Journal of Volcanology and Geothermal Research, Sep 1, 2008
This study aims to contribute a possible explanation for magma migration within volcanoes located... more This study aims to contribute a possible explanation for magma migration within volcanoes located in contractional tectonic settings, based on field data and physically-scaled experiments. The data demonstrate the occurrence of large stratovolcanoes in areas of coeval reverse faulting, in spite of the widely accepted idea that volcanism can develop only in extensional/transcurrent tectonic settings. The experiments simulate the propagation
SUMMARYField investigations show that Plio‐Quaternary Mexican and Quaternary Ecuadorian volcanic ... more SUMMARYField investigations show that Plio‐Quaternary Mexican and Quaternary Ecuadorian volcanic arcs are coeval with intra‐arc transcurrent or transtensional tectonics with motions along faults parallel or subparallel to the arc. This relationship can also be observed in the Quaternary Kamchatka arc. These arcs have an anomalously wide distribution of volcanic centres which cannot be explained simply by a low dip in the subducting lithosphere. Comparison with the intra‐arc tectonics and geometry of other Quaternary arcs reveals that strike‐slip fault zones, parallel to the arc, favour magma rising in a broad surficial zone and may channel magma feeding mainly huge stratovolcanoes.
this manuscript presents an analysis of an interesting landslide site near a large water reservoi... more this manuscript presents an analysis of an interesting landslide site near a large water reservoir. The site is well described but the core part (as presented in this manuscript) is relatively weak. The geophyisical survey is not adapted to the scale of the site and not this kind of mass movement investigation. GPR is commonly used in paleoseismic studies where only one fault scarp is analysed. In this context here, it does not provide any useful information and the results are unclear (and even contradictory for one site). The numerical modelling is most likely not a ’numerical modelling’ but just a pseudostatic analysis of stability of a slope section performed with a software. So, these two
Dykes (Mode I extension fractures) supply magma from deep reservoirs to the surface and subject t... more Dykes (Mode I extension fractures) supply magma from deep reservoirs to the surface and subject to their propagation paths, they can sometimes reach the surface and feed volcanic eruptions. Most of the times they mechanically stall in the heterogeneous crust or deflect through pre-existing fractures forming sills. Although several studies have explored dyking in heterogeneous regimes, the conditions under which dykes propagate in glacial-volcanotectonic regimes remain unclear.Here, we coupled field observations with FEM numerical modelling using the software COMSOL Multiphysics (v5.6) to explore the mechanical and geometrical conditions that promote (or not), dyke-sill propagation in glacial-tectonic conditions. We used as a field example the Stardalur cone sheet-laccolith system, located in the Esja peninsula proximal to the western rift zone. The laccolith is composed of several vertical dykes that bend into sills and form a unique stacked sill ‘flower structure’. We modelled a heterogeneous crustal segment composed of lavas (top) and hyaloclastites (bottom). We then studied the emplacement of a dyke with varied overpressure values (Po = 1-10 MPa) and regional extension (Fe = 0.5-3 MPa) loading conditions at the lava/hyaloclastite contact. In the second stage, we added an ice cap as a body load to explore dyking subject to unloading due to glacier thickness variations (0-1 km).Our results have shown that the presence of the ice cap can affect the dyke-sill propagation and the spatial accumulation of tensile and shear stresses below the cap. The observed field structure in non-glacial regimes has been formed either due to the mechanical contrast (Young’s modulus) of the studied contact, a compressional regime due to pre-existing dyking or faulting, or finally, high overpressure values (Po ≥ 5 MPa). Instead, in a glacial regime, the local extensional stress field below the ice cap encourages the formation of the laccolith when the ice cap becomes thinner (lower vertical loads). Our models can be applied to universal volcanoes related to glacier thickness variation and sill emplacement.
Measuring surface deformation is critical in analogue modelling of Earth science phenomena. Here,... more Measuring surface deformation is critical in analogue modelling of Earth science phenomena. Here, we present a novel application of the Microsoft Kinect sensor to measure vertical deformation in a scaled analogue model of Nisyros volcano (Greece), simulating two magmatic sources and related surface deformation. The Kinect permits capture of real time, 640 × 480 pixel, true‐colour images (RGB) and a grid of distances to the modelled surface with a horizontal and vertical resolution of ±1 mm. Using recorded distances permits quantification of vertical deformation in terms of maximum and average down‐ and uplift during deflation and inflation phases respectively, which is of crucial importance for defining the kinematics of faults formed during the modelling, determined from interpretation of the RGB images. Although other techniques have demonstrated similar or higher accuracy, our study demonstrates the cost‐effectiveness of the Kinect in analogue modelling of volcanoes.
Journal of Volcanology and Geothermal Research, Sep 1, 2008
This study aims to contribute a possible explanation for magma migration within volcanoes located... more This study aims to contribute a possible explanation for magma migration within volcanoes located in contractional tectonic settings, based on field data and physically-scaled experiments. The data demonstrate the occurrence of large stratovolcanoes in areas of coeval reverse faulting, in spite of the widely accepted idea that volcanism can develop only in extensional/transcurrent tectonic settings. The experiments simulate the propagation
SUMMARYField investigations show that Plio‐Quaternary Mexican and Quaternary Ecuadorian volcanic ... more SUMMARYField investigations show that Plio‐Quaternary Mexican and Quaternary Ecuadorian volcanic arcs are coeval with intra‐arc transcurrent or transtensional tectonics with motions along faults parallel or subparallel to the arc. This relationship can also be observed in the Quaternary Kamchatka arc. These arcs have an anomalously wide distribution of volcanic centres which cannot be explained simply by a low dip in the subducting lithosphere. Comparison with the intra‐arc tectonics and geometry of other Quaternary arcs reveals that strike‐slip fault zones, parallel to the arc, favour magma rising in a broad surficial zone and may channel magma feeding mainly huge stratovolcanoes.
this manuscript presents an analysis of an interesting landslide site near a large water reservoi... more this manuscript presents an analysis of an interesting landslide site near a large water reservoir. The site is well described but the core part (as presented in this manuscript) is relatively weak. The geophyisical survey is not adapted to the scale of the site and not this kind of mass movement investigation. GPR is commonly used in paleoseismic studies where only one fault scarp is analysed. In this context here, it does not provide any useful information and the results are unclear (and even contradictory for one site). The numerical modelling is most likely not a ’numerical modelling’ but just a pseudostatic analysis of stability of a slope section performed with a software. So, these two
Dykes (Mode I extension fractures) supply magma from deep reservoirs to the surface and subject t... more Dykes (Mode I extension fractures) supply magma from deep reservoirs to the surface and subject to their propagation paths, they can sometimes reach the surface and feed volcanic eruptions. Most of the times they mechanically stall in the heterogeneous crust or deflect through pre-existing fractures forming sills. Although several studies have explored dyking in heterogeneous regimes, the conditions under which dykes propagate in glacial-volcanotectonic regimes remain unclear.Here, we coupled field observations with FEM numerical modelling using the software COMSOL Multiphysics (v5.6) to explore the mechanical and geometrical conditions that promote (or not), dyke-sill propagation in glacial-tectonic conditions. We used as a field example the Stardalur cone sheet-laccolith system, located in the Esja peninsula proximal to the western rift zone. The laccolith is composed of several vertical dykes that bend into sills and form a unique stacked sill ‘flower structure’. We modelled a heterogeneous crustal segment composed of lavas (top) and hyaloclastites (bottom). We then studied the emplacement of a dyke with varied overpressure values (Po = 1-10 MPa) and regional extension (Fe = 0.5-3 MPa) loading conditions at the lava/hyaloclastite contact. In the second stage, we added an ice cap as a body load to explore dyking subject to unloading due to glacier thickness variations (0-1 km).Our results have shown that the presence of the ice cap can affect the dyke-sill propagation and the spatial accumulation of tensile and shear stresses below the cap. The observed field structure in non-glacial regimes has been formed either due to the mechanical contrast (Young’s modulus) of the studied contact, a compressional regime due to pre-existing dyking or faulting, or finally, high overpressure values (Po ≥ 5 MPa). Instead, in a glacial regime, the local extensional stress field below the ice cap encourages the formation of the laccolith when the ice cap becomes thinner (lower vertical loads). Our models can be applied to universal volcanoes related to glacier thickness variation and sill emplacement.
Measuring surface deformation is critical in analogue modelling of Earth science phenomena. Here,... more Measuring surface deformation is critical in analogue modelling of Earth science phenomena. Here, we present a novel application of the Microsoft Kinect sensor to measure vertical deformation in a scaled analogue model of Nisyros volcano (Greece), simulating two magmatic sources and related surface deformation. The Kinect permits capture of real time, 640 × 480 pixel, true‐colour images (RGB) and a grid of distances to the modelled surface with a horizontal and vertical resolution of ±1 mm. Using recorded distances permits quantification of vertical deformation in terms of maximum and average down‐ and uplift during deflation and inflation phases respectively, which is of crucial importance for defining the kinematics of faults formed during the modelling, determined from interpretation of the RGB images. Although other techniques have demonstrated similar or higher accuracy, our study demonstrates the cost‐effectiveness of the Kinect in analogue modelling of volcanoes.
This paper deals with some points raised in a comment by Newfield and Oppenheimer on our previous... more This paper deals with some points raised in a comment by Newfield and Oppenheimer on our previous article concerning two previously unrecognized written sources relating the effects in North Africa of two Icelandic eruptions. In our article Brugnatelli and Tibaldi (2020), we did not enter into all the details concerning the already known sources, since they had already been dealt with by a number of scholars, including Newfield and Oppenheimer, as one can see in the text and in the references. We limited ourselves to point out that some of the examined "witness statements" are not as straightforward as one could expect, either concerning the dating of the events recorded or their description. This paper deals more thoroughly with the sources commented on by Newfield and Oppenheimer.
The physical processes that operate within, and beneath, a volcano control the frequency, duratio... more 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 magmafilled 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.
Uploads
Papers by Alessandro Tibaldi