Jet flow dynamics of explosive eruptions: laboratory and numerical investigation of shock-tube experiments

Explosive eruptions represent the most powerful and hazardous manifestations of volcanic activity on Earth. During such events, a high-velocity gas/pyroclast mixture is injected in the atmosphere, producing ash columns that can reach altitudes of tens of kilometres. Depending on atmospheric conditions and eruption intensity, these ash clouds can travel thousands of kilometres, potentially disrupting the air-traffic and the climate worldwide.

Jet flow dynamics of explosive eruptions are affected by several parameters, including pressure gradient, temperature of the magmatic mixture, particle mass and size distribution, and vent geometry. However, most of these parameters cannot be measured directly during an eruption. Conversely, some of the characteristics of the volcanic jets, such as exit velocity, jet dimension, and acoustic signals, can be collected by volcanic monitoring systems.

To correlate jet flow characteristics with magmatic conditions below the vent of the conduit, we investigated jet flow dynamics using a combination of shock-tube experiments and numerical simulations. Data from laboratory experiments were collected using a high-speed camera to capture the evolution of the jet at high temporal resolution, as well as acoustic signals from microphones. Schlieren shadow photography has also been adopted to visualise shock waves and density contrasts within the gas during the experiments. Using this setup we investigated the role of particles on jet flow characteristics. Preliminary results indicate that in the supersonic regime, both the amplitude of acoustic signals and the spectral properties of the signal are influenced by solid loading. Finally, transient numerical simulations of the shock-tube experiments were also performed to correlate the evolution of the jet features with the internal thermodynamic conditions of the gas/pyroclast mixture.