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Whalebacks are convex landforms created by the smoothing of bedrock by glacial processes. Their formation is attributed to glacial abrasion either by bodies of subglacial sediment sliding over bedrock or by individual clasts contained within ice. This paper reports field measurements of sediment depth around two whaleback landforms in order to investigate the relationship between glacigenic deposits and whaleback formation. The study site, at Lago Tranquilo in Chilean Patagonia, is situated within the Last Glacial Maximum (LGM) ice limits. The two whalebacks are separated by intervening depressions in which sediment depths are generally 0.2 to 0.3 m. Two facies occur on and around the whalebacks. These facies are: (1) angular gravel found only on the surface of the whalebacks, interpreted as bedrock fracturing in response to unloading of the rock following pressure release after ice recession, and (2) sandy boulder-gravel in the sediment-filled depressions between the two whalebacks, interpreted as an ice-marginal deposit, with a mixture of sediment types including basal glacial and glaciofluvial sediment. Since the whalebacks have heavily abraded and striated surfaces but are surrounded by only a patchy and discontinuous layer of sediment, the implication is that surface abrasion of the whalebacks was achieved primarily by clasts entrained in basal ice, not by subglacial till sliding. [ABSTRACT FROM AUTHOR]

Basal ice samples were collected from ice exposures in a natural subglacial cavity beneath an outlet glacier of Øksfjordjøkelen, North Norway. Sediment and cation (Ca2+, Mg2+, Na+, K+) concentrations were then determined, and indicate stacking of basal ice units producing a repeat pattern of 'clean firnification ice' overlying sedimentrich ice. All measured cations show correlation with sediment concentration indicating weathering reactions to be the dominant contributor of cations. Regressions of specific sediment surface area per unit volume with cation concentration are performed and used to predict cation concentrations. These predicted values provide an indication of cation relocation within the basal ice sequence. The results suggest limited melting and refreezing resulting in the relocation of predominantly monovalent cations downward through the profile. Exchange of cations into solution during the melting of sediment-rich ice samples has previously been suggested as a source of error in such investigations. Analyses of sediment-free regelation ice spicules formed at the bed show cation concentrations above firnification ice levels and comparable, in many instances, to the basal ice samples. [ABSTRACT FROM AUTHOR]