scholarly journals Influence of debris-rich basal ice on flow of a polar glacier

2014 ◽  
Vol 60 (223) ◽  
pp. 989-1006 ◽  
Author(s):  
Erin C. Pettit ◽  
Erin N. Whorton ◽  
Edwin D. Waddington ◽  
Ronald S. Sletten
Keyword(s):  
Low Temperatures ◽  
Ablation Rate ◽  
Surface Velocity ◽  
Inverse Theory ◽  
Limited Data ◽  
Outlet Glacier ◽  
Basal Ice ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Taylor Glacier

AbstractAt Taylor Glacier, a cold-based outlet glacier of the East Antarctic ice sheet, observed surface speeds in the terminus region are 20 times greater than those predicted using Glen’s flow law for cold (–17°C), thin (100 m) ice. Rheological properties of the clean meteoric glacier ice and the underlying deformable debris-rich basal ice can be inferred from surface-velocity and ablation-rate profiles using inverse theory. Here, with limited data, we use a two-layer flowband model to examine two end-member assumptions about the basal-ice properties: (1) uniform softness with spatially variable thickness and (2) uniform thickness with spatially variable softness. We find that the basal ice contributes 85–98% to the observed surface velocity in the terminus region. We also find that the basal-ice layer must be 10–15 m thick and 20–40 times softer than clean Holocene-age glacier ice in order to match the observations. Because significant deformation occurs in the basal ice, our inverse problem is not sensitive to variations in the softness of the meteoric ice. Our results suggest that despite low temperatures, highly deformable basal ice may dominate flow of cold-based glaciers and rheologically distinct layers should be incorporated in models of polar-glacier flow.

scholarly journals Present dynamics and future prognosis of a slowly surging glacier

2011 ◽  
Vol 5 (1) ◽  
pp. 299-313 ◽  
Author(s):  
G. E. Flowers ◽  
N. Roux ◽  
S. Pimentel ◽  
C. G. Schoof
Keyword(s):  
Mass Balance ◽  
Force Balance ◽  
Surface Velocity ◽  
Internal Dynamic ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Ice Surface ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Negative Balance

Abstract. Glacier surges are a well-known example of an internal dynamic oscillation whose occurrence is not a direct response to the external climate forcing, but whose character (i.e. period, amplitude, mechanism) may depend on the glacier's environmental or climate setting. We examine the dynamics of a small (∼5 km2) valley glacier in Yukon, Canada, where two previous surges have been photographically documented and an unusually slow surge is currently underway. To characterize the dynamics of the present surge, and to speculate on the future of this glacier, we employ a higher-order flowband model of ice dynamics with a regularized Coulomb-friction sliding law in both diagnostic and prognostic simulations. Diagnostic (force balance) calculations capture the measured ice-surface velocity profile only when non-zero basal water pressures are prescribed over the central region of the glacier, coincident with where evidence of the surge has been identified. This leads to sliding accounting for 50–100% of the total surface motion in this region. Prognostic simulations, where the glacier geometry evolves in response to a prescribed surface mass balance, reveal a significant role played by a bedrock ridge beneath the current equilibrium line of the glacier. Ice thickening occurs above the ridge in our simulations, until the net mass balance reaches sufficiently negative values. We suggest that the bedrock ridge may contribute to the propensity for surges in this glacier by promoting the development of the reservoir area during quiescence, and may permit surges to occur under more negative balance conditions than would otherwise be possible. Collectively, these results corroborate our interpretation of the current glacier flow regime as indicative of a slow surge that has been ongoing for some time, and support a relationship between surge incidence or character and the net mass balance. Our results also highlight the importance of glacier bed topography in controlling ice dynamics, as observed in many other glacier systems.

scholarly journals Strain-induced phase changes within cold basal ice from Taylor Glacier, Antarctica, indicated by textural and gas analyses

2005 ◽  
Vol 51 (175) ◽  
pp. 611-619 ◽  
Author(s):  
Denis Samyn ◽  
Sean J. Fitzsimons ◽  
Reginald D. Lorrain
Keyword(s):  
Thermal Conditions ◽  
Significant Loss ◽  
Phase Changes ◽  
Ductile Deformation ◽  
Geochemical Evolution ◽  
Gas Composition ◽  
Outlet Glacier ◽  
Basal Ice ◽  
Gas Measurements ◽  
Taylor Glacier

AbstractThis paper reports detailed textural and gas measurements conducted in cold basal ice (–17°C from the margin of Taylor Glacier, an outlet glacier of the East Antarctic ice sheet. The analyzed samples were retrieved from a basal ice sequence excavated at the end of a subglacial tunnel dug near the glacier snout. The basal sequence exhibits two contrasting ice facies, defined as the englacial and stratified facies. On the one hand, analysis of ice crystal textures from the basal ice sequence provides evidence for localized ductile deformation, especially within the stratified facies where significant dynamic recrystallization was detected. On the other hand, high-resolution gas analyses reveal that strong changes in gas composition occurred at the structural interfaces of the stratified facies. These gas composition changes are typical of melting–refreezing processes but are not associated with any significant loss of gas volume. Given the specific subglacial thermal conditions at the margin of Taylor Glacier, we interpret this phenomenon as resulting from microscopic phase changes involving selective gas redistribution through the pre-melt phase. It is argued that such processes may play an important role in the post-genetic geochemical evolution of cold debris-laden ice and may be enhanced through intense strain conditions.

scholarly journals Buried ice in Kennar Valley: a late Pleistocene remnant of Taylor Glacier

2017 ◽  
Vol 29 (3) ◽  
pp. 239-251 ◽  
Author(s):  
Kate M. Swanger
Keyword(s):  
Late Pleistocene ◽  
Ice Cores ◽  
Dry Valleys ◽  
Patterned Ground ◽  
Outlet Glacier ◽  
Air Bubble ◽  
Isotopic Analyses ◽  
Stable Isotopic ◽  
Glacier Ice ◽  
Taylor Glacier

AbstractBuried glacier ice is common in the McMurdo Dry Valleys and under ideal climatic and geomorphological conditions may be preserved for multimillion-year timescales. This study focuses on the analysis of ~300 m2 of buried glacier ice in lower Kennar Valley, Quartermain Range. The mapped ice is clean,<10 m thick and covered by a~25 cm sandy drift. The mouth of Kennar Valley is occupied by a lobe of Taylor Glacier, an outlet glacier from Taylor Dome. Based on ice–sediment characteristics, air bubble concentrations and stable isotopic analyses from three ice cores, the lower Kennar Valley ice is glacial in origin. These data coupled with a previously reported exposure age chronology indicate that the buried ice was deposited by a late Pleistocene advance of Taylor Glacier, probably during an interglacial interval. The surface of the buried glacier ice exhibits a patterned ground morphology characterized by small, dome-shaped polygons with deep troughs. This shape possibly reflects the final stages of ice loss, as stagnant, isolated ice pinnacles sublimate in place. This study highlights how polygon morphology can be used to infer the thickness of clean buried ice and its geomorphological stability throughout Antarctica, as well as other in cold, arid landscapes.

scholarly journals A ten-year record of supraglacial lake evolution and rapid drainage in West Greenland using an automated processing algorithm for multispectral imagery

2013 ◽  
Vol 7 (4) ◽  
pp. 3543-3565 ◽  
Author(s):  
B. F. Morriss ◽  
R. L. Hawley ◽  
J. W. Chipman ◽  
L. C. Andrews ◽  
G. A. Catania ◽  
...  
Keyword(s):  
Surface Velocity ◽  
Lake Area ◽  
Ice Flow ◽  
Outlet Glacier ◽  
West Greenland ◽  
Subglacial Environment ◽  
Supraglacial Lakes ◽  
Automated Method ◽  
Modis Imagery ◽  
Glacier Flow

Abstract. The rapid drainage of supraglacial lakes introduces large pulses of meltwater to the subglacial environment and creates moulins, surface-to-bed conduits for future melt. Introduction of water to the subglacial system has been shown to affect ice flow, and modeling suggests that variability in water supply and delivery to the subsurface play an important role in the development of the subglacial hydrologic system and its ability to enhance or mitigate ice flow. We developed a fully automated method for tracking meltwater and rapid drainages in 78 large, perennial lakes along an outlet glacier flow band in West Greenland from 2002 to 2011 using ETM+ and MODIS imagery. Results indicate interannual variability in maximum coverage and spatial evolution of total lake area. We identify 238 rapid drainage events, occurring most often at low and middle elevations during periods of net filling or peak lake coverage. We observe a general progression of both lake filling and draining from lower to higher elevations but note that the timing of filling onset, peak coverage, and dissipation are also variable. While lake coverage is sensitive to air temperature, warm years exhibit greater variability in both coverage evolution and rapid drainage. Mid elevation drainages in 2011 coincide with large surface velocity increases at nearby GPS sites, though the relationships between iceshed-scale dynamics and meltwater input are still unclear.

scholarly journals Structures within the surge front at Bakaninbreen, Svalbard, using ground-penetrating radar

1997 ◽  
Vol 24 ◽  
pp. 122-129 ◽  
Author(s):  
Tavi Hodson ◽  
Daniel L. Gooch ◽  
Graham W. Stuart
Keyword(s):  
Ground Penetrating Radar ◽  
Shear Zones ◽  
Hot Water ◽  
Important Process ◽  
Glacier Surface ◽  
Basal Ice ◽  
Extensive Region ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Ground Penetrating

Bakaninbreen, Svalbard, started to surge during 1985–86, and developed a surge front up to 60 m high. Associated with down-glacier propagation of this surge front was the formation of shear zones and thrust faults, some of which revealed basally derived debris at the glacier surface. Hot water drilling and sampling of basal material showed the glacier bed to be soft sediment more than 1 m thick. A high-resolution ground-penetrating radar (GPR) survey at 100 MHz was conducted along three 500 m lines parallel to glacier flow on the surge front. The aims were to investigate the internal geometry of the thrust features, and the processes of entrainment of basal debris into bulk glacier ice.A strong linear reflector was seen on the survey, but it is about 15–20 m above the bed as identified from drilling depths. It probably represents the upper interface of a layer of debris-rich basal ice. Several extensive englacial reflectors were interpreted as debris-laden emergent thrust features, varying in thickness from 0.1 to 1.1 m. These features were mapped at the glacier surface, and drilling and sediment sampling verified the interpretation. Other englacial features included regions of incipient thrusting at the basal reflector, and an extensive region of scattering up to 30 m above the basal reflector that we interpret as folds, or blind thrusts that terminate englacially. Our results clearly demonstrate the potential of GPR for mapping internal glacial structure, and suggest that thrusting is an important process by which sediment is incorporated into glacier ice in the highly compressive region at the surge front.

scholarly journals The relative strengths of debris-laden basal ice and clean glacier ice: some evidence from Taylor Glacier, Antarctica

1996 ◽  
Vol 23 ◽  
pp. 270-276 ◽  
Author(s):  
Wendy Lawson
Keyword(s):  
Compressive Strength ◽  
Uniaxial Compressive Strength ◽  
Mechanical Behaviour ◽  
Deformation Mechanism ◽  
Basal Ice ◽  
Basal Zone ◽  
Dominant Deformation Mechanism ◽  
Glacier Ice ◽  
Pressure Melting ◽  
Taylor Glacier

An understanding of the mechanical behaviour of the basal zone of an ice mass is fundamental to understanding the overall dynamics of that ice mass. Despite the fact that debris-laden ice is found in the basal zones of many glaciers and ice sheets, its mechanical behaviour is only poorly understood. This paper attempts to expand our knowledge of the mechanical behaviour of debris-laden ice by examining the uniaxial compressive strength of debris-laden basal ice sampled from the snout of the Taylor Glacier, Antarctica. The mechanical behaviour of debris-laden ice (debris content 5–20% by volume) under uniaxial compression, and the relationship between the behaviours of debris-laden basal ice and ‘clean’ glacier ice, is complex and variable. At the relatively warm temperatures at which uniaxial compressive strength tests were conducted in the field, debris-laden ice was generally weaker than clean glacier ice. At these temperatures, between 0° and −5°C, pressure melting was the dominant deformation mechanism in the debris-laden ice and cracking the dominant deformation mechanism in clean ice. At −25°C, however, debris-laden ice reached higher strengths than lite clean glacier ice and cracking was the dominant deformation mechanism in both ice types. The change in relationship between the strengths of debris-laden and clean ice with temperature is inferred to be attributable to the temperature dependence of the rate of pressure melting. These results suggest that the dynamic effects and significance of the presence of a debris-laden ice layer in the basal zone of an ice mass are likely to be highly variable in space and time.

scholarly journals Structures within the surge front at Bakaninbreen, Svalbard, using ground-penetrating radar

1997 ◽  
Vol 24 ◽  
pp. 122-129 ◽  
Author(s):  
Tavi Hodson ◽  
Daniel L. Gooch ◽  
Graham W. Stuart
Keyword(s):  
Ground Penetrating Radar ◽  
Shear Zones ◽  
Hot Water ◽  
Important Process ◽  
Glacier Surface ◽  
Basal Ice ◽  
Extensive Region ◽  
Glacier Ice ◽  
Glacier Flow ◽  
Ground Penetrating

Bakaninbreen, Svalbard, started to surge during 1985–86, and developed a surge front up to 60 m high. Associated with down-glacier propagation of this surge front was the formation of shear zones and thrust faults, some of which revealed basally derived debris at the glacier surface. Hot water drilling and sampling of basal material showed the glacier bed to be soft sediment more than 1 m thick. A high-resolution ground-penetrating radar (GPR) survey at 100 MHz was conducted along three 500 m lines parallel to glacier flow on the surge front. The aims were to investigate the internal geometry of the thrust features, and the processes of entrainment of basal debris into bulk glacier ice. A strong linear reflector was seen on the survey, but it is about 15–20 m above the bed as identified from drilling depths. It probably represents the upper interface of a layer of debris-rich basal ice. Several extensive englacial reflectors were interpreted as debris-laden emergent thrust features, varying in thickness from 0.1 to 1.1 m. These features were mapped at the glacier surface, and drilling and sediment sampling verified the interpretation. Other englacial features included regions of incipient thrusting at the basal reflector, and an extensive region of scattering up to 30 m above the basal reflector that we interpret as folds, or blind thrusts that terminate englacially. Our results clearly demonstrate the potential of GPR for mapping internal glacial structure, and suggest that thrusting is an important process by which sediment is incorporated into glacier ice in the highly compressive region at the surge front.

scholarly journals Three-dimensional surface velocities of Storstrømmen glacier, Greenland, derived from radar interferometry and ice-sounding radar measurements

2003 ◽  
Vol 49 (165) ◽  
pp. 201-209 ◽  
Author(s):  
Niels Reeh ◽  
Johan Jacob Mohr ◽  
Søren Nørvang Madsen ◽  
Hans Oerter ◽  
Niels S. Gundestrup
Keyword(s):  
Steady State ◽  
Vertical Velocity ◽  
Three Dimensional ◽  
Greenland Ice Sheet ◽  
Mass Conservation ◽  
Ablation Rate ◽  
Radar Interferometry ◽  
Surface Velocity ◽  
Outlet Glacier ◽  
Dimensional Surface

AbstractNon-steady-state vertical velocities of up to 5 m a−1 exceed the vertical surface-parallel flow (SPF) components over much of the ablation area of Storstrømmen, a large outlet glacier from the East Greenland ice sheet. Neglecting a contribution to the vertical velocity of this magnitude results in substantial errors (up to 20%) also on the south–north component of horizontal velocities derived by satellite synthetic aperture radar interferometry (InSAR) measurements. In many glacier environments, the steady-state vertical velocity component required to balance the annual ablation rate is 5–10 m a−1 or more. This indicates that the SPF assumption may be problematic also for glaciers in steady state. Here we derive the three-dimensional surface velocity distribution of Storstrømmen by using the principle of mass conservation (MC) to combine InSAR measurements from ascending and descending satellite tracks with airborne ice-sounding radar measurement of ice thickness. The results are compared to InSAR velocities previously derived by using the SPF assumption, and to velocities obtained by in situ global positioning system (GPS) measurements. The velocities derived by using the MC principle are in better agreement with the GPS velocities than the previously calculated velocities derived with the SPF assumption.

scholarly journals A ten-year record of supraglacial lake evolution and rapid drainage in West Greenland using an automated processing algorithm for multispectral imagery

2013 ◽  
Vol 7 (6) ◽  
pp. 1869-1877 ◽  
Author(s):  
B. F. Morriss ◽  
R. L. Hawley ◽  
J. W. Chipman ◽  
L. C. Andrews ◽  
G. A. Catania ◽  
...  
Keyword(s):  
Surface Velocity ◽  
Lake Area ◽  
Ice Flow ◽  
Outlet Glacier ◽  
West Greenland ◽  
Subglacial Environment ◽  
Supraglacial Lakes ◽  
Automated Method ◽  
Modis Imagery ◽  
Glacier Flow

Abstract. The rapid drainage of supraglacial lakes introduces large pulses of meltwater to the subglacial environment and creates moulins, surface-to-bed conduits for future melt. Introduction of water to the subglacial system has been shown to affect ice flow, and modeling suggests that variability in water supply and delivery to the subsurface play an important role in the development of the subglacial hydrologic system and its ability to enhance or mitigate ice flow. We developed a fully automated method for tracking meltwater and rapid drainages in large (> 0.125 km2) perennial lakes and applied it to a 10 yr time series of ETM+ and MODIS imagery of an outlet glacier flow band in West Greenland. Results indicate interannual variability in maximum coverage and spatial evolution of total lake area. We identify 238 rapid drainage events, occurring most often at low (< 900 m) and middle (900–1200 m) elevations during periods of net filling or peak lake coverage. We observe a general progression of both lake filling and draining from lower to higher elevations but note that the timing of filling onset, peak coverage, and dissipation are also variable. Lake coverage is sensitive to air temperature, and warm years exhibit greater variability in both coverage evolution and rapid drainage. Mid-elevation drainages in 2011 coincide with large surface velocity increases at nearby GPS sites, though the relationships between ice-shed-scale dynamics and meltwater input are still unclear.

scholarly journals Response of glacier flow and structure to proglacial lake development and climate at Fjallsjökull, south-east Iceland

2019 ◽  
Vol 65 (250) ◽  
pp. 321-336 ◽  
Author(s):  
REBECCA DELL ◽  
RACHEL CARR ◽  
EMRYS PHILLIPS ◽  
ANDREW J. RUSSELL
Keyword(s):  
Satellite Imagery ◽  
Surface Velocity ◽  
Outlet Glacier ◽  
Lake Development ◽  
Glacier Terminus ◽  
Air Temperatures ◽  
Glacier Dynamics ◽  
Proglacial Lake ◽  
Glacier Flow ◽  
Structural Architecture

ABSTRACTOver recent decades, the number of outlet glaciers terminating in lakes in Iceland has increased in line with climate warming. The mass-balance changes of these lake-terminating outlet glaciers are sensitive to rising air temperatures, due to altered glacier dynamics and increased surface melt. This study aims to better understand the relationship between proglacial lake development, climate, glacier dynamics and glacier structure at Fjallsjökull, a large, lake-terminating outlet glacier in south-east Iceland. We used satellite imagery to map glacier terminus position and lake extent between 1973 and 2016, and a combination of aerial and satellite imagery to map the structural architecture of the glacier's terminus in 1982, 1994 and 2011. The temporal evolution of ice surface velocities between 1990 and 2018 was calculated using feature tracking. Statistically significant increases in the rate of terminus retreat and lake expansion were identified in 2001, 2009 and 2011. Our surface velocity and structural datasets revealed the development of localised flow ‘corridors’ over time, which conveyed relatively faster flow towards the glacier's terminus. We attribute the overall changes in dynamics and structural architecture at Fjallsjökull to rising air temperatures, but argue that the spatial complexities are driven by glacier specific factors, such as basal topography.

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