Death Valley 2009 #1
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The Mysterious "Sailing" Rocks Of Racetrack Playa
Hypotheses For Movement Of Rocks Across The Lakebed
Several hypotheses have been proposed to explain the sliding ("sailing") rocks of Devil's Racetrack in Death Valley National Park, but no one has actually filmed this remarkable phenomenon in motion or observed it in real time. GPS measurements indicate that the rocks have moved across the lakebed (playa) in different directions. Most authorities agree with at least two conditions necessary for the movement of rocks. (1) Occasional heavy rains and runoff from nearby slopes producing a slick surface on the fine clays of the lakebed. (2) Gail force, multidirectional winds of at least 100 miles per hour, strong enough to push the rocks across the surface in different directions. (3) A third hypothesis builds upon the previous ones and appears to be necessary for larger rocks weighing up to 700 pounds. Freezing nighttime winter temperatures that produce a floating ice sheet on the muddy clay surface. As the lakebed dries, the clay mud shrinks and cracks into a mosaic of interlocking polygons. When the playa fills with water, the fine bentonite? clay imbibes water and the polygonal cracks coalesce into a sticky surface. Another hypothesis describes colonies of cyanobacteria living in the surface clay that also imbibe water and become mucilaginous, possibly contributing to the slippery surface.

There are additional hypotheses to explain the movement of rocks, however, most of these can be discounted. Gravity can be ruled out since the north end of the lakebed is 1.5 inches (4 cm) higher than the southern end, and most of the rocks traveled slightly uphill. Pranksters during wet years is a possibility, except they left no footprints in the soft, muddy clay surface adjacent to the rocks. Another hypothesis involves aliens from another planet who visited this playa during exceptional wet years.

Sailing rock on Devil's Racetrack Playa showing grooved track in its wake.

The sailing rocks on Devil's Racetrack move in different directions.

As the lakebed dries, the clay mud shrinks and cracks into a mosaic of interlocking polygons.

Close-up view of dried, cracked mud of Devil's Racetrack Playa.

Stones with rough bottoms leave striated tracks in their wake. In next image colors are inverted to normal.

The steep slope in upper left is the source of the angular rocks.

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