ALASKA VOLCANO OBSERVATORY STATUS REPORT
U.S. Geological Survey
Saturday, July 22, 2017, 12:45 PM AKDT (Saturday, July 22, 2017, 20:45 UTC)

GREAT SITKIN VOLCANO (VNUM #311120)
52°4'35" N 176°6'39" W, Summit Elevation 5709 ft (1740 m)
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN

An increase in seismic activity was detected at Great Sitkin starting with seismic tremor on July 21 16:17 AKDT (July 22 00:17 UTC). After about an hour, tremor transitioned to discrete earthquakes. Small earthquakes continue at present at a much decreased rate of several per hour. No anomalous airwaves were detected at the Adak infrasound array, and nothing was observed in satellite data above weather cloud tops, which were at about 10,000 ft asl. AVO continues to monitor Great Sitkin with a local seismic network, distal infrasound networks and with satellite observations.

Great Sitkin Volcano is a basaltic andesite volcano that occupies most of the northern half of Great Sitkin Island, a member of the Andreanof Islands group in the central Aleutian Islands. It is located 43 km (26 miles) east of the community of Adak. The volcano is a composite structure consisting of an older decapitated volcano and a younger parasitic cone with a 2-3 km diameter summit crater. A steep-sided dome occupies the center of the crater. Great Sitkin erupted at least three times in the 20th century, most recently in 1974 when a lava dome formed in the crater accompanied by at least one ash cloud that reached ~10,000 ft. above sea level. A poorly documented eruption occurred in 1945, also producing a lava dome that was partially destroyed in the 1974 eruption. Within the past 280 years a large explosive eruption produced pyroclastic flows that partially filled the Glacier Creek valley on the southwest flank.

OTHER ALASKA VOLCANOES

Information on all Alaska volcanoes is available at : http://www.avo.alaska.edu.

For definitions of Aviation Color Codes and Volcano Alert Levels, see: http://www.avo.alaska.edu/color_codes.php

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CONTACT INFORMATION:

Michelle Coombs, Scientist-in-Charge, USGS
mcoombs@usgs.gov (907) 786-7497

Jeff Freymueller, Coordinating Scientist, UAF
jfreymueller@alaska.edu (907) 322-4085

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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