Tillie Doyle
Playas and pans are often used interchangeably to refer to dry lake beds, especially in Mexico and the western United States. Playas are flat-bottomed depressions found in interior desert basins, which are periodically covered by water that either filtrates into the groundwater system or evaporates, leaving deposits of salt, sand, and mud. Pans, or salt pans, are the term used in most of South Africa for these dry lake beds. The terms takyr, sabkha, and kavir are used in Central Asia, Saudi Arabia, and Iran, respectively, while in South America, salar or salina (Spanish for salt pan) is used. These landforms are important sources of dust and salts and are also critical habitats for rare species.
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What You'll Learn
Playas are flat-bottomed depressions found in desert basins
Playas are flat-bottomed depressions found in interior desert basins and adjacent to coasts within arid and semiarid regions. They are among the flattest known landforms, with slopes generally less than 0.2 meters per kilometre. Playas are periodically covered by water that slowly filtrates into the groundwater system or evaporates into the atmosphere, causing the deposition of salt, sand, and mud along the bottom and around the edges of the depression. This process results in the formation of saline crusts, similar to those found in saline flats along coasts, lakeshores, and deltas.
Playas are formed when shallow lakes in basins eventually evaporate, leaving behind salt-surfaced lake beds. They are also known as sinks, pans, or salt flats and can be hundreds of kilometres wide. The term "playa" comes from the Spanish word for "beach" or "shore". Playas are often the only source of water available to wildlife in the desert, and they are important sources of dust and salts, which are blown to the surrounding uplands.
The surfaces of playas consist of silt and clay deposited by floodwaters that enter closed basins during occasional flow events. Very large playas may exhibit dry, sediment-dominated sections and moist, salt-dominated sections. The salt deposits of a salt pan are zoned, with less-soluble sulfates and carbonates at the outer margin and highly soluble sodium chloride at the centre. This process of salt crystallization is similar to the evaporation of brine in a dish.
Playas can be affected by occasional surface floods and are usually dry. The supply of water, basin depth, and duration of accumulation contribute to variations in the thickness of playa deposits. Playas with thicker sequences may have alternating layers of lacustrine clays and salt beds, reflecting periods of high floodwater runoff and arid climatic phases, respectively. Playas are also susceptible to threats such as pollution from concentrated animal feeding operations and invasive plant species, which can crowd out native vegetation and impact the standing water.
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Pans are also known as dry lake beds
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). 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.
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. This occurs when water fills the playa, 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.
Dry lake beds are commonly ringed by shadscale, saltbrush, and other salt-tolerant plants that provide critical winter fodder for livestock and other herbivores. 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.
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Playas are also known as salt pans
Playas are formed when water slowly filtrates into the groundwater system or evaporates into the atmosphere, leaving behind salt, sand, and mud deposits along the bottom. This process of inundation is what develops and maintains the characteristic flatness of playas. The occurrence of different minerals, such as loughlinite, has also been observed in the pan sediments of playas.
The terminology used to describe playas can be quite confusing due to the various local names. In addition to "playa," these landforms may be referred to as pans, salt lakes, salt pans, salt flats, or dry lake beds. The specific term used often depends on the region and the characteristics of the playa. For example, in Australia and South Africa, small playas are generally referred to as pans, while in Central Asia, Saudi Arabia, and Iran, different terms like "takyr," "sabkha," and "kavir" are applied.
Playas play an important role in the surrounding ecosystem. They serve as a source of dust and salts, which are blown to the surrounding uplands. Additionally, playas are often the only source of water available to wildlife in the desert, attracting antelope and other animals after rainstorms. However, they can also pose a threat to these environments due to pollution from concentrated animal feeding operations and the invasive shrub Kochia prostrata, which can crowd out native vegetation.
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Playas are affected by occasional surface floods
Playas are flat-bottomed depressions found in interior desert basins and adjacent to coasts within arid and semiarid regions. They are characterised by their flatness, lack of vegetation, and the presence of salt, sand, and mud along their bottoms. Playas are usually dry, but they are affected by occasional surface floods.
The occurrence of occasional surface floods in playas results in the deposition of silt and clay on their surfaces. These sediments are carried by floodwaters that enter the closed basins during flow events. As the floodwaters slowly recede, the water in the centre of the basin evaporates, leading to the formation of salt deposits. This process contributes to the unique characteristics of playas, including their flatness and lack of vegetation.
The flooding events in playas can be influenced by various factors. One factor is the inflow of water from nearby bodies of water, such as during storms or surges. Additionally, groundwater flow plays a role in supplying water to closed basins, which can impact the moisture levels and sediment composition of playas. The interaction between groundwater and surface water influences the hydrological dynamics of these landforms.
The effects of occasional surface floods on playas are not limited to sediment deposition and evaporation patterns. The presence of water in playas also creates habitats for various organisms, including rare species found only in these inhospitable environments. For example, the giant fairy shrimp, discovered in 2006, thrives in the murky waters of playas in southwest Idaho, Nevada, and Utah due to the fine clay load. Playas, with their seasonal flooding, become crucial water sources for wildlife in the desert, attracting antelope and other animals after rainstorms.
Understanding the dynamics of surface floods in playas is essential for preserving their unique ecological characteristics and the rare species that depend on them. While playas are generally dry, the occasional floods shape their geological and ecological features, contributing to the diverse and specialised environments found in arid and semiarid regions.
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Pans are found in the Kalahari Basin
The Makgadikgadi Pan is technically not a single pan but many pans with sandy desert in between, the largest being the Sua (Sowa), Ntwetwe, and Nxai Pans. These salt pans are very inhospitable, with only a thin layer of blue-green algae as plant life. The fringes of the pan are salt marshes, which are then circled by grassland and shrubby savanna. The pan is home to one of only two breeding populations of greater flamingos in southern Africa, as well as ostriches, chestnut-banded plovers, and Kittlitz's plovers. During the wet season, the pan becomes an important habitat for migrating animals, including wildebeest and one of Africa's biggest zebra populations, as well as large predators such as lions, cheetahs, and leopards.
The pans in the Kalahari Basin are the terminal features of desert drainage systems, or "dry lakes" at the end of ephemeral streams. They are flat surfaces devoid of vegetation that are gleaming white when dry, hardened by the cementing action of soluble minerals. On occasion, they are covered by a shallow layer of standing water. The pans are remnant features from a period of greater precipitation, with very little water ever flowing to the sea from the Kalahari. Instead, each stream ended its course in a slightly lower depression from which there was no outlet, and the fine silt particles and soluble minerals were deposited as the stream dried up.
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Frequently asked questions
A playa is a flat-bottomed depression found in interior desert basins and adjacent to coasts within arid and semiarid regions. They are periodically covered by water that slowly filtrates into the groundwater system or evaporates into the atmosphere, causing the deposition of salt, sand, and mud along the bottom. Playas are usually dry and are affected by occasional surface floods.
A pan, or salt pan, is a dry lake bed formed when a playa has no paleo lacustrine heritage. Small salt pans in South Africa, called vokils, are of this type. Salt pans are zoned like bathtub rings, with less-soluble sulfates and carbonates at the outer margin and highly soluble sodium chloride at the centre.
No, pans and playas are not the same. Pans are a type of playa. Playas are also known as pans, flats, dry lakes, or salt lakes.
Pans and playas are found in arid and semiarid regions. The largest concentration of dry lakes (nearly 22,000) is in the southern High Plains of Texas and eastern New Mexico. Playas are also found in New Mexico, Puerto Rico, Cuba, and Egypt. In South Africa, small types of playas are referred to as pans.
