Browsing by Author "Fierro, D"
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- ItemBackground measurements in the Environmental Radioactivity Measurement Centre Low-Level Gamma Laboratory at ANSTO(Australian Nuclear Science and Technology Organisation, 2012-10-18) Fierro, D; Heijnis, HAt SPERA 2010, the results of a study on the low-level building materials including a special concrete mix for the development of a basement gamma spectrometry laboratory at Ansto were presented. Since the completion of the Environmental Radioactivity Measurement Centre using these ideal materials at ANSTO in early 2012, there has been a reduction of approximately 30% in the background counts. In this presentation, the success in achieving the reductions will be compared to the previous gamma laboratory setting. This will reflected particularly through the radionuclides tested using an IAEA Quality Assurance method, as well as the counts per second across a broad energy range for the detectors in the laboratory.
- ItemComparison of Be-7 analysis using two gamma spectrometry systems and software packages(South Pacific Radioactivity Association, 2008-11-26) Zawadzki, A; Mokhber-Shahin, L; Fierro, D; Shamnugarajah, K; Ciufici, JNaturally occurring radioisotope, Be-7, can be used to study short term deposition and resuspension cycle of surficial bed sediments. The activity of Be-7 can be determined by gamma spectrometry. Due to Be-7 short half life, samples must be analysed within a few days of collection on several gamma spectrometry systems. To test the precision of Be-7 data from two gamma spectrometry systems and software packages, multiple analysis of a sediment sample was performed over 6 months. A statistical procedure was used to investigate the precision of the analytical data as the activity of Be-7 decreases over time. The sample was prepared from a sediment sample spiked with Be-7 activity, collected from fresh rain water, and counted on High Purity Germanium (HPGe) gamma spectrometry systems from EG&G Ortec and Canberra. Software packages Gamma Vision and Genie-PC were employed to determine peak areas and activity calculations. Calculations were also performed manually by visual determination of the Be-7 peak region of interest and simple gamma spectrometry calculation procedure.
- ItemComparison of radium-228 determination in water among Australian laboratories(Elsevier, 2017-11) Zawadzki, A; Cook, M; Cutmore, B; Evans, F; Fierro, D; Gedz, A; Harrison, JJ; Loosz, T; Medley, P; Mokhber-Shahin, L; Mullins, S; Sdraulig, SThe National Health and Medical Research Council and Natural Resource Management Ministerial Council of Australia developed the current Australian Drinking Water Guidelines which recommend an annual radiation dose value of 1 mSv year−1. One of the potential major contributors to the radiation dose from drinking water is radium-228, a naturally occurring radionuclide arising from the thorium decay series. Various methods of analysing for radium-228 in water have been established and adapted by analytical radiochemistry laboratories. Seven laboratories in Australia participated in analysing radium-228 spiked water samples with activity concentrations ranging from 6 mBq L−1 to 20 Bq L−1. The aim of the exercise was to compare and evaluate radium-228 results reported by the participating laboratories, the methods used and the detection limits. This paper presents the outcome of the exercise. Crown Copyright © 2017 Published by Elsevier Ltd.
- ItemThe determination of the efficiency of a Compton suppressed high purity germanium detector using Monte Carlo simulations(South Pacific Radioactivity Association, 2010-09-01) McNamara, AL; Heijnis, H; Fierro, D; Reinhard, MIThe low level radiochemistry laboratory at the Australian Nuclear Science and Technology Organisation (ANSTO) performs radioactivity measurements of various environmental samples for a broad range of low level radionuclides. The laboratory's low-level gamma-spectrometry facility contains two Compton suppressed high purity Germanium (HPGe) detector systems. A Compton suppressed HPGe detector is well suited to the analysis of small environmental samples, however the nature of these samples (range of different geometries, densities and compositions) can make it difficult to construct an efficiency curve for the instrument. Currently, efficiency calibrations are f, carried out using reference materials packed into a particular geometry, e.g. a petri-dish. This makes the analysis of samples with different geometries difficult and time-consuming. Monte Carlo simulations can be a powerful tool in estimating the efficiency of the detector, especially for complicated detector systems and unusual sample compositions and geometries, provided enough geometric information on the system is available. Monte Carlo radiation transport simulations can also be used to determine self absorption, random and coincidence summing corrections, cascade and background effects. We model the gamma-Compton suppressed system using the simulation toolkit Geant4 for the efficiency calibration and compare the calculated efficiencies with the measurement of standard radionuclides in the low energy region of ~ 40 to 1500 keV. The calculated I7 efficiencies have the same dependence on energy as the measured values and the discrepancies between the two values can be attributed to incomplete knowledge of the detector geometry.
- ItemThe determination of the efficiency of a Compton suppressed HPGe detector using Monte Carlo simulations(Elseiver, 2012-04-01) McNamara, AL; Heijnis, H; Fierro, D; Reinhard, MICompton suppressed high-purity germanium (HPGe) detector is well suited to the analysis of low levels of radioactivity in environmental samples. The difference in geometry, density and composition of environmental calibration standards (e.g. soil) can contribute to excessive experimental uncertainty to the measured efficiency curve. Furthermore multiple detectors, like those used in a Compton suppressed system, can add complexities to the calibration process. Monte Carlo simulations can be a powerful complement in calibrating these types of detector systems, provided enough physical information on the system is known. A full detector model using the Geant4 simulation toolkit is presented and the system is modelled in both the suppressed and unsuppressed mode of operation. The full energy peak efficiencies of radionuclides from a standard source sample is calculated and compared to experimental measurements. The experimental results agree relatively well with the simulated values (within similar to 5 - 20%). The simulations show that coincidence losses in the Compton suppression system can cause radionuclide specific effects on the detector efficiency, especially in the Compton suppressed mode of the detector. Additionally since low energy photons are more sensitive to small inaccuracies in the computational detector model than high energy photons, large discrepancies may occur at energies lower than similar to 100 keV. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
- ItemDetermining flow patterns and emplacement dynamics from tsunami deposits with no visible sedimentary structure(John Wiley and Sons, 2016-09-16) Kain, CL; Wassmer, P; Goff, JR; Chagué-Goff, C; Gomez, C; Hart, DE; Fierro, D; Jacobsen, GE; Zawadzki, AIn the absence of eyewitness reports or clear sedimentary structures, it can be difficult to interpret tsunami deposits or reconstruct tsunami inundation patterns. The emplacement dynamics of two historical tsunami deposits were investigated at seven transects in Okains Bay, New Zealand, using a combined geospatial, geomagnetic and sedimentological approach. The tsunami deposits are present as layers of sand and silt intercalated between soils and become finer and thinner with distance inland. The deposits are attributed to the 1960 and possibly the 1868 tsunamis, based on radiometric dating and correlation with historical records. Measurements of Magnetic Fabric (MF: Anisotropy of Magnetic Susceptibility) and particle size were used to reconstruct the evolution of flow dynamics laterally and vertically. A combination of statistical methods, including spatial autocorrelation testing, Spearman's rank order correlation, Principal Component Analysis (PCA) and K-means cluster analysis, was applied to examine relationships between MF parameters and sediment texture, and infer depositional hydrodynamics. Flow patterns deduced from MF show the estuary channel acted as a conduit for inundation, with flow commonly aligned sub-perpendicular to the estuary bed. MF and sediment data suggest deposition occurred from settling during laminar flow. Evidence of both uprush and backwash deposition, as well as wave reflection from infrastructure, was found. Statistical analysis of data showed significant relationships between grain size parameters and MF parameters associated with flow speed and magnetic fabric type. PCA and cluster analysis differentiated samples into two primary hydrodynamic groups: (1) samples deposited from laminar flow; and (2) samples deposited close to the limit of inundation, which includes samples deposited further inland, those affected by flow convergence, and those in the upper part of tsunami deposits. This approach has potential as a tool for reconstructing hydrodynamic conditions for palaeotsunamis and by combining spatial and statistical analyses, large-scale investigations can be more easily performed. Copyright © 2016 John Wiley & Sons, Ltd.
- ItemEnvironmental radioactivity in building materials for the environmental radioactivity measurement centre at ANSTO(South Pacific Radioactivity Association, 2010-09-01) Fierro, D; Heijnis, HThe successful use of gamma-spectrometry to measure very low level radioactivity relies on several factors, including the actual system and shielding, as well as environmental factors. A low-level laboratory needs to be in a geographic location with low background radiation, built with low background materials. The laboratory should ideally be built underground to minimize the interference from cosmic radiation. Plans for a new Environmental Radioactivity Measurement Centre at ANSTO were developed in late 2009. The plans included the replacement of the Low Level Radiochemistry Laboratory which was built in the early 1960's and a new Gamma-spectrometry laboratory to be located in the basement of the new building. The design of a new Gamma-spectrometry room triggered a comprehensive study of Australian building materials. Initially the building material study focused on the choice between high density concrete and local Hawkesbury sandstone. It was found that the naturally occurring gamma-emitting isotopes K-40, Pb-210, Ra-226, Ra-228 (Ac—228), Th-228 and U-238 were at similar activities for both local sandstone and commercially (standard) concrete. The levels exceeded 500 Bq/kg for K-40, 20 Bq/kg for the U-238 series isotopes and 70 Bq/kg for the Th-232 by series isotopes. The study proceeded by breaking down the components of the concrete and studying 5 different sources of cement, aggregate and sand. We also sourced different commercially available grades of sandstone and the local sandstone at different depths (2 and 4 m below surface). The benchmark for the study was a special concrete mix used in the building of a gamma-basement in Germany which was of much value to our study. We needed to find building materials of either sandstone or a special concrete mix to be below the following values: K-40 less than 30 Bq/kg, both U-238 and Th-232 series less than 10 Bq/kg. Following an extensive sourcing of building materials, a "low-level" concrete mix was found. The sandstone shielding option was discarded. Other materials in or near the Gamma-spectrometry basement were also analysed. The room design shows a glass wall barrier between the office and the actual instrument room. The glass sample was analysed and found relatively low levels of the radioisotopes of interest. A list of building materials best avoided in building a low background gamma-facility will be presented, showing that by choosing incorrect building materials one can easily reach the dose-limits for external and internal hazard.
- ItemEstimating the inundation limits of small historical tsunamis(Geological Society of Australia, 2014-07-10) Judd, K; Chagué-Goff, C; Goff, JR; Zawadzki, A; Gadd, PS; Fierro, DThere has been considerable progress in tsunami research in recent years, yet most work has been focussed on identifying and understanding the evidence of large events. This talk discusses the evidence for small historical tsunamis in Lyttelton Harbour, New Zealand. The study area has been inundated by numerous relatively small historical tsunamis without depositing any notable sedimentary evidence. However, excavations of shallow soil profiles revealed discontinuous layers of small grey mud clasts, most likely transported from the nearby harbour, at various depths across the study area. The origin of these mud clast layers was investigated using a multi-proxy approach comprising sedimentological, geochemical and diatom analyses complemented by radiometric dating and 179 historical data. Subtle variations consistent with inclusions of marine mud, such as a decrease in organic content and magnetic susceptibility and increases in geochemical markers (e.g. potassium, calcium) were found in the sedimentary profile. Variations in diatom assemblages suggesting marine influence were also recorded at similar depths, aligning with layers of mud clasts. Using 137Cs dating and historical data, these deposits were attributed to the 1960 Chile and possibly 1964 Alaska tsunamis. Sedimentary evidence for the 2010 Chile tsunami was not found at the study site, but geochemical analysis of surface samples revealed marked changes in calcium, chlorine, strontium and titanium concentrations, indicative of a change from terrestrial to marine influence. This was used to identify the landward extent of inundation. Ultimately, this study shows that a broad multi-proxy analysis can distinguish even the subtle signatures of an inconspicuous deposit laid down by a small tsunami.
- ItemIdentifying tsunami deposits in the absence of sand(American Geophysical Union, 2015-12-16) Chagué-Goff, C; Judd, K; Goff, JR; Gadd, PS; Fierro, D; Zawadzki, ATsunamis originating in South America are known to have affected Lyttelton Harbour, New Zealand, in the recent past. However, while there was clear evidence of inundation, in particular in 1960 and 2010, there was no report of any sand left behind. Our study aimed to search for evidence of these small historical tsunamis, in the absence of any visible sand layer. Shallow trenches revealed discontinuous layers of small grey mud clasts at various depths across the study area, most likely transported from the nearby harbour. The origin of these mud clast layers was investigated using sedimentological, geochemical and diatom analyses complemented by dating from 137Cs activity profiles and historical data. Subtle variations consistent with inclusions of marine mud such as a decrease in organic content and magnetic susceptibility and increases in geochemical markers (e.g. Ca, K, K/Rb, Si/Rb and Sr/Rb) were found in the sediment profile. Variations in diatom assemblages suggesting a marine influence were also recorded at similar depths, aligning with layers of mud clasts. Based on 137Cs activity profiles and historical data, these deposits were attributed to the 1960 Chile and 1964 Alaska tsunamis, and we also found evidence for an older deposit, possibly associated with the 1868 Arica tsunami. Sedimentary evidence for the 2010 Chile tsunami was not found at the study site, but our study revealed spatial variations in Ca, Cl and Sr concentrations that were inversely related to Ti concentrations. This was used to identify the landward extent of inundation by the 2010 event. We show that a broad multi-proxy analysis can distinguish even the subtle signatures of an inconspicuous deposit laid down by a small tsunami. © 2014 American Geophysical Union.
- ItemITRAX core scanner capabilities combined with other geochemical and radiochemical techniques to evaluate environmental changes in a local catchment, South Sydney, NSW, Australia(Springer, 2015-07-22) Gadd, PS; Heijnis, H; Chagué-Goff, C; Zawadzki, A; Fierro, D; Atahan, P; Croudace, IW; Goralewski, JIn this study, geochemical and radioanalytical techniques are used together with the ITRAX core scanner to reconstruct the environmental history of Mill Creek catchment, located on the south-western fringes of Sydney. This ITRAX capability study was undertaken to investigate environmental changes in a local catchment which incorporates a nuclear research reactor, a small legacy nuclear waste burial ground, extensive new housing developments, a large rubbish tip, as well as quarries. This catchment changed from being near pristine in the 1950’s to an extensively developed catchment with wide ranging land uses. This rapid development has led to silting up near the mouth of the creek, and there is also evidence of periodic siltation triggered by catchment disturbance from local bushfires, associated with peaks in magnetic susceptibility. The sedimentary environment changed from a creek system to a mangrove swamp and saltmarsh. Changes in Cu, Zn and Pb distributions over the last 60 years suggest an anthropogenically-driven input, although concentrations measured by WD-XRF indicate that the level of urbanisation is lower in the study area than in many of the more industrialised and urbanised neighbouring catchments of Sydney estuary and Botany Bay. The activities of 239 + 240Pu and 241Am in the sediment are below detection limit, which strongly suggests that the legacy nuclear waste has not entered the creek system. © 2015, Springer.
- ItemLate Holocene environmental changes and anthropogenic impact in Dee Why Lagoon, New South Wales(Taylor & Francis, 2019-02-02) Chagué, C; Edwards, D; Ruszczyk, J; Gadd, PS; Zawadzki, A; Jacobsen, GE; Fierro, D; Goralewski, J; Clement, L; Albani, ALate Holocene environmental changes were examined in Dee Why Lagoon, New South Wales, based on the sedimentological, geochemical and geochronological analysis of six cores collected from the fluvial delta and lagoon basin. The lagoon formed about 7300–7200 cal yr BP, following the post-glacial marine transgression and establishment of a sand barrier. Infilling of the lagoon occurred at a rate of 0.09–0.15 mm/yr until about 3300–3200 cal yr BP, when the barrier closed, resulting in mostly freshwater conditions, as evidenced by a change from pyrite-rich units to sediment containing little sulfur and a lack of foraminifera. Sedimentation rates increased to 0.23 then 0.43 mm/yr until about 100 years ago. Post-European land clearance led to an increase in sedimentation rates to 1.0–1.3 mm/yr on the fluvial delta, which are lower than those from other wave-dominated estuaries in New South Wales as well as those estimated by previous studies in Dee Why Lagoon. Our study shows that the fluvial delta started forming much earlier than originally thought, based on results of radiometric dating, and confirmed using sedimentological and geochemical data, as well as a critical examination of historic aerial photographs. Human impact has resulted in an increase in heavy metal (Cu, Pb, Zn) and metalloid (As) concentrations in the recent sediment, most likely attributed to stormwater discharge. Pb and As concentrations are above the ANZECC high sediment quality guideline values at the site closest to the stormwater outlet, with As-based pesticides one of the possible sources. Using the mean enrichment quotient, which is based on normalised Cu, Pb and Zn concentrations over their normalised background concentrations, we show that the surface sediments in Dee Why Lagoon are severely enriched, reflecting the recent anthropogenic impact that has also led to an increase in sedimentation rates. Copyright © 2019 Informa UK Limited
- ItemLow-level gamma-spectrometry by using Compton suppression — testing the performance of two systems at the ANSTO low level radiochemistry laboratory(South Pacific Radioactivity Association, 2008-11-25) Heijnis, H; Zawadzki, A; Fierro, DThe successful use of gamma-spectrometry to measure very low level radioactivity relies on several factors, including the actual system and shielding, as well as environmental factors. A low-level laboratory needs to be in a geographic location with low back ground radiation, built with low background materials. The laboratory should ideally be built underground to minimize the interference from cosmic radiation. Compton suppressed systems have been designed to reduce background caused by Compton scattering. The background can be reduced by the use of Compton Suppression. This is achieved by introducing a second detection system. This second detection system, consisting of a large single crystal Nal annulus, detects the escaping energy from partial absorbed photons in the primary detector, the High purity Germanium detector. As set of standards tests to check the performance of the Compton suppression systems has b n devised by the Monaco Laboratory ( J-F Commanducci, 2003). These tests have been carried out on both ANSTO systems and show a considerable improvement in Compton to peak ratios in the testing and an overall decrease in background due to the shipping of incomplete photon absorption in the primary detector. The two systems allow small environmental samples to be analysed for isotopes such as Pb-210, Cs-137 and Be-7, without compromising the detection limit too much. J-F Commanducci, 2003: Construction du Laboratoire Souterrain et des Spectrometres a coincindences “faibre bruit” destines a la surveillance de L’Environrnent Marin. IAEA-MEL Document. PP 69.
- ItemMeasurement of fallout radionuclides, 239,240Pu and 137Cs, in soil and creek sediment: Sydney Basin, Australia(Elsevier, 2016-01-01) Smith, BS; Child, DP; Fierro, D; Harrison, JJ; Heijnis, H; Hotchkis, MAC; Johansen, MP; Marx, SK; Payne, TE; Zawadzki, ASoil and sediment samples from the Sydney basin were measured to ascertain fallout radionuclide activity concentrations and atom ratios. Caesium-137 (137Cs) was measured using gamma spectroscopy, and plutonium isotopes (239Pu and 240Pu) were quantified using accelerator mass spectrometry (AMS). Fallout radionuclide activity concentrations were variable ranging from 0.6 to 26.1 Bq/kg for 137Cs and 0.02–0.52 Bq/kg for 239+240Pu. Radionuclides in creek sediment samples were an order of magnitude lower than in soils. 137Cs and 239+240Pu activity concentration in soils were well correlated (r2 = 0.80) although some deviation was observed in samples collected at higher elevations. Soil ratios of 137Cs/239+240Pu (decay corrected to 1/1/2014) ranged from 11.5 to 52.1 (average = 37.0 ± 12.4) and showed more variability than previous studies. 240Pu/239Pu atom ratios ranged from 0.117 to 0.165 with an average of 0.146 (±0.013) and an error weighted mean of 0.138 (±0.001). These ratios are lower than a previously reported ratio for Sydney, and lower than the global average. However, these ratios are similar to those reported for other sites within Australia that are located away from former weapons testing sites and indicate that atom ratio measurements from other parts of the world are unlikely to be applicable to the Australian context. © 2015, Elsevier Ltd.
- ItemMulti-proxy evidence for small historical tsunamis leaving little or no sedimentary record(Elsevier, 2017-01-01) Judd, K; Chagué-Goff, C; Goff, JR; Gadd, PS; Zawadzki, A; Fierro, DThere has been considerable progress in tsunami research in recent years, yet most work has been focussed on identifying and understanding the evidence of large events. This study aimed to identify the evidence of small historical tsunamis in Lyttelton Harbour, New Zealand. The study area has been inundated by multiple relatively small historical tsunamis that left atypical sedimentary evidence (no sand) or no sediment. Shallow trenches revealed discontinuous layers of small grey mud clasts at various depths across the study area, most likely transported from the nearby tidal flats. The origin of these mud clast layers was investigated using a multi-proxy approach comprising sedimentological, geochemical and diatom analyses complemented by dating from 137Cs activity profiles and historical data. Subtle variations consistent with inclusions of marine mud such as a decrease in organic content and magnetic susceptibility and increases in geochemical markers (e.g. Ca/kcps, K/kcps, K/Rb, Si/Rb and Sr/Rb) were found in the sediment profile. Variations in diatom assemblages suggesting a marine influence were also recorded at similar depths, aligning with layers of mud clasts. Using 137Cs activity profiles and historical data, these deposits were attributed to the 1960 Chile Valdivia and 1964 Alaska tsunamis, as well as a possible earlier event. Sedimentary evidence for the 2010 Chile Maule tsunami was not found at the study site, but geochemical analysis of surface samples revealed marked changes in Ca, Cl, Sr and Ti concentrations, indicative of a change from a terrestrial to marine influence. This was used to identify the landward extent of inundation by the 2010 event. Ultimately, this study shows that a broad multi-proxy analysis can distinguish even the subtle signatures of an inconspicuous deposit laid down by a small tsunami. © 2017, Elsevier B.V.
- ItemMulti-proxy evidence for trans-Pacific tsunamis in the Hawai'ian Islands(Elsevier, 2012-03-01) Chagué-Goff, C; Goff, JR; Nichol, SL; Dudley, W; Zawadzki, A; Bennett, JW; Mooney, SD; Fierro, D; Heijnis, H; Dominey-Howes, D; Courtney, CThe origin of two sand layers buried in Pololū wetland, on the northeast coast of the island of Hawai'i, was investigated using a multi-proxy approach, including radiometric dating, sedimentology, geochemistry, micropalaeontology, palynology and historical records. Based on 210Pb, 137Cs and pollen data, the lower sand unit extending 250 to 350 m inland is attributed to the 1946 Aleutian tsunami, while the upper sand unit was laid down by the 1957 Aleutian tsunami. Chronological information does not appear to support any link between these deposits and historical storm events. Furthermore, sedimentological, geochemical, diatom and pollen results suggest deposition of marine and near-beach sediments under high energy conditions typically associated with tsunami inundation. This work presents the first conclusive sedimentary evidence for distantly-generated tsunamis on the Hawai'ian Islands, opening the way for more comprehensive historical and palaeotsunami studies. Indeed, a brief review of archaeological data suggests that the Hawai'ian coast may have experienced similar large magnitude events in the past, from both local and distant sources. © 2012 Elsevier
- ItemRadioanalytical method developments to determine polonium-210 and radium-226 activities in bone samples to be used in forensic studies(Australian Nuclear Science and Technology Organisation, 2012-10-16) Zawadzki, A; Goralewski, J; Heijnis, H; Fierro, D; Lee, G; Watling, J; May, C210Pb dating on human skeletal remains has been proposed in forensic studies for the determination of time since death (TSD) or post-mortem intervals. 210Pb and its granddaughter 210Po enter the human body from two main sources, direct ingestion in foodstuffs and the decay of ingested 226Ra which is retained in the bone and bony tissue [1]. One of the methods in dating human bones is based on the decay unsupported 210Pb (total 210Pb minus supported 210Pb) since the time of death. Total 210Pb can be determined from 210Pb granddaughter, 210Po, and supported 210Pb from 210Pb grandparent, 226Ra. A reliable and sensitive method of determining 210Po and 226Ra activities in bone samples is required in order to produce reliable postmortem intervals. A method was developed, using pig bone samples, to analyse these radionuclides by alpha spectrometry. In this presentation, the methodology employed is discussed, along with some of the difficulties encountered and how these were overcome.
- ItemRe-constructing the sedimentation and pollution signatures of Mill Creek (NSW) by ITRAX core-scanning, geochemical and radiochemistry techniques(Australian Nuclear Science and Technology Organisation, 2012-10-16) Gadd, PS; Heijnis, H; Goralewksi, J; Fierro, D; Zawadzki, AIn this study, we combine ITRAX Core Scanning, Grain size and Radiochemistry (Pb-210, Cs-137 and Pu-239/240) techniques to investigate pollution and age of sedimentation in Mill Creek. The creek drains a catchment containing the Lucas Heights Waste Management facility, the Lucas Heights Science precinct and the Little Forest Burial Ground. The ITRAX core scanner non-destructively collects optical and X-radiographic images, and provides high-resolution elemental profiles that are invaluable for guiding sample selection for further detailed sampling. The core from the creek was first scanned on the ITRAX core scanner and further sampled for the other techniques. The chronology for the sediment core was developed using Pb-210, Ra-226 and Cs-137 analysis.
- ItemThe Waikari River tsunami: New Zealand's largest historical tsunami event(Elsevier, 2019-02-16) Donaldson, G; Goff, JR; Chagué, C; Gadd, PS; Fierro, DThe Waikari River tsunami was caused by a landslide triggered by the 1931 Hawke's Bay earthquake, New Zealand's deadliest natural disaster to date. Although it was reported in newspapers and personal diaries at the time, this is the first study to examine the tsunami using a multi-proxy approach aimed at investigating the physical evidence of this event. Sedimentological, geochemical, chronological and microfossil analyses were carried out on an anomalous gravel layer within the sedimentary sequence of Waikari Station located in a meander bend close to the river mouth. The chronology was established by extrapolation from 137Cs data coupled with historical artefacts found within the gravel layer. Diatoms within the deposit were brackish, and most probably sourced from the adjacent tidally-influenced Waikari River. Principal component analysis performed on geochemical data showed that the anomalous gravel layer at all sites is associated with a cluster of elements not related to detrital input nor organic matter, but indicative of an estuarine source. A second, older, gravel layer was also identified. It is considered to have been deposited by an earlier tsunami, quite likely caused by a landslide generated by the 1863 Hawke's Bay earthquake. The deposit has similar sedimentological, geochemical and microfossil characteristics to the gravel layer deposited by the 1931 event. This study adds valuable insights into the poorly understood topic of landslide generated tsunamis by investigating the largest historical event of its kind to occur in New Zealand. © 2019 Elsevier B.V.