Deadly mudslide in Washington

This image, taken from an airplane, shows the best view I’ve seen of a mudslide just east of the town of Oso in rural, northwestern Washington State.

The mudslide occurred at about 10:45 a.m. on the morning of Saturday, March 22nd along the Stillaguamish River. As of the time of this writing, there have been 8 people confirmed dead but today searchers stunned the press by reporting that the list of potential missing includes up to 108 names.

The searchers stress that the list includes vague descriptions like “John who once lived in this neighborhood”, so the total of missing should not be immediately interpreted as a possible death toll. The mudslide hit 49 different lots containing property, at least ½ of which were believed to be occupied full time, and buried Highway 530 – the only route to a nearby town of 1,359 called Darrington.

The slide also completely blocked the Stillaguamish River, reducing its output to a trickle. When landslides occur, they can completely block rivers, creating lakes behind them that eventually overtop the dam leading to a major flood. Flood warnings have been issued on the river, but most likely some degree of digging/dredging will open up a flow path to let the water slowly pass through.

The rocks that collapsed appear to be loosely-consolidated, possibly-glacial sediments. Similar events are common in this area; the state of Washington recently completed a $13 million project to stabilize a portion of hillslope on the opposite side of the river from this slide. Additionally, this area has endured significant rainfalls over the past several weeks, although there was no specific storm right before this slide. Instead, the amount of rain caused buildup of groundwater pressures in the area, and eventually this groundwater pressure allowed the hillslope to give way. Rainfall totals during the month of March in this area are about 300% above the average totals for the month.

Layering in the disrupted central block appears somewhat intact and can be seen in this photo; the slide broke away along an arcuate scarp and left debris piles that are reportedly up to 4.5 meters (15 feet) thick.

From here, search teams will have to simply dig through significant portions of that sediment to try to locate and identify those missing, in addition to digging through that big pile of dirt to prevent flooding on the river.

-JBB

Image credit: Washington State DOT via Reuters/NBC
http://www.nbcnews.com/storyline/deadly-mudslide/washington-mudslide-toll-rises-eight-least-18-missing-n59981

Read more:
http://blogs.agu.org/landslideblog/2014/03/23/oso-landslide-1/
http://news.nationalgeographic.com/news/2014/03/140324-mudslides-natural-disasters-geology-science/
http://www.slate.com/blogs/future_tense/2014/03/24/oso_wash_mudslide_climate_change_may_bring_more_such_disasters.html
http://www.cnn.com/2014/03/23/us/washington-landslide/
http://www.latimes.com/nation/nationnow/la-na-washington-mudslide-108-missing-search-20140324,0,7984706.story#axzz2wu5DV3ch
http://www.stltoday.com/news/national/voices-crying-for-help-stop-in-washington-mudslide/article_7802d13b-177e-5bff-9ec3-117f9dd494e5.html

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Washington State Mudslide from Above

A few days ago, a hillside above Oso, Washington collapsed after weeks of heavy rain, sending a wall of mud and debris across a small valley of the Stillaguamish River. The neighborhood below the hillside was destroyed, and more than 100 properties damaged, resulting in at least 14 verified deaths.

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Officials Raise Death Toll to 29 in Washington State Mudslide Tragedy

Officials Raise Death Toll to 29 in Washington State Mudslide Tragedy

Before-and-after photo of the mudslide area (BING/AP)

Officials have now confirmed the deaths of 29 people in the mudslide in rural Washington state, although only 22 have been officially identified in information released Wednesday morning by the Snohomish County medical examiner’s office. (more…)

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Death toll rises in Washington landslide

At least eight people have been killed by a huge landslide that buried cars and houses in mud and debris.

US authorities say the death toll from a massive landslide in rural Washington state has doubled to eight.

Eighteen people were still missing on Sunday after rain-soaked embankments along State Route 530 near Oso, about 90km northeast of Seattle, gave way a day earlier and washed out at least six homes.

The slide in the foothills of the Cascade Mountains along the Stillaguamish River piled mud, rock and debris up to 5 meters deep in some places.

Rescue crews were able to get out to the muddy, tree-strewn area after geologists flew over in a helicopter and determined it was safe enough for emergency responders and technical rescue personnel to search for possible survivors, the Associated Press news agency quoted Snohomish County Fire District 21 Chief Travis Hots as saying.

“We didn’t see or hear any signs of life out there today,” he said, adding that they did not search the entire debris field, only drier areas safe to traverse.

Despite that, Hots said crews were still in a “search and rescue mode. It has not gone to a recovery mode at this time.”

Rescuers’ hopes of finding more survivors had been buoyed late Saturday when they heard people yelling for help from within the debris field, but they were unable to reach anyone. The mud was so thick and deep that searchers had to turn back.

The slide wiped through what neighbours described as a former fishing village of small homes, some nearly 100 years old.

Some of the missing may have been able to get out on their own, authorities said. The number unaccounted for could change because some people may have been in cars and on roads when the slide hit, Hots added.

The slide blocked the flow of the river, creating floods and a backup of water behind a natural dam of mud and debris. (6)

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