| barchan dune (bär-kän') A large, crescent-shaped dune lying at right angles to the prevailing wind and having a steep, concave leeward side with the crescent tips pointing downwind. Barchan dunes form on flat, hard surfaces where the sand supply is limited. They can reach heights of up to 30 m (98 ft) and widths of 350 m (1,148 ft). See illustration at dune. |