Description and interpretation of the composition of fluid and alteration mineralogy in the geothermal system,at Svartsengi,Iceland

The bulk composition and mineralogy of hydrothermally altered tholeiite, along with the composition and speciation of fluid, have been determined for a well-defined alteration zone at 240°C and 110 bars at Svartsengi, Iceland. Mass balances between the geothermal fluid and altered tholeiite, relative to a seawater/fresh water mixture and unaltered tholeiite, indicate the overall reaction per 1000 cm³ is: 1325 gm plagioclase + 1228 gm pyroxene + 215 gm oxide-minerals break down to form 685 gm chlorite + 636 gm albite + 441 gm quartz + 249 gm epidote + 266 gm calcite + 201 gm oxide-minerals + 15 gm pyrite, requiring an influx of 123 gm CO₂, 10 gm H₂S and 4 gm Na₂O and a release of 57 gm SiO₂, 35 gm FeO, 21 gm CaO, 8 gm MgO and 4 gm K₂O.Principal reactions, deduced from textural evidence, include Na-Ca exchange in plagioclase, precipitation of quartz, calcite and anhydrite, and formation of chlorite and epidote by reactions between groundmass minerals and fluid.Thermodynamic analyses of authigenic minerals and downhole fluid indicate that the fluid maintains a state close to equilibrium with the secondary mineral phases chlorite, epidote, albite, quartz, calcite, prehnite, anhydrite, pyrite and magnetite, whereas remnant primary labradorite and augite are out of equilibrium with the fluid.Water/rock ratios for the system are determined under a variety of assumptions. However, the open nature of the system makes comparisons with experimental and theoretical closed system studies ambiguous.     

The role of horizontal impulses of the faulting continental slope in generating the 26 December 2004 tsunami

For a long time, people have believed that the vertical displacement of seafloor due to undersea earthquakes is the primary cause of tsunami genesis. However, seismically-inverted seafloor deformation of the 2004 Sumatra–Andaman earthquake shows that the total vertical displacement is not enough to have generated the powerful Indian Ocean tsunami. Based on the seismically-inverted data and a three-dimensional ocean general circulation model (OGCM), we show that the momentum force, transferred by the horizontal impulses of the faulting continental slope in that earthquake, has accounted for two thirds of the satellite-observed tsunami height and generated kinetic energy 5 times larger than the potential energy due to the vertical displacement. The asymmetric tsunami pattern, recorded by tide-gauges showing leading-elevation waves toward Sri Lanka and leading-depression waves toward Thailand, is best explained by the horizontally-forced mechanism. The same mechanism has also explained the March 2005 Nias earthquake and tsunami data, suggesting that the horizontal motions of faulting have played more important roles in tsunami genesis than previously thought.     

In situ atomic force microscopy measurements of biotite basal plane reactivity in the presence of oxalic acid

We have used a direct imaging technique, in situ atomic force microscopy (AFM), to observe the dissolution of the basal biotite surface by oxalic acid over a range of temperatures close to ambient conditions, using a specially designed AFM liquid cell and non-invasive intermittent contact mode of operation. From the 3-dimensional nanometre-resolution data sets, we observe a process characterised by the slow formation of shallow etch pits in the (0 0 1) surface and fast growth of etch pits from the resulting steps, which represent proxies for the {h k 0} surface. Measurements of dissolution rates as a function of temperature allow a determination of an apparent activation energy (E_a,app) for the process, via mass-loss calculations from image analysis. We obtain a value of E_a,app = 49 ± 2 kJ mol⁻¹, which is consistent with separate calculations based on planar area etch pit growth, and measurements of etch pit perimeters, indicating that this value of E_a,app is representative of {h k 0} surface dissolution. The measurement of etch pit perimeters also enables an estimation of apparent activation energy as a function of step density indicating substantially higher apparent activation energy, up to E_a,app = 140 kJ mol⁻¹, on extrapolation towards a pristine surface with no defects. We suggest that this higher value of E_a,app represents the slow formation of etch pits into the (0 0 1) surface.     

Spatio-temporal evaluation of event detection and measurement coherence among satellite rainfall products for ensembled dataset generation

Theoretical and Applied Climatology - Selection of a best suited satellite-based gridded rainfall product (SGRP) is challenging due to their significant variations at spatial and temporal scale....     

Strain estimation from single forms of distorted fossils — A computer graphics and MATLAB approach

Most of the existing methods of strain analysis can estimate strain in a single form of distorted brachiopod, or trilobite provided independent evidence, such as the association of the fossil with cleavage and/or stretching lineation is available for inferring the direction of maximum principal strain. This article proposes a simple computer graphics based method and its MATLAB code that determine the minimum amount of strain in a single distorted fossil form even if data for inferring the maximum principal strain direction are lacking. Our method is a rapid computer-graphics alternative to some of the existing analytical methods. In a distorted fossil form of original bilateral symmetry, the relative senses of angular shears along the hinge line and the median line are mutually opposite to each other. It follows, therefore, that the maximum principal strain direction lies within the acute angle between the hinge and the median lines in the plane of the fossil. Using this principle, our method performs several simulations such that each simulation retrodeforms the distorted fossil by assuming a particular orientation, lying within the acute angle between the hinge line and the median line, as the potential direction of the maximum principal strain. Each simulation of retrodeformation yields a potential strain ratio. The distribution of all the potential strain ratios, obtained by assuming different orientations as the potential directions of the maximum strain, is typically a parabola-like curve with a distinct vertex that corresponds to the minimum amount of strain in the distorted fossil. An entirely computer graphical approach is somewhat time-intensive because it involves a large number of retrodeformational simulations. We, therefore, give a MATLAB code, namely, the Minstrain, that rapidly retrodeforms the fossil and determines the minimum strain with precision.     

Quantitative Determination of Soil Erosion and Prioritization of Micro-Watersheds Using Remote Sensing and GIS

Soil erosion which occurs at spatially varying rate is a widespread threat to sustainable resource management at watershed scale. Thus estimation of soil loss and identification of critical area for implementation of best management practice is central to success of soil conservation programme. The present study focuses application of most widely used Universal Soil Loss Equation (USLE) to determine soil erosion and prioritization of micro-watersheds of Upper Damodar Valley Catchment (UDVC) of India. Annual average soil loss for the entire basin is 23.17 t/ha/yr; for micro-watersheds. High soil loss is observed in 345 micro-watersheds, medium in 159 micro-watersheds and low soil loss is observed in 201 micro-watersheds. It is found that, out of 705 micro-watersheds of UDVC, 453 micro-watersheds are in agreement with AISLUS suggested priority which is based on observed sediment yield, 116 micro-watersheds under predict and 136 micro-watersheds over predict the priority. Geographic Information System (GIS) is applied to prepare various layers of USLE parameters which interactively estimate soil erosion at micro-watershed level. The main advantage of the GIS methodology is in providing quick information on the estimated value of soil loss for any part of the investigated area.     

Soil erosion assessment in Rangit catchment,India through a process-based model in the geospatial environment

The accurate assessment of soil erosion in the spatial environment can give valuable input in designing reservoirs and for preparing watershed management action plans. Rangit River in northeastern India is affected by severe soil erosion, causing reduction in its reservoir capacity. The main aim of the paper is to estimate the soil erosion in the Rangit catchment, India through a process-based soil erosion model that integrates remote sensing and field data in the geospatial domain, and also to identify the problem areas for further watershed management action plans. Various topographic parameters that were derived from land use, soil texture and a digital elevation model were used for the estimation of soil erosion. The Morgan, Morgan and Finny model was used to compute soil erosion. Based on the drainage pattern, the catchment was divided into eight sub-catchments for detailed study. Annual soil erosion was estimated for four years from 2002 to 2005 using the corresponding year’s meteorological data. Estimated soil erosion was compared with the field data in each year and found very good correlation.     

Bioavailable copper and manganese in soils from Iceland and their relationship with scrapie occurrence in sheep

The bioavailability of trace metals can be directly linked with many common animal and human diseases. It is easier to correlate regional geochemical trends with disease distribution in the developing world because local populations and animals live from the land. In the western world, humans tend to live from the global food market whereas animals graze on the land. Recent biochemical studies have shown that the prion protein needs copper to keep its structure. If copper is not available, the prion protein can take up manganese and unfold. Preliminary results for trace metals in soil samples from scrapie-affected areas in Iceland show that bioavailable manganese manganese (easily reducible and exchangeable Mn) is very high whereas soluble copper and free copper are very low.