A study of the tsunami effects of two landslides in the St. Lawrence Estuary

Abstract

The Lower St. Lawrence Estuary (LSLE) is a 230 km long by 50 km wide trough with a broad, flat floor with maximum water depths of 400 m and "shelves" that sit in water depths of < 60 m. It is partly filled with thick glaciomarine and post-glacial sediments and lies within close proximity to the Charlevoix Seismic Zone, the most seismically active region of eastern Canada. The purpose of this paper is to present the modelled tsunami effects of two submarine landslides from the LSLE. A regional seafloor mapping project revealed several submarine landslides on the slopes and channel floor of the LSLE. The tsunamigenic effects of two instability features in the area were investigated. The features chosen were: (1) a blocky submarine landslide that covers an area of ∼3 km2, a run-out distance of 1.2 km and maximum slab thickness of 20 m; and (2) a lateral spread feature with a 4 km long headwall escarpment and a maximum slab thickness of 10.5 m, which may be a candidate for a future landslide. Using a numerical wave tank, the nonlinear shallow water equations were solved for motions induced by the submarine instability features. The equations are solved numerically by the finite volume method, and the code is able to model accurately tsunami runup and drawdown. © Springer Science + Business Media B.V. 2010.