Reconstructing terrestrial ice sheet retreat dynamics from hummocky topography using multiscale evidence: An example from central Ireland

The research reported here combines high-resolution digital elevation models (DEMs) derived from airborne LiDAR with ground-penetrating radar (GPR) surveys and macro-and micro-scale sedimento-logical analyses to study the geomorphology and internal structure and composition of ridges and mounds within an area of hummocky topography in the Brosna basin, central Ireland. Our evidence indicates that much of the hummocky topography consists of fragmented mega-scale glacial lineations (MSGLs) indicating a phase of accelerated ice flow, overlain by groups of small ridges composed of subglacially derived till and sediment gravity flow deposits. Subtle differences in ridge morphology indicate they may be multi-genetic and formed both ice-marginally as moraines and subglacially as small ribbed moraine. We interpret MSGL-ridge associations as a subglacial bedform continuum reflecting the evolution from a deforming bed to brittle deformation, due to changing thermal and hydrological con-ditions at the ice-bed interface during ice sheet retreat. Adjacent glaciofluvial landforms indicate initial en-and supra-glacial meltwater drainage, possibly directly related to changing basal thermal/hydro-logical characteristics and subglacial ridge formation. Subsequently a subglacial conduit system evolved, and later retreat involved formation of ice-marginal ridges. The partially preserved landsystem reflects formation at a polythermal to active temperate ice marginal zone, rather than the stagnating temperate margin previously assumed for this area. Our work demonstrates the usefulness of hummocky topog-raphy in identifying changes in ice sheet bed thermal/hydrological characteristics during deglaciation and the importance of combining multiple evidence strands in reconstructing the processes involved in glacial landform construction.(c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

This study utilizes high-resolution digital elevation models (DEMs) derived from airborne LiDAR, ground-penetrating radar (GPR) surveys, and sedimentological analyses to investigate the geomorphology and composition of ridges and mounds in the Brosna basin, central Ireland. The findings suggest that the hummocky topography is composed of fragmented mega-scale glacial lineations (MSGLs) overlain by groups of small ridges formed by subglacial till and sediment gravity flow deposits. The research indicates that the formation of these landforms reflects changes in ice sheet bed thermal/hydrological characteristics during deglaciation.