Uncovering Hidden Eruptive Activity from Mount Michael Volcano, South Sandwich Islands with Long-Range Multi-Year Infrasound Detection

Mount Michael is a remote stratovolcano in the South Sandwich Islands, with eruptive activity observed only by limited geological expeditions and sporadic satellite imagery. At 1,672 km, the IMS infrasound station array IS27, Antarctica, has been continuously recording infrasound since 2004. We use IS27 infrasound records from 2004 to 2020, revealing unobserved episodes of persistent eruptive activity from Mount Michael during two main periods: May 2005 to January 2008 and May 2016 to April 2018. We also find other interesting signal features, like seasonal microbaroms and intermittent glacier calving during the warmest months of the Antarctic summer. We model the expected systematic backazimuth variation of the infrasound detections at IS27 by combining ray-tracing with empirical climatologies, showing that the observed backazimuth variation broadly follows the modeled annual effects of changing stratospheric propagation conditions on a source at Mount Michael. We also characterize the observed signal amplitudes as moderate explosive eruptions, similar to or greater than the small phreatic explosion at Mount St. Helens, WA, USA, on 8 March 2005. Finally, we highlight a selection of infrasound signals corresponding to satellite observation of eruptions and include examples of other typical infrasound detection sources from the multi-year analysis.