(a) (i) Define weathering (ii) State two types of weathering (b) Discuss briefly four factors which influence weathering

Answer Details

(a)(i) Definition of weathering: Weathering is the gradual breaking down, disintegration and decomposition of rocks into smaller particles and eventually into soil, in their place of origin (in situ), through the action of physical, chemical and biological agents.

(a)(ii) Two types of weathering:

• Physical (mechanical) weathering
• Chemical weathering

(Biological weathering is a recognised third type.)

(b) Four factors that influence weathering:

1. Temperature: Alternate heating and cooling causes rock minerals to expand and contract at different rates. This sets up stresses that crack and flake the rock, so areas with wide temperature ranges weather faster.
2. Water (rainfall): Water carries out chemical reactions such as hydrolysis, hydration and solution that decompose rock minerals. Rain water also seeps into cracks and, on freezing or through flow, widens them and washes away loosened particles.
3. Living organisms: Plant roots grow into cracks and prise rocks apart, while burrowing animals, lichens, bacteria and decaying organic matter release acids that dissolve and break down the rock.
4. Nature (composition and structure) of the rock: Soft, porous and jointed rocks with easily soluble minerals weather quickly, whereas hard, compact rocks with resistant minerals weather slowly.

Other influencing factors include wind (abrasion and removal of particles) and topography/relief (steep slopes expose fresh rock to rapid weathering).