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Climate change: Too much rain caused deadly mudslide on unstable ground

Massive mudslide in Washington
Massive mudslide in Washington
AP Lindsey Wasson

Authorities confirm 14 dead and 176 missing on Monday from the massive landslide that rolled through the rural neighborhood of Oso/Darrington north of Seattle on Saturday covering a square-mile area with mud and mangled trees as it laid waste to 50 structures.

Experts say the cause of the landslide, which wasn’t the first in the area, appears to be ground saturation after receiving double the normal rainfall for March, the sixth-wettest recorded since 1922, as explained by Johnny Burg, a meteorologist from Seattle’s National Weather Service.

The March rainfall was followed by a drier-than-normal 4 month spell.

“That kind of heavy rain really saturates the ground to the point where it cannot hold any more water,” said Burg. “And that creates instability, especially on steep hillsides.”

King5 News reported on Monday more than twice the amount of rain was measured near the Stillaguamish River in a region with geological soils from glacial remnants over 20,000 years old composed of rock and loose sand, which was rendered unstable by the permeation of vast amounts of water.

According to a ThinkProgress report, climate models predict the Pacific Northwest will experience rising temperatures and increasing rainfall, which will cause changes in the regions snowpack and annual snowmelt.

Increasing landslides is also a prediction, bringing a rise in human toll and economic cost.

“If the climate changes in a way that we get a lot more rainfall you would expect to see a lot more landslides,” Dave Montgomery, a geologist at the University of Washington, told EarthFix this week. “The character of the rainfall that we get, whether it’s more high intensity rain or more of the long soak would actually influence the type and style of landslides that we might expect to get but the short answer is, you know, if we get more rainfall we ought to expect to see more landslides and this region already is landslide-prone.”

A similar landslide happened in 2006, which threatened about 12 homes, but caused no fatalities, the Seattle Times reported.

At that time, the Washington State Department of Transportation and The Army Corps of Engineers worked to redirect the river and fortify the area, but it was no match for the wall of mud that crashed across the landscape on Saturday, which was described as a tsunami.

“The slide is about a mile wide. Entire neighborhoods are just gone. When the slide hit the river, it was like a tsunami,” said an unidentified firefighter.

The region has a history of landslides, but permits keep getting issued to build homes, which has been a source of alarm to one local geomorphologist, who has documented the unstable conditions.

“We’ve known it would happen at some point,” Daniel J. Miller told The Seattle Times on Monday. “We just didn’t know when.”

Miller, working with his wife Lynne, submitted a report in 1997 to the Washington Department of Ecology, which warned of soil instability.

Add a changing climate with increasing rain predicted and it boils down to a recipe for disaster if the country keeps allowing new-home construction in the area, not to mention increased floods.

Rescue efforts in the mudslide area are quickly becoming a search and recovery project with up to 60 volunteers and possible help from trained disaster dogs to begin on Monday as teams renew efforts to find people before rain moves back into the area.

Gov. Jay Inslee's office released a statement saying that FEMA will be moving quickly with a "limited emergency declaration for direct federal assistance to assist in the response to the Oso mudslide."

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