Cascade Range Current Update

Thursday, March 10, 2005 9:35 a.m. PST (1735 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, episodic changes in the level of activity can occur over days to months. The eruption could also 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 southeastward at higher altitudes, but remain very near the volcano at lower altitudes.

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 fall in trace amounts 100 miles or more downwind.

Recent observations: The volcano is clear this morning and sporting an intermittent steam plume. There have been no explosive events since 5:25 p.m. local time on Tuesday. After the event Tuesday, seismicity returned to a level similar to that in the several hours prior to the explosion, and it remains at about that level at this time. Yesterday, the new dome was found to be remarkably intact. Ballistics up to ~1 m in diameter were hurled as far as the northern flank of the old dome. No ballistics were found along or beyond the crater rim. Ash deposits were found along a narrow eastward swath. Ash up to ~1 inch thick was deposited along the east flank of the volcano. Although no obvious vent was observed, the distribution of ballistics and ash suggest the explosion emanated from a source very near that of the October 1, 2004 and January 16, 2005 explosions. Today, crews will conduct more visual observations, measure gases, do routine maintenance on some far-field instrument stations, and redeploy GPS units.

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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