(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20210417/2049Z)
(3) Volcano:	Semisopochnoi (VNUM #311060)
(4) Current Color Code:	ORANGE
(5) Previous Color Code:	RED
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2021/A165
(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:	Eruptive activity at Semisopochnoi has declined over the last 24 hours. Satellite views of the volcano have been mostly obscured, but a recent clearing suggests activity has declined and no significant ash plume was observed. As a result, AVO is lowering the Color Code to ORANGE and the Alert Level to WATCH. It is likely that low-level eruptive activity continues and may not be detected by regional infrasound sensors or above the low clouds in satellite data. AVO will continue to monitor the situation. Small eruptions producing minor ash deposits within the vicinity of the volcano and ash clouds under 10,000 ft above sea level are typical of activity at this volcano.
(12) Volcanic cloud height:	unknown
(13) Other volcanic cloud information:	unknown
(14) Remarks:	Semisopochnoi is monitored by satellite data, regional infrasound, and lightning detection instruments. An infrasound array on Adak Island may detect explosive emissions from Semisopochnoi with a slight delay (approximately 13 minutes) if atmospheric conditions permit.
(15) Contacts:	Aaron Wech, Acting Scientist-in-Charge, USGS awech@usgs.gov (907) 786-7497 Jessica Larsen, Acting Coordinating Scientist, UAF jflarsen@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: WATCH
Previous Volcano Alert Level: WARNING

Current Aviation Color Code: ORANGE
Previous Aviation Color Code: RED

Issued: Saturday, April 17, 2021, 12:49 PM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2021/A165
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary: Eruptive activity at Semisopochnoi has declined over the last 24 hours. Satellite views of the volcano have been mostly obscured, but a recent clearing suggests activity has declined and no significant ash plume was observed. As a result, AVO is lowering the Color Code to ORANGE and the Alert Level to WATCH. It is likely that low-level eruptive activity continues and may not be detected by regional infrasound sensors or above the low clouds in satellite data. AVO will continue to monitor the situation.

Small eruptions producing minor ash deposits within the vicinity of the volcano and ash clouds under 10,000 ft above sea level are typical of activity at this volcano.




Recent Observations:
[Volcanic cloud height] unknown
[Other volcanic cloud information] unknown

Hazard Analysis:
[Ash cloud] unknown
[Ashfall] unknown

Remarks: Semisopochnoi is monitored by satellite data, regional infrasound, and lightning detection instruments. An infrasound array on Adak Island may detect explosive emissions from Semisopochnoi with a slight delay (approximately 13 minutes) if atmospheric conditions permit.

Contacts: Aaron Wech, Acting Scientist-in-Charge, USGS
awech@usgs.gov (907) 786-7497

Jessica Larsen, Acting Coordinating Scientist, UAF
jflarsen@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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