Cascade Range Current Update

MOUNT ST. HELENS UPDATE
Wednesday, March 9, 2005 8:00 p.m. PST (03/10, 0200 UTC)

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 east-northeastward early in the day and shift to an east-southeastward drift later in the afternoon.

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: A small but significant explosive event occurred at 5:25 pm PST on 03/08, creating a steam-and-ash plume that reached an altitude of 36,000 feet above sea level within minutes. Within minutes of the onset of this event, we lost communication with 7 monitoring stations in the crater, but not with any stations outside the crater. The event followed a few hours of slightly increased seismicity that was noted but not interpreted as precursory activity. There were no other indications of an imminent change in activity. There were reports of fine dustings of ash falling in Ellensberg, Yakima, and Toppenish, Washington between 7pm and 9pm yesterday. According to the Washington Volcano Ash Advisory Center, a faint and diffuse ash cloud was last detected in satellite imagery at 3:30 am PST on 03/09 over western Montana.

Today, field crews made observations in the crater, sampled ash along the flanks, recovered two damaged monitoring stations, and installed a new seismometer. Observations in the crater found no obvious vent source for the 5:25 pm explosion, and the new dome was found to be remarkably intact. Ballistics up to ~1 m in diameter were seen at distances as far as the northern flank of the old dome, including at all locations where monitoring stations were lost. No ballistics were found along or beyond the rim. Ash deposits in the crater indicate that the plume was very narrow and directed primarily eastwards. Ash up to ~1 inch thick was deposited along the Plains of Abraham east of the volcano. 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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