The geomorphology and sedimentology of eskers in north-central Ireland

Abstract

Abstract Eskers are common glacial landforms in Ireland and form regionally-extensive networks that reflect stages of ice retreat of this sector of the late Devensian (Weichselian) British–Irish ice sheet. However, the sedimentary structures and composition of these eskers are poorly known, despite being able to offer valuable insight into subglacial hydrological processes during deglaciation. This study presents detailed morphological and sedimentary evidence from six esker systems in north-central Ireland, where adjacent and interacting ice domes were characterized by changes in ice-bed thermal and hydrological properties as well as significant ice dome centre migration. Morphologically, esker ridges in this area vary in length, size and continuity, with some esker systems ascending over hills (thus crossing watersheds) whereas other systems are confined to basin settings. Esker systems commonly appear to feed terminal outwash and glaciolacustrine deltas, but several systems do not show a clear terminus. The internal sediments within eskers vary from concentrically-bedded sands and gravels formed within enclosed tunnels, to interbedded sands, gravels and diamictons, occasionally with water-induced soft-sediment deformations, that are likely formed in interlobate settings. In contrast with some previous glacier models that assume that esker systems are isochronous and were formed in solely subglacial settings, the esker systems described here are interpreted as being of different ages, formed in variously subglacial to ice-marginal settings, and thus cannot be used as a single snapshot of the disposition of ice domes during stages of late Devensian ice retreat.