Geoengineering has attracted large attention over recent years as to being a possible way to ameliorate some of the effects of climate change. One of the proposals, involving injecting sulphate aerosols into the stratosphere in order to cool Earth's temperature back to pre-industrial levels, has been assessed as one of the leading geoengineering proposals. Despite this, large uncertainties remain in both the physical and social sciences. Small scale trials of sulphate aerosol injection are not seen as ways to provide large amounts of useful data to inform on the climate response to stratospheric sulphate aerosol loading (whilst also facing many social and ethical barriers). Large scale trials involving injecting amounts of aerosol more comparable to what would be required to cool the Earth's temperature back to pre-industrial levels are viewed as too risky. Assessments of the climate effects of sulphate aerosol geoengineering by the scientific community therefore have largely relied on climate modelling studies. The thesis begins by reviewing sulphate aerosol geoengineering and the modelling that have been conducted to date. In light of the need to verify modelling results with observations the thesis seeks to understand the effects of nature's analogue to sulphate aerosol geoengineering: large volcanic eruptions. When a volcano erupts it can inject large amounts of SO2 gas into the stratosphere, which then undergo conversion to form sulphate aerosol, cooling the Earth in a way analogous to sulphate aerosol engineering. The ability of the climate models submitted to the Coupled Model Intercomparison Project 5 (CMIP5) database is assessed, with a particular focus on dynamical changes in the Northern Hemisphere winter period. These models fail to capture the observed NH dynamical response following eruptions, which is of concern for the accuracy of geoengineering modelling studies that assess the atmospheric response to sulphate aerosol geoengineering. Simulations of volcanic eruptions are then performed with high-top and low-top configurations of the HadGEM2-CC climate model. The high-top version of HadGEM2-CC, with enhanced vertical resolution and model height, gives a markedly improved and statistically significant post-volcanic winter dynamical simulation to its low-top counterpart. The post-winter dynamical simulation in the high-top model agrees with the observed response following volcanic eruptions. Accordingly, mechanisms involved in the dynamical changes are analysed and it is concluded that the HadGEM2-CC high-top model would give more confident simulations of sulphate aerosol geoengineering over its low-top counterpart. Given the identification of a more suitable model for geoengineering simulations following extensive investigation, the final chapter analyses simulations of the HadGEM2-CC high-top model for asymmetries between the climate response to an immediate onset of geoengineering and a rapid cessation of geoengineering - known as a 'termination' of geoengineering. The project is summarised and discussed, and future work is proposed, involving a large host of projects.

Volcanic eruptions and unrest have the potential to have large impacts on society causing social, economic and environmental losses. One of the primary goals of volcanological studies is to understand a volcano’s behaviour so that future instances of unrest or impending eruptions can be predicted. Despite this, our ability to predict the onset, location and size of future periods of unrest remains inadequate and one of the main problems in forecasting is associated with the inherent complexity of volcanoes. In practice, most reliable forecasts have employed a probabilistic approach where knowledge of volcanic activity triggers have been incorporated into scenarios to indicate the probability of unrest. The proposed relationship between large earthquakes and volcanic activity may, therefore, indicate an important precursory signal for volcanic activity forecasting. There have been numerous reports of a spatial and temporal link between volcanic activity and high magnitude seismic events and it has been suggested that significantly more periods of volcanic unrest occur in the months and years following an earthquake than expected by chance. Disparities between earthquake-volcano assessments and variability between responding volcanoes, however, has meant that the conditions that influence a volcano’s response to earthquakes have not been determined. Using data from the MODVOLC algorithm, a proxy for volcanic activity, this research examined a globally comparable database of satellite-derived volcanic radiant flux to identify significant changes in volcanic activity following an earthquake. Cases of potentially triggered volcanic activity were then analysed to identify the earthquake and volcano parameters that influence the relationship and evaluate the mechansisms proposed to trigger volcanic activity following an earthquake. At a global scale, this research identified that 57% [8 out of 14] of all large magnitude earthquakes were followed by increases in global volcanic activity. The most significant change in volcanic radiant flux, which demonstrates the potential of large earthquakes to influence volcanic activity at a global scale, occurred between December 2004 and April 2005. During this time, new thermal activity was detected at 10 volcanoes and the total daily volcanic radiant flux doubled within 52 days. Within a regional setting, this research also identified that instances of potentially triggered volcanic activity were statistically different to instances where no triggering was observed. In addition, assessments of earthquake and volcano parameters identified that earthquake fault characteristics increase the probability of triggered volcanic activity and variable response proportions at individual volcanoes and regionally demonstrated the critical role of the state of the volcanic system in determining if a volcano will respond. Despite the identification of these factors, this research was not able to define a model for the prediction of volcanic activity following earthquakes and, alternatively, proposed a process for response. In doing so, this thesis confirmed the potential use of earthquakes as a precursory indicator to volcanic activity and identified the most likely mechanisms that lead to seismically triggered volcanic unrest.

No description available.

O Complexo Vulcânico Yate (CVY) está localizado na Zona Vulcânica Sul dos Andes, Chile. É constituído pelos vulcões Yate, Hornopirén e Gualaihué, além de um conjunto de cones monogênicos conhecido como Centros Eruptivos Cordón Cabrera; aflora em uma área de aproximadamente 400 km2, representado por uma sequência vulcânica de mais de 2.000 metros de sessão vertical contínua. O Vulcão Yate é o maior dos vulcões do complexo, correspondendo a um tipo combinado constituído por cinco unidades litoestratigráficas que se estendem no tempo desde o Pleistoceno Superior (c. 122 ka) até o Holoceno. O Vulcão Hornopirén corresponde a um vulcão estromboliano com registro de atividade eruptiva mais antiga, no Pleistoceno Inferior-Médio (c. 1,4-0,26 Ma), estendendo-se até Holoceno. Por fim, o Vulcão Gualaihué corresponde a um vulcão tipo escudo com atividades efusiva, restrita ao Pleistoceno Médio (c. 440 ka), e freatomagmática no Holoceno. A assinatura geoquímica diversificada das rochas do CVY levou à individualização de quatro tipos de basaltos e andesitos basálticos (BABs) com associações mineralógicas particulares: (i) de alto alumínio e baixo magnésio (BAB-A), com olivina-clinopiroxênio-plagioclásio; (ii) de baixo alumínio e alto magnésio (BAB-AM), com olivina-plagioclásio; (iii) de alto magnésio (BO), com olivina; e (iv) de alto potássio (BAB-K), com coexistência de duas associações mineralógicas incongruentes, olivinaplagioclásio e plagioclásio-clinopiroxênio-orotopiroxênio. A assinatura isotópica desses BABs diferenciase apenas em termos da razão 87Sr/86Sr, em parte acompanhada pelas razões 06Pb/204Pb; as razões 143Nd/144Nd, no entanto, são pouco variáveis. Quando comparados, os BAB-A são as rochas mais radiogênicas, sendo que as razões isotópicas de Sr (> 0,70440) não se correlacionam com a razão Rb/La, sugerindo que o enriquecimento isotópico não teria relação com contaminação crustal. A modelagem quantitativa sugere que esses BABs poderiam ser produto de graus variáveis de fusão parcial de um manto peridotítico, na presença de água (c. 1%). Modelo petrogenético semelhante é proposto para os BAB-AM e BO, todavia com volume de água menor. Já os BAB-K apresentam claras evidências de desequilíbrio mineral, sugerindo a atuação de ambos assimilação e mistura de magmas na sua gênese.Com respeito às rochas mais evoluídas (ABSiO2, andesitos e dacitos), presentes exclusivamente no Vulcão Yate, as características texturais e químicas são pouco conclusivas, sendo as tendências geoquímicas divergentes daquelas típicas de cristalização fracionada. O comportamento geoquímico, endossado pelas texturas de desequilíbrio mineral comuns a esses magmas, mostra mistura (mixing ou mingling) de magmas como um mecanismo importante em suas histórias petrogenéticas. Por fim, a gênese dos riolitos (com anfibólio) parece sugerir fusão parcial de uma crosta anfibolítica ou cristalização fracionada a partir de um magma andesítico, a ~12 km de profundidade. A evolução magmática no CVY, desde o Pleistoceno Inferior-Médio até o Holoceno, incluiria atividade eruptiva de magmas básicos (BABs), ao longo de estruturas N-S (Vulcão Hornopirén) e NE-SW (Vulcão Gualaihué), os quais também devem ter interagido com uma câmara magmática em evolução (Vulcão Yate, c. 10 km de profundidade), provavelmente disposta na junção destas estruturas. Essa interação teria produzido graus variáveis de mistura, cristalização fracionada e assimilação crustal de seus produtos. / The Yate Volcanic Complex (CVY) is located in the Southern Volcanic Zone of the Chilean Andes, at 42°30S, comprising the Yate, Gualaihué and Hornopirén volcanoes. The Yate volcano is a major compound type in which effusive activity occurred since Upper Pleistocene (c. 122 ka) until Holocene. Hornopirén and Gualaihué are minor, and represent strombilian- and shield-type volcanoes, respectively. Effusive activity in Hornopirén extended since Lower to Middle Pleistocene (c. 1,4 Ma to 260 ka), and in Gualaihué was around Middle Pleistocene (c. 440 ka), with subordinate phreatomagmatic eruptions during Holocene. Four types of basalt and basalt andesite associations (BABs) were recognized in YVC: (i) a high-Al and low-Mg group (BAB-A), with olivine-clinopyroxene-plagioclase phenocrystal assembly; (ii) a high-Mg and low-Al group (BAB-AM), with olivine-plagioclase; (iii) a high-Mg group (BO), with olivine and, (iv) a K-rich group (BAB-K) including two incongruent mineral assemblies, olivineplagioclase and clinopyroxene-orthopyroxene. Sr (and Pb) isotopic ratios show different patterns for BABs. When compared together, BAB-A is the most radiogenic group, with 87Sr/86Sr ratios higher than 0.70440 showing no correlation with Rb/La ratios. This suggests that isotopic (and incompatible element) enrichment may not be exactly related to crustal contamination. Quantitative modeling points to partial melting, in c. 1% water (slab-derived fluids), of an enriched peridotite as a possible mechanism involved in the genesis of BAB-A magmas. Similar petrogenetic model is envisaged for BAB-AM and BO; however, minor water contents during melting should be required for. Striking features of mineral disequilibrium suggest each (K-rich) crust assimilation and magma mixing influenced compositional signature of the BAB-K magmas. Magma mixing and mingling seems to be also an important petrogenetic mechanism in genesis of the evolved magmas (silica-rich basalt andesites, andesites, dacites) from the YVC, as shown by petrographic (olivine-clinopyroxene [Mg# 0,8], coexisting with clinopyroxene-orthopyroxene [Mg# 0,76-0,63]) and geochemical features. Genesis of amph-riolites, however, can be explained to each partial melting of amphibolite crust or ~12 km-deep fractional crystallization from an andesitic magma. In summary, the magmatic evolution of YVC, from the Middle Pleistocene to Holocene, is dominated by geochemically distinct basic magmas emplaced along NS- and SW-trending structures. Chemical and mechanical interaction between these magmas occurred into the magma chamber, located at the junction of those structures. In addition, partial melting of the crust produced the most evolved magmas of the complex.

Abstract Major water soluble ions (Cl-, NO3-, SO42-, CH3SO3-, Na+, K+, NH4+, Mg2+, Ca2+) were determined and the results interpreted from a 121 m long ice core drilled at the summit of the Lomonosovfonna dome, Svalbard. The core covers about the past 800 years. The reliability of anion chemistry for paleoenvironmental studies, and various insoluble particles were also investigated. The ice core studied in this Thesis is the first relatively deep ice core from the central Svalbard that has been analyzed and the results interpreted and published at high resolution for all major ions. One of the clearest features of the ion profiles is anthropogenic impact. SO42- and NO3- concentrations show significant increases by the mid-20th century with slight increases already at the end of the 19th century. In addition excess Cl- and NH4+ from anthropogenic sources are detected arriving after the mid-20th century. Anthropogenically derived SO42- and NO3- have different sources on Lomonosovfonna. NO3- is correlated with NH4+ and requires interpretation in terms of both natural and anthropogenic NH4NO3 sources. The ice core ionic load consists mostly of sea salt ions (Na+, Cl-, K+ and Mg2+). Water soluble Ca2+ are mostly terrestrial in origin. Ion balance together with the Na+/Cl- ratio shows considerable change about 1730 that is most probably due to Na2CO3 input to the ice cap before 1730. Marine biogenic CH3SO3- concentrations are high and stable during the Little Ice Age. CH3SO3- concentrations show a clear change in concentrations in 1920, that is the end of the Little Ice Age in Svalbard. Regardless of anthropogenic impact, marine biogenic SO42- is appreciable in total SO42- budget even in the 20th century. The Laki volcanic eruption in Iceland in 1783 is identified in the ice core as a volcanic tephra layer and high SO42- concentration and acidity peaks. These show that SO42- arrived to the Lomonosovfonna ice cap 6–12 months later than insoluble tephra and the SO42- aerosol caused a drop in temperature. The reliability of ice core ion chemistry analyses was estimated – for the first time in an ice core using two different analytical procedures on 500 adjacent samples from the same depth. Small-scale inhomogeneity in ion concentrations shows that information from ice core layers is representative of the regional environmental and suitable for paleoclimate studies.

Mapping of the north-eastern portion of the Bird1s River Complex revealed that two large xenoliths composed of pyroclastic rocks and sandstone of the Cave Sandstone Stage have reacted with the dolerite. All the reaction phenomena normally associated with Karroo Dolerite are encountered. These are: (a) Metasomatism during the stage of iron enrichment of the dolerite with the production of a pyroxene-plagioclase metasomatic granophyre (b) Metasomatism during the stage of alkali enrichment of the dolerite with the production of a potassium feldspar adinole C c) Assimilation 'vi th the production of contaminated doleri tes Cd) Fusion 'vi th the production of glassy rocks including buchi tes (e) The production of rheomorphic veins

A multi-prong approach was taken in this dissertation to understand volcanic processes from both a long-term and more immediate hazard perspective. In the long-term, magma sources within the crust may produce measurable surficial response and long-wavelength gravity anomalies that provide information about the extent and depth of this magma. Long-term volcanic hazard forecasting is also improved by developing as complete a record as possible of past events. In the short-term, a long-standing question has been on the casting of precursory volcanic activity in terms of future volcanic hazards. Three studies are presented in this dissertation to address these issues. Inversion of high-resolution ground magnetic data in Amargosa Valley, NV indicates that anomaly B could be generated by a buried shield volcano. This new information changes the event count in this region which in turn affects the overall volcanic hazard estimation. Through the use of Finite Element Models (FEM) an in-depth characterization of the surficial response to magma underplating is provided for the Tohoku Volcanic Arc, Japan. These models indicate that surficial uplift was dominantly driven by mid-crustal intrusions and the magnitude and wavelength of this uplift was mainly controlled by the elastic layer thickness. In Dominica, seismic data were used as weights in spatial intensity maps to generate dynamic volcanic hazard maps influenced by changes in seismicity. These maps show an increasing trend in the north that may be indicative of an increase in earthquake and volcanic hazards.

Four papers are presented in this thesis each one reporting on studies relating to volcanic ash with special reference to soils. The first paper reviews a) some of the phenomena relating to the ejection and deposition of ash that are important in interpreting the significance of its occurrence, b) the significance of ash layers to workers in the Quaternary, c) the techniques available for the characterization and recognition of tephra, d) the literature on ash deposits in western Canada and compiles the noted occurrences. In addition this paper presents the data from a study to determine the amount of ash retained by soils within and beyond the major areas of deposition indicated in the literature. The presence of ash in soils was found to be widespread though the amounts present may be limited for identification purposes, in some cases. The second paper describes two soils derived from Bridge River volcanic ash and their underlying paleosols and presents selected physical and chemical analyses. The analyses indicate that in the youthful soils studied the physical properties of the ash soils are inherited from the parent material. The colloidal and chemical properties are initially imparted by organic matter with some influence from ash weathering products especially aluminum. Shallow surface additions of volcanic ash to soils influence soil properties to varying degrees depending on pedogenic environment and depth of material. The third paper evaluates a number of methods that have been used to identify podzolic B horizons and the influence of surface additions of volcanic ash on the podzolic characteristics of soils. Pyrophosphate, pyrophosphate dithionite, citrate dithionite bicarbonate extractions, phosphate sorption capacity and pH-dependent cation exchange capacity determinations all highlighted the podzol B horizons while acid ammonium oxalate extractions and pH determined in NaF did not. The presence of surface additions of Bridge River ash may influence acid ammonium Oxalate or NaF criteria but it was not found to reduce the value of the other diagnostic criteria examined in this study. The final paper studies the amorphous material and clay mineral characteristics of the two aforementioned soils and examines some of the methods of extraction and isolation of clay materials in soils. All of the chemical treatments applied to the soils were found to result in some dissolution of secondary and primary soil materials. The treatments used to extract amorphous materials indicated that the Si to Al ratios of extracted materials was greater than 2. As this value approaches 2 the formation of allophane and imogolite will take place. This situation is indicated as having taken place in isolated capillaries as evidenced by the limited occurrence of imogolite-like material. Chlorite is the dominant clay mineral in the ash soils and is believed to be the weathering product of primary biotite, horneblende and pyroxene. / Land and Food Systems, Faculty of / Graduate

M.Sc. / Please refer to full text to view abstract

During the long, dark night of a volcanic winter, a young man clashes with his father over the fate of five desperate survivors who have arrived outside the gates of the family compound. Yet he soon discovers true darkness lies within.