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The colonisation of Iceland around 870 A.D. saw the influx of Norse settlers to a previously uninhabited island, resulting in large-scale ecological changes. Human impacts on the landscape vary in time and are spatially complex, making it difficult to accurately assess how Iceland was affected. To improve our knowledge about the spatial and temporal patterns of landscape changes in Iceland, this thesis uses quantitative approaches to analyse existing palaeoenvironmental data from Iceland. A meta-analysis was used to determine the spatial bias in and the temporal quality of Icelandic pollen sites. Relative pollen productivity (RPP) estimates are calculated for seven ecologically important taxa, by analysing pollen-vegetation relationships at eighteen sites. The RPPs serve as input for quantitative pollen-based reconstruction models, the Multiple Scenario Approach. Landscape reconstructions totalling 3825 km² were generated for three sites (Mývatn, Reykholtsdalur, and Skálholt) and three time slices (577-877 CE, 877-1077 CE, and 1077-1277 CE). The analysis of spatial bias shows that pollen sites in Iceland are closer to farms and have a higher annual mean temperature and precipitation than a sample of random sites. The RPPs of Icelandic taxa are lower than RPPs in comparable areas. Different spatial patterns in vegetation cover emerge from the reconstruction model outputs, Mývatn remains wooded throughout the time slices, while Reykholtsdalur becomes mostly deforested from 1077 CE onwards. The spatial analysis shows the need for thorough analysis of the representativeness of current palynological datasets, which helps identify where future sampling should take place to create more representative datasets. The characterisation of pollen-vegetation relationships shows that there is much more to be understood about the mechanics behind differences in RPP estimates in different locations. Quantitative reconstruction methods provide a useful tool for gaining insight into differences in land cover changes in Iceland, and to visualise different spatial patterns in the landscape.

The overall aim of this thesis is to assess the use of tephra layer morphology to infer surface qualities of past landscapes. By examining how environmental processes affect the development of an enduring tephra record, this thesis assesses the potential of using tephra layer morphology to infer surface environmental conditions of the past. A variety of processes operate at both the land surface and in the near sub-surface that can impact the preservation of tephra layers, and this thesis examines whether this is expressed in layer thickness, morphology and grain size distribution (GSD). A preserved tephra layer may have been fundamentally shaped by the nature of the surface environment at the time the tephra was deposited. These are assessed by examining different tephra layers (up to 20 cm thick) in a variety of different environmental settings in Iceland, collecting over 10,000 individual measurements, combined with controlled experiments in Scotland. A series of case-studied are used: 1) assessing the relationship between tephra layer thickness and GSD with the rate at which the surface tephra deposit is buried and preserved. 2) assessing the effect of small scale topographic features (cryogenic landforms found in Iceland - thúfur) on tephra layer morphology and GSD. 3) identifying the effects of slope angle on the movement of different tephra and the influence of different slope angles on layer formation. 4) evaluating morphological and GSD changes in tephra layers across cultural landscapes to infer land use and 5) testing new ways in which tephra layer morphology can measured and visualised using CT scanning. Results indicate that there are circumstances when environmental processes taking place in the days, weeks, months and years post deposition can indeed alter tephra layer morphology. Therefore, the variable preservation of tephra layers do record aspects of environmental processes and thus may enhance palaeoenvironmental reconstruction. Areas with rapid rates of burial preserve a greater proportion of the original fallout than areas with slower soil accumulation rates. The burial rate itself does not appear to correlate to the variability within the layer, indicating that processes occurring soon after the eruption are more influential. Small-scale landscape features such as thúfur formations that include locally steep slope angles (above the relevant angle of repose) can alter the thickness and grain size distribution of tephra layers across the features themselves, meaning that the variability of the layers provide evidence of micro-topographic features being present on the surface at the time of tephra deposition. Within a uniform vegetation cover that subsumes the tephra deposit, significant movement of tephra downslope only occurs when the slope angle is above the critical angle of movement. Tephra layer thickness variation is associated with changes in vegetation coverage onto which the tephra was initially deposited and thus tephra layer morphology which may be used as an indication of past land management. Due to human interventions, tephra deposits in areas actively managed (such as on occupied farms) may be actively cleared of fallout and farmed after an eruption. Combining the analysis of tephra layer morphology with historical data on social status and farming practice provides a novel insight into land use at the time of an eruption and in the years after. Whilst layer thickness (and thus mass loading) is a useful metric, grain size distribution does not appear to be an indicator of different land uses. Testing CT scanning as a method to visualise preserved tephra layers was successful and indicates that this technique can be used in future studies of tephra morphology changes to complement and extend the insights possible with studies of soil micromorphology. This work adds to the growing body of research that is using tephra layers for more than chronology in the science of environmental reconstruction. It also highlights the ways that surface environmental processes may affect the preservation of tephra deposits in subtle yet pervasive ways that may be unrecognised by those using tephra layers to reconstruct volcanic processes. Environmental controls on tephra layer morphology are therefore widespread and are likely to occur on all tephra layers as they are preserved into the stratigraphy. This has significant implications for inferences of volcanic process made using tephra, which should be taken account of in future volcanological research.

The Icelandic mantle is lithologically and chemically heterogeneous. This had led to the identification of geochemically enriched and depleted domains within the Icelandic mantle. Enriched domains have been prescribed to the presence of recycled oceanic lithosphere in the form of pyroxenite. Halogens are highly incompatible and fluid mobile elements which are concentrated in the Earth's crust, particularly in altered oceanic crust and serpentinised oceanic lithosphere from hydrothermal alteration. During subduction these halogen-rich domains are returned to the mantle in the down-going slab. Therefore halogens are potentially excellent tracers of recycled oceanic lithosphere in the mantle. This thesis uses the halogen concentration of melt inclusions and basaltic glasses from Iceland and the Reykjanes Ridge to address this potential. Firstly, the influence of pyroxenite-derived melts to melt compositions across Iceland is assessed. Pyroxenite-derived melts have the greatest influence in the flank zones of Iceland, far from the rift and plume centre. Concentrations of halogens measured in melt inclusions and glasses from Iceland are highest in the flank zones. Additionally, the highest halogen concentrations in glasses from the Reykjanes Ridge are in those closest to Iceland and correlate with enriched melt compositions. Therefore halogen concentrations appear to be a promising tracer of the influence of recycled oceanic lithosphere, with higher concentrations indicating higher influence on erupted melt compositions. Ratios of halogens to elements of similar compatibility show a different behaviour to the concentrations. The influence of recycled oceanic lithosphere has no influence on these ratios and they cannot be used as tracers of its contribution. Heterogeneity in the ratios can be used to identify recycled mantle domains with differing ratios. Differences in the ratios may be caused by individual recycled lithologies retaining unique halogen contents which can be identified in high density study of particular locations. On a global scale halogens are likely recycled throughout MORB and OIB mantle domains. Recycled oceanic lithosphere is likely present in the upper mantle and recycling is not confined to entrainment of residue slabs at the core-mantle boundary. Over time this recycling has created mantle halogen ratios which are similar to that of MORB. Thus on a global scale mantle halogen ratios are consistent, however smaller scale studies with high sampling density are able to identify heterogeneities which may reflect heterogeneity in subducted lithologies.

The Icelandic plume, a major convective upwelling, has had a considerable influence on the geological evolution of the North Atlantic region. Direct manifestations of this major convective upwelling include positive residual depth anomalies and long wavelength free-air gravity anomalies, both of which reach from Baffin Island to Norway and from Newfoundland to Svalbard. Signifi cant shear wave velocity anomalies, observed in full-waveform tomographic models between 100 km and 200 km depth, show the Icelandic plume has a complex, irregular planform. These anomalies suggest about fi ve horizontal fi ngers radiate away from the central plume conduit. The best imaged fingers lie beneath the British Isles, southern Scandinavia and Greenland, extending ~1,000 km from the Icelandic plume. It is proposed that these radial miscible fi ngers develop due to the Saffman-Taylor instability, a fluid dynamical phenomenon which occurs when a less viscous fluid is injected into a more viscous fluid. Mobility ratio (i.e. the ratio of fluid viscosities), Peclet number (i.e. the ratio of advective and diffusive transport rates) and thickness of the horizontal layer into which the fluid is injected, together control the presence of fi ngering due to the Saffman-Taylor instability. Estimates for the Icelandic plume suggest the mobility ratio is at least 15, the Peclet number is ~ 2 x 10⁴, and the asthenospheric channel thickness is 100 ± 50 km. Appropriately scaled laboratory experiments play a key role in developing a quantitative understanding of the spatial and temporal evolution of mantle plume planforms. My results prove that the presence or absence of radial miscible fi ngering due to the Saffman-Taylor instability is controlled by changes in mobility ratio, Peclet number and horizontal layer thickness. At large horizontal thicknesses, gravity has an increasingly important influence and acts to damp the production of radial viscous miscible fi ngers. Observed values from the Icelandic plume suggest the fluid dynamics may be more complex than the Saffman-Taylor instability alone. Additional processes, such as interaction with the base of the lithospheric plate, along with the Saffman-Taylor instability, may be the origin of the fingers.

Microseismicity offers an opportunity to image subsurface deformation at exceptionally high spatial and temporal resolution. This may be related to a diverse range of processes, including fore- and aftershocks to destructive earthquakes on large faults, magma movement at volcanoes, or the gradual advance of glaciers. Microearthquakes at faults might also signal more exotic behaviour, including due to transient events such as fluid injections or pulses of aseismic fault creep. The study of small earthquakes has advanced significantly over the past decades, as seismology has entered the digital age. Denser networks, with larger numbers of more sensitive seismometers allow ever smaller seismic events to be detected and analysed. The study of larger numbers of earthquakes brings a raft of benefits, including more robust statistical analyses, higher temporal resolution, and the opportunity to achieve significantly greater spatial resolution by harnessing the power of relative relocation algorithms. However, the fundamental task has remained the challenge of extracting an earthquake catalogue from continuous waveform recordings. I present new software that offers a powerful, efficient, and highly automatable method to produce exceptionally complete and robust earthquake catalogues from continuous seismic data. Instead of reducing the information contained in waveforms to "picks" - discrete timestamps marking candidate phase arrival times - within QuakeMigrate the seismic data is transformed to continuous functions which are then combined across the network by migration. Retaining as much information as possible until the point of comparing the recordings from across the entire array allows phase arrivals at or below the signal-to-noise ratio to be successfully associated with events, improving both detection capability and location resolution. I use QuakeMigrate to detect and locate microseismicity in the Northern Volcanic Zone, Iceland, from 13 years of continuous seismic data recorded on a dense local network. Through comparison with a comprehensive catalogue of previously analysed events, I demonstrate that this new, automated algorithm is capable of location accuracy equal to or surpassing the widely held gold standard of manually refined earthquake locations. Within my new catalogue of more than 155,000 events, including related to magma ascent and intrusion in the lower crust, shallow geothermal activity, and seismicity triggered by fluid injection, I focus on persistent earthquake swarms that delineate a network of faults surrounding Askja volcano. Tightly constrained earthquake hypocentres, refined by cross correlation and relative relocation, reveal an intricate mesh of strike-slip faults, with fine-scaled structures resolved at length-scales of 10's of metres. This comprehensive image of the subsurface fault structure fills in the gaps between manually analysed events, and combined with tightly-constrained fault plane solutions reveals kinematics which point to a complex deformation field, and the role of elevated pore pressures or mechanical anisotropy in generating anomalous fault geometries. Comparison of the temporal evolution of the major sources of deformation with the seismicity provides evidence that deflation of a shallow magma reservoir in Askja caldera plays a principal role in driving these earthquakes. Within individual earthquake swarms, seismicity systematically migrates along fault planes, indicating the role of aseismic processes in controlling their evolution. Analysis of the migration velocities and b-value statistics points to transient creep events as the primary driving mechanism, indicating the role of unusual frictional properties. Aseismic slip has recently been recognised as an important process in releasing strain at subduction zone interfaces, as well as on faults at a range of depths both in the oceans and within the continents. Such well-resolved examples of this process are crucial in gaining a deeper understanding of the wide spectrum of fault behaviour, and the links between slow and largely silent, and fast and potentially devastating fault slip. The Bárðarbunga-Holuhraun dike intrusion provides a unique opportunity to analyse the triggering of seismic swarms due an extremely well-resolved static stress change. As the dike intruded towards Askja, a surge in swarm seismicity was observed across the network of faults studied in this dissertation. In the absence of complicating factors present in the study of stress changes caused by large earthquakes, I determine that swarms initiated at Coulomb stress increases of as small as 0.025 MPa. Furthermore, swarms do not show any seasonal tendency in occurrence, despite strong seasonal loading of the crust, which dominates measurements of relative crustal velocity changes. This further indicates that these faults experience very low effective normal stresses. Together, these observations indicate that this network of faults possess an exotic rheology. The absence of seismicity triggered elsewhere by the dike intrusion provides confidence in my observation of their spatial extent, which is consistent with earthquake catalogues derived from analogue seismic recordings extending back to the 1970s. I suggest the potential roles of fluids released at sites of vigorous hydrothermal activity in Askja volcano, and from numerous melt feeders in the lower crust, in producing the conditions that allowed these faults to develop, setting this area apart from the remainder of the Northern Volcanic Zone, which is otherwise largely aseismic during the current inter-rift period.

The plate tectonic cycle is fundamental to our dynamic Earth, encompassing the formation and evolution of new lithosphere at divergent, mid-ocean ridges, all the way to its eventual return to, and re-equilibration with, the mantle in subduction zones. I investigate the structure of the crust and upper mantle of the Earth in two regions that represent different endmembers in this cycle through the analysis of microseismicity and seismic anisotropy, seeking to learn more about the stresses in these environments and how they are manifest in the structure of the subsurface. In Iceland, new oceanic crust is accreted episodically within the volcanic rift zones that delineate the subaerial portion of the Mid-Atlantic Ridge, the divergent margin between the North American and the Eurasian plates. Northern Borneo, conversely, exhibits the tectonic signatures of not one but two terminated subduction zones, where oceanic lithosphere was once being actively recycled into the Earth's mantle. As part of this work, I have helped to deploy and service two passive seismic experiments-the Cambridge Volcano Seismology network in Iceland and the northern Borneo Orogeny Seismic Survey (nBOSS) network in Sabah-from which I have derived my results. Seismic anisotropy is manifest on a vast range of scales, from swathes of the crust and mantle, all the way down to the scale of single mineral crystals. It has the potential to inform on the dynamic state of the mantle, the structural fabric of fault zones, layering in sedimentary basins, and the distribution of partial melt in the subsurface, to name a few applications. Here, I seek new insights into the stress state and structure of nascent oceanic crust as it is accreted at a mid-ocean ridge, and the volcanic systems found therein, in Iceland. I also look to piece together the interplay between past tectonic events, subduction termination, and the present-day state of the mantle in northern Borneo. In the first part of my dissertation, I apply shear-wave splitting analysis to a microseismic catalogue (spanning the period 2008-2018) in the Northern Volcanic Zone of Iceland in order to investigate the relationship between seismic anisotropy and the tectonic stresses arising from extension and plate spreading, microseismicity, and the presence of melt. I find the upper 3-4 km of the Icelandic crust to be seismically anisotropic. Modelling of the stresses in the upper crust arising due to plate spreading and active deformation around Askja volcano, I find this anisotropic layer can be explained through a mechanism of stress-aligned microcracks within the porous crust. I then use earthquakes that occur within the lower, ductile crust-associated with the movement of melt within the volcanic plumbing system-and effective elastic media modelling to explore the role of melt in the generation of seismic anisotropy below 10 km depth, finding a strong correlation between my observations and the presence of melt as inferred from seismic tomography. I synthesise these observations with recent works examining the seismic anisotropic structure of the Icelandic crust from ambient noise observations to construct a conceptual model for the mechanisms generating anisotropy throughout the Icelandic crust. In the second part of my dissertation, I step back in terms of scale to investigate how tectonic processes related to subduction (and post-subduction) are manifest in the form of seismic anisotropy by applying shear-wave splitting analysis to teleseismic core-refracted seismic phases. My results, in conjunction with a recent tomographic model of the region, constrain the seismic anisotropy to the lithosphere and reflect recent (past ∼20 Myr) events in the tectonic history of northern Borneo. In north-west Sabah, my observations of seismic anisotropy are aligned with the orogenic belt running down the north-west coast (the Crocker Range), which formed during the termination of subduction of the proto-South China Sea. Conversely, in south-west Sabah my observations suggest extension has played an important role in the subsequent tectonic evolution of northern Borneo following subduction of the Celebes Sea and the opening of the Sulu Sea. I supplement this work with the first detailed study of seismic activity on a network of faults around Mount Kinabalu, a 4100 m tall mountain within the Crocker Range of northern Borneo. For this, I developed and used QuakeMigrate, a new Python package for the automatic detection and location of earthquakes using waveform migration and stacking. These new observations indicate ongoing extension in the region around Mount Kinabalu and allow, for the first time, for this network of faults to be mapped and explored in detail.

Measuring the travel times of seismic waves is one of the most important tools for uncovering Earth’s structure and dynamics. In recent years, the discovery that surface wave dispersion could be estimated from ambient noise has introduced new possibilities into the field of seismic imaging, such as performing passive source tomography in regions where it was not previously possible with a dense azimuthal ray path coverage. In this work, I leverage the new possibilities introduced by this method to investigate the crust in Iceland in a number of ways, including tomographic imaging as well as azimuthal and radial anisotropy analyses in both the lower and upper crust. Understanding accretion and deformation processes at mid-ocean ridges is crucial because they control the resulting oceanic crustal structure, which covers two-thirds of the Earth’s surface. Iceland, which is uplifted by a convective mantle plume and has an active spreading ridge system exposed above sea level, offers a unique opportunity for studying this phenomenon. I first use a dataset of Love and Rayleigh wave dispersion measurements with dense azimuthal coverage to constrain seismic anisotropy in the Icelandic crust. I show that seismic anisotropy in the lower crust is controlled by crystal preferred orientation, providing a direct observation of lower crustal flow. Furthermore, since shear is needed to align the crystals, our result reveals that crustal flow cannot be a simple translation of mass and requires internal deformation. This finding has important implications for how thick, hot oceanic crust, as found in volcanic rifted margins and near plume-ridge interactions, can accrete and deform. Despite the growing use of ambient noise in measuring crustal properties, extensive comparisons between ambient noise results and those obtained from local earthquakes remain elusive. To address this, I measure Love and Rayleigh group velocity using ambient noise recorded around Askja, a large active volcano in central Iceland, explore its velocity structure and anisotropy and compare my findings to those from local earthquake studies. I show that crack properties estimated using surface wave anisotropy strongly correlate with local shear wave splitting and outcrop mapping, indicating the method is highly effective for such analyses. Next, I show that VSV models derived from Rayleigh waves can be significantly faster than VS extracted from body waves, which has important implications for viii jointly exploiting these two classes of data. Furthermore, 3D VSV and VSH models constrained by the data through a two-step inversion procedure resolve a shallow slow anomaly consistent with a magma chamber predicted by geodetic studies, but not imaged by local earthquake body wave tomography. I then measure Love and Rayleigh phase velocities from ambient noise in Iceland in the period range 7 - 16 s from more than 3000 station pairs. This involves the development and use of an automatic method for extracting phase velocities from noise cross-correlation functions (NCF). The phase travel times are then inverted for phase velocity maps. I present the first Love phase velocity maps of Iceland and show that like Rayleigh phase velocities, Love phase velocities display slow anomalies along the rift zones with the lowest velocities in the neighbourhood large volcanic centres, which I attribute to the presence of partial melt.

In his first verse, the precocious poet Egill Skallagrímsson declares ‘eigi mun þú finna betra þrevetran óðarsmið mér’ (‘you will not find a better poetry-smith of three years than me’). Such metaphors are highly conventional in the skaldic poetry of the Viking Age and beyond. However, the link between the composition of verse and the construction of material objects was regarded as a topic of particular importance by Scandinavian poets such as Egill. In fact, connections between poets, craftsmen, their arts and their products resonate across the corpus of Old Norse literature—not only in skaldic metaphor, but also in historical, mythological and saga material. To judge by the frequency of their appearance in this literary corpus, these connections were clearly considered to be highly significant in Viking-Age and medieval Scandinavia. Nevertheless, they have received little attention in scholarship to date. This thesis investigates the nature and extent of the links between poets and craftsmen, and between poetic composition and material crafting. It investigates both what the origins of these connections were, and what they suggest about the artisans and creative processes concerned. This thesis begins by establishing precisely which poets and craftsmen form the focus of this investigation. As these figures appear in a large variety of different sources, it is also important to discuss the different categories of evidence considered in this thesis, and to confront any difficulties involved in their use. The first chapter proceeds by considering the links between poets, craftsmen, their arts and their products which are made in skaldic poetry. In the second chapter, skaldic poetry, sagas and archaeological material are analysed to build a picture of the links between historical poets and craftsmen working in late Viking-Age Scandinavia. This chapter considers the similar ways in which these figures interacted with the political elite, and the correspondences between the creation, dissemination and use of their products. The third chapter considers what skaldic and eddic poetry as well as Snorra Edda reveal about the mythological configuration of poetic composition, crafting and their practitioners. It explores the shared association of poetry and crafted goods with the distant past and with geographically remote spaces in the Old Norse cosmos, and the implications of these associations. In the fourth chapter, the shared characteristics of poetic composition, crafting and their practitioners are considered in the context of the Íslendingasögur. As many of the connections explored in the earlier chapters recur in this corpus, it constitutes appropriate evidence with which to draw the investigation to a close. In my conclusion, I reconsider the findings of each of the chapters and suggest that a deep conceptual similarity between poetic composition and skilled crafting runs throughout Old Norse literature, and that this encouraged the frequent associations between them which can be detected in this corpus. I also argue that poets and craftsmen were frequently connected on account of their shared role as threatening but highly necessary creator figures.

The focus of this thesis is the development and application of a new method of diffusion chronometry known as DFENS (Diffusion chronometry using Finite Elements and Nested Sampling). This method combines a flexible finite element numerical model with a nested sampling Bayesian inversion to provide robust uncertainty estimates and account for observations from multiple elements within a single phase, or multiple phases. In this thesis, the DFENS methodology is applied to three eruptions from Iceland with different compositions and storage depths in order to characterise the timescales of pre-eruptive residence and transport: the Skuggafjöll eruption, Bárðarbunga volcanic system; the Borgahraun eruption, Theistareykir volcanic system; and the Laki eruption, Grímsvötn volcanic sytem. These findings are then synthesised within an Icelandic and global framework. The Skuggafjöll eruption contains zoned macrocrysts of olivine and plagioclase that record a shared magamatic history of growth from trace element depleted melts followed by sequestration in a crystal mush environment and then entrainment into a trace element enriched melt prior to eruption. Equilibrated plagioclase core Mg profiles suggest storage in a mush that was colder than the original primitive liquid, but hotter than the final carrier liquid. Olivine and plagioclase DFENS models indicate that mush disaggregation and mixing took place approximately 1 year before eruption. Petrological observations have shown the monognetic Borgarhraun eruption was fed by mixed primary magmas that ponded near the Moho (approximately 24 km depth). Diffusion chronometry conducted on olivine macrocrysts show that crystal entrainment into the carrier-liquid took place approximately 13 days before eruption with some crystals having residence times of less than 5 days. This is the first estimate of Moho to surface transport times anywhere on the global spreading ridge system and implies a rapid connection between the lower and upper crust with melt transport rates of 0.01 to 0.06 m s⁻¹. Spinel crystals contained in Borgarhraun wehrlite nodules are zoned in Cr and Al. The core composition and degree of disequilibrium observed in the spinel crystals within each nodule correlates with their size suggesting diffusion is responsible for the zoning. Diffusive exchange in these spinels is primarily driven by cooling and exchange with the interstitial mush liquid. 2D diffusion modelling of Cr-Al exchange in the spinels indicates that the crystal mush was stored for approximately 1500 years. This is the first direct estimate of the storage times of primary magmas in the lower crust and for active basaltic mushes in general. The Laki eruption contains several populations of plagioclase crystals within its crystal cargo. Those with oscillatory zoned mantles and high-anorthite cores are equilibrated in terms of their Mg content and indicate storage in a mush environment that was colder than the final carrier liquid. Large equilibrated crystals of 3 mm diameter indicate minimum storage times under these conditions of 2100 years. Crystals with simpler zoned mantles have Mg core disequilibria that record diffusion timescales of 60 to 150 years before eruption. It is likely that the Laki crystal cargo was incrementally assembled over a protracted period of time. Diffusion timescales of final entrainment for olivine and plagioclase macrocrysts from different eruptive fissures are typically less than 20 days, which is shorter than the average interval between eruptive episodes, and supports the concept of pulsed mush disaggregation throughout the eruption. Combined, the observations and modelling results of this thesis suggest there is a dichotomy in the temporal evolution of basaltic systems. Long-term crystal storage in colder mush environments on the order of hundreds to thousands of years throughout the crust are interspersed with periods of rapid magma transport (days to weeks).

Understanding dykes is vital as they serve both as bodies that build the crust and as conduits that feed eruptions. The 2014-15 Bárðarbunga-Holuhraun rifting event comprised the best-monitored dyke intrusion to date and the largest eruption in Iceland in 230 years. Over a 13 day period magma propagated laterally from the subglacial Bárðarbunga volcano, Iceland, along a 48 km path before erupting in the Holuhraun lava field on 29 August 2014. A huge variety of seismicity was produced, including over 30,000 volcano-tectonic earthquakes (VTs) associated with the dyke propagation at ∼ 6 km depth below sea level, and long-period seismicity - both long-period earthquakes (LPs) and tremor - associated with the eruption processes. The Cambridge University seismic network in central Iceland recorded the dyke seismicity in unprecedented detail, allowing high resolution analyses to be carried out. This dissertation comprises two parts: study of 1) the volcano-tectonic dyke-induced seismicity and 2) the long-period seismicity associated with eruption processes. Volcano-tectonic earthquakes induced by the lateral dyke intrusion were relocated, using cross-correlated, sub-sample relative travel times. The ∼ 100 m spatial resolution achieved reveals the complexity of the dyke propagation pathway and dynamics (jerky, segmented), and allows us to address the precise relationship between the dyke and seismicity. The spatio-temporal characteristics of the induced seismicity can be directly linked in the first instance to propagation of the tip and opening of the dyke, and following this - after dyke opening - indicate a relationship with magma pressure changes (i.e. dyke inflation/deflation), followed by a general 'post-opening' decay. Seismicity occurs only at the base of the dyke, where dyke-imposed stresses - combined with the background tectonic stress (from regional extension over > 200 years since last rifting) - are sufficient to induce failure of pre-existing weaknesses in the crust, while the greatest opening is at shallower depths. Emplacement oblique to the spreading ridge resulted in left-lateral shear motion along the distal dyke section (studied here), and a prevalence of left-lateral shear failure. Fault plane strikes are predominately independent of the orientation of lineations delineated by the hypocenters, indicating that they are controlled by the underlying host rock fabric. Long-period earthquakes and tremor were systematically detected and located during the dyke propagation phase and the first week of the eruption. Clusters of highly similar, repetitive LPs were identified, with a peak frequency of ∼ 1 Hz and clear P and S phases followed by a long-duration coda. The source mechanisms were remarkably consistent between clusters and also fundamentally different to those of the VTs. The clusters were accurately located near each of three ice cauldrons (depressions formed by basal melting) that were observed on the surface of Dyngjujökull glacier above the path of the dyke. Most events were in the vicinity of the northernmost cauldron, at shallower depth than the VTs associated with lateral dyke propagation. At the two northerly cauldrons, periods of shallow seismic tremor following the clusters of LPs were also observed. Given that the LPs occurred at ∼ 4 km depth and in swarms during times of dyke-stalling, it is inferred that they result from excitation of magmatic fluid-filled cavities and indicate magma ascent. The tremor may then represent the climax of the vertical melt movement, arising from either rapid, repeated excitation of the same LP cavities, or sub-glacial eruption processes. This long-period seismicity therefore highlights magma pathways between the depth of the dyke-VT earthquakes and the surface. Notably, no tremor is detected associated with each cauldron, despite melt reaching the base of the overlying ice cap, a concern for hazard forecasting.

Earth's volatiles (e.g. CO₂ and H₂O) are thought to be stored largely in the interior of the planet. The partitioning of these volatile elements between Earth's surface and interior controls the evolution of our atmosphere and oceans, acting as a regulator on our planet's long term climate. Basalt geochemistry is our most direct probe of Earth's convecting mantle, however the tendency of volatile elements to form vapour phases deep within volcanic systems obscures the mantle volatile signals inherited by basalts. This thesis explores the extent to which basalts may preserve mantle volatile signals, places new constraints on volatile heterogeneity within the Icelandic plume, and considers the role of mantle convection in establishing deep Earth volatile cycles. Volatile- trace element systematics in suites of basaltic glass and melt inclusions have been widely used to infer volatile abundances in the depleted mantle, but have resulted in a large diversity of estimates. In this thesis a new statistical treatment of such datasets is developed, using simple numerical models for concurrent magma mixing and degassing. It is demonstrated that the role of magma degassing was previously underestimated, and the variability in apparent mantle volatile concentrations is largely a result of variability in magma mixing and degassing. Using a large new dataset of Icelandic melt inclusions sampling diverse mantle components, alongside a compilation of existing suites, the gross structure of the global melt inclusion array is shown to be controlled by magma degassing and olivine decrepitation. By applying the new statistical treatment of the data developed here, the presence of at least three mantle components with distinct volatile chemistry are demonstrated to contribute Icelandic magmas. With a novel combination of geophysical and geochemical constraints, the thermal structure and mineralogy of the melting region beneath Iceland is constrained. The role of mineralogical heterogeneity in the long term storage of mantle volatiles is critically assessed.

Volcanic eruption rates in Iceland during the last deglaciation increased 5--30 fold from the steady-state rates. This has been understood by the unloading of ice, which increases the decompression rates in the mantle, causing enhanced mantle melting rates. However, existing theoretical work cannot account for large variations of Rare Earth Element (REE) concentrations in the Icelandic lavas. Lavas erupted during the last deglaciation are depleted in REEs by up to 70\%; whereas, existing models can only produce at most 20\% depletion. This dissertation attempts to find the causes of this mismatch and provides the first models that take account of the diachronous response of volcanism to deglaciation. Numerical models of mantle flow and mantle melting response to the glaciation and deglaciation are developed. A time-lag sampler is incorporated to represent the time lag between the melt production at depths and the eruption on the Earth's surface due to finite rate of melt transport. The model results for the last deglaciation in Iceland show that the variations of REE concentrations are strongly dependent on the melt ascent velocity. This explains the REE concentration mismatch between the previous theoretical work and the observations. Comparison between the model results (timing of the bursts in volcanic eruptions, REE concentration variations, and volume proportions of the subglacial, finiglacial and postglacial eruptions) and the observational data suggests that the melt ascent velocity during the last deglaciation beneath Iceland is of the order of ~100~m/year. The effects of glacial loading during the last glacial period on mantle melting are also investigated. It is found that glacial loading suppresses mantle melting and modulates the average REE concentrations in the melts due to the depth-dependent profile of mantle melting suppression. In addition, this dissertation explores how different deglaciation histories can result in different REE concentrations in the early-postglacial lavas. This may explain why lava shields formed during the Termination~II have different geochemical compositions from that formed during the Termination~I. Lastly, predictions for the future of the Icelandic volcanic eruption rates are made based on given estimated deglaciation rates of the current Icelandic glaciers.

The thesis delves into the social dynamics of music-making in Iceland. It builds on this researcher's twenty-year long career as a music journalist in his native country, making use of the knowledge, connections and insights accumulated therein. This research project has made use of participant observation, in-depth interviews, historical documents as well as ethnography. Thirty musicians from the current Icelandic pop/rock world were interviewed, focussing on how they manoeuvre themselves within a relatively small society. The thesis was inspired by Ruth Finnegan's book, The Hidden Musicians - Music-Making in an English Town, similarly looking at the structure of a tightly knit music community, and how place shapes and informs its residents. Iceland's small size (pop. 350,000) is a defining factor; its "village" feel feeds into the shaping of its music culture. My theoretical framework is built around classic socio-musicological theories (derived from Pierre Bourdieu and Howard Becker), more recent research carried out by Sara Cohen, Tia De Nora, and Nick Prior, as well as theories on the difference between professional and amateur music-making (based on the work of, among others, Canadian sociologist Robert A. Stebbins). A grounded theory arose from the interview data, confirming the impact of a "village" factor, which simultaneously liberates and restricts artistic work. The peculiarities of Iceland's pop/rock world manifests themselves in interrelated aspects, such as its status as a micro-nation and this shapes much of the dynamism of its popular music culture. Co-operation across different genres is high, and a lack of formal bureaucracy in terms of doing things was significant. Support from institutions like the radio, music competitions and music offices is effective and strong, making for a relative easy market access domestically and facilitating an optimistic outlook from the interviewees towards their chosen field. The musicians' inner need to make music, perform and release it was scrutinised and the small size of Iceland's population - and therefore, the Icelandic popular music world - gives rise to a fuzzy distinction between amateur and professional. This fact underscores the aforementioned prolific levels of activity in Iceland's musical community. Yet in spite of these positive elements, active Icelandic musicians also admitted to experiencing much precarity and unpredictability in terms of their creative work. All of these elements, detailed here, make for a vibrant and active music scene, with participants effectively "punching above their weight".

The thesis is a comparative and multidisciplinary study of legendary genealogies in the historical writing of northern England and Iceland c. 1120 – c. 1241. Historical writing was produced in abundance over this period in both areas and the frequent contact between England and Scandinavia, as well as shared use of early medieval insular sources make them especially suitable for comparison. The Viking invasions and settlement in England had a significant impact on English culture, language and literature and changed attitudes to their own legendary past. The Danish conquest of England in the early eleventh-century also brought the insular and Scandinavian worlds closer together, and even after the Norman Conquest in 1066, England and Scandinavia engaged in scholarly and textual exchange The theoretical framework for the thesis combines approaches from religious history, art history, political history, literature history and gender history. The main research questions of the thesis consider the dissemination, development, and purpose of legendary genealogies. The sources are a collection of Durham related manuscripts with illuminations of the pagan god Woden (c. 1120–88) in two historical works De Primo Saxonum Aduentu and De Gestis Regum; Genealogia Regum Anglorum (Rievaulx, 1153x54) by Aelred of Rievaulx; two works attributed to Snorri Sturluson’s Prose Edda (Iceland, 1220s) and Heimskringla (Iceland, 1225x35). Common to the sources is the inclusion of genealogies that stretch from legendary generations to living individuals at the time of writing. Thus, genealogies connected dynasties and civilisations in mutual descent from pagan, Trojan and biblical ancestors. By analysing textual dissemination as well as political contexts, literary patronage and mechanisms in legitimisation of power, the thesis address amalgamations of origin myths, the use and significance euhemerised pagan gods, and female generations in genealogies.

In recent decades there has been an increased interest in the carbon content of Earth’s geochemical reservoirs due to the impact of atmospheric carbon on the habitability of our planet. Earth’s interior likely hosts a greater mass of carbon than that of the oceans, atmosphere and crust combined, which has buffered the carbon content of the atmosphere over geological time. Yet only a few direct measurements of carbon from the upper mantle, and none from the lower mantle, have been made. Undegassed basalts erupted at mid-ocean ridges have previously been used to estimate the carbon content of the upper mantle. However, due to the low solubility of carbon within silicate melt, these undegassed basalt suites are rare. The majority of basalts have lost their mantle carbon information en route to eruption through the crust. Various crustal processes act to modify the geochemistry of melts before eruption, therefore it is important to be able to characterise the effect of these processes to better interpret the volatile signals preserved in erupted products. Pressure, and therefore depth, is a key parameter controlling volatile solubility and can be estimated using a variety of igneous barometers. This thesis presents results from crys- tallisation experiments conducted on basaltic glass from the Miðfell eruption, Iceland. The experiments provide new data that has been used to test a variety of barometers and crystalli- sation models used by igneous petrologists, and could aid future barometer recalibration. A key part of this work was the development of an experimental method for stabilising 5 kbar conditions in a piston cylinder apparatus. The experiments have shown that clinopyroxene- liquid barometry is more reliable than multi-reaction barometry. However, knowledge of equilibrium clinopyroxene compositions is crucial for accurately determining pressure using the clinopyroxene-liquid barometer. More experiments conducted at mid-crustal pressures are required for a full recalibration of these barometers. The results of testing igneous barometers and crystallisation models have been applied to two suites of olivine-hosted melt inclusions from the Kistufell and Miðfell eruptions to help determine the melt evolution history of these basalts. These eruptions were targeted due to previously measured noble gas isotopic ratios that suggest a primordial mantle component present in their melting regions, and therefore evoking the possibility that they could hold information about deep mantle carbon. Barometry suggests that Miðfell phases equilibrated, and therefore crystallised, at mid-crustal pressures (5–7 kbar), which could allow for the entrapment of undegassed melt inclusions within olivine. The two melt inclusion suites were found to differ in trace element variability, with the observation that the more trace element enriched eruption, Kistufell, had lower relative trace element variability than the more depleted eruption, Miðfell. Several processes, both in the crust and the mantle, are likely responsible for the level of trace element enrichment and variability, including extent of mantle melting, source heterogeneity, and melt transport. The depleted nature of the Miðfell melt inclusions has allowed them to preserve some of the highest CO$_2$/Ba and CO$_2$/Nb ratios ever recorded in basaltic glass, with ratios over five times greater than undegassed mid-ocean ridge basalt values. This carbon enrichment is not due to any crustal melt modification process, but rather pertaining to lower mantle carbon-rich lithologies that have been tapped by the Icelandic mantle plume. The carbon reservoir beneath Miðfell is estimated to contain 744 $\pm$ 188 ppm carbon, 15 times greater than the depleted upper mantle. This value matches estimates of bulk mantle carbon from planetary mass balance calculations and provides evidence for carbon-rich domains within the Earth.

On 16 August 2014 an unusual sequence of earthquakes began near the southeastern rim of the ice-covered Bárðarbunga caldera in central Iceland. Over the course of two weeks a dyke propagated 48 km beneath the glacier northeastwards and into the Holuhraun lava field, where it erupted for six months, becoming the largest eruption in Iceland for over 200 years. During this time, a gradual, incremental caldera collapse took place in the central volcano. The rifting episode was captured both geodetically and seismically. In this thesis, I analyse the seismic response to the event, both due to the dyke propagation, and the subsequent caldera collapse. This gives an insight into the underlying processes controlling rifting events, and the nature of the responding crust. The Cambridge seismic network recorded the 2014-15 Bárðarbunga-Holuhraun rifting episode in exceptional detail. I discuss the deployment and operation of this dense seismic network in the remote Icelandic highlands, as well as the campaign deployments on the volcano caldera, on the glacier (above the dyke path) and around the eventual eruption site, as a first response to the crisis. Using this dataset I have accurately located, and analysed, 47,000 earthquakes during the pre-intrusive, intrusive, eruptive and post-eruptive periods. Approximately 4,000 of the recorded earthquakes are associated with the caldera collapse, delineating faults accommodating the subsidence and showing good correlation with geodetic data. The seismicity reveals activation of both inner and outer caldera faults with 60 inward dipping planes on the northern and southern side, indicating a symmetric caldera structure. Detailed analysis of the earthquake source mechanisms shows that 90% can be explained by a double-couple solution, which is in contrast to results from previous studies of Bárðarbunga. I find the dominant failure mechanism during the collapse to be steep normal faulting, with sub-vertical P-axes, striking sub-parallel to the caldera rim. The northern and southern sides of the caldera, however experienced very different seismicity rates, highlighted by the order of magnitude difference in the cumulative seismic moments. The southeastern part of the caldera, whilst experiencing less activity, shows a mixture of failure mechanisms, owing to the interaction of the caldera collapse and the dyke exit. Therefore, this thesis presents evidence of a complex asymmetric caldera collapse, not controlled by a single caldera ring fault. Of the 47,000 earthquakes located, 31,000 delineate the segmented, lateral dyke intrusion as it fractured a pathway through the crust, utilizing pre-existing weaknesses. Despite the extensional rift setting, the dyke emplacement generated exclusively doublecouple earthquakes. At the leading edge of the propagation, earthquake source mechanisms show exclusively strike-slip faulting, in contrast to the conventional model of normal faulting above a propagating dyke. I observe right-lateral strike-slip faulting as the dyke propagates to the NE, and an abrupt change to left-lateral strike-slip faulting as the dyke turns and propagates in a more northerly direction into the northern volcanic zone. This shows that the direction of fault motion is determined by the opening of the dyke, rather than by the regional extension. I am also able to define the thickness of the seismogenic crust under Bárðarbunga as 7 km, based on the depth extent of observed seismicity. The bulk of the seismicity in the volcano is located at 1-4 km below the surface, whereas the dyke exited the caldera at 4-6 km depth, propagating at 6-8 km b.s.l. I hypothesise that the magma storage region is likely located at 4-6 km b.s.l. (6-8 km below the caldera surface), just below the most active caldera seismicity and at similar depth levels to the dyke. Thus, this thesis details the melt distribution and movement at depth from a large basaltic central volcano, and the coupled deformation of the subsiding caldera with the dyke intrusion and eruption.

The aim of this thesis is to understand the role of geomorphological change in the abandonment of Norse harbours in the North Atlantic. Nodes of maritime activities that were established by Norse settlers during the Scandinavian Viking Age often developed into important towns and cities. Some of these, however, disappeared for unknown reasons. Norse harbours in the North Atlantic varied in scale. They ranged from small landing beaches used by small boats for local use through to much larger anchorages handling considerable trade and being important nodes on the transatlantic trading network. Changes in coastal geomorphology necessitated a response from seafarers. In this thesis, a conceptual framework for the formation, recovery and stability of headland-dominated sandy beaches in high-energy environments is established, based on empirical observation and on the use of the MIKE21 numerical sediment transport model. Under persistent calm climatic conditions, nearshore seabed gradient is a weak control on beach formation and persistence in embayments. However, under persistent stormy conditions, nearshore sea bed gradient becomes the prominent control. Embayments with nearshore gradients of > 0.025 m/m inhibit beach recovery on a sub-annual timescale, while gradients < 0.025 m/m promote beach recovery. These ideas are assessed in the Shetland Islands, using numerical modelling, geomorphology and OSL dating on sand blow deposits. In the late Norse era beach landing sites in Unst became prone to depletion and destruction because of increased storminess. Numerical modelling (MIKE21) supports the idea that the recovery time of different sandy beaches on Unst is dependent on average nearshore slope. The beach at Sandwick has shallow nearshore gradients and recovers quickly in the face of storminess, but beach stability at Lunda Wick is more uncertain, and thus Lunda Wick represents a more problematic landing place. The Norse harbour of The Bishop's seat at Garðar in the Eastern Settlement of Greenland is assessed to evaluate the impacts of gradual long term geomorphological change on coastlines that lack soft-sediment. A high resolution, near shore bathymetric survey shows that, due to relative sea level rise of 1 m/500 years, the landing site became more difficult to access during the later period of Norse settlement and key onshore infrastructure was disrupted. The possible role of terrestrial supplies of sediment in changing the viability of landing places is assessed through an evaluation of the Norse trading centre of Gásir in northern Iceland. Geomorphological mapping and analysis of fluvial connectivity indicate that the delta on which Gásir is located is prone to aggradation from large, irregular pulses of sediment derived from landslides in the catchment. Written sources and geomorphological mapping indicate geomorphological changes around the same time that trade was shifting to the use of boats with a deeper draft. Cultural change and environmental changes would have reinforced each other in rendering the harbour site nonviable. Geomorphological forces acting on varying spatial and temporal scales have the potential to disrupt the use of landing sites. Whether environmental changes led to the abandonment of a landing site was strongly influenced by the seafarers' competence and available technology. Higher levels of competence would enable more problematic landing sites to be used, but there are limits to this adaptation. Technological changes, such as the use of larger and deeper draft boats, would have changed the geomorphic requirements for harbour sites, and thus may have led to a passive abandonment of the site over time rather than active abandonment such as that in the face of a catastrophic change of the shoreline. Coastal geomorphology was a critical factor affecting the use of Norse harbours, as it interacted with the wider cultural and economic developments in the North Atlantic realm. This thesis demonstrates that numerical sediment transport analysis is a powerful tool in coastal archaeological research as it can illuminate processes driving observable changes in the empirical record.

This thesis examines the memorial meaning attributed to royal power in the Icelandic legal tradition, as it is textually negotiated in sources extant from the period c. 1250-1500. It discusses the significance and functions of the Norwegian king's legal authority as part of the Icelanders' collective remembrance of their country's legal past (spanning the years c. 870-1302), and as a defining element in the creation of the Icelandic identity as a community of law. The scope of analysis covers thirteenth- to fifteenth-century legal sources (sections of law-books and legal texts preserving legal arrangements between Iceland and Norway made in the eleventh century and in the period c. 1260-1302), and a fourteenth-century account of the Norwegian king's involvement in a settlement dispute in ninth-century Iceland. These main sources are analysed against the background of several auxiliary sources (saga narratives, diplomas) from a New Philological perspective and scrutinised using the methods developed in cultural memory studies. This provides a novel perspective on the primary sources, filling a gap in recent scholarship on cultural memory in Old Norse literature and historiography. Both categories of texts, drawing on oral and written traditions of law-making and story-telling, are vehicles for multi-faceted culturally meaningful and often contradictory memories of the Norwegian king. The Icelandic laws preserve provisions bestowed upon the Icelanders by the Norwegian monarchs, whereas the sagas convey semi-mythological images of the monarchs, who act as legislators, negotiators of legal agreements with the Icelanders, and as law-keepers. By analysing the memorial functions of royal power in the primary sources, the thesis argues for the complexity of the Icelanders' self-definition as a kingless community of law, who nevertheless incorporate and actively engage with royal power, which shapes the collective memory of the country's legal tradition.

There is increasing evidence for high magnitude dust storms in high latitude environments. Yet, Aeolian processes in these areas have been largely understudied and therefore our knowledge of these systems is limited. Understanding dust emission processes from the high latitudes regions is of increasing importance because future climate scenarios indicate a reduction in terrestrial ice masses and an expansion in glacial outwash plains which are the main dust sources in high latitude environments. Of these regions, Iceland is the most researched high latitude dust source region, however our understanding of processes which lead to dust events are still poorly understood. This thesis examines the interlinking relationship between dust source and dust particle sedimentology and the physical and meteorological drivers which promote or inhibit dust emission in Iceland. This is achieved through active aeolian monitoring at source during two monitoring periods at Markarfljot, South Iceland. These measurements are complimented using secondary data sources (e.g. meteorological and satellite data), sedimentological mapping and particle analysis and laboratory abrasion experiments. This thesis is the first high resolution multi event record of dust emissions in the high latitudes and concludes by showing that potential dust concentrations and dust particle size are driven by the interlinking relationship between wind speed, sediment texture and surface moisture. Factors that affect the potential sediment availability for dust events are more important in the high latitudes than in the subtropics in driving spatial and temporal variability in dust emission. Measurements presented in this thesis are required to verify and tune regional and global modelling attempts to quantify the potential contribution of high latitude dust in the Earth system. However, further measurements are required to fully understand seasonal changes in dust emissions, across a variety of dust source units within all high latitude dust source regions.

The Icelandic mantle plume has had a profound influence on the development of the North Atlantic region over its 64 Myr existence. Long-wavelength free-air gravity anomalies and full waveform tomographic studies suggest that the planform of the plume is highly irregular, with up to five fingers of hot asthenosphere radiating away from Iceland beneath the lithospheric plates. Two of these fingers extend beneath the British Isles and southern Scandinavia, where departures from crustal isostatic equilibrium and anomalous uplift have been identified. In this study, the spatial extent of present-day dynamic support associated with the Icelandic plume is investigated using receiver function analysis. Teleseismic events recorded at nine temporary and 59 permanent broadband, three-component seismometer stations are used to calculate 3864 P-to-S crustal receiver functions. The amplitude and arrival time of particular converted phases are assessed, and H-k stacking is applied to estimate bulk crustal properties. Sub-selections of receiver functions are jointly inverted with Rayleigh wave dispersion data to obtain crustal VS profiles at each station. Both inverse- and guided forward modelling techniques are employed, as well as a Bayesian, trans-dimensional algorithm. Moho depths thus obtained are combined with seismic wide-angle and deep reflection data to produce a comprehensive crustal thickness map of northwestern Europe. Moho depth is found to decrease from southeast (37 km) to northwest (26 km) in the British Isles and from northeast (46 km) to southwest (29 km) in Scandinavia, and does not positively correlate with surface elevation. Using an empirical relationship, crustal shear wave velocity profiles are converted to density profiles. Isostatic balances are then used to estimate residual topography at each station, taking into account these novel constraints on crustal density. Areas of significant residual topography are found in the northwestern British Isles (1400 m), southwestern Scandinavia (464 m) and Denmark (620 m), with convective support from the Icelandic plume as its most likely source. Finally, the irregular planform of the Icelandic plume is proposed to be a manifestation of radial viscous fingering due to a Saffman-Taylor instability. This fluid dynamical phenomenon occurs when less viscous fluid is injected into a layer of more viscous fluid. By comparing the thermal and convective characteristics of the plume with experimental and theoretical results, it is shown that viscous fingering could well explain the present-day distribution of plume material.

Iceland possesses numerous subglacial volcanoes (tuyas and tindars) that act as geological records of the thick ice sheets that once spanned across the country. Flat topped volcanic summits, which were able to penetrate through the covering ice, provide an estimate of the ice sheet's minimum thickness at the time the volcano was in its final eruptive stage. Iceland not only provides a large number of potential subglacial edifices to sample but is geologically interesting as it sits above a magmatic hotspot and spreading ridge, providing a long term record of volcanism during considerable climate variability. However, it is unknown exactly in which glacial cycle these volcanic edifices formed, due to the lack of accurate and reliable eruption ages. Helium isotopes are valuable tracers of the mantle source for the origin of volcanic rocks. Helium isotopes are comprised of a mixture of magmatic helium trapped whilst in the mantle, cosmogenic helium built up by interaction with cosmic rays during surface exposure and radiogenic helium produced from the in situ decay of U and Th. These helium components yield invaluable information on the mantle source, time of eruption and length of exposure respectively. The principle aim of this study is to determine whether reliable and accurate eruption ages of basaltic subglacial volcanoes in Iceland are possible, by applying a relatively new geochronological tool: U-Th/He dating. These eruption ages combined with cosmogenic derived 3He surface exposure ages of the summits helps to establish ice surface elevation and thickness fluctuations over time. Olivine bearing basalt samples were acquired from 14 tuyas, 4 tindars and 1 shield volcano across the Western and Northern Volcanic Zones in Iceland (WVZ and NVZ). Samples were collected from the base of each edifice for U-Th/He dating and the summits of 3 tuyas for cosmogenic 3He surface exposure dating. Olivine phenocrysts were hand-picked and analysed on two noble gas mass spectrometers (VG5400 and Helix-MC instruments). As part of the analytical procedure for these techniques, magmatic helium trapped in the olivine grains is also analysed. The mantle helium isotope ratios indicate that nearly all edifices sampled obtain a MORB-like source (1-18RA) except for an OIB-like (24RA) centrally located tuya, Bláfell. The helium ratios acquired in the NVZ are lower (4-11RA) than those in the WVZ (8-20RA). There are no significant differences seen in the mantle components between the different types of edifice sampled. Mantle helium isotope ratios confirm the heterogeneity of the mantle beneath Iceland. The cosmogenic 3He exposure ages of Hlöđufell and Bláfell in the WVZ and Gaesafjöll in the NVZ are determined as 0.5±7.4ka, 67±0.7ka and 108±46ka respectively. This study presents the first 3He cosmogenic exposure age determined to be over 20ka in Iceland. The low concentrations of U and Th observed in Icelandic olivines (0.002-0.04 nmol/g and 0.01-0.1 nmol/g respectively) prevent any reliable disequilibrium ages to be established. Minimum secular equilibrium U-Th/He ages are determined and provide a range of erroneously large eruption ages (0.4 - 80.4 Ma), due to potential helium implantation and under-detection of 3He released during sample analysis. Progress can be made towards determining accurate eruption ages for Icelandic basalts if certain factors are adhered to and various sources of helium are separated effectively.

Virkisjökull is an outlet glacier of the Öræfajökull icecap in SE Iceland and currently covers 60% of its catchment, though this is reducing. Fieldwork and catchment monitoring activities for this project over the last 4 years includes measurement of ice ablation, proglacial discharge, dye-tracing of flow pathways, and deployment of three automatic weather stations at altitudes up to 880 m. These data calibrate a distributed hydrological model (WaSIM) to project potential river regime during stages of glacier retreat. Results show: (1) glacier hypsometry sensitizes the catchment to a disproportionately rapid increase in runoff as the snowline rises resulting in a potential annual increase in river discharge of up to 37% ; (2) a dominantly channelized glacial drainage system in all seasons with a rapid runoff response to melt: englacial flow of 0.58 m s-1 is comparable to the proglacial river velocity; and (3) that longer-term, reduced glacier cover and snow storage will lead to a discharge regime dominated by short-term precipitation events in all seasons, and a reduced influence of the seasonal meltwater discharge peak. The study demonstrates the importance of glacier hypsometry above the present ELA as an influence on catchment hydrological response to potential climate warming. This study demonstrates the importance of considering changes at the catchment scale when discussing hydrological changes forced by enhanced glacier melt. Field work at Virkisjokull has revealled catchment-specific hydrological behaviour in the proglacial foreland that may have a large influence on the river regime as the glacier retreats.

This thesis offers the first detailed palaeoenvironmental analysis of wetland areas within sub-Arctic enclosed homefield’s. Significance of meadows were previously mentioned only briefly in the literature, suggesting influences in settlement site selection as well as importance in quality fodder production, producing up to two thirds of total hay resources in a somewhat marginal agricultural landscape. Given the importance of hay resources in Iceland it seems unusual these areas have received so little attention to date, despite extensive research on all other aspects of the Norse farm system. The organic sediments within the meadows, given their development in-situ over extended time periods, have the ability to record aspects of the intimate relationship between societal and environmental change, and so in a robust and holistic way our methods set integrates radiocarbon measurement, tephrochronology, palynology and thin section micromorphology from the same core; reflecting these findings against existing paleoclimate and archaeological site data. This combined application of the core techniques – palynology and soil micromorphology, has proven successful in creating effective human ecodynamic records from each of the study farms. Records obtained from the three farm sites in northwest and northern Iceland exposed the varying importance and differing utilisation of these wetland areas. Meadows would appear to have played an import role in choice of settlement site across northern Iceland, through the provision of open areas, and additional and immediately available fodder resources at settlement, in a landscape dominated by dense scrub. Meadows were found to have been in continuous use, albeit at varying levels of intensity, from settlement to the present day. In this respect the semi-natural resources are found to be remarkably resilient, demonstrating little alterations to their composition following severe climatic downturns, including that of the Little Ice Age, and volcanic eruption. Acting as a robust resource and safety buffer for settlements, contributing to fodder resources where reliability of other resources is jeopardised by environmental conditions. Research in the more marginal northwest peninsula provides the first evidence of artificially created wet meadows in Iceland, developed to give sustained fodder production for over-wintering livestock in an environment that inherently had a short growing season and lacked soil fertility. A further example of the nuanced land management practices adopted in the agriculturally fragile farmscapes of the Norse North Atlantic. The findings of the thesis have wider implications for understanding the emergence of resilient and sustainable communities in agriculturally marginal environments; to this end there remains many opportunities to use palaeoenvironmental research to study ecosystem responses to natural and anthropogenic stresses, giving us a better understanding of capacities to withstand future stresses.