Volcano-Magnetic Signal Reveals Rapid Evolution of the Inner Structure of Piton de la Fournaise

Near-real time analysis of magnetization can provide important information for the imaging of volcano systems and their spatiotemporal evolution. This study focuses on the contribution of volcano-magnetic signals from reiterations of ground magnetic measurements to investigate the evolution of active structures at the Piton de la Fournaise volcano from 2017 to 2020. Changes are demonstrated by magnetic anomalies along a reference profile by means of the reiteration periods. These variations are first modeled qualitatively in 2D using electrical resistivity constraints in order to investigate the evolution of magnetization at depth through time, and the model is subsequently compared with the 3D intrusive activity from depth up to the surface from Interferometric Synthetic Aperture Radar (InSAR) inverse modeling. The shallow areas of demagnetization modeled from one reiteration to another are consistent with the geometry and location of the underlying intrusions revealed by the 3D InSAR models, suggesting strong thermal, stress, and electrokinetic effects due to magmatic activity not only at the surface but also at depth, along the main magmatic paths. It also raises a question as to the extent of the associated thermal diffusion processes at the scale of individual magma injections. This study confirms that detecting resistivity and magnetization anomalies, and quantifying their spatiotemporal evolution, can provide powerful tools for imaging volcanic systems at various scales and for providing warning of associated hazards. It also highlights the necessity for 4D monitoring of volcanic edifices using this method to provide greater precision, an important issue that is now made possible by the use of Unmanned Aerial Vehicle measurements.