This dissertation explores the combination of Interferometric Synthetic Aperture Radar (InSAR) results with field data to provide additional constraints on the processes controlling deformation signals observed at Galeras volcano (Colombia) and Santorini volcano (Greece). InSAR measurements during 2007-2008 at Galeras reveal a subsidence signal on its northeast flank. I model InSAR and gravity data to determine the best-fit parameters for the subsidence source and suggest this signal was caused by deflation of the magma chamber associated with the January 2008 eruption. In January 2011, Santorini volcano entered a period of unrest characterised by earthquake swarms and caldera-wide uplift. I analyse satellite data over a period incorporating both the preceding phase of quiescence (1993-2010) and the phase of unrest (2011-2012). A subsidence signal is confirmed on the intra-caldera island of Nea Kameni during 1993-2010. I investigate several possible scenarios for its source, with my preferred explanation being a combination of cooling and contraction of historic lava flows, and loading from these flows inducing relaxation of the substrate. I also use a joint InSAR/GPS inversion technique to model the caldera-wide uplift observed during 2011-2012. I determine the optimal parameters for the deformation source and the temporal variation in volume change within the shallow magma chamber. The renewed activity offered an opportunity to observe how soil-gas emissions would respond to an influx of magma to a shallow reservoir. I employ a new approach (222Rn-δ¹³C systematics) to identify and quantify the source of diffuse degassing at Santorini during the period of unrest. Finally, I present a new high-resolution merged LiDAR-Bathymetry grid, enabling detailed mapping of both onshore and offshore historic lava flows emplaced in the centre of Santorini caldera. Updated lava volumes provide new extrusion rate estimates and a means of estimating both the size and duration of future dome-building eruptions at Santorini.

Surface displacements resulting from upper-crustal intrusion of melt are a paramount concern for communities and facilities located in or near active volcanic areas (e.g. Campi Flegrei, Yucca Mtn.). Study of active intrusions such as Campi Flegrei, Italy west of Mt. Vesuvius, is limited to remote observations through geophysical/geodetic procedures. While the surface displacement due to melt emplacement at depth can easily be determined, the geometries and depth of intrusions are often based on simplified assumptions (e.g. spheres and prolate or oblate ellipsoids). These models benefit from data constraining both the geometries of the individual intrusions, and the kinematics and mechanics of deformation within the superstructure overlying the intrusions. Mount Ellsworth, a partially exposed sub-volcanic system, is an ideal natural laboratory for the study of near surface intrusions. The intrusions of the Henry Mountains are ideal because they were emplaced into relatively flat-lying stratigraphy of the Colorado Plateau, at a time when the stress field was largely isotropic. Previous geologic work done in the Henry Mountains, conducted by C.B. Hunt (1953) and Marie Jackson and Dave Pollard (1988), presents competing emplacement models (i.e. large batch intrusion or incremental sill growth), as well as, differing geologic map data and interpretations. Through a combination of 1:5000 scale field mapping and profile-oriented gravity study, we have produced detailed geologic maps and cross sections of Mt. Ellsworth assess the previous work done on Mt. Ellsworth with new datasets, as well as, evaluate criteria refining various emplacement models. Mapping results demonstrate that several of the assumptions made in models theorized by Hunt (1953) and Jackson and Pollard (1988), were inappropriately applied on Mt. Ellsworth. These assumptions include the thickness and separation of stratigraphic units, the size and distribution of sills and smaller intrusions, structural attitudes of beds and sills, and the presence of exposure of the main body of the intrusion. Gravity data collected on similar intrusions presented in Corry (1988) demonstrates the difficulty of obtaining a gravity anomaly on the wavelength of the assumed size of the intrusion. Forward gravity modeling of various potential geometries beneath Mount Ellsworth suggests that the anomalies are similar in shape with a magnitude between 16 and 20 mGal. Results from the gravity profiles collected for this study fail to predict an anomaly on the wavelength of the Mount Ellsworth intrusion and record a much more complicated anomaly than is presented by the forward models. By combining the stratigraphic data, structural data, and cross sections, it can be determined that the Mount Ellsworth intrusion is a laccolith with a floor 1.5 kilometers beneath the topographic surface, is 1 kilometer thick at its maximum, and has dimensions of 4 kilometers wide by 6 kilometers long.

A series of analogue flume experiments are used to investigate initiation, flow and deposition of static piles of polymict materials, the sorting during transport, and the three dimensional geometry of the resulting deposits. Sequential charges are used to investigate the effects and extent of reworking. The particle heterogeneity is designed to simulate typical PDC make-up, with analogues for juvenile pumice and lithic clasts, as well as the fine-grained pumiceous material which makes up the bulk of the flow. Analogue flume experiments are used to investigate the generation of complex facies variations typical of pyroclastic density current (PDC) deposits. Polymict charges are developed to behave as analogues for the particle size and density contrasts present in PDC (i.e. lithic and juvenile pumice clasts), and investigate the effect of granular sorting during flow on the geometry of deposit architectures. Multiple charges are used to simulate pulses or sequences of separate PDC in order to assess the extent and effects of reworking. 3D visualisation of the resulting deposits reveals stratigraphies analogous to those seen in PDC, including pumice ‘rafting' or over-passing and inverse grading of pumice, and normal grading of lithics by simple gravitational granular sorting. Reworking between differentially-coloured layers makes several complex shear-derived Kelvin-Helmholtz instability features apparent, from fully developed rotational eddies, to less developed recumbent flame structures. The implications for the formation of these in PDC are assessed, including the potential influences on temperature proxy data, radiogenic dating by included phenocrysts (40Ar/39Ar) or charcoals (14C), calculation of eruptive volumes, sedimentation rates and flow velocity.

The volcanic stratigraphy and petrography is described for a 46 km2 area on the southern flank of Mount Jefferson in the north-central part of the Oregon High Cascades. Here, volcanic processes have been active throughout Quaternary time, resulting in complex stratigraphic relationships. In addition, three formerly recognized glaciations and a two-phase period of neoglaciation have eroded the terrain, depositing tills in contact or interstratified with the volcanic units. Collectively, these processes and the resulting deposits are characteristic of High Cascades development.

The world-class Buchans Mining Camp hosts a number of high-grade, low-tonnage volcanogenic massive sulfide (VMS) deposits. The Lundberg and Engine House zones form the lower-grade stockwork to the Lucky Strike deposit and have yet to be mined. A detailed study of the Lundberg and Engine House zones was conducted to establish the stratigraphic setting of the deposits, to determine the petrology of the host volcanic rocks and distribution of alteration facies, and to characterize the mineralization with the goal of improving exploration for polymetallic massive sulfide deposits in the Buchans camp.

The world-class Buchans Mining Camp hosts a number of high-grade, low-tonnage volcanogenic massive sulfide (VMS) deposits. The Lundberg and Engine House zones form the lower-grade stockwork to the Lucky Strike deposit and have yet to be mined. A detailed study of the Lundberg and Engine House zones was conducted to establish the stratigraphic setting of the deposits, to determine the petrology of the host volcanic rocks and distribution of alteration facies, and to characterize the mineralization with the goal of improving exploration for polymetallic massive sulfide deposits in the Buchans camp.

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.

The world-class Buchans Mining Camp hosts a number of high-grade, low-tonnage volcanogenic massive sulfide (VMS) deposits. The Lundberg and Engine House zones form the lower-grade stockwork to the Lucky Strike deposit and have yet to be mined. A detailed study of the Lundberg and Engine House zones was conducted to establish the stratigraphic setting of the deposits, to determine the petrology of the host volcanic rocks and distribution of alteration facies, and to characterize the mineralization with the goal of improving exploration for polymetallic massive sulfide deposits in the Buchans camp.

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.)--Aberdeen University, 2009. / Title from web page (viewed on June 3, 2009). Includes bibliographical references.