Modeling the subglacial hydrology of the James Lobe of the Laurentide Ice Sheet |
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| Institution: | 1. Department of Geosciences, Oregon State University, Corvallis, OR 97331, USA;2. WERI, University of Guam, Mangilao, GU 96923, USA;1. Yale University, Department of Geology and Geophysics, PO Box 208109, New Haven, CT 06520-8109, USA;2. University of Maryland, Department of Geology, College Park, MD 20742, USA;1. LHyGeS, Université de Strasbourg/EOST – CNRS, 1 rue Blessig, F-67000 Strasbourg, France;2. CEA-Laboratoire de Modélisation des Transferts dans l’Environnement, Bât. 225, F-13108 Saint Paul lez Durance cedex, France;1. Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA;2. Mathematics and Geoscience, 181 Smeal Building, Penn State DuBois, College Place, DuBois, PA 15801, USA;3. Department of Geosciences, 517 Deike Building, Pennsylvania State University, University Park, PA 16802, USA;4. Goddard Earth Sciences Technology and Research (GESTAR), USA;5. Cryospheric Sciences Laboratory, Mail Code 615, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA;1. Department of Geography and Earth Sciences, Aberystwyth University, Wales SY23 3DB, UK;2. School of Geography, University of Leeds, LS2 9JT, UK;3. SUERC, East Kilbride, UK;4. Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK;5. Department of Geosciences, Hamilton College, Clinton, NY 13323, USA;1. Key Laboratory of Engineering Geomechanics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. University of Chinese Academy of Sciences, 100049 Beijing, China |
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| Abstract: | To investigate the drainage conditions that might be expected to develop beneath soft-bedded ice sheets, we modeled the subglacial hydrology of the James Lobe of the Laurentide Ice Sheet from Hudson Bay to the Missouri River. Simulations suggest the James Lobe had little effect on regional groundwater flow because the poorly conductive Upper-Cretaceous shale that occupies the upper layer of the bedrock would have functioned as a regional aquitard. This implies that general northward groundwater flow out of the Williston Basin has likely persisted throughout the Quaternary. Moreover, the simulations indicate that the regional aquifer system could not have drained even the minimum amount of basal meltwater that might have been produced from at the glacier bed. Therefore, excess drainage must have occurred by some sort of channelized drainage network at the ice–till interface. Using a regional groundwater model to determine the hydraulic conductivity for an equivalent porous medium in a 1-m thick zone between the ice and underlying sediment, and assuming conduit dimensions from previous theoretical work, we use a theoretical karst aquifer analog as a heuristic approach to estimate the spacing of subglacial conduits that would have been required at the ice–till interface to evacuate the minimum water flux. Results suggest that for conduits assumed to be on the order of a tenth of a meter deep and up to a meter wide, inter-conduit spacing must be on the order of tens–hundreds of meters apart to maintain basal water pressures below the ice overburden pressure while evacuating the hypothesized minimum meltwater flux. |
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