| Popis: |
The last British Ice Sheet has been a focus of research for over a century, and yet we have only a generalised picture of its extent and internal geometry. This is a remarkable situation compared to knowledge of the larger former ice sheets of North America and Fennoscandia. The central tenet of this thesis is that the glacial landform record has been neglected as a source of spatial information, hindering our attempts to reconstruct the characteristics of the ice sheet. This motivated systematic mapping of glacial landforms (subglacial bedforms, moraines, eskers, and meltwater channels) for the whole of Britain, yielding the first consistent and countrywide glacial maps. Mapping was achieved primarily using a high resolution (5 m horizontal) digital elevation model to visualise the landscape. Over 60,000 features were identified and mapped, greatly expanding the known distribution and pattern of glacial landforms. Analysis of the landform data permitted a country-wide reconstruction of the pattern of ice sheet retreat. A database of just over 400 dates, compiled from the literature, was used to arrange the pattern of retreat in time. This exercise highlighted various incompatibilities between the presently available dates. Examination of landform patterns enabled the elucidation of some pre-deglacial configurations of ice divides and flow geometry, including ice streams. This revealed the existence of both transient (migrating) and persistent ice divides. In contrast to other and larger palaeo-ice sheets, the majority of flow evidence in Britain exhibits a particularly close association with topography, indicative of an ice sheet thickness comparable with the amplitude of subglacial relief. The retreat pattern, flow geometries and divide configurations that have been identified from this research provide a set of evidence-based constraints at ice sheet scale for future numerical ice sheet modelling experiments. |
