ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, August 27, 2021, 12:26 PM AKDT (Friday, August 27, 2021, 20:26 UTC)
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
The eruption of lava in the summit crater of Great Sitkin Volcano continued over the past week. Satellite data showed that the new lava dome widened from approximately 860 m (~2800 ft) across on August 19 to about 880 m (~2900 ft) on August 24. Steam and gas plumes have been visible to local observers and in satellite images, but no explosive activity or ash emissions have been detected. Sulfur dioxide plumes were detected daily by satellite throughout week. Small earthquakes have been detected that are likely associated with the lava effusion.
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 Volcano 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.
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
Explosions from the north crater of Mount Cerberus, detected by seismic and infrasound sensors, generally occurred several times a day throughout the past week. Ash and steam emissions were confirmed in rare clear web camera images and by nearby observers and were detected in satellite images. The plumes were all below 10,000 feet above sea level and resulted in minor ash deposits on Semisopochnoi Island. Sulfur dioxide emissions were also detected by satellite daily this week.
Small eruptions producing minor ash deposits within the vicinity of the active north crater of Mount Cerberus and ash clouds under 10,000 feet 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.
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
Low-level eruption continues at Pavlof Volcano. Elevated surface temperatures, increased seismicity and infrasound, and small explosions were detected on August 24–26 (Tuesday–Thursday). The volcano was otherwise relatively quiet. Minor ash emissions to 12,000 ft from one explosion were reported by a passing aircraft.
The explosions that have occurred during Pavlof Volcano's current period of activity have been short-lived, with ash deposits confined to the flanks of the volcano. 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 Volcano 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 ASL have been generated by past eruptions of Pavlof, and during the March 2016 eruption, ash plumes as high as 40,000 feet 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.
CLEVELAND VOLCANO
(VNUM #311240)
52°49'20" N 169°56'42" W,
Summit Elevation 5676 ft (1730 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW
Unrest continues at Cleveland volcano. Elevated surface temperatures at the volcano's summit were observed in satellite images frequently throughout the past week. Steam and sulfur dioxide emissions were also occasionally observed. Earthquake activity has remained low and no explosions were detected in seismic or infrasound data.
Episodes of lava effusion and explosions can occur without advance warning. Explosions from Cleveland 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 occur less frequently.
Cleveland volcano is monitored by only one seismic station, 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, local and regional 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.
ATKA VOLCANIC COMPLEX
(VNUM #311160)
52°19'51" N 174°8'20" W,
Summit Elevation 5030 ft (1533 m)
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN
Earthquake activity associated with the seismic swarm that began on August 10 has returned to background levels over the past week. In response to this decrease in seismicity, the Aviation Color Code and Alert Level were lowered to GREEN/NORMAL earlier today (August 27).
The Atka volcanic complex is monitored by local seismic and infrasound sensors, satellite data, and regional lightning detection instruments.
The Atka volcanic complex forms the northern part of Atka Island, located about 16 km north of the community of Atka and 1,761 km southwest of Anchorage. The Atka volcanic complex includes a possible older caldera and several younger vents, including Korovin Volcano, Mount Kliuchef, and Sarichef Volcano. Korovin Volcano, a 1553-m-high (5030 ft) stratovolcano, has been the site of most historical volcanic activity, and has a small, roiling crater lake that occasionally produces energetic steam emissions. Korovin has erupted several times in the past 200 years, including 1973, 1987, and 1998, and has likely had small ash emissions as recently as 2005. Typical recent Korovin eruptions produce minor amounts of ash and occasional but small lava flows. Reports of the height of the ash plume produced by the 1998 eruption ranged as high as 10,600 m (35,000 feet) above sea level. Mount Kliuchef is composed of a series of five vents aligned northeast–southwest. The two main summit vents of Kliuchef appear relatively young and the easternmost was probably the source of an 1812 eruption that is sometimes attributed to Sarichef.
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.