Class 9 Social Science Chapter 2: Shaping of the Earth’s Surface – Complete Notes
New NCERT Book: Understanding Society: India and Beyond – Part 1
PART 1: CHAPTER NOTES – FULL CHAPTER EXPLANATION
What is Shaping of the Earth’s Surface?
The surface of the Earth is not the same everywhere. At some places there are high mountains, at some places flat plains, at some places deep valleys and at some places deserts. All these are called landforms.
The Earth’s surface keeps changing slowly with time. Sometimes the change is very slow, like a river cutting a valley in thousands of years. Sometimes the change is very fast, like an earthquake or a landslide in a few seconds.
These changes happen because of forces inside the Earth and forces outside the Earth. Inside forces are called Endogenic forces and outside forces are called Exogenic forces.
Structure of the Earth
The Earth is made of three main layers.
- Crust: Crust is the outermost and thinnest layer of the Earth. We live on the crust. It is made of solid rocks. Under the oceans, the crust is thin, and under the continents, it is thick.
- Mantle: Mantle is the middle layer below the crust. It is very hot and the rocks here are in a semi-molten state, which means they are partly solid and partly liquid. This hot material is called Magma.
- Core: Core is the innermost layer of the Earth. It is divided into Outer Core and Inner Core. It is made mainly of Iron and Nickel and it is extremely hot.
The crust is not one single piece. It is broken into many big pieces called Tectonic Plates. These plates float and move very slowly on the mantle.
Plate Tectonics and Movement of Plates
Tectonic plates move in different directions. When two plates move towards each other, they collide. This is called Convergent Movement. When plates collide, mountains are formed and sometimes earthquakes also happen. The Himalayas were formed like this.
When two plates move away from each other, it is called Divergent Movement. When plates move away, new crust is formed and sometimes volcanoes are formed in the oceans.
When two plates slide past each other, it is called Transform Movement. In this movement, earthquakes happen because plates rub against each other.
That is why earthquakes mostly happen near the edges of plates, which are called Plate Boundaries.
Endogenic Forces – Forces Inside the Earth
Endogenic forces work inside the Earth. They create big landforms like mountains, plateaus and plains.
Volcano: When hot magma comes out of the Earth through a crack, it is called a Volcano. Lava comes out, cools down and becomes solid rock. After many eruptions, a volcanic mountain is formed.
Earthquake: When plates suddenly move or break inside the Earth, the ground shakes. This shaking is called an Earthquake. The point inside the Earth where the earthquake starts is called Focus, and the point on the surface just above it is called Epicentre.
Fold Mountains: When two plates collide, the rocks bend and fold like a cloth. These folded rocks form Fold Mountains. The Himalayas, Alps and Andes are fold mountains.
Block Mountains: Sometimes rocks break and one part goes up and the other part goes down. The part which goes up forms Block Mountains.
Exogenic Forces – Forces Outside the Earth
Exogenic forces work on the surface of the Earth. They wear down high landforms and fill up low areas. The main exogenic processes are Weathering, Erosion and Deposition.
Weathering: Weathering means breaking down of rocks at the same place by heat, cold, water, wind and plants. The rock breaks into small pieces but does not move from its place.
Erosion: Erosion means wearing away and carrying away of rock pieces by running water, wind, glaciers and sea waves. In erosion, material moves from one place to another.
Deposition: Deposition means dropping down of the material carried by rivers, wind and glaciers at a new place. When a river slows down, it deposits sand and soil and forms plains and deltas.
Landforms Formed by Rivers
Rivers are the most important agents of erosion and deposition.
In the upper course, in mountains, the river flows fast and cuts deep valleys. It forms V-shaped valleys and waterfalls.
In the middle course, the river becomes slower and forms meanders, which are big bends in the river.
In the lower course, near the sea, the river deposits a lot of sand and soil and forms a Delta. The Sundarbans Delta formed by Ganga and Brahmaputra is the largest delta in the world. Fertile plains formed by rivers are very good for farming.
Landforms Formed by Wind
In deserts, wind is the main agent of erosion and deposition because there is very little water and very few plants.
Wind carries sand from one place to another and forms Sand Dunes, which are hills of sand.
When wind erodes rocks, it forms Mushroom Rocks, which are narrow at the bottom and wide at the top.
In India, the Thar Desert in Rajasthan has many sand dunes.
Landforms Formed by Glaciers
A Glacier is a big moving mass of ice. Glaciers move very slowly in mountains and in very cold areas.
Glaciers erode valleys and make them U-shaped. When glaciers melt, they deposit rocks and soil and form Moraines.
In India, glaciers are found in the Himalayas. The Gangotri Glacier is the source of the river Ganga.
Landforms Formed by Underground Water
Rainwater goes inside the Earth through cracks in limestone rocks. This water dissolves the rock and forms caves.
Inside caves, limestone deposits form Stalactites, which hang from the roof, and Stalagmites, which rise from the floor.
Landforms Formed by Sea Waves
Sea waves continuously hit the coast and erode rocks. They form Sea Cliffs, Sea Caves, Sea Arches and Sea Stacks.
When sea waves deposit sand, they form Beaches.
Natural Disasters Related to Landforms
Earthquakes, landslides, avalanches, GLOFs and dust storms are natural disasters related to the shaping of the Earth.
Landslide: When rocks and soil suddenly slide down a mountain slope due to heavy rain or earthquake, it is called a Landslide. Landslides mostly happen in hilly areas like the Himalayas and Western Ghats.
Avalanche: When a big mass of snow suddenly slides down a mountain, it is called an Avalanche.
GLOF: GLOF means Glacial Lake Outburst Flood. When a glacial lake suddenly breaks, a huge amount of water flows down and causes floods.
Dust Storm: In dry areas, strong winds carry a lot of dust and sand. This reduces visibility and affects health and farming.
We cannot stop these disasters completely, but we can reduce their damage by early warning, planting trees, not cutting hills, and building houses in safe places.
Quick Revision Notes:
Earth has three layers: Crust, Mantle and Core.
Crust is broken into Tectonic Plates.
Plates move in three ways: Convergent, Divergent and Transform.
Endogenic forces work inside the Earth, Exogenic forces work on the surface.
Weathering is breaking of rocks, Erosion is carrying away, Deposition is dropping down.
Rivers form V-shaped valleys, Meanders and Deltas.
Wind forms Sand Dunes and Mushroom Rocks.
Glaciers form U-shaped valleys and Moraines.
Earthquake Focus is inside the Earth, Epicentre is on the surface.
Himalayas are Fold Mountains formed by collision of plates.
NCERT TEXTBOOK QUESTIONS AND ANSWERS
Note: These are the in-text questions and activities given in the NCERT textbook.
Q1. Let’s Analyse: Observe the land around your school or home. Is it flat, hilly or uneven? What do you think made it like this?
Ans. The land around my home is mostly flat. It is a plain formed by deposition of soil by rivers over a long time. Rivers, wind and human activities like farming and construction have shaped this land.
Q2. Why do earthquakes happen more in some parts of India than in others?
Ans. Earthquakes happen more in areas near plate boundaries and in the Himalayan region because the Indian plate is still colliding with the Eurasian plate. That is why Jammu and Kashmir, Himachal Pradesh, Uttarakhand, North-East India and Gujarat are more earthquake-prone.
Q3. How are mountains formed?
Ans. Mountains are mostly formed when two tectonic plates collide with each other. The rocks between them fold and rise up and form fold mountains like the Himalayas. Some mountains are also formed by volcanoes and by faulting of rocks.
Q4. What is the difference between Weathering and Erosion?
Ans. Weathering is breaking down of rocks at the same place, the material does not move. Erosion is wearing away and carrying away of rock material from one place to another by water, wind or glaciers.
Q5. Why are river plains very fertile and good for farming?
Ans. River plains are fertile because rivers deposit fine soil called alluvium on the plains every year. This soil is soft, rich in minerals and holds water well, so crops grow very well there.
Q6. How does wind shape the land in deserts?
Ans. In deserts, wind erodes rocks and carries sand from one place to another. It forms sand dunes and mushroom rocks. Wind deposits sand in new places and changes the shape of the desert again and again.
Q7. What is a Glacier? How does it change landforms?
Ans. A glacier is a large moving mass of ice. It moves slowly and erodes the valley below it and makes it U-shaped. When it melts, it deposits rocks and soil and forms moraines.
Q8. Why should we be careful while building houses on mountain slopes?
Ans. We should be careful because mountain slopes are prone to landslides and avalanches, especially during heavy rain and earthquakes. Cutting trees and digging hills makes landslides more dangerous.
Q9. What is the difference between Focus and Epicentre of an earthquake?
Ans. Focus is the point inside the Earth where the earthquake starts. Epicentre is the point on the surface of the Earth directly above the Focus. Damage is maximum near the Epicentre.
Q10. Let’s Explore: With the help of a map, locate the Himalayas, the Thar Desert, the Western Ghats and the Sundarbans Delta. What type of landform is each of these?
Ans. The Himalayas are fold mountains, the Thar Desert is a desert landform formed by wind, the Western Ghats are mountains and hills, and the Sundarbans Delta is a delta formed by deposition by rivers Ganga and Brahmaputra.
Q11. How can we reduce the damage caused by landslides and earthquakes?
Ans. We can reduce damage by planting more trees, not cutting hills unnecessarily, building earthquake-resistant houses, following early warning, and not building houses in very risky areas.
EXTRA QUESTIONS FOR EXAM
Very Short Answer Questions
Q1. What are the three layers of the Earth?
Ans. Crust, Mantle and Core.
Q2. What are Tectonic Plates?
Ans. Tectonic Plates are big broken pieces of the Earth’s crust which move slowly on the mantle.
Q3. What is the outermost layer of the Earth called?
Ans. Crust.
Q4. What is Magma?
Ans. Hot, semi-molten rock material inside the Earth is called Magma.
Q5. What are Endogenic forces?
Ans. Forces which work inside the Earth are called Endogenic forces.
Q6. What are Exogenic forces?
Ans. Forces which work on the surface of the Earth are called Exogenic forces.
Q7. What is Weathering?
Ans. Breaking down of rocks at the same place is called Weathering.
Q8. What is Erosion?
Ans. Carrying away of rock material by water, wind or glaciers is called Erosion.
Q9. What is Deposition?
Ans. Dropping down of material carried by rivers, wind or glaciers at a new place is called Deposition.
Q10. Give one example of Fold Mountains.
Ans. The Himalayas.
Short Answer Questions
Q1. Explain the structure of the Earth.
Ans. The Earth has three layers. Crust is the outermost thin layer on which we live. Mantle is the middle layer, which is very hot and semi-molten. Core is the innermost layer, made of Iron and Nickel, and it is extremely hot.
Q2. Explain the three types of plate movements.
Ans. In Convergent movement, plates move towards each other and collide, forming mountains. In Divergent movement, plates move away from each other and new crust is formed. In Transform movement, plates slide past each other and earthquakes happen.
Q3. What is the difference between Weathering, Erosion and Deposition?
Ans. Weathering is breaking of rocks at the same place. Erosion is carrying away of broken rock material by water, wind or glaciers. Deposition is dropping down of this material at a new place and forming new landforms like plains and deltas.
Q4. How do rivers shape landforms in different courses?
Ans. In the upper course, rivers cut V-shaped valleys and waterfalls. In the middle course, they form meanders. In the lower course, they deposit soil and form fertile plains and deltas.
Q5. Why are earthquakes and landslides dangerous? How can we reduce their damage?
Ans. Earthquakes shake buildings and cause loss of life and property. Landslides bury roads and houses in hilly areas. We can reduce damage by planting trees, building strong houses, following early warning and not building in risky areas.
Long Answer Questions
Q1. Explain the structure of the Earth and Plate Tectonics. How do plate movements form mountains and cause earthquakes?
Ans. The Earth has three layers – Crust, Mantle and Core. The crust is broken into tectonic plates which move slowly on the mantle.
When two plates collide, fold mountains like the Himalayas are formed. When plates move away, new crust and volcanoes are formed. When plates slide past each other, they rub and cause earthquakes. Most earthquakes happen at plate boundaries. The Focus is inside the Earth and the Epicentre is on the surface above it.
Q2. Explain Weathering, Erosion and Deposition with examples. How do rivers, wind and glaciers shape the Earth’s surface?
Ans. Weathering breaks rocks at the same place by heat, water and wind. Erosion carries this broken material away. Deposition drops it at a new place.
Rivers cut V-shaped valleys in mountains, form meanders in plains and deltas near the sea. Wind forms sand dunes and mushroom rocks in deserts. Glaciers form U-shaped valleys and moraines in cold and mountain areas. All these agents together keep changing the Earth’s surface.
Q3. Explain the landforms formed by rivers, wind, glaciers, underground water and sea waves.
Ans. Rivers form V-shaped valleys, waterfalls, meanders, plains and deltas. Wind forms sand dunes and mushroom rocks in deserts. Glaciers form U-shaped valleys and moraines. Underground water forms caves, stalactites and stalagmites in limestone areas. Sea waves form sea cliffs, sea caves, sea arches, sea stacks and beaches on the coast.
These landforms show that both inside forces and outside forces shape the Earth continuously.
Case Based Questions
Case 1:
In a hilly village, it rained heavily for three days. Suddenly, a large amount of rocks and soil slid down the slope and blocked the road. Many trees were also cut on that slope last year for construction.
Q1. What is this phenomenon called?
Ans. Landslide.
Q2. What were the two reasons for this landslide?
Ans. Heavy rain and cutting of trees on the slope.
Q3. How can such disasters be reduced in future?
Ans. By planting more trees, not cutting hills unnecessarily, and not building houses and roads in very risky areas.
Case 2:
Riya lives near the Thar Desert. She sees big hills of sand near her village. Sometimes strong winds blow sand everywhere and it becomes difficult to see. Her grandfather says these sand hills keep changing their place.
Q1. What are these hills of sand called?
Ans. Sand Dunes.
Q2. Which agent forms these sand dunes?
Ans. Wind.
Q3. Why do sand dunes keep changing their place?
Ans. Because wind continuously carries sand from one place to another and deposits it at a new place.
WORKSHEET FOR PRACTICE
Try to solve this worksheet yourself without seeing the answers above. This will help you in exams.
A. Multiple Choice Questions (MCQ)
Q1. Which is the outermost layer of the Earth?
a) Mantle
b) Core
c) Crust
d) Magma
Q2. Which of the following is an Endogenic force?
a) River
b) Wind
c) Volcano
d) Glacier
Q3. When two plates move towards each other, it is called:
a) Divergent movement
b) Convergent movement
c) Transform movement
d) Erosion
Q4. Which landform is formed by deposition of rivers near the sea?
a) Sand Dune
b) Delta
c) Moraine
d) Waterfall
Q5. Sand Dunes are formed by:
a) Rivers
b) Glaciers
c) Wind
d) Sea waves
Q6. U-shaped valleys are formed by:
a) Rivers
b) Wind
c) Glaciers
d) Underground water
Q7. The point on the surface above the Focus is called:
a) Core
b) Epicentre
c) Crust
d) Mantle
Q8. Which of these is a Fold Mountain?
a) Thar Desert
b) Himalayas
c) Sundarbans Delta
d) Beach
B. True or False
Q1. The crust is the innermost layer of the Earth.
Q2. Tectonic plates move very slowly.
Q3. Weathering and Erosion are the same process.
Q4. Rivers form deltas near the sea.
Q5. Landslides mostly happen in hilly areas during heavy rain.
C. Fill in the Blanks
Q1. The Earth has three layers: Crust, Mantle and ______.
Q2. The hot semi-molten material inside the Earth is called ______.
Q3. ______ is breaking of rocks at the same place.
Q4. Rivers form ______ valleys in the mountains.
Q5. Wind forms ______ in deserts.
D. Assertion – Reason Questions
Read the statements and choose the correct option:
a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
b) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
c) Assertion is true but Reason is false.
d) Assertion is false but Reason is true.
Q1. Assertion: Earthquakes mostly happen near plate boundaries.
Reason: Plates move and collide or slide past each other at plate boundaries.
Q2. Assertion: River plains are good for farming.
Reason: Rivers deposit fertile soil called alluvium on the plains.
Q3. Assertion: Landslides happen more when trees are cut on slopes.
Reason: Roots of trees hold the soil and prevent it from sliding down.
E. Match the Following
Match Column A with Column B:
Column A Column B
- Crust a) Sand Dunes
- Mantle b) Outermost layer of Earth
- River c) U-shaped valley
- Wind d) Middle layer of Earth
- Glacier e) Delta
F. Short and Long Answer Questions
Q1. What are Tectonic Plates? Explain any two types of plate movements.
Q2. What is the difference between Weathering and Erosion?
Q3. How do rivers form different landforms?
Q4. Explain any two natural disasters related to landforms.
Q5. Why is the Himalayan region more prone to earthquakes? Explain in 4-5 lines.
G. Case Based Question
In a coastal town, sea waves hit the rocks every day. After many years, caves and arches were formed in the rocks. Sand was also deposited on the shore and a beach was formed.
Q1. Which agent is shaping the land in this town?
Q2. Name any two landforms formed by sea waves.
Q3. Why does the shape of the coast keep changing?
Worksheet Answer Key
MCQ Answers: 1-c, 2-c, 3-b, 4-b, 5-c, 6-c, 7-b, 8-b
True or False Answers: 1-False, 2-True, 3-False, 4-True, 5-True
Fill in the Blanks Answers: 1-Core, 2-Magma, 3-Weathering, 4-V-shaped, 5-Sand Dunes
Assertion-Reason Answers: 1-a, 2-a, 3-a
Match the Following Answers: 1-b, 2-d, 3-e, 4-a, 5-c