A - Brachan dunes are crescent shaped. They occur where sand supply is limited and wind direction is fairly constant. Barchans generally form around shrubs or large rocks, which serve as minor barriers to sand transportation. The horns (tips) of barchans point downwind.

B - Transverse dunes occur where sand supply is greater. They form as ridges perpendicular to the prevailing wind direction. The crests of transverse dunes generally are sinuous to very sinuous.

C - Parabolic dunes somewhat resemble barchans. However, their horns point the opposite direction - upwind. Parabolic dunes always form adjacent to blowouts, oval depressions from which come the sandy sediments that form the parabolic dunes.

D - Longitudinal dunes occur in some modern deserts where sand is abundant and cross winds merge to form these high, elongated dunes. They can be quite large, up to 200 km long and up to 100 m high. The crests of longitudinal dunes generally are stright to slightly sinuous.

E - Barchanoid ridge dunes are barchan dunes that form ridges perpendicular to wind direction.

F - Star dunes form when wind blows in many directions.