Mount St. Helens Update October 5, 2004

International Glaciospeleological Survey

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

Mount St. Helens Update 5 October 2004 7:00 A.M.

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

Yesterday visitors to Mount St. Helens witnessed a 30-minute-long steam-and-ash emission starting at 9:43 a.m. PDT and a 10- minute-long steam-and-ash emission starting at 14:10 p.m. PDT. The larger one dusted roads to the the SE of the volcano with ash. Maximum thickness of the ash at 8 km (about 5 miles) was 0.2 mm (less than 1/8 of an inch). Neither event generated 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 yesterday’s and other steam and ash emissions of the past few days is now covered by a bubbling lake. Since yesterday's emissions, earthquake energy has slowly increased to previous high values.

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. Thermal surveys of the dome confirms the deformation. Hot cracks (40-50° C; about 100-120° F, well below magmatic temperatures) in the dome are opening, and dome rocks are avalanching off the dome into the lake and onto the south crater floor. The north flank of the dome appears thermally stable.

Yesterday’s gas-sensing flight detected carbon dioxide, often in association with hydrogen sulfide peaks and occasional sulphur dioxide peaks, at numerous sites around the dome and crater floor.

Today field crews will take additional thermal images of the dome and crater, conduct gas-sensing and geologic-observation flights, and continue hardening GPS sites. Two additional GPS stations were lowered by helicopter onto the 1980-86 lava dome yesterday to aid in measuring deformation of the dome.

Wind forecasts from the National Oceanic and Atmospheric Administration (NOAA), combined with eruption models, show that morning winds will are from the south and west and any ash clouds will drift northward and easterly.

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.

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

Mount St. Helens Update, October 5, 2004, 6:45 p.m, PDT

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

This morning the rate of seismicity was at a high, sustained level when, shortly after 9:00 a.m. PDT, the most vigorous steam and ash emission of the current period of unrest began. The emission originated from the same vent as have others this past week, as well as from another nearby new vent in the intensely deforming area on the south side of the 1980-86 lava dome. For more than one hour, steam clouds billowed from the crater. The ash content varied with intensity of steam jetting from the vent. For the first time, ash content was sufficient that it was detected by National Weather Service Doppler Radar. Steam and ash clouds reached about 12,000 feet and drifted north-northeastward. Ash forecasts warned downwind residents. Media reports indicate that a light dusting of ash fell in Morton, Randle, and Packwood, Washington, towns about 30 miles from the volcano. Nearby traffic on U.S. 12 stirred up the ash, slightly reducing visibility. We have no reports of ash falling at greater distances.

The rate of seismicity dropped during and the emission and has stayed at relatively low rates. We infer that magma is at a very shallow level and could soon be extruded from a vent 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.

Results of field work are pending. Crews worked on GPS and seismic stations and made thermal and visual observations during and after the steam and ash emission.

Wind forecasts from the National Oceanic and Atmospheric Administration (NOAA), combined with eruption models, show winds this evening will remain southerly and any ash clouds will drift north-northeastward.

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.

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