Following the seismic swarm that began at Bogoslof around October 22, 2023 the frequency of earthquakes has now subsided to background levels. During the swarm 5 to 10 events per hour and up to a total of ~1,100 earthquakes were recorded in one week. The decline in seismicity has been observed over the past 3 weeks, with the last moderate earthquake (M2.7) recorded on November 9. No other signs of volcanic unrest have been detected. In response, AVO is lowering the Aviation Color Code and Volcano Alert Level to UNASSIGNED.
Bogoslof volcano is monitored using a single local seismic station, distant seismic and infrasound instruments, satellite data, and lightning networks.
At least nine historical eruptions have been documented at Bogoslof volcano. The most recent occurred from December 2016 to August 2017 and produced seventy main explosive events that generated volcanic ash clouds that rose as high as 42,500 ft (13 km) above sea level, and greatly modified the topography of Bogoslof Island. Previous eruptions of the volcano have lasted weeks to months and have on occasion produced ash fall on the community of Unalaska. Eruptions of the volcano are often characterized by multiple explosive ash-producing events as well as the growth of lava domes.
Bogoslof Island is the largest of a cluster of small, low-lying islands making up the summit of a large submarine stratovolcano. The highest point above sea level is about 490 ft (150 m); however, the volcano is frequently altered by both eruptions and wave erosion and has undergone dramatic changes in historical time. The two main islands currently above sea level are Fire Island and Bogoslof Island, both located about 61 miles (98 km) northwest of Unalaska/Dutch Harbor, 76 miles (123 km) northeast of Nikolski, and 93 miles (149 km) northeast of Akutan. The volcano is situated slightly north (behind) the main Aleutian volcanic front. Bogoslof volcano is within the U.S. Fish and Wildlife Service Alaska Maritime National Wildlife Refuge and is habitat for marine mammals and seabirds (https://www.fws.gov/refuge/alaska_maritime/).
Matt Loewen, Acting Scientist-in-Charge, USGS email@example.com (907) 786-7497
David Fee, Coordinating Scientist, UAFGI firstname.lastname@example.org (907) 378-5460
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.
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