The thermal regime of sub-polar glaciers mapped by multi-frequency radio-echo sounding

Helgi Björnsson*, Yngvar Gjessing, Svein Erik Hamran, Jon Ove Hagen, Olav Liestøl, Finnur Pálsson, Björn Erlingsson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

200 Citations (Scopus)

Abstract

Radio-echo soundings provide an effective tool for mapping the thermal regimes of polythermal glaciers on a regional scale. Radar signals of 320-370 MHz penetrate ice at sub-freezing temperatures but are reflected from the top of layers of ice which are at the melting point and contain water. Radar signals of 5-20 MHz, on the other hand, see through both the cold and the temperate ice down to the glacier bed. Radio-echo soundings at these frequencies have been used to investigate the thermal regimes of four polythermal glaciers in Svalbard: Kongsvegen, Uvérsbreen, Midre Lovénbreen and Austre Brøggerbreen. In the ablation area of Kongsvegen, a cold surface layer (50-160m thick) was underlain by a warm basal layer which is advected from the temperate accumulation area. The surface ablation of this cold layer may be compensated by freezing at its lower cold-temperate interface. This requires that the free water content in the ice at the freezing interface is about 1 % of the volume. The cold surface layer is thicker beneath medial moraines and where cold-based hanging glaciers enter the main ice stream. On Uvérsbreen the thermal regime was similar to that of Kongsvegen. A temperate hole was found in the otherwise cold surface layer of the ablation area in a surface depression between Kongsvegen and Uvérsbreen where meltwater accumulates during the summer (near the subglacial lake Setevatnet, 250 m a.s.l.). Lovénbreen was frozen to the bed at the snout and along all the mountain slopes but beneath the central part of the glacier a warm basal layer (up to 50m thick) was fed by temperate ice from two cirques. On Austre Brøggerbreen, a temperate basal layer was not detected by radio-echo soundings but the basal ice was observed to be at the melting point in two boreholes.

Original languageEnglish
Pages (from-to)23-32
Number of pages10
JournalJournal of Glaciology
Volume42
Issue number140
DOIs
Publication statusPublished - 1996

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