The Earth is a dynamic system changed by internal and external processes. The external (exogenetic) processes are the consequence of solar energy and gravitational forces, whereas the internal processes are an outcome of the Earth's internal heat. This lesson covers weathering and gradation – the work of rivers, underground water, glaciers, wind and sea waves.
1. Weathering
Weathering is the breaking, disintegration and decomposition of materials of the Earth's crust by their exposure to the atmosphere. Its three types are physical, chemical and biological.
Physical Weathering
The breakdown of rocks without changing their chemical composition, through physical forces such as constant freezing and thawing, which cause expansion and contraction.
| Type | Process |
|---|---|
| Exfoliation | Alternate heating and cooling peels rounded rock surfaces layer by layer like an onion; sheeting and shattering are its other forms |
| Granular disintegration | In crystalline rocks the grains become loose and fall out, due to temperature |
| Block disintegration | Repeated expansion and contraction by day and night stresses the joints of rocks |