(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20180701/1837Z)
(3) Volcano:	Great Sitkin (VNUM #311120)
(4) Current Color Code:	YELLOW
(5) Previous Color Code:	GREEN
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:
(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:	Earthquake activity at Great Sitkin Volcano has increased above background levels over the past day. Numerous small, shallow earthquakes are occurring beneath the summit at rates as high as 10-20 per hour. It is uncertain if this unrest will lead to any eruptive activity but this remains a possibility given the general degree of unrest at Great Sitkin over the past several months. Thus AVO is raising the Aviation Color Code and Alert Level to YELLOW /ADVISORY. AVO detected a brief steam and ash explosion at Great Sitkin on June 10, and earthquake activity then declined to background levels over a period of about 2 weeks. Over the past several days, nothing significant has been observed in satellite data and no other signs of unrest have been detected or reported to AVO. Great Sitkin Volcano is monitored by a five-station seismic network on Great Sitkin Island and with additional seismic stations on the nearby islands of Igitkin, Adak, Kagalaska, and Kanaga. A six-element infrasound array to detect explosions (atmospheric pressure waves) was installed on Adak Island in June, 2017, although it is currently (June 2018) only partly operational. AVO also uses satellite imagery to monitor Great Sitkin Volcano.
(12) Volcanic cloud height:	not applicable
(13) Other volcanic cloud information:	Unknown
(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. 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. A seismic swarm occurred from July 2016 through the end of 2017.
(15) Contacts:	Michelle Coombs, Scientist-in-Charge, USGS mcoombs@usgs.gov (907) 786-7497 Jeff Freymueller, Coordinating Scientist, UAFGI jfreymueller@alaska.edu (907) 322-4085
(16) Next Notice:

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AVO/USGS Volcanic Activity Notice

Volcano: Great Sitkin (VNUM #311120)

Current Volcano Alert Level: ADVISORY
Previous Volcano Alert Level: NORMAL

Current Aviation Color Code: YELLOW
Previous Aviation Color Code: GREEN

Issued: Sunday, July 1, 2018, 10:37 AM AKDT
Source: Alaska Volcano Observatory
Notice Number:
Location: N 52 deg 4 min W 176 deg 6 min
Elevation: 5709 ft (1740 m)
Area: Aleutians

Volcanic Activity Summary: Earthquake activity at Great Sitkin Volcano has increased above background levels over the past day. Numerous small, shallow earthquakes are occurring beneath the summit at rates as high as 10-20 per hour. It is uncertain if this unrest will lead to any eruptive activity but this remains a possibility given the general degree of unrest at Great Sitkin over the past several months. Thus AVO is raising the Aviation Color Code and Alert Level to YELLOW /ADVISORY.

AVO detected a brief steam and ash explosion at Great Sitkin on June 10, and earthquake activity then declined to background levels over a period of about 2 weeks. Over the past several days, nothing significant has been observed in satellite data and no other signs of unrest have been detected or reported to AVO.

Great Sitkin Volcano is monitored by a five-station seismic network on Great Sitkin Island and with additional seismic stations on the nearby islands of Igitkin, Adak, Kagalaska, and Kanaga. A six-element infrasound array to detect explosions (atmospheric pressure waves) was installed on Adak Island in June, 2017, although it is currently (June 2018) only partly operational. AVO also uses satellite imagery to monitor Great Sitkin Volcano.

Recent Observations:
[Volcanic cloud height] not applicable
[Other volcanic cloud information] Unknown

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. 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. A seismic swarm occurred from July 2016 through the end of 2017.

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

Jeff Freymueller, Coordinating Scientist, UAFGI
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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