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U.S. Geological Survey, Vancouver, Washington
University of Washington, Pacific Northwest Seismograph Network, Seattle, Washington
Mount St. Helens Update, October 13, 2004, 7:00 a.m, PDT
Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
Seismic activity remained at a low, but slightly increasing level overnight. Yesterdays 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 on October 11 were hampered by steam clouds. Conditions appeared similar to those of October 11, 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 on October 12 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, which is proving useful in interpreting very small seismic events that do not appear at more distant stations. Today, field crews will take new thermal images of the crater floor and dome, make gas-sensing measurements, perform routine maintenance of GPS sites, and take hydrological measurements.
Wind forecasts from the National Oceanic and Atmospheric Administration (NOAA), combined with eruption models, show generally northerly winds. Any ash clouds will drift southward 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 extruding onto the surface. Incandescence from hot rock or gases reflects off steam clouds and is 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.
Todays media briefing will be held at the Headquarters of the Gifford Pinchot National Forest at 10:30 a.m.
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