Salar de Uyuni: The Flattest Place on Earth

Imagine an area 130 km (80 mi) long and 100 km (60 mi) wide – larger than 30 separate countries – that is blanched completely white and so flat that the variance in height from any single point to another is less than metre.  Such an area exists – the world’s largest salt flat, the Salar de Uyuni in Bolivia’s Altiplano region, the widest part of the Andes.  The salar is the product of numerous prehistoric lakes that formed and dried over thousands of years; as the lakes evaporated due to the lack of precipitation and external drainage in the plateau, they left behind salt and other materials that coalesced in a giant salt pan.  Salar de Uyuni contained a phenomenal 10 billion tonnes of salt; just 25 000 tonnes are taken annually from the pan.


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While not as dry as the nearby Atacama just across the Chilean border, precipitation here is minimal, averaging 1–3 mm (0.039–0.12 in) per month in winter and peaking at 70 mm (2.8 in) in January.  Eleven months of the year, the salar sees less than five days of rain per month.  As the salar has no natural outflow, when it does rain the salar floods with an extremely thin layer of water (barely ankle deep even at its most extreme), creating what is essentially the world’s largest mirror.  Depending on where you are located within the salar, it can be very difficult to discern where the sky ends and the surface begins.  Pink flamingos are found in large numbers wherever and whenever there is water, feeding on pink algae.

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Source: YoshiVic, http://commons.wikimedia.org/wiki/File:Salar_de_Uyuni_lake.jpg.  Licensed under the Creative Commons Attribution 2.0 Generic licence.

Source: P. Pavanelli, http://www.flickr.com/photos/patpavanelli/4141331321/.  Licensed under the Creative Commons Attribution ShareAlike 2.0 Generic licence.

Despite the arid conditions, it’s not really that hot in the Salar; the average summer high is 21°C (70°F), and night time temperatures drop all the way to the -9-5°C (16-41°F) range.  Altitude plays a large role in that, as the salar sits 3 656 m (11 995 ft) above sea level.  It’s this altitude that also can also help aid your GPS and television signals, believe it or not.  With the high-altitude clear skies, low humidity, and almost unerring flatness, space agencies actually use the salar to calibrate their satellites since surface reflectivity off of the immense salt flat is five times better than that of an ocean (no waves to deal with). NASA have already used the salar to calibrate their ICESat satellite for measuring ice sheet change in the Arctic.  Where there is undulation in the salar, it’s tiny (a few centimetres at most) and is tied not to the shape of the underlying bedrock far below but to gravity.  When floods occur, the salt-in-solution moves to areas with higher gravitational potential.

The Salar de Uyumi, for all of its ‘featurelessness’, is actually home to a large number of attractions, both natural and manmade, and sees a decent amount of tourist action as a result.  In the western half of the salar, a few islands rise above the flat; these are the tops of ancient buried volcanoes that break through the salt crust.  The most notable are Incahuasi(‘Inca house’), the largest of Uyuni’s islands that has long been a in the middle of the salar, and Isla del Pescado (‘Fish Island’), named for its supposed resemblance to a fish when viewed at a great distance.  These rocky outcrops are covered in cacti that are hundreds and even thousands of years old, growing at the rate of a centimetre per year.  Numerous hot springs and geysers rim the edges of the salar.  The most famous attraction is perhaps the Palacio de Sal, a.k.a. the famous ‘Salt Hotel’ (which will be explored further in the next update in its own entry), made entirely of salt blocks taken from the salar. And the salt flats make for a ready-made highway for vehicles cross the Altiplano, so the salar sees plenty of visitors even without direct tourism.

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Incahuasi (Inkawasi).  Click to expand (8827×1235).  Source: Julia W, http://en.wikipedia.org/wiki/File:Salar_de_Uyuni_D%C3%A9cembre_2007_-_Panorama_1_edit.jpg.  Licensed under the Creative Commons Attribution-Share Alike 3.0 Unported licence.

Isla del Pescado, surrounded by a sea of white.

Much as a layer of ice covers a frozen lake, the salt crust of the Salar de Uyuni (which can be anywhere from tens of centimetres to a few metres thick) covers an underlying pool of brine 2 to 20 m (7 to 66 ft) deep.  The brine is the world’s largest stockpile of lithium, containing at least 43 percent of the world’s known reserves (perhaps 9 million tonnes, weighted toward the east-central and southeastern part of the salar).  The lithium is believed to have come from the various hot springs in the region.  Because of the nearly exponential growth in the number of batteries used each year around the world, these lithium resources will get increasingly more attention as society requires more and more batteries for its expanding electronic base (and if hybrid cars indeed begin denting the mainstream).  Production at the moment, however, is minimal, with the current government advocating locally-owned cooperative lithium mining rather than seeing potential monies flow outward to foreign corporations. Potassium and magnesium are also present in relatively high densities, and the ratio of lithium to magnesium does present an elevated extraction cost compared to other lithium reserves.  But as demand increases, Bolivia could find itself at the heart of a geoeconomic power struggle based upon what lies beneath the Salar de Uyuni.

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Source: L. Hirth, http://upload.wikimedia.org/wikipedia/commons/thumb/b/b6/Salar_de_Uyuni_4.jpg/640px-Salar_de_Uyuni_4.jpg.

Further Reading

Ericksen, G.E. (1978).  Chemical composition and distribution of lithium-rich brines in salar de Uyuni and nearby salars in southwestern Bolivia.  Energy3(3): 355-363.

Fricker, H.A. et al.(2005).  Assessment of ICESat performance at the salar de Uyuni, Bolivia.  Geophysical Research Letters 32(L21S06): 1-5.  Available at http://icesat.gsfc.nasa.gov/icesat/publications/GRL/fricker-2.pdf.  Accessed 15 November 2011.

Hand, E. (2007).  The salt flat with curious curves.  Nature, 30 November 2007.  Available at http://www.nature.com/news/2007/071130/full/news.2007.315.html.  Accessed 15 November 2011.

Keating, J. (2009).  Bolivia’s Lithium-Powered Future.  Foreign Policy, 21 October 2009.  Available at http://www.foreignpolicy.com/articles/2009/10/21/bolivias_lithium_powered_future.  Accessed 15 November 2011.

Mason, G. (2006).  The incredible Salar de Uyuni, largest salt flats in the world. TravelBlog, 2 May 2006.  Available at http://www.travelblog.org/South-America/Bolivia/Potosi-Department/Salar-de-Uyuni/blog-56252.html.  Accessed 15 November 2011.

Reuder, J. et al. (2008).  Investigations on the effect of high surface albedo on erythemally effective UV irradiance: Results of a campaign at the Salar de Uyuni, Bolivia.  Journal of Photochemistry and Photobiology B: Biology 87(1): 1-8.  Available at http://www.lfabolivia.org/wp-content/uploads/2008/12/final-uyuni.pdf.  Accessed 15 November 2011.

Tahil, W. (2007).  The Trouble with Lithium: Implications of Future PHEV Production for Lithium Demand.  London: Meridian International Research.  Available at http://www.inference.phy.cam.ac.uk/sustainable/refs/nuclear/TroubleLithium.pdf.  Accessed 15 November 2011.

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