December 30, 2004
Playas, Playa Lakes, Salt Lakes and Salt Flats
The latest entry from our expedition researcher Ben Foster!
A playa is “a flat, central area of an undrained desert basin (Tarbuck and Lutgens, 1990).”
A playa lake is “a temporary lake in a playa (Tarbuck and Lutgens, 1990).”
A more detailed definition of playa comes from the Dictionary of Physical Geography by John Whittow: “A Spanish term referring to a level or almost level area occupying the centre of an enclosed basin in which a temporary lake forms periodically. It is generally composed of stratified beds of clay or silt, deposited within the lake, that usually contain large amounts of soluble salts (Whittow, 1984).”
Occasionally, abundant rainfall will fall over a desert. If this falls in the area of a desert basin, a shallow lake may form. Such a lake is known as a playa lake. Usually, these lakes will last only a few days, sometimes up to a few weeks. Evaporation and infiltration are the reasons the lake soon disappears. Once the lake evaporates, a dry, flat lakebed remains. That lakebed is known as a playa. Fine silts and clays usually make up the lakebed. These would have been carried here by the water running from the upper slopes of the basin and deposited by the water when coming to rest in the lake. Salt often encrusts the playa. These salts would have precipitated out of the water as it evaporated (Tarbuck and Lutgens, 1990).
The deposits associated with the playa may be a few meters thick or may be hundreds of meters thick. The thickness depends on how long the deposition has been going on, the material supply and the basin’s depth (Selby, 1991).
A salt lake is a lake with a high level of salinity. Such lakes are most often found in very arid areas where rates of evaporation are high. Salt lakes are usually found within playas that are located in basins (Whittow, 1984). A salt lake may be similar to a playa lake but may be more permanent, such as the Great Salt Lake in Utah.
A salt flat is “the dried-up bed of a former salt lake (Whittow, 1984).”
The world’s largest salt flat is the Salar de Uyuni in Bolivia. Located in the central Andean Altiplano (high plateau) of Bolivia is this 9000 km2 salt flat. The Salar is located in a basin. The Cordillera Occidental lies to the west and the Cordillera Oriental lies to the east. The Salar is amazingly smooth because of alternately wet and dry periods. The climate of the area is semiarid and the Salar sees an average annual rainfall of about 300 mm. The rainy season stretches from December to March. At this time, the Salar may have a 25 cm deep layer of salty water (brine). This brine evaporates in the dry season to a level at or below the surface. (Arthur Bowman, 2004).
The elevation of the Salar de Uyuni is around 3600 meters (Arthur Bowman). Temperatures in the area can be below freezing at night and scorching in the day. The flat is impossibly white. Previously, WAY previously (25,000 – 40, 000 years ago), a lake known as Lago Minchin covered the area. Rains originally formed the lake as they ran down the surrounding volcanic landscape into the basin. Lago Minchin dried up and the basin was lake-less for 14,000 years until a new lake formed and remained for another 1000 years. At that point, the lake mostly dried up again, leaving the salt flats of Coipasa and Uyuni, as well as two smaller lakes whose names are Lagos Poopö & Uru Uru and which are remnants of the once great Lago Minchin (Lisa & Andre Ismael, 2004).
The Salar is important to the local economy, both in attracting tourists and for it’s salt extraction. At the Salar’s perimeter, the salt may be 20 to 30 centimeters thick. The salt can be be 6-8 meters thick in the centre of the Salar. The salt is cut out in blocks by pickaxe or shovel. Less than 25, 000 tones is harvested each year. There is an estimated 10 billion tones of salt in the Salar. The harvested salt may be packed on llamas and taken to Tarija where it can be traded. The salt may be traded for many things including honey, maize, wood, coca leaves or money (Lisa & Andre Ismael, 2004).
For more interesting reading on the Salar de Uyuni, refer to the following websites:
http://www.zuvuya.net/sites/babylontravel/english/ecology/e-index_salardeuyuni.htm
http://www.duke.edu/~bsb3/bolivia/aj.htm
Bibliography
Ismael, Lisa & Andre. “Bolivia: A ride across the Salar de Uyuni.” www.zuvuya.net, 2004.
Bowman, Arthur. “The Salar de Uyuni.” http://www.duke.edu/~bsb3/bolivia/aj.htm, 2004.
Selby, M.J.. Earth’s Changing Surface. Oxford: Clarendon, 1991
Tarbuck, Edward J., and Frederick k. Lutgens. The Earth: An Introduction to Physical Geology. Toronto: Merrill, 1990.
Whittow, John. The Penguin Dictionary of Physical Geography. Toronto: Penguin, 1984.
