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571.
Pierre Delmelle Minoru Kusakabe Alain Bernard Tobias Fischer Simon de Brouwer Esfeca del Mundo 《Bulletin of Volcanology》1998,59(8):562-576
The hydrologic structure of Taal Volcano has favored development of an extensive hydrothermal system whose prominent feature
is the acidic Main Crater Lake (pH<3) lying in the center of an active vent complex, which is surrounded by a slightly alkaline
caldera lake (Lake Taal). This peculiar situation makes Taal prone to frequent, and sometimes catastrophic, hydrovolcanic
eruptions. Fumaroles, hot springs, and lake waters were sampled in 1991, 1992, and 1995 in order to develop a geochemical
model for the hydrothermal system. The low-temperature fumarole compositions indicate strong interaction of magmatic vapors
with the hydrothermal system under relatively oxidizing conditions. The thermal waters consist of highly, moderately, and
weakly mineralized solutions, but none of them corresponds to either water–rock equilibrium or rock dissolution. The concentrated
discharges have high Na contents (>3500 mg/kg) and low SO4/Cl ratios (<0.3). The Br/Cl ratio of most samples suggests incorporation of seawater into the hydrothermal system. Water
and dissolved sulfate isotopic compositions reveal that the Main Crater Lake and spring discharges are derived from a deep
parent fluid (T≈300 °C), which is a mixture of seawater, volcanic water, and Lake Taal water. The volcanic end member is
probably produced in the magmatic-hydrothermal environment during absorption of high-temperature gases into groundwater. Boiling
and mixing of the parent water give rise to the range of chemical and isotopic characteristics observed in the thermal discharges.
Incursion of seawater from the coastal region to the central part of the volcano is supported by the low water levels of the
lakes and by the fact that Lake Taal was directly connected to the China sea until the sixteenth century. The depth to the
seawater-meteoric water interface is calculated to be 80 and 160 m for the Main Crater Lake and Lake Taal, respectively. Additional
data are required to infer the hydrologic structure of Taal. Geochemical surveillance of the Main Crater Lake using the SO4/Cl, Na/K, or Mg/Cl ratio cannot be applied straightforwardly due to the presence of seawater in the hydrothermal system.
Received: 12 February 1997 / Accepted: 26 January 1998 相似文献
572.
Alain Plouffe 《Environmental Geology》1998,33(2-3):183-196
Abundant cinnabar (HgS) mineralization is associated with the Pinchi Fault in central British Columbia. Two formerly producing
mercury mines have been developed on this fault: Pinchi and Bralorne Takla. The mercury content of till (a sediment type directly
deposited by glaciers) in the area of this fault is primarily controlled by the occurrence of cinnabar mineralization in bedrock
and the direction of ice flow. Cinnabar-bearing bedrock was eroded by glaciers, transported in the direction of ice flow,
and deposited "down-ice" from its source. An example of such a dispersal train is documented for the Pinchi Mine area where
mercury ore was transported over a distance of 12 km, as measured in the clay-sized fraction (< 0.002 mm) of till, and could
have been transported over 24 km according to heavy mineral concentrates (specific gravity >3.3) of this same sediment. Antimony,
chromium, and nickel dispersal trains were also detected in the region. These data indicate that natural glacial processes
can result in the "mobilization" of metals in the surficial environment, a factor which has to be considered at mine sites
in glaciated terrain, where mine reclamation and remediation measures are now required.
Received: 31 October 1996 · Accepted: 27 May 1997 相似文献
573.
Hervé Nouzé Isabelle Contrucci Jean-Paul Foucher Bruno Marsset Yannick Thomas Estelle Thereau Alain Normand Éliane Le Drezen Stéphane Didailler Jean-Pierre Regnault Sandie Le Conte Stéphanie Guidart Wim Lekens Simon Dean Alexandre Throo 《Comptes Rendus Geoscience》2004,336(13):1181-1189
The Storegga slides, off Norway, are among the largest submarine slides ever known on a continental slope. The HYDRATECH cruise on N/O Le Suroît aimed at a high-resolution survey of an area at the northern boundary of the slides. This survey images in great detail the bottom simulating reflector (BSR) extent and properties, the various fluid escape structures and the sediment deformations. The combination and the quality of the data help to understand the still poorly constrained relationships between fluid escapes, gas hydrates and slope stability in the survey area. To cite this article: H. Nouzé et al., C. R. Geoscience 336 (2004). 相似文献
574.
Alain Dupont Jacqueline Vander Auwera Christian Pin Ştefan Marincea Tudor Berza 《Mineralium Deposita》2002,37(6-7):568-586
575.
Two-dimensional numerical simulations were conducted of the growth of thermal plumes from a point heat source at Rayleigh
numbers up to 108 and Prandtl numbers up to 1000. Scaling the convection equations by the free fall velocity rather than the
thermal diffusivity, increased the Prandtl number range available to numerical simulation by one order of magnitude from Prandtl
number 100 to 1000. We present animations showing how the plumes grow with time for different Prandtl numbers. Plumes with
Prandtl numbers around 7 (water) were found to be unstable to sinuous instabilities; whereas those at Prandtl numbers of 1000
had straight stems and fewer sinuous instabilities. Wavelet analysis was used to analyze the scales at which plumes initiated,
and the scales at which sinuous instabilities occurred. The scale of both the plume structures and instabilities was found
to decrease with Prandtl number. 相似文献
576.
Franois Anctil Renaud Mathieu Lon-tienne Parent Alain A. Viau Mathali Sbih Masoud Hessami 《Journal of Hydrology》2002,260(1-4):30-37
The aim of this study was to characterise fine scale patterns of organic soil moisture content in the top 5 cm by means of semi-variogram modelling. Soil moisture content was observed along a transect on 2 occasions, early in the 1999 growing season to avoid any influences originating from vegetation and cultural practices. Soil moisture values were found to be normally distributed and were not significantly correlated with the soil organic matter content. Many similarities were depicted between the exponential semi-variograms characteristics of this study and another one in mineral soils, reported in the literature, except for the much higher sills associated with organic soils. Of particular interest were similar correlation lengths, indicating that a correlation range of the order of 100 m should be expected for mineral soils and for the level of moisture and organic matter contents found in this study. 相似文献
577.
Gravity waves associated with stably stratified layers were observed in the planetary boundary layer at two locations in France. Using an array of three monostatic Doppler acoustic sounders, the wave speeds and directions were found. A quantitative study of the waves has been performed to determine their physical characteristics. Based on their dynamics, a classification into three types was possible. Most were found to be trapped beneath a critical level. 相似文献
578.
Reservoir lifetime and heat recovery factor in geothermal aquifers used for urban heating 总被引:1,自引:0,他引:1
Alain C. Gringarten 《Pure and Applied Geophysics》1978,117(1-2):297-308
Simple models are discussed to evaluate reservoir lifetime and heat recovery factor in geothermal aquifers used for urban heating. By comparing various single well and doublet production schemes, it is shown that reinjection of heat depleted water greatly enhances heat recovery and reservoir lifetime, and can be optimized for maximum heat production. It is concluded that geothermal aquifer production should be unitized, as is already done in oil and gas reservoirs.Nomenclature
a
distance between doublets in multi-doublet patterns, meters
-
A
area of aquifer at base temperature, m2 drainage area of individual doublets in multidoublet patterns, m2
-
D
distance between doublet wells, meters
-
h
aquifer thickness, meters
-
H
water head, meters
-
Q
production rate, m3/sec.
-
r
e
aquifer radius, meters
-
r
w
well radius, meters
-
R
g
heat recovery factor, fraction
-
S
water level drawdown, meters
- t
producing time, sec.
-
T
aquifer transmissivity, m2/sec.
-
v
stream-channel water velocity, m/sec.
-
actual temperature change, °C
-
theoretical temperature change, °C
-
water temperature, °C
-
heat conductivity, W/m/°C
- r
rock heat conductivity, W/m/°C
- aCa
aquifer heat capacity, J/m3/°C
- aCr
rock heat capacity, J/m3/°C
- WCW
water heat capacity, J/m3/°C
-
aquifer porosity, fraction 相似文献
579.
580.
The spectral density of temperature fluctuations in the boundary layer has been studied in the range 0.2 to 2 Hz. It is shown that the temperature spectrum is strongly variable from one minute to the next and that the spectral slope tends to increase with the standard deviation of temperature fluctuations and with the stability of the medium. It is shown that C
T
2
values computed from short time series (30 s) tend to be smaller than the C
T
2
values computed from several minutes of record.Formerly at Laboratoire de Météorologie Dynamique du C.N.R.S. (Paris). 相似文献