Ice stream shear margin moraines

The distribution and pattern of subglacial bedforms provides valuable insights into the configuration and behaviour of former ice sheets and recent work has begun to address the landform assemblages of palaeo-ice streams. In this paper, we focus on subglacially formed ice stream shear margin moraines; these landforms are thought to form in the shear zone between fast-flowing stream-ice and slow-moving sheet-ice. Using satellite imagery and aerial photographs, we identify four ice stream shear margin moraines associated with the former M'Clintock Channel Palaeo-Ice Stream, Victoria Island, Arctic Canada, The moraines range in length from I I to 22 km, maintain fairly constant widths of around 500 in, and range in height from 10 to 50 m above the surrounding terrain. They are composed of carbonate drift of a similar composition as the ice stream bedforms and have been laid down irrespective of local and regional topography. Two of the moraines display a lateral offset and are thought to reflect minor migrations of the ice stream margin. We explore their possible mode of formation and suggest that they occur when erosion at the ice stream margin provides a surplus of sediment which is 'smeared out' in the downstream direction. The identification of other palaeo-ice stream shear margin moraines has probably been hampered by their interrupted continuity which can only be appreciated at the large scale. It is hoped that the descriptions presented in this paper will help to identify these landforms and increased detection of palaeo-ice streams will reveal other ice stream shear margin moraines. Copyright (C) 2002 John Wiley Sons, Ltd.