Brief communication : subglacial lake drainage beneath Isunguata Sermia, west Greenland : geomorphic and ice dynamic effects

We report three active subglacial lakes within 2 km of the lateral margin of Isunguata Sermia, West Greenland, identified by differencing time-stamped ArcticDEM strips. Each lake underwent one drainage–refill event between 2009 and 2017, with two lakes draining in < 1 month in August 2014 and August 2015. The 2015 drainage caused a ∼ 1-month down-glacier slowdown in ice flow and flooded the foreland, aggrading the proglacial channel by 8 m. The proglacial flooding confirms the ice-surface elevation anomalies as subglacial water bodies and demonstrates how their drainage can significantly modify proglacial environments. These subglacial lakes offer accessible targets for geophysical investigations and exploration

Brief Communication: Outburst floods triggered by periodic drainage of subglacial lakes, Isunguata Sermia, West Greenland

We report three active subglacial lakes within 2 km of the lateral margin of Isunguata Sermia, West Greenland, identified by differencing time-stamped ArcticDEM strips. Each lake underwent one drainage-refill event between 2009 and 2017, with two lakes draining in < 1 month during August 2014 and August 2015, and all three characterised by 2–3-year refill periods. The 2015 drainage flooded the foreland aggrading 8 m of the proglacial channel, confirming the ice-surface elevation anomalies as subglacial water bodies and demonstrating how subglacial lake drainages can significantly modify proglacial environments. These subglacial lakes offer accessible targets for future geophysical investigations and exploration

Sinuous ridges and the history of fluvial and glaciofluvial activity in Chukhung Crater, Tempe Terra, Mars

International audience&lt;p&gt;We explore the origins of a complex assemblage of sinuous ridges in Chukhung crater (38.47&amp;#176;N, 72.42&amp;#176;W), Tempe Terra, Mars, and discuss the implications of the landsystem for post-Noachian fluvial and glaciofluvial activity in this location [1].&lt;/p&gt;&lt;p&gt;We produced a geomorphic map of Chukhung crater using a basemap of 6&amp;#160;m/pixel Context Camera (CTX) images and a 75&amp;#160;m/pixel High Resolution Stereo Camera digital elevation model (DEM). We used 25&amp;#160;cm/pixel High Resolution Imaging Science Experiment images, and a 24 cm/pixel DEM generated from CTX stereopair images [2] to aid classifications of sinuous ridges into four morpho-stratigraphic subtypes. We constrained an age envelope of ~2.1&amp;#8211;3.6 Ga for Chukhung crater using modelled ages (from crater size-frequency analyses) of units above and below it in the regional stratigraphy. We derived a minimum model age of ~330&amp;#160;Ma for viscous flow features (putative debris-covered glaciers) in southern Chukhung crater.&lt;/p&gt;&lt;p&gt;Sinuous ridges in southern Chukhung crater emerge from moraine-like deposits associated with the debris-covered glaciers. Sinuous ridges in northern Chukhung crater extend from dendritic fluvial valley networks on the crater wall. The northern sinuous ridges are most likely to be inverted palaeochannels, which comprise subaerial river sediments exhumed as ridges by erosion of surrounding materials.&lt;/p&gt;&lt;p&gt;Both sinuous ridge subtypes in southern Chukhung crater have numerous esker-like properties. Eskers are ridges of glaciofluvial sediment deposited in meltwater tunnels within or beneath glacial ice. One of the ridge subtypes in southern Chukhung crater is best explained as eskers because these ridges ascend the sides of their host valleys and, in places, escape over them onto adjacent plains. Post-depositional processes can cause inverted paleochannels to cross local undulations in the contemporary topography [3] but the ascent and escape over larger, pre-existing topographic divides is (as yet) not adequately explained by these mechanisms. Eskers, in contrast, form under hydraulic pressure in ice-confined tunnels, and commonly ascend valley walls and cross topographic divides. The esker-like properties of the second sinuous ridge subtype in southern Chukhung crater can also be explained under the inverted palaeochannel hypothesis so the origins of these ridges remain more ambiguous.&lt;/p&gt;&lt;p&gt;Chukhung crater has undergone protracted and/or episodic modification by liquid water since its formation between the early Hesperian and early Amazonian. This falls after the Noachian period (&gt;3.7&amp;#160;Ga), when most major fluvial activity on Mars occurred. Esker-forming wet-based glaciation in Chukhung crater might have occurred as recently as the mid Amazonian (&gt;330&amp;#160;Ma), when climate conditions are thought to have been cold and hyper-arid. Rare occurrences of eskers associated with Amazonian-aged glaciers in Mars&amp;#8217; mid-latitudes are attributed to transient, localised geothermal heating within tectonic rift/graben settings [4]. The location of Chukhung crater between major branches of the large Tempe Fossae volcano-tectonic rift system is consistent with this hypothesis.&lt;/p&gt;&lt;p&gt;References: [1] Butcher et al. 2021, Icarus 357, 114131. [2] Mayer and Kite 2016, Lunar Planet. Sci. Conf. Abstract #1241. [3] Lefort et al. 2012, J. Geophys. Res. Planets 117, E03007. [4] Butcher et al. 2017, J. Geophys. Res. Planets 122, 2445&amp;#8211;2468.&lt;/p&gt

Eskers associated with buried glaciers in Mars' mid latitudes: recent advances and future directions

Until recently, the influence of basal liquid water on the evolution of buried glaciers in Mars' mid latitudes was assumed to be negligible because the latter stages of Mars' Amazonian period (3 Ga to present) have long been thought to have been similarly cold and dry to today. Recent identifications of several landforms interpreted as eskers associated with these young (100s Ma) glaciers calls this assumption into doubt. They indicate basal melting (at least locally and transiently) of their parent glaciers. Although rare, they demonstrate a more complex mid-to-late Amazonian environment than was previously understood. Here, we discuss several open questions posed by the existence of glacier-linked eskers on Mars, including on their global-scale abundance and distribution, the drivers and dynamics of melting and drainage, and the fate of meltwater upon reaching the ice margin. Such questions provide rich opportunities for collaboration between the Mars and Earth cryosphere research communities

Morphometry and pattern of a large sample (>20,000) of Canadian eskers and implications for subglacial drainage beneath ice sheets

Ice sheet flow is strongly influenced by the nature and quantity of meltwater entering the subglacial system. Accessing and monitoring contemporary drainage systems beneath ice sheets is notoriously difficult, but it is possible to utilise the exposed beds of palaeo-ice sheets. In particular, eskers record deposition in glacial drainage channels and are widespread on the exposed beds of former ice sheets. However, unlike some other common glacial landforms (e.g. drumlins) there have been relatively few attempts to investigate and quantify their characteristics at the ice sheet scale. This paper presents data on the distribution, pattern, and morphometry of a large (>20,000) sample of eskers in Canada, formed under the Laurentide Ice Sheet, including quantification of their length, fragmentation, sinuosity, lateral spacing, number of tributaries, and downstream elevation changes. Results indicate that eskers are typically very long (hundreds of km) and often very straight (mean sinuosity approximates 1). We interpret these long esker systems to reflect time-transgressive formation in long, stable conduits under hydrostatic pressure. The longest eskers (in the Keewatin sector) are also the least fragmented, which we interpret to reflect formation at an ice margin experiencing stable and gradual retreat. In many locations, the lateral distance between neighbouring eskers is remarkably consistent and results indicate a preferred spacing of around 12 km, consistent with numerical models which predict esker spacing of 8–25 km. In other locations, typically over soft sediments, eskers are rarer and their patterns are more chaotic, reflecting fewer large R-channels and rapidly changing ice sheet dynamics. Comparison of esker patterns with an existing ice margin chronology reveals that the meltwater drainage system evolved during deglaciation: eskers became more closely spaced with fewer tributaries as deglaciation progressed, which has been interpreted to reflect increased meltwater supply from surface melt. Eskers show no preference to trend up or down slopes, indicating that ice surface was an important control on their location and that the conduits were, in places, close to ice overburden pressure

Increased channelization of subglacial drainage during deglaciation of the Laurentide Ice Sheet

The configuration of subglacial meltwater is a critical control on ice sheet dynamics, and the presence of pressurized water distributed across the bed can induce dynamic instabilities. However, this process can be offset by efficient evacuation of water within large subglacial channels, and drainage systems beneath alpine glaciers have been shown to become increasingly channelized throughout the melt season in response to the increased production of meltwater. This seasonal evolution has recently been inferred beneath outlet glaciers of the Greenland Ice Sheet, but the extent to which this process occurs across much larger spatial and temporal scales is largely unknown, introducing considerable uncertainty about the evolution of subglacial drainage networks at the ice sheet scale and associated ice sheet dynamics. This paper uses an unprecedented data set of over 20,000 eskers to reconstruct the evolution of channelized meltwater systems during the final deglaciation of the Laurentide Ice Sheet (13–7 kyr B.P.). We demonstrate that eskers become more frequent during deglaciation and that this coincides with periods of increased rates of ice margin recession and climatic warming. Such behavior is reminiscent of the seasonal evolution of drainage systems observed in smaller glaciers and implies that channelized drainage became increasingly important during deglaciation. An important corollary is that the area of the bed subjected to a less efficient pressurized drainage system decreased, which may have precluded dynamic instabilities, such as surging or ice streaming

A map of large Canadian eskers from Landsat satellite imagery

Meltwater drainage systems beneath ice sheets are a poorly understood, yet fundamentally important environment for understanding glacier dynamics, which are strongly influenced by the nature and quantity of meltwater entering the subglacial system. Contemporary sub-ice sheet meltwater drainage systems are notoriously difficult to study, but we can utilise exposed beds of palaeo-ice sheets to further our understanding of subglacial drainage. In particular, eskers record deposition in glacial drainage channels and are widespread on the exposed beds of former ice sheets. This paper presents a 1:5,000,000 scale map of >20,000 large eskers (typically > 2 km long) deposited by the Laurentide Ice Sheet (LIS), mapped from Landsat imagery of Canada, in order to establish a dataset suitable for analysis of esker morphometry and drainage patterns at the ice sheet scale. Comparisons between eskers mapped from Landsat imagery and aerial photographs indicate that, in most areas, approximately 75% of eskers are detected using Landsat. The data presented in this map build on and extend previous work in providing a consistent map of an unprecedented sample of eskers for quantitative analysis. It offers an alternative perspective on the problems surrounding ice-sheet meltwater drainage and can be used for: (i) detailed investigations of esker morphometry and distribution from a large sample size; (ii), testing of numerical models of meltwater drainage routing that predict esker characteristics (e.g. channel spacing, sinuosity), (iii) assessment of the factors that control esker location and formation; and (iv), a refined understanding of ice margin configurations during retreat of the LIS

Crevasse-squeeze ridge corridors: diagnostic features of late stage palaeo-ice stream activity

A 200-km-long and 10-km-wide linear assemblage of till-filled geometrical ridges on the bed of the Maskwa palaeo-ice stream of the late Wisconsinan southwest Laurentide Ice Sheet are interpreted as crevasse-squeeze ridges (CSR) developed during internal flow unit reorganization, immediately prior to ice stream shutdown. Ridge orientations are predominantly orientated WNW–ESE, with a subordinate WSW–ENE alignment, both indicative of ice fracture development transverse to former ice stream flow, as indicated by NNE–SSW aligned MSGL. Subglacial till injection into basal and/or full depth, mode I and II crevasses occurred at the approximate centreline of the ice stream, in response to extension and fracturing. Landform preservation indicates that this took place during the final stages of ice streaming, immediately prior to ice stream shutdown. This linear zone of ice fracturing therefore likely represents the narrowing of the fast-flowing trunk, similar to the plug flow identified in some surging valley glaciers. Lateral drag between the final active flow unit and the slower moving ice on either side is likely recorded by the up-ice bending of the CSR limbs. The resulting CSR corridor, here related to an individual ice stream flow unit, constitutes a previously unreported style of crevasse infilling and contrasts with two existing CSR patterns: (1) wide arcuate zones of CSRs related to widespread fracturing within glacier surge lobes; and (2) narrow concentric arcs of CSRs and recessional push moraines related to submarginal till deformation at active temperate glacier lobes

An ice-sheet scale comparison of eskers with modelled subglacial drainage routes

Eskers record the signature of channelisedmeltwater drainage during deglaciation providing vital information on the nature and evolution of subglacial drainage. In this paper, we compare the spatial pattern of eskers beneath the former Laurentide Ice Sheet with subglacial drainage routes diagnosed at discrete time intervals from the results of a numerical ice-sheet model. Perhaps surprisingly,we showthat eskers predominantly occur in regions where modelled subglacial water flow is low. Eskers and modelled subglacial drainage routes were found to typically match over distances of b10 km, and most eskers show a better agreement with the routes close to the ice margin just prior to deglaciation. This supports a time-transgressive esker pattern, with formation in short (b10km) segments of conduit close behind a retreating ice margin, and probably associated with thin, stagnant or sluggish ice. Esker-forming conduits were probably dominated by supraglacially fed meltwater inputs. We also show that modelled subglacial drainage routes containing the largest concentrations of meltwater show a close correlation with palaeo-ice stream locations. The paucity of eskers along the terrestrial portion of these palaeo-ice streams and meltwater routes is probably because of the prevalence of distributed drainage and the high erosion potential of fast-flowing ice