Multiscale analysis of the landforms and sediments of palaeo-ice streams.

Abstract

Ice streams play a fundamental role in the stability and dynamics of ice sheets. They are defined by their rapid flow and this is enabled by conditions and processes at the icebed interface. A significant limitation to our understanding of this environment is that most studies, of both contemporary and palaeo-ice streams, have focussed on only one or two, discrete spatial scales of analysis and so integration between scales is restricted. This thesis investigates palaeo-ice streams at multiple scales in order to examine their subglacial processes and characteristics, and to assess the links between and the application of different spatial scales of analysis. Seven palaeo-ice streams from the British and Laurentide ice sheets were investigated at the macroscale, which involved geomorphological mapping, spatial analysis of subglacial lineations and examination of bed characteristics. Two ice streams were also investigated at smaller scales, which included sedimentological analysis (mesoscale) and micromorphological analysis (microscale). Macroscale results showed that subglacial lineations display certain spatial characteristics, including: clustering according to elongation ratio; distribution of low elongation ratios throughout the ice streams; and a decrease in maximum elongation ratio towards the ice stream lateral margins. The latter of which is considered to reflect the transverse distribution of ice velocity. In some cases, a decline in subglacial lineation concentration and elongation ratio coincided with topographic obstacles at the ice stream bed. The most common bed characteristics identified were: widespread till, fine grained sedimentary bedrock with a moderate permeability, low relief and a flat topographic curvature. Key subglacial processes identified included deformation, which was observed at all three scales, and high pore water pressures, for which multiple lines of evidence were found at the meso and micro scales. Spatial variability in both strain and pore water pressure was also common. The multiscale approach allowed robust interpretations of fast flow mechanisms, which furthers knowledge of the sediment and landform characteristics that may result from these flow mechanisms. A summary of the processes that can be identified at each of the spatial scales is given