WorldWide Drilling Resource®

23 WorldWide Drilling Resource ® AUGUST 2020 Geotechnical Drilling at Mount St. Helens Adapted from Information by the U.S. Forest Service The Gifford Pinchot National Forest Supervisor announced plans to proceed with geotechnical studies of the Spirit Lake area within Mount St. Helens National Volcanic Monument, in Skamania County, Washington. When Mount St. Helens erupted in 1980, the debris and lava flow dammed up Spirit Lake which had been feeding the North Fork of the Toutle River. Blown-down timber entered the lake resulting in a floating log mat which still occupies about 25% of the lake’s surface. Officials feared if the natural dam broke, it would send massive amounts of water and debris to the cities in its path. The U.S. Army Corps of Engineers and the Forest Service built a temporary pumping station to help stabilize the lake level, an access road, and storage facility. They also installed a 1.6- mile, 11-foot-diameter tunnel which drains water from Spirit Lake into South Fork Coldwater Creek, which feeds into the Nork Fork Toutle River. The tunnel, which was built under emergency condi- tions, has been repaired numerous times over the years. It has deteriorated and must be replaced. When repairs were being made to the tunnel, experts noticed the lake levels rose to dangerously high levels. This is why engineers also want to build a spillway to act as a backup to the tunnel, of- fering additional protections for the Toutle, Toutle Lake, Toledo, Lexington, and Castle Rock communities, as well as the cities of Kelso and Longview. Before any of the work can begin, engineers need to study the pyroclastic deposit, debris avalanche, as well as the underlying rock, to get a better understanding of the geology of this particular area. The only data currently available is over 35 years old. The plan includes gathering core samples, four inches in diameter, from about 30 locations. Approximately 3-5 rigs will be used to gather samples from 100-350 feet deep. A temporary submersible pump or floating pump will be installed in Spirit Lake (in the area of the historical pump station). This pump will be used to fill a tank near the lakeshore for the drilling operation to use. Casing from a borehole drilled in the 1980s, which was only two feet aboveground, is now exposed due to erosion of the debris field. Scientists reading a piezometer in a previously drilled borehole. C&G