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

Abstract

Robserson, S. (2008). Structural composition and sediment transfer in a composite cirque glacier: Glacier de St. Sorlin, France. Earth Surface Processes and Landforms 33(13), 1931-1947This paper considers the links between structure, sediment transport and sediment delivery at Glacier de St. Sorlin, France. Sediment transported by the glacier is concentrated at flow-unit boundaries as medial moraines, controlled by the position of bedrock outcrops in the accumulation area. Rockfall entrained within primary stratification is tightly folded at flow-unit boundaries under high cumulative strains and laterally compressive stress. High cumulative strains and laterally compressive stresses lead to the development of longitudinal foliation from primary stratification. Folding elevates subglacial sediments into foliation-parallel debris ridges, which are exposed in the ablation area. Crevasses and shear planes within the glacier have little control on sediment transport. Debris stripes in the proglacial area are morphologically similar to foliation-parallel debris ridges; however, they are not structurally controlled, but formed by fluvial erosion. The conclusion of this study is that at Glacier de St. Sorlin proglacial sediment-landform associations are subjected to intense syn- and post-depositional modification by high melt-water discharges, hence their composition does not reflect that of sediments melting out at the terminus. The action of melt water limits the potential of the sedimentary record to be used to constrain numerical models of past glacier dynamics in debris-poor glacierized Alpine catchments. Copyright ? 2008 John Wiley & Sons, Ltd.Peer reviewe

Structural glaciology of a temperate maritime glacier: lower fox glacier, new zealand

“…They appear to originate close to the bed of the glacier and are interpreted as thrust planes formed by longitudinal compression near the snout, along reactivated crevasse traces. Ice crystals within these thrust planes (Table 1) appear to be indicative of the dynamic recrystallization of large crystals under shear as outlined by Roberson (2008). In some instances, the thrust planes are debris-rich, and although direct observation of thrusting was not observed, the thrusts do appear to form topographic 'steps' on the ice surface ( Fig.…”

Application of borehole optical televiewing to investigating the 3-D structure of glaciers: implications for the formation of longitudinal debris ridges, midre Lovénbreen, Svalbard

“…8b) indicative of vertical displacement along the plane (Hudleston, 1989); (2) they are composed of fine-grained bubble-rich ice, indicative of dynamic recrystallization (C. Wilson and B. Marmo, http://web.earthsci.unimelb.edu.au/wilson/ice1; and (3) the vertical displacement of up-glacier ice units relative to down-glacier ice units indicates that the ice is subject to high compressive stresses parallel to the ice-flow vector (Souchez, 1967;Rees and Arnold, 2007). Structurally, S 3 shear planes are similar to arcuate fractures identified in the terminal zone of other valley glaciers (Hambrey and others, 1996;others, 1998, 2003;Roberson, 2008), where it has frequently been suggested that compressive brittle failure is facilitated by pre-existing structural weaknesses, for example strongly anisotropic crystal fabrics or rotated fractures (Nye, 1952;Weiss and Schulson, 2000).…”

Former dynamic behaviour of a cold-based valley glacier on Svalbard revealed by basal ice and structural glaciology investigations

“…Similar to Roberson (2008) and Roberson and Hubbard (2010), S 2 arcuate fracture traces are interpreted as shear planes based on the evidence that: (1) they cut across S 0 /S 1 layering at low angles and in places displace it vertically, and (2) the fine material within S 2 has a strong linear component (Fig. 9d), or stretching lineation (Fleming and others, 2013), indicative of shear in the direction of ice flow (Table 2; Fig.…”