Transverse englacial debris-rich ice bands at Kvíárjökull, southeast Iceland

Abstract

Thick exposures of debris-rich ice at various Icelandic glaciers are central to the debate over the prevalence of glacial sediment transfer by glaciohydraulic supercooling. We present physical analyses of ice and debris at Kvíárjökull, a temperate glacier in southeast Iceland with a terminal glacier-bed overdeepening, where stratified debris-rich ice forms up to metre-thick transverse englacial bands. Our results are not consistent with debris-rich ice formation predominantly by supercooling because: (1) 137Cs was absent from sediment filtered from debris-rich ice; (2) isotopic analysis ( δD and δ 18O) demonstrated no clear pattern of isotopic enrichment of debris-rich ice with respect to englacial ice; and (3) melt-out debris from debris-rich ice included large striated clasts from both fluvial and basal sources. We support transverse englacial debris-rich ice band formation by the thickening and elevation of basal materials in a region of longitudinally compressive ice flow situated between the reverse slope of the overdeepening and the base of an ice fall. Debris band form and distribution are likely to be controlled by thrusting along transverse englacial foliae associated with the formation of band ogives on the glacier surface.