Is This Remote Desert Actually the World’s Largest Mirror?

Even if you don’t know the Salar de Uyuni by name, there’s a good chance you’ve seen a photo of it. Tourists flock to this massive salt flat in Bolivia to snap pictures of its mirror-like surface, only visible when covered with a thin layer of water.

Salar de Uyuni is the world’s largest salt desert, and for years, people have assumed it’s also the world’s largest natural mirror. I mean, check it out for yourself—you’ll see what I mean in the video below.

The wetted surface is incredibly reflective. That said, no one had ever set out to scientifically prove that it’s the world’s largest natural mirror—until recently.

Is Salar de Uyuni Really a Giant Mirror?

In a new study published September 19 in the journal Nature Communications Earth & Environment, researchers used data from the European Space Agency’s Sentinel-3 satellites to search for empirical evidence of Salar de Uyuni’s mirror-ness, or its specular reflection. They used satellite data because the vast interior of the salt flat is often inaccessible during the wet season, making it difficult to study this phenomenon.

Each of these twin Earth-observing satellites is equipped with radar altimeters—instruments that beam radar pulses down to Earth and measure how long it takes for the signal to bounce back. The stronger the return signal, the smoother—and more reflective—the surface below.

The researchers, led by Stefano Vignudelli of the National Research Council of Italy’s Institute of Biophysics, analyzed more than 390,000 radar measurements taken between 2016 and 2024. In February 2024—peak wet season—they conducted field tests to validate their satellite observations, using an optical tool to measure the smoothness of the water’s surface. Drone photography also provided visual confirmation of smoothness by capturing images of the Sun’s reflection off the water.

The verdict? It’s complicated

The researchers’ findings show that despite its appearance to the naked eye, Salar de Uyuni is not a uniform mirror at radar wavelengths. Therefore, it probably isn’t a uniform mirror for optical wavelengths either. Rather, the reflectivity of the water’s surface evolves spatially and temporally.

The most mirror-like conditions occur after significant rainfall and before the water has had a chance to evaporate, according to the researchers. The correlation between periods of heavy rain and the mirror effect suggests it is a direct result of regional climate patterns, leading the authors to conclude that the best time to see the mirror is from late January to early March.

Because this phenomenon only arises under specific conditions and does not affect the entire Salar de Uyuni at once, it’s difficult to say whether it’s actually the world’s largest natural mirror at any given time. That doesn’t mean it isn’t exceptionally cool, however.

One of the most intriguing findings from this study is that wind doesn’t disturb the mirror effect, probably because the water is so shallow that ripples cannot form. The researchers hope future studies will investigate this and offer more insight into the unique characteristics that give rise to this natural wonder.