The last glaciation of Aran Island and Cruit Island, Co. Donegal, north-west Ireland

Abstract:This paper describes geomorphological and sedimentary evidence from Aran Island and Cruit Island (County Donegal, north-west Ireland), informed by evidence from across west Donegal, which helps to show the processes of ice advance and retreat and subglacial conditions during the last (late Midlandian) glaciation. Extensive abraded rock surfaces show clear evidence for ice overtopping of the islands. Erosional landforms include striae, flutes developed in bedrock, whalebacks, roches mountonnées and meltwater channels. Depositional landforms include erratic boulders and a single marginal moraine on Aran Island. Glacial or glacially-influenced sediment deposition that does not have a geomorphic expression took place into bedrock hollows during an ice advance stage, probably around the time of the last glacial maximum. The dominance of erosional signatures likely reflects the stripping by ice of a surficial cover of weathered pre-glacial granite debris. The general absence of subglacial and ice-marginal sediments across the region likely reflects the granite substrate and coarse granitic weathering products, which did not favour development of a thick deformable sediment pile.