Laboratory observations of elasto-acoustic signals of rock fragmentation, fluid-filled cavities formation, stick-slip motion and mass flux dynamics

In a novel combination of experimental methods, the style of conduit dynamics developed during rapid decompression of volcanic materials is deduced. For the first time, shock-tube decompression experiments are combined with direct visual observations of rock fragmentation and mass flux dynamics, and a time series parameterization of pressure, elasto-acoustic signals and conduit elastic deformation. A transparent autoclave enabled the high-speed filming of the overall processes, whereas seven high-dynamic piezoelectric sensors distributed along the autoclave registered elasto-acoustic signals, and two dynamic pressure transducers recorded the internal pressure, all simultaneously. From the data correlation with visual observations of fragmentation and mass flux driven by gas expansion two contrasting dynamics emerged: continuous and discontinuous. These dynamics are determined by the initial pressure and sample properties, the energy distribution and the internal changes in the conduit geometry such as the formation and resonance of fluid-filled cavities, and the stick-slip motion. Mass flux dynamics depend on the way in which the sample is fragmented and how the particles flow along the conduit. All processes in continuous and discontinuous dynamics operate at their own spatio-temporal scale, yet they are interconnected and reflected in the elasto-acoustic signals characterized by a wide frequency 100–25,000 Hz bandwidth, revealing tremor and harmonic signals. These results are useful to interpret and identify from seismic signals the physical processes that determine conduit behavior and the associated eruptive style in active volcanoes.