Geomorphological Signature of Topographically Controlled Glacier Flow-Switching

Abstract

Glacier flow-switching, which can involve changes in ice flow velocity and direction, is crucial to a full understanding of ice masses and their response to climate change. A topographically controlled glacier flow switch was recently documented at Breiðamerkurjökull, southeast Iceland, where the central flow unit migrated eastward in response to variations in subglacial topography and the influence of Jökusarlon glacial lagoon.Uncrewed aerial vehicle-(UAV) derived data was used to assess the geomorphic response to this switching and related processes across a 1.5 km² area of the central flow unit uncovered between 2010-2023. From 2010 to 2017, the landscape featured streamlined subglacial material, a stable subglacial esker system and proglacial lakes (Landsystem A), shifting to a spillway-dominated system between 2018 to 2023 (Landsystem B). Since 2018 the glacier has been retreating across a reverse slope bed, resulting in the formation of quasi-annual ice-marginal spillways. Meltwater impoundment at the ice margin, formed ice-contact lakes which eventually initiated ice-margin parallel spillways draining proglacial meltwater along the local land-surface gradient, towards Jökulsárlón. Once the ice retreats, an ice-contact lake forms again at the new margin and initiates the erosion of the next ice-marginal spillway. The geomorphological signature demonstrates how subglacial topography and ice-flow switching can significantly influence ice and meltwater dynamics.Since the glacier flow-switch, part of the central unit is now lake-terminating with areas of the margin evolving into a stagnant system, as it is now cut off from the accumulation centre. Therefore, Landsystem B could be analogous to regions of ice stream shut down and regions where ice masses retreated across reverse slope beds like the Pakowki Lake region of Southeastern Alberta, which displays a similar landform assemblage. Such insights are important for assessing the efficacy of ice sheet models in reconstructing the finer scale dynamics of past ice sheets during retreat.

Keywords: glacial geomorphology, Iceland, Laurentide Ice Sheet, UAV.