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VOLCANO ACTIVITY NOTIFICATION

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(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued: (20201120/1900Z)
(3) Volcano: Semisopochnoi (VNUM #311060)
(4) Current Color Code: UNASSIGNED
(5) Previous Color Code: YELLOW
(6) Source: Alaska Volcano Observatory
(7) Notice Number: 2020/A1265
(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: No eruptive activity has been detected at Semisopochnoi since mid-June. Seismicity has persisted above background levels since that time, but had decreased to very low levels before a satellite link for transmitting seismic data failed on November 11, 2020. Since that time, no changes have been observed in satellite data, and no explosions have been detected from the Adak Island infrasound array. AVO is lowering the Aviation Color Code to UNASSIGNED and Alert Level to UNASSIGNED for Semisopochnoi due to the lack of evidence for ongoing unrest. Low-level seismic unrest may be continuing undetected. The satellite link is not likely to be reestablished without a site visit.

Despite the lack of eruptive activity since mid-June, Semisopochnoi has been in a state of unrest since September 2018, producing sporadic low-level explosions and elevated seismicity. Future small explosions may occur without warning and typically generate small clouds of volcanic ash that are a hazard in the immediate vicinity of the erupting vent at North Cerberus. More significant ash emissions may be possible, but have not been observed during the 2018–2020 eruptive period.
(12) Volcanic cloud height: n/a
(13) Other volcanic cloud information: n/a
(14) Remarks: The seismic monitoring network for Semisopochnoi has been offline since November 11, but if atmospheric conditions permit an infrasound array on Adak Island may detect explosion signals from Semisopochnoi with a 13 minute delay. Semisopochnoi is also monitored remotely with satellite observations and lightning sensors.
(15) Contacts: Matt Haney, Acting Scientist-in-Charge, USGS
mhaney@usgs.gov (907) 786-7497

David Fee, Coordinating Scientist, UAFGI
dfee1@alaska.edu (907) 322-4085
(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

AVO/USGS Volcanic Activity Notice

Volcano: Semisopochnoi (VNUM #311060)

Current Volcano Alert Level: UNASSIGNED
Previous Volcano Alert Level: ADVISORY

Current Aviation Color Code: UNASSIGNED
Previous Aviation Color Code: YELLOW

Issued: Friday, November 20, 2020, 10:00 AM AKST
Source: Alaska Volcano Observatory
Notice Number: 2020/A1265
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary: No eruptive activity has been detected at Semisopochnoi since mid-June. Seismicity has persisted above background levels since that time, but had decreased to very low levels before a satellite link for transmitting seismic data failed on November 11, 2020. Since that time, no changes have been observed in satellite data, and no explosions have been detected from the Adak Island infrasound array. AVO is lowering the Aviation Color Code to UNASSIGNED and Alert Level to UNASSIGNED for Semisopochnoi due to the lack of evidence for ongoing unrest. Low-level seismic unrest may be continuing undetected. The satellite link is not likely to be reestablished without a site visit.

Despite the lack of eruptive activity since mid-June, Semisopochnoi has been in a state of unrest since September 2018, producing sporadic low-level explosions and elevated seismicity. Future small explosions may occur without warning and typically generate small clouds of volcanic ash that are a hazard in the immediate vicinity of the erupting vent at North Cerberus. More significant ash emissions may be possible, but have not been observed during the 2018–2020 eruptive period.


Recent Observations:
[Volcanic cloud height] n/a
[Other volcanic cloud information] n/a

Remarks: The seismic monitoring network for Semisopochnoi has been offline since November 11, but if atmospheric conditions permit an infrasound array on Adak Island may detect explosion signals from Semisopochnoi with a 13 minute delay. Semisopochnoi is also monitored remotely with satellite observations and lightning sensors.

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

David Fee, Coordinating Scientist, UAFGI
dfee1@alaska.edu (907) 322-4085

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.
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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