Esker Ridge Research Articles

Glacial geomorphology of Newfoundland, Canada

ABSTRACT We present a synthesis of glacial geomorphology comprising Newfoundland and the surrounding continental shelf. During the last glaciation, this region was encompassed by the Newfoundland Ice Cap that coalesced with the Laurentide Ice Sheet and extended to the continental shelf edge. The subglacial geomorphic signal of terrestrial and marine portions of this ice sheet has been mapped using aerial photography, satellite imagery, SRTM DEMs, multibeam bathymetric data and onshore field mapping over the last 50 years. Here, we build on this, digitizing ∼146,380 features identified in published literature. Using newly available digital elevation data and multibeam bathymetric data, we identify ∼38,550 new features, such as undocumented ice thrust, crevasse and esker ridges and meltwater channels. This updated geomorphological map provides a record of paleo landforms over Newfoundland, enabling future efforts to reconstruct the dynamics, timing and erosion history of ice advance and retreat during the last glacial period..

Glacial geomorphology of the northwest Laurentide Ice Sheet on the northern Interior Plains and western Canadian Shield, Canada

ABSTRACT The majority of the Northwest Territories of mainland Canada was covered by the Laurentide Ice Sheet during the Last Glacial Maximum. The increasing coverage of high resolution remotely sensed data provides new opportunities to map the glacial geomorphology and study the glacial history of this remote location. Here we present a comprehensive map of glacial landforms within the northern Interior Plains and adjacent areas of the Canadian Shield, comprising around 6% of the Laurentide Ice Sheet bed. Twelve landform types were mapped from the high resolution ArcticDEM: ice flow parallel lineations, subglacial ribs, crevasse-squeeze ridges, major and minor moraine crests, hummocky terrain complexes and ridges, shear margin moraines, major, minor and lateral and submarginal meltwater channels, esker ridges and complexes, glaciofluvial complexes, perched deltas, raised shorelines and aeolian dunes. Together, these landforms provide a record of the highly dynamic behaviour of the northwest sector of the Laurentide Ice Sheet.

Limnogenesis of large l akes in the North-West of the Russian Plain

Abstract. The issues of the formation of the largest lakes in Europe - Ladoga and Onega are considered in the article. The main aim was to identify features of the basins development from their origin to modern condition. The newest geological and geophysical data obtained in 2014-2021 was used to achieve the goal. Both depressions, in which modern lake basins are located, were formed in the Late Proterozoic. In the Late Quaternary, the glacier significantly modeled the pre-Quaternary relief. Glacial tongues significantly expanded the negative forms of the pre-glacial relief. At the same time, the glacier also formed positive landforms, such as moraines and esker ridges. Such ridges intersect the Lake Ladoga center and mark the position of the Neva stage. Structural features of the supraglacial section are considered in detail. It is shown that in both lakes the structure of the upglacial section is approximately the same and is associated with the gradual retreat of the glacier from the lake basins. Thus, it is shown that, despite the similarity of the main stages of paleogeographic development, each lake basin was characterized by its own features and their development itself occurred asynchronously.

Classification of esker morphology on soft beds in the area of the Saalian and Elsterian Glaciations in Poland

The study provides a morphologic classification of eskers formed on a soft bed in Poland during the Saalian and Elsterian Glaciations. The classification is based on morphometry, including esker fragmentation, length, sinuosity, ridge elongation and presence of tributary ridges. Five esker types and a total of ten subtypes were distinguished. The most common esker types to the south of the LGM in Poland include 1a – continuous, short, straight esker ridges, 1b – continuous, short, sinuous esker ridges, and 4c – segmented, long, sinuous eskers. The eskers were formed in subglacial N-, R-, N-R and open channels. A synchronous model of esker formation was dominant, but some time-transgressively formed eskers consisting of beads also occur. The analysed eskers have common features with eskers on a hard bed and some of them originated in a similar way, but many eskers exhibit dissimilarity due to different conditions of their formation. The study shows that current esker morphogenetic classifications need to be extended to also include the character of eskers on soft beds.

A rare signature of subglacial outburst floods developed along structural ice weaknesses in the southern sector of the Scandinavian Ice Sheet during the Drenthian Glaciation, S Poland

We present the study of a subglacial drainage system that developed in the base of the Scandinavian Ice Sheet at the border of the Silesian Lowland and Silesian Upland (southern Poland) during the Drenthian Glaciation as a result of large outburst flood events. This drainage system was characterised by a spatially complex structure, i.e. it was composed of an individual an N-channel (tunnel channel) incised in Mesozoic rocks, i.e. Cretaceous and Triassic marls and limestones, and an R-channel, deposits of which form a set of large esker ridges which also occur on bedrock in the SE prolongation of the tunnel channel. Unlike most known cases of the co-occurrence of such forms, the studied tunnel channel and eskers are directly related, having been formed during the same flow events. The studied forms are unique within the entire southern sector of the Scandinavian Ice Sheet, which, in Central Europe, advanced mainly over soft unconsolidated Quaternary and Neogene sediments. The tunnel channel was formed as a result of enormous erosion of the ice sheet bed. The material eroded from the channel was partially deposited in a subsequent part of the drainage system. The location and orientation of the drainage system did not result directly from water pressure gradients, but was strongly determined by the internal structure of the ice sheet, i.e. it presumably developed along the marginal part of the ice stream supplying the Upper Odra ice lobe, which represented distinct weaknesses within the ice sheet. The development of the drainage system was the effect of the drainage of meltwater stored in the ice sheet system, most probably as a supraglacial lake. Gravelly-sandy rhythms recorded within the esker succession indicate that the process of lake drainage took place in several stages, or that the lake developed and drained several times.

In the footsteps of the ice sheet in the area of the planned geopark postglacial land of the Drawa and Dębnica rivers (the Drawskie Lakeland, Poland)

The article presents 20 geosites located on five geotourist paths and their closest vicinity, constituting the initial part of the planned geopark Postglacial land of Drawa and Dębnica. Geosites represent the most valuable abiotic resources, proving the large geodiversity of the studied area. These are: 1. glacial and fluvioglacial accumulation forms (e.g.: terminal end-moraine of the Parsęta lobe, undulating moraine uplands, glacial deposits including erratic border boulders, esker ridges), 2. glacial and fluvioglacial erosive forms (e.g.: channel and melt-out-depressions), 3. other (like e.g.: deep erosive and erosional-denudation valleys, erosive forms of groundwater or 1st order watershed between the Odra and Parsęta catchments). The purpose of the geosites characteristics in this paper is to support the development of geotourism in the peripheral tourist area.

Interlobate esker aquifer characterization by high resolution seismic reflection method with landstreamer in SW Finland

The Virttaankangas interlobate esker with 100 m thick sediments has a complex depositional history. It is one of the largest groundwater reserves in Finland and hosts a managed artificial recharge plant providing potable water for the 300,000 inhabitants of the Turku region. We researched the characteristics of the esker aquifer both on a major fracture valley and on an esker ridge with a low groundwater table. This study presents the results of the first landstreamer-based high-resolution seismic reflection survey in Finland conducted in 2011. The esker core (main aquifer) position was delineated accurately throughout the entire area with continuous seismic data compared to a previous sedimentological model, gravimetric data and reference drillings. New features related to the widening of the coarse-grained unit of the esker core as well as a previously unknown daughter esker adjacent to the main esker core were revealed. These new findings are in agreement with the existing 3-D hydrogeological model. Our research provides valuable data on the high-resolution seismic reflection surveying of thick interlobate glaciofluvial deposits on two areas with differing bedrock topography on crystalline basement rocks.

Postglacial seismogenic deformations of an esker in the Northern Karelian Isthmus (south-east Fennoscandia)

The research area is located in the Northern part of the Karelian Isthmus between Lake Ladoga and the Gulf of Finland of the Baltic Sea. The terrain features are closely related to the tectonic structure of the crystalline basement, partially covered with thin deposition layer of the Last Glaciation and Holocene mostly. Accumulative forms are rarely but strongly correlated with the tectonic structure also. Most expressive features of accumulative topography are esker ridges that stretch for tens of kilometers. Analysis of eskers spatial distribution shows their close connection with the structural plan of the crystalline basement. One of the ridges under study was described in three sections where a lot of deformations in soft sediments, accompanied by deformations of the esker’s topography (in one case) were found. The nature and stratigraphic position of deformations indicates their appearance during the period of existence of the Baltic Ice Lake after the retreat of the ice sheet. Post-sedimentary deformations were accompanied by partial re-deposition of sedimentary strata. Deformations are represented by several types and generations. The ensembles of faults and fold deformations in the esker deposition kinematically connected with each other and coinciding along the strike with the structural lineaments demonstrate the influence of the activated tectonic structure to the formation of the sedimentary cover. The conjugation of normal and thrust faults, the presence of several “event horizons” with traces of liquefaction testify to the seismotectonic genesis of deformations and several strong earthquakes that occurred at different stages of the existence of the Baltic Ice Lake in the period 13.0–11.6 thousand years BP.

Complex kame belt morphology, stratigraphy and architecture

AbstractThe development of glacier karst at the margins of melting ice sheets produces complex glaciofluvial sediment‐landform assemblages that provide information on ice sheet downwasting processes. We present the first combined geomorphological, sedimentological and geophysical investigation of the Brampton Kame Belt, an important glaciofluvial depositional zone at the centre of the last British‐Irish Ice Sheet. Ground‐penetrating radar (GPR) data allow the broad scale internal architecture of ridges (eskers) and flat‐topped hills (ice‐walled lake plains) to be determined at four sites. In combination with sediment exposures, these provide information on lateral and vertical variations in accretion styles, depositional boundaries, and grain size changes. Building on existing work on the subject, we propose a refined model for the formation of ice‐walled lake plains resulting from the evolution and collapse of major drainage axes into lakes as stable glacier karst develops during deglaciation. The internal structure of esker ridges demonstrates variations in sedimentation that can be linked to differences in ridge morphologies across the kame belt. This includes low energy flow conditions and multiple accretion phases identified within large S‐N oriented esker ridges; and fluctuating water pressures, hyperconcentrated flows, and significant deformation within a fragmented SW–NE oriented esker ridge. In combination with updated geomorphological mapping, this work allows us to identify two main styles of drainage within the kame belt: (1) major drainage axes aligned broadly S‐N that extend through the entire kame belt and collapsed into a chain of ice‐walled lakes; and (2) a series of smaller, fragmented SW–NE aligned esker ridges that represent ice‐marginal drainage as the ice sheet receded south‐eastwards up the Vale of Eden. Our study demonstrates the importance of integrated geomorphological, sedimentological and geophysical investigations in order to understand complex and polyphase glaciofluvial sediment‐landform assemblages. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.

The geomorphology and sedimentology of eskers in north-central Ireland

Eskers are common glacial landforms in Ireland and form regionally-extensive networks that reflect stages of ice retreat of this sector of the late Devensian (Weichselian) British–Irish ice sheet. However, the sedimentary structures and composition of these eskers are poorly known, despite being able to offer valuable insight into subglacial hydrological processes during deglaciation. This study presents detailed morphological and sedimentary evidence from six esker systems in north-central Ireland, where adjacent and interacting ice domes were characterized by changes in ice-bed thermal and hydrological properties as well as significant ice dome centre migration. Morphologically, esker ridges in this area vary in length, size and continuity, with some esker systems ascending over hills (thus crossing watersheds) whereas other systems are confined to basin settings. Esker systems commonly appear to feed terminal outwash and glaciolacustrine deltas, but several systems do not show a clear terminus. The internal sediments within eskers vary from concentrically-bedded sands and gravels formed within enclosed tunnels, to interbedded sands, gravels and diamictons, occasionally with water-induced soft-sediment deformations, that are likely formed in interlobate settings. In contrast with some previous glacier models that assume that esker systems are isochronous and were formed in solely subglacial settings, the esker systems described here are interpreted as being of different ages, formed in variously subglacial to ice-marginal settings, and thus cannot be used as a single snapshot of the disposition of ice domes during stages of late Devensian ice retreat.

Actively evolving subglacial conduits and eskers initiate ice shelf channels at an Antarctic grounding line

Ice-shelf channels are long curvilinear tracts of thin ice found on Antarctic ice shelves. Many of them originate near the grounding line, but their formation mechanisms remain poorly understood. Here we use ice-penetrating radar data from Roi Baudouin Ice Shelf, East Antarctica, to infer that the morphology of several ice-shelf channels is seeded upstream of the grounding line by large basal obstacles indenting the ice from below. We interpret each obstacle as an esker ridge formed from sediments deposited by subglacial water conduits, and calculate that the eskers’ size grows towards the grounding line where deposition rates are maximum. Relict features on the shelf indicate that these linked systems of subglacial conduits and ice-shelf channels have been changing over the past few centuries. Because ice-shelf channels are loci where intense melting occurs to thin an ice shelf, these findings expose a novel link between subglacial drainage, sedimentation and ice-shelf stability.

Sukcesja osadowa i etapy formowania ozu gostynińskiego, Równina Kutnowska, centralna Polska

Artykuł nie zawiera streszczenia w języku polski.

Rapid subglacial streamlined bedform formation at a calving bay margin

ABSTRACTUsing the LiDAR‐derived Swedish national height model we have identified previously undescribed shallow streamlined glacial bedforms, small‐scale drumlins, on the Närke plain in south‐central Sweden. These drumlins could only be detected with high‐resolution LiDAR, due to both their subtle size and forest cover. In this area the ice margin receded in a subaqueous environment with a proglacial water depth in the order of 100 m during the last deglaciation. As indicated by the configuration of marginally formed De Geer moraine ridges draping the drumlinoids, the receding ice margin formed deeply indented calving bays. These were located around subaqueous outlets of the subglacial melt‐water drainage, with their apex position marked geomorphologically by beaded esker ridges. The mapped small‐scale drumlins are aligned perpendicular to the reconstructed ice sheet margin and suggest formation along flow lines adjusted to the configuration of these calving embayments as they propagated up‐flow with ice margin retreat. Based on these geometric relationships we argue that the emplacement of the drumlins was near‐marginal, ∼7.7–1 km from the margin, on a short timescale (∼5–35 years).

Towards a morphogenetic classification of eskers: Implications for modelling ice sheet hydrology

Validations of paleo-ice sheet hydrological models have used esker spacing as a proxy for ice tunnel density. Changes in crest type (cross-sectional shape) along esker ridges have typically been attributed to the effect of changing subglacial topography on hydro- and ice-dynamics and hence subglacial ice-tunnel shape. These claims assume that all eskers formed in subglacial ice tunnels and that all major subglacial ice tunnels produced a remnant esker. We identify differences in geomorphic context, sinuosity, cross-sectional shape, and sedimentary architecture by analysing eskers formed at or near the margins of the last Cordilleran Ice Sheet on British Columbia's southern Fraser Plateau, and propose a morphogenetic esker classification. Three morphogenetic types and 2 subtypes of eskers are classified based on differences in geomorphic context, ridge length, sinuosity, cross-sectional shape and sedimentary architecture using geophysical techniques and sedimentary exposures; they largely record seasonal meltwater flows and glacial lake outburst floods (GLOFs) through sub-, en- and supraglacial meltwater channels and ice-walled canyons.General principles extracted from these interpretations are: 1) esker ridge crest type and sinuosity strongly reflect meltwater channel type. Eskers formed in subglacial conduits are likely to be round-crested with low sinuosity (except where controlled by ice structure or modified by surging) and contain faults associated with flank collapse. Eskers formed near or at the ice surface are more likely to be sharp-crested, highly sinuous, and contain numerous faults both under ridge crest-lines and in areas of flank collapse. 2) Esker ridges containing numerous flat-crested reaches formed directly on the land-surface in ice-walled canyons (unroofed ice tunnels) or in ice tunnels at atmospheric pressure, and therefore likely record thin or dead ice. 3) Eskers containing macroforms exhibiting headward and downflow growth likely record flood-scale flows (possibly GLOFs where a lake can be inferred). These conclusions suggest that esker crest type, sinuosity and geomorphic context, when understood along with sedimentary architecture, largely reflect formational position with respect to the ice-surface. Reconstructions of ice sheet hydrology need to account for variation in esker morphology because basing hydrodynamic inferences on the presence or absence of an esker alone ignores encoded differences in water source, supply, flow magnitude and frequency, and conduit position.

Digital landscapes of deglaciation: identifying Late Quaternary glacial lake outburst floods using LiDAR

AbstractHigh resolution DEMs obtained from LiDAR topographic data have led to improved landform inventories (e.g. landslides and fault scarps) and understanding of geomorphic event frequency. Here we use airborne LiDAR mapping to investigate meltwater pathways associated with the Tweed Valley palaeo ice‐stream (UK). In particular we focus on a gorge downstream of Palaeolake Milfield, previously mapped as a sub‐glacial meltwater channel, where the identification of abandoned headcut channels, run‐up bars, rock‐cut terrace surfaces and eddy flow features attest to formation by a sub‐aerial glacial lake outburst flood (GLOF) caused by breaching of a sediment dam, likely an esker ridge. Mapping of these landforms combined with analysis of the gorge rim elevations and cross‐section variability revealed a two phase event with another breach site downstream following flow blockage by higher elevation drumlin topography. We estimate the magnitude of peak flow to be 1–3 × 103 m3/s, duration of the event to range from 16–155 days, and a specific sediment yield of 107–109 m3/km2/yr. We identified other outburst pathways in the lower Tweed basin that help delineate an ice margin position of the retreating Tweed Valley ice stream. The results suggest that low magnitude outburst floods are under‐represented in Quaternary geomorphological maps. We therefore recommend regional LiDAR mapping of meltwater pathways to identify other GLOFs in order to better quantify the pattern of freshwater and sediment fluxes from melting ice sheets to oceans. Despite the relatively low magnitude of the Till outburst event, it had a significant impact on the landscape development of the lower Tweed Valley through the creation of a new tributary pathway and triggering of rapid knickpoint retreat encouraging new regional models of post‐glacial fluvial landscape response. Copyright © 2015 John Wiley & Sons, Ltd.

The role of sediment supply in esker formation and ice tunnel evolution

Meltwater is an important part of the glacier system as it can directly influence ice sheet dynamics. Although it is important that ice sheet models incorporate accurate information about subglacial meltwater processes, the relative inaccessibility of contemporary ice sheet beds makes direct investigation challenging. Former ice sheet beds contain a wealth of meltwater landforms such as eskers that, if accurately interpreted, can provide detailed insight into the hydrology of former ice sheets. Eskers are the casts of ice-walled channels and are a common landform within the footprint of the last Laurentide and Cordilleran Ice Sheets. In south-western Alberta, esker distribution suggests that both water and sediment supply may have been important controls; the longest esker ridge segments are located within meltwater valleys partially filled by glaciofluvial sediments, whereas the shortest esker ridge segments are located in areas dominated by clast-poor till. Through detailed esker ridge planform and crest-type mapping, and near surface geophysics we reveal morpho-sedimentary relationships that suggest esker sedimentation was dynamic, but that esker distribution and architecture were primarily governed by sediment supply. Through comparison of these data with data from eskers elsewhere, we suggest three formative scenarios: 1) where sediment supply and flow powers were high, coarse sediment loads result in rapid deposition, and rates of thermo-mechanical ice tunnel growth is exceeded by the rate of ice tunnel closure due to sediment infilling. High sedimentation rates reduce ice tunnel cross-sectional area, cause an increase in meltwater flow velocity and force ice tunnel growth. Thus, ice tunnel growth is fastest where sedimentation rate is highest; this positive feedback results in a non-uniform ice tunnel geometry, and favours macroform development and non-uniform ridge geometry. 2) Where sediment supply is limited, but flow power high, the rate of sedimentation is less than the rate of thermo-mechanical ice tunnel growth. Here the ice tunnel enlarges faster than it fills with sediment and its evolution is independent of sedimentation, resulting in more uniform ice tunnel geometry. In these cases esker architecture is dominated by extensive vertical accretion of tabular units and ridge geometry is more uniform. 3) Where sediment is truly supply-limited the sedimentation rate is negligible regardless of water supply and, like scenario 2, ice tunnel growth is independent of sediment deposition, forming a relatively uniform ice tunnel (or eroding the bed). Because meltwater flows transport few gravel clasts the ice tunnel is not completely filled with gravel and, instead, saturated and pressurized diamicton or bedrock (if deformable) from beneath the surrounding ice is “squeezed” into the relatively low pressure ice tunnel during waning flow (or after ice tunnel shutdown), resulting in deformation of limited gravels deposited within the ice tunnel and a landform cored with diamicton or deformed bedrock, and with a relatively uniform ridge geometry. Our data demonstrate that an esker map is a minimum map of ice-walled channel location and that continued detailed investigation of morpho-sedimentary relationships is essential to gaining a complete picture of esker forming processes. Validating the morpho-sedimentary relationships identified in south-western Alberta (and other areas) with a larger data set may allow improved remote predictive esker mapping over larger areas and inferences to be made about spatial and temporal variations in esker depositional environments and ice tunnel evolution.

Directions of ice flow during the last glaciation in counties Meath, Westmeath and Cavan

Ice flow direction indicators in north-west County Meath and adjacent parts of Westmeath and Cavan are described. Drumlins. striae, roche moulonnees. and oilier streamlined features, as well as till fabrics, suggest a general How during glacial maximum of north-west to south-east when combined with erratic carriage data. Analysis of the configuration of ice marginal moraines and subglacially deposited esker ridges deposited during glacial retreat, as well as till fabric analysis of deglacial sediments, suggest a more complicated retreat of ice, with margins oriented south-wesI to north-east prevailing in the south and cast of the study area. Further to the west and south-west there seems to be an element of retreat towards the west, with a north-south trending ice margin. This is suggested as providing evidence for a decoupling of the ice into separate lobes in that area.

Time-lapse electrical resistivity tomography of a water infiltration test on Johannishus Esker, Sweden

Managed aquifer recharge (MAR) is an efficient way to remove organic matter from raw water and, at the same time, reduce temperature variation. Two MAR sites were constructed by Karlskrona municipality on Johannishus Esker in Sweden. One of these sites, Vang, was monitored for electrical conductivity and electrical resistivity (using electrical resistivity tomography - ERT) during a 9-week tracer infiltration test. The aim of the monitoring was to map the pathways of the infiltrated water, with the overall goal to increase the efficiency of the MAR. ERT proved useful in determining both the nature of the esker formation and the water migration pathways. In Vang, the esker ridge follows a tectonically controlled paleo-valley. The fault/fracture zone in the bedrock along this paleo-valley was mapped. During the tracer test, the infiltrated water was detected in the area close to the infiltration ponds, whereas far-situated observation wells were less affected. For sequential infiltration and recharge periods in MAR, the timing of the well pumping is another important factor. Natural groundwater flow direction was a determinant in the infiltration process, as expected. ERT measurements provide supplementary data for site selection, for monitoring the functionality of the MAR sites, and for revealing the geological, hydrogeological and structural characteristics of the site.

Underdispersion and overdispersion of traits in terrestrial snail communities on islands.

Understanding and disentangling different processes underlying the assembly and diversity of communities remains a key challenge in ecology. Species can assemble into communities either randomly or due to deterministic processes. Deterministic assembly leads to species being more similar (underdispersed) or more different (overdispersed) in certain traits than would be expected by chance. However, the relative importance of those processes is not well understood for many organisms, including terrestrial invertebrates. Based on knowledge of a broad range of species traits, we tested for the presence of trait underdispersion (indicating dispersal or environmental filtering) and trait overdispersion (indicating niche partitioning) and their relative importance in explaining land snail community composition on lake islands. The analysis of community assembly was performed using a functional diversity index (Rao's quadratic entropy) in combination with a null model approach. Regression analysis with the effect sizes of the assembly tests and environmental variables gave information on the strength of under- and overdispersion along environmental gradients. Additionally, we examined the link between community weighted mean trait values and environmental variables using a CWM-RDA. We found both trait underdispersion and trait overdispersion, but underdispersion (eight traits) was more frequently detected than overdispersion (two traits). Underdispersion was related to four environmental variables (tree cover, habitat diversity, productivity of ground vegetation, and location on an esker ridge). Our results show clear evidence for underdispersion in traits driven by environmental filtering, but no clear evidence for dispersal filtering. We did not find evidence for overdispersion of traits due to diet or body size, but overdispersion in shell shape may indicate niche differentiation between snail species driven by small-scale habitat heterogeneity. The use of species traits enabled us to identify key traits involved in snail community assembly and to detect the simultaneous occurrence of trait underdispersion and overdispersion.

Transient subglacial hydrology of a thin ice sheet: insights from the Chasm esker, British Columbia, Canada

Glacier drainage systems are never steady state; instead they fluctuate over time and space in response to variation in water input. In order to improve numerical models of glacier hydrology it is important to fully understand the processes controlling subglacial drainage system evolution, but contemporary ice sheet beds are typically inaccessible. Thus, esker distribution, morphology, and sedimentology have been used to infer the dynamics and hydrology of former ice sheets. However, debate remains as to the processes responsible for esker formation and most theoretical investigations have assumed that they formed due to processes that operated beneath thick ice despite many field investigations to the contrary. We investigate esker formation during the final stages of the thin, inactive, and rapidly decaying Cordilleran Ice Sheet (CIS) in interior British Columbia, Canada. A combination of geomorphological, ground-penetrating radar (GPR) and electrical resistivity tomography (ERT) data suggest esker ridge sedimentary architecture is consistent with synchronous formation during a glacial lake outburst flood (GLOF). These data reveal esker ridge deposition most likely took place within an ice tunnel that evacuated late-waning stage flow, following erosion and partial fill of a broader meltwater corridor. Esker ridge sedimentary architecture reveals this depositional environment was dynamic, reflecting complex interaction between ice thickness, ice structure, ice tunnel geometry, flow conditions, and sediment supply. Under these thin, inactive ice conditions ice tunnel location was initially governed by structural weaknesses in the ice and/or equipotential gradient. Because creep closure rates were low, the ice tunnel evolved through feedbacks between conduit growth via frictional melting/mechanical ice excavation, and conduit closure due to sediment infilling, rather than ice creep. This resulted in a non-uniform ice tunnel that enlarged in an upglacier direction and locally unroofed to form open channels during its final stages. These data suggest that eskers may record unsteady, rather than steady flows in a drainage network and so the assumptions often made when using eskers to inform hydrological components of ice sheet models may not be applicable to all ice sheet settings.