(a) (i) Define weathering (ii) State two types of weathering
(b) Discuss briefly four factors which influence weathering
Explanation
Weathering is the breaking down of rock masses (rock minerals) into simpler forms through the agents of physical, chemical and biological processes. (a)(i) Types of weathering include: (i) Physical weathering (ii) Chemical weathering. (b) Factors which influence weathering are: 1. Climatic factors: (a) Temperature (b) Rainfall/ Water (c) Wind. 2. biological factors / Living organisms: (a) Man (b) Plant (c) Animals 3. Topography 4. Parent Materials 5. Time.
1. Climate: (a)Temperature: (i) changes in temperature bring about cracks in rocks. (ii) these differences in temperature cause aggregates onerals of which rocks are made up to expand to varying degrees since they have different coefficients or expansion. The rocks are stressed, hence peeled and cracked.
b. Rainfall/Water: (i) when water falls on rocks in form of rain, it moves or transports weathered rock and rock particles down the ground, thereby, exposing unweathered part of the rock to other agents. e.g. temperature changes for further weathering. (ii) The rock particles carried down the rok sides by rainwater are abrassive, thereby, causing mechanical breakdown of rock surfaces which carried along with it rain water down the drain. (iii) in temperate countries and other areas with temperate climate, ice is formed in cracks from water collected in such cracks. Since water increases in volume when it freezes, the ice serves as a wedge, thereby, widening the cracks, and cause promoting rock disintegration. (iv) water dissolves minerals in rocks, thereby, causing weathering. (v) involves the attachment of water molecules to the substance or chemical compound being attacked. This may lead to the weakening of the rock mineral concerned, and in turn, weaken the rock which contains that minerals: leading to its breakdown. Wind is more active in arid regions. (1). It also carnes rock particles which collides against each other, thereby causing abrassions and chipping off of particles
2. Biological factors or living organisms: (i) activities of man e.g.in road construction, mining, farming breakdown rocks physically. (ii) plants contribute immensely to weathering of rocks through their roots. (iii) roots of trees and shrubs growing by the side of rocks or on the rocks, penetrate into cracks in the rocks. These widen and break-down the rocks. (iv) plants' roots exude certain susbtances or chemicals which cause the dissolution of rock minerals. (v) burrowing animals, e.g. earthworms, rodents, e.t.c. cause weathering by their activities.
3. Topography: (i) the gradient of the land affects the velocity of the running water or ice on the rock. (ii) this affects the rates, the force ( pressure) of collision of these particles when they are moved or transported from their original position.
4. Parent Materials: (i). the type of parent material affects the rate of weathering. (ii) softness/hardness of the material affects the rate of weathering.
5. Time: (i) the longer the rocks are exposed to weathering processes, the more the rock will weather