Thin sheets of ice push rocks across the desert when conditions are just right
Racetrack Playa is home to an enduring Death Valley mystery. Littered across the surface of this dry lake, also called a "playa," are hundreds of rocks - some weighing as much as 320 kilograms (700 pounds) - that seem to have been dragged across the ground, leaving synchronized trails that can stretch for hundreds of meters.
What powerful force could be moving them? Researchers have investigated this question since the 1940s, but no one has seen the process in action - until now.
In a paper published in the journal PLOS ONE on Aug. 27, a team led by Scripps Institution of Oceanography, UC San Diego, paleobiologist Richard Norris reports on first-hand observations of the phenomenon.
Because the stones can sit for a decade or more without moving, the researchers did not originally expect to see motion in person. Instead, they decided to monitor the rocks remotely by installing a high-resolution weather station capable of measuring gusts to one-second intervals and fitting 15 rocks with custom-built, motion-activated GPS units. (The National Park Service would not let them use native rocks, so they brought in similar rocks from an outside source.)
The experiment was set up in winter 2011 with permission of the Park Service. Then - in what Ralph Lorenz of the Applied Physics Laboratory at the Johns Hopkins University, one of the paper's authors, suspected would be "the most boring experiment ever" - they waited for something to happen.