Wind
A sand dune is a deposit of wind-blown sand. Wind causes erosion by deflation and abrasion. Deflation is the process by which wind removes surface materials. Abrasion by wind-carried sand can polish rock, but causes little erosion. All of the sediment picked up by wind eventually falls to the ground. Wind erosion and deposition may form sand dunes and loess deposits. Wind-deposited sediment is loess ( les ). Sediment that is finer than sand, such as particles of clay and silt, is sometimes deposited in layers far from its source. Many area with thick loess deposits are valuable farmlands.