laboratory experiments simulating the geomorphic response to tectonic uplift 1 we present the results of an experimental study of topography dynamics under conditions of constant precipitation and uplift rate the experiment is designed to develop a complete drainage network by the growth and propagation of erosion instabilities in response to tectonic perturbations the quantitative analysis of topographic evolution is made possible by using telemetric lasers that perform elevation measurements at an excellent level of precision we focus our study on the effect of initial surface organization and of uplift rate on both the transient dynamics and the steady state forms of topography we show that the transient phase is strongly dependent on the initial internally drained area which is found to decrease exponentially with time the topography always reaches a steady state whose mean elevation depends linearly on uplift rate with a strictly positive value when uplift is zero steady state surfaces are characterized by a well defined slope area power law with a constant exponent of 0 12 and an amplitude that depends linearly on uplift rate with a strictly positive value when uplift is zero these results are consistent with a stream power law erosion model that includes a nonnegligible threshold for particle detachment uncertainty regarding the sediment transport length is resolved by calibrating the transient dynamics with a surface process model reappraising published results on the linear dependency between mean elevation or relief and denudation rate we suggest that an erosion threshold is worth considering for large scale systems

control of pre rift lithospheric structure on the architecture and evolution of continental rifts insights from the main ethiopian rift east africa we investigate the along axis variations in architecture segmentation and evolution of the main ethiopian rift mer east africa and relate these characteristics to the regional geology lithospheric structure and surface processes we first illustrate significant along axis variations in basin architecture through analysis of simplified geological cross sections in different rift sectors we then integrate this information with a new analysis of ethiopian topography and hydrography to illustrate how rift architecture basin symmetry asymmetry is reflected in the margin topography and has been likely amplified by a positive feedback between tectonics flexural uplift and surface processes fluvial erosion unloading this analysis shows that 70 of the 500 km long mer is asymmetric with most of the asymmetric rift sectors being characterized by a master fault system on the eastern margin we finally relate rift architecture and segmentation to the regional geology and geophysical constraints on the lithosphere we provide strong evidence that rift architecture is controlled by the contrasting nature of the lithosphere beneath the homogeneous strong somalian plateau and the weaker more heterogeneous ethiopian plateau differences originating from the presence of pre rift zones of weakness on the ethiopian plateau and likely amplified by surface processes the data provided by this integrated analysis suggest that asymmetric rifts may directly progress to focused axial tectonic magmatic activity without transitioning into a symmetric rifting stage these observations have important implications for the asymmetry of continental rifts and conjugate passive margins worldwide

post oligocene river incision southern sierra madre occidental mexico the sierra madre occidental of western mexico consists of a granitic basement covered by oligocene ignimbrites that define a reference surface from which to estimate late cenozoic river incision a 90 m grid digital elevation model was used to characterize contemporary topography and interpolate the late oligocene surface of the ignimbrite plateau from a surface fit to the highest points in the relatively undissected uplands between major river valleys long term river incision rates calculated from the difference between this reference surface and longitudinal profiles of 11 rivers that flow toward the tepic zacoalco rift zone range from about 0 01 to 0 2 mm year 1 river profiles of this region also show evidence of river capture driven by flexural uplift along the flank of the rift zone river profile concavity values in the sierra madre occidental range from 0 22 to 0 63 a range similar to that reported previously for a wide range of environments in contrast the empirically constrained ratio of exponents in the stream power model of river incision m n ranges from 0 44 to 0 52 close to the expected theoretical value of 0 5 the wider range of observed values may illustrate how can differ from the driving values of m n in non steady state bedrock river systems

the influence of surface and tectonic processes on landscape evolution of the iberian chain spain quantitative geomorphological analysis and geochronology abstract in tectonically active areas the landscape response to tectonic forcing is described and possibly quantified by regional topographic and hydrographic features as well as by spatial variation in rates of surface processes we investigated the recent landscape evolution of the iberian chain ne spain an intraplate thrust belt formed in cenozoic times and characterized by a dome shaped topography in its central sector the landscape is dominated by low relief surfaces late neogene in age presently standing at an average altitude of 1300 m a recent regional uplift controlled the organization of the present fluvial network and dissection of the landscape in this framework we investigated the geomorphic responses to tectonic forcing by the calculation of morphometric parameters focusing on topography map of local relief swath profiles and hydrography basin hypsometric curve and integral basin asymmetry factor river longitudinal profiles and relative indices and using srtm dem the results of morphometric analysis have been coupled with radiometric uranium series dating of calcareous tufas lying on fluvial strath terraces the obtained ages allow the estimation of incision rate along the high tajo and martin rivers our results indicate that uplift and rock type erodibility are the main factors influencing landscape evolution of the study area the incision rates are very similar throughout the central sector of the range indicating that despite subtle local variation the rivers are responding to a main tectonic input the regional uplift in conclusion the iberian chain landscape is in a transient state in response to a recent dome like uplift indeed the fluvial processes that weakly incised this landscape at a rate of 0 6 mm yr are approaching a radial pattern on the basis of geological and geomorphic constraints we hypothesize that the uplift started around or after 3 ma

river networks of southern africa scaling laws governing their geometry and deviations from scaling 1 africa is tectonically and hypsometrically different to all other continents and therefore provides a unique natural laboratory for the study of river network geometry southern africa is one of the more unusual geomorphological regions of this continent hence our interest in the geometry of the rivers draining this region the 14 river basins analyzed here come from the larger networks of the orange and limpopo rivers as well as from the southernmost section of the continent where rivers meander through an exhumed belt of folded paleozoic mountains basic scaling laws such as horton s laws and hack s law hold for the rivers studied here but the parameters governing these relationships vary between networks a strong inverse correlation between horton s ratio of stream numbers and mean source stream slope is observed we believe this is the first time such a relation has been reported horton s ratio of basin areas is proportional to that of stream numbers but always greater than it this contradicts existing models that equate the two parameters an expression for the ratio of stream lengths in terms of the ratio of stream numbers is derived theoretically and verified for the available data the parameter governing hack s law h varies not only between networks but also with scale inside each network existing models provide up to four scaling regimes given the spatial resolution of this study the two regimes at the middle scales are visible here these are termed the short range and randomness regimes with a crossover occurring at a drainage area of approximately 800 km2 the values for h in the smaller short range regime have an inverse correlation with the roughness of the topography observed values for h imply basins appear more elongated with increasing area this would be more pronounced in rivers draining a smooth topography in the randomness regime the values of h are lower mostly between 0 5 and 0 6 with a weak positive correlation to topography roughness this range of h corresponds to self similar basins but a more detailed analysis of individual stream fractality is necessary before such a conclusion can be made

optimal channel networks a framework for the study of river basin morphology optimal channel networks ocns are dendritic structures obtained by minimizing the local and global rates of energy dissipation in a continuously fed in space and time plane aggregation system reminiscent and based on the properties of the planform of three dimensional natural drainage networks geomorphological and fractal properties of ocns are known from earlier studies by the authors this paper explores further the structures derived by optimization of energy dissipation rates optimality of subnetworks and of basin shapes is investigated as a by product of competition for drainage a new perspective on the possible prediction of the width function of a basin network and hence of its hydrologic response is obtained by exploiting ocn techniques requiring only the definition of the outer boundaries of the basin the interplay between hillslope processes and the development of drainage networks is addressed aiming at the relative role and the mutual interrelations of geology and optimal organization in the structure of mature river basins also addressed is the issue of multiscaling and multifractality in the spatial organization of the network it is concluded that ocn approaches provide a comprehensive framework for the study of the morphology of geophysical structures

runoff generation and hydrologic response via channel network geomorphology recent progress and open problems abstract recent theoretical emphasis on quantifying the processes of runoff generation in space time in river basins has given a new focus to the fundamental importance of channel network geomorphology in river basin hydrology of particular significance in this context is the need for a comprehensive quantitative theory of channel networks in three dimensions reflecting the constraints of space filling and available potential energy as well as climatic hydrologic and geologic controls which are in dynamical equilibrium with channel network forms recent progress related to these issues is discussed in a nontechnical way and illustrated with examples and important open problems are identified

evaluation of a distributed catchment scale water balance model the validity of some of the simplifying assumptions in a conceptual water balance model is investigated by comparing simulation results from the conceptual model with simulation results from a three dimensional physically based numerical model and with field observations we examine in particular assumptions and simplifications related to water table dynamics vertical soil moisture and pressure head distributions and subsurface flow contributions to stream discharge the conceptual model relies on a topographic index to predict saturation excess runoff and on philip s infiltration equation to predict infiltration excess runoff the numerical model solves the three dimensional richards equation describing flow in variably saturated porous media and handles seepage face boundaries infiltration excess and saturation excess runoff production and soil driven and atmosphere driven surface fluxes the study catchments a 7 2 km2 catchment and a 0 64 km2 subcatchment are located in the north appalachian ridge and valley region of eastern pennsylvania hydrologic data collected during the machydro 90 field experiment are used to calibrate the models and to evaluate simulation results it is found that water table dynamics as predicted by the conceptual model are close to the observations in a shallow water well and therefore that a linear relationship between a topographic index and the local water table depth is found to be a reasonable assumption for catchment scale modeling however the hydraulic equilibrium assumption is not valid for the upper 100 cm layer of the unsaturated zone and a conceptual model that incorporates a root zone is suggested furthermore theoretical subsurface flow characteristics from the conceptual model are found to be different from field observations numerical simulation results and theoretical baseflow recession characteristics based on boussinesq s groundwater equation

the relationship between catchment and hillslope properties implications of a catchment evolution model abstract a recently proposed model of catchment evolution is used as the basis to study the relationships between catchment and hillslope properties the results highlight the interaction of the large scale and small scale features of the landscape tectonic uplift influences the catchment gradient in turn influencing the hillslope gradient and thus the drainage density but equally the hillslope ad channel gradients are related by sediment transport continuity so that catchment gradient is influenced by hillslope gradient neither the hillslope nor the channel network can be studied independently of the other catchment gradients are explicitly related to regional climatic and geologic conditions hillslope gradient and lenght are related via runoff and soil erosional properties if hillslope gradient is known then hillslope lenght and drainage density can be determined in turn drainage density can also be related to catchment scale properties via drainage density it is then possible to obtain an explicit relationship between hillslope length and catchment gradient and area lingking the basin s small and large scale features

controls on the strength of coupling among climate erosion and deformation in two sided frictional orogenic wedges at steady state 1 many important insights regarding the coupling among climate erosion and tectonics have come from numerical simulations using coupled tectonic and surface process models however analyses to date have left the strength of the coupling between climate and tectonics uncertain and many questions unanswered we present an approximate analytical solution for two sided orogenic wedges obeying a frictional rheology and in a condition of flux steady state that makes explicit the nature and sensitivity of the coupling between climate and deformation we make the simplifying assumption that the wedge grows in a self similar fashion consistent with airy isostasy such that topographic taper is invariant with orogen width tectonic influx rate and climate we illustrate first how and why the form of the erosion rule matters to orogen evolution and then derive a physically based orogen scale erosion rule we show that steady state orogen width crest elevation and crustal thickness are controlled by the ratio of accretionary flux to erosional efficiency to a power dictated by the erosion process remarkably we show that for most combinations of parameters in the erosion law rock uplift rate is more strongly controlled by erosional efficiency than it is by the accretionary flux further assuming frontal accretion with no underplating the spatial distribution of erosional efficiency dictates the relative rock uplift rates on the pro wedge and retro wedge and the time averaged trajectories of rocks through the orogen the restriction to invariant frictional properties is conservative in these respects systems subject to positive feedback between erosion and rheology will exhibit even stronger coupling among climate erosion and deformation than shown here

solute sources and chemical weathering in the owens lake watershed eastern california 1 chemical and strontium isotope analyses of solutes in a series of streams representing the bulk of the water reaching the 8500 km2 owens lake watershed provide a unique opportunity to evaluate factors that control stream chemistry on a regional scale the streams drain terrain that is dominated by mesozoic granitoids of the sierra nevada batholith but that also contains irregularly distributed roof pendants of paleozoic metasedimentary sequences mass balance modeling indicates that plagioclase feldspar weathering is the dominant contributor to stream chemistry and that carbonate dissolution is also a significant source of solutes for most streams the calculated ratio of plagioclase to carbonate is highly sensitive to the assumed weathering product of plagioclase kaolinite versus smectite and we suggest that the importance of carbonate could be exaggerated in cases where only the plagioclase to kaolinite reaction is considered strontium isotope 87sr 86sr ratios range from 0 70685 to 0 71958 with a flow weighted mean of 0 70911 to the extent that this value represents the water that would be flowing into owens lake were it not diverted by the los angeles aqueduct system the flow weighted mean 87sr 86sr ratio is consistent with ratios measured in owens lake core carbonates ranging in age up to 25 kyr the overall sr budget of the watershed is determined by the relative contributions of carbonate dissolution and plagioclase feldspar weathering and is dominated by reactions related to pyrite oxidation and hydrothermal fluid input from just two subbasins the impact of these processes needs to be considered when modeling regional and global riverine sr budgets climate related shifts in the relative importance of silicate mineral weathering reactions appear to be only second order effects on a regional scale

scaling relationships of channel networks at large scales examples from two large magnitude watersheds in brittany france abstract we present a statistical analysis on two watersheds in french brittany whose drainage areas are about 10 000 and 2000 km 2 the channel system was analysed from the digitised blue lines of the 1 100 000 map and from a 250 m dem link lengths follow an exponential distribution consistent with the markovian model of channel branching proposed by smart 1968 the departure from the exponential distribution for small lengths that has been extensively discussed before results from a statistical effect due to the finite number of channels and junctions the strahler topology applied on channels defines a self similar organisation whose similarity dimension is about 1 7 that is clearly smaller than the value of 2 expected for a random organisation the similarity dimension is consistent with an independent measurement of the horton ratios of stream numbers and lengths the variables defined by an upstream integral drainage area mainstream length upstream length follow power law distributions limited at large scales by a finite size effect due to the finite area of the watersheds a special emphasis is given to the exponent of the drainage area a a that has been previously discussed in the context of different aggregation models relevant to channel network growth we show that a a is consistent with 4 3 a value that was obtained and analytically demonstrated from directed random walk aggregating models inspired by the model of scheidegger 1967 the drainage density and mainstream length present no simple scaling with area except at large areas where they tend to trivial values constant density and square root of drainage area respectively these asymptotic limits necessarily imply that the space dimension of channel networks is 2 equal to the embedding space the limits are reached for drainage areas larger than 100 km 2 for smaller areas the asymptotic limit represents either a lower bound drainage density or an upper bound mainstream length of the distributions because the fluctuations of the drainage density slowly converge to a finite limit the system could be adequately described as a fat fractal where the average drainage density is the sum of a constant plus a fluctuation decreasing as a power law with integrating area a fat fractal hypothesis could explain why the similarity dimension is not equal to the fractal capacity dimension as it is for thin fractals the physical consequences are not yet really understood but we draw an analogy with a directed aggregating system where the growth process involves both stochastic and deterministic growth these models are known to be fat fractals and the deterministic growth which constitutes a fundamental ingredient of these models could be attributed in river systems to the role of terrestrial gravity

fluvial landscape response time how plausible is steady state denudation whether or not steady state topography and denudation are probable states depends on the timescale of system response to tectonic and climatic perturba tions relative to the frequency of those perturbations this paper presents analytical derivations of algebraic relations for the response time of detachment limited fluvial bedrock channel systems both to tectonic and climatic perturbations detachment limited fluvial erosion is described by the stream power incision model and the derivations are limited to the applicability of that model all factors likely to influence system response time that are not adequately captured by the stream power incision model will tend to increase the response time the calculations presented thus provide minimum estimates of landscape response time and therefore over predict the prob ability of attaining and sustaining steady state topography and denudation the central range of taiwan is used as a case study to estimate response times in a landscape often argued to be in steady state model parameters are fit to modern stream profiles by assuming that the topography represents a quasi steady state form estimated response times generally range from 0 25 to 2 5 ma depending on the non linearity of the incision rule and the magnitude and type of perturbation thus it may be reasonably argued that steady state topography and denudation are likely to prevail during periods of climatic stability response time is sufficiently short compared with plate tectonic timescales however rapid climatic fluctuation in the quaternary appears to preclude the attainment of steady state conditions in modern orogens motivation

transient fluvial incision in the headwaters of the yellow river northeastern tibet china 1 we utilize topographic analysis of channel profiles combined with field measurements of erosion rates to explore the distribution of channel incision in the anyemaqen shan a broad mountainous region in the northeastern tibetan plateau tributary channels to the yellow river display systematic downstream increases in channel gradient associated with convex upward longitudinal profiles steep lower reaches of channels are associated with rapid 1 m ka incision rates along the yellow river while upstream reaches are associated with relatively slow 0 05 0 1 m ka erosion of soil mantled uplands covariance between erosion rates and channel steepness indices suggest that channels are adjusted to match long wavelength differential rock uplift across the range geologic constraints indicate that rapid incision downstream of the range is associated with excavation of basin fill driven by changes in relative base level farther downstream the upstream limit of this wave of transient incision is marked by a series of knickpoints that are found at nearly the same elevation throughout the watershed consistent with knickpoint migration as a kinematic rather than diffusional wave tributary channel gradients downstream of knickpoints however display a progressive adjustment to increased incision rates that may reflect the influence of increased sediment flux comparison of observed channel profiles to a stream power model of fluvial behavior reveals that the rate of knickpoint propagation can only be explained if the erosional efficiency coefficient k increases during incision our results thus highlight the utility of channel profile analysis to reconstruct the fluvial response to both active tectonism and external changes in base level

a nonlocal theory of sediment buffering and bedrock channel evolution 1 bedrock erosion in mountain river channels ultimately sets the erosion rate of the surrounding hillslopes and the rate of sediment supply to the channels the supply of coarse bed sediment acts as a dampening effect on further erosion by depositing an alluvial cover that temporarily obscures the bedrock for landscapes where the residence time of the alluvial bed cover is comparable to the timescale of bedrock incision coarse sediment supply and transport generate a strong negative feedback on fluvial downcutting and the coupled process of hillslope channel erosion is inherently self buffering here we study a simple model of self buffered bedrock channel erosion that incorporates the spreading of bed sediment cover downstream in a way that allows for a broad tailed power law probability distribution of transport velocities of bed sediment over the long term this leads us to consider a nonlocal transport law fractional advection parameterized by a scaling exponent 0 1 which collapses to local advection for 1 for strong sediment buffering we find that nonlocality 1 has a direct control on the power law scaling of channel slope s with upstream area a giving s a 1 2 at steady state empirical observations of slope area scaling are consistent with 1 and nonlocal transport in general the model predicts linear logarithmic or power law stream profiles depending on the extent of buffering the degree of nonlocality and the scaling of the bedrock erosion law it also predicts somewhat counterintuitively that bed cover should thicken with distance x downstream slower than linearly as x i e the more nonlocal the bed sediment spreading process 0 the slower the bed cover increases downstream we deduce that long range heterogeneous transport of coarse sediment in mixed bedrock alluvial rivers may be a key element of landscape scaling and an important factor in landscape dynamics

self organized river basin landscapes fractal and multifractal characteristics in recent years a new theory of the evolution of drainage networks and associated landscapes has emerged mainly in connection with the development of fractal geometry and of self organized criticality soc concepts this theory has much improved our understanding of the mechanisms which determine the structure of natural landscapes and their dynamics of evolution in the first part of this paper the main ideas in the theory of landscape self organization are outlined and some remarkable features of the resulting structures are presented in the second part we apply theoretical tools developed in the context of multifractal fields to the study of the scaling properties of the field of elevations of soc landscapes we observe that such landscapes appear to be more complex than simple self affine fractals although in some cases a simple fractal framework may be adequate for their description we also show that multiple scaling may emerge as a result of heterogeneity in the field properties reflecting climate and geology

using slope area and apatite fission track analysis to decipher the rock uplift pattern of the yumu shan new insights into the growth of the ne tibetan plateau abstract studies have shown that the growth of the qilian shan the northeastern margin of the tibetan plateau started 10 ma ago however when and how it expanded northwards is still under debate here we focus on the rock uplift pattern of the yumu shan an active fault related fold in the hexi corridor north to the qilian shan normalized channel steepness achieved from the analysis of river longitudinal profiles shows a spatially variant rock uplift pattern with higher rates in the middle part and lower rates towards the west and east tips the compression of the mountain is typically accommodated by fault fold related shortening and vertical thickening apatite fission track thermochronology reveals that the growth of the yumu shan started 4 ma ago similar to the work on active tectonics combining the onset ages of the growth of the qilian shan 10 ma laojunmiao anticline 3 4 ma baiyanghe anticline 3 4 ma wenshu shan 4 5 ma and heli shan 2 ma we draw an conclusion that the ne margin of the tibetan plateau initiated growth in the mid miocene and expanded to the hexi corridor and to the south of the alxa block in the early pleistocene

correlation between channel and hillslope lengths and its effects on the hydrologic response summary in the geomorphologic approach based on width functions the instantaneous response function irf is completely determined once the distributions of hillslope and channel lengths in addition to flow parameters are assigned the relative contributions of hillslopes and channels to the variance of the travel times have been analyzed in the literature and three different variance producing mechanisms namely geomorphologic kinematic and hydrodynamic have been identified in this study the width function approach is employed to investigate a dispersive mechanism of geomorphologic and kinematic nature due to the existence of a relevant correlation between hillslope and channel lengths distributions the effects of this correlation on the variance of the irf were neglected in previous works assuming that the two distributions are uncorrelated here several basins of different size in the central apennines italy have been studied finding that both positive and negative values of correlation can occur their absolute values being seldom negligible the sign of the correlation is related to the distribution of slopes within the basin thus appearing to be influenced by typical morphologic signatures such as the presence of canyons or alluvial valleys in particular basins with large flat areas located near the outlet generally show negative values of correlation and are consequently more prone to produce peaked flow hydrographs finally an analytical expression is proposed to investigate the size of the catchments whose hydrologic response can be considerably affected by the hillslope channel correlation

beryllium 7 in soils and vegetation along an arid precipitation gradient in owens valley california 1 beryllium 7 is a potentially powerful tracer of atmospheric deposition and recent sediment transport but the quantity and distribution of 7be on arid landscapes have not been described we measured 7be in soil vegetation and dust in owens valley california and describe its distribution in aridisols and mollisols to evaluate its potential as a sediment tracer in desert environments beryllium 7 in vegetation and the upper few cm of soil is low but detectable 20 becquerels bq m 2 surface inventories of 7be at sites on the valley floor vary by a factor of five between the end of the rainy season april and the end of the dry season november in mollisols live grasses hold 50 bq 7be m 2 which is on the order of half of the total springtime surface inventory we find that within site variability at the 5 m scale is 5 to 22 1 relative standard error and can be explained by localized rain shadowing and erosion but between site variability at the km scale can be explained by differences in rainfall our alpine site has more than triple the inventory that is predicted from the rainfall 7be flux relationship that we generate using our springtime soil measurements and previously reported deposition data dust deposition does not appear to contribute significantly to 7be inventories but anomalously high 7be on the eastern flank of the sierras may be explained by a higher altitude air mass source and better scavenging efficiency of snow

scaling and elevation in river networks the analysis of large river networks obtained from digital elevation models has given insight into the variation of channel slope with scale investigators have recently suggested that channel slopes are self similar with magnitude or area as a scaling parameter our data indicates otherwise in particular the variance of channel slope is larger than that predicted by simple self similarity this suggests multiscaling the scaling exponent for the standard deviation is approximately half the corresponding exponent in the relationship of the slope mean to magnitude or area a model for channel slopes based on a point process of elevation drops along the channel is presented the model reproduces observed multiscaling properties when the density of elevation increments is related to area or magnitude as a

fractal techniques and the surface roughness of talus slopes linear plots of log n against log g where n is the number of steps of length g to span a transit are conventionally used as evidence that geomorphic surfaces are self similar fractals i e the surfaces have a constant fractal dimension in this study 42 transits on talus slope surfaces in niagara and letchworth gorges western new york are investigated to ascertain whether they are self similar log n log g plots which r2 values in excess of 0 99 suggest are linear are found upon more rigorous testing to be curvilinear it is concluded that the talus slope surfaces are not self similar and that log n log g plots are relatively insensitive to departures from self similarity the curvilinearity of the log n log g plots is explained with the aid of a randomized square wave model of the talus slope surfaces this model is used to extend the range of measurement beyond that which was possible in the empirical analysis the negative of the gradient of the log n log g relation at a point is the fractal dimension d measurements made upon the randomized square wave model indicate that the relation between d and scale of measurement has an asymmetrical wave shape with a peak i e maximum d where the scale of measurement is equal to the characteristic scale of roughness in other words the value of d for a surface is not absolute but depends on the scale of measurement relative to the scale of roughness linear regression analysis reveals that at the scale of measurement employed in this study d is positively correlated with particle size this is because the values of d fall on the right hand tail of the wave shaped relation between d and scale of measurement transects normal to the direction of slope are found to have higher values of d than profiles parallel to the direction of slope and this is explained in terms of particle orientation shape and juxtaposition because d varies continuously with scale of measurement there are considerable difficulties in using it to characterize and compare the surface roughness of talus slopes generalizing from talus slopes to other ground surfaces it is evident that to the extent that any natural ground surface has a characteristic scale of roughness it will depart from self similarity and d should be used with caution in quantifying the roughness of the surface geomorphologists are therefore urged to be more rigorous in their testing of self similarity before employing d to characterize surface roughness

saltating particles playa crusts and dust aerosols at owens dry lake california as part of the multinational lake owens dust experiment lode we have studied the generation of dust storms on the south sand sheet of owens dry lake california an anthropogenically desiccated playa reported to be the single greatest source of particulate matter in north america during march 1993 we performed an intensive field study including eight significant dust storms building on our prior work 1978 1984 and preliminary studies 1991 1992 we studied sources and magnitude of coarse saltating particles the meteorological conditions that allow them to become mobile across the flat playa of owens dry lake and how the motion of saltating particles across different types of playa surfaces results in the generation of pm10 dusts aerosol particles smaller than 10 m aerodynamic diameter saltating grains of lacustrine sand and broken crust abrade and disaggregate the playa surface into fine aerosols and the resulting pm10 concentrations recorded during major dust storms are among the highest ever recorded in north america on 23 march 1993 we measured a 2 h concentration on the playa of 40 620 g m 3 as far as we can determine the highest ambient pm10 value ever recorded in the u s a abrasion of salt silt clay crusts by saltation is shown to be responsible for all but a small part of one dust storm the quantity sand run saltating particle transport multiplied by wind run is shown to be very closely correlated with dust aerosol concentration finally we have established that on lake bed studies are essential for quantitative prediction of dust events on the owens dry lake bed despite the difficult conditions encountered

channel networks a geomorphological perspective the study of channel networks has been dominated since 1966 by the random model however recent work has shown 1 that although the topological properties of small networks conform to the random model more closely than those of large ones even small networks exhibit systematic deviations from topological randomness and 2 that the topological and length properties of channel networks are controlled to a large degree by the spatial requirements of subbasins and the need for these subbasins to fit together in space by the size sinuosity and migration rate of valley bends and by the length and steepness of valley sides the factors that control the density properties of channel networks vary with the scale of the investigation and the geomorphic processes governing channel initiation although progress has been made toward a satisfactory stream junction angle model further work is needed the evolution of channel networks has been investigated by a variety of methods including the development of conceptual and simulation models the monitoring of small scale badland and experimental drainage basins and the substitution of space for time the morphology of most channel networks is largely inherited from the past or strongly influenced by inherited forms inasmuch as there is no way of ever knowing the origin or complex history of such networks the use of stochastic models in their study seems unavoidable

effects of orographic precipitation variations on the concavity of steady state river profiles the concavity or curvature of river profiles has long been taken to be a fundamental indicator of the underlying processes governing fluvial erosion and thereby of landscape evolution however erosion laws have generally been derived without accounting for the strong orographically driven gradients in precipitation typically found in mountainous regions in addition field measurements have found discrepancies between the form of measured stream profiles and theoretically derived values introducing a simple physically based feedback we find that orographically induced variations in precipitation strongly affect the curvature of steady state river profiles this feedback complicates efforts to infer the form of erosion laws from observed profile concavities but could help explain discrepancies between observations and theory our results demonstrate a strong feedback through which climate influences the form of river profiles and show how such climatic effects act to limit the relief of unglaciated mountain ranges

beryllium 7 wet deposition variation with storm height synoptic classification and tree canopy state in the mid atlantic usa short lived fallout isotopes such as beryllium 7 7be are increasingly used as erosion and sediment tracers in watersheds 7be is produced in the atmosphere and delivered to the earth s surface primarily in precipitation however relatively little has been published about the variation in 7be wet deposition caused by storm type and vegetation cover our analysis of precipitation throughfall and sediments in two forested headwater catchments in the mid atlantic usa indicates significant variation in isotope deposition with storm type and storm height individual summer convective thunderstorms were associated with 7be activity concentrations up to 5 0 bq l 1 in precipitation and 4 7 bq l 1 in throughfall while single event wet depositional fluxes reached 168 bq m 2 in precipitation and 103 bq m 2 in throughfall storms originating from the continental usa were associated with lower 7be activity concentrations and single event wet depositional fluxes for precipitation 0 7 1 2 bq l 1 and 15 8 65 0 bq m 2 and throughfall 0 1 0 3 bq l 1 and 13 5 98 9 bq m 2 tropical systems had relatively low activity concentrations 0 2 0 5 bq l 1 in precipitation and 0 2 1 0 bq l 1 in throughfall but relatively high single event depositional fluxes due to large rainfall volumes 32 8 67 6 bq m 2 in precipitation and 25 7 134 bq m 2 in throughfall the largest sources of 7be depositional variation were attributed to storm characteristics including precipitation amount and maximum storm height 7be activity associated with fluvial suspended sediments also exhibited the highest concentration and variability in summer 175 1450 bq kg 1 we conclude the dominant source of variation on event level 7be deposition is storm type our results illustrate the complex relationships between 7be deposition in precipitation and throughfall and demonstrate event scale relationships between the 7be in precipitation and on suspended sediment copyright 2015 john wiley sons ltd

wetland mapping in the congo basin using optical and radar remotely sensed data and derived topographical indices article i nfo this study reports results of a classification tree approach to mapping the wetlands of the congo basin focusing on the cuvette centrale of the congo river watershed an area of 1 176 000 km 2 regional expert knowledge was used to train passive optical remotely sensed imagery of the landsat thematic mapper tm and enhanced thematic mapper plus etm sensors jers 1 active radar l band imagery and topographical indices derived from 3 arc sec elevation data of the shuttle radar topography mission srtm all data inputs were resampled to a common 57 m resolution grid a classification tree bagging procedure was employed to produce a final map of per grid cell wetland probability thirty bagged trees were ranked and the median result was selected to produce the final wetland probability map thresholding the probability map at 0 5 yielded a proportion of wetland cover for the study area of 32 equivalent to 360 000 km 2 wetlands predominate in the carpe lake tele lake tumba landscape located in the western part of the democratic republic of the congo and the south eastern republic of congo where they constitute 56 of the landscape local topography depicting relative elevation for sub catchments proved to be the most valuable discriminator of wetland cover however all sources of information i e optical radar and topography featured prominently in contributing to the classification tree procedure reinforcing the idea that multi source data are useful in the characterization of wetland land cover the method employed freely available data and a fully automated process except for training data collection comparisons to existing maps and in situ field observations indicate improvements compared to previous efforts

geomorphic expression of active tectonics in a rapidly deforming forearc sila massif calabria southern italy we examine the tectonic geomorphology of la sila calabria southern italy a high standing 1500 m plateau surrounded by crustal extension with map dem and field data these data are used to constrain a simple geodynamic model that describes short wavelength deformation of the plateau rim topographic metrics including drainage patterns river longitudinal profiles and swath profiles are consistent with field stratigraphic relationships collectively suggesting that local tectonic deformation is embedded within a broader regional uplift that has increased the mean elevation of the sila plateau during the quaternary the concavity steepness and length gradient index of modeled river longitudinal profiles proved to be the most useful metrics for recording the effects of locally active faults a previously unrecognized horst on the northeastern portion of the plateau was identified with these data nevertheless the core of the sila plateau remains relatively undeformed with respect to its flanks which are characterized by steep fault bounded escarpments active extension has dropped base level for and unloaded the plateau rim causing deep fluvial incision and associated flexural uplift of the footwall this footwall uplift helps maintain a separate external and nearly radial drainage away from the plateau along its flanks and a nearly closed drainage for the plateau interior a drainage divide roughly correlates with the plateau rim inhibiting the process of drainage integration through the sila interior and subsequent landscape dissection as a result geomorphic processes driving erosion of the sila upland are lagging behind the tectonic processes that have driven rock uplift leading to an overall increase in mean surface elevation these results underscore the importance of the lag times a landscape may endure in transforming from one tectonic and base level condition to another we conclude that the calabrian forearc has a similar geomorphic evolution as the more northern apennines consistent with the emerging view that growth of apennine topography has been recent quaternary rapid and possibly decoupled from rock deformation in the orogenic wedge

spatial relationship between topography and rock uplift patterns in asymmetric mountain ranges based on a stream erosion model abstract the spatial relationship between topography and rock uplift patterns in asymmetric mountain ranges was investigated using a stream erosion model in which the asymmetric rock uplift was given and erosion rates were proportional to the m th power of the drainage area and the n th power of the channel gradient the model conditions were simple and thus the effects of horizontal rock movement diffusional processes and erosion thresholds were neglected and spatially uniform precipitation lithology and vegetation were assumed in asymmetric mountain ranges under realistic exponent conditions m n and the above assumptions the surface erosion rate is faster on the steeper side and slower on the gentler side the topographic axis migrates away from the rock uplift axis toward the center of the mountain range owing to the contrast in erosion rates this migration continues until the erosion is balanced with rock uplift in a dynamic steady state the topographic pattern is independent of the rock uplift rate as indicated by an analytical solution and is prescribed by the rock uplift pattern and the exponents m and n as the asymmetry of the rock uplift pattern increases the topographic axis migrates a greater distance the location of the topographic axis is related to the location of the rock uplift axis by a simple logarithmic function for a wide range of m and n the fit of the numerical results and the logarithmic function is particularly good when m 0 5 and n 1 0 if the rock uplift pattern in asymmetric mountain ranges is known the value of n 5 m 4 can be constrained based on the logarithmic relation assuming a dynamic steady state on the other hand if the value of n 5 m 4 is known in an asymmetric mountain range the rock uplift pattern can be estimated directly from the topography this relation was applied to the suzuka range in central japan and the value of n 5 m 4 was estimated for an assumed reverse fault motion

a new experimental material for modeling relief dynamics and interactions between tectonics and surface processes abstract we developed a new granular material mativ to study experimentally landscape evolution in active mountain belt piedmonts its composition and related physical properties have been determined using empirical criteria derived from the scaling of deformation erosion transport and sedimentation natural processes mativ is a water saturated composite material made up with 4 granular components silica powder glass microbeads plastic powder and graphite whose physical mechanical and erosion related properties were measured with different laboratory tests mechanical measurements were made on a modified hubbert type direct shear apparatus erosion related properties were determined using an experimental set up that allows quantifying the erosion sedimentation budget from tilted relaxation topographies for mativ we also investigated the evolution of mean erosion rates and stream power erosion law exponents in 1d as a function of slope our results indicate that mativ satisfies most of the defined criteria it deforms brittlely according to the linear mohr coulomb failure criterion and localizes deformation along discrete faults its erosion pattern is characterized by realistic hillslope and channelized processes slope diffusion mass wasting channel incision during transport eroded particles are sorted depending on their density and shape which results in stratified alluvial deposits displaying lateral facies variations to evaluate the degree of similitude between model and nature we used a new experimental device that combines accretionary wedge deformation mechanisms and surface runoff erosion processes results indicate that mativ succeeded in producing detailed morphological and sedimentological features drainage basin channel network terrace syntectonic alluvial fan geometric kinematic and dynamic similarity criteria have been investigated to compare precisely model to nature although scaling is incomplete it yields particularly informative orders of magnitude with all these characteristics mativ appears as a very promising material to investigate experimentally a wide range of scientific questions dealing with relief dynamics and interactions between tectonics erosion and sedimentation processes

on the multifractal characterization of river basins abstract the spatial organization and scaling properties of a number of physical variables in river basins are analyzed within the framework of the multifractal formalism using data from digital elevation maps these variables include energy expenditure slopes discharges and the channel initiation function a measure of the processes that trigger channelization in the field the spatial distribution of these variables have multifractal properties which can be described in terms of a multifractal spectrum the analysis of nine very different basins in the united states shows that the multifractal spectra for each of the variables are very similar across basins revealing a common structure of organization this structure is compared to networks generated with scheidegger s stochastic model of river basins and the differences are discussed

on the description of the basin effective drainage structure abstract the relationships between the local properties of the morphological elements of a drainage basin and its drainage structure are analysed two theoretical approaches are used for which hydro dynamics and basin morphology are respectively assumed to represent the lowest and the highest starting scale level the results show a convergence toward the idea of slope scaling with contributing area in river networks this concept is then used as an indicator of channel initiation and maintenance for the identification of the effective drainage structure of the basin on the basis of existing digital elevation models dems integral properties of the single dem pixel are finally introduced to reduce the noise owing to a possible dem low accuracy e g in the estimation of the local slope value from the elevation data set the resulting network is characterized by a non uniform drainage density as expected for natural river networks

testing of the siberia landscape evolution model using the tin camp creek northern territory australia field catchment the siberia landscape evolution model was used to simulate the geomorphic development of the tin camp creek natural catchment over geological time measured hydrology erosion and geomorphic data were used to calibrate the siberia model which was then used to make independent predictions of the landform geomorphology of the study site the catchment located in the northern territory australia is relatively untouched by europeans so the hydrological and erosion processes that shaped the area can be assumed to be the same today as they have been in the past subject to the caveats regarding long term climate fluctuation a qualitative or visual comparison between the natural and simulated catchments indicates that siberia can match hillslope length and hillslope profile of the natural catchments a comparison of geomorphic and hydrological statistics such as the hypsometric curve width function cumulative area distribution and area slope relationship indicates that siberia can model the geomorphology of the selected tin camp creek catchments copyright 2002 environmental research institute of the supervising scientist commonwealth of australia

short term soil mixing quantified with fallout radionuclides soil mixing plays a significant role in contaminant transport carbon sequestration and landscape evolution yet the rates and driving mechanisms are poorly constrained here we use depth profiles and advection diffusion modeling of fallout nuclides to quantify differences in short term 7 be and weapons derived isotopes and quantify mixing with a steady state model of vertical 210 pb transport on a forested landscape in the bega valley in southeastern australia and on grasslands in marin county california where bioturbation is documented as the dominant sediment transport mechanism we calculate diffusion like mixing coefficients of 1 2 cm 2 yr 1 in montane forest soils of northern new england we observe little field evidence of short term mixing and find that the traditional advection diffusion model fails to describe 210 pb profiles because nuclide profiles here can be described with a simple model of litterfall organic matter decay and radioactive decay we argue that diffusion like processes are barely active on short time scales and that the advection diffusion model overestimates diffusion like transport while animal bioturbation and soil freezing cycles have little effect on the fate of elements in new england physical soil mixing drives transport at bega valley and marin county we suggest that the absence of soil stirring that we quantify in new england forests may explain the slow physical erosion here 0 2 cm k y relative to the actively bioturbated soils of bega valley and marin county 5 10 cm k y

orographic precipitation and the relief of mountain ranges 1 the influence of climate on the relief of mountain ranges has long been supposed but has received little quantitative investigation the simplified system of a longitudinal river profile in a bedrock channel coupled to a physically based model of orographic precipitation is used to explore how orographically influenced patterns of precipitation affect the relief of fluvially sculpted mountain ranges it is shown that the impact on the orography depends on the nature of the precipitation regime significant changes in relief also occur for imposed temperature changes of realistic magnitude although the ability of the relief to respond to any given change depends sensitively on its response time and the timescale of the forcing

distribution of active rock uplift along the eastern margin of the tibetan plateau inferences from bedrock channel longitudinal profiles 1 current models of long term river incision into bedrock suggest that the local rate of differential rock uplift should exert a primary control on the gradient of channel longitudinal profiles however discrimination of this effect from the influence of variations in substrate erodibility sediment flux precipitation and transient changes in profile shape has proved difficult in practice here we investigate the controls on the spatial distribution of bedrock channel gradients adjacent to the sichuan basin in an effort to assess the degree and nature of active deformation along this margin of the tibetan plateau analysis of river longitudinal profiles utilizing a channel steepness index a measure of profile gradient normalized for drainage area reveals a zone of anomalously steep channels adjacent to the topographic front of the plateau margin channel profiles are systematically less steep in their headwater reaches on the plateau and in their lower reaches east of the plateau margin comparison of steepness indices to mapped lithologic variations reveals that lithology has only a limited influence on channel gradient in this field area we observe no systematic relationship between steepness indices and upstream drainage area channels of all size are steeper near the plateau margin we argue that these systematic changes are not readily explained as a consequence of increased sediment flux or of orographic precipitation we are led to conclude that steep channel profiles along the topographic front of the plateau reflect active differential rock uplift between this region and the foreland

in situ development of high elevation low relief landscapes via duplex deformation in the eastern himalayan hinterland bhutan prior studies have proposed tectonic and climatic mechanisms to explain surface uplift throughout the bhutan himalaya while the resulting enigmatic low relief landscapes elevated above deeply incised canyons are a popular setting to test ideas of interacting tectonic and climatic forces when and why these landscapes formed is still debated we test the idea that these landscapes were created by a spatially variable and recent increase in rock uplift rate associated with the formation of structural duplexes at depth we utilize a new suite of erosion rates derived from detrital cosmogenic nuclide techniques geomorphic observations and a landscape evolution model to demonstrate the viability of this hypothesis low relief landscapes in bhutan are eroding at a rate of 70 m ma while basins from surrounding steep landscapes yield erosion rates of 950 m ma demonstrating that this portion of the range is in a transient period of increasing relief applying insights from our erosion rates we explore the influence of an active duplex on overlying topography using a landscape evolution model by imposing a high rock uplift rate in the middle of a mountain range our simulations show that low relief landscapes with thick alluvial fills form upstream of convex knickpoints as rivers adjust to higher uplift rates downstream a pattern consistent with geologic geomorphic and thermochronometric data from bhutan with our new erosion rates reconstructed paleo river profiles and landscape evolution simulations we show that the low relief landscapes were formed in situ as they were uplifted 800 m in the past 0 8 1 ma

geomorphic constraints on uplift history in the aspromonte massif southern italy abstract the landscape morphology of the aspromonte massif southern italy shows hanging low relief surfaces that correlate with uplifted landsurfaces which are preserved all around the massif the drainage network has deeply incised the high standing low relief landscapes seen here as being the remnants of phases of relief smoothing prior to strong uplift that has affected the area since the middle pleistocene gis aided estimation of the rock volumes eroded since the late early pleistocene indicate high variability in denudation rates between the gently rolling landscapes and the river valleys in this framework longitudinal river profiles are examined for 42 river channels to constrain multiple non equilibrium conditions and to reconstruct the long term uplift history of the massif most profiles consist of three four segments separated by knickpoints and suggest a complex incision pattern longitudinal profiles reveal two upper low gradient channel segments a zone of steep channels further down the low relief landsurface margin and a very steep lower channel segment particularly in the western quadrant upper channel segments correspond to the relict landscape rlandscape a high standing landsurface on top of the massif and the hanging landscape hlandscape a landsurface surrounding the rlandscape respectively steeper middle and lower segments are the result of two phase river incision that is linked to changes in regional uplift rates and subordinately to rock strength properties indeed analysis of river longitudinal profiles could indicate initially relatively slow aspromonte uplift during the early pleistocene and then pulses of rapid uplift during the middle late pleistocene multi segment river longitudinal profiles are therefore evidence of the transient landscapes of aspromonte in response to pulsed massif uplift

mesoscale fluvial erosion parameters deduced from modeling the mediterranean sea level drop during the messinian late miocene 1 after a base level drop rivers are the first components of the landscape to respond by incising into topography a base level drop results in a knickpoint in the downstream part of river longitudinal profiles whether knickpoints are preserved or erased during the upstream propagation of incision is still debated preservation and erasure of knickpoints are two end member processes that work in natural systems at different timescales different length scales and different places the huge 1500 m and fast tens of kiloyears sea level drop in the mediterranean during the messinian resulted in the fast propagation of incision far inland this is especially the case in the rhone valley southern france where the knickpoint is 300 km from the mediterranean coast numerical modeling of this event has been performed using the ros model which simulates both erosional and depositional processes in rivers the best fit between numerical results and geological data is obtained for a nonlinear relation between incision and drainage area and for a small transport length of sediment this small transport length at least 2 orders of magnitude lower than the length of the rhone suggests that the longitudinal profile relaxed in a diffusive way so that the initial knickpoint was not preserved finally after a base level fall the propagation of fluvial incision is very fast at geological timescales hundreds of kiloyears despite this the diffusive response implies that the time required for restoration of an equilibrium profile is very long

a physically based interpolation method for fluvially eroded topography 1 interpolation of elevation data from fluvially eroded topography is difficult for available methods because of the inherent roughness and drainage properties of the fine scale surface we propose a new method that produces an interpolation surface by adapting a simulated topography to a given set of point elevation data the simulated surface is produced by a simple model that rapidly simulates topography in dynamic equilibrium including the effects of tectonic uplift fluvial incision and hillslope diffusion agreement between the simulated topography and the elevation data is improved by iteratively adjusting a spatially varying erodability parameter when the iterative procedure terminates the simulated surface is in close but not in exact agreement with the observations exact agreement can usually be produced by distorting the simulated surface in a way that does not introduce local depressions interpolation surfaces generated by the proposed method have realistic drainage patterns without unrealistic depressions in addition the textural properties of the interpolation surfaces including the distributions of slopes and curvatures are better than those generated by other interpolation methods

catchment drainage network scaling laws found experimentally in overland flow morphologies the scaling relation between the drainage area and stream length hack s law along with exceedance probabilities of drainage area discharge and upstream flow network length is well known for channelized fluvial regions we report here on a laboratory experiment on an eroding unconsolidated sediment for which no channeling occurred laser scanning was used to capture the morphological evolution of the sediment high intensity spatially nonuniform rainfall ensured that the morphology changed substantially over the 16 hr experiment based on the surface scans and precipitation distribution overland flow was estimated with the d8 algorithm which outputs a flow network that was analyzed statistically the above mentioned scaling and exceedance probability relationships for this overland flow network are the same as those found for large scale catchments and for laboratory experiments with observable channels in addition the scaling laws were temporally invariant even though the network dynamically changed over the course of experiment

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

pre processing algorithms and landslide modelling on remotely sensed dems abstract terrain analysis applications using remotely sensed digital elevation models dems nowadays easily available permit to quantify several river basin morphologic and hydrologic properties e g slope aspect curvature flow path lengths and indirect hydrogeomorphic indices e g specific upslope area topographic wetness index able to characterize the physical processes governing the landscape evolution e g surface saturation runoff erosion deposition such dems often contain artifacts and the automated hydrogeomorphic characterization of the watershed is influenced by terrain analysis procedures consisting in artificial depression pit and flat area treatment approaches combined with flow direction methods in shallow landslide deterministic models when applied using topographic dataset at medium scale e g 30 m of resolution the choice of the most suitable dem processing procedure is not trivial and can influence model results this also affects the selection of most critical areas for further finer resolution studies or for the implementation of countermeasures aiming to landslide risk mitigation in this paper such issue is investigated using as topographic input the aster dems and comparing two different combinations of dem correction and flow routing schemes the study areas comprise ten catchments in italy for which hydrogeomorphic processes are significant aims of this paper are 1 to introduce a parameter estimation procedure for the physically based dem correction method pem4pit physical erosion model for pit removal 2 to investigate the influence of different terrain analysis procedures on results of the slope stability model shalstab shallow landsliding stability using remotely sensed aster dems 3 trying to assess which of terrain analysis methods is more appropriate for describing terrain instability

beryllium 7 and lead 210 chronometry of modern soil processes the linked radionuclide accumulation model lrc abstract soil systems are known to be repositories for atmospheric carbon and metal contaminants but the complex processes that regulate the introduction migration and fate of atmospheric elements in soils are poorly understood this gap in knowledge is attributable in part to the lack of an established chronometer that is required for quantifying rates of relevant processes here we develop and test a framework for adapting atmospheric lead 210 chronometry 210 pb half life 22 years to soil systems we propose a new empirical model the linked radionuclide accumulation model lrc aka lark that incorporates measurements of beryllium 7 7 be half life 54 days to account for 210 pb penetration of the soil surface during initial deposition a process which is endemic to soils but omitted from conventional 210 pb models e g the constant rate of supply crs model and their application to sedimentary systems we validate the lrc model using the 1963 1964 peak in bomb fallout americium 241 241 am half life of 432 years as an independent corroborating time marker in three different soils we locate a sharp 241 am weapons horizon at disparate depths ranging from 2 5 to 6 cm but with concordant ages averaging 1967 4 via the lrc model similarly at one site contaminated with mercury hg t we find that the lrc model is consistent with the recorded history of hg emission the close agreement of pb am and hg behavior demonstrated here suggests that organo metallic colloid formation and migration incorporates many trace metals in universal soil processes and that these processes may be described quantitatively using atmospheric 210 pb chronometry the 210 pb models evaluated here show that migration rates of soil colloids on the order of 1 mm yr 1 are typical but also that these rates vary systematically with depth and are attributable to horizon specific processes of leaf litter decay eluviation and illuviation we thus interpret 210 pb models to quantify i exposure of the soil system to atmospheric aerosol deposition in the context of ii organic carbon assimilation colloid production and advection through the soil profile the behavior of some other elements such as cs diverges from the conservative colloid behavior exemplified by pb and am and in these cases the value of empirical 210 pb chronometry models like lrc and crs is as a comparator rather than as an absolute chronometer we conclude that 210 pb chronometry is valuable for tracing colloidally mediated transport of pb and similarly refractory metals as well as the mobile pool of carbon in soils

groundwater controls on episodic soil erosion and dust emissions in a desert ecosystem feedbacks between vegetation soils and sediment transport processes maintain arid landscapes in geomorphically active degraded states or in more biologically productive and geomorphically stable states landscape evolution models and resource management strategies require a detailed understanding of thresholds that limit sediment transport in deserts but it can be difficult to quantify geomorphic responses to abrupt environmental change here we use measurements of fallout radionuclides and salt content in soils horizontal sediment fluxes vegetation cover and saturated zone depth in owens valley california usa to quantify the geomorphic response of a desert landscape to changes in groundwater availability owens valley has a well documented history of surface water diversions and pumping during the a d 1987 1992 drought and we studied 11 sites having a gradient of 0 5 m to 8 m of groundwater decline during this time we show that short length scale 50 m sediment redistribution is active in areas with a range of environmental histories but centimeter scale net soil loss occurred when photosynthetic vegetation cover declined to 20 where local groundwater remained shallow enough to produce evaporite salts erosion and dust emissions are most severe in central owens valley when groundwater falls below the 2 m effective rooting depth of native meadow vegetation but remains shallow enough 6 m so that capillary action maintains loose erodible sediment at the surface

constraints on the long term colluvial erosion law by analyzing slope area relationships at various tectonic uplift rates in the siwaliks hills nepal 1 the large database of topographic form and uplift rates that exists for the siwaliks hills central nepal makes possible a thorough analysis of the long term erosion model the study especially focuses on drainage areas larger than 5 10 3 km2 fixed by the database resolution and smaller than 1 km2 above which a fluvial signature is recorded this area range corresponds to colluvial valleys in which the dominant erosion process is likely debris flow we evaluate a phenomenological model wherein erosion is considered to depend on drainage area and slope we test this model by assuming that the uplift rate is in approximate equilibrium with erosion the stream power law model formulated by analogy to river incision and transport problems is found to be consistent with data since an inverse power law relationship between slope and drainage area is systematically observed between 7 10 3 and 1 km2 with little variability on the exponent 0 24 thanks to the range of uplift rates we obtain constraints on the slope dependency of erosion law which appears linear and which predicts a significant erosion threshold the linear dependence on slope in the debris flow zone is consistent with findings by kirby and whipple 2001 in the fluvial downstream zone and with the linear relationship between local relief and uplift rate documented by hurtrez et al 1999 the transition between this colluvial channel regime and the fluvial regime appears quite sharp in contrast with recent studies but the latter regime is not sufficiently documented to derive definite conclusions

climatic influences on profile concavity and river incision 1 longitudinal profiles of alluvial and bedrock rivers are typically concave up and the precise shape of their concavity is known to integrate tectonic climatic and channel grain size distribution factors we isolate climatic hydrologic effects on profile concavity through a spatial analysis of large watersheds with mixed bedrock alluvial trunk channels spanning a steep climatic hydrologic gradient in a tectonically stable landscape forty watersheds on the eastern american high plains were selected to minimize variability in base level relief vegetation rock type and drainage area we calculate stream concavity by two complementary methods an area normalized stream concavity index sci and the slope of a line regressed through log log plot of channel slope and basin area the sci and covary more importantly a positive correlation exists between profile concavity and climatic hydrologic factors such as precipitation intensity and peak annual discharge however modeled profile steepness has no correlation to climate or watershed hydrology we conclude that in tectonically stable settings higher intensity rainfall and greater mean annual precipitation lead to more concave profiles we do not have data to know if the concavity changes reflect primarily bedrock or alluvial grain size processes but generally a doubling of rainfall intensity on the high plains leads to a tripling in concavity manifest as tens of meters of incision such climatically influenced profile concavity could explain some of the often cited late cenozoic incision and increase in local relief for the high plains and rocky mountains traditionally ascribed to tectonics

the uplift of the adriatic flank of the apennines since the middle pleistocene new insights from the tronto river basin and the acquasanta terme travertine central italy abstract the apennines chain is an active neogene fold and thrust belt resulting from the westward subduction of the adriatic microplate starting from the end of the early pleistocene the chain was affected by an increase in regional uplift recent gps data resolved uplift rates of 1 2 mm yr for the whole apennines whereas in the adriatic flank several studies estimated rates between 0 3 and 0 5 mm yr over the last 1 myr a number of works investigated the evolution of the drainage systems along the periadriatic margin of the apennines providing long term incision rates studies from the northern part of this sector reported uplift rates varying from 0 2 to 1 1 mm yr whereas only few studies concentrated on the central sector of the adriatic flank of the apennines focusing mainly on the evolution of the lower reach of major rivers this work aims to quantify the long term rock uplift and incision rates of the eastern portion of the central apennines through the analysis of the tronto river basin because of its geologic and geomorphological configurations this basin is an ideal test site to investigate the influence of tectonics and climate on the recent topographic evolution of the central apennines the basin extends with a roughly wsw ene direction from the inner sector of the chain to the adriatic coast crossing several tectonic structures such as the amatrice extensional basin and the acquasanta and montagna dei fiori anticlines in particular in the acquasanta terme area the right flank of the tronto river valley is characterized by fluvial and travertine deposits organized and exposed in several levels in this work we investigated the hydrography river longitudinal profiles and topography swath profile slope and local relief of the tronto river basin coupling these data with field observations and geochronological analysis on the continental sediments fluvial deposits and travertines outcropping in the acquasanta terme area to better characterize the nature of travertines we performed geochemical characterization of three travertine forming thermal springs obtaining their physico chemical parameters the percentage of dissolved gases and the isotopes content finally we applied a knickpoint celerity model to chronologically constrain the geomorphological evolution of the whole drainage system the results show the occurrence of a continuous tectonic uplift 0 5 mm yr across the study area since middle pleistocene the uplift together with climate fluctuations drove the incision 0 6 mm yr of the landscape and the delineation of the present drainage network these data are consistent with previous estimates of uplift and incision rates in adjacent areas and provide new constraints on the quaternary evolution of the central apennines this study highlights how the coupling of field surveys with morphometric and topographic analyses of a drainage system is crucial to understand and quantify the influence of tectonic and climate changes in shaping the landscape

under what conditions do parallel river networks occur abstract geologists have long recognized that channel networks can deviate from a typical dendritic form when they develop under certain geologic or topographic constraints one such deviation is the parallel form which is thought to occur when networks develop on sloping surfaces the objectives of this research are to determine the specific conditions under which parallel networks occur and the nature of the transition between dendritic and parallel networks natural and simulated channel networks are considered in this study the natural networks were obtained from the digital elevation models of basins that include remnants of the preexisting topographic surface these remnants were identified as locations with small drainage areas and topographic curvatures that are close to zero for each basin the average slope of the preexisting surface was calculated and the channel network was classified using an existing method that can distinguish five network types including dendritic and parallel based on measures that are derived from scaling invariance the natural networks become consistently parallel when the average slope of the preexisting surface exceeds about 3 simulated channel networks were also generated using a detachment limited model for fluvial erosion the parameters of the model were determined to imitate the natural basins and the average slopes of the observed preexisting surfaces were used for the slopes of the initial surfaces in the simulations the model can also produce a transition between dendritic and parallel networks for an initial slope around 3 but this transition depends on the roughness of the initial surface and the boundary conditions

role of channel and floodplain cross section geometry in the basin response 1 we investigate the role of cross section geometry in flow routing by developing an analytical framework based on the instantaneous response function irf and relationships of river basin geomorphology the cross section geometry is included explicitly within the framework by assuming a power law cross section that is in turn used to derive expressions for the at a site hydraulic geometry the analysis performed using the illinois river basin indicates that the cross section geometry takes on different roles depending on whether flows are in the channel or floodplain the cross section geometry where width dominates over depth width dominant i e the at a site width depth ratio increases with increasing depth tends to produce a larger network celerity and dispersion for the channel and the trend reverses for the high floodplain flows we found that the cross section geometry can influence the relative contribution of hydrodynamic and kinematic dispersion for the channel the depth dominant cross section produces a lower hydrodynamic dispersion than the width dominant cross section and vice versa for the floodplain we found that the nonlinear dependence of the irf on effective rainfall expressed in the irf time to peak and peak flow may vary depending on the cross section geometry with the nonlinearity decreasing for the width dominant cross sections additionally the effect of cross section geometry on the basin response can alter the relative contribution of the stream network and hillslopes to the basin dispersion the derived framework has potential as an a priori tool for incorporating channel and floodplain geometry into distributed rainfall runoff models

morphotectonic analysis of the lunigiana and garfagnana grabens northern apennines italy implications for active normal faulting abstract this work integrates existing structural geology data with new detailed geomorphic analyses of the fluvial network to characterize active and potentially seismogenic faults bordering the lunigiana and garfagnana basins in the northern apennines of italy these two basins are nw se oriented asymmetric grabens bordered by several normal faults with a poorly known but probable recent slip history several strong earthquakes m 5 0 6 5 have occurred in the area in the last millennium demonstrating that this is one of the most seismically active areas of the northern apennines however the lack of reliable instrumental data for strong earthquakes generally low deformation rates and poor exposures of faulted quaternary sediments render the characterization of active seismogenic faults problematic here we quantify the relationships between faults and watershed scale geomorphology using 10 m digital topography to extract channel and basin metrics such as steepness concavity and stream length gradient indices of modeled river longitudinal profiles in particular convex segments of longitudinal profiles knickpoints are investigated in the spatial context of suspected active faults several knickpoints arise locally from juxtaposed rock types of different erodibility however many others mapped along major normal faults have a clear tectonic origin in fact the height of the footwall knickpoints the closest to the fault trace varies along strike the fault increasing toward the fault center and tapering off toward the fault tips mimicking the expected displacement profile of a fault in these cases we consider the knickpoint height as a proxy of the fault throw accumulated by the youngest fault activity probably during the late quaternary the along strike distribution of knickpoint heights helps in defining the likely segmentation pattern of the fault system the identified active normal fault segments have lengths ranging from 9 5 to 28 5 km the inferred late quaternary throw rate ranges from 0 3 to 0 8 mm a however the absence of any offset datable material limits our ability to assign precise numeric ages and rates of offset to the faulting

beryllium 7 the cinderella of fallout radionuclide sediment tracers current concern for the sustainable management of soil resources and the many adverse effects of increased sediment loads on streams and river systems has generated a need for more information on rates and patterns of soil loss and an improved understanding of catchment sediment budgets traditional measurement techniques are frequently unable to meet the requirements and fallout radionuclides have been shown to offer considerable potential for tracing the mobilization transfer redistribution and storage of soil and sediment within catchments and river systems caesium 137 and lead 210 have been the most widely used fallout radionuclide sediment tracers but their half lives mean that the information that they provide is in most instances limited to the medium term e g 25 120 years the need for information on shorter timescales has directed attention to the potential for using beryllium 7 which has a considerable shorter half life for tracing soil and sediment redistribution over short timescales e g days weeks to date however there have been relatively few attempts to exploit this potential this situation is likely to be in part a reflection of the emphasis of early work on 137cs and 210pb and the more recent nature of work using 7be however it may also reflect the limitations and constraints imposed by the nature of 7be fallout and the short half life of this radionuclide this contribution explores recent work in using 7be as a sediment tracer and the constraints imposed by its origin and behaviour attention is directed to fallout inputs the application of 7be to tracing soil and sediment redistribution on slopes and on river floodplains its use as a source fingerprint and other related applications the likely future potential of 7be as a sediment tracer is assessed copyright 2012 john wiley sons ltd

the evolution towards steady state erosion in a soil mantled drainage basin semi quantitative data from a transient landscape in the swiss alps abstract this paper presents semi quantitative data concerning the pattern of erosion under present day humid climatic conditions for a ca 10 km2 large soil mantled drainage basin located in the northern foothills of the central swiss alps the present day pattern of erosion was presumably initiated at ca 15 ka at the time when the last glacial period was terminated present day erosional processes are characterized by fluvial dissection and hillslope mass failure resulting in linear geomorphic features as fluvial dissection proceeds the rivers tend to adapt steady state longitudinal stream profiles in this case the stream profiles display power law relationships between channel gradient and upstream size of the drainage basin our study shows that establishment of steady state longitudinal stream profiles requires a balanced mass flux between processes on hillslopes and in channels this situation is interpreted for locations where the downslope flux of mass on hillslopes does not exceed the erosional potential and the transport capacity in channels consequently the development of steady state drainage systems appears to be controlled by erosional processes in channels as they dictate the elevation of the base level in contrast systems that are at transient states of longitudinal stream profile development very often display non balanced mass flux between processes in channels and on hillslopes specifically low mechanical strength of the bedrock e g glacial till marls results in a downslope flux of mass that exceeds the transport capacity and the erosional potential in the channel causing the elevation of the channel floor to increase in this case processes on hillslopes are not necessarily coupled with erosion in channels and appear to control the evolution of the drainage basin for a limited time interval besides interpretations of controls on surface erosion this paper also estimates post glacial sediment yield for the analyzed drainage basin these estimates are achieved by determination of the difference between the elevation of the glacial and the present day surface the data show that ca 30 of the analyzed drainage basin experiences present day surface erosion furthermore average post glacial sediment yield measures ca 4 6 m ka if the post glacial volume of sediment is related to the area that has experienced surface erosion or ca 1 4 m ka if it is related to the whole drainage basin interestingly the erosional efficiency appears to be significantly higher for systems that display steady state stream profiles than for transient rivers

the geometry of listric normal faults and deformation in their hangingwalls abstract in cross sections containing listric extensional faults area balancing techniques for depth to decollement are usually based on either bed length conservation or displacement conservation listric fault geometry may be constructed from a hangingwall roll over profile using the chevron construction this construction based on conservation of heave necessitates a reduction in fault displacement with decreasing fault dip a modification of this construction utilizing conservation of fault displacement predicts a listric fault that detaches at a shallower depth a new construction based on slip lines uses fault perpendicular displacement segments to generate listric fault shape fault propagation strain may be responsible for anomalous hangingwall geometries and these can be predicted by forward modelling using either a modified chevron construction or a slip line construction

short residence time and fast transport of fine detritus in the judean desert clues from 7be in settled dust 1 the cosmogenic isotope 7be t1 2 53 3d was measured in sediments collected from dust traps deployed in the judean desert which is part of the dead sea drainage basin the results show that a the 7be dry deposition flux in the dead sea region is 2 0 0 6 104 atoms cm 2 y 1 during summer and winter and 5 3 0 7 104 atoms cm 2 y 1 during fall b the residence time of dust in the dead sea drainage basin is less than one year c the recycled component of the cosmogenic isotope 10be t1 2 1 39 106y in judean desert dust is potentially small and d the 7be inventory atoms cm 2 in dust settled in the drainage basin did not reach steady state between consecutive rare events of desert winter floods suggesting a short transport rate of fine detritus material from the marginal terraces into the dead sea provided 10be behaves similarly as implied by the common geochemistry and cosmogenic origin of 7be and 10be we suggest 10be in lake lisan pleistocene dead sea detrital sediments as a potential proxy for paleo flood frequency and dust transport

the importance of spatially heterogeneous erosivity and the cumulative area distribution within a basin evolution model abstract topography reflects the terrain composition and the forces to which it is exposed the elements that control this shape are intuitive precipitation wind soil composition geologic activity lithology and vegetation each of these elements varies naturally in space a model of basin evolution is shown to produce quantitatively different topography for different relative magnitudes of diffusive and incisive erosion processes spatial heterogeneities in erosivity also influence the simulated topography the calibration of this evolution model is compared to observed topography the calibration process ultimately hinges on quantification of the aggregation pattern of the basin through analysis of the cumulative area distribution the effect of spatially heterogeneous erosivity is shown to be crucially important to reproduce the cumulative area distribution of observed topography

transient channel incision along bolinas ridge california evidence for differential rock uplift adjacent to the san andreas fault 1 the rates and spatial distribution of active deformation provide critical constraints on the geodynamics of deforming lithosphere yet such data are often difficult to acquire in eroding landscapes where poor preservation of geomorphic or stratigraphic markers hinders strain reconstruction recent advances in understanding of the relationship between bedrock channel profile form and erosion rate have led to their use as an index of rock uplift rate in steady state landscapes here we extend this analysis to landscapes experiencing a transient increase in erosion rate using an example from the marin county region of northern california we characterize channel and hillslope gradients in a series of small watersheds along a monolithologic portion of the franciscan terrane in marin county channel steepness indices vary strongly from north to south along the ridge and correspond with the progressive development of relief on threshold hillslopes along valley walls these patterns argue that recent channel incision has engendered a transient adjustment of hillslope gradient as incision outpaces soil production rates these differences in landscape form and inferred incision rate are explained by differential rock uplift within the region east of the san andreas fault relationships between channel gradient and incision rate suggest a threefold to fivefold difference in incision rate across the region and place a minimum bound on differential rock uplift rates our study highlights how landscape analysis can place bounds on the distribution of earth deformation in both space and time and thus lends insight into the processes driving that deformation

cover effect in bedrock abrasion a new derivation and its implications for the modeling of bedrock channel morphology the sediment load of a bedrock river plays an important role in the fluvial incision process by providing tools for abrasion the tools effect and by covering and thereby protecting the bed the cover effect we derive a new formulation for the cover effect in which the fraction of exposed bed area falls exponentially with increasing sediment flux or decreasing transport capacity and explore its consequences for the model of bedrock abrasion by saltating bed load erosion rates predicted by the model are higher than those predicted by earlier models in a closed system the maximum erosion rate is predicted to occur when sediment supply is equal to transport capacity for a flat bed by optimizing the channel geometry to minimize the potential energy of the stream and using representative values for both discharge and grain size we derive equations for the geometry of a bedrock river and explore how predictions for width slope and bed cover vary as functions of drainage area rock uplift rate and rock strength the equations predict a dependence of channel width on drainage area similar to the relations using a simple shear stress incision law the slope area relationship is predicted to be concave up in a log log regime with a curvature dependent on uplift rate however this curvature does not deviate sufficiently from a straight line to allow discrimination between models using empirical data dependence of channel width and slope on rock uplift rate can be separated into two domains for low uplift rates channel geometry is largely insensitive to uplift rate due to a threshold effect at high uplift rates there is a power law dependence bed cover is predicted to increase progressively downstream and to increase with increasing uplift rate in our model the width to depth ratio is a function of both tectonic and climatic forcing this indicates that the scaling between channel width and bed slope is neither a unique indicator of tectonic forcing at steady state nor a signature of transience or steady state we conclude that sediment effects need to be taken into account when modeling bedrock channel morphology

the design of post mining landscapes using geomorphic principles nature can provide analogues for post mining landscapes in terms of landscape stability and also in terms of the rehabilitated structure blending in with the surrounding undisturbed landscape in soil mantled landscapes hillslopes typically have a characteristic pro le that has a convex upper hillslope pro le with a concave pro le lower down the slope in this paper hillslope characteristic form is derived using the area slope relationship from pre mining topography at two sites in western australia using this relationship concave hillslope pro les are constructed and compared to linear hillslopes in terms of sediment loss using the siberia erosion model it is found that concave hillslopes can reduce sediment loss by up to ve times that of linear slopes concave slopes can therefore provide an alternative method for the construction of post mining landscapes an understanding of landscape geomorphological properties and the use of erosion models can greatly assist in the design of post mining landscapes copyright 2003 john wiley sons ltd

incision and channel morphology across active structures along the peikang river central taiwan implications for the importance of channel width river morphology and dynamics are strongly influenced by active tectonics we report channel dynamics for the peikang river which flows through the hsuehshan range in central taiwan using a digital elevation model and field surveys we constrain channel morphology for an 90 km stretch of river to calculate unit stream power and boundary shear stress along the river path incision rates are estimated with optically stimulated luminescence dating of sand deposited on strath terraces we find a strong correlation between unit stream power shear stress and incision rate but only if variation in channel width is considered a calibrated river incision rule implies river incision rates of 9 13 5 mm yr upstream of the meiyuan and tili faults and suggests that one or both of these structures are presently active our results indicate that the shuilikeng fault is also actively deforming as incision rates increase to 6 10 mm yr across it compared to 1 4 mm yr in adjacent reaches prominent narrowing across the shuilikeng fault and the absence of significant gradient variation indicate that channel width is a first order morphological adjustment to differential incision only when the channel width to depth ratio reaches a minimum does the channel slope significantly adjust to local changes in base level as is the case upstream of the meiyuan and tili faults

evolution and selection of river networks statics dynamics and complexity moving from the exact result that drainage network configurations minimizing total energy dissipation are stationary solutions of the general equation describing landscape evolution we review the static properties and the dynamic origins of the scale invariant structure of optimal river patterns optimal channel networks ocns are feasible optimal configurations of a spanning network mimicking landscape evolution and network selection through imperfect searches for dynamically accessible states ocns are spanning loopless configurations however only under precise physical requirements that arise under the constraints imposed by river dynamics every spanning tree is exactly a local minimum of total energy dissipation it is remarkable that dynamically accessible configurations the local optima stabilize into diverse metastable forms that are nevertheless characterized by universal statistical features such universal features explain very well the statistics of and the linkages among the scaling features measured for fluvial landforms across a broad range of scales regardless of geology exposed lithology vegetation or climate and differ significantly from those of the ground state known exactly results are provided on the emergence of criticality through adaptative evolution and on the yet unexplored range of applications of the ocn concept

use of digital elevation model data for the derivation of the geomorphological instantaneous unit hydrograph the use of digital elevation models dems allows the automatic derivation of channel networks and the quantitative description of the geomorphic characteristics of basins a common method of channel network extraction from dem data is based on the specification of a threshold area at that is the minimum support area required to drain to a point for a channel to form usually an arbitrary constant threshold area value is chosen for channel network extraction in this study the effects of threshold area selection both on the morphometric and scaling properties such as drainage density total channel length horton laws and fractal dimension of a channel network and the associated hydrological response function are analysed the response is obtained following the geomorphological instantaneous unit hydrograph theory two different probabilistic models are used they both relate the characteristic response function of the basin to its dem data derived networks one is derived assuming a strahler stream ordering system and the other is obtained by averaging a flow equation with respect to the network structure described by the width function applications are shown for three mountainous basins in the italian alps a sensitivity analysis is performed to study the influence of the variability of morphometric properties with respect to at on the hydrological response obtained it is shown that the model based on the width function is able to reduce the effects of this variability on the simulated response 1997 by john wiley sons ltd

a physical explanation for an observed area slope elevation relationship for catchments with declining relief a general relationship between the contributing area slope and mean elevation of catchments with relief declining after a tectonic uplift event is presented this relationship is based on the continuity equation for runoff and erosion processes in the catchment the key hypothesis underlying this relationship is that as a catchment declines the nondimensionalized catchment approaches a constant form this hypothesis is verified for computer simulated catchments the area slope elevation relationship covers several cases catchments declining toward a peneplain catchments declining from a high slope dynamic equilibrium resulting from a high rate of tectonic uplift to a low slope one resulting from a lower rate of tectonic uplift and catchments declining from an elevated initial condition as for example in the decline of a mine spoil heap a previously published relationship between slope and area for catchments in dynamic equilibrium and based on runoff and erosion physics is shown to be a special case of this general relationship the new area slope elevation relationship is compared with data from simulated catchments and a field catchment it is thus shown that for declining catchments the area slope elevation relationship is a good predictor of catchment form for catchments with declining relief it is argued that the slope area elevation relationship is sufficient with the planiform drainage pattern to completely define the elevation properties of the catchment such as for instance the hypsometric curve

revisiting the hypsometric curve as an indicator of form and process in transport limited catchment hypsometry has historically been used as an indicator of geomorphic form of catchments and landforms yet there has been little work aimed at relating hypsometry to landform process and scale this paper uses the siberia catchment evolution model to explore linkages between catchment process and hypsometry siberia generates results that are qualitatively and quantitatively similar to observed hypsometric curves for physically realistic parameters however we show that not only does the hypsometry reflect landscape runoff and erosion process but it is strongly dependent on channel network and catchment geometry we show that the width to length ratio of the catchment has a significant influence on the shape of the hypsometric curve though little on the hypsometric integral for landforms dominated by fluvial sediment transport the classic strahler mature hypsometric curve is only generated for catchments with roughly equal width and length narrow catchments show a hypsometric curve more similar to strahler s monadnock form for landscapes dominated by diffusive transport the simulated hypsometric curve is concave down everywhere this being consistent with curves reported for some example catchments in france because the transition between diffusive dominance to fluvial is scale dependent with larger catchments exhibiting greater fluvial dominance then the hypsometric curve is a scale dependent descriptor of landforms experimental results for simulated landforms from a small scale rainfall erosion simulator are reported it is shown that siberia yields satisfactory fits to the data confirming its ability to predict the form of the hypsometric curve from a simple model of geomorphic processes 1998 john wiley sons ltd

a physical explanation of an observed link area slope relationship an observed log log linear relationship between channel slope and contributing area is explained by the erosional physics that lead to catchment form it is postulated that tectonic uplift is in balance with the fluvial erosion down wasting that dominates catchment erosion and it is shown that this relationship results in the observed log log linear relationship at dynamic equilibrium in addition it has been observed that there are deviations from this log log linear relationship near the catchment divide with observed slopes being lower than those predicted from the relationship this is explained by noting that for small areas fluvial erosion effects are dominated by soil creep and rain splash modeled by diffusive physics the area at which this deviation from log log linearity occurs is that point on the hillslope at which diffusive physics like soil creep and rain splash begin to dominate fluvial erosion these predictions are confirmed by numerical simulations using a catchment evolution model

investigating a floodplain scaling relation using a hydrogeomorphic delineation method 1 floodplains are critical landscape features that are highly distinguished from neighboring uplands in terms of their hydrologic geomorphologic biogeochemical and ecological processes thus an essential step in floodplain studies is the determination of the lateral floodplain extent and its variability within a basin recent advances in topographic mapping and gis based analysis provide a means for developing automated techniques to determine floodplain extent in this study we propose a hydrogeomorphic floodplain delineation which links a simplified inundation algorithm with the river basin properties we utilize the method to investigate the physical controls on floodplain formation as captured by scaling relations between floodplain width and contributing area our hypothesis is that an efficient delineation grounded in hydrogeomorphic theory can improve our understanding of floodplain geometry across a range of conditions we test the method for two distinct watersheds a humid catchment in italy and an ephemeral basin in new mexico and note the existence of power law scaling of the floodplain width after averaging over stream orders an analysis of the algorithm parameters is conducted to identify possible limitations further systematic tests are needed to establish the generality of the floodplain scaling and its control on floodplain processes

topography of large scale watersheds fractal texture and global drift application to the mississippi basin the topography of large scale hydrographic basins is assumed to involve two components a meso scale isotropic fractal pattern and a polarized large scale trend which is oriented by large scale tectonics and supports the global drainage an algorithm is developed which splits up topography into a fractional brownian function and a trend gradient c focusing on the large scales a logarithmic profile and a rectangular planform are detected through either the relationship between the gradient c and the normalized elevation e or by the basin hypsometric curve and the inertia tensor of the basin area this is successfully applied to the digital terrain model of eight large scale sub basins of the mississippi the profile belonging to the basin main valley is also logarithmic but its slope is twice smaller than that of the mean profile denoting a trend surface with converging slopes towards the mid valley the scaling transition is investigated through angular distributions this is synthesized by a ternary diagram involving the following poles according to increasing scales a pure isotropic fractal f a transient off centred fractal o and a tilted tectonic plane t the fractal parameters are the intensity at scale s 1 km and the hurst exponent h over a basin area h is constant while is proportional to the trend slope c whatever the elevation e this implies a constant horizontal scale f for each basin around 30 km separating the fractal dominated topography from the trend dominated topography

meteoric cosmogenic beryllium 10 adsorbed to river sediment and soil applications for earth surface dynamics abstract rainfall scavenges meteoric cosmogenic 10be from the atmosphere 10be falls to the earth s surface where it binds tightly to sediment particles in non acidic soils over the life span of those soils as such meteoric 10be has the potential to be an excellent geochemical tracer of erosion and stability of surfaces in a diverse range of natural settings meteoric 10be has great potential as a recorder of first order erosion rates and soil residence times even though this tracer was first developed in the late 1980s and showed great promise as a geomorphic tool it was sidelined in the past two decades with the rise of the sister nuclide in situ 10be which is produced at a known rate inside quartz minerals since these early days substantial progress has been made in several areas that now shed new light on the applicability of the meteoric variety of this cosmogenic nuclide here we revisit the potential of this tracer and we summarize the progress 1 the atmospheric production and fallout is now described by numeric models and agrees with present day measurements and paleo archives such as from rain and ice cores 2 short term fluctuations in solar modulation of cosmic rays or in the delivery of 10be are averaged out over the time scale soils accumulate 3 in many cases the delivery of 10be is not dependent on the amount of precipitation 4 we explore where 10be is retained in soils and sediment 5 we suggest a law to account for the strong grain size dependence that controls adsorption and the measured nuclide concentrations and 6 we present a set of algebraic expressions that allows calculation of both soil or sediment ages and erosion rates from the inventory of meteoric 10be distributed through a vertical soil column the mathematical description is greatly simplified if the accumulation of 10be is at a steady state with its export through erosion in this case a surface sample allows for the calculation of an erosion rate explored further this approach allows calculation of catchment wide erosion rates from river sediment similar to the approach using 10be produced in situ in contrast to the in situ 10be approach however these analyses can be performed on any sample of fine grained material even where no quartz minerals are present therefore this technique may serve as a tool to date sediment where no other chronometer is available to track particle sources and to measure earth surface process rates in soil suspended river sediment and fine grained sedimentary deposits

a statistic for testing the elevation characteristics of landscape simulation models there is an urgent need to test recently constructed conceptual models of landscape evolution and geomorphology against field data many statistics that have commonly been used such as strahler statistics are poorly suited to this testing being unable to potentially falsify the models when applied in controlled conditions the relations between these statistics and catchment mass movement processes are in many cases indirect moreover they are sensitive to unknowable inputs e g initial conditions one of the main differences among the competing landscape evolution models is their representation of mass movement and erosion processes so that statistics that are directly linked to these processes or their geomorphic signature are needed this paper examines the use of a log log linear relation between catchment area slope and elevation this relation has been previously derived quantitatively from the catchment erosion and hydrologic processes for dynamic and declining geomorphic equilibria using a catchment evolution model this paper shows that the relation is robust against deviations from the assumptions of spatial and temporal homogeneity of erosion climate and tectonic uplift made in its derivation the sensitivity of the geomorphology to time varying tectonic uplift and climate and spatially variable soil erodability is examined it is thus asserted that the relation between area slope and elevation is suitable for testing of models against field data where spatial and temporal homogeneity of erosion climate and tectonic uplift are only approximately true in the case of variable soil erodability planar drainage patterns exhibit self organization with the high elevation regions of the catchment having low soil erodability consequently a downstream increasing erodability of the soil material consistent with a downstream fining type of behavior is observed it is further argued that the equilibria relation is fundamental and uniquely defines the elevation form of catchments so that all other elevation statistics are derived from it

a comparison of experimental and natural drainage basin morphology across a range of scales 1 numerous quantitative models have been developed to simulate the long term evolution of river basin topography most of these models reach an equilibrium state when the base level is lowered at a constant rate and the substrate and climate are constant in time at equilibrium the erosion balances the base level lowering so the topography remains frozen in time however some recent laboratory experiments contradict this behavior in these experiments the space time mean erosion rate balances the base level lowering rate but the actual erosion rates are highly variable in space and time consequently the channel networks are substantially mobile the experimental flow conditions are approximately similar but not dynamically equivalent to those in nature so it is unclear whether the observed dynamics are representative this paper examines whether the processes occurring in the experiments produce basins that are geometrically similar to typical natural basins to make this comparison the conceptual framework of scaling invariance is used many similarities are observed but we find that the experimental basins are slightly more elongated across a range of scales than the natural basins we consider and the relationship between channel slope and drainage area exhibits a break that is not found in the natural basins we analyze in the experiments the slopes of small channels also depend on the proximity of large channels this dependency is more pronounced for experiments with more mobile channel networks and it is not observed in most of the natural basins we analyze

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

using 7be measurements to estimate the relative contributions of interrill and rill erosion abstract rapid and reliable methods for estimating the relative contribution of interrill and rill erosion during a rainfall event are needed to provide an improved understanding of soil erosion processes and to develop process based soil erosion prediction models use of the radionuclide 7 be in controlled experiments provides a means of addressing this need and this paper reports an experimental study aimed at refining and testing procedures employed to estimate the relative contribution of the two components of erosion four experimental plots area 5 2 m and 10 15 20 and 25 slope filled with a loessial soil manually tilled and kept free of weeds with herbicides were subjected to high intensity rainfall 91 8 120 6 mm h 1 in order to induce rill development the evolution of the rill network was documented photographically during the rainfall events and the runoff and sediment output from the plots were collected and measured the sediment was recovered from the runoff and its mass and 7 be activity were measured the yang model reported previously was used to estimate the relative contributions of interrill and rill erosion from the 7 be activity of the exported sediment and this model was further refined to take account of the dynamic growth of the rills during the rainfall event the results from the experiments were also used to develop a simple empirical linear model for estimating the relative contributions of interrill and rill erosion from the 7 be measurements a comparison of the results provided by the three models showed some differences in the estimates of the magnitude of the relative contributions although their trend during the event was similar the estimates provided by the empirical linear model tended to be higher than those obtained using the refined model and lower than those generated by the yang model but were closer to those provided by the refined model which was seen as being theoretically the most accurate model the basis of the empirical linear model was simpler than that of other models since only a few easily obtained parameters were required in practical terms the empirical linear model therefore has important advantages and is judged to provide acceptable results further work is required to test its applicability under a wider range of conditions

late cenozoic uplift of the eastern cordillera bolivian andes abstract this paper analyses late cenozoic uplift in the bolivian andes using the morphology of well preserved regional paleosurfaces in the eastern cordillera that define three axially draining braided river catchments that formed between 12 and 9 ma rock uplift since the formation of the paleodrainage systems which has been quantified using four different methods is 1705 695 m with a mean erosion of 230 90 m as a consequence of entrenchment of the drainage systems the lack of faulting or tilting in the regions immediately farther west strongly suggest that rock uplift of the paleodrainage systems also extends to the western margin of the eastern cordillera balanced structural cross sections require crustal deformation at depth beneath the eastern cordillera in order to accommodate underthrusting of the brazilian shield beneath the thin skinned fold and thrust belt on the eastern margin of the bolivian andes in this case the observed uplift of the eastern cordillera is easily explained by sliding up a ramp in the major decollement dipping in the range 4 16 w as a consequence of the observed 60 110 km of shortening farther east in the subandean zone contemporaneous uplift of the western margin of the eastern cordillera is easily explained in terms of crustal thickening as a result of ductile squeezing in the lower crust accommodating at depth the subandean shortening it remains unclear how this uplift relates to that of the regions farther west in the altiplano and volcanic arc except that uplift in the eastern cordillera coincides with a phase of intense shortening in the northern altiplano commencing at 9 5 ma and continuing to 2 7 ma and possibly younger

martian geomorphology from fractal analysis of drainage networks 1 an alternative approach to conventional planetary terrain analysis is proposed martian terrains represented by topography based on the mars orbiter laser altimetry mola data are represented as a series of drainage basins regardless of the historical presence or absence of actual fluid flow a fractal analysis of each drainage network computationally extracted from an underlying terrain yields a network descriptor a list of four numbers that describes the traits of a network network descriptors are used for a quantitative characterization and classification of martian surfaces we have extracted and analyzed 387 drainage networks from 74 martian locations representing all major epochs and geological units to investigate whether their network descriptors are capable of differentiation between different epochs and geological units we have found that our approach can distinguish morphologically different terrains but only in a statistical sense in particular the method could be used to measure the degree of surface cratering and thus the age of the surface in addition for surfaces that are not heavily cratered the method is capable of distinguishing between different geological units we have found no global trends in the character of martian drainage networks their network descriptors show no systematic dependence on location or elevation our analysis reveals that all noachian surfaces grouped in the npld geological unit have very similar network descriptors regardless of prominence and integration of their visible fluvial features the comparison between statistical description of npld and terrestrial drainage networks shows overall similarities but also some marked differences because of these differences the notion of sustained rainfall on mars during the noachian epoch is inconsistent with our findings but a limited rainfall is compatible with our results