A decades-old mystery has finally been laid to rest in Death Valley, California.

Black dolomite boulders, known as the sailing stones, are located on the dry lake bed known as Racetrack Playa within Death Valley.  The rocks appeared to move on their own, indicated by a lengthy trail etched into the dirt behind each one; however, no one had actually seen the stones move, leading to a number of theories on how a rock could possibly inch its way across  vast, flat earth.

A multitude of ideas sought to explain the phenomenon, from Earth’s magnetic field to gale-force winds to slippery algae.  Now, after a time-lapse photography and GPS tracking experiment, the mystery of the sailing stones has been revealed.

According to Discovery News, the group of scientists who conducted the experiment concluded that jagged plates of thin ice, resembling panels of broken glass, bulldozed the rocks across the flooded playa.  Driven by gentle winds, the rocks seem to hydroplane atop the mud.

“I have to confess I was surprised,” study co-author Ralph Lorenz, who has authored several studies suggesting thick ice carries the playa rocks, told Discovery News.  “I really expected buoyancy to be required, and it clearly wasn’t.  The ice was thinner than I thought would be needed. It was amazing to see the process actually happen.”

As expected, ice formation in a desert is fleeting.  Live Science explains that, “the playa occasionally floods in winter, from rain or melted snow.  Sitting at 3,608 feet (1,100 meters) above sea level and ringed by mountains, nighttime temperatures can drop below freezing, sheeting the temporary lake in thin ice or freezing it solid.”  Temperatures drop at night due to low humidity and lack of cloud cover, but come morning the sheet of ice quickly thaws and evaporates, leaving no trace of a force capable of shifting the rocks.

Racetrack Playa is characterized by strange geography in itself.  The dry lake bed is three miles long, flat as a tabletop, and littered with several hundred boulders which come to rest on the lake bed after tumbling from one of the surrounding hillsides.  The sizes of the rocks range from small, baseball-sized stones to 700 lb. boulders; despite their varying sizes, each trails a long path behind it.

“I’m amazed by the irony of it all,” James Norris, a research engineer and one of the leaders of the study, told the Los Angeles Times. “In a place where rainfall averages two inches a year, rocks are being shoved around by mechanisms typically seen in arctic climates.”

Norris added, “I know there are people who like the mystery of it and will probably be somewhat disappointed that we’ve solved it.  It’s a fascinating process, and in many ways I hope that there’s more to be discovered. Never say never.”