Mount Meager, a glaciated volcano in a changing cryosphere : hazards and risk challenges

Abstract : Mount Meager is a glacier-clad volcanic complex in British Columbia, Canada. It is known for its landslides, of which the 2010 is the largest Canadian historical landslide. In this thesis we investigated slope instability processes at Mount Meager volcano and the effects of ongoing deglaciation. We used a variety of methods including field and remote, geological, geomorphological and structural mapping to characterize glacial and landslide activity at Mount Meager. We used Structure from Motion photogrammetry (SfM) and Lidar to produce digital surface models and InSAR to monitor slope deformation. We applied SfM to historic photography to document glacier and landslide activity at Mount Meager. We discussed a model of growth and erosion of a volcano in glacial and interglacial periods, and the scientific and dissemination value of historic 3D topographic reconstruction. We described the 2010 Mount Meager landslide deposit to interpret emplacement dynamics and kinematics. The 2010 landslide separated in water-rich and water-poor phases that had different runout and distinct deposits. We analyzed historic airphotos to constrain the slope deformation prior to the 2010 collapse. The glacier near the toe of the slope retreated in the failure lead up, the collapse evolved in four subfailures involving the whole volcanic sequence and some basement rocks. We estimated 6 × 106 m3 of water in the slope, that allowed the separation of the frontal water-rich phase. The total failure volume was 53 ± 3.8 × 106 m3. We identified 27 large (>5×105 m2) unstable slopes at Mount Meager and calculated ~1.3 km3 of ice loss since 1987. The west flank of Plinth peak and Devastation Creek valley moved up to -34±10 mm and -36±10 mm, respectively, over a 24-day period during the summer of 2016. The failure of these slopes could impact infrastructures and communities downstream of the volcano. The resulting decompression on the volcanic edifice after the failure of Plinth peak would affect the stress field to a depth of 6 km and up to 4 MPa. This sudden decompression could lead to hydrothermal or magmatic eruptions.
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Gioachino Roberti. Mount Meager, a glaciated volcano in a changing cryosphere : hazards and risk challenges. Earth Sciences. Université Clermont Auvergne, 2018. English. ⟨NNT : 2018CLFAC040⟩. ⟨tel-02010551⟩

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