ABSTRACT: A grove-ploughing theory for the production of mega-scale glacial lineations, and implications for ice-stream mechanics.

CGRG Bibliography of Canadian Geomorphology
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Abstract

Mega-scale lineations (MSGLs) are longitudinally aligned corrugations (ridge-groove structures 6-100 km long) in sediment produced subglacially. They are indicators of fast flow and a common signature of ice-stream beds. We develop a qualitative theory that accounts for their formation, and use numerical modeling, and observations of ice-stream beds to provide supporting evidence. ice in contact with a rough (scale of 10-103 m) bedrock surface will mimic the form of the bed. Because of flow acceleration and convergence in ice-steam onset zones, the ice-base roughness elements experience transverse strain, transforming them from irregular bumps into longitudinally aligned keels of ice protruding downwards. Where such keels slide across a soft sedimentary bed, they plough through the sediments, carving elongate grooves, and deforming material up into intervening ridges. This explains MSGLs and has important implications for ice-stream mechanics. Groove ploughing proves the means to acquire new lubricating sediment and to transport large volumes of it downstream. Keels may provide basal drag in he force budget of ice streams, thereby playing a role in flow regulation and stability. We speculate that groove ploughing permits significant ice-stream widening, thus facelifting high-magnitude ice discharge.

Bibliography of Canadian Geomorphology