Bedrock controls on subglacial landform distribution and geomorphological processes : evidence from the Late Devensian Irish Sea Ice Stream

Ice streams play an important role as regulators of the behaviour of modern ice sheets, taking the form of corridors of fast flowing ice. Similar zones of fast moving ice have also been recognised draining the margins of the Late Devensian British and Irish Ice Sheet. Although the geomorphological and sedimentary signatures of palaeo ice streams have received significant attention, allowing the identification of these former ice streams, the influence of bedrock geology on the processes occurring beneath these palaeo ice streams is less well understood, even though subglacial geology has been shown to control the location ice streams within the West Antarctic Ice Steam. This paper highlights the role played by bedrock geology on landform distribution beneath a much older ice stream, the Late Devensian Irish Sea Ice Stream. The spatial relationships displayed between subglacial landforms and bedrock geology are described from Anglesey, northwest Wales, and the Rhins of Galloway, southwest Scotland; both sites occur close to the eastern margin of this Irish Sea Ice Stream. A link has been established between landform morphology and distribution, and the disposition of the main tectonostratigraphical units within the bedrock. Changes in landform morphology are shown to have been locally controlled by large-scale faults and/or major lithological boundaries, with less durable bedrock lithologies controlling the location and lateral extent of relatively faster flowing portions of the ice stream.