(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20210507/1916Z)
(3) Volcano:	Semisopochnoi (VNUM #311060)
(4) Current Color Code:	YELLOW
(5) Previous Color Code:	ORANGE
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2021/A231
(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 ash emissions or explosions from Semisopochnoi have been detected in satellite or infrasound data since April 26. Partly cloudy satellite views this week have shown no recent ash deposits or elevated surface temperatures, and only steam was observed within the north crater of Mount Cerberus. Sulfur dioxide emissions were observed this week on May 1 and 5, signifying continued volcanic unrest. AVO is therefore lowering the Aviation Color Code and Volcano Alert Level to YELLOW/ADVISORY. AVO will continue to monitor activity at Semisopochnoi with satellite and regional infrasound data. When occurring, 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 activity at Semisopochnoi.
(12) Volcanic cloud height:	N/A
(13) Other volcanic cloud information:	N/A
(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:	Matt Haney, Acting Scientist-in-Charge, USGS mhaney@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: ADVISORY
Previous Volcano Alert Level: WATCH

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

Issued: Friday, May 7, 2021, 11:16 AM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2021/A231
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary: No ash emissions or explosions from Semisopochnoi have been detected in satellite or infrasound data since April 26. Partly cloudy satellite views this week have shown no recent ash deposits or elevated surface temperatures, and only steam was observed within the north crater of Mount Cerberus. Sulfur dioxide emissions were observed this week on May 1 and 5, signifying continued volcanic unrest. AVO is therefore lowering the Aviation Color Code and Volcano Alert Level to YELLOW/ADVISORY. AVO will continue to monitor activity at Semisopochnoi with satellite and regional infrasound data.

When occurring, 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 activity at Semisopochnoi.




Recent Observations:
[Volcanic cloud height] N/A
[Other volcanic cloud information] N/A

Hazard Analysis:
[Ash cloud] N/A

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: Matt Haney, Acting Scientist-in-Charge, USGS
mhaney@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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