Mt. St. Helens Update 10/04/04

[Windy]

.S. Geological Survey, Vancouver, Washington
University of Washington, Pacific Northwest Seismograph Network, Seattle, Washington

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

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

This morning visitors to Mount St. Helens witnessed a 40-minute-long steam-and-ash emission starting at 9:43 PDT. Steam clouds carrying minor ash billowed out of the crater to an altitude of 10,000 to perhaps 12,000 feet. The event did not generate earthquakes or an explosion signal. We infer that hot rock was pushed up into the glacier, melted ice, and generated the steam. Part of the vent for today’s and other steam and ash emissions of the past few days is now covered by a boiling lake. The emission occurred during a time of gradually increasing seismicity, which dropped slightly after the emission, but continued to increase gradually through the afternoon. Another period of smaller steam and ash bursts occurred between 2:10 and 2:40 P.M. Visual observations show that the area of uplift, which includes part of the glacier and a nearby segment of the south flank of the lava dome, continues to rise. We infer that magma is at a very shallow level and could soon be extruded into the vent or elsewhere in the deforming area. Additional steam and ash emissions are likely and could occur at any time without warning. Conditions suggest that there is also an increased probability of larger-magnitude and more ash-rich eruptions in coming days.

Yesterday’s gas-sensing flight detected slightly lower concentrations of carbon dioxide in the crater, but for the first time the airborne instruments detected the presence of hydrogen sulfide. Wind conditions during today’s flight should permit the first estimation of the rate of gas flux.

Today field crews took additional thermal images of the dome and crater and conducted gas-sensingand geologic-observation flights. Two additional GPS stations were lowered by helicopter onto the 1980-86 lava dome to aid in measuring deformation of the dome.

Wind forecasts from the National Oceanic and Atmospheric Administration (NOAA), combined with eruption models, show winds this evening will be from the west and any ash clouds will drift eastward. By tomorrow morning the wind will shift to the south and any ash clouds will drift northward.

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. The morning press conference is at 9:30 AM.

[HurricaneGirl]