(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20210519/0518Z)
(3) Volcano:	Semisopochnoi (VNUM #311060)
(4) Current Color Code:	ORANGE
(5) Previous Color Code:	YELLOW
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2021/A274
(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:	Several small explosions were detected in regional infrasound data earlier today and a small ash cloud was observed in a satellite image from 15:21 (23:21 UTC) on May 17. As a result AVO is raising the Color Code to Orange and the Alert Level to Watch. Small eruptions producing minor ash deposits within the vicinity of the active north crater of Mount Cerberus and ash clouds under 10,000 ft above sea level are typical of recent activity at Semisopochnoi. Weather clouds up to 15,000 ft above sea level currently obscure the volcano.
(12) Volcanic cloud height:	unknown
(13) Other volcanic cloud information:	Small ash clouds are likely being generated during explosions and are likely under 10,000 ft asl.
(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:	Michelle Coombs, Scientist-in-Charge, USGS mcoombs@usgs.gov (907) 786-7497 David Fee, Coordinating Scientist, UAF 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: WATCH
Previous Volcano Alert Level: ADVISORY

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

Issued: Tuesday, May 18, 2021, 9:18 PM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2021/A274
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary: Several small explosions were detected in regional infrasound data earlier today and a small ash cloud was observed in a satellite image from 15:21 (23:21 UTC) on May 17. As a result AVO is raising the Color Code to Orange and the Alert Level to Watch.

Small eruptions producing minor ash deposits within the vicinity of the active north crater of Mount Cerberus and ash clouds under 10,000 ft above sea level are typical of recent activity at Semisopochnoi. Weather clouds up to 15,000 ft above sea level currently obscure the volcano.

Recent Observations:
[Volcanic cloud height] unknown
[Other volcanic cloud information] Small ash clouds are likely being generated during explosions and are likely under 10,000 ft asl.

Hazard Analysis:
[Ash cloud] Explosions detected in infrasound data and confirmed in satellite imagery.

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: Michelle Coombs, Scientist-in-Charge, USGS
mcoombs@usgs.gov (907) 786-7497

David Fee, Coordinating Scientist, UAF
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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