The four agents of erosion are water, ice, wind and waves. Each of these agents is able to weather rocks, causing them to break apart after being worn down. Of the four agents of erosion, water is considered to be the most important and commonly occurring.
The most effective form of water in erosion is as running water in a stream or river. However, raindrops can also cause small-scale and large-scale sheet erosion as they pool together. Erosion caused by wind is typically found in desert areas where it shifts sand and wears down rocks. Ice erosion occurs through the movement of glaciers, which wears down and freezes surfaces over which it travels. Waves cause erosion at the coasts as they erode rock and sand through pure energy and chemical composition.