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Erosion of Grooves by Subglacial Melt-Water Streams

Abstract The shape of the former Laurentide ice sheet in what is now northern Ohio and southern Ontario is calculated and the subglacial hydrological potential field computed. Subglacial water flow is found to be concentrated over high points in the bed, such as what is now Kelleys Island in Lake Erie. Some 1010 litres of subglacial melt water per year passed over Kelleys Island. It is argued that the “glacial” grooves on Kelleys Island are subglacial melt-water channels. Assuming that the subglacial melt water attained saturation with respect to CaCO3, in passing over the limestone of Kelleys Island, the material formerly occupying the grooves could have been dissolved in 102 years. This is a much shorter time than glacier occupancy and the assumption of chemical equilibrium is not critical. The features on Kelleys Island are fluted valleys about 6 m across and each flute is about 0.1 m in width. Each flute represents a subglacial channel but only one or two of these channels operated at any one time. Blockages, perhaps caused by basal debris, caused the rivers to make minor course changes and in many instances it is possible to determine the order of channel occupancy. The channels were striated after abandonment by water when moving basal debris or debris-laden ice occupied the channels. From the Gauckler-Manning formula and the potential gradient obtained from the ice-sheet model the river velocity is calculated to be about 4 m s–1, in rough agreement with the water flux calculated earlier. The grooves support the concept that subglacial water flows in “Nye” channels, and raise the suggestion that subglacial erosion by solution is of widespread importance.