Glacial Debris and Saturated Soil: A Geological Recipe For Mudslides

Mar 26, 2014

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.


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The death toll from Saturday's massive landslide near the small town of Oso in Washington state is at least 16. Emergency managers say they've located other bodies under the mud, but will add them to the official total only after they've been recovered. Dozens of people are still listed as missing or unaccounted for. From the HERE AND NOW Contributors Network, Tom Banse has this report.

TOM BANSE, BYLINE: Business is understandably slow right now at the small upholstery shop where Leila Hoffman works. That leaves lots of time to think. Hoffman is about three miles down the road from the landslide.

LEILA HOFFMAN: Yeah. It's been kind of nerve-wracking. And you can't ever put it out of your mind, because all day long, the helicopters are going, you know? And I guess not that you should put it out of your mind at this point.

BANSE: Those search-and-rescue helicopters are flying to and from the square mile of mud and debris. Saturday's slide crashed down on a rural neighborhood of fisherman's cabins, farm houses and regular homes.

HOFFMAN: You know, my life goes on, and I kind of feel guilty about it, you know? It's, like, if I was younger and stronger, I'd be up there volunteering - not that they need any more now.

BANSE: Local volunteers familiar with the landscape and skilled with chainsaws are helping what is now a massive emergency response. The National Guard has arrived. A federal urban search and rescue team is on scene. Hovercraft skitter on water around the perimeter. FEMA communications trucks are parked in neighboring towns. Backhoes and bulldozers are clearing paths into the debris.


BANSE: Frequent rain showers are making it challenging for both professional and volunteer responders to move across the square mile of soupy, slippery debris. Rescuers are employing high-tech electronics to help locate buried victims. Snohomish County emergency management director John Pennington says some searchers are carrying sensitive receivers to detect mobile phone signals.

JOHN PENNINGTON: They're trying to ping for cellphones for the purposes of essentially locating individuals in the debris. And there are technologies that can further refine where that ping came from. And I know that process is actually going on right now.

BANSE: Other technical rescue teams are armed with listening devices and small cameras to probe voids in the mudflow. But old-fashioned tools have actually worked best, according to local fire chief Travis Hots.

TRAVIS HOTS: The last three days, the most effective tool has been dogs, and just our bare hands and shovels uncovering people. But the dogs are the ones that are pinpointing a particular area to look, and we're looking, and that's how we're finding people.

BANSE: Unfortunately, Hots says there have been no survivors or signs of life detected since Saturday night. Cadaver dogs have joined the search dogs. Hots has dark circles under his eyes after four nights of little sleep. But he promises the large number of families still awaiting word about missing loved ones, the search will continue, as he puts it, on all eight cylinders, until everyone is accounted for. For HERE AND NOW, I'm Tom Banse in Arlington, Washington. Transcript provided by NPR, Copyright NPR.