ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, February 10, 2023, 11:37 AM AKST (Friday, February 10, 2023, 20:37 UTC)
Lava continued to erupt within the summit crater of Great Sitkin at a low rate over the past week. Weather conditions were cloudy at the volcano for most of the week obscuring views of the summit; however, steam emissions could be seen in clear views on Wednesday; Feb 8. Satellite-based radar from Feb. 6, showed that the lava flow at the summit continues advancing to the east into the remaining summit crater icefield. Small earthquakes have been occurring on some days, but seismic activity overall remains very low.
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 mi (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 1.5 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.
Activity continued this week at the north crater of Mount Young at Semisopochnoi volcano. Seismicity was elevated throughout the week with faint tremor observed early in the week and small local earthquakes in recent days. A steam plume from Mount Young was observed every day there were clear web camera views. No eruptive activity was observed in satellite images.
The volcano has been erupting sporadically since 2018 and activity has been characterized by eruption of ash to heights usually less than 10,000 ft (3 km) above sea level.
Semisopochnoi 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. 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.
The ongoing earthquake swarm near Takawangha volcano continued over the past week. AVO analysts located several small earthquakes (less than magnitude 2) during the last week. No volcanic activity was observed in satellite data.
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, 1,449 m (4,754 ft)-high stratovolcano located on the northeast portion of Tanaga Island, roughly 95 km (59 miles) 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.
OTHER ALASKA VOLCANOES
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