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U.S. Geological Survey, Vancouver, Washington
University of Washington, Pacific Northwest Seismograph Network, Seattle, Washington
October 17, 2004 10:45 am PDT (1745 UTC)
MOUNT ST. HELENS VOLCANO
Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
Growth of the new lava dome inside the crater of Mount St. Helens continues. As long as this eruption is in progress, episodic changes in the level of activity can occur over days, weeks, or even months. Increase in the intensity of eruption could occur suddenly or with very little warning and may include explosive events that produce hazardous conditions within several miles of the volcano. Under current conditions, small lahars (volcanic debris flows) could suddenly descend the Toutle River valley if they are triggered by heavy rain or by interaction of hot rocks with snow or glacier ice. Such lahars pose negligible hazard below the Sediment Retention Structure (SRS), but could pose a hazard to people along the river channel upstream of the SRS. Owing to weather and stream-flow conditions at this time of year, it is not unusual for rivers draining the volcano to contain high concentrations of sediment that turn the water murky. Although considered less likely at this time, eruptive activity could evolve into a more explosive phase that affects areas farther from the volcano and sends significant ash thousands of feet above the crater where it could be a hazard to aircraft and to downwind communities.
Wind forecasts from the National Oceanic and Atmospheric Administration (NOAA), coupled with eruption models, show that any ash clouds that rise above the crater rim today will drift northeastward to eastward later in the day.
Seismicity has increased slightly in the past 24 hours, but remains at a low level overall. Some of the higher seismicity is due to storm noise. Overnight, rainfall triggered a small debris flow that flowed north from the crater and changed rapidly to muddy streamflow within 5 km of the volcano. Global Positioning System (GPS) measurements continue to indicate only minor deformation of the northern part of the 1980-86 lava dome and no deformation of the outer flanks of the volcano. Poor weather yesterday prevented geological observations.
The current level and character of seismicity are consistent with a continuing rise of magma driving uplift of the crater floor and feeding the surface extrusion of lava. Low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor.
Field crews will not be out in today's poor weather. When weather conditions improve, we will continue geologic observations, thermal imaging, and making improvements in telemetry systems.
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