Full Notification

Volcano: Shishaldin (VNUM #311360)

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

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


Issued: Monday, September 25, 2023, 12:34 PM AKDT
Source: Alaska Volcano Observatory
Notice Number: 2023/A1431
Location: N 54 deg 45 min W 163 deg 58 min
Elevation: 9373 ft (2857 m)
Area: Aleutians

Volcanic Activity Summary:

Activity at Shishaldin Volcano has declined significantly. Seismicity decreased rapidly around 06:00 AKDT (14:00 UTC) and no significant ash emissions from the volcano are being observed in satellite data at this time. In response, AVO is lowering the Aviation Color Code to ORANGE and the Alert Level to WATCH. 

The ash cloud from this morning’s eruption detached from the volcano around 07:00 AKDT (15:00 UTC) and is drifting east-southeast at an altitude of 45,000 ft above sea level.  Ash emissions continued at a lower altitude of about 20,000–25,000 ft above sea level until about 08:20 AKDT (16:20 UTC). Small explosions are currently being detected in infrasound data and likely represent low-level eruptive activity near the vent area.

Trace to minor amounts of ashfall were reported by the communities of False Pass, King Cove, Cold Bay and Sand Point.  Ashfall occurred during rainfall in all four communities. No ashfall is expected from the current small explosions that are being detected in infrasound. Refer to the National Weather Service SIGMET for the drifting ash cloud (https://www.weather.gov/aawu/sigmets) and the Ashfall Advisory and Special Weather Statement for trace to minor amounts of ashfall on communities on the lower Alaska Peninsula and surrounding waters (https://www.weather.gov/afc/).

Based on previous eruption cycles, pyroclastic flows 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.  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] 9,500 ft above sea level
[Other volcanic cloud information] Drifting cloud from the main explosion moving east-southeast of the volcano

Hazard Analysis:
[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 [email protected] (907) 786-7497

David Fee, Coordinating Scientist, UAFGI [email protected] (907) 378-5460