Discussion
Which of these is an example of physical rather than chemical weathering?
Answer: D
Correct answer: Frost shattering of rock
Frost shattering is physical, or mechanical, weathering: rock is broken into smaller pieces with no change in its chemical composition. Water seeps into a crack, freezes, and expands by about nine per cent, prising the crack wider; repeated cycles split the rock apart. It is most effective where temperatures cross freezing point frequently, as on high mountains, and produces the scree slopes below cliffs. The other three are chemical processes, which alter the minerals themselves. Carbonation dissolves limestone in weakly acidic rainwater, creating caves and karst; oxidation rusts iron-bearing minerals and gives lateritic soils their red colour; and hydrolysis converts feldspar into clay, which is the commonest chemical reaction in the crust. The two reinforce each other: physical weathering breaks rock into fragments and so multiplies the surface area available for chemical attack. Physical weathering dominates in cold and arid climates, chemical in hot and humid ones.
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