Alaska Volcano Observatory - AVO Volcano Activity Notification

AVO VOLCANO ACTIVITY NOTIFICATION

AVO/USGS Volcanic Activity Notice

Volcano: Shishaldin (VNUM #311360)

Current Volcano Alert Level: WARNING
Previous Volcano Alert Level: WATCH

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

Issued: Saturday, July 22, 2023, 11:43 PM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2023/A1122
Location: N 54 deg 45 min W 163 deg 58 min
Elevation: 9373 ft (2857 m)
Area: Aleutians

Volcanic Activity Summary:

An ash cloud from Shishaldin Volcano reaching 30,000 ft. (9 km) was observed in satellite data and pilot reports at 11:30 pm AKDT (07:30 UTC on July 23). This follows a several-hour increase in observed eruptive activity. In response, the aviation Color Code is being raised to RED and the Volcano Alert Level is being raised to WARNING. The National Weather Service has issued a SIGMET for this ash cloud, and a Special Weather Statement has been issued for possible trace ash on False Pass.

Based on previous eruption cycles, significant ash emissions are likely to continue for an hour or more. Pyroclastic and mudflows are likely on the immediate flanks of the volcano.

Shishaldin Volcano is monitored by local seismic and infrasound sensors, web cameras, and a telemetered geodetic network. The local monitoring network has been partially impaired over the last few weeks due to telecommunications issues but seismic stations and web cameras south of the volcano were brought back online on July 19. In addition to the local monitoring network, AVO uses nearby geophysical networks, regional infrasound and lighting data, and satellite images to detect eruptions.

Recent Observations:
[Volcanic cloud height] 30,000 ft. (9 km) above sea level
[Other volcanic cloud information] Plume is moving northeast

Hazard Analysis:
[Ash cloud] 30,000 ft. (9 km) above sea level moving northeast, see SIGMET
[Ashfall] Trace ashfall possible downwind of the volcano, see Special Weather Statement
[Pyroclastic flow] Likely on all flanks
[Mud flow] Likely on all flanks

Remarks:

Shishaldin Volcano, located near the center of Unimak Island in the eastern Aleutian Islands, is a spectacular symmetric cone with a base diameter of approximately 10 miles (16 km). A 660 ft. (200 m) wide funnel-shaped summit crater typically emits a steam plume and occasional small amounts of ash. Shishaldin is one of the most active volcanoes in the Aleutian volcanic arc, with at least 54 episodes of unrest including over 26 confirmed eruptions since 1824. Most eruptions are relatively small, although the April-May 1999 event generated an ash column that reached 45,000 ft. (14 km) above sea level.

Contacts:

Chris Waythomas, Acting Scientist-in-Charge, USGS, cwaythomas@usgs.gov, (907) 786-7497

David Fee, Coordinating Scientist, UAFGI, dfee1@alaska.edu, (907) 378-5460

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.

(1) VOLCANO OBSERVATORY NOTICE FOR AVIATION (VONA)
(2) Issued:	(20230723/0743Z)
(3) Volcano:	Shishaldin (VNUM #311360)
(4) Current Color Code:	RED
(5) Previous Color Code:	ORANGE
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2023/A1122
(8) Volcano Location:	N 54 deg 45 min W 163 deg 58 min
(9) Area:	Aleutians
(10) Summit Elevation:	9373 ft (2857 m)
(11) Volcanic Activity Summary:	An ash cloud from Shishaldin Volcano reaching 30,000 ft. (9 km) was observed in satellite data and pilot reports at 11:30 pm AKDT (07:30 UTC on July 23). This follows a several-hour increase in observed eruptive activity. In response, the aviation Color Code is being raised to RED and the Volcano Alert Level is being raised to WARNING. The National Weather Service has issued a SIGMET for this ash cloud, and a Special Weather Statement has been issued for possible trace ash on False Pass. Based on previous eruption cycles, significant ash emissions are likely to continue for an hour or more. Pyroclastic and mudflows are likely on the immediate flanks of the volcano. Shishaldin Volcano is monitored by local seismic and infrasound sensors, web cameras, and a telemetered geodetic network. The local monitoring network has been partially impaired over the last few weeks due to telecommunications issues but seismic stations and web cameras south of the volcano were brought back online on July 19. In addition to the local monitoring network, AVO uses nearby geophysical networks, regional infrasound and lighting data, and satellite images to detect eruptions.
(12) Volcanic cloud height:	30,000 ft. (9 km) above sea level
(13) Other volcanic cloud information:	Plume is moving northeast
(14) Remarks:	Shishaldin Volcano, located near the center of Unimak Island in the eastern Aleutian Islands, is a spectacular symmetric cone with a base diameter of approximately 10 miles (16 km). A 660 ft. (200 m) wide funnel-shaped summit crater typically emits a steam plume and occasional small amounts of ash. Shishaldin is one of the most active volcanoes in the Aleutian volcanic arc, with at least 54 episodes of unrest including over 26 confirmed eruptions since 1824. Most eruptions are relatively small, although the April-May 1999 event generated an ash column that reached 45,000 ft. (14 km) above sea level.
(15) Contacts:	Chris Waythomas, Acting Scientist-in-Charge, USGS, cwaythomas@usgs.gov, (907) 786-7497 David Fee, Coordinating Scientist, UAFGI, dfee1@alaska.edu, (907) 378-5460
(16) Next Notice: