The effect of pre-existing craters on the initial development of explosive volcanic eruptions: An experimental investigation

Most volcanic eruptions occur in craters formed by previous activity. The presence of a crater implies specific confinement geometries, variably filled by loose fragmental deposits, which are expected to exert a strong, yet poorly studied, control on the violent gas expansion that drives the eruption. Here we analyze patterns of ejection from buried explosions in analog experiments, in order to investigate how the presence of a crater and changes in explosion depth and intensity may affect the formation of eruptive ejecta jets. Results show that scaled depth (charge burial depth divided by the cubic root of charge energy) controls the velocity and, partly, spread angle of eruptive jets independently of the presence of a pre-existing crater. Conversely, for a fixed scaled depth, the presence of a pre-existing crater limits the development of a laterally expanding annulus of the jet. These results are directly applicable to interpretation of volcanic explosions. Key Points Analysis of ejection patterns from intra- and extra-crater buried explosions Velocity and spread angle of ejecta jet are sensitive to explosion scaled depth Radially expanding annulus of the jet is sensitive to pre-existing crater