USGS Volcano Notice - DOI-USGS-AVO-2023-10-03T11:47:46-08:00

A significant explosive eruption of Shishaldin started at 5:47 AKDT (13:47 UTC) today and lasted until about 9:00 AKDT (17:00 UTC). It was preceded by about 9 hours of escalating seismic unrest, lava fountaining, pyroclastic flow activity on the volcano's flanks, and minor ash emissions. The explosive eruption produced an initial ash cloud as high as 40,000 ft asl, with subsequent ash emissions to between 20,000 and 25,000 ft asl. The eruption was observed in satelite images, webcams, lightning, and seismic and infrasound data. 

AVO raised the Aviation Color Code and Volcano Alert Level to RED/WARNING for the explosive eruption; they have since been lowered to ORANGE/WATCH. The National Weather Service issued a SIGMET for the ash cloud, and a Special Weather Statement was issued for possible ashfall on Unimak Island and the lower Alaska Peninsula, including False Pass, Cold Bay, and Sand Point. AVO received reports of trace ashfall in Cold Bay. 

Since the event, seismic and infrasound activity has quieted substantially, and clear webcam views show steaming at the summit vent. Redistributed airborne volcanic ash is present to several thousand feet asl near the volcano, and additional collapse of accumulated lava near the summit crater can occur without warning and generates hot mass flows on the upper flanks and small volcanic ash clouds that dissipate quickly.  

This the is 12th explosive event at Shishaldin since July 12, 2023. These events have been preceded by increases in seismicity in the hours to days before they occur. It is unknown how long this period of ongoing activity will last. However, previous eruptions of Shishaldin Volcano have lasted weeks to months with repeated cycles of eruptive activity like those seen since July.

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. Weakly elevated surface temperatures were observed overnigt by satellite. Clear webcam views showed light steaming at the summit. 

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 was low with a few local earthquakes detected over the past day. No volcanic activity was noted in clear satellite or web camera images, although resuspended ash from the 1912 eruption of Katmai is visible in the region.

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.   

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