Denudation - Questions & Answers
EXERCISES I. Choose the correct option:1. The process of breaking and removing the rocks from the surface of the earth:
(a) Erosion (b) Mass movement (c) Denudation (d) Weathering
Answer: (c) Denudation
2. Denudation is the process that wears away landmass and reshapes the surface of the earth. Which of the following process is NOT involved in it?
(a) Weathering (b) Erosion (c) Deposition (d) Mass wasting
Answer: (c) Deposition
3. The disintegration of rocks by atmospheric agents at or near the surface of the earth:
(a) Erosion (b) Weathering (c) Mass movement (d) Denudation
Answer: (b) Weathering
4. The displacement of rocks by agents like wind, water or ice:
(a) Deposition (b) Transportation (c) Erosion (d) Mass wasting
Answer: (c) Erosion
5. The large-scale movement of loose materials (rock-waste) down the slope on account of gravity:
(a) Mass movement (b) Deposition (c) Denudation (d) Weathering
Answer: (a) Mass movement
6. Assertion (A): In the upper course the dominant activity of a river is erosion.
Reason (R): The river flows swiftly as the gradient is steep.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
7. The laying down of material that has been weathered, eroded and transported by natural processes such as water, wind and ice.
(a) Physical Weathering (b) Deposition (c) Denudation (d) Tributary
Answer: (b) Deposition
8. The streams or small rivers which join the main river are called:
(a) Transporteries (b) Tributaries (c) Distributaries (d) Meanders
Answer: (b) Tributaries
9. When a river divides into channels or smaller rivers they are called its:
(a) Tributaries (b) Distributaries (c) Meanders (d) Transporteries
Answer: (b) Distributaries
10. Assertion (A): River meanders are bends of longitudinal courses.
Reason (R): Meanders are the result of both erosion and deposition under conditions of a gentle slope and sufficient water in rivers.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (b) Both A and R are true but R does not explain A.
11. In the upper course the dominant activity of a river is:
(a) Valley (b) Meander (c) Erosion (d) Mass wasting
Answer: (c) Erosion
12. In the middle course of a river the gradient is gentle so the flow of the river slows down such that it appears like a snake over its floodplains forming which of the following?
(a) Deltas (b) Gorges (c) Meanders (d) Rapids
Answer: (c) Meanders
13. Barchans are moon-shaped dunes.
(a) Dunes (b) Sand Dunes (c) Barchans (d) Seifs
14. Stationary, long and narrow sand-ridges which grow parallel to the direction of the prevailing wind and remain in a fixed position.
(a) Dunes (b) Sand Dunes (c) Barchans (d) Seifs
Answer: (d) Seifs
15. The lowering of land, rounding of exposed rock surfaces and levelling of the peaks:
(a) Denudation (b) Erosion (c) Mass wasting (d) Deposition
Answer: (a) Denudation
16. Assertion (A): In the lower course of the river all the ideal conditions for depositional landforms exist.
Reason (R): The load-transporting capacity is drastically reduced due to sluggish flow as well as division of a river into many distributaries.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (a) Both A and R are true and R is the correct explanation of A.
17. Which amongst the following is not a factor affecting work of a river?
(a) Velocity of water (b) Quality of water (c) Volume of water (d) Load of water
Answer: (b) Quality of water
18. How do migratory dunes damage towns and villages?
(a) They cover all surfaces with thick layers of sand.
(b) The large mass of sand shifts further.
(c) They can be checked by building walls.
(d) All of the above.
Answer: (a) They cover all surfaces with thick layers of sand.
19. Assertion (A): Barchan are moon-shaped live dunes.
Reason (R): The migration of the barchans is a threat to desert life.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (b) Both A and R are true but R does not explain A.
20. Name the landform that is formed as a result of the action of wind wherein loose materials are lifted and blown off to be deposited outside the desert margins.
(a) Sand Dunes (b) Barchans (c) Deflation Hallows (d) Seifs
Answer: (c) Deflation Hallows
21. See the above figure of a barchan and identify the direction of the wind.
(a) A (b) B (c) Both A and B (d) Neither A nor B.
Answer: (a) A
| Effect on the river | Work of the river | Effect on land | |
|---|---|---|---|
| Young Stage (Upper Course) |
Formation of gorge, rapids and waterfalls. | Mainly erosion. | Formation of V-shaped valleys. |
| Maturity Stage (Middle Course) |
meanders river cliffs |
transportation (some deposition) |
Valley Widening Open, wide gentle-sloping valley |
| Old Stage (Lower Course) |
deltas flood plains ox-bow lakes |
deposition | Alluvium Deposition very gently-sloping, smooth, wide valley |
1. What do you mean by denudation?
Answer: Denudation is the comprehensive process of breaking and removing rocks from the surface of the earth. It refers to the wearing away of landmass by various natural processes like weathering, erosion, mass movement, and transportation, which ultimately results in lowering the level of the land, rounding exposed rock surfaces, and levelling the peaks.
2. Name the factors which affect work of a river.
Answer: The factors that affect the work of a river are: (i) Velocity of water, (ii) Volume of water, and (iii) Load of sediments.
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 or dominant activity of a river in its upper course is erosion (specifically down-cutting). The significant landforms formed in the upper course are V-shaped valleys, gorges, waterfalls, and rapids.
4. How is a waterfall formed?
Answer: A waterfall is generally formed due to large differences in the rate of erosion. When the water flows over the edge of a hard resistant rock that has a soft rock layer at its bottom, the soft rock gets eroded quickly, creating a hollow basin called a plunge pool. This process results in a vertical fall of water of enormous volume from a great height.
5. State the two characteristics of a river in its middle course.
Answer: The two characteristics of a river in its middle course are: (i) lateral cutting (widening) is more active than down cutting, and (ii) the volume of water in the river increases due to many tributaries joining it.
6. How are meanders formed? Give one example of a meander.
Answer: Meanders result from both the erosional and depositional work of rivers. They generally form under conditions of a gentle slope and sufficient water, where the river flow is diverted by an obstruction, allowing it to perform lateral erosion work. An example of meanders can be seen in the Ganga in India and the Mississippi in the USA.
7. Name one landform in the lower course of a river. How is it formed?
Answer: Delta. It is formed when the river divides into many distributaries due to a drastically reduced load-transporting capacity from sluggish flow. This leads to widespread deposition of sediments near the mouth of the river, creating a triangular-shaped formation over a large area.
8. Where is wind erosion most predominant?
Answer: Wind erosion is most predominant in arid and desert regions, as there is little vegetation or moisture to bind the loose surface materials together.
9. What are known as Deflation Hollows?
Answer: Deflation hollows are depressions created by the lowering of the land surface. They are formed when wind lifts and blows away loose surface materials like sands and pebbles from the ground.
10. Name two chief landforms formed by wind erosion.
Answer: The two chief landforms formed by the active erosion, transportation, and depositional work of wind are Deflation Hollows and Sand Dunes.
11. Name two chief types of sand dunes.
Answer: The two chief types of sand dunes found in tropical deserts are: (a) Barchan and (b) Longitudinal Dunes or Seifs.
12. State any two characteristics of barchans.
Answer: (i) They are moon-shaped live dunes that advance steadily before winds that blow from a particular direction. (ii) Their windward side is convex and gently-sloping while the leeward side (sheltered side) is concave and steep.
1. (a) State the difference between weathering and denudation.
Answer: Weathering refers only to the disintegration of rocks by atmospheric agents at or near the surface of the earth without any movement of the resulting particles. Denudation is a much broader process meaning the laying bare of landmasses; it involves breaking and removing rocks through weathering, but also actively includes erosion, mass movement, and transportation.
(b) Name the various processes involved in denudation. What are the results of denudation?
Answer: The processes involved in denudation are Weathering, Erosion, Mass Movement (Mass Wasting), Transportation, and Deposition. The overall result of denudation is the lowering of the level of land, the rounding of exposed rock surfaces, and the levelling of mountain peaks.
(c) Give a geographical reason for each of the following:
(i) Erosion is the dominant activity of a river in its upper course.
Answer: Because the river originates in the hills or mountains, the gradients are very steep. This causes the river to flow swiftly, providing it with immense force for effective erosion under the impact of the rushing water and the load it carries.
(ii) Landforms of deposition are more prominent in the middle course of a river.
Answer: As the river enters the plains in its middle course, the gradient is reduced and the water flows more slowly. The energy is drastically reduced to just enough to drag larger particles, making depositional work more prevalent than erosional down-cutting.
(iii) All the rivers do not form deltas.
Answer: Because delta formation strictly depends on specific ideal conditions that all rivers do not possess, such as a nearly calm sheltered sea, a massive amount of sediment supply, and a reasonable size of the river.
(d) Describe the work of wind erosion and state two important landforms of wind erosion.
Answer: Wind erosion involves the lifting, carrying, and blowing away of loose surface materials like sand and pebbles. It works as an active agent primarily in arid regions. Two important landforms generated by the work of wind are Deflation Hollows and Sand Dunes (like Barchans and Seifs).
2. (a) Briefly describe the factors which affect the work of a river.
Answer: The work of a river depends on: (i) Velocity of water: higher velocity causes maximum erosion and transportation, whereas low velocity causes deposition. (ii) Volume of water: a larger volume increases the power of erosion and transportation. (iii) Load: the material transported by the river does all the work of deepening valleys and shaping new landforms.
(b) Describe the three stages of a river.
Answer: The profile of a river is divided into: (i) Upper Course (Young Stage), where steep gradients cause swift flow leading to dominant vertical erosion and landforms like gorges and waterfalls. (ii) Middle Course (Maturity Stage), where the gradient is gentle, lateral cutting widens the valley, and transportation and initial deposition form meanders. (iii) Lower Course (Old Stage), characterized by sluggish flow, drastically reduced transport capacity, and large-scale deposition resulting in deltas and flood plains.
(c) Give a geographical reason for each of the following:
(i) The effects of wind erosion are more pronounced in desert areas.
Answer: Because there is extremely little vegetation or moisture in desert regions to bind the loose surface materials together against the wind.
(ii) Migratory sand dunes are uncertain and dangerous.
Answer: Because when they migrate with the wind, they can suddenly encroach upon oases, bury palm trees or houses, and inflict heavy damage upon towns and villages.
(iii) Long rooted trees and sand holding grasses are grown bordering fields near deserts.
Answer: They are planted to halt the unchecked advance of shifting sand dunes, thereby protecting the fertile lands and settlements from being buried and devastated.
(d) State the factors on which the shape and size of dunes depend.
Answer: The shape and size of dunes depend on: (a) The direction and force of wind, (b) The speed of wind carrying the dust and sand particles, (c) The nature and amount of sand brought by the wind, (d) Water features like lakes or streams in the close-by area, (e) The nature of vegetation on the land, and (f) The nature of the surface where the dune forms.
3. Given below is a photograph of Purwa Waterfall on the River Tamsa in Madhya Pradesh. Answer the following questions:
(a) What stage is the River Tamsa in to cause formation of this waterfall? Give reasons to support your answer.
Answer: The River Tamsa is in its Upper Course (Young Stage). The reason is that waterfalls are a product of severe vertical erosion which is the dominant activity only in the upper course due to a steep gradient and swift water flow.
(b) What other landforms would a river make in this stage?
Answer: A river would also form V-shaped valleys, gorges, and rapids in this stage.
(c) What landforms would the River Tamsa make in the next stage of its flow?
Answer: In the next stage (Maturity Stage / Middle Course), it would make meanders, river cliffs, and ox-bow lakes.
(d) Besides being a tourist attraction waterfalls are important sources of energy. Elucidate.
Answer: Waterfalls involve an enormous volume of water falling vertically from a great height. The kinetic energy generated by this falling water is immense and is highly valuable for harnessing and generating hydroelectric power.
1. What is the relationship between denudation, weathering and erosion? Give examples to support your answer.
Answer: Denudation is the broad, overall process of wearing away the earth's landmass. It represents the combined effects of both weathering and erosion. Weathering breaks down the rocks statically (e.g., changes in temperature cracking a rock), and erosion acts dynamically to displace those broken rocks (e.g., a river cutting a gorge). Together, weathering provides the loose material, and erosion transports it, resulting in denudation.
2. While travelling from Haridwar to Prayagraj, the course of which river did you follow? List the landforms associated with it along the course you followed.
Answer: You followed the course of the River Ganga. Along this course, associated landforms transition from the upper stage features like gorges, rapids, and V-shaped valleys (around Haridwar) to middle course features like meanders, ox-bow lakes, and broad open valleys (as it reaches Prayagraj).
1. On the outline map of the world mark one of the following in each continent (i) Rivers which form deltas; (ii) Desert.
Answer: (Self-directed map activity for the student based on geography atlas marking.)
2. Prepare a power point presentation on the effects of rising sea levels due to global warming in the world's most populated delta — the Ganga Brahmaputra delta.
Answer: (Self-directed practical activity requiring students to create a presentation detailing coastal flooding and habitat loss.)
3. In this chapter you have studied the action of winds that results in desertification in arid areas. Make a list of activities that could prevent and reverse desertification.
Answer: Activities to prevent and reverse desertification include planting long-rooted trees and sand-holding grasses as windbreaks, reducing overgrazing by domestic animals, conserving ground water reserves, and adopting sustainable irrigation to keep the soil bound together.