Weathering - the breakdown of rock and minerals.

Erosion - the movement of these weathered materials.

Physical weathering - the breakdown of rock and minerals by mechanical stress.

Types of Physical Weathering

1. Frost fracture - water gets into cracks in rocks, freezes and expands, causing rocks to crack.

2. Heat expansion - rocks expand when heated and contract when cooled. Different minerals expand and contract at different rates, causing stress along mineral boundaries. Also the outside expands more than the inside.

3. Exfoliation: as internal pressure is released from certain rocks, it can cause layers to split and fall off.

4. Biological weathering can include:

Plant growth: expansion of cracks due to root growth.

Burrowing animals: tunneling by animals can increase the size of existing cracks.

Chemical weathering - breaks down rock with chemical reactions often including water.

Types of Chemical Weathering

1. Solution - rainwater absorbs CO2 , SO2, and other chemicals from the atmosphere along with organic acids from the soil which then reacts with rock and minerals causing some to dissolve and move away.

2. Hydrolysis - carbonic acid reacts with silicates in some rocks leaving a soft clay from which potassium, sodium and magnesium are subsequently leached.

3. Oxidation - the reaction of metallic minerals to oxygen (mainly in water). This results in the formation of oxides, which tend to be softer than the original mineral. For example, rust on iron.

Environmental conditions affect the rate of weathering.Physical weathering will increase in areas that are cold and dry.Chemical weathering will increase in areas that are warm and wet.