The origin and significance of debris‐charged ridges at the surface of storglaciären, northern sweden

Abstract

Storglaciären is a 3.2 km long polythermal valley glacier in northern Sweden. Since 1994 a number of small (1–2 m high) transverse debris‐charged ridges have emerged at the ice surface in the terminal zone of the glacier. This paper presents the results of a combined structural glaciological, isotopic, sedimentological and ground‐penetrating radar (GPR) study of the terminal area of the glacier with the aim of understanding the evolution of these debris‐charged ridges, features which are typical of many polythermal glaciers. The ridges originate from steeply dipping (50–70°) curvilinear fractures on the glacier surface. Here, the fractures contain bands of sediment‐rich ice between 0.2 and 0.4 m thick composed of sandy gravel and diamicton, interpreted as glaciofluvial and basal glacial material, respectively. Structural mapping of the glacier from aerial photography demonstrates that the curvilinear fractures cannot be traced up‐glacier into pre‐existing structures visible at the glacier surface such as crevasses or crevasse traces. These curvilinear fractures are therefore interpreted as new features formed near the glacier snout. Ice adjacent to these fractures shows complex folding, partly defined by variations in ice facies, and partly by disseminated sediment. The isotopic composition (δ18O) of both coarse‐clear and coarse‐bubbly glacier ice facies is similar to the isotopic composition of the interstitial ice in debris layers that forms the debris‐charged ridges, implying that none of these facies have undergone any significant isotopic fractionation by the incomplete freezing of available water. The GPR survey shows strong internal reflections within the ice beneath the debris‐charged ridges, interpreted as debris layers within the glacier. Overall, the morphology and distribution of the fractures indicate an origin by compressional glaciotectonics near the snout, either at the thermal boundary, where active temperate glacier ice is being thrust over cold stagnant ice near the snout, or as a result of large‐scale recumbent folding in the glacier. Further work is required to elucidate the precise role of each of these mechanisms in elevating the basal glacial and glaciofluvial material to the ice surface.

Dye tracing to determine flow properties of hydrocarbon-polluted Rabots glaciär, Kebnekaise, Sweden

“…Throughflow velocities range from 0.04 to 0.28 m s −1 for the glacier-based experiments (Table 2), which fall within the range of values previously inferred from experiments on Storglaciären (Seaberg et al, 1988;Hock and Hooke, 1993). A threshold of 0.2 m s −1 is proposed by Theakstone and Knudsen (1981) and Nienow (2011) to distinguish between fast and slow flow.…”

“…Dye tracing has been applied successfully in the alpine environment in several studies and has contributed substantially to understanding of subglacial drainage systems, for example, Storglaciären in the Kebnekaise mountains in northern Sweden (e.g. Seaberg et al, 1988;Hock and Hooke, 1993), glaciers in the European Alps (e.g. Nienow et al, 1998), the High Artic (e.g.…”

“…Stenborg, 1965Stenborg, , 1973Nilsson and Sundblad, 1975;Schytt, 1981;Holmlund, 1988;Jansson, 1996;Schneider, 1999;Glasser et al, 2003, Fountain et al, 2005, and an understanding of its hydrological system has been extremely limited until now. The majority of dye tracing experiments in moulins on Storglaciären have been conducted in the lower ablation zone below a riegel in the bedrock topography (e.g.…”

“…The majority of dye tracing experiments in moulins on Storglaciären have been conducted in the lower ablation zone below a riegel in the bedrock topography (e.g. Seaberg et al, 1988;Hock and Hooke, 1993;Kohler, 1995), as the overdeepened trough upstream of the riegel results in a largely englacial drainage system Pohjola, 1994;Fountain et al, 2005) and an absence of surface meltwater input points. Dye tracing experiments conducted in crevasses, moulins or boreholes at elevations above the riegel on Storglaciären have thus been limited and produced very attenuated, or, in some cases, no dye return Jansson, 1996).…”

Structural composition and sediment transfer in a composite cirque glacier: Glacier de St. Sorlin, France

“…The processes leading to medial moraine formation at Glacier de St. Sorlin have been identified in studies of other warm-based Alpine glaciers (Goodsell et al, 2005;Small, 1987), and at polythermal Arctic glaciers of a similar size (Glasser et al, , 2003. Glacier de St. Sorlin can be considered 'debris poor'.…”