Evidence for and reconstruction of a Nahanagan Stade glacier at Croloughan Lough, Derryveagh Mountains, Co. Donegal

Abstract:Some characteristics of a large arcuate ridge of granite boulders at Croloughan Lough, Derryveagh Mountains, Co. Donegal, and the adjacent terrain are outlined, and possible origins for the ridge are discussed. The ridge does not conform to generally accepted criteria for classification as a protalus rampart or protalus rock glacier. Certain characteristics suggest the ridge may be a product of rock-slope failure, but others do not support this hypothesis. Several lines of evidence point towards a glacial origin, and it is inferred that the ridge is the end moraine of a small glacier that developed at the site during the Nahanagan Stade (11–10ka 14C BP). A map-based reconstruction of the glacier indicates it had a small surface area (0.15km2), an equilibrium line altitude of 325m OD and an accumulation area ratio of 43%. The glacier was probably nourished in part by snow blown from the plateau above and to the south of the site. The ridge and adjacent area provide the first recorded evidence for occurrence of a Nahanagan Stade glacier in the Donegal highlands.