High on the Andean plateau of southwestern Bolivia lies one of the most otherworldly places on Earth: the Salar de Uyuni. Spanning more than 10,000 square kilometers, it is the largest salt flat in the world. To stand here is to step into a dreamscape where the horizon disappears, and the sky appears to merge seamlessly with the land. When covered by a thin layer of water after seasonal rains, the surface becomes so reflective that travelers often call it the “world’s largest natural mirror.”
For years, this claim has captivated the imagination of tourists, photographers, and scientists alike. Images of people seemingly walking among the clouds or standing on a flawless glassy surface have traveled the globe. But until recently, much of the evidence for this phenomenon was purely anecdotal. Now, thanks to a new study published in Communications Earth & Environment, researchers have revealed the scientific truth behind this extraordinary spectacle—and it turns out to be even more fascinating than anyone expected.
The Challenge of Studying the Mirror Effect
Despite its fame, the mirror-like quality of the Salar de Uyuni has never been rigorously measured on a large scale. The main difficulty is accessibility. During the wet season, when rainfall turns the salt crust into a shallow lake, much of the salt flat becomes treacherous to reach. Vehicles can sink, and heavy rains make fieldwork nearly impossible. For scientists seeking to verify the mirror effect, this presented a serious obstacle.
To overcome this, researchers designed a two-part strategy that combined satellite observations with on-the-ground fieldwork. Their goal was simple yet ambitious: to determine if the Salar truly behaves like the massive natural mirror that the world believes it to be.
Satellites Scanning the Salt Desert
The first part of the study relied on data collected from the European Space Agency’s Sentinel-3 satellites. These satellites carry radar altimeters, instruments that send pulses of radar energy toward Earth and measure how much signal bounces back. Smooth surfaces reflect stronger signals, while rough surfaces scatter the energy.
By analyzing more than 390,000 radar measurements taken between 2016 and 2024, the scientists could map out the reflective qualities of Salar de Uyuni over both space and time. This enormous dataset offered an unprecedented window into how the salt flat behaves under different weather conditions.
Ground Truth: Testing the Mirror in Real Time
Still, satellite data alone was not enough. To validate their findings, the research team traveled to Bolivia during the peak wet season in February 2024—precisely timed to coincide with a Sentinel-3 satellite passing overhead. Armed with optical instruments, drones, and cameras, they measured the actual smoothness of the water’s surface and observed how it reflected sunlight.
The results were striking. Whenever the satellite registered a strong radar return, the ground team found that the surface was indeed mirror-like, reflecting the sky with astonishing clarity. This confirmed that the satellite data could reliably detect the phenomenon, bridging the gap between technological measurement and human experience.
The Mirror Revealed as Complex and Dynamic
The study’s findings, however, came with a twist. Contrary to the popular notion that Salar de Uyuni is one vast, uniform mirror, the researchers discovered that its reflective quality is far more complex. The surface changes significantly from one area to another and varies over time depending on rainfall and evaporation.
The most perfect mirror conditions occur after heavy rains, when a shallow sheet of water covers the salt crust before beginning to dry. This stage, fleeting and delicate, produces the breathtaking reflections captured in countless photographs. The team found a strong correlation between rainfall patterns and the strength of the mirror effect, demonstrating that climate, not chance, governs the phenomenon.
When and Why the Mirror Appears
The researchers concluded that the best time to witness the Salar’s mirror is from late January to early March, during the peak of the rainy season. This is when the balance between rainfall and evaporation produces an even, glassy surface across vast stretches of the flat.
One surprising result challenged intuition: wind did not disrupt the mirror. Normally, a breeze across a shallow lake would create ripples that break up reflections. But in Salar de Uyuni, the water is often only a few millimeters deep—too shallow to allow waves to form. As a result, even in windy conditions, the surface remains an unbroken canvas for the sky.
Beyond Beauty: Why It Matters
Understanding the Salar de Uyuni is not only about marveling at its beauty. The salt flat is a vital natural resource, holding some of the world’s largest reserves of lithium, a critical element for batteries and renewable energy technology. Knowing how water behaves across its surface can help researchers understand its hydrology, ecology, and potential environmental vulnerabilities.
Moreover, this study showcases the power of combining space-based technology with direct fieldwork. By linking satellite data with on-the-ground observations, scientists can uncover truths about remote and challenging environments—truths that deepen both scientific knowledge and human wonder.
A Mirror of Earth and Sky
The Salar de Uyuni remains one of nature’s most breathtaking spectacles. Science has now confirmed what travelers have long felt in their hearts: that walking across the Salar during the wet season is like stepping into infinity, where the Earth reflects the heavens in a seamless embrace. Yet, as this research shows, the mirror is not a static feature but a dynamic interplay of rain, salt, and sunlight.
In the end, the Salar’s magic lies not only in its visual perfection but in the delicate conditions that create it. It is a reminder that the most extraordinary wonders of our planet often emerge from the fragile balance of nature—a balance we are only beginning to understand.
More information: Stefano Vignudelli et al, Satellite radar altimetry reveals spatial and temporal changes in water surface smoothness in the Salar de Uyuni, Bolivia, Communications Earth & Environment (2025). DOI: 10.1038/s43247-025-02715-1
