Chapter 1 – Exogenetic processes and resultant landforms

WBBSE Class 10 Geography Chapter 1 Exogenetic Processes Questions and Answers

Content Structure

1. Multiple choice questions and answers (MCQs)
2. Very short-type questions and answers
- 2A. Fill in the blanks
- 2B. True or false
- 2C. Very short-type questions and answers
3. Short-type questions and answers
4. Analytical questions and answers
5. Explanatory questions and answers

1. Multiple choice questions and answers (MCQs) [1 mark each]

1. Who first used the term “Gradation”?
a) W.M. Davis
b) G.K. Gilbert
c) Alexander von Humboldt
d) James Hutton

Ans: b) G.K. Gilbert

2. In which course does deposition dominate?
a) Upper course
b) Middle course
c) Lower course
d) Mountain course

Ans: c) Lower course

3. Which force acts from outside the earth’s surface?
a) Endogenetic force
b) Exogenetic force
c) Tectonic force
d) Volcanic force

Ans: b) Exogenetic force

4. Which process raises land by deposition?
a) Denudation
b) Aggradation
c) Weathering
d) Attrition

Ans: b) Aggradation

5. Which river is considered an ideal river?
a) Nile
b) Amazon
c) Mississippi
d) Ganga

Ans: c) Mississippi

6. Which process lowers the height of land by erosion?
a) Aggradation
b) Degradation
c) Sedimentation
d) Accumulation

Ans: b) Degradation

7. Which valley is formed by a glacier?
a) V-shaped valley
b) U-shaped valley
c) Rift valley
d) Structural valley

Ans: b) U-shaped valley

8. Which glacier is the largest in India?
a) Gangotri Glacier
b) Yamunotri Glacier
c) Siachen Glacier
d) Zemu Glacier

Ans: c) Siachen Glacier

9. What is the ice-free mountain peak in an ice sheet called?
a) Moraine
b) Nunatak
c) Cirque
d) Arete

Ans: b) Nunatak

10. Which landform is formed by wind deposition?
a) Gorge
b) Canyon
c) Sand dune
d) Delta

Ans: c) Sand dune

11. What is the highest waterfall in the world?
a) Niagara Falls
b) Angel Falls
c) Victoria Falls
d) Jog Falls

Ans: b) Angel Falls

12. Which desert landform is crescent shaped?
a) Seif dune
b) Barchan
c) Loess
d) Wadi

Ans: b) Barchan

13. Which river process forms potholes?
a) Abrasion
b) Attrition
c) Deposition
d) Weathering

Ans: a) Abrasion

14. Which river course is dominated by erosion?
a) Upper course
b) Middle course
c) Lower course
d) Delta course

Ans: a) Upper course

15. What is the triangular deposit formed at the mouth of a river called?
a) Flood plain
b) Delta
c) Gorge
d) Basin

Ans: b) Delta

2. Very short-type questions and answers

2A. Fill in the blanks [1 mark each]

1. The word gradation was first used by __________. (G.K. Gilbert)
2. The removal of loose sand particles by wind is called __________. (Deflation)
3. The process of lowering the land surface by erosion is called __________. (Degradation)
4. The highest waterfall in the world is __________.(Angel Falls)
5. Fine wind-blown silt deposits are called __________. (Loess)
6. The valley formed by glacier erosion is __________ shaped.(U)
7. A dry river valley in desert regions is called __________. (Wadi)
8. The area drained by a river and its tributaries is called a river __________. (Basin)

2B. True or false [1 mark each]

1. Exogenetic forces originate inside the earth. (False)
2. Angel Falls is the highest waterfall in the world. (True)
3. A U-shaped valley is formed by river erosion. (False)
4. A delta is formed at the mouth of a river. (True)
5. A V-shaped valley is formed in the upper course of a river. (True)
6. Loess is a fine wind-blown deposit of silt. (True)

2C. Very short-type questions and answers [1 mark each]

1. Name the highest waterfall in the world.
Ans: The highest waterfall in the world is Angel Falls in Venezuela.

2. Name the largest continental glacier in the world.
Ans: The largest continental glacier in the world is the Antarctic Ice Sheet.

3. In which part of the course of a river depositional activity is most prominent?
Ans: Depositional activity is most prominent in the lower course of a river.

4. Give an example of ‘Himalayan glacier’.
Ans: Gangotri Glacier is an example of a Himalayan glacier.

5. Who first used the word ‘Gradation’?
Ans: The word gradation was first used by G. K. Gilbert.

6. Give an example of ‘Mountain glacier’.
Ans: Siachen Glacier is an example of a mountain glacier.

7. Give an example of ‘ideal river’.
Ans: The Mississippi River is an example of an ideal river.

8. What is the shape of the valley carved out by a glacier?
Ans: A glacier carves a U-shaped valley.

9. What is deflation?
Ans: Deflation is the process of wind erosion in which loose sand, dust and fine particles are lifted and removed from the land surface, leaving behind heavier materials.

10. Name the largest glacier in India.
Ans: The largest glacier in India is the Siachen Glacier.

11. What is the name of ice-free mountain peak situated in the continental glacier or ice sheet?
Ans: An ice-free mountain peak within a continental glacier is called a Nunatak.

12. What is desertification?
Ans: Desertification is the process by which fertile land gradually becomes dry, barren and desert-like due to factors such as deforestation, overgrazing, soil erosion and climatic changes.

13. What is weathering?
Ans: Weathering is the breaking down and decomposition of rocks at or near the earth’s surface by physical, chemical or biological processes, without the movement of the rock materials.

14. What is erosion?
Ans: Erosion is the process of wearing away and removal of the earth’s surface materials by natural agents such as rivers, wind, glaciers and sea waves.

3. Short-Type Questions and Answers [2 marks each]

1. What is ‘Aggradation’?
Ans: Aggradation is the process of building up the land by filling in low-lying areas. When a river or the wind slows down, it loses the energy needed to carry sand, mud, and gravel. It drops these materials into valleys or plains, which gradually raises the level of the ground.

2. What is ‘gradation’?
Ans: Gradation is the process of leveling the Earth’s surface. It works through two opposite actions:

Aggradation: Low lands (like valleys) are filled up by the deposition of sand and silt. Result: Over millions of years, these forces work together to create a relatively level surface called a “grade.”
Degradation: High lands (like mountains) are worn down by erosion and weathering.

3. What is ‘Degradation’?
Ans: Degradation is the natural process where the Earth’s high land surfaces, like mountains and hills, are slowly worn down and lowered. This happens because external forces like flowing water, wind, and moving ice constantly chip away at the rock and soil. Over millions of years, this continuous cutting and carrying away of material reduces the overall height of the landscape.

4. What is ‘River basin’?
Ans: A river basin is the entire area drained by a river and its tributaries. It includes all the land from where rainwater and small streams flow into a particular river.

5. What is ‘Water divide’?
Ans: A water divide is a high land or ridge that separates two river basins. It acts as a natural boundary that directs rainwater to flow into different rivers on either side so water falling on one side flows to one river, while water on the other side flows to another river.

6. What is ‘Pot hole’?
Ans: A pothole is a circular hole formed in the river bed due to the grinding action of pebbles and stones carried by the river. These stones move round and round with the flowing water and slowly drill holes in the rocky layer of the river.

7. How is a waterfall formed?
Ans: A waterfall is created when a river flows over a sudden drop in the land. This usually happens when the river passes from a layer of very hard rock onto a layer of softer rock. The water eats away at the soft rock much faster, creating a vertical ledge.

8. What is lateral moraine?
Ans: Lateral moraine is the debris deposited along the sides of a glacier. These materials are carried by the glacier and get piled up along its edges as the glacier moves down the valley.

9. What is ‘glacier’?
Ans: A glacier is a slow moving mass of ice formed by the accumulation and compaction of snow in high mountains or polar regions. As layers of snow press together and turn into ice, the heavy mass slowly moves down the slope under the force of gravity.

10. What is snow line?
Ans: The snow line is the height above which snow remains permanently throughout the year. Below this level the snow melts during summer, but above this height the temperature remains low and snow stays throughout the year.

11. What is ‘plunge pool’?
Ans: A plunge pool is a deep hollow formed at the base of a waterfall due to the erosional action of falling water. The strong force of falling water and the movement of stones and pebbles gradually deepen the hollow and make it wider over time.

12. What is hanging valley?
Ans: A hanging valley is a tributary valley which remains at a higher level than the main valley formed by a glacier. It is called a hanging valley because the smaller valley seems to hang above the deeper main valley.

4. Analytical questions and answers [3 marks each]

1. Why are deltas not formed by all rivers?
Ans: Deltas are not formed by all rivers because:

Deep sea near the river mouth: When a river enters a deep sea or ocean, the sediments carried by the river sink quickly to the bottom and cannot accumulate to form a delta.
Strong sea waves and ocean currents: Powerful waves and currents wash away the sediments brought by the river, so they do not settle and form a delta.
Less sediment load in the river: If a river carries very little sand, silt and clay, there is not enough material to build a delta.
Fast flow of water near the mouth: When the river water flows very fast near the mouth, the sediments are carried far into the sea instead of being deposited there.

2. What is the difference between alluvial fan and delta?
Ans:

Feature	Alluvial Fan	Delta
Meaning	An alluvial fan is a fan-shaped deposit of sand, gravel and silt formed by a river.	A delta is a landform formed by the deposition of sediments at the mouth of a river.
Place of formation	Formed at the foot of mountains where a river comes down to the plain.	Formed at the mouth of a river where it enters a sea or ocean.
Surface of deposition	Deposited on the land surface.	Deposited in a sea, ocean or large lake.
Shape	Has a fan-shaped structure spreading outward from the mountain front.	Usually triangular, arcuate or bird-foot shaped.
River flow	Formed when the river suddenly loses speed after leaving the mountains.	Formed when the river slows down on meeting the sea and deposits sediments.
Example	Common along the Himalayan foothills.	Example: Ganga–Brahmaputra Delta.

3. Write the differences between barkhans and seifs.
Ans:

Feature	Barkhans	Seifs
Meaning	Barkhans are crescent-shaped sand dunes formed by wind action.	Seifs are long, narrow sand dunes formed by wind deposition.
Shape	Crescent or half-moon shaped with two pointed ends.	Long, straight or slightly curved ridges of sand.
Wind direction	Formed where wind blows mainly in one direction.	Formed where winds blow from two different directions.
Size and structure	Usually smaller and isolated sand dunes.	Usually longer and may extend for many kilometres.
Region of occurrence	Common in desert regions with limited sand supply.	Found in large sandy deserts with abundant sand.
Example of region	Seen in deserts like the Thar Desert.	Seen in large deserts such as the Sahara Desert.

4. How is an ox-bow lake formed?
Ans: An ox-bow lake is formed in the middle or lower course of a river where the land is relatively flat and the river flows more slowly. In these regions the river develops large bends called meanders due to continuous lateral erosion on the outer banks and deposition on the inner banks. As erosion continues, the bends become larger and the neck between two loops of a meander gradually becomes narrower. During floods or periods of high water flow, the river may cut across this narrow neck and take a shorter and straighter path. The abandoned curved portion of the river gets separated from the main channel and forms a crescent-shaped water body known as an ox-bow lake.

5. What are the causes of desertification?
Ans: Major causes of desertification include:

Deforestation: Cutting down large numbers of trees removes the natural vegetation cover. Without trees and plants, the soil becomes loose and dry, making it more vulnerable to erosion and gradually turning the land into desert.
Overgrazing: When too many animals graze in the same area, they destroy grasses and small plants. This reduces vegetation cover and leaves the soil exposed to wind and water erosion.
Excessive cultivation: Continuous farming without proper soil management reduces soil fertility. Overuse of land for agriculture can dry out the soil and make it unsuitable for crop growth.
Soil erosion: Strong winds and running water remove the fertile topsoil. When the top layer of soil is lost, the land becomes barren and less productive.
Climatic changes and drought: Long periods of low rainfall and increasing temperatures dry up the soil and vegetation. This lack of moisture gradually leads to the spread of desert conditions.

6. How do exogenetic processes act upon the earth’s surface?
Ans: Exogenetic processes are external processes that act on the earth’s surface through natural agents such as running water, wind, glaciers and sea waves. These agents constantly change the shape of the land by breaking down rocks and carrying the materials from one place to another. Through processes like weathering, erosion, transportation and deposition, rocks are gradually worn away and their particles are moved and deposited elsewhere. As a result, highlands and mountains are slowly reduced in height, while the eroded materials are deposited in lowlands, valleys and plains. Over a long period of time, these processes help to level the uneven land surface through the process known as gradation.

7. Distinguish between river valley and glacial valley.
Ans:

Feature	River Valley	Glacial Valley
Agent of formation	Formed by the erosional action of running water (river).	Formed by the movement and erosion of glaciers.
Shape	Usually V-shaped valley.	Usually U-shaped valley.
Width	Generally narrow.	Much wider than river valleys.
Depth and sides	Deep with sloping sides.	Wide with steep and straight sides.
Region where found	Commonly found in plains and mountainous regions where rivers flow.	Mostly found in high mountain regions where glaciers move.

8. How is an alluvial fan formed?
Ans: An alluvial fan is formed when a river flowing down from a mountainous region reaches a plain. In the mountain region the river flows very fast and carries a large amount of sediments such as sand, gravel and pebbles. When the river comes down to the plain, the slope suddenly becomes gentle and the river loses its speed. Due to the decrease in velocity, the river can no longer carry the heavy materials and begins to deposit them. These deposited materials spread out widely at the foot of the mountains in a fan-like shape. Over time, repeated deposition of sediments builds up a broad fan-shaped landform known as an alluvial fan.

9. Distinguish between works of a river and works of wind.
Ans:

Feature	River Work	Wind Work
Region of occurrence	Occurs mainly in humid regions where rivers flow.	Occurs mainly in desert and dry regions.
Agent of action	Water acts as the main transporting and eroding agent.	Air (wind) acts as the transporting and eroding agent.
Landforms formed	Forms valleys, flood plains, deltas and waterfalls.	Forms sand dunes, loess deposits and desert landforms.
Availability of material	Carries sand, silt, pebbles and other sediments in water.	Carries fine sand and dust particles through wind.
Example of region	Seen along major rivers like the Ganga and Nile.	Seen in deserts like the Sahara and Thar Desert.

5. Explanatory questions and answers [5 marks each]

1. What is river erosion? Discuss the main processes of river erosion.
Ans: River erosion is the process by which a river wears away the land surface while flowing from higher land to lower land. As the river flows, it removes soil, rocks and other materials from its bed and banks. This continuous wearing away gradually deepens and widens the river channel and helps in the formation of various landforms such as valleys, gorges and potholes. The main processes of river erosion are explained below:

1. Hydraulic Action – Hydraulic action is the erosion caused by the force of flowing water. The fast moving water strikes the river banks and bed with great pressure and loosens rock particles. Water also enters cracks in the rocks and gradually breaks them apart.
2. Abrasion (Corrasion) – Abrasion is the wearing away of rocks by friction. The river carries sand, pebbles and stones which rub and scrape against the river bed and banks. This continuous rubbing gradually erodes the rocks and makes the channel deeper and wider.
3. Attrition – Attrition occurs when rock fragments carried by the river collide with each other. Because of constant collision, the rocks break into smaller, smoother and rounder pieces. This reduces the size of the materials transported by the river.
4. Solution (Corrosion) – Solution is the process in which soluble minerals and rocks such as limestone dissolve in river water. These dissolved substances are carried away by the river in solution form, contributing to the erosion of the land surface.

2. How are three landforms formed by glacial erosion? Explain.
Ans: Glaciers are large masses of moving ice that slowly move down mountain slopes. As glaciers move, they scrape, pluck and wear away rocks from the land surface. Through these processes, glaciers create several landforms in mountainous regions. Three important landforms formed by glacial erosion are explained below.

1. Cirque (Corrie) – A cirque is a bowl-shaped hollow formed at the upper end of a glacial valley. It is created when glacier ice slowly moves and scrapes the rock surface. Processes like plucking and abrasion remove rock materials from the valley head, gradually deepening and widening the hollow. After the glacier melts, the cirque may sometimes be filled with water to form a small lake called a tarn.
2. U-Shaped Valley – A U-shaped valley is formed when a glacier moves through a pre-existing river valley. The moving ice scrapes and cuts the valley floor and sides, making it wider and deeper. As a result, the narrow V-shaped river valley is transformed into a broad valley with a flat floor and steep sides, giving it a U-shaped appearance.
3. Hanging Valley – A hanging valley is formed where a smaller tributary glacier joins a larger main glacier. The main glacier erodes its valley more deeply than the smaller tributary glacier. When the glaciers melt, the tributary valley remains at a higher level than the main valley. Because it appears to hang above the main valley, it is called a hanging valley, and waterfalls are often found at its edge.

3. What landforms are formed by the erosional work of a river? Describe them.
Ans: Rivers continuously wear away and cut down the land surface as they flow from higher land to lower land. This wearing away of land mainly takes place through vertical cutting and sideways cutting of the river. As a result, several landforms are created along the course of the river.

1. Interlocking Spurs – In mountainous regions, the river flows through steep valleys. The river winds its way around resistant rocks, forming a series of projecting ridges called interlocking spurs. These ridges appear to overlap each other on both sides of the river.

2. Rapids – Rapids are parts of a river where the water flows very fast over a steep and uneven rocky bed. The sudden change in slope and presence of hard rocks cause the water to move turbulently and rapidly.
3. Waterfalls – Waterfalls are formed where the river flows over a sudden vertical drop in the river bed. This may occur when a river flows from hard rock to soft rock or when there is a steep cliff. The falling water creates a plunge pool at the base and gradually erodes the rocks.

4. Gorges and Canyons – Continuous erosion by the river deepens the valley over a long period of time. This process forms deep narrow valleys called gorges. In plateau regions, wider and deeper valleys with steep sides are formed, which are known as canyons.

4. Explain the main landforms created by the wearing away action of rivers.
Ans: ivers continuously wear away the land as they flow from higher land to lower land. This wearing away mostly occurs in the upper course of the river, where the land is steep and the river flows very fast. Because of this strong flow, the river cuts into the land and forms different erosional landforms.

1. V-shaped Valleys – In the upper course, the river mainly cuts downward into the land. This strong downward cutting forms deep and narrow valleys with sloping sides, which look like the letter “V”.

2. Gorges and Canyons – When a river continues to cut deeply into the land for a long time, it forms a very deep and narrow valley called a gorge. In plateau regions, the valley may become wider with steep sides and is known as a canyon.
3. Waterfalls and Rapids – Waterfalls are formed where the river flows over a sudden vertical drop in the river bed. The falling water strikes the rocks below and gradually deepens a hollow at the base. Rapids occur where the river flows very fast over a steep and uneven rocky bed.
4. Potholes – Potholes are circular holes formed in the river bed. They are created when pebbles and small stones carried by the river rotate in swirling water and gradually drill holes into the rocky layer.

5. What landforms are formed by the depositional work of wind? Explain.
Ans: Wind is an important agent of deposition in desert and dry regions. When the speed of wind decreases, it cannot carry sand and dust particles any further. As a result, these materials are deposited on the ground and different landforms are formed. The main depositional landforms formed by wind are:

1. Sand Dunes – Sand dunes are mounds or hills of sand formed by the deposition of wind-blown sand. Wind carries loose sand from one place to another and when its speed decreases, the sand gets deposited in heaps. Over time these heaps grow larger and form sand dunes.
Types of sand dunes include:
- Barchans: Crescent-shaped sand dunes formed by wind blowing mainly in one direction.
- Seif dunes: Long, narrow sand dunes formed by winds blowing from two different directions.
2. Loess Deposits – Loess is a fine yellow coloured wind-blown silt deposit. It is formed when very fine dust particles carried by wind are deposited over large areas. Loess soil is very fertile and supports agriculture in many parts of the world, such as in China and parts of Europe.
3. Sand Sheets – Sand sheets are large flat areas covered with thin layers of wind-deposited sand. They form when wind spreads sand evenly over a wide region instead of forming dunes.