ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, May 8, 2009, 4:17 PM AKDT (Saturday, May 9, 2009, 00:17 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

Growth of the lava dome continued this past week and is now roughly equivalent in size to the largest dome that was emplaced during the 1989-90 eruption. As the dome grows larger it is increasingly unstable with a growing likelihood of a complete or partial dome failure. Currently AVO considers renewed explosive activity and dome destruction as the most likely outcome of the current episode of dome growth. The return to explosive behavior may occur with little or no advanced warning and would produce a significant ash cloud and lahars and/or flooding in the Drift River valley. There is also a possibility that the current episode of dome growth will slowly diminish and no further explosive activity will occur. Based on our knowledge of past eruptions at Redoubt AVO considers this outcome to be less likely.

Seismicity has varied in its frequency, magnitude, and source characteristics over the past week, but remains consistent with continued dome growth. Numerous rock falls off the unstable north flank of the dome have been observed in seismic and web camera images this week, and have produced minor ash plumes that have reached heights of 12,000 ft above sea level (several thousand feet above the volcano). Vigorous venting of steam and other volcanic gases has been observed, and broad regions of sulfur dioxide gas have been detected by airborne gas measurement flights and in satellite images extending for hundreds of miles from the volcano. Thermal anomalies related to dome growth were observed in satellite data throughout the week.

AVO is monitoring the situation closely and the observatory is staffed 24/7. AVO will provide frequent updates of the volcano's status and the earliest possible warning of significant explosive activity and other hazardous phenomena.

VENIAMINOF VOLCANO (VNUM #312070)
56°11'52" N 159°23'35" W, Summit Elevation 8225 ft (2507 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Seismic activity began to increase significantly above normal background levels on the morning of May 6 at Veniaminof Volcano. This increase caused AVO to raise the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY on the afternoon of May 7. Seismicity continues at an elevated rate with numerous small magnitude earthquakes being registered across the entire seismic network. Visual observations from residents of Perryville over the past several days indicate no change in the typical steaming from the summit caldera cone that has been the site of activity over recent years. Satellite images show no evidence of increased heat flow or ash emissions.

Given the elevated seismicity, it is possible that low-level ash emissions could occur with little or no additional warning. Ash emissions from typical eruptions of Veniaminof are relatively minor, and usually do not rise much higher than 15,000 ft above sea level. These ash plumes can extend for tens of miles and could be hazardous to aircraft in the vicinity of the volcano. Ash fall is typically confined to the summit caldera and the upper flanks of the volcano.





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, 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.

---