Playa

A playa (or pan) is a dry or ephemeral lakebed, generally extending to the shore, or a remnant of, an endorheic lake. Such flats consist of fine-grained sediments infused with alkali salts. Playas are also known as alkali flats, sabkhas, dry lakes or mud flats. If the surface is primarily salt then they are called salt pans, salt lakes or salt flats.

Their surface is typically dry, hard and smooth during the dry season, but wet and very soft in the rainy season. Playas may be small, round depressions in the surface of the landscape. A playa lake is formed when rain fills this hole with water, creating a small lake. Playas can also form when the water table intersects the surface and water seeps into them.

Playas are typically formed in semi-arid to arid regions of the world. The largest concentration of playa lakes in the world (nearly 22,000) is on the southern High Plains of Texas and eastern New Mexico. While most playa lakes are very small, other examples of playa lakes include Lake Alablab in Suguta, Kenya, and Wild Horse Lake, Oklahoma, USA. Salar de Uyuni in Bolivia, near Potosí, is the largest salt flat in the world at 4,085 square miles (10,582 square km).

Many playas contain shallow lakes during the rainy season, especially so during wet years. If the layer of water is thin and is moved around the playa 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.

Geological curiosity

Racetrack Playa is a place in Death Valley National Park, very famous for its 'sailing stones', rocks that mysteriously move across its surface.

Ecology

While the playa itself will 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.

Threats to playas include pollution from concentrated animal feeding operations such as cattle feedlots and dairies, erosion, fertilizer, pesticide and sediment runoff from farms, and overgrazing.

Human use

The extremely flat, smooth and hard surfaces of playas make them ideal surfaces for motor vehicles and bicycles. Large-sized playas are further excellent spots for pursuing land speed records, as the smoothness of the surface allows low-clearance vehicles to travel very fast without risk of disruption by surface irregularities, and the trajectory need not be precise to avoid obstacles. The playas at Bonneville Salt Flats in Utah and Black Rock Desert in Nevada have both been used for setting land speed records. Dry lake beds that do not fill with water at any time are sometimes used as locations for air bases, for similar reasons. Examples include Area 51 in Nevada, and Edwards Air Force Base in California.

Terminology

The Spanish word "playa" (IPA2|ˈplaʝa) literally means "beach". Alkali flats are known by this name in some parts of Mexico and the western United States (pronEng|ˈplaɪə). On the Llano Estacado and other parts of the Southern High Plains, "playa" refers to a playa lake, a smaller seasonal depression.

"Pan" is the term used in most of southern 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.

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.

Gallery

References

* cite journal
last = Briere
first = Peter R.
year = 2002
month = May
title = Playa, playa lake, sabkha: Proposed definitions for old terms
journal = Journal of Arid Environments
volume = 45
issue = 1
pages = 1–7
publisher = Elsevier
doi = 10.1006/jare.2000.0633
accessdate = 2008-05-20

ee also

* Salt lake
* Soil salinity
* Cienega

External links

* [http://www.lbk.ars.usda.gov/wewc/biblio/bar.htm The Bibliography of Aeolian Research]