DSpace Community: 04.01. Earth Interior

Effects of wall-rock elasticity on magma flow in dykes during explosive eruptions

Thu, 29 Oct 2009 22:58:59 GMT

Title: Effects of wall-rock elasticity on magma flow in dykes during explosive eruptions

Authors: Costa, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Sparks, R. S. J.; Department of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK; Macedonio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Melnik, O.; Department of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK ; Institute of Mechanics, Moscow State University, Moscow, Russia

Abstract: Magma flow during explosive volcanic eruptions has been described assuming rigid conduits with simple cylindrical or planar geometries. Here we study the dynamics of explosive volcanic flows to take account of the role of elastic deformation of the conduit influenced by local magmatic pressure. Three cases are investigated: a dyke with elliptical cross-section, a cylindrical conduit and a deep dyke connected to a shallow cylinder. The model CPIUC (Macedonio et al., 2005) was used for simulations and generalized to account for elastic deformations of the conduit cross-section area due to magmatic overpressure. Fragmentation level is typically deeper in a dyke than in a cylinder. For flows in wide dykes pressure at the fragmentation depth can be lower than the surrounding lithostatic pressure by several tens of MPa, indicating that the wall-rocks of the dyke will be unstable, constraining the dyke width and eventually blocking the eruption. On the other hand, when the fragmentation level is shallow the corresponding lithostatic pressure is not large enough to close the dyke and eruptions from wide dykes are possible. The behaviour changes drastically when we assume the conduit is a dyke at depth that evolves to a cylinder near the surface. In this case even very wide dykes can be stable because the fragmentation level moves into the cylindrical region where deformation is negligible.

EMSO: European multidisciplinary seafloor observatory

Fri, 10 Apr 2009 22:58:59 GMT

Title: EMSO: European multidisciplinary seafloor observatory

Authors: Favali, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Beranzoli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia

Abstract: EMSO has been identified by the ESFRI Report 2006 as one of the Research Infrastructures that European members and associated states are asked to develop in the next decades. It will be based on a European-scale network of multidisciplinary seafloor observatories from the Arctic to the Black Sea with the aim of long-term real-time monitoring of processes related to geosphere/biosphere/hydrosphere interactions. EMSO will enhance our understanding of processes, providing long time series data for the different phenomenon scales which constitute the new frontier for study of Earth interior, deep-sea biology and chemistry, and ocean processes. The development of an underwater network is based on past EU projects and is supported by several EU initiatives, such as the on-going ESONET-NoE, aimed at strengthening the ocean observatories’ scientific and technological community. The EMSO development relies on the synergy between the scientific community and industry to improve European competitiveness with respect to countries such as USA, Canada and Japan. Within the FP7 Programme launched in 2006, a call for Preparatory Phase (PP) was issued in order to support the foundation of the legal and organisational entity in charge of building up and managing the infrastructure, and coordinating the financial effort among the countries. The EMSO-PP project, coordinated by the Italian INGV with participation by 11 institutions from as many European countries, started in April 2008 and will last four years.

New geological insights and structural control on fluid circulation in La Fossa cone (Vulcano, Aeolian Islands, Italy)

Wed, 29 Oct 2008 22:58:59 GMT

Title: New geological insights and structural control on fluid circulation in La Fossa cone (Vulcano, Aeolian Islands, Italy)

Authors: Barde-Cabusson, S.; Dipartimento di Scienze della Terra, Università Degli Studi di Firenze, Italy; LMV, Université Blaise Pascal, Clermont-Ferrand, France; Finizola, A.; Laboratoire GéoSciences Réunion, UR, IPGP, UMR 7154, Saint-Denis, La Réunion, France; Istituto Nazionale di Geofisica e Vulcanologia, Palermo, Italy; Revil, A.; Colorado School of Mines, Dept. of Geophysics, Golden, CO, USA; CNRS-LGIT (UMR 5559), University of Savoie, Equipe Volcan, Chambéry, France; Ricci, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Piscitelli, S.; IMAA-CNR, Laboratory of Geophysics Tito Scalo (PZ), Italy; Rizzo, E.; IMAA-CNR, Laboratory of Geophysics Tito Scalo (PZ), Italy; Angeletti, B.; CNRS-CEREGE, Université Paul Cézanne, Aix en Provence, France; Balasco, M.; IMAA-CNR, Laboratory of Geophysics Tito Scalo (PZ), Italy; Bennati, L.; Dept. of Earth & Atmospheric Sciences, Purdue University, West Lafayette, USA; Byrdina, S.; LMV, Université Blaise Pascal, Clermont-Ferrand, France; Equipe de Géomagnétisme, IPGP, UMR 7154, 4, Place Jussieu, 75005 Paris, France; Carzaniga, N.; Dipartimento di Scienze della Terra, Università Degli Studi di Firenze, Italy; Crespy, A.; CNRS-CEREGE, Université Paul Cézanne, Aix en Provence, France; Di Gangi, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Morin, J.; Laboratoire GéoSciences Réunion, UR, IPGP, UMR 7154, Saint-Denis, La Réunion, France; Université Paris 1, Panthéon-Sorbonne, Paris, France; Perrone, A.; IMAA-CNR, Laboratory of Geophysics Tito Scalo (PZ), Italy; Rossi, M.; Dipartimento di Geoscienze, Università di Padova, Italy; Università Milano-Bicocca, Milan, Italy; Roulleau, E.; GEOTOP-UQAM-McGill, Montréal, Canada; Suski, B.; Université de Lausanne (UNIL), Institut de Géophysique, Lausanne, Switzerland; CNRS-CEREGE, Université Paul Cézanne, Aix en Provence, France; Villeneuve, N.; Institut de Recherche pour le Développement, US 140 ESPACE, La Réunion, France

Abstract: Electric resistivity tomography (ERT), self-potential (SP), soil CO2 flux, and temperature are used to study the inner structure of La Fossa cone (Vulcano, Aeolian Islands). Nine profiles were performed across the cone with a measurement spacing of 20 m. The crater rims of La Fossa cone are underlined by sharp horizontal resistivity contrasts. SP, CO2 flux, and temperature anomalies underline these boundaries which we interpret as structural limits associated to preferential circulation of fluids. The Pietre Cotte crater and Gran Cratere crater enclose the main hydrothermal system, identified at the centre of the edifice on the base of low electrical resistivity values (b20 Ω m) and strong CO2 degassing, SP, and temperature anomalies. In the periphery, the hydrothermal activity is also visible along structural boundaries such as the Punte Nere, Forgia Vecchia, and Palizzi crater rims and at the base of the cone, on the southern side of the edifice, along a fault attributed to the NW main tectonic trend of the island. Inside the Punte Nere crater, the ERT sections show an electrical resistive body that we interpret as an intrusion or a dome. This magmatic body is reconstructed in 3D using the available ERT profiles. Its shape and position, with respect to the Pietre Cotte crater fault, allows replacing this structure in the chronology of the development of the volcano. It corresponds to a late phase of activity of the Punte Nere edifice. Considering the position of the SP, soil CO2 flux, and temperature maxima and the repartition of conductive zones related to hydrothermal circulation with respect to the main structural features, La Fossa cone could be considered as a relevant example of the strong influence of preexisting structures on hydrothermal fluid circulation at the scale of a volcanic edifice.

Unveiling seismic and density structure beneath the Vrancea seismogenic zone, Romania

Wed, 11 Nov 2009 22:58:59 GMT

Title: Unveiling seismic and density structure beneath the Vrancea seismogenic zone, Romania

Authors: Tondi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Achauer, U.; EOST, Strasbourg - France; Landes, M.; Indiana University, Indiana - USA; Davi', R.; University College Dublin, Dublin - IRELAND; Besutiu, L.; Romanian Academy, Bucharest - Romania

Abstract: The Vrancea seismogenic zone in Romania exhibits an intense intermediate-depth seismicity, confined to a relatively small, roughly cylindrical and elongated region, whose origin is still under debate. Our three-dimensional P and S wave velocity and density images put additional physical constraints on the existing tectonic models to a depth of 200 km. The results appear to substantiate a combination of lithospheric delamination and oceanic subduction. For our analysis, we apply the tomographic inversion method of sequential integrated inversion (SII) to P and S first arrivals from active source data collected during the VRANCEA99 and VRANCEA2001 seismic refraction experiments, local earthquake data collected during the Carpathian Arc Lithosphere X-Tomography (CALIXTO) experiment and recent gravity measurements of the studied area. The reconstructed models, which explain both travel times and gravity data, show a subducting slab which exhibits fast Vp, fast Vs, high density, and a low Vp/Vs ratio consistent with the cold downgoing plate. We associate intermediate-depth seismicity with the observed sharp lateral Vp/Vs variations presumably generated by contact between the dense and cold slab and the lithospheric mantle in the shallower part or the asthenosphere in the deeper part. This contrast is particularly evident between 100 and 150 km depth, where the maximum historical seismic energy release is concentrated. Our results indicate the diagnostic power of a combined interpretation of 3-D Vp, Vs, Vp/Vs, and density models.

Description: An edited version of this paper was published by AGU. Copyright (2009) American Geophysical Union