RTZ Copper Mine landslide triggered quakes

The April 10, 2013, landslide at Rio Tinto-Kennecott Utah Copper's Bingham Canyon mine contains enough debris to bury New York City's Central Park 66 feet deep, according to a new University of Utah study. 

The slide happened in the form of two rock avalanches 95 minutes apart. 

The first rock avalanche included grayer bedrock material seen around the margins of the lower half of the slide. 

The second rock avalanche is orange in color, both from bedrock and from waste rock from mining. 

The new study found the landslide triggered 16 small quakes. Such triggering has not been noted previously. 

The slide likely was the largest nonvolcanic landslide in North America's modern history. 

Credit: Kennecott Utah Copper.

Last year's gigantic landslide at a Utah copper mine probably was the biggest nonvolcanic slide in North America's modern history, and included two rock avalanches that happened 90 minutes apart and surprisingly triggered 16 small earthquakes, University of Utah scientists discovered.

The landslide – which moved at an average of almost 70 mph and reached estimated speeds of at least 100 mph – left a deposit so large it "would cover New York's Central Park with about 20 meters (66 feet) of debris," the researchers report in the January 2014 cover study in the Geological Society of America magazine GSA Today.

While earthquakes regularly trigger landslides, the gigantic landslide the night of April 10, 2013, is the first known to have triggered quakes.

The slide occurred in the form of two huge rock avalanches at 9:30 p.m. and 11:05 p.m. MDT at Rio Tinto-Kennecott Utah Copper's open-pit Bingham Canyon Mine, 20 miles southwest of downtown Salt Lake City. Each rock avalanche lasted about 90 seconds.

While the slides were not quakes, they were measured by seismic scales as having magnitudes up to 5.1 and 4.9, respectively. The subsequent real quakes were smaller.

Kennecott officials closely monitor movements in the 107-year-old mine – which produces 25 percent of the copper used in the United States – and they recognized signs of increasing instability in the months before the slide, closing and removing a visitor center on the south edge of the 2.8-mile-wide, 3,182-foot-deep open pit, which the company claims is the world's largest man made excavation.

Landslides – including those at open-pit mines but excluding quake-triggered slides – killed more than 32,000 people during 2004-2011, the researchers say.

Fortunate;y, no one was hurt or died in the Bingham Canyon slide. The slide damaged or destroyed 14 haul trucks and three shovels and closed the mine's main access ramp until November.

Kris Pankow

"This is really a geotechnical monitoring success story," says the new study's first author, Kris Pankow, associate director of the University of Utah Seismograph Stations and a research associate professor of geology and geophysics.

"No one was killed, and yet now we have this rich dataset to learn more about landslides."

There have been much bigger human-caused landslides on other continents, and much bigger prehistoric slides in North America, including one about five times larger than Bingham Canyon some 8,000 years ago at the mouth of Utah's Zion Canyon.

More Information: Massive landslide at Utah copper mine generates wealth of geophysical data - GSA Today