Spirit Lake Outflow Current System

After the 1980 eruption, the U.S. Army Corps of Engineers mobilized to address flooding and sediment concerns at Spirit Lake and newly created Castle and Coldwater lakes. The Gifford Pinchot National Forest is responsible for operating, maintaining and repairing the 1.6 mile Spirit Lake tunnel, and the engineered channels at Castle and Coldwater lakes. The tunnel and the engineered channels that provide outflow for Castle and Coldwater lakes make up the Mount St. Helens Protective Works managed by the U.S. Forest Service.

To address annual tunnel operation in this dynamic volcanic landscape and to contribute to geologic hazard risk reduction to downstream communities, the Forest Service works cooperatively with federal, state and local partners. The Forest Service invests annually in:

  • tunnel inspections and subsequent repairs
  • studies to increase information crucial to lake level management
  • log and debris management
  • emergency response planning
  • analysis of long-term outflow options

Through interagency agreements, the U.S. Geological Survey focuses on lake level and tunnel flow sensors to make sure the agencies can monitor Spirit Lake. The U.S. Army Corps of Engineers provides technical and contracting support to address repairs and maintenance of the Spirit Lake tunnel.

Pacific NW Research Station​ Publication: August 2019 Science Update featuring analysis of Spirit Lake (.pdf)

Spirit Lake Outflow and Protective Works Story Map

Learn more about Spirit Lake and lasting impacts of the 1980 eruption on the Toutle River watershed:

View Full-size story map