Erosion is the physical removal and transport of material by mobile agents such as water, wind, ice, waves, and gravity. The four common agents of erosion are:

• Water: Water is the most efficient and effective agent for erosion. Erosion by water commonly occurs in two different geologic settings: coastlines and streams/rivers. Erosion on coastlines is due to the action of ocean currents, waves, and tides. Erosion along streams and rivers commonly occurs along the bank of the stream. A stream is any size channelized body of running water.

• Wind: Wind is a very powerful erosional agent. Wind erosion, or aeolian erosion, occurs when strong winds knock soil or rock particles loose and blow them somewhere else. This type of erosion is responsible for creating landscape features such as sand dunes, ventifacts, and desert varnish.

• Ice: Ice is another agent of erosion. Most glaciers erode the land beneath them by plucking and abrasion. Plucking occurs when meltwater penetrates the cracks in rocks and freezes, causing the rock to break off. Abrasion occurs when rocks and sediment carried by the glacier scrape against the bedrock, smoothing and polishing it.

• Gravity: Gravity and mass movement are also agents of erosion. Gravity can cause landslides, rockfalls, and other types of mass movement that can transport large amounts of sediment downhill.

These agents of erosion are mobile at the Earth’s surface and are responsible for the transport of sediment. Erosion and mass wasting appear to be similar processes but have distinctly different causes. The movement of sediment by erosion requires mobile agents such as water, wind, and ice. That is, the sediment is transported by the movement of the agents.