Sediment fingerprinting and the mode of formation of singular and composite annual moraine ridges at two glacier margins, Jotunheimen, southern Norway

Abstract

Sedimentary variation within and between annual moraine ridges formed at Storbreen and Styggedalsbreen, Jotunheimen, during the 1980s and 1990s is investigated with a focus on processes and mechanisms of moraine-ridge formation. Tops and bottoms of sediment slabs, deposited either as single annual moraines or incorporated into composite moraine ridges formed of several annual increments, were analysed and compared with possible source sediments with a view to sediment fingerprinting. Clast roundness and shape indicated mainly subglacial sediment origins while textural variability was mainly inherited from proglacial sediment sources, and macrofabrics and micromorphological characteristics revealed overprinting by various glaciofluvial, glaciolacustrine and periglacial processes. The evidence suggests one dominant mechanism of moraine-ridge formation involving the annual freeze-on and subsequent melt-out of overridden proglacial sediment slabs. This mechanism provides the basis of a simple model encompassing both singular and composite annual moraine-ridge formation, which appears appropriate for temperate glacier snouts characterized by deep seasonally frozen ground, close to the lower altitudinal limit of the zone of alpine permafrost.

Sub-annual moraine formation at an active temperate Icelandic glacier

“…Worsley, 1974;Birnie, 1977;Matthews et al, 1979;Sharp, 1984;Chandler et al, 2016a), while moraines formed by submarginal freeze-on have internal sedimentary architectures characterized by distinct sediment slabs (cf. Krüger, 1993Krüger, , 1995Krüger, , 1996Matthews et al, 1995;Evans and Hiemstra, 2005;Reinardy et al, 2013;Hiemstra et al, 2015;Chandler et al, 2016a). These characteristics are not apparent in moraine FJA-06.…”

“…Annual moraines have been reported by numerous researchers (e.g. Thórarinsson, 1967;Worsley, 1974;Karlén and Denton, 1975;Gordon and Timmis, 1992;Schomacker et al, 2012;Hiemstra et al, 2015;Luckman, 2017), but detailed insights into linkages between annual moraine-forming processes and glaciological, environmental and other boundary conditions remain relatively limited (e.g. Sharp, 1984;Boulton, 1986;Krüger, 1995;Evans and Hiemstra, 2005;Lukas, 2012;Reinardy et al, 2013;Chandler et al, 2016a;Wyshnytzky, 2017).…”

Spatial distribution of cold-ice within a temperate glacier – implications for glacier dynamics, sediment transport and foreland geomorphology

“…Basal freeze-on occurs particularly during winter when liquid water content at the bed is diminished and energy production through friction and internal deformation is reduced. Sediments are entrained at the base of the glacier snout and then melt out during the ablation season (Sharp, 1984;Krüger, 1993;1995;1996;Matthews et al, 1995;Krüger et al, 2002;15 Bradwell, 2004;Evans and Hiemstra, 2005;Winkler and Matthews, 2010;Reinardy et al, 2013;Hiemstra et al, 2015). This growing body of evidence suggests that cold-ice processes within primarily temperate-glacier systems may influence marginal depositional processes and landforms.…”

Very low inheritance in cosmogenic surface exposure ages of glacial deposits: A field experiment from two Norwegian glacier forelands

“…Their lower marginal zones, however, experience seasonal freezing onto the substrate (Hiemstra et al, 2015;Winkler and Matthews, 2010b) and discontinuous permafrost exists in their headwall rock faces (Hipp et al, 2014).…”

“…Austanbotnbreen has not been monitored but terrain age is reasonably well known as recent reference points are provided by recessional moraines inferred to have been deposited in c. AD 1930 and 2000 by analogy with neighbouring Jotunheimen glaciers (cf. Hiemstra et al, 2015;Matthews and Winkler, 2011;Winkler and Matthews, 2010b).…”