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.
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.
- David Montgomery, professor of geology at University of Washington.
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