Geomorphic Processes: Weathering & Erosion – NDA Geography PYQs

Consider the following statements:

1. Crystallisation is a form of mechanical weathering.
2. Hydration causes granular disintegration.
3. Frost action is synonymous with freeze-thaw action.

Which of the statements given above are correct?
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

Answer: (c) 1 and 3 only
Statement 1 is correct — crystallisation of minerals inside rock pores physically stresses the rock and is a mechanical weathering process. Statement 2 is wrong — hydration causes chemical change in minerals (they absorb water and change structure), not granular disintegration which is a physical process. Statement 3 is correct — frost action and freeze-thaw action describe the same process of water freezing and expanding in rock cracks.

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Question 2 [NDA 2014-I]
Statement I: Chemical weathering processes are found more active in hot and humid environment.
Statement II: High temperature and rainfall help in the process of decomposition of rocks.

(a) Both true and II explains I
(b) Both true but II does not explain I
(c) I true but II false
(d) I false but II true

Answer: (a) Both true and II explains I
Chemical weathering requires both water (for chemical reactions) and heat (to speed up reactions). Hot and humid climates provide both — making chemical weathering most vigorous there. Statement II correctly explains why Statement I is true.

Question 3 [NDA 2014-I]
Why is hydrolysis an effective form of chemical decomposition of bedrock in humid tropics?

1. Humid tropics experience high temperature and humidity.
2. There is high diurnal range in temperature.

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Answer: (a) 1 only
High temperature and humidity both accelerate hydrolysis — the chemical reaction between water and minerals. The humid tropics are effective for hydrolysis because of these two factors. The diurnal (day-night) temperature range in the tropics is actually LOW — tropical regions have consistently warm temperatures throughout the day and night.

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Question 4 [NDA 2018-I]
Chemical weathering of rocks is much greater in a place with:
(a) Cold and dry climate
(b) Hot and humid climate
(c) Hot and dry climate
(d) Cold and humid climate

Answer: (b) Hot and humid climate
Chemical weathering needs both heat (to speed up chemical reactions) and water (for solution, hydrolysis, oxidation, and carbonation). Hot and humid climates provide the maximum of both. Hot and dry climates have heat but lack water. Cold and humid have water but lack heat.

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Question 5 [NDA 2018-II]
Which one of the following is not a process of chemical weathering?
(a) Solution
(b) Carbonation
(c) Oxidation
(d) Exfoliation

Answer: (d) Exfoliation
Exfoliation is a physical (mechanical) process — the outer layers of rock peel off due to temperature changes, without any change in chemical composition. Solution, carbonation, and oxidation are all chemical weathering processes that change the mineral composition of rocks.

Question 6 [NDA 2019-I]
Which one of the following is an example of Salt-Crystal growth?
(a) Chemical weathering
(b) Physical weathering
(c) Biological weathering
(d) Bio-chemical weathering

Answer: (b) Physical weathering
Salt crystal growth (haloclasty) is physical weathering — the growing salt crystals mechanically push rock apart without changing the rock’s chemical composition. The pressure from crystal growth causes cracks to widen and fragments to break off.

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Question 7 [NDA 2021-I]
The process whereby certain minerals absorb water, expand and change is called:
(a) Hydration
(b) Oxidation
(c) Hydrolysis
(d) Carbonation

Answer: (a) Hydration
Hydration is the absorption of water molecules into the crystal structure of minerals, causing them to expand and change their chemical properties. Hydrolysis is different — it involves water chemically reacting with and breaking down mineral bonds. These two processes are distinct.

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Question 8 [NDA 2022-I]
While travelling to a hilly region, you notice a massive boulder which was loosened by heavy rains and moved downhill. This has resulted due to which of the following processes?

1. Mass wasting
2. Erosion
3. Weathering

(a) 1 only
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1, 2 and 3

Answer: (a) 1 only
The downhill movement of the boulder under gravity is mass wasting. Heavy rain may have contributed to loosening (weathering effect), but the movement itself is driven by gravity acting directly — which is the definition of mass wasting. Erosion requires a transporting agent (water, wind, ice) actively carrying material — gravity alone moving a boulder is mass wasting.

Question 9 [NDA 2022-I]
Which of the following statements in respect of landslides are correct?

1. These occur only on gentle slopes during rain.
2. They generally occur in clay-rich soil.
3. Earthquakes trigger landslides.

(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3

Answer: (c) 2 and 3 only
Statement 1 is wrong — landslides occur on steep slopes, not gentle ones. Gentle slopes are less susceptible to landslides. Statement 2 is correct — clay-rich soil becomes very weak and slippery when saturated with water, making it prone to sliding. Statement 3 is correct — earthquakes shake unstable slopes and trigger landslides frequently.

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Question 10 [NDA 2022-I]
Consider the following features about a geographical phenomenon:

1. Torrents of snow and ice roaring down a steep mountain side.
2. It is hazardous to skiers and mountaineers.
3. It involves a mix of falling, rolling, sliding and flowing of materials.

Which of the following phenomena can be identified with the above features?
(a) Slump and earthflow
(b) Avalanche
(c) Landslide
(d) Rockslide

Answer: (b) Avalanche
All three features describe an avalanche — the rapid downward movement of snow and ice on a steep mountain slope. Landslides involve rock and soil. Slumps involve rotational movement. Avalanches specifically involve snow and ice and are the characteristic hazard of alpine environments.

Question 11 [NDA 2022-I]
Weathering, mass wasting, erosion and transportation are indicators of which one of the following processes?
(a) Denudation
(b) Endogenetic process
(c) Diastrophism
(d) Mountain building

Answer: (a) Denudation
Denudation is the collective term for all surface processes that wear down and lower the Earth’s surface. It includes weathering (breaking down), mass wasting (gravity movement), erosion (transport by agents), and transportation (moving material to lower areas). Endogenetic processes build up the surface rather than wearing it down.

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Question 12 [NDA 2022-II]
Which of the following is most likely to be the most prevalent form of weathering in hot-tropical desert areas?
(a) Mechanical
(b) Chemical
(c) Biological
(d) Leaching

Answer: (a) Mechanical weathering
Hot deserts have very little water, so chemical weathering — which requires water — is limited. But they have extreme daily temperature variation — very hot during the day and cold at night. This repeated thermal expansion and contraction breaks rocks apart mechanically without any chemical change.

Question 13 [NDA 2025-I]
Which of the following is/are the applied forces in mechanical weathering process?

1. Gravitational force
2. Expansion force
3. Force due to water pressure

(a) 1 only
(b) 1 and 2 only
(c) 2 and 3 only
(d) 1, 2 and 3

Answer: (d) 1, 2 and 3
All three forces operate in mechanical weathering. Gravity causes mass movement of loosened rock fragments. Expansion forces arise from freeze-thaw action, salt crystal growth, and thermal expansion. Water pressure in cracks contributes to crack widening. All three are legitimate mechanical forces.

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Practice Question 1 (Important for NDA)
Statement I: The hills with dense vegetation cover do not experience heavy soil erosion.
Statement II: The vegetation cover helps infiltration of rainwater and binding of soils.

(a) Both true and II explains I
(b) Both true but II does not explain I
(c) I true but II false
(d) I false but II true

Answer: (a) Both true and II explains I
Dense vegetation reduces soil erosion in two ways — plant roots bind the soil and prevent it from being washed away, and vegetation cover slows down rainwater, allowing more infiltration and reducing surface runoff. Statement II correctly explains why Statement I is true.