Massive landslide in Alaska sweeps over glacier

[July 13, 2012]  ANCHORAGE, Alaska (AP) -- Even by Alaska standards, the rock slide in Glacier Bay National Park was a huge event.

It was a monumental geophysical event that was almost overlooked until a pilot happened to fly over where the cliff collapsed and snapped some photographs nearly a month later.

When the cliff collapsed in the national park in southeast Alaska on June 11, it sent rock and ice coursing down a valley and over a lovely white glacier in what perhaps was the largest landslide recorded in North America.

The rumbling was enough so that it showed up as a 3.4-magnitude earthquake in Alaska. The seismic event also was recorded in Canada. The massive landslide occurred in a remote valley beneath the 11,750-foot Lituya Mountain in the Fairweather Range about six miles from the border with British Columbia.

"I don't know of any that are bigger," Marten Geertsema, a research geomorphologist for the provincial Forest Service in British Columbia, said Thursday, when comparing the landslide to others in North America.

If someone had been standing in front of the slide, the air blast alone would have flattened that person, said Geertsema, who studies natural hazards resulting from geophysical processes on the earth's surface.

"I think they would be blown over by the air blast," he said.

Despite the extraordinary size of the landslide, which was estimated at a half-mile wide and 5 1/2 miles long, it went virtually unnoticed until air taxi pilot Drake Olson flew over it on July 2. The landslide, which rolled over the glacier, is not very noticeable to the thousands of cruise ship passengers that visit Glacier Bay National Park near Juneau each summer. That is because it is about 12 to 15 miles up the glacier from the bay.

While this one was huge by North American standards, bigger ones have occurred, including a September 2002 landslide in Russia that extended for 20 miles, Geertsema said.

Lituya Mountain has been the scene of extraordinary geophysical events before. In 1958, a landslide on the other side of the mountain produced a wave estimated at 1,700 feet.

One fishing vessel was able to ride out the wave.

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

Another boat with two people aboard disappeared.

One of Olson's photos of the June landslide shows a huge dent in the side of an ice-covered peak. Another shows a river of rock and ice that flowed out of a valley. The landslide triggered numerous avalanches.

Glacier Bay National Park Superintendent Susan Boudreau said visitors to the 3.2-million acre park won't notice anything different in the landscape this summer, but the rock and ice likened to a river of black syrup moving toward the bay is on the move. How fast it is moving is still the question, she said.

"It is going to come down but we don't know the speed of that," Boudreau said.

There are several factors that contribute to the likelihood of mountains collapsing, Geertsema said. Sometimes it is caused by a general weakening of the rock. Other times it could be due to a very large snowpack that melts quickly.

Scientists also are looking at the role of climate change.

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

Permafrost is ground that stays perpetually frozen.

Geertsema said Swiss scientists are becoming increasingly convinced that climate change is playing a role in the frequency of rock slides, after looking at data from instruments measuring temperature and the widening and narrowing of gaps in the rocks in the Alps.

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

Park ecologist Lewis Sharman said the landslide is a reminder of why Glacier Bay National Park is special.

"These types of events to me are welcome reminders that this place is one of the coolest on earth," he said.

[Associated Press; By MARY PEMBERTON]

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