Formation
The surface of a dry lake is typically dry, hard and rough during the dry season, but wet and very soft in the rainy season. Dry lakes are generally small, round depressions in the surface of the landscape.
A playa lake is formed when rain fills a round depression in the landscape, creating a small lake. The water is generally freshwater, When all of the water evaporates, a playa is formed. The playa appears as a flat bed of clay, generally encrusted with precipitated salts. These evaporate minerals are a concentration of weathering products that have been left behind. Some examples of evaporite minerals are sodium carbonate, borax, and other salts. Playas are often found in bajadas, a depositional landform of desert environments.
Dry lakes can also form when the water table intersects the surface and water seeps into them.
Dry lakes are typically formed in semi-arid to arid regions of the world. The largest concentration of dry lakes in the world (nearly 22,000) is in the southern High Plains of Texas and eastern New Mexico.
Most dry lakes are small, however Salar de Uyuni in Bolivia, near PotosÃ, the largest salt flat in the world is of 4,085 square miles (10,582 square km).
The Racetrack Playa, located in Death Valley, California, features "sailing stones" that leave linear "racetrack" imprints. The sailing stones are a geological phenomenon found in the playa. The stones slowly move across the surface, leaving a track as they go, without human or animal intervention. They have never been seen or filmed in motion. The stones only move once every two or three years and most tracks last for three or four years.
Many dry lakes contain shallow water during the rainy season, especially during wet years. If the layer of water is thin and is moved around the dry lake by wind, an exceedingly hard and smooth surface may develop. Thicker layers of water may result in a "cracked-mud" surface and "teepee" structure desiccation features. Very little water can result in dune formation.
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