Cascade Range Current Update

MOUNT ST. HELENS UPDATE
Thursday, January 20, 2005 10:00 a.m. PST (1800 UTC)

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, 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: 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.

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.

For additional information, background, images, and other graphics: http://vulcan.wr.usgs.gov/News/framework.html

For seismic information: http://www.pnsn.org/HELENS/welcome.html

For a definition of alert levels: http://vulcan.wr.usgs.gov/News/framework.html

For a webcam view of the volcano: http://www.fs.fed.us/gpnf/volcanocams/msh/

Telephone recordings with the latest update on Mount St. Helens and phone contacts for additional information can be heard by calling:

Media (360) 891-5180

General public (360) 891-5202

OTHER CASCADE VOLCANOES

All other volcanoes in the Cascade Range are all at normal levels of background seismicity. These include Mount Baker, Glacier Peak, Mount Rainier, and Mount Adams in Washington State; Mount Hood, Mount Jefferson, Three Sisters, Newberry, and Crater Lake, in Oregon; and Medicine Lake, Mount Shasta, and Lassen Peak in northern California.

USGS Cascades Volcano Observatory, the Pacific Northwest Seismograph Network at the University of Washington, and the USGS Northern California Seismic Network and Volcano Hazards Team in Menlo Park, California, monitor the major volcanoes in the Cascade Range of northern California, Oregon, and Washington.



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