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A MYSTERY for more than 70 years has been solved: What prompts rocks, some weighing hundreds of pounds, to move across Racetrack Playa of Death Valley?
Racetrack Playa is a dry mud surface of Death Valley National Park. It’s almost completely flat, gets no more than 2 in. of rain annually, yet at an elevation of 3708 feet is known for extremes of heat and cold.
The playa has been studied since 1948 when researchers sought to explain its odd phenomenon of rocks that, immobile for years, would seemingly get up one day and move around leaving a trail of dried mud. Hypotheses for this errant behavior suggested “dust devils,” winds of hurricane force, films of slick algae, floating sheets of ice, pranksters and (no surprise, here) UFOs.
In 2011, Richard D. Norris, of the Scripps Institution of Oceanography, and his cousin James M. Norris, of the R&D firm Interwoof, set up the Slithering Stones Research Initiative. They and colleagues installed a weather station and time-lapse camera near the playa.
Also, the researchers installed GPS devices in rocks and set them on the playa. And they waited. For more than two years, no rock moved anywhere.
Then, in November 2013, a freak storm hit the playa with freezing rain and snow. In late December, a perfect combination of conditions set the stones in motion. In fact, the Norrises captured their movement on camera (http://goo.gl/SK0eEo).
First, rain flooded a portion of the playa and turned its normally hard surface into a mud pond. Then, night brought freezing temperatures before the water could evaporate. A portion of the playa was covered in panes of ice, as thin as 1/4 in. and hundreds of feet across.
The next morning, the sun caused portions of the ice to thaw, with huge cracking sounds, and a light wind set these ice floes into movement. Rocks atop them meandered at about 15 ft./min. across the playa. More than 60 rocks traipsed around on December 20, 2013. Within a month, some of the instrumented rocks traveled as much as 735 ft. in whimsical patterns wrought by breeze and terrain.
The Norrises and colleagues published “Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion” in the research journal Plos One.
“There was a side of me that was wistful,” James Norris said, “because the mystery was no more.” ds
© Dennis Simanaitis, SimanaitisSays.com, 2014