ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, February 13, 2009, 2:24 PM AKST (Friday, February 13, 2009, 23:24 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. This week, seismicity has been dominated by periods of tremor with variable amplitudes and small discrete earthquakes. These data are likely indicative of movement of shallow fluids (including heated ground water) and gases within the volcano.

Web camera views have been obscured by clouds and snow since Tuesday. Clear web camera views and reports from staff observers in the field during the past week reported intermittent steam plumes from the area of the 1989-90 lava dome and from a new melt hole, continued melting of the upper Drift glacier, and continued water discharge along the lower Drift glacier and into the Drift River. Airborne gas measurements on February 7 recorded levels of the magmatic gas CO2 about two times greater than the values recorded on January 31 and February 2, 2008. Sulfur dioxide (SO2) levels remained low indicating that the gas is being absorbed by shallow groundwater near the volcano's summit.

AVO personnel installed a GPS instrument near Redoubt and collected water samples and temperature data with an infrared camera. Sulfur odor was detected during sampling, which is consistent with the water carrying dissolved sulfur gas emitted in the active fumarolic zone. Exposed rock in the active fumaroles is warm (about 80 F)and the outflow stream on the west side of the Drift Glacier was frozen.

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 estimate that the magma is still relatively deep (greater than 5 km or ~3 miles) although a small amount of the magma may have risen to shallower depths (within 2 km, or about a mile, of the surface) in late January when seismicity, degassing, and melting intensified. At present, the current period of elevated unrest could persist for some time, possibly many months. However, as long as substantial volcanic-gas emission, prolonged periods of tremor, and intermittent discrete, shallow earthquakes occur, notable escalation of activity immediately prior to an eruption might only be on the order of hours or less. On the basis of current activity, we consider the most likely scenario is an eruption similar to or smaller than the 1989-90 eruption.

Staff continue to monitor the volcano 24 hours a day. We will issue further information as it becomes available. An Information Statement summarizing AVO's current analysis of unrest at Redoubt Volcano was released 13 February at 10:12AM AKST (today) and can be found on our web site: http://www.avo.alaska.edu/


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.

More information about Redoubt Volcano can be found at http://www.avo.alaska.edu/activity/Redoubt.php

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 about Cleveland activity during the last week. Low-level ash emissions may occur with little or no warning. Satellite views have been mostly cloudy over the past 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.

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

The Alaska Volcano Observatory lowered the Aviation Color Code to GREEN and the Alert Code to NORMAL at Shishaldin volcano on 11 February.

Seismic levels at Shishaldin volcano have decreased to background levels and have been at this level since late December 2008. A very weak thermal anomaly was last detected on February 3, 2009. Reports of steam issuing from the summit crater continue to be received although this is not anomalous activity at this volcano; steaming is typical.



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.

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.

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