Mount Steele landslide 1 of the 10 largest of the year: researcher

Experts say they aren't surprised about a massive landslide on Mount Steele in southwest Yukon earlier this month, but that doesn't mean they know what triggered it. 

The St. Elias Mountains are young, steep and heavily glaciated, which makes them more susceptible to slides, says Jeff Bond, manager of surficial geology at Yukon Geological Survey. 

"This is a highly active area," he says. 

On Oct. 11, 45 million tons of rock, snow and ice came thundering off Mount Steele, a 5,067 metre peak in the remote icefields of the St. Elias Mountains, in Kluane National Park and Reserve. The debris — which NASA compared to the weight of approximately 700 aircraft carriers — fell approximately one kilometre and slid about twice that distance on the Steele glacier. 

This is the second significant slide in the area in less than a decade. A 2007 slide on Mount Steele is considered one of the largest known landslides in western Canada. 

Bond says the recent slide may be smaller, but it's still thrilling. 

"It's always exciting to see mother nature in high-speed action," he said. "This is geology on steroids, so to speak, where things are happening quickly and catastrophically."

'Actually a very large event'

The recent landslide was discovered by Goran Ekstrom, a seismologist and professor at Columbia University who tracks seismic data worldwide. 

The force of millions of tons of rock and ice coming off the mountain caused seismic waves measuring similar to a magnitude five (moderate) earthquake, he says. 

"It's actually a very large event. We don't have a full list of large landslides, but I would say this will be in the top 10 of 2015. Worldwide," said Ekstrom. "It might even be higher up on the list."

He says the scientific community doesn't know if there is a "special condition" with Mount Steele that caused two significant events in a short period of time. He says, although ground shaking can case landslides, there were no earthquakes in the region the day of this slide, nor were there other obvious triggers. 

Ekstrom says many people are surprised to hear that a landslide of this scale could go almost undetected, but he says if it weren't for the satellite images from NASA, that likely would have been the case with this one. Shortly after Ekstom detected the Mount Steele slide, his colleague Colin Stark tracked down NASA images that show Mount Steele before and after the slide.

"In a few weeks, there will probably be snow on top of these deposits and nobody would ever have known that there was a landslide." said Ekstrom.

Ekstrom says researchers think there might have been another large landslide south of Mount Steele in Alaska last week, but researchers have been unable to confirm the slide using satellite images due to cloudy weather. 

Geologists say Kluane is one of the most seismically active regions in the Yukon because of the Duke and Denali faults. Although Mount Steele is in a remote area accessible only by aircraft, a small landslide did occur much closer to the the beaten path in August 2014.

CBC contacted Kluane National Park and Reserve for comment, but did not hear back.