Geophysical events

Abstract

Mount St. Helens Volcano, Cascade Range, southern Washington, USA (46.20°N, 122.18° W). All times are local (GMT‐8 h). March eruptive activity from Mt. St. Helens was limited to occasional emission of small steam clouds, at least one of which contained ash. However, significant deformation was measured within the crater, and there was a slight increase in volcanic seismicity during the second half of March. Geologists announced that another eruptive episode was likely if the deformation and seismic trends continued, but none had occurred by SEAN's April 8 press time.The U.S. Geological Survey‐University of Washington seismic net recorded 15 bursts of seismicity in March and five more bursts during the first 6 days of April. In the past, similar signals have often been correlated with episodes of steam emission, but because of poor weather, correlations with only two such episodes could be confirmed in March: a minor puff on March 9 at 1549, and a steam cloud containing some ash on March 27 at 1441. Newly fallen ash (made up of reworked dome material) observed NE of the volcano March 25 may have been ejected during a burst of seismicity the previous day.