What do you think of this fact?
In Death Valley National Park, there’s a dried-up lake bed where rocks leave long tracks behind them, as if someone had dragged them through the mud. Nobody was pushing them. For decades, nobody had even seen one move.
A mystery since the 1940s
The place is called Racetrack Playa. Some of its rocks weigh up to 320 kilograms, and their trails can stretch for hundreds of meters. People have been trying to explain them since the 1940s; according to the study, the first report dates to 1948. Ideas ranged from dust devils and strong winds to water and ice.
In winter 2011, a team led by Richard Norris of the Scripps Institution of Oceanography set up a weather station and placed 15 rocks fitted with motion-activated GPS units on the playa. The National Park Service says the team expected to wait five to ten years for any movement. It took two.
Pushed by windowpane ice
In winter 2013/2014, a shallow pond formed on the playa, no more than 7 centimeters deep. A thin sheet of ice formed on top, only a few millimeters thick. When that ice broke up during the day, light winds pushed huge floating panels of ice across the water, and those panels shoved the rocks along the soft mud.
The rocks didn’t fly. They crept at a few meters per minute, and some moved for just a few seconds, others for up to 16 minutes. In one event, at least 60 rocks moved at once. One GPS rock covered 224 meters in total over at least two separate events. No hurricane, no magic, just ice as thin as a windowpane and a breeze.
Bonus fact: Movement is so rare that, according to co-author Ralph Lorenz, the rocks may be moving only about one millionth of the time.
The rocks themselves look completely ordinary. Their secret is a shallow pond, a thin layer of ice and a light breeze, all lining up in the middle of a desert.