Landslides, stratigraphy, and surficial geology of the Hydraulic map sheet (NTS 93A/12) British Columbia, Canada




Bichler, Ahren Johannes

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The landslides, stratigraphy, and surficial geology of the Hydraulic map sheet (NTS 93A/12), located in the interior of British Columbia, were examined. The research centred on landslide processes within the upper Quesnel River valley. It consists of three major components, each conducted at a different scale. At the smallest scale, surficial geological mapping was conducted at a scale of 1:50 000. Three hundred and twenty eight terrain polygons were identified, of which 32% were verified by fieldwork. Polygons containing morainal sediment as its primary surficial material make up 86% of the surficial area. Glaciofluvial and colluvial sediments, confined to the major valleys, are also important units. Glaciolacustrine sediment was rarely identified as the primary sediment but underlies all glaciofluvial terraces within the valleys. Bi-directional ice flow indicators show a strong northwest-southeast orientation while limited uni-directional data indicate flow to the northwest. The medium scale part of the project was a stratigraphic assessment of sediment within the Quesnel and Cariboo River valleys and the description of landslide processes. Twenty four natural exposures were investigated, including nine landslides. Nine stratigraphic units were identified, of which only three are actively involved in modem landslide processes. Advance-phase glaciolacustrine sediment, of the Fraser Glaciation, hosts two styles of failure: I) long-lived, flow dominated failures that occur as a series of smaller events and 2) short-lived, rapid, slide dominated failures. A third style of landsliding was recognized within an upper clay unit and Fraser till. These landslides are short-lived, rapid events that are the most fluid-like failures found within the region. The largest scale research was a detailed site investigation of a landslide using a variety of geophysical methods. Ground penetrating radar techniques offered detailed information on the upper 20 m of surficial material including the internal structure of individual units as well as the ability to image the surface of rupture and the surface of separation. Direct current electrical resistivity and seismic surveys yielded data on the geometries of the stratigraphic units to depths of 40 m and 80 m respectively. Direct current electrical resistivity was further able to image the surfaces of rupture and separation based on the juxtaposition of stratigraphic units. Through the integration of geophysical data with stratigraphy and digital terrain models a three-dimensional structural model of the landslide was created.



landslides, geology, British Columbia