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Berlin Brandenburg

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  • American Geophysical Union (CrossRef)  (12)
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  • 1
    In: Eos, Transactions American Geophysical Union, 21 August 2012, Vol.93(34), pp.328-328
    Description: The largest source of natural gas in the United States, the Marcellus shale, underlies a 95,000‐square‐mile area from Virginia to New York and from Ohio to Pennsylvania. Since 2005, about 5000 wells have been drilled in Pennsylvania alone, and about 2500 of these are now producing gas. While many welcome the shale gas jobs, others worry about environmental impacts. A workshop was convened at Pennsylvania State University to coordinate the collection of data for water quality and quantity in regions of hydrofracturing. The purpose of the event was to encourage participants to use and contribute data to a growing database of water quality and quantity for regions of shale gas development ().
    Keywords: Shale Gas ; Water ; Marcellus ; Database
    ISSN: 0096-3941
    E-ISSN: 2324-9250
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  • 2
    In: Eos, 06/05/2015, Vol.96
    ISSN: Eos
    E-ISSN: 2324-9250
    Source: American Geophysical Union (via CrossRef)
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  • 3
    In: Eos, Transactions American Geophysical Union, 04 September 2012, Vol.93(36), pp.346-346
    ISSN: 0096-3941
    E-ISSN: 2324-9250
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  • 4
    In: Journal of Geophysical Research: Earth Surface, June 2009, Vol.114(F2), pp.n/a-n/a
    Description: Weathering of rocks as a result of exposure to water and the atmosphere can cause significant changes in their chemistry and porosity. In low‐porosity rocks, such as basalts, changes in porosity, resulting from chemical weathering, are likely to modify the rock's effective diffusivity and permeability, affecting the rate of solute transport and thus potentially the rate of overall weathering to the extent that transport is the rate limiting step. Changes in total porosity as a result of mineral dissolution and precipitation have typically been used to calculate effective diffusion coefficients through Archie's law for reactive transport simulations of chemical weathering, but this approach fails to account for unconnected porosity that does not contribute to transport. In this study, we combine synchrotron X‐ray microcomputed tomography (CT) and laboratory and numerical diffusion experiments to examine changes in both total and effective porosity and effective diffusion coefficients across a weathering interface in a weathered basalt clast from Costa Rica. The CT data indicate that below a critical value of ∼9%, the porosity is largely unconnected in the basalt clast. The CT data were further used to construct a numerical pore network model to determine upscaled, effective diffusivities as a function of total porosity (ranging from 3 to 30%) for comparison with diffusivities determined in laboratory tracer experiments. By using effective porosity as the scaling parameter and accounting for critical porosity, a model is developed that accurately predicts continuum‐scale effective diffusivities across the weathering interface of the basalt clast.
    Keywords: Effective Porosity ; Diffusivity ; Basalt Weathering
    ISSN: 0148-0227
    E-ISSN: 2156-2202
    Source: John Wiley & Sons, Inc.
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  • 5
    In: Geophysical Research Letters, 01 January 2000, Vol.27(1), pp.5-8
    Description: The fluxes, concentrations, and carbon isotopic compositions of soil CO were measured along the Parkfield segment of the San Andreas fault (SAF). Single or double‐peak CO flux anomalies (〉 18 g m d) were observed along 12 of 16 fault‐crossing transects at five sites. Flux anomalies did not coincide with concentration anomalies. Flux anomalies paralleled the fault trace, suggesting zones of high diffusivity/permeability. One flux anomaly may have been accentuated by a 0.3 mm creep event. However, values of δC (‐23.7 to ‐21.6 ‰) and C (110.5 to 111.9 pmC) for soil gas CO are characteristic of CO of biogenic origin. The CO flux anomalies are therefore consistent with fault‐related biogenic gas flow and do not yield evidence for degassing of deeply derived CO.
    Keywords: Quaternary Geology ; Anomalies ; C-13/C-12 ; C-14 ; California ; Carbon ; Carbon Dioxide ; Fluid Pressure ; Gases ; Isotope Ratios ; Isotopes ; Monterey County California ; Parkfield California ; Pore Pressure ; Radioactive Isotopes ; San Andreas Fault ; Soils ; Stable Isotopes ; United States ; Volcanism;
    ISSN: 0094-8276
    E-ISSN: 1944-8007
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  • 6
    In: Water Resources Research, April 2011, Vol.47(4), pp.n/a-n/a
    Description: Although changes in bulk electrical conductivity () in aquifers have been attributed to microbial activity, has never been used to infer biogeochemical reaction rates quantitatively. To explore the use of electrical conductivity to measure reaction rates, we conducted iron oxide reduction experiments of increasing biological complexity. To quantify reaction rates, we propose composite reactions that incorporate the stoichiometry of five different types of reactions: redox, acid‐base, sorption, dissolution/precipitation, and biosynthesis. In batch experiments and the early stages of a column experiment, such reaction stoichiometries inferred from a few chemical measurements allowed quantification of the Fe oxide reduction rate based on changes in electrical conductivity. The relationship between electrical conductivity and fluid chemistry did not hold during the latter stages of the column experiment when increased while fluid chemistry remained constant. Growth of an electrically conductive biofilm could possibly explain this late stage increase. The measured increase is consistent with a model proposed by analogy from percolation theory that attributes the increased conductivity to growth of biofilms with conductivity of ∼5.5 S m in at least 3% of the column pore space. This work demonstrates that measurements of and flow rate, combined with a few direct chemical measurements, can be used to quantify biogeochemical reaction rates in controlled laboratory situations and may be able to detect the presence of biofilms. This approach may help in designing future field experiments to interpret biogeochemical reactivity from conductivity measurements.
    Keywords: Biogeophysics ; Electrical Conductivity ; Iron Reduction
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 7
    Language: English
    In: Journal of Geophysical Research: Solid Earth, 07/10/1995, Vol.100(B7), pp.12881-12894
    Description: Two types of periodic textures observed in veins from the Kodiak accretionary prism attest to cyclic fluid flow through a regionally extensive fracture network buried at 8-12 km depth: (1) crack-seal microstructures with bands of mica inclusions and (2) collapse microstructures with jagged bands of residue embedded within euhedral crystals of quartz. The difference in texture reflects the closure of cracks: crack-seal microstructures record the complete chemical sealing of the crack after each fracture event, whereas the collapse features record longer fluid-filled periods followed by more rapid draining of fractures. Collapse features consist of pressure solution selvages trapped within veins and in the wall rock adjacent to euhedral growth terminations; the high concentrations of immobile elements in these selvages indicate that these fractures closed by collapse and penetration of quartz crystals into wall rock. Analysis of chemical composition on either side of four large euhedral growth veins and whole rock analysis of slates across the Kodiak Formation reveal local depletion of silica adjacent to veins but no evidence for long-distance silica transport within the system. Both crack-seal and collapse textures are observed in a regionally extensive vein system that displays a regular geometry, with thin, closely spaced (0.5-3 cm), near-vertical crack-seal veins that connect vertically and laterally with thicker euhedral growth veins arranged in widely spaced ( approximately 500 mm) southeast dipping en echelon sets. The mesoscopic distribution and textural variability of the vein network suggests that the development of the vein system involved early nucleation and growth of vertical hydrofractures. As the fracture density increased, arrays of fractures locally provided zones of weakness and southeast dipping brittle-ductile shear zones nucleated. These en echelon cracks remained open and provided small reservoirs of fluid. Textures show that en echelon fractures remain open but periodically grow by upward and downward propagation. Crack tips are then sealed with locally derived silica, and fluid drains back into en echelon fracture arrays. This local fluid movement is punctuated by less frequent events where the system links up over a greater distance, fractured reservoirs become interconnected, and the fluid within reservoirs is drained upward or laterally. Periodic inflation and deflation of en echelon arrays may reflect periodic slip on crosscutting faults and rupture of the seals that separate reservoirs. Copyright 1995 by the American Geophysical Union.
    Keywords: Igneous And Metamorphic Petrology ; Structural Geology ; Accretionary Wedges ; Afognak Island ; Alaska ; Chemical Composition ; Circulation ; Cretaceous ; Deformation ; Fluid Phase ; Fractures ; Kodiak Accretionary Complex ; Kodiak Formation ; Mesozoic ; Petrography ; Pressure Solution ; Silica ; Solutions ; Southwestern Alaska ; Structural Analysis ; Textures ; United States ; Upper Cretaceous ; Veins;
    ISSN: Journal of Geophysical Research: Solid Earth
    E-ISSN: 01480227
    E-ISSN: 21562202
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  • 8
    Language: English
    In: Journal of Geophysical Research: Solid Earth, 05/10/1994, Vol.99(B5), pp.9505-9522
    Description: Samples of the subglacial lake in the crater of the tholeiitic basaltic caldera Grimsvoetn in Iceland were obtained by using a hot-water drill to sink two boreholes through the 250-m-thick ice shelf covering the lake. The lake generally shows an increase in solutes with increased depth, as solutes are added from the lake's bottom and dilute glacial meltwater is added continuously from above. The crater lake temperature ranges from 0 degrees C in the upper part to temperatures of 1 degrees C to 4 degrees C near the bottom of the lake. The lake water pH ranges between 7.0 and 5.7. The crater lake is assumed to be closed, with respect to volatile components released from subsurface magma, except for periodic draining by joekulhlaups. From the periodicity and water chemistry of the joekulhlaups, we have estimated the volcano's average release rates of carbon, sulfur, chlorine and fluorine between 1954 and 1991 and corrected these rates for dissolution of bedrock into the lake water and seepage of solutes to groundwater. The corrected mean release rates are 5.3 X 10 (super 7) kg C yr (super -1) , 5.3 X 10 (super 6) kg S yr (super -1) , 6.6 X 10 (super 5) kg Cl yr (super -1) , and 1.5 X 10 (super 5) kg F yr (super -1) . The emission rate estimates for Grimsvoetn, one of the most active volcanoes in Iceland, are the longest integrated estimates obtained for an active volcano and are equal to or lower than those of other major active volcanoes worldwide. This difference may imply that published release rates for other volcanoes are overestimated, because they are usually not integrated over time. The values of the S/Cl and F/Cl ratios for noneruptive periods are 0.53 + or - 0.20 and 0.013 + or - 0.003, and for the two eruptive events are 0.69 and 2.14, and 0.034 and 0.041, respectively. The response of the elemental ratios to eruptive events, followed by the return to lower ratios, supports the assumption of steady state, because no long-term accumulation of volatiles occurs. The energy output from the volcano, estimated from the amount of ice melted by hydrothermal heat, is 4250 MW over the last four decades. Using the energy output to calculate magma solidification rates and maximum possible volatile release rates, we observe that emissions of F and S are strongly suppressed at Grimsvoetn, while a significant portion of available Cl and C are released. These calculations also reveal that coverage of a volcano by a glacier, and subsequent raising of the water table, may cause significant scrubbing of magmatic gases so that these gases do not reach the atmosphere. Copyright 1994 by the American Geophysical Union.
    Keywords: Quaternary Geology ; General Geochemistry ; Atmosphere ; Calderas ; Chemical Composition ; Europe ; Fresh Water ; Gases ; Glacial Features ; Glacial Lakes ; Grimsvotn ; Iceland ; Lakes ; Magmas ; Rates ; Volatiles ; Volcanic Features ; Volcanoes ; Western Europe;
    ISSN: Journal of Geophysical Research: Solid Earth
    E-ISSN: 01480227
    E-ISSN: 21562202
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  • 9
    Language: English
    In: Journal of Geophysical Research, 1992, Vol.97(B13), p.20043
    Description: Steady state models of overgrowth and vein formation are developed using kinetic data for quartz dissolution and precipitation and estimates of fluid advection, pore-fluid and grain-boundary diffusion. Application of these models to overgrowths and veins in the Kodiak accretionary complex suggests that the Kodiak Formation deformed continuously by a grain-boundary diffusion-limited mechanism, accompanied by episodic pore fluid diffusion of quartz from the matrix to vertical fluid-filled fractures near the base of the accretionary wedge. These processes produced two types of syntectonic crystal textures within the Kodiak Formation: overgrowths containing displacement-controlled fibers, and throughgoing veins composed of face-controlled elongate blocky quartz crystals. Based on textural observations, displacement-controlled quartz growth in overgrowths is rate-limited by either diffusion along a cohesive interface or the rate of matrix strain. The magnitude of elongation recorded by displacement-controlled crystal growth varies smoothly (elongation of 1 to 3) from the shallowest to the deepest structural levels of the Kodiak Formation, suggesting that the diffusional component of deformation in the accretionary wedge increases with depth. In contrast, face-controlled quartz growth is largely restricted to Veins within the deepest level, where the cleavage is subhorizontal and deformation involves a component of simple shear, suggesting proximity to a decollement. The face-controlled quartz veins represent mode I cracks which seal periodically and contain continuous planar solid inclusion bands, cracks which partially seal periodically and contain discontinuous solid inclusion bands, or cracks that remain open and contain euhedral quartz crystals with no solid inclusions. The initial crack aperture, inferred from spacing of inclusion bands, varies from 8 mu m in crack seal features to much larger values in euhedral growth veins. Euhedral growth veins remain open throughout their development (10 (super 5) to 10 (super 6) years), and crack seal veins develop as a consequence of many crack-seal events over a 10 (super 3) - 10 (super 6) year period. In both cases, textural evidence suggests that most transport of silica occurs by local pore-fluid diffusion from matrix to vein. Wall rock inclusion bands suggest that "crack" events and "seal" events each occurred within periods of 10 (super 2) - 10 (super 4) years. A picture emerges of intermittent fluid flow upward from the decollement into a branching hierarchy of vertical fractures in the accretionary wedge during hydrofracturing events, followed by local transport and precipitation of silica causing sealing of the fractures at depth and propagation of pulses of fracture fluid upward. Copyright 1992 by the American Geophysical Union.
    Keywords: Structural Geology ; Mineralogy Of Silicates ; Accretionary Wedges ; Afognak Island ; Alaska ; Cracks ; Cretaceous ; Crystal Growth ; Deformation ; Diffusion ; Fluid Dynamics ; Fractures ; Framework Silicates ; Grain Boundaries ; Kinetics ; Kodiak Formation ; Mesozoic ; Metamorphic Rocks ; Metasedimentary Rocks ; Overgrowths ; Periodicity ; Pore Water ; Quartz ; Quartz Veins ; Silica Minerals ; Silicates ; Subduction Zones ; United States ; Upper Cretaceous ; Veins;
    ISSN: 0148-0227
    E-ISSN: 21562202
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  • 10
    Language: English
    In: Eos, Transactions American Geophysical Union, 12/11/2007, Vol.88(50), pp.560-560
    Description: Biological, physical, and chemical processes transform bedrock and sediments into soil at the Earth's surface. All terrestrial life on Earth is supported in the aptly named “critical zone” (CZ), where air, water, rock materials, and biota interact. The CZ is bounded at the top by the vegetative canopy and at the bottom by the lower limits of groundwater. Processes within this zone regulate the transformation of minerals, solubilize nutrients for biota, buffer toxins, create water pathways, and ultimately sculpt the landscape on which we live. Forty scientists from many disciplines attended a workshop recently at Pennsylvania State University to discuss needs for data and information systems to investigate the CZ.
    ISSN: Eos, Transactions American Geophysical Union
    E-ISSN: 00963941
    E-ISSN: 23249250
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