Cascade Range Current Update

November 22, 2004 10:15 am PST (1815 UTC)

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 southeastward.

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 the extrusion of lava onto the surface, where it builds a dome. 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.

Recent observations: The only field work conducted yesterday was continued construction on a new site west of the volcano to improve and strengthen our radio-telemetry network. Saturday’s field work during ideal conditions produced good sets of photographic, thermal-imaging, and gas-sensing data. The welt, the broad area of uplift south of the 1980-86 lava dome, has now reached the crater wall on the southeast and south and has also expanded to the southwest. It also appears to be moving northward into the southern part of the 1980-86 lava dome. The new lava dome, which lies within the welt, continues to expand upward and outward. The dome expansion is accompanied by growth of fractures creating weak zones. The steep west face of the dome is crumbling piecemeal, but, as fractures grow, there is an increasing chance of large slabs of hot rock toppling westward and forming ash clouds that drift out of the crater and hot avalanches, or pyroclastic flows. The flows would sweep over, erode, and melt snow and ice and produce lahars, or volcanic debris flows, that pour northward out of the crater onto the Pumice Plain. The three instrument packages, called Spiders, that were lowered from a helicopter into the crater on Saturday are operating well and sending back data in real time. The GPS site placed near the top of the new lava dome is moving at an impressive rate southeastward and upward. In 24 hours it moved about 10 meters (33 feet) southeastward and 2 meters (6.5 feet) upward, confirming visual and photographic observations. Gas measurements made on Saturday were of high quality and show that daily gas emissions remain at a more or less constant rate of a couple hundred tons of sulfur dioxide, about 1000 tons of carbon dioxide, and several tons of hydrogen sulfide.

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