Subglacial drainage by groundwater-channel coupling,and the origin of esker systems: Part 1—glaciological observations |
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| Institution: | 1. British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK;2. British Geological Survey, West Mains Road, Edinburgh, EH9 3LA, UK;1. Department of Geography, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada;2. Department of Geography, University of Calgary, 2500 University Drive, Calgary, AB, T2N 1N4, Canada;1. Department of Earth and Environmental Sciences, University of Waterloo, Ontario N2L 3G1, Canada;2. National Research Institute of Astronomy and Geophysics, Helwan, Cairo, Egypt;1. CAGE - Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geosciences, UiT the Arctic University of Norway, 9037, Tromsø, Norway;2. Department of Geography and Earth Science, Aberystwyth University, Wales, SY23 3DB, UK;3. Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, 10964, USA;4. Department of Geological Sciences, Stockholm University, Stockholm, 106 91, Sweden;1. Department of Geography, Durham University, Durham DH1 3LE, UK;2. Department of Geography, University of the Fraser Valley, Abbotsford, B.C., Canada;3. Department of Geography, University of Sheffield, UK;4. Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA, USA |
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| Abstract: | OverallThis work is presented in two parts. Part I presents observations on the coupling between subglacial channel flow and groundwater flow in determining subglacial hydraulic regime and creating eskers from an Icelandic glacier that is suggested as an analogue for many parts of Pleistocene ice sheets. Part II develops a theory of perennial subglacial stream flow and the origin of esker systems, and models the evolution of the subglacial stream system and associated groundwater flow in a glacier of the type described in Part I. It is suggested that groundwater flow may be the predominant mechanism whereby meltwater at the glacier bed finds its way to the major subglacial streams that discharge water to glacier margins.Part IBoreholes drilled through an Icelandic glacier into an underlying till and aquifer system have been used to measure variations in head in the vicinity of a perennial subglacial stream tunnel during late summer and early winter. They reveal a subglacial groundwater catchment that is drained by a subglacial stream along its axis. The stream tunnel is characterised by low water pressures, and acts as a drain for the groundwater catchment, so that groundwater flow is predominantly transverse to ice flow, towards the channel.These perennial streams flow both in summer and winter. Their portals have lain along the same axes for the 5 km of retreat that has occurred since the end of the Little Ice Age, 100 years ago, suggesting that the groundwater catchments have been relatively stable for at least this period. In the winter season, stream discharges are largely derived from basal melting, but during summer, water derived from the glacier surface finds its way, via fractures and moulins, to the glacier bed, where it dominates the meltwater flux. Additional subglacial streams are created in summer to help drain this greater flux from beneath the glacier, through poorly integrated and unstable networks. Summer streams cease to flow during winter and tend not to form in the same places in the following summer. Perennial streams are the stable component of the system and are the main sources of extensive esker systems.Strong flow of groundwater towards low-pressure areas along channels and the ice margin is a source of major upwelling that can produce sediment liquefaction and instability. A theory is developed to show how this could have a major effect on subglacial sedimentary processes. |
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