Author : Johnson, A.L. Date : 2003. Title : -Snow Avalanche Impact Landform Geomorphology in the Southern Canadian Cordillera. Publication : Unpublished MSc thesis. University of Victoria, Victoria. Issue : Page(s) :
Snow avalanche impact landforms (SAIL's) are typically elliptical-shaped depressions located at the base of avalanche tracks bounded by an arcuate crescent-shaped ridge. The purpose of this research was to determine the surface age and stability of SAIL's in the southern Canadian Cordillera. To achieve this, three sites were studied in detail: Blackhorn SAIL in the Central Coast Mountains, Spoon Lake SAIL in the Northern Cascade Mountains, and Peyto Lake SAIL in the southern Canadian Rocky Mountains. SAIL morphology is similar to other impact landforms, and in this study is compared with submarine plunge pools and meteorite impact craters.SAIL geomorphology is described and an explanation of the development is provided for each site. Each tells a distinct story. The geomorphology of these features is controlled by variations in topography of the avalanche track, the availability of unconsolidated debris in the impact area, and the ability of the avalanche impact pressure force to displace the available debris in the trajectory path of avalanche flow. Ground-based snow avalanches move debris by bulldozing, and airborne snow avalanches move sediment by explosion on impact. High-magnitude events that maintain SAIL form are induced by local climatic conditions. Dendrochronology and lichenometry proved to be effective techniques for dating more recent high-magnitude snow avalanche events at these sites. Evidence of long-term SAIL development (e.g., well-developed soil horizons, debris stratification) and present stability (e.g., well- vegetated, lichen abundance) was observed and supports the theory of formation through episodic, high-magnitude snow avalanche events.