Seismic and infrasound signals from the 2023 explosive eruption sequence of Shishaldin Volcano, Alaska

David Fee , Darren Tan, Matt Haney, Karenna Merritt, John Lyons, Aaron Wech, Matthew Loewen, Eleanor Boyce, Logan Scamfer

Shishaldin Volcano, Alaska erupted in 2023 with 13 explosive paroxysms over a 4 month period, producing notable seismic and low frequency acoustic (infrasound) signals recorded on a local geophysical network. We describe the pre-, syn-, and post-eruptive seismoacoustic signals from the 2023 eruption sequence. Using a recently developed machine learning classifier, we detect and categorize diverse seismicity, including sustained precursory tremor that began months before the first eruption. Explosive events exhibit similar repose periods and relatively consistent high-amplitude, broadband seismic tremor, building over hours to days and at times enabling short-term eruption forecasts. In contrast, co-eruptive infrasound consists of complex mixtures of weak to energetic discrete events and continuous tremor or jetting. The infrasound characteristics suggest that the paroxysmal phase of some eruptions was driven by discrete, energetic Strombolian explosions rather than sustained fountaining, highlighting variability among basaltic explosive styles. The seismoacoustic observations align with a foam-reservoir mechanism, where deep gas flux formed a foam that collapsed periodically to drive eruptions, while a late-stage shallow intrusion increased leakage and continuous degassing and seismicity. These results have important implications for eruption forecasting and hazard monitoring and demonstrate the utility of combining seismic and infrasound data to understand eruption dynamics.