 ¡@ ¡@ SandStorm along the Mohave River near Daggett, California, October 24, 1919 (photo. by D.G. Thompson) From USGS ¡@ Violent wind forms the sandstorms that can block the source of sunlight, cover up the roads, oases or wells. A sandstorm starts with a mist of suspended dust and sand. When the mist clears up, the heavy particles move like a think carpet over the desert close to the ground. The air above the " carpet" is clear, where heads of people appear as walking in water. The sand blast effect is greatest at ground level and insignificant above 18 inches (46cm). The sand storms can last for many hours or days. It may cause suffocation and dehydration of animals and humans. As the sand grains move along by wind, they attack the rock surfaces. Softer parts are eroded first, resulting in a mushroom shape or various strange shapes. In sandy deserts, dunes are created by wind action. At the boundaries, the sand layer is irregular and shallower. Right: Delicate Arch, Arches National Park, Utah (photo. by Peter Kresan) From USGS |
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  Crescentic dunes (also know as barchans and transverse dunes) are wider than long, They are formed by unidirectional wind. ¡@ Left: Algodunes Sand Sea of southeastern California. The dunes can move as much as 5m per year. (photo. by Peter Kresan) From USGS Right: The crescentic dunes of coastal Peru are moving to the left. (photo. by John McCauley) From USGS |
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 Star dunes are formed from multidirectional winds. The dunes grows upwards instead of laterally. (photo. by George Gerster) From USGS |
 Linear dunes are sand
ridges with much longer lengths than the widths. They maybe 160 km long, occur as isolated
ridges. Some merge to form Y-shaped compound dunes by bidirectional wind.(photo. by Carol Breed) From USGS ¡@ |
 Sand dunes in Death Valley, California (photo. by Richard Frear) From USGS |
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