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AVO VOLCANO ACTIVITY NOTIFICATION

ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, November 12, 2021, 1:49 PM AKST (Friday, November 12, 2021, 22:49 UTC)


SEMISOPOCHNOI VOLCANO (VNUM #311060)
51°55'44" N 179°35'52" E, Summit Elevation 2625 ft (800 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Small explosions producing low-level ash clouds from the north crater of Mount Cerberus on Semisopochnoi Island occurred multiple times per day throughout the last week. These explosions were detected on local seismic sensors, local and regional infrasound sensors, and, when weather conditions allowed, webcam and satellite images. Most ash emissions were from ~1.5 to 3.0 km (5,000 to 10,000 ft) above sea level and typically dissipated within 50 km (30 mi) of the volcano, but a plume this morning may have reached slightly above 3.5 km (12,000 ft) and was tracked 80 km (50 mi).

Small eruptions producing minor ash deposits within the vicinity of the active north crater of Mount Cerberus and ash clouds typically under 10,000 ft above sea level have characterized the recent activity and show no signs of abating.

Semisopochnoi is monitored by local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.


Remote 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 miles (65 km) northeast of Amchitka Island and 130 miles (200 km) west of Adak.

GREAT SITKIN VOLCANO (VNUM #311120)
52°4'35" N 176°6'39" W, Summit Elevation 5709 ft (1740 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Lava effusion likely continued this week at Great Sitkin, but poor weather obscured most satellite images. Last night a clear satellite image indicated elevated surface temperatures consistent with lava effusion. Very little earthquake activity was detected over the last week, which has been typical of lava effusion since July. No explosions were detected in seismic, infrasound, or satellite data.

Erupted lava has overtopped the summit crater rim and is flowing into small valleys on the south, west, and north flank of the volcano. The terrain is steep in these areas, and blocks of lava and lava rubble could detach from the terminus of the flow lobes without warning and form small rock avalanches in these valleys. Such avalanches may liberate ash and gas and could travel several hundred meters beyond the lava flows; they would be hazardous to anyone in those areas.

There is no indication of how long lava effusion will continue during the current eruption, and it is possible that explosive activity could occur with little or no warning.

Great Sitkin is monitored by local seismic and infrasound sensors, satellite data, web cameras, and remote 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 43 km (26 miles) 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 3 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 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.

PAVLOF VOLCANO (VNUM #312030)
55°25'2" N 161°53'37" W, Summit Elevation 8261 ft (2518 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE

Seismicity was elevated during the past week at Pavlof. Tremor and explosion levels observed in seismic and infrasound data temporarily increased during the early part of the week; however, no widespread ash clouds or deposits were noted when weather conditions allowed satellite or webcam views of the volcano. A small lava flow was first noted in satellite data near the southeast vent on November 8. On November 10 a 2 km-long (1.2 mi) lahar deposit was visible in satellite images below the active southeast crater. A high-resolution satellite image on November 11 showed the lava flow extending 200 m (650 ft) below the active southeastern vent, while the lahar deposit from the previous day likely originated from a hot steaming area 1 km (0.6 mi) below the active crater.

The explosions that have occurred during the current period of activity at Pavlof have been short-lived, with ash deposits confined to the flanks of the volcano. Collapse of lava flows on the steep flank of Pavlof could result in small pyroclastic flows downslope and generate lahars in drainages to the coast. Eruptive activity is focused at a vent on the upper southeast flank of the volcano, near the location of the eruptive vent in 2007. The level of unrest at Pavlof 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 remote infrasound and lightning networks.


Pavlof Volcano is a snow- and ice-covered stratovolcano located on the southwestern end of the Alaska Peninsula about 953 km (592 mi) southwest of Anchorage. The volcano is about 7 km (4.4 mi) in diameter and has active vents on the north and east sides 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 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 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 48 km (30 miles) to the southwest of Pavlof.

OTHER ALASKA VOLCANOES

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CONTACT INFORMATION:

Michelle Coombs, Scientist-in-Charge, USGS, mcoombs@usgs.gov (907) 786-7497

David Fee, Coordinating Scientist, UAF, dfee1@alaska.edu (907) 322-4085


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.
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