Distribution and characteristics of landslides in the Fraser River Corridor, Southwestern British Columbia, Canada

Abstract

Landslides are major drivers of landscape evolution. Mass-wasting events connect hillslope and channel processes through the downslope transferal of sediment, which can impact fluvial systems in a multitude of ways. Coarse sediment delivered into the channel can impact flow dynamics, alter river incision rates through the tools and cover effect, deflect reach-scale river alignment, and disrupt riverine ecosystems. The feedbacks between landslides, fluvial processes, and landscape evolution remain largely unexplored despite increasingly detailed landslide inventories, enabled by the availability of airborne lidar mapping and high-resolution topographic data. To better understand the nature of these feedbacks across varying lithologies, tectonic conditions and valley morphologies we explore post-glacial landslides (~14 ka to present) in the Fraser River valley in southwest British Columbia, Canada. We created a landslide inventory using existing literature and 2,560 km2 of new airborne lidar along the Fraser Canyon corridor, a 375-km stretch of the Fraser River, which flows through multiple regions with distinct climate, morphology, and geology. We documented ~300 landslides with areas between 2 x 103 and 2 x 106 m2. Failure types include translational bedrock slides, earthflows, and rock avalanches, which vary systematically with bedrock geology and valley morphometrics. We find more translational bedrock and earthflow failures in the broader, U-shaped valley of the northern Fraser River canyons, where sedimentary, metasedimentary, and volcanic bedrock are more common. Rock avalanches are more common in the southern Fraser River canyon, where valley walls are composed of plutonic and metamorphic rocks, however the southern region has fewer landslide features overall. These findings suggest individual failures and their combined impact on the post-glacial evolution of the Fraser River are sensitive to both the geologic and glacial history of a particular stretch of river.