LIFTING OF THE CLAST BY WATER AND ICE: AN EXPLANATION FOR THE TRAILS OF THE RACETRACK AND BONNIE CLAIRE PLAYAS

The sliding rocks of the Racetrack and Bonnie Claire playas have puzzled researchers for nearly a century. Rock fragments seem to race over a desiccated layer of sediment in the desert of Death Valley, California, leaving only their infamous trails as proof of their enigmatic movement. Interestingly, no one has ever witnessed the movement of these rocks. Furthermore, the mechanism responsible for moving the rocks and creating the trails has not yet been fully explained. A series of observations and measurements of this phenomenon at Racetrack and Bonnie Claire were conducted by NASA’s Lunar and Planetary Science Academy interns, and coordinating NASA researchers, in June, 2010. The dolomite and granite rocks have masses ranging from 0.5 kg to 300 kg. The trails are parallel on occasion, but are more commonly chaotic, with some as long as 0.5 km. Each rock has a mound of raised clay on one side and a trail depression on the other. A number of trails have no rocks at the end, with only a mound of solid clay where a rock once could have rested. Analysis of trail width and length measurements has revealed that the trails often widen towards the distal end of the trail. Additionally, some trails are much wider than their associated rock, while others are much narrower. Field observations and measurements of the moisture content and temperature of the sediment point towards a unique mechanism, involving increased buoyancy, and possible rock uplift through a combination of water influx and “ice collar” formation. Additionally, miniature icebergs floating over the playa may have created some trails without rocks, during hydroperiods with ponded water.