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Comparison of oxygen isotope records from radiocarbon dated groundwater and U-Th dated flowstone
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Using geochemistry to characterise tsunami deposits and identify the tsunami inundation limited
No full textMuch advance has been made in the last 10 years or so in tsunami research, mostly as a response to the devastating events that have also provided the opportunity to study large tsunamis and their impact in different settings. We are thus now better equipped to identify tsunami deposits in the geological record, and this should help us being better prepared for the future. Geochemistry is one of the recent proxies which are being increasingly adopted by tsunami researchers. However, its value is not always recognised, and this mostly because the information it provides is not often straightforward.
Chemical signatures can reflect the occurrence of shell hash and/or microfossils; they can also be salinity indicators, thus helping to identify the marine source of the deposit. The chemical composition of sandy deposits also reflects their mineralogy and is thus site-specific. The preservation potential of salinity indicators in particular is dependent on the presence of organic matter and fine material as salts are leached readily through the porous sand and will be diluted by rainfall. Studies of recent events show that they can be retained in the underlying soil, thus corroborating the marine source of the overlying sandy deposit.
Another recent advance has been the use of geochemical signatures as markers of the tsunami inundation limit, beyond the extent of the visible (sandy) deposit. Until recently, researchers had relied on the extent of sandy units within soil and mud, to estimate the inundation limit of previous tsunamis. This has led to an underestimation of the magnitude of these precursor events, with catastrophic outcomes. Geochemical signatures, including stable isotopes, can help distinguish the mud left behind by a tsunami from the terrestrial mud in which it was deposited. This will allow us to redraw tsunami inundation maps, with important implications for tsunami risk assessment and preparedness.
Nevertheless, it is recommended to use geochemistry in association with other proxies. While geochemistry can provide the missing clue, we most often need a full suite of diagnostic criteria to be able to gain a better understanding of previous events. © Copyright 2014 The Geological Society of America (GSA)
Evaluation of soil and fluid structure interaction in blast modelling of the flying plate test
No full textThe influence of the soil properties on the structural integrity of impacted structures is important in light of the increased use of improvised explosive devices (IED’s) and buried explosives. The study deduces material parameters for the Federal Highway Authority (FHWA) soil model in LS-DYNA and comparisons are made with the ConWep and two commonly used soil models. The softening behaviour of semi-cohesive prairie soils due to pore pressure development and the reduction of the cohesion angle are highlighted. The flying plate test is used for validation with very good agreement found, capturing the plate’s kinematic and structural responses. © 2015, Elsevier Ltd
Evaluation of a hydrocode in modelling NATO threats against steel armour
No full textHaving identified relevant constitutive models and the likely fracture mechanisms, a benchmarking study was undertaken to numerically compute a perforation solution based on the work by Børvik et al [1]. Material strength of ductile metals subjected to high strain phenomena is often described through the Johnson-Cook model [2] or the Zerilli-Armstrong [3] relation; both describe strain rate sensitivity, strain hardening and thermal softening albeit by different means. Phenomenological models like Johnson and Cook’s [2] and the associated fracture criterion by the same authors [4] have been extensively used [1,5-8] across a number of research areas. Whilst useful in capturing the main deformation and failure mechanisms, the author’s note the inherent deficiencies present in these models and resolve to calculating conservative solutions.
The study also evaluates the blast response of an elasto-plastic plate using the commercial FEA code LS-DYNA[10]. The peak displacement of each plate is compared to literature [11] through two blast analysis techniques, namely the CONWEP blast code which is embedded in the hydrocode and the computationally expensive, but more accurate, technique of fluid structure coupling via a multi-material ALE formulation. The blast threat is a 6 kg TNT mine modelled using the steel pot test criteria set out by the NATO standard in AEP-55 Vol.2. The ALE formulation is competently described in [12] and we apply it to validate wether it’s applicable for near field blast analysis. We aim to shed some light on the nuances and the problems associated with modelling highly dynamic problems. In the words of Jean Lemaitre and Rodrigue Desmorat [14]:
“Very accurate calculations are too often made with a very poor accuracy of the material parameters
New Constraints on the Geometry and Kinematics of Active Faults in the Hinterland of the Northwest Himalaya
No full textThe geometry and kinematics of the active, and potentially seismogenic, fault structures within the hinterland of the Himalaya have proven challenging to constrain in the past, primarily because active faults in this region tend to be buried beneath the subsurface and active seismicity often does not align with surficially mapped fault traces. Here we present a series of complementary datasets, including results from low temperature thermochronology, basin-wide erosion rates from 10Be concentrations, and topographic and longitudinal profile analyses, that place constraints on the spatial distribution of fault-related rock uplift and erosion across a ~400-km long region of the lower and high Himalaya of northwest India. Results from our analyses reveal that hillslope morphology and channel steepness are relatively invariant parallel to strike but vary significantly across strike, with the most prominent and abrupt variations occurring at the physiographic transition between the lower and high Himalaya (PT2), near the axial trace of the ramp-flat transition in the Main Himalayan Thrust (MHT). The cross-strike changes in geomorphology observed across the PT2 correlate with an order of magnitude northward increase in basin-wide erosion rates (~0.06-0.8 mm/a) and a corresponding decrease in apatite (~5-2 Ma) and zircon (U-Th)/He (~10-2 Ma) cooling ages. Combined with published geophysical and seismicity data, we interpret these results to reflect spatial variations in rock uplift and exhumation induced by a segment of the MHT ramp-flat system that is at least ~400 km long and ~125 km wide. The relatively young (U-Th)/He ages (<10 Ma) greater than 20 km south of the MHT ramp-flat transition preliminarily suggest that the kinematics of this system are best explained by a model which incorporates an accreting duplex on the MHT ramp but additional forthcoming analyses, including thermal modeling, will confirm if this hypothesis is robust
Using 3D geological modelling and geochemical mixing to characterise alluvial aquifer recharge sources in the upper Condamine River catchment, Queensland, Australia
No full textThe influence of mountain front recharge on the water balance of alluvial valley aquifers located in upland catchments of the Condamine River basin in Queensland, Australia, is investigated through the development of an integrated hydrogeological framework. A combination of three-dimensional (3D) geological modelling, hydraulic gradient maps, multivariate statistical analyses and hydrochemical mixing calculations is proposed for the identification of hydrochemical end-members and quantification of the relative contributions of each end-member to alluvial aquifer recharge.
The recognised end-members correspond to diffuse recharge and lateral groundwater inflows from three hydrostratigraphic units directly connected to the alluvial aquifer. This approach allows mapping zones of potential inter-aquifer connectivity and areas of groundwater mixing between underlying units and the alluvium. Mixing calculations using samples collected under baseflow conditions reveal that lateral contribution from a regional volcanic aquifer system represents the majority (41%) of inflows to the alluvial aquifer. Diffuse recharge contribution (35%) and inflow from two sedimentary bedrock hydrostratigraphic units (collectively 24%) comprise the remainder of major recharge sources.
A detailed geochemical assessment of alluvial groundwater evolution along a selected flowpath of a representative subcatchment of the Condamine River basin confirms mixing as a key process responsible for observed spatial variations in hydrochemistry. Dissolution of basalt-related minerals and dolomite, CO2 uptake, ion-exchange, precipitation of clay minerals, and evapotranspiration further contribute to the hydrochemical evolution of groundwater in the upland alluvial aquifer.
This study highlights the benefits of undertaking an integrated approach that combines multiple independent lines of evidence. The proposed methods can be applied to investigate processes associated with inter-aquifer mixing, including groundwater contamination resulting from depressurisation of underlying geological units hydraulically connected to the shallower water reservoirs. © 2016, Elsevier B.V
Timing and importance of arboriculture and agroforestry in a temperate East Polynesia Society, the Moriori, Rekohu (Chatham Island)
No full textIdentifying arboriculture and agroforestry in Polynesian Societies has usually relied heavily upon the ethnographic record in the absence of direct archaeological evidence. In this paper we outline a multi-proxy research design, including ethnography, palynology, anthracology, archaeology and a high precision chronology to evaluate arboriculture and agroforestry as components of Moriori subsistence practices before the arrival of Europeans in 1791. The colonisers of Rekohu brought with them a mainland New Zealand endemic tree, Corynocarpus laevigatus, and the technology to propagate the tree in a less than ideal climate and to process its drupe into a storable source of carbohydrate in what was a difficult environment for Polynesian cultivation practices. We also present a conceptual model of forest change due to Moriori fuel selection practices which suggests that Moriori were actively managing these forest spaces for food, fuel, medicine, construction material and as a habitation space, therefore making agroforestry an important component of Moriori subsistence. © 2016, Elsevier Ltd
Is percent ‘projected natural vegetation soil carbon’ a useful indicator of soil condition?
No full textThe concentration of Soil Organic Carbon (SOC) is often used as an indicator of soil condition and soil health. To be useful as an indicator, SOC must be considered in context, with soil type, climatic region, local rainfall, slope, and land use history influencing measured amounts of SOC. The concept of Percent Projected Natural Vegetation Soil Carbon (PNVSC) implicitly incorporates these context variables. Percent PNVSC is defined as a simple percentage comparing the contemporary measured soil carbon against a hypothetical amount of soil carbon that would be observed in the local landscape today, if the areas under managed agroecosystems remained under natural vegetation (which in this study is dry sclerophyll forest). The term ‘natural’ used in the PNVSC concept approximates with the natural system prior to agrarian settlement. Percent PNVSC was calculated for a 22,000 ha sub-catchment of the Hunter Valley, Australia and it showed a spatially weighted average of 73, indicating substantial soil carbon loss as a result of cumulative land use change over more than 100 years. The Percent PNVSC map highlights changes in soil carbon distribution across the landscape with mid-slope positions lower in the catchment showing the greatest loss of soil carbon. Viticulture has resulted in half of the original SOC being lost, compared to a 75 % PNVSC for unimproved pasture and an 83 % PNVSC for improved pasture. Average soil carbon loss due to mixed land-use change in this sub-catchment is 13,331 kg C/ha. © 2014, Springer International Publishing Switzerland
Applications of geochemistry in tsunami research: a review
No full textMuch progress has been made since the first published studies of tsunami deposits nearly 30 years ago. Geochemistry is now a much more widely used proxy in tsunami research, mainly due to its increasingly recognised value in the identification of historical and/or prehistorical deposits, at times even providing the conclusive proof when other proxies are missing or equivocal, but also its significance in environmental impact assessments following recent tsunamis. The rapid advance in analytical techniques has also made it a more approachable and popular method, as it is now often faster and cheaper. Here we provide a review of the applications of geochemistry, including the techniques used, as well as a database of studies that used chemical proxies in their investigation of recent and old events, including onshore and offshore tsunami deposits. Chemical signatures are often used as markers of marine inundation, either as salinity indicators, where they can also allow the identification of the limit of tsunami inundation, or tracers of the incorporation of marine-sourced carbonates. Their applications as indicators of source material are nevertheless expanding, thereby potentially providing additional information on the hydrodynamic processes associated with tsunami inundation, although they are largely site-specific. The effects of post-depositional changes in different climatic regimes are examined, with a particular emphasis on water-leachable components and implications for post-event recovery of coastal ecosystems. We demonstrate the usefulness of chemical proxies in studies of the geological record of tsunamis extending back thousands of years, suggest new approaches and discuss limitations and existing knowledge gaps. © 2016, Elsevier B.V
Recent development of wildlife transfer databases
Get PDFThe transfer of radionuclides to wildlife in the environmental radiological assessment models developed over the last two decades is most often described by the whole organism concentration ratio (CRwo-media). This parameter relates whole organism activity concentrations to those in environmental media (typically soil for terrestrial ecosystems and water for aquatic ecosystems). When first released in 2007, the ERICA Tool contained the most comprehensive and well documented CRwo-media database available for wildlife. It was subsequently used in the US DOE RESRAD-BIOTA model and formed the initial basis for the international wildlife transfer database (WTD; www.wildlifetransferdatabase.org/?) developed to support IAEA and ICRP activities. Subsequently, many additional data were input to the WTD, including the outputs of a review of Russian language literature and data from Canadian monitoring programmes associated with nuclear power plants, U-mining and related industries. Summarised data from the WTD in 2011 were used to provide CRwo values in ICRP 114 and the IAEA's handbook on wildlife transfer parameters (http://www-ns.iaea.org/projects/emras/emras2/working-groups/working-group-five.asp?s=8&l=63). This paper provides an update on the development of the WTD subsequent to 2011 and its application to derive revised default CRwo-media parameter values of the ERICA Tool. Since 2011, some circa 17,000 additional CRwo-media values have been added to the WTD. The new inputs include original data for: representative species of the ICRPs Representative Animals and Plants (RAPs) from a UK forest; monitoring data from Japanese estuaries and Finland; Canadian wildlife; plutonium uptake data from US weapons testing programme sites; wild plants and invertebrates from north western USA; refereed literature published after 2011. Additionally, data already in the WTD from Australia were reviewed with reference to original source reports not previously considered and amended where required. The revised WTD was quality checked by considering the degree of variation in the data for each organism-element combination and the change between the WTD versions. This identified a number of errors (e.g. double entry of data, unit conversion errors and entries based on a dry matter rather than the required fresh weight basis) all of which have now been rectified. Statistical analyses of the WTD have demonstrated that there is currently no justification to subdivide CRwo-media from e.g. mammal to mammal herbivore and mammal carnivore etc.. In revising the ERICA Tool, a more generic categorisation of organisms has subsequently been used. Even with the increase in available data, there are still many radionuclide-organism combinations for which data are lacking. To provide default values where there are no data, a set of rules have been derived including the use of Bayesian statistics. (authors