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5-mile-long landslide in Alaska national park; warming eyed as possible culprit

FlyDrake.com via Glacier Bay National Park

Rock and debris from a landslide lie along five miles of what had been an ice-white glacier inside Glacier Bay National Park.

A massive landslide sent tons of rock and debris tumbling more than five miles down a glacier in Alaska, the National Park Service reported in an event that could be yet another sign of a warming world.

Located in a remote area of Glacier Bay National Park, the slide was so big it registered on earthquake monitors as a magnitude 3.4 event.

Officials noticed the monitor blip on June 11 but it wasn't until July 2 that a pilot passing over the site took photos that showed just how large it was, Glacier Bay National Park announced on its Facebook page.

"It's certainly the largest that we're aware of" inside the park, Glacier Bay ecologist Lewis Sharman told msnbc.com.

Larger landslides have happened over geologic time, Marten Geertsema, a natural hazards researcher for the Forest Service in nearby British Columbia, told msnbc.com, but it definitely was "one of the longest runout landslides on a glacier in Alaska and Canada in recent times."

Moreover, the force was enormous, Geertsema said. No one was present, but had anyone been there they probably "would be blown over by the air blast," he told the Associated Press. 

Officials ruled out an earthquake as the trigger that caused part of the nearly 12,000-foot Lituya Mountain to give way, smothering the ice-white Johns Hopkins Glacier with dark rock and debris over an area a half-mile wide and 5.5 miles long.

Drake Olson / FlyDrake.com via AP

The landslide is viewed from above the Johns Hopkins Glacier.

One possibility is that thawing permafrost, which is ground that stays frozen for two more our years, caused the slide.

"We are seeing an increase in rock slides in mountain areas throughout the world because of permafrost degradation," said Geertsema. 

"I don't know whether permafrost degradation played a role here, but we can be almost certain that permafrost exists on Lituya Mountain," said Geertsema, who reviewed aerial photos of the mountain and slide area. "Certainly this type of event could happen from permafrost degradation."

Many areas of mountain permafrost have been thawing in recent decades as temperatures warm, and some experts are becoming convinced that thawing is a factor in the frequency of rock slides, Geertsema said, pointing to data by Swiss scientists studying the Alps.

Marten Geertsema and Drake Olson

The section of rock and ice that slid off Lituya Mountain is seen here. Marten Geertsema estimates it was 200 meters, or about 600 feet, wide.

"It plays an important role," Geertsema said of climate change. "I think we have been underestimating the role it might play." 

Sharman, the park ecologist, echoed that sentiment, saying he's heard from experts that "they would not be surprised" to see more such landslides inside the national park if temperatures continue to warm.

"Certainly we are seeing an increase in large landslides over the past decades," Geertsema said, citing his 2006 study that found between 1973 and 2003 the average in northern British Columbia increased from 1.3 large landslides per year to 2.3.

Moreover, he said, most of the slides in northern British Columbia are happening in the warmest years.

Landslides like this one can also be triggered by other factors, Geertsema added, such as a combination of large snowpack and a cold spring that results in a delayed and then rapid melt.

The slide itself was miles from areas used by park visitors, most of whom see Glacier Bay by cruise ship. 

"You can't see it from a boat or the bay. You've got to be up flying. And it's not on a typical flying route," park service spokesman John Quinley told Reuters. "It would have been pretty horrific if you'd been camped on the glacier."

And it won't reach the bay for a long time.

The frozen ground that covers the top of the world has been thawing rapidly over the last three decades. But there is cause for concern beyond the far north, because the carbon released from thawing permafrost could raise global temeratures even higher. NBC's Anne Thompson reports for "Changing Planet," produced by NBC Learn in partnership with the National Science Foundation.

"The landslide is approximately 12-14 miles up the glacier," the park said on its Facebook page, and the glacier itself moves material towards the bay only about 10-15 feet a day. "So this debris may not reach the face of the glacier for many years," it added.

Officials are currently trying to estimate the volume of material that fell in the slide.

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In 1958, a nearby landslide, this one above Lituya Bay and triggered by a 7.7 earthquake, created a wave hundreds of feet high that washed 1,720 feet up a narrow inlet. Two people on a fishing boat vanished and three others on land were killed. 

One fishing vessel was able to ride out the wave, Geertsema noted.

"They looked below them and they could see the tops of the Sitka spruce trees way below," he said. "The other boat disappeared."

Last month's slide covered more land area than the 1958 incident, but even so it probably won't go down as the biggest one by volume in North America.

"We do not know the volume of the recent landslide on the Johns Hopkins Glacier yet, but it is unlikely to break the volume record," Rex Baum, a U.S. Geological Survey expert, told msnbc.com.

What is the record? That, said Baum, would be the 2.8 cubic kilometer rock slide avalanche from the May 18, 1980, eruption of Mount St. Helens in Washington state.  

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