Unique documentation,analysis of origin and development of an undrained depression in a subsidence basin caused by underground coal mining (Kozinec,Czech Republic)

This article aims to explain and demonstrate the origin and development of a subsidence basin caused by coal mining as well as to point out important aspects of this phenomenon in engineering geology. Engineering geology needs to deal with a number of issues related to the origin and development of subsidence basins in areas affected by deep coal mining. An interesting case study from the Upper-Silesian Basin in the northeast of the Czech Republic near the Polish border is presented in this paper. There is a clear time chronological succession in the ground surface changes manifested by a ground subsidence gradation, both in their absolute values as well as in their spatial distribution. The phenomenon is documented by aerial photo time series, which optimally depict the origin and development of the subsidence. In the study area, there are changes in the landscape elements and it is essential to be considered in future land use plans. The marginal conditions of the Quaternary geological structure and hydrogeological conditions are responsible for an unconfined aquifer which manifests there as a water body in an undrained depression in the course of the ground subsidence.     

Star formation sustained by gas accretion

Numerical simulations predict that metal-poor gas accretion from the cosmic web fuels the formation of disk galaxies. This paper discusses how cosmic gas accretion controls star formation, and summarizes the physical properties expected for the cosmic gas accreted by galaxies. The paper also collects observational evidence for gas accretion sustaining star formation. It reviews evidence inferred from neutral and ionized hydrogen, as well as from stars. A number of properties characterizing large samples of star-forming galaxies can be explained by metal-poor gas accretion, in particular, the relationship among stellar mass, metallicity, and star-formation rate (the so-called fundamental metallicity relationship). They are put forward and analyzed. Theory predicts gas accretion to be particularly important at high redshift, so indications based on distant objects are reviewed, including the global star-formation history of the universe, and the gas around galaxies as inferred from absorption features in the spectra of background sources.     

Seismic-event-based methodology to obtain earthquake-induced translational landslide regional hazard maps

A seismic-event-based methodology to generate earthquake-induced translational landslide maps using Newmark method is proposed. The steps are: (1) to construct a GIS-based geotechnical database; (2) to identify those areas that are susceptible to the occurrence of translational landslides based on available geological information; (3) to compute a static safety factor; (4) to compute the critical acceleration that defines the threshold acceleration required to cause a displacement; (5) to characterize the seismic hazard as a set of stochastic events, collectively exhaustive and mutually exclusive, that fully describes the hazard spatial distribution and annual frequency of occurrence (in accordance with the earthquake location, depth and magnitude) with the appropriate ground-motion prediction equations; (6) to compute the Newmark displacement; and finally, (7) to carry out a probabilistic translational landslide hazard analysis to estimate an exceedance rate of a given displacement. This methodology is applied to Mexico, and maps for return periods of 150 and 500 years are presented. Results shown in maps are estimations of where translational landslides may occur and should be useful to carry out local studies to elaborate recommendations of site specific hazard reduction plans as well as to calculate insurance rates. In addition, these results are useful to identify civil protection actions, risk management at regional and local level, and land use planning, as well as for promoting more detailed vulnerability and risk studies at different scales.     

Mobility of heavy metals from coal fly ash

The mobility of Cd, Co, Cu, Ni, Pb, Sb, and Zn from six different coal-fired power plant fly ashes that show a wide compositional range was examined using a sequential extraction procedure in order to assess their mobility when these wastes are ponded or landfilled. The extraction sequence was as follows: (1) water extractable, (2) cation exchangeable (CH₃COONH₄ at pH 7), (3) surface oxide-bound cations (CH₃COONH₄ at pH 5), (4) Fe oxide-bound cations (HONH₃Cl), and (5) residual (HF, HCl, HNO₃, 211). The heavy metal contents in the extraction solutions were determined by anodic (Cd, Cu, Pb, Sb, and Zn) and cathodic (Ni and Co) stripping voltammetry. The results reveal differences in the total contents of the selected trace elements among the fly ash samples, which must be related to differences in coal composition and combustion technology. The extractable fraction under natural conditions ranges from 1.5 to 36.4 percent of the total element content. Cadmium, Co, Cu, and Zn show the highest extractable fraction (10.8–18.9 percent on average). Cadmium is the most easily water-extractable element, while Co, Cu, and Zn increase their mobility as the severity of the extraction increases. Cobalt, Ni, Pb, and Zn are mainly associated with the surface oxide-bound and Fe oxide-bound fractions. Nickel, Pb, and Sb have low mobility potentials (5.3–6.6 percent as extractable fraction), but Sb presents a relatively high water-extractable fraction.     

Long-Term Profiles of Wind and Weibull Distribution Parameters up to 600 m in a Rural Coastal and an Inland Suburban Area

An investigation of the long-term variability of wind profiles for wind energy applications is presented. The observations consists of wind measurements obtained from a ground-based wind lidar at heights between 100 and 600 m, in combination with measurements from tall meteorological towers at a flat rural coastal site in western Denmark and at an inland suburban area near Hamburg in Germany. Simulations with the weather research and forecasting numerical model were carried out in both forecast and analysis configurations. The scatter between measured and modelled wind speeds expressed by the root-mean-square error was about 10 % lower for the analysis compared to the forecast simulations. At the rural coastal site, the observed mean wind speeds above 60 m were underestimated by both the analysis and forecast model runs. For the inland suburban area, the mean wind speed is overestimated by both types of the simulations below 500 m. When studying the wind-speed variability with the Weibull distribution, the shape parameter was always underestimated by the forecast compared to both analysis simulations and measurements. At the rural coastal site although the measured and modelled Weibull distributions are different their variances are nearly the same. It is suggested to use the shape parameter for climatological mesoscale model evaluation. Based on the new measurements, a parametrization of the shape parameter for practical applications is suggested.     

Accurate pressure gradient calculations in hydrostatic atmospheric models

Most models of atmospheric flow which use the primitive equations require a diagnostic equation to determine local total pressure. In hydrostatic models, this equation is the vertically integrated hydrostatic equation. A frequently used approximation to this integration is to hold the temperature constant within model layers yielding a linear proportionality between p or (Exner's function) and z. This procedure yields static pressures with errors on the order of 10^–3mb.If terrain following coordinates are used, terms arise in the horizontal momentum equations involving the gradient of total pressure along the coordinate surface, less a correction for the variation of the hydrostatic pressure along a sloped surface. Erroneous horizontal accelerations are common in these models which result from spurious pressure gradients that are due to inaccurate computation of the static pressure. This error may be amplified if the computation of the slope correction term of the horizontal pressure gradient is not consistent with the method of calculating the total pressure.We derive a methodology to be used in the vertical pressure integrations that is exact if the potential temperature lapse rate is constant between integration limits. The method is applied to both the integration of the hydrostatic equation and the computation of the slope correction term in the horizontal pressure gradient. The method employs a fixed vertical grid and a dynamic one defined by the significant levels in the vertical temperature distribution. With this methodology, the error in calculation of the horizontal pressure gradient acceleration is greatly reduced, especially in situations where the isothermal surfaces are not parallel to the vertical coordinate surfaces. The problem of aliasing and the treatment of significant temperature levels is described.     

A new sulphur isotopic study of some Iberian Pyrite Belt deposits: evidence of a textural control on sulphur isotope composition

The sulphide deposits of the Iberian Pyrite Belt (IPB) represent an ore province of global importance. Our study presents 113 new sulphur isotope analyses from deposits selected to represent the textural spectrum of ores. Measured ³⁴S values range from −26 to +10‰ mostly for massive and stockwork ores, in agreement with data previously published. In situ laser ³⁴S analyses reveals a close correlation of ³⁴S with texture. Primary diagenetic textures are dominated by relatively low ³⁴S (−8‰ to −2‰), whereas stockwork feeder textures are dominated by higher ³⁴S (∼+3‰ to +5‰). Intermediate textures (mainly coarse textures in stratiform zones) have intermediate ³⁴S, although they are mostly dominated by the high ³⁴S component. Rare barite has a homogeneous ³⁴S around +18‰, which is consistent with direct derivation from Lower Carboniferous seawater sulphate. A dual source of sulphide sulphur in the IPB deposits has been considered. A hydrothermal source, derived from reduction of coeval seawater sulphate in the convective systems, is represented by sulphide in the feeder zones. Here variations in ³⁴S are caused by variations in the extent of the sulphate reduction, which governs the SO₄:H₂S ratio. The second end-member was derived from the bacterial reduction of coeval seawater sulphate at or near the surface, as reflected in the primary textures. A distinct geographical variation in ³⁴S and texture from SW (more bacteriogenic and primary textures) to NE (more hydrothermal textures and ³⁴S) which reflects a variation in the relative input of each source was likely controlled by local geological environments. Given that the sulphur isotope characteristics of the IPB deposits are unlike most VMS and Kuroko deposits, and noting the dominance of a mixed reduced sedimentary and volcanic environment, we suggest that the IPB could represent an ore style which is intermediate between volcanic and sedimentary hosted massive sulphide types. Received: 8 October 1997 / Accepted: 14 May 1998     

Ion--neutral friction as a model for magnetic relaxation

It is generally admitted that a plasma in the absence of forcing will relax to a minimum energy state compatible with appropriate constraints. Usually this is a force-free state, which, in two dimensions, implies a potential magnetic field except by the possible presence of current sheets. The precise mechanism of this relaxation, and in particular the plasma velocity, are generally ignored. There exists, however, a physically well-defined process that should produce magnetic relaxation: ion--neutral (or ambipolar) friction. While there is no guarantee of the existence of a limit of this process when t?→?∞, there exists a family of sequential limits for whom the Lorentz force tends to zero. To analyze the configuration of these limit states, we study the evolution of several moments of the magnetic energy. We prove that for as long as the enstrophy remains bounded, the current density energy also remains bounded in two dimensions: this excludes all classical configurations of current sheets across which the magnetic field reverses direction. Hence, these sheets cannot be the limit of ion--neutral diffusion unless the flow becomes increasingly irregular over time.     

The significance of Chara vegetation in the precipitation of lacustrine calcium carbonate

A significant portion of calcium carbonate is deposited in lake sediments as a result of biological processes related to the photosynthetic activity of phytoplankton in the pelagic realm and, in addition, macrophytes in the littoral zone. Lake Wigry, one of the largest lakes in Poland (north‐east Poland), is characterized by: (i) carbonate sediments with a CaCO₃ content exceeding 80% within the littoral zone; and (ii) large areas of submerged vegetation dominated by charophytes (macroscopic green algae, Characeae family). It is claimed that charophytes are highly effective in utilizing HCO₃^? and forming thick CaCO₃ encrustations. Thus, this study was aimed at evaluating the CaCO₃ production by dense Chara stands overgrowing the lake bottom reaching a depth of 4 m. In late July 2009, the fresh and dry mass of plants, the percentage contribution of calcium carbonate and the production of CaCO₃ per 1 m² were investigated along three transects at three depths (1 m, 2 m and 3 m, with each sample area equal to 0·0625 m²) per transect. The composition and structure of phytoplankton and the physico‐chemical properties of the water analysed in both the littoral and pelagic zones served as the environmental background and demonstrated moderately low fertility in the lake. The greatest dry plant mass exceeded 1000 g m^?2 and CaCO₃ encrustations constituted from 59% to over 76% of the charophyte dry weight. Thus, the maximum and average values of carbonates precipitated by charophytes were 685·5 and 438 g m^?2, respectively, which exceeded previously reported results. A correlation of carbonate production with the depth of Chara stands was detected, and intermediate depths offered the most favourable conditions for carbonate precipitation (589 g m^?2 on average). As precipitated carbonates are ultimately stored in bottom deposits, the results highlight the significance of charophytes in lacustrine CaCO₃ sedimentation.