Cascade Range Current Update

CASCADES VOLCANO OBSERVATORY WEEKLY UPDATE
Friday, July 11, 2008 11:08 PDT (Friday, July 11, 2008 18:08 UTC))

MOUNT ST. HELENS VOLCANO (CAVW#1201-05-)
46.20°N 122.18°W, Summit Elevation 8363 ft (2549 m)
Volcano Alert Level: NORMAL
Aviation Color Code: GREEN

SUMMARY:

As discussed in yesterday's update, the more than three-years-long, lava-dome eruption of Mount St. Helens that began in autumn 2004 and paused in late January of this year appears to have ended. Earthquakes, volcanic gas emissions, and ground deformation are all at pre-eruptive background levels.

Even with the end of lava dome growth, some hazards persist. The new lava dome remains hot in places-capable of producing small hot avalanches or minor explosions that could dust areas with ash up to tens of miles downwind. Rock fall from the crater walls can produce clouds of dust that rise above the crater rim, especially during dry, windy days, as has happened in the past. Also, heavy rainfall or rapid snowmelt can send small debris flows onto the Pumice Plain north of the crater.

RECENT OBSERVATIONS:

This week field crews made repairs to monitoring equipment, continued the summer GPS campaign, and hauled out damaged equipment and spent batteries. They observed a conspicuous deposit of a recent rock and snow avalanche that fell from the south crater wall, just west of the top of the south flank Climbers Trail. Upon reaching the crater floor, the avalanche swept for about 200 meters (650 feet) across the west arm of Crater Glacier, hugging the base of the new lava dome. The exact timing of the avalanche is uncertain, but we know that it happened sometime between June 26 and July 8. Such events underscore the hazards in the crater posed by rock falls and avalanches from the steep crater walls.

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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