toward a boot strap hypothesis of plate tectonics feedbacks between plates the asthenosphere and the wavelength of mantle convection abstract the solid earth system is characterized by plate tectonics a low viscosity zone beneath plates the asthenosphere and long wavelength flow in the convecting mantle we use suites of numerical experiments to show 1 how long wavelength flow and the operation of plate tectonics can generate and maintain an asthenosphere and 2 how an asthenosphere can maintain long wavelength flow and plate tectonics plate subduction generates a sub adiabatic temperature gradient in the mantle which together with temperature dependent viscosity leads to a viscosity increase from the upper to the lower mantle this allows mantle flow to channelize in a low viscosity region beneath plates an asthenosphere forms dynamically flow channelization in turn stabilizes long wavelength convection the degree of dynamic viscosity variations from the upper to the lower mantle increases with the wavelength of convection and drops toward zero if the system transitions from plate tectonics to a single plate planet the plate margin strength needed to initiate that transition increases for long wavelength cells long wavelength flow allows plate tectonics to exist over a wider range of plate margin strength the coupled feedbacks allow for a linked causality between plates the asthenosphere and the wavelength of mantle flow with none being more fundamental than the others and the existence of each depending on the others under this hypothesis the asthenosphere is defined by an active process plate tectonics which maintains it and is maintained by it and plate tectonics is part of an emergent self sustaining flow system that bootstraps itself into existence

efficient cooling of rocky planets by intrusive magmatism the earth is in a plate tectonics regime with high surface heat flow concentrated at constructive plate boundaries other terrestrial bodies that lack plate tectonics are thought to lose their internal heat by conduction through their lids and volcanism hotter planets io and venus show widespread volcanism whereas colder ones modern mars and mercury are less volcanically active however studies of terrestrial magmatic processes show that less than 20 of melt volcanically erupts with most melt intruding into the crust signatures of large magmatic intrusions are also found on other planets yet the influence of intrusive magmatism on planetary cooling remains unclear here we use numerical magmatic thermo mechanical models to simulate global mantle convection in a planetary interior in our simulations warm intrusive magmatism acts to thin the lithosphere leading to sustained recycling of overlying crustal material and cooling of the mantle in contrast volcanic eruptions lead to a thick lithosphere that insulates the upper mantle and prevents efficient cooling we find that heat loss due to intrusive magmatism can be particularly efficient compared to volcanic eruptions if the partitioning of heat producing radioactive elements into the melt phase is weak we conclude that the mode of magmatism experienced by rocky bodies determines the thermal and compositional evolution of their interior rocky planets dominated by intrusive magmatism can cool more efficiently than those dominated by extrusive volcanism according to numerical simulations of mantle convection

power series solution for ponded infiltration on sloping surfaces summary recently it has been shown that the philip power series solution can also be applied for falling head ponded infiltration mollerup and hansen 2007 or more generally for variable head vh ponded infiltration on flat surfaces mollerup 2007 in this study it is shown that the power series solution can also be applied for vh ponded infiltration on sloping surfaces numerical simulations have been made for a guelph loam for a vh scenario the power series solution was compared with a 2d fem solution of richards equation with good agreement using the developed series solutions a vh scenario was compared with constant head ch simulations with both a ponding depth of zero and the average ponding depth as used in the vh simulations especially the latter gave small differences in the cumulative infiltration compared with the vh results simulations showed that cumulative infiltration normal to the slope as function of time is decreasing with increasing slope angles for similar vertical ponding depths corresponding to equal amount of surface water on a given horizontal slope section in contrast the infiltration on a given projected horizontal area increases with the slope angle

geological consequences of super sized earths 1 the discovery of terrestrial scale extrasolar planets and their calculated abundance in the galaxy has prompted speculation on their surface conditions and thermal structure both are dependent on the tectonic regime of a planet which is itself a function of the balance between driving forces and the resistive strength of the lithosphere here we use mantle convection simulations to show that simply increasing planetary radius acts to decrease the ratio of driving to resisting stresses and thus super sized earths are likely to be in an episodic or stagnant lid regime this effect is robust when associated increases in gravity are included as the more dominant effect is increased fault strength rather than greater buoyancy forces the thermo tectonic evolution of large terrestrial planets is more complex than often assumed and this has implications for the surface and conditions habitability of such worlds

formation of ridges in a stable lithosphere in mantle convection models with a viscoplastic rheology numerical simulations of mantle convection with a viscoplastic rheology usually display mobile episodic or stagnant lid regimes in this study we report a new convective regime in which a ridge can form without destabilizing the surrounding lithosphere or forming subduction zones using simulations in 2 d spherical annulus geometry we show that a depth dependent yield stress is sufficient to reach this ridge only regime this regime occurs when the friction coefficient is close to the critical value between mobile lid and stagnant lid regimes maps of convective regime as a function of the parameters friction coefficients and depth dependence of viscosity are provided for both basal heating and mixed heating situations the ridge only regime appears for both pure basal heating and mixed heating mode for basal heating this regime can occur for all vertical viscosity contrasts while for mixed heating a highly viscous deep mantle is required

convection scaling and subduction on earth and super earths super earths are the smallest class of discovered extra solar planets owing to their relatively small mass some might resemble earth and perhaps be habitable because of the connection to habitability through thermal evolution we investigate the tectonic regime of massive terrestrial planets two independent studies o neill c lenardic a oct 2007 geological consequences of super sized earths grl 34 l19204 valencia d o connell r j sasselov d d nov 2007a inevitability of plate tectonics on super earths apjl 670 l45 l48 have reached opposing conclusions about the likelihood of plate tectonics here we offer possible reasons for the discordant findings and address three key aspects of sustaining plate tectonics deformation on faults negative buoyancy and energy dissipation during subduction we show that in general the ratio of driving force to plate resistance increases with planetary mass this is a consequence of increasing convective stresses thinning plates and similar plate structure we conclude that even though the strength of dry and wet of faults increases for massive terrestrial planets the convective stress increases even more allowing deformation to take place also despite shorter timescales for plate cooling rocky super earths achieve negative buoyancy at subduction zones finally by investigating the effects of energy dissipation during subduction we find that massive terrestrial planets dissipate less energy during subduction and hence provide a positive feedback to sustain active lid tectonics in conclusion rocky super earths have more favorable conditions than earth for the subduction of plates and hence for sustaining plate tectonics

a suspended sediment stratification correction for combined wave and current flows a simple model for the near bottom combined wave and current flow over a moveable sediment bed is presented the model is an extension of the grant and madsen 1979 combined wave and current model with moveable bed effects on the physical bottom roughness included as by grant and madsen 1982 the unsteady conservation of fluid momentum and sediment mass equations which are coupled through an eddy diffusivity closure scheme are solved for the wave and current velocity profiles along with the suspended sediment concentration and transport profiles sample runs are presented to illustrate the effect of varying wave conditions on the current the mean sediment concentration and the mean sediment transport results show that for fine to medium sands self stratification of the flow can be important during storms owing to the large amount of sediment suspended by the waves and the enhanced turbulent mixing associated with the wave current interaction the theory easily can be generalized for inclusion in a full ekman layer model

similarity in catchment response 2 moving rainstorms the influence of storm motion on runoff is explored with a focus on dimensionless hydrologic similarity parameters one and two dimensional physically based runoff models are subjected to moving rainstorms a dimensionless storm speed parameterute lp where u is the storm speed te is the runoff plane kinematic time to equilibrium and lp is the length of the runoff plane is identified as a similarity condition storm motion effects on the peak discharge are greatest when the storm is traversing a one dimensional runoff plane in the downslope direction at a dimensionless speed of ute lp 0 5 this conclusion holds for all values of the dimensionless storm sizes ls lp where ls is the length of the storm in the direction of motion simulations with a two dimensional rainfall runoff model confirm the applicability of this similarity parameter on natural watershed topography results indicate that the detailed simulation of storm motion is necessary when the storm is moving near the velocity of maximum effect which is considerably slower than typical storm velocities

scale effects on the estimation of erosion thresholds through a distributed and physically based hydrological model abstract slope incision and subsequent development of rills gullies and channels are responsible for significant soil losses and are often irreversible with very high restoration costs particularly in semiarid environments the location of potential areas of erosion where these processes occur is vital to land management and conservation the study of the relationship between the local slope s and the drainage area a through the geomorphological relationship s a b combined with hydrologic simulation models has proved to be appropriate for the identification and characterisation of potential areas of incision especially when it takes into account the spatial distribution of soil properties and the evolution of hydrological processes however physical properties of soil digital elevation models dems and flow algorithms used may affect the results this study employs a distributed physically based hydrological model to evaluate the infiltration runoff relationships and their influence on selecting critical area from three dems with different resolutions the results show a significant scale effect on flow distribution and the location of threshold points on slopes the results obtained from a 30 m dem significantly differ from those obtained from 10 and 5 m dems because the former was unable to capture the spatial variability of geomorphic processes the selected set of critical points shows high s a correlations for different values of critical shear stress the physical model confirmed the dominance of surface runoff in the study site and was validated from field identification of erosion risk areas although for incision areas

dem based modelling of surface runoff using diffusion wave equation a digital elevation model dem based overland flow routing model was developed for computation of surface runoff for isolated storm events the model operates on a grid or cell basis and routes the rainfall excess generated over the cells following the dem derived drainage paths to the catchment outlet the rainfall excess for each cell of the catchment was computed using the philip two term infiltration model utilizing the physical properties of the cell the overland flow was described by a finite volume based numerical solution of the diffusion wave approximation of the st venant equations the cell physical properties such as topographic characteristics land use soil etc were extracted from published maps for discretized cells of the catchment using a geographic information system the results of model application indicate that the model satisfactorily predicted the runoff hydrograph the cell based structure of the model allowed for generation of spatially distributed catchment information in terms of the model computed variables such as the depth of flow and discharge

a storm event watershed model for surface runoff based on 2d fully dynamic wave equations the main purpose of this work concerns the development and testing of an overland flow model based on the two dimensional fully dynamic shallow water equations three key aspects fundamental to get accurate efficient and robust computation of surface runoff at basin scale are discussed by transferring the main findings obtained by the recent research on the topic of dam break wave and flood propagation in the context of rainfall runoff modelling in particular attention is focused on the numerical flux and bottom slope source terms computation on a numerical treatment of friction slope terms and on an algorithm for dealing with wetting drying fronts the performances of the numerical model have been preliminarily evaluated using experimental or ideal tests characterized by very critical conditions for the stability of a numerical model then attention was focused on a real event occurred in a sub basin of reno river in italy to analyse the suitability of the model in simulating real flood situations the numerical results highlight the good performances of the model in all the simulations discussed in the paper copyright 2012 john wiley sons ltd

hysteresis in mantle convection plate tectonics systems 1 we use simulations of mantle convection with surface yielding to show that multiple tectonic regimes are possible for equivalent system parameter values models with the same lithospheric strength parameters and the same vigor of convection can display different modes of tectonics within the region of multiple solutions the evolutionary pathway of the system is the dominant factor that determines the tectonic mode e g whether mantle convection operates in a plate tectonic like mode the extent of the multiple regimes window is found to increase with the temperature dependent viscosity contrast across the system the implication for models that seek to predict the tectonic regimes of planets is that the temporal evolution of the planet needs to be taken into account a further implication is that modeling studies can lead to different conclusions regarding the tectonic state of a planet extra solar planets in particular despite the final model parameter values remaining equivalent

self consistent generation of tectonic plates in time dependent three dimensional mantle convection simulations 1 presented here are self consistent three dimensional simulations of mantle convection some of which display an approximation of plate tectonic behavior that is continuous in space and time plate behavior arises through a reasonable material description of silicate deformation with a simple yield stress being sufficient to give first order plate like behavior however the required yield strength or fault frictional coefficient is much less than experimentally determined values toroidal poloidal ratios are within geologically observed limits the sensitivity of the system to yield strength and the form of strength envelope is systematically investigated optimum plate character is obtained in a narrow range of yield strength below which diffuse boundaries and above which episodic behavior and eventually a rigid lid are observed models with mobile lids develop very long wavelength horizontal structure the longest wavelength possible in the domain two dimensional models display much greater time dependence than three dimensional models

a comparison of drainage networks derived from digital elevation models at two scales abstract automated generation of drainage networks has become increasingly popular with powerful analytical functions in geographic information systems gis and with the increased availability of digital elevation models dems this paper compares drainage networks derived from dems at two scales 1 250 000 250k and 1 24 000 24k using various drainage parameters common in hydrology and geomorphology the comparison of parameters derived from the 250k dems with those from the 24k dems in 20 basins ranging from 150 to 1000 km2 in west virginia shows that the goodness of fit between parameter estimates based on the dems varies results clearly show that superior estimations are produced from the 24k dems better estimates can be obtained from the 250k dems for stream length and frequency parameters than for gradient parameters however the estimation of the mean gradient parameters based on the 250k dems seems to improve with increasing terrain complexity finally basin size does not strongly affect the accuracy of parameter estimates based on the 250k dems

the effect of rheological parameters on plate behaviour in a self consistent model of mantle convection abstract in a three dimensional numerical model of mantle convection we have explored the self consistent formation and evolution of plates this was done by investigating the influence of temperature stress and pressure dependence of the viscosity on plate like behaviour further the role of a depth dependent thermal expansivity and of internal heating was examined first order self consistent plate tectonics can be obtained for temperature and stress dependent viscosity we observe virtually undeformed moving plates and the phenomenon of trench migration however plate motion only appears during short intervals which are interrupted by long phases characterised by an immobile lid an improvement is achieved by adding pressure dependence of the viscosity and of the thermal expansivity to the model this leads to extended plates with continuous plate motion and the appearance of a low viscosity zone internal heating accelerates subduction and gives an increase in plate velocity the plates are otherwise left intact we find that the surface velocity is largely determined by subduction rather than by upwellings plate like behaviour is restricted to a narrow parameter window the window is bordered by an episodic or a stagnant lid type of flow on the one side and by a domain in which convection is akin to constant viscosity flow on the other side with these different convective regimes the behaviour of various terrestrial planets can be described self consistently occasionally even a change from the plate regime to the stagnant lid regime occurs such a type of transition has possibly changed the style of tectonics on some terrestrial planets such as mars

the energetics and convective vigor of mixed mode heating velocity scalings and implications for the tectonics of exoplanets the discovery of large terrestrial 1 earth mass me to 10 me extrasolar planets has prompted a debate as to the likelihood of plate tectonics on these planets canonical models assume classic basal heating scaling relationships remain valid for mixed heating systems with an appropriate internal temperature shift those scalings predict a rapid increase of convective velocities vrms with increasing rayleigh numbers ra and non dimensional heating rates q to test this we conduct a sweep of 3 d numerical parameter space for mixed heating convection in isoviscous spherical shells our results show that while vrms increases with increasing thermalrait does so at a slower rate than predicted by bottom heated scaling relationships further the vrms decreases asymptotically with increasing q these results show that independent of specific rheologic assumptions e g viscosity formulations water effects lithosphere yielding the differing energetics of mixed and basally heated systems can explain the discrepancy between different modeling groups high temperature or young planets with a large contribution from internal heating will operate in different scaling regimes compared to cooler temperature or older planets that may have a larger relative contribution from basal heating thus differences in predictions as to the likelihood of plate tectonics on exoplanets may well result from different models being more appropriate to different times in the thermal evolution of a terrestrial planet as opposed to different rheologic assumptions as has often been assumed

the pressure weakening effect in super earths consequences of a decrease in lower mantle viscosity on surface dynamics 1 the quest to identify habitable planets has raised interest in the surface dynamics of terrestrial bodies in this context super earths a new class of exoplanets have become of special interest in the past decade scalings to super earth sizes when compared to the earth suggest changes to convective stresses and mantle temperatures which can cause either an increase in surface mobility or in plate resistance mantle viscosity which depends on temperature stress and pressure plays a critical role in both cases new mineralogical assumptions suggest that the viscosity in super earths acts differently than in the earth and what had been assumed for super earths in planets larger than the earth pressure will become so high that pressure weakening and a decrease of viscosity in the lowermost mantle results we present a numerical convection study featuring this viscosity decrease and find that this leads to a reduction in surface mobility

convection in three dimensions with surface plates generation of toroidal flow this work presents numerical calculations of mantle convection that incorporate some of the basic observational constraints imposed by plate tectonics the model is three dimensional and includes surface plates it allows plate velocity to change dynamically according to the forces which result from convection we show that plates are an effective means of introducing a toroidal component into the flow field after initial transients the plate motion is nearly parallel to transform faults and in the direction that tends to minimizes the toroidal flow field the toroidal field decays with depth from its value at the surface the poloidal field is relatively constant throughout the layer but falls off slightly at the top and bottom boundaries layered viscosity increasing with depth causes the toroidal field to decay more rapidly effectively confining it to the upper low viscosity layer the effect of viscosity layering on the poloidal field is relatively small which we attribute to its generation by temperature variations distributed throughout the system the generation of toroidal flow by surface plates would seem to account for the observed nearly equal energy of toroidal and poloidal fields of plate motions on the earth a low viscosity region in the upper mantle will cause the toroidal flow to decay significantly before reaching the lower mantle the resulting concentration of toroidal flow in the upper mantle may result in more thorough mixing there and account for some of the geochemical and isotopic differences proposed to exist between the upper and lower mantles

a contour based topographic model for hydrological and ecological applications a digital model for discretizing three dimensional terrain into small irregularly shaped polygons or elements based on contour lines and their orthogonals is described from this subdivision the model estimates a number of topographic attributes for each element including the total upslope contributing area element area slope and aspect this form of discretization of a catchment produces natural units for problems involving water flow as either a surface or subsurface flow phenomenon the model therefore has wide potential application for representing the three dimensionality of natural terrain and water flow processes in the fields of hydrology sedimentology and geomorphology three example applications are presented and discussed they are the prediction of zones of surface saturation the prediction of the distribution of potential daily solar radiation and the prediction of zones of erosion and deposition in a catchment

diffusion wave model for simulating storm water runoff on highway pavement surfaces at superelevation transition on a curved section of highway the cross slope of the road is often designed to be superelevated to balance the centrifugal force and gravity applied on vehicles the accumulation of storm water runoff sheet flow near superelevation transitions may significantly increase due to the extended flow path and converging flow lines a two dimensional finite volume based diffusion wave model is developed to simulate the sheet flow on these geometrically complex surfaces both dirichlet and neumann type boundary conditions are developed for open boundaries based on kinematic wave theory results show that the distribution of sheet flow is closely related to the cross slope longitudinal slope rainfall intensity and the width of the road the analysis of sheet flow characteristics on superelevation transition areas suggests that the optimal longitudinal slope in the range of 0 3 0 4 minimizes the depth of storm water runoff on the road surface

effects of surface roughness and rainfall impact on overland flow bed roughness and rainfall impact affect hydraulic friction in overland flow the relationship between friction velocity discharge and channel slope was examined for the case of shallow spatially varied flow on rough surfaces rainfall was simulated on artificially roughened surfaces in a laboratory measured flow velocities were compared to theoretical velocities computed from a dynamic equation for spatially varied flow and from the darcy weisbach uniform flow equation the measurements showed that the constant that relates the darcy weisbach friction coefficient to reynolds number can become larger than the theoretical value for smooth laminar flow an analysis of the dynamic equation showed that frictional forces were much larger than forces resulting from changes in hydrostatic pressure and momentum water surface profiles based on the darcy weisbach friction equation nearly matched those from the dynamic equation for spatially varied flow a regression was developed from the darcy weisbach equation the regression accurately predicted flow velocity when absolute roughness rainfall rate channel discharge slope slope length and viscosity were known

geoframework coupling multiple models of mantle convection within a computational framework solver coupling can extend the capability of existing modeling software and provide a new venue to address previously intractable problems a software package has been developed to couple geophysical solvers demonstrating a method to accurately and efficiently solve multiscale geophysical problems with reengineered software using a computational framework pyre pyre is a modeling framework capable of handling all aspects of the specification and launching of numerical investigations we restructured and ported citcoms a finite element code for mantle convection into the pyre framework two citcoms solvers are coupled to investigate the interaction of a plume at high resolution with global mantle flow at low resolution a comparison of the coupled models with parameterized models demonstrates the accuracy and efficiency of the coupled models and illustrates the limitations and utility of parameterized models

an in situ erosion rate for a fine grained marine sediment near bottom current and particulate concentration data and a theoretical model of sediment resuspension together have led to inferences about the erosional response of a fine grained sediment to bottom stress tidal boundary layer observations made 5 m from the bottom in the main basin of puget sound washington show that currents with speeds exceeding 40 cm s cause an increase in concentration as much as sixfold from a background level of 1 mg 1 when the erosion rate e is given a power law dependence on bottom stress in accord with laboratory fine sediment entrainment measurements the field data and theoretical model together suggest that 4 0 and 1 7 10 6 g cm2 s uncertainty in these values stemming from a variety of factors is discussed the analysis also points to sediment resuspension of material with relatively large settling velocity ws 0 1 cm s taking place against a background of much finer particles and a depth of sediment reworking of approximately 0 3 mm under typical strong flow conditions comparison of this in situ erosion rate with previous laboratory rate estimates shows it to be comparable to rates measured for some freshwater sediments

power series solution for falling head ponded infiltration with evaporation 1 assumptions for many of the derived analytical infiltration models are either a constant infiltration rate or a constant head at the soil surface for many realistic infiltration situations a falling head boundary condition is more appropriate philip showed that both the wetting profiles and the cumulated infiltration in one dimensional infiltration into homogenous soil with constant head at the upper boundary can be written as a power series in t presently it is shown that a power series solution can be applied for falling head infiltration with evaporation when comparing with the constant head solution the falling head solution differs only from the second term i e the sorptivity remains unchanged a result which can be applied to falling head infiltrometer technique the effect of a constant evaporation rate in the falling head scenario appears from the third term in the presented numerical examples the retention model by van genuchten and the hydraulic conductivity model by mualem are applied by comparing the wetting profiles obtained with a fem solution it is shown that the discrepancies between the models are very small also the estimation of the time at which the pond is emptied is concordant the infiltration model is compared with a model by parlange and colleagues and a simple infiltrometer method for determining the saturated hydraulic conductivity is proposed

physical modeling of sheet flow on rough impervious surfaces this paper presents results from an extensive experimental study of sheet flow on rough impervious surfaces that are used to represent highway pavement experiments were performed on three surfaces under no rainfall and simulated rainfall conditions and with slopes of 1 2 and 3 measurements include flow depth and unit discharge turbulent boundary layer theory for a rough surface is used to describe the depth discharge relationship resulting in a model with a single parameter directly related to the surface roughness comparisons are made with manning s equation and the variability of the manning coefficient is assessed hydraulic effects of rainfall are generally found to be small compared to other factors

the effects of internal heating and large scale climate variations on tectonic bi stability in terrestrial planets abstract we use 3d mantle convection and planetary tectonics models to explore the links between tectonic regimes and the level of internal heating within the mantle of a planet a proxy for thermal age planetary surface temperature and lithosphere strength at both high and low values of internal heating for moderate to high lithospheric yield strength hot and cold stagnant lid single plate planet states prevail for intermediate values of internal heating multiple stable tectonic states can exist in these regions of parameter space the specific evolutionary path of the system has a dominant role in determining its tectonic state for low to moderate lithospheric yield strength mobile lid behavior a plate tectonic like mode of convection is attainable for high degrees of internal heating i e early in a planet s thermal evolution however this state is sensitive to climate driven changes in surface temperatures relatively small increases in surface temperature can be sufficient to usher in a transition from a mobile to a stagnant lid regime once a stagnant lid mode is initiated a return to mobile lid is not attainable by a reduction of surface temperatures alone for lower levels of internal heating the tectonic regime becomes less sensitive to surface temperature changes collectively our results indicate that terrestrial planets can alternate between multiple tectonic states over giga year timescales within parameter space regions that allow for bi stable behavior any model based prediction as to the current mode of tectonics is inherently non unique in the absence of constraints on the geologic and climatic histories of a planet

shift a distributed runoff model using irregular triangular facets abstract shift sistema hidrologico de facetas triangulares is a computational system that allows for the 1 creation editing and visualization of a watershed digital elevation model dem based on the triangular irregular network tin concepts 2 input and interpolation of soil river bed and rainfall data and 3 calculation and routing of runoff in all the facets and reaches the tin dem model is constructed from a set of points where the slope changes abruptly afterwards the drainage network is automatically identified and an interactive editor allows the addition or deletion of points to eliminate network discontinuities rainfall data are interpolated by means of a procedure based on the minimization of the bending energy of a thin plate in order to calculate and route the runoff the system determines the routing sequence of river segments and for each one identifies the facets forming the contributing area and determines a cascade of overland flow planes then for each element and time interval the system calculates the infiltration and routes the resultant runoff by a numerical solution of the kinematic wave equations this information is saved and the user can see the hydrograph for any facet or reach

a regime diagram of mobile lid convection with plate like behavior abstract terrestrial planetary bodies that undergo solid state convection can exhibit a variety of tectonic styles from stagnant lid one plate planets to those with a mobilized lithosphere for modeled planetary convection the de facto mode of recycling of lithosphere into the planetary interior is typically achieved through 2 sided and symmetric downwelling flows however lithosphere recycling on earth occurs in a distinctly 1 sided mode known as subduction using numerical models of mantle convection in which the viscosity of planetary mantle material is strongly temperature dependent yet maintains a finite material strength as dictated by its yield stress we investigate the continuum of mobile lid convection with plate like behavior the models span a parameter space of rayleigh number and plate strength and explore convective systems with low yield stresses resulting in weak subduction hinges that bend easily and highly deformable subducted slabs three distinct modes are found to occur in convective systems with weak plates the stagnant lid mode 2 sided downwelling mode and a mode that alternates between 1 sided subduction and 2 sided downwellings we classify the style of convective downwelling for a range of models and show that mode selection strongly depends on the combination of surface mobility and strength of the downgoing plate using these measurements we have developed a regime diagram that can predict whether a particular system will be in one of those three modes

numerical experiments on thermal convection of highly compressible fluids with variable viscosity and thermal conductivity implications for mantle convection of super earths abstract we conduct a series of numerical experiments of thermal convection of highly compressible fluids in a two dimensional rectangular box in order to study the mantle convection on super earths the thermal conductivity and viscosity are assumed to exponentially depend on depth and temperature respectively while the variations in thermodynamic properties thermal expansivity and reference density with depth are taken to be relevant for the super earths with 10 times the earth s from our experiments we identified a distinct regime of convecting flow patterns induced by the interplay between the adiabatic temperature change and the spatial variations in viscosity and thermal conductivity that is for the cases with strong temperature dependent viscosity and depth dependent thermal conductivity a deep stratosphere of stable thermal stratification is formed at the base of the mantle in addition to thick stagnant lids at their top surfaces in the deep stratosphere the fluid motion is insignificant particularly in the vertical direction in spite of smallest viscosity owing to its strong dependence on temperature our finding may further imply that some of super earths which are lacking in mobile tectonic plates on their top surfaces may have deep stratospheres at the base of their mantles

scaling laws for convection with temperature dependent viscosity and grain damage numerical experiments of convection with grain damage are used to develop scaling laws for convective heat flow mantle velocity and plate velocity across the stagnant lid and plate tectonic regimes three main cases are presented in order of increasing complexity a simple case wherein viscosity is only dependent on grainsize a case where viscosity depends on temperature and grainsize and finally a case where viscosity is temperature and grainsize sensitive and the grain growth or healing is also temperature sensitive in all cases convection with grain damage scales differently than newtonian convection due to the effects of grain damage for the fully realistic case numerical results show stagnant lid convection fully mobilized convection that resembles the temperature independent viscosity case and partially mobile or transitional convection depending on damage to healing ratio rayleigh number and the activation energies for viscosity and healing applying our scaling laws for the fully realistic case to earth and venus we demonstrate that increasing surface temperature dramatically decreases plate speed and heat flow essentially shutting down plate tectonics due to increased healing in lithospheric shear zones as proposed previously contrary to many previous studies the transitional regime between the stagnant lid and fully mobilized regimes is large and the transition from stagnant lid to mobile convection is gradual and continuous thus planets could exhibit a full range of surface mobility as opposed to the bimodal distribution of fully mobile lid planets and stagnant lid planets that is typically assumed

finite volume two dimensional unsteady flow model for river basins the paper presents a two dimensional unsteady flow model rbfvm 2d based on the finite volume method with a combination of unstructured triangular and quadrilateral grids in a river basin system the attractive feature of this model is that it calculate of the mass and momentum flux across each side of elements as a riemann problem which is solved using the osher scheme this feature enables this model to deal with the wetting and drying processes for flood plain and wetland studies dam breaking phenomena involving discontinuous flows subcritical and supercritical flows and other cases the computations of tributary inflows and regulated flows through gates weirs and culverts or bridges are also included sample applications of this model to two dam break problems showed fairly satisfactory results also this model was applied to a portion of the kissimmee river basin in florida for flow simulations and the results agreed well with the field and laboratory data in a physical model study of this ri

slabs in the lower mantle and their modulation of plume formation numerical mantle convection models indicate that subducting slabs can reach the core mantle boundary cmb for a wide range of assumed material properties and plate tectonic histories an increase in lower mantle viscosity a phase transition at 660 km depth depth dependent thermal expansivity and depth dependent thermal diffusivity do not preclude model slabs from reaching the cmb we find that ancient slabs could be associated with lateral temperature anomalies 500 c cooler than ambient mantle plausible increases of thermal conductivity with depth will not cause slabs to diffuse away regional spherical models with actual plate evolutionary models show that slabs are unlikely to be continuous from the upper mantle to the cmb even for radially simple mantle structures the observation from tomography showing only a few continuous slab like features from the surface to the cmb may be a result of complex plate kinematics not mantle layering there are important consequences of deeply penetrating slabs our models show that plumes preferentially develop on the edge of slabs in areas on the cmb free of slabs plume formation and eruption are expected to be frequent while the basal thermal boundary layer would be thin however in areas beneath slabs the basal thermal boundary layer would be thicker and plume formation infrequent beneath slabs a substantial amount of hot mantle can be trapped over long periods of time leading to mega plume formation we predict that patches of low seismic velocity may be found beneath large scale high seismic velocity structures at the core mantle boundary we find that the location buoyancy and geochemistry of mega plumes will differ from those plumes forming at the edge of slabs various geophysical and geochemical implications of this finding are discussed

plate tectonics on super earths equally or more likely than on earth abstract the discovery of extra solar super earths has prompted interest in their possible mantle dynamics and evolution and in whether their lithospheres are most likely to be undergoing active plate tectonics like on earth or be stagnant lids like on mars and venus the origin of plate tectonics is poorly understood for earth likely involving a complex interplay of rheological compositional melting and thermal effects which makes it challenging to make reliable predictions for other planets nevertheless as a starting point it is common to parameterize the complex processes involved as a simple yield stress that is either constant or has a byerlee s law dependence on pressure because the simplifying assumptions made in developing analytical scalings may not be valid over all parameter ranges numerical simulations are needed one numerical study on super earths finds that plate tectonics is less likely on a larger planet o neill and lenardic 2007 in apparent contradiction of an analytical scaling study valencia et al 2007 to try and understand this we here present new calculations of yielding induced plate tectonics as a function of planet size focusing on the idealized end members of internal heating or basal heating as well as different strength profiles and compared to analytical scalings in the present study we model super earths as simple scaled up versions of earth i e assuming constant physical properties keeping the ratio of core mantle radii constant and applying the same temperature difference between top bottom boundaries and the same internal heating rate effects that originate outside of the planet such as tidal forces meteor impacts and intense surface heating from a nearby star are not considered we find that for internally heated convection plate tectonics is equally likely for terrestrial planets of any size whereas for basally heated convection plate tectonics becomes more likely with increasing planet size this is indicated both by analytical scalings and the presented numerical results which agree with each other when scalings are adjusted to account for increasing mean density with increasing planet size plate tectonics becomes more likely with increasing planet size for all scenarios the influence of the pressure variation of viscosity thermal expansivity and conductivity may however act in the opposite sense and needs to be determined in future studies at least in the simplest case factors other than planet size such as the presence of surface water are likely most important for determining the presence or absence of plate tectonics

the influence of mantle internal heating on lithospheric mobility implications for super earths abstract super earths a recently discovered class of exoplanets have been inferred to be of a similar rock and metal composition to the earth as a result the possibility that they are characterised by the presence of plate tectonics has been widely debated however as the super earths have higher masses than earth it is assumed that they will also have higher rayleigh numbers and non dimensional heating rates accordingly we conduct a systematic 2d study to investigate the influence of these parameters on the surface behaviour of mantle convection the main focus of our work considers the response of surface motion to the mantle s internal heating however we also include an analysis of other parameters scaling with planet mass such as viscosity in agreement with the findings of valencia and o connell 2009 and van heck and tackley 2011 we find plate like surface mobilisation for increased rayleigh numbers but increasing the internal heating leads to the formation of a strong stagnant lid because the mantle heating effects thermally activated viscosity additionally viscosity is affected by the increased pressures and temperatures of super earths in total our findings indicate that surface mobility will likely be reduced on super sized earths our numerical models show that the interior temperature of the convecting system is of vital importance in planets with a hotter interior plate tectonics is less likely

analysis procedure for and application of a device for simulating sediment entrainment abstract the problem of estimating entrainment rates for cohesive bed sediments has been approached an analysis procedure was developed for characterizing entrainment of cohesive bed sediments using a device called a particle entrainment simulator pes which simulates bed shear effects on sediment entrainment while most of the available techniques to calculate entrainment rates are based on theoretical parameterizations using the flow field the pes technique and its method of analysis provide a tool to directly measure entrainment under controlled laboratory settings representative of existing or predicted conditions of bed stress sediment compaction and cohesion and if any bioturbation the analysis procedure calculates entrainment rates using data generated from experiments conducted on sediment cores with the pes the procedure was applied to determine entrainment rates for two different marine sites the first in puget sound was used to validate the procedure with field data for a tidally dominated period of time entrainment rates were calculated at a second site on hudson shelf valley where storm generated wave and current effects are important suspended sediment concentration distributions in the water column were calculated at both sites using pes generated entrainment stress functions good agreement was reached between the calculated and observed suspended sediment concentrations at 5 m above the bed for the puget sound application observations were not available for suspended sediment concentration comparisons for the hudson shelf valley application