Spirit Lake Outlet and Tunnel
Spirit Lake Tunnel Background
Debris flow during the 1980 eruption of Mount St. Helens blocked the natural outlet to Spirit Lake to the North Fork of the Toutle River. The lake level must be controlled to prevent the water from over-topping the outlet and potentially causing large-scale mudflow down the Toutle River Valley.
In 1985 the U.S. Army Corps of Engineers constructed a 1.6 mile, 11-ft diameter tunnel bored horizontally through rock to systematically release water and maintain a safe water level in Spirit Lake. Read more about outlet tunnel construction and monitoring from the U.S. Army Corps of Engineers.
The dynamic geology of our area has caused ongoing problems for the tunnel, however. After routine inspections revealed damage to a portion of the tunnel, a contract was awarded and short-term critical repairs were completed in the March 2016.
Over the next several months, long-term options are being considered along with alternative solutions. The process has brought together land managers, scientists, engineers, and community stakeholders to identify a sustainable solution in an area marked by change. The National Academy of Sciences, Engineering, and Medicine (NASEM) assembled an independent scientific committee to engage stakeholders, hold committee meetings, and share their findings. This effort’s focus will be the continued safety of the downstream communities and the protection of local and regional ecology and economic activities.
Watch a short video showing the tunnel outlet before and after the gate is opened back up following repairs.
View Repair Photos