Barkhan

A barkhan (also spelled barchan or barkhane) is a crescent-shaped sand dune produced by the action of wind predominately from one direction. Barkhans are common in sandy deserts all over the world and on Mars. They are characterized by a gently sloping windward side and a steep, concave slipface on the leeward side. The "horns" or arms of the crescent point downwind, indicating the direction of sand movement.

Barkhans typically form where there is a limited supply of sand, a relatively flat, hard ground surface, and a consistent wind direction. The size of a barkhan can vary greatly, ranging from a few meters to hundreds of meters in height and width.

The formation process begins with a small obstacle on the desert surface that disrupts the wind flow, causing sand to accumulate. As the sand pile grows, the wind scours the windward side, carrying sand grains over the crest to the slipface. Sand then avalanches down the steep slipface, resulting in the downwind migration of the dune. The shape of the crescent is a result of the faster movement of sand at the dune's edges (horns) where there is less resistance.