Which one of the following is likely to be the most prevalent form of weathering in hot-tropical desert areas?
- (a)Mechanical
- (b)Chemical
- (c)Biological
- (d)Leaching
Correct — A, Mechanical. In hot tropical deserts the most prevalent weathering is mechanical (physical) weathering. The very large difference between day and night temperatures makes rock surfaces expand and contract repeatedly, causing them to crack, flake and disintegrate (thermal or insolation weathering and exfoliation). The scarcity of water suppresses chemical weathering, which needs moisture.
- (b)Chemical — Chemical weathering, such as hydrolysis and carbonation, needs water and is most active in warm, humid climates; deserts are too dry for it to dominate.
- (c)Biological — Biological weathering depends on abundant plant roots and organisms, which are sparse in deserts.
- (d)Leaching — Leaching is the washing-down of soluble minerals by percolating water — a wet-climate process, not a desert one.
Weathering is the in-place breakdown of rock. Physical (mechanical) weathering fragments rock without changing its chemistry, while chemical weathering alters mineral composition and needs water. Climate decides which dominates: hot deserts favour mechanical processes, warm humid regions favour chemical ones.
The tempting wrong answer is chemical, since deserts are hot and heat speeds up chemical reactions. But chemical weathering also needs water, which deserts lack — so the large daily temperature swings make mechanical weathering dominate.
- Mechanical weathering breaks rock physically, without changing its chemistry.
- Large diurnal temperature ranges in deserts drive thermal expansion and contraction, causing exfoliation and granular disintegration.
- Chemical weathering requires moisture, which is scarce in deserts.
- Warm, humid climates — not deserts — favour chemical weathering.
- Choosing chemical weathering because deserts are hot — chemical weathering also needs water, which is lacking.
- Confusing weathering (in-place breakdown) with erosion (removal and transport).
Asks the dominant weathering type in a stated climate — match hot desert to mechanical weathering.
Consider the following statements: Statement-I: Rainfall is one of the reasons for weathering of rocks. Statement-II: Rain water contains carbon dioxide in solution. Statement-III: Rain water contains atmospheric oxygen. Which one of the following is correct in respect of the above statements?
- (a) Both Statement-II and Statement-III are correct and both of them explain Statement-I
- (b) Both Statement-II and Statement-III are correct, but only one of them explains Statement-I
- (c) Only one of the Statements II and III is correct and that explains Statement-I
- (d) Neither Statement-II nor Statement-III is correct
Answer(a) Both Statement-II and Statement-III are correct and both of them explain Statement-I
Same theme — weathering of rocks. That item is about water-driven chemical weathering; this one asks why physical (mechanical) weathering instead dominates in dry deserts.
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
Same concept — mechanical (physical) weathering. That item lists the forces that drive it; this one asks why it is the dominant type in hot deserts.
- practice — not a real PYQ
Chemical weathering is generally most intense in which type of climate?
- (a)Hot and dry
- (b)Warm and humid
- (c)Cold and dry
- (d)Polar
Answer(b) Warm and humid — heat and abundant moisture speed up chemical reactions.
- practice — not a real PYQ
Exfoliation of rocks in deserts is mainly caused by
- (a)heavy rainfall
- (b)large daily temperature changes
- (c)glacial ice
- (d)acid rain
Answer(b) large daily temperature changes — repeated expansion and contraction peel off rock layers.