Barchans sand dunes, are crescent-shaped sand dune produced by the action of wind predominately from one direction. One of the commonest types of dunes, it occurs in sandy deserts all over the world.
Barchans are convex facing the wind, with the horns of the crescent pointing downwind and marking the lateral advancement of the sand. These dunes are markedly asymmetrical in cross section, with a gentle slope facing toward the wind and a much steeper slope, known as the slip face, facing away from the wind. Barchans may be 9–30 m (30–100 feet) high and 370 m (1,214 feet) wide at the base.