Lava flow hazards are one of the few constant themes across the wide spectrum of volcanic research in the solar system. These dynamic hazards are controlled by the location of the eruption, the topography and material properties of the land upon which the flow spreads, and the properties of the lava (e.g., volume, temperature, and rheology). Understanding the influences on eruption location and how lava flows modify the landscape are important steps to accurately forecast volcanic hazards. Three studies are presented in this dissertation that address di˙erent aspects of modeling and assessing vent opening and lava flow hazards. The first study uses hierarchical clustering to explore the distribution of activity at Craters of the Moon (COM) lava field on the eastern Snake River Plain (ESRP). Volcanism at COM is characterized by 53 mapped eruptive vents and 60+ lava flows over the last 15 ka. Temporal, spatial, and spatio-temporal clustering methods that examine different aspects of the distribution of volcanic vents are introduced. The sensitivity of temporal clustering to different criteria that capture the age range of magma generation and ascent is examined Spatial clustering is dictated by structures on the ESRP that attempt to capture the footprint of an emplacing dike. A combined spatio-temporal is the best approach to understanding the distribution of linked eruptive centers and can also provide insight into the evolution of volcanism for the region. Spatial density estimation is used to visualize the differences between these models. The goal of this work is to improve vent opening forecasting tools for use in assessing lava flow hazards. The second study presents a new probabilistic lava flow hazard assessment for the U.S. Department of Energy’s Idaho National Laboratory (INL) nuclear facility that (1) explores the way eruptions are defined and modeled, (2) stochastically samples lava flow parameters from observed values for use in MOLASSES, a lava flow simulator, (3) calculates the likelihood of a new vent opening within the boundaries of INL, (4) determines probabilities of lava flow inundation for INL through Monte Carlo simulation, and (5) couples inundation probabilities with recurrence rates to determine the annual likelihood of lava flow inundation for INL. Results show a 30% probability of partial inundation of the INL given an e˙usive eruption on the ESRP, with an annual inundation probability of 8.4×10^−5 to 1.8×10^−4. An annual probability of 6.2×10^−5 to 1.2×10^−4 is estimated for the opening of a new eruptive center within INL boundaries. The third study models thermo-mechanical erosion of a pyroclastic substrate by flow-ing lava on Volcán Momotombo, Nicaragua. It describes the unique morphology of a lava flow channel using TanDEM-X/TerraSAR-X and terrestrial radar digital elevation models. New methods for modeling paleotopography on steep-sided cones are introduced to mea-sure incision depths and document cross-channel profiles. The channel is incised ~35 m into the edifice at the summit and transitions into a constructional feature halfway down the ~1,300 m high cone. An eroded volume of ~4×10^5 m3 was calculated. It is likely that a lava flow eroded into the cone as it emplaced during an eruption in 1905. There is not suÿcient energy to thermally erode this volume, given the observed morphology of the flow. Models are tested that explore the relationship of shearing and material properties of the lava and substrate against measured erosion depths and find that thermo-mechanical erosion is the most likely mode of channel formation. Additionally, it is likely that all forms of erosion via lava flow are impacted by thermal conditions due to the relationship between temperature and substrate hardness. The evolution of these structures (their creation and subsequent infilling) plays an important role in the growth of young volcanoes and also controls future lava flows hazards, as seen by the routing of the 2015 flow into the 1905 channel.

Mafic eruptions have been the dominant form of volcanic activity in central Oregon throughout the Holocene. These eruptions have produced cinder cones, extensive lava flows, and tephra blankets. In most cases, the extent and volume of the tephra blankets has not been determined, despite the fact that future tephra production would pose considerable hazards to transportation, infrastructure, and public health. The economy of the region, which is largely based in tourism, would also be negatively impacted. For this reason, developing a better understanding of the extent and dynamics of tephra production at recent mafic vents is critical, both in terms of mitigating the hazards associated with future eruptions and in improving our scientific understanding of explosive mafic activity. Here I present detailed field and laboratory studies of tephra from recent mafic vents at Newberry Volcano and in the central Oregon High Cascades. Studies of Newberry vents show that eruption style is strongly correlated with eruptive volume, that extensive magma storage and assimilation occurred prior to the eruption of these vents, and that minimum pre-magmatic water content as recorded by plagioclase was 2.5 wt.%. Detailed mapping and physical studies of tephra deposits from High Cascades vents show that several recent eruptions produced extensive tephra deposits. These deposits are physically similar to well-documented historic eruptions that have been characterized as violent strombolian. At least one Cascade cinder cone (Sand Mountain) produced a tephra deposit that is unusually large in volume and characterized by uniformly fine-grained clasts, which is interpreted as evidence for syn-eruptive interaction with external water. Microtextural characteristics of tephra, along with an evaluation of possible water sources, support this interpretation. These investigations demonstrate that magma storage and eruption style at mafic vents is both variable and complex. Additionally, these studies show that cinder cones in central Oregon have the potential to erupt much more explosively than previously assumed. The results of this study will be an important tool for developing comprehensive regional hazard assessments. This dissertation includes previously published and unpublished co-authored material.

This thesis attempts to develop our understanding of volcanic magma plumbing systems and the magmatic processes that operate within them, such as fractional crystallisation, crustal partial melting, assimilation, and magma mixing. I utilise petrology, rock and mineral geochemistry, and isotope systematics to seek to improve our ability to forecast the eruptive frequency and style of active volcanoes, an aspect often lacking in current volcano monitoring efforts. In particular, magma reservoir dynamics are investigated from a mineral scale at Katla volcano in Iceland, to a sub-mineral scale at Merapi, Kelud, and Toba volcanoes in Indonesia. The magma plumbing architecture of Katla volcano on Iceland is explored in the first part of this thesis. Crystalline components within tephra and volcanic rock preserve a record of the physical and chemical evolution of a magma, and are analysed through oxygen isotopic and thermobarometric techniques to temporally constrain changes in reservoir depth and decode the petrogenesis of the lavas. We find both prolonged upper crustal magma storage and shallow level assimilation to be occurring at Katla. The results generated from combining these analytical strands reveal the potential for unpredictable explosive volcanism at this lively Icelandic volcano. The second part of this thesis examines the magma plumbing systems of Merapi, Kelud and Toba volcanoes of the Sunda arc in Indonesia at higher temporal and petrological resolution than possible for Katla (e.g., due to the crystal poor character of the rocks). For this part of the thesis, minerals were analysed in-situ to take advantage of sub-crystal scale isotopic variations in order to investigate processes of shallow-level assimilation in the build-up to particular eruptions. We find that intra-crystal analyses reveal an otherwise hidden differentiation history at these volcanoes, and establish a better understanding as to how they may have rapidly achieved a critical explosive state. The outcomes of this thesis therefore deepen our knowledge of evolutionary trends in magma plumbing system dynamics, and highlight the importance of understanding the geochemical processes that can prime a volcano for eruption. Lastly, I emphasise the vital contribution petrology can make in current volcano monitoring efforts.

Ruapehu is an active volcano located on the North Island of New Zealand, with the most recent major eruptions occurring in 1945, 1969, 1975, and 1995/96. Ruapehu is also home to the three major North Island ski areas, Whakapapa, Turoa, and Tukino. Because of the high frequency of eruptions, there is a significant volcanic hazard at the ski areas particularly from lahars which can form even after minor eruptions. Most recently, lahars have affected Whakapapa ski area in 1969, 1975, and 1995/96. The most significant risk at Turoa is from ballistic bombs due to the proximity of the top two T-Bars to the crater. Ash fall has also caused disruption at the ski areas, covering the snow and causing damage to structures. There is yet to be a death at the ski areas from a volcanic event; however the risk at the ski areas is too high to be completely ignored. The ski areas at Whakapapa and Turoa are currently operated by Ruapehu Alpine Lifts (RAL), who have been significantly improving their commitment to providing volcanic hazard training for their staff and preparing for handling a volcanic eruption. RAL is joined by the Institute of Geological Sciences (GNS) and the Department of Conservation (DoC) in trying to mitigate this risk through a range of initiatives, including an automated Eruption Detection System (EDS), linked to sirens and loudspeakers on Whakapapa ski areas, as well as by providing staff training and public education. The aim of this study was to provide RAL with recommendations to improve their staff training and warning system response. Staff induction week at both Turoa and Whakapapa ski areas was observed. Surveys were distributed and collected from staff at both ski areas, and interviews were conducted with staff at Whakapapa ski area. Data obtained from staff interviews and surveys provided the author with insight into staff's mental models regarding a volcanic event response. A simulation of the warning system was observed, as well as a blind test, to collect data on the effectiveness of training on staff response. Results indicated permanent and seasonal staff were knowledgeable of the volcanic hazards that may affect the ski areas, but had differing perspectives on the risk associated with those hazards. They were found to be confident in the initial response to a volcanic event (i.e. move to higher ground), but were unsure of what would happen after this initial response. RAL was also found to have greatly improved their volcanic hazard training in the past year, however further recommendations were suggested to increase training effectiveness. A training needs analysis was done for different departments at the ski areas by taking a new approach of anticipating demands staff may encounter during a volcanic event and complementing these demands with existing staff competencies. Additional recommendations were made to assist RAL in developing an effective plan to use when responding to volcanic events, as well as other changes that could be made to improve the likelihood of customer safety at the ski areas during an eruption.

This thesis presents a new GIS-based scenario volcanic risk assessment model called RiskScape Volcano (RSV) that has been designed for the RiskScape program to advance the field of volcanic risk assessment. RiskScape is a natural hazards risk assessment software tool being developed in New Zealand by GNS Science and NIWA. When integrated into RiskScape, RSV will add proximal volcanic hazard risk assessment capability, and enhanced inventory design; it presently operates outside of RiskScape by combining volcanic hazard models’ output spatial hazard intensity (hazard maps) with inventory databases (asset maps) in GIS software to determine hazard exposure, which is then combined with fragility functions (relationships between hazard intensity and expected damage ratios) to estimate risk. This thesis consists of seven publications, each of which comprises a part of the development and testing of RSV: 1) results of field investigation of impacts to agriculture and infrastructure of the 2006 eruption of Merapi Volcano, Indonesia; 2) agricultural fragility functions for tephra damage in New Zealand based on the observations made at Merapi; 3) examination of wind patterns above the central North Island, New Zealand for better modeling of tephra dispersal with the ASHFALL model; 4) a description of the design, components, background, and an example application of the RSV model; 5) test of RSV via a risk assessment of population, agriculture, and infrastructure in the Rotorua District from a rhyolite eruption at the Okataina Volcanic Centre; 6) test of RSV via a comparison of risk to critical infrastructure in Mammoth Lakes, California from an eruption at Mammoth Mountain volcano versus an eruption from the Inyo craters; and 7) a survey of volcanic hazard awareness in the tourism sector in Mammoth Lakes. Tests of the model have demonstrated that it is capable of providing valid and useful risk assessments that can be used by local government and emergency management to prioritise eruption response planning and risk mitigation efforts. RSV has provided the RiskScape design team with a more complete quantitative volcanic risk assessment model that can be integrated into RiskScape and used in New Zealand and potentially overseas.

Ruapehu is an active volcano located on the North Island of New Zealand, with the most recent major eruptions occurring in 1945, 1969, 1975, and 1995/96. Ruapehu is also home to the three major North Island ski areas, Whakapapa, Turoa, and Tukino. Because of the high frequency of eruptions, there is a significant volcanic hazard at the ski areas particularly from lahars which can form even after minor eruptions. Most recently, lahars have affected Whakapapa ski area in 1969, 1975, and 1995/96. The most significant risk at Turoa is from ballistic bombs due to the proximity of the top two T-Bars to the crater. Ash fall has also caused disruption at the ski areas, covering the snow and causing damage to structures. There is yet to be a death at the ski areas from a volcanic event; however the risk at the ski areas is too high to be completely ignored. The ski areas at Whakapapa and Turoa are currently operated by Ruapehu Alpine Lifts (RAL), who have been significantly improving their commitment to providing volcanic hazard training for their staff and preparing for handling a volcanic eruption. RAL is joined by the Institute of Geological Sciences (GNS) and the Department of Conservation (DoC) in trying to mitigate this risk through a range of initiatives, including an automated Eruption Detection System (EDS), linked to sirens and loudspeakers on Whakapapa ski areas, as well as by providing staff training and public education. The aim of this study was to provide RAL with recommendations to improve their staff training and warning system response. Staff induction week at both Turoa and Whakapapa ski areas was observed. Surveys were distributed and collected from staff at both ski areas, and interviews were conducted with staff at Whakapapa ski area. Data obtained from staff interviews and surveys provided the author with insight into staff's mental models regarding a volcanic event response. A simulation of the warning system was observed, as well as a blind test, to collect data on the effectiveness of training on staff response. Results indicated permanent and seasonal staff were knowledgeable of the volcanic hazards that may affect the ski areas, but had differing perspectives on the risk associated with those hazards. They were found to be confident in the initial response to a volcanic event (i.e. move to higher ground), but were unsure of what would happen after this initial response. RAL was also found to have greatly improved their volcanic hazard training in the past year, however further recommendations were suggested to increase training effectiveness. A training needs analysis was done for different departments at the ski areas by taking a new approach of anticipating demands staff may encounter during a volcanic event and complementing these demands with existing staff competencies. Additional recommendations were made to assist RAL in developing an effective plan to use when responding to volcanic events, as well as other changes that could be made to improve the likelihood of customer safety at the ski areas during an eruption.

This thesis presents a new GIS-based scenario volcanic risk assessment model called RiskScape Volcano (RSV) that has been designed for the RiskScape program to advance the field of volcanic risk assessment. RiskScape is a natural hazards risk assessment software tool being developed in New Zealand by GNS Science and NIWA. When integrated into RiskScape, RSV will add proximal volcanic hazard risk assessment capability, and enhanced inventory design; it presently operates outside of RiskScape by combining volcanic hazard models’ output spatial hazard intensity (hazard maps) with inventory databases (asset maps) in GIS software to determine hazard exposure, which is then combined with fragility functions (relationships between hazard intensity and expected damage ratios) to estimate risk. This thesis consists of seven publications, each of which comprises a part of the development and testing of RSV: 1) results of field investigation of impacts to agriculture and infrastructure of the 2006 eruption of Merapi Volcano, Indonesia; 2) agricultural fragility functions for tephra damage in New Zealand based on the observations made at Merapi; 3) examination of wind patterns above the central North Island, New Zealand for better modeling of tephra dispersal with the ASHFALL model; 4) a description of the design, components, background, and an example application of the RSV model; 5) test of RSV via a risk assessment of population, agriculture, and infrastructure in the Rotorua District from a rhyolite eruption at the Okataina Volcanic Centre; 6) test of RSV via a comparison of risk to critical infrastructure in Mammoth Lakes, California from an eruption at Mammoth Mountain volcano versus an eruption from the Inyo craters; and 7) a survey of volcanic hazard awareness in the tourism sector in Mammoth Lakes. Tests of the model have demonstrated that it is capable of providing valid and useful risk assessments that can be used by local government and emergency management to prioritise eruption response planning and risk mitigation efforts. RSV has provided the RiskScape design team with a more complete quantitative volcanic risk assessment model that can be integrated into RiskScape and used in New Zealand and potentially overseas.

Les groupes ethniques minoritaires sont parmi les secteurs de la société qui sont menacés en permanence par des risques plus élevés de catastrophes. Le fondement d'un tel constat est les impacts négatifs disproportionnés de catastrophes passées. Il est de ce fait nécessaire d'intégrer tous les groupes ethniques en particuliers les minorités dans la réduction des risques de catastrophe (RRC). Pourtant, la communauté scientifique a peu étudié le rôle de l’ethnicité dans la vulnérabilité et la capacité des populations exposées à divers aléas. Ainsi les praticiens sur le terrain et les organisations non-gouvernementales (ONG), ne possèdent pas de méthodes et d’outils appropriés pour intégrer les minorités ethniques dans la RRC. En plus, des exemples de méthodologies et de politiques visant à rendre cet objectif opérationnel et institutionnalisés sont également limités. Cette étude vise à répondre à ces lacunes, en prenant l’exemple des communautés multiethniques autour de Mont Kanlaon situé sur l'île de Negros aux Philippines. La zone d'étude se caractérise par une grande diversité ethnique composé d'au moins trois grands groupes ethniques (Ilonggos, Cebuanos et Bukidnons). Les résultats de cette étude suggèrent que cette mosaïque constitue une dimension importante de la RRC puisque chaque groupe ethnique possède ses propres formes de vulnérabilité et de capacité face aux aléas volcaniques et d’autres origines. Ces minorités ethniques sont parmi les secteurs les plus vulnérables de la société philippine en raison de leur statut marginalisés. En outre, les résultats de cette étude suggèrent que chaque groupe ethnique possède des capacités issues en grande partie de ressources locales qui sont utiles aux fins de la RRC. / The ethnic minority groups are among the sectors of the society who are permanently threatened by higher risk of disasters. The basis of such claim is the disproportionate negative impacts of both major and minor disasters. There is thus a pressing need to integrate ethnic minority groups in disaster risk reduction (DRR). However, within the scientific community, there are limited studies in the current literature of disaster that investigated the role of ethnicity in shaping the vulnerability and capacity of the ethnic groups. The authorities, non-government organizations (NGOs), and researchers have limited defined methods and tools to make such as objective operational in the field. Finally, plans, actions and policies to make such objective institutionalized are also limited. This study aimed to fulfill those gaps. The study has adapted an integrated DRR framework and a methodology that follows the ideals and principles of Community-Based Disaster Risk Reduction (CBDRR). The present study focuses on the multiethnic communities surrounding Mt. Kanlaon located in the island of Negros, Philippines. The study area is characterized by a great ethnic diversity composed of at least three major ethnic groups (Ilonggos, Cebuanos, and Bukidnons). The results of the study suggest that this ethnic mosaic constituted a major dimension of DRR because each ethnic group portrays different vulnerabilities and capacities in the face of volcanic hazards and other natural hazards. These ethnic minorities are among the most vulnerable sectors of the Philippine society due to their marginalized and minority status. In addition, the results of this study also suggest that each ethnic group possesses capacities derived from local resources that are useful for the purpose of DRR.

Pendant une éruption volcanique sur des sommets englacés, des coulées de débris syn-eruptifs,dénommées lahars, peuvent être générées par la fonte partiale de glaciers. Ce phénomène estbien connu sur le volcan Cotopaxi, Equateur. La présente étude concerne trois vallées et un cônede déjection sur le flanc sud-ouest de ce volcan. Une première analyse a été conduite par relevésde formes géomorphologiques dans ces vallées qui témoignent des processus d’érosion et desédimentation lors du passage de lahars dans le passé, notamment ceux du dernier événementéruptif datant de 1877 AD. Bien que les types des formes géomorphologiques déterminées sontles mêmes, leur distribution spatiale varie d’une vallée à l’autre en fonction d’une interaction deparamètres morphologiques locaux. Les conditions environnementales individuelles déterminentégalement le volume de l’écoulement, paramètre crucial dans la délimitation de zones de risques delahars dans les plaines adjacentes. Pour cela, une deuxième étude a été menée à grande échelle surle cône de déjection à l’exutoire de la vallée la plus au Sud des trois. Une analyse intégrale de la morphologiede surface et des affleurements naturels a été complétée par des données stratigraphiquesde subsurface obtenues via un sondage avec un Géoradar. Reconstituer l’architecture sédimentairede ce cône permet de visualiser la distribution spatiale de formes érosives et de dépôts. L’étude àrévélé que différentes parties du cône sont actives à des moments distincts et les épaisseurs dedépôts de lahars sont variables en fonction du type d’écoulement et de son volume. Ceci permetde relier les dynamiques géomorphologiques des plaines alluviales aux zones d’initiation de laharssur les flancs du volcan. Enfin, cette étude a débouché sur la mise en place d’une nouvelle fonctiondans le logiciel de modélisation de lahars LAHARZ prenant en compte l’incorporation progressive desédiment dans un contexte érosif dans les vallées, ce qui permet une meilleure délimitation de zonesde risque de lahars sur le cône. / During a volcanic eruption at ice capped volcanoes, syn-eruptive volcanic debris flows, lahars, canbe triggered through the partial melting of the glaciers. This phenomenon is well known to have happenedat Cotopaxi volcano, Ecuador, where the present study has been realized. The latter concernsthree drainages on the southwestern flank of the volcano and one alluvial fan. A first analysis hasbeen conducted assessing geomorphologic features in the drainages testifying from erosional anddepositional processes during past lahars, in particular of those generated during the last eruptiveevent dating back to 1877 AD. Although the types of determined geomorphologic features are thesame, their spatial distribution varies among the three valleys as a function of an interplay of localmorphologic parameters. The individual environmental conditions determine also the flow volumeof such lahars, a critical parameter when to delineating hazard zones in the adjacent lowlands. Thesecond analysis has therefore be performed at large scale on the alluvial fan forming at the mouthof the southernmost of the three drainages. An integral study of the surface morphology and naturalexposures was enriched with subsurface stratigraphic information obtained through a ground penetratingradar survey. The sediment architecture of the fan provides valuable insights on the distributionof erosional features and deposits. Different fan parts appear to be active at different times andlahar deposit thicknesses are highly variable as a function of flow type and volume. This allows torelate floodplain dynamics to the initiation zone of lahars on the upper flanks of the volcano. At last,this research led to integrate a new bulking function acknowledging for erosional processes in thevalleys into the lahar-modeling software LAHARZ allowing to better delineate lahar hazard zones onthe fan.

Tephra deposits are one of the possible outcomes of explosive volcanic eruptions and are the result of vertical settling of volcanic particles that have been expelled from the volcanic vent into the atmosphere, following magma fragmentation within the volcanic conduit. Tephra fallout represents the main volcanic hazard to populated areas and critical facilities. Therefore, it is crucial to better understand processes that lead to tephra transport, sedimentation and hazards. In this study, and based on detailed mapping and sampling of the tephra deposit of the 2450 BP Plinian eruption of Pululagua volcano (Ecuador), I investigate tephra deposits through a variety of approaches, including empirical and analytical modeling of tephra thickness and grain size data to infer important eruption source parameters (e.g. column height, total mass ejected, total grain size distribution of the deposit). I also use a statistical approach (smoothed bootstrap with replacement method) to assess the uncertainty in the eruptive parameters. The 2450 BP Pululagua volcanic plume dynamics were also explored through detailed grain size analysis and 1D modeling of tephra accumulation. Finally, I investigate the influence of particle shape on tephra accumulation on the ground through a quantitative and comprehensive study of the shape of volcanic ash. As the global need for energy is expected to grow in the future, many future natural hazard studies will likely involve the assessment of volcanic hazards at critical facilities, including nuclear power plants. I address the potential hazards from tephra fallout, pyroclastic flows and lahars for the Bataan Nuclear Power Plant (Philippines) posed by three nearby volcanoes capable of impacting the site during an explosive eruption. I stress the need for good constraints (stratigraphic analysis and events dating) on past eruptive events to better quantify the probability of future events at potentially active volcanoes, the need for probabilistic approaches in such volcanic hazard assessments to address a broad range of potential eruption scenarios, and the importance of considering coupled volcanic processes (e.g. tephra fallout leading to lahars) in volcanic hazard assessments.