For nearly a century Death Valley’s dancing rocks have amazed visitors and stumped scientists. Despite etching trails longer than football fields into the dried mud, no one had ever seen the stones move.
Last winter researchers employed GPS trackers and time-lapse photography to monitor dozens of rocks ranging from petite pebbles to hefty boulders. On December 20, they caught more than 60 stones sliding in unison at slothlike speeds of 2 to 5 meters per minute. The team describes the event August 27 in PLOS ONE.
Numerous explanations have been proposed for the mass movements over the years, ranging from earthquakes to aliens. Tagging the rocks revealed that ice and wind power the locomotion. During some winters, rainwater pools in the normally bone-dry lakebed and freezes into thin rafts of floating ice. As the wind blows against these rafts, the ice shoves against the rocks, forcing them to grind along the mud and leave behind the telltale tracks.