The rocks break and undergo decay under the influence of the atmospheric agencies like wind, sun, frost, water and organisms. This phenomenon is known as weathering. Weathering and erosion act together to lower the mountains and produce sediments. The weathering can be defined as process which tends to break and decompose rocks. It consists of two processes; physical breaking or disintegration and chemical decay or decomposition.
Erosion is a process which destroys the existing rocks and removes the product from the site of destruction. Transport plays important role in erosion. It is usually done by water, wind and ice.
The combined effect of erosion and weathering is called denudation. It results in general wearing down of the surface of earth.
The physical weathering process in which large sheets of rock peel off from an outcrop is known as exfoliation. During this process, reduction in pressure due to removal of overlying rock plays important role. When each slab breaks off, weight from the underlying mass is released and outer layers expand and separate from the rock mass. The process of exfoliation is normally seen in granite and other homogeneous rocks.
If an outcrop of jointed rock is subjected to chemical weathering, the boulders are produced which are rounded shaped. This process of weathering is called spherical weathering. It is similar to exfoliation except that it takes place on much smaller scale. During this process, the minerals in the rock weather to clay and increase in size due to hydration.
In physical weathering, a rock is broken down into smaller pieces without involving any chemical change. It involves application of mechanical forces. The main agents of physical weathering are frost, heating, cooling and organisms.
In chemical weathering or decomposition, the rocks are broken down by chemical decay of minerals. During this process, the sets of chemical reactions act on rocks and change the minerals to more stable forms. The principal agents of chemical weathering are water and organisms.
Biological weathering is type of weathering which involves various activities of living organisms. It can contribute to further degradation of rocks by making them vulnerable to environmental factors which include both biotic and abiotic components.
The rate at which a rock weathers depends on many factors like particle size of rocks, its mineral composition, order of crystallization and climatic factors.
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