An ice-sheet scale comparison of eskers with modelled subglacial drainage routes

Stephen J Livingstone,Robert D Storrar,John K Hillier,Chris R Stokes,Chris D Clark,Lev Tarasov

doi:10.1016/j.geomorph.2015.06.016

Abstract

Eskers record the signature of channelised meltwater drainage during deglaciation providing vital information on the nature and evolution of subglacial drainage. In this paper, we compare the spatial pattern of eskers beneath the former Laurentide Ice Sheet with subglacial drainage routes diagnosed at discrete time intervals from the results of a numerical ice-sheet model. Perhaps surprisingly, we show that eskers predominantly occur in regions where modelled subglacial water flow is low. Eskers and modelled subglacial drainage routes were found to typically match over distances of <10km, and most eskers show a better agreement with the routes close to the ice margin just prior to deglaciation. This supports a time-transgressive esker pattern, with formation in short (<10km) segments of conduit close behind a retreating ice margin, and probably associated with thin, stagnant or sluggish ice. Esker-forming conduits were probably dominated by supraglacially fed meltwater inputs. We also show that modelled subglacial drainage routes containing the largest concentrations of meltwater show a close correlation with palaeo-ice stream locations. The paucity of eskers along the terrestrial portion of these palaeo-ice streams and meltwater routes is probably because of the prevalence of distributed drainage and the high erosion potential of fast-flowing ice.

Highlights

Eskers are slightly sinuous ridges composed of glaciofluvial sand and gravel that are deposited in subglacial, englacial, or supraglacial drainage channels (e.g., Banerjee and McDonald, 1975; Brennand, 2000; Storrar et al, 2014a)
In this study our aim is to compare the expression of eskers on the bed of the former Laurentide Ice Sheet (LIS) with subglacial drainage routes predicted from the results of a numerical ice sheet model
We explore a new approach that compares the expression of eskers beneath the former LIS with subglacial drainage routes predicted from the results of a numerical ice-sheet model at specific time steps during deglaciation

Summary

Introduction

Eskers are slightly sinuous ridges composed of glaciofluvial sand and gravel that are deposited in subglacial, englacial, or supraglacial drainage channels (e.g., Banerjee and McDonald, 1975; Brennand, 2000; Storrar et al, 2014a) They can extend for tens to hundreds of kilometres (taking into account small gaps), reach in excess of 50 m in height, and are typically arranged roughly parallel to each other (e.g., Prest et al, 1968; Banerjee and McDonald, 1975; Shilts, 1984; Shreve, 1985a,b; Aylsworth and Shilts, 1989; Clark and Walder, 1994; Boulton et al, 2009; Storrar et al, 2014a,b). Because of the difficulties in directly observing the drainage of water at the bed of ice masses, we have a limited understanding of the distribution and geometry of the subglacial drainage network and a lack of data at the spatial and temporal scales necessary to constrain or test subglacial hydrological models (e.g., Hewitt, 2011; Werder et al, 2013)

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