The role of tectonism in the distribution, appearance and dynamic behaviour of debris-rich basal ice

The aim of this thesis is to examine the role of tectonic deformation upon various aspects of the debris-rich basal ice layer (BIL). These include the distribution, composition and dynamic behaviour of the BIL. Although the potential influence of tectonic deformation has been acknowledged since the end of the last century, little work has subsequently been focused towards this aim.Three main field sites were selected for detailed investigation in order to examine the influence of tectonic deformation in a variety of different glaciological settings. In chronological order of study these included: the Matanuska Glacier, Alaska; Skeiðarárjökull, southern Ireland, and; the Russell Glacier, south-west Greenland.At each field site, a variety of study sites were selected and subjected to detailed and systematic observation. In particular, the thickness and composition of the BIL was noted, along with the presence of any tectonic structures. In addition, a series of sedimentological techniques were applied to the basal ice under examination, including: classification and logging of the facies present, debris-concentration analysis, particle-size analysis, clast fabric analysis and shape and roundness analyses. Finally, two attempts were made to collect quantitative movement data from the BIL. This was finally successful at the Russell Glacier.The results of this study show the influence of tectonic deformation upon the BIL to be both prevalent and profound in nature. Work at Skeiðarárjökull in particular showed tectonic processes to be highly influential in affecting the spatial distribution of the BIL, whilst observation at the Russell Glacier suggested that tectonic deformation may have a profound influence upon the facies composition of the BIL. As a result, a tectonic model of facies evolution was devised which relies on only two processes, to explain the observed facies variability, namely initial entrainment and subsequent tectonism. The quantitative dataset obtained at the Russell Glacier showed basal sliding to be the dominant dynamic mechanism in operation. Comparatively little deformation was therefore accommodated within the BIL itself.It is therefore argued that the distribution and appearance of debris-rich basal ice is a function not only of the formational processes in operation, but also of the tectonic processes that have subsequently affected that ice. Further work is required to ascertain the effect basal ice may have on glacier dynamics.