DSpace Collection:

High resolution finite volume central schemes for a compressibile two-phase model

Sat, 31 Dec 2011 23:00:00 GMT

Title: High resolution finite volume central schemes for a compressibile two-phase model Authors: La Spina, G.; Dipartimento di Matematica L.Tonelli, University of Pisa, Italy; De' Michieli Vitturi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia Abstract: A modi_cation of the Kurganov, Noelle, Petrova central-upwind scheme [A. Kurganov et al., SIAM J. Sci. Comput., 23 (2001), pp. 707{740] for hyperbolic systems of conservation laws is presented. In this work, the numerical scheme is applied to a single-temperature model for compressible two-phase ow with pressure and velocity relaxations [E. Romenski et al., J. Sci. Comput., 42 (2010), pp. 68{95]. The system of governing equations of this model are expressed in conservative form, which is the necessary condition to use a central scheme. The numerical scheme presented is not based on the complete characteristic decomposition, but only on the information about the local speeds of propagation given by the maximum and minimum eigenvalue of the Jacobian of the uxes. We propose to use the numerical ux formulation of the central-upwind scheme in conjunction with a second-order reconstruction of the primitive variables and the MUSCL-Hancock method, where the boundary extrapolated values are evolved by half time step before the computation of the numerical uxes. To investigate the accuracy and robustness of the proposed scheme, two 1D Riemann-problems of an air/water mixture and a 2D shock-bubble-interaction problem are presented. Furthermore, a detailed comparison with the second order GFORCE scheme and the _rst order Lax-Friedrichs scheme is shown. To integrate the source terms an operator splitting approach is used and, under suitable conditions, it is shown that this integration can be computed analytically.

Evidence for a recent change in the shallow plumbing system of Mt. Etna (Italy): Gas geochemistry and structural data during 2001–2005

Mon, 31 Dec 2012 23:00:00 GMT

Title: Evidence for a recent change in the shallow plumbing system of Mt. Etna (Italy): Gas geochemistry and structural data during 2001–2005 Authors: Giammanco, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Salerno, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Caltabiano, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Burton, M. R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Longo, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia Abstract: We analyzed crater SO2 fluxes from Mt Etna, together with soil CO2 effluxes from the volcano's flanks, in the period from 2001 to 2005. Between the 2001 and 2002–2003 eruptions, persistently low values of both parameters suggest that no new gas-rich magma was accumulating at shallow depth (b5 km) within Etna's central conduit, whereas very high SO2 sin-eruptive fluxes during the two eruptions indicated sudden decompression of an un-degassed magma rising along newly-formed eccentric conduits. In November 2003, soil CO2 data indicate migration of gas-rich magma from deep (>10 km) to shallow (b5 km) portions of the feeding conduits, preceded by an increase in crater SO2 fluxes. A similar behavior was observed also during and after the following 2004–2005 eruption. This degassing style matches a period of increased structural instability of the volcanic edifice caused by acceleration of spreading that affected both its eastern and southern flanks. Spreading could have triggered progressively deeper depressurization in the central conduit, inducing release of the more soluble gas (SO2) first, and then of CO2, contrary to what was observed before the 2001 eruption. This suggests that the edifice has depressurized, promoting ascent of fresh-magma and increasing permeability favouring release of CO2 flux. By integrating geochemical and structural data, previous degassing models developed at Mt. Etna have been updated to advance the understanding of eruptive events that occurred in recent years.

The high-temperature P21/m -> C2/m phase transitions in synthetic amphiboles along the richterite-(BMg)-richterite join

Fri, 31 Dec 2010 23:00:00 GMT

Title: The high-temperature P21/m -> C2/m phase transitions in synthetic amphiboles along the richterite-(BMg)-richterite join Authors: Iezzi, G.; Università degli studi G. D'annunzio, Chieti Pescara, Italy; Tribaudino, M.; Università degli studi di Parma, Parma, Italy; Ventura, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Margiolaki, I. Abstract: The thermal behavior of three amphiboles along the join “Mg-richterite” [MRIC: ANaB(NaMg) CMg5TSi8O22W(OH)2]–richterite [RIC: ANaB(NaCa)CMg5TSi8O22W(OH)2] was investigated by in situ synchrotron radiation powder diffraction between 90 and 873 K. The studied samples have B-site compositions Na1Mg1 (sample RN1), Na0.97Mg0.8Ca0.24 (sample RN2), and Na0.97 Mg0.58Ca0.45 (sample RN6). The evolution of cell parameters as a function of T shows a discontinuity in the two Mg-richer samples (RN1 and RN2), which is interpreted as evidence of a P21/m → C2/m phase transition, whereas the Ca-richer sample (RN6) shows no evidence of a phase transition. The transition in samples RN1 and RN2 follows a different thermodynamic behavior, being tricritical in end-member “Mg-richterite” (RN1) and second order in the BCa-bearing amphibole RN2. A thermodynamic analysis done according to the Landau formalism and allowing for order parameter saturation, gives Tc = 462(3) and 378(1) K, and saturation temperature 𝛉s =116(21) and 141(7) for RN1 and RN2, respectively. Comparison with data from literature shows that the thermal strain of C-centered amphiboles with constant A-, C-, T-, and W-site occupancy equal to Na, Mg5, Si8, and (OH)2, respectively, and a B-site occupied by variable amounts of Li, Na, Mg, and/or Ca, mainly expands about 70° from c toward the a cell-edge onto the 010 plane. Conversely, the spontaneous strain accompanying the thermal transition shows that the maximum expansion is oriented about 25° from c and is coupled with a contraction close to the a cell direction. On the other side, transition induced by solid solution at room-T follows an almost opposite deformation pattern. The present data confirm the hypothesis of a first-order character of the transition induced by the increase of the B-site dimension for increasing BCa contents, similarly to the closely related P21/c → C2/c transition in pyroxenes.

Magma convection and mixing dynamics as a source of Ultra-Long-Period oscillations

Sat, 31 Dec 2011 23:00:00 GMT

Title: Magma convection and mixing dynamics as a source of Ultra-Long-Period oscillations Authors: Longo, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Papale, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Vassalli, M.; School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland; Saccorotti, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Montagna, C. P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Cassioli, A.; Dipartimento di Sistemi e Informatica, Università di Firenze, Firenze, Italy; Giudice, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Boschi, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia Abstract: Many volcanic eruptions are shortly preceded by injection of new magma into a pre-existing, shallow (<10 km) magma chamber, causing convection and mixing between the incoming and resident magmas. These processes may trigger dyke propagation and further magma rise, inducing long-term (days to months) volcano deformation, seismic swarms, gravity anomalies, and changes in the composition of volcanic plumes and fumaroles, eventually culminating in an eruption. Although new magma injection into shallow magma chambers can lead to hazardous event, such injection is still not systematically detected and recognized. Here, we present the results of numerical simulations of magma convection and mixing in geometrically complex magmatic systems, and describe the multiparametric dynamics associated with buoyant magma injection. Our results reveal unexpected pressure trends and pressure oscillations in the Ultra-Long-Period (ULP) range of minutes, related to the generation of discrete plumes of rising magma. Very long pressure oscillation wavelengths translate into comparably ULP ground displacements with amplitudes of order 10−4–10−2 m. Thus, new magma injection into magma chambers beneath volcanoes can be revealed by ULP ground displacement measured at the surface.

Adventive hydrothermal circulation on Stromboli volcano (Aeolian Islands, Italy) revealed by geophysical and geochemical approaches: Implications for general fluid flow models on volcanoes

Thu, 31 Dec 2009 23:00:00 GMT

Title: Adventive hydrothermal circulation on Stromboli volcano (Aeolian Islands, Italy) revealed by geophysical and geochemical approaches: Implications for general fluid flow models on volcanoes Authors: Finizola, A.; Laboratoire GéoSciences Réunion, UR, IPGP, UMR 7154, Saint Denis, La Réunion, France; Ricci, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Deiana, R.; Dipartimento di Geoscienze, Università degli Studi di Padova, Padova, Italy; Barde Cabusson, S.; Dipartimento di Scienze della Terra, Università di Firenze, Firenze, Italy; Rossi, M.; Dipartimento di Geoscienze, Università degli Studi di Padova, Padova, Italy; Praticelli, N.; Dipartimento di Geoscienze, Università degli Studi di Padova, Padova, Italy; Giocoli, A.; Laboratorio di Geofisica, IMAA-CNR, Tito Scalo, Potenza, Italy; Romano, G.; Tito Scalo, Potenza, Italy; Delcher, E.;; Suski, B.; Institut de Géophysique, Université de Lausanne, Lausanne, Switzerland; Revil, A.; Colorado School of Mines, Illinois St. Golden, Colorado, USA; CNRS-LGIT, UMR 5559, Université de Savoie, Equipe Volcan, Le Bourget du Lac, France; Menny, P.; Laboratoire Magmas et Volcans, Université Blaise Pascal, Clermont-Ferrand, France; Di Gangi, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Letort, J.; Ecole et Observatoire des Sciences de la Terre, Université de Strasbourg, France; Peltier, A.; Institut de Physique du Globe de Paris, UMR 7154, Paris, France; Villasante-Marcos, V.; Instituto Geografico Nacional, Madrid, Spain; Douillet, G.; Ecole et Observatoire des Sciences de la Terre, Université de Strasbourg, France; Avard, G.; Department of Geological Sciences, University of Missouri, USA; Lelli, M.; Istituto di Geoscienze e Georisorse, CNR, Pisa, Italy Abstract: On March 15th 2007 a paroxysmal explosion occurred at the Stromboli volcano. This event generated a large amount of products,mostly lithic blocks, someofwhich impacted the ground as far as down to 200 m a.s.l., about 1.5 kmfaraway fromthe active vents. Two days after the explosion, a newvapouremissionwas discovered on the north-eastern flank of the volcanic edifice, at 560 m a.s.l., just above the area called “Nel Cannestrà”. This new vapour emission was due to a block impact. In order to investigate the block impact area to understand the appearance of the vapour emission, we conducted on May 2008 a multidisciplinary study involving Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR), Self-Potential (SP), CO2 soil diffuse degassing and soil temperature surveys. This complementary data set revealed the presence of an anomalous conductive body, probably related to a shallow hydrothermal level, at about 10–15 m depth, more or less parallel to the topography. It is the first time that such a hydrothermal fluid flow,with a temperature close to thewater boiling point (76 °C) has been evidenced at Stromboli at this low elevation on the flank of the edifice. The ERT results suggest a possible link between (1) the main central hydrothermal system of Stromboli, located just above the plumbing system feeding the active vents, with a maximum of subsurface soil temperature close to 90 °C and limited by the NeoStromboli summit crater boundary and (2) the investigated area of Nel Cannestrà, at ~500 m a.s.l., a buried eruptive fissure active 9 ka ago. In parallel, SP and CO2 soil diffuse degassingmeasurements suggest in this sector at slightly lower elevation fromthe block impact crater a magmatic and hydrothermal fluid rising system along the N41° regional fault. A complementary ERT profile, on May 2009, carried out from the NeoStromboli crater boundary downto the block impact crater displayed a flank fluid flowapparently connected to a deeper system. The concept of shallow hydrothermal level have been compared to similar ERT results recently obtained onMount Etna and La Fossa cone of Vulcano. This information needs to be taken into account in general fluid flow models on volcanoes. In particular, peripheral thermal waters (as those bordering the northeastern coast of Stromboli) could be contaminated by hydrothermal and magmatic fluids coming from regional faults but also from the summit.

Insights into fluid circulation across the Pernicana Fault (Mt. Etna, Italy) and implications for flank instability

Wed, 31 Mar 2010 22:00:00 GMT

Title: Insights into fluid circulation across the Pernicana Fault (Mt. Etna, Italy) and implications for flank instability Authors: Siniscalchi, A.; Dipartimento di Geologia e Geofisica, Università degli Studi di Bari, via Orabona, 4-70125, Bari-Italy; Tripaldi, S.; Dipartimento di Geologia e Geofisica, Università degli Studi di Bari, via Orabona, 4-70125, Bari-Italy; Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Giammanco, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Piscitelli, S.; Istituto di Metodologie per l' Analisi Ambientale, CNR, Tito (PZ), Italy; Balasco, M.; Istituto di Metodologie per l' Analisi Ambientale, CNR, Tito (PZ), Italy; Behncke, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Magri, C.; Dipartimento di Geologia e Geofisica, Università degli Studi di Bari, via Orabona, 4-70125, Bari-Italy; Naudet, V.; Université Bordeaux 1, Geosciences Hydrosciences Material and Constructions, GHYMAC-EA 4134, Talence, F-33405, France; Rizzo, E.; Istituto di Metodologie per l' Analisi Ambientale, CNR, Tito (PZ), Italy Abstract: We conducted geophysical–geochemical measurements on a ∼2 kmN–S profile cutting across the Pernicana Fault, one of the most active tectonic features on the NE flank of Mt. Etna. The profile passes from the unstable E flank of the volcano (to the south) to the stable N flank and significant fluctuations in electrical resistivity, self-potential, and soil gas emissions (CO2, Rn and Th) are found. The detailed multidisciplinary analysis reveals a complex interplay between the structural setting, uprising hydrothermal fluids, meteoric fluids percolating downwards, ground permeability, and surface topography. In particular, the recovered fluid circulation model highlights that the southern sector is heavily fractured and faulted, allowing the formation of convective hydrothermal cells. Although the existence of a hydrothermal system in a volcanic area does not surprise, these results have great implications in terms of flank dynamics at Mt. Etna. Indeed, the hydrothermal activity, interacting with the Pernicana Fault activity, could enhance the flank instability. Our approach should be further extended along the full extent of the boundary between the stable and unstable sectors of Etna for a better evaluation of the geohazard in this active tectonic area.

Interpretation of data from the monitoring thermal camera of Stromboli volcano (Aeolian Islands, Italy)

Tue, 30 Jun 2009 22:00:00 GMT

Title: Interpretation of data from the monitoring thermal camera of Stromboli volcano (Aeolian Islands, Italy) Authors: Zanon, V.; Centro de Vulcanologia e Avaliac¸ ˜ao de Riscos Geol´ogicos, Universidade dos Ac¸ores, Rua M˜ae de Deus, 9501-801 Ponta Delgada, Portugal; Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Pecora, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia Abstract: Twenty eruptive events from the Northeast Crater of Stromboli volcano recorded by a thermal monitoring camera in early 2004 were analysed in order to understand the eruptive dynamics. Selected eventswere chosen to be typical of explosions that characterize the steady activity of Stromboli in terms of jet height and duration. Most of the explosions consisted of clast-rich single bursts, originating from the same vent inside the Northeast Crater. Conspicuous ash emission was scarce. Eruptions were preceded by the flashing of a perturbation wave characterized by low temperatures and an average propagation velocity of about 35–100 m s−1. This perturbation was thought to be caused by the bursting of the gas slug at the bottom of the crater and is interpreted as an air wave. This was immediately followed by the expansion of a jet of ‘hot’ gas and particles, at a velocity of 35–75 m s−1. Ejecta coarser than 138 cm appeared ∼1.6–2 s after the onset of the explosion, moving at a variable velocity (30–60 m s−1). Eruptive events were either vertical or inclined 7–13◦ towards the NNW. This inclination is thought to be a consequence either of the morphology of the conduit, following modest rock falls that partially obstructed the uppermost part of the crater, or of the displacement of the internal conduit due to the explosive activity of the volcano. The instability of the summit area is a further possible cause of the deformation of the conduit.

Volcanic Eruptions:Cyclicity during Lava Dome Growth

Thu, 03 Jul 2008 22:00:00 GMT

Title: Volcanic Eruptions:Cyclicity during Lava Dome Growth Authors: Melnik, O.; Institute of Mechanics, Moscow State University,; Sparks, R. S. J.; Earth Science Department, University of Bristol,; Costa, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Barmin, A.; Institute of Mechanics, Moscow State University, Abstract: We consider the process of slow extrusion of very viscous magma that forms lava domes. Dome-building eruptions are commonly associated with hazardous phenomena, in- cluding pyroclastic flows generated by dome collapses, explosive eruptions and volcanic blasts. These eruptions commonly display fairly regular alternations between pe- riods of high and low or no activity with time scales from hours to years. Usually hazardous phenomena are asso- ciated with periods of high magma discharge rate, thus, understanding the causes of pulsatory activity during ex- trusive eruptions is an important step towards forecasting volcanic behavior, especially the transition to explosive ac- tivity when magma discharge rate increases by a few orders of magnitude. In recent years the risks have increased be- cause the population density in the vicinity of many active volcanoes has increased.

Modeling the interplay of fO2 and fS2 along the FeS-silicate melt equilibrium

Mon, 31 Dec 2007 23:00:00 GMT

Title: Modeling the interplay of fO2 and fS2 along the FeS-silicate melt equilibrium Authors: Moretti, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Baker, Don R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: In this paper we will discuss a simplified thermodynamic description for the saturation of FeS, either liquid or solid, in magmatic melts. The Conjugated-Toop–Samis–Flood–Grjotheim model [Moretti R. and Ottonello G., 2005. Solubility and speciation of sulfur in silicate melts, the Conjugated-Toop–Samis–Flood–Grjotheim (CTSFG) model. Geochimica et Cosmochimica Acta, 69, 801–823] has furnished the theoretical reference frame, since it already accounts for the solubility of gaseous sulfur and the speciation and oxidation state of sulfur in silicate melts. We provide a new model to predict the saturation of magmatic silicate melts with an FeS phase that is internally consistent with these previous parameterizations. The derived model provides an effective sulfogeobarometer, which is superior with respect to previous models. For magmas rising from depth to surface, our appraisal of molar volumes of sulfur-bearing species in silicate melts allows us to model oxidation–reduction processes at different pressures, and sulfur concentrations for saturationwith either liquid or solid phases. In this respect, the nature of the oxygen fugacity buffer is critical. On the basis of model results on some typical compositions of volcanological interest, the sulfur contents at sulfide saturation (SCSS) have been calculated and the results duplicate the experimental observations that the SCSS is positively correlatedwith pressure forwatersaturated acidic melts and negatively correlated with pressure for water-poor basaltic melts. This new model provides fO2–fS2 pairs of FeS saturation of natural silicatemelts. In caseswhere the redox constraint is lacking, the model can be used to investigate whether the dissolved sulfur content approaches SCSS or not, and if so, to estimate at which fO2 value the silicate melt is saturated with a sulfide phase

The 2007 eruption of Stromboli volcano: Insights from real-time measurement of the volcanic gas plume CO2/SO2 ratio

Mon, 31 Dec 2007 23:00:00 GMT

Title: The 2007 eruption of Stromboli volcano: Insights from real-time measurement of the volcanic gas plume CO2/SO2 ratio Authors: Aiuppa, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Federico, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Giudice, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Giuffrida, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Guida, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Gurrieri, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Liuzzo, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; Moretti, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Papale, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia Abstract: The recent eruption of Stromboli in February–April 2007 offered a unique chance to test our current understanding of processes driving the transition from ordinary (persistent Strombolian) to effusive activity, and the ability of instrumental geophysical and geochemical networks to interpret and predict these events. Here, we report on the results of two years of in-situ sensing of the CO2/SO2 ratio in Stromboli's volcanic gas plume, in the attempt to put constraints on the trigger mechanisms and dynamics of the eruption. We show that large variations of the plume CO2/SO2 ratio (range, 0.9–26) preceded the onset of the eruption (since December 2007), interrupting a period of relatively-steady and low ratios (time-averaged ratio, 4.3) lasting from at least May to November 2006. By contrasting our observations with numerical simulations of volcanic degassing at Stromboli, derived by use of an equilibrium saturation model, we suggest that the pre-eruptive increase of the ratio reflected an enhanced supply of deeply-derived CO2-rich gas bubbles to the shallowplumbing system. This larger-than-normal ascent of gas bubbles was likely sourced by a 1–3 km deep gas– melt separation region (probably a magma storage zone), and caused faster convective overturning of magmas in the shallow conduit; an increase in the explosive rate and in seismic tremor, and finally the collapse of the la Sciara del Fuoco sector triggering the effusive phase. The high CO2/SO2 ratios (up to 21) observed during the effusive phase, and particularly in the days and hours before a paroxysmal explosion on March 15, 2007, indicate the persistence of the same gas source; and suggest that de-pressurization of the same 1–3 km deep magma storage zone could have been the trigger mechanism for the paroxysm itself