Thrusting and debris entrainment in a surging glacier: Bakaninbreen, Svalbard

Abstract

Bakaninbreen, a 17 km long glacier terminating in fjord waters in central Spitsbergen (77°45′ N, 17°20′E), began to surge between the springs of 1985 and 1986. By summer 1994 the surge front had reached a position 3 km from the terminus and had almost ceased propagation. Structural investigations were undertaken to characterise the tectonic evolution of this thermally complex surge-type glacier, and the role played by thrusting and its effect on debris entrainment. Much of the glacier surface, particularly within and below the surge front, displayed transverse high-angle thrusts, defined by discrete fractures bounded by coarse clear ice. Some fractures were associated with a film of mud, whereas in others a discrete laver of diamicton, with interstitial ice several decimetres thick, was evident. Within the surge front, and genetically related to the thrusts, was a number of shear zones several metres wide. These were defined by fine-grained ice that was the product of the grinding up of crystals during shear (mylonitization). Three main sedimentary facies are associated with the thrusts: mud, gravelly mud and clast-rich muddy diamicton. The diamicton has the character of basal glacial debris: grain-size distribution ranging from clay to cobble size, clasts with a predominance in the sub-angular and sub-rounded classes, and striated and faceted clasts. Hot-water drilling through the glacier revealed several englacial layers above the surge front, and debris brought up on the drill stem suggests a basal origin. At least some of these englacial layers are probably the sub-surface continuations of the thrusts. The observed facies indicate that the glacier is moving over a soft, deformable bed and that thrusting is an important process in transferring debris to the surface, especially when the surge front is propagating down-glacier.

Ice-cored moraine degradation mapped and quantified using an unmanned aerial vehicle: A case study from a polythermal glacier in Svalbard

“…Evans, 2009) ('hummocky moraine') in relation to the stacking of englacial material along thrusts planes (e.g. Hambrey et al, 1996;1997;Bennett et al, 1998;Graham, 2002;Midgley et al, 2007). The processes described in these papers may, in part, be responsible for areas of surface hummocks…”

Structural glaciology of Austre Brøggerbreen, northwest Svalbard

“…The upwards migration of equilibrium lines and pronounced surface lowering of glaciers in Svalbard have revealed the internal structure of many ice masses in unprecedented detail. Recent structural glaciological research in Svalbard has primarily focused on structural controls on entrainment and transport of debris in polythermal and cold-based glaciers (Bennett, Hambrey, Huddart, & Ghienne, 1996;Boulton, van der Meer, Beets, Hart, & Ruegg, 1999;Hambrey & Glasser, 2003;Hambrey, Dowdeswell, Murray, & Porter, 1996;Hambrey, Bennett, Dowdeswell, Glasser, & Huddart, 1999;Hambrey et al, 2005;Hubbard, Glasser, Hambrey, & Etienne, 2004;Lovell et al, 2015). The map described in this paper documents the glacier-wide structural characteristics of Austre Brøggerbreen, a cold-based valley glacier in Svalbard.…”

Late Holocene palaeoceanography in Van Mijenfjorden, Svalbard

“…This is inferred from findings of strandlines and laminated lacustrine silts up to 22 m above current sea level, suggesting a lake with a volume of approximately 0.8 km 3 . A trunk of the PGS, Bakaninbreen (Bakanin Glacier), surged recently (1985)(1986)(1987)(1988)(1989)(1990), but the surge front failed to reach the tidewater terminus (Hambrey et al 1996).…”