the influence of ambient groundwater discharge on exchange zones induced by current bedform interactions summary we use numerical modeling to investigate the interactions between laminar flow in a water column current bedform induced flow in underlying permeable sediments and discharge of deep groundwater to the water column groundwater discharge reduces the spatial extent of current induced exchange zones within the sediments and may completely prevent the development of current bedform induced flow at high groundwater discharge although exchange zone size is reduced by groundwater discharge the reduction in exchange flux is not significant suggesting reduced residence times of materials cycled through these smaller zones fluid exchange zones tend to be centered around the reattachment points of eddies that also mark the location of flow divides within the sediments while deep groundwater is discharged preferentially along troughs exchange zone depth and the water column reynolds number are functionally related through a morgan mercer flodin model the relationship between the current induced flux through the sediments and the reynolds number is described by low order monotonic polynomial functions

fire and the evolution of steep soil mantled landscapes recent burns in the western united states attest to the signif icant geomorphic impact of fire in mountainous landscapes yet we lack the ability to predict and interpret fire related erosion over millennial time scales a diverse set of geomorphic processes is often invoked following fire the magnitude of postfire erosional processes coupled with temporal variations in fire frequency dic tate the extent to which fires affect sediment production and land scape evolution in the oregon coast range several models for long term rates of soil production and transport have been tested and calibrated although treatment of fire related processes has been limited following recent fires in the oregon coast range we observed extensive colluvial transport via dry ravel localized bed rock emergence due to excess transport and talus like accumula tion in adjacent low order valleys soils exhibited extreme but dis continuous hydrophobicity and no evidence for rilling or gullying was observed using a field based data set for fire induced dry rav el transport we calibrated a physically based transport model that indicates that soil flux varies nonlinearly with gradient the post fire critical gradient 1 03 which governs the slope at which flux increases rapidly is lower than the previously estimated long term value 1 27 reflecting the reduction of slope roughness from in cineration of vegetation by using a high resolution topographic data set generated via airborne laser swath mapping we modeled the spatial pattern of postfire and long term erosion rates postfire erosion rates exceed long term rates which average 0 1 mm yr 21 by a factor of six and subtle topographic variations generated local patches of rapid postfire erosion commonly 1 mm yr 21 our sim ulations indicate that fire related processes may account for 50 of temporally averaged sediment production on steep hillslopes our analysis provides a mechanistic explanation for the coincident early holocene timing of increased fire frequency and regional ag gradation in oregon coast range drainage basins given the sen sitivity of steep hillslopes to fire driven transport changes in cli mate and fire frequency may affect soil resources by perturbing the balance between soil transport and production

glassy dynamics of landscape evolution soil creeps imperceptibly downhill but also fails catastrophically to create landslides despite the importance of these processes as hazards and in sculpting landscapes there is no agreed upon model that captures the full range of behavior here we examine the granular origins of hillslope soil transport by discrete element method simulations and reanalysis of measurements in natural landscapes we find creep for slopes below a critical gradient where average particle velocity sediment flux increases exponentially with friction coefficient gradient at critical gradient there is a continuous transition to a dense granular flow rheology slow earthflows and landslides thus exhibit glassy dynamics characteristic of a wide range of disordered materials they are described by a two phase flux equation that emerges from grain scale friction alone this glassy model reproduces topographic profiles of natural hillslopes showing its promise for predicting hillslope evolution over geologic timescales

fitting degradation of shoreline scarps by a nonlinear diffusion model the diffusion model of degradation of topographic features is a promising means by which vertical offsets on holocene faults might be dated in order to calibrate the method we have examined present day profiles of wave cut shoreline scarps of late pleistocene lakes bonneville and lahontan it may be assumed that these scarps were initially at least as steep as the angle of repose offsets range from 1 to 12 m and present slope angles range from 9 to 29 a parameter called apparent diffusion age defined as half the mean square horizontal extent of the slope function of each profile is plotted as a function of scarp offset the points show a clear trend of apparent age increasing nearly linearly with offset if linear diffusion held and scarps were initially vertical apparent diffusion age would be the same for all the shoreline profiles the increasing trend can only partly be explained by nonvertical initial scarp slope and therefore the rate of transport of material downslope must increase significantly faster than a linear law in the range of slopes spanned by the data the transport law must become linear at small slope to reduce scatter between profiles with varying ambient slopes the transport law adopted for the purpose of dating is k0 1 5s2 where s is local slope the transport coefficient k0 is correlated inversely with fan slope suggesting that there is a dependence on the particle size distribution a table is included that allows easy application of the model to scarps with simple initial shape

sediment transport by dry ravel 1 dry ravel is a general term that describes the rolling bouncing and sliding of individual particles down a slope and is a dominant hillslope sediment transport process in steep arid and semiarid landscapes during fires particles can be mobilized by the collapse of sediment wedges that have accumulated behind vegetation on a daily basis particles may be mobilized by bioturbation and by small landslides experiments on a dry ravel flume indicate that a basic expression of the momentum equation predicts the distance traveled by particles propelled down a rough surface this equation is further elaborated to produce a nonlinear slope dependent transport equation for dry ravel that represents the rate at which sediment crosses a contour width of slope sediment traps installed on two hillslope transects near santa barbara california measured the flux from dry ravel initiated by bioturbation and the data support the form of the equation additionally a physical model based on the infinite slope stability analysis is proposed for the initiation of dry ravel by landsliding the analytical result from this model is supported by experiments and field data reported by others

ice storms tree throw and hillslope sediment transport in northern hardwood forests in december 2008 694 trees uprooted within a 108 ha 1 08 km2 watershed in central massachusetts due to a severe ice storm resulting in the displacement of 1300 m3 of root material unconsolidated sediment and fractured bedrock overall we find that uprooting and tree throw is often grouped in clusters and cascades conifers displace more material than deciduous trees areas with abundant mature hemlock and steep slopes are more susceptible to tree throw with clusters as dense as 125 per hectare and failure is predominantly downhill suggesting that ice storms promote efficient downslope hillslope sediment transport in northern hardwood forests combining the recurrence interval of severe storms in new england 20 75 years with the forest response presented here we calculate a sediment transport rate of 2 5 10 5 m3 m 1 a 1 averaged over the entire watershed forest susceptibility to tree throw differed based on location in the watershed some areas experienced up to 30 higher than average sediment transport rates while others experienced no tree throw two severe storms following the 2008 ice storm hurricane in 2011 snow storm in october 2012 did not result in significant tree throw within the study area highlighting that the coupling of storm severity and forest susceptibility controls the amount of tree throw during a given forest disturbance in addition to recent tree throw from the 2008 ice storm widespread pit and mound microtopography in the study area indicates that tree throw is a recurrent process in this landscape two factors emerge that will influence future ice storms related hillslope sediment transport in the steep forested hillslopes of new england regional climate gradients and changing climate determine the size intensity and recurrence of ice storms forest management practices and health control the tree age and type copyright 2015 john wiley sons ltd

tree root mounds and their role in transporting soil on forested landscapes the growth and decay of tree roots can stir and transport soil this is one process that contributes to the mass movement of soil on hillslope to explore the efficiency of this process we document the mounding of soil beside ponderosa and lodgepole pine trees in the forests that dominate the mid elevations of colorado s boulder creek watershed mounds are best expressed around ponderosa pines reaching vertical displacements above the far field slopes of order 10 20 cm fading into the slope by roughly 100 cm distance from the trunks with common diameters of 30 cm positive mounding occurs on all sides of trees on slopes indicating that the mounding is not attributable to deflection of a creeping flow of soil around the tree but rather to the insertion of root volume on all sides in the subsurface mounding is commonly asymmetric even on cross slope profiles significant variation in the mound sizes results in no clear relationship between tree diameter and root volume displaced these observations motivated the development of a discrete element model of tree root growth using the liggghts model in which grains we specified to be root cells were allowed to enlarge within the simulated granular matrix mounding could be reproduced with the majority of the vertical displacement of the surface being attributable to reduction of the bulk density due to dilation of the granular matrix during root enlargement finally we develop a previous analysis of the role of roots in transporting soil during growth and decay cycles we find that even in shallow soils the root cycle can drive significant soil transport down forested montane slopes copyright 2013 john wiley sons ltd

sediment transport by burrowing mammals marin county california abstract field observations suggest that burrowing activity is the primary mode of sediment transport currently active in a small grassland drainage basin in marin county california spatial concentrations of the 1 150 gopher mounds surveyed vary from 0 16 mounds m on interfluves to 0 32 mounds m on sideslopes and in the topographic hollow with localized concentrations of up to 2 88 mounds m on the margins of the colluvial deposit simple models of sediment transport by burrowing activity yield estimates of between 0 91 and 2 33 cm3 cm yr for the basin as a whole with absolute minimum and maximum rates of 048 and 6 31 cm3 cm yr i these values are similar to those previously estimated for this area lehre 1982 and are nearly an order of magnitude less than average long term sediment transport rates at the same site reneau 1988 key words sediment transport erosion rates bioturbation introduction burrowing animals disturb and transport soil in environments ranging from alpine tundra to humid grasslands hansen and morris

using hilltop curvature to derive the spatial distribution of erosion rates 1 erosion rates dictate the morphology of landscapes and therefore quantifying them is a critical part of many geomorphic studies methods to directly measure erosion rates are expensive and time consuming whereas topographic analysis facilitates prediction of erosion rates rapidly and over large spatial extents if hillslope sediment flux is nonlinearly dependent on slope then the curvature of hilltops will be linearly proportional to erosion rates in this contribution we develop new techniques to extract hilltop networks and sample their adjacent hillslopes in order to test the utility of hilltop curvature for estimating erosion rates using high resolution 1 m digital elevation data published and new cosmogenic radionuclide analyses in the feather river basin california suggest that erosion rates vary by over an order of magnitude 10 to 250 mm kyr 1 hilltop curvature increases with erosion rates allowing calibration of the hillslope sediment transport coefficient which controls the relationship between gradient and sediment flux having constraints on sediment transport efficiency allows estimation of erosion rates throughout the landscape by mapping the spatial distribution of hilltop curvature additionally we show that hilltop curvature continues to increase with rising erosion rates after gradient limited hillslopes have emerged hence hilltop curvature can potentially reflect higher erosion rates than can be predicted by hillslope gradient providing soil production on hilltops can keep pace with erosion finally hilltop curvature can be used to estimate erosion rates in landscapes undergoing a transient adjustment to changing boundary conditions if the response timescale of hillslopes is short relative to channels

chronology and rates of faulting of ventura river terraces california new evidence concerning the chronology of four late pleistocene terraces of the ventura river near oak view california that are vertically offset and tilted by reverse and reverse flexural slip faults provides a means of estimating rates of fault movement and downcutting by the ventura river radiocarbon ages of charcoal contained within terrace deposits date two of the terraces correlation of soils that have developed on terrace deposits and extrapolation of the rate of vertical displacement of the arroyo parida santa ana fault not a flexural slip fault date the others resulting age estimates for the four main late pleistocene terraces are qt5b 30 000 qt6a 38 000 qt6b 54 000 and qt6c 92 000 yr b p vertical slip rates on flexural slip faults range from 0 3 to 1 1 mm yr and apparently are related to the rate form and mechanics of folding of the north limb of the ayers creek canada larga syncline average rates of downcutting of the ventura river for several intervals during the late pleistocene estimated from the chronology and relative elevation of river terraces north of the arroyo panda santa ana fault upstream from the zone of faulting vary from 0 5 to 1 3 mm yr the range in rates probably reflects variations in local uplift as well as adjustments to changing eustatic sea level climatic conditions and or regional deformation of the western transverse ranges the average rate of downcutting of the ventura river north of the zone of flexural slip faulting is 0 8 mm yr compared with 1 2 to 2 2 mm yr in the deformation zone immediately to the south this apparently indicates that during tectonic deformation there is an approximate balance between the rate of uplift due to faulting and folding and the rate of downcutting by the fluvial system

new probabilistic strong seismic ground motion maps of canada new probabilistic strong seismic ground motion maps of canada are derived by applying the cornell mcguire method to 32 earthquake source zones in canada and adjacent regions peak horizontal acceleration and peak horizontal velocity are mapped to depict strong ground motion in the frequency ranges near 5 hz and near 1 hz respectively some earthquake source zones are well defined on the basis of both tectonics and average seismicity rates but a lack of understanding of the near field effects of the large earthquakes prohibits accurate estimates of ground motion in their vicinity some source zones have no known large scale crustal features or zones of weakness that can explain the seismicity and must therefore be defined simply as concentrations of seismic activity with no geological or geophysical controls on the boundaries other source zones lack information on low magnitude seismicity that would be representative of longer periods of time a significant source of uncertainty in the ground motion estimates is introduced by the uncertainty in strong ground motion attenuation relations particularly in the near field of large earthquakes and particularly in eastern canada where no strong motion data are available for earthquakes larger than magnitude 5 valid estimates can be made of relative levels of probabilistic strong ground motion on a regional basis at moderate probabilities however the simple peak ground motion parameters are not sufficient for engineering design purposes in the immediate vicinity of large earthquakes a comparison of the new probabilistic ground motion estimates at the canada united states border with equivalent estimates made in the united states reveals that peak acceleration contours match well in the british columbia washington state yukon alaska and lake ontario border regions canadian peak velocities are a factor of two higher near the british columbia washington state border canadian peak accelerations are higher in the border regions of eastern canada influenced by the charlevoix zone and in regions of the alaska panhandle british columbia border influenced by the active queen charlotte and fairweather fault zones the new ground motion estimates are used to produce new peak acceleration and peak velocity zoning maps to replace the 1970 peak acceleration zoning map in the national building code of canada the acceleration and velocity maps provide independent ground motion reference levels for small rigid structures and taller flexible structures respectively compared to the 1970 map with four zones the new maps with seven zones have a finer subdivision of zoning in moderate risk areas and additional zones in the high risk areas a change in probability of exceedence from 0 01 per annum on the 1970 map to 10 per cent in 50 yr on the new maps and the addition of velocity as a zoning parameter have necessitated changes in the seismic design provisions these revisions will be incorporated into the 1985 edition of the code

advective flow through the upper continental shelf driven by storms buoyancy and submarine groundwater discharge data from monitoring wells on the carolina usa continental shelf require a reevaluation of pore water exchange across the seafloor temperature salinity and 226ra data from 3 offshore wells require rapid and frequent pore water exchange to depths of several meters through sands and other permeable sediments the exchange is driven by tidal pumping storms buoyancy and submarine groundwater discharge tidal pumping causes semidiurnal temperature cycles in one well that can only be explained by rapid fluid flow the effect of large storms is evident in sudden temperature changes 2 4 m below the seabed in two wells these changes require considerable pore water exchange sudden cooling of the ocean may cause pore waters to become buoyant with respect to the ocean and trigger pore water convection to several meters depth as observed in one well the wells also display frequent large factor of ten changes in 226ra activity this requires a substantial input of 226ra enriched fluids to replace 226ra that is lost during exchange events these data support a fourth flow process which is groundwater seeping from the underlying limestone the pore spaces in the overlying sand provide a temporary reservoir for these fluids we conclude that pore water residence times in 2 4 m thick sands on this continental margin are on the order of a few months or less

rate weakening friction characterizes both slow sliding and catastrophic failure of landslides abstract catastrophic landslides cause billions of dollars in damages and claim thousands of lives annually whereas slow moving landslides with negligible inertia dominate sediment transport on many weathered hillslopes surprisingly both failure modes are displayed by nearby landslides and individual landslides in different years subjected to almost identical environmental conditions such observations have motivated the search for mechanisms that can cause slow moving landslides to transition via runaway acceleration to catastrophic failure a similarly diverse range of sliding behavior including earthquakes and slow slip events occurs along tectonic faults our understanding of these phenomena has benefitted from mechanical treatments that rely upon key ingredients that are notably absent from previous landslide descriptions here we describe landslide motion using a rate and state dependent frictional model that incorporates a nonlocal stress balance to account for the elastic response to gradients in slip our idealized one dimensional model reproduces both the displacement patterns observed in slow moving landslides and the acceleration toward failure exhibited by catastrophic events catastrophic failure occurs only when the slip surface is characterized by rate weakening friction and its lateral dimensions exceed a critical nucleation length h h that is shorter for higher effective stresses however landslides that are extensive enough to fall within this regime can nevertheless slide slowly for months or years before catastrophic failure our results suggest that the diversity of slip behavior observed during landslides can be described with a single model adapted from standard fault mechanics treatments

comparing the smooth parabolic shapes of interfluves in continental slopes to predictions of diffusion transport models abstract computer models of stratigraphic development at continental margins often include elements in which sediment topography evolves according to a diffusion equation representing effects of down slope sediment transport however there has been little effort to verify the model for example by showing whether deposit geometries are as expected from it or by considering whether transport is consistent with the model s assumptions the issue is important for understanding transport erosion and deposition in continental slopes more generally and the extent to which such processes are recorded in seabed morphology examples of slope topography illustrating diffusive like characteristics are examined here in the uppermost slope of the usa central atlantic margin sandy areas between canyon heads are smoothly convex upwards and almost parabolic a morphology similar to subaerial soil mantled hillslopes known to evolve according to a diffusion equation other data of interfluves in muddy sediment from both atlantic and pacific usa margins also show this smooth convex upwards form in subaerial hill crests the upwards convex parabolic shape arises where steady erosion by streams along channels provide constant flux boundary conditions i e the parabola is the steady state solution to the diffusion equation although submarine processes will likely be different the similar morphology of submarine interfluves prompts the question as to whether erosion along channels and movements of sediment between channels can also sometimes occur to cause a diffusive like evolution of topography the discussion therefore focuses on submarine processes affecting erosion and deposition in particular to address whether the morphology results from true diffusion which requires that sediment moves down slope with a transport flux proportional to local bed gradient or is fortuitous sediment transport is instead unrelated to local bed gradient and the morphology arises from other effects on accumulation rates

using chemical tracers in hillslope soils to estimate the importance of chemical denudation under conditions of downslope sediment transport 1 we present a model of hillslope soils that couples the evolution of topography soil thickness and the concentration of constituent soil phases defined as unique components of the soil with collective mass equal to the total soil mass the model includes both sediment transport and chemical denudation a simplified two phase model is developed the two phases are a chemically immobile phase which has far lower solubility than the bulk soil and is not removed through chemical weathering for example zircon grains and a chemically mobile phase that may be removed from the system through chemical weathering chemical denudation rates in hillslope soils can be measured using the concentration of immobile elements but the enrichment of these immobile elements is influenced by spatial variations in chemical denudation rates and spatial variations in the chemical composition of a soil s parent material these considerations cloud the use of elemental depletion factors and cosmogenic nuclide based total denudation rates used to identify the relationship between physical erosion and chemical weathering if these techniques do not account for downslope sediment transport on hillslopes where chemical denudation rates vary in space estimates of chemical denudation using techniques that do not account for downslope sediment transport and spatial variations in chemical denudation rates may be adequate where the chemical denudation rate is a significant fraction of the total denudation rate but are inadequate in regions where chemical weathering rates are small compared to the total denudation rate we also examine relationships between transient mechanical and chemical denudation rates soil particle residence times may affect chemical weathering rates and the relationship between total landscape lowering rates and soil particle residence times can thus be quantified

numerical model on the flow dynamics around the sediment water interface in the tidal coastal area abstract investigating flow dynamics around the sediment water interface is one of difficult issues in marine environment it has important significance to study the physical chemical and biological activities between the overlying water and sedimentary layer with tidal forcing in this study we established a numerical model to investigate the flow dynamics around the sediment water interface in the tidal coastal area the model reflected the hydrodynamics of periodic reciprocating unsteady flow in the overlying water layer and the fully coupled simulation of flow movement between the overlying water layer and sedimentary layer a sedimentary layer an overlying water layer and an air layer were all treated as the fluid zone the unsteady reynolds averaged navier stokes equations and the reynolds stress model with porosity were solved by the finite volume method moreover the drag source term in the momentum equation was modified as the darcy forchheimer extended form the model showed a strong performance in simulating the hydrodynamics of coupled flow around the sediment water interface with tidal forcing in a coastal area with considering the sedimentary layer the benthic boundary layer velocity distributions were more accurate than those obtained by a wall function model around the sediment water interface there was inertial loss in the flow furthermore velocity increased with increasing porosity and velocity gradient became larger compared with models with darcy s law the numerical model in this study had better performance in the turbulent characteristics of sediment water interface layer the model can lead to better understanding of the exchange mechanisms of oxygen nitrogen and nutrient between overlying water and sediment

quantification of soil production and downslope creep rates from cosmogenic 10be accumulations on a hillslope profile average soil transport rates over a period of 3500 yr on a convex soil mantled hillslope have been quantified using a mass balance model that incorporates the soil concentration of the cosmogenic isotope 10 be the 10 be model results support the assumption used in most geomorphic models that the soil creep rate is proportional to surface gradient the predicted diffusion coefficient is 360 55 cm 3 yr 1 cm 1 contour length and the average rate of soil production is 0 026 0 007 cm yr within the uncertainty of this technique the data do not reject g k gilbert9s hypothesis that some hillslopes may exist in a condition of dynamic equilibrium with a uniform soil production rate however the model does not require an assumption of dynamic equilibrium and may be an approach that uniquely allows the quantification of a local soil production rate law

near source attenuation of peak horizontal acceleration strong motion data recorded within 50 km of the rupture zone were used to study near source attenuation characteristics of horizontal peak ground acceleration for worldwide earthquakes of magnitudes 5 0 to 7 7 the data base consisted of 229 horizontal components of peak acceleration recorded from 27 earthquakes including the 15 october 1979 imperial valley earthquake these data were found to be adequately represented by the functional relationship pga a exp b m r c m d where pga represents the mean of the peak values scaled from the two horizontal components of each recording m is richter magnitude and r is distance from the fault rupture zone peak acceleration was found to be lognormally distributed with a standard error representing a 45 per cent increase in the median estimate the regression analysis statistically confirmed the results of earthquake simulation studies that have predicted peak acceleration to become independent of magnitude and distance in the near field an extensive sensitivity study showed that predictions based on our attenuation relationships are stable with respect to reasonable model and parameter variations an analysis of residuals was used to investigate the behavior of peak acceleration with respect to various earthquake site and recording parameters the more significant findings being 1 a similarity in the level of acceleration recorded on soil or rock 2 larger than average accelerations recorded at sites located on shallow soils or in areas of steep topography 3 larger than average accelerations associated with earthquakes having reverse fault mechanisms and 4 lower than average accelerations recorded in large embedded structures

the soil production function a brief history and its rediscovery abstract in 1877 g k gilbert reasoned that the rate at which bedrock is converted to soil reaches a maximum under an optimal soil depth that facilitates contact between bedrock and water such that freeze thaw and chemical weathering are maximised in doing so he outlined the functional dependence of soil production bedrock weathering on local soil depth however the concept of a soil production function does not appear to have been utilised until well into the following century when carson and kirkby carson m a kirkby m j 1972 hillslope form and process cambridge university press cambridge 475 pp expressed it as a notional relationship they also noted that at depths less than optimum instability exists that will either drive soil depth to the optimal weathering depth or to zero depth more recent work has also described a declining exponential soil production function in which the highest rate is at zero soil depth despite dealing with a fundamental issue in soil science viz soil formation the soil production concept has been applied mostly to landscape evolution studies the situation is ripe for its use in soil science and developments in techniques such as cosmogenic nuclides will assist this

martian gullies a comprehensive review of observations mechanisms and insights from earth analogues upon their discovery in 2000 martian gullies were hailed as the first proof of recent i e less than a few million years flowing liquid water on the surface of a dry desert planet many processes have been proposed to have formed martian gullies ranging from liquid water seepage from aquifers melting of snow ice and frost to dry granular flows potentially lubricated by co2 terrestrial analogues have played a pivotal role in the conception and validation of gully formation mechanisms comparison with the terrestrial landscape argues for gully formation by liquid water debris flows originating from surface melting however limited knowledge of sediment transport by sublimation is a critical factor in impeding progress on the co2 sublimation hypothesis we propose avenues towards resolving the debate a laboratory simulations targeting variables that can be measured from orbit b applications of landscape evolution models c incorporation of the concept of sediment connectivity d using 3d fluid dynamic models to link deposit morphology and flow rheology and e a more intense exchange of techniques between terrestrial and planetary geomorphology including quantitative and temporal approaches finally we emphasize that the present may not accurately represent the past and that martian gullies likely formed by a combination of processes

advective transport affecting metal and nutrient distributions and interfacial fluxes in permeable sediments abstract our laboratory flume experiments demonstrate that advective porewater flows produce biogeochemical reaction zones in permeable sediments leading to specific and reproducible complex patterns of fe mn and nutrients oxygenated water forced into the sediment when boundary flows were deflected by protruding sediment structures generated distinct zones of nitrification and ferric iron precipitation this inflow was balanced by ammonium rich porewater ascending from deeper sediment layers thereby creating an anoxic channel where dissolved fe2 and mn2 could reach the surface between the zones of ferric iron precipitation and fe2 upwelling a layer with increased manganese oxide and solid phase fe ii concentrations formed indicating redox reaction between these components the establishment of topography on the previously smooth sediment surface reversed the net interfacial flux of solutes while the smooth control core was found to be a sink for metals and nutrients the sediment with mounds acted as a source for these substances our experiments show that in sandy sediment with an oxidised surface layer reduced metal species can be released to the water column by flow topography interactions we conclude that advective transport processes constitute an important process controlling biogeochemical zonations and fluxes in permeable sea beds

the effects of bioturbation on soil processes and sediment transport abstract plants and animals exploit the soil for food and shelter and in the process affect it in many different ways for example uprooted trees may break up bedrock transport soil downslope increase the heterogeneity of soil respiration rates and inhibit soil horizonation in this contribution we review previously published papers that provide insights into the process of bioturbation we focus particularly on studies that allow us to place bioturbation within a quantitative framework that links the form of hillslopes with the processes of sediment transport and soil production using geometrical relationships and data from others work we derive simple sediment flux equations for tree throw and root growth and decay

erosion and mobility in granular collapse over sloping beds 1 we describe laboratory experiments of granular material flowing over an inclined plane covered by an erodible bed designed to mimic erosion processes of natural flows travelling over deposits built up by earlier events two controlling parameters are the inclination of the plane and the thickness of the erodible layer we show that erosion processes can increase the flow mobility i e runout over slopes with inclination close to the repose angle of the grains r by up to 40 even for very thin erodible beds erosion efficiency is shown to strongly depend on the slope of the topography entrainment begins to affect the flow at inclination angles exceeding a critical angle c r 2 runout distance increases almost linearly as a function of the thickness of the erodible bed suggesting that erosion is mainly supply dependent two regimes are observed during granular collapse a first spreading phase with high velocity followed by a slow thin flow provided either the slope or the thickness of the erodible bed is high enough surprisingly erosion affects the flow mostly during the deceleration phase and the slow regime the avalanche excavates the erodible layer immediately at the flow front waves are observed behind the front that help to remove grains from the erodible bed steep frontal surges are seen at high inclination angles over both rigid or erodible bed finally simple scaling laws are proposed making it possible to obtain a first estimate of the deposit and emplacement time of a granular collapse over a rigid or erodible inclined bed

approaches to dynamic equilibrium in theoretical simulations of slope development the model slop3d is used to identify characteristic aspects of slope development under different conditions a series of slopes along the kall valley in the northern eifel is reproduced by a developmental sequence of model slopes the spatial and temporal variations of the components of slope development systems relief slope form weathering rates denudation rates are discussed by means of mass movement and wash denudation models the negative feedbacks between system components create a tendency towards the establishment of a dynamic equilibrium which is reached however only if the endogenic and exogenic conditions remain constant for the required relaxation time the latter is shown to be a function of slope length of the rate of uplift of the denudational process type and of the intensity of exogenic inputs e g precipitation varying rock resistance leads to the development of shield inselbergs only if the rate of denudation becomes higher than the maximum possible weathering rate of the resistant bedrock

sediment disentrainment and the concept of local versus nonlocal transport on hillslopes 1 a local formulation of the sediment flux on a hillslope describes the flux as a unique function of local hillslope conditions at any contour position x whereas a nonlocal formulation must take into account nonlocal upslope or downslope conditions that influence the flux at x local formulations are reasonable when particle motions involve small length scales associated with localized bioturbation of the soil column or with proximal surface transport such as rain splash nonlocal formulations may be more appropriate in steeplands where patchy intermittent motions involve large travel distances mostly over the surface once sediment motions are initiated the disentrainment process determines the distribution of particle travel distances which in turn forms the basis of nonlocal formulations that involve a convolution of hillslope surface conditions for example the land surface slope the kernel in the convolution integral which weights the effect of land surface conditions e g slope at all positions upslope or downslope of x derives from the formulation of the disentrainment rate and characterizes whether particle travel distances depend on conditions at the position where motions originate or vary as particles experience changing surface conditions during their downslope motions if hillslope properties controlling transport e g surface slope are defined or measured at a specified resolution then motions smaller than this resolution cannot be attributed to these properties resolved at a smaller scale in essence the relative importance of local and nonlocal transport depends on the scale of particle motions compared to the relevant scale of hillslope properties that drive transport

how long is a hillslope hillslope length is a fundamental attribute of landscapes intrinsically linked to drainage density landslide hazard biogeochemical cycling and hillslope sediment transport existing methods to estimate catchment average hillslope lengths include inversion of drainage density or identification of a break in slope area scaling where the hillslope domain transitions into the fluvial domain here we implement a technique which models flow from point sources on hilltops across pixels in a digital elevation model dem based on flow directions calculated using pixel aspect until reaching the channel network defined using recently developed channel extraction algorithms through comparisons between these measurement techniques we show that estimating hillslope length from plots of topographic slope versus drainage area or by inverting measures of drainage density systematically underestimates hillslope length in addition hillslope lengths estimated by slope area scaling breaks show large variations between catchments of similar morphology and area we then use hillslope length relief structure of landscapes to explore nature of sediment flux operating on a landscape distinct topographic forms are predicted for end member sediment flux laws which constrain sediment transport on hillslopes as being linearly or nonlinearly dependent on hillslope gradient because our method extracts hillslope profiles originating from every ridgetop pixel in a dem we show that the resulting population of hillslope length relief measurements can be used to differentiate between linear and nonlinear sediment transport laws in soil mantled landscapes we find that across a broad range of sites across the continental united states topography is consistent with a sediment flux law in which transport is nonlinearly proportional to topographic gradient

attenuation of strong ground motion in canada from a random vibrations approach abstract theoretical relations are developed for the attenuation of horizontal peak ground acceleration pga and velocity pgv in canada with emphasis on eastern canada the theoretical basis is a composite of several approaches at intermediate epicentral distances results from random vibration theory hanks and mcguire 1981 boore 1983 which can be used to describe pga and pgv in terms of shear radiation implied by brune9s 1970 source model are applied to canadian earthquakes motions are extended into the near source region using arguments concerning magnitude scaling joyner and boore 1981 at distances greater than two crustal thicknesses ground motions are attributed largely to the lg phase and are attenuated accordingly nuttli 1982 the resulting attenuation relations for pga and pgv in eastern canada are in excellent agreement with strong motion data from moderate eastern canadian and central united states earthquakes compared to empirical attenuation relationships based on modified mercalli intensity the theoretical model predicts a stronger dependence of peak ground motions on magnitude in other respects amplitude levels and distance decay empirical and theoretical predictions are similar the model predicts that eastern events will have higher peak accelerations but similar peak velocities in comparison to their western counterparts of the same moment magnitude this arises from the relative enrichment of eastern earthquakes in higher frequencies

statistical description of slope dependent soil transport and the diffusion like coefficient 1 for hillslopes undergoing diffusive soil transport it is often assumed that the soil flux is proportional to the local land surface gradient where the coefficient of proportionality is like a diffusion coefficient inasmuch as transport involves quasi random soil particle motions related to biomechanical mixing and similar dilational processes a slope dependent relation arises from a balance between particle fluxes that tend to loft a soil and gravitational settling of particles into available pore space a specialized form of the fokker planck equation adapted to such particle motions clarifies how the particle flux involves advective and diffusive parts this in turn contributes to a kinematic description of the diffusion like coefficient ingredients of this coefficient include an active soil thickness a characteristic particle size the porosity in excess of a consolidated porosity and the rate of particle activation as a function of depth these last two ingredients vertical porosity structure and activation rate in effect characterize the magnitude and frequency of settling particle motions related to biological activity and thereby set the rate constant of the transport process the significance of land surface slope is that it is a measure of the downslope component of slope normal lofting that is balanced by settling because the diffusion like coefficient contains the soil thickness the analysis suggests that the soil flux is proportional to the depth slope product the analysis is consistent with published profiles of soil creep displacement and with published estimates of soil flux obtained by downslope integration of soil production rates for hillslopes in california and australia

a granular physics based view of fault friction experiments rate and state dependent friction rsf equations are commonly used to describe the time dependent frictional response of fault gouge to perturbations in sliding velocity among the better known v

how well can hillslope evolution models explain topography simulating soil transport and production with high resolution topographic data the morphology of hillslopes is a direct refl ection of tectonic forcing and climatic and biologic processes that drive soil production mobilization and transport soil transport on hillslopes affects river incision by providing tools for channel abrasion and controls the distribution of sediment that infl uences aquatic habitat although numerous hillslope transport relationships have been proposed over the past 60 years a comprehensive analysis of model predictions for a real landscape has not been performed here we use high resolution topographic data obtained via airborne laser swath mapping alsm to simulate the long term evolution of oregon coast range hillslopes and test three published transport models and a new model that accounts for nonlinear depth and slopedependent transport analysis of one dimensional steady state solutions for these four models suggests that plots of gradient curvature may be diagnostic for distinguishing model predictions to evaluate two dimensional model predictions for our fi eld site we assumed local steady state erosion for a 72 000 m 2 sequence of hillslopes and valleys after calibrating each of the four models we imposed constant base level lowering for cells within the valley network simulated 500 000 yr of soil production and transport and determined which transport model best preserved morphologic patterns that describe the current landscape form models for which fl ux varies proportionally with hillslope gradient generated broadly convex hilltops inconsistent with the sharp crested steep sided slopes of our study site whereas the two nonlinear slope dependent models produced convex planar slopes consistent with current hillslope form our proposed nonlinear slope and depth dependent model accounts for how soil thickness controls the magnitude of biogenic disturbances that drive transport this model best preserved the current landscape form particularly the narrow sharply convex hilltops characteristic of the oregon coast range according to our formulation which provides an explicit linkage for relating the distribution of biota to hillslope processes the degree of hilltop convexity varies nonlinearly with the ratio of erosion rate to maximum soil production rate highlighting the profound infl uence of soil depth on hillslope evolution

responses of soil mantled hillslopes to transient channel incision rates 1 channel incision drives hillslope morphology in humid soil mantled landscapes when channel incision rates change numerous hillslope soil properties e g erosion rates soil thickness and soil production adjust in response to this change here we investigate the timescales of adjustment of hillslope soil properties when channel incision rates change in time an idealized soil mantled hillslope linear sediment flux law and soil density equal to bedrock density is investigated and the transient evolution of this hillslope is determined analytically this analysis reveals two dominant adjustment timescales the longer of these two timescales determines the rate at which the entire hillslope adjusts to a change in channel incision rates and is proportional to 4 2 2d where is the length of the hillslope and d is the sediment diffusivity numerical simulations are then used to examine responses of hillslopes that involve nonlinear behavior e g hillslopes that experience nonlinear sediment transport or have soil thicknesses that respond to the soil production function using these numerical models we show that the ratio between the soil density s and the density of the soil parent material can alter the long term response of the hillslope such that the characteristic timescale becomes 4 2 2d s in addition we show that the adjustments of the soil erosion rate the soil production rate and the soil thickness have different characteristic response timescales hillslopes that experience sediment flux that is proportional to the depth slope product respond on longer timescales than hillslopes that experience a linear sediment flux law when channel incision rates increase we illustrate how the spatial pattern of hillslope response to changes in channel incision rates can be used to constrain either channel incision histories or hillslope response timescales if the hillslope response timescale is known the pattern of hillslope disturbance can be used to constrain the celerity of a incision wave as it moves upstream through a channel if the channel incision history is known the hillslope response timescale may be evaluated on the basis of the spatial pattern of hillslope disturbance

the driving forces of porewater and groundwater flow in permeable coastal sediments a review abstract advective flows rapidly transport water solutes and particles into and out of permeable sand beds and significantly affects the biogeochemistry of coastal environments in this paper we reviewed the drivers of porewater and groundwater advection in permeable shelf sediments in an attempt to bridge gaps among different disciplines studying similar problems we identified the following driving forces 1 terrestrial hydraulic gradients 2 seasonal changes in the aquifer level on land moving the location of the subterranean estuary 3 wave setup and tidal pumping 4 water level differences across permeable barriers 5 flow and topography induced pressure gradients 6 wave pumping 7 ripple and other bed form migration 8 fluid shear 9 density driven convection 10 bioirrigation and bioturbation 11 gas bubble upwelling and 12 sediment compaction while these drivers occur over spatial scales ranging from mm to km and temporal scales ranging from seconds to years their ultimate biogeochemical implications are very similar i e they are often a source of new or recycled nutrients to seawater and transform organic carbon into inorganic carbon drivers 2 12 result in no net water input into the ocean taking all these mechanisms into account we conservatively estimate that a volume equivalent to that of the entire ocean is filtered by permeable sediments at time scales of about 3000 years quantifying the relative contribution of these drivers is essential to understand the contribution of sediments to the global cycles of matter

solute exchange by convection within estuarine sediments the rates of material transport through sediments are central to determining the biochemical status of sediments transport within sediments can occur by molecular diffusion through porewaters and by the activities of burrowing biological organisms but a number of physical processes can enhance transport within porewaters here convection is investigated as a mechanism for solute transport within sediments convection will occur as the gravitational adjustment to the occurrence of porewater which is of lower salinity and density than the water at the sediment surface this process could be important for exchange between sediments and the water column in regions subject to significant temporal variations in salinity such as estuaries

evaluating hillslope diffusion and terrace riser degradation in new zealand and idaho 1 the relationship of sediment flux to surface slope is a predominant control on the evolution of transport limited hillslopes although both linear and nonlinear sediment flux models have been proposed and widely debated this functional relationship remains one of the outstanding questions in geomorphology we examine degradation of fluvial terrace risers in new zealand and idaho in order to test the linear diffusion model and to better understand the relationship between sediment flux and slope we implement three techniques based on the linear diffusion model as well as a geometric scaling method that uses proportional relationships in riser geometry rather than a specific transport equation model to assess rates of degradation we show that techniques that utilize the riser midpoint slope as the primary metric of degradation as opposed to the full scarp profile offer the simplest and most reliable assessment of riser degradation our findings suggest that the linear diffusion model does not accurately describe terrace riser degradation except for low angle risers for which linear and nonlinear forms are indistinguishable results from the geometric scaling method show that degradation rates in both regions differ by a factor of two between equator and pole facing risers and that diffusion ages of idaho risers are approximately 2 times those of new zealand risers similar geometric trends in riser evolution from both regions reveal that terrace riser degradation is governed by a widely applicable relationship between sediment flux and slope

evolution of the santa cruz mountains california through tectonic growth and geomorphic decay i describe a strategy for modeling a specific large scale topographic feature that recognizes the discrepancy between tectonic and geomorphic scales and allows for important feedbacks between these processes in the geomorphic model the largest channel in each 4 4 km cell is explicitly treated the channel incision being driven by a stream power rule hillslopes internal to each cell respond rapidly to incision of the local channel prompting their treatment in the model as steady state forms i present analytic expressions for the local relief which is controlled by the local channel incision rate and rate constants associated with the dominant hillslope process either diffusive or landsliding initial conditions include any preexisting topography and a lightly etched a channel network the model is illustrated using the santa cruz mountains california i show that an earlier hypothesis that the santa cruz mountains are due to advection of topography past an uplift source related to a restraining bend in the san andreas fault remains viable when more specific geomorphic processes are considered the local tectonics are represented by crustal thickening necessitated by conservation of mass in the bend right lateral translation of crust with respect to the bend and flexural response to the distributed load the model produces reasonable geographic and statistical distributions of topography using rates of tectonic and geomorphic processes that are within the range of those measured locally this argues that this restraining bend is a long lived feature of the san andreas fault the slightly higher crest and shorter length of the southern santa cruz mountains may potentially be explained by slightly faster slip of the crust west of the fault with respect to the bend than of that to the east deflection is minimal beneath these relatively small mountains disallowing the interesting feedback of erosionally driven uplift the predicted pattern of exhumation could be used to guide the search for fission track sites that could aid in the testing of the model

integration of geochemical mass balance with sediment transport to calculate rates of soil chemical weathering and transport on hillslopes 1 we developed a process oriented hillslope soil mass balance model that integrates chemical and physical processes within hillslope soils the model explicitly factors that soil chemical weathering at any hillslope position is related to the flux of soil eroded from upslope as well as soil production from underlying bedrock the model was merged with measurements of soil elemental chemistry and cosmogenic radionuclide based saprolite to soil conversion rates along a 50 m transect of a semiarid granodiorite hillslope in the southeastern australian highlands inverse modeling results in the simultaneous quantification of the rates of soil chemical weathering and soil transport as a function of hillslope position soil chemical weathering rates per land surface area systematically varied along the transect from losses of 0 035 kg m 2 yr 1 on the ridge to gains of 0 035 kg m 2 yr 1 at the lowest slope position the mass loss via soil chemical weathering would have been overestimated by 40 if the impact of soil transport on soil chemistry was ignored the chemical mobility of elements combined with biological nutrient demand controlled the spatial redistribution of individual elements p and ca were preferentially retained relative to si al and fe within the hillslope base the calculated soil transport rate is linearly related to the product of soil thickness and slope gradient instead of slope alone soil residence time was determined by calculating the time length for a 3 dimensional box volume 1 m2 surface area soil thickness to be entirely removed by mass flux of soil transport 4 ka on the ridge to 0 9 ka at the hillslope base these soil residence times combined with soil chemical weathering rates indicate that a 1 m2 area of soil loses 1 800 kg via chemical weathering while passing through the upslope portion of the hillslope but that it regains 90 kg probably via clay precipitation and biological retention of cations during its passage through the lower segments of the transect this study provides a previously unrecognized linkage between physical soil transport and soil chemical weathering that have implications for hillslope evolution as well as biogeochemistry

the influence of climate and microclimate aspect on soil creep efficiency cinder cone morphology and evolution along the eastern mediterranean golan heights although hillslope evolution has been subject to much investigation for more than a century the effect of climate on the morphology of soil mantled hillslopes remains poorly constrained in this study we perform numerical simulations of volcanic cinder cones in the golan heights eastern mediterranean to estimate soil transport efficiency across a significant north south gradient in mean annual precipitation 1100 to 500 mm we use the initial cinder cone morphology constrained by stratigraphy the modern hillslope form surveyed with sub meter accuracy and the eruption age based on 40ar 39ar chronology to predict the best fit value of the soil transport coefficient diffusivity based on a nonlinear transport model our results indicate that the best fit diffusivity k varies from 1 to 6 m2 ka 1 among the five cinder cones in our field area diffusivity k values vary systematically with precipitation and hillslope aspect specifically k is higher on south facing drier hillslopes and decreases with mean annual precipitation we interpret this climate dependency to reflect vegetation driven variations in apparent soil cohesion which increases with root network density and attenuation of rain splash and overland flow erosion which increases with vegetative ground cover to assess how vegetative root mass and ground cover vary with precipitation and aspect we quantified the spatial distribution of ndvi normalized difference vegetation index from aster satellite images and observed spatial variations that correlate with our calibrated values of k analysis of previously studied cinder cones in the usa can be used to extend our framework to arid domains this endeavor suggests a humped relationship between k and precipitation with maximum diffusivity at mean annual precipitation of 400 600 mm copyright 2017 john wiley sons ltd

biotic origin for mima mounds supported by numerical modeling article i nfo mima mounds are 1 m high hillocks found on every continent except antarctica despite often numbering in the millions within a single field their origin has been a mystery with proposed explanations ranging from gla cialprocesses to seismic shaking one hypothesisproposes that mounds innorth america are built by burrowing mammals to provide refuge from seasonally saturated soils we test this hypothesis with a numerical model parameterized with measurements of soil transport by gophers from a california mound field that couples animal behavior with geomorphic processes the model successfully simulates the development of the mounds as well as key details such as the creation of vernal pools small intermound basins that provide habitat for en demic species furthermore we demonstrate that the spatial structure of the modeled mound fields is similar to actual mound fields and provides an example of self organized topographic features we conclude that scaled by body mass mima mounds are the largest structures built by nonhuman mammals and may provide a rare example of an evolutionary coupling between landforms and the organisms that create them

the search for a topographic signature of life landscapes are shaped by the uplift deformation and breakdown of bedrock and the erosion transport and deposition of sediment life is important in all of these processes over short timescales the impact of life is quite apparent rock weathering soil formation and erosion slope stability and river dynamics are directly influenced by biotic processes that mediate chemical reactions dilate soil disrupt the ground surface and add strength with a weave of roots over geologic time biotic effects are less obvious but equally important biota affect climate and climatic conditions dictate the mechanisms and rates of erosion that control topographic evolution apart from the obvious influence of humans does the resulting landscape bear an unmistakable stamp of life the influence of life on topography is a topic that has remained largely unexplored erosion laws that explicitly include biotic effects are needed to explore how intrinsically small scale biotic processes can influence the form of entire landscapes and to determine whether these processes create a distinctive topography

interactions between soil biota and the effects on geomorphological features abstract the interaction of animals with abiotic features of their environment has long been known to cause alterations to geomorphic features and these interactions may cause feedback loops that further alter geomorphic features and animal communities this paper samples the literature on selected burrowing animals in western north america and discusses the interactions of animals with abiotic features of the environment and with each other and the resulting impacts on geomorphic features and each other as expected burrowing characteristics of animals influence geomorphological processes for example pocket gophers and certain ground squirrels that burrow horizontal tunnels on sloping grounds seem to have significant impacts on horizontal movement of soils whereas prairie dogs and harvester ants have more impact on vertical movement of soils burrowing animals in general increase the patchiness of the environment which creates localized patch habitat for other plants and animals thereby increasing biodiversity at the landscape scale burrowing animals influence and are influenced by microbes sylvatic plague wiped out large populations of prairie dogs earthworms cause major changes in soil microflora pocket gophers and harvester ants cause changes in mycorrhizal communities which in turn impact plant communities

influence of lithology on hillslope morphology and response to tectonic forcing in the northern sierra nevada of california 1 many geomorphic studies assume that bedrock geology is not a first order control on landscape form in order to isolate drivers of geomorphic change e g climate or tectonics yet underlying geology may influence the efficacy of soil production and sediment transport on hillslopes we performed quantitative analysis of lidar digital terrain models to examine the topographic form of hillslopes in two distinct lithologies in the feather river catchment in northern california a granodiorite pluton and metamorphosed volcanics the two sites separated by 2 km and spanning similar elevations were assumed to have similar climatic histories and are experiencing a transience in landscape evolution characterized by a propagating incision wave in response to accelerated surface uplift c 5 ma responding to increased incision rates hillslopes in granodiorite tend to have morphology similar to model predictions for steady state hillslopes suggesting that they adjust rapidly to keep pace with the incision wave by contrast hillslopes in metavolcanics exhibit high gradients but lower hilltop curvature indicative of ongoing transient adjustment to incision we used existing erosion rate data and the curvature of hilltops proximal to the main channels where hillslopes have most likely adjusted to accelerated erosion rates to demonstrate that the sediment transport coefficient is higher in granodiorite 8 8 m2 ka 1 than in metavolcanics 4 8 m2 ka 1 hillslopes in both lithologies get shorter i e drainage density increases with increasing erosion rates

toward a unifying constitutive relation for sediment transport across environments abstract landscape evolution models typically parse the environment into different process domains each with its own sediment transport law e g soil creep landslides and debris flows and river bed load and suspended sediment transport sediment transport in all environments however contains many of the same physical ingredients albeit in varying proportions grain entrainment due to a shear force that is a combination of fluid flow particle particle friction and gravity we present a new take on the perspective originally advanced by bagnold that views the long profile of a hillsope river shelf system as a continuous gradient of decreasing granular friction dominance and increasing fluid drag dominance on transport capacity recent advances in understanding the behavior and regime transitions of dense granular systems suggest that the entire span of granular to fluid regimes may be accommodated by a single phase rheology this model predicts a material flow effective friction or viscosity that changes with the degree of shear rate and confining pressure we present experimental results confirming that fluid driven sediment transport follows this same rheology for bed and suspended load surprisingly below the apparent threshold of motion we observe that sediment particles creep in a manner characteristic of glassy systems we argue that this mechanism is relevant for both hillslopes and rivers we discuss the possibilities of unifying sediment transport across environments and disciplines and the potential consequences for modeling landscape evolution

nonlocal sediment transport on steep lateral moraines eastern sierra nevada california usa available for download is the author s version of the paper the final publisher s version is available at https dx doi org 10 1002 2017jf004325 the dataset doi is https doi org 10 15695 vudata cee 1

dynamics of slow moving landslides from permanent scatterer analysis high resolution interferometric synthetic aperture radar insar permanent scatterer data allow us to resolve the rates and variations in the rates of slow moving landslides satellite to ground distances range changes on landslides increase at rates of 5 to 7 millimeters per year indicating average downslope sliding velocities from 27 to 38 millimeters per year time series analysis shows that displacement occurs mainly during the high precipitation season during the 1997 1998 el nino event rates of range change increased to as much as 11 millimeters per year the observed nonlinear relationship of creep and precipitation rates suggests that increased pore fluid pressures within the shallow subsurface may initiate and accelerate these features changes in the slope of a hill resulting from increases in the pore pressure and lithostatic stress gradients may then lead to landslides

preserving the palaeoenvironmental record in drylands bioturbation and its significance for luminescence derived chronologies luminescence osl dating has revolutionised the understanding of late pleistocene dryland activity however one of the key assumptions for this sort of palaeoenvironmental work is that sedimentary sequences have been preserved intact enabling their use as proxy indicators of past changes this relies on stabilisation or burial soon after deposition and a mechanism to prevent any subsequent re mobilisation as well as a dating technique osl especially at the single grain level can be used to gain an insight into post depositional processes that may distort or invalidate the palaeoenvironmental record of geological sediment sequences this paper explores the possible impact of bioturbation the movement of sediment by flora and fauna on luminescence derived chronologies from quaternary sedimentary deposits in texas and florida usa which have both independent radiocarbon chronologies and archaeological evidence these sites clearly illustrate the ability of bioturbation to rejuvenate ancient weathered sandy bedrock and or to alter depositional stratigraphies through the processes of exhumation and sub surface mixing of sediment the use of multiple osl replicate measurements is advocated as a strategy for checking for bioturbated sediment where significant osl heterogeneity is found caution should be taken with the derived osl ages and further measurements at the single grain level are recommended observations from the linear dunes of the kalahari show them to have no bedding structure and to have osl heterogeneity similar to that shown from the bioturbated texan and florida sites the kalahari linear dunes could have therefore undergone hitherto undetected post depositional sediment disturbance which would have implications for the established osl chronology for the region

modelling hillslope evolution linear and nonlinear transport relations many recent models of landscape evolution have used a diffusion relation to simulate hillslope transport in this study a linear diffusion equation for slow quasi continuous mass movement e g creep which is based on a large data compilation is adopted in the hillslope model transport relations for rapid episodic mass movements are based on an extensive data set covering a 40 yr period from the queen charlotte islands british columbia a hyperbolic tangent relation in which transport increases nonlinearly with gradient above some threshold gradient provided the best fit to the data model runs were undertaken for typical hillslope profiles found in small drainage basins in the queen charlotte islands results based on linear diffusivity values defined in the present study are compared to results based on diffusivities used in earlier studies linear diffusivities adopted in several earlier studies generally did not provide adequate approximations of hillslope evolution the nonlinear transport relation was tested and found to provide acceptable simulations of hillslope evolution weathering is introduced into the final set of model runs the incorporation of weathering into the model decreases the rate of hillslope change when theoretical rates of sediment transport exceed sediment supply the incorporation of weathering into the model is essential to ensuring that transport rates at high gradients obtained in the model reasonably replicate conditions observed in real landscapes an outline of landscape progression is proposed based on model results hillslope change initially occurs at a rapid rate following events that result in oversteepened gradients e g tectonic forcing glaciation fluvial undercutting steep gradients are eventually eliminated and hillslope transport is reduced significantly

effects of current bed form induced fluid flow on the thermal regime of sediments 1 heat transport associated with current bed form fluid exchange affects biogeochemical and ecological process in a variety of aquatic settings we simulate turbulent flow over dunes induced darcy flow in sediments and sediment heat transport forced by a diel variation of water column temperature heat conduction dominates when the water column current cannot induce rapid fluid exchange heat advection becomes important with increasing sediment permeability and or current velocity resulting in a complicated space time temperature pattern weak temperature variations are found beneath dune crests where water upwells out of the sediments strong variations are located below dune stoss faces where water downwells the relative dominance of heat conduction versus advection is captured by a global peclet number that depends on dune geometry and hydrodynamic and thermal properties including the period of thermal forcing thermally induced fluid viscosity variations cause periodic but nonsymmetric changes in fluid flux through the sediments but do not significantly influence temperature patterns

from divots to swales hillslope sediment transport across divers length scales 1 in soil mantled steeplands soil motions associated with creep ravel rain splash soil slips tree throw and rodent activity are patchy and intermittent and involve widely varying travel distances to describe the collective effect of these motions we formulate a nonlocal expression for the soil flux this probabilistic formulation involves upslope and downslope convolutions of land surface geometry to characterize motions in both directions notably accommodating the bidirectional dispersal of material on gentle slopes as well as mostly downslope dispersal on steeper slopes and it distinguishes between the mobilization of soil material and the effect of surface slope in giving a downslope bias to the dispersal of mobilized material the formulation separates dispersal associated with intermittent surface motions from the slower bulk behavior associated with small scale bioturbation and similar dilational processes operating mostly within the soil column with a uniform rate of mobilization of soil material the nearly parabolic form of a hillslope profile at steady state resembles a diffusive behavior with a slope dependent rate of mobilization the steady state hillslope profile takes on a nonparabolic form where land surface elevation varies with downslope distance x as xa with a 3 2 consistent with field observations and where the flux increases nonlinearly with increasing slope the convolution description of the soil flux when substituted into a suitable expression of conservation yields a nonlinear fokker planck equation and can be mapped to discrete particle models of hillslope behavior and descriptions of soil grain transport by rain splash as a stochastic advection dispersion process

the zoogeomorphic characteristics of burrows and burrowing by nine banded armadillos dasypus novemcinctus abstract burrowing animals act like a geomorphic disturbance changing the environment through soil excavation landform creation and bioturbation the potential zoogeomorphic effects of these actions include modification of surficial features increased soil erosion changes in the growth and distribution of vegetation and modifications to soil fertility the burrowing ninebanded armadillo dasypus novemcinctus migrated to north america prior to the 1850s and has since continued to expand its habitat to the american southeast and parts of the midwest little data are available on the zoogeomorphic impact of the burrowing nature of this species making it difficult to predict future implications of this animal as it continues to migrate into new regions on the university of south alabama campus in mobile alabama armadillos are present on a 35 hectare unprotected forested preserve used by the university community for outdoor activities and research to understand the potential zoogeomorphic impact of armadillo burrows on the local environment morphometric measurements were recorded on 187 burrows located in the study area using dimensions of burrow entrances and minimum lengths of tunnels in calculations armadillos excavated approximately 0 029 m 3 to 0 04 m 3 of soil from each burrow the entrances to burrows averaged 33 5 in slope and tended to be located in a microhabitat of a fallen tree exposed tree roots or a sideslope persistent fall of forest litter and anthropogenic modifications makes positive identification of spoil mounds possible in approximately half of the burrow sites surface modification by armadillos is ongoing in the study area with over half of the burrows classified as active during the four month project we concluded that for southern alabama armadillos prefer to excavate burrows into sideslopes and that given the lack of ground cover sandy soil and humid climate armadillos are an important zoogeomorphic agent in the region

bedrock erosion by root fracture and tree throw a coupled biogeomorphic model to explore the humped soil production function and the persistence of hillslope soils 1 in 1877 g k gilbert reasoned that bedrock erosion is maximized under an intermediate soil thickness and declines as soils become thinner or thicker subsequent analyses of this humped functional relationship proposed that thin soils are unstable and that perturbations in soil thickness would lead to runaway thinning or thickening of the soil to explore this issue we developed a numerical model that simulates the physical weathering of bedrock by root fracture and tree throw the coupled biogeomorphic model combines data on conifer population dynamics rootwad volumes tree throw frequency and soil creep from the pacific northwest usa although not hardwired into the model a humped relationship emerges between bedrock erosion and soil thickness the magnitudes of the predicted bedrock erosion rates and their functional dependency on soil thickness are consistent with independent field measurements from a coniferous landscape in the region imposed perturbations of soil erosion during model runs demonstrate that where bedrock weathering is episodic and localized hillslope soils do not exhibit runaway thinning or thickening the pit and mound topography created by tree throw produces an uneven distribution of soil thicknesses across a hillslope thus although episodes of increased erosion can lead to temporary soil thinning and even the exposure of bedrock patches local areas of thick soils remain these soil patches provide habitat for trees and serve as nucleation points for renewed bedrock erosion and soil production model results also suggest that where tree throw is a dominant weathering process the initial mantling of bedrock is not only a vertical process but also a lateral process soil mounds created by tree throw flatten over time spreading soil over bedrock surfaces

pore water chemistry in mangrove sediments relationship with species composition and developmental stages french guiana spatial and seasonal variability of sedimentary salinity ph redox potential and solid phase sulphide concentration were investigated in a range of mangrove communities along the coast of french guiana seasonal depth distributions of these parameters and organic content were compared within avicennia rhizophora and mixed mangrove stands at different stages of plant development mangrove communities and variable surface water inputs strongly impact sediment and ground water properties in the upper sediment changes in salinity are mainly controlled by seasonal conditions transpiration and proximity of fresh water influx whereas we suggest that constant basal salinity results from an accumulation of salt that has migrated as a result of density driven convection processes there are no clear differences between the depth distributions of salinity obtained beneath avicennia germinans and rhizophora mangle stands implying that plant zonations are not primarily controlled by soil salinity in this environment nevertheless r mangle grows in places subjected to the greatest variability in freshwater influxes suggesting that rhizophora might require or withstand occasional inundation by fresh water beneath rhizophora stands sediment properties reflect anaerobic and sulphidic conditions close to the sediment surface in contrast beneath avicennia stands sediment geochemistry mostly depends on the stages in forest development on contents in sedimentary organic matter and on seasonal changes in the early stage of avicennia settlement the sediment at the level of radial pneumatophore bearing cable roots displays permanent suboxic conditions with eh values reaching 400 mv these high ehs are interpreted as an effect of the oxidation produced by the cable root system the development of mature avicennia stands results in accumulation of sedimentary organic matter and promotes low ehs and the reduction of pore water sulphate near cable root level the oxidation process observed in pioneer mangroves results in a reoxidation of solid sulphides produced previously during dry conditions the desiccation of the upper sediment adds its oxidation effects to those of root activity as a result suboxic processes dominate in the upper 20 cm thick layer organic matter decomposition and sulphur oxidation strongly acidify the sediment below 20 cm the sediment is anaerobic and sulphidic hence sulphide concentrations depend on the edaphic conditions controlling decay processes and appear to be a consequence rather than a cause of the observed zonation of vegetal species the small size of a germinans propagules might have a significant influence on the extensive development of this plant community along the highly dynamic coastline of the guianas this study demonstrates that the different properties of pore water were intimately linked and that the explanation of the evolution of this forest reflects a combination of multiple parameters moreover it appeared that the organic content played a key role along with the species composition and the seasonal variations waterlogging desiccation

trouble with diffusion reassessing hillslope erosion laws with a particle based model 1 many geomorphic systems involve a broad distribution of grain motion length scales ranging from a few particle diameters to the length of an entire hillslope or stream studies of analogous physical systems have revealed that such broad motion distributions can have a significant impact on macroscale dynamics and can violate the assumptions behind standard local gradient flux laws here a simple particle based model of sediment transport on a hillslope is used to study the relationship between grain motion statistics and macroscopic landform evolution surface grains are dislodged by random disturbance events with probabilities and distances that depend on local microtopography despite its simplicity the particle model reproduces a surprisingly broad range of slope forms including asymmetric degrading scarps and cinder cone profiles at low slope angles the dynamics are diffusion like with a short range thin tailed hop length distribution a parabolic convex upward equilibrium slope form and a linear relationship between transport rate and gradient as slope angle steepens the characteristic grain motion length scale begins to approach the length of the slope leading to planar equilibrium forms that show a strongly nonlinear correlation between transport rate and gradient these high probability long distance motions violate the locality assumption embedded in many common gradient based geomorphic transport laws the example of a degrading scarp illustrates the potential for grain motion dynamics to vary in space and time as topography evolves this characteristic renders models based on independent stationary statistics inapplicable an accompanying analytical framework based on treating grain motion as a survival process is briefly outlined

experimental evidence for hillslope control of landscape scale landscape evolution theory suggests that climate sets the scale of landscape dissection by modulating the competition between diffusive processes that sculpt convex hillslopes and advective processes that carve concave valleys however the link between the relative dominance of hillslope and valley transport processes and landscape scale is difficult to demonstrate in natural landscapes due to the episodic nature of erosion here we report results from laboratory experiments combining diffusive and advective processes in an eroding landscape we demonstrate that rainsplash driven disturbances in our experiments are a robust proxy for hillslope transport such that increasing hillslope transport efficiency decreases drainage density our experimental results demonstrate how the coupling of climate driven hillslope and valley forming processes such as bioturbation and runoff dictates the scale of eroding landscapes

attenuation relations for strong seismic ground motion in canada abstract strong seismic ground motion attenuation relations based primarily on western united states data in conjunction with intensity data from eastern and western canada are employed to derive new attenuation relations for horizontal strong seismic ground motion for application throughout canada the following peak acceleration a p and peak velocity v p relations are proposed for use in western canada a p cm sec 2 10 e 1 3 m r 1 5 v p cm sec 1 0 00040 e 2 3 m r 1 3 where m is magnitude and r hypocentral distance km the difference in the distance attenuation of modified mercalli intensity in eastern and western canada and an assumption of equivalent strong motion in the near field in the two regions is applied to the western relations to derive the following relations proposed for use in eastern canada a p cm sec 2 3 4 e 1 3 m r 1 1 v p cm sec 1 0 00018 e 2 3 m r 1 0 the proposed relations are in reasonable agreement with the small amount of strong motion data available for western and eastern canada within the accuracy justified by very scattered experimental data peak vertical and sustained horizontal acceleration and velocity can be estimated as 2 3 of the peak horizontal values the magnitude and distance dependence of acceleration and velocity parameters are sufficiently different that the relative levels of ground motion bounds in different frequency ranges will depend on the dominant magnitudes of and distance ranges to the earthquakes contributing risk in various regions of canada the results indicate the importance of mapping risk for parameters in addition to simple peak acceleration and suggest alternative methods of deriving ground motion bounds required for the development of design response spectra

rates of surface processes on slopes slope retreat and denudation results taken from 270 publications on rates are summarized and collated with those from 149 publications reviewed previously young 1969 1974 the data are classified by major climatic zone normal or steep relief and consolidated or unconsolidated rocks representative rates and their ranges are given for soil creep solifluction surface wash solution chemical denudation rock weathering slope retreat cliff free face retreat marine cliff retreat and denudation the last being compared with representative rates of uplift solifluction is of the order of 10 times faster than soil creep but both cause only very slow ground loss solution is an important cause of ground loss for siliceous rocks on which it may be half as rapid as on limestones total denudation brought about mainly by surface wash reaches a maximum in the semi arid and probably also the tropical savanna zones acceleration of natural erosion rates by human activities ranges from 2 3 times with moderately intense land use to about 10 times with intensive land use and considerably higher still where there is recognized accelerated soil erosion where there is active uplift typical rates are of the order of 10 times faster than denudation although in some high steep mountain ranges these may approach equality

gophers as geomorphic agents in the colorado front range subalpine zone abstract gophers are significant geomorphic agents in many landscapes we document activity of the northern pocket gopher thomomys talpoides in two small subalpine meadows 1050 1800 m2 of the front range colorado usa we tracked locations and volumes of mounds and subnivean infilled tunnels over one year and probed the thickness of the biomantle within one meadow we infer that only 5 7 gophers occupied each meadow implying a gopher density of 28 67 ha 1 fractional areal coverage of the meadows by diggings suggests that within 49 95 years gophers would fully resurface the meadows annual volumes of excavated soil correspond to the equivalent of 1 mm of material spread evenly over the meadows probed meadow resistance depths reveal a pattern we interpret to be stone lines at roughly 15 cm depths implied vertical turnover times are therefore roughly 150 years these spatial and temporal patterns imply that gophers should be able to churn the biomantle on approximately century timescales and should fully resurface the meadow areas in similar timescales these field data also contribute to an investigation of lateral sediment transport given the local slope of the landscape gopher driven sediment transport within our two study sites suggests a landscape diffusivity of 0 008 m2y 1 at no time do gophers occupy the forest as evidenced by subnivean infilled tunnels winter activity is restricted to the upslope and hence upwind meadow edges which correspond to high snow cover and warm 0 c shallow subsurface soil temperatures subsequent activity expands downhill into the meadows and shows a distinct pulse of mound activity in late summer through early fall prior to snowfall local forest fire history has led to much more extensive meadows in the past suggesting that the geomorphic influence of gophers in the landscape is much more widespread than the present distribution of meadows and may cover the entire subalpine region of the front range on millennial timescales

soil creep the driving factors evidence and significance for biogeomorphic and pedogenic domains and systems a critical literature review abstract soil and regolith creep have been analyzed for at least the last 140 years using many methodological configurations and temporal and spatial scales the general concept of creeping soil and its mechanism first proposed by w m davis and g k gilbert at the end of the 19th century evolved since the 1940s towards theoretical models and precise short and long term field measurements this fruitful epoch continued with results enhanced at the turn of the 20th century by the application of new research methods e g radiometry and a redefinition of the term soil creep to encompass the sum of stochastic shallow subsurface and near surface processes causing net downslope movement of soil or regolith simultaneously another possibility of creep detection was noticed in dendrochronology and since the 1970s in the formally defined discipline of dendrogeomorphology indirect evaluations of creep activity were performed based on tree ring analyses of bent trees this method found many followers but was also heavily criticized as imprecise and lacking in evidence of which kind of tree trunk curvature e g pistol butt like deformation s shape curvature could be ascribed to creep movement from the beginning soil creep was associated with the activity of living organisms on hillslopes however this aspect of creep studies has never been fully developed in spite of the solid foundations and directions of potential studies pointed out by charles darwin at the end of the 19th century in this paper we focus on the historical context of soil creep studies and highlight forest ecosystems as probably the most active environment of biogenic creep mainly due to tree uprooting and other biomechanical effects of living and dead trees root channel infilling tree root mounding etc that are a factors in biotransport in the final sections the position of biogenic creep in the structure of biogeomorphic systems is discussed in relation to such important conceptual frameworks as the biogeomorphic ecosystem biogeomorphic feedback window and ecosystem engineering we also describe several hypotheses that should be carefully tested in the future and propose several research methods that have the ability to further our knowledge about soil creep radiometry laser scanning and soil micromorphology

quantifying sediment transport across an undisturbed prairie landscape using cesium 137 and high resolution topography soil erosion is a global environmental problem and anthropogenic fallout radionuclides offer a promising tool for describing and quantifying soil redistribution on decadal time scales to date applications of radioactive fallout to trace upland sediment transport have been developed primarily on lands disturbed by agriculture grazing and logging here we use 137cs to characterize and quantify soil erosion at the konza prairie long term ecological research lter site an undisturbed grassland in northeastern kansas we report on the small scale 10 m and landscape scale 10 to 1000 m distribution of fallout 137cs and show significant variability in the concentrations and amounts of 137cs in soils at our site 137cs soil concentrations and amounts typically vary by 10 to 30 on small scales which most likely represents the spatial heterogeneity of the depositional processes landscape scale variability of soil 137cs was significantly higher than small scale variability most notably soils collected on convex divergent landforms had 137cs inventories of 2500 to 3000 bq m 2 which is consistent with the expected atmospheric inputs to the study area during the 1950s and 1960s concave landforms however had statistically lower inventories of 1800 to 2300 bq m 2 the distribution of 137cs on this undisturbed landscape contrasts significantly with distributions observed across disturbed sites which generally have accumulations of radioactive fallout in valley bottoms because the upslope contributing area at each sampling point had a significant negative correlation with the soil inventory of 137cs we suggest that overland flow in convergent areas dominates soil erosion at konza on time scales of decades very few points on our landscape had 137cs inventories significantly above that which would be predicted from direct deposition of 137cs on the soil surface we conclude therefore that there is little net sediment storage on this undisturbed landscape

particle motion on burned and vegetated hillslopes climate change is causing increasingly widespread frequent and intense wildfires across the western united states many geomorphic effects of wildfire are relatively well studied yet sediment transport models remain unable to account for the rapid transport of sediment released from behind incinerated vegetation which can fuel catastrophic debris flows this oversight reflects the fundamental inability of local continuum based models to capture the long distance particle motions characteristic of steeplands probabilistic particle based nonlocal models may address this deficiency but empirical data are needed to constrain their representation of particle motion in real landscapes here we present data from field experiments validating a generalized lomax model for particle travel distance distributions the model parameters provide a physically intuitive mathematical framework for describing the transition from light to heavy tailed distributions along a continuum of behavior as particle size increases and slopes get steeper and or smoother we show that burned slopes are measurably smoother than vegetated slopes leading to 1 lower rates of experimental particle disentrainment and 2 runaway motion that produces the heavy tailed travel distances often associated with nonlocal transport our results reveal that surface roughness is a key control on steepland sediment transport particularly after wildfire when smoother surfaces may result in the preferential delivery of coarse material to channel networks that initiate debris flows by providing a first order framework relating the statistics of particle motion to measurable surface characteristics the lomax model both advances the development of nonlocal sediment transport theory and reveals insights on hillslope transport mechanics

a 20 000 year record of ocean circulation and climate change from the santa barbara basin much of the evidence for climate driven fluctuations in ocean circulation during the past 20 000 years has come from studies of the north atlantic region1 6 the extent to which such interactions have occurred in other ocean basins and any associated teleconnec tions between basins is poorly understood here we present high resolution palaeoclimate and palaeoceanographic records from a 20 000 year sedimentary sequence from the santa barbara basin on the eastern margin of the north pacific ocean the sequence shows oscillations of the benthic environment between low oxygen conditions laminated sediments during periods of warm climate and higher oxygen conditions non laminated bioturbated sediments during cool intervals age differences between coexisting benthic and planktonic foraminifers indicate climate related changes in the age and source and hence oxygen content of basin bottom waters relatively young bottom waters are associated with the cooler intervals and are considered to reflect high proportions of intermediate waters derived from proximal sources conversely older bottom waters are associated with the warmer intervals and were derived from more distal sources these climate driven variations in ocean circulation appear to be synchronous with the main ocean climate fluctuations in the north atlantic region1 6 suggesting that a tight coupling mechanism operates between the two basins

gopher bioturbation field evidence for non linear hillslope diffusion it has generally been assumed that diffusive sediment transport on soil mantled hillslopes is linearly dependent on hillslope gradient fieldwork was done near santa barbara california to develop a sediment transport equation for bioturbation by the pocket gopher thomomys bottae and to determine whether it supports linear diffusion the route taken by the sediment is divided into two parts a subsurface path followed by a surface path the first is the transport of soil through the burrow to the burrow opening the second is the discharge of sediment from the burrow opening onto the hillslope surface the total volumetric sediment flux as a function of hillslope gradient is found to be qs cm3 cm 1 a 1 176 dz dx 3 189 dz dx 2 68 dz dx 34 dz dx 0 4 this result does not support the use of linear diffusion for hillslopes where gopher bioturbation is the dominant mode of sediment transport a one dimensional hillslope evolution program was used to evolve hillslope profiles according to non linear and linear diffusion and to compare them to a typical hillslope the non linear case more closely resembles the actual profile with a convex cap at the divide leading into a straight midslope section copyright 2000 john wiley sons ltd

how steady are steady state landscapes using visible near infrared soil spectroscopy to quantify erosional variability although topographic steady state is often used as a simplifying assumption in sediment yield studies and landscape evolution models the temporal and spatial scales over which this assumption applies in natural landscapes are poorly defined we used visible near infrared visnir spectroscopy to measure the weathering of hilltop soils and quantify local erosional variability in two watersheds in the oregon coast range united states one watershed appears adjusted to base level lowering driven by rock uplift in the cascadia forearc while the other is pinned by a gabbroic dike that locally slows river incision and hillslope erosion models for uniformly eroding hillslopes imply uniform soil residence times instead we observe significant variability around the mean value of 18 8 k y 31 2 11 8 k y for our adjusted watershed the magnitude of erosional variability likely reflects the time scales associated with stochastic processes that drive bedrock weathering soil production and soil transport e g tree turnover the residence time distribution for our pinned watershed has a mean value of 72 9 k y 165 6 50 6 k y and is highly skewed with a substantial fraction of long residence time soils we speculate that this pattern results from the lithologic control of base level and lateral divide migration driven by erosional contrasts with neighboring catchments our novel and inexpensive methodology enables us to quantify for the first time the magnitude of erosional variability in a natural landscape and thus provides important geomorphic context for studies characterizing regolith development more generally we demonstrate that soils can record catchment scale landscape dynamics that may arise from lithologic controls or forcing due to climate or tectonics

rain splash of dry sand revealed by high speed imaging and sticky paper splash targets 1 rain splash transport of sediment on a sloping surface arises from a downslope drift of grains displaced ballistically by raindrop impacts we use high speed imaging of drop impacts on dry sand to describe the drop to grain momentum transfer as this varies with drop size and grain size and to clarify ingredients of downslope grain drift the splash of many grains involves ejection of surface grains accelerated by grain to grain collisions ahead of the radially spreading front of a drop as it deforms into a saucer shape during impact for a given sand size splash distances are similar for different drop sizes but the number of displaced grains increases with drop size in proportion to the momentum of the drop not infiltrated within the first millisecond of impact we present a theoretical formulation for grain ejection which assumes that the proportion of ejected grains within any small azimuthal angular interval dq about the center of impact is proportional to the momentum density of the spreading drop within dq and that the momentum of ejected grains at angle q is on average proportional to the momentum of the spreading drop at q this formulation consistent with observed splash distances suggests that downslope grain transport involves an asymmetry in both quantity and distance more grains move downslope than upslope with increasing surface slope and on average grains move farther downslope this latter effect is primarily due to the radial variation in the surface parallel momentum of the spreading drop surface parallel transport increases approximately linearly with slope

burial and turbulent transport by bioturbation a 27 year experiment in southeast australia in order to assess the net effect and relative importance of geomorphic processes at two natural woodland sites in southeast australia 100 small tiles were placed on the soil surface in 1979 and their movement was monitored over the course of nearly three decades rates of tile burial and other tile displacement were considerable but also markedly random being largely inconsistent with expected patterns of displacement by orthodox creep and rainwash processes this included substantial upslope displacement and burial depths that ranged from zero to 5 cm we suggest that such turbulent transport in the topsoil has mostly been caused by the direct and indirect transfer of soil and clasts by animals and plants i e bioturbation in addition to direct evidence of biota interacting with tiles the effectiveness of bioturbation at our sites has been well established and the overall tile burial rate of 0 25 to 0 4 mm yr 1 is comparable to rates of surface mounding patterns of tile movement are generally consistent with soils geomorphic theory regarding the biomantle and bioturbation driven stonelayer formation and provide further evidence that soil transfer and slope movement in many situations are markedly random and complex processes copyright 2010 john wiley sons ltd

lateral migration of hillcrests in response to channel incision in soil mantled landscapes 1 we investigate lateral migration of hillcrests in response to vertical offsets or transient incision rates of channels bordering these hillcrests in soil mantled landscapes for hillslopes undergoing sediment transport that is linearly proportional to the slope the hillcrest offset distance is one quarter of the ratio of the vertical offset between the channels to the relief of the symmetric hillslope if channels are downcutting at different rates the speed of hillcrest migration will depend on the ratio of the downcutting rates and the density ratio which is the ratio of the bulk density of the bedrock to the bulk density of the soil the density ratio plays a fundamental role in determining the transient response of the hillcrest lower density ratios lead to faster transient responses to changes in channel downcutting rates other parameters that affect the transient response of the hillcrest are the magnitude of transient differences in downcutting between the two channels the time averaged incision rate and a ratio of the elevation of the hillslope to a length that characterizes the decay in soil production with increasing soil thickness different parameters will be important for different sediment flux laws the profile of soil thickness reacts to transient changes in downcutting at a different rate than surface topography hillslopes experiencing transient channel downcutting may have surface topography that is symmetric about the hillcrest but will at the same time have a soil thickness profile that is asymmetric

process based model linking pocket gopher thomomys bottae activity to sediment transport and soil thickness burrowing organisms assist in shaping earth surfaces and are simultaneously affected by the environment they inhabit however a conceptual framework is not yet available to describe this feedback we introduce a model that connects the population density of soil burrowing animals to sediment transport via energy the model combined with avail able data from california hillslopes where soil erosion is driven by pocket gophers thom omys bottae suggests that a gopher annually expends 9 kj of energy or 1 of re ported burrowing energy expenditure in generating sediment transport the model is used to evaluate the case that gophers prefer to populate thicker soils the results suggest that this behavior may drastically dampen the spatial and temporal variations of soil thickness and gopher populations implying that burrowing organisms may create landscapes dis tinct from those affected by abiotic processes

particle trajectories on hillslopes implications for particle age and 10be structure many geomorphic systems act as conveyor belts onto which material is loaded at a particular rate and is transported in one direction toward another system that serves as a sink as the material travels it ages it changes in grain size it accumulates cosmogenic radionuclides it adsorbs or releases nutrients and it weathers here i address the hillslope conveyor as many geochemical processes are depth dependent the depth history of a particle becomes important to know i calculate soil particle trajectories in the horizontal depth plane and address three cases one in which horizontal speeds decline exponentially with depth a second in which they are uniform with depth and a third in which horizontal speeds are also uniform but all profile values are vertically well mixed vertical speeds are governed by continuity in an incompressible medium and by the boundary condition of zero vertical particle speed at the soil surface particle trajectories must therefore become surface parallel at the surface knowledge of soil particle trajectories allows calculation of residence times and concentration profiles of 10be in the soil the results inform strategies for interpretation of nuclide concentrations in soils and stream sediments and for inference of transport rate profiles in all steady cases the particle age and 10be structure is uniform with distance from the divide when significant vertical gradients in horizontal speed occur the patterns of particle age and of 10be concentration are dominated by the depth scale of the transport process in unmixed cases the particle age and 10be concentration in near surface samples can greatly exceed the vertically averaged values reflecting the fact that the vertical speeds of particles slow dramatically as they near the surface in cases in which horizontal speed varies significantly with depth the vertically averaged concentration of 10be within the soil can significantly under predict the mean 10be concentration of sediment delivered to the channel proper averaging requires weighting by particle speed these results provide the backdrop for addressing chemical evolution of soil on a hillslope

residual strength of clays in landslides folded strata and the laboratory the post peak drop in drained shear strength of an overconsolidated clay may be considered as taking place in two stages first at relatively small displacements the strength decreases to the fully softened or critical state value owing to an increase in water content dilatancy second after much larger displacements the strength falls to the residual value owing to reorientation of platy clay minerals parallel to the direction of shearing if the clay fraction is less than about 25 the second stage scarcely comes into operation the clay behaves much like a sand or silt with angles of residual shearing resistance typically greater than 20 degrees conversely when the clay fraction is about 50 residual strength is controlled almost entirely by sliding friction of the clay minerals and further increase in clay fraction has little effect the angles of residual shearing resistance of the three most commonly occurring clay minerals are approximately 15 degrees for kaolinite 10 degrees for illite or clay mica and 5 degrees for montmorillonite when the clay fraction lies between 25 and 50 there is a transitional type of behaviour residual strength being dependent on the percentage of clay particles as well as on their nature the post peak drop in strength of a normally consolidated clay is due only to particle reorientation measurements of strength on natural shear surfaces agree within practical limits of variation with values derived from back analysis of reactivated landslides this field residual strength can be recovered by multiple reversal shear box tests on cut plane samples but in high clay fraction materials it is typically somewhat higher than the strength measured in ring shear tests residual strength is little affected by variation in the slow rates of displacement encountered in reactivated landslides and in the usual laboratory tests but at rates faster than about 100 mm min qualitative changes take place in the pattern of behaviour a substantial gain in strength is followed with increasing displacement by a fall to a minimum value in clays and low clay fraction silts this minimum is not less than the slow or static residual but in clayey silts with clay fractions around 15 25 according to tests currently in progress the minimum can be as low as one half of the static value author trrl

evidence for nonlinear diffusive sediment transport on hillslopes and implications for landscape morphology steep soil mantled hillslopes evolve through the downslope movement of soil driven largely by slope dependent transport processes most landscape evolution models represent hillslope transport by linear diffusion in which rates of sediment transport are proportional to slope such that equilibrium hillslopes should have constant curvature between divides and channels on many soil mantled hillslopes however curvature appears to vary systematically such that slopes are typically convex near the divide and become increasingly planar downslope this suggests that linear diffusion is not an adequate model to describe the entire morphology of soil mantled hillslopes here we show that the interaction between local disturbances such as rainsplash and biogenic activity and frictional and gravitational forces results in a diffusive transport law that depends nonlinearly on hillslope gradient our proposed transport law 1 approximates linear diffusion at low gradients and 2 indicates that sediment flux increases rapidly as gradient approaches a critical value we calibrated and tested this transport law using high resolution topographic data from the oregon coast range these data obtained by airborne laser altimetry allow us to characterize hillslope morphology at 2 m scale at five small basins in our study area hillslope curvature approaches zero with increasing gradient consistent with our proposed nonlinear diffusive transport law hillslope gradients tend to cluster near values for which sediment flux increases rapidly with slope such that large changes in erosion rate will correspond to small changes in gradient therefore average hillslope gradient is unlikely to be a reliable indicator of rates of tectonic forcing or baselevel lowering where hillslope erosion is dominated by nonlinear diffusion rates of tectonic forcing will be more reliably reflected in hillslope curvature near the divide rather than average hillslope gradient