Weathering

Weathering is the gradual breakdown of rocks when they are exposed to the air. Weathering affects surface rocks the most, but water trickling into the ground can weather rocks 200 m down.

The more extreme the climate, the faster weathering takes place, whether the climate is very cold or very hot.

In tropical Africa the basal weather front (the lowest limit of weathering underground) is often 60 m down.

Weathering works chemically (through chemicals in rainwater) , mechanically (through temperature changes) and organically (through plants and animals).

Chemical weathering is when gases dissolve in rain to form weak acids that corrode rocks such as limestone.

The main form of mechanical weathering is frost shattering - when water expands as it freezes in cracks in the rocks and so shatters the rock.

Thermoclastis is when desert rocks crack as they get hot and expand in the day, then cool and contract at night.

Exfoliation is when rocks crack in layers as weight of rock or ice above them is removed.