Ending a half-century of geological speculation, scientists have finally seen the process that causes rocks to move atop Racetrack Playa, a desert lake bed in the mountains above Death Valley, California. Researchers watched a pond freeze atop the playa, then break apart into sheets of ice that — blown by wind — shoved rocks across the lake bed.
Until now, no one has been able to explain why hundreds of rocks scoot unseen across the playa surface, creating trails behind them like children dragging sticks through the mud.
“It’s a delight to be involved in sorting out this kind of public mystery,” says Richard Norris, an oceanographer at the Scripps Institution of Oceanography in La Jolla, California, who led the research with his cousin James Norris, an engineer at Interwoof in Santa Barbara, California. The work was published on 27 August in PLoS ONE1.
Geologists previously speculated that some combination of wind, rain and ice would have a role. But few expected that the answer would involve ice as thin as windowpanes, pushed by light breezes rather than strong gales.