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A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. [1]
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.
Barrier island – Coastal dune landform that forms by wave and tidal action parallel to the mainland coast; Bay – Recessed, coastal body of water connected to an ocean or lake; Baymouth bar – low and narrow strip of alluvial land made from sand or pebbles
Landform Description Image Dunes: 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]
Dune collisions [5] [6] and changes in wind direction spawn new barchans from the horns of the old ones and govern the size distribution of a given field. [7] As barchan dunes migrate, smaller dunes outpace larger dunes, catching-up the rear of the larger dune and eventually appear to punch through the large dune to appear on the other side.
Aeolian landforms preserved in the formation range from damp sandsheet and lake paleosol (fossil soil) beds to thin, chaotically arranged dune sets to equilibrium erg construction, with dunes 300 to 400 meters (980 to 1,310 ft) wide migrating over still larger draas. The draas survived individual climate cycles, and their interdunes were sites ...
Barrier island contrasted with other coastal landforms. Barrier islands are a coastal landform, a type of dune system and sand island, where an area of sand has been formed by wave and tidal action parallel to the mainland coast. [1] They usually occur in chains, consisting of anything from a few islands to more than a dozen.
Ridge and swale, or in dunal areas dune and swale, is a landform consisting of regular, parallel ridges alternating with marshy depressions. [1] Ridge-and-swale landscapes are most commonly formed by the gradual movement of a beach, for example as a result of gradually fluctuating water levels, or the shifting meanders of a river.