Submarine slope failures and tsunami hazard in coastal British Columbia: Douglas Channel and Kitimat Arm

Abstract

A new analysis of multibeam swath bathymetry data reveals evidence of large submarine slope failures in southern Douglas Channel, British Columbia. Specifically, two rotational submarine slides (A and B) formed by the failure of scallop-shaped blocks derived from the eastern margin of the fiord wall are identified. Slide A has an estimated minimum volume of 32 000 000 m3 and Slide B of 31 000 000 m3. The toes of the failures are buried by a thick cover of mud deposited from suspension, as are the edges of the slide masses, suggesting that the failures occurred during early to mid-Holocene time, i.e. 5000 to 10 000 years BP. Although the causes of the failures are not known at this time, their close proximity to an apparently active fault presents the possibility that they may have been triggered by ground motion or surface rupture of the fault during past earthquake events. Additional geological research is required to better delineate the age of the submarine failures, their triggers, and their mechanisms of emplacement. Nested failures, retrogressive and incipient slide blocks, and steep slopes are characteristic of the southeastern margin of Douglas Channel and present conditions conducive to future submarine failures. Each of the newly identified slide volumes exceed that of the 25 000 000 m3 slope failure that took place on 27 April 1975 along the inner slope of Kitimat Arm to the northwest of Douglas Channel. This latter failure generated a tsunami with a maximum recorded wave height of 8.2 m and damaged a First Nations village on the opposite side of the inlet. A fine-scale numerical model using high-resolution seafloor topography and detailed slide-volume characteristics has been initiated to better assess the generation, propagation, and along-channel impacts of tsunami waves that may have resulted from the Douglas Channel slope failures. The findings will provide important information needed to manage the potential impacts of any future event and to support the safe and sustainable development of the region.