bar·chan dune 
(bär-kän)
(bär-kän)n.
A crescent-shaped dune, reaching heights of up to 30 meters (98 feet) and widths of 350 meters (1,148 feet), and having a steep, concave leeward side with crescent tips pointing downwind.
[Russian barkhan, barchan dune, from Kazakh barxan; akin to Uyghur bargan, dune that moves.]