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CGG-02 Subglacial environments: Processes, sediments, landforms, modelling and experiments
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Instantaneous end moraine and sediment wedge formation during the 1890 glacier surge of Brúarjökull, Iceland
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Ívar Örn Benediktsson, University of Iceland (Iceland)
Per Moller, Lund University (Sweden)
Olafur Ingolfsson, University of Iceland (Iceland)
Jaap van der Meer, Queen Mary University of London (United Kingdom)
Kurt H Kjćr, University of Copenhagen (Denmark)
Johannes Krüger, University of Copenhagen (Denmark)
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The lack of data on landsystem evolution and sedimentary environments has hitherto hampered our contemporary understanding of the behaviour of surging glaciers and ice streams. This study on the ice-marginal environment of the surge-type Brúarjökull in Iceland provides us with new information about subglacial and ice-marginal processes operating during a surge. During the 1890 surge, Brúarjökull advanced 10 km in 3-4 months with flow rates of 100-120 m/day. The interaction between this very dynamic ice and sediment/landform associations is highlighted by a detailed investigation on the sediment distribution in the glacier forefield, as well as the morphology, sedimentology and tectonic architecture of the 1890 end moraine.
As a result of substrate/bedrock decoupling during the 1890 surge, subglacial sediment was dislocated across the bedrock surface and deformed compressively, leading to gradual substrate thickening and the formation of a sediment wedge in the marginal zone. A drop in subglacial porewater pressure at the very end of the surge led to coupling at the substrate/bedrock interface and a stress transfer up into the sediment sequence, causing it to deform in brittle manner. The moraine-ridge formation was initiated by the plough of the glacier toe into the topmost part of the marginal sediment wedge. Fine-grained and incompetent sediment deformed in ductile manner, resulting in a narrow moraine dominated by rooted folds, while coarse-grained and competent sediment deformed in brittle fashion, resulting in a wider, thrust-block dominated moraine. A new sequential model illustrates the stepwise formation of a surging-glacier marginal sediment wedge and an instantaneous end moraine - a twofold, inseparable marginal end-product formed during the last ∼5 days of the 1890 surge.
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