Cascade Range Current Update

Friday, February 29, 2008 10:26 PST (Friday, February 29, 2008 18:26 UTC)
MOUNT ST. HELENS WEEKLY UPDATE
Volcanic-Alert Level ADVISORY - Aviation Color Code YELLOW:

SUMMARY:

The pause in lava dome growth continues, and all our monitoring instruments show trifling or nil volcanic-related activity. This pause, which began in late January 2008, was recognized by absence of measurable growth among successive fixed-camera images, nearly quiescent seismicity, and the absence of tilt signals that might characterize extrusion of lava from the conduit.

We continue to monitor closely for evidence of renewed extrusion or other activity. The new lava dome remains hot in places; thus, it is 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 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.

RECENT OBSERVATIONS:

On a daily basis, a small steam plume rises above the active spine but usually dissipates before reaching crater-rim height. Under optimal atmospheric conditions this plume may ascend above the rim and be visible to residents and travelers in southwest Washington and northwest Oregon. This morning a small lenticular cloud formed above the volcano, owing to a changing weather system.

This past week field crews took advantage of good weather to repair a GPS antenna at Johnston Ridge Observatory, improve a radio connection for data transmission from Coldwater Ridge visitor center, and replace a bent antenna at one of our voice-communication repeater sites.

For the past month, locatable earthquakes at Mount St. Helens have been fewer than one per day, all smaller than magnitude 2. Ground tilt measurements show an overall sluggish subsidence in the area of the new dome. A GPS receiver on the active spine settles about 2 cm daily on a southward path.

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.

INFORMATION:

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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