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ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, March 20, 2009, 1:02 PM AKDT (Friday, March 20, 2009, 21:02 UTC)


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

On Sunday, March 15, 2009, AVO raised the color code and alert level to ORANGE/Warning during an abrupt increase in seismicity and following a burst of steam and ash that was observed by airborne AVO staff. High volcanic gas emissions were measured during the event. After several hours, seismicity and steam emissions declined, and remained low for the next several days. The color code and alert level was subsequently reduced to YELLOW/Advisory on March 18, 2009.

Seismic activity at Redoubt has been low over the remainder of the week but remains above background levels. The seismicity consists of occasional short periods of low amplitude volcanic tremor and small discrete earthquakes. A burst of several dozen larger events occurred Friday morning.

Mostly clear weather at the volcano this week has provided good satellite and web camera images, and these showed nothing unusual. A steam plume rising just above the summit of the volcano has been visible most of the week.

It is still possible for unrest at the volcano to change rapidly, and seismic activity or other signs of unrest could escalate over time periods as short as 24 hours or less. AVO continues to monitor Redoubt closely, but the AVO operations center in Anchorage is no longer formally staffed 24 hours per day, although someone is on duty 24 hours per day and can be contacted by calling 907-786-7497.


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 new reports of activity at Cleveland over the past 24 hours. Satellite views have been obscured by clouds.

OKMOK VOLCANO (VNUM #311290)
53°23'49" N 168°9'58" W, Summit Elevation 3520 ft (1073 m)
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN

AVO reduced the Aviation Color Code to GREEN and the Volcanic Alert Level to NORMAL for Okmok volcano earlier today.

Seismic activity at Okmok has been at low to near background levels and satellite views show no activity over the past two weeks. AVO has received no reports of activity.





Okmok volcano was in vigorous eruption from July 12 through mid-August, 2008. Energetic, intermittent ash emission from several vents within the caldera blanketed much of the northeast portion of Umnak Island with ash and dusted Unalaska/Dutch Harbor with fine ash on several occasions. Rain-induced remobilization of debris from high on the volcano's flanks produced lahars down many drainages, forming new deltas at the coastline. A new, 200-300 m-high (660-980 ft) tephra cone developed inside the caldera at the primary eruption site. Since late August 2008, seismicity at Okmok has generally declined. The last confirmed ash emission at Okmok occurred on August 19, 2008.

Okmok volcano is a 6-mile-wide caldera that occupies most of the eastern end of Umnak Island, located 75 miles southwest of Unalaska/Dutch Harbor in the eastern Aleutian Islands. Okmok has had several eruptions in historic time typically consisting of ash emissions occasionally to over 30,000 feet ASL but generally much lower; lava flows crossed the caldera floor in 1945 and 1958. Prior to 2008, the volcano last erupted in February 1997 producing lava flows and intermittent ash emissions over the course of several months.

The nearest settlement is Nikolski, population about 35, roughly 45 miles west of the volcano. A ranch caretaker family lives at Fort Glenn on the flank of the volcano about 6 miles east of the caldera rim.


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, 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.