HISTORICAL LANDSLIDE EVENTS AND LANDSLIDE SUSCEPTIBILITY MAPPING ALONG THE SEA TO SKY CORRIDOR, BRITISH COLUMBIA, CANADA

The scenic Sea to Sky Highway, road to the 2010 winter Olympics, has historically been vulnerable to landslides. More than 18% of Canada’s total landslide related deaths (>600) have occurred along this corridor. Over the last 154 years, we have counted 155 reported landslide events. The observed trend in landslide frequency has a peak period during the 1980s and 1990s at approximately 40 events per decade. The early part of the trend is heavily influenced by data censoring due to an incomplete record prior to the 1980s. This inventory documents the geographical distribution, the types, and the impacts of landslides on people and infrastructure. The most abundant types of landslides are debris flows and rock falls, which are highly concentrated in the southern part of the corridor between Horseshoe Bay and Porteau, along the coast of Howe Sound. A distribution of reported landslide events, based on the time of year, demonstrates that rock falls occur throughout the year, but are especially abundant in the fall and early winter, which could likely be linked to freeze/thaw temperature cycles. Furthermore, debris flows are more concentrated in the fall and early winter months also but do not seem to occur during the dryer seasons. Certain historical events became pivotal points in triggering adaptation measures for the Sea to Sky Corridor, namely, the M-Creek debris flow (ca. 1981) and the Just rock fall event (ca. 1982).

Subsequent to the landslide inventory and the surficial geology mapping, a landslide susceptibility mapping method was applied for the most abundant types of landslides. A qualitative parametric method was applied separately for rock falls/rock slides and debris flows because of different causal factors for each type of landslide. The objective of this study was to help reduce risk of landslides to people and infrastructure. Preliminary results indicate a good correlation with the distribution of historical events and zones of medium-high to high landslide susceptibility.