Geology Rocks

emlocke:

Seismicity and the Strange Rubbing Boulders of the Atacama Desert

[The half-ton to 8-ton boulders] appeared to be rubbed very smooth about their midsections. What could cause this in a place where Earth’s most common agent of erosion—water—is as almost nonexistent? … Over the approximately two million years that these rocks have been sitting on their sandy plain perhaps they were jostled by seismic waves. They caused them gradually grind against each other and smooth their sides. It made sense, but [University of Arizona geologist Jay Quade] never thought he’d be able to prove it.

Then, on another trip to the Atacama, Quade was standing on one of these boulders, pondering their histories when a 5.3 magnitude earthquake struck. The whole landscape started moving and the sound of the grinding of rocks was loud and clear.

“It was this tremendous sound, like the chattering of thousands of little hammers,” Quade said. He’d probably have made a lot more observations about the minute-long event, except he was a bit preoccupied by the boulder he was standing on, which he had to ride like a surfboard … “I was just astonished when this earthquake came along and showed us how it worked,” Quade said. Quade will explain the phenomenon on Tuesday, 11 Oct., at the annual meeting of The Geological Society of America in Minneapolis.

(via GSA press release - The Strange Rubbing Boulders of the Atacama)