New Insights from a Multi-Method Geophysical Investigation on a Very Large, Slow-Moving Landslide (Hell Bourg, Reunion Island)
Résumé
Hell Bourg landslide (Salazie, Reunion Island) is a large, inhabited, slow-moving landslide (>200 Mm3). This landslide covers and remobilizes debris from former volcanic flank collapses. The volume, lithology, structure and evolution through time of these ancient deposits make the Hell Bourg landslide particularly complex. To understand the dynamics and improve the hazard related to its displacements, geodetic, geomorpho-logic, and geologic investigations have been undertaken on this landslide for more than 20 years. Complementary investigations have been required to acquire a precise definition of this large landslide’s subsurface geometry and hydrogeology, necessary for a better understanding of its dynamics. In the present study, we combine different geophysical approaches (airborne electromagnetics, passive and active seismic data) to investigate the internal structure of the landslide. This method delivers accurate 3D images that provide useful additional information about the subsurface of the landslide. The models obtained of the subsurface are consistent with geomorphological and geological observations and allow the derivation of a new conceptual model of the 3D structure of the landslide. Thanks to this approach, new insights into the origin and mechanisms of the Hell Bourg landslide have been gained. This study shows the relevance of the multi-method approach for understanding large complex landslides. The work carried out on the Hell Bourg landslide opens up new avenues of research into large landslide mechanisms in a volcanic tropical environment.