Unloading And Expansion
Removal of overlying rock load because of continued erosion causes vertical pressure release with the result that the upper layers of the rock expand producing disintegration of rock masses. Fractures will develop roughly parallel to the ground surface. In areas of the curved ground surface, arched fractures tend to produce massive sheets or exfoliation slabs of rock.
- Exfoliation sheets resulting from expansion due to unloading and pressure release may measure hundreds or even thousands of meters in horizontal extent. Large, smooth rounded domes called exfoliation domes result due to this process.
TEMPERATURE CHANGES AND EXPANSION
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With a rise in temperature, every mineral expands and pushes against its neighbour and as temperature falls, a corresponding contraction takes place.
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Because of diurnal changes in the temperatures, this internal movement among the mineral grains of the superficial layers of rocks takes place regularly.
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This process is most effective in dry climates and high elevations where diurnal temperature changes are drastic. These movements are very small still they make the rocks weak due to continued fatigue.
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The surface layers of the rocks tend to expand more than the rock at depth and this leads to the formation of stress within the rock resulting in heaving and fracturing parallel to the surface.
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Due to differential heating and resulting expansion and contraction of surface layers and their subsequent exfoliation from the surface results in smooth rounded surfaces in rocks. In rocks like granites, smooth-surfaced and rounded small to big boulders called tors form due to such exfoliation.