(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20190918/2110Z)
(3) Volcano:	Semisopochnoi (VNUM #311060)
(4) Current Color Code:	YELLOW
(5) Previous Color Code:	ORANGE
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:
(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:	Seismicity at Semisopochnoi has decreased over the past few weeks with no observations of seismic tremor since September 15. Low-level sulfur dioxide emissions continue to be observed when conditions permit. Other than the ongoing refilling of the crater lake, no changes in surface features have been observed since the small, shallow cone that formed around August 24. Due to the decrease in activity, AVO is lowering the color code/activity level to YELLOW/ADVISORY.
(12) Volcanic cloud height:	No cloud observed
(13) Other volcanic cloud information:	No cloud observed
(14) Remarks:	Semisopochnoi is monitored with an on-island seismic network, and remotely by satellite and lightning sensors. An infrasound array on Adak Island could detect explosive emissions from Semisopochnoi with a 13 minute delay if atmospheric conditions permit.
(15) Contacts:	Michelle Coombs, Scientist-in-Charge, USGS mcoombs@usgs.gov (907) 786-7497 David Fee, Coordinating Scientist, UAFGI 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: Wednesday, September 18, 2019, 1:10 PM AKDT
Source: Alaska Volcano Observatory
Notice Number:
Location: N 51 deg 55 min E 179 deg 35 min
Elevation: 2625 ft (800 m)
Area: Aleutians

Volcanic Activity Summary: Seismicity at Semisopochnoi has decreased over the past few weeks with no observations of seismic tremor since September 15. Low-level sulfur dioxide emissions continue to be observed when conditions permit. Other than the ongoing refilling of the crater lake, no changes in surface features have been observed since the small, shallow cone that formed around August 24. Due to the decrease in activity, AVO is lowering the color code/activity level to YELLOW/ADVISORY.

Recent Observations:
[Volcanic cloud height] No cloud observed
[Other volcanic cloud information] No cloud observed

Remarks: Semisopochnoi is monitored with an on-island seismic network, and remotely by satellite and lightning sensors. An infrasound array on Adak Island could detect explosive emissions from Semisopochnoi with a 13 minute delay if atmospheric conditions permit.

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

David Fee, Coordinating Scientist, UAFGI
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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