Researchers have solved a longstanding mystery that has befuddled scientists and tourists alike: why rocks on a dry lake bed in Death Valley National Park in California occasionally move.

The explanation for the phenomenon at Racetrack Playa — named for the long trails that the rocks, some of which weigh hundreds of pounds, leave in the mud — is that the stones are pushed by wind-driven ice that forms and then breaks up under certain conditions.

“It’s a very rare phenomenon,” said Richard D. Norris, a paleobiologist at the Scripps Institution of Oceanography and lead author of a paper describing it in PLOS One. “A brief moment in time.”