(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20210608/1743Z)
(3) Volcano:	Gareloi (VNUM #311070)
(4) Current Color Code:	YELLOW
(5) Previous Color Code:	GREEN
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2021/A338
(8) Volcano Location:	N 51 deg 47 min W 178 deg 47 min
(9) Area:	Aleutians
(10) Summit Elevation:	5161 ft (1573 m)
(11) Volcanic Activity Summary:	A slight increase in seismic activity was observed at Mount Gareloi (Gareloi volcano) on May 18, and beginning May 27 there has been a sustained increase in the rate and size of small volcanic earthquakes. Because the level of seismic activity is now above background, AVO is raising the aviation color code to YELLOW and the Volcano Alert Level to ADVISORY. There have been no other notable changes at the volcano in satellite data or web camera views. Sulfur dioxide gas was detected in satellite imagery from Gareloi over the past week and is consistent with measurements from the last several years. No activity was observed by an AVO field crew flying over the summit on May 23. Gareloi volcano persistently emits magmatic gases from a fumarole field on the south crater and commonly exhibits low-level seismic activity. These observations suggest the presence of shallow magma and potential interaction with a hydrothermal system. The current increase in seismicity likely reflects a change to the magmatic-hydrothermal system, but it is not clear that the likelihood of a volcanic eruption has increased. AVO will continue to monitor activity to determine if the recent changes are related to influx of new magma or other changes to the magma system. Gareloi is monitored by a local seismic and infrasound network, satellite data, and regional infrasound and lightning-detection networks.
(12) Volcanic cloud height:	None
(13) Other volcanic cloud information:	n/a
(14) Remarks:	Mount Gareloi, which makes up all of Gareloi Island, is a stratovolcano located in the Delarof Islands group of the Aleutian Islands, about 2,000 km (1,242 mi) west-southwest of Anchorage and about 150 km (93 mi) west of Adak, the westernmost community in Alaska. This small volcano is 10 × 8 km (6.2 × 5.0 mi) in diameter at its base with two summits, separated by a narrow saddle. The northern, slightly higher peak contains crater about 300 m (1,000 ft) across. The southern summit has a crater open to the south and a persistent degassing vent (fumarole) on its western rim. Gareloi has been one of the most active in the Aleutians since the 1740s, with 16 reports of eruptive activity at Gareloi since 1760. In 1929, its largest historical eruption produced sixteen small south- to southeast-trending craters that extend from the southern summit to the coast, as well as lava flows and pyroclastic deposits on the southeastern flank of the volcano. Eruptions of Gareloi commonly produce ash clouds and lava flows, and the primary hazard is airborne clouds of ash that could affect aircraft. Since seismic instruments were installed in 2003, they have detected small but consistent seismic signals from beneath Mount Gareloi’s edifice.
(15) Contacts:	Michelle Coombs, Scientist-in-Charge, USGS mcoombs@usgs.gov (907) 786-7497 David Fee, Coordinating Scientist, UAF dfee1@alaska.edu (907) 322-4085
(16) Next Notice:

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AVO/USGS Volcanic Activity Notice

Volcano: Gareloi (VNUM #311070)

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

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

Issued: Tuesday, June 8, 2021, 9:43 AM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2021/A338
Location: N 51 deg 47 min W 178 deg 47 min
Elevation: 5161 ft (1573 m)
Area: Aleutians

Volcanic Activity Summary: A slight increase in seismic activity was observed at Mount Gareloi (Gareloi volcano) on May 18, and beginning May 27 there has been a sustained increase in the rate and size of small volcanic earthquakes. Because the level of seismic activity is now above background, AVO is raising the aviation color code to YELLOW and the Volcano Alert Level to ADVISORY. There have been no other notable changes at the volcano in satellite data or web camera views. Sulfur dioxide gas was detected in satellite imagery from Gareloi over the past week and is consistent with measurements from the last several years. No activity was observed by an AVO field crew flying over the summit on May 23.

Gareloi volcano persistently emits magmatic gases from a fumarole field on the south crater and commonly exhibits low-level seismic activity. These observations suggest the presence of shallow magma and potential interaction with a hydrothermal system. The current increase in seismicity likely reflects a change to the magmatic-hydrothermal system, but it is not clear that the likelihood of a volcanic eruption has increased. AVO will continue to monitor activity to determine if the recent changes are related to influx of new magma or other changes to the magma system.

Gareloi is monitored by a local seismic and infrasound network, satellite data, and regional infrasound and lightning-detection networks.

Recent Observations:
[Volcanic cloud height] None
[Other volcanic cloud information] n/a

Remarks: Mount Gareloi, which makes up all of Gareloi Island, is a stratovolcano located in the Delarof Islands group of the Aleutian Islands, about 2,000 km (1,242 mi) west-southwest of Anchorage and about 150 km (93 mi) west of Adak, the westernmost community in Alaska. This small volcano is 10 × 8 km (6.2 × 5.0 mi) in diameter at its base with two summits, separated by a narrow saddle. The northern, slightly higher peak contains crater about 300 m (1,000 ft) across. The southern summit has a crater open to the south and a persistent degassing vent (fumarole) on its western rim. Gareloi has been one of the most active in the Aleutians since the 1740s, with 16 reports of eruptive activity at Gareloi since 1760. In 1929, its largest historical eruption produced sixteen small south- to southeast-trending craters that extend from the southern summit to the coast, as well as lava flows and pyroclastic deposits on the southeastern flank of the volcano. Eruptions of Gareloi commonly produce ash clouds and lava flows, and the primary hazard is airborne clouds of ash that could affect aircraft. Since seismic instruments were installed in 2003, they have detected small but consistent seismic signals from beneath Mount Gareloi’s edifice.

Contacts: Michelle Coombs, Scientist-in-Charge, USGS mcoombs@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.

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