The U.S. Forest Service is proposing to resume using an abandoned three-mile road across the pumice plain north of Mount St. Helens to collect core samples and reach the the Spirit Lake Outflow for maintenance purposes.
Tedd Huffman, manager of the Mount St. Helens National Volcanic Monument, sent out a letter in mid-March explaining the proposal and seeking written comments by April 14.
The agency wants to have limited administrative access to the southwest shore of Spirit Lake.
The area was used from 1982 to 1985 in a pumping operation by the U.S. Army Corps of Engineers to stabilize Spirit Lake until a drainage tunnel was completed.
Access to the lake in the 1980s — and potentially again — would be via an extension of Gifford Pinchot National Forest road No. 99 from a gate at Windy Ridge Viewpoint parking lot for approximately 2 miles to a small parking lot available to researchers.
From the researchers’ parking lot, the 1980s pumice plain access route would be improved temporarily for use one or two field seasons by tracked drilling equipment to retrieve core samples and to do long-term maintenance of the Spirit Lake Outflow.
A narrow, administrative-use only trail would lead from the southwest shore of the lake to the inlet of the Spirit Lake tunnel.
The extension of road No. 99 beyond Windy Ridge parking lot is used by the Forest Service as a hiking and cycling trail. It is popular with mountain bike riders plus hikers heading to Loowit Falls or Loowit trail No. 216 circling Mount St. Helens.
The road also gets use by researchers along with emergency medical service and law enforcement when necessary.
Debris flow during the May 1980 eruption blocked the natural outlet of Spirit Lake to the North Fork of the Toutle River. The lake level needs to be controlled to prevent the water from overtopping the outlet and potentially causing a large mudflow down the Toutle River.
The 11-foot-diameter tunnel completed in 1985 is 1.6 miles bored horizontally through rock under Harry’s Ridge.
As the tunnel has aged, it has experienced periodic fracturing of its lining and uplifting of the tunnel floor.
Short-term critical repairs to a partial blockage of a 30-foot section of the tunnel were completed in the winter of 2016. The Forest Service is working on developing long-term options for a sustainable solution to the lake outlet.
The drilling of core samples will provide more information about the geologic structure of the debris blockage.
Work in the past year has highlighted the need for an alternative to helicopter access to the tunnel inlet. Bad weather can restrict helicopter access, making motorized access important for the safety of personnel working on the tunnel.
TO COMMENT
• Written comments may be emailed to comments-pacificnorthwest-giffordpinchot-mtsthelensnvm@fs.fed.us or mailed to Tedd Huffman, manager; Mount St. Helens National Volcanic Monument, 42218 NE Yale Bridge Road, Amboy, Wash., 98601.
For more information, contact Chris Strebig, project lead, at 360-891-5052 or by email to cstrebig@fs.fed.us.
