Surface displacement at volcanic edifices is related to subsurface processes associated with magma movements, fluid transfers within the volcano edifice and gravity-driven deformation processes. Understanding of associated ground displacements is of importance for assessment of volcanic hazards. For example, volcanic unrest is often preceded by surface uplift, caused by magma intrusion and followed by subsidence, after the withdrawal of magma. Continuous monitoring of the surface displacement at volcanoes therefore might allow the forecasting of upcoming eruptions to some extent. In geophysics, the measured surface displacements allow the parameters of possible deformation sources to be estimated through analytical or numerical modeling. This is one way to improve the understanding of subsurface processes acting at volcanoes. Although the monitoring of volcanoes has significantly improved in the last decades (in terms of technical advancements and number of monitored volcanoes), the forecasting of volcanic eruptions remains puzzling. In this work I contribute towards the understanding of the subsurface processes at volcanoes and thus to the improvement of volcano eruption forecasting. I have investigated the displacement field of Llaima volcano in Chile and of Tendürek volcano in East Turkey by using synthetic aperture radar interferometry (InSAR). Through modeling of the deformation sources with the extracted displacement data, it was possible to gain insights into potential subsurface processes occurring at these two volcanoes that had been barely studied before. The two volcanoes, although of very different origin, composition and geometry, both show a complexity of interacting deformation sources. At Llaima volcano, the InSAR technique was difficult to apply, due to the large decorrelation of the radar signal between the acquisition of images. I developed a model-based unwrapping scheme, which allows the production of reliable displacement maps at the volcano that I used for deformation source modeling. The modeling results show significant differences in pre- and post-eruptive magmatic deformation source parameters. Therefore, I conjecture that two magma chambers exist below Llaima volcano: a post-eruptive deep one and a shallow one possibly due to the pre-eruptive ascent of magma. Similar reservoir depths at Llaima have been confirmed by independent petrologic studies. These reservoirs are interpreted to be temporally coupled. At Tendürek volcano I have found long-term subsidence of the volcanic edifice, which can be described by a large, magmatic, sill-like source that is subject to cooling contraction. The displacement data in conjunction with high-resolution optical images, however, reveal arcuate fractures at the eastern and western flank of the volcano. These are most likely the surface expressions of concentric ring-faults around the volcanic edifice that show low magnitudes of slip over a long time. This might be an alternative mechanism for the development of large caldera structures, which are so far assumed to be generated during large catastrophic collapse events. To investigate the potential subsurface geometry and relation of the two proposed interacting sources at Tendürek, a sill-like magmatic source and ring-faults, I have performed a more sophisticated numerical modeling approach. The optimum source geometries show, that the size of the sill-like source was overestimated in the simple models and that it is difficult to determine the dip angle of the ring-faults with surface displacement data only. However, considering physical and geological criteria a combination of outward-dipping reverse faults in the west and inward-dipping normal faults in the east seem to be the most likely. Consequently, the underground structure at the Tendürek volcano consists of a small, sill-like, contracting, magmatic source below the western summit crater that causes a trapdoor-like faulting along the ring-faults around the volcanic edifice. Therefore, the magmatic source and the ring-faults are also interpreted to be temporally coupled. In addition, a method for data reduction has been improved. The modeling of subsurface deformation sources requires only a relatively small number of well distributed InSAR observations at the earth’s surface. Satellite radar images, however, consist of several millions of these observations. Therefore, the large amount of data needs to be reduced by several orders of magnitude for source modeling, to save computation time and increase model flexibility. I have introduced a model-based subsampling approach in particular for heterogeneously-distributed observations. It allows a fast calculation of the data error variance-covariance matrix, also supports the modeling of time dependent displacement data and is, therefore, an alternative to existing methods. / Oberflächenverschiebungen an Vulkanen können einerseits durch unterirdische Magmen- oder Fluidbewegungen oder andererseits durch Gravitation verursacht werden. So sind insbesondere vor Eruptionen oft Aufwölbungen an Vulkanen zu beobachten, verursacht durch Magmenintrusion in die Erdkruste. Nach Eruptionen hingegen sinkt das Vulkangebäude aufgrund von Magmenextrusion wieder. Kontinuierliche Messungen an Vulkanen ermöglichen es, Eruptionen teilweise bis auf wenige Tage vorherzusagen. Die gemessenen Oberflächenverschiebungen können in analytischen oder numerischen Modellierungen genutzt werden, um Parameter eines möglichen Quellprozesses abzuschätzen. Auf diese Art und Weise kann das Verständnis über die unterirdischen Prozesse, die an Vulkanen stattfinden, verbessert werden. Obwohl es in den letzten Jahrzehnten eine enorme Entwicklung und Verbesserung der Überwachung von Vulkanen gab, sind viele Vorhersagen sehr vage und ungenau. Mit dieser Arbeit möchte ich einen Beitrag zum Verständnis von unterirdischen Prozessen an Vulkanen und auf lange Sicht gesehen, zur Vorhersage von Eruptionen leisten. Ich habe die Vulkane, Llaima in Chile und Tendürek im Osten der Türkei, mit Hilfe der Interferometrie von Radardaten (InSAR) untersucht. Die somit gemessenen Verschiebungen an der Erdoberfläche ermöglichen es, durch Modellierung der möglichen Deformationsquellen, Informationen über die Untergrundstrukturen dieser beiden bisher kaum erforschten Vulkane zu bekommen. Obwohl unterschiedlich in Aufbau, Gesteinszusammensetzung und Entstehung, zeigen beide Vulkane Anzeichen dafür, dass jeweils mehrere interagierende Deformationsquellen im Untergrund existieren. Am Vulkan Llaima war es schwierig, aufgrund der starken Dekorrelation des Radarsignals zwischen den Satellitenaufnahmen, die InSAR Methode anzuwenden. Ich entwickelte eine Methode um die doppeldeutigen relativen Phasenwerte der Interferogramme modellbasiert in eindeutige relative Phasenwerte umzurechnen. Die damit erzeugten Oberflächenverschiebungskarten am Vulkan eigneten sich nun für eine anschließende Modellierung der Deformationsquelle. Die Modellierungsergebnisse zeigen signifikante Unterschiede zwischen den Parametern der präeruptiven- und posteruptiven Deformationsquellen. Demzufolge könnten zwei unterschiedliche, interagierende Magmenkammern unter Llaima existieren, eine tiefe, posteruptiv aktive Kammer und eine flache, durch den Aufstieg von Magma präeruptiv aktive Kammer. Am Vulkan Tendürek ist eine langfristige, kontinuierliche Senkung des Vulkangebäudes zu beobachten, die mit einem großen, aufgrund von Kühlung sich kontrahierenden, magmatischen Sill, erklärbar ist. Unter Hinzunahme von hochauflösenden, optischen Daten jedoch, sind bei genauerer Untersuchung bogenförmige Strukturen an der Erdoberfläche sichtbar. Diese sind Anzeichen dafür, dass Verwerfungen existieren, die das gesamte Vulkangebäude in einem elliptischen Ring umgeben. Dabei ist zu beobachten, dass die Ringstörungen über Jahrtausende, möglicherweise sogar kontinuierlich, geringe Magnituden von Versatz aufweisen. Bei langer, kontinuierlicher Aktivität über mehrere zehntausende von Jahren, könnte dies ein weiterer Mechanismus zur Entstehung von Calderastrukturen an Vulkanen darstellen, der jedoch sehr langsam verläuft. Im Gegensatz dazu ist die heutige weit verbreitete Auffassung, dass Calderen als Folge katastrophaler Einstürze von Vulkangebäuden entstehen. Um zu untersuchen welche Geometrie die vorgeschlagenen Strukturen Sill und Ringstörungen an Tendürek im Untergund haben könnten, vollführte ich eine weitaus komplexere numerische Modellierung. Diese zeigt, dass die Größe des Sills ohne Berücksichtigung der Ringstörung um ein Vielfaches überschätzt ist. Die Orientierung und Geometrie der Ringstörungen ist jedoch nicht eindeutig nur mit Oberflächenverschiebungsdaten auflösbar. Unter der Berücksichtigung von geologischen und physikalischen Gesichtspunkten sind nach Außen einfallende Aufschiebungen im Westen und nach Innen einfallende Abschiebungen im Osten die plausibelste Erklärung. Außerdem habe ich eine Methode zur Datenreduzierung entwickelt. Abhängig vom zu untersuchenden Prozess sind für die Modellierung von unterirdischen Deformationsquellen verhältnismäßig wenige gut verteilte Messpunkte an der Erdoberfläche ausreichend. Satelliten gestützte Radaraufnahmen haben jedoch oft mehrere Millionen dieser Punkte. Deshalb müssen diese riesigen Datensätze auf eine Art und Weise reduziert werden, dass keine oder nur möglichst wenige Informationen verloren gehen. Für diesen Zweck habe ich, ausgehend von einem existierenden Algorithmus, eine modellbasierte Methode zur Reduzierung von besonders heterogen verteilten Oberflächendaten entwickelt. Diese Methode ist besonders gut auf Zeitreihendatensätze anwendbar und stellt somit eine Alternative zu existierenden Algorithmen dar.

Volcanic activity, and the resultant deposits and structures at the Earth's surface, are the outcome of the inner workings of underground magmatic plumbing systems. These systems, essentially, consist of magma reservoirs which supply magma to the surface through volcanic conduits feeding volcanic eruptions. The mechanics and structure of plumbing systems remain largely unknown due to the obvious challenges involved in inferring volcanic processes occurring underground from observations at the surface. Nevertheless, volcanologists are beginning to gain a deeper understanding of the workings and architecture of magmatic plumbing systems from geophysical observations on active volcanoes, as well as from geological studies of the erosional remnants of ancient volcanic systems. In this work, I explore the relationship between the structure and mechanics of shallow plumbing systems and the volcanic eruptions these systems produce. I attempt to contribute to the understanding of this complex relationship by linking geological and geophysical observations of an eroded basaltic subvolcanic system, and the eruptive and tectonic activity of an active volcano, with mathematical models of magma ascent and stress transfer. The remarkable exposures of the Carmel outcrop intrusions, near the San Rafael swell, southeast Utah, U. S. A., allow detailed geological and geophysical observations of the roots of volcanic conduits that emerge from a subhorizontal magma feeder reservoir. These observations reveal a new mechanism for magma ascent and eruption triggering through gravitational instabilities created from an underlying feeding sill, and shed light on the mechanics of sill emplacement. Geophysical and geological observations of the 1999 and xii 1992 eruptions of the Cerro Negro volcano, Nicaragua, are used to explore the coupling between changes in the stress field and the triggering of volcanic eruptions, and magma ascent through the shallow crust. Modeling results of stress transfer and conduit flow highlight the importance of the surrounding stress field and geometry of the volcanic conduits that comprise shallow plumbing systems.

Ce manuscrit de thèse résume trois ans de travaux sur l’utilisation des méthodes d’apprentissage statistique pour l’analyse automatique de signaux naturels. L’objectif principal est de présenter des outils efficaces et opérationnels pour l’analyse de signaux environnementaux, en vue de mieux connaitre et comprendre l’environnement considéré. On se concentre en particulier sur les tâches de détection et de classification automatique d’événements naturels.Dans cette thèse, deux outils basés sur l’apprentissage supervisé (Support Vector Machine et Random Forest) sont présentés pour (i) la classification automatique d’événements, et (ii) pour la détection et classification automatique d’événements. La robustesse des approches proposées résulte de l’espace des descripteurs dans lequel sont représentés les signaux. Les enregistrements y sont en effet décrits dans plusieurs espaces: temporel, fréquentiel et quéfrentiel. Une comparaison avec des descripteurs issus de réseaux de neurones convolutionnels (Deep Learning) est également proposée, et favorise les descripteurs issus de la physique au détriment des approches basées sur l’apprentissage profond.Les outils proposés au cours de cette thèse sont testés et validés sur des enregistrements in situ de deux environnements différents : (i) milieux marins et (ii) zones volcaniques. La première application s’intéresse aux signaux acoustiques pour la surveillance des zones sous-marines côtières : les enregistrements continus sont automatiquement analysés pour détecter et classifier les différents sons de poissons. Une périodicité quotidienne est mise en évidence. La seconde application vise la surveillance volcanique : l’architecture proposée classifie automatiquement les événements sismiques en plusieurs catégories, associées à diverses activités du volcan. L’étude est menée sur 6 ans de données volcano-sismiques enregistrées sur le volcan Ubinas (Pérou). L’analyse automatique a en particulier permis d’identifier des erreurs de classification faites dans l’analyse manuelle originale. L’architecture pour la classification automatique d’événements volcano-sismiques a également été déployée et testée en observatoire en Indonésie pour la surveillance du volcan Mérapi. Les outils développés au cours de cette thèse sont rassemblés dans le module Architecture d’Analyse Automatique (AAA), disponible en libre accès. / This manuscript summarizes a three years work addressing the use of machine learning for the automatic analysis of natural signals. The main goal of this PhD is to produce efficient and operative frameworks for the analysis of environmental signals, in order to gather knowledge and better understand the considered environment. Particularly, we focus on the automatic tasks of detection and classification of natural events.This thesis proposes two tools based on supervised machine learning (Support Vector Machine, Random Forest) for (i) the automatic classification of events and (ii) the automatic detection and classification of events. The success of the proposed approaches lies in the feature space used to represent the signals. This relies on a detailed description of the raw acquisitions in various domains: temporal, spectral and cepstral. A comparison with features extracted using convolutional neural networks (deep learning) is also made, and favours the physical features to the use of deep learning methods to represent transient signals.The proposed tools are tested and validated on real world acquisitions from different environments: (i) underwater and (ii) volcanic areas. The first application considered in this thesis is devoted to the monitoring of coastal underwater areas using acoustic signals: continuous recordings are analysed to automatically detect and classify fish sounds. A day to day pattern in the fish behaviour is revealed. The second application targets volcanoes monitoring: the proposed system classifies seismic events into categories, which can be associated to different phases of the internal activity of volcanoes. The study is conducted on six years of volcano-seismic data recorded on Ubinas volcano (Peru). In particular, the outcomes of the proposed automatic classification system helped in the discovery of misclassifications in the manual annotation of the recordings. In addition, the proposed automatic classification framework of volcano-seismic signals has been deployed and tested in Indonesia for the monitoring of Mount Merapi. The software implementation of the framework developed in this thesis has been collected in the Automatic Analysis Architecture (AAA) package and is freely available.

Le Permien et le Trias (ca. 300 à 200 Ma) sont caractérisés par une réorganisation globale de la dynamique des enveloppes externes de la Terre et en particulier de la biosphère qui traverse l'une de ses plus grandes crises à la transition entre le Permien le Trias. L'évaluation du rôle du domaine Est Téthysien (actuelle Asie du Sud Est) dans les perturbations des enveloppes externes est mal établie en raison d'une mauvaise compréhension de son évolution paléogéographique au Permien et au Trias. Des éléments nouveaux sur la paléogéographie et l'évolution géodynamique du domaine Est Téthysien ont été déduits d'analyses sédimentologiques, géochronologiques et géochimiques réalisées dans les bassins sédimentaires de Luang Prabang (Laos), Sam Nua et Song Da (Nord du Vietnam). Ces études ont montré qu'un ensemble continental majeur du domaine Est Téthysien, le bloc Indochinois, est bordé par deux zones de subduction au Permien supérieur et au Trias inférieur, puis entre en collision avec le bloc Chine du Sud au Trias moyen tandis que le fonctionnement de l'autre zone de subduction, au niveau du Bassin de Luang Prabang, se poursuit jusqu'au Trias supérieur. Les arcs magmatiques liés à la présence des zones de subductions représentaient alors probablement des reliefs topographiques importants dans une zone située à faible latitude. La présence d'un écosystème continental relativement diversifié au Trias inférieur dans le Bassin de Luang Prabang suggère que ces reliefs aient pu constituer des zones refuges favorables au maintient et/ou au renouvellement de la biosphère lors de la crise biologique permo-triasique. / The Permian and the Triassic (ca. 300 to 200 Ma) are characterized by a global change that has impacted the hydrosphere, the atmosphere and especially the biosphere that has underwent one of its biggest crisis at the permian-triassic boundary. Assessing the role of the East Tethyan domain (present day South East Asia) in the reorganization of the biosphere is hampered by a poor understanding of its paleogeographic evolution. Examination of the Luang Prabang Basin (Laos) Sam Nua and Song Da Basin (Vietnam) using sedimentological, geochronological and geochemical analysis brings new information about the geodynamic evolution of the Indochina bloc. These studies revealed the existence of two subduction zones bordering the Indochina bloc during the Late Permian and the Early Triassic, followed by a collision with the Indochina bloc during the Middle Triassic while the other subduction zone was still active up to the Late Triasic. The magmatic arcs related to the subduction zones might have representedimportant topographic heights in an area located at a low latitude. The occurrence of a rather diversified continental ecosystem in the Luang Prabang Basin during the Lower Triassic suggests that these topographic heights could have formed a refuge zone suitable to the maintaining and/or the recovery of the biosphere during or slightly after the Permian-triassic biotic crisis.

Two-thirds of submarine volcanism in the Earth's ocean basins is manifested along mid-ocean ridges and the remaining one-third is revealed along intraoceanic arcs and seamounts. Hydrothermal systems and the circulation patterns associated with these volcanic settings remove heat from the solid Earth into the deep ocean. Hydrothermal circulation continues to remove and redistribute heat in the crust as it ages. The heat and mass fluxes added to the deep ocean influence mixing in the abyssal ocean thereby affecting global thermohaline circulation. In addition to removing heat, hydrothermal processes extract chemical components from the oceanic and carry it to the surface of the ocean floor, while also removing certain elements from seawater. The resulting geochemical cycling has ramifications on the localized mineral deposits and also the biota that utilize these chemical fluxes as nutrients. In this dissertation, I analyze observed conductive heat flow measurements in the Panama Basin and borehole thermal measurements in Brothers Volcano and use mathematical models to estimate advective heat and mass fluxes, and crustal permeability. In the first manuscript, I use a well-mixed aquifer model to explain the heat transport in a sediment pond in the inactive part of the Ecuador Fracture Zone. This model yields mass fluxes and permeabilities similar to estimates at young upper oceanic crust suggesting vigorous convection beneath the sediment layer. In the second manuscript, I analyze the conductive heat flow measurements made in oceanic between 1.5 and 5.7 Ma on the southern flank of the Costa Rica Rift. These data show a mean conductive heat deficit of 70%, and this deficit is explained by various hydrothermal advective transport mechanisms, including outcrop to outcrop circulation, transport through faults, and redistribution of heat by flow of hydrothermal fluids in the basement. In the third manuscript, I analyze the borehole temperature logs for two sites representative of recharge and discharge areas of hydrothermal systems in the Brothers Volcano. I develop upflow and downflow models for fluids in the borehole and formation resulting in estimated of flow rates and permeabilities. All three independent research works are connected by the common thread of utilizing relatively simple mathematical concepts to get new insights into hydrothermal processes in oceanic crust. / PHD / Two-thirds of underwater volcanic activity in the Earth’s ocean basins is exhibited in areas where new material for Earth’s outer shell is created and the remaining one-third is displayed along areas where the outer shell is destroyed. In these areas, hot springs that are under water and their water movement patterns remove heat from the solid outer shell and puts it into the deepest parts of the ocean. Hot water circulation continues to remove and redistribute heat and various chemical elements in the shell as it grows old. This heat and chemical elements, which get added to the deep ocean water, influences the way water mixes and forms layers in the world oceans. This also affects the movement of ocean currents. The chemical elements removed from the shell by hot water gets deposited as minerals on the ocean floor in places where hot springs arise. This variety of minerals provides nutrients for different marine organisms. In this work done during my PhD studies, I examine the heat and temperature that was measured in the Panama Basin and Brothers Volcano. I utilize these examinations to build simple math models to find out how much heat and chemical components are being added to the deep ocean water. I also find out the methods in which the hot water springs appear on the ocean floor and the patterns in which the hot water circulates in the Earth’s outer shell. All of these estimates will help the scientists who are studying the patterns and changes in ocean currents by giving them a number on how much heat is released from the inside of the Earth.

Fractional crystallization, magma mixing, assimilation of continental crust, and how those processes modify volatile budgets, control the evolution of magma. As a consequence, the understanding of these processes, their magnitudes, and timescales is critical for interpreting ancient magma systems, their eruptions, and the potential future volcanic activity. In this dissertation I present the results of three projects. The first explores how magmatic processes affect magma reservoirs and eruption dynamics. The second explores where in the storage system and how often these processes occur. The third explores how volatile budgets are modified by processes such as crystallization, mixing, and assimilation. Volcán Popocatépetl (central México) erupted ~14100 14C yr BP producing the Tutti Frutti Plinian Eruption (TFPE). The eruption tapped two different silicic magmas that mixed just prior and during the eruption. The influx of mass and volatiles generated during the mixing of both magmas overpressured the reservoir, which was weakened at the top. The weakened reservoir relaxed while magma was tapped and collapsed to form a caldera at the surface. Although it is known that fractional crystallization, mixing, and assimilation can greatly modify magmas, the frequency and intensity of these events is not known. I investigated the magmatic processes responsible for the evolution of magmas erupted during five Plinian events of Popocatépetl volcano. Results show that during the last 23 ky magma was stored in two different zones, and was variably modified by replenishments of mafic magma. Interestingly, little evidence for large mafic inputs triggering explosive eruptions was found. Each of these processes alters the abundances of volatiles and introduces different types of volatiles to the system. Hence, the volatile budget of magma can have a rich and complex history. To investigate how volatile budgets evolve in active magma systems, I analyzed the abundances of volatiles (H2O, CO2, F, Cl, and S) in numerous glass inclusions trapped in phenocrysts. Results show that the magmas that produced the last five Plinian eruptions at Popocatépetl volcano evolved by crystallization and magma mixing, assimilation of the local carbonate basement is not chemically appreciable. Mixing with mafic magmas added substantial CO2 and S to the system, dewatered the magma, yet produced little change in the F contents of the magmas. / text

Adam Bobbette Cultures of Forecasting: Volatile and Vulnerable Nature, Knowledge, and the Future of Uncertainty Summary This dissertation is a cultural history and ethnography of volatile nature forecasting. It looks at the ways that the future of nature is known in highly unpredictable contexts through a broad history of modernist nature forecasting and an ethnography of state scientists, shamans, and a sultans retinue on the active volcano, Mount Merapi, Indonesia. The project aims to understand how practices of forecasting generate futures, mobilize, and organise anticipation, how time is known, and populations governed. It looks at the way that publics emerge through forecasting technologies, and how futures and nature-culture relations are contested. It follows the practices of scientists in volcano and tsunami observatories, in planes tracking tropical storms, and bunkers dug into active volcanoes; at how instruments and technologies such as seismographs, windows, globes, speakers, and electrical tomography, mediate and transform relations with nature, the future, and governance. It considers too, the role of architecture, shamanism, and the state in appropriating and governing uncertainty. By following the fieldwork of geophysicists and volcanologists in observatories and the edge of the caldera of Mount Merapi, as well as spirit possession practices, and the ritual offerings of a sultan, I demonstrate how practices of forecasting are making contested futures lived in the present, and forging infrastructures and tools for their longevity. Forecasting, I demonstrate, is a cultural technique that negotiates the porous borders between the human, nature, and the future.

How people pereceive the risks associated with natural hazards contributes to their willingness to take protective action. Such action may be constrained by prevailing socio-economic and place-specific conditions that restrict or inform the choice of protective measures available to the individual. Vulnerability to the impacts of extreme geophysical events increases when the range of alternatives is limited or misinformed. Many evacuees from a potentially violent volcanic eruption in Ecuador returned to their home town of Banos while it was still under an evacuation order in 2000 and considered to be a high risk area by officials. The research examined four main questions: (1) What economic conditions confronted Baños evacuees? (2) What political or other social events occurred while they were evacuated that limited their perceived range of options? (3) What information was available about prior eruptions of the volcano and other local natural hazards? and (4) What were the characteristics of the economic base of Baños? These questions were investigated using data from interviews with evacuees, government and non-governmental officials, census and other statistical information, scholarly texts and newspaper reports. The research suggests that economic conditions made it extremely difficult for people to relocate to other communities. When a violent eruption did not occur immediately, and few direct impacts of the eruptions were experienced in Baños, many people chose to return home in an effort to reestablish themselves economically. These people perceived the volcano hazard in Baños to be far less threatening than the economic destitution associated with evacuation. This perception may have been influenced by factors other than the socio-economic context, including efforts of political leaders and tourist business owners to effect the town's economic recovery. These efforts included an aggressive publicity campaign that minimized the risk posed by the volcano. Besides encouraging tourists to return, the campaign also encouraged evacuees to do so. Finally, among some residents, religious beliefs may have contributed to perceptions that they would not be harmed in the event of an explosive eruption.

No description available.

North Crater occupies the north-western quadrant of the Tongariro Volcanic Centre and represents one of at least eleven vents which have been active on Tongariro since the last glacial maximum. The most recent cone-forming activity at North Crater is thought to have occurred between 14-12 ka ago to produce the distinct, wide, flattopped andesite cone. This project focused mainly on the cone-building eruptions at North Crater, including stratigraphic correlations with distal tephra, interpreting eruptive processes, and establishing the sequence of events during cone construction. Detailed field work identified key stratigraphic sections and facies in the proximal, medial and distal environments. These sections allowed stratigraphic correlations to be made between proximal cone-building facies and distal sheet-forming facies at North Crater, and established a complete North Crater eruption stratigraphy. In the proximal environment, welded and non to poorly welded facies formed from fallout of a lava-fountain, pyroclastic flow or as fallout from a convecting plume. In the medial and distal environment, the lithofacies consist of fallout from a convecting plume and minor pyroclastic flow. Convective fall and non to poorly welded pyroclastic flow deposits dominate the lower eruption stratigraphy suggesting explosive eruptions involving a gas-rich magma. A change to welded deposits produced from lava-fountaining occurs later in the cone-building sequence and suggest a change to lower explosively and eruption of gas-poor magma. Grain size, componentry data, density, petrography and SEM analysis were carried out on representative samples to characterise the different facies, and reveal information about eruption processes. The non to poorly welded deposits are typically made up of vesicular pumice, scoria and mingled clasts of sub-rounded bombs and lapilli. The welded facies are relatively dense and clast outlines are often difficult to distinguish. The eruptives are porphyritic with abundant plagioclase gt clinopyroxene gt orthopyroxene gt opaques. Quartzofeldspathic crustal xenoliths are common and indicate crustal assimilation. Mingled clasts of light and dark glass were found to have microlites present in the dark glass, but were absent in the light glass. Electron microprobe analyses found that the dark and light glass components in a single clast had similar compositions, showing that the contrasting physical appearance of the glass is not due to a different chemical composition. Forty three whole rock XRF analyses showed that the magmas ranged from basaltic andesite to andesite, and Harker variation plots display linear trends typical of magma mixing. Magma mixing as the most important magmatic process is supported by disequilibrium of phenocryst compositions and phenocryst textures. Magma viscosity, bulk density and temperature was determined using MAGMA (Kware), and indicate that they fall into the range of typical andesites. Eruptive activity involved vigorous lava-fountaining, minor convecting eruption plumes and dominant collapsing eruption plumes. This activity has produced welded and non-welded pyroclastic flow and fall deposits to form the large cone seen today. There are significant volcanic hazards associated with this style of activity at North Crater, characterised by lava-fountaining, eruption plume fallout, and widespread pyroclastic flows and lahars extending beyond the ring plain. These could all be potentially devastating to the central North Island of New Zealand.