Dry lake

For other uses, see Dry Lake (disambiguation).

File:Hows-e Sultan.jpg

Namak Lake, Qom Province, Iran

A dry lake is an ephemeral lakebed, or a remnant of an endorheic lake. Such flats consist of fine-grained sediments infused with alkali salts. Alternative names for the dry lake include alkali flat, alkali sink and playa.

A playa lake may cover a wide area, but it is never deep. Most water in it evaporates, leaving a layer of salt on the surface. These salt covered stretches are called saltpans.

If its basin is primarily salt then the dry lake is called a salt pan, pan, hardpan, or salt flat (the latter is a remnant of a salt lake). Other dry lake types include the sabkha and the mudflat.

Terminology

File:Tunisia 10-12 - 141 - Salt Flats (6609472321).jpg

The Chott el Djerid in Tunisia

The Spanish word playa (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 also used on the Llano Estacado and other parts of the Southern High Plains.

In South America, the usual term for a dry lake 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, which are sometimes employed for land speed record attempts. It is also used in Australia. Distinguished are salt pans and clay pans.

Hardpan is a dry terminus of an internally drained basin in a dry climate, typically used in the Great Basin of the western US.

In Arabic, an alkali 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.

Formation

Salt harvesting in Salar de Uyuni, Bolivia, the world's largest salt flat

File:2006 1205 135618-DVNP-RACETRACK.jpg

Sailing stone in Racetrack Playa

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 water from rain or other sources flows into a dry depression in the landscape, creating a pond or lake. If the total annual evaporation rate exceeds the total annual inflow, at some time the depression will become dry again, forming a playa. Salts dissolved in the water remain and gradually build up over time. The playa appears as a flat bed of clay, generally encrusted with precipitated salts. These evaporite minerals are a concentration of weathering products that have been left behind. Some examples of evaporite minerals are sodium carbonate, borax, and other salts. In deserts, a playa may be found in an area ringed by bajadas.

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 Potosí, 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. These rocks have been recently filmed in motion by the Scripps Institution of Oceanography at UC San Diego and are due to a perfect concatenation 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.

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.

Ecology

While the dry lake itself will typically be devoid of vegetation, they are commonly ringed by shadscale, saltbrush and other salt-tolerant plants that provide critical winter fodder for livestock and other herbivores.

File:Seasonally flooded playa in SW Idaho.JPG

Playa in southwest Idaho, home to a number of rare species that occur nowhere else including Lepidium davisii (Davis' peppergrass) and Branchinecta raptor - a recently discovered giant fairy shrimp.

In southwest Idaho and parts of Nevada and Utah are a number of rare species that occur nowhere else but the inhospitable environment of seasonally flooded playas. A new species of giant fairy shrimp was found in 2006- and though a large predatory species- it evaded detection because of the playa's murkiness when filled because of winds and fine clay. It is also a species able to regenerate using tiny undetectable cysts that can remain in a dry lake bed for years until conditions are optimum for the species to hatch.

Lepidium davisii is another rare species- a perennial plant- whose habitat is restricted to playas in southern Idaho and northern Nevada.

Oftentimes in the desert this is the only available water to wildlife away from major rivers or lakes, antelope and other wildlife take advantage of close by playas for drinking water after rainstorms.

Threats to dry lakes include pollution from concentrated animal feeding operations such as cattle feedlots and dairies, 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, capable of crowding out natives and draining a playa's standing water because of root growth and the Kochia plants' use of it when available.

Human use

The Mosaic Company chemical plant processes brines from Searles Dry Lake to make such products as trona

The extremely flat, smooth and hard surfaces of dry lakes make them ideal for motor vehicles and bicycles. Furthermore, large-sized dry lakes are excellent spots for pursuing land 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 lakes at Bonneville Salt Flats in Utah and Black Rock Desert in Nevada have both been used for setting land speed records. Lake Eyre and Lake Gairdner in South Australia have also been used for various land speed record attempts. Dry lake beds that very rarely fill with water are sometimes used as locations for air bases, for similar reasons. Examples include Groom Lake at Area 51 in Nevada, and Edwards Air Force Base (originally known as Muroc Dry Lake) in California.

Brines from the subsurface of dry lakes are often exploited for valuable minerals in solution. See, for example Searles Dry Lake and Lithium resources.

United States regulation

Under United States law, a "playa lake" may be considered isolated wetlands, 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).

Gallery

• Devil's Golf Course in Death Valley NP.jpg

  Devil's Golf Course in Death Valley National Park, western United States

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  The dry lake and shore of Lake Hart, an endorheic desert lake in South Australia.
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  A closeup photograph of salt growths on the crust of a dry lake.
• EtoshaPan 2005-06 comparison.jpg

  Etosha pan in northern Namibia

See also

• List of drying lakes
• Cienega
• Salt storm
• Soil salinity

Bibliography

• John H. Wellington, Southern Africa: a geographical study, Chapter 16 LAKES AND PANS