Observations of Coastal Landslide-Generated Tsunami Under an Ice Cover: The Case of Lac-des-Seize-Îles, Québec, Canada

On April 15 2014, a landslide occurred on the east shore of a lake in the municipality of Lac-des-Seize-Iles, about 100 km north of Montreal, Quebec, Canada. The coastal landslide, with a length of 94 m and a width of 55 m, had a volume of about 30,500 m3 of sandy to gravelly till. It was likely triggered by a significant amount of water infiltration caused by a heavy rain coincident with an accelerated snow melt. The displaced mass spread on the lake floor and triggered a tsunami that broke and partly lifted the ice cover. Water and ice damaged several seasonal residences and boathouses on the periphery of the lake, in an area extending 450 m north and 500 m south of the landslide debris location. Observations on aerial photographs taken shortly after the event revealed the existence of radial structures on the ice cover in the affected area resulting from the evolution of the tsunami wave. Investigations carried out on east and west shores showed evidences of net marks on tree trunks explained by a maximum inundation height which can be as much as 1.8 m directly in front of the landslide position on the west shore.