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ENGINEERING GEOLOGY, ELECTRICAL RESISTIVITY TOMOGRAPHY AND DISPLACEMENT MONITORING OF THE DAWSON CITY LANDSLIDE,YUKON.
Session: Landslides and Slope Stability V / Mouvements de terrain et stabilité des pentes V
Marc-Andre Brideau, BGC Engineering Inc. (Canada)
Alexandre Bevington, BC Ministry of Forests, Lands and Natural Resources Operations (Canada)
Antoni Lewkowicz, University of Ottawa (Canada)
Doug Stead, Simon Fraser University (Canada)
The Dawson City landslide is a pre-historic slope failure located at the northern city limit of Dawson City, Yukon. The landslide occurred at the faulted contact between an older ultramafic rock unit that is thrust on top of a younger metasedimentary rock unit. The fault damage zone results in the very blocky nature (five main discontinuity sets) of the failed rock mass and led to an initial pseudo-circular slope failure mechanism. The landslide deposit is composed dominantly of ultramafic rocks. A series of split trees, disturbed soil exposing stretched roots, and trenches, all indicate movement in both the headscarp and deposit. Monitoring since 2006 confirms annual surface displacement rates in these areas in the cm to decimetre range. A 200 m long electrical resistivity tomography profile conducted in the lower part of the deposit is interpreted as a thick active layer over permafrost, suggesting that ongoing deformation is due to the creep of permafrost containing ground ice. As such, the lower part of the landslide can be regarded as a rock glacier.
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