USGS Update 2004-Nov-11 11:00
Growth of the new lava dome inside the crater of Mount St. Helens continues, and is accompanied by intermittent emissions of steam and ash. 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 high above the crater rim today would drift west-northwestward.
Clear views this morning show that a steam plume is rising passively and drifting westward out of the crater. The plume occasionally contains minor ash, which falls out in the crater and on the flank of the volcano, darkening the snow.
Seismicity 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. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.
Yesterday field crews repaired the DomeCam, the time-lapse camera that is aimed at the new lava dome from a site near the crater mouth, and conducted visual and thermal-imaging observations and a gas-sensing flight. Strong winds made interpretation of gas data difficult. Good viewing conditions revealed continued growth of the lava dome. Current estimates are that the welt, the broad area of deformation, is about 600 m (about 1950 feet) in diameter. The new lava dome, which occupies the central and western parts of the welt, is about 400 by 180 m (1300 by 600 feet). The highest point on the new lava dome is about 250 m (820 feet) above the former surface of the glacier that occupied that point in mid-September. Maximum surface temperatures on the new dome remain at about 700 degrees C (1300 degrees F). GPS instruments on the welt show rates of movement of up to several meters per day, while GPS instruments on the 1980-86 lava dome show movements of up to 1-2 cm (less than one inch) per day northward, away from the growing welt and new dome.
Growth of the new lava dome inside the crater of Mount St. Helens continues, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. During such eruptions, episodic changes in the level of activity can occur over days to months. The eruption could also intensify suddenly or with little warning and produce explosions that cause hazardous conditions within several miles of the crater and farther downwind. Small lahars could suddenly descend the Toutle River if triggered by heavy rain or by interaction of hot rocks with snow and ice. These lahars pose a negligible hazard below the Sediment Retention Structure (SRS) but could pose a hazard along the river channel upstream.
Potential ash hazards to aviation: Under current eruptive conditions, small, short-lived explosions may produce ash clouds that exceed 30,000 feet in altitude. Ash from such events can travel 100 miles or more downwind.
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.
My intent with this page is to provide a clearning house for links to the current activity at Mt.St.Helens. Please send me any links of interest that you may come across, whether for permanent sites or for news reports. I'm not going to be able to do this all alone and all help will be appreciated.
(Disclaimer I have no association with anyone or any organization, and speak only for myself. Links and quotes are provided for information only.)