Cascade Range Current Update

Wednesday, May 31, 2006       11:00 a.m. PDT (1800 UTC)

MOUNT ST. HELENS UPDATE    

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, 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 that rise above the crater rim today would drift northward to north northeastward.  

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 volcano is clear and free of visible fuming this morning.  Field crews yesterday measured gas emission, did a survey of temperature at the dome, installed 6 global positioning stations on the flanks of the volcano, and examined deposits of Monday’s large rockfall.  Gas emission and thermal character of the dome are similar to those measured in recent months.  The rockfall on Monday generated an avalanche, now visible from the north as a dark tongue, that came from the east side of the growing spine (sometimes called “the fin”), descended northward around the east side of the 80s dome and down onto the amphitheater floor next to the east arm of the crater glacier.  Ash associated with the avalanche lightly dusted the volcano’s upper northeast flank.  Seismicity and repeat photographs from remote cameras show that the spine continues to grow.  The growing spine is now sufficiently steep and fractured that a rockfall- avalanche similar in size to that of Monday is possible within the next week or so.  Such an event could generate an ash plume that would rise above the crater rim and drift 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.

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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