1,721,079 research outputs found
Mercury Emissions Associated with Volcanoes and Geothermal Sources
No full textThere is some debate at present regarding the quantity of mercury naturally released by
volcanoes and its relative significance to the natural Hg budget. In order to better understand
the role of volcanoes in the global mercury budget a number of field campaigns were carried
out to evaluate the Hg/S ratios in volcanic gases around the world. Measurements have been
made of emissions of Masaya (Nicaragua), Etna and Vulcano (Italy), Tatun (Taiwan), Taal
and Makiling (Philippines) and Kilauea (Hawaii, USA). Emissions from open vents,
fumaroles, hot springs, bubbling mud pools and altered ground were investigated at these sites
and concentrations of mercury elevated above background levels were observed on most
occasions. A Lumex 915+ portable mercury vapour spectrometer was employed to record
real-time gaseous elemental mercury (GEM) concentrations alongside a Multi-GAS sensor
, H S, CO , humidity, temperature and pressure. These
box developed to monitor SO
2 2 2
measurements were carried out in parallel with the collection of GEM on gold coated sand
traps, particulate Hg (Hg(p)) on quartz mini-traps, reactive gaseous Hg (RGM) on glass
denuders and sulphur on filter packs. As observed in studies of background air Hg, most of
the GEM was the dominant form in the volcanic gases. While RGM and Hg(p) represent only
a few % of the Hg present, concentrations of these species in volcanic air was several orders
of magnitude higher than levels observed in background and industrial air studies. Hg/S ratios
volcanic flux to estimate Hg fluxes.
were determined and used in conjunction with the SO
2
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and 10 . If
Hg/S ratios in open vent emissions at Masaya and Etna were between 10
representative of other volcanoes, these results suggest degassing of basaltic magma plays an
important part of the global atmospheric Hg budget.
With these new measurements, we shall
critically revisit the status of the global volcanic mercury emissions budget, and its
uncertainties
Preliminary estimates of volcanic gaseous and particulate-phase mercury emissions at Mt. Etna and Vulcano Island
No full text
Plume chemistry and potential impacts of the plume from the recent activity at Halema’uma’u, Kilauea, USA.
No full textSince the 19 March 2008 explosion within Halema‘uma‘u that formed the new vent at Kilauea’s summit,
degassing rates have been greatly elevated above the levels typical of previous years. The location and
subsequent dispersion of this new degassing presents its own specific problems compared to that in the
east rift zone. For example, throughout 2008 the Halema’uma’u plume was generally blown through the
Kau desert, directly affecting downwind communities. In this study we present measurements made in July
and halogens (HF, HCl, HBr and HI) in the new
2008. We characterize the gas chemistry in terms of SO
2
plume from Halema’uma’u in order to compare them with other plumes worldwide, including those from
subduction zone settings and other emissions from Kilauea itself. Further to this we characterize the
plume’s chemistry in terms of emissions of environmentally important metallic species both in the size-
segregated aerosol (important for determining atmospheric lifetime and potential speciation) and in the
case of Hg in the gas phase (both in the elemental form and reactive forms). To complement this plume
characterization we also looked at preliminary environmental samples of grasses, rainwater and fog in
order to investigate potential future avenues for research into the environmental consequences of Kilauea’s
volcanic emissions
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
Understanding cyclic seismicity and ground deformation patterns at volcanoes: intriguing lessons from Tungurahua volcano, Ecuador
Full text linkCyclic seismicity and ground deformation patterns are observed on many volcanoes worldwide where seismic swarms and the tilt of the volcanic flanks provide sensitive tools to assess the state of volcanic activity. Ground deformation at active volcanoes is often interpreted as pressure changes in a magmatic reservoir, and tilt is simply translated accordingly into inflation and deflation of such a reservoir. Tilt data recorded by an instrument in the summit area of Tungurahua volcano in Ecuador, however, show an intriguing and unexpected behaviour on several occasions: prior to a Vulcanian explosion when a pressurisation of the system would be expected, the tilt signal declines significantly, hence indicating depressurisation. At the same time, seismicity increases drastically. Envisaging that such a pattern could carry the potential to forecast Vulcanian explosions on Tungurahua, we use numerical modelling and reproduce the observed tilt patterns in both space and time. We demonstrate that the tilt signal can be more easily explained as caused by shear stress due to viscous flow resistance, rather than by pressurization of the magmatic plumbing system. In general, our numerical models prove that if magma shear viscosity and ascent rate are high enough, the resulting shear stress is sufficient to generate a tilt signal as observed on Tungurahua. Furthermore, we address the interdependence of tilt and seismicity through shear stress partitioning and suggest that a joint interpretation of tilt and seismicity can shed new light on the eruption potential of silicic volcanoes
The arc arises: The links between volcanic output, arc evolution and melt composition
Full text linkSubduction initiation is a key process for global plate tectonics. Individual lithologies developed during subduction initiation and arc inception have been identified in the trench wall of the Izu–Bonin–Mariana (IBM) island arc but a continuous record of this process has not previously been described. Here, we present results from International Ocean Discovery Program Expedition 351 that drilled a single site west of the Kyushu–Palau Ridge (KPR), a chain of extinct stratovolcanoes that represents the proto-IBM island arc, active for ∼25 Ma following subduction initiation. Site U1438 recovered 150 m of oceanic igneous basement and ∼1450 m of overlying sediments. The lower 1300 m of these sediments comprise volcaniclastic gravity-flow deposits shed from the evolving KPR arc front. We separated fresh magmatic minerals from Site U1438 sediments, and analyzed 304 glass (formerly melt) inclusions, hosted by clinopyroxene and plagioclase. Compositions of glass inclusions preserve a temporal magmatic record of the juvenile island arc, complementary to the predominant mid-Miocene to recent activity determined from tephra layers recovered by drilling in the IBM forearc. The glass inclusions record the progressive transition of melt compositions dominated by an early ‘calc-alkalic’, high-Mg andesitic stage to a younger tholeiitic stage over a time period of 11 Ma. High-precision trace element analytical data record a simultaneously increasing influence of a deep subduction component (e.g., increase in Th vs. Nb, light rare earth element enrichment) and a more fertile mantle source (reflected in increased high field strength element abundances). This compositional change is accompanied by increased deposition rates of volcaniclastic sediments reflecting magmatic output and maturity of the arc. We conclude the ‘calc-alkalic’ stage of arc evolution may endure as long as mantle wedge sources are not mostly advected away from the zones of arc magma generation, or the rate of wedge replenishment by corner flow does not overwhelm the rate of magma extraction
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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