On a dried-up lake bed in Death Valley are dozens of rocks that have puzzled us for decades. The rocks have each left a dusty trail, evidence of some unknown force propelling them forward. Scientists have now finally observed the rocks moving and settled on an explanation: Thin ice and a gentle breeze.
Speculation about the origin of these sailing stones has ranged from hurricane-force winds to slippery algae films. In contrast, the rocks are actually being pushed around by delicate sheets of ice skating on sand, a solution that's just gentle and non-grandiose enough to be true. The idea doesn't come out of the blue; back in 2011, a scientist published his ice raft model after experimenting with sand in a Tupperware container.
What is really remarkable is that in a study published today in PLOS ONE, scientists observed the rocks actually moving for the first time. The whole experiment actually started four years ago, when a team of scientists—including our aforementioned Tupperware experimenter—set up cameras and actually GPS-tracked rocks on the dried lakebed of Racetrack Playa. They had no idea if the cameras and GPS would actually capture anything.
A GPS-tagged rock scooting on Racetrack Playa. Credit Jim Norris
Then in December 2013, a perfect storm of ice and wind set hundreds of rocks sliding along the lakebed. The researchers observed the cracking of a thin layer of ice that had formed on Racetrack Playa. A light but steady wind then pushed the ice pieces around, where they would accumulate behind rocks and push them forward. The rocks traveled as much as 200 feet and as fast as 10 mph. For the first time, this was all captured on camera.
Image credit: Jim Norris
But is this the whole story? The scientists point out that the largest boulders didn't budge during this perfect wind storm—there could be another explanation for how they move. There could still be mysteries yet at Racetrack Playa. [PLOS]
Top image: Nagel Photography/Shutterstock