The Salar de Uyuni – the contiguous remains of an ancient lake, covering more than 10,000 square kilometers in the Andes Mountains of Bolivia, South America – is now a vast, flat white salt basin.
In the rainy season, when water collects on the impermeable crystalline crust of the salt pan and forms a large shallow pool, a natural mirror is formed. The resulting natural mirror reflects the sky below as if it were flat – almost perfectly; Hence, space agencies use these flats/complexes to test their satellite altimeters. In addition to being beautiful, this natural mirror also sits atop a large body of brine containing high levels of lithium; Therefore, the Salar de Uyuni represents a unique intersection between a geological phenomenon, an atmospheric event and today’s technology.
How Salar de Uyuni in Bolivia turned into the world’s largest natural mirror?
The extreme flatness of the Salar de Uyuni, characterized by an elevation change of less than 1 meter across an area of 10,582 square kilometres, enables it to become a completely flat surface. The area is inundated with water from runoff from the surrounding mountains during the rainy season (December to April), creating a thin layer of uniform water due to the impermeability of the salt crust and the completely flat land. That is, the water layer is very shallow (a few centimeters thick), creating a liquid lens that reflects the sky and clouds, creating a uniform horizon.
Why NASA and the European Space Agency are looking to Bolivia to repair their satellites
In addition, the natural mirror of the Salar de Uyuni is very large and chemically stable. As a result, it is essential to the science of observing Earth from space. For example, NASA and ESA’s spacecraft use the submerged Salar de Uyuni to calibrate satellite radar and laser altimeters. In addition, because the water surface is a perfect, highly reflective “plane,” scientists can compare satellite measurements with a precisely surveyed ground elevation of the surface to verify the accuracy of the data; Therefore, the Bolivian Desert is a very important geodetic benchmark for satellite sensors in terms of measuring sea level change and land ice cover change.
The 40,000-year transformation: How ancient lakes became a modern mirror
The mirror effect is the culmination of a 40,000-year geological history. The Salar de Uyuni was created by evaporation from several ancient lakes, such as Lake Minchin and Lake Tauca. When these lakes dried up due to the high Andean sun, they left behind large amounts of sodium chloride and other minerals. Underneath this white crust are very large deposits of lithium-rich brine. The high concentration of minerals in the water during the rainy season increases the density of the brine, preventing ripples to create a more consistent reflection for today’s visitors.
Why is thin air ideal for reflections?
The dry air of the Altiplano, located at 3,656 meters above sea level, is remarkably low in humidity, which is key to the clarity of the mirror. With minimal water vapor and pollution in the atmosphere, light can pass through with little scattering, thanks to the lack of aerosols and moisture. When the water is completely still, a white color effect appears, blurring the line between land and sky.This phenomenon is caused by the specular reflection of sunlight off the smooth surface of the water, which is reflected at a fixed angle, recreating the planetarium directly under the observer’s feet.