Cascade Range Current Update

Saturday, August 20, 2005 9:45 a.m. PDT (1645 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 northeasterly.

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: Early morning pictures from the Sugarbowl camera indicate that dome growth continues, with continued slumping of the middle part of the new dome complex and westwards as well as vertical motion of the latest lava spine located at the western edge of the complex. Over the last week seismicity levels have gradually dropped from an earthquake every 5-10 minutes to one every 10-20 minutes. No other significant changes in seismicity or deformation have occurred over the last 24 hours. A rockfall yesterday evening at 1925 PDT created a small ash cloud that rose over the rim and was briefly visible from the Portland area before it rapidly dissipated to the northeast. Yesterday field crews installed more temporary seismic instruments in the northern part of the crater floor, repositioned several GPS spider stations on the western lobe of the crater glacier, recovered ash samples out of an ash spider placed on the southern side of the old dome, grabbed new rock samples from near the vent, and did geologic mapping along the flanks.

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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