Scientist Takes Close Look at Alaska Landslide

May 16, 2013

A buildup of moisture in the soil likely caused a large landslide near the town of Sitka, according to a federal scientist who is taking a close look at Sunday’s slide in southeast Alaska.

U.S. Forest Service soil scientist Jacquie Foss told the Daily Sitka Sentinel that the landslide that destroyed the Redoubt Lake cabin, blocked the river and covered the surrounding area was likely caused by last week’s warm weather that melted snow on the mountainside. The soil on top of the underlying bedrock was unable to hold given the added moisture to the soil, she said.

Rain on Saturday and Sunday added to the weight of the soil on the steep slope, and at a certain point the soil separated from the bedrock and gravity did the rest.

“This has to do with overloading the slope with water,” Foss said.

She estimated the slide started at between 900 and 1,100 feet in elevation, and was 1,400 feet long and about 700 feet wide.

“This gives a conservative estimate of about 20 acres in area,” Foss said in an email. “This is a very large slide by Tongass standards – most of our landslides are 5 acres or less.”

The slide happened Sunday just as Kevin Knox, 41, and his girlfriend, Maggie Gallin, 28, returned from fishing in a rowboat to the National Forest Service cabin at Redoubt Lake, about 15 miles southwest of Sitka.

The cabin is surrounded by mountain slopes and rocky cliffs that go up about 4,000 feet above the lake.

Knox said Maggie was in the cabin when a huge piece of the mountain let loose. He yelled for her to get out of the cabin and the two ran for the beach, with Knox’s 10-year-old border collie, Luna, by his side. The couple and others have searched for the dog, but she remains missing.

Knox said the cabin and all the couple’s belongings ended up under about 20 feet of debris.

Foss said that while rockslides and debris avalanches are not uncommon on the Tongass, this one was unusual for its timing. Typically the Forest Service sees “lots and lots” of landslides in the fall following the heavy rains of October and September.

“To me, this is an odd time of year, with nice weather, it’s warming up,” she said. “It’s pretty amazing that all at once a failure would occur.”

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