Shock wave hazards during explosive volcanic eruptions: an experimental investigation

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Shock waves in explosive volcanic eruptions are poorly investigated. Several issues concerning their generation and propagation are still objects of great debate, and the associated hazards are currently downplayed in active volcanic area risk assessment. Evidence for such phenomena was recently recovered from one of the villages destroyed by the 1982 eruption of El Chichón volcano (Mexico). Micrometric craters produced by the impact of volcanic ash particles were found on the surface of a steel pole. The velocities of the impacts, was calculated by analytical methods as up to 980 m/s, similar to those reported theoretically and numerically for shock waves accompainying volcanic eruptions. The main goal of this proposal is to gain better insight into the mechanisms by which volcanic particles of different size/mass can be accelerated by shock waves, either given efficient momentum coupling with a gas phase or due to changes in the shock structure at the contact with particles. We plan to reproduce experimentally the impact craters on metal targets. Questions to be answered are: 1) What is the main process responsible for particle acceleration in the presence of shock waves? 2) What is the relationship between the grain-size, the mass load, the shape of the particles, and the high velocities calculated? 3) Is the steel’s temperature at the moment of impact an important factor in determining the magnitude of “cratering”? The results expected from this investigation, will 1) elucidate the processes associated with shock wave propagation during explosive eruptions, and 2) help to raise awareness about the hazards related to these phenomena while improving specific response strategies.