On 6 August 2010, a large (~50 Mm 3) debris avalanche occurred on the flank of Mount Meager in the southern Coast Mountains of British Columbia, Can ada. We studied the deposits to infer the morphodynamics of the landslide from initiation to emplacement. Structure from motion (SfM) photogram metry, based on oblique photos taken with a standard SLR camera during a low heli copter traverse, was used to create highresolution orthophotos and base maps. Interpretation of the images and maps allowed us to recognize two main rheological phases in the debris avalanche. Just below the source area, in the valley of Capricorn Creek, the landslide separated into two phases, one waterrich and more mobile, and the other waterpoor and less mobile. The waterrich phase spread quickly, achieved high superelevation on the val ley sides, and left distal scattered deposits. The main waterpoor phase moved more slowly, did not superelevate, and formed a thick continuous deposit (up to ~30 m) on the valley floor. The waterpoor flow deposit has structural fea tures such as hummocks, brittleductile faults, and shear zones. Our study, based on a freshly emplaced deposit, advances understanding of large mass movements by showing that a single landslide can develop multiple rheol ogy phases with different behaviors. Rheological evolution and separation of phases should always be taken into account to provide better risk assessment scenarios.
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