Alaska Volcano Observatory - AVO Volcano Activity Notification

AVO VOLCANO ACTIVITY NOTIFICATION

(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20210723/2225Z)
(3) Volcano:	Great Sitkin (VNUM #311120)
(4) Current Color Code:	ORANGE
(5) Previous Color Code:	YELLOW
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2021/A553
(8) Volcano Location:	N 52 deg 4 min W 176 deg 6 min
(9) Area:	Aleutians
(10) Summit Elevation:	5709 ft (1740 m)
(11) Volcanic Activity Summary:	A satellite radar image from last night July 22, 9:32 PM local (July 23 05:32 UTC) shows a small ~50 m (~150 ft) diameter area of uplift in the center of the crater at Great Sitkin suggestive of rising magma near the surface. This lava dome-like feature appears to have been emplaced sometime between July 14 and 22. As a result AVO is raising the the Aviation Color Code to ORANGE and the Volcano Alert Level to WATCH. Seismicity has been at relatively low levels this week compared to last week and we suspect that the lava dome-like feature was emplaced last week. Moderately elevated surface temperatures consistent with this feature were observed in satellite data on July 22. Cloudy conditions have obscured views of the volcano by satellite most of the past week. AVO will continue to closely monitor this new uplift feature. The prognosis for eruptive activity is uncertain. Continued growth of the lava dome feature, additional explosive events, or a return to non-eruptive behaviors are all possible. AVO will report on significant changes and observations in monitoring data should they occur. 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:	None
(13) Other volcanic cloud information:	n/a
(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:	Matt Haney, Acting Scientist-in-Charge, USGS mhaney@usgs.gov (907) 786-7497 David Fee, Coordinating Scientist, UAF dfee1@alaska.edu (907) 322-4085
(16) Next Notice:

AVO/USGS Volcanic Activity Notice

Volcano: Great Sitkin (VNUM #311120)

Current Volcano Alert Level: WATCH
Previous Volcano Alert Level: ADVISORY

Current Aviation Color Code: ORANGE
Previous Aviation Color Code: YELLOW

Issued: Friday, July 23, 2021, 2:25 PM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2021/A553
Location: N 52 deg 4 min W 176 deg 6 min
Elevation: 5709 ft (1740 m)
Area: Aleutians

Volcanic Activity Summary: A satellite radar image from last night July 22, 9:32 PM local (July 23 05:32 UTC) shows a small ~50 m (~150 ft) diameter area of uplift in the center of the crater at Great Sitkin suggestive of rising magma near the surface. This lava dome-like feature appears to have been emplaced sometime between July 14 and 22. As a result AVO is raising the the Aviation Color Code to ORANGE and the Volcano Alert Level to WATCH. Seismicity has been at relatively low levels this week compared to last week and we suspect that the lava dome-like feature was emplaced last week. Moderately elevated surface temperatures consistent with this feature were observed in satellite data on July 22. Cloudy conditions have obscured views of the volcano by satellite most of the past week. AVO will continue to closely monitor this new uplift feature.

The prognosis for eruptive activity is uncertain. Continued growth of the lava dome feature, additional explosive events, or a return to non-eruptive behaviors are all possible. AVO will report on significant changes and observations in monitoring data should they occur.

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.

Recent Observations:
[Volcanic cloud height] None
[Other volcanic cloud information] n/a
[Lava flow/dome] New ~50 m (~150 ft) diameter lava dome-like feature present in the summit crater.

Hazard Analysis:
[Lava flow/dome] Continued growth of the lava dome-like feature is possible.

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.

Contacts: Matt Haney, Acting Scientist-in-Charge, USGS mhaney@usgs.gov (907) 786-7497

David Fee, Coordinating Scientist, UAF dfee1@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.