Physical weathering, also known as mechanical weathering, refers to the process of breaking down rocks into smaller pieces without changing their chemical composition. It typically involves several stages and mechanisms:
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Freeze-Thaw Cycle (Frost Wedging): Water seeps into cracks in the rock. When temperatures drop, the water freezes and expands, exerting pressure on the rock. This repeated freezing and thawing causes the rock to crack and break apart.
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Thermal Expansion and Contraction: Changes in temperature can cause rocks to expand when heated and contract when cooled. This repeated cycle can lead to the development of cracks and eventually break the rock apart, particularly in desert environments where temperature shifts are more extreme.
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Exfoliation: This process occurs when layers or sheets of rock begin to peel away from the underlying rock. It often happens in igneous rocks like granite as a result of a reduction in pressure during erosion or when temperatures change.
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Abrasion: This involves the mechanical scraping or wearing away of rock surfaces as a result of friction from wind, water, or ice carrying sediments. Over time, this can smooth and round the edges of rocks.
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Biological Activity: The growth of plant roots can cause rocks to fracture as the roots expand into cracks, and animals burrowing can also contribute to the physical weathering of rocks.
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Salt Crystal Growth: In arid environments, saltwater can seep into cracks in rocks. As the water evaporates, the remaining salt crystals can grow and expand, exerting pressure on the rock and causing it to break apart.
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Shock and Impact: Physical forces, such as the impact of falling rocks or debris, can cause fracturing and breaking of rocks, contributing to physical weathering.
These processes typically occur simultaneously or in conjunction with chemical weathering, and they significantly contribute to the landscape and soil formation over time.
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