(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20210920/0558Z)
(3) Volcano:	Semisopochnoi (VNUM #311060)
(4) Current Color Code:	RED
(5) Previous Color Code:	ORANGE
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2021/A811
(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:	Ash emissions from the ongoing eruption at Semisopochnoi have increased in frequency and intensity. Satellite images show an ash cloud at an estimated altitude of 15,000 ft. above sea level extending approximately 60 miles (100 km) to the southeast through 05:00 UTC. Explosions have been observed throughout the day and increased sulfur dioxide gas emissions have been observed in satellite data this afternoon. These observations represent an increase in eruptive activity and Aviation Color Code and Volcano Alert level are being increased to RED/WARNING. Increasing high clouds over Semisopochnoi will likely obscure satellite views of ash emissions within the hour. Seismic and infrasound monitoring will continue to provide notice of ongoing explosive activity, however it cannot determine the height or extent of ash emissions. The Alaska Volcano Observatory will continue to closely monitor all available data. Please visit the NWS Alaska Aviation Weather Unit for current information about the volcanic ash cloud forecast. https://www.weather.gov/aawu/sigmets
(12) Volcanic cloud height:	15,000 ft. asl
(13) Other volcanic cloud information:	Ash and sulfur dioxide observed in satellite extending 60 miles to the SE
(14) Remarks:	Semisopochnoi is monitored by a local seismic and infrasound network, local web cameras, regional lightning and infrasound sensors, and satellite data.
(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: WARNING
Previous Volcano Alert Level: WATCH

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

Issued: Sunday, September 19, 2021, 9:58 PM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2021/A811
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary: Ash emissions from the ongoing eruption at Semisopochnoi have increased in frequency and intensity. Satellite images show an ash cloud at an estimated altitude of 15,000 ft. above sea level extending approximately 60 miles (100 km) to the southeast through 05:00 UTC. Explosions have been observed throughout the day and increased sulfur dioxide gas emissions have been observed in satellite data this afternoon. These observations represent an increase in eruptive activity and Aviation Color Code and Volcano Alert level are being increased to RED/WARNING.

Increasing high clouds over Semisopochnoi will likely obscure satellite views of ash emissions within the hour. Seismic and infrasound monitoring will continue to provide notice of ongoing explosive activity, however it cannot determine the height or extent of ash emissions. The Alaska Volcano Observatory will continue to closely monitor all available data.

Please visit the NWS Alaska Aviation Weather Unit for current information about the volcanic ash cloud forecast. https://www.weather.gov/aawu/sigmets

Recent Observations:
[Volcanic cloud height] 15,000 ft. asl
[Other volcanic cloud information] Ash and sulfur dioxide observed in satellite extending 60 miles to the SE
[Lava flow/dome] none
[Lava flow] none

Hazard Analysis:
[Ash cloud] A 15,000 ft. high ash is observed extending 100 km (60 miles) southeast of the volcano.
[Ashfall] Ashfall is expected on Semisopochnoi island and in the marine waters under the ash cloud southeast of the volcano.
[Volcanic gas] SO2 emissions detected on occasion

Remarks: Semisopochnoi is monitored by a local seismic and infrasound network, local web cameras, regional lightning and infrasound sensors, and satellite data.

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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