Numerical simulation of the 30--45 ka debris avalanche flow of Montagne Pelée volcano, Martinique: from volcano flank collapse to submarine emplacement

International audienceWe simulate here the emplacement of the debris avalanche generated by the lastflank collapse event of Montagne Pele´e volcano (30–45 ka), Martinique, Lesser Antilles.Our objective is to assess the maximum distance (i.e., runout) that can be reached by thistype of debris avalanche as a function of the volume involved. Numerical simulations areperformed using two complementary depth-averaged thin-layer continuum models becauseno complete models were available in the literature. The first model, SHALTOP, accuratelydescribes dry granular flows over a 3D topography and may be easily extended todescribe submarine avalanches. The second model, HYSEA, describes the subaerial andsubmarine parts of the avalanche as well as its interaction with the water column. However,HYSEA less accurately describes the thin-layer approximation on the 3D topography.Simulations were undertaken testing different empirical friction laws and debris avalanchevolume flows. Our study suggests that large collapses (~25 km3) probably occurred inseveral times with successive volumes smaller than about 5 km3 entering the sea. Thisresult provides new constraints on the emplacement processes of debris avalanches associatedwith these collapses which can drastically change the related hazard assessment suchas the generated tsunami, in a region known for its seismic and volcanic risks