Tuesday, January 07, 2014 8:09 pm
Utah avalanche was largest in modern history
By PAUL FOYAssociated Press
The April 2013 rockslide sent 165 million tons of debris into a nearly mile-deep pit where it cracked bedrock and triggered unprecedented earthquakes, the researchers said in a newly published study.
"We don't know of any case until now where landslides have been shown to trigger earthquakes," said Jeff Moore, assistant professor of geology and geophysics.
There were no injuries or deaths as the slide temporarily shut down a copper mine, burying 14 giant haul trucks and leading to a series of layoffs and buyouts at Kennecott Utah Copper Corp.
"It was a creeping movement that had been developing over many months along an old fault line," Moore said Tuesday. Kennecott had been monitoring the area and evacuated workers ahead of the danger, he said.
The disaster didn't involve a volcanic explosion and was actually a pair of related slides about 90 minutes apart, said Moore, who co-authored the study together with Kris Pankow, associate director of the university's seismograph stations.
The peer-reviewed research was published Monday in the Geological Society of America's magazine, GSA Today.
The debris slides falling as fast as 100 mph crashed to earth with such force that they registered as magnitude-5 earthquakes and then triggered 16 smaller quakes where the bedrock cracked, Moore said.
Mother Nature has put on bigger shows, the scientists noted.
The 1980 eruption of Mount St. Helens in Washington unleashed a landslide 57 times larger than Kennecott's.
Another slide about 8,000 years ago at the mouth of Zion Canyon in southern Utah was five times as large.