Patterns and Controls of Cross-section Morphology for the Glaciated Bow River Valley, Canadian Rockies

Glaciers are powerful agents of erosion that can broaden and deepen valley floors, steepen valley sides and enhance local relief. The objective of this research is to analyze downvalley patterns in valley cross-section profiles in the Canadian Rocky Mountains to infer information about controls on glacial valley genesis. This study focuses on the Bow River valley, located on the east side of the Great Divide in the Canadian Rockies. The valley is mainly situated parallel to overall geologic structure, with some valley locations oriented perpendicular to structure. The last glacial advance to affect the area was late-Pleistocene. Eleven valley cross-sections along the Bow River valley were extracted from a 30m DEM for analysis. Cross- sections were analysed using different mathematical models: (i) power law; (ii) quadratic; and (iii) variable width/depth ratio. As the shape of the valley in the present day is influenced by post-glacial filling, we also defined best-fit equations that estimate the erosional form, rather than the present day valley, by fitting equations for cross-sections to data points restricted to the valley sides. Equations were thus extrapolated below the surface deposits of the valley floor to estimate the depth of valley fill. No strong downvalley trend in steepness for the valley sidewalls is visible in the data, although two groups are evident; one group for cross-sections with steep valley walls and one for those with less steep valley walls. There is a possible decreasing trend in valley width in the downvalley direction, although the signal is weak. When cross-section data were analyzed in relation to geological structure, cross-sections oriented perpendicular to structure are found to be steeper and narrower than those which are not. This finding suggests a strong preconditioning on the cross-section form by geological structure. When the best-fit equations were extrapolated below the surface deposits to estimate the depth of valley fill, the strength of the best-fit curves is increased. Using this approach, maximum depths of valley fill up to order 100m were defined. Additional field studies will help determine the accuracy of valley fill estimates made in this manner.