USGS Volcano Notice - DOI-USGS-AVO-2023-08-18T10:11:55-08:00

The seventh explosive event of Shishaldin Volcano's most recent eruption culminated on Tuesday, August 15, 2023, at about 2:40 AKDT (10:40 UTC). The eruption produced an ash cloud that reached as high as 30,000-36,000 feet above sea level. The ash cloud extended to the northeast about 60 miles (100 km) but produced no reported ash fall on the communities of False Pass and Cold Bay. An associated sulfur dioxide cloud traveled over parts of Alaska and western Canada, remnants of which are still apparent in satellite data. The eruption produced significant seismicity and explosions detected by the local AVO seismic and infrasound networks, as well as volcanic lightning detected by the World Wide Lightning Location Network (WWLLN).

After the eruption, elevated seismicity and ash emissions continued for several hours and gradually declined. Currently, the volcano is quiet, seismic levels are low but still above the background, and no significant emissions are occurring. Elevated surface temperatures were observed in satellite data throughout the week. The elevated temperatures are caused by hot eruptive material (pyroclastic debris and lava) that has accumulated around the summit.

Shishaldin has had seven periods of explosive eruptive activity resulting in significant ash emissions since July 12. It is unknown how long this eruptive period will last. Previous eruptions of Shishaldin Volcano have lasted weeks to months with repeated cycles of activity similar to those seen since July 12. Before the current activity, the 2019–2020 eruption of Shishaldin was the first to result in lava flows outside the crater area since 1976. Minor eruptions in 2004 and 2014 erupted lava confined to the summit crater. Previous eruptions of Shishaldin have produced ash clouds like those seen during the current eruption, most recently in January 2020. Routine evaluations of satellite, seismic, and infrasound data provide warning of unrest associated with the production of ash clouds. In addition, ashfall forecast models are kept up to date on the public activity page (https://avo.alaska.edu/activity/Shishaldin.php).  

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 lightning data, and satellite observations to detect eruptions.  

Slow eruption of lava is likely continuing at Great Sitkin Volcano. This week, the volcano was challenging to observe as clouds and fog obscured satellite and web camera views. Earthquake activity remained slightly elevated this week.

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.  

The volcano is monitored by local seismic, geodetic, and infrasound sensors, web cameras, regional infrasound and lightning networks, and satellite data. 

Earthquake activity continued at Cleveland volcano this week, although at a low level, with occasional local earthquakes detected, especially during a brief increase in local seismicity on August 17. Clouds obscured satellite images of the volcano over much of the week, preventing direct observation. Steam and gas emissions from the summit crater were observed in web camera images several times throughout the week. These are normal and do not indicate a significant change in unrest. 

Episodes of lava effusion and explosions can occur without warning. Explosions from Mount Cleveland are typically short-duration and typically present a hazard to aviation near the volcano. Significant explosions could produce a more widespread aviation hazard but are less likely and occur less frequently.  

Cleveland volcano is currently monitored by a local seismic network, infrasound sensors and web cameras. In addition to the local monitoring network, AVO uses nearby geophysical networks, regional infrasound and lighting data, and satellite observations to detect eruptions. Based on past events, explosive eruptions of Cleveland may occur with little or no warning. Rapid detection of an ash-producing eruption may be possible using a combination of seismic, infrasound, web camera, lightning, and satellite data.

Earthquake activity beneath Trident Volcano remained slightly elevated over the past week, with multiple local low-frequency earthquakes, regular volcanic earthquakes, and deep tremor noted most days. Clear views of the volcano in satellite and web camera data showed nothing indicative of escalating unrest.    

The current period of seismic unrest began on August 24, 2022. Earthquake depths at the beginning of the swarm were mainly deep, around 16 miles (25 km) below sea level, and became progressively shallower to around 3 miles (5 km) over the following four days. Since late August 2022, most earthquakes have occurred within the shallow crust, with depths less than 4 miles (6 km) below sea level; however, an increasing number of earthquakes have been occurring deeper (greater than 9 miles or 15 km depth). Starting in May 2023 an increase in low-frequency earthquakes and tremor has been observed—in addition to the regular earthquakes—near Trident Volcano. Such low-frequency events are often associated with the movement of magma or volcano-related fluids within the ground. Ground uplift at Trident Volcano has also been detected in satellite radar data. Snow cover prohibits winter observations, which limits our ability to provide precise timing, but data from June 3, 2023, indicates that about 2 in (5 cm) of ground uplift has occurred since October 6, 2022. Uplift is most significant on the volcano’s south flank.  

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.