Rolling stones are all very well, but rocks that sail on by? The so-called ‘sailing stones’ of Death Valley National Park, California, remain one of the strangest phenomena of the natural world.
Stones as heavy as a large vending machine travel across the valley floor, as if by magic, leaving deep trails in their wake. Death Valley is so famous for its sailing stones and the mark they make on the landscape that their location is called ‘Racetrack Playa’ – playa meaning ‘dry lake bed’. Different rocks sometimes trace a parallel course, turning corners and zigzagging back again, creating a spooky pattern.
They have been the subject of scientific investigation since 1948. But it wasn’t until the winter of 2013-14 that Twilight Zone theories were replaced by hard facts when a research team led by paleobiologist Richard Norris from the Scripps Institution of Oceanography, UC San Diego, caught the stones in action. Having set up time-lapse cameras and attached GPS trackers to rocks back in 2011, the team’s patience was finally rewarded. They discovered that it wasn’t magnetic forces, hurricane-force winds or slippery algae that caused them to slide about, as had been previously suggested – the real culprit was ice: thin, floating windowpanes of it.
Death Valley, which is the hottest, driest and lowest American national park, can be scorching by day but, when the nights are cold enough to freeze the shallow film of water that can cover the playa following rain or snow melt (often in March), it can turn into an ice rink for rocks.
When these ice sheets start to melt and create floes around the rocks and there’s at least a light breeze, even large stones that have sat in the same place for decades can be sent sailing off at heady speeds of about 5m per minute.
Okay, so you won’t see them whizzing past like something out of The X Files. But they gradually travel a course that can take them over 200m from their original location.
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