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Radially symmetrical, star dunes are pyramidal sand mounds with slipfaces on three or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes. Star dunes grow upward rather than laterally. They dominate the Grand Erg Oriental of the Sahara

Oval or circular mounds that generally lack a slipface, dome dunes are rare, and these occur at the far upwind margins of sand seas. U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. These dunes are formed from blowout dunes where the erosion of vegetated sand leads to a U-shape




00.11, 24.11.12.   Wik 

causes of sandstorms ... As the force of wind passing over loosely held particles increases, particles of sand first start to vibrate, then to saltate ("leap"). As they repeatedly strike the ground, they loosen and break off smaller particles of which then begin to travel in suspension. At wind speeds above that which causes the smallest to suspend, there will be a population of sand grains moving by a range of mechanisms: suspension, saltation and creep

A recent study finds that the initial saltation of sand particles induces a static electric field by friction. Saltating sand acquires a negative charge relative to the ground which in turn loosens more sand particles which then begin saltating

Gust fronts may be produced by the outflow of rain-cooled air from an intense thunderstorm, or they may represent a dry cold front, that is, a cold front that is moving into a dry air mass and is producing no precipitation. This is the type of dust storm which was common during the dustbowl  years . Following the passage of a dry cold front, convective instability resulting from cooler air riding over heated ground can maintain the dust storm initiated at the front. In desert areas, sand storms are most commonly caused by either thunderstorm outflows, or by strong pressure gradients which cause an increase in wind velocity