Age and origin of ice-cored moraines in Jotunheimen and Breheimen, southern Norway: insights from Schmidt-hammer exposure-age dating

Abstract

2014. Age and origin of ice-cored moraines In Jotunheimen and Breheimen, Southern Norway: insights from Schmidt-Hammer exposure-age dating.ABSTRACT. High-precision Schmidt-hammer exposureage dating (SHD) is applied to ice-cored moraine-ridge complexes at three high-alpine glaciers in Jotunheimen and Breheimen, southern Norway. Local calibration curves were established using moraine ridges dating from the last 50 years and bedrock surfaces deglaciated ∼9700 years ago. SHD ages, with 95% statistical confidence intervals, ranged from 3920 ± 790 years to a negative (futuristic) age of -890 ± 580 years at Gråsubreen, 420 ± 700 to 260 ± 710 years at Vesle-Juvbreen and 2250 ± 450 to 1605 ± 410 years at Østre Tundradalskyrkjabreen. Negatively skewed R-value distributions were interpreted as the result of weathered boulders from reworked surfaces. This leads to the interpretation of these SHD ages as maximum estimates of moraine-ridge age. Østrem's hypothesis (that the proximal ridges are the oldest and survived being overridden many times) is rejected on the basis of our SHD ages. Although ice-cored moraine ridges resemble the flow structures of rock glaciers, Barsch's hypothesis (that these icecored moraine complexes are rock glaciers) is also rejected. Instead, the ice-cored moraine-ridge complexes are considered to be glaciotectonic structures produced by the interaction of polythermal glaciers and alpine permafrost over the late Holocene. All the individual ridges were essentially formed during the 'Little Ice Age' glacier advance from material deposited earlier by multiple neoglacial events. The considerable size of the moraine complexes is attributed not only to the accumulation of material from these different events over a long period of time but also to their survival in the landscape during phases of glacier retreat when ice cores do not melt and fluvial and other destructive processes remain ineffective in the permafrost environment.

Internal Structure and Current Evolution of Very Small Debris-Covered Glacier Systems Located in Alpine Permafrost Environments

“…These so-called push moraines are very common at the cold glacier margins in permafrost environments (Etzelmüller and Hagen, 2005;Matthews et al, 2014;Dusik et al, 2015). As it currently occurs in the study sites (Figures 6B, 7), differential flow and ablation induce the progressive disconnection between rock glaciers and the upslope glacier zones in negative mass balance periods (Ackert, 1998;Ribolini et al, 2010;Lilleøren et al, 2013).…”

“…The genesis of the studied systems has to be considered in light of the numerous Holocene climatic oscillations, although their current structures are mainly related to the last glacial pulse (LIA and subsequent decay; Ackert, 1998;Matthews et al, 2014;Monnier et al, 2014). Indeed, the extent of both glacier and debris-covered zones probably continuously oscillated over the last millennia in relation to climatic variations (e.g., IvyOchs et al, 2009).…”

Improved Schmidt-hammer exposure ages for active and relict pronival ramparts in southern Norway, and their palaeoenvironmental implications

“…The equations used for age calibration, including the calculation of 95% confidence intervals around predicted SHD ages, are as follows (see also Matthews et al, 2014). The calibration equation is a standard linear regression equation of the form:…”

“…As SHD age reflects the average age of the surface boulders (cf. Matthews et al, 2014), it provides information on: (1) the status of ramparts that are currently active, (2) a maximum age estimate for the time elapsed since the stabilisation of relict ramparts, and (3) a minimum age estimate for the time elapsed since the beginning of rampart development.…”

Glacier change from the early Little Ice Age to 2005 in the Torngat Mountains, northern Labrador, Canada

“…Oversized moraines in front of small cirque glaciers found in Scandinavia have been interpreted as being ice-cored based on their unique morphometry, showing a distinct change in curvature and elevation relative to the adjacent glacier (e.g., Lilleøren and Etzelmüller, 2011;Lilleøren et al, 2013;Østrem, 1964, 1971. In Norway, for example, the elevation of local ice-cored moraines has been interpreted as the height of the former glacier surface during the LIA (Matthews et al, 2014). Ice-cored moraines, and the frequently encountered ice-cored debris fields, are classified as controlled moraines that are indicative of permafrost being present in the ice-marginal zone (e.g., Evans, 2009;Sollid and Sørbel, 1988).…”