Erosion is the process of the movement of materials from one place to another, and generally occurs when the material is exposed to ice, water or wind, and gravity.
Weathering is a process by which rocks and minerals are gradually broken down into smaller and smaller particles.
Weathering of rocks is caused by chemical and mechanical means. Slightly acidic rainwater can react with rock surfaces, dissolving them over time. Rocks can also be affected by organic sources of chemical reactants. Heat from the sun can cause differences in temperature between the surface and the interior of a rock which can cause a loosening of the surface called exfoliation. Liquid water penetrates cracks in the rocks surface where it can freeze and expand, opening up the cracks for further attack in tandem with acidic rainwater. Plant root growth can also cause cracks to further expand, making them more vulnerable to frost expansion and chemical attack. Underlying rock which is exposed due to erosion of the overlying rock becomes free of the pressure it was previously exposed to, causing the rock to expand and break apart. Other means of weathering include the expansion of crystallizing salts that have been taken in by a rock surface, expansion due to the absorption of water, and hydraulic action from crashing waves on seashore rock formations.