Adry lake bed, also known as aplaya (/ˈplaɪ-ə/), is a basin ordepression 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 analkali flat. If covered with salt, it is known as asalt flat.
If its basin is primarilysalt, then a dry lake bed is called asalt pan,pan, orsalt flat (the latter being a remnant of asalt lake).Hardpan is the dry terminus of an internally drained basin in a dry climate, a designation typically used in theGreat Basin of the western United States.[citation needed]
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Another term for dry lake bed isplaya. The Spanish wordplaya (pronounced[ˈplaʝa]) 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 theLlano Estacado and other parts of the SouthernHigh Plains and is commonly used to addresspaleolake sediments in theSahara likeLake Ptolemy.
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In South America, the usual term for a dry lake bed issalar orsalina, Spanish forsalt pan.
Pan is the term used in most of South Africa. These may include the small roundhighveld pans, typical of theChrissiesmeer area, to the extensive pans of theNorthern Cape province.
Terms used in Australia includesalt pans (whereevaporite minerals are present) andclay pans.[1]
In Arabic, a salt flat is called asabkha (also spelledsabkhah,subkha orsebkha) orshott (chott). In Central Asia, a similar "cracked mud" salt flat is known as atakyr. InIran salt flats are calledkavir.
A dry lake is formed when water from rain or other sources, like intersection with a water table, flows into a dry depression in the landscape, creating a pond or lake. If the total annual evaporation rate exceeds the total annual inflow, the depression will eventually become dry again, forming a dry lake. Salts originally dissolved in the water precipitate out and are left behind, gradually building up over time. A dry lake appears as a flat bed of clay, generally encrusted with precipitated salts. These evaporite minerals are a concentration of weathering products such as sodium carbonate, borax, and other salts. In deserts, a dry lake may be found in an area ringed bybajadas.
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 ofTexas and easternNew Mexico.[citation needed] Most dry lakes are small. However,Salar de Uyuni inBolivia, nearPotosí, the largest salt flat in the world, comprises 4,085 square miles (10,582 square km).[2]
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 andteepee structure desiccation features. If there is very little water,dunes can form.
TheRacetrack Playa, located inDeath 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 theScripps Institution of Oceanography at theUniversity 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.[3] The stones only move once every two or three years and most tracks last for three or four years.[4]
While a dry lake bed is itself typically devoid of vegetation, they are commonly ringed byshadscale,saltbrush and other salt-tolerant plants that provide critical winter fodder forlivestock and otherherbivores.
In southwestIdaho and parts ofNevada andUtah there are a number of rare species that occur nowhere else but in the inhospitable environment of seasonally flooded playas. A new species ofgiant 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.[5]
Lepidium davisii is another rare species, a perennial plant whose habitat is restricted to playas insouthern Idaho and northern Nevada.[6]
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 cattlefeedlots and dairies. Results are erosion; fertilizer, pesticide and sediment runoff from farms; andovergrazing.[6] 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 is capable of crowding out native vegetation and draining a playa's standing water because of its root growth.
The extremely flat, smooth, and hard surfaces of dry lake beds make them ideal for fast motor vehicles and motorcycles. Large-sized dry lakes are excellent spots for pursuingland speed records, as the smoothness of the surface allows low-clearance vehicles to travel very fast without any risk of disruption by surface irregularities, and the path traveled has no obstacles to avoid. The dry lake beds atBonneville Salt Flats in Utah andBlack Rock Desert inNevada have both been used for setting land speed records.Lake Eyre andLake Gairdner inSouth Australia have also been used for various land speed record attempts. Dry lake beds that rarely fill with water are sometimes used as locations for air bases for similar reasons. Examples includeGroom Lake atArea 51 in Nevada andEdwards Air Force Base (known initially as Muroc Dry Lake) in California.
Brines from the subsurface of dry lakes are oftenexploited for valuable minerals in solution. See, for example,Searles Dry Lake andLithium resources.
Under United States law, a "playa lake" may be considered isolatedwetlands and may be eligible to enroll in the new wetlands component of theConservation Reserve Program, enacted in the2002 farm bill (P.L. 107–171, Sec. 2101).[7]
TheBurning Man yearly event takes place in a playa in theBlack Rock Desert in western Nevada every year.
Fangfang Yao et al (2023),[8] 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.[9]
{{cite journal}}: CS1 maint: multiple names: authors list (link)A temporary lake created in the lowest elevation of a basin in an arid area that has no surface drain into another water body, such as a perennial stream or river. Lake water is removed either by evaporation into the air or seepage into the ground.
