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David Graham, Loughborough University (United Kingdom)
Darrel Swift, Sheffield University (United Kingdom)
Nicholas Midgley, Nottingham Trent University (United Kingdom)
Simon Cook, University of Aberystwyth (United Kingdom)
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Evidence is presented for the englacial transport of significant quantities of basal debris at two temperate glaciers in southeast Iceland. The ablation areas of both glaciers are fed by steep ice falls and exhibit strong transverse-arcuate foliation. Near the terminus, this foliation is intimately associated with laterally extensive upglacier-dipping debris-rich ice layers that comprise traction zone debris and a significant quantity of rounded and well-rounded striated clasts. Glacier-bed overdeepenings support basal ice formation by glaciohydraulic supercooling at the terminus of both glaciers; however, the distribution of the debris layers, the close association with arcuate foliation, the high calibre of the rounded debris, and the abundance of striations on rounded debris, all indicate that the englacial structures were formed by the active incorporation of basal ice and debris upglacier of the reverse slope of the overdeepening. The englacial structures are therefore most likely to have been formed by folding and/or thrusting at the base of the icefall and/or against the reverse slope of the overdeepening. Nevertheless, the origin of the rounded debris remains unclear. The results of structural and sedimentological investigations of debris layer and proglacial sediment properties are presented that demonstrate the longevity and importance of these structures in the glacial sediment budget and highlight some of the problems associated with their origin.
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