constraints on the lateral strength of slabs from three dimensional dynamic flow models if the viscosity of subducted lithosphere is described purely by temperature and pressure it should remain considerably more viscous than the surrounding material as it descends through the upper mantle many dynamic models of the long wavelength geoid associated with slabs require an increase in viscosity from the upper to the lower mantle but assume the perturbation to the lateral viscosity structure arising from the slabs themselves can be ignored previous studies indicate that strong and localized viscosity variations should have a dramatic influence on the geoid we present 3d finite element models of the regional geoid of the western pacific subduction zones slab buoyancies and viscosities are defined using the distribution of seismicity the geoid is very sensitive to the lateral strength of the slab very viscous slabs penetrating a low viscosity mantle generate significant 10 50 m long wavelength geoid lows opposite to the geoid high which is observed over slabs to obtain a geoid high comparable to that observed the lower mantle viscosity must be 60 200 times greater than the upper mantle viscosity and the slab must be in contact with the lower mantle these strict requirements suggest that slabs have been weakened and cannot act as stress guides from the deep mantle to the surface

measuring floodplain spatial patterns using continuous surface metrics at multiple scales abstract interactions between fluvial processes and floodplain ecosystems occur upon a floodplain surface that is often physically complex spatial patterns in floodplain topography have only recently been quantified over multiple scales and discrepancies exist in how floodplain surfaces are perceived to be spatially organised we measured spatial patterns in floodplain topography for pool 9 of the upper mississippi river usa using moving window analyses of eight surface metrics applied to a 1 1 m 2 dem over multiple scales the metrics used were range sd skewness kurtosis cv sd curv rugosity and vol area and window sizes ranged from 10 to 1000 m in radius surface metric values were highly variable across the floodplain and revealed a high degree of spatial organisation in floodplain topography moran s i correlograms fit to the landscape of each metric at each window size revealed that patchiness existed at nearly all window sizes but the strength and scale of patchiness changed within window size suggesting that multiple scales of patchiness and patch structure exist in the topography of this floodplain scale thresholds in the spatial patterns were observed particularly between the 50 and 100 m window sizes for all surface metrics and between the 500 and 750 m window sizes for most metrics these threshold scales are 15 20 and 150 of the main channel width 1 2 and 10 15 of the floodplain width respectively these thresholds may be related to structuring processes operating across distinct scale ranges by coupling surface metrics multi scale analyses and correlograms quantifying floodplain topographic complexity is possible in ways that should assist in clarifying how floodplain ecosystems are structured

spatial prediction of river channel topography by kriging topographic information is fundamental to geomorphic inquiry and spatial prediction of bed elevation from irregular survey data is an important component of many reach scale studies kriging is a geostatistical technique for obtaining these predictions along with measures of their reliability and this paper outlines a specialized framework intended for application to river channels our modular approach includes an algorithm for transforming the coordinates of data and prediction locations to a channel centered coordinate system several different methods of representing the trend component of topographic variation and search strategies that incorporate geomorphic information to determine which survey data are used to make a prediction at a specific location for example a relationship between curvature and the lateral position of maximum depth can be used to include cross sectional asymmetry in a two dimensional trend surface model and topographic breaklines can be used to restrict which data are retained in a local neighborhood around each prediction location using survey data from a restored gravel bed river we demonstrate how transformation to the channel centered coordinate system facilitates interpretation of the variogram a statistical model of reach scale spatial structure used in kriging and how the choice of a trend model affects the variogram of the residuals from that trend similarly we show how decomposing kriging predictions into their trend and residual components can yield useful information on channel morphology cross validation analyses involving different data configurations and kriging variants indicate that kriging is quite robust and that survey density is the primary control on the accuracy of bed elevation predictions the root mean square error of these predictions is directly proportional to the spacing between surveyed cross sections even in a reconfigured channel with a relatively simple morphology sophisticated methods of spatial prediction are no substitute for field data copyright 2007 john wiley sons ltd

spin state of ferric iron in mgsio3 perovskite and its effect on elastic properties abstract recent studies have indicated that a significant amount of iron in mgsio 3 perovskite pv is fe 3 fe 3 fe 10 60 due to crystal chemistry effects at high pressure p and that fe 3 is more likely than fe 2 to undergo a high spin hs to low spin ls transition in pv in the mantle we have measured synchrotron mossbauer spectroscopy sms x ray emission spectroscopy xes and x ray diffraction xrd of pv with all iron in fe 3 in the laser heated diamond anvil cell to over 100 gpa fe 3 increases the anisotropy of the pv unit cell whereas fe 2 decreases it in pv synthesized above 50 gpa fe 3 enters into both the dodecahedral a and octahedral b sites approximately equally suggesting charge coupled substitution combining sms and xes we found that the ls population in the b site gradually increases with pressure up to 50 60 gpa where all fe 3 in the b site becomes ls while fe 3 in the a site remains hs to at least 136 gpa fe 3 makes pv more compressible than mg endmember below 50 gpa because of the gradual spin transition in the b site together with lattice compression the completion of the spin transition at 50 60 gpa increases bulk modulus with no associated change in density this elasticity change can be a useful seismic probe for investigating compositional heterogeneities associated with fe 3

mapping gravel bed river bathymetry from space 1 understanding river form and behavior requires an efficient means of measuring channel morphology this study evaluated the potential to map the bathymetry of two clear flowing shallow 3 m deep gravel bed rivers 60 m wide from 2 m pixel worldview2 satellite images direct measurements of water column optical properties were used to quantify constraints on depth retrieval the smallest detectable change in depth was 0 01 0 04 m and the maximum detectable depth was 5 m in green bands but 2 m in the near infrared lower sensor radiometric resolution yields less precise estimates over a smaller range an algorithm for calibrating a band ratiox to field measurements of depth d proved effective when applied to spectra extracted from images r2 0 822 and 0 594 for the larger and smaller stream respectively or measured in the field r2 0 769 and 0 452 this procedure also identified optimal wavelength combinations but different bands were selected for each site accuracy assessment of bathymetric maps produced using various calibration approaches and image types indicated that 1 a linear d vs xrelation provided depth estimates nearly as accurate as a quadratic formulation 2 panchromatic and pan sharpened multispectral images with smaller 0 5 m pixels did not yield more reliable depth estimates than the original images and 3 depth retrieval was less reliable in pools due to saturation of the radiance signal this investigation thus demonstrated the feasibility as well as the limitations of measuring the bathymetry of clear shallow gravel bed rivers from space

deepest mantle viscosity constraints from earth rotation anomalies 1 the radial variation of viscosity from earth s surface to the core mantle boundary is most accurately determined on the basis of observations related to the glacial isostatic adjustment gia process beneath a depth of approximately 1250 km the primary constraints available pertain to the anomalies in earth s rotational state that have previously been shown to be intimately linked to the same gia process responsible for postglacial sea level variability it is demonstrated that these anomalies are capable of resolving a difference between d viscosity and that of the overlying region which extends upwards to the 1250 km depth horizon a trade off is shown to exist between the viscosities in these deepest mantle layers that may be resolved by the observed direction of true polar wander

geostatistical analysis of ground survey elevation data to elucidate spatial and temporal river channel change a digital elevation model dem of a fluvial environment represented landform surface variability well and provided a medium for monitoring morphological change over time elevation was measured above an arbitrary datum using a ground based three dimensional tacheometric survey in two reaches of the river nent uk in july 1998 october 1998 after flood conditions and june 1999 a detailed geostatistical analysis of the elevation data was used to model the spatial variation of elevation and to produce dems in each reach and for each survey period maps of the difference in elevation were produced and volumetric change was calculated for each reach and each survey period the parameters of variogram models were used to describe the morphological character of each reach and to elucidate the linkages between process and the form of channel change operating at different spatial and temporal scales the analysis of channel change on the river nent shows the potential of geostatistics for investigating the magnitude and frequency of geomorphic work in other rivers a flood modified the channel features but low magnitude and high frequency flows rationalized the morphology in spite of relatively small amounts of net flux the channel features changed as a consequence of the reworking of existing material the blocking of chute entrances and redirection of the channel had a considerable effect on the behaviour of the channel such small changes suggested that the distributary system was sensitive to variation in sediment regime plots of the kriging variances against sampling intervals were used to quantify the temporal variation in sampling redundancy ranging between 11 per cent and 93 per cent these curves illustrated the importance of bespoke sampling designs to reduce sampling effort by incorporating anisotropic variation in space and geomorphic information on flow regime variation in the nugget parameter of the variogram models was interpreted as sampling inaccuracy caused by variability in particle size and is believed to be important for future work on surface roughness copyright 2003 john wiley sons ltd

quantifying submerged fluvial topography using hyperspatial resolution uas imagery and structure from motion photogrammetry quantifying the topography of rivers and their associated bedforms has been a fundamental concern of fluvial geomorphology for decades such data acquired at high temporal and spatial resolutions are increasingly in demand for process oriented investigations of flow hydraulics sediment dynamics and in stream habitat in these riverine environments the most challenging region for topographic measurement is the wetted submerged channel generally dry bed topography and submerged bathymetry are measured using different methods and technology this adds to the costs logistical challenges and data processing requirements of comprehensive river surveys however some technologies are capable of measuring the submerged topography through water photogrammetry and bathymetric lidar are capable of reasonably accurate measurements of channel beds in clear water whilst the cost of bathymetric lidar remains high and its resolution relatively coarse the recent developments in photogrammetry using structure from motion sfm algorithms promise a fundamental shift in the accessibility of topographic data for a wide range of settings here we present results demonstrating the potential of so called sfm photogrammetry for quantifying both exposed and submerged fluvial topography at the mesohabitat scale we show that imagery acquired from a rotary winged unmanned aerial system uas can be processed in order to produce digital elevation models dems with hyperspatial resolutions c 0 02 m for two different river systems over channel lengths of 50 100 m errors in submerged areas range from 0 016 m to 0 089 m which can be reduced to between 0 008 m and 0 053 m with the application of a simple refraction correction this work therefore demonstrates the potential of uas platforms and sfm photogrammetry as a single technique for surveying fluvial topography at the mesoscale defined as lengths of channel from c 10 m to a few hundred metres this article is protected by copyright all rights reserved

uas based remote sensing of fluvial change following an extreme flood event the effects of large floods on river morphology are variable and poorly understood in this study we apply multi temporal datasets collected with small unmanned aircraft systems uass to analyze three dimensional morphodynamic changes associated with an extreme flood event that occurred from 19 to 23 june 2013 on the elbow river alberta we documented reach scale spatial patterns of erosion and deposition using high resolution 4 5 cm pixel orthoimagery and digital elevation models dems produced from photogrammetry significant bank erosion and channel widening occurred with an average elevation change of 0 24 m the channel pattern was reorganized and overall elevation variation increased as the channel adjusted to full mobilization of most of the bed surface sediments to test the extent to which geomorphic changes can be predicted from initial conditions we compared shear stresses from a two dimensional hydrodynamic model of peak discharge to critical shear stresses for bed surface sediment sizes we found no relation between modeled normalized shear stresses and patterns of scour and fill confirming the complex nature of sediment mobilization and flux in high magnitude events however comparing modeled peak flows through the pre and post flood topography showed that the flood resulted in an adjustment that contributes to overall stability with lower percentages of bed area below thresholds for full mobility in the post flood geomorphic configuration overall this work highlights the potential of uas based remote sensing for measuring three dimensional changes in fluvial settings and provides a detailed analysis of potential relationships between flood forces and geomorphic change copyright 2015 john wiley sons ltd

development of channel organization and roughness following sediment pulses in single thread gravel bed rivers large episodic inputs of coarse sediment sediment pulses in forested mountain streams may result in changes in the size and arrangement of bed forms and in channel roughness a conceptual model of channel organization delineates trajectories of response to sediment pulses for many types of gravel bed channels channels exhibited self organizing behavior to various degrees based on channel gradient presence of large in channel wood or other forcing elements the size of the sediment pulse and the number of bed mobilizing flows since disturbance typical channel changes following a sediment pulse were initial decreases in water depth in variability of bed elevations and in the regularity of bed form spacing trajectories of change subsequently showed increased average water depth more variable and complex bed topography and increased uniformity of bed form spacing bed form spacing in streams with abundant forcing elements developed at a shorter spatial scale two to five channel widths than in streams without such forcing mechanisms five to 10 channel widths channel roughness increased as bed forms developed

temporal and spatial variability in thalweg profiles of a gravel bed river this study used successive longitudinal thalweg profiles in gravel bed rivers to monitor changes in bed topography followingfloodsandassociatedlargesedimentinputs variationsinchannelbedelevations distributionsofresidualwater depths percentage of channellengthoccupied byriffles andaspatial autocorrelationcoefficient moran si wereused to quantify changes in morphological diversity and spatial structure in redwood creek basin northwestern california bed topographyinredwoodcreekanditsmajortributariesconsistsprimarilyofaseriesofpoolsandriffles thesize frequency and spatial distribution of the pools and riffles have changed significantly during the past 20 years following large floods and highsediment input inredwood creek and its tributaries in 1975 variation in channelbed elevations was low and the percentageofthechannellengthoccupiedbyriffleswashigh overthenext20years variationinbedelevationsincreased while the length of channel occupied by riffles decreased an index standard deviation of residual water depth bankfull depth 100 wasdevelopedtocomparevariationsinbedelevationoverarangeofstreamsizes withahigherindexbeing indicativeofgreatermorphologicaldiversity spatialautocorrelationinthebedelevationdatawasapparentatbothfineand coarsescalesinmanyofthethalwegprofilesandtheobservedspatialpatternofbedelevationswasfoundtoberelatedtothe dominant channel material and the time since disturbance river reaches in which forced pools dominated and in which large woody debris and bed particles could not be easily mobilized exhibited a random distribution of bed elevations in contrast in reaches where alternate bars dominated and both wood and gravel were readily transported regularly spaced bed topography developed at a spacing that increased with time since disturbance this pattern of regularly spaced bed featureswasreversedfollowinga12 yearfloodwhenbedelevationsbecamemorerandomlyarranged copyright 1999 john wiley sons ltd

yin yang grid an overset grid in spherical geometry 1 a new kind of overset grid named yin yang grid for spherical geometry is proposed the yin yang grid is composed of two identical component grids that are combined in a complemental way to cover a spherical surface with partial overlap on their boundaries each component grid is a low latitude part of the latitude longitude grid therefore the grid spacing is quasi uniform and the metric tensors are simple and analytically known one can directly apply mathematical and numerical resources that have been written in the spherical polar coordinates or latitude longitude grid the complemental combination of the two identical component grids enables us to make efficient and concise programs simulation codes for geodynamo and mantle convection simulations using finite difference scheme based on the yin yang grid are developed and tested the yin yang grid is suitable for massively parallel computers

a geostatistical framework for quantifying the reach scale spatial structure of river morphology 1 variogram models related metrics and relation to channel form abstract fluvial geomorphology is fundamentally concerned with the association between form and process in rivers examining these interactions in complex natural channels requires a means of quantifying the variability and organization of bed topography this paper introduces a geostatistical framework for characterizing reach scale spatial structure transformation to a channel centered coordinate system allows topographic variations to be resolved into along and across stream components dimensionless variables obtained by scaling distances by the mean channel width and de trended elevations by the mean bankfull depth account for channel size and allow spatial patterns to be compared over time or among sites these patterns are effectively described by the variogram a spatial statistic that expresses dissimilarity as a function of distance fitting a parametric model to the sample variogram provides a rich description of channel form for example multiple nested structures can be combined to account for anisotropy with varying degrees of spatial variability observed over different length scales along and across the channel integral metrics derived from the variogram model yield a more compact summary and variogram maps a useful visualization to guide interpretation of these metrics i used a simple channel builder to isolate the effects of specific aspects of river morphology on the variogram this analysis indicated that geostatistical models were sensitive to changes in the size shape and orientation of channel features but not to a pure translation of the morphology the results also highlighted the importance of considering streamwise and transverse components jointly rather than in isolation

spin state transition and partitioning of iron effects on mantle dynamics experimental studies at pressure and temperature conditions of the earth s lower mantle have shown that iron in ferropericlase fp and in mg silicate perovskite pv undergoes a spin state transition this electronic transition changes elastic and transport properties of lower mantle minerals and can play an important role in mantle convection here we focus on the geodynamic effect of the spin induced density modifications caused by the volume collapse of fp and by the variation of fe partitioning kpv fp between fp and pv since kpv fp behavior strongly depends on alumina content we explore two end member compositions one al bearing with 4 7 wt al2o3 in pv and the other al free we use the theoretical model by sturhahn et al 2005 to calculate the spin configuration of fp over a range of pressure temperature conditions and use experimental results to model fe partitioning we then apply the mie gruneisen debye equation of state to obtain the density of the mineral assemblages the calculated amplitude of the density change across the spin state transition is less than 1 consistent with experiments by mao et al 2011 our density profiles differ from prem by less than 1 5 the spin induced density variations are included in a three dimensional convection code stag3d for a compressible mantle we find small temperature differences between models with and without spin state transitions since over billions of years the relative temperature difference is less than 50 k however the relative rms vertical velocity difference is up to 15 for an al free system but only less than 6 for an al bearing system c 2015 elsevier b v all rights reserved

sinking slabs below fossil subduction zones abstract the fate of sinking lithospheric slabs following the cessation of subduction is examined using a two dimensional numerical model of mantle convection the model incorporates rigidly moving oceanic plates which recycle through the underlying viscous mantle and rigid continental plates which cannot be subducted due to their inherent buoyancy the model is used to study the effects of the cessation of subduction due to the accretion of a 4000 km wide block of continental crust to the margin of a large stationary continent e g the india asia collision we model a continental block representative of greater india that is carried along with an oceanic plate towards a subduction zone at the leading edge of a much larger stationary continent which represents asia prior to continental collision subducted oceanic plate material under rides the margin of the larger continent for several hundred kilometres before peeling away from the surface boundary layer and descending into the mantle as a cold narrow slab consequently once a moving continental block arrives at the continental margin and closes over the original subduction zone the surface location of the continental suture lies several hundred kilometres seaward of the location of the cold remnant of the sinking slab the ongoing convective flow in the subcontinental mantle adjusts to accommodate the change in mechanical boundary condition at the upper surface a step increase in viscosity at 660 km depth slows the rate of slab descent substantially but cannot account for mid mantle thermal anomalies attributed to subduction zones that became extinct more than 140 my ago the horizontal displacement of the slab remnants relative to the continental crustal suture depends on the relative motion of the fossil plate boundary at the surface and the underlying mantle over riding of an intra oceanic subduction zone or the indenting of a smaller subcontinent into a larger continental mass can cause the tomographically observed cold anomalies to be displaced laterally by thousands of kilometers from the location of the former converging plate boundary

recent large magnitude floods and their impact on valley floor environments of northeastern yellowstone abstract the lamar river watershed of northeastern yellowstone contains some of the most diverse and important habitat in the national park broad glacial valley floors feature grassland winter range for ungulates riparian vegetation that provides food and cover for a variety of species and alluvial channels that are requisite habitat for native fish rapid neogene uplift and quaternary climatic change have created a dynamic modern environment in which catastrophic processes exert a major influence on riverine riparian ecosystems uplift and glacial erosion have generated high local relief and extensive cliffs of friable volcaniclastic bedrock as a result steep tributary basins produce voluminous runoff and sediment during intense precipitation and rapid snowmelt recent major floods on trunk streams deposited extensive overbank gravels that replaced loamy soils on flood plains and allowed conifers to colonize valley floor meadows tree ring dating identifies major floods in 1918 ca 1873 and possibly ca 1790 in 1996 and 1997 discharge during snowmelt runoff on soda butte creek approached the 100 year flood estimated by regional techniques with substantial local bank erosion and channel widening indirect estimates show that peak discharges in 1918 were approximately three times greater than in 1996 with similar duration and much greater flood plain impact nonetheless 1918 peak discharge reconstructions fall well within the range of maximum recorded discharges in relation to basin area in the upper yellowstone region the 1873 and 1918 floods produced lasting impacts on the channel form and flood plain of soda butte creek channels may still be locally enlarged from flood erosion and net downcutting has occurred in some reaches leaving the pre 1790 flood plain abandoned as a terrace gravelly overbank deposits raise flood plain surfaces above levels of frequent inundation and are well drained therefore flood plain soils are drier noncohesive gravels also reduce bank stability and may have persistent effects on channel form overall floods are part of a suite of catastrophic geomorphic processes that exert a very strong influence on landscape patterns and valley floor ecosystems in northeastern yellowstone

phase boundaries in finite amplitude mantle convection summary phase boundaries are included in dynamical finite element models of mantle convection they are represented by point chains which act as additional sources of buoyancy forces when distorted and as additional source or sink of heat the influence of the exothermic olivine spinel transition is studied in both shallow and deep convection models the flow is only slightly enhanced by the transition the increase of temperature due to latent heat release is step like in the deep model in the case of shallow convection it is more diffuse other quantities like ocean floor topography gravity anomalies and stress distribution are no more than moderately affected in a further investigation the effect of spinel post spinel transition whether endothermic or exothermic on deep convection is examined the effect on the flow is negligibly small in both cases

the impacts of mantle phase transitions and the iron spin crossover in ferropericlase on convective mixing is the evidence for compositional convection definitive new results from a yin yang overset grid based control volume model high resolution seismic tomographic images from several subduction zones provide evidence for the inhibition of the downwelling of subducting slabs at the level of the 660 km depth seismic discontinuity furthermore the inference of old 140 myr sinking slabs below fossil subduction zones in the lower mantle has yet to be explained we employ a control volume methodology to develop a new anelastically compressible model of three dimensional thermal convection in the mantle of a terrestrial planet that fully incorporates the influence of large variations in material properties the model also incorporates the influence of 1 multiple solid solid pressure induced phase transitions 2 transformational superplasticity at 660 km depth and 3 the high spin low spin iron spin transition in ferropericlase at midmantle pressures the message passing interface parallelized code is successfully tested against previously published benchmark results the high resolution control volume models exhibit the same degree of radial layering as previously shown to be characteristic of otherwise identical 2 d axisymmetric spherical models the layering is enhanced by the presence of moderate transformational superplasticity and in the presence of the spin crossover in ferropericlase stagnation of cold downwellings occurs in the range of spin crossover depths 1700 km although this electronic spin transition has been suggested to be invisible seismically recent high pressure ab initio calculations suggest it to have a clear signature in body wave velocities which could provide an isochemical explanation of a seismological signature involving the onset of decorrelation between vp and vs that has come to be interpreted as requiring compositional layering

mantle phase transitions and layered chaotic convection we report preliminary results from a sequence of very high resolution simulations of the mantle convection process based upon an axisymmetric anelastically compressible spherical model with both olivine spinel and spinel post spinel phase transitions our analyses strongly suggest that at earth like rayleigh numbers near 107 the circulation may be quite strongly layered although a very long timescale transient exists that is characterized by brief excursions into the whole mantle state we suggest the use of a new diagnostic tool that may be employed to determine whether or not the layered state is characteristic of the present day earth

the missing dimension effects of lateral variation on 1 d calculations of fluvial bedload transport most calculations of bedload transport in rivers including those in numerical models of aggradation and degradation are 1 d all hydraulic and transport rate calculations are averaged over the channel width because bedload transport laws are nonlinear width averaged calculations will underestimate the true bedload flux if there is any local spatial variation in either the bed or the flow this paper analyses the effects on bedload transport capacity of spatial variation in applied and critical c shear stress separately and in combination a simple but versatile statistical model is used to represent variability in with allowance for differences between sand and gravel bed rivers and for below bankfull flow bedload flux is shown to increase greatly with the variance of especially in gravel bed rivers variability in c through bed patchiness may increase reduce or make little difference to bedload flux depending on the correlation between and c simple width averaging leads to severe underestimation of bedload transport in most conditions some alternatives are considered the findings have implications for sediment routing models srms but further research is needed to explore the issue fully

introduction to the special issue on discontinuity of fluvial systems abstract fluvial systems include natural and human created barriers that modify local base level as such these discontinuities alter the longitudinal flux of water and sediment by storing releasing or changing the flow path of those materials even in the absence of distinct barriers fluvial systems are typically discontinuous and patchy the size of fluvial discontinuities ranges across scales from 10 0 m such as riffles to 10 4 m such as lava dams or major landslides the frequency of occurrence appears to be inversely related to size with creation and failure of the small features such as beaver dams occurring on a time scale of 10 0 to 10 1 years and a frequency of occurrence at scales as low as 10 1 m in contrast larger scale discontinuities such as lava dams can last for time scales up to 10 5 years and have a frequency of occurrence of approximately 10 4 m the heterogeneity generated by features is an essential part of river networks and should be considered as part of river management therefore we suggest that natural dams are a useful analog for human dams when evaluating options for river restoration this collection of papers on the studies of natural dams includes bedrock barriers log jams and beaver dams the collection also addresses the discontinuity generated by a floodplain in the absence of an obvious barrier in the channel and tools for evaluation of riverbed heterogeneity it is completed with a study of impact of human dams on floodplain sedimentation these papers will help geomorphologists and river managers understand the factors that control river heterogeneity across scales and around the world

melting of the fefeo and the fefes systems at high pressure constraints on core temperatures melting temperatures of feo fes and fes2 have been accurately determined in a hydrostatic inert pressure environment up to about 0 5 mbar using a new yttrium lithium fluoride ylf heating laser the melting curve for feo is in perfect agreement with data obtained from multi anvil experiments at 160 kbar 1 but is in stark disagreement with previous laser heating experiments 2 preliminary measurements show strong melting depression on mixtures of fe and fes whereas mixtures of fe and feo were observed to melt close to the melting curve of iron the kraut kennedy melting relationship 3 in which the melting temperature is a linear function of volume is successfully tested in this study for li na k fe fes fes2 and feo to compressions up to 30 at 1 36 mbar core mantle boundary cmb feo fe and fes are estimated to melt at 3670 3260 and 3060 100 k respectively assuming outer core compositions with about 60 fe and about 40 feo or fes and a solid solution system the melting temperature at the cmb on the core side would be 3300 k 200 k compared to a temperature at the bottom of the mantle of 2650 100 k if these systems exhibit eutectic behaviour the melting gradient through the outer core would have to be substantially higher than the adiabatic gradient in order to maintain a thermal boundary at the cmb the present melting data and experimental constraints on the adiabatic gradient in the outer core suggest a temperature at the inner core outer core boundary of nearly 4200 k

tethyan subducted slabs under india abstract tomographic imaging of the mantle under tibet india and the adjacent indian ocean reveals several zones of relatively high p wave velocities at various depths under the hindu kush region in northeastern afghanistan and southern tajikistan a regional northward dipping slab is seen in the entire upper 600 km of the mantle and is apparently still attached to the lithosphere of the indian plate under northern pakistan this same slab shows a roll over structure with the deeper portion overturned and dipping southward as can also be seen in the distribution of earthquake hypocenters farther east southeast e g in the vicinity of nepal a well resolved anomaly below 450 km depth is connected to the slab under the hindu kush but seems to be separated from the lithosphere above 350 km these upper mantle anomalies are interpreted as the remnants of delaminated sub continental lithosphere that went down when greater india continued to converge northward with asia after 45 ma the deeper high velocity anomalies under the indian sub continent appear clearly separated from the shallower ones as well as from each other and are inferred to represent remnants of oceanic lithospheric slabs that have sunk into the lower mantle and were subsequently overridden by the indian plate they occur at depths between 1000 and 2300 km and occasionally descend down to the core mantle boundary the anomalies form three parallel wnw ese striking zones we interpret the two southern zones as remnants of oceanic lithosphere that was subducted when the neo tethys ocean closed between india and tibet in the cretaceous and earliest tertiary the northern deep mantle zone under northern afghanistan the himalayas and the lhasa block in southern tibet may represent the last subducted remnant of the paleo tethys ocean which is thought to have closed before the hauterivian stage of the early cretaceous the middle zone continues southeastward as a rather straight high velocity zone towards sumatra where it becomes convex southward and parallel to the subduction zone under the sunda arc comparison of this straight middle zone near india with the shallower upper 600 1000 km northern zone which displays a cusp like shape near the yunnan sw china syntaxis of the eastern himalayas supports the notion that the shallow northern zone represents later subduction than the deeper middle zone the suggestion of a counterclockwise rotation 20 of the indian plate during tertiary indentation of asia is supported by these features the present day latitudes of 5 35 n of the deep slabs under india and adjacent areas correspond to the approximate paleolatitudes of the cretaceous subduction zones the slab remnants in the middle mantle occur therefore near the ancient locations where they started their downward journey which implies that lateral movements in the deeper mantle were not large

a conceptual model for meander initiation in bedload dominated streams a simple analytic model is presented relating local sediment transport capacity to variance in the transverse shear stress distribution in a stream channel the model is used to develop a physically based conceptual model for the initiation of meandering in straight bedload dominated streams as a result of a feedback mechanism the feedback maximizes the cross sectional shear stress variance and in order to achieve stability ultimately minimizes the energy slope at repeated locations along the channel subject to steady state mass flux and the stability of the channel boundary these locations develop into pools in a fully developed meandering channel they represent attractor states wherein sediment continuity is satisfied using the least possible energy expenditure per unit length of channel however since the cross sectional geometry of a pool and the adjacent bar is asymmetric these attractor states are only conditionally stable requiring strong curvature induced secondary circulation to maintain their asymmetry between two successive pools a stream occupies a metastable higher energy state corresponding to a riffle that requires greater energy expenditure per unit length of channel to transport the same volume of sediment the model we present links processes at the scale of a channel width to adjustments of the channel sinuosity and slope at the scale of a channel reach we argue that the reach scale extremal hypotheses employed by rational regime models are mathematical formalisms that permit a one dimensional theory to describe the three dimensional dynamics producing stream morphology our model is consistent with the results from stream table experiments with respect to both the rate of development of meandering and the characteristics of the equilibrium channel morphology copyright 2006 john wiley sons ltd

characterising the relaxation distance of nearshore submarine morphology a southern baltic sea case study abstract a method for defining the length of coast with alongshore uniformity of nearshore submarine morphology is required in many shore normal nearshore profile modelling approaches here we introduce a new variable the relaxation distance to describe the alongshore spacing between two adjacent shore normal profiles characterised by distinct morphologies within this distance alongshore morphological changes are too small to distinguish so the nearshore submarine morphology is regarded as uniform along the coast we apply a semi variogram approach which expresses decreased spatial correlation of the nearshore submarine morphology with alongshore distance to quantify relaxation distances we apply this morphological variable to analyse 225 measured shore normal submarine profiles at 500 m intervals in three distinct sites of the tideless wave dominated southern baltic coast swina eba and hel the relaxation distances of these three sites are approximately 4500 m 3000 m and 2200 m of the three sites swina has the smoothest nearshore submarine morphology and the weakest wave energy the relaxation distances of different quasi straight segments at each site appear similar but those at different sites decrease with enlarged morphological perturbations which are residuals resulting from detrending the shore normal profiles the standard deviations of these morphological perturbations are correlated with the incidence wave angles and wave energy we also found that large perturbations such as longshore bars and channels have a significant impact on the estimation of underwater volume using shore normal profile trends therefore relaxation distance can indicate morphological smoothness the length of shore parallel uniform nearshore submarine morphology and the impact of local processes on submarine morphology

sediment supply and the development of the coarse surface layer in gravel bedded rivers the bed surface of most gravel rivers is considerably coarser than the sub surface or the gravel load transported over it a phenomenon affecting river dynamics morphology and ecology the coarse surface layer often called an armour or pavement has been attributed to an inherent tendency for small grains to settle between larger ones during active transport of all sizes1 2 and to selective erosion or trapping of finer particles when the coarse grains are relatively immobile3 4 where bedload supply is cut off below dams selective erosion causes coarsening5 6 using a simple quantitative model we propose that surface coarsening develops in gravel bedded rivers when local bedload supply from upstream is less than the ability of the flow to transport that load we present laboratory results which support this hypothesis and show that supply reduction causes changes in bedforms and progressive confinement of active bedload transport to a narrow band of finer bed surface bordered by a coarse less active bed it may therefore be possible to relate the degree of river bed surface coarsening to sediment supply resulting from land use

bar resistance in gravel bed streams at bankfull stage total flow resistance in gravel bed streams with high width depth ratios and low sinuosities is primarily a result of grain and bar roughnesses the relative importance of these two roughness elements has not been established the relative importance of grain and bar resistance is examined for 12 straight and divided gravel bed reaches at bankfull stage by using the keulegan equation to determine a resistance division of energy slope the remaining slope is assumed to represent the relative importance of bar resistance bar resistance accounts for 50 to 75 of the total resistance in these reaches calculated values of reach averaged bar slope correlate closely with field measurements of bar magnitude

large scale tectonic features induced by mantle avalanches with phase temperature and pressure lateral variations of viscosity a more general expression for the mantle vorticity equation is proposed for convection using axisymmetrical spherical geometry both the main mantle phase changes and radial and lateral variations of viscosity due to temperature and pressure four series of computations have been performed with 1 both the latent heat releases of the 400 km exothermic and the 670 km endothermic phase change and uniform and constant mantle viscosity 2 the 670 km phase change alone and viscosity jumps of 10 or 30 between upper and lower mantle phases 3 the 670 km endothermic phase change a viscosity contrast of 30 and temperature and pressure dependent viscosity law and 4 both 400 km and 670 km phase changes a viscosity jump of 30 and a temperature and pressure dependent viscosity the 400 km exothermic phase change modifies the global structure from partly layered to whole mantle convection this effect is opposite to the effect obtained by increasing the viscosity jump at 670 km however both effects induce unrealistic thermal behavior which will not appear with temperature dependent laws for viscosity the mantle avalanches which suddenly inject huge quantities of cold material into the lower mantle have effects at the surface and at the core mantle boundary cmb they induced heat flow crises which explain the huge volcanic events high rates of mid oceanic ridge accretion and periods of low frequency magnetic reversal the surface heat flow proceeds directly from the upper mantle return flow along with the avalanches the temperature dependent viscosity tends to decrease the strength of the avalanches the bottom heat flow and the birth of cmb plumes may be considered as the consequences of cold upper mantle material arrival at the cmb the lower mantle and the upper mantle transit times depend on the thickness of upper and lower mantles but also on the phase changes and on the viscosity the cmb and surface perturbations may be simultaneous to a few tens of million years the temporal evolution of the convection pattern during an avalanche allows us to propose self consistent mechanisms for slab migration above the 670 km discontinuity for the birth and disappearance of ridges the rising of powerful plumes from the cmb and the creation of low viscosity zones which may act as a lubricant under continents for fast migration these results show that the main mantle phase changes combined with temperature and pressure dependent viscosity induce convective behavior which provides an explanation for most of the past and present large scale dynamic behavior of the earth s global tectonics

paleogeographic maps of the continents bordering the indian ocean since the early jurassic paleomagnetic data from the african plate from the early jurassic onward are critically re evaluated and updated resulting in a set of 30 paleopoles from which an apparent polar wander path is derived using 20 ma intervals this path is then used in conjunction with kinematic models of the indian and atlantic oceans to place other continents bordering the indian ocean eurasia india islands and plateaus madagascar seychelles mascarene and blocks involved in the collision of india with eurasia south tibet indochina in an absolute paleogeographic frame fixed with respect to africa paleogeographic maps are presented for the early jurassic pre breakup the jurassic cretaceous boundary anomaly ml5 the early cretaceous m2 the late cretaceous a 34 the cretaceous tertiary boundary a 29 the early eocene a 24 the middle eocene a 21 and the oligocene miocene boundary a 6 observed and predicted paleomagnetic directions for landmasses other than africa i e for western europe china korea india and australia which are not used in deriving the maps are found to be in very satisfactory agreement the quality of reconstructions as measured by rms discrepancies between observed and predicted paleolatitudes is of the order of 5 the main features of the paleogeographic maps are discussed with the aim of relating oceanic and on land geodynamic events the constraints provided by tibetan data on the india asia collision and the 20 ma reorganization of geology and plate boundaries in a band extending from the south china sea through tibet to the red sea system are discussed in more detail we emphasize the episodic nature of the breakup of gondwanaland and formation of the indian ocean and subsequent interaction with eurasia in which six major discrete events are identified separated by 30 ma phases of rather uniform plate motion

changes of the earth s rotation axis owing to advection of mantle density heterogeneities polar wander the secular motion of the earth s rotation axis relative to its surface has been studied for many years dynamical arguments1 3 show that polar wander can arise from the redistribution of mass in a plastic deformable earth the rate depending on both the rate of mass redistribution and the rate at which the earth s rotational bulge can readjust to the changing rotation axis here we use a viscosity structure obtained through geoid modelling4 a mantle flow field consistent with tomographic anomalies5 and time dependent lithospheric plate motions6 to calculate the advection of mantle density heterogeneities and corresponding changes in the degree two geoid during the cenozoic era we show that the rotation axis will follow closely any imposed changes of the axis of maximum non hydrostatic moment of inertia the resulting path of the rotation axis agrees well with palaeomagnetic results7 with the model predicting a current rate of polar motion that explains 40 of that observed geodetically8

a geostatistical framework for quantifying the reach scale spatial structure of river morphology 2 application to restored and natural channels abstract alluvial rivers are shaped by interactions between the bed topography the flow field and the movement of sediment to help refine our understanding of these connections between form and process i developed a geostatistical framework for quantifying the reach scale spatial structure of river morphology described in a companion paper in this study i applied this approach to a restored channel and three disparate reaches of a dynamic natural stream repeat topographic surveys of each site were used to examine relationships between channel change and the variability and organization of the topography for the restored river the development of point bars increased overall morphologic diversity primarily because of greater cross sectional asymmetry the three natural reaches experienced a variety of adjustments ranging from 1 gradual bar growth and bank erosion to 2 extensive deposition followed by channel abandonment and 3 chute cutoff and incision of a new channel in both the restored and natural streams geostatistical analysis which involved variogram modeling calculation of integral metrics and inspection of variogram maps provided an effective informative summary of the observed channel changes the use of dimensionless variables accounted for channel size highlighted differences in spatial structure and enabled a comparison among sites the restored reach had not yet achieved the same degree of heterogeneity as the more pristine channels emphasizing variability and spatial pattern via this geostatistical framework could yield insight on form process interactions and help to quantify geomorphic complexity and habitat heterogeneity in the applied context of river restoration

partial melting in a thermo chemical boundary layer at the base of the mantle abstract seismological detections of complex structures in the lowermost mantle boundary layer the d region motivate a conceptual model of a compositionally stratified thermo chemical boundary layer tcbl within which lateral temperature variations sustained by large scale mid mantle flow cause variations of partial melt fraction partial melt fractions of from 0 to 30 in the tcbl occur due to the eutectic of the boundary layer material lying below the high temperature at the core mantle boundary cmb coupled with the presence of steep thermal gradients across the boundary layer regions of the tcbl with the highest temperatures have extensive partial melting producing lateral chemical variations and strong effects on seismic velocities and boundary layer dynamics this tcbl concept provides a relatively simple framework that can plausibly account for diverse seismological observations such as predominance of large scale volumetric elastic wave velocity heterogeneity in the boundary layer laterally extensive but intermittent abrupt shear and compressional velocity increases and decreases at the top of the d region small scale topography of d velocity discontinuities thin ultra low velocity zones at the cmb widespread shear wave anisotropy in d bulk sound velocity anomalies detected in low shear velocity regions of d and large scale upwellings from the most extensively melted regions of the boundary layer neutral or negative buoyancy of the partial melt in the tcbl is required along with an increase in bulk modulus and some density increase of the boundary layer material relative to the overlying mantle more complex models in which the partially melted chemical boundary layer is laterally displaced by mid mantle downwellings are also viable but these appear to require additional special circumstances such as a phase change efficient segregation of slab crustal material or abrupt onset of anisotropy in order to account for rapid velocity increases at the top of d the precise nature of the compositional anomaly or anomalies in d and the eutectic composition of this zone are yet to be determined but it appears likely that partial melting within the lowermost mantle plays a paramount role in the observed seismic velocity heterogeneity increased resolution geodynamic calculations of dense boundary layer structures with partial melting and attendant viscosity reductions and chemical heterogeneity are needed to quantify this tcbl concept

fire and alluvial chronology in yellowstone national park climatic and intrinsic controls on holocene geomorphic processes we employed a systemwide approach a large and robust set of radiocarbon ages and modern process analogs to interpret the holocene history of forest fire related sedimentation and overall alluvial activity in northeastern yellowstone national park debris flow and flood events following the 1988 fires provided facies models for interpreting the stratigraphic record of fire related sedimentation within valley side alluvial fans of soda butte creek fire related deposits make up approximately 30 of the late holocene fan alluvium fifty 14 c ages on fire related events cluster within the intervals of 3300 2900 2600 2400 2200 1800 and 1400 800 yr b p and suggest earlier episodes of large fires and fan aggradation around 7500 5500 and 4600 4000 yr b p a major pulse of fire related debris flow activity between 950 and 800 yr b p coincided with the height of the widely recognized medieval warm period ca a d 1050 1200 instrumental climate records over the last 100 yr in yellowstone imply that the intensity and interannual variability of summer precipitation are greater during warmer periods enhancing the potential for severe short term drought major forest fires and storm generated fan deposition along lower soda butte creek fill cut terrace treads were created by lateral migration of channels and accumulation of overbank sediments ca 8000 yr b p terrace level t1a 7000 5600 t1b 3100 2600 t2 2000 1300 t3 and post 800 yr b p t4 these periods coincide with overbank sedimentation on slough creek and the lamar river but alternate with intervals of fire related fan deposition implying a strong climatic control local paleoclimatic data suggest cooler effectively wetter conditions during terrace tread formation in warmer drier intervals reduced average runoff in axial streams results in meander belt narrowing concurrent channel incision may be caused by infrequent large floods greater resistance to downcutting however allowed fewer terraces to be formed along slough creek and the lamar river alluvial systems in northeastern yellowstone show a clear response to millennial scale climatic cycles wherein alluvial fans aggrade and prograde over flood plains in drier periods axial streams widen their flood plains and trim back the fans during wetter periods small scale climatic fluctuations of the holocene thus had substantial impact on postglacial landscapes in northeastern yellowstone

intermittent layered convection in a model mantle with an endothermic phase change at 670 km it is not yet known whether convection in the earth s mantle occurs in cells that extend throughout the entire depth of the mantle or if the upper and lower mantle convect in independent layers both possibilities seem to be consistent with geochemical and seismologi cal observations1 4 it is generally accepted however that the seismologically observed boundary between the upper and lower mantle at 670 km depth arises from the endothermic phase change spinel perovskite mgo here we investigate the results of including this phase change in a model of mantle convection for realism and to eliminate scaling problems our calculations use commonly accepted values of geophysical parameters for a clapeyron slope y 2 106 a value close to experimental results and theoretical expectations we observe local intermittent mixing between the upper and lower mantle such behaviour may offer a way to reconcile the existence of geophysical evidence for both whole mantle and layered convection

spectral and geophysical consequences of 3 d spherical mantle convection with an endothermic phase change at the 670 km discontinuity abstract numerical computations of 3 d compressible convection have been conducted in a spherical earth s mantle with an endothermic phase change at the 670 km discontinuity the results validate the trends of layering of mantle convection induced by the phase change indeed partial layering and two layer convective circulation prevail for the same value of clapeyron slope as was observed with an axisymmetrical approach these 3 d results show that as far as the purely 3 d effects of convection are not concerned the 2 d geometry allows relevant conclusions in particular on the cylindrical shape of the avalanches of upper mantle material into the lower mantle which were observed at the poles of the axisymmetrical numerical simulations however the 3 d simulations allow direct computations of the geophysical consequences of mantle flows as thermal anomalies topographical deflections of the bottom upper and internal surfaces and the resulting geoid anomalies two layered or intermittently layered convection induces geophysical anomalies that are in qualitative agreement with the real geophysical date whereas surface topographies computed from one layer convection models or whole mantle circulation models are too large compared with observations it is possible to generate a satisfactory geoid and topography when a realistic phase change is considered at the 670 km discontinuity this property is verified both for a layered and an intermittently layered structure of convection in the earth s mantle

characteristics of turbulent unidirectional flow over rough beds double averaging perspective with particular focus on sand dunes and gravel beds 1 we address some unsolved methodological issues in modeling of natural rough bed flows by critically examining existing approaches that parameterize rough bed flows these often utilize loosely defined variables here we suggest that double averaging in time and in a volume occupying a thin slab in a plane parallel to the mean bed provides a rigorous straightforward alternative that can aid in the parameterization process we further present two examples two dimensional bed form and gravel bed flows we argue that the double averaging approach based on momentum equations should serve as a better methodological basis for modeling phenomenological developments and parameterizations these equations explicitly include drag terms and form induced momentum fluxes due to spatial heterogeneity of the time averaged flow in the near bed region they also provide a solid basis for better definitions of basic flow variables including the shear stress partitioning into turbulent and form induced momentum fluxes skin friction and pressure form drag we show that for a range of rough bed flows the vertical distribution of the double averaged velocity consists of two distinct regions 1 a linear region below roughness tops and 2 a logarithmic region above them