Salar de Atacama is the largest salt flat in Chile. It is located 55 km (34 mi) south of San Pedro de Atacama, is surrounded by mountains, and has no drainage outlets. In the east it is enclosed by the main chain of the Andes, while to the west lies a secondary mountain range of the Andes called Cordillera de Domeyko. Large volcanoes dominate the landscape, including the Licancabur, Acamarachi, Aguas Calientes and the Láscar. The last is one of the most active volcanoes in Chile. All of them are located along the eastern side of the Salar de Atacama, forming a generally north-south trending line of volcanoes that separate it from smaller endorheic basins.
The salt flat encompasses 3,000 km2 (1,200 sq mi), is about 100 km (62 mi) long and 80 km (50 mi) wide, which makes it the third largest in the world, after Salar de Uyuni in Bolivia (10,582 km2 (4,086 sq mi)). and Salinas Grandes in Argentina (6,000 km2 (2,300 sq mi)). Its average elevation is about 2,300 m above sea level. The topography of the core portion of the salar exhibits a high level of roughness, the result of evaporation and ephemeral surface water, unlike the most other salt flats, as for example the Salar de Uyuni, which is periodically covered with shallow water.
Some areas of the salt flat form part of Los Flamencos National Reserve. The Laguna Cejar is a sink hole lake in the Salar de Atacama, 18 km from San Pedro, Chile. It has a salt concentration that ranges from 5 to 28% (50 to 280 parts per thousand), producing at the higher end of the range an effect of floating like the Dead Sea.
Salar de Atacama is part of a larger depression hosting other salt flats. This depression, called "La gran fosa" by Reinaldo Börgel is bounded by north-south structures. At present this larger depression conforms a subsiding sedimentary basin. Comparing with neighboring areas of the Andes the depression is a major topographical anomaly thought to be caused by a lithospheric block that due to its high density has remained at lower position than the rest of the Andes. The high density would derive from the times the Salar de Atacama depression was a westward rift arm of the Salta Rift Basin located further east in Argentine territory.
Salar de Atacama basin is bordered on the north by the Salado River basin, which is a sub-basin of the Loa River basin. To the east, the drainage divide approximately coincides with the international border with Bolivia until the Portezuelo del Cajón. The dividing range includes the volcanoes Cerros de Tocorpuri, Sairecabur, Curiquinca, Licancabur and Juriques. Going southward, the water divide runs along a chain of volcanoes that lie entirely in Chilean territory. To the west, the Cordillera Domeyko separates the Salar de Atacama basin from arheic areas.
The volcanoes east of Salar de Atacama may be responsible for contaminating the incoming streams with salts.
Salar de Atacama is the world's largest and purest active source of lithium, containing 27% of the world's lithium reserve base, and as of 2017 provided about 36% of the world's lithium carbonate supply, followed by China with 23%. High lithium concentration in its brine (2,700 parts per million), a high rate of evaporation (3,500 mm per year), and extremely low annual rainfall (<30 mm average per year) make Atacama's finished lithium carbonate easier and cheaper to produce than from the neighboring Salar de Uyuni, which is estimated to have half of the lithium reserves in the world. Salar de Atacama's evaporation rate is the highest in the lithium industry, followed by Puna de Atacama, Argentina (2,600 mm per year), and the Salar de Uyuni (1,300–1,700 mm per year). Extraction of lithium-rich brines is causing conflict with water use by local communities and is damaging the ecosystem, including the Andean flamingo.
In the Salar de Atacama, boron is also extracted from brines as boric acid (up to 0.85 g/l as B). The natural removal of boron and lithium from present-day brines possibly occurs as ulexite and lithium-sulfate, this latter as double and/or triple salts.
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