The Mystery of Death Valley's Sliding Rocks, Solved

Slate in motion.
Aug. 29 2014 4:17 PM

Ice, Ice Baby

The mystery of Death Valley's sliding rocks, solved.

screen_shot_20140829_at_10.53.52_am

While the mysterious tracks carved into the dry lake bed of Racetrack Playa in Death Valley were long ago attributed to sliding rocks, an explanation for what causes the "sailing stones" to move—thereby leaving their famous trails in the dirt—has remained elusive to researchers for some time.

But, according to a study published in the journal PLoS ONE, the mystery is no more. The culprit is neither powerful dust devils, nor hurricane-force winds—it's something far more subtle: the combination of thin layers of ice and wind.

By inserting GPS tags into rocks, researchers were able to monitor their movements, and then, after comparing those results with information gathered at their weather station, finally pin down exactly what was happening. Basically: When the conditions are just right, ice gathers behind the rocks, and the friction that creates—when combined with a light breeze—causes the rocks to move.

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For this to happen, several events must occur in tandem (which helps explain why years, and sometimes decades, separate suspected movements). Temperatures need to fluctuate at the right levels, the ice can't be too thick, and, most important, there needs to water in the playa. Considering that the lake bed is dry 99 percent of the time and the area receives less than 2 inches of annual rainfall, the team's ultimate conclusion is a fitting answer to the long-enigmatic phenomenon.

“The process of ice breaking up and shoving rocks around happens every year if you go up into Saskatchewan or Ontario, but you don’t normally associate it with a hot, dry place like Death Valley,” said paleoceanographer Richard Norris, one of the main researchers behind the study. “And yet here’s the same kind of process unfolding occasionally—very occasionally—in this place that we associate with a very different kind of climate.”

Watch the video above for a more thorough explanation of the science behind the sliding rocks, and how, exactly, Norris and his team were finally able to put the mystery to bed.

A.J. McCarthy is a Slate video blogger.

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