USGS Volcano Notice - DOI-USGS-AVO-2023-03-17T12:20:46-08:00

Earthquake activity beneath Takawangha volcano, which began in the fall of 2022, peaked on March 9 – 11 and has declined slowly since. More than 800 earthquakes have been located over the past week beneath Tanaga Island, with depths less than 9 km (5.5 miles) below sea level. Most of the recent earthquakes locate between Takawangha volcano and nearby Tanaga Volcano, which is about 8 km (5 miles) west of Tanaga Volcano on Tanaga Island. Earthquake activity is ongoing, with multiple magnitude M2 events recorded since March 11. 

The decline in earthquake activity and lack of additional signs of unrest in other monitoring data indicates a decreased potential for eruption at the volcano. In response, AVO lowered the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY on March 16. 

Because seismic activity is also elevated at nearby Tanaga Volcano, if an eruption were to occur, it is unclear at this stage whether it would come from Takawangha volcano or Tanaga Volcano. No eruptive signals or other signs of unrest have been detected in other data streams or in satellite data. 

AVO continues to monitor the activity closely and seismic analysts are locating events as time permits. Earthquakes are occurring under Tanaga Island at a rate of up to several per minute. We expect a renewed increase in shallow seismicity and possibly other signs of unrest, such as gas emissions, elevated surface temperatures, and surface deformation to precede any future eruption.   

Takawangha is monitored with a local seismic network, a single local infrasound sensor, regional infrasound and lightning sensors, and satellite imagery. 

Earthquake activity beneath Tanaga Volcano, which began on March 4, peaked on March 9 – 11 and has declined slowly since. Over the past week, more than 800 earthquakes have been located beneath Tanaga Island, with depths less than 9 km (5.5 miles) below sea level. Most of the recent earthquakes locate between Tanaga Volcano and nearby Takawangha volcano, which is about 8 km (5 miles) east of Tanaga Volcano. Earthquake activity is ongoing, with multiple magnitude M2 events recorded since March 11. 

The decline in earthquake activity and lack of additional signs of unrest in other monitoring data indicates a decreased potential for eruption at the volcano. In response, AVO lowered the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY on March 16. 

Because seismic activity is also elevated at nearby Takawangha volcano, if an eruption were to occur, it is unclear at this stage whether it would come from Tanaga Volcano or Takawangha volcano. No eruptive signals or other signs of unrest have been detected in other data streams or in satellite data. 

AVO continues to monitor the activity closely and seismic analysts are locating events as time permits. Earthquakes are occurring under Tanaga Island at a rate of up to several per minute. We expect a renewed increase in shallow seismicity and possibly other signs of unrest, such as gas emissions, elevated surface temperatures, and surface deformation to precede any eruption.    

Tanaga is monitored with a local seismic network, a single local infrasound sensor, regional infrasound and lightning sensors, and satellite imagery. 

Lava likely continued to erupt within the summit crater of Great Sitkin at a low rate over the past week. Satellite imagery from late February showed the lava flow advancing to the east and south within the summit crater. Seismicity was at very low levels throughout the week. Slightly elevated surface temperatures were observed on one day in satellite imagery. No other signs of unrest were seen in satellite and webcam views. 

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

Earthquake activity slowed over the past week but continues above background levels. The largest earthquakes had magnitudes between M2 and M3. The earthquakes are occurring below the center of the caldera and to the east of the volcano at depths shallower than about 6 km (4 miles). Satellite ground surface deformation data through March 11 shows possible uplift within the central portion of the caldera. No eruptive activity observed in satellite views.  

There is no indication that an eruption of Aniakchak is imminent, or that one will occur. 

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

AVO monitors Aniakchak with a local network, which consists of six seismometers, a web camera, and a single infrasound sensor, as well as satellite remote sensing data and regional infrasound and lightning networks. Several of the seismic stations, however, stopped transmitting data on March 4 due to low power levels. Two stations remain in operation, but we are unable to locate smaller earthquakes due to the outage.

Seismicity beneath Trident Volcano slowed over the past week but remains above background levels. One M2 earthquake was recorded with a depth of 4 km (2.5 miles), although most of the earthquakes over the past week have been small, below M1. No eruptive activity or other signs of unrest were seen in satellite and webcam views. 

The current period of seismic unrest began on August 24, 2022. Earthquake depths at the beginning of the swarm were mostly deep, around 25 km (16 miles) below sea level and became progressively shallower to around 5 km (3 miles) over the following four days. Since late August 2022, most earthquakes have occurred within the shallow crust, with depths less than 6 km below sea level. Since January 1, 2023, earthquakes under Trident are occurring at an average rate of about ten per day or less.    

Increases in seismic activity have been detected previously at Trident Volcano and 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 surface deformation to precede any future eruption, if one were to occur.   

AVO monitors Trident Volcano with a local network of seismometers, a webcam, remote sensing data, and regional infrasound and lightning networks. 

Seismic activity was very low at Semisopochnoi volcano over the past week. No unusual activity was observed in infrasound data. No steaming or ash emissions from Mount Young were observed in webcam views or in satellite views, although cloudy conditions obscured clear views throughout the week.  

Although the active north cone of Mount Young continues to produce a robust steam plume when views are clear, no ash emissions or explosive activity have been detected at Semisopochnoi volcano since late January. The level of seismic activity has also decreased over the past month.  

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 have characterized the recent activity. Additional ash-producing events could occur again with little warning.   
  
Semisopochnoi volcano is monitored by local seismic and infrasound sensors, satellite data, web cameras, and regional infrasound and lightning networks.