The largest salar (salt flat) in the world

The largest salar (salt flat) in the world, Salar de Uyuni, is located within the Altiplano of Bolivia in South America. The Altiplano is a high plateau formed during uplift of the Andes Mountains. The plateau harbors fresh and saltwater lakes, together with salars, that are surrounded by mountains with no drainage outlets—all at elevations greater than 3,659 meters (12,000 feet) above mean sea level. The Salar de Uyuni covers approximately 8,000 square kilometers (3,100 square miles), and it is a major transport route across the Bolivian Altiplano due to its flatness.

This astronaut photograph features the northern end of the salar and the dormant volcano Mount Tunupa (image center). 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. The dark volcanic rocks comprising Mt. Tunupa are in sharp contrast with the white, mineral-crusted surface of the salar. The major minerals are halite—common table salt—and gypsum—a common component of drywall.

Relict shorelines visible in the surface salt deposits (lower right of the image) attest to the occasional presence of small amounts of water in the salar. Sediments in the salar basin record fluctuations in water levels that occurred as the lake that once occupied the salar evaporated. These sediments provide a valuable paleoclimate record for the region. The dynamic geological history of the Altiplano is recorded in isolated “islands” within the salt flat (image left); these islands are typically built from fossil coral reefs covered by Andean volcanic rocks.

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The largest salar (salt flat or playa) in the world, Salar de Uyuni, is located within the Altiplano of Bolivia. Covering 10,582 square kilometers (4,086 square miles), the mineral-crusted salar is about the same size as the “Big Island” of Hawaii.

While the almost perfectly flat expanse of white can seem endless in photographs from the ground, this unique photograph offers a view on the playa as seen from the vantage point of an astronaut on the International Space Station. The smaller Salar de Coipasa is also visible to the northwest. The flat, white surfaces are comprised mainly of halite (common table salt) and gypsum, a soft mineral that is widely used in plaster and fertilizer. Several mountains, including the dormant volcano Mount Tunupa, cast long shadows across the salars.

The salars owe their existence to several large, ancient lakes that covered the plateau several thousand years ago. During the Late Pleistocene, most of this area was covered by Lago Minchin. About 15,000 years ago, Minchin had shrunk significantly, depositing large quantities of calcium carbonate in the basin and enriching the remaining water with gypsum, halite, and other minerals. Since it was trapped in a closed basin with no outlets, this briny water evaporated slowly during dry periods, providing the perfect conditions for salts and other evaporites to form. Over several thousand years, thick crusts have built up. In many areas, the salt crusts are more than 10 meters (33 feet) thick.

In addition to providing an exotic backdrop for photographers, the unusually flat surface has served as an ideal location for testing newly-launched satellite sensors. For instance, scientists working with both ICESat and Envisat have taken advantage of Salar de Uyuni to calibrate sensors on board. Salt flats make ideal locations for calibration because they are large, stable surfaces with strong reflection, much like ice sheets.