An ignimbrite veneer deposit: The trail-marker of a pyroclastic flow

The term “ignimbrite veneer deposit” (IVD) is proposed for a new kind of pyroclastic deposit which is found associated with, and passes laterally into, Taupo ignimbrite of valley pond type in New Zealand. It forms a thin layer mantling the landscape over 15,000 km², and is regarded as the deposit from the trailing “tail” of a pyroclastic flow, where a relaxation of shear stress favoured the deposition of the basal part of the flow. The IVD differs little in grain-size from the associated ignimbrite, but it shows a crude internal stratification attributed to the deposition of a succession of layers, one after the passage of each pulse of the pyroclastic flow. It locally contains laterally-discontinuous lenses of coarse pumice (“lee-side lenses”) on the far-vent side of topographic obstacles. In nearvent exposures the Taupo IVD shows lensoid and cross-stratified bed-forms even where it stands on a planar surface, attributed to deposition from a flow travelling at an exceedingly high velocity.An IVD can be distinguished from a poorly sorted pyroclastic fall deposit because the beds in it show more rapid lateral variations in thickness, it may show a low-angle cross-stratification, and it contains carbonised wood from trees not in the position of growth; from the deposit of a wet base surge because it lacks vesicles and strong antidune-like structures and contains carbonised vegetation, and from a hot and dry pyroclastic surge deposit because it possesses a high content of pumice and “fines”.The significance of an IVD is that it records the passage of a pyroclastic flow, where the flow itself has moved farther on.     

PAI-OFF: A new proposal for online flood forecasting in flash flood prone catchments

The Process Modelling and Artificial Intelligence for Online Flood Forecasting (PAI-OFF) methodology combines the reliability of physically based, hydrologic/hydraulic modelling with the operational advantages of artificial intelligence. These operational advantages are extremely low computation times and straightforward operation. The basic principle of the methodology is to portray process models by means of ANN. We propose to train ANN flood forecasting models with synthetic data that reflects the possible range of storm events. To this end, establishing PAI-OFF requires first setting up a physically based hydrologic model of the considered catchment and – optionally, if backwater effects have a significant impact on the flow regime – a hydrodynamic flood routing model of the river reach in question. Both models are subsequently used for simulating all meaningful and flood relevant storm scenarios which are obtained from a catchment specific meteorological data analysis. This provides a database of corresponding input/output vectors which is then completed by generally available hydrological and meteorological data for characterizing the catchment state prior to each storm event. This database subsequently serves for training both a polynomial neural network (PoNN) – portraying the rainfall–runoff process – and a multilayer neural network (MLFN), which mirrors the hydrodynamic flood wave propagation in the river. These two ANN models replace the hydrological and hydrodynamic model in the operational mode. After presenting the theory, we apply PAI-OFF – essentially consisting of the coupled “hydrologic” PoNN and “hydrodynamic” MLFN – to the Freiberger Mulde catchment in the Erzgebirge (Ore-mountains) in East Germany (3000 km²). Both the demonstrated computational efficiency and the prediction reliability underline the potential of the new PAI-OFF methodology for online flood forecasting.     

Space physics coordinate transformations: the role of precession

Raw data on spacecraft orbits and attitude are usually supplied in “inertial” coordinates. The normal geocentric inertial coordinate system changes slowly in time owing to the effects of astronomical precession and the nutation of the Earth’s rotation axis. However, only precession produces a change that is significant compared with the errors in determining spacecraft position. We show that the transformations specified by Russell (1971) and Hapgood (1992) are strictly correct only if the epoch-of-date inertial system is used. We provide a simple formula for estimating the error in the calculated position if the inertial system for some other epoch is used. We also provide a formula for correcting inertial coordinates to the epoch-of-date from the standard fixed epoch of J2000.0.     

The effect of microporosity on transport properties in porous media

Sizeable amounts of connected microporosity with various origins can have a profound effect on important petrophysical properties of a porous medium such as (absolute/relative) permeability and capillary pressure relationships. We construct pore-throat networks that incorporate both intergranular porosity and microporosity. The latter originates from two separate mechanisms: partial dissolution of grains and pore fillings (e.g. clay). We then use the reconstructed network models to estimate the medium flow properties. In this work, we develop unique network construction algorithms and simulate capillary pressure–saturation and relative permeability–saturation curves for cases with inhomogeneous distributions of pores and micropores. Furthermore, we provide a modeling framework for variable amounts of cement and connectivity of the intergranular porosity and quantifying the conditions under which microporosity dominates transport properties. In the extreme case of a disconnected inter-granular network due to cementation a range of saturations within which neither fluid phase is capable of flowing emerges. To our knowledge, this is the first flexible pore scale model, from first principles, to successfully approach this behavior observed in tight reservoirs.     

Effects of sampling microhabitats with low coverage within the STAR/AQEM macroinvertebrate sampling protocol on stream assessment

In the STAR/AQEM protocol microhabitats covering less than 5% of the sampling area were neglected. Driven by an ongoing discussion on the importance of these underrepresented microhabitats we tested the influence of sampling them. We investigated 48 streams representing 14 different stream types from all over Germany. Macroinvertebrates of underrepresented microhabitats were sampled in addition to the STAR/AQEM protocol. To ensure the method remains feasible in routine monitoring programmes the total sampling and sorting effort of additional sampling was limited to 20 min. Particularly those taxa were picked, which were not recognised during the routine STAR/AQEM sorting.To identify the effect of additional sampling on stream assessment results, we calculated the stream type-specific Multimetric Index (MMI) with the “main” and the “main+additional” data for each sample. The mean and median difference in MMI values between “main” and “main+additional” samples was 0.02 and 0.01, respectively. In seven of 48 samples (14.6%) a different ecological quality class was calculated with the “main+additional” dataset. Regarding common metrics within the MMI as well as intercalibration metrics differences between “main” and “main+additional” samples were analysed. The values differed most in richness metrics (e.g., number of EPTCBO Taxa, number of Trichoptera Taxa). The results of the present study show that additional sampling of underrepresented microhabitats could alter multimetric assessment results.     

Inertial effects during irreversible meniscus reconfiguration in angular pores

In porous media, the dynamics of the invading front between two immiscible fluids is often characterized by abrupt reconfigurations caused by local instabilities of the interface. As a prototype of these phenomena we consider the dynamics of a meniscus in a corner as it can be encountered in angular pores. We investigate this process in detail by means of direct numerical simulations that solve the Navier–Stokes equations in the pore space and employ the Volume of Fluid method (VOF) to track the evolution of the interface. We show that for a quasi-static displacement, the numerically calculated surface energy agrees well with the analytical solutions that we have derived for pores with circular and square cross sections. However, the spontaneous reconfigurations are irreversible and cannot be controlled by the injection rate: they are characterized by the amount of surface energy that is spontaneously released and transformed into kinetic energy. The resulting local velocities can be orders of magnitude larger than the injection velocity and they induce damped oscillations of the interface that possess their own time scales and depend only on fluid properties and pore geometry. In complex media (we consider a network of cubic pores) reconfigurations are so frequent and oscillations last long enough that increasing inertial effects leads to a different fluid distribution by influencing the selection of the next pore to be invaded. This calls into question simple pore-filling rules based only on capillary forces. Also, we demonstrate that inertial effects during irreversible reconfigurations can influence the work done by the external forces that is related to the pressure drop in Darcy’s law. This suggests that these phenomena have to be considered when upscaling multiphase flow because local oscillations of the menisci affect macroscopic quantities and modify the constitutive relationships to be used in macro-scale models. These results can be extrapolated to other interface instabilities that are at the origin of fast pore-scale events, such as Haines jumps, snap-off and coalescence.     

Hydromagnetic spectroscopy of the magnetosphere with Pc3 geomagnetic pulsations along the 210° meridian

Analysis of Pc3 observational data along the 210° magnetic meridian showed a complicated frequency-latitude structure at middle latitudes. The observed period-latitude distributions vary between events with a “noisy source”: the D component has a colored-noise spectrum, while the spectrum of H component exhibits regular peaks that vary with latitude, and events with a “band-limited source”: the spectral power density of the D component is enhanced at certain frequencies throughout the network. For most ULF events a local gap of the H component amplitude has been exhibited at both conjugate stations at L ≃ 2.1. A quantitative interpretation has been given assuming that band-limited MHD emission from an extra-magnetospheric source is distorted by local field line resonances. Resonant frequencies had been singled out with the use of the asymmetry between spectra of H and D components. Additionally, a local resonant frequency at L ≃ 1.6 was determined by the quasi-gradient method using the data from nearly conjugate stations. The experimentally determined local resonance frequencies agree satisfactorily with those obtained from a numerical model of the Alfven resonator with the equatorial plasma density taken by extrapolation of Carpenter-Anderson model. We demonstrate how simple methods of hydromagnetic spectroscopy enable us to monitor simultaneously both the magnitude of the IMF and the magnetospheric plasma density from ULF data.     

Basaltic volcanism in the northern sector of the main Ethiopian rift

The different basalt types related to rift structure development have been investigated, starting from the pre-rift stage in the northern Ethiopian rift and its eastern escarpment and plateau.The basic volcanic rocks are represented mainly by transitional basalts, both in the pre-rift (plateau) and rift (escarpment and rift floor) stages. A striking feature is that although the plateau basalts show clear tholeiitic affinity and the rift basalts reveal a somewhat pronounced “alkaline” character, the REE and LILE element abundances, however, progressively decrease from the “tholeiitic” basalts of the plateau to the “alkaline” basalts of the rift.All data support the view that such contrasting features may be attributed to a continuous depletion of hygromagmatophile (REE, LILE) elements in the mantle source material, related to the large volumes of magmas produced in the early phase of rift structure development. The transition from “tholeiitic” (plateau) to “alkaline” (rift) transitional basalts is related to decreasing intensity of extensional movements.     

3-D inversion of borehole-to-surface electrical data using a back-propagation neural network

The “fluid-flow tomography”, an advanced technique for geoelectrical survey based on the conventional mise-à-la-masse measurement, has been developed by Exploration Geophysics Laboratory at the Kyushu University. This technique is proposed to monitor fluid-flow behavior during water injection and production in a geothermal field. However data processing of this technique is very costly. In this light, this paper will discuss the solution to cost reduction by applying a neural network in the data processing. A case study in the Takigami geothermal field in Japan will be used to illustrate this. The achieved neural network in this case study is three-layered and feed-forward. The most successful learning algorithm in this network is the Resilient Propagation (RPROP). Consequently, the study advances the pragmatism of the “fluid-flow tomography” technique which can be widely used for geothermal fields. Accuracy of the solution is then verified by using root mean square (RMS) misfit error as an indicator.     

Footings under seismic loading: Analysis and design issues with emphasis on bridge foundations

The paper provides state-of-the-art information on the following aspects of seismic analysis and design of spread footings supporting bridge piers: (1) obtaining the dynamic stiffness (“springs” and “dashpots”) of the foundation; (2) computing the kinematic response; (3) determining the conditions under which foundation–soil compliance must be incorporated in dynamic structural analysis; (4) assessing the importance of properly modeling the effect of embedment; (5) elucidating the conditions under which the effect of radiation damping is significant; (6) comparing the relative importance between kinematic and inertial response. The paper compiles an extensive set of graphs and tables for stiffness and damping in all modes of vibration (swaying, rocking, torsion), for a variety of soil conditions and foundation geometries. Simplified expressions for computing kinematic response (both in translation and rotation) are provided. Special issues such as presence of rock at shallow depths, the contribution of foundation sidewalls, soil inhomogeneity and inelasticity, are also discussed. The paper concludes with parametric studies on the seismic response of bridge bents on embedded footings in layered soil. Results are presented (in frequency and time domains) for accelerations and displacements of bridge and footing, while potential errors from some frequently employed simplifications are illustrated.     

Stationary magnetospheric convection on November 24, 1981. 2.Small-scale structures in the dayside cusp/cleft

A case study of the dayside cusp/cleft region during an interval of stationary magnetospheric convection (SMC) on November, 24, 1981 is presented, based on detailed measurements made by the AUREOL-3 satellite. Layered small-scale field-aligned current sheets, or loops, superimposed to a narrow V-shaped ion dispersion structure, were observed just equatorward from the region of the “cusp proper”. The equatorward sheet was accompanied by a very intense and short (less than 1 s) ion intensity spike at 100 eV. No major differences were noted of the characteristics of the LLBL, or “boundary cusp”, and plasma mantle precipitation during this SMC period from those typical of the cusp/cleft region for similar IMF conditions. Simultaneous NOAA-6 and NOAA-7 measurements described in Despirak et al. were used to estimate the average extent of the “cusp proper” (defined by dispersed precipitating ions with the energy flux exceeding 10⁻³ erg cm⁻² s⁻¹) during the SMC period, as ≈0.73∼ ILAT width, 2.6–3.4 h in MLT, and thus the recently merged magnetic flux, 0.54–0.70 × 10⁷ Wb. This, together with the average drift velocity across the cusp at the convection throat, ≈0.5 km s⁻¹, allowed to evaluate the cusp merging contribution to the total cross-polar cap potential difference, ≈33.8–43.8 kV. It amounts to a quite significant part of the total cross-polar cap potential difference evaluated from other data. A “shutter” scenario is suggested for the ion beam injection/penetration through the stagnant plasma region in the outer cusp to explain the pulsating nature of the particle injections in the low- and medium-altitude cusp region.     

Express Assessment of Water Toxicity Based on Bioassaying: Case Study of Surface-Water Bodies in St. Petersburg

A system of efficient on-line monitoring of the state of water in surface water bodies is developed. The expediency of using new general-purpose bioassays for the integral express evaluation of the natural-water toxic impact on living organisms is substantiated. Fundamentally new methods of bioassaying with gasteropoda from special laboratory cultures (“PRM-TESTS”) used as test organisms are presented. The results of complex hydrochemical and biological (toxicological) investigations with PRM-TESTS as applied to water bodies in St. Petersburg are discussed.__________Translated from Vodnye Resursy, Vol. 32, No. 4, 2005, pp. 425–434.Original Russian Text Copyright © 2005 by Kurilenko, Zaitseva.     

Inversion approach for thermal data from a convecting hydrothermal system

Hydrothermal systems are often studied by collecting thermal gradient data and temperature/depth curves. These data contain important information about the flow field, the evolution of the hydrothermal system, and the location and nature of the ultimate heat sources. Thermal data are interpreted by the “forward” method; the thermal field is calculated based on selected initial conditions and boundary conditions such as temperature and permeability distributions. If the calculated thermal field matches the data, the chosen conditions are inferred to be possibly correct. Because many sets of initial conditions may produce similar thermal fields, users of the “forward” method may inadvertently miss the correct set of initial conditions. Analytical methods for “inverting” data also allow the determination of all the possible solutions consistent with the definition of the problem. In this paper we suggest an approach for inverting thermal data from a hydrothermal system, and compare it to the more conventional approach. We illustrate the difference in the methods by comparing their application to the Salton Sea Geothermal Field by Lau (1980a) and Kasameyer, et al. (1984). In this particular example, the inverse method was used to draw conclusions about the age and total rate of fluid flow into the hydrothermal system.     

Magmatismes basiques dits “orogeniques” et “anorogeniques” et teneurs entro2: Les associations “Isotitanees” et “anisotitanfes”

The patterns of variation of TiO₂ conent during magmatic evolution are different in the so called “orogenic” and “anorogenie” basic associations; these last terms, which are the cause of much misunderstanding, can be replaced by the terms “isotitaniferous” and “anisotitaniferous”.     

Growth and evolution of an emergent tuff cone: Considerations from structural geology, geomorphology and facies analysis of São Roque volcano, São Miguel (Azores)

The syn-eruptive and post-eruptive history of São Roque tuff cone, its geological setting and volcanological features were studied in detail to understand the role played by the different factors that contributed to the morphological evolution of this relatively simple and small volcanic edifice.In addition, attention was also focused on the series of natural changes that affected the tuff cone during the course of the years and that finally led to its structural disassembly. A novel model is proposed to explain this process.The São Roque volcanic centre, located on the island of São Miguel (Azores), consists of two well-consolidated bodies and numerous small islets that formed more than 4700 years ago during the hydromagmatic activity that took place along an intruding dyke, whose NNW–SSE trend is in agreement with the regional tectonic pattern. The eruptive vents probably migrated progressively from SSE to NNW, forming small edifices through the rapid accumulation of sediments during alternating phases of “dry” and “wet” magmatic emissions. Syn-eruptive partial collapses greatly modified the original morphological structure of these edifices, probably allowing sea water to continuously flow into the vents. The complex interaction of these factors controlled the depth of magma fragmentation, producing different types of deposits, in which the ash-lapilli ratio varies considerably. The high-water saturation degree of these deposits caused syn-eruptive and post-eruptive remobilization which resulted in collapses and some small-scale landslides.Post-eruptive, WNW–ESE trending transtensional and extensional tectonic activities operated during the initial dissection of the cone, generating instability. Furthermore, the rapid accumulation of “wet” tephra, and its following consolidation, caused selective collapses that favoured the fragmentation of the deposit and caused the formation of numerous islets separated by radially-arranged channels. Collapses also involved the lava units emplaced in more recent times around the tuff cone, which show that brittle deformation has been significant in the area for a prolonged period.     

Ar/Ar dating of the Bandelier Tuff and San Diego Canyon ignimbrites, Jemez Mountains, New Mexico: Temporal constraints on magmatic evolution

The Jemez Mountains volcanic field (JMVF), located in north-central New Mexico, has been a site of basaltic to rhyolitic volcanism since the mid-Miocene with major caldera forming eruptions occurring in the Pleistocene. Eruption of the upper Bandelier Tuff (UBT) is associated with collapse of the Valles Caldera, whereas eruption of the lower Bandelier Tuff (LBT) resulted in formation of the Toledo Caldera. These events were previously dated by K-Ar at 1.12 ± 0.03 Ma and 1.45 ± 0.06 Ma, respectively. Pre-Bandelier explosive eruptions produced the San Diego Canyon (SDC) ignimbrites. SDC ignimbrite “B” has been dated at 2.84 ± 0.07 Ma, whereas SDC ignimbrite “A”, which underlies “B”, has been dated at 3.64 ± 1.64 Ma. Both of these dates are based on single K-Ar analyses.⁴⁰Ar/³⁹Ar dating of single sanidine crystals from these units indicates revision of the previously reported dates. Isochron analysis of 26 crystals from the UBT gives a common trapped ⁴⁰Ar/³⁶Ar component of 304.5, indicating the presence of excess ⁴⁰Ar in this unit, and defines an age of 1.14 ± 0.02 Ma. Isochron analysis of 26 crystals from the LBT indicates an atmospheric trapped component and an age of 1.51 ± 0.03 Ma. An age of 1.78 ± 0.04 Ma, based on the weighted mean of 5 individual analyses, is indicated for SDC ignimbrite “B”, whereas 3 analyses from SDC ignimbrite “A” give a weighted mean age of 1.78 ± 0.07 Ma. Evidence for xenocrystic contamination in the SDC ignimbrites comes from analyses of a correlative air-fall pumice unit in the Puye Formation alluvial fan giving ages of 1.75 ± 0.08 and 3.50 ± 0.09 Ma. The presence of xenocrysts in bulk separates used for the original K-Ar analyses could account for the significantly older ages reported.Geochemical data indicate that SDC ignimbrites are early eruptions from the magma chamber which evolved to produce the LBT, as compositions of SDC ignimbrite “B” are virtually identical to least evolved LBT samples. Differentiation during the 270-ka interval between eruption of SDC ignimbrite “B” and the LBT produced an array of high-silica rhyolite compositions which were erupted to form the LBT. Mixed pumices associated with eruption of the LBT indicated an influx of more mafic magma into the system which produced shifts in some incompatible trace-element ratios. Lavas and tephras of the Cerro Toledo Rhyolite record the geochemical evolution of the Bandelier magma system during the 370-ka interval between eruption of the LBT and the UBT.The combined geochronologic and geochemical data place the establishment and evolution of the Bandelier silicic magma system within a precise temporal framework, beginning with eruption of the SDC ignimbrites at 1.78 Ma, and define a periodicity of 270–370 ka to ash-flow eruptions in the JMVF. These intervals are comparable to those in other multicyclic caldera complexes and are a measure of the timescales over which substantial fractionation of large silicic magma bodies occur.     

Nankai Trough, Japan Trench and Kuril Trench: geochemistry of Fluids sampled by submersible “Nautile”

Deep-water samples collected during the Kaiko project are often associated with biological communities located on geological structures favorable to fluid venting. The evidence of fluid venting are the temperature anomalies, the decrease in sulfate concentrations, the content in methane and the lowC₁(C₂ +C₃) ratio of light hydrocarbons. Because of large dilution by ambiant seawater during sampling it is difficult to compute the composition of the advected end-member pore fluid. Part of this fluid should originate in the “petroleum window”, i.e. at temperature about 60°C. Modeling the upward flow of water, taking into account the anomalies of temperature measured on the seafloor and the geochemical anomalies, leads to non-steady-state advection of the pore fluid. The occurrence of a deep component in the fluid has implications for the geological and tectonic models of the subduction zones off Japan.     

Two-dimensional simulations of katabatic layers observed during the GIMEX experiment

The hydrostatic model SALSA is used to simulate a particular event observed during the Greenland Ice Margin EXperiment “GIMEX” (on July 12th, 1991). The time evolution of the large-scale flow was incorporated in the model through time dependent boundary conditions which were updated using the closest upwind sounding. A turbulent scheme for the stable boundary layer and an appropriate parametrization of the surface fluxes implemented in the same model, are used for this study. The simulation results are discussed and compared to the available observations. The computed turbulent fluxes are correctly estimated. The model predicts a mixing zone of about 1500 m high which is in good agreement with tundra site observations. Over the ice cap, the katabatic layer is correctly simulated by the model. Its height of 80–300 m is well estimated. The comparison between the simulation and observations taken at ice cap sites is reasonably valid. The ablation computed along the ice cap corresponds well to the values reconstructed of observations at sites 4 and 9. Finally, a sensibility study to a specified westward geostrophic wind (2 ms⁻¹) shows that the consideration of this latter improves the simulated tundra wind evolution.     

Transformation between gravimetric and GPS/levelling-derived geoids using additional gravity information

The transformation from the gravimetric to the GPS/levelling-derived geoid using additional gravity information for the covariance function of geoid height differences has been investigated in a test area in south-western Canada. A “corrector surface” model, which accounts for datum inconsistencies, long-wavelength geoid errors, vertical network distortions and GPS errors, has been constructed using least-squares collocation. The local covariance function of geoid height differences is usually obtained from residual values between the GPS/levelling and gravimetric geoid heights after the elimination of all known systematic distortions. If additional gravity data (in the form of gravity anomalies) are available, the covariance function of geoid height differences can be determined by the following steps: (1) transforming the GPS/levelling-derived geoid heights into gravity anomalies; (2) forming differences between the computed in step 1 and given gravity anomalies; (3) determining the parameters of the local covariance function of the gravity anomaly differences; (4) constructing an analytical covariance model for the geoid height differences from the covariance function of the gravity anomaly differences using the parameters derived in step 3. The advantage of the proposed method stems from the great number of gravity data used to derive the empirical covariance function. A comparison with the least-squares adjustment shows that the standard deviation of the residuals of the predicted geoid height differences with respect to the control point values decreases by 2.4 cm.     

Magma rates in feeding conduits of different volcanic centres

A quasi-stationary magma flow rate in asthenospheric and crustal conduits of central type volcanoes and volcanic centres was studied analytically under the following conditions. Magma rises through cylindrical channels in which the magma temperature does not change with time, but the wall rocks are gradually heated. The magma rates were calculated for basaltic, andesitic and dacitic volcanoes using the “continental” and “oceanic” geotherms. It follows from these calculations that the magma supply rate may determine the kind of activity of a volcanic centre, being constant for large and very active volcanoes, intermittent for usual volcanic centres of island arcs or sporadic for volcamic fields, clusters of cinder cones and areal volcanism. Theoretical conclusions are consistent with observational data.