Hydrogeology of the Kabul Basin (Afghanistan), part I: aquifers and hydrology   总被引：1，自引：0，他引：1  

Georg Houben  Nadege Niard  Torge Tünnermeier  Thomas Himmelsbach 《Hydrogeology Journal》2009,17(3):665-677

Shallow groundwater represents the main source for water supply in Kabul, Afghanistan. Detailed information on the hydrogeology of the Kabul Basin is therefore needed to improve the current supply situation and to develop a sustainable framework for future groundwater use. The basin is situated at the intersection of three major fault systems of partially translational and extensional character. It comprises three interconnected aquifers, 20–70 m thick, consisting of coarse sandy to gravely detritus originating from the surrounding mountains. The aquifers were deposited by three rivers flowing through the basin. The coarse aquifer material implies a high permeability. Deeper parts are affected by cementation of pore spaces, resulting in formation of semi-diagenetic conglomerates, causing decreased well yields. Usually the aquifers are covered by low-permeability loess which acts as an important protection layer. The main groundwater recharge occurs after the snowmelt from direct infiltration from the rivers. The steadily rising population is estimated to consume 30–40 million m³ groundwater per year which is contrasted by an estimated recharge of 20–45 million m³/a in wet years. The 2000–2005 drought has prevented significant recharge resulting in intense overexploitation indicated by falling groundwater levels.  相似文献   

Variations in fluid chemistry and membrane phospholipid fatty acid composition of the bacterial community in a cold storage groundwater system during clogging events     

Alexandra Vetter  Kai Mangelsdorf  Markus Wolfgramm  Kerstin Rauppach  Georg Schettler  Andrea Vieth-Hillebrand 《Applied Geochemistry》2012

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Integrated Water Resources Management under different hydrological,climatic and socio-economic conditions   总被引：2，自引：2，他引：0  

Edda Kalbus  Thomas Kalbacher  Olaf Kolditz  Elisabeth Krüger  Jörg Seegert  Gunda Röstel  Georg Teutsch  Dietrich Borchardt  Peter Krebs 《Environmental Earth Sciences》2012,65(5):1363-1366

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Numerical Modeling of the Near‐Field Hydraulics of Water Wells     

Georg J. Houben  Sarah Hauschild 《Ground water》2011,49(4):570-575

Numerical flow models can be a useful tool for dimensioning water wells and to investigate the hydraulics in their near‐field. Fully laminar flow can be assumed for all models calculated up to the screen. Therefore models can be used to predict—at least qualitatively, neglecting turbulent losses inside the well—the spatial distribution of inflow into the well and the overall hydraulic performance of different combinations of aquifer parameters and technical installations. Models for both horizontal (plan view) and vertical flow (cross section) to wells were calculated for a variety of setups. For the latter, this included variations of hydraulic conductivity of the screen, pump position, and aquifer heterogeneity. Models of suction flow control devices showed that they indeed can homogenize inflow, albeit at the cost of elevated entrance losses.  相似文献   

Submarine hydrothermal activity and gold-rich mineralization at Brothers Volcano, Kermadec Arc, New Zealand     

Cornel E. J. de Ronde  Gary J. Massoth  David A. Butterfield  Bruce W. Christenson  Junichiro Ishibashi  Robert G. Ditchburn  Mark D. Hannington  Robert L. Brathwaite  John E. Lupton  Vadim S. Kamenetsky  Ian J. Graham  Georg F. Zellmer  Robert P. Dziak  Robert W. Embley  Vesselin M. Dekov  Frank Munnik  Janine Lahr  Leigh J. Evans  Ken Takai 《Mineralium Deposita》2011,46(5-6):541-584

Brothers volcano, of the Kermadec intraoceanic arc, is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world. It has two distinct vent fields, known as the NW Caldera and Cone sites, whose geology, permeability, vent fluid compositions, mineralogy, and ore-forming conditions are in stark contrast to each other. The NW Caldera site strikes for ??600?m in a SW?CNE direction with chimneys occurring over a ??145-m depth interval, between ??1,690 and 1,545?m. At least 100 dead and active sulfide chimney spires occur in this field and are typically 2?C3?m in height, with some reaching 6?C7?m. Their ages (at time of sampling) fall broadly into three groups: <4, 23, and 35?years old. The chimneys typically occur near the base of individual fault-controlled benches on the caldera wall, striking in lines orthogonal to the slopes. Rarer are massive sulfide crusts 2?C3?m thick. Two main types of chimney predominate: Cu-rich (up to 28.5?wt.% Cu) and, more commonly, Zn-rich (up to 43.8?wt.% Zn). Geochemical results show that Mo, Bi, Co, Se, Sn, and Au (up to 91?ppm) are correlated with the Cu mineralization, whereas Cd, Hg, Sb, Ag, and As are associated with the dominant Zn-rich mineralization. The Cone site comprises the Upper Cone site atop the summit of the recent (main) dacite cone and the Lower Cone site that straddles the summit of an older, smaller, more degraded dacite cone on the NE flank of the main cone. Huge volumes of diffuse venting are seen at the Lower Cone site, in contrast to venting at both the Upper Cone and NW Caldera sites. Individual vents are marked by low-relief (??0.5?m) mounds comprising predominately native sulfur with bacterial mats. Vent fluids of the NW Caldera field are focused, hot (??300°C), acidic (pH????2.8), metal-rich, and gas-poor. Calculated end-member fluids from NW Caldera vents indicate that phase separation has occurred, with Cl values ranging from 93% to 137% of seawater values. By contrast, vent fluids at the Cone site are diffuse, noticeably cooler (??122°C), more acidic (pH?1.9), metal-poor, and gas-rich. Higher-than-seawater values of SO₄ and Mg in the Cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water/rock interactions. Iron oxide crusts 3?years in age cover the main cone summit and appear to have formed from Fe-rich brines. Evidence for magmatic contributions to the hydrothermal system at Brothers includes: high concentrations of dissolved CO₂ (e.g., 206?mM/kg at the Cone site); high CO₂/³He; negative ??D and ??¹⁸O_H2O for vent fluids; negative ??³⁴S for sulfides (to ?4.6??), sulfur (to ?10.2??), and ??¹⁵N₂ (to ?3.5??); vent fluid pH values to 1.9; and mineral assemblages common to high-sulfidation systems. Changing physicochemical conditions at the Brothers hydrothermal system, and especially the Cone site, occur over periods of months to hundreds of years, as shown by interlayered Cu?+?Au- and Zn-rich zones in chimneys, variable fluid and isotopic compositions, similar shifts in ³He/⁴He values for both Cone and NW Caldera sites, and overprinting of ??magmatic?? mineral assemblages by water/rock-dominated assemblages. Metals, especially Cu and possibly Au, may be entering the hydrothermal system via the dissolution of metal-rich glasses. They are then transported rapidly up into the system via magmatic volatiles utilizing vertical (??2.5?km long), narrow (??300-m diameter) ??pipes,?? consistent with evidence of vent fluids forming at relatively shallow depths. The NW Caldera and Cone sites are considered to represent stages along a continuum between water/rock- and magmatic/hydrothermal-dominated end-members.  相似文献   

Nuclear and incommensurate magnetic structure of NaFeGe2O6 between 5?K and 298?K and new data on multiferroic NaFeSi2O6     

G��nther J. Redhammer  Anatoliy Senyshyn  Martin Meven  Georg Roth  Sebastian Prinz  Astrid Pachler  Gerold Tippelt  Clemens Pietzonka  Werner Treutmann  Markus Hoelzel  Bj?rn Pedersen  Georg Amthauer 《Physics and Chemistry of Minerals》2011,38(2):139-157

The compound NaFeGe₂O₆ was grown synthetically as polycrystalline powder and as large single crystals suitable for X-ray and neutron-diffraction experiments to clarify the low temperature evolution of secondary structural parameters and to determine the low temperature magnetic spins structure. NaFeGe₂O₆ is isotypic to the clinopyroxene-type compound aegirine and adopts the typical HT-C2/c clinopyroxene structure down to 2.5?K. The Na-bearing M2 polyhedra were identified to show the largest volume expansion between 2.5?K and room temperature, while the GeO₄ tetrahedra behave as stiff units. Magnetic susceptibility measurements show a broad maximum around 33?K, which marks the onset of low-dimensional magnetic ordering. Below 12?K NaFeGe₂O₆ transforms to an incommensurately modulated magnetic spin state, with k?=?[0.323, 1.0, 0.080] and a helical order of spins within the M1-chains of FeO₆ octahedra. This is determined by neutron-diffraction experiments on a single crystal. Comparison of NaFeGe₂O₆ with NaFeSi₂O₆ is given and it is shown that the magnetic ordering in the latter compound, aegirine, also is complex and is best described by two different spin states, a commensurate one with C2??/c?? symmetry and an incommensurate one, best being described by a spin density wave, oriented within the (1 0 1) plane.  相似文献   

Eoalpine tectonics of the Eastern Alps: implications from the evolution of monometamorphic Austroalpine units (Schneeberg and Radenthein Complex)     

Kurt Krenn  Walter Kurz  Harald Fritz  Georg Hoinkes 《Swiss Journal of Geoscience》2011,104(3):471-491

Monometamorphic metasediments of Paleozoic or Mesozoic age constituting Schneeberg and Radenthein Complex experienced coherent deformation and metamorphism during Late Cretaceous times. Both complexes are part of the Eoalpine high-pressure wedge that formed an intracontinental suture and occur between the polymetamorphosed Ötztal–Bundschuh nappe system on top and the Texel–Millstatt Complex below. During Eoalpine orogeny Schneeberg and Radenthein Complexes were south-dipping and they experienced a common tectonometamorphic history from ca. 115 Ma onwards until unroofing of the Tauern Window in Miocene times. This evolution is subdivided into four distinct tectonometamorphic phases. Deformation stage D1 is characterized by WNW-directed shearing at high temperature conditions (550–600°C) and related to the initial exhumation of the high-pressure wedge. D2 and D3 are largely coaxial and evolved during high- to medium-temperature conditions (ca. 450 to ≥550°C). These stages are related to advanced exhumation and associated with large-scale folding of the high-pressure wedge including the Ötztal-Bundschuh nappe system above and the Texel–Millstatt Complex below. For the area west of the Tauern Window, F2/F3 fold interference results in the formation of large-scale sheath-folds in the frontal part of the nappe stack (formerly called “Schlingentektonik” by previous authors). Earlier thrusts were reactivated during Late Cretaceous normal faulting at the base of the Ötztal–Bundschuh nappe system and its cover. Deformation stage D4 is of Oligo-Miocene age and accounted for tilting of individual basement blocks along large-scale strike-slip shear zones. This tilting phase resulted from indentation of the Southern Alps accompanied by the formation of the Tauern Window.  相似文献   

TiO2 exsolution from garnet by open-system precipitation: evidence from crystallographic and shape preferred orientation of rutile inclusions     

Alexander Proyer  Gerlinde Habler  Rainer Abart  Richard Wirth  Kurt Krenn  Georg Hoinkes 《Contributions to Mineralogy and Petrology》2013,166(1):211-234

We investigated rutile needles with a clear shape preferred orientation in garnet from (ultra) high-pressure metapelites from the Kimi Complex of the Greek Rhodope by electron microprobe, electron backscatter diffraction and TEM techniques. A definite though complex crystallographic orientation relationship between the garnet host and rutile was identified in that Rt[001] is either parallel to Grt<111> or describes cones with opening angle 27.6° around Grt<111>. Each Rt[001] small circle representing a cone on the pole figure displays six maxima in the density plots. This evidence together with microchemical observations in TEM, when compared to various possible mechanisms of formation, corroborates a precipitate origin. A review of exchange vectors for Ti substitution in garnet indicates that rutile formation from garnet cannot occur in a closed system. It requires that components are exchanged between the garnet interior and the rock matrix by solid-state diffusion, a process we refer to as “open-system precipitation” (OSP). The kinetically most feasible reaction of this type will dominate the overall process. The perhaps most efficient reaction involves internal oxidation of Fe²⁺ to Fe³⁺ and transfer from the dodecahedral to the octahedral site just vacated by $ {\text{Ti}}^{ 4+ }: 6\,{\text{M}}^{ 2+ }_{ 3} {\text{TiAl}}\left[ {{\text{AlSi}}_{ 2} } \right]{\text{O}}_{ 1 2} + 6\,{\text{M}}^{ 2+ }_{ 2, 5} {\text{TiAlSi}}_{ 3} {\text{O}}_{ 1 2} = 10\,{\text{M}}^{ 2+ }_{ 3.0} {\text{Al}}_{ 1. 8} {\text{Fe}}_{0. 2} {\text{Si}}_{ 3} {\text{O}}_{ 1 2} + {\text{M}}^{2+} + 2 {\text{e}}^{-} + 1 2\,{\text{TiO}}_{ 2} . $ OSP is likely to occur at conditions where the transition of natural systems to open-system behaviour becomes apparent, as in the granulite and high-temperature eclogite facies.  相似文献   

Identification of maars and similar volcanic landforms in the West Eifel Volcanic Field through image processing of DTM data: efficiency of different methods depending on preservation state     

Nadine Seib  Jonas Kley  Georg Büchel 《International Journal of Earth Sciences》2013,102(3):875-901

The West Eifel Volcanic Field comprises 98 maars, tuff rings, and scoria rings of volcanoes younger than 700 ka. Digital Terrain Models (DTMs) allow to automatically measure morphologic parameters of volcanic edifices such as slope angles, diameters, elevations, floor, and slope surface areas. Based on their morphological characteristics, we subdivided the West Eifel volcanoes into five morphometric groups which reflect different stages of erosion. Group I, II, and IV comprise clear ring-shaped structures. The difference between these groups is that a tephra ring is well preserved in Group I, partially preserved in Group II and absent in Group IV. The original shapes of Group III maars have been lost more substantially than in Groups I, II, or IV, but they nevertheless retain a negative shape (a depression) and have characteristic channel systems, which can be used as search criteria. Maar-diatremes of Group V are eroded down to their feeder pipes and form hills. In order to locate potential volcanic depressions that are likely to be maar volcanoes, we defined common search criteria such as circular negative landforms or particular drainage system patterns for all groups except the least well-preserved Group V. These criteria were taken as the basis for further processing of the DTM data. The first processing step consisted of constructing a residual relief calculated as the difference between a filtered (smoothed) topographic surface and the original DTM data. This identifies local topographic features. We propose a method for regulating the degree of smoothing which is based on filtering of local maxima according to their distance from a surface constructed from local minima. The previously defined search criteria for Groups I to IV such as specific ranges of curvature, slope, circularity, density of the drainage network were then applied to the residual relief in order to extract maar shapes. Not all criteria work equally well for all morphological groups. Combinations of multiple search criteria therefore yield the best results and efficiently identify most known maars. They also separate some probable new, hitherto unrecognized maars from a large number of other local depressions. We also compared the erosional state of maars to their absolute ages. Published estimates of erosion rates for maars in the French Massif Central suggest a general trend of erosion rates decreasing with time elapsed since eruption. However, this cannot explain the strongly varying ages for maars of the same morphometric group (i.e., similar preservation state) in the West Eifel Volcanic Field. The spatial distribution of the morphometric groups shows some regularity. For example, strongly eroded maars are concentrated in the Gerolstein area (where maar density is highest), whereas most well-preserved maars are located east of the Eifel North–South Depression (ENSD). Most maars affected by fluvial erosion lie near the Kyll and Kleine Kyll streams. These observations suggest differential recent uplift of the West Eifel Volcanic Field, with stronger uplift occurring west of the ENSD.  相似文献   

Modeling the water exchanges between the Venice Lagoon and the Adriatic Sea     

Debora Bellafiore  Georg Umgiesser  Andrea Cucco 《Ocean Dynamics》2008,58(5-6):397-413

A hydrodynamic model of the Venice Lagoon and the Adriatic Sea has been developed in order to study the exchanges at the inlets of the Venice Lagoon, a complex morphological area connecting the sea and the lagoon. The model solves the shallow water equations on a spatial domain discretized by a staggered finite element grid. The grid represents the Adriatic Sea and the Venice Lagoon with different spatial resolutions varying from 30 m for the smallest channels of the lagoon to 30  km for the inner areas of the central Adriatic Sea. Data from more than ten tide gauges displaced in the Adriatic Sea have been used in the calibration of the simulated water levels. After the calibration, the tidal wave propagation in the North Adriatic and in the Venice Lagoon is well reproduced by the model. To validate the model results, empirical flux data measured by acoustic Doppler current profiler probes installed inside the inlets of Lido and Malamocco have been used and the exchanges through the three inlets of the Venice Lagoon have been analyzed. The comparison between modeled and measured fluxes at the inlets outlines the efficiency of the model to reproduce both tide- and wind-induced water exchanges between the sea and the lagoon. Even in complex areas, where highly varying resolution is needed, the model is suitable for the simulation of the dominating physical processes.  相似文献