scholarly journals The role of Edge-Driven Convection in the generation of volcanism I: a 2D systematic study

2020 ◽  
Author(s):  
Antonio Manjón-Cabeza Córdoba ◽  
Maxim Ballmer
Keyword(s):  
Numerical Models ◽  
High Volume ◽  
Oceanic Lithosphere ◽  
Companion Paper ◽  
Small Scale ◽  
Continental Lithosphere ◽  
Transient Phenomenon ◽  
Mantle Viscosity ◽  
Wide Range

Abstract. The origin of intraplate volcanism is not explained by the plate tectonic theory, and several models have been put forward for explanation. One of these models involves Edge-Driven Convection (EDC), in which cold and thick continental lithosphere is juxtaposed to warm and thin oceanic lithosphere to trigger convective instability. To test whether EDC can produce long-lived high-volume magmatism, we run numerical models of EDC for a wide range of mantle properties and edge (i.e., the oceanic-continental transition) geometries. We find that the most important parameters that govern EDC are the rheological paramaters mantle viscosity η0 and activation energy Ea. However, even the maximum melting volumes found in our models are insufficient to account for island-building volcanism on old seafloor, such as at the Canary Islands and Cape Verde. Also, beneath old seafloor, localized EDC-related melting commonly transitions into widespread melting due to small-scale sublithospheric convection, inconsistent with the distribution of volcanism at these volcanic chains. In turn, EDC is a good candidate to sustain the formation of small seamounts on young seafloor, as it is a highly transient phenomenon that occurs in all our models soon after initiation. In a companion paper, we investigate the implications of interaction of EDC with mantle-plume activity.

scholarly journals The role of edge-driven convection in the generation of volcanism – Part 1: A 2D systematic study

Solid Earth ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 613-632
Author(s):  
Antonio Manjón-Cabeza Córdoba ◽  
Maxim D. Ballmer
Keyword(s):  
Numerical Models ◽  
High Volume ◽  
Oceanic Lithosphere ◽  
Companion Paper ◽  
Rheological Parameters ◽  
Small Scale ◽  
Transient Phenomenon ◽  
Mantle Viscosity ◽  
Wide Range

Abstract. The origin of intraplate volcanism is not explained by plate tectonic theory, and several models have been put forward for explanation. One of these models involves edge-driven convection (EDC), in which cold and thick continental lithosphere is juxtaposed with warm and thin oceanic lithosphere to trigger convective instability. To test whether EDC can produce long-lived high-volume magmatism, we run numerical models of EDC for a wide range of mantle properties and edge (i.e., the oceanic–continental transition) geometries. We find that the most important parameters that govern EDC are the rheological parameters mantle viscosity η0 and activation energy Ea. However, even the maximum melting volumes predicted by our most extreme cases are insufficient to account for island-building volcanism on old seafloor, such as at the Canary Islands and Cabo Verde. Also, beneath old seafloor, localized EDC-related melting commonly transitions into widespread melting due to small-scale sublithospheric convection, inconsistent with the distribution of volcanism at these volcano chains. In turn, EDC is a good candidate to sustain the formation of small seamounts on young seafloor, as it is a highly transient phenomenon that occurs in all our models soon after initiation. In a companion paper, we investigate the implications of interaction of EDC with mantle plume activity (Manjón-Cabeza Córdoba and Ballmer, 2021).

Coupled Thermo-Hydro-Geochemical Models of Engineered Barrier Systems: The Febex Project

2000 ◽  
Vol 663 ◽  
Author(s):  
J. Samper ◽  
R. Juncosa ◽  
V. Navarro ◽  
J. Delgado ◽  
L. Montenegro ◽  
...  
Keyword(s):  
Large Scale ◽  
Reference Model ◽  
Numerical Models ◽  
Full Scale ◽  
Small Scale ◽  
Model Parameters ◽  
In Situ Test ◽  
Wide Range ◽  
Engineered Barrier

ABSTRACTFEBEX (Full-scale Engineered Barrier EXperiment) is a demonstration and research project dealing with the bentonite engineered barrier designed for sealing and containment of waste in a high level radioactive waste repository (HLWR). It includes two main experiments: an situ full-scale test performed at Grimsel (GTS) and a mock-up test operating since February 1997 at CIEMAT facilities in Madrid (Spain) [1,2,3]. One of the objectives of FEBEX is the development and testing of conceptual and numerical models for the thermal, hydrodynamic, and geochemical (THG) processes expected to take place in engineered clay barriers. A significant improvement in coupled THG modeling of the clay barrier has been achieved both in terms of a better understanding of THG processes and more sophisticated THG computer codes. The ability of these models to reproduce the observed THG patterns in a wide range of THG conditions enhances the confidence in their prediction capabilities. Numerical THG models of heating and hydration experiments performed on small-scale lab cells provide excellent results for temperatures, water inflow and final water content in the cells [3]. Calculated concentrations at the end of the experiments reproduce most of the patterns of measured data. In general, the fit of concentrations of dissolved species is better than that of exchanged cations. These models were later used to simulate the evolution of the large-scale experiments (in situ and mock-up). Some thermo-hydrodynamic hypotheses and bentonite parameters were slightly revised during TH calibration of the mock-up test. The results of the reference model reproduce simultaneously the observed water inflows and bentonite temperatures and relative humidities. Although the model is highly sensitive to one-at-a-time variations in model parameters, the possibility of parameter combinations leading to similar fits cannot be precluded. The TH model of the “in situ” test is based on the same bentonite TH parameters and assumptions as for the “mock-up” test. Granite parameters were slightly modified during the calibration process in order to reproduce the observed thermal and hydrodynamic evolution. The reference model captures properly relative humidities and temperatures in the bentonite [3]. It also reproduces the observed spatial distribution of water pressures and temperatures in the granite. Once calibrated the TH aspects of the model, predictions of the THG evolution of both tests were performed. Data from the dismantling of the in situ test, which is planned for the summer of 2001, will provide a unique opportunity to test and validate current THG models of the EBS.

scholarly journals Dynamics of Orographically Triggered Banded Convection in Sheared Moist Orographic Flows

2007 ◽  
Vol 64 (10) ◽  
pp. 3542-3561 ◽  
Author(s):  
Oliver Fuhrer ◽  
Christoph Schär
Keyword(s):  
Small Amplitude ◽  
Three Dimensional ◽  
Horizontal Resolution ◽  
Small Scale ◽  
Mean Flow ◽  
Topographic Roughness ◽  
Wide Range ◽  
Orographic Convection ◽  
Wind Profiles

Abstract Shallow orographic convection embedded in an unstable cap cloud can organize into convective bands. Previous research has highlighted the important role of small-amplitude topographic variations in triggering and organizing banded convection. Here, the underlying dynamical mechanisms are systematically investigated by conducting three-dimensional simulations of moist flows past a two-dimensional mountain ridge using a cloud-resolving numerical model. Most simulations address a sheared environment to account for the observed wind profiles. Results confirm that small-amplitude topographic variations can enhance the development of embedded convection and anchor quasi-stationary convective bands to a fixed location in space. The resulting precipitation patterns exhibit tremendous spatial variability, since regions receiving heavy rainfall can be only kilometers away from regions receiving little or no rain. In addition, the presence of banded convection has important repercussions on the area-mean precipitation amounts. For the experimental setup here, the gravity wave response to small-amplitude topographic variations close to the upstream edge of the cap cloud (which is forced by the larger-scale topography) is found to be the dominant triggering mechanism. Small-scale variations in the underlying topography are found to force the location and spacing of convective bands over a wide range of scales. Further, a self-sufficient mode of unsteady banded convection is investigated that does not dependent on external perturbations and is able to propagate against the mean flow. Finally, the sensitivity of model simulations of banded convection with respect to horizontal computational resolution is investigated. Consistent with predictions from a linear stability analysis, convective bands of increasingly smaller scales are favored as the horizontal resolution is increased. However, small-amplitude topographic roughness is found to trigger banded convection and to control the spacing and location of the resulting bands. Thereby, the robustness of numerical simulations with respect to an increase in horizontal resolution is increased in the presence of topographic variations.

The formation, preservation and seismic signatures of chemical heterogeneities in the lower mantle

2020 ◽  
Author(s):  
Anna J. P. Gülcher ◽  
Maxim D. Ballmer ◽  
Paul J. Tackley ◽  
Paula Koelemeijer
Keyword(s):  
Physical Properties ◽  
Lower Mantle ◽  
Numerical Models ◽  
Bulk Composition ◽  
Oceanic Lithosphere ◽  
Global Scale ◽  
Seismic Velocities ◽  
Mantle Dynamics ◽  
Wide Range ◽  
Scientific Challenge

<p>Despite stirring by vigorous convection over billions of years, the Earth’s lower mantle appears to be chemically heterogeneous on various length scales. Constraining this heterogeneity is key for assessing Earth’s bulk composition and thermochemical evolution, but remains a scientific challenge that requires cross-disciplinary efforts. On scales below ~1 km, the concept of a “marble cake” mantle has gained wide acceptance, emphasising that recycled oceanic lithosphere, deformed into streaks of depleted and enriched compositions, makes up much of the mantle. On larger scales (10s-100s of km), compositional heterogeneity may be preserved by delayed mixing of this marble cake with either intrinsically-dense or intrinsically-strong materials. Intrinsically dense materials may accumulate as piles at the core-mantle boundary, while intrinsically viscous domains (e.g., enhanced in the strong mineral bridgmanite) may survive as “blobs” in the mid-mantle for large timescales, such as plums in the mantle “plum pudding”<sup>1,2</sup>. While many studies have explored the formation and preservation of either intrinsically-dense (recycled) or intrinsically-strong (primordial) heterogeneity, only few if any have quantified mantle dynamics in the presence of different types of heterogeneity with distinct physical properties.<span> </span></p><p>To address this objective, we use state-of-the-art 2D numerical models of global-scale mantle convection in a spherical-annulus geometry. We explore the effects of the <em>(i)</em> physical properties of primordial material (density, viscosity), <em>(ii)</em> temperature/pressure dependency of viscosity, <em>(iii)</em> lithospheric yielding strength, and <em>(iv)</em> Rayleigh number on mantle dynamics and mixing. Models predict that primordial heterogeneity is preserved in the lower mantle over >4.5 Gyr as discrete blobs for high intrinsic viscosity contrast (>30x) and otherwise for a wide range of parameters. In turn, recycled oceanic crust is preserved in the lower mantle as “marble cake” streaks or piles, particularly in models with a relatively cold and stiff mantle. Importantly, these recycled crustal heterogeneities can co-exist with primordial blobs, with piles often tending to accumulate beneath the primordial domains. This suggests that the modern mantle may be in a hybrid state between the “marble cake” and “plum pudding” styles.<span> </span></p><p>Finally, we put our model predictions in context with recent discoveries from seismology. We calculate synthetic seismic velocities from predicted temperatures and compositions, and compare these synthetics to tomography models, taking into account the limited resolution of seismic tomography. Convection models including preserved bridgmanite-enriched domains along with recycled piles have the potential of reconciling recent seismic observations of lower-mantle heterogeneity<sup>3</sup> with the geochemical record from ocean-island basalts<sup>4,5</sup>, and are therefore relevant for assessing Earth’s bulk composition and long-term evolution.<span> </span></p><p><sup>1</sup> Ballmer et al. (2017), <em>Nat. Geosci</em>., 10.1038/ngeo2898<br><sup>2</sup> Gülcher et al. (in review), <em>EPSL</em>: Variable dynamic styles of primordial heterogeneity preservation in Earth’s lower mantle <br><sup>3</sup> Waszek et al. (2018), <em>Nat. Comm., </em>10.1038/s41467-017-02709-4 <br><sup>4</sup> Hofmann (1997), <em>Nature, </em>10.1038/385219a0; <br><sup>5</sup> Mundl et al. (2017), <em>Science, </em>10.1126/science.aal4179</p>

Numerical Models of Wind Effects on Temperature Loaded Object

2017 ◽  
Vol 738 ◽  
pp. 69-78
Author(s):  
Vladimira Michalcova ◽  
Lenka Lausova ◽  
Iveta Skotnicova ◽  
Sergej Kuznetsov
Keyword(s):  
Transport Model ◽  
Numerical Models ◽  
Simulation Models ◽  
Lower Atmosphere ◽  
Small Scale ◽  
Ansys Fluent ◽  
Eddy Simulation ◽  
Wide Range ◽  
Shear Stress Transport Model ◽  
The Difference

Wind climate influencing wind loads on buildings and other structures, as well as the dispersion of pollutants from various surfaces is essentially determined by small-scale motions and processes occurring in the atmospheric boundary layer (ABL). The physical and thermal properties of the underlying surface, in conjunction with the dynamics and thermodynamics of the lower atmosphere influence the distribution of wind velocity in thermally stratified ABL. Atmospheric turbulence is characterized by a high degree of irregularity, three-dimensionality, diffusivity, dissipation, and a wide range of motion scales. This article describes a change of selected turbulent variables in the surroundings of flow around a thermally loaded object. The problem is solved numerically in Ansys Fluent 13.0 software using LES (Large eddy simulation) models as well as the Transition SST (Shear Stress Transport) model that is able to take into account the difference between high and low turbulence at the interface between the wake behind an obstacle and the free stream. The results are mutually compared and verified with experimental measurements in the wind tunnel.

scholarly journals A MODEL OF THE EVOLUTION OF THE LITHOSPHERE OF THE HIMALAYAN-TIBETAN OROGEN

2021 ◽  
pp. 89-107
Author(s):  
R.S. Alekseev, ◽  
◽  
Yu.L. Rebetsky ◽  
Keyword(s):  
Upper Mantle ◽  
Subduction Zones ◽  
Oceanic Lithosphere ◽  
Indian Plate ◽  
Tibet Plateau ◽  
Small Scale ◽  
Continental Lithosphere ◽  
Principal Stresses ◽  
Vertical Movements ◽  
Reference Parameters

The Himalayan-Tibetan orogen is one of the active orogens on Earth. The processes caused by the collision of two continents have attracted attention of many researchers, and over the past decades, a large amount of geological and geophysical data has accumulated, on which models of the evolution of the region are based. The paper presents a model of the evolution of the Tibet plateau and the adjacent mountain chains, which complies with the modern concepts of the structure of the crust. The reference parameters of this model are the data on the values of stresses and on the patterns of the spatial distribution of principal stresses obtained in our own tectonophysical studies in region, as well as in other intracontinental orogens and in subduction zones between lithospheric plates. The basic assumptions of the model are the factors of the long stage of the Indian plate underthrusting beneath the Eurasian continent, metamorphic processes in the submerged slab (oceanic lithosphere) and in the continental lithosphere above it, combination of absolute horizontal movements of the Eurasian and Indian plates, small-scale convection in the upper mantle and vertical movements of matter, both in the continental lithosphere itself and in the upper mantle.

scholarly journals Artistic explorations of Lviv artists of decorative and applied arts in small-scale plastics of the second half of the 20th century: image of a human being

2021 ◽  
Vol IX(258) (47) ◽  
pp. 10-14
Author(s):  
V. Honcharuk
Keyword(s):  
20Th Century ◽  
Art Criticism ◽  
Fine Arts ◽  
Decorative Arts ◽  
Small Scale ◽  
Human Being ◽  
Applied Art ◽  
Wide Range ◽  
Characteristic Features

The present article examines the special characteristics of the development of small-scale sculpture as an independent phenomenon in Lviv fine arts of the second half of the 20th century within the framework of the interpretation of a human being image, since the following problem has not been sufficiently studied in Ukrainian art criticism. In particular, the research focuses on the specific features of artistic experiments of the representatives of decorative and applied art in the field of anthropomorphic sculpture; traces characteristic features of conceptual and modelling solutions; identifies artistic and stylistic features and peculiarities of the representation of a human being image. The author stresses upon the role of Lviv Ceramic and Sculpture Factory that largely set trends in the development of small-scale sculpture. In addition, as based on works of famous representatives of Lviv school of decorative arts, the author identifies the variety of interpretations and wide range of modelling means as well as traces the most vivid anthropomorphic designs.

scholarly journals Numerical models of sunspot formation and fine structure

2012 ◽  
Vol 370 (1970) ◽  
pp. 3114-3128 ◽  
Author(s):  
Matthias Rempel
Keyword(s):  
Magnetic Field ◽  
Fine Structure ◽  
Large Scale ◽  
Numerical Models ◽  
Dynamical Evolution ◽  
Solar Interior ◽  
Small Scale ◽  
Wide Range ◽  
Umbral Dots ◽  
The Magnetic Field

Sunspots are central to our understanding of solar (and stellar) magnetism in many respects. On the large scale, they link the magnetic field observable in the photosphere to the dynamo processes operating in the solar interior. Properly interpreting the constraints that sunspots impose on the dynamo process requires a detailed understanding of the processes involved in their formation, dynamical evolution and decay. On the small scale, they give an insight into how convective energy transport interacts with the magnetic field over a wide range of field strengths and inclination angles, leading to sunspot fine structure observed in the form of umbral dots and penumbral filaments. Over the past decade, substantial progress has been made on both observational and theoretical sides. Advanced ground- and space-based observations have resolved, for the first time, the details of umbral dots and penumbral filaments and discovered similarities in their substructures. Numerical models have advanced to the degree that simulations of entire sunspots with sufficient resolution to resolve sunspot fine structure are feasible. A combination of improved helioseismic inversion techniques with seismic forward modelling provides new views on the subsurface structure of sunspots. In this review, we summarize recent progress, with particular focus on numerical modelling.

scholarly journals Interstellar and intergalactic dynamos

2012 ◽  
Vol 8 (S294) ◽  
pp. 225-236
Author(s):  
M. Hanasz ◽  
D. Woltanski ◽  
K. Kowalik
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Numerical Models ◽  
Rotation Period ◽  
Cosmic Ray ◽  
Small Scale ◽  
Galactic Rotation ◽  
Galaxy Mergers ◽  
Wide Range

AbstractWe review recent developments of amplification models of galactic and intergalactic magnetic field. The most popular scenarios involve variety of physical mechanisms, including turbulence generation on a wide range of physical scales, effects of supernovae, buoyancy as well as the magnetorotational instability. Other models rely on galaxy interaction, which generate galactic and intergalactic magnetic fields during galaxy mergers. We present also global galactic-scale numerical models of the Cosmic Ray (CR) driven dynamo, which was originally proposed by Parker (1992). We conduct a series of direct CR+MHD numerical simulations of the dynamics of the interstellar medium (ISM), composed of gas, magnetic fields and CR components. We take into account CRs accelerated in randomly distributed supernova (SN) remnants, and assume that SNe deposit small-scale, randomly oriented, dipolar magnetic fields into the ISM. The amplification timescale of the large-scale magnetic field resulting from the CR-driven dynamo is comparable to the galactic rotation period. The process efficiently converts small-scale magnetic fields of SN-remnants into galactic-scale magnetic fields. The resulting magnetic field structure resembles the X-shaped magnetic fields observed in edge-on galaxies.

scholarly journals Evidence of oceanic plate delamination in the Northern Atlantic

2021 ◽  
Author(s):  
Joao Duarte ◽  
Nicolas Riel ◽  
Chiara Civiero ◽  
Sonia Silva ◽  
Filipe Rosas ◽  
...  
Keyword(s):  
Plate Tectonics ◽  
Numerical Models ◽  
Oceanic Lithosphere ◽  
Continental Lithosphere ◽  
Subduction Initiation ◽  
Passive Margins ◽  
Velocity Anomaly ◽  
New Class ◽  
Lisbon Earthquake ◽  
Mountain Belts

Abstract The Earth’s surface is constantly being recycled by plate tectonics. Subduction of oceanic lithosphere and delamination of continental lithosphere constitute the two most important mechanisms by which the Earth’s lithosphere is recycled into the mantle. Delamination or detachment in continental regions typically occurs below mountain belts due to a weight excess of overthickened lithospheric mantle, which detaches from overlying lighter crust, aided by the existence of weak layers within the continental lithosphere. Oceanic lithosphere is classically pictured as a rigid plate with a strong core that does not allow for delamination to occur. Here, we propose that active delamination of oceanic lithosphere occurs offshore Southwest Iberia. The process is assisted by the existence of a lithospheric serpentinized layer that allows the lower part of the lithosphere to decouple from the overlying crust. Tomography images reveal a sub-lithospheric high-velocity anomaly below this region, which we interpret as a delaminating block of old oceanic lithosphere. We present numerical models showing that for a geological setting mimicking offshore Southwest Iberia delamination of oceanic lithosphere is possible and may herald subduction initiation, which is a long-unsolved problem in the theory of plate tectonics. We further propose that such oceanic delamination is responsible for the highest-magnitude earthquakes in Europe, including the M8.5-8.7 Great Lisbon Earthquake of 1755 and the M7.9 San Vincente earthquake of 1969. In particular, our numerical models, in combination with calculations on seismic potential, provide a solution for the instrumentally recorded 1969 event below the flat Horseshoe abyssal plain, away from mapped tectonics faults. Delamination of old oceanic lithosphere near passive margins constitutes a new class of subduction initiation mechanisms, with fundamental implications for the dynamics of the Wilson cycle.

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