Theory question 307
Weathering, Erosion and Mass Movement(a) What is weathering? (b) Explain the following processes of mechanical weathering: (i) frost action; (ii) exfoliation.
Show the model answer
Model answer
(a) Weathering is the breaking down and decay of rocks in their original place by physical, chemical and biological processes.
(b)(i) Frost action: water fills cracks in rock; at night it freezes and expands; the pressure widens the cracks; repeated freezing and thawing splits off angular fragments (scree).
(ii) Exfoliation: in hot deserts rocks heat strongly by day and cool quickly at night; the outer layer expands and contracts more than the inside; stresses create cracks parallel to the surface; outer shells peel off like onion skins, leaving rounded rocks.
Explanation
Mention heating and cooling for exfoliation.