discovery of jarosite within the mawrth vallis region of mars implications for the geologic history of the region abstract analysis of visible to near infrared reflectance data from the mro crism hyperspectral imager has revealed the presence of an ovoid shaped landform approximately 3 by 5 km in size within the layered terrains surrounding the mawrth vallis outflow channel this feature has spectral absorption features consistent with the presence of the ferric sulfate mineral jarosite specifically a k bearing jarosite kfe3 so4 2 oh 6 terrestrial jarosite is formed through the oxidation of iron sulfides in acidic environments or from basaltic precursor minerals with the addition of sulfur previously identified phyllosilicates in the mawrth vallis layered terrains include a basal sequence of layers containing fe mg smectites and an upper set of layers of hydrated silica and aluminous phyllosilicates in terms of its fine scale morphology revealed by mro hirise imagery the jarosite bearing unit has fracture patterns very similar to that observed in fe mg smectite bearing layers but unlike that observed in the al bearing phyllosilicate unit the ovoid shaped landform is situated in an east west bowl shaped depression superposed on a north sloping surface spectra of the ovoid shaped jarosite bearing landform also display an anomalously high 600 nm shoulder which may be consistent with the presence of goethite and a 1 92 m absorption which could indicate the presence of ferrihydrite goethite jarosite and ferrihydrite can be co precipitated and or form through transformation of schwertmannite both processes generally occurring under low ph conditions ph 2 4 to date this location appears to be unique in the mawrth vallis region and could represent precipitation of jarosite in acidic sulfur rich ponded water during the waning stages of drying

tectonics and topography for a lithosphere containing density heterogeneities the purpose of this paper is to clarify the dynamic role of lithospheric density heterogeneities in particular with respect to mountain building and other processes of intraplate deformation density anomalies within or just beneath the lithosphere constitute major sources for tectonic stress fields the product of their magnitude by their depth is shown to characterize their ability to induce deformation this rule of the density moment directly yields the lithospheric thickening or thinning rate when applied to structures of large lateral extent for anomalies of lateral extent that is small in comparison with their depth the deformation is vertically inhomogeneous and has been computed with the help of simple physical models of a stratified viscous newtonian lithosphere the analytical treatment is based on fourier transform continent continent collision thickens not only the crust but the entire lithosphere the cold root underlying a mountain chain induces strong regional compressive stresses able to sustain the mountain bulding process without further help from forces transmitted from far away thus the continental lithosphere is in a somewhat metastable mechanical state adiabatic i e rapid thickening or thinning tends to grow further once initiated tectonic phases of strong compression correspond to the climax of such instabilities the response of models with cold lithospheric roots of various intensities has been computed both in two and three dimensions they yield velocity distributions and stress fields instructive comparisons are made with earthquake focal mechanisms and in situ stress measurements in the alpine and appalachian regions in the presence of lateral variations of the mechanical properties of the lithosphere the tectonic style is not only function of the local topography and of the nature of its compensation deformations in neighbouring provinces are coupled as shown by 3 dimensional models for example thickening sustained by a cold lithospheric root may generate extension in peripheral zones of weakness these last results illustrate the point that the computation of regional tectonic stresses requires the knowledge of the density anomalies within the lithosphere on the one hand and of geometrical constraints related to lateral mechanical heterogeneities on the other

reports venus identification of banded terrain in the mountains of ishtar terra high resolution images obtained with the arecibo radar system at a wavelength of 12 6 centimeters reveal numerous parallel 10 to 20 kilometer wide bands of high radar backscatter situated on and oriented parallel to the major mountain ranges of the ishtar terra region of venus geometric and morphological characteristics suggest that the bands represent earth like tectonic deformational features such as folds and faults

venus gravity anomalies and their correlations with topography this report provides a summary of the high resolution gravity data obtained from the pioneer venus orbiter radio tracking data gravity maps covering a 70 latitude band through 360 of longitude are displayed as line of sight and vertical gravity topography converted to gravity and bouguer gravity maps are also shown in both systems topography to gravity ratios are made over several regions of the planet there are markedly different ratios for the aphrodite area as compared to the beta and atla areas

evidence for divergent plate boundary characteristics and crustal spreading on venus detailed examination of the topography and morphology of western aphrodite terra reveals numerous features that are similar to terrestrial divergent plate boundary characteristics individual domains between fracturezone like discontinuities contain a variety of bilaterally symmetrical topographic elements that suggest that topographic features have been created at rise crests rifted and separated and moved laterally to their present symmetrical positions the topographic and morphologic similarities together with strikingly similar mirror image map patterns on both sides of the rise axis suggest that western aphrodite terra shares the characteristics of oceanic divergent plate boundaries and is the site of crustal spreading on venus topographic profiles are consistent with spreading rates of the order of several centimeters per year

self similar dynamics of liquid injected into partially saturated aquifers the injection of liquid from a central well into a partially saturated aquifer of finite thickness is described using similarity solutions the solutions illustrate that injection leads to a growing zone around the source in which the fluid fills the whole depth of the aquifer beyond this zone the current adjusts to the depth in the far field as the fluid slumps under gravity the radial extent of the zone in which the aquifer is fully flooded depends on the ratio of the buoyancy driven flow speed to the pressure driven flow speed associated with the injection new laboratory experiments using a model porous medium support the model predictions in the case of an initially unsaturated layer the analysis is then developed to allow for a fully saturated aquifer containing fluid of lower density than the injectate and a further class of similarity solutions is developed again these are shown to be consistent with new laboratory experiments in concluding we briefly consider how the results may be combined to explore the self similar dynamics of a relatively dense fluid injected into an aquifer which is partially saturated with fluid of smaller density

mantle flow tectonics the influence of a ductile lower crust and implications for the formation of topographic uplands on venus convective flow within the interiors of terrestrial planets is a primary source of large scale topographic and tectonic features we treat the crust and mantle as a layered viscous half space and find solutions for flow driven by a buoyancy force distribution within the mantle and by relief at the surface and crust mantle boundary the crust initially responds to mantle upwelling with uplift but continued flow causes significant crustal thinning and subsidence downwelling leads to initial subsidence and subsequent crustal thickening and surface uplift changes in crustal thickness are driven by 1 vertical normal stresses due to mantle flow and 2 shear coupling of horizontal mantle flow into the crust the degree and time scale of crustal deformation are sensitive to crustal thickness and viscosity and the presence of elastic layers in the upper crust and mantle deformation can occur on time scales less than several hundred million years for reasonable values of these parameters strong or elastic upper crustal layers enhance crustal thinning or thickening while large viscosity contrasts between the lower crust and upper mantle or elastic mantle layers tend to diminish deformation for time dependent mantle flow due to a rising or sinking diapiric body crustal deformation depends upon the ratio of diapir radius to crustal thickness and the ratio of crustal to mantle viscosity a sinking diapir can lead to crustal thickening elevated topography and a specific sequence of time varying deformation while regions such as beta regio have long been suggested to result from convective upwelling in the venus mantle we suggest that a mantle downwelling origin is consistent with many of the characteristics of the compressional mountain ranges of western ishtar terra

on the role of caprock and fracture zones in dispersing gas plumes in the subsurface 1 waste stored in a geological disposal facility can generate gas and depending on the geological environment this gas may migrate into the rock mass here we develop a simplified physical model to describe the initial stages of the dispersal of a gas plume as it rises from such a geological disposal facility located at a depth of many hundreds of meters below the surface typically the plume becomes confined below a low permeability layer and then spreads laterally until reaching a fault or fracture zone when it may continue rising upward since the gas is soluble in the groundwater the gas may partially dissolve as it displaces the groundwater in addition in the generic geology considered herein since the source of gas gradually wanes with time the spreading plume tends to thin out leading to some residual trapping of the gas behind the plume we show that depending on the distance of the fault or fracture zone from the geological disposal facility different fractions of the source gas may be diverted farther upward into the formation rather than being trapped in the original layer this can have an important impact on the subsequent pattern of dispersal of the gas by the groundwater flows which may be key information in any safety assessment

geology of a rift zone on venus beta regio and devana chasma beta regio is a region of rifting and volcanism on venus the nature of beta a major topographic rise and rift zone is herein characterized using pioneer venus arecibo and venera 15 16 data high resolution 1 2 km arecibo and venera radar images reveal details of faulting and volcanism and pioneer venus altimetry illustrates the density and location of faults in relation to topography faults are distributed throughout beta but are concentrated in devana chasma where they are spaced 5 20 km apart the pattern of faulting and distribution and sequence of volcanic activity in beta can be used to help understand how the rift has evolved including the origin of the high topography of beta and the origin and nature of devana chasma on the basis of geologic mapping relations and map patterns beta appears to have formed as a result of doming in response to a mantle anomaly at the same time rhea mons a major shield volcano was formed formation of devana chasma followed with extensive faulting in the rift trough geometry of the trough and fault patterns suggests that some degree of lithospheric stretching has occurred later volcanism produced a second major shield volcano theia mons which is superimposed on the western bounding fault of the rift zone both uplift and extension have been involved in forming devana chasma and beta regio and may be important in the formation of other equatorial high land regions with systems of chasmata on venus such as aphrodite terra the bifurcation of devana chasma in the vicinity of theia mons and the extension of the rift system south to phoebe regio and west toward aphrodite terra suggest that their origins may be linked

a mechanism for tectonic deformation on venus in the absence of identifiable physiographic features directly associated with plate tectonics alternate mechanisms are sought for the intense tectonic deformation observed in radar images of venus one possible mechanism is direct coupling into an elastic lithosphere of the stresses associated with convective flow in the interior spectral green s function solutions have been obtained for stresses in an elastic lithosphere overlying a newtonian interior with an exponential depth dependence of viscosity and a specified surface density distribution driving the flow at long wavelengths and for a rigid elastic fluid boundary condition horizontal normal stresses in the elastic lid are controlled by the vertical shear stress gradient and are directly proportional to the depth of the density disturbance in the underlying fluid the depth and strength of density anomalies in the venusian interior inferred by analyses of long wavelength gravity data suggest that stresses in excess of 100 mpa would be generated in a 10 km thick elastic lid unless a low viscosity channel occurring beneath the lid or a positive viscosity gradient uncouples the flow stresses the great apparent depth of compensation of topographic features argues against this however thus supporting the importance of the coupling mechanism if there is no elastic lid stresses will also be very high near the surface providing also that the viscosity gradient is negative

buoyancy driven flow from a waning source through a porous leaky aquifer we develop a series of models to describe the migration of a buoyant fluid through a layered permeable rock following release from a localized waning source in particular if the fluid is injected into a high permeability layer bounded above by a layer of lower permeability a plume migrates along the interface with some draining into the low permeability layer if the current is sufficiently deep to overcome the capillary entry pressure we show the motion of the fluid is controlled by a number of key factors with the dominant dimensionless numbers being the time scale for the source to decay compared to the time scale for draining through the low permeability layer the residual saturation of the gas and water in the formation as that phase is displaced by the other phase and the capillary entry pressure as measured by the critical depth of the current required for draining as compared to the initial depth of the current simplified analytical models are presented to illustrate some of the key controls on and transitions in the flow and the models are used to explore leakage and trapping prior to flow reaching a fault zone

venus comparison of gravity and topography in the vicinity of beta regio the doppler tracking data obtained from the pioneer venus orbiter when it passed near beta regio yielded a peak vertical anomaly of 150 mgal when analyzed by our two stage procedure a comparison of maps of the gravity and topography at comparable resolution shows a striking correlation a scatter plot shows that the observed gravity anomaly is approximately 0 4 of that expected from uncompensated topography of half the mean density of venus however the spectral admittance shows that the gravity anomalies can not be explained either by airy compensation at fixed depth or by a model comprising an elastic plate atop an inviscid fluid the gravity and topography variations may signify deep compensation or dynamic support for beta regio and more shallow compensation for other features

comment on impact craters of venus a continuation of the analysis of data from the venera 15 and 16 spacecraft by a t basilevsky et al

venus limited extension and volcanism along zones of lithospheric weakness three global scale zones of possible tectonic origin are described as occurring along broad low rises within the equatorial highlands on venus lat 50 n to 50 s long 60 to 310 the two longest of these tectonic zones the aphrodite beta and themis atla zones extend for 21 000 and 14 000 km respectively several lines of evidence indicate that beta and atla regiones located at the only two intersections of the three major tectonic zones are dynamically supported volcanic terranes associated with currently active volcanism rift valleys south of aphrodite terra and between beta and phoebe regiones are characterized by 75 to 100 km widths raised rims and extensions of only a few tens of kilometers about the same magnitudes as in continental rifts on the earth horizontal extension on venus was probably restricted by an early choking off of plate motion by high crustal and upper mantle temperatures and the subsequent loss of water and an asthenosphere

the geology and geomorphology of the venus surface as revealed by the radar images obtained by veneras 15 and 16 a region by region condensed description of almost all of the area that was radar photographed by veneras 15 and 16 is presented using some generalizations the diversity of terrain was reduced to a discrete set from which a geological morphological map was constructed the predominant type of terrain of the studied area is a plain that was tentatively subdivided into five morphological types ridge and band patchy rolling plain dome and butte plain smooth plain and high smooth plain stratigraphically the ridge and band plains are the oldest and the smooth plains are the youngest the stratigraphic position of the other types is yet to be determined large sections of the plains show similarities to the mare type basaltic plains of the moon mercury and mars other types of terrain are combinations of ridges and grooves in various patterns linear parallel orthogonal diagonal or chevron like and chaotic in some places the ridge and groove terrain is stratigraphically below the plain material but in other places it appears to be plain material that has been subsequently deformed near the eastern and western boundaries of ishtar terra large several hundred kilometers in diameter ring like features can be seen that are named coronae or ovoids evidence of tectonic deformation and the presence of flow like patterns support their designation as volcano tectonic features beta regio seems to be an uplifted plain showing evidence of rifting and volcanism all types of terrain are sparesely peppered with craters of obvious impact morphology their average density gives the plain an age range of 0 5 to 1 109 years the fact that many impact craters are still in the pristine state indicates a very low rate of surface reworking at least for the last 0 5 to 1 109 years no evidence for water erosion sedimentation processes has been found the tectonic activity of venus has no equivalent on the moon mercury or even mars and can be compared only with that of the earth intensive horizontal deformation previously known only on earth occurs on venus but in a characteristic venusian style

hydrochemical performance and mineralogical evolution of a dispersed alkaline substrate das remediating the highly polluted acid mine drainage in the full scale passive treatment of mina esperanza sw spain acid mine drainage remediation is an unresolved matter in abandoned mining districts around the world development and implementation of passive treatment systems in these areas are commonly focused on engineering and water quality aspects neoformed mineral phases precipitated within the reactive material of these passive treatments account for the removal of pollutants but also can cause clogging and passivation of the reactive substrate after 20 months of operation and monitoring the limestone based passive treatment system implemented in mina esperanza sw spain was sampled to study the relationship between water chemistry mineral composition of the neoformed precipitates and treatment performance water chemical profiles show the existence of three precipitation zones controlled by fe al and zn hydrochemistry and also a migration with time of precipitation zones downward into the reactive material these precipitation zones were also confirmed by a mineral study performed on the solid samples where either schwertmannite and goethite or hydrobasaluminite and zn rich green rust were the mineral phases that controlled the metal removal in the three precipation fe al or zn zones iron and al precipitates were observed to play a critical role in the time evolution of the reactive material hydraulic conductivity furthermore al precipitates passivated to some extent the limestone grains by armoring although migration of the fe precipitation zone and al redissolution later activated the limestone grains a higher proportion of limestone in the reactive mixture and the addition of new reagents to the bottom section of the reactive material to enhance the reducing environment and to promote divalent metal removal are proposed on the basis of this hydrochemical and mineralogical study for a future design for the mina esperanza passive treatment system

seasonal variations in the formation of al and si rich fe stromatolites in the highly polluted acid mine drainage of agua agria creek tharsis sw spain abstract the study of the different biotic and abiotic processes involved in the current formation of fe stromatolites in rivers affected by acid mine drainage amd is essential not only to understand this unique and extreme environment but also to achieve a better understanding of the past iron formation on the earth and on mars the fe stromatolites studied in the highly polluted amd in tharsis sw spain revealed a unique mineral assemblage with jarosite and rostite as the most unexpected fe and al phases and goethite and schwertmannite as the main constituents seasonal variations in this region greatly affected the composition of the precipitates and the distribution of diatoms within the fe stromatolites drought and flood events were also recognized in the sedimentary textures and in the mineral assemblages observed of particular layers within the fe stromatolites the characterization of the chemical and mineralogical composition of fe stromatolites in tharsis as well as the different formation mechanisms proposed complement the existing literature on newly formed fe stromatolites and provides new observations to increase our understanding of those extreme environments

characterization of venera 15 16 geologic units from pioneer venus reflectivity and roughness data abstract geologic units have been defined for the surface of venus from venera 15 16 image data a characterization of these geologic units is carried out using information on surface properties derived from pioneer venus pv reflectivity and rms slope data the geologic context provided by venera 15 16 units allows additional more specific interpretations of surface radar properties to be made characterization of venera units results in the definition of four groups of venera units i smooth rocky units ii rough rocky units iii rough high dielectric units and iv diffusely scattering units on the basis of correlations of surface morphology to spatial and statistical distributions in rms slope and reflectivity data we test models for the origin of the surface properties of some units we conclude that plains and tectonic units can be contrasted in terms of the average roughness of the surface and that tectonic deformation appears to roughen the surface at 0 5 to 10 m and 5 to 50 cm scales this tectonic weathering process appears to dominate the erosional regime of venus unlike earth or mars production and transport of soils dominates only a small portion 5 of the surface some of the venera units display distinctive spatial and statistical distributions of pv radar data in particular apparent low reflectivity in the tesserae appears to be caused by small 5 50 cm rock fragments on the surface which cause diffuse scattering at pioneer venus wavelenghts analysis of models for the formation of these fragments suggests that they are due to the pervasive deformation undergone by the tesserae finally aspects of this study have been used to extend results of venera image data analysis southward of 30 n lat resulting in a prediction of the distribution of tessera such results can aid in magellan investigations

geochemistry of dissolved aluminum at low ph hydrobasaluminite formation and interaction with trace metals silica and microbial cells under anoxic conditions abstract the precipitation of dissolved aluminum is among the most important geochemical processes affecting the water chemistry and trace metal dynamics of acid mine drainage amd in this study we focus on the in situ formation of al precipitates and their subsequent interaction with trace metals dissolved silica and microbial cells under anoxic conditions e g deep strata of pit lakes flooded underground mines in the presence of sulfate 0 1 0 2 m dissolved aluminum precipitates at ph 4 0 and forms an amorphous globular hydroxysulfate precipitate with composition corresponding to hydrobasaluminite this proto hydrobasaluminite shows an important capacity to incorporate sio 2 aq divalent metal cations fe ii pb ii be ii and many anion forming trace elements as cr sb v se u by coprecipitation removal efficiencies obtained experimentally with freshly formed hydrobasaluminite under anoxic and oxic conditions were consistent with metal profiles obtained in the pit lakes and suggest that the behaviour of many toxic metals is closely linked to the al particles detailed transmission electron microscopy tem shows that hydrobasaluminite may coexist with more crystalline minerals like gibbsite bayerite and or allophane which are present as nanocrystals embedded in the amorphous matrix and appear to form by transformation of the former hydrobasaluminite precipitation is favoured by the activity of iron and sulfate reducing microbes in the water column and at the sediment water interface our study shows that at solubility equilibrium microbial cells often serve as nuclei for al precipitation further chemical mapping of al coated cells by scanning tem shows an important incorporation of sio 2 fe 2 valence confirmed by electron energy loss spectroscopy and other metal cations e g mg 2 in the al cell coatings as compared to al particles presumed to form via abiotic precipitation these al cell coatings are amorphous to x rays and their compositions likely result from coprecipitation of sio 2 and fe 2 resulting in si rich and fe ii rich hydrobasaluminite the disparity between field and laboratory data the serendipitous detection of nontronite like smectite in precipitates formed in the acidic waters under laboratory conditions and the apparent saturation with respect to different clay minerals e g kaolinite halloysite are all evidences suggesting thermodynamic feasibility of aluminosilicate precursor formation in these systems

sorption of trace metals to an aluminum precipitate in a stream receiving acid rock drainage snake river summit county colorado the quality of water in streams that are contaminated by acid drainage from mines and from the weathering of mineralized rocks improves as the water flows downstream the purpose of this study was to investigate the geochemical processes that occur in one such stream and to determine the fate of the trace metals that are removed from the water the stream chosen for this purpose was the snake river summit county colorado which is affected by natural acid rock drainage ard containing so4 al fe and various trace elements such as zn cu pb ni and others most of the fe in the snake river is removed from solution by the oxidation of fe2 to fe3 and the subsequent precipitation of fe oxyhydroxides that form a massive ferricrete deposit near the springs that feed the river further downstream the snake river ph 3 0 mixes with water from deer creek ph 7 0 thereby increasing its ph to 6 3 and causing so4 rich precipitates of al oxyhydroxide to form the precipitates and associated organic c complexes sorb trace metals from the water and thus have high concentrations of certain elements including zn 540 11 400 ppm cu 34 221 ppm pb 90 340 ppm and ni 11 197 ppm the concentrations of these elements in the precipitates that coat the streambed rise steeply in the zone of mixing and then decline downstream the trace element concentrations of the water in the mixing zone at the confluence with deer creek decrease by 75 or more and are up to 3 orders of magnitude lower than those of the precipitates sorption curves for zn cu pb ni and so4 were derived by stepwise neutralization of a sample of snake river water collected above the confluence with deer creek and indicate that the trace metals are sorbed preferentially with increasing ph in the general order pb cu zn and ni sulfate is removed between ph 4 and 5 to form an al hydroxysulfate and or by sorption to microcrystalline gibbsite the sorption data determined from the neutralization experiment were used to account for the downstream decrease of trace metal concentrations in the precipitates the results of this study demonstrate that the partitioning of trace metals in the snake river is not only a function of ph but also depends on the progressive removal of trace metals as the water of the snake river flows through its confluence with deer creek the chemical composition of the water also determines what compounds precipitate with increasing ph

gravity driven deformation of the crust on venus intense horizontal deformation features are observed on the surface of venus despite the apparent absence of terrestrial style plate tectonics high surface temperature low erosion rate and regions of elevated terrain suggest that gravity spreading may be responsible for some of these features gravity spreading on the earth is known to cause extensive deformation in certain thin skinned tectonic regions where the uppermost layers become detached along a decollement while the high pore pressures and soft sedimentary rocks frequently observed along decollements on the earth are not plausible for venus temperature induced regions of ductile deformation may exist simple viscous models of gravity spreading above a ductile region of the crust are developed to examine the effects of rheology thermal gradient surface slope and crustal thickness on deformation for a reasonable range of parameters the models show that surface slope driven ductile deformation at relatively shallow depths in the crust is possible and may be capable of detaching the uppermost rigid portion of the crust resulting in horizontal translation

aluminum mobility in mildly acidic mine drainage interactions between hydrobasaluminite silica and trace metals from the nano to the meso scale abstract aluminum precipitates control the hydrochemistry and mineralogy of a broad variety of environments on earth e g acid mine drainage amd coastal wetlands boreal and alpine streams tropical acid sulfate soils laterites and bauxites however the geochemical and mineralogical processes controlling al and other associated metals and metalloids transport and removal in those environments are not fully understood the geochemical system of paradise portal colorado usa comprises sulfate rich mildly acidic waters the hydrochemistry of which is directly controlled by the massive precipitation of hydrobasaluminite al4 so4 oh 10 12 36h2o three connected but discernible aluminum precipitation stages were identified and described 1 nanoparticle formation and size decrease along the creek 2 hydrobasaluminite neoformation on the riverbed and 3 precipitate accretion and accumulation on the riverbed leading to al and fe banded formations the co occurrence of al and si in the system was observed recording significant amounts of si accompanying the three different components of the system i e nanoparticles and fresh and aged al precipitates also abrupt and minor changes in the sedimentary record were described and proposed to be the response of the system to seasonal and interannual changes in amd chemistry concerning the mobility of other metals and metalloids p th v w ti and b showed a tendency to be preferentially incorporated into hydrobasaluminite while others like be as se or ba tend to remain dissolved in the water

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

capillary entry pressure and the leakage of gravity currents through a sloping layered permeable rock we examine the motion of a buoyant fluid injected into a water saturated porous rock as it spreads along a thin inclined low permeability barrier we account for leakage of the fluid across the barrier once the current is sufficiently deep so that the pressure exceeds the capillary threshold we show that at some distance from the source the pressure decreases below this threshold and all the remaining flux spreads laterally along the barrier we examine the controls on the partitioning of the flow between the draining flux and the laterally spreading flux and also the controls on the lateral extent of the draining region for the case of an instantaneous release and a maintained release of fluid we consider the implications of our work for the dispersal of co 2 plumes which may be sequestered in deep saline aquifers

the effect of drainage on the capillary retention of co2 in a layered permeable rock buoyant plumes of co 2 spreading through water saturated permeable rock bounded by layers of lower permeability tend to spread laterally as they advance they may gradually leak through fractures or discontinuities in the lower permeability boundary leading to a gradual waning of the original plume and dispersal of co 2 higher in the formation with a finite release of co 2 the trailing edge of the plume recedes with time and capillary forces tend to trap a fraction of this co 2 within the pore space this also leads to a gradual waning of the plume with time and limits the mass of co 2 which can leak through the boundary and rise higher into the formation we explore the balance between these two effects and calculate some of the controls on the fraction of the co 2 plume which becomes trapped within the original layer of rock

iron and aluminum hydroxysulfates from acid sulfate waters acid sulfate waters are produced mostly by the oxidation of common sulfide minerals such as pyrite chalcopyrite pyrrhotite and marcasite in rocks soils sediments and industrial wastes this spontaneous process of mineral weathering plays a fundamental role in the supergene alteration of ore deposits the formation of acid sulfate soils and the mobilization and release of acidity and metals to surface and ground waters the purely natural process of acid rock drainage is often intensified by human activities related to mining mineral processing construction soil drainage and dredging geochemical reaction rates are accelerated because physical disturbance gives greater exposure of mineral surfaces to air and water and to microbes that catalyze the reaction process large quantities of reactive sulfides are also concentrated and exposed to air as a result of mining and mineral processing acid sulfate waters produce a number of fairly insoluble hydroxysulfate and oxyhydroxide minerals that precipitate during oxidation hydrolysis and neutralization the objective of this chapter is to describe the formation properties fate and environmental implications of the nano to microphase hydroxy sulfates of fe and al that are precipitated from acid sulfate waters these minerals are commonly of poor crystallinity and difficult to characterize much remains to be learned about their occurrence formation and properties mine drainage the best known examples of acid sulfate waters are those released from mines where coal and metallic sulfide ores have been exploited ash et al 1951 barton 1978 nordstrom 1982a rose and cravotta 1998 nordstrom and alpers 1999 there may be as many as 500 000 inactive or abandoned mine sites in the united states alone lyon et al 1993 although most of these pose no immediate water quality problem kleinmann 1989 estimated that about 19 300 km of streams and more than 72 000 ha of lakes and reservoirs have been

on the flow of buoyant fluid injected into a confined inclined aquifer we study the dispersal of a plume of incompressible buoyant fluid injected into a confined sloping aquifer which has an outflow at a single fault which may be up dip up slope or down dip down slope from the point of injection we develop a long time asymptotic solution for the motion of the injected fluid we show that for the case in which the outflow fault is up dip from the point of injection there is a critical injection rate above which the injected fluid floods the full depth of the aquifer and we show that for the case in which the outflow fault is down dip from the point of injection there is a critical injection rate below which all injected fluid initially flows up dip our analysis leads to expressions for the lateral extent of the injected fluid as a function of time and we consider the implications of the model for the dispersal of supercritical carbon dioxide injected into deep saline aquifers the work also indicates that the geometry of the system may have a significant effect on i the total volume of carbon dioxide which it is possible to sequester in a faulted aquifer and ii the interpretation of the dispersed position of any injected tracers

plate tectonics on venus the high surface temperature of venus implies a permanently buoyant lithosphere and a thick basaltic crust terrestrial style tectonics with deep subduction and crustal recycling is not possible overthickened basaltic crust partially melts instead of converting to eclogite because mantle magmas do not have convenient access to the surface the 40 ar abundance in the atmosphere should be low venus may provide an analog to archean tectonics on the earth

topographic controls on gravity currents in porous media we present a theoretical and experimental study of the propagation of gravity currents in porous media with variations in the topography over which they flow motivated in part by the sequestration of carbon dioxide in saline aquifers we consider cases where the height of the topography slopes upwards in the direction of the flow and is proportional to the nth power of the horizontal distance from a line or point source of a constant volumetric flux in two dimensional cases with n 1 2 the current evolves from a self similar form at early times when the effects of variations in topography are negligible towards a late time regime that has an approximately horizontal upper surface and whose evolution is dictated entirely by the geometry of the topography for n 0 result in a transition from an early time similarity solution towards a topographically controlled regime that has an approximately horizontal free surface we also analyse the evolution over topography that can vary with different curvatures and topographic exponents between the two horizontal dimensions finding that the flow transitions towards a horizontally topped regime at a rate which depends strongly on the ratio of the curvatures along the principle axes finally we apply our mathematical solutions to the geophysical setting at the sleipner field concluding that topographic influence is unlikely to explain the observed non axisymmetric flow

venus gravity analysis of beta regio radio tracking data acquired over beta regio were analyzed to obtain a surface mass distribution from which a detailed vertical gravity field was derived in addition a corresponding vertical gravity field was evaluated solely from the topography of the beta region a comparison of these two maps confirms the strong correlation between gravity and topography which was previously seen in line of sight gravity maps it also demonstrates that the observed gravity is a significant fraction of that predicted from the topography alone the effective depth of complete isostatic compensation for the beta region is estimated to be 330 km which is somewhat deeper than that found for other areas of venus