Suchergebnisse

Uncertainty remains about how the surface hydrology of the Greenland ice sheet influences its subglacial drainage system, affecting basal water pressures and ice velocities, particularly over intraseasonal and interseasonal timescales. Here we apply a high spatial (200m) and temporal (1h) resolution subglacial hydrological model to a marginal (extending ~25km inland), land-terminating, ~200km$^{2}$ domain in the Paakitsoq region, West Greenland. The model is based on that by Hewitt (2013) but adapted for use with both real topographic boundary conditions and calibrated modeled water inputs. The inputs consist of moulin hydrographs, calculated by a surface routing and lake-filling/draining model, which is forced with distributed runoff from a surface energy-balance model. Results suggest that the areal density of lake-bottom moulins and their timing of opening during the melt season strongly affects subglacial drainage system development. A higher moulin density causes an earlier onset of subglacial channelization (i.e., water transport through channels rather than the distributed sheet), which becomes relatively widespread across the bed, whereas a lower moulin density results in a later onset of channelization that becomes less widespread across the bed. In turn, moulin density has a strong control on spatial and temporal variations in subglacial water pressures, which will influence basal sliding rates, and thus ice motion. The density of active surface-to-bed connections should be considered alongside surface melt intensity and extent in future predictions of the ice sheet's dynamics. ; This work was funded through a UK Natural Environment Research Council Doctoral Training grant (LCAG/133), a Bowring Junior Research Fellowship (St Catharine's College, Cambridge), and a Leverhulme/Newton Trust Early Career Fellowship, all awarded to A.F.B. I.J.H. was supported by a Marie Curie FP7 Career Integration Grant within the 7th European Union Framework Programme.

Viscous flow features (VFF) occur in the mid-latitudes of Mars and have characteristics consistent with being glaciers. Climate models suggest that martian glaciers are cold-based systems in which meltwater has never been widely produced. VFF are common in Phlegra Montes, a mountain range in the mid-latitudes of the northern hemisphere of Mars. However, in Phlegra Montes, the presence of an esker associated with an extant Amazonian Period VFF provides evidence that warm-based glacial processes did formerly operate. The problem at the centre of this paper is that the glacial meltwater responsible for this esker could have been produced as a consequence of its setting in a graben, with locally enhanced geothermal heating having been the driver of melt, not systemic heating associated with a regional warm-based regime. Given this uncertainty, this paper aims to determine if there are indicators of more widespread warm-based glacial processes in Phlegra Montes. The paper briefly describes the distribution and characteristics of VFF across the region, before focussing on the search for key landforms considered diagnostic of erosion by warm-based glaciers. From our observations, including discriminant morphometrics, we conclude that the landscape of Phlegra Montes is indicative of widespread warm-based glacial processes, including subglacial scour, linear abrasion and the incision of subglacial meltwater channels. Our findings have significance in constraining the contexts and process environments within which liquid water has been produced during the Amazonian Period on Mars and point to several lines of future research into martian glaciation, climate and landscape evolution. ; FEGB is part of the PALGLAC research team supported by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant agreement No. 787263). FEGB also acknowledges funding from the Science and Technology Facilities Council (STFC) grant ST/N50421X/1.

Glaciers in High Mountain Asia, many of which exhibit surface debris, contain the largest volume of ice outside of the polar regions. Many contain supraglacial pond networks that enhance melt rates locally, but no large-scale assessment of their impact on melt rates exists. Here we use surface energy balance modeling forced using locally measured meteorological data and monthly satellite-derived pond distributions to estimate the total melt enhancement for the four main glaciers within the 400-km2 Langtang catchment, Nepal, for a 6-month period in 2014. Ponds account for 0.20 ± 0.03 m/year of surface melt, representing a local melt enhancement of a factor of 14 ± 3 compared with the debris-covered area, and equivalent to 12.5 ± 2.0% of total catchment ice loss. Given the prevalence of supraglacial ponds across the region, our results suggest that effective incorporation of melt enhancement by ponds is essential for accurate predictions of future mass balance change in the region. ; Gates Cambridge Trust, Trinity College (Cambridge), Philip Lake and William Vaughn Lewis Fund (Cambridge). B.B. Roberts Fund (Cambridge). European Research Council under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 676819). USAID (United States Agency for International Development) High Mountain Glacier Watershed Programs Climber-Scientist Grant (CCRDCS0010) Swiss National Science Foundation project UNCOMUN (SNF 200021L146761).

We present a systematic, metre-scale characterisation of the 3D morphometry of an esker on Mars, and the first attempt to reconstruct the multi-stage dynamics of esker formation on Mars. Eskers are sinuous ridges comprising sediment deposited by meltwater draining through ice-confined tunnels within or beneath glaciers. Detailed morphometric insights into eskers on Mars are important for (i) informing morphometric tests of whether sinuous ridges elsewhere on Mars are eskers, and (ii) informing modelling experiments which aim to reconstruct the glaciological and environmental controls on esker formation on Mars. We use a digital elevation model generated from High Resolution Imaging Science Experiment (HiRISE) images to characterise the height and width of an extremely rare esker associated with a late-Amazonian-aged viscous flow feature (debris-covered glacier) in NW Tempe Terra, Mars. Our measurements suggest that the NW Tempe Terra esker is a 'stacked' formation comprising an underlying 'lower member' ridge that is superposed by a narrower 'upper member' ridge. We used a novel morphometric approach to test whether the apparent stacking records two distinct esker deposition regimes (either within the same drainage episode, or within temporally-separated drainage episodes). This approach posits that esker crest morphology is controlled by primary esker formation processes and, by extension, that portions of eskers with similar crest morphologies should have similar morphometric relationships. We predicted the morphometric relationships described by the constituent upper and lower member ridges based on 'reference relationships' observed for morphologically-similar portions of the esker where no evidence of stacking was observed. Our observations corresponded well with the predicted relationships, supporting our stacked esker hypothesis. We propose conceptual models, which invoke spatial and temporal variations in sediment supply and meltwater discharge, to explain the stacked morphology. These models are informed by morpho-sedimentary relationships observed along eskers on Earth. ; This work was un-dertaken at The Open University as part of a PhD studentship held by FEGB and funded by the Science Technology and Facil-ities Council (STFC) grant ST/N50421X/1. Manuscript preparation was supported by The Open University (internal funding) and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (ERC Advanced Grant PALGLAC 787263). We also gratefully acknowledge UK Space Agency grants ST/L00643X/1, ST/R001413/1, and ST/R001383/1 (MRB); ST/R001405/1, ST/P001262/1, and ST/S00145X/1 (SRL); and ST/R/001375 (AH). SJC is supported by the French space agency, CNES.