|(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)|
|(3) Volcano:||Great Sitkin (VNUM #311120)|
|(4) Current Color Code:||ORANGE|
|(5) Previous Color Code:||RED|
|(6) Source:||Alaska Volcano Observatory|
|(7) Notice Number:||2021/A299|
|(8) Volcano Location:||N 52 deg 4 min W 176 deg 6 min|
|(10) Summit Elevation:||5709 ft (1740 m)|
|(11) Volcanic Activity Summary:||A short-duration (1-2 minutes) explosive eruption occurred at 21:04 AKDT Tuesday May 25 (5:04 UTC 26 May) and resulted in an ash cloud up to 15,000 ft asl. Since that explosion, seismicity has decreased and satellite images show no further ash emissions. Thus, AVO is reducing the Aviation Color Code ORANGE and the Volcano Alert Level to WATCH. Additional explosive events are possible, but not certain.
The ash cloud from the initial explosive eruption is still visible in satellite images. See the NWS Alaska Aviation Weather Unit web page for current information. https://www.weather.gov/aawu/sigmets
Great Sitkin is monitored with a local real-time seismic network, which will typically allow AVO to detect changes in unrest that may lead to an explosive eruption. Rapid detection of an ash-producing eruption would be accomplished using a combination of seismic, infrasound, lightning, and satellite data.
|(12) Volcanic cloud height:||No current emissions|
|(13) Other volcanic cloud information:||Drifting ash cloud still visible in satellite data|
|(14) Remarks:||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.|
|(15) Contacts:||Michelle Coombs, Scientist-in-Charge, USGS
email@example.com (907) 786-7497
David Fee, Coordinating Scientist, UAF
firstname.lastname@example.org (907) 322-4085
|(16) Next Notice:|
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