No description available.

No description available.

The aim of this thesis is to establish useful methods of morphological analysis for the radio-echo data stored at the Scott Polar Research Institute, Cambridge, and to apply these to a poorly known area o the subglacial Antarctic surface - the Gamburtsev Mountains beneath the centre of the East Antarctic ice sheet. These mountains could have a profound influence on the behaviour of the current ice sheet, as well as on the development of models for the establishment and growth of the ice sheet. A morphological explanation of these mountains is thus of some importance. A first step towards these aims is to prepare a contour map. The problems of achieving bed altitude figures, the errors involved in the calculation and the contouring processes are examined and a new contour map of the Gamburtsev Mountains is presented as a considerable improvement in detail over previous reconstructions of this surface. This must be accompanied by a morphological analysis for further explanation and this has been approached using analogue for the surface, and by a division into macro- and meso-scale studies. The nature of the radio-echo data precludes many established methods of morphological analysis and poses problems for three-dimensional interpretation. After examination of available methods the macro-scale study of relief is divided into vertical and horizontal components. The mean and standard deviation of altitudes are used to study vert ical variations in relief across the mountains, with the distances between neighbouring peaks, and the recurrence intervals of altitudes being applied to the horizontal component. The meso-scale study concentrates on the valleys in the Gamburtsev mountain surface, with the examination of top widths, depths, basal widths, and vertical and horizontal asymmetry being examined. Relationships and ratios between these parameters are analysed. These macro- and meso-scale studies are compared throughout with the results of repeating the measurements on other, exposed, glaciated land surfaces (West Greenland, East Greenland, Baffin Island, the Dry Valleys area, McMurdo Sound, and other parts of the Transantarctic Mountains), in order to establish known controls on our interpretation of the Gamburtsev surface measurements. This analysis leads to the presentation of a morphological classification of the Gamburtsev surface which complements the contour map and is used in an explanation of the nature of the surface in terms of geological history, the history of glacierisation and the current ice sheet conditions. A model of East Antarctic ice sheet growth including the role of the Gamburtsev Mountains is integrated with existing models. The mountains played a crucial part in the establishment of ice sheet conditions, and their morphology reflects this role together with their long and complex geological history.

No description available.

Glacial isostatic adjustment (GIA) describes the Earth’s response to changing ice and water loads as ice sheets grow and diminish. GIA is difficult to model in Antarctica due to limited knowledge of ice history and Earth properties. The signal confounds satellite gravity measurements of present-day ice-mass change and needs to be accurately removed, but remains the biggest uncertainty. One problem with current Antarctic GIA models is that they neglect ice-mass changes over the past few thousand years, which, in regions of low viscosity mantle, may dominate the present-day bedrock uplift. This study investigates deficiencies in millennial-scale GIA models arising from omission of Late Holocene and present-day ice-mass changes. In the Antarctic Peninsula increasing accumulation observed in ice cores since the 1850s has been shown to cause loading and present-day GIA-related subsidence, although results are dependent on the Earth model. This missing signal may help to reconcile the misfit between GIA model predictions and GPS-observed uplift. GPS records from the northern Peninsula provide an opportunity to place bounds on the regional Earth properties. Since 1995 several ice shelves have collapsed triggering ice-mass unloading that invokes a solid Earth response. However, non-linear GPS-observed uplift cannot be explained by elastic deformation alone. Using a viscoelastic model to predict uplift due to recent ice loss and testing the fit to GPS time series, an Earth model has been constrained with upper mantle viscosity much lower than previously suggested. Elsewhere, the stagnation of Kamb Ice Stream on the Siple Coast ~165 years ago has caused localised thickening of ice which may cause significant GIA-related subsidence if the regional mantle viscosity is low. Combining with an LGM deglacial history and comparing with an empirically-derived GIA model shows large misfits, indicating that the regional mantle viscosity is high and highlighting potential errors in the LGM deglacial model.

No description available.

No description available.

Within the vast bounds of geographical study the author has held two major interests, those of glacial geomorphology and the wider topic of the application of statistical techniques in geographical analysis. Through this research it has been possible to combine these two interests in a lengthy study. However, it should be noted at the outset that the thesis that follows bears little resemblance to the work that was originally intended. The work was planned to be concerned solely with an in depth quantitative analysis of drumlins with the hope of gaining insights into the fundamental problem of explaining drumlin formation. An area of Galloway in south-west Scotland was selected but initial field work revealed considerable problems in the interpretation of the glacial history of the chosen region. It rapidly became apparent that the work on drumlins could not proceed without firstly producing a satisfactory re-appraisal of that glacial history.

Considerable work to date on orogenic systems has focussed on active orogens, whereas relatively little research has looked at inactive, post-orogenic systems. This study begins to redress this balance by considering the post-orogenic Pyrenean mountain belt. The relative importance of the controls of tectonics, lithology and climate on the resultant geomorphology of the post-orogenic system are considered, as well as quantifying the degree and timing of post-orogenic exhumation. This is achieved through the use of digital elevation data, field observations and low temperature thermochronology. Extraction of morphometric parameters from digital elevation data at a catchment scale reveals a north-south asymmetry within the Pyrenees, with northern catchments having steeper slopes and lower minimum elevations than their southern counterparts. This is attributed to an inherited tectonic control, with the original asymmetric form that was developed during active orogenesis being preserved through post-orogenic erosion. The distribution of erosion-resistant crystalline massifs within the Axial Zone of the Pyrenees provides a first order control on the position of the principal drainage divide. This resistance to erosion compared to the surrounding lithologies allows the massifs to define the high elevations within the chain. Climate has also played a role, with an enhanced glaciation on the northern side of the orogen brought about by orographic precipitation and reduced solar radiation. This has resulted in glaciation in northerly catchments reaching lower elevations than their southerly counterparts and permitting glaciers to extend further into the foreland in the north than those in the south during larger glaciations. Apatite fission track and apatite (U-Th)/He thermochronometers and associated thermal modelling document an asymmetry in the exhumation and erosional history of the Pyrenees. Results show that vertical profiles in northerly draining catchments record rapid exhumation at 30 Ma, with 1 km or less of exhumation after this time. In contrast, samples to the south of the main drainage divide, whilst also showing rapid exhumation at around 30 Ma, show considerably more exhumation after this time (~2.5 km). Therefore, these thermochronometers also document the transition from a syn- to a post-orogenic system recording a gradual, diachronous shutdown across the orogen. This evidence suggests that some isolated regions of the orogen remained active after 20 Ma and possibly as late as 10 Ma, considerably later than previously documented. No evidence is recorded for an acceleration in erosion related to climate change in the last 4 Ma. Modelling work has also highlighted the importance of evolving topography and the associated deformation of isotherms that influence thermochronometric analysis in mountainous terrain.

This research demonstrates the impact that glaciations had on the geomorphology and sediment deposition of the NW Irish continental margin, including both sides of the Rockall Trough and the Rockall Bank. A modern hydrographic, geophysical and sedimentological approach is used to analyse and interpret new and historical datasets, including multi beam, sidescan sonar, seismic and core data. New methodologies such as CUBE and Geocoder algorithms for multi beam bathymetry and backscatter data processing, 3D visualisations, ArcGIS Spatial and Hydrological Analysis and digital X-Ray scanning are used to deliver an accurate geomorphological and sedimentological interpretation and to understand the changes that occurred in the sedimentary processes from shelf edge to basin floor since the last glaciation, through deglaciation and in the Holocene. This research demonstrates a number of correlations between glacial geomorphology observed on the continental shelf and the various geomorphological and sedimentary features observed along the NW Irish continental slope and trough. It also provides extensive evidence that the Rockall Bank was scoured by several generations of icebergs and acted as a natural barrier against which icebergs coming from the western Atlantic Ocean grounded. Near seabed geophysical investigation throughout the Irish Rockall Trough is used to classify the area into six sedimentary provinces, each characterised by different depositional processes. This also provides new evidence of previously undetected mass transport deposits and extensive fluid-migration on a wide area of the trough. Finally, the study of sediment cores along two major canyons and across the trough provides a regional perspective on the sedimentary processes that took place since the last glaciation on the north-eastern margin of the Rockall Trough. The study reveals that margin physiography, distance from the ice sheet grounding zone, style of glaciation on the shelf and strength of deep sea circulation are the main controlling factors over the depositional processes.