The breakdown and decay of rocks in situ (in place) at or near the Earth's surface by physical, chemical, and biological action, without large-scale transport of the broken material.
- Physical (mechanical) weathering disintegrates rock without changing its chemistry: frost action (freeze-thaw), exfoliation (peeling of surface layers from heating and cooling), and salt crystallisation.
- Chemical weathering decomposes rock by altering its minerals: oxidation (rusting of iron), carbonation (acidic rainwater dissolving limestone), hydration, and hydrolysis; it is most active in warm, humid climates.
- Biological weathering is by living things: roots prising cracks open, burrowing animals, and acids from lichens.
- Weathering is the first stage that produces the regolith and ultimately soil; it prepares material that erosion then carries away.
- The dominant type depends on climate: physical weathering dominates in cold and arid regions, chemical weathering in hot wet regions.
The physical versus chemical distinction, the named processes (exfoliation, carbonation, oxidation), and the climate control on type are standard geomorphology facts and the basis of soil formation.
Weathering (breakdown in place, no transport) versus erosion (breakdown plus removal and transport); physical (no chemical change) versus chemical (mineral change); carbonation dissolves limestone to form karst features.
In-place breakdown of rock by physical, chemical, and biological action; the first step before erosion and soil formation.