ABSTRACT
On the North shore of the St. Lawrence Estuary (Québec, Canada), near the Betsiamites river delta, a large subaerial-submarine landslide complex was mapped using multibeam bathymetry, LiDAR and photogrammetric data. Previous analysis of this landslide complex revealed that at least four different landsliding events occurred to form the present morphology, in which over 2 km3 of material have been mobilized. Of particular interest here is the Betsiamites 7.25 kyr cal BP landslide that is entirely submarine, and mobilized about 1.3 km3 of material deposited over an area of 54 km2. This is, to date, the largest landslide scar identified on the St. Lawrence estuary seafloor. Previous studies showed that this landslide may have been triggered by a strong earthquake that liquefied a sandy layer interbedded between clayey layers.
Submarine landslides that mobilized that kind of volume within a short time may have triggered tsunamis. In order to be able to evaluate the tsunami potential of the 7250 cal BP landslide, a kinematic analysis needs to be done. This kinematic analysis is presented in this paper. The pre-failure and post-failure topographies are available via a morphologic analysis of the multibeam data. The morphology of the deposit is well described by the present morphology and an analysis of seismic profiles. Relations between geotechnical properties (from samples taken in cores) and empirical rheological relationships are used to determine the rheology of the materials. The BING model, that simulates the propagation of the mass using bilinear or Herschel-Bulkley rheology, and that takes into account the presence of water, is used in order to simulate the post-failure behavior of the Betsiamites submarine landslide.
