USGS Update 2004-Dec-21 08:55

Potential ash hazards: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 south-southeastward.

Recent observations: Clouds again obscure the mountain, but better weather is forecast for later in the week. According to field sensors, there is no significant change in the eruptive activity. When the weather improves, field crews will service seismic stations, continue repairs to radio transmitters, and install more GPS units. Preliminary analyses from a gas-sensing flight last week suggest that emissions of SO2 may be slightly elevated, but within the range of past measurements; confirmation of results awaits further analysis. As of the end of November, the “whaleback” measured about 500 m long, about 200 m wide, and its highest point, which extends above the old lava dome, reached about 275 m above the old crater floor. The volumetric change associated with emplacement of new lava (the new dome, uplift, and glacier deformation) was about 28 million cubic meters. The old lava dome, which grew from 1980-86, has a volume of about 80 million cubic meters.

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Standard USGS Update

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.)

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