Weathering refers to the in-situ disintegration and decomposition of rocks at or near the Earth’s surface. It is classified into three types: physical weathering, chemical weathering, and biological weathering.
Physical weathering, also known as mechanical weathering, involves the breakdown of rocks without altering their chemical composition. Key mechanisms include thermal expansion and contraction, where temperature fluctuations cause rocks to expand during the day and contract at night, leading to stress and fractures. This is prominent in arid regions like the Thar Desert. Frost action occurs in temperate or high-altitude areas, where water seeps into rock cracks, freezes, and expands, exerting pressure on the rock. This process is significant in the Himalayas. Salt crystallization involves the growth of salt crystals in porous rocks, common in coastal regions like Gujarat and Tamil Nadu, where saline groundwater evaporates, leaving salts that wedge apart mineral grains.
Chemical weathering alters the chemical composition of rocks through reactions with water, oxygen, and acids. Oxidation occurs when minerals like iron react with oxygen, leading to rust-like deposits, as seen in lateritic soils of Karnataka and Odisha. Hydrolysis involves the reaction of minerals with water, forming new compounds; for example, feldspar in granite weathers into clay minerals. Carbonation is the reaction of carbonate rocks like limestone with carbonic acid (formed when CO2 dissolves in water), leading to the creation of karst landscapes such as the Krem Liat Prah caves in Meghalaya. Acid rain, caused by industrial emissions, accelerates chemical weathering in urban areas, damaging historical monuments like the Taj Mahal.
Biological weathering results from the activities of living organisms. Plant roots grow into rock fractures, exerting pressure and splitting rocks—a process common in the Western Ghats. Burrowing animals like earthworms and termites expose rocks to further weathering. Lichens and microorganisms secrete organic acids that dissolve minerals, contributing to soil formation. Human activities such as mining and deforestation also accelerate biological weathering by disturbing rock structures.