The phenomenon, which was discovered in the 1940s, pertains to the inexplicable movement of extremely heavy boulders across a dry lake bed situated in Death Valley National Park.
Nobody has ever seen the boulders move directly but long trails left behind them in the sand seem to suggest that they have somehow traversed significant distances all by themselves. Some of the rocks that have shifted even weigh upwards of 320kg.
In an effort to solve the mystery once and for all a team of scientists from Scripps Institution of Oceanography visited the site in 2011 and set up a high-resolution weather station and 15 rocks fitted with GPS devices to measure even the slightest movements with impeccable accuracy.
It would take a further two years for anything to happen, but eventually during a visit to the site in December 2013 the team discovered that the area had been submerged in 3 inches of water.
As it turned out the movement of the rocks occurs under a very specific set of circumstances that requires there to be just enough water to cover the ground but not enough to submerge the rocks. The actual movement occurs due to a combination of strong winds, the freezing of the water during the night and the thawing of the ice by the hot sun during the day.
“It’s possible that tourists have actually seen this happening without realising it,” said co-author Jim Norris. “It is really tough to gauge that a rock is in motion if all the rocks around it are also moving.”