In November, after receiving reports of increased emissions of volcanic gases, melting of snow and ice near the summit and an increase in seismicity, AVO raised the concern levels to "warning" and the aviation code to "yellow." AVO increased concern levels after seismic stations on the volcano showed an increase in intensity and numbers of localized small earthquakes.

AVO has seven stations on or near Redoubt, including four that can be accessed through the Redoubt Web page at www.avo.alaska.edu/activity/Redoubt.php. Seismic stations also are on other volcanoes, such as Mount Spurr.

"We think the activity is pretty shallow and localized below the summit," said Michelle Coombs, a geologist with the U.S. Geological Survey, Anchorage. "It's well above background, but they aren't able to be felt at the more distant stations."

Increased seismic activity on distant stations could be a sign of an eruption. During the 1989-90 eruption of Redoubt, Spurr's seismometers showed explosive activity on Redoubt.

"Those are the kinds of things we'd expect to see if the volcano was having eruptive activity," Coombs said.

Scientists have been monitoring Redoubt 24-hours a day. This week, scientists flew over Redoubt on Sunday and Monday. On Monday, new outflows of muddy debris were seen on a glacier down slope of the summit. A web camera was installed at AVO's Redoubt Hut, about 7.5 miles from the summit. A web cam on Spurr was turned toward Redoubt. Scientists made gas measurements on a flight on Monday and noted an increase in sulfur dioxide. Sulfur dioxide which smells like rotten eggs carbon dioxide and hydrogen sulfide are all gases associated with an upwelling of magma.

Redoubt is a noisy volcano, with lots of seismic activity due to moving glaciers, rockfalls and other more common natural events. The latest earthquake activity is different.

"The number we see now is much greater than that," Coombs said. "The type of earthquake has changed. It's not just an increase in the number of earthquakes, but a change in the type of earthquake as well."

Scientists are seeing more low-frequency earthquakes or volcanic tremor associated with the movement of gases. The gases can be from magma heating water in Redoubt's hydrothermal system or gases from the magma itself.

Seismic activity has ebbed and flowed this week, but remains of concern, AVO said in its latest alerts on Wednesday. The greatest concern in an eruption is ashfall and mudflows that could affect the Drift River oil facility. Ash is particularly hazardous to aviation. During the last Redoubt eruption, a Boeing 747 jet flew into an ash cloud on Dec. 18, 1989, causing all four engines to stop. The jet fell about 10,000 feet before the pilot restarted the engines.

Ash also can be hazardous to people and animals, particularly people with respiratory problems like asthma or emphysema. The Alaska Department of Health and Human Services issued a notice Tuesday advising people to take care if ash does fall. Contact-lens wearers should remove contacts, and anyone going outside should wear dust masks. For more information on health impacts, visit the HHS Web page at www.hss.state.ak.us. The Kenai Peninsula Borough Office of Emergency Management also has information on its Web page at www.borough.kenai.ak.us/emergency/default.htm.

If Redoubt erupts, the most likely scenario is an eruption similar to that of 1989-90, with a dusting to a trace amount of ash deposited on local communities, Coombs said. Larger eruptions are possible, but it would take a very large eruption to blanket towns in inches of ash. The 1989-90 eruption deposited about -inch of ash on Kenai.

The AVO Web site has links to ash trajectory projections, as well as links to Anchorage International Airport, ashfall and emergency preparedness information and the National Weather Services. A link to a Dec. 22, 2005, Homer News archive article, "Get out the panty hose: What to do if Augustine blows," has information about preparing for volcanoes, and can be found at www.homernews.com.

The Alaska Volcano Observatory is a cooperative program with the U.S. Geological Survey, the University of Fairbanks Geophysical Institute and the Alaska Division of Geological and Geophysical Surveys.

Michael Armstrong can be reached at michaelarmstrong.@homernews.com.