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Glacial Debris and Saturated Soil: A Geological Recipe For Mudslides

The official death toll from Saturday’s massive landslide near Oso, Wash., now stands at at least 16.

Emergency managers say they have located other bodies under the mud, and will add them to the total only after they’re recovered.

Dozens of people are still listed as missing or unaccounted for.

From the Here & Now Contributors Network, Tom Banse of the Northwest News Network reports on the ongoing rescue and recovery efforts.

And as search efforts intensify, geologists are looking into causes of the rapid collapse of the 1,500 foot wide segment of hillside in Snohomish County that suddenly cut away and crushed the homes and roads below.

The chief culprit appears to have been the glacial composition of the hillside, which is made of silt, clay and soil, and very little rock, which tends to be very loose.

When these collapse they create something called a “rotational slide,” meaning that the land turns on itself, with the base of the hills moving upward as the top collapses.

David Montgomery, a geologist at University of Washington explains the geological circumstances behind the mudslide.

Guests

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Crews work on Washington State Route 530 to clear debris from a mudslide on March 25, 2014 in Oso, Washington. (Ted S. Warren/Getty Images)
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Crews work on Washington State Route 530 to clear debris from a mudslide on March 25, 2014 in Oso, Washington. (Ted S. Warren/Getty Images)
(King County Sheriff's Office - Air Support Unit)
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(King County Sheriff's Office - Air Support Unit)
(King County Sheriff's Office - Air Support Unit)
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(King County Sheriff's Office - Air Support Unit)
(King County Sheriff's Office - Air Support Unit)
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(King County Sheriff's Office - Air Support Unit)
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