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U.S. Geological Survey, Vancouver, Washington
University of Washington, Pacific Northwest Seismograph Network, Seattle, Washington
Mount St. Helens Update, October 12, 2004, 5:45 p.m, PDT
Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
Seismic activity remained at a low, but gradually increasing level today. This morning’s visual observations and thermal imaging of the 1980-86 lava dome, the intensely deforming and uplifting area on the south side of the dome, and the new lava extrusion first seen yesterday afternoon were hampered by steam clouds. Conditions appeared similar to those of yesterday afternoon, with high temperatures (up to 600 degrees C) around the fin-shaped lava extrusion in the western part of the uplift. The area of high temperature appears to have increased in size. Abundant steam continued to rise from the fin area to the crater rim, from which it was dispersed southeastward by strong winds.
A new instrument array was lowered onto the uplifting area this afternoon by helicopter. It contains telemetered seismic, GPS, and tilt instruments, as well as a microphone. It will provide critical information on rate of movement of the uplift as well as a close-in seismic station. Other field work concentrated on improving satellite and radio telemetry systems.
Wind forecasts from the National Oceanic and Atmospheric Administration (NOAA), combined with eruption models, show variable wind directions tonight, but generally northerly. Any ash clouds will drift southwestward to southeastward.
As a result of the intense unrest of the past two and one-half weeks and recent observations, we infer that magma is at a very shallow level and is likely extruding onto the surface. As last night, incandescence from hot rock or gases could reflect off steam clouds and be visible from north of the volcano. During times of unrest, Mount St. Helens and similar volcanoes elsewhere typically go through episodic changes in level of unrest over periods of days to weeks, or even months. Such changes are in part driven by variations in the rate of magma movement. We expect fluctuations in the level of unrest to continue during coming days. Escalation in the degree of unrest could occur suddenly or with very little warning. There may be little time to raise the alert level before a hazardous event occurs. Therefore, we continue to monitor the situation closely and will issue additional updates and changes in alert level as warranted.
Tomorrow’s media briefing will be held at the Headquarters of the Gifford Pinchot National Forest at 10:30 a.m.
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