Mechanical stability of Mount Pelée volcano: insights from elasto-plastic numerical models.

Mount Pelée volcano (Martinique) is under unrest since 2019, characterized by an increase in shallow seismicity and surface deformation. To date, an explanation for this unrest is the presence of a shallow inflating source beneath the western flank of the volcano. The objective of this study is to develop more realistic mechanical models than those traditionally used to explain the observed deformation.

In this work, we investigate the mechanical stability of the volcanic edifice using Drucker-Prager elasto-plastic rheology. The mechanical model is constructed by interpolating topography and bathymetric data around the volcano over a distance of 30 km, with lateral boundaries set in free-slip, bottom face blocked and a free top surface. The elastic properties of the crust are derived from the P- and S-wave average velocities. We explore two extreme effective strengths of the crustal domain in the gravity field, as well as the response to a compliant shallow inflating source (30 MPa at 0 km depth).

Our models show that gravitational loading alone can reproduce the magnitude and pattern of the observed surface deformation. Progressively decreasing the effective crustal strength generates stress and deformation over distances larger than those observed with the geodetic measurements over the edifice, but compatible to what a giant landslide could produce. In addition, incorporating a shallow inflating source within the gravity field produces specific shear stress and strain patterns that also correlate with the observed seismicity during the unrest period, as well as surface deformation consistent with geodetic observations. Differentiating between gravitational or inflation-driven mechanisms requires higher-resolution geodetic and seismic observations.

Overall, our results indicate that the western flank of the volcanic edifice is prone to surface deformation and failure, while the eastern flank concentrates shear stress and strain at depth, highlighting potential hazard on both flanks. In this framework, deformation is primarily controlled by the strength parameters of the crust. Incorporating visco-plasto-elastic behavior with layered parameters consistent to a complete velocity model, together with inferred faults and landslide scars, should further improve our understanding of Mount Pelée’s mechanical behavior.