The beating sound of passive degassing at an open-vent volcano captured by combined infrasonic and SO2 flux observations

Volcanic degassing is a key manifestation of volcanic activity, and offers crucial insights into the subtle changes in volcano behavior during unrest and prior to eruption. However, accurately assessing gas emission rates remains difficult, and the implementation of gas flux sensing techniques is one of the most pressing challenges in modern volcanology. Here, we present two years of continuous measurements (April 2017–March 2019) of the SO2 flux and infrasound associated with volcanic degassing at Stromboli volcano (Italy). We show that degassing can be tracked in space and time following changes in infrasonic activity during persistent Strombolian activity. By modeling gas expansion within the conduit, we convert ~10 million infrasonic signals into equivalent gas fluxes associated with puffing and spattering activity. Our results and calculations from both methodologies indicate a total magmatic gas emission rate ranging between 10 and 100 m³/s. We find this volumetric rate to be almost entirely accounted for by the acoustically-derived gas flux, both in terms of total volume released and the spatial distribution of the degassing sources. Our results open new avenues to interpreting passive degassing at open-vent volcanoes, and demonstrate the potential of infrasound as a valuable tool for quantifying gas emissions in such systems.