You missed the world's largest natural landslide since 2010.
If no one's around to see a landslide, does it make a noise? You bet. 030514 OUTDOORS 1 Capital City Weekly You missed the world's largest natural landslide since 2010.

Drake Olson Photo

Haines pilot Drake Olson was the first person to see the world's largest natural landslide since 2010. One face of Mount La Perouse collapsed, spreading debris across Brady Glacier.

Drake Olson Photos

Mount La Perouse and Brady Glacier are seen after the slide.

Drake Olson Photos

Olson prepares to climb the slide after his landing his small plane at its foot.

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Wednesday, March 05, 2014

Story last updated at 3/5/2014 - 2:02 pm

If no one's around to see a landslide, does it make a noise? You bet.

You missed the world's largest natural landslide since 2010.

Don't worry - you're not alone. When an estimated 70 million metric tons of rock and ice fell off Mount La Perouse, no one was there to see it. In fact, the sight went unseen for five days, even though seismologists knew from the first instant that something unusual was afoot.

"They saw a big signal and they knew it was somewhere in Southeast Alaska," said Martin Geertsema, a professor at the University of Northern British Columbia and a landslide expert for the British Columbian government.

The "they" in this case was a team of researchers from Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y.

In March last year, that team published a the results of an experiment using the world's network of earthquake sensors. Instead of looking for earthquakes, they used the sensors to search for the signals given off by landslides.

The results were astounding. From thousands of miles away, they could tell the size and duration of a landslide - even how far it traveled across the landscape.

That information had never been seen before, because seismologists weren't looking for it.

"Because all our sensors and computers are tuned for earthquake signals ... our particular organization, we are not looking for landslide signals," explained Natalia Ruppert, a seismologist at the Alaska Geophysical Institute.

Imagine a set of field glasses aimed at a distant ridge. Looking at that ridge, you'd miss what was happening on the next ridge over.

The Lamont-Doherty team shifted the field glasses and saw something new.

In June 2012, with their paper months from publication, they detected an enormous avalanche at Mount Lituya in Glacier Bay National Park.

According to the scientists' measurements, the landslide involved almost 30 million metric tons of rock - but no one saw it because of its remote location.

One month later, Haines pilot Drake Olson was running a flightseeing tour when he shot the first aerial photos of the slide. "I started getting excited," he said, "and (the passengers) were getting excited because they saw I was getting excited."

Olson sent his photographs to fascinated scientists and stayed connected with them.

When the ground moved on Feb. 16, the recordings indicated a slide three times the size of Lituya.

Four days later, word of the slide reached Olson. What he didn't know was where. "I said, OK, if it's three times the size of Lituya, where is it? And they said the Panhandle."

Olson had encountered one of the problems with the new system - as built, it lacks precision. Colin Stark, one of the key figures on the Lamont-Doherty team, said Feb. 26 that his group needed satellite imagery to confirm the slide's location.

Without that confirmation, they knew only that it was within a 30-mile by 30-mile space of Glacier Bay National Park.

Olson didn't want to wait. He called Geertsema, who he knew from the 2012 slide, and took off.

"I almost didn't go because it's cloudy and I'm so flipping busy I need to stay on the ground and do ground stuff," he said. "I got up there to about 12,000 feet, and I could see off in the distance that (the sky) was open."

He flew on, over the magnificent scenery of Glacier Bay.

"There was nothing obvious. I thought, I might as well just enjoy this," he said.

Forty minutes later, he saw it, smack in the middle of Brady Glacier. "It stuck out like a sore thumb," he said.

Snow had partially covered the avalanche, but 60 million metric tons of rock and ice is hard to hide.

According to pictures, the slide started about 9,000 feet up. It tore down a steep slope, ran up the side of the mountain opposite, then cascaded downhill, creating a streak almost 5 miles long on the glacier.

"It's an amazing mix of crushed snow and ice and rock in a slurry craziness," Olson said.

The debris is 30 feet thick in places, cemented in place with ice that melted under the friction of the slide, then refroze.

He landed his plane at the foot of the slide and took out his skis.

"When you're out there, and you know you're all alone ... It's really neat and scary too," he said. "I probably walked up two-thirds of it, then the mountain started shedding some more of it."

Olson took off, carrying his pictures back to Haines.

There's no telling what caused the slide, but Geertsema said it was probably a combination of factors. "Techtonics, thermal stresses ... all these things kind of combine," he said.

The area is prone to landslides, and January's mild weather may have been the straw that broke the mountain's back.

In the long run, he said, scientists are seeing more large slides in the mountains. "I think it's in part due to better detection, but we are seeing an increased trend of these things," he said.

That matters for Alaskans throughout Southeast. While this slide took place on a glacier, others are possible closer to tidewater.

"These kind of things happened in safe areas, but they just as likely could have been rockslides into inlets. That could impact coastal communities or cruise ships, for example," Geertsema said.

In 1958, a slide fell into Lituya Bay and created a tsunami estimated at 1,500 feet high. In May 2012, a landslide fell into Nepal's Seti River, causing a tsunami that killed 72 people.

To date, research has focused on detecting slides in remote areas. Detection will allow scientists to gather more data and come closer to predicting future landslides. "I guess one of the questions we have is where is the next one going to be? That question is a lot more difficult," Geertsma said.