Multi-Phased Flow Modeling of Vulcanian Explosions with Fountain Collapse on Montserrat

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VoightEAR-0073761Numerous short-duration explosions occurred during August, September and October 1997, at the Soufriere Hills Volcano, Montserrat, West Indies. These eruptions were accompanied by gravity collapse of heavy parts of the eruption column, that produced pumice and ash flows (pyroclastic flows) and "ash hurricanes" that moved sideways, into adjacent farmlands and formerly populated areas. Many of these eruptions were predicted, and we and other staff of Montserrat Volcano Observatory closely documented the eruptions by continuous seismic monitoring, measured surveys of the eruption clouds,photography, and video. Such data are rare, and in this project, we aim to quantify these eruptions, including the speed and trajectory of the explosion clouds, and then to compare these field-based data to sophisticated models of the eruptions. In our modeling, we will attempt to identify the magma and gas ratios in the eruption conduit before the explosion, and the pressure distribution. Then we will use this information as the starting condition for a "multi-phase" explosion model, in which separated solid and gas phases are allowed to expand dynamically upon release from the conduit tube. We can track the speeds and trajectories of the particles emitted from the conduit, and the particle densities of theerupting particle-and-gas cloud. We hope from this study to establish the main conditions in the conduit that control whether the clouds will continue to rise vertically, or will collapse to form dangerous pyroclastic flows. Pyroclastic flows are the major cause of loss of life in explosive eruptions worldwide, and the improved understanding obtained from this project should help to reduce hazards at a number of locations in this country and abroad.