FLUTE-FORMING CONDITIONS IN ALBERTA AND NORTH DAKOTA: A COMPARISON USING ICE SHEET RECONSTRUCTIONS AND FIELD TECHNIQUES

The morphologically similar Saskatchewan Glacier Valley in Alberta, Canada, and the Kiwa Glacier Valley in British Columbia, Canada, were compared using field and laboratory techniques, to determine why glacial flutes were developed in the former and not the latter. Using similar techniques, these areas were then compared to an area of continental ice sheet flutes northwest of the Martin Moraine in north-central North Dakota. By applying the equations of existing glacier longitudinal profile lines to a terminus downvalley from the Saskatchewan and Kiwa Glaciers, and using mathematical approximations for equations of former glacier longitudinal profile lines when ice was at the Martin Moraine position in North Dakota, former glacier surfaces could be reconstructed. After subtracting the elevation of the land surface from that of the reconstructed glacier surface, and calculating former ice surface slope, resulting ice thickness and basal shear stress distribution plots were possible. Results show basal shear stress values, representing the minimum strength of sediment during flute formation, range from zero to more than 35 kPa for Saskatchewan Glacier reconstructions, and zero to more than 2 kPa for Martin Moraine reconstructions. Data for the Saskatchewan Glacier and Martin Lobe seem reasonable but differences in valley morphology between the existing Kiwa Glacier and the downvalley terminus result in questionable ice thickness and basal shear stress plots. Approximation of sediment strength using Coulomb's equation, and observation of the similarity in reconstructed ice thickness for the Saskatchewan and North Dakota studies, indicate the development of porewater pressure is crucial for flute formation. Sediment texture and the location of flutes on a topographic high, downglacier from a proglacial lake basin, allowed high porewater pressures to develop as glaciers extended to terminus positions. Lack of flutes in the Kiwa Glacier area is attributed to the absence of a similar topographic high.