Description of the Volcanic Event: More Details

After May 18, 1980

A. Elevation—8,365 ft.; more than 1300 feet lower than the old summit B. Steam pit formations 1. 300o C pumice covered glacier water and ice. The water and ice formed steam and burst through the pumice creating steam explosion pits. 2. Within days of the eruption, more than three dozen steam pits formed; the largest one was 125 ft. deep, 2,300 ft. long, and 1,000 ft. wide. C. Spirit Lake 1. Both the debris on the lake bottom and the debris dam caused the lake to rise and increase in size to almost twice the size of the pre-eruption lake and more than 250 feet above its original altitude. 2. A mudflow on March 19, 1982 breached the deposits and caused substantial erosion of what is called the "Little Grand Canyon." a) Some of the individual canyons have depths of 140 feet cut through pumice and landslide debris. b) The channel was breached in a meandering path. c) The Little Grand Canyon is a one-fortieth scale replica of the Grand Canyon. 3. The size of Spirit Lake was reduced to normal size by man-made pumps. D. Subsequent eruptions 1. May 25, 1980 2. June 12, 1980 3. July 22, 1980 4. August 7, 1980 5. October 17, 1980 E. Formation of the lava dome began subsequent to the October 17 eruption.

Reference
Austin, Lumsden, Morris, and Vardiman. Mt. St. Helens Tour Guidebook. Institute for Creation Research, 1997.