Search results for "Circulation"
showing 10 items of 1137 documents
Steam and gas emission rate from La Soufriere volcano, Guadeloupe (Lesser Antilles): Implications for the magmatic supply during degassing unrest
2014
Abstract Since its last magmatic eruption in 1530 AD, La Soufriere andesitic volcano in Guadeloupe has displayed intense hydrothermal activity and six phreatic eruptive crises. Here we report on the first direct quantification of gas plume emissions from its summit vents, which gradually intensified during the past 20 years. Gas fluxes were determined in March 2006 and March 2012 by measuring the horizontal and vertical distributions of volcanic gas concentrations in the air-diluted plume and scaling to the speed of plume transport. Fluxes in 2006 combine real-time measurements of volcanic H2S concentrations and plume parameters with the composition of the hot (108.5 °C) fumarolic fluid at …
Halogens in Mafic and Intermediate-Silica Content Magmas
2018
As volatile and variably mobile components, halogens play key roles in magmatic, metasomatic, mineralizing, and volcanic processes by influencing the physical and chemical properties of melts, fluids, and minerals. Volcanic emission of halogens to the atmosphere leads to long- and short-term impacts on atmospheric chemistry that range from global perturbation of the stratospheric O3 budget to more localized life-threatening contamination of soils and fresh water. The concentrations of F, Cl, Br, and I in melts, fluids, and minerals provide crucial geochemical information and insights into magmatic processes ranging from partial melting to volcanic eruptions. Halogen research is useful for e…
First gas and thermal measurements at the frequently erupting Gamalama volcano (Indonesia) reveal a hydrothermally dominated magmatic system
2020
Abstract The first gas and thermal measurements at the summit of the Gamalama volcano indicate that the system is dominated by hydrothermal processes. This is highlighted by the prevalence of H2S over SO2 (H2S/SO2 = 2–8), a high CO2/SO2 ratio (76–201), and a low heat transfer (3.0 MW) to the surface. A relative variation in gas composition is observed along the degassing fracture zone, possibly due to partial S scrubbing. Despite this surface hydrothermal signature, the system exhibits high gas equilibrium temperatures (425–480 °C), indicating that fluids are not exclusively derived from a boiling hydrothermal aquifer, but also sourced by cooling and crystallizing basaltic magma at deep tha…
Mercury concentration, speciation and budget in volcanic aquifers: Italy and Guadeloupe (Lesser Antilles)
2009
Abstract Quantifying the contribution of volcanism to global mercury (Hg) emissions is important to understand the pathways and the mechanisms of Hg cycling through the Earth's geochemical reservoirs and to assess its environmental impacts. While previous studies have suggested that degassing volcanoes might contribute importantly to the atmospheric budget of mercury, little is known about the amount and behaviour of Hg in volcanic aquifers. Here we report on detailed investigations of both the content and the speciation of mercury in aquifers of active volcanoes in Italy and Guadeloupe Island (Lesser Antilles). In the studied groundwaters, total Hg (THg) concentrations range from 10 to 500…
Mercury content and speciation in the Phlegrean Fields volcanic complex: evidence from hydrothermal system and fumaroles
2009
Abstract Mercury is outstanding among the global environmental pollutants of continuing concern. Although degassing of active volcanic areas represents an important natural source of mercury into the atmosphere, still little is known about the amount and behaviour of Hg in volcanic aquifers, especially regarding its chemical speciation. In order to assess the importance of mercury emissions from active volcanoes, thermal waters were sampled in the area surrounding La Solfatara, Pozzuoli bay. This is the most active zone of the Phlegrean Fields complex (coastal area north–west of Naples), with intense hydrothermal activity at present day. Studied groundwaters show total Hg (THg) concentratio…
Influence of the pH on the synthesis of reduced graphene oxide under hydrothermal conditions
2012
Here we describe the important role played by the pH on the morphology and structure of the reduced graphite oxide (rGO) samples obtained by hydrothermal treatment of the previously prepared GO. The nature of the resulting samples has been studied on the basis of a complete battery of experimental techniques.
Magma Degassing at Piton de la Fournaise Volcano
2015
Since about 1860 AD, magmatic gas release at Piton de la Fournaise volcano is very weak during intra-eruptive phases and essentially occurs during the relatively short-lived eruptions. Recent gas measurements performed during an eruption in October 2010, combined with detailed review of melt and fluid inclusion composition in magmas erupted over the past 50 kyrs, indicate that most PdF eruptions extrude magmas having variably degassed at shallow depth (P 1 kbar) and the shallow magmas, whose fluids are efficiently scrubbed by the hydrothermal system and the water table. Quantification of SO2 fluxes permits to track syn-eruptive magma ascent at shallow level (above sea level). Deeper exsolut…
Blood Flow and Tissue Oxygenation of Human Tumors: An Update
1992
It is generally accepted that tumor microcirculation, blood flow, oxygen and nutrient supply, tissue pH distribution, and the bioenergetic status (factors which are usually closely linked and which define the so-called cellular microenvironment) can markedly influence the therapeutic response of malignant tumors. Tumor blood flow is the major determinant for intra-tumor pharmacokinetics and (through modulation of the cellular microenvironment) of pharmacody-namics. The oxygen supply greatly determines the radiosensitivity of the tumors to be treated. The oxygen enhancement ratio, i.e., the ratio of doses with and without oxygen to produce the same biological effect is 2.7 to 3.0. O2 partial…
GEOCHEMICAL AND MINERALOGICAL FINGERPRINTS OF THE SEDIMENTS SUPPLY AND EARLY DIAGENETIC PROCESSES IN THE BIZERTE LAGOON (TUNISIA)
2016
International audience; The Bizerte Lagoon (Tunisia) functions as a sedimentation environment characterized by receiving allochthonous sediments mainly transported by the Ben Hassine, Rharek and Guenich streams, as well as marine sediments from the Mediterranean Sea. It is subjected to significantenvironmental changes due to the natural and anthropic influences altering the natural patterns of circulation, extraction and/or deposition of mineralogical materials. The aim of this investigation is to analyze the sediments supply and early diagenetic processes in Bizerte Lagoon. Thephyicochemical parameter of the sediment pore water, as well as their texture, mineralogical composition (X-Ray di…
m.quadriceps statisku slodzi pavadošās hemodinamiskās reakcijas augšstilba maģistrālo artēriju gultnēs
2013
m.quadriceps statisku slodzi pavadošās hemodinamiskās reakcijas augšstilba maģistrālo artēriju gultnēs Pētījums veltīts perifēro artēriju un pretestības asinsvadu tonusa regulācijas īpatnību izpētei, reģionālai muskuļu asinsvadu gultnei iekļaujoties dažāda rakstura hemodinamiskās reakcijās. Promocijas darba pirmajā etapā tika veikti tālākā pētījumā izmantojamo metožu teorētiskā pamatojuma un praktiskās realizācijas pilnveidojumi: fotopletizmogrāfijas metodei – audu tilpuma pulsa un atsevišķas artērijas pulsa reģistrācijas metožu informativitātes salīdzinājums, artēriju ultrasonogrāfijas metodei – oriģinālas programmatūras izstrāde un aprobācija artērijas morfometrisko un asins plūsmas param…