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U.S. Geological Survey
Tuesday, May 26, 2009, 12:22 PM AKDT (Tuesday, May 26, 2009, 20:22 UTC)

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


The 2009 eruption of Redoubt Volcano has entered its 10th week. Lava continues to erupt from a vent in the summit crater feeding a blocky, rubbly lava dome that extends out of the summit crater and more than 500 m (1640 ft) down the north flank of the volcano. Although volcanic seismicity has declined somewhat in the last few weeks, it remains elevated above pre-eruption background. Volcanic gas emissions also remain elevated. The growing lava dome is potentially unstable and the possibility of a full or partial collapse remains high. Such a collapse would likely be accompanied by a large ash plume and lahars in the Drift River Valley. This event could occur with little or no warning. Consequently, AVO continues to monitor the volcano 24 hours per day and the aviation color code remains ORANGE and the alert level WATCH.

Recent Observations

The current lava dome is estimated to be roughly 40 million cubic meters in volume based on analyses of thermal and satellite images and aerial photographs. This amount of material would fill approximately 11 Louisiana Superdomes. Using measurements from a Worldview satellite image on May 17, the dome and tongue of lava that extends to the north is about 950 m (3115 ft) long (north-to-south), 460 m (1510 ft) wide (east-to-west), and 200 m (655 ft) tall. Over time, the dome is growing in size primarily to the north but to the east and west as well. There is a slight overhang developing at the very front (northernmost part) of the lava tongue in the upper Drift gorge.

Nighttime images from the AVO webcam continue to show occasional incandescence or glow as rockfalls expose hot interior dome rock. Thermal images obtained during helicopter overflights indicate portions of the surface of the lava dome exceed 350 degrees C. This value reflects the temperature of the cooling crust and is not a direct measurement of actual lava temperature as it emerges from the vent. Temperatures of fresh lava of this composition should be considerably higher (~850 to 950 degrees C).

Seismic activity at Mount Redoubt remains elevated with numerous small volcanic earthquakes and signals from small rock avalanches recorded on the stations closest to the volcano. Many of these small rock falls generate minor ash plumes that may rise several thousand feet above the crater rim and produce localized fallout.

Airborne gas measurements over the past several weeks indicate that Redoubt's emissions remain high. For the month of May, preliminary calculations indicate that average emissions are in excess of 8,000 tonnes/day of SO2 and 15,000 tonnes/day of CO2 . These values are similar to the range of values measured during the early dome building phase of the 1989-90 Redoubt eruption and are consistent with strong degassing expected during active lava extrusion.

Reviewing data on erupted lava composition, seismicity, and deformation (as measured by high-precision GPS measurements made in the vicinity of the volcano), AVO scientists infer that magmas feeding the lava dome are rising from at least two main staging locations at 3 to 5 km (2-3 mi) depth below the surface and 8 to more than 15 km (5-9 mi) depth. The processes of magma ascent and eruption have produced a variety of mixed andesitic magmas sampled by AVO since the start of the eruption in March.

Prognosis and Ongoing Hazards

The last explosive event of the current eruption occurred on the morning of April 4 destroying the lava dome that had grown in the summit crater in late March and early April. The current lava dome has now been growing for 53 days and is similar in size to the larger domes emplaced during the 1989-90 eruption. During the 1989-90 eruption, the longest period of dome growth between explosions was 36 days. Based on the size of the current lava dome and the likelihood of increasing instability as it extends down the steep upper Drift gorge, AVO expects it will most likely be destroyed either through gravitational collapse or an explosion from within the shallow vent system.

The Redoubt eruption is expected to continue for additional weeks to months. During this time, a cycle of relatively quiet periods of lava dome growth followed by brief explosive episodes of dome destruction will likely take place. Future explosions pose an ongoing threat of lahars in the Drift River Valley, trace to minor ash fall throughout south-central Alaska, and ash-related impacts to aviation. However, the possibility remains that the lava dome growth rate may slowly diminish and the dome itself will stabilize and no further explosive activity will occur.

For more information and recent photographs including animations of dome growth, please see our web site: http://www.avo.alaska.edu/activity/Redoubt.php

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 significantly disrupted 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
tlmurray@usgs.gov (907) 786-7497

Steve McNutt, Coordinating Scientist, UAF
steve@giseis.alaska.edu (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.
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