temporal buffering of climate driven sediment flux cycles by transient catchment response abstract the marine sedimentary record can exhibit a systematic cyclicity that is consistent with climate variability driven by milankovitch scale forcing milankovitch band cyclicity is widely interpreted in the hemipelagic and pelagic sediments of the marine realm and in terrestrial paleoenvironments has been observed in lacustrine sediments soils and river floodplain successions it remains unclear however if and how mountain catchments as a primary sediment source respond to these high frequency 6 yr climatic cycles and whether particulate sediment flux signals can be expected to be recorded in the clastic sedimentary record of adjacent basin fills recent field and theoretical studies suggest that mountain catchments respond transiently to high frequency forcing and so sediment discharge from the catchment is a non linear function of forcing variables using a catchment basin model we demonstrate that climate driven cyclicity in particulate sediment discharge is strongly damped when the period of climate variability is shorter than the response timescale of the eroding landscape given that the response timescale of landscapes is of the order of 10 6 yr and that milankovitch driven climate cyclicity is of the order of 10 4 10 5 yr it is likely that climate driven perturbation of upland catchments at these periods will be strongly damped by transient landscape behaviour our results therefore suggest that stratigraphy built by particulate fluxes from upland catchments and long term trends in the sediment delivery to the ocean may be relatively insensitive to short term climate variability

quaternary landscape evolution in the san jacinto fault zone peninsular ranges of southern california transient response to strike slip fault initiation well constrained case studies of transient landscape response to external forcing are needed to improve our understanding of erosion processes in tectonically active mountain belts the peninsular ranges portion of the san jacinto fault zone sjfz is an excellent location for such a study because it displays pronounced geomorphic disequilibrium resulting from initiation of a major strike slip fault in the past 1 0 to 2 5 million years we recognize two geomorphic domains in this region 1 a relict low relief upland domain consisting of broad flat valleys and low gradient streams and 2 very steep rough topography with deeply incised canyons and retreating erosional knickpoints pleistocene sediments exposed along and near the sjfz include fluvial conglomerate sandstone and mudstone with weak paleosols and west to nw directed paleocurrents these sediments accumulated in a lowgradient stream system represented by domain 1 during an early phase of slip in the sjfz prior to the modern phase of erosion and degradation domain 2 late pliocene or early pleistocene initiation of the sjfz triggered a wave of headward erosion and stream capture that is still migrating nw along the fault zone using the total distance that capture points have migrated along the fault zone and a range of possible ages for fault initiation the rate of knickpoint retreat is estimated at 12 to 44 km my to explore the signal of transient geomorphic response to fault initiation we analyzed 23 tributaries along an 20 km portion of the main fault valley within domain 2 the analysis reveals three zones with distinctive morphologies 1 strongly convex longitudinal profiles in the nw 2 a large ca 5 6 km 2 landslide in the central zone and 3 concave tributaries in the se with profile complexity decreasing and catchment area increasing from nw to se the distribution of these zones suggests close spatial and temporal association of active fault slip bedrock incision deep seated landslides and erosional modification the fundamental driving force behind these processes is profound geomorphic disequilibrium resulting from initiation of the sjfz we suggest that landslides may have played a significant role in shaping the morphology of this fault zone and that the influence of landslides may be underestimated in areas where characteristic landforms and deposits are obscured by later erosion and faulting d 2005 elsevier b v all rights reserved

submarine hydrogeology of the hawaiian archipelagic apron 2 numerical simulations of coupled heat transport and fluid flow we perform numerical simulations of buoyancy driven pore fluid flow in the hawaiian archipelagic apron and underlying oceanic crust in order to determine the extent to which heat redistributed by such flow might cause conductive heat flow measurements to underrepresent the true mantle heat flux we also seek an understanding of undulations observed in finely spaced heat flow measurements acquired north of oahu and maro reef with wavelengths of 10 to 100 km and amplitudes of 2 to 7 mw m 2 we find that pore fluid flow can impart significant perturbations to seafloor heat flow from the value expected assuming a constant mantle flux in the simplest scenario moat wide circulation driven by bathymetric relief associated with the volcanic edifice recharges a fluid system over the moat and discharges the geothermally heated water through the volcanic edifice the existing heat flow data are unable to confirm the existence of such a flow regime in that it produces prominent heat flow anomalies only on the steep flanks of the volcano where heat flow probes cannot penetrate however this flow system does not significantly mask the mantle flux for reasonable permeabilities and flow rates another numerical simulation in which the upper oceanic basement acts as a aquifer for a flow loop recharged at basement outcrops on the flexural arch and discharged within a permeable volcanic edifice is capable of almost uniformly depressing conductive heat flow across the entire moat by 15 large heat flow anomalies 20 mw m 2 are located over the recharge and discharge zones but are beyond the area sampled by our data presumably finely spaced heat flow measurements over the flexural arch could test for the existence of the predicted recharge zone we demonstrate that the prominent shorter wave undulations in heat flow across the oahu and maro reef moats are too large to be explained solely by relief in the upper oceanic basement more likely shallower large scale turbidites or debris flows also serve as aquifers within the less permeable moat sediments with our limited information on the structural geology of the moat permeability structure of its major geologic units and their variations in the third dimension we are not able to exactly match the spatial distribution of heat flow anomalies in our data but spectral comparisons look promising

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

on the response of the ocean to a moving storm the nonlinear dynamics abstract a novel and efficient numerical method is used to investigate the nonlinear equations of motion for the upper layer of a two layer ocean in which the lower layer is infinitely deep and at rest the efficiency is achieved by seeking solutions that are in a steady state translating in equilibrium with the storm oscillations are found in the wake of the storm two features of the response are attributed to the nonlinear terms in the equation of motion 1 a rapid transition from a maximum in the downwelling phase to a maximum in the upwelling phase of each oscillation followed by a gradual relaxation to the next downwelling maximum and 2 a displacement of the maximum response usually to the right of the storm track by 40 km it is shown that the horizontal pressure gradient terms can be neglected from the momentum equations for fast large storms in which case a lagrangian integration can be performed following fluid particles this enables feature 1 to be attributed to the along tra

heat flow variations correlated with buried basement topography on the juan de fuca ridge flank systematic heat flow variations are commonly observed on sedimented flanks of mid ocean ridges these variations have been attributed to the convective circulation of pore fluids within the oceanic crust and have been used to estimate the scale and pattern of this circulation here we report similar systematic variations observed in a detailed heat flow and seismic reflection survey over sediment covered 3 myr old sea floor on the eastern flank of the juan de fuca ridge we find that heat flow peaks are located above buried basement ridges and adjacent to two minor basement outcrops heat flow lows are found where thick sediments fill basement valleys the simple inverse relationship between heat flow and sediment thickness defined by the data indicates that hydrothermal circulation sealed within the permeable portion of the oceanic crust is vigorous enough to maintain approximately isothermal 10 k conditions at the sediment crust interface as no systematic variations in estimated basement temperatures are observed it seems that at this location the heat flow variations result only from sediment thickness variations and do not reflect a particular convective pattern

heat flow on hot spot swells evidence for fluid flow 1 we examine variability observed in heat flow determinations collected on hot spot swells we find substantial scatter in heat flow at wavelengths of a few hundred kilometers and less at both hawaii and reunion where closely spaced data exist and large variability in the regional heat flow surveys at cape verde bermuda and crozet our preferred interpretation is that the observed variability is due to fluid flow the presence of fluid flow admits the possibility that some heat is lost through advection such that the mean observed heat flow is less than the actual mantle flux if so the full magnitude of sublithospheric thermal variations may not be observed this interpretation has important implications for understanding heat flow determinations made on hot spot swells and resulting geodynamic inferences we suggest fluid flow may be masking variations in sublithospheric heat flux making available surface heat flow values a poor discriminator between geodynamic models for hot spot swells future field programs methods of data analysis and models should be designed to help extract a low frequency mantle flux disguised by a high noise surface filter

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

flankflux an experiment to study the nature of hydrothermal circulation in young oceanic crust the sediment buried eastern flank of the juan de fuca ridge provides a unique environment for studying the thermal nature and geochemical consequences of hydrothermal circulation in young ocean crust just 18 km east of the spreading axis where the sea floor age is 0 62 ma sediments lap onto the ridge flank and create a sharp boundary between sediment free and sediment covered igneous crust farther east beneath the nearly continuous turbidite sediment cover of cascadia basin the buried basement topography is extremely smooth in some areas and rough in others at a few isolated locations small volcanic edifices penetrate the sediment surface an initial cruise in 1978 and two subsequent cruises in 1988 and 1990 on this sedimented ridge flank have produced extensive single channel seismic coverage detailed heat flow surveys co located with seismic lines and pore fluid geochemical profiles of piston and gravity cores taken over heat flow anomalies complementary multichannel seismic reflection data w

off axis hydrothermal circulation parametric tests of a refined model of processes at deep sea drilling project ocean drilling program site 504 we have developed a refined model of coupled heat and fluid flow to numerically simulate off axis hydrothermal circulation through the upper oceanic crust the new representation includes mesh elements with curved sides and noncentered nodes these curvilinear elements allow improved simulation of topography at the seafloor and within underlying sediment and basaltic layers curvilinear simulations of circulation at deep sea drilling project ocean drilling program site 504 confirm the broad conclusions derived from the rectilinear simulations of fisher et al 1990 but also suggest that permeability within the upper few hundred meters of crust around hole 504b must be concentrated within several narrow zones this interpretation is consistent with core observations and wireline logs from hole 504b within these highly permeable zones absolute permeability may be several orders of magnitude higher than the bulk permeability measured for the upper crust as a whole a series of detailed parametric simulations was conducted to determine the quantitative importance of basal heat flow seafloor bathymetry basement relief and differential sediment thickness in modifying the geometry and intensity of off axis hydrothermal circulation these studies reveal that basement relief and differential sediment thickness are more important than seafloor bathymetry in enhancing off axis convection within the seafloor observed natural correlations between seafloor bathymetry and heat flow may exist because bathymetry is a proxy for the other two important parameters basement relief and differential sediment thickness off axis convection at geochemically significant velocities is possible even with heat input appropriate for some of the oldest oceanic crust a thick sediment layer over older crust may cause enough conductive refraction at the seafloor to mask the variations in seafloor heat flow often associated with off axis hydrothermal convection

fluvial landsculpting and the fractal dimension of topography abstract quantitative models of landform development can help us to understand the evolution of mountains and regional topography and the effects of tectonic motions and climate on landscape including its fractal geometry this paper presents a general and powerful three dimensional model of fluvial erosion and deposition at hill to mountain range scale the model works by accumulating the effects of randomly seeded storms or floods precipitons that cause diffusional smoothing then move downslope on digital topography grids that erode portions of elevation differences that transport a slope limited amount of eroded material and that deposit alluvium when their sediment carrying capacity is exceeded the iteration of these simple and almost linear rules produce very complicated simulated landscapes demonstrating that complex landscapes do not require complex laws each process implemented in the model is affected differently by changes in horizontal scale erosion a scale free process roughens topography at all wavelengths this roughening is balanced by diffusive processes scaling as 1 l 2 at short wavelengths and deposition scaling scaling as 1 l 2 at long wavelenghts such a mixture of scale free and scale dependent processes can produce multifractal behavior in the models the fractal dimension of the model topography is much more sensitive to climatic variables than to tectonic uplift landscape evolution may be fractal but it does not seem to be chaotic analysis of topography of areas in southern arizona using variograms shows approximately fractal behavior with mean fractal dimension around 2 2 2 3 departures from an exact fractal relatioship imply that the topography is in detail multifractal the fractal dimension at short wavelengths is less than that at long wavelengths this variation could either be caused by the relative strengths of diffusive and erosional processes shaping the topography or a result of changes in climatic or tectonic conditions still preserved in the landscape

seismic reflectivity anomalies in sediments at the eastern flank of the juan de fuca ridge evidence for fluid migration a high resolution seismic survey was carried out in the vicinity of ocean drilling program odp leg 168 drill sites at the eastern flank of the juan de fuca ridge three seismic systems with different source frequencies up to 4000 hz were used simultaneously along each seismic line the data sets were combined to provide the best possible resolution at any given depth level an integrated interpretation of narrow zones of low reflection amplitudes is presented which are related to basement highs but are independent of seafloor topography the effect is most pronounced above a buried basement ridge in the vicinity of odp sites 1030 and 1031 where higher porosity values are present higher porosities can reduce seismic impedance contrasts and may therefore cause the observed low reflection amplitudes in addition biot stoll s biot 1956a b stoll 1989 model suggests that attenuation coefficients are porosity dependent and reflection amplitudes are further decreased at higher seismic frequencies when porosity increases since zones of higher porosities are potential pathways for fluids they may be associated with hydrothermally driven fluid discharge which was previously predicted above the buried basement ridge it is therefore proposed that the observed seismic amplitude reduction in the vicinity of odp sites 1030 and 1031 indicates zones of upward fluid migration

on the implementation of passive open boundary conditions for a general circulation model the barotropic mode the objective of this study is to evaluate the performance of several open boundary conditions applied to the princeton ocean model the focus is on passive open boundary conditions applied to the external mode i e conditions that are applied when the mean flow at the open boundary is unknown and the values of the variables must be assumed or extrapolated from the interior solution three types of open boundary conditions obcs are tested 1 radiation conditions 2 characteristic methods 3 relaxation schemes numerical experiments are conducted in a zonal channel that include different forms of bottom topography the experiments are designed to emphasize flow conditions dominated by direct wind forcing or wave radiation three sets of experiments are discussed 1 forcing by a uniform alongshelf wind stress 2 the barotropic adjustment of an initial perturbation in the sea surface elevation and 3 forcing by a traveling storm the results of these experiments are compared with analytical solutions and the results of experiments using cyclic boundary conditions or expanded domains according to our results all radiation schemes of orlanski s type perform poorly in either flows with strong nonlinear components or when the model response is dominated by the propagation of dispersive wave packets the characteristic method recommended by roed and cooper 1987 provided reasonable responses in most cases but we found problems in handling dispersive waves or variable wind forcing at the open boundaries although there were limitations in all the obcs that we tested the best overall performances were for the conditions proposed by flather 1976 combined with a local solution approach proposed by roed and smesdtad 1984 and the flow relaxation scheme developed by martinsen and engedahl 1987

oceanic basement structure sediment thickness and heat flow near hole 504b a new seismic reflection survey around hole 504b the deepest borehole in ocean crust reveals active faulting possible volcanic centers and a lateral change in the relationship of heat flow and basement structure near the borehole migration of single channel and multichannel seismic profiles collected in a 25 by 25 km grid with a 1 km line spacing significantly improved the resolution of basement structure and sediment thickness west of hole 504b heat flow is high above east west lineated basement ridges whereas heat flow to the east is normal above ridges and high above two buried basement knolls the difference is probably due to lateral variations in sediment thickness small buried basement knolls are common and may have been point sources for lava flows hole 504b lies in a flat floored basin that slopes gently upward to the west a recently active fault 1 1 1 2 km south of hole 504b is indicated by sediment reflector discontinuities that extend up to the seafloor the fault strikes east west and crosses a buried volcanic knoll where holes 678b and 896a were drilled regionally basement relief north of hole 504b is 100 to 150 m lower than to the south which we attribute to an increased spreading rate obtained from dating published local magnetic anomaly patterns with a recent timescale we find at least five graben structures resembling failed rifts which may have formed in response to asymmetric spreading or to the change in tectonic stress accompanying the spreading rate change south facing scarps on basement ridges are as common as north facing scarps sediment thickness is highly correlated to basement depth due to preferential deposition in topographic lows when the crust was 1 2 ma old and to later winnowing

spatial and temporal analysis of hillslope channel coupling and implications for the longitudinal profile in a dryland basin author s michaelides katerina hollings rory singer michael bliss nichols mary h nearing mark a

controls on valley spacing in landscapes subject to rapid base level fall what controls the architecture of drainage networks is a fundamental question in geomorphology recent work has elucidated the mechanisms of drainage network development in steadily uplifting landscapes but the controls on drainage network morphology in transient landscapes are relatively unknown in this paper we exploit natural experiments in drainage network development in incised plio quaternary alluvial fan surfaces in order to understand and quantify drainage network development in highly transient landscapes i e initially unincised low relief surfaces that experience a pulse of rapid base level drop followed by relative base level stasis parallel drainage networks formed on incised alluvial fan surfaces tend to have a drainage spacing that is approximately proportional to the magnitude of the base level drop numerical experiments suggest that this observed relationship between the magnitude of base level drop and mean drainage spacing is the result of feedbacks among the depth of valley incision mass wasting and nonlinear increases in the rate of colluvial sediment transport with slope gradient on steep valley side slopes that lead to increasingly wide valleys in cases of larger base level drop we identify a threshold magnitude of base level drop above which side slopes lengthen sufficiently to promote increases in contributing area and fluvial incision rates that lead to branching and encourage drainage networks to transition from systems of first order valleys to systems of higher order branching valleys the headward growth of these branching tributaries prevents the development of adjacent ephemeral drainages and promotes a higher mean valley spacing relative to cases in which tributaries do not form model results offer additional insights into the response of initially unincised landscapes to rapid base level drop and provide a preliminary basis for understanding how varying amounts of base level change influence valley network morphology copyright 2015 john wiley sons ltd

on the implementation of open boundary conditions for a general circulation model the three dimensional case this article discusses the results of an experimental survey on the performance of a select group of open boundary conditions obcs for three dimensional primitive equation models the focus is on passive conditions where the model response at the open boundaries is dictated by the interior dynamics the performance of the obcs is tested in a series of numerical experiments conducted in a rotating channel which includes variable bottom topography and density stratification the experiments are sele cted to enhance nonlinear phenomena that comprises advection and the propagation of dispersive waves the first two experiments study coastal upwelling with constant and time varying wind forcing the third experiment analyses the barotropic and baroclinic response of a coastal ocean due to the passage of a traveling storm the open boundary condition with the best overall performance is the flow relaxation scheme on sea surface elevation and transport a radiation condition for internal velocities and a combined scheme of flow advection and relaxation for the temperature field a modified gravity wave radiation scheme provides reasonable responses when combined with radiation conditions for internal velocities and an advection equation for temperature if the forcing is not changing direction rapidly at the open boundary schemes using the method of characteristics or traditional wave advection schemes fail when combined with radiation conditions for the baroclinic mode

a regional model of the semidiurnal internal tide on the australian north west shelf a fully three dimensional nonlinear primitive equation model is applied to a study of the semidiurnal internal tide on the australian north west shelf a region of strong barotropic and baroclinic tide the model shows a significant internal tide over most of the continental slope region predominantly between 100 and 1000 m depths energy flux is highly variable with regions of onshore flux and regions of offshore flux corresponding to regions of subcritical and supercritical seabed slopes a comparison between the model and detailed observations from one region shows reasonable agreement in vertical displacement currents and depth integrated energy flux the comparison also highlights the difficulty in obtaining appropriate observations to provide a rigorous verification of internal tide models the m2 and s2 internal tides show similar patterns of flow with energy in the s2 internal tide about 25 of that in the m2 constituent estimates of the total baroclinic m2 energy are about 2 2 gw for the north west shelf nearly an order of magnitude larger than suggested by earlier studies this represents about 5 of the dissipation of the m2 barotropic tide in the model domain the seasonal variability in the baroclinic energy flux is about 20 from the mean the baroclinic energy extracted from the tide is expected to make a significant contribution to mixing in the region

fracture induced hydrothermal convection in the oceanic crust and the interpretation of heat flow data small scale seafloor heat flow variations with a characteristic wavelength of about 1200 m have been observed on a profile over a sediment sealed ridge flank two theories have been advanced to explain them low aspect ratio hydrothermal convection in a highly permeable basement layer 600 m thick or high aspect ratio convection in an anisotropic permeable layer 200 m thick induced by 20 m topographic variations with a 1000 m half wavelength neither theory is totally satisfactory the first requires a very thick highly permeable zone while the absence of any resolvable basement relief on a complementary seismic survey limits the credibility of the second we hypothesize that sub critical hydrothermal convection in normal upper oceanic crust driven by discrete fractures can cause the observed heat flow anomalies we test the hypothesis by using a finite element code to solve the coupled time dependent heat transport and fluid flow differential equations discrete fractures are incorporated explicitly we show that the inclusion of fractures in layers 2a and 2b promotes convection fluid flow through fractures causes horizontal thermal gradients and initiates and maintains sub critical convection within the upper basalts the predicted heat flow variations are comparable with the observed data

relief rejuvenation and topographic length scales in a fluvial drainage basin napf area central switzerland this paper explores how and to what extent a phase of relief rejuvenation modifies the mode of surface erosion in an approximately 63 km2 drainage basin located at the northern border of the swiss alps luzern area in the study area the retreat of the alpine glaciers at the end of the last glacial maximum lgm caused base level to lower by approximately 80 m the fluvial system adapted to the lowered base level by headward erosion this is indicated by knickzones in the longitudinal stream profiles and by the continuous upstream narrowing of the width of the valley floor towards these knickzones in the headwaters above these knickzones processes are still to a significant extent controlled by the higher base level of the lgm there frequent exposure of bedrock in channels and especially on hillslopes implies that sediment flux is to a large extent limited by weathering rates in the knickzones however exposure of bedrock in channels implies that sediment flux is supply limited and that erosion rates are controlled by stream power the morphometric analysis reveals the existence of length scales in the topography that result from distinct geomorphic processes along the tributaries where the upstream sizes of the drainage basins exceed 100 000 200 000 m2 the mode of sediment transport and erosion changes from predominantly hillslope processes i e landsliding creep of regolith rock avalanches and to some extent debris flows to processes in channels fluvial processes and debris flows this length scale reflects the minimum size of the contributing area for channelized processes to take over in the geomorphic development i e threshold size of drainage basin this threshold size depends on the ratio between production rates of sediment on hillslopes and export rates of sediment by processes in channels consequently in the headwaters erosion rates and sediment flux and hence landscape evolution rates are to a large extent limited by weathering processes in contrast in the lower portion of the drainage basin that adjusts to the lowered base level rates of channelized erosion and relief formation are controlled mainly by stream power hence this paper shows that base level lowering headward erosion and establishment of knickzones separate drainage basins in two segments with different controls on rates of surface erosion sediment flux and relief formation

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

dynamic interactions between erosion deposition and three dimensional deformation in compressional fold belt settings 1 this study investigates whether the three dimensionality of erosion and deposition can influence three dimensional folding even when compression is purely convergent this problem is studied by employing a three dimensional mathematical model incorporating dynamic thin plate deformation coupled with fluvial and hillslope sediment transport the approach taken is to impose several fundamentally different sediment routing patterns by changing the initial regional topographic slope and the ratio of the characteristic timescales for deformation to fluvial surface processes r and to investigate how deformation responds numerical results indicate that when and or r are small i e initial topography is regionally flat and or rates of surface processes are slow compared to rate of imposed deformation folding is two dimensional and unaffected by surface processes since loads created by surface processes are imposed after deformation this situation favors development of small scale drainage networks transporting sediment from anticlines to adjacent basins when and or r are relatively large the development of a large scale transverse drainage network which can be maintained during folding is able to strongly amplify and localize folding this leads to interesting features where the largest transverse rivers coincide with the greatest structural and topographic amplitude of doubly plunging folds which is caused by erosion enhanced deformation for intermediate parameter values folding and surface processes interact in a complex manner giving rise to three dimensional en echelon structures that migrate in a transient manner this study demonstrates that under some circumstances one can anticipate major two way interaction between surface processes and three dimensional deformation

time scales of tectonic landscapes and their sediment routing systems abstract in regions undergoing active tectonics the coupling between the tectonic displacement field the overlying landscape and the redistribution of mass at the earth9s surface in the form of sediment routing systems is particularly marked and variable coupling between deformation and surface processes takes place at a range of scales from the whole orogen to individual extensional fault blocks or contractional anticlines at the large scale the attainment of a steady state between the overlying topography and the prevailing tectonic conditions in active contractional orogens requires an efficient erosional system with a time scale dependent on the vigour of the erosional system generally in the range 10 6 10 7 years the catchment fan systems associated with extensional fault blocks and basins of the western usa are valuable natural examples to study the coupling between tectonic deformation landscape and sediment routing systems even relatively simple coupled systems such as an extensional fault block and its associated basin margin fans have a range of time scales in response to a tectonic perturbation these response times originate from the development of uniform steady state relief during the accumulation of displacement on a normal fault c 10 6 years the upstream propagation of a bedrock knickpoint in transverse catchments following a change in tectonic uplift rate c 10 6 years or the relaxation times of the integrated catchment fan system in response to changes in climatic and tectonic boundary conditions 10 5 10 6 years the presence of extensive bedrock or alluvial piedmonts increases response times significantly the sediment efflux of a mountain catchment is a boundary condition for far field fluvial transport but the fluvial system is much more than a simple transmitter of the sediment supply signal to a neighbouring depocentre fluvial systems appear to act as buffers to incoming sediment supply signals with a diffusive time scale c 10 5 10 6 years dependent on the length of the system and the extent of its floodplains stream channels and proximal gravel fans the vocabulary for explaining landscapes would benefit from a greater recognition of the importance of the repeat time and magnitude of perturbations in relation to the response and relaxation times of the landscape and its sediment routing systems landscapes are best differentiated as buffered or reactive depending on the ratio of the response time to the repeat time of the perturbation furthermore landscapes may be regarded as steady or transient depending on the ratio of the response time to the time elapsed since the most recent change in boundary conditions the response of tectonically and climatically perturbed landscapes has profound implications for the interpretation of stratigraphic architecture

from grain size to tectonics 1 regional grain size trends in fluvial successions can reveal important information regarding the dynamics of sediment routing systems self similar solutions for down system grain size fining have recently been proposed to explore how key variables such as the spatial distribution of deposition sediment discharge and sediment supply characteristics control spatial distribution of grain size in fluvial successions over time scales of 104 106 years we explore the sensitivity of these solutions to changes in key variables and assess their applicability to ancient fluvial successions several sensitivity analyses are presented to investigate the relative control of the key model variables on the spatial pattern of down system grain size fining in fluvial successions sensitivity analyses demonstrate that 1 an increase in the initial value of sediment discharge to a basin causes a decrease in the rate of grain size fining in fluvial successions an effect that becomes nonlinear for large values of initial sediment discharge 2 a short wavelength high amplitude subsidence regime generates a greater rate of down system grain size fining and a long wavelength lower amplitude subsidence regime generates a lesser rate of down system grain size fining in fluvial successions and 3 an increase in the spread of grain sizes in the sediment supply generates a greater rate of down system grain size fining we apply this modeling technique to grain size data sets collected from two time surfaces within conglomerates of the upper eocene montsor fan succession of the pobla basin spanish pyrenees these data sets exhibit approximately self similar grain size distributions further the observed increase in down system grain size fining associated with smaller depositional system lengths provides support for the application of self similar solutions to fluvial successions by applying these solutions to carefully collected grain size data from fluvial successions we are able to relate explicitly the initial grain size supplied to the system the spatial distribution of subsidence and the sediment discharge into the basin to the rate of grain size fining in fluvial successions this method thus offers a powerful means of elucidating sediment routing system dynamics over time

timescales of alluvial fan development by precipitation on mars 1 dozens of large low gradient alluvial fans are present within impact crater basins on the cratered highlands of mars the timescales and climate conditions that were required to generate such fans are unknown but testable through our understanding of terrestrial hill slope erosion in the presence of precipitation previous estimates of fan formation time vary from years to millions of years here we use an idealised physical model of 2 d catchment fan evolution to present a framework within which the development of martian alluvial fans should be considered we simplify the erosional and depositional system so that there are only three variables erodibility due to gravity amount of water runoff due to precipitation and catchment fan boundary elevation within this framework to generate large low gradient 108 yr if the substrate is extremely erodible relative to terrestrial examples

earth s surface responses during geodynamic evolution numerical insight from the southern east china sea continental shelf basin west pacific abstract the interaction between the earth s surface and deep geodynamic processes has a great influence on sedimentary patterns and characteristics of sedimentary systems especially in the continental margin such as the southern part of the east china sea continental shelf basin ecscsb however the exact processes and dynamics are poorly understood the numerical tool badlands was adopted to simulate the geological evolution of the southern ecscsb during the mesozoic transitional regime of the west pacific continental margin between 200 and 100 ma the numerical model involving four dimensional 4d sequence stratigraphy was validated by comparing with the tectono morphology sedimentary environments and sediment distribution according to our findings the transition was mainly controlled by three structural stages the first transitional stage of the southern ecscsb was mainly controlled by lithospheric scale tectonic evolution in the second stage the dynamic topography contributed to slow regional uplift while the last stage showed mantle induced dynamic subsidence the model results on 4d geomorphic characteristics sediment distribution of basin evolution and deep dynamic topography provided a quantitative image for geological evolution of the west pacific continental margin in the mesozoic

channel initiation and the problem of landscape scale since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape this threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head a field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth undissected hillslopes and the valley bottoms to which they drain this finding contradicts assertions that landscapes are scale independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization

the influence of bedrock orientation on the landscape evolution surface morphology and denudation 10be at the niesen switzerland landscape evolution and surface morphology in mountainous settings are a function of the relative importance between sediment transport processes acting on hillslopes and in channels modulated by climate variables the niesen nappe in the swiss penninic prealps presents a unique setting in which opposite facing flanks host basins underlain by identical lithologies but contrasting litho tectonic architectures where lithologies either dip parallel to the topographic slope or in the opposite direction i e dip slope and non dip slope the north western facing diemtigen flank represents such a dip slope situation and is characterized by a gentle topography low hillslope gradients poorly dissected channels and it hosts large landslides in contrast the south eastern facing frutigen side can be described as non dip slope flank with deeply incised bedrock channels high mean hillslope gradients and high relief topography results from morphometric analysis reveal that noticeable differences in morphometric parameters can be related to the contrasts in the relative importance of the internal hillslope channel system between both valley flanks while the contrasting dip orientations of the underlying flysch bedrock has promoted hillslope and channelized processes to contrasting extents and particularly the occurrence of large landslides on the dip slope flank the flank averaged beryllium 10 10be derived denudation rates are very similar and range between 0 20 and 0 26 mm yr 1 in addition our denudation rates offer no direct relationship to basin s slope area steepness or concavity index but reveal a positive correlation to mean basin elevation that we interpret as having been controlled by climatically driven factors such as frost induced processes and orographic precipitation our findings illustrate that while the landscape properties in this part of the northern alpine border can mainly be related to the tectonic architecture of the underlying bedrock the denudation rates have a strong orographic control through elevation dependent mean annual temperature and precipitation

modelling channel incision and alpine hillslope development using laser altimetry data this paper presents a new approach to simulate drainage basin evolution and demonstrates that high resolution elevation data can be used as useful tool for a dynamic simulation of alpine landscape development in which channel incision is incorporated in high spatial detail a vector channel incision model cim uses 1 m high resolution laser altimetry data for simulation of longitudinal profile development the cim is combined with a grid cell based hillslope erosion model to incorporate the hillslope response to incising bedrock rivers in a simulation of landscape evolution the combined simulation model is applied to a geologically diverse alpine catchment to simulate landscape development from reconstructed late glacial conditions towards the current situation the model is time efficient and realistically adapts to contrasting geological substrata while spatially and temporally variable incision values knick point recession and variable hillslope development result in a realistic simulation of post glacial landscape evolution high resolution elevation data in combination with dynamic geomorphological simulation models facilitate research of complex and difficult to access alpine terrain at greater detail than before it potentially paves the way for more efficient landscape evolution research and can contribute to increasing the understanding of the functioning of geo ecological systems

problems with imaging cellular hydrothermal convection in oceanic crust heat flow variations are commonly used to infer the existence of hydrothermal convection in young oceanic crust and in special cases the geometry and vigor of convection in a small area on the eastern flank of the juan de fuca ridge where the sea floor and seismic basement relief are only about 10 m a coherent pattern of heat flow variation having 40 mw m 2 peak to peak amplitude and half wavelength of about 600 m has been previously observed and interpreted to be caused by cellular convection within the extrusive layer 2a of the oceanic crust in august 1995 new seismic reflection and heat flow data were collected to define better the structure of basement in this area and to determine the planform of the heat flow variations revealed along the single transect of the earlier observational study the new higher resolution seismic results show considerable intra crustal structure in particular the uppermost crust is reverberant beneath areas of lower heat flow and a diffractive character extends close to the basement surface beneath areas of higher heat flow this relationship suggests that the heat flow variations may be caused by variations in depth to the top of a high permeability intracrustal zone that is not coincident with acoustic basement where relatively uniform temperatures are maintained by vigorous hydrothermal circulation of unresolved planform if this is the case the search that began in the 1970 s for heat flow variations that might reveal the scale of cellular convection and hence by inference the penetration depth of hydrothermal circulation in the oceanic crust may have been frustrated once again

on the semidiurnal internal tide at a shelf break region on the australian north west shelf abstract the properties of the semidiurnal internal tide in the region of the shelf break at a location on the australian north west shelf are discussed information is derived from an analysis of thermistor chain and current meter data collected over six months at the shelf break and slope locations the work is an extension of an earlier study the internal tide is described in terms of modes finding that the firm mode dominates propagating onshore at an angle of 30 from normal to the bathymetry with a rapid decay in amplitude of nearly five times from the shelf slope to the shelf break a distance of 22 5 km or approximately one wavelength the loss of energy flux from this decay gives rise to vertical mixing with a vertical eddy viscosity of 1 4 10 4 m2 s 1 the amplitude at the m2 tidal frequency dominates over the s2 amplitude giving an s2 m2 amplitude ratio significantly smaller than for the barotropic tidal motion the internal tide appears to have a three dimensional structure at the sh

near inertial ocean response to tropical cyclone forcing on the australian north west shelf the regional ocean modeling system roms was applied to the australian north west shelf nws to hindcast the ocean response to four intense historical tropical cyclones tcs while the four cyclones had very different trajectories across the nws all passed within 150 km of a long term vertical mooring located on the continental shelf in 125 m depth the observed ocean response at this relatively shallow southern hemisphere shelf site was characterized by the development of a peak in the counter clockwise ccw near inertial kinetic energy mixed layer deepening and subsequent restratification strong near inertial isotherm oscillations were also observed following two of the cyclones roms reproduced these features and also showed that the peak in the near inertial ccw kinetic energy was observed on the left side of each cyclone trajectory the time rate of change of near inertial kinetic energy depended strongly on the storm rossby number i e defined based on the storm speed the storm length scale and the coriolis frequency the shallow water depth on the nws resulted in first a more rapid decay of near inertial oscillations than in the deep ocean and second a generation efficiency the ratio of near inertial power to the rate of wind work of up to 10 smaller than found for cyclones propagating across deeper water the total energy put into near inertial motions is nevertheless large compared to the background tidal energy the rapid decay of near inertial motions emphasizes the importance of frictional effects in characterizing the response to cyclone forcing in shallow seas

topographic evolution and morphology of surfaces evolving in response to coupled fluvial and hillslope sediment transport 1 this paper quantifies how the ratio of sediment transport on hillslopes to sediment transport in channels influences surface and channel network morphologies and the dynamics of topographic evolution this problem is investigated by development and investigation of a simple deterministic model incorporating mass balance of sediment and runoff coupled with a law combining dispersive and concentrative sediment transport processes our analysis includes the identification of a new nondimensional parameter de that is a function of rainfall system size rock type and hydraulic regime and that is a measure of the relative importance of fluvial and hillslope sediment transport we show that de has an important influence on the surface morphology e g total exposed surface area and interface width which reflects surface roughness and relief channel network form e g channel sinuosity channel spacing and timescale of surface evolution surface and channel network morphologies are also strongly influenced by the overall surface slope relative to the magnitude of initial topographic roughness topographic evolution occurs in distinct phases of relief growth and decay the transition between which is controlled by a saturation phenomenon related to the growth of spatial correlations the scaling behavior of simulated topography with respect to both time and space is obtained and is shown to be independent of de roughness exponents are found to be independent of de but dependent on the magnitude of initial roughness interface width is shown to grow and decay as a logarithm of time

uplift shortening and steady state topography in active mountain belts we present a tectonic surface process model used to investigate the role of horizontal shortening in convergent orogens and the effects on steady state topography the tectonic model consists of a specified velocity field for the earth9s surface and includes a constant uplift rate and a constant horizontal strain rate which varies to reflect the relative importance of frontal accretion and underplating in an orogenic wedge the surface process model includes incision of a network of rivers formed by collection of applied precipitation and diffusive hillslope mass transfer three non dimensional parameters describe this model a ratio of the maximum horizontal velocity to the vertical velocity a peclet number expressing the efficiency of the hillslope diffusion relative to the uplift rate and a fluvial erosion number reflecting the fluvial incision efficiency relative to the uplift rate a series of models are presented demonstrating the resultant steady state landforms parameterized by these three numbers a finite velocity ratio results in an asymmetric form to the model mountain range although the magnitude of the asymmetry also depends on the peclet number topographic steady state is achieved faster for models with no horizontal component to the velocity field with finite horizontal velocity topographic steady state is achieved only at the scale of the entire mountain range even the first order drainage basins are unstable with time in the presence of horizontal shortening we compare our model results to topographic profiles from active mountain ranges in taiwan new zealand and the olympic mountains of washington state all these examples exhibit asymmetric topographic form with the asymmetry consistent with the polarity of subduction suggesting that horizontal tectonic motion is affecting the macro geomorphic form of these ranges

hydrodynamic description for advective sediment transport processes and rill initiation a physically based model for advective sediment transport during rill initiation is developed based on 1 a short wavelength rescaling of the momentum balance equations for the surface water flux 2 a deforming coordinate system which characterizes local morphological changes of the surface during erosion and 3 a generalized transport function for the surface sediment flux which distinguishes the contributions of diffusive and advective transport a linear stability analysis of the coupled system indicates that an intrinsic minimum transverse length scale for rill initiation is forced by the cross slope pressure gradient in the surface water the wavelength of this initial rill spacing is dependent upon the relative significance of the advective component of sediment transport and the hydraulic efficiency of the surface water flux and is independent of the total length of the hillslope the hydrodynamic model presented can also be used to evaluate the nonlinear development of rills and rill networks subsequent to initiation

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

slope control on the aspect ratio of river basins although it is traditionally thought that drainage basins are geometrically similar we present new results which indicate that the aspect ratio of weakly dissected river basins at large scales 10 103 km2 depends on the surface slope steeper surfaces develop narrower and lengthier basins whereas more gently dipping surfaces develop more equant and wider basins this relationship is interpreted to be related to the nature of water flow over rough surfaces with steeper slopes causing less flow convergence and lengthier and narrower basins we derive an empirical relationship that can be used to infer the slope of a surface on which a river basin acquired its geometry based solely on a measure of its basin form this relation provides a unique means of inferring the relative chronology of river basin development with respect to surface tilting and therefore provides a direct link between river basin morphology and tectonics

a composite analysis of the core of a mature hurricane abstract an unusually large quantity of aircraft data was obtained within the core of hurricane frederic 1979 these data are combined with powell s surface observations of the same storm and composited the data are sufficiently abundant to allow three dimensional kinematic analyses of poorly documented parameters such as divergence and vertical velocity patterns of related but independently determined parameters such as radar reflectivities cloud water concentrations and kinematically derived vertical velocities agree well diagnostic budget analyses of sensible heat and angular momentum are computed for the storm inflow layer the analysis provides a unique quantitative picture of the inflow layer of a mature asymmetric hurricane the depth of the inflow layer decreases with decreasing radius as a result surface drag coefficients derived from angular momentum budgets do not appear to increase with increasing wind speed the sensible heat budget shows downward subgrid scale heat fluxes near cloud

influences of surface processes on fold growth during 3 d detachment folding in order to understand the interactions between surface processes and multilayer folding systems we here present fully coupled three dimensional numerical simulations the mechanical model represents a sedimentary cover with internal weak layers detached over a much weaker basal layer representing salt or evaporites applying compression in one direction results in a series of three dimensional buckle folds of which the topographic expression consists of anticlines and synclines this topography is modified through time by mass redistribution which is achieved by a combination of fluvial and hillslope erosion as well as deposition and which can in return influence the subsequent deformation model results show that surface processes do not have a significant influence on folding patterns and aspect ratio of the folds nevertheless erosion reduces the amount of shortening required to initiate folding and increases the exhumation rates increased sedimentation in the synclines contributes to this effect by amplifying the fold growth rate by gravity the main contribution of surface processes is rather due to their ability to strongly modify the initial topography and hence the initial random noise prior to deformation if larger initial random noise is present folds amplify faster which is consistent with previous detachment folding theory variations in thickness of the sedimentary cover in one or two directions also have a significant influence on the folding pattern resulting in linear large aspect ratio folds our simulation results can be applied to folding dominated fold and thrust belt systems detached over weak basal layers such as the zagros folded belt

development and response of a coupled catchment fan system under changing tectonic and climatic forcing sediment fans are a potentially useful and underexploited recorder of earth s climatic and tectonic history but historical observations have led to conflicting views on the importance of tectonic climatic and lithologic variables in controlling fan morphology and deposition a one dimensional model of a sediment fan and its associated catchment is used to explore the sensitivity of such simple sediment routing systems to perturbations in fault slip and precipitation rates a transport limited catchment is coupled to a fan whose surface slope is set by the balance between catchment sediment efflux and the available tectonically generated basin accommodation rock uplift rate is spatially variable across the model space increasing the fault slip rate or decreasing the precipitation rate leads to an increase in fan slope temporary back stepping of the fan toe and a pronounced angular unconformity conversely a decrease in slip rate or an increase in precipitation rate results in a decrease in fan slope and progradation and eventual stabilization of the fan toe once perturbed the system evolves toward a new equilibrium state with time constants of 0 5 to 2 myr these response times are insensitive to slip rate but are strongly dependent on precipitation rate variations in fan slope are well described by a dimensionless parameter that expresses equilibrium slope as a function of slip rate precipitation rate system size and catchment lithology this parameter holds promise as a predictive tool in inverting the morphology of natural fans for environmental variables

the qs problem sediment volumetric balance of proximal foreland basin systems although the stratigraphy of sedimentary basins depends on the balance between the magnitude and grain size characteristics of the sediment supply qs and the spatial distribution of tectonic subsidence generating accommodation x qs is problematical to measure in present day sediment routing systems and formidably difficult to predict in their ancient counterparts this challenge was tackled by treating the sediment discharge from the outlet of mountain catchments as the result of incision by a drainage network with a bulk diffusivity based on the length over which the mean annual rainfall is concentrated the size relief and slope of palaeo catchments acting as feeders for sediment routing systems are used to run simulations of sediment discharge and bulk diffusivity for a range of annual precipitation values a wide range of observable geological phenomena can be used to converge on the most likely solutions for qs including depositional volumes in the basin and bedrock thermochronology and detrital cosmogenic nuclide dating to constrain catchment erosion rates modelled sediment discharges can be checked with estimates derived from global regressions the sediment efflux of mountain catchments serves as a boundary condition for down system sediment transport and deposition variations in the volumetric ratio of sediment supply to available accommodation qs x determines patterns of transverse versus longitudinal axial sediment dispersal the volumetric ratio may change as a result of variations in climatic parameters tectonic uplift rate and catchment expansion an abrupt climate change to higher precipitation values promotes higher qs x but transient landscape response causes a return to values close to the baseline generating a distinctive down system extension of a gravel spike catchment expansion has a similar but more prolonged effect on gravel progradation in contrast a change in tectonic forcing such as an increase in slip rate on a border fault causes little change in qs x because increased subsidence compensates for the increased sediment supply studies of mid eocene oligocene sediment routing systems in the south central pyrenees allow the discrimination of different types of proximal wedge top sedimentary systems on the basis of the volumetric ratio of qs to accommodation x i small steep local fan systems in tectonically ponded underfilled basins supplied by low sediment discharges ii tectonically guided long range axial systems fed by large sediment discharges from widely spaced palaeovalleys and iii large shallow sloping transverse megafans burying underlying defunct or active tectonic structures supplied by high to very high sediment discharges understanding the role of variations in qs helps to explain the syntectonic evolution of proximal foreland basin systems the oligocene miocene north alpine foreland basin switzerland is qualitatively identified as a high qs example the miocene recent northern apennines of italy as a low qs example and the eocene oligocene southern pyrenees of spain as intermediate in character

two approaches to modeling the initiation and development of rills in a man made catchment 1 surface erosion rills are dominant structures in young developing ecosystems and as such they fundamentally affect water flows for example by channeling surface runoff or by locally changing the infiltration capacity of the soil to successfully model the systems hydrology it is indispensable to take the development of erosion rills into account the goal of this study was to model the emergence of an erosion rill network with total length of 6 km formed during the last few years in the 6 ha large artificial catchment chicken creek near cottbus germany the length and connectivity of the evolving network were quantified from aerial images this analysis showed that the major rill network established already during the first year of ecosystem development we adapted two model approaches to simulate the emergence of erosion rills first we used a self organized critical network approach with soil erosion and sediment deposition governed by a local critical shear stress the second approach based on manning s equation was developed to compare the results of the self organized critical network approach with results from a simple but more physically based approach erosion was triggered in the case of high local shear stress and deposition was calculated from settling velocity of the suspended particles both models were able to reproduce the observed rill network geometric characteristics such as network length and rill depth were simulated in the right order of magnitude the models also managed to describe the position and temporal evolution of the main erosion rills in the catchment

a study of tropical cyclone influence on the generation of internal tides 1 an investigation is made into modifications of the semidiurnal internal tide on the western australian shelf by a passing tropical cyclone current mooring observations are presented taken during the passage of tropical cyclone bobby 1995 over these mooring locations the observations reveal large vertical excursions at near inertial frequency of the isotherm during and following the cyclone s passage this coincides with diminishing semidiurnal baroclinic tides to gain dynamical insight into the observations a fully three dimensional free surface nonlinear hydrostatic model is applied to the western australian shelf the model is initialized with realistic stratification and forced by representative tides and cyclone winds the wind forcing is derived from an idealized analytical cyclone model prescribed from observed cyclone track and central pressure data and the tidal forcing allows for the generation of internal tides the cyclone modifies stratification by turbulent mixing upwelling downwelling and density advection up or down the shelf slope this results in significant changes to internal tide characteristic paths and hence the internal tide generation process on the continental slope mixing is enhanced over the shelf due to shallow topography with respect to the shelf slope region creating a strong density front at the shelf edge observations and modeling show that the water column response to the cyclone passage is most abrupt in shallow water at 125 m then at 300 m depth the model reproduces the main features of the observed inertial oscillations concomitant with the dampening of m2 internal tides after the passage of the cyclone

controls on the spacing and geometry of rill networks on hillslopes rain splash detachment initial hillslope roughness and the competition between fluvial and colluvial transport 1 rill networks have been a focus of study for many decades but we still lack a complete understanding of the variables that control the spacing of rills and the geometry of rill networks e g parallel or dendritic on hillslopes in this paper we investigate the controls on the spacing and geometry of rill networks using numerical modeling and comparison of the model results to terrestrial laser scanner derived topographic data from rill networks formed in physical experiments the landscape evolution model accounts for the transport of sediment due to rain splash and fluvial entrainment as well as the deposition of sediment being advected by the overland flow in order to develop realistic rill networks in the model we find that it is necessary to incorporate the effects of raindrop impact within the fluvial sediment transport process model results are only consistent with those of experiments when raindrop aided fluvial sediment transport is accounted for dendritic networks are often predicted by the model in cases of high initial topographic roughness and high rates of advective fluvial sediment transport relative to diffusive colluvial transport parallel networks form within numerical experiments in low roughness cases under a wide range of relative advective and diffusive transport rates as well as in high roughness cases in which diffusive sediment transport is high relative to advective transport the transition from dendritic to parallel rill networks is shown to occur gradually rather than being associated with a particular threshold finally based on a balance between diffusive and advective sediment transport processes we predict that the mean spacing between parallel rills scales with the square root of the ratio of diffusivity to channel erodibility

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

large scale geomorphology classical concepts reconciled and integrated with contemporary ideas via a surface processes model linear systems analysis is used to investigate the response of a surface processes model spm to tectonic forcing the spm calculates subcontinental scale denudational landscape evolution on geological timescales 1 to hundreds of million years as the result of simultaneous hillslope transport modeled by diffusion and fluvial transport modeled by advection and reaction the tectonically forced spm accommodates the large scale behavior envisaged in classical and contemporary conceptual geomorphic models and provides a framework for their integration and unification the following three model scales are considered micro meso and macroscale the concepts of dynamic equilibrium and grade are quantified at the microscale for segments of uniform gradient subject to tectonic uplift at the larger meso and macroscales which represent individual interfluves and landscapes including a number of drainage basins respectively the system response to tectonic forcing is linear for uplift geometries that are symmetric with respect to baselevel and which impose a fully integrated drainage to baselevel for these linear models the response time and the transfer function as a function of scale characterize the model behavior numerical experiments show that the styles of landscape evolution depend critically on the timescales of the tectonic processes in relation to the response time of the landscape when tectonic timescales are much longer than the landscape response time the resulting dynamic equilibrium landscapes correspond to those envisaged by hack 1960 when tectonic timescales are of the same order as the landscape response time and when tectonic variations take the form of pulses much shorter than the response time evolving landscapes conform to the penck type 1972 and to the davis 1889 1899 and king 1953 1962 type frameworks respectively the behavior of the spm highlights the importance of phase shifts or delays of the landform response and sediment yield in relation to the tectonic forcing finally nonlinear behavior resulting from more general uplift geometries is discussed a number of model experiments illustrate the importance of fundamental form which is an expression of the conformity of antecedent topography with the current tectonic regime lack of conformity leads to models that exhibit internal thresholds and a complex response

regional heat flow variations across the sedimented juan de fuca ridge eastern flank constraints on lithospheric cooling and lateral hydrothermal heat transport seafloor heat flow has been estimated continuously along a transect on the sedimented eastern flank of the juan de fuca ridge to provide constraints on the scale and rate of lateral heat and fluid transport in the upper igneous crust and on the total flux from the young lithosphere beneath the profile extends from 20 km east of the ridge axis where turbidite sediments lap onto the oceanic crust at an age of less than 1 ma and ends 110 km east of the axis over 3 6 ma crust estimated heat flow is derived from the combination of the depth to igneous basement determined from seismic reflection profiles and basement temperatures measured in nine ocean drilling program boreholes along the transect the strategy is based on the knowledge that in this young area upper basement temperatures are locally homogenized by vigorous hydrothermal circulation and hence vary smoothly between drilling sites at the young end of the transect near the region of extensive outcrop heat flow is only 15 of that predicted for lithosphere of this age heat flow increases systematically to the east reaching the full predicted level about 20 km from the point of sediment basement onlap the anomaly can be accounted for by mixing and or eastward flow of cool water in the upper igneous crust beneath the sediment at a darcian rate of the order of 1 m yr a geochemical signature of fresh seawater in basement is observed many tens of kilometers farther to the east although the thermal signature is no longer present along the remainder of the transect the heat flow conforms very well to that predicted by simple boundary layer cooling theory once the thermal effects of rapid sedimentation on this ridge flank are accounted for

transformation of tectonic and climatic signals from source to sedimentary archive sedimentary rocks reflect past tectonic and climatic events numerical simulations suggest that changes in precipitation and in the rate of tectonic uplift affect the grain size and the distribution of sediments deposited downstream

empirical relationship between river slope and the elongation of bars in braided rivers a potential tool for paleoslope analysis from subsurface data abstract paleoslope of ancient river systems is a fundamental parameter needed to reconstruct paleohydrology and paleoclimate from the fluvial sedimentary record the shape of braid bars in 22 modern rivers yields a relationship between average bar elongation length width and river slope steep rivers display more elongated bars than gently dipping reaches this relationship has potential application to ancient braided systems preserved in the subsurface and imaged by 3d seismic data the average elongation of bars identified on a stratal slice through the dagang river deposits in north east china yields a slope prediction which combined with empirical data on grain size and slope of alluvial rivers predicts a median grain size of between 0 1 and 1 mm for the considered river sediment in agreement with grain size data in an adjacent isochronous belt this study provides an additional approach for paleohydraulics in sedimentary basins and grain size prediction in exploration

impact of seafloor sediment permability and thickness on off axis hydrothermal circulation juan de fuca ridge eastern flank sediment permeability plays a key role in controlling both the flux of solute and heat through marine sediments and patterns of hydrothermal circulation within the underlying oceanic crust interlayered silt rich and clay rich sediments almost completely bury basement on the eastern flank of the juan de fuca ridge laboratory measurements indicate that silt rich sediment permeability is 1 to 2 orders of magnitude greater than clay rich sediment permeability at similar depths numerical simulations of coupled fluid flow and heat transfer using a simplified model of a sedimented ridge flank with smooth basement topography illustrate how differences in permeability between the two sediment types can influence patterns of hydrothermal circulation and the flux of heat and solute across the seafloor the layered structure of the model domain is inferred from reflection seismic and seafloor heat flow data two distinct patterns of hydrothermal circulation are obtained depending on whether silt rich or clay rich sediments compose the sediment layer above a permeable upper basement aquifer a clay rich sediment column nearly isolates circulation within the basement aquifer resulting in closed convection computed seafloor heat flow profiles resemble heat flow measurements made on the eastern flank of the juan de fuca ridge computed vertical fluid fluxes across the sediment column are small in agreement with fluid fluxes estimated from sediment geochemical profiles when the sediments are silt rich 17 of the flow within a convection cell crosses the sediment column open convection where basement topography is smooth is probably rare because sediment columns overlying oceanic crust are unlikely to be entirely silt each pattern of convection persists over a wide range of sediment thicknesses for a given sediment permeability and basal heat flow a transition from open to closed convection occurs when the effective permeability of the sediment column is only slightly less than that of an entirely silt rich column thus the addition of only a small amount of clay to an otherwise silt rich sediment column may effectively isolate the crustal aquifer from the ocean

thermomechanical implications of sediment transport for the architecture and evolution of continental rifts and margins erosion and deposition redistribute mass as a continental rift evolves which modifies crustal loads and influences subsequent deformation surface processes therefore impact both the architecture and the evolution of passive margins here we use coupled numerical models to explore the interactions between the surface crust and lithosphere this interaction is primarily sensitive to the efficiency of the surface processes in transporting mass from source to sink if transport is efficient there are two possible outcomes 1 faulting within the zone of extension is longer lived and has larger offsets this implies a reduction of the number of faults and the width of the proximal domain 2 efficient transport of sediment leads to significant deposition and hence thermal blanketing this will induce a switch from brittle to ductile deformation of the upper crust in the distal domains the feedbacks between these two outcomes depend on the extension history the underlying lithospheric rheology and the influence of submarine deposition on sediment transport high erosion sedimentation during early faulting leads to abrupt crustal necking while intermediate syntectonic sedimentation rates over distal deep submarine hotter crust leads to unstructured wide distal domains in models where rheological conditions favor the formation of asymmetric conjugate margins only subaerial transport of sediments into the distal domains can increase conjugate symmetry by plastic localization these models suggest that passive margin architecture can be strongly shaped by the solid earth structure sea level and climatic conditions during breakup

a dynamic model to investigate coupling between erosion deposition and three dimensional thin plate deformation 1 this paper presents a mathematical model developed to investigate fully coupled interactions between erosion deposition and dynamic three dimensional deformation within fold belt settings the mechanical part of the model is an elastic plastic thin plate overlying an inviscid substrate this plate can be compressed from the side and responds by the development of buckle folds the surface topography is advected along with the underlying deforming plate and can be modified through time by a combination of fluvial and hillslope sediment transport the resulting mass redistribution creates loads on the plate which then feed back and influence subsequent deformation erosion and deposition preliminary results calculated with the model indicate that erosion and deposition have two main effects on deformation the first is to decrease the amount of shortening required to initiate folding while the second is to increase the fold wavelength both effects result from the ability of erosion and deposition to reduce the influence of gravity on deformation in the extreme case of efficient erosion and deposition deformation becomes localized on a single large scale mega anticline as opposed to being distributed on a train of anticlines and synclines this study indicates that erosion and deposition play a major role in governing the deformation and topography of fold belts and the sediment routing system acting within such a setting

a three dimensional barotropic model of the response of the australian north west shelf to tropical cyclones abstract a three dimensional barotropic model using a coordinate or depth transformation and forced with tropical cyclone wind and atmospheric pressure fields has been applied to the continental shelf and slope regions of the australian north west shelf the atmospheric pressure field of the cyclone causes a nearly isostatic sea level response and weak currents in an unbounded ocean the wind field would produce currents that circulate around the center of the cyclone and eject water thus tending to reduce sea level the coastline forms a boundary for the ejected water resulting in a large sea level rise and strong currents between the cyclone path and the coastline the model provides a good description of the vertical current shear as observed at a number of moorings during two different cyclones sea level rises are accurately modeled and a reasonable description of observed current strengths is achieved however the predicted currents and sea level changes at offshore stations are sensitive to the

internal tide observations from the australian north west shelf in summer 1995 abstract observations are presented of the internal tide over the continental shelf and slope from a cross section on the australian north west shelf data collected from moored instruments and repeated profile measurements during the summer months of 1995 show an energetic large amplitude shoreward propagating semidiurnal internal tide multiple generation sites are suggested coinciding with near critical bottom slopes in water less than approximately 200 m deep the vertical structure of the internal tide is predominantly a first vertical mode whereas in deeper water over the slope the vertical structure is more complicated with currents and vertical displacements intensified in the lower part of the water column the internal tide is largely confined to a region approximately 100 km wide from water depths between 70 and 1000 m strong generation and dissipation of the internal tide energy is observed over this region and there is evidence that the dissipated energy impacts on the vertical mixing

shaping post orogenic landscapes by climate and chemical weathering the spacing of hills and valleys reflects the competition between disturbance driven or diffusive transport on hillslopes and concentrative or advective transport in valleys although the underlying lithologic tectonic and climatic controls have not been untangled here we measure geochemical and geomorphic properties of catchments in kruger national park south africa where granitic lithology and erosion rates are invariant enabling us to evaluate how varying mean annual precipitation map 470 mm 550 mm and 730 mm impacts hill valley spacing or landscape dissection catchment averaged erosion rates based on 10be concentrations in river sands are low 3 6 m m y and vary minimally across the three sites our lidar derived slope area analyses reveal that hillslopes in the dry site are gentle 3 and short such that the terrain is low relief and appears highly dissected with increasing rainfall hillslopes lengthen and increase in gradient 6 8 resulting in less dissected higher relief catchments the chemical depletion fraction of hilltop regoliths increases with rainfall from 0 3 to 0 7 reflecting a climate driven increase in chemical relative to physical erosion soil catenas also vary systematically with climate as we observe relatively uniform soil properties in the dry site that contrast with leached sandy crests and upper slopes coupled with downslope clay accumulation zones in the intermediate and wet sites the geomorphic texture of this slow eroding granitic landscape appears to be set by climate driven feedbacks among chemical weathering regolith fabric differentiation hydrological routing and sediment transport that enhance the vigor of hillslope sediment transport relative to valley forming processes for wetter climates 2013 geological society of america

fluvial and slope wash erosion of soil mantled landscapes detachment or transport limited many numerical landform evolution models assume that soil erosion by flowing water is either purely detachment limited i e erosion rate is related to the shear stress power or velocity of the flow or purely transport limited i e erosion deposition rate is related to the divergence of shear stress power or velocity this paper reviews available data on the relative importance of detachment limited versus transport limited erosion by flowing water on soil mantled hillslopes and low order valleys field measurements indicate that fluvial and slope wash modification of soil mantled landscapes is best represented by a combination of transport limited and detachment limited conditions with the relative importance of each approximately equal to the ratio of sand and rock fragments to silt and clay in the eroding soil available data also indicate that detachment entrainment thresholds are highly variable in space and time in many landscapes with local threshold values dependent on vegetation cover rock fragment armoring surface roughness soil texture and cohesion this heterogeneity is significant for determining the form of the fluvial slope wash erosion or transport law because spatial and or temporal variations in detachment entrainment thresholds can effectively increase the nonlinearity of the relationship between sediment transport and stream power results from landform evolution modeling also suggest that aside from the presence of distributary channel networks and autogenic cut and fill cycles in non steady state transport limited landscapes it is difficult to infer the relative importance of transport limited versus detachment limited conditions using topography alone copyright 2011 john wiley sons ltd

free surface effects on the near inertial ocean current response to a hurricane abstract during the passage of hurricane frederic in 1979 four ocean current meter arrays in water depths of 100 950 m detected both a baroclinic and a depth independent response in the near inertial frequency band although the oceanic response was predominately baroclinic the hurricane excited a depth independent component of 5 11 cm s 1 the origin and role of the depth independent component of velocity is investigated using a linear analytical model and numerical simulations from a 17 level primitive equation model with a free surface both models are forced with an idealized wind stress pattern based on the observed storm parameters in hurricane frederic in an analytical model the green s function k0 is convolved with the wind stress curl to predict a sea surface depression of approximately 20 cm from the equilibrium position the near inertial velocities are simulated by convolving the slope of the sea surface depression with a second green s function the barotropic current velocities rotate

influence of surface processes and initial topography on lateral fold growth and fold linkage mode elongation of randomly distributed fold segments and their potential linkage are important for hydrocarbon exploration because it can greatly influence the morphology of the reservoir and both migration and accumulation of hydrocarbons in antiformal traps here we study the effects of surface processes and the presence of a topographic slope on the different linkage modes that can occur and how these parameters affect the required horizontal offset for perturbations to link the proposed numerical model represents a sedimentary cover detached over a much weaker basal decollement layer the upper surface is modified by mass redistribution which is achieved by a combination of fluvial and hillslope processes several series of simulations were performed 1 without surface processes or regional slope 2 with regional slope only 3 with fluvial incision and hillslope processes and 4 with hillslope processes only model results show that the presence of a regional slope reduces the critical distance required for the transition between linkage and no linkage modes whereas erosion and redeposition of sediments on the contrary increase this distance the location of the saddle point where fold segments link and its vertical distance to the crests of the anticlines are different compared to the case without erosion or initial topographic slope which potentially can affect the morphology of hydrocarbon traps moreover both erosion and redeposition of sediments enhance the fold elongation growth along the fold axis once the erosion velocity exceeds the folding velocity model results have been compared to the zagros fold belt

numerical treatment of cross shelf open boundaries in a barotropic coastal ocean model abstract using a barotropic coastal ocean model with a straight coastline and uniform cross shelf bottom slope seven different cross shelf open boundary conditions four of which are applied in either implicit or explicit form are compared in three numerical experiments 1 a mound of water is allowed to collapse and radiate waves toward the open boundaries 2 a uniform alongshelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment 3 a uniform cross shelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment the boundary condition which is most transparent to waves consists of a sponge at the outer edge of the model domain with an orlanski radiation condition at the outer edge of the sponge several open boundary conditions perform adequately in the wind stress experiments but the orlanski radiation condition alone without a sponge appears to give the best total performance of thes

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

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

results from a new model of river basin evolution this paper briefly describes a model of the erosional development of catchments and their channel networks the model differentiates between the dominant transport processes in hillslope and channels the development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms the growth of a river basin is qualitatively described the model concepts are used to study the basin during periods of growth transient periods as well as during dynamic equilibrium this leads to hypotheses about the relationship between slopes relief tectonic uplift erodability runoff and catchment area it is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation

inception of channelization and drainage basin formation upstream driven theory the ubiquitous presence of river drainage basins in the terrestrial environment suggests that distributed overland flow generated by rainfall tends to spontaneously organize itself into dendritic systems of discrete channels several recent numerical models describe the evolution of complete drainage basins from the initial condition of rainfall on a flat tilted plateau the surface of which has been provided with random elevation perturbations these analyses model overland flow via the assumption of a perfect balance between gravitational and frictional terms i e in terms of normal flow linear stability analysis applied to the normal flow model has been shown however to fail to select a wavelength corresponding to a finite distance of separation between incipient basins this suggests that the normal flow model may not be a sufficient basis for studying drainage basin development especially at the finest scales of morphologic significance here the concept of a threshold condition for bed erosion is combined with an analysis of the full equations of shallow overland flow in order to study wavelength selection classical linear stability analysis is shown to be inadequate to analyse the problem at the level of inception an alternative linear analysis of bed perturbations based on the threshold condition is developed and shown to lead to the selection of finite wavelength of the correct order of magnitude the analysis here is driven from the upstream direction in that bed erosion is first caused only when sufficient flow has gathered from upstream due to rainfall a downstream driven theory of incipient channelization that is not necessarily dependent upon rainfall is presented in izumi 1993 and is presently in preparation for publication

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

a numerical study of the storm surge generated by tropical cyclone jane abstract in 1983 tropical cyclone jane crossed the north west coast of australia generating a storm surge currents associated with this storm surge were recorded at two offshore moorings south of the cyclone track the data from these moorings are suggestive of the propagation of a continental shelf wave between the two stations this hypothesis is tested by carrying out a numerical simulation of this storm surge based on the depth integrated shallow water equations with wind wave enhanced bottom friction analysis of the numerical results shows that the storm surge can be interpreted as due to continental shelf waves

the influence of surface slope on the shape of river basins comparison between nature and numerical landscape simulations we investigate the influence of initial conditions of slope and surface roughness on the shape length to width aspect ratio of incipient drainage basins in numerical experiments of simple tilted surfaces using the cascade code of landscape evolution comparison with data on the shape of river basins in nature shows that simple rules of the steepest descent routing of water are sufficient to account for a natural range of incipient drainage basin shape independently of the erosion processes at work to produce numerical basins that respect the main aspect ratio of natural drainage basins one must use very low initial regional surface slopes of less than 1 at the scale of the entire drainage basins and a local roughness slope of less than 3 at the scale of local surface irregularities numerical studies addressing real study cases may take advantage of the relation between local roughness and regional slope in order to produce catchment aspect ratios similar to the natural studied cases

role of river incision in enhancing deformation many active compressional belts contain examples of transverse rivers intersecting anticlines at their highest structural and topographic position this unusual association between rivers and doubly plunging anticlines at relatively small scales is usually explained by some form of antecedence or superposition in this article i suggest an alternative explanation i e that river erosion unloads the crust and that this process causes local deformation to be enhanced in the vicinity of rivers i show the plausibility of this hypothesis with the aid of a coupled three dimensional mechanical surface process mathematical model the conclusion is that river incision can have a major influence on deformation of the surrounding crust if incision occurs at the same time that the crust is deforming plastically in response to regional compression in this case incision amplifies background deformation at a relatively small scale leading to the formation of noncylindrical folds with culminations coinciding with river incision in the absence of regional deformation the response of the crust to river incision is small and of long wavelength because it is governed by flexural isostasy of relatively rigid elastic crust thus whether rivers exert an influence on local deformation depends critically on the timing between river incision and regional deformation this point may explain why in some cases rivers appear to have had no significant influence on local deformation whereas in other cases they have