Salar de Uyuni

Long ago, a giant lake covered this land.

The water had no way to flow out. Slowly, the water dried up into the air. The salt in the water stayed behind. Now there is a big white crust of salt.

The salt flat was once a huge lake. During the last part of the Ice Age, much of this area was covered by a lake that scientists call Lago Minchin. The lake sat in a closed basin, a low area with no river flowing out, so its water could leave only by evaporating, drying up into the air.

By about 15,000 years ago the lake had shrunk a lot. As the water evaporated, the salts dissolved in it were left behind. Over thousands of years, thick salt crusts built up. In many places the crust is now more than 10 meters thick.

NASA's Earth Observatory (2014) explains that the salars owe their existence to several large ancient lakes. During the Late Pleistocene most of the area lay under Lago Minchin; by about 15,000 years ago Minchin had shrunk significantly, depositing large quantities of calcium carbonate and enriching the remaining water in gypsum, halite and other minerals. Trapped in a closed basin with no outlets, the brine evaporated slowly in dry periods, ideal conditions for evaporites to form, and over several thousand years crusts built up more than 10 m thick in many areas. Copernicus (2017) dates the giant prehistoric lake that dried out here to some 40,000 years ago.

NASA (2005) notes that relict shorelines show the occasional return of small amounts of water, and that sediments in the basin record the falling lake levels, a valuable paleoclimate record. The basin is still closed today: climate scientist René Garreaud told NASA in 2022 that all of the rain and snow falling in it feeds the Uyuni and Coipasa dry lakes.

Rocky islands stand up out of the salt. Many are made of very old coral, covered with rock from volcanoes.

A mountain called Tunupa stands at the north end. Rain on its sides gives water to small villages. People who live nearby have collected salt here for a very long time.

Rocky islands rise out of the white salt. NASA says these islands are usually made of fossil coral reefs, the remains of living things, covered with volcanic rock.

At the north end of the salar stands Mount Tunupa, a sleeping volcano. Enough rain falls on its slopes to give water to small communities at its base. Salt from the flat has long been collected by the local Aymara people, who still make up most of the people in the area.

NASA's Earth Observatory (2005) describes isolated islands within the flat that are typically built from fossil coral reefs covered by Andean volcanic rocks, a record of the region's dynamic geological history. It also notes that the dormant volcano Mount Tunupa is high enough to carry a summit glacier and that rain on its windward slopes supplies small communities along its base.

In Landsat images of the flooded salar in January 2022, NASA noted discolored water and salt, which it says could be due to runoff, volcanic sediments, and microbes or algae thriving in the water. People are part of the landscape too: Copernicus (2017) writes that salt has traditionally been harvested by the local Aymara people, who still predominate in the area, and NASA (2022) adds that some of the salar's minerals have been harvested since at least the 1600s.

The salt flat holds useful things.

There is salt, and a metal called lithium that goes into batteries. Scientists also use the flat to test the tools on satellites in space.

Under and in the salt are useful minerals. Besides table salt, there is gypsum, used in plaster, and lithium, a light metal used to make batteries, including batteries for electric cars. Copernicus says Uyuni is one of the richest lithium deposits in the world. From space you can see large evaporation ponds, where water is dried off to collect lithium from salty brine.

The salar is useful to space scientists too. Because it is huge, flat, steady and very bright, they use it to check and adjust instruments on satellites.

NASA (2022) lists the salar's minerals as lithium, halite, and ulexite and gypsum, used for fertilizer and plaster. Copernicus (2017) describes Uyuni as one of the richest lithium deposits in the world, at an estimated 9 million tonnes, and identifies geometric shapes in its satellite image as the evaporation ponds of the national lithium plant, where lithium is isolated from salt brine. At the scale of the whole country, the U.S. Geological Survey's 2025 Mineral Commodity Summaries puts Bolivia's measured and indicated lithium resources at 23 million tons.

The flat also serves science. NASA (2014) reports that teams working with the ICESat and Envisat satellites used it to calibrate sensors, because salt flats are large, stable surfaces with strong reflection, much like ice sheets. Copernicus adds that its less-than-1-meter relief makes it ideal for calibrating radar altimeters such as those on ESA's CryoSat and the Sentinel-3 satellites.

Salar de Uyuni is very high up.

Up high, there is less air to breathe, so visitors go slowly and rest. The sun is strong too. Visitors go with a good tour company, and in the rainy season they listen to local advice.

At about 3,660 meters, the salar is very high, and the UK government's travel advice names the Salar de Uyuni as a place where altitude sickness is a risk. Health experts at the CDC explain that travelers who sleep higher than about 2,450 meters can get altitude illness, and that going up gradually gives the body time to adjust. The first few days are the most important, so visitors take it easy at first. The CDC also notes that sunlight carries more ultraviolet rays up high.

Rain falls mostly in the southern summer. In early 2022, so much rain fell that local newspapers reported flooding and short bans on travel across the salar. The UK travel advice suggests getting local advice, using only reputable tour companies, and carrying food, water and warm clothing in case bad weather causes delays.

The CDC Yellow Book warns that any unacclimatized traveler sleeping at or above about 2,450 m can develop altitude illness, lists La Paz in Bolivia (about 3,650 m) among high destinations, and says the acute adjustment over the first 3 to 5 days is crucial. It advises ascending gradually and doing only mild exercise for the first 48 hours, and lists increased ultraviolet radiation among high-altitude exposures.

Weather matters too. René Garreaud told NASA in 2022 that Altiplano rain falls mostly in the austral summer and that the rest of the year is bone dry. In early 2022 the salar filled almost to its edges; hydrologist Jorge Molina Carpio of the Universidad Mayor de San Andrés called the filling above normal, and local newspapers reported flooding and temporary bans on travel across the flat. The UK Foreign, Commonwealth and Development Office notes that Bolivia has no official minimum standards for tour operators, including salt flat tours, and advises getting local advice and using only reputable companies; in the November to March rainy season roads can be blocked, so travelers carry food, water and warm clothing.