Wind, water, volcanoes and glaciers cause natural erosion. Accelerated erosion is caused by unusual events, such as earthquakes, cyclones or human activity, like deforestation. The main forms of erosion are soil erosion, fluvial erosion, mass-movement erosion and stream bank erosion. Each form has a different effect on the landscape.
Soil erosion occurs when soil particles wash or blow off the land's surface as a results of rain, blowing wind or when freeze and thaw cycles detach the particles from the surface. Soil erosion is divided into two categories: sheet erosion and wind erosion. Sheet erosion occurs when rain falls on bare or sparsely covered soil, which loosens the fine particles that get carried downhill as runoff. Wind erosion removes the valuable topsoil on the land's surface.
Fluvial erosion occurs when running water gouges shallow channels or deep gullies into the soil. Fluvial erosion is categorized as rill erosion, gully erosion or tunnel gullying. Mass-movement erosion happens when gravity, in conjunction with heavy rain or earthquakes, causes entire slopes to slump, slip or slide. Types of mass-movement erosion include slips, mudslides, earth flows and scree erosion. Steam bank erosion occurs on the banks of waterways, particularly those that experience periodic flooding.