Modeling infrasonic sources related to density currents

Pyroclastic Density Currents (PDCs) are among the most impressive, and hazardous phenomena of volcanic activity. Understanding their dynamics remains a major challenge. Gravity driven flows, dominated by the fluidparticles interaction, are in fact difficult to access for field measurements and complex to model and describe numerically. To date, the use of infrasonic arrays has shown to be able to detect and track PDC’s run-out automatically and in real-time, strongly improving the monitoring of this dangerous volcanic activity. However, relying only infrasonic (or seismic) signal we are not able yet to quantify physical parameters of the PDC, strongly limiting our ability to timely assess the correct volcanic hazard. We here present a new integrated approach that, by the aid of computational modeling, aims to find theoretical and empirical relations between the geophysical signal and the dynamical properties of the flow. In particular we show that, for a dilute PDC the upper and turbulent part of the flow is well developed and coupled with the atmosphere and thus is very effective in generating infrasound. We use the ASHEE model to simulate the dynamic evolution of the gas-particle density current, including the infrasound generation and propagation process. The relationship between PDCs dynamics and acoustic wave-field is explored by varying both numerical and initial conditions in a stratified atmosphere. Comparing synthetic signal with real infrasound recorded associated with density currents activity, we find a strong correlation between the frequency content of the signal and the dimensions of the density current. Our study may have strong implication in terms of hazard assessment. Infrasonic signals could be used to remotely estimate physical properties of PDCs dynamics providing data to constrain observations and improve our ability to monitor such phenomena.