Long-term, coupled muon measurements to track density changes at La Soufrière de Guadeloupe volcano
Résumé
Volcanic hydrothermal systems give rise to unpredictable hazards such as hydrothermal explosions, partial edifice collapse, mudflows and sudden emission of toxic gases. Characterizing the dynamics of these systems is thus critical for developing efficient risk assessment.
Here we present the use of continuous muon measurements at La Soufrière de Guadeloupe volcano as a novel methodology to characterize the spatio-temporal dynamics of its hydrothermal system. Six muon telescopes acquire data continuously around the lava dome since 2015. In this work a set of more than 1.5 years of continuous measurements acquired with two muon detectors is analyzed. The two telescopes scan two different zones of the dome with large overlapping volumes. Characterizing the time changes in the outgoing muon flux in different regions allows us to study the density changes caused by steam formation, condensation, water infiltration and storage. First, we define these regions according to the different geological structures in the volcano presenting characteristic behaviors: active/non-active fumarolic zones, and shallow/deeper sections of the system. We then perform a principal component analysis of the temporal series to identify which lines-of-sight of the two telescopes present coherent temporal variations. Finally, we make use of calibrated static muon radiographies to determine the changes in opacity implied by the muon-flux changes observed. This strategy allows us to spatially constrain the three-dimensional location of the coherent density changes and to improve the quantification of the associated mass changes.