DEATH VALLEY NATIONAL PARK, Calif. — For years
scientists have theorized about how large rocks — some weighing
hundreds of pounds — zigzag across Racetrack Playa in Death Valley
National Park, leaving long trails etched in the earth.
Now two researchers at the Scripps Institution of Oceanography
at the University of California, San Diego, have photographed these
"sailing rocks" being blown by light winds across the former lake
bed.
Cousins Richard Norris and James Norris said the movement is
made possible when ice sheets that form after rare overnight rains
melt in the rising sun, making the hard ground muddy and slick.
On Dec. 20, 2013, the cousins catalogued 60 rocks moving across
the playa's pancake-flat surface.
"Observed rock movement occurred on sunny, clear days, following
nights of sub-freezing temperatures," they wrote in a report
published Wednesday in the online scientific journal PLOS ONE.
The conclusion proves theories that have been floated since
geologists began studying the moving rocks in the 1940s.
The phenomenon doesn't happen often because it rarely rains in
the notoriously hot and dry desert valley.
The rocks move about 15 feet per minute, according to the
report.
Richard Norris, 55, a paleobiologist at Scripps, and James, 59,
a research engineer, launched their "Slithering Stones Research
Initiative" in 2011, the Los Angeles Times reported
(http://lat.ms/VNVWou).
After getting permits from the National Park Service, they
installed a weather station in the area and placed 15 stones
equipped with global positioning devices on the playa.
The "GPS stones," which were engineered to record movement and
velocity, were stationed at the southern end of the playa where
rocks begin their strange journeys after tumbling down a cliff.
At the end of last year, Richard and James Norris returned to
inspect the instruments.
"We found the playa covered with ice," Richard told the Times.
"We also noticed fresh rock trails near shards of thin ice stacked
up along the shoreline."
The following afternoon, "we were sitting on a mountainside and
admiring the view when a light wind kicked up and the ice started
cracking," he said. "Suddenly, the whole process unfolded before
our eyes."
This undated photo provided by the National Park Service shows
rocks that have moved across a dry lake bed in Death Valley
National Park in California's Mojave Desert. For years scientists
have theorized about how the large rocks — some weighing hundreds
of pounds — zigzag across Racetrack Playa leaving long trails
etched in the earth. Now two researchers at the Scripps Institution
of Oceanography have photographed these "sailing rocks" being blown
by light winds across the former lake bed. Cousins Richard Norris
and James Norris say the movement is made possible when ice sheets
that form after rare overnight rains melt in the rising sun, making
the hard ground muddy and slick
