Quantification of sediment transport during glacier surges and its impact on landform architecture

Category Sedimentology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Kjوr, Kurt H.۱; Korsgaard, Niels J.۱; Benediktsson, Ivar ضrn۲; Schomacker, Anders۲
Holding Date 11 October 2008

Multi-temporal DEMs (Digital Elevation Models) of glaciers and ice streams have successfully been used for extraction of changes in ice volume over time. In this study, we analysed DEMs of the Brúarjökull glacier forefield for 1945, prior to the last surge in 1964, and for 2003 in order to assess the effect of the surge on the sediment architecture in the forefield. The pre- and post-surge DEMs allow direct quantification of the sediment volumes that were re-distributed in the forefield by the surging ice mass in 1964.
The surge-type Brúarjökull has experienced six surges during the last four centuries; these are the largest surges known to have occurred in Iceland with the most recent surge event in 1963-64. During this surge, the glacier advanced 8 km over a period of c. 3 months with a maximum ice flow velocity of 5 m/hr, and 700 km3 of ice and firn were moved downglacier. The continued recession of Brúarjökull since the 1963/64 surge reveals a young landscape consisting of widely spaced and elongated bedrock hills interspaced with shallow sedimentary basins. The majority of the forefield is covered with a basal till sheet or glaciofluvial outwash fans.
Mapping of the sediment thickness in the glacier forefield shows higher accumulation along ice marginal positions related to wedge formation during extremely rapid ice flow, which was sustained by overpressuried water causing decoupling beneath a thick sediment sequence that was coupled to the glacier. Elevation differences between the terrain surface in 1945 and 2003 confirm this scenario as huge quantities of sediment was eroded, deformed and transported during surge events. On the scale of individual landforms, it appears for a drumlin surface that is has been lowered 20 m from 1945-2003. Dead-ice melting can explain roughly 8 m of this lowering. Thus, the drumlin must have experienced 12 m of subglacial erosion during the 1964 surge.
The imprint of at least four landform generations is seen on the present terrain surface. The simplest landscape architecture occurs outside the 1810 ice margin, where the 1890 surge advanced over hitherto undeformed sediments. Proximal to the 1810 ice margin, the landscape have been transgressed by two overriding glaciers (in 1890 and 1964). The most complex landscape architecture is found proximal to the 1964 ice margin, where the impact of four surges is evident. Thus, the landscape at Brúarjökull is a product of multiple generations of superimposed landforms associated with extensive sediment transport through subglacial deformation.