BACHELOR OF SCIENCE IN GEOGRAPHY

GEOMORPHOLOGY

BGEOS-11

SEMESTER-I

Department of Geography,
School of Sciences
Tamil Nadu Open University
577, Anna Salai, Saidapet, Chennai - 600 015
www.tnou.ac.in

January 2022
Name of Programme: B.Sc Geography

Course Code: BGEOS-11

Course Title: Geomorphology

Course Design: Dr. K. Katturajan

Assistant Professor,
Department of Geography,
School of Sciences,
Tamil Nadu Open University, Chennai -600 015

Course Writer: Dr. P. Arul

Associate Professor,
Department of Geography,
Government Arts College (Autonomous),
Salem -636 007.

Course Coordinator & Editor: Dr. K. Katturajan

January 2022 (First Edition)

ISBN No: 978-93-95914-72-7

© Tamil Nadu Open University, 2022

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 04.01.2022

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 BGEOS-11 Geomorphology

Syllabus

BLOCK 1 Introduction to Geomorphology

1. Nature, Scope, Key concepts, and Systems approach
2. Earth: Interior Structure
3. Rock Types: Igneous Sedimentary and Metamorphic
4. Types of Folds and Faults
BLOCK 2 Theories of Geomorphology
5. Theory of isostasy
6. Wegner’s Continental drift theory
7. Seafloor spreading
8. Plate Tectonics Theory
BLOCK 3 Geomorphic Processes
9. Earthquakes and Volcanoes.
10. Weathering and Mass Wasting
BLOCK 4 Cycle of Erosion
11. Cycle of Erosion: Davis
12. Cycle of Erosion: Penck
BLOCK 5 Evolution of Landforms
13. Evolution of Landforms (Erosional and Depositional): Fluvial and Karst
14. Evolution of Landforms (Erosional and Depositional): Aeolian and Glacial
15. Evolution of Landforms (Erosional and Depositional): Coast.
16. Application of Geomorphology in Mineral Exploration and Coastal Zone
Management.
References
1. Summerfield M. A. (2013): Global Geomorphology, Routledge, New York
2. Khullar, D.R., (2012) Physical Geography, Kalyani Publishers, New Delhi.
3. Christopherson, R. W. and Birke land, G. H., (2012) Geosystems: An Introduction
to Physical Geography (8th edition), Pearson Education, New Jersey.
4. Huggett, R.J. (2007) Fundamentals of Geomorphology, Routledge, New York.
5. Das Gupta, A., and Kapoor, A.N, Principles of Physical Geography, S.C. Chand &
Company Ltd, 2001.
6. Lobeck. A.K. (1939) An Introduction to the study of Landscapes, McGraw –Hill
Book company
7. Thorn Bury.D.(1984) - Principles of Geomorphology, Wiley Eastern Ltd, New
Delhi, 1984
 BGEOS-11 Geomorphology

Unit Page
Contents
No Number

Block 1: Introduction to Geomorphology

1 Nature, scope, Concept and System Approach of Geomorphology 01

2 Earth: Interior Structure 10

3 Rock Types: Igneous, Sedimentary and Metamorphic 20

4 Types of Folds and Faults 28

Block 2: Theories of Geomorphology

5 Theory of Isostasy 35

6 Wegner’s Continental drift theory 43

7 Sea Floor Spreading 51

8 Plate Tectonic Theory 60

Block 3: Geomorphic Processes

9 Earthquakes and Volcanoes 67

10 Weathering and Mass Wasting 80

Block 4: Cycle of Erosion

11 The cycle of Erosion: Davis 89

12 The cycle of Erosion: Penck 98

Block 5: Evolution of Landforms

Evolution of Landforms (Erosional and Depositional) Fluvial and

13 104
Karst

Evolution of Landforms (Erosional and Depositional) Glacial and

14 120
Aeolian

15 Evolution of Landforms (Erosional and Depositional): Coast 132

Application of Geomorphology in Mineral Exploration and Coastal

16 139
Zone Management
 Unit 1
Nature, scope, Concept and System
Approach of Geomorphology
Structure
1.1 Overview
Learning Objectives
1.2 Nature of Geomorphology
1.3 Scope and Concept of Geomorphology
1.4 Significance of Geomorphology
1.5 The System Approach in Geomorphology
Let us sum up
Glossary
Check Your Progress
Suggested Readings

1.1 Overview
The word “geomorphology" comes from the Greek roots "geo, “morph,”
and “logos,” meaning “earth,” “form,” and “study,” respectively. Therefore,
geomorphology is literally “the study of earth forms.” Geomorphologists
are concerned primarily with the earth’s surficial features, including their
origin, history, composition, and impact on human activity. Geomorphology
concentrates primarily on Quaternary (Pleistocene and Holocene)
features. Earth’s landforms reflect the local and regional balance between
hydrologic, tectonic, aeolian, glacial, atmospheric, and marine processes.
Let us see the Learning Objectives of this unit.
Learning Objectives
After studying this unit, you should be able to:
• Meaning, scope, Concept, and significance of the Geomorphology
• Key concepts of Geomorphology
• The system Approach in Geomorphology

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1.2 Nature of Geomorphology:
Geomorphology is a branch of Physical Geography, the word
Geomorphology is derived from the Greek language, in the Greek
language “geo” refers to “Earth” “morphe” refers to “form” and “logos”
refers to the “study”. Geomorphology is the scientific study of the origin
and evolution of topographic (Topography is a term used to describe the
land surface) and bathymetric (Bathymetry is the study of the "beds" or
"floors" of water bodies, including the ocean, rivers, streams, and lakes)
features created by physical, chemical, or biological processes operating
at or near the Earth's surface. Simply the subject Geomorphology is the
study of landforms, their processes, form, and sediments at the surface of
the Earth. Besides, the study includes looking at landscapes to work out
how the earth's surface processes, such as air, water, and ice, can mould
the landscape. Landforms are produced by erosion or deposition, as rock
and sediment are worn away by these earth-surface processes and
transported and deposited to different localities. The different climatic
environments produce different suites of landforms. The landforms of
deserts, such as dunes and ergs, are a world apart from the glacial and
periglacial features found in polar and sub-polar regions.
A person who studies geomorphology is known as Geomorphologists their
major job is to map the distribution of these landforms to understand better
their occurrence.

1.3 Scope and Concept of Geomorphology:

Geomorphology is the scientific study of landforms and the processes that
shape them. Geomorphologists seek to understand why landscapes look
the way they do: to understand landform history and dynamics and predict
future changes through a combination of field observation, physical
experiments, and numerical modelling. Geomorphology is practiced within
geology, engineering geology, geodesy, geography, archaeology, and
geological engineering.
The fundamental concepts of geomorphology are as follows:
Concept 1:

The same physical processes and laws that operate today operated
throughout geologic time, although not necessarily with the same intensity
as now.

This is the important principle of geology and is known as the principle of

uniformitarianism. It was first enunciated by Hutton in 1785. According to
Hutton "the present is the key to the past". According to him, geologic

2|Page
processes operated throughout geologic time with the same intensity as
now. We know that it is not true. Glaciers were much more significant
during the Pleistocene and during other periods of geologic time than now;
world climates have not always been distributed as they now are, and,
thus, regions that are now humid have been deserted and areas now
desert have been humid. Numerous examples show that the intensity of
various geologic processes has varied through geologic time.
Concept 2: ‘Geologic Structure is a dominant control factor in the
evolution of landforms, and it's reflected in them’.

The above concept demonstrates the imposing influence of geological

structure on primary and secondary landforms produced by the exogenetic
denudational process. The geologic structure is a dominant control factor
in the evolution of landforms and is reflected in them. The major controlling
factor in landform development is structure and process. Here the term
structure includes not only the folds, faults, etc. but all those ways in which
the earth materials out of which landforms are carved differ from one
another in their physical and chemical attributes. it includes such as rock
attitudes; presence or absence of joints, bedding planes, faults, and folds;
rock massiveness; hardness of constituent minerals; the susceptibility of
the mineral constituents to chemical alteration; permeability and
impermeability of rocks; and various other ways by which the rocks of the
earth crust differ from one another. The term structure also has
stratigraphic implications, and knowledge of the structure of a region
implies the appreciation of rock sequence, both in outcrop and in the
subsurface, as well as the regional relationship of the rock strata. In
general, the structures are much older than the geomorphic forms
developed upon them. Such major structural features as folds and faults
may go back to far distant periods of diastrophism.
Concept 3: ‘Geomorphic processes leave their distinctive imprints upon
landforms and each geomorphic process develops its characteristic
assemblage of landforms.’
Geomorphologic processes and geomorphic agents are considered
separately for different meanings by a few geomorphologists. Geomorphic
processes include all those physical and chemical changes which affect
the earth’s surface and are involved in the evolution and development of
landforms of varying sizes and magnitudes. While the geomorphic agent is
a medium through which eroded materials are transported from the place
of erosion to the place of deposition.

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Concept 4: “As the different erosional agencies act on the earth’s surface
there is produced a sequence of landforms having distinctive
characteristics at the successive stages of their development.”
Geomorphic processes leave their distinctive imprint upon landforms, and
each geomorphic process develops its characteristic assemblage of
landforms. The term process applies to the many physical and chemical
ways by which the earth's surface undergoes modification. In general,
endogenetic processes (originate from forces within the earth crust such
as diastrophism and volcanism) tend to build up or restore areas that have
been worn down by the exogenetic processes (results from external forces
like weathering, mass wasting, erosion); otherwise, the earth's surface
would finally become largely featureless. Just like plants and animals,
landforms have their distinguishing features depending upon the
geomorphic process responsible for their development. A proper
appreciation of the significance of process in landform evolution not only
gives a better picture of how individual landforms develop but also
emphasizes the genetic relationships of landform assemblages.
Landforms are not haphazardly developed concerning one another but
certain forms may be expected to be associated with each other. Thus, the
concept of certain types of the terrain becomes basic in the thinking of
geomorphologists. Most landscape is the products of a group of
processes. The complex geomorphic processes and agents which operate
under a particular set of climatic conditions have been termed a
morphogenetic system.
Concept 5: “Geomorphic scale is a significant parameter in the
interpretation of landform development and landform characteristics of
geomorphic systems.”

As the different erosional agents act upon the earth's surface there is
produced an orderly sequence of landforms. The landforms possess
distinctive characteristics depending upon the stage of their development.
This idea was most stressed by W. M. Davis and out of this idea grew his
concept of the geomorphic cycle and its concomitant stages of youth,
maturity, and old age culminating in a topographic surface of low relief
called peneplain. Use of the term geomorphic cycle will carry with it an
implication of orderly and sequential development but there will be no
implication that designation of the topography to a certain area as youthful,
mature, or old means that the topography of another region in the same
stage of development has fully comparable characteristics. Under varying
conditions of geology, structure, and climate landform characteristics may

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vary greatly even though the geomorphic processes may have been acting
for comparable periods. Partial cycles are more likely to occur than
completed ones, for much of the earth's crust is restive and subject to
intermittent and differential uplifts.
Concept 6: A Simple Geomorphological equation may be envisaged as a
vehicle for the explanation of landforms as follows the complexity of
geomorphic evolution is more common than simplicity. Usually, most of
the topographic details have been produced during the current cycle of
erosion, but there may exist within as area remnants of features produced
during prior cycles. Commonly we can recognize the dominance of one
cycle. Horberg (1952) divided the landscapes into five major categories:
(1) simple, (2) compound, (3) monocyclic, (4) multicyclic, and (5)
exhumed. Simple landscapes are those which are the product of a single
dominant geomorphic process, compound landscapes are those in which
more than one geomorphic process has played a major role in the
development of existing topography. Monocyclic landscapes are those that
bear the imprint of only one cycle of erosion; multicyclic landscapes have
been produced during more than one cycle of erosion. Much of the earth's
topography bears the imprints of more than one period of erosion.
Exhumed or resurrected landscapes are those which were formed during
some past period of geological time, then buried beneath a cover mass of
igneous or sedimentary origin, then still later exposed through the removal
of the cover. Topographic features now being exhumed may date back as
far as the Precambrian or they may be as recent as Pleistocene.
Concept 7: ‘Complexity of geomorphic evolution is more common than
simplicity.’
Generally, landform characteristics are explained based on the most
dominant controlling factor on the basic premise that most landforms are
simple and have less complex geomorphic evolution but, most of the
landforms are the result of poly-factor rather than mono-factor.

Concept 8: “Little of the earth’s topography is older than Tertiary and most
of it no older than Pleistocene.”
According to this concept majority of geomorphologists that most of the
present-day landforms are the result of geomorphic processes that
operated in the Tertiary and Quaternary times as the landforms older than
Tertiary have been either obliterated by the dynamic wheels of
denudational processes or have been so greatly modified that they have
lost their original shapes and cannot be properly and accurately identified.
Proper interpretation of present-day landscape is impossible without a full

5|Page
appreciation of the manifold influences of the geologic and climatic
changes during the Pleistocene. Pleistocene diastrophism has played a
most significant role in the shaping of present-day landscapes.
Concept 9: “Each climatic type produces its characteristic assemblage of
landforms.”
An appreciation of world climate is necessary for a proper understanding
of the varying importance of the different geomorphic processes. Climatic
variations may affect the operation of geomorphic processes either
indirectly or directly. The indirect influences are largely related to how
climate affects the amount, kind, and distribution of the vegetal cover. The
direct controls are such as the amount and kind of precipitation, its
intensity, the relation between precipitation and evaporation and the daily
range of temperature, weather, and how frequently the temperature falls
below. There are, however, other climatic factors whose effects are less
obvious, such as how long the ground is frozen, exceptionally heavy
rainfalls and their frequency, seasons of maximum rainfall, frequency of
freeze and thaw days, differences in climatic conditions as related to
slopes facing the sun and those not so exposed, the differences between
conditions on the windward and leeward sides of topographic features
transverse to the moisture-bearing winds, and the rapid changes in
climatic conditions with an increase in altitude.
Concept 10: Geomorphology, although concerned primarily with present-
day landscapes, attains its maximum usefulness by historical extension.
Geomorphology, although concerned primarily with present-day
landscapes, attains its maximum usefulness by historical extension.
Geomorphology concerns itself primarily with the origins of the present
landscape but in most landscapes, there are present forms that date back
to previous geological epochs or periods. A geomorphologist is thus forced
to adopt a historical approach if he is to interpret properly the geomorphic
history of a region. Paleogeomorphology covers the identification of
ancient erosion surfaces and the study of ancient topographies.

1.4 Significance of Geomorphology

Geomorphology is the study of Earth’s landforms created by mostly
physical processes, including physical or chemical changes, and those
changes influenced by biological processes, including land use.
Geographers apply geomorphological principles to study how landforms
have changed in the past, but increasingly such principles are important
for modern applications. Over long geological periods, plate

6|Page
tectonics have shaped continents. Earthquakes and volcanic activity
represent the active change that relates to plate tectonic movements.
Fluvial, or those involving water, change is among the most significant
physical factors that shape the Earth at generally small scales. The
importance of geomorphology for physical geographers is not only
important in understanding Earth’s physical changes but also in preparing
for hazards. For instance, understanding issues of deforestation, soil
properties, and seasonal precipitation can better assess the frequencies
of flooding events and their potential danger. Also, Geomorphology
knowledge is essential for the following reasons such as
• To understand the geomorphological processes of the various
environment.

• To detect natural and environmental hazards efficiently, e.g.,

earthquake, flooding, landslide, tsunami, Volcanism, etc.
• To identify various landform features and landscapes
• To identify various landform features from satellite images
• Coastal and river research
• Vulnerability studies
• Geology, Geography, Archeology, Engineering, various planning
measures, Mining, Construction, and Urban study.
In the present-day context, applied geomorphologic knowledge has
become very important for a better understanding of natural hazards. The
knowledge of geomorphology helps in mitigating various hazards or
reducing the impact to a great extent.

1.5 The System Approach in Geomorphology

A systems approach in geomorphology has a long and varied history that
tracks developments in physics, chemistry, biology, and ecology. Four
related stages started with classical mechanics and moved through
classical thermodynamics and open systems to non-equilibrium
thermodynamics and dissipative systems. New ideas emerged in each of
the stages that led to fresh concepts about the dynamics of geomorphic
systems. Classical mechanics and classical thermodynamics promoted
the idea of equilibrium, open systems thermodynamics fostered the idea of
steady-state and dynamic equilibrium, and non-equilibrium thinking
generated the linked ideas of complexity and disorder.

7|Page
Let Us Sum Up
Geomorphology: Geomorphology is concerned with the nature and origins
of Earth’s surface features. Literary, a study of Earth form.
Geomorphology is generally understood to embrace the study of
landforms and landscapes.
Significance of Geomorphology:
Geomorphology knowledge is essential for the following reasons as

• To understand the geomorphological processes of various

environments.
• To detect natural and environmental hazards efficiently, e.g.,
earthquake, flooding, landslide, tsunami, Volcanism, etc.
• To identify various landform features and landscapes
• To identify various landform features from satellite images • Coastal
and river research
• Vulnerability studies
• Geology, Geography, Archeology, Engineering, various planning
measures, Mining, Construction, and Urban study.
Scope of Geomorphology: To understand landform history and dynamics
and predict future changes through a combination of field observation,
physical experiment, and numerical modelling.
The System Approach in Geomorphology: A systems approach in
geomorphology has a long and varied history that tracks developments in
physics, chemistry, biology, and ecology.

Glossaries
1. Topography is a term used to describe the land surface) and
2. Bathymetry is the study of the "beds" or "floors" of water bodies,
including the ocean, rivers, streams, and lakes
3. Geomorphologists A person who studies geomorphology
4. Uniformitarianism is the assumption that the same natural laws and
processes that operate in our present-day scientific observations have
always operated in the universe in the past and apply everywhere in the
universe.

5. Endogenetic processes: originate from forces within the earth's crust

such as diastrophism and volcanism.

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6. Exogenetic processes: results from external forces like weathering,
mass wasting, erosion

Check Your Progress

1. Geomorphology-Define.

2. Who are Geomorphologists?

3. State the Significance of Geomorphology.
4. What did you understand from the System Approach is
Geomorphology?

Answers to Check Your Progress

1. Geomorphology is concerned with the nature and origins of Earth’s
surface features

2. For a person who studies geomorphology their major job is to map the
distribution of these landforms to understand better their occurrence.
3. Geomorphology knowledge is essential to understand the
geomorphological processes of various Environment
4. A systems approach in geomorphology has a long and varied history
that tracks developments in physics, chemistry, biology, and ecology.

Suggested Readings
1. Chorley, R.J.: Spatial Analysis in Geomorphology.
2. King, L.C.: The Morphology of the Earth.
3. Singh, Savindra – Bhooakrity Vigyan
4. Sparks, B.W.: Geomorphology
5. Tharnbury, W.D.: Principles of Geomorphology.
6. Worcester: A Text Book of Geomorphology

9|Page
 Unit 2
Earth: Interior Structure
Structures
2.1 Overview
Learning Objectives
2.2 History of Study:
2.3 The internal structure of the Earth

2.4 Interior of Earth

2.4.1 The Crust
2.4.2 The Mantle
2.4.3 Core
2.4.3.1 Outer Core
2.4.3.2 The Inner Core
Let us sum up
Glossary
Check your progress

Suggested readings

2.1 Overview
In Units 1, you have learned about nature, scope, and the basic concepts
of Geomorphology. In this Unit, we will focus on the interior of the Earth,
its structure, and composition. We begin the unit with the geological
history of the earth and get into the interior structure and its composition.
There is more to the Earth than what we can see on the surface. If you
were able to hold the Earth in your hand and slice it in half, you'd see that
it has multiple layers. But of course, the interior of the Earth continues to
hold some mysteries for us. However, advances in seismology have
allowed us to learn a great deal about the Earth and the many layers that
make it up. Each layer has its properties, composition, and characteristics
that affect many of the key processes of our planet. They are, in order
from the exterior to the interior – the crust, the mantle, the outer core, and
the inner core. Let's look at them and see what they have going on. Earth

10 | P a g e
has four layers → the outer crust that we live on, the plastic-like mantle,
the liquid outer core, and the solid inner core. Many geologists believe that
as the Earth cooled the heavier, denser materials sank to the centre and
the lighter materials rose to the top. Because of this, the crust is made of
the lightest materials (rock- basalts and granites) and the core consists of
heavy metals (nickel and iron).

Learning Objectives
After studying this unit, you should be able to:
• A brief history of the Study.
• Source of information of the Earth’s interior and different layers
• Earth’s internal structure as propounded by different Earth
scientists.

2.2 History of Study:

In 1912, Alfred Wegener proposed the theory of Continental Drift, which
suggested that the continents were joined together at a certain time in the
past and formed a single landmass known as Pangaea. Following this
theory, the shapes of continents and matching coastline geology between
some continents indicated they were once attached.
Research into the ocean floor also led directly to the theory of Plate
Tectonics, which provided the mechanism for Continental Drift.
Geophysical evidence suggested lateral motion of continents and that
oceanic crust is younger than continental crust. This geophysical evidence
also spurred the hypothesis of palaeomagnetism, the record of the
orientation of the Earth's magnetic field recorded in magnetic minerals.
Model of a flat Earth, with the continents modelled in a disk shape and
Antarctica as an ice wall. Credit: Wikipedia Commons
Then there was the development of seismology, the study of earthquakes
and the propagation of elastic waves through the Earth or other planet-like
bodies, in the early 20th century. By measuring the time of travel of
refracted and reflected seismic waves, scientists were able to gradually
infer how the Earth was layered and what lay deeper at its core.

For example, in 1910, Harry Fielding Ried put forward the "elastic rebound
theory", based on his studies of the 1906 San Fransisco earthquake. This
theory, which stated that earthquakes occur when accumulated energy is
released along a fault line, was the first scientific explanation for why

11 | P a g e
earthquakes happen and remain the foundation for modern tectonic
studies.
Then in 1926, English scientist Harold Jeffreys claimed that below the
crust, the core of the Earth is liquid, based on his study of earthquake
waves. And then in 1937, Danish seismologist Inge Lehmann went a step
further and determined that within the earth's liquid outer core, there is a
solid inner core.
By the latter half of the 20th century, scientists developed a
comprehensive theory of the Earth's structure and dynamics had formed.
As the century played out, perspectives shifted to a more integrative
approach, where geology and Earth sciences began to include the study
of the Earth's internal structure, atmosphere, biosphere, and hydrosphere
into one.
This was assisted by the development of space flight, which allowed for
Earth's atmosphere to be studied in detail, as well as photographs taken of
Earth from space. In 1972, the Landsat Program, a series of satellite
missions jointly managed by NASA and the U.S. Geological Survey,
began supplying satellite images that provided geologically detailed maps,
and have been used to predict natural disasters and plate shifts.

2.3 The internal structure of the Earth

Scientific understanding of the internal structure of Earth is based on
observations of topography and bathymetry, observations of rock in
outcrop, samples brought to the surface from greater depths by volcanoes
or volcanic activity, analysis of the seismic waves that pass-through Earth,
measurements of the gravitational and magnetic fields of Earth, and
experiments with crystalline solids at pressures and temperatures
characteristic of Earth's deep interior. Sources of Information about the
interior of the earth
Sources of information about the earth’s interior can get directions as well
as indirectly.
Direct Sources:

Deep earth mining and drilling reveal the nature of rocks deep down the
surface. But as mining and drilling are not practically possible beyond a
certain depth, they don’t reveal much information about the earth’s interior.

Mponeng gold mine (deepest mine in the world) and TauTona gold
mine (second deepest mine in the world) in South Africa are the deepest
mines reaching a depth of only 3.9 km. And the deepest drilling is only

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about a 12 km deep hole bored by the Soviet Union in the 1970s over
the Kola Peninsula. Volcanic eruption forms another source of obtaining
direct information.

Indirect sources:
• Temperature and pressure patterns through mining activity: An
increase in temperature and pressure with depth means an increase in
density as well. Hence it becomes possible to determine the rate of
change of characteristics of the material of earth. This has led to the
knowledge of the layers of earth.

• Meteors: These are extra-terrestrial masses reaching the earth’s

surface. They have material and structures similar to earth and give
information about the materials of which earth is formed.

• Gravitation force(g): The force exerted by the Earth on all things in its
range is not the same along all latitudes, it is variable over different
places. Observations suggest that gravitational force is greater at
poles and lesser at the equator. This is due to the increased distance
from the core. This difference in (g) is also attributed to the uneven
material mass distribution.
• Magnetic surveys: The distribution of magnetic materials gives an idea
of the magnetic field of the earth which indicates the density and type
of material present in the interior of the earth.
• Seismic activity: This gives the most important evidence of the interior
of the earth. Earthquakes give a fair idea of the interior of the earth.
We shall investigate the details of the Earthquake Unit.

2.4 Interior of Earth

The Earth can be divided into one of two ways – mechanically or
chemically. Mechanically – archaeologically, meaning the study of liquid
states – it can be divided into the lithosphere, asthenosphere,
mesospheric mantle, outer core, and inner core. But chemically, which is
the more popular of the two, it can be divided into the crust, the mantle
(which can be subdivided into the upper and lower mantle), and the core –
which can also be subdivided into the outer core, and inner core.
The inner core is solid, the outer core is liquid, and the mantle is
solid/plastic. This is due to the relative melting points of the different layers
(nickel-iron core, silicate crust, and mantle) and the increase in
temperature and pressure as depth increases. At the surface, the nickel-
iron alloys and silicates are cool enough to be solid. In the upper mantle,

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the silicates are generally solid but localized regions of melt exist, leading
to limited viscosity.

Fig.2.1 The Earth’s layers (strata) are shown to scale.

Credit: pubs.usgs.gov
In contrast, the lower mantle is under tremendous pressure and therefore
has a lower viscosity than the upper mantle. The metallic nickel-iron outer
core is liquid because of the high temperature. However, the intense
pressure, which increases towards the inner core, dramatically changes
the melting point of the nickel-iron, making it solid.
2.4.1 The Crust
The crust is the outermost layer of the earth making up 0.5-1.0 per cent of
the earth’s volume and less than 1 per cent of Earth’s mass. Density
increases with depth an average density is about 2.7 g/cm3 (the average
density of the earth is 5.51 g/cm³). The thickness of the crust varies in the
range of 5-30 km in the case of the oceanic crust and 50-70 km in the
case of the continental crust. The continental crust can be thicker than 70
km in the areas of major mountain systems. It is as much as 70-100 km
thick in the Himalayan region. The temperature of the crust increases with
depth, reaching values typically in the range from about 200 °C to 400 °C
at the boundary with the underlying mantle. The temperature increases by
as much as 30 °C for every kilometre in the upper part of the crust. The
outer covering of the crust is of sedimentary material and below that lie
crystalline, igneous and metamorphic rocks which are acidic.
The lower layer of the crust consists of basaltic and ultra-basic rocks. The
continents are composed of lighter silicates: silica and aluminium

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called sial and it is composed of lighter (felsic) sodium, potassium,
aluminium silicate rocks like granite. The oceans have the heavier
silicates: silica and magnesium called sima and it is composed of dense
(mafic) iron magnesium silicate igneous rocks, like basalt.
Lithosphere
The lithosphere is the rigid outer part of the earth with thickness varying
between 10-200 km. It is including the crust and the upper part of the
mantle. The lithosphere is broken into tectonic plates (lithospheric
plates), and the movement of these tectonic plates cause large-scale
changes in the earth’s geological structure (folding, faulting). The source
of heat that drives plate tectonics is the primordial heat left over from the
planet’s formation as well as the radioactive decay of uranium, thorium,
and potassium in Earth’s crust and mantle.
2.4.2 The Mantle
The mantle covers about 83 per cent of the earth’s volume and holds 67%
of the earth’s mass. It is also known as the ‘mesosphere’ located at the
boundary between the lower crust and upper parts of the mantle. The
speed of seismic waves is 6.9 kilometres per second at the base of the
lower crust. It rises rapidly to 8.1 kilometres per second due to
discontinuity. This zone of separation was discovered by a Yugoslavian
seismologist named Andrija Mohorovicic in 1909. Thereafter, it came to be
known as ‘Mohorovicic Discontinuity’ or ‘Moho Discontinuity’.
The density of the upper mantle varies between 2.9 g/cm3 and 3.3 g/cm3.
The lower mantle extends beyond the asthenosphere in a solid state. The
density ranges vary from 3.3 g/cm3 to 5.7 g/cm3 in the lower mantle. The
mantle is composed of silicate rocks that are rich in iron and
magnesium relative to the overlying crust. Regarding its constituent
elements, the mantle is made up of 45% oxygen, 21% silicon, and 23%
magnesium (OSM). In the mantle, temperatures range from approximately
200 °C at the upper boundary with the crust to approximately 4,000 °C at
the core-mantle boundary. Convective material circulation occurs in the
mantle due to temperature differences. Convection of the mantle is
expressed at the surface through the motions of tectonic plates. High-
pressure conditions ought to inhibit seismicity in the mantle.
Asthenosphere
The upper portion of the mantle is called the asthenosphere (astheno
means weak). It lies just below the lithosphere extending up to 80-200 km.
It is highly viscous, mechanically weak, and ductile and its density is

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higher than that of the crust. These properties of the asthenosphere aid in
plate tectonic movement and isostatic adjustments (the elevated part at
one part of the crust area is counterbalanced by a depressing part at
another). It is the main source of magma that finds its way to the surface
during volcanic eruptions

Fig.2.2 Two different views of the interior of the Earth

2.4.3 Core
2.4.3.1 Outer Core
The core is the deepest and most remote zone in the Earth’s interior. It is
also known as ‘barysphere’ and its extent at a depth of 2900 kilometres
from lower parts of the mantle to the Earth’s centre at a depth of 6371
kilometres. It is marked by the boundary known as ‘Weichert-Gutenberg
Discontinuity’ between the lower mantle and upper parts of the core and it
marks the rapid change in the density from 5.5 g/cm3 to 10.0 g/cm3. It is
also supported and marked by an increase in the speed of the primary
seismic waves to 13.6 kilometres per second. The density of the outer
core ranges from 9.9 g/cm3 to 12.2 g/cm3. The temperature of the outer
core ranges from 4400 °C in the outer regions to 6000 °C near the inner
core. Dynamo theory suggests that convection in the outer core, combined
with the Coriolis effect, gives rise to Earth’s magnetic field.

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 Fig.2.3 Temperature with depth in the Earth
By Bkilli1 (Own work) [CC BY-SA 3.0(link is external)]
2.4.3.2 The Inner Core
The inner core extends from the centre of the earth to 5100 km below the
earth’s surface. The inner core is generally believed to be composed
primarily of iron (80%) and nickel (nife). Since this layer can transmit shear
waves (transverse seismic waves), it is solid. (When P-waves strike the
outer core – inner core boundary, they give rise to S-waves). Earth’s
inner core rotates slightly faster relative to the rotation of the surface. The
solid inner core is too hot to hold a permanent magnetic field. The density
of the inner core ranges from 12.6 g/cm3 to 13 g/cm3. The core (inner
core and the outer core) accounts for just about 16 per cent of the earth’s
volume but 33% of the earth’s mass. Scientists have determined the
temperature near the Earth’s centre to be 6000֯ C, 1000֯ C hotter than
previously thought. At 6000°C, this iron core is as hot as the Sun’s
surface, but the crushing pressure caused by gravity prevents it from
becoming liquid.

Let Us Sum Up
Crust: The outermost solid layer of a rocky planet or natural satellite.
Chemically distinct from the underlying mantle.
Mantle: A layer of the Earth (or any planet large enough to support
internal stratification) between the crust and the outer core. It is chemically

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distinct from the crust and the outer core. The mantle is not liquid. It is,
however, ductile, or plastic, which means that on very long-time scales
and under pressure it can flow. The mantle is mainly composed of
aluminium and silicates.
Core: The innermost layers of the Earth. The Earth has an outer core
(liquid) and an inner core (solid). They are not chemically distinct from
each other, but they are chemically distinct from the mantle. The core is
mainly composed of nickel and iron.

Glossaries
• Seismic Waves: an elastic wave in the earth produced by an
earthquake or other means.
• Barysphere: the heavy interior portion of the earth within the
lithosphere

• Asthenosphere: a zone of a celestial body (such as the earth) that

lies beneath the lithosphere and within which the material is believed
to yield readily to persistent stresses
• Bathymetry: the measurement of water depth at various places in a
body of water

Check Your Progress

1. What are the three main layers of the Earth?
Ans: The crust, the mantle, and the core.
2. How does pressure change as you go from the surface to the
centre of the Earth?
Ans: Pressure increases.
3. How does temperature change as you go from the surface toward the
centre of the Earth?
Ans: Temperature increases.
4. What are both parts of the core made of?
Ans: Iron and nickel.
5. What are the two types of crust calling that make up Earth's outer
skin?
Ans: Oceanic crust and Continental crust.

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Suggested Readings
1. 1. Chorley, R.J.: Spatial Analysis in Geomorphology.
2. 2. King, L.C.: The Morphology of the Earth.
3. 3. Singh, Savindra – Bhooakrity Vigyan
4. 4. Sparks, B.W.: Geomorphology
5. 5. Tharnbury, W.D.: Principles of Geomorphology.
6. 6. Worcester: A Text Book of Geomorphology
7. https://pubs.usgs.gov/gip/interior/
8. https://www.e-education.psu.edu/marcellus/node/870
9. https://phys.org/news/2015-12-earth-layers.html
10. https://www.e-education.psu.edu/marcellus/node/870

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 UNIT 3
ROCK TYPES: IGNEOUS, SEDIMENTARY
AND METAMORPHICS

Structures
3.1 Overview
Learning Objectives
3.2 Definition
3.3 Types of rocks

3.3.1 Igneous rocks

3.3.2 Sedimentary rocks
3.3.3 Metamorphic rocks
3.4 Rock Cycle
3.4.1 Significance of Rock Cycle
3.4.2 Process involve in Rock Cycle

Let us sum up
Glossary
Check your progress
Suggested readings

3.1 Overview
Rocks are very important to mankind because they are one of the best
sources of fuel and power. For example, we derive coal, petroleum, and
even natural gas from rocks. Minerals are extracted from rocks. This is
one of the obvious advantages of rocks. The scientific study of rocks is
called petrology. Minerals are extracted from rocks. This is one of the
obvious advantages of rocks. Many important minerals such as gold and
diamond are mined directly from rocks. Salt can be extracted from rocks.
The salt mined from rocks can be used to preserve food or to season food.
Rocks also serve as a source of water supply. Many springs and wells all
over the world get their sources from rocks. In the absence of rocks, these
springs will not exist. Rocks are one of the beauties of nature and

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therefore can serve as a tourist attraction. Some rocks contain vast
amounts of clay. The clay derived from some rocks is used in producing
ceramics.
Learning Objectives
After studying this unit, you will learn about,
• Types of rocks

• Rock Cycle
• Significance of Rock Cycle
• The process involves in Rock Cycle

3.2 Definition
Rocks are the hard substance or solid material that forms part of the main
surface of the Earth. A rock is any naturally occurring solid mass or
aggregate of minerals matter. Simply rock is any naturally occurring solid
mass or aggregate of minerals or mineraloid matter. It is categorized by
the minerals including their chemical composition and how it is formed.

3.3 Types of rock

There are three basic types of rocks: igneous, sedimentary, and
metamorphic. Rocks are categorized by the minerals including
their chemical composition and how it is formed. Rocks are commonly
divided into three major classes according to the processes that resulted
in their formation. These classes are
3.3.1 Igneous rocks
which have solidified from molten material called magma; In terms of
modes of occurrence, igneous rocks can be either intrusive (plutonic and
hypabyssal) or extrusive (volcanic). Intrusive igneous rocks make up most
igneous rocks and are formed from magma that cools and solidifies within
the crust of a planet (known as plutons), surrounded by pre-existing rock
(called country rock); the magma cools slowly and, as a result, these rocks
are coarse-grained. The mineral grains in such rocks can generally be
identified with the naked eye. Intrusive rocks can also be classified
according to the shape and size of the intrusive body and its relation to the
other formations into which it intrudes. Typical intrusive formations
are batholiths, stocks, laccoliths, sills, and dikes. When the magma
solidifies within the earth's crust, it cools slowly forming coarse textured
rocks, such as granite, gabbro, or diorite. Extrusive igneous rocks, also
known as volcanic rocks, are formed at the crust's surface because of the

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partial melting of rocks within the mantle and crust. Extrusive igneous
rocks cool and solidify more quickly than intrusive igneous rocks. They are
formed by the cooling of molten magma on the earth's surface. The
magma, which is brought to the surface through fissures or volcanic
eruptions, solidifies at a faster rate. Hence such rocks are smooth,
crystalline, and fine-grained. Basalt is a common extrusive igneous rock
and forms lava flows, lava sheets and lava plateaus. Some kinds of basalt
solidify to form long polygonal columns. The Giant's Causeway in Antrim,
Northern Ireland is an example.

3.3.2 Sedimentary rocks

Sedimentary rocks are types of rock that are formed by the accumulation
or deposition of small particles and subsequent cementation of mineral or
organic particles on the floor of oceans or other bodies of water at the
Earth's surface. Sedimentary rocks are the most common rocks exposed
on the Earth’s surface but are only a minor constituent of the entire crust,
which is dominated by igneous and metamorphic rocks. Sedimentary
rocks are produced by the weathering of preexisting rocks and the
subsequent transportation and deposition of the weathering products.
Sedimentary rocks are the product of 1) weathering of preexisting rocks,
2) transport of the weathering products, 3) deposition of the material,
followed by 4) compaction and 5) cementation of the sediment to form a
rock. The most significant examples of Sedimentary rocks are sandstone,
conglomerates, clay rock, shale gypsum, salt rock, limestones, dolomites,
coals, and peats.
3.3.3 Metamorphic rocks
Metamorphic rocks have been derived from either igneous or sedimentary
rocks under conditions that caused changes in mineralogical composition,
texture, and internal structure. These three classes, in turn, are subdivided
into numerous groups and types based on various factors, the most
important of which are chemical, mineralogical, and textural attributes.
Igneous rock (derived from the Latin word igneous, the meaning of
fire, from ignis meaning fire) is formed through the cooling
and solidification of magma or lava. Igneous rocks are formed
when magma cools in the Earth's crust, or lava cools on the ground
surface or the seabed. Sedimentary rocks are formed at the earth's
surface by the accumulation and cementation of fragments of earlier
rocks, minerals, and organisms.

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The sedimentary rocks are formed by diagenesis or lithification of
sediments, which in turn are formed by the weathering, transport, and
deposition of existing rocks. The metamorphic rocks are formed when
existing rocks are subjected to such large pressures and temperatures
that they are transformed this process is called metamorphism, meaning
to "change in form". Agents of Metamorphism are 1. Heat: Heat is the
most important factor for the development of metamorphic rocks from pre-
existing parents’ rocks. It may be pointed out that mineral composition is
entirely changed due to intense heat, but the rocks are seldom melted. 2.
Compression resulting from convergent horizontal movement caused by
endogenetic forces causes folding in rock beds. Thus, the resultant
pressure from compressive forces and consequent folding changes the
form and composition of parent rocks. 3. Solution-chemically active hot
gases and water while passing through the rocks change their chemical
composition. Magmatic water and water confined in the beds of
sedimentary rocks also help in introducing chemical changes in the rocks.
The most significant examples of metamorphic rocks are marbles are
generally formed due to changes in limestone because of temperature
changes. Schist is a fine-grained metamorphic rock and is characterized
by well-developed foliation Mica is changed as Schist. Slates are formed
due to the dynamic regional metamorphism of shales and other
argillaceous rocks. Conglomerates change as Gneiss and Sandstone
change as Quartzite.

3.4 Rock Cycle

Meaning: The rock cycle is a basic concept in geomorphology that
describes transitions through geologic time among the three
main rock types: The rock cycle is a series of processes that create and
transform the types of rocks in Earth’s crust. The rock components of the
crust are slowly but constantly being changed from one form to another
and the processes involved are summarized in the rock cycle.
3.4.1 Significance of Rock Cycle
Our world is constantly changing. Evidence from fossils and rock samples
have shown scientists that at one point all our continents were connected.
Because our world changes, it is important for our planet to have the rock
cycle. The rock cycle is driven by two forces: (1) Earth’s internal heat
engine, which moves material around in the core and the mantle and leads
to slow but significant changes within the crust, and (2) the hydrological
cycle, which is the movement of water, ice, and air at the surface, and is
powered by the sun. The rock cycle is still active on Earth because our

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core is hot enough to keep the mantle moving, our atmosphere is relatively
thick, and we have liquid water. On some other planets or their satellites,
such as the Moon, the rock cycle is virtually dead because the core is no
longer hot enough to drive mantle convection and there is no atmosphere
or liquid water.

Fig.3.1 Rock Cycle

3.4.2 Process involve in Rock Cycle

As already discussed, there are three main types of rocks: sedimentary,
igneous, and metamorphic. Each of these rocks is formed by physical
changes—such as melting, cooling, eroding, compacting, or deforming—
that are part of the rock cycle. Sedimentary rocks are formed from pieces
of other existing rock or organic material. There are three different types of
sedimentary rocks: clastic, organic (biological), and chemical. Clastic
sedimentary rocks, like sandstone, form from clasts, or pieces of other
rock. Organic sedimentary rocks, like coal, form from hard, biological
materials like plants, shells, and bones that are compressed into rock. The
formation of clastic and organic rocks begins with the weathering or
breaking down, of the exposed rock into small fragments. Through the
process of erosion, these fragments are removed from their source and
transported by wind, water, ice, or biological activity to a new location.
Once the sediment settles somewhere, and enough of it collects, the
lowest layers become compacted so tightly that they form solid rock.

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Chemical sedimentary rocks, like limestone, halite, and flint, form from
chemical precipitation. A chemical precipitate is a chemical compound—
for instance, calcium carbonate, salt, and silica—those forms when the
solution it is dissolved in, usually water, evaporates and leaves the
compound behind. This occurs as water travels through Earth’s crust,
weathering the rock and dissolving some of its minerals, transporting it
elsewhere. These dissolved minerals are precipitated when the water
evaporates.
Metamorphic rocks are rocks that have been changed from their original
form by immense heat or pressure. Metamorphic rocks have two classes:
foliated and nonfoliate. When a rock with flat or elongated minerals is put
under immense pressure, the minerals line up in layers, creating foliation.
Foliation is the aligning of elongated or platy minerals, like hornblende or
mica, perpendicular to the direction of pressure that is applied. An
example of this transformation can be seen with granite, an igneous rock.
Granite contains long and platy minerals that are not initially aligned, but
when enough pressure is added, those minerals shift to all points in the
same direction while getting squeezed into flat sheets. When granite
undergoes this process, like at a tectonic plate boundary, it turns into
gneiss (pronounced “nice”). Non-foliated rocks are formed the same way,
but they do not contain the minerals that tend to line up under pressure
and thus do not have the layered appearance of foliated rocks.
Sedimentary rocks like bituminous coal, limestone, and sandstone, given
enough heat and pressure, can turn into nonfoliate metamorphic rocks like
anthracite coal, marble, and quartzite. Nonfoliate rocks can also form
metamorphism, which happens when magma encounters the surrounding
rock.

Igneous rocks (derived from the Greek word for fire) are formed when
molten hot material cools and solidifies. Igneous rocks can also be made
in a couple of different ways. When they are formed inside of the earth,
they are called intrusive, or plutonic, igneous rocks. If they are formed
outside or on top of Earth’s crust, they are called extrusive, or volcanic,
igneous rocks. Granite and diorite are examples of common intrusive
rocks. They have a coarse texture with large mineral grains, indicating that
they spent thousands or millions of years cooling down inside the earth, a
time course that allowed large mineral crystals to grow. Alternatively, rocks
like basalt and obsidian have very small grains and a relatively fine
texture. This happens because when magma erupts into lava, it cools
more quickly than it would if it stayed inside the earth, giving crystals less
time to form. Obsidian cools into the volcanic glass so quickly when

25 | P a g e
ejected that the grains are impossible to see with the naked eye. Extrusive
igneous rocks can also have a vesicular, or “holey” texture. This happens
when the ejected magma still has gases inside of it so when it cools, the
gas bubbles are trapped and end up giving the rock a bubbly texture. An
example of this would be pumice.

Let Us Sum Up
Rocks are the hard substance or solid material that forms part of the main
surface of the Earth. Rocks are categorized by the minerals including
their chemical composition and how it is formed. There are three main
types of rocks: sedimentary, igneous, and metamorphic. Each of these
rocks is formed by physical changes—such as melting, cooling, eroding,
compacting, or deforming—that are part of the rock cycle. The rock cycle
is a series of processes that create and transform the types of rocks in
Earth’s crust

Glossaries
• Petrology is a scientific study of rocks
• Igneous rock is formed through the cooling and solidification of
magma or lava.
• Sedimentary rocks are formed by diagenesis or lithification of
sediments.

• Metamorphic rocks are rocks that have been changed from their
original form by immense heat or pressure.
• Rock cycle is a series of processes that create and transform the
types of rocks in Earth’s crust

Check Your Progress

1. Rock- Define.
Rocks are the hard substance or solid material that forms part of the
main surface of the Earth.
2. What is meant by Petrology?
Petrology is a scientific study of rocks

3. Mention the types of rocks.

There are three main types of rocks: sedimentary, igneous, and
metamorphic.

4. Write a note on the Rock Cycle.

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 The Rock cycle is a series of processes that create and transform the
types of rocks in Earth’s crust.

Suggested Readings
1. Das Gupta, A & Kapoor, A.N., (2001) Principles of Physical
Geography, S.C. Chand & Company Ltd. New Delhi.
2. Khullar, D.R., (2012) Physical Geography, Kalyani Publishers, New
Delhi.

3. Brown, J.H. (2005) Biogeography, Sinauer Associates Inc,

Sunderland.
4. Seddon, B.A. (1971) Overview to Biogeography, Duckworth, London.

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 UNIT 4
Types of Folds and Faults

Structures
4.1 Overview
Learning Objectives

4.2 Endogenic processes

4.3 Diastrophic forces and movements
4.4 Exogenic processes

4.5 Folds
4.5.1 Types of Folds
4.6 Faults
4.6.1 Types of faults
Let us sum up
Glossary
Check your progress
Suggested readings

4.1 Overview
The study of forces affecting the crust of the earth or geological processes
is of paramount significance because these forces and resultant
movements are involved in the creation, destruction, recreation and
maintenance of geomaterials and numerous types of relief features of
varying magnitudes. These forces very often affect and change the earth’s
surface. The geological changes are generally two types e.g. (1) long
period changes and (2) short-period changes. Long-period changes occur
so slowly that the main is unable to notice such changes during his life
period. On the other hand, short-period changes take place so suddenly
that these are noticed within a few seconds to a few hours, e.g., seismic
events, volcanic eruptions etc. The forces, which affect the crust of the
earth are divided into two broad categories based on their source of origin
e.g. (I) endogenetic forces and (II) exogenetic forces.

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Learning Objectives
After learning this unit, students would be learning
• the exogenic forces of the earth: types of fold and fault.

4.2 Endogenic processes

The forces coming from within the earth are called endogenic forces which
causes two types of movements in the earth viz. (1) horizontal movements
and (II) vertical movements. These movements motored by the
endogenetic forces introduce various types of vertical irregularities which
give birth to numerous varieties of relief features on the earth’s surface
(e.g. mountains, plateau, plains, lakes, faults, folds, etc). Volcanic
eruptions and seismic events are also expressions of endogenetic forces.
Such movements are called sudden movements and forces responsible
for their origin are called sudden forces. The endogenetic forces and
movements are divided, based on intensity, into two major categories viz.
(1) diastrophic forces and (2) sudden forces.
Sudden forces and movements: They are caused by sudden endogenetic
forces coming from deep within the earth, causing such sudden and rapid
events that these cause massive destructions at and below the earth’s
surfaces. Such events like volcanic eruptions and earthquakes are called
‘extreme events’ and become disastrous hazards when they occur in
densely populated localities.

4.3 Diastrophic forces and movements

They include both vertical and horizontal movements which are caused
due to forces deep within the earth. These diastrophic forces and
movements are further subdivided into two groups viz. (1) epirogenetic
movements and (II) orogenetic movements. epirogenetic movements
cause upliftment and subsidence of continental masses through upward
and downward movements respectively. Orogenetic movements caused
due to endogenetic movements forces working in horizontal manner folds
and faults are the result of these movements.

4.4 Exogenic processes

The exogenetic forces or processes also called denudational processes,
or destruction forces are originated from the atmosphere. These forces are
continuously engaged in the destruction of the relief features created by
the endogenetic forces through their weathering, erosional and
depositional activities. Denudations include both weathering and erosion
where weathering being a static process includes the disintegration and

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decomposition of rocks in sit whereas erosion is a dynamic process that
includes both, removal of materials and their transportation to different
destinations. Weathering is of three types viz. 1. Physical or mechanical
weathering (II) chemical weathering and (iii) biological weathering.
Weathering is very important for the biospheric ecosystem because
weathering of parent rocks results in the formation of soils which are very
essential for the sustenance of the biotic lives in the biosphere. The
erosional process includes running water, groundwater, sea waves,
glaciers, and wind. These natural agents erode the rocks, transport the
eroded materials and deposit them in suitable places and thus form
several types of erosional and depositional landforms of different
magnitudes and dimensions.

4.5 Folds
Wave-like bends are formed in the crystal rocks due to tangential
compression force resulting from horizontal movement caused by the
endogenetic force originating deep within the earth. Such bends are called
folds wherein some parts are bent up and some parts are bent down. The
up folded rock strata in the arch-like form are called anticlines while the
down folded structure forming trough-like feature is called a syncline.
Folding: A fold is a bend in the rock strata resulting from the compression
of an area in the Earth’s crust. Folding occurs when the lithospheric plate
pushes up against another plate. In folding, the land between the two
tectonic plates, acting towards each other, rises. Fold mountains such as
the Himalayas have been formed due to folding.
4.5.1 Types of Folds
The nature of folds depends on several factors e.g., the nature of rocks,
the nature and intensity of compressive forces, duration of the operation of
compressive forces etc.

(1) Symmetrical folds are simple, the limbs both of which incline uniformly.
These folds are an example of an open fold.
(2) Asymmetrical folds are characterized by unequal and irregular limbs.
Both the limbs incline at different angles. One limb is relatively larger and
the inclination is moderate and regular while the other limb is relatively
shorter with a steep inclination. Thus, both the limbs are symmetrical in
terms of inclination and length.

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(3) Monoclinal folds are those in which one limb inclines moderately with
regular slope while the other limb inclines steeply at right angles and the
slope is almost vertical.
(4) Isoclinal folds are formed when the compressive forces are so strong
that both the limbs of the fold become parallel but not horizontal.
(5) Recumbent folds are formed when the compressive forces are so
strong that both the limbs of the fold become parallel as well as horizontal.

Fig. 4.1 Types of Fold

https://cameroongcerevision.com/wp-Structure/uploads/2020/03/summary-
of-folds.jpg

4.6 Faults
When the crystal rocks are displaced, due to tensional movement caused
by the endogenetic forces, along a plane the resultant structure is called a
fault. Faulting: At times, when the crustal rocks are subjected to horizontal
compressional pressure, they do not get folded. Instead, they develop
fractures or cracks along the line of weakness. These lines of fracture are
known as faults. The movement of the crustal rocks of the earth’s crust
along the line of fault is known as faulting. Block Mountains are formed
due to faulting.

4.6.1 Types of faults

The different types of faulting of the crystal rocks are determined by the
direction of motion along the fracture plane. (1) Normal faults are formed
due to the displacement of both the rock blocks in opposite directions due
to fracture consequent upon greatest stress. The fault plane is usually
between 450. (2) Reverse faults are formed due to the movement of both
the fractured rock blocks towards each other. The fault plane, in a reverse

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fault, is usually inclined at an angle between 40 degrees and other
horizontal 0 degrees. (3) Lateral or strike-slip faults are formed when the
rock blocks are displaced horizontally along the fault plane due to
horizontal movement. (4) Step faults: when a series of faults occur in any
area in such a way that a slope of all the fault planes of all the faults is in
the same direction. Rift Valley and Graben: Rift valley is a major relief
feature resulting from faulting activities, Rift valley represents a trough,
depression, or basin between two crustal parts.

Fig.4.2 Types of faults

https://gharpedia.com/wp-Structure/uploads/2019/03/Types-of-Faults-01-
0207030001.jpg

Let Us Sum Up
The earth's surface is being continuously subjected to
external forces originating within the Earth’s atmosphere and by
internal forces from within the earth. The external forces are known as
exogenic forces, and the internal forces are known as endogenic forces.
Wave-like bends are formed in the crystal rocks due to tangential
compression force resulting from horizontal movement caused by the
endogenetic force originating deep within the earth. The nature of folds
depends on several factors e.g., the nature of rocks, the nature and
intensity of compressive forces, duration of the operation of compressive
forces etc., When the crystal rocks are displaced, due to tensional
movement caused by the endogenetic forces, along a plane the resultant
structure is called a fault.

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Glossaries
Endogenic processes the forces coming from within the earth are called
endogenic forces.
Exogenetic forces are originated from the atmosphere.
Faulting is the movement of the crustal rocks of the earth’s crust along
the line of fault.
Folding a fold is a bend in the rock strata resulting from the compression
of an area in the Earth’s crust.
Anticlines refer that the up folded rock strata in an arch-like form
Syncline refers that the down folded structure forming trough-like feature

Check Your Progress

1. Name the natural forces that affect the earth crust.
The forces, which affect the crust of the earth are divided into two
broad categories based on their source of origin e.g. (I) endogenetic
forces and (II) exogenetic forces.
2. Examine the importance of sudden forces and movements on the
earth crust.

They are caused by sudden endogenetic forces coming from deep

within the earth, causing such sudden and rapid events that these
cause massive destructions at and below the earth’s surfaces.
3. State the types of folds.
The nature of folds depends on several factors e.g., the nature of
rocks, the nature and intensity of Compressive forces, duration of the
operation of compressive forces etc., Symmetrical folds, Asymmetrical
folds, Monoclinal folds, Isoclinal folds, Recumbent folds.
4. Enumerate the types of faults.

The different types of faulting of the crystal rocks are determined by

the direction of motion along the fracture plane Normal faults, Reverse
faults, Lateral or strike-slip faults, Step faults, Rift Valley and Graben

Suggested Readings
1. Khullar, D.R., (2012) Physical Geography, Kalyani Publishers, New
Delhi.
2. Brown, J.H. (2005) Biogeography, Sinauer Associates Inc,

33 | P a g e
 Sunderland.
3. Seddon, B.A. (1971) Overview to Biogeography, Duckworth, London.
4. Thornbury W.D. (2002), Principles of Geomorphology, CBS Publishers
& Distributors, New Delhi, India.

34 | P a g e
 UNIT 5
Theory of Isostasy
Structures
5.1 Overview
5.1.1 Definition
Learning Objectives

5.2 Significance of the Study

5.3 Conceptual evolution of the Isostasy Theory
5.4 Evidence to the Isostasy theory

5.5 Points to be remembered in Theory of Isostasy

5.6 Understanding the Concept of Theory of Isostasy
5.7 Postulations of Airy (Theory of Isostasy)

5.8 Postulations of Pratt (Theory of Isostasy)

Let us sum up
Glossary
Check your progress
Suggested readings

5.1 Overview
Isostasy is a fundamental concept in Geomorphology. It is the idea that
the lighter crust must be floating on the denser underlying mantle. It is
invoked to explain how different topographic heights can exist on the
Earth's surface. Isostatic equilibrium is an ideal state where the crust and
mantle would settle in absence of disturbing forces. The waxing and
waning of ice sheets, erosion, sedimentation, and extrusive volcanism are
examples of processes that perturb isostasy. The physical properties of
the lithosphere (the rocky shell that forms Earth's exterior) are affected by
the way the mantle and crust respond to these perturbations. Therefore,
understanding the dynamics of isostasy helps us figure out more complex
phenomena such as mountain building, sedimentary basin formation, the
break-up of continents and the formation of new ocean basins.

35 | P a g e
Learning Objectives
After studying this unit, students would be able to understand the
• Conceptual evolution of the Isostasy Theory
• Evidence to the Isostasy theory
• Postulations of Airy and Pratt (Theory of Isostasy)

5.1.1 Definition
The term “Isostasy” is derived from “Isostasios”, a word of Greek language
meaning the state of being in balance or equal standing or equipoise. The
theory of isostasy explains the tendency of the earth’s crust to attain
equilibrium and the distribution of the material in the earth’s crust which
conforms to the observed gravity values. Isostasy or isostatic equilibrium
is the state of gravitational equilibrium between Earth's crust (or
lithosphere) and mantle such that the crust "floats" at an elevation that
depends on its thickness and density. Isostasy, the ideal theoretical
balance of all large portions of Earth’s lithosphere as though they were
floating on the denser underlying layer, the asthenosphere, a section of
the upper mantle composed of weak, plastic rock that is about 110 km (70
miles) below the surface.
Isostasy controls the regional elevations of continents and ocean floors by
the densities of their underlying rocks. Imaginary columns of the equal
cross-sectional area that rise from the asthenosphere to the surface are
assumed to have equal weights everywhere on Earth, even though
their constituents and the elevations of their upper surfaces are
significantly different. This means that an excess of mass seen as material
above sea level, as in a mountain system, is due to a deficit of mass, or
low-density roots, below sea level. Therefore, high mountains have low-
density roots that extend deep into the underlying mantle.

5.2 Significance of the Study

The concept of isostasy played an important role in the development of the
theory of plate tectonics. The theory of isostasy explains the tendency of
the earth’s crust to attain equilibrium and the distribution of the material in
the earth’s crust which conforms to the observed gravity values.

5.3 Conceptual evolution of the Isostasy Theory

There are two main ideas, developed in the mid-19th century, on the way
isostasy acts to support mountain masses. In Pratt's theory, there are
lateral changes in rock density across the lithosphere. Assuming that the

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mantle below is uniformly dense, the less dense crustal blocks float higher
to become mountains, whereas the denser blocks form basins and
lowlands. On the other hand, Airy's theory assumes that across the
lithosphere, the rock density is approximately the same, but the crustal
blocks have different thicknesses. Therefore, mountains that shoot up
higher also extend deeper roots into the denser material below. Both
theories rely on the presumed existence of a denser fluid or plastic layer
on which the rocky lithosphere floats. This layer is now called the
asthenosphere and was verified in the mid-20th century to be present
everywhere on Earth due to analysis of earthquakes - seismic waves,
whose speed decrease with the softness of the medium, pass relatively
slowly through the asthenosphere. Both theories predict a relative
deficiency of mass under high mountains, but Airy's theory is now known
to be a better explanation of mountains within continental regions,
whereas Pratt's theory essentially explains the difference between
continents and oceans, since the continental crust is large of granitic
composition which is less dense than the basaltic ocean basin.

5.4 Evidence to the Isostasy theory

Since isostasy predicts deficiencies of mass under higher topological
regions, one way to test isostasy on the planetary scale is to measure the
variation of the local gravitational field. A simple pendulum can be utilized
to measure the local strength of gravity; indeed, this was how the first
gravity measurements in the U.S. were performed. Nowadays, physical
geodesy, the study of physical properties of the gravity field of Earth,
utilizes relative and absolute gravimeters for gravity surveys. Modern
absolute gravimeters work by measuring the acceleration rate of a free-
falling mass in a vacuum - the mass includes a retroflector which acts as
one arm of a Michelson interferometer; thus, the velocity of the mass can
be inferred from the interference fringes. Modern relative gravimeters
mostly use quartz zero-length springs and are calibrated to absolute
gravimeters. A portable spring-based gravimeter can now measure the
earth's gravitational field up to accuracies of nanometer per second
squared.
Due to self-rotation, the Earth bulges at its equator, roughly forming an
ellipsoid, hence at sea level the value of gravity is dependent on the
latitude and is less at latitudes near the equator than at latitudes near the
poles. This value of gravity at a particular point on the ellipsoid is called
the theoretical value for that point. Subtracting the theoretical value of
gravity from the observed value of gravity at a point gives a difference

37 | P a g e
called the "gravity anomaly." After correcting both for elevation and the
gravitational attraction of the rocks between the instrument and the
ellipsoid, the measured value of gravity minus the theoretical value is
called the "Bouguer gravity anomaly."

5.5 Points to be remembered in Theory of Isostasy

1. Theory of Isostasy was developed from gravity surveys in the
mountains of India, in 1850. The term was first proposed by Clarence
Dutton, an American geologist in 1889.
2. This doctrine states that wherever equilibrium exists in the earth’s
surface, equal mass must underlie equal surface areas; in other words, a
great continental mass must be formed of lighter material than that
supposed to constitute the ocean floor.
3. Thus, there exists a gravitational balance between crustal segments of
different thicknesses.
According to Dutton, the elevated masses are characterized by rocks of
low density and the depressed basins by rocks of higher density.
4. To compensate for its greater height these lighter continental materials
must extend downward to some distance under the continent and below
the ocean-floor level so that unit areas beneath the oceans and continents
may remain in stable equilibrium.
5. Accordingly, a level of uniform pressure is thought to exist where the
pressure due to elevated masses and depressed areas would be equal.
This is known as the ‘Isopiestic-Level ‘.

5.6 Understanding the Concept of Theory of Isostasy

It is invoked to explain how different topographic heights can exist on the
Earth’s surface. Isostatic equilibrium is an ideal state where the crust and
mantle would settle in absence of disturbing forces. These are the
examples of processes that perturb isostasy: -
• The waxing and waning of ice sheets,
• Erosion, sedimentation, and Extrusive volcanism
The physical properties of the lithosphere (the rocky shell that forms
Earth’s exterior) are affected by the way the mantle and crust respond to
these perturbations.
Therefore, understanding the dynamics of isostasy helps us figure out
more complex phenomena such as: -

38 | P a g e
 • Mountain building,
• Sedimentary basin formation,
• The break-up of continents and

• The formation of new ocean basins

5.7 Postulations of Airy (Theory of Isostasy)

According to him the crust of relatively lighter material is floating in the
substratum of denser material. In other words, ‘sial’ is floating in ‘sima’.

He considered the density of different columns (plains, plateaus,

mountains, etc.) to be the same. Hence, he proposed the idea
of ‘Uniform density with varying thicknesses.

Fig. 5.1 Model of Uniform Density with varying Density

5.8 Postulations of Pratt (Theory of Isostasy)

Pratt considered land blocks of various heights to be different in terms of
their density. The taller landmass has lesser density and smaller height
features to be denser. If there is a higher column, density will be lesser
and if there is a shorter column, density will be higher. He accepted that all
blocks of different heights get compensated at a certain depth into the

39 | P a g e
substratum. Thus, he denounced the root concept of Airy and accepted
the ‘concept of a level of compensation.

Fig. 5.2 Model of Level of Compensation

Let Us Sum Up
The theory of Isostasy was developed from gravity surveys in the
mountains of India, in 1850. The term was first proposed by Clarence
Dutton, an American geologist in 1889. This doctrine states that wherever
equilibrium exists in the earth’s surface, equal mass must underlie equal
surface areas; in other words, a great continental mass must be formed of
lighter material than that supposed to constitute the ocean floor. Thus,
there exists a gravitational balance between crustal segments of different
thicknesses.
According to Dutton, the elevated masses are characterized by rocks of
low density and the depressed basins by rocks of higher density. To
compensate for its greater height these lighter continental materials must
extend downward to some distance under the continent and below the
ocean-floor level so that unit areas beneath the oceans and continents
may remain in stable equilibrium. Accordingly, a level of uniform pressure
is thought to exist where the pressure due to elevated masses and
depressed areas would be equal. This is known as the ‘Isopiestic-Level ‘.

Glossaries
Asthenosphere: the upper layer of the earth's mantle, below the
lithosphere, in which there is relatively low resistance to plastic flow and
convection is thought to occur.
Lithosphere: the rigid outer part of the earth, consisting of the crust and
upper mantle, "the lithosphere comprises several plates".
Sial: the material of the upper or continental part of the earth's crust,
characterized as relatively light and rich in silica and alumina.

40 | P a g e
Sima: the material of the lower part of the earth's crust, underlying both
the ocean and the continents, characterized as relatively heavy and rich in
silica and magnesia.
Gravimeter: A portable spring-based gravimeter can now measure the
earth's gravitational field to accuracies of nanometer per second squared.
‘Isopiestic-Level’: a level of uniform pressure is thought to exist where
the pressure due to Elevated masses and depressed areas would be
equal. This is known as the Isopiestic- Level ‘.

Check Your Progress

1. Give a brief account of Isostasy.

The theory of isostasy explains the tendency of the earth’s crust to attain
equilibrium and the distribution of the material in the earth’s crust which
conforms to the observed gravity values.

2. Bring out the significance of Isostasy.

Isostasy controls the regional elevations of continents and ocean floors by
the densities of their underlying rocks. Imaginary columns of the equal
cross-sectional area that rise from the asthenosphere to the surface are
assumed to have equal weights everywhere on Earth, even though
their constituents and the elevations of their upper surfaces are
significantly different
3. Isopiestic-Level-Define.
Mountain building, Sedimentary basin formation, the break-up of
continents and the formation of new ocean basins. a level of uniform
pressure is thought to exist where the pressure due to Elevated masses
and depressed areas would be equal. This is known as the ‘Isopiestic-
Level

Suggested Readings
[1] A. B. Watts, Isostasy and Flexure of the Lithosphere (Cambridge,
2001).
[2] O. S. Boyd, C. H. Jones, and A. F. Sheehan, "Foundering Lithosphere
Imaged Beneath the Southern Sierra Nevada, California, USA,"
Science 305, 660 (2004).

[3] C. Ollier and C. Pain, The Origin of Mountains (Routledge, 2000).

41 | P a g e
[4] J. Gilluly, "Crustal Deformation in the Western United States," in The
Maga tectonics of Continents and Oceans, ed. by H. Johnson and B. L.
Smith (Rutgers, 1970), p. 47.
[5] G. Zandt et al., "Active Foundering of a Continental arc Root Beneath
the Southern Sierra Nevada in California," Nature 431, 41 (2000)

42 | P a g e
 UNIT 6
Wegner’s Continental drift theory
Structures
6.1 Overview
Learning Objectives
6.2 Points to be remembered in Continental Drift Theory
6.3 Evidence supporting the Continental Drift Theory
6.3.1 The Geographical similarity in the coasts of the Atlantic Ocean
6.3.2 Rocks & Paleontological evidence

6.3.3 Tillite
6.3.4 Placer Deposits
6.3.5 Distribution of Fossils
6.4 Forces behind the drifting of continents, according to Wegner
6.5 Criticism of the Continental Drift Theory
Let Us Sum Up
Glossaries
Check Your Progress
Suggested Readings

6.1 Overview
Alfred Wegener (November 1880–November 1930) was a German
meteorologist, climatologist, and geophysicist at the University of Graz in
Austria. Who introduced a revolutionary scientific theory in the year 1912
on continental drift and formulated the idea that a supercontinent known
as Pangaea, a Greek term meaning "all lands,”? The Continental Drift
theory explains that the continents had all originally been a part of one
enormous landmass or supercontinent about 240 million years ago before
breaking apart and drifting to their current locations. Based on the work of
previous scientists who had theorized about the horizontal movement of
the continents over the Earth's surface during different periods of geologic
time and based on his observations drawing from different fields of
science, Wegener postulated that about 200 million years ago, a

43 | P a g e
supercontinent that he called Pangaea (which means "all lands" in Greek)
began to break up. Over millions of years the pieces separated, first into
two smaller supercontinents, Laurasia and Gondwanaland, during the
Jurassic period and then by the end of the Cretaceous period into the
continents we know today. In the Triassic Period, Pangaea fragmented,
and the parts began to move away from one another. The westward drift
of the Americas opened the Atlantic Ocean, and the Indian block drifted
across the Equator to merge with Asia.

Fig. 6.1 Continental Drift

Sources: http://www-
das.uwyo.edu/~geerts/cwx/notes/chap15/ancient_files/image002.gif
Learning Objectives
After studying this unit, students would be able to understand the following
• Evidence supporting the Continental Drift Theory
• The Geographical similarity in the coasts of the Atlantic Ocean

• Forces behind the drifting of continents, according to Wegner

• Criticism of the Continental Drift Theory

6.2 Points to be remembered in Continental Drift

Theory
The theory deals with the distribution of the oceans and the continents.

44 | P a g e
It was first put forward by Abraham Ortelius in 1596 before fully being
developed by Albert Wegener.
According to Wegener’s Continental Drift theory, all the continents were
one single continental mass (called a Super Continent) – Pangaea and a
Mega Ocean surrounded this supercontinent. The mega ocean is known
by the name Panthalassa.

Although Wagner’s initial theory did not cover mantle convection until
Arthur Holmes later proposed the theory.
The supercontinent was named Pangaea and the Mega- Ocean was
called Panthalassa.
According to this theory, the supercontinent, Pangaea, began to split some
two hundred million years back.

Pangaea first split into 2 big continental masses known as

Gondwanaland and Laurasia forming the southern and northern
modules respectively.
Later, Gondwanaland and Laurasia continued to break into several smaller
continents that exist today.

Fig. 6.1 This map of the world shows the earth’s major tectonic plates.
Arrows indicate the direction of plate movement. This map only shows the
15 largest tectonic plates. Image courtesy of United States Geological
Survey (USGS)

45 | P a g e
6.3 Evidence supporting the Continental Drift Theory

6.3.1 The Geographical similarity in the coasts of the

Atlantic Ocean:
The Matching of Continents (Jig-Saw-Fit): (i) The outlines of the coasts on
the two sides of the Atlantic Ocean are such that they can be easily joined
together, the eastern coast of South America can be fitted against the
western coast of Africa. This was called the ‘Jigsaw-fit’ of the opposing
coasts of the Atlantic Ocean by Wegener. (ii) The Northern tip of Australia
can very well fit into the Bay of Bengal.
(iii) On the same principle the bulge of Ethiopia and Eritrea on the East
Coast of Africa may be said to fit in the curve of the coastline of Western
India and Pakistan.
6.3.2 Rocks & Paleontological evidence:
The radiometric dating methods have helped in correlating the formation of
rocks present in different continents across the ocean. The ancient rocks
belts on the coast of Brazil match with those found in Western Africa. The
old marine deposits found on the coasts of South America and Africa
belong to the Jurassic Age. This implies that the ocean never existed
before that time. This evidence was further supported by a series of
Geological similarities observed on the opposite sides of the Atlantic
Ocean. The study of fossils, fauna and flora also confirmed this. Wegener
concluded on this basis that in the ‘Paleozoic Era’ all the continents were
part of the ‘Pangaea’ but in the ‘Permocarboniferous’ period this landmass
was broken into two parts north and south of the Sea of Tethys which
used to flow where its remnant-the Mediterranean Sea now lies.
6.3.3 Tillite
It is the sedimentary rock formed out of deposits of glaciers. The
Gondwana system of sediments from India is known to have its
counterparts in six different landmasses of the Southern Hemisphere. At
the base, the system has thick tillite indicating extensive and prolonged
glaciation. Counterparts of this succession are found in Africa, Falkland
Island, Madagascar, Antarctica, and Australia besides India. The overall
resemblance of the Gondwana type sediments demonstrates that these
landmasses had remarkably similar histories. The glacial tillite provides
unambiguous evidence of palaeoclimates and the drifting of continents.

46 | P a g e
6.3.4 Placer Deposits
The occurrence of rich placer deposits of gold in the Ghana coast and the
absolute absence of source rock in the region is an amazing fact. The
gold-bearing veins are in Brazil, and it is obvious that the gold deposits of
Ghana derived from the Brazil Plateau when the two continents lay side by
side. The widespread distribution of Permo-Carboniferous glacial
sediments in South America, Africa, Madagascar, Arabia, India,
Antarctica, and Australia was one of the major pieces of evidence for the
theory of continental drift. The continuity of glaciers, inferred from oriented
glacial striations and deposits called tillites, suggested the existence of the
supercontinent of Gondwana, which became a central element of the
concept of continental drift.
6.3.5 Distribution of Fossils
When identical species of plants and animals adapted to living on land or
in freshwater are found on either side of the marine barriers, a problem
arises regarding accounting for such distribution. The observations that
Lemurs occur in India, Madagascar and Africa led some to consider a
contiguous landmass “Lemuria” linking these three landmasses.
Mesosaurus was a small reptile adapted to shallow brackish water. The
skeletons of these are found only in two localities: the Southern Cape
province of South Africa and Traver formations of Brazil. The two localities
presently are 4,800 km apart with an ocean in between them.

Fig. 6.2 Distribution of Fossils. Source:

https://media.nationalgeographic.org/assets/photos/305/757/e606b8ef-
5d37-4f2e-b563-c2bac8f7e517.jpg

47 | P a g e
6.4 Forces behind the drifting of continents
According to Wegener, the drift was in two directions:
equator wards due to the interaction of forces of gravity, pole-fleeing force
(due to centrifugal force caused by earth’s rotation) and buoyancy (ship
floats in water due to buoyant force offered by water), and
Westwards due to tidal currents because of the earth’s motion (earth
rotates from west to east, so tidal currents act from east to west, according
to Wegener).
Wegener suggested that tidal force (gravitational pull of the moon and to a
lesser extent, the sun) also played a major role.

The polar-fleeing force relates to the rotation of the earth. Earth is not a
perfect sphere; it has a bulge at the equator. This bulge is due to the
rotation of the earth (greater centrifugal force at the equator).

The centrifugal force increases as we move from poles towards the

equator. This increase in centrifugal force has led to pole fleeing,
according to Wegener.
The tidal force is due to the attraction of the moon and the sun that
develops tides in oceanic waters (tides explained in detail in
oceanography).
According to Wegener, these forces would become effective when applied
over many million years, and the drift is continuing.

6.5 Criticism of the Continental Drift Theory:

There was much opposition to Wegener's theory for several reasons. For
one, he was not an expert in the field of science in which he was making
a hypothesis, and for another, his radical theory threatened conventional
and accepted ideas of the time. Furthermore, because he was making
multidisciplinary observations, there were more scientists to find fault with
them. One of the biggest faults of Wegener’s continental drift theory was
that he did not have a viable explanation for how continental drift could
have occurred. He proposed two different mechanisms, but each was
weak and could be disproven. One was based on the centrifugal force
caused by the rotation of the Earth, and the other was based on the tidal
attraction of the sun and the moon.
The theory does not indicate any force adequate to bring about the drift of
continents. The continents can only drift due to a tidal force 10,000 million
times as strong as it is at present. But such a force seems impossible

48 | P a g e
because such a thing would stop the rotation of the earth in one year.
This will also produce radioactivity and convection currents in the SIMA.
This theory presupposes SIMA to be in a liquid state and SIAL is
supposed to be floating over it. This is in stark contradiction to the
assumption that SIMA buckled the edges of the drifting masses. The two
positions are Paradoxical because the former presupposes the SIMA to be
liquid while the latter regard it as sufficiently solid.
Several critics have found fa laws with the ‘Jig-saw fit’ element in the
theory. They say that the different continents can fit in each other to a
certain extent only. According to Wegener, the only logical alternative was
that the continents themselves had been joined and had since drifted
apart. In addition, those Coastlines are a temporary feature and are liable
to change. Several other combinations of fitting in of unrelated landforms
could be attempted. Continental Drift Theory shifts India’s position too
much to the south, distorting its relationship with the Mediterranean Sea
and the Alps. The mountains do not always exhibit geological affinity.
In addition that the following are mainly cited by the scholars to the
weakness of this theory Wegener failed to explain why the drift began only
in the Mesozoic era and not before, The theory doesn’t consider oceans,
Proofs heavily depend on assumptions that are generalistic Forces like
buoyancy, tidal currents and gravity are too weak to be able to move
continents, Modern theories (Plate Tectonics) accept the existence of
Pangaea and related landmasses but give a very different explanation to
the causes of drift, Though scientifically unsound on various grounds,
Wegener’s theory is a significant milestone in the study of tectonics, and it
laid a strong foundation for future the theories like seafloor spreading and
plate tectonics.

Let Us Sum Up
Continental drift theory deals with the distribution of the oceans and the
continents. According to Wegener’s Continental Drift theory, all the
continents were one single continental mass (called a Super Continent) –
Pangaea and a Mega Ocean surrounded this supercontinent. The mega
ocean is known by the name Panthalassa. The supercontinent was named
Pangaea (Pangea) and the Mega- Ocean was called Panthalassa.
According to this theory, the supercontinent, Pangaea, began to split some
two hundred million years back. Pangaea first split into 2 big continental
masses known as Gondwanaland and Laurasia forming the southern and
northern modules respectively. Later, Gondwanaland and Laurasia
continued to break into several smaller continents that exist today.

49 | P a g e
Glossaries
Pangaea: one single continental mass
Panthalassa: The Mega-Ocean
Gondwanaland: North landmass

Laurasia: South Landmass

Tidal force: due to the attraction of the moon and the sun

Check Your Progress

1. Who is Alfred Wegener?

A German meteorologist, climatologist, and geophysicist at the

University of Graz in Austria.
2. Pangaea-Define
A Greek term meaning "all lands”
3. What is meant by centrifugal force?
The centrifugal force is caused by the rotation of the Earth.
4. What is tidal force?
The tidal force is caused by the tidal attraction of the sun and the
moon.

Suggested Readings
1. B. Watts, Isostasy and Flexure of the Lithosphere (Cambridge, 2001).
2. O. S. Boyd, C. H. Jones, and A. F. Sheehan, "Foundering Lithosphere
Imaged Beneath the Southern Sierra Nevada, California, USA,"
Science 305, 660 (2004).
3. A. Ollier and C. Pain, The Origin of Mountains (Routledge, 2000).
4. J. Gilluly, "Crustal Deformation in the Western United States," in The
Magatectonics of Continents and Oceans, ed. by H. Johnson and B. L.
Smith (Rutgers, 1970), p. 47.
5. G. Zandt et al., "Active Foundering of a Continental arc Root Beneath
the Southern Sierra Nevada in California," Nature 431, 41 (2000)

50 | P a g e
 UNIT 7
Sea Floor Spreading
Structures
7.1 Overview
Learning Objectives
7.2 Conceptual Evolution
7.3 Significance of Seafloor spreading
7.4 Explanation of the theory
7.4.1 Mid-Ocean Ridges
7.4.2 Geomagnetic Reversals
7.4.3 Geographic Features
7.4 Conclusion
7.5 Let us sum up
7.6 Glossary
7.7 Check your progress
7.8 Suggested readings

7.1 Overview
Our Earth is a warm planet sailing through cold space. Much of the rocky
interior (the mantle) of our planet is hot enough to flow like a candy bar
kept too long in one’s pocket. The surface of the Earth, however, is chilled
by the cold of space, and so the familiar rocks of the Earth’s surface are
hard and brittle. The cold outer layer of our planet, which holds together as
a rigid shell, is not made of one solid piece. Instead, this shell is broken
into many separate pieces, or tectonic plates, that slide around atop the
mobile interior. The tectonic plates are in motion. They are driven by the
flowing mantle below and their motions are controlled by a complex puzzle
of plate collisions around the globe. There are three types of plate-plate
interactions based upon relative motion: convergent, where plates collide,
divergent, where plates separate, and transform motion, where plates
simply slide past each other. Seafloor Spreading is the usual process at
work at divergent plate boundaries, leading to the creation of a new ocean
floor. As two tectonic plates slowly separate, molten material rises from

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within the mantle to fill the opening. In this way, the rugged volcanic
landscape of a mid-ocean ridge is created along the plate boundary.
Learning Objectives
After learning this unit, students would be understanding,
• Conceptual evolution and significance of the theory
• Explanation of the theory

• Faults

7.2 Conceptual Evolution

The seafloor spreading hypothesis was proposed by the American
geophysicist Harry H. Hess in 1960. Seafloor spreading is the theory
that oceanic crust forms along submarine mountain zones, known
collectively as the mid-ocean ridge system, and spreads out laterally away
from them. This idea played a pivotal role in the development of the theory
of plate tectonics, which revolutionized geologic thought during the last
quarter of the 20th century.

7.3 Significance of Seafloor spreading

Seafloor spreading helps explain continental drift in the theory of plate
tectonics. When oceanic plates diverge, tensional stress causes fractures
to occur in the lithosphere. The motivating force for seafloor spreading
ridges is tectonic plate slab pull at subduction zones, rather than magma
pressure, although there is typically significant magma activity at
spreading ridges. Plates that are not subducting are driven by gravity
sliding off the elevated mid-ocean ridges a process called ridge push. At a
spreading centre, basaltic magma rises the fractures and cools on the
ocean floor to form a new seabed. Hydrothermal vents are common at
spreading centres. Older rocks will be found farther away from the
spreading zone while younger rocks will be found nearer to the spreading
zone.
Spreading rate is the rate at which an ocean basin widens due to seafloor
spreading. (The rate at which new oceanic lithosphere is added to each
tectonic plate on either side of a mid-ocean ridge is the spreading half-
rate and is equal to half of the spreading rate). Spreading rates determine
if the ridge is fast, intermediate, or slow. Generally, fast ridges have
spreading (opening) rates of more than 90 mm/year. Intermediate ridges
have a spreading rate of 40–90 mm/year while slow-spreading ridges have
a rate less than 40 mm/year. The highest known rate is over 200 mm/yr in
the Miocene on the East Pacific Rise. In the 1960s, the record

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of geomagnetic reversals of Earth's magnetic field was noticed by
observing magnetic stripe "anomalies" on the ocean floor. This results in
broadly evident "stripes" from which the past magnetic field polarity can be
inferred from data gathered with a magnetometer towed on the sea
surface or from an aircraft. The stripes on one side of the mid-ocean ridge
were the mirror image of those on the other side. By identifying a reversal
with a known age and measuring the distance of that reversal from the
spreading centre, the spreading half-rate could be computed. In some
locations spreading rates be asymmetric; the half rates differ on each side
of the ridge crest by about five per cent. This is thought due to
temperature gradients in the asthenosphere from mantle plumes near the
spreading centre.

7.4 Explanation of the theory

According to this theory that oceanic crust forms along
submarine mountain zones, known collectively as the role in the
development of the theory of plate tectonics, which revolutionized geologic
thought during the last quarter of the 20th century. Based on Tharp’s
efforts and other discoveries about the deep-ocean floor, Hess postulated
that molten material from Earth’s mantle continuously wells up along the
crests of the mid-ocean ridges that wind for nearly 80,000 km (50,000
miles) through all the world’s oceans. As the magma cools, it is pushed
away from the flanks of the ridges. This spreading creates a successively
younger ocean floor, and the flow of material is thought to bring about the
migration, or drifting apart, of the continents. The continents bordering
the Atlantic Ocean, for example, are believed to be moving away from the
Mid-Atlantic Ridge at a rate of 1–2 cm (0.4–0.8 inches) per year, thus
increasing the breadth of the ocean basin by twice that amount. Wherever
continents are bordered by deep-sea trench systems, as in the Pacific
Ocean, the ocean floor is plunged downward, underthrusting the
continents and ultimately reentering and dissolving in Earth’s mantle, from
which it had originated.
A veritable legion of evidence supports the seafloor spreading hypothesis.
Studies conducted with thermal probes, for example, indicate that the heat
flow through bottom sediments is generally comparable to that through the
continents except over the mid-ocean ridges, where at some sites
the heat flow measures three to four times the normal value. The
anomalously high values are considered to reflect the intrusion of molten
material near the crests of the ridges. Research has also revealed that the
ridge crests are characterized by anomalously low seismic

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wave velocities, which can be attributed to thermal expansion and micro
fracturing associated with the upwelling magma. Investigations of
oceanic magnetic anomalies have further corroborated the seafloor
spreading hypothesis. Such studies have shown that the strength of
the geomagnetic field is alternately anomalously high and low with
increasing distance away from the axis of the mid-ocean ridge system.
The anomalous features are nearly symmetrically arranged on both sides
of the axis and parallel the axis, creating bands of parallel anomalies.

Fig 7.1 Sea Floor Spreading

Measurements of the thickness of marine sediments and absolute age
determinations of such bottom material have provided additional evidence
for seafloor spreading. The oldest sediments so far recovered by a variety
of methods—including coring, dredging, and deep-sea drilling—date only
to the Jurassic Period, not exceeding about 200 million years in age. Such
findings are incompatible with the doctrine of the permanency of the ocean
basins that had prevailed among Earth scientists for so many years.
Seafloor spreading is a geologic process in which tectonic plates—large
slabs of Earth's lithosphere—split apart from each other. Seafloor
spreading and other tectonic activity processes are the results of mantle
convection. Mantle convection is the slow, churning motion of
Earth’s mantle. Convection currents carry heat from the lower mantle
and core to the lithosphere. Convection currents also “recycle” lithospheric
materials back to the mantle. Seafloor spreading occurs at divergent plate
boundaries. As tectonic plates slowly move away from each other, heat
from the mantle’s convection currents makes the crust more plastic and
less dense. The less-dense material rises, often forming a mountain or

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elevated area of the seafloor. Eventually, the crust cracks.
Hot magma fueled by mantle convection bubbles up to fill these fractures
and spills onto the crust. This bubbled-up magma is cooled
by frigid seawater to form igneous rock. This rock (basalt) becomes a new
part of Earth’s crust.
7.4.1 Mid-Ocean Ridges
Seafloor spreading occurs along mid-ocean ridges—large mountain
ranges rising from the ocean floor. The Mid-Atlantic Ridge, for instance,
separates the North American plate from the Eurasian plate, and the
South American plate from the African plate. The East Pacific Rise is a
mid-ocean ridge that runs through the eastern Pacific Ocean and
separates the Pacific plate from the North American plate, the Cocos
plate, the Nazca plate, and the Antarctic plate. The Southeast Indian
Ridge marks where the southern Indo-Australian plate forms a divergent
boundary with the Antarctic plate. Seafloor spreading is not consistent at
all mid-ocean ridges. Slowly spreading ridges are the sites of tall, narrow
underwater cliffs and mountains. Rapidly spreading ridges have a much
gentler slope. The Mid-Atlantic Ridge, for instance, is a slow-spreading
centre. It spreads 2-5 centimetres (.8-2 inches) every year and forms
an ocean trench about the size of the Grand Canyon. The East Pacific
Rise, on the other hand, is a fast-spreading centre. It spreads about 6-16
centimetres (3-6 inches) every year. There is not an ocean trench at the
East Pacific Rise, because the seafloor spreading is too rapid for one to
develop. The newest, thinnest crust on Earth is located near the centre of
the mid-ocean ridge—the actual site of seafloor spreading. The age,
density, and thickness of oceanic crust increase with distance from the
mid-ocean ridge.

Fig 7.2 Word Mid-Oceanic Ridges

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7.4.2 Geomagnetic Reversals
The magnetism of mid-ocean ridges helped scientists first identify the
process of seafloor spreading in the early 20th century. Basalt, the once-
molten rock that makes up the newest oceanic crust, is a magnetic
substance, and scientists began using magnetometers to measure the
magnetism of the ocean floor in the 1950s. What they discovered was that
the magnetism of the ocean floor around mid-ocean ridges was divided
into matching “stripes” on either side of the ridge. The specific magnetism
of basalt rock is determined by the Earth’s magnetic field when the magma
is cooling. Scientists determined that the same process formed the
perfectly symmetrical stripes on both sides of a mid-ocean ridge. The
continual process of seafloor spreading separated the stripes in an orderly
pattern.
7.4.3 Geographic Features
Oceanic crust slowly moves away from mid-ocean ridges and sites of
seafloor spreading. As it moves, it becomes cooler, denser, and thicker.
Eventually, older oceanic crust encounters a tectonic boundary
with continental crust. In some cases, oceanic crust encounters an active
plate margin. An active plate margin is an actual plate boundary, where
the oceanic crust and continental crust crash into each other. Active plate
margins are often the site of earthquakes and volcanoes. Oceanic crust
created by seafloor spreading in the East Pacific Rise, for instance, may
become part of the Ring of Fire, the horseshoe-shaped pattern of
volcanoes and earthquake zones around the Pacific Ocean basin. In other
cases, oceanic crust encounters a passive plate margin. Passive margins
are not plated boundaries, but areas where a single tectonic
plate transitions from the oceanic lithosphere to the continental
lithosphere. Passive margins are not sites of faults or subduction zones.
Thick layers of sediment overlay the transitional crust of a passive margin.
The oceanic crust of the Mid-Atlantic Ridge, for instance, will either
become part of the passive margin on the North American plate (on the
east coast of North America) or the Eurasian plate (on the west coast of
Europe). New geographic features can be created through seafloor
spreading. The Red Sea, for example, was created as the African Plate
and the Arabian plate tore away from each other. Today, only the Sinai
Peninsula connects the Middle East (Asia) with North Africa.
Eventually, geologists predict, seafloor spreading will separate the
two continents—and join the Red and Mediterranean Seas.

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 Mid-ocean ridges and seafloor spreading can also influence sea levels.
As oceanic crust moves away from the shallow mid-ocean ridges, it cools
and sinks as it becomes denser. This increases the volume of the ocean
basin and decreases the sea level. For instance, a mid-ocean ridge
system in Panthalassa—an ancient ocean that surrounded
the supercontinent Pangaea—contributed to shallower oceans and higher
sea levels in the Paleozoic era. Panthalassa was an early form of the
Pacific Ocean, which today experiences less seafloor spreading and has a
much less extensive mid-ocean ridge system. This helps explain why sea
levels have fallen dramatically over the past 80 million years.

7.4 Conclusion
Seafloor spreading disproves an early part of the theory of continental
drift. Supporters of continental drift originally theorized that the continents
moved (drifted) through unmoving oceans. Seafloor spreading proves that
the ocean itself is a site of tectonic activity. Keeping Earth in Shape
Seafloor spreading is just one part of plate tectonics. Subduction is
another. Subduction happens when tectonic plates crash into each other
instead of spreading apart. At subduction zones, the edge of the denser
plate subducts, or slides, beneath the less dense one. The denser
lithospheric material then melts back into the Earth's mantle. Seafloor
spreading creates a new crust. Subduction destroys old crust. The two
forces roughly balance each other, so the shape and diameter of the Earth
remain constant.

Let Us Sum Up
The seafloor spreading hypothesis was proposed by the American
geophysicist Harry H. Hess in 1960. Seafloor spreading is the theory
that oceanic crust forms along submarine mountain zones, known
collectively as the mid-ocean ridge system, and spreads out laterally away
from them. Seafloor Spreading is the usual process at work at divergent
plate boundaries, leading to the creation of a new ocean floor. Seafloor
spreading helps explain continental drift in the theory of plate tectonics.
When oceanic plates diverge, tensional stress causes fractures to occur in
the lithosphere. The motivating force for seafloor spreading ridges is
tectonic plate slab pull at subduction zones, rather than magma pressure,
although there is typically significant magma activity at spreading
ridges. Plates that are not subducting are driven by gravity sliding off the
elevated mid-ocean ridges a process called ridge push. Seafloor
spreading disproves an early part of the theory of continental drift.

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Supporters of continental drift originally theorized that the continents
moved (drifted) through unmoving oceans.

Glossaries
Geophysicist: a person who studies geophysics

Panthalassa: an ancient ocean that surrounded the supercontinent

Pangaea: contributed to shallower oceans and higher sea levels in the
Paleozoic era.
Subduction: the sideways and downward movement of the edge of a
plate of the earth's crust into the mantle beneath another plate.
Geomagnetic field: geomagnetic field is the magnetic field that extends
from the Earth's interior out into space, where it interacts with the solar
wind, a stream of charged particles emanating from the Sun.
Mid-Ocean ridges: a long, seismically active submarine ridge system
situated in the middle of an ocean basin and marking the site of the
upwelling of magma associated with sea-floor spreading. An example is
the Mid-Atlantic Ridge.

Check Your Progress

1. What is the seafloor spreading theory deal with?
Seafloor spreading is the theory that oceanic crust forms along
submarine mountain zones, known collectively as the mid-ocean ridge
system, and spreads out laterally away from them.
2. Bring out the significance of the seafloor spreading theory.
Seafloor spreading helps explain continental drift in the theory of plate
tectonics. When oceanic plates diverge, tensional stress causes fractures
to occur in the lithosphere. The motivating force for seafloor spreading
ridges is tectonic plate slab pull at subduction zones, rather than magma
pressure, although there is typically significant magma activity at
spreading ridges.
3. Write a note on Harry H. Hess.

The American geophysicist Harry H. Hess in 1960 the seafloor

spreading hypothesis was proposed

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Suggested Readings
1. Charles F. Kahle, Plate Tectonics- Assessments and Reassessments
2. The dynamic earth: textbook in geosciences: Wyllie, P. J. New York,
John Wiley
3. Hess, H. H., 1960, Evolution, ocean basin: Princeton Univ. Press
Preprint for "The sea, ideas and observations,"
4. A. B. Watts, Isostasy and Flexure of the Lithosphere (Cambridge,
2001).

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 UNIT 8
PLATE TECTONIC THEORY
Structures
8.1 Overview
Learning Objectives
8.2 Significance of the Theory

8.3 Explanation of Plate Tectonic Theory:

8.3.1 Divergent Boundaries
8.3.2 Convergent Boundaries

8.3.3 Transform Boundaries

8.3.4 Rates of Plate Movement
8.3.5 Force for the Plate Movement
8.3.6 Movement of the Indian Plate
8.4 Conclusion
Let us sum up
Glossary
Check your progress
Suggested readings

8.1 Overview
The concept of Plate Tectonics was first coined by the German
geophysicist Alfred Wegener back in 1915, but several ideas of continental
drift date back many years before. Plate Tectonic theory is, in fact, the
outcome of the combined efforts of many scientists of different countries
working together and separately. This theory came to light in the year
1960. Today we almost take for granted our knowledge of how the Earth’s
crust shifts and regenerates on a continual cycle; but the theory of plate
tectonics wasn’t widely accepted until the 1960s! It was in 1967, McKenzie
Parker and Morgan, independently collected the available ideas and came
out with another concept termed Plate Tectonics. The term ‘Plate’ was first
used by Canadian Geologist J.T.Wilson in the year 1965.

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Learning Objectives
After learning this unit, students would be learning the Significance and
the explanation of Plate Tectonic Theory:

8.2 Significance of the Theory

Plate tectonic theory is a comprehensive theory that is used to explain the
structure of the Earth’s crust and offers an explanation for various relief
features and tectonic events viz. mountain building, folding, faulting,
continental drift, volcanic activity, seismic events etc. The theory belongs
to a host of scientists of different disciplines.

8.3 Explanation of Plate Tectonic Theory

According to this theory, the rigid lithosphere is split into 7 major ‘plates’
that slowly move on top of the underlying asthenosphere (mantle). This
branch of geology studies the faulting and folding of the crust along the
various boundaries; convergent, divergent, subduction, and conservative.
A tectonic plate (also called a lithospheric plate) is a massive, irregularly
shaped slab of solid rock, generally composed of both continental and
oceanic lithosphere. Plates move horizontally over the asthenosphere as
rigid units. The lithosphere includes the crust and top mantle with its
thickness range varying between 5-100km in oceanic parts and about 200
km in the continental areas. A plate may be referred to as the continental
plate or oceanic plate depending on which of the two occupy a larger
portion of the plate. The Pacific plate is largely oceanic whereas the
Eurasian plate may be called a continental plate. The theory of plate
tectonics proposes that the earth’s lithosphere is divided into seven major
and some minor plates. Young Fold Mountain ridges, trenches, and/or
faults surround these major plates.

The major plates are as follows :(i) Antarctica and the surrounding oceanic
plate (ii) North American (with western Atlantic floor separated from the
South American plate along with the Caribbean islands) plate (iii) South
American (with western Atlantic floor separated from the North American
plate along with the Caribbean islands) plate (iv) Pacific plate (v) India-
Australia-New Zealand plate (vi) Africa with the eastern Atlantic floor plate
(vii) Eurasia and the adjacent oceanic plate. Some important minor plates
are listed below: (i) Cocos plate: Between Central America and Pacific
plate (ii) Nazca plate: Between South America and Pacific plate (iii)
Arabian plate: Mostly the Saudi Arabian landmass (iv) Philippine plate:
Between the Asiatic and Pacific plate (v) Caroline plate: Between the
Philippine and Indian plate (North of New Guinea) (vi) Fuji plate: North-

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east of Australia. These plates have been constantly moving over the
globe throughout the history of the earth. It is not the content that moves
as believed by Wegener. Continents are part of a plate and what moves is
the plate. Moreover, it may be noted that all the plates, without exception,
have moved in the geological past, and shall continue to move in the
future as well. Wegener had thought of all the continents to have initially
existed as a supercontinent in the form of Pangaea. However, later
discoveries reveal that the continental masses, resting on the plates, have
been wandering all through the geological period, and Pangaea was a
result of the converging of different continental masses that were parts of
one or the other plates. Scientists using the palaeomagnetic data have
determined the positions held by each of the present continental
landmasses in different geological periods (Fig 8.1). The position of the
Indian subcontinent (mostly Peninsular India) is traced with the help of the
rocks analysed from the Nagpur area.

Fig.8.1 Types of Plate Boundaries

Plate boundaries are the edges where two plates meet. Most geologic
activities, including volcanoes, earthquakes, and mountain building, take
place at plate boundaries. How can two plates move relative to each
other?
There are three types of plate boundaries:
• Divergent plate boundaries: the two plates move away from each
other.
• Convergent plate boundaries: the two plates move towards each
other.

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• Transform plate boundaries: the two plates slip past each other.
8.3.1 Divergent Boundaries
Where the new crust is generated as the plates pull away from each other.
The sites where the plates move away from each other are called
spreading sites. The best-known example of divergent boundaries is the
Mid-Atlantic Ridge. At this, the American Plate(s) is/are separated from the
Eurasian and African Plates.
8.3.2 Convergent Boundaries
Where the crust is destroyed as one plate dived under another. The
location where the sinking of a plate occurs is called a subduction zone.
There are three ways in which convergence can occur. These are: (i)
between an oceanic and continental plate; (ii) between two oceanic plates;
and (iii) between two continental plates.
8.3.3 Transform Boundaries
Where the crust is neither produced nor destroyed as the plates slide
horizontally past each other. Transform faults are the planes of separation
generally perpendicular to the mid-oceanic ridges. As the eruptions do not
take all along the entire crest at the same time, there is a differential
movement of a portion of the plate away from the axis of the earth. Also,
the rotation of the earth affects the separated blocks of the plate portions.
How do you think the rate of plate movement is determined?
8.3.4 Rates of Plate Movement
The strips of the normal and reverse magnetic fields that parallel the mid-
oceanic ridges help scientists determine the rates of plate movement.
These rates vary considerably. The Arctic Ridge has the slowest rate (less
than 2.5 cm/yr), and the East Pacific Rise near Easter Island, in the South
Pacific about 3,400 km west of Chile, has the fastest rate (more than 15
cm/yr).
8.3.5 Force for the Plate Movement
At the time that Wegener proposed his theory of continental drift, most
scientists believed that the earth was a solid, motionless body. However,
concepts of seafloor spreading, and the unified theory of plate tectonics
has emphasised that both the surface of the earth and the interior are not
static and motionless but are dynamic. The fact that the plates move is
now a well-accepted fact. The mobile rock beneath the rigid plates is
believed to be moving circularly. The heated material rises to the surface,
spreads, begins to cool, and then sinks back into deeper depths. This

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cycle is repeated over and over to generate what scientists call a
convection cell or convective flow. Heat within the earth comes from two
main sources: radioactive decay and residual heat. Arthur Holmes first
considered this idea in the 1930s, which later influenced Harry Hess’
thinking about seafloor spreading. The slow movement of the hot, softened
mantle that lies below the rigid plates is the driving force behind the plate
movement.
8.3.6 Movement of the Indian Plate
The Indian plate includes Peninsular India and the Australian continental
portions. The subduction zone along the Himalayas forms the northern
plate boundary in the form of continent-continent convergence. In the east,
it extends through the Rakinyoma Mountains of Myanmar towards the
island arc along the Java Trench. The eastern margin is a spreading site
lying to the east of Australia in the form of an oceanic ridge in the SW
Pacific. The Western margin follows the Kirthar Mountain of Pakistan. It
further extends along the Makrana coast and joins the spreading site from
the Red Sea rift southeastward along the Chagos Archipelago. The
boundary between India and the Antarctic plate is also marked by an
oceanic ridge (divergent boundary) running in roughly W-E direction and
merging into the spreading site, a little south of New Zealand. India was a
large island situated off the Australian coast, in a vast ocean. The Tethys
Sea separated it from the Asian continent till about 225 million years ago.
India is supposed to have started her northward journey about 200 million
years ago at the time when Pangaea broke. India collided with Asia about
40-50 million years ago causing rapid uplift of the Himalayas. The
positions of India from about 71 million years till the present. It also shows
the position of the Indian subcontinent and the Eurasian plate. About 140
million years before the present, the subcontinent was located as south as
50oS Latitude. The two major plates were separated by the Tethys Sea
and the Tibetan block was closer to the Asiatic landmass. During the
movement of the Indian plate towards the Asiatic plate, a major event was
that occurred the outpouring of lava and formation of the Deccan Traps.
This started somewhere around 60 million years ago and continued for a
long period. Note that the subcontinent was still close to the equator. From
40 million years ago and thereafter, the event of formation of the
Himalayas took place. Scientists believe that the process is continuing,
and the height of the Himalayas is rising even to this date.

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8.4 Conclusion
Plate tectonic theory is a revolutionary theory it helps to understand that
from the deepest ocean trench to the tallest mountain, plate tectonics
explains the features and movement of Earth's surface in the present and
the past. Plates of the lithosphere move because of convection currents in
the mantle. One type of motion is produced by seafloor spreading. Plate
boundaries can be located by outlining earthquake epicentres. Plates
interact at three types of plate boundaries: divergent, convergent and
transform. Most of the Earth’s geologic activity takes place at plate
boundaries. At a divergent boundary, volcanic activity produces a mid-
ocean ridge and small earthquakes. At a convergent boundary with at
least one oceanic plate, an ocean trench, a chain of volcanoes develops,
and many earthquakes occur. At a convergent boundary where both
plates are continental, mountain ranges grow, and earthquakes are
common. At a transform boundary, there is a transform fault and massive
earthquakes occur but there are no volcanoes. Processes acting over long
periods create Earth’s geographic features.

Let Us Sum Up
Plate Tectonic theory is, in fact, the outcome of the combined efforts of
many scientists of different countries working together and separately.
This theory came to light in the year 1960. Plate tectonic theory is a
comprehensive theory that is used to explain the structure of the Earth’s
crust and offers an explanation for various relief features and tectonic
events viz. mountain building, folding, faulting, continental drift, volcanic
activity, seismic events etc. There are three types of plate boundaries:
Divergent plate boundaries: the two plates move away from each other.
Convergent plate boundaries: the two plates move towards each other.
Transform plate boundaries: the two plates slip past each other.

Glossaries
Asthenosphere: zone of Earth's mantle lying beneath the lithosphere and
believed to be much hotter and more fluid than the lithosphere.
The asthenosphere extends from about 100 km (60 miles) to about 700
km (450 miles) below Earth's surface. Cross-section of a tectonic plate.

Lithospheric plate: A tectonic plate is a massive, irregularly shaped slab

of solid rock, generally composed of both continental and oceanic
lithosphere.
Subduction zone: Subduction is a geological process that takes place at
convergent boundaries of tectonic plates where one plate moves under

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another and is forced to sink due to high gravitational potential energy into
the mantle.
Plate boundaries: Which are the edges where two plates meet.

Transform plate boundaries: the two plates slip past each other.

Check Your Progress

1. Write a note on Alfred Wegner.
The concept of Plate Tectonics was first coined by the German
geophysicist Alfred Wegener back in 1915.
2. State different kinds of boundaries.
There are three types of plate boundaries:

• Divergent plate boundaries: the two plates move away from each
other.
• Convergent plate boundaries: the two plates move towards each
other.
• Transform plate boundaries: the two plates slip past each other.
3. Bring out the significance of Plate Tectonic Theory.

Plate tectonic theory is a comprehensive theory that is used to explain the

structure of the Earth’s crust and offers an explanation for various relief
features and tectonic events viz. mountain building, folding, faulting,
continental drift, volcanic activity, seismic events etc. The theory belongs
to a host of scientists of different disciplines.

Suggested Readings
1. 1. Das Gupta, A & Kapoor, A.N., (2001) Principles of Physical
Geography, S.C. Chand & Company Ltd. New Delhi.
2. Khullar, D.R., (2012) Physical Geography, Kalyani Publishers, New
Delhi.

3. Brown, J.H. (2005) Biogeography, Sinauer Associates Inc,

Sunderland.
4. Seddon, B.A. (1971) Overview to Biogeography, Duckworth, London.

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 UNIT 9
Earthquakes and Volcanoes
Structures
9.1 Overview
Learning Objectives

9.2 Earthquakes
9.3 Causes of Earthquakes
9.3.1 Tectonic earthquake
9.3.2 Volcanic earthquake

9.3.3 Explosion earthquake

9.4 World distribution of Earthquakes
9.5 Tsunami

9.6 volcanoes
9.6.1. Volcanic Material
9.6.2 Types of Volcanoes:
9.7 World Distribution of Volcanoes
9.7.1 Forecast of volcanicity
Let us sum up
Glossary
Check your progress
Suggested readings

9.1 Overview
Earth’s surface, on which humankind lives, exhibits an endless variability
in morphological forms. The continental exteriors vary from mountain belts
and volcanic chains to hilly areas and flat lowlands, the oceanic bottom
rises from large abyssal plains to seamounts and ridges and falls to
narrow trenches. All this variability is an expression of the ever-present
competition of two classes of energetic sources. The first class is the heat
production in Earth’s interior that generates forces known in geology as
internal or endogenous. The internal forces drive all the vertical and

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horizontal movements of the Earth’s crust and are responsible for some
severe disasters such as earthquakes or volcanic eruptions. The second
class—the external or exogenous forces—is generated by energetic input
from the Sun. They trigger emotions in Earth’s hydrosphere and
atmosphere and tend, through weathering, erosion, and sedimentation, to
decrease the morphological expressiveness created by internal forces.
This is an expression of the second theorem of thermodynamics predicting
dissipative exchange of energy between systems that are in mutual
disequilibrium. Generally, if there were no atmosphere and hydrosphere
on Earth, the internal forces would produce extremely rugged surface
morphology with any kind of steep positive or negative forms that could
sustain gravitational forces. On the other hand, if there were no internal
forces, erosion would quickly diminish all morphological variations and
Earth would become a boringly flat spheroid body.
Learning Objectives
After studying this unit, you will learn about, Volcanoes, types, causes and
consequences and the World Distribution of Volcanoes.

9.2 Earthquakes
An earthquake is a sudden shaking or trembling of the earth which lasts
for a very short time. It is caused by a disturbance deep inside the earth’s
crust. Earthquakes occur all the time, all over the earth. They are not even
noticed. Major earthquakes are much less frequent. They can cause
immense damage to buildings, bridges, dams, and people. There can be a
great loss to life and property. Earthquakes can cause floods, landslides,
and tsunamis. About 50,000 earthquakes large enough to be noticed
without the aid of instruments occur annually over the entire Earth. Of
these, approximately 100 are of sufficient size to produce substantial
damage if their centres are near areas of habitation. Very great
earthquakes occur on average about once per year. Over the centuries
they have been responsible for millions of deaths and an incalculable
amount of property damage. Little was understood about earthquakes until
the emergence of seismology at the beginning of the 20th
century. Seismology, which involves the scientific study of all aspects of
earthquakes, has yielded answers to such long-standing questions as to
why and how earthquakes occur.
An earthquake can be defined as any sudden shaking of the ground
caused by the passage of seismic waves through Earth’s rocks. Seismic
waves are produced when some form of energy stored in Earth’s crust is
suddenly released, usually when masses of rock straining against one

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another suddenly fracture and “slip.” Earthquakes occur most often along
geologic faults, narrow zones where rock masses move about one
another. The major fault lines of the world are located at the fringes of the
huge tectonic plates that make up Earth’s crust.

9.3 Causes of Earthquakes

Mainly, there are four types of earthquakes namely tectonic, volcanic,
collapse and explosion.
9.3.1 Tectonic earthquake:
This occurs when geological forces on rocks and the adjoining plate’s
cause’s a physical and chemical change and result in the breaking of the
Earth's crust. Earthquakes are caused by the sudden release
of energy within some limited region of the rocks of the Earth. The energy
can be released by elastic strain, gravity, chemical reactions, or even the
motion of massive bodies. Of all these the release of elastic strain is the
most important cause, because this form of energy is the only kind that
can be stored in sufficient quantity on the Earth to produce major
disturbances. Earthquakes associated with this type of energy release are
called tectonic earthquakes.
9.3.2 Volcanic earthquake:
Results from tectonic forces occur in conjunction with volcanic activity.
Volcanic activity is one of the major causes of earthquakes. In other
words, each volcanic eruption is followed by earthquakes and many of the
severe earthquakes cause volcanic eruptions. Collapse earthquakes are
generally small earthquakes that occur in underground caverns and mines
caused by the seismic waves which are produced from the explosion of
rock on the surface.
9.3.3 Explosion earthquake:
Occur due to the detonation of a nuclear or chemical device.

Seismology is the science that studies various aspects of seismic waves

generated during the occurrence of earthquakes. Seismic waves are
recorded with the help of an instrument known as a Seismograph. The
place of the occurrence of an earthquake is called ‘focus’ and the place
which experiences the seismic event first is called ‘epicentre’. Which is
located on the earth’s surface and is always perpendicular to the ‘focus’.
On the other hand, the focus, or the place of the origin of the earthquake is
always inside the earth. The instrumental scales used to describe the size
of an earthquake began with the Richter magnitude scale in the 1930s. It

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is a relatively simple measurement of an event's amplitude, and its use
has become minimal in the 21st century. Seismic waves travel through
the Earth's interior and can be recorded by seismometers at great
distances. The surface wave magnitude was developed in the 1950s to
measure remote earthquakes and to improve the accuracy for larger
events. The moment magnitude scale not only measures the amplitude of
the shock but also considers the seismic moment (total rupture area,
average slip of the fault, and rigidity of the rock). The Japan
Meteorological Agency seismic intensity scale, the Medvedev–
Sponheuer–Karnik scale and the Mercalli intensity scale are based on the
observed effects and are related to the intensity of shaking.
The different types of tremors and waves generated during the occurrence
of an earthquake are called ‘seismic waves which are generally divided
into 3 broad categories e.g., primary waves, secondary waves and surface
waves.

(i) Primary waves are also called Longitudinal waves or compressional

waves or simply ‘P’ waves, are analogous to sound waves wherein
particles move both to and fro in the line of the propagation of the ray. ‘P’
waves travel at the fastest speed through solid materials. Though they are
also pass-through liquid materials, their speed is slowed down. In the
upper crust, P-waves travel in the range of 2–3 km per second in soils and
unconsolidated sediments, increasing to 3–6 km per second in solid rock.
In the lower crust, they travel at about 6–7 km per second; the velocity
increases within the deep mantle to about 13 km per second. In the
Earth's interior, the shock- or P-waves travel much faster than the S-
waves.

Fig.9.1 Seismic waves

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(ii) Secondary waves are also called Transverse waves or simply ‘S’
waves. These are analogous to water ripples or light waves wherein the
particles move at right angles to the rays. ‘S’ waves cannot pass through
liquid materials. The velocity of S-waves ranges from 2–3 km per second
in light sediments and 4–5 km per second in the Earth's crust up to 7 km
per second in the deep mantle. Consequently, the first waves of a distant
earthquake arrive at an observatory via the Earth's mantle. S-waves and
later arriving surface waves do most of the damage compared to P-waves.
S-waves shake the ground up and down and back and forth.

(iii) Surface waves are also called long-period waves or simply ‘L’ waves.
These waves generally affect only the surface of the earth and die out at
smaller depths. These waves cover the longest distances of all the seismic
waves through their speed is lower than ‘P’ and ‘S’ waves, these are most
violent and destructive.

9.4 World distribution of earthquakes:

Earth’s major earthquakes occur mainly in belts coinciding with the
margins of tectonic plates. This has long been apparent from early
catalogues of felt earthquakes and is even more readily discernible in
modern seismicity maps, which show instrumentally determined
epicentres. The most important earthquake belt is the Circum-Pacific Belt,
which affects many populated coastal regions around the Pacific Ocean—
for example, those of New Zealand, New Guinea, Japan, the Aleutian
Islands, Alaska, and the western coasts of North and South America. It is
estimated that 80 per cent of the energy presently released in earthquakes
comes from those whose epicentres are in this belt. The seismic activity is
by no means uniform throughout the belt, and there are several branches
at various points. Because at many places the Circum-Pacific Belt is
associated with volcanic activity, it has been popularly dubbed the
“Pacific Ring of Fire.”
A second belt, known as the Alpine Belt, passes through the
Mediterranean region eastward through Asia and joins the Circum-Pacific
Belt in the East Indies. The energy released in earthquakes from this belt
is about 15 per cent of the world total. There also are striking connected
belts of seismic activity, mainly along oceanic ridges—including those in
the Arctic Ocean, the Atlantic Ocean, and the western Indian Ocean—and
along the rift valleys of East Africa. This global seismicity distribution is
best understood in terms of its plate tectonic setting.

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 Fig. 9.2 World Distribution of Earthquakes
Sources: https://www.geo41.com/

9.5 Tsunami
Tsunami, (Japanese: “harbour wave”) also called seismic sea
wave or tidal wave, catastrophic ocean wave, usually caused by a
submarine earthquake, an underwater or coastal landslide, or
a volcanic eruption. The term tidal wave is frequently used for such a
wave, but it is a misnomer, for the wave has no connection with the tides.
A tsunami is a series of ocean waves that sends surges of water,
sometimes reaching heights of over 100 feet (30.5 meters), onto land.
These walls of water can cause widespread destruction when they crash
ashore.
What Causes a Tsunami?
The giant waves are typically caused by large,
undersea earthquakes at tectonic plate boundaries. When the ocean floor
at a plate boundary rises or falls suddenly, it displaces the water above it
and launches the rolling waves that will become a tsunami. Most
tsunamis–about 80 per cent–happen within the Pacific Ocean’s “Ring of
Fire,” a geologically active area where tectonic shifts make volcanoes and
earthquakes common. Tsunamis may also be caused by underwater
landslides or volcanic eruptions. They may even be launched, as they

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frequently were in Earth’s ancient past, by the impact of a large meteorite
plunging into an ocean. Tsunamis can travel across the sea at up to 500
miles (805 kilometres) an hour—about as fast as a jet aeroplane. At that
speed, they can cross the entire expanse of the Pacific Ocean in less than
a day. And their long wavelengths mean they lose very little energy along
the way.

Fig. 9.3 Types of faults

In the Deep Ocean, tsunami waves may appear only a foot or so high. But
as they approach the shoreline and enter shallower water they slow down
and begin to grow in energy and height. The tops of the waves move
faster than their bottoms do, which causes them to rise precipitously. A
tsunami’s trough, the low point beneath the wave’s crest, often reaches
shore first. When it does, it produces a vacuum effect that sucks coastal
water seaward and exposes harbour and sea floors. This retreating of
seawater is an important warning sign of a tsunami because the wave’s
crest and its enormous volume of water typically hit shore five minutes or
so later. Recognizing this phenomenon can save lives. The Pacific
Tsunami Warning System, a coalition of 26 nations headquartered in
Hawaii, maintains a web of seismic equipment and water level gauges to
identify tsunamis at sea. Similar systems are proposed to protect coastal
areas worldwide.

Types of faulting in tectonic earthquakes in normal and reverse faulting,

rock masses slip vertically past each other. In strike-slip faulting, the rocks
slip past each other horizontally.

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9.6 volcanoes
A mountain or hill, typically conical, has a crater or vent through which
lava, rock fragments, hot vapour, and gas are or have been erupted from
the earth's crust otherwise it can be defined as A volcano on Earth is a
vent or fissure in the planet's crust through which lava, ash, rock and
gases erupt. A volcano is also a mountain formed by the accumulation of
these eruptive products. A volcanologist is a geologist who studies the
processes involved in the formation and eruptive activity of volcanoes and
their current and historic eruptions, known as volcanology.

Fig. 9.4 Components of Volcanoes

• Magma: Molten rock beneath Earth’s surface.

• Parasitic Cone: A small cone-shaped volcano formed by an
accumulation of volcanic debris
• Sill: A flat piece of rock formed when magma hardens in a crack in a
volcano
• Vent: An opening in Earth’s surface through which volcanic materials
escape.
• Flank: The side of the volcano
• Lava: Molten rock that erupts from a volcano that solidifies as it cools.
• Crater: Mouth of Volcano-surrounds a volcanic vent
• Conduit: underground passage magma travels through.
• Summit: Highest point; apex
• Throat: Entrance of a volcano. The part of the conduit that ejects lava
and volcanic ash

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• Ash: Fragments of Lava or rock smaller than 2 mm in size that is
blasted into the air by volcanic explosions.
• Ash Cloud: A cloud of ash formed by volcanic explosions.
9.6.1. Volcanic Material
1. Vapour and gases: Steam and vapour constitute 60 to 90% of total
gases discharged during a volcanic eruption. The gases include. Water
vapour is typically the most abundant volcanic gas, followed by carbon
dioxide and sulfur dioxide. hydrogen sulfide, hydrogen chloride,
and hydrogen fluoride. hydrogen, carbon monoxide, halocarbons, organic
compounds, and volatile metal chlorides.
2. Magma and lava: Generally molten rock material below the earth
surface is called magma while they are called lava when they come to the
earth’s surface. The mineral composition of the magma is the most
important factor determining the nature of a volcanic eruption. Types of
Lava: 1. Basic laves: There are highly fluid. They are dark coloured like
basalt, rich in iron and magnesium but poor in silica. They are affected in
extensive areas, spreading out as thin sheets. The resultant volcano is
gently sloping with a wide diameter and form a flattened shield or dome. 2.
Acid lavas: These lavas are highly viscous with a melting point. They are
light-coloured, of low density, and have a high percentage of silica. They
flow light-coloured, of low density, and have a high percentage of silica.
They slowly and seldom travel far. The resultant cone is therefore steep-
sided. Geysers are springs that throw boiling water high in the air. They
are caused by volcanic heat warming trapped groundwater.
3. Pyroclastic or fragmental material: There is pyroclastic material,
volcanic ash, lapilli, blocks and volcanic “bombs.”
9.6.2Types of Volcanoes:
Generally, volcanoes are classified as active, dormant, and extinct.
An active volcano that erupts regularly is considered an active volcano
otherwise an active volcano has erupted since the last ice age (i.e., in the
10,000 years). Current active volcanoes around the world include Mount
Fujiyama in Jpan, Mount Etna (Sicily, Italy); Mount Nyiragongo (the
Democratic Republic of the Congo); and Mount Kilauea (Hawaii, United
States.
A dormant volcano would then not have erupted in the past 10,000
years, but it is expected to erupt again other words it can be defined as a
dormant volcano as any volcano that is not showing any signs of unrest
but could become active again. Examples of dormant volcanoes include

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Krakatoa in Indonesia, Mount Pelee in the Caribbean Island Four-Peaked
Mountain (Alaska, United States); Mount Pinatubo (Philippines), and
Soufriere Hills (Montserrat).
An extinct volcano is a volcano that is no longer active. An extinct
volcano has not erupted over the last ice age, which ended approximately
10,000 years ago, and is not expected to erupt again in the future.
Volcanoes believed to be extinct around the world include Zuidwal
Volcano (Netherlands); the Emperor-Seamount chain (Hawaii, United
States); and Mount Kulal (Kenya).

Volcanologists classify eruptions into several different types some of the

most common types of eruptions:
Hawaiian Eruption: In a Hawaiian eruption, fluid basaltic lava is thrown
into the air in jets from a vent or line of vents (a fissure) at the summit or
on the flank of a volcano.
Strombolian Eruption: Strombolian eruptions are distinct bursts of fluid
lava from the mouth of a magma-filled summit conduit. The explosions
usually occur every few minutes at regular or irregular intervals. The
explosions of lava, which can reach heights of hundreds of meters, are
caused by the bursting of large bubbles of gas, which travel upward in the
magma-filled conduit until they reach the open air.
Vulcanian Eruption: A Vulcanian eruption is a short, violent, relatively
small explosion of viscous magma. Vulcanian eruptions create powerful
explosions in which material can travel faster than 350 meters per second
(800 mph) and rise several kilometres into the air.
Plinian Eruption: The largest and most violent of all the types of volcanic
eruptions are Plinian eruptions. They are caused by the fragmentation of
gassy magma and are usually associated with very viscous magmas.
Lava Domes: Lava domes form when very viscous, rubbly lava is
squeezed out of a vent without exploding. The lava piles up into a dome,
which may grow by inflating from the inside or by squeezing out lobes of
lava.

9.7 World Distribution of Volcanoes

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There is a close relationship between volcanic activity, earthquakes, and
plate tectonics, with many volcanoes located above subduction zones and
in axial rifts. Around 80% of volcanic activity is found along subduction
boundaries. Mid-ocean spreading centres and continental rifts account for
around 15% of volcanic activity. Rest is intra-plate volcanism.

Fig.9.4 World Distribution of Volcanoes

There is a close relationship between volcanic activity, earthquakes, and
Mid-Atlantic belt: A few basaltic volcanoes of fissure eruption type also
occur along the mid-oceanic ridge, where seafloor spreading is in
progress.
Circum-Pacific ring of fire: Most of the high volcanic cones and volcanic
mountains are found in this belt, where there is active subduction of the
Pacific, Nazca, Cocos, and Juan de Fuca plates. One good example is the
volcanic of Sumatra and Java, which lies over the subduction zone
between the Australian Plate and the Eurasian plate.

Mid-Continental belt: It includes volcanoes of the alpine mountain chains

and the Mediterranean Sea and those in the fault zone of Eastern Africa.
Here volcanoes are caused due to the collision of African, Eurasian, and
Indian plates.

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Intra-plate volcanoes are scattered in the inner parts of plates away from
the margins. There are also called Hot spot volcanoes as they occur in the
middle of plate boundaries where magma exits from weaknesses in the
earth’s surface. The Hawaiian Islands are an example of hot spot
volcanoes.
9.7.1 Forecast of volcanicity
By studying the type of materials and distribution of deposits geologists
can learn a lot about the activity of volcanoes. Eruptions can be predicted
in several ways: Tiltmeters are very sensitive devices that are used to
identify any bulging of the sides of a volcano. The increased pressure
causes the volcano’s sides to bulge out indicating an eruption may be
about to happen. Gases or steam coming out of vents in the volcano, or
the appearance of geysers could suggest an eruption will soon follow.
Seismometers are used to detect vibrations in the rock. These could be
caused by the movement of the magma or the cracking of rocks due to
increased heat both would indicate an eruption being imminent.

Let Us Sum Up
The internal forces drive all the vertical and horizontal movements of the
Earth’s crust and are responsible for some severe disasters such as
earthquakes or volcanic eruptions. An earthquake is a sudden shaking or
trembling of the earth which lasts for a very short time. Mainly, there are
four types of earthquakes namely tectonic, volcanic, collapse and
explosion. The different types of tremors and waves generated during the
occurrence of an earthquake are called ‘seismic waves which are
generally divided into 3 broad categories e.g., primary waves, secondary
waves and surface waves. A volcano on Earth is a vent or fissure in the
planet's crust through which lava, ash, rock, and gases erupt. Generally,
volcanoes are classified as active, dormant, and extinct.

Glossaries
Seismograph: Seismic waves are recorded with the help of an
instrument.
‘focus’: The place of the occurrence of an earthquake is called
‘epicentres’ the place which experiences the seismic event first is called.
Crater: Mouth of Volcano-surrounds a volcanic vent.
Lava: Molten rock that erupts from a volcano that solidifies as it cools.

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A volcanologist is a geologist who studies the processes involved in the
formation and eruptive activity of volcanoes and their current and historic
eruptions, known as volcanology.
Tilt meters are very sensitive devices that are used to identify any bulging
of the sides of a volcano.
A tsunami is a series of ocean waves that sends surges of water

Seismology: which refers that the scientific study of all aspects of

earthquakes.

Check Your Progress

1. Earthquake-Define.

An earthquake is a sudden shaking or trembling of the earth which

lasts for a very short time.
2. State the causes of earthquakes.

Causes of Earthquakes are mainly, there are four types of earthquakes

namely tectonic, volcanic, collapse and explosion.
3. Write a note on Seismology.
Seismology is the science that studies various aspects of seismic
waves generated during the occurrence of earthquakes.
4. Write about the focus and epicentre.
The place of the occurrence of an earthquake is called ‘focus’ and. the
place which experiences the seismic event first is called ‘epicentre’.

Suggested Readings
1. Huggett, R.J. (2007) Fundamentals of Geomorphology, Routledge,
New York.
2. Das Gupta, A., and Kapoor, A.N, Principles of Physical Geography,
S.C. Chand & Company Ltd, 2001.

3. Lobeck. A.K., An Overview to the study of Landscapes, McGraw –Hill

Book Company, 1939
4. Thorn Bury.D., - Principles of Geomorphology, Wiley Eastern Ltd, New
Delhi, 1984

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 UNIT 10
Weathering
Structures
10.1 Overview
Learning Objectives
10.2 Weathering
10.3 Significance of weathering
10.4 Controlling factors of Weathering
10.5 Types of Weathering

10.5.1 Physical weathering

10.5.1.1 Thermal weathering
10.5.1.2 Frost Wedging
10.5.1.3 Exfoliation
10.5.2 Chemical Weathering
10.5.3 Biological Weathering
10.6 Mass wasting
10.6.1.2 Slump
10.6.1.3 Debris Slide
10.6.1.4 Debris flows
10.6.1.5 Soil creep
Let us sum up

Glossary
Check your progress
Suggested Readings

10.1 Overview
Rocks are disintegrated and decomposed and ultimately are broken down
into smaller pieces due to the operation of different weathering processes.
Weathering helps erosional processes by weathering processes loosens
the rocks by disintegration and decomposing them and thus paves the

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way for erosional processes to operate easily. Continuous removal and
transfer of weathered materials through different processes of mass
translocation of rock wastes such as landslides, debris slides, rockfall,
rockslides, talus creep etc. Differential weathering helps in the evolution of
landforms and their modifications.
Learning Objectives
After studying this unit, you will learn the causes and consequences of
Weathering processes and Mass wasting.

10.2 Weathering
Weathering is the breakdown of rocks at the Earth’s surface, by the action
of rainwater, extremes of temperature, and biological activity. It does not
involve the removal of rock material. Simply it can be defined as the
process of disintegration and decomposition of rocks. It is due to the
action of climate, plants, animals, and other living organisms which cause
the rocks to break down physically, chemically, and biologically.

10.3 Significance of weathering

Weathering processes are responsible for breaking down the rocks into
smaller fragments and preparing the way for the formation of not only
regolith and soils but also erosion and mass movements. Biomes and
biodiversity is a result of forests (vegetation) and forests depend upon the
depth of weathering mantles. Erosion cannot be significant if the rocks are
not weathered. That means weathering aids mass wasting, erosion and
reduction of relief and changes in landforms are a consequence of
erosion. Weathering of rocks and deposits helps in the enrichment and
concentrations of certain valuable ores of iron, manganese, aluminium,
copper etc., which are of great importance for the national economy.
Weathering is an important process in the formation of soils.

10.4 Controlling factors of Weathering

The nature and magnitude of weathering differ from place to place and
region to region. Weathering of rocks is affected and controlled by the
agents of weathering, lithological and structural characteristics of rocks,
height, and slope factors. The mineralogical composition of rock will
determine the rate of alteration or disintegration. The texture of the rock
will affect the type of weathering that is most likely to occur. Fine-grain
rock will usually be more susceptible to chemical alteration but less
susceptible to physical disintegration. The pattern of joints, fractures, and
fissures within rock may provide an avenue for water to penetrate. Thus,

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shattered, and fractured rock masses are more likely to undergo
weathering than are monolithic structures. Climate will also control the
type and rate of weathering by affecting the likelihood of freeze-thaw
cycles and chemical reactions.

10.5 Types of Weathering

There are three types of weathering. They are physical weathering,
chemical weathering, and biological weathering.
10.5.1 Physical weathering
Physical Weathering is the disintegration of rock mainly induced by
elements of weather. It produces smaller, angular fragments of the same
rock. It is caused by the change in temperature, pressure, water, and
wind. Physical weathering is further divided into different categories. They
are thermal weathering, frost wedging and exfoliation.

Fig 10.1 Thermal Weathering Fig.10.2 Chemical Weathering

10.5.1.1 Thermal weathering

In arid and semi-arid areas, the temperature increases, heating up and
expanding the rocks during the day and contract the rock materials when
cooling at night. Under extreme temperature conditions, due to alternate
expansion and contraction, the rocks crack and eventually split. Thermal
weathering is of two types. They are; (a) Granular disintegration and
(b) Block disintegration alternate expansion and contraction of minerals
of varying properties in the rocks due to temperature changes, making the
rocks break down into small pieces (Figure 10.2). Due to this, the breakup
of rocks occurs, grain by grain. This is known as granular disintegration.
Block disintegration occurs in rocks such as granite rock. So, in the areas
of jointed igneous or layered sedimentary rocks due to the great diurnal

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range of temperature, the rocks may break up along the joints and cracks
into a large rectangular shaped block.
10.5.1.2 Frost Wedging
Almost all liquids contract when frozen, but when water freezes it becomes
larger or takes up more space. As water expands it puts great pressure on
rocks. When water enters the cracks of rocks and freezes, the pressure
exerted on the rock is enough to wedge the walls of the crack farther
apart, thus expanding and deepening the crack. Thus, frost wedging
results in weathering of rock.
10.5.1.3 Exfoliation
Rocks generally heat or cool more on the surface layers. The alternate
changes in temperature could cause their outer layers to peel off from the
main mass of the rock in concentric layers just as the skin of an onion. The
process by which curved layers of rock break away from the rock beneath
them leaving behind dome-shaped monoliths is called exfoliation (Figure
10.3). It is also called ‘onion weathering’. Exfoliation occurs commonly in
arid areas.

Fig 10.3 Exfoliation

10.5.2 Chemical Weathering
Chemical weathering is more likely to occur and to be more effective in
humid tropical climates, and disintegration of rock from freeze-thaw cycles
is more likely to take place and to be more effective in sub-Arctic climates.
Chemical weathering is the decomposition of rock. For example, it creates
altered rock substances, such as kaolinite (China clay) from granite. The
types of chemical weathering are as follows: i. Solution: Some soluble
minerals in the rock get dissolved when meeting water. Over a long

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period, minerals get washed away from rock and sometimes leading to the
formation of caves. ii. Oxidation: When oxygen combines with water and
iron, it weakens the rock and breaks it. Example, rusting of iron. iii.
Hydrolysis: It is the chemical breakdown of a rock substance when
combined with water and forms an insoluble precipitate like clay mineral.
The most common example of hydrolysis is feldspar found in granite
changing to clay. iv. Carbonation: Carbonation is the mixing of water with
carbon dioxide to make carbonic acid. This acid reacts with minerals in the
rocks. This type of weathering is important in the formation of caves. v.
Hydration: It is the absorption of water into the mineral structure of the
rock. Hydration expands volume and results in rock deformation. A good
example of hydration is the absorption of water by anhydrite, resulting in
the formation of gypsum.

Fig 10.4 Oxidation

10.5.3 Biological Weathering:

Biological weathering would include the effect of animals, plants and man
on the landscape. Biological weathering is the alteration of rock by the
action of plants, animals, and man. Burrowing and wedging by organisms
like earthworms, termites, rodents, etc., help in exposing the rock surfaces
to chemical changes with the penetration of moisture and air. Human
beings by removing vegetation for agriculture and other activities also help
in mixing and creating new contacts between air, water, and minerals in
the rock materials. Plant roots make great pressure on the rock materials
mechanically breaking them apart. Recently, man has become the most

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powerful weathering agent because of the development of modern
technologies. Biological weathering thus is divided into 3 types e.g. (i)
faunal weathering (ii) floral weathering (iii) anthropogenic weathering.

Fig 10.5 Biological weathering Trees Fig 10.6 Biological Weathering

animal
10.6 Mass wasting
Mass wasting is the movement of a large mass of rock, soil and debris
downward by the pull of gravity. It is also called a mass movement or
slope movement. It may happen suddenly or slowly. Generally, mass
wasting is classified by the type of material involved (mud, soil, and rock)
and type of motion (fall-free-falling pieces, slide material moves along the
rock slope and flow–material mixed with water). Mass wasting, also known
as slope movement or mass movement, is the geomorphic process by
which soil, sand, regolith, and rock move downslope typically as a solid,
continuous or discontinuous mass, largely under the force of gravity,
frequently with characteristics of a flow as in debris flows and mudflows.
Types of mass wasting include creep, slides, flows, topples, and falls,
each with its characteristic features, and taking place over timescales from
seconds to hundreds of years.
10.6.1 Types of Mass Wasting
Following are the types of mass wasting: Rockfalls occur when pieces of
rock break from a cliff. Frost wedging may also eventually loosen large
blocks causing them to fall. The accumulation of rock debris at the base of
a steep slope is called the talus.
10.6.1.1 Rockslides:
Rockslides usually follow a zone of weakness. The presence of water
increases slippage. Collisions down the slope generally break the rock
mass into rubble that eventually results in rockslides. Landslides:

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Landslides occur when a large piece of rock breaks off and slides
downhill. It is often initiated by earthquakes and very heavy rain.

Fig 10.6 Rockslides Fig 10.7 Massive Land Slide

10.6.1.2 Slump
The great mass of bedrock moves downward by a rotational slip from a
high cliff is known as a slump. The most common reason for slumping is
erosion at the base of the slope which reduces the support for overlying
sediments.

Fig 10.0 Mud Flow Fig 10.9 Debris Flow

10.6.1.3 Debris Slide
Debris slide is more extensive and occurs on a larger scale than slump but
there is a little amount of water. The materials involved in the debris slide
are a mixture of soil and rock fragments.
10.6.1.4 Debris flows
Debris flow is defined as the mass-wasting event in which turbulence
occurs throughout the mass. Debris flow includes earth flows, mudflows,
and debris avalanches. Debris flow occurs when the rock or soil mass

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loses coherency when lots of water is involved. Debris becomes mixed up
completely and flows as liquid mud.
10.6.1.5 Soil creep
It is a slow and long-term mass movement. The combination of small
movements of soil or rock in different directions over time is directed by
gravity gradually downslope. The steeper the slope, the faster the creep

Let Us Sum Up
Weathering helps erosional processes by weathering processes loosens
the rocks by disintegration and decomposing them and thus paves the
way for erosional processes to operate easily Weathering is the
breakdown of rocks at the Earth’s surface, by the action of rainwater,
extremes of temperature, and biological activity. There are three types of
weathering. They are physical weathering, chemical weathering, and
biological weathering. The great mass of bedrock moves downward by a
rotational slip from a high cliff is known as a slump. Debris slide is more
extensive and occurs on a larger scale than slump but there is a little
amount of water Debris flow includes earth flows, mudflows, and debris
avalanches.

Glossaries
Exfoliation: The process by which curved layers of rock break away from
the rock beneath them leaving behind dome-shaped monoliths is called
exfoliation
Weathering is the breakdown of rocks at the Earth’s surface, by the action
of rainwater, extremes of temperature, and biological activity.
Mass movement is the geomorphic process by which soil, sand, regolith,
and rock move downslope.

Landslides: Landslides occur when a large piece of rock breaks off and
slides downhill.

Check Your Progress

1. Weathering-Define.

Weathering is the process of disintegration of rocks by various natural

agents.
2. State the types of Weathering.
There are three types of weathering. They are physical weathering,
chemical weathering, and biological weathering.

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3. Write a note on Mass wasting.
Mass Movement is defined as the downslope movement of rock and
regolith near the Earth's surface mainly due to the force of gravity.
4. List the types of Mass wasting.
Types of mass wasting are rockfall, soil creep, debris slide, Slump,
debris slide and debris creep.

Suggested Readings
1. A Textbook of Geomorphology (Hardcover) by P. Dayal
2. The Study of Landforms: A Textbook of Geomorphology by R.J.
Small

3. Geomorphology (Paperback) by Savindra Singh

4. The Encyclopedia of Geomorphology by Rhodes W. Fairbridge

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 UNIT 11
The cycle of Erosion: Davis
11.1 Overview
Learning Objectives
11.2 Significance of the Study

11.3 Assumptions of Davisian model of ‘geographical cycle

11.4 ‘Trio of Davis’ and his concept
11.5 Explanation of the Theory

11.5.1 Youthful stage

11.5.2 Mature stage
11.5.3 Old Stage
11.6 Evaluation of the Davisian Model
11.6.1 Positive Aspects of Davis’ Model
11.6.2 Negative Aspects of Davis Model
11.7 Conclusion
Let us sum up
Glossary
Check your progress
Suggested readings

11.1 Overview
William Morris Davis was born on 12th February 1850 in Philadelphia,
Pennsylvania, an American geographer, geologist, geomorphologist, and
meteorologist often called the "father of American geography". He had
sound knowledge of geography, geology, and meteorology, thus calling
him Father of the American Geography. W.M.Davis was a professor at
Harvard University. He was the first Geomorphologist to present a general
theory of “Landform Development” through this cycle of erosion. From his
field observations and studies made by the original nineteenth-century
surveyors of the western United States, he devised his most influential
scientific contribution: the "geographical cycle". His theory was first defined
in his 1889 article, The Rivers and Valleys of Pennsylvania, Cyclic

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concepts are one of the most persuasive ideas of landform evolution. It
originated with Hutton’s dictum, "no vestige of a beginning, no prospect of
an end"; evolved with uniformitarianism and finally saw the hues with
Davis' "Cycle of Erosion" propounded in 1899. Davis postulated his
concept of the ‘geographical cycle’ popularly known as the ‘cycle of
erosion’ in 1899 to present a genetic classification and systematic
description of landforms.
Learning Objectives
After studying this unit, you will learn about,
• Assumptions of Davisian model of ‘geographical cycle
• ‘Trio of Davis’ and his concept
• Explanation of the Theory
• Evaluation of the Davisian Model

11.2 Significance of the Study

The Davisian model of the geographical cycle and the general theory of
landform development was to provide the basis for a systematic
description and genetic classification of landforms. The reference system
of Davisian general theory of landform development is ‘that landforms
change in an orderly manner as processes operate through time such that
under uniform external environmental conditions an orderly sequence of
landform develops’., which was a model of how rivers erode uplifted land
to base level,

11.3 Assumptions of Davisian model of ‘geographical

cycle’
(1) Landforms are the evolved products of the interactions of endogenetic
(diastrophic) forces originating from within the earth and the external or
exogenetic forces originating from the atmosphere (denudational
processes, agents of weathering and erosion-rivers, wind, groundwater,
sea waves, glaciers, and periglacial processes).

(2) The evolution of landforms takes place in an orderly manner in such a

way that a systematic sequence of landforms is developed through time in
response to an environmental change.

(3) Streams erode their valleys rapidly downward until the graded
condition is achieved.

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(4) There is a short-period rapid rate of upliftment in landmass. It may be
pointed out that Davis also described slower rates of upliftment if so
desired.
(5) Erosion does not start until the upliftment is complete. In other words,
upliftment and erosion do not go hand in hand. This assumption of Davis
became the focal point of severe attacks by the critics of the cyclic
concept.
According to Davis three factors viz. structure, process and time play
important roles in the origin and development of landforms of a particular
place. These three factors are called as ‘Trio of Davis’ and his concept is
expressed as follows:

11.4 ‘Trio of Davis’ and his concept

“Landscape is a function of the structure, process and time” Structure
means lithological (rock types) and structural characteristics (folding,
faulting, joints etc.) of rocks. Time was not only used in temporal context
by Davis but it was also used as a process itself leading to an inevitable
progression of change of landforms. Process means the agents of
denudation including both, including weathering, and erosion (running
water in the case of the geographical cycle).

11.5 Explanation of the Theory

Davisian theory may be explained as follows:
There are sequential changes in landforms through time (passing through
youth, mature and old stages) and these sequential changes are directed
towards a well-defined end product-development of peneplain.’
His ‘geographical cycle’ has been defined in the following manner:
‘Geographical cycle is a period during which an uplifted landmass
undergoes its transformation by the process of land-sculpture ending into
low featureless plain or peneplain (Davis called peneplane).”
Davis has described his model of geographical cycle through a graph
below (fig. 11.1):
The cycle of erosion begins with the upliftment of the landmass. There is a
rapid rate of short-period upliftment of landmass of homogeneous
structures. This phase of upliftment is not included in the cyclic time as this
phase is, in fact, the preparatory stage of the cycle of erosion.
Fig. 11.1 represents the model of the geographical cycle wherein UC
(upper curve) and LC (lower curve) denote the hilltops or crests of water

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divides (absolute reliefs from mean sea level) and valley floors (lowest
reliefs from mean sea level) respectively.

fig. 11.1

fig. 11.1 Geographical cycle

The horizontal line denotes time whereas the vertical axis depicts altitude
from sea level. AC represents maximum absolute relief whereas BC
denotes initial average relief. Initial relief is defined as a difference
between the upper curve (summits of water divides) and the lower curve
(valley floors) of a landmass. In other words, relief is defined as the
difference between the highest and the lowest points of a landmass. ADG
line denotes base level which represents sea level. No river can erode its
valley beyond base level (below sea level).
Thus, the base level represents the limit of maximum vertical erosion (val-
ley deepening) by the rivers. The upliftment of the landmass stops after
point C (fig. 11.1) as the phase of upliftment is complete.
Now erosion starts and the whole cycle passes through the following three
stages:

Fig. 11.2 Three Stages of Davisian Cycle: Youth, Mature and Old Stage

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11.5.1 Youthful stage:
Erosion starts after the completion of the upliftment of the landmass. The
top surfaces or the summits of the water divides are not affected by
erosion because the rivers are small and widely spaced. Small rivers and
short tributaries are engaged in head-ward erosion due to which they
extend their lengths.
The process is called stream lengthening (increase in the lengths of the
rivers). Because of steep slope and steep channel gradient rivers actively
deepen their valleys through vertical erosion aided by pothole drilling and
thus there is a gradual increase in the depth of river valleys. This process
is called valley deepening. The valleys become deep, and narrow
characterized by steep valley side slopes of the convex plan.
The youthful stage is characterized by the rapid rate of vertical
erosion and valley deepening because:
(i) The channel gradient is very steep,

(ii) Steep channel gradient increases the velocity and kinetic energy of the
river flow,
(iii) Increased channel gradient and flow velocity increases the
transporting capacity of the rivers,
(iv) Increased transporting capacity of the rivers allow them to carry big
boulders of high calibre (more angular boulders) which help in valley
incision (valley deepening through vertical erosion) through pothole
drilling.
The lower curve (LC valley floor) falls rapidly because of valley deepening
but the upper curve (UC summits of water divides or inter stream areas)
remains almost parallel to the horizontal axis (AD, in fig. 16.1) because the
summits or upper parts of the landmass are not affected by erosion. Thus,
relative relief continues to increase till the end of the youthful stage when
ultimate maximum relief is attained.
In nutshell, the youthful stage is characterized by the following char-
acteristic features:
(i) Absolute height remains constant (CF is parallel to the horizontal axis)
because of insignificant lateral erosion.

(ii) Upper curve (UC) representing summits of water divides is not affected
by erosion.

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(iii) Lower curve (LC) falls rapidly because of the rapid rate of valley-
deepening through vertical erosion.
(iv) Relief (relative) continues to increase.
(v) Valleys are of V shape characterized by convex valley side slopes.
(vi) Overall valley form is gorge or canyon.
(vii) Long profiles of the rivers are characterized by rapids and waterfalls
which gradually diminish with the march of time and this practically
disappear by the end of late youth. The main river is graded.
11.5.2 Mature stage
The early mature stage is heralded by marked lateral erosion and a well-
integrated drainage network. The graded conditions spread over a larger
area and most of the tributaries are graded to the base level of erosion.
Vertical erosion or valley deepening is remarkably reduced. The summits
of water divides are also eroded and hence there is a marked fall in the
upper curve (UC) i.e., there is a marked lowering of absolute relief.
Thus, absolute relief and relative relief, both decreases. The lateral
erosion leads to valley widening which transforms the V-shaped valleys of
the youthful stage into wide valleys with uniform or rectilinear valleys
sides. The marked reduction in valley deepening (vertical erosion or valley
incision) is because by a substantial decrease in channel gradient, flow
velocity and transporting capacity of the rivers.
11.5.3 Old Stage
The old stage is characterized by the almost total absence of valley
incision, but lateral erosion and valley widening is still active process.
Water divides are more rapidly eroded. Water divides are reduced in
dimension by both, down-wasting, and back-wasting. Thus, the upper
curve falls more rapidly, meaning thereby there is a rapid rate of decrease
in absolute height. Relative or available relief also decreases sharply
because of active lateral erosion but no vertical erosion. The near absence
of valley, deepening is due to extremely low channel gradient and
remarkably reduced kinetic energy and maximum entropy.
The valleys become almost flat with concave valley side slopes. The entire
landscape is dominated by graded valley-sides and divides crests, broad,
open, and gently sloping valleys having extensive flood plains, well-
developed meanders, residual convexo-concave monadnocks and the
extensive undulating plain of extremely low relief. Thus, the entire
landscape is transformed into a peneplain. As revealed by fig. 16.1 the

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duration of the old stage is many times as long as youth and maturity
combined.

11.6 Evaluation of the Davisian Model

Davisian model of geographical cycle received worldwide recognition and
the geomorphologists readily applied his model in their geomorphological
investigations. Even though this theory was widely appreciated criticized
by the Geomorphologists as follows:
11.6.1 Positive Aspects of Davis’ Model
(1) Davis’ model of the geographical cycle was highly simple and
applicable.

(2) He presented his model in a very lucid, compelling and disarming style
using very simple but expressive language. Commenting on the language
of Davis used in his model Bryan remarked, “Davis rhetorical style is just
admired and several generations of readers became, slightly bemused by
long though mild intoxication of the limpid prose of Davis remarkable
essay.”

(3) Davis based his model on detailed and careful field observations.
(4) Davis’ model came as a general theory of landform development after
a long gap after Hutton’s cyclic nature of the earth history.
(5) This model synthesized the current geological thoughts. In other
words, Davis incorporated the concept of ‘base level’ and genetic
classification of river valleys, the concept of ‘graded streams’ of G.K.
Gilbert and French engineers’ concept of ‘profile of equilibrium’ in his
model.
(6) His model is capable of both predictions and historical interpretation of
landform evolution.
11.6.2 Negative Aspects of Davis Model
(1) Davis concept of upliftment is not acceptable. He has described a rapid
rate of upliftment of short duration but as evidenced by plate tectonics
upliftment is exceedingly a show and long-continued process.
(2) Davis’ concept of the relationship between upliftment and erosion is
erroneous. According to him no erosion can start unless upliftment is
complete. Can erosion wait for the completion of upliftment? It is a natural
process that as the land rises, erosion begins. Davis has answered this
question.

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(3) Overemphasizing the time: Davis relatively ignored the importance of
structure and process which are important factors of landform
development.
(4) The initial phase, sudden upliftment, and erosion start only after
completion of upliftment are not practical.
(5) Davis ignored the role of deposition and weathering in landform
development and overemphasized the erosion factor.
(6) As per Davis, the erosional cycle gets completed after the old stage
and peneplains formation, but landform development is a never-ending
process.
(7) Ignored the role of climate in landform development.

11.7 Conclusion
Various models were developed based on this reference system e.g., the
normal cycle of erosion, the arid cycle of erosion, the glacial cycle of
erosion, the marine cycle of erosion etc. Thus, ‘geographical cycle’ is one
of the several possible models based on Davis’ reference system of
landform development., However, the theory Normal Cycle of Erosion has
brought sea-level changes in geomorphological study

Let Us Sum Up
William Morris Davian an American geographer, geologist,
geomorphologist, and meteorologist is often called the "father of American
geography". Davis postulated his concept of the ‘geographical cycle’
popularly known as the ‘cycle of erosion’ in 1899 to present a genetic
classification and systematic description of landforms. basic assumptions
of the Davisian model are a landmass evolved from the beneath of the sea
level, homogenous characteristics, depressions, due to the rainfall origin
of small streams and lakes, three stages are youth, mature and old stage,
evaluation of the theory with positive and negative point of views.

Glossary
Diastrophic: forces originating from within the earth

Exogenetic forces: originating from the atmosphere

Denudational processes: agents of weathering and erosion-rivers, wind,
groundwater, sea waves, glaciers, and periglacial processes
Uniformitarianism: doctrine deals with the ‘Present is key to the past’.

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Peneplain: end product-development of Davisian concept and plain
region.
Monadnock: Residual hills of the old stage

Check Your Progress

1. Write a note on Father of American Geography.
William Morris Davis for his outstanding contribution in the field of
Geology, Geomorphology and Meteorology

2. Bring out the significance of the Normal Cycle of erosion in the

geomorphological study.
The Davisian model of the geographical cycle and the general theory of
landform development was to provide the basis for a systematic
description and genetic classification of landforms.
3. State the Basic Assumptions of Davis.
A huge landmass evolved from beneath the sea surface having
homogenous characteristics with small depression.
4. List the stages of the Davisian Concept
According to Davis, there were three stages youthful, mature, and old
stages.

Suggested Readings
5. A Textbook of Geomorphology (Hardcover) by P. Dayal
6. The Study of Landforms: A Textbook of Geomorphology by R.J. Small
7. Geomorphology (Paperback) by Savindra Singh
8. The Encyclopedia of Geomorphology by Rhodes W. Fairbridge

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 UNIT 12
CYCLE OF EROSION: PENCK

12.1 Overview
Learning Objectives
12.2 Points to be remembered in Penck Concept:
12.2.1 Pedeplain or (Primarumpf)

12.2.2 Waxing erosion or (Aufsteigende Entwickelung)

12.2.3 Uniform erosion or (Gleichformige Entwickelung)
12.2.4 Waning erosion or (Absteigende Entwickelung)

12.2.5 End plain or (endruiripf)

12.3 Views of Penck
12. 5 Positive Points of Penck’s concept

12.6 Drawbacks of Penck’s Concept

12.7 Conclusion
Let us sum up
Glossary
Check your progress
Suggested Readings

12.1 Overview
Walther Penck was a geologist and geomorphologist known for his
theories on landscape evolution. Penck is noted for criticizing key
elements of the Davisian cycle of erosion, concluding that the process of
uplift and denudation occur simultaneously, at gradual and continuous
rates. Penck's idea of parallel slope retreat led to revisions of Davis's cycle
of erosion.

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12.2 Penck Concept
12.2.1 Pedeplain or (Primarumpf)
As per Penck, initially, there is a featureless surface that Penck called
"Primarumpf" or primary Pedeplain.

• It is a prior stage of landform development.

• In this stage, a landscape with no landform’s development.
• No mountain, no mountain in this stage.

• The upper curve and the lower curve are the same.
12.2.2 waxing erosion or (Aufsteigende Entwickelung)
• Landforms start developing.

• Mountains are suddenly rising

• Valleys are deepening hence narrow valleys are created.
• Relief increases and convex and free face slope developed.
• A gap between the upper curve and the lower curve is increasing.
• Endogenic force >> Exogenic force.
12.2.3 Uniform erosion or (Gleichformige Entwickelung)
Three-part in this stage
• In the first part, uplifting is greater than erosional
• The highest peak will be formed in the upper curve.
• Second part upliftment and erosional nearly the same.
• Last parts, upliftment lasted and loosing slowly both valley and
mountain.
12.2.4Waning erosion or (Absteigende Entwickelung)
• Summit or upper curve erodes faster.
• The river becomes graded and reaches rectilinear slope development.

• Formation of conical shape Inselburge.

12.2.5 End plain or (endruiripf)
• Landform development stops.

• Pediplain developed
• Upperparts erosional and lower part deposition.

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12.3 Views of Penck
Walter Penck studied the Davis erosional cycle model and agreed the
most of Davis's thoughts but disagreed on the process and stages
components (i.e. trio of Davis are the structure, process, and stages) of
Davis erosional model. Penck rejected that stage is not sequential and
there may be interrupted by rejuvenation.
Penck made certain deviations from the views of Davis. One, the erosion
does not remain suspended till the uplift is complete. He said, the
geomorphic forms are an expression of the phase and rate of uplift about
the rate of degradation, and that interaction between the two factors, uplift
and degradation is continuous. Two, the rate of the uplift process is on
changing.
Penck proposed three types of valley slopes based on erosional intensity
acting on crustal movements.
1. Straight slope:
Indicating uniform erosion intensity and uniform development of landforms
or ‘Gleichformige Entwickelung’ in German.
2. Convex slope:
Indicating waxing erosion intensity and a waxing development of
landforms or ‘Aufsteigende Entwickelung.
3. Concave slope:
Indicating waning erosion intensity and a waning development of
landforms or ‘Absteigende Entwickelung.’
12.4 Penck’s Cycle of Erosion

Fig. 12.1 The cycle of Erosion (Penck): Stages

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Stage 1:
With uplift, the interfluves, as well as the lower parts, rise. There is a lack
of brisk undercutting. Penck used the term ‘Primarumpf’ to represent the
characteristic landscape before upliftment. Primarumpf is the initial surface
or primary peneplane representing either a newly emerged surface from
below sea level or a ‘fastenbene’ or ‘peneplane’ type of land surface
converted into featureless landmass by uplift.
Stage 2:
Here, the rate, of downcutting is less than the rate of uplift. There is not
much change in relief.
Stage 3:
The rate of down cutting becomes equal to the rate of uplift. Again, there is
not much change in relief.
Stage 4:
The uplift comes to an end and the down-cutting further intensifies. The
height of the interfluves decreases. The deepening of valleys accelerates.
A convex slope results: this is the stage of waxing erosion or
(Aufsteigende Entwickelung).
Stage 5:
The downcutting and the deepening of valleys slow down. The interfluves
are rounded and further lowered. A concave slope results: this is the stage
of waning erosion or (Absteigende Entwickelung).
Stage 6:
Uniform erosion or (Gleichformige Entwickelung) characterises the product
(endruiripf) or end plain.

12. 5 Positive Points of Penck’s concept

1. Penck followed a deductive approach and did not restrict himself to any
condition.
2. Compared to the Davisian cycle, Penck’s approach was forward-
looking.
3. Penck, quite appropriately, emphasised the mutual relation between
uplift and the deepening of valleys. This indicates Penck’s respect for
geological evidence. Penck’s third stage is evident in the Middle Alps.

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12.6 Drawbacks of Penck’s Concept
1. Penck gave too much importance to the role of endogenetic forces.
2. The orderliness in landform changes, as assumed by Penck, may be
difficult to achieve.
3. Inadequate knowledge about the initial pristine landscape does not
allow much verification.
4. The concept of the geographical cycle of erosion itself has been
criticised by many since many of the cyclic generalisations are based on
untested assumptions. An overemphasis on historical and evolutionary
studies in landforms results in the reconstruction of stages of evolution
becoming the focus of study.

12.7 Conclusion:
Penck is perhaps the most misunderstood geomorphologist in the world. It
is not yet sure whether he used the word ‘cycle’ or not in his model of
landform development. Penck’s views could not be known in true sense
and could not be interpreted in right perspective because of (i) His
incomplete work due to his untimely death, (ii) His obscure composition in
difficult German language, (iii) Ill-defined terminology, (iv) Misleading
review by W.M. Davis, and (v) Some contradictory ideas.

Let Us Sum Up
Walter Penck gave a morphological system model in 1924 also known as
the cycle of erosion. As per Walter Penck, the Endogenic force also
interferes with the cycle of erosion through Rejuvenation. Hence, the
erosion cycle is a never-ending process. The erosional cycle is not time
dependent as Davis proposed. The main goal of Penck’s model of
morphological system was to find out the mode of development and
causes of crustal movement based on exogenetic processes and
morphological characteristics. The reference system of Penck’s model is
that the characteristics of landforms of a given region are related to the
tectonic activity of that region.

Glossaries
Primarumpf: Pedeplain
Gleichformige Entwickelung: Uniform erosion
Absteigende Entwickelung: waning erosion

Aufsteigende Entwickelung: waxing erosion

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Endruiripf: End plain

Check Your Progress

1. Write a note on Walther Penck.
Walther Penck was a geologist and geomorphologist known for his
theories on landscape evolution.
2. State the main point of the Penck Concept.
The Endogenic force also interferes with the cycle of erosion through
Rejuvenation.
3. Pedeplain-Define
An almost plain region without a difference
4. Mention the major slopes of the Penck concept.
Straight, convex, and concave slopes

Suggested Readings
1. Christopherson, R. W. and Birkeland, G. H., (2012) Geosystems: An
Overview to Physical Geography (8/E), Pearson Education, New Jersey.
2. Das Gupta, A &Kapoor, A.N., (2001) Principles of Physical Geography,
S.C. Chand & Company Ltd. New Delhi.
3. Khullar, D.R., (2012) Physical Geography, Kalyani Publishers, New
Delhi.
4. Brown, J.H. (2005) Biogeography, Sinauer Associates Inc, Sunderland.

5. Seddon, B.A. (1971) Overview to Biogeography, Duckworth, London.

6. Thornbury W.D. (2002), Principles of Geomorphology, CBS Publishers
& Distributors, New Delhi, India

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 UNIT 13
Evolution of Landforms (Erosional and
Depositional) Fluvial and Karst
Structure
13.1 Overview
Learning Objectives

13.2 Running Water (Fluvial Topography)

13.2.1 Erosion
13.2.2 Transportation

13.2.3 Deposition
13.3 Fluvial Erosional Landforms:
13.4 Depositional Landforms:
13.5 Karst topography
13.5.1 Distribution of Karst Areas:
13.5.2 Conditions for the development of Karst Topography:
13.6 Karst: Erosional Landforms
13.7 Karst: Depositional features
Let us sum up
Glossary
Check your progress
Suggested readings

13.1 Overview
We are all aware that our planet Earth is a dynamic evolving system.
Many cyclic processes are acting on the surface of the earth. They are
done by aerial agents like air, wind, water, ice and waves. They are called
geographical agents. They create a lot of landforms on the surface of the
earth. One such agent is the running water. Generally, it is called streams
or rivers. Rivers are powerful and dynamic geological agents. The water
flowing through a stream performs three kinds of geographical works
erosion, transportation, and deposition. Hence, a river is considered

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one of the geographical agents on earth. The flowing water has the force,
velocity, and power to generate electricity.
In humid regions, which receive heavy rainfall running water is considered
the most important of the geomorphic agents in bringing about the
degradation of the land surface. There are two components of running
water. One is an overland flow on the general land surface as a sheet.
Another is linear flow as streams and rivers in valleys. The work of running
water in the form of surface runoff of overland flow and the stream is the
most important of all the exogenetic or plantation processes because
running water is the most widespread exogenetic process on this planet
earth. The landforms either carved out or built up by running water are
called fluvial landforms and the running waters which shape them are
called the fluvial process which includes overland flow and steam flow.
Learning Objectives
After studying this unit, you will learn about the erosional, transportation
and depositional features of River and Karst Topography.

13.2 Running Water (Fluvial Topography)

In humid regions, which receive heavy rainfall running water is considered
the most important of the geomorphic agents in bringing about the
degradation of the land surface. Do You Know Denudation is the
combined action of the various processes that cause the wearing away of
the Earth’s surface and causes a general lowering and levelling out of the
surface? It is carried out in four phases- weathering, transportation,
erosion, and deposition. The adjective 'fluvial' (from Latin fluvius river)
refers to the work of rivers but in the context of landscape development, it
includes the work of both overland flow and streamflow. Thus, landforms
shaped by running water (i.e., by the fluvial processes of overland flow
and streamflow) are called fluvial landforms. Fluvial landforms and
processes dominate the continental land surface.
13.2.1 Erosion
Erosion by any river is a very important aspect for mankind. The rate of
erosion is higher in mountains as compared to that in plains. Rivers carry
the particles/ debris formed by weathering and deposit it at another place.
The particles that rivers carry are stones, rocks, sand particles etc., which
help in the erosional process.
13.2.1.1 Erosion may be divided into two parts:
1. Vertical Erosion:

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This is also known as downward (cut) erosion, which results in the
deepening of the valley. This, erosional activity is dominantly vertical.
Rivers flow from mountains to low slopes, eroding the bedrocks vertically.
Because the flow is fast and the slope (gradient) is steep, this process
goes on, till the river reaches its mouth and results in the formation of ‘V-
shaped valleys.
2. Lateral Erosion:
This is a sideway erosional process. It starts when the river enters from
mountains to plains. Speed of water/flow decreases, and the river starts
‘sideway’ erosion and further it leads to widening of the valley.
13.2.2.2 Factors Controlling Erosion:
(i) Velocity of Running Water:

The process of erosion depends upon the velocity of the river. If the
gradient is steep, the velocity of the river will be higher which leads to
more erosion. In plains, the velocity of the river is low, erosion is also
comparatively less.
There is a law about the erosional capacity of running water, if the velocity
of the river is doubled or multiplied by two its capacity of carrying the
material rises by 64 times its original capacity. This is known as ‘Gilbert’s
sixth power law’. Erosion Capacity increases during flooding while it lies
low in a dry patch of weather.
(ii) Volume of Water in River:
The higher the volume of water in the river, the more will be erosion. As
the volume increases the presence of rocks, stones, soil particles, debris
etc. also rises. Higher volume results in the deepening of riverbeds and
broadening of banks. All this leads to the widening of the valley by eroding
riverbeds and walls or sides of the river.

(iii) Load of River:

If the number of rocks, stones, soil particles is high in rivers, it will
accelerate the process of erosion and friction.
(iv) Nature of Rocks:
The erosion process on limestones and sandstones rocks is faster as
these are soft rocks. On the other hand, the erosion process on Granite
and Basalt is slow and tougher comparatively, these being hard rocks.
Rivers carry out the process of erosion and friction based on load,
gradient, and type of rocks. Most of the erosional landforms made by

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running water are associated with vigorous and youthful rivers flowing over
steep gradients. With time, stream channels over steep gradients turn
gentler due to continued erosion, and consequently, lose their velocity,
facilitating active deposition. There may be depositional forms associated
with streams flowing over steep slopes. But these phenomena will be on a
small scale compared to those associated with rivers flowing over medium
to gentle slopes. The gentler the river channels in gradient or slope, the
greater is the deposition. When the stream beds turn gentler due to
continued erosion, downward cutting becomes less dominant and lateral
erosion of banks increases and consequently the hills and valleys are
reduced to plains. Overland flow causes sheet erosion. Depending upon
irregularities of the land surface, the overland flow may concentrate into
narrow to wide paths. Because of the sheer friction of the column of
flowing water, minor or major quantities of materials from the surface of
the land are removed in the direction of flow and gradually small and
narrow rills will form. These rills will gradually develop into long and wide
gullies; the gullies will further deepen, widen, lengthen, and unite to give
rise to a network of valleys.
In the early stages, down-cutting dominates during which irregularities
such as waterfalls and cascades will be removed. In the middle stages,
streams cut their beds slower, and lateral erosion of valley sides becomes
severe. Gradually, the valley sides are reduced to lower and lower slopes.
The divides between drainage basins are likewise lowered until they are
almost completely flattened leaving finally a lowland of faint relief with
some low resistant remnants called monadnocks standing out here and
there. This type of plain forming because of stream erosion is called a
peneplain (an almost plain). The characteristics of each of the stages of
landscapes developing in running water regimes may be summarised as
follows: Streams are few during this stage with poor integration and flow
over original slopes showing shallow V-shaped valleys with no floodplains
or with very narrow floodplains along trunk streams. Streams divides are
broad and flat with marshes, swamps, and lakes.
Meanders if present develops over these broad upland surfaces. These
meanders may eventually entrench themselves into the uplands.
Waterfalls and rapids may exist where local hard rock bodies are exposed.
Mature During this stage streams are plenty with good integration. The
valleys are still V-shaped but deep; trunk streams are broad enough to
have wider floodplains within which streams may flow in meanders
confined within the valley. The flat and broad inter stream areas and
swamps and marshes of youth disappear and the stream divides turn

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sharp. Waterfalls and rapids disappear. Old Smaller tributaries during old
age are few with gentle gradients. Streams meander freely over vast
floodplains showing natural levees, oxbow lakes, etc. Divides are broad
and flat with lakes, swamps, and marshes. Most of the landscape is at or
slightly above sea level.
13.2.2 Transportation:
The river carries rocks, stones, soil particles etc. from one place to
another. This process of carrying materials is known as transportation. It is
carried out in the middle course of a river.

Rivers carry out debris in different ways:

(i) Traction:
Large materials such as boulders are rolled and pushed along the riverbed
by the force of river water.
(ii) Solution:
Dissolved materials are also carried by a river. This happens often in
areas where the limestone is dissolved by slightly acidic water. Some
chemicals and salt also dissolve in river waters.
(iii) Load in Suspension/Suspended Load:
When materials made of very fine particles such as clay and silt is lifted as
the result of turbulence and transported by river. Faster flowing turbulent
rivers carry more suspended materials, that is why rivers appear muddy.
Transportation of fine material is faster than coarse material.
13.2.3 Deposition:
This process begins when gradients are low and the velocity of river water
decreases. At this stage deposition of materials carried by the river take
place, which helps in levelling of low-lying areas. The process of erosion
and deposition is completed at this stage.

Fast-flowing rivers carry the material for a long time and distance. On the
other hand, rivers that flow slow, start the deposition work on their way.
Sometimes when rivers change their directions, the deposition process
begins.

13.3 Fluvial Erosional Landforms:

Valleys start as small and narrow rills; the rills will gradually develop into
long and wide gullies; the gullies will further deepen, widen and lengthen
to give rise to valleys. Depending upon dimensions and shape, many

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types of valleys like V-shaped valleys, gorges, canyons, etc. can be
recognized. A gorge is a deep valley with very steep to straight sides and
a canyon is characterized by steep step-like side slopes (Figure 13.1) and
maybe as deep as a gorge. A gorge is almost equal in width at its top as
well as its bottom. In contrast, a canyon is wider at its top than at its
bottom. A canyon is a variant of a gorge. Valley types depend upon the
type and structure of rocks in which they form. For example, canyons
commonly form in horizontal bedded sedimentary rocks and gorges form
in hard rocks. Figure 13.1: The Valley of Kaveri River near Hogenekal,
Dharmapuri district, Tamilnadu in the form of the gorge.

Fig.13.1 Gorge
Potholes and Plunge Pools Over the rocky beds of hill-streams circular
depressions called potholes form because of stream erosion aided by the
abrasion of rock fragments. Once a small and shallow depression forms,
pebbles and boulders get collected in those depressions and get rotated
by flowing water and consequently the depressions grow in dimensions. A
series of such depressions eventually join, and the stream valley gets
deepened. At the foot of waterfalls also, large potholes, quite deep and
wide, form because of the sheer impact of water and rotation of boulders.
Such large and deep holes at the base of waterfalls are called plunge
pools. These pools also help in the deepening of valleys. Waterfalls are
also transitory like any other landform and will recede gradually and bring
the floor of the valley above waterfalls to the level below.
Incised or Entrenched Meanders In streams that flow rapidly over steep
gradients, normally erosion is concentrated on the bottom of the stream

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channel. Also, in the case of steep gradient streams, lateral erosion on the
sides of the valleys is not much when compared to the streams flowing on
low and gentle slopes. Because of active lateral erosion, streams flowing
over gentle slopes develop sinuous or meandering courses. It is common
to find meandering courses over floodplains and delta plains where stream
gradients are very gentle. But very deep and wide meanders can also be
found cut in hard rocks. Such meanders are called incised or entrenched
meanders (Figure 13.2). Meander loops develop over original gentle
surfaces in the initial stages of development of streams and the same
loops get entrenched into the rocks normally due to erosion or slow,
continued uplift of the land over which they start. They widen and deepen
over time and can be found as deep gorges and canyons in hard rock
areas. They give an indication of the status of original land surfaces over
which streams have developed.

Fig. 13.2 Enriched Meanders

What are the differences between incised meanders and meanders over
flood and delta plains?
River Terraces River terraces are surfaces marking old valley floor or
floodplain levels. They may be bedrock surfaces without any alluvial cover
or alluvial terraces consisting of stream deposits. River terraces are
products of erosion as they result due to vertical erosion by the stream into
its depositional floodplain. There can be several such terraces at different
heights indicating former riverbed levels. The river terraces may occur at
the same elevation on either side of the rivers in which case they are

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called paired terraces (Figure 7.3). Figure 7.3: Paired and unpaired river
terraces When a terrace is present only on one side of the stream and with
none on the other side or one at quite a different elevation on the other
side, the terraces are called unpaired terraces. Unpaired terraces are
typical in areas of slow uplift of land or where the water column changes
are not uniform along both the banks. The terraces may result due to (i)
receding water after a peak flow; (ii) change in hydrological regime due to
climatic changes; (iii) tectonic uplift of land; (iv) sea-level changes in case
of rivers closer to the sea.

13.4 Depositional Landforms

Rivers deposit sediments in different parts of their courses and thus form
various types of landforms which are called constructional landforms such
as alluvial fans and alluvial cones, sandbanks, natural levees, flood plains,
sand bars and deltas. Alluvial fans are formed when streams flowing from
higher levels break into foot slope plains of low gradient. Normally very
coarse load is carried by streams flowing over mountain slopes. This load
becomes too heavy for the streams to be carried over gentler gradients
and gets dumped and spread as a broad low to high cone-shaped deposit
called an alluvial fan.
Usually, the streams which flow over fans are not confined to their original
channels for long and shift their position across the fan forming many
channels called distributaries. Alluvial fans in humid areas show normally
low cones with a gentle slope from a low cone. Unlike in alluvial fans, the
deposits making up deltas are very well sorted with clear stratification. The
coarsest materials settle out first and the finer fractions like silts and clays
are carried out into the sea. As the delta grows, the river distributaries
continue to increase in length and the delta continues to build up into the
sea. Floodplains, Natural Levees and Point Bars Deposition develop a
floodplain just as erosion makes valleys. Floodplain is a major landform of
river deposition. Large-sized materials are deposited first when the stream
channel breaks into a gentle slope. Thus, normally, fine-sized materials
like sand, silt and clay are carried by relatively slow-moving waters in
gentler channels usually found in the plains and deposited over the bed
and when the waters spill over the banks during flooding above the bed.

A riverbed made of river deposits is the active floodplain. The floodplain

above the bank is inactive. Inactive floodplain above the banks contains
two types of deposits — flood deposits and channel deposits. In plains,
channels shift laterally and change their courses occasionally leaving cut-
off courses that get filled up gradually. Such areas over flood plains built

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up by abandoned or cut-off channels contain coarse deposits. The flood
deposits of spilled waters carry relatively finer materials like silt and clay.
The flood plains in a delta are called delta plains.
Natural levees and point bars are some of the important landforms found
associated with floodplains. Natural levees are found along the banks of
large rivers. They are low, linear, and parallel ridges of coarse deposits
along the banks of rivers quite often cut into individual mounds. During
flooding as the water spills over the bank, the velocity of the water comes
down and large-sized and high specific gravity materials get dumped near
the bank as ridges. They are high nearer the banks and slope gently away
from the river. The levee deposits are coarser than the deposits spread by
floodwaters away from the river. When rivers shift laterally, a series of
natural levees can form.
Deltas are like alluvial fans but develop at a different location. The load
carried by the rivers is dumped and spread into the sea. If this load is not
carried away far into the sea or distributed along the coast, it spreads and
accumulates. Classification of Delta: Deltas are generally classified based
on common characteristics of shape, structure, size growth etc. The shape
of deltas is determined by the physical conditions such as discharge of
water, the velocity of streamflow, supply and amount of sediments, rate of
subsidence, tidal waves, sea waves, oceanic currents, rate of growth etc.
Generally, deltas are divided on the following two bases.
(1) based on shape (i) arcuate delta (ii) bird-foot delta (iii) estuarine delta
(iv) truncated delta
(2) based on growth (i) growing delta (ii) blocked delta
(i) Arcuate delta: Such deltas are like an arc of a circle or a bow such
deltas are formed when the river water is as dense as the seawater. The
arcuate or semi-circular shape is also given to such deltas by sea waves
and oceanic currents. The Nile Delta is the best example of arcuate deltas.
(ii) Bird-foot Delta: Bird foot deltas resembling the shape of the foot of a
bird are formed due to deposition of finer materials that are kept in
suspension in the river water which is lighter than the seawater. The rivers
with high velocity carry suspended finer load to greater distances inside
the oceanic water. The fine materials after encountering saline oceanic
water settle down on either side of the main channel and thus a linear
delta is formed. It is otherwise called a finger delta. (iii) Estuarine delta:
The deltas formed due to the filling of estuaries of rivers are called
estuarine deltas. Those mouths of the rivers are called estuaries which are

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submerged under marine water and sea waves and oceanic currents
remove the sediments brought by the rivers. There is a continuous
struggle between the rivers and seas. The deltas of Narmada and Tapi
rivers of India are the examples of estuarine deltas. (iv) Truncated delta:
Sea waves and ocean currents modify and even destroy deltas deposited
by the river through their erosional work. Thus, eroded and dissected
deltas are called truncated deltas. (v) Blocked Delta: These are the
deltas are whose seaward growth is blocked by sea waves and ocean
currents through their erosional activities. (vi) Abandoned delta: When
the rivers shift their mouths in the seas and oceans, new deltas are
formed, while the previous deltas are left unnourished, such deltas are
called abandoned deltas.

Sundarbans Delta: Arcuate River delta Mississippi: Bird foot Delta

Photo Courtesy: NASA

13.5 Karst topography:

Landforms produced by chemical weathering or chemical erosion of
carbonate rocks mainly calcium carbonate and magnesium carbonate by
surface and subsurface water are called Karst topography which refers
to characteristic landforms produced by chemical erosion on crystalline
jointed limestone of Karst region of erstwhile Yugoslavia situated along the
eastern margin of Adriatic Sea.
13.5.1 Distribution of Karst Areas
Karst topography generally develops in those areas where thick beds of
massive limestone lie just below the layer of surficial materials. Besides,
karst topography also develops on dolomite, dolomites limestones and
chalks. Besides the typical karst region of erstwhile Yugoslavia, Karst
topography has well developed in cause region of southern France.

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13.5.2 Conditions for the development of Karst
Topography:
The following conditions alone favour the development of true karstic
topography.
(1) The limestone must be massive, thickly bedded, hard and tenacious,
well cemented, and well jointed.

(2) Limestones should not be porous wherein permeability is largely

controlled by joints and not by the mass of rocks because if limestones are
porous, the water may pass through the rock mass and thus whole rock
mass will become weak and will collapse.
(3) The position of limestone should be above the groundwater table so
that surface drainage may disappear through sinks, blind valleys and
sinking creeks to have subterranean drainage so that caves, passages
and galleries and associated features may be formed.
(4) The limestones should be widely distributed in both areal and vertical
dimensions.
(5) The carbonate rocks should be very close to the ground surface so that
rainwater may easily and quickly infiltrate into the beds of limestones and
may corrode the rocks to form solutional landforms.
(6) The limestones should be highly folded fractured or faulted.
(7) There should be enough rainfall so that the required amount of water is
available to dissolve carbonate rocks.

13.6 Karst: Erosional Landforms

Lapies: The highly corrugated and rough surface of limestone lithology
characterized by low ridges and pinnacles, narrow clefts and numerous
solution holes are called lapies. Lapies are generally formed due to
corrosion of limestones along their joints when limestones are well
exposed at the ground surface.

The weathering residues left at the surface are called terra rosa which
means red residual soils or red earth. Chemically active rainwater
dissolves limestones and other carbonate rocks along their joints and thus
numerous types of solution holes are developed at the ground surface
when limestones are directly exposed to the atmospheric processes.
Smaller holes are called sinkholes which are generally of two types (i)
funnel-shaped sinkholes and (ii) cylindrical sinkholes. Gradual
enlargement of sinkholes due to the continuous dissolution of limestones

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results in the coalescence of closely spaced sinkholes into one larger hole
which is called a swallow hole. Some swallow holes are further enlarged
due to continuous solution into larger depression enlarged which are
called dolines.

Fig. 13.3 Limestone features

The solution holes enlarged due to the collapse of some portion of the
upper surface because of the formation of cavities below the ground
surface are called collapse sinks. A feature almost like doline in
appearance but with shallow depth and larger areal extent is called
solution pan. Sometimes the floor of doloines is plugged due to
deposition of clay, with the resulting water cannot percolate dolines full of
water are called karst lakes. Rocks-walled steep depressions caused by
the collapse of the ground surface are called cockpits. Karst window is
formed due to the collapse of the upper surface of sinkholes or domains.
Extensive depressions are called uvalas which are up to one KM across.
Smaller uvalas are called jamas. Most extensive, larger than dolines,
depressions are called ‘poljes’.
Sinking creek-The surface of the karst plain looks like a sieve because of
the development of closely spaced numerous sinkholes. These sinkholes
act as funnels because surface water disappears to go underground
through these holes. When surface water disappears through numerous
sinkholes located in a line, the resultant feature is s called a sinking creek
and the point through which water goes downward is called a sink. Blind
valley refers to the valley of that surface stream that disappears in
limestone formation through a swallow hole or sinkhole. In other words,
that valley is called a blind valley the flow of which terminates at a swallow
hole and the valley looks dry valley. Karst valley –Surface streams
develop their U-shaped vaa limestone formationormations. Such wide U-

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shaped valleys developed on limestones are called solution valleys or
karst valleys. Caves or Caverns are voids of large dimensions below the
ground surface. Caves are the most significant landforms produced by
erosional work of groundwater in limestone lithology. The vertical pipe-like
passages that connect the caves and the swallow holes are called
‘Ponores’. Natural Bridge in limestone areas is formed in two ways (1)
due to collapse of the roofs of caves and (2) due to disappearance of
surface streams as subterranean streams, formation of valleys below the
ground surface and reappearance of the disappeared stream on the
ground surface.

13.7 Karst: Depositional features

All types of deposits in the caverns are collectively called speleothems of
which calcite is the common constituent. Banded calcareous deposits are
called travertines whereas the calcareous deposits, softer than travertine,
at the mouth of the caves are called tufa or calc-tufa. The calcareous
deposits from the dripping of water in dry caves are called dripstones.
The columns of dripstones hanging from the cave ceiling are called
stalactites while the calcareous columns of dripstones growing upward
from the cave floor are known as stalagmites. Cave pillars are formed
when stalactites and stalagmites meet. The dripstones growing sideward
from stalactites and stalagmites are called helictites and heligmites
respectively. The helictites of the globular structure are called globulites.
Floor deposits caused by seepage water and water flow out of stalagmites
are called flowstones.

Let Us Sum Up
Our planet Earth has a dynamic evolving system. Many cyclic processes
are acting on the surface of the earth. They are done by aerial agents like
air, wind, water, ice and waves. They are called geographical agents.
They create a lot of landforms on the surface of the earth. The landforms
either carved out or built up by running water are called fluvial landforms
and the running waters which shape them are called the fluvial processes
which include overland flow and steam flow. Erosion by any river is a very
important aspect for mankind. The river carries rocks, stones, soil particles
etc. from one place to another. This process of carrying materials is known
as transportation. Rivers deposit sediments in different parts of their
courses and thus form various types of landforms which are called
constructional landforms such as alluvial fans and alluvial cones,
sandbanks, natural levees, flood plains, sand bars and deltas.

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Landforms produced by chemical weathering or chemical erosion of
carbonate rocks mainly calcium carbonate and magnesium carbonate by
surface and subsurface water are called Karst topography. Lapies are
generally formed due to corrosion of limestones along their joints when
limestones are well exposed at the ground surface. The weathering
residues left at the surface are called terra rosa. All types of deposits in
the caverns are collectively called speleothems of which calcite is the
common constituent. The columns of dripstones hanging from the cave
ceiling are called stalactites while the calcareous columns of dripstones
growing upward from the cave floor are known as stalagmites. Cave
pillars are formed when stalactites and stalagmites meet.

Glossaries
• Fluvial: Latin word refers to the work of rivers

• Monadnocks: a lowland of faint relief with some low resistant

remnants called standing out here and there.
• Peneplain: This type of plain forming because of stream erosion (an
almost plain).
• Gorge: A gorge is a deep valley with very steep to straight sides
• Canyon: a canyon is characterized by steep step-like side slopes and
maybe as deep as a gorge.
• A river delta: A river delta is so named because the shape of the Nile
River's delta approximates the triangular uppercase Greek letter delta
is a landform created by deposition of sediment that is carried by
a river as the flow leaves its mouth and enters Slower-moving or
stagnant water

• Karst topography refers to characteristic landforms produced by

chemical erosion on crystalline jointed limestone of Karst region of
erstwhile Yugoslavia.

• Cave pillars are formed when stalactites and stalagmites meet.

• Stalactites the columns of dripstones hanging from the cave ceiling
Blind valley refers to the valley of that surface stream that disappears
in limestone formation through a swallow hole or sinkhole.
• Dolines Some swallow holes are further enlarged due to continuous
solution into larger depression enlarged which are formed.

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Check Your Progress
1. Fluvial landforms-Define
Latin word refers to the work of rivers.
2. List the types and factors controlling the erosional process.

Lateral and vertical, Volume of water, speed, nature of rock and load of
river
3. State the erosional landforms of the river.
Waterfalls, potholes, V-shaped valley, gorge, and canyon,
4. Mention the various transportation processes of rivers.
The solution, Traction, and load in suspension
5. What are the depositional features of rivers?
Depositional features of rivers are alluvial fans and alluvial cones,
sandbanks, natural levees, flood plains, sand bars and deltas.

6. Karst topography-Define
Landforms produced by chemical weathering or chemical erosion of
carbonate rocks mainly calcium carbonate and magnesium carbonate
by surface and subsurface water.
7. Examine the essential conditions for the development of Karst
Topography.
The limestone must be massive, thickly bedded, hard and tenacious,
well cemented, and well jointed
8. Name the landforms produced by the work of underground water.
Sink holes, Dolines, Lapies, Dolines, Vuvala and Terra Rosa
9. What are the landforms produced by the depositional process of
Underground water?

Stalactite, Stalagmite, Cave pillars, natural bridge, Karst Valley.

Suggested Readings
1. Strahler, A. H. and Strahler, A N., (2001) Modern Physical Geography
(4/E), John Wiley and Sons, Inc., New York.
2. Christopherson, R. W. and Birkeland, G. H., (2012) Geosystems: An
Overview to Physical Geography (8/E), Pearson Education, New
Jersey.

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3. Das Gupta, A &Kapoor, A.N., (2001) Principles of Physical Geography,
S.C. Chand & Company Ltd. New Delhi.
4. Khullar, D.R., (2012) Physical Geography, Kalyani Publishers, New
Delhi.
5. Brown, J.H. (2005) Biogeography, Sinauer Associates Inc,
Sunderland.

6. Seddon, B.A. (1971) Overview to Biogeography, Duckworth, London.

7. Thornbury W.D. (2002), Principles of Geomorphology, CBS Publishers
& Distributors, New Delhi, India.

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 UNIT 14
Evolution of Landforms (Erosional and
Depositional) Glacial and Aeolian
Structure
14.1 Overview
Learning Objectives

14.2 Types of Glaciers

14.2.1 Erosional landforms of Glacier
14.2.2 Transportation and Depositional landforms of Glacier

14.3 Aeolian landforms

14.3.1 Erosional works of wind
14.3.2 Erosional Landforms of wind
14.3.3 Transportation work of wind
14.3.4 Depositional work of wind
14.3.5 Depositional landforms of wind
Let us sum up
Glossary
Check your Progress
Suggested readings

14.1 Overview
Glaciers are moving bodies of ice that can change entire landscapes. They
sculpt mountains, carve valleys, and move vast quantities of rock and
sediment. In the past, glaciers have covered more than one-third of Earth's
surface, and they continue to flow and shape features in many places.
Glaciers and the landscapes they have shaped provide
invaluable information about past climates and offer keys to understanding
climate change today.
Work of glaciers: The moving ice mass downslope under the impact of
gravity is called a glacier. About 10% of the earth’s surface is now covered

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by glaciers. Glaciers are formed due to the accumulation of ice above the
snow line under extreme cold climates. A snow line is generally defined as
a zone between permanent and seasonal snow. The area of accumulation
of huge volume of ice is called snowfields which generate glaciers of
different dimensions.
Learning Objectives
After learning this unit, students would be learning the following,
• Glacial erosional and depositional Landforms
• Aeolian erosional and depositional Landforms

14.2 Types of Glaciers

Glaciers are generally divided into 2 broad categories viz. (i) mountain or
valley glaciers and (ii) continental glaciers.
Ice sheets or ice caps-The biggest glaciers on the earth’s land surface
are called ice sheets which are broad domes with flattened cross-sections
covering thousands of square kilometres. These are hundreds of
kilometres in width. They submerge underlying topography.

Continental glaciers are extensive ice sheets. These are called

continental because they cover most of the continent. Extensive ice sheets
radiate outward the centre and move downslope. At present, the biggest
continental glaciers are Antarctic and Greenland ice sheets.
Mountain or valley glaciers-The body of ice moving downslope under
the impact of gravity through the valley bordered by rock valley walls in the
mountains is called mountain glacier or valley glacier of Alpine glacier.

Fig.14.1 Valley Glacier

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14.2.1 Erosional landforms of Glacier
The erosional work of the glaciers is accomplished through the
mechanisms of abrasion, plucking and polishing. Pure ice mass is
geomorphologically inactive but when coarse debris is carried by the
glacier at its base it becomes an active agent of erosion. Thus, the glacier
erodes its bed and side walls with the help of tools of erosion through the
mechanism of abrasion. Large particles of well-jointed rocks are detached
by the moving glacial ice. This mechanism is called plucking. The
landforms carved out of glacial erosion include U-shaped valleys, hanging
valleys, Cirques, arêtes, horns, nunataks, crag and tail, glacial stairway,
Roches moutonnee, trough lakes, tarn, fiords etc.
U-shaped valleys-The cross-section of glacial valleys or glacial troughs of
mountain glaciers is U-shaped which is characterized by steep valley walls
with concave slopes and broad and flat valley floor. Sometimes, valleys
are associated with tributary valleys called hanging valleys. The valleys
of tributary glaciers that join the main glacial valleys of much greater depth
are called hanging valleys.
Cirques-the armchair-shaped off amphitheatric cirque or corrie is a
horseshoe-shaped, steep-walled depression representing a glaciated
valley head.

Fig.14.2 Glacier Erosional Features

Nunatak-The highest peaks and mounds surrounded by ice from all sides
are called nunataks. They look like scattered small islands amid extensive
ice masses. That is why they are also called glacial islands.

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Crag and Tail-A peculiar landform having vertical eroded steep side up
glacial side and tail-like appearance with lower height down glacial side is
called crag and tail. Such landform is developed over old volcanic or
basaltic plugs which project above the ground surface as resistant in the
flow direction of glacial ice and hence the side facing the direction from
which the ice comes becomes step due to erosion and is called crag. On
the other hand, the other side being sheltered by glacial ice becomes
elongated with a gentle slope and appears like a tail.
Roches moutonnees are streamlined asymmetrical hillocks, mounds or
hills having one side smoothly moulded with a gentle slope and steepened
and craggy ice side. The landform looks like the streamlined rocky
eminences resembling a sheep in a lying posture. Glacial stairways knew
as giant stairways or cyclopean stairs. The plucking of rocks at the foot of
faults forms vertical cliffs. Smaller depressions are formed at the bases of
cliffs. These depressions become lakes when they are filled with
meltwater. Glacial grooves-small-scale streamlined depressions are
called glacial grooves individual grooves may measure 12km in length,
100mt in width and 30 mt in depth. Fiords are glacial troughs that have
been occupied by the sea. Fiords are the arms of the sea which have
occupied U-shaped glaciated valleys which were dug out below sea level
through the mechanisms of abrasion and plucking by valley glaciers
descending from coastal mountains. Fiords are characterized by steep
sidewalls and several hanging valleys. They are very deep towards the
coastal land and become shallow for some distance towards the sea, but
they again become deep.

14.2.2 Transportation and Depositional landforms of

Glacier
The rock debris carried by the glaciers is collectively called glacial drifts.
Sometimes the term moraine is used for the debris transported by the
glaciers and also for the landforms made by the deposition of glacial
debris. Depositional landforms formed due to the setting down of glacial
drifts include moraines or moronic ridges and drumlins. Moraines are
ridge-like depositional features of glacial tills. They are long but narrow
ridges with a height of more than 30 mt.
1. Outwash Plain: when the glacier reaches its lowest point and melts, it
leaves behind a stratified deposition material, consisting of rock debris,
clay, sand, gravel etc. This layered surface is called till plain or an
outwash plain and a downward extension of the deposited clay material
is called a valley train.

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2. Eskars is a winding ridge of unasserted deposition of rock, gravel, clay
etc. running along a glacier in a till plain. The eskers resemble the features
of an embankment and are often used for making roads. If the melting of
the glacier has been punctuated, it is reflected in a local widening of the
esker and here it is called a beaded esker.
3. Kame Terraces are the broken ridges or unasserted deposition looking
like hummocks in a till plain
4. Drumlin is an inverted boat-shaped deposition in a till plain caused by
deposition. The erosional counterpart is called a Roche moutonne.
5. Kettle Holes can be when the deposited material in a till plain gets
depressed locally and forms a basin
6. Moraine is a general term applied to rock fragments, gravel, sand etc.
carried by a glacier. Depending on its position, the moraine can be ground,
lateral, medial, or terminal moraine. When two glaciers join their lateral
moraines also join near their confluences and are called medial moraines.

14.3 Aeolian landforms

The wind is, no doubt, an important geomorphic agent but it is not as
effective a process of erosion as rivers and sea waves. “Wind is a
comparatively minor agent of geomorphic change because of the low
density of air as compared to rock and water”. Aeolian processes involving
erosion of dry, loose and unprotected geomaterials, transportation and
deposition of fine sediments mainly sand, are most active in arid and semi-
arid regions of tropical and temperate environments. Desert environments
are characterized by very low mean annual rainfall (less than 250mm,
average being 100mm), practical absence of vegetation, very high daily
and annual ranges of temperature, dust storms, high-velocity winds, the
dominance of sands, highly variable annual rainfall, occasional torrential
rainfall through strong rainstorms resulting into stream floods and sheets
floods etc. The deserts having mobile sands are called erg. The tropical
desert areas are characterized mainly by mechanical weathering which
includes the processes of block disintegration due to temperature change
granular disintegration due to temperature change, shattering due to
occasional light shower during the daytime, exfoliation due to heat and
wind etc. Besides chemical weathering involving the decomposition of
rocks during occasional wet conditions also become effective.

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14.3.1 Erosional works of wind
Wind erosion in the arid and semi-arid regions is assisted by mechanical
weathering. Expansion of rocks due to high daytime and summer
temperature and contraction consequent upon lower night and winter
temperature result in the disintegration of crystalline rocks which facilitates
Aeolian erosion. Wind erosion is largely controlled and determined by (i)
wind velocity (ii) nature and the number of sands, dust and pebbles, (iii)
composition of rocks (iv) nature of vegetation and (v) humidity, rainfall and
temperature. Unlike rivers and glaciers, winds erode the rocks from tall
sides because of their variable directions. Wind erosion occurs in three
ways viz. (1) deflation, (abrasion) or sandblasting and (3) attrition. The
process of removing, lifting the blowing away dry and loose particles of
sands and dust by wind is called deflation. Long continued deflation
removes most loose materials and thus depressions or hollows were
known as blowouts are formed and bedrocks are exposed to wind
abrasion. Deflation also attacks rock surfaces but the process of
depression in rock surfaces mainly of sandstones, detaches small
fragments and helps in forming small depressions in rock surfaces but the
process of depression formation through deflation in bedrock surface is
exceedingly slow. Since deflation removes mostly fine particles larger
particles such as gravel are left over the surface. Thus, the accumulation
of gravels over thousands of years from desert pavements protect the
rocks below from further wind erosion. Wind armed with entrained sand
grains as tools of erosion attacks the rocks and erodes them through the
mechanisms of abrasion, fluting, grooving, pitting and polishing. The
combined effects of these mechanisms are collectively called abrasion or
sandblasting. Attrition involves mechanical tears and wears off the
particles suffered by themselves while they are being transported by wind
through the processes of saltation and surface creep. Saltation involves
the movement of sands and gravels through the mechanisms of bouncing,
jumping and hopping by turbulent airflow. Saltating grains frequently rise
to a height of 50 cms over a sand bed and up to 2mts over the pebbly
surface by the combined action of aerodynamic lift and the impact of other
saltating grains which return to the ground surface. Surface creep
involves the movement of relatively bigger particles along the ground
surface by strong winds.

14.3.2 Erosional Landforms of wind

Long-continued erosional works through the mechanisms of abrasion or
sandblasting and deflation produces some characteristics of landforms in

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desert areas such as blowouts or deflation basins, mushroom rocks or
pedestal rocks, inselbergs, demoiselles, yardangs, zeugen, ventifacts,
dreikanters, stone lattice, wind windows etc., Deflation Basins-
Depressions formed in the deserts due to removal of sands through the
process of deflation are called deflation basins or blow-outs Or desert
hollows.
Mushroom rocks: The rocks having a broad upper part and narrow base
resembling an umbrella or mushroom are called mushroom rocks or
pedestal rocks or pilzfelsen. Inselbergs are referring that the rising
residual hill above the flat surfaces in the arid regions are also called
Bernhardt. Demoiselles represent rock pillars having relatively resistant
rocks at the top and soft rocks below. These features are formed due to
differential erosion of hard rocks and soft rocks. Zeugen-Rock masses of
a tabular form resembling a capped inkpot standing on a softer rock
pedestal of shale, mudstone etc. are called zeugen.

Fig.14.3 Yardangs
Yardangs are steep sided deeply undercut overhanging rock ridges
separated from one another by long grooves or corridors or passageways
cut in desert floors of relatively softer rocks. Yardangs are also called
cockscomb in some countries. Dreikanter-Faceted rock boulders,
cobbles and pebbles abraded by long periods of wind erosion are called
ventifacts. A ventifact or faceted rock block may have as many as eight
abraded facets. The rock pieces having three abraded facets are called
dreikanter while the boulders with two abraded facets are called
zweikanter. Stone lattice-The rocks of varying compositions and
resistance when abraded by powerful wind charged with erosion tools
become of uneven surface as the powerful wind abrades weaker sections
of rocks and removes the abraded materials while relatively resistant
sections are least affected by abrasion. Such pitted and fluted rock

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surfaces are called stone lattices. Wind bridges and wind windows-
Holes are formed due to continuous abrasion of the stone lattice by a
powerful wind. These holes are gradually widened and ultimately, they
reach the opposite side of the rocks. Such holes are formed through
abrasion across the rocks are called wind windows.

14.3.3 Transportation work of wind

The transportation work of wind differs from other agents of erosion
substantially because the direction of the wind is highly variable. Wind
transport involves the entrainment of loosened grains of sands and dust in
the air and their movement to new locations of deposition. Wind
transports the materials through the mechanisms of suspension,
saltation and traction. Very fine materials with a diameter of less
than0.2mm are kept in suspension by upward moving air. Such materials
kept in suspension are called dust and extremely fine particulate matters
are called haze or smoke. The suspended matters are carried by the wind
for greater distances. The materials larger than 0.2mm in diameter are
transported through the mechanism of bouncing, leaping, or jumping. This
mechanism of wind transport is called saltation. The transport loosened
materials on the ground surface are called surface creep or traction
wherein the materials always touch the ground and move forward without
saltating.

14.3.4 Depositional work of wind

The depositional work of wind is geomorphologically important because
significant features like dunes and loess are formed. Deposition of
windblown sediments occurs due to marked reduction in wind speed and
obstructions caused by bushes, forests, marshes and swamps, lakes, big
rives, walls etc. Sands are deposited on both windward and leeward sides
of fixed obstructions. The accumulated sand mounds on either side of the
obstruction are called sand shadows. Accumulation of sands between
obstacles is called sand drifts.

14.3.5 Depositional landforms of wind

Ripple marks are small-scale depositional features of sands. These
wave-like features are formed mainly by saltation impact. Ripples are
divided into (i) transverse ripples and (ii) longitudinal ripples. Sand Dunes
are heaps or mounds of sands are generally called dunes or simply dunes.
Though dunes are significant depositional features of desert areas, they
are also formed in all those areas where sands are available in profusion
and wind is capable of transporting and depositing them in suitable areas.

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There is a wide range of variations in the shape, size and structure of
different types of dunes. Most dunes are mobile landforms as they
generally move forward in the direction of the wind. If they are formed in
groups, they are called a dune complex, dune colony or dune chain.
Dunes are classified on various bases viz. morphology, structure,
orientation, location ground pattern, internal structure, number of slip faces
etc. Longitudinal sand dunes-Sand dunes formed parallel to the wind
direction are called longitudinal dunes. They are extending hundreds of km
in length with an average height of several hundred meters. Longitudinal
dunes are also called linear dunes, sand ridges, seif, lab dunes etc.
Transverse sand dunes-They appear wave-like features. Dunes formed
transverse to the direction of prevailing winds are called transverse dunes.

Fig. 14.4 Types of dunes

Dunes of crescentic shape having two horns are called Barchans.

Barchans are special types of transverse dunes. Parabolic dunes
generally develop in partially stabilized sandy terrains. They are usually

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U-shaped having a convex nose that migrates downwind. These dunes
are much longer and narrower than barchans but are always associated
with a blowout. Other forms of dunes-The dunes having multiple slip faces,
high central peak, radially extending three or more arms are called star
dunes. The dunes formed of coarser sands left behind due to the
migration of longitudinal dunes are called whalebacks or whaleback
dunes. Loess is an example of the most significant windblown deposits.
Loess means loose or unconsolidated material. Loess deposits generally
occur at very distant places from the source areas of their sediment
supply.

Let us sum up
Aeolian is a term about the wind; hence windborne, windblown or wind
deposited materials are often referred to as aeolian landforms. The wind is
not an effective agent in eroding the landscape, but it can transport loose,
unconsolidated fragments of sand and dust. Winds vary considerably in
strength from one moment in time to the next and are thus able to lift and
transport rock debris for only short periods. Wind action is quite
pronounced in the arid and semi-arid areas of the world where the
absence of vegetation cover and the presence of extensive desolate rocks
help in the erosional, transportation and depositional processes. The wind
brings changes over the earth surface through the process of erosion,
transportation, and deposition.
Glaciers are formed due to the accumulation of ice above snowlines under
extreme cold climates. To understand global warming and sea level
changing concepts knowledge on glaciers has become essential. Glaciers
are classifiable in three main groups: (1) glaciers that extend in continuous
sheets, moving outward in all directions, are called ice sheets if they are
the size of Antarctica or Greenland and ice caps if they are smaller; (2)
glaciers confined within a path that directs the ice movement are
called mountain glaciers; and (3) glaciers that spread out on the level
ground or the ocean at the foot of glaciated regions are
called piedmont glaciers or ice. The landforms carved out of glacial
erosion include bumps and depressions. U-shaped valleys, hanging
valleys, cirques, aretes, horns, nunataks, crag and tail, glacial stairway,
rochesmoutonnees, trough lakes, tarn, fiords etc., Depositional landforms
formed due to settling down of glacial drifts (glacial sediments of varying
sizes) include moraines or morainic ridges and drumlins.

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Glossaries
Aeolian: It is a term about the wind; hence windborne, windblown or wind
deposited materials are often referred to as aeolian landforms.
Desert: A desert is a barren area of landscape where little precipitation
occurs and consequently, living conditions are hostile for plant and animal
life. The lack of vegetation exposes the unprotected surface of the ground
to the processes of denudation. About one-third of the land surface of the
world is arid or semi-arid.
Pediplains: When the high relief structures in deserts are reduced to low
featureless plains by the activities of wind, they are called Pediplains.
Alpine (valley) glacier: Alpine glaciers begin high up in the mountains in
bowl-shaped hollows called cirques
Continental glacier: Continental glaciers are continuous masses of ice
that are much larger than alpine glaciers. Small continental glaciers are
called ice fields.
Glacial erratic: A glacial erratic is glacially deposited rock differing from
the size and type of rock native to the area in which it rests. "Erratics"
take their name from the Latin word errare (to wander) and are carried
by glacial ice.

Check your Progress

1. Describe the landforms produced by the erosion of glaciers.
The landforms carved out of glacial erosion include bumps and
depressions. U-shaped valleys, hanging valleys, cirques, aretes,
horns, nunataks, crag and tail, glacial stairway, rochesmoutonnees,
trough lakes, tarn, fiords etc.,
2. Elucidate the landforms produced by the depositional process of
glaciers.
Depositional landforms formed due to settling down of glacial drifts
(glacial sediments of varying sizes) include moraines or morainic
ridges, drumlins Eskers and Outwash Plains
3. State the work of wind in an arid region.
Aeolian erosion develops through two principal processes: deflation
removal of material and its transport as fine grains in atmospheric
suspension and abrasion mechanical wear of coherent material.
4. Describe the landforms produced by the action of wind in an arid

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 region.
The landforms that result from aeolian erosion include ventifacts, ridge
and swale systems yardangs, desert depressions, and inverted relief.

Suggested Readings
1. Strahler, A. H. and Strahler, A N., (2001) Modern Physical Geography
(4/E), John Wiley and Sons, Inc., New York.
2. Christopherson, R. W. and Birkeland, G. H., (2012) Geosystems: An
Overview to Physical Geography (8/E), Pearson Education, New Jersey.
3. Das Gupta, A &Kapoor, A.N., (2001) Principles of Physical Geography,
S.C. Chand & Company Ltd. New Delhi.

4. Khullar, D.R., (2012) Physical Geography, Kalyani Publishers, New

Delhi.
5. Brown, J.H. (2005) Biogeography, Sinauer Associates Inc, Sunderland.
6. Seddon, B.A. (1971) Overview to Biogeography, Duckworth, London.
7. Thornbury W.D. (2002), Principles of Geomorphology, CBS Publishers
& Distributors, New Delhi, India

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 UNIT 15
Evolution of Landforms (Erosional and
Depositional): Coastal
15.1 Coastal landforms
Learning Objectives
15.2 Sea Coast and Sea Shore

15.3 Coastal landforms: Processes and Mechanism of Marine erosion

15.4 Erosional Landforms:
15.5 Depositional Landforms:

Let us sum up
Glossary
Check your progress
Suggested readings

15.1 Coastal landforms

The work of seawater is performed by several marine agents like sea
waves, oceanic currents, tidal waves, and tsunamis but the sea waves are
the most powerful and effective erosive agents of coastal areas. Sea
waves are defined as undulations of seawater characterized by well-
developed crests and troughs. The mechanism of the origin of sea waves
is not precisely known but it is commonly believed that waves are
generated due to friction on the water surface caused by blowing winds.
The height of wind-generated sea waves depends on (i) wind speed (ii)
the duration of wind from one direction and (iii) the extent of fetch which
represents the length of water surface over which the wind blows. Sea
waves are classified into two types based on the depth of oceanic water
viz. (1) waves in deep waters are called oscillatory waves and (2) waves
of shallow water are called translator waves. From a geomorphological
point of view, sea waves are divided into two major types viz. (1)
constructive waves and (2) destructive waves. Low-frequency waves
approaching the shore and beach are constructive because they lose
volume and energy rapidly while moving up the beach. After all, water

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percolates in the shingles and other beach materials and thus the
backwash is weakened. It is, thus obvious that low-frequency waves help
in the building of beaches. On the other hand, high-frequency waves with
short wavelengths and high wave crests occurring on a more steeply
sloping shore are destructive because instead of spilling they plunge and
generate a powerful backwash that combs down and the beach.
Learning Objectives
After learning this unit, students would be able to be understanding the
• Coastal landforms: Processes and Mechanism of Marine erosion
• Erosional, and Depositional Landforms

15.2 Sea Coast and Sea Shore

Generally, seacoast and seashore are taken as synonymous but
geomorphologically these two terms have quite different meanings.
Seashore represents the zone of land between high tidewater and low
tidewater. While the shoreline represents the actual landward limit of
seawater at a given moment. ‘The shoreline is the line of demarcation
between land and water’. The shore zone or simply shore is divided into e
zones: (1) back shore represents the beach zone starting from the limit of
frequent storm waves to the cliff base; (2) foreshore extends from low
tidewater to high tidewater and (3) offshore represents the zone of the
shallow bottom of the continental slope.

15.3 Processes and Mechanism of Marine erosion

Hydraulic action: It refers to the impact of moving water on the coastal
rocks. Large storm waves attack the coastal rocks with enormous hammer
blows. The waves can dislodge larger fragments of rocks weighing several
tones in weight. This process of displacement of rock fragments is called
quarrying and plucking. Abrasion or corrosion is another effective
mechanism of coastal erosion by marine waves with the help of tools of
erosion (coarse sands, pebbles, cobbles, and sometimes boulders).
Corrosion or solution refers to the chemical alteration of rocks mainly
carbonate rocks due to their contact with seawater. Besides hydraulic
action, abrasion and corrosion, coastal rocks are also weakened and
disintegrated due to alternate processes of wetting and drying because
these promote a wide range of chemical processes which help in the
disintegration and decomposition of coastal rocks.

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 Fig. 15.1 Coastal Features

15.4 Erosional Landforms:

Significant coastal features formed due to marine erosion by sea waves
and other currents and solutional processes include cliffs, coves, caves,
indented coastline, stacks, chimneys, arch, inlets wave-cut platforms etc.
Cliffs: Steep rocky coast rising almost vertically above seawater is called
sea cliff which is very precipitous with overhanging crest. The formation of
sea cliffs begins with the erosion of coastal rocks through the mechanisms
of hydraulic actions and abrasion by breaker waves.

Fig. 15.2 Cliff and Wave cut platform

Wave-Cut Platform: Rock-cut flat surfaces in front of cliffs are called
wave-cut platforms or simply shore platforms which are slightly concave

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upward. The origin and development of wave-cut platforms are related to
cliff recession. These are called wave-cut benches. Sea Caves: Sea
caves are formed along the coast due to gradual erosion of weak and
strongly jointed rocks by up rushing breaker waves. The joints are
widened into large cavities and hollows which are further enlarged due to
gradual wave erosion into well-developed coastal caves. When the caves
are enlarging to such an extent that their roofs become remarkably thin,
they ultimately collapse and fall, and the debris is removed by powerful
backwash and thus resultant long narrow inlets are called ‘geo’ in
Scotland. Sometimes, the air in the cave is compressed by up rushing
powerful storm waves and finding no other route to escape it breaks open
the roof of the cave and appears with great force making unique whistling.
Such holes are called natural chimneys or blow holes or gloup. Stocks
are also called needles, columns, pillars, skerries etc.

Fig. 15.3 Wave Erosional Features

15.5 Depositional Landforms:

Significant depositional landforms developed by sea waves include sea
beaches, bars, and barriers, offshore and longshore bars, spits, hooks,
loops, connecting bars, loped bars, tombolo, barrier island, tidal inlets,
winged headlands, progradation, wave-built platforms etc. Beaches:
Temporary or shore-lived deposits of marine sediments consisting of
sands, shingles, cobbles etc. on the seashore are called beaches.
Beaches are generally formed when the sea is calm, and winds are of low
velocity. Beach materials consist of fine to coarse sands, shingles
(pebbles), cobbles and boulders. The major sources of the supply of
beach materials are erosion of headlands and cliffs, sediments brought by
the rivers and nallas at their mouths, mass wasting and mass movement.
An ideal beach consists of two main elements e.g., upper beach and
lower beach and several minor elements e.g., storm beach, beach

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ridges, or berms, beach cusps, small channels, ripples, ridges,
runnels etc.
Beaches are generally classified based on beach materials into (1) sand
beach sand grains ranging in size between 0.5 to 2 mm), (2) shingle
beach (composed of pebbles ranging in size from 2 to 100mm) and (3)
boulder beach (more than 100mm in diameter) The ridges, embankments
or mounds of sands formed by sedimentation through sea waves parallel
to the shoreline are called bars. The larger forms of bars are called
barriers. The formation of bars and barriers starts with the development of
shoals due to the deposition of sands. The shoals grow in height by the
addition of sediments until they appear above sea level. Bars and barriers
may be formed near the coast or away from the coast, parallel to the
coastline or transverse to the coast. There are different forms of sand bars
and barriers. If the bars are formed in such a way that they are parallel to
the coast but are not attached to the land, they are called offshore or
longshore bars. If the sand bars are formed in such a way that one end
is attached to the land while the other end projects or opens out towards
the sea, they are called spits. High-energy storms waves very often modify
the shape of spits by bending them towards the coast. The curved spits
assume the shape of a hook and thus such spits are called hooked spits
or simply hooks. Hooks are stabilized when there is an equilibrium
between constructive and destructive waves.
When the opposing currents become more dominant than the littoral
currents, the spits are bent to such an extent that they are attached to the
mainland and thus form a complete loop that encloses seawater in the
form of lagoons. Such a form of a spit is called a loop. When such a loop
is formed around an island, it is called a looted bar. Connection bars are
formed when bars are so extended that they either join two headlands or
two islands. A bar connecting two headlands is called connecting bar while
a bar becomes a tombolo when it connects the mainland with an island or
connects a headland with the island. Lagoons are formed when the coves
or bays are completely enclosed by bars. Flat and rolling marshy lands
developed in the coastal areas of humid tropics are called coastal
wetlands, which are generally formed behind spits or bars. Flat and rolling
marshy lands developed in the coastal areas of humid tropics are called
coastal wetlands which are generally formed behind spits or bars.
Depositional coastal areas having a flat surface in the dry tropic zones are
called sabkhas which are flat but barren coastal lands.

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Let Us Sum Up
The work of seawater is performed by several marine agents like sea
waves, oceanic currents, tidal waves, and tsunamis but the sea waves are
the most powerful and effective erosive agents of coastal areas. Seashore
represents the zone of land between high tidewater and low tidewater.
While the shoreline represents the actual landward limit of seawater at a
given moment. The waves can dislodge larger fragments of rocks
weighing several tones in weight. This process of displacement of rock
fragments is called quarrying and plucking. Significant coastal features
formed due to marine erosion by sea waves and other currents and
solutional processes include cliffs, coves, caves, indented coastline,
stacks, chimneys, arch, inlets wave-cut platforms etc. Lagoons are
formed when the coves or bays are completely enclosed by bars. Flat and
rolling marshy lands developed in the coastal areas of humid tropics are
called coastal wetlands.

Glossaries
Cliffs: Steep rocky coast rising almost vertically above seawater is called
sea cliff which is very precipitous with overhanging crest.
Sea Caves: Sea caves are formed along the coast due to gradual erosion
of weak and strongly jointed rocks by up rushing breaker waves.
Wave-Cut Platform: Rock-cut flat surfaces in front of cliffs are called
wave-cut platforms or simply shore platforms.
Lagoons are formed when the coves or bays are completely enclosed by
bars.
Beaches: Temporary or shore-lived deposits of marine sediments
consisting of sands, shingles, cobbles etc.,

Tombolo: A bar connecting two headlands is called Tombolo.

Check Your Progress

1. Name the agents of seawater involved in erosional works.
The work of seawater is performed by several marine agents like sea
waves, oceanic currents, tidal waves, and tsunamis but the sea waves
are the most powerful and effective erosive agents of coastal areas.
2. State the process involve in the erosional process of sea waves.

This process of displacement of rock fragments is called quarrying and

plucking.

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3. What are landforms are formed by the erosion of sea waves?
Significant depositional landforms developed by sea waves include
sea beaches, bars, and barriers, offshore and longshore bars, spits,
hooks, loops, connecting bars, loped bars, tombolo, Barrier Island,
tidal inlets, winged headlands, progradation, wave-built platforms etc.
4. Beaches-Define.

Temporary or shore-lived deposits of marine sediments consisting of

sands, shingles, cobbles etc. on the seashore are called beaches.
5. Write a note on Cliff.

Steep rocky coast rising almost vertically above seawater is called sea
cliff which is very precipitous with overhanging crest.

Suggested Readings
1. Strahler, A. H. and Strahler, A N., (2001) Modern Physical Geography
(4/E), John Wiley and Sons, Inc., New York.
2. Christopherson, R. W. and Birkland, G. H., (2012) Geosystems: An
Overview to Physical Geography (8/E), Pearson Education, New
Jersey.
3. Das Gupta, A &Kapoor, A.N., (2001) Principles of Physical Geography,
S.C. Chand & Company Ltd. New Delhi.
4. Khullar, D.R., (2012) Physical Geography, Kalyani Publishers, New
Delhi.
5. Brown, J.H. (2005) Biogeography, Sinauer Associates Inc,
Sunderland.
6. Seddon, B.A. (1971) Overview to Biogeography, Duckworth, London.
7. Thornbury W.D. (2002), Principles of Geomorphology, CBS Publishers
& Distributors, New Delhi, India.

138 | P a g e
 UNIT 16
. Application
of Geomorphology in Mineral
Exploration and Coastal Zone Management

16.1 Overview
Learning Objectives
16.2 Geomorphology and Mineral Exploration

16.3 Geomorphology and Engineering Works

16.4 Geomorphology and Regional Planning
16.5 Geomorphology and Urbanization

16.6 Geomorphology and Hazard Management

16.7 Other Applications of Geomorphology
16.8 Application of Geomorphology in Coastal Zone Management
Let us sum up
Glossary
Check your progress
Suggested readings

16.1 Overview
There has been increasing recognition of the practical application of
geomorphic principles and the findings of geomorphological research to
human beings who are influenced by and, in turn, influence the surface
features of the earth. Continuous increase in population has led to
pressure on land resources, an extension of agriculture to hilly and
marginal lands resulted in man-induced catastrophes like soil erosion,
landslides, sedimentation, and floods. A proper interpretation of landforms
throws light upon the geologic history, structure, and lithology of a region.
As geology becomes more specialized there is a growing possibility that
the application of geomorphology to problems of applied geology will be
overlooked. The role of applied geomorphology relates mainly to the
problems of analyzing and monitoring landscape forming processes that
may arise from human interference. Human beings have over time tried to
tame and modify geomorphic/environmental processes to suit their

139 | P a g e
economic needs. Geomorphology has diverse applications over a large
area of human activity while Geomorphologist may serve more effectively
the need of society.
Learning Objectives
After learning this unit, students would be understanding the following,
• Geomorphology and Mineral Exploration
• Geomorphology and Engineering Works:
• Geomorphology and Regional Planning:
• Geomorphology and Urbanization:
• Geomorphology and Hazard Management:
• Other Applications of Geomorphology

16.2 Geomorphology and Mineral Exploration

There is a close association of geological structure and minerals deposits.
Characteristic landscapes of specific areas could indicate these geological
structures. Economic geologist has not appreciated the exploration of
some minerals in the name of understanding the geomorphic features and
history of a region. In search for mineral deposits, these three points may
serve for Geomorphic features as (I) some minerals have a direct
topographic expression for its deposits; (2) the geologic structure and
topography of an area have correlation which clues the accumulation of
minerals; (3) geomorphic history indicates the physical condition under
which the minerals accumulated or were enriched of a particular area.
Surface expression of ore bodies Some ore bodies have surface
expression, but many do as topographic forms, as outcrops of ore,
gossan, or residual minerals, or as such structural features as faults,
fractures, and breccia zones. Not all ore outcrops need to be reflected in
positive topographic forms.
Though no generalization can be made about the exact type of topography
necessary for the iron ore accumulation, distinct topographic expression is
needed for a particular deposit. Residual iron deposits are the results of
the concentration of iron due to long periods of weathering, and thus for
their accumulation, old erosion and weathering surfaces are favourable
sites. Weathering residues Geomorphology can play an important role for
several important economic minerals which are essentially weathering
residues of present or ancient geomorphic cycles. Apart from iron
deposits, materials like clay minerals, caliche, bauxite and some

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manganese and nickel ores are of this nature. Recent weathering surfaces
may exhibit residual weathering products, or they may lie upon ancient
weathering surfaces which are now buried. Peneplain or near peneplain
surfaces are most commonly surfaces upon which they form. In general,
such minerals are to be found upon remnants of tertiary erosional surfaces
above present base levels of erosion.
Geomorphic processes are the main cause of placer concentration of
minerals, found in specific positions with distinctive topographic
expression the deposition of placers affected by the type of rock-forming
the bedrock floor. There are as many as nine types of placer deposits.
They are residual or ‘seam diggings’, colluvial, eolian, bajada, beach,
glacial including those in end moraines and valley trains, and buried and
ancient placers. The most important among them is alluvial placers. The
other name of Residual placers is ‘seam diggings’ which are residues from
the weathering of quartz stringers or veins, are usually of partial amount,
and grade down into lodes. Creep downslope is the main reason to
produce colluvial placers and are thus transitional between residual
placers and alluvial placers. The most important minerals like gold, tin and
diamonds are obtained from alluvial placers Placer deposits have a total
share of around 20 per cent of the world’s diamonds.
In oil exploration, several oil fields have been discovered because of their
striking topographic expression. These oil fields are characterized by
anticlinal structures which are strikingly reflected in the topography. When
viewed from aerial photographs, many of the Gulf Coast salt dome
structures are evident in the topography. For the student of
geomorphology, it is a good working principle to suspect that
topographically high areas may also be structurally high, where
possibilities of topographical inversion at the crest of a structural high may
result in weak beds.

16.3 Geomorphology and Engineering Works

Evaluation of geologic factors of one type or another is often involved in
most engineering projects, among all the factors terrain characteristics is
most common. A detailed study of the geomorphic history of an area may
support the proper evaluation of surficial materials and the bedrock profile
configuration. Road Construction Topographic features of an area
determined the most feasible highway route. Road engineering faces
several problems by different types of terrain that includes geologic
structure, geomorphic history of the area, lithological and stratigraphic
characteristics, and strength of the surficial deposits. An area like the karst

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plain required repeated cut and fill, if not done then the road will be
flooded after heavy rains with surface runoff from the sinkholes. The
presence of enlarged solutional cavities in the karst region emphasises the
designer of roads in such a way that roads should not be weakened. A
region like glacial terrain presents several engineering problems. Road
construction in flat till plain is topographically ideal but in other areas
where moraines, eskers, kames or drumlins like features exist there is a
need for cut and fill to avoid circuitous routes. Areas that are characterized
by late, youth and maturity of relief will require more bridge construction
and many cuts and fills. These types of areas are consistently facing
problems like landslides, earth flows, and slumping. Landslides and
different types of mass-wasting present problems not only in different
phases of engineering but in highway construction also. Subgrade or the
soil beneath a road surface has become more significant because of its
control over the drainage beneath a highway, therefore the construction
design of the highway should be in such a way to carry heavy traffic. Two
factors largely determine the lifetime of a highway under moderate loads is
the quality of the aggregate used in the highway and the soil texture and
subgrade drainage. The type of parent material and the relationships of
soils to its varying topographic conditions are more essential in modern
road construction. The most serious problem encountered by highway
engineers is Pumping which means expulsion of water from beneath road
slabs through joints and cracks. Pumping is particularly greater over
glacial till than over permeable materials such as wind-blown sand and
outwash gravel. Poor drainage in a subgrade is mainly responsible for
pumping. Poor and best performance of the highway is characterized by
silty-clay subgrades with a high-water table and granular materials with a
low water table respectively.
Dam site selection a synthesis of knowledge concerning the
geomorphology, lithology, and geologic structure of terrains has greatly
helped while selecting sites for dam construction. According to Bryan, five
main requirements of good reservoir sites depend on geologic conditions:
(1) adequate size water-tight basin; (2) a narrow outlet of the basin with a
foundation that will permit economical construction of a dam; (3) to build
an adequate and safe spillway to carry excess waters; (4) availability of
resources needed for dam construction (earthen dams); and (5)
Assurance that excessive deposition of mud and silt will not shorten the
life of a reservoir. Constructing a dam in a Limestone terrain may prove a
difficult one, for instance, the Hondo reservoir was built over limestone in
southeastern New Mexico with a water table some 20 feet below the

142 | P a g e
surface. Rapid Leakage was the cause of the abandonment of the
reservoir. Building a dam in a valley may not be a good dam site from the
standpoint of the size of the dam. Buried bedrock valleys containing sand
and gravel fills are common in glaciated areas, which may not depict an
adequate picture of surface conditions. Making a dam on those sites
where subsurface topography is not supported with the buried preglacial
valley with sand and gravel in it would have a chance of leakage.

16.4 Geomorphology and Regional Planning

Geomorphologic information can be utilized at various levels of planning.
The combination of topographic information, soils, hydrology, lithology,
terrain characteristics and engineering included on terrain maps make it
suitable for regional planning. Applied geomorphology has a distinct place
in regional planning. At the broadest scale, it can be used as delineate
areas for the forest, mountain, plateau, recreational, rural, and urban
areas. Balanced growth of a country’s economy requires a careful
understanding of its natural resources and human resources. Rural or
underdeveloped terrain fulfils a variety of recreational needs. There is a
transformation from a terrain map into land-use suitability maps to develop
rural and urban areas. Detailed information on topography enlightened
regional planners who may then advise development projects best suited
for the separate region.

16.5 Geomorphology and Urbanization

There is a separate branch known as urban geomorphology applied to
urban development. According to R.U. Cooke, this branch of
geomorphology is concerned with “the study of landforms and their related
processes, materials and hazards, ways that are beneficial to planning,
development and management of urbanized areas where urban growth is
expected”. Geomorphic features decide the stability, safety, basic needs
and even its expansion. That means city or towns entirely depends on
lithological and topographical features, hydrological conditions, and
geomorphic features. Urban geomorphologists commence even before
urban development through field survey, terrain classification,
identification, and selection of alternative sites for settlements irrespective
of plain or hilly areas. These urban geomorphologists would be concerned
with the impact of natural events on the urban community and that of
urban development on the environment.
When geomorphological problems are not understood by the planners and
engineers then it leads to destruction and damage to urban settlements in

143 | P a g e
different environmental regions. Settling of foundation material in the dry
or glacial region, weathering process, damages of roads and buildings
through floods in many parts of the world are not recent phenomena.
These problems arise due to a misunderstanding of the geomorphological
conditions. In developing countries, attention has not been given to the
geomorphological conditions before the development of existing urban
centres. This leads to the haphazard growth of cities with squatter
settlements and shantytowns with urban morphology.

16.6 Geomorphology and Hazard Management

Hazards can be put in natural or man-induced where the tolerable level or
unexpected nature exceeds. According to Chorley, the geomorphic hazard
may be defined as “any change, natural or man-made, that may affect the
geomorphic stability of a landform to the adversity of living things”. These
hazards may arise from immediate and sudden movements like volcanic
eruptions, earthquakes, landslides, avalanches, floods, etc. Faulting,
folding, warping, uplifting, subsidence, or vegetation changes and
hydrologic regime due to climatic change arise from the long-term factors.
Areas having past case histories of volcanism and seismic events help in
making predictions of possible eruptions and earthquakes respectively.
Regular monitoring of seismic waves, measurement of the temperature of
craters lakes, hot springs, geysers, and changes in the configuration of
volcanoes whether dormant or extinct can reduce the hazard to some
extent. Detailed knowledge of topography can predict the path of lava flow
and its eruptions points in advance.
The behaviour of a river system can be well understood by its geomorphic
knowledge through its channel, morphology, flow pattern, river
metamorphosis and so on. It may help control excess water in rivers and
control measures during flood season. Prior knowledge of erosion in the
upper catchment area and carrying sediments to its proportion may help in
understanding the gradual rise in the riverbed, which may lead to levee
breaches and cause sudden floods. Earthquakes may be man-induced or
natural geomorphic hazards. Detailed study of seismic waves region
would help in identifying and mapping the zones of high to low intensity to
reduce the risk of human life.

16.7 Other Applications of Geomorphology

Some of the applications of geomorphic principles have been used in
applied geomorphology but there are other fields where geomorphic
knowledge of the terrain is more important. Soils maps to some extent are

144 | P a g e
topographic maps and differences in soil series fundamentally rest upon
topographic conditions under which each portion of soil series developed.
Soil erosion related problem is essentially a problem involving the
recognition and proper control of such geomorphic processes as sheet
wash erosion, gullying, mass-wasting, and stream erosion. The angle of
slope is not a single factor that determined the severity of erosion. With
the Overview of air photographs and satellite imageries, preparation of
specialized maps and interpreting them has become easier and more
accurate. Nowadays, aerial photographs are being used for evaluating
landforms and land use for city developmental plans, construction
projects, highways etc. Another tool i.e., Remote sensing is necessary for
sustainable management of natural resources like soil, forest, crops,
oceans, urban and town planning etc. At present Geographical Information
Systems (GIS) technology has been used along with Remote Sensing
techniques in geomorphic features interpretation. All fields discussed in
this chapter should be sufficient to show an understanding of geomorphic
principal, besides the geomorphic history of a particular region,
geomorphic features may contribute in applied geology to the solutions of
problems. To control the adverse effects of human activities on
geomorphic forms and processes, the application of geomorphology can
be of immense use.

16.8 Application of Geomorphology in Coastal Zone

Management
Coastal zones are not linear as a boundary between land and water rather
viewed as a dynamic region of the interface of land and water. The major
threat to the fragile coastal zone is its deteriorating coastal environment
through shoreline erosion, loss of natural beauty, pollution and extinction
of species coastal zone management requires an integrated approach.
The most widespread material is beach sand, found mainly in low
latitudes. Beach sand and gravel is widely used in the construction
industry. Geomorphologists have made some significant contributions
towards an understanding of shoreline equilibrium in Eastern Australia
where considerable development of sand mining for heavy minerals has
been done. Some measures have been designed for coast protection
including sea-defence structures such as seawalls, breakwaters, jetties
and groynes. To protect the sea backshore zone from direct erosion cut,
sea walls are designed since these walls are impermeable, they increase
the backwash and produce a destructive wave effect. Breakwaters can be
built either normal or parallel to the coast. It is necessary to monitor and
quantify wave conditions, tidal currents, and sediment movement in the

145 | P a g e
nearshore zone to evaluate how sea defences and other man-made
structures affect shoreline equilibrium.
In the context of coastal zone management Hails emphasizes that applied
geomorphology must be concerned with quantitative and not descriptive
research to obtain relevant and accurate data on (i) natural erosion and
deposition rate (ii) at what rates and amount the sediment transport from
the river catchments to the nearshore zone; (iii) variations in sediment
composition and offshore distribution; (iv) sand supply sources and
shoreline equilibrium; (v) interchange rate of sand between beaches and
dune systems; (vi) the effects of constructing sea defences; (vii) offshore
sediment dispersal and the dredging effects of seabed morphology,
sediment transport and wave refraction; and (viii) analysis of landform
including the topography of the nearshore zone, a form of the continental
shelf and relict coastlines, particularly in terms of rock outcrops. The
above investigation provides relevant baseline data needed for the
systematic planning process and monitoring programmes but also land-
use schemes.
The coastal zone represents varied and highly productive ecosystems
such as mangroves, coral reefs, seagrasses and dunes. These
ecosystems are under pressure on account of increased anthropogenic
activity on the coast, because of globalization. It is necessary to protect
these coastal ecosystems to ensure sustainable development. This
requires information on habitats, landforms, coastal processes, water
quality, and natural hazards on a repetitive basis. The coastal zone of the
world is under increasing stress due to the development of industries,
trade and commerce, tourism and resultant human population growth and
migration, and deteriorating water quality. This region is of very high
biological productivity and thus an important component of the global life
system. Coastal ecosystems harbour a wealth of species and genetic
diversity, store and cycle nutrients, filter pollutants and help to protect
shorelines from erosion and storms. Marine ecosystems play a vital role in
regulating climate and they are a major carbon sink and oxygen source.
The industrial development of the coast has resulted in the degradation of
coastal ecosystems and diminishing the living resources of the Exclusive
Economic Zone (EEZ) in form of coastal and marine biodiversity and
productivity. More than half population lives within 60 km of the coast and
would rise to almost three quarters by 2020 (Anon, 1992). Episodic
events, such as cyclones, floods, pose a serious threat to human life and
property in the coastal zone. Human activities also induce certain changes
or accelerate the process of change.

146 | P a g e
Thus, there is an urgent need to conserve the coastal ecosystems and
habitats including individual plant species and communities so,
settlements, recreation, environment, and agriculture. To ensure
sustainable development, it is necessary to develop accurate, up-to-date
and comprehensive scientific databases on habitats, protected areas,
water quality, environmental indicators and carry out a periodic
assessment of the health of the system.
The management of coastal zone requires data on varied aspects as
discussed earlier. Information exists in form of thematic maps as well as
non-spatial format. Thus, it is difficult to integrate these data
conventionally. It is, therefore, necessary to develop a computer-based
information system composed of a comprehensive and integrated set of
data designed for decision-making. In this remote-sensing-based
management plan, basic input about coastal areas is derived from remote
sensing data. Integration of this thematic data with other secondary data
would lead to the identification of suitable sites, initial zoning, sea
protection plan, eco-system conservation, etc.

Let Us Sum Up
The role of applied geomorphology relates mainly to the problems of
analyzing and monitoring landscape forming processes that may arise
from human interference. Human beings have over time tried to tame and
modify geomorphic/environmental processes to suit their economic needs.
Geomorphology has diverse applications over a large area of human
activity while Geomorphologist may serve more effectively the need of
society. There is a close association of geological structure and minerals
deposits. Geomorphic processes are the main cause of placer
concentration of minerals, found in specific positions with distinctive
topographic expression the deposition of placers affected by the type of
rock-forming the bedrock floor. Dam site selection a synthesis of
knowledge concerning the geomorphology, lithology, and geologic
structure of terrains has greatly helped while selecting sites for dam
construction. To ensure sustainable development, it is necessary to
develop accurate, up-to-date, and comprehensive scientific databases on
habitats, protected areas, water quality, environmental indicators and carry
out a periodic assessment of the health of the system. Remote sensing is
necessary for sustainable management of natural resources like soil,
forest, crops, oceans, urban and town planning etc.

147 | P a g e
Glossaries
1. Catastrophes: the natural process like soil erosion, landslides,
sedimentation, and floods.
2. Seam diggings: which are residues from the weathering of quartz
stringers or veins
3. Lithology: Study about the rocks
4. Geomorphic hazard: It may be defined as “any change, natural or
man-made, that may affect the geomorphic stability of a landform to the
adversity of living things”.
5. Episodic events: Periodic climate-related disasters such as cyclones,
floods.

Check Your Progress

1. Write a note on Applied Geomorphology
Applied geomorphology relates mainly to the problems of analyzing and
monitoring landscape forming processes that may arise from human
interference.
2. Bring out the significance of Urban Geomorphology.

Urban geomorphology applied to urban development. According to R.U.

Cooke, this branch of geomorphology is concerned with “the study of
landforms and their related processes materials and hazards, ways that
are beneficial to planning, development and management of urbanized
areas where urban growth is expected”.
3. Dam site selection requires multiple subject knowledge-Why?
Dam site selection a synthesis of knowledge concerning the
geomorphology, lithology, and geologic structure of terrains has greatly
helped while selecting sites for dam construction. According to Bryan, five
main requirements of good reservoir sites depend on geologic conditions:
(1) adequate size water-tight basin; (2) a narrow outlet of the basin with a
foundation that will permit economical construction of a dam; (3) to build
an adequate and safe spillway to carry excess waters; (4) availability of
resources needed for dam construction (earthen dams); and (5)
Assurance that excessive deposition of mud and silt will not shorten the
life of a reservoir.

148 | P a g e
4. Coastal Zone Management-Define
The coastal zone represents varied and highly productive ecosystems
such as mangroves, coral reefs, seagrasses, and dunes.

Suggested Readings
1. Strahler, A. H. and Strahler, A N., (2001) Modern Physical Geography
(4/E), John Wiley and Sons, Inc., New York.
2. Christopherson, R. W. and Birkeland, G. H., (2012) Geosystems: An
Overview to Physical Geography (8/E), Pearson Education, New
Jersey.
3. Das Gupta, A &Kapoor, A.N., (2001) Principles of Physical Geography,
S.C. Chand & Company Ltd. New Delhi.
4. Khullar, D.R., (2012) Physical Geography, Kalyani Publishers, New
Delhi.

5. Brown, J.H. (2005) Biogeography, Sinauer Associates Inc,

Sunderland.
6. Seddon, B.A. (1971) Overview to Biogeography, Duckworth, London.
7. Thornbury W.D. (2002), Principles of Geomorphology, CBS Publishers
& Distributors, New Delhi, India.

149 | P a g e
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 About Tamil Nadu Open University

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Headquarters at Chennai was established in 2000 by an
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