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Journal articles on the topic 'Subglacial bedforms'

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Author: Grafiati

Published: 10 December 2022

Last updated: 28 January 2023

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1

Vérité, Jean, Édouard Ravier, Olivier Bourgeois, Stéphane Pochat, Thomas Lelandais, Régis Mourgues, Christopher D. Clark, Paul Bessin, David Peigné, and Nigel Atkinson. "Formation of ribbed bedforms below shear margins and lobes of palaeo-ice streams." Cryosphere 15, no. 6 (June 28, 2021): 2889–916. http://dx.doi.org/10.5194/tc-15-2889-2021.

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Abstract. Conceptual ice stream land systems derived from geomorphological and sedimentological observations provide constraints on ice–meltwater–till–bedrock interactions on palaeo-ice stream beds. Within these land systems, the spatial distribution and formation processes of ribbed bedforms remain unclear. We explore the conditions under which these bedforms may develop and their spatial organization with (i) an experimental model that reproduces the dynamics of ice streams and subglacial land systems and (ii) an analysis of the distribution of ribbed bedforms on selected examples of palaeo-ice stream beds of the Laurentide Ice Sheet. We find that a specific kind of ribbed bedform can develop subglacially through soft-bed deformation, where the ice flow undergoes lateral or longitudinal velocity gradients and the ice–bed interface is unlubricated; oblique ribbed bedforms develop beneath lateral shear margins, whereas transverse ribbed bedforms develop below frontal lobes. We infer that (i) ribbed bedforms strike orthogonally to the compressing axis of the horizontal strain ellipse of the ice surface and (ii) their development reveals distinctive types of subglacial drainage patterns: linked cavities below lateral shear margins and efficient meltwater channels below frontal lobes. These ribbed bedforms may act as convenient geomorphic markers to reconstruct lateral and frontal margins, constrain ice flow dynamics, and infer meltwater drainage characteristics of palaeo-ice streams.

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2

Knight, Jasper, G. McCarron Stephen, and A. Marshall McCabe. "Landform modification by palaeo-ice streams in east-central Ireland." Annals of Glaciology 28 (1999): 161–67. http://dx.doi.org/10.3189/172756499781821616.

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AbstractIn eastern Ireland, subglacial bedforms including drumlins and Rogen moraines were modified by headward erosion along two ice streams which had overlapping flow tracks. The ice streams, which had tidewater termini, are dated by geochronometric and morphostratigraphic methods to <15.014 C kyr BP (Castleblaney ice stream) and ~13.814C kyr BP (Armagh ice stream). Bedforms along ice-stream tracks show a morphological continuum which reflects a down-ice increase in the degree of modification by ice-stream activity (i.e. resulting in unmodified →remoulded/overprinted →crosscut →streamlined bedforms). The down-ice changes in bedform types are inferred to relate to changes in subglacial drainage and sediment-transport mechanisms. Bedform and sedimentary evidence suggest that discrete subglacial meltwater channels which developed up- ice changed in a down-ice direction to unchannelized flows which deepened towards the ice margin. Meltwater release from subglacial cavities, and produced by strain heating at sheared ice-stream margins, probably helped support ice-stream flow, which ended as the volume of subglacial meltwater discharge decreased. Dated millennial-scale cycles of ice activity may be related to instability at tidewater margins, followed by complex thermal and hydraulic responses within the ice mass.

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3

Menzies, J., and J. Rose. "Subglacial bedforms—an introduction." Sedimentary Geology 62, no. 2-4 (May 1989): 117–22. http://dx.doi.org/10.1016/0037-0738(89)90111-5.

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4

Riverman, Kiya L., Sridhar Anandakrishnan, Richard B. Alley, Nicholas Holschuh, Christine F. Dow, Atsuhiro Muto, Byron R. Parizek, Knut Christianson, and Leo E. Peters. "Wet subglacial bedforms of the NE Greenland Ice Stream shear margins." Annals of Glaciology 60, no. 80 (December 2019): 91–99. http://dx.doi.org/10.1017/aog.2019.43.

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AbstractWe describe elongate, wet, subglacial bedforms in the shear margins of the NE Greenland Ice Stream and place some constraints on their formation. Lateral shear margin moraines have been observed across the previously glaciated landscape, but little is known about the ice-flow conditions necessary to form these bedforms. Here we describe in situ sediment bedforms under the NE Greenland Ice Stream shear margins that are observed in active-source seismic and ground-penetrating radar surveys. We find bedforms in the shear margins that are ~500 m wide, ~50 m tall, and elongated nearly parallel to ice-flow, including what we believe to be the first subglacial observation of a shear margin moraine. Acoustic impedance analysis of the bedforms shows that they are composed of unconsolidated, deformable, water-saturated till. We use these geophysical observations to place constraints on the possible formation mechanism of these subglacial features.

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5

Shaw, John. "The meltwater hypothesis for subglacial bedforms." Quaternary International 90, no. 1 (April 2002): 5–22. http://dx.doi.org/10.1016/s1040-6182(01)00089-1.

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6

Greenwood, Sarah L., and Chris D. Clark. "Subglacial bedforms of the Irish Ice Sheet." Journal of Maps 4, no. 1 (January 2008): 332–57. http://dx.doi.org/10.4113/jom.2008.1030.

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7

Rea, Brice R., David J. A. Evans, Tom S. Dixon, and W. Brian Whalley. "Contemporaneous, localized, basal ice-flow variations: implications for bedrock erosion and the origin of p-forms." Journal of Glaciology 46, no. 154 (2000): 470–76. http://dx.doi.org/10.3189/172756500781833197.

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AbstractA detailed study of a proglacial bedrock site and a subglacial cavity of an outlet of Øksfjordjøkelen, Norway, is presented together with observations from the foreland of Konowbreen, Spitsbergen. Striation directions and subglacial observations indicate that local ice-flow paths were highly variable, deviating at angles of approximately 90° from the main ice-flow direction. Stepped bedrock topography appears conducive to the production of highly variable ice-flow paths, because the high bed roughness creates a locally variable stress regime within the ice, including low-pressure, lee-side areas into which ice can flow. If ice flow is sustained along a specific path and the ice contains debris, then abrasion should produce an erosional bedform. Models are proposed whereby locally variable ice-flow patterns could produce erosional bedforms, which would be described as p-forms, purely through mechanical abrasion.

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8

STOKES, CHRIS R., MARTIN MARGOLD, and TIMOTHY T. CREYTS. "Ribbed bedforms on palaeo-ice stream beds resemble regular patterns of basal shear stress (‘traction ribs’) inferred from modern ice streams." Journal of Glaciology 62, no. 234 (May 10, 2016): 696–713. http://dx.doi.org/10.1017/jog.2016.63.

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Rapidly-flowing ice streams are an important mechanism through which ice sheets lose mass, and much work has been focussed on elucidating the processes that increase or decrease their velocity. Recent work using standard inverse methods has inferred previously-unrecognised regular patterns of high basal shear stress (‘sticky spots’ >200 kPa) beneath a number of ice streams in Antarctica and Greenland, termed ‘traction ribs’. They appear at a scale intermediate between smaller ribbed moraines and much larger mega-ribs observed on palaeo-ice sheet beds, but it is unclear whether they have a topographic expression at the bed. Here, we report observations of rib-like bedforms from DEMs along palaeo-ice stream beds in western Canada that resemble both the pattern and dimensions of traction ribs. Their identification suggests that traction ribs may have a topographic expression that lies between, and partly overlaps with, ribbed moraines and much larger mega-ribs. These intermediate-sized bedforms support the notion of a ribbed bedform continuum. Their formation remains conjectural, but our observations from palaeo-ice streams, coupled with those from modern ice masses, suggest they are related to wave-like instabilities occurring in the coupled flow of ice and till and modulated by subglacial meltwater drainage. Their form and pattern may also involve glaciotectonism of subglacial sediments.

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9

Baltrūnas, Valentinas, Richard I. Waller, Vaidotas Kazakauskas, Stasys Paškauskas, and Valentas Katinas. "A comparative case study of subglacial bedforms in northern Lithuania and south-eastern Iceland." Baltica 27, no. 2 (February 20, 2014): 75–92. http://dx.doi.org/10.5200/baltica.2014.27.18.

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This paper aims to compare the dynamics of the subglacial environment as determined by an analysis of the structure and sedimentology of both Pleistocene and modern glacial deposits. Investigations focused on subglacial sediments in areas of streamlined relief in northern Lithuania (Ruopiškiai megascale subglacial lineations - MSGL) and south-eastern Iceland (drumlinised terrain exposed by the recent retreat of Skeiðarárjökull glacier). Sedimentological analyses involved granulometry, till macrofabrics, and the anisotropy of magnetic susceptibility (AMS) of micro-clasts. Comparative investigations of subglacial bedforms exposed at Ruopiškiai and Skeiðarárjökull highlighted differences in their formation and post-genetic transformation. In both cases, their initiation was associated with ice advance and subglacial sediment deformation. However, subsequent dynamics were different.

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10

Hillier, J. K., M. J. Smith, C. D. Clark, C. R. Stokes, and M. Spagnolo. "Subglacial bedforms reveal an exponential size–frequency distribution." Geomorphology 190 (May 2013): 82–91. http://dx.doi.org/10.1016/j.geomorph.2013.02.017.

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11

Hughes, Anna L. C., Chris D. Clark, and Colm J. Jordan. "Subglacial bedforms of the last British Ice Sheet." Journal of Maps 6, no. 1 (January 2010): 543–63. http://dx.doi.org/10.4113/jom.2010.1111.

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12

Clark, Chris D. "Emergent drumlins and their clones: from till dilatancy to flow instabilities." Journal of Glaciology 56, no. 200 (2010): 1011–25. http://dx.doi.org/10.3189/002214311796406068.

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AbstractSubglacial bedforms are a range of landforms (10-105m long) shaped mostly in glacial sediments and are abundant on ice-sheet beds. Numerous explanations for their generation, especially of drumlins, have been proposed. Rather than viewing them as resulting from erosion or deposition directly by ice, Smalley and Unwin (1968) proposed that both might occur simultaneously if, beneath the glacier, a layer of lubricating sediment existed and ‘flowed’, conducting geomorphic work (erosion, deposition, shaping) of its own. This idea appears to have steered the field, leading perhaps to final resolution of the centuries-old problem of drumlin genesis. Here I trace how the idea evolved, leading to the conclusion that subglacial bedforms are emergent phenomena arising from self-organization in the coupled flow of ice, sediment and water. The ubiquity and patterning of bedforms appears to be well explained by a naturally arising flow instability in the subglacial system, and which has been demonstrated by analytical and numerical modelling. A problem for the instability theory is an apparent mismatch between predicted and observed sedimentological properties of bedforms. A distinction is made between emergent drumlins, drumlin clones and obstacle drumlins which helps explain some apparent contradictions, and a conceptual framework is erected that might form a basis for confronting the theory with the wealth of observational evidence that exists.

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13

Tinkler, K. J. "Fluvially sculpted rock bedforms in Twenty Mile Creek, Niagara Peninsula, Ontario." Canadian Journal of Earth Sciences 30, no. 5 (May 1, 1993): 945–53. http://dx.doi.org/10.1139/e93-079.

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Sculpted rock bedforms (s-forms) on Whirlpool Sandstone are described from the bed of Twenty Mile Creek. The morphologies identified (undulating surfaces, rises, furrows, comma forms, spindles, potholes, and transverse troughs) are those described for sculpted bedrock forms (p-forms, s-forms) developed in subglacial environments. Additional morphologies identified are undercut downsteps and quarried surfaces in the lee of bedrock rises. Morphological differences between the subglacial and fluvial forms are attributed to the difference between confined conduit flow in the subglacial case and open-channel flow in the fluvial examples. In fluvial systems the descending bedrock surface presents rock differently to oncoming flows and favours certain s-forms (quarried lee faces and undulating surfaces). In a strong-flow fluvial environment s-forms develop by wear. Dominant sediment-transport modes are large clasts (up to metre dimensions) and suspended silt–clay with a small (< 7%) hard or heavy-mineral component. Hydraulic quarrying, which removes fracture-delimited blocks from the bed, interrupts the process. Although fluvial s-forms are similar to subglacial s-forms, large stable vortices may not exist in the fluvial context over the range of effective stages. Upper regime flow is common over bedrock reaches, and flow acceleration at small downsteps (knickpoints) magnifies the duration and spatial extent of wear effective velocities.

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14

Schoof, Christian. "Basal perturbations under ice streams: form drag and surface expression." Journal of Glaciology 48, no. 162 (2002): 407–16. http://dx.doi.org/10.3189/172756502781831269.

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AbstractClassical sliding theories consider ice sliding over obstacles which are much shorter than the thickness of overlying ice. Here we present a theory which considers “form drag” generated under ice streams by large obstacles such as subglacial bedforms, which may have lengths comparable to ice thickness. We also investigate how perturbations at the surface of an ice stream can be generated by such bedforms, and develop a mathematical framework for separating the effects of such local (kilometre-scale) variations in ice flow from the bulk flow of the ice stream.

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15

Stokes, Chris R., and Chris D. Clark. "Are long subglacial bedforms indicative of fast ice flow?" Boreas 31, no. 3 (September 1, 2002): 239–49. http://dx.doi.org/10.1080/030094802760260355.

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16

Ely, Jeremy C., Chris D. Clark, Matteo Spagnolo, Chris R. Stokes, Sarah L. Greenwood, Anna L. C. Hughes, Paul Dunlop, and Dale Hess. "Do subglacial bedforms comprise a size and shape continuum?" Geomorphology 257 (March 2016): 108–19. http://dx.doi.org/10.1016/j.geomorph.2016.01.001.

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17

STOKES, CHRIS R., and CHRIS D. CLARK. "Are long subglacial bedforms indicative of fast ice flow?" Boreas 31, no. 3 (June 28, 2008): 239–49. http://dx.doi.org/10.1111/j.1502-3885.2002.tb01070.x.

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18

Fowler, A. C. "Instability modelling of drumlin formation incorporating lee-side cavity growth." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 465, no. 2109 (June 17, 2009): 2681–702. http://dx.doi.org/10.1098/rspa.2008.0490.

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It is proposed that the formation of the subglacial bedforms known as drumlins occurs through an instability associated with the flow of ice over a wet deformable till. We pose a mathematical model that describes this instability, and we solve a simplified version of the model numerically in order to establish the form of finite-amplitude two-dimensional waveforms. A feature of the solutions is that cavities frequently form downstream of the bedforms; we allow the model to cater for this possibility and we provide an efficient numerical method to solve the resulting free boundary problem.

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19

Lamsters, Kristaps, and Vitālijs Zelčs. "Subglacial bedforms of the Zemgale Ice Lobe, south-eastern Baltic." Quaternary International 386 (November 2015): 42–54. http://dx.doi.org/10.1016/j.quaint.2014.10.006.

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20

Fowler, A. C. "The formation of subglacial streams and mega-scale glacial lineations." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 466, no. 2123 (April 21, 2010): 3181–201. http://dx.doi.org/10.1098/rspa.2010.0009.

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The instability theory of drumlin formation has been very successful in predicting the existence of ribbed moraine, as well as its amplitude and wavelength. However, the theory as it stands has not yet been shown to have the capability of predicting the existence of three-dimensional bedforms—drumlins—or their more extreme cousins, mega-scale glacial lineations. We extend the instability theory to include a dynamic description of the local subglacial drainage system, and in particular, we show that a uniform water-film flow between ice and deformable subglacial till is unstable, and that as a consequence, lineations will form. Predictions of the transverse wavelengths are consistent with observations.

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21

Fowler, A. C., and M. Chapwanya. "An instability theory for the formation of ribbed moraine, drumlins and mega-scale glacial lineations." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2171 (November 8, 2014): 20140185. http://dx.doi.org/10.1098/rspa.2014.0185.

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We present a theory for the coupled flow of ice, subglacial water and subglacial sediment, which is designed to represent the processes which occur at the bed of an ice sheet. The ice is assumed to flow as a Newtonian viscous fluid, the water can flow between the till and the ice as a thin film, which may thicken to form streams or cavities, and the till is assumed to be transported, either through shearing by the ice, squeezing by pressure gradients in the till, or by fluvial sediment transport processes in streams or cavities. In previous studies, it was shown that the dependence of ice sliding velocity on effective pressure provided a mechanism for the generation of bedforms resembling ribbed moraine, while the dependence of fluvial sediment transport on water film depth provides a mechanism for the generation of bedforms resembling mega-scale glacial lineations. Here, we combine these two processes in a single model, and show that, depending largely on the granulometry of the till, instability can occur in a range of types which range from ribbed moraine through three-dimensional drumlins to mega-scale glacial lineations.

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22

LIVINGSTONE, STEPHEN J., CHRIS R. STOKES, COLM Ó COFAIGH, CLAUS-DIETER HILLENBRAND, ANDREAS VIELI, STEWART S. R. JAMIESON, MATTEO SPAGNOLO, and JULIAN A. DOWDESWELL. "Subglacial processes on an Antarctic ice stream bed. 1: Sediment transport and bedform genesis inferred from marine geophysical data." Journal of Glaciology 62, no. 232 (March 17, 2016): 270–84. http://dx.doi.org/10.1017/jog.2016.18.

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ABSTRACTThe spatial pattern and morphometry of bedforms and their relationship to sediment thickness have been analysed in the Marguerite Bay Palaeo-ice stream Trough, western Antarctic Peninsula. Over 17 000 glacial landforms were measured from geophysical datasets, and sediment thickness maps were generated from acoustic sub-bottom profiler data. These analyses reveal a complex bedform pattern characterised by considerable spatial diversity, influenced heavily by the underlying substrate. The variability in length and density of mega-scale lineations indicates an evolving bedform signature, whereby landforms are preserved at different stages of maturity. Lineation generation and attenuation is associated with regions of thick, soft till where deformation was likely to be the greatest. The distribution of soft till and the localised extent of grounding-zone wedges (GZWs) indicate a dynamic sedimentary system characterised by considerable spatio-temporal variability in sediment erosion, transport and deposition. Formation of GZWs on the outer shelf of Marguerite Trough, within the error range of the radiocarbon dates, requires large sediment fluxes (upwards of 1000 m3 a−1 (m grounding line width)−1), and a >1 m thick mobile till layer, or rapid basal sliding velocities (upwards of 6 km a−1).

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23

Ng, Felix S. L., and Anna L. C. Hughes. "Reconstructing ice-flow fields from streamlined subglacial bedforms: A kriging approach." Earth Surface Processes and Landforms 44, no. 4 (November 20, 2018): 861–76. http://dx.doi.org/10.1002/esp.4538.

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24

WALLER, RICHARD I., THAIENNE A. G. P. VAN DIJK, and ÓSKAR KNUDSEN. "Subglacial bedforms and conditions associated with the 1991 surge of Skeiðarárjökull, Iceland." Boreas 37, no. 2 (May 2008): 179–94. http://dx.doi.org/10.1111/j.1502-3885.2007.00017.x.

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25

Schroeder, Dustin M., Robert G. Bingham, Donald D. Blankenship, Knut Christianson, Olaf Eisen, Gwenn E. Flowers, Nanna B. Karlsson, Michelle R. Koutnik, John D. Paden, and Martin J. Siegert. "Five decades of radioglaciology." Annals of Glaciology 61, no. 81 (March 9, 2020): 1–13. http://dx.doi.org/10.1017/aog.2020.11.

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AbstractRadar sounding is a powerful geophysical approach for characterizing the subsurface conditions of terrestrial and planetary ice masses at local to global scales. As a result, a wide array of orbital, airborne, ground-based, and in situ instruments, platforms and data analysis approaches for radioglaciology have been developed, applied or proposed. Terrestrially, airborne radar sounding has been used in glaciology to observe ice thickness, basal topography and englacial layers for five decades. More recently, radar sounding data have also been exploited to estimate the extent and configuration of subglacial water, the geometry of subglacial bedforms and the subglacial and englacial thermal states of ice sheets. Planetary radar sounders have observed, or are planned to observe, the subsurfaces and near-surfaces of Mars, Earth's Moon, comets and the icy moons of Jupiter. In this review paper, and the thematic issue of the Annals of Glaciology on ‘Five decades of radioglaciology’ to which it belongs, we present recent advances in the fields of radar systems, missions, signal processing, data analysis, modeling and scientific interpretation. Our review presents progress in these fields since the last radio-glaciological Annals of Glaciology issue of 2014, the context of their history and future prospects.

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26

Vérité, Jean, Édouard Ravier, Olivier Bourgeois, Paul Bessin, Stephen J. Livingstone, Christopher D. Clark, Stéphane Pochat, and Régis Mourgues. "Formation of murtoos by repeated flooding of ribbed bedforms along subglacial meltwater corridors." Geomorphology 408 (July 2022): 108248. http://dx.doi.org/10.1016/j.geomorph.2022.108248.

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27

Ó Cofaigh, Colm, Carol J. Pudsey, Julian A. Dowdeswell, and Peter Morris. "Evolution of subglacial bedforms along a paleo-ice stream, Antarctic Peninsula continental shelf." Geophysical Research Letters 29, no. 8 (April 2002): 41–1. http://dx.doi.org/10.1029/2001gl014488.

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28

Fannon, J. S., A. C. Fowler, and I. R. Moyles. "Numerical simulations of drumlin formation." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, no. 2204 (August 2017): 20170220. http://dx.doi.org/10.1098/rspa.2017.0220.

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We summarize the present form of the instability theory for drumlin formation, which describes the coupled subglacial flow of ice, water and sediment. This model has evolved over the last 20 years, and is now at the point where it can predict instabilities corresponding to ribbed moraine, drumlins and mega-scale glacial lineations, but efforts to provide numerical solutions of the model have been limited. The present summary adds some slight nuances to previously published versions of the theory, notably concerning the constitutive description of the subglacial water film and its flow. A new numerical method is devised to solve the model, and we show that it can be solved for realistic values of most of the parameters, with the exception of that corresponding to the water film thickness. We show that evolved bedforms can be three-dimensional and of the correct sizes, and we explore to some extent the variation of the solutions with the model’s parameters.

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29

Jorge, Marco G., and Tracy A. Brennand. "Semi-automated extraction of longitudinal subglacial bedforms from digital terrain models – Two new methods." Geomorphology 288 (July 2017): 148–63. http://dx.doi.org/10.1016/j.geomorph.2017.04.001.

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30

Spagnolo, Matteo, Edward C. King, David W. Ashmore, Brice R. Rea, Jeremy C. Ely, and Chris D. Clark. "Looking through drumlins: testing the application of ground-penetrating rada." Journal of Glaciology 60, no. 224 (2014): 1126–34. http://dx.doi.org/10.3189/2014jog14j110.

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AbstractGround-penetrating radar (GPR) is becoming a commonly applied technique in geomorphology. However, its use in the study of subglacial bedforms has yet to be fully explored and exploited. This paper presents the results of a GPR feasibility study conducted on a drumlinized terrain in Cumbria, UK, where five drumlins were investigated using multiple radar antenna frequencies. The site was selected for the presence of nearby bedrock outcrops, suggesting a shallow drumlinized diamict–bedrock contact and a permeable lithology. Despite the clayey sediment and unfavourable weather conditions, a considerable penetration depth of ~12 m was achieved when using a 50 MHz antenna, with a separation of 1 m, trace spacing of 1 m and 128-fold vertical stack. Results indicate that the drumlinized diamict is in direct erosional contact with the bedrock. While the internal drumlin geometry is generally chaotic on the stoss side, evidence of layering dipping downflow at an angle greater than the drumlin surface profile was found on the lee side. The inter-drumlin areas comprise ~4 m of infill sediment that masks part of the original drumlin profile. Overall, this study indicates that GPR can be deployed successfully in the study of glacial bedform sedimentary architecture.

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31

Frydrych, Małgorzata. "Complex genesis of N-channel eskers illustrated with the example of an esker near Tosie (east-central Poland)." Acta Universitatis Lodziensis. Folia Geographica Physica, no. 20 (December 30, 2021): 13–25. http://dx.doi.org/10.18778/1427-9711.20.02.

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The study presents the problem of complex genesis of eskers formed in N-channels on the example of an esker located near Tosie in east-central Poland. The lithofacies analysis revealed a high diversity of structural and textural characteristics of sediments in this form. The esker consists of three sedimentation units. Coarse sediments of the esker core were deposited in the subenvironment of a subglacial tunnel, as an effect of bedforms migration under hydrostatic pressure. Opening of the tunnel resulted in the forming of an open crevasse, in which the cover of the esker core sediments was accumulated. These deposits recorded a significant variability of flow energy and sedimentation mechanisms, which indicates a strong influence of the ice-sheet ablation dynamics. During the final deglaciation stage, a part of the esker was covered with diamicton. Numerous soft-sediment deformation structures were identified within the esker. The sediments were dislocated vertically to the elevation of more than 8 metres. They constitute the record of buried dead-ice masses melting in the esker core sediments. Melting of the masses resulted in vertical displacement of sediments and formation of "the dead-ice structure". The complexity of esker genesis is characteristic of postglacial areas in Poland, where most eskers were formed in subglacial N-channels. Numerous research results confirm a considerably more frequent occurrence of the facies sequence of subglacial tunnel and open crevasse in eskers formed in N-channels than R-channels. This is indicated by a much greater dissimilarity of processes during different stages of esker formation on soft bed and solid substratum.

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32

Le Heron, Daniel Paul, Christoph Kettler, Bethan J. Davies, Lars Scharfenberg, Lukas Eder, Michael Ketterman, Gerit E. U. Griesmeier, et al. "Rapid geomorphological and sedimentological changes at a modern Alpine ice margin: lessons from the Gepatsch Glacier, Tirol, Austria." Journal of the Geological Society 179, no. 3 (October 28, 2021): jgs2021–052. http://dx.doi.org/10.1144/jgs2021-052.

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The Gepatsch Glacier in Tirol (Austria) is a rapidly retreating valley glacier whose host valley and forefield reveal subglacial, proglacial, and reworked sediment–landform assemblages. Structures include roches moutonées develop on gneiss, compound bedrock-sediment bedforms (crag and tail structures), flutes, and small diamicton ridges. The glacial sediments and landforms are undergoing incision and terrace development by meltwater streams. Glacial geomorphological and surface geological maps, in concert with elevation models of difference between July 2019 and July 2020 highlight considerable changes to the forefield over a 12-month time period. Till exposed within the last 20 years has undergone substantial mass wasting and re-deposition as subaerial mass flows, or reworked into stream deposits. The lee sides of many roches moutonées completely lack subglacial sediment, and instead contain a sand and gravel deposit interpreted to result from glaciofluvial deposition. Thus, insights into the rates of erosion and deposition in a complex, proglacial setting, allow some of these processes to be quantified for the first time. Repeated monitoring of glacier forefields is expected to yield a better understanding of the preservation potential of proglacial sedimentary facies, and hence their preservation potential in Earth's sedimentary record.Supplementary material: A comparison of 3D model parameters for 2019 and 2020 data is available at https://doi.org/10.6084/m9.figshare.c.5664299

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Reinardy, Benedict T. I., Robert D. Larter, Claus-Dieter Hillenbrand, Tavi Murray, John F. Hiemstra, and Adam D. Booth. "Streaming flow of an Antarctic Peninsula palaeo-ice stream, both by basal sliding and deformation of substrate." Journal of Glaciology 57, no. 204 (2011): 596–608. http://dx.doi.org/10.3189/002214311797409758.

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AbstractAcoustic sub-bottom profiler surveys on the northeast Antarctic Peninsula shelf indicate that parts of the seabed are underlain by an acoustically transparent layer that is thin on the inner shelf and becomes thicker and more extensive towards the outer shelf. Sedimentological and geophysical data are combined to construct a bed model where streaming ice flow, by both deformation and basal sliding, took place within cross-shelf troughs. The model suggests only limited deformation contributed to fast flow on the inner shelf, i.e. in the onset zone of ice streaming, where the bed was predominantly underlain by a stiff till. Thus, fast ice flow in this area might have been by basal sliding, with deformation confined to discontinuous patches of soft till <40 cm thick. Towards the middle and outer shelf, extensive, thick sequences of soft till suggest a change in the dominant subglacial process towards widespread deformation. This downstream change from basal sliding to subglacial deformation is manifest in the transition from stiff-till dominance to soft-till dominance, while a downstream increase in ice flow velocity is evident from the complex geomorphic imprint on the inner shelf evolving to the more restricted set of bedforms on the outer shelf.

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O'Brien, P. E., L. De Santis, P. T. Harris, E. Domack, and P. G. Quilty. "Ice shelf grounding zone features of western Prydz Bay, Antarctica: sedimentary processes from seismic and sidescan images." Antarctic Science 11, no. 1 (March 1999): 78–91. http://dx.doi.org/10.1017/s0954102099000115.

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Several grounding zone wedges were left on the floor and flanks of Prydz Channel in western Prydz Bay by the Lambert Glacier during the last glacial cycle. Seismic profiles indicate that vertical accretion at the glacier bed was the most important depositional process in forming the wedges, rather than progradation by sediment gravity flows. Sidescan sonographs reveal extensive development of flutes on the sea floor inshore from the wedges, indicating deformable bed conditions beneath the ice. The region inshore of the east Prydz Channel wedge features extensive dune fields formed by currents flowing towards the grounding zone. This orientation is consistent with models of circulation beneath ice shelves in which melting at the grounding line generates plumes of fresher water that rise along the base of the ice shelf, entraining sea water into a circulation cell. The Lambert Deep is surrounded by a large composite ridge of glacial sediments. Internal reflectors suggest formation mostly by subglacial accretion. The sea floor in the Lambert Deep lacks dune fields and shows evidence of interspersed subglacial cavities and grounded ice beneath the glacier. The absence of bedforms reflects sea floor topography that would have inhibited the formation of energetic melt water-driven circulation.

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BRINER, JASON P. "Supporting evidence from the New York drumlin field that elongate subglacial bedforms indicate fast ice flow." Boreas 36, no. 2 (April 2007): 143–47. http://dx.doi.org/10.1111/j.1502-3885.2007.tb01188.x.

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36

Möller, Per, and Thomas P. F. Dowling. "Streamlined subglacial bedforms on the Närke plain, south-central Sweden – Areal distribution, morphometrics, internal architecture and formation." Quaternary Science Reviews 146 (August 2016): 182–215. http://dx.doi.org/10.1016/j.quascirev.2016.04.007.

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37

King, Edward C. "The precision of radar-derived subglacial bed topography: a case study from Pine Island Glacier, Antarctica." Annals of Glaciology 61, no. 81 (April 2020): 154–61. http://dx.doi.org/10.1017/aog.2020.33.

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AbstractRecent advances in the measurement of bedforms beneath active ice streams have been made using ground-based grid profiling using impulse radar systems operating with centre frequencies in the 3–5 MHz range. Surveys of Rutford Ice Stream and Pine Island Glacier have shown that features such as mega-scale glacial lineations with topographic relief of as little as 3 m can be traced for many kilometres downstream under more than 2 km of fast-moving ice. In the discussion of these data, it is often asked ‘How is it possible to map such fine-scale topography with such a low-frequency radar’. In answering that question, the key point is the distinction between the precision of a radar range measurement to a single, isolated reflective interface and the ability to resolve the presence of two closely-spaced interfaces of similar reflectivity (commonly referred to as the vertical resolution). This paper will discuss and illustrate this distinction and use the case study of data acquired over Pine Island Glacier to examine the limits of precision of the radar range measurement.

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Chen, Xiaoshuai, Hongwei Kuang, Yongqing Liu, Yuchong Wang, Zhenrui Yang, Thomas Matthew Vandyk, Daniel Paul Le Heron, et al. "Subglacial bedforms and landscapes formed by an ice sheet of Ediacaran-Cambrian age in west Henan, North China." Precambrian Research 344 (July 2020): 105727. http://dx.doi.org/10.1016/j.precamres.2020.105727.

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39

Sjogren, D. B., and R. B. Rains. "Glaciofluvial erosional morphology and sediments of the Coronation–Spondin Scabland, east-central Alberta." Canadian Journal of Earth Sciences 32, no. 5 (May 1, 1995): 565–78. http://dx.doi.org/10.1139/e95-048.

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Spatially discontinuous meltwater channel networks on the Canadian Prairies are usually interpreted as having formed subaerially in front of the retreating Laurentide ice sheet. Evidence in the Coronation–Spondin scabland, east-central Alberta, supports an alternative formation by progressive channelization of a subglacial sheetflow of water. The scabland is an integrated channel network with varying degrees of anabranching, the channels having highly variable sizes, shapes, and orientations. Enhanced scour at some channel confluences reflects contemporaneous channel utilization. Channels also display convex-up, concave-up, and undulatory along-channel profiles, with some junctions at the same elevations. Longitudinal grooves in large-scale channels are associated with numerous boulder deposits. Residual hills, demarcated by channels, display composite and streamlined forms. Superimposed on residuals are erosional transverse bedforms, longitudinal grooves, and undulating surfaces that indicate submergence for all but the last phase of channelization. Glaciofluvial deposits are found as pendant bars on the distal end of some large, flat-topped residuals, or as mantles superimposed on some residuals. The scabland is interpreted to have formed as a waning, subglacial sheetflood diverted around hummocky terrain to the southwest. A rapidly subsiding ice roof, and instability in the flow, eventually concentrated meltwater into discrete channels. Abrupt cessation of flow left discontinuous gravel–boulder deposits, and ice sheet loading formed small-scale glaciotectonic features as the ice recoupled to its bed. Subsequent deglaciation barely modified the scabland, leaving it straddling part of the modern topographic divide between the Battle and Red Deer river basins.

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Larter, Robert D., Alastair G. C. Graham, Karsten Gohl, Gerhard Kuhn, Claus-Dieter Hillenbrand, James A. Smith, Tara J. Deen, Roy A. Livermore, and Hans-Werner Schenke. "Subglacial bedforms reveal complex basal regime in a zone of paleo–ice stream convergence, Amundsen Sea embayment, West Antarctica." Geology 37, no. 5 (May 2009): 411–14. http://dx.doi.org/10.1130/g25505a.1.

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41

Brennand, Tracy A. "Macroforms, large bedforms and rhythmic sedimentary sequences in subglacial eskers, south-central Ontario: implications for esker genesis and meltwater regime." Sedimentary Geology 91, no. 1-4 (June 1994): 9–55. http://dx.doi.org/10.1016/0037-0738(94)90122-8.

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42

Benvenuti, Antonio, and Andrea Moscariello. "High-resolution seismic geomorphology and stratigraphy of a tunnel valley confined ice-margin fan (Elsterian glaciation, Southern North Sea)." Interpretation 4, no. 4 (November 1, 2016): T461—T483. http://dx.doi.org/10.1190/int-2016-0026.1.

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The deep Middle Pleistocene subglacial incisions of the Southern North Sea (SNS) are commonly infilled by northward gently dipping clinoforms oriented toward the former ice-sheet core. We have focused on the terminal sector of the largest tunnel valley (TV) of the SNS and offer the first high-resolution reconstruction of the geomorphology and stratigraphy of the infill of the glacial incision, as well as the detailed geomorphology of the incision to better understand the genetic mechanisms of these uncommon but peculiar large-scale (up to 13 km in length) bedforms. For this study, high-resolution 3D seismic data, the grain-size distribution from ditch cutting samples, and the gamma-ray wireline log of borehole K14-12 are used. The TV formed in the subglacial environment by steady state flows in a time-transgressive fashion. Meltwater flow transports the eroded material southward and eventually deposits it at the ice-sheet margin, in the lightly grounded ice-sheet environment where the adverse slope forces the flow to wane. The process results in an elongated ice-margin fan made of clinoforms, whose grain-size distribution fines progressively southward, in the downstream direction. The formation and filling of the TV occurred during the retreat of the ice-sheet margin and cyclic fluctuations of the meltwater mass flow rate, which affected the internal stratigraphy and created an undulated top of the clinoforms’ unit. Sparsely distributed, horizontally layered units interpreted as distal proglacial lacustrine deposits filled depressions on the top of the clinoforms-bearing unit. The sequence was then sealed by a chaotic seismic-stratigraphic unit that probably belongs to postglacial times. The ice-sheet-oriented clinoforms were thus formed by sustained meltwater flow resulting from large-size Scandinavian and British convergent ice sheet flows in the freshwater environment of SNS developed between the complex ice margins and the topographic highs inherited from continental Europe.

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43

JAMIESON, STEWART S. R., CHRIS R. STOKES, STEPHEN J. LIVINGSTONE, ANDREAS VIELI, COLM Ó COFAIGH, CLAUS-DIETER HILLENBRAND, and MATTEO SPAGNOLO. "Subglacial processes on an Antarctic ice stream bed. 2: Can modelled ice dynamics explain the morphology of mega-scale glacial lineations?" Journal of Glaciology 62, no. 232 (March 14, 2016): 285–98. http://dx.doi.org/10.1017/jog.2016.19.

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ABSTRACTMega-scale glacial lineations (MSGLs) are highly elongate subglacial bedforms associated with ice streaming. However, the link between MSGLs and rapid ice flow is largely qualitative, and there have been few attempts to quantitatively link their formation to ice flow characteristics (e.g. ice velocity, thickness, basal shear stress). We take measurements of MSGLs from a palaeo-ice stream that once occupied Marguerite Trough, Antarctic Peninsula and explore a range of possible correlations with ice dynamics generated from an ensemble of numerical modelling experiments that reproduce the deglaciation of the ice stream. Our results confirm that high mean ice velocities and a weak bed correlate with longer MSGLs. Furthermore, the height of MSGLs are low (2–3 m) where modelled basal shear stress is low, but their height tends to be higher and more variable where basal shear stress is larger. The mean density of MSGLs decreases as ice flux increases. Our analysis further suggests that the length of MSGLs is a function of basal ice velocity and time. Although our data/model correlations confirm the importance of ice velocity in MSGL formation, a significant challenge remains if we are to employ MSGLs as a quantifiable measure of past ice stream velocity.

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44

Brennand, T. A., J. Shaw, and D. R. Sharpe. "Regional-scale meltwater erosion and deposition patterns, northern Quebec, Canada." Annals of Glaciology 22 (1996): 85–92. http://dx.doi.org/10.3189/1996aog22-1-85-92.

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Glaciofluvial ridges, several hundred kilometres long, are commonly referred to as interlobate moraines because they appear to have formed at the convergence of two distinct ice lobes. Flow convergence is indicated by patterns of striations, streamlined forms and eskers. The so-called interlobate moraines are also thought to have formed asynchronously as the ice margin retreated. By contrast, we argue that the Harricana moraine of northern Quebec, Canada, formed following flow convergence in a regional-scale subglacial outburst flood. Flowlines constructed from streamlined bedforms mapped on the glacial map of Canada, reinterpretation of these streamlined forms as products of meltwater erosion, and field records of erosional marks (S-forms) in bedrock and glaciofluvial deposits to the lee of bedrock highs support this model. The effects of this flow convergence on the ice-sheet topography and drainage controlled the location of the broad conduit in which the Harricana moraine was deposited. Continued flow in this conduit and melting of the conduit walls explain the local patterns of striae, the supply of debris to the conduit, and the morphological and sedimentary characteristics of the moraine itself. From these characteristics, we conclude that the moraine was formed synchronously. This conclusion, if correct, is instructive regarding the deglacial hydrological organization of a large sector of the Laurentide ice sheet.

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45

Brennand, T. A., J. Shaw, and D. R. Sharpe. "Regional-scale meltwater erosion and deposition patterns, northern Quebec, Canada." Annals of Glaciology 22 (1996): 85–92. http://dx.doi.org/10.1017/s0260305500015251.

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Glaciofluvial ridges, several hundred kilometres long, are commonly referred to as interlobate moraines because they appear to have formed at the convergence of two distinct ice lobes. Flow convergence is indicated by patterns of striations, streamlined forms and eskers. The so-called interlobate moraines are also thought to have formed asynchronously as the ice margin retreated. By contrast, we argue that the Harricana moraine of northern Quebec, Canada, formed following flow convergence in a regional-scale subglacial outburst flood. Flowlines constructed from streamlined bedforms mapped on the glacial map of Canada, reinterpretation of these streamlined forms as products of meltwater erosion, and field records of erosional marks (S-forms) in bedrock and glaciofluvial deposits to the lee of bedrock highs support this model. The effects of this flow convergence on the ice-sheet topography and drainage controlled the location of the broad conduit in which the Harricana moraine was deposited. Continued flow in this conduit and melting of the conduit walls explain the local patterns of striae, the supply of debris to the conduit, and the morphological and sedimentary characteristics of the moraine itself. From these characteristics, we conclude that the moraine was formed synchronously. This conclusion, if correct, is instructive regarding the deglacial hydrological organization of a large sector of the Laurentide ice sheet.

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46

Holschuh, N., K. Christianson, J. Paden, R. B. Alley, and S. Anandakrishnan. "Linking postglacial landscapes to glacier dynamics using swath radar at Thwaites Glacier, Antarctica." Geology 48, no. 3 (January 3, 2020): 268–72. http://dx.doi.org/10.1130/g46772.1.

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Abstract Ice sheets reshape Earth’s surface. Maps of the landscape formed by past ice sheets are our best tool for reconstructing historic ice sheet behavior. But models of glacier erosion and deposition that explain mapped features are relatively untested, and without observations of landforms developing in situ, postglacial landscapes can provide only qualitative insight into past ice sheet conditions. Here we present the first swath radar data collected in Antarctica, demonstrating the ability of swath radar technology to map the subglacial environment of Thwaites Glacier (West Antarctica) at comparable resolutions to digital elevation models of deglaciated terrain. Incompatibility between measured bedform orientation and predicted subglacial water pathways indicates that ice, not water, is the primary actor in initiating bedform development at Thwaites Glacier. These data show no clear relationship between morphology and glacier speed, a weak relationship between morphology and basal shear stress, and highlight a likely role for preexisting geology in glacial bedform shape.

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Clark, Chris D. "Glaciodynamic context of subglacial bedform generation and preservation." Annals of Glaciology 28 (1999): 23–32. http://dx.doi.org/10.3189/172756499781821832.

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AbstractSubglacially-produced drift lineations provide spatially extensive evidence of ice flow that can be used to aid reconstructions of the evolution of former ice sheets. Such reconstructions, however, are highly sensitive to assumptions made about the glaciodynamic context of lineament generation; when during the glacial cycle and where within the ice sheet were they produced. A range of glaciodynamic contexts are explored which include: sheet-flow submarginally restricted; sheet-flow pervasive; sheet- flow patch; ice stream; and surge or re-advance. Examples of each are provided. The crux of deciphering the appropriate context is whether lineations were laid down time-trans-gressively or isochronously. It is proposed that spatial and morphometric characteristics of lineations, and their association with other landforms, can be used as objective criteria to help distinguish between these cases.A logically complete ice-sheet reconstruction must also account for the observed patches of older lineations and other relict surfaces and deposits that have survived erasure by subsequent ice flow. A range of potential preservation mechanisms are explored, including: cold- based ice; low basal-shear stresses; shallowing of the deforming layer; and basal uncoupling.

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Hillier, John K., Ioannis A. Kougioumtzoglou, Chris R. Stokes, Michael J. Smith, Chris D. Clark, and Matteo S. Spagnolo. "Exploring Explanations of Subglacial Bedform Sizes Using Statistical Models." PLOS ONE 11, no. 7 (July 26, 2016): e0159489. http://dx.doi.org/10.1371/journal.pone.0159489.

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49

Jorge, Marco G., and Tracy A. Brennand. "Measuring (subglacial) bedform orientation, length, and longitudinal asymmetry – Method assessment." PLOS ONE 12, no. 3 (March 20, 2017): e0174312. http://dx.doi.org/10.1371/journal.pone.0174312.

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50

Dowling, Thomas P. F., Per Möller, and Matteo Spagnolo. "Rapid subglacial streamlined bedform formation at a calving bay margin." Journal of Quaternary Science 31, no. 8 (November 2016): e2912. http://dx.doi.org/10.1002/jqs.2912.

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