IMPLICATIONS OF ESKER FORMATION FOR ICE-MARGINAL MELTWATER AND SEDIMENT ROUTING

Eskers are highly distinctive landforms which are the product of meltwater and sediment transport through glacial systems. Despite the ubiquity of eskers in the sediment and landform record little attention has been paid to the geomorphic and sedimentary role that eskers play during deglaciation. Once melted-out, large eskers may alter patterns of meltwater movement and storage within the recently deglaciated environment. We aim to assess the role that esker ridges play in modifying meltwater and sediment routing following glacier retreat. Skeidarárjökull, southeast Iceland is currently retreating and has a large number of eskers in its foreland.

Ridges composed of sand and gravel recently exposed on the proximal side of an ice contact slope at the margin of Skeidarárjökull exhibit pseudo-anticlinally bedded clast-supported gravels diagnostic of deposition within a conduit. A carapace of subglacial till on the esker suggests that the ridges have been preserved subglacially. Esker bases are approximately 30 m below current sandur elevation and lack any connecting proglacial outwash fans, suggesting that they were deposited when the sandur was at a lower level, with the ice-marginal and proglacial expression of these eskers buried by subsequent sandur aggradation.

The development of an ice contact slope associated with de-coupling of the glacier from the proglacial outwash system has forced meltwater flow along the glacier margin, where eskers ridges are ponding meltwater and trapping sediment within a series of proglacial lakes.

Our study demonstrates the importance of subglacial esker formation for proglacial and ice-marginal sedimentary processes during glacier recession. Our modern analogue will be applicable to Quaternary glacial systems subject to rapid proglacial sandur aggradation and/or the presence of an over-deepened subglacial basin.