Identification of Regime Transitions in Umbrella Cloud Growth for Short- and Long-Lived Eruptions

Abstract:

The ability to characterize the transition between fluid dynamic regimes in an umbrella cloud as it spreads as a gravity current is important for volcanologists and atmospheric scientists. It would allow a better understanding of how ash behaves and spreads in the atmosphere and therefore better estimate the location and propagation of the ash during an eruption. We tested a new gravity current model that allows us to study the transition from one flow regime to another in data plume growth data from several eruptions. It was found that previous asymptotic models of umbrella cloud growth only treat one part of the evolution of the cloud. The new model allows for the study of the duration of different regimes and the timing of transitions during growth of the umbrella cloud. It was found, by testing the effect of the different input parameters of the model, that the duration of release from the volcanic source has a larger impact than the drag force and the initial radius of the intrusion on the initial and downwind spreading.