Insights into Acoustic Sources from Pyroclastic Density Currents

Pyroclastic Density Currents (PDCs) are deadly, highly destructive, fast-moving, ground-hugging, mixtures of hot gas and volcanic particles. PDC high velocities, dynamic pressures, and temperatures make direct field measurements extremely challenging. Due to the combination of high-impact to the natural and built environment, and the difficulty of obtaining direct measurements, remote detection methods would be of benefit to their study and early warning systems. Acoustic methods have been proposed in the past for this application, however, due to sparse field data, there remains a limited understanding of the fundamental question regarding the source of the recorded acoustic signals. The Pyroclastic flow Eruption Large-scale Experiment (PELE) is a large-scale experimental facility designed to synthesize pyroclastic density currents (PDCs) within a laboratory environment. PELE has been augmented with acoustic sensors allowing for the direct observation of physical properties and the location of the experimental flow with time-synchronized acoustic data.This study examines the location and source of the acoustic signals that have been previously identified in field data.  Combining signal cross-correlation between sensors with known offsets within the experimental channel, and high speed imaging of the experimental flow, the resulting dataset showed that there are multiple pulses of signal sources within a single flow. These signals seem to be associated with the interface of the flow and the atmosphere. This result highlights that, while previously the source of the field signals was attributed to the front of the flow, there are multiple sources within the flow. Further research should be undertaken to further explore the role of these different sources and topography and path in the field. Additionally, this insight should be taken into account for sensor deployment design and early warning system development.