An article published in the science journal PLOS ONE on August 27th by scientists from the Scripps Institution of Oceanography has finally put to rest the mystery of the ‘sliding’ rocks of Racetrack Playa in Death Valley.
One of the many rocks photographed that seemed to have slid across Racetrack Playa in Death Valley. The phenomenon was first noticed in the 1940s. Many hypotheses have been made at to the cause of the phenomenon, including that perhaps it is an elaborate hoax. Racetrack Playa is located in the northwestern portion of Death Valley National Park and rests at an elevation of 3,708’ (1,130 m). Photo by Meera Dolasia and taken in 2009.
For years people have been mystified by the apparent movement of rocks, some weighing over 100 pounds, over hundreds of feet along the flat surface of Racetrack Playa in Death Valley leaving long tracks etched in the ground as they move. Richard D. Norris and his cousin James M. Norris launched an investigation into the mystery beginning in 2011 with their ‘Slithering Stones Research Initiative’ sponsored by NASA and Scripps among others. They established a weather station in the area near the playa (with permission from the Death Valley National Park Service, not an easy accomplishment!) and placed 15 stones attached with GPS tracking units in the vicinity of the existing ‘sliding stones’ that first triggered the mystery.
Location of weather station in Death Valley overlooking the GPS-instrumented rock zone on Racetrack Playa. Map from PLOS ONE article.
One of the GPS-instrumented rocks and its track across the playa. The GPS unit, with its battery pack, was placed in a cavity bored into the top of the rock. Photo from PLOS ONE article.
Using time-lapse photography they caught on camera the rocks sliding across the playa at the surprisingly fast pace of up to 15 feet (3-5 meters) per minute on December 4th and December 20th, 2013 as well as other occasions. In all cases rainfall preceded the events, which froze just beneath the playa surface. During the mornings after the rainfalls and freeze-up they relate what happened:
” Steady light winds and morning sun caused floating ice to break-up near mid day, accompanied by widespread popping sounds from fragmenting ice panels. Ice initially broke into floating panels tens of meters in size that became increasingly fragmented and separated by open rippled water as melting continued. Floating ice sheets driven by wind stress and flowing water, pushed rocks resting on the playa surface, in some cases moving >60 rocks in a single event...Two rocks recorded movements on December 4; one trail was 65.6 m long (stone mass 16.6 kg) and the other of 64.1 m (stone mass 8.2 kg). Both movements lasted 16 minutes starting at 11:05 am local time. These rocks were originally located ~153 meters apart, and began motion within 6 seconds of each other. Both rocks initially reached velocities of 5–6 m/minute that fell to 3–4 m/minute by 6 minutes into the move event. The December 20 event is recorded by one rock (stone mass 15.4 kg) with a 39.1 m movement over 12.3 minutes starting at 11:37 am. The rock initially achieved a velocity of 2–3 m/minute, then nearly stopped 4 minutes into the move, resumed a minute later, and traveled 5 m/minute to the end of the move event.”
Graphic of weather conditions measured at the weather station established just above the play for the period of November 19, 2013-January 9, 2014. At the top of the graph are the dates of major rock movements. From PLOS ONE article.
An overview photo (from the ‘Source Hill’ shown in the map earlier) displaying the dozens of GPS-instrumented rocks that slid across the playa on December 20, 2013. Photo from PLOS ONE article.
Although this hypothesis has been made before (along with many others) this is the first time peer-reviewed proof of the phenomenon and what causes it has been confirmed by scientific investigation.
The entire article in PLOS ONE (a fascinating read) may be found here.
REFERENCE: ‘Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion’ by Richard D. Norris, James M. Norris, Ralph D. Lorenz, Jib Ray, Brian Jackson, PLOS ONE, August 27, 2014.
Christopher C. Burt
Weather Historian
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