ABSTRACT: ~Hydrogeomorphic hazards in northern British Columbia.

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Abstract

The varied and remote landscape of northern British Columbia (BC) is largely unstudied in terms of Quaternary history and geomorphology. This thesis is a compilation of a series of recent studies of this landscape’s geomorphic hazards. The thesis focuses on various aspects of landslides and outburst floods, and considers the influence of climate change on hazard regimes. Chapter 2 provides an overview of large catastrophic landslides in the period 1973 to 2003. The landslides are grouped into three categories – rock, soil, and rock and soil. Catastrophic landslides have increased from an average of 1.3 landslides per year between 1973 and 2003 to 2.3 landslides per year in the last decade of the study period, suggesting a link to climate change. Chapters 3 and 4 are case studies of individual long runout landslides. Chapter 3 gives a very detailed description of a landslide involving quick clays in glaciomarine sediment. Zones within the landslide are distinguished on the basis of morphology, and inferred direction and style of movement. The wet antecedent climatic conditions associated with the landslide are considered in the context of prehistoric landslides during a wet climatic period and future climate change scenarios. A wetter projected future climate suggests more landslides can be expected in the decades to come. Chapter 4 is a case study of a 2 km long rock slide – debris avalanche. The slide occurred on the limb of an anticline with significant preslide deformation. The initial rock slide impacted and entrained fine grained soil that resulted in a thin distal spreading of debris. The main landslide runout was modelled using Voellmy and Bingham rheologies. While Voellmy rheologies are well-suited for modelling most rock avalanches, the fine texture of the entrained debris resulted in Bingham flow. Chapters 5 and 6 have to do with glacier and landslide dams, respectively. Chapter 5 is a study of jökulhlaups (glacial outburst floods) from a glacier in northwestern BC. The study shows how self-dumping glacial lakes have developed out of phase with each other in response to glacier thinning and retreat. A partial record of the last century demonstrates that the lakes go through a jökulhlaup cycle of growth and decay. The study implies that more lakes may form and drain catastrophically as glaciers continue to retreat under a projected warming future climate. Chapter 6 provides a 1000 year record of landslides and landslide dams from a watershed in northeastern BC. AMS radiocarbon dating of wood in landslide debris, and from drowned forests buried in deltaic sediment in former landslide dammed lakes, is used to date the events. The limited 1000 year record suggests that older records are removed from the small watershed by erosion and mass transport. Chapter 7 considers the impacts of the landslide, as a natural disturbance agent, on biophysical diversity. Landslides increase diversity by changing site, soil, and vegetation conditions, setting back the ecological clock, and providing important habitat for a variety of organisms. The final chapter provides a synthesis of the previous chapters, and briefly considers the changing landscape of northern BC already being impacted by forest insect epidemics, increasing the susceptibility to forest fire and landslides. Under a predicted warmer and wetter future climate landslides and glacial outburst floods are expected to continue to increase.

Bibliography of Canadian Geomorphology