Death Valley National Park

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The Racetrack Playa, or The Racetrack, is a scenic dry lake feature with "sailing stones" that inscribe linear "racetrack" imprints. It is located above the northwestern side of Death Valley, in Death Valley National Park, Inyo County, California, U.S..<br />
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The sailing stones are a geological phenomenon found in the Racetrack. Slabs of dolomite and syenite ranging from a few hundred grams to hundreds of kilograms inscribe visible tracks as they slide across the playa surface, without human or animal intervention. The tracks have been observed and studied since the early 1900s, yet until 2014 no one had ever seen the stones in motion. Racetrack stones only move once every two or three years and most tracks last for three or four years. Stones with rough bottoms leave straight striated tracks while those with smooth bottoms wander.<br />
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The sailing stones were originally thought to be moved by strong winter winds, in the upwards of 90 mph, once it had rained enough to fill the playa with just enough water to make the clay slippery. The prevailing southwest winds across Racetrack playa blow to northeast. Most of the rock trails are parallel to this direction, lending support to this hypothesis.<br />
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An alternate theory suggests that as rain water accumulates, strong winds blow thin sheets of water quickly over the relatively flat surface of the playa. Sheets of ice form on the surface as night temperatures fall below freezing. Wind then drives these floating ice floes, their aggregate inertia and large area providing the necessary force required to move both small and large stones. Rock trails would again remain parallel to the southwest winds. According to investigator Brian Dunning, "Solid ice, moving with the surface of the lake and with the inertia of a whole surrounding ice sheet, would have no trouble pushing a rock along the slick muddy floor."<br />
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Another hypothesis is focused on observations and measurements of narrowing trails, heat conductivity of the playa's rocks, water, ice and sediments, missing rocks from ends of the trails, and an intermittent spring system in the playa. Kletetschka with his team identified three groups of Racetrack playa spring lineaments, Spinal Springs, Edge Springs, and Gindarja Springs, through which additional water flows into the playa once the ice forms on the water inside the playa. This mechanism, in addition to the raft hypothesis,allows lifting the rocks by adding additional amount of water via these springs.<br />
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The most recent research and observations of moving stones indicates that ice collars form around rocks and the rocks along with ice are buoyantly floated off the soft bed. The minimal friction allows the rocks to be moved by arbitrarily light winds.<br />
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In a study released in August, 2014, researchers observed rock movements using GPS and time-lapse photography. They documented a rock movement on December 20, 2013 that involved more than 60 rocks, with some rocks moving up to 224 meters between December 2013 and January 2014 in multiple move events. This study contradicted earlier hypotheses of winds or thick ice floating rocks off the surface. Instead, rocks move when ice sheets just a few millimeters thick start to melt during periods of light wind. These thin floating ice panels ice shove the rocks at up to five meters per minute.

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The Racetrack Playa, or The Racetrack, is a scenic dry lake feature with "sailing stones" that inscribe linear "racetrack" imprints. It is located above the northwestern side of Death Valley, in Death Valley National Park, Inyo County, California, U.S..

The sailing stones are a geological phenomenon found in the Racetrack. Slabs of dolomite and syenite ranging from a few hundred grams to hundreds of kilograms inscribe visible tracks as they slide across the playa surface, without human or animal intervention. The tracks have been observed and studied since the early 1900s, yet until 2014 no one had ever seen the stones in motion. Racetrack stones only move once every two or three years and most tracks last for three or four years. Stones with rough bottoms leave straight striated tracks while those with smooth bottoms wander.

The sailing stones were originally thought to be moved by strong winter winds, in the upwards of 90 mph, once it had rained enough to fill the playa with just enough water to make the clay slippery. The prevailing southwest winds across Racetrack playa blow to northeast. Most of the rock trails are parallel to this direction, lending support to this hypothesis.

An alternate theory suggests that as rain water accumulates, strong winds blow thin sheets of water quickly over the relatively flat surface of the playa. Sheets of ice form on the surface as night temperatures fall below freezing. Wind then drives these floating ice floes, their aggregate inertia and large area providing the necessary force required to move both small and large stones. Rock trails would again remain parallel to the southwest winds. According to investigator Brian Dunning, "Solid ice, moving with the surface of the lake and with the inertia of a whole surrounding ice sheet, would have no trouble pushing a rock along the slick muddy floor."

Another hypothesis is focused on observations and measurements of narrowing trails, heat conductivity of the playa's rocks, water, ice and sediments, missing rocks from ends of the trails, and an intermittent spring system in the playa. Kletetschka with his team identified three groups of Racetrack playa spring lineaments, Spinal Springs, Edge Springs, and Gindarja Springs, through which additional water flows into the playa once the ice forms on the water inside the playa. This mechanism, in addition to the raft hypothesis,allows lifting the rocks by adding additional amount of water via these springs.

The most recent research and observations of moving stones indicates that ice collars form around rocks and the rocks along with ice are buoyantly floated off the soft bed. The minimal friction allows the rocks to be moved by arbitrarily light winds.

In a study released in August, 2014, researchers observed rock movements using GPS and time-lapse photography. They documented a rock movement on December 20, 2013 that involved more than 60 rocks, with some rocks moving up to 224 meters between December 2013 and January 2014 in multiple move events. This study contradicted earlier hypotheses of winds or thick ice floating rocks off the surface. Instead, rocks move when ice sheets just a few millimeters thick start to melt during periods of light wind. These thin floating ice panels ice shove the rocks at up to five meters per minute.