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Denudation:
Denudation refers to the processes that wear away the Earth’s surface, leading to the reduction in elevation and relief of landforms. It encompasses weathering, mass wasting, and erosion. Weathering, a crucial part of denudation, breaks down rocks at or near the Earth’s surface through physical and chemical processes.
Types of Weathering
A. Physical Weathering: This type involves the mechanical breakdown of rocks without altering their chemical composition.
1. Frost Action: Water seeps into cracks in rocks, freezes, and expands, causing the rock to break apart. This process is common in cold climates where freeze-thaw cycles are frequent.
2. Thermal Action: Temperature fluctuations cause rocks to expand when heated and contract when cooled. Repeated cycles of expansion and contraction can cause the outer layers of rocks to peel off, a process known as thermal stress weathering.
3. Exfoliation: This occurs when rocks formed under high pressure deep within the Earth are exposed at the surface. The release of pressure causes the rock to expand and crack in layers or sheets.
4. Biological Action: Organisms like plants, animals, and microbes contribute to weathering. Plant roots grow into rock cracks, exerting pressure and causing them to split. Animals burrowing can also disturb and break down rock material.
B. Chemical Weathering: This type involves the chemical alteration of the minerals within rocks, leading to their decomposition.
1. Hydrolysis: This reaction involves water and minerals in the rock, leading to the formation of new minerals and the breakdown of the rock. For instance, feldspar minerals can transform into clay minerals through hydrolysis.
2. Oxidation: Oxygen reacts with minerals, particularly those containing iron, to form oxides. This process can weaken the rock, making it more susceptible to further weathering. Rust formation in iron-bearing rocks is a common example.
3. Acid Action: Acids, particularly carbonic acid, play a significant role in weathering. Carbonic acid is a weak acid formed when carbon dioxide dissolves in water, and it is commonly found in rainwater, soil water, and stream water. This acid slowly dissolves some types of minerals, such as calcite in limestone, in a process called carbonation. This leads to the formation of karst landscapes and the creation of features like sinkholes and caves.
