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The Hindu Kush–Karakoram Himalaya (HKKH) hold the largest ice mass outside of the poles. It is estimated that 1.9 billion people depend on the major rivers that are partially sustained by meltwater from these glaciers. Glacier mass loss has accelerated over the last decade and predictions indicate that this will continue over the next century, though vary widely and are based on relatively simplistic representations of climate and glacier behaviour. The aim of this thesis is to investigate the impact of climatic drivers on glacier mass balance, and how a robust representation of mass balance influences longer-term evolution of debris-covered Khumbu Glacier in the Nepal Himalaya. A cross-disciplinary modelling approach is adopted, utilising meteorological observations and regional climate models to aid downscaling of presentday and future climate, which is used to force a distributed energy balance model. The distributed mass balance results are integrated into a 3D higher-order ice flow model to study glacier evolution under historical and future atmospheric forcing. Energy balance modelling results demonstrate that the meteorological drivers of Khumbu Glacier mass balance vary substantially over space and time. The seasonality is more marked at lower elevations, where net shortwave radiation provides much of the energy available for melt, though net longwave radiation contributes appreciably during the monsoon. Despite temperatures remaining below freezing in the Western Cwm, ablation through sublimation is simulated. The calculation of a sub-debris ablation curve for Khumbu Glacier is applied to simulated clean-ice mass balance, improving glacier-wide and altitudinal ablation rates relative to observations. By 2100, temperature is found to increase by 1.8? to 3.9? depending on the emission scenario, with highest warming in the winter. Over the coming 80 years, precipitation increases by 15%, though varies substantially between models, demonstrating the high uncertainty regarding future precipitation trends. The value of forcing the ice flow model with distributed mass balance is seen in the simulated present-day velocities, particularly of the Khumbu icefall, which match closely with remote-sensing observations. The results indicate that the stagnant debris-covered tongue has already dynamically, and perhaps physically, detached from the active Khumbu Glacier. The significant recent warming means that the active section of Khumbu Glacier is committed to a 22% volume loss by 2100, and 34% by 2300. Future increased precipitation can act to offset the impact of moderate warming on glacier mass balance. However, under the most extreme warming scenario, mass loss is significant, particularly during the monsoon. Despite having the world's highest accumulation area, Khumbu Glacier may cease to exist by 2160.

There has been a progressive increase in the number and area of ice-marginal lakes along the western margin of the Greenland Ice Sheet (GrIS) since the late 1980s. Ice-marginal lake formation and growth have been widely associated with accelerated rates of mass loss and terminus recession at alpine glaciers, yet their impacts on the GrIS have remained unquantified. This thesis therefore investigated the influence of ice-marginal lakes on ice-margin dynamics in west Greenland at multiple spatial and temporal scales, using both established remote sensing techniques and the novel integration of time-lapse photography with Structure-from-Motion and Multi-View Stereo. A regional-decadal scale analysis of ice-margin change along a ~5000 km length of the GrIS revealed that lake-terminating ice-margins receded faster than their terrestrial counterparts between 1987 and 2015. In addition, the rate of recession at lake-terminating ice-margins accelerated over the study period and increasingly outpaced recession at terrestrial ice-margins. Altitude, latitude, lake area and the length of the lake – ice-margin interface were also identified as significant controls on rates of lake-terminating ice-margin recession. Local-seasonal scale ice-margin dynamics were investigated using the first continuous year-round volumetric record of calving at a lacustrine ice-margin. These data highlighted two distinct calving regimes; with melt-undercutting driving high calving rates under ice-free lake conditions, and force imbalances at the ice-cliff driving low calving rates when the lake was frozen. These results are important because they demonstrate that ice-marginal lakes are key regulators of ice-margin dynamics at the GrIS. The quantitative data derived through this study provide an empirical foundation upon which modelling efforts can incorporate the influence of ice-marginal processes. This is particularly pertinent given that rates of mass loss and recession at lake-terminating margins of the GrIS are likely to accelerate in coming decades in response to continued ice-marginal lake expansion and a lengthening melt season.

Accurate projection of the future evolution of the Greenland and Antarctic ice sheets is a key challenge of glaciology and climate science. Ice sheet flow is dominated by ice streams; narrow corridors of fast flow bounded laterally by slower flowing ice, discharging the majority of ice from an ice sheet. These ice streams are particularly vulnerable to retreat, and their behaviour evolves along with the ice sheet as a whole. These interactions contribute to uncertainty in projections of ice sheet evolution. In part, this uncertainty can be addressed by examining the palaeo record, providing information on ice stream behaviour over thousands of years. This thesis presents a series of simulations of the British-Irish Ice Sheet using the latest generation BISICLES ice sheet model. Model simulations are used to determine the role of ice streams in the demise of the British-Irish Ice Sheet. First, BISICLES is used to examine the dynamical processes that control the retreat of a major ice stream of the British-Irish Ice Sheet, and this demonstrates vulnerability of the ice stream to Marine Ice Sheet Instability. Then a new basal sliding scheme is implemented coupled with thermo-mechanics, and this successfully models the placement and spacing of the majority of British-Irish Ice Sheet ice streams. Finally, simulations of the deglaciation style of the North Sea demonstrate the significant influence of the Norwegian Channel Ice Stream. Through these simulations, in combination with novel model-data comparison techniques, the considerable role of ice streams in the demise of the British-Irish Ice Sheet is shown. Ice stream evolution and interaction with other factors driving deglaciation needs to be adequately considered in the aim of projecting the future evolution of the Antarctic and Greenland ice sheets. Research such as presented here, modelling and reconstructing palaeo ice sheets, continues to advance this aim.

An accurate characterization of the inaccessible subglacial environment is key to accurately modelling the dynamic behaviour of ice sheets and glaciers, crucial for predicting sea-level rise. The composition and water content of subglacial material can be inferred from measurements of shear wave velocity (Vs) and bulk electrical resistivity (R), themselves derived from Rayleigh wave dispersion curves and transient electromagnetic (TEM) soundings. Conventional Rayleigh wave and TEM inversions can suffer from poor resolution and non-uniqueness. In this thesis, I present a novel constrained inversion methodology which applies a Markov chain Monte Carlo implementation of Bayesian inversion to produce probability distributions of geophysical parameters. MuLTI (Multimodal Layered Transdimensional Inversion) is used to derive Vs from Rayleigh wave dispersion curves, and its TEM variant, MuLTI-TEM, for evaluating bulk electrical resistivity. The methodologies can include independent depth constraints, drawn from external data sources (e.g., boreholes or other geophysical data), which significantly improves the resolution compared to conventional unconstrained inversions. Compared to such inversions, synthetic studies suggested that MuLTI reduces the error between the true and best-fit models by a factor of 10, and reduces the vertically averaged spread of the Vs distribution twofold, based on the 95% credible intervals. MuLTI and MuLTI-TEM were applied to derive Vs and R profiles from seismic and TEM electromagnetic data acquired on the terminus of the Norwegian glacier Midtdalsbreen. Three subglacial material classifications were determined: sediment (Vs < 1600 m/s, 50 Ωm < R < 500 Ωm), permafrost (Vs > 1600 m/s, R > 500 Ωm) and weathered/fractured bedrock containing saline water (Vs > 1900 m/s, R < 50 Ωm). These algorithms offer a step-change in our ability to resolve and quantify the uncertainties in subsurface inversions, and show promise for constraining the properties of subglacial aquifers beneath Antarctic ice masses. MuLTI and MuLTITEM have both been made publicly available via GitHub to motivate users, in the cryosphere and other environmental settings, for continued advancement.

In this thesis, I develop and demonstrate a system for monitoring fluctuations in the speed of Greenland ice sheet outlet glaciers with high temporal frequency from imagery acquired by a range of satellite missions. This work is motivated by an ambition to utilise a new era of operational satellites to better understand how environmental changes are affecting the flow and mass of Greenland's outlet glaciers. First, I exploited the systematic and frequent acquisition schedule of the Sentinel-1 satellite constellation to track weekly variations in the speed of four fast-flowing, marine-terminating glaciers - Jakobshavn Isbræ, Petermann Glacier, Zachariæ Isstrøm and Nioghalvfjerdsfjorden - between 2015-2017. By combining the Sentinel-1 data with an eight-year time-series derived from TerraSAR-X, I produced a decadal record of variations in glacier flow. On a technical level, I was able to demonstrate the value of Sentinel-1's 6-day revisit time for glaciology, because it leads to an increase in the degree of correlation between consecutive images and also to improved tracking of movement near to the glacier calving fronts. On a scientific level, I was able to demonstrate that a strong correlation exists between iceberg calving events and glacier speedup, and to show for the first time that Jakobshavn Isbræ has begun to slow down. Next, I assessed the capability of the Sentinel-1 constellation to detect and chart seasonal changes in the speed of five slow-flowing glaciers situated in a 14,000 km2 land-terminating sector of central-west Greenland. These new measurements offer significantly improved spatial and temporal resolution when compared to previous missions, in all seasons. I was able to show that there are marked differences in the degree of seasonal speedup of the five glaciers - with summertime increases in ice flow ranging from 21 to 49 % - reinforcing the need for comprehensive monitoring and the challenges of making regional extrapolations. Thanks to the high temporal frequency afforded by Sentinel-1, I was also able to document for the first time the detailed spatial pattern of speedup persistence, and to show that short- lived peaks of melting match transient spikes in glacier velocity. Finally, I explored the added value and complementarity of the Sentinel-2 multi- spectral instrument (MSI) for tracking ice motion. I was able to combine measurements acquired by Sentinel-1 and Sentinel-2 to detect short-term changes in iceberg drift, iceberg calving, ice motion, and supraglacial lake area at Jakobshavn Isbræ. I also showed that measurements of glacier flow determined from both satellites are in good agreement, and that the spatial coverage they afford is greatest in opposing seasons, illustrating the promise of Sentinel-2 for glaciology.

Glacial runoff often contains nitrate far in excess of nitrogen (N) concentrations in snow. ‘Excess’ nitrate is likely produced by nitrifying bacteria in subglacial environments, yet the source of the additional N has not been identified. In this thesis, rocks are investigated as an N source to subglacial microbial ecosystems following their comminution by glacial erosion and leaching with meltwater. Weathering processes involving the release of N and micronutrients, iron (Fe) and manganese (Mn), from rock to glacial environments were evaluated using a combination of field studies in Adventdalen (Svalbard) and rock weathering experiments. Attempts were also made to constrain isotope fractionation during weathering to improve the use of stable isotopes to trace N provenance. The sedimentary geological succession underlying glaciers in the study area contained significant N (up to 0.21 wt. %), particularly in organic rich, siltstones and shales. Fe and Mn were largely found within oxide and carbonate minerals while significant pyrite bound Fe (max. 5.2 wt. %) was present in organic rich sediments. In simulated glacial weathering experiments, nitrogen was almost entirely liberated as ammonium with much of it absorbed to mineral surfaces rather than dissolved in solution. Pyrite oxidation liberated Fe and generated acidity which drove i) silicate dissolution releasing N and ii) carbonate dissolution yielding dissolved Mn. The largest N yields were associated with rocks containing abundant organic N which may have been liberated via oxidative weathering, protonation of amines and/or organic matter degradation by free radicals produced during crushing. Liberated ammonium was partly lost as ammonia gas when the solution pH exceeded 8 and also absorbed to sediment, particularly when clay minerals were abundant. Further experiments demonstrated an isotope enrichment in adsorbed ammonium of up to 10‰ δ15N relative to bedrock N, caused by fractionation from a combination of adsorption and volatilisation processes. In Svalbard, up to 89% of nitrate in glacial runoff was derived from non-snowpack sources. Solute was acquired into snowmelt via chemical weathering of rock talus in ice marginal moraines largely via coupled sulphide oxidation and silicate dissolution. When oxygen was available, ammonium released from rock was converted to nitrate via microbial nitrification. This assertion is supported by nitrate δ18O values of close to 0‰, vastly different from atmospheric oxygen. However, when flowpaths were anoxic, nitrate was absent likely due to microbial denitrification. Geological variations may control the magnitude of nutrient export by weathering in glacial catchments. For instance, N and Mn were particularly enriched in water from the Longyearbreen catchment which overlies shales enriched in these elements. Furthermore, clay minerals in bedrock significantly influences the distribution of N (as ammonium) between dissolved and particulate phases through ion exchange reactions.

In this thesis I develop novel methods and datasets, based on the processing of CryoSat-2 satellite radar altimeter data, to improve the understanding of retrieving measurements of surface elevation and elevation change over the Antarctic and Greenland ice sheets. First, I used 6 years of CryoSat-2 altimetry to create a model of the surface height of the Antarctic Ice Sheet and ice shelves. Posted at a resolution of 1 km, 94 % of the grounded ice sheet and 98 % of the floating ice shelves are observed, and the remaining grid cells North of 88 ° S are interpolated using ordinary kriging. Taking into account slope-dependent errors and the distribution of slopes across the ice sheet, I estimated the average accuracy of the DEM to be 9.5 m - a value that is comparable to, or better than that of other models derived from satellite radar and laser altimetry. Next, I developed a new technique to retrieve estimates of the depth distribution of radar backscatter from CryoSat-2 altimeter waveforms using a backscatter model. I then applied this model to chart spatial and temporal variatibility in radar backscatter and, for the first time, explicitly estimate radar penetration depth across the interior of the Greenland Ice Sheet. I then used this information to correct for artefacts in elevation trends derived from Cryosat-2 pulse-limited altimetry resulting from an episodic melt event which reset the radar scattering horizon. Incorporating the penetration depth into the surface height retrieval, I find improved agreement when compared to independent airborne laser altimeter data recorded over the same time period. Finally, I used CryoSat-2 altimetry to estimate seasonal elevation changes in the Greenland Ice Sheet. Using regional climate model simulations of height fluctuations due to surface process alone, I demonstrate that CryoSat-2 observations track elevation changes driven by melting and snowfall accumulation in the ice sheet ablation zone. I then mapped spatial and temporal variations in seasonal elevation change, demonstrating the ability of CryoSat-2 to monitor changes in Greenland which arise due to its meteorology.

During the mid- to late Neogene (20 - 2.5 million years ago), episodic retreat of the Antarctic Ice Sheet (AIS) coincided with periods of higher-than-present atmospheric CO2, indicating ice sheet sensitivity to climatic conditions similar to those projected for the coming decades. Understanding Antarctic climate and vegetation during such a period of AIS retreat is crucial for our fundamental understanding of high latitude environments in warmer-than-present climate scenarios. This thesis presents a detailed geochemical study of sediments and plant fossils from the terrestrial Sirius Group of Oliver Bluffs, Transantarctic Mountains, located at 85 °S today and during the Neogene. Biomarker analysis of the sediments show strong evidence for a warmer Antarctica, where summer temperatures reached 5 °C. These relatively favourable conditions sup- ported a low diversity mixed vegetation. In contrast to the macrofossil record, there is geochemical evidence for conifers, suggesting that Antarctic vegetation was strongly controlled by local environmental variability. The warmer conditions are associated with a dynamic carbon cycle, evidenced by anomalously high and variable atmospheric 13C and possibly linked to atmospheric CO2 levels. Precipitation isotopes are reconstructed from plant compound isotope analysis of the fossils, and indicate markedly different hydrological cycling. This result is supported by climate modelling experiments which suggest that Antarctic hydrological cycling is most strongly governed by the extent of the ice sheet rather than by greenhouse gas radiative forcing. This thesis presents a new approach to exploring Antarctic climate and vegetation and provides important novel information on this crucial region of the world.

New Zealand fills a large geographic gap in the global glacial record, with landforms and near-surface deposits preserving a remarkable footprint of Quaternary glaciation. As one of the few land masses in the Southern Hemisphere, the record of glacial geomorphology is of great importance for research into the natural behaviour of the Earth’s climate system. This thesis presents a 3D simulation of the New Zealand Southern Alps glaciers at the Last Glacial Maximum (LGM, c. 30 to 18 ka) in an attempt to constrain glacial geometry of that period. To achieve this, the REVOLTA (Reconstruction of Volume and Topography Automation) model was developed, a Python script tool for ArcGISTM that requires just a DEM of glacier bed conditions and the down-valley extent of glaciation as initial inputs. Ice thickness is initially estimated at points along an automatically generated centreline network based on the perfect-plasticity rheology assumption, taking into account a valley side drag component of the force balance equation. Distributed ice thickness is subsequently interpolated using a glaciologically correct algorithm. Results indicate a total LGM ice volume of 6771.9 km3, in good correspondence of previous studies using a climate-driven ice dynamics approach. Combined with an estimate of contemporary ice volume (50.67 km3), this result reinforces the notion that New Zealand has lost almost the entirety (99.25 %) of its glacial ice since the LGM, although this volume has contributed to just 17.02 mm of global sea level rise. Analysis of the LGM distributed ice thickness output shows a large number of nunataks and exposed ridges in the central Mt. Cook and northern regions, with a localised icefield in the Fiordland area. LGM Equilibrium Line Altitudes (ELAs) automatically calculated using the Accumulation Area Ratio (AAR) method reveals an average lowering of 1074 m from present, with those to the west of main divide 461m lower than those to the east on average. LGM climatic conditions were estimated using the ELAs and scaled versions of contemporary temperature and precipitation distributions, suggesting a temperature reduction of between 5.6°C to 10.3°C and precipitation change of +4.3 % to +100.4% from present. When considering these new estimates in conjunction with critically evaluated previous evidence, an average LGM cooling of 6.5 °C to 8°C is proposed, a refinement on the wide range of previously published values. Importantly, there is large spatial variability between catchments, with eastern regions experiencing significantly greater cooling and greater precipitation increases (or less decrease) than their western counterparts. Increased westerly circulation and reduced sea level altering the relative position of the orographic barrier is a suggested potential mechanism for the predicted precipitation pattern changes, whilst increased southerly flow bringing cool air up the east coast is a possible cause of the temperature change differential predicted. The proportion of precipitation falling as snow or rain was also found to be an important factor when considering New Zealand LGM conditions, with up to 50% estimated to be falling as rain at the LGM ELA, with a strong east-west differential. Input dataset generation for REVOLTA resulted in several important research outcomes. A DEM approximating LGM bed conditions was created, using a variety of novel techniques to modify the existing DEM. These included the estimation of contemporary ice thickness distribution using the VOLTA (Volume and Topography Automation) model for removal from the DEM, merging offshore and lake bathymetry and considering Holocene in-fill sediments. Furthermore, an in-depth review of the most up to date literature and datasets regarding the lateral extent of LGM glaciation was also carried out, generating an updated ‘outline’ of LGM glaciation.

The main aim of this research project was to improve our understanding of the diversity, function and ecology of glacial microbiomes. Snow and ice algae are critical players in supraglacial habitats and form extensive blooms in spring and summer. Here I present results on the diversity and the function of snow and ice algae on 21 glaciers in 4 Arctic settings: Greenland, Iceland, Svalbard and Sweden. For the first time, I have evaluated the full microbial community composition (i.e., algae, bacteria, archaea) in the main supraglacial habitats, namely green snow, red snow, biofilms, dirty ice, and cryoconite holes. I have cross-correlated these data with metabolic analyses (i.e., metabolomics, pigments, fatty acids) and critical physico-chemical parameters. I found that snow and ice algae were the first communities to appear after the onset of melting and they showed positive net photosynthetic rates indicating accumulation of organic matter. Furthermore, for the first time I have described these communities in Iceland. My data reveal that red pigmented snow algae are cosmopolitan, and independent of location specific geochemical and mineralogical factors. Only six taxa made up >99% of the algal communities: two uncultured Chlamydomonadaceae, Chloromonas polyptera, Chloromonas nivalis, Chloromonas alpina and Raphidonema sempervirens. In contrast, the composition of green snow varied between the studied locations with higher relative abundance of Raphidonema sempervirens and Microglena sp. in Svalbard, and Chloromonas polyptera in Sweden. Furthermore, I show that green and red snow are not successive stages but two independent phenomena with different adaptation strategies. In all sites, bacteria were mostly represented by the phyla Bacteriodetes, Proteobacteria and Cyanobacteria. The bacterial community composition varied between the different habitats on the phylum level, whereas on the class level they also showed strong biogeography. Archaea showed overall low species diversity. The synthesis of pigments and fatty acids in snow and ice algae were mainly driven by nitrogen and less so by phosphorus limitation. This is especially important for pigments which cause a darkening of glacial surfaces. I show that snow and ice algae dramatically decrease surface albedo which will eventully result in higher melting rates of glaciers.

In this thesis, I use synthetic aperture radar (SAR) and radar altimeter data to make new observations of Antarctic and Greenland ice sheet grounding lines. I use ERS SAR data acquired between 1992 and 2011 to map the Petermann Glacier grounding line on 17 occasions using quadruple difference interferometric SAR (QDInSAR). Over the 19-year period, the grounding line position varied by 0.5 km, on average, with no significant trend over time. Although tidal forcing explains a fraction (34 %) of the movement, localised variations in the glacier thickness could explain it all were they to alter the glaciers hydrostatic balance as they advect downstream – a hitherto unconsidered possibility that would reduce the accuracy with which changes in grounding line position can be detected. Next, I developed a new technique for detecting grounding lines using differential range direction offset tracking (DRDOT) in incoherent SAR data. I then applied this technique to a sequence of 11 TerraSAR-X images acquired in 2009 over Petermann Glacier. The DRDOT technique is able to reproduce the shape and location of the grounding line with an estimated lateral precision of 0.8 km and, although this is 30 times poorer than QDInSAR, provides a complementary method given the paucity of coherent SAR data. Finally, I developed another new method for detecting the grounding line as the break in ice sheet surface slope computed from CryoSat-2 elevation measurements. I then applied this technique to map grounding lines in the sectors of Antarctica buttressed by the Filchner-Ronne, Ekström, Larsen-C, and Amundsen Sea ice shelves. The technique is able to map the grounding line to within 4.5 km, on average, and, although this is far poorer than either QDInSAR or DRDOT, it is computationally efficient and can succeed where SAR-based methods fail, offering an additional complementary approach.

Supraglacial lakes (SGLs) form when runoff (meltwater + rain) pools in depressions on the Greenland ice sheet (GrIS). SGLs can collectively affect seasonal ice sheet flow rates when they drain episodically; although the net impact on flow speed is uncertain. In this thesis: 1) a new model of SGL Initiation and Growth (the SLInG model) is presented, 2) existing SGL observations are evaluated and combined to form a single optimised dataset, 3) these data are used to evaluate the model and 4) this model is used to investigate past trends in SGL evolution in south west Greenland. SLInG is a 2-dimensional transient hydrology model which routes runoff, which has been simulated using a regional climate model, over a digital elevation model (DEM) of the ice sheet surface. Water is routed using Darcy’s law for flow through a porous medium and Manning’s equation for open channel flow, and is allowed to collect in depressions in the DEM, thus forming SGLs. Observations of SGLs can be temporally sparse and variation in reported lake frequency can be significant between datasets. Three observational datasets of SGLs, automatically derived from satellite data, were found to omit a sizeable (29 to 48%) fraction of lakes identified manually. These datasets were combined using a hierarchical scheme, leading to a 67% increase in the number of lakes reported. By comparison with satellite observations, SLInG is found to be 19 times more likely to correctly predict the location, or absence, of a lake, than not. In addition, simulated and observed lake onset dates are highly correlated (r= ~0.8) and model estimates of the rate of growth of lake covered area are, on average, just 14% greater than observed values. SLInG was forced with 40 years of reanalysis data in order to investigate historical variation in the temporal evolution of SGLs. SLInG shows that SGLs have responded to recent dramatic changes in local climate by migrating inland by 150 m a.s.l. (3.75 m a.s.l. per year) during 1971-2010. This modelled trend is in good agreement with recent satellite observations and suggests that SGLs, by forming and draining at higher elevations, where pre-existing surface-bed conduits such as moulins and crevasses are rare, may contribute more significantly to ice sheet dynamics in the future.

Landscape change in the jokulhlaup-prone proglacial system at Solheimajokull has been quantified at multiple spatio-temporal scales with the aim of assessing the relative geomorphic importance of the 1999 j6kulhlaup and the controls on proglacial landscape development. A time-series of high-resolution orthophotographs, photogrammetric digital elevation models (DEMs) and LiDAR data were used to quantify planform and volumetric rates of change both pre- and post-j6oulhlaup. Proglacial sedimentological and stratigraphic characteristics were investigated using ground penetrating radar (GPR), sediment logging and clast analysis. Depth-averaged two-dimensional hydrodynamic modelling was used to reconstruct jokulhlaup flow hydraulics, sediment transport and within-flood bed elevation change.

This thesis examines how microstructures in glaciogenic sediments reflect the processes forming them, and how these microstructures then affect the conditions around them, through a series of field studies, laboratory tests, models, and statistical analyses. Following literature reviews, a deformational chronology is developed for diamictons at Criccieth, North Wales, and their microstructures are used to indicate the stress, hydraulic, and environmental changes the materials have undergone. Microstructures of the lowest diamict indicate clast lodgement. The processes reflected in the microstructures of this lowest diamict are built into a quantitative model that estimates its residual strength (20 - 50 kPa) and the ice velocity during lodgement (20 - 50 m a-1). The response of sediment to glacial stress is further examined by triaxial testing of diamict from Yorkshire, and the subsequent examination of its micromorphology. Shears in the material are disrupted by clasts, and this may be responsible for work hardening seen during the tests. Fabric compression, and the development of immobilised shears or hydraulic fractures buffer pore fluid pressure to ~470 kPa. The information from previous chapters is then used to analyse other material from the Yorkshire coast. This analysis confirms the presence in the area of meltout tills that have undergone low strain, as well as providing evidence for the decoupling of the ice and sediment in this region, and the nature of drainage systems within and above the diamicts during glaciation. Overall this thesis details the processes forming three ‘classic’ microstructures found in glacial sediments; omnisepic fabrics, lattisepic fabrics, and melanges, and provides evidence for the processes involved in forming diamict pebbles and skelsepic fabrics. In addition this thesis details how such structures reflect coupling and decoupling processes between glaciers and their beds, and examines the manner in which microstructures affect the response of a subglacial sediment body to stress and hydraulic conditions.