Modelling the impact of a hypothetical sub-Plinian eruption at La Soufrière of Guadeloupe (Lesser Antilles)

This paper describes the development and application of an impact model for a future hypothetical sub-Plinian eruption of La Soufrière of Guadeloupe. The model was designed to assess the impact from either a single or multiple eruption scenarios, each defined in terms of a map of the intensity of three volcanic hazards; volcanogenic earthquake, tephra fallout and pyroclastic density currents. The impact from the three hazards can be assessed independently or alternatively the joint impact of the three hazards can be assessed. The outputs that are produced from the model are; the number of buildings with collapsed roofs, and the number of fatal and non-fatal casualties.Two versions of the impact model were developed, one that uses a spreadsheet and another that is implemented using a Geographical Information System (GIS). Both versions use the same types of hazard inputs and vulnerability functions to derive the number of building collapses and casualties, but have different spatial resolution of the final outputs. The spreadsheet version aggregates the results at a zone level defined specifically for this project whereas the GIS was designed to produce results using 250 m grid-squares. The outputs from the two versions, when using the same eruption scenario, produced somewhat different results, highlighting the importance of defining the appropriate spatial resolution.The vulnerability functions were developed using data on the building stock that was collected by a local survey, in which data on the form of construction, condition, location and types of openings and the variation of these parameters across the affected area were collected. The vulnerability functions incorporated new assessments of fire risks induced by pyroclastic density currents.The model was applied to La Soufrière using a range of input hazard scenarios based on reconstruction of the most recent sub-Plinian magmatic eruption which occurred in 1530 AD. A sensitivity analysis of the model was carried out choosing the inputs from a range of defined input values. The effect on losses and casualties of a range of possible mitigation measures was assessed by running the original model and the modified model using the same input eruption scenario. A separate casualty treatment model was also developed and tested.