ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, March 24, 2023, 11:35 AM AKDT (Friday, March 24, 2023, 19:35 UTC)
Low-level eruptive activity resumed at Semisopochnoi volcano over the past week. On March 18, a vapor plume extending 90 mi (150 km) from Mount Young was observed with no detected seismicity and no significant ash emissions. On March 19, a series of small explosions were detected in seismic and infrasound data and accompanied by minor ash emissions prompting AVO to raise the Aviation Color Code and Volcano Alert Level to ORANGE/WATCH. One small explosion was detected in seismic and infrasound data on March 21. No ash emissions have been observed since March 19 although views of the volcano by satellite and web camera have been mostly obscured by cloud cover. One web camera view on March 22 showed low-level steaming from Mount Young.
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.
Semisopochnoi volcano occupies the largest, young volcanic island in the western Aleutians. The volcano is dominated by a 5-mile (8 km) diameter caldera that contains a small lake and several post-caldera cones and craters. The age of the caldera is not known with certainty but is likely early Holocene. Prior to 2018, the previous known historical eruption of Semisopochnoi occurred in 1987, probably from Sugarloaf Peak on the south coast of the island, but details are lacking. Another prominent, young post-caldera landform is Mount Young, a three-peaked cone cluster in the southwest part of the caldera. Mount Young has been intermittently active since 2018. The island is uninhabited and part of the Alaska Maritime National Wildlife Refuge. It is located 40 mi (65 km) northeast of Amchitka Island and 130 mi (200 km) west of Adak.
Lava continued to erupt within the summit crater of Great Sitkin at a low rate over the past week. Satellite imagery from March 23 showed the lava flow advancing to the east within the summit crater. Seismicity was at very low levels throughout the week. No signs of unrest were seen in partly cloudy satellite and webcam views.
Great Sitkin is monitored by local seismic and infrasound sensors, satellite data, web cameras, and regional infrasound and lightning networks.
Great Sitkin Volcano is a basaltic andesite volcano that occupies most of the northern half of Great Sitkin Island, a member of the Andreanof Islands group in the central Aleutian Islands. It is located 26 miles (43 km) east of the community of Adak. The volcano is a composite structure consisting of an older dissected volcano and a younger parasitic cone with a ~1 mile (1.5 km)-diameter summit crater. A steep-sided lava dome, emplaced during the 1974 eruption, occupies the center of the crater. That eruption produced at least one ash cloud that likely exceeded an altitude of 25,000 ft (7.6 km) above sea level. A poorly documented eruption occurred in 1945, also producing a lava dome that was partially destroyed in the 1974 eruption. Within the past 280 years a large explosive eruption produced pyroclastic flows that partially filled the Glacier Creek valley on the southwest flank.
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 300 earthquakes have been located beneath Tanaga Island, with depths less than 5.5 miles (9.5 km) below sea level. Most of the recent earthquakes locate between Tanaga Volcano and nearby Takawangha volcano, which is about 5 miles (8 km) east of Tanaga Volcano on Tanaga Island. Earthquake activity is ongoing, with multiple magnitude M2 events recorded since peak activity began to decline on March 11. Radar satellite data through March 20 shows recent surface deformation near Sajaka volcano (a subfeature of Tanaga Volcano) suggestive of magma intrusion and consistent with earthquake activity.
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. We expect a renewed increase in shallow seismicity and possibly other signs of unrest, such as gas emissions, elevated surface temperatures, and additional changes in 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.
Tanaga Island lies in the Andreanof Islands approximately 62 miles (100 km) west of the community of Adak and 1260 miles (2025 km) SW of Anchorage. The northern half of the island is home to the Tanaga volcanic complex, comprising three main volcanic edifices. Tanaga Volcano is the tallest of these (5,925 ft or 1,806 m) and lies in the center of the complex. The last reported eruption of Tanaga occurred in 1914 and earlier eruptions were reported in 1763-1770, 1791, and 1829. Reports of these eruptions are vague, but deposits on the flanks of the volcano show that typical eruptions produce blocky lava flows and occasional ash clouds. Eruptions have occurred both from the summit vent and a 5,197 ft (1,584 m)-high satellite vent on the volcano's northeast flank. Immediately west of Tanaga volcano lies Sajaka, a 4,443 ft (1,354 m)-high compound edifice with an older cone to the east that collapsed into the sea within the last few thousand years, and a new cone that has grown in the breach. The new cone is 4,305 ft (1,312 m) high and consists of steeply dipping, interbedded cinders and thin, spatter-fed lava flows. To the east of Tanaga lies Takawangha, which is separated from the other active volcanic vents by a ridge of older rock. No historical eruptions are known from Sajaka or Takawangha; however, field work shows that recent eruptions have occurred, and it is possible that historic eruptions attributed only to Tanaga may instead have come from these other vents.
Earthquake activity beneath Takawangha volcano, which began in the fall of 2022, peaked on March 9–11 and has declined slowly since. More than 300 earthquakes have been located over the past week beneath Tanaga Island, with depths less than 5.5 miles (9 km) below sea level. Most of the recent earthquakes locate between Takawangha volcano and nearby Tanaga Volcano, which is about 5 miles (8 km) west of Takawangha volcano on Tanaga Island. Earthquake activity is ongoing, with multiple magnitude M2 events recorded since peak activity began to decline on March 11.
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. 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.
Takawangha is a remote, 4,754 ft (1,449 m)-high stratovolcano located on the northeast portion of Tanaga Island, roughly 59 miles (95 km) west of Adak in the Andreanof Islands. Takawangha's summit is mostly ice-covered, except for four young craters that have erupted ash and lava flows in the last few thousand years. Parts of Takawangha's edifice are hydrothermally altered and may be unstable, possibly leading to localized debris avalanches from its flanks. Takawangha lies across a saddle from historically active Tanaga volcano to the west. No historical eruptions are known from Takawangha; however, field work shows that recent eruptions have occurred, and it is possible that historic eruptions attributed to Tanaga may instead have come from Takawangha.
Seismicity beneath Aniakchak volcano remained above background levels. The largest earthquakes during the past week 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 4 miles (6 km). Radar satellite data through March 23 shows rapid uplift of the ground surface within the central portion of the caldera, consistent with magma intrusion at about 4 km depth. No eruptive activity observed in satellite views.
Increases in seismic activity and surface deformation 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 additional changes in 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.
Aniakchak volcano, located in the central portion of the Alaska Peninsula, consists of a stratovolcano edifice with a 6 miles (10 km) diameter summit caldera. The caldera-forming eruption occurred around 3,500 years ago. Postcaldera eruptions have produced lava domes, tuff cones, and larger spatter and scoria cone structures including Half-Cone and Vent Mountain all within the caldera. The most recent eruption occurred in 1931 and created a new vent and lava flows on the western caldera floor while spreading ash over much of southwestern Alaska. Aniakchak volcano is 15 miles (25 km) southeast of the nearest community, Port Heiden, and 416 miles (670 km) southwest of Anchorage, Alaska.
Seismicity beneath Trident Volcano remained above background levels, although most of the earthquakes over the past week have been small (less than ~M1. No eruptive activity or other signs of unrest were seen in satellite or 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 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 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.
Trident is one of the Katmai group of volcanoes located within Katmai National Park and Preserve on the Alaska Peninsula. Trident consists of a complex of four cones and numerous lava domes, all andesite and dacite in composition, that reach as high as 6,115 ft (98 km) above sea level. An eruption beginning in 1953 constructed the newest cone, Southwest Trident, and four lava flows on the flank of the older complex. This eruption continued through 1974 and produced ash (an initial plume rose to 30,000 ft or 48 km asl), bombs, and lava at various times. Fumaroles remain active on the summit of Southwest Trident and on the southeast flank of the oldest, central cone. Trident is located 92 miles (148 km) southeast of King Salmon and 273 miles (440 km) southwest of Anchorage.
OTHER ALASKA VOLCANOES
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Michelle Coombs, Scientist-in-Charge, USGS firstname.lastname@example.org (907) 786-7497
Pavel Izbekov, Acting Coordinating Scientist, UAFGI email@example.com (907) 378-5460
The Alaska Volcano Observatory is a cooperative program of the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys.