AVO/USGS Volcanic Activity Notice

Volcano: Semisopochnoi (VNUM #311060)

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

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


Issued: Monday, November 7, 2022, 1:08 PM AKST
Source: Alaska Volcano Observatory
Notice Number: 2022/A1242
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary:

Small explosions have been detected in geophysical data over the past week from the north crater of Mount Cerberus at Semisopochnoi. In addition, volcanic tremor has resumed during the same time period. Ash emissions have not been observed. However, the type of unrest we detected was associated with ash emissions during previous periods of unrest and, if occurring, such ash emissions are likely below 10,000 ft above sea level. These events are similar to eruptive activity observed over the last year at Semisopochnoi, but not since September 14. The Aviation Color Code and Volcano Alert Level are being raised to ORANGE/WATCH.

Small eruptions producing minor ash deposits within the vicinity of the active north crater of Mount Cerberus and ash clouds usually under 10,000 ft (3 km) above sea level have characterized the recent activity and more ash-producing events could occur again with little warning. 

Semisopochnoi is monitored by a local seismic and infrasound network, local web cameras, regional lightning and infrasound sensors, and satellite data. 

Recent Observations:
[Volcanic cloud height] less than 10,000 ft. above sea level
[Other volcanic cloud information] none
[Ballistics] none
[Lava flow/dome] none
[Lava flow] none

Hazard Analysis:
[General hazards] Likely airborne ash at altitudes <10,000 feet above sea level and local ash fall in the vicinity of the north crater of Mount Cerberus
[Ash cloud] less than 10,000 ft. above sea level
[Ashfall] trace ashfall likely on the flanks of the north crater of Mount Cerberus

Remarks:

Remote Semisopochnoi volcano occupies the largest, young volcanic island in the western Aleutians. The uninhabited island is part of the Alaska Maritime National Wildlife Refuge. It is located 65 km (40 mi) northeast of Amchitka Island and 200 km (130 mi) west of Adak, Alaska. Semisopochnoi volcano is dominated by an 8-km (5-mile) diameter caldera that contains a small lake and several post-caldera cones and craters. The age of the caldera is not known with certainty but is likely early Holocene. The north cone of Mount Cerberus, in the southwest part of the caldera, is the site of the current eruption, which began in 2018. The last known eruption prior to 2018 was in 1987 from Sugarloaf Peak on the south coast of the island.

Contacts:

Kristi Wallace, Acting Scientist-in-Charge, USGS, kwallace@usgs.gov, (907) 786-7497

David Fee, Coordinating Scientist, UAFGI, dfee1@alaska.edu, (907) 378-5460

Next Notice:

A new VAN will be issued if conditions change significantly or alert levels are modified. While a VAN is in effect, regularly scheduled updates are posted at http://www.avo.alaska.edu.

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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(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20221107/2208Z)
(3) Volcano:	Semisopochnoi (VNUM #311060)
(4) Current Color Code:	ORANGE
(5) Previous Color Code:	YELLOW
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2022/A1242
(8) Volcano Location:	N 51 deg 55 min E 179 deg 35 min
(9) Area:	Aleutians
(10) Summit Elevation:	2625 ft (800 m)
(11) Volcanic Activity Summary:	Small explosions have been detected in geophysical data over the past week from the north crater of Mount Cerberus at Semisopochnoi. In addition, volcanic tremor has resumed during the same time period. Ash emissions have not been observed. However, the type of unrest we detected was associated with ash emissions during previous periods of unrest and, if occurring, such ash emissions are likely below 10,000 ft above sea level. These events are similar to eruptive activity observed over the last year at Semisopochnoi, but not since September 14. The Aviation Color Code and Volcano Alert Level are being raised to ORANGE/WATCH. Small eruptions producing minor ash deposits within the vicinity of the active north crater of Mount Cerberus and ash clouds usually under 10,000 ft (3 km) above sea level have characterized the recent activity and more ash-producing events could occur again with little warning.  Semisopochnoi is monitored by a local seismic and infrasound network, local web cameras, regional lightning and infrasound sensors, and satellite data.
(12) Volcanic cloud height:	less than 10,000 ft. above sea level
(13) Other volcanic cloud information:	none
(14) Remarks:	Remote Semisopochnoi volcano occupies the largest, young volcanic island in the western Aleutians. The uninhabited island is part of the Alaska Maritime National Wildlife Refuge. It is located 65 km (40 mi) northeast of Amchitka Island and 200 km (130 mi) west of Adak, Alaska. Semisopochnoi volcano is dominated by an 8-km (5-mile) diameter caldera that contains a small lake and several post-caldera cones and craters. The age of the caldera is not known with certainty but is likely early Holocene. The north cone of Mount Cerberus, in the southwest part of the caldera, is the site of the current eruption, which began in 2018. The last known eruption prior to 2018 was in 1987 from Sugarloaf Peak on the south coast of the island.
(15) Contacts:	Kristi Wallace, Acting Scientist-in-Charge, USGS, kwallace@usgs.gov, (907) 786-7497 David Fee, Coordinating Scientist, UAFGI, dfee1@alaska.edu, (907) 378-5460
(16) Next Notice:	A new VAN will be issued if conditions change significantly or alert levels are modified. While a VAN is in effect, regularly scheduled updates are posted at http://www.avo.alaska.edu.

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