Cascade Range Current Update

Wednesday, December 14, 2005      10:30 a.m. PST (18:30 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 ash clouds that rise up to about 15,000 feet above the crater rim (about 23,000 feet above sea level) today would drift southwestward to northwestward; higher-altitude ash clouds would drift east-southeastward.   

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:   Small rock falls continue from the growing lava dome.  Larger ones may produce ash plumes that are visible above the crater rim.  Patterns of earthquakes and ground deformation remain unchanged from recent trends.  The volume of the dome measured on October 24, 2005, was 70 million cubic meters—about 90% of the volume of the 1980-to-1986 dome.

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/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.



Three Sisters, Oregon, Information Statement
December 14, 2005

This Information Statement provides an update about ongoing investigations of the broad area in the Three Sisters region of central Oregon that has been gradually swelling since late 1997. Field surveys indicate that the swelling, or uplift, is continuing but may have slowed somewhat during the past year. The area of uplift is about 12 miles (20 kilometers) in diameter and is centered 3 miles (5 kilometers) west of South Sister volcano. The middle of the uplift has been rising at an average rate of about one inch (25 millimeters) per year as a result of intrusion of a modest volume of magma, or molten rock, about 4 miles (7 kilometers) below the ground surface. Seismic activity related to the uplift has been scant, except for a swarm of more than 300 small earthquakes in late March 2004. Volcanic gases released from the intruding magma dissolve in ground water so water in local springs and streams is slightly enriched in chemical components derived from volcanic gases.

Results of this year’s investigations show that:
(1) Earthquakes continue at a low rate. Only 5 small (maximum magnitude 1.5) earthquakes were located in the uplift area in 2005.
(2) The chemical composition of local spring and stream water remains unchanged from that of the past 5 years.
(3) Uplift of the ground surface continues, but seems to have slowed from the rate observed in past years. Results of three techniques used to measure ground deformation all have a degree of uncertainty, but together they suggest that the rate decreased in 2004-2005, perhaps by as much as one half. If so, the rate of intrusion of magma has declined as well.

Scientists believe that periods of intrusion similar to the present one have occurred in the area before. The duration and outcome of the current episode are impossible to forecast, and only continued monitoring will show whether or not this episode of intrusion is slowly ending. Intrusions in volcanic areas require close scrutiny because some eventually lead to eruption, but only after weeks to months of intensifying unrest. Scientists will work with the U.S. Forest Service to enhance monitoring networks as needed, and continue to work with local agencies to develop a plan for responding to any future volcanic events.

For additional information see:
http://volcanoes.usgs.gov,
http://vulcan.wr.usgs.gov, and
http://www.ess.washington.edu/SEIS/PNSN/SISTERS/welcome.html.

U.S. GEOLOGICAL SURVEY
CASCADES VOLCANO OBSERVATORY
BUILDING 10, SUITE 100
1300 SE CARDINAL COURT
VANCOUVER, WA 98683
(360) 993-8900
http://vulcan.wr.usgs.gov and http://volcanoes.usgs.gov



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