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ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, March 5, 2021, 12:25 PM AKST (Friday, March 5, 2021, 21:25 UTC)
56°11'52" N 159°23'35" W,
Summit Elevation 8225 ft (2507 m)
Current Volcano Alert Level: WATCH
Current Aviation Color Code: ORANGE
Low-level eruptive activity continues at Veniaminof. The first signs of unrest came from satellite observations of increased sulfur dioxide degassing Monday, followed by elevated surface temperatures observed in satellite data overnight on Wednesday. Regional infrasound sensors detected a small explosion from Veniaminof volcano Thursday morning at 14:13 UTC (05:13 local time), and subsequent satellite and webcam views indicated continuous low-level (< 10,000 ft asl) ash emissions, prompting AVO to raise the Aviation Color Code to ORANGE and the Volcano Alert Level to WATCH. Minor ash deposits were also visible at the volcano's summit. Clouds obscured views of the volcano Thursday evening. No additional explosions were detected overnight, but clear views earlier this morning show that low-level (< 10,000 ft asl) ash emissions continue.
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.
The local seismic data remains offline since December 8, 2020 due to an outage of a satellite link at Port Heiden. However, the Alaska Volcano Observatory continues to monitor Veniaminof with satellite and webcam data and remote infrasound, 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).
51°55'44" N 179°35'52" E,
Summit Elevation 2625 ft (800 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW
No volcanic activity has been detected at Semisopochnoi in mostly cloudy satellite data or regional infrasound data this week.
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 sensors. An infrasound array on Adak Island could detect explosive emissions from Semisopochnoi with a 13 minute delay 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.
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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Dave Schneider, Acting Scientist-in-Charge, USGS
firstname.lastname@example.org (907) 786-7497
David Fee, Coordinating Scientist, UAFGI
email@example.com (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.