Experimental insights into transient volcanic eruption

Abstract:

The explosive expansion of mixtures of pressurized gases and pyroclasts within volcanic conduits and volcanic flows is a complex process that cannot be directly observed. Here, we present the results of shock-tube experiments with volcanic particles which exhibit remarkable similarities to the ejection dynamics of transient eruptions. Upon rapid decompression (from 2-11 MPa argon pressure to atmospheric pressure Pa = 0.1 MPa), loose particles are vertically accelerated and ejected into a large tank filled with air at atmospheric conditions. Our experimental results show that: 1) time-scales of the mechanical coupling between pyroclasts and the gas phase control the mixture dynamics and different regimes can be defined in terms of the Stokes number according to the particles grain-size; 2) As suggested by previous studies, we found that the pseudo-gas approximation is a reasonable approximation in transient eruptions only under certain conditions (constrained here experimentally); 3) the non-linear decay of the particles velocities with time is related with the conduit depth and the initial volume of the expanding material. Our results broaden the impact of previous experimental studies and provide fundamental information for numerical models of eruptive dynamics.