Factors determining desert dune type

While most observers recognize four elemental types of desert dunes (longitudinal, transverse, barchan and star 1–3 ) there is little agreement about which factors determine these types. The angular relationships between the resultant of sand shifting winds and both the crest and principal slipfaces of the elemental types have been discussed qualitatively for many decades. These relationships have been quantified but the wide range of dune types that combine the elemental forms, and the juxtaposition of different dune types, show that wind regime is not the only determinant; for example, sand availability has been considered important. We have now quantified the importance of both wind regime and sand availability as determinants of dune type. We show here that the four elemental types occur in areas uniquely defined by both the equivalent sand thickness of sediments held in the dunes and a measure of directional variability of sand-moving winds. Wind strength does not appear to be important, vegetation has an ambiguous role, and the particle size of dune sediments is unimportant.