modelling shoreface profile evolution current knowledge of hydro sediment and morpho dynamics in the shoreface environment is insufficient to undertake shoreface profile evolution modelling on the basis of first physical principles we propose a simple panel type model to map observed behaviour the internal dynamics are determined by slope dependent wave induced cross shoreface transports while the external driving factors are lateral sediment supply and sea level rise this model concept is tested with reasonable success against the observed behaviour of the central holland coast considering two hindcast periods one covering the evolution over the last century the other the subboreal subatlantic evolution a limitation of this model is that the cross shoreface dynamics are solely steered by the variations of shoaling short waves since a variety of other wave and current dynamics may be expected to be present in the coastal boundary layer it may well be that the effects of the mechanisms and conditions which are not represented are hidden in the coefficients of the sediment transport formula this limits the accuracy of the coefficients as used and our findings should be considered as an order of magnitude estimate only indeed behaviour oriented modelling implies that generalization of results to arbitrary situations and conditions is not straightforward yet we expect that some of the conclusions are more generally applicable this concerns the substantiation of the assumption that the upper shoreface responds on a much smaller time scale than the lower shoreface and the idea that the shoreface profile is not always and everywhere in equilibrium with its forcing a worthwhile observation from the holland coast application is that the bottom slope effect on the transport is only important at geological time scales the profile evolution at the engineering time scales say 10 to 100 years is effectively quasi static in that there is no feedback between the long term averaged transport and the state of the profile this implies that at these smaller scales the profile changes can be predicted on the basis of a static sediment balance this does not mean that the gravitational downslope transport is unimportant as a physical phenomenon in coastal profile evolution it is only unimportant if a highly aggregated model like this is applied at relatively short time scales

the influence of climate on the tectonic evolution of mountain belts simple physical arguments analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate however obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging spatial correlations between intense precipitation or glaciation and zones of rapid rock uplift have indeed been documented in numerous mountain ranges and are consistent with model predictions more compelling evidence such as tectonic changes in response to rather than just coincident with climate change has however rarely been documented triggered by a climate driven increase in erosion rate friction dominated mountain ranges are expected to show a number of simultaneous responses a decrease in the width of the range a temporary increase in sediment yield a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins the most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the european alps and the st elias range of alaska field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view

landsliding and the evolution of normal fault bounded mountains much of the tectonic and climatic history in high relief regions such as the mountains of the western u s basin and range province is contained in the morphology of hillslopes drainage networks and other landforms that range in scale from 10 1 to 101km to understand how these landforms evolve we have developed a numerical landscape evolution model that combines a detailed tectonic displacement field with a set of physically based geomorphic rules bedrock landsliding long recognized as a significant geomorphic process in mountainous topography is for the first time explicitly included in the rule set in a series of numerical experiments we generate synthetic landscapes that closely resemble mountainous topography observed in the basin and range the production of realistic landscapes depends critically on the presence of bedrock landslides and landsliding yields rates of long term erosion that are comparable in magnitude to those of fluvial erosion the erosive efficiency of bedrock landsliding implies that hillslopes may respond very quickly to changes in local base level and that fluvial erosion is the rate limiting process in steady state experimental landscapes our experiments generate power law distributions of landslide sizes somewhat similar to both field and laboratory observations thus even a simple model of bedrock landsliding is capable of quantitatively reproducing mountainous topography and landslide distributions and represents a significant step forward in our understanding of the evolution of normal fault bounded ranges

forward and back diffusion through argillaceous formations the exchange of solutes between aquifers and lower permeability argillaceous formations is of considerable interest for solute and contaminant fate and transport we present a synthesis of analytical solutions for solute diffusion between aquifers and single aquitard systems validated in well controlled experiments and applied to several datasets from laboratory and field scale problems with diffusion time and length scales ranging from 10 2 108 years and 10 2 102 m one dimensional diffusion models were applied using the method of images to consider the general cases of a finite aquitard bounded by two aquifers at the top and bottom or a semi infinite aquitard bounded by an aquifer the simpler semi infinite equations are appropriate for all domains with dimensionless relative diffusion length zd 0 7 at dimensionless length scales above this threshold application of semi infinite equations to aquitards of finite thickness leads to increasing errors and solutions based on the method of images are required measured resident solute concentration profiles in aquitards and flux averaged solute concentrations in surrounding aquifers were accurately modeled by appropriately accounting for generalized dynamic aquifer aquitard boundary conditions including concentration gradient reversals dimensionless diffusion length scales were used to illustrate the transferability of these relatively simple models to physical systems with dimensions that spanned 10 orders of magnitude the results of this study offer guidance on the application of a simplified analytical approach to environmentally important layered problems with one or two diffusion interfaces

formation mechanisms for self organized kilometer scale shoreline sand waves the feedbacks between morphology and waves through sediment transport are investigated as a source of kilometer scale shoreline sand waves in particular the observed sand waves along srd holmslands tange denmark are examined we use a linear stability model based on the one line approximation linking the bathymetry to the perturbed shoreline previous models that consider the link by shifting the equilibrium profile and neglecting the curvature of the depth contours predict a positive feedback only if the offshore wave incidence angle c is above a threshold c 42 considering curvilinear depth contours and using a linearly decaying perturbation in bed level we find that c can vary over the range 0 90 depending on the background bathymetric profile and the depth of closure dc associated to the perturbed wave refraction there are two sources of instability the alongshore gradients in wave angle wave angle mechanism and the alongshore gradients in wave energy induced by wave crest stretching wave energy mechanism the latter are usually destabilizing but the former are destabilizing only for large enough dc steep foreshores and gently sloping shorefaces the critical angle comes out from the competition between both mechanisms but when both are destabilizing c 0 in contrast with earlier studies the model predicts instability for the holmslands tange coast so that the observed sand waves could have emerged from such instability the key point is considering a larger dc that is reasonably supported by both observations and wave climate which brings the wave angle mechanism near the destabilizing threshold

interplay between mass movement and fluvial network organization an example from southern apennines italy abstract relationships between landslides and drainage network arrangement have been investigated by classical and quantitative geomorphological analysis in an intermountain valley i e the upper valley of the sinni river of the southern italian apennines the 120 km 2 wide test area is characterized by very low grade metamorphic rocks mainly shale and associated crystalline metamorphic rocks which underwent high exhumation and uplift rates during quaternary times we recognized and mapped 534 landslides through the stereoscopic interpretation of one set of 20 panchromatic aerial photographs 1 33 000 scale landslides were classified according to both type of movement and relative age we detected and mapped 35 new landslides after a long rainfall period during the winter 2008 2009 the percentage of area affected by landslides d l of the area has a high value about 37 analysis of distribution of landslides areas within different age classes suggests that recent present day landslide distribution is strongly influenced by the legacy of widespread large and ancient landslides probably generated within a different morpho climatic setting a quantitative geomorphological analysis of the drainage network has been performed to evaluate the influence of landslide processes on morphometric properties of the drainage network in particular the degree of hierarchical organization of the drainage network is assessed through the hierarchical anomaly density a measure of the number of anomalous confluences i e channels of u order not flowing in channels of order u 1 in drainage basins on the basis of statistical relationships between morphometric indices of the drainage network and d l we argue that the activity of more recent mass movements rather than very old landslides can act as a disturbing element within the development of the drainage network generating anomalous confluences of the 1st order empirical relationships between suspended sediment yield and some geomorphic parameters of the drainage network allowed the estimation of short term denudation rates in the study area the comparison between uplift and denudation rates suggests that the landscape system has not reached a steady state between uplift and erosion in which tectonic uplift can represent a disturbing element within the recent morphogenesis on the basis of the data presented large mass movements in the study area are mainly linked to the relief growth promoted by quaternary tectonics whereas litho structural and morpho climatic factors assume a minor role

prediction of cross shore sediment transport at different spatial and temporal scales abstract coastal sediment transport and associated morphological change can be examined at many spatial and temporal scales these scales range from instantaneous movement of single grains on a time scale of the local turbulence to seasonal and long term movement of large sand bodies such as longshore bars and tidal deltas researchers have begun to recognize that a first principles microscale approach to calculating long term and large scale megascale coastal change may not be possible or even adequate therefore new approaches are being sought to advance quantitative understanding and prediction of large scale coastal behavior the present paper opens with a discussion of compatible spatial and temporal scales for calculating sediment transport and morphology change motivation is given for the need to calculate morphologic change at scales greater than the typical one of microscale example calculations are made at different scales showing the assumptions and approximations of each the main conclusion is that calculations at different scales can be related and reconciled if limitations in prediction of initial and boundary conditions and in the fluid forcing are recognized

a viscoelastic earthquake cycle model for taiwan 1 while recent geophysical measurements including global positioning system gps surveys have clarified the mechanisms of active mountain building in the taiwan arc continent collision the geometry of faults beneath the island remains unclear in this paper we use gps data collected before the 1999 chi chi earthquake to image the geometry of active faults under taiwan and estimate slip rates on these faults we invert the data using kinematic and mechanical earthquake cycle models consisting of faulting in an elastic lithosphere overlying a viscoelastic asthenosphere in the kinematic model uniform slip is prescribed on the faults at a constant rate while in the mechanical model the faults slip in response to shear stresses in the lithosphere these models explain the essential features of both the horizontal and vertical gps velocity fields we find a 27 39 km thick elastic lithosphere overlying a viscoelastic asthenosphere with maxwell relaxation time of 15 80 years or viscosity of 0 5 4 1019 pa s the models produce a combined slip rate of 30 50 mm yr on the frontal thrusts in western taiwan and 60 80 mm yr of slip on the longitudinal valley fault inversion of the data using both models indicates a decollement dipping 10 under western taiwan and increasing in dip by no more than 10 under the central ranges and eastern taiwan

anisotropy of magnetic susceptibility of the jingou river section implications for late cenozoic uplift of the tian shan better constraints on the uplift history of tian shan will increase our understanding of both mountain building processes and deformation patterns related to the india asian collision anisotropy of magnetic susceptibility ams holds great potential to track variations in tectonic strain which is ultimately responsible for mountain uplift here we present an ams record spanning the interval of 28 4 ma from the fluviolucastrine jingou river section in the tian shan foreland rock magnetic measurements show that the ams are dominated by antiferromagnetic hematite and some paramagnetic minerals both of which have a crystallographic preferred orientation and therefore the ams sequence may be applied to reconstruct tectonic strain although the principal minimum k min direction is nearly perpendicular to the bedding plane indicative of a predominantly sedimentary fabric for the section the tightly grouped principal maximum k max parallel to the fold axis suggests that the section was subject to an embryonic deformation at least since the late oligocene the k max direction is most likely associated with the n s strain caused by the india asian collision during the intervals of 23 3 20 0 ma and 16 5 14 0 ma the strain markedly increased as evidenced by more tightly grouped k max directions and k min largely distributed within a clear n s girdle these two intervals are accompanied by changes in sedimentary facies higher energy conditions and doubled sedimentation rates and are interpreted as the periods when the tian shan experienced significant uplift a conceptual model is tentatively proposed to reconcile various timings for the tian shan uplift

evaluation of depth of closure using data from duck nc usa using 12 years of frequent high precision profiles collected on a wave dominated sandy oceanic beach to 8 m depth the characteristics and interpretation of depth of closure or the seaward limit of significant profile change is critically examined this includes evaluation of the predictive capability of d1 the seaward boundary of the littoral zone as originally defined by hallermeier 1981 hallermeier r j 1981 a profile zonation for seasonal sand beaches from wave climate coastal eng 4 253 277 depth of closure during major erosional events is usually produced by the seaward limit of offshore bar movement following the original recommendation of hallermeier 1981 d1 based on 12 h exceeded wave height and a reference depth of mean low water provides a robust limit to the observations using a 6 cm change criterion empirically the observed depth of closure is 69 of d1 although the scatter is large this scatter is partly controlled by pre event profile shape most particularly bar configuration depth of closure under accretional conditions can also be measured but it is time scale dependent as accretion is a slow steady process d1 underpredicts closure for accretional situations time interval e g annual depth of closure represents the integral effect of erosional and accretional events an important observation of the data is that depth of closure increases with time scale however the full population of time interval observations is not resolved at duck due to the measurement limit 8 m depth as time interval increases from 1 year to 8 years less cases close most non closing time interval cases coincide with the periods influenced by the most energetic wave events however time interval closures are generally deeper than the biggest event closure in the period showing that it represents more than the largest event the frequency distribution of the data suggests that most if not all of these missing data simply represent closures deeper than 8 m depth up to a 4 year time interval d1 t appears to provide a reasonable limit to the quantified observations it is an interesting result that d1 an event based approach might provide a limit to closure over periods up to 4 years as these time interval closures are generally larger than those produced by single storms therefore the general applicability of this result for more complete data sets or on rapidly evolving i e eroding or accreting coasts is uncertain the present data also suggest that on swell dominated coastlines where accretional processes are dominant d1 may underpredict closure suggesting an important limitation to this approach but as sediment would be moving onshore this may not be a practical problem therefore within the limits of the data set hallermeier s 1981 approach is found to define robust estimates of depth of closure particularly for individual erosional events this useful result is expected to find widespread application in coastal geology and engineering

accelerated relative sea level rise and rapid coastal erosion testing a causal relationship for the louisiana barrier islands abstract the role of relative sea level rise as a cause for the rapid erosion of louisiana s barrier island coast is investigated through a numerical implementation of a modified bruun rule that accounts for the low percentage of sand sized sediment in the eroding louisiana shoreface shore normal profiles from 150 km of coastline west of the mississippi delta are derived from bathymetric surveys conducted during the 1880s 1930s and 1980s an rms difference criterion is employed to test whether an equilibrium profile form is maintained between survey years only about half the studied profiles meet the equilibrium criterion this represents a significant limitation on the potential applicability of the bruun rule the profiles meeting the equilibrium criterion along with measured rates of relative sea level rise are used to hindcast shoreline retreat rates at 37 locations within the study area modeled and observed shoreline retreat rates show no significant correlation thus in terms of the bruun approach relative sea level rise has no power for hindcasting and presumably forecasting rates of coastal erosion for the louisiana barrier islands

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

hummocky cross stratification tropical hurricanes and intense winter storms most previous workers have inferred a storm origin for hummocky cross stratification which typically occurs in shallow marine deposits on the modern earth the only storms capable of profoundly affecting shallow marine depositional environments are severe tropical cyclones hurricanes and mid latitude winter wave cyclones intense winter storms this paper examines the palaeogeographic distribution including palaeolatitude and palaeogeographic setting of 107 occurrences of hummocky cross stratification ranging in age from the proterozoic to recent in each of these stratigraphic units both palaeolatitude and palaeogeography are consistent with a direct storm influence associated with the passage of hurricanes or winter storms directly over the site of deposition this palaeogeographic evidence lends support to the inferred storm origin for hummocky cross stratification further the distribution of the structure suggests that most occurrences 73 were generated by tropical hurricanes the remaining 27 being generated by intense mid latitude winter storms the preferential generation of hummocky cross stratification by hurricanes is consistent with 1 the known differences in the nature of the bottom flows generated by the two major storm types and 2 the inferred nature of the flows which form hummocky cross stratification hurricanes couple less effectively with the water column than do intense winter storms due to this ineffective coupling hurricane generated bottom flows tend to be oscillatory or multidirectional dominant with only minor unidirectional components of motion in contrast intense winter storms generally do couple effectively with the water column generating bottom flows which possess a dominant or significant unidirectional component most previous workers have suggested that hummocky cross stratification forms under oscillatory or multidirectional dominant flow thus it is conceptually reasonable that the vast majority of ancient occurrences of hummocky cross stratification were probably hurricane generated as suggested by the aforementioned palaeogeographic distribution the proterozoic palaeozoic neogene and quaternary were times when global climate was similar to that of today the distribution of hummocky cross stratification deposited during these times suggests that both hurricanes and intense winter storms occupied latitudinal belts during these times which were essentially identical to those occupied by their modern counterparts the mesozoic and palaeogene were non glacial times when global climate was much warmer than that of today the distribution of hummocky cross stratification deposited during this interval suggests that hurricanes occurred more frequently at higher latitudes during non glacial times than they do at present the possibility of a broadened hurricane belt during the mesozoic and palaeogene is consistent with climatic considerations a limited number of mesozoic and palaeogene rock units containing hummocky cross stratification were deposited in palaeogeographic settings that preclude a direct hurricane influence these examples were deposited in the middle latitudes suggesting that intense winter storms continued to form hummocky cross stratification in the middle latitudes during these much warmer times some previous workers have suggested that tsunamis may be capable of generating hummocky cross stratification the palaeogeographic distribution of the structure does not support an origin due to tsunamis lacustrine examples of hummocky cross stratification reported herein are the first known non marine occurrences they suggest that storm effects strongly influence the sedimentary record of some lakes

high angle wave instability and emergent shoreline shapes 1 modeling of sand waves flying spits and capes 1 contrary to traditional findings the deepwater angle of wave approach strongly affects plan view coastal evolution giving rise to an antidiffusional high wave angle instability for sufficiently oblique deepwater waves with angles between wave crests and the shoreline trend larger than the value that maximizes alongshore sediment transport 45 a one contour line numerical model shows that a predominance of high angle waves can cause a shoreline to self organize into regular quasiperiodic shapes similar to those found along many natural coasts at scales ranging from kilometers to hundreds of kilometers the numerical model has been updated from a previous version to include a formulation for the widening of an overly thin barrier by the process of barrier overwash which is assumed to maintain a minimum barrier width systematic analysis shows that the wave climate determines the form of coastal response for nearly symmetric wave climates small net alongshore sediment transport cuspate coasts develop that exhibit increasing relative cross shore amplitude and pointier tips as the proportion of high angle waves is increased for asymmetrical wave climates shoreline features migrate in the downdrift direction either as subtle alongshore sand waves or as offshore extending flying spits depending on the proportion of high angle waves numerical analyses further show that the rate that the alongshore scale of model features increases through merging follows a diffusional temporal scale over several orders of magnitude a rate that is insensitive to the proportion of high angle waves the proportion of high angle waves determines the offshore versus alongshore aspect ratio of self organized shoreline undulations

simulation of large scale coastal change using a morphological behaviour model abstract quantitative simulation of large scale coastal behaviour lscb is possible using a model based only on principles of sand mass conservation and geometric rules for shoreface and active sand body morphology dynamic processes are subsumed into a set of parameters that define the geometry of the active cross shore profile which in turn can represent an entire coastal cell the parameters together with a set of local behaviour rules governing adjustments at discrete points along the profile provide a simple formulation that is constrained by sediment mass balance to yield emergent numerical solutions for profile kinematics the emergent qualities of this shoreface translation model are exemplified in simulation experiments on changes to sand deposits on the southeastern australian coast and shelf during the post glacial marine transgression in another example the model is used to simulate lscb over engineering time scales at an idiosyncratic site both examples illustrate the over riding importance of small residual sand movements that accumulate through time to cause lscb in comparison to gross sand movements the residuals are too small to measure directly or predict on the basis of available theory exploratory inverse simulation provides a quantitative method for side stepping these limitations the shoreface translation model therefore is used as a tool to explore possible forms of coastal behaviour through an approach that incorporates available data along with theoretical considerations validation is not strictly possible for this type of inverse approach so the degree to which a simulation reproduces observed features in nature is a measure of its success

simulating the evolution of coastal morphology and stratigraphy with a new morphological behaviour model geombest abstract a new morphological behaviour model is used to simulate evolution of coastal morphology associated with cross shore translations of the shoreface barrier and estuary the model encapsulates qualitative principles drawn from established geological concepts that are parameterized to provide quantitative predictions of morphological change on geological time scales order 10 3 years as well as shorter time scales applicable for long term coastal management order 10 1 to 10 2 years changes in sea level and sediment volume within the shoreface barrier and estuary drive the model behaviour further parameters defining substrate erodibility sediment composition and time dependent shoreface response constrain the evolution of the shoreface towards an equilibrium profile results from numerical experiments are presented for the low gradient autochthonous setting of north carolina and the steep allochthonous setting of the washington shelf simulations in the currituck region of north carolina examined the influence of sediment supply substrate composition and substrate erodibility on barrier transgression results demonstrate that the presence of a lithified substrate reduces the rate of barrier transgression compared to scenarios where an erodible sand rich substrate exists simulations of the washington coast 20 km north of the columbia river confirmed that the model can reproduce complex stratigraphy involving regressive and transgressive phases of coastal evolution results suggest that the first major addition of sediment to the shelf occurred around 12 900 years ago and resulted from the rapid addition of sediment volume from the columbia river attributed to the missoula floods this was followed by a period where little or no sediment was added 12 400 9100 bp and a third period when most sediment was added to the shelf 9100 bp to present from the columbia river comparing results from each setting demonstrates an indirect control that substrate slope has on shoreface transgression rates shoreface transgression is shown to be sensitive to the rate of estuarine sedimentation with the sensitivity increasing as substrate slope decreases

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

thermochronological analysis of the dynamics of the southern alps new zealand the isotopic ages of material exposed close to the alpine fault in the southern alps new zealand vary in a consistent fashion along the orogen for the k ar system muscovite and biotite ages display two distinct spatial trends that meet in the area of fox glacier where a strong relationship is observed between k ar age and altitude excess argon is present in samples between mount kinnaird and haast pass in the southwest of the southern alps giving unrealistically old inconsistent k ar ages across this region incorporation of excess argon appears to be highly variable however and minimization of its influence on dynamical interpretations of thermochronology is possible through considering only the youngest age from a given area such treatment indicates that excess argon contamination does not play an important role in the systematic k ar age variation identified along the southern alps the observed age distribution is consistent with estimates of the modern rapid uplift and exhumation of the southern alps beginning ca 5 ma k ar mica ages older than this south of the copland valley indicate that substantial late cenozoic exhumation occurred along the southern alps prior to the development of the modern tectonic regime but at rates lower than at present total exhumation during the current phase of tectonism in the southern alps decreases from the whataroa river southward north of fox glacier the southern alps have attained a dynamical steady state such that the observed distribution of exhumation will not change significantly with further deformation and denudation under current conditions

thermal and kinematic modeling of bedrock and detrital cooling ages in the central himalaya 1 we introduce a new method that convolves detrital mineral cooling ages with digital elevation models to test numerical models of erosion in collisional orogens along a trans himalayan transect in central nepal we develop a kinematic and thermal model to predict variations in bedrock cooling ages in modern himalayan topography the model assumes a thermal steady state and utilizes a simple ramp and flat style decollement representing the main himalayan thrust the model also assumes a topographic steady state such that overthrusting is balanced by erosion to maintain a constant topographic profile erosion rates display strong spatial variations as a function of the angle between the slope of the topographic surface and the trajectories of rock particles approaching the surface to predict the detrital cooling age signal we combine the distribution of bedrock cooling ages within a catchment with the rate of erosion and distribution of muscovite predicted cooling age distributions are compared with detrital 40ar 39ar muscovite data to assess varying tectonic and erosion scenarios such cooling age distributions are very sensitive to how much of the total plate convergence is expressed as erosion of the overthrusting plate the best fit model assigns 4 6 km myr 1 of overthrusting equivalent to as much as 1 5 2 km myr 1 of vertical erosion to the asian plate although a trade off exists between ramp geometry along the decollement and the best fit rate only a narrow range of ramp dips decollement depths and erosionally compensated overthrusting rates are compatible with the observed detrital ages

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

on steady states in mountain belts the dynamic system of tectonics and erosion contains important feedback mechanisms such that orogenic systems tend toward a steady state this concept is often invoked but the nature of the steady state is commonly not specified we identify four types of steady state that characterize the orogenic system and illustrate these cases by using numerical model results and natural examples these types are 1 flux steady state 2 topographic steady state 3 thermal steady state and 4 exhumational steady state they refer to the erosional flux the topography the subsurface temperature field and the spatial pattern of cooling ages respectively models suggest that the topography will reach a steady mean form at the scale of an orogenic belt but perfect topographic steady state is unlikely to be achieved at shorter length scales thermal steady state is a precondition for exhumational steady state and in the case of temperature dependent deformation topographic steady state exhumational steady state is characterized by reset age zones spatially nested according to closure temperature as illustrated in natural systems from new zealand the cascadia accretionary margin and taiwan

the effects of lithology and base level on topography in the northern alpine foreland abstract the evolution of topography is driven by climate and tectonics and strongly influenced by substrate properties and different base levels the contributions of these factors may vary in space and time and are thus difficult to disentangle our study area the hausruck kobernauserwald range has a rather uniform climatic and tectonic history but is drained by rivers with different base levels and consists of contrasting sedimentary rocks mainly due to different sedimentation environments this makes them an ideal location to study the effects of lithology and base level on topography to decipher the roles of these influences we used a high resolution digital elevation model and performed a series of morphometric analyses longitudinal river profiles indicate that all channels in the study area independent from base level bed rock and overall morphological expression are well graded hypsometry shows no evidence for base level effects on the present topography while variations in the hypsometric curves coincide with lithological differences this is also reflected in contrasts of mean elevation and slope distributions lithology dependent variations in channel concavity and catchment wide hypsometric integrals show that lithology controls both channel incision and hillslope processes in the study area our results further indicate that variations in channel and catchment metrics are not linked to the prevalence of different rock types alone but to different successions of lithological units along the channels and within the catchments variations in channel slope and geomorphological mapping suggest that lithology dependent landsliding is the dominant process causing the observed large scale landscape diversity in the hausruck kobernauserwald range

restraining bend tectonics in the santa cruz mountains california imaged using 10be concentrations in river sands reverse faults frequently generate large and destructive earthquakes yet their seismic hazard remains diffi cult to assess with traditional paleoseismic tools because their surface expressions are often complex and subtle this contribution assesses the utility of millennial scale denudation rates derived from in situ cosmogenic 10be for revealing the spatial patterns and magnitudes of rock uplift produced by slip along reverse faults we present seventeen basin averaged denudation rates from rivers draining the santa cruz mountains along the san andreas fault california usa which closely reproduce known uplift rate patterns associated with a restraining bend along the fault an additional component of vertical deformation appears to be superposed on the uplift due to the restraining bend this may result from regional transpression further irregularities in the fault trace or interactions with neighboring faults our results indicate that 10be derived denudation rates can reveal patterns of rock uplift adjacent to reverse faults over length scales relevant for characterizing their seismic hazard potential

application of multivariate statistical techniques in alongshore differentiation of coastal barriers abstract this paper investigates the existence of statistical correlations and relationships between geological and oceanographic parameters along a coastal barrier system in southern brazil the existence of few statistical studies on coastal barriers motivated the use of multivariate statistical techniques that take environmental parameters such as coastal morphological sedimentary features and their morphometric measurements into account the hierarchical cluster analysis hca and principal component analysis pca were used to assess the spatial variations of fourteen parameters driving the current and past behavior of this coastal barrier system at fourteen locations through the application of hca these locations were divided into four groups groups 1 2 3 and 4 the hca results were analyzed using pca the first pc1 and the second pc2 principal components together explained at least 76 4 of the variability of all four groups the most important geological and oceanographic parameters that were correlated to pc1 and pc2 were different in each group in general the shoreface slope and shoreface dimensions were common to all groups as pc1 correlated parameters being the most important ones regarding data variability in addition for the progradational groups 1 and 4 retrogradational group 2 and aggradational barriers group 3 pca indicated that shoreline orientation wave exposure and beach type are secondary but relevant factors controlling the past and current behavior of coastal barriers in southern brazil

late quaternary sea level change and evolution of belfast lough northern ireland new offshore evidence and implications for sea level reconstruction the interplay of eustatic and isostatic factors causes complex relative sea level rsl histories particularly in paraglacial settings in this context the past record of rsl is important in understanding ice sheet history earth rheology and resulting glacio isostatic adjustment field data to develop sea level reconstructions are often limited to shallow depths and uncertainty exists as to the veracity of modelled sea level curves we use seismic stratigraphy 39 vibrocores and 26 radiocarbon dates to investigate the deglacial history of belfast lough northern ireland and reconstruct past rsl a typical sequence of till glacimarine and holocene sediments is preserved two sea level lowstands both max 40 m are recorded at c 13 5 and 11 5k cal a bp each is followed by a rapid transgression and subsequent periods of rsl stability the first transgression coincides temporally with a late stage of meltwater pulse 1a and the rsl stability occurred between c 13 0 and c 12 2k cal a bp younger dryas the second still slowstand occurred between c 10 3 and c 11 5k cal a bp our data provide constraints on the direction and timing of rsl change during deglaciation application of the depth of closure concept adds an error term to sea level reconstructions based on seismic stratigraphic reconstructions

modes of cross shore sediment transport on the shoreface of the middle atlantic bight the mechanisms responsible for onshore and offshore sediment fluxes across the shoreface zone seaward of the surf zone were examined in a 3 year field study the study was conducted in the southern part of the middle atlantic bight in the depth region 7 17 m using instrumented tripods supporting electromagnetic current meters pressure sensors suspended sediment concentration sensors and sonar altimeters the observations embraced fairweather moderate energy swell dominated and storm conditions cross shore mean flows ranged from near zero during fairweather to 20 cm s 1 during the storm oscillatory flows were on the order of 10 cm s 1 during fairweather and 100 cm s 1 during the storm suspended sediment concentrations at about 10 cm above the bed were 5 kg m 3 during the storm three methods were applied to evaluate the relative importance of incident waves long period oscillations mean flows and gravity in effecting shoreward or seaward sediment flux 1 an energetics transport model was applied to instantaneous near bottom velocity data 2 higher moments of near bottom flows were estimated and compared and 3 suspended sediment fluxes were estimated directly from the instantaneous products of cross shore velocity and suspended sediment concentration the results show that measurable contributions were made by all four of the processes most significantly mean flows were seen to dominate and cause offshore fluxes during the storm and to contribute significantly to onshore and offshore flux during fairweather and moderate energy incident waves were in all cases the major source of bed shear stress but also caused shoreward as well as seaward net sediment advection low frequency effects involving wave groups and long period waves made secondary contributions to cross shore sediment flux contrary to expectations low frequency fluxes were just as often shoreward as seaward whereas cross correlations between suspended sediment concentration and the instantaneous near bottom current speed were high and in phase under storm conditions they were weak and out of phase during fairweather conditions this suggests that simple energetics models are probably inadequate for predicting fairweather transport of suspended sediment

wave angle control of delta evolution 1 wave influenced deltas with large scale arcuate shapes and demarcated beach ridge complexes often display an asymmetrical form about their river channel here we use a numerical model to demonstrate that the angles from which waves approach a delta can have a first order influence upon its plan view morphologic evolution and sedimentary architecture the directional spread of incoming waves plays a dominant role over fluvial sediment discharge in controlling the width of an active delta lobe which in turn affects the characteristic rates of delta progradation oblique wave approach and a consequent net alongshore sediment transport can lead to the development of morphologic asymmetry about the river in a delta s plan view form this plan form asymmetry can include the development of discrete breaks in shoreline orientation and the appearance of self organized features arising from shoreline instability along the downdrift delta flank such as spits and migrating shoreline sand waves features observed on natural deltas somewhat surprisingly waves approaching preferentially from one direction tend to increase sediment deposition updrift of the river this morphodynamic groin effect occurs when the delta s plan form aspect ratio is sufficiently large such that the orientation of the shoreline on the downdrift flank is rotated past the angle of maximum alongshore sediment transport resulting in preferential redirection of fluvial sediment updrift of the river mouth

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

rollover drowning and discontinuous retreat distinct modes of barrier response to sea level rise arising from a simple morphodynamic model we construct a simple morphodynamic model to investigate the long term dynamic evolution of a coastal barrier system experiencing sea level rise using a simplified barrier geometry the model includes a dynamic shoreface profile that can be out of equilibrium and explicitly treats barrier sediment overwash as a flux with barrier behavior primarily controlled by the maximum potential overwash flux and the rate of shoreface response the modeled barrier system demonstrates four primary behaviors height drowning width drowning constant landward retreat and a periodic retreat height drowning occurs when overwash fluxes are insufficient to maintain the landward migration rate required to keep pace with sea level rise on the other hand width drowning occurs when the shoreface response rate is insufficient to maintain the barrier geometry during overwash driven landward migration during periodic barrier retreat the barrier experiences oscillating periods of rapid overwash followed by periods of relative stability as the shoreface resteepens this periodic retreat which occurs even with a constant sea level rise rate arises when overwash rates and shoreface response rates are large and of similar magnitude we explore the occurrence of these behaviors across a wide range of parameter values and find that in addition to the maximum overwash flux and the shoreface response rate barrier response can be particularly sensitive to the sea level rise rate and back barrier lagoon slope overall our findings contrast with previous research which has primarily associated complex barrier behavior with changes in external forcing such as sea level rise rate sediment supply or back barrier geometry

can barrier islands survive sea level rise quantifying the relative role of tidal inlets and overwash deposition barrier island response to sea level rise depends on their ability to transgress and move sediment onto and behind the barrier either through flood tidal delta deposition or via overwash our understanding of these processes over decadal or longer timescales however is limited here we use a recently developed barrier island model brie to better understand the interplay between tidal dynamics overwash fluxes and sea level rise on barrier coasts and barrier island stratigraphy model results suggest that in microtidal environments with large alongshore sediment transport fluxes tidal inlets are ephemeral and migrate rapidly these conditions lead to effective deposition of flood tidal deltas and allow inlets to constitute most of the landward sediment flux whether barrier islands can survive sea level rise depends on the combined landward sediment flux from overwash and flood tidal delta deposition likely making barrier islands with artificially stabilized inlets via jetty construction or maintenance dredging more vulnerable to sea level rise

equilibrium and time scales in geomorphology application to sand bed alluvial streams equilibrium is defined as a single valued temporally invariant functional relationship between the values of an output variable and the values of the input variable s in a geomorphic system disequilibrium occurs if the output deviates from the functional relationship by more than a consensual degree natural geomorphic variables are characterized by a relaxation time output variables are insensitive to cyclical inputs with frequencies much greater than the relaxation time but can respond completely for sufficiently low frequencies rapid trends recent step changes or pulse inputs and intermediate frequency inputs can cause disequilibrium the gradient of sand bed alluvial channels the output variable is determined by sediment and water delivery from slopes the input variables and changes in this hydraulic regime require regrading by erosion and deposition initial stages of adjustment to changed regime in a long unbranched channel with sediment and water delivery only at the upstream end propagate downstream but later stages of adjustment occur simultaneously throughout the reach in a dendritic channel network the gradient responds rather uniformly throughout the network to changes in regime during all stages of adjustment the time scale of adjustment to changed regime depends upon the size of the channel network or stream length the sediment and water discharges and to a lesser degree upon the magnitude of the change grade as defined by mackin 1948 is synonymous with equilibrium as used in this paper if a period of years is replaced by a time period commensurate with the relaxation time of the gradient the use of the term grade is best restricted to a single valued relationship between channel gradient and the hydraulic regime

a long term decadal scale evolution model for microtidal barrier systems abstract a model is presented to simulate the long term decadal evolution of microtidal spit barrier systems the model has been derived from the analysis of coastal processes taking place along the trabucador la banya complex in the ebro delta spanish mediterranean coast it is composed of two submodels to simulate the evolution of the seaside and bayside barrier shorelines the outer coast submodel is of the one line type but formulated in curvilinear coordinates to reproduce the evolution of strongly curved coasts which is a common configuration for spits the model makes use of a long term parameterization of the longshore sediment transport rate which is formulated in terms of a morphological wave and a local transport constant the inner coast submodel is based on a morphological equilibrium approach it considers the overwash transport to be the dominant driving term contributing to the sediment budget of the inner coast it makes use of the concept of critical barrier width to estimate the conditions under which overwash is able to contribute to bayside shoreline accretion the model has been verified calibrated for the trabucador la banya system and it has been used to simulate its evolution under different climatic scenarios

observations and a model of undertow over the inner continental shelf abstract onshore volume transport stokes drift due to surface gravity waves propagating toward the beach can result in a compensating eulerian offshore flow in the surf zone referred to as undertow observed offshore flows indicate that wave driven undertow extends well offshore of the surf zone over the inner shelves of martha s vineyard massachusetts and north carolina theoretical estimates of the wave driven offshore transport from linear wave theory and observed wave characteristics account for 50 or more of the observed offshore transport variance in water depths between 5 and 12 m and reproduce the observed dependence on wave height and water depth during weak winds wave driven cross shelf velocity profiles over the inner shelf have maximum offshore flow 1 6 cm s 1 and vertical shear near the surface and weak flow and shear in the lower half of the water column the observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the su

complexities in barrier island response to sea level rise insights from numerical model experiments north carolina outer banks using a morphological behavior model to conduct sensitivity experiments weinvestigate the sea level rise response of a complex coastal environment to changes ina variety of factors experiments reveal that substrate composition followed in rankorder by substrate slope sea level rise rate and sediment supply rate are the mostimportant factors in determining barrier island response to sea level rise we find thatgeomorphic threshold crossing defined as a change in state e g from landward migratingto drowning that is irreversible over decadal to millennial time scales is most likely tooccur in muddy coastal systems where the combination of substrate composition depth dependent limitations on shoreface response rates and substrate erodibility mayprevent sand from being liberated rapidly enough or in sufficient quantity to maintain asubaerial barrier analyses indicate that factors affecting sediment availability such aslow substrate sand proportions and high sediment loss rates cause a barrier to migratelandward along a trajectory having a lower slope than average barrier island slope therebydefining an effective barrier island slope other factors being equal such barrierswill tend to be smaller and associated with a more deeply incised shoreface therebyrequiring less migration per sea level rise increment to liberate sufficient sand to maintainsubaerial exposure than larger less incised barriers as a result the evolution of larger lessincised barriers is more likely to be limited by shoreface erosion rates or substrateerodibility making them more prone to disintegration related to increasing sea level riserates than smaller more incised barriers thus the small deeply incised north carolinabarriers are likely to persist in the near term although their long term fate is less certainbecause of the low substrate slopes that will soon be encountered in aggregate results point to the importance of system history e g previous slopes sediment budgets etc in determining migration trajectories and therefore how a barrier island will respondto sea level rise although simple analytical calculations may predict barrier responsein simplified coastal environments e g constant slope constant sea level rise rate etc our model experiments demonstrate that morphological behavior modeling is necessary toprovide critical insights regarding changes that may occur in environments havingcomplex geometries especially when multiple parameters change simultaneously

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

modern sedimentation on the shoreface and inner continental shelf at wrightsville beach north carolina u s a abstract the geologic framework and surficial morphology of the shoreface and inner continental shelf off the wrightsville beach north carolina barrier island were mapped using high resolution sidescan sonar bathymetric and seismic reflection surveying techniques a suite of over 200 diver vibracores and extensive seafloor observations by divers the inner shelf is a sediment starved active surface of marine erosion modern sediments where present form a patchy veneer over tertiary and quaternary units the lithology of the underlying units exerts a primary control on the distribution texture and composition of surficial sediments as well as inner shelf bathymetry the shoreface is dominated by a linear cross shore morphology of rippled scour depressions rsds extending from just seaward of the surf zone onto the inner shelf on the upper shoreface the rsds are incised up to 1 m below surrounding areas of fine sand and have an asymmetric cross section that is steeper sided to the north on the inner shelf the rsds have a similar but more subdued cross sectional profile the depressions are floored primarily by shell hash and quartz gravel vibracore data show a thick up to 1 5 m sequence of rsd sediments that unconformably overlies ancient coastal lithosomes in this sediment starved inner shelf setting rippled scour depressions probably form initially on preexisting coarse sediment substrates such as modern lag deposits of paleofluvial channel lithosomes or ancient tidal inlet thalwegs interannual observations of seafloor morphologic change and the longer term record contained in vibracores suggest that the present seafloor morphology is either relatively stable or represents a recurring preferential morphologic state to which the seafloor returns after storm induced perturbations the apparent stability is interpreted to be the result of interactions at several scales that contribute to a repeating self reinforcing pattern of forcing and sedimentary response which ultimately causes the rsds to be maintained as sediment starved bedforms responding to both along shore and across shore flows sediment accumulation from over 30 years of extensive beach nourishment at wrightsville beach appears to have exceeded the local shoreface accommodation space resulting in the leaking of beach and shoreface sediment to the inner shelf a macroscopically identifiable beach nourishment sediment on the shoreface and inner shelf was used to identify the decadal scale pattern of sediment dispersal the nourishment sediment is present in a seaward thinning wedge that extends from the beach over a kilometer onto the inner shelf to waters depths of 14 m this wedge is best developed offshore of the shoreline segment that has received the greatest volume of beach nourishment

the tectonic evolution of the southern alps new zealand insights from fully thermally coupled dynamical modelling summary we present here the results of numerical models of the southern alps in which the thermal and dynamical developments of the orogen are fully coupled to one another this interlinkage allows the use of a wide range of thermal and physical features of the orogen as constraints on the applicability of our models in particular the thermal aspect of this method enables the prediction of the distribution of thermochronological ages at the surface of the model perturbation of the geothermal structure due to rapid uplift and exhumation causes an intrinsic weakening and concentration of strain along the equivalent of the alpine fault zone in these models this thermal weakening of the crust also produces a zone of high strain antithetic to the alpine fault in the upper crust that is comparable to the main divide fault zone within the southern alps the introduction of orographic rainfall and erosional processes into the model leads to the development of high asymmetric topography comparable to that of the southern alps this topographic profile results from the capture of available precipitation by the windward side of the orogen and the resultant rain shadow on the leeward side due to the time required to accumulate suycient topography for this rain capture evect to become significant the establishment of this high asymmetric topography lags the initiation of surface uplift by several million years comparison of the observed thermal history of the southern alps with that seen in models based on divering hypotheses of the tectonic evolution of the south island shows that the present tectonic regime of the orogen most probably developed in a single rapid reorganization of plate motions at approximately 5 ma with relative stability of the tectonic regime since that time the variation in isotopic ages along the southern alps is consistent with that expected from variation in accumulated uplift and exhumation along the orogen arising from the obliquity of convergence of the australian and pacific plates

analytic solution for the morphology of a soil mantled valley undergoing steady headward growth validation using case studies in southeastern arizona 1 the geomorphic literature contains many analytic solutions for the topographic evolution of gently sloping soil mantled hillslopes responding to base level changes most of these solutions are limited to vertical base level changes and or to simplified geometries however in this paper we present an analytic solution for the morphology of a valley and its adjacent hillslopes undergoing steady headward growth the mathematics of this problem were first solved by ivantsov 1947 in the context of heat flow near a parabolic solidification boundary here we test whether the ivantsov solution provides an accurate first order prediction of the morphology of valley heads and their adjacent hillslopes by comparing the model predictions to survey data from two study sites in southeastern arizona the model predicts that elevation contours of valley heads are parabolas and that topographic transects normal to contour lines are error functions high resolution digital elevation models dems were constructed for the two study sites using real time kinematic global positioning system rtk gps measurements and a terrestrial laser scanner tls our analyses show that the model reproduces the first order morphology of headward growing valleys and their adjacent hillslopes we also show that by analyzing hillslope profiles at different distances from the valley head the model framework can be used to infer likely changes in the valley head migration rate through time

continental crust under compression a seismic refraction study of south island geophysical transect i south island new zealand 1 the 1996 south island geophysical transect sight active source seismic survey was designed to show the style of lithospheric thickening due to late cenozoic oblique convergence across the australian pacific plate boundary in new zealand as part of this study two seismic refraction lines were shot across central south island and offshore extensions of the continental crust in the tasman sea and pacific ocean we present the data and a 603 km long seismic velocity profile of the crust and uppermost mantle along one of these seismic transects a tomographic inversion of 62 563 travel times from crustal and upper mantle refractions and wide angle reflections resulted in a model with a two layer crust upper crustal velocities were between 5 9 and 6 3 km s and lower crustal velocities were between 6 5 and 7 0 km s continental compression has locally reduced the seismic velocities in the pacific plate crust by 0 2 0 3 km s a possible effect of high strain and fluids in the crust the thickening of the crust from 28 km at the east coast of south island to 37 km beneath the southern alps can account for about 25 of the 80 110 km shortening of pacific plate crust while the rest must be accounted for by rapid erosion of mesozoic sedimentary rocks on the west side of the orogen in our model the lower crust forms a continuous 2 6 km thick layer beneath central south island the asymmetric topography of the southern alps is reflected in the crustal root which has a steeper flank at the west coast this observation is consistent with westward underthrusting of pacific lower lithosphere beneath south island that has been suggested in earlier studies

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

on the causes and modes of exhumation and lateral growth of the alps 1 a compilation of the apatite and zircon fission track ages of the alpine chain points to markedly different patterns of cooling and exhumation of the eastern alps compared to the central and western alps the site of exhumation and shortening in the western alps migrated outward whereas it was more stationary in the eastern alps where it created a narrower metamorphic belt a correlation of these observations to the deep structure of the orogen suggests that north directed lower crustal wedging induces northward propagation of the deformation and exhumation front in the middle and upper crust of the central and western alps the absence of such lower crustal wedges in the eastern alps does not induce a similar shift of deformation but rather a long term localization of shortening and exhumation in one and the same area namely the axial zone of the orogen a critical review of the temporal correlations between inferred changes in the erosional efficiency of the alps and tectonic phases points to a negative correlation and hence no erosional control on the shifts of the deformation front of the alps therefore we conclude that changes in the deep structure and rheology of the orogen instead of changes in its erosional efficiency exerted the prime control on the lateral growth of the alps

controls of local geology and cross shore longshore processes on embayed beach shoreline variability 10 shoreline variability along the 3 6 km long narrabeen beach embayment in se australia is 11 investigated over a 5 year period we apply the one line shoreline change model lx shore 12 which couples longshore and cross shore processes and can handle complex shoreline 13 planforms non erodible emerged headlands and submerged rocky features the model 14 skilfully reproduces the three dominant modes of shoreline variability which are by 15 decreasing order of variance cross shore migration rotation and a third mode possibly 16 related to breathing model results confirm previous observations that longshore processes 17 primarily contribute to the rotation and third modes on the timescales of months to seasons 18 while cross shore processes control the shoreline migration on shorter timescales from hours 19 storms to months additional simulations simplifying progressively the bathymetry show 20 how the inherent geology strongly modulates the spatial modes of shoreline variability the 21 offshore central rocky outcrop is found to limit the rotation in contrast the submerged rocky 22 platforms that extend from the headlands enhance the shoreline rotation mode and increase 23 alongshore variability of the cross shore migration mode owing to increased alongshore 24 variability in wave exposure offshore wave transformation across large scale submerged 25 rocky features and headland shape are therefore critical to contemporary shoreline dynamics 26 2

geomorphological analysis of the drainage system on the growing makran accretionary wedge abstract the morphology of six adjacent major catchments draining the onshore makran accretionary wedge in southeast iran and southwest pakistan was studied to examine how the channel pattern and the length profiles may reflect the recent and active growth of the wedge qualitative field surveys were combined with the quantitative analysis of channel steepness and concavity measured from digital elevation models these profiles were compared with modelled profiles using a stream power approach assuming homogeneously uplifting uniform rock substratum results show a distinct difference between the studied western and eastern catchments the three western rivers are in morphological equilibrium whereas the two eastern rivers exhibit profiles with prominent convexities and knickpoints thus notably diverging from equilibrium concave up shapes all the studied catchments share the same base level flow on similar lithologies and developed under uniform climate conditions therefore we interpret the morphometric differences in terms of differential rock uplift rate as a response to local tectonic activity this interpretation is consistent with both uplift rates of marine terraces along the coast of makran and the recorded seismicity the geomorphological analysis presented here extends coastal information to wide inland areas and documents longer term tectonic behaviour than the seismotectonic record hence the steeper surface slope and faster surface uplift rates recorded by the eastern catchments compared to equilibrium of the western catchments are regional long term signals relevant for a wide part of the makran accretionary wedge we attribute the regional geomorphic difference to quaternary variations in tectonic regimes that forced differential uplift rates of the wedge surface we hypothesize that the different tectonic regimes are related to different subduction rates

fluvial and marine controls on combined subaerial and subaqueous delta progradation morphodynamic modeling of compound clinoform development 1 fluviodeltaic systems commonly display a compound clinoform geometry that consists of a subaerial subaqueous delta couplet the extent of subaqueous delta development varies significantly and in modern systems is a function of fluvial input and basin hydrodynamics we present a model of fluviodeltaic progradation in which the repeated occurrence of characteristic terrestrial floods and large coastal storms drives fluvial and shallow marine morphodynamics respectively we couple fluvial and shallow marine sediment dynamics via the surf zone which we collapse to a shock condition and treat as a moving boundary with steady sediment supply and sea level and simple basin geometry our model naturally develops prograding deltas with compound clinoform geometries the subaerial delta grows via fluvial aggradation and shoreface progradation whereas the subaqueous delta expands through foreset progradation with only minor topset aggradation the interplay of fluvial input with the wave current field controls the basic partitioning of sediment between subaerial and subaqueous deltas and by extension the compound clinoform geometry increasing the frequency or magnitude of coastal storms decreasing flood frequency or discharge and reducing grain size all increase the fraction of sediment delivered to the shallow marine environment and the extent of subaqueous delta progradation relative to subaerial delta development our model which emphasizes the intrinsic coupling of fluvial and shallow marine sediment dynamics and downplays the importance of allogenic fluctuations can explain many of the first order morphologic features of natural delta systems including significant lateral separation of the shoreline and clinoform rollover and differing rates of subaerial and subaqueous delta progradation

storm and fair weather wave base a relevant distinction surface waves are an important mechanism for the redistribution of sediment on shallow marine shelves and are commonly interpreted as comprising two distinct populations fairweather waves and storm waves the latter of which are generally thought to penetrate to greater water depths here we used 2 3 10 6 spectral density estimates for the surface ocean collected between 1996 and 2008 from 32 buoys in the caribbean the gulf of mexico and the western atlantic to test the hypothesis that surface waves in the modern ocean comprise two size modes although distinct wave size classes occur in some individual measurements and over the time scales of some individual storms time averaged frequency distributions of wave size are unimodal thus there is no empirical basis for presupposing a distinct bimodal separation in the size of fair weather and storm waves or in the manifestation of such differences in stratigraphic successions instead there is a continuously increasing probability that a wave will reach the bottom with decreasing water depth and a separate probability that describes the hydrodynamic state of the sediment water interface wave size does however exhibit signifi cant geographic bimodality locations in the relatively protected gulf of mexico and caribbean regions have modal wavelengths that are 50 m less than waves at locations along the western atlantic time integrated estimates of the depth of wave penetration provide empirical constraints on the paleo water depths of ancient sedimentary deposits and highlight differences between sheltered shelf environments such as those that characterized many ancient epeiric seas and open ocean facing narrow continental shelves

numerically simulating alpine landscapes the geomorphologic consequences of incorporating glacial erosion in surface process models abstract a numerical model that simulates the evolution of glaciated mountain landscapes is presented by employing a popular sliding based glacial erosion model many common glacial landforms are created the numerical model builds on earlier work as it is fully two dimensional and employs the first order forcing on mountain evolution these forcings include tectonic uplift isostasy hillslope processes fluvial processes and glacial processes a climate dependent model of ice dynamics is employed to determine ice coverage and ice flux two simulations are presented one with generic model parameters and a second with parameters that correspond to conditions in the southern alps of new zealand landforms that are produced by the model include climate climate dependent elevation lowering similar to what might be expected by a glacial buzz saw valley overdeepening terminal moraines and valley retreat the model also predicts that current rates of sedimentation are higher than the long term average and that several tens of thousands of years are required for the landscape to adjust to a change in the dominant erosional forcing therefore glaciated orogens are unlikely to achieve topographic steady state over milankovitch timescales

effects of tectonic deformation and landslides in the erosion of a mountain plateau in the transitional zone between the central and patagonian andes

geology of the wrightsville beach north carolina shoreface implications for the concept of shoreface profile of equilibrium abstract nearly 300 km of 3 5 khz subbottom profile and 100 khz sidescan sonar data a suite of over 100 short 2 m percussion cores and vibracores have been collected on the shoreface and inner continental shelf off wrightsville beach north carolina sidescan sonar images were analyzed for acoustic backscatter to delineate the surface sediment distribution groundtruth data for the sidescan sonar interpretations were provided by surface grab samples cross shore sediment transport by combined waves and currents is the predominant sedimentologic signature on this shoreface the shoreface is dominated by a shore normal system of rippled scour depressions that begin in 3 4 m water depth and extend to the base of the shoreface about 1 km offshore at 10 m depth the depressions are 40 100 m wide and up to 1 m deep they are floored by coarse rippled shell hash and gravel some are separated by rock underlain fine sand ridges on the inner shelf the bathymetric and sedimentary fabrics become shore oblique due to a series of relict ridges with 1 2 m of relief the ridges are coarse on their landward sides and covered on their seaward flanks by thin veneers of fine sand field evidence from the wrightsville beach shoreface demonstrates that a shoreface equilibrium profile as defined by dean 1991 and others does not exist here for example 1 the grain size varies widely and inconsistently over the profile 2 shoreface profile shape is controlled predominantly by underlying geology including tertiary limestone outcrops and oligocene silts and 3 sediment transport patterns cannot be explained by simple diffusion due to wave energy gradients and that transport occurs seaward of the assumed engineering closure depth of 8 5 m this has several implications for the application of equilibrium profile based numerical models used to investigate coastal processes and design coastal engineering projects at wrightsville beach the most important practical implication is that a number of assumptions required by existing analytical and numerical models e g dean 1991 genesis sbeach used for the design of shore protection projects and large scale coastal modeling over decadal time scales cannot be met

role of waves and tides on depth of closure and potential for headland bypassing abstract depth of closure is a fundamental concept used to define the seaward extent of a morphodynamically active shoreface at a particular temporal scale the estimation of this limit in relation to the depth in front of the bounding headlands along embayed coastlines allows questioning whether embayments often deemed closed sediment cells experience more headland bypassing than expected wave based parameterisations developed for microtidal beaches are most widely used to estimate closure depth however a re evaluation of the concept for shorefaces influenced by geological control presence of headlands and or bedrock and strong tidal currents is appropriate here we use the macrotidal embayed and high energy coastline of sw england to identify the active nearshore limits with a multi method approach that includes observations of shoreface morphology and sedimentology offshore inshore wave formulations and bed shear stress computations we identify the basal limit of significant i e 0 14 m morphological change depth of closure doc and a maximum depth of extreme bed activity and sediment transport depth of transport dot observations of doc correspond closely to the values predicted by existing formulations based on inshore wave conditions 10 15 m for the study area relative to mean low water spring water level in this case the computed dot represented by the upper plane bed transition attained under extreme conditions exceeds 30 m depth in the study area the significant implication is that even though many headlands appear sufficiently prominent to suggest a closed boundary between adjacent embayments significant wave and tide driven sediment transport is likely to occur beyond the headland base during extreme events especially at low water levels the maximum depth for significant sediment transport dot was computed across a broad wave current parameter space further highlighting that tidal currents can increase this closure depth estimate by 10 m along macrotidal coastlines representing a 30 increase compared to tideless settings this work illustrates the importance of tidal currents in depth of closure calculations and challenges the notion that embayed beaches are generally closed cells as headland bypassing may be more wide spread than commonly assumed along exposed coastlines globally

sediment supply to beaches cross shore sand transport on the lower shoreface many beaches have been built by an onshore supply of sand from the shoreface and future long term coastal evolution critically depends on cross shore sediment exchange between the upper and the lower shorefaces even so cross shore sediment supply remains poorly known in quantitative terms and this reduces confidence in predictions of long term shoreline change in this paper field measurements of suspended sediment load and cross shore transport on the lower shoreface are used to derive a model for sediment supply from the lower to the upper shoreface at large spatial and temporal scales data collection took place at five different field sites that exhibit a wide range of wave conditions and sediment characteristics data analysis shows that both suspended sediment load and cross shore sediment transport scale with the grain related mobility number which ranged up to 1000 in the measurements while the effect of orbital velocity skewness is more limited a 1 year long simulation of sediment transfers between the lower and the upper shorefaces on a natural beach compares well with transport rates estimated from long term bar migration patterns and aeolian accretion on the same beach

a unifying framework for shoreline migration 1 multiscale shoreline evolution on sedimentary coasts 1 a unifying framework for shoreline migration is presented which synthesizes problems from coastal engineering geomorphology and stratigraphy into a common quantitative basis consideration of characteristic problems from these fields reveals that multiscale shoreline evolution problems naturally break into three classes on the basis of the morphologic unit of evolution shoreface bed versus shoreline planform versus stratigraphic shoreline trajectory shoreline evolution models correspondingly break into morphodynamic morphokinematic and hybrid approaches a generalized shoreline continuity equation is derived the shoreline exner equation which subsumes equilibrium profile models commonly used in geomorphology and engineering and provides a natural framework for interpreting shoreline trajectories preserved in the sedimentary record the shoreline exner equation provides a rigorous basis for geometric and moving boundary models which have significant untapped potential for shoreline migration problems recent advances in computational methods for evolving interface problems make hybrid models particularly attractive for problems of large scale planform shoreline dynamics such as delta evolution

controls on the spacing of first order valleys 1 many landscapes are composed of ridges and valleys that are uniformly spaced even where valley locations are not controlled by bedrock structure models of long term landscape evolution have reproduced this phenomenon yet the process by which uniformly spaced valleys develop is not well understood and there is no quantitative framework for predicting valley spacing here we use a numerical landscape evolution model to investigate the development of uniform valley spacing we find that evenly spaced valleys arise from a competition between adjacent drainage basins for drainage area a proxy for water flux and that the spacing becomes more uniform as the landscape approaches a topographic equilibrium valley spacing is most sensitive to the relative rates of advective erosion processes such as stream incision and diffusion like mass transport such as soil creep and less sensitive to the magnitude of a threshold that limits the spatial extent of stream incision analysis of a large number of numerical solutions reveals that valley spacing scales with a ratio of characteristic diffusion and advection timescales that is analogous to a peclet number we use this result to derive expressions for equilibrium valley spacing and drainage basin relief as a function of the rates of advective and diffusive processes and the spatial extent of the landscape the observed scaling relationships also provide insight into the cause of transitions from rill like drainage networks to branching networks the spatial scale of first order drainage basins the contributing area at which hillslopes transition into valleys and the narrow range of width to length ratios of first order basins

barrier island evolution middle atlantic shelf u s a part i shoreface dynamics abstract in part i of this paper near bottom fluid velocity and sediment concentration measurements from the shoreface of a middle atlantic barrier long island coast are analyzed to provide insight into the dynamics of erosional shoreface retreat in part ii these data are combined with observations of coastal stratigraphy in order to construct a model for the evolution and behavior of middle atlantic barriers wave motions on the long island shoreface tend to drive sediment onshore calculations of the onshore sediment flux driven by asymmetrical shoaling waves show that for the wave states commonly encountered on the middle atlantic shelf values become strongly positive landward of approximately 10 m water depth upper shoreface but drop to very low values shortly seaward of that isobath on the lower shoreface and inner shelf floor fair weather wave current interaction tends to cause a landward creep of sediment even though the wave orbital component of the near bottom velocity field is nearly symmetrical this movement occurs because the wave approach direction generally lies within 90 of the direction up coast or down coast of the alongshore wind driven current therefore fluid shear stress acting on the sediments tends to be reinforced during the shoreward stroke of the wave orbital motion and partially cancelled during the seaward stroke during major storms the rate of sediment transport increases by at least an order of magnitude and the role of wind driven currents becomes important much more sediment is resuspended by the wave orbital current component because storm waves are more powerful than fair weather swells but the wind driven flow component is also much stronger and is now available for transporting the resuspended sediment storm flows over the shoreface occur in distinct dynamic zones surf zone friction dominated zone transition zone geostrophic zone the zones are defined by dynamical considerations and expand or contract with the intensity of the causative wind stress during peak flow events the characteristic length scales of the friction dominated and geostrophic zones tend to correspond with the morphologic zones of the shoreface and inner shelf the storm intensified wind driven alongshore flows of the lower shoreface are frequently jet like in nature and may be upwelling or downwelling wind driven coastal flows with a strong downwelling component occur during most storms on the long island coast and are particularly important to the coastal sand budget during these events sand is entrained by the storm intensified upper shoreface circulation system of wave driven alongshore currents and rip currents and is fed into the main wind driven coastal current because of the offshore component of bottom flow sand is swept down the lower shoreface and onto the adjacent inner shelf fair weather processes may be unable to return storm deposited sand to the beach from such an offshore position the shoreface transport regime of the long island barrier coast thus consists of long periods of time months during which sand moves slowly toward the beach punctuated by short intense periods hours or days during which sand is transferred from the shoreface to the adjacent inner shelf the long term sense of movement of the shoreface whether retreating the long island case or prograding must depend on the loss or gain of sand by shoreface with respect to the inner shelf the data shows that the coastal sand budget is controlled not only by the upper shoreface cycle withdrawl of sand from the beach prism storage in the breakpoint bar and its subsequent return to the beach but by a cycle of larger spatial and temporal scale in which sand is exchanged between the shoreface as a whole and the adjacent inner shelf

inundation of a barrier island chandeleur islands louisiana usa during a hurricane observed water level gradients and modeled seaward sand transport large geomorphic changes to barrier islands may occur during inundation when storm surge exceeds island elevation inundation occurs episodically and under energetic conditions that make quantitative observations difficult we measured water levels on both sides of a barrier island in the northern chandeleur islands during inundation by hurricane isaac wind patterns caused the water levels to slope from the bay side to the ocean side for much of the storm modeled geomorphic changes during the storm were very sensitive to the cross island slopes imposed by water level boundary conditions simulations with equal or landward sloping water levels produced the characteristic barrier island storm response of overwash deposits or displaced berms with smoother final topography simulations using the observed seaward sloping water levels produced cross barrier channels and deposits of sand on the ocean side consistent with poststorm observations this sensitivity indicates that accurate water level boundary conditions must be applied on both sides of a barrier to correctly represent the geomorphic response to inundation events more broadly the consequence of seaward transport is that it alters the relationship between storm intensity and volume of landward transport sand transported to the ocean side may move downdrift or aid poststorm recovery by moving onto the beach face or closing recent breaches but it does not contribute to island transgression or appear as an overwash deposit in the back barrier stratigraphic record the high vulnerability of the chandeleur islands allowed us to observe processes that are infrequent but may be important at other barrier islands

free stream velocity descriptions under waves with skewness and asymmetry abstract in shallow water when waves shoal their orbital velocities exhibit skewness velocity skewness and asymmetry acceleration skewness in response to corresponding changes in the free surface near the bed changes in the skewness and asymmetry of the time varying velocities have important consequences for the residual velocities spun up by the bottom friction and for sediment transport in the wave boundary layer where the largest sediment transport often occurs there is a need to represent the free stream velocity the orbital velocity at the edge of the wave boundary layer in a systematic way such that it can be mimicked in wave tunnel experiments and wave boundary layer models which usually do not represent the free surface since there is no readily accessible dynamical theory for shoaling waves that includes both skewness and asymmetry it is necessary to synthesize the shoaling effect in a free stream velocity description that is general enough to fit observed velocity time series this paper reviews previous free stream velocity descriptions including the description of abreu et al 2010 and introduces a new description based on generalising a sawtooth wave shape the paper quantifies all the relevant measures of skewness and asymmetry for each description it then demonstrates that abreu et al s 2010 description represents the most general one and improves upon their fitting techniques to observed free stream velocities to further simplify it when this description is used in conjunction with a characterisation of the velocity for irregular waves such as that of elfrink et al 2006 it is possible to relate velocity skewness and asymmetry directly to the non dimensional wave and beach parameters wave height surface wavelength and surf similarity parameter as a proxy for beach slope matlab scripts are provided for the improved description of abreu et al 2010 and elfrink et al s 2006 characterisation

coastal profile response to sea level rise a process based approach prevailing ideas and calculations of coastal response to sea level rise slr are often based on the bruun model bruun p sea level rise as a cause of shore erosion journal waterways harbors division asce88 117 130 1962 that predicts upward and landward transfer of an equilibrium profile during slr through offshore sediment transport on the shoreface the model is based on a number of assumptions of questionable validity as well as outdated concepts on how sediment is transported across the shoreface this contribution takes a numerical modelling approach that is based on first order processes contributing to the movement of sediment across the shoreface using a wave transformation model that predicts hydrodynamic processes driving cross shore sediment transport and an energetics based model for the coupling between hydrodynamics and sediment transport we show that cross shore sediment transport is mainly onshore directed at the boundary between the lower and the upper shoreface in agreement with the model proposed by davidson arnott conceptual model of the effects of sea level rise on sandy coasts journal of coastal research21 1166 1172 2005 the transition from onshore to offshore directed transport is located well within the surf zone and with a rising sea level this transition point becomes displaced landward and upward tests also show that substrate slope is of fundamental importance to the manner in which beaches react to rising sea level copyright 2012 john wiley sons ltd

origin of the highly elevated pyrenean peneplain 1 peneplanation of mountain ranges is generally considered the result of long term erosional processes that smooth relief and lower elevation near sea level therefore peneplain remnants at high elevation in mountain ranges are used to infer posttectonic surface uplift such an interpretation has been proposed for the pyrenees where high elevation low relief erosional surfaces rose up to more than 2000 m because the pyrenean foreland basins are filled with very thick continental deposits which have buried the early jagged landscape we challenge this hypothesis by pointing out that relief applanation does not necessarily require elevation lowering we propose an alternative interpretation in which piedmont aggradation of detrital sediment that comes from erosion of the high chain induces the rise of the base level of the range therefore reducing strongly the erosive efficiency of the drainage system and resulting in the progressive smoothing of the relief such a process allows a high elevation low relief erosional surface to develop at the scale of the range in the pyrenees occurrence of high elevation low relief erosional surface remnants does not imply a posttectonic uplift but is instead due to the dissection of the initial miocene high elevation low relief surface by the recent drainage system the erosive activity of which has been enhanced by global climate change from the late pliocene onward

evidence of episodically accelerated denudation on the tibetan namche barwa massif by megafloods abstract megafloods cause widespread mobilization of sediments that have strong potential to control the geodynamic evolution of the namche barwa nb massif by changing the landscape morphology within a short time however the impact of catastrophic events on the denudation of the massif over the longer time scale has not been explored in detail this contribution assesses the impact of catastrophic floods on the denudation style of the namche barwa nb massif over millennial time scales towards this 21 optical ages and 1700 detrital thermochronometric ages of zircon and apatite minerals extracted from paleoflood sediments downstream of the massif were integrated with decadal sediment load and aggradation data to estimate the minimum denudation rate during paleoflood events the results indicate that the 7 ka flood eroded 71 m of material from the nb massif this denudation is equivalent to the material that would be produced over 8000 years of erosion at a rate of 9 mm a the 3 5 ka flood eroded 24 m of material equaling 2500 years worth of erosion at a rate of 9 mm a such relatively instantaneous denudations are three orders of magnitude higher than averaged denudation rates over million year time scale this study therefore provides the first evidence of the strong interplay of catastrophic flood events and tectonics for the rapid exhumation of the namche barwa massif megafloods from the failure of dammed lakes provide valuable information to understand the flood surge risk for human settlements in the siang and the assam valleys

uplift histories from river profiles 1 longitudinal river profiles where elevation of a river bed is plotted as a function of distance along the river bed contain information about uplift rate when a region adjacent to a reference level e g sea level is uplifted a rapid change in gradient occurs near the river mouth the erosional process causes this change in gradient to migrate upstream thus a river profile is effectively a tape recording of the uplift rate history provided that the erosional process can be adequately parameterized here we use a non linear equation to relate the shape of a river profile z x to uplift rate history u t if erosion is assumed to be dominated by knickpoint retreat an inverse model can be formulated and used to calculate uplift rate histories our model builds upon standard stream profile analysis which focuses on the relationship between profile slope and drainage area we have applied this analytical approach to river profiles from the bie dome angola calculated uplift rate histories agree with independent geologic estimates

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

gravity driven sediment transport on the continental shelf implications for equilibrium profiles near river mouths an analytical model is developed for equilibrium bathymetric profiles off river mouths associated with the shoreward convex upward portion of subaqueous deltas and clinoforms the model builds on recent field results demonstrating that gravity driven flux of suspended mud is important on shelves provided that wave induced suspension of sediment supports the requisite turbid hyperpycnal layer because the maximum sediment load is determined by the critical richardson number the results are independent of the properties of the suspended mud or the bed the model assumes the equilibrium state to represent a balance between the supply of sediment by a river at the coast and the downslope bypassing of sediment to deep water within wave supported turbid near bed layers progressive seaward increases in bed slope across the convex shelf profile allow the attenuation of wave agitation with depth to be compensated for by a downslope increase in the contribution of gravity the model is consistent with shelf profiles off the mouths of the eel california ganges brahmaputra bangladesh waiapu new zealand po italy and rhone france rivers the equilibrium profile is predicted to be a function of wave climate and riverine sediment supply only with deeper and broader profiles associated with decreasing sediment supply increasing wave height and or increasing wave period

exploring shoreface dynamics and a mechanistic explanation for a morphodynamic depth of closure using energetics based formulations for wave driven sediment transport we develop a robust methodology for estimating the morphodynamic evolution of a cross shore sandy coastal profile in our approach wave driven cross shore sediment flux depends on three components two onshore directed terms wave asymmetry and wave streaming and an offshore directed slope term in contrast with previous work which applies shallow water wave assumptions across the transitional zone of the lower shoreface we use linear airy wave theory the cross shore sediment transport formulation defines a dynamic equilibrium profile and by perturbing about this steady state profile we present an advection diffusion formula for profile evolution morphodynamic peclet analysis suggests that the shoreface is diffusionally dominated using this depth dependent characteristic diffusivity timescale we distinguish a morphodynamic depth of closure for a given time envelope even though wave driven sediment transport can and will occur at depths deeper than this morphodynamic closure depth the rate of morphologic bed changes in response to shoreline change becomes asymptotically slow linear wave theory suggests a shallower shoreface depth of closure and much sharper break in processes than shallow water wave assumptions analyzing hindcasted wave data using a weighted frequency magnitude approach we determine representative wave conditions for selected sites along the u s coastline computed equilibrium profiles and depths of closure demonstrate reasonable similarities except where inheritance is strong the methodology espoused in this paper can be used to better understand the morphodynamics at the lower shoreface transition with relative ease across a variety of sites and with varied sediment transport equations

late holocene shoreline responses to competing shelf bay and beach accommodation spaces under conditions of relative sea level change and the potential for future catastrophic beach retreat in the columbia river littoral cell washington and oregon usa abstract the columbia river littoral cell crlc 160 km in length provides opportunities to compare competing accommodation space relations under different conditions of relative sea level change the crlc system includes abundant littoral sand supply from the large columbia river late holocene prograded beach plains and barrier spits 0 5 5 km in width two large marine dominated estuaries willapa bay and grays harbor and a high wave energy inner shelf littoral sand accumulation rates in prograded beach plains and barrier deposits are based on paleo shoreline positions that are dated by great earthquake catastrophic beach retreat scarps n 10 from 0 3 to 5 0 ka the retreat scarp timelines are mapped in across shore gpr transects n 79 yielding timeline bounded polygons n 247 the polygons are evaluated for littoral sand volume and bounding ages yielding volume accretion rates m3 ka 1 which are summed for the four crlc subcells clatsop plains 27 4 106 m3 ka 1 long beach 19 8 106 m3 ka 1 grayland plains 15 9 106 m3 ka 1 north beaches 11 7 106 m3 ka 1 major submarine sinks of littoral sand including the inner shelf and large marine dominated estuaries are evaluated for increased littoral sand accommodation space that could result from potential future sea level rise of 1 2 and 3 m during the next century or two the estimated beach and nearshore sand erosion needed to fill the increased submarine accommodation space from a 2 0 m rise in relative sea level would result in averaged beach retreat values of 0 7 km clatsop plains 1 2 km long beach and 1 3 km grayland plains about 30 50 larger than previous estimates based on the brunn method these catastrophic shoreline retreat distances 0 7 1 3 km represent 25 50 of the present widths of prograded barrier spits and beach plains they serve as warnings about future catastrophic beach erosion resulting from potential future slr in other similar barrier spit and beach plain shorelines worldwide

equilibrium responses of cliffed coasts to changes in the rate of sea level rise abstract basic formulae have long been used to predict the effects of sea level rise on coastal recession for instance the geometric bruun rule and its modifications has often been applied to sandy coasts both low lying and steep however the behavior of rocky coasts whether strongly or poorly lithified should be significantly different than that of sandy coasts given that rocky coast evolution depends upon the irreversible breakdown of rock whereas sandy and depositional systems are controlled by the transport and related transport gradients of mobile sediment here we investigate the basis of a modeled relationship which suggests with a number of caveats that the equilibrium soft rock cliff recession rate can be estimated by the square root of the relative change in sea level rise rate although this relationship was derived using the numerical model scape soft cliff and platform erosion which simulates a broad soft rock cliffed coastal system driven by stochastic environmental forces here we show that a simplified modeling approach also reproduces the relationship we then extend this approach to develop a general theoretical framework within which it is possible to consider the potential responses of the different types of cliffed coasts to changes in the rate of sea level rise although a wide variety of processes affect different coastal settings this framework demonstrates how the strength and the nature of feedbacks within cliffed system control their response to sea level rise this suggests that cliffed environments controlled by different processes can still respond in similar ways to changes in the rate of sea level rise most rocky coasts would be expected to respond as a damped or negative feedback system between the extremes of a no feedback system that is unresponsive to sea level rise rate and an instant response system characterized by a linear response similar to the bruun rule this framework suggests that a potential inverse feedback case could also exist in which increased rates of sea level rise reduce the rate of coastal recession in almost all cases it is apparent that cliffed coast response to sea level rise depends not only upon the total elevation change of sea level but on the rate of the sea level rise these theoretical investigations and the classifications presented provide a framework to understand the behavior of systems affected by a wide array of processes and provide expectations that can be tested using more complex models of cliffed coast evolution in a variety of environments whether sandy or rocky hard or soft

equilibrium shoreface profiles a sediment transport approach abstract large scale coastal behaviour models use the shoreface profile of equilibrium as a fundamental morphological unit that is translated in space to simulate coastal response to for example sea level oscillations and variability in sediment supply despite a longstanding focus on the shoreface profile and its relevance to predicting coastal response to changing environmental conditions the processes and dynamics involved in shoreface equilibrium are still not fully understood here we apply a process based empirical sediment transport model combined with morphodynamic principles to provide new insight into equilibrium shoreface profile development and shape the quantitative model is based on field measurements and shows that a balance between onshore sediment transport due to oscillatory wave motion and offshore sediment transport due to gravity produces profile shapes that are similar to natural shoreface profiles from the danish north sea coast and the southeast australian coast model predictions of equilibrium profile response to the effects of climate change such as rising sea level or changing wave climates are examined implementation of the model is straightforward there is no tuning or calibration and computation times are short it is therefore easily implemented with repeated iterations to manage uncertainty

effects of closure depth changes on coastal response to sea level rise insights from model experiments in southern brazil abstract this study focuses on the impacts of variable shoreface closure depth limits on coastal responses to increases in sea levels along a sandy barrier in southern brazil upper and lower shoreface limits for sediment exchanges are largely regulated by the wave climate and they tend to move offshore as the temporal scale increases therefore because closure depth limits are a source of uncertainty in simulations of coastal response to sea level rise to elucidate how important changes in these limits are under such conditions four simulation experiments were performed with variable combinations of upper and lower shoreface closure depth values direct methods for closure depth delineation require long term data sets with field surveys which are rarely available therefore indirect approaches are applied widely to calculate closure depth values here we apply hallermeier s equations using two wave data sources one measured via wave buoys and one modeled wave watch iii and simulating waves nearshore model wwiii swan evaluation of coastal response under rising sea levels was possible via application of an aggregated coastal modeling approach using the random shoreface translation model ranstm shoreline retreat distances resulting from each combination of upper hc and lower hi shoreface closure depth values cases in model simulations were compared case 1 hc 7 4 m hi 42 1 m case 2 hc 7 4 m hi 35 7 m case 3 hc 6 2 m hi 35 7 m and case 4 hc 6 2 m hi 42 1 m statistical analysis via the kruskal wallis test demonstrated that shoreline retreat was significantly affected at p

plio plistocene in sequence thrust propagation along the main central thrust zone kumaon garhwal himalaya india new thermochronological data abstract the kumaon and garhwal himalayas nw india have similar geologic tectonic topographic and precipitation pattern however low temperature thermochronological age pattern varies significantly along the strike as well as across the strike of major faults here we interpret the new set of thermochronological age data across the strike of major faults namely vaikrita thrust vt munsiari thrust mt berinag thrust bt and the baijnath nappe along pindari valley in the kumaon garhwal himalaya in the present work 18 new apatite fission track aft ages of samples collected along a north south transect have been reported ages in the hanging wall of vt which range from 2 1 0 2 to 4 2 0 7 ma have been found to be becoming younger linearly with distance from north to the vt this trend crosses the vt with significant jump in ages in the south of the vt ages are lying between 0 3 0 1 and 3 9 0 8 ma and show linear variation with distance from the vt to bt no significant jump in ages across the mt is observed and the linear trend of younging southward is continuing till the bt the break and displacement in age pattern with youngest ages close to thrusts possibly indicate progressive late thrust movement it reflects sequential uplift and cooling towards the south from the vt to bt which is consistent with an in sequence style of thrust propagation we compare our new data to the published thermochronological data from its adjacent traverses along the goriganga and dhauliganga valleys 25 km away from the present traverse towards east and west respectively in the kumaon garhwal himalaya in order to understand potential along strike variations in the kinematics our observations indicate a dynamic coupling between tectonic and surface processes in the garhwal kumaon himalaya and support that the geometry of crustal scale faults and their associated kinematics control exhumation pathways of rocks

very slow erosion rates and landscape preservation across the southwestern slope of the ladakh range india erosion rates are key to quantifying the timescales over which different topographic and geomorphic domains develop in mountain landscapes geomorphic and terrestrial cosmogenic nuclide tcn methods were used to determine erosion rates of the arid tectonically quiescent ladakh range northern india five different geomorphic domains are identified and erosion rates are determined for three of the domains using tcn 10be concentrations along the range divide between 5600 and 5700 m above sea level asl bedrock tors in the periglacial domain are eroding at 5 0 0 5 to 13 1 1 2 meters per million years m m y principally by frost shattering at lower elevation in the unglaciated domain erosion rates for tributary catchments vary between 0 8 0 1 and 2 0 0 3 m m y bedrock along interfluvial ridge crests between 3900 and 5100 m asl that separate these tributary catchments yield erosion rates 850 ky respectively these results highlight the persistence of very slow erosion in different geomorphic domains across the southwestern slope of the ladakh range which on the scale of the orogen records spatial changes in the locus of deformation and the development of an orogenic rain shadow north of the greater himalaya copyright 2014 john wiley sons ltd

orogeny and metamorphism a model for deformation and pressure temperature time paths with applications to the central and southern appalachians a model is presented for deformation uplift and exhumation in convergent orogens based on the following premises 1 foreland basin subsidence monitors the distribution in time and space of overthrust loads added to an orogen 2 the presence of an inherited rifted margin plays an important role in the subsequent history of an orogen by forming a basement ramp or buttress that must be surmounted in order for thrusts to advance on the craton on the seaward side of this transition up to 20 km of overthrusts can be accumulated without creating topography 3 critical shape theory can be applied to orogens as a whole allowing predictions to be made concerning dynamic balance between mass addition and loss uplift exhumation and growth of topography and 4 pressure temperature time p t t data can be used to reconstruct particle paths within the deforming orogen three states of overthrust orogens can be defined based on the relative rates of mass loss and mass addition as monitored by the foreland rapid exhumation of metamorphic terranes is most likely in the steady state where erosion balances accretion a constructive state where mass addition is greater than mass loss results in crustal thickening and initially little exhumation a destructive state where mass loss outweighs mass addition results in slow exhumation or subsidence of metamorphic rocks in the orogen depending on whether mass is removed by erosion or by extension p t t data on peak metamorphism pluton emplacement uplift exhumation and cooling can be used in conjunction with data from the foreland to distinguish among these various states the topography and strength of the inherited rifted margin play an important role in localizing zones of exhumation and uplift within the orogen application of this model to the central and southern appalachians suggests that during the constructive phases of the taconian and acadian orogenies overthrust loads accumulated mainly on the seaward side of the ocean continent transition as marked by the bouguer gravity gradient between the acadian and alleghanian orogenies the appalachian orogen was probably in a steady state with uplift and exhumation of rocks in the orogen but little subsidence of the foreland or advance of thrusts toward the craton the constructive stage of the alleghanian orogeny achieved the critical topography necessary to drive crystalline thrust sheets over the craton this resulted in widespread uplift and westward transport of older metamorphic rocks post orogenic unroofing of the southern appalachians is compatible with the predictions of flexural models the post orogenic unroofing history of the central appalachians and ouachitas probably reflects mesozoic extension in these areas

lowstand tempestites depositional model for cretaceous skeletal limestones western interior basin high resolution sedimentologic paleontologic and stratigraphic data were collected for three cenomanian turonian skeletal limestone packages in the western interior basin results of the study have significant implications for sequence stratigraphy in fine grained basinal facies 1 skeletal limestones represent calcareous tempestites deposited at or near storm wave base and their stratigraphic distribution provides a constraint on paleobathymetry 2 skeletal limestones are widely traceable and can be correlated to coeval progradational retrogradational shoreface deposits placing them in a relative sea level context 3 skeletal limestone origin can be described by a comprehensive depositional model the model incorporates effects of winnowing erosion on relative fall and sediment starvation condensation on subsequent rise relating both to the absence of an effective depositional gradient 4 application of the model suggests a reinterpretation of relative sea level history for the cenomanian turonian in the western interior that is better constrained than previous estimates

timing of low temperature mineral formation during exhumation and cooling in the central alps switzerland abstract construction of the new gotthard rail base tunnel through the central alps provided a truly unique sample of a fissure assemblage formed during exhumation and cooling of the central alps the base of the tunnel is at 500 m a s l and the overburden at the sampling locality amounts to 2000 m the fissure assemblage apophyllite kf laumontite and quartz occurs within the southern aar granite it formed during exhumation and erosion of the alpine orogen apophyllite and laumontite mark very late fissure minerals in the central swiss alps only followed by stilbite hematite and calcite the data from a combined study of 40 ar 39 ar age dating of apophyllite apatite fission track analysis and the petrology of rock samples from tunnel and the from the mountains above the tunnel reflect the late stages of an aging orogen apatite fission track analysis yields an exhumation rate of 0 46 mm yr a cooling rate of 12 3 c m y and a geothermal gradient of 27 c km at the time of apophyllite formation combining these data with the 40 ar 39 ar plateau age of 2 ma for the formation of apophyllite a minimum formation temperature and depth of 68 c at 2550 m below the present day erosion surface follow at this time the position of the sample location was 550 m below the tunnel level assemblage stabilities and computed temperature time evolution of fissures in the aar massif indicate that laumontite formed between 11 and 2 ma ago at temperatures between 180 and 70 c chemical components for forming laumontite were provided from dissolution of minerals of the alpine greenschist facies variscan granitoid rocks of the aar massif basement systematic variations in the composition of laumontite are an effect of decreasing temperature