Formation and reorientation of structure in the surge‐type glacier Kongsvegen, Svalbard

Abstract

Kongsvegen, a surge-type glacier in Spitsbergen, Svalbard, shares a tide-water margin with the glacier Kronebreen. The complex has been in retreat since a surge advance of Kongsvegen around 1948. The surface of Kongsvegen displays suites of deformational structures highlighted by debris-rich folia. These structures are melting out to form a network of sediment ridges in the grounded terminal area. The structures are also visible in a marginal, 1 km long, 5-20 m high cliff-face at the terminus. Current models for the evolution of deformational structures at Kongsvegen divide the structures into suites based on their orientation and dip, before assigning a mechanism for genesis based on structure geometry. Interpretation of aerial photographs and field mapping of surface structures suggest that many structures were reorientated or advected during the surge. We suggest that many of the deformational structures highlighted by debris-rich folia represent reorientated, sediment-filled crevasses. Some evidence of thrusting is apparent but the process is not as ubiquitous as previously suggested. Many deformational structures also appear to have been offset by more recent structures. Mechanisms of structural development must, therefore, be considered within the context of distinct stages of glacier flow dynamics and multiple surge episodes. Furthermore, evidence for thrusting and folding within the glacier systems of Svalbard has been used as the basis for interpreting Quaternary glacial landforms in the UK. The findings of this paper, therefore, have implications for interpretations of the Quaternary record.

Debris entrainment and landform genesis during tidewater glacier surges

“…These include crevasse squeeze structures that formed during a previous surge and have then been slowly reoriented in a down-ice direction during the quiescent phase Woodward et al, 2002]. Such inclined till-filled structures present a favorably oriented slip plane that can be exploited during a subsequent surge by TSD [Rea and Evans, 2011], particularly under conditions of very high basal water pressures that force the fracture open and allow the injection of water and saturated debris.…”

“…This material is then exposed during the quiescent phase as characteristic landformsediment assemblages or surge landsystems [cf., Rea, 1999, 2005]. Sediment is also exposed within the ice as englacial debris inclusions or bands [e.g., Glasser et al, 1998;Woodward et al, 2002], hereafter referred to as debris-rich englacial structures. Better understanding of the links between surging, debris entrainment, and geomorphology is important as it can help to provide an insight into processes acting at the bed [Christoffersen et al, 2005;Larsen et al, 2006].…”

“…Two main mechanisms have been proposed for the origin of upglacier-dipping structures: (1) debris-bearing thrust faults originating from the bed in a zone of longitudinal compression [e.g., Hambrey and Dowdeswell, 1997;Glasser et al, 1998;Lønne, 2006;Larsen et al, 2010] and (2) the deformation of structures initially formed as vertical crevasse squeezes, which are then reoriented in a down-ice direction during quiescent phase ice flow. This forms a favorably inclined slip plane along which thrust-style displacement (TSD) can occur during a subsequent surge Woodward et al, 2002;Rea and Evans, 2011]. In all cases, formation is related to tectonic processes active during surges and the availability of soft, deformable basal material.…”

‘A test of the englacial thrusting hypothesis of “hummocky” moraine formation: case studies from the northwest Highlands, Scotland’: Comments

“…In his review of models of moraine formation, Lukas cited Woodward et al (2002; who questioned the significance of thrusting in debris elevation in Svalbard glaciers based on observations at Kongsvegen, Svalbard. However, he failed to acknowledge that this work has been severely criticised by Glasser et al (2003) for misrepresenting earlier structural-glaciological work, for over-interpreting the nature of changing flow dynamics from aerial photographs, and for presenting no new data to support their alternative hypothesis (injection of saturated sediment into basal crevasses).…”

Glacier ice structures influence on moraines developement (Hørbye glacier, Central Spitsbergen)

“…In the fi rst one material derives from the substrateare incorporated by folding and thrusting mechanism (Woodward et al, 2002).…”