Analysis of gas jetting and fumarole acoustics at Aso Volcano, Japan

This work is an in-depth investigation of a specific acoustic signal, volcanic jet noise, also referred to as volcanic jetting or simply, jet noise. Volcanoes generate jet noise at a variety of scales, from low-level gas jetting to violent subplinian-plinian volcanic jets. Research on jet noise produced by jet engines and rockets has shown there is a relationship between jet noise and the jet's parameters (i.e. jet velocity, temperature, nozzle diameter, etc.) that continues to evolve with increased understanding. Jets have been observed to be self-similar; in other words, they scale. This scaling implies that lessons learned in human-made jet noise studies could be applied to volcanic jets. The challenge lies in that volcanoes are not jet engines with smooth surfaces, easily measurable features, and comparatively constant shape; rather they are dynamic and complex, with varying surrounding topography and flow features. This varied nature is what makes them not only fascinating but also dangerous to the local populous and global air traffic. Although the length scales of laboratory and volcanic jets are vastly different, the acoustic features should scale similarly. This suggests that studying smaller-scale volcanic jets, such as from gas jetting fumaroles, is useful. A fumarole is a vent in an active volcanic environment that issues steam and other volatiles (i.e. carbon dioxide, sulfur dioxide, etc.) at temperatures greater that 100°C. Here is an example from Mt. Griggs, Alaska. Fumaroles are more accessible and easier to characterize, and should scale to large, less frequent and more hazardous volcanic jets with plumes that reach 10 to 30+ km in the atmosphere. In the past fumaroles have been recorded but not investigated in depth. Our aim for this work was to understand fumarole acoustics and its relation to degassing to better understand volcanic jetting and its relationship to other eruptive activity. To achieve this we characterized the acoustic signal from a gas-jetting fumarole at Aso volcano, Japan, investigated the path effects and estimated the volatile flux using the acoustic data, thermal infrared images and published gas composition data. More details can be found on the poster below presented at AGU Fall Meeting 2015 and the paper McKee et al. (2017).