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111.
Geochemical modeling of magma mixing allows for evaluation of volumes of magma storage reservoirs and magma plumbing configurations.
A new analytical expression is derived for a simple two-component box-mixing model describing the proportions of mixing components
in erupted lavas as a function of time. Four versions of this model are applied to a mixing trend spanning episodes 3–31 of
Kilauea Volcano’s Puu Oo eruption, each testing different constraints on magma reservoir input and output fluxes. Unknown
parameters (e.g., magma reservoir influx rate, initial reservoir volume) are optimized for each model using a non-linear least
squares technique to fit model trends to geochemical time-series data. The modeled mixing trend closely reproduces the observed
compositional trend. The two models that match measured lava effusion rates have constant magma input and output fluxes and
suggest a large pre-mixing magma reservoir (46±2 and 49±1 million m3), with little or no volume change over time. This volume is much larger than a previous estimate for the shallow, dike-shaped
magma reservoir under the Puu Oo vent, which grew from ∼3 to ∼10–12 million m3. These volumetric differences are interpreted as indicating that mixing occurred first in a larger, deeper reservoir before
the magma was injected into the overlying smaller reservoir.
Electronic Supplementary Material Supplementary material is available at and is accessible for authorized users. 相似文献
112.
Patrick A. Hesp Sergio Rebello Dillenburg Eduardo Guimaraes Barboza Luiz C. P. Clerot Luiz J. Tomazelli Ricardo Norberto Ayup Zouain 《地球表面变化过程与地形》2007,32(3):407-414
The surface morphology of the transgressive dunefield barrier extending from Itapeva to Tramandai along the northern littoral of Rio Grande do Sul, is examined and an attempt is presented to link morphological changes across the barrier to Holocene sea level changes. The 4·5 km wide Holocene barrier displays two typical morphologies: an inner part dominated by large‐scale, continuous alongshore, overlapping dunefield phases comprising sand sheets, dunes, deflation plains and precipitation ridges; and an outer part dominated by discontinuous, medium‐ to small‐scale, triangular to lobate transgressive dunefield phases, cut by both active and relict (palaeo‐) creeks or washouts. Holocene sea level in the region rose to c. +1 to +3 m above present reaching a maximum around 5100 years bp and then progressively fell to the present level. We argue that the effect on barrier development was to suppress the development of a drainage system during the rising and maximum stages, and encourage the development of an organized drainage system in the form of regularly spaced washouts during the falling period, and that this change in sea level from rising to falling therefore produced the large‐scale differences in barrier morphology. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
113.
Plinian plumes erupt with a bulk density greater than that of air, and depend upon air entrainment during their gas-thrust phase to become buoyant; if entrainment is insufficient, the column collapses into a potentially deadly pyroclastic flow. This study shows that strombolian ash plumes can be erupted in an initially buoyant state due to their extremely high initial gas content, and in such cases are thus impervious to column collapse. The high gas content is a consequence of decoupled gas rise in the conduit, in which particles are ultimately incidental. The relations between conduit gas flow, eruption style and plume density are explored here for strombolian scenarios and contrasted with conventional wisdom derived from plinian eruptions. Considering the inherent relation between gas content and initial plume density together with detailed measurements of plume velocities can help unravel ambiguities surrounding conduit processes, eruption styles and hazards at poorly understood volcanoes. Analysis of plume dynamics at Santiaguito volcano, Guatemala adds further support for a model involving decoupled gas rise in the conduit. 相似文献
114.
本文聚焦于人类活动在印度洋和中、高纬度大洋中遥远岛屿的表象,着重阐述了人类行为对自然生态系统的影响,文章通过对建筑、采矿、生物引进,以及旅游业开发等人类活动的若干方面的观察和考证,总结认为世界上不存在孤立地域,没有哪一个环境能够保持与世界的经济和政治体系毫不相干。 相似文献
115.
116.
The need for full‐scale dynamic tests, which are recognized as the most reliable method to evaluate a structure's vibration properties, is increasing as new analysis techniques are developed that take into account the complex interaction phenomenons that occur in dam–reservoir–foundation systems. They are extremely useful to obtain reliable data for the calibration of newly developed numerical methods. The Earthquake Engineering and Structural Dynamics Research Center (CRGP) at the University of Sherbrooke has been developing and applying dynamic testing methods for large structures in the past 10 years. This paper presents the experimental evaluation of the effects of the varying water level on the dynamic response of the 180 m Emosson arch dam in Switzerland. Repeated forced‐vibration tests were carried out on the dam during four different periods of the reservoir's filling cycle during a one‐year span. Acceleration and hydrodynamic pressure frequency responses were obtained at several locations while the dam was subjected to horizontal harmonic loading. The variation of the resonant frequencies as a function of the reservoir level is investigated. A summary of the ongoing numerical correlation phase with a three‐dimensional finite element model for the dam–reservoir–foundation system is also presented. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
117.
Pierre Le Hir Andre Ficht Ricardo Silva Jacinto Patrick Lesueur Jean-Paul Dupont Robert Lafite Isabelle Brenon Benedicte Thouvenin Philippe Cugier 《Estuaries and Coasts》2001,24(6):950-963
A comprehensive study of fine sediment transport in the macrotidal Seine estuary has been conducted, including observations of suspended particulate matter (SPM), surficial sediment, and bathymetric data, as well as use of a three dimensional mathematical model. Tide, river regime, wind, and wave forcings are accounted. The simulated turbidity maximum (TM) is described in terms of concentration and location according to tidal amplitude and the discharge of the Seine River. The TM is mainly generated by tidal pumping, but can be concentrated or stretched by the salinity front. The computed deposition patterns depend on the TM location and are seasonally dependent. The agreement with observations is reasonable, although resuspension by waves may be overestimated. Although wave resuspension is likely to increase the TM mass, it generally occurs simultaneously with westerly winds that induce a transverse circulation at the mouth of the estuary and then disperse the suspended material. The resulting effect is an output of material related to wind and wave events, more than to high river discharge. The mass of the computed TM remains stable over 6 months and independent of the river regime, depending mainly on the spring tide amplitude. Computed fluxes at different cross-sections of the lower estuary show the shift to the TM according to the river flow and point out the rapidity of the TM adjustment to any change of river discharge. The time for renewing the TM by riverine particles has been estimated to be one year. 相似文献
118.
The WGS84 (World Geodetic System 1984) reference system is, originally, mathematically defined from the NSWC-9Z2 (Naval Surface Weapons Center — 9Z2) reference system. The WGS84 associated realization, called in this paper WGS84-D, is a 1 meter consistency NNSS (US Navy Navigation Satellite System) Doppler realized reference frame. In contrast, the ITRF (IERS Terrestrial Reference Frame) is a 1 centimeter consistency reference frame realized through the most accurate techniques of Space Geodesy. This work intends to improve the transformation parameters between the WGS84-D and the ITRF through the use of both a NSWC-9Z2/Doppler realization and an extension of the ITRF network. A strong linear correlation was also modeled between the Doppler determined scale factor and the mean smoothed sunspot number, due to uncompensated ionospheric effects. This correction improved NSWC-9Z2 (i.e. WGS84) Doppler realization consistency. The uncertainty of adjusted transformation parameters between the ITRF and the WGS84-D is improved by a factor 2 over previous determinations. 相似文献
119.
Dissolved Ba, Cd, Co, Mn, Mo, Ni, Rb, Sb, Sr, U and V were measured in the Oubangui river (Central African Republic) during a complete flood period. The dissolved concentrations vary by factors ranging from 1.4 to 8.2 as a function of river discharge: Sr, Ba, Rb and Mo concentrations decrease with rising stage; Ni, U, Sb, Cd, V and Mn concentrations increase with rising stage. These distributions are explained by a mixing of quick flow, mostly surface runoff with delayed flow, mostly groundwater. The dual origin of stream waters is demonstrated by the major element ratios, which are close to a silicate end-member during the high-flow period and trend towards a carbonate end-member during the low-flow period. Moreover, geological heterogeneities in the Oubangui basin may play a role in the variation of concentrations observed at the basin outlet. The previously indicated presence of a subsurface carbonate sequence in the lower part of the basin is confirmed. Cd, V, Mn and Co show peak concentrations during decreasing stage. We suggest that biological processes such as release from phytoplanktonic material and dissolution of oxides or carbonate phases may explain this maximum. 相似文献
120.
A complete yearly record (1988) of surface measurements is used to examine the atmospheric diurnal secondary circulations over the entire area of Hong Kong in conjunction with spatial and temporal variations of surface temperature, wind speed and rainfall. Evidence of atmospheric diurnal secondary circulations is found at 10 sites. The occurrence of a summer morning rainfall maximum over the coast results from the interaction of the large-scale summer monsoon and local mesoscale secondary circulations. The afternoon onshore secondary circulation accelerates the advection of warm, humid unstable air and, coupled with the upward orographic lifting, produces enhanced rainfall along windward mountain ridges.Dynamical and scaling considerations suggest that the blocking effect is negligible and the primary forcing mechanism is land-sea temperature difference, but terrain effects are also important. Although the secondary circulation system's strength and timing vary, the circulation behaves like a classic sea-land breeze circulation, complicated by superimposed mountain-valley breezes. 相似文献