Trails left by rocks are seen in a shallow lake in Death
Valley's Racetrack Playa. REUTERS/Scripps Institution of
Oceanography, University of California, San Diego
A solution to the longstanding mystery of why rocks move
erratically across an isolated patch of California's Death
Valley finally emerged today, when researchers published a
study showing the driving force was sheets of wind-driven ice.
Trails from the movement of the rocks, which show them
changing direction suddenly in their movement across the
so-called Racetrack Playa, have long befuddled scientists and
the general public. People wondered: How were the rocks
Paleobiologist Richard Norris of the Scripps Institution of
Oceanography, who led the study, saw the rare phenomenon
first-hand last December while standing with his cousin,
engineer James Norris, at the spot.
They published their findings on Thursday in the journal PLOS
One, showing that even though the stones can sit for a decade
or more without moving, on certain occasions they go on a
slow trip that results from an unusual combination of ice and
wind in an area normally known for scorching hot
That happens when the dry lake bed they are in freezes over
with a thin layer of ice which then breaks apart in a light
wind, sending large sheets of ice against the rocks with
enough force to move them a few yards per minute, Norris
Because of the ability of the large ice sheets to catch the
wind, and aided by the underlying flow of water, the rocks,
which weigh as much as 318kg, are pushed along in a way that
could not occur from the force of the wind alone, he said.
A scientific theory dating back to the 1950s had suggested
that thick ice and heavy winds could be behind the movement
of the rocks, but the study published today found the ice is
far thinner and the wind much lighter than first thought.
Popular theories for what drives the rocks have ranged from a
sudden tilting of the Earth to the action of giant magnets
under the surface of the ground.
"I think it has massive popular appeal because it is one of
these things that's very widely known about but kind of
marvelled at," Norris said.
Norris said other people might have seen the rare phenomenon
of wind-driven ice pushing the Death Valley rocks, but they
probably did not understand what they were seeing because it
happens so slowly and the trail the rocks leave is obscured
until the water dries out.
His team used motion-activated GPS units built into rocks and
also cameras to document the phenomenon in preparation for
publishing their findings.