For a century, Death Valley's sailing stones that creep across Racetrack Playa have kept visitors and scientists wondering and speculating. The boulders, which are made up of black dolomite, seemed to be moving on their own, leaving trails behind as they slide uphill across the flat lakebed. So far, the trails are the only known evidence of the rocks' mysterious movement. No one has yet seen the rocks moving right before their eyes.
Since there is a lack of evidence, several theories have been made to explain this natural phenomenon. Some have thought that the stones were pulled by magnetic fields or were blown by strong winds. Others, perhaps more desperate than the rest, blamed everything on pranksters and even on aliens.
In 2011, a group of researchers and volunteers attempted to solve the mystery by placing 15 rocks with GPS units attached in Racetrack Playa which is the dry lake formation where the moving rocks are found. They sat back and waited for something to happen.
One of the researchers, physicist Dr. Ralph Lorenz of Johns Hopkins University, described the project as "the most boring experiment ever."
Things started to become interesting two years later. In the latter part of November 2013, a small pond made up of significant amounts of rain and snow was formed in the south end of the playa. The following month, the rocks which are GPS-embedded started to move. The heaviest among them weighed 35 lbs. The rocks moved at an average speed distance of 9 to 16 feet for every minute. All of these were caught on camera.
The mechanism that pushes the rocks to move across the Racetrack Playa is then explained on paper. First, the rain creates a shallow layer of water on the playa's dry terrain. Next, this layer of water freezes overnight. By morning, the formed ice breaks apart into thin sheets. Lastly, the thin sheets of ice were pushed against the rocks by the wind. The ice acts like a 'sail' and made the rocks slide slowly over the moist and muddy terrain.
"Science sometimes has an element of luck," says paleobiology professor Richard Norris of the Scripps Institution of Oceanography. "We expected to wait five or ten years without anything moving, but only two years into the project, we just happened to be there at the right time to see it happen in person."
According to the researchers, the rocks would move in fits and starts. The direction of their movement is sometimes altered when there's a shift in the winds. It is speculated that the frequency of rock movement had declined since the 1970s because of climate change.
