Browsing by Author "Browning, John"

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    Conditions for caldera collapse in complex volcano-tectonic settings
    (2025) Villarroel Lastra, Matías Andrés; Browning, John; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    Comprender los mecanismos y las condiciones que gobiernan la formación de calderas es crucial para avanzar en la evaluación de riesgos volcánicos, la exploración de recursos y nuestro conocimiento de los procesos volcánicos. Los modelos analógicos y numéricos han proporcionado valiosas perspectivas sobre las estructuras y procesos asociados, en condiciones que de otra manera sería difícil acceder. Sin embargo, estos modelos a menudo se basan en suposiciones simplificadas y no consideran las complejidades del sistema magmático ni las interacciones volcánico-tectónicas. Esta tesis investiga la interacción entre la geometría de la cámara magmática, los esfuerzos tectónicos regionales, la presión de fluidos en los poros y las estructuras regionales pre y post colapso en el control de la evolución de las calderas de colapso en contextos volcánico-tectónicos complejos. A través de un enfoque integrador que combina experimentos analógicos y modelos utilizando el Método de Elementos Discretos y el Método de Elementos Finitos, esta investigación explora cómo estos factores influyen en las condiciones de esfuerzo requeridas para la nucleación de fallas, los umbrales de colapso y la arquitectura de las fallas. Este estudio revela que las cámaras magmáticas apiladas verticalmente dentro de sistemas transcorticales tienen más probabilidades de generar condiciones de esfuerzo favorables para la nucleación de fallas de caldera. El régimen extensional favorece fallas de mayor ángulo y, combinados con la presión de fluidos en los poros, inicios de colapso más tempranos, mientras que el régimen compresional retrasa el colapso y promueve fallas de ángulo más bajo. Las estructuras regionales pre y post colapso, pueden promover la reactivación de fallas, influir en el umbral del colapso y, dictar la forma de la caldera y su arquitectura interna. Estos resultados proporcionan nuevas perspectivas sobre la mecánica del colapso de calderas, destacando la importancia de los factores geológicos regionales y locales en su evolución. Al integrar observaciones de campo con técnicas de modelado de vanguardia, esta tesis contribuye a un marco más completo para comprender los sistemas de calderas en diversos ambientes volcánico-tectónicos y condiciones corticales.
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    Correction to: Depths of magma chambers at three volcanic provinces in the Karlıova region of Eastern Turkey
    (2018) Karaoğlu, Özgür; Browning, John; Salah, Mohamed K.; Elshaafi, Abdelsalam; Gudmundsson, Agust
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    Crustal folds alter local stress fields as demonstrated by magma sheet - Fold interactions in the Central Andes
    (2021) Clunes, Matías; Browning, John; Cembrano, José; Marquardt, Carlos; Gudmundsson, Agust
    For magma chambers to form or volcanic eruptions to occur magma must propagate through the crust as dikes, inclined sheets and sills. Most models that investigate magma paths assume the crust to be either homogeneous or horizontally layered, often composed of rocks of contrasting mechanical properties. In regions that have experienced orogenesis, like the Andes, the crust has been deformed over several million years, resulting in rock layers that are commonly folded and steeply dipping. The assumption of homogeneous properties or horizontal layering then does not capture all of the potential magma path-crustal interactions. Here we tackle this problem by determining the effect of a crust made of steeply inclined layers in which sills and inclined sheets are emplaced. We combine field observations from a sill emplaced in the core of an anticlinal fold at El Juncal in the Chilean Central Andes, including lithologies, sill and fold limbs attitude, length and thickness with a suite of finite element method models to explore the mechanical interactions between inclined layers and magma paths. Our results demonstrate that the properties of the host rock layers as well as the contacts between the layers and the geometry of crustal structures all play an important role in magma propagation and emplacement at shallow levels. Sill propagation and emplacement in heterogeneous and anisotropic crustal segments change the crustal stress field promoting sill arrest, deflection or further propagation. Specifically, sills are more likely to be deflected when encountering shallow dipping layers rather than steeply dipping layers of a fold. Mechanically weak contacts encourage sill deflection due to the related rotation of the stress field and this effect is attenuated when the folded layers are steeper. These processes may change the amount and style of recorded surface deformation, with implications for monitoring of active volcanoes. (C) 2021 Elsevier B.V. All rights reserved.
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    Dilatation and shearing in tectono-volcanic systems from poro-elasto-plastic models set in the Southern Andes Volcanic Zone context, inferences on geofluid flow
    (2022) Gerbault, Muriel; Saez, Felipe; Ruz Ginouves, Javiera; Cembrano, José; Iturrieta, Pablo; Hurtado, Daniel; Hassani, Riad; Browning, John
    Geothermal fields near volcanic complexes and active crustal-scale fault zones require an understanding of the mechanical interactions that control variations in pore fluid pressure at a crustal scale. Crustal faults can trigger and modify fluid flow depending mostly on their geometry and mechanical properties. In turn, fluid flow reduces normal stresses causing either shearing or dilation through the rock mass, concomitant with hydraulic fracturing or seismic fault reactivation. The Southern Andes Volcanic Zone (SAVZ) documents widespread geofluid migration through the crust within a bulk regional transpressive regime. We address here the key role of dilatational domains potentially hosting geothermal fluids, in close relation to shear zones, by using elasto-plastic and poro-elasto-plastic models. First we define models considering Drucker-Prager elasto-plasticity, that account for either: 1) an inflating magmatic cavity or 2) a dextral slipping fault zone ca. 4 km apart, to assess the rheological conditions leading to brittle failure of the bedrock around the fault zone and the cavity, respectively. This setup is applied to the San-Pedro Tatara volcanic complex in the SAVZ. Parametric tests of Young’s moduli and frictional strength provide not only the conditions for macro-scale shear failure, but also shows the development of diffuse domains of dilatational strain in the intervening bedrock. Both void opening and/or volumetric cracking may lead to an increase in porosity and/or permeability, allowing over-pressurized geofluids to migrate within these domains. Our results (Ruz Ginouves et al., JVGR, 2021) show that generally, shallow magma chambers (~< 4 km) and fault zones must be close enough to trigger bedrock failure of the other counterpart (< 4 km), unless the magma chamber is deeper than 10 km, the magma overpressure is high or the regional strength is very low. We argue that alternating strike-slip faulting and magmatic overpressure promote a variety of stress fields that may explain observations of transient fluid pathways on seemingly independent timescales along the Andean margin. To gain further insights into these processes, we develop a numerical scheme to quantify stress and fluid flow with a coupled poro-mechanical approach implemented using Python’s Opensource FEM library FeniCS. Benchmarks are first presented to validate our poro-elasto-plastic approach. Then a synthetic setup shows how fluids get channelized around a fault zone several days after an imposed fault slip motion. Preliminary results are discussed in comparison to a high enthalpy geothermal system associated with another volcanic complex in the SAVZ.
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    Fault intersection-related stress rotation controls magma emplacement at the Nevados de Chill´ an Volcanic Complex
    (2025) Espinosa Leal, Javier; Browning, John; Cembrano, José; Mitchell, Thomas; Rojas, Flavia; Moorkamp, Max; Griffith, W. Ashley; Meredith, Philip
    It has been suggested that fracture and fault intersections promote enhanced transport of fluids in the brittle crust by forming zones of increased permeability. However, the underlying mechanisms that control the emplacement of magma at fault intersections remain poorly understood. To better understand the relation between magma emplacement, volcano development and fault zone intersections, we examine the Nevados de Chillán Volcanic Complex (NChVC, 36.8°S) in the Southern Andean Volcanic Zone. The complex is thought to be located atop the intersection between two sets of NE-right lateral strike-slip faults and a seismically active regional scale NW-oriented inherited structure, also interpreted as a regional fault zone. We collected data on the orientation and frequency of tens of dykes and thousands of fractures, at the volcano scale, from representative outcrops using three-dimensional digital image correlation techniques, with images taken from Unmanned Aerial Vehicles (UAVs). We use these data to generate a conceptual model of the response of the different fracture sets to regional loads and the potential consequence in terms of magma emplacement. In our conceptual model, N-S to NW-SE striking fractures become reactivated by fault intersection-related local stress field rotations. This, in turn, favors NW-SE aligned magma emplacement, and the evolution of NW-SE aligned volcanoes. Our findings provide a mechanical explanation for rotated magma emplacement pathways, which do not necessarily require a transient stress state imposed by unlocking the megathrust.
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    Field observations and numerical models of a Pleistocene-Holocene feeder dyke swarm associated with a fissure complex to the east of the Tatara-San Pedro-Pellado complex, Southern Volcanic Zone, Chile
    (2020) Ruz Ginouves, Javiera Andrea; Browning, John; Cembrano, José; Iturrieta, Pablo; Gerbault, Muriel; Sielfeld, Gerd
    Magma is transported through the lithosphere as dykes which, during periods of unrest, may feed eruptions at the surface. The propagation path of dykes is influenced by the crustal stress field and can be disturbed by crustal heterogeneities such as contrasting rock units or faults. Moreover, as dykes propagate, they themselves influence the surrounding stress field through processes of stress transfer, crustal deformation and seismic failure. The result is the formation of arrested dykes, as well as contrasting strike and dip angles and dyke segmentation. Here, we study the mechanisms of dyke injection and the role played in modifying the stress field and potential propagation paths of later dyke injections. To do this we combine field data from an eroded and well-exposed shallow feeder dyke swarm with a suite of two-dimensional FEM numerical models. We mapped 35 dyke segments over a ~1 km long dyke swarm exposed ~5 km to the East of Pellado Volcano, in the Tatara-San Pedro-Pellado (TSPP) volcanic complex, Southern Volcanic Zone of the Andes. Detailed mapping of the swarm elucidates two preferential strike orientations, one ~N80°E and the other ~N60°E. Our numerical models simulate both the TSPP volcanic complex and the studied dyke swarm as zones of either magmatic excess pressure or as a rigid inclusion. The crustal segment hosting the volcanic complex and dykes is modelled using an elastic domain subjected to regional compression in select model cases. Model outputs provide the stress and strain fields resulting from the different geometries and applied boundary loads. The model results indicate that individual dyke injections can locally rotate the principal stresses such as to influence the range of orientations over which later dykes will form. The orientation of σ1 at the dyke tip ranges over 60° (±30° either side of the dyke tip) indicating that the strike orientation of later dykes will fall within this range. The effect of adding a bulk regional compression is to locally increase the magnitude of favorably oriented tensile stresses in the bedrock but to reduce the range of σ1 orientations to 40° (±20°). This implies that under a far-field transpressive stress regime, as is common in Andean settings, regional dyke swarms will tend to maintain their strike orientation parallel to the regional bulk stress. These results should be accounted for when studying periods of volcanic unrest in order to discern the location and orientation of potential fissure eruptions in active volcanic areas such as the Southern Volcanic Zone of the Andes.
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    Fluid flow in the Nevados de Chillán Geothermal System as an example of fractured reservoir, Southern Andes
    (2024) Arancibia Hernández, Gloria Cecilia; Mura Toledo, Valentina Rossana; López Contreras, Camila Andrea; Oyarzo Cespedes, Isa Paz Belen; Browning, John; Healy, David; Maza, Santiago; Morata, Diego
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    Historical accounts provide insight on the geological evolution of the 20th century eruptions at Santorini volcano, Greece
    (2023) Drymoni, Kyriaki; Browning, John; Pomonis, Panagiotis; Magganas, Andreas
    The 20th century eruptions of the Santorini volcano in Greece are the most recent activity of the volcano’s long lifespan. While the different eruptions taking place between 1925 and 1950 have traditionally been considered to exhibit similar eruptive styles, aspects of their evolution and precise information related to the individual eruption dynamics were poorly constrained. This study collates field reports and historical accounts, mainly from the Greek national scientific committee, which was assigned to study the volcanic activity in Nea Kameni Island with recent field campaigns. This analysis provides further insight into these eruptions and attempts to unravel the timing and style of explosive and effusive episodes that took place. Reconstruction of the recent geological evolution and of the eruptive history allow a more complete description of the eruption dynamics and associated unrest. These include fumarolic behaviour, explosion intensity, direction and volume of the lava flows, eruption duration, vent morphological changes (such as craters, domes, and horseshoe ramparts), textural characteristics and lava morphologies, as well as surface fracturing. Specific features related to first-hand accounts of the eruptions and associated products, in conjunction with our in situ post-eruptive geological study, allow an improved reconstruction of activity, both prior to and during the historical eruptions, which contributes to understanding the development of the eruption and enhances the forecast of potential future eruptions from patterns of precursory activity.
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    Intertwining volcanoes and society in Chile through arts and interdisciplinary connections
    (2024) Acuna, Valentina; Clunes, Matias; Valdebenito, Sebastian Riffo; Browning, John
    The conceptual distance between nature and society has been a concern within social sciences and interdisciplinary debates. We contribute to this discussion illustrating how arts have played an important role in demonstrating the entanglement of Earth and society through their ability to frame and shape the dynamics of the Earth across sensations. Through an examination of artistic representations in Chile, we seek to show how the proximity of Chilean society to the presence of volcanoes has been eloquently conveyed through various artistic styles across different historical epochs. Our study extends from the birth of the Chilean nation in 1818 to the year 2021, and examines a wide range of artistic representations, that encompass national symbols, image-making techniques, sculpture, art installations, poetry, music, and audiovisual works. Our research represents a pioneering effort to explore the diverse representations of volcanoes in Chile and has uncovered a remarkable diversity of artistic expressions that reflects the deep connection between Chilean society and volcanic processes and landscapes. Ever-present and often breathtaking, volcanoes have served as enduring symbols of national identity and as sources of inspiration for artists of diverse disciplines and aesthetic sensibilities. We illustrate how the arts reveal the relationship between volcanoes and social life and provide the basis for a detailed analysis that explores the temporal and spatial contexts in the representation of volcanoes and the human perception of geological phenomena in Chilean culture.
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    Nature and geometry of halobearing hydrothermal veins: Insights into the mechanics of fracture propagation in the Upper Crust
    (2024) Hofer Apostolidis, Karin Andrea; Cembrano, José; Browning, John; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    Comprender los procesos físicos y geológicos fundamentales críticos que gobiernan la formación de halos de alteración en sistemas de fallas-venas es valioso para comprender diversos procesos geológicos. Esta tesis tiene como objetivo desentrañar la naturaleza de los mecanismos de generación de halos de alteración, la relación geométrica de escala entre los anchos de halo y vena, y la interacción entre fluidos y rocas dentro de fracturas llenas hidrotermalmente. Estos halos de alteración representan huellas detectables que se pueden usar para inferir trayectorias de fluidos, ya sea que resulten de un flujo advectivo (producto de la interacción entre fluido y roca dentro de la zona de daño en los alrededores de la propagación de una fractura impulsada por fluido) o por procesos de transferencia de masa por difusión (producto de gradientes de presión, temperatura o químicos). Estudié venas con halos encontradas en cuatro floramientos en la Cordillera de la Costa de Chile, y en muestras de mano de la Región de Fujian provenientes del sudeste de China. Para abordar los objetivos específicos, este estudio se llevó a cabo siguiendo cuatro metodologías. En el campo, mapeé la geometría y cinemática de venas portadoras de halos a varias escalas, desde milímetros hasta decenas de metros. Se prestó especial atención a la relación de contacto entre halos, venas y su roca de caja. A partir de imágenes de alta resolución tomadas en el campo, medí los anchos de halo y vena utilizando el software de análisis y procesamiento de imágenes ImageJ. Se analizaron cortes transparentes de muestras de mano obtenidas en terreno para identificar la petrografía y composición mineral de la vena, utilizando microscopía óptica y el uso de la técnica de difracción de electrones dispersados (EBSD). Los resultados permiten identificar relaciones de escala linear en un gráfico logarítmico entre los anchos de halo y vena, lo que es consistente con el modelo de propagación elasto-plástica de fracturas de Irwin-Orowan.
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    Post-fragmentation vesiculation timescales in hydrous rhyolitic bombs from Chaitén volcano
    (2020) Browning, John; Tuffen, H.; James, M. R.; Owen, J.; Castro, J. M.; Halliwell, S.; Wehbe, K.
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    Receiver function imaging of mantle transition zone discontinuities and the origin of volcanism beneath Libya
    (2019) Lemnifi, A. A.; Browning, John; Elshaafi, A.; Aouad, N. S.; Yu, Y.
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    Reconciling the location of lava domes and eruption centers in Paleocene-Eocene calderas in northern Chile
    (2021) Clunes, Matías; Browning, John; Marquardt, Carlos; Cembrano, José; Villarroel, Matías; Rivera, Orlando; Mpodozis, Constantino
    In the Atacama Desert, at the Precordillera of northern Chile, a series of Paleocene-Eocene caldera deposits and ring-faults are exceptionally well-preserved1. Here we aim to build on previous mapping efforts to consider the location, timing and style of pre, syn and post caldera volcanism in the region. We focus on the partially nested caldera complexes of Lomas Bayas and El Durazno2,3 where deposits record several stages of caldera evolution (pre-collapse, collapse/intra-caldera and extra-caldera, resurgence and post-collapse eruptive deposits). The pre-caldera basement is a thick sequence of early Paleocene mafic lavas4, 5. The caldera complex formed between around 63 and 54 Ma4, 5. Both calderas constitute subcircular structures approximately 13 km in diameter and are cut by several NNW to NNE-trending felsic dikes which are spatially related to felsic domes interpreted as resulting from post caldera formation unrest1,4. These calderas have been interpreted as part of the Carrizalillo megacaldera complex2 . We combine field observations, such as the attitude of dikes, as well as information on their dimension and composition, the size, location and composition of domes and lava flows, as well as the evidence of the regional stress field operating during the caldera evolution from measurements of fault kinematics. This data will be used as the input to finite element method models to investigate the effect of nested caldera geometry, ring-faults and crustal heterogeneities on the location of domes and eruptive centers generated during caldera unrest. The results will be potentially useful for constraining models of eruption forecasting during periods of unrest in calderas and ore deposition models which have been shown to be linked to caldera structure and magma emplacement
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    Thermal fluid circulation around the Karliova triple junction: Geochemical features and volcano-tectonic implications (Eastern Turkey)
    (2019) Karaoğlu, Özgür; Bazargan, Mohsen; Baba,Alper; Browning, John
    The Karlıova triple junction (KTJ) in eastern Turkey has been subjected to incremental deformation resulting in complex kinematic and mechanical interactions throughout the upper crust. These interactions have generated tectonic inversions and uplift, extensive seismicity and volcanism. The regional tectonics generate local stresses, some of which are favorable to magma transport and thermal water circulation throughout the lithosphere. Here we evalauate hydrogeochemical, geological and numerical results relating to the mechanism of thermal fluid circulation around the KTJ. Hydrogeochemistry of the samples indicates that the thermal water springs are probably heated by steam. Volcanic rocks at the site appear to be the host rock owing to the enrichment of Na+ and Cl− ions in water and the abundance of these elements in minerals of the volcanic rocks. In addition, it is clear that the thermal fluids are sourced from depth and migrate through permeable networks of faults. The effects of crustal heterogeneities, in particular the geometry and mechanical properties of many faults and layers, on thermal fluid circulation in relation to active magma chambers were investigated under a variety of different mechanical conditions. The numerical results indicate very close relationships between the stress field causing faulting and thermal fluid movement in the KTJ. The effect of thermal transfer was modeled with depth throughout the crust and along the the crustal surface. The models show that some faults encourage thermal fluid circulation below the Varto and Özenç volcanoes. Hydrogeochemical, geological and numerical results suggest that magmas residing beneath both the Varto caldera and the Özenç volcano are the main heat source for thermal fluid in the Varto region. Fluid-solid interactions and fluid circulation models show that the permeable faults are important factors affecting heat transport and fluid circulation. In a series of thermal fluid flow models we probe the mechanism for fluid and gas transport from the 900 °C ‘hot’ zone around the deep magma chambers and investigate how heat is lost throughout the crust on the way to the surface and so eventually creates water channels of temperatures between 50 to 60 °C.
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    Variable elastic anisotropy controls stress in shallow crown pillars
    (2025) Cortez, Jorge; Browning, John; Marquardt, Carlos; Clunes, Matías; Carmona, Nicolás; Benson, Philip; Koor, Nick
    As easily accessible natural resources become depleted, it is necessary to extract material from deeper levels and so mines may opt to develop a process of transition from open-pit to underground mining methods. In some cases, however, the process develops in the opposite direction where shallower resources from historic underground districts are mined by surface extraction methods. In both cases, it is necessary to maintain a crown pillar to ensure the stability of the pit and underground infrastructure. The dimensions of these crown pillars are typically designed using a combination of empirical methods and numerical modelling. In both methodologies, rocks are often treated as elastic and isotropic materials, even when they exhibit a clear direction of anisotropy caused by bedding planes, foliation, or closely spaced joints. To explore the role of this anisotropy in the stress state surrounding and within crown pillars, a series of two-dimensional finite element models were built using the code FEniCS. The results of this study show that tectonic loading leads to significantly higher compressive stresses, 2 to 4 times greater than gravitational loads alone. Tensile stress also increases notably, with values reaching almost -11 MPa compared to −1 MPa under gravitational loads. Therefore, the degrees of anisotropy and its orientation is likely to play a significant role in stress distribution. Our findings highlight the importance of constraining the in-situ stress, the geology of the host rock and the degree of anisotropy at laboratory scale for adequately addressing the risk of crown pillar failure and mining subsidence.
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    Volcanotectonics: the tectonics and physics of volcanoes and their eruption mechanics
    (2022) Gudmundsson, Agust; Drymoni, Kyriaki; Browning, John; Acocella, Valerio; Amelung, Falk; Bonali, Fabio L.; Elshaafi, Abdelsalam; Galindo, Ines; Geshi, Nobuo; Geyer, Adelina; Heap, Michael J.; Karaoğlu, Özgür; Kusumoto, Shigekazu; Marti, Joa; Pinel, Virginie; Tibaldi, Alessandro; Thordarson, Thorvaldur; Walter, Thomas R.
    The physical processes that operate within, and beneath, a volcano control the frequency, duration, location and size of volcanic eruptions. Volcanotectonics focuses on such processes, combining techniques, data, and ideas from structural geology, tectonics, volcano deformation, physical volcanology, seismology, petrology, rock and fracture mechanics and classical physics. A central aim of volcanotectonics is to provide sufficient understanding of the internal processes in volcanoes so that, when combined with monitoring data, reliable forecasting of eruptions, vertical (caldera) and lateral (landslide) collapses and related events becomes possible. To gain such an understanding requires knowledge of the material properties of the magma and the crustal rocks, as well as the associated stress fields, and their evolution. The local stress field depends on the properties of the layers that constitute the volcano and, in particular, the geometric development of its shallow magma chamber. During this decade an increasing use of data from InSAR, pixel offset and structure-from-motion, as well as dense, portable seismic networks will provide further details on the mechanisms of volcanic unrest, magma-chamber rupture, the propagation of magma-filled fractures (dikes, inclined sheets and sills) and lateral and vertical collapse. Additionally, more use will be made of accurate quantitative data from fossil and active volcanoes, combined with realistic numerical, analytical and machine-learning studies, so as to provide reliable models on volcano behaviour and eruption forecasting.