|
U.S. Geological Survey, Vancouver, Washington
University of Washington, Pacific Northwest Seismograph Network, Seattle, Washington
October 19, 2004 10:00 am PDT (17:00 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. Small lahars (volcanic debris flows) could suddenly descend the Toutle River valley if triggered by heavy rain or by interaction of hot rocks with snow or glacier ice. These lahars pose a negligible hazard below the Sediment Retention Structure (SRS), but could pose a hazard to people along the river channel upstream of the SRS. 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, the current 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 ash clouds that rise above the crater rim today would drift to the northwest, north, and northeast from the volcano.
In the past 24 hours, seismicity has not changed significantly and remains at a low level overall. Continuing storm noise explains some of the higher background signal observed. We have no new Global Positioning System (GPS) measurements to report. Poor weather yesterday again 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.
When weather conditions improve, we will continue geologic observations, thermal imaging, and making improvements in telemetry systems.
We continue to monitor the situation closely and will issue additional updates and changes in alert level as warranted.
|
