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Chapter 10

Denudation

Class 9 - Total Geography Morning Star


Short Answer Questions

Question 1

What do you mean by denudation?

Answer

Denudation is the process of breaking and removing the rocks from the surface of the earth. It includes weathering, erosion, mass movement and transportation.

Question 2

Name the factors which affect work of a river.

Answer

The factors which affect work of a river are-

  1. Velocity of water
  2. Volume of water
  3. Load

Question 3

What is the main function of a river in its upper course? Name the landforms formed in the upper course of a river.

Answer

The main function of a river in its upper course is erosion. It erodes its bed and banks and carries large boulders of rock with it.

The landforms formed in the upper course of a river are V-shaped valley and waterfall.

Question 4

How is a waterfall formed?

Answer

A waterfall is generally formed due to large differences in the rate of erosion. The water that falls down the edge of a hard resistant rock may have at the bottom a soft rock. It is this soft rock that gets eroded fast and creates a hollow basin called plunge pool.

Question 5

State the two characteristics of a river in its middle course.

Answer

The two characteristics of a river in its middle course are-

  1. The lateral cutting is more active than down cutting.
  2. The volume of water in the river increases due to many tributaries joining it.

Question 6

How are meanders formed? Give one example of a meander.

Answer

Meanders generally form under conditions of a gentle slope and sufficient water in rivers. The river flow is diverted by an obstruction allowing the river to do lateral erosion work.

The Ganga in India is famous for its meanders.

Question 7

Name two landforms in the lower course of a river.

Answer

Two landforms in the lower course of a river are delta and estuary.

Question 8

Where is wind erosion most predominant?

Answer

Wind erosion is most predominant in arid regions such as deserts.

Question 9

What are known as Deflation Hollows?

Answer

Deflation results in the lowering of the land surface to create depressions called deflation hollows.

Question 10

Name two chief landforms of wind deposition.

Answer

Two chief landforms of wind deposition are sand dunes and loess deposits.

Question 11

Name two chief types of sand dunes.

Answer

Two chief types of sand dunes are-

  1. Barchan
  2. Longitudinal dunes or Seifs

Question 12

State any two characteristics of barchans.

Answer

Two characteristics of barchans are-

  1. They occur transversely to the wind, so that their horns thin out and become lower in the direction of the wind.
  2. The windward side is convex and gentle-sloping while the leeward side is concave and steep.

Structured Questions

Question 1(a)

State the difference between weathering and denudation.

Answer

WeatheringDenudation
Weathering is the process of breaking down of rocks but not its removal.Denudation is the process of breaking and removing the rocks from the surface of the earth.
It is only a part of denudation cycle.It includes weathering, erosion, mass movement and transportation.
Weathering is a short-term process.Denudation is a long-term process.
The main agents of weathering are temperature, moisture, frost action, wind, oxygen, organic acids etc.The four active agents of denudation are water, wind, waves and glacial ice.

Question 1(b)

Name the various processes involved in denudation. What are the results of denudation?

Answer

The various processes involved in denudation are-

  1. Weathering
  2. Erosion
  3. Mass movement or mass wasting
  4. Transportation
  5. Deposition

The results of denudation are the formation of erosional or depositional landforms on the surface of the earth.

Question 1(c)

Give a geographical reason for each of the following:

(i) Erosion is the dominant activity of a river in its upper course.

(ii) Landforms of deposition are more prominent in the middle course of a river.

(iii) All the rivers do not form deltas.

Answer

(i) Erosion is the dominant activity of a river in its upper course because at this stage, the river flows swiftly, for the gradients are steep. Under the impact of rush of water and the load the river carries, erosion action is swift and effective.

(ii) Landforms of deposition are more prominent in the middle course of a river because at this stage, the gradient is reduced and the river flows more slowly. The energy required to transport the materials is just enough to drag large particles and the lateral cutting is more active than down cutting.

(iii) All the rivers do not form deltas because there are certain conditions for the formation of deltas, which include nearly calm sheltered sea, large amount of sediment supply and a reasonable size of the river.

Question 1(d)

Describe the work of wind erosion and state two important landforms of wind erosion.

Answer

Wind picks up loose debris like sand and pebbles and transports as well as deposits them in another location. Wind can lift and carry sand grains away. When the speed of wind slows down, the sediments brought by the wind begin to drop on the ground. This process continues and forms various landforms on the surface of the earth.

Two important landforms of wind erosion are deflation hollows and sand dunes.

Question 2(a)

Briefly describe the factors which affect the work of a river.

Answer

The factors which affect the work of a river are-

1. Velocity of water — Erosion and transportation are both maximum when the velocity of water is high. Deposition takes place when the velocity of water is low.

2. Volume of water — The larger the volume of water, the greater is the power of erosion and transportation. Deposition takes place better when there is reduced volume of water and when the load is greater.

3. Load — The load of the river does all the work of erosion and deposition. Mass wasting, deepening of river valleys and formation of landforms depend on the load a river carries.

Question 2(b)

Describe the three stages of a river.

Answer

The three stages of a river are-

1. Upper course — At this stage, the river flows swiftly, for the gradients are steep. This course generally lies in a hilly area and the river flows a considerable distance over a steep slope.

Along its course, it erodes its bed and banks, and carries large boulders of rock with it. The erosion action is swift and effective. V-shaped valleys and waterfalls are formed in the upper course of the rivers.

2. Middle course — At this stage, the gradient is reduced, and the river flows more slowly. In the middle course of the river, the energy required to transport the materials is just enough to drag large particles.

The lateral cutting is more active and the volume of water in the river increases due to many tributaries joining it. Meanders and oxbow lakes are formed in the middle course of the rivers.

3. Lower course — In this stage, the rover flows sluggishly and makes many landforms. All the ideal conditions for depositional landforms exist but the load-transporting capacity is drastically reduced due to the sluggish flow as well as division of a river into many distributaries.

Deltas are formed in the lower course of rivers.

Question 2(c)

Give a geographical reason for each of the following:

(i) The effects of wind erosion are more pronounced in desert areas.

(ii) Migratory sand dunes are uncertain and dangerous.

(iii) Long rooted trees and sand holding grasses are grown bordering fields near deserts.

Answer

(i) The effects of wind erosion are more pronounced in desert areas since there is little vegetation or moisture to bind the loose surface materials.

(ii) Migratory sand dunes are uncertain and dangerous because when they migrate with the wind, they damage towns and villages.

(iii) Long rooted trees and sand holding grasses are grown bordering fields near deserts to halt the advance of the dunes in order to prevent the fertile land from being devastated.

Question 2(d)

State the factors on which the shape and size of dunes depend?

Answer

The factors on which the shape and size of dunes depend are:

  1. The direction and force of wind.
  2. The speed of wind, carrying the dust and sand particles.
  3. The nature and amount of sand brought by the wind.
  4. Water features like lakes, streams etc., in the close-by area.
  5. The nature of vegetation on the land.
  6. The nature of the surface, where the formation of a sand dune takes place.
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