ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, June 9, 2023, 11:53 AM AKDT (Friday, June 9, 2023, 19:53 UTC)
Lava continued to slowly erupt at Great Sitkin over the past week, adding to a thick lava flow confined to the summit crater. A Satellite image obtained on June 6 confirmed the ongoing eruption of lava and elevated surface temperatures were observed in satellite imagery from June 8. Only a few small local earthquakes were detected at Great Sitkin during the week. No other noteworthy activity was observed in cloud-obscured views of the volcano in satellite and web camera data.
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 Aniakchak volcano was lower than the previous week but remained above the background. Satellite data from June 3 indicated continued uplift within Aniakchak caldera. Satellite and web camera data obtained over the past week showed no signs of unrest.
Increases in seismic activity and ground movement 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 ground movement 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. Another seismometer on the volcano stopped transmitting data on April 21 due to presumed snow cover and low power levels. A new seismometer was installed in Port Heiden on April 12, so two local seismic stations are now in operation. We are unable to locate smaller earthquakes due to the outages. A new webcam was also deployed in Port Heiden.
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.
The level of activity at Semisopochnoi remained low over the past week. The last evidence of ash emission from the volcano was on May 5 and consisted of a light dusting of ash on the northwest flank of the north crater of Mount Young. Satellite and web camera views of the volcano obtained throughout the week were obscured by clouds.
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 eruptive 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 volcano 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 miles (65 km) northeast of Amchitka Island and 130 miles (200 km) west of Adak.
Earthquake activity beneath Takawangha volcano continued over the past week. The number of earthquakes located each day beneath Tanaga Island varied slightly, but the rate was lower compared to previous weeks.
No other signs of volcanic unrest were observed in cloudy satellite data over the last week, and no new satellite radar data were available to verify if recent ground movement has continued.
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 Tanaga Volcano or Takawangha volcano.
An increase in shallow seismicity and possibly other signs of unrest, such as gas emissions, elevated surface temperatures, and additional changes in ground movement, will likely precede any eruption if one were to occur.
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.
Earthquake activity beneath Tanaga volcano continued over the past week. The number of earthquakes located each day beneath Tanaga Island varied slightly, but the rate was lower compared to previous weeks.
No other signs of volcanic unrest were observed in cloudy satellite data over the last week, and no new satellite radar data were available to verify if recent ground movement has continued.
Because the 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.
An increase in shallow seismicity and possibly other signs of unrest, such as gas emissions, elevated surface temperatures, and additional changes in ground movement, will likely precede any eruption if one were to occur.
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.
Seismicity beneath Trident Volcano remained elevated over the past week with numerous earthquakes detected each day. The largest earthquake of the past week was a magnitude 3 on June 4. No eruptive activity or other signs of unrest were reported in satellite or web camera views.
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.
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 ground movement, 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 (1,864 m) 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 9 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.
A little after 5:00 pm AKDT on Monday, June 5, AVO detected seismic and pressure sensor signals associated with a sizeable non-volcanic avalanche on the eastern flank of Iliamna Volcano. The Aviation Color Code and Volcano Alert Level were briefly raised to Yellow/Advisory when precursory seismicity was detected and returned back to Green/Normal once the avalanche occurred and seismic activity ended. Further analysis of seismic data and comparison to similar events indicated that an escalation of volcanic activity was unlikely. Snow and rock avalanches occur regularly at this volcano, and there is no indication of any volcanic activity associated with the avalanche.
Iliamna volcano is located on the western side of lower Cook Inlet in the Lake Clark National Park. Iliamna is a snow-covered stratovolcano which rises 10,020 feet above sea level. Although steam plumes occur on its eastern flanks, there has been no historic volcanic activity at Iliamna. Iliamna is located 225 km (140 miles) southwest of Anchorage and 113 km (70 miles) northwest of Homer.
Chris Waythomas Acting Scientist-in-Charge, USGS cwaythomas@usgs.gov (907) 786-7497
David Fee, Coordinating Scientist, UAFGI dfee1@alaska.edu (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.