formation mechanism deformation characteristics and stability analysis of wujiang landslide near centianhe reservoir dam abstract wujiang landslide which is an ancient landslide has a total volume of approximately 1 327 10 7 m 3 its downstream boundary is approximately 300 and 590 m away from the new dam and axis of the dam respectively while the upstream boundary is approximately 1000 m away from the dam the relative relief of the landslide ranges from 380 to 480 m with moderately steep terrain and well developed gullies in this study we have investigated the geotechnical characteristics of the landslide and analyzed its formation conditions and evolution process we conclude that the landslide can be classified into the bedrock crack bedding slip mode and is an ancient landslide where creep deformation still exists although it has undergone repeated sliding evolution we have further analyzed its deformation characteristics the landslide is currently in a slow creep deformation state with the deformation larger at the leading edge and smaller at the trailing edge hence the disintegration of the superficial part or the slip of the shallow upper part of the landslide is likely to occur conversely the possibility of the whole slope sliding down is relatively low finally based on morgenstern price assumptions we have developed a rigorous three dimensional analysis method that can analyze the stability and identify the dominant sliding direction of the landslide during the impoundment of the reservoir

long term talus flatirons formation in the hyperarid northeastern negev israel abstract colluvial sediments of talus relicts talus flatirons around mesas preserve a record that sheds light on slope forming processes at temporal scales 103 yr the sedimentology and soil stratigraphy of two groups of talus flatirons in the northeastern hyperarid negev desert reveal four deposition events in the younger talus and at least two in the older one numerical modeling of high resolution 10be depth profiles suggests that these taluses were deposited during the middle pleistocene the younger talus group first depositional event occurred at 551 142 80 ka and its abandonment occurred at 270 38 17 ka the abandonment of the older talus group and stabilization of its surface occurred at 497 114 176 ka these ages indicate that the development of the studied talus sequence is not specifically associated with pleistocene glacial interglacial cycles the 10be modeled concentrations indicate significant differences in the average inheritance of talus flatirons of different groups these differences can be attributed to variability in the transport distance and duration of gravel exposure during transport but could also reflect some temporal variability in cliff retreat our results also demonstrate that talus slopes in hyperarid areas despite their steepness can store sediment for long periods 500 ka and thus constitute a valuable archive

quaternary scale evolution of sequences of talus flatirons in the hyperarid negev article i nfo talus flatiron sequences are ubiquitous landforms in arid and semiarid regions characterized by horizontal erodible rocks capped by more resistant rocks alternating phases of deposition and erosion lead to the formation of generations of talus flatirons in which ancient ones are located farther from the source cliff the existing conceptual model of this systematic spatial distribution of talus flatirons is related to glacial interglacial climatic cycles and to relatively high rates of cliff retreat three groups of talus flatirons were analyzed in the northeastern hyperarid negev desert the analyses include mapping age determination using optically stimulated luminescence and cosmogenic nuclide exposure dating electrical resistivity tomography and sedimentological and soil analyses all talus flatirons contain gypsic salic soil catena typical to hyperarid climate b80 mm yr 1 no pedogenic indicators of past wetter environments such as buried calcic soil 10 be exposure ages of the talus flatirons suggest that they were deposited during the middle pleistocene 610 ka and 170 ka for the oldest and intermediate aged talus flatiron groups respectively these ages combined with the present location of the talus flatirons relative to the source cliff yield retreat rates of 6 12 and 200 m ma 1 for the bedrock cliff and talus flatiron apex respectively and in opposite directions our results show that a climatic changes at glacial interglacial time scales are not the main controls over the formation of talus flatiron generation and b that significant cliff retreat is not the main cause for the systematic spatial distribution of talus flatiron generations relative to the cliff our results indicate that the process of talus flatiron formation in the negev desert must be associated with the balance between production deposition and removal of clasts under hyperarid conditions with only a minor cliff retreat

cosmogenic 3he exposure ages of pleistocene debris flows and desert pavements in capitol reef national park utah abstract the quaternary history of the capitol reef area utah is closely linked to the basaltic andesite boulder deposits that cover much of the landscape understanding the age and mode of emplacement of these deposits is crucial to deciphering the quaternary evolution of this part of the colorado plateau using cosmogenic 3 he exposure age dating we obtained apparent exposure ages for several key deposits in the capitol reef area coarse boulder diamicts capping the johnson mesa and carcass creek terraces are not associated with the bull lake glaciation as previously thought but were deposited 180 15 to 205 17 ka minimum age and are the result of debris flow deposition desert pavements on the johnson mesa surface give exposure ranging from 97 8 to 159 14 ka and are 34 96 kyears younger than the boulder exposure ages the offset between the boulder and pavement exposure ages appears to be related to a delay in pavement formation until the penultimate glacial interglacial transition or periodic burial and exposure of pavement clasts since debris flow deposition incision rates for the capitol reef reach of the fremont river calculated from the boulder exposure ages range from 0 40 to 0 43 m kyear 1 maximum rates and are some of the highest on the colorado plateau

repartition de la sedimentation dans le golfe proterozoique superieur du schisto calcaire au congo et gabon implications en afrique centrale abstract on the eastern border of the central africa craton the nw se directed nyanga niari basin formed a gulf cross cutting the precambrian chaillu massif this basin was linked to the ne sw directed comba basin the western extension of the sangha aulacogen in these two basins the late proterozoic schisto calcaire cycle comprises a transgressive zone with marls and conglomerates a condensed dolomite section pink dolomite and a high sea level stand zone with a carbonate ramp and barrier prograding sw ne towards the aulacogen between the comba and nyanga niari basins submarine dunes and infratidal giant stromatolites overlain by oncolitic dolomites were formed an internal shelf was isolated by an oolitic barrier an evaporitic dolomite lagoon with algal mats appeared in the nyanga niari basin and in the western part of the comba basin the lagoon was bordered by a shoal preceding a deepening of the internal shelf towards the aulacogen the foreshore sedimentation started with a thin conglomeratic layer and continued with the oolithe de kisantu characterized by a high frequency of talc oncolites in the nearshore zone black pseudo oolitic dolomite and algal mats were formed with thinly laminated algal deposits near the tidal flat in the northwestern part of the nyanga niari basin the continental serie de la biloua contains a continuous tidal breccia bar prograding towards the ne in the southern part of the comba basin fluvial channel deposits occur consisting of alluvial levees crevasse splays and tidal breccia located in the estuary in the neighbourhood of the channel mouth the sedimentation is disturbed most of the facies described here are present in many other proterozoic basins north and south of the central african craton everywhere shelf carbonate ramps seem prograding towards the sangha aulacogen the continental slope deposits of the same age cannot be interpreted as the lower part of the pan african molasse in all these sedimentary environments algal mats appear to be the main cause of organic matter productivity and of the primary carbonate precipitation finally the lagoonal environment was probably very similar to present day carbonate lagoons

the significance of scarp retreat for cenozoic landform evolution on the colorado plateau u s a since the beginning of the cenozoic period several hundreds of metres of the sedimentary cover have been removed from the colorado plateau palaeoclimatic considerations show that the colorado plateau has been dominated by dry climates throughout the cenozoic with the possible exception of the early palaeocene today in the still prevailing arid climate which strongly accentuates differences in rock resistance the relief shows a structurally controlled cuesta scarp topography in the slightly deformed strata of alternating resistance in examining whether the denudational efficiency of scarp retreat was sufficient to account for the wide erosional gaps in the sedimentary cover rates of scarp retreat were determined by using the information of dated volcanic material and by applying a new method which calculates the amount of retreat from the width of beheaded valleys of known age rates of retreat range from 0 5 to 6 7 km my 1 the results show that the rates of retreat are controlled by the thickness and resistance of the caprocks a model of cenozoic scarp retreat demonstrates that the rates of recession calculated for the scarps in upper cretaceous rocks were sufficient to bring them into their present positions from the centre of the monument uplift on the central colorado plateau the late eocene positions of the cliffs in the early tertiary formations give an indication of their maximal extent after the upper cretaceous sediments had been removed from the uplifts erosion cut through successively older rocks and activated scarps in stratigraphically lower positions scarp retreat can operate simultaneously and independently at different levels which enabled this erosional mechanism to remove great proportions of the sedimentary cover of the colorado plateau during the cenozoic

evaluation of simplified methods for predicting earthquake induced slope displacements in earth dams and embankments abstract this paper provides a review and comparison of existing simplified displacement based sliding block models analyses were performed to evaluate the relative accuracy of fifteen of these simplified models for predicting earthquake induced displacements to accomplish this task the predictive capability of the models was assessed by comparing model predictions with the actual displacements that were observed after earthquake shaking in 122 case histories of earth dams and embankments the results indicate that the model predictions of displacement were less than the observed displacement for a large majority of the case histories that were examined the difference between the observed and predicted displacements was relatively large for a significant percentage of the cases for each model that was examined the shapes and positions of the models relative error cumulative distribution functions did not change significantly if the case histories were filtered to include only those with intermediate levels of observed displacement i e 0 01 m

rapid incision of the colorado river in glen canyon insights from channel profiles local incision rates and modeling of lithologic controls the colorado river system in southern utah and northern arizona is continuing to adjust to the baselevel fall responsible for the carving of the grand canyon estimates of bedrock incision rates in this area vary widely hinting at the transient state of the colorado and its tributaries in conjunction with these data we use longitudinal profiles of the colorado and tributaries between marble canyon and cataract canyon to investigate the incision history of the colorado in this region we find that almost all of the tributaries in this region steepen as they enter the colorado river the consistent presence of oversteepened reaches with similar elevation drops in the lower section of these channels and their coincidence within a corridor of high local relief along the colorado suggest that the tributaries are steepening in response to an episode of increased incision rate on the mainstem this analysis makes testable predictions about spatial variations in incision rates these predictions are consistent with existing rate estimates and can be used to guide further studies we also present cosmogenic nuclide data from the henry mountains of southern utah we measured in situ10be concentrations on four gravel covered strath surfaces elevated from 1 m to 110 m above trachyte creek the surfaces yield exposure ages that range from approximately 2 5 ka to 267 ka and suggest incision rates that vary between 350 and 600 m my these incision rates are similar to other rates determined within the high relief corridor available data thus support the interpretation that tributaries of the colorado river upstream of the grand canyon are responding to a recent pulse of rapid incision on the colorado numerical modeling of detachment limited bedrock incision suggests that this incision pulse is likely related to the upstream dipping lithologic boundary at the northern edge of the kaibab upwarp copyright 2009 john wiley sons ltd

considerations on the chronological and causal relationships between talus flatirons and palaeoclimatic changes in central and northeastern spain abstract talus flatirons are relatively common landforms in arid and semiarid areas they are frequent in the duero tajo and ebro tertiary basins in spain the generation of a flatiron requires the alternation of periods with a prevalence of accumulation processes followed by periods with a preponderance of erosion processes in the three tertiary basins considered here talus flatirons have been found in numerous places and up to five stages of slope evolution have been recognised in some locations the second youngest stage s 2 has been dated in several places in the ebro and duero basins through 14 c the age of this stage ranges from 2529 52 to 3590 40 14 c ybp the third youngest stage s 3 has yielded dates of 27 862 444 radiocarbon years bp in the ebro basin and 28 550 130 14 c ybp in the duero basin s 4 has been dated in the ebro basin to 35 570 490 14 c ybp the s 2 slope facets correspond to the iron and bronze age cold stages the s 3 and s 4 flatirons may be correlated with the heinrich events h 3 and h 4 these dates may indicate that the accumulation periods on the slopes correspond to cold global events the dates obtained for the stages s 3 and s 4 in the central and northeastern sectors of spain and their good correlation with heinrich events suggest that flatirons could be related to climatic sequences in the upper pleistocene and holocene

palaeoclimatic considerations of talus flatirons and aeolian deposits in northern fuerteventura volcanic island canary islands spain abstract fuerteventura volcanic island has been subject to considerable aeolian activity since the late pleistocene the aeolian record includes inactive aeolian deposits with interbedded entisols whose age by osl dating ranges between 46 and 26 ky bp the corralejo active dune field where sand sheets nebkhas coppice dunes blowouts barchans and transverse dunes have been described constitutes a more recent aeolian deposit here the age is about 14 ky bp on fuerteventura island aeolian dust has been deposited on valleys and slopes this last type of accumulation has been affected by gully incision producing talus flatirons samples taken on the apex of these palaeo slopes indicate an osl age of 30 and 50 ky bp a palaeoclimatic succession has been interpreted during which a prevailing arid period took place in ois 4 with the accumulation of aeolian dust a humid period occurred in ois 2 during which slopes were dissected and formed talus flatirons an arid period about 14 ky bp gave rise to the corralejo dune field which has continued until present with slight climatic oscillations

giant subtidal stromatolites forming in normal salinity waters we report here the discovery of giant lithified subtidal columnar stromatolites 2 m high growing in 7 8 m of clear oceanic water in current swept channels between the exuma islands on the eastern bahama bank they grow by trapping ooid and pelletal carbonate sand and synsedimentary precipitation of carbonate cement within a field of giant megaripples the discovery is important to geologists and biologists because similar organo sedimentary structures built by a combination of cementation and the trapping of sediment by microbes were the dominant fossil types during the precambrian stromatolites are thought to have been responsible for the production of free oxygen and thus the evolution of animal life1 2 until the discovery of small lithified subtidal columnar stromatolites in the bahamas3 the only subtidal marine examples known to be living while undergoing lithification were in the hypersaline waters of hamelin pool at shark bay western australia4 7 shark bay stromatolites range from intertidal to the shallow subtidal with the larger columns reaching 1 m in height the shark bay stromatolites have strongly influenced geological interpretation by analogy many ancient stromatolites have been considered to have grown in intertidal and or hypersaline conditions8 although hypersalinity was not a necessity for growth during the precambrian because grazing metazoan life had not then evolved

colorado river chronostratigraphy at lee s ferry arizona and the colorado plateau bull s eye of incision abstractlee s ferry arizona united states lies at an important geo logic transition between the grand canyon margin and the canyon lands center of the colorado plateau it marks a knickpoint along the colorado river at the top of the steep grand canyon and it is central to debate about the patterns of erosion and sources of uplift in this famous landscape new chronostratigraphic data from the suite of ll terraces here indicate a strong uvial response to climate driv ers superimposed upon an integrated mid to late pleistocene incision rate of 350 m m y a regional compilation of well constrained results over the same timescale reveals that this is intermediate between slower rates downstream in grand canyon and even faster rates in the central colorado plateau which taper off again farther upstream near the plateau s eastern edge this bull s eye pattern of rapid inci sion in the central colorado plateau does not match proposed sources of uplift from mantle dynamics at the south and west ank of the pla teau nor patterns of river steepness and energy instead we suggest that this incision pattern is primarily driven by transient response to drainage integration and isostatic feedback from the deep exhuma tion of weak rocks in the central plateau introduction

cosmogenic dating of fluvial terraces fremont river utah absolute dating of river terraces can yield long term incision rates clarify the role of climate in setting times of aggradation and incision and establish the rates of pedogenic processes while surface exposure dating using cosmogenic 10be and 26al would seem to be an ideal dating method the surfaces are composed of individual clasts each with its own complex history of exposure and burial the stochastic nature of burial depth and hence in nuclide production in these clasts during exhumation and fluvial transport and during post depositional stirring results in great variability in clast nuclide concentrations we present a method for dealing with the problem of pre depositional inheritance of cosmogenic nuclides we generate samples by amalgamating many individual clasts in order to average over their widely different exposure histories depth profiles of such amalgamated samples allow us to constrain the mean inheritance to test for the possible importance of stirring and to estimate the age of the surface working with samples from terraces of the fremont river we demonstrate that samples amalgamated from 30 clasts represent well the mean concentration depth profiles show the expected shifted exponential concentration profile that we attribute to the sum of uniform mean inheritance and depth dependent post depositional nuclide production that the depth dependent parts of the profiles are exponential argues against significant post depositional displacement of clasts within the deposit our technique yields 10be age estimates of 60 9 102 16 and 151 24 ka for the three highest terraces corresponding to isotope stages 4 5d and 6 respectively the mean inheritance is similar from terrace to terrace and would correspond to an error of 30 40 ka if not taken into account the inheritance likely reflects primarily the mean exhumation rates in the headwaters of order 30 m ma

sediment dynamics below retreating cliffs the retreat of cliffs may constitute the dominant erosional response to base level fall in arid settings underlain by horizontally bedded sedimentary rock these vertical cliffs typically loom above a relatively straight bedrock slope plinth that is mantled with a thin layer of sediment and perched near the angle of repose in detail a plinth consists of a system of quasi parallel ridges and channels we ask how the sediment supplied from a retreating cliff influences the erosion of the plinth hillslopes and channels and how this affects the rate of cliff retreat motivated by field observations and high resolution topographic data from two sites in western colorado we develop a two dimensional 2d rules based numerical model to simulate the erosion of channels draining a plinth and diffusive erosion of the intervening interfluves in this model retreat of a cliffband occurs when the height of the vertical cliff exceeds a threshold due to incision by channels on the plinth below debris derived from cliff retreat is distributed over the model plinth according to the local topography and distance from the source this debris then weathers in place and importantly can act to reduce local bedrock erosion rates protecting both the plinth and ultimately the cliff from erosion in this paper we focus on two sets of numerical model experiments in one suite we regulate the rate of rockfall to limit the cliff retreat rate in most cases this results in complete loss of the plinth by erosion in a second suite we do not impose a limit on the cliff retreat rate but instead vary the weathering rate of the rockfall debris these runs result in temporally steady cliff plinth forms and retreat rates both depend on the weathering rate of the debris copyright 2011 john wiley sons ltd

a shaking table model test on a rock slope anchored with adaptive anchor cables abstract to determine the load transfer mechanism and dynamic response characteristics of an adaptive anchor cable aac equipped with a mechanical energy dissipation device a shaking table model test was conducted on rock slope test models anchored with a system consisting of several aacs that were fabricated based on a landslide mass in xiangjiapo during the test the strain of the aac structure and the dynamic response of the slope model were monitored to determine the anchoring mechanism of the aac system and the dynamic characteristics of the aac system anchored slope model the sliding sleeve energy dissipation device of the aac automatically adjusted its tension or deformation to allow its deformation to be consistent with that of the rock and earth mass thereby buffering the impact at the instant of the start of seismic loading the constant sliding resistance of the aac determined its working conditions under a certain seismic loading condition when the constant sliding resistance was set excessively high the energy dissipation device was ineffective under the seismic loading when the constant sliding resistance was set too small the aac slid at the instant of the start of seismic loading however when the constant sliding resistance and the sliding distance were set to proper values the aac slid gradually in a stepwise motion and its peak strain was significantly lower the test results can be used as a reference for designing cut slopes in regions of high seismicity and in selecting anti seismic engineering measures for these slopes

coupled numerical analytical approach to landscape evolution modeling the earth s topography is shaped by surface processes that operate on various scales in particular river processes control landscape dynamics over large length scales whereas hillslope processes control the dynamics over smaller length scales this scale separation challenges numerical treatments of landscape evolution that use space discretization large grid spacing cannot account for the dynamics of water divides that control drainage area competition and erosion rate and slope distribution small grid spacing that properly accounts for divide dynamics is computationally inefficient when studying large domains here we propose a new approach for landscape evolution modeling that couples irregular grid based numerical solutions for the large scale fluvial dynamics and continuum based analytical solutions for the small scale fluvial and hillslope dynamics the new approach is implemented in the landscape evolution model dac divide and capture the geometrical and topological characteristics of dac s landscapes show compatibility with those of natural landscapes a comparative study shows that even with large grid spacing dac predictions fit well an analytical solution for divide migration in the presence of horizontal advection of topography in addition dac is used to study some outstanding problems in landscape evolution i the time to steady state is investigated and simulations show that steady state requires much more time to achieve than predicted by fixed area calculations due to divides migration and persistent reorganization of low order streams ii large scale stream captures in a strike slip environment are studied and show a distinct pattern of erosion rates that can be used to identify recent capture events iii three tectono climatic mechanisms that can lead to asymmetric mountains are studied each of the mechanisms produces a distinct morphology and erosion rate distribution application to the southern alps of new zealand suggests that tectonic advection precipitation gradients and non uniform tectonic uplift act together to shape the first order topography of this mountain range copyright 2014 john wiley sons ltd

evolution and environmental conditions of conophyton jacutophyton associations in the atar dolomite upper proterozoic mauritania within the upper proterozoic sedimentary cover of the west african craton well exposed in the atar area mauritania the carbonate rich atar formation exhibits a peculiar development of stromatolites this formation is subdivided into 6 units based on lithology and stromatolite content units 1 3 and 5 are mainly terrigenous shales and silts and contain carbonate layers of different facies laminated and structureless micrite microbially laminated and detrital carbonates stromatolitic layers the environmental conditions were characterized by low energy sporadically increasing and shallow water with rare desiccation features units 2 and 4 contain conophyton jacutophyton and tilemsina unit 6 has a succession of conophyton jacqueti to baicalia these carbonate units were deposited under water in low energy conditions without any allochthonous sediment supply the rhythmic alternation of terrigenous and carbonate units corresponds to rhythmic variations in environmental conditions related to sea level or climatic changes the morphological diversity of stromatolites is not related systematically to changes in the environment some of the morphological variations are controlled by the evolution of the biological community e g the evolution of conophyton shape with time and its eventual disappearance new forms of stromatolite are described baicalia safia conophyton jacqueti jaculophyton sahariensis and tilemsina agdeireia

a very efficient o n implicit and parallel method to solve the stream power equation governing fluvial incision and landscape evolution abstract we present a new algorithm to solve the basic stream power equation which governs channel incision and landscape evolution in many geomorphic settings the algorithm is highly efficient because computation time increases linearly with the number of points used to discretize the landscape and is ideally suited to parallelization it is also unconditionally stable because it uses an implicit scheme for the time integration of the landscape evolution equation which means that large time steps can be used without sacrificing accuracy in this paper we describe the algorithm and present results that demonstrate its efficiency and accuracy

influence of earthquakes on the stability of slopes earthquakes are a major trigger for instability of natural and man made slopes often the instability of slopes due to an earthquake causes more destruction and kills more people than the actual earthquake itself a comparison is made between different methodologies to analyze the potential stability of slopes during earthquakes theoretically it seems simple to calculate the stability of a slope during an earthquake in reality however the stability is influenced by so many parameters that are either not known or which influence is so poorly known that a decent estimation of stability cannot be made offshore the situation is worse because proper data required for stability calculations are even less available than onshore on and offshore erosion and weathering create continuously slopes that may become unstable during a future earthquake offshore also sedimentation creates continuously new slopes another fundamental problem in stability analysis is the complicated and largely unknown behavior of seismic waves in three dimensions in natural materials the lack of accurate data and the unknown behavior of seismic waves in three dimensions make estimations of slope stability during an earthquake unreliable

relict slope rings and talus flatirons in the colorado piedmont origin chronology and paleoenvironmental implications abstract in the colorado piedmont talus flatiron chronosequences are associated with buttes that consist of erodible arkosic sandstone and resistant caprock following the removal of the caprock some buttes evolve into crater like relict slope rings resulting from the differential erosion of the soft bedrock in the core of the hills these unique landforms are only documented in the colorado piedmont their development is attributed to the unusually high erodibility contrast between the low cohesion sandy bedrock and the bouldery colluvial armor the talus flatiron sequences and relict slope rings mapped in the three studied areas record alternating periods of accumulation and incision in the slopes that are likely controlled by changes in moisture availability and vegetation cover density the obtained osl dates place slope accumulation phases at 124 ka and ca 73 ka 50 40 ka 15 ka and 10 6 ka a comparison of these geochronological data with paleoclimatic records from the region suggests that colluvium deposition occurred during periods of denser vegetation cover which are controlled by climate changes further investigations including additional and more accurate geochrological data from the relict slopes will help to better understand the paleoclimatic significance of these largely unknown morphostratigraphic features

erosional dynamics flexural isostasy and long lived escarpments a numerical modeling study erosional escarpments are common features of high elevation rifted continents fission track data suggest that these escarpments form by base level lowering and or marginal uplift during rifting followed by lateral retreat of an erosion front across tens to hundreds of kilometers previous modeling studies have shown that this characteristic pattern of denudation can have a profound impact upon marginal isostatic uplift and the evolution of offshore sedimentary basins yet at present there is only a rudimentary understanding of the geomorphic mechanisms capable of driving such prolonged escarpment retreat in this study we present a nonlinear two dimensional landscape evolution model that is used to assess the necessary and sufficient conditions for long term retreat of a rift generated escarpment the model represents topography as a grid of cells with drainage networks evolving as water flows across the grid in the direction of steepest descent the model accounts for sediment production by weathering fluvial sediment transport bedrock channel erosion and hillslope sediment transport by diffusive mechanisms and by mass failure numerical experiments presented explore the effects of different combinations of erosion processes and of dynamic coupling between denudation and flexural isostatic uplift model results suggest that the necessary and sufficient conditions for long term escarpment retreat are 1 incising bedrock channels in which the erosion rate increases with increasing drainage area so that the channels steepen and propagate headward 2 a low rate of sediment production relative to sediment transport efficiency which promotes relief generating processes over diffusive ones 3 high continental elevation which allows greater freedom for fluvial dissection and 4 any process including flexural isostatic uplift that helps to maintain a drainage divide near an escarpment crest flexural isostatic uplift also facilitates escarpment retreat by elevating topography in the vicinity of an eroding escarpment thereby increasing channel gradients and accelerating erosion which in turn generates additional isostatic uplift of all the above conditions high continental elevation is common to most rift margin escarpments and may ultimately be the most important factor

dynamic reorganization of river basins river networks evolve as migrating drainage divides reshape river basins and change network topology by capture of river channels we demonstrate that a characteristic metric of river network geometry gauges the horizontal motion of drainage divides assessing this metric throughout a landscape maps the dynamic states of entire river networks revealing diverse conditions drainage divides in the loess plateau of china appear stationary the young topography of taiwan has migrating divides driving adjustment of major basins and rivers draining the ancient landscape of the southeastern united states are reorganizing in response to escarpment retreat and coastal advance the ability to measure the dynamic reorganization of river basins presents opportunities to examine landscape scale interactions among tectonics erosion and ecology

scarp retreat rates in semiarid environments from talus flatirons ebro basin ne spain abstract triangular slope facets or talus flatirons are presented as a useful tool for the calculation of scarp retreat rates in arid regions in the central sector of the ebro basin sequences of talus flatirons have been developed around mesas capped by miocene limestone these talus flatirons are grouped in four stages of slope evolution s2 s3 s4 s5 by the extrapolation of the relict talus profiles with the adjusted log functions the position of the scarp for each one of the stages is located the mean values obtained indicate a scarp retreat of 23 m between stages s3 and s2 8 m between s4 and s3 and 26 m between s5 and s4 the ages obtained by radiocarbon dating are 2529 52 b p and 2930 60 b p for stage s2 27 864 444 b p for s3 and 35 570 490 b p for s4 consequently the mean scarp retreat rates are 0 9 mm yr for the s2 s3 interval and 1 mm yr for s3 s4 the scarp retreat rate is related to the lithological and structural features of both the caprock and the underlying clay sediments and to the palaeoclimatic evolution of the region that controls the intensity of weathering and water erosion processes that affect the slope system

mise en evidence de complexes ophiolitiques dans la chaine du mayombe gabon angola et nouvelle interpretation geotectonique abstract the precambrian mayombian belt was formed by the closure of an oceanic basin by subduction processes during late kibarian time 1000 ma ago this closure led to a collision between a western eburnean craton 2000 ma and two older eastern cratons the chaillu in the north 2500 ma and the kasai in the south 2700 ma after this collision marked by the tectonic emplacement of ophiolitic complexes and the generation of palingenetic granites the nyanga and niari eastern miogeosyncline was formed between 1000 and 600 ma ago the deformations of the miogeosynclinal sequence resulted from the late orogenic phases and the uplift of the axis of the belt this new model of the evolution is similar to those recently proposed for the pan african damara ribeira orogens south of the equator and the pharusian dahomeyan west africa

chronology and paleoenvironmental interpretation of talus flatiron sequences in a sub humid mountainous area tremp depression spanish pyrenees talus flatirons are debris covered relict slopes disconnected from the source area which are relatively common in arid and semi arid areas talus flatiron sequences record the alternation of accumulation and incision phases these chronosequences may be used for infer temporal changes in the morphogenetic processes acting on the slopes as well as information on the local paleoclimatic history talus flatiron sequences developed in the tremp depression eastern spanish pyrenees are analysed from the geomorphological chronological and paleoenvironmental perspective the two groups of relict slopes differentiated by means of detailed geomorphological mapping have been dated by optically stimulated luminescence osl and radiocarbon dating at 25 20 kyr s3 and 5 4 1 7 cal kyr s2 the talus flatiron group s3 is correlated with a fluvial terrace of the noguera pallaresa river c 23 kyr bp the comparison of the ages obtained in the tremp depression with chronologies published for talus flatiron sequences in semi arid areas and other paleoclimatic proxies suggests that the aggradation phases in the slopes occurred during periods with higher humidity and vegetation cover the chronological differences observed between semi arid spain and the tremp depression may be partly related to the more humid climate of the latter mountain area copyright 2013 john wiley sons ltd

evolution sedimentaire et tectonique du bassin proterozoique superieur de comba congo stratigraphie sequentielle du supergroupe ouest congolien et modele d amortissement sur decrochements dans le contexte de la tectogenese panafricaine abstract the comba trough infilled by the upper proterozoic west congolian supergroup trends n60 e and cuts across the congo zaire archean craton the trough is perpendicular to the nyanga niari basin which itself represents the foreland of the pan african mayombe belt moreover the comba trough was connected to other troughs extending further east beneath the mesozoic cenozoic of the congolian basin the tectono sedimentary evolution of the comba basin was initiated between 950 and 700 ma the trough was formed by a nw se extension it was filled up by periglacial fluvio lacustrine sediments which correspond to the deltaic formations of the bouenza group and the upper diamictite tillite superieurerd respectively then a general climatic warm up produced a rise of the eustatic sea level which flooded the lake of comba as well as the lakes and shelves of the congo zaire craton this marine sedimentation is represented by the schisto calcaire group which in terms of sequence stratigraphy we interpret as a transgressive system tract red marls of the lower part of the scia facies a condensed section pink dolomite of the upper part of the scia facies a highstand system tract deposited along a carbonate ramp the latter corresponds to a lateral facies variation and not a vertical facies succession as it was classically assumed this highstand system tract was composed of an external shelf scib facies a barrier scic facies a lagoon scii facies a beach kisantu oolithe of the sciiia facies and sciiib facies a tidal flat sciiic facies with fluvial sciv facies and tidal niari breccia facies channels between 700 and 600 ma a first compressive phase was responsible further west for the eastward pan african mayombian thrusting this phase was accompanied by the deposition of a thick molassic formation mpioka formation on the foreland belt and extending into the comba basin a late shortening phase of the mayombian belt propagated into the comba basin which was affected by strike slip deformation along its southern edge this strike slip deformation induced important disruptions of the regional mayombian tensor and a particular structural pattern of the comba basin characterized by strike slip damping structures sections of these structures are interpreted as positive negative and dual flowers this particular structural pattern provides an explanation of the combian structures as they reflect local deviation of the pan african shortening axes as a conclusion the evolutionary stages of the comba basin are discussed in the wider context of the upper proterozoic of the congo zaire craton

multiple talus flatirons variations of scarp retreat rates and the evolution of slopes in almazan basin semi arid central spain abstract we studied a group of talus flatirons situated at the foot of structural platforms capped by miocene limestones in the almazan basin a southeastern extension of the tertiary duero basin in northern spain this group of talus flatirons exhibits five different stages of slope evolution s 1 s 2 s 3 s 4 and s 5 they are concave slopes separated from the limestone scarp by a distance that increases with the age of the slope we measured their profiles and fitted them to mathematical functions by extrapolating these functions we obtained the intersection point with the scarp at every stage this gives different distances retreated by the scarp during each interval between consecutive stages of slope evolution remains of charcoal found in the debris slopes corresponding to stages s 1 s 3 and s 4 have been dated by means of 14 c to 1090 40 3590 40 and 28 550 130 bp respectively these values allowed us to calculate the following rates of scarp retreat 0 5 mm year during the time interval between stages s 4 and s 3 and 10 5 mm year for the interval between s 3 and s 1 there is a good correlation between the ages of the slope accumulations and cold periods s 3 is correlated with the middle bronze age cold epoch and s 4 may correspond to the heinrich event h 3 these correlations seem to confirm that talus flatirons in arid environments are good climatic indicators

statistical analysis of an earthquake induced landslide distribution the 1989 loma prieta california event the 1989 loma prieta california earthquake moment magnitude m 6 9 generated landslides throughout an area of about 15 000 km2 in central california most of these landslides occurred in an area of about 2000 km2 in the mountainous terrain around the epicenter where they were mapped during field investigations immediately following the earthquake the distribution of these landslides is investigated statistically using regression and one way analysis of variance anova techniques to determine how the occurrence of landslides correlates with distance from the earthquake source slope steepness and rock type the landslide concentration defined as the number of landslide sources per unit area has a strong inverse correlation with distance from the earthquake source and a strong positive correlation with slope steepness the landslide concentration differs substantially among the various geologic units in the area the differences correlate to some degree with differences in lithology and degree of induration but this correlation is less clear suggesting a more complex relationship between landslide occurrence and rock properties

palaeogeographic significance of stromatolitic buildups on late proterozoic platforms the example of the west congo basin abstract the west congo basin equatorial africa is filled with a late proterozoic sedimentary succession its middle part is made up of the schisto calcaire shale limestone group a study of the lower part of this group has resulted in a model of carbonate sedimentation a stromatolite buildup very similar to the present barrier reefs and cut by tidal and or swell channels separates an intertidal and supratidal inner platform from a subtidal outer one the inner platform is characterized by deposition of dolomitic limestones containing gypsum crystals epigenetically replaced by calcite and chalcedony the outer platform is made up of stromatolite biostromes arranged in elongate domes parallel to marine currents alternating with limestones with thin shale stringers in proterozoic basins stromatolitic barrier reefs mark transitions either between inner and outer platforms or between platform and deep basin subtidal stromatolite biostromes with an elongation of ten to hundreds of meters locally encroached upon some of the slowly subsiding flat bottomed epicontinental basins

geomorphological features and 3d modelling of montelparo mass movement central italy abstract the ancient village of montelparo marche region central italy is affected by a large translational mass movement the relief is modeled on arenaceous and arenaceous pelitic units overlying pelitic arenaceous terrains the bedding strata form a gently dipping monocline the translational slide is about 1100 m long and 500 700 m wide the upper boundary between the stable area and the sliding mass is marked by a large active trench near the hilltop the main sliding surface is located at a depth ranging between 65 and 100 m in the politic arenaceous unit we studied the mechanism of the slope instability along the stratigraphic contact between a rigid arenaceous unit and an underlying ductile pelitic unit the uncovering of the contact caused by the intense downcutting processes of the river at the hill foot during the holocene favoured the onset of the movement this was enhanced by the fractured bedrock and especially by the jointing we created a numerical model based on the finite differences code flac 3d by using a specific approach for mesh generation the model suggests a further enlargement and deepening of the trench and a sliding direction not aligned with the slope dip direction failure in the model concentrates at and around the main trench all the other elements staying in an elastic state and inducing a rigid sliding the model shows that both the failure onset and the current evolutionary state can be explained by the geological and static conditions of the slope

an uplift history of the colorado plateau and its surroundings from inverse modeling of longitudinal river profiles 1 it is generally agreed that a region encompassing the colorado plateau has been uplifted by sub crustal processes admittance calculations tomographic studies and receiver function analyses suggest that dynamic support is generated by some combination of convective upwelling and lithospheric thickness changes notwithstanding advances in our understanding of present day setting uplift rate histories are poorly constrained and debated an improved history will aid discrimination between proposed models here we show that a regional uplift rate history can be obtained by inverting longitudinal river profiles we assume that the shape of a river profile is controlled by uplift rate and moderated by erosion in our model uplift rate is allowed to vary smoothly as a function of space and time upstream drainage area is invariant with time simultaneous inversion of river profiles from the colorado rio grande columbia and mississippi catchments shows that three phases of regional uplift occurred the first phase occurred between 80 and 50 myrs when 1 km of uplift was generated at a rate of 0 03 mm yr a second phase occurred between 35 and 15 myrs when 1 5 km of uplift was generated at a faster rate of 0 06 mm yr a final phase of uplift commenced 5 myrs ago these distinct phases of late cretaceous and oligocene uplift are corroborated by stratigraphic considerations by thermochronometric data and by stratigraphic evidence of periodic clastic efflux delivered into the gulf of mexico an episodic uplift history is consistent with staged removal of thick lithospheric mantle beneath a large region which is currently centered on yellowstone

geochronology of sedimentary and metasedimentary precambrian rocks of the west african craton abstract this contribution summarizes current knowledge of the geochronology of the upper proterozoic sedimentary rocks covering the west african craton this was done by using direct dating methods correlations between the northern edge of the tindouf basin and the northern and southern part of the taoudeni basin as well as the volta basin are proposed an important depositional lack over almost the entire craton is confirmed between 1 7 ga which represents the time of the latest eburnean activities or cooling effects and about 1 0 ga which is the start of the general upper proterozoic sedimentation this lack is remarkable as the other cratons from gondwana continent are covered by middle proterozoic sediments the upper proterozoic sedimentation on the west african craton may be divided into a basal mainly sandstone period ca 1000 900 ma a middle mainly limestone period ca 900 750 ma and an upper mainly siltstone period ca 750 650 ma tectonic volcanic and thermal activities in connection with the pan african orogeny are recorded only around the craton they induced either sedimentation lacks in morocco or sedimentation excesses in hoggar unsolved problems such as the precise stratigraphic position of the uppermost proterozoic tillitic episode and the correlation within the moroccan anti atlas are also raised

geochemical characterization of the marinoan cap carbonate of the niari nyanga basin central africa abstract despite recent works on the schisto calcaire group of the west congolian supergroup in central africa neoproterozoic cap carbonate have not been well documented in the niari nyanga basin that extends from gabon to angola the couplet cap carbonate scia and upper diamictite that is a marker of the snowball earth event was studied in 5 sections from the niari nyanga basin and in one section from the external zone of the mayombe folded belt mfb our paper presents a high resolution data set based on results from petrography geochemistry mineralogy and stable isotope studies performed on cap carbonate samples the estimation of the illite crystallinity indexes indicates different degrees of post sedimentary transformations evolving from deep diagenesis in the syncline basin to an epimetamorphism in the external zone of the mfb thin sections of rocks sampled in this latter section display metamorphic features materialized by recrystallization of minerals in a s1 cleavage plane despite such an observation all our samples clearly show preservation of primary petrographic structures such as biolaminations fenestrae and peloids geochemical data leads us to highlight that the cap carbonate is composed by a variety of carbonate types these results support the fact that the cap carbonate was derived from a combination of biological and chemical processes organomineralization and chemical precipitation from supersaturated solutions with a negligible impact of post depositional transformations for all the studied sections stable isotope profiles display a drop in 13c values from about 2 6 to 4 associated with 18o values ranging from 6 to 10 moreover the similarity of the isotopic profiles of the studied cap carbonate from the niari nyanga basin and the mfb and the close fit to the expected neoproterozoic 13c and 18o seawater values constitute a strong indication of a weak impact of a diagenetic to epimetamorphic evolution on the carbon isotopic signature of the scia cap carbonate in the light of this data set our isotopic records must be considered as a reliable tracer of the marinoan glaciation within the west congolian supergroup

determining three dimensional non spherical critical slip surface in earth slopes using an optimization method abstract determination of the three dimensional 3 d critical slip surface with the minimum factor of safety in earth slopes is one of the important and difficult problems of the optimization methods counting the spherical slip surface in the stability analysis of 3 d slopes not only is easy but also provides for a better understanding although such slip surfaces cannot be adequately compatible with the actual slip surfaces found in nature this paper is an attempt to obtain the non spherical critical slip surface that is more consistent with the actual slip surface in nature by using the three dimensional alternating variable local gradient tdavlg optimization method tdavlg is a new approach in optimization process and it is based on the univariate method the factor of safety is calculated using the limit equilibrium method the optimization process can turn the initial slip surface into a non spherical critical slip surface in all types of slopes with different soil properties the resulting three dimensional non spherical slip surface not only has the minimum factor of safety but is also the most compatible with respect to the actual slip surface emerging in nature the non spherical critical slip surface obtained in the examples proves the efficiency and precision of the suggested method

stability analysis of three dimensional seismic landslides using the rigorous limit equilibrium method abstract in this paper a new method combining the rigorous limit equilibrium method and the pseudo dynamic method is proposed to investigate stability of 3d seismic landslides in which the force equilibrium conditions along three coordinate axes and the overall moment equilibrium conditions around three coordinate axes are all strictly satisfied moreover sinusoidal cosinusoidal wave is applied to simulate earthquake displacement and an amplification factor of peak seismic acceleration is referred to as the amplification of seismic wave when it propagates from the bottom to the top of landslides the pseudo dynamic factor of safety of 3d seismic landslides is determined using trust region reflective iterative algorithm the effects of the parameters of the seismic landslides on the stability are analyzed by the bp neural network algorithm in which a database to investigate the stability of 3d seismic landslides is established in addition the stability of donghekou landslide is studied to verify the accuracy and precision of the present method

dynamic process analysis for the initiation and movement of the donghekou landslide debris flow triggered by the wenchuan earthquake the donghekou landslide debris flow was a remarkable geological disaster triggered by the wenchuan earthquake in 2008 the dynamic process of a rapid landslide debris flow is very complicated and can be divided into two aspects the slope dynamic response of the earthquake and the mass movement and accumulation process a numerical method combined with a finite difference method fdm and discrete element method dem for simulation of landslide debris flow under seismic loading is presented the fdm and dem are coupled through the critical sliding surface initiation time and velocity the dynamic response of the slope is simulated by the finite difference method and critical sliding surface is determined using the earthquake response spectrum method the landslide initiation time and the velocity are determined by time history analysis the mass movement and accumulation process is simulated using the discrete element method simulation results demonstrate that the maximum amplification coefficient of dynamic acceleration for the donghekou slope is approximately 3 909 the initiation time of landslide is approximately 6 0 s and the average initial velocity of the sliding mass is approximately 0 85 m s the failure of the slope is the result of elevation orientated amplification effect and the sliding mass triggered with a small initial velocity the numerical simulated result of the maximum sliding velocity is approximately 66 35 m s and the mass is disintegrated rapidly because of collision and free fall the landslide velocity decreases when the flowing mass reaches a lower slope angle and gradually comes to a stop and the total travel distance is approximately 2400 m c 2013 elsevier ltd all rights reserved

platform to basin facies evolution the carbonates of late proterozoic vendian gourma west africa abstract during the vendian uppermost proterozoic the gourma basin was an east west intracratonic feature that opened eastward into an ocean the southern edge of the gourma basin preserves facies belts representing land to deep basin environments shoreward facies consist of tidal belts of microbially laminated dolomites or porostromata dolomites interstratified with clastic carbonates of local origin landward supratidal facies consist of finely laminated sedimentary rocks with sizeable desiccation features but no evaporites the upper part of this unit is affected by a periodic emersion resulting in a complex succession of paleosol profiles offshore of the tidal facies are lagoon facies rocks that were protected from the open sea by a carbonate buildup composed of a framework of stromat lite bioherms associated with detrital dolomites indicating a high energy environment slope facies consist of a thick succession of ribbon limestones with some graded beds synsedimentary slumping and faulting of the ribbon limestones indicate a significant depositional slope allochthonous deposits are sporadically interstratified with the ribbon limestones and consist of muds with small grains derived from the platform deposits polygenic breccias conglomerates composed only of ribbon limestone intraclasts and oolitic calcarenites shelf facies rocks are pervasively dolomitized but original textures are well preserved including fine grained structures the ribbon limestones on the other hand are not dolomitized except for dolomitic layers caused by pressure solution the distribution of facies in gourma basin carbonates corresponds well with ideal models of wilson 1975 comparisons with present day facies distributions are less satisfactory especially considering the dominance of cyanobacteria over all environments for which there is no modern day counterpart comparisons with the modern environment however suggest a subtropical semi arid climate during deposition of the gourma strata

sedimentary talc in neoproterozoic carbonate successions abstract mineralogical petrographic and sedimentological observations document early diagenetic talc in carbonate dominated successions deposited on two early neoproterozoic 800 700 million years old platform margins in the akademikerbreen group svalbard talc occurs as nodules that pre date microspar cements that fill molar tooth structures and primary porosity in stromatolitic carbonates in the upper fifteenmile group of the ogilvie mountains nw canada the talc is present as nodules coated grains rip up clasts and massive beds that are several meters thick to gain insight into the chemistry required to form early diagenetic talc we conducted precipitation experiments at 25 c with low so4 synthetic seawater solutions at varying ph mg2 and sio2 aq our experiments reveal a sharp and reproducible ph boundary at 8 7 only above which does poorly crystalline mg silicate precipitate increasing mg2 and or sio2 aq alone is insufficient to produce the material the strong ph control can be explained by mg silica complexing activated by the deprotonation of silicic acid above 8 6 8 7 ft ir tem and xrd of the synthetic precipitates reveal a talc like 2 1 trioctahedral structure with short range stacking order hydrothermal experiments simulating burial diagenesis show that dehydration of the precipitate drives a transition to kerolite hydrated talc and eventually to talc this formation pathway imparts extensive layer stacking disorder to the synthetic talc end product that is identical to neoproterozoic occurrences early diagenetic talc in neoproterozoic carbonate platform successions appears to reflect a unique combination of low al concentrations and by inference low siliciclastic input near modern marine salinity and mg2 elevated sio2 aq and ph 8 7 because the talc occurs in close association with microbially influenced sediments we suggest that soluble species requirements were most easily met through microbial influences on pore water chemistry specifically ph and alkalinity increases driven by anaerobic fe respiration

episodic sediment delivery and landscape connectivity in the mancos shale badlands and fremont river system utah usa abstract the fremont river drains about 1000 km 2 of mancos shale badlands which provide a large percentage of the total sediment load of its middle and lower reaches factors controlling sediment movement include weathering that produces thin paralithic soils mass movement events that move the soil onto locations susceptible to fluvial transport intense precipitation events that move the sediment along rills and across local pediments and finally fremont river floods that move the sediment to the main stem colorado river a forty year erosion pin study has shown that down slope creep moves the weathered shale crust an average of 5 9 cm yr weather records and our monitoring show that wet winters add large slab failures and mudflows recent sediment trap studies show that about 95 of sediment movement across pediments is accomplished by high intensity summer convective storms between 1890 and 1910 a series of large autumn floods swept down the fremont river eroding its floodplain and transforming it from a narrow and meandering channel to a broad braided one beginning about 1940 the fremont s channel began to narrow sequential aerial photos and cross sections suggest that floodplain construction since about 1966 has stored about 4000 to 8000 m 3 of sediment per kilometer per year these data suggest that it will take two centuries to restore the floodplain to its pre 1890 condition which is in line with geologic studies elsewhere on the colorado plateau the various landscape elements of slope pediment and floodplain are semi independent actors in sediment delivery each with its own style accelerated mass movement on the slopes has an approximate 20 year recurrence sediment movement from slope across pediments to master stream is episodic and recurs more frequently the slope to pediment portion of the system appears well connected however sediment transport through the floodplain is not well connected in the decadal time scale but increases in the century and millennial time scales and changes over time depending on the cycle of arroyo cutting and filling

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

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