USGS Volcano Notice - DOI-USGS-AVO-2023-09-16T12:05:35-08:00

An explosive event began at 5:10 p.m. AKDT on September 15, 2023 (01:10 UTC on Sept 16) after a period of rapidly increasing seismicity. The explosive event produced an ash-rich cloud that the National Weather Service estimated reached an altitude of 42,000 ft  (12.8 km) above sea level and was accompanied by volcanic lightning. The Alaska Volcano Observatory raised the Aviation Color Code and Volcano Alert Level to RED/WARNING. This upper level cloud detached from the vent around 18:30 AKDT (0230 UTC), drifted towards the east, and can now be observed over the Gulf of Alaska. Trace ash fall was reported in the community of False Pass between 18:00 and 20:30 AKDT (0200 to 0430 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.

As the upper-level volcanic cloud detached from the vent, seismicity began to decrease dramatically. Beginning around 19:30 AKDT (0330 UTC), lightning resumed, indicating continued ash emissions, but at a lower level. The meteorological cloud deck over the volcano was then at about 22,500 ft (6.8 km) above sea level and ash emissions are 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. Seismicity and volcanic lightning continued to decrease until 21:00 AKDT on September 15, 2023 (05:00 UTC on Sept 16).

Seimicity is now at pre-eruptive levels and the Alaska Volcano Observatory lowered the Aviation Color Code and Volcano Alert Level to ORANGE/WATCH. 

There have been ten periods of elevated eruptive activity resulting in significant ash emissions and mass flows of volcanic debris on the volcano's flanks since the onset of the current eruption. These periods of elevated eruptive activity have been preceded by increases in seismicity in the hours before they occur. Collapse of accumulated lava near the summit crater can occur without warning and generate hot mass flows on the upper flanks and small volcanic ash clouds. The ongoing eruptive period started on July 12, and it is unknown how long this eruptive episode will last. However, previous eruptions of Shishaldin Volcano have lasted weeks to months with repeated cycles of activity like those seen over the last month.

Local seismic and infrasound sensors, web cameras, and a geodetic network monitor Shishaldin Volcano. In addition to the local monitoring network, AVO uses nearby geophysical networks, regional infrasound and lighting data, and satellite images to detect eruptions.

Slow eruption of lava in the summit crater likely continues. Seismicity remains low with a few earthquakes detected over the past day. Clouds obscured views of the volcano by satellite and web camera today.

The current lava flow at Great Sitkin Volcano began erupting in July 2021. No explosive events have occurred since a single event in May 2021.

Local seismic and infrasound sensors, web cameras, regional infrasound and lightning networks, and satellite data are used to monitor the volcano.

Seismic activity near Trident Volcano remained elevated over the past day with some earthquakes detected. No activity was observed in mostly cloudy satellite views and clear web camera views over the past day.

The current period of seismic unrest began on August 24, 2022. Increases in seismic activity have been detected previously at Trident Volcano and other similar volcanoes and did not result in eruptions. We expect additional shallow seismicity and other signs of unrest, such as gas emissions, elevated surface temperatures, and ground movement, to precede any future eruption if one were to occur.   AVO issued an Information Statement on July 25 providing a more detailed update on the volcanic unrest at Trident Volcano and the broader Katmai volcanic cluster (https://www.avo.alaska.edu/news.php?id=1595).

Trident Volcano is monitored by local seismic sensors, web cameras, regional infrasound and lightning networks, and satellite data.