Your best initial guess is that it is a frozen lake covered with snow. Look again and you see that it is too dry to be snow, and the temperature is not as cold as it should be.
In fact you are not looking at snow, but salt. You have stumbled upon Salar de Uyuni – the salt flats of Uyuni in Bolivia. It’s the world’s largest salt flat and it’s a blindingly white area about 50 miles by 60 miles – a little less that the size of Connecticut. You’ve seen or heard of smaller versions in the southwestern United States.
Uyuni, one of the more difficult travel destinations in the world, is extremely remote. The usual way to get there is to drive four hours from Bolivia’s capital, La Paz, and take a seven-hour train ride to the city of Uyuni at the crest of the Andes, about 11,000 feet.
A salt flat is a lake is completely comprised of minerals – mainly salt mineral in the form of halite (rock salt). Salt, the most common of substances and necessary for human life, is a crystal made up of two oppositely charged ions, sodium and chloride. These ions disassociate in water to move freely among water molecules.
If a body of water is trapped (no drainage into ground or river) and the rate of evaporation is greater than the local precipitation (rain), then the amount of water decreases over a long period of time. Left behind are the minerals, like the salt on your skin when your sweat evaporates.
If this happens year after year, the concentration of salt increases, building up layer upon layer until it becomes a slat flat. Windy areas are good candidates for slat flats because wind can boost the evaporation rate.
As you walk across the salt lake’s surface you see unusual polygonal shapes, like honeycombs but less regular, or soap bubbles trapped between two panes of glass – a lot of hexagons mainly but also pentagons, heptagons and octagons. The shapes are ridges of salt crystals a few inches high, most likely formed during the evaporation process.