International Glaciospeleological Survey
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U.S. Geological Survey, Vancouver, Washington October 20, 2004 11:00 am PDT (18:00 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 west and southwest from the volcano. In the past 24 hours, seismicity has decreased somewhat and remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. Last night, glow from this new lava was intermittently visible on the U.S. Forest Service web camera. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor. Poor weather yesterday again prevented geological observations. When last seen during an overflight on October 14, estimated dimensions of the new lava extrusion were approximately 110 x 70 meters (360 x 230 ft) in length and height and about 18 m (58 ft) in width. The maximum temperature recorded on October 14 during the last successful overflight of the crater area, was 761 degrees C (1400 degrees F). Today, weather conditions have improved considerably and field crews are flying this morning to obtain new photographs, video, thermal images, and other data. Preliminary reports from the field indicate that the new lava dome has increased in width since October 14 and much of the fin-shaped lava spine described earlier has collapsed. Some ash likely related to small avalanches from the spine and possibly small ash emissions is visible on snow inside the crater. A vigorous steam plume is rising to approximately 10,000 feet above sea level. A gas measurement flight is planned for later in the day. Other field crews are conducting maintenance on instrumentation and improving our telemetry systems. The U.S. Geological Survey and the University of Washington continue to monitor the situation closely and will issue additional updates and changes in alert level as warranted. |
