Forvitring

Forvitring, or weathering, is the breakdown and chemical alteration of rocks and minerals at or near the Earth’s surface. It occurs in place (in situ) and contrasts with erosion, which removes and transports weathered material by wind, water, or ice. Weathering is a key process in soil formation and in the long-term cycling of elements between the lithosphere and biosphere.

Weathering is commonly divided into physical (mechanical) weathering, chemical weathering, and biological weathering. Physical weathering breaks rocks into smaller pieces without changing their mineral composition, through processes such as freeze–thaw cycles, thermal expansion and contraction, pressure release (unloading), and abrasion. Chemical weathering alters the minerals themselves via reactions with water and atmospheric gases; common processes include dissolution (for example, carbonic acid dissolving limestone), hydrolysis (feldspars turning into clays), and oxidation of iron-bearing minerals. Biological weathering involves organisms and their byproducts, such as plant roots growing into cracks, lichens producing acids, and microbial activity, which can both physically disrupt and chemically alter rocks.

The rate and extent of forvitring depend on climate (temperature and moisture), rock properties (mineralogy, grain size, existing fractures), topography, and time. Warmer, wetter conditions generally accelerate chemical weathering, while mechanical weathering can dominate in cooler or drier settings where cracks and fractures are more effectively exploited. The products of weathering include clays and oxides, dissolved ions enriching soils and waters, and altered rock masses that contribute to soil horizons and regolith. Weathering drives landscape evolution, soil formation, and the availability of nutrients in ecosystems.