For decades scientists have been baffled by moving rocks atop Racetrack Playa, a lake bed located in the mountains above Death Valley, California. These rocks can create tracks hundreds of feet long and make sudden turns.

Most popular theories on the rocks’ movement center around a combination of wind and water making the rocks sail across the ground.

Other theories suggested thick ice sheets lifted the rocks and moved them across the lake bed. The ice sheet theory was on the right track, but new research says thin clear sheets of ice helped by a light breeze pushed the rocks slowly. The research was published by the journal PLOS ONE.

The scientists had a bit of luck on their side as Racetrack Playa is dry nearly all the time. The group travelled to Playa in December 2013 to check instruments.

“On Dec. 21, 2013, ice breakup happened just around noon, with popping and cracking sounds coming from all over the frozen pond surface,” said Richard Norris in a press statement. “I said to Jim, ‘This is it!’”

As the ice cracked, it shoved the rocks gently. After the ice melted away that afternoon, the scientists found trails from more than 60 rocks.

“Science sometimes has an element of luck,” Richard Norris said. “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.”

Richard Norris explains their findings in the video below.

Here’s another video showing the moving rocks in action. Fast forward to around 3 minutes to see it.

Image credit: Mike Hartmann via Scripps Oceanography

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