ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, January 20, 2023, 11:29 AM AKST (Friday, January 20, 2023, 20:29 UTC)
Activity continued this week at the north crater of Mount Young at Semisopochnoi volcano. Seismicity was elevated throughout the week with small local earthquakes and weak tremor. Weak seismic and infrasound signals were recorded on Tuesday, indicating minor explosive activity, but no ash emissions were observed in clear webcam views. However, a persistent steam plume from Mount Young, rising up to 5,000 ft above sea level, was observed all week when webcam views were clear. No eruptive activity was observed in satellite views.
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.
Weakly elevated surface temperatures at the summit of Great Sitkin Volcano were observed in satellite data on Wednesday, suggesting that lava likely continues to erupt within the volcano's summit crater at a low rate. The active lava is advancing primarily to the south, burying earlier 2021–2022 lava, and east into the remaining summit crater icefield. The last high-resolution radar image showing lava growth was obtained on January 15. Small earthquakes have been occurring daily, but seismic activity overall remains 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 most recent significant eruption in 1974, 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.
Eruptive activity at Pavlof Volcano has stopped. Seismicity has decreased to background levels, and no explosions have been detected since December 11, 2022. Weakly elevated surface temperatures and minor steaming from the recently active vent continue to be observed intermittently in satellite and web camera imagery, consistent with cooling of previously erupted lava. Due to the decrease in activity to background levels, AVO lowered the Aviation Color Code to Green and the Volcano Alert Level to Normal on January 20.
Previous eruptions of Pavlof indicate that the level of unrest can change quickly and the progression to more significant eruptive activity can occur with little or no warning. Pavlof is monitored by local seismic and infrasound sensors, satellite data, web cameras, and regional infrasound and lightning networks.
Pavlof Volcano is a snow- and ice-covered stratovolcano located on the southwestern end of the Alaska Peninsula about 592 mi (953 km) southwest of Anchorage. The volcano is about 4.4 mi (7 km) in diameter and currently has an active vent on the east side close to the summit. With over 40 historic eruptions, it is one of the most consistently active volcanoes in the Aleutian arc. Eruptive activity is generally characterized by sporadic Strombolian lava fountaining continuing for a several-month period. Ash plumes as high as 49,000 ft (15 km) above sea level have been generated by past eruptions of Pavlof, and during the March 2016 eruption, ash plumes as high as 40,000 ft (12.2 km) above sea level were generated and the ash was tracked in satellite data as distant as eastern Canada. The nearest community, King Cove, is located 30 mi (48 km) to the southwest of Pavlof.
The ongoing earthquake swarm near Takawangha volcano continued but slowed over the past week. AVO analysts located 13 small earthquakes (less than magnitude 2) during the last 7 days. Nearly all of them occurred at depths less than 6 miles (9 km) below sea level. 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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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.