Cascade Range Current Update

Friday, December 17, 2004 9:50 a.m. PST (1750 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 ash clouds that rise above the crater rim today would drift east-southeastward.

Recent observations: We got clear views of the crater mid-day yesterday during a thermal-imaging flight. The new dome has noticeably broadened and the prominent fracture system along its top continues to widen. Hot cracks emit ash intermittently. During the night of December 15 (Wednesday) ash emitted from the east side of the dome formed a cloud that swept down the east arm of the glacier and over east side of the old lava dome, leaving a dark smear of ash on the snow on its north face. This smear is visible on the USFS VolcanoCam. The flow was relatively cool as it did not melt much snow. We were also able to repair an important radio-telemetry site that was severely damaged during the recent windstorm and do other needed maintenance. Owing to a late start caused by lingering fog in the metro area, we were not able to fit in a gas-sensing flight. That flight will begin shortly today. This morning the volcano is emitting a vapor plume that is drifting over the southeast crater rim. Four earthquakes of about magnitude 3 occurred overnight amidst the ongoing pattern of frequent smaller earthquakes. Swarms of similar-sized events have occurred on several occasions during the past month.

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.

For additional information, background, images, and other graphics: http://vulcan.wr.usgs.gov/News/framework.html

For seismic information: http://www.pnsn.org/HELENS/welcome.html

For a definition of alert levels: http://vulcan.wr.usgs.gov/News/framework.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.



Past Updates

News - Mount St. Helens Current Information