Abstract
Catastrophic collapses of the flanks of stratovolcanoes constitute a major hazard threatening numerous lives in many countries. Although many such collapses occurred following the ascent of magma to the surface, many are not associated with magmatic reawakening but are triggered by a combination of forcing agents such as pore-fluid pressurization and/or mechanical weakening of the volcanic edifice often located above a low-strength detachment plane. The volume of altered rock available for collapse, the dynamics of the hydrothermal fluid reservoir and the geometry of incipient collapse failure planes are key parameters for edifice stability analysis and modelling that remain essentially hidden to current volcano monitoring techniques. Here we derive a high-resolution, three-dimensional electrical conductivity model of the La Soufrière de Guadeloupe volcano from extensive electrical tomography data. We identify several highly conductive regions in the lava dome that are associated to fluid saturated host-rock and preferential flow of highly acid hot fluids within the dome. We interpret this model together with the existing wealth of geological and geochemical data on the volcano to demonstrate the influence of the hydrothermal system dynamics on the hazards associated to collapse-prone altered volcanic edifices.
Highlights
Laterally-directed explosions on a smaller scale caused 63 fatalities at Ontake volcano in 201411 and could have caused many fatalities at Tongariro in 201210,12
Knowledge of the subsurface structure and dynamics of the volcanic hydrothermal system and other structures that contribute to edifice instability such as faults, detachment planes and areas of mechanically weak rock is crucial for risk assessment in volcanic systems[9,15,16]
We provide estimates for the potential volume of material involved for different scenarios and compare these to past edifice collapses studied at La Soufrière de Guadeloupe[30,31,41]
Summary
Laterally-directed explosions on a smaller scale caused 63 fatalities at Ontake volcano in 201411 and could have caused many fatalities at Tongariro in 201210,12. Imaging of the hydrothermal system, together with geophysical and geochemical monitoring data, helps to construct a functional dynamic model of the volcanic edifice linking observables, hidden states of the hydrothermal-magmatic system, and possible eruptive outcomes[18] This knowledge contributes to reduce epistemic uncertainty in modelling constraints (e.g. volume, overpressure, path) for hazard and risk-oriented simulations of partial edifice collapse (for example19,20), associated laterally-directed explosions and potentially tsunamigenic debris avalanches at volcanoes in populated areas (for example[21]). Electromagnetic geophysical methods, such as electrical resistivity tomography, are sensitive to electric conductivity anomalies associated with fluid-saturated rocks and have been widely used to image fluid presence and migration[22]. We provide estimates for the potential volume of material involved for different scenarios and compare these to past edifice collapses studied at La Soufrière de Guadeloupe[30,31,41]
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