Dune

Mesquite Sand Dunes - Death Valley California

In physical geography, a dune is a hill or ridge of sand, usually deposited by eolian processes (wind) or sometimes by the flow of water. Dune fields cover large parts of some deserts, and some beaches have dunes. Mars has many dunes. Sand dunes have different forms and sizes based on their interaction with the wind. Sometimes they migrate downwind.

Dune Media

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  Dune fields in the Australian desert.

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  Sand dunes of the Empty Quarter to the east of Liwa Oasis, United Arab Emirates

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  Sand hitting sand is more likely to stick; sand hitting a more coherent surface is more likely to bounce (saltation). This exacerbating feedback loop helps sand accumulate into dunes.

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  Isolated barchan dunes on the surface of Mars. Dominant wind direction would be from left to right.

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  Star dunes with a rough pyramidal shape and ridges at Great Sand Dunes National Park and Preserve

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  Schematic of coastal parabolic dunes

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  Reversing dune showing short minor slipface atop the major stoss (upwind) face

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  Dune Nine in Sossusvlei, Namibia, is over 300m high.

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  Coastal dunes covered in grasses around the mouth of the Liver Å river in Denmark

• Newborough Dune Rejuvenation, Wales; video of work done by Natural Resources Wales; 2015

• Sea dune erosion at Talacre, Wales