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Thursday, 31 August 2006

Snow White Lakes...But No Snow

Written by Dr. Ronald Francis
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salt flatYour 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.



You decide to take a drive on it in order to get to Fish Island, where you’ve heard there are great views of the lakes through interesting rock formations. You feel like you are driving to the end of the world because it is so flat for so long, and so uniformly white. The complete and utter flatness makes depth perception difficult, and you record the strange visual effects in photographs.

You wonder how Salar de Uyuni was originally formed. Uyuni used to be part of a prehistoric lake called Minchin 40,000 years ago. When Minchin dried up, it left smaller lakes and two salts flats. Uyuni is one of the salt flats.

You can walk on the 10 meter deep flat during the winter, but in the summer heavy objects like a truck, have been known to occasionally “lose ground” on the salt surface and drop into a hidden mud pit.

After a rain, the rainwater sits on the surface of the salt flat creating a dramatic mirror-like effect. This makes for magnificent views.

saltYou’re glad you’ve done your research beforehand, since there are limited resources in the general area of Uyuni. There are, however, several tourist agencies that offer trips to Uyuni.

You’re near the end of your stay. Despite the grueling trip to get here, you’re glad to have seen one of the earth’s most interesting natural surfaces.


For a satellite picture of the area see,com_google_maps/Itemid,38/lang,en/



Have a question for our resident physicist to answer in his next column?  Send to: mail [at] intravelmag [dot] com


©Dr. Ronald Francis


Last modified on Sunday, 16 December 2012

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