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A dry lake bed, also known as a playa (), is a basin or depression that formerly contained a standing surface water body, which disappears when evaporation processes exceed recharge. If the floor of a dry lake is covered by deposits of alkaline compounds, it is known as an alkali flat. If covered with salt, it is known as a salt flat.
Another term for dry lake bed is playa. The Spanish word playa () literally means "beach". Dry lakes are known by this name in some parts of Mexico and the western United States. This term is used e.g. on the Llano Estacado and other parts of the Southern High Plains and is commonly used to address paleolake sediments in the Sahara like Lake Ptolemy.
In South America, the usual term for a dry lake bed is salar or salina, Spanish for salt pan.
Pan is the term used in most of South Africa. These may include the small round highveld pans, typical of the Chrissiesmeer area, to the extensive pans of the Northern Cape province.
Terms used in Australia include salt pans (where evaporite minerals are present) and clay pans.Twidale, C.R. & Campbell, E.M. (2005, revised edition): Australian landforms: understanding a low, flat, arid and old landscape. Rosenberg Publishing. Pp. 227, 235, 237, 239.
In Arabic, a salt flat is called a sabkha (also spelled sabkhah, subkha or sebkha) or shott ( chott). In Central Asia, a similar "cracked mud" salt flat is known as a takyr. In Iran salt flats are called kavir.
Dry lakes are typically formed in semi-arid to arid regions of the world. The largest concentration of dry lakes (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 Potosí, the largest salt flat in the world, comprises 4,085 square miles (10,582 square km). "Uyuni Salt Flat" ''Encyclopædia Britannica
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 bed 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. If there is very little water, can form.
The Racetrack Playa, located in Death Valley, California, features a geological phenomenon known as "sailing stones" that leave "racetrack" imprints as they slowly move across the surface without human or animal intervention. These rocks have been recently filmed in motion by the Scripps Institution of Oceanography at the University of California, San Diego and are due to a perfect coincidence of events. First, the playa has to fill with water, which must be deep enough to form floating ice during winter, but still shallow enough that the rocks are exposed. When the temperature drops at night, this pond freezes into thin sheets of "windowpane" ice, which then must be thick enough to maintain strength, but thin enough to move freely. Finally, when the sun comes out, the ice melts and cracks into floating panels; these are blown across the playa by light winds, propelling the rocks in front of them. The stones only move once every two or three years and most tracks last for three or four years.
In southwest Idaho and parts of Nevada and Utah there are a number of rare species that occur nowhere else but in the inhospitable environment of seasonally flooded playas. A new species of giant fairy shrimp was found in 2006. Although a large predatory species, it evaded detection because of the murkiness of the playa's water caused by winds and a fine clay load. This shrimp species is able to regenerate using tiny undetectable cysts that can remain in a dry lake bed for years until conditions are optimum for hatching.
Lepidium davisii is another rare species, a perennial plant whose habitat is restricted to playas in southern Idaho and northern Nevada.
Far from major rivers or lakes, playas are often the only water available to wildlife in the desert. Antelope and other wildlife gather there after rainstorms to drink.
Threats to dry lakes include pollution from concentrated animal feeding operations such as cattle and dairies. Results are erosion; fertilizer, pesticide and sediment runoff from farms; and overgrazing. A non-native shrub that has been used for rangeland restoration in the west, Kochia prostrata, also poses a significant threat to playas and their associated rare species, as it capable of crowding out native vegetation and draining a playa's standing water because of its root growth.
from the subsurface of dry lakes are often solution mining for valuable minerals in solution. See, for example, Searles Dry Lake and Lithium resources.
Under United States law, a "playa lake" may be considered isolated and may be eligible to enroll in the new wetlands component of the Conservation Reserve Program, enacted in the 2002 farm bill (P.L. 107–171, Sec. 2101).
The Burning Man yearly event takes place in a playa in the Black Rock Desert in western Nevada every year.
Fangfang Yao et al (2023), at the University of Virginia reported that more than half of the world's large lakes are drying up. They assessed almost 2,000 large lakes using satellite measurements combined with climate and hydrological models. They found that unsustainable human use, changes in rainfall and run-off, sedimentation, and rising temperatures have driven lake levels down globally, with 53% of lakes showing a decline from 1992 to 2020.
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