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Unit 2
Land and
Oceans

Learning Objectives
• To understand the continents and oceans.
• T
 o learn about the characteristic features of different landforms
and oceans.
• To know about the classification of landforms.
• To understand the oceans and its features.

Pathway
This lesson focuses on land and oceans found on the Earth. It deals with the
classification of landforms - first, second and third order landforms.

The teacher enters the classroom with

giant-sized envelopes. The students are
enthusiastic to know the content of the
envelopes. Teacher asks the children to sit
in groups and explains the activity. Each
group is given an envelope which contains
seven jig-saws and a chart paper. The
teacher asks them to paste the jig-saws
(continents) close to each other leaving no
gap between them. Teacher asks them to
colour the remaining places in blue.
A group pastes the continents and comes
first with the chart without any gaps in
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between the continents. The teacher 1. First order landforms

then puts the chart on the board and the
Continents and oceans are grouped as first
children applaud.
order landforms. The vast land masses on
"What kind of picture is this? Once I have
Earth are called Continents and huge
seen one like this in the atlas, " says Yazhini.
water bodies are called Oceans. There are
"You are right. This is Pangea, the seven continents. They are Asia, Africa,
Super Continent, and the Sea around is North America, South America,
Panthalasa. It was 200 million years ago, Antarctica, Europe and Australia. Asia
when these landmasses moved away is the largest continent, whereas Australia
from each other to gain the present is the smallest one.
position as continents and oceans."
says the teacher.
GEO CONNECT:
"What makes it to move madam?" asks
Land classification - Sangam period
Nila.
1. Kurinji - Mountain and its
"Nothing other than the internal heat of
environs
the Earth," says the teacher and continues,
“this lesson deals about the continents and 2. Mullai - Forest and its
oceans in detail” surroundings
The Earth is covered by water which 3. Marutham - Agricultural land and
occupies 71 percent and land that its adjoining areas.
occupies 29 percent of the Earth’s 4. Neithal - Sea and its environs
surface. The surface of the Earth is not 5. Palai - Desert region
even, because it has lofty mountains,
Which of the above land form
deep oceans and other landforms. These
category do you belong to?
landforms can be classified as

Classification of landforms
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Apart from continents, there are five 2. Second order landforms

oceans located on the Earth’s surface.
The second order landforms are
They are the Pacific, Atlantic, Indian,
categorised as mountains, plateaus and
Southern and Arctic Ocean. Among
plains.
these oceans, the Pacific Ocean is the
largest and the Arctic Ocean is the smallest.

Activity:
Required materials Plateau
Plain

• A round plate Valley

Hill
Cave River
Stream
• 7 slices of one carrot Lake

Island

• A glass of water Pond

Procedure Ocean
Beach

Write the abbreviations As, Af, NA,

Second order Landforms:
SA, An, Eu and Au on each slice in
Mountains, Plateaus and Plains
descending order of its size.
The teacher hangs a wall map of the
world. 2.1 Mountains
The students have the expansion of A landform that rises
each abbreviation written on the board. 600 metre above its
surroundings and has
Students now try to place the slices
steep slopes is called a
on the plate matching the position of
mountain. Mountains
the continents in the map.
are found in isolation
They pour some water.
or in groups. If the mountains extend
The teacher shows the oceans. for a larger area continuously, it is
Accordingly the students put their called a mountain range. These ranges
fingers in the respective places stretch for hundreds or thousands of
and repeat the names of the ocean kilometre. The Himalayas of Asia, the
stirring the water. Rocky Mountains of North America and
The students learn the position,
comparative size of the continent
and the position of oceans. HOTS:
December 11 International
Isthumus : A narrow strip Mountain Day
of land which connects Prepare slogans, posters and
two large landmasses or placards to celebrate International
separates two large waterbodies. Mountain Day.

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Activity: 2.2 Plateaus

Complete the given table with the help of an atlas. Plateaus are the elevated portions of the
Follow the example. Earth that have flat surfaces bounded by
S.No. Mountain Peaks Continents Elevation steep slopes. The elevation of plateaus
Ranges (m)
may be a few hundred metre or several
1. The Everest Asia 8,848
thousand metre. Tibetan Plateau is the
­ imalayas
H
2. The highest plateau in the world. So, it is called
Rockies as the ‘Roof of the world’. The flat topped
3. The part of the plateau is called Tableland.
Andes The plateaus are generally rich in minerals.
4. The Alps
The Chotanagpur Plateau is one of the
5. The
mineral rich plateaus in India. Therefore,
Eastern
Ghats mining is one of the major activities of the
people living here. The Deccan Plateau in
peninsular India is of volcanic origin.
the Andes of South America are such
examples. The Andes mountain in South
America is the longest mountain range Dharmapuri Plateau,
(7,000 km) in the world. The highest Coimbatore Plateau and
point of a mountain is known as peak. Madurai Plateau are found
Mt. Everest is the highest peak (8,848 m) in Tamil Nadu.
in the world. Which country is Mt. Everest
located in? 2.3 Plains
Plains are a flat and relatively low-lying
lands. Plains are usually less than 200
HOTS: You know the importance of metre above sea level. Sometimes they
conservation of forests. Do you think may be rolling or undulating. Most plains
conservation of mountains is also are formed by rivers and their tributaries
equally important? and distributaries. These plains are used
extensively for agriculture due to the
availability of water and fertile soil. They
Mountains are the sources of rivers.
They provide shelter to flora and fauna.
The plains have been
Here, tourism is an important activity.
the cradle of civilisations
During summer, people go to mountain
from the earliest times.
regions to enjoy the pleasing cool
For example: the Indus in India, the
weather. Udhagamandalam, Kodaikanal,
Nile valley in Egypt are some of the
Kolli hills, Yercaud and Yelagiri are some
early civilisations which developed
of the hill stations found in Tamil Nadu.
and flourished.

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are most suitable for human inhabitation. beaches and sand dunes are some examples
Hence, they are the highly populated of third order landforms.
regions of the world. The oldest civilisations
like the Mesopotamian and the Indus
civilisations developed in river plains. The
Valley
Indo-Gangetic plain in North India is one
of the largest plains in the world. The
plains formed by river Cauvery and Vaigai
are important plains found in Tamil Nadu.
Coastal plains are the low lying lands
adjacent to oceans and seas.

Activity:
Complete the given table with the help of an atlas. Beach
Follow the example.
S.No. Continents Plateaus Plains
1. Asia Tibetan Yangtze Plain
Plateau
2. North
America
3. South
America
4. Australia
Sand
5. Europe
Dune
6. Africa

Activity:
•M
 ake a model of different
landforms.
Erosion is the process of removal
•P
repare an album of people’s
of surface material from the Earth's
activities in different landforms.
crust. The eroded materials are
transported and deposited on the low
lying areas. This process is called as
3. Third order landforms
Deposition.
Third order landforms are formed on
mountains, plateaus and plains mainly
HOTS: When you are walking on the
by erosional and depositional activities of
Marina beach in Chennai, which order
rivers, glaciers, winds and waves. Valleys,
of landform are you on?

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4. Oceans spreads for about 168.72 million sq.km.

It is bounded by Asia and Australia in
The Earth looks blue when we see it from
its west and North America and South
space. This is because, two-thirds of it
America in its east. It stretches from the
is covered by water. The water is found
Arctic Ocean in the north to the Southern
in oceans and seas. Oceans are vast
Ocean in the south.
expanse of water. Seas are water bodies
partially or fully enclosed by land. As you
have studied previously, there are five If Mount Everest,
main oceans in the world. which is the highest
point (8,848 metres)
was plugged into the
Pacific Ocean
Mariana Trench, still there would
Atlantic Ocean
be 2,146 metres of water left.
Indian Ocean
Southern Ocean The depth in meters from mean sea
Arctic Ocean level is denoted as m-

Area of Oceans (%)

This ocean’s shape is roughly
triangular with its apex in the north at
4.1 The Pacific Ocean
the Bering Strait which connects the
The Pacific Ocean is the
Pacific Ocean with the Arctic Ocean. The
largest and deepest
Bering Sea, the China Sea, the Sea of
ocean on the Earth. It
Japan, Tasman Sea and the Philippine
covers about one-third of
Sea are some of the marginal seas of the
the Earth’s total area and
Pacific Ocean. Indonesia, Philippines,
Japan, Hawaii, New Zealand are some
of the islands located in this Ocean.
The deepest point Mariana Trench is
10,994 m - and is located in the Pacific
Ocean. A chain of volcanoes is located
around the Pacific Ocean called the
Pacific Ring of Fire.

The Spanish navigator

Ferdinand Magellan
named the ocean
Pacific, meaning calm
or tranquil.
Pacific Ocean and its Marginal Seas

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• Smallest Ocean
• It is the largest continent in
• It remains frozen for most of the year.
size.
• Eurasian basin is the deepest point.
• It ranks first in total • Surrounds the continents of Antartica.
population of the world. • It is bourdered by southern parts of
• The second largest ocean. Pacific
• Shape of the ocean resembles the letter ‘S’. Atlantic and the Indian Oceans.
• The largest and deepest ocean. • it is the busiest shipping route between the • It is the second smallest • Deepest point-South Sandwich trench.
• The deepest point-Mariana Trench Eastern and Western hemispheres. continent in size.
(10.994m). • It ranks third in total
• Chain of volcanoes-”Ring of fire’ present population of the world. • It is the named after India.
• Third Largest Ocean
• Triangle in shape

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• It is the third largest

continent in size.
• It ranks fourth in total
population of the
world.

• It is the second largest

continent in size.
• It ranks second in
total population of the
• It is the fourth largest world. • It is the smallest
continent in size. continent in size.
• It ranks fifth in total • It ranks sixth in total
population of the world. population of the
• It is the fifth largest world.
continent in size.
• No permenant residents.
• Researchers around
4000 people stay here.
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4.2 The Atlantic Ocean Mediterranean Sea are important marginal

The Atlantic Ocean is the second largest seas of the Atlantic Ocean. St. Helena,
ocean on the Earth. It covers one sixth Newfoundland, Iceland and Falkland are
of the Earth’s total area and spreads for some of the islands found in this ocean.
about 85.13 million sq.km . It is bounded
4.3 The Indian Ocean
by North America and South America in
The Indian Ocean is the third largest ocean
the west and Europe and Africa in the
on the Earth’s surface. It covers an area of
east. Like the Pacific, it stretches from
about 70.56 million sq.km. It is named after
the Arctic Ocean in the north to the
India. It is triangular in shape and bounded
Southern Ocean in the south. The shape
by Africa in the west, Asia in the north and
of the Atlantic Ocean resembles the letter
Australia in the east. The Andaman and
‘S’. The Strait of Gibraltar connects the
Nicobar Islands, Lakshadweep, Maldives,
Sri Lanka, Mauritius and the Reunion Islands
are some of the islands located in the Indian
Ocean. Malacca strait connects the Indian
Ocean and the Pacific Ocean.

Palk Strait connects the Bay of

Bengal and Palk Bay.

The Bay of Bengal, the Arabian Sea, the

Persian Gulf and the Red Sea are some of
the important marginal seas of the Indian
Ocean. The Java trench (7,725 m-) is the
deepest point in the Indian Ocean.

Atlantic Ocean and its Marginal Seas

Atlantic Ocean with the Mediterranean

Sea. The Atlantic Ocean is the busiest
shipping route between the Eastern and
Western hemispheres. The deepest point
is the Milwaukee Deep in the Puerto
Rica Trench. It has a depth of about 8600
m-. The Caribbean Sea, the Gulf of Mexico,
the North Sea, the Gulf of Guinea and the

HOTS: Why are the Red Sea, Dead

Sea and Black Sea named so?
Indian Ocean and its Marginal Seas

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this ocean is very cold. Much of it is covered

• 6° Channel
by sea ice. The deepest point in this ocean
separates Indira
is South Sandwich Trench with a depth
Point and Indonesia
of 7,235 m-.
• 8° Channel separates Maldives
and Minicoy islands
HOTS: When you travel from Japan to
• 9° Channel separates
California, which ocean would you travel
Lakshadweep Islands and Minicoy
across?
islands
• 10° Channel separates Andaman
and Nicobar Islands
4.5 The Arctic Ocean
The Arctic Ocean is the smallest ocean.
4.4 The Southern Ocean It covers an area of 15.56 million sq.km.
The Southern Ocean surrounds the continent It lies within the Arctic Circle. It remains
of Antarctica and is enclosed by the 60°S frozen for most of the year. The Norwegian
latitude. It covers an area of 21.96 million Sea, the Greenland Sea, the East Siberian
sq.km. It is bordered by the southern parts Sea and the Barents Sea are some of the
of the Pacific, the Atlantic and the Indian marginal seas of this ocean. Greenland,
Oceans. The Ross Sea, the Weddell Sea New Siberian Island and Novaya Zemlya

Southern Ocean and its Marginal Seas

Arctic Ocean and its Marginal Seas

and the Davis Sea are the marginal seas Island are some of the islands located
of this Ocean. Farewell Island, Bowman in the Arctic Ocean. The North Pole is
Island and Hearst Island are some of the situated in the middle of the Arctic Ocean.
islands located in this ocean. The water in The Eurasian Basin is the deepest

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point in the Arctic Ocean, which is about • Valleys, beaches and sand dunes are
5,449 m- in depth. the third order landforms.
• Many islands and marginal seas are
Activity: found in the oceans.
Complete the given table with the help of an atlas.
Follow the example.
Sl.No. Name Area Trenches Depth
of the (million (m)
Ocean sq.km)
• Island - A land surrounded by water
1. Pacific 168.72 Mariana 10,994
Ocean on all sides.
2. Atlantic • Bay - A broad inlet of the sea where
Ocean
the land curves inwards.
3. Indian
Ocean • Strait - A narrow stretch of water
4. Southern linking two large water bodies.
Ocean
5. Arctic
• Trench - The deepest part of the
Ocean ocean.
• Peninsula - The land surrounded by
water on three sides.
HOTS: When you arrange the
continents in ascending order according Exercises
to their size, which ranks third?
A. Choose the correct answer
1. Which of the following is the
smallest ocean on Earth?
Wrap-up
a. The Pacific Ocean
• The surface of the Earth is covered by
b. The Indian Ocean
71 percent of water and 29 percent of
c. The Atlantic Ocean
land.
d. The Arctic Ocean
• The landforms are classified as first
order, second order and third order 2. The Malacca Strait connects
landforms. a. The Pacific and Atlantic Oceans
• Continents and oceans are the first b. The Pacific and Southern Oceans
order landforms. c. The Pacific and Indian Oceans
• There are seven continents and five d. The Pacific and
oceans on the Earth’s surface. Arctic Oceans
• Mountains, plateaus and plains are
the second order landforms.

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3. Which of the following oceans is D. Match the following

the busiest ocean?
A B
a. The Pacific Ocean
1. T
 he South a) T
 he Atlantic
b. The Atlantic Ocean -
Sandwich Trench Ocean
c. The Indian Ocean 2. T
 he Milwaukee b) T
 he Southern
-
Trench Ocean
d. The Arctic Ocean
3. T
 he Mariana c) The Indian Ocean
4. The frozen continent is -
Trench
a. North America b. Australia 4. T
 he Eurasian basin - d) T he Pacific Ocean
c. Antarctica d. Asia 5. T
 he Java Trench - e) The Arctic Ocean
5. A narrow strip of water that
connects two large water bodies E. i) Consider the following
statements.
a. A Strait b. An Isthmus
1. Plains are formed by rivers.
c. An Island d. A Trench
2. 
The ‘South Sandwich Trench’ is
found in the Indian Ocean.
B. Fill in the blanks. 3. Plateaus have steep slopes.
1. The world’s largest continent is     Choose the correct answer using
2.       is the mineral rich plateau the codes given below.
in India a. 1 and 3 b. 2 and 3
3. The largest ocean is          c. 1, 2 and 3 d. 2 only
4. Deltas are      order landforms.
ii) Consider the following
5. The Island continent is       
statements.

C. Circle the odd one out. 

Statement I: Mountains are second
order landforms.
1. Africa, Europe, Australia, Sri Lanka
2. The Arctic Ocean, the Mediterranean Statement II: The Mariana Trench

Sea, the Indian Ocean, the Atlantic is the deepest trench in the world.
Ocean
Which of the statement(s) is/are
3. Plateau, Valley, Plain, Mountain true?
4. The Bay of Bengal, the Bering Sea, a. I is true; II is wrong
the China Sea, the Tasman Sea. b. I is wrong; II is true
5. The Andes, the Rockies, the Everest, c. Both the statements are true
the Himalayas d. Statements I and II are wrong.

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F. Answer in a word
1. Which is the highest plateau in the
world?
2. Name a second order landform.
3. Which ocean is named after a country?
4. Name the island located in the Arabian
Sea.
5. What is the deepest part of the ocean 3. Which activity of river is this landform
called as? formed by?

G. Answer in brief. K. i) Activity

1. What is a continent? 1. Trip to the nearby area to appreciate
2. Name the continents which surround the physical features of any kind of
the Atlantic Ocean. landform.

3. What are oceans? 2. Conduct a quiz on landforms and

oceans.
4. List out the names of continents
according to their size ii) Activity
5. Name the oceans which surround 1. Give examples for the following using
North America and South America. an Atlas.

H. Distinguish between a. Bay:     ,     ,     

1. A Mountain and a Plateau b. Gulf:     ,     ,     

2. An ocean and a sea c. Island:     ,     ,     

d. Straits:     ,     ,    
I. Answer the following questions in
2. Map reading (with the help of atlas)
detail
a. A sea in the east of India
1. Write down the classification of land
forms. b. Continents in the west of Atlantic Ocean

2. Write a note on plateaus. c. Continents in the south of Arctic Ocean

3. Plains are highly populated. Give d. A strait between India and Sri Lanka
reasons f. Oceans which surround Australia
4. Give the important features of the g. Find out the Isthumusses
Pacific Ocean. (Create more questions)
5. Write down the importance of oceans. 3. On the given outline map of the world,
label the continents and mountain
J. Picture Study
ranges.
1. Name the landform.
4. On the given outline map of the world,
2. What order of a landform is this?
label oceans, seas, isthumus and straits.

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Map Activity

Not to Scale

Not to Scale

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Unit -I

Interior of the
Earth

Learning Objectives

To acquaint ourselves with

™™To know about the interior of the earth
™™To understand the role of plates
™™To learn about earthquakes and volcanoes

Introduction 1. The Crust

The earth, our homeland, is a dynamic The crust is the outermost layer of the earth.
planet. The earth’s surface has lofty mountains, Its average thickness varies from 5 to 30 km. It
high plateaus, large plains and deep valleys etc. is about 35 km on the continental masses and
The earth’s surface is constantly undergoing only 5 km on the ocean floors. Despite greater
changes inside and outside. Have you ever thickness, the continental crust is less dense
wondered what lies in the interior of the earth? than the oceanic crust because it is made of both
What is the earth made up of? light and dense rock types. The oceanic crust is
composed mostly of dense rocks such as basalt.
Interior of the Earth
The structure of the earth may be compared to that
Earth is called as blue
of an apple. The earth too has shells like that of an
Planet. 71% of the earth
apple. If we cut a section through the earth, we will
is covered by water.
get a view as shown in figure. On the basis of the
study of earthquake waves the spherical earth is
found to be three concentric layers. They are: The crust comprises two of distinct parts. The
1. The crust, upper part consists of granite rocks and forms the
2. The mantle and continents. It has the main mineral constituents
3. The core. of silica and alumina. So it is collectively referred
to as Sial. It has an average density of 2.7g/cm3.
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The lower part is a continuous zone of denser high temperature and pressure. It extends from
basaltic rocks forming the ocean floors, 5,150 km to 6,370 km. The average density of
comprising mainly of silica and magnesium. It is core is 13.0 g/cm3
therefore called Sima. It has an average density
• The crust forms only 1 per
of 3.0g/cm3. The sial and the sima together form
cent of the volume of the
the earth’s crust. Since the sial is lighter than the
earth, 84 % consists of the
sima, the continents can be said to be ‘floating’
mantle and 15 % makes the
on a sea of denser sima.
core.
• The radius of the earth is
6371 km.

The Earth Movements

The lithosphere is broken into a number
of plates known as the Lithospheric plates.
Each plate, oceanic or continental moves
independently over the asthenosphere.The
movement of the Earth’s lithospheric plates
is termed as tectonic movements. The energy
2. The Mantle required to move these plates is produced by
the internal heat of the earth. These plates
The next layer beneath the crust is called the
move in different directions at different
mantle. It is separated from the crust by a
speed.
boundary called Mohorovicic discontinuity. The
mantle is about 2,900 km thick. It is divided into
two parts. (i) The upper mantle with a density of
3.4 – 4.4g/cm3. extends down to 700 km. (ii) The
lower mantle having a density of 4.4– 5.5g/cm3
extends from 700 to 2,900 km.

3. The Core
The innermost layer of the earth is called
Lithospheric Plates
the core. It is also known as barysphere.
It is separated from the mantle by a boundary At places, these plates move away
called Weichart-Gutenberg discontinuity. The from each other creating wide rifts on the
core is also divided into two parts. (i) The outer earth’s surface. At some places, these plates
core, which is rich in iron, is in liquid state. come closer and collide. When an oceanic plate
It extends between 2,900 – 5,150 km. (ii) The collides with a continental plate, the denser
inner core, composed of Nickel and Ferrous oceanic plate is forced below the continental
(Nife), is solid in state. The central core has very plate. As a result of the pressure from above
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the rocks heats up and melt. The molten rocks Fault Scarp
Fault trace
rise again forming volcanic mountains along
the continental edge. Alternatively, a trench
may be formed between two plates. In some
cases when two continental plates converge, Epicentre
neither plate can be forced under the other.
Seismic Focus
Instead, folds may be created. Great mountain Waves

ranges like the Himalayas have been formed

in this way. Fault Plane

Earthquake
Asthenosphere - The asthenosphere
The earthquake waves are recorded by
is the part of the mantle that flows
an instrument known as seismograph. The
and moves the plates of the earth.
magnitude of an earthquake is measured by the
Richter scale. The numbers on this scale range
The movement of these plates causes
from 0 to 9.
changes on the surface of the earth. The earth
movements are divided on the basis of the • An earthquake of 2.0 on
forces which cause them. The forces which Richter scale or less can be felt
act in the interior of the earth are called as only a little. An earthquake over
Endogenic forces and the forces that work on 5.0 on Richter scale can cause
the surface of the earth are called as Exogenic damage from things falling. A 6.0 on Richter
forces. scale or higher magnitude is considered very
Endogenic forces sometimes produce strong and 7.0 on Richter scale is classified as
sudden movements and at the other times a major earthquake.
produce slow movements. Sudden movements Causes of Earthquake
like earthquakes and volcanoes cause mass
The chief cause of earthquake is the sudden
destruction over the surface of the earth.
slipping of the portion of the earth’s crust
Earthquake along fractures or faults. The movement of the
molten rocks underneath the surface produce
A sudden movement of a portion of
strains which break the rocks apart. The
the earth’s crust which produces a shaking
sudden shifting of landmass causes upheavals
or trembling is known as an earthquake.
in the crust of the earth sending vibrations or
Earthquakes may cause widespread damage
waves into the surrounding portions of the
to life and property. The point where these
earth. Sometimes the surface of the earth itself
vibrations originate is called the focus of the
cracks.
earthquake. The point of the earth’s surface
directly above the focus is called the epicentre of Another cause of earthquake is volcanic activity.
the earthquake. From the focus, the earthquake A violent or explosive eruption often causes the
vibrations travel in different directions in the earth in its vicinity to quake. Earthquakes are
form of seismic waves. often common in most volcanic areas.
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Effects of Earthquakes On 26th Dec 2004 TSunami

Earthquakes may cause changes in the in the Indian Ocean swept
earth’s surface. Vibrations often set landslides coastal area of Indonesia,
in mountainous regions.A greater danger in an India, Srilanka, Thailand
earthquake is the falling of buildings. Most of etc., They caused immense damage to life
the houses which collapsed were made of mud and property in the coastal area
and bricks and proved to be death traps. Fire is
another great danger. Underground water system Distribution of Earthquakes
is naturally disturbed by such movements. The world’s distribution of earthquakes
coincide very closely with that of volcanoes.
There are three types of
earthquake waves: Regions of greatest seismicity are circum-Pacific
1. P waves or longitudinal waves areas, with the epicenters and the most frequent
2. S waves or transverse waves occurrences along the Pacific Ring of Fire. It is
3. L waves or surface waves said that about 68 percent of earthquakes occur
in this belt. Another 31 % of earthquakes take
An earthquake which originates below or place in the Mediterranean-Himalayan belt
near the sea causes great disturbance in the including Asia Minor, the Himalayas and parts
water. The floods and waves cause great loss of north-west China. The remaining percent of
of life, sometimes more than the earthquake earthquakes are occur in Northen Africa and
itself. Tsunami, a Japanese term, is the name Rift valley areas of the Red sea and Dead sea.
given to the huge wave caused in the sea by an In India, the Himalayan region and the
earthquake. Tsunamis are quite common along Ganga-Brahamaputra valley are prone to
the coasts of Japan and other regions in the earthquakes. A number of earthquakes have been
Pacific Ocean. experienced in this region. Some of them were

World Distribution of Earthquakes

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very severe and caused extensive damage, e.g., the basin, it is called a caldera. Calderas are caused
earthquake of Uttar Kashi in 1991 and Chamoli by violent explosions which blow away entire
in 1999. The Deccan Plateau, which was supposed tops of great cones.
to be comparatively free from the dangers of
the earthquakes, has experienced two severe Causes of Volcanic Activity
earthquakes in the past, the Koyna earthquake in The temperature increases as the depth
1967 and the Latur earthquake in 1993. increases at the rate of 1ºc for every 35 metres.
Volcanoes There is also great pressure. At a depth of about
15 km the pressure is about 5 tonnes per cm2of
A volcano is a vent or an
rock. Under these circumstances, the interior of
opening in the earth’s crust
the earth is in a semi-molten state called magma.
through which hot magma
The magma, under great pressure has the
erupts from deep below
capacity to dissolve great volume of gas; some
the surface. The opening
gases are also combustible. This makes volcanic
is usually circular in form.
material burst forth through the weak spots in
Volcanic eruptions may also take place through
the earth’s crust.
a long crack or fissure through which steam and
other materials flow out. Fact : The scientific study of valcanoes
are called volcanology. People
who study valcanoes are called
volcanologists.

Nature of volcanic eruptions

Sometimes, magma rises slowly to the
surface and spreads over a vast area. This is
known as fissure eruption. Some plateaus
and plains have been formed in this way, e.g.,
Deccan Plateau in India and the Colombian
Plateau in North America. If the magma rises
quickly to the surface, lava is thrown high into
The molten rock material within the earth,
the atmosphere. Besides lava, ash, steam, gases
together with gases, is called magma. After it
and pieces of rocks are also thrown out. This
rises to the surface, it is called as lava. In course
type of eruption is known as explosive eruption.
of time, lava and other materials flow out of a
The terrible explosion on the island of Krakatoa
volcano accumulate around the opening and
(27th August 1883) in Indonesia is an example
form a conical hill or a mountain vent is an
for explosive type of eruption.
openning or mouth of a volcano. The top of
this cone is usually marked by a funnel-shaped Lava flow is affected by viscosity. For
depression, which is called a crater. If the crater example, honey has high viscosity, so it flows
of a volcano is of great size and is shaped like a slowly, whereas water has low viscosity, so it
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flows easily. The viscosity of lava is determined force throwing them several kilometres up
by the amount of silica and water in magma. into the atmosphere. Such volcanoes have
Highly viscosity lava is rich in silica and has steep slopes and are made of cinder and ash.
little water. Low viscosity lava has little silica, They are known as cinder-cone volcanoes.
but a lot of water. It moves rapidly forming Many volcanoes of Mexico and Central
smooth flows. America belong to this group.

Barren island is situated in

the Andaman Sea, and lies
about 138 km northeast
of the territory's capital. It
is only in active volcano along the chain Cinder - Cone Valcano
from sumatra to myanmar. Last eruption
occurred in 2017. 3. Composite volcano: Composite volcanoes
are made of alternate layers of lava, cinder
Types of Volcanoes and ash. They are also called strato volcano.
St. Helens is an example of composite
The shape of a volcano depends on the
volcano.
type of lava and the force of the eruption. On
the basis of shape, there are three types of
volcanoes. They are:
1. Shield volcano
2. Cinder-cone volcano
3. Composite volcano
1. Shield volcano: A shield volcano is formed
by quiet eruption of lava with a low silica Volcanoes are also grouped according to
content. Such a volcano has a wide base and their periodicity of eruptions such as active,
a cone with gentle slopes. Volcanoes of the dormant and extinct. These names refer to
Hawaii islands are of this type. the state of activity rather than the types of
volcanoes.

Active Valcanoes that erupt frequently

are called active volcanoes. Most of the active
volcanoes lie in the Pacific Ring of Fire belt
which lies along the Pacific coast. There are
2. Cinder-cone volcano: Silica-rich magma about 600 active volcanoes in the world, such as
traps gases inside the volcano until enough Mt. Stromboli in Mediterranean Sea, St.Helens
pressure is built to push the magma out of in USA, Pinatubo in Philippines. Mauna Loa in
the earth’s crust. When this type of volcano Hawaii (3,255m.) is the world’s biggest active
erupts, it shoots gases, ash, etc. with great volcano.
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extinct ones. They occur along the coastal

Stramboli is known mountain ranges, as off-shore islands and
as the ‘light house of in the midst of oceans, but there are a few in
Mediterranean sea’ the interior of continents. The volcanic belts
are also the principal earthquake belts of the
Dormant volcanoes have shown no world. There are three major zones of volcanic
sign of activity for many years but they may activities in the world. They are:
become active at any time. It is also called
1. The Circum – Pacific belt
Sleeping Volcano Vesuvius mountain of
2. The Mid continental belt
Italy, Mt Fujiyama in Japan, Mt. Krakatoa of
Indonesia are famous examples of this types. 3. The Mid Atlantic belt

Extinct The top of extinct volcanic 1. Circum Belt

mountains have been eroded. Mt Popa This is the volcanic zone of the convergent
of Myanmar and Mt. Kilimanjaro and Mt. oceanic plate boundary. It includes the
Kenya of Africa are examples of extinct volcanoes of the eastern and western coastal
volcanoes. areas of Pacific Ocean. This zone is popularly
termed as the Pacific Ring of Fire which has
Distribution of Volcanoes in the world been estimated to include two-thirds of the
Volcanoes are located in a clearly-defined world’s volcanoes.
pattern around the world. They are closely
2. Mid continental belt
related to regions that have been intensely
folded or faulted. There are about 500 active This is the volcanic zone of convergent
volcanoes and thousands of dormant and continental plate boundaries that includes

ARCTIC OCEAN

ASIA
EUROPE NORTH
AMERICA
ATLANTIC
OCEAN
AFRICA

PACIFIC
OCEAN
SOUTH
INDIAN AMERICA
OCEAN
AUSTRALIA

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the volcanoes of Alpine mountain chains, the ™™The crust is the outer-most layer of the
Mediterranean Sea and the fault zone of eastern Africa. earth.
The important volcanoes are Vesuvius, Stromboli, ™™The upper part of the earth crust is SIAL.
Etna, Kilimanjaro and Kenya. Surprisingly, the ™™The lower part of the earth crust is SIMA.
Himalayas have no active volcanoes at all.
™™The mantle is about 2900km thick.

3.Mid Atlantic Belt ™™The lithosphere is broken into a number of

plates known as the lithospheric plates
This belt represents the divergent
™™The earthquake waves are recorded by an
boundary of plates located along the mid-
instrument known as seismograph.
Atlantic ridges. Volcanoes of this area are
mainly of fissure eruption type. Iceland is the ™™Tsunami is caused by an underwater
most active volcanic area and is located on earthquake.
the mid-Atlantic ridge. St. Helena and Azores ™™A volcano is a vent or opening in the earth
Island are other examples. crust.
™™The Shape of a volcano depends on the
WRAP UP type of lava and force of the eruption.
™™The Earth’s interior structure is compared ™™There are three major zone of volcanic
with that of an apple activity in the world.

Glossary
1. Core The inner most layer of the earth கரு
2. Mantle The second layer beneath the crust கவசம்
3. Mohorovicic Boundary that separated the mantle from ம�ோஹ�ோர�ோவிசிக்
discontinuity the crust எல்லை
4. Land slide Downward movements of rock debris of the நிலச்சரிவு
mountain
5. Seismograph Instrument to measures the magnitude of an சீஸ்மோகிராப்
earthquake
6. Tsunami Sea waves caused by an underwater ஆழிப்பேரலை
earthquake or a volcanic eruption under sea.
7. Vent An opening a the earth surface from which எரிமலைத் துளை
volcanic material is emitted
8. Magma The molten state of rocks பாறைக்குழம்பு
9. Lava The solidified form of magma after it எரிமலைக்குழம்பு
reaches the surface of the earth
10. Viscosity A liquids resistance to flow பாகுத்தன்மை

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™™ 7. __________ belt is known as the “Ring of

Evaluation Fire”.
a. Pacific b. Atlantic
I. Choose the correct answer c. Arctic d. Antarctic

1. Nife is made up of ___________ .

a. Nickel and ferrous II. Fill in the blanks
b. Silica and aluminum
1) The core is separated from the mantle by a
c. Silica and magnesium boundary called ______________.
d. Iron and magnesium
2) The earthquake waves are recorded by an
2. Earthquake and volcanic eruption occur near instrument known as __________.
the edges of ______________. 3) Magma rises to the surface and spreads over
a. Mountain b. Plains a vast area is known as __________.

c. Plates d. Plateaus 4) An example for active volcano

______________.
3. The magnitude of an earthquake is measured
5) Seismology is the study of __________.
by ______________.
a. Seismograph b. Richter scale
c. Ammeter d. Rotameter III. Circle the odd one

1) crust, magma, core, mantle

4. The narrow pipe through which magma flow
out is called a ______________. 2) focus, epicenter, vent, seismic waves
a. Vent b. Crater 3) Uttar Kashi, Chamoli, Koyna, Krakatoa
c. Focus d. Caldera
4) lava, caldera, silica, crater

5. Lava cones are _____________ 5) Stromboli, Helens, Hawaii, Fujiyama

a. mountains of accumulation
b. mountains of deformation
IV. Match the following
c. relicit mountains
1) Earth quake - Japanese term
d. fold mountains
2) Sima - Africa
6. T he top of the cone of a volcanic moun-
tain has a depression known as the 3) Pacific Ring of Fire- Sudden movement
___________ 4) Tsunami - Silica and magnesium
a. crater b. lopith
5) Mt. Kenya - World volcanoes
c. caldera d. sill

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V. Consider the following statement and ( ) 5) What is a volcano?

Tick the appropriate answer 6) Name the three types of volcanoes based on
1. Assertion (A): There structure of the earth shape.
may be compared to that of anApple.
VIII. Give reason
Reason (R): The interior of the earth con-

1) No one has been able to take samples from
sists of crust, mantle and core.
the interior of the earth
a. A and R are correct and A explains R
b. A and R are correct but A does not explain R 2) The Continent crust is less dense than the
oceanic crust
c. A is incorrect but R is correct
d. Both A and R are incorrect IX. Distinguish between
Assertion (A): The Pacific Ocean includes
2.  1) SIAL and SIMA
two thirds of the world’s volcanoes.
2) Shield volcano and composite volcano
Reason (R): The boundary along the Eastern
and Western coast areas of the Pacific Ocean is 3) Active volcano and dormant volcano
known as the Pacific Ring of Fire.
X. Answer the following questions in detail
a. A and R are correct and A explains R
b. A and R are correct but A does not explain R 1) Write about the effects of an earthquake?

c. A is incorrect but R is correct 2) Describe the classification of volcanoes

d. Both A and R are incorrect based on the eruptions.

3) Name the major zones of volcanic activity

VI. Answer in a word
and explain any one.
1) Name the outer most layer of the earth.
XI. HOTs
2) What is SIAL?
1) The earth’s interior is very hot. Why?
3) Name the movement of the Earth’s lithospheric
plates? 2) Are Volcones Destructive (or) Constructive?

4) Give an example of extinct volcano 3) How does volcaone make on Island?

XII. Activity
VII. Answer the following briefly
1) On an outline map of the world, mark
1) What is mantle?
the Pacific Ring of Fire
2) Write note on the core of the earth?
2) Label the parts of volcano.
3) Define Earthquake?
3) Prepare an album on earthquake and
4) What is a Seismograph? volcanoes.

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PUZZLE

Across Down
1. Point of origin of Earthquake 2. Extinct volcano in Europe
4. Molten rock under the surface 3. Top layer of the Earth
5. Waves triggered by deep ocean earthquake 4. Middle layer of Earth
6. Inner layer of the Earth

WORLD MAP

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LABEL THE PARTS OF VOLCANO

Reference

Majid Husain, Physical Geography Anmol Publication Pvt Ltd

A Das Gupta, A.N. Kapoor, Principles of Physical Geography, S. Chand & Company Ltd., New Delhi
Goh Cheng Leong, certificate Physical and Human Geography, Oxford University press.
Savindra Singh (2015) physical Geography Pravalika publications Allahabad.

ICT CORNER Interior of the Earth

select full screen mode and play the game

with descriptions

PROCEDURE

Step 1: Open the Browser and type the URL given below (or) Scan the QR Code.
Step 2: Click on the Map to start
Step 3: select full screen mode and play the game with descriptions

Interior of the Earth URL:

http://world-geography-games.com/earth/index.html

*Pictures are indicative only

*If browser requires, allow Flash Player or Java Script to load the page.

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GEOGRAPHY

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UNIT Lithosphere – I
Endogenetic Processes
1
Learning Objectives

„„To know about the spheres of the Earth

„„To illustrate the internal structure of the Earth
„„To study the rock types and its cycle
„„To explain the internal processes of the Earth
„„To understand the processes of Earthquakes and volcanoes

Introduction 1.1 Spheres of the Earth

The Earth is a unique planet of the Earth’s surface is a vast area of
Solar family. The Earth is composed of four 510 million sq.km, where four spheres of the
spheres namely, the lithosphere, the Earth interact. The abiotic spheres are the
atmosphere, the hydrosphere and the lithosphere, atmosphere and hydrosphere.
biosphere. This lesson focuses on the The biotic sphere is the biosphere. Together,
internal processes of the Earth. The these spheres constitute the planet, Earth.
sequence of lessons generally follows
the spheres of the Earth system in a 1.2 Structure of the Earth
comprehensive manner.
The outer surface and inner core of the
Earth are totally different in their nature and
Have you ever wondered what our Earth
structure. The structure of the Earth’s interior
is made up of? Or what lies underneath the
is divided into three layers namely the crust,
Earth’s surface?
the mantle and the core.

“The Earth can physically be described

as a ball of rock (the lithosphere), partly
covered by water (the hydrosphere)
and wrapped in an envelope of air
(the atmosphere). To these three
physical zones it is convenient to add
a biological zone which includes all
the living organisms (the biosphere).”
Arthur Holmes Spheres of the Earth

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The lithosphere is the solid outer The terms ‘lithosphere’ and

part of the Earth. ‘crust’ are not the same.
The atmosphere is a thin layer of The lithosphere includes
gases that surrounds the Earth. the crust and the uppermost
part of the mantle.
The hydrosphere is the watery
part of the Earth’s surface including oceans, All terrestrial planets have
rivers, lakes and water vapour lithosphere. The lithospheres of Mercury,
Venus, and Mars are much thicker and
The biosphere is the layer of Earth more rigid than that of the Earth.
where life exists.

Crust
Crust is the outer layer of the Earth,
where we live. It is the skin of our Earth, which
Oceanic Crust
Continental Crust

ranges between 5 to 30 km. It is the solid

and rigid layer of the Earth. The thickness Upper Mantle

of the crust is greater below the continents

than the ocean floor. The crust is classified Continental Crust And Oceanic Crust

as continental crust and oceanic crust. The Continental Crust is made up of SIAL and
major elements of crust SIAL are Silica (Si) Oceanic Crust is made up of SIMA
and Aluminium (Al) and SIMA (Si - Silica
and MA - Magnesium)

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Mantle Types of Rock

The interior part beneath the crust is Based on formation, rocks are classified as:
called mantle, which is about 2,900 km
Igneous,
thick. In the upper part of the mantle, the
„
rock remains solid, whereas in the lower part „ Sedimentary and
of the mantle, rocks are in molten form. „ Metamorphic.
This molten rock inside the Earth is
called ‘magma’. Fact
Core The ancient city of Petra in Jordan is an
Th e core is the innermost and example of an entire city carved out of rocks.
hottest layer of the Earth which lies There are many specimens of magnificent
below the mantle. It is composed mainly rock-cut architecture in India, like the Ajanta
of Nickel (Ni) and Iron (Fe). Hence it is and Ellora caves in Maharashtra, the Aihole
called NIFE. The core is divided into and Badami temples in Karnataka, the
Solid inner core and Liquid outer core. Konark temple in Odisha and
The presence of large quantities of iron Mamallapuram in Tamil Nadu.
in the core is responsible for the Earth’s
gravitational force. As the Earth rotates
Igneous Rocks
on its axis, the liquid outer core spins over
the solid inner core and generates the The word ‘igneous’ is derived from
Earth’s magnetic field. This is responsible for the Latin word Ignis meaning ‘Fire’. The
the functioning of the magnetic compass. interior of the Earth contains very hot molten
Due to high pressure, the materials in material called ‘Magma’. When the magma
the inner core are unable to move and reaches the Earth’s surface, it is referred to
hence remain solid. as ‘Lava’. The lava on the surface cools down
and gets solidified as rocks called igneous
rocks. Granite and basalt are examples of such
1.3 Rocks
rocks. Igneous rocks are also called Primary
The crust is a storehouse of rocks. An or Mother rocks because all other rocks are
aggregate of minerals on the Earth’s crust is directly or indirectly formed from them.
called ‘rock’. It may be hard and compact like
‘granite’ or soft as ‘clay’ or loose as ‘sand’.
Sedimentary Rocks
These sedimentary rocks are named
Th e D e e p est Pl ac e
after the latin word 'sediment' meaning
ever reached by human
' settle. Rivers, glaciers and winds carry
technology vary from time bits of rock and soil and deposit them in
to time. Till 2011 Kola layers. After a few million years, these
Super Hole (12,262m) deposits harden into compact rocks and
in Murmansk, Russia was the deepest are called Sedimentary rocks.
place. But in 2012, Z-44 Chavyo Well
The bodies of plants and animals that fall
(12,376m) broke the record, and is on the deposits get embedded in the layers
supposed to be 15 times the height of and form Fossils. Sandstone, limestone,
Burj Khalifa in Dubai.The exploration chalk, gypsum, coal and conglomerate are
of Earth’s interior continues. examples of sedimentary rocks.

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Metamorphic Rocks down into relatively low elevated plains

and shapes the landform created by
The term ‘metamorphic’ is derived
Endogenetic process.
from the word ‘metamorphosis’, which
means, ‘change of form’. When igneous or Internal Processes
sedimentary rocks are subjected to extreme
heat and pressure, they undergo a complete The internal processes
change in their form and character .i.e., in generate heat and eject
course of time, granite may get transformed materials from deep below
to gneiss, basalt to schist, limestone to marble the Earth’s crust. Internal
and sandstone to quartzite. radioactivity is the
principal source of power
Rock Cycle for this process.
The Rock cycle is a continuous process Plate Tectonics
through which igneous, sedimentary and The lithosphere is divided into a number
metamorphic rocks are transformed from one of huge slabs of rocks called ‘Tectonic
form to another. plates.’ These tectonic plates are divided into
major and minor plates. These plates float
independently over the mantle. Collisions
Weathering
and erosion of these plates produce mountain ranges
Slow uplift to
Transport
and and other irregular surface features, both on
deposition
the surface
land and the ocean floor. This phenomenon
is called ‘plate tectonics’. The movement
Igneous rock
Sedimentation

Crystallization
of magma
of tectonic plates is due to thermal energy
Magma
Sedimentary rock
from the mantle. Now we have a better
understanding about the plate movements
Melting
Metamorphic rock
Burial, high temperatures
and pressures
and its relation to Earthquake and volcanic
Magma from molten
crust and mantle
activities.
Types of Plate Boundaries
Activity Convergent Boundary - Here the plate moves
Narrate the processes involved in the toward each other and sometimes, a plate
given rock cycle diagram in your own sinks under another. The location where the
words. sinking of a plate occurs is called a subduction
zone (eg) Fold Mountain-Himalayas.

1.4 Geomorphic Processes

The forces that act from the Earth’s
interior towards the Earth’s surface are
called Internal processess or Endogenetic
processes. These forces build the landscape Divergent Boundary – Here the plates pull
and create topographic relief. away from each other as magma pushes up
from the mantle (eg) Mid Atlantic Ridge
The forces that act on the surface of
the Earth due to natural agents like running
water, glacier, wind, waves etc. are called
External processes or Exogenetic processes.
These external processes tear the landscape

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Conservative/Transform Boundary – Here lofty mountain ranges such as the Himalayas

the plates slide horizontally past each other. and the Alps
(eg) San Andres Fault. According to plate tectonics, the plates
are in constant motion with an average rate
of few centimetres per year. The movement
might seem slow, but over millions of years,
the plates and the continents riding on them
move a long way. For example, about 250
Movements of Continental Plates million years ago, the Indian Plate was a part
Due to lateral compressional forces, of the Gondwana land, which comprised of
the plates are forced to move upwards modern Africa, Australia, Antarctica, and
and downwards. This is called ‘Folding’. South America.
Mountains formed by folding are called fold
mountains. The process of folding creates
Convergent
Transform Divergent Continental Rift zone
plate boundary
plate boundary plate boundary (young plate boundary)
Convergent
plate boundary

Trench
Strato Oceanic crust
Strato Trench
volcano Continental crust
volcano
Lithosphere Oceanic crust

Hot spot Subducting

Asthenosphere plate

Plate boundaries and associated features

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Approximately 140 million years Seismic Waves

ago, the Indian plate broke away from the Earthquakes generate seismic waves. The
ancient super continent ‘Gondwana’ and nature, force and speed of these seismic waves
began moving north and collided with Asia. depend on the nature of the medium through
The collision with the Eurasian Plate along which it passes. Accordingly, there are three
the boundary between India and Nepal major types of waves.
formed the Orogenic belt that created the
Primary or P-waves are the fastest of all
Tibetan Plateau and the mighty Himalayan
the Earthquake waves and the first to reach
Mountains.
the epicentre. These waves pass through solids,
liquids and gases, either through push or pull
Activity with an average velocity of 5.3km per second to
Here is a list of a few mountains. 10.6 km per second.
• Ural Mountains, Andes Mountains, Fact
Vindhya Range, Alps mountains,
C.F. Richter devised a scale to measure
• S atpura range, Rocky Mountains,
the magnitude of Earthquakes. This
Sierra Nevada.
scale relates to the energy released at the
• Identify and Locate with help of atlas epicentre and provides an estimation of
the severity of an Earthquake. It is an open
Earthquake ended scale. The highest magnitude ever
Earthquakes are generally caused by recorded is 9.5 on Richter scale (Bio-Bio,
the sudden vibrations in the Earth’s crust, Chile in 1960).
which spreads outward in all directions as Secondary or S-waves travel only
waves from the source of disturbance. The through solids. These transverse waves shake
point of origin of an Earthquake is called the ground perpendicular to the direction in
‘Focus’ (Hypocenter) which generates a which they propagate. The average velocity of
series of elastic waves. ‘Epicentre’ is a point these waves is 1Km per second to 8 km per
on the Earth’s surface that lies directly above second.
the focus. The impact of the Earthquake is felt Surface Waves (or) L-waves are similar
the most at the epicentre. to P-waves but they travel primarily along
the ground surface. These waves travel
Profile of an Earthquake
comparatively slower and are the most
destructive waves. The average velocity of
these waves are 1 km per second to 5 km per
second.
The instrument which
records the Earthquake waves
Distance from Epicentre
Epicentre is called ‘seismograph’ or
Soil at the Site ‘seismometer’. The science
Di
st
an
ce
Fault that deals with Earthquakes is called
fro
m Depth ‘seismology’.
Fo
cu
s
Focus or
Magnitude
Tsunami
Earthquake
Magnitude The word ‘Tsunami’ is a Japanese term,
meaning harbour waves. It is adopted to describe
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large seismically generated sea waves caused iv. Crater - a bowl shaped depression found
by Earthquakes, submarine explosions and at the top of the volcano through which
landslides. These waves travel at a great speed the magma flows out.
(more than 500 km per hour) and the length of Based on the periodicity of eruptions,
the waves exceeds 600 km. These waves reach to volcanoes are classified into
a height of more than 15 m near the sea shore (i) Active volcano, (ii) Dormant volcano, (iii)
and are capable of causing destruction along the
Extinct volcano.
coastal area.
The 2004 Indian Ocean Earthquake that The term ‘volcano’ is derived
caused tsunami is the sixth-deadliest natural from the Latin term VULCAN,
disaster which travelled at a speed of 600 which is the name of Roman
km per hour with an estimated death toll of “God of Fire”.
2,80,000. The Earthquake which occurred
near Indonesia at 00.58 hours took nearly 7
hours to reach Chennai.

On 26 December 2004 a
tsunami occurred in the
Indian Ocean. It was the result
of the Indio-Australian Plate
subducting below the Eurasian
Plate. It was caused by an Earthquake
measuring a magnitude of above 9 in the
Richter scale. The Earthquake caused the
seafloor to uplift, displacing the seawater a. Active Volcano
above.
Active volcanoes
are those which
Volcanoes constantly eject
A volcano is a vent or an opening on the volcanic lava, gases
surface of the Earth crust, through which hot and fragmented
solid, liquid and gaseous materials (Magma) materials. (eg.) Mount
erupt out to the surface from the Earth’s St. Helens in the United States.
interior. Magma rises up and ejects on the
b. Dormant Volcano (or) Sleeping
surface as Lava. Volcanoes are also formed
when plates move apart. Volcano
Volcanoes that
Volcanoes generally have the following
do not show any sign
major components. They are:
of volcanic activity for
i. Magma chamber - a large pool of liquid a long period of time
rock found beneath the surface of the are known as dormant
Earth volcanoes. Sometimes there may be a sudden
ii. Vents - an opening serving as an outlet explosion which may cause unimaginable loss
for air, smoke, fumes, magma etc to life and property (e.g.) Mt. Fuji , Japan
iii. Volcanic cone - a landform built by the
magma ejected from the vent in the c. Extinct or Dead Volcano
shape of a cone. When a volcano permanently
stops its volcanic activity, then it is
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called as extinct or dead volcano boundaries. One such area is the Circum-Pacific
(e.g.) Mt. Kilimanjaro, Tanzania. Ring of Fire, where the Pacific Plate meets many
surrounding plates. The Ring of Fire is the most
Activity seismically and volcanically active zone in the
Take a bottle filled with soda. Shake world. The other distinctive major belts are Mid-
the bottle twice or thrice. Now twist the Oceanic Ridges ,Mid-Continental Belts and
cap open. What do you observe? Alpine - Himalayan belt.

Volcanoes can also be classified based on Effect Of Volcanoes

their structure and composition as composite Constructive Effects
volcano, shield volcano and dome volcano Volcanic materials enrich the soil fertility that
promotes agricultural activities. The hot volcanic
d. Composite Volcano
region helps in generating geothermal energy.
Composite volcano, also known as strata Many dormant and active volcanoes are the most
volcano, is a conical volcano built by many attractive tourist spots of the world. Most of the
layers of hardened lava, pumice and volcanic volcanic materials are used as building materials.
ash. These are commonly found in the Pacific Destructive Effects
Ocean Eg. Mt. Fuji, Japan
Volcanic eruption causes Earthquakes, flash
e. Volcanic Dome floods, mud slide and rock fall. Lava can travel very
far and burn, bury, or damage anything in its path.
A lava dome or volcanic dome is roughly The large amount of dust and ash makes breathing
a circular mound formed due to the slow hard and irritable. Volcanic eruptions can alter the
ejection of viscous lava from a volcano. As the weather conditions and disrupt transport (Iceland
lava is rich in silica with intense viscosity, it is volcanic eruption) in and around the volcanic
prevented from flowing far from its vent. e.g. region.
Parícutin, Mexico
Hots Recap
Pacific Ring of Fire — Most seismically and „ The spheres of the Earth are the
volcanically active. Why? lithosphere, atmosphere, hydrosphere
and biosphere.
f. Shield Volcano
„ Earth’s interior is divided into three
Shield volcanoes layers - Crust, Mantle and Core.
are formed by intense „ Based on composition, the crust,
viscous lava. mantle and core are referred to as
These are shallow SIAL, SIMA and NIFE respectively.
depositions with „ The formation and deformation of
gently sloping sides. landforms on the surface of the Earth
Hence the lava are due to continuous internal and
external processes.
flows out in all directions to create a shield.
„ The lithosphere is composed of major
E.g., Mauna Loa, Hawaii
and minor tectonic plates.
Distribution of Earthquakes and „ Earthquake is the shaking or
Volcanoes trembling of the Earth’s crust.
Most Earthquakes and volcanic eruptions „ Earthquake and volcanoes are useful
do not strike randomly, but occur along the plate to understand the Earth’s interior.

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EXERCISE
9. The point of origin of an Earthquake is called
the _________
I Choose the a. epicentre b. focus
correct answer c. seismic wave d. magnitude
1.       is the rigid outer layer of the II. Match the following
Earth. 1. Endogenetic — Seismograph
a. core b. mantle process
c. Crust d. inner core 2. Mantle — Subduction Zone
2.       layer is made up of 3. Convergent — Volcanic
liquid iron boundaries
a. Inner core b. Outer core 4. Earthquake — Pacific Ocean
c. Mantle d. Crust 5. Composite — SIMA
3. Magma is found in the  volcano

a. crust b. mantle III. C

 onsider the given
c. core d. None of the above statements
1. i. Mt. Fuji is a dormant volcano.
4. 
The movement of tectonic plates is
induced by       energy. ii. Mt. Kil imanjaro is a dormant

a. hydel b. thermal volcano.
c. wave d. tidal iii M
 t. Tanzania is a dormant volcano.
5. In the ancient period, Which of the statement(s) is/are true?
Gondwanaland moved towards a. i is true b. ii is true
      direction. c. iii is true d. i, ii, iii are true
2. Statement: Magma gushes out when it
a. north b. south
finds vents.
c. east d. west
Reason: Interior of the Earth contains
6. Many million years ago , India was a
compressed hot magma
part of the super continent      
a. Statement & reason are true
a. Gondwana b. Laurasia
b. Statement is true, reason is false
c. Panthalasa d. Pangea.
c. Statement is false reason is true
7. T he movement of plates that creates
stress and tension in the rocks causing d. Statement & reason are false
them to stretch and cracks result 3. Statement I: Mountain ranges are formed
in      . by the collision of tectonic plates
a. fold b. fault Statement II: The movement of
c. mountain d. earthquake tectonic plates is due to the thermal
8. 
    refers to a bowl-shaped depression energy from the mantle
found at the top of the volcano. a. Statement I is false II is true
a. crater b. vent b. Statement I and II are false
c. chamber d. volcanic cone c. Statement I is true II is false
d. Statement I and II are true

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IV. A
 nswer in brief: VIII. Map Skill
1. Write a brief note on the various spheres On the given outline map of the world,
of the Earth. mark the following:
2. Mention the layers of the interior of the a. Pacific Ring of fire
Earth. b. Earthquake prone zones (any two)
3. Define Plate tectonics. c. Locate any two active volcanoes of the
4. What is Tsunami? world.
d. Himalayas and Alps ranges
5. What is a Volcano? Mention its major
components.
IX. Life Skills
6. What is an Earthquake and how it occurs?
Imagine that you feel tremors or shocks in
7. What are seismic waves and mention its
your locality. What will be your role in saving
types? lives from destruction? List out the Do’s and
8. Write about the Pacific Ring of fire. Don’ts.

V. Give Reasons for the

­following:
1. Igneous rocks are also called Primary
Rocks or Mother rocks.

VI. Distinguish between

1. Core and crust.
2. Epicentre and Hypocentre
3. Divergent and convergent boundaries.
4. Primary waves and Secondary waves.
5. Shield volcano and volcanic Dome.

VII. Write answers in a Paragraph

1. Describe the structure of the Earth.
2. Write a note on the internal and external
processes of Earth.
3. How are volcanoes classified based on
the periodicity of their eruptions?
4. Explain the effects of Volcanoes.

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Unit 3

Lithosphere:
Endogenic Processes

Chapter Outline Learning Objectives:

3.1 Introduction • Understand the structure and
3.2 Interior of the Earth
composition of the Earth.
3.3 Continental Drift Theory
3.4 Plate Tectonics • Develop an insight into the
3.5 Plate boundaries Continental Drift Theory.
3.6 Convection Cell • Describe the concept of Plate
3.7 Fold Tectonic movement.
3.8 Fault • List and compare the characteristics
3.9 Earthquake and distribution of the earth’s
3.10 Volcano
internal forces
3.11 Rocks
3.12 Rock Cycle • Explain rock types and rock cycle

3.1 Introduction
Do you know that the Russians tried to dig
through the centre of the Earth? It indeed
is a daring attempt.
While the famous Voyager 1 satellite
took 26 years to exit our Solar System
(16.5 billion km away), almost the same
amount of time (24 years) was taken for
man to dig out a mere 12.3 km into the
earth’s surface.
Russia drilled Kola Super Deep bore Figure 3.1 Kola Super Deep
hole between 1970 and 1994. The deepest Borehole, Russia
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8.9 KM HIGH
MOUNT EVEREST
are collectively known as geomorphic
processes. (Figure.3.3)
The process by which the earth’s surface
is reshaped through rock movements and
SEA LEVEL

DEEPEST ACTIVE MINE

displacement is termed as diastrophism.
Diastrophism includes both orogenic and
3.9 KM DEEP
KIMBERLITE

12.3 KM DEEP MARIANA TRENCH

epeirogenic processes.
KOLA SUPERDEEP BOREHOLE 10.9 KM DEEP

Our knowledge of the earth is mostly

Figure 3.2 Extreme points of the earth limited to its surface. But the earth has
a complicated interior. The earth is
part of it, named 'SG-3 (Star Gate), extends composed of lithosphere, atmosphere,
12.3 km into the Earth. Look at figure 3.2 hydrosphere, and biosphere.
and amaze the highest and deepest points The lithosphere is the outermost rigid
of the earth. rocky shell of the earth. It comprises the
The earth’s surface is being continuously crust and the upper portion of the mantle.
reshaped by both the internal (Endogenic The word lithosphere is derived from
forces) and external forces (Exogenic the Greek words lithos meaning rocky
forces). The changes that the endogenic and sphaira meaning sphere. The term
and exogenic forces bring about in the lithosphere was introduced by Joseph
appearance of the surface of the earth Barrel, an American Geologist.

Earth
movements

Endogenetic Exogenetic

Slow Movements Sudden

Movements
Weathering Erosion
(Diastrophism)
(Catastrophism)

Orogenic or Mountain building Earthquakes Physical Glacier

Epeirogenic or Continent
forming

Tension Volcanoes Chemical River Water

Upward
movement
Compression Biological Waves
Downward
movement
Wind

Underground
water (Karst)

Figure 3.3 Earth's Forces

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Figure 3.4 Layers of the Earth

3.2 Interior of the Earth 70 km thick in the Himalayan region. The
The interior of the earth is composed density of the crust is less than 2.7 g/cm3.
of many minerals both in the solid and 3.2.2 The mantle
liquid state. The temperature in general The mantle is composed of silica, magnesium
increases at the rate of 1° C for every 32 and iron. It lies between the lower crust
metres towards the earth’s interior. and the outer core. It extends for about
Look at the figure.3.4 the layers of the 2,900 km. It is divided into upper mantle
earth. Earth’s interior can be divided into and lower mantle. The mantle generally is
the crust, upper mantle, lower mantle, in a solid state. The upper part of the mantle
outer core, and inner core. is called asthenosphere. The word Asthen
in Greek means weak. It extends up to
3.2.1 The Crust 400 km and it is the main source of magma.
The crust is further divided into upper The Mohorovicic is the boundary which
crust (continental crust), composed of divides the lower crust and the upper mantle.
silica and aluminum (sial) and the lower The density of the mantle is 3.9 g/cm3.
crust (oceanic crust) made up of silica and
magnesium (sima). The boundary between 3.2.3 The core
the upper crust and the lower crust is termed The core forms the centre of the earth. Its
as ‘Conorod boundary’. The thickness density is 13.0 g/cm3. Its temperature is
of the crust varies from oceanic areas to about 5500° C to 6000° C. The core has
continental areas. Oceanic crust is thinner two parts namely the outer core and the
when compared to the continental crust. inner core. The boundary between the
The mean thickness of oceanic crust is 5 km lower mantle and the outer core is called
while the continental crust is around 30 km. Guttenberg margin.
The continental crust is thicker in the areas The outer core and inner core are
of major mountain systems. It is as much as separated by Lehmann boundary. The
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outer core is in the liquid state while the 3.3 Continental Drift Theory
inner core is in the solid state. Generally, In 1912 Alfred Wegener (1880-1930)
the core is composed of Nickel and Ferrous postulated that all the continents once
(Iron) which is called NiFe (Barysphere). were together forming a single continent.
The core is extended from 2,900 km to 6,370 According to him, about 250 million years
km from the surface of the earth.

L A U R A S IA

Equator TETHYS SEA Equator

TETHYS SEA

GO
ND
WA
NA
LA
ND

PERMIAN TRIASSIC
250 million years ago 200 million years ago

Equator Equator TETHYS SEA

TETHYS SEA

JURASSIC CRETACEOUS
145 million years ago 65 million years ago

NORTH ASIA
AMERICA

INDIA

AFRICA
Equator
SOUTH
AMERICA
AUSTRALIA

ANTARCTICA

PRESENT DAY

Figure 3.5 Continental Drift

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ago, the earth was made up of a single the western side of Africa and the
landmass called Pangaea (meaning "all eastern side of South America fit
lands"), and a single ocean surrounding it together.
called as Panthalassa. Over a long period
of time, probably 220 million years ago, 'Enchanted rock is a
they drifted apart and gradually moved to pink' coloured ancient
form their present position. First, Pangaea Granite rock located
broke into two landmasses namely in Texas Which
Laurasia in the north and Gondwana in attractes tourists
the south.
Laurasia further split into Eurasia and
North America. Gondwana land split
Africa
into Africa, South America, Antarctica, South America
Australia, and India.
Wegener put forward certain evidences
to support the continental drift theory. Let
us deal with it in detail.
South
3.3.1 Evidences to support continental pole
drift theory India
The continental drift theory is supported
by the following evidences.
1. Certain identical rare fossils have been Antarctica
found in different continents.
The fossils of Mesosaurus (a small
Permian reptile), for example, have
been found only in Africa and South
Australia
America.
2. The fossil of a Fern tree, about 360
million year old, has been found only Figure 3.6 Evidence of continents split
in India and Antarctica. from the same land mass
3. Rocks of similar type, formation, and age
have been found in Africa and Brazil. 3.4 Plate Tectonics
Have you heard about diving between
4. Geological structure in Newfoundland
two continents? It is possible in the Silfra
matches with that of Ireland, Scotland
rift of Iceland. Look at Figure.3.7. It is
and Scandinavia. Geological Structure
located in the Tingvellir National Park.
of Appalachian Mountains matches with
It is in the boundary between the North
Morocco and Algeria in North Africa.
American plate and the Eurasian plate. It
5. The corresponding edges of the is the visible boundary between these two
continents fit together. For example, plates.

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Gnss (Global Navigation Satellite System)

measures the speed of
plate movement. Rate of
seafloor spreading ranges
from 1 to 2 centimetres
per year along the oceanic
ridge in the northern Atlantic Ocean to
more than 15 cm per year along the East
Figure 3.7 Silfra rift, Tingvellir, Iceland Pacific Rise.

Web link for Silfra drift

https://www.youtube.com/watch?
Lithospheric plates are sometimes
v=U3eT0qmPJbw
called as crustal plates or tectonic plates.
Earth's lithosphere is divided into a
3.5 Plate boundaries series of major and minor mobile plates.
Plate boundaries are the zones where Eurasian plate, Indo-Australian plate,
two or more plates move about. Plate North American plate, South American
tectonics describes the distribution and plate, Pacific plate, African plate and
motion of the plates. The earth's surface Antarctic plate are the major plates.
is composed of rigid lithospheric slabs Arabian plate, Caribbean plate, Cocas
technically called “plates”. The word plate and Scotia plate are the examples of
tectonic is derived from the Greek word minor plates. Plates move at the rate of 2
tekton meaning builders. to 3 centimeters per year.

W E

NORTH AMERICAN EURASIAN PLATE

PLATE
PHILIPPINE
JUAN DE FUCA COCOS CARIBBEAN PLATE
PLATE PACIFIC
PLATE PLATE PLATE
ARABIAN
PLATE INDIAN
PACIFIC PLATE
PLATE
AFRICAN
SOUTH
NAZCA PLATE
EASTER PLATE AMERICAN
PLATE AUSTRALIAN PLATE
PLATE

JUAN FERNANDEZ
PLATE

ANTARCTICA PLATE
SCOTIA PLATE
Not to scale

Figure 3.8 Distribution of tectonic plates

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Student activity
Look at the map given below. Label the plates or number them. Identify and colour
the oceanic plates.
1. Pacific plate 9. North American plate
2. African plate 10. South American plate
3. Eurasian plate 11. Juan de Fuca plate
4. Arabian plate 12. Indian plate
5. Australian plate 13. Antarctic plate
6. Caribbean plate 14. Philippine plate
7. Cocas plate 15. Nasca plate
8. Scotia plate
1. Name the plates bordering the Indo-Australian plate.

2. Which sea lies between African plate and Arabian plate?

3. Which two continents, you think, may fit together?

W E

Not to scale

Figure 3.9 Tectonic plates

Plates are composed of the continental Plate margins mark the occurrence of
or oceanic landmass. The subduction the most significant landforms, including
of the oceanic plates results in the volcanoes, fold mountains, island arcs
occurrence of earthquakes and volcanoes and deep-sea trenches. There are three
adjacent to trenches. principal types of plate boundaries. They
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are divergent, convergent, and transform

Volcanic
arc
boundaries.

ch
en
Tr
3.5.1 Divergent plate boundaries Oceanic Crust
Continental
crust
Divergent plate boundary is the margin Lithosphere Lithosphere
where two plates move apart. For
instance, the African plate and South Asthenosphere

American plate move apart and form a

divergent plate boundary. Narrow oceans Figure 3.10 Divergent margin
High
represent young divergent boundaries

Ra ntain
islands such as the Azores, Ascension, St.
Plateau

e
ng
and wide oceans are indications of

u
Helena and Tristan da Cunha.

Mo
old ocean basins. Ocean ridges are Continental crust
Continental crust

the boundaries between plates of the Web link: Mid Atlantic Ridge
Lithosphere Lithosphere

lithosphere. www.britanica.com/place/
atlanticocean
Atlantic Ocean Astheno sphere

is widening at an
Secondly, rift valley is formed when
estimated rate of 1 to
two plates move apart. If a divergent
10 cm a year
boundary runs through the continent,
A fissure is created when oceanic the continent splits apart and rift valley
lithosphere separates along the oceanic is formed. The African Rift Valley of East
plate boundary. The gap is filled by magma Africa is an example.
that rises from the asthenosphere. The
3.5.2 Convergent plate boundary
magma cools and solidifies to create a new
Convergent plate boundary is the margin
oceanic crust. Hence, the divergent plate
where two plates collide with one another.
boundary is termed as the constructive
For instance, the South American plate
plate boundary. It is also called as accreting
and Nazca plate collide with each other.
plate margin.
There are two kinds of surface features
Let us see what happens in the divergent
associated with the convergent margin.
plate boundary. Firstly, submarine
The first is the ocean trench that forms a
mountain ridge is formed through the
line between the two colliding plates.
fissures in the oceanic crust when the
plates move apart.
The Mid-Atlantic Ridge is an ideal Wadati-Benioff
example of a submarine mountain ridge zones are nothing but
in the Atlantic Ocean. It is the longest Subduction zone
mountain ridge in the world.
It extends for about 16,000 km, in a 'S'
shaped path, between Iceland in the north
and Bouvet Island in the south. It is about A trench is a narrow and deep depression of
80 to 120 km wide. It reaches above the the ocean floor. It is formed when the oceanic
sea level in some places thus forming the plate slides down underneath continental

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plate as the oceanic plate is denser than the 3.5.3 Transform plate boundaries
continental plate. For instance, Mariana Transform plate boundary is the margin
Trench in the Pacific Ocean, is the deepest where two plates move side by side. The
trench in the world. It is formed when the lithosphere is neither destroyed nor created
Pacific plate sinks down the Eurasian plate. It is by the transform plate boundary. Hence
about 10,994 metres (10.99 km) deep. Mariana it is called as the Conservative or passive
Trench stretches for more than 2,540 km with plate boundary. The San Andreas Fault,
a width of 69 km. California, is a transform boundary that
You could take Mount Everest and separates the North American plate and
sink it in the Mariana Trench, the deepest Pacific Plates.
point in the ocean, and still you have a km Subduction zone

of depth to reach the surface of the ocean. oceanic

Cascade
ridge
When a continental plate and an oceanic Juan
Range

plate collide with each other, denser oceanic De Fuca North

plate sinks below the lighter continental Plate American
plate, subduction zone is formed. Transform Plate
boundary San Francisco
San
A subduction zone is a boundary where Plate motion direction Andreas
one plate sinks under the other plate. It was Los Angeles fault

first identified by Kiyoo Wadati and Benioff. Pacific

Plate Gulf of
Secondly fold mountain is formed when California

two plates collide each other. For instance, Figure 3.12 Transform plate boundary
the Himalayas were formed when the Indian
plate collided with the Eurasian plate. The 3.6 Convection Cell
zone marking the boundary of the two Now you may think why plates keep
colliding plates is known as suture line. moving. The plate movements are caused
Volcanic
arc

by the convection cells. Convection cell

h

As the crust is less dense than the

nc
e

is the circulation of the molten materials

Tr

mantle,
Oceanicthe
Crustnewly formed magma will
Continental

caused by the heat derived from the core.

crust
tendLithosphe
to rise re to the Earth’s surface, where
Lithosphe re
it may form volcanoes. The area in the When looking at the figure.3.13 you will
Asthenosphere
subduction zone where most earthquakes understand how and why plates move in
occur is known as the Benioff zone. different directions.
High When the molten materials( magma)
Ra ntain

circulate in different directions, they push

Plateau
e
ng
u
Mo

Continental crust
or pull the plates in different directions.
Continental crust
Thus, the plates move towards each other,
Lithosphere
Lithosphere
move away from one another and move
side by side. The plate movements cause
Asthenosphere
the formation of fold, fault, earthquake, and
volcano to occur. Let us see the cause, effects,
Figure 3.11 Convergent plate boundaries and distribution of the internal forces.

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Mid-Oceanic Ridge

Ocean
Trench
Subduction

Continental Oceanic
Lithosphere Lithosphere

Cold
Convection
Cell
Hot
Outer
core

Inner
core

Figure 3.13 Convection Cell

Axial Planes
3.7.1 Parts of a Fold
Hinge Lines
(fold axes) Axis Up thrown part of a fold is called anticline.
Down thrown part of a fold is syncline.
Hinge
line
b
Lim

The side of the fold is a limb. The top

b
Li
m
b
Lim of the fold is the crest. The plane which
Li m

Li m b
bisects the angle between two limbs is
b

Anticline Syncline Anticline

called the axis of fold or axial plane. The
Figure 3.14 Parts of the Fold fold is formed by the plate movements.

3.6.1 Internal forces 3.7.2 Types of Folds

The internal forces are also called as the The type of fold depends on the nature of
tectonic forces. They generally occur in the rock, the intensity of compression forces,
the plate boundaries. They are caused by etc. The types of the fold can be many but
convection cell and plate movement. They we will deal with five of the following.
form fold, fault, earthquake and volcano. 1. When compressional force is equal
from both sides, the angle of the limb
3.7 Fold
is same on both sides. Such a fold is
Horizontal movements are produced
called symmetrical fold.
by forces of compression and tension.
Folding is the bending of rock strata due 2. When compressional force is more
to compression. Folding on a large scale from one end, one limb is steeper
results in mountain building generally than the other. Such a fold is called
referred to as orogeny. asymmetrical fold.

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A. Open (Symmetrical) B. Asymmetrical C. Overturned

D. Recumbent E. Isoclinal

Figure 3.15 Types of Fold

3. Isoclinal folds are similar to symmet- So isoclinal folds are symmetrical and
rical folds, but these folds both have aligned in a parallel fashion.
the same angle and are parallel to each 4. When one limb of the fold is pushed
­other. 'iso' means 'the same' (symmet- over the other limb of the fold, it is
rical), and 'cline' means 'angle,' so this called as over turned fold. Limbs are
name literally means 'the same angle.' seldom horizontal.

Figure 3.16 The Fold mountains of the world

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Student activity
From the map given above, name the plates causing the formation of fold mountains
given below.
S. No Fold Mountain Two Converging Plates

1. The Andes

2. The Rockies

3. The Atlas

4. The Himalayas

5. The Alps

5. When one side of the fold is pushed so The fault plane is the flat surface
much that it lies positioned over the along which broken blocks of rock slide
other, such a fold is called recumbent past one another. A fault dip is an angle
fold. between the fault plane and horizontal
plane. Up thrown side represents the
When plates converge, the weak
uppermost block of a fault. Down thrown
rocks and sediments lying between two
side represents the lowermost block of a
plates get squeezed and folded. Parallel
fault. Sometimes it becomes difficult to
folds form long chains of fold mountain
find out, which block has really moved
ranges with high peaks. The fold
along the fault plane. Hanging wall is the
mountains are characterised by peaks and
upper wall of a fault. Foot wall represents
valleys. The tops of anticlines become
the lower wall of a fault.
the peaks and synclines become the
valleys. Intermontane plateaus (plateau A fault scarp is the steep wall like slope
surrounded by the mountain ranges all caused by faulting of the crustal rocks.
sides) may be found between the high Sometimes the fault scrap is so steep that
ranges. Example, Tibet. it resembles a cliff.

3.8 Fault 3.8.1 Types of Faults

A fault is a break in earth’s crust where Based on how plates move about, the fault
blocks of rock crust slide past each other. can be divided into as follow:
Usually it occurs along plate 3.8.1.1 Normal Fault
boundaries, where the forces of plate Vertical displacement of the crust is called a
motion compress, pull or shear the crust normal fault. The normal fault is caused by
that breaks the crust. Energy release tensional forces where plates diverge. One
associated with rapid movement on active block lies above the other (hanging wall). The
faults is the cause of most earthquakes. other block lies below the fault (footwall).

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Hanging Wall Block

Footwall Block

Footwall Block Hanging Wall Block

Reverse Fault
Normal Fault
Figure 3.18 Narmada Rift Valley, India
word meaning ‘trough’. A Rift Valley may
subsequently get filled by water and a
river may flow through it. Normally, a rift
Hanging Wall Block valley is long, narrow and very deep. For
Footwall Block example,
all Block i. Rhine rift Valley is flanked by two
Reverse Fault Block Mountains namely the Vosges
and the Black Forest.
Figure 3.17 Normal fault and Reverse fault
When movement occurs along a normal ii. The rift of River Narmada in India lies
fault, the hanging wall slips downward. between the Vindhyas and Satpura
block mountains.
Landforms made by Normal fault are: iii. The great rift valley of Africa.
1. Rift Valley or Graben The Great Rift Valley of Africa is
When a narrow block of land drops or the longest rift valley in the world. It
subsides between two parallel normal stretches for 6,400 km from Mozambique
faults, rift valley (Graben) is formed. in the south to Syria in the north. The
Graben originates from the German depressions have become lakes. The lakes

Volcano (e.g. Mt.Kilimanjaro) Fault Scarps

Parallel Faults (F = Faults)

Plate pulled apart Central

block Plate pulled apart
(horst)
Multiple fracturing F F Rift Valley F F FF
Magma
F Rift Valley Multiple fracturing
Lakes on valley floors (e.g. Lake Tanganyika)

Figure 3.19 Rift valley and Block Mountain

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Horst

Graben

Tectonic Stress

Figure 3.20 Horst (Left) and Vindhya Block Mountain (Right)

of Africa, Dead Sea of Israel and the Red convergent plate boundaries. One side of
Sea form the parts of the Great Rift Valley. the fault lies at an angle above the other.

2. Horst 3.8.1.3 Shear Fault / Transform Fault/

When a block of land between two faults Strike – Slip Fault
is pushed up, block mountain or horst is It is created by shearing along transform
formed. In this case, the central block is boundaries. Rocks on either side of fault
not only up thrown but the side blocks slip past each other sideways with little up
are also relatively downthrown so that the or down motion. It mostly occurs in the
whole central mass appears like a dome. ocean basin and connects offsets in the
In India, specifically the mountain mid ocean ridge.
ranges of Vindhya and Satpura found in
the central western part of the India are 3.9 Earthquake
block mountains. Earthquake is a sudden shaking of the
earth’s surface. Focus is the location
3.8.1.2 Reverse Fault inside the earth where the earthquake
A reverse fault is a horizontal displacement originates. Epicenter is the point on the
of the crust. It is formed where two earth's surface vertically above the focus
fractured blocks move towards each other. of an earthquake. Earthquake results from
It is caused by compressional forces along the sudden release of pressure which
Left lateral strike - slip Fault
has slowly built up within the earth’s
crust. Energy is released in the form of
shockwaves known as seismic waves. The
seismic waves can broadly be classified
into two types namely Body waves and
surface waves.
I. Body Waves are the waves that travel
through the interior of the earth. They
are further divided into the following.

Figure 3.21 Transform fault

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Fault Scarp
Fault trace

Epicenter

Seismic
Waves Focus

Fault Plane

Figure 3.22 Parts of an Earthquake

a. P or Primary or Compressional waves Love waves shake the ground side to

are the fastest seismic waves (6 km/ side like S wave.
sec. in the upper crust). They cause Rayleigh waves displace the ground
the matter to oscillate forward and like rolling ocean waves. The ground
backward, parallel to the motion of rolls forward and up and then down and
the seismic wave front. P waves push backwards. This is similar to a p wave but
(compress) and pull (dilate) the rock with the extra up-down motion.
that they pass through. They pass
through all medium. 3.9.1 Measuring the earthquake
b. S or Secondary or Shear waves are It is estimated that about 100,000
slower than the primary waves (3.5 earthquakes occur but all cannot be felt. A
km/sec. in the upper crust). They few earthquakes may be severe causing huge
cause matter to oscillate side to side, damage to property. Earthquake magnitude
perpendicular to the motion of the is measured on the Richter scale (named
wave front. S waves shear the rock that after the seismologist who devised it), which
they pass through. They pass through rates them on a scale of 1 to 10. Earthquake
only solid medium. intensity is measured on the modified Mercalli
II. Surface Waves are the waves that scale, which ranges from 1 to 12, depending
travel along the earth's surface. They upon the intensity. The seismograph is an
are slower than body waves. They instrument used to detect and record seismic
cause damage during earthquakes. waves created by the earthquakes.

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3.9.2 Description of effects of earthquake in Richter scale

MODIFIED MERCALLI SCALE RICHTER SCALE

I. Felt by almost no one. 2.5. Generally not felt, but
II. Felt by very few people. recorded on seismometers.
III. Tremor noticed by many, but they often 3.5. Felt by many people
do not realize it is an earthquake.
IV. Felt indoors by many, Feels like a truck
has struck the building.
V. Felt by nearly everyone: many people
awakened. Swaying trees and poles
may be observed.
VI. Felt by all; many people run outdoors. 4.5. Some local damage
Furniture moved, slight damage occurs. may occur.
VII. Everyone runs outdoors. Poorly built
Structures considerable damaged; Slight
damage elsewhere.
VIII. Specially designed structures damaged 6.0. A destructive earthquake.
Slightly, others collapse.
IX. All buildings considerably damaged, many
shift off foundations, Noticeable cracks in
ground.
X. Many structures destroyed. Ground is 7.0. A major earthquake.
badly cracked.
XI. Almost all structures fall. Very wide cracks 8.0. Great Earthquakes.
in ground. and
XII. Total destruction. Waves seen on ground up
surfaces, objects are tumbled and tossed.

Table 3.1 The Mercalli and Richter scales

3.9.3 Causes of Earthquakes 3. Fires in the forest and urban areas.
There are many factors controlling the 4. Flash floods.
occurrence of the earthquake. Some of the
5. Tsunami - The high amplitude oceanic
major factors include:
waves caused by submarine earthquake
1. Plate Tectonic Movements
(measuring more than 7 on Richter
2. Volcanic Eruptions.
scale). The seismic waves travel through
3. Construction of large dams results
seawater generates high sea waves. They
in earthquake. Example. Koyna dam,
cause severe loss of life and property.
Maharashtra.
For instance, on 26th December 2004, a
4. Other Reasons: The nuclear
tsunami originating from a magnitude
explosions also release massive energy
8.9 earthquake in northern Sumatra
to cause tremors in the earth crust.
killed over 1,50,000 people in countries
When underground cave collapses,
surrounding the Indian Ocean.
earthquake may occur.
3.9.5 Distribution of earthquakes
3.9.4 Effects of the Earthquakes
1. Damage to buildings, roads, rails, 1. Circum-Pacific region: This region
factories, dams, bridges etc. includes all the coastal areas around
2. Landslides caused by earthquakes the Pacific Ocean. It extends through
damage infrastructure. the coasts of Alaska, Aleutian Islands,

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W E

Not to scale

Figure 3.23 World Distribution of Earthquakes and Volcanoes

Japan, Philippines, New Zealand, west
coast of North and South America.
This zone accounts for 68% of all
earthquakes on the surface of the earth. EARTHQUAKE MIDDLE EAST
2. Mediterranean-Himalayan region: NEAR THE IRAN/IRAQ BORDER/NOV.12.2017-9:18P.M.LOCAL TIME

This region extends from Alps

mountain to the Himalayan Mountains Tehran
and Tibet to China. About 31% of
❂
MAGNITUDE:7.2
world's earthquakes occur in this
region.
3. Other Areas: These include Northern ❂
Baghdad
Africa and Rift Valley areas of the Red
Sea and the Dead Sea. ✵ ✵
IRAQ IRAN
3.10 Volcano
A volcano is an opening in the earth's crust
through which magma, gases and ash are
released to the earth's surface. The molten Figure 3.24 Earthquake,Iran-Iraq
rock material found in the interior of the border, 2017
earth is called magma. It can be noted that On 12th November 2017, an earthquake
when magma reaches the earth’s surface, it with a magnitude of 7.2 on the Richter
scale occurred on the Iran–Iraq border.
is known as lava (Figure. 3.25). Vent is an Areas affected: Iran and Iraq.
opening or mouth of a volcano. Fumaroles Max. intensity: 8 (Severe)
are the gushing fumes through the gap Fault: Arabian and Eurasian plates.
in the volcano. Crater is a saucer shaped Casualties: 630 dead; above 8,100
depression in the mouth of a volcano. injured; above 70,000 homeless. Depth:
When the crater is widened, it is called as 19.0 km.

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Crater (if filled with water,

a crater lake is formed). Fact File
Mt. Krakatau
Cone
Vent Lava
The greatest volcanic explosion
Ash Side
Vent
known to humans is perhaps
Fumarole Mt. Krakatau in August 1883.

Crust Krakatau is a small volcanic island

in the Sunda Straits, between Java
and Sumatra.
Figure 3.25 Volcano The explosion could be heard in
Caldera. Volcanic ash consists of fragments Australia, almost 4,000 km away.
of pulverized rock, minerals and volcanic The vibration set up enormous waves
glass, created during volcanic eruptions. over 30 m high which drowned
Volcano generally erupts either through the 36,000 people in the coastal districts
vent (E.g. Mt. Fujiyama, Japan) or fissure of Indonesia.
(The Deccan Plateau, India).
Pumice is a volcanic rock produced when
lava with a very high content of water and Cotopaxi in Ecuador
gases is discharged from a volcano. is the world’s highest
active volcano.
3.10.1 Causes of Volcanic Eruptions
The following are the causes of volcanic
eruptions: 1. Active Volcanoes: Volcanoes which
Weak Zones in the Earth Crust: The erupt frequently are called active
parts of the earth where two tectonic volcanoes. Generally, their vent remains
plates collide against or drift apart from open. Mount Etna of Italy, Cotopaxi in
each other are considered very weak. Ecuador are some examples.
Volcanoes may erupt in such zones, for 2. Dormant Volcanoes: These volcanoes
example, African and Eurasian plates. may not have erupted in the recent past
Magma Saturated with Gases: The but there is a possibility of eruption
magma, in the interior of the earth, is often at any time. In other words, they may
found saturated with gases like carbon lie dormant awaiting active eruption
dioxide, and hydrogen sulphide. These anytime. Sometimes gases and steam
gases together with water vapour make the come out of them. They cause great
magma highly explosive. Magma is forced destruction to life and property once
out as lava on the surface of the earth due they become active again. Mt. Vesuvius
to the pressure exerted by these gases. of Italy and Mt. Fujiyama of Japan are
examples.
3.10.2 Types of Volcanoes 3. Extinct Volcanoes: These volcanoes
Based on the frequency of eruption, there have exhausted their energy and have
are three types of volcanoes:
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not erupted during the known geological 3.10.3 Effects of Volcanic Activities
period. The vent of these volcanoes Destructive effects of volcano
remains closed with solidified lava. Showers of cinders and bombs can cause
The formations such as craters may be damage to life and properties. Sometimes
filled with water and crater lakes may be ash can precipitate under the influence of
formed. The slopes of these landforms rain and completely cover large areas.
may be covered with vegetation. Popa in The volcanic gases pose potential
Myanmar and Mt. Kenya in eastern Africa hazard to people, animals; agriculture,
are the examples of extinct volcano. while sulphur dioxide gas can lead to acid
On the basis of nature of eruption rain and air pollution.
and form developed on the surface, they
are classified into following types: Positive Effects of Volcanoes
Volcanism creates new landforms.
a) Shield Volcanoes: These are made up
Volcanic rocks yield very fertile soil upon
of basalt, a type of lava that is very fluid
weathering and decomposition.
when erupted. They become explosive
when water gets into the vent. They The Kimberlite rock of South Africa,
develop into a cinder cone. Hawaiian the source of diamonds, is the pipe of an
volcano is an example of this category. ancient volcano.

b) Composite cone volcanoes: They are In the vicinity of active volcanoes,

also called 'strato volcanoes'. They waters in the depth are heated from contact
are cone-shaped volcanoes composed with hot magma giving rise to springs and
of layers of lava, ash and rock debris. geysers. The Puga valley in Ladakh region
Mount Vesuvius and Mount St. Helens and Manikaran (Himachal Pradesh) are
are examples of composite volcanoes. promising spots in India for the generation
of geothermal electricity.
c) Cinder Cone Volcano : It forms when
magma is thrown out to the surface, 3.10.4 Distribution of Volcanoes across
cooled in to ash and cinders and settled the World
around the mouth of volcano. It is less Most known volcanic activity and the
dangerous than other volcanoes. earthquakes occur along converging plate
d) Lava Dome: Unlike composite and margins and mid-oceanic ridges. The
shield volcanoes, lava domes are of major regions of volcanic distributions are
significantly smaller structure. They as follows.
are formed when the lava is too viscous
1. Pacific Ring of Fire
to flow to a great distance. As the lava
Circum-Pacific region, popularly termed
dome slowly grows, the outer surface
the ‘Pacific Ring of Fire’, has the greatest
cools and hardens as the lava continues
concentration of active volcanoes.
to pile within. Eventually, the internal
Volcanic belt and earthquake belt closely
pressure can shatter the outer surface,
overlap along the ‘Pacific Ring of Fire’. It
causing loose fragments to spill down
is estimated to include two-thirds of the
its sides.
world’s volcanoes.

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2. Mid Atlantic Region 3.11.1 Rock Types

The Mid Atlantic Region coasts has Based on their origin, the rocks are
comparatively fewer active volcanoes classified as follows:
but many dormant or extinct volcanoes, There are three types of rocks
example. St. Helena, Cape Verde Islands 1. Igneous Rocks
and the Canary Islands. But the volcanoes 2. Sedimentary Rocks
of Iceland and the Azores are active. 3. Metamorphic Rocks
3. The Great Rift valley of Africa
I. Igneous Rocks
In Africa some volcanoes are found along
Igneous rocks are formed out of magma and
the East African Rift Valley. Kilimanjaro
lava and they are known as primary rocks. If the
and Mt. Kenya are extinct volcanoes. The
magma cools slowly at great depths, mineral
only active volcano in West Africa is Mt.
grains increase in their size. Sudden cooling (at
Cameroon.
the surface) results in small and smooth grains.
4. Mediterranean Region The igneous rocks are the oldest of all the rocks.
Volcanoes of the Mediterranean region Granite, pegmatite, basalt, etc are some of the
are mainly associated with the Alpine examples of igneous rocks. There are two types
folds. Example, Mt. Vesuvius and of igneous rocks: intrusive rocks (Granite) and
Mt. Stromboli (known as the Light House extrusive rocks (Basalt-Deccan Traps).
of the Mediterranean Sea).
Granite is less dense and is lighter in
5. Other Regions colour than basalt rocks.
Elsewhere in the interiors of continents
of Asia, North America and Europe active 3.11.2 Intrusive Igneous rocks
volcanoes are rare. There are no volcanoes Intrusive Igneous rocks are formed when
in Australia. magma rises and cools within the crust.
The intrusive activity of volcanoes gives
Volcanoes in India rise to various forms. We see them one by
There are no volcanoes in the Himalayan one as follow.
region of India. However, Barren Island,
1. Batholiths
lying 135 km north-east of Port Blair
Batholiths are large rock masses formed due
became active in 1991 and 1995.
to cooling and solidification of hot magma
However, the other volcanic island in inside the earth. It is granitic in origin.
Indian Territory is Narcondam (Andaman
2. Laccoliths
and Nicobar Islands) It is probably extinct.
Laccoliths are large dome-shaped intrusive
Its crater wall has been completely destroyed.
rock connected by a pipe-like conduit
3.11 Rocks from below. These are basically intrusive
Rock is the solid mineral material forming counterparts of an exposed domelike
the surface of the earth. Petrology is batholiths. The Karnataka plateau is
the science of rocks. The age of the rock is spotted with dome hills of granite rocks.
determined based on Carbon-14 dating. Most of these, now exfoliated, are examples
of laccoliths.

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3. Lapoliths II. Sedimentary Rocks

When the magma moves upwards, a Sedimentary rocks are also called as
saucer shape, concave shaped body called detrital rocks. They are formed as a result
Lapolith is formed. of denudation. These deposits through
4. Sill compaction turn into sedimentary rocks.
Sill is a solidified sheet-like horizontal They occupy only 5 percent of the earth.
lava layer inside the earth. The near They are layered or stratified of varying
horizontal bodies of the intrusive igneous thickness. Example: sandstone, shale etc. Ice
rocks are called sill or sheet, depending on deposited sedimentary rocks is called Till.
the thickness of the material. The thinner Wind-deposited sediments are called Loess.
ones are called sheets while the thick Depending upon the mode of formation,
horizontal deposits are called sills. sedimentary rocks are classified into
1. Mechanically formed sedimentary
5. Dyke rocks: sandstone, conglomerate,
When the magma makes its way through limestone, shale, loess, etc.
cracks and the fissures developed in the 2. Organically formed sedimentary rocks:
land, it solidifies almost perpendicular geyserites, chalk, limestone, coal etc.
to the ground. It gets cooled in the same
3. Chemically formed: halite, potash, etc.
position to develop a wall-like structure.
Such structures are called dikes. III. Metamorphic Rocks
These are the most commonly found The word metamorphic means ‘change
intrusive forms in the western Maharashtra of form’. The metamorphic rocks form
area. These are considered the feeders for under the action of pressure, volume and
the eruptions that led to the development temperature (PVT) change.
of the Deccan traps.

Volcano Lava flows &

Pyroclastic deposits

Volcanic neck
Dyke Sill Laccolith
Sill
Lapolith

Stock
Dyke

Dyke

Batholith

Figure 3.26 Intrusive Volcanic structure

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Students’ activity
Place the appropriate number given in the diagram in the bracket
Lacolith (  )

Batholith (  )
5

Dyke (  ) 1 6

Sill (  )
4

Chamber (  ) 3

Lapolith (  )
2

Figure 3.27 Intrusive Volcanic Structures

Table 3.2 Metamorphosis processes

Igneous/ Sedimentary rock Influence Metamorphosed rock
Granite Pressure Gneiss
Clay, Shale Pressure Schist
Sandstone Heat Quartzite
Clay, Shale Heat Slate or Phyllite
Coal Heat Anthracite or Graphite
Coal Heat and Pressure Diamond
Limestone Heat Marble

Metamorphism is a process by which or metamorphic rocks. The fragments derived

the already consolidated rocks undergo out of igneous and metamorphic rocks form
recrystallisation and reorganization of into sedimentary rocks.
materials within original rocks. Gneiss, Igneous and sedimentary rocks can
slate, schist, diamond, marble, quartzite change into metamorphic rocks. The
etc. are some examples of metamorphic crustal rocks (igneous, sedimentary and
rocks. The igneous and metamorphic rocks metamorphic) may be carried down into
together account for 95 percent of the earth. the mantle (interior of the earth) through
subduction process and the same melt and
3.12 Rock Cycle turn into magma, the original source for
Rock cycle is a continuous process through igneous rocks. In this way the rock cycle
which old rocks are transformed into new ones. is a continuous process.
Igneous rocks can be changed into sedimentary

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Magma
melting
crystallization

melting Metamorphic Rock

Igneous Rock

heat & pressure

heat & pressure

weathering, erosion &
weathering, erosion &
deposition
deposition

Sedimentary Rock
Sediment

compaction & cementation

Figure 3.28 The Rock Cycle

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Evaluation
I. Multiple choice
1. Orogeny: structural deformation of questions
lithosphere due to interaction between
tectonic plates. 1. The term “Lithosphere”
2. Conorod boundary: Margin between was introduced by
the upper crust and the lower crust. a. Alfred Wegener
3. Shearing fault: the fault is created by b. Joseph Barrel
shearing along the plate boundary.
c. Alexander Von Humbolt
4. Laccoliths: are large dome-shaped
intrusive rock connected by a pipe. d. Kiyoo Wadati
5. Lapolith: When the magma moves 2. The boundary between the upper crust
upwards, a saucer shape, concave and lower crust is termed as
shaped body called lapolith. a. Guttenberg margin
6. Syncline: down slope of a fold
b. Lehmann Boundary
7. Crest: the top of the fold.
c. Conorod boundary
8. Catasrophism: sudden movements of
the earth caused by plate movements. d. Mohorovicic boundary
9. Metamorphism: the process by which 3. Who postulated the continental drift
both igneous and sedimentary rocks theory?
get changed into metamorphic rocks.
a. Kober b. Holmes
10. Rock cycle: a continuous process
through which old rocks are c. Taylor d. Wegener
transformed into new ones.

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4. Odd one out 10. Solidified sheet-like horizontal lava

a. The Eurasian plate layer inside the earth is called as
b. The North American plate a. Dyke
c. The Pacific plate b. Batholith
d. The African plate c. Sill
5. One among the given is the deepest d. Lacolith
trench in the world.
a. The Mariana Trench II. Brief answer
b. The Sandwich Trench 11. Define Diastrophism.
c. The Puerto Rico Trench 12. Why is the inner core solid?
d. The Sunda Trench
13. Distinguish between Mohorovicic
6. It is a type of fold where one limb is boundary and Lehman boundary.
steeper than the other. 14. Write the significance of the Ring of
a. Symmetrical fold Fire.
b. Asymmetrical fold 15. List the types of volcano based on their
c. Over turned fold frequency of eruption .
d. Recumbent fold
7. The longest rift valley in the world is III. Short answer
a. The Narmada rift valley 16. Write a short note on the Convection
b. The African rift valley cell.
c. The Baikal rift valley 17. Name the types of plate boundary.
d. The Rhine rift valley 18. Why do plates keep moving?
8. One of the following zones accounts 19. Name the types of fold.
for 68% of the earthquakes on the 20. Draw a volcano and label its parts.
surface of the earth.
a. The Mediterranean – Himalayan zone IV. Detailed answer
b. The Circum Pacific zone
21. Describe the Interior of the Earth with
c. The Mid Atlantic zone a diagram.
d. The African rift valley zone 22. Explain continental drift theory.
9. One among the given is the world’s 23. Explain the types of plate boundaries.
highest active volcano.
24. Draw a diagram and describe the stages
a. Mt. Vesuvius of the rock cycle.
b. Mt. Stromboli 25. On the outline map of the world, mark
c. Mt. Cotopaxi the distribution of volcanoes and
d. Mt. Krakatau describe briefly about them.

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V. Practice 3. Fundamentals of Geomorphology

1. Prepare in the cardboard sheet Richard John Huggett
jigsaw puzzle of fitting plates in their
Web Reference
respective boundaries.
2. Prepare a working model of the active 1. h t t p s : / / 3 . b p . b l o g s p o t . c o m /
volcano and demonstrate in the class. O 1 f RT h Z c WC g / V 7 n m Ump O i d I /
AAAAAAAAAmY/xyFJKGV04
3. Make a model of types of Fold and
ysOG275yupB5JhGnbDU0l_JwCLcB/
Fault using available resources, label
s1600/Dis.png
them, and present to the class.
2. h t t p s : / / w w w . y o u t u b e . c o m /
watch?v=_5q8hzF9VVE
Reference
3. h t t p s : / / v o l c a n o e s . u s g s . g o v / . . . /
1. Physical geography: fundamentals of This_D ynamic_Planet-Teaching_
the physical environment V. Ettwein Companion_Packet.pd
and M. Maslin
4. h t t p s : / / w w w . y o u t u b e . c o m /
2. Introducing Physical Geography, John watch?v=PDrMH7RwupQ
Wiley & Sons.

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ICT CORNER
Lithosphere Morphing Boundaries

Through this activity you will

identify the land masses formed
by Endogenic processes.

Steps
• Use the URL to land on ‘Google Earth’ or scan the QR code from your smartphone.
• Open “Google Earth” app and type “Everest” in the search box to explore the
folded mountain structure created by tectonic collision.
• Type volcano name in search box and explore the landscape formed by its eruption.
• Roll over the globe using your mouse and zoom in and zoom out to explore the
land mass and its tectonic plate extensions.

Step 1 Step 2

Step 3 Step 4

Google Earth’s URL:

https://earth.google.com/web/

*Pictures are indicative only.

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