2005-04-04

 

USGS Update 2005-Apr-04 10:30

Potential ash hazards: 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 would drift eastward at lower altitude and southeastward at higher altitude.

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.

Recent observations: As has happened on several occasions during the lava-dome-building phase of the eruption, a series of large (equal to or greater than magnitude 3) earthquakes are being produced, in addition to the typical array of smaller events. Three large earthquakes occurred during the past 24 hours. The largest, magnitude 3.4, at 10:45 p.m. (PDT) last night is the largest recorded at St. Helens since early October. The exact cause of these larger events is unknown, but they are usually associated with time periods during which the whaleback portion of the lava dome is breaking up. The earthquakes don’t represent the surficial disintegration or sliding of rock slabs off the dome, but rather slip on fractures deeper in the dome or conduit. Such behavior may be the result of increased resistance to extrusion as the whaleback gets longer, steeper, or pushes against the crater wall.





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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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