Origin of overdeepened bedrock basins and valleys in ice sheet settings

Understanding the controls on focused glacial erosion is important given its impact on ice sheet development and dynamics. Previous work has assumed that large glacial erosional landforms such as troughs and overdeepenings are morphologically distinct from glaciofluvial landforms such as tunnel valleys. However, there are many examples of large-scale glacial bedrock incisions (channelised glacioerosional bedrock landform (CGBL)) that are difficult to categorise as either glacial or subglacial-fluvial, and process-based morphological criteria for distinguishing between the two are lacking. This thesis presents the findings of a semi-automated GIS-based morphological analysis of both the long- and cross-profiles of CGBL features identified in foreland or foreland-like settings. The thesis identifies over 13,900 individual bedrock CGBLs and analyses changes in average cross-sectional morphologies of CGBL features in four main study regions (northern Switzerland; Finger Lakes; Humboldt glacier; and British Columbia) against erosional end-member examples (glacial, subaerial fluvial, and subglacial fluvial). Changes in cross sectional morphology are further analysed along features in relation to changes in bed slope and the regional context (e.g. bedrock erodibility, faulting, topographic confinement) in Northern Switzerland and the Finger Lakes. The results show that CGBL features are found across most currently and previously glaciated foreland-settings, and that these have average cross-sectional morphologies that range from subaerial fluvial eroded V-shaped to glacially eroded U-shaped. The results also show that CGBL development is highly influenced by the bed slope morphology and regional contextual factors. The major conclusion is that CGBL features such as “overdeepenings” and “tunnel valleys” are part of a continuum of features which form from both glacial and subglacial fluvial erosive processes, and that the relative level of influence of these processes are highly influenced by a wide range of contextual factors including geology and topography.