Smooth Desert Boulders May Be Quakes’ Work

Smooth Desert Boulders May Be Quakes’ Work - Across the Atacama Desert in Chile are thousands of peculiar boulders that look as if they were rubbed smooth across their midsections.

How did it happen? Normally rocks become smooth by rubbing against one another in a body of water, but the Atacama is one of the driest places on the planet. Now a team led by Jay Quade, a University of Arizona geologist, has suggested an answer.

At the annual meeting of the Geological Society of America in Minneapolis, Dr. Quade and his colleagues Peter Reiners and Kendra Murray reported that the boulders rolled down from the hills above, dislodged by earthquakes.
Boulders in a Chilean desert appear to be rubbed smooth.

Over millions of years, the large boulders, each up to 10 tons, accumulated across the desert and began rubbing against one another during earthquakes, resulting in the smooth midsections.

Around the world, earthquakes typically result in water damage, in the form of floods and tsunamis, Dr. Quade said. But because the Atacama is so dry, water does not enter the picture.

“This provides a snapshot into a process we geologists don’t normally recognize — the role of seismicity,” he said.

The researchers estimate that since about two earthquakes occur in the region every year, it took about a million years for the boulders to gain their smooth belts.

Dr. Quade added that with some searching, similar boulders might be found on the Moon and on Mars and other planets where water is scarce. ( )

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