Cascade Range Current Update

Mount St. Helens Update 4 October 2004 7:00 A.M.

Current status is Volcano Alert (Alert Level 3); aviation color code RED

Overnight seismic activity increased until a steam (and possibly ash) event occurred about 10:40 P.M. Observers at Coldwater Ridge could see the steam plume, which barely made it to the crater rim, in the moonlight. Since then, the seismicity has been significantly lower as after prior steam-and-ash events. Earthquakes are occurring at a rate of about 1 per minute and the largest since the steam event have been in the magnitude 2s. All locations remain shallow.

Results from GPS measurements indicate no significant deformation of the outer flanks of the volcano. However, visual observations and photographic analysis show large-scale uplift (10’s of meters) of part of the glacier and a nearby segment of the lava dome. Yesterday a field crew installed a new GPS instrument on the dome and also measured the distance from the Johnston Ridge Observatory to the dome.

Yesterday’s gas flight continued to detect carbon dioxide and low levels of hydrogen sulfide.

Two telemetered microphones are now in operation to detect explosions.

Today we will receive a remotely operated video camera that will be installed on the crater rim from the USGS Hawaiian Volcano Observatory. Today field crews will work at installing additional seismometers on the flanks of the volcano and will continue to harden the GPS sites and download data. Time permitting, additional flights to acquire thermal imagery and gas measurements will occur.

Wind forecasts from the NOAA, combined with eruption models show winds today will be from the east and southeast and any ash clouds would drift to the west and northwest.

We continue to be concerned that additional steam-and-ash eruptions could occur at any time. The principal hazard from these types of events is for ash reaching altitudes that could affect aviation. If the current unrest continues there is also an increased probability of larger magnitude and more ash-rich eruptions.

We continue to monitor the situation closely and will issue additional updates and Alert Level changes as warranted.

Press conferences will continue to be held at the Headquarters office of the Gifford Pinchot National Forest. Press conferences are held at 9:30 A.M. and 2:30 P.M.



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