Scientists capture first ever time lapse video of Death Valley's Sailing Stones moving across the desert.
The sailing stones of Death Valley are a staple on alien conspiracy theory lists and discussions about baffling Earth phenomena. Stones on the Racetrack Playa in Death Valley National Park, ranging in size from pebbles to boulders, move across the flat surface, leaving tracks. The phenomenon is made stranger by the fact that multiple stones appear to have moved synchronously, turning or reversing in concert. Scientists have now captured the first video of a sailing stone in motion. In an article published August 27 in the journal PLOS One, the mechanism behind the motion of the rocks gets a complete scientific explanation.
The rocks have been generating discussion and theories about the cause of their movement since at least 1949, when the first report of the rocks was published. Many theories have been presented to explain how the rocks move, but scientists agree that the rocks are most likely to move when the playa is wet, and that wind is involved. Scientists have previously used GPS mapping to show that the rocks move in short spurts. For the study, a weather station, several time lapse cameras, and GPS-equipped rocks were installed at the Racetrack Playa.
Rarely, enough rain will fall on the playa that shallow ponds will form, and in winter the pond will freeze. The shallow pond leaves the tops of the rocks exposed, sticking up through the ice. A pond formed on the Racetrack Playa in November 2013, and remained there, freezing and thawing, until February 2014. The study reports that rock movement happened on sunny days following freezing nights. The sunlight melts some of the ice, creating a layer of water and mud. The floating ice breaks into panels that can be moved by winds and by the flowing water underneath. As a result, the rocks are pushed by the moving ice sheets, trapped in the ice but able to slide across the wet playa.
The study records one ice sheet moving more than 60 rocks at once. The rocks move slowly for only a few minutes, between 1 to 4 meters per minute (3 to 13 feet per minute), and the trails they leave only become visible once all the ice has melted and the water has evaporated. Ice sheets may collide, break up against large rocks, or further fracture as they move, explaining how some rocks seem to move in parallel for part of a track, and then take independent paths. Sustained winds are needed to cause the rock movement, with wind speeds of 3 to 4.5 meters per second (10 to 15 feet per second) recorded. The combination of the low friction of the muddy surface below the rocks, the floating fragmented ice sheets, and sustained winds can move even large boulders.
While the explanation is not as exciting as alien life sending us cryptic, rock-based messages, the sailing stones are still a fascinating natural event. What's your favorite strange Earth phenomenon?
Source: PLOS One