Outwash plains are formed as a result of deposition by meltwater from glaciers or ice sheets. When a glacier or ice sheet melts, it produces large volumes of water that can carry sediment away from the ice margin. This sediment is deposited as the water slows down and spreads out, forming an outwash plain. Outwash plains are typically composed of sand and gravel, but they can also contain silt and clay. They are often found in front of glaciers or ice sheets, and they can extend for many kilometers.