The mysterious sailing stones at Racetrack Playa
How does a big heavy rock move on its own across the desert? The reason is partially due to ice. Researchers have investigated this question since the 1940s, but no one has seen the process in action — until now.
Because the stones can sit for a decade or more without moving, the UC San Diego 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 experiment was set up in winter 2011 with permission of the Park Service. Then — in what they called “the most boring experiment ever” — the team waited for something to happen.
But in December 2013, Norris and co-author and cousin Jim Norris arrived in Death Valley to discover that the playa was covered with a pond of water seven centimeters (three inches) deep. Shortly after, the rocks began moving.
Their observations show that moving the rocks requires a rare combination of events. First, the playa fills with water, which must be deep enough to form floating ice during cold winter nights but shallow enough to expose the rocks. As nighttime temperatures plummet, the pond freezes to form thin sheets of “windowpane” ice, which must be thin enough to move freely but thick enough to maintain strength. On sunny days, the ice begins to melt and break up into large floating panels, which light winds drive across the playa, pushing rocks in front of them and leaving trails in the soft mud below the surface.
Read more about the discovery here →