Death Valley's Racetrack Playa has held a strange secret for decades. Stones, including quite heavy stones, seem to slide across the dry lake bed of their own accord. Just how it happens has been anyone's guess. Until recently, that is.
Death Valley is a place of extremes, hitting triple-digit heat in the day only to drop below freezing at night. Scientists started coming up with some theories, including that hurricane-force winds push the stones along or that thick algal films help to push them on their way. But the one theory that seemed to hold the most logic is that on the rare occasions when water makes its way to the playa, it freezes at night enough to make a slippery surface over which the wind can blow the stones. It wasn't until last year that the theory was proven that just a little bit of ice and just a little bit of wind can make the strange activity happen.
Sci-News reported, "First, the playa fills with water, which must be deep enough to form floating ice during cold winter nights but shallow enough to expose the stones. As nighttime temperatures plummet, the pond freezes to form thin sheets of ‘windowpane’ ice, which must be thin enough to move freely but thick enough to maintain strength. On sunny days, the ice begins to melt and break up into large floating panels, which light winds drive across the playa, pushing rocks in front of them and leaving trails in the soft mud below the surface."
The researchers ultimately proved the theory by installing a weather station that tracks gusts of wind at one-second intervals and fitting 15 stones with motion-activated GPS units. By collecting data over months, they found that it takes a very particular set of circumstances but when all the ingredients align, stones slide across the playa almost perfectly in sync with each other.
While technically the mystery has been solved, witnessing the stones resting at the end of their tracks -- with no visual evidence for how they moved -- is still an amazing natural wonder to behold.