117,617 research outputs found
Rheomorphic structures in a high-grade ignimbrite: The Nuraxi tuff, Sulcis volcanic district (SW Sardinia, Italy)
No full textDeposits of the 15.8 Ma Nuraxi explosive eruption crop out in the Sulcis volcanic district, southwestern Sardinia. They consist of a decimeter-thick pumice fallout layer overlain, with no apparent temporal break, by several tens of meters thick, high-grade ignimbrite. The eruption was from a vent probably located ∼20-30 km north of S. Pietro island, and it tapped a compositionally uniform, rhyolite magma reservoir (SiO2 70-72 wt.%) bearing about 20 vol.% crystals. The ignimbrite consists of: (a) a Lower Ignimbrite (LI), <2-m-thick, fine-grained and glassy grading upward into a partly devitrified lapilli-tuff, and (b) an Upper Ignimbrite (UI) that is an intensely welded to lava-like lapilli-tuff. The deposit has an inferred maximum runout of about 80 km and overall dispersal/thickness characteristic of a low aspect-ratio ignimbrite. Over most of its outcrop the tuff rests on a flat, horizontal paleosurface and forms an ignimbrite plateau with uniform thickness and structural characteristics. However, in some areas it shows extensive folding and over-thickening as a result of rheomorphic flow into topographic depressions. Structural analysis of the ignimbrite reveals the presence of a pervasive foliation and lineation as well as macroscopic and microscopic flow structures. Occurrence of abundant, widely distributed stretched cavities in the tuff indicates that a substantial amount of gas was trapped in the tuff during aggradation. The observed pattern of structures of the ignimbrite plateau accords well with a conceptual model in which syn-depositional structures are formed during non-particulate, basal laminar flow due to agglutination of juvenile particles within the lower part of the pyroclastic density current. The flow was controlled by the substantial transfer of momentum from the high-speed, particulate upper part of the current to the top of the non-particulate part of the current and the onset of a complex relationship between welding, flow and sedimentation processes. It is proposed in particular that elongated gas pockets played a major role in guiding the laminar shear within the non-particulate part of the current in flat, horizontal areas, eventually promoting brittle failure of the deforming tuff mass along shear planes
Magma and tephra characteristics for the 17–25 May 2016 Mt Etna eruption
No full textWe provide the dataset associated with the research data article “Shallow factors controlling the explosivity of basaltic magmas: The 17–25 May 2016 eruption of Etna Volcano (Italy)” Edwards et al. This dataset contains major element data for groundmass glass, plagioclase, olivine and clinopyroxene phenocrysts, and melt inclusions within these phenocrysts, found within tephra and lava from this eruption. We also provide the grain size dataset from the fallout deposits
Campylopus introflexus Brid.
No full textCampylopus introflexus (Hedw.) Brid. − 2A, versants de la Montagne de Cagna, en forêt communale de Pianotoli Caldarello/Zerubia, dans la sapinière dont l’association est à rapprocher du Poo –Fagetum sylvaticae abietietosum, 18.6.2008, Pioli , A. (Hb. privé 20080618002); 2B, forêt communale de Moltifao, tourbière de Valdo [UTM: NM128031], sur des touradons d’ Osmunda regalis, dans une association s’apparentant à l’ Hyperico-Alnetum osmundetosum, pas de bryophytes compagnes, 4.6.2010, Pioli , A. (Hb. privé 20100604001). Espèce invasive, signalée jusqu’ici en forêt territoriale de Melaghia (SOTIAUX et al., 2008).Published as part of Pioli, Achille, 2015, Contribution à l'inventaire des bryophytes de corse: nouvelles données sur la présence de quelques espèces nouvelles, rares ou peu fréquentes, pp. 101-107 in Candollea 70 (1) on page 104, DOI: 10.15553/c2015v701a9, http://zenodo.org/record/568437
Transient explosions at open-vent volcanoes: The case of Stromboli (Italy)
No full textStromboli is a persistently active, open-vent basaltic volcano whose activity is controlled by
the balance between magma supply, outgassing, and eruptive rates, and is characterized by low-intensity, regular Strombolian explosions. However, two types of large, transient, violent explosive eruptions suddenly occur with no clear precursory activity. These explosions, called “major” and “paroxysmal” depending on size, cover a large variability in intensity and mag- nitude, but are all marked by short duration. Paroxysms have significantly larger intensities (>106 kg/s) than major explosions (104 kg/s) and fundamental differences in the characteris- tics (composition, crystallinity, vesicularity) of the erupted tephra, suggesting that different sources feed these two eruption types. Paroxysms are generated by the explosive fragmen- tation of low-porphyricity (LP) magma mingled with high-porphyricity resident magma in the shallow reservoir, whereas major eruptions are likely associated with destabilization of the lower portion of the shallow magmatic system, continuously hybridized by the arrival of LP magma. In general, the intensity of these explosions is related to the amount of the LP magma erupted (>107 kg in paroxysms and 104–105 kg in major explosions), suggesting that the magma plays a major role in the fragmentation mechanism. Despite its primary impor- tance in the hazards of Stromboli, the total amount of magma erupted in these events in the past 10 years is less than 1% of the total mass erupted by the volcano
Author Correction: Reliability of Total Grain-Size Distribution of Tephra Deposits (Scientific Reports, (2019), 9, 1, (10006), 10.1038/s41598-019-46125-8)
No full textAn amendment to this paper has been published and can be accessed via a link at the top of the paper
Breutelia chrysocoma Lindb.
No full textBreutelia chrysocoma (Hedw.) Lindb. − 2A, ForêtcommunaledeCorrano,peuplementcomposé d’un taillis sous futaie de chêne vert avec maquis à bruyère et arbousier, dans le vallon de Morodesi (thalweg), dans une zone claire de maquis bas composé par Erica arborea, Phyllerea latifolia, Quercus ilex, Smilax aspera, Rubia peregrina, dont l’association relève de l’ Erico-Arbutetum phillyreetosum latifoliae, exposition nord-ouest, substrat granitique, sol acide, aucun pied avec sporophyte, 400 m, 2.3.2011, Pioli, A. (Hb. privé 20110302002); 2A. ForêtcommunaledeCorrano, le long de la route départementale D757, sur le talus rocheux, granitique, à végétation vasculaire composée d’une futaie de chêne vert avec maquis, dont l’association s’apparente à l’ Erico-Arbutetum phillyreetosum latifoliae, aucun pied avec sporophyte, 7.3.2011, Pioli, A. (Hb. privé 20110307016). Espèce peu fréquente en Corse, connue de la région d’Ajaccio, de Cauro, Bastia (Teghime), et retrouvée dans la région de Porto et dans les Calanche de Piana (HÉBRARD, 1986). Elle occupe de grandes surfaces sur les stations répertoriées.Published as part of Pioli, Achille, 2015, Contribution à l'inventaire des bryophytes de corse: nouvelles données sur la présence de quelques espèces nouvelles, rares ou peu fréquentes, pp. 101-107 in Candollea 70 (1) on pages 103-104, DOI: 10.15553/c2015v701a9, http://zenodo.org/record/568437
Reliability of Total Grain-Size Distribution of Tephra Deposits
No full textTotal Grain-Size Distribution (TGSD) of tephra deposits is key to the characterization of explosive volcanism, plume-dispersal modeling, and magmatic fragmentation studies. Nonetheless, various aspects that includes deposit exposure and data fitting make its determination extremely complex and affect its representativeness. In order to shed some lights on the reliability of derived TGSDs, we examine a large TGSD dataset in combination with a sensitivity analysis of sampling strategies. These analyses are based both on a well-studied tephra deposit and on synthetic deposits associated with a variety of initial eruptive and atmospheric conditions. Results demonstrate that TGSDs can be satisfactorily fitted by four distributions (lognormal, Rosin-Rammler, and power-law based either on the absolute or cumulative number of particles) that capture different distribution features. In particular, the Rosin-Rammler distribution best reproduces both the median and the tails of the TGSDs. The accuracy of reconstructed TGSDs is strongly controlled by the number and distribution of the sampling points. We conclude that TGSDs should be critically assessed based on dedicated sampling strategies and should be fitted by one of the mentioned theoretical distributions depending on the specific study objective (e.g., tephra-deposit characterization, physical description of explosive eruptions, tephra-dispersal modeling)
Magnetic fabric, welding texture and strain fabric in the Nuraxi Tuff, Sardinia, Italy
No full textAnisotropy of magnetic susceptibility (AMS) has been used to interpret flow directions in ignimbrites, but no study has demonstrated that the AMS fabric corresponds to the flow fabric. In this paper, we show that the AMS and strain fabric coincide in a high-grade ignimbrite, the Nuraxi Tuff, a Miocene rhyolitic ignimbrite displaying a wide variability of rheomorphic features and a well-defined magnetic fabric. Natural remanent magnetization (NRM) data indicate that the magnetization of the tuff is homogeneous and was acquired at high temperatures by Ti-magnetite crystals. Comparison between the magnetic fabric and the deformation features along a representative section shows that AMS and anisotropy of isothermal remanent magnetization (AIRM) fabric are coaxial with and reproduce the shape of the strain ellipsoid. Magnetic tests and scanning electron microscopy observations indicate that the fabric is due to trails of micrometer-size, pseudo-single domain, magnetically interacting magnetite crystals. Microlites formed along discontinuities such as shard rims and vesicle walls mimicking the petrofabric of the tuff. The fabric was thus acquired after deposition, before late rheomorphic processes, and accurately mimics homogeneous deformation features of the shards during welding processes and mass flow. © Springer-Verlag 2008
Buxbaumia viridis Moug. & Nestl.
No full textBuxbaumia viridis (DC.) Moug. & Nestl. − 2B, Forêt communale d’Asco, peuplements composés de pin laricio s’apparentant au Galio – Pinetum laricii anthyllidetosum hermanniae, station située dans la zone humide de Valentinu [NM948951], à association se rapprochant de l’ Athyrio-Gentianetum gentianetosum, en exposition nord, 1160 m, quatre pieds sur un talus suintant tapissé par les restes très décomposés d’un tronc de pin laricio au sol, pas de bryophytes compagnes à proximité, 28.7.2010, Pioli, A. observation; 2B, Forêt communale d’Albertacce, canton de Calasima [NM922976], forêt de pin laricio à exposition nord-est, 1310 m, sept pieds sur un tronc de pin laricio au sol, pas de bryophytes compagnes à proximité, végétation vasculaire s’apparentant au Galio-Pinetum laricii anthyllidetosum hermanniae, 29.6.2011, Pioli, A. observation; 2B, Forêt communale de Vivario, vallée du Manganello, au lieu dit Grottacia [NM072677], forêt mélangée de hêtre et de pin laricio, exposition nord, 1150 m, quatre pieds sur une souche de pin laricio, pas de bryophytes compagnes à proximité, seuls quelques thalles primaires de Cladonia, végétation vasculaire s’apparentant au Poo-Fagetum sylvaticae fagetosum, 1.6.2011, Pioli, A. observation; 2B, Forêt communale de Vivario, station proche de la précédente dans la Vallée du Manganello, sur le GR 20 [NM073677], peuplements mélangés de hêtre et de pin laricio d’altitude, exposition nord, 1100 m, treize pieds sur une souche de pin laricio, colonisée par les mousses Hypnum cupressiforme, Dicranum tauricum et le lichen Cladonia coniocraea, végétation vasculaire s’apparentant au Poo-Fagetum sylvaticae fagetosum, 1.6.2011, Pioli, A. observation. Espèce protégée (annexe 2 de la directive européenne «Habitats»). Peu fréquente, connue des hêtraies-sapinières et des forêts de pin laricio, dans les forêts d’Aitone, Valdoniellu, Rospa Sorba, Noceta, Restonica, Vizzavona, Marmano, San Antone et Palneca (HÉBRARD, 2005; PIOLI, 2006). Les nouvelles stations ont été découvertes dans des forêts où nous suspections sa présence.Published as part of Pioli, Achille, 2015, Contribution à l'inventaire des bryophytes de corse: nouvelles données sur la présence de quelques espèces nouvelles, rares ou peu fréquentes, pp. 101-107 in Candollea 70 (1) on page 104, DOI: 10.15553/c2015v701a9, http://zenodo.org/record/568437
Controls on the explosivity of scoria cone eruptions: Magma segregation at conduit junctions
No full textViolent strombolian (transitional) eruptions are common in mafic arc settings and are characterized by simultaneous explosive activity from scoria cone vents and lava effusion from lateral vents. This dual activity requires magma from the feeder conduit to split into vertical and lateral branches somewhere near the base of the scoria cone. Additionally, if the flow is separated, gas and liquid (+ crystals) components of the magma may be partitioned unevenly between the two branches. Because flow separation requires bubbles to move independently of the liquid over time scales of magma ascent separation is promoted by low magma viscosities and by high magma H2O content (i.e. sufficiently deep bubble nucleation to allow organization of the gas and liquid phases during magma ascent). Numerical modeling shows that magma and gas distribution between vertical and horizontal branches of a T-junction is controlled by the mass flow rate and the geometry of the system, as well as by magma viscosity. Specifically, we find that mass eruption rates (MERs) between 103 and 105 kg/s allow the gas phase to concentrate within the central conduit, significantly increasing explosivity of the eruption. Lower MERs produce either strombolian or effusive eruption styles, while MER > 105 kg/s prohibit both gas segregation and lateral magma transport, creating explosive eruptions that are not accompanied by effusive activity. These bracketing MER constraints on eruptive transitions are consistent with field observations from recent eruptions of hydrous mafic magmas. © 2009 Elsevier B.V. All rights reserved
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