ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, February 27, 2009, 1:31 PM AKST (Friday, February 27, 2009, 22:31 UTC)

REDOUBT VOLCANO (VNUM #313030)
60°29'7" N 152°44'38" W, Summit Elevation 10197 ft (3108 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Unrest at Redoubt Volcano continues. No eruption has occurred.

Relatively low-amplitude volcanic tremor and intermittent discrete earthquakes characterized seismic activity at Redoubt from February 21-24. During this time, clear weather allowed many web camera and satellite views that showed nothing out of the ordinary.

On Wednesday, February 25, a broad-spectrum seismic signal at 9:29 AM AKST was likely associated with a small mud flow originating from a melt hole in the Drift glacier at about 5600 feet above sea level. This dark deposit was seen in a web camera image from 10:03 AM AKST that morning, and observers on an overflight the next day reported that the deposit was several hundred meters in length. Later the same day, at 3:37 PM AKST, tremor amplitude increased sharply and remained elevated for approximately one hour. This tremor was strong enough to be recorded on all seismic stations on Redoubt Volcano as well as many stations surrounding Cook Inlet. At 10:40 PM AKST the same night, the number of discrete earthquakes increased and remained elevated for about four hours.

On Thursday, February 26, a flurry of earthquakes began at 5:30 PM AKST and lasted for roughly one hour. These events were accompanied by the emplacement of a mudflow that covered a large portion of the upper Drift glacier, as viewed in web camera images beginning at 6:04 PM AKST. An ASTER thermal infrared satellite image from last night shows this deposit stretching several kilometers down the Drift glacier.

The recent variations in seismic activity coupled with increased melt water discharge on the upper Drift glacier indicate that conditions have changed at shallow depths beneath the volcano. It is possible that magma has moved to shallower levels in the volcanic edifice, but recent changes may be due instead to changes in degassing pathways from a deeper magma body. AVO is currently analyzing this seismic activity and will issue further information as it becomes available. A gas-measurement flight is currently underway.

Because of the clear weather this past week, AVO was able to undertake several flights to Redoubt to measure gas (February 21, and today) and perform upgrades to the monitoring network (February 21, 22, and today). Results from the February 21 gas flight reveal that the emission rates of CO2 and SO2 have not changed since February 7 and both remain high. Upgrades to the network include addition of a broadband seismometer on the volcano's west flank, installation of a pressure sensor (to detect airwaves) north of the volcano, and improvements to the power supply at the AVO hut.

AVO continues to monitor Redoubt Volcano closely, and the observatory is staffed 24 hours a day.


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.

CLEVELAND VOLCANO (VNUM #311240)
52°49'20" N 169°56'42" W, Summit Elevation 5676 ft (1730 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

AVO has received no reports of activity at Cleveland in the past week. Nothing unusual has been observed in mostly to partly cloudy satellite images. Low-level ash emissions may occur with little or no warning.

Cleveland volcano forms the western half of Chuginadak Island, a remote and uninhabited island in the east central Aleutians. It is located about about 75 km (45 mi.) west of the community of Nikolski, and 1500 km (940 mi.) southwest of Anchorage. The volcano's most recent significant eruption began in February, 2001 and had 3 explosive events that produced ash clouds as high as 12 km (39,000 ft) above sea level. This eruption also produced a rubbly lava flow and hot avalanche that reached the sea. The most recent minor ash emissions were observed in January 2009.

OTHER ALASKA VOLCANOES

Seismic activity is monitored in real time at 31 volcanoes in Alaska. Satellite images of all Alaskan volcanoes are analyzed daily for evidence of ash plumes and elevated surface temperatures. Some volcanoes may currently display anomalous behavior but are not considered to be at a dangerous level of unrest. Akutan, Aniakchak, Augustine, Dutton, Fisher, Fourpeaked, Gareloi, Great Sitkin, Griggs, Iliamna, Isanotski, Kanaga, Katmai, Korovin, Mageik, Makushin, Martin, Novarupta, Okmok, Pavlof, Shishaldin, Snowy, Spurr, Tanaga, Trident, Ugashik-Peulik, Ukinrek Maars, Veniaminof, Westdahl, and Wrangell volcanoes are in color code GREEN and volcano alert level Normal. All are at or near normal levels of background seismicity. AVO did not detect ash plumes or significant elevated surface temperatures in the vicinity of any volcano.

Please see http://www.avo.alaska.edu/color_codes.php for complete definitions of Aviation color codes and Volcano alert levels.

VOLCANO INFORMATION ON THE INTERNET: http://www.avo.alaska.edu
RECORDING ON THE STATUS OF ALASKA'S VOLCANOES (907) 786-7478

CONTACT INFORMATION:

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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