Report on St. Helens (United States) — October 1982
Scientific Event Alert Network Bulletin, vol. 7, no. 10 (October 1982)
Managing Editor: Lindsay McClelland.
St. Helens (United States) SO2 emission declines; no deformation
Please cite this report as:
Global Volcanism Program, 1982. Report on St. Helens (United States) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 7:10. Smithsonian Institution.
46.2°N, 122.18°W; summit elev. 2549 m
All times are local (unless otherwise noted)
Seismicity remained at background levels through early November, and no significant deformation has been measured. SO2 emission ranged from 20 to 70 t/d in October, the lowest rate since the eruption of 18 May 1980.
Geological Summary. Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fujisan of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to 2,200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older edifice, but few lava flows extended beyond the base of the volcano. The modern edifice consists of basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the north flank, and were witnessed by early settlers.
Information Contacts: T. Casadevall, D. Swanson, USGS CVO, Vancouver, WA; S. Malone, University of Washington.