Abstract

Vulcanian eruptions are small explosive volcanic eruptions, which occur frequently at many volcanoes worldwide. This eruptive style presents a significant natural hazard in terms of ash deposition and pyroclastic flow development, and may form the initial and waning phases of larger more explosive eruptions. The eruption plumes generated by Vulcanian events are both unsteady and turbulent, and difficult to measure directly, due to their short duration and the low temporal resolution of field monitoring methods. An appropriate methodology for investigating the fundamental dynamics and testing the predictions of theoretical models is the use of laboratory analogue experiments. In this study, appropriately-scaled laboratory experiments are used to investigate the dynamics of short duration, high pressure releases of buoyant fluid. Pressurized mixtures of water and alcohol were released into fresh water, producing short-lived plumes which exhibited a range of behaviour. The experiments identified the total momentum and buoyancy of the release as independent controlling parameters over a wide range of initial conditions, and this was confirmed by scaling analysis. This presentation focuses on using laboratory observations to constrain the development of predictive models for unsteady flows resulting from finite-volume fluid releases. The scaling laws derived from the experimental observations are applied to volcanic hazard prediction to estimate the mass of ash produced in a single eruptive event, and form the basis of an algorithm for measuring ash distribution within eruption plumes using UV-imaging. These applications are illustrated with field observations from Soufriere Hills Volcano, Montserrat, and Volcan Santiaguito, Guatemala.