Infrasound Radiation From Impulsive Volcanic Eruptions: Nonlinear Aeroacoustic 2D Simulations

Abstract

Infrasound observations are increasingly used to constrain properties of volcanic eruptions. In order to better interpret infrasound observations, however, there is a need to better understand the relationship between eruption properties and sound generation. Here we perform two‐dimensional computational aeroacoustic simulations where we solve the compressible Navier‐Stokes equations for pure‐air with a large‐eddy simulation approximation. We simulate idealized impulsive volcanic eruptions where the exit velocity is specified and the eruption is pressure‐balanced with the atmosphere. Our nonlinear simulation results are compared with the commonly used analytical linear acoustics model of a compact monopole source radiating acoustic waves isotropically in a half space. The monopole source model matches the simulations for low exit velocities (<100 m/s or M0.3333em≈0.3333em0.3 where M is the Mach number); however, the two solutions diverge as the exit velocity increases with the simulations developing lower peak amplitude, more rapid onset, and anisotropic radiation with stronger infrasound signals recorded above the vent than on Earth's surface. Our simulations show that interpreting ground‐based infrasound observations with the monopole source model can result in an underestimation of the erupted volume for eruptions with sonic or supersonic exit velocities. We examine nonlinear effects and show that nonlinear effects during propagation are relatively minor for the parameters considered. Instead, the dominant nonlinear effect is advection by the complex flow structure that develops above the vent. This work demonstrates the need to consider anisotropic radiation patterns and jet dynamics when interpreting infrasound observations, particularly for eruptions with sonic or supersonic exit velocities.

Analog field-scale acoustic study of volcanic eruption directivity using a tiltable liquid nitrogen-charged water cannon

“…Ichihara et al (2009) discusses a related case of lake water surface explosions (not confined by conduit walls). In addition, our source is conceptually similar to the directed blast numerical simulations of Watson et al (2021). We note that Watson et al (2021) observed enhanced high frequencies in the downstream blast direction (i.e., above the vertically directed source), consistent with our observations.…”

Ultra and Very Long Period Seismic Signatures of Unsteady Eruptions Predicted From Conduit Flow Models

“…There is an opportunity to use simulations of the eruptive jet and atmospheric response (Cerminara et al., 2016; Koyaguchi et al., 2018; Ogden et al., 2008; Watson et al., 2021) as part of the forward modeling workflow to bypass assumptions and biases that may be introduced when using simple source models (e.g., point monopoles or dipoles; point mass, energy, and momentum sources) that are only indirectly linked to eruptive processes. To pursue this approach, we must develop coupled models of conduit flow and the response of a compressible atmosphere.…”

Volcano infrasound: progress and future directions

“…Matoza et al 2009aMatoza et al , 2013. Numerical simulations (Taddeucci et al 2014;Cerminara et al 2016;Brogi et al 2018;Watson et al 2021a) and laboratory studies (Swanson et al 2018;Peña Fernández et al 2020) have examined volcanic jets, which are complex, directional sources, and provide a first step towards more realistic source models. Significant advances are likely to come from adapting and integrating results from modern aeroacoustic and jet noise studies into the volcano infrasound community (Matoza et al 2009a), as well as from combining simulation and laboratory results with field observations to investigate infrasound source processes and quantify uncertainties.…”

“…Elevation contour units are meters. Modified from Fee et al (2021) demonstrated that neglecting nonlinear effects may result in inaccurate infrasound-derived estimates of eruption properties (Anderson 2018;Brogi et al 2018;Dragoni and Santoro 2020;Maher et al 2020;Watson et al 2021a). For example, aeroacoustic simulations by Watson et al (2021a) show that changes to waveform shape due to nonlinear effects can lead to underestimation of total erupted volume (Fig.…”

“…Field observations should be combined with analogue experiments (e.g., Medici et al 2014;Cigala et al 2017;Peña Fernández et al 2020;Schmid et al 2020), numerical modeling (e.g. Ogden et al 2008;Cerminara et al 2016;Watson et al 2021a), and new data types such as continual radio frequency, which Méndez-Harper et al (2018) recently suggested is caused by shock structures in volcanic jet flows.…”