Geomorphic Hazards

Introduction

Geomorphic hazards are natural disasters directly linked to the Earth's dynamic
physical processes, altering its surface over time. These hazards, often
catastrophic, have significant implications for both the environment and human
societies. Key geomorphic hazards discussed below are: Earthquakes,
Tsunamis, Landslides, and Avalanches.

1. Earthquakes

An earthquake is a sudden shaking of the Earth's surface, caused by the

release of energy from the Earth's lithosphere. This energy, stored due to stress
and strain in the Earth’s crust, is released when rocks break or slip along a fault
line. Earthquakes can have devastating impacts on infrastructure, the economy,
and human lives, particularly in densely populated areas.

Causes of Earthquakes

● Tectonic Plate Movements:

○ Convergent Boundaries: When two tectonic plates collide, the

denser plate is forced beneath the other, leading to the formation of
subduction zones. Earthquakes are frequent here due to the
immense pressures involved, such as in the Pacific Ring of Fire.
○ Divergent Boundaries: Plates move apart at mid-ocean ridges,
creating new crust. The friction between moving plates causes
moderate earthquakes. Examples include the Mid-Atlantic Ridge.
○ Transform Faults: Plates slide past each other. The San Andreas
Fault in California is a classic example, where the North American
Plate moves past the Pacific Plate, causing frequent earthquakes.
 ● Human-induced Earthquakes:

○ Reservoir-induced Seismicity: Large reservoirs behind dams alter

the Earth's stress and strain, occasionally triggering earthquakes, as
seen in Koyna, India.
○ Mining and Drilling Activities: Human activities can cause small to
moderate tremors by disturbing the natural equilibrium of rock
layers.

Focus and epicenter

● The point where the energy is released is called the focus or the
hypocentre of an earthquake.
● The point on the surface directly above the focus is called epicenter (first
surface point to experience the earthquake waves).
● A line connecting all points on the surface where the intensity is the same
is called an isoseismal line

Earthquake Magnitude and Intensity

 ● Magnitude: Measured on the Richter Scale, the magnitude quantifies the
energy released at the epicenter. Each increase by one unit represents a
32-fold increase in energy release.
● Intensity: Assessed using the Mercalli Intensity Scale, this measure
reflects the earthquake's effects on people, buildings, and the Earth's
surface.

Seismic Waves and Types

● Primary Waves (P-waves): These are the fastest waves, traveling

through both solid and liquid layers of the Earth. They cause ground
particles to move in the same direction as the wave.
● Secondary Waves (S-waves): Slower than P-waves, they can only move
through solids and cause particles to move perpendicular to the direction
of the wave.
● Surface Waves: These waves cause the most damage as they move
along the Earth's surface, resulting in rolling and swaying ground motion.

Global Distribution of Earthquakes

● Pacific Ring of Fire: Encompasses several tectonic plate boundaries

around the Pacific Ocean, leading to frequent seismic and volcanic activity.
● Alpine-Himalayan Belt: Stretches from the Mediterranean to Southeast
Asia, including areas like the Himalayas and Alps, where tectonic plates
collide.
Earthquake Hazards

● Ground Shaking: Causes building collapse, road destruction, and loss of

life. The degree of shaking depends on the distance from the epicenter,
magnitude, and local geology.
● Surface Rupture: Fault lines can break the Earth’s surface, damaging
infrastructure like bridges and pipelines.
● Liquefaction: During intense shaking, water-saturated soils lose strength
and behave like liquids, undermining the foundations of buildings and
roads.
● Tsunamis: Underwater earthquakes can generate massive ocean waves
that flood coastal areas.

Earthquake Risk Reduction

 ● Earthquake-resistant Infrastructure: Reinforced concrete and
steel-frame buildings can withstand seismic forces better than traditional
structures.
● Seismic Hazard Mapping: Identifying and zoning high-risk areas for
planning and preparedness.
● Public Awareness and Preparedness: Conducting drills, educating
communities on evacuation routes, and creating early warning systems.

2. Volcanic Hazards – Nature, Causes, and Impact

Volcanoes are fascinating yet dangerous natural features formed by the

movement of molten rock (magma) from within the Earth to the surface. When
magma reaches the Earth’s surface, it is called lava, which flows down the
volcano's slope, often accompanied by gases, ash, and rock fragments.

Nature and Causes of Volcanic Eruptions

1. Magma and Lava

● Magma: A complex mixture of

molten rock, gases, and often
crystallized minerals that exist
beneath the Earth’s crust. It remains
under high temperature and
pressure.
● Lava: Once magma reaches the
surface and loses its dissolved gases,
it is referred to as lava. Lava flows from volcanic vents and can vary in
temperature and composition.

2. Causes of Volcanic Eruptions

Volcanoes erupt due to the following primary causes:

 1. Buoyancy of Magma: Magma is less dense than the surrounding solid
rocks, causing it to rise toward the surface.
2. Pressure Release: As magma moves upward, the pressure decreases, and
gases dissolved within the magma form bubbles. These bubbles expand,
propelling the magma further upward, eventually leading to an eruption
when it reaches the Earth’s crust.

3. Types of Eruptions

Volcanoes can erupt in two primary modes:

1. Explosive Eruptions: In this type, magma has high gas content and is
thick and viscous. The sudden release of pressure leads to violent
explosions that eject magma as hot fragments and gases into the
atmosphere.
2. Effusive Eruptions: Here, the gas content is lower, and the magma is less
viscous, allowing lava to flow smoothly out of the vent without violent
explosions.

Types of Volcanoes Based on Eruptions

1. Plinian Eruptions:
○ Most violent,
characterized by
powerful upward
explosions of
gases and
magma.
○ Example: Mount
Pinatubo in the
Philippines
(1991) sent volcanic ash more than 30 km into the atmosphere.
2. Pelean Eruptions:
 ○ When magma is obstructed by a dome of solid lava, the pressure
builds until it finds a weak point, resulting in a lateral blast.
○ Example: Mount St. Helens, USA (1980).
3. Hawaiian Eruptions:
○ Occurs in regions under crustal tension, where deep fissures allow
magma to flow freely, producing extensive lava sheets.
○ Example: Kilauea, Hawaii (1960).
4. Vulcanian Eruptions:
○ Named after Vulcano Island, Italy, where more viscous lava forms a
crust between eruptions. These eruptions produce dense volcanic
clouds.
5. Strombolian Eruptions:
○ Named after Stromboli, Italy, known for moderate, continuous gas
explosions ejecting clotted lava bombs.

Impact and Hazards Associated with Volcanoes

Volcanic eruptions pose both primary and secondary hazards. These hazards
can cause widespread destruction and loss of life, and their intensity varies
depending on the type of eruption and proximity to populated areas.

1. Primary or Direct Hazards

1. Lava Flows:
○ Slow-moving molten rock that can destroy everything in its path.
○ While not usually life-threatening due to their slow speed, lava
flows can bury homes, roads, and farmlands.
2. Pyroclastic Flows:
○ Fast-moving avalanches of hot ash, rock fragments, and gases that
can incinerate everything in their path.
○ These flows are one of the deadliest volcanic hazards due to their
speed and temperature.
3. Air-Fall Tephra:
 ○ Rock fragments, including ash, ejected into the air during an
eruption.
○ Ashfall can damage crops, collapse buildings, and disrupt air travel.
4. Volcanic Gases:
○ Volcanic gases, including water vapor, carbon dioxide (CO₂), sulfur
dioxide (SO₂), and hydrogen sulfide (H₂S), are released during
eruptions.
○ These gases can be toxic, cause respiratory issues, and contribute to
acid rain.

2. Secondary or Indirect Hazards

1. Lahars (Volcanic Mudflows):

○ Mixtures of water, rock, and mud that rush down valleys, often after
snow or ice is melted by volcanic heat.
○ Lahars can travel long distances, uprooting trees and buildings and
posing significant risks to human settlements.
2. Landslides:
○ Volcanic landslides are rapid downhill movements of rock, ice, and
snow.
○ Triggered by eruptions, earthquakes, or even heavy rainfall, these
landslides can devastate communities living on or near volcanoes.
3. Tsunamis:
○ Volcanic eruptions beneath the ocean or along coastlines can trigger
tsunamis, which are powerful ocean waves that flood coastal areas.
○ While rare, tsunamis generated by volcanic eruptions can be
catastrophic, as seen in the Krakatoa eruption of 1883.

Regional Distribution of Volcanoes

Volcanic activity is found on every continent except Australia. However, it is

concentrated in areas where tectonic plates converge, diverge, or where there
are hotspots in the Earth’s crust.
1. Tectonic Settings for Volcanic Activity

1. Subduction Zones:
○ Where one tectonic plate is thrust beneath another, leading to
explosive volcanoes.
○ Example: Mount Fuji (Japan), Mount Vesuvius (Italy).
2. Rift Zones:
○ Volcanoes form where tectonic plates are diverging, such as along
mid-ocean ridges.
○ Example: Iceland, where rift volcanoes dominate.
3. Hotspot Volcanoes:
○ Formed where plumes of hot magma rise from deep within the
mantle, far from tectonic plate boundaries.
○ Example: Hawaiian Islands.

3. Tsunamis

A tsunami is a series of ocean waves caused by the sudden displacement of

water, usually due to underwater earthquakes, volcanic eruptions, or landslides.
These waves can travel across entire ocean basins, reaching coasts thousands
of kilometers away from the point of origin.

Causes of Tsunamis

● Underwater Earthquakes: The majority of tsunamis are triggered by

seismic activity, particularly in subduction zones, where tectonic plates
collide and one is forced under the other. The sudden vertical movement
of the ocean floor displaces vast quantities of water, leading to waves
that can reach heights of over 30 meters.
● Volcanic Eruptions: Explosive eruptions, especially those causing the
collapse of a volcano's caldera, can displace enough water to generate
tsunamis.
● Landslides: Both underwater and coastal landslides can displace large
volumes of water, generating tsunamis. An example is the 1929 Grand
Banks tsunami in Newfoundland, caused by a submarine landslide.

Mechanism of a Tsunami

1. Initiation: The sudden vertical displacement of the ocean floor, usually

due to an earthquake, triggers a tsunami.
2. Wave Propagation: Tsunami waves travel at high speeds in deep waters
(up to 800 km/h) but are usually low in height (1-2 meters).
3. Wave Shoaling: As the tsunami approaches shallow coastal areas, its
speed decreases, but the wave height increases dramatically due to
energy conservation.
4. Inundation: The waves crash onto shorelines, causing widespread
flooding and destruction.

Tsunami Hazards

● Inundation and Flooding: Low-lying coastal areas can be inundated by

waves, displacing populations and destroying infrastructure.
 ● Loss of Life: Tsunamis are notorious for their high death tolls, as they
strike with little warning and immense force. The 2004 Indian Ocean
Tsunami killed over 230,000 people across 14 countries.
● Environmental Destruction: Tsunamis can strip vegetation, erode
coastlines, and contaminate freshwater sources.

Tsunami Risk Reduction

● Tsunami Early Warning Systems: Technologies such as the DART

(Deep-ocean Assessment and Reporting of Tsunamis) system detect
seismic activity and relay data to monitoring centers, allowing for timely
warnings.
● Coastal Evacuation Plans: Governments must establish clear evacuation
routes and shelters for communities living in tsunami-prone areas.
● Tsunami-Resilient Construction: Buildings in tsunami-prone regions
should be elevated or designed to allow water to flow through without
causing structural collapse.

4. Landslides

A landslide refers to the movement of rock, soil, and debris down a slope under
the influence of gravity. Landslides are common in mountainous or hilly regions
and can be triggered by factors such as heavy rainfall, earthquakes, volcanic
eruptions, and human activities.

Types of Landslides

● Slides:
○ Rotational Slides: The movement occurs along a curved surface,
often creating a stepped profile.
○ Translational Slides: Movement occurs along a planar surface, often
involving large blocks of material.
 ● Falls: Sudden vertical movement of rock or debris, often occurring on
steep cliffs. Falls are typically triggered by freeze-thaw cycles or
earthquakes.
● Flows:
○ Debris Flows: Rapid movements of loose soil, rocks, and organic
material, often triggered by intense rainfall.
○ Mudflows: Similar to debris flows, but with a higher water content,
causing faster and more fluid movement.
○ Creep: The slow, gradual movement of soil downhill due to
seasonal changes or freeze-thaw cycles.

Causes of Landslides

● Natural Factors:
○ Rainfall: Heavy rainfall saturates the soil, reducing its stability and
causing it to slide downhill.
○ Earthquakes: Seismic activity can weaken slopes and trigger
landslides, particularly in mountainous regions.
 ○ Volcanic Activity: Volcanic eruptions, especially in combination with
rain, can cause lahars (volcanic mudflows) and landslides.

● Human Factors:
○ Deforestation: The removal of vegetation destabilizes slopes,
increasing the likelihood of landslides.
○ Construction: Road building, mining, and improper land use can
weaken slopes and trigger landslides.

Landslide Hazards

● Loss of Life: Large landslides can bury entire communities, as seen in the
Malpa landslide of 1998, which killed over 300 people.
● Infrastructure Damage: Roads, bridges, and buildings in landslide-prone
areas are frequently destroyed, leading to high economic costs for
reconstruction.
● Environmental Degradation: Landslides can strip away vegetation,
destroy habitats, and alter river courses, leading to long-term ecological
damage. In fragile ecosystems, this can cause loss of biodiversity and
disrupt water cycles.
● Economic Loss: Landslides can lead to massive economic losses due to
damage to infrastructure like roads, bridges, homes, and utilities. The cost
of repairs, along with loss of agricultural land and livelihoods, can be
overwhelming, especially in mountainous and rural regions.

Risk Reduction and Mitigation for Landslides

● Hazard Zonation Mapping: Identifying areas prone to landslides through

geographic and geological surveys helps in land-use planning and risk
reduction.
● Afforestation and Vegetation: Planting trees and maintaining vegetation
cover on slopes increases soil stability and reduces the risk of landslides.
 ● Retaining Walls and Drainage Systems: Engineering solutions such as
constructing retaining walls and improving drainage systems can help in
preventing water buildup and landslide occurrences.
● Relocation of Vulnerable Communities: In areas with a high risk of
landslides, especially in densely populated or developing regions,
relocation of settlements can be a life-saving measure.
● Community Education: Awareness programs and disaster preparedness
can help communities recognize early warning signs and take necessary
actions to minimize casualties.

5. Avalanches

An avalanche refers to the rapid flow of

snow down a slope, often triggered by a
disturbance in the snowpack. Avalanches
are common in mountainous regions,
especially during the winter months, and
they can vary in size from small slides to
large, devastating events that sweep
entire mountainsides.

Types of Avalanches

● Surface Avalanches: These occur when the top layer of snow slides over
a more stable layer underneath. This is often triggered by weather
changes or minor disturbances.
● Full-Depth Avalanches: These involve the movement of the entire
snowpack down to the ground, causing more extensive damage.
● Slab Avalanches: A large slab of cohesive snow breaks away and slides
as a single block. These are among the most dangerous types of
avalanches, as they can involve large volumes of snow.
 ● Loose Snow Avalanches: Occur when snow particles lose cohesion and
slide individually, starting small and accumulating more snow as they
descend.
● Wet Avalanches: Caused by melting snow and water seepage, reducing
the snowpack’s stability. These are slower-moving but can carry large
amounts of debris.
● Cornice Avalanches: Formed by the collapse of overhanging snow, often
triggered by wind or gravitational forces.

Causes of Avalanches

● Terrain: Avalanches occur more frequently on slopes with angles

between 25-45 degrees. The profile and surface roughness of the slope,
whether smooth or rugged, play a role in determining the snow’s stability.
● Weather and Snowfall: Heavy snowfall, wind direction, and sudden
temperature changes are major triggers. Rapid accumulation of snow can
create unstable layers, which are prone to sliding.
● Earthquakes and Vibrations: In tectonically active areas like the
Himalayas, seismic activity can trigger avalanches by disturbing
snowpacks. Human activities like skiing, snowmobiling, or construction
work can also cause vibrations that lead to avalanches.
● Human Activity: Activities such as skiing, hiking, or military movement in
avalanche-prone areas significantly contribute to triggering avalanches.

Avalanche Hazards

● Loss of Life: Avalanches are lethal, often burying victims under meters of
snow. Those caught in an avalanche are at risk of asphyxiation, trauma
from impact, or hypothermia. The Siachen Glacier Avalanche in 2016,
which buried 10 Indian soldiers, highlights the deadly nature of these
hazards.
 ● Damage to Infrastructure: Avalanches destroy buildings, roads, and
utilities, particularly in mountainous communities that depend on these
infrastructures for connectivity and survival.
● Economic Impact: Mountain resorts, tourism, and local economies often
suffer significant losses due to avalanches. The disruption to daily life, as
well as the cost of rescue and recovery, can be immense.

Risk Reduction and Mitigation for Avalanches

● Forecasting and Early Warnings: Predicting avalanches is crucial,

particularly in areas where tourists or residents are at risk. The Snow
Avalanche Study Establishment (SASE) in India plays a key role in
monitoring snow conditions and issuing warnings. Advanced systems like
satellite imaging, ground-based radar, and Digital Terrain Models
(DTMs) are used for accurate forecasting.
● Structural Measures: Protective structures such as snow nets, fences,
and avalanche dams are used to prevent or control avalanches. These
barriers help break the snow’s momentum, reducing the force of the
avalanche as it descends.
● Afforestation and Reforestation: Planting trees along vulnerable slopes
helps stabilize the snow and soil, preventing large-scale snow
movements.
● Controlled Avalanches: In some regions, small avalanches are
deliberately triggered under controlled conditions to prevent the buildup
of snow that could lead to a larger and more destructive event.
● Public Education and Safety Training: Educating communities and
tourists about avalanche risks, safe zones, and emergency protocols is
essential for reducing casualties. Rescue teams are also trained in rapid
response and the use of avalanche beacons for locating victims.