Strong explosive eruption at Shishaldin volcano, ash reaches 12.8 km (42 000 feet) a.s.l., Alaska

On September 15, 2023, around 01:10 UTC, an explosive eruption at Shishaldin Volcano sent an ash-rich cloud soaring to an altitude of 12.8 km (42 000 feet), accompanied by volcanic lightning. The eruption followed a several-hour increase in seismicity. The Aviation Color Code and Volcano Alert Level were raised to RED/WARNING.

The upper-level cloud detached from the vent around 02:30 UTC and was drifting towards the east. Beginning around 03:30 UTC, lightning resumed indicating continued ash emssions. At the time, the meteorological cloud deck over the volcano was over the volcano at about 6.8 km (22 500 feet) above sea level and ash emissions were not visible in satellite data. Explosions continued to be detected in infrasound data, at a lower level than during the most energetic phase of this event.

Trace ash fall was reported in the community of False Pass between 02:00 to 04:30 UTC. The National Weather Service has issued a SIGMET for the drifting ash cloud, and a Special Weather Statement has been issued for trace ash on False Pass.

Seismicity started decreasing rapidly around 02:30 UTC, but it remained elevated until 05:00 UTC.  During this period of waning seismicity, volcanic lightning continued to be detected, indicating continued ash production.  The last detection of volcanic lighting was at 04:48 UTC and seismicity has returned to pre-eruptive levels, indicating that significant ash emissions have ended. Thus, the Aviation Color Code and Volcano Alert Level were lowered to ORANGE/WATCH.

References:

¹ AVO/USGS volcanic activity notices issued on September 16, 2023

Featured image: AVO ISLZ webcam