Massive boulders in Death Valley California have been known to move as much as several hundred feet on their own. Despite decades of study, no one knew how. That is until Scripps geoscience professor Richard Norris drilled GPS trackers into the rocks and pointed video cameras at them as part of his “Slithering Stones Research Initiative” in 2011.
Here’s what his team discovered:
“The largest observed rock movement involved >60 rocks on December 20, 2013 and some instrumented rocks moved up to 224 m between December 2013 and January 2014 in multiple move events. In contrast with previous hypotheses of powerful winds or thick ice floating rocks off the playa surface, the process of rock movement that we have observed occurs when the thin, 3 to 6 mm, ‘windowpane’ ice sheet covering the playa pool begins to melt in late morning sun and breaks up under light winds of ~4–5 m/s. Floating ice panels 10 s of meters in size push multiple rocks at low speeds of 2–5 m/min. along trajectories determined by the direction and velocity of the wind as well as that of the water flowing under the ice.”
The GPS units were placed inside the rocks along with a battery back. A magnet set nearby triggered a switch that would log the boulder’s position once movement was detected.
The findings were released this week in the journal Plos One.