MELTWATER LANDFORM PERSPECTIVES ON SUBGLACIAL HYDROLOGICAL PROCESSES: INSIGHTS FROM HIGH-RESOLUTION MAPPING IN NORTHERN CANADA

The configuration and evolution of meltwater drainage under ice sheets is a key control on ice flow, erosion, sedimentation and frontal ablation. Meltwater landforms allow the properties of meltwater drainage to be reconstructed, typically over centennial to millennial time-scales and spatially over 100s of km. They therefore have enormous potential for informing our understanding of modern day subglacial hydrological processes, which are difficult to observe directly. Recently, the availability of high resolution (2 m) digital elevation models (e.g. ArcticDEM) has facilitated the discovery and mapping of meltwater imprints at an unprecedented level of detail and scale.

This presentation summarises recent holistic mapping efforts, which reveal diverse meltwater traces forming an integrated network across northern Canada. Eskers are typically surrounded and joined by wider meltwater corridors (100s to 1000s m wide) that comprise both erosional and depositional forms (such as hummocks, ridges, murtoos), including subglacial bedforms (e.g. ribbed moraine tracts). We suggest that meltwater corridors formed by the exchange of water and sediment between a conduit (esker) or efficient core and the surrounding hydraulically-connected distributed drainage system (corridor) in response to variable melt inputs. The landform signature of meltwater corridors is likely influenced by different styles of drainage (e.g. from laterally constrained floods to distributed drainage) and coupling with the ice above. Eskers are interpreted to record a composite signature of ice marginal drainage. This interpretation is based on the close 1:1 association between beaded eskers (series of aligned sediment mounds) and De Geer moraine (i.e., each bead is associated with a corresponding ridge) in Keewatin, which suggests that they are quasi-annual ice-marginal deposits formed time-transgressively at the mouth of subglacial conduits during deglaciation.