ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, November 11, 2022, 12:00 PM AKST (Friday, November 11, 2022, 21:00 UTC)
Pavlof Volcano continues to erupt from the active vent just below the summit on its east flank. Explosions were detected on several days of the week in seismic and infrasound data. Nearly continuous volcanic tremor was recorded throughout the week on local seismic stations and elevated surface temperatures were observed in satellite data on November 5, 6, 8, and 10. Web cameras views were usually obscured by clouds during the week, but a few clear images showed nothing of note.
Periods of lava spatter and fountaining from the vent on the volcano’s upper east flank have been occurring since mid-November 2021. This activity has built a small cone and sent lava flows down the flank that melt the snow and ice and produce variable amounts of meltwater. The meltwater typically incorporates loose debris on the flank of the volcano and forms thin (less than 2 m thick) lahars. The lahar deposits extend down the east-southeast flank for several kilometers, not quite to the base of the volcano.
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.
Low-level eruptive activity at Semisopochnoi volcano resumed earlier this past week and continues. Small explosions were detected in geophysical data on October 31 and November 7 from the north crater of Mount Cerberus at Semisopochnoi, and volcanic tremor was also observed on November 5 and 6. Steaming was seen in web camera images on November 4. Ash emissions have not been seen in satellite imagery or web camera views. However, the type of activity AVO detected was associated with ash emissions during previous periods of unrest and, if occurring, such ash emissions are likely lower than 10,000 ft (3 km) above sea level. The explosive events were similar to eruptive activity observed over the last year at Semisopochnoi, albeit with a brief pause since September 14. For these reasons, AVO raised the Aviation Color Code and Volcano Alert Level to ORANGE/WATCH on November 7. Since then, seismicity has been at low levels and nothing significant has been observed in satellite imagery or web camera views.
The volcano has been erupting sporadically since 2018 and activity has been characterized by eruption of ash to levels 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.
Slow eruption of lava within the summit crater of Great Sitkin Volcano continued this week. Elevated surface temperatures were observed on November 5, 6, and 9. Slow growth of the lava flow field continues, with flow lobes extending more than 2000 ft (~600 m) to the east and 1400 ft (~430 m) to the south of the vent. Weak seismic activity consistent with the slow, continued lava eruption was observed over the past 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.
Low-level unrest continues at Cleveland volcano. Elevated surface temperatures were observed in satellite data on November 1 and 5. No significant activity has been observed in seismic data or mostly cloudy web camera views.
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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