USGS Update 2005-Jan-20 10:00

Aerial views taken on 2005-Jan-19

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 northeastward early in the day and eastward later.

Recent observations: Yesterday a crew investigated the effects of an event that occurred about 3 a.m. (PST) on 16 January. Pictures are posted on our web site. The 17-minute-long event was an explosive emission of ash and blocks from the vent area at the north end of the growing lava dome. A shower of ballistic fragments pockmarked a snow-covered area up to several hundred meters northeast of dome with craters up to one meter in diameter. New instruments deployed on 14 January were severely damaged, as was an older GPS instrument. Ash fell thickly in east and west parts of the crater and drifted eastward over the rim depositing a thin layer of gray ash on the east flank outward for at least 3 kilometers. The scale and impact of the explosion was similar to that of 1 October 2004, which was witnessed in clear weather. Analysis of a digital-elevation model made from photographs taken on 3 January provides new information about the size of the growing welt and lava dome. Since last measured on 11 December 2004, the lava dome has maintained its 475-meter length, which is constrained by the old lava dome and crater wall, but has widened from 310 m to 410 m. Its highest point is 7 m higher. The entire welt and dome has increased in volume from 30 to 34 million cubic meters, an average rate of about 2 cubic meters per second. These results suggest that the rate of lava extrusion has decreased from autumn 2004 rates.

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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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