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Monday, March 16, 2009 2:40 PM AKDT (Monday, March 16, 2009 2240 UTC)

Redoubt Volcano
60°29'7" N 152°44'38" W, Summit Elevation 10197 ft (3108 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Current Status and Observations

Seismic activity at Mount Redoubt increased at about 1:05 AKDT Sunday afternoon (March 15, 2009) and approximately 4 hours of continuous volcanic tremor ensued. The onset of the tremor was associated with a small explosion that produced a plume of gas and ash that rose to about 15,000 feet above sea level and deposited a trace amount of ash over the summit-crater floor and down the south flank of the volcano to about 3,000 feet. AVO responded to this increase in activity by raising the color code and alert level to ORANGE/WATCH at 2:50 PM AKDT. At this time it does not appear that the increase in activity heralds a significant eruption in the short term, but conditions may evolve rapidly.

An AVO overflight Sunday witnessed activity from 11:30 AM until about 3:00 PM and was able to document ash emission from a new vent, just south of the 1990 lava dome and west of the prominent ice collapse feature near the north edge of the summit crater. Although ash emission was short lived, it represents the first documented ash fall during the current episode of unrest at Mount Redoubt.

About twenty minutes after the initial steam and ash burst, a sediment-laden flow occurred from a small area in the ice at about 7000 feet on upper Drift glacier. This flow descended about 1500 feet and produced a distinctive seismic signature seen across the Redoubt network.

Although the intent of the overflight was make airborne gas measurements, only a few such measurements were possible due to the uncertain nature of the activity and potential for further ash emission. The measurements that were made indicated at least a qualitative increase in SO2 emission relative to levels measured previously. The gas data are currently being processed and will be available soon.

Interpretation of New Activity and Possible Outcomes

Although preliminary, it is likely that the plume observed just after 1:00 PM AKDT on Sunday, March 15, 2009 was produced by a steam explosion in the shallow hydrothermal system of the volcano. Without examination of the ash we cannot say with certainty if the ash represents new magma or if it is merely pulverized old material from the surface of the volcano.

Steam-driven explosions are not unexpected events at Redoubt given the amount of heat that is being released at the surface. It is possible that more such explosions can occur with little or no warning. It is possible that these plumes can reach above 20,000 feet, and may contain minor amounts of fine ash.

Relatively rapid increases in seismic activity, and an overall waxing and waning pattern to the seismicity at Redoubt may persist for weeks to months. Increases in seismicity may or may not be associated with other volcanic phenomena, such as minor ash emission, and vigorous steaming. The burst of activity at Redoubt on March 15, 2009 indicates that the volcano is still in a restless condition.

AVO plans to visit Redoubt later this week to attempt collection of ash samples, retrieve GPS data and do some routine maintenance of seismic and other equipment.

AVO has resumed 24 hour per day staffing of the AVO operations center in Anchorage.

Heavily ice-mantled Redoubt volcano is located on the western side of Cook Inlet, 170 km (106 mi) southwest of Anchorage and 82 km (51 mi) west of Kenai, within Lake Clark National Park. Redoubt is a stratovolcano which rises to 10,197 feet above sea level. Recent eruptions occurred in 1902, 1966-68, and 1989-90. The 1989-90 eruption produced mudflows, or lahars, that traveled down the Drift River and partially flooded the Drift River Oil Terminal facility. The ash plumes produced by the 1989-90 eruption affected international air traffic and resulted in minor or trace amounts of ash in the city of Anchorage and other nearby communities.

Tom Murray, Scientist-in-Charge, USGS (907) 786-7497

Steve McNutt, Coordinating Scientist, UAF (907) 474-7131

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