ALASKA VOLCANO OBSERVATORY INFORMATION STATEMENT
GREAT SITKIN VOLCANO
U.S. Geological Survey
Friday, March 6, 2020, 12:24 PM AKST (Friday, March 6, 2020, 21:24 UTC)
52°4'35" N 176°6'39" W,
Summit Elevation 5709 ft (1740 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW
A relatively large magnitude 3.5 earthquake occurred at Great Sitkin this morning at 6:31 AM AKST (15:31 UTC). It was located approximately 1 km east-southeast of the summit at shallow depths (not more than 2 km below sea level). Since the quake, seismic activity has returned to lower levels, and no eruptive activity has been detected in infrasound or satellite data today. Although this earthquake represents a significant increase in the seismic activity at the volcano, it does not mean that an eruption is imminent. AVO is closely monitoring the volcano for other signs of unrest that may indicate increased activity or likelihood of an eruption.
Great Sitkin is monitored with a network of local seismic sensors, satellite data and distant lightning networks. In addition, a local infrasound sensor on Great Sitkin, as well as an infrasound array on nearby Adak Island, may detect explosive emissions if atmospheric conditions permit.
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 dissected volcano and a younger parasitic cone with a 3-km-diameter summit crater. A steep-sided lava dome, emplaced during an eruption in 1974, occupies the center of the crater. Great Sitkin erupted at least three times in the 20th century, most recently in 1974. That eruption produced at least one ash cloud that likely exceeded an altitude of 25,000 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
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Michelle Coombs, Scientist-in-Charge, USGS
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David Fee, Coordinating Scientist, UAFGI
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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.