Cascade Range Current Update

Mount St. Helens Update, October 1, 2004, 7:00 P.M.

Current status is Alert-Level 2-Volcano Advisory

The increasingly energetic seismic swarm of the past week culminated in a small 25-miunute-long eruption around noon today from a vent just south of the lava dome. The vent opened in a portion of the glacier that had become increasingly crevassed and uplifted over the past few days. This deformation was probably driven by piston-like uplift of a portion of the lava dome and crater floor. The eruption sent a steam and minor ash plume to an altitude of about 10,000 ft. It drifted southwestward accompanied by minor ashfall in areas close to the volcano. Seismicity dropped to a low level for several hours after the eruption, but is gradually increasing with earthquakes (maximum Magnitude about 3) occurring a rate of 1-2 per minute. We infer that the system is repressurizing. As a result, additional steam-and-ash eruptions similar to today’s could occur at any time.

Field crews in a helicopter took thermal images of the dome and crater both during and several hours after the eruption. Results will be available tomorrow. Another crew began deployment of two broadband seismometers that will provide useful data for in-depth scientific studies. Today’s explosion disabled both the seismometer and GPS instrument on the lava dome.

Updated wind forecasts from the National Oceanographic and Atmospheric Administration coupled with an eruption model indicate that the wind direction will be variable from the north to east so that any ash clouds produced tonight will drift southwestwardly or westwardly.



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