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'''Salar de Uyuni''' (or "Salar de Tunupa")<ref>{{cite web|title=Salar de Tunupa|url=http://www.irisentoreopreis.nl/tunupa_map.shtml|website=Iris en Tore op reis|access-date=26 February 2016|date=29 July 2011|archive-date=19 January 2016|archive-url=https://web.archive.org/web/20160119054358/http://www.irisentoreopreis.nl/tunupa_map.shtml|url-status=dead}}</ref> is the world's largest [[Salt pan (geology)|salt flat]], or [[Dry lake|playa]], at
The Salar was formed as a result of transformations between several prehistoric lakes that existed around forty thousand years ago but had all evaporated over time.{{r|NASA2019}} It is now covered by a few meters of salt crust, which has an extraordinary flatness with the average elevation variations within one meter over the entire area of the Salar. The crust serves as a source of salt and covers a pool of [[brine]], which is exceptionally rich in [[lithium]]. The large area, clear skies, and exceptional flatness of the surface make the Salar ideal for calibrating the [[altimeter]]s of Earth observation satellites.<ref name=nature2/><ref name=geo/><ref name=refl/><ref>{{cite news |bibcode=2002AGUFMOS52A0193B |title=GPS Survey of the salar de Uyuni, Bolivia, for Satellite Altimeter Calibration |last=Borsa |first=A. A |publisher=American Geophysical Union, Fall Meeting |year=2002 |display-authors=etal}}</ref><ref name=ieee>{{cite journal
|last1=Lamparelli |first1=R. A. C. |title=Characterization of the Salar de Uyuni for in-orbit satellite calibration |journal=[[IEEE Geoscience and Remote Sensing Society|IEEE Trans. Geosci. Remote Sens.]] |volume=41 |issue=6 |pages=1461–1468 |year=2003 |doi=10.1109/TGRS.2003.810713 |display-authors=1 |last2=Ponzoni |first2=F. J. |last3=Zullo |first3=J. |last4=Queiroz Pellegrino |first4=G. |last5=Arnaud |first5=Y. |bibcode = 2003ITGRS..41.1461C |s2cid=18716304
The Salar serves as the major transport route across the Bolivian [[Altiplano]] and is a prime breeding ground for several species of [[flamingo]]s. Salar de Uyuni is also a climatological transitional zone since the towering tropical [[Cumulus congestus cloud|cumulus congestus]] and [[cumulonimbus incus]] clouds that form in the eastern part of the salt flat during the summer cannot permeate beyond its drier western edges, near the Chilean border and the [[Atacama Desert]].{{citation needed|date=June 2016}}
The Salar has been used as a filming ___location for movies such as ''[[Star Wars: The Last Jedi]]'' (2017; as planet Crait),<ref>{{cite web |title=Crait: The Salar de Uyuni Star Wars Planet |url=https://www.salardeuyuni.com/salar-de-uyuni-star-wars/ |website=salardeuyuni |date=24 August 2018 |publisher=salardeuyuni.com |access-date=11 April 2020}}</ref><ref>{{cite web |last1=Butler |first1=Alex |title=Star Wars: The Last Jedi filming locations around the world |url=https://www.lonelyplanet.com/articles/star-wars-the-last-jedi-filming-locations |website
==Formation, geology, and climate==
[[File:Uyuni landsat.JPG|thumb|''Salar de Uyuni'' as viewed from space, with [[Coipasa Lake|''Salar de Coipasa'']] in the top left corner]]
Salar de Uyuni is part of the [[Altiplano]] of Bolivia in South America. The Altiplano is a high plateau, which was formed during uplift of the Andes mountains. The plateau includes fresh and saltwater lakes as well as salt flats and is
===History===
[[File:Salar_de_Uyuni,_Bolivia,_2016-02-04,_DD_10-12_HDR.JPG|thumb|left|Mountains surrounding the Uyuni salt flat during sunrise, [[Daniel Campos Province]], [[Potosí Department]], southwestern [[Bolivia]], not far from the crest of the [[Andes]]]]
The geological history of the Salar is associated with a sequential transformation between several vast lakes. Some 30,000 to 42,000 years ago, the area was part of a giant prehistoric lake, [[Lake Tauca|Lake Minchin]]. Its age was estimated by [[radiocarbon dating]] shells from outcropping [[sediment]]s and [[Carbonate platform|carbonate reefs]] and varies between reported studies. Lake Minchin (named after Juan B. Minchin of Oruro)<ref>{{cite journal|author=Bowman, Isaiah |jstor=201641 |title=Results of an Expedition to the Central Andes |journal=Bulletin of the American Geographical Society |volume=46 |issue=3 |pages=161–183 |year=1914 |doi=10.2307/201641}}</ref> later transformed into [[Lake Tauca|Paleo Lake Tauca]] having a maximal depth of {{convert|140|m|sp=us}}, and an estimated age of 13,000 to 18,000 or 14,900 to 26,100 years, depending on the source. The youngest prehistoric lake was Coipasa, which was radiocarbon dated to 11,500 to 13,400 years ago. When it dried, it left behind two modern lakes, [[Lake Poopó|Poopó]] and [[Lago Uru Uru|Uru Uru]], and two major salt deserts, [[Lago Coipasa|Salar de Coipasa]] and the larger Salar de Uyuni. Salar de Uyuni spreads over 10,582 km<sup>2</sup>, which is roughly 100 times the size of the [[Bonneville Salt Flats]] in the United States. Lake Poopó is a neighbor of the much larger [[Lake Titicaca]]. During the wet season, Titicaca overflows and discharges into Poopó, which in turn, floods Salar De Coipasa and Salar de Uyuni.<ref name=nature>{{cite journal |journal=[[Nature (journal)|Nature]] |title=Tropical climate changes at millennial and orbital timescales on the Bolivian Altiplano |first1=P. A. |last1=Baker |volume=409 |year=2001 |pmid=11217855 |display-authors=1 |last2=Rigsby |first2=C. A. |last3=Seltzer |first3=G. O. |last4=Fritz |first4=S. C. |last5=Lowenstein |first5=T. K. |last6=Bacher |first6=N. P. |last7=Veliz |first7=C. |issue=6821 |pages=698–701 |doi=10.1038/35055524 |bibcode=2001Natur.409..698B |s2cid=4394703 |url=http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1046&context=geosciencefacpub}}</ref>
Lacustrine mud that is interbedded with salt and saturated with brine underlies the surface of Salar de Uyuni. The brine is a saturated solution of [[sodium chloride]], [[lithium chloride]], and [[magnesium chloride]] in water. It is covered with a solid salt crust varying in thickness between tens of centimeters and a few meters. The center of the Salar contains a few islands, which are the remains of the tops of ancient volcanoes submerged during the era of Lake Minchin. They include unusual and fragile coral-like structures and deposits that often consist of fossils and algae.<ref name=trav1/>
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The area has a relatively stable average temperature with a peak at {{cvt|21|°C}} in November to January, and a low of {{cvt|13|°C}} in June. The nights are cold all through the year, with temperatures between {{convert|-9|and|5|°C|°F|abbr=on}}. The relative humidity is rather low and constant throughout the year at 30% to 45%. The rainfall is also low at {{convert|1|to|3|mm|in|abbr=on}} per month between April and November, but it may increase up to {{convert|80|mm|in|abbr=on}} in January. However, except for January, even in the rainy season the number of rainy days is fewer than 5 per month.<ref name=ieee/>
{{Wide image|Gringo Trail banner Salar de Uyuni.JPG|1100px|{{center|During the rainy season (December to April) the flat turns into a shallow lake and becomes the world's largest natural mirror, featuring a stunning reflection to the sky.}}}}
==Economic influence==
[[File:Salt production Uyuni.JPG|thumb|Salt production at the Salar|alt=]]
Located in the [[Lithium Triangle]], the Salar contains a large amount of [[sodium]], [[potassium]], [[lithium]] and [[magnesium]] (all in the chloride forms of [[Sodium chloride|NaCl]], [[Potassium chloride|KCl]], [[Lithium chloride|LiCl]] and [[Magnesium chloride|MgCl<sub>2</sub>]], respectively), as well as [[borax]].<ref name=trav1/>
|title=Lithium Statistics and Information|publisher=[[USGS]]}} ([https://www.usgs.gov/centers/national-minerals-information-center/lithium-statistics-and-information other Lithium statistics from USGS])</ref>
Lithium is concentrated in the brine under the salt crust at a relatively high concentration of about 0.3%. It is also present in the top layers of the porous [[halite]] body lying under the brine; however, the liquid brine is easier to extract, by boring into the crust and pumping out the brine.{{citation needed|date=June 2020}} The brine distribution has been monitored by the [[Landsat program|Landsat]] satellite and confirmed in ground drilling tests. Following those findings, an American-based international corporation has invested $137 million to developing lithium extraction.<ref>{{cite book |url=https://books.google.com/books?id=j0QrAAAAYAAJ&pg=PA60 |page=60 |title=Science and technology for development: prospects entering the twenty-first century : a symposium in commemoration of the twenty-fifth anniversary of the U.S. Agency for International Development |publisher=National Academies |year=1988 |author=National Research Council (U.S.). Board on Science and Technology for International Development, National Research Council (U.S.). Office of International Affairs|isbn=9780309320023 }}</ref> However, lithium extraction in the 1980s and 1990s by foreign companies met strong opposition from the local community. Locals believed that the money infused by mining would not reach them.<ref name="BBC_electric_car">{{cite news |title=Bolivia holds key to electric car future |url=http://news.bbc.co.uk/1/hi/business/7707847.stm |website=[[BBC News|BBC]]|date=9 November 2008 }}</ref> The lithium in the salt flats contains more impurities, and the wet climate and high altitude make it harder to process.<ref>{{cite web |last1=Eisler |first1=Matthew |title=Bolivian lithium: why you should not expect any 'white gold rush' in the wake of Morales overthrow |url=https://theconversation.com/bolivian-lithium-why-you-should-not-expect-any-white-gold-rush-in-the-wake-of-morales-overthrow-127139 |website=[[The Conversation (website)|The Conversation]] |date=15 November 2019 |language=en}}</ref>
No mining plant is currently at the site, and the Bolivian government does not want to allow exploitation by foreign corporations. Instead, it intends to reach an annual production of 35,000 t by 2023 in a joint venture with ACI Systems Alemania GmbH.<ref>{{Cite news |date=3 December 2018 |title=Bolivia's Almost Impossible Lithium Dream |url=https://www.bloomberg.com/news/features/2018-12-03/bolivia-s-almost-impossible-lithium-dream |access-date=26 March 2019 |newspaper=[[Bloomberg News|Bloomberg]]}}</ref><ref name="BBC_electric_car"/><ref name="ACISA">{{cite web |title=Lithium – ACI Systems Alemania GmbH |date=August 2019 |url=https://www.acisa.de/lithium/ |access-date=11 January 2020}}</ref>
Salar de Uyuni is estimated to contain 10 billion tonnes (9.8 billion long tons; 11 billion short tons) of salt, of which less than 25,000 t is extracted annually. All miners working in the Salar belong to [[Colchani, Potosí|Colchani's]] cooperative. Because of its ___location, large area, and flatness, the Salar is a major car transport route across the Bolivian [[Altiplano]],<ref name=nasa/> except when seasonally covered with water.{{citation needed|date=June 2016}}
==Name==
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[[File:SalarDeUyuniSaltProduction.jpg|thumb|Traditional salt production at Salar. Such salt blocks are used for building [[Palacio de Sal|salt hotel]]s]]
Salar de Uyuni is a popular tourist destination, and consequently a number of hotels have been built in the area. Due to lack of conventional construction materials, many of them are almost entirely (walls, roof, furniture) built with salt blocks cut from the Salar. The first such hotel, named [[Palacio de Sal]], was erected in 1993–1995<ref name=lick2>{{cite web|url=http://www.hotelchatter.com/story/2009/1/26/231522/848/hotels/Bolivian_Hotel_Truly_Is_the_Salt_of_the_Earth|work=hotelchatter.com|title=Bolivian Hotel Truly Is the Salt of the Earth|date=27 January 2009|access-date=16 October 2009|archive-date=15 May 2013|archive-url=https://web.archive.org/web/20130515053921/http://www.hotelchatter.com/story/2009/1/26/231522/848/hotels/Bolivian_Hotel_Truly_Is_the_Salt_of_the_Earth|url-status=dead}}</ref><ref name=lick1>{{cite web |url=http://www.tripcrazed.com/702316570/dont-lick-the-walls-of-the-salt-hotel/ |title=Don't Lick the Walls of the Salt Hotel |website=Tripcrazed.com |date=19 May 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090523140538/http://www.tripcrazed.com/702316570/dont-lick-the-walls-of-the-salt-hotel/ |archive-date=23 May 2009}}</ref> in the middle of the salt flat,<ref name=lick3>{{cite web |first=Peter |last=McFarrren |publisher=The [[Associated Press]] |url=http://www.seattlepi.com/getaways/030499/salt04.html |title=Salt hotel has a rule: No licking |date=4 March 1999 }}{{Dead link|date=April 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref name=book1>{{cite book |url=https://archive.org/details/peruboliviaecuad00benb |url-access=registration |page=[https://archive.org/details/peruboliviaecuad00benb/page/378 378] |title=Peru, Bolivia & Ecuador |first1=Ben |last1=Box |author2=Kunstaetter, Robert |author3=Kunstaetter, Daisy |author4=Groesbeck, Geoffrey |publisher=Footprint Travel Guides |year=2007 |isbn=978-1-906098-06-3}}</ref> and soon became a popular tourist destination.<ref name=ng>{{cite web |url=http://news.nationalgeographic.com/news/2007/07/070725-salt-hotel.html |archive-url=https://web.archive.org/web/20070728022241/http://news.nationalgeographic.com/news/2007/07/070725-salt-hotel.html |url-status=dead |archive-date=28 July 2007 |title=Photo in the News: New Salt Hotel Built in Bolivia |publisher=The [[National Geographic]] |date=25 July 2007 |access-date=1 September 2009}}</ref> However, its ___location in the center of a desert caused sanitation problems, as most waste had to be collected manually. Mismanagement caused serious environmental pollution and the hotel had to be dismantled in 2002.<ref>{{cite book |url=https://books.google.com/books?id=peBeMlMgcD4C&pg=PA259 |page=259 |title=The Rough Guide to South America |first=Harry |last=Adès |publisher=[[Rough Guides]] |year=2004 |isbn=1-85828-907-6}}</ref><ref name=german>{{cite web |language=de |work=hbernreuther.de |url=http://www.hbernreuther.de/Brasilien_Bolivien/Palacio_del_Sal/palacio_del_sal.html |title=Palacio del Sal |url-status=dead |archive-url=https://web.archive.org/web/20081206050825/http://www.hbernreuther.de/Brasilien_Bolivien/Palacio_del_Sal/palacio_del_sal.html |archive-date=6 December 2008}}</ref>
Around 2007, a new hotel was built,<ref name=ng/> under the name Palacio de Sal, in a new ___location
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===Train cemetery===
One major tourist attraction is an antique train cemetery. It is {{convert|3|km|mile|abbr=on}} outside Uyuni and is connected to it by the old train tracks. The town served in the past as a distribution hub for the trains carrying minerals en route to Pacific Ocean ports. The rail lines were built by British engineers arriving near the end of the 19th century and formed a sizeable community in Uyuni. The engineers were invited by the British-sponsored Antofagasta and Bolivia Railway Companies, now [[Ferrocarril de Antofagasta a Bolivia]]. The rail construction started in 1888 and ended in 1892. It was encouraged by Bolivian President [[Aniceto Arce]], who believed Bolivia would flourish with a good transport system, but it was
{{Wide image|Uyuni Décembre 2007 - Cimetière de Trains 1.jpg|1100px|Cemetery of trains near the town of [[Uyuni]]}}
===Incidents===
==Satellite calibration==
Salt flats are ideal for calibrating the distance measurement equipment of satellites because they are large, stable surfaces with strong reflection, similar to that of ice sheets. As the largest salt flat on Earth, Salar de Uyuni is especially suitable for this purpose.<ref name="NASA2019" /> In the low-rain period from April to November, due to the absence of industry and its high elevation, the skies above Salar de Uyuni are very clear, and the air is dry (relative humidity is about 30%; rainfall is roughly {{convert|1|mm|disp=or}} per month). It has a stable surface, smoothed by seasonal flooding — water dissolves the salt surface and thus keeps it leveled.<ref>{{cite journal |last1=Borsa |first1=A. A. |last2=Bills |first2=B. G. |last3=Minster |first3=J. B. |year=2008 |title=Modeling the topography of the salar de Uyuni, Bolivia, as an equipotential surface of Earth's gravity field |journal=Journal of Geophysical Research: Solid Earth |volume=113 |issue=B10 |doi=10.1029/2007jb005445|bibcode=2008JGRB..11310408B |s2cid=140609728 |url=https://escholarship.org/content/qt0fr1z3fs/qt0fr1z3fs.pdf?t=lnr314 }}</ref>
As a result, the variation in the surface elevation over the {{convert|10582|sqkm|sp=us|adj=on}} area of Salar de Uyuni is less than {{convert|1|m|sp=us}} normal to the Earth's circumference, and there are few square kilometers on Earth that are as flat. The surface reflectivity ([[albedo]]) for ultraviolet light is relatively high at 0.69 and shows variations of only a few percent during the daytime.<ref name=refl>{{cite journal |journal=Journal of Photochemistry and Photobiology B |volume=87 |issue=1 |year=2007 |pages=1–8 |title=Investigations on the effect of high surface albedo on erythemally effective UV irradiance: Results of a campaign at the Salar de Uyuni, Bolivia |doi=10.1016/j.jphotobiol.2006.12.002 |first1=Joachim |last1=Reuder |url=http://www.lfabolivia.org/wp-content/uploads/2008/12/final-uyuni.pdf |format=free-download pdf |pmid=17227712 |display-authors=1 |last2=Ghezzi |first2=F. |last3=Palenque |first3=E. |last4=Torrez |first4=R. |last5=Andrade |first5=M. |last6=Zaratti |first6=F. |bibcode=2007JPPB...87....1R |url-status=dead |archive-url=https://web.archive.org/web/20140414175025/http://www.lfabolivia.org/wp-content/uploads/2008/12/final-uyuni.pdf |archive-date=14 April 2014}}</ref> The combination of all these features makes Salar de Uyuni about five times better for satellite calibration than the surface of an ocean.<ref name=nature2>{{Cite news |title=The salt flat with curious curves |first=Eric |last=Hand |date=30 November 2007 |publisher=[[Nature (journal)|Nature]] |url=http://www.nature.com/news/2007/071130/full/news.2007.315.html}}</ref><ref name=geo>{{cite journal |title=Assessment of ICESat performance at the salar de Uyuni, Bolivia |first=H. A. |last=Fricker |journal=[[Geophysical Research Letters]] |volume=32 |page=L21S06 |doi=10.1029/2005GL023423 |year=2005 |issue=21 |bibcode=2005GeoRL..3221S06F |s2cid=13173970 |doi-access=
|url=https://books.google.com/books?id=CeLCxydgA8UC&pg=PA22 |page=22 |title=Satellite-based Estimates of Sea Ice Volume Flux: Applications to the Fram Strait Region |first=Gunnar |last=Spreen |publisher=GRIN Verlag |year=2008 |isbn=978-3-640-13064-1}}</ref>
By using data from [[Multi-angle imaging spectroradiometer|MISR]] to perform passive optical [[bathymetry]] when the flat is flooded and calibrating the resultant water depth model with topographical data from the laser altimeter of [[ICESat]], it has been shown that the Salar de Uyuni is not perfectly flat. The 2006 analysis revealed previously missed features: ridges between {{convert|20
{{Clear}}
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File:Salar Uyuni au02.jpg|Llamas in the Salar
File:Reflection on the Salar de Uyuni, bolivia.jpg|Reflection on the Salar de Uyuni
File:Salar de Uyuni
</gallery>
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