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VOLCANO ACTIVITY NOTIFICATION

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ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, April 30, 2021, 10:44 AM AKDT (Friday, April 30, 2021, 18:44 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

SO2 and (or) low-level ash emissions from Semisopochnoi were observed in satellite views on Saturday, Sunday, and Monday of this past week. Those plumes generally drifted to the south at altitudes of roughly 10,000 ft above mean sea level. Generally cloudy conditions prevailed for the rest of the week, obscuring most satellite views of the volcano. No activity was detected by regional infrasound arrays. AVO will continue to monitor the situation closely.

Small eruptions producing minor ash deposits within the vicinity of the volcano 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.

VENIAMINOF VOLCANO (VNUM #312070)
56°11'52" N 159°23'35" W, Summit Elevation 8225 ft (2507 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW

Seismicity was relatively low over the past week, and no unusual activity was observed in satellite and web camera views. Pauses in eruptions are common, and lava flows and eruption of minor ash plumes could resume suddenly with little or no warning.

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.

Only two seismic stations in the local network at Veniaminof are currently transmitting data. While the full network of eight stations has not been fully restored, the data from the two functioning seismic stations will aid in the detection of changes in unrest that may precede a more significant explosive eruption. The Alaska Volcano Observatory continues to monitor Veniaminof with satellite and webcam data and remote infrasound, regional seismic and lightning networks.


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).

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. Clouds obscured most satellite and web camera images throughout the week; occasional clear views showed elevated surface temperatures at the volcano's summit. No activity was observed 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.

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:

Matt Haney, Acting Scientist-in-Charge, USGS
mhaney@usgs.gov (907) 786-7497

Jessica Larsen, Acting Coordinating Scientist, UAF
jflarsen@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.
VOLCANO ALERT LEVELS
NORMAL
Volcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.
ADVISORY
Volcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.
WATCH
Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway but poses limited hazards.
WARNING
Hazardous eruption is imminent, underway, or suspected.
AVIATION COLOR CODES
GREEN
Volcano is in typical background, noneruptive state or, after a change from a higher level, volcanic activity has ceased and volcano has returned to noneruptive background state.
YELLOW
Volcano is exhibiting signs of elevated unrest above known background level or, after a change from a higher level, volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.
ORANGE
Volcano is exhibiting heightened or escalating unrest with increased potential of eruption, timeframe uncertain, OR eruption is underway with no or minor volcanic-ash emissions [ash-plume height specified, if possible].
RED
Eruption is imminent with significant emission of volcanic ash into the atmosphere likely OR eruption is underway or suspected with significant emission of volcanic ash into the atmosphere [ash-plume height specified, if possible].
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Page modified: January 4, 2021 11:16
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