The Salar was formed as a result of transformations between several prehistoric lakes. It is covered by a few meters of salt crust, which has an extraordinary flatness with the average altitude variations within one meter over the entire area of the Salar, it is the world’s largest salt flat.
The Salar contains large amounts of sodium, potassium, lithium and magnesium as well as borax. Of those, lithium is arguably most important as it is a vital component of many electric batteries. Salar de Uyuni attracts tourists from around the world.
As it is located far from the cities, a number of hotels have been built in the area. Due to lack of conventional construction materials, many of them are almost entirely (walls, roof, furniture) built with salt blocks cut from the Salar.
The first such hotel was erected in 1993–1995 in the middle of the salt flat, and soon became a popular tourist destination. However, its location in the center of a desert caused sanitation problems, as most waste had to be collected manually.
As the largest salt flat on Earth, Salar de Uyuni is especially suitable for this purpose. In the low-rain period from April to November, due to the absence of industry and its high elevation, the skies above Salar de Uyuni are very clear, and the air is dry.
It has a stable surface which is smoothed by seasonal flooding (water dissolves the salt surface and thus keeps it leveled). As a result, the variation in the surface elevation over the 10,582-square-kilometer (4,086 sq mi) area of Salar de Uyuni is less than 1 meter (3 ft 3 in), and there are few square kilometers on Earth that are as flat.
The Salar de Uyuni occupies what was once the deepest part of an enormous lake, known as Lago Tauca, which covered the southern Altiplano until 12,000 years ago. Reaching depths of up to 70m, Lago Tauca existed for a thousand years and covered the area now occupied by Lago Poopó, the Salar de Coipasa and the Salar de Uyuni – and was itself the successor to an earlier lake, Lago Minchín.
In the dry season, the surface of the Salar, up to a depth of 10–20cm, becomes extremely hard and dry. Beneath this crust, though, the salt remains saturated with water.
As the top layer dries, it contracts, forming cracks which draw the underlying salt water up by capillary action, thereby forming the strange polygonal lines of raised salt that cover the Salar in the dry season.
The salar was formerly occupied by a series of large lakes. The youngest was a shallow palaeolake, ‘Coipasa’, radiocarbon-dated between 11,500 and 13,400 calendar years before present (cal. yr bp).
The youngest deep palaeolake, ‘Tauca’, was previously dated using carbonate fossils from outcropping sediments and carbonate bioherms (reefs) that mark past high stands. This astronaut photograph features the northern end of the salar and the dormant volcano Mount Tunupa (center of the image).
This mountain is high enough to support a summit glacier and enough rain falls on the windward slopes to provide water for small communities along the base.