Several valleys on the southern slopes of the western Uinta Mountains exhibit stepped erosional profiles.These profiles consist of tall, steep, cliffs (~10m high) separated by low relief areas, which are often occupied by lakes.Directly opposite these valleys, on the northern slopes of the range, the profiles are quite different.Here, the terrain is less steep with intermittent short cliffs (~1m) separating broad, low relief areas.I propose that the difference in morphology between these areas is a direct result of the contrasting angles at which the bedding planes intersect the valley floor.To test this hypothesis, I examined three pairs of valleys, each to the north and south of an LGM local ice divide, and made up of quartzite beds dipping ~5⁰NW.In the south valleys, this results in beds dipping up-valley, while in the north they dip down-valley.I hypothesize that this makes south valley more susceptible to erosion by quarrying because the opposing angle of the bedding makes the valley floor more prone to cavities.In contrast, the north valley is more prone to abrasion, since the ice generally slides along the bedding planes, abrading the surfaces.Field observations and GIS analysis show a prevalence of steep cliff features in the south and low-slope polished surfaces in the north; features that support the dominance of quarrying and abrasion respectively.Furthermore, I use a numerical model of glacial erosion to examine the roles of spatial variability of resistance to erosion and bedding slope on an idealized environment, with results showing that the slope of weaker beds with respect to the ground surface has an effect on the resulting morphology.
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Influence of structural variability on glacially-eroded steps, Uinta Mountains, UT
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