Browsing by Author "Browning, John"

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    A new anisotropic poroelasticity model to describe damage accumulation during cyclic triaxial loading of rock
    (2022) Lyakhovsky, Vladimir; Panteleev, Ivan; Shalev, Eyal; Browning, John; Mitchell, Thomas; Healy, David; Meredith, Philip G.
    Crustal rocks undergo repeated cycles of stress over time. In complex tectonic environments where stresses may evolve both spatially and temporally, such as volcanoes or active fault zones, these rocks may experience not only cyclic loading and unloading, but also rotation and/or reorientation of stresses. In such situations, any resulting crack distributions form sequentially and may therefore be highly anisotropic. Thus, the tectonic history of the crust as recorded in deformed rocks may include evidence for complex stress paths, encompassing different magnitudes and orientations. Despite this, the ways in which variations in principal stresses influence the evolution of anisotropic crack distributions remain poorly constrained. In this work, we build on the previous non-linear anisotropic damage rheology model by presenting a newly developed poroelastic rheological model which accounts for both coupled anisotropic damage and porosity evolution. The new model shares the main features of previously developed anisotropic damage and scalar poroelastic damage models, including the ability to simulate the entire yield curve through a single formulation. In the new model, the yield condition is defined in terms of invariants of the strain tensor, and so the new formulation operates with directional yield conditions (different values for each principal direction) depending on the damage tensor and triaxial loading conditions. This allows us to discern evolving yield conditions for each principal stress direction and fit the measured amounts of accumulated damage from previous loading cycles. Coupling between anisotropic damage and anisotropic compaction along with the damage-dependent yield condition produces a reasonable fit to the experimentally obtained stress–strain curves. Furthermore, the simulated time-dependent cumulative damage is well correlated with experimentally observed acoustic emissions during cyclic loading in different directions. As such, we are able to recreate many of the features of the experimentally observed directional 3-D Kaiser ‘damage memory’ effect.
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    Conditions for fracture arrest in layered rock sequences
    (2020) Forbes Inskip, Nathaniel D.; Browning, John; Meredith, Philip G.; Gudmundsson, Agust
    Fracture arrest in layered rock sequences is important in many geodynamic processes, such as dyke-fed volcanic eruptions, earthquake ruptures, landslides, and the evolution of plate boundaries. Yet it remains poorly understood. For example, we do not fully understand the conditions for dyke arrest (preventing potential eruptions) or hydraulic-fracture arrest in gas shales (preventing potential aquifer pollution). Here we present new numerical results on the conditions for arrest of fluid-driven (mode-I) vertical fractures in layered rock sequences when the tips of the fractures approach the interface between two layers of contrasting mechanical properties. In particular, we explore the stress-field effects of variations in layer stiffness, proximity of fracture tip to layer interface, and layer thickness. When the layer hosting the fracture tip is stiffer, fracture arrest normally occurs at the interface with the more compliant layer. By contrast, when the layer above the interface is stiffer, fracture arrest may occur within the host layer well below the interface. These conclusions are supported by field observations of arrested fluid-driven joints and dykes and, therefore, provide a better understanding of the mechanical conditions for dyke-fed eruptions.
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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. The vast majority of models that investigate magma paths assume the crust to be either homogeneous or horizontally layered, often composed of rocks of contrasting mechanical properties. In subduction 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, such as lithologies, sill and fold limbs attitude, sill length and layers and sill 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 crustal geometry all play an important role on magma propagation and emplacement at shallow levels. Sill propagation and emplacement through heterogeneous and anisotropic crustal segments changes the crustal stress field promoting sill arrest, deflection or 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 maximum principal compressive stress and this effect is attenuated when the fold layers are more steeply dipping. This processes may change the amount and style of surface deformation recorded, with significant implications for monitoring of active volcanoes.
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    Damage zone heterogeneity on seismogenic faults in crystalline rock; a field study of the Borrego Fault, Baja California
    (2020) Ostermeijer, G. A.; Mitchell, T. M.; Aben, F. M.; Dorsey, M. T.; Browning, John; Rockwell, T. K.; Fletcher, J. M.; Ostermeijer, F.
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    Depths of magma chambers at three volcanic provinces in the karla +/- ova region of Eastern Turkey
    (2018) Karaoglu, Ozgur; Browning, John; Salah, Mohamed K.; Elshaafi, Abdelsalam; Gudmundsson, Agust
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    Descifrando la volcanología física de secuencias volcánicas miocenas de Los Andes de Chile Central
    (2023) Leiva Gilberto, Camila Andrea; Browning, John; Marquardt R., Carlos; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    La geología del área de Farellones ubicada en la Cordillera Principal de los Andes de Chile central, entre los 2 mil y 3 mil m.s.n.m., consiste en una secuencia de rocas volcánicas y volcanoclásticas del Mioceno, las cuales están localmente intruidas por rocas plutónicas graníticas a dioríticas del mismo periodo o cubiertas por depósitos sedimentarios de origen glaciar, aluvial y coluvial del Cuaternario. La ocurrencia de centros de erupción puntuales en la secuencia volcánica Miocena, aunque ya ha sido sugerida, sigue siendo enigmática, a pesar de existir estudios de sistemas volcánicos en el arco volcánico activo. En este trabajo se determinó la presencia de un estratovolcán caracterizado por 1.7 km de intercalación de flujos de lavas andesíticas a basálticas con depósitos piroclásticos dacíticos a riolíticos indicando eventos de colapso gravitacional en forma de flujo de bloques y cenizas, flujos de densidad piroclástica y caída de cenizas. El tramo superior de la secuencia está conformado por lavas riolíticas con esferulitas, que representan la parte superior del estratovolcán con el Complejo de Domos Cerro Colorado. En el flanco oeste del estratovolcán Cerro Colorado, una fuente de magma y fluidos hidrotermales interactuaron, promoviendo explosiones y colapsos estructurales locales, desarrollando el sistema de maar-diatrema Quebrada Lunes. Este sistema está formado por 700 m de brechas piroclásticas y tobas de composición andesítica a dacítica intercaladas con lavas andesíticas. Toda esta secuencia se encuentra intruida por diques y sills, y afectada por fallas normales. Los resultados indican que los centros eruptivos del Mioceno en Los Andes de Chile central exhibieron un volcanismo diverso entre procesos efusivos y explosivos, así como constructivos y destructivos.
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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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    Diversity of volcanism and evidence of discrete eruption centres in the Miocene Andes of Central Chile
    (2023) Leiva, Camila; Browning, John; Marquardt, Carlos; Clunes, Matias; Villarroel, Matias; Espinosa, Javier; Meyer, Martin; Payacán, Italo; Mpodozis, Constantino
    The geology of the Farellones region in the Andean Cordillera of central Chile, comprise a thick sequence of volcanic and volcaniclastic Miocene rocks. The occurrence of discrete eruption centres within this sequence, whilst suggested, has been difficult to stablish, as in the modern volcanic systems of the SVZ to the southeast of the study area. Here we report, for the first time a previously uncharacterized composite (Cerro Colorado Volcano) associated to a series of intercalated lava flows and pyroclastic deposits of basaltic to rhyolitic composition of Miocene age. Eruptive sequences reach 1.7 km in vertical section, yet the lateral continuity of units is interrupted by a major faults, and gravity collapse deposits. We document a series of large pyroclastic block and ash flows, which are overlain by rhyolitic pyroclastic density currents, ash fall and crystal, lithic and vitric tuffs, all making up more than 300 m of the sequence. A further 300 m thick unit of spherulite-bearing rhyolitic lavas represent the upper most section of the Cerro Colorado volcano. During the early stages of its construction magmas and hydrothermal fluids interacted to form a maar-diatreme system (Quebrada Lunes maar-diatreme). Much of the volcanic units are intruded by E-W and NW-SE striking andesitic and rhyolitic dikes One of the dikes exhibits internal pyroclastic textures evidence of shallow conduit fragmentation. This pyroclastic dike is further evidence of magma-fluid interaction and related explosivity. Similar pyroclastic breccias described elsewhere related to porphyry copper mineralization. Our results indicate that Miocene volcanism in the Andes of Central Chile is linked to discrete eruptive centres which can be identified and characterized through careful field mapping.
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    Evidence of eruptive style transitions from a fossilised conduit on the flank of the Nevados de Chillán volcanic complex
    (2023) Rojas Guzmán, Flavia Jael; Cembrano, José; Browning, John; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    Las transiciones de estilos eruptivos son frecuentes en volcanes silíceos y una mejor comprensión de sus controles transicionales es necesaria para la prevención de riesgos. Ejemplos de erupciones híbridas donde se producen simultáneamente comportamientos eruptivos explosivos y efusivos han llevado a reexaminar los modelos de transiciones utilizados para comprender estos procesos complejos y poco conocidos. Los conductos fosilizados expuestos registran evidencias de procesos magmáticos y ofrecen una gran oportunidad para examinar estructuras y texturas relacionadas con estas transiciones. El objetivo de esta investigación es comprender cómo interactúan y evolucionan las fases eruptivas efusivas y explosivas durante un mismo evento eruptivo y determinar el mecanismo principal que impulsa su transición. Para abordar este objetivo, se analiza un conducto de 2.5 m de ancho situado en el flanco SE del Complejo Volcánico Nevados de Chillán, Chile. Este conducto registra dominios bandeados, porosos y densos intercalados y yuxtapuestos. El trabajo se realizó combinando análisis texturales cualitativos y cuantitativos, mediciones de porosidad con picnómetro de helio y mediciones del contenido de agua total con espectroscopia de transformada de Fourier. Los resultados permitieron identificar cinco etapas principales en la evolución del conducto: (1) una fase explosiva en la que el conducto se rellena de material piroclástico, (2) un proceso cíclico de fragmentación y densificación dentro del conducto que genera la intercalación de los dominios porosos y densos, conduciendo a una fase híbrida explosiva-efusiva, (3) la formación de un tapón magmático denso que sella el conducto y deforma las vesículas y bandas, (4) la compactación del dominio piroclástico debido al ascenso del tapón generando una reducción de la porosidad (hasta un 4% en bandas densas), micropliegues, fiamme vítreos y una fase principalmente efusiva, y una etapa final (5) de relajación de las vesículas tras la densificación, devolviéndoles su forma regular, principalmente redondeada. Los resultados fueron comparados con otros conductos expuestos y examinados para proponer el modelo de evolución de conductos en erupciones de corta duración.
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    Field analysis Vs boat-based photogrammetry derived data in volcanotectonics: an example from the Santorini dyke swarm
    (2020) Drymoni, Kyriaki; Bonali, Fabio Luca; Browning, John; Gudmundsson, Agust; Fallati, Luca; Antoniou, Varvara; Nomikou, Paraskevi
    Field studies are vital for mapping and understanding active geological processes on Earth. Such studies commonly inform analogue and numerical modelling setups and provide insights over a variety of scales. However, geological field studies have several limitations as they are sensitive both to field-based conditions (e.g. weather conditions, geomorphology, weathering, erosion and access) and the experience of the researchers conducting the work. All of these limitations can add significant error or uncertainty to geological measurements. At the same time, new geological measurement techniques (e.g. photogrammetry) are easy to access, fast and friendly to use, but also often depend on ground truthing parameters.In this study, we compared two different methods for mapping and surveying volcanotectonic processes related to dyking events: classical field analysis and boat-based photogrammetry. We tested the two approaches on dykes located within a section of a steep cliff face that makes up part of the Santorini caldera. The caldera wall is accessible by land only in the upper most parts and so most measurements require access by boat or by abseiling down the cliff faces. The latter is very dangerous and not recommended.The core of the work is to carefully compare field data with the equivalents collected on photogrammetry-derived 3D model, focusing on the sea level area in order to compare reliable dataset. Data comparison is focused on dyke attitudes, thicknesses, petrological descriptions, along the 4-km length profile of the northern caldera wall of Santorini volcano.We collected a series of high-resolution images, around 800 pictures in total, aimed at 3D modelling the dyke swarm using photogrammetry methods. They have been collected using a 20 MPX hand-held camera equipped with commercial GPS from a boat, moving parallel and to a constant distance from to the caldera wall.Comparison of both datasets allowed insights into 1) the completeness and, 2) the limitations of each technique. Here we assess the various advantages to design a novel multidimensional methodology that allows fast, accurate and low-cost data generation in difficult working conditions, such as at steep cliff faces and flooded terrains.
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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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    Fracture growth and damage zone evolution in fault-vein systems determined through scaling relations in alteration halo-bearing hydrothermal veins
    (2024) Hofer Apostolidis, Karin Andrea; Cembrano Perasso, José Miguel; Browning, John; Pérez-Flores, Pamela; Mitchell, Thomas M.; Meredith, Philip G.; Rojas Guzmán, Flavia Jael; Tao Xu
    Understanding how fluids flow to form halo-bearing veins is essential to assess the fundamental processes involved in fracture propagation and the formation of hydrothermal ore deposits. Haloes may mimic damage zones during fracture propagation, contributing to the identification of scaling relations between halo width and fracture displacement. In this work, we examine geometry, kinematics and mineral composition of well-exposed halo-bearing fault-vein network field samples. We studied a total of 18 veins from Iron-Oxide Copper Gold (IOCG) deposits in the Chilean Atacama Desert and from the Chinese Cathaysia tectonic block. Vein length and width and halo width were measured directly at the outcrop and later under optical microscope. We established a scaling relation, over five orders of magnitude, between halo width (HW) and vein width (VW) of the form which suggests that the majority of analyzed haloes were formed as a result of crack tip process zone damage. Such ratios and scaling relationships, apart from elucidating the physical mechanisms driving halo/damage zone formation, have potential implications for a more reliable estimation of the nature and size of ore grade variations away from high-grade mineralized veins to the relatively lower grade surrounding wall rock volumes.
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    Habilitación de un marco de carga de biaxial para el ensayo de materiales análogos a rocas
    (2021) Hidalgo Ávila, Tomás Emilio Felipe; Sáez Robert, Esteban; Browning, John; Pontificia Universidad Católica de Chile. Escuela de Ingeniería
    El método de diseño de minería subterránea denominado block caving fragmenta el cuerpo de roca colapsándola con su peso iniciando así la minería. Este trabajo evaluó el comportamiento de un material análogo a roca en marco de trayectorias biaxiales habilitado para tales condiciones en probetas de 120 × 60 × 19 cm. El objetivo de este dispositivo es medir el rol de las fracturas durante la propagación del caving. El material análogo se compone de yeso, agua y retardante de yeso (RP). Representa las características de roca dura frágil con propiedades reducidas y se caracterizó mediante ensayos de laboratorio uniaxiales y velocidades de onda para luego ser comparados con los resultados biaxiales, obteniendo módulos de Poisson y Young similares y dentro del rango que Heuer y Hendron (1969) proponen. Se rehabilitó un marco de carga biaxial desde aspectos técnicos de funcionamiento como mangueras y conexiones, hasta adecuaciones del equipo para ensayar cuatro probetas confeccionadas con este material análogo. Se utilizaron transductores de desplazamiento en dos orientaciones sobre la superficie de la probeta para controlar las deformaciones. Estas mediciones directas fueron complementadas y comparadas con mediciones indirectas mediante correlación de imágenes. Se realizaron dos ensayos exploratorios verificando la capacidad del equipo para otorgar las tensiones y desplazamientos necesarios para que la probeta lograra una falla frágil. Establecido el protocolo de cargas, se realizaron dos ensayos con diferentes niveles de confinamiento: 0.2 y 1 MPa. Los principales resultados demostraron que el marco biaxial rediseñado y el material análogo son adecuados para representar aspectos del comportamiento de deformación y fracturamiento en condiciones de tensiones horizontales elevadas. En el futuro, se espera que el equipo pueda utilizarse para estudiar los procesos fundamentales relacionados con la fractura de roca durante block caving.
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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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    Implications of longitudinal ridges for the mechanics of ice-free long runout landslides
    (2021) Magnarini, Giulia; Mitchell, Thomas M.; Goren, Liran; Grindrod, Peter M.; Browning, John
    The emplacement mechanisms of long runout landslides across the Solar System and the formation mechanisms of longitudinal ridges associated with their deposits remain subjects of debate. The similarity of longitudinal ridges in martian long runout landslides and terrestrial landslides emplaced on ice suggests that an icy surface could explain both the reduction of friction associated with the deposition of long runout landslides and the development of longitudinal ridges. However, laboratory experiments on rapid granular flows show that ice is not a necessary requirement for the development of longitudinal ridges, which instead may form from convective cells within high-speed flows. These experiments have shown that the wavelength (S) of the ridges is 2-3 times the thickness (T) of the flow, which has also been demonstrated at field scale on a tens-of-kilometre martian long runout landslide. Here, we present the case study of the 4-km-long, ice-free El Magnifico landslide in Northern Chile which exhibits clear longitudinal ridges, and show for the first time on a terrestrial landslide that the S/T ratio is in agreement with the scaling relationship found for both laboratory rapid granular flows and a previously measured martian long runout landslide. Several outcrops within the landslide allow us to study internal sections of the landslide deposit and their relationship with the longitudinal ridges in order to shed light on the emplacement mechanism. Our observations include interactions without chaotic mixing between different lithologies and the presence of meters-sized blocks that exhibit preserved original bedding discontinuities. We associate these observations with fluctuations in stress, as they are qualitatively similar to numerically modelled rapid granular slides, which were suggested, to some degree, to be associated with acoustic fluidization. Our results suggest that 1) the mechanism responsible for the formation of longitudinal ridges is scale- and environment-independent; 2) while the internal structures observed do not necessarily support a mechanism of convective-style motion, their interpretation could also point to a mechanism of internal deformation of the sliding mass derived from pattern-forming vibrations. Our novel observations and analysis provide important insights for the interpretation of similar features on Earth and Mars and for discerning the underlying mechanisms responsible for the emplacement of long run out landslides
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    Lithospheric layering beneath northern Central Africa by S-to-P receiver functions
    (2020) Lemnifi, A. A.; Liu, L..; Browning, John
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    Magmatic overpressures, volatile exsolution and potential explosivity of fissure eruptions inferred via dike aspect ratios
    (2020) Geshi, Nobuo; Browning, John; Kusumoto, Shigekazu
    Buoyant magmas abundant in exsolved volatiles (bubbles) drive the rapid upward-propagation of feeder dikes from magma chambers. The consequence of a feeder dike reaching the surface can result in an explosive volcanic eruption depending, partly, on the retention of volatiles. Therefore, timely detection of the vesicularity and overpressure of the magma during feeder dike ascent is critical for the prediction of the explosivity of any future eruption. In this study, we evaluated the explosivity of eruptions based on field investigations of the erupted products and the overpressure of magma in the conduit based on the dimensions of exposed feeder dikes. We found a positive correlation between the explosivity of eruptions and the magma overpressure generated in the conduit during recent fissure eruptions of Miyakejima volcano. Because the buoyancy of low-density magma produces positive overpressure at the dike’s top, feeder dikes with highly-vesiculated magmas possess high amounts of overpressure. An enlargement of the opening width of a feeder dike by magmatic overpressure results in a higher flux of vesiculated magma, which causes vigorous explosive activity. Our results suggest the possibility of forecasting the explosivity of an impending eruption if the width (or opening) of an ascending feeder dike is monitored in real-time through measurements of ground deformation and seismicity induced by the dike.