1,721,771 research outputs found
A CO2-rich gas trigger of explosive paroxysms at Stromboli basaltic volcano, Italy
No full textIn addition to rhythmic slug-driven Strombolian activity, Stromboli volcano occasionally produces discrete explosive paroxysms (2 per year on average for the most frequent ones) that constitute a major hazard and whose origin remains poorly elucidated. Partial extrusion of the volatile-rich feeding basalt as aphyric pumice during these events has led to consider their triggering by the fast ascent of primitive magma blobs from possibly great depth. Here I propose instead that most of the paroxysms could be triggered and driven by the fast upraise of CO2-rich gas pockets generated by bubble foam growth and collapse in the sub-volcano plumbing system. Data for the SO2 and CO2 crater plume emissions with the magma sulphur content are used to show that Stromboli’s feeding magma originally may contain as much as 2 wt% of carbon dioxide and early coexists with an abundant CO2-rich gas phase with high CO2/SO2 molar ratio (60 at 10 km depth below the vents, compared to ~7 in time-averaged crater emissions). Pressure-related modelling indicates that the time-averaged crater gas composition and output are well accounted for by closed system decompression of the basalt-gas mixture until about the volcano-crust interface (~3 km depth), followed by open degassing and crystallization in the volcano conduits. However, both the low viscosity and high vesicularity of the basaltic magma permit bubble segregation and bubble foam growth at deep sill-like feeder discontinuities and at shallower physical boundaries (the volcano-crust interface) where the gas-rich aphyric basalt interacts with the unerupted crystal-rich, viscous magma drained back from the volcano conduits. Gas pressure build up and bubble foam collapse at these boundaries will intermittently trigger the sudden upraise of CO2-rich gas blobs that constitute the main driving force of the paroxysms. Deeper-sourced gas blobs, driving the most powerful explosions, will be the richest in CO2 and have highest CO2/SO2 ratios. This mechanism is shown to account well for the dynamic, seismic and petrologic features of Stromboli’s paroxysms and, hence, to provide a potential alternative interpretation for their genesis and their forecasting. Enhanced bubble foam leakage prior to a paroxysm, or foam emptying in several steps, should lead indeed to precursory upstream of CO2-rich gas and increasing CO2/SO2 ratio in crater plume emissions. The recent detection of such signals prior to two explosions in December 2006 and March 2007 strongly supports this expectation and the model proposed in this study.In press1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcaniJCR Journalreserve
Arles au XIXe siècle. Allard P. (1992), Arles et ses terroirs, 1820-1910
No full textCourtot Roland. Arles au XIXe siècle. Allard P. (1992), Arles et ses terroirs, 1820-1910. In: Méditerranée, tome 78, 3-4-1993. La Camargue et le Rhône, hommes et milieux, sous la direction de Mireille Provansal . p. 111
Arles au XIXe siècle. Allard P. (1992), Arles et ses terroirs, 1820-1910
No full textCourtot Roland. Arles au XIXe siècle. Allard P. (1992), Arles et ses terroirs, 1820-1910. In: Méditerranée, tome 78, 3-4-1993. La Camargue et le Rhône, hommes et milieux, sous la direction de Mireille Provansal . p. 111
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Seismic tremor evidence for a deep gas trigger of the 5 April 2003 paroxysmal explosion on Stromboli volcano, Italy
No full textIn addition to strombolian-type mild-explosive activity, Stromboli volcano intermittently
produces discrete paroxysmal blasts (2-3 per year) that constitute a major hazard
for tourists, volcanologists, and occasionally the local population. These events
have no recognized activity precursors, are currently unforecasted, and their triggering
mechanism remains poorly elucidated. An emblematic example of such events
has been the 5 April 2003 explosion, which happened during a period of lava flow
outpouring and a few months after a tsunami-generating flank collapse. Here we report
the first evidence of a progressive and then rapid increase of seismic tremor within
the few hours that just preceded this event. We show that this seismic signal is compatible
with the collapse of a deep-seated bubble foam layer, followed by adiabatic
and fast ascent of large blobs of CO2-dominated gas + liquid, in agreement with the
triggering mechanism proposed by Allard (2007, and in press) for most of the paroxysms
on Stromboli. We develop a quantitative approach encompassing geochemical,
petrologic and seismic data, which points that the 5 April 2003 explosion resulted
from the accumulation of a huge CO2-dominated gas amount at great depth and its
sudden discharge from a small-size sill-like magma body or reservoir. A main fall of
our seismic data and our modelling is that the timing of gas coalescence and slug ascent
to the surface can be estimated quite accurately. Therefore, this work provides
new perspectives for a combined seismic and geochemical forecasting of future large
paroxysms on Stromboli
He, C and S isotopes in subaerial and submarine fumaroles from the caldera of Phlaegrean Fields, Italy
No full textFirst in-situ sensing of volcanic gas plume composition at Boiling Lake (Dominica, West Indies)
Full text linkDominica, a small Caribbean island between Martinique (to the South) and
Guadeloupe (to the North), is, because of the high number of potentially active volcanic centres,one of the most susceptible sites to volcanic risk in the Lesser Antilles arc. Seven major volcanic centres, active during the last 10ka, are considered likely to erupt again, and one of these is the
Valley of Desolation volcanic complex. This is an area of 0.5 km2, located in on SW Dominica, where a number of small explosion craters, hot springs,bubbling pools and fumaroles testify for vigorous and persistent hydrothermal activity. Two main phreatic explosions have been documented in historical time (1880 and 1997), and the most likely centre of future activity is the
Boiling Lake, a nearby high-T volcanic crater lake produced by an undated phreatic/phreatomagmatic explosion. Hot (80 to 90°C) and acidic (4-6) waters normally characterize the steady-state activity of the lake, whereby which vigorous gas upwelling in the lake’s centre feeds a persistent steaming plume. Stability of the Boiling Lake has occasionally been interrupted in the
past (since 1876) by crises, the most recent in 2004, involving rapid draining of the lake and changes in water temperature and pH, likely as a result of drastic decrease of hydrothermal fluid input into the lake. While the chemical and isotopic composition of the lake waters is well
characterised, there are no compositional data available for the gas plume leaving the lake, due to
inherent difficulties in direct gas sampling. Here, we present the results of the first direct measurements of the Boiling Lake’s plume, performed by using the MultiGAS technique in February 2012. We acquired 0.5 Hz time-series of H2O, CO2, H2S and SO2 plume concentrations,which were seen to peak (with maximum background-corrected concentrations of 3680, 101 and 25 ppm for respectively H2O, CO2 and H2S) during phases of visible increase in lake outgassing.
SO2 was virtually absent in the plume. From the concentration data, the characteristic CO2/H2S (5.2±0.4) and H2O/CO2 (31.4±6) volatile ratios in the Boiling lake’s atmospheric plume were
derived. This reveals similar C to S signature for Boiling lake and Valley of Desolation (for which we also obtained data using the same technique), likely indicative of common source reservoir.
The Boiling lake’s plume is far more H2O-rich than the Valley of Desolation gas, suggesting that a significant fraction of in-plume H2O in the former originates from re-evaporation of the lake water itself. Our data here provide a first compositional baseline for quiescent volcanic gas emissions at
Boiling Lake, and may form the basis to stimulate emerging geochemical monitoring programs in the area
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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