ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, August 31, 2012, 3:35 PM AKDT (Friday, August 31, 2012, 23:35 UTC)

LITTLE SITKIN VOLCANO (VNUM #311050)
51°57'11" N 178°32'8" E, Summit Elevation 3898 ft (1188 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

A swarm of high-frequency earthquakes began at Little Sitkin volcano on the evening of August 29, 2012 and continued through the night prompting AVO to elevate the Aviation Color Code/Volcano Alert Level to YELLOW/ADVISORY. The rate of anomalous seismicity has varied over the last two days, with the two most active periods being the morning of August 30 and at about 04:00 am AKDT (12:00 UTC) on August 31. The rate of earthquakes began to decline about 06:00 am AKDT (14:00 UTC) on August 31 and currently remains in decline. No eruptive activity occurred. Clouds have obscured satellite images of the area.

AVO is closely monitoring the situation and will issue further updates as conditions change.

Although a 4-station seismic network was installed on Little Sitkin Island in 2005, the volcano has not formally been on AVO's list of seismically monitored volcanoes because of chronic telemetry problems resulting in intermittent and sporadic recording of seismic data. Recent work in June 2012 on the receiving station on Amchitka Island resolved most of the communication issues, and data from the 4 stations on Little Sitkin Island are currently recorded and processed, and AVO continues efforts to establish background seismic levels at the volcano.



Little Sitkin volcano occupies Little Sitkin Island in the western Aleutian Islands, and is within the Aleutian Island National Wildlife Refuge. The active stratovolcano rises 1188 m (3898 ft) in the center-northeastern part of the island. The island is 330 km (200 mi) northwest of the community of Adak, 377 km (234 mi) southeast of Attu, and 2173 km (1350 mi) southwest of Anchorage, Alaska. Little Sitkin has no confirmed historical eruptions, although eruptive activity near the turn of the last century seems probable based on vegetation cover of the youngest-looking lava flows. Three long-lived fumarolic and hot springs areas are known including a cluster of boiling, acidic pools on the west flank of the volcano.


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

Although cloudy conditions obscured satellite views over most of the past week, images from August 17 show that the summit crater of Cleveland is tephra-covered, funnel-shaped, and contains no lava dome. No activity was reported this week.

Sudden explosions of blocks and ash remain possible with little or no warning. Associated ash clouds could exceed 20,000 feet above sea level. If a large ash-producing event occurs, nearby seismic, infrasound, or volcanic lightning networks should detect the event and alert AVO staff. There is no real-time seismic monitoring network on Mount Cleveland and AVO is unable to track activity in real time.

ILIAMNA VOLCANO (VNUM #313020)
60°1'55" N 153°5'30" W, Summit Elevation 10016 ft (3053 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Satellite and webcam views of Iliamna over the past week were clear to cloudy. No unusual activity was observed or reported. Seismicity remains slightly above background levels.

The current level of activity at Iliamna does not indicate an imminent or certain eruption. Seismic activity, along with gas emissions, appear to be declining gradually. A similar seismic swarm occurred at Iliamna Volcano in 1996-1997 and was not followed by eruptive activity. Prior to an eruption, AVO would expect to see a significant increase in earthquake activity beneath the volcano.


OTHER ALASKA VOLCANOES

Seismic activity is monitored in real time at 29 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, Isanotski, Kanaga, Katmai, Mageik, Makushin, Martin, Novarupta, Okmok, Pavlof, Redoubt, Shishaldin, Snowy, Spurr, Tanaga, Trident, Ugashik-Peulik, Ukinrek Maars, Veniaminof, and Westdahl 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 of these volcanoes.

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:

John Power, Scientist-in-Charge, USGS
jpower@usgs.gov (907) 786-7497

Jeff Freymueller, Coordinating Scientist, UAFGI
jeff.freymueller@gi.alaska.edu (907) 978-5458

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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