Reports of rocks apparently moving across dry lakebeds in Death Valley, California, have been circulating for over a century. With some ‘sailing stones’ weighing over 300kg and leaving trails hundreds of metres long, scientists have long struggled to find a plausible explanation.
That changed in 2014, when researchers led by Richard Norris at Scripps Institution of Oceanography showed that during the winter, rain turns to ice on the lakebeds, which then cracks during the daytime, forming large panels. These sometimes catch the wind, lift up and start moving – shoving even large boulders ahead of them across the soft mud. But conditions must be just right: if the ice is too thick, it doesn’t break into panels; too thin, and it can’t shove the rocks.
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