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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

The Middle Pleistocene development of the rivers Severn and Avon

Maddy, Darrel January 1989 (has links)
No description available.
12

A Lateglacial plateau icefield in the Monadhliath Mountains, Scotland : reconstruction, dynamics and palaeoclimatic implications

Boston, Clare Mary January 2012 (has links)
The complex record of glaciogenic landforms and sediments in Britain relating to the last British-Irish Ice Sheet provides the opportunity to reconstruct former ice extents, ice dynamics, retreat patterns and examine their links to climate change. Yet in Scotland, as in the rest of Britain, a previously fragmentary approach to palaeoglaciological research has limited our understanding of glacier dynamics and their relationship to climate, particularly during the Last Glacial-Interglacial Transition. The Monadhliath Mountains in the Central Scottish Highlands are dominated by an extensive plateau area that has received little research attention in the past. The few examples of research include work by British Geological Survey officers in the early 1900s and J.R. Young in the 1970s. These studies focussed primarily on the geomorphology and sedimentology of isolated valleys and therefore this PhD research provides the first systematic mapping of the region as a whole. Results of remote and field mapping demonstrate that two coalescent plateau icefields, together covering an area of c. 280 km2, occurred over the southwest and central sector of the Monadhliath Mountains during the Younger Dryas. Equilibrium line altitudes calculated for the icefield are of comparable magnitude to those reconstructed for nearby Younger Dryas ice masses, such as in Drumochter and Creag Meagaidh, but indicate slightly lower precipitation in the Monadhliath Mountains. ELAs of individual outlet glaciers rise steeply from west to east across the plateau, indicating a strong local precipitation gradient. Significant variations in the geomorphology on the plateau and within outlet valleys allowed an examination of former thermal regime and differences in ice dynamics during retreat. In-depth analysis of moraine retreat patterns enabled a detailed insight into palaeoglaciological controls on deglaciation for the first time, concluding that valley morphology and gradient were the most influential factors on the retreat dynamics of the plateau icefield.
13

Multiscale analysis of the landforms and sediments of palaeo-ice streams

Channon, Heather January 2013 (has links)
Ice streams play a fundamental role in the stability and dynamics of ice sheets. They are defined by their rapid flow and this is enabled by conditions and processes at the icebed interface. A significant limitation to our understanding of this environment is that most studies, of both contemporary and palaeo-ice streams, have focussed on only one or two, discrete spatial scales of analysis and so integration between scales is restricted. This thesis investigates palaeo-ice streams at multiple scales in order to examine their subglacial processes and characteristics, and to assess the links between and the application of different spatial scales of analysis. Seven palaeo-ice streams from the British and Laurentide ice sheets were investigated at the macroscale, which involved geomorphological mapping, spatial analysis of subglacial lineations and examination of bed characteristics. Two ice streams were also investigated at smaller scales, which included sedimentological analysis (mesoscale) and micromorphological analysis (microscale). Macroscale results showed that subglacial lineations display certain spatial characteristics, including: clustering according to elongation ratio; distribution of low elongation ratios throughout the ice streams; and a decrease in maximum elongation ratio towards the ice stream lateral margins. The latter of which is considered to reflect the transverse distribution of ice velocity. In some cases, a decline in subglacial lineation concentration and elongation ratio coincided with topographic obstacles at the ice stream bed. The most common bed characteristics identified were: widespread till, fine grained sedimentary bedrock with a moderate permeability, low relief and a flat topographic curvature. Key subglacial processes identified included deformation, which was observed at all three scales, and high pore water pressures, for which multiple lines of evidence were found at the meso and micro scales. Spatial variability in both strain and pore water pressure was also common. The multiscale approach allowed robust interpretations of fast flow mechanisms, which furthers knowledge of the sediment and landform characteristics that may result from these flow mechanisms. A summary of the processes that can be identified at each of the spatial scales is given.
14

Spatial and temporal dynamics of three East Antarctic outlet glaciers and their floating ice tongues

Wuite, Jan, January 2006 (has links)
Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 241-249).
15

Hydrology and dynamics of a land-terminating Greenland outlet glacier

Bartholomew, Ian David January 2012 (has links)
The purpose of this thesis is to investigate the hydrology and dynamics of a land-terminating outlet glacier on the western margin of the Greenland Ice Sheet (GrIS). The investigations are motivated by uncertainty about the effect of meltwater on rates of ice flow in the GrIS and the possibility that hydrologically forced changes in ice velocity might increase mass loss from the ice sheet significantly in response to climate warming. The impact of meltwater on fluctuations in ice flow has been a research focus for glaciologists studying Alpine and Arctic glaciers for decades. In these settings, one of the main controls on the relationship between surface melting and ice velocity is the structure of the subglacial drainage system, which evolves spatially and temporally on a seasonal basis in response to inputs of meltwater from the glacier surface. In this thesis we present three years of field observations of glacier velocity, surface ablation and hydrology from a land-terminating glacier in west Greenland. These data are supplemented by satellite data and the use of simple models to constrain surface melting. We find that hydrologically forced ice acceleration occurs each year along a 115 km transect, first at sites nearest the ice sheet margin and at locations further inland following the onset of surface melting at higher elevations. At sites near the ice sheet margin, the relationship between surface melting and ice velocity is not consistent throughout the melt season, and ice velocity becomes less sensitive to inputs of meltwater later in the summer. This is explained by development in the efficiency of the subglacial drainage system, in a manner similar to Alpine glaciers. We perform a hydrological study which indicates that an efficient subglacial drainage system expands upglacier over the course of the melt season, in response to inputs of water from the ice sheet surface. At higher elevation sites, however, thicker ice and colder temperatures mean that it is harder to generate enough water to reach the ice-bed interface and this only occurs once enough water has accumulated to propagate fractures through thick ice to the bed. One mechanism which allows this is drainage of supraglacial lakes. Inter-annual comparison shows that increased rates of annual ablation lead to higher annual ice velocities. At high elevation sites (>1000 m), timing of drainage of meltwater to the ice-bed interface appears to be the main control on the the overall magnitude of summer acceleration. At lower elevations, although development in the structure of the subglacial drainage system limits the overall summer acceleration signal, short-term variability in meltwater input can sustain high ice velocities even once the subglacial drainage system has become channelised. Overall, the research presented in this thesis suggests that hydrologically-forced acceleration can increase mass loss from the GrIS in a warmer climate due to inland expansion of the area of the ice sheet bed which is subject to inputs of meltwater from the ice sheet surface. The relationship between surface melting and ice velocity is mediated, however, by the structure of the subglacial drainage system and variations in the rate of meltwater drainage to the ice bed interface. Insights from this work can help in the development of numerical ice sheet models which aim to predict the future contribution to sea-level rise from the Greenland Ice Sheet.
16

Influence of rock glaciers on stream hydrology, La Sal Mountains, Utah, U.S.A

Geiger, Stuart T. January 2008 (has links)
Thesis (M.A.)--University of Wyoming, 2008. / Title from PDF title page (viewed on August 6, 2009). Includes bibliographical references (p. 44-46).
17

Seasonal evolution of a glacial hydrologic system observations of borehole water levels from the Bench Glacier, Alaska /

Tschetter, Timothy J. January 2008 (has links)
Thesis (M.S.)--University of Wyoming, 2008. / Title from PDF title page (viewed on July 15, 2009). Includes bibliographical references.
18

New techniques for the investigation of deformation mechanisms in flow of fine-grained ice Ih /

McDaniel, Shannon M. January 2005 (has links)
Thesis (Ph. D.)--University of Washington, 2005. / On t.p. "h" is subscript. Vita. Includes bibliographical references (leaves 113-125).
19

Borehole measurements of dynamic basal drainage adjustments during sliding accelerations Bench Glacier, Alaska /

Meierbachtol, Toby Warren. January 2007 (has links)
Thesis (M.S.)--University of Montana, 2007. / Title from title screen. Description based on contents viewed Aug. 16, 2007. Includes bibliographical references (p. 77-79).
20

Modelling the impact of surface melt on the hydrology and dynamics of the Greenland Ice Sheet

Koziol, Conrad Pawel January 2018 (has links)
Increasing surface runoff from the Greenland Ice Sheet due to a warming climate not only accelerates ice mass loss by altering surface mass balance, but may also lead to increased dynamic losses. This is because surface melt draining to the bed can reduce ice-bed coupling, leading to faster ice flow. Understanding the impact of surface melt on ice dynamics is important for constraining the contribution of the Greenland Ice Sheet to sea level rise. The aim of this thesis is to numerically model the influence of surface runoff on ice velocities. Three new models are presented: an updated supraglacial hydrology model incorporating moulin and crevasse drainage, along with lake drainage over the ice surface via channel incision; an ice sheet model implementing a numerically efficient formulation of ice flow; an adjoint code of the ice flow model based on automatic differentiation. Together with a subglacial hydrology model, these represent the key components of the ice sheet system. The supraglacial hydrology model is calibrated in the Paakitsoq region. Model output shows the partitioning of melt between different drainage pathways and the spatial distribution of surface drainage. Melt season intensity is found to be a relevant factor for both. A key challenge for simulations applying a coupled ice-flow/hydrology model is state and parameter initialization. This challenge is addressed by developing a new workflow for incorporating modelled subglacial water pressures into inversions of basal drag. A current subglacial hydrology model is run for a winter season, and the output is incorporated into the workflow to invert for basal drag at the start of summer in the Russell Glacier area. Comparison of the modelled subglacial system to observations suggests that model output is more in line with summer conditions than winter conditions. A multicomponent model integrating the main components of the ice sheet system is developed and applied to the Russell Glacier area. A coupled ice-flow/hydrology model is initialized using the proposed workflow, and driven using output from the supraglacial hydrology model. Three recent melt seasons are modelled. To a first order, predicted ice velocities match measured velocities at multiple GPS sites. This affirms the conceptual model that summer velocity patterns are driven by transitions between distributed and channelized subglacial hydrological systems.

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