equilibrium disequilibrium and nonequilibrium landforms in the landscape abstract landscapes are composed of a diversity of landforms that may be characterized as equilibrium disequilibrium or nonequilibrium equilibrium is a constant relation between input and output or form toward which a landform tends or around which it fluctuates in time because of recent environmental changes and long relaxation times however many landforms are not adjusted to present inputs disequilibrium landforms are those that tend toward equilibrium but have not had sufficient time to reach such a condition some landforms called nonequilibrium do not tend toward equilibrium even with relatively long periods of environmental stability but rather undergo frequent and large change in form nonequilibrium may be caused by high magnitude thresholds that cause low frequency weather events to dominate form positive feedbacks and or nonlinearities that result in deterministic chaos landscapes contain mixtures of equilibrium disequilibrium and nonequilibrium landforms and these types of landforms interact in geomorphic systems such as sediment cascades the three types of behavior may coexist in the same landscape and the outputs of such mixed geomorphic systems reflect the combined effects of equilibrium disequilibrium and nonequilibrium subsystems this classification provides a framework for analysis and modeling of complex landscapes

a rudimentary mechanistic model for soil production and landscape development a rudimentary mechanistic model for soil production and landscape development is proposed the continuity equation of the model assumes that the change in soil thickness over time depends on the production of soil from the weathering of bedrock and the transport of soil through natural surface erosion the parameters for the model include the weathering rate and erosive diffusivity weathering rate is expressed as an exponential decay function of soil thickness which represents mechanical weathering erosive diffusivity can be estimated from soil erosion models the model is solved numerically using the finite difference approach and is applied to a numerical example simulation is performed for a hypothetical landscape with a series of hills and valleys results show the development rate of soil initially is very large and slows down until it reaches a steady state defined by a constant change in soil thickness the model also exhibits the characteristics of a nonlinear dynamic system nonlinearity of soil thickness and curvature and initial randomness appears to cause chaos instability in the system the results show promising progress in quantitative modelling of pedogenesis the limitations and suggested improvements of the model are also presented

relation between soil age and silicate weathering rates determined from the chemical evolution of a glacial chronosequence long term weathering rates rlt were determined from base cation depletion in soil profiles developed on six granitic glacial moraines varying in age from 0 4 to 297 ka in the wind river mountains wyoming weathering rates were found to decrease with soil age t according to the power law equation rlt 15 t 0 71 where rlt is in meq m 2 yr 1 and t is in ka comparable data from the literature are consistent with this function and it is similar to power law equations describing changes in laboratory weathering rates with time on the basis of our study we predict that for a catchment unaffected by anthropogenic inputs and in a steady state with respect to the organic and cation exchange pools rlt should be higher than present day weathering rates derived from stream fluxes rpd by a factor of about 3 4

modeling the tor dotted crests bedrock edges and parabolic profiles of high alpine surfaces of the wind river range wyoming abstract broad low curvature surfaces common to many alpine landscapes and particularly well expressed in the laramide ranges of the western usa appear to be roughly in steady state with respect to the current surface processes uniform thin order 1 m regolith covers the crystalline bedrock with the exception of occasional tors at ridgecrests the surfaces are commonly edged by bedrock lips at the tops of cliffs that bound the intervening glacial troughs regolith production is low order 10 m year on bare bedrock and reaches a maximum under tens of centimeters of regolith all of these characteristics may be accounted for with a numerical model that is faithful to the periglacial surface processes presently operating on these surfaces hillslope transport is modeled assuming the dominant process is frost creep transport efficiency depends linearly upon local slope and appropriately vanishes in the absence of regolith frost frequency scales the rate of motion while the ratio of frost penetration depth to regolith thickness dictates the degree to which the process is curtailed by available regolith initial conditions include initial mean slope and bedrock roughness and a uniform regolith cover boundary conditions are imposed by dictating that the edges of the calculation space be lowered at a rate appropriate for glacial incision broad convex surfaces emerge over time scales of order 1 million years all surfaces rapidly decouple from the bounding glacial troughs as the high negative curvature at the edges disallows accumulation of regolith these bedrock edges lower at a few microns per year while the troughs lower at many times this rate as the bedrock edges therefore serve as the effective boundary condition for the remaining surface the surfaces operate independently of both lowering and widening of the glacial troughs for a reasonable set of transport and weathering rates the final steady state landscape is sensitive to the initial condition in particular the steeper the initial landscape the more likely tors are to develop as the high curvature disallows accumulation of regolith these tors in turn limit the lowering rate of the crest and the landscape retains significant local relief low relief initial conditions more likely lead to parabolic surfaces that lack tors that tors are more likely on the crests reflects the high initial curvature at the crest tors on the side slopes are eliminated the present high surfaces in the laramide ranges of the western usa imply operation of periglacial surface processes over millions of years the occasional tors imply a steeper rather than flatter initial landscape the strong decoupling of surfaces from glacial troughs justifies their use as local geomorphic markers that allow calculation of relief production since glacial incision was initiated on the other hand their present low curvature does not require a landscape history in which these surfaces were once joined as an initially widespread erosion surface

sediment transport mechanisms on soil mantled hillslopes landscape evolution is modeled widely using a simple creep law for complex processes of sediment transport here field data show how a new transport model combined with an exponential soil production law better captures spatial variations of soil thick ness on hillslopes we combine parameterizations of simple and depth dependent creep with overland flow to predict soil thickness and suggest how soil distribution evolves in response to climatic and tectonic forcing we present an empirical expression for the response time of the system to external forcing that shows strong dependence on relief and is independent of soil production rate we suggest that this parameterization may be used to quantify upland carbon storage and removal and predict impacts of defor estation or rapid climatic changes

scale issues in weathering studies a review of the major scale issues in weathering studies reveals concerns over the fundamental spatio temporal distributions of weathering phenomena as well as issues of upscaling microscope based observations and linking different scales of observations in explanations of landform development various strategies are proposed which can be used to tackle these issues many rooted in non linear dynamical systems ideas as an initial step spatio temporal scale distributions are estimated here for weathering processes landforms and controls based on a range of empirical data two case studies of phytokarst in grand cayman and blistering and scaling of building stones are presented to illustrate the types of data that might be used to establish more convincing scale linkages in weathering investigations

the spatial variation of weathering and soil depth across a triassic sandstone outcrop in this study we used an archive of borehole logs from the british geological survey to collect information on the spatial structure of weathering that extends from the surface to competent bedrock across the triassic sherwood sandstone group outcrop 750 km2 in the east midlands uk the borehole logs were used to estimate the thickness of the soil n 280 and soil and saprolite ss the overburden of ice may have increased sub glacial pore water pressure with the fractures and faults acting as a drainage system for the removal of dissolved weathering products

pedologic and geomorphic impacts of a tornado blowdown event in a mixed pine hardwood forest abstract biomechanical effects of trees on soils and surface processes may be extensive in forest environments two blowdown sites caused by a november 2005 tornado in the ouachita national forest arkansas allowed a case study examination of bioturbation associated with a specific forest blowdown event as well as detailed examination of relationships between tree root systems soils and underlying bedrock the sites occur within mixed shortleaf pine and hardwood forests more than 95 of trees in the severe blowdown areas were either uprooted or suffered trunk break with uprooting more common than breakage within the most heavily damaged areas all uprooted trees were pines while all trees left standing were hardwoods root wads of uprooted trees had a mean surface area of about 3 m 2 and volume of about 2 m 3 though individual sizes were quite variable nearly 4 of the ground surface area was affected by uprootings with a soil volume equivalent to a disturbance of the entire surface area to a depth of 2 4 cm tree size as measured by diameter at breast height was significantly related to the area and volume of root wads r 2 0 55 0 71 respectively with volume of uprooted soil varying as diameter to the 3 power suggesting that the timing of blowdown events relative to tree age or growth stage significantly influences the area of disturbance and the mass and volume of material involved in 93 of cases the roots of the uprooted trees contacted or penetrated the underlying bedrock and in all those cases bedrock was quarried by uprooting only 11 of the tree throws showed evidence of general lateral root turning at the soil bedrock interface in most cases roots penetrated bedrock along joints the propensity for tree roots to penetrate bedrock joints facilitate weathering and excavate bedrock during uprooting supports the idea that tree roots play a predominant role in locally deepening soils

estimates of the rate of regolith production using and from an alpine hillslope abstract the production of regolith is a fundamental geomorphic process because most surface processes transport only unconsolidated material we use concentrations of the cosmogenic radionuclides crns 10 be and 26 al in regolith and bedrock to deduce the rate of production of regolith on an alpine hillslope in the wind river range wy these calculations are based on a theoretical model which we develop here this model shows that it is important to consider dissolution of regolith in regolith production and in basin averaged erosion rate studies rates of production of regolith are uniform along the hillslope and the mean rates for the entire hillslope deduced from 10 be and 26 al are 14 3 4 0 and 13 0 4 0 m ma 1 respectively rates of production of regolith deduced from 10 be concentrations in regolith mantled bedrock support the rates deduced from regolith concentrations in the alpine environment examined here the rate of production of regolith beneath 90 cm of regolith is nearly twice as fast as the average rate of production of regolith on bare rock surfaces which small et al small e e anderson r s repka j l finkel r 1997 erosion rates of alpine bedrock summit surfaces deduced from in situ 10 be and 26 al earth and planetary science letters 150 413 425 previously documented rock mantled with regolith probably weathers more rapidly than bare rock because the water required for frost weathering is limited on bare rock surfaces because the hillslope examined here is convex with constant curvature and regolith production and thickness are uniform down the slope the regolith volume flux must be proportional to the local slope of the hillside therefore our results are consistent with gilbert s gilbert g k 1909 the convexity of hilltops journal of geology 17 344 350 steady state hillslope hypothesis if tor height and the difference between rates of weathering on bare and regolith mantled rock provide a fair estimate of the age of summit flats steady state hillslope conditions have been attained in less than several million years

slope gradient and aspect effects on soils developed from sandstone in pennsylvania abstract this study was initiated to determine the basic characteristics and genesis of soils on gentle to very steep slopes on two contrasting slope aspects two transects a southwest sw and a northwest nw transect were laid out on a sandstone ridge across the summit and steepest convex shoulder positions the thickness of the o a and e horizons was not related to slope gradient across soils on all slope gradients and aspects this indicates that the present rate of soil formation is greater than erosion the influence of erosion on steep slopes could be off set by lateral movement of through flow water above the b horizon or the process of tree throw masks slope gradient effects solum depth b horizon thickness clay fe and al indexes decreased with increasing slope for both the nw and sw aspects organic carbon index decreased with increasing slope for the sw aspect decreases in effective precipitation over relatively larger surface areas at steep versus lower slope gradients a longer influence of periglacial erosion following the wisconsinan glacial advance and present slow but significant soil creep could cause these differences in soil development across the slope solum depth b horizon thickness clay fe and al indexes showed a smaller decrease across the nw compared to the sw slope organic carbon did not decrease across the nw slope the e horizon was also slightly thicker on the nw compared to the sw slope these aspect differences were probably caused by less evaporation on shaded nw compared to sunny sw slopes which produce generally higher moisture levels and more effective eluviation and illuviation on the nw slope

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

stream channel responses and soil loss at off highway vehicle stream crossings in the ouachita national forest article this study investigates the geomorphic effects of ford type stream crossings in an off highway vehicle ohv trail complex in the ouachita national forest arkansas at a total of 15 crossing sites we used a disturbed vs un disturbed study design to assess soil truncation and an upstream vs downstream design to assess in channel ef fects the 15 sites ranged from ohv crossings active for over 20 years to those on trails that have been closed to regular use for n5 years all of the sites designated for ohv use 14 sites exhibit soil loss of 30 to 45 cm within the trail segments on either side of the crossings in channel responses attributable to the crossings were ob served at 14 93 of the sites and include increased bank erosion increased mud coatings on coarse channel clasts increased in channel fine sediment accumulations changes in the size distributions of coarse bed materi al and occurrence of large channel filling sediment plugs however while every site but one shows at least one channel impact only one site exhibits all of them despite the relatively homogeneous geographic area sampled only limited generalizations are evident sediment impacts seem to predominate over runoff impacts from the trails small channels basin areas b0 4 km 2

meteorological causes of harmattan dust in west africa we investigated the temporal dynamics of dust entrainment in the bodele depression central sahara to better understand the intra annual variability of aerosol emission in the world s largest dust source the linkages between dust entrainment and large scale meteorological factors were examined by correlating several meteorological variables in the mediterranean and africa north of the equator with the aerosol concentrations in the bodele depression separately for winter and summer the methodological tools applied are ncep ncar reanalysis data and the aerosol index of the total ozone mapping spectrometer toms ai available for 15 years from 1978 to 1993 we found that dust mobilisation during the harmattan season is highly dependent on air pressure variability in the mediterranean area high pressure to the north of the bodele intensifies the ne trade winds leading to an increased entrainment of dust in the bodele depression in summer dust mobilization cannot be explained by the large scale meteorological conditions this highlights the importance of local to regional wind systems linked to the northernmost position of the intertropical convection zone itcz during this time

geomorphic controls of soil spatial complexity in a primeval mountain forest in the czech republic abstract soil diversity and complexity is influenced by a variety of factors and much recent research has been focused on interpreting or modeling complexity based on soil topography relationships and effects of biogeomorphic processes we aimed to i describe local soil diversity in one of the oldest forest reserves in europe ii employ existing graph theory concepts in pedocomplexity calculation and extend them by a novel approach based on hypothesis testing and an index measuring graph sequentiality the extent to which soils have gradual vs abrupt variations in underlying soil factors and iii reveal the main sources of pedocomplexity with a particular focus on geomorphic controls a total of 954 soil profiles were described and classified to soil taxonomic units stu within a 46 ha area we analyzed soil diversity using the shannon index and soil complexity using a novel graph theory approach pairwise tests of observed adjacencies spectral radius and a newly proposed sequentiality index were used to describe and quantify the complexity of the spatial pattern of stus this was then decomposed into the contributions of three soil factor sequences sfs i degree of weathering and leaching processes ii hydromorphology and iii proportion of rock fragments six reference soil groups and 37 second level soil units were found a significant portion of pedocomplexity occurred at distances shorter than the 22 m spacing of neighbouring soil profiles the spectral radius an index of complexity of the pattern of soil spatial adjacency was 14 73 to which the individual sfs accounted for values of 2 0 8 0 and 3 5 respectively significant sequentiality was found for degree of weathering and hydromorphology exceptional overall pedocomplexity was particularly caused by enormous spatial variability of soil wetness representing a crucial soil factor sequence in the primeval forest moreover the soil wetness gradient was partly spatially correlated with the gradient of soil weathering and leaching suggesting synergistic influences of topography climate hydro geology and biomechanical and biochemical effects of individual trees the pattern of stony soils random in most respects resulted probably from local geology and quaternary biogeomorphological processes thus while geomorphology is the primary control over a very locally complex soil pattern microtopography and local disturbances mostly related to the effects of individual trees are also critical considerable local pedodiversity seems to be an important component of the dynamics of old growth mixed temperate mountain forests with implications for decreasing pedodiversity in managed forests and deforested areas

climatic impact on isovolumetric weathering of a coarse grained schist in the northern piedmont province of the central atlantic states the possible impact of periglacial climates on the rate of chemical weathering of a coarse grained plagioclase muscovite quartz schist has been determined for a small watershed near baltimore maryland the isovolumetric chemical weathering model formulated from the geochemical mass balance study of the watershed shows that the weathering front advances at a velocity of 9 1 m m y if the modern environmental parameters remain the same back through time however recent surficial geological mapping demonstrates that periglacial climates have impacted the area such an impact significantly affects two key chemical weathering parameters the concentration of co2 in the soil and groundwater moving past the weathering front depending upon the assumptions used in the model the rate of saprolitization varies from 2 2 to 5 3 m m y the possible impact of periglacial processes suggested by the chemical weathering rates indicates a need to reconsider theories of landscape evolution as they apply to the northern piedmont province of the mid atlantic states i suggest that from the late miocene to the present that the major rivers have become incised in their present locations this incision has enhanced groundwater circulation and chemical weathering such that crystalline rocks beneath interfluvial areas remain mantled by saprolite and the saprolite mantle has been partially stripped as periglacial conditions alternate with humid temperate conditions

soil production on a retreating escarpment in southeastern australia the functional dependence of bedrock conversion to soil on the overlying soil depth the soil production function has been widely recognized as essential to understanding landscape evolution but was quantified only recently here we report soil production rates for the first time at the base of a retreating escarpment on the soil mantled hilly slopes in the upper bega valley southeastern australia concentrations of 10 be and 26 al in bedrock from the base of the soil column show that soil production rates decline exponentially with increasing soil depth these data define a soil production function with a maximum soil production rate of 53 m m y under no soil mantle and a minimum of 7 m m y under 100 cm of soil thus constraining landscape evolution rates subsequent to escarpment retreat the form of this function is supported by an inverse linear relationship between topographic curvature and soil depth that also suggests that simple creep does not adequately characterize the hillslope processes spatial variation of soil production shows a landscape out of dynamic equilibrium possibly in response to the propagation of the escarpment through the field area within the past few million years in addition we present a method that tests the assumption of locally constant soil depth and lowering rates using concentrations of 10 be and 26 al on the surfaces of emergent tors

a possible bistable evolution of soil thickness the analysis of the dynamical evolution of soil depth is of crucial importance to the understanding of landform processes in soil mantled landscapes such as soil production bedrock weathering landscape lowering and sediment yield the temporal evolution of the regolith thickness is studied through a stochastic model incorporating the dynamics of both soil production and erosion serious and extreme erosive processes e g landslides are considered as random forcings acting discontinuously and abruptly the dynamics of soil production is described by a deterministic function of the soil depth and different hypotheses are considered that express such a dependence the probability distribution of soil depth is analytically estimated as a function of the relative rates of the processes of soil erosion and bedrock weathering it is found that for different and likely values of the parameters the dynamics can be either transport limited or weathering limited intermediate conditions correspond to bistable systems having two preferential states that are both explored by the process the conditions controlling the occurrence of bistable systems are also discussed with respect to the steady state linear stability of a companion deterministic model the existence in the deterministic model of two possible stable states separated by a range of unstable configurations is found to be a condition necessary but not sufficient to the emergence of double modes in the soil depth distribution in the stochastic process suggested by this paper

late quaternary erosion in southeastern australia a field example using cosmogenic nuclides late quaternary rates of apparent soil production bedrock incision and average erosion are determined for the southeastern highlands of australia using in situ produced cosmogenic nuclide concentrations of 10 be and 26 al apparent soil production rates define a steep inverse exponential function of soil depth with a maximum of 143 m ma 1 under zero soil depth there were no observed soil depths between about 25 cm and zero however such that the maximum observed rate is about 50 m ma 1 the bredbo river catchment average erosion rate is 157 1mm a 1 and is similar to the average hillslope erosion rate of 167 1mm a 1 bedrock incision rates average 9 mma 1 and suggest that the higher rates of hillslope erosion may be in response to a pulse of incision perhaps generated by knickpoint propagation bedrock erosion rates inferred froma tor profile average 3 8 mma 1 with higher rates on other more weathered tor tops an aboveground tor profile of nuclide concentrations is consistent with a simple model of rapid stripping of the surrounding saprolite supporting the view that at least one episodic period of increased denudation has affected the landscape evolution of the highlands we test this hypothesis by using a simple landscape evolution model to reasonably predict the spatial variation of soil depth as well as the emergence of tors r 2001 elsevier science ltd and inqua all rights reserved

cosmogenic nuclides topography and the spatial variation of soil depth abstract if the rate of bedrock conversion to a mobile layer of soil depends on the local thickness of soil then hillslopes on uniform bedrock in a landscape approaching dynamic equilibrium should be mantled by a uniform thickness of soil conversely if the depth of soil varies across an actively eroding landscape then rates of soil production will also vary and consequently the landscape will not be in morphologic equilibrium the slow evolution of hillslopes relative to the tempo of climatic variations and tectonic adjustments would suggest that local morphologic disequilibrium may be expected in many landscapes here we explore this issue of equilibrium landscapes through a previously developed model that predicts the spatial variation in thickness of soil as a consequence of the local balance between soil production and erosion first we confirm the assumption in the model that soil production varies inversely with the thickness of soil using two independent methods one method uses the theoretical prediction that at local steady state soil production equals removal the depth of soil should vary inversely with hillslope curvature the second method relies on direct measurements of in situ produced concentrations of cosmogenic 10 be and 26 al in bedrock at the base of the soil column for our study site in northern california the two methods agree and yield the expression that the rate of soil production declines exponentially with the thickness of soil from 0 077 mm year with no soil mantle to 0 0077 mm year under 1 m of soil we then use this function of soil production in a coupled production and diffusive model of sediment transport to explore the controls on the spatial variation of the depth of soil on four separate spur ridges noses where we measured the data for the function of soil production model predictions are sensitive to boundary conditions grid scale and run time nonetheless we found good agreement between predicted and observed depths of soil as long as we used the observed function of soil production the four noses each have spatially varying curvature and consequently have varying depths of soil implying morphologic disequilibrium we suggest that our study site has been subjected to a wave of incision and varying intensities of erosion because of tectonic and climatic oscillations that have a frequency shorter than the morphologic response time of the landscape

origins and implications of soil layering abstract layering is common in soils due to a variety of pedologic and geologic processes and has important consequences for the interpretation of soils and landscapes layering can derive from original sedimentary layering depositional upbuilding episodic surface erosion deposition and stability soil production by weathering vertical or lateral translocation bioturbation and various combinations of these complex and polygenetic models incorporate both geogenic and pedogenic processes and allow for physical and biological processes as well as both vertical and horizontal movements we review these conceptual frameworks and synthesize them into a vertical contrast model vcm for interpreting layered surficial materials the vcm incorporates a variety of geologic and pedologic processes which may create destroy enhance or obscure vertical contrasts the model is illustrated via application to sites in the ouachita mountains usa and northwest saxonian lowlands germany the examples illustrate the importance of a comprehensive pedogeomorphic interpretation of layering since neither standard stratigraphic or top down pedogenetic principles necessarily apply the examples also show that the same process can sometimes contemporaneously both create and destroy vertical contrasts

delayed delivery from the sediment factory modeling the impact of catchment response time to tectonics on sediment flux and fluvio deltaic stratigraphy the sediment flux from a catchment is driven by tectonics and climate but is moderated by the geomorphic response of the landscape system to changes in these two boundary conditions consequently catchment response time and the non linear behavior of landscapes in response to boundary condition change control the downstream propagation of climatic or tectonic perturbations from catchments to neighboring basins in order to investigate the impact of catchment response time on sediment flux we integrated a spatially lumped numerical model pacmod with new routines simulating the evolution of landscape morphology and erosion rates under tectonic and climatic forcing we subsequently applied the model to reconstruct the sediment flux from a tectonically perturbed catchment in central italy finally we coupled our model to deltasim a process response model simulating fluvio deltaic stratigraphy and investigated the impact of catchment response time on stratigraphy using both synthetic scenarios and a real world system fucino basin central italy our results demonstrate that the differential response of geomorphic elements to tectonic and climatic changes induces a complex sediment flux signal and produces characteristic stratigraphic architectures and shoreline trajectories copyright 2014 john wiley sons ltd

local topography and erosion rate control regolith thickness along a ridgeline in the sierra nevada california the ridgelines of mountain ranges are a source of geomorphic information unadulterated by the arrival of sediment from upslope studies along ridgecrests therefore can help identify and isolate the controls on important regolith properties such as thickness and texture a 1 5 km section of ridgeline in the sierra nevada ca with a tenfold decrease in erosion rate inferred from ridgetop convexity provided an opportunity to conduct a high resolution survey of regolith properties and investigate their controls we found that regolith along the most quickly eroding section of the ridge was the rockiest and had the lowest clay concentrations furthermore a general increase in regolith thickness with a slowing of erosion rate was accompanied by an increase in biomass changes in vegetation community broader ridgeline profiles and an apparent increase in total available moisture the greatest source of variation in regolith thickness at the 10 100 m scale however was the local topography along the ridgeline with the deepest regolith in the saddles and the thinnest on the knobs because regolith in the saddles had higher surface soil moisture than the knobs we conclude that the hydrological conditions primarily driven by local topography i e rapid vs slow drainage and water storage potential provide the fundamental controls on regolith thickness through feedbacks incorporating physical weathering by the biota and chemical weathering moreover because the ridgeline saddles are the uppermost extensions of first order valleys we propose that the fluvial network affects regolith properties in the furthest reaches of the watershed

podzolization of soils under individual tree canopies in southwestern british columbia canada abstract on burnaby mountain in the coastal rainforest of british columbia there are concentric circular belts of podzolised soils around the stems of douglas fir and western hemlock trees the most acid soils occur near each stem and soils showing the greatest contrast in chroma between the eluvial and illuvial horizons occur beneath the periphery of the canopy of each tree these circular belts of soils appear to be associated with limited flow of a very acid water from precipitation down a stem and much greater flow of less acid water from the periphery of the canopy

nonequilibrium regolith thickness in the ouachita mountains abstract interpretations of regolith and soil thickness in the context of landscape evolution are typically based on the notion that thickness is controlled by the interaction of weathering rates and erosion and tuned to topography on sideslopes of the ouachita mountains arkansas however there is a high degree of local spatial variability that is largely unrelated to topography this indicates nonequilibrium in the sense that there is no evidence of a balance between rates of weathering and removal as is postulated in some conceptual models in geomorphology and pedology johnson s soil thickness model is applied as an alternative to interpret local variations in regolith thickness at the study sites regolith thickness is not generally related to slope curvature elevation or pedogenic development in the solum this indicates that variability in thickness is related chiefly to processes and controls acting in the lower regolith below the solum the primary controls of variability are local lithol

modelling soil landscape genesis a time split approach for hummocky agricultural landscapes abstract here we present a scheme for modelling soil landscape development in hummocky agricultural landscapes of formerly glaciated terrains soil landscape development is regarded as discontinuous over time long term progressive soil development during the holocene was replaced abruptly by an intense period of regressive pedogenesis during the last 50 years which is deduced from published 137 cs data and catchment scale mass balances consequently our primary working hypothesis is that the recent soil pattern is mainly a result of human influence during the last 50 years the paradigm behind our approach is that we have to couple geological historical information with recent dynamics of relevant processes to understand soil landscape development spatially distributed erosion and sedimentation are the most important processes during that period the intensity and extent of these processes is however also a function of the spatial pattern of soils erodibility which evolved in the progressive period therefore we developed a time split modelling approach for the progressive period relevant pedogenic processes de carbonatization silicate weathering clay translocation have to be quantified by a spatially distributed coupled water flow and solute transport model based on reconstructed initial and upper boundary conditions geomorphic units climate history relevant outputs e g topsoil textural properties are used as a spatially distributed input for the model of the regressive period for the latter we use a modified version of the dynamic physically based erosion 3d model schmidt j von werner m michael a 1996 erosion 2d 3d a computer model to simulate water erosion in german sachsische landesanstalt fur landwirtschaft dresden which allows spatially distributed modelling of water related soil erosion and deposition relevant topsoil properties are iteratively adapted to the rates of spatially distributed erosion and deposition preliminary results suggest that a coupling with tillage erosion plays an important role in our landscapes explicit analyses of the soil pattern using digital soil mapping techniques will be applied for model validation

stability of creeping soil and implications for hillslope evolution the geomorphic behavior of a soil mantled hillslope undergoing diffusive creep involves a coupling between changes in land surface elevation soil transport rates soil production and soil thickness a linear stability analysis suggests that the coupled response of the soil mantle to small perturbations in soil thickness or surface topography is influenced by two factors the diffusive like behavior of soil creep has a stabilizing effect wherein perturbations in land surface elevation are damped the relation between the soil production rate and soil thickness may be either stabilizing or destabilizing a monotonically decreasing production rate with soil thickness reinforces the stabilizing effect of diffusive land surface smoothing an increasing production rate with soil thickness has a destabilizing effect wherein perturbations in soil thickness or the soil bedrock interface are amplified despite the presence of diffusive land surface smoothing this coupled behavior is insensitive to the transport relation whether the soil flux is proportional to the land surface gradient or to the product of the soil thickness and land surface gradient the latter type of relation nonetheless could lead to a more complex hillslope form than might otherwise be expected for purely diffusive transport moreover the response to periodic sinusoidal variations in the rate of stream downcutting at the lower hillslope boundary involves upslope propagation of coupled damped waveforms in the land surface and the soil bedrock interface the distance of upslope propagation goes with the square root of the product of the transport diffusion like coefficient and the period of the downcutting rate the upper part of the hillslope is therefore insensitive to relatively high frequency variations in stream downcutting so together with a stable behavior of the coupled soil mantle bedrock system this part of the hillslope may exhibit a tendency toward uniform lowering while the lower part behaves transiently conversely in the presence of low frequency variations in stream downcutting hillslope morphology and soil thickness variations are more likely to reflect unsteady conditions over the entirety of the hillslope

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

paleomagnetism of middle proterozoic mafic intrusions and upper proterozoic nankoweap red beds from the lower grand canyon supergroup arizona abstract paleomagnetic data from lavas and dikes of the unkar igneous suite 16 sites and sedimentary rocks of the nankoweap formation 7 sites grand canyon supergroup gcsg arizona provide two primary paleomagnetic poles for laurentia for the latest middle proterozoic ca 1090 ma at 32 n 185 e dp 6 8 dm 9 3 and early late proterozoic ca 850 900 ma at 10 s 163 e dp 3 5 dm 7 0 a new 40ar 39ar age determination from an unkar dike gives an interpreted intrusion age of about 1090 ma similar to previously reported geochronologic data for the cardenas basalts and associated intrusions the paleomagnetic data show no evidence of any younger middle late proterozoic tectonothermal event such as has been revealed in previous geochronologic studies of the unkar igneous suite the pole position for the unkar group cardenas basalts and related intrusions is in good agreement with other ca 1100 ma paleomagnetic poles from the keweenawan midcontinent rift deposits and other sw laurentia diabase intrusions the close agreement in age and position of the unkar intrusion ui pole with poles derived from rift related rocks from elsewhere in laurentia indicates that mafic magmatism was essentially synchronous and widespread throughout laurentia at ca 1100 ma suggesting a large scale continental magmatic event the pole position for the nankoweap formation which plots south of the unkar mafic rocks is consistent with a younger age of deposition at about 900 to 850 ma than had previously been proposed consequently the inferred 200 ma difference in age between the cardenas basalts and overlying nankoweap formation provides evidence for a third major unconformity within the grand canyon sequence

soil formation rates on silicate parent material in alpine environments different approaches different results abstract high mountain soils develop in particularly sensitive environments consequently deciphering and predicting what drives the rates of soil formation in such environments are a major challenge in terms of soil production or formation from chemical weathering the predominating perception for high mountain soils and cold environments is often that the chemical weathering portion of soil development is temperature inhibited often to the point of non occurrence several concepts exist to determine long term rates of soil formation and development we present three different approaches 1 quantification of soil formation from minimally eroded soils of known age using chronosequences known surface age and soil thickness sast 2 determination of soil residence times srt and production rates through chemical weathering using un stable isotopes e g 230 th 234 u activity ratios and 3 a steady state approach using cosmogenic isotopes e g 10 be for each method data from different climate zones and particularly from high mountains alpine environment are compared the sast and steady state approach give quite similar results for alpine environments european alps and the wind river range rocky mountains usa using the srt approach soil formation rates in mountain areas but having a temperate climate do not differ greatly from the sast and steady state approaches independent of the chosen approach the results seem moderately comparable soil formation rates in high mountain areas alpine climate range from very low to extremely high values and show a clear decreasing tendency with time very young soils have up to 3 4 orders of magnitude higher rates of development than old soils 10 5 to 10 6 yr this apparently is a result of kinetic limits on weathering in regions having young surfaces and supply limits to weathering on old surfaces due to the requirement for chemical weathering to occur soil production rates cannot be infinitely high consequently a speed limit must exist in the literature this limit has been set at about 320 to 450 t km 2 a our results from the sast approach show however that in alpine areas soil formation easily reaches rates of up to 800 2000 t km 2 a these data are consistent with previous studies in mountain regions demonstrating that particularly young soils intensively weather even under continuous seasonal snowpack and thus that the concept of temperature controlled soil development soil forming intervals in alpine regions must be reconsidered

a process based model for colluvial soil depth and shallow landsliding using digital elevation data a model is proposed for predicting the spatial variation in colluvial soil depth the results of which are used in a separate model to examine the effects of root strength and vertically varying saturated conductivity on slope stability the soil depth model solves for the mass balance between soil production from underlying bedrock and the divergence of diffusive soil transport this model is applied using high resolution digital elevation data of a well studied site in northern california and the evolving soil depth is solved using a finite difference model under varying initial conditions the field data support an exponential decline of soil production with increasing soil depth and a diffusivity of about 50 cm 2 yr the predicted pattern of thick and thin colluvium corresponds well with field observations soil thickness on ridges rapidly obtain an equilibrium depth which suggests that detailed field observations relating soil depth to local topographic curvature could further test this model bedrock emerges where the curvature causes divergent transport to exceed the soil production rate hence the spatial pattern of bedrock outcrops places constraints on the production law the infinite slope stability model uses the predicted soil depth to estimate the effects of root cohesion and vertically varying saturated conductivity low cohesion soils overlying low conductivity bedrock are shown to be least stable the model may be most useful in analyses of slope instability associated with vegetation changes from either land use or climate change although practical applications may be limited by the need to assign values to several spatially varying parameters although both the soil depth and slope stability models offer local mechanistic predictions that can be applied to large areas representation of the finest scale valleys in the digital terrain model significantly influences local model predictions this argues for preserving fine scale topographic detail and using relatively fine grid sizes even in analyses of large catchments

the convenient fiction of steady state soil thickness abstract steady state regolith or soil thickness ssst whereby surface removals are approximately balanced by production of new soil by bedrock weathering is a common assumption in most models of hillslope and landscape evolution ssst is also a fundamental assumption in the use of cosmogenic radionuclides crn to estimate erosion and weathering rates the steady state concept is based on feedbacks between soil thickness and weathering at the base of the regolith such that sometimes after an optimal or threshold thickness is achieved thicker soils lead to lower weathering rates and vice versa ssst is thus only applicable to soils formed chiefly from weathering of the underlying bedrock where sufficient time has elapsed for regolith accumulation and where effects of processes other than weathering and surface removals on thickness are negligible even within this domain the widespread occurrence of deep weathering profiles regolith stripping and inherited regolith features makes ssst problematic as a conceptual model for pedogenesis or weathering profile development the ratio of soil thickness to total weathering profile thickness is proposed as a simple index of steady state steady state profiles formed on weathered bedrock should exhibit ratios close to unity data from the cumberland plateau region of eastern kentucky show that soil weathering profile ratios in shallow 20 m and generally significantly greater than soil thicknesses in the region suggesting ratios convenient fiction facilitating the use of some models and tools the potential pitfalls arise from the possibility that the utility of ssst as a convenient fiction in some contexts may be mistaken for a realistic representation of the dynamics of pedogenesis and weathering profile evolution