Last week, we showed you this mystery image. What was it? As a number of readers—including Brad Halderman (comment #3), Budi Prasteya (comment #7), and others—correctly guessed, you’re looking at a cropped version of one of the famous “sailing stone” tracks located on the Racetrack Playa in Death Valley National Park.
Since the 1940s, researchers have documented the distinctive furrows behind rocks at a number of dried out lake beds in Death Valley. Yet, nobody has actually seen the rocks move or proven definitively how the tracks form. Animals, earthquakes, and gravity have all been ruled out. Some researchers have suggested that the composition of the rock might be a factor, but tests have shown most of the boulders are run-of-the mill dolomites, basalts, limestones, gneisses, and schists that aren’t unusually slippery.
One of the best theories left standing: a combination of wind, mud, and ice. The area receives strong gusts of wind, and episodic bursts of rain that can create slicks of mud for brief periods. During cold weather, thin layers of ice can carpet the playa, and many scientists believe that wind, with the help of ice and mud underneath—has enough force to slide the boulders.
Though science journalist Brian Dunning has an interesting video that shows the movement of ice on the playa, no one has filmed wind actually moving the rocks. In the meantime, researchers (including a recent group sponsored by NASA) continue to investigate the phenomenon, as a NASA news story reported earlier this summer.
–Adam Voiland, NASA’s Earth Science News Team