Cascade Range Current Update

Saturday, July 7, 2007 09:52 PDT (Saturday, July 7, 2007 16:52 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 ENE.

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: Evidence from AFM stations, crater seismometers, and increased turbidity measured downstream in the Toutle suggest an abrupt but minor increase in water flow out of the crater between 6pm and 9pm local time on Friday July 6. AFM stations downstream at Hoala on the pumice plain and at Elk Rock did not register increases associated with this event. The AFM flow monitor at Loowit Falls shows that after 9pm water flow returned to near normal but at this hour still registers a slightly elevated flow volume, compared to levels before the event. The increased flow event may have been triggered by high summer temperatures affecting the crater glaciers. No explosion or large rockfall signal preceded the increased water flow. Seismicity remains at normal levels. The flow event registered on crater seismic stations as a number of subtle low-amplitude signals lasting several minutes between 6pm and 9pm local time.

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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