Newest Volcano Notice Including Semisopochnoi

Two episodes of elevated eruptive activity occurred at Shishaldin Volcano over the past week on August 2, and August 3-4. The Aviation Color Code and Volcano Alert Level was raised to RED/WARNING for this second event which is ongoing. Low-level eruption of lava confined to the summit crater as well as a short duration pause in the eruption occurred between these events.

On August 2, an ash plume was observed by pilots north of Shishaldin from the ground surface to 9000 ft (2.7 km) above sea level.  Overall seismic activity was low at this time, however, small explosive events consistent with low level strombolian activity were detected.

On August 3 at about 9:00 am AKDT (18:00 UTC), seismic activity began to increase in intensity.  Cloudy conditions obscured satellite and web camera observations.  There was a steady increase in seismicity throughout the day and the Alaska Volcano Observatory issued a Volcanic Activity Notice announcing the lead up to explosive activity at 5:36 pm AKDT (01:36 UTC August 4).  Seismic activity continued to increase through the night with strongly elevated surface temperatures observed through cloud cover suggesting lava was active at the surface.  Satellite images indicated low-level ash emissions by 5:20 am (13:20 UTC) as cloud cover cleared. Ash emission gradually increased and the Alaska Volcano Observatory issued a second Volcanic Activity Notice while remaining at Aviation Color Code and Volcano Alert Level ORANGE/WATCH at 9:04 am AKDT (17:04 UTC).  Over the next hour, the height of the plume increased to 30,000 ft above sea level with the plume extending over 100 km (62 miles) to the northeast. At 10:17 am AKDT (18:17 UTC), the Aviation Color Code and Volcano Alert Level/Alert Level was raised to RED/WARNING where it currently remains.  Trace to minor tephra fallout is expected to the northeast of Shishaldin. 

Prior to each of these events during the week, seismic activity had remained above background.  Elevated surface temperatures were observed most days throughout the week consistent with low-level eruption or recent cooling deposits. 

Shishaldin has now had six periods of elevated eruptive activity resulting in significant ash emissions during the current eruption which started on July 12.  It is unknown how long this eruption will last, but previous eruptions of Shishaldin Volcano have lasted weeks to months with repeated cycles of activity similar to those seen in the last three weeks. Before the current activity, the 2019–2020 eruption of Shishaldin was the first to result in lava flows outside of the crater area since 1976. Minor eruptions in 2004 and 2014 erupted lava confined to the summit crater. Eruptions from Shishaldin have produced ash clouds in the past like those seen during the current eruption, most recently in January 2020. Satellite, seismic, and infrasound data is routinely monitored for signs of explosions that might produce ash clouds. In addition, ashfall forecast models are kept up to date on the public activity page (https://avo.alaska.edu/activity/Shishaldin.php). 

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. 

Slow eruption of lava continued at Great Sitkin over the past week, adding to a thick lava flow in the summit crater. Satellite radar data through August 1 show the eastern lobe of the lava flow continuing to advance into glacial ice surrounding the crater and causing it to deform and crack. Earthquake activity remained slightly elevated this week. Weakly elevated surface temperatures were observed in satellite data on July 29.  

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 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 and tremor detected.  Clouds obscured satellite images of the volcano over much of the week, but normal steam and gas emissions from the summit crater were observed in web camera images on July 24, 27, and 28. 

Episodes of lava effusion and explosions can occur without advance warning. Explosions from Mount Cleveland are normally short-duration and only present a hazard to aviation in the immediate vicinity of the volcano. Larger explosions that present a more widespread hazard to aviation are possible but are less likely and occur less frequently. 

Cleveland volcano is currently monitored with a five-station real-time seismic network and three nearby web cameras. 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 elevated over the past week with multiple local low-frequency earthquakes and tremor noted each day. No eruptive activity or other signs of unrest were observed in clear satellite and web camera images.  

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. 

Earthquake activity beneath Aniakchak volcano was low over the past week. Several small earthquakes were detected daily. No unusual activity was observed in mostly clear webcam and satellite images of the volcano. Satellite radar data from July 21 showed no detectable surface changes. 

The current period of seismic unrest began in October 2022. Increases in seismic activity have been detected previously at other similar volcanoes, with no subsequent eruptions. We expect additional shallow seismicity and other signs of unrest, such as gas emissions, elevated surface temperatures, and additional surface deformation to precede any future eruption, if one were to occur. 

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

Due to recently low levels of volcanic unrest at Semisopochnoi volcano, the Alaska Volcano Observatory lowered the Aviation Color Code to GREEN and Volcano Alert Level to NORMAL on Thursday, August 3, 2023. The last evidence of possible eruptive activity was observed on May 5 and consisted of a light dusting of ash on the northwest flank of Mount Young. The last detection of possible explosions in monitoring data was April 25, 2023. Since this time, earthquake activity has been at low levels. Steam plumes continue from the north crater of Mount Young and were observed this week on July 31 and August 1. Although steaming was not observed from this vent prior the start of this eruption, it is common for steam plumes to persist at volcanoes for years following an eruption as the volcano slowly cools.   

The current eruption sequence at Semisopochnoi began in September 2018 and has consisted of small eruptions producing minor ash deposits within the vicinity of the active north crater of Mount Young and ash clouds usually under 10,000 ft (3 km) above sea level with occasional periods of continuous ash production. While current observations indicate that this eruption may be over, it is also possible activity could resume, and small ash-producing events could occur with little warning. The Alaska Volcano Observatory will continue to closely monitor Semisopochnoi and report on any changes in activity.  

Semisopochnoi is monitored by a local seismic and infrasound network, local web cameras, regional lightning and infrasound sensors, and satellite data.