ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, February 6, 2009, 1:05 PM AKST (Friday, February 6, 2009, 22:05 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, though no eruption has yet occurred. Seismic activity at the volcano remains above background levels and has waxed and waned over the last week. Yesterday from 11:18 to about 16:00 AKST, there were several periods of more intense seismic tremor. Since then, nearly continuous low-level seismic tremor has been recorded.

Clear web camera images currently show no activity at the volcano. Observers on overflights during the past week reported intermittent steam plumes from the area of the 1989-90 lava dome, continued melting of the upper Drift glacier, and increased water discharge along the lower Drift glacier and into the Drift River. Airborne gas measurements on January 31 and February 2 recorded levels of the magmatic gas CO2 several times greater than the value recorded on November 2, 2008.

Gas and heat flux, combined with ongoing seismic activity, suggest that new magma has been emplaced within the crust below Redoubt and that it is actively degassing. We do not know the exact depths or volume of the magma; nor is it certain that the magma will continue to rise to the surface. On the basis of current activity, however, the most likely scenario is an eruption similar to or smaller than the 1989-90 eruption. It is somewhat less likely that no eruption will occur or that the volcano has an eruption larger than that of 1989-90.

AVO personnel installed two new seismic instruments near Redoubt over the past week, and improved signals coming in from the Redoubt seismic network at AVO's facility in Homer.

Staff continue to monitor the volcano 24 hours a day. We will issue further information as it becomes available.



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 10,198 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.

SHISHALDIN VOLCANO (VNUM #311360)
54°45'19" N 163°58'16" W, Summit Elevation 9373 ft (2857 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Seismicity at Shishaldin is unchanged over the last seven days and weak tremor continues.

The last thermal anomaly visible at Shishaldin in satellite imagery was on January 26. Snow and ice continue to obscure web camera views.




Shishaldin volcano, located near the center of Unimak Island in the eastern Aleutian Islands, is a spectacular symmetric cone with a base diameter of approximately 10 miles (16 km). A small summit crater typically emits a noticeable steam plume with occasional small amounts of ash. Shishaldin is one of the most active volcanoes in the Aleutian volcanic arc, erupting atleast 28 times since 1775. Most of Shishaldin's eruptions have consisted of small ash and steam plumes, although the most recent eruption in April-May 1999 produced an ash column that reached a height of 45,000 ft above sea level.

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

The last thermal anomaly seen at Cleveland was on January 23. AVO has received no reports about Cleveland during the last week.

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, 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.

---