| Summary: | The riverbanks within the upper reaches of the Moose River estuary have been analysed to determine their stratigraphy, geotechnical properties and stability. Rotational slumps, translational slides, block falls and earth flows are the forms of mass movement identified within the study area. Rotational slumps are the most common failure type and are particularly concentrated along the north mainland banks characterized by a basal glaciomarine unit (Tyrrell Sea clay) overlain by a thick silt unit and capped by a thin organic soil layer. The rotational slumps commonly occur in the spring and are associated with the sensitive basal stratigraphic unit (Tyrrell Sea clay). The tidal inundation and exposure of the clay twice a day encourages instability by promoting cracking which weakens the unit. Undercutting by the river flow and the scouring by river ice during spring breakup further destabilizes the bank. Coupled with an increase in pore-water pressure during snowmelt (thereby decreasing the shear strength of the sediment), and the rapid drawdown effect following the spring freshet, particularly after an ice jam, a loss of sediment strength and change in support by the river results, and large-scale failures occur.
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