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Eric Rignot - One of the best experts on this subject based on the ideXlab platform.
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iceberg calving of thwaites glacier west antarctica full stokes modeling combined with linear elastic fracture mechanics
The Cryosphere, 2016Co-Authors: Eric Rignot, Mathieu Morlighem, Helene SeroussiAbstract:Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades. Here, we present a study of its calving dynamics combining a two-dimensional flow-band full-Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model Crevasse propagation and ice fracturing. We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom Crevasses that are consistent with the distribution of depth and width of surface and bottom Crevasses observed by NASA's Operation IceBridge radar depth sounder and laser altimeter, whereas HO/LEFM and SSA/LEFM do not generate Crevasses that are consistent with observations. We attribute the difference to the nonhydrostatic condition of ice near the grounding line, which facilitates Crevasse formation and is accounted for by the FS model but not by the HO or SSA models. We find that calving is enhanced when pre-existing surface Crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the timescale of calving events. It is more prominent for glaciers with rapid calving rates than for glaciers with slow calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback to calving events. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line of a glacier for constraining Crevasse formation and iceberg calving.
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Iceberg calving of Thwaites Glacier, West Antarctica: Full-Stokes modeling combined with linear elastic fracture mechanics
2016Co-Authors: Eric Rignot, Mathieu Morlighem, Helene SeroussiAbstract:Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades. Here, we present a study of its calving dynamics combining a two-dimensional flowband Full Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model Crevasse propagation and ice fracturing. We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom Crevasses that match the distribution of Crevasse depth and width observed from NASA's Operation IceBridge radar depth sounders, whereas HO/LEFM and SSA/LEFM do not generate Crevasses that match observations. We attribute the difference to the non-hydrostatic condition of ice near the grounding line, which facilitates Crevasse formation, and is accounted for by the FS model but not by the HO or SSA model. We also find that calving is enhanced when pre-existing surface Crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the time scale of calving events. It is more prominent for glaciers with rapid calving rates than glaciers with slow calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line for constraining Crevasse formation and iceberg calving.
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Full-Stokes modeling of grounding line dynamics, ice melt and iceberg calving for Thwaites Glacier, West Antarctica
2016Co-Authors: Eric Rignot, Mathieu Morlighem, Helene SeroussiAbstract:Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past three decades. Here we present a two-dimensional, Full-Stokes (FS) modeling study of the grounding line dynamics and iceberg calving of TG. First, we compare FS with two simplified models, the higher-order (HO) model and the shallow-shelf approximation (SSA) model, to determine the impact of changes in ice shelf basal melt rate on grounding line dynamics. Second, we combine FS with the Linear Elastic Fracture Mechanics (LEFM) theory to simulate Crevasse propagation and iceberg calving. In the first experiment, we find that FS requires basal melt rate consistent with remote sensing observations to reach steady state at TG’s current geometry while HO and SSA require unrealistically high basal melt rate. The grounding line of FS is also more sensitive to changes in basal melt rate than HO and SSA. In the second experiment, we find that only FS can produce surface and bottom Crevasses that match radar sounding observations of Crevasse width and height. We attribute the difference to the non- hydrostatic conditions of ice near the grounding line, which facilitate Crevasse formation and are not accounted for in HO and SSA. Additional experiments using FS indicate that iceberg calving is significantly enhanced when surface Crevasses exist near the grounding line, when ice shelf is shortened, or when the ice shelf front is undercut. We conclude that FS yields substantial improvements in the description of ice flow dynamics at the grounding line under high basal melt rate and in constraining Crevasse formation and iceberg calving.
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Basal Crevasses on the Larsen C Ice Shelf, Antarctica: Implications for meltwater ponding and hydrofracture
Geophysical Research Letters, 2012Co-Authors: Daniel Mcgrath, Konrad Steffen, Harihar Rajaram, Ted Scambos, Waleed Abdalati, Eric RignotAbstract:A key mechanism for the rapid collapse of both the Larsen A and B Ice Shelves was meltwater-driven Crevasse propagation. Basal Crevasses, large-scale structural features within ice shelves, may have contributed to this mechanism in three important ways: i) the shelf surface deforms due to modified buoyancy and gravitational forces above the basal Crevasse, creating >10 m deep compressional surface depressions where meltwater can collect, ii) bending stresses from the modified shape drive surface crevassing, with Crevasses reaching 40 m in width, on the flanks of the basal-Crevasse-induced trough and iii) the ice thickness is substantially reduced, thereby minimizing the propagation distance before a full-thickness rift is created. We examine a basal Crevasse (4.5 km in length, ∼230 m in height), and the corresponding surface features, in the Cabinet Inlet sector of the Larsen C Ice Shelf using a combination of high-resolution (0.5 m) satellite imagery, kinematic GPS and in situ ground penetrating radar. We discuss how basal Crevasses may have contributed to the breakup of the Larsen B Ice Shelf by directly controlling the location of meltwater ponding and highlight the presence of similar features on the Amery and Getz Ice Shelves with high-resolution imagery. © 2012. American Geophysical Union. All Rights Reserved.
David J.a. Evans - One of the best experts on this subject based on the ideXlab platform.
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Crevasse squeeze ridge corridors diagnostic features of late stage palaeo ice stream activity
Geomorphology, 2016Co-Authors: David J.a. Evans, Robert D Storrar, Brice R. ReaAbstract:A 200-km-long and 10-km-wide linear assemblage of till-filled geometrical ridges on the bed of the Maskwa palaeo-ice stream of the late Wisconsinan southwest Laurentide Ice Sheet are interpreted as Crevasse-squeeze ridges (CSR) developed during internal flow unit reorganization, immediately prior to ice stream shutdown. Ridge orientations are predominantly orientated WNW–ESE, with a subordinate WSW–ENE alignment, both indicative of ice fracture development transverse to former ice stream flow, as indicated by NNE–SSW aligned MSGL. Subglacial till injection into basal and/or full depth, mode I and II Crevasses occurred at the approximate centreline of the ice stream, in response to extension and fracturing. Landform preservation indicates that this took place during the final stages of ice streaming, immediately prior to ice stream shutdown. This linear zone of ice fracturing therefore likely represents the narrowing of the fast-flowing trunk, similar to the plug flow identified in some surging valley glaciers. Lateral drag between the final active flow unit and the slower moving ice on either side is likely recorded by the up-ice bending of the CSR limbs. The resulting CSR corridor, here related to an individual ice stream flow unit, constitutes a previously unreported style of Crevasse infilling and contrasts with two existing CSR patterns: (1) wide arcuate zones of CSRs related to widespread fracturing within glacier surge lobes; and (2) narrow concentric arcs of CSRs and recessional push moraines related to submarginal till deformation at active temperate glacier lobes.
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an assessment of surge induced crevassing and the formation of Crevasse squeeze ridges
Journal of Geophysical Research, 2011Co-Authors: Brice R. Rea, David J.a. EvansAbstract:[1] Evidence for extensive crevassing is preserved on the deglaciated forelands of many surging glaciers as Crevasse squeeze ridges (CSRs). At some point these Crevasses make direct connection with the bed in order to become sediment filled, and full-depth connections have been inferred from turbid water up-wellings in Crevasses and the formation of concertina eskers. The dynamics of seven surging glaciers are assessed, using a linear elastic fracture mechanics approach, to determine the likely directions of fracture and controlling parameters for Mode I Crevasses. Extensional surface strain rates are insufficient to promote top-down full-depth penetration. For small Crevasse spacing (<5 m), surface strain rates are sufficient for top-down crevassing to depths of 4–12 m, explaining the extensive surface crevassing associated with glacier surging. As has been shown in other settings, top-down, full-depth crevassing is only possible when water is added and approaches 97% of the Crevasse depth. The provision of sufficient meltwater to facilitate this is problematic due to the extensive surface crevassing, unless water can move along connected Crevasses to a dominant water capturing Crevasse. For ice thicknesses greater than ∼200 m, basal water pressures in excess of 80–90% of flotation are required for full-depth, bottom-up crevassing. Field evidence suggests that this is the default for surging glaciers and that, on occasion, water pressures may even become artesian. CSRs, found across many surging glacier forelands and ice margins, most likely result from the infilling of basal Crevasses, driven for the most part, bottom-up, by high basal water pressures.
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An assessment of surge-induced crevassing and the formation of Crevasse squeeze ridges
Journal of Geophysical Research, 2011Co-Authors: Brice R. Rea, David J.a. EvansAbstract:[1] Evidence for extensive crevassing is preserved on the deglaciated forelands of many surging glaciers as Crevasse squeeze ridges (CSRs). At some point these Crevasses make direct connection with the bed in order to become sediment filled, and full-depth connections have been inferred from turbid water up-wellings in Crevasses and the formation of concertina eskers. The dynamics of seven surging glaciers are assessed, using a linear elastic fracture mechanics approach, to determine the likely directions of fracture and controlling parameters for Mode I Crevasses. Extensional surface strain rates are insufficient to promote top-down full-depth penetration. For small Crevasse spacing (
Steven A Arcone - One of the best experts on this subject based on the ideXlab platform.
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velocity field in the mcmurdo shear zone from annual ground penetrating radar imaging and Crevasse matching
Cold Regions Science and Technology, 2020Co-Authors: Laura E. Ray, Steven A Arcone, James H Lever, L M Kaluzienski, Madeleine Jordan, Benjamin J Walker, Peter Ortquist Koons, Gordon S HamiltonAbstract:Abstract The McMurdo shear zone (MSZ) is strip of heavily Crevassed ice oriented in the south-north direction and moving northward. Previous airborne surveys revealed a chaotic Crevasse structure superimposed on a set of expected Crevasse orientations at 45 degrees to the south-north flow (due to shear stress mechanisms). The dynamics that produced this chaotic structure are poorly understood. Our purpose is to present our field methodology and provide field data that will enable validation of models of the MSZ evolution, and here, we present a method for deriving a local velocity field from ground penetrating radar (GPR) data towards that end. Maps of near-surface Crevasses were derived from two annual GPR surveys of a 28 km2 region of the MSZ using Eulerian sampling. Our robot-towed and GPS navigated GPR enabled a dense survey grid, with transects of the shear zone at 50 m spacing. Each survey comprised multiple crossings of long (> 1 km) Crevasses that appear in echelon on the western and eastern boundaries of the shear zone, as well as two or more crossings of shorter Crevasses in the more chaotic zone between the western and eastern boundaries. From these maps, we derived a local velocity field based on the year-to-year movement of the same Crevasses. Our velocity field varies significantly from fields previously established using remote sensing and provides more detail than one concurrently derived from a 29-station GPS network. Rather than a simple velocity gradient expected for Crevasses oriented approximately 45 degrees to flow direction, we find constant velocity contours oriented diagonally across the shear zone with a wavy fine structure. Although our survey is based on near-surface Crevasses, similar crevassing found in marine ice at 160 m depth leads us to conclude that this surface velocity field may hold through the body of meteoric and marine ice. Our success with robot-towed GPR with GPS navigation suggests we may greatly increase our survey areas.
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Crevasse initiation and history within the McMurdo Shear Zone, Antarctica
Journal of Glaciology, 2019Co-Authors: L M Kaluzienski, Gordon S Hamilton, Ellyn M. Enderlin, Peter O. Koons, Zoe Courville, Steven A ArconeAbstract:While large-scale observations of intensified fracture and rifting can be observed through remote-sensing observations, understanding Crevasse initiation may best be achieved with small-scale observations in which Crevasses can be directly observed. Here we investigate the kinematic drivers of Crevasse initiation in the McMurdo Shear Zone (MSZ), Antarctica. We delineated 420 Crevasses from ~95 km of 400 MHz frequency ground-penetrating radar data and compared these data with kinematic outputs derived from remotely-sensed ice surface velocities to develop a statistical method to estimate Crevasse initiation threshold strain rate values. We found the MSZ to be dominated by simple shear and that surface shear strain rates proved best for predicting Crevasse features, with regions of higher shear strain rate more likely to have a greater number of Crevasses. In the surveyed portion of our study region, values of shear strain rate and vorticity rate derived from the MEaSUREs2 velocity dataset range between 0.005–0.020 and 0.006–0.022 a −1 , respectively, with Crevasses located at ≥0.011 and ≥0.013 a −1 . While threshold values from this study cannot be directly applied to other glacial environments, the method described here should allow for the study of shear margin evolution and assessment of localized damage and weakening processes in other locations where in situ data are available.
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ground penetrating radar profiles of the mcmurdo shear zone antarctica acquired with an unmanned rover interpretation of Crevasses fractures and folds within firn and marine ice
Geophysics, 2016Co-Authors: Steven A Arcone, Laura E. Ray, James H Lever, Benjamin S Walker, Gordon S Hamilton, L M KaluzienskiAbstract:ABSTRACTThe Crevassed firn of the McMurdo shear zone (SZ) within the Ross Ice Shelf may also contain Crevasses deep within its meteoric and marine ice, but the surface crevassing prevents ordinary vehicle access to investigate its structure geophysically. We used a lightweight robotic vehicle to tow 200- and 400-MHz ground-penetrating radar antennas simultaneously along 100 parallel transects over a 28 km2 grid spanning the SZ width. Transects were generally orthogonal to the ice flow. Total firn and meteoric ice thickness was approximately 160 m. Firn Crevasses profiled at 400 MHz were up to 16 m wide, under snow bridges up to 10 m thick, and with strikes near 35°–40° to the transect direction. From the top down, 200-MHz profiles revealed firn diffractions originating to a depth of approximately 40 m, no discernible structure within the meteoric ice, a discontinuous transitional horizon, and at least 20 m of stratified marine ice; 28–31 m of freeboard found more marine ice exists. Based on 10 consecutiv...
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strain rate estimates for Crevasse formation at an alpine ice divide mount hunter alaska
Annals of Glaciology, 2013Co-Authors: Seth Campbell, Steven A Arcone, S G Roy, Karl J Kreutz, E C Osterberg, P O KoonsAbstract:Crevasse initiation is linked to strain rates that range over three orders of magnitude (0.001 and 0.163 a -1 ) as a result of the temperature-dependent nonlinear rheological properties of ice and from water and debris inclusions. Here we discuss a small cold glacier that contains buried Crevasses at and near an ice divide. Surface-conformable stratigraphy, the glacier's small size, and cold temperatures argue for limited rheological variability at this site. Surface ice-flow velocities of (1.2-15.5) � 0.472 m a -1 imply classic saddle flow surrounding the ice divide. Numerical models that incorporate field-observed boundary conditions suggest extensional strain rates of 0.003-0.015 a -1 , which fall within the published estimates required for Crevasse initiation. The occurrence of one Crevasse beginning at 50 m depth that appears to penetrate close to the bed suggests that it formed at depth. Field data and numerical models indicate that a higher interior stress at this Crevasse location may be associated with steep convex bed topography; however, the dynamics that caused its formation are not entirely clear.
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GPR images of hidden Crevasses in Antarctica
Eighth International Conference on Ground Penetrating Radar, 2000Co-Authors: Steven A Arcone, Allan J. DelaneyAbstract:ABSTRACT GPR IMAGES OF HIDDEN CrevasseS IN ANTARCTICASteven A. Arcone and Allan J. DelaneyU. S. Army Cold Regions Research and Engineering Laboratory72 Lyme Road, Hanover, NH 03755sarcone@crrel.usace.army.mil delaney@crrel.usace.army.mil EQUIPMENT AND PROCEDURESWe have used airborne and ground-based GPR at400500 MHz to image hidden Crevasses in Antarctica. Theradar antennas were either pushed in front of a snowmobile, or cantilevered from a helicopter flying at about 6 malutude and speeds near 15 m/s. We used a high trace acquisition rate, long time ranges, and migration to show snow bridge depth, Crevasse width, septums between Crevasses, connecting cavities and associated folded strata inthe ground-based proffles. The Crevasse images are formedby the discontinuities in reflections from the stratified firn.Diffractions from Crevasse walls are strongly single-sided,originate from point and linear discontinuities, and provideadvance warning. Airborne recorded images are similar, butless detailed than surface images. An increased trace ratecould improve airborne imaging and allow greater profiles-s.Key words: radar, Crevasses, AntarcticaWe used a GSSI, models lOa or b control unit and8W peak power 400500 MHz antenna transducers, whichproduce a 22.5 cycle pulse. For a ground-based antennatheoretical subsurface patterns in urn of density, p 0.5-0.9
Helene Seroussi - One of the best experts on this subject based on the ideXlab platform.
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iceberg calving of thwaites glacier west antarctica full stokes modeling combined with linear elastic fracture mechanics
The Cryosphere, 2016Co-Authors: Eric Rignot, Mathieu Morlighem, Helene SeroussiAbstract:Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades. Here, we present a study of its calving dynamics combining a two-dimensional flow-band full-Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model Crevasse propagation and ice fracturing. We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom Crevasses that are consistent with the distribution of depth and width of surface and bottom Crevasses observed by NASA's Operation IceBridge radar depth sounder and laser altimeter, whereas HO/LEFM and SSA/LEFM do not generate Crevasses that are consistent with observations. We attribute the difference to the nonhydrostatic condition of ice near the grounding line, which facilitates Crevasse formation and is accounted for by the FS model but not by the HO or SSA models. We find that calving is enhanced when pre-existing surface Crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the timescale of calving events. It is more prominent for glaciers with rapid calving rates than for glaciers with slow calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback to calving events. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line of a glacier for constraining Crevasse formation and iceberg calving.
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Iceberg calving of Thwaites Glacier, West Antarctica: Full-Stokes modeling combined with linear elastic fracture mechanics
2016Co-Authors: Eric Rignot, Mathieu Morlighem, Helene SeroussiAbstract:Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades. Here, we present a study of its calving dynamics combining a two-dimensional flowband Full Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model Crevasse propagation and ice fracturing. We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom Crevasses that match the distribution of Crevasse depth and width observed from NASA's Operation IceBridge radar depth sounders, whereas HO/LEFM and SSA/LEFM do not generate Crevasses that match observations. We attribute the difference to the non-hydrostatic condition of ice near the grounding line, which facilitates Crevasse formation, and is accounted for by the FS model but not by the HO or SSA model. We also find that calving is enhanced when pre-existing surface Crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the time scale of calving events. It is more prominent for glaciers with rapid calving rates than glaciers with slow calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line for constraining Crevasse formation and iceberg calving.
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Full-Stokes modeling of grounding line dynamics, ice melt and iceberg calving for Thwaites Glacier, West Antarctica
2016Co-Authors: Eric Rignot, Mathieu Morlighem, Helene SeroussiAbstract:Abstract. Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past three decades. Here we present a two-dimensional, Full-Stokes (FS) modeling study of the grounding line dynamics and iceberg calving of TG. First, we compare FS with two simplified models, the higher-order (HO) model and the shallow-shelf approximation (SSA) model, to determine the impact of changes in ice shelf basal melt rate on grounding line dynamics. Second, we combine FS with the Linear Elastic Fracture Mechanics (LEFM) theory to simulate Crevasse propagation and iceberg calving. In the first experiment, we find that FS requires basal melt rate consistent with remote sensing observations to reach steady state at TG’s current geometry while HO and SSA require unrealistically high basal melt rate. The grounding line of FS is also more sensitive to changes in basal melt rate than HO and SSA. In the second experiment, we find that only FS can produce surface and bottom Crevasses that match radar sounding observations of Crevasse width and height. We attribute the difference to the non- hydrostatic conditions of ice near the grounding line, which facilitate Crevasse formation and are not accounted for in HO and SSA. Additional experiments using FS indicate that iceberg calving is significantly enhanced when surface Crevasses exist near the grounding line, when ice shelf is shortened, or when the ice shelf front is undercut. We conclude that FS yields substantial improvements in the description of ice flow dynamics at the grounding line under high basal melt rate and in constraining Crevasse formation and iceberg calving.
Brice R. Rea - One of the best experts on this subject based on the ideXlab platform.
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Crevasse squeeze ridge corridors diagnostic features of late stage palaeo ice stream activity
Geomorphology, 2016Co-Authors: David J.a. Evans, Robert D Storrar, Brice R. ReaAbstract:A 200-km-long and 10-km-wide linear assemblage of till-filled geometrical ridges on the bed of the Maskwa palaeo-ice stream of the late Wisconsinan southwest Laurentide Ice Sheet are interpreted as Crevasse-squeeze ridges (CSR) developed during internal flow unit reorganization, immediately prior to ice stream shutdown. Ridge orientations are predominantly orientated WNW–ESE, with a subordinate WSW–ENE alignment, both indicative of ice fracture development transverse to former ice stream flow, as indicated by NNE–SSW aligned MSGL. Subglacial till injection into basal and/or full depth, mode I and II Crevasses occurred at the approximate centreline of the ice stream, in response to extension and fracturing. Landform preservation indicates that this took place during the final stages of ice streaming, immediately prior to ice stream shutdown. This linear zone of ice fracturing therefore likely represents the narrowing of the fast-flowing trunk, similar to the plug flow identified in some surging valley glaciers. Lateral drag between the final active flow unit and the slower moving ice on either side is likely recorded by the up-ice bending of the CSR limbs. The resulting CSR corridor, here related to an individual ice stream flow unit, constitutes a previously unreported style of Crevasse infilling and contrasts with two existing CSR patterns: (1) wide arcuate zones of CSRs related to widespread fracturing within glacier surge lobes; and (2) narrow concentric arcs of CSRs and recessional push moraines related to submarginal till deformation at active temperate glacier lobes.
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an assessment of surge induced crevassing and the formation of Crevasse squeeze ridges
Journal of Geophysical Research, 2011Co-Authors: Brice R. Rea, David J.a. EvansAbstract:[1] Evidence for extensive crevassing is preserved on the deglaciated forelands of many surging glaciers as Crevasse squeeze ridges (CSRs). At some point these Crevasses make direct connection with the bed in order to become sediment filled, and full-depth connections have been inferred from turbid water up-wellings in Crevasses and the formation of concertina eskers. The dynamics of seven surging glaciers are assessed, using a linear elastic fracture mechanics approach, to determine the likely directions of fracture and controlling parameters for Mode I Crevasses. Extensional surface strain rates are insufficient to promote top-down full-depth penetration. For small Crevasse spacing (<5 m), surface strain rates are sufficient for top-down crevassing to depths of 4–12 m, explaining the extensive surface crevassing associated with glacier surging. As has been shown in other settings, top-down, full-depth crevassing is only possible when water is added and approaches 97% of the Crevasse depth. The provision of sufficient meltwater to facilitate this is problematic due to the extensive surface crevassing, unless water can move along connected Crevasses to a dominant water capturing Crevasse. For ice thicknesses greater than ∼200 m, basal water pressures in excess of 80–90% of flotation are required for full-depth, bottom-up crevassing. Field evidence suggests that this is the default for surging glaciers and that, on occasion, water pressures may even become artesian. CSRs, found across many surging glacier forelands and ice margins, most likely result from the infilling of basal Crevasses, driven for the most part, bottom-up, by high basal water pressures.
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An assessment of surge-induced crevassing and the formation of Crevasse squeeze ridges
Journal of Geophysical Research, 2011Co-Authors: Brice R. Rea, David J.a. EvansAbstract:[1] Evidence for extensive crevassing is preserved on the deglaciated forelands of many surging glaciers as Crevasse squeeze ridges (CSRs). At some point these Crevasses make direct connection with the bed in order to become sediment filled, and full-depth connections have been inferred from turbid water up-wellings in Crevasses and the formation of concertina eskers. The dynamics of seven surging glaciers are assessed, using a linear elastic fracture mechanics approach, to determine the likely directions of fracture and controlling parameters for Mode I Crevasses. Extensional surface strain rates are insufficient to promote top-down full-depth penetration. For small Crevasse spacing (