Sailing stones, sliding rocks, and moving rocks all refer to a geological phenomenon where rocks move and inscribe long tracks along a smooth valley floor without human or animal intervention.The stones move only every two or three years and most tracks develop over three or four years. Stones with rough bottoms leave straight striated tracks while those with smooth bottoms tend to wander. Stones sometimes turn over, exposing another edge to the ground and leaving a different track in the stones wake.Trails differ in both direction and length. Rocks that start next to each other may travel parallel for a time, before one abruptly changes direction to the left, right, or even back to the direction from which it came. Trail length also varies – two similarly sized and shaped rocks may travel uniformly, then one could move ahead or stop in its track.Tracks of sliding rocks have been observed and studied in various locations, including Little Bonnie Claire Playa in Nevada, and most notably Racetrack Playa, Death Valley National Park, California, where the number and length of tracks are notable. At Racetrack Playa, these tracks have been studied since the early 1900s, yet the origins of stone movement were not confirmed and remained the subject of research for which several hypotheses existed. However, as of August 2014, timelapse video footage of rocks moving has been published, showing the rocks moving at low wind speeds within the flow of thin, melting sheets of ice. The scientists have thus identified the cause of the moving stones to be ice shove. After more than seventy years of attempts to solve the mystery of Death Valley’s sailing stones, U.S. researchers led by Dr Brian Jackson of Boise State University have finally caught the stones in action. Thin sheets of ice push rocks across a dry lake in Death Valley when conditions are just right. Image credit: Norris RD et al. Thin sheets of ice push rocks across a dry lake in Death Valley when conditions are just right. Image credit: Norris RD et al.One of the most interesting mysteries of Death Valley National Park is the sliding stones at Racetrack Playa (a playa is a dry lake bed).These stones can be found on the floor of the playa with long trails behind them. Somehow the stones slide across the playa, cutting a furrow in the sediment as they move.Remarkably, multiple stones commonly show parallel tracks, including apparently synchronous high angle turns and sometimes reversals in travel direction.Some of the stones weigh more than 300 kg. That makes the question: “what powerful force could be moving them?” Scientists have investigated this question since the first report in 1948, but no one has seen the phenomenon in action – until now.
Posted on: Fri, 26 Sep 2014 07:04:29 +0000
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