Spirit Lake Outflow and Tunnel


Erosion in the Mount St. Helens drainageLog barrier protecting Spirit Lake OutletColorado School of Mines geologists collecting field data for seismic site analysisSpirit Lake Outlet tunnel joining Spirit Lake with Coldwater Creek


BACKGROUND – A massive debris flow during the 1980 eruption of Mount St. Helens created Castle and Coldwater lakes, and blocked the natural outflow from Spirit Lake. To maintain a safe water level in Spirit Lake, in 1985 the U.S. Army Corps of Engineers (USACE) constructed a tunnel, completed a 1.6 mile, 11-ft diameter shaft bored horizontally through rock on the Mount St. Helens National Volcanic Monument.

As the tunnel ages its components require repair and replacement, and total deferred maintenance is in the tens of millions of dollars. The 2017 National Academies of Science, Engineering, &Medine report provides recommendations for improved understanding of options for long-term management of the outflow from Spirit Lake.


Where is the Spirit Lake Outflow  Area?    


Spirit Lake Drainage Map


SPIRIT LAKE PROJECT WORK –  Spirit Lake and the Toutle River drainage system affects many local and downstream partners and people.  Some of the recent project work completed by the Forest Service, USACE, and U.S. Geological Survey includes:

  • critical repairs to a section of the tunnel
  • installed a log debris barrier to protect Spirit Lake outlet
  • added a new tunnel flow sensor in addition to other investments to reduce risk and improve safety
  • developed an emergency operations plan and held table top exercises to practice plan
  • completed a comprehensive risk assessment


Current Spirit Lake surface elevation


Lakes and drainages around Mount St. Helens


National Academies of Sciences, Engineering, Medicine Consensus Study Report:  A Decision Framework For Managing The Spirit Lake And Toutle River System At Mount St. Helens


The Geologic, geomorphic, & hydrologic context underlying options for long-term management of the Spirit Lake outlet near Mount St. Helens, WA.


Mount St. Helens Volcanocam



Project Manager: Chris Strebig, 360-891-5052

Project Planner: Michelle King, 360-891-5021