barchan

1. (geology, also attributive) An arc-shaped shifting sand dune comprising well-sorted (uniformly sized) sand.Examples: "The sand is usually very well sorted in barchans, for it is constantly re-worked as the dune 'marches'. The marching also causes cross-bedding inside the barchan, with a dip parallel to the sand-fall face."; "But to follow the dunes around the foot of their slopes is also tedious and one can walk for half a kilometre east or west, finding one barchan linked to another and no easy way through, and the unverifiable suspicion grows that one has been driven by insensible curves actually southwards."; "The structure out here was revealed immediately—desert punctuated by oases in a geography of cruelty, barkhans or traveling sand-dunes a hundred feet high, which might or might not possess consciousness, […]"alsoattributive