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AVO/USGS Volcanic Activity Notice

Volcano: Semisopochnoi (VNUM #311060)

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

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


Issued: Thursday, September 29, 2022, 2:57 PM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2022/A1082
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary:

Although the active north cone of Mount Cerberus continues to produce a vapor plume and elevated seismic tremor, no ash emissions or explosive activity have been detected at Semisopochnoi volcano since September 14. The level of seismic activity is still elevated but has decreased. Thus, we are lowering the Aviation Color Code to YELLOW and Volcano Alert Level to ADVISORY. 

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. 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] none
[Other volcanic cloud information] none
[Ballistics] none
[Lava flow/dome] none
[Lava flow] none

Hazard Analysis:
[General hazards] Explosive activity and ash emissions at Semisopochnoi could increase again at any time.

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:

Michelle Coombs, Scientist-in-Charge, USGS, mcoombs@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">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.

VOLCANO ALERT LEVELS
NORMAL
Volcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.
ADVISORY
Volcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.
WATCH
Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway but poses limited hazards.
WARNING
Hazardous eruption is imminent, underway, or suspected.
AVIATION COLOR CODES
GREEN
Volcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.
YELLOW
Volcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.
ORANGE
Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway with no or minor volcanic-ash emissions [ash-plume height specified, if possible].
RED
Eruption is imminent with significant emission of volcanic ash into the atmosphere likely OR eruption is underway or suspected with significant emission of volcanic ash into the atmosphere [ash-plume height specified, if possible].
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Page modified: January 4, 2021 11:16
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