While orbiting over South America” on March 17, 2019, an astronaut aboard the
International Space Station (ISS) shot this photograph of the Atacama Desert, the driest non-polar desert in the world, and the numerous salt flats in the Andes Mountains along the border of Chile and Bolivia. The centerpiece is the Salar de Uyuni, the largest salt flat on Earth.
Salar de Uyuni regularly captures the attention of astronauts due to its high contrast against the brown landscape, according to NASA.
Salar de Uyuni from the International Space Station (ISS). Salar de Uyuni and its smaller neighbor, Salar de Coipasa, have darker tones along their edges in this image. These dried lake beds are typically bright white in color, but rainfall can bring an influx of dark volcanic sediments. The region experienced rainfall in early February 2019, which caused temporary discoloration of the salars. By the time this image was taken in March 2019, the flats had started to shift back to their lighter colors. Image source: NASA Earth Observatory webpage
Salar de Uyuni from the International Space Station (ISS), annotated version. Nearby, the much smaller Laguna Colorada displays bright hues thanks to algae that thrive in the salty water. To the west and northwest of the lake, some of the white dots are snow-capped volcanoes and mountains. The salars receive less than 200 millimeters of rainfall per year. In contrast, the cloud-covered parts of Bolivia (north of the salars) see more than 1,750 mm of rain annually. The Andes Mountains create a rain shadow effect along the coast of northern Chile and western Bolivia, as air masses carrying moisture from the east drop most of their water before cooling and moving up over the mountains. Along the coast, the Atacama Desert is one of the driest places on Earth, sometimes going years without rainfall. NASA uses the Atacama Desert to test rovers and other instruments because the area is a good analog for future astrobiological exploration of Mars. Image source: NASA Earth Observatory webpage Salar de Uyuni salt flat
At 10,582 square kilometers (4,086 sq mi), Salar de Uyuni is the world’s largest salt flat. It has an elevation of 3,656 meters (11,995 feet) above sea level (
Salar means salt flat in Spanish).
Because of its location, large area, and flatness, it is a major car transport route across the Bolivian Altiplano, except when seasonally covered with water.
The area has a relatively stable average temperature with a peak at 21 °C (69.8 °F) in November to January and a low of 13 °C (55.4 °F) in June. The nights are cold all through the year, with temperatures between -9 °C (15.8 °F) and 5 °C (41 °F).
Some 30,000 to 42,000 years ago, the area was part of a giant prehistoric lake, Lake Minchin, which was named after Juan B. Minchin, the Bolivian geologist and engineer of the 19th-century. This lake later transformed into Paleo-Lake Tauca having a maximal depth of 140 meters (460 ft).
The youngest prehistoric lake was Coipasa, which was radiocarbon dating to 11,500 to 13,400 years ago. When it dried, it left behind two modern lakes, Poopó and Uru Uru, and two major salt deserts, Salar de Coipasa and the larger Salar de Uyuni.
During the rainy season (December to March) the Salar de Uyuni salt flat gets covered with a layer of water. As the water evaporates under largely still conditions, the salt forms hexagonal shapes (optimal for heat transfer) on its surface known as Bénard cells, an example of the Rayleigh-Bénard convection phenomena. On the horizon is the conical Tunupa Volcano (5,321 meters/17,457 feet high from sea level), an important point of reference when navigating the salt flat. One legend holds that Tunupa is a female volcano whose child was stolen and her tears created the salt flat. Photo by Dan Lundberg on Flickr. CC BY-SA 2.0
Salar de Uyuni
on Wikipedia “Salt Flats, Mountains, and Moisture” on NASA Earth Observatory
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