slip system domains 2 kinematic aspects of fabric development in polycrystalline aggregates abstract in the first paper of the present series cobbold and gapais 1986 we develop theoretical models of plane strain domainal deformation by slip along inextensible and indestructible fibres for such extreme mechanical conditions we show that deformation is largely controlled by kinematic factors we use our models to explain domainal patterns of natural slip systems including bedding and foliation planes faults ductile shear zones and lattice planes the present paper focusses on kinematic aspects of fabric development in polycrystalline aggregates a three dimensional kinematic model is developed it reveals that common quartz fabrics may develop domainally by reorientation and selection of inextensible slip directions a axes or slip planes with initially random orientation stable orientations of slip directions are close to both surfaces of no finite extension and orientations of large amount of shear we explain 1 1 common patterns of quartz a and c axis fabrics e g small circles and crossed girdles 2 2 characteristic differences between fabric patterns according to the shape of the finite strain ellipsoid 3 3 development of asymmetric fabrics during non coaxial deformation histories this last process involves selective destruction or replacement of certain orientation domains so that a preferred orientation of slip lines develops close to the bulk shear direction rotation recrystallization is shown to be an efficient natural selection mechanism the models also account for many microstructural features found in oriented polycrystalline rocks especially 1 1 alternating band like or kink like domains of twinned preferred orientations 2 2 individual grains or clusters of grains with retort like shapes and extensive recrystallisation at boundaries 3 3 small scale shear bands formed by strain partitioning and shear localization

numerical simulation of strain within lava domes abstract a new analytical and numerical method is presented to assess 3d deformation within lava domes the method allows any simultaneous combination of strain components even that of a pure shear and six elementary simple shear components the method s practical use is presented model results provide the following information for lava dome strain patterns in the upper part of a dome stretching is perpendicular to flow direction and in the lower part it is parallel flinn parameter values indicate a flattening strain ellipsoid through the dome except in a small zone in the centre where it is a constriction ellipsoid

empirical prediction of debris flow mobility and deposition on fans a new method to predict the runout of debris flows is presented a data base of documented sediment transporting events in torrent catchments of austria switzerland and northern italy has been compiled using common classification techniques with this data we test an empirical approach between planimetric deposition area and event volume and compare it with results from other studies we introduce a new empirical relation to determine the mobility coefficient as a function of geomorphologic catchment parameters the mobility coefficient is thought to reflect some of the flow properties during the depositional part of the debris flow event the empirical equations are implemented in a geographical information system gis based simulation program and combined with a simple flow routing algorithm to determine the potential runout area covered by debris flow deposits for a given volume and starting point of the deposits a monte carlo technique is used to produce flow paths that simulate the spreading effect of a debris flow the runout zone is delineated by confining the simulated potential spreading area in the down slope direction with the empirically determined planimetric deposition area the debris flow volume is then distributed over the predicted area according to the calculated outflow probability of each cell the simulation uses the arc objects environment of esri and is adapted to run with high resolution 2 5 m 2 5 m digital elevation models generated for example from lidar data the simulation program called toprundf is tested with debris flow events of 1987 and 2005 in switzerland copyright 2009 john wiley sons ltd

groundwater contamination from an inactive uranium mill tailings pile 2 application of a dynamic mixing model at riverton wyoming low ph process waters from an abandoned uranium mill tailings pile have been infiltrating into and contaminating the shallow water table aquifer the contamination process has been governed by transient infiltration rates saturated unsaturated flow as well as transient chemical reactions between the many chemical species present in the mixing waters and the sediments in the first part of this two part series white et al 1984 we presented field data as well as an interpretation based on a static mixing model as an upper bound we estimated that 1 7 of the tailings water had mixed with the native groundwater in the present work we present the results of numerical investigation of the dynamic mixing process the model dynamix dynamic mixing couples a chemical speciation algorithm phreeqe with a modified form of the transport algorithm trump specifically designed to handle the simultaneous migration of several chemical constituents the overall problem of simulating the evolution and migration of the contaminant plume was divided into three sub problems that were solved in sequential stages these were the infiltration problem the reactive mixing problem and the plume migration problem the results of the application agree reasonably with the detailed field data the methodology developed in the present study demonstrates the feasibility of analyzing the evolution of natural hydrogeochemical systems through a coupled analysis of transient fluid flow as well as chemical reactions it seems worthwhile to devote further effort toward improving the physicochemical capabilities of the model as well as to enhance its computational efficiency

control on the emplacement of the andesite lava dome of the soufriere hills volcano montserrat by degassing induced crystallization lava solidification is controlled by two mechanisms external cooling and gas exsolution the latter inducing crystallization due to increasing liquidus temperature the andesite lava dome of the soufriere hills volcano montserrat is an extrusion dominated by crystallization caused by gas exsolution where cooling is unimportant in controlling emplacement in the magma chamber the magma has an estimated viscosity of 7 106 pa s during ascent gas exsolution caused the magma to extrude in a highly crystalline state with only 5 15 residual melt viscosities in the range 1013 1014 pa s and mechanical strength 1 mpa deformation can be heterogeneous with extrusion along shear zones rheological stiffening in the upper conduit also causes large overpressures shallow seismicity and cyclic patterns of dome extrusion gas rich porphyritic andesites tend to be the least mobile kind of lava because transition from magma into hot crystalline material was reached during ascent

a probabilistic model of debris flow delivery to stream channels demonstrated for the coast range of oregon usa debris flows are important geomorphic agents in mountainous terrains that shape channel environments and add a dynamic element to sediment supply and channel disturbance identification of channels susceptible to debris flow inputs of sediment and organic debris and quantification of the likelihood and magnitude of those inputs are key tasks for characterizing spatial and temporal patterns found in channel conditions and associated habitats in a river network widely available digital elevation and land cover data 10 m dems and 25 m satellite imagery offer the potential to assess debris flow runout paths over regional extents this paper presents a model for using these data to calculate empirical probabilities for debris flow runout over dem determined flow paths and shows how these probabilities can be combined over all sources to estimate the potential for debris flow delivery to stream reaches throughout entire channel networks the model is calibrated and model predictions are compared to field mapped debris flow travel paths from study sites in the coast range of oregon usa this model predicts debris flow probability over channel reach scales that can be aggregated to basin scale measures of debris flow potential it offers unprecedented ability to characterize debris flow effects over channel networks providing a tool for risk assessment and for generating hypotheses that relate topographic and forest cover controls on debris flow runout to the types and abundance of channel habitats in a river basin

the formation and failure of debris flow dams background key factors and model tests case studies from china temporary dams can be formed by the sudden injection of debris flow into main streams by some favorable geomorphologic and hydraulic conditions resulting in extensive inundations upstream and catastrophic floods downstream due to dam breaches and consequently dramatic changes of channels and valleys expeditious means of assessing dam forming potential are necessary particularly in geologically active regions complete blockages or dam formations are significantly related to the discharge ratio and velocity ratio between the tributary and the main stream the bulk density of the debris flow confluent angles and the degree of unevenness of grain sizes in order to set up a critical index c for dam formation 19 groups of flume tests were conducted the results showed that there were three types of blockage in the intersections and dam forming processes were mainly controlled by the product of the dimensionless momentum ratio and the degree of unevenness of grain sizes in the debris flow complete blockages or dam formations occurred when c 83 4 whereas semi blockages were formed or no dams were formed when c 71 5 which had been judged to be feasible by historical instances of dam formation in china dam failures commonly resulted from overtopping no piping was observed in the course of dam failure and the time elapsed between dams can be denoted by a linear relation with the momentum ratio

endogenous growth of dacite dome at unzen volcano japan 1993 1994 a dacite dome at unzen volcano grew mainly exogenously when it was small and the effusion rate was high but endogenously when the dome became large and the effusion rate declined the endogenous dome that has grown since late 1993 shows a shape classified as pelean whereas the earlier stage had a low lava dome shape the carapace of the endogenous dome moved like the crust of a basaltic lava pillow although the dome is several hundred times larger than such pillows the surface carapace was carried from the inside of the dome where it had been produced and it thickened as it cooled the crater floor was strongly deformed by the advancing endogenous dome the movement and crater floor deformation can be compared to that of a tractor tread moving on unconsolidated ground

coarse grained debris flow dynamics on erodible beds a systematic set of flume experiments is used to investigate the features of velocity profiles within the body of coarse grained debris flows and the dependence of the transport sediment concentration on the relevant parameters runoff discharge bed slope grain size and form the flows are generated in a 10 m long laboratory flume initially filled with a layer consisting of loose debris after saturation a prescribed water discharge is suddenly supplied over the granular bed and the runoff triggers a debris flow wave that reaches nearly steady conditions three types of material have been used in the tests gravel with mean grain size of 3 and 5 mm and 3 mm glass spheres measured parameters included triggering water discharge volumetric sediment discharge sediment concentration flow depth and velocity profiles the dynamic similarity with full sized debris flows is discussed on the basis of the relevant dimensionless parameters concentration data highlight the dependence on the slope angle and the importance of the quasi static friction angle the effects of flow rheology on the shape of velocity profiles are analyzed with attention to the role of different stress generating mechanisms a remarkable collapse of the dimensionless profiles is obtained by scaling the debris flow velocity with the runoff velocity and a power law characterization is proposed following a heuristic approach the shape of the profiles suggests a smooth transition between the different rheological regimes collisional and frictional that establish in the upper and lower regions of the flow and is compatible with the presence of multiple length scales dictated by the type of contacts instantaneous or long lasting between grains

structure and emplacement of a rhyolitic obsidian flow little glass mountain medicine lake highland northern california many rhyolitic obsidian flows show consistent stratigraphic relations among textural units exposed in the flow fronts of undissected flows and in cross sections of older flows the stratigraphy of the holocene little glass mountain rhyolitic obsidian flow consists of from bottom to top air fall tephra deposits basal breccia coarsely vesicular pumice obsidian finely vesicular pumice and surface breccia slightly crystalline rhyolite occurs near the vent areas a model of obsidian flow emplacement based on these textural relations is presented this stratigraphy may reflect the distribution of volatiles within the magma source region with the interlayered contact between coarsely vesicular pumice and overlying obsidian indicating stratification of volatiles in the magma body the distribution of pumiceous and glassy zones along with the orientations of flow banding can be used to map the surface structure of rhyolitic obsidian flows this complex structure as mapped on the little glass mountain flow reflects both the initial flow stratigraphy and subsequent deformational processes during emplacement of the lava three processes disrupt the initial flow configuration the rise of coarse pumice diapirs from the base of the flow the inward propagation of fractures in areas of extension and surface folding in sites of flow parallel compression subvertical flow banding in vent areas indicates that fracturing accompanies the emergence of lava most of the observed upper surface of a dome originates as a fracture plane the structure of domes that form over vent areas may reflect the orientation of dike like conduits as well as the local state of stress during extrusion

deformation of partially molten granite a review and comparison of experimental and natural case studies experimental and natural investigations of partially molten granite are compared and reviewed experiments suggest that deformation of partially molten granite with low viscosity melt 104 pa s exhibits a rheological critical melt percentage rcmp in case of high viscosity melts 108 pa s however the relationship between melt fraction and log viscosity of the partially molten granite may be linear considerations about viscosity rheological thresholds and segregation of natural melts suggest that low viscosity melt experiments simulate natural conditions more realistically therefore an rcmp is to be expected under natural conditions both diffusion creep and dislocation creep may occur under natural conditions whereas cataclastic flow is only observed under experimental conditions a melt induced transition from dislocation creep to diffusion creep occurs under experimental and natural conditions melt topology is controlled by the magnitude of differential stress under experimental conditions if differential stress is higher than 100 150 mpa melt pockets are elongate and oriented at a low angle to the maximum compressive stress in contrast in nature melt pockets tend to be oriented subparallel to the foliation plane i e presumably at a high angle to the maximum compressive stress

rheology and microstructure of experimentally deformed plagioclase suspensions we present the result of the first deformation experiments at high temperatures and high pressures on synthetic magmatic suspensions of strongly anisometric particles the results highlight the interplay between the rheological response and the development of microstructures and they demonstrate the critical importance of the shape of crystals on the mechanical behaviour of magmas plagioclase suspensions with two crystal fractions 0 38 and 0 52 were deformed both in compression and in torsion in a paterson apparatus with increasing crystal fraction the rheological behaviour of the magmatic suspension evolves from nearly steady state flow to shear weakening this change being correlated with a microstructural evolution from a pervasive strain to a strain partitioning fabric magmatic suspensions of plagioclase have viscosities approximately five orders of magnitude higher than suspensions of equivalent crystallinities made of isometric particles such as quartz

coaxial progressive deformation textures in extrusive and shallow intrusive rocks southwest japan abstract fine grained rocks from an andesite dyke a dacite dome and a basalt flow contain microshear zones overprinting an aligned microlitic groundmass in each case the shear zones comprise conjugate sets bisected by the plane of crystal alignment this texture indicates coaxial or pure shear flow in contrast to simple shear which is generally considered to be the dominant kinematic flow type in extrusive and shallow intrusive rocks this is interpreted as resulting from a change from non coaxial to coaxial flow coinciding with increasing viscosity during emplacement this suggests that deformation of extrusive and shallow intrusive rocks in the near solid state during the latter stages of emplacement may be more important in the development of aligned rock textures than fluid state flow of the magma as is commonly envisaged

dynamics of an unusual cone building trachyte eruption at pu u wa awa a hualālai volcano hawai i the pu u wa awa a pyroclastic cone and pu u anahulu lava flow are two prominent monogenetic eruptive features assumed to result from a single eruption during the trachyte dominated early post shield stage of hual lai volcano hawai i pu u wa awa a is composed of complex repetitions of crudely cross stratified units rich in dark dense clasts which reversely grade into coarser pumice rich units pyroclasts from the cone are extremely diverse texturally ranging from glassy obsidian to vesicular scoria or pumice in addition to fully crystalline end members the 100 m thick pu u anahulu flow is in contrast entirely holocrystalline using field observations coupled with whole rock analyses this study aimed to test whether the pu u wa awa a tephra and pu u anahulu lava flows originated from the same eruption as had been previously assumed crystal and vesicle textures are characterized along with the volatile contents of interstitial glasses to determine the origin of textural variability within pu u wa awa a trachytes e g magma mixing vs degassing origin we find that 1 the two eruptions likely originated from distinct vents and magma reservoirs despite their proximity and similar age 2 the textural diversity of pyroclasts forming pu u wa awa a can be fully explained by variable magma degassing and outgassing within the conduit 3 the pu u wa awa a cone was constructed during explosions transitional in style between violent strombolian and vulcanian involving the formation of a large cone and with repeated disruption of conduit plugs but without production of large pyroclastic density currents pdcs and 4 the contrasting eruption styles of hawaiian trachytes flow cone and pdc forming are probably related to differences in the outgassing capacity of the magmas prior to reaching the surface and not in intrinsic compositional or temperature properties these results further highlight that trachytes are kinetically faster magmas compared to dacites or rhyolites likely degassing and crystallizing more rapidly

flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

a geochemical transport model for redox controlled movement of mineral fronts in groundwater flow systems a case of nitrate removal by oxidation of pyrite a one dimensional prototype geochemical transport model was developed in order to handle simultaneous precipitation dissolution and oxidation reduction reactions governed by chemical equilibria total aqueous component concentrations are the primary dependent variables and a sequential iterative approach is used for the calculation the model was verified by analytical and numerical comparisons and is able to simulate sharp mineral fronts at a site in denmark denitrification has been observed by oxidation of pyrite simulation of nitrate movement at this site showed a redox front movement rate of 0 58 m yr 1 which agreed with calculations of others it appears that the sequential iterative approach is the most practical for extension to multidimensional simulation and for handling large numbers of components and reactions however slow convergence may limit the size of redox systems that can be handled

the mechanism of flow and fabric development in mechanically anisotropic trachyte lava anisotropy of magnetic susceptibility ams and electron back scattered diffraction ebsd of magnetite and sanidine fabrics throughout an eroded trachyte lava dome in tertiary volcanic province of the nw czech republic revealed two fabric types the high degree of ams fabric is associated with sanidine textural domains similar to normal kink bands type i fabric and occupies the whole body except the sw margin folded fabric and low anisotropy of ams also in the sw margin reveals sanidine alignment domains resembling reverse kink bands type ii fabric the flow of trachyte lava occurred via simultaneous slip of sanidine crystals along their 010 planes and also by readjustment of the textural domain boundaries according to the fibre slip theory this microfabric study suggests that the type ii fabrics resulted from collapse of vertically anisotropic trachyte crystal mush above the feeding conduit type i fabric is interpreted to originate from type ii fabrics by further stretching of highly attenuated fold limbs asymmetric type i fabrics along margins of the dome are related to outflow of trachyte lava away from the conduit region due to divergent flow the trachyte fabric zonality is interpreted to reflect the process of successive emplacement of progressively rotated trachyte lava lobes within a lava dome that locally preserves the collapsed and folded vertical fabrics

analysis and simulation of reactive transport of metal contaminants in ground water in pinal creek basin arizona abstract large scale mining activities have generated a plume of acidic ground water more than 15 km long in the regional aquifer of the pinal creek basin a one dimensional reactive transport model was developed using phreeqc to aid in the analysis of transport and chemical processes in the plume and to determine the uses and limitations of this type of modeling approach in 1984 the acidic part of the plume had a ph as low as 3 4 and contained milligram per liter concentrations of iron copper aluminum and other metals from 1984 to 1994 concentrations of contaminants in the alluvial aquifer in pinal creek basin arizona decreased as a result of mixing recharge remedial pumping and chemical reactions for reactions involving gypsum and rhodochrosite the equilibrium modeling assumption of a local geochemical equilibrium was generally valid from 1984 to 1990 water along the simulated flow path was at equilibrium or slightly supersaturated with gypsum and gypsum equilibria controlled dissolved concentrations of calcium and sulfate beginning in 1991 water in the acidic part of the plume became increasingly undersaturated with respect to gypsum indicating that the gypsum available for dissolution in the aquifer may have been completely consumed by about 1991 rhodochrosite precipitation was thought responsible for the measured attenuation in dissolved manganese in the neutralized zone for reactions involving calcite the assumption of a local geochemical equilibrium was generally not valid dissolution of calcite in the transition zone was not sufficient to establish equilibrium although following neutralization the calcite saturation index decreased to 1 2 in 1986 calcite undersaturation decreased along the flow path in the neutralized zone and equilibrium was attained about 7 km downgradient of the transition zone the assumption of a local geochemical equilibrium was not valid for oxidation reduction reactions that involved iron oxides and manganese oxides kinetically controlled oxidation reduction reactions continued in the acidic part of the flow path for years following the passage of the transition zone although the equilibrium approach helped to provide an increased understanding of contaminant transport at pinal creek future work will require a kinetic modeling approach to more accurately simulate selected reactions between the plume and aquifer materials

strain partitioning during partial melting and crystallizing felsic magmas abstract the rheology of partly molten felsic systems changes dramatically during the onset of melting and through crystallization solid to liquid and liquid to solid transitions are not rheologically identical contradicting the concept of a unique rheological critical melt percentage we use four thresholds separating the successive stages according to the melt fraction for the melting transition 1 the liquid percolation threshold connects the melt pockets at about 8 of melt thus allowing local magma displacement at the metric scale and 2 for greater melt percentages 20 25 a melt escape threshold corresponds to the onset of transport over large distances of the melt and part of the residual solid phase leading ultimately to granitic bodies for the solidification transition 3 the first formation of a rigid framework of crystals which can accumulate stress although the melt can still flow corresponds to the rigid percolation threshold 55 solids and 4 the system becomes totally locked at about 72 75 solid which corresponds to the particle locking threshold the present paper focuses on strain partitioning induced by the coexistence of two contrasting rheological phases between these thresholds on a variety of scales non coaxial deformation is preferentially accommodated by the lower viscosity melt which increases the vorticity in the melt phase and reinforces asymmetries in the flow pattern strain partitioning also increases the scale length of the weakest phase during melting and magma ascent whereas strain partitioning decreases the scale length during crystallizing strain partitioning also affects the migration of melt by raising the particle locking threshold and lowering the melt escape threshold for three dimensional deformations such as transpression the direction of melt segregation e g horizontal may differ from the direction of melt migration e g vertical

crustal and uppermost mantle structure of the bohemian massif based on celebration 2000 data 1 the deep structure of the bohemian massif bm the largest stable outcrop of variscan rocks in central europe was studied using the data of the international seismic refraction experiment central european lithospheric experiment based on refraction celebration 2000 the data were interpreted by seismic tomographic inversion and by two dimensional 2 d trial and error forward modeling of p and s waves additional constraint on crustal structure was given by amplitude modeling using the reflectivity method and gravity modeling though consolidated the bm can be subdivided into several tectonic units separated by faults shear zones or thrusts reflecting varying influence of the cadomian and variscan orogeneses the saxothuringian barrandian moldanubian and moravian velocity models determine three types of crust mantle transition in the bm reflecting variable crustal thickness and delimiting contacts of tectonic units in depth the nw area the saxothuringian has a highly reflective lower crustal layer above moho with a strong velocity contrast at the top of this layer this reflective laminated lower crust reaches depths of 26 35 km and is characteristic for the saxothuringian unit which was subject to eastward subduction the moldanubian in the central part is characterized by the deepest 39 km and the most pronounced moho within the whole bm with a strong velocity contrast 6 9 8 1 km s 1 a thick crust mantle transition zone in the se with velocity increase from 6 8 to 7 8 km s 1 over the depth range of 23 40 km seems to be the characteristic feature of the moravian overthrusted by the moldanubian during variscan collision

magnetic fabric transposition in folded granite sills in variscan orogenic wedge abstract new approach involving evaluation of anisotropy of magnetic susceptibility ams data in stereoplots and jelinek s p j t space vollmer s eigenvalue and microstructural analyses is proposed to discriminate between homogeneous and superposed deformation in granites this method is used to decipher the internal ams fabric and microstructural evolution of a folded array of granitic sills the studied major sill shows a fabric and microstructural zonality marked by submagmatic and high temperature type i planar linear fabric developed at sill margins and the transpositional type ii subsolidus fabrics that formed at high to medium temperature deformation in the sill core while type i fabric is associated with dip slip magnetic lineations type ii subsolidus fabrics are marked by subhorizontal magnetic lineations striking parallel to the long axis of the sill the structural reconstruction of the fabrics in the granite and the host rocks as well as new u pb zircon ages suggest coeval emplacement of horizontal and vertical sills accounting for significant weakening of the host rock magma multilayer the model of folding of such multilayer and extrusion of residual magma parallel to axial planes is discussed with respect to structural record in other syn contractional granite sill arrays forming sheeted plutons worldwide

do gravel bed river size distributions record channel network structure 1 bed load sediment particles supplied to channels by hillslopes are reduced in size by abrasion during downstream transport the branching structure of the channel network creates a distribution of downstream travel distances to a given reach of river and thus may strongly influence the grain size distribution of the long term bed load flux through that reach here we investigate this hypothesis using mass conservation and the sternberg exponential decay equation for particle abrasion to predict bed material variability at multiple scales for both natural and artificial drainage networks we assume that over a sufficiently long timescale no net deposition occurs and that grains less than 2 mm are swept away in suspension we find that abrasion during fluvial transport has a surprisingly small effect on the bed load sediment grain size distribution for the simple case of spatially uniform supply of poorly sorted hillslope sediments this occurs because at any point in the channel network local resupply offsets the size reduction of material transported from upstream thus river bed material may essentially mirror the coarse component of the size distribution of hillslope sediment supply furthermore there is a predictable distance downstream at which the bed load grain size distribution reaches a steady state in the absence of net deposition due to selective transport large scale variability in bed material such as downstream fining must then be due primarily to spatial gradients in hillslope sediment production and transport characteristics a second key finding is that average bed load flux will tend to stabilize at a constant value independent of upstream drainage area once the rate of silt production by bed load abrasion per unit travel distance is equal to the rate of coarse sediment supply per unit channel length q bed load flux equilibrates over a distance that scales with the inverse of the fining coefficient in the abrasion rate law and can be approximated simply as q 3 thus the efficiency of particle abrasion sets a fundamental length scale shorter for weaker rocks and longer for harder rocks which controls the expression in the river bed of variability in sediment supply we explore the role of the abrasion length scale in modulating the influence of sediment supply variability in a number of channel network contexts including individual tributary junctions a sequence of tributary inputs along a main stem channel and variable basin shapes and network architecture as expressed by the width function these findings highlight the need for both data and theory that can be used to predict the grain size distributions supplied to channels by hillslopes

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

emplacement dynamics of phonolite magma into maar diatreme structures correlation of field thermal modeling and ams analogue modeling data abstract emplacement mode and original shape and dimensions of a well exposed phonolite body in the ceske st edoho i mountains czech republic were reconstructed using combined techniques of structural analysis of magmatic fabrics and columnar jointing together with analogue and thermal mathematical modeling of cooling for different shapes of experimental bodies phreatomagmatic rocks in the vicinity of some phonolite stocks in the area of interest suggest that the phonolite bodies were likely emplaced into maar diatremes our modeling revealed that intrusion of magma into phreatomagmatic maar diatreme craters can result in cryptodomes extrusive domes lava lakes or branched intrusions the fabric and columnar jointing pattern of the selected phonolite body reveals best fit with an asymmetric extrusive dome emplaced into the maar crater the scaling analysis and thermal modeling also suggest that the phonolite extrusion could have formed within 6 66 days and cooled to the background temperature after 10 000 years combined analogue and thermal modeling also revealed that the phonolite extrusions into maar diatreme craters are marked by upper tier collonade of vertical columns and lower tier of curved and outward flaring columns both tiers in the phonolite extrusions are divided by a subhorizontal suture

some remarks on fabric overprints and constrictional ams fabrics in igneous rocks during the ascent emplacement and post emplacement deformation of igneous rocks two or more phases of deformation that overprint each other are often depicted these overprints when magnetic minerals are present are recorded in magnetic fabric in this contribution overprints are studied by means of numerical modeling following several basic scenarios common to igneous rocks biotite and amphibole that occur often together in igneous rocks are considered as carriers of the anisotropy of magnetic susceptibility modeling shows that 1 a constrictional fabric with a low degree of anisotropy as commonly recorded in magmatic rocks may result from a deformation overprint and not necessarily from an extensional transtensional regime and 2 that the constrictional ams fabrics originates from orthogonal superimposition of a deformation event on an ams fabric inherited from earlier magma emplacement history therefore the interpretation of a constrictional fabric must be performed with caution numerical modeling may provide a suitable help in strengthening the interpretation of real magnetic fabric data

gis based cell model for simulating debris flow runout on a fan summary a gis based cell model based on a kinematic approach is proposed to simulate debris flow routing on a fan the sediment water mixture is modeled as a monophasic continuum and the flow pattern is discretized by square cells 1 m in size that coincide with the dem cells flow occurs from cells with a higher mixture free surface to those with a lower mixture free surface a uniform flow law is used if the elevation of the former cell is higher than that of the latter otherwise the flow is simulated using the broad crested weir law erosion and deposition are simulated using an empirical law that is adjusted for a monophasic continuum the sediment concentration in the routing volume is computed at each time step and controls both erosion and deposition the cell model is used to simulate a debris flow that occurred on the rio lazer dolomites north eastern italian alps on november 4th 1966 furthermore the hydrologic and the hydraulic conditions for the initiation of debris flow are simulated providing the solid liquid hydrograph of the resulting debris flow a number of simulations has been carried out with physically reasonable parameters the results are compared with the extension of the debris flow deposition area and the map of observed depths of deposited sediments this comparison shows that the proposed model provides good performance the analysis of sensitivity carried out by systematically varying the model parameters shows that lower performances are associated with parameter values that are not physically reasonable the same event is also simulated using a cellular automata model and a finite volume two dimensional model the results show that the two models provide a sediment deposition pattern less accurate than that provided by the present cell model

solidification and morphology of submarine lavas a dependence on extrusion rate the results of recent laboratory experiments with wax extruded beneath relatively cold water may be extrapolated to predict the surface morphology of submarine lavas as a function of the extrusion rate and melt viscosity the experiments with solidifying wax indicated that the surface morphology was controlled by a single parameter the ratio of the time taken for the surface to solidify and a time scale for lateral flow for submarine basalts a solution of the cooling problem which is dominated by conduction in the lava but convective heat transfer in the water and estimates of lava viscosities place this parameter within the empirically determined pillowing regime over a wide range of extrusion rates this result is consistent with the observation that pillow basalts are the most common products of submarine eruptions smoother surfaces corresponding to the various types of submarine sheet flows are predicted for sufficiently rapid extrusions of basaltic magma still higher eruption rates in regions of low topographic relief may produce submarine lava lakes minimum emplacement times can be calculated for submarine volcanic constructs of a single lava flow type

nitrate reduction in an unconfined sandy aquifer water chemistry reduction processes and geochemical modeling nitrate distribution and reduction processes were investigated in an unconfined sandy aquifer of quaternary age ground water chemistry was studied in a series of eight multilevel samplers along a flow line deriving water from both arable and forested land results show that plumes of nitrate contaminated groundwater emanate from the agricultural areas and spread through the aquifer the aquifer can be subdivided into an upper 10 to 15 m thick oxic zone that contains o2 and no3 and a lower anoxic zone characterized by fe2 rich waters the redox boundary is very sharp which suggests that reduction processes of o2 and no3 occur at rates that are fast compared to the rate of downward water transport nitrate contaminated groundwater contains total contents of dissolved ions that are two to four times higher than in groundwater derived from the forested area the persistence of the high content of total dissolved ions in the no3 free anoxic zone indicates the downward migration of contaminants and that active nitrate reduction is taking place nitrate is apparently reduced to n2 because both nitrite and ammonia are absent or found at very low concentrations possible electron donors in the reduced zone of the aquifer are organic matter present as reworked brown coal fragments from the underlying miocene and small amounts of pyrite at an average concentration of 3 6 mmol kg electron balances across the redoxcline based on concentrations of o2 no3 so42 and total inorganic carbon tic indicate that pyrite is by far the dominant electron donor even though organic matter is much more abundant groundwater transport and chemical reactions were modeled using the code phreeqm which combines a chemical equilibrium model with a one dimensional mixing cell transport model only the vertical component of the water transport was modeled since in contrast to rates along flow lines the vertical rates are close to constant as required by the one dimensional model average vertical transport rates of water in the saturated zone were obtained by tritium dating the modeling process is a two step procedure first the sediment column is initialized with natural water containing only oxygen as electron acceptor and subsequently agricultural waters containing both oxygen and nitrate are fed into the column the nitrate concentration of agricultural waters entering the saturated zone varies with time and an input function was therefore constructed by linear mixing of natural waters and agricultural waters this input function was fed into the column initialized with natural water and the model run forward in time to the year 1988 where field data are available comparison with field data shows that the variation in groundwater chemistry is well described by the model when reduction of oxygen and reduction of nitrate by pyrite oxidation are the only redox reactions occurring finally predictions are made for the distribution of water chemistry in the year 2003 downward progression of the redoxcline is accelerated by a factor of five due to nitrate pollution of the aquifer but absolute rates remain small of the order of a few centimeters per year the controlling factor for nitrate migration through the aquifer once it has reached the anoxic zone is the concentration and distribution of pyrite in the sediments

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

redox processes in the oderbruch polder groundwater flow system in germany abstract large scale redox processes were investigated in a river recharged aquifer in the oderbruch polder alongside the river oder in north eastern germany major hydraulic and hydrochemical processes were identified qualitatively as a result of intensive drainage activities in the past 250 a the groundwater level within the polder is situated below the river water level and a levee prevents flooding of the lowland as a consequence river water permanently infiltrates into the shallow confined aquifer a sequence of redox reactions driven by organic matter degradation can be observed during infiltration of oxic river water into the groundwater up to 3 km from the river reduction processes from o2 respiration to so2 4 reduction dominate the groundwater chemistry while reduction of fe and mn hydr oxides is the source of the high amounts of dissolved fe2 and mn2 carbonate dissolution precipitation reactions control the actual groundwater concentration of mn2 the first order rate constant for so2 4 reduction was found to be 0 0169 a 1 fe2 is released into the groundwater at a rate of 0 0033 mmol l 1 a 1 the groundwater chemistry is strongly linked to the hydraulic conditions near the river the groundwater is confined and recharged by bank filtration only in contrast in the central polder the groundwater is unconfined and percolation of rainwater through the dried loam is possible because of texture changes such as shrinkage fissures geogenic pyrite present within the alluvial loam is oxidised and large amounts of so2 4 are released into the groundwater

anisotropy of magnetic susceptibility in the ponta grossa dyke swarm brazil and its relationship with magma flow direction abstract measurements of anisotropy of magnetic susceptibility ams in 95 mafic dykes mainly tholeiites 10 200 m in width from the mesozoic ponta grossa swarm southern brazil revealed two main types of magnetic fabric type i fabric plane k 1 k 2 parallel to the dyke plane represents magma flow within the dykes whereas type ii plane k 1 k 3 parallel to the dyke plane is compatible with a fabric pattern reflecting vertical compaction of the magma column fabric type i dominates 51 of the dykes within the swarm whereas type ii 38 of the dykes concentrates mainly in the western region where the dykes intrude sediments considering the dykes with type i fabrics it is concluded that 58 of the dykes were fed by horizontal or sub horizontal k 1 inclinations less than 30 magmatic flow and 42 were fed by inclined to vertical k 1 inclinations more than 30 magma flow the latter are more frequent in the southeastern part of the swarm suggesting a magma source close to this area although there may have been other sources in other regions where dykes with inclined flow and distinct chemical characteristics are also found

flow direction and groundmass shear zones in dykes shimane peninsula japan the groundmass of andesitic dykes at sezaki southwest japan has trachytic texture and contains microscopic shear zones the shear zones comprise a conjugate pair formed by flattening of the solidifying dyke rock probably caused by the magma pressure of the still molten part of the dyke this pressure shortened the solidifying rock perpendicular to the dyke margins and caused it to extrude parallel to the magma flow direction the groundmass shears indicate that locally the magma flowed 60 upward in the dykes it is concluded that while groundmass shears are a useful indicator of flow direction in dykes phenocryst alignment in dykes is strongly influenced by magma pressure flattening and thus may be a poor indicator of flow direction

relevance of erosion processes when modelling in channel gravel debris flows for efficient hazard assessment abstract a storm composed of two delayed cells hit the monte antelao slopes dolomites north eastern italy in the early morning of july 18th 2009 the resulting runoff triggered two consecutive debris flows along the rovina di cancia channel the detailed topographic data collected before and just after this event allowed an accurate reconstruction of the morphological changes experienced by the channel bed these data are here used as benchmark to test the ability of numerical models to reproduce the dynamics of a real event taking into account the morphology changes of the channel bed the aim is to provide an efficient model for engineering applications on large scales such as those required by debris flow hazard assessment a rainfall runoff transformation is applied to reconstruct the solid liquid hydrograph needed for computing the debris flow propagation two routing models are used a gis based movable bed model and a widely used fixed bed model flo 2d although similar results are obtained in terms of areas subjected to deposition significant differences emerge in terms of mobilized volumes only the simulation of both the deposition and entrainment processes allows to reliably reproduce the sediment volumes estimated from the pre and post event topographic data this information is fundamental in any hazard assessment because the volume of sediment mobilized by debris flow events exerts a fundamental control on the extension of areas subjected to inundation and on the thickness of sediment deposits the capability to reproduce correctly the mobilized volumes also entails a more reliable simulation of the evolution of the peak and volume of the solid liquid hydrograph as the debris flow propagates downstream allowing the identification of the channel reach where banks could be overflowed conversely adopting a fixed bed model leads mainly to an underestimation of the both the transported sediments volumes and the area subjected to deposition as a consequence the maximum debris flow depth in the portion of the channel subjected to erosion is underestimated and that in the portion of the channel subjected to deposition is overestimated all these types of information are of great importance for an effective hazard assessment

shear thickening dilatancy in crystal rich flows abstract rheological models of molten rock are mostly based on behaviours in which viscosity is constant with respect to strain rate e g newtonian bingham plastic or viscosity decreases with increasing strain rate pseudo plastic or shear thinning rheological models in which viscosity increases with increasing strain rate shear thickening or dilatant models have rarely been used yet such behaviour is common in particulate systems whereas magmas with low crystal content may be appropriately modelled by the former behaviours greater crystal content may lead to particle interactions resulting in shear thickening behaviour the effect is illustrated using a powdered rhyolitic rock mixed with water which exhibits extreme shear thickening behaviour caused by particles moving apart as they move past each other the expansion of the grain fabric during flow is opposed by the applied loads such that dilatancy is invariably associated with shear thickening rheology crystal rich lava may exhibit shear thickening dilatancy a proposition supported by observations of glass rich microscopic shear zones disrupting crystal fabrics plutonic crystal mush may also exhibit shear thickening dilatancy which can explain synplutonic intrusion involving brittle fracture followed by ductile disruption in general strain rate is an important contributor to the transition from ductile to brittle behaviour in crystal rich igneous rocks

contaminant transport at a waste residue deposit 2 geochemical transport modeling contaminant transport in an aquifer at an incinerator waste residue deposit in denmark is simulated a two dimensional geochemical transport code is developed for this purpose and tested by comparison to results from another code the code is applied to a column experiment and to the field site the ongoing geochemical processes and any unknown geochemical parameters are obtained through simulation of the column experiment that used soil and leachate from the field site the application of the code to the field site which has been monitored for more than 15 years use this geochemical information along with the flow and nonreactive transport parameters obtained by the inverse modeling procedure described in the first paper sonnenborg et al this issue of this two paper series the simulation results of the site model are compared with several measured component breakthroughs at monitoring wells contamination was first controlled by transport and later by transport and ion exchange in both the column and field site simulations the code is used to identify the controlling transport processes physical or geochemical ion exchange and mineral precipitation and to estimate the involved parameters primarily ion exchange selectivity coefficients

depositional systems and sequence stratigraphy of coarse grained deltas in a shallow marine strike slip setting the bohemian cretaceous basin czech republic deposits of coarse grained gilbert type deltas showing varying degrees of reworking of foresets by basinal currents were identified in middle turonian to early coniacian sandstones of the bohemian cretaceous basin the progradation of the deltaic packages earlier interpreted as large scale subaqueous dunes shelf ridges or subaqueous fault scarp accumulation terraces was controlled by high and low frequency relative sea level changes in a relatively slowly subsiding intracontinental strike slip basin end member types of the bohemian cretaceous coarse grained deltas are deep water deltas characterized by thick 50 80 m foreset packages with steep 10 30 foresets and shallow water deltas which deposited thin 15 m packages with foresets typically between 4 and 10 the differences in thickness and foreset slope angle were controlled predominantly by the accommodation available during progradation the depositional regime of the deltas was governed by i the fluvial input of abundant sand bedload with a minor proportion of gravel ii gravity flows most probably caused by liquefaction of the upper part of the unstable foreset slope and iii migration of sandy bedforms on the foreset slopes the bedform migration was driven by unidirectional currents of possible tidal origin individual foreset packages represent systems tracts or parts of systems tracts of depositional sequences a variety of stacking patterns of high frequency sequences exists in the basin caused by low frequency relative sea level changes as well as by local changes in sediment input because of generally low subsidence rates fluvial or beach topset strata were not preserved in the cases studied the absence of preserved fluvial facies which has been one of the main arguments against the fluvio deltaic origin of the sandstone bodies is explained by erosion of the topsets during transgression and their reworking into coarse grained lags of regional extent covering ravinement surfaces

field observations of a debris flow event in the dolomites a debris flow event occurred in june 1997 in the dolomites eastern alps italy the phenomenon was directly observed in the field and recorded by a video camera near its initiation area the debris flow originated shortly after an intense rainstorm 25 mm in 30 min whose runoff mobilised the loose coarse debris that filled the bottom of the channel in its upper part the analysis of the steep headwater basin indicates a very short concentration time 9 14 min that fits the quick hydrological response observed in the field the debris flow mobilisation was not contemporaneous with the arrival of the peak water discharge in the initiation area probably due to the time required for the saturation of the highly conductive channel bed material channel cross section measurements taken along the flow channel indicate debris flow peak velocity and discharge ranging from 3 1 to 9 0 m s and from 23 to 71 m3 s respectively samples collected immediately after deposition were used to determine the water content and bulk density of the material channel scouring fines enrichment and transported volume increase testify erosion and entrainment of material along the flow channel field estimates of the rheological properties based on open channel flow of bingham fluid indicate a yield strength of 5000 400 pa and relatively low viscosity 60 326 pa s probably due to a high percentage of fines approx 30

reactivity of pyrite and organic carbon as electron donors for biogeochemical processes in the fractured jurassic lincolnshire limestone aquifer uk abstract in this study the weathering profiles of limestone blocks in the jurassic lincolnshire limestone uk are used to determine the spatial variation in concentration of electron donors organic carbon and pyrite that might drive subsurface microbial respiration including denitrification organic carbon concentrations were found to be constant throughout the block transects in contrast sulphur and pyrite iron concentrations were significantly higher in the unweathered zones in comparison to the weathered zones moreover acid extractable iron concentrations were significantly higher in the weathered zones in comparison to those of the unweathered zones this suggests that pyrite is operating as the main electron donor in this system and that organic carbon is unreactive therefore potentially beneficial microbial processes such as denitrification of agrochemically contaminated groundwater will be limited not by availability of organic carbon but by availability of pyrite

sulfide oxidation and sulfate reduction in a shallow groundwater system oderbruch aquifer germany abstract detailed groundwater monitoring was carried out over a period of two years in an anoxic river recharged aquifer of the oderbruch polder north eastern germany isotope data from wells located in a 5 km transect along the flow direction was used to determine sources and sinks of so 4 2 in the aquifer the so 4 2 originates from river water infiltration and from oxidative dissolution of fes 2 within the alluvial loam covering the aquifer sands a change of confined hydraulic conditions near the river to unconfined conditions in the central polder effects the hydrochemistry of the aquifer the confined areas are dominated by sulfate reduction increasing 34 s so 4 values suggest continuous but slow t 1 2 50 years sulfate reduction from the beginning of inflow onwards with 34 s so 4 values ranging from 1 8 to 44 7 versus cdt and an enrichment factor of 33 a zone with a strong sulfate depletion 34 s so 4 of up to 85 7 exists in a shallow microenvironment rich in solid phase organic carbon between river and levee in the unconfined areas of the central polder a so 4 2 plume with concentrations exceeding the original river water content indicates fes 2 oxidation by o 2 and or no 3 within the alluvial loam the lowered 34 s so 4 value reflects the input of the isotopically lighter so 4 2 from the sulfide

internal strain within lava flows from analogue modelling internal strain within lava flows can be measured in the field from deformed bubbles or vesicle foliations preferred crystal orientation or ams studies these measurements have important implications for the determination of vertical velocity profiles and flow directions recent field studies show very contrasting strain patterns especially in vertical profiles an experimental study was conducted to relate variations in internal strain to different boundary conditions during flow results show that viscous flow in a straight channel along a basal slope produces three successive stretch trajectories in vertical flow planes these trajectories are related to the distribution with time of a simple shear component and a pure shear component viscous flow in a straight channel along a horizontal base reveals convex stretch trajectories in the vertical flow plane radial spreading at the mouth of a straight channel reveals concentric stretching perpendicular to the radial direction of displacement in the upper part of the flow strain components deduced from experiments may also explain fold formation during motion these experimental results provide a few end member strain patterns which may facilitate the interpretation of strain measurements in natural lava flows in terms of emplacement mechanisms

internal kinematics of salt diapirs the internal structure of intrusive and extrusive salt bodies elucidates their external shape and the mechanism and history of diapiric emplacement information relevant to petroleum exploration trace amounts of brine can act like heat to weaken salt and promote geologic creep by solution transfer mechanisms we compare natural strain markers in salt with the artificial markers used by fluid dynamicists stream lines are the smooth flow paths followed by fluid particles stream surfaces separate flow laminae and contain the stream lines grain shape fabrics in salt anneal readily and have strain memories so short that lineations map the stream lines and foliations map the stream surfaces of the last stages of deformation by contrast larger structures like folded beddi g have much longer strain memories as a result multiple generations of tonguelike recumbent flow folds formed by unsteady flow in the mother source layer rotate to upright sheath folds or spines in the stems of diapirs here they are constricted and refolded into steep curtain folds to form crescentic and other interference patterns visible in the roofs of salt mines mature diapirs can form crestal bulbs which may be balloon or mushroom shaped and which potentially form larger petroleum traps than previously supposed screens of country rock may be entrained between the stem and peripheral overhanging lobes caused by episodic sedimentation

internal fabric development in complex lava domes abstract viscous lava extrusions were modeled using plaster of paris with admixed magnetite dust which served as a tracer of the internal anisotropy of magnetic susceptibility fabric in model lava domes used analogue material showed pseudoplastic behavior and yield strength level proportional to increasing mixing ratio of plaster powder and water a series of models ranging from simple gravity flows to complex lava domes showing combined endogenous and exogenous growth were created by intrusion of plaster into a sandbox the similarity of model bodies is compared with natural lava domes on the basis of dynamic scaling analysis growth dynamics exogenous growth and internal fabric development in natural lava domes is critically discussed using the experimental results

propagation and deposition of stony debris flows at channel confluences the fluid dynamics of stony debris flows generated in two small tributaries adjacent to each other and flowing into a main receiving channel was analyzed experimentally at a laboratory scale the analysis on the propagation along the tributaries and deposition in the main channel provide information about sediment water mobility dangerous damming and potential hazard debris flows were generated by releasing a preset water discharge over an erodible layer of saturated gravels material as a consequence the debris flow sediment concentration varied accordingly to the entrainment rate which in turn was strongly controlled by the tributary slope the data collected by acoustic level sensors pore fluid pressure transducers and a load cell were used to characterize the evolution of bulk density and solid concentration of the sediment water mixture these two parameters were relevant to assess the stony debris flow mobility which contributes to determine the shape of sediment deposits in the main channel the detailed bed topography surveys carried out in the main channel at the end of each experiment provided information on the morphology of these deposits and on the interplay of adjacent confluences the influences of confluence angle tributary slopes and triggering conditions have been investigated for a total of 18 different configurations within the investigated range of parameters the slope angle was the parameter that mainly influences the stony debris flow mobility while for adjacent confluences the degree of obstruction within the receiving channel was strongly influenced by the triggering scenario

textural evidence for dilatant shear thickening rheology of magma at high crystal concentrations investigation of the rheology of magmas at high crystal concentrations by experimental means has proved problematic an alternative approach is to study textures of igneous rocks that not only preserve evidence of the kinematics of magma flow such as flow direction but can also preserve evidence of rheology flow textures in multiply intruded trachyte dykes on fraser island eastern australia record evidence of dilatant flow during solidification this conclusion is reached by interpretation of microscopic ductile shear zones that disrupt the groundmass of aligned feldspar laths detailed three dimensional investigation demonstrates that the dihedral angle between conjugate micro shear zones is approximately 65 this conjugate angle is equivalent to that observed in dilatant granular materials such as sand dilatant behaviour is synonymous with shear thickening rheology indicating that the magma flow is time dependent and resists high flow rates some of the dykes contain autobrecciation fragments that may represent localities where the ductile flow rate threshold was exceeded newtonian or pseudoplastic shear thinning rheology of crystal poor magmas must progressively give way to shear thickening rheology during cooling and increasing crystal concentration

progressive growth of the cerro bayo cryptodome chachahuen volcano argentina implications for viscous magma emplacement cryptodome and dome collapse is associated with volcanic hazards such as explosive eruptions pyroclastic flows and volcanic edifice collapse study of the growth and evolution of volcanic domes

experiments on internal strain in lava dome cross sections simple experiments have been conducted to study the strain evolution in lava dome cross sections a viscous fluid is injected vertically from a reservoir into a feeding conduit silicone putty is used as analogue magma two dimensional experiments allow the assessment of the internal strain within the dome particle paths are symmetrical on either side of a central line passing through the feeding conduit and display parabolic trajectories the highest strain zone is located above the extrusion zone in cross sections stretch trajectories show a remarkable concentric pattern wrapping around the extrusion zone of the analogue magma to the lateral margins a triple junction of stretch trajectories defines an isotropic point in the strain field in the main central part of the dome an intermediate zone of reversed sense of shearing is caused by a change in the sign of the velocity gradient with respect to that in the upper and lower zones knowledge of this evolving strain pattern can provide a better understanding of the evolution of natural domes also it can help to unravel the kinematic history of ancient domes partly removed by erosion

possible role of fluids in the process of earthquake swarm generation in the west bohemia vogtland seismoactive region abstract the west bohemia vogtland region in the western part of the bohemian massif known for periodic occurrence of earthquake swarms is also characterised by 0 2 0 5 ma old quaternary volcanoes rich co2 emissions anomalies of mantle derived he mineral springs and moffets the detailed analysis of the time space pattern of seismicity during the january 1997 swarm demonstrates the gradual and ordered migration of micro seismic activity suggesting the step by step penetration of fluids into a small fractured volume this scenario is supported by the similarity of the source mechanisms of the natural events of the january 1997 swarm with artificial injection induced micro earthquakes during the german deep drilling project ktb in neighbouring ne bavaria also the comparison of the west bohemia vogtland earthquake swarm region with other intraplate earthquake swarm regions and with earthquake swarms induced by current volcanic processes indicates a role of intrusions of magma and related fluids in generation process of earthquake swarms

geochemical calculations and observations on salt water intrusions i a combined geochemical minxing cell model abstract a combined geochemical mixing cell flow model has been developed the geochemical model is based on the computer program eq 3 6 wolery 1982 has been modified to include cation exchange reactions and is incorporated in a one dimensional mixing cell model for stationary one dimensional transport dispersion or diffusion is calculated by mixing the cell contents with neighbouring cells relationships between mixing factors and dispersivity and diffusion coefficients are derived the model is used to simulate concentration changes during salt water intrusions fundamental differences are shown to exist between diffusion of salt water from a stagnant water body and dispersive intrusions during marine transgressions or flooding events with dispersive flow characteristic water compositions develop in space and time as a result of cation exchange with diffusion these steep concentration gradients are smoothed out and mixed compositions occur the concept that characteristic concentrations occur during dispersive flow is used to obtain paleohydrological information in a dutch polder the depth of the fresh salt water interface before polder development is deduced from a simulation of observed exchange reactions in the polder groundwater

a reactive transport model of neptunium migration from the potential repository at yucca mountain abstract characterization and performance assessment studies for the potential high level nuclear waste repository at yucca mountain have identified 2 3 7 np as a radionuclide of concern for the proposed repository to predict the migration of neptunium after a repository breach an understanding of the relevant hydrologic and geochemical processes is required the hydrologic flow in the unsaturated zone at yucca mountain is dependent on the infiltration rate the stratigraphy of the vadose zone and the heat generated by the decaying radioactive waste the geochemical processes that strongly affect 2 3 7 np migration include solubility limited release of 2 3 7 np from the near field environment aqueous speciation of neptunium into non sorbing carbonate hydroxy complexes and the sorbing npo 2 cation sorption of neptunium onto the zeolitic tuffs via an ion exchange mechanism and radioactive decay the finite element heat and mass transfer fehm code was used to investigate the coupled effects of chemical interactions and heat on neptunium transport from the potential repository to the water table the selective coupling method is introduced to solve these reactive transport problems the simulations indicate that in the absence of irreversible changes in the hydrologic and transport properties the heat pulse does not significantly affect the migration of neptunium as the time scale of heat pulse propagation is shorter than the time scales associated with neptunium release and migration water chemistry particularly ph calcium and sodium concentration significantly affect the retardation of neptunium by the zeolitic rocks between the repository and the water table

the perfect debris flow aggregated results from 28 large scale experiments 1 aggregation of data collected in 28 controlled experiments reveals reproducible debris flow behavior that provides a clear target for model tests in each experiment 10 m3 of unsorted water saturated sediment composed mostly of sand and gravel discharged from behind a gate descended a steep 95 m flume and formed a deposit on a nearly horizontal runout surface experiment subsets were distinguished by differing basal boundary conditions 1 versus 16 mm roughness heights and sediment mud contents 1 versus 7 percent dry weight sensor measurements of evolving flow thicknesses basal normal stresses and basal pore fluid pressures demonstrate that debris flows in all subsets developed dilated coarse grained high friction snouts followed by bodies of nearly liquefied finer grained debris mud enhanced flow mobility by maintaining high pore pressures in flow bodies and bed roughness reduced flow speeds but not distances of flow runout roughness had these effects because it promoted debris agitation and grain size segregation and thereby aided growth of lateral levees that channelized flow grain size segregation also contributed to development of ubiquitous roll waves which had diverse amplitudes exhibiting fractal number size distributions despite the influence of these waves and other sources of dispersion the aggregated data have well defined patterns that help constrain individual terms in a depth averaged debris flow model the patterns imply that local flow resistance evolved together with global flow dynamics contradicting the hypothesis that any consistent rheology applied we infer that new evolution equations not new rheologies are needed to explain how characteristic debris flow behavior emerges from the interactions of debris constituents

interpretation of domainal groundmass textures in basalt lavas of the southern lamington volcanics eastern australia the arrangement of crystals vesicles and glass in the matrix of a volcanic rock records information about the kinematics accompanying its formation simple rock textures involve homogeneous distributions of features such as aligned crystals whereas more complex rock textures involve inhomogeneous distributions comprising subregions or domains of homogeneous textural types in the groundmass of volcanic rocks two types of domainal textures are defined by 1 differences in the degree of alignment or direction of alignment of crystals and 2 different concentrations of crystals a petrographic survey of basalt lavas of the tertiary lamington volcanics in northeast new south wales australia reveals the presence of both crystal alignment and crystal concentration domainal textures alignment domains are interpreted as shear zones overprinting homogenous aligned textures during flow the formation of crystal concentration domains appears to involve multiple processes including 1 crystal clustering during flow 2 complex overprinting of dilatant groundmass shear zones 3 melt segregations due to stress or 4 postvesiculation processes

effectiveness of various cover scenarios on the rate of sulfide oxidation of mine tailings long term environmentally sound disposal of the millions of tons of mining residue is a serious challenge to the international mining industry this paper evaluates through a numerical investigation the potential performance of desulfurized tailings as a cover material for the reduction of acidic drainage from sulfidic tailings this evaluation is facilitated through a comparison of various cover types as decommissioning options the cover types considered consist of a desulfurized tailings material cover exposed to ambient climate conditions a water cover flooded tailings and a combination cover type as part of the evaluation of cover performances the effect of climatic variability on the potential rate of sulfide oxidation in tailings with an open ground surface was also assessed the numerical analysis was conducted using the model pyrox which was modified to allow for variably saturated conditions time varying moisture contents and to account for the temperature dependence of henry s law and gas diffusion in the case study presented here the benign cover material consists of a low sulfide waste stream cassiterite float tails cft a by product of the production of tin concentrate cassiterite sno2 modelling results after a simulation period of 100 years indicate that a water cover alone or an exposed cft cover alone are both less effective options than the combined cover type a water cover alone leads to a reduction of approximately 99 1 in the oxidation rate relative to uncovered tailings while the combined cover type results in the lowest potential extent of sulfide oxidation after mine closure an approximately 99 8 reduction importantly a cft cover exposed to ambient environmental conditions can still substantially reduce the sulfide oxidation rate by approximately 75 82 over a 100 year time period relative to uncovered tailings variability in precipitation and hence percent saturation of the surface layer had less of an effect on the potential sulfide oxidation rate than did the cover type the performance of the exposed cft cover varied by less than 10 within the range of climatic conditions expected at the renison bell mine site in southwest tasmania australia although the modelling results indicate that the combined water and cft cover is the best option this approach achieves only a minor improvement over the water cover alone

magnetic fabric and inferred flow direction of dikes conesheets and sill swarms isle of skye scotland abstract we have measured the ams of 16 dikes 35 conesheets and three sills associated with the cuillin hills magmatic center of the isle of skye in the inner hebrides of scotland and of nine dikes located in the regional dike swarm of skye sixty three intrusives totalling 734 samples were studied to determine the plumbing of the skye volcanic system low field susceptibility versus temperature k t identified three different mineral phases in the area namely ti rich magnetite pyrrhotite and titanomaghemite the petrofabrics of the 63 intrusives yielded coherent flow azimuths regardless of their time of emplacement three main types of magnetic fabric a c were found fabric type a plane kmax kint parallel to the dike plane represents the magma flow direction within the intrusives and is the dominant fabric 55 of all the intrusives within the cuillin hills magmatic center and its regional dike swarm the kmax inclinations show that 55 of the intrusives were fed by horizontal to sub horizontal ams inclination of the kmax axis is equal or less than 30 magma fluxes and the rest of them were fed by inclined to vertical fluxes horizontal magma flow means lateral magma injection inside fractures and becomes more probable as the source is located further away

the triggering of debris flow due to channel bed failure in some alpine headwater basins of the dolomites analyses of critical runoff the debris deposits at the bottom of very steep natural channels and streams in high mountain areas can be mobilized by runoff triggering a water sediment mixture flow known as debris flow the routing of debris flow through human settlements can cause damage to civil structures and loss of human lives the prediction of such an event or the runoff discharge that triggers it assumes an interest in risk analyses and the planning of defence measures the object of this study is to find a method to determine the critical runoff value that triggers debris flow as a result of channel bed failure historical and rainfall data on 30 debris flows that occurred in six watersheds of the dolomites north eastern italian alps were collected from different sources field investigations at the six sites together with the hydrologic response to the rainfalls that triggered the events were performed to obtain a realistic scenario of the formation of the debris flow there occurred field observations include a survey along the channel of the triggering reach of debris flow with measurements of the channel slope and cross section and sampling of debris deposits for grain size distribution simulated runoff discharge values based on the rainfall recorded by pluviometers were then compared with values obtained through experimental criteria on the initiation and formation of debris flow by bed failure the results are discussed to provide a plausible physical based method for the prediction of the triggering of debris flow by channel bed failure copyright 2007 john wiley sons ltd

slip system domains i plane strain kinematics of arrays of coherent bands with twinned fibre orientations abstract slip system in rocks often occupy domains each of uniform slip system orientation examples are conjugate faults shear zones folded bedding and crystal lattices domainal behaviour in plane strain is modelled as simple shearing along inextensible fibres an array of alternating band domains with coherent boundaries can undergo a uniform bulk strain with local perturbations in the domains if 1 domain boundaries are planes of mirror symmetry with respect to fibre attitude and 2 domains have alternating fractional widths a and 1 a motion in the models is shown to be a combination of three independent modes plus a bulk rigid motion during mode 1 motion domain boundaries stretch but do not migrate during mode 2 they do not stretch but migrate by lateral translation during mode 3 they migrate by translation and rotation orientation distribution functions odfs are defined by assigning frequencies a and 1 a to orientations and changes in are shown to be due to mode 1 alone changes in a to mode 2 alone mode 3 has no effect on an odf combinations of modes 1 2 and 3 can be used to accommodate an imposed bulk motion two examples are discussed a bulk simple shear and a rigid motion large amounts of simple shear are possible if fibres are on average parallel to the imposed shear direction if modes 1 and 2 are operative the resulting odf has a maximum peak close to the shear direction this may explain the asymmetry of preferred lattice orientations and the occurrence of unique fault sets in rocks that have undergone a progressive simple shear

characterization of the reactivity of riverine heterogeneous sediments using a facies based approach the rhine meuse delta the netherlands large groundwater resources are found in densely populated lowland areas which consist often of young unconsolidated and reduced sediments when anthropogenic activities lead to oxygenation of the aquifer breakdown of the main reduced fractions i e sedimentary organic matter som and pyrite could lead to severe groundwater deterioration such as acidification heavy metal mobilization and increased hardness the characterization of the reactive properties of these sediments is important in predicting groundwater deterioration but is often complicated by the high degree of heterogeneity of these sediments in this study the potential reduction capacity prc based on som and pyrite content the potential buffer capacity pbc based on carbonate content potential acidification capacity pac based on the potential acid production by sulfide oxidation and the measured reduction capacity mrc of five facies which are typical of the riverine sediments in the rhine meuse delta the netherlands were determined a universal facies classification model was used to classify the deposits into more homogeneous sub units based on lithologic and geogenic properties with a further sub division into oxic or anoxic redox environment based upon groundwater data and field observations the bulk chemical data show strong variation across facies for the median values of prc 186 9093 mmol o2 kg 1 pbc 17 132 mmol o2 kg 1 and pac 36 1530 mmol h kg 1 the mrc was measured as reactivity to molecular o2 exposure and was 0 5 567 3 mmol o2 kg 1 steady state oxidation rates were in the wide range of 0 001 10 355 mmol o2 kg 1 day 1 but were typically about 3 8 times faster in fine facies than in coarse facies both the prc and mrc depend strongly on grain size but also on the syn post depositional environment and redox conditions the main part of the prc consists of som but pyrite reactivity is higher than som reactivity as shown by the relative depletion of pyrite in oxic subfacies and the preferential oxidation during the oxidation experiments some facies are very prone to acidification because the pac is higher than the pbc but the oxidation experiments also show that acidification could already start before the prc is fully exhausted this study is one of the few that combines bulk chemical data groundwater data and reactivity measurements and shows that a facies based approach is a practical tool in characterizing the reactivity of heterogeneous deposits 2007 elsevier ltd all rights reserved

deformation and magnetic fabrics in ductile shear zones a review abstract the anisotropy of magnetic susceptibility ams is a well established petrofabric tool for indicating relative strain and microstructural character and has been validated on various rock types and different structural settings the magnetic susceptibility of a rock k depends primarily on the nature and abundance of magnetic minerals the physical arrangement and lattice preferred orientation of these magnetic minerals give rise to magnetic anisotropy the ams scalar parameters most commonly used to constrain strain include the corrected degree of anisotropy p 1 a proxy for fabric intensity and the shape factor 1 t 1 an indicator of the magnetic fabric symmetry prolate vs oblate a number of studies have shown that a positive correlation generally exists between p and strain thus the ams shows a great potential as a tool for examining deformation in geologic structures characterized by large strain gradients such as shear zones however a number of caveats exist i the increase of p with strain cannot be solely attributed to deformation because p also increases with k regardless of deformation ii strain across shear zones is typically heterogeneous and is often localized in units of different lithology thus making the separation of the lithological and strain controls on ams difficult also deformation is commonly accompanied by mineral segregation or fluid rock interaction that induces changes in magnetic mineralogy iii even if the undeformed lithology was uniform across a shear zone variations in strain rate or temperature may result in different deformation mechanisms hence the relationship between p and strain depends strongly on both the mineral carriers of ams and on deformation mechanisms and iv the ams is unable to resolve composite fabrics such as those resulting from s c structures where minerals on the c and s planes respectively contribute to ams

microshear zones in a miocene submarine dacite dome of southwest japan microscopic shear zones have been found in the groundmass of glassy rocks of a miocene submarine dacite dome in southwest japan similar textures have been reported previously but only in dykes these textures give a valuable insight into the deformation of the dome during its emplacement by recording the orientations of the principal strains detailed textural analysis indicates that the microshear zones formed as a result of flattening and stretching of the magma simultaneously with quenching measured stretching directions are near parallel suggesting the magma flowed in one dominant direction rather than in a radial pattern the strain is believed to also be influenced by high magma pressure inside the dome being imposed on the high viscosity outer part of the dome

rheology of concentrated granular suspensions and possible implications for debris flow modeling 1 granular suspensions are of major relevance for many geophysical flows we investigated the rheological behavior of three samples taken from a debris flow deposit at varying solid concentration from 38 0 to 54 2 by volume and grain size distribution experiments were performed first on the fraction finer than 0 075 mm and then on suspensions with fine sand up to 0 425 mm in size and percentages varying from 10 to 50 a vane apparatus connected to a rotational rheometer was used and experiments showed a reproducibility within 12 results were processed by the tikhonov regularization method in order to convert the shear stress versus rotation velocity curves to shear stress versus shear rate flow curves at shear rates lower than 3 5 s 1 shear stress is rate independent at higher shear rates the shear stress increases depending on the maximum grain particles included within the suspension we used the herschel bulkley and bingham models to describe the monotonous increase of the flow curves varying the grain size distribution of the samples the power and consistency indexes range within 0 75 1 35 and 0 44 40 8 pa s n where n is the exponent of the viscosity coefficient varies from 1 0 to 47 2 pa s and the shear stress varies from 28 to 1959 pa for materials mainly composed of silt and clay with a variable sand content 1 an increase in the particle size changes the rheological behavior from shear thinning to shear thickening and 2 the percentage of sand affects both the frictional character of the flow and the magnitude of the rheological parameters

ams measurements on obsidian from the inyo domes ca a comparison of magnetic and mineral preferred orientation fabrics abstract measurements of the anisotropy of magnetic susceptibility ams on lavas can yield information concerning flow directions deformation regimes and relative shear rates here we report results of measurements made on samples of rhyolitic obsidian collected from obsidian dome ca comparisons of ams measurements with previously determined 3d microlite orientation distributions in these samples serve as a calibration of the ams technique despite the low values of bulk susceptibility 1 06 7 04 10 3 si found in the dome relative to typical values in basalts 10 2 si the degree of anisotropy is extremely high in all specimens 3 4 10 7 furthermore susceptibility tensors exhibit a wide range of shapes varying from prolate to triaxial and flattened ellipsoids b parameter from 8 6 to 6 4 corresponding to various degrees of microlite dispersion our results also indicate that despite the tight clustering of principal susceptibility axes obtained on each site bulk flow directions inferred from the orientations of k max axes may be misleading because the orientation of the local extension changes from place to place within the dome however it is shown that the ams of each specimen provides a good measure of the direction of local extension consequently it is possible to interpret spatial variations in flow regime from systematic changes in the orientation of principal susceptibility axes as the proposed association between the local deformation regime and ams is strongly dependent on the aspect ratio of the crystals embedded in the flowing lava some caution must be exerted when interpreting ams results from other flows and a direct comparison between different flows may not be granted in many occasions

surface slopes velocity profiles and fluid pressure in coarse grained debris flows saturated with water and mud data on the internal velocity distribution of flowing sediment fluid mixtures such as debris flows are rare but necessary for model development and testing a probe to measure the mean particle velocity at different depths and different locations within experimental debris flows in a 4 m diameter rotating drum was developed in addition the flow depth basal normal stress and basal pore fluid pressure were also measured results show that for a given sediment fluid mixture the velocity profiles collapse to distinct non dimensional profiles macroscopic flow behaviour shows great similarity with mean surface slopes weakly dependent on the shear rate for water saturated gravel but strongly shear rate dependent when pores are filled with mud poorly sorted material with a high content of fines produced fluid pressures close to normal stress and sidewall friction had a strong effect on the flow pattern our results reveal variability in profile characteristics for flows displaying similar macro dynamics and provide data for model testing

the processes and mechanism of failure and debris flow initiation for gravel soil with different clay content clay content can influence gravel soil mass failure and debris flow initiation significantly but quantification of the clay content influence in the published literature is lacking this paper describes the experiments carried out to explore soil mass failure and debris flow initiation with different clay contents the whole process of gravel soil mass failure and debris flow initiation can be grouped into five phases i infiltration excess runoff ii fracture extending iii initial slip iv large scale slip v debris flow triggering in the experiments when the clay content of soil mass is lower than 2 5 no soil failure and debris flow are triggered only the soil masses with moderate clay contents 5 10 show the clear processes of the five phases that need the shortest rainfall duration among different clay contents soil masses with high clay content 10 and low clay content 2 5 5 need longer rainfall duration to cover the five phases for partially triggering soil failure and debris flows clay content is closely linked with the soil failure and debris flow initiation under rainfall the key mechanism can be grouped into two reasons i the clay particles absorb the moisture and dilate to fill the soil pores and the content of the clay has a direct link with the filled pores ii the gravel soil masses with different clay content differ in their structure for the low clay content soil mass group 2 5 5 the coarse grains of the gravel soil form large pores and saturated clay particles are too few to block most soil pores as a result pore water pressure of soil mass is released easily in the raining process therefore inner friction holds strong and soil mass is hard to mobilize into slip and debris flows on the other hand for soil masses with high 10 clay contents soil failure and debris flow are triggered under the aid of surface runoff flux to reduce the cohesion of the soil whereas only for the soil masses with moderate clay contents 5 10 large scale soil failure and debris flow can be triggered within the shortest duration in this case the debris flow is of the form of soil mechanics which is triggered after soil masses slip and liquefaction the others are of the form of hydraulic mechanics the experiments provide valuable evidence for quantifying clay content impact on gravel soil failure and debris flow initiation because they were carried out in a flume the research results are applicable to the soil failure and debris flow initiation in bedrock gully situations

new views of granular mass flows concentrated grain fluid mixtures in rock avalanches debris flows and pyroclastic flows do not behave as simple materials with fixed rheologies instead rheology evolves as mixture agitation grain concentration and fluid pressure change during flow initiation transit and deposition throughout a flow however normal forces on planes parallel to the free upper surface approximately balance the weight of the superincumbent mixture and the coulomb friction rule describes bulk intergranular shear stresses on such planes pore fluid pressure can temporarily or locally enhance mixture mobility by reducing coulomb friction and transferring shear stress to the fluid phase initial conditions boundary conditions and grain comminution and sorting can influence pore fluid pressures and cause variations in flow dynamics and deposits

deformation patterns in a high viscosity lava flow inferred from the crystal preferred orientation and imbrication structures an example from salina aeolian islands southern tyrrhenian sea italy shape preferred orientation and imbrication structures of crystals have been measured on samples representative of the base centre and top of a highly viscous lava flow on salina aeolian islands southern tyrrhenian sea the data allow zones with different deformation patterns to be identified in the base and top of the flow deformation leads to the development of discrete preferred orientation and imbrication of the elongate crystals the sense of shear is right lateral at the base and left lateral at the top of the flow shear strain can be estimated by the analysis of crystal preferred orientation deformation increases from the flow centre to the outer more viscous boundary layers random orientation of crystals in the inner zone supports the presence of plug flow in a pseudoplastic lava the textural features of the studied lava may be related to different mechanisms i e lateral expansion we conclude that the observed crystal alignments and imbrication structures may be related to a plug flow moving between two non deforming walls the walls are represented by the solidified broken upper and basal crust of the flow the low shear strain values calculated in the outer margins of the flow are indicative of the last deformation event crystal preferred orientation and imbrication structures may be related to the occurrence of velocity gradients existing between the inner zone of the flow and its solidus or near solidus outer margins

terrestrial sedimentary pyrites as a potential source of trace metal release to groundwater a case study from the emsland germany abstract pyrite is a common minor constituent of terrestrial freshwater sediments and a sink for trace elements different amounts and morphological types framboids and euhedral crystals of sedimentary pyrites were found in the heavy mineral fraction of cores obtained from several drillholes located in the emsland region nw germany their trace element contents were investigated to assess their potential for groundwater contamination after oxidation e g induced by dewatering or autotrophic denitrification nickel arsenic and cadmium were found in significant concentrations in pyrite geochemical modeling showed that elevated trace metal concentrations in groundwater potentially exceeding drinking water standards should preferentially occur in a less than 1 m thick zone situated around the depth of the redoxcline where nitrate is reduced by pyrite this was confirmed by depth specific groundwater sampling in the emsland and by previously published studies the absolute concentration of released trace metals depends on their content in the pyrite but also strongly on the nitrate load of groundwater

structures and lithofacies of inferred silicic conduits in the parana etendeka lip southernmost brazil abstract extensive silicic units in the parana etendeka lip have been long interpreted as pyroclastic density currents rheomorphic ignimbrites derived from the messum complex in namibia in recent literature however they have been characterized as effusive lava flows and domes in this paper we describe structures and lithofacies related to postulated silicic lava feeder conduits at mato perso sao marcos and jaquirana cambara do sul areas in southern brazil inferred conduits are at least 15 25 m in width and the lithofacies include variably vesicular monomictic welded and non welded breccias in the margins to poorly vesicular banded spherulitic and microfractured vitrophyres in the central parts flat lying coherent vitrophyres and massive obsidian are considered to be the subaerial equivalents of the conduits large scale regional tectonic structures in southern brazil include the ne sw aligned porto alegre suture leao and acotea faults besides the antas lineament a curved tectonic feature accompanying the bed of antas river south of the antas lineament smaller scale nw se lineaments limit the exposure areas of the inferred conduits ne sw and subordinate nw se structures within this smaller scale lineaments are represented by the main postulated conduit outcrops and are parallel to the dominant sub vertical banding in the widespread banded vitrophyre lithofacies upper lava flows display flat lying foliation pipe like and spherical vesicles and have better developed microlites petrographic characteristics of the silicic vitrophyres indicate that crystal poor magmas underwent distinct cooling paths for each inferred conduit area the vitrophyre chemical composition is defined by the evolution of trachydacitic dacitic vitrophyres with 62 65 wt sio 2 to rhyodacite and rhyolite with 66 68 wt sio 2 the more evolved rocks are assigned to the latest intrusive grey vitrophyre outcropping in the center of the conduits degassing pathways formed during fragmentation and fracturing episodes within the conduits may have helped to inhibit the explosivity of the eruptions based on the documented lithofacies architecture we attribute the source of the silicic lava flows in the studied localities to tectonic controlled local conduits rather than pyroclastic density currents from distant vent areas

the rheological transition in plagioclase bearing magmas 1 volcanological processes such as melt segregation ascent and eruption are directly dependent on the rheological behavior of magmatic suspensions an increase of the crystal fraction of the suspension leads to the formation of a solid particle network which abruptly increases magma viscosity the crystal fraction at which this rheological transition occurs depends on parameters such as the strain rate and the size shape and sorting of particles to determine the influence of the crystal shape on the rheological transition suspensions of plagioclase a representative anisometric crystal have been investigated at high temperatures and pressures synthetic suspensions with crystal fractions s ranging from 0 38 to 0 75 were deformed both in compression and torsion in a paterson apparatus at 300 mpa 900 c and 800 c and for strain rates between 1 0 10 5 and 1 0 10 3 s 1 all suspensions exhibit a non newtonian shear thinning rheological behavior the experimental results coupled with existing data and models at low crystal fractions s 0 3 allow several rheological domains to be identified from steady state flow to strain weakening each characterized by a specific microstructure in particular a progressive evolution from a pervasive to a strain partitioning fabric is found when increasing the crystal fraction our results highlight the influence of both the strain rate and the shape of crystals on the rheological behavior of magmas during crystallization magmatic suspensions of anisometric minerals such as plagioclase would develop a solid particle network earlier s 0 3 than suspensions of isometric minerals s 0 5 our study shows that localization of strain early in the crystallization history of mushy zones in the magma chamber near the conduit margins and at the base of lava flows would facilitate the mobilization the transfer and the final emplacement at the surface of highly viscous feldspar rich magmas

redox controlled multiple species reactive chemical transport 2 verification and application a redox controlled multiple species multidimensional reactive chemical transport model dynamix has been presented in part 1 of this paper in part 2 the model is checked against two other independently developed reactive chemical transport codes simulated results from dynamix agree reasonably well with those obtained from the other two models two approaches for simulating redox reactions an external approach based on hypothetical electron activity and an effective internal approach based on conservation of electrons have been examined the results show that in the external approach the simulated redox front is smeared out by diffusion and dispersion whereas in the effective internal approach the redox front is sharp and is controlled by the redox reactions the evolution of solid phases from the two approaches give markedly different mineral assemblages it is suggested that the external approach is of relevance in industrial processes such as electrometallurgy in which mineral dissolution is driven by externally supplied electric power the effective internal approach is applicable to hydrogeochemical systems groundwater contamination diagenesis ore formation rock weathering and soil genesis in which redox potential is dictated by the states of the redox species the results also suggest that in the presence of precipitation and consequent retardation of the concentration front spreading due to hydrodynamic dispersion may be significantly inhibited to demonstrate the applicability of dynamix for realistic field problems two field cases are simulated by this model in the first case the supergene enrichment of copper at butte montana the simulated mineral assemblages and their distributions agree reasonably with the mineral assemblages and the ore grade observed in the field in the second case involving two dimensional contaminant transport in a hypothetic aquifer the simulated results suggest that dynamix is capable of handling a realistic multi dimensional field problem with several hundred grid blocks and time scales of practical interest

folds produced by gravity spreading of a banded rhyolite lava flow abstract recumbent folds near the top of the minyon falls banded rhyolite flow in northeastern new south wales australia indicate lateral radial extension of lava as it flowed from the vent under the influence of gravity these structures occur near the vent of the flow and differ from the upright folds commonly observed near the tops of lava flows farther from the vent the fold patterns indicate lateral radial shortening and shearing as the spread of lava was impeded interpretation of the folds leads to a kinematic model of coaxial flow near the vent grading to simple shear and sub simple shear away from the vent

dynamics of obsidian flows inferred from microstructures insights from microlite preferred orientations the flow of obsidian lava leads to crystal alignments that reflect both the accumulated strain and the type of flow across the surface microlite preferred orientations are used to investigate the emplacement dynamics strain history and structural evolution of obsidian dome eastern california measurements of three dimensional microlite trend and plunge in samples from the near vent region distal flow and flow front show 1 the flow directions along the dome margins 2 the deformation style e g pure versus simple shear at the dome margins and 3 the variation in strain as a function of position within the flow microlites form well developed lineations in the plane of flow banding in all samples stereographic projections indicate that lineations trend normal to the western flow front and plunge shallowly away from the margin the radial flow pattern indicated by measurements made along the western margin suggests that extrusion was from a roughly elliptical vent these results highlight a strong correlation between microlite trend and the bulk flow direction inferred from the geometry of the flow along most of the eastern periphery lineations trend parallel to the margin and likely reflect the local flow direction as influenced by compression against the thickening flow crust marginal talus piles and topography orientation distributions imply that radial spreading accompanied by flattening was the dominant mechanism for flow emplacement comparisons of measured orientation distributions with theoretical predictions suggest that microlite fabrics in flow front and nearvent samples developed in a pure shear flow microstructures in a sample from near the distal flow base records a component of simple shear variance in microlite trend provides a measure of the amount of strain acquired during flow standard deviation in trend decreases from the near vent region to the flow margins reflecting progressive alignment of microlites during transport pure shear strain inferred from orientation distributions increases from approximately 0 3 near the vent to about 1 1 at the flow front the difference between these strains 0 8 is an estimate of the strain associated with flow emplacement such strain is similar in size to that estimated from mesoscopic structures v1 and for horizontal spreading of a fluid whose volume is equal to that of obsidian dome v1 6 this suggests that flow on the surface was sufficient to produce observed microlite preferred orientations in the flow front these techniques can be applied to interpret older dissected lavas where erosion has erased much of the original flow front or where larger scale structures indicative of flow directions are poorly preserved fl 2002 elsevier science b v all rights reserved

field tracer test for denitrification in a pyrite bearing schist aquifer abstract a small scale artificial tracer test performed on a schist aquifer in brittany has helped clarify mechanisms and kinetics of in situ autotrophic denitrification no 3 was injected as a pulse simultaneously with a conservative tracer br during the test which lasted 210 h 73 of the injected br was recovered as against only 47 of the no 3 the 26 difference in the recovery of the two injected species is interpreted as being the result of denitrification in part due to the direct oxidation of pyrite present in the solid aquifer according to the reaction 5fes 2 14no 3 4h 7n 2 10so 4 2 5fe 2 2h 2 o and in part due to subsequent iron oxidation according to the reaction no 3 5fe 2 6h 1 2n 2 5fe 3 3h 2 o despite the potential increase in so 4 and fe resulting from denitrification through pyrite oxidation the concentrations of these elements in the groundwater remain moderate due to the precipitation of minerals such as jarosite and or natroalunite tracer transfer takes place in a heterogeneous medium which according to the breakthrough curves can be simplified to a dual porosity aquifer comprising a high permeability fractures or large fissures medium of low porosity from which only minor denitrification of circulating no 3 bearing water was observed and a low permeability small fissures medium of high porosity which induces a higher denitrification rate in the circulating no 3 bearing water the kinetics of the denitrification reaction are high compared with results obtained for other environments and can be described by a first order model with a half life of 7 9 days for the low porosity medium and only 2 1 days for the high porosity medium

experimental study of bedrock erosion by granular flows 1 field studies suggest that bedrock incision by granular flows may be the primary process cutting valleys in steep unglaciated landscapes an expression has been proposed for debris flow incision into bedrock which posits that erosion rate depends on stresses due to granular interactions at the snout of debris flows here we explore this idea by conducting laboratory experiments to test the hypothesis that bedrock erosion is related to grain collisional stresses which scale with shear rate and particle size we placed granular material in a 56 cm diameter rotating drum to explore the relationship between erosion of a synthetic bedrock sample and variables such as grain size shear rate water content and bed strength grain collisional stresses are estimated as the inertial stress using the product of the squares of particle size and vertical shear rate our uniform granular material consisted of 1 mm sand and quartzite river gravel with means of 4 6 or 10 mm in 67 experimental runs the eroded depth of the bed sample varied with inertial stresses in the granular flow to a power less than 1 0 and inversely with the bed strength the flows tended to slip on smooth boundaries resulting in higher erosion rates than no slip cases we found that lateral wall resistance generated shear across the channel producing two cells whose widths depended on wall roughness while the hypothesized inertial stress dependency is supported with these data wear mechanics needs to account for grain dynamics specifically at the snout and possibly to include lateral shear effects

the influence of debris flows on channels and valley floors in the oregon coast range u s a debris flows are one of the most important processes which influence the morphology of channels and valley floors in the oregon coast range debris flows that initiate in bedrock hollows at heads of first order basins erode the long accumulated sediment and organic debris from the floors of headwater first and second order channels this material is deposited on valley floors in the form of fans levees and terraces in channels deposits of debris flows control the distribution of boulders the stochastic nature of sediment supply to alluvial channels by debris flows promotes cycling between channel aggradation which results in a gravel bed morphology and channel degradation which results in a mixed bedrock and boulder bed morphology temporal and spatial variability of channel bed morphology is expected in other landscapes where debris flows are an important process

silicic lava dome growth in the 1934 1935 showa iwo jima eruption kikai caldera south of kyushu japan the 1934 1935 showa iwo jima eruption started with a silicic lava extrusion onto the floor of the submarine kikai caldera and ceased with the emergence of a lava dome the central part of the emergent dome consists of lower microcrystalline rhyolite grading upward into finely vesicular lava overlain by coarsely vesicular lava with pumice breccia at the top the lava surface is folded and folds become tighter toward the marginal part of the dome the dome margin is characterized by two zones a fracture zone and a breccia zone the fracture zone is composed of alternating layers of massive lava and welded oxidized breccia the breccia zone is the outermost part of the dome and consists of glassy breccia interpreted to be hyaloclastite the lava dome contains lava with two slightly different chemical compositions the marginal part being more dacitic and the central part more rhyolitic the fold geometry and chemical compositions indicate that the marginal dacite had a slightly higher temperature lower viscosity and lower yield stress than the central rhyolite the high temperature dacite lava began to effuse in the earlier stage from the central crater the front of the dome came in contact with seawater and formed hyaloclastite during the later stage low temperature rhyolite lava effused subaerially as lava was injected into the growing dome the fracture zone was produced by successive fracturing ramping and brecciation of the moving dome front in the marginal part hyaloclastite was ramped above the sea surface by progressive increments of the new lava the central part was folded forming pumice breccia and wrinkles subaerial emplacement of lava was the dominant process during the growth of the showa iwo jima dome

structural analysis of flow related textures in lavas abstract the textures of coherent volcanic rocks including lavas and volcanic intrusives commonly contain features that are attributed to flowage previous applications of structural analysis to volcanic rocks are expanded here to provide a framework for analysis textures defined as the crystallinity granularity and shapes and arrangements of the components crystals glass and voids of a rock together with structures defined as individual features composed of the disposition attitude arrangement or relative positions of the components of a rock are first described second the spatial fabrics shapes and arrangements of the components of a rock and the orientation of textures and structures are identified third textures structures and fabrics are placed in the spatial and temporal geological context finally detailed interpretations of the kinematics and rheology of structures and fabrics is made leading to an integrated flow history of the rock illustrative case studies include rhyolite from the basal part of the tertiary minyon falls dome northeastern new south wales australia which has a texture comprising planar domains of differing crystal abundance flow bands multiple folds of these domains relatively homogeneous crystal alignment parallel to the fold axes and microfolding of these domains in the zone of interaction between phenocrysts and matrix including retrorotation of phenocrysts on short limbs of inequant folds trachyte dykes on fraser island queensland australia have a texture comprising crystal alignment planar concentration domains banding two planar domains of crystal alignment interpreted to be conjugate shear zones phenocrysts influence the spacing and distribution of the domains and interacted with shear zones by undergoing small amounts of rotation the shear zones overprinted a homogeneous crystal alignment during the last stage of flow before solidification as a result of dilatant granular interactions lava from miocene submarine banded silicic mafic domes on katsurajima on the coast of the shimane peninsula southwestern japan has a texture comprising crystal alignment irregular domains interpreted as the result of quenching local internal deformation of crystals including brittle boudinage and elongate vesicles and amygdales dacite from the late stages of the 1991 1995 eruption of mount unzen in western kyushu japan has a texture comprising crystal alignment deformation of phenocrysts and their surrounding matrix producing voids by mechanical means with the possible involvement of vapour phases the pervasive mechanical failure of the flowing magma may have triggered frontal collapse and the ensuing pyroclastic eruptions a spectrum of increasingly intense flow related textures can be recognised from simple planar alignments of crystals and vesicles to overprinting effects and domainal textures such as banding and shear zones and deformed domains pervasive ductile tearing and ultimately brittle fracture record flow during the transition from ductile magma to brittle rock the development of these flow related textures is controlled by the interplay of driving forces magma pressure gravity and resisting forces viscosity where driving forces are strong flow related textures are well developed when viscous resistance exceeds the driving forces flow and the development of flow related textures ceases