Cascade Range Current Update

Thursday, February 21, 2008 10:10 PST (Thursday, February 21, 2008 18:10 UTC)
MOUNT ST. HELENS WEEKLY UPDATE
Volcanic-Alert Level ADVISORY - Aviation Color Code YELLOW:

SUMMARY:

Growth of the new lava dome inside the crater of Mount St. Helens, which began in October 2004, appears to have paused during the past month. Therefore, we are lowering the alert level from Watch to Advisory and the aviation color code from Orange to Yellow, which signifies that volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase. The rate of lava extrusion as determined by repeated aerial photography has been declining since late 2004, and other indicators of eruptive activity have also declined significantly. Comparison of photographs taken by remote cameras between late January and mid-February 2008 shows no evidence of extrusion. In addition, very few earthquakes have been recorded since late January, gas emissions are barely detectable, and daily ground-tilt events have stopped. These changes may only reflect a temporary pause in the eruption. The new lava dome remains hot in places and capable of producing hot avalanches or small steam explosions that could cause hazardous conditions in and around the crater. Sudden melting of snow and ice or intense rainfall could send small lahars onto the Pumice Plain and perhaps down the Toutle River as far as the Sediment Retention Structure (SRS). Ash clouds from explosions could affect aircraft. Until conditions warrant a change, Cascades Volcano Observatory will issue weekly updates on Fridays, rather than our current daily updates.

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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