Factors affecting distribution of landslides along rivers in southern Alberta

Abstract

A regional study of the distribution and characteristics of landslides along four major rivers in southern Alberta was undertaken in order to relate landslide activity to geologic and physiographic factors such as bedrock outcrop, groundwater, river sinuosity, and the aspect of valley slope. This provides greater insight into the factors controlling slides in the study region, particularly in the Cretaceous bedrock.The study was based on an analysis of air photos, augmented by surficial and bedrock geologic maps and hydrogeologic and bedrock topographic maps. The area is underlain by a thick sequence of gently dipping sedimentary strata of Upper Cretaceous age. Late Pleistocene glaciation deranged the drainage to some extent and the rivers studied now occupy postglacial channels in some reaches and are re-excavating preglacial channels in other reaches.The results of the study indicate that the bedrock type is of considerable importance since there is marked difference in valley wall stability between relatively unstable marine formations and the relatively stable nonmarine formations. Areas of comparatively high groundwater exert an obvious influence on landsliding. The importance of buried valleys in locally drawing down the water table is clearly evident. More than 90% of the landslides occur in meander bends and are related to river erosion.Failures in the bedrock appear to be translational whereas those higher on the valley wall in Pleistocene sediments are largely rotational. The data have been assembled on a profile of the river and present a regional picture of landslide activity over a large area.