(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20210713/0014Z)
(3) Volcano:	Semisopochnoi (VNUM #311060)
(4) Current Color Code:	ORANGE
(5) Previous Color Code:	YELLOW
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2021/A490
(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:	Continuous volcanic tremor (constant shaking) began to be observed at ~2000 UTC (12 pm AKDT) and continues through the present time. Ash emissions were visible in satellite data beginning around 2100 UTC (1 pm AKDT) to an altitude of less than 5,000 feet asl (based on wind direction). Satellite observations from yesterday afternoon showed a robust steam plume and sulfur dioxide gas emissions. These observations indicate an increase in unrest and the Aviation Color Code is being increased to ORANGE, and the Volcano Alert Level is being increased to WATCH. Additional ash emissions are probable, but not certain. 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:	Less than 5,000 ft asl.
(13) Other volcanic cloud information:	Observed in GOES-17 satellite
(14) Remarks:	Semisopochnoi is monitored by a local seismic and infrasound network, 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: WATCH
Previous Volcano Alert Level: ADVISORY

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

Issued: Monday, July 12, 2021, 4:14 PM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2021/A490
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary: Continuous volcanic tremor (constant shaking) began to be observed at ~2000 UTC (12 pm AKDT) and continues through the present time. Ash emissions were visible in satellite data beginning around 2100 UTC (1 pm AKDT) to an altitude of less than 5,000 feet asl (based on wind direction). Satellite observations from yesterday afternoon showed a robust steam plume and sulfur dioxide gas emissions. These observations indicate an increase in unrest and the Aviation Color Code is being increased to ORANGE, and the Volcano Alert Level is being increased to WATCH. Additional ash emissions are probable, but not certain.

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] Less than 5,000 ft asl.
[Other volcanic cloud information] Observed in GOES-17 satellite

Remarks: Semisopochnoi is monitored by a local seismic and infrasound network, 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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