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Sediment Transport in Dry-Based Glaciers: An Assessment of the Sedimentary Signatures Imprinted by Glacial Modification

Sarah Mager & Sean Fitzsimons
Department of Geography, University of Otago, Dunedin, New Zealand

 
Abstract

The processes of erosion and entrainment for dry-based glaciers are poorly understood.  Until recently it had been assumed that dry-based glaciers were largely incapable of basal erosion because low basal temperatures create an environment which strictly limits the availability of water and excludes or limits the possibility of sliding. However, observations in the Dry Valleys, Victoria Land, Antarctica have identified morainic ridges adjacent to small cold-based glaciers.  This paper presents data on the analysis of entrained sediment extracted from four small alpine glaciers in the Dry Valleys.  The approach of this study is to examine whether sedimentary signatures of entrained basal debris can be used to elucidate processes of debris entrainment and transportation.  

The main techniques employed in this study are particle size, shape and roundness analysis of sediments from the glacier substrate, different basal ice facies and proglacial deposits.  The results show that samples from basal ice tend to have sedimentary signatures very similar to parent characteristics with regard to roundness and shape, but there were significant differences in mean particle size and an increase in the number of modes in particle size distributions.  These characteristics suggest that some crushing of the entrained debris may have occurred.  However, the absence of more angular particles in the basal ice is not consistent with this interpretation.  An alternative interpretation is that increased modality of the particle size distributions has been caused by abrasion and that a "textural maturity" in roundness and shape is achieved very quickly over a short transport path.  Samples from blocks of sediment entrained in basal ice which retained their parent sedimentary and bedding structures were also analysed.  In some instances "tails" of material extended downstream from sediment blocks.  Examination of these "tails" revealed no significant change in clast shape or roundness with increasing distance from the source.  There was, however, a decrease in mean particle size and an increase in the number of modes within the particle size distributions.

 
Reference

Mager, S. 1996. Sediment transport in dry-based glaciers : an assessment of sedimentary signatures imprinted by glacial transportation. Unpublished BSc (hons) dissertation, in Geography, at the University of Otago, Dunedin, New Zealand. 78 pp.

Mager, S. and Fitzsimons, S. 2001. Sediment transport in dry-based glaciers: an assessment of the sedimentary signatures imprinted by glacial modification [Abstract]. Presented at: 2001 Geography A Spatial Odyssey, Joint Conference of the New Zealand Geographical Society and the Institute of Australian Geographers in Dunedin, in February 2001.

© 2009 Department of Geography, University of Otago, Dunedin, New Zealand