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Weathering is the break down of rocks to form sediment.

There are different types of weathering including;


Results in the alteration of the chemical composition of the weathered material due to a reaction which alters:

- the composition of rock minerals
- the volume of the rock
- the strength and coherence of the rock
Examples of this process include Hydration water is added to a rock, weakening its structure and Carbonation weak carbonic acids slowly dissolve rocks such as Limestone


This is the breakdown of rocks and minerals, which remain the same

Examples of this include Freeze / Thaw action: effect of water in cracks, freezing and expanding in volume by around 10% (in fact 9.05%) breaks the rock and Thermal/exfoliation weathering repeated heating and cooling of rocks causes the rock to expand and contract and breakup.


The effect of living things breaking up rocks

Tree roots: as a tree grows, its roots are extended into the ground. As they grow and thicken, rocks are prised apart. Also occurs on a slower, smaller scale by mosses and lichens.

Respiration by plant roots increases carbon dioxide in soil and assists the formation of weak acid as rainwater filters through the soil.

Burrowing animals e.g. moles, fauna break rock, and bring material to the surface

We can measure this by using a visual measure called Rahn's Index of weathering. This shows the various extent to which the stones have been weathered. This is dependent on lithology (rock type), exposure and the time that the stones have been standing.
Biological weathering

1 Unweathered
2 Slightly Weathered - faint rounding of corners of letters
3 Moderately Weathered - rough surfaces, letters legible
4 Badly Weathered - letters difficult to read
5 Very badly Weathered - letters almost indistinguishable
6 Extremely Weathered - no letters left, scaling

Find out more;

Watch this Ice wedging animation

Watch a range of animations on all different types of weathering

Watch how weathering can create minerals

Take a simple quiz