The Salar de Uyuni desert is famous for its vast surface water that resembles a giant mirror and its hexagonally patterned salt crust, beneath which lies over 10 million tons of high-value lithium.
Salar de Uyuni is the largest salt flat on Earth, covering an area of 10,400 km2 in the Andes Plateau. The desert has an average elevation of 3,660 meters above sea level, but it hasn’t always been this way. About 5 million years ago, the area where the Andes Mountains now stand was at a low elevation, and the climate became arid, according to Sarah McKnight, an assistant professor of hydrogeology at the University of Dayton in Ohio.
Salar de Uyuni in Bolivia is the largest salt flat on the planet. (Photo: Helen Filatova).
Over time, extreme temperatures and scarce rainfall caused ancient lakes in the region to evaporate, leaving behind sediment and salt deposits. Tectonic processes and volcanic activity subsequently pushed these deposits upward, forming the plateau and shaping the current landscape. Compared to other salt flats like the Salar de Atacama in Chile, which has salt crusts over 1,000 meters thick in some areas, Salar de Uyuni’s crust is relatively thin, measuring only 3 to 10 meters.
The accumulation of salt on the salt flat depends on the area’s geology, and the tectonic activity beneath Salar de Uyuni is far less than that under Salar de Atacama. The salt crust of Salar de Uyuni covers a layer of extremely salty water known as brine. However, in some areas, fresh water also sits above the crust due to a process called water upwelling.
“The salt flat is surrounded by snow-capped mountains and volcanoes that supply meltwater to the edge of the salt crust. Freshwater seeps below the crust but immediately separates from the brine due to differences in salinity. Since freshwater is less dense than brine, it rises above the saline water,” McKnight explains.
Water upwelling occurs when fresh water rises through the crust and spreads across the surface, forming lakes on the salt flat. Salar de Uyuni has 6 to 8 such lakes, which play a crucial role for wildlife living in the desert. The size of these lakes varies with the seasons and during droughts.
The freshwater flowing down from the surrounding mountains is why Salar de Uyuni is one of the largest lithium reserves on Earth. Hydrothermal and volcanic activity in the Andes means the mountains are rich in minerals, including lithium, which is carried away by water as it flows through the rocks. The salt flat is located in a mountainous region often referred to as the “lithium triangle,” which includes areas in Bolivia, Argentina, and Chile, containing 75% of the world’s lithium supply, according to the Harvard International Review.
Salar de Uyuni is believed to contain 10.2 million tons of lithium, which is approximately 38% of the known lithium supply worldwide, according to a 2012 study. The United States Geological Survey estimates that the salt flat holds about a quarter of the world’s lithium supply. While resource exploration companies are very interested in Salar de Uyuni, the lithium is too widely dispersed across the salt flat for them to currently have the technology to extract it economically.
