Alaska Volcano Observatory

From Orr and others, 2024: "Beginning on August 10, 2021, AVO detected a swarm of earthquakes at Atka volcanic complex that lasted several days before tapering off. In response to this local seismicity, AVO raised the Aviation Color Code and Volcano Alert Level to YELLOW and ADVISORY on August 11.
"AVO analysts located 204 earthquakes between August 10 and 12; these events had epicenters approximately 3-9 km [2-6 mi] west-southwest of Mount Kliuchef and typical depths of 2-5 km [1.2-3 mi] below sea level. The largest earthquake took place on August 11 and had an ML of 2.5. Five other earthquakes exceeded ML 2.0. The rate of earthquakes began to decline after August 12 and returned to background levels by the end of the month. In response, AVO changed the Aviation Color Code and Volcano Alert Level of Atka volcanic complex to GREEN and NORMAL on August 27. Satellite imagery and infrasound sensors detected no anomalous activity or unrest around the time of the earthquake swarm, in contrast with observations from October 2020, when satellite data showed detectable SO2 emissions from the volcano in close conjunction with an increase in earthquake activity (Cameron and others, 2023)."