LAND FORMATION In desert

• Mountain ranges influence the development of deserts by creating rain shadows.

• As moisture-laden winds flow upward over the windward slopes, they cool and lose their moisture in the form of rain and snow.
• Dry air descending over the leeward slopes evaporates moisture from the soil.
• The Great Basin, a desert of North America, results from the rain shadow produced by the Sierra Nevada.
• The desert landscape is stark, shaped by wind and, paradoxically, water.
• When rains do come to the desert, the soil, unprotected by vegetation, easily erodes. Canyons called arroyos form where water rushes down from the hills.
• From the eroded angular peaks of more resistant rocks, alluvial fans lead away to deposit large slopes of debris, called bajadas, at the base.
• These slopes level off to form low basins called playas. During the infrequent rains, the basins fill with water.
• The rainwater then evaporates, leaving behind on the surface a layer of glistening salt dissolved from the ground. Such salt lakes are a common feature of some deserts.
• In the Great Salt Lake of Utah, a remnant of an inland sea fed by some inflow of fresh water, evaporation is never complete, but it is sufficient to concentrate salt in the lake water.
• Winds literally sandblast rocks into unusual shapes and also build up dunes. In sandy deserts such as the Sahara and parts of the North American desert, sand dunes are typical features.
• Wind-built mounds of sand can reach heights of more than 200 m (more than 650 ft) in the Sahara, Arabian, and Iranian deserts.
• In deserts where prevailing winds are strong and sand is relatively scarce, as in the coastal deserts of Peru, dunes may take on regular crescent shapes that move continuously across the desert floor.
• Dunes may be longitudinal ridges resulting from winds blowing only in one direction, or they may be star shaped in regions where the wind blows from all directions.