the stone and boulder content of swedish forest soils abstract stone and boulder content has a strong influence on many soil processes and is a crucial factor to take into account when estimating element pools in this paper we present the results of a large scale inventory of the stone and boulder content of forest soils which employed a surface penetration method viro s method in 1943 plots across sweden the volume of stones and boulders was 43 4 on average although it was 47 6 for the most common soil type on glacial till parent material the variation was spatially correlated and there were regional patterns which were related to bedrock composition and quaternary development a stoniness function was developed for the upper 30 cm of the mineral soil and this was used to translate the penetration depths into stone and boulder content the function was based on a reference data set of 200 soil pits a relationship was found between stone and boulder content and surface boulder frequency but the strength of the relationship varied regionally in some regions surface boulders may provide an indicator of stone and boulder content in the soil

coupling of thermal evolution and despinning of early iapetus abstract the cassini mission revealed two spectacular characteristics of iapetus 1 a geologically old and high equatorial ridge which is unique in the solar system and 2 a large flattening of 35 km consistent with the equilibrium figure for a hydrostatic body rotating with a period of 16 h whereas the current spin period is 79 33 days this study describes three dimensional simulations of solid state convection within an undifferentiated iapetus it investigates the implications for the evolution of the interior thermal structure and its spin rate and global shape using radially layered viscoelastic models the role of the concentration in the short lived radiogenic element 26 al just after accretion is completed is specifically addressed the first result is to show that whatever the 26 al value convection occurs as suggested by castillo rogez et al castillo rogez j matson d sotin c johnson t lunine j thomas p 2007 icarus 190 179 202 convection reduces the warming of the interior compared to the conductive evolution and therefore limits the conditions for despinning in our calculations two conceptual linear viscoelastic models are used when considering a maxwell rheology the interior temperature viscosity never reaches a value high low enough to induce despinning in order to promote dissipation at low temperature a burgers rheology which includes an additional dissipation peak is introduced for favorable parameter values this latter rheology leads to despinning however only models associated with large amounts of short lived radiogenic elements 26 al 25 ppb lead to the observed flattening this suggests that the accretion process needs to be completed shortly after the formation of cais calcium aluminum rich inclusions 4 myr for 26 al varying between 72 and 46 ppb the observed flattening is obtained only for a limited range of initial spin period between 9 5 and 10 2 h for 26 al ranging between 30 and 15 ppb initial spin rates smaller than 8 5 h are required for smaller values of 26 al the body is too cold and viscous to acquire a significant flattening even if a rotation period close to the body disruption limit is considered even with a thin lithosphere during the early stage our simulations show that iapetus never reaches the equilibrium figure for a hydrostatic body due to the non zero rigidity of the lithosphere the 35 km value of the flattening is the result of the partial relaxation of an ancient larger flattening ranging between 45 and 80 km depending on the evolution of the lithosphere thickness mainly controlled by the radiogenic content a thin lithosphere is consistent with an early building of the equatorial ridge the lithosphere thickening due to interior cooling can explain the preservation of the ridge throughout the remaining evolution of iapetus

simplified models of spreading flow of dry granular material shallow flow integrated numerical models of landslide and avalanche motion have recently experienced rapid development an important aspect of model development is verification to show that models

rheological properties of water ice applications to satellites of the outer planets 1 abstract the icy moons of the outer solar system have not been quiescent bodies in part because many have a substantial water component and have experienced significant internal heating we can begin to understand the thermal evolution of the moons and the rate of viscous relaxation of surface topography because we now have good constraints on how ice in several of its polymorphic forms flows under deviatoric stress at planetary conditions details of laboratory derived flow laws for pure polycrystalline ice are reviewed in detail one of the more important questions at hand is the role of ice grain size grain size may be a dynamic quantity within the icy moons and it may or may not significantly affect rheology one recent beneficiary of revelations about grain size sensitive flow is the calculation of the rheological structure of europa s outer ice shell which may be no thicker than 20 km

two phase natural convection implications for crystal settling in magma chambers abstract crystal settling is no longer thought to be the most likely mechanism operating in the formation of layered igneous intrusions the main objection raised against its feasibility is the prediction that crystal settling velocities are likely to be orders of magnitude smaller than convective velocities and that vigorous convection would therefore keep crystals well mixed within the interior of a magma chamber in previous theoretical and numerical investigations of crystal settling no account has been taken of compositional buoyancy gradients created by the interpenetration of crystals and melt this paper includes these effects the results of two dimensional numerical simulations show that parameter regimes exist in which effective crystal settling occurs in infinite prandtl number thermally convecting two phase fluids even for small ratios of settling to convective velocity

assessing textural variation in laminated sands using digital image analysis of thin sections although between laminae parameter variations in sediments have been studied in the past measured parameters were generally limited to grain size distribution and total porosity the magnitude and directional characteristics of physical properties of laminated sediments also depend on the shape and orientation of particles packing pore size characteristics and properties of the pore network leaving out a complete characterization of granular sediment in models of physical properties could result in a systematic mismatch between modeled and measured values however tools for high resolution quantification of these spatial variable parameters are not readily available in order to provide such a tool an image analysis procedure is presented based on digital images of thin sections the procedure defines a sequence of rectangular measurement windows with their long sides oriented parallel to stratification and measures the sediment characteristics for each window logs of parameters values oriented perpendicular to stratification are thus created after verification of the image analysis procedure using comparative laboratory measurements the procedure is applied to two thin section images of unconsolidated fine grained laminated sands the quantitative variations observed in the logs of grain and pore characteristics correlate well with bedding observed on the original images overall the image analysis procedure proved to be a useful and versatile tool for quantifying variations of textural characteristics on sub lamina scale

thermal convection in a volumetrically heated infinite prandtl number fluid with strongly temperature dependent viscosity implications for planetary thermal evolution parameterized models of the thermal evolution of planets are usually based on the assumption that the lithosphere convecting mantle boundary can be defined by an isotherm at a temperature below which viscosity is infinite on geologic timescales recent experimental results argue against this assumption we have investigated both the definition of the lithosphere convecting mantle boundary and the power law relation describing convecting heat transfer based on numerical experiments of thermal convection in a volumetrically heated fluid with temperature dependent viscosity other recent studies have treated only the heating from below but volumetric heating is likely to be the dominant mode of heating in planetary mantles either as a consequence of radioactive heating or as a proxy for secular cooling convection can occur either in the whole box or be located under a stagnant lid in the lid regime convection is driven by a temperature contrast depending on the rheology of the fluid and the interior temperature this result in agreement with experimental studies indicates that boundary between the stagnant lid and the convecting layer similar to the lithosphere convecting mantle boundary cannot be defined as a fixed isotherm during thermal evolution of planets the viscosity contrast in the convecting mantle remains constant not the temperature at the bottom of the lithosphere we present an example showing that the evolution of planets is strongly dependent on the criterion chosen to define the lithosphere convecting mantle boundary for reasonable values of the activation energy for thermally activated creep the temperature defining the lithosphere convecting mantle boundary the mantle temperature and the thickness of the lithosphere could be larger than expected from previous models which treat the base of the lithosphere as a fixed isotherm

effects of dispersed particulates on the rheology of water ice at planetary conditions we have investigated the effects of initial grain size and hard particulate impurities on the transient and steady state flow of water ice i at laboratory conditions selected to provide more quantitative constraints on the thermomechanical evolution of the giant icy moons of the outer solar system our samples were molded with particulate volume fractions of 0 001 to 0 56 and particle sizes of 1 to 150 m deformation experiments were conducted at constant shortening rates of 4 4 10 7 to 4 9 10 4 s 1 at pressures of 50 and 100 mpa and temperatures 77 to 223 k for the pure ice samples initial grain sizes were 0 2 0 6 mm 0 75 1 75 mm and 1 25 2 5 mm stress strain curves of pure ice i under these conditions display a strength maximum u at plastic strains e 0 01 after initial yield followed by strain softening and achievement of steady state levels of stress ss at e 0 1 to 0 2 finer starting grain size in pure ice generally raises the level of u petrography indicates that the initial transient flow behavior is associated with the nucleation and growth of recrystallized ice grains and the approach to ss evidently corresponds to the development of a steady state grain texture effects of particulate concentrations 0 1 are slight at these concentrations a small but significant reduction in u with respect to that for pure water ice occurs mixed phase ice with 0 1 is significantly stronger than pure ice the strength of samples with 0 56 approaches that of dry confined sand the magnitude of the strengthening effect is far greater than expected from homogeneous strain rate enhancement in the ice fraction or from pinning of dislocations orowan hardening this result suggests viscous drag occurs in the ice as it flows around the hard particulates mixed phase ice is also tougher than pure ice extending the range of bulk plastic deformation versus faulting to lower temperatures and higher strain rates the high pressure phase ice ii formed in 0 56 mixed phase ice during deformation at high stresses bulk planetary compositions of ice rock 0 4 0 5 are roughly 2 orders of magnitude more viscous than pure ice promoting the likelihood of thermal instability inside giant icy moons and possibly explaining the retention of crater topography on icy planetary surfaces

soil containing rock fragments effects on infiltration abstract infiltration is a very complex process rock fragments affect infiltration by their presence in the soil matrix and on the soil surface procedures for quantifying soil and surface rock fragments are reviewed within the soil the physical properties and hydraulic properties that affect infiltration are shown to be influenced by rock fragments physical properties discussed are bulk density porosity and water content hydraulic properties that affect infiltration are water retention saturated conductivity and unsaturated conductivity rock fragments on the soil surface have been reported to both increase or decrease infiltration rates and amounts

origin of ice diapirism true polar wander subsurface ocean and tiger stripes of enceladus driven by compositional convection abstract we consider the scenario in which the presence of ammonia in the bulk composition of enceladus plays a pivotal role in its thermochemical evolution because ammonia reduces the melting temperature of the ice shell by 100 k below that of pure water ice small amounts of tidal dissipation can power an ammonia feedback mechanism that leads to secondary differentiation of enceladus within the ice shell this leads to compositionally distinct zones at the base of the ice shell arranged such that a layer of lower density and compositionally buoyant pure water ice underlies the undifferentiated ammonia dihydrate ice layer above we then consider a large scale instability arising from the pure water ice layer and use a numerical model to explore the dynamics of compositional convection within the ice shell of enceladus the instability of the layer can easily account for a diapir that is hemispherical in scale as it rises to the surface it co advects the warm internal temperatures towards the outer layers of the satellite this advected heat facilitates the generation of a subsurface ocean within the ice shell of enceladus this scenario can simultaneously account for the origin of asymmetry in surface deformation observed on enceladus as well as two global features inferred to exist a large density anomaly within the interior and a subsurface ocean underneath the south polar region

evolutionary structures in double diffusive convection in magma chambers finite amplitude solutions to subcritical time dependent double diffusive convection d d c applicable for magma chambers are obtained by a two dimensional finite element method based on stream function temperature and compositional fields grid refinement is used for resolving the disparately scaled thermal and chemical boundary layers present for large ratios of the thermal to chemical diffusivity lewis number characteristic of magmas the occurrence of layered convection depends strongly on the initial conditions of the temperature and composition it is shown that in the infinite prandtl number limit a local transition from a diffusive to a finger like regime can take place for large enough lewis numbers this time dependent finding suggests that a strict categorization of d d c into the finger and diffusive regimes requires modification in geological applications

early stage weathering systematics of pb and nd isotopes derived from a high alpine holocene lake sediment record highlights deglacial chemical weathering monitored by adsorbed isotopic and elemental signals resilience of authigenic geochemical signals towards variable lake redox conditions pronounced early deglacial weathering of labile accessory minerals remarkably congruent uranogenic and reduced thorogenic pb isotope release anthropogenic atmospherically deposited pb pollution since over 2000 years abstract radiogenic pb and nd isotopes are well established tools in paleoceanographic science tracing ambient climate and continental runoff to the oceans down to sub millennial timescales particularly in case of pb isotopes a clear climate dependency of continental isotopic runoff on glacial interglacial transitions has been observed pb isotopes were reported to be released incongruently during initial chemical weathering this incongruent release implies that pb isotopic runoff compositions differ from the bulk catchment pb isotopic signal yet only little is known about the processes leading to the incongruent release and the timescales of weathering on the continents in this study we targeted the adsorbed trace metal signature in sediments from a swiss high alpine lake that have accumulated since the retreat of the large alpine ice domes during the last deglaciation to investigate initial pb and nd isotope weathering processes in a granitic environment additionally selected adsorbed element concentrations and ratios were analysed to complement the isotopic physico chemical weathering information the integrity of the presented isotope records is supported by further investigation into the lake environment e g oxic anoxic conditions and its potential influence on the isotopic record the pb isotope records during the early lake phase witnessed high amplitude isotopic fluctuations linked to the initial chemical weathering of fine glacial substrate this finding is also supported by the lithology of the core and rapidly decreasing adsorbed th and u concentrations following this early lake phase the majority of the holocene traced congruent release of 207pb 204pb and 206pb 204pb and a significant depletion of 208pb 204pb in the adsorbed phase these findings corroborate earlier suggestions of more effective weathering of uranogenic minerals yet also call for the presence of more weathering resistant thorogenic minerals in the lake catchment the latest 2 2 ka of the record are significantly overprinted by anthropogenic pb deposition coinciding with the rise and fall of the roman empire finally our data suggest that nd isotopes are equally affected by incongruent weathering during the initial deglacial weathering processes albeit at smaller magnitude than seen for pb isotopes

three layered models of ganymede and callisto compositions structures and aspects of evolution abstract three layered structural models are determined for ganymede and callisto each consists of a rock core a mixed ice rock lower mantle and a pure ice upper mantle this structure results from differentiation subsequent to accretional melting attention is given to evaluating various candidates for the rock component and three alternatives representing various degrees of silicate hydration and oxidation are modeled and incorporated structures are calculated on the basis of a 250 k isotherm which is a reasonablev approximation to the gentle adiabats expected to occur in icy satellites differentiation of an ice rock satellite generally involves an increase in radius and the three layered approach allows this process to be examined in some detail it is determined that satellite expansion is most significant early in the process and much less so as differentiation proceeds to completion if tectonics are due to global expansion distinguishing on this basis between a completely differentiated satellite and one that is only partially differentiated is difficult the postaccretional global expansion of ganymede which may have left a tectonic record was probably limited to 1 in radius in agreement with observed limits useful quantities such as silicate mass and volume fraction uncompressed density j2 c22 binding energy and surface heat flow are also determined nonhydrostatic contributions to j2 and c22 are estimated and shown to be nonnegligible encounters with jupiter orbiting spacecraft are unlikely to determine callisto s degree of central condensation we conclude by calculating the relative likelihood of postaccretional melting caused by radiogenic heating three layered satellites have generally hotter interiors because additional thermal boundary layers divide the separately convecting upper and lower mantles inhibiting heat transport ganymedes and callistos that are less than about 1 3 differentiated by mass should experience a second episode of melting as these boundary layers are either above the level of the water ice minimum melting temperature or intersect the melting curve at deeper levels runaway differentiation to at least a depth corresponding to a pressure in the ice v stability field is likely the main point here is that if satellite tectonics are tied to differentiation by melting or its aftermath as in the instability following ocean closure of kirk and stevenson moderate or small amounts of accretional differentiation are unlikely to explain an absence of tectonics as in callisto because extensive differentiation ultimately occurs

sample size for determination of coarse fragment content in a stony soil abstract particle size analysis of soils containing coarse fragments requires sufficient amounts of soil material we tried to quantify the sample volume for coarse fragment measurements in a rendzina soil with more than 50 coarse fragment content a monolith of 50 cm 80 cm was excavated to a depth of 160 cm hardened with an epoxy resin and cut into six cross sections the coarse fragment contents were determined on the cross sections by counting the aerial fractions belonging to the fine earth fine gravel and gravel classes additionally 24 samples with a volume of 3 2 to 4 5 1 were sieved to determine the coarse fragment content the contents estimated from the cross sections equalled the contents measured with particle size analysis the data were evaluated in terms of the representative elementary area and volume the coarse fragment content as a function of the sampling size exhibited the features of the representative elementary volume graph the side length of the representative elementary area ranged from 11 to 19 cm the estimated representative elementary volume ranged from 400 to 2 100 cm 3

the savage hutter avalanche model how far can it be pushed the savage hutter sh avalanche model is a depth averaged dynamical model of a fluid like continuum implementing the following simplifying assumptions i density preserving ii shallowness of the avalanche piles and small topographic curvatures iii coulomb type sliding with bed friction angle delta and iv mohr coulomb behaviour in the interior with internal angle of friction phi or delta and an ad hoc assumption reducing the number of mohr s circles in three dimensional stress states to one we scrutinize the available literature on information regarding these assumptions and thus delineate the ranges of validity of the proposed model equations the discussion is limited to relatively large snow avalanches with negligible powder snow component and laboratory sand avalanches starting on steep slopes the conclusion of the analysis is that the sh model is a valid model for sand avalanches but its mohr coulomb sliding law may have to be complemented for snow avalanches by a second velocity dependent contribution for very small snow avalanches and for laboratory avalanches starting on moderately steep and bumpy slopes it may not be adequate

a model for the interior structure evolution and differentiation of callisto abstract the recently measured dimensionless moment of inertia moi factor for callisto of 0 3549 0 0042 anderson et al 2001 icarus 153 157 161 poses a problem its value cannot be explained by a model in which callisto is completely differentiated into an ice shell above a rock shell and an iron core such as its neighboring satellite ganymede nor can it be explained by a model of a homogeneous undifferentiated ice rock satellite we show that callisto may be incompletely differentiated into an outer ice rock shell in which the volumetric rock concentration is close to the primordial one at the surface and decreases approximately linearly with depth an ice mantle mostly depleted of rock and an about 1800 km rock ice core in which the rock concentration is close to the close packing limit the ice rock shell thickness depends on uncertain rheology parameters and the heat flow and can be roughly 50 to 150 km thick we show that if callisto accreted from a mix of metal bearing rock and ice and if the average size of the rocks was of the order of meters to tens of meters then callisto may have experienced a gradual but still incomplete unmixing of the two components an ocean in callisto at a depth of 100 200 km is difficult to obtain if the ice is pure h2o and if the ice rock lithosphere is 100 km or more thick a water ocean is more plausible for ice contaminated by ammonia methane or salts or for pure h2o at a depth of 400 600 km

convection and lithospheric strength in dione an icy satellite of saturn abstract finite element numerical simulations for the structure of convection cells within a self gravitating boussinesq fluid sphere with variable viscosity are used to determine temperature distribution stream functions velocities and intensities of the stresses within dione an icy satellite of saturn a non newtonian i e stress dependent viscosity is considered but the numerical simulation according to u r christensen 1984a geophys j r astron soc 77 343 384 is carried out knowing that the properties of power law convection can be closely simulated by newtonian flow with a reduced value of the activation enthalpy the initial temperature profile has been determined taking into account the amount of energy trapped as heat during the accumulation process and the other energy source is the radioactivity of the long lived isotopes the obtained results seem to show a long duration endogenic activity in agreement with the geological observations the intensities of the stress are able to fracture the icy crust both in extensional and in compressional regimes the thickness of the mechanical lithosphere evolves in a way determined by the complex interplay of the lithospheric temperature gradient and the strain rate

estimating stone and boulder content in forest soils evaluating the potential of surface penetration methods abstract given the amount and variation of stones and boulders in forest soils it is remarkable that little attention has been paid to this property in the analysis and modelling of soil processes this study aims a to investigate the stoniness relative volume of stones and boulders of representative forest soils in central sweden b to evaluate the possibilities to predict soil stoniness with non destructive surface penetration methods particularly the rod penetration method suggested by viro in 1952 the content of stones and boulders down to 0 4 m depth in forest till were quantified in 200 systematically distributed pits the mean content of stones and boulders was 0 50 with a range of 0 14 0 78 penetration depths were useful as predictors only for cases of stoniness below 0 50 where 75 of the variation could be explained the general evaluation of surface penetration methods revealed that large errors in very stony soils cannot be avoided the major source of error is inherent in the method and not caused by sampling this conclusion may lower expectations that ground penetrating radar systems will become useful for predicting stoniness

limiting stress states in granular avalanches the savag e hutter theory for granular avalanches assumes that the granular material is in either of two limiting stress states depending on whether the motion is convergent or divergent at transitions between convergent and divergent regions ajump in stress occurs which necessarily implies that there is ajump in the ava lanche velocity and or its thickness in this paper a regularization scheme is used which smoothly switches from one stress state to the other and avoids the generation of such singular surfaces the resulting algorithm is more stable than previous numerical meth ods but shocks can still occur during rapid convergence in the run out zone results are presented from two di mensional calculations on complex geometry which illustrate that some necking features observed in laboratory experiments can be explained by the regu larized savage rutter model

effects of rock fragments on soil erosion by water at different spatial scales a review this paper reviews the various effects of rock fragments on soil erosion by water since these effects are scale dependent they are investigated at three different nested spatial scales the microplot 4 10 6 100m2 the mesoplot 10 2 102 m2 and the macroplot 101 104 m2 for each scale the corresponding process mechanisms are discussed particular attention is paid to the effects of rock fragment cover on the intensity of soil erosion processes at the mesoplot scale i e on interrill areas rock fragments at the soil surface can have negative as well as positive effects on sediment yield these ambivalent effects are conditioned by the type of fine earth porosity soil surface slope vertical position and size of rock fragments and by the occurrence of horseshoe vortex erosion at the microplot scale i e the soil surface area which is covered by a single rock fragment and at the macroplot scale i e upland areas where both interrill and rill erosion takes place rock fragments at the soil surface have a negative effect on sediment yield in these two scales rock fragments can thus be considered as natural soil surface stabilizers at the macroplot scale the mean decrease of relative interrill and rill sediment yield with rock fragment cover can be expressed by an exponential decay function the scatter of the data indicates that a given rock fragment cover can have different efficiencies in reducing interrill and rill sediment yield depending on the varying intensities of the hydrological and erosion subprocesses these findings have implications for erosion modelling and soil conservation

the shape of enceladus as explained by an irregular core implications for gravity libration and survival of its subsurface ocean 1 enceladus global shape is not consistent with a simultaneously hydrostatic and fully differentiated body but its geophysical hyperactivity strongly implies that it is differentiated enceladus surface conforms to a triaxial shape consistent with relaxation to a global geoid but its rocky core need not be hydrostatic a modestly irregular core either in terms of topography or density and dynamically aligned would act to enhance the global geoid explaining the full global shape of enceladus requires 10 km of excess core polar flattening and 4 km of excess core equatorial distortion for a uniform density core the stresses associated with this excess topography can be sustained indefinitely but because the rocky core is not hydrostatic enceladus degree 2 gravity coefficients j2 and c22 will not conform to the hydrostatic ratio of 10 3 testable by cassini gravity notably core polar axes could be depressed by up to 4 6 km with respect to internal isobars such a topographic variation could help preserve polar ocean remnants for example if enceladus ocean undergoes secular freezing it will first ground near the tidal axes polar seas would be the last to freeze and survival of a south polar sea may be one reason why enceladus activity today is concentrated at high southern latitudes isostatic variations in the thickness or density of a floating ice shell may also contribute to enceladus nonhydrostatic shape but a strength supported nonisostatic icy lithosphere is argued here to be unlikely given enceladus record of regional high heat flows faulting and viscous relaxation

element pool balances in soils containing rock fragments abstract the quantification of element pools and their changes in time is an important part of the analysis of ecosystems this quantification is more difficult in soils with rock fragments because of their heterogeneity and because of the difficult analysis of the rock fraction for the pool substance repeated sampling and geostatistical analysis were used to quantify spatial heterogeneity in rock fragment content 137 cs measurements were used to quantify fine earth contamination of dry sieved and washed rock fragments because they are nondestructive and allowed for repeated analysis of the same sample after different treatments 239 240 pu c and n were determined for comparison they are typical for substances that are difficult to be determined directly in rock fragments and they also occur mainly in topsoils small distance heterogeneity may cause an error in rock fragment content of 10 with similar errors biasing the determination of other pools after dry sieving up to 10 of the 137 cs pool may still adhere to the rock fragments washing could remove a further 9 but 1 still remained on the rock fragments these fractions will normally be ignored in analyses which cannot be applied to the rock fragment fraction pu c and n were distributed similarly to 137 cs between the fine earth from dry sieving and the wash off the 137 cs technique therefore allows an easy and less laborious estimation of the part of other element pools associated with rock fragments than direct measurement which in many cases is difficult where the 137 cs technique is used to estimate past erosion since the beginning of nuclear bomb testing errors of several 100 t ha 1 soil loss may result if heterogeneity and cs contamination of rock fragments are ignored

oceans in the icy galilean satellites of jupiter abstract equilibrium models of heat transfer by heat conduction and thermal convection show that the three satellites of jupiter europa ganymede and callisto may have internal oceans underneath ice shells tens of kilometers to more than a hundred kilometers thick a wide range of rheology and heat transfer parameter values and present day heat production rates have been considered the rheology was cast in terms of a reference viscosity 0 calculated at the melting temperature and the rate of change a of viscosity with inverse homologous temperature the temperature dependence of the thermal conductivity k of ice i has been taken into account by calculating the average conductivity along the temperature profile heating rates are based on a chondritic radiogenic heating rate of 4 5 pw kg 1 but have been varied around this value over a wide range the phase diagrams of h2o ice i and h2o 5 wt nh3 ice have been considered the ice i models are worst case scenarios for the existence of a subsurface liquid water ocean because ice i has the highest possible melting temperature and the highest thermal conductivity of candidate ices and the assumption of equilibrium ignores the contribution to ice shell heating from deep interior cooling in the context of ice i models we find that europa is the satellite most likely to have a subsurface liquid ocean even with radiogenic heating alone the ocean is tens of kilometers thick in the nominal model if tidal heating is invoked the ocean will be much thicker and the ice shell will be a few tens of kilometers thick ganymede and callisto have frozen their oceans in the nominal ice i models but since these models represent the worst case scenario it is conceivable that these satellites also have oceans at the present time the most important factor working against the existence of subsurface oceans is contamination of the outer ice shell by rock rock increases the density and the pressure gradient and shifts the triple point of ice i to shallower depths where the temperature is likely to be lower then the triple point temperature according to present knowledge of ice phase diagrams ammonia produces one of the largest reductions of the melting temperature if we assume a bulk concentration of 5 wt ammonia we find that all the satellites have substantial oceans for a model of europa heated only by radiogenic decay the ice shell will be a few tens of kilometers thinner than in the ice i case the underlying rock mantle will limit the depth of the ocean to 80 100 km for ganymede and callisto the ice i shell on top of the h2o nh3 ocean will be around 60 to 80 km thick and the oceans may be 200 to 350 km deep previous models have suggested that efficient convection in the ice will freeze any existing ocean the present conclusions are different mainly because they are based on a parameterization of convective heat transport in fluids with strongly temperature dependent viscosity rather than a parameterization derived from constant viscosity convection models the present parameterization introduces a conductive stagnant lid at the expense of the thickness of the convecting sublayer if the latter exists at all the stagnant lid causes the temperature in the sublayer to be warmer than in a comparable constant viscosity convecting layer we have further modified the parameterization to account for the strong increase in homologous temperature and therefore decrease in viscosity with depth along an adiabat this modification causes even thicker stagnant lids and further elevated temperatures in the well mixed sublayer it is the stagnant lid and the comparatively large temperature in the sublayer that frustrates ocean freezing

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

on convection in ice i shells of outer solar system bodies with detailed application to callisto it has been argued that the dominant non newtonian creep mechanisms of water ice make the ice shell above callisto s ocean and by inference all radiogenically heated ice i shells in the outer solar system stable against solid state convective overturn conductive heat transport and internal melting oceans are therefore predicted to be or have been widespread among midsize and larger icy satellites and kuiper belt objects alternatively at low stresses where non newtonian viscosities can be arbitrarily large convective instabilities may arise in the diffusional creep regime for arbitrarily small temperature perturbations for callisto ice viscosities are low enough that convection is expected over most of geologic time above the internal liquid layer for plausible ice grain sizes a few mm the alternative for early callisto a conducting shell over a very deep ocean 450 km is not compatible with callisto s present partially differentiated state moreover if convection is occurring today the stagnant lid would be quite thick 100 km and compatible with the lack of active geology nevertheless callisto s steady state heat flow may have fallen below the convective minimum for its ice i shell late in solar system history in this case convection ends the ice shell melts back at its base and the internal ocean widens considerably the presence of such an ocean of order 200 km thick is compatible with callisto s moment of inertia but its formation would have caused an 0 25 radial expansion the tectonic effects of such a late slow expansion are not observed so convection likely persists in callisto possibly subcritically ganymede due to its greater size rock fraction and full differentiation has a substantially higher heat flow than callisto and has not reached this tectonic end state titan if differentiated and triton should be more similar to ganymede in this regard pluto like callisto may be near the tipping point for convective shutdown but uncertainties in its size and rock fraction prevent a more definitive assessment

oceans inside jupiter s moons both the voyager and galileo space missions have told us a great deal about io europa ganymede and callisto the moons of jupiter there has been previous evidence for water on these moons but the best yet indicating the existence of subsurface oceans on europa and callisto comes from the galileo magnetometer experiment the interiors of these two bodies are electrically conducting and the most obvious explanation is that water with electrolytic conductivity is present

modeling of two dimensional overland flow a two dimensional hydrodynamic and numerical model for overland flow is developed in this paper the model allows spatial variations in hillslope physical characteristics including surface roughness infiltration and microtopography the accuracy of the model is tested by comparison with characteristic based solutions and experimental data the results of these tests indicate that the model is accurate and has good stability and convergence properties the application of the model to two dimensional overland flow on hillslopes is demonstrated by applying it to surfaces with spatially variable roughness infiltration and microtopography these simulations show that microtopography is the dominant factor causing spatial variation in overland flow depth velocity and direction

shock waves dead zones and particle free regions in rapid granular free surface flows shock waves dead zones and particle free regions form when a thin surface avalanche of granular material flows around an obstacle or over a change in the bed topography understanding and modelling these flows is of considerable practical interest for industrial processes as well as for the design of defences to protect buildings structures and people from snow avalanches debris flows and rockfalls these flow phenomena also yield useful constitutive information that can be used to improve existing avalanche models in this paper a simple hydraulic theory first suggested in the russian literature is generalized to model quasi two dimensional flows around obstacles exact and numerical solutions are then compared with laboratory experiments these indicate that the theory is adequate to quantitatively describe the formation of normal shocks oblique shocks dead zones and granular vacua such features are generated by the flow around a pyramidal obstacle which is typical of some of the defensive structures in use today

compositional diapirism as the origin of the low albedo terrain and vaporization at midlatitude on ceres recent observations of ceres made using the heterodyne instrument for the far infrared on board the european space agency s herschel space observatory have shown that water vapor is emanated from the low albedo midlatitude regions based on the supposition that some dark spots on europa may be caused by diapirism we explored whether ceres environment also can induce compositional diapirism and whether an upwelling diapir could explain the origin and distribution of the dark spots and vaporization of ceres if the density of the rock that constitutes ceres is around 2700 kg m 3 the undifferentiated crust is stable over geological time periods at less than 180 k at a surface temperature of 170 k a diapir can reach the surface if the crust is a few tens of kilometers thick alternatively if the surface temperature is 150 k a large contrast in viscosity would prevent diapirs from reaching the surface the relatively moderate surface temperature in the midlatitude regions of ceres may be the reason for the formation of dark terrains occurring only in such areas our finite difference calculations do not show that diapirism melts the surface ice because the temperature gradient changes very little however if the observed vapor emission is caused by the sublimation of fresh ice compositional diapirism could be the mechanism that transports the fresh ice to the surface in addition to other mechanisms such as cryovolcanism diapirism is a valid hypothesis for explaining the dark terrain and vapor emissions of ceres

the effects of rock fragment shapes and positions on modeled hydraulic conductivities of stony soils abstract mountainous soils usually contain a large number of rock fragments particles with a diameter larger than 2 mm which can influence soil hydraulic properties that are required to quantitatively describe soil water movement in stony soils the objective of this study was to numerically estimate both the saturated hydraulic conductivity of a stony soil and its dependence on a relative content of rock fragments stoniness and the shape position and distribution of rock fragments in a soil matrix the assessment method was based on a numerical version of darcy s classic experiment that involved steady state flow through a porous material under a unit hydraulic gradient our experiments involving hypothetical stony soils in this particular case were simulated using mainly the two dimensional 2d numerical model hydrus 2d a limited number of simulations were carried out using a three dimensional hydrus model three different shapes of hypothetical rock fragments were used in the study a sphere an ellipsoid with two different positions and a pyramid all represented by their 2d cross sections i e a circle an ellipse and a triangle respectively the mean relative effective saturated hydraulic conductivity k rs for the same stoniness was almost the same for all simulated scenarios and fine soil textures a stoniness between 0 07 and 0 5 cm 3 cm 3 can cause a decrease of k rs in the range of 0 17 0 70 numerical experiments were divided into 3 scenarios the largest and the smallest values of k rs were different for different shapes of rfs scenario a different orientations of the slab sided elliptical rfs scenario b and regular or irregular distributions of spherical rfs scenario c the largest difference between k rs values 0 26 was found in scenario b when the slab sided elliptical rfs were oriented either horizontally or vertically for stoniness of 0 24 or 0 31 cm 3 cm 3 simulated k rs values were underestimated in all scenarios as compared to the ravina and magier 1984 function the smallest differences 1 1 2 5 between numerically simulated and calculated the corring and churchill 1961 method for a cylindrical shape of rfs k rs values were found for scenario a with its 2d representation of spherical rock fragments calculated the corring and churchill 1961 method for a spherical shape of rfs k rs values corresponded well with those simulated using a 3d representation of spherical rock fragments numerical models provide a unique opportunity to evaluate the effects of different factors on the saturated hydraulic conductivity of stony soils that may be nearly impossible to measure in practice

viscosity of rock ice mixtures and applications to the evolution of icy satellites theory and experiments are used to establish lower and upper bounds on the ratio of actual viscosity to pure ice viscosity for a suspension of rock particles in a water ice matrix for typical conditions encountered in icy satellites this ratio is of order ten or possibly larger depending on unknown factors such as the particle size distribution it is shown that even this modest increase in viscosity may be enough to have caused a failure of solid state convective self regulation early in the evolution of a homogeneous rock water ice satellite provided the satellite is large enough and sufficiently silicate rich the criteria for this failure are satisfied by ganymede and are marginal for callisto if the silicates are hydrated failure of self regulation means that the viscosity is too high for the interior to remain completely solid and eliminate the heat production of long lived radioisotopes by solid state convection partial melting of the ice then occurs it is further shown that satellites of this size may then undergo runaway differentiation into a rock core and almost pure ice mantle because the gravitational energy release is sufficient to melt nearly all the ice and the rayleigh taylor instability time scale is short although the high pressure phases of ice melt the resulting water quickly refreezes at a higher level it is conjectured that these results explain the striking surface dissimilarity of ganymede and callisto if these satellites accreted cold and undifferentiated ganymede may have gone supercritical melted and differentiated because of a failure of self regulation whereas callisto remained undifferentiated to the present day like all proposed explanations for the ganymede callisto dichotomy this conjecture cannot be quantified with confidence because of inadequate or incomplete observations theory and experimental data

a model for the runout analysis of rapid flow slides debris flows and avalanches runout analyses are used for risk assessment and design of remedial measures against rapid landslides such as debris flows debris avalanches rockslide avalanches large scale liquefaction failure

creep of water ices at planetary conditions a compilation many constitutive laws for the flow of ice have been published since the advent of the voyager explorations of the outer solar system conflicting data have occasionally come from different laboratories and refinement of experimental techniques has led to the publication of laws that supersede earlier ones in addition there are unpublished data from ongoing research that also amend the constitutive laws here we compile the most current laboratory derived flow laws for water ice phases i ii iii v and vi and ice i mixtures with hard particulates the rheology of interest is mainly that of steady state and the conditions reviewed are the pressures and temperatures applicable to the surfaces and interiors of icy moons of the outer solar system advances in grain size dependent creep in ices i and ii as well as in phase transformations and metastability under differential stress are also included in this compilation at laboratory strain rates the several ice polymorphs are rheologically distinct in terms of their stress temperature and pressure dependencies but with the exception of ice iii have fairly similar strengths hard particulates strengthen ice i significantly only at high particulate volume fractions ice iii has the potential for significantly affecting mantle dynamics because it is much weaker than the other polymorphs and its region of stability which may extend metastably well into what is nominally the ice ii field is located near likely geotherms of large icy moons

tidal heating and the long term stability of a subsurface ocean on enceladus abstract tidal dissipation has been suggested as the heat source for the south polar thermal anomaly on enceladus we find that under present day conditions and assuming maxwellian behavior tidal dissipation is negligible in the silicate core dissipation may be significant in the ice shell if the shell is decoupled from the silicate core by a subsurface ocean we have run a series of self consistent convection and conduction models in 2d axisymmetric and 3d spherical geometry in which we include the spatially variable tidal heat production we find that in all cases the shell removes more heat from the interior than can be produced in the core by radioactive decay resulting in cooling of the interior and the freezing of any ocean under likely conditions a 40 km thick ocean made of pure water would freeze solid on a 30 ma timescale an ocean containing other chemical components will have a lower freezing point but even a water ammonia eutectic composition will only prolong the freezing not prevent it if the eccentricity of enceladus were higher e 0 015 in the past the increased dissipation in the ice shell may have been sufficient to maintain a liquid layer we cannot therefore rule out the presence of a transient ocean as a relic of an earlier era of greater heating if the eccentricity is periodically pumped up the ocean may have thickened and thinned on a similar timescale as the orbital evolution provided the ocean never froze completely we conclude that the current heat flux of enceladus and any possible subsurface ocean is not in steady state and is the remnant of an epoch of higher eccentricity and tidal dissipation

ocean worlds in the outer solar system many outer solar system bodies are thought to harbor liquid water oceans beneath their ice shells this article first reviews how such oceans are detected we then discuss how they are maintained when they formed and what the oceans likely characteristics are we focus in particular on europa ganymede callisto titan and enceladus bodies for which there is direct evidence of subsurface oceans we also consider candidate ocean worlds such as pluto and triton

evaluation of laboratory dolomite core sample size using representative elementary volume concepts the adequacy for laboratory testing of four dolomite cores from the culebra dolomite of the rustler formation at the waste isolation pilot plant near carlsbad new mexico were evaluated using representative elementary volume rev theory gamma ray computerized tomography created three dimensional grids of bulk density and macropore index over volumes from 1 4 10 7 to 1 6 l three different methods for both volume averaging and rev analysis were applied and compared both density and macropore index converged to single values with increasing volume which meets the most common qualitative definition of a rev statistical test results for the relatively homogeneous samples indicate that volumes larger than 1 to 7 ml have constant properties contrarily a highly varied sample required 250 and 373 ml to achieve invariant density and macropore characteristics respectively prismatic volume averaging was found to be better than slice averaging while a qualitative test for the rev provided similar results as a rigorous statistical method all cores were larger than the rev but were significantly different from one another this implies that multiple cores are necessary to determine the entire range of transport properties within the rock

surface sealing as affected by various rock fragment covers in west africa field studies on the influence of rock fragments on surface sealing hence infiltration remain scarce and contradictory to document this issue rainfall simulation experiments were carried out on 37 undisturbed 1 m2 plots located along a pedo climatic transect across west africa an important part of the variability of infiltration coefficient r2 0 71 could be explained by a simple model based on the position of rock fragments in the top layer and accounting for the areal percentages of three types of soil surface 1 bare surface 2 soil surface covered with rock fragments embedded in the soil surface and 3 surface with rock fragments resting on top of the soil surface an even higher determination coefficient r2 0 76 was gained when rock fragment size were accounted for in combination with vesicular porosity furthermore a positive linear relationship was obtained between infiltration coefficient and mean annual rainfall suggesting that additional factors related to climate might be involved including organic matter content and clay mineralogy two main regions could thus be differentiated in the arid and semi arid zones coarse gravel and cobbles embedded in a seal are predominant and generate high runoff conversely fine and medium gravel mainly free at soil surface are dominant in the wetter zone favouring therefore higher infiltration rate

calculating dense snow avalanche runout using a voellmy fluid model with active passive longitudinal straining a quasi one dimensional dense snow avalanche model has been developed to predict avalanche runout and flow velocity in a general two dimensional terrain the model contains three different dense snow avalanche flow laws these are 1 a voellmy fluid flow law with longitudinal active passive straining 2 a voellmy fluid flow law advanced by russian researchers in which the coulomb like dry friction is limited by a yield stress and 3 a modified criminale ericksen filby fluid model proposed by norwegian researchers the application of the voellmy fluid law with active passive straining to solve practical avalanche dynamics problems is evaluated by applying the model to simulate laboratory experiments and field case studies the model is additionally evaluated by comparing simulation results using the russian and norwegian models in a final analysis the influence of the initial conditions on avalanche runout is investigated we conclude that the model resolves many of the shortcomings of the voellmy salm model which is traditionally used in switzerland to predict avalanche runout furthermore since the model contains the three well calibrated parameters of the swiss guidelines on avalanche calculation it can be readily applied in practice we discuss why we believe the russian and norwegian models are not ready for practical application finally we show that many problems remain such as the specification of the initial release conditions we conclude that numerical models require a more detailed description of initial fracture conditions

subsurface oceans on europa and callisto constraints from galileo magnetometer observations magnetic field perturbations measured during galileo flybys of europa and callisto are consistent with dipole fields induced by the temporal variations of the ambient jovian magnetospheric field these fields are close to those expected for perfectly conducting moons we investigate the implications of these observations for the electrical structure of the moon s interiors using a simple shell model it is found that europa and callisto must possess regions where the conductivity exceeds 0 06 and 0 02 s m at a depth of less than 200 and 300 km below the surface respectively this conductivity is unattainable in ice or silicates unless the ice layer is at least partially molten or very large temperature gradients can be maintained below the ice an ionosphere or a cloud of pick up ions are probably also insufficiently conductive global earth like oceans under the surface of both moons could account for the observations provided they are at least a few kilometers thick c 2000 academic press

ceres evolution and current state 1 we modeled several thermal evolution scenarios for ceres to explore the nature of large wet protoplanets and to predict current day evidence that might be found by close inspection such as by the dawn mission the density for ceres is near 2 1 suggesting a water content between 17 and 27 by mass short and long lived radioactive nuclide heating is considered even if only long lived radionuclide heating is assumed the water ice in ceres melts quickly and a water mantle forms but an approximately 10 km crust does not melt the circulating warm water would alter the silicates as heat is lost by conduction through the frozen crust water begins to freeze out at the base of the crust solid state convection begins and transports more heat as well as perhaps material dissolved or entrained in the water to or near the surface ceres water layer eventually but perhaps not entirely freezes forming a layered density structure with perhaps some liquid water remaining today our differentiated models are in agreement with the recently measured difference between the equatorial and polar radii we find that ceres existence and evolution depend critically on it containing water at formation and this depends strongly on the combination of when it accreted and the amount of 26al present in the pre ceres 1 km sized objects slightly more 26al or earlier accretion produces a dry vesta like object melting and freezing plus mineralization would lead to several dimensional changes over time creating topographic features zones of weakness and perhaps disruptions in the crust

stability of ice rock mixtures with application to a partially differentiated titan titan s moment of inertia calculated assuming hydrostatic equilibrium from gravity field data obtained during the cassini huygens mission implies an internal mass distribution that may be incompatible with complete differentiation this suggests that titan may have a mixed ice rock core possibly consistent with slow accretion in a gas starved disk which may initially spare titan from widespread ice melting and subsequent differentiation a partially differentiated titan however must still efficiently remove radiogenic heat over geologic time we argue that compositional heterogeneity in the major saturnian satellites indicates that titan formed from planetesimals with disparate densities the resulting compositional anomalies would quickly redistribute to form a vertical density gradient that would oppose thermal convection we use elements of the theory of double diffusive convection to create a parameterized model for the thermal evolution of ice rock mixtures with a stabilizing compositional gradient to account for large uncertainties in material properties and accretionary processes we perform simulations for a wide range of initial conditions ultimately for realistic density gradients double diffusive convection in the ice rock interior can delay but not prevent ice melting and differentiation even if a substantial fraction of potassium is leached from the rock component consequently titan is not partially differentiated

quantifying representative elementary volume of connectivity for translucent granular materials by light transmission micro tomography aquifers composed of granular materials are major repositories of groundwater resource in which water can flow freely and be stored abundantly undoubtedly exploring connectivity of granular materials is essential to understand the mechanism of water and contaminant migration in subsurface environment while characterizing the connectivity remains a difficult task currently this study proposes a new light transmission micro tomography ltm with high resolution to address this problem the new approach relies on scanning micro structure by light transmission through translucent granular materials in given thickness an experiment of light transmission through a two dimensional 2d sandbox packed by heterogeneous translucent silica is conducted to examine the efficiency of ltm in capturing all the features of connectivity including porosity n density solid phase pores interface area asp and tortuosity considering the importance of representative elementary volume rev in characterizing the representativeness and reliability of connectivity associated rev scales of characteristic variables are also estimated using a criterion of relative gradient error egi results suggest that the frequencies of minimum rev sizes of connectivity are close to gaussian distribution in 0 0 12 0 mm and the rev size of approximately 10 0 mm is available to represent connectivity of translucent silica then the quantification of connectivity and the corresponding rev estimates are significant for accurate simulation of fluid migration and for associated optimal design of contaminant remediation in subsurface environment more important this study provides the possibility of rapid handy and economical on site measurements of connectivity for translucent materials

in situ stress conditions at iodp site c0002 reflecting the tectonic evolution of the sedimentary system near the seaward edge of the kumano basin offshore from sw japan this paper presents a complete set of in situ stress calculations for depths of 200 1400 mbsf meters below seafloor at iodp site c0002 near the seaward margin of the kumano forearc basin offshore from southwest japan the vertical stress component was obtained by integrating bulk density calculations from moisture and density logging data and the two horizontal components were stochastically optimized by minimizing misfits between a probabilistic model and measured breakout widths for every 30 m vertical segment of the wellbore our stochastic optimization process reveals that the in situ stress regime is decoupled across an unconformity between an accretionary complex and the overlying kumano forearc basin the stress condition above the unconformity is close to the critical condition for normal faulting while below the unconformity the geologic system is stable in a normal to strike slip fault stress regime the critical state of stress demonstrates that the tectonic evolution of the sedimentary system has been achieved mainly by the regionally continuous action of a major out of sequence thrust fault during sedimentation in the forearc basin the stable stress condition in the accretionary prism is interpreted to have resulted from mechanical decoupling by the accommodation of large displacement along the megasplay fault

comparison of measured xrpd and modeled a2m soil mineralogies a study of some swedish forest soils in the context of weathering rate predictions abstract quantitative soil mineralogy has been identified as a key factor influencing profile weathering estimates and is often calculated with normative methods such as the analysis to mineralogy a2m model in sweden and other countries there is a large request for accurate base cation weathering estimates in order to establish how sustainable harvest of biomass should be performed in the future however there is a lack of knowledge around the accuracy of the arithmetic mean output of a2m estimates the most common a2m solution used in weathering studies to our knowledge a thorough investigation of how a2m input data affect the arithmetic mean output center of gravity of the a2m solution space is missing in this study the indirect geochemical normative method a2m was compared with a direct x ray powder diffraction method xrpd to quantify soil mineralogy at two sites and 8 soil profiles at a 10 cm depth interval we explored the hypothesis that normative calculations performed with a2m produce an output in closer agreement with the mineralogy obtained from xrpd if site specific mineralogical input data are used rather than regional data site specific mineralogical input data consisted of mineral stoichiometry data measured by electron microprobe analysis empa and mineral identity determined by xrpd whereas regional mineral input data were based on previously reported data on mineral stoichiometry and mineral identity derived from three geological regions in sweden the results from this comparison showed that the site specific approach yielded relatively low average biases and root mean square errors rmse for most minerals with the exception of quartz average bias of 4 8 wt rmse of 5 3 wt at the asa site the regional approach yielded deviating results for k feldspar and dioctahedral mica with high average biases and rmse for dioctahedral mica asa 7 8 wt 9 0 wt flakaliden 12 8 wt 15 5 wt and for k feldspar asa 5 2 wt 6 1 wt flakaliden 5 6 wt 6 7 wt the results from this study were supported by a close agreement between measured geochemistry and normalized geochemistry derived from a back calculation of the xrpd mineralogy i e mineral budgeting in conclusion our findings suggest that a2m results in combination with site specific mineralogical input data are improved independent of study site and soil profile however for future weathering studies it might be beneficial to find constraints of how to select a solution from the entire a2m solution space which is in better agreement with the xrpd mineralogy

constraints on gas giant satellite formation from the interior states of partially differentiated satellites an icy satellite whose interior is composed of a homogeneous ice rock mixture must avoid melting during its entire history including during its formation when it was heated by deposition of accretional energy and short lived radioisotopes estimates of the temperature rise associated with radiogenic and accretional heating coupled with limits on satellite melting can be used to constrain the timing of formation of a partially differentiated satellite relative to the origin of the calcium aluminum rich inclusions cai s as a function of its accretion timescale and the protosatellite disk temperature td geological characterization and spacecraft radio tracking data suggest that callisto the outermost regular satellite of jupiter and saturn s mid sized satellite rhea are partially differentiated if their interiors are in hydrostatic equilibrium because the specific conditions during the satellites formation are uncertain we determine accretional temperature profiles for a range of values for td and accretion time scales with the limiting assumption that impactors deposit all their energy close to the surface leading to maximally effective radiative cooling we find that callisto can remain unmelted during formation if it accreted on a time scale longer than 0 6 myr considering both radiogenic and accretional heating callisto must have finished accreting no earlier than 4 myr after formation of cai s for td 100 k warmer disks or larger impactors that deposit their energy at depth in the satellite would require longer and or later formation times if rhea accreted slowly in 10 5

simulation of dnapl migration in heterogeneous translucent porous media based on estimation of representative elementary volume when the dense nonaqueous phase liquid dnapl comes into the subsurface environment its migration behavior is crucially affected by the permeability and entry pressure of subsurface porous media a prerequisite for accurately simulating dnapl migration in aquifers is then the determination of the permeability entry pressure and corresponding representative elementary volumes rev of porous media however the permeability entry pressure and corresponding representative elementary volumes rev are hard to determine clearly this study utilizes the light transmission micro tomography ltm method to determine the permeability and entry pressure of two dimensional 2d translucent porous media and integrates the ltm with a criterion of relative gradient error to quantify the corresponding rev of porous media as a result the dnapl migration in porous media might be accurately simulated by discretizing the model at the rev dimension to validate the quantification methods an experiment of perchloroethylene pce migration is conducted in a two dimensional heterogeneous bench scale aquifer cell based on the quantifications of permeability entry pressure and rev scales of 2d porous media determined by the ltm and relative gradient error different models with different sizes of discretization grid are used to simulate the pce migration it is shown that the model based on rev size agrees well with the experimental results over the entire migration period including calibration verification and validation processes this helps to better understand the microstructures of porous media and achieve accurately simulating dnapl migration in aquifers based on the rev estimation

pressure coefficient in dam break flows of dry granular matter abstractthe propagation of dry granular flows such as rock and snow avalanches can be described by depth averaged models different from classical shallow water equations these models take into account the anisotropy of normal stresses inside the flowing pile through using an earth pressure coefficient in the pressure term a new regularization function for calculating the pressure coefficient in the savage hutter type models at the early stages of dam break flows and collapses is proposed in such circumstances the flow lines are significantly curved with respect to the basal surface and a special treatment of the earth pressure coefficient is required for obtaining a satisfactory agreement with experimental data the comparison between numerical simulations and laboratory experimental data shows an apparent improvement in describing the early stages of dam break waves over rough beds the comparison with experiments over smooth bed surface exhibits minor evidence of improvement nonetheless in this

spatial distribution of surface rock fragments along catenas in semiarid arizona and nevada usa improved techniques for estimating soil erosion by water have shown that soil surface cover is a major component in the estimate of soil loss erosion prediction models require the user to input slope gradient and soil profile descriptions if equations expressing the relations between slope gradient soil profile rock fragment content and surface rock fragment cover were embedded in these models then direct user input could be reduced field measurements of slope gradient soil profile rock fragment content surface rock fragment cover and vegetation type and cover were made on 12 soil slope complexes on catenas in southeastern arizona usa correlation analysis showed that both slope gradient and soil profile rock fragment content were significantly p 0 01 correlated to surface rock fragment cover additional analysis indicated that the combined effects of slope gradient and soil profile rock content were better defined by a soil slope factor ssf two equations were developed to estimate surface rock fragment cover a logarithmic relation using slope gradient as the independent variable and a hyperbolic equation using the ssf as the independent variable these equations were used to estimate surface rock fragment cover from a soil slope complex in southern nevada the ssfrfc equation gave better estimates of the measured surface rock fragment cover these relations developed for catenas in southeastern arizona may be site specific but they do show that a relation exists for this semiarid area and suggest that similar relations may exist in areas with similar geology and climate such as parts of africa asia australia and south america development of simple relations describing important erosion processes will improve erosion estimates while simultaneously decreasing time and costs associated with using erosion prediction models

influence of rock fragments on the water retention and water percolation in a calcareous soil abstract the water retention properties of a calcareous soil containing rock fragments have been determined in the laboratory thanks to pressure plate measurements done on both the fine earth and the rock fragments from the soil the available water content awc has been calculated from these data we have shown that when the rock fragments are neglected the awc can be overestimated by 39 when we do not neglect their volume but when their hydraulic properties are not considered the awc can be underestimated by 34 by using a reservoir model we have also calculated the effect of rock fragments on water percolation to groundwater depending of the climatic characteristics of the year the underestimation of percolation when we neglect the rock fragments can reach up to 14 9 and the overestimation when we neglect their hydraulic properties can be equal to 15 8 these findings emphasise the role of the rock fragments on the water supply in stony soils

determination of mineral surface area in relation to the calculation of weathering rates the release of base cations by the weathering of soil minerals provides the primary buffer against the detrimental impact of acid deposition on the soil the rate of release of base cations will be governed by mineral composition and the exposed surface area of mineral grains in theory it is possible to calculate the surface area of a mixture of grains on the basis of particle size and geometry an alternative is the use of correlations it has been suggested sverdrup et al 1990 nordic council of ministers 98 that mineral surface area can be related to soil particle size distribution via a simple empirical equation this contribution compares the surface areas of soils as calculated by geometric equations and sverdrup s equation with actual bet measurements the equations tested do not appear to be applicable to the soils used in the current work modified versions of the equation suggested by sverdrup applied to subsets of our data based on sites and soil types yield better results for the soils used in the current work statistically significant improved fits are obtained when soil mineralogy as well as soil texture is taken into account