Spelling suggestions: "subject:"glacier""
131 |
The effects of solutes, debris and temperature on the shear strength of basal ice in cold-based glaciersSirota, Paul, n/a January 2008 (has links)
Isotropic ice samples containing measured concentrations of solutes and debris similar to basal material found in several cold-based glaciers in the McMurdo Dry Valleys, Antarctica, were manufactured in a laboratory and tested for peak shear strength at constant strain rates with a direct-shear device. The shear tests show that differences in rheology and shear strength appear to be related to impurity content and concentration. Debris-laden ice becomes more ductile with greater concentrations of solutes, whereas, low solute-concentrations and high debris-concentrations are associated with increases in shear strength and brittle behaviour. Stress exponents from Glen�s flow law calculated for isotropic solute and debris-laden ice ranged between 4 and 5, leading to the conclusion that higher rates of deformation may be expected in dirty basal ice than predicted for glacial ice models that use stress exponents where, n = 3. Observations of both natural and synthetic samples tested over a range of temperatures between -25�C and -5�C showed that natural basal ice samples containing high solute and debris concentrations were highly sensitive to temperature change. These tests showed an approximate 10 % loss in shear strength for every 1�C increase in temperature between -25�C and -10�C. In addition, contrasts in rheology and rates of deformation within basal ice are responsible for the development of debris-laden ice structures in the basal zones of cold-based glaciers that flow over unconsolidated substrates. As layered sedimentary bedding was preserved in frozen blocks within the deforming basal ice of several of these glaciers, the evidence suggests that at some point each glacier has interacted with its bed and entrained portions of the substrate material. Empirical shear strength data and observations of rheological changes attributed to composition together with evidence acquired during fieldwork in Antarctica help to support the argument that cold-based glaciers flowing over unconsolidated sediment are capable of affecting geomorphic change. Hence, isotropic ice models that exclude basal processes may need to be adjusted, especially where small increases in the temperature of the basal zones of cold glaciers may occur. In conclusion, palaeo-climate inferences based purely upon small amounts of geomorphic evidence, which suggest warmer climate conditions, may need to be re-evaluated in order to portray more accurate renditions of formerly glaciated landscapes.
|
132 |
A compositional approach to understanding the formation of basal ice in the Antartic glaciersMager, Sarah M., n/a January 2006 (has links)
The composition of ice from four case studies based on the facies, solute, stable isotope, and debris content reveals compositional differences reflective of different modes of ice formation. In Southern McMurdo Sound, there is a distinctive geochemical signature that differentiates between meteoric-origin and marine-origin ice. Analysis of the basal ice of three glaciers from the McMurdo Dry Valleys shows that liquid water does contribute to its formation. The basal ice sequences are structurally and compositionally different and are reflective of different modes of formation or entrainment active at the glacier margins. In the cases of the Rhone and Wright Lower glaciers marginal sediments and liquid water are key to understanding the accretion of debris-rich ice and both have basal facies consistent with refreezing in subzero conditions. The liquid water is formed by ephemeral melt during the summer. In the Rhone Glacier, melt water refreezes on the apron and is entrained into the advancing glacier. By contrast, by the Wright Lower Glacier adjacent streams or ponds saturate unconsolidated sediments which are entrained during ice advance. In the Taylor Glacier, the basal ice is comprised of a thick sequence of intercalated layers of clean clear ice and fine-grained debris layers. These laminated facies have a solute composition consistent with evaporites formed from a relict seawater intrusion. The combination of entrained debris, high solutes and laminations is consistent with interaction at the glacier bed and regelation. Interpreting empirically derived co-isotopic slopes is problematic, as highlighted in the case study of the Taylor Glacier where laminated facies have all the hallmarks of refrozen ice, yet plot on a co-isotopic slope that is typically interpreted as meteoric. Similarly, ice from the McMurdo Ice Shelf shows a clear difference in absolute isotope values which is interpreted as being refrozen from seawater, yet its co-isotopic plot is statistically indistinguishable from the meteoric water line. The ice compositional approach has highlighted several shortcomings. Firstly, solutes deposited in inland areas have limited solute pathways and do not distinguish between different types of ice but are useful in distinguishing between marine and continental salts. Secondly, co-isotopic analysis to reconstruct freezing history is dependent on statistically-derived interpretations which do not explain slopes that lie between physically-based models of meteoric and freezing slopes. In empirical studies, slopes between 5 and 8 are common, and are probably cosmopolitan samples. Finally, ice composition is inconsistent between similar ice types in the McMurdo Dry Valleys, as similar facies have different ice compositions, and origins. This underlines the problem with the premise that structurally similar ice facies are formed by the same process.
|
133 |
An assessment of regional climate trends and changes to the Mt. Jaya glaciers of Irian JayaKincaid, Joni L. 17 September 2007 (has links)
Over the past century, glaciers throughout the tropics have predominately retreated.
These small glaciers, which respond quickly to climate changes, are becoming
increasingly important in understanding glacier-climate interactions. The glaciers on Mt.
Jaya in Irian Jaya, Indonesia are the last remaining tropical glaciers in the Western
Pacific region. Although considerable research exists investigating the climatic factors
most affecting tropical glacier mass balance, extensive research on the Mt. Jaya glaciers
has been lacking since the early 1970s.
Using IKONOS satellite images, the ice extents of the Mt. Jaya glaciers in 2000,
2002, 2003, 2004, and 2005 were mapped. The mapping indicates that the recessional
trend which began in the mid-19th century has continued. Between 1972 (Allison, 1974;
Allison and Peterson, 1976) and 2000, the glaciers lost approximately 67.6% of their
area, representing a reduction in surface ice area from 7.2 km2 to 2.35 km2. From 2000
to 2005, the glaciers lost an additional 0.54 km2, representing approximately 24% of the
2000 area. Rates of ice loss, calculated from area measurements for the Mt. Jaya glaciers
in 1942, 1972, 1987, and 2005, indicate that ice loss on Mt. Jaya has increased during
each subsequent period. Preliminary modeling, using 600 hPa atmospheric temperature, specific humidity,
wind speeds, surface precipitation, and radiation values, acquired from the NCEP
Reanalysis dataset, indicates that the only climate variable having a statistically-significant
change with a magnitude great enough to strongly affect ice loss on these
glaciers was an increase in the mean monthly atmospheric temperature of 0.24ðC
between 1972 and 1987. However, accelerated ice loss occurring from 1988-2005
without large observed changes in the weather variables indicates that a more complex
explanation may be required. Small, though statistically-significant changes were found
in regional precipitation, with precipitation decreasing from 1972-1987 and increasing
from 1988-2005. While, individually, these changes were not of sufficient magnitude to
have greatly affected ice loss on these glaciers, increased precipitation along with a
rising freezing level may have resulted in a greater proportion of the glacier surface
being affected by rain. This may account for the increased recession rate observed in the
latter period.
|
134 |
Ice-atmosphere interactions in the Canadian high arctic : implications for the thermo-mechanical evolution of terrestrial ice masses /Wohlleben, Trudy M. H. January 1900 (has links)
Thesis (Ph. D.)--University of Alberta, 2009. / A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Dept. of Earth and Atmospheric Sciences, University of Alberta. Includes bibliographical references. Also available via the Internet.
|
135 |
Flow obstructions in valley glaciersCaruso, Raven, University of Lethbridge. Faculty of Arts and Science January 2007 (has links)
Valley glaciers often occur within complex dendritic systems where tributary glaciers
contribute ice mass and blocking potential to the trunk glacier. Analysis of glacier
inventories and maps in the regions of Svalbard, East Greenland, Yukon Territory and the
Thompson Glacier system indicates that trunk - tributary intersections commonly occur at
angles between 45° and 90°. An analogue material with flow properties similar to creep
in pure ice has been used to simulate flow in a model valley glacier. The model and a
series of blockages were constructed based on dimensions derived from the inventory and
map analysis. The angled blockage indicates lower overall velocity rates and appears to
have a funnelling rather than blocking affect on the analogue material. The perpendicular
obstruction that blocked half the width of the model valley caused a piling up of analogue
material prior to a release into the unobstructed side of the valley. / ix, 149 leaves : ill. ; 29 cm.
|
136 |
Determination of changes of surface height, 1957-1967, of the Gilman Glacier, North Ellesmere Island, Canada.Arnold, K. C. (Keith C.) January 1968 (has links)
No description available.
|
137 |
Ice ablation measured by stakes and by terrestrial photogrammetry : a comparison on the lower part of the White Glacier, Axel Heiberg Island, Canada / Ablation measured by stakes and photogrammetry.Arnold, K. C. (Keith C.) January 1978 (has links)
No description available.
|
138 |
Quantitative controls on the routing of supraglacial meltwater to the bed of glaciers and ice sheetsClason, Caroline January 2012 (has links)
The influence of seasonal influx of supraglacial meltwater on basal water pressures and consequent changes in ice surface velocity has been a focus of research spanning over three decades, particularly focussing on alpine glaciers. Now, with increased recognition for a need to better include glacial hydrology within models of ice dynamics and ice sheet evolution, the ability to predict where and when meltwater is delivered to the subglacial system is paramount, both for understanding the dynamics of alpine glaciers, and of large Arctic ice masses. Studies of the dynamics of outlet glaciers on the Greenland Ice Sheet have received particular attention in recent years, as links between ice acceleration and increased surface melt production are explored. Responses of horizontal and vertical ice velocities to meltwater generated suggest efficient transmission of meltwater from the supraglacial to subglacial hydrological systems. Indeed, in the case of meltwater transfer through the drainage of supraglacial lakes, it has been shown that such build-ups of stored meltwater can force crevasse penetration through many hundreds of metres of ice. This thesis presents a new modelling routine for the prediction of moulin formation and delivery of meltwater to the ice-bed interface. Temporal and spatial patterns of moulin formation through propagation of crevasses and drainage of supraglacial lakes are presented, and quantitative controls on water-driven crevasse propagation are investigated through a series of sensitivity tests. The model is applied to two glacial catchments: the Croker Bay catchment of Devon Ice Cap in High Arctic Canada; and Leverett Glacier catchment of the southwest Greenland Ice Sheet. Through model application to these sites, sensitivities to crevasse surface dimensions, ice tensile strength, ice fracture toughness and enhanced production of surface meltwater are investigated. Model predictions of moulin formation are compared with field observations and remotely sensed data, including ice surface velocities, dynamic flow regimes, and visible surface features. Additionally, model quantification of meltwater delivered to the ice-bed interface of Leverett Glacier is compared with profiles of measured proglacial discharge. Moulin formation is predicted at increasingly high elevation with time into the ablation season in both4catchments, and furthermore, the model predicts an increase in both the number of moulins and the number of lake drainages in response to increased melt scenarios. Sensitivity testing confirms that the model is most sensitive to factors influencing the rate at which meltwater fills a crevasse, and results highlight the importance of accurate parameterisation of crevasse surface dimensions and the tensile strength of the ice. Further applications of the model are discussed, with a focus on incorporation into coupled models of glacial hydrology and dynamics, including larger scale ice sheet modelling. The inclusion of spatially distributed points of temporally varying meltwater delivery to the subglacial system is imperative to fully understand the behaviour of the subglacial drainage system. Furthermore, dynamic response to future climatic change and increased melt scenarios, and the consequent evolution of ice masses, including those in the Canadian Arctic and Greenland, cannot be fully understood without first understanding the glacial hydrological processes driving many of these changes.
|
139 |
The effects of solutes, debris and temperature on the shear strength of basal ice in cold-based glaciersSirota, Paul, n/a January 2008 (has links)
Isotropic ice samples containing measured concentrations of solutes and debris similar to basal material found in several cold-based glaciers in the McMurdo Dry Valleys, Antarctica, were manufactured in a laboratory and tested for peak shear strength at constant strain rates with a direct-shear device. The shear tests show that differences in rheology and shear strength appear to be related to impurity content and concentration. Debris-laden ice becomes more ductile with greater concentrations of solutes, whereas, low solute-concentrations and high debris-concentrations are associated with increases in shear strength and brittle behaviour. Stress exponents from Glen�s flow law calculated for isotropic solute and debris-laden ice ranged between 4 and 5, leading to the conclusion that higher rates of deformation may be expected in dirty basal ice than predicted for glacial ice models that use stress exponents where, n = 3. Observations of both natural and synthetic samples tested over a range of temperatures between -25�C and -5�C showed that natural basal ice samples containing high solute and debris concentrations were highly sensitive to temperature change. These tests showed an approximate 10 % loss in shear strength for every 1�C increase in temperature between -25�C and -10�C. In addition, contrasts in rheology and rates of deformation within basal ice are responsible for the development of debris-laden ice structures in the basal zones of cold-based glaciers that flow over unconsolidated substrates. As layered sedimentary bedding was preserved in frozen blocks within the deforming basal ice of several of these glaciers, the evidence suggests that at some point each glacier has interacted with its bed and entrained portions of the substrate material. Empirical shear strength data and observations of rheological changes attributed to composition together with evidence acquired during fieldwork in Antarctica help to support the argument that cold-based glaciers flowing over unconsolidated sediment are capable of affecting geomorphic change. Hence, isotropic ice models that exclude basal processes may need to be adjusted, especially where small increases in the temperature of the basal zones of cold glaciers may occur. In conclusion, palaeo-climate inferences based purely upon small amounts of geomorphic evidence, which suggest warmer climate conditions, may need to be re-evaluated in order to portray more accurate renditions of formerly glaciated landscapes.
|
140 |
Structure and deformation in a propagating surge front /Pfeffer, William Ted. January 1988 (has links)
Thesis (Ph. D.)--University of Washington, 1988. / Map on folded leaf in pocket. Vita. Bibliography: leaves [133]-134.
|
Page generated in 0.069 seconds