Description: From Orr and others, 2023: "A series of small earthquakes thought to be associated with glacial activity took place near the summit of Isanotski Volcano in the spring of 2019. Around 13,000 earthquakes were detected from March 12 to May 11, forming several swarms that each lasted hours to days. Tremor bursts were also recorded within a few days after some of the swarms. Sporadic seismicity continued into the summer, although this seismicity was less significant than that of the spring. Most earthquakes recorded near Isanotski Volcano in 2019 were too small to be located, so their local magnitudes could not be determined. However, a larger event on May 1 was located close to the surface near the summit of Isanotski Volcano and had an ML of −0.3. These traits are consistent with a glacial seismicity source. Photographs taken in August 2019 show crevasses in the ice on the north side of Isanotski Volcano that may be related to the spring seismicity.
"The 2019 seismic sequence began on March 12 at 05:20 UTC (March 11 at 21:20 AKDT). For the first four days, the earthquakes in the sequence had low amplitudes, but on March 16, events suddenly increased in amplitude and decreased in rate. These events continued until late on March 21. After a 3-hour pause, in the early morning of March 22, a 4-minute-long tremor burst followed the earthquakes. A second swarm began several hours later and ended on March 25. The seismicity resumed on March 31 with a third earthquake swarm that continued for about a day and a half. This was followed by a series of short tremor bursts and LP earthquakes on April 4.
"Another series of earthquake swarms, each lasting less than a day, took place on April 12-16. These were followed by a 1.5-minute-long tremor burst on April 18. The last large swarm of the sequence started on April 21 and continued until May 9. Like the opening swarm in March, the earthquakes of this final swarm sharply increased in amplitude after about 5 days. The swarm was also followed by a 6-minute-long tremor burst on May 12. Although the tremor burst concluded the main sequence, tremor was also noted on May 30 and June 1. Occasional earthquakes occurred during the pauses between the March-May swarms, and more occurred afterward until at least July. These sporadic events are difficult to describe thoroughly because they typically had very low amplitudes (which could easily be masked by noise) and because local monitoring is limited."