ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, April 15, 2022, 12:57 PM AKDT (Friday, April 15, 2022, 20:57 UTC)

EDGECUMBE VOLCANO (VNUM #315040)
57°3'3" N 135°45'40" W, Summit Elevation 3202 ft (976 m)
Current Volcano Alert Level: UNASSIGNED
Current Aviation Color Code: UNASSIGNED

A swarm of earthquakes that began about 2:00 AM AKDT on April 11 has been detected beneath Kruzof Island near Mount Edgecumbe volcano. Several hundred earthquakes have been detected since April 11, and the largest was a Magnitude 2.8 on April 11. This earthquake activity has been slowly declining since early on April 12, although as many as several small earthquakes continue to be detected every hour. The magnitudes of individual earthquakes in this continuing activity have ranged from about M1.7 down to M0.5 or smaller. The current earthquakes are located in the shallow crust (less than 10 km depth), though their exact locations and depths are hard to pinpoint since there is no local seismic network on the island. Preliminary analysis of earthquake activity over the past several years suggests that the current swarm may have been preceded by a slow increase in activity beginning as early as 2020. This earthquake activity is unusual for Mount Edgecumbe and the cause is currently unknown. It may reflect volcanic activity, tectonic processes, or a combination of sources.

AVO does not have local seismic instruments in the area, and the closest station is in Sitka, about 15 miles (25 km) to the east of the volcano. Because the volcano is not instrumented, it currently has an Aviation Color Code and Volcano Alert Level (for ground hazards) of UNASSIGNED/UNASSIGNED. AVO has brought additional distant seismic stations from the regional network into its analysis system to better monitor the seismic swarm and is conducting additional retrospective analyses of seismic data. Satellite images from high resolution sensors and web camera images (from the FAA) show no surficial changes related to volcanic unrest. Analysis of Synthetic Aperture Radar (SAR) data is underway to evaluate if topographic changes have occurred over the past several years.

The prognosis for Mount Edgecumbe is unclear at present. Many volcanoes experience earthquake swarms that taper off without an eruption. If renewed volcanic activity were to occur, we would expect that many more earthquakes would be observed. AVO has no plans to supplement the regional seismic network at this point but has this capability should conditions warrant.

Mount Edgecumbe is a 976 m (3202 ft) high stratovolcano on Kruzof Island located 24 km (15 mi) west of Sitka, Alaska, and is part of a broader volcanic field of lava domes and craters on southern Kruzof Island and surrounding submarine vicinity. Mount Edgecumbe and the surrounding volcanic field lies within the Tongass National Forest. There are no written observations of eruptions from the volcanic field; Tlingit oral history describes small eruptions from about 800 years ago. Geologic investigations show that eruptions 13,000 to 14,500 years ago produced at least one widespread regional tephra layer around 1 m thick near Sitka and over 30 m thick on parts of Kruzof Island. The youngest eruption preserved in the geologic record was about 4,500 years ago. The volcanic field has erupted a wide range of basalt to rhyolite compositions from numerous vents over the past 600,000 years.

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

Slow lava effusion from a vent within the summit crater of Great Sitkin Volcano likely continues. The volcano was obscured by clouds throughout the week, which prevented observations in satellite images. Satellite radar can observe the ground surface through clouds, but there have been no new images collected this past week. Seismic activity remains low.

The terrain is steep near the terminus of the lava flow lobes, and blocks of lava could detach without warning and form small rock avalanches in these valleys. These 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.

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 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 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 (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.

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

Pavlof Volcano continues to erupt from the east vent near the volcano’s summit. Seismic tremor, consistent with continued low-level activity, was present throughout the week. No explosions were detected in local geophysical data. Satellite and web cameras views were obscured for most of week. A satellite image from April 14th showed the typically elevated surface temperatures. No ash emissions were observed in cloudy satellite or web camera data.

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 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 remote 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 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 (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.

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

The eruption at Semisopochnoi volcano continued during the last week, with small explosions observed occasionally in local geophysical data. Seismicity remains elevated with ongoing periods of seismic tremor. Satellite and webcam observations were obscured by clouds, and no ash emissions were observed. It is likely that intermittent ash emissions have continued but were not observed due to poor viewing conditions.

Small explosions have characterized the recent activity and show no signs of abating. These produce minor ash deposits within the vicinity of the active north crater of Mount Cerberus, with ash clouds typically lower than 10,000 ft (3 km) above sea level.

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

DAVIDOF VOLCANO (VNUM #311040)
51°57'15" N 178°19'34" E, Summit Elevation 1076 ft (328 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

An earthquake swarm in the vicinity of Davidof volcano that began on Monday, January 24, continues, with a few small earthquakes over the past week. The rate of earthquakes was steady over the course of the week. The cause of this earthquake activity remains uncertain due to lack of local monitoring capabilities and the inherent uncertainty in earthquake swarm behavior. The earthquakes could be associated with volcanic unrest but may also be the result of regional tectonic activity. Satellite observations were obscured by clouds over the past week.

There is no real-time seismic monitoring network at Davidof volcano. The closest seismometers are approximately 9 miles (15 km) to the east of the volcano on Little Sitkin Island. Davidof is also monitored by satellite data and remote infrasound and lightning networks.


Davidof volcano is a mostly submerged stratovolcano in the Rat Islands group in the western Aleutian Islands, about 218 miles (350 km) west of Adak. The subaerial part of the volcano comprises Davidof, Khvostof, Pyramid, and Lopy islands, which encircle Crater Bay, a 1.5-mile (2.5 km) diameter caldera. The islands are built up from interbedded lava flows and explosive deposits. The volcano has been sparsely studied, but visits by Alaska Volcano Observatory geologists in 2021 documented thick sequences of rhyolite to dacite pyroclastic flow and fall deposits that represent the most recent explosive eruptions. The age of these deposits is unknown, but they appear older than Holocene deposits from nearby Segula and Little Sitkin. There are no known historical eruptions from Davidof.

OTHER ALASKA VOLCANOES

Information on all Alaska volcanoes is available at: http://www.avo.alaska.edu.

For definitions of Aviation Color Codes and Volcano Alert Levels, see: http://www.avo.alaska.edu/color_codes.php

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CONTACT INFORMATION:

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

David Fee, Coordinating Scientist, UAFGI, 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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