Phreatic Eruption Dynamics and Risk in the Antilles

ended

Phreatic or hydrothermal eruptions are relatively frequent phenomena on active volcanoes hosting shallow hydrothermal systems, where heat and fluids are transferred from the magmatic source to the surface through a porous and fractured rock. Such a flow of fluids promotes the increase of interstitial pressure as well as the alteration and weakening of the host rock, potentially leading to conditions of mechanical failure. The deriving phreatic explosions are able to generate jets of gas and particles, often accompanied by intense fallout of large (10-40 cm) lithic blocks. Due to the complex interaction of the magmatic and hydrothermal systems, phreatic explosions are among the most sudden and unpredictable volcanic phenomena. Their study is hindered by the largely incomplete stratigraphic record, the partial understanding of the underlying physical processes, and by the fact that such eruptions often manifest few, low-amplitude and unclear precursors in geophysical and geochemical signals. This project aims to develop a new physical and numerical model for the simulation of phreatic eruptions, and to apply it to the estimate of volcanic hazard and risk at La Soufrière de Guadeloupe (Lesser Antilles, FR), where the recent unrest episodes have increased the alert level for the resident population and for tourists, who increasingly visit the volcanic area. The project will focus on 1) aspects related to establishment and stability of initial conditions in the porous and fractured environment hosting the hydrothermal system; 2) the role of liquid water in the explosion, involving the explosive phase transition (flashing) of overheated water; 3) the 3D simulation of the phreatic explosion dynamics, with focus on potential blast generation and ballistic ejection. The scientific objective is to better understand the mechanism that triggers the explosion of the hydrothermal system under forcing by a deep magmatic source and to predict its dangerous effects.