Geophysical events


  • Anonymous


Mount St. Helens Volcano, Cascade Range, southern Washington, U.S.A. (46.20°N, 122.18°W). All times are local (GMT − 7 h). After the devastating May 18 eruption, smaller but significant explosions occurred on May 25, June 12, July 22, and August 7. The lava dome that grew in the bottom of the crater for a few days after the June 12 eruption was destroyed by explosions on July 22, but a second dome was emplaced, following the August 7 explosions.

U.S. Geological Survey personnel measured temperatures of 647° in the August 7 pyroclastic flow deposits near the crater and 639° near their distal margin the day after emplacement. By August 8 a lava dome had filled the inner crater that was formed during the July 22 explosions to about half its former depth of almost 100 m. More than 20 m of additional dome growth had taken place by the morning of August 9. Occasional bursts of vapor and ash rose to 3–6-km altitude on August 8, accompanied by small seismic events. Sulfur dioxide emission increased from about 900 tons/day on August 8 to at least 2000 tons/day on the 9th, but explosive bursts had ended and the level of seismic activity was very low.