Geodetic modelling of a multi-source deformation pattern retrieved through Sentinel-1 DInSAR measurements: the 11-15 August 2019 Piton de la Fournaise (La Réunion Island) eruption case-study

The Piton de la Fournaise volcano is located on the southeastern part of La Réunion Island and is inserted in the tectonic framework of the Indian Ocean. It is one of the most active worldwide volcanoes and it can be classified as a hot-spot basaltic one.

In this work, we focus on the eruption occurred from 11 to 15 August 2019 on the southern-southeastern flank of this volcano, inside the Enclos Fouqué caldera. In particular, this distal event was characterized by the opening of two eruptive fissures and accompanied by shallow volcano-tectonic earthquakes.

Firstly, we investigate the surface deformations induced by the occurred eruptive activity, by exploiting Differential Synthetic Aperture Radar Interferometry (DInSAR) measurements; they are obtained by processing the data collected by the Sentinel-1 satellite of the Copernicus European Program along ascending and descending orbits. Due to the position of the island in the southern hemisphere, the processed S1 interferograms are characterized by a 12-days temporal baseline; for this reason, they measure the ground deformations generated during both the pre- and co-eruptive phases. Then, we analyze the distribution of the relocated hypocenters to recognize the activated structures and to furnish further constraints to our model. Finally, we perform an analytical modelling to the computed coseismic DInSAR displacements, with the aim of investigating the volcanic source/s responsible for the measured surface deformation field.

The retrieved results reveal that several volcanic sources (one sill and four dikes, in particular) have been active during the pre- and the co-eruptive phases, allowing the magma transport towards the surface; their action can justify the complexity of the observed deformation pattern. Our findings are in good agreement with the seismicity recorded by the Observatoire Volcanologique du Piton de la Fournaise network and with several geophysical evidences, such as the comparison between the volume of the retrieved sources and the erupted magma volumes, and the fissures location.