ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, January 6, 2023, 12:40 PM AKST (Friday, January 6, 2023, 21:40 UTC)
Eruptive activity continued this week at the active north crater of Mount Cerberus, now known as Mount Young. Minor ash deposits on the flanks of Mount Young were observed on fresh snow extending ~2 km (~1.2 miles) south-southwest of the active crater when web camera images were clear on January 1 and January 3. 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 periods of elevated seismicity and infrasound signals observed on the local geophysical network, which were likely due to weak explosive activity. Infrasound signals from the direction of Mount Young were observed at a regional array in Adak once during the last week.
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.
Earlier this week, the Don Young Recognition Act was signed into law. This Act renamed Mount Cerberus to Mount Young in honor of long-time Alaska Congressman Don Young. For more information, see: AVO">https://avo.alaska.edu/news.php?id=1590">AVO News (alaska.edu).
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, now known as 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.
Lava continued to erupt within the summit crater of Great Sitkin Volcano this week. Weakly elevated surface temperatures were observed once in satellite data during the week, although most views of the summit were obscured by clouds. A high-resolution satellite image from Monday showed continued slow growth of the lava flow field. The active lava is currently advancing primarily to the south, over earlier 2021–2022 lava, and east into the remaining summit crater icefield. A small swarm of earthquakes occurred 6 km (4 mi) east of the summit and at depths less than 6 km (4 mi) on Monday and Tuesday, including earthquakes with magnitudes of 2.3 and 1.5. Besides this brief swarm, overall seismicity was 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.
Seismicity remains above background levels and is characterized by weak, low-frequency earthquakes. No eruptive activity was observed over the past week and no explosions have been detected since December 7, 2022. Weakly elevated surface temperatures and minor steaming from the active vent were observed in satellite data and web camera views several times during the week and may be related to the cooling of lava around the vent.
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 over the past week, although seismic data from the local network experienced an outage over the past day which was resolved this morning. AVO analysts located 17 small earthquakes (less than magnitude 1.5) during the last 7 days. All of them occurred at with depths less than 6 miles (9 km) below sea level. Nothing significant was observed in satellite data this week, including some mostly clear and partly cloudy views.
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.
Due to a reduction of volcanic unrest at Cleveland Volcano over the past few months, on Thursday Alaska Volcano Observatory downgraded the Aviation Color Code and Volcano Alert Level from YELLOW/ADVISORY to UNASSIGNED/UNASSIGNED.
Elevated surface temperatures and sulfur dioxide emissions had prompted AVO to raise the Aviation Color Code and Volcano Alert Level from UNASSIGNED/UNASSIGNED to YELLOW/ADVISORY on May 11, 2022. That activity continued throughout the summer, but all signs of unrest ceased or declined in recent months. Elevated surface temperatures in the summit crater are occasionally being observed but at reduced frequency and strength. Sulfur dioxide emissions have not been detected in satellite data since July 29, 2022. Minor steaming from the summit crater was observed over the past week but is considered to represent background activity for Cleveland. The last eruptive activity at Cleveland volcano was a short-lived explosion on the evening (local time) of June 1, 2020.
Despite the current pause, the eruptive period at Cleveland, dating back to 2001, remains ongoing and future explosions are likely. These occur without warning and typically generate small clouds of volcanic ash that are a hazard in the immediate vicinity of the volcano, though more significant ash emissions are possible.
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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