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Class 9 Social Science Chapter 2

Shaping of the Earth’s Surface

Understanding Society: India and Beyond | Grade 9 – Part 1

Chapter Summary

The Earth’s surface is constantly changing because of forces working inside and outside the Earth. The theory of plate tectonics explains how large pieces of the Earth’s lithosphere move slowly over the semi-molten asthenosphere.

Movement of tectonic plates produces mountains, volcanoes, earthquakes, valleys and ocean basins. The three main types of plate boundaries are convergent, divergent and transform boundaries.

External processes such as weathering, erosion and deposition also shape the Earth’s surface. Running water, waves, glaciers, wind and underground water create different landforms.

Landforms influence human settlements, agriculture, transport, trade, tourism and other activities. At the same time, some landforms are associated with hazards such as landslides, avalanches, GLOFs and dust storms.

Understanding these processes helps us understand the changing Earth, reduce disaster risks and develop a safer relationship with our environment.

The Big Questions

What shapes the Earth’s surface?
What is plate tectonics? What are the effects of plate movement?
How are landforms formed and how are they classified?
How are humans and other living beings connected to these landforms?
How do disasters associated with different landforms impact human lives?

1. Plate Tectonics

Plate tectonics is a theory that explains the movement of the Earth’s crust. The outer part of the Earth is divided into large and small pieces called tectonic plates.

These plates move slowly over the semi-molten layer beneath them. Their movement causes major physical features and natural events.

Plate Tectonics: The theory that Earth’s lithosphere is divided into moving plates whose movements shape the Earth’s surface.

Major Effects of Plate Movement

Mountains
Formed mainly when plates collide.

Earthquakes
Common near moving plate boundaries.

Volcanoes
May form where plates collide or separate.

Ocean Basins
Can develop through plate movement.

2. Interior of the Earth

Layer	Easy Explanation
Crust	Outermost layer on which we live.
Mantle	Very thick and hot layer below the crust.
Core	Innermost and extremely hot part of the Earth.
Lithosphere	Rigid outer layer made of the crust and upper mantle.
Asthenosphere	Hot, mobile and partially molten layer below the lithosphere.
Outer Core	Fluid layer mainly made of iron and nickel.
Inner Core	Solid, hot and very dense metallic part.

Key Point: The lithosphere is broken into tectonic plates. The asthenosphere allows these plates to move.

3. Types of Tectonic Plates

Continental plates: Carry continents.
Oceanic plates: Carry ocean floors.
Mixed plates: Carry both continents and oceans.

Major Plates Mentioned in the Chapter

Pacific Plate, Eurasian Plate, African Plate, North American Plate, South American Plate, Indo-Australian Plate and Antarctic Plate.

4. Why Do Tectonic Plates Move?

Heat from the Earth’s core heats material in the mantle. Hot material rises and cooler material sinks. This continuous movement produces convection currents.

Convection Currents: Continuous movement in the mantle in which hot material rises and cooler material sinks.

These currents push and pull tectonic plates, causing them to move in different directions.

5. Types of Plate Boundaries

Boundary	Plate Movement	Main Effects	Example
Convergent	Plates move towards each other.	Mountains, earthquakes and volcanic activity.	Himalaya
Divergent	Plates move away from each other.	New crust and mid-ocean ridges.	Mid-Atlantic Ridge
Transform	Plates slide past each other.	Mainly earthquakes.	San Andreas Fault

LET’S MAP

Pick any two plates from the map above and complete the table given below.

Name of the plate	Continents	Ocean
Pacific Plate	Mostly oceanic; touches several continental margins.	Pacific Ocean
Eurasian Plate	Europe and most of Asia	Parts of Atlantic, Arctic and other surrounding oceans

6. Earthquakes, Volcanoes and the Ring of Fire

Most earthquakes and volcanoes occur along plate boundaries. The area around the Pacific Ocean with a large concentration of earthquakes and volcanoes is called the Ring of Fire.

Remember: Plate boundaries are important zones for earthquakes and volcanic activity.

LET’S EXPLORE

Examine the plate map (Fig. 2.3) with the earthquake and volcano map (Fig. 2.4). What correlation do you observe?

Answer: Earthquakes and volcanoes are concentrated mainly near tectonic plate boundaries. This shows a strong relationship between plate movement and these natural phenomena.

LET’S EXPLORE

Observe the map showing the distribution of earthquakes and volcanoes (Fig. 2.4). Can you identify which continents and countries are located around the Ring of Fire with the help of an atlas or a globe?

Answer: The Ring of Fire mainly surrounds the Pacific Ocean. It includes parts of North America, South America, Asia and Oceania. Countries such as Japan, Indonesia, the Philippines, New Zealand, Chile and parts of the western Americas lie in or near this zone.

LET’S EXPLORE

Does India have a risk of earthquakes?

Answer: Yes. India has experienced several major earthquakes. Himalayan regions and some other parts of India are particularly vulnerable because of active tectonic movements.

Can you find out which region is more vulnerable to earthquakes? Why do you think human lives are at risk?

Answer: The Himalayan region is highly vulnerable because of active plate movements. Human lives are at risk because earthquakes can damage buildings, roads, bridges and other infrastructure, especially in densely populated areas.

Indian Knowledge and Earthquakes

In early times, earthquakes were known as ‘bhūkampa’, meaning the shaking of the Earth.

In the Bṛihatsaṁhitā, Varāhamihira discussed earthquakes and connected observations of wind, rain, clouds, animal behaviour and planetary alignments with them.

He associated earthquakes with four elemental forces: Vāyu, Agni, Indra and Varuṇa.

The passage shows an early attempt to understand earthquakes through observation and cosmological reasoning.

LET’S EXPLORE

Look carefully at this photograph and answer the following questions:

What do you think caused this situation?
What could that grey powder be?
What does it tell us about the Earth’s internal forces?

Answer:

The situation was likely caused by a volcanic eruption.
The grey powder could be volcanic ash and fine volcanic material.
It shows that powerful internal forces can bring hot material from inside the Earth to its surface.

India’s Mud Volcano

The mud volcano at Baratang Island in the Andaman and Nicobar Islands is a rare natural feature.

Unlike fiery volcanoes, mud volcanoes release mud because of underground gases and pressure.

7. Weathering

Weathering: The breaking down of rocks into smaller pieces at or near the Earth’s surface without movement of the broken material.

Type	Cause
Physical weathering	Temperature changes, frost, wind, water and ice expansion.
Chemical weathering	Reactions involving water, air or acids change minerals.
Biological weathering	Plants, animals and microorganisms break rocks.

Weathering helps shape the Earth’s surface and contributes to soil formation.

8. Erosion

Erosion: The wearing away and movement of soil, rocks and other surface materials from one place to another by natural agents.

Type	Main Agent
Water erosion	Rivers, rain and ocean waves
Wind erosion	Strong winds
Glacial erosion	Moving ice
Coastal erosion	Sea waves

Weathering vs Erosion: Weathering breaks rocks down. Erosion also involves movement of the broken material.

Effects of Erosion on Human Life

Farmers may lose fertile topsoil.
Crop production may decrease.
Rivers and coastal areas may lose land.
Houses and roads may be damaged.
Construction and mining areas may become unstable.
Fishing and tourism can also be affected.

LET’S EXPLORE

Observe the photographs (Fig. 2.9) and also note the types of erosion. How are farmers affected by erosion due to water and wind?

Answer: Water and wind erosion remove fertile topsoil. This reduces soil fertility and can lower crop yields. Severe erosion may also damage agricultural land.

Soil and Water Conservation

Method	Easy Meaning
Contouring	Digging trenches along contour lines to slow rainwater and reduce erosion.
Bunding	Building earthen embankments to slow surface runoff and increase infiltration.
Terracing	Creating step-like fields on hillsides to reduce soil erosion.
Check dams	Small barriers that slow water flow, reduce erosion and help groundwater recharge.

The chapter also mentions traditional water-management practices associated with the Sindhu-Sarasvatī civilisation and the Zabo system of Nagaland.

9. Agents of Gradation

Agents of gradation are natural forces that wear down, transport and deposit materials, gradually modifying the Earth’s surface.

Running Water
Forms valleys, plains and deltas.

Glaciers
Carve U-shaped valleys and transport debris.

Wind
Shapes deserts through erosion and deposition.

Waves
Shape cliffs, beaches, caves and arches.

Groundwater
Creates caves and sinkholes.

Landforms and Human Civilisations

Fertile river plains supported agriculture and early cities.
Mountains acted as barriers and also provided routes through passes.
Deserts limited settlements but encouraged trade routes.
Coasts and harbours supported trade and cultural contact.

Thus, landforms have influenced settlement, agriculture, trade, wars, travel and cultural development.

10. Running Water

Rivers shape land through erosion, transportation and deposition.

River Course	Important Landforms
Upper course	V-shaped valleys, waterfalls and rapids
Middle course	Meanders, oxbow lakes and floodplains
Lower course	Deltas, levees and alluvial fans

Waterfall

A waterfall is a place where a river flows over a steep cliff or vertical drop.

It commonly forms where hard rock resists erosion while softer rock below is worn away.

Waterfalls can support tourism, recreation and sometimes hydroelectric power generation.

Meander

A meander is a winding curve or bend in a river, commonly formed by lateral erosion and deposition.

The outer bank is generally eroded while sediments are deposited on the inner bank.

Meanders can support agriculture, settlements, irrigation, navigation and tourism.

Important Example: Grand Anicut, also called Kallanai, in Tamil Nadu shows the use of a river for irrigation.

Delta

A delta forms at the mouth of a river when the river deposits sediments as it enters a sea, ocean or lake.

Usually has fertile alluvial soil.
Supports agriculture.
Provides habitats for aquatic life.
May support fishing and settlements.
Can become a centre of trade and transport.
May also be vulnerable to floods.

LET’S EXPLORE

Have you heard about the Sundarbans delta? Try and explore its uniqueness and find out why it is popular with tourists.

Answer: The Sundarbans is a large delta region associated with the Ganga-Brahmaputra-Meghna river system. It is famous for its mangrove forests, rich biodiversity and distinctive landscape, which attract tourists.

11. Waves and Currents

Waves and currents constantly reshape coastal areas. They create landforms such as:

Beaches

Sand bars

Sea cliffs

Sea caves

Arches

Stacks

Beach

A beach is a landform made of sand, pebbles or rocks along a shoreline. It is mainly formed through deposition by waves.

Beaches support tourism, recreation and fishing and may also provide some protection to coastal settlements.

Coastal Erosion Landforms

Landform	How it Forms
Sea cliff	Waves erode and undercut the base of the coast.
Wave-cut platform	Flat surface left as a cliff retreats.
Sea cave	Waves erode weak parts of rocks.
Sea arch	Caves on opposite sides of a headland meet.
Sea stack	Rock pillar left after an arch collapses.

12. Glaciers

Glaciers slowly move over land and erode, transport and reshape the landscape.

Glacial Landform	Easy Explanation
U-shaped valley	Glacier widens and deepens an existing valley.
Cirque	Bowl-shaped depression at the head of a glacier.
Arete	Sharp ridge between glacial valleys.
Hanging valley	Smaller glacial valley meeting a larger one.
Fjord	Deep, narrow inlet formed when the sea floods a glacial valley.

Glaciers are important sources of fresh water and can support tourism, agriculture, fishing and other activities.

Moraines

Moraines are deposits of rocks, soil and debris called till, carried and left behind by glaciers.

Type	Location
Lateral moraine	Along the sides of a glacier.
Terminal moraine	At the end of a glacier, marking its furthest advance.
Medial moraine	In the middle where two glaciers meet and their lateral moraines join.

THINK ABOUT IT

A devastating flood struck the Chamoli district in Uttarakhand in February 2021 in which many people and livestock lost their lives. There was severe damage to buildings, roads, bridges, and hydel projects, and connectivity to villages was adversely affected. Can you find out the reasons that led to the sudden and unexpected flood?

Answer: The disaster was associated with a sudden release of water and debris in a steep Himalayan region. Factors discussed in relation to the event include a high-altitude slope failure, melting or movement of ice and rock, and the sudden flow of water and debris downstream. Such events can be extremely destructive in narrow mountain valleys.

13. Wind

Strong winds pick up and carry loose sand and soil, causing wind erosion.

Landform	Easy Explanation
Yardang	Streamlined rock ridge carved by wind.
Ventifact	Rock polished and shaped by wind-blown sand.
Deflation hollow	Depression formed when loose material is removed by wind.
Desert pavement	Surface left after finer particles are blown away.

Dunes

Dunes are hills or ridges of sand formed by wind in deserts or along sandy coasts.

Type	Feature
Barchan	Crescent-shaped dunes.
Longitudinal	Long ridges parallel to the prevailing wind.
Star	Have several arms where winds come from different directions.
Parabolic	U-shaped dunes often stabilised by vegetation.

14. Underground Water

Underground water can dissolve soluble rocks such as limestone. This creates Karst topography.

Caves
Hollow spaces formed by dissolution of rock.

Stalactites
Formations hanging from cave ceilings.

Stalagmites
Formations rising from cave floors.

Sinkholes
Depressions formed when the ground collapses.

Underground rivers
Rivers flowing through cave systems.

Memory Trick: Stalactites hang from the ceiling; stalagmites rise from the ground.

LET’S EXPLORE

Observe the landforms around your school or residence and try to identify which agent may have created them.

Suggested Approach: Observe slopes, valleys, river deposits, exposed rocks, soil, drainage channels and nearby water bodies. Decide whether water, wind, glaciers, waves or groundwater is the most likely agent.

15. Landforms and Disasters

Different landforms and natural processes are associated with different disasters. The chapter discusses four important disasters:

Landslides
Sudden movement of soil and rock down a slope.

Avalanches
Sudden movement of snow down a mountain slope.

GLOFs
Sudden release of water from a glacial lake.

Dust Storms
Strong winds carrying large amounts of dust and sand.

Landslides

Landslides occur when slopes become unstable and soil, rocks or debris suddenly move downward.

Main Causes

Heavy and continuous rainfall
Earthquakes
Volcanic activity
Steep slopes
Loose or weathered rocks
Deforestation
Mining
Road construction
Unplanned construction
Poor drainage

Book Activity

Prone areas:

Himalayan and other steep mountainous regions are commonly landslide-prone.

Mitigation measures:

Improve drainage, control deforestation, stabilise slopes, avoid unsafe construction and use vegetation to strengthen soil.

Recent examples:

Students can record a recent landslide reported in newspapers and note its causes and effects.

Avalanches

Avalanches occur when unstable snow suddenly moves down steep mountain slopes.

Causes

Heavy snowfall
Weak layers of snow
Sudden rise in temperature
Strong winds
Earthquakes and vibrations
Human activities such as skiing, trekking or construction

Prone areas:

High mountain regions with heavy snowfall, such as parts of the Himalayas, are vulnerable.

Mitigation measures:

Monitor snow conditions, restrict movement in dangerous periods, use warning systems and follow avalanche safety instructions.

Recent examples:

Students can record a recent avalanche reported in newspapers or other reliable sources.

Glacial Lake Outburst Floods (GLOFs)

A GLOF occurs when a large amount of water suddenly escapes from a glacial lake.

Main Causes

Rapid melting of glaciers
Rising temperatures
Heavy rainfall
Intense snowfall
Earthquakes
Avalanches or landslides
Collapse of natural ice or moraine dams

Prone areas:

High Himalayan areas containing glacial lakes are particularly vulnerable.

Mitigation measures:

Monitor glacial lakes, use early-warning systems, assess risky lakes and prepare downstream communities for evacuation.

Recent examples:

Students can record a recent GLOF event from reliable news sources.

Dust Storms

Dust storms occur when strong winds lift large amounts of loose, dry soil and sand into the air.

Main Causes

Prolonged drought
Low rainfall
Loose and dry soil
Sparse vegetation
Deforestation
Overgrazing
Poor farming practices
Extreme weather conditions

Prone areas:

Desert and semi-arid regions are more prone to dust storms.

Mitigation measures:

Increase vegetation, protect soil, reduce overgrazing, use suitable farming methods and follow weather warnings.

Recent examples:

Students can record a recent dust storm reported in newspapers.

Chapter Conclusion

The Earth’s surface is constantly changing because of internal and external forces.

Internal forces such as earthquakes, volcanic eruptions, folding and faulting help create major landforms. External forces such as weathering, erosion and deposition gradually modify them.

Running water, waves, glaciers, wind and underground water are important agents of gradation.

Landforms influence human settlements, agriculture, resources, trade, transport and culture. Understanding these processes also helps people prepare for natural disasters.

Before we move on…

The Earth is made up of layers, namely, the crust, mantle, and core.
Interior forces of the Earth (earthquakes, volcanoes, folding, and faulting) are responsible for the movement of the crust.
External forces like weathering and erosion carve smaller landforms over the Earth’s surface which affect human life in multiple ways.
The surface of the Earth is carved by agents of gradation like running water, waves and tides, glaciers, wind, and underground water.
Disasters like landslides, avalanches, glacial lake outflows, and sandstorms are associated with specific landforms.

Questions and Activities

1. What are the sources of energy that are required to cause movements associated with the internal forces of the Earth?

Answer: The main source is the Earth’s internal heat. Heat from the Earth’s interior produces convection currents in the mantle, which help move tectonic plates.

2. Relate various physiographic divisions you have studied in the earlier grades with various endogenic forces responsible for their origin.

Answer: Mountains such as the Himalayas are related to plate collision and folding. Volcanic features are related to volcanic activity. Faulting and tectonic movements also create valleys and other relief features.

3. Why and where do earthquakes occur frequently? Is it possible to predict earthquakes?

Answer: Earthquakes occur frequently near active tectonic plate boundaries because plates move, collide or slide past one another. Exact prediction of the time and place of an earthquake is not currently possible, but scientists can identify earthquake-prone regions and assess risk.

4. “Plate movements are responsible for the distribution of earthquakes and volcanoes.” Explain.

Answer: Most earthquakes and volcanoes occur near plate boundaries. Converging, diverging and sliding plates create stress or allow magma to rise. Therefore, plate movements strongly influence the global distribution of earthquakes and volcanoes.

5. Draw and label a diagram of a meander and a delta.

Answer: Draw a winding river for a meander and label the river, steep bank, bar and oxbow lake. For a delta, draw a river dividing into distributaries near the sea and label the river, distributaries, islands/bars and sea.

6. How are deforestation and erosion associated with each other? Explain.

Answer: Trees and vegetation hold soil together with their roots. Deforestation removes this protection. As a result, rainwater and wind can carry away more soil, increasing erosion.

7. Develop a plan to protect the land in your local area from erosion.

Answer: Plant more trees and grass, protect existing vegetation, build contour trenches and bunds on slopes, use terraces where needed, improve drainage and avoid unnecessary removal of soil.

8. Which disasters do you think you might experience in your region? Discuss a mitigation plan in your classroom.

Answer: Possible disasters depend on the region. A suitable mitigation plan should include awareness, early warnings, safe buildings, emergency kits, evacuation routes, communication systems and regular disaster-preparedness drills.

9. Prepare a model of landforms created by underground water.

Answer: Prepare a model showing a limestone cave with a cave mouth, stalactites, stalagmites, a sinkhole and an underground river. Use cardboard, clay or other safe materials.

10. What precautionary measures will you take if you are staying in an earthquake-prone region?

Answer: Use earthquake-resistant buildings, secure heavy objects, keep an emergency kit, identify safe places and exits, practise earthquake drills and follow official warnings. During shaking, protect the head and stay away from windows and falling objects.

11. Prepare a map showing landform-associated disasters that happened in the current calendar year.

Answer: Mark the locations of recent landslides, avalanches, GLOFs and dust storms on an outline map of India and the world. Add a small legend showing each disaster type.

12. Create a poster showing landforms that are considered to be sacred or important in your region, and add the folk stories associated with them.

Answer: Select an important mountain, river, cave, lake or other landform in your region. Draw or paste its picture and write its name, location, importance and a short local folk story associated with it.

13. Document a case of a disaster that hit your region in the past, highlighting its effects on various human activities.

Answer: Select one local disaster and record its date, location, causes and effects. Explain how it affected houses, roads, agriculture, schools, transport, livelihoods and communication. Add photographs or newspaper reports if available.

14. Translate the given poster on landslide into your native language and display it in your home.

Answer: Translate the safety instructions on the given landslide poster clearly into your native language. Display the translated poster where family members can easily read it.

15. Divide the class into three groups. Each group will work on one project (water, wind, and glacier). The project should highlight the causes, impact on human life and the environment, and mitigation

Answer:

Water Group: Study erosion, floods, river landforms and water conservation. Explain their effects on people and the environment and suggest measures such as afforestation, drainage improvement and soil conservation.

Wind Group: Study wind erosion, dunes and dust storms. Explain their effects and suggest vegetation protection, soil conservation and suitable land-use practices.

Glacier Group: Study glacial erosion, moraines, avalanches and GLOFs. Explain their effects and suggest monitoring, early-warning systems, safe planning and preparedness.

Quick Revision

Topic	Remember
Plate tectonics	Moving tectonic plates shape the Earth’s surface.
Convergent boundary	Plates move towards each other.
Divergent boundary	Plates move away from each other.
Transform boundary	Plates slide past each other.
Weathering	Breakdown of rocks without movement.
Erosion	Removal and movement of material.
River	Creates valleys, meanders, oxbow lakes and deltas.
Waves	Create beaches, cliffs, caves, arches and stacks.
Glaciers	Create U-shaped valleys, cirques, aretes and moraines.
Wind	Creates dunes, yardangs and other desert landforms.
Groundwater	Creates caves, sinkholes, stalactites and stalagmites.
Major disasters	Landslides, avalanches, GLOFs and dust storms.

class 9 social science 1 chapter 2 notes and book solutions

Class 9 Social Science Chapter 2

Chapter Summary

The Big Questions

1. Plate Tectonics

Major Effects of Plate Movement

2. Interior of the Earth

3. Types of Tectonic Plates

Major Plates Mentioned in the Chapter

4. Why Do Tectonic Plates Move?

5. Types of Plate Boundaries

LET’S MAP

6. Earthquakes, Volcanoes and the Ring of Fire

LET’S EXPLORE

LET’S EXPLORE

LET’S EXPLORE

Indian Knowledge and Earthquakes

LET’S EXPLORE

India’s Mud Volcano

7. Weathering

8. Erosion

Effects of Erosion on Human Life

LET’S EXPLORE

Soil and Water Conservation

9. Agents of Gradation

Landforms and Human Civilisations

10. Running Water

Waterfall

Meander

Delta

LET’S EXPLORE

11. Waves and Currents

Beach

Coastal Erosion Landforms

12. Glaciers

Moraines

THINK ABOUT IT

13. Wind

Dunes

14. Underground Water

LET’S EXPLORE

15. Landforms and Disasters

Landslides

Main Causes

Book Activity

Avalanches

Causes

Glacial Lake Outburst Floods (GLOFs)

Main Causes

Dust Storms

Main Causes

Chapter Conclusion

Before we move on…

Questions and Activities

Quick Revision