Subglacial bedforms of the Irish ice sheet

Abstract

The last Irish Ice Sheet has a long history of investigation, but its most basic properties are still debated. A palaeo-glaciological 'inversion' of the glacial geomorphological record has elsewhere proven an effective means to reconstruct former ice sheets at ice sheet scale. To this end, this paper describes new glacial geomorphological mapping of the Irish landscape, using Digital Elevation Models, Landsat ETM+ and SPOT satellite images, with the objective of achieving a thorough and systematic documentation of the form, spatial distribution and arrangement of glacial landforms in Ireland. A resulting map, presented here at a scale of 1:425,000, identifies ~33,000 subglacial bedforms. Glacial lineations (drumlins, mega-scale glacial lineations and crag and tails) and ribbed moraine comprise the bulk of the bedform population, although a wide spectrum of bedform types, shapes and sizes is observed. In particular, a suite of enigmatic bedforms were mapped which were not classified either as streamlined lineations or transverse ridges; rather, they are quasi-circular in form. This map is the first to document the subglacial bedform record of Ireland at the scale of individual landforms, and countrywide. In so doing, it reveals the extent and complexity of superimposed and cross-cutting bedform relationships, which demand an ice sheet reconstruction depicting marked changes in ice sheet geometry, conffguration and behaviour through its evolution. This map forms the basis for a palaeo-glaciological reconstruction which addresses and attempts to incorporate the complexity of ice ow history revealed by the subglacial bedforms of Ireland.