Cascade Range Current Update

Wednesday, April 11, 2007 9:42 PDT (Tuesday, April 11, 2007 16:42 UTC)

MOUNT ST. HELENS UPDATE

Current Volcanic- Alert Level WATCH ; 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 rising above the crater rim today would drift to the east at high altitudes early in the day and to the north-northwest at high altitudes later in the day. At low altitudes, any ash clouds would drift to the northwest.

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: It is another quiet day here at Mount St. Helens, with good visibility into the crater of the volcano this morning. Seismicity and deformation remain at low levels, though lava continues to extrude onto the south crater floor. Several small earthquakes (M 2) have occurred in the past 24 hours, although these are not unusual.

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

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, April 11, 2007

This report provides an update of U.S. Geological Survey (USGS) and partners’ (chiefly the Pacific Northwest Seismic Network at the University of Washington and University of Oregon) activities to monitor and assess ongoing volcanic unrest in the Three Sisters region, which began in late 1997 or early 1998. It was discovered in 2001, when analysis of satellite radar data (using a technique called InSAR) revealed that an area about 10 miles in diameter had risen about 4 inches at its center, which lay 3 miles west of the summit of South Sister volcano. Uplift continued at average rates of about 1 inch per year through 2004.

Two continuously recording GPS receivers and annual field surveys during summer 2005 and 2006 confirm that over the past two years this rate has slowed somewhat. InSAR and leveling measurements indicate that the rate of vertical motion has slowed by about one-half, while GPS measurements also show that the rate of vertical motion has slowed, but not by as much. The uplift and extension are likely driven by intrusion of a modest volume of magma, or molten rock, at a depth of about 4 miles. Slowing of ground deformation implies a decrease in the rate of magma intrusion.

Work by USGS scientists in 1990 showed that magmatic heat and gas influenced spring-water temperature and chemistry in this same area. Therefore, the area may be affected episodically by intrusions. The current episode has not yet had a measurable effect on spring waters, which are sampled and analyzed yearly. Seismicity continues at the low rate typical since the March 2004 earthquake swarm, which was located near Middle and South Sisters and tallied more than 300 small earthquakes over several days. In the past year, 7 small earthquakes were located in and near the area of uplift; maximum magnitude was 1.8. Since 2001, scientists have installed 7 additional seismic stations in the area. Two more will come on line this summer and improve our ability to detect and accurately locate future earthquakes. The duration and outcome of the current episode of intrusion is impossible to forecast, and only continued monitoring can track future developments. Intrusions in volcanic areas require close scrutiny because some eventually lead to eruption, but only after weeks to months of intensifying unrest involving earthquakes, ground uplift, and release of volcanic gases. 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 future volcanic events.

For additional information see:
http://vulcan.wr.usgs.gov/Volcanoes/Sisters/,
http://www.ess.washington.edu/SEIS/PNSN/SISTERS/welcome.html, and
http://volcanoes.usgs.gov,
or call the Cascades Volcano Observatory (360) 993-8973

Mount St. Helens Current Eruption Menu