SR 504 near Mount St. Helens closed indefinitely after mudslide

May 23, 2023, 2:30 PM

Mount St. Helens mudslide...

Following a mud slide on Sunday, May 14, crews closed the gates to the upper reaches of SR 504/Spirit Lake Memorial Highway. The closure will remain in place until further notice. (Photo from Washington State Department of Transportation)

(Photo from Washington State Department of Transportation)

Days before the 43rd anniversary of the Mount St. Helens eruption, a mudslide wiped out an entire road and closed a popular tourist site.

Washington Department of Transportation (WSDOT) spokesperson Tamara Greenwell said a massive mudslide Sunday night was so big it demolished the 85-foot Spirit Lake Outlet Bridge and closed the road at milepost 43.

Eleven people and a dog were evacuated by helicopter after being stranded overnight on the far side of the Johnston Ridge observatory.

11 people, dog rescued at Mount St. Helens after mudslide blocks road

“We learned that there were some folks trapped on the other side [of the mountain], and Skamania County and King County assisted with the rescue of several people who are all safe now,” Greenwell said.

“Monday morning, our crews got better eyes on the slide…what we’re calling a massive landslide. It took out an 85-foot bridge structure completely,” Greenwell continued. “Yeah, I was out there yesterday. And I was able to see sort of mangled and tangled bridge rebar. Like about half a mile downstream. It is a massive landslide.”

The damage was so bad that crews could not assess how long the repairs would take.

“We got some drone video of it yesterday to get a broad scope of what we’re dealing with,” Greenwell said. “So, there’s still a lot of work and safety assessment that has to be done before we can develop a plan to reopen the roadway.”

One of the biggest impacts is on the Johnston Ridge observatory because the wiped-out road takes visitors to the center; additionally, some of the buildings have reportedly lost access to the power grid.

Greenwell thinks this event will impact tourism in the short term; however, folks can still go up to Mount St. Helens, just nothing past milepost 43.

“I was up there yesterday, there are some beautiful lookout points that you can pull off at, to see the mountain,” Greenwell said. “And I think, you know, as long as folks are staying away from sort of the upper section of the highway, they’ll still be tourists going up there.”

It’s too soon to say the cause of the landslide, but the initial assessment from geotechnical engineers is that the unseasonably hot temperatures drastically melted the snowpack, which then oversaturated the soils — loosening it enough to cascade down the mountain and taking out the bridge.

How does WA mountain snowpack water supply look this year?

WSDOT is working in coordination with the U.S. Forest Service, U.S. Army Corps of Engineers, U.S. Geological Survey, and Skamania and Cowlitz counties to determine what needs to be done to stabilize the soil in the area and rebuild the roadway.

“Additional safety analysis is needed, but due to the ongoing geological instability in the area, it’s too soon to tell when we’ll be able to safely do that work,” said Brad Clark, WSDOT Southwest Region Maintenance Manager. “We appreciate everyone’s patience during this emergency.”

On Monday, May 22, WSDOT Engineering Geologists began site reconnaissance of the slide area to collect ground data which will be used to cross-reference with the LIDAR information. Engineering Geologists are processing LIDAR data this week and will begin analysis work next week. This information will help inform when cleanup and repair work could begin.

There is currently no timeline for work to reopen the highway, and WSDOT said that travelers should plan for the highway to be closed for an extended period.

Follow Micki Gamez on Twitter or email her here.

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SR 504 near Mount St. Helens closed indefinitely after mudslide