Cascade Range Current Update

Monday, December 3, 2007 10:45 PST (Monday, December 3, 2007 18:45 UTC)

MOUNT ST. HELENS UPDATE

Current Volcanic- Alert Level WATCH; 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, changes in the level of activity can occur over days to months. The eruption could 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 any ash clouds rising above the crater rim today would drift northeast.

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: The active spine of the lava dome continues to extrude, according to our in-crater tiltmeter. This instrument shows small inflation-deflation events every few hours, which we interpret as dome growth pulses. The wind from winter storms has increased the noise on seismometers close to or in the crater, saturating them relative to the sparse small earthquakes that have characterized the eruption as of late. No in-crater GPS results are available this morning. Views from all volcano cams in the past 24 hours have been useless for assessing eruptive activity, owing to poor weather.

The discharge from streams exiting the crater has increased greatly, as measured by acoustic flow monitors, and the area is receiving substantial rain this morning. At this time the AFM signals are characteristic of increasing water flow, not lahars. Stream flow at lower elevations in the drainages surrounding Mount St. Helens increased abruptly early this morning. These results can be found online at the National Water Information System Web site (search string “NWIS” and follow links to Real-time Data).

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/Volcanoes/MSH/Eruption04/

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

For a definition of alert levels:
http://vulcan.wr.usgs.gov/Volcanoes/Cascades/CurrentActivity/volcano_warning_scheme.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

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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