Sailing Stones

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The sailing stones are a geological phenomenon where rocks move in long tracks along a smooth valley floor without human or animal intervention. They have been recorded and studied in a number of places around Racetrack Playa, Death Valley, where the number and length of travel grooves are notable. The force behind their movement is not understood and is subject to research. Racetrack stones only move 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 wander. Stones sometimes turn over, exposing another edge to the ground and leaving a different track in the stone's wake. Sliding rock trails fluctuate in direction and length. Some rocks which start next to each other start out traveling parallel, but one may abruptly change direction to the left, right, or even back the direction it came from. Length also varies because two similarly sized and shaped rocks could travel uniformly, then one could burst ahead or stop dead in its track. Speed is an unknown variable. Since these stones are rarely transported and nobody has witnessed the movement, the speeds the rocks travel at are not known. Physicists studying the phenomenon in 1995 found that winds blowing on playa surfaces can be compressed and intensified. They also found that boundary layers (the region just above ground where winds are slower due to ground drag) on these surfaces can be as low as 2 inches (5 cm). This means that stones just a few inches high feel the full force of ambient winds and their gusts, which can reach 90 mph (145 km/h) in winter storms. Such gusts are thought to be the initiating force while momentum and sustained winds keep the stones moving, possibly as fast as a moderate run as only half the force required to start a stone sailing is needed to keep it in motion. [READ THE REST OF THIS ARTICLE]





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