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Directly observing glacial drainage systems (englacial and subglacial) is challenging. The distribution, morphology and internal structure of eskers can provide valuable information about the glacial drainage system and meltwater processes. This work presents the annual evolution (meltout) and internal structure of an esker emerging from the Breiðamerkurjökull ice margin, southeast Iceland. Changes in esker morphology have been repeatedly mapped over a 1‐year period using high temporal and spatial resolution data acquired by an uncrewed aerial vehicle (UAV). The internal architecture of the esker was investigated using ground‐penetrating radar (GPR) surveys. These data are used to identify the dominant processes driving the formation of this englacial esker and to evaluate the preservation potential. The englacial esker was up to 2.6 m thick and ice‐cored. A large moulin upglacier of the esker, which evolved into an englacial conduit, supplied meltwater to the englacial channel. Upglacier dipping debris‐filled basal hydrofractures, formed by pressurised subglacial meltwater rising up the retrograde bed slope, likely supplied sediment to the englacial conduit. Over the 1‐year period of observation the crest morphology evolved from flat‐ to sharp‐crested and the esker footprint increased by a factor of 5.7 in response to post‐depositional processes. The findings presented here indicate that englacial eskers may have low preservation potential due to post‐depositional reworking such as slumping through ice‐core meltout and erosion by later meltwater flow. As englacial eskers may not be preserved in the landscape, they could represent important glacial drainage system components that are not currently captured in palaeo‐ice sheet reconstructions. This work highlights the value of creating a time series of high‐temporal resolution data to quantify morphological evolution and improve glacial process‐form models. [ABSTRACT FROM AUTHOR]

The availability of a bathymetric database that covers about 80% of the Icelandic shelf has made it possible to produce a geomorphological map of the glacial landforms. The digital elevation model of the bathymetry was analyzed as a series of shaded relief images. Trough edges, bulging trough mouths, moraines, eskers, melt water channels, streamlined bedrock and streamlined drift, mostly hitherto unmapped, distributed all around the island have been identified. Moraines are found on the shelf, within troughs and inside fjords. Streamlined landforms are always confined to the bottom of troughs. Troughs appear to have been cut by ice streams draining an ice sheet that likely covered the entire shelf. At the shelf break, most troughs terminate with contours that bulge in a convex-outwards fashion. This suggests that an ice stream eroded, transported and finally deposited large amounts of sediment at the trough mouth. Overall, the glacial morphology of the shelf highlights a radial pattern that indicates a main ice divide near the centre of Iceland. [ABSTRACT FROM AUTHOR]

Ice low-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 ice flow switch near a glacier margin 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 Jökulsárlón glacial lagoon. This site provides an opportunity to study the geomorphic response to ice-margin reconfiguration. Investigating contemporary processes can offer valuable insights into analogous landforms created during the deglaciation of palaeo-ice sheets. The landform assemblage and topographic setting of our Icelandic study site is compared to a palaeo-example from Alberta, Canada, which was once covered by the Laurentide ice sheet. 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 which deglaciated between 2010 and 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 and 2023 (Landsystem B). Since 2018 this section of Breiðamerkurjökull 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. As 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 where ice masses retreated across reverse slope beds. For example, the Pakowki Lake region of Southeastern Alberta displays a similar landform assemblage and is presented as a palaeo-example in this work. Such insights are important for assessing the efficacy of numerical models in reconstructing the finer scale dynamics of past ice sheets during retreat. • Landform mapping at Breiðamerkurjökull (Iceland) from UAV-derived data reveals two distinct landform assemblages. • Landsystem A (2010-2017): flat subglacial bed, subglacial eskers and proglacial lakes. • Landsystem B (2018-2023): reverse slope bed and ice-marginal spillways. • Landsystem B is analogous to SE Alberta, providing support for existing spillway reconstructions in the region. • The geomorphic response highlights the significance of subglacial topography on ice and meltwater dynamics. [ABSTRACT FROM AUTHOR]