ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, May 14, 2021, 11:37 AM AKDT (Friday, May 14, 2021, 19:37 UTC)
GREAT SITKIN VOLCANO
(VNUM #311120)
52°4'35" N 176°6'39" W,
Summit Elevation 5709 ft (1740 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW
The status of Great Sitkin was raised to Aviation Color Code YELLOW and Volcano Alert Level ADVISORY on Wednesday, May 12 due to observations of increased volcanic gas emissions and elevated surface temperatures at the summit. In addition, a slight increase in local seismicity beginning Sunday, May 9 has been observed. No activity has been observed in cloudy satellite data or web camera images since Wednesday. A few small earthquakes were observed on Thursday and today.
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: ADVISORY
Current Aviation Color Code: YELLOW
Semisopochnoi remains at Aviation Color Code and Volcano Alert Level YELLOW/ADVISORY. No ash emissions or explosions from Semisopochnoi were detected in satellite or infrasound data over the past week.
Small eruptions producing minor ash deposits within the vicinity of the volcano and ash clouds under 10,000 ft above sea level are typical of activity during unrest at Semisopochnoi since September 2018. Local seismic stations have been offline since November 11, 2020. New explosions could occur at any time with no warning.
Semisopochnoi is monitored remotely by satellite and lightning detection sensors. An infrasound array on Adak Island may detect explosive emissions from Semisopochnoi with a slight delay (approximately 13 minutes) if atmospheric conditions permit.
Remote Semisopochnoi volcano occupies the largest, young volcanic island in the western Aleutians. The volcano is dominated by an 5-mile (8-km) diameter caldera that contains a small lake and a number of 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 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.
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
Seismicity remains above background with occasional events detected on the local seismic stations over the past week. No activity was observed in mostly cloudy satellite imagery or detected in regional infrasound arrays.
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 are less likely and occur less frequently.
Cleveland volcano is monitored by only two 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.
VENIAMINOF VOLCANO
(VNUM #312070)
56°11'52" N 159°23'35" W,
Summit Elevation 8225 ft (2507 m)
Current Volcano Alert Level: UNASSIGNED
Current Aviation Color Code: UNASSIGNED
The status of Veniaminof was downgraded to Aviation Color Code and Volcano Alert Level UNASSIGNED/UNASSIGNED on Wednesday, May 12. No eruptive activity has been observed in satellite or infrasound data since early April. The UNASSIGNED status is a result of several seismic station outages impairing the ability of the AVO to assess seismic unrest at the volcano. These stations may come back online as snowpack decreases. Any eruptive activity or unrest may still be detected with the remaining seismic stations, in regional infrasound networks, through detection of lightning, and/or monitoring of satellite images.
Eruptive activity at Veniaminof usually consists of minor ash emissions, lava fountaining and lava flows from the small cone in the summit caldera. Ash emissions are typically confined to the summit crater, but larger events can result in ash fall in nearby communities and drifting airborne ash.
Mount Veniaminof volcano is an andesitic stratovolcano with an ice-filled 10-km diameter summit caldera located on the Alaska Peninsula, 775 km (480 mi) southwest of Anchorage and 35 km (22 mi) north of Perryville. Veniaminof is one of the largest (~300 cubic km; 77 cubic mi) and most active volcanic centers in the Aleutian Arc and has erupted at least 14 times in the past 200 years. Recent eruptions in 1993-95, 2005, 2013, and 2018 all occurred at the intracaldera cone and lasted for several months. These eruptions produced lava spattering and fountaining, minor emissions of ash and gas, and small lava flows into intracaldera icefield. Minor ash-producing explosions occurred nearly annually between 2002 and 2010. Previous historical eruptions have produced ash plumes that reached 15,000 to 20,000 ft above sea level (1939, 1956, and 2018) and ash fallout that blanketed areas within about 40 km (25 mi) of the volcano (1939, 2018).
UGASHIK-PEULIK VOLCANO
(VNUM #312130)
57°45'1" N 156°22'12" W,
Summit Elevation 4836 ft (1474 m)
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN
The status of Ugaskik/Peulik was moved from UNASSIGNED/UNASSIGNED to GREEN/NORMAL on Wednesday, May 12. Communications with seismic stations in the local network have been reestablished allowing the Alaska Volcano Observatory to resume locating earthquakes and detecting unrest at these volcanoes.
UKINREK MAARS VOLCANO
(VNUM #312131)
57°50'2" N 156°30'50" W,
Summit Elevation 299 ft (91 m)
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN
The status of Ukinrek Maars was moved from UNASSIGNED/UNASSIGNED to GREEN/NORMAL on Wednesday, May 12. Communications with seismic stations in the local network have been reestablished allowing the Alaska Volcano Observatory to resume locating earthquakes and detecting unrest at the volcano..
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, 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.