The term “blue-sky eruption” (BSE) can be used to describe eruptions which are unexpected or have no detected precursory activity. Case study analyses indicate that they have a diverse range of characteristics and magnitudes, providing both direct and indirect hazards and occur in both under-developed and developed countries. BSEs can be a result of physical triggers (e.g. the lack of physically detectable precursors or a lack of understanding of the eruption model of the volcano), social triggers (such as an inadequate monitoring network), or a combination of the two. As the science of eruption forecasting is still relatively young, and the variations between individual volcanoes and individual eruptions are so great, there is no effective general model and none should be applied in the absence of a site-specific model. Similarly, as methods vary between monitoring agencies, there are no monitoring benchmarks for effective BSE forecasting. However a combination of seismic and gas emission monitoring may be the most effective. The United States began a hazard and monitoring review of their volcanoes in 2005. While the general principles of their review would be beneficial in a monitoring review of New Zealand’s volcanoes, differences in styles of volcanism, geographic setting and activity levels mean changes would need to be review to fully appreciate the risk posed by New Zealand’s volcanoes. Similarly, the monitoring benchmarks provided in the U.S. review may not be fully applicable in New Zealand. While advances in technology may ultimately allow the effective forecasting of some BSEs, the immediate threat posed by unexpected eruptions means that effective management and mitigation measures may be the only tools currently at our disposal to reduce the risks from BSEs.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references (leaves 158-175).

Thesis (Ph. D.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 204-228).

Typescript. Includes vita and abstract. Includes bibliographical references (leaves 109-114). Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.

In this thesis, we assess various climatic impacts of stratospheric aerosol injection (SAI), a geoengineering proposal that aims to cool Earth by enhancing the sunlight-reflecting aerosol layer in the lower stratosphere. To this end, we employ simpleradiative transfer models, a detailed radiative transfer code (SOCRATES), and two Hadley Centre general circulation models (HadGEM2-CCS and HadGEM2-ES). We find that the use of a light-absorbing aerosol (black carbon) for SAI would result in significant stratospheric warming and an unprecedented weakening of the hydrological cycle. Conversely, we find that SAI with sulphate or titania aerosol could counteract many of the extreme climate changes exhibited by a business-as-usual scenario (RCP8.5) by the end of this century. In a separate investigation, we show that volcanic aerosol dispersion following low-altitude volcanic eruptions can exhibit high sensitivity to the ambient weather state. Volcanic aerosol may get 'trapped' in a single hemisphere or transported to the opposite hemisphere depending simply on the meteorological conditions on the day of the eruption. In a final study, we investigate the impacts of SAI on North Atlantic tropical storm frequency. We find that SAI exclusively promoted in the southern hemisphere would increase North Atlantic storm frequency, and vice versa for northern hemisphere SAI. The results of this thesis should promote further research into SAI, which could conceivably be deployed to maintain global-mean temperature below the COP21 target of +1.5 K above pre-industrial levels, whilst society transitions onto a sustainable energy pathway. Conversely, the possibility of SAI being weaponised, for instance, to specifically increase North Atlantic tropical storm frequency, should motivate policymakers to implement effective regulation and governance to deter unilateral SAI deployments.

Explosive volcanic eruptions are propelled to the surface by the exsolution of vapour bubbles from magma due to decompression. A long-held view is that the amount of H₂O dissolved in the magma at depth controls the intensity of an explosive eruption. Growing evidence from studies reporting H₂O concentrations of melt inclusions (MIs) do not support this view. Instead, the rate at which magma ascends to the surface may play an important role in modulating the eruption style. Slow magma ascent allows the vapour bubbles to rise ahead of the magma, thereby diffusing the driving force for an explosive eruption, whereas for fast magma ascent, the bubbles remain essentially trapped within the magma, causing acceleration and the potential for an explosive eruption. Chapter 1 presents a new modelling approach to constrain magma decompression rate based on the incomplete diffusive re-equilibration of H₂O in olivine-hosted melt inclusions. We apply this chronometer to two contrasting eruptions at Cerro Negro volcano in Nicaragua: the 1992 VEI 3 and 1995 VEI 2 eruptions. Both eruptions have the same basaltic composition (SiO₂ ∼ 50 wt%) and maximum volatile concentrations (H₂O ∼ 4.7 wt%). However, MIs from the less explosive 1995 eruption appear to have experienced more water loss compared to those from the 1992 eruption, which is consistent with slower magma ascent. We present a parameterization of the numerical diffusion model in chapter 2, which significantly reduces the calculation time, facilitating the use of Monte Carlo simulations to evaluate uncertainties. We use this parameterization to create a regime diagram that can be used to guide when melt inclusions may be used as magma hygrometers and when they are better suited to act as magma speedometers. We develop diagnostic tools to recognize where and when water loss has occurred in a magma’s ascent history, and we outline quantitative tools that may be used to restore the primary and/or pre-eruptive water content. We find that one of the largest sources of uncertainty in modelling diffusive re-equilibration of H₂O in MIs and olivines is the diffusivity of H+ in olivine. We present new experimental constraints on H+ diffusivity in olivines from Cerro Negro (1992 eruption) and Etna (3930 BP ‘Fall Stratified’ eruption) (chapters 1 and 3, respectively). Our results show that H+ diffusion is highly anisotropic with the diffusivity along the [100] direction more than an order of magnitude faster than along [010] or [001], implying a large role for the ‘proton-polaron’ diffusion mechanism, which shares this anisotropy. We also find that the lower forsterite (Fo ~ 80) olivines from Cerro Negro have significantly faster H+ diffusivity than higher forsterite (Fo ~ 90) olivines from Etna. The results for Etna agree well with other estimates on high forsterite olivines from San Carlos and Kilauea, suggesting that the Fe content of the olivine strongly affects the H+ diffusivity. In chapter 4, we apply the methods from the first three chapters to an unusually explosive eruption of picritic magma at Etna, Sicily in 3930 BP (termed the ‘Fall Stratified’ eruption). MIs from this eruption show limited evidence for water loss and so cannot be modelled to determine decompression rate. Instead, we model H+ diffusion profiles within the olivine crystals themselves and determine rapid ascent rates of ~15 m/s. We perform rehomogenization experiments on the MIs to accurately assess their pre-eruptive CO₂ concentrations, and find nearly 1 wt.% CO₂. Solubility modelling indicates that these MIs must have been trapped at near Moho depths (24–30 km). The magma’s high CO₂ concentration and deep initial pressures may have been responsible for the magma’s rapid ascent, which ultimately led to its great eruption intensity.

No description available.

Eruption dynamics are sensitive to ash aggregation, and ash aggregates (e.g. accretionary lapilli) are commonly found in eruptive deposits, yet few experiments have been conducted on aggregation phenomena using natural materials. Experiments were developed to produce a probabilistic relationship for the efficiency of ash aggregation with respect to particle size, collision kinetic energy and atmospheric water vapor. The laboratory experiments were carried out in an enclosed tank designed to allow for the control of atmospheric water vapor. A synthetic ash proxy, ballotini, and ash from the 2006 eruption of Tungurahua, in Ecuador, were examined for their aggregation potential. Image data was recorded with a high speed camera and post-processed to determine the number of collisions, energy of collisions and probability of aggregation. Aggregation efficiency was dominantly controlled by collision kinetic energy and little to no dependence on atmospheric water vapor was seen in the range of relative humidity conditions tested, 20 to 80%. Equations governing the relationships between aggregation efficiency and collision kinetic energy and the related particle Stokes number, respectively, were determined for implementation into large scale numerical volcanic models.

Η Νίσυρος είναι ένα στρωματοηφαίστειο δομημένο από Πλειοκαινικά ηφαιστειακά προϊόντα που αποτελούνται κυρίως από ανδεσίτες και βασαλτικούς ανδεσίτες πάνω στους οποίους αποτέθηκαν ασβεσταλκαλικά ηφαιστειακά προϊόντα δακιτικής – ρυοδακιτικής σύστασης με την μορφή πυροκλαστικών αποθέσεων, ροών λάβας και δόμων λάβας. Οι νησίδες του Γυαλιού, της Στρογγυλής, της Παχειάς και της Περγούσας, αποτελούνται από Πλειοκαινικούς δόμους ρυολιθικής (Γυαλί), ανδεσιτικής (Στρογγυλή) και δακιτικής σύστασης (Παχειά και Περγούσα) οι οποίοι φιλοξενούν πυροκλαστικές αποθέσεις της ανώτερης κίσσηρης του Γυαλιού (Στρογγυλή) και ενότητες του τόφφου της Κω και της Παναγιάς Κυράς (Παχειά και Περγούσα). Στην εργασία παρουσιάζουμε την ιστορία γένεσης και φωτογραφίες από τη Νίσυρο, ακολουθώντας πέντε μόνο διαδρομές. / In the present dissertation we are recording the geological monuments of Nisyros island. We present the geological history of the island, providing photos of five routes we have followed.

Soputan volcano is one of the few basaltic volcanoes among 127 active volcanoes in Indonesia. It is part of the Sempu-Soputan volcanic complex located south of Tondano Caldera, North Sulawesi and commonly produces both explosive eruptions with VEI 2-3 and effusive lava dome and flow eruptions. Over the last two decades, Soputan had thirteen eruptions, the most recent in 2016. Most eruptions started explosively, followed by dome growth and in some cases pyroclastic flows. Our study focuses on understanding the magmatic system of Soputan and what processes are responsible for its highly explosive eruptions, which are typically uncommon for a basaltic magma composition. Our study includes tephra samples predating the 1911 eruptions, lava flow samples from the 2015 eruption, and ash from a 2015 fallout deposit. Our whole rock major and trace element composition are virtually identical to lava flow and select pyroclastic deposit compositions of Kushendratno et al. (2012) for the 1911-1912 and 1991-2007 eruptions. Bulk rocks contain 49 to 51 wt.% SiO2, whereas 2015 ash samples are slightly more silicic with 53 wt.% SiO2, consistent with segregation of groundmass from phenocrysts in the eruption cloud. Mantle normalized incompatible trace elements indicate strongly depleted HFSE (High Field Strength Elements) and REE (Rare Earth Elements) signatures but with spikes at Pb and Sr and mild enrichment of Rb and Ba. In comparison of data of this study with what was reported by Kushendratno et al. (2012), Fo68-79 olivine-hosted melt inclusions range from basaltic (48-52 wt.% SiO2) to basaltic andesite (54-55 wt.%) as compared to 54 - 65 wt.% SiO2 glass in Fo68-74 olivines. The compositional range of melt inclusions is consistent with 50% fractionation of multiple minerals including observed phenocrysts of olivine, plagioclase, pyroxene and oxides. Compositional trends with an inflection point likely reflect a change in the crystallizing assemblage, where early crystallization includes clinopyroxene and plagioclase, while later crystallization is dominated by plagioclase. New volatile concentration data from melt inclusions (S max. 0.35 wt.%, Cl max. 0.17%, H2O max. 5.2 wt.% from FTIR analyses) are higher than previously reported from younger samples (S max. ~0.07 wt.%, Cl max. 0.2%, H2O max. ~1 wt.%). H2O is relatively constant (~1-4 wt.%) for individual tephra samples (data by FTIR and water by difference method). Our inclusion data suggest that more volatile-rich magmas exist at depth and this is consistent with a model whereby recharge of deep, volatile-rich magmas into a more degassed and crystal-rich magma initiates a new, highly explosive eruption.