ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, December 30, 2022, 12:49 PM AKST (Friday, December 30, 2022, 21:49 UTC)
Eruptive activity resumed on Tuesday, December 27, at the active north crater of Mount Cerberus. Minor ash deposits on the flanks of Mount Cerberus were observed on fresh snow extending up to ~1 km (~1000 yards) from the vent when web camera images were clear on December 27 and 28. No ash plumes have been observed in web camera or satellite imagery, but a persistent steam plume rising up to 5,000 ft above sea level from the active crater may now be carrying minor volcanic ash within it. The observation of ash deposits this week was accompanied by a minor increase in seismic tremor observed on most days. The resumption of eruptive activity led the Alaska Volcano Observatory to raise the Aviation Color Code to ORANGE and Volcano Alert Level to WATCH on Wednesday, December 28.
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 Cerberus, 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.
Lava continued to erupt within the summit crater of Great Sitkin Volcano this week. Elevated surface temperatures and a steam plume could be seen when satellite and web camera views were clear. High resolution satellite imagery showed continued slow growth of the lava flow field over the course of the week. The active lava is currently advancing primarily to the south over earlier 2021–2022 lava, and east into the remaining summit crater icefield. Seismicity associated with the current lava eruption is low with no significant activity noted in geophysical data during the week.
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.
Seismicity remains above background levels. A handful of small earthquakes were detected, only one of which was large enough to locate. Low-level seismic tremor was also observed December 28 through 30. No explosions have been detected since December 7, 2022. Elevated surface temperatures and minor steaming from the active vent have been observed when satellite and web camera views have been clear throughout the week. A high-resolution satellite image on December 27 showed a small spot of strongly elevated temperatures within the recently active vent on the upper eastern flank of the volcano but no sign of eruptive activity.
Periods of lava spatter and fountaining from the vent on the volcano’s upper east flank have been occurring since mid-November 2021.
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 continues. AVO analysts located 48 small earthquakes (less than magnitude 2.5) during the past week, with depths nearly all less than 6 miles (9 km) below sea level. Clouds obscured satellite views most days this week, although no other signs of volcanic unrest were observed in partly cloudy views on Dec 27.
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.
Low-level volcanic unrest continued at Cleveland volcano this week. A persistent steam plume was observed in partly cloudy satellite and web camera views, but no elevated surface temperatures were seen. Low-level seismicity was observed with small local earthquakes detected on December 27 and 28.
Episodes of lava eruption and explosions can occur at Cleveland without advance warning. Explosions are normally short duration and only present a hazard to aviation in the immediate vicinity of the volcano. Larger explosions that present a more widespread hazard to aviation are possible but are less likely and occur less frequently.
When operational, Cleveland volcano is monitored by only three seismic stations, which restricts AVO's ability to precisely locate earthquakes and detect precursory unrest that may lead to an explosive eruption. Rapid detection of an ash-producing eruption may be possible using a combination of seismic, infrasound, lightning, and satellite data.
Cleveland volcano forms the western portion of Chuginadak Island, a remote and uninhabited island in the east central Aleutians. The volcano is located about 45 miles (75 km) west of the community of Nikolski, and 940 miles (1500 km) southwest of Anchorage. The most recent significant period of eruption began in February 2001 and produced 3 explosive events that generated ash clouds as high as 39,000 ft (11.8 km) above sea level. The 2001 eruption also produced a lava flow and hot avalanche that reached the sea. Since then, Cleveland has been intermittently active producing small lava flows, often followed by explosions that generate small ash clouds generally below 20,000 ft (6 km) above sea level. These explosions also launch debris onto the slopes of the cone producing hot pyroclastic avalanches and lahars that sometimes reach the coastline.
OTHER ALASKA VOLCANOES
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