Geologists mapping out Mount St. Helens mudslide to assess road damage, needed repairs

Part of State Route 504 near Mount St. Helens remains buried following a powerful mudslide last week that damaged the route and stranded 12 people and a dog overnight.

The group, which was on the side of the Johnston Ridge Observatory, had to be evacuated off the mountain by a King County Sheriff’s Office chopper.

The mudslide washed out an 85-foot bridge, damaged the road, and cut power to the Johnston Ridge Observatory.

The upper SR 504/Spirit Lake Memorial Highway is closed between mileposts 43 and 51. Federal agencies and the Washington State Department of Transportation are warning hikers not to go beyond the closure because the hillside is dangerously unstable.

The slide happened after a stretch of warm weather and significant snowmelt.

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Mudslide on SR 504 to Mount St. Helens A mudslide on SR 504, the highway to and from Mount St. Helens, left 12 people and a dog stranded overnight from Sunday, May 14 to Monday, May 15, 2023. Tim Uhler, one of the people who was stranded, took video of the slide with his drone. (Tim Uhler)

Geologists are now working with some of the most sophisticated technical methods in the world to map out how much damage was done.

An incident management team that includes the U.S. Army Corps of Engineers will also find out how long it could take to clean up and repair the highway.

A plane equipped with LIDAR — or light detection and ranging — flew over the area Friday. LIDAR uses lasers to create a high-resolution 3D map, in this case of the slide area.

Information was also collected by WSDOT engineering geologists on the ground.

According to officials, there are still recreational opportunities for visitors. SR 504 is open up to milepost 43 near the Science and Learning Center at Coldwater. Several scenic viewpoints are open, including Elk Rock and Castle Lake.

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