Thursday, August 28, 2014

An Icy Solution To The Mystery Of The Slithering Stones

A century ago, miners working in California's Death Valley reported seeing boulders on the desert floor with long trails behind them — as if the stones had been pushed across the sand. But despite 60 years of trying, no one ever saw what moved them.


Now scientists think they've solved the mystery of the "slithering rocks of Death Valley." Using GPS tags pasted to the boulders, and a video camera, a geologist from Scripps Institution of Oceanography and his engineer cousin have evidence that broad, jagged panes of melting ice push the stones across the desert, nudged in one direction or another by the breeze. The team details their results in the current issue of the journal Plos One.
For decades, scientists trekked out to a dry lake bed in Death Valley called the Racetrack to see these rocks for themselves. Some of the stones weigh as much as 500 pounds. And many do indeed leave a long trail in the sand; some paths are straight, some zigzag. "They do things like ... take high-angle turns," says Richard Norris. "Sometimes they reverse course."
Norris, a geologist at Scripps, was just as puzzled as everyone else when he first saw the rock trails. Some were even parallel, as if the rocks had moved in tandem. "They are just going every which way out there," he says, "but in a very regular kind of fashion — like they're moving in fleets."
Fleets of boulders mysteriously sliding across the lake bed, or playa — a small community of scientists became rather obsessed with the phenomenon. "Every couple of years," Norris says, "somebody goes out there and tries to figure out what's going on."
Some scientists said windstorms were behind it. In 1953, a guy landed a plane on the lake bed and tried moving the rocks with the wash from his propellers. No go. Though a few stones rolled, they didn't slide. The trails were clearly not the sort made by rolling rocks. npr

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