Cascade Range Current Update

Wednesday, May 4, 2005 10:15 a.m. PDT (1715 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 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: Yesterday’s good weather allowed field crews to obtain thermal and visual observations of the growing lava dome and to resurvey some targets that were placed on the dome two weeks ago. All data suggest that lava extrusion continues at a rate similar to that of recent months, even though the rate of seismic activity has declined somewhat over the past few weeks. We infer that this is the result of the recent breakup of the long whaleback-shaped spine that was being pushed southward and upward by extruding lava since late January. Under current conditions, the extruding lava is beginning to form a new, but much smaller, whaleback-shaped spine that is evidently easier to push. Therefore the accompanying seismicity is much less intense.

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

General public (360) 891-5202

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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