Is stress modeling able to forecast intrusions and slip events at Piton de la Fournaise volcano?

Widespread evidence indicates that the stress field and the presence of major discontinuities control the magma trajectory and the stability of volcanic edifices. These latter factors affect two major volcanic hazards: eruptions and flank slip events. Here, we use a catalog of 60 intrusions at Piton de la Fournaise (Reunion Island) to document the link between stress inherited from intrusions and slip events, and the location of subsequent events. Our study spans two periods, 1998-2007 and 2007-2021, separated by a collapse of the summit crater and a 1.4 meter flank slip in 2007. The 1998-2007 intrusive sequence cannot be explained by stress interaction. On the contrary, the location of intrusions in the 2007-2021 sequence is consistent with a decrease in normal stresses (unclamping) induced by previous intrusions. Progressive rift zone unclamping, and Coulomb stress increase on previously recognized structures explain the migration of activity from the summit to distal areas, the alternation between intrusions in the northern and the southern flanks, as well as the occurrence of flank slip events. Stress analysis documents a positive feedback between rift zone and flank slip events. In the long term, both magma intrusions and flank slip events contribute to the occurrence of catastrophic flank collapses through unclamping and Coulomb stress increase at the base of an unstable sector.