Skip to Main Content
The geologic, geomorphic, and hydrologic context underlying options for long-term management of the Spirit Lake outlet near Mount St. Helens, WashingtonAuthor(s): Gordon E. Grant; Jon J. Major; Sarah L. Lewis
Source: Gen. Tech. Rep. PNW-GTR-954. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 151 p.
Publication Series: General Technical Report (GTR)
Station: Pacific Northwest Research Station
PDF: View PDF (5.0 MB)
DescriptionThe 1980 eruption of Mount St. Helens produced a massive landslide and consequent pyroclastic currents, deposits of which blocked the outlet to Spirit Lake. Without an outlet, the lake began to rise, threatening a breaching of the blockage and release of a massive volume of water. To mitigate the hazard posed by the rising lake and provide an outlet, in 1984–1985 the U.S. Army Corps of Engineers bored a 2.6-km (8,500-ft) long tunnel through a bedrock ridge on the western edge of the lake. Locally, the tunnel crosses weak rock along faults, and external pressures in these weak zones have caused rock heave and support failures, which have necessitated periodic major repairs. During its more than 30-year lifetime, the tunnel has maintained the level of Spirit Lake at a safe elevation. The lake approaches its maximum safe operating level only when the tunnel closes for repair. The most recent major repair in early 2016 highlights the need for a reliable outlet that does not require repeated and expensive interventions and extended closures. The U.S. Forest Service, U.S. Army Corps of Engineers, and U.S. Geological Survey developed, reviewed, and analyzed an array of options for a long-term plan to remove the threat of catastrophic failure of the tunnel. In this report, we (1) provide background on natural hazards that can affect existing and alternative infrastructure; (2) evaluate the potential for tunnel failure and consequent breaching of the blockage posed by the current tunnel infrastructure; (3) evaluate potential consequences to downstream communities and infrastructure in the event of a catastrophic breaching of the blockage; (4) evaluate potential risks associated with alternative lake outlets; and (5) identify data and knowledge gaps that need to be addressed to fully evaluate options available to management.
- You may send email to email@example.com to request a hard copy of this publication.
- (Please specify exactly which publication you are requesting and your mailing address.)
- We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
- This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
CitationGrant, Gordon E.; Major, Jon J.; Lewis, Sarah L. 2017. The geologic, geomorphic, and hydrologic context underlying options for long-term management of the Spirit Lake outlet near Mount St. Helens, Washington. Gen. Tech. Rep. PNW-GTR-954. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 151 p.
KeywordsRisk assessment, natural dam, potential failure mode analysis, Mount St. Helens, Toutle River, Spirit Lake, flood, lahar, debris flow, volcano, earthquake.
- Applying online WEPP to assess forest watershed hydrology
- Dams and water developments
- Investigating potential effects of heli-skiing on golden eagles in the Wasatch Mountains, Utah
XML: View XML