PLAYA

((Spanish: shore or beach), ) also called pan, flat, or dry lake, flat-bottom depression found in interior desert basins and adjacent to coasts within arid and semiarid regions, periodically covered by water that slowly filtrates into the ground water system or evaporates into the atmosphere, causing the deposition of salt, sand, and mud along the bottom and around the edges of the depression. Playas are among the flattest known landforms. Their slopes are generally less than 0.2 metre per kilometre. When filled with only a few centimetres of water, many kilometres of surface may be inundated. It is the process of inundation that develops and maintains the near-perfect flatness so characteristic of these arid-region landforms. Playas occupy the flat central basins of desert plains. They require interior drainage to a zone where evaporation greatly exceeds inflow. When flooded, a playa lake forms where fine-grained sediment sand salts concentrate. Terminology is quite confused for playas because of many local names. A saline playa may be called a salt flat, salt marsh, salada, salar, salt pan, alkali flat, or salina. A salt-free playa may be termed a clay pan, hardpan, dry lake bed, or alkali flat. In Australia and South Africa small playas are generally referred to as pans. The low-relief plains of these lands contrast with the mountainous deserts of North America, resulting in numerous small pans instead of immense playas. The terms takyr, sabkha, and kavir are applied in Central Asia, Saudi Arabia, and Iran, respectively. Saline flats are specialized forms located adjacent to large bodies of water, as, for example, along coasts, lakeshores, and deltas. They flood during storms, either with surface runoff or with surges from the nearby body of water. The saline crusts of saline flats are quite similar to those that develop in playas. also called Pan, Flat, or Dry Lake, flat-bottom depression found in interior desert basins and adjacent to coasts within arid and semiarid regions, periodically covered by water which slowly filtrates into the ground water system or evaporates into the atmosphere, causing the deposition of salt, sand, and mud along the bottom and around the edges of the depression. Playa (Spanish: shore or beach) is applied in the English-speaking world to a wide range of topographic depressions and desiccated lakes, but its nomenclature will vary according to individual depressions and regions of the world. Playas are called shotts or sabkhas in North Africa and Arabia, kavirs in Iran, takyrs in Central Asia, solonchaks in the Caspian Sea region, and pans in South Africa and Australia. In North America the terms salt flat, salt marsh, salt plain, and salina are used in reference to playas containing saline deposits, while a salt-free playa is sometimes called a clay pan, hardpan, or dry lake, and the term alkali flat is used for both saline and non-saline playas. Playas found within interior drainage basins vary in size from tens of metres to tens of kilometres across. Coastal playas or saline flats are usually only a few hundred feet wide, but sometimes they may extend several hundred miles along a coastal plain with widths exceeding 30 km (18 miles). The majority of the approximately 50,000 playas in the world are small. Fewer than 1,000 exceed 65 square km (25 square miles), and fewer than 100 exceed 520 square km (200 square miles). Most small playas are almost circular in shape, and the typical playa will have a length-width ratio of 2:1 or 3:1. Coastal playas will usually be elongated parallel to the shoreline, but the configuration of all playas will vary according to the local topography and climate. Playas can be distinguished from intermittent lakes by the amount of time that water is contained in the depression. A depression in which water is present for less than one-fourth of the year should be called a playa. Perhaps the most famous playas are those of Lake Bonneville in Utah, U.S., where the almost horizontal surface is ideal, when dry, for automobile speed trials. Additional reading A useful collection of scientific papers is James T. Neal (ed.), Playas and Dried Lakes: Occurrence and Development (1975). The playas of Death Valley, California, are described by Charles B. Hunt, Death Valley: Geology, Ecology, and Archaeology (1975). Victor R. Baker