Scientists captured the movement of stones along the Racetrack Playa in Death Valley National Park. With this evidence, they can now explain the mechanism behind the rocks' mysterious motion.
"As it turns out, the movement requires the perfect concatenation of
events. First, the playa has to fill with water, which must be deep
enough to form floating ice during winter, but still shallow enough that
the rocks are exposed.
When the temperature drops at night, this
pond freezes into thin sheets of "windowpane" ice, which then must be
thick enough to maintain strength, but thin enough to move freely.
when the sun comes out, the ice melts and cracks into floating panels;
these are blown across the playa by light winds, propelling the rocks in
front of them.
And it's surprisingly gentle: the sheets of ice
are only 0.25in (3-5mm) thick, moving under winds of 10mph (3-5 metres
per second), pushing the rocks along at a speed of only a few inches per
second -- a speed which is almost imperceptible at a distance unless
you know what to look for."
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