(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20210416/0315Z)
(3) Volcano:	Semisopochnoi (VNUM #311060)
(4) Current Color Code:	RED
(5) Previous Color Code:	ORANGE
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2021/A161
(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:	Satellite data suggests ash emissions from Semisopochnoi volcano have been ongoing since early this morning and are continuing with no decrease in intensity. The ash cloud extends more than 217 mi (350 km) southeast of the volcano with heights up to 20,000 feet (6 km) above sea level. Based on the length and height of the ash plume and sustained nature of ash emissions, AVO is raising the Color Code to RED and the Alert Level to WARNING. AVO will continue to monitor the situation.
(12) Volcanic cloud height:	20,000 feet above sea level or less.
(13) Other volcanic cloud information:	Continuous ash cloud extends more than 350 km from volcano.
(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: WARNING
Previous Volcano Alert Level: WATCH

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

Issued: Thursday, April 15, 2021, 7:15 PM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2021/A161
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary: Satellite data suggests ash emissions from Semisopochnoi volcano have been ongoing since early this morning and are continuing with no decrease in intensity. The ash cloud extends more than 217 mi (350 km) southeast of the volcano with heights up to 20,000 feet (6 km) above sea level. Based on the length and height of the ash plume and sustained nature of ash emissions, AVO is raising the Color Code to RED and the Alert Level to WARNING. AVO will continue to monitor the situation.


Recent Observations:
[Volcanic cloud height] 20,000 feet above sea level or less.
[Other volcanic cloud information] Continuous ash cloud extends more than 350 km from volcano.

Hazard Analysis:
[Ash cloud] Continuous ash cloud extends more than 350 km from volcano.
[Ashfall] Ashfall is expected on the flanks of the volcano and onto marine waters under the ash cloud southeast of the volcano.

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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