Boulders appear to move on their own and leave defined trails in the Racetrack Playa area of Death Valley National Park. The phenomenon has been documented since 1948 and several potential explanations for how rocks that can weigh as much as 40 pounds can move 800 feet have been presented. The mystery of the ‘sailing stones’ of Death Valley has been solved by a team of researchers led by Richard D. Norris from Scripps Institution of Oceanography in La Jolla, California. The discovery was published in the Aug. 27, 2014, edition of the journal Public Library of Science.
A variety of explanations have been presented by scientists and lay people over the last 70 years for the apparent movement of rocks by themselves. No serious person has claimed any unnatural cause but until now no exacting study has been made of the phenomenon. The rocks do move because the tracks of their motion remain as evidence of the movement.
High winds, liquid water, and ice have been offered as an explanation but no person has actually seen the rocks move until Norris and colleagues filmed the rocks moving. GPS also documented the movement of the “mysterious” rocks. As many as 60 rocks moved a distance of 734 feet between Dec. 2013 and Jan. 2014 in multiple move events. A video of the rocks moving can be seen here.
The answer to the mystery is ice, sun, and wind. Thin ice sheets are deposited on the ground of Racetrack Playa. The early morning sun partially melts the ice. Flat ice sheets carry the rocks in the direction of the prevailing winds at a given time. The rocks can travel as fast as 16 feet per minute with winds that can reach five meters per minute in velocity. The tracks are produced by ice and the rocks as the ice melts. The ice is only a few millimeters thick.