Dome building at Mount St. Helens



After an unusually long period of dormancy, Mount St. Helens erupted between May 23 and June 10 of this year, adding 7 million m3 of magma to its dome. As Eos went to press, the eruption ranked as “the most voluminous eruptive event at [Mount] St. Helens since June of 1980,” according to one U.S. Geological Survey (USGS) geologist. The accompanying level of seismicity was also unusually high, with earthquakes of magnitude 2.0 to 2.8 occurring every 5—10 minutes between May 27 and June 2 (Eos, July 2, 1985, p. 537).