Browsing by Author "Gudmundsson, Agust"
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- ItemConditions for fracture arrest in layered rock sequences(2020) Forbes Inskip, Nathaniel D.; Browning, John; Meredith, Philip G.; Gudmundsson, AgustFracture 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.
- ItemCorrection 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
- ItemCrustal 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, AgustFor 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.
- ItemDepths 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
- ItemField 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, ParaskeviField 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.
- ItemModelling of interactions between dykes, inclined sheets and faults at Santorini volcano(2021) Drymoni, Kyriaki; Browning, John; Gudmundsson, AgustDykes and inclined sheets are known occasionally to exploit faults as parts of their paths, but the conditions that allow this to happen are still not fully understood. Here we report field observations from a well-exposed dyke swarm of the Santorini volcano, Greece, that show dykes and inclined sheets deflected into faults and the results of analytical and numerical models to explain the conditions for deflection. The deflected dykes and sheets belong to a local swarm of 91 dyke/sheet segments that was emplaced in a highly heterogeneous and anisotropic host rock and partially cut by some regional faults and a series of historic caldera collapses, the caldera walls providing, excellent exposures of the structures. The numerical models focus on a normal-fault dipping 65° with a damage zone composed of parallel layers or zones of progressively more compliant rocks with increasing distance from the fault rupture plane. We model sheet-intrusions dipping from 0˚ to 90˚ and with overpressures of alternatively 1 MPa and 5 MPa, approaching the fault. We further tested the effects of changing (1) the sheet thickness, (2) the fault-zone thickness, (3) the fault-zone dip-dimension (height), and (4) the loading by, alternatively, regional extension and compression. We find that the stiffness of the fault core, where a compliant core characterises recently active fault zones, has pronounced effects on the orientation and magnitudes of the local stresses and, thereby, on the likelihood of dyke/sheet deflection into the fault zone. Similarly, the analytical models, focusing on the fault-zone tensile strength and energy conditions for dyke/sheet deflection, indicate that dykes/sheets are most likely to be deflected into and use steeply dipping recently active (zero tensile-strength) normal faults as parts of their paths
- ItemSpatial and temporal volcanotectonic evolution of Santorini volcano, Greece(2022) Drymoni, Kyriaki; Browning, John; Gudmundsson, AgustVolcanic and tectonic activities in the Aegean region have controlled the evolution of Santorini volcano, including changes in the shape and size of the island through time. Previous studies associate much of the island’s volcanic activity with the presence of regional faults, but a comprehensive volcanotectonic study that clarifies the relationship between dyking and faulting in the island has not been made. Here we present a detailed structural analysis focused on the northern caldera wall of Santorini, where numerous dykes and faults outcrop and can be studied in the mesoscale. To augment our discussion of dyke and fault interactions, we combine previous volcanological and geophysical observations with our structural analysis to report the volcanotectonic evolution of the northern part of the island and design a conceptual spatial-temporal model. We mapped 91 dyke segments and 15 faults and classified the latter, where possible, with respect to their observed or recorded kinematics, their size, and the active stress field under which they were formed based on prior geophysical data. We relate our observations to a mechanical unconformity within the northern caldera wall. Our field observations, coupled with previous numerical, geophysical, and volcanological studies, offer insights on the interaction between dykes and faults and indicate the conditions under which the faults facilitated magma emplacement, or not, during the volcano’s activity. Our analysis attempts to answer an essential question: under what conditions do crustal faults facilitate or inhibit magma propagation to the surface, with application to the island of Santorini
- ItemStresses Induced by Magma Chamber Pressurization Altered by Mechanical Layering and Layer Dip(2024) Clunes Squella, Matías; Browning, John; Cortez Campaña, Jorge Osvaldo; Cembrano Perasso, José Miguel; Marquardt Roman, Carlos Jorge; Kavanagh, Janine L.; Gudmundsson, AgustUnderstanding the stress distribution around shallow magma chambers is vital for forecasting eruption sites and magma propagation directions. To achieve accurate forecasts, comprehensive insight into the stress field surrounding magma chambers and near the surface is essential. Existing stress models for pressurized magma chambers often assume a homogenous elastic half-space or a heterogeneous crust with varying mechanical properties in horizontal layers. However, as many volcanoes have complex, non-horizontal, and heterogeneous layers, we enhance these assumptions by considering mechanically stratified layers with varying dips. We employed the Finite Element Method (FEM) to create numerical models simulating three chamber geometries: circular, sill-like and prolate. The primary condition was a 10 MPa excess pressure within the magma chamber, generating the stress field. Layers dips by 20-degree increments, with differing elastic moduli, represented by stiffness ratios of the successive layers (EU/EL) ranging from 0.01 to 100. Our findings validate prior research on heterogeneous crustal modeling, showing that high stiffness ratios disrupt stress within layers and induce local stress rotations at mismatched interfaces. Layer dip further influences stress fields, shifting the location of maximum stress concentration over varying distances. This study underscores the significance of accurately understanding mechanical properties, layer dip in volcanoes, and magma chamber geometry. Improving forecasting of future eruption vents in active volcanoes, particularly in the Andes with its deformed, folded, and non-horizontal stratified crust, hinges on this knowledge. By expanding stress models to incorporate complex geological structures, we enhance our ability to forecast eruption sites and magma propagation paths.
- ItemVolcanotectonic interactions between inclined sheets, dykes, and faults at the Santorini Volcano, Greece(2021) Drymoni, Kyriaki; Browning, John; Gudmundsson, AgustDykes and inclined sheets are known occasionally to exploit faults as parts of their paths, but the conditions that allow this to happen are still not fully understood. In this paper, we report field observations from a swarm composed of 91 segments of dykes and inclined sheets, the swarm being particularly well-exposed in the mechanically layered caldera walls of the Santorini volcano, Greece. Here the focus is on dykes and sheets in the swarm that are seen deflected into faults and the mechanical conditions that encourage such deflections. In particular, we present new analytical and numerical models to explain the mechanical principles of dyke/sheet deflections into faults. The numerical models are applied to a normal-fault dipping 65° with a damage zone composed of parallel layers or zones of progressively stiffer rocks with increasing distance from the fault rupture plane. We model a sheet-intrusion, dipping from 0° to 90° and with an overpressure of alternatively 1 MPa and 5 MPa, approaching the fault. We further tested the effects of changing (1) the thickness of the sheet-intrusion, (2) the fault-zone thickness, (3) the fault-zone dip-dimension (height), and (4) the loading by, alternatively, regional tension and compression. We find that the stiffness of the fault core, where a compliant core characterises recently active fault zones, has pronounced effects on the orientation and magnitudes of the local stresses and, thereby, on the likelihood of dyke/sheet deflection into the fault zone. Similarly, the analytical models, focusing on the fault-zone tensile strength and energy conditions for dyke/sheet deflection, indicate that dykes/sheets are most likely to be deflected into and use steeply dipping recently active (zero tensile-strength) normal faults as parts of their paths.
- ItemVolcanotectonics: 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.