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2023 South Coldwater Slide

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2023 South Coldwater Slide
Destruction of the Spirit Lake Outlet Bridge
DateMay 14, 2023 (2023-05-14)
LocationMount St. Helens National Volcanic Monument
CauseSoil saturation due to heavy rainfall and snowmelt
Deaths0
Non-fatal injuries0
Missing12 (temporarily stranded)

The 2023 South Coldwater Slide is a mudslide that occurred in May 2023 near Mt. St. Helens. The volume of debris, and subsequent destruction of a bridge, closed off Washington State Route 504 and access to the Mount St. Helens National Volcanic Monument.

History

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On May 14, 2023, a mudslide and debris flow, given the moniker "South Coldwater Slide" by the U.S. Forest Service (USFS),[1] destroyed the 85-foot (26 m) Spirit Lake Outlet Bridge and severed SR 504 northeast of Johnston Ridge Observatory at milepost 49. Twelve people were airlifted from the area beyond the mudslide; the observatory's seasonal reopening was postponed and the highway east of Coldwater Lake was closed to all traffic.[2][3] Three days later, the closure was temporarily expanded further west to milepost 43 due to potential hazards revealed by geotechnical engineers during their investigation; access to Coldwater Lake and local trails was restored in June after the closure was moved back to milepost 49 at the site of the slide.[4][5]

A team composed of USFS staff and volunteers hiked to the observatory to retrieve scientific equipment and supplies so that observation of the volcano could proceed at the Coldwater Science and Learning Center.[6] The center was outfitted with exhibits and other facilities as a temporary alternative to the Johnston Ridge Observatory, providing the continuation of services for visitors to the area while cleanup and repairs were underway.[7] Washington State Department of Transportation (WSDOT) contractors cleared debris over the highway by July and created a temporary gravel road to access Johnston Ridge for vehicle retrieval and to prepare for reopening in 2024.[8][9] Power was restored to the observatory and monitoring equipment of the volcano was declared as back to "full functionality".[10] Marie Gluesenkamp Perez, the U.S. Representative of the district, toured the slide in August and co-sponsored the renewal of the National Landslide Preparedness Act the following year.[11]

Road closure for the South Coldwater Slide, 2024

The interim roadway was washed out in November 2023 after the replacement culverts failed due to heavy rainfall and erosion which was unrelated to the prior South Coldwater Slide event. There were no changes to the admittance of previously reopened recreation areas but the timeline to fully reopen SR 504 to the observatory in 2024 was called into doubt by the USFS.[12] Further investigation of the site by WSDOT engineers revealed difficulties in making additional repairs to the bypass. A temporary fix was considered to be uneconomical and it would further delay a permanent rebuild. Delays in temporarily or permanently reopening the bridge and highway for regular use is also due to a combination of the limited construction schedule based on weather, high elevation, and the steep slope of the area.[13]

The USFS announced that the highway and access to the observatory was to remain closed until late 2026.[14] After the loss of the bypass, the closure of SR 504 was listed between milepost 45.2 and 51, and the observatory is without power.[15] With construction not slated until April 2026, WSDOT revised the planned reopening of both the road and observatory to April 2027.[16]

Cause

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The slide, measured at 300,000 cubic yards (230,000 m3),[10] was determined not to be associated with seismic or volcanic activity, but caused by the cumulative effects of melting snow and the oversaturation of the volcanic soil in the area.[17]

References

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  1. ^ The Chronicle staff (May 23, 2023). "Forest Service Hopes to Provide 'Alternative' Recreation at Mount St. Helens as Surveys of South Coldwater Slide Continue". The Chronicle. Retrieved February 6, 2024.
  2. ^ Kauffman, Brennen (May 15, 2023). "Debris slide blocks SR 504 near Coldwater Lake; a dozen people rescued". The Daily News. Longview, Washington. Retrieved February 6, 2024.
  3. ^ Greenwell, Tamara (May 16, 2023). "Upper SR 504/Spirit Lake Memorial Highway closed until further notice" (Press release). Washington State Department of Transportation. Retrieved February 6, 2024.
  4. ^ The Chronicle staff (May 16, 2023). "Cause, Timeline Undetermined After 'Catastrophic' Slide on Road to Mount St. Helens". The Chronicle. Retrieved February 6, 2024.
  5. ^ KOMO News staff (June 19, 2023). "Coldwater Lake Recreation Area at Mount St. Helens reopens following SR 504 landslide". KOMO News (Seattle, Washington). Retrieved February 6, 2024.
  6. ^ Ellenbecker, Lauren (May 25, 2023). "Landslide prompts trek for Mount St. Helens observatory supplies". The Columbian. The Seattle Times. Retrieved February 12, 2024.
  7. ^ Day, Hayley (June 9, 2023). "Another landslide blocks access to Mount St. Helens". The Daily News. Longview, Washington. Retrieved February 6, 2024.
  8. ^ "Mount St. Helens mudslide cleared enough for drivers to retrieve stranded vehicles". The Oregonian. July 15, 2023. Retrieved February 6, 2024.
  9. ^ Brown, Sydney (July 17, 2023). "Motorists retrieve vehicles stranded by landslide on highway to Mount St. Helens". The Columbian. Retrieved February 6, 2024.
  10. ^ a b The Oregonian staff (July 15, 2023). "Drivers finally able to retrieve vehicles stranded at Mount St. Helens". The Seattle Times. The Oregonian. Retrieved February 6, 2024.
  11. ^ The Chronicle staff (May 3, 2024). "House of Representatives approves extension to landslide protection system". The Chronicle. Retrieved May 7, 2024.
  12. ^ Vander Stoep, Isabel (November 16, 2023). "Temporary 'fix' after landslide on Spirit Lake Highway has failed, WSDOT says". The Chronicle. Retrieved February 6, 2024.
  13. ^ KGW staff (February 6, 2024). "Mount St. Helens' Johnston Ridge Observatory closed until 2026 after landslide on Spirit Lake Highway". KGW 8 News (Portland, Oregon). Retrieved February 7, 2024.
  14. ^ Barker, Cade (May 13, 2024). "Volcano Awareness Month: Numerous activities available in person, social media". The Reflector. Retrieved May 20, 2024.
  15. ^ "Johnston Ridge Observatory at Mount St. Helens will likely stay closed until at least 2026". The Chronicle. February 7, 2024. Retrieved February 8, 2024.
  16. ^ Spykerman, Monica (August 7, 2024). "Johnston Ridge Observatory and Spirit Lake Highway are slated to reopen in spring of 2027". The Columbian. Retrieved August 13, 2024.
  17. ^ Vander Stoep, Isabel (May 19, 2023). "43 Years After Eruption, Mount St. Helens Continues to 'Reveal New Mysteries'". The Chronicle. Retrieved February 6, 2024.
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