This research was able to identify a wide range of elements present in fresh volcanic ash from a 2010 eruption in Indonesia using varied instrumental neutron activation analysis techniques. The ash was then leached into slightly acidic distilled water meant to simulate rainwater. This thesis focuses both on the methods used to identify the elements present in the ash, as well as the possible impacts of the results. The research included the use of both thermal and epithermal neutron irradiations from the University of Texas's TRIGA research reactor in conjunction with a high purity germanium detector (HPGe) with a Compton suppression system. The leachate was analyzed by an inductively coupled plasma mass spectrometer (ICP-MS), and the results were compared to the original material present in the ash. Several potentially toxic metals and metalloids leached out of the system at relatively high rates. For example, 2.7% of the original antimony present in the ash leached into the simulated rainwater, as well as 1.7% of the original nickel, and 0.71% of the original arsenic. However, the concentrations of the elements identified in the ash were mostly similar to average crustal rock, and the concentrations of the elements identified in the leachate were not determined to be at toxic levels. The total amount of each element released during the eruption was also calculated based on the estimate of 160 million tonnes of ash released during the eruption, which was determined by a different study. / text

Fluid flow rates and pathways in partially-welded, fractured, unsaturated tuff are investigated in a sloping borehole (DSB-1) cored from the surface to a perched aquifer at the Apache Leap near Superior, Arizona. Suspected water-bearing fractures were identified in the borehole using video and geophysical logs. Pore water extracted from cores associated with these fractures proved to have elevated ¹⁴C activity relative to pore waters from intermediate depths. Pore water from the deepest fracture interval contained post-bomb ¹⁴C. Low tritium concentrations in most samples indicates imbibition from each flow is small relative to the volume of water in the pores, but cumulative imbibition over time is significant based on ¹⁴C distribution through the unsaturated zone. The saturated zone beneath DSB-1 is a mixture of fracture flows with older aquifer water. Estimates based on ¹⁴C and ³H data indicate half of the water in the local aquifer originated from fractures near DSB-1. Geochernical models incorporating pore-water, surface-runoff, aquifer-water and mineral chemistry suggest that fracture flow may also be the predominant source of recharge for the older aquifer water. Water and carbon are extracted from core samples using uni-axial compression and a new vacuum distillation technique. Distillation is shown to be an effective method when carbon extraction is not possible by other methods. Mass yields from distillation provide evidence that there may be a substantial reservoir of carbon adsorbed to mineral phases. Carbon-14 activity of formation air samples from intervals with low air permeability reflect the composition of water imbibed from fracture flows at those depths. In zones of higher permeability, atmospheric contamination is suspected even though SF₆ (injected as a tracer during drilling) concentrations had not diminished. An independent investigation on the carbon isotopic composition of soil-zone CO₂ demonstrates the need to correct soil-respired CO₂ samples for CO₂ contamination in base reagents and for fractionation during sample collection. The minimum δ¹³C-shift from soil CO₂ to soil-respired CO₂ is also shown to be a function of the δ¹³C of soil organic material rather than a fixed 4.4%₀ as previously thought.

The thermal evolution of pyroclastic density currents (PDCs) is the result of entrainment of ambient air, particle concentration, and initial eruptive temperature, which all impact PDC dynamics and their hazards, such as runout distance. The associated hazards and opaqueness of PDCs make it impossible for in-situ entrainment efficiencies or concentration measurements that would provide critical information on the thermal evolution and physical processes of PDCs. The thermal evolution of explosive eruptive events such as volcanic plumes and pyroclastic density currents (PDCs) is reflected in the textures of the material they deposit. A multiscale model is developed to evaluate how the rinds of breadcrust bombs can be used as a unique thermometer to examine the thermal evolution of PDCs. The multiscale, integrated model examines how bubble growth, pyroclast cooling, and dynamics of PDC and projectile pyroclasts form unique pyroclast morphology. Rind development is examined as a function of transport regime (PDC and projectile), transport properties (initial current temperature and current density), and pyroclast properties (initial water content and radius). The model reveals that: 1) rinds of projectile pyroclasts are in general thicker and less vesicular than those of PDC pyroclasts; 2) as the initial current temperature decreases due to initial air entrainment, the rinds on PDC pyroclasts progressively increase in thickness; and 3) rind thickness increases with decreasing water concentration and decreasing clast radius. Therefore, the modeled pyroclast’s morphology is dependent not only on initial water concentration but also on the cooling rate, which is determined by the transport regime. The developed secondary thermal proxy is then applied to the 2006 PDCs from the Tungurahua eruption to constrain the entrainment efficiency and thermal evolution of PDCs. A three-dimensional multiphase Eulerian-Eulerian-Lagrangian (EEL) model is coupled to topography and field data such as paleomagnetic data and rind thicknesses of collected pyroclasts to study the entrainment efficiency and thus the thermal history of PDCs at Tungurahua volcano, Ecuador. The modeled results that are constrained with observations and thermal proxies demonstrate that 1) efficient entrainment of air to the upper portion of the current allows for rapid cooling, 2) the channelized pyroclastic density currents may have developed a stable bed load region that was inefficient at cooling and 3) the PDCs had temperatures of 600-800K in the bed load region but the upper portion of the currents cooled down to ambient temperatures. The results have shown that PDCs can be heterogeneous in particle concentration, temperature, and dynamics and match observations of PDCs down a volcano and the thermal proxies. Lastly, the entrainment efficiencies of PDCs increases with increasing PDC temperature and entrainment varies spatially and temporally. Therefore, the assumption of a well-mixed current with a single entrainment coefficient cannot fully solve the thermal evolution and dynamics of the PDC.

Volcanic eruptions produce a range of concurrent, sequential and recurrent hazards which can impact society and critical infrastructure. For daily activities, modern societies are reliant on dependable functioning critical infrastructure, such as electrical supply; water supply; wastewater; transportation; communication networks; buildings; air conditioning and ventilation systems; and electronic equipment. In addition, during volcanic eruptions these sectors are vital for effective emergency response and recovery. Despite the importance of critical infrastructure, the systematic quantification of their vulnerability to volcanic hazards, a key aspect of volcanic risk management, has received little research attention. Successful volcanic risk management and disaster risk reduction are cost effective investments in preventing future losses during eruptions and increasing resilience to volcanic hazard impacts. Effective volcanic risk management requires the characterisation of both hazards and vulnerabilities to the same level of detail. This thesis develops a methodological framework to quantitatively assess the vulnerability of critical infrastructure sectors to volcanic hazard impacts. The focus is on fragility and vulnerability functions which provide quantitative relationships between impact (damage and disruption) and volcanic hazard intensity. The framework details how post-eruption infrastructure impact data, compiled in a newly established infrastructure impacts database, can be classified by hazard and impact intensity to derive vulnerability and fragility functions. Using the vulnerability framework, fragility functions for several critical infrastructure sectors for volcanic tephra fall impacts are derived. These functions are the first attempt to quantify the vulnerability of critical infrastructure sectors using a systematic approach. Using these fragility functions, risk is estimated for the electrical transmission network in the North Island of New Zealand using a newly developed probabilistic tephra fall hazard assessment. This thesis and framework provide a pathway forward for volcanic risk scientists to advance volcanic vulnerability assessments such that comprehensive and robust quantitative volcanic risk assessments are commonplace in infrastructure management practices. Improved volcanic vulnerability and risk assessments leads to enhanced risk-based decision making, prioritisation of risk reduction investment and overall reduction in volcanic risk.

Io, the innermost Galilean satellite of Jupiter, exhibits a wide variety of complex phenomena such as interaction with Jupiter’s magnetosphere, volcanic activity, and a rarefied multi-species sublimating and condensing atmosphere with an ionosphere. Io’s orbital resonance with Jupiter and the other Galilean satellites produces intense tidal heating. This makes Io the most volcanically active body in the solar system with plumes that rise hundreds of kilometers above the surface. In the present work, the interaction of Io’s atmosphere with the Jovian plasma torus is simulated via the Direct Simulation Monte Carlo (DSMC) method and the aurora produced via electron-neutral excitation collisions is examined using electron transport Monte Carlo simulation. The electron-transport Monte Carlo simulation models the electron collisions with the neutral atmosphere and their transport along field lines as they sweep past Io, using a pre-computed steady atmosphere and magnetic field. As input to the Monte Carlo simulation, the neutral atmosphere was first modeled using prior 2D sunlit continuum simulations of Io’s atmosphere produced by others. In order to justify the use of a sunlit atmosphere for eclipse, 1D two-species (SO2 and a non-condensable) DSMC simulations of Io’s atmospheric dynamics during and immediately after eclipse were performed. It was found that the inclusion of a non-condensable species (SO or O2) leads to the formation of a diffusion layer which prevents rapid collapse. The degree to which the diffusion layer slowed the atmospheric collapse was found to be extremely sensitive to both the initial non-condensable mole fraction and the reaction (or sticking) probability on the surface of the “non-condensable”. Furthermore, upon egress, vertical stratification of the atmosphere occurred with the non-condensable species being lifted to higher altitudes by the rapid sublimation of SO2 as the surface warms. Simulated aurorae (specifically the [OI] 6300 Å and the S2, SO, and SO2 molecular band emission in the middle ultraviolet) show good agreement with observations of Io in eclipse and an attempt was made to use the simulations to constrain the upstream torus electron temperature and Io’s atmospheric composition, structure, and volcanic activity. It is found that the position of the bright [OI] 6300 Å wake spot relative to Io’s equator depends on the position of Io relative to the plasma torus’ equator and the asymmetric electron number flux that results. Using HST/STIS UV-Vis spectra, the upstream electron temperature is weakly constrained to be between 3 eV and 8 eV depending on the flux of a low energy (35 eV), non-thermal component of the plasma (more non-thermal flux requires lower thermal plasma temperatures to fit the spectrum). Furthermore, an upper limit of 5% of the thermal torus density (or 180 cm−3 based on the Galileo J0 plasma density at Io) is obtained for the low energy non-thermal component of the plasma. These limits are consistent with Galileo observations of the upstream torus temperature and estimates for the the non-thermal component. Finally, plume activity and S2 content during eclipse observations with HST/STIS were constrained by examining the emission intensity along the spatial axis of the aperture. During the August 1999 UV-Vis observations, the auroral simulations indicate that the large volcanoes Pele and Surt were inactive whereas Tvashtar was active and that Dazhbog and possibly Loki were also actively venting gas. The S2 content inferred for the large Pele-type plumes was between 5% (Tvashtar) and 30% (Loki, if active), consistent with prior observations (Spencer et al., 2000; Jessup et al., 2007). A 3D DSMC simulation of Io’s sublimation and sputtered atmosphere including photo- and plasma-chemistry was developed. In future work these atmospheric simulations will replace the continuum target atmosphere in the auroral model and thus enable a better match to the observed high altitude auroral emission. In the present work, the plasma interaction is modeled by a flux of ions and electrons which flow around and through Io’s atmosphere along pre-computed fields and interact with the neutral gas. A 3D DSMC simulation of Io’s atmosphere assuming a simple thermal model for the surface just prior to ingress into eclipse and uniform frost coverage has been performed in order to understand how Io’s general atmospheric dynamics are affected by the new plasma model with chemistry and sputtering. Sputtering was found to supply most of the nightside atmosphere (producing an SO2 column of ~5×1013 cm−2); however, the dense dayside sublimation atmosphere was found to block sputtering of the surface. The influence of the dynamic plasma pressure on the day-to-night circumplanetary flow was found to be quite substantial causing the day-to-night wind across the dawn terminator to flow slightly towards the equator. This results in a region of high density near the equator that extends far (~2000 km for the condensable species) onto the nightside across the dawn terminator. Thus, even without thermal lag due to rotation or variable surface frost, highly asymmetric equatorial column densities relative to the subsolar point are obtained. The non-condensable O2, which is a trace species on the dayside, is the dominant species on the nightside despite increased SO2 sputtering because the loss rate of O2 is slow. Finally, a very intriguing O2 flow feature was observed near the dusk terminator where the flow from the leading hemisphere (pushed by the plasma) meets the flow from the dayside trailing hemisphere. Since the O2 does not condense on the surface, it slowly convects towards the poles and then back onto the nightside, eventually to be dissociated or stripped away by the plasma. / text

published_or_final_version / Earth Sciences / Master / Master of Philosophy

No description available.

The Ngatamariki Geothermal Field is located 20 km north of Taupo in the Taupo Volcanic Zone and has a boundary of 12 km² as delineated by magneto-telluric surveys (Urzua 2008). Rhyolitic deposits, derived from the Maroa Volcanic Centre, dominate the geology of the area with the 186 AD (Wilson et al. 2009) Taupo pumice mantling stream valleys in the area. The majority of thermal features at Ngatamariki are located along the Orakonui Stream on the western boundary of the field; the stream area is dominated by a 50x30 m geothermal pool filling a hydrothermal eruption crater. This crater was formed during a hydrothermal eruption in 1948, with a subsequent eruption in April 2005. Orakei Korako is located 7 km north of Ngatamariki and has one of the largest collections of thermal features in New Zealand. The geology at Orakei Korako is similar to Ngatamariki, but the area is dominated by a series of south-west trending normal faults which create sinter terraces on the eastern bank of Lake Ohakuri. Water samples from springs and wells at Ngatamariki and Orakei Korako were taken to assess the nature of both fields. Spring waters at Ngatamariki have chloride contents of 56 to 647 mg/l with deep waters from wells ranging from 1183 to 1574 mg/l. This variation is caused by mixing of deep waters with a steam heated groundwater, above clay caps within the reservoir. Stable isotopic results (δ¹⁸O and δD) suggest that reservoir waters are meteoric waters mixed with magmatic (andesitic) water at Ngatamariki. Reservoir water chemistry at Orakei Korako exhibits low chloride contents, which is anomalous in the Taupo Volcanic Zone. Chloride content in well and spring waters is similar ranging from 546 to 147 mg/l, due to mixing of reservoir fluids with a ‘hot water’ diluent at depth. Isotopic compositions of spring waters suggest that they are meteoric waters which mix with magmatic (rhyolitic) water, more enriched in δ¹⁸O and δD than ‘andesitic’ water. Relationships between major ion concentrations and known subsurface geology suggest there is no hydraulic connection between the two fields.

The Tahorakuri Formation was introduced as a stratigraphic term to simplify the sometimes complex and inconsistent naming conventions in subsurface deposits within the geothermal fields of the central Taupo Volcanic Zone (TVZ). It consists of all volcaniclastic and sedimentary deposits between the ~350 ka Whakamaru-group ignimbrites and the greywacke basement that cannot be correlated with known ignimbrites. As such, it represents a long period in which relatively little is known about the volcano-tectonic history of the TVZ. The thesis focuses on the Tahorakuri Formation at Ngatamariki and Rotokawa geothermal fields and the implications for the volcano-tectonic evolution of the TVZ. Drill cuttings from wells NM5 and NM6 are re-examined, and new U-Pb zircon dates from the Tahorakuri Formation are presented and implications discussed. Potassium feldspars identified in the drill cuttings from NM5 were examined by Raman spectroscopy and electron microprobe (EMP) analysis. Although petrographically many of the feldspars appear similar to sanidine, a primary volcanic mineral phase, this showed them to be adularia which formed during hydrothermal alteration. Raman spectroscopy was found to be ideal for analysing a large number of grains quickly, with the spectral peak at ~140 cm⁻¹ being particularly useful for identifying adularia as it is absent in sanidine. EMP analysis was found to be somewhat slower, but definitively identified the feldspars as adularia, with typical potassium-rich compositions of Or₉₄-Or₉₉. U-Pb dating shows that the Tahorakuri Formation formed over a very long time, with pyroclastic deposits ranging from 1.89 - 0.70 Ma. This was followed by a period with little or no explosive volcanism until ~0.35 Ma during which sediments were deposited at Ngatamariki. The periods at ~1.9 Ma and ~0.9 Ma were particularly active phases of pyroclastic deposition, with the second phase likely correlating with the Akatarewa ignimbrite. The oldest deposits overlie a large andesitic composite cone volcano. Significant subsidence of the andesite must have preceded emplacement of the silicic deposits, indicating that rifting within the central TVZ may have started earlier than previously thought. While the origin of the deposits is uncertain, the distribution of the oldest deposits outcropping at the surface, as well as the likely early initiation of rifting, would suggest a source within the TVZ is likely.

This thesis aims to create a specific and robust geotechnical data set for the Lyttelton Volcanic Group, and investigate the effect of emplacement and post-emplacement mechanisms on geotechnical characteristics. The thesis provides an engineering geological model of a representative section of the Lyttelton Volcanic Complex, which, in conjunction with field observations, informed the subdivision of the main lithological groups into geotechnical sub-units. The sub-units account for the geological variations within the rock types of this study. Eighteen geotechnical sub-units were identified, sampled and characterised: 1trachytic dykes, 2trachytic domes, 3trachytic lava, 4brecciated basaltic ignimbrite, 5moderately welded basaltic ignimbrite, 6highly welded basaltic ignimbrite, 7red ash, 8crystal dominated tuff, 9lithic dominated tuff, 10rubbly basaltic breccia, 11unweathered basaltic lava, 12slightly to moderately weathered basaltic lava, 13highly to completely weathered basaltic lava, 14highly vesicular basaltic lava bomb, 15basaltic dyke, 16blocky basaltic lava, 17volcanogenic conglomerate and 18volcanogenic tuffaceous sandstone. Thirteen units were able geotechnically tested. Sample preparation and geotechnical testing followed ASTM and ISRM guidelines respectively. Geotechnical testing included: uniaxial compressive strength (σci), point load strength index (Is(50)), porosity (n), density (ρd), P and S wave velocities (Vp and Vs), slake durability (Id2), Young’s Modulus (E), Poisson’s Ratio (υ), shear modulus (G) and bulk modulus (K). The igneous lithologies included in this study have been characterised using the Detailed Engineering Geological Igneous Descriptive Scheme, developed purposely for the needs of the thesis. The results of laboratory testing showed many strong trends with geological characteristics and relationships between geotechnical parameters. Parameters such as porosity, density, P-wave velocities, Young’s Modulus and point load strength showed very strong correlations with uniaxial compressive strength. Variability in the physical and mechanical properties is attributed to the geological factors, which dictate the material behaviour. These include texture, grain size, composition, welding, lithification, flow banding, percentage and size of phenocrysts/clasts/lithics. Geological factors affecting geotechnical behaviour are a function of emplacement mechanism. Four distinct emplacement mechanisms were identified in this study: lava flows, pyroclastic density currents, intrusions (dykes) and airfall deposits. Typically, lava flows and intrusions have higher strength, durability, density and lower porosity than pyroclastics and airfall deposits. Importantly, the data illustrates a considerable variability in some geotechnical parameters within the same unit (e.g. 58-193 MPa strength variation in the unweathered basaltic lava). Variability within rocks with similar emplacement mechanisms is attributed to the effects of post-emplacement mechanisms and processes (e.g. weathering, alteration and micro/macro fracturing leading to lower strength). Evaluation of engineering geological and geotechnical parameters of rock and soil materials are required for engineering purposes, specifically when any form of design is required. This study has highlighted the importance and necessity to identify volcanic lithologies and features correctly as there are consequences for geotechnical behaviour, and that volcanic data from literature data should not be used without the correct degree of ground-truthing and geological context. Location-specific engineering geological data are necessary for the quantitation of variability in engineering geological characterisation for engineering geological models, designs and simulations in the Port Hills Volcanics.