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No description available.

Since reaching their LIAMs, Himalayan glaciers have generally undergone a period of retreat, evident from large moraines left at former ice limits. Currently, however, detailed assessments of Himalayan glacier fluctuations over the past century are limited and fail to compare spatially or temporally to records available in Central Europe, North America and Scandinavia. Consequently, the variability and magnitude of glacial change across the Himalayas, which is a key indicator of climatic change in this region, is yet to be fully understood. Against a background of poor data availability, Corona imagery and historic GLIMS glacier outlines now offer an opportunity to assess glacier extent for regions of the Himalayas pre-1980. Corona imagery, acquired by a US space-borne reconnaissance mission operational from 1960 to 1970, represents a particularly unique dataset offering high resolution imagery (~1.8 m) with stereo-scopic capabilities. Utilising Corona imagery, there is an opportunity to produce detailed maps of Himalayan glacier extent and extract ice surface elevation estimations, in some instances, for the first time. Despite having been de-classified in 1995, the use of Corona data in the Himalayas has been neglected, mainly because of orthorectification challenges related to its unique geometric distortions. Hence, there remains a need to develop a low cost and easily replicable method of accurately orthorectifying Corona imagery enabling its use as a large-scale glacier mapping tool in the Himalayas. In response to this need, Corona images are orthorectified in this study through the use of: (1) a non-metric photogrammetry approach; and (2) horizontal and vertical reference data acquired from ortho-ASTER imagery and the freely available ASTER GDEM. By comparing glacier measurements derived from Corona imagery, GLIMS data and more contemporary ASTER data, changes in glacier area, length and in some instances volume, between the 1960/70s and early 2000s, were quantified for glaciers selected within four study areas located in Uttarakhand, India and Central Nepal. Importantly, this cross-regional glacier change dataset both complements and enhances current Himalayan records. Most notably, results indicate that glaciers selected in the Bhagirathi and Pindar/Kali basins, Uttarakhand, reduced in area by a relatively small 7.97±0.29% and 7.54±0.26%, respectively. Contrastingly, glaciers selected in the more easterly located Seti and Trisula basins reduced in area by 29.78±0.2% and 50.55±0.08%, respectively. Comparisons of Corona DEM (derived from Corona stereo-pairs) and ASTER Global DEM elevations at the terminus regions of four glaciers revealed extensive surface lowering, ranging from 87±27 m to 142±27 m. For Corona processing, the methods applied were shown to orthorectify Corona images to an accuracy that allows comparable glacier outlines to be delineated, further demonstrating the mapping potential of this dataset. However, for Corona DEM extraction, the use of ASTER spatial control data was shown to be inadequate and the presence of large vertical errors in the DEMs generated hindered the measurement of glacier volume change. For this purpose, it is therefore recommended that the methods developed are tested with the use of very high resolution spatial control data.

This project was desgined to ascertain the origin of debris-bearing basal ice exposed in thick sequences at the margin of the Greenland ice sheet; an understanding of basal processes is fundamental to realistic modelling both of ice sheet behaviour and of the development of glaciated landscapes. Stratigraphic, isotopic (delta18O, deltaD), structural, dynamic and sedimentological analyses of ice and debris from the ice sheet margin indicate two zones of basal ice formation and debris entrainment beneath the ice. At some point in the interior, water freezes to the bed in small increments across a transition zone between warm and cold based areas. This interior derived basal ice re-crystalises during flow, may undergo pressure melting and regelation, and appears at the ice sheet margin as an isotopically distinctive ice facies with large clear crystals and with gas and debris pockets at crystal boundaries. Close to the margin, particularly in zones of faster flowing ice, some of this basal ice melts from the bed. Water derived from this melting, and from penetration of surface meltwater, re-freezes at the bed in a narrow freezing zone at the very edge of the ice sheet, forming a sequence several metres thick of ice and debris laminae. Compressive flow at the margin, related to seasonal freezing as well as to marginal thinning of the ice, causes folding and thrust-faulting within the glacier. This thickens the basal sequence, and raises material from the basal layers and from the basal transport zone into the body of the glacier to form debris bands. At the very margin, accumulations of snow, superimposed ice, and debris are overriden and incorporated into the lowest part of the basal sequence. These findings have implications for basal thermal conditions, ice rheology, the distribution of zones of sub-glacial geomorphic activity, and the structure of ice sheet sediments.

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.

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.

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.

The principal aim of the thesis is to determine the Late Quaternary glacial history of the South Patagonian Icefield at Torres del Paine (51°S, 73°W), Chile. The secondary aim is to compare this glacial history with palaeoclimatic records from elsewhere to test the theory that climate change over the last glacial-interglacial cycle was synchronous between the two polar hemispheres. Synchronous climate change cannot be explained as an atmospheric response to insolation changes unless fundamental ocean-atmosphere reorganisations occurred (Broecker and Denton, 1990). Empirical glacial-geologic data from southern South America is therefore used to test recent models of global climate change. The global pattern of climate change over the last glacial-interglacial cycle is assessed by reviewing proxy palaeoclimate records including isotope records from polar ice cores and deep sea sediment cores, and glacial geologic records from the southern Andes. Conclusions from this review form the basis for hypotheses about what 'should' have happened at Torres del Paine. To test these hypotheses glacial geologic investigations were undertaken on site. Geomorphological evidence is used to define eight icesheet, deglaciation and valley glacier stages; ice extended ca.50km east of the modern South Patagonian Icefield margin during the last glaciation. Basal dates from peat bogs provide dating control for some glacial stages. Pumice fragments associated with glacial deposits were derived from an eruption of Volcan Reclus ca.12,000 yr BP and therefore constrain the Lateglacial depositional sequence. Models of the glacial history are constructed. Evidence that climate change at Torres del Paine was synchronous with other sites is equivocal. However, significant results are: (a) evidence of a Late-Lateglacial ('Younger Dryas') advance - the first such site in Patagonia; (b) evidence that deglaciation occurred slowly; and (c) evidence that the greatest extent of ice did not necessarily coincide with the coldest part of the last glaciation.

No description available.

Groundwater-surface water exchange significantly impacts proglacial hydrology and ecology. This study applies a multidisciplinary approach to investigate groundwater-surface water exchange in the proglacial zones of two retreating glaciers in SE Iceland. Mapping of decadal changes in the extent of proglacial groundwater seeps in the large outwash plain of Skeiðarársandur has shown a 97% decline, as well as substantial falls in groundwater levels. Field and laboratory measurements suggested high spatial variability in hydraulic conductivity at the Skaftafellsjökull foreland. The highest hydraulic conductivity was measured in areas underlain by glaciofluvial deposits whilst the lowest hydraulic conductivities were associated with glacial tills and lacustrine deposits. Precipitation was identified as an important control on groundwater levels on various temporal scales. Automated monitoring of meltwater and groundwater levels also identified fluctuations in meltwater level as an important control on hydraulic heads, whose importance on groundwater levels has been observed during various flow regimes. The close connection between meltwater and groundwater levels suggest high meltwater-aquifer exchange. However, high meltwater-aquifer exchange is contested by significantly different geochemical and isotopic composition of groundwater and meltwater. Hydrogeological flux estimates suggest high spatial variability in groundwater seepage into the Instrumented Lake, which was attributed to the high variability in hydraulic conductivity around the lakeshores. These are also supported by high –resolution temperature mapping at the lake bed, which suggested that groundwater upwelling in the fine-grained lakeshore took place at discrete locations. This study suggests climate and glacier margin fluctuations as primary controls on proglacial groundwater-surface water exchange. It also highlights the importance of groundwater contributions to water quality and ecology, with groundwater-fed bodies possibly sustaining important ecological niches. However, proglacial groundwater-fed features are transient and are threatened by changes in precipitation and glacier retreat. Further declines in groundwater-fed hydrological systems are therefore projected to adversely impact proglacial groundwater-surface water interaction.