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  • 1
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    Dynamics of magmatic intrusion: what can we learn from the comparison of analog and numerical models? (2024)
    Presse universitaires de Strasbourg
    Details
    Publication Date: 2024-03-11
    Description: This study investigates the dynamics of magmatic intrusions based on the joint analysis of analog and numerical models. By injecting different fluids from the bottom of a solidified gelatin block, we simulate the propagation of magmatic intrusions through the crust and record their shapes, trajectories, and velocity as they rise towards the surface. Additionally, we make use of a 2D fluid-filled crack propagation model constrained by our experimental observations. The numerical simulations demonstrate that our viscous fluid-filled crack experiments, conducted with silicon-oil injections, propagate in the same regime as typical basaltic intrusions. The comparison between analog and numerical results allow us to define the domain of validity of the numerical model and its limit of applicability. This study provides new insights into the processes that control the propagation of magmatic intrusions and our ability to reproduce them using analog and numerical models.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    On the Propagation Path of Magma‐Filled Dikes and Hydrofractures: The Competition Between External Stress, Internal Pressure, and Crack Length (2019)
    Wiley
    Details
    Publication Date: 2021-03-09
    Description: Mixed‐mode fluid‐filled cracks represent a common means of fluid transport within the Earth's crust. They often show complex propagation paths which may be due to interaction with crustal heterogeneities or heterogeneous crustal stress. Previous experimental and numerical studies focus on the interplay between fluid over-pressure and external stress but neglect the effect of other crack parameters. In this study, we address the role of crack length on the propagation paths in the presence of an external heterogeneous stress field. We make use of numerical simulations of magmatic dike and hydrofracture propagation, carried out using a two‐dimensional boundary element model, and analogue experiments of air‐filled crack propagation into a transparent gelatin block. We use a 3‐D finite element model to compute the stress field acting within the gelatin block and perform a quantitative comparison between 2‐D numerical simulations and experiments. We show that, given the same ratio between external stress and fluid pressure, longer fluid‐filled cracks are less sensitive to the background stress, and we quantify this effect on fluid‐filled crack paths. Combining the magnitude of the external stress, the fluid pressure, and the crack length, we define a new parameter, which characterizes two end member scenarios for the propagation path of a fluid‐filled fracture. Our results have important implications for volcanological studies which aim to address the problem of complex trajectories of magmatic dikes (i.e., to forecast scenarios of new vents opening at volcanoes) but also have implications for studies that address the growth and propagation of natural and induced hydrofractures.
    Description: Published
    Description: 2064–2081
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: JCR Journal
    Keywords: Magmatic dykes ; hydrofractures ; Numerical symulations ; Analogue experiments ; 04.08. Volcanology ; 05.05. Mathematical geophysics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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    PAPER (OA)
  • 3
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    A two-step model for dynamical dike propagation in two dimensions: Application to the July 2001 Etna eruption (2020)
    Wiley Agu
    Details
    Publication Date: 2020-10-16
    Description: We developed a hybrid numerical model of dike propagation in two dimensions solving both for the magma trajectory and velocity as a function of the source overpressure, the magma physical properties (density and viscosity), and the crustal density and stress field. This model is used to characterize the influence of surface load changes on magma migration toward the surface. We confirm that surface loading induced by volcanic edifice construction tends both to attract the magma and to reduce its velocity. In contrast, surface unloading, for instance, due to caldera formation, tends to divert the magma to the periphery-retarding eruption. In both cases the deflected magma may remain trapped at depth. Amplitudes of dike deflection and magma velocity variation depend on the ratio between the magma driving pressure (source overpressure as well as buoyancy) and the stress field perturbation. Our model is then applied to the July 2001 eruption of Etna, where the final dike deflection had been previously interpreted as due to the topographic load. We show that the velocity decrease observed during the last stage of the propagation can also be attributed to the local stress field. We use the dike propagation duration to estimate the magma overpressure at the dike bottom to be less than 4 MPa. This approach can be potentially used to forecast if, where, and when propagating magma might reach the surface when having knowledge on the local stress field, magma physical properties, and reservoir overpressure.
    Description: Published
    Description: 1107-1125
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    How caldera collapse shapes the shallow emplacement and transfer of magma in active volcanoes (2020)
    Elsevier
    Details
    Publication Date: 2020-10-16
    Description: Calderas are topographic depressions formed by the collapse of a partly drained magma reservoir. At volcanic edifices with calderas, eruptive fissures can circumscribe the outer caldera rim, be oriented radially and/or align with the regional tectonic stress field. Constraining the mechanisms that govern this spatial arrangement is fundamental to understand the dynamics of shallow magma storage and transport and evaluate volcanic hazard. Here we show with numerical models that the previously unappreciated unloading effect of caldera formation may contribute significantly to the stress budget of a volcano. We first test this hypothesis against the ideal case of Fernandina, Galápagos, where previous models only partly explained the peculiar pattern of circumferential and radial eruptive fissures and the geometry of the intrusions determined by inverting the deformation data. We show that by taking into account the decompression due to the caldera formation, the modeled edifice stress field is consistent with all the observations. We then develop a general model for the stress state at volcanic edifices with calderas based on the competition of caldera decompression, magma buoyancy forces and tectonic stresses. These factors control: 1) the shallow accumulation of magma in stacked sills, consistently with observations; 2) the conditions for the development of circumferential and/or radial eruptive fissures, as observed on active volcanoes. This top-down control exerted by changes in the distribution of mass at the surface allows better understanding of how shallow magma is transferred at active calderas, contributing to forecasting the location and type of opening fissures.
    Description: Published
    Description: 257-293
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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    PAPER (OA)
  • 5
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    Understanding the link between circumferential dikes and eruptive fissures around calderas based on numerical and analog models (2020)
    Wiley Agu
    Details
    Publication Date: 2020-10-16
    Description: Active calderas are seldom associated with circumferential eruptive fissures, but eroded magmatic complexes reveal widespread circumferential dikes. This suggests that, while the conditions to emplace circumferential dikes are easily met, mechanisms must prevent them from reaching the surface. We explain this discrepancy with experiments of air injection into gelatin shaped as a volcano with caldera. Analog dikes show variable deflection, depending on the competition between overpressure, P e , and topographic unloading, P l; when P l /P e = 4.8–5.3, the dikes propagate orthogonal to the least compressive stress. Due to the unloading, they become circumferential and stall below the caldera rim; buoyancy is fundamental for the further rise and circumferential fissure development. Numerical models quantitatively constrain the stress orientation within the gelatin, explaining the observed circumferential dikes. Our results explain how dikes propagate below the rim of felsic and mafic calderas, but only in the latter they are prone to feed circumferential fissures.
    Description: Published
    Description: 6212–6219
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
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    Characterizing the physical properties of gelatin, a classic analog for the brittle elastic crust, insight from numerical modeling (2021)
    Elsevier
    Details
    Publication Date: 2023-10-31
    Description: Precise characterization of the mechanical properties of gelatin, a classic analog of the elastic crust, is necessary for scaling the mechanical models of the Earth's crust behavior in laboratory experiments. Here we reassess how to accurately calculate the Young modulus (E) of gelatin contained in experimental tanks. By means of dedicated analog experiments and finite element simulations, we estimate the bias introduced by using equations appro­ priate for a half-space to interpret the subsidence due to a cylindrical surface load applied on the gelatin. In the case of a standard experimental setup with gelatin adhering to the tank wall, we find E is overestimated by at least 5% for a box with lateral size smaller than 20 times the cylinder diameter. In addition, we deduce a correction factor to be applied when using an analytical formula. We confirm that measuring the shear velocity leads to accurate estimates for the rigidity of gelatin. We also propose a new method for in situ Young's modulus estimation, relying on the length of air-filled propagating crack. Indeed, for a given injected volume, this length depends only on the density contrast between air and gelatin and on the Young's modulus of the gelatin. The fracture toughness of the gelatin is estimated independently. Direct comparison between fracture toughness and Young's modulus shows that for a given Young's modulus, salted gelatin has a higher fracture toughness than unsalted gelatin.
    Description: Published
    Description: 228901
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 7
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    Magma ascent at floor-fractured craters diagnoses the lithospheric stress state on the Moon (2020)
    Elsevier
    Details
    Publication Date: 2023-10-31
    Description: On the Moon, floor-fractured craters (FFCs) present evidence of horizontal crater-centred magmatic intrusions. Crater floor uplift and moat formation indicate that these sill intrusions occur at shallow depths ( 〈 10 km). While a recent study has demonstrated that magma ascent below FFCs and mare-filled craters was triggered by crater unloading, the mechanism leading to the emplacement of shallow sills is still poorly understood. Here we show that the local stress field due to crater unloading is also responsible for the horizontalisation of the magma flow leading to sill-like intrusions. On Earth, caldera formation has been shown to similarly affect magma trajectories, inducing the formation of a sill-shaped storage zone. Magma ascent to shallow depths below FFCs was however made possible because of a regional tensional stress caused by mare loading on the lunar lithosphere. We show that the tensional stress generated by elastic lithosphere deformation caused by mare loading combined to the local crater stress field can explain the distribution of FFCs on the Moon, with the smallest FFCs being located over a larger distance range from the mare. In particular, FFCs distribution around Oceanus Procellarum is consistent with an average load thickness of ∼ 1 km. This study suggests that magma trajectory in the crust of terrestrial planets can provide a diagnostic of the lithospheric structure and state of stress.
    Description: Published
    Description: 115889
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 8
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    Buoyancy Versus Local Stress Field Control on the Velocity of Magma Propagation: Insight From Analog and Numerical Modelling (2023)
    Frontiers Media S.A.
    Details
    Publication Date: 2023-03-06
    Description: Magmatic dykes interact with heterogeneous crustal stress. As a result, their propagation towards the surface can be tortuous and their propagation velocity may vary. While the deflection of dykes in response to the local stress field has been addressed by several studies, less has been done about the effect on their propagation velocity. Understanding under which conditions an intrusion may accelerate or decelerate due to crustal stress heterogeneities has obvious important implications in terms of forecasting the timing of the onset of the eruption. Here we analyse the velocity of fluid-filled crack propagation in a gelatin block characterized by a heterogenous stress field considering the case study of a load applied at the surface. We find that a crack deflected towards the load and its underlying compressive stress field is decelerated. By comparing experimental results with numerical solutions, we evidence the potential complementary role played by stress field variations and changes in trajectory orientation, controling the buoyancy, on the velocity of magma propagation. We also show that the energy release estimated along the crack path by simplified numerical models appears to be a good proxy for the velocity. We conclude that numerical models allowing for magma path estimations could also be used to infer magma velocity variations. In addition, 1D numerical models solving for the fluid flow along a prescribed path, provide velocity variation as a function of the surrounding stress field and the magma driving pressure.
    Description: Published
    Description: 838318
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Keywords: magma propagation, analog experiments, numerical modelling, volcanic hazard, hydraulic fracture ; 04.08. Volcanology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 9
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    Modeling the Shape and Velocity of Magmatic Intrusions, a New Numerical Approach (2023)
    Wiley-AGU
    Details
    Publication Date: 2023-04-17
    Description: Dykes are magma-filled fractures propagating through the brittle crust. Understanding the physics of dyking process is essential to mitigate the volcanic hazard associated with the opening of new eruptive fissures at the surface. Often, physics-based models view either fracturing of the host rock or viscous flow of the magma as the dominating energy sink during dyke propagation. Here, we provide a numerical model that captures the coupling of fracturing at the crack tip and the transport of a viscous fluid. Built with the boundary element technique, our model allows for computation of the shape and velocity of a growing fluid-filled crack accounting for the viscosity of the fluid: the fluid flow induces a viscous pressure drop acting at the crack walls, and modifies the shape of the crack. The energy conservation equation provides the constraints to solve for the crack growth velocity, assuming that brittle fracturing and viscous flow are the main processes that dissipate energy. Using a parameter range that represents typical magmatic intrusions, we obtain crack shapes displaying some typical characteristics, including a tear-drop head and an open tail that depend on rock rigidity, magma viscosity, and buoyancy. We show that viscous forces significantly contribute to the energy dissipated during the propagation of magmatic dykes. Applied to the 1998 intrusion at Piton de la Fournaise (La Réunion Island), we provide ranges of dyke lengths and openings by adjusting the numerical velocity to the one deduced from the migration of volcano-tectonic events.
    Description: Published
    Description: e2022JB025697
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 10
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    Dynamics of magmatic intrusion: what can we learn from the comparison of analog and numerical models? (2024)
    Presses universitaires de Strasbourg
    Details
    Publication Date: 2024-02-27
    Description: This study investigates the dynamics of magmatic intrusions based on the joint analysis of analog and numerical models.By injecting different fluids from the bottom of a solidified gelatin block, we simulate the propagation of magmatic intrusions through the crust and record their shapes, trajectories, and velocity as they rise towards the surface. Additionally, we make use of a 2D fluid-filled crack propagation model constrained by our experimental observations. The numerical simulations demonstrate that our viscous fluid-filled crack experiments, conducted with silicon-oil injections, propagate in the same regime as typical basaltic intrusions. The comparison between analog and numerical results allow us to define the domain of validity of the numerical model and its limit of applicability. This study provides new insights into the processes that control the propagation of magmatic intrusions and our ability to reproduce them using analog and numerical models.
    Description: Published
    Description: 67-87
    Description: OSV1: Verso la previsione dei fenomeni vulcanici pericolosi
    Description: N/A or not JCR
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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