Seismic swarm at Mount Saint Helens (as of 3:00 pm PDT, 9/30/04).
| The figure shown is a computer-based display of vertical seismic velocity recorded at the June Lake seismic station near the volcano (see http://www.geophys.washington.edu/SEIS/PNSN/WEBICORDER/GREEN/welcome.html). The most recent data has shown that these earthquakes are shallow and are in or just below the lava dome in the crater created by the major 1980 eruption of the mountain. Two hypotheses are that new magma is involved, or that the earthquakes are due to hydrothermal overpressure. In either case, disruption of the lava dome accompanied by a small to medium sized eruption appears probable at this point. A future Image of the Week will follow up on this evolving volcanic activity. In general, seismologists and other Earth scientists have made great strides in successfully assessing volcanic hazards in the two decades since the 1980 eruption. A significant component of this progress has been in the improved monitoring and interpretation of volcano seismicity. Figure courtesy of the University of Washington and the U.S. Geological survey. Submitted by Rick Aster, New Mexico Tech. |
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