Thursday, August 28, 2014

One of Geology's Little Mysteries Solved: The Sliding Stones of Racetrack Playa in Death Valley

Bonnie Claire Playa in Nevada
There are side shows that happen in the sciences. There are the big mysteries of the cosmos and earth history that take many years and the work of dozens or hundreds of the greatest minds to solve: atomic theory, quantum physics, plate tectonics, DNA sequencing and so on. In geology, there are the big picture mysteries of how the continents have moved through time, the patterns of evolution of life on the planet, the origins of rock sequences. It's the great human adventure of exploration that carries us into a fascinating future.

And then there are those nagging little mysteries. Why does bread fall with the buttered side down? Why do cats land right side up? It's the kinds of things that have kept the Mythbusters at work for years. Well, it seems that one of those nagging little mysteries in geology has been solved. For years, stones have left mysterious trackways on the surface of Racetrack Playa in Death Valley National Park. They have been noted more than half a century, and have been the subject of a number of studies, but in all those years no one has seen it happen, or provided a convincing explanation of how it could happen. There have been numerous hypotheses, and of course outlandish ideas like magnetic force lines and alien interventions.
Bonnie Claire Playa, Nevada
But now, we are learning that Richard D. Norris, James M. Norris, Ralph D. Lorenz, Jib Ray, and Brian Jackson have shed light on the mystery, and produced digital images of the rocks in action. In their just released article, Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion, they document the conditions that resulted in the movement of numerous stones on the playa, especially during the winter of 2013-2014. The article can be read in its entirety here: (and thank you for the open access!).

In essence, the researchers marked the location of stones, and outfitted many with GPS trackers. When storms filled part of the playa surface, a thin sheet of ice formed on the water. As the ice began to melt during the day, large sheets of ice were seen moving and pushing the stones.  The winds recorded were not nearly as powerful as expected, as stones were moved when the winds were no more than 4-5 meters per second (9-11 mph). You can see the process happening in the video here:

I was sure all along that UFOs were swooping down and playing a form of ice hockey with complicated rules, but actually the phenomenon the researchers described made good sense. Racetrack Playa is not the only place where rocks have left trails. I've not been to Racetrack Playa yet, but I've seen tracks on Bonnie Claire Playa northeast of Death Valley National Park, and along Highway 50 in the Carson Sink of western Nevada. There were certain factors in common with each site: relatively high altitude, a source of rocks (the roadbed of Highway 50 was one source), and winters that occasionally have freezing conditions and high winds. Ice was suggested as a factor because many of the trails were parallel to each other as if the rocks were locked together.

I've been joking all day that my life feels empty now that the stones have been explained. But does solving the mystery of the sliding stones take away from our sense of wonder at the world? No, it doesn't. It is a marvelous example of how science works. I love to see mysteries solved by good old-fashioned hard work and persistence. 

This also allows me to say to the vandals and felons who have stolen the sliding stones from the surface of the Racetrack, thinking they have some taken possession of a magical key to the supernatural worlds encompassed within: "Guess what, moron! You've stolen a rock. You are an idiot".

Citation: Norris RD, Norris JM, Lorenz RD, Ray J, Jackson B (2014) Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion. PLoS ONE 9(8): e105948. doi:10.1371/journal.pone.0105948

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