ALASKA VOLCANO OBSERVATORY WEEKLY UPDATE
U.S. Geological Survey
Friday, November 20, 2020, 11:38 AM AKST (Friday, November 20, 2020, 20:38 UTC)
52°22'54" N 174°9'55" W,
Summit Elevation 5030 ft (1533 m)
Current Volcano Alert Level: ADVISORY
Current Aviation Color Code: YELLOW
Low-level seismicity, composed of occasional small, mainly low-frequency earthquakes, was recorded at Korovin Volcano throughout the past week. No eruptive activity was detected by infrasound sensors or in satellite views of the volcano.
Korovin is monitored by local seismic and infrasound sensors, satellite data, and regional lightning detection instruments.
Korovin Volcano is a 1553-m-high (5030 ft) stratovolcano located on the northern part of Atka Island in the central Aleutian Islands, about 21 km (13 mi) north of the community of Atka, 538 km (350 mi) west of Dutch Harbor, and 1760 km (1100 mi) southwest of Anchorage. The volcano has two distinct summit vents about 0.6 km (2000 ft) apart, that have been the sites of eruptive activity in historical time. The most recently active of the vents maintains a small, roiling, lake that occasionally produces energetic steam emissions. Thermal springs and fumaroles located on and near the volcano indicate an active hydrothermal system. 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 from 4,900 to 10,600 m (16,000 to 35,000 feet) above sea level.
51°55'44" N 179°35'52" E,
Summit Elevation 2625 ft (800 m)
Current Volcano Alert Level: UNASSIGNED
Current Aviation Color Code: UNASSIGNED
No eruptive activity was detected in infrasound data or in satellite views of the volcano this week. A local seismic data outage began on Wednesday, November 11, when a satellite link for transmitting seismic data failed. The satellite link is not likely to be reestablished without a site visit. Because seismicity had decreased to very low levels before the outage and no eruptive activity has been detected since mid-June, AVO lowered the Aviation Color Code to UNASSIGNED and Alert Level to UNASSIGNED for Semisopochnoi earlier today. Low-level seismic unrest may be continuing undetected.
Semisopochnoi is normally monitored by local seismic sensors, satellite data, and regional infrasound and lightning detection instruments. 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. The last 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
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Matt Haney, Acting Scientist-in-Charge, USGS
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David Fee, Coordinating Scientist, UAFGI
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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.