Aeroacoustics of volcanic jets: An overview

Abstract

Explosive volcanic eruptions can inject large volumes of ash into heavily traveled air corridors; they pose a significant societal and economic hazard. They also generate large amplitude atmospheric infrasound waves (~0.01-20 Hz), which can be recorded at thousands of kilometers from the eruption and can provide detailed information on the timing, duration, and relative vigor of the volcanic explosions. In order to provide more detail about the eruption process based on acoustic signals, a quantitative model for the acoustic source process within the volcanic eruption column is needed. Volcanic eruption columns are modeled by a momentum-driven jet flow, transitioning with altitude into a thermally buoyant plume. Infrasound recordings from such activity resemble the large-scale turbulence similarity spectrum, indicating that large-scale volcanic jet flows generate an infrasonic form of jet noise. However, volcanic jet noise deviates from pure-air laboratory jet noise because of complexities such as multiphase flow (especially loading with ash particles); nozzle/crater geometry and roughness; buoyancy effects; and high temperature and density effects. We propose a new framework for understanding acoustic sources at volcanoes based on aeroacoustics research, which is being developed through multi-disciplinary integration of field, numerical, and laboratory studies.