Salar de Uyuni
Salar de Uyuni is the biggest salt flat in the world. It covers an area of over 10,500 square km in the high Andes of Bolivia, around 3,650 metres above sea level. The whole place is covered in a thick crust of salt, blindingly white in the dry season and turned into a perfect mirror in the rainy season. It is one of the most beautiful and strange landscapes on Earth.
- CountryBoliviaIn the high Andes of South America
- Area10,582 km²About the size of Jamaica
- Altitude3,656 metresHigher than most ski resorts
- Salt depthUp to 120 metresIn the centre. The crust is hard enough to drive on
- Lithium under50 to 70% of world reservesA key metal for batteries
- Famous forThe mirror effectWhen the rains come, the surface reflects the sky
How big is Salar de Uyuni?
Salar de Uyuni is the biggest salt flat in the world, ahead of Tunisia's Chott el Jerid, India's Rann of Kutch and the Bonneville Salt Flats in the United States.
What is Salar de Uyuni?
A salt flat is a flat plain covered in salt. They form when a lake with no outflow dries up. The water evaporates but the salt that was dissolved in it stays behind. Over time the salt builds up into a thick crust on the ground.
Salar de Uyuni was once a giant prehistoric lake called Lake Minchin, around 40,000 years ago. The climate changed, the lake dried up, and a huge layer of salt was left behind. The salt has been compressed and added to ever since, until today it is in places over 100 metres thick. The whole salt flat sits at over 3,600 metres altitude, on the high Bolivian plateau called the Altiplano.
The mirror effect
The most famous feature of Salar de Uyuni is its mirror effect. During the brief rainy season (December to April), a thin layer of water sits on top of the salt. The water is so smooth and so shallow (a few centimetres) that it reflects the sky perfectly. The line between the ground and the sky disappears completely, and photos taken from the right angle make people and objects look like they are floating in the clouds.
In the dry season, the surface forms huge polygonal patterns of cracked salt, like a giant honeycomb. Both versions of the Salar are visually striking.
The lithium underneath
Beneath the salt of Salar de Uyuni lies one of the largest deposits of lithium in the world. Lithium is a soft silvery metal used in the rechargeable batteries that power phones, laptops and electric cars. The Salar holds between 50 and 70% of the world's known lithium reserves. As the world moves to electric vehicles, demand for lithium is soaring, which puts Bolivia at the centre of a global resource race.
Mining the lithium is controversial. The traditional method (evaporating salty water in giant pools) uses enormous amounts of water in an already dry region. Local indigenous communities (the Quechua and Aymara peoples) have voiced concerns. The Bolivian government, which has owned the lithium since 2008, is now experimenting with newer technologies that use less water.
Visiting the Salar
Most tourists visit on a three or four-day tour by 4x4 from the small Bolivian town of Uyuni. Highlights include the famous Salt Hotel (built entirely from salt blocks), Incahuasi Island (a rocky outcrop in the middle of the salt flats covered in giant cacti), and the Eduardo Avaroa National Reserve to the south with its flamingo-filled red and green lagoons.
Deeper dive: Lake Minchin, the Andean Plateau and the lithium triangle
Salar de Uyuni and its smaller neighbour Salar de Coipasa are the remains of an ancient lake system in the Bolivian Altiplano. The largest of these ancient lakes, Lake Minchin (active around 40,000 to 25,000 years ago), once covered an area larger than England. As the global climate became drier at the end of the last ice age, the lake repeatedly evaporated and refilled, then finally dried up almost completely around 12,000 years ago, leaving behind the salt flats. The crust of salt is composed mostly of halite (rock salt) with significant deposits of gypsum, sylvite and other evaporite minerals.
The Salar lies on the Altiplano, the second largest high plateau on Earth (after the Tibetan Plateau), with an average elevation of around 3,750 metres. The Altiplano was lifted up over the last 25 million years by the collision of the Nazca tectonic plate with the South American plate, the same collision that built the Andes mountains. The high altitude is what makes the climate dry: most of the Pacific moisture is rained out on the western side of the Andes before reaching the plateau.
Salar de Uyuni is the largest component of what is sometimes called the lithium triangle, a region across northern Argentina, southern Bolivia and northern Chile containing roughly half of the world's known lithium resources. The brine method of lithium extraction involves pumping salty water from beneath the salt crust into shallow evaporation pools, where the sun and wind concentrate the lithium over 12 to 18 months. The water is then chemically processed to produce lithium carbonate or lithium hydroxide. The process is much cheaper than mining hard-rock lithium but uses around 2 million litres of water per tonne of lithium produced, a serious issue in such a dry region.
The country is Bolivia. Another high-altitude landmark in the same region is Machu Picchu.