One of the largest landslides ever recorded in North America, probably the longest, struck Alaska’s 11,924-foot Lituya Mountain in June but wasn’t discovered until a week or so ago by air taxi pilot Drake Olsen. The slide occurred in Glacier Bay National Park and ran for 5.5 miles along the Johns Hopkins Glacier, covering the ice with dark black soil and rock.
Unlike a 1958 landslide at the same site, which killed five in a giant wave that washed across Lituya Bay, the most recent event was not triggered by an earthquake — but it was large enough to be recorded on seismic sensors with a magnitude of 3.4. Experts speculated that global warming might have had a hand in causing it.
“I don’t know whether permafrost degradation played a role here, but we can be almost certain that permafrost exists on Lituya Mountain,” said Dr. Martin Geertsema, a natural hazards researcher for the Forest Service in nearby British Columbia. “We are seeing an increase in rock slides in mountain areas throughout the world because of permafrost degradation…Certainly this type of event could happen from permafrost degradation.”
The occurrence of large landslides in northern British Columbia increased 77 percent between 1973 and 2003, Geertsema reported in a 2006 study.
The Lituya slide was so powerful, it create snow avalanches along its flanks, and an air blast exploded 1,500 vertical feet up a nearby mountain. Geologists are still calculating the volume of debris, but despite the size is it was neither the longest recently record or the biggest. The former was a 2002 slide in Russia, the latter a slide on Mt. St. Helens in 1980, which released 2.8 cubic kilometers of material.
Photos via National Park Service by Drake Olsen, data by Dr. Martin Geertsema