Plinian fall deposits from Vulsini Volcanic District (Central Italy)

Stratigraphic investigations of the Vulsini Volcanic District indicate the existence of five prominent plinian fall deposits, deposited over a period of about 0.34 Ma. The oldest deposit (Basal pumices) crops out mainly in the peripheral areas and is one of the largest plinian events in the Vulsini District, with a volume of about 9 km³ and a calculated column height exceeding 30 km. Subcircular patterns of isopachs and isopleths around the Bolsena lake indicate emplacement in wind-free conditions and suggest a source vent location in the northernmost sector of the present Bolsena lake, where it is possible that an older central volcanic structure existed. The four younger plinian fall deposits are related to Bolsena activity. The oldest of these, named the Ponticello and Orvieto-Bagnoregio pumices, are mainly distributed on the north-eastern sector of the Vulsini District. Their volumes are an order of magnitude lower than that of the basal unit, and the estimated column heights do not exceed 20 km. The younger Ospedaletto pumice deposit has a NE-SW dispersal axis, whereas the youngest Casetta pumice deposit is found only in the north-eastern sector of the district. Their estimated volumes are respectively 1.2 and 0.1 km³, whereas the inferred vent areas appear to be located slightly to the east of the Ponticello and Orvieto-Bagnoregio pumice deposit source areas. The chronology of the Ospedaletto and Casetta pumices indicates that the final plinian activity from the Bolsena complex is contemporaneous with the Latera activity. The decreasing volumes from the oldest to the youngest units, together with the progressive shifting northeastwards of the source vents, may be related to the volcano-tectonic subsidence of the Bolsena area. The source vents for the post-Basal pumices events are mainly clustered just north of Bolsena village where the greatest displacement during subsidence occurred. Accordingly, source vent shifting appears to be related to the progressive opening of normal faults from the inner to the outer margin of the Bolsena depression.     

Bayesian event tree for eruption forecasting (BET_EF) at Vesuvius,Italy: a retrospective forward application to the 1631 eruption

Reliable forecasting of the next eruption at Vesuvius is the main scientific factor in defining effective strategies to reduce volcanic risk in one of the most dangerous volcanic areas of the world. In this paper, we apply a recently developed probabilistic code for eruption forecasting to new and independent historical data related to the pre-eruptive phase of the 1631 eruption. The results obtained point out three main issues: (1) the importance of “cold” historical data (according to Guidoboni 2008) related to pre-eruptive phases for evaluating forecasting tools and possibly refining them; (2) the BET_EF code implemented for Vesuvius would have forecasted the 1631 eruption satisfactorily, marking different stages of the pre-eruptive phase; (3) the code shows that pre-eruptive signals that significantly increase the probability of eruption were likely detected more than 2 months before the event.     

Reconstruction of the eruptive activity on the NE sector of Stromboli volcano: timing of flank eruptions since 15 ka

A multidisciplinary geological and compositional investigation allowed us to reconstruct the occurrence of flank eruptions on the lower NE flank of Stromboli volcano since 15 ka. The oldest flank eruption recognised is Roisa, which occurred at ~15 ka during the Vancori period, and has transitional compositional characteristics between the Vancori and Neostromboli phases. Roisa was followed by the San Vincenzo eruption that took place at ~12 ka during the early stage of Neostromboli period. The eruptive fissure of San Vincenzo gave rise to a large scoria cone located below the village of Stromboli, and generated a lava flow, most of which lies below sea level. Most of the flank eruptions outside the barren Sciara del Fuoco occurred in a short time, between ~9 and 7 ka during the Neostromboli period, when six eruptive events produced scoria cones, spatter ramparts and lava flows. The Neostromboli products belong to a potassic series (KS), and cluster in two differently evolved groups. After an eruptive pause of ~5,000 years, the most recent flank eruption involving the NE sector of the island occurred during the Recent Stromboli period with the formation of the large, highly K calc-alkaline lava flow field, named San Bartolo. The trend of eruptive fissures since 15 ka ranges from N30°E to N55°E, and corresponds to the magma intrusions radiating from the main feeding system of the volcano.     

Magnetite activities across the MgAl2O4-Fe3O4 spinel join,with application to thermobarometric estimates of upper mantle oxygen fugacity

The activity of Fe₃O₄ component in MgAl₂O₄-Fe₃O₄ spinels has been measured at 900° and 1000° C and 1 atm total pressure using a zirconia oxygen electrolyte. As previously reported for the dilute Fe₃O₄ concentration region (Mattioli and Wood 1986a), magnetite activity at 1000° C is greater than at 900° C at constant Fe₃O₄ mole fraction, for compositions across the MgAl₂O₄-Fe₃O₄ join between 20 and 80 mol% Fe₃O₄ component. The 1-atm solvus crest lies between 900° and 1000° C and, at 900° C the limbs are at Fe₃O₄ mole fractions of 0.2 and 0.6 approximately.Application of the O'Neill and Navrotsky (1983, 1984) cation distribution model indicates that the unusual activity — composition behavior of Fe₃O₄ is caused by changes in the equilibrium state of disorder of mixed MgAl₂O₄-Fe₃O₄ spinels relative to the disordered Fe₃O₄ standard state. In addition, both stoichiometric volumes (Mattioli et al. 1987) and activities across the MgAl₂O₄-Fe₃O₄ join suggest that short range order is significant for this binary. Excess free energy terms must be added to ideal Fe₃O₄ activities formulated from equilibrium cation distributions in complex MgAl₂O₄-Fe₃O₄ spinels in order to increase Fe₃O₄ activities to values consistent with observation and to generate the apparent region of immiscibility at 900° C.We have applied our activity data to the estimation of upper mantle spinel-lherzolite oxygen fugacities. We calculated that minimum 's are about 2 log units below the synthetic QFM buffer at 15 kbar total pressure for Fe₃O₄ concentration of 2 mol%, in a Cr-free spinel phase. If a preliminary calibration of an additional 25 mol% Fe²⁺-substitution as FeCr₂O₄ or FeAl₂O₄ component is incorporated into Fe₃O₄ activity, then olivine-orthopyroxene-spinel assemblages of depleted-Type 1-spinel-lherzolite xenoliths indicate 's close to QFM at 15 kbar. This is in good agreement with previous thermobarometric estimates and in sharp contrast to 1 atm intrinsic measurements near IW.     

New results of 40Ar/39Ar dating constrain the timing of transition from fissure-type to central volcanism at Mount Etna (Italy)

Recent geological studies performed at Etna allow reassessing the stratigraphic frame of the volcano where distinct evolutionary phases are defined. This stratigraphic reconstruction was chronologically constrained on the basis of a limited number of U–Th and K–Ar age determinations whose uncertainty margins are sometimes too wide. For this reason, we successfully adopted at Etna the ⁴⁰Ar/³⁹Ar technique that allowed obtaining more precise age determinations. The incremental heating technique also gives information on sample homogeneity, and potential problems of trapped argon. Five samples were collected from stratigraphically well-controlled volcanic units in order to chronologically define the transition between the fissure-type volcanism of the Timpe phase to the central volcanism of the Valle del Bove Centers. Isotopic ages with an uncertainty margin of 2–4% have been obtained emphasizing that this transition occurred (130–126 ka) without significant temporal hiatus.     

Analytical expressions for three-phase generalized relative permeabilities in water- and oil-wet capillary tubes

We analyze three-phase flow of immiscible fluids taking place within an elementary capillary tube with circular cross-section under water- and oil-wet conditions. We account explicitly for momentum transfer between the moving phases, which leads to the phenomenon of viscous coupling, by imposing continuity of velocity and shear stress at fluid-fluid interfaces. The macroscopic flow model which describes the system at the Darcy scale includes three-phase effective relative permeabilities, K _{i j,r} , accounting for the flux of the ith phase due to the presence of the jth phase. These effective parameters strongly depend on phase saturations, fluid viscosities, and wettability of the solid matrix. In the considered flow setting, K _{i j,r} reduce to a set of nine scalar quantities, K _{i j,r} . Our results show that K _{i j,r} of the wetting phase is a function only of the fluid phase own saturation. Otherwise, K _{i j,r} of the non-wetting phase depends on the saturation of all fluids in the system and on oil and water viscosities. Viscous coupling effects (encapsulated in K _{i j,r} with i ≠ j) can be significantly relevant in both water- and oil-wet systems. Wettability conditions influence oil flow at a rate that increases linearly with viscosity ratio between oil and water phases.     

Centropages typicus (Crustacea,Copepoda) reacts to volatile compounds produced by planktonic algae

Volatile organic compounds (VOCs) may play the role of infochemicals and trigger chemotaxis and ecologically relevant responses in freshwater and marine invertebrates. Aquatic grazers use these signals as chemical cues to trace the presence of their food or to detect their predators. However, detailed data are still needed to fully understand the role of these relationships in marine plankton. We investigated the ability of the copepod Centropages typicus to perceive the odour of three planktonic diatoms (Skeletonema marinoi, Pseudonitzschia delicatissima and Chaetoceros affinis) and a dinoflagellate (Prorocentrum minimum). This information is ecologically relevant for orientation, habitat selection, predator avoidance and communication. In addition, as the pH of the medium influences the perception of chemical cues in aquatic environments, we tested the effect of seawater acidification resulting from increasing levels of CO₂, and its influences on the olfactory reactions of copepods. For this reason, our tests were repeated in normal (pH 8.10) and acidified (pH 7.76) seawater in order to simulate future ocean acidification scenarios. Using replicated chemokinetic assays we demonstrated that VOCs produced by Ps. delicatissima and Pr. minimum attract copepods at normal pH, but this effect is lowered in acidified water. By contrast, the odour of S. marinoi mainly induces a reaction of repulsion, but in acidified water and at higher concentrations this toxic diatom becomes attractive for copepods. Our experiments demonstrate, for the first time, that copepods are sensitive to the volatile compounds contained in various microalgae; VOCs prompt chemokinesis according to algal species and odour concentrations. However, seawater acidification induces changes in copepods' perception of odours. These findings highlight the sensitivity of chemically mediated interactions to global changes