Explain the following processes of weathering:

KCSE Geography Paper 1 2012 Section B Question 8.

(a) Explain the following processes of weathering:
(i) hydration; 
(ii) oxidation; 
(iii) frost action. 

• (i) Hydration: In hydration certain rock minerals absorb water and expand.
• This causes internal stress in the rock and it eventually disintegrates. 
• (ii) Oxidation: Oxidation takes place in rocks that contain iron.
• The iron combines with oxygen forming iron oxides/Ferric oxide
• Such rocks change colour and crumble easily. 
• (iii) Frost action
•  In temperate/high mountain areas, water may occupy services/cracks in the rocks during the day.
•  At night the temperatures drop below freezing point causing the water to freeze/expand, exerting pressure in the cracks.
•  During the day, temperatures rise, causing the ice to melt thus releasing pressure in the cracks.
•  This alternate freeze-thaw action weakens the rock causing it to disintegrate.

(b) Describe how an exfoliation dome is formed.

• In arid/semi arid areas, there is large diurnal ranges of temperature.
• During the day, a homogenous rock is intensely heated/at night, the rock looses heat rapidly.
• The differential heating causes the outer layer to expand/contract faster than the inner layer.
• When this expansion and contraction takes place repeatedly, stress develops in the outer layer of rocks. Cracks appear on the surface layer.
• Eventually, the outer layer peels off.
• The peeling off leaves behind a rounded mass of rock known as exfoliation dome.

​(c) Explain three physical factors that enhance movement of materials along a slope due to gravity.

Nature of materials.

• Heavy and large materials move faster on a slope as they are more likely to be overcome by gravity/thinly bedded layers have a tendency to move faster.

Angle of slope.

• The steeper the slope, the faster the rate of movement/where rocks are dipping steeply, movement is faster.

Climatic factors/amount of water.

• The more saturated the rock/soil/materials is, the more likely it is to move as water adds weight and lubricates/alternate freezing and thawing encourages movement.

Vegetation cover

• Bare surfaces are more likely to experience mass wasting because there is no vegetation to bind the materials together. .

Earth movements.

• Earthquakes/volcanic eruptions/isostatic adjustments cause vibrations which may trigger widespread movement of weathered rock materials.

​(d) (i) Give two processes of rapid mass movement. 

• landslides/slumping/rockslide/rockfall/debris slide/debris fall/avalanche
•  mudslides/mudflow
•  Earthflows/earthslide 

​(ii) State four indicators of occurrence of soil creep in an area.

• Telephone/fence poles that are inclined down a slope/bent tree trunks.
•  Accumulated soil at the foot of a sloop/behind obstacles such as walls.
•  Existence of bare rock/exposed upper slope.
•  Presence of a ribbed/stepped pattern across the slope.
•  Presence of dipped rock strata in the direction of the slope.
•  Presence of overhanging banks above roads/rivers.
•  Presence of slope retreat.

​Related Geography Searches on external land forms, weathering Form 3 Level

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