How Death Valley's 'sailing stones' move on their own
Images: Clockwise from left: Lgcharlot/Wikimedia; mikenorton/Shutterstock; Jon Sullivan; Wikimedia

Located above the northwestern side of Death Valley in Eastern California's Mojave Desert, an exceptionally flat dried lake called Racetrack Playa contains a peculiar phenomenon. Dozens of large stone stabs made of dolomite and syenite - often weighing as much as 318 kilograms - move across the cracked mud, leaving a series of smooth trails behind them. 

Some of these trails stretch for a whopping 250 metres. They often form a nice, lightly curved line, but sometimes they form sharp, zig-zagging angles, implying a sudden shift to the right or left. These ‘sailing stones’, as they’ve been nicknamed, are so common on the the Racetrack Playa, they make it look like a well-worn racetrack, hence the name. (Playa is another word for ‘dried lake’.)

It’s obvious that these stones are moving because of the trails, but how? No one knew. Since the 1900s researchers and casual observers were fascinated by the stones but no one could explain how they moved. And the biggest factor that kept the answer obscured over a century was that to this day, no one’s ever seen them move.

According to Marc Lallanilla at LiveScience, while the less informed guesses included everything from aliens and magnetic fields to good old-fashioned pranksters, a popular theory among researchers was that dust devils, which are strong, relatively long-lived whirlwinds, were pushing the stones around as they swept across the playa. But this theory, and others that cropped up, were all disproved. 

And then in 2006, planetary scientist Ralph Lorenz from the Johns Hopkins University Applied Physics Laboratory in the US started investigating the sailing stones. He came to the Racetrack Playa with an interest in studying its similarities to a hydrocarbon lake on Saturn’s moon, Titan, and stayed to put an end to a long-standing mystery. 

To do so, all he needed was a small rock, some water, and an ordinary Tupperware container. Lorez put the small rock in the bottom of the Tupperware container and filled it with a few centimetres of water. Then he put the whole thing in the freezer.

Marc Lallanilla at LiveScience explains what happened next:

"After putting the container in the freezer, Lorenz ended up with a small slab of ice with a rock embedded in it. By placing the ice-bound rock in a large tray of water with sand at the bottom, all he had to do was gently blow on the rock to get it to move across the water.

And as the ice-embedded rock moved, it scraped a trail in the sand at the tray's bottom. Lorenz devised his clever experiment by researching how the buoyancy of ice can cause large rocks, when encased in ice, to move by floating along tidal beaches in the Arctic Sea."

Calculations by Lorenz and his colleagues of the weather conditions in Death Valley during the winter months appeared to support his theory. "Calculations show that, in this scenario, the ice causes virtually no friction on the water, so the stones are able to glide with just a slight breeze,” Joseph Stromberg reported at Smithsonian Magazine. "The team argues that their model accounts for the movement far better than any other, since it doesn’t require massive wind speeds or enormous ice sheets."

They published their research in the American Journal of Physics.

While the evidence is circumstantial because no one has actually seen it happen, Lorenz's research remains the most likely explaination for the sailing stones of Death Valley.