Exposure of a coastal city to a landslide tsunami: a case study of Cassis, France

Abstract

The rise of sea level will enhance erosion of cliffs that will be in the reach of storm waves in the distant future. We analyse the possible consequences of erosion-driven collapse of the cliff of Cap Canaille, located approximately 20 km from Marseille, France. A resulting fall of large amount of rocks (several millions m 3 ) into the sea (or a subaerial landslide of an equal volume) may generate a local tsunami that will endanger the adjacent seaside resort Cassis. The propagation of waves, created by this hypothetic event, is simulated using the fully non-linear Boussinesq wave model FUNWAVE. The maximum elevation in Cassis may reach 3.6 m and it only weakly depends on the particular scenario of the collapse. The largest source of danger is the short arrival time (3-3.5 min) of the first wave that is also the highest one. This requires implementation of non- traditional means for building resilience of the local coastal community with respect to such events.