The internal structure of volcanoes controls their volcano-tectonic evolution, especially during flank failure events. At Piton de la Fournaise volcano (La Réunion), offshore debris avalanche deposits, recent eastern flank slip events, and a seaward spoon-shaped preferential intrusion zone, demonstrate the recurrence of destabilization processes at different timescales. The stability of the eastern flank is therefore one of the major concerns at that volcano. To constrain the flank structures and destabilization mechanics, we compare the pattern of morphologic lineaments with recently published InSAR deformation measurement and modelling, magnetic anomalies, and seismicity data. We identify several structural discontinuities distributed in two families striking N50-80 ° and N120-160 ° . Their spatial location being limited to the eastern flank, we suspect the discontinuity as being the result of local intra-caldera processes or inheritance from caldera formation. Among these discontinuities, a major N65 ° discontinuity runs through the middle of the eastern flank, separating a north-western block from a south-eastern block. The north-western block shows low seismic velocities and is affected by sheared sill intrusions, while the south-eastern block shows higher seismic velocities and is affected by fault slip and creep. Both blocks probably lie between 0.5-2 km depth, at the base of a previously identified spoon-shaped intrusion zone around sea level. Both observed slip behaviours (sheared sill and faults) could be due (1) to an underlying intrusive complex creating a mechanical contrast and forming the N65 ° fault, or (2) to an edifice decoupling due to the N65 ° fault. Whatever the origin of the identified discontinuities, their presence and their interactions with the volcanic activity could lead to complex dismantling dynamics that should be accounted for in flank failure hazard assessment. • We assess Piton de la Fournaise’s east flank structure thanks to published data. • We compare morphologic lineaments with deformation, magnetic and seismic data. • A network of N50-80 ° and N120-160 ° shallow structural discontinuities is identified. • A major N65 ° discontinuity separates a SE block affected by fault slip and creep. • The most unstable SE block should be accounted for flank failure hazard assessment.
Dumont et al. (Sun,) studied this question.