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
Current Aviation Color Code: RED

Issued: Friday, August 25, 2023, 8:20 PM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2023/A1319
Location: N 54 deg 45 min W 163 deg 58 min
Elevation: 9373 ft (2857 m)
Area: Aleutians

Volcanic Activity Summary:

Explosive eruptive activity is continuing at Shishaldin Volcano. An ash cloud continues to be observed in satellite data at an altitude of 21,000 ft (6.4 km) above sea level moving towards the northeast. This is a decrease in altitude from earlier today. Seismic tremor decreased rapidly around 5:30 pm AKDT (0130 UTC) and is approaching levels observed prior to the onset of ash emissions.

Based on previous eruption cycles, it is likley that ash emissions are starting to decrease and may end over the next few hours. Pyroclastic and mudflows are likely on the immediate flanks of the volcano. Minor to trace amounts of ash fall are likely to the north of the volcano and in the water immediately offshore. No ash fall is expected in populated areas.

The National Weather Service is responsible for tracking the drifting ash cloud and SIGMETs have been issued throughout the day. See https://www.weather.gov/aawu/SIGMETs for current information for aviation.

Shishaldin Volcano is monitored by local seismic and infrasound sensors, web cameras, and a telemetered geodetic network. 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] 21,000 ft msl
[Other volcanic cloud information] Observed in satellite data moving northeast

Hazard Analysis:
[Ash cloud] Drifting at about 30,000 ft (9 km) above sea level.
[Ashfall] Possible on Unimak Island and in nearshore waters north of the volcano
[Pyroclastic flow] likely on the immediate flanks of the volcano
[Mud flow] likely on the immediate flanks of the volcano

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:

Matt Haney, Scientist-in-Charge, USGS mhaney@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:	(20230826/0420Z)
(3) Volcano:	Shishaldin (VNUM #311360)
(4) Current Color Code:	RED
(5) Previous Color Code:	RED
(6) Source:	Alaska Volcano Observatory
(7) Notice Number:	2023/A1319
(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:	Explosive eruptive activity is continuing at Shishaldin Volcano. An ash cloud continues to be observed in satellite data at an altitude of 21,000 ft (6.4 km) above sea level moving towards the northeast. This is a decrease in altitude from earlier today. Seismic tremor decreased rapidly around 5:30 pm AKDT (0130 UTC) and is approaching levels observed prior to the onset of ash emissions. Based on previous eruption cycles, it is likley that ash emissions are starting to decrease and may end over the next few hours. Pyroclastic and mudflows are likely on the immediate flanks of the volcano. Minor to trace amounts of ash fall are likely to the north of the volcano and in the water immediately offshore. No ash fall is expected in populated areas. The National Weather Service is responsible for tracking the drifting ash cloud and SIGMETs have been issued throughout the day. See https://www.weather.gov/aawu/SIGMETs for current information for aviation. Shishaldin Volcano is monitored by local seismic and infrasound sensors, web cameras, and a telemetered geodetic network. 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:	21,000 ft msl
(13) Other volcanic cloud information:	Observed in satellite data 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:	Matt Haney, Scientist-in-Charge, USGS mhaney@usgs.gov (907) 786-7497 David Fee, Coordinating Scientist, UAFGI dfee1@alaska.edu (907) 378-5460
(16) Next Notice: