Seismic data from station KOWE showing a quake and tremor sequence at Atka volcanic complex on the evening of March 27 (~03:35 March 28 UTC). There was also an explosion signal noted in infrasound data from the Atka network a few seconds after the first seismic signal. The top panel of this figure shows the waveform of the seismic data and the bottom panel is a spectrogram, which shows the frequency information of the seismic data as a heat map.
On March 28, 2024, AVO raised the alert levels at the Atka volcanic complex to YELLOW/ADVISORY, stating: "A small, short-lived explosion was detected at the Atka volcanic complex this evening at 19:36 AKDT March 27 (03:36 UTC March 28), and AVO is increasing the Aviation Color Code to YELLOW and the Volcano Alert Level to ADVISORY. The event was detected in local infrasound and seismic data and was followed by a few minutes of elevated seismic tremor. Processing of the local infrasound data indicates the explosion originated from the summit crater of Korovin, one of several volcanoes within the Atka volcanic complex. No ash emissions have been observed in satellite images."
For a few days afterwards, seismic activity continued above background levels. There were low-frequency earthquakes and periods of seismic tremor.
By April 9th, seismicity had returned to background levels. Therefore, AVO returned the alert levels to GREEN/NORMAL on that day.