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A dune is a large pile of wind-blown material, typically sand or snow. As the pile accumulates, its larger surface area increases the rate of deposition in a positive feedback loop until the dune collapses under its own weight. This process causes dunes to move in the direction of the wind over time. [6] [7] Death Valley Mesquite Flats sand dunes.
Generally, blowouts do not form on actively flowing dunes because the dunes need to be bound to some extent, for instance by plant roots. These depressions usually start on the higher parts of stabilized dunes on account of the more considerable desiccation and disturbances occurring there, which allows for greater surface drag and sediment ...
Erg Chebbi, Morocco Major dune seas of the Sahara in yellow, Great Sand Sea.Red dashed line shows approximate limit of the Sahara. Sand seas and dune fields generally occur in regions downwind of copious sources of dry, loose sand, such as dry riverbeds and deltas, floodplains, glacial outwash plains, dry lakes, and beaches.
An interdunal wetland, interdunal pond or dune slack is a water-filled depression between coastal sand dunes. It may be formed either by wind erosion or by dunal encroachment on an existing wetland. [1] The wind erosion process involves wind scooping out sufficient sand to reach the water table, and typically occurs behind the first line of ...
The Physics of Blown Sand and Desert Dunes is a scientific book written by Ralph A. Bagnold. [1] The book laid the foundations of the scientific investigation of the transport of sand by wind. [2] It also discusses the formation and movement of sand dunes in the Libyan Desert.
A large dune complex is called a dune field, [7] while broad, flat regions covered with wind-swept sand or dunes, with little or no vegetation, are called ergs or sand seas. [ 8 ] [ 9 ] [ 10 ] Dunes occur in different shapes and sizes, but most kinds of dunes are longer on the stoss (upflow) side, where the sand is pushed up the dune, and have ...
the subscript refers to the sand fraction, s represents the ratio / where is the sand fraction density, () is the RGF as a function of the sand level within the gravel bed, is the bed shear stress available for sand transport and is the critical shear stress for incipient motion of the sand fraction, which was calculated graphically using the ...
Cross-bedding forms during deposition on the inclined surfaces of bedforms such as ripples and dunes; it indicates that the depositional environment contained a flowing medium (typically water or wind). Examples of these bedforms are ripples, dunes, anti-dunes, sand waves, hummocks, bars, and delta slopes. [1]