ABSTRACT
The case of the Betsiamites-Colombier slides is one of the large submarine mass movements in Canada for which some detailed geotechnical investigations were also undertaken, largely because of the slide extension onto the coastal area. It resulted from at least two major slide events which mobilized an estimated total volume of 2000 million m3 (2 km3) of sediments. Linkage between offshore and onshore geophysical investigations with borehole data and in situ testing allows reconstruction of the architecture of the Betsiamites River delta area and leads to the identification of the main failure events. A first landslide dated at 7250 cal BP mobilized a volume of 1300 million m3 over an area of 54 km2: the Betsiamites submarine slide event. It prepared the ground for the second major slide event of February 5th 1663 slide: the Colombier slide. This slide involved four successive failure phases: one submarine (flow) and three subaerial (two flowslides and a spread), for a total volume of about 530 million m3 over an area of 20 km2. The Colombier landslide event is among the largest documented historic landslides in Canada. The presence of submarine scars, left by the early Holocene event, acted as predisposition factors for the development of the failure while the earthquake of 1663 probably was the main triggering of the Colombier slide.
