Intermittent volcanic seismicity continues to be recorded at Redoubt.
Volcanic unrest continues at Redoubt. Seismicity currently remains above background and the possibility of an eruption exists.

LEAD: All four engines of a KLM Boeing 747 temporarily shut down yesterday when the jumbo jet flew through a cloud of ash from the erupting Redoubt Volcano in Alaska, Government officials reported.

All four engines of a KLM Boeing 747 temporarily shut down yesterday when the jumbo jet flew through a cloud of ash from the erupting Redoubt Volcano in Alaska, Government officials reported.

The huge airliner descended from 25,000 feet to 12,000 feet in eight minutes before the crew was able to restart two of the engines, and all four were operating when the plane, traveling from Amsterdam to Tokyo, landed at 12:25 P.M. in Anchorage, where it had been scheduled to stop for refueling.

None of the 231 passengers and 14 crew members on board the plane, Flight 867, were hurt.

Interpretation and Hazards

Based on our current understanding of Redoubt's past eruptions, both historical and from the geologic record, and our analysis of the current episode of unrest, AVO considers the following future scenarios as possible:

1) Failed Eruption: No eruption occurs because magma does not reach the surface. Earthquake activity, gas output, and steaming slowly decrease over several weeks or months. Continued heat flux may cause continued, modest melting of snow and ice on the edifice and subsequent increased, but not hazardous outflow into the Drift River.

2) Eruption similar to or smaller than 1989-90: Unrest continues to escalate culminating in an eruption that is similar to or smaller than the one that occurred in 1989-90. An eruption such as this would likely spread volcanic ash throughout Cook Inlet and other parts of south-central Alaska depending upon the prevailing winds. Communities around the volcano, especially to the east, northeast, and southeast, would likely experience trace to several millimeters (less than 0.4 inches) of ash fall as a result of discrete explosive events. Such events could also generate pyroclastic flows that swiftly melt snow and ice to form mudflows, or lahars, that would likely travel east down Drift River, possibly reaching and flowing into Cook Inlet. If summit lava domes form, as they did in 1989-90, they may repeatedly collapse and generate pyroclastic flows that would likely travel north from the summit crater and form lahars. Smaller lahars could also form in other drainages if hot debris accumulated on other flanks of the volcano. An eruption consisting of multiple explosive events, episodic lava-dome growth and collapse, and lahars may last weeks to months

3) Larger Explosive Eruption: A significantly larger eruption could occur, perhaps similar to eruptions that are thought to have taken place prehistorically. Such an eruption might involve the production of larger ash clouds, pyroclastic flows on several flanks of the volcano, and larger lahars more frequently reaching Cook Inlet down Drift River and affecting other drainages around the volcano as well.

4) Flank Collapse: The intruding magma or other processes could destabilize a portion of the Redoubt edifice that could result in a large volcanic landslide. At least twice in the last 10,000 years, debris flows generated by such landslides have reached Cook Inlet. It is also likely that a landslide of this type would be accompanied by an eruption. Because of the scarcity of these events in the geologic record, a flank collapse and eruption is considered very unlikely. A flank collapse may be accompanied by visible deformation of the edifice and AVO will be looking for such signs.

Based on all available monitoring data and AVOs knowledge of the volcano, scenario number two, an eruption similar to or smaller than that of 1989-90, appears to be the most probable outcome at this time. We consider one and three to be somewhat less likely, and scenario four to be much less likely.

Comparing the time frame of pre-eruptive activity in 1989-90 (the only other eruption for which seismic data were available) with the current unrest, we would expect such an eruption to begin within the next few days or weeks. It is likely that the onset of an explosive eruption would be preceded by a further increase in seismicity. An explosive eruption would be accompanied by a sharp increase in seismicity. Should earthquake activity or other monitoring data suggest that an eruption is expected within hours, or is underway, AVO would move Redoubt from its current Aviation Color Code ORANGE to RED, and Alert Level WATCH to WARNING.
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2009-01-29 08:01:58
Seismicity remains above background levels and appears to have increased slightly over the last few hours.

AVO is currently staffed 24 hours per day to monitor Redoubt Volcano. The Aviation Color Code remains at ORANGE and the Volcano Alert Level remains at WATCH.