Cascade Range Current Update

U.S. Geological Survey, Vancouver, Washington
University of Washington, Pacific Northwest Seismograph Network, Seattle, Washington

November 11, 2004 11:00 am PST (1900 UT)

MOUNT ST. HELENS VOLCANO

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, and is accompanied by intermittent emissions of steam and ash. As long as this eruption is in progress, episodic changes in the level of activity can occur over days, weeks, or even months. Increase in the intensity of eruption could occur suddenly or with very little warning and may include explosive events that produce hazardous conditions within several miles of the volcano. Small lahars (volcanic debris flows) could suddenly descend the Toutle River valley if triggered by heavy rain or by interaction of hot rocks with snow or glacier ice. These lahars pose a negligible hazard below the Sediment Retention Structure (SRS) but could pose a hazard to people along the river channel upstream of the SRS. At this time of year, it is not unusual for rivers draining the volcano to contain high concentrations of sediment that turn the water murky.

Although considered less likely at this time, the current eruptive activity could evolve into a more explosive phase that affects areas farther from the volcano and sends significant ash thousands of feet above the crater where it could be a hazard to aircraft and to downwind communities.

Wind forecasts from the National Oceanic and Atmospheric Administration (NOAA), coupled with eruption models, show that ash clouds that rise high above the crater rim today would drift west-northwestward.

Clear views this morning show that a steam plume is rising passively and drifting westward out of the crater. The plume occasionally contains minor ash, which falls out in the crater and on the flank of the volcano, darkening the snow.

Seismicity remains at a low level compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.

Yesterday field crews repaired the DomeCam, the time-lapse camera that is aimed at the new lava dome from a site near the crater mouth, and conducted visual and thermal-imaging observations and a gas-sensing flight. Strong winds made interpretation of gas data difficult. Good viewing conditions revealed continued growth of the lava dome. Current estimates are that the welt, the broad area of deformation, is about 600 m (about 1950 feet) in diameter. The new lava dome, which occupies the central and western parts of the welt, is about 400 by 180 m (1300 by 600 feet). The highest point on the new lava dome is about 250 m (820 feet) above the former surface of the glacier that occupied that point in mid-September. Maximum surface temperatures on the new dome remain at about 700 degrees C (1300 degrees F). GPS instruments on the welt show rates of movement of up to several meters per day, while GPS instruments on the 1980-86 lava dome show movements of up to 1-2 cm (less than one inch) per day northward, away from the growing welt and new 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/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

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