Shortly after 9 p.m. Sunday, May 14, more than 300,000 cubic yards of debris from an adjacent hillside fell approximately 2,000 feet above SR 504 and covered the roadway with rock, mud, ice and water, causing catastrophic damage to the 85-foot Spirit Lake Outlet Bridge at milepost 49.
What to expect
UPDATE - Nov. 2023 -
On Nov. 5, WSDOT staff received information that the temporary bypass was eroding. WSDOT staff worked in the days following to assess the infrastructure, determine scope of the problem and identify the cause. Here is what we know:
- This was not a new debris flow or landslide event. There is no relation between the original debris flow of the landslide on May 14 and this localized event.
- The material surrounding the two installed culvert pipes became compromised in a localized event due to water flow, resulting in water eroding the structural integrity of the roadway and causing the culverts to collapse.
- This culvert failure was related to rainfall, flow of water and erosion at the roadway location itself.
- There is no evidence of impact to the Spirit Lake outlet tunnel. The channel is clear and flow is normal.
- There is no relation between the culverts failing and the recent minor seismic activity in the Mount St. Helens National Volcanic Monument.
Given the harsh weather conditions at high elevations in the upper portion of SR 504 during the rain and snow season, WSDOT has determined it is appropriate, out of an abundance of caution, to remove the culverts, guardrail, asphalt and fill material that made up the temporary access to avoid the possibility of impacts to the Spirit Lake outlet tunnel. An emergency contract began Nov. 17 to complete this work.
The next few months will include many discussions across multiple state and federal agencies regarding timelines for temporary and permanent access to JRO. At this time, there is no timeline for public access being restored to JRO.
Several visitor centers, trails, and viewpoints remain open to the public on SR 504 (subject to seasonal closures and winter hours) including Mount St. Helens Visitor Center at Silver Lake, the Forest Learning Center, Elk Rock and Castle Lake Viewpoints, the Science and Learning Center at Coldwater, Coldwater Lake Recreation Area, Hummocks Trail, and the South Coldwater Trailhead. These activities in no way impact current travelers as SR 504 is closed at the winter gate, milepost 45.2, and there are no impacts to U.S. Forest Service facilities other than JRO.
UPDATE - Aug. 2023 -
From the end of June and throughout July 2023, WSDOT's emergency contractor, Scarsella Brother's, Inc., completed initial slide area stability assessments and subsequent debris removal.
This was followed by the installation of replacement culverts and the construction of a temporary one-lane bypass road alongside SR 504, providing administrative and emergency access to the observatory.
WSDOT engineers are currently assessing the situation and developing a plan for permanent repairs. First, engineering geologists will need to analyze soil samples to assess the stability of the original highway route and surrounding area before recommending a design to replace the washed-out bridge and restore the two-lane highway.
Additionally, utility lines were severed at the debris slide site, resulting in the absence of services at the observatory. Repairs to the power and data lines are underway with no current estimated timeline for completion.
What can the public expect moving forward?
The upper portion of SR 504 between mileposts 45.2 and 51 will remain closed to the public for the remainder of the year and into spring 2024.
Because the debris slide area still poses potential risk to the public, access to the temporary bypass road is limited to administrative and emergency access only, as the U.S. Forest Service works to restore utility and visitor services, including monitoring equipment, and it also allows WSDOT to collect further field information for the design and construction of a new permanent highway alignment.
While the precise cause of the landslide is yet to be determined, preliminary assessments suggest that unseasonably high temperatures likely led to significant melting of the snowpack. Consequently, the saturated soils and channels on the slopes became overwhelmed with debris mixing with the increased water flow. Ultimately, this accumulation of debris and water broke free, cascading downstream and causing the destruction of the 85-foot bridge span and roadway.
Please visit the Gifford Pinchot National Forest website for information about accessing U.S. Forest Service facilities.
On Sunday, May 14, 2023, 300,000 cubic yards of rock, mud, ice, and water slid 2,000 feet down to State Route (SR) 504 bridge at milepost 49, destroying the Spirit Lake Outlet Bridge and highway. This debris flow fully blocked access to Johnston Ridge Observatory (JRO) located on the north side the Mount St. Helens National Volcanic Monument. The current closure point remains at milepost 45.2, also called the winter gate. Local agencies are working together to address the impacts of the slide and repair the highway.