(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20210219/1828Z)
(3) Volcano:	Semisopochnoi (VNUM #311060)
(4) Current Color Code:	YELLOW
(5) Previous Color Code:	ORANGE
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2021/A24
(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 significant volcanic activity has been detected at Semisopochnoi in satellite or regional infrasound data since February 6 and 7 when several small ash deposits were observed in satellite imagery. As a result, the Alaska Volcano Observatory is decreasing the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY. Small eruptions producing minor ash deposits within the vicinity of the volcano are typical of activity during unrest at Semisopochnoi since September 2018. Local seismic stations have been offline since November 11, 2020. New explosions could occur at anytime with no warning.
(12) Volcanic cloud height:	n/a
(13) Other volcanic cloud information:	n/a
(14) Remarks:	Semisopochnoi is monitored remotely by satellite and lightning sensors. An infrasound array on Adak Island could detect explosive emissions from Semisopochnoi with a 13 minute delay if atmospheric conditions permit.
(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

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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: Friday, February 19, 2021, 9:28 AM AKST
Source: Alaska Volcano Observatory
Notice Number: 2021/A24
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary: No significant volcanic activity has been detected at Semisopochnoi in satellite or regional infrasound data since February 6 and 7 when several small ash deposits were observed in satellite imagery. As a result, the Alaska Volcano Observatory is decreasing the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY.

Small eruptions producing minor ash deposits within the vicinity of the volcano are typical of activity during unrest at Semisopochnoi since September 2018. Local seismic stations have been offline since November 11, 2020. New explosions could occur at anytime with no warning.

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

Hazard Analysis:
[Ash cloud] none observed
[Ashfall] none observed since February 8

Remarks: Semisopochnoi is monitored remotely by satellite and lightning sensors. An infrasound array on Adak Island could detect explosive emissions from Semisopochnoi with a 13 minute delay if atmospheric conditions permit.

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.

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