August 29, 2014
Scientists Solve The Mystery Of Death Valley’s “Sailing Stones”
Chuck Bednar for redOrbit.com - Your Universe Online
For nearly 80 years, scientists have been puzzled by the “sailing stones” of Death Valley National Park – massive rocks, some weighing 500 pounds or more, that inexplicably have long trails behind them as though they had been pushed through the dry, flat mud surface of the region known as Racetrack Playa.According to National Geographic’s Jason Bittel, these “sailing stones” (also known as the “sliding rocks” of Death Valley) were first documented by miners more than a century ago and appear to change location all on their own, with the lengthy, sometimes zigzag pattern trailing after them the only evidence that the boulders had even moved.
Bittel said that scientists have been working to solve this mystery since 1948, and had submitted numerous theories claiming that “dust devils, flooding, ice sheets, hurricane-force winds, and algal films” could have been to blame. Now, the authors of a new study published Wednesday in the journal PLOS ONE have discovered the real reason for this unusual phenomenon.
Richard Norris, a paleobiologist at the Scripps Institution of Oceanography in La Jolla, California, and his colleagues traveled to the site in 2011 in order to monitor the rocks remotely using a combination of a high-resolution weather station, time-lapse cameras and motion-activated GPS units. The researchers said that they were prohibited from using native rocks by the US National Park Service, so they brought in similar boulders from an external source.
Since the stones can remain in place for more than a decade without moving, Norris and his colleagues did not expect to actually observe the motion in person. In fact, in a statement, co-author Ralph Lorenz of the Johns Hopkins University’s Applied Physics Laboratory predicted that their work would be “the most boring experiment ever.”
In December 2013, however, the research team’s efforts paid off. A day of rain caused a thin sheet of ice to form on the desert surface, said NPR’s Christopher Joyce. As the sun came up the following day, the ice started melting in the center of the playa, popping and cracking throughout the playa until finally the sheets of ice began to move.
Joyce said that the sheets were thin and approximately 40 to 50 feet across. The ice began sliding on top of a film of melted water, pushing the rocks along the muddy desert surface at a rate of several feet per minute. By the end of the day, some of them had moved hundreds of feet, and since the ice and water had evaporated before the afternoon, patterns indicating the trails taken by the rocks were left behind in the now-dry sand, he added.
“Science sometimes has an element of luck. We expected to wait five or ten years without anything moving, but only two years into the project, we just happened to be there at the right time to see it happen in person,” Norris said. As he explained to Joyce, it was just a case of lucking into the right conditions – rain, followed by cold and sunshine, accompanied by a wind that was steady but not too blustery and mud that had the right amount of slipperiness.
Norris and his team later returned to the site along with Lorenz, who had been studying the site since 2007, and managed to capture video footage and photographic evidence of the event, said Hannah Marsh of The Telegraph. In all, the scientists reported observing five movement events involving hundreds of rocks in a span of approximately 10 weeks.
“It's so much fun!” Norris told NPR. “Pretty much everybody was out there because it was a neat problem, and it was fun to do. And I think there's no purer form of science than that.”
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