Série du marégraphe de Marseille : mesures de températures de surface de la mer de 1895 à 1956 : une correction

In 2007, a daily temperature series, which has been collected from 1885 to 1967 at the Marseilles tide recorder, was published here. Upon the available information provided by the data managing office, they were considered as sea-surface temperatures. Unfortunately they were not but air temperature inside the building. In the present paper, the authors correct this error by studying the true seawater temperature series which had been dug out after the publication of the precedent paper. The study of this slightly shorter series (1895–1956) leads to close conclusions. Along these 61 years, the warming trend of the surface seawater rises to +1.6 °C, to +1.3 °C if only January to May and December are selected and +2.2 °C during the June to November period. In the first half part of the series (1895–1925), the average value of each month distributions (except January) and annual minimal (except 1956) are significantly lower than along the second (1925–1956).     

Marine sediment contamination of an industrial site at Port of Bagnoli, Gulf of Naples, Southern Italy

For almost one century an important steel plant has been active at the Bagnoli industrial area (Naples, Southern Italy). The environmental survey of near shore and offshore sediments has been carried out as fundamental part of a clean up project. The characteristics of the area, supposed type of pollution, national and international protocols in force were taken into consideration in designing sampling schemes and selecting analytical parameters. For this work, sediment grain size, PAHs, PCBs, trace elements, total hydrocarbons and organic matter were considered. Factor analysis evidenced two main types of pollution in the proximity of the industrial plant, both probably attributable to the activity of the industrial site. The first one, due to Cd, Pb, Zn and Mn seems determined by localised activities at the southern part of the plant. The second one, due to Fe and Mn, appears directly linked to the whole contaminated area.     

Eruption of a helically twisted prominence

In this paper we analyze the eruption of a prominence, characterized by a helical-like structure and by a non-linear rising motion. We approximated the prominence as a cylindrical curved flux tube and estimated the behaviour of several geometrical parameters during the activation and the eruption phases. We determined that, at the onset of the activation, the number N of turns of a magnetic field line over the whole length of the prominence was 5.0, while the value of the ratio P/r ₀ between the pitch of the magnetic field lines and the prominence width was 0.45. These values are in good agreement with those predicted by the kink-mode instability. Moreover, we found a decrease of the total twist of one helical thread from 10 to 2 during the prominence eruption, indicating a relaxation of the magnetic field towards a less twisted configuration. We conclude that the prominence was initially destabilized by the kink-mode instability and, not succeeding in finding a new equilibrium configuration, it erupted.     

Crystal chemistry, cation ordering and thermoelastic behaviour of CoMgSiO4 olivine at high temperature as studied by in situ neutron powder diffraction

The thermal expansion, structural changes and the site partitioning of Co and Mg in synthetic CoMgSiO₄ olivine have been studied by in situ time-of-flight neutron powder diffraction as a function of temperature, between 25 and 1,000°C. Thermal expansion of the unit cell dimensions and volume are linear within this temperature range and give no indications of a phase transition, although the thermoelastic behaviour indicates a slight strain minimum around 700°C. Co²⁺ shows a strong preference for the M1 site throughout this temperature range with an oscillatory behaviour; it decreases slightly at about 300°C, climbing up to nearly its original value at around 800°C and then decreasing by about 30% at 1,000°C. This behaviour is in contrast with that of (Fe, Mg)₂SiO₄ olivine, in which the initial Fe²⁺ site preference for the M1 site switches to the M2 site beyond a cross-over temperature. The oscillatory site preference in (CoMg)-olivine as a function of temperature is reflected in the M–O polyhedral volume changes and M–O bond lengths, as well as, thermoelastic strain and atomic thermal displacement parameters. The imbalance between the increasing vibrational and decreasing configurational entropy contributions, together with covalent bonding effects rather than crystal field contributions, seem to drive the cation partitioning in (CoMg)-olivine.     

Geochemistry of tholeiites from Lanai,Hawaii

Lanai is the third smallest of the fifteen principal subaerial shield volcanoes of the Hawaiian hotspot. This volcano apparently became extinct during the shield-building stage of volcanism, as shown by the absence of both alkalic cap and post-erosional lavas. Major and trace element analyses of 22 new samples collected primarily from 3 stratigraphic sections show that Lanai tholeiites span a large range in composition. Some Lanai lavas are unique geochemically among Hawaiian tholeiites in having the lowest abundances of incompatible trace elements of any Hawaiian lavas and well-developed positive Eu anomalies. The geochemical characteristics of these low-abundance Lanai tholeiites are not the result of alteration, differences in mantle source modal mineralogy, the presence of residual accessory mantle phases or fractional crystallization of such phases, assimilation of depleted [MORB] wall-rock, or accumulation/resorption of phenocrysts or xenocrysts. Incompatible trace element ratios (e.g., Nb/La, Nb/Th, La/Th, La/Hf, Ce/Pb) in Lanai tholeiites span considerable ranges and form coherent trends with each other and with absolute abundances of these elements. Large variations in La/Sm, La/Yb, and absolute REE abundances at constant MgO suggest that Lanai tholeiites formed by variable amounts of partial melting. However, large ranges in incompatible element ratios cannot be explained solely by variations in partial melting of a geochemically homogeneous source, but must reflect geochemical heterogeneities in the Lanai source. Partial melting modeling indicates that the mixed Lanai source is probably LREE-enriched [i.e., (La/Yb)_CN>1]. One component in the Lanai source, exemplified by the low-abundance tholeiites, has markedly lower REE/HFSE, Th/HFSE, alkali/HFSE, and Ce/Pb ratios than other Lanai or Hawaiian tholeiites and may indicate the presence of recycled residual subduction zone materials in the Hawaiian plume source. The positive Eu anomalies that characterize the low-abundance Lanai tholeiites are not the result of plagioclase accumulation or assimilation but are a feature of this source component. Progressive temporal geochemical variations in Lanai tholeiites from 2 stratigraphic sections indicate that the source composition of these lavas probably evolved over time. This change could have resulted from a progressive decrease in the extent of partial melting of the Lanai source. The compositional variability of Lanai tholeiites suggests that geochemical heterogeneities in their source are larger than the scale of partial melting. Lanai tholeiites could not have formed by smaller degrees of partial melting of plume material than did the larger-volume Hawaiian shields. Therefore, volume differences between Hawaiian shields must be controlled primarily by differences in the volume of supplied plume material rather than by differences in the degree of partial melting. The premature cessation of eruptive activity at Lanai may be attributed to relatively large degrees of partial melting of a small plume.     

Pressure-induced coordination change of Ti in silicate glass: a XANES study

The effect of pressure on titanium coordination in glasses, with composition K₂TiSi₄O₁₁, quenched isobarically from liquids equilibrated at high pressure (5, 10, 15, 20, 25, 30 kbar respectively) and T=1600° C has been investigated by X-ray absorption spectroscopy (XAS). The XANES spectra collected at the Ti K-edge clearly show a variation with pressure that is related to changes in the geometrical environment around the Ti atoms. By comparison with spectra of standard materials, the XANES spectra of the glasses suggest a relatively low average coordination number (near 5) in samples quenched at low pressure and a higher coordination number (near 6) in samples quenched from the highest pressure. The combination of XANES data with density and compressibility measurements supports the idea that a mixture of 6- and lower coordinated (4- and/ or 5-coordinated) Ti geometries are present in the 1 bar glass, and an increasing proportion of 6-coordinated Ti occurs in the glasses synthesized at progressively higher pressures.     

Distribution of some heavy metals in the Gulf of Fos

Measurements of copper, lead, cadmium and zinc were determined using the differential pulse anodic stripping voltametry technique in a marine industrialized area, the Gulf of Fos, near Marseilles. Results show an important contamination of the whole area, with particularly high values near the coast. Comparing our results with those of the literature, we see that the Gulf of Fos is probably one of the most polluted areas in Europe.     

The 1983 Etna eruption: Event chronology and morphological evolution of the lava flow

The event chronology of the 1983 Etna eruption is summarized, and the development of a compound lava field at different time intervals during the eruption is described as observed from aerial photographs.The morphological evolution of the lava fronts has been compared with effusion rate and principal modifications occurring in the main channel, and it has been inferred that the development of the lava flow units is related to the formation of lava tunnels and particularly of lava channels. The total volume of lava emitted has been estimated to be 100±20×10⁶ m³ according to two different methods. Finally, the comparison with previous historical eruptive activity shows a good correlation to other quiet eruptions.     

The effect of water on the viscosity of a haplogranitic melt under P-T-X conditions relevant to silicic volcanism

 The viscosities of hydrous haplogranitic melts synthesized by hydrothermal fusion at 2 kbar pressure and 800 to 1040° C have been measured at temperatures just above the glass transition and at a pressure of 1 bar using micropenetration techniques. The micropenetration viscometry has been performed in the viscosity range of 10⁹ Pa s to 10¹² Pa s. The samples ranged in water content from 0.4 to 3.5 wt%. For samples with up to 2.5 wt% H₂O, the water contents have been determined using infrared spectroscopy obtained before and after each viscometry experiment to be constant over the duration of the measurements. Above this water content a measurable loss of water occurs during the viscometry. The viscosity data illustrate an extremely nonlinear decrease in viscosity with added water. The viscosity drops drastically with the addition of 0.5 wt% of water and then shallows out at water contents of 2 wt%. An additional viscosity datum point obtained from the analysis of fluid inclusions in a water-saturated HPG8 confirms a near invariance of the viscosity with the addition of water between 2 and 6 wt%. These measurements may be compared directly with the data of Hess et al. (1995, in press) for the effects of excess alkali and alkaline earth oxides on the viscosity of HPG8 (also obtained at 1 bar). The viscosity of the melts, compared on an equivalent molar basis, increases in the order H₂O<(Li₂O<Na₂O< K₂O<Rb₂O,Cs₂O<BaO<SrO<CaO<MgO< BeO). The extraordinary decrease in melt viscosity with added water is poorly reproduced by the calculation scheme of Shaw (1972) for the range of water contents investigated here. The speciation of water in the quenched glasses can be used to quantify the dependence of the viscosity on hydroxyl content. Considering only the hydroxyl groups as active fluidizers in the hydrous melts the nonlinearity of the viscosity decrease and the difference with the effects of the alkali oxides becomes larger. Consequences for degassing calcalkaline rhyolite are discussed. Received: 17 August 1995/Accepted: 8 January 1996     

The influence of trace amounts of water on the viscosity of rhyolites

 As a major volatile in volcanic systems, water has a significant influence on the rheological properties of silicic magmas. This is especially so at minor water contents relevant to the emplacement of silicic lavas. To investigate the influence of water on the viscosity of natural rhyolitic obsidians, a novel strategy has been adopted employing parallel-plate and micropenetration techniques. Viscosities have been determined on three types of material: (a) raw water-bearing obsidians; (b) remelted (1650  °C, 1 atm) degassed glasses of the obsidians; and (c) hydrothermally hydrated (1300  °C, 3 kbar) obsidians. Ten natural rhyolitic obsidians (peraluminous, calc-alkaline and peralkaline) were employed: seven originated from lava flows and contained <0.2 wt.% H₂O, two samples were F-rich from pyroclastic successions, and one was an obsidian cobble with 1.5 wt.% water also associated with pyroclastic units. Melt compositions and water contents were stable during viscometry. The measured decreases in activation energies of viscous flow and viscosity with small amounts of water are much greater than the Shaw calculation scheme predicts. In addition, a marked non-linear decrease in η exists with increasing water content. In contrast to the case for peralkaline rhyolites, 0.1–0.2 wt.% water decreases activation energies significantly (up to 30%) for calc-alkaline compositions. These results have important implications for the ease of near-surface degassing of silicic magmas during emplacement and permit the testing of calculational models for viscosity, largely based on synthetic systems. Received: 7 July 1997 / Accepted: 6 April 1998