investigating multiple fault rupture at the salar del carmen segment of the atacama fault system northern chile fault scarp morphology and knickpoint analysis this study presents a new geomorphological approach to investigate the past activity and potential seismic hazard of upper crustal faults at the salar del carmen segment of the atacama fault system in the northern chile forearc our contribution is based on the analysis of a large set of topographic profiles and allows extrapolating fault analysis from a few selected locations to distances of kilometers along strike of the fault we detected subtle changes in the fault scarp geometry which may represent the number of paleoearthquakes experienced by the structure and extracted the cumulative and last incremental displacement along strike of the investigated scarps we also tested the potential of knickpoints in channels crossing the fault scarps as markers for repeated fault rupture and proxies for seismic displacement the number of paleoearthquakes derived from our analysis is 2 3 well in agreement with recent paleoseismological investigations which suggest 2 3 earthquakes mw 6 5 6 7 at the studied segments knickpoints record the number of events for about 55 of the analyzed profile pairs only few knickpoints represent the full seismic displacement while most retain only a fraction of the displacement the along strike displacement distributions suggest fault growth from the center toward the tips and linkage of individual ruptures our approach also improves the estimation of paleomagnitudes in case of multiple fault rupture by allowing to quantify the last increment of displacement separately paleomagnitudes calculated from total segment length and the last increment of displacement mw 6 5 7 1 are in agreement with paleoseismological results

the effects of large organic debris on sediment processes and stream morphology in vermont abstract research conducted on a small third order stream in the green mountains of vermont suggests that large organic debris lod has an important influence on areal sorting and storage of sediment spacing of pool riffle sequences and channel geometry large organic debris forms local base levels that trap over 26 cubic meters of sediment and cause over 14 percent of the vertical drop along a 412 meter study reach on tiger brook vermont the local base levels created by large organic debris accumulations are the most important control on sediment storage between large bedrock knickpoints along the study reach focusing fine grained sediment deposition in areas stable at low and moderate discharges the micro steps created by these lod local base levels dominate gradient and sediment storage at short time scales between the slowly evolving large bedrock macrosteps the relation that exists among the volumes of standing timber adjacent to the channel lod and sediment stored behind lod seems to indicate that large organic debris causes a negative feedback type mechanism where channel degradation leads to increased standing timber recruitment and large organic debris sediment storage sites

criterion delineating the mode of headcut migration two modes of headcut migration are generally recognized 1 rotating headcuts that tend to flatten as they migrate and 2 stepped headcuts that tend to retain nearly vertical faces a mathematical description of the sediment detachment potential immediately upstream and downstream of the headcut is used to delineate these modes of migration the delineating parameter is the ratio of the time required to erode the headcut face from above to the time required to undermine the headcut face from below this erosional time scale ratio is a dimensionless function of flow sediment and geometry parameters for the limiting case of homogeneous cohesive soils the time scale ratio is a simple function of a froude number and the aspect ratio of drop height to normal flow depth this relationship is calibrated using original laboratory experiments of headcut migration in initially vertical headcuts and verified by independent field experiments of headcuts propagating in four different homogeneous cohesive soils

effect of soil stratification on the development and migration of headcuts in upland concentrated flows 1 experiments were conducted to examine the effect of vertical stratification in soil erodibility on the development and migration of steady state headcut scour holes in upland concentrated flows typical of agricultural fields packed soil beds with a preformed step were subjected to identical simulated rainstorms and clear water overland flow rates which resulted in predictable actively migrating headcut scour holes with nearly identical characteristics when an erosion resistant layer was incorporated into the packed soil bed at a depth that exceeded this expected plunge pool scour depth the erosion and hydraulic processes of the migrating headcuts remained unchanged when the erosion resistant layer was placed so as to intersect this potential headcut scour depth the erosivity of the reattached wall jet was unable to erode this layer and the depth of scour the nappe entry angle and sediment efflux all were reduced inversely proportional to the relative depth of the resistant layer these data were successfully predicted using modified jet impingement theory for headcut scour holes and demonstrate further the effects of soil management and tillage practices on total soil losses from agricultural fields

inversion of fluvial channels for paleorock uplift rates in taiwan the transient response of erosion to changes in rock uplift rate leads to the preservation of rock uplift history in the long profiles of rivers however extracting this information is nontrivial as changes in channel steepness are the result of both spatial and temporal changes in rock uplift rate as well as other factors such as climate and rock type we exploit an analytical linear solution for river channel profile evolution in response to erosion and tectonic uplift to investigate the rock uplift history of taiwan the analytical approach allows us to solve the linear inverse problem efficiently extracting rock uplift as a function of space and time from digital elevation data we assess the potential of fluvial topography to resolve rock uplift rates using three approaches 1 a synthetic resolution test 2 analysis of the forward model to demonstrate where in space and time the fluvial topography constrains rock uplift rate and 3 interpretation of the model resolution matrix furthermore the potential to analyze large data sets reduces the influence of stochastic processes such as landslides small scale river network reorganization and also local lithological variability in taiwan our analysis suggests that current rock uplift rates exceed erosion rates across much of the island and that there has been an increase in rock uplift rates since 0 5 ma across the central range

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

waterfalls on the eastern side of rocky mountain national park colorado usa abstract we examined 30 waterfalls on the eastern side of rocky mountain national park in colorado usa to evaluate whether drainage area or bedrock properties as reflected in joint characteristics correlate more strongly with the location and characteristics of individual waterfalls longitudinal profiles tend to be more concave for larger drainages to have a smaller proportion of total elevation loss in waterfalls and to have vertical drops rather than angled or ramp waterfalls we interpret these trends to indicate greater overall incisional capability for larger catchments shape of individual waterfalls and height of drop correlate more strongly with bedrock properties waterfalls in bedrock lacking prominent vertical joints perpendicular to flow are more likely to have a single drop rather than multiple drops and taller waterfalls correlate with more widely spaced horizontal joints waterfalls also noticeably correspond to resistant bedrock outcrops that form steep segments along hillslopes adjacent to the channel we interpret these results to indicate that the location and characteristics of waterfalls along headwater streams in the study area reflect primarily a limited ability to incise through more resistant segments of the underlying bedrock

an empirical stream power formulation for knickpoint retreat in appalachian plateau fluviokarst summary hydrologically abandoned caves on tributaries of the upper cumberland river tennessee usa record a wave of river incision that advanced up the drainage basin in the late pliocene and early pleistocene geomorphic and geologic evidence suggests that incision occurred as a migrating knickpoint generated by sudden base level lowering the passage of a knickpoint up the cumberland river tributaries was modeled as a perturbation to steady state incision according to the stream power law e kq m s n and tested using dated incision events recorded in cave sediments knickpoint migration rates generated by this model were 0 1 0 18 m yr over the entire stream network and 4 0 m yr for the mainstem cumberland river channel the ratio m n 0 79 was consistent with previously published parameters however the values of m 1 91 and n 2 39 were much higher than those reported in previous field studies these results suggest the stream power model may be used to model knickpoint migration in the study area provided values for the constants m and n are larger this may be due to the influence of fluviokarst where surface drainage is interrupted due to diversion into the underlying karst aquifer field measurements of channel and basin geometry in fluviokarstic tributaries to the upper cumberland river show 1 a stronger variance between channel slope and discharge 2 a nonlinear relationship between discharge and drainage area and 3 stream width to be nearly invariant as opposed to non karst watersheds because the stream power model relies heavily on the substitution of discharge for drainage area the behavior of channel incision and knickpoint migration in fluviokarst may differ substantially from that of non karst channels

scale dependence of lithological control on topography bedrock channel geometry and catchment morphometry in western scotland abstract we propose that a scale dependent topographic signature of erodibility arises due to fluvial and glacial erosion acting on different parts of the landscape at different times for 14 catchments in western scotland we define three levels of substrate erodibility in order of decreasing resistance quartzite rocks nonquartzite rocks and zones of fault related fracture then using digital topographic and planimetric data coupled with field measurements we identify regression based scaling relationships between substrate erodibility and morphometric parameters at two spatial scales catchment scale morphometry shows a weak to variable relationship with substrate metrics overall erodibility can be inferred from catchment steepness indices i e channel steepness index and relief ratio but the existence of multiple exceptions could confound a more general application of this approach nonetheless major valley troughs trace fault zones and nonquartzite rocks leaving much of the higher and stee

original forms and initial modifications of the galway lake road scarp formed along the emerson fault during the 28 june 1992 landers california earthquake a remarkable scarp formed southeast of the galway lake road during the mw 7 3 landers california earthquake over the first 11 months following the earthquake we repeated topographic surveys and ground stereoscopic photography and interpreted the observations of original forms and initial modifications of the faulted landforms the complexity of the surface rupture influenced the geomorphic responses the principal shear zone consisted of en echelon right and left lateral generally left stepping fault segments with cumulative offsets of 5 m right lateral and 2 5 m vertical typical fault scarp profiles have different slope angles above and below the surface rupture and a small free face the surface rupture formed steep irregular knickpoints in channels crossing the scarp the original channel surfaces were warped as they stepped down over tilted and rotated fracture bounded blocks the landforms were modified measurably by the above average winter 1992 1993 rainfall over surfaces controlled by hillslope processes only fault scarp erosion was controlled by rainsplash and slumping originally sharp corners were rounded and loose sediment collected in colluvial wedges surface flows over simple ramp steps in channel profiles caused incision that drove knick points back by as much as 50 cm over more complex portions of the principal shear zone flow was diverted into open fractures and little modification of the scarp occurred the pre earthquake topography at the site provided no clear evidence of the last similar slip event simple diffusion erosion models of the time required to bring the new scarp to its pre landers event configuration indicate that the last major rupture may have been several thousand years ago

incision of alluvial channels in response to a continuous base level fall field characterization modeling and validation along the dead sea abstract the dramatic lake level drop of the dead sea during the twentieth century 30 m provides a field scale experiment in transport limited incision of gravel bed channels in response to quasi continuous base level fall at approximately constant rate we apply a one dimensional numerical incision model based on a linear diffusion equation to seven ephemeral channels draining into the dead sea the model inputs include the measured twentieth century lake level curve annual shoreline location i e annual channel lengthening following the lake level drop reconstructed longitudinal profiles of each of the channels based on mapped and surveyed terraces and the current profiles of the active channels the model parameters included the diffusion coefficient and the upstream derived sediment flux both were first calibrated using a set of longitudinal profiles of known ages and then validated using additional sets of longitudinal profiles the maximum at station total incision observed at each of the studied channels was significantly less then the total lake level drop and varied in response to both drainage area and lake bathymetry the model applied predicted degradation rates and the pattern of degradation with high accuracy this suggests that sediment flux in the modeled channels is indeed linearly dependent on slope further support for this linear dependency is provided by a linear correlation between the diffusion coefficient and the mean annual rain volume over each basin a proxy for discharge the model presented could be a valuable tool for planning in rapid base level fall environments where incision may risk infrastructure

evidence for late stage fluvial activity in kasei valles mars 1 two inner channels in the southern branch of kasei valles are among the best preserved examples of fluvial erosion on mars attributes of the channels include arcuate alcoves perched boulders and a concave up longitudinal profile all of which are consistent with the interpretation that these channels were carved by a newtonian fluid the sharp concavity of the longitudinal profile is comparable to a terrestrial alluvial system with a minimum work profile the shape of the profile suggests that the system was in a quasi equilibrium state but was not active long enough to achieve grade associated with these channels is a platy meter scale texture identified in high resolution mars orbiter camera images although a lava flow could explain many of the material properties of the platy surface texture we speculate that this texture in the immediate proximity to the southern kasei valles inner channels may be related to waning floodwaters moving through the inner channels and is a mudflow deposit

from extension to transpression quaternary reorganization of an extensional related drainage network by the alhama de murcia strike slip fault eastern betics abstract the complex present day drainage network of the lorca totana area records the changing tectonic setting from extension to transpression in the eastern betics through a detailed morphometric analysis we evaluate the topographic response to this major change in the tectonic setting and the influence in the drainage of miocene extension and middle pleistocene to present day transpression the present day drainage network preserves geomorphic features inherited from late miocene extension that are being overprinted by a new transverse fluvial system this new system advanced towards the nw since the middle pleistocene in response to a localized base level drop related to the ne sw oriented alhama de murcia sinistral reverse fault geomorphic indexes calculated in this work suggest the present day activity of the alhama de murcia fault and the sierra de la tercia anticline the two major tectonic structures in the area the landscape rejuvenation associated with this process results in contrasting mountain front sinuosity values between old and new mountain fronts high slk index anomalies convex shaped and complex hypsometric curves knickpoints in river profiles contrasting slope area plots and high steepness index values this fluvial reorganization was driven progressively by successive fluvial captures preserved as wind gaps in the present day drainage network

erosion rates of waterfalls in post volcanic fluvial systems around aso volcano southwestern japan estimation of the recession rate of waterfalls is a crucial issue in bedrock river erosion because waterfall recession can cause a major impact on bedrock incision especially when waterfall recession rates are high areas of active volcanoes are often characterized by many waterfalls in the volcanic edifice this study examines recession rates of waterfalls in welded aso 1 ignimbrite from the aso volcano in southwestern japan using an empirical equation which comprises a force resistance index composed of measurable geomorphic parameters the estimated recession rates are on the order of 0 01 0 07 m a 1 the estimated rates are then validated by examining the duration and distance of their recession the duration of waterfall recession is derived from eruptive ages of the aso ignimbrites giving waterfall recession distances of approximately 10 km although the original locations of the waterfalls suggested by the recession distances exceed the downstream limit of the present aso 1 ignimbrite remnants along valley floors features of the surrounding topography are consistent with these localities being where the waterfalls formed the use of an equation to estimate recession rates is therefore considered to be valid and practical the contrast between the highly dissected landforms downstream of the present waterfalls and the gentle landscapes upstream of the waterfalls suggests that the rapid recession of the waterfalls is the major cause of post eruptive fluvial erosion into ignimbrites copyright 2007 john wiley sons ltd

a model for knickpoint migration in first and second order streams we introduce a new theoretical framework for knickpoint migration in unventilated flows prevalent in channelized semicohesive first and second order streams characterized by a sequence of constrictions and expansions in the channel cross section a key feature of the framework is the inclusion of shear induced fluvial erosion due to flow suction at the nappe as the key mechanism driving migration channel surveys water stage time lapse photography and laser scans from mud creek iowa usa confirm this unventilated erosive mechanism and reveal a dual advective diffusive mode of retreat we treat the fluvial bed shear stress as being similar to the flow on the lee side of a submerged obstacle and derive a governing equation which is a generalized burgers equation the equation is solved to successfully simulate knickpoints monitored in two sites iowa and mississippi and a modified peclet number is used to analyze the advective diffusive nature of the knickpoint migration

origin and development of theater headed valleys in the atacama desert northern chile morphological analogs to martian valley networks abstract understanding planetary landforms including the theater headed valleys box canyons of mars usually depends on interpreting geological processes from remote sensing data without ground based corroboration here we investigate the origin and development of two mars analog theater headed valleys in the hyperarid atacama desert of northern chile previous workers attributed these valleys to groundwater sapping based on remote imaging topography and publications on the local geology we evaluate groundwater sapping and alternative hypotheses using field observations of characteristic features strength measurements of strata exposed in headscarps and estimates of ephemeral flood discharges within the valleys the headscarps lack evidence of recent or active seepage weathering such as spring discharge salt weathering alcoves or vegetation their welded tuff caprocks have compressive strengths multiple times those of the underlying epiclastic strata flood discharge estimates of cubic meters to tens of cubic meters per second derived using the manning equation are consistent with the size of transported clasts and show that the ephemeral streams are geomorphically effective even in the modern hyperarid climate we interpret that headscarp retreat in the quebrada de quisma is due to ephemeral flood erosion of weak miocene epiclastic strata beneath a strong welded tuff with erosion of the tuff facilitated by vertical jointing the quebrada de humayani headscarp is interpreted as the scar of a giant landslide maintained against substantial later degradation by similar strong over weak stratigraphy this work suggests that theater headed valleys on earth and mars should not be attributed by default to groundwater sapping as other processes with lithologic and structural influences can form theater headscarps

structural control on drainage network and catchment area geomorphology in the dead sea area an evaluation using remote sensing and geographic information systems in the wadi zerka ma in catchment area jordan the geology of jordan is characterized by fault systems with three major trends 1 nw se the oldest 2 wnw ese and 3 nnw sse the youngest the drainage network of the wadi zerka ma in catchment area located in the middle of the dead sea rift parallels these structural orientations a regional transtensive fault with embedded normal faults bounds the lower and middle part of the catchment area the topographic profile of the zerka ma in river exhibits two major knickpoints where it crosses two major embedded normal faults the second major knickpoint developed as a result of the dramatic lowering of the lisan lake water level a lake that pre dates the dead sea the decreased water level triggered river incision into the clastic sandstone units of wadi zerka ma in we performed a morphotectonic analysis study to investigate how the rock structures control the drainage network and the catchment area geomorphology according to the transverse topographic symmetry factor t the catchment area is highly asymmetric the major basin asymmetry trend is se oriented parallel to the oldest set of fault systems the catchment area displays a convex hypsometric curve indicating a very recent stage in the geomorphologic cycle our study indicates that the lisan lake catchment area shrinkage and structures growth controlled and shaped the wadi zerka ma in catchment area geomorphology the combined use of a geographic information system gis and remote sensing was shown to be very efficient in unraveling the evolution of the drainage network and catchment area geomorphology

climatic and tectonic controls on fluvial incision and aggradation in the spanish pyrenees the influences of tectonic and climatic changes on upland river systems are investigated using data from plio pleistocene terraces of the rio cinca river in the southern pyrenees this river runs transverse to the main thrust fault structures and is a major conduit for sediment delivery to the ebro basin detailed field mapping combined with long profile and palaeohydraulic reconstructions yields a comprehensive picture of changes in palaeoriver character during the plio pleistocene as the area is over 150 km from the basin outlet in the mediterranean sea changes in base level are unlikely to have influenced terrace development although tectonic activity has exerted a strong control on the position of the river the main period of thrust propagation pre dates the terraces and activity has waned from the pliocene through to the present it is concluded that the main control on incision in this area is climate through its influence on sediment supply rivers which are starved of sediment by climate change will have the power to incise whereas aggradational phases are linked to periods of increased sediment flux

the influence of bedrock geology on knickpoint development and channel bed degradation along downcutting streams in south central indiana geologic controls on knickpoint development and the mechanics of channel bed degradation were eluci dated by comparison of downcutting streams in south central indiana developed in lithologically homoge neous carbonate units and layered siliciclastic strata knickpoints formed in a single lithologic unit are stepped each step consists of a knickpoint face and tread the height of each step is equal to and controlled by bed thickness spatially knickpoints in homogeneous terrain are limited to jointed strata that dip 1 upstream or 2 downstream at angles less than the channel gradient knickpoints observed in lithologically layered strata are characterized by a single step in which resistant jointed rocks overlie and protect weaker units total knickpoint relief is influenced by thickness of the weaker strata knickpoints in layered siliciclastic strata are spatially limited to bedrock reaches produced by differential rates of channel incision knickpoint distribution is also influenced by joint

convergent evolution of abrading flow obstacles insights from analogue modelling of fluvial bedrock abrasion by coarse bedload upstream facing convex surfaces ufcs are formed by bedload abrasion in bedrock rivers and indicate the recent significant action of bedload abrasion in causing channel incision beyond this little is known of the dynamics of ufcs and the effect of substrate and bedload properties on rates and distribution of bedload abrasion for these bed roughness elements grain size populations from 1 to 8 cm b axis in 1 or 2 cm bin widths were used to bombard preshaped marble and limestone targets bolted to the base of an annular flume the control of initial shape and lithology of the target and the erodent grain size and lithology were investigated by monitoring the evolution of the target form using laser scanning at predefined time intervals eleven experiment suites were carried out containing three initial target shapes constructed from two lithologies four bedload erodent grain sizes of either granodiorites or limestone or clear water flow all 10 targets abraded by bedload evolved from their initial form into a steady state time invariant form producing ufcss steady state forms were closely similar for all targets despite different initial conditions bedload grain size has a strong control on this equilibrium form related to the transit path of the grains when moving over the target whilst initial target form has only a weak control steady state morphology is achieved more rapidly with harder erodent bedload particles and or softer targets upstream facing convex surface stoss sides were characterised by a brighter sugary granular appearance on the rock forming grain scale increasing erodent grain size for a fixed bedload mass increased the bulk abrasion rate at fixed flow speed and discharge no detectable erosion occurred for a limestone block in clear water flows under the same flow conditions indicating solution and cavitation were insignificant mechanisms of erosion in this study during the experiment suites suspended load abrasion was also found to be an insignificant mechanism in eroding lee or lateral sides in natural settings the initial formation of ufcss can occur for homogenous and or jointed substrates in close association with plucking or alternatively for heterogeneous substrates by variation in substrate erodibility

self formed bedrock waterfalls waterfalls are inspiring landforms that set the pace of landscape evolution as a result of bedrock incision they communicate changes in sea level or tectonic uplift throughout landscapes or stall river incision disconnecting landscapes from downstream perturbations here we use a flume experiment with constant water discharge and sediment feed to show that waterfalls can form from a planar homogeneous bedrock bed in the absence of external perturbations in our experiment instabilities between flow hydraulics sediment transport and bedrock erosion lead to undulating bedforms which grow to become waterfalls we propose that it is plausible that the origin of some waterfalls in natural systems can be attributed to this intrinsic formation process and we suggest that investigations to distinguish self formed from externally forced waterfalls may help to improve the reconstruction of earth history from landscapes

fluvial incision into bedrock insights from morphometric analysis and numerical modeling of gorges incising glacial hanging valleys western alps france bedrock gorges incising glacial hanging valleys potentially allow measurements of fluvial bedrock incision in mountainous relief using digital elevation models topographic maps and field reconnaissance we identified and characterized 30 tributary hanging valleys incised by gorges near their confluence with trunk streams in the romanche watershed french western alps longitudinal profiles of these tributaries are all convex and have abrupt knickpoints at the upper limit of oversteepened gorge reaches we reconstructed initial glacial profiles from glacially polished bedrock knobs surrounding the gorges in order to quantify the amount of fluvial incision and knickpoint retreat from morphometric analyses we find that mean channel gradients and widths as well as knickpoint retreat rates display a drainage area dependence modulated by bedrock lithology however there appears to be no relation between horizontal retreat and vertical downwearing of knickpoints assuming a postglacial origin of these gorges our results imply high postglacial fluvial incision 0 5 15 mm yr 1 and knickpoint retreat 1 200 mm yr 1 rates that are however consistent with previous estimates numerical modeling was used to test the capacity of different fluvial incision models to predict the inferred evolution of the gorges results from simple end member models suggest transport limited behavior of the bedrock gorges a more sophisticated model including dynamic width adjustment and sediment dependent incision rates predicts present day channel geometry only if a significant supply of sediment from the gorge sidewalls 10 mm yr 1 is triggered by gorge deepening combined with pronounced inhibition of bedrock incision by sediment transport and deposition

channel incision in the rio atenguillo jalisco mexico defined by 36cl measurements of bedrock abstract the jalisco block of western mexico has undergone uplift in the tertiary in response to subduction tectonics the atenguillo river interior to the jalisco block has incised the bedrock units of the jalisco block including cretaceous ash flow tuff granite as well as younger volcanic lava flows to study incision rates knickpoint propagation and the uplift rate of the region samples from nine different points along the atenguillo channel were collected for 36 cl exposure age dating exposure ages along the length of the channel are high near the head of the basin where the river meanders in a broad plain ages are younger at the knickpoints and downstream where the river cuts deeply and forms a canyon incision rates measured at different points along the channel also correlate with channel slope and age low incision rates are measured in the oldest part of the channel near the head station b 2 5 mm year and just above the knickpoints station c 0 6 mm year and station g 1 4 mm year the incision rates are highest just below the knickpoints station f 2 4 mm year and farther downstream stations h and i 5 6 and 2 9 mm year respectively the high incision rates can be attributed to subduction related uplift of the jalisco block other features attributable to uplift are emergent paleoshorelines and uplifted marine sediments along the coast and relatively lower incision rates were measured north of the jalisco block

an automated method for producing synoptic regional maps of river gradient variation procedure accuracy tests and comparison with other knickpoint mapping methods abstract the study of abrupt changes in longitudinal river profiles or knickpoints is currently approached through an empirical power law the slope area relationship results based on digital elevation model dem analyses and stream extractions are generally intended to determine crustal uplift rates and identify transient landscape conditions in this article we present an alternative geomorphometric method for locating knickpoints and knickzones based on local slope gradient and curvature attributes intended as a rapid regional scale automated knickpoint detection technique the accuracy of this slope curvature method is tested on two digital elevation grids nasa s srtm ground resolution of 90 m resampled here to 75 m and the aster dem 15 m in the sierra nacimiento new mexico usa a basement cored mountain range recently exhumed by waves of headward drainage integration in response to remote tectonic deformation in the adjacent rio grande rift out of every 10 gradient anomalies detected by the srtm derived numeric routine up to 8 are certifiable knickpoints recognized among a population of georeferenced occurrences surveyed in the field an independent comparison with the slope area method provided a further accuracy test which was particularly useful at sites that could not be validated in the field for practical reasons given the low tectonic activity of the study area the majority of knickpoints was also found to coincide with lithologic boundaries making it difficult without further geomorphological data to single out dynamic knickpoints directly caused by the upstream propagation of channel instabilities relating to base level change

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

fluvial adjustment of the lower jordan river to a drop in the dead sea level water utilization in the upper part of the jordan basin has led to a significant reduction in inflow to the dead sea over the last 70 years a drop of about 22 m in mean sea level has occurred and has resulted in a continual adjustment of the lower jordan river the impacts of this lowering on the channel morphology of the lower jordan river were examined using aerial photographs until the late 1970s the drop in the sea level was small but still led to channel extension since the early 1980s a rapid drop in sea level took place leading to major changes in channel morphology and deep incisions the greatest change in channel width was recorded near the river mouth between 1850 and 1980 there were only insignificant changes in channel sinuosity but subsequently a 25 increase of channel sinuosity has been recorded most of changes in the channel sinuosity were recorded in the newly exposed area over the last 30 years the active channel width has narrowed by almost four times until the late 1980s the channel was relatively stable with minor bank collapses and only one bar detected near the jisr abdallah during the 1990s a number of bars developed along the channel the downcutting is in parallel with the sea level drop resulting in the development of terraces along the lower part of the study reach in 1983 the channel incision reached 8 km upstream and by 1993 it was about 11 km

regional analysis of bedrock stream long profiles evaluation of hack s sl form and formulation and assessment of an alternative the ds form the equilibrium form of the fluvial long profile has been used to elucidate a wide range of aspects of landscape history including tectonic activity in tectonic collision zones and in continental margin and other intraplate settings as well as other base level changes such as due to sealevel fluctuations the hack sl form of the long profile which describes a straight line on a log normal plot of elevation normal versus distance logarithmic is the equilibrium long profile form that has been most widely used in such studies slope area analysis has also been used in recent years we show that the sl form is a special case of a more general form of the equilibrium long profile here called the ds form that can be derived from the power relationship between stream discharge and downstream distance and the dependence of stream incision on stream power the ds form provides a better fit than the sl form to river long profiles in an intraplate setting in southeastern australia experiencing low rates of denudation and mild surface uplift we conclude that if an a priori form of the long profile is to be used for investigations of regional landscape history the ds form is preferable in particular the ds form in principle enables equilibrium steepening due to an increase in channel substrate lithological resistance parallel shift in the ds plot to be distinguished from disequilibrium steepening due to long profile rejuvenation disordered outliers on the ds plot slope area analysis and the slope distance ds approach outlined here are complementary approaches reflecting the close relationship between downstream distance and downstream catchment area copyright 2006 john wiley sons ltd

erosion rates and mechanisms of knickzone retreat inferred from 10be measured across strong climate gradients on the northern and central andes western escarpment escarpment edge deep gorges and distinct knickzones in river profiles characterize the landscape on the western escarpment of the andes between 5 s and 18 s northern peru to northern chile th

geomorphic and cosmogenic nuclide constraints on escarpment evolution in an intraplate setting darling escarpment western australia the 900 km long darling scarp in western australia is one of the most prominent linear topographic features on earth despite the presence of over steepened reaches in all westerly flowing streams crossing the scarp and significant seismic activity within 100 km of the scarp there is no historical seismicity and no reported evidence for quaternary tectonic displacements on the underlying darling fault consequently it is unclear whether the scarp is a rapidly evolving landform responding to recent tectonic and or climatic forcing or a more slowly evolving landform in order to quantify late quaternary rates of erosion and scarp relief processes we obtained measurements of the cosmic ray produced nuclide beryllium 10 10be from outcropping bedrock surfaces along the scarp summit and face in valley floors and at stream knickpoints erosion rates of bedrock outcrops along the scarp summit surface range from 0 5 to 4 0 m myr 1 these are in the same range as erosion rates of 2 1 to 3 6 m myr 1 on the scarp face and similar to river incision rates of 2 6 to 11 0 m myr 1 from valley floor bedrock straths indicating that the darling scarp is a slowly eroding steady state landform without any significant contemporary relief production over the last several 100 kyr and possibly several million years knickpoint retreat rates determined from 10be concentrations at the bases of two knickpoints on small streams incised into the scarp are 36 and 46 m myr 1 if these erosion rates were sustained over longer timescales then associated knickpoints may have initiated in the mid tertiary to early neogene consistent with early mid tertiary marginal uplift ongoing maintenance of stream disequilibrium longitudinal profiles is consistent with slow regional base level lowering associated with recently proposed continental scale tilting as opposed to differential uplift along discrete faults cosmogenic 10be analysis provides a useful tool for interpreting the palaeoseismic history of intraplate near fault landforms over 105 to 106 years copyright 2010 john wiley sons ltd

longitudinal profile development into bedrock an analysis of hawaiian channels analysis of topographic maps of rivers incised into dated hawaiian lava flows shows that the long term average bedrock erosion rate along certain reaches is linearly related to stream power field observations suggest that two processes may control hawaiian channel downcutting 1 stream power dependent erosion including abrasion of the channel bed by transported particles and 2 step wise lowering caused by knickpoint propagation modeling results indicate that a simple stream power dependent erosion law predicts the straight to weakly convex longitudinal profiles characteristic of kauai channels but is insufficient to predict two other characteristic features the upslope propagation of knickpoints and the straight 5 8 channel slopes below the knickpoints thus more than this single transport law is apparently required to model bedrock channel incision field surveys also indicate that significant portions of the channel lengths below the knickpoints are mantled with large boulders we propose that

analogue modeling of transverse drainage mechanisms fifteen physical experiments on a stream table replicated four general mechanisms proposed to explain transverse drainage development namely antecedence superimposition overflow and piracy the experimental design encompassed multiple strategies to effectively replicate the different mechanisms these experiments roughly emulate natural fluvial processes including aggradation lateral erosion degradation knickpoint retreat ponding and overflow the experiments address landscape morphology and depositional field criteria associated with antecedence overflow and piracy antecedence experiments showed that defeat of streams by a tectonically growing structure could result from a combination of upstream ponding and diversion into a trunk drainage insufficiently fast retreating knickpoints and downstream deposition of eroded sediments piracy can result from stream aggradation until it overtops a low divide by headward erosion of a stream through a divide and by sapping processes for piracy driven by headward erosion asymmetrically sloped ridges allow the drainage divide across the ridge to retreat from headward erosion but a symmetric divide hinders the ability of a stream to retreat across the ridge apex aggradationally driven piracy is potentially hindered because the slope across the divide needs to be sufficiently steep compared to the uncaptured stream otherwise deposition occurs across the divide and a levee is formed which prevents capture for transverse drainages produced by overflow knickpoints retreat across the overflow outlet producing a high probability of downstream flooding a positive feedback develops where added discharge to the drainage from lake water increases erosion and knickpoint retreat further eroding and undermining the basin outlet and releasing even more lake water the result is rapid incision and dramatic flooding downstream of the bedrock high during lake outlet erosion two superimposition experiments were unsuccessful most of the field criteria for antecedence overflow and piracy were either directly replicated or implied based on observations during each experimental run

geomorphic response of lillooet river british columbia to meander cutoffs and base level lowering abstract a detailed record of channel profiles slopes and stream discharge on lillooet river provides an opportunity to study the effects of natural and artificial channel changes that have occurred over the past century we analyze the long term effects of channel alterations that may affect flood hazard in the mid 1940s several meanders were artificially severed side channels blocked off and the level of downstream lillooet lake was lowered these measures were thought to increase hydrologic efficiency and decrease flood risk in the largely agricultural valley between 1947 and 1994 average channel width in the upper reaches decreased by 50 most of which occurred by the late 1950s between 1945 and 1969 lillooet river degraded its bed elevation by 3 4 m 12 5 to 16 7 cm a 1 in the upper reaches and up to 2 m 8 3 cm a 1 in the lower reaches this sudden and profound degradation compares to average bed elevation increases of 2 4 cm a 1 prior to the engineering works between 1969 and 1985 the cross section area increased by 22 in the upper reaches and 13 in the lower reaches and decreased to 12 and 8 respectively for the time period 1985 to 2000 the increased sediment supply that was caused by channel straightening accelerated delta advance in lillooet lake from 7 m a 1 1858 to 1948 to 30 m a 1 for the five year period following the 1948 channel works these rates have decreased over time but with a current advance rate of 10 5 m a 1 1986 2009 are still above the long term average prior to the channel changes this study demonstrates the time scale direction and magnitude of channel changes following significant artificial river alterations while the initial goal of decreasing flood risk had been achieved in the short term the lower river apparently is slowly returning to an overall aggradational phase ongoing delta advance will ultimately increase channel elevations in the lower reaches and lead to significant flood hazards for populated areas

stream channel convexity induced by continuous base level lowering the dead sea israel abstract the dead sea level has dropped from 388 4 m in 1896 to 417 2 m in 2004 and continues to fall rapidly reaching a record of 1 m y drop such a dramatic base level fall on time scales of several tens of years makes the dead sea area a unique field laboratory the aim of this study is to examine the effect of the lowering dead sea as a base level on the longitudinal profiles of channels on the formation of knick points and on the sinuosity field studies were made along the lower courses of creeks which drain lakeward precise longitudinal profile measurements and their fitting to linear and logarithmic curves show they are planar to slightly convex the short convexity the absence of hydrological or lithological control and former experimental results of profile response to base level fall suggest that the convexity results from the recent continuous rapid drop of the dead sea the convexity is also an inheritance of the paleo morphology i e the original convex front of the fan deltas and coastal scarps following channel incision slope displacement and diffusion the erodible substrate and the high stream power prevented preservation of nickpoints along the main channels sinuosity of the meandering thalwegs remained low 1 1 1 2 indicating no response to the base level lowering along the steep slopes although the stream channels are incised in soft sediments the base level induced entrenchment dies out within 1000 m or less from the receding shoreline the channel profiles demonstrate different phases of adjustment to the lowering base level the uniqueness of the dead sea case is that contrary to former field and experimental studies the system is in a continuous relaxation period without reaching a final adjustment the channels are trapped in their convex form following a rapid on going base level fall upon exposed paleo fan deltas

recession rates of waterfalls in boso peninsula japan and a predictive equation rates of waterfall recession and major factors that influence the rate were studied using waterfalls in boso peninsula japan the mean rate of waterfall recession was estimated by determining the age and original location the principal factor in determining the rate of waterfall recession is the ratio of the erosive force of stream to the bedrock resistance this is expressed in terms of measurable variables which include the discharge drainage area and precipitation the width and height of the waterfall and the unconfined compressive strength of the bedrock an empirical equation connecting the force resistance ratios and the rates of waterfall recession is derived copyright 2003 john wiley sons ltd

petrologic structural and geochronologic characteristics of the acadian metamorphic overprint on the taconide zone in part of southwestern new england

inner gorge slot canyon system produced by repeated stream incision eastern alps significance for development of bedrock canyons abstract many inner bedrock gorges of the alps show abrupt downstream changes in gorge width as well as channel type and gradient as a result of epigenetic incision of slot canyons many slot canyons also are associated with older gorge reaches filled with quaternary deposits the age of slot canyons and inner bedrock gorges however commonly is difficult to constrain for the inner bedrock gorge system of the steinberger ache catchment eastern alps active slot canyons as well as older abandoned gorge reaches filled with upper wurmian proglacial deposits record three phases of gorge development and slot canyon incision a 234u 230th age of cement of 29 7 1 8 ka in fluvial conglomerates onlapping the flank of an inner gorge fits with late wurmian valley bottom aggradation shortly before pleniglacial conditions in addition the age indicates that at least the corresponding canyon reach must be older during advance of ice streams in the buildup of the last glacial maximum lgm the catchment was blocked and a proglacial lake formed bedrock gorges submerged in that lake were filled with fluviolacustrine deposits during the lgm the entire catchment was overridden by ice during post glacial reincision streams largely found again their preexisting inner bedrock canyons in some areas however the former stream course was missed and a slot canyon formed the distribution of pleistocene deposits the patterns of canyon incision and the mentioned u th cementation age however together record a further discrete phase of base level rise and stream incision well before the lgm the present course of steinberger ache and its tributaries is a patchwork of 1 slot canyons incised during post glacial incision 2 vestiges of slot canyons cut upon an earlier middle to late wurmian cycle of base level rise and fall 3 reactivated reaches up to 200 m in width of inner bedrock gorge that are watershed at present and more than at least 30 ka in age and 4 abandoned sediment filled reaches of bedrock canyons that also must be older than 30 ka and that are exposed alongside the active streams multi cyclic bedrock canyon systems composed of reaches of markedly different ages may be common in mountain ranges subject to glaciations and or mass wasting

epeirogenic controls on canadian river incision and landscape evolution great plains of northeastern new mexico abstract the canadian river has carved a deep bedrock canyon into the great plains of northeastern new mexico in response to a complex interaction of post laramide epeirogenic rock uplift processes along the jemez lineament and downstream baselevel fall caused by late tertiary and quaternary evaporite dissolution broad slow bulging along the jemez lineament a lithospheric scale structure with prolific late cenozoic volcanism along its trend helps drive incision in the canyon canadian river canyon fluvial terraces mapped and correlated according to soils elevation and rock type criteria reveal longitudinal profiles that appear broadly warped across the jemez lineament and converge to the modern channel profile both upstream and downstream of the canyon similarly the modern channel long profile is distinctly and broadly convex through its great plains reach a unique feature among major rivers draining the eastern flank of the southern rocky mountain front radiocarbon dated charcoal from terrac

experimental study of headcut erosion in cohesive soils under different consolidation types and hydraulic parameters headcut is a change in stream channel elevation where there is concentrated flow most of the past studies focus on non cohesive soils although many problems on the streams occur because of cohesive beds and banks in this study eight samples of cohesive soils with a different composition of silt and clay for different waterfall heights and flow velocity under long and short term natural consolidation conditions were tested in one of the tests a sand layer was settled on the headcut bed to investigate its impact on headcut erosion by increasing clay content the headcut will remain vertical as it moves backward result showed that the effect of clay content reduction was more noticeable under the long term consolidation condition in general the effect of clay percentage variation on the measured parameters is much higher than the effects of waterfall height or flow velocity and the effect of consolidation type and adding a sand layer on the measured values is much higher than the effect of clay percentage variation on the waterfall height and flow velocity

macroscale dynamics of experimental landscapes abstract we review results from laboratory scale modelling of erosion and relief dynamics under variable uplift and rainfall rates under constant values of these forcing parameters an experimental landscape typically evolves towards a steady state between uplift and erosion and we show how the geometry of the steady state landscape adjusts to the rates of uplift and rainfall the comparison between these laboratory scale landscapes and the natural ones is not straightforward because contrary to analogue modelling in tectonics natural conditions of relief evolution cannot be downscaled to the laboratory without any scale distortions laboratory scale modelling in geomorphology is therefore only experimental not analogue despite these limitations experimental models may be used to provide physical tests for numerical models and they give insights into first order behaviours and directions for future research

experimental study of knickpoint and longitudinal profile evolution in cohesive homogeneous material a series of experiments were conducted in homogeneous bedrock to study knickpoint and longitudinal profile evolution knickpoints are created by successive drops in base level which simulate intermittent uplift channel morphology and flow characteristics vary systematically along a knickpoint reach as the knickpoint lip is approached width decreases but depth velocity and bottom shear stress increase as a result knickpoints are rapidly destroyed through the process of 1 knickpoint replacement and 2 subsequent knickpoint inclination knickpoint replacement consists of two morphologically distinct erosional reaches the knickpoint face below the knickpoint lip which decreases in slope and an incising reach above the knickpoint lip which increases in slope knickpoint replacement is a significant process in the evolution of knickpoints in homogeneous bedrock within experimental limits this study supports the notion that knickpoints do not undergo parallel head ward retreat in homogeneous bedrock given intermittent uplift except in those possible cases of extensive and pervasive bedrock jointing only the erosional sediment transport discontinuity above the knickpoint is developed in cohesive sediments below the knickpoint a steep bedrock channel slope low sediment load and rapid decrease in grain size of sediment load preclude development of the aggradational sediment transport discontinuity knickpoint evolution can be characterized by three general models parallel retreat replacement and inclination these models are based on the following criteria within the knickpoint reach 1 relationship between bottom shear stress 0 and critical shear stress needed to initiate motion c 2 nature of the bed load transport discontinuities and 3 spatial variability of bedrock resistance to fluvial erosion

large climate driven changes of oceanic oxygen concentrations during the last deglaciation during the last glacial termination the solubility of gases in the ocean decreased as ocean temperatures rose however marine sediments have not unanimously recorded ocean deoxygenation throughout this time some records show increasing oxygenation since the last glacial maximum particularly in the deep sea while many document abrupt oxygenation changes often associated with apparent changes in the formation rate of north atlantic deep water here we present a global compilation of marine sediment proxy records that reveals remarkable coherency between regional oxygenation changes throughout deglaciation the upper ocean generally became less oxygenated but this general trend included pauses and even reversals reflecting changes in nutrient supply respiration rates and ventilation the most pronounced deoxygenation episode in the upper ocean occurred midway through the deglaciation associated with a reinvigoration of north atlantic deep water formation at this time the upper indo pacific ocean was less oxygenated than today meanwhile the bulk of the deep ocean became more oxygenated over the deglaciation reflecting a transfer of respired carbon to the atmosphere the observed divergence from a simple solubility control emphasizes the degree to which oxygen consumption patterns can be altered by changes in ocean circulation and marine ecosystems

landscape evolution valley excavation and terrace development following abrupt postglacial base level fall many high latitude fluvial systems are adjusting to base level changes since the last glaciation channels that experienced base level fall may still be incising often through glacial diamictons tills these tills can be quite competent behaving more like weak bedrock than unconsolidated sediment and erode at a fast pace thus providing a unique opportunity to test models of channel incision and knickpoint migration in transient systems here we integrate light detection and ranging lidar topography strath terrace chronology and numerical modeling to determine knickpoint migration and incision history of the le sueur river in central minnesota usa results indicate that the le sueur river is best modeled as a detachment limited channel with downstream coarsening related to lag clasts from tills playing a critical factor in longitudinal profile development the le sueur river meanders as it incises so we coupled the best fit incision model to a meander model to determine valley excavation history the excavation history was used to determine a natural background erosion rate prior to land use changes associated with settlement and agricultural expansion in the mid 1800s we compared background fine sediment silt and clay erosion rates with historic decadal average annual suspended loads results show that modern fine sediment contributions from sources associated with valley excavation are three times higher than modeled presettlement loads recent changes in hydrology associated with land use and climate change have increased flows in rivers leading to higher sediment loads not just from field erosion but from increased bank and bluff erosion in the deeply incised valleys

seismic assessment of the weihe graben central china insights from geomorphological analyses and 10be derived catchment denudation rates abstract the tectonic activity and potential for linkage of adjacent active faults are crucial for seismic assessment as the two largest faults that bound the weihe graben central china the qinling northern piedmont fault qnf 200 km and the huashan piedmont fault hpf 150 km are mainly responsible for seismic risk in this densely populated area where the 1556 m 8 5 huaxian earthquake occurred with 830 000 fatalities however their tectonic activity and the degree of interaction remain poorly constrained hampering an adequate seismic risk assessment of the weihe graben here we integrate 23 new 10be derived catchment averaged denudation rates of 0 06 0 32 mm yr with topographic metrics to evaluate the seismic risk the results demonstrate that the landscape of the qinling and huashan mountains is in transient state in response to the tectonic perturbations of the qnf and the hpf with tectonic knickpoints formed along main streams and tributaries and widespread unstable drainage divides these two faults have comparable tectonic activity and are potentially capable of generating earthquakes with the maximum magnitude of mw 7 7 7 9 moreover they have likely started linking posing a greater seismic risk than previously estimated

escarpment evolution on high elevation rifted margins insights derived from a surface processes model that combines diffusion advection and reaction experiments with a surface processes model of large scale 1 1000 km long term 1 100 m y erosional denudation are used to establish the controls on the evolution of a model escarpment that is related to the rifting of a continent the model describes changes in topographic form as a result of simultaneous short and long range mass transport representing hillslope diffusive processes and fluvial transport advection respectively fluvial entrainment is modeled as a first order kinetic reaction which reflects the credibility of the substrate and therefore the fluvial system is not necessarily carrying at capacity one dimensional and planform models demonstrate that the principal controls on the evolution of an initially steep model escarpment are 1 antecedent topography drainage 2 the timescale or equivalently a length scale in the fluvial entrainment reaction 3 the flexural response of the lithosphere to denudation and 4 the relative efficiencies of the short and long range transport processes when rainfall and substrate lithology are uniform a significant amount of discharge draining over the escarpment top causes it to degrade only when the top of the model escarpment coincides with a drainage divide can escarpment retreat occur for these conditions an additional requirement for retreat of a model escarpment without decline is a long reaction time scale for fluvial entrainment this corresponds to a substrate that is hard to detach by fluvial erosion and therefore to fluvial erosion that is not transport limited continuous backtilting of an escarpment due to flexural isostatic uplift in response to denudational unloading helps maintain the scarp top as a divide it is essential if the escarpment gradient is to be preserved during retreat in a uniform lithology low flexural rigidities promote steep and slowly retreating escarpments for given rainfall and substrate conditions the morphology of a retreating model escarpment is determined by the ratio of the short range diffusive and long range advective transport efficiencies a low ratio which is interpreted to correspond to a relatively arid climate and weathering limited conditions promotes steep sharp topped escarpments with straight main slopes and escarpment retreat occurs over a wide range of height scales a high ratio interpreted to correspond to a more humid temperate climate produces a convex upper slope and concave lower slope morphology and only major escarpments are predicted to preserve a high scarp gradient lithological contrasts in the model produce more complex morphologies and predict the formation of scarps crowned by an erosionally resistant caprock however resistant caprocks are not an essential requirement for model scarps to retreat we conclude that the inferred controls and model behavior are both consistent with the present day morphology of rifted continental margins and with modern conceptual models of landscape evolution

drainage organization on the newly emerged dead sea bed israel abstract the organization of distributary drainage systems on the emerging coastal areas of the dead sea was studied following a rapid base level fall of 24 m during the period 1945 2002 which made the emerging pristine coastal zone a natural field laboratory photogrammetric digital elevation models were extracted to identify different emerged areas and to quantify erosion and deposition processes visual interpretation of orthophotos was used in order to recognize different drainage networks and to delineate the receding shoreline the remotely sensed data were backed by field surveys including measurement of longitudinal profiles the study demonstrates the spatial variability of runoff allocation from prograding fans to the emerging areas and the variable drainage responses three distinct environments were revealed on the emerged areas from the coast to the land deeply incised channels which are the main transmitters of the base level effect headward dendritic coalescing systems that are the reversal of the diverging channel system on alluvial fans and areas with unconfined sheet flowouts which are detached from base level control the threshold gradient of erosion on the emerged areas is 3 headward erosion was uncoupled with the lake level drop i e the rate of headward entrenchment increased with time despite an almost constant base level fall

bathymetry of lake lisan controls late pleistocene and holocene stream incision in response to base level fall abstract this paper examines the millennial scale evolution of the longitude profile of nahal wadi zin in the dead sea basin in the northern arava valley israel nahal zin has incised 50 m into relatively soft late pleistocene lake lisan sediments incision was forced by the regressive 10 km lake level fall of a total of 200 m of lake lisan from its highest stand at 25 ka and exposure of the lake floor sediments to fluvial and coastal processes alluvial cut terraces of the incising channel are well preserved along the 17 5 km of the lowermost reach of nahal zin at its outlet into the dead sea basin nahal zin deposited a holocene alluvial fan at the base of a 10 80 m high escarpment in unconsolidated sediments the escarpment is associated with the amazyahu fault which forms the southern structural boundary of the present dead sea basin geomorphic mapping optically stimulated luminescence osl ages and soil stratigraphy allowed correlation of terrace remnants and reconstruction of several past longitudinal profiles of nahal zin and its incision history together with the published lake level chronology these data provide an opportunity to examine stream incision related to base level lowering at a millennial scale osl ages of the terraces fit relatively well with the established lake level chronology and follow its regression and fall for a few thousands of years the longitudinal profile response to the lake level fall was downstream lengthening onto the exposed former lake bed most of the incision 40 m occurred later when the lake level reached the top of the amazyahu fault escarpment and continued to drop the incision was a relatively short episode at about 17 ka and cut through this escarpment almost to its base the fast incision its timing and the profiles of the incising channels indicate that the escarpment was an underwater feature and was not formed after the lake retreated this fairly simple scenario of regressive lake level fall and knickpoint exposure and incision is modeled here using a one dimensional numerical incision model based on a linear diffusion equation the calculated diffusion coefficient fits earlier results and data obtained from other streams in the area and confirms the upscaling of this simple model to the millennial scale

late quaternary stream incision and uplift in the forearc of the cascadia subduction zone western oregon documentation of a latest pleistocene earliest holocene episode of strath formation and fluvial aggradation in the oregon coast range provides a datum from which long term bedrock stream incision rates are determined variations in long term incision rates probably reflect cumulative differential uplift in the forearc of the cascadia subduction zone although factors such as bedrock and climatic controls and isostatic adjustments to erosion obscure the precise relationship between surface uplift and stream incision patterns of differential incision are most striking near the latitude of newport where a steep gradient divides a region of higher rates 0 6 0 9 mm yr in the northern coast range from a region of lower rates 0 1 0 3 mm yr in the central coast range the steep incision gradient is nearly coincident with abrupt changes in marine terrace 80 125 kyr uplift rates the locations of quaternary faults and the southern flank of a saddle of low historic 40 70 years uplift the exact causes of these variable patterns of incision uplift are unknown analogies with uplift patterns in other subduction zones and comparisons with other neotectonic data in the region indicate that patterns of differential incision probably are caused by variations in permanent strain accumulation along the cascadia subduction zone such variations may be related to differences in seismic moment release during individual earthquakes to changes in plate geometry or rates of wedge accretion to segmentation of earthquake ruptures and or to deformation on active structures in the north american plate and accretionary wedge

colorado river long profile metrics knickzones and their meaning abstract the numerical analysis of river long profiles has a rich history and is experiencing a rejuvenation with the advent of improved terrain models and computational tools the highly variable profile and the unusual hydrology of the green colorado river system crossing the colorado plateau provide an example that is germane to debates about transient versus equilibrium knickzone features about the controls of baselevel change due to drainage integration or differential uplift and the role of adjustments to climate hydrology and changing bedrock in order to explore these controls in more detail we define objective geologic study reaches along the green colorado river calculate unit stream power and develop a discharge adjusted steepness index kqsn that avoids the scaling assumptions in substituting contributing area for discharge which are erroneous in this dryland setting determining the nature of knickzones is key and the colorado plateau is a prime setting for study because of the legacy of previous work and a burst of new research and debate the four canyon knickzones along the green colorado are characterized by energy expenditure an order of magnitude greater than in intervening reaches and our kqsn proxy tracks stream power well the strong coincidence of the grand canyon cataract canyon and eastern uinta knickzones with stronger bedrock and mass movement inputs suggests they are pinned equilibrium adjustments to greater bed resistance with the possible exception of desolation canyon as a transient feature marked by anomalous profile convexity along the trunk drainage the knickzone anomalies become greater downstream this and patterns of kqsn in headwater tributaries correspond to some proposed sources of broad mantle driven uplift but they do not match other proposed uplift patterns thus a poorly understood decoupling of topography and proposed uplift exists in some regions

timescales and the role of inheritance in long term landscape evolution northern new england australia landscape evolution in northern new england is characterized by the persistence of landforms over long time periods the topography in the study area was initiated by paleozoic diapiric intrusion of granitic rocks as highs within metasedimentary and volcanic rocks this framework was probably reinforced by differences in the resistance of the massive igneous and the fractured metasedimentary rocks to erosion as a result both the tertiary and present day relief of the area consists of uplands developed on granitic rocks partly overlain by paleozoic volcanic rocks and lowlands developed on paleozoic metasediments extensive volcanism in the tertiary had only a minimal effect on this relationship a significant impact of tertiary volcanism however was the diversion of major streams across topographic highs despite 19 35 ma of incision these streams are still far from establishing equilibrium profiles and dissecting the highs the persistence of topography for a timescale of the same order of magnitude as that conventionally thought to be required for planation is due to reduced denudation rates in a passive tectonic setting and the presence of erosion resistant paleozoic igneous units the latter influence is indicated by knickpoint persistence for 19 35 ma on streams diverted across these rocks since it is generally considered that such disequilibria are short lived features formed by quaternary or ongoing deformation this knickpoint persistence has important implications for landscape analyses that use disequilibria to assess recent tectonism in a landscape