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91.
Fumarolic activity of Avachinsky and Koryaksky volcanoes, Kamchatka, from 1993 to 1994 总被引:1,自引:0,他引:1
Yuri A. Taran Charles B. Connor Vyacheslav N. Shapar Alexandre A. Ovsyannikov Arthur A. Bilichenko 《Bulletin of Volcanology》1997,58(6):441-448
Volcanic gas and condensate samples were collected in 1993–1994 from fumaroles of Koryaksky and Avachinsky, basaltic andesite
volcanoes on the Kamchatka Peninsula near Petropavlovsk–Kamchatsky. The highest-temperature fumarolic discharges, 220 °C
at Koryaksky and 473 °C at Avachinsky, are water-rich (940–985 mmol/mol of H2O) and have chemical and isotopic characteristics typical of Kamchatka–Kurile, high- and medium-temperature volcanic gases.
The temperature and chemical and water isotopic compositions of the Koryaksky gases have not changed during the past 11 years.
They represent an approximate 2 : 1 mixture of magmatic and meteoric end members. Low-temperature, near-boiling-point discharges
of Avachinsky Volcano are water poor (≈880 mmol/mol); Their compositions have not changed since the 1991 eruption, and are
suggested to be derived from partially condensed magmatic gases at shallow depth. Based on a simple model involving mixing
and single-step steam separation, low water and high CO2 contents, as well as the observed Cl concentration and water isotopic composition in low-temperature discharges, are the
result of near-surface boiling of a brine composed of the almost pure condensed magmatic gas. High methane content in low-temperature
Avachinsky gases and the 220 °C Koryaksky fumarole, low C isotopic ratio in CO2 at Koryaksky (–11.8‰), and water isotope data suggest that the "meteoric" end member contains considerable amounts of the
regional methane-rich thermal water discovered in the vicinity of both volcanoes.
Received: 2 May 1996 / Accepted: 5 November 1996 相似文献
92.
93.
Morphological expression of bedforms formed by supercritical sediment density flows on four fjord‐lake deltas of the south‐eastern Canadian Shield (Eastern Canada) 下载免费PDF全文
Alexandre Normandeau Patrick Lajeunesse Antoine G. Poiré Pierre Francus 《Sedimentology》2016,63(7):2106-2129
High‐resolution swath bathymetry data collected in fjord‐lakes Pentecôte, Walker and Pasteur (eastern Québec, Canada) allowed imaging in great detail the deltas of four rivers in order to understand the factors controlling the formation and downslope evolution of bedforms present on their slopes. The morphometry and morphology of 199 bedforms reflect the behaviour of sediment density flows. The shape of the bedforms, mostly crescentic, and the relationships between their morphological properties indicate that they were formed by supercritical density flows and that they are cyclic steps. The crescentic shape suggests an upslope migration while the aspect ratios and increasing wavelengths with distance from the shore (and decreasing slopes) are compatible with a cyclic step origin. At the rollover point, the acceleration of the density flows on steep slopes produces tightly spaced hydraulic jumps and favours short wavelength and symmetrical bedforms. Further downslope, decreasing slopes and increasing specific discharge increase the wavelength and asymmetry of the bedforms. The wavelength and asymmetry are increased because density flows require longer distances to become supercritical again on lower slopes after each successive hydraulic jump. Bedform morphometry and morphology are used to reconstruct density flow behaviour downslope. Froude numbers are high near the rollover point and gradually decrease downslope as the slope becomes gentler. Conversely, the specific discharge and flow depth are low near the rollover point and gradually increase downslope as the flow either erodes sediments or becomes more dilute due to sediment deposition and water entrainment. The supercritical density flows are believed to be triggered mainly by hyperpycnal flows but some evidence of delta‐front slope failures is also observed. The differences in delta morphology and bedform development between the four deltas are linked to basin morphology and watershed hydrology, but also mainly to the fjord heritage of the lakes that allowed the focusing of sediment at the delta front. 相似文献
94.
95.
Julien Maes Ann H. Muggeridge Matthew D. Jackson Michel Quintard Alexandre Lapene 《Computational Geosciences》2016,20(3):581-594
The in-situ upgrading (ISU) of bitumen and oil shale is a very challenging process to model numerically because of the large number of components that need to be modelled using a system of equations that are both highly non-linear and strongly coupled. Operator splitting methods are one way of potentially improving computational performance. Each numerical operator in a process is modelled separately, allowing the best solution method to be used for the given numerical operator. A significant drawback to the approach is that decoupling the governing equations introduces an additional source of numerical error, known as the splitting error. The best splitting method for modelling a given process minimises the splitting error whilst improving computational performance compared to a fully implicit approach. Although operator splitting has been widely used for the modelling of reactive-transport problems, it has not yet been applied to the modelling of ISU. One reason is that it is not clear which operator splitting technique to use. Numerous such techniques are described in the literature and each leads to a different splitting error. While this error has been extensively analysed for linear operators for a wide range of methods, the results cannot be extended to general non-linear systems. It is therefore not clear which of these techniques is most appropriate for the modelling of ISU. In this paper, we investigate the application of various operator splitting techniques to the modelling of the ISU of bitumen and oil shale. The techniques were tested on a simplified model of the physical system in which a solid or heavy liquid component is decomposed by pyrolysis into lighter liquid and gas components. The operator splitting techniques examined include the sequential split operator (SSO), the Strang-Marchuk split operator (SMSO) and the iterative split operator (ISO). They were evaluated on various test cases by considering the evolution of the discretization error as a function of the time-step size compared with the results obtained from a fully implicit simulation. We observed that the error was least for a splitting scheme where the thermal conduction was performed first, followed by the chemical reaction step and finally the heat and mass convection operator (SSO-CKA). This method was then applied to a more realistic model of the ISU of bitumen with multiple components, and we were able to obtain a speed-up of between 3 and 5. 相似文献
96.
Alexandre Anozé Emerick 《Computational Geosciences》2016,20(1):35-47
Ensemble-based methods are becoming popular assisted history matching techniques with a growing number of field applications. These methods use an ensemble of model realizations, typically constructed by means of geostatistics, to represent the prior uncertainty. The performance of the history matching is very dependent on the quality of the initial ensemble. However, there is a significant level of uncertainty in the parameters used to define the geostatistical model. From a Bayesian viewpoint, the uncertainty in the geostatistical modeling can be represented by a hyper-prior in a hierarchical formulation. This paper presents the first steps towards a general parametrization to address the problem of uncertainty in the prior modeling. The proposed parametrization is inspired in Gaussian mixtures, where the uncertainty in the prior mean and prior covariance is accounted by defining weights for combining multiple Gaussian ensembles, which are estimated during the data assimilation. The parametrization was successfully tested in a simple reservoir problem where the orientation of the major anisotropic direction of the permeability field was unknown. 相似文献
97.
98.
Alexandre Cunha Costa Saskia Foerster José Carlos de Araújo Axel Bronstert 《水文研究》2013,27(7):1046-1060
Scarcity of hydrological data, especially streamflow discharge and groundwater level series, restricts the understanding of channel transmission losses (TL) in drylands. Furthermore, the lack of information on spatial river dynamics encompasses high uncertainty on TL analysis in large rivers. The objective of this study was to combine the information from streamflow and groundwater level series with multi‐temporal satellite data to derive a hydrological concept of TL for a reach of the Middle Jaguaribe River (MJR) in semi‐arid north‐eastern Brazil. Based on this analysis, we proposed strategies for its modelling and simulation. TL take place in an alluvium, where river and groundwater can be considered to be hydraulically connected. Most losses certainly infiltrated only through streambed and levees and not through the flood plains, as could be shown by satellite image analysis. TL events whose input river flows were smaller than a threshold did not reach the outlet of the MJR. TL events whose input flows were higher than this threshold reached the outlet losing on average 30% of their input. During the dry seasons (DS) and at the beginning of rainy seasons (DS/BRS), no river flow is expected for pre‐events, and events have vertical infiltration into the alluvium. At the middle and the end of the rainy seasons (MRS/ERS), river flow sustained by base flow occurs before/after events, and lateral infiltration into the alluvium plays a major role. Thus, the MJR shifts from being a losing river at DS/BRS to become a losing/gaining (mostly losing) river at MRS/ERS. A model of this system has to include the coupling of river and groundwater flow processes linked by a leakage approach. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
99.
Alain Vauchez Marcos Egydio‐Silva Marly Babinski Andra Tommasi Alexandre Uhlein Dunyi Liu 《地学学报》2007,19(4):278-286
Pervasive melting of the middle crust, as inferred in Tibet and the Altiplano, probably influences the deformation of the lithosphere. To constrain strain distribution in a pervasively molten crust, we analysed the deformation in an eroded analogue of these orogens. The Ribeira‐Araçuaí orogen (SE Brazil) comprises a stack of allochthons containing large volumes of anatectic and magmatic rocks. The upper allochton (∼300 km long, 50–100 km wide and >10 km thick) involves peraluminous diatexites and leucogranites resulting from partial melting of the middle crust. It overlies another allochthon containing huge early‐ to syn‐collisional plutons intruding metasediments. Both anatexites and magmatic intrusions display a pervasive strain‐induced magmatic fabric. Homogeneous strain distribution suggests inefficient localization. U–Pb ages of ∼575 Ma imply that anatexite melting was synchronous to the early‐ to syn‐collisional magmatism. Similarity in ages magmatic and solid‐state fabrics indicates that intrusions and anatexites deformed coherently with solid‐state rocks while still molten, in response to a combination of gravity‐driven and collision‐driven deformation. 相似文献
100.