http://hdl.handle.net/2122/264 Sat, 25 May 2013 13:30:00 GMT 2013-05-25T13:30:00Z http://hdl.handle.net/2122/8609 Title: Enhanced crystal fabric analysis of a lava flow sample by neutron texture diffraction: A case study from the Castello d’Ischia dome Authors: Walter, J. M.; Mineralogisch-Petrologisches Institut, Universität Bonn, Poppelsdorfer Schloss, D-53115, Bonn,; Iezzi, G.; Dipartimento di Ingegneria e Geologia (INGEO), Università G. d’Annunzio, Chieti, Italy; Albertini, G.; Dipartimento di Fisica e Ingegneria dei Materiali e del Territorio, Università Politecnica delle Marche,; Gunther, M. E.; Department of Geological Sciences, University of Idaho, Moscow, Idaho, USA; Piochi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Ventura, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Jansen, E.; Mineralogisch-Petrologisches Institut, Universität Bonn, Bonn, Germany; Fiori, F.; Di.S.C.O., Sez. di Biochimica, Biologia e Fisica, Università Politecnica delle Marce, Ancona, Italy Abstract: The crystal fabric of a lava has been analyzed for the first time by neutron texture diffraction. In this study we quantitatively investigate the crystallographic preferred orientation of feldspars in the Castello d’Ischia (Ischia Island, Italy) trachytic exogenous dome. The crystallographic preferred orientation was measured with the monochromatic neutron texture diffractometer SV7 at the Forschungszentrum Jülich in Germany and a Rietveld refinement was applied to the sum diffraction pattern. The complementary thin section analysis showed that the three-dimensional crystal shape and the corresponding shape preferred orientation are in agreement with the quantitative orientation distributions of the neutron texture data. The (0k0) crystallographic planes of the feldspars are roughly parallel to the local flow bands, whereas the other corresponding pole figures show that a pivotal rotation of the anorthoclase and sanidine crystals was active during the emplacement of this lava dome. In combination with scanning electron microscopy investigations, electron probe microanalysis, XRF, and X-ray diffraction, the Rietveld refinement of the neutron diffraction data indicates a slow cooling dynamic on the order of several months during their crystallization under subaerial conditions. Results attained here demonstrate that neutron texture diffraction is a powerful tool that can be applied to lava flows. Wed, 30 Jan 2013 23:00:00 GMT http://hdl.handle.net/2122/8609 2013-01-30T23:00:00Z http://hdl.handle.net/2122/8373 Title: An analytical model for gas overpressure in slug-driven explosions: Insights into Strombolian volcanic eruptions Authors: Del Bello, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Llewellin, E. W.; University of Durham; Taddeucci, J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Scarlato, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Lane, S.; Lancaster University Abstract: Strombolian eruptions, common at basaltic volcanoes, are mildly explosive events that are driven by a large bubble of magmatic gas (a slug) rising up the conduit and bursting at the surface. Gas overpressure within the bursting slug governs explosion dynamics and vigor and is the main factor controlling associated acoustic and seismic signals. We present a theoretical investigation of slug overpressure based on magma-static and geometric considerations and develop a set of equations that can be used to calculate the overpressure in a slug when it bursts, slug length at burst, and the depth at which the burst process begins. We find that burst overpressure is controlled by two dimensionless parameters: V′, which represents the amount of gas in the slug, and A′, which represents the thickness of the film of magma that falls around the rising slug. Burst overpressure increases nonlinearly as V′ and A′ increase. We consider two eruptive scenarios: (1) the “standard model,” in which magma remains confined to the vent during slug expansion, and (2) the “overflow model,” in which slug expansion is associated with lava effusion, as occasionally observed in the field. We find that slug overpressure is higher for the overflow model by a factor of 1.2–2.4. Applying our model to typical Strombolian eruptions at Stromboli, we find that the transition from passive degassing to explosive bursting occurs for slugs with volume >24–230 m3, depending on magma viscosity and conduit diameter, and that at burst, a typical Strombolian slug (with a volume of 100–1000 m3) has an internal gas pressure of 1–5 bars and a length of 13–120 m. We compare model predictions with field data from Stromboli for low-energy “puffers,” mildly explosive Strombolian eruptions, and the violently explosive 5 April 2003 paroxysm. We find that model predictions are consistent with field observations across this broad spectrum of eruptive styles, suggesting a common slug-driven mechanism; we propose that paroxysms are driven by unusually large slugs (large V′). Thu, 09 Feb 2012 23:00:00 GMT http://hdl.handle.net/2122/8373 2012-02-09T23:00:00Z http://hdl.handle.net/2122/8313 Title: Rapid differentiation in a sill-like magma reservoir: a case study from the campi flegrei caldera Authors: Pappalardo, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Mastrolorenzo, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia Abstract: In recent decades, geophysical investigations have detected wide magma reservoirs beneath quiescent calderas. However, the discovery of partially melted horizons inside the crust is not sufficient to put constraints on capability of reservoirs to supply cataclysmic eruptions, which strictly depends on the chemical-physical properties of magmas (composition, viscosity, gas content etc.), and thus on their differentiation histories. In this study, by using geochemical, isotopic and textural records of rocks erupted from the high-risk Campi Flegrei caldera, we show that the alkaline magmas have evolved toward a critical state of explosive behaviour over a time span shorter than the repose time of most volcanic systems and that these magmas have risen rapidly toward the surface. Moreover, similar results on the depth and timescale of magma storage were previously obtained for the neighbouring Somma-Vesuvius volcano. This consistency suggests that there might be a unique long-lived magma pool beneath the whole Neapolitan area. Sat, 31 Dec 2011 23:00:00 GMT http://hdl.handle.net/2122/8313 2011-12-31T23:00:00Z http://hdl.handle.net/2122/8306 Title: Crystal fractionation, magma step ascent, and syn-eruptive mingling: the Averno 2 eruption (Phlegraean Fields, Italy) Authors: Fourmentraux, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Métrich, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Bertagnini, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Rosi, M.; Dipartimento di Scienze della Terra, Pisa, Italy Abstract: The 3.7 ka year-old Averno 2 eruption is one of the rare eruptions to have occurred in the northwest sector of the Phlegraean Fields caldera (PFc) over the past 5 ka. We focus here on the fallout deposits of the pyroclastic succession emplaced during this eruption. We present major and trace element data on the bulk pumices, along with major and volatile element data on clinopyroxene-hosted melt inclusions, in order to assess the conditions of storage, ascent, and eruption of the feeding trachytic magma. Crystal fractionation accounts for the evolution from trachyte to alkali-trachyte magmas; these were intimately mingled (at the micrometer scale) during the climactic phase of the eruption. The Averno 2 alkali trachyte represents one of the most evolved magmas erupted within the Phlegraean Fields area and belongs to the series of differentiated trachytic magmas erupted at different locations 5 ka ago. Melt inclusions record significant variations in H2O (from 0.4 to 5 wt%), S (from 0.01 to 0.06 wt%), Cl (from 0.75 up to 1 wt%), and F (from 0.20 to >0.50 wt%) during both magma crystallization and degassing. Unlike the eruptions occurring in the central part of the PFc, deep-derived input(s) of gas and/or magma are not required to explain the composition of melt inclusions and the mineralogy of Averno 2 pumices. Compositional data on bulk pumices, glassy matrices, and melt inclusions suggest that the Averno 2 eruption mainly resulted from successive extrusions of independent magma batches probably emplaced at depths of 2–4 km along regional fractures bordering the Neapolitan Yellow Tuff caldera. Thu, 31 May 2012 22:00:00 GMT http://hdl.handle.net/2122/8306 2012-05-31T22:00:00Z http://hdl.handle.net/2122/8299 Title: Morphometric analysis of lava flow units: Case study over LIDAR-derived topography at Mount Etna, Italy Authors: Tarquini, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Favalli, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Mazzarini, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Isola, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Fornaciai, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia Abstract: High resolution, LIDAR-derived digital elevation models of volcanic areas can significantly improve knowledge of lava flow morphology and emplacement mechanisms. Here we focus on single flow units, presenting a new semi-automatic procedure which provides a quantitative analysis of their shape. The method relies on the automatic processing of the elevation profiles obtained on transects orthogonal to the flow unit axis. The initial phase of the Mount Etna flank eruption from September 2004 is taken as test case, and the procedure is applied on an active lava flow, which was emplaced on the eastern flank of the volcano. The main topographic dataset used is a 2-m-resolution digital elevation model obtained from a LIDAR survey. Starting from the axis of a lava flow unit, our method yields morphometric data on the flow unit at a 2 m spacing, calculating parameters including flow width, channel width, the heights of the levees, inward and outward slope of levees, and estimating pre-emplacement slope along the axis. The procedure is embedded in a customized GIS, which allows easy processing, handling and displaying of data. The procedure has also been applied to another flow unit emplaced during the October–November 1999 overflow from the Bocca Nuova crater. Results show that the channel width seems to accommodate first‐order trends of the pre-emplacement slope along the flow unit axis, while it is little affected by high frequency changes in slope; in contrast, flow unit width and flow unit thickness are apparently influenced by small‐scale changes in slope. The different emplacement conditions of the two flow units are reflected by the overall contrasting morphologies, as shown by the different average thickness and by the different ratios between (i) flow width vs. channel width and (ii) flow unit section area vs. channel width. The new method provides an enhanced, systematic and thorough morphometric description of flow units, which may improve the understanding of the emplacement mechanisms of lava flows on Earth and other planets. Tue, 31 Jul 2012 22:00:00 GMT http://hdl.handle.net/2122/8299 2012-07-31T22:00:00Z http://hdl.handle.net/2122/8287 Title: Degassing behaviour of vesiculated basaltic magmas: an example from Ambrym volcano, Vanuatu Arc Authors: Polacci, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Baker, D. R.; Earth and Planetary Sciences, McGill University, Montreal, QC H3A2A7, Canada; La Rue, A.; Earth and Planetary Sciences, McGill University, Montreal, QC H3A2A7, Canada; Mancini, L.; Sincrotrone Trieste S.C.p.A., 34149 Basovizza (Trieste), Italy; Allard, P.; Institut de Physique du Globe, Paris Sorbonne Cité, CNRS UMR7154, Paris, France Abstract: Ambrym is one of the most actively erupting basaltic volcanoes in the Vanuatu island arc. Scoria clasts collected from a fallout deposit in the inner terrace of its Benbow active crater were analyzed through series of synchrotron X-ray computed microtomographic experiments, as well as permeability measurements and simulations. Our goal was to reconstruct and visualize scoria textures in 3D and to quantify vesicularity, permeability, vesicle sizes and distributions in order to understand how gas moves in and out of Ambrym basaltic magma. We find that vesicle size distributions in the volume range between ~ 103 and 1010 μm3 define two scoria classes. Vesicle size distributions in the low-to-moderately (0.44–0.67) vesicular samples can be fit by power laws with an exponent of 1 ± 0.2; distributions in the highly vesicular (0.86–0.88) samples can be fit by power laws with a higher exponent (1.4 to 1.7), as well as by exponential fits. Highly vesicular samples exhibit a very pronounced large vesicle, consisting of networks of smaller, interconnected vesicles, that is more than three orders of magnitude larger in volume than all other vesicles in each distribution. This type of vesicle is not found in the low-to-moderately vesicular samples. In addition, vesicle number density negatively correlates with vesicularity: less vesicular samples have the highest number density and vice versa, and contain far more numerous small-to-medium-sized vesicles than highly vesicular samples. Measured and calculated viscous (Darcian) permeabilities overlap in the range 10− 13 and 10− 9 m2, with higher values in the more vesicular samples. We ascribe these differences in the textural and physical properties of the scoria clasts to their derivation from distinct magma portions in the conduit that were driven by convective overturn and underwent different vesiculation histories and gas transport dynamics. Comparing basaltic scoria clasts from Ambrym to those from mild explosive activity at Stromboli volcano (Italy) reveals that differences in their vesicle size distributions may result from the influence of different crystal contents and shapes on the vesiculation and permeability of the respective magmas. Finally, we highlight how rheological properties have a fundamental role in determining the degassing behaviour of basaltic magma at Ambrym and other volcanoes in general. Sat, 30 Jun 2012 22:00:00 GMT http://hdl.handle.net/2122/8287 2012-06-30T22:00:00Z http://hdl.handle.net/2122/8281 Title: Xenopumices from the 2011–2012 submarine eruption of El Hierro (Canary Islands, Spain): Constraints on the plumbing system and magma ascent Authors: Meletlidis, S.; Centro Geofísico de Canarias, Instituto Geográfico Nacional, Santa Cruz de Tenerife, Spain; Di Roberto, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Pompilio, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Bertagnini, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Iribarren, I.; Centro Geofísico de Canarias, Instituto Geográfico Nacional, Santa Cruz de Tenerife, Spain; Felpeto, A.; Centro Geofísico de Canarias, Instituto Geográfico Nacional, Santa Cruz de Tenerife, Spain; Torres, P. A.; Centro Geofísico de Canarias, Instituto Geográfico Nacional, Santa Cruz de Tenerife, Spain; D'Oriano, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia Abstract: Textures, petrography and geochemical compositions of products emitted during the onset of the 2011–2012 submarine eruption (15 October, 2011) off the coast of El Hierro have been investigated to get information on interaction mechanism between the first rising magma and the crust during the onset of the eruption as well as to get information on magma storage and plumbing systems beneath El Hierro volcano. Studied products consist of 5–50 cm bombs with an outer black to greenish, vesicular crust with bulk basanite composition containing pumiceous xenoliths (xenopumices). Our results show that xenopumices are much more heterogeneous that previously observed, since consist of a macro-scale mingling of a gray trachyte and white rhyolite. We interpreted xenopumices as resulting from the interaction (heating) between the basanitic magma feeding the eruption, a stagnant trachytic magma pocket/s and an associated hydrothermally altered halo with rhyolitic composition. Our findings confirm the importance of the study of the early products of an eruption since they can contain crucial information on the plumbing system geometry and the mechanism of magma ascent. Mon, 10 Sep 2012 22:00:00 GMT http://hdl.handle.net/2122/8281 2012-09-10T22:00:00Z http://hdl.handle.net/2122/8248 Title: The Mt. Moio eruption (Etna): Stratigraphy, petrochemistry and 40Ar/39Ar age determination with inferences on the relationship between structural setting and magma intrusion Authors: Del Carlo, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Branca, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; De Beni, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Lo Castro, M. D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Wijbrans, J. R.; Faculteit Aard-en Levenswetenschappen, Vrije Universiteit, Amsterdam, The Netherlands Abstract: Mt. Moio is the most peripheral scoria cone of Etna volcano and rises above the Peloritani Mountains sedimentary basement, 18 km north of the volcano summit. Geological and tephrostratigraphic studies and 40Ar/39Ar age determinations were used to characterize the eruption and constrain its occurrence to ~ 29 ka ago, during the activity of the Ellittico volcano, the volcanic edifice active before the actual one, the Mongibello volcano. The Mt. Moio eruption formed a large scoria cone and a widespread tephra fallout deposit, indicating that vigorous explosive activity produced an eruptive plume; minor effusive activity produced a small lava flow at the end of the eruption. Geochemical data indicate that the composition of erupted magma became less evolved during the eruption (mugearite → basalt–hawaiite); thus Mt. Moio deposits have been divided into Lower and Upper Sequences characterized by similar depositional facies. Based on the classification of Etna flank eruptions available in the literature, Mt. Moio can be classed as an eccentric (sensu Rittmann) and Class B eruption. Historic flank eruptions (e.g. 1669, 1763, 2001, 2002–03) formed deposits that are petrochemically and stratigraphically similar to those of Mt. Moio. The general trend of the Mt. Moio eruptive fissure corresponds to that of extensional neotectonic lineaments in the Apenninic–Maghrebian Chain, indicating that the structure of the basement played a role in controlling the ascent of the volatile-rich magma during Ellittico volcano activity. Sun, 30 Sep 2012 22:00:00 GMT http://hdl.handle.net/2122/8248 2012-09-30T22:00:00Z http://hdl.handle.net/2122/8187 Title: Evidence of basaltic magma intrusions in a trachytic magma chamber at Pantelleria (Italy) Authors: Romengo, N.; Università di Palermo; Landi, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Rotolo, S. G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia Abstract: In the last 50 ka basalts have erupted outside the margin of the young caldera on the island of Pantelleria. The inner portion of the caldera has instead been filled by trachyte lavas, pantellerite lavas and pumice fall deposits. This paper focuses on a low-volume benmoreite lava topping the trachyte lava pile in the middle of the young caldera. The mineral chemistry, including trace elements in clinopyroxene (LA-ICP-MS), suggests that benmoreite is a hybrid product resulting from mixing between a trachytic magma and a basaltic end member even more primitive than those erupted during the past 50 ka. The principal inference is that basaltic magmas intruded the trachytic magma chamber below the caldera and were erupted in recent times within the caldera and not only beyond, as the distribution of basaltic centers would suggest. Data are used to discuss the relationship between felsic and mafic magmas at Pantelleria. Sat, 31 Dec 2011 23:00:00 GMT http://hdl.handle.net/2122/8187 2011-12-31T23:00:00Z http://hdl.handle.net/2122/8101 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. Mon, 31 Dec 2012 23:00:00 GMT http://hdl.handle.net/2122/8101 2012-12-31T23:00:00Z