Regular Patterns in Frictional Resistance of Ice-Stream Beds Seen by Surface Data Inversion

Science ◽  
2013 ◽  
Vol 342 (6162) ◽  
pp. 1086-1089 ◽  
Author(s):  
O. V. Sergienko ◽  
R. C. A. Hindmarsh
Keyword(s):  
Frictional Resistance ◽  
Data Inversion ◽  
Ice Stream ◽  
Surface Data ◽  
Stream Beds ◽  
Regular Patterns

scholarly journals Ribbed bedforms on palaeo-ice stream beds resemble regular patterns of basal shear stress (‘traction ribs’) inferred from modern ice streams

2016 ◽  
Vol 62 (234) ◽  
pp. 696-713 ◽  
Author(s):  
CHRIS R. STOKES ◽  
MARTIN MARGOLD ◽  
TIMOTHY T. CREYTS
Keyword(s):  
Shear Stress ◽  
Ice Sheets ◽  
Western Canada ◽  
Coupled Flow ◽  
Ice Streams ◽  
Ice Stream ◽  
Stream Beds ◽  
Basal Shear ◽  
Subglacial Meltwater ◽  
Regular Patterns

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.

scholarly journals The periodic topography of ice stream beds: Insights from the Fourier spectra of mega-scale glacial lineations

2017 ◽  
Vol 122 (7) ◽  
pp. 1355-1373 ◽  
Author(s):  
Matteo Spagnolo ◽  
Timothy C. Bartholomaus ◽  
Chris D. Clark ◽  
Chris R. Stokes ◽  
Nigel Atkinson ◽  
...  
Keyword(s):  
Ice Stream ◽  
Stream Beds ◽  
Fourier Spectra

Ribbed bedforms, markers of palaeo-ice stream margins, basal meltwater drainage and ice flow dynamic

2021 ◽  
Author(s):  
Jean Vérité ◽  
Édouard Ravier ◽  
Olivier Bourgeois ◽  
Stéphane Pochat ◽  
Thomas Lelandais ◽  
...  
Keyword(s):  
Flow Direction ◽  
Local Stress ◽  
Sediment Surface ◽  
Shear Stresses ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Stream ◽  
Physical Experiments ◽  
Stream Beds ◽  
Ice Water

<p>Over the three last decades, great efforts have been undertaken by the glaciological community to characterize the behaviour of ice streams and better constrain the dynamics of ice sheets. Studies of modern ice stream beds reveal crucial information on ice-meltwater-till-bedrock interactions, but are restricted to punctual observations limiting the understanding of ice stream dynamics as a whole. Consequently, theoretical ice stream landsystems derived from geomorphological and sedimentological observations were developed to provide wider constraints on those interactions on palaeo-ice stream beds. Within these landsystems, the spatial distribution and formation processes of subglacial periodic bedforms transverse to the ice flow direction – ribbed bedforms – remain unclear. The purpose of this study is (i) to explore the conditions under which these ribbed bedforms develop and (ii) to constrain their spatial organisation along ice stream beds.  </p><p>We performed physical experiments with silicon putty (to simulate the ice), water (to simulate the meltwater) and sand (to simulate a soft sedimentary bed) to model the dynamics of ice streams and produce analog subglacial landsystems. We compare the results of these experiments with the distribution of ribbed bedforms on selected examples of palaeo-ice stream beds of the Laurentide Ice Sheet. Based on this comparison, we can draw several conclusions regarding the significance of ribbed bedforms in ice stream contexts:</p><ul><li>Ribbed bedforms tend to form where the ice flow undergoes high velocity gradients and the ice-bed interface is unlubricated. Where the ribs initiate, we hypothesize that high driving stresses generate high basal shear stresses, accommodated through bed deformation of the active uppermost part of the bed.</li> <li>Ribbed bedforms can develop subglacially from a flat sediment surface beneath shear margins (i.e., lateral ribbed bedforms) and stagnant lobes (i.e., submarginal ribbed bedforms) of ice streams, while they do not develop beneath surging lobes.</li> <li>The orientation of ribbed bedforms reflects the local stress state along the ice-bed interface, with transverse bedforms formed by compression beneath ice lobes and oblique bedforms formed by transgression below lateral shear margins.</li> <li>The development of ribbed bedforms where the ice-bed interface is unlubricated reveals distinctive types of discontinuous basal drainage systems below shear and lobe margins: linked-cavities and efficient meltwater channels respectively.</li> </ul><p>Ribbed bedforms could thus constitute convenient geomorphic markers for the reconstruction of palaeo-ice stream margins, palaeo-ice flow dynamics and palaeo-meltwater drainage characteristics.</p>

scholarly journals Bayesian estimation of basal conditions on Rutford Ice Stream, West Antarctica, from surface data

2011 ◽  
Vol 57 (202) ◽  
pp. 315-324 ◽  
Author(s):  
Mélanie Raymond Pralong ◽  
G. Hilmar Gudmundsson
Keyword(s):  
Steady State ◽  
Surface Topography ◽  
Surface Elevation ◽  
Surface Velocity ◽  
West Antarctica ◽  
Elevation Change ◽  
Surface Geometry ◽  
Inference Problem ◽  
Ice Stream ◽  
Surface Data

AbstractThe determination of basal properties on ice streams from surface data is formulated as a Bayesian statistical inference problem. The theory is applied to a flowline on Rutford Ice Stream, West Antarctica. Estimates of bed topography and basal slipperiness are updated using measurements of surface topography and the horizontal and vertical components of the surface velocity. The surface topography is allowed to vary within measurement errors. We calculate the transient evolution of the surface until rates of surface elevation change are within limits given by measurements. For our final estimation of basal properties, modelled rates of elevation change are in full agreement with estimates of surface elevation changes. Results are discarded from a section of the flowline where the distribution of surface residuals is not consistent with error estimates. Apart from a general increase in basal slipperiness toward the grounding line, we find no evidence for any spatial variations in basal slipperiness. In particular, we find that short-scale variability (<10 × ice thickness) in surface topography and surface velocities can be reproduced by the model by variations in basal topography only. Assuming steady-state conditions, an almost perfect agreement is found between modelled and measured surface geometry, suggesting that Rutford Ice Stream is currently close to a steady state.

scholarly journals The relationship between sticky spots and radar reflectivity beneath an active West Antarctic ice stream

2014 ◽  
Vol 55 (67) ◽  
pp. 29-38 ◽  
Author(s):  
David W. Ashmore ◽  
Robert G. Bingham ◽  
Richard C.A. Hindmarsh ◽  
Hugh F.J. Corr ◽  
Ian R. Joughin
Keyword(s):  
Free Water ◽  
Radar Data ◽  
Force Balance ◽  
Ice Streams ◽  
West Antarctic ◽  
Ice Stream ◽  
Surface Data ◽  
Fast Flow ◽  
The Relationship ◽  
Modelling Approach

AbstractIsolated areas of high basal drag, or ‘sticky spots’, are important and poorly understood features in the force balance and dynamics of West Antarctic ice streams. Characterizing sticky spots formed by thin or drying subglacial till using ice-penetrating radar is theoretically possible, as high radar bed-returned power (BRP) is commonly related to an abundance of free water at the ice/bed interface, provided losses from englacial attenuation can be estimated. In this study we use airborne radar data collected over Evans Ice Stream to extract BRP profiles and test the sensitivity of BRP to the adopted englacial attenuation correction. We analyse 11 ~ 2 0 km profiles in four fast-flow areas where sticky spots have been inferred to exist on the basis of model and surface data inversions. In the majority of profiles we note that the increase in basal drag is accompanied by a decrease in BRP and suggest that this is evidence both for the presence of a sticky spot in those locations and that local variations in subglacial hydrology are responsible for their existence. A comparison is made between empirical and numerical modelling approaches for deriving englacial attenuation, and our findings generally support previous studies that advocate a modelling approach.

scholarly journals A groove-ploughing theory for the production of mega-scale glacial lineations, and implications for ice-stream mechanics

2003 ◽  
Vol 49 (165) ◽  
pp. 240-256 ◽  
Author(s):  
Chris D. Clark ◽  
Slawek M. Tulaczyk ◽  
Chris R. Stokes ◽  
Miquel Canals
Keyword(s):  
Qualitative Theory ◽  
Transverse Strain ◽  
Supporting Evidence ◽  
Ice Streams ◽  
Flow Acceleration ◽  
High Magnitude ◽  
Ice Stream ◽  
Roughness Elements ◽  
Stream Beds ◽  
Fast Flow

AbstractMega-scale glacial lineations (MSGLs) are longitudinally aligned corrugations (ridge–groove structures 6–100 km long) in sediment produced subglacially. They are indicators of fast flow and a common signature of ice-stream beds. We develop a qualitative theory that accounts for their formation, and use numerical modelling, and observations of ice-stream beds to provide supporting evidence. Ice in contact with a rough (scale of 10–103 m) bedrock surface will mimic the form of the bed. Because of flow acceleration and convergence in ice-stream onset zones, the ice-base roughness elements experience transverse strain, transforming them from irregular bumps into longitudinally aligned keels of ice protruding downwards. Where such keels slide across a soft sedimentary bed, they plough through the sediments, carving elongate grooves, and deforming material up into intervening ridges. This explains MSGLs and has important implications for ice-stream mechanics. Groove ploughing provides the means to acquire new lubricating sediment and to transport large volumes of it downstream. Keels may provide basal drag in the force budget of ice streams, thereby playing a role in flow regulation and stability. We speculate that groove ploughing permits significant ice-stream widening, thus facilitating high-magnitude ice discharge.

scholarly journals Formation of ribbed bedforms below shear margins and lobes of palaeo-ice streams

2021 ◽  
Vol 15 (6) ◽  
pp. 2889-2916
Author(s):  
Jean Vérité ◽  
Édouard Ravier ◽  
Olivier Bourgeois ◽  
Stéphane Pochat ◽  
Thomas Lelandais ◽  
...  
Keyword(s):  
Spatial Organization ◽  
Longitudinal Velocity ◽  
Frontal Lobes ◽  
Lateral Shear ◽  
Ice Streams ◽  
Ice Flow ◽  
Drainage Patterns ◽  
Ice Stream ◽  
Stream Beds ◽  
Land Systems

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.

Crescentic scours on palaeo-ice stream beds

2016 ◽  
Vol 46 (1) ◽  
pp. 221-222 ◽  
Author(s):  
A. G. C. Graham ◽  
K. A. Hogan
Keyword(s):  
Ice Stream ◽  
Stream Beds

scholarly journals Ribbed bedforms in palaeo-ice streams reveal shear margin positions, lobe shutdown and the interaction of meltwater drainage and ice velocity patterns

2020 ◽  
Author(s):  
Jean Vérité ◽  
Édouard Ravier ◽  
Olivier Bourgeois ◽  
Stéphane Pochat ◽  
Thomas Lelandais ◽  
...  
Keyword(s):  
Local Stress ◽  
Laurentide Ice Sheet ◽  
Ice Streams ◽  
Ice Flow ◽  
Drainage Patterns ◽  
Velocity Gradients ◽  
Ice Stream ◽  
Stream Beds ◽  
Local Stress State ◽  
Ice Velocity

Abstract. Conceptual ice stream landsystems derived from geomorphological and sedimentological observations provide constraints on ice-meltwater-till-bedrock interactions on palaeo-ice stream beds. Within these landsystems, the spatial distribution and formation processes of ribbed bedforms remain unclear. We explore the conditions under which these bedforms develop and their spatial organisation with (i) an experimental model that reproduces the dynamics of ice streams and subglacial landsystems and (ii) an analysis of the distribution of ribbed bedforms on selected examples of paleo-ice stream beds of the Laurentide Ice Sheet. We find that a specific kind of ribbed bedforms can develop subglacially from a flat bed beneath shear margins (i.e., lateral ribbed bedforms) and lobes (i.e., submarginal ribbed bedforms) of ice streams. These bedforms initiate where the ice flow undergoes high velocity gradients and the ice-bed interface is unlubricated. We suggest that (i) their orientation reflects the local stress state along the ice-bed interface and (ii) their development reveals distinctive types of subglacial drainage patterns below these two kinds of margins: linked-cavities and efficient meltwater channels respectively. These ribbed bedforms are thus convenient geomorphic markers to reconstruct palaeo-ice stream margins and constrain palaeo-ice flow dynamics and palaeo-meltwater drainage characteristics.

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