Editing Dune (section)

====Barchan or crescentic====
{{main|barchan}}
[[File:Barchan in Noachis.jpg|thumbnail|right|Isolated barchan dunes on the surface of [[Mars]]. Dominant wind direction would be from left to right.]]
Barchan dunes are crescent-shaped mounds which are generally wider than they are long. The lee-side slipfaces are on the concave sides of the dunes. These dunes form under winds that blow consistently from one direction (unimodal
winds).<ref name=dkp>{{cite book|title=The Ultimate Visual Family Dictionary|chapter=Geology, Geography, and Meteorology|page=282–283|publisher=[[DK (publisher)|D.K. Pub.]]|year=2012|location=New Delhi|language=en|isbn=978-0-1434-1954-9}}</ref> They form separate crescents when the sand supply is comparatively small. When the sand supply is greater, they may merge into barchanoid ridges, and then transverse dunes (see below).<ref name=Mangimeli/>

Some types of crescentic dunes move more quickly over [[desert]] surfaces than any other type of dune. A group of dunes moved more than 100 metres per year between 1954 and 1959 in [[China]]'s [[Ningxia Province]], and similar speeds have been recorded in the [[Western Desert (Egypt)|Western Desert]] of [[Egypt]]. The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than three kilometres, are in China's [[Taklamakan Desert]].<ref name="USG Types of Dunes">{{cite web|title=Types of Dunes|url=http://pubs.usgs.gov/gip/deserts/dunes/|access-date=8 March 2012|url-status=live|archive-url=https://web.archive.org/web/20120314161113/http://pubs.usgs.gov/gip/deserts/dunes/|archive-date=14 March 2012 |publisher=[[U.S. Geological Survey]] |date=29 October 1997}}</ref>