The Glacial Isostatic Adjustment (GIA) of the British Isles is of interest due to the constraints that can be provided on key model parameters such as regional ice sheet history, viscoelastic earth structure and the global meltwater (eustatic) signal. Many past studies have used as their primary observable the high quality relative sea level (RSL) data from this region. However, as indicated in these studies, the data are notoriously difficult to fit due to the highly complex non-monotonic nature of the observed sea level change. In addition, the model predictions show a strong sensitivity to both regional ice and earth model parameters as well as the global meltwater history, resulting in a high degree of non-uniqueness when seeking an optimum model solution. The principle aim of this thesis is to address this inherent non-uniqueness in the British Isles GIA problem and reduce the viable solution parameter space by considering additional datasets that display distinct sensitivities to local and global components of the GIA signal. This was achieved in a number of stages, using a combination of relative sea level data from both near and far-field sites, Continuous GPS data and the most recent geomorphological field constraints. GPS observations of present day vertical crustal motion at sites across Great Britain are employed to provide an independent constraint on the choice of regional earth model parameters (viscoelastic earth structure). It was shown that the data are relatively insensitive to plausible variations in both the regional and global ice model history and as such, the data are used to identify an optimum range of earth model parameters for the region. Using a set of previously un-modelled far-field sea level data from China and Malay-Thailand, a revised model of eustatic sea level change over the Holocene was developed. Constraining the eustatic component of sea level change is useful since it provides a direct measure of continental ice volume that can be compared to results from oxygen isotope methods. Additionally, inference of the eustatic signal over the mid-late Holocene, which was the primary focus of one aspect of this thesis can provide information on both: (i) the rate and timing of major ice melting at the end of the last deglaciation and (ii) the magnitude of melting during the late Holocene, which is an important baseline that can be compared to estimates of global sea-level rise in the 20th century. This new global ice model is characterised by an initial slowdown in the rate of eustatic sea level rise at 7 kyr BP, followed by a continuing rise, until 2 kyr BP, driven by continued melting from the Antarctic Ice sheet. A new British-Irish Ice sheet model over the most recent glacial cycle was produced. This model was constrained to fit to most recent geomorphological field constraints and includes an extensive two-stage glaciation across the North Sea basin, with a greatly thickened and extended ice sheet within the Irish Sea, out along the NE Atlantic margin and across Ireland. During deglaciation, the Irish ice sheet now undergoes a very rapid thinning and retreat. These results have been combined to produce a final new GIA model for the region, which has been constrained, for the first time, using an extended RSL database which includes observations from both Great Britain and Ireland. This new model captures reasonably well the regional trends in the observed sea level, with previous unresolved misfits relating to the timing and height of the Holocene highstand now largely removed.

This thesis provides a comprehensive study of the Axial Volcanic Ridge (AVR) at 45˚30 N on the Mid-Atlantic Ridge. A number of datasets were collected over the area, including: EM120 ship based bathymetry, TOBI sidescan sonar, Isis high-resolution bathymetry, Isis video and sampling dives and crustal magnetisation surveys. In this thesis I seek to explore the questions of the volcanic building blocks of AVRs and their spatial and temporal evolution in a number of ways. Very detailed volcanological mapping of the seafloor is used to provide semi-quantitative estimates of the relative proportions of different lava morphologies on and off the AVR and within the upper oceanic crust. I find that the AVR is characterised by predominantly pillow lavas while the flatter areas of seafloor around the AVR are covered by higher effusion rate lava morphologies. These observations are combined with the bathymetry and sidescan sonar datasets to elucidate the detailed nature of the building blocks of AVRs, which I find to be volcanic hummocks, composed predominantly of pillow lavas. These hummocks are morphologically the same as pillow mounds described at intermediate-spreading rate ridges. From these observations we identify common collapse scarps and associated talus deposits, which if buried may contribute significantly to increased porosity and lower seismic velocity in seismic layer 2A. Sediment cover is used as a proxy for seafloor age, and suggests that both the AVR and the flat seafloor around it are a similar age. Statistical analysis of the distribution and size of volcanic hummocks on the AVR finds their numbers to have been vastly underestimated in previous studies. I also show that hummock density is very variable across the AVR, possibly corresponding to many discrete melt sources. Evidence from 45˚N does not support either a uniform, long period life cycle model as has been proposed, or a steady state AVR. Instead I suggest that the AVR is the surface representation of robust magma supply, and irregular nature of this melt supply will control the surface appearance of the AVR.

An inversion of the glacial geomorphological record provides an effective means to reconstruct former ice sheets at ice sheet-scale. The last Irish Ice Sheet has a long history of investigation, but its most basic properties are debated. Much previous research, based on an incremental development of knowledge through field observation of glacigenic landforms and deposits, has locally yielded high levels of detail but this detail is spatially fragmented across the former ice sheet bed. The evidence-base for ice sheet reconstruction is therefore patchy and incomplete, and its internal inconsistencies make an ice sheet reconstruction, via this approach, problematic. This thesis explores new opportunities for palaeo-glaciological reconstruction offered by remotely sensed data. Systematic glacial landform mapping has been conducted throughout Ireland from a variety of satellite imagery and digital elevation models, and yields new Glacial Maps for Ireland comprising >39,000 landforms. These landform maps are the building blocks for a palaeo-glaciological reconstruction of the ice sheet. Adopting a 'flowset' approach, the full population of landform data is summarised as discrete cartographic units - flowsets - and their spatial, temporal and glaciodynamic information is extracted. The flowset record, integrated with the wealth of evidence and dating constraints in the literature, stimulates a reconstruction describing seven broad stages of ice sheet history. These provide a framework for the evolution of the last Irish Ice Sheet. Key elements of the reconstruction confirm and extend an early advance from a British ice source, a maximum period likely dominated by large ice streams, fragmentation of the ice sheet into separate ice bodies during retreat, and final decay in western mountain groups. The pattern of ice sheet evolution is both asymmetric and asynchronous. A range of scales of ice sheet behaviour are observed, from first-order, fundamental changes in ice sheet geometry (centres of mass and ice flow structure) to more local-scale high-frequency fluctuations of ice flow patterns. This new model acts as a framework for continued investigation of the evolution of the Irish Ice Sheet, and the observed ice sheet behaviour demands further exploration of the sensitivities and role of ice sheets in the wider ice - climate system.

<I>In-situ</I> cosmogenic <SUP>10</SUP>Be, <SUP>26</SUP>A1 and <SUP>21</SUP>Ne concentrations from locations in central Namibia and the Transantarctic Mountains, Antarctica have been used to investigate rates of landscape change in passive margin settings and contrasting hot and cold arid conditions. Concentrations of cosmogenic <SUP>10</SUP>Be and <SUP>26</SUP>A1 in quartz separated from 14 samples from the Gamsberg in central Namibia have been measured using accelerator mass spectrometry. The Gamsberg is a flat-topped residual forming part of the Great Escarpment of central Namibia. Rates of summit denudation range from 0.2 to 0.8 m Ma<SUP>-1</SUP> and rates of slope retreat have been ˜10 m Ma<SUP>-1</SUP> over the past 0.04 to 1.5 Ma. The data indicate that backwearing is much more significant than downwearing but that summit denudation is occurring. Low rates of escarpment retreat of ˜10 m Ma<SUP>-1</SUP> are incompatible with the idea that retreat from the coast has been at a uniform rate since rifting occurred ˜130 Ma BP. The data are consistent with geological evidence and data from apatite fission track thermochronology that suggest that the escarpment retreated rapidly soon after rifting but has not retreated significantly during the Tertiary. Measurements of cosmogenic <SUP>10</SUP>Be and <SUP>26</SUP>A1 from three granite borhardts on the coastal plain of Namibia seaward of the Great Escarpment in the arid/hyper-arid central Namib Desert indicate mean rates of summit lowing ranging from2.2 to 6.3 m Ma<SUP>-1</SUP> over the pat 1-3 x 10<SUP>5</SUP> a. Low variability in estimated denudation rates between the sampling sites and the long term persistence of an arid climate implies that a rate of summit lowering of ˜5 m Ma<SUP>-1</SUP> has characterised bedrock exposures in the central Namib for at least the past 10 Ma. It has been demonstrated that <I>in-situ</I> cosmogenic isotope analysis can provide unobtainable data on denudation rates over timescales intermediate between short-term process studied and long-term estimates from techniques such as thermochronology. Cosmogenic isotopes analysis has significant potential for evaluating controls on denudation rates in a range of geomorphic settings and constraining models of long-term landscape evolution.

No description available.

The links between depositional fabrics, diagenesis and fracture patterns are explored for the Barremian-Aptian Jurf and Qishn formations of central east Oman. Field, petrographic and analytical (oxygen and carbon isotopic ratios, clumped isotopes, strontium isotopes, major and trace elements, tensile strength) data were acquired. The excellent outcrop exposures allow the investigation of the geometries, dimensions and spatial distributions of sedimentary bodies, diagenetic bodies and fractures at the inter-well scale (one kilometre). It is suggested that in the Late Barremian, storm and wave reworking and transport were the dominant sedimentary processes operating in the peritidal environment of the southern Tethyan platform. The stratigraphic distribution of the parasequences and discontinuity surface types suggest some regional sea level control on the peritidal carbonate cyclicity. Pervasive dolomite is restricted to the Jurf Formation transgressive systems tract, which is characterized by a peritidal environment rich in microbial mats. Other system tracts, despite being composed of peritidal facies with evidence for high salinities, were not dolomitized, suggesting that the presence of microbial mats, i.e. the depositional fabric, exerted a major control on dolomite distribution. Spacing and orientation of fractures in limestones also depend strongly on the depositional fabric. Grain-supported facies, such as grainstones and rudstones, develop closely and evenly spaced northwestsoutheast oriented stratabound fractures; whereas mud-supported facies develop widely and unevenly spaced throughgoing fractures predominantly oriented north-south. It is suggested that fractures developed until fracture saturation in early cemented grain-supported facies during the Late Cretaceous. As burial increased, the bedding interfaces become stronger allowing for the development of throughgoing fractures that cross-cut mud-supported beds, which remained undersaturated with respect to fractures. This study shows that diagenetic heterogeneities of the Jurf and Qishn formations are strongly linked to depositional heterogeneities, and that both the depositional fabric and early diagenesis control the distribution of fracture heterogeneities.

This thesis considers the interface between three related fields of scientific research, all of which are concerned with glaciers and glacial deposits. The three main research areas which acted as stimuli! for the work are glacial geomorphology, glaciology and sedimentary geology. Glacial depositional geomorphology lags behind other areas of geomorphological research, particularly those of slope and fluvial geomorphology. During the last century the main focus of Western European glacial geomorphology (both erosional and depositional) has been the study of Pleistocene landforms and chronologies. According to Price (1973), the former (the study of landforms) has developed as "an inexact science", which Sugden and John (1976) attribute to the lack of studies of process-form relationships, the lack of application of polar evidence to glacial problems, and the paucity of research links between glaciology and glacial geomorphology (Sugden and John 1976, p.3). Such criticisms prompted the study of process-form relationships within a currently glacierized zone of the polar regions. The recent glaciological literature contains numerous articles on "surging glaciers". These glaciers appear to differ markedly from other glaciers in their mechanism of movement (Paterson 1969) and dynamics of self-regulation (Miller 1973)" perhaps to such an extent that the depositional landforms and landfox-m associations produced by their activity may differ from those created by non-surging glaciers (liller 1973). One way of testing this suggestion is to collect field data relating to landforms from the snout areas of surging glaciers, and subsequently compare the results with existing knowledge relating to landforms and landform associations produced by non-surging glaciers. A major criticism of much work on the Pleistocene landforms and deposits in Britain is that workers too often rely on intuitive guesswork to ascertain process-form relationships, basing their interpretation on form alone. Whilst this approach may be successful to a large degree, the amount of controversy arising from contrasting interpretations leads to scepticism about the method (litchell et al. 1973). An increasing number of workers turn to particle size analysis of deposits to add objectivity and scientific support to their interpretation. (British Geomorphological Research Group Current Research in Geomorphology Series 1973-5). Their argument is that different types of material, attributable to different depositional processes, can be separated by particle size analysis. This approach is a well tried and tested method in sedimentary geology, where workers are dealing with deposits for which modern process-form relationships are well established. This is not the case in glacial sedimentology, where there is a need for basic data on the textural characteristics of glacial material from areas where the depositional processes and environments can be clearly linked to a particular deposit (siatt 1971) This thesis sets out to examine the depositional landforms, landform associations and particle size characteristics of sedimentary deposits associated with surging glaciers. The first part of the work critically examines the current state of knowledge with regard to surging glaciers, in the light of current glacier movement theories (Chapters 1 ,2 and 3) the subsequent sections deal with process-landform links by, firstly, examining the glacier debris cascade system of non-surging glaciers, and secondly, by applying the fundamentals of this modelling approach to the known features of surging glaciers. The first part terminates with a discussion of the context within which the particle size analysis of glacial deposits is set. The second part is concerned with data collection and presentation. Data were collected from two surging glacier snout areas: Battyebreen in the High Arctic area of Svalbard, and tr Eyjabakkajokull in the maritime area of Iceland. The morphology and proglacial features of Battyebreen strongly suggest that it is a surging glacier (see below: Chapter 1), although there are ii no records of a surge event. The surges of Byjabakkajokull in Iceland are better documented (Thorarinsson 1938, 1964, 1969) and this glacier is known to have surged twice during the last century. The most recent surge occurred between October 1972 and October 1973. Two types of data were collected in accordance with the aims of the thesis: depositional landforms and landforming processes in the stagnant zone of Battyebreen and the proglacial n area of Eyjabakkajokull were mapped, and samples of sediment from these landforms collected and subsequently analysed. The results of each data collection are presented in Chapters 5, 6 and 7. In the third part of the thesis the results of the field and laboratory work are reviewed in the light of publications by authors in related fields. A general model of the development of depositional landforms resulting from glacier surges and the effect of surges on the texture of glacial and fluvioglacial sediments are presented. In the final chapter (Chapter 11) the work as a whole is reviewed, and several conclusions drawn.

Evidence resulting from the detailed mapping of the glacial geomorphology and deposits of an area in south east Aberdeenshire is presented and discussed and a model of glaciation and deglaciation is produced. Landforms of glacial erosion are partly masked by the drift cover but glacially abraded and striated bedrock, ice moulded topography and swarms of rock drumlins are all recognised and used in order to determine the amount and mechanisms of glacial erosion that have taken place. Glacial till forms a uniform cover of 2-4m over the entire area and three separate tills are identified. A lodgement till/meltout till couplet of local origin and a meltout till deriving from a sediment source offshore are postulated and the field relations and distribution of these tills suggest that the two parent ice bodies merged in the coastal zone. Meltwater channels are classified and found to be largely of subglacial origin. Deposits of fluvio-glacial material are similarly classified and include terraces, eskers and kames most of which are also interpreted as being of sub-glacial ice-contact oringin. A spatial analysis of all fluvio-glacial phenomena is undertaken incorporating the evidence produced in the discussion of individual channels and deposits. On the basis of this a reconstruction of the hydrological sub-system operating at the base of the former ice-sheet in the area is suggested. This consists of a west to east orientated meltwater system merging with a south to north orientated system in the coastal zone Deposits of glacio-lacustrine and glacio-marine origin are identified and a suggested classification outlined. The low level coastal deposits are interpreted as being marine whilst most of the others are interpreted as being either sub- or supra-glacial lacustrine deposits. Two deposits are interpreted as ice-contact proglacial deposits formed marginal to the ice. No evidence indicating higher sea levels was found in the area. All this information is integrated and compared with theoretical models and with other interpretations for thearea and a new model of glaciation and deglaciation is built up. All deposits, in the area are interpreted as belonging to the last glaciation to effect the area which is believed to be the Devensian. Three main directions of ice movement are idicated a primary easterly direction and two secondary southeasterly and northerly directions. Erosion by the ice is considered to have been more significant than has formerly been thought. The meltwater system is compared with theoretical models based on ice maxima conditions and the pattern of meltwater features in the area is interpreted as reflecting such a system. It is concluded that the ice in the area was temperate and wet based and that the ice margin must have lain some considerable distance away. The hypothesis of both moraireless Buchan and the Aberdeen readvance are both considered and rejected. It is concluded that deglaciation must have taken place by a process of widespread stagnation of ice in situ and that the coastal zone, being an area of ice merging, became an area of very early and rapid deglaciation causing widespread deposition of eskers and kames in this zone. Deglaciation was early, certainly well before 11,500 B.P., and proba.bly before 13,000 B.P. The suggested sequence of events that is produced involves an initial advance of ice from the north west followed by a period of easterly flowing ice merging with a northerly moving ice stream along the coast. Deglaciation took place earliest in this zone. This sequence of events is placed into a suggested regional context.

The distribution of ice-scoured landscapes correlates with zones of basal ice melting as reconstructed for a Pleistocene Scottish ice sheet. Areas of no apparent ice sheet erosion are associated with a zone of basal ice freezing. The morphological and morphometric characteristics of ice-scoured landscapes and landforms are more closely- related to bedrock lithology and structure, in particular to patterns of bedding plane strikes and dips, joints and faults, than to ice-movement directions . Where the latter were perpendicular to the strike of bedrock structures dipping up-ice, hierarchies of typical roche moutonnee forms are developed with plucked and cliffed lee-side facets. However, where the ice flow direction and the strike of the structures were sub-parallel, the plucked and cliffed facets occur parallel to the former. In some massive rocks fresh fracturing of the bedrock may occur on the lee sides of obstacles and is thought to be related to a process of glacier crushing. The correlation structure of a number of cirque morphometric variables indicates that as cirque size increases, the degree of enclosure in plan, profile and overall dimensions increases. Also length tends to increase relative to amplitude, but' length to breadth ratio remains relatively constant. A space-time transformation suggests that dimensional cirque equilibrium forms are not present. However, dimensionless equilibrium forms appear to be developed in plan and also at an overall level. Cirque headwall retreat proceeds slightly faster than downcutting, but there is no evidence for widespread landscape destruction by cirque erosion. The form of the pre-glacial relief may be more important in explaining variationa in the character of cirque landscapes. Variations in cirque morphometry tend to be a function of local-scale factors, in particular the maximum altitude of the area draining into each cirque.

This contribution utilises a multifaceted approach to investigate the physical processes responsible for the onshore migration of ebb tidal sandbanks at an estuarine inlet dominated by low energy waves. A coastal video system was used to obtain two-weekly quantitative measurements of the position, plan form and crest depth of the landward migrating sandbanks over a five year period which encompassed four consecutive events. These data were supplemented with a 35 year photographic record of the inlet's development. Onshore sandbank migration was characterised by mean and maximum rates of I to 2 m. day&quot;1 and 5 m. day&quot; 1 respectively. The migration rate was found to be highly correlated (R2 = 0.7) with, and linearly related to the ratio of the incident wave height to the crest depth particularly prior to shore-attachment. The plan form, area and crest depth of the sandbanks are a function of the sediment availability. In the inlet's current morphologic mode two plan form geometries are typically observed. These are crescentic and elongate forms (high aspect ratios) where the latter have their major axis transversely-orientated with respect to the coast. Which of these forms develops is dependent on the chronology of wave energy and the crest depth in relation to the tidal water level variation. Elongate transverse morphologies are associated with low relief sandbanks which are synonymous with periods of relatively low sediment availability. Conversely the crescentic morphologies typically occur when sediment availability is higher and the depth to the sandbank crests is shallower. A unique set of in-situ measurements of waves, currents and sediment transport were obtained from four positions on a sandbank in the mid term of its onshore migration. Analysis of the data revealed that the sandbank was dominated by onshore directed sediment transport in the shallow surf zone where current maxima occurred. The gradients in transport were highest on the flood tide. An energetics analysis of the data revealed that short wave stirring and wave driven mean flows were the physical processes responsible for morphological change. The mean flows are in effect longshore currents since they are generated by strong refraction and focussing of the incident waves by the morphologies. These generate a zone of wave convergence over the sandbanks when in the submerged state and very oblique wave breaking along the flanks when the features are exposed by the tide. A numerical model (MIKE 21) was subsequently applied in order to simulate the wave driven patterns of erosion and deposition over the sandbanks using both idealised and measured boundary conditions. The numerical experiments determined that there exists a dichotomy in the patterns of erosion and deposition which are laterally constrained in the submerged state and divergent in the exposed state. Morphological evolution was therefore governed by the variable residence times of the causative wave driven processes at different tidal elevations. It was found that low energy waves when combined with neap tides promoted shoreward elongation through the dominance of the patterns of deposition in the shallow submerged state. Higher energy conditions were predicted to promote a degree of broadening in the longshore dimension and increased crest elevation. This was caused by the patterns of deposition being dominated by both the laterally constrained (high tide) and divergent (low tide) patterns due to their longer residence times.