Question 4
- (i)
- List three landforms found in limestone regions.
(ii) Draw a well labeled diagram to show the underground features of a limestone region.
2 Outline three ways by which limestone is beneficial to man.
The question was not so popular among the candidates and their performance was just fair. Quite a good proportion of the candidates who answered the question were able to correctly define weathering as the disintegration or decomposition of rocks in situ by physical chemical or biological processes. However, quite a good proportion of the candidates could not identify correct factors that affect weathering. The factors that affect weathering are:
- temperature changes/climate
- rainfall/moisture/climate
- types /nature of rocks
- living organisms (plants and animals)
- relief/topography
- time
The Description of the processes of exfoliation goes thus:
- Physical/mechanical weathering
- occurs in desert/arid regions
- plutonic rocks are exposed to the surface by erosion
- the removal of the heavy overlying rock materials relax the pressure on the rock
- the rocks expand slightly in volume around the exposed surfaces
- the expansion makes the exposed side weak and more vulnerable to external forces
- expansion causes cracks parallel to the surface
- thin layers on the exposed surface peel off and are called sheeting structures
- the process also involves variations in day and night temperatures
- high temperatures at day causes outer layers of exposed rocks to expand
- expansion of rocks is intense on the outer layers than the inner layers
- drop in temperatures at night causes outer layers of rocks to contract faster than the inner layers
- repeated changes in temperatures cause alternate expansion and contraction
- stress is built up in rocks as a result of the repeated expansion and contraction
- the stress results in the peeling off of the rock in layers
- outer rocks peel off like onion layers/concentric layers and the process is called exfoliation