A preliminary assessment of the occurrence of submarine slope failures in coastal British Columbia by analysis of swath multibeam bathymetric data collected 2001-2011

Abstract

An inventory of submarine slope instability features has been compiled for coastal areas of British Columbia based on morphologic analysis of regional multibeam bathymetric data. The slope instability features are classified as submarine slides, debris flows, rock avalanches and associated features including fan deltas, sediment cones and channel complexes. In addition, the study provides an initial assessment of the size and distribution of these geohazards, with a particular focus on identifying large features that are the result of a single failure event because these would have the greatest potential to generate a damaging tsunami. Submarine landslide deposits have been identified in all fjords and inlets examined including Bute, Knight, Toba and Jervis Inlets and Howe Sound. Douglas Channel, Kitimat Arm and Alberni Inlets also have significant landslide derived sediment bodies on the margin and floors of these inlets. In the Strait of Georgia extensive failures have been identified along the Fraser River delta and on slopes where sediment accretion has occurred in the Holocene, including spits and other coastal landforms. The locus of nearly all submarine slope failures in Juan de Fuca Strait has been along the edge of a terrace landform associated with sea level lowstand. Whereas the age of some features can be tentatively inferred by association with modern or postglacial morphology, the exact age of the instability features documented in this study cannot be determined from this morphologic analysis alone. The accompanying ArcGIS document allows each instability feature to be located and queried for information such as morphologic classification, surface area, possible age, and other details.