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Relation between secondary structures in Athabasca Glacier and laboratory deformed iceStanley, Alan David January 1965 (has links)
Glacier movement produces numerous secondary structures
including layers formed by different types of ice and the preferred crystallographic orientation of constituent grains. This thesis describes structures on Athabasca Glacier and shows how they are related to systems of stress that produce glacier flow.
The surface of Athabasca Glacier can be divided into an area of prominent layers of coarse ice near the glacier margin and another formed by less distinct thick layers of fine ice in the central quarter of the ice tongue to within 800 m of the terminus. The coarse layers trend subparallel with the glacier walls and dip steeply towards the centre. In contrast, layers of fine ice near the glacier centre are near vertical and trend parallel with the direction of flow. The layers are deformed about a transverse vertical plane into a series of "similar" folds with limbs commonly separated by narrow cracks subparallel with the axial plane.
Because the coarse layers near the margins, and the fine layers near the centre do not change in shape, size or attitude down the length of the glacier they must be formed at or near their present position.
Cv measurements of ice grains at 25 locations on the ablation surface give fabric diagrams that represent real
stress fabrics that have two or more areas of concentration containing up to 7% of the data. The diagrams may be separated into two distinct groups according to their location on the ice surface.
Fabric diagrams from coarse layers near the margins have two or more maxima clustered near the pole to the layering. Diagrams from contorted fine layers near the middle of the glacier have most data concentrated in the north east quadrant, but maxima are independent of the attitude of any ice layers. In most diagrams, maxima fall on the locus of a small circle of constant radius. The observed radius lies between 30° and 50°, and the centre, located in approximately the same position in all diagrams, represents a line subparallel with the direction of glacier flow.
The two types of ice and their distinct fabric indicate that two different stress systems exist in a glacier. Ice near the margin is under shear while that near the centre is under compression.
In laboratory experiments, increase in the rate of creep may be attributed to some process of recrystallization. Test specimens that have recrystallized under compression are composed of small grains with Cv axes that tend to be oriented in a small circle about the unique stress axis.
Fabrics of compressed ice are identical to those obtained from ice near the centre of many glaciers and show that if ice deforms most readily by glide within the
basal plane, the final orientation fabric depends upon the local plane of movement and not the plane of maximum resolved shear stress. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate
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Flow Dynamics of a Soft-Bedded Glacier in Southeast Iceland During Basal Sliding EventsMarkus, Julie T. 22 July 2011 (has links)
No description available.
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Evolution of Seasonal Variations in Motion of the Kaskawulsh Glacier, Yukon TerritoryHerdes, Emilie January 2014 (has links)
Differential GPS data from 2007-2014 are used to assess horizontal and vertical velocity variations of the Kaskawulsh Glacier at interannual and intra-annual timescales. These indicate that an upglacier propagating high velocity event occurs every spring at the onset of melt, and that a downglacier propagating high velocity event occurs every fall or winter after melt has finished. These events suggest that the subglacial drainage system alternates between a distributed system in the winter and channelized system in the summer and fall. In addition, there is a strong negative correlation between summer melt and velocity the following fall and winter, with strong melt years resulting in low velocities. For each additional metre of summer melt, an 8.6% average decrease in velocity is observed on the glacier the following fall-winter. These results suggest that changes in the subglacial drainage system limit the sensitivity of glacier motion to increased meltwater inputs. Glacier motion will likely show a net decrease under a warming climate due to the negative correlation between surface melt rates and ice motion and a decrease in driving stresses as a result of reduced ice thicknesses. In addition, future fall-winter velocity patterns could be accurately predicted from only a month or two of summer melt data, with May-June melt providing the best indication of fall-winter motion. This study also suggests that the common assumption that glaciers are ‘stable’ in the late fall and winter is incorrect.
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Reconstructing the Surge History and Dynamics of Fisher Glacier, Yukon, 1948-2022Partington, Gabriel 22 June 2023 (has links)
Glacier surges are periods of dynamic instabilities which result in semi-regular alternating periods of slow flow, termed the quiescent phase, and fast flow, termed the active phase. This study uses remotely sensed imagery, digital elevation models, glacier velocity datasets, and in situ oblique photographs to reconstruct the surge history and dynamics of Fisher Glacier to better characterize surging in the southwest Yukon and assess the risk posed by this glacier’s surges on surrounding regions. Fisher Glacier has previously been identified as a surge-type glacier but, until now, it had not been the focus of any detailed studies.
We find evidence that Fisher Glacier underwent two surges during the study period from 1948 to 2022. Visual analysis of characteristic surge features on the glacier surface show that the glacier was in quiescence from <1948 to at least 1963. In 1972, an advanced terminus position, intense surface crevassing, and high point velocities suggest that a surge had recently terminated, corroborating a previous report of a surge occurring around 1970. This was followed by a 40-year quiescent phase from ~1973-2013 during which the terminus underwent consistent retreat, totaling a terminus-wide average of 2058 ± 8 m (up to 3567 ± 8 m in certain sections). Velocities during the quiescent phase were low (generally <50 m yr⁻¹), but underwent a slow multidecadal increase starting around 1985, spreading from the center of the glacier towards the head and the terminus. A pre-surge buildup phase beginning in ~2008-2010 resulted in velocities of up to ~200 m yr⁻¹. The active phase of the surge initiated in winter 2013/14 and was characterised by a velocity increase to ~1500 m yr⁻¹ that propagated both up- and down-glacier from the surge nucleus in the mid-region (~22 km upglacier from the terminus). Velocities peaked at >2100 m yr⁻¹ in the winter/early spring of 2016 at ~12 km from the terminus. The surge resulted in a mean terminus-wide advance of 868 ± 8 m, intense surface crevassing and a downglacier transfer of mass from the reservoir zone to the receiving zone. The terminus area increased in elevation by a mean of ~80 m. In July 2016, the surge rapidly terminated within a period of ~1 month, although velocities at the head and the terminus took a few more months to slow to quiescent values. Since then, average annual velocities along the centerline have been lower than pre-surge velocities, the crevasses have closed up, and the rate of ice surface elevation change has been negative across the entire glacier.
Fisher Glacier’s surge dynamics suggest predominantly hydrologically controlled surging, but with some aspects more representative of thermally controlled surging. Thus, we propose that more than one mechanism might be at play in controlling its surges, although further research is required to confirm this. Under current climate conditions, it is unlikely that Fisher Glacier could dam the nearby Alsek River and cause a glacier lake outburst flood.
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Finite element simulations of ice mass flowWatts, Leonard Gary January 1988 (has links)
No description available.
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The mathematical and numerical modelling of Antarctic ice streamsJohnson, Clare January 1995 (has links)
No description available.
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The hydrology of debris-covered glaciersFyffe, Catriona Louise January 2012 (has links)
Studies of glacier-hydrology have focused on clean Alpine glaciers, and recently ice sheet outlet glaciers, but there are few studies on debris-covered glaciers. It is known debris affects ablation rates, and that debris-covered glaciers evolve differently to their debris-free counterparts, but how the debris influences the hydrology is poorly understood. This thesis aims to understand the influence of the debris on the hydrological system and water balance of Miage Glacier, Western Italian Alps. The supraglacial hydrology was studied by modelling ablation using a distributed energy balance melt model, and measuring supraglacial stream discharges; the structure and evolution of the englacial and subglacial network was investigated using dye tracing and water chemistry monitoring; and the proglacial runoff was examined through detailed hydrograph analysis. Glacier velocity measurements were used to investigate the debris’ influence on the glacier dynamics. High ablation rates occurred on clean ice and beneath thin debris on the upper glacier, resulting in large supraglacial streams which led into an efficient drainage system. Glacier velocities had a greater magnitude and variability close to the upper glacier moulins. Thick debris on the lower glacier reduced ablation, and consequently the discharge of supraglacial streams and efficiency of the hydrological network. Despite locally inefficient subglacial drainage, glacier velocities on the lower glacier remained subdued, partly because the debris attenuated water inputs. This attenuation reduced the occurrence of high amplitude diurnal cycles in the proglacial runoff and confined them to particularly warm weather. Lag times from peak air temperature to peak runoff were long relative to comparable debris-free glaciers. Evaporation of rainfall from debris-surfaces was high, and dependant on the debris permeability, suggesting this is an important water balance component. Under climate warming, it is predicted the ablation of Miage Glacier will increase, but this may be negated given an increase in debris cover.
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A geological framework for temporal sedimentary dynamicsNoll, Christian John 15 May 2009 (has links)
Geophysical, geochemical and geotechnical methods were used to investigate the spatial and
temporal aspects of sediment distribution, accumulation, post-depositional alterations, and seafloor
response and recovery to major events in a temperate, paraglacial, turbid outwash fjord. The goals of this
study are to generate a complete geological model and compare the results to the global distribution of
fjords. The over arching theme of this study is that the ratio of the area of the watershed to the area of the
receiving basin can provide a first order indicator of many factors including glacial mass; the timing of
glacial retreat; sediment input, accumulation, and preservation; and other factors. Temporal observations
reveal the change of this fjord from a glaciated basin to and estuarine environment. These observations
become important when viewed in the context of global climate change and the continued loss of ice.
Preserved strata provide a 2800 yr record of changing modes of sedimentation as the system evolved from
a glaciated basin to a non-glaciated fjord revealing a detailed chronology of change between end-member
systems which can be used to infer changes as glaciers retreat from other fjords. Short lived radio isotopes
were used to investigate post-depositional alteration of modern sediments. Without an understanding of
how biological and physical processes work to modify sedimentary fabric during preservation, changes
seen in sediment and rock core data cannot be accurately resolved. Physical processes can cause erosion
and lateral transport; winnowing and armoring; and instantaneous sedimentation, all of which may be
preserved. Biological processes can modulate the preservation of strata by destroying sedimentary fabric
and integrating signals. The final fundamental need is to investigate the seafloor response and recovery to these events. Massive earthquakes are frequent in the study area and cause perturbations to sediment input
and preservation. By understanding how lakes and deltas modulate sediment discharge after the event;
how shorelines are modified after the event; and where sediment is deposited we can determine the
influence these changes have on the environment and on humans.
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Spatial and temporal distributions of accumulation rates on the catchment of Thwaites Glacier, West AntarcticaLeuro, Erick 26 August 2015 (has links)
We make a first-order calculation of accumulation rates in the catchment of Thwaites Glacier (TG), West Antarctica using the Nye and Daansgard-Johnson methodologies. Both formulations compute accumulations as a function of the age-depth relationship, including a thinning correction due to ice flow. For this purpose, I track and firn-correct two continuous, shallow ice layers obtained from radio echo soundings surveyed during the 2004-05 AGASEA expedition. The layers range from 60 to 700 meters depth between the ice divide and the coast. Dating of layers come from the ice core WDC06A, located on the West Antarctic Ice Sheet (WAIS) ice divide, which have ages 548 and 725 years, respectively. We compare our accumulation results with four independent datasets: 1)IceBridge snow radar (2009-2010), optimized for tracking near-surface layers; 2) a contemporary model of snowfall precipitation, 3) an interpolation of ice core data using satellite passive microwave; 4) ice cores data. We test the hypothesis that accumulation rates have increased since the beginning of the industrial era, a change that has not been observed. Indeed, I find that observations indicate that accumulation rates in the TG catchment have not changed during the past ~700 years. From here I assess the mass balance of the system and analyze what it tells about the history of the glacier. / text
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The role of microbial extracellular polymeric substances in psychrotolerance and geochemistry of subglacial environmentsBaker, Matthew G Unknown Date
No description available.
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