When visitors stumbled upon scores of heavy stones that appeared to have moved across the dried lake bed of Racetrack Playa in California’s Death Valley National Park, leaving a tell-tale trail in their wake, scientists were baffled. How had so many boulders, some weighing 300kg, moved as much as 250m across this remote part of the valley?
Adding to the mystery, some trails were gracefully curved, while others were straight with sudden shifts to the left or right. Who, or what, had moved the stones? A slew of theories emerged, from magnetic fields to alien intervention to dust devils to pranksters.
It took a NASA scientist to crack the case. In 2006, Ralph Lorenz developed a kitchen table model using a small rock frozen in an inch of water in a Tupperware container to demonstrate ice shove, the phenomenon behind the mysterious sailing stones.
In winter, Racetrack Playa fills with water and the lakebed’s stones become encased in ice. Thanks to ice’s buoyancy, even a light breeze can send those frozen boulders sailing across the muddy bottom of the lakebed. Stones with rough bottoms leave straight tracks, while those with smooth bottoms drift and digress. Warmer months melt the ice and evaporate the water, leaving only the stones and their mysterious trails.
Visitors can see these sailing stones in a few locations, including Little Bonne Claire Playa in Nevada and most famously, Death Valley’s Racetrack Playa.