TEST OF PRACTICAL KNOWLEDGE QUESTION (a) Define weathering. (b) ldentiry three factors that affect weathering. (c) Describe the processes of exfoliation.

Answer Details

(a) Definition of weathering

Weathering is the breakdown, decay or disintegration of rocks in situ (at or near the earth's surface) by physical, chemical and biological processes, without the transportation of the resulting materials. It is distinct from erosion, which involves movement of the loosened material.

(b) Three factors that affect weathering

1. Climate: temperature range and moisture control the type and rate; alternate heating and cooling favours physical weathering, while heat and rainfall favour chemical weathering.
2. Nature of the rock (rock type and structure): hardness, mineral composition and the presence of joints and bedding planes determine how easily a rock breaks down.
3. Vegetation and living organisms: plant roots prise rocks apart and decaying organic matter produces acids that attack minerals.

(Relief/slope and time are also acceptable.)

(c) The process of exfoliation

Exfoliation is a form of physical weathering common in hot deserts and tropical regions with large diurnal temperature ranges. The process is:

• By day, intense heating causes the outer surface layer of the rock to expand more than the cooler interior.
• At night the surface cools rapidly and contracts.
• This repeated expansion and contraction sets up stresses between the outer shell and the inner rock, weakening the bond between them.
• In time the outer curved layers peel or flake off like the layers of an onion, a process aided by slight chemical action of dew.
• The result is smooth, rounded rock masses such as exfoliation domes, with the peeling shells accumulating at the base.