It’s a little more complicated than that – and it’s not the only way to trigger a glacial period – but this is the most likely explanation for the dry climate that led to the salt flats of Crait. (Diego Delso/Wikimedia Commons) Diego Delso/Wikimedia Commons CC BY-SA 4.0 These wobbles sometimes conspire to cause a planetary chill by affecting the temporal and geographical distribution of solar radiation Earth receives, which can bring about an ice age. Crait probably experiences Milankovich cycles much like Earth, which describe how our planet wobbles in three different ways across three different time periods as it spins around the Sun. Once upon a time, the climate was far warmer and wetter, but this world may have experienced an ice age of its own. That, in a nutshell, is what’s going on at Crait. The limited amount of water quickly settles atop the flat marvel, and until it's thieved back by the Sun’s radiation, it resembles a colossal mirror. We’re in an interglacial period right now – and thanks to anthropogenic climate change, we might be for far longer than nature intended – so rain once again visits the locale. Small pockets survived longer than others, but a major portion of it evolved into the Salar de Uyuni. At the zenith of the last glacial period - the glacial maximum - around 21,000-27,000 years ago, all the salt within it was left behind, and layer upon layer of accumulated where the great lake once was. So, over thousands of years, the water within Lake Minchin evaporated away faster than it could be replenished by precipitation. Less surface water meant fewer clouds, which often meant no rain. This meant that in plenty of places, including South America, the regional climate dried, as there wasn’t anywhere near as much water left on the surface to evaporate and form clouds. At the height of the last glacial period, however, massive volumes of water were locked up in ice, and the planet was covered in frozen shards. It’s remarkably flat, so much so that the water in the gigantic lake – Lake Minchin – couldn’t drain away and it continued to increase in size for many millennia. It is, or at least was, positioned on the Altiplano, a high plateau that formed during the uplift of the famous Andes Mountains. It’s not clear how it formed – various hypotheses, including a sudden increase in local precipitation and glacial meltwater, have been proposed – but either way, it was gigantic, and small fresh and saltwater lakes still dotting the region hint at their more sizeable past.

Around 40,000 years ago, the area was a segment of a gigantic lake. Covering an area of 10,582 square kilometers (4,086 square miles), it’s a profoundly ancient sedimentary deposit. Here you can see Salar de Uyuni, as well as the dormant volcano Mount Tunupa, from space.

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