laboratory earthquakes the sub rayleigh to supershear rupture transition we report on the experimental observation of spontaneously nucleated supershear rupture and on the visualization of sub rayleigh to supershear rupture transitions in frictionally held interfaces the laboratory experiments mimic natural earthquakes the results suggest that under certain conditions supershear rupture propagation can be facilitated during large earthquake events

denudational isostatic rebound of intraplate highlands the lachlan river valley australia a range of evidence from the lachlan valley in the southeast australian highlands is consistent with neogene isostatic rebound in response to denudational unloading this evidence is found along the inland edge of the highlands in the transition zone between the highlands proper and the lachlan s inland alluviated valley and the intracratonic murray basin the amounts and rates of uplift indicated by offsets of suballuvium bedrock profiles and the long profiles of tertiary valley filling basalts are consistent with modelling of denudational rebound using known rates of highland denudation and basinal sedimentation and reasonable crustal properties the modelling shows that weak to moderately strong strong lithosphere effective elastic thickness te 1 25 km and strong lithosphere te 100 km are all consistent with the observed amounts of rebound strong lithosphere must be broken however to be consistent with the field data even in the australian setting which is characterized by very low rates of denudation isostatic rebound in response to denudational unloading must be a significant factor in maintaining highland elevation and must be incorporated in models of long term landscape evolution it would be expected that denudational isostatic rebound would be an even more significant component of long term landscape evolution in areas of higher denudation rates

long term landscape evolution early miocene and modern rivers in southern new south wales australia basaltic lavas that flowed into river valleys draining westward from the uplands of southern new south wales have preserved the early miocene landscape to a remarkable degree the reconstruction of this landscape shows that the major topographic features of the highest part of the australian continent had taken on essentially their present form by the mid tertiary and that some of these features were formed during the mesozoic plateau surfaces have been lowered by only about 2 to 5 m ma and most major streams have incised by only about 5 to 18 m ma with a maximum incision of 30 m ma since the early miocene despite the passage of 20 ma stream gradients have not waned nor have major breaks in profiles been eliminated on the contrary the modern stream profiles are strikingly similar to their early miocene counterparts suggesting that the evolution of the profiles has been determined mainly by variations in stream power rather than by the headward retreat of nickpoints through the drainage system

new physical evidence of the role of stream capture in active retreat of the blue ridge escarpment southern appalachians abstract the blue ridge escarpment of the southern appalachian mountains is a striking and rugged topographic feature of the ancient passive margin of eastern north america the crest of the escarpment generally coincides with an asymmetric regional drainage divide separating steep streams of the escarpment face from low gradient streams of the blue ridge upland recent exhumation and erosion rate studies suggest that the escarpment has evolved by inland erosional retreat but the mechanism timing and magnitude of retreat remain poorly understood longitudinal stream profiles and slope drainage area relationships of several upland basins draining the divide have led to the identification of 14 previously unknown fluvial terrace deposits preserved at the escarpment crest these relict terraces and the associated beheaded drainages indicate the role of large stream capture events in producing ongoing escarpment retreat through landward divide migration and subsequent topographic adjustment terrace location and preservation suggest that rectilinear drainage patterns and divide asymmetry generate discrete high order captures and episodes of rapid localized retreat that collectively produce slower evolution of the escarpment at large while overall retreat magnitude and rate remain unknown roundness of terrace alluvium suggests that the most recent captures have locally produced tens of kilometers of retreat within the limited preservation lifetime of the deposits in contrast with recent numerical modeling and cosmogenic studies these data show the potential for stream capture and divide migration to sustain passive margin escarpment evolution long after the cessation of rifting the fluvial record of divide retreat preserved atop the blue ridge escarpment suggests the potential for using field methods to better constrain the histories of younger taller and potentially more dynamic passive margin escarpments

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

early tertiary palaeogeography landform evolution and palaeoclimates of the southern monaro n s w australia the age of the southern highlands of australia has long been controversial recent field investigations around bombala in southern new south wales have shed some light on this as well as on the early tertiary palaeoclimates in southern australia late palaeocene basalts were extruded on a landscape with a relief of at least 400 m and possibly as much as 800 m showing that the region had a substantial relief by the beginning of the tertiary fluvial and lacustrine sediments deposited on the earlier or prebasaltic landscape have been preserved by the basalt and contain palynofloras and fossil wood as do sediments deposited between basalt flows in the lower parts of the basalt pile the palynomorphs are representative of the lygistepollenites balmei zone in the upper late paleocene ca 58 60 ma the pollen and fossil wood indicate the region was covered by cool temperate rainforest podocarps and araucarian conifers were significant components of these forests in addition to nothofagus ferns were prominent in some localities the fossil wood is dominated by gymnosperms comparison of the palynofloras with bioclimatic data of a number of descendant extant species has shown that most belong to the mesotherm response category with mean annual temperatures in the range 14 20 c there is little evidence that frosts were significant data from tree rings support this and show that climates were markedly seasonal the annual rings are very thin suggesting cool climates their uniformity shows that conditions varied little from year to year

geomorphic controls on andean denudation rates abstract to predict erosion rates throughout the andes we conducted a multiple regression analysis of the sediment discharge from 47 drainage basins in the bolivian andes and various topographic climatologic and geologic parameters these mountainous basins are typically large 17 81 000 km2 documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm mean 11 000 end document km2 often have decades of measurement data on daily water and sediment discharge and display an extraordinary range of denudation 0 01 6 9 mm yr

incision and differential bedrock uplift along the indus river near nanga parbat pakistan himalaya from 10be and 26al exposure age dating of bedrock straths abstract well preserved river cut bedrock surfaces straths abandoned by the progressive incision of the indus river in northern pakistan were dated using in situ cosmogenic 10 be and 26 al exposure age dating measurements on young and modern straths show no significant ingrowth of 10 be and 26 al implying that strath exposure ages closely approximate their abandonment age strath exposure ages range up to 65 ka and increase with height above the river the straths can be divided into two groups low straths dated at about 7 ka which yield very rapid bedrock incision rates 9 12 m ka and high straths 7 ka in age which yield somewhat slower incision rates 1 6 m ka incision rates for both groups increase by 1 3 m ka downstream toward an active reverse fault the raikot fault that forms the western border of the nanga parbat haramosh massif nphm the downstream increases in incision rates for the low straths mimic downstream increases in the modern gradient suggesting that bedrock incision rates have been proportional to stream power over the last 7 ka gradient increases are probably the result of the creation of knickpoints by bedrock uplift along the raikot fault the longitudinal profile and steep gorge of the indus river in the study area indicate that bedrock incision appears to keep pace with differential vertical motions between the nphm and surrounding regions thus the 1 3 m ka difference in incision rates likely reflects the differential bedrock uplift rate between the nphm and the skardu basin the differential incision rate is consistent with differential exhumation rates obtained from apatite fission track ages assuming geotherms of 80 90 c km in the nphm and 35 c km in the skardu basin this relation suggests that rapid bedrock incision of at least 1 3 m ka has persisted within the nphm for the last 0 5 ma the acceleration of incision rates throughout the study area since 15 ka is likely to be a climatic signal that records an increase in the discharge and or sediment load of the indus river in the study area related to deglaciation of the surrounding terrane

crustal constraints on the evolution of the continental divide of eastern australia the continental drainage divide of eastern australia follows major negative bouguer gravity anomalies for more than 3000 km this relation indicates that there have been major crustal constraints on the evolution of the divide and that traditional explanations that were couched in terms only of stream capture or diversion during successive cycles of erosion are no longer tenable comparable evidence from elsewhere in australia and the appalachians of the united states suggests that many apparent anomalies in large scale drainage patterns may be attributable to long lasting or resurgent crustal influences

slope aspect slope length and slope inclination controls of shallow soils vegetated by sclerophyllous heath links to long term landscape evolution abstract on upland triassic sandstone slopes of the western blue mountains nonswamp sclerophyllous heath shrub dominated vegetation on shallow soils is commonly found downslope and adjacent to sclerophyllous forest on deeper soils some consider heath and thus shallow soils as favouring west facing slopes which are expected to experience drier microclimates due to insolation strong and desiccating winds and severe summer fires however our analysis of extensive areas with heath on shallow soils based on vegetation and topographic maps and fieldwork of uplands with various degrees of dissection suggests that aspect is a poor predictor of shallow soils rather shallow soils and heath are found on short slopes and the lower segments of longer slopes with the latter significantly steeper than forested segments the shallow deep soil boundary marked by contrasting modern vegetation structures does not signify a catchment area threshold and correspondingly the vegetation patterns are not in balance with distributary catchment processes as short slopes are mantled exclusively by shallow soils instead the soil depth boundary represents the propagation of base level lowering signals which takes place not only by the headward retreat of knickpoints but also via increased lowering of slope segments adjacent to drainage lines this leads to steep slopes immediately adjacent to canyons narrow gorges and small steep valleys that are mantled by shallow discontinuous soils undergoing rapid erosion these steep slopes persist in the landscape for 10 my after upland stream rejuvenation until incision of more weatherable permian sediments underlying the triassic cliff forming sandstones triggers rapid lateral expansion of gorges once shallowly mantled and steeper slopes adjacent to streams are consumed by gorge widening slopes adjacent to wide gorge clifflines reflect former upland drainage patterns rather than the redirected flow to rapidly widening gorges hence modern vegetation patterns reflect a significant phase of landform development perhaps combined with enhanced erosion during the last glacial period that is compounded by a humped soil production function on bedrock

a new surface processes model combining glacial and fluvial erosion we have developed a new surface processes model incorporating large scale fluvial processes local hill slope processes and glacial erosion ice thickness and velocity are calculated under a shallow ice approximation simulation experiments in fast growing orogens comparing the efficiencies of fluvial and glacial erosion where the two are operating simultaneously over several glacial cycles show that glacial landscapes can support greater ice masses than fluvial landscapes glacial valley and lake shapes create a disequilibrium between landform and land forming process that leads to pulses of high erosion at the end of glacial periods glacial erosion rates can reach a constant value in a uniformly growing orogen and glacial erosion is capable of eroding drainage divides when the ice is moderately thick

implications of the shear stress river incision model for the timescale of postorogenic decay of topography 1 the reason for the survival of mountainous topography in ancient orogenic belts is a long standing problem in geomorphology and geodynamics we explore the geomorphologic controls on the timescale for the postorogenic decay of topography to address the question of whether there is a viable geomorphologic explanation for the persistence of topography in ancient orogenic belts or whether alternative geodynamic explanations must be sought using both approximate analytical solutions and numerical simulations we show that the standard detachment limited stream power river incision model predicts for reasonable initial topographies relatively short postorogenic decay times of 1 10 myr additional layers of complexity are introduced to this simplest model including isostasy and flexural strength a transition to transport limited conditions during decline and the incorporation of the combined effects of a critical threshold for erosion and the stochastic variability of flood magnitudes each of these additional factors acts to lengthen the decay timescale pure airy isostatic rebound of a thick crustal root results in decay times that are at most a factor of 6 longer than the detachment limited result the transition to transport limited conditions involves partial protection of the bed by a thin layer of alluvium which inhibits erosion and therefore increases decay times by a factor of 2 3 in our analysis finally including critical shear stress results increases decay time by approximately a factor of 20 for the parameter values in our example calculation more importantly however a significant portion of topography remains after predicted lowering rates have dropped to values less than measured rates of denudation in weathering limited low relief environments thus a model combining isostasy a transition to transport limited conditions and a critical shear stress for erosion could account for the presence of residual topography for hundreds of million years all three of these factors can be expected to play a role in natural settings

southeast australian late mesozoic and cenozoic denudation rates a test for late tertiary increases in continental denudation throughout the tertiary average rates of erosion of southeast australia have been uniformly low about 10 3 mm yr of surface lowering indicating that this part of the australian continent did not contribute to a rapid increase in ocean basin sedimentation over the past 15 or 20 m y somewhat higher mesozoic rates may be the result of minor tectonism but explanation for the generally low cenozoic and mesozoic erosion rates may be sought in the forest cover and general tectonic stability of southeast australia over this time period australia9s gradually increasing aridity climatic seasonally over the past 20 m y has apparently not resulted in higher average rates of erosion of the continent except perhaps in the very latest tertiary and quaternary

pattern and tempo of great escarpment erosion extensive geological geophysical structural and geochronological data suggest that the locations of great escarpments bordering passive margins are exceptionally stable and are probably determined by crustal structure together the data do not support the established paradigm of ongoing significant and parallel escarpment retreat rather thermochronologic data and sedimentary sequences in ocean basins suggest that initial tectonically controlled rift escarpments undergo rapid and significant erosion only during the earliest stages of seafloor spreading development of stable passive margin escarpments follows this period of intense erosion escarpments increase in sinuosity as embayments retreat more rapidly than interfluves measurements of 24 escarpments suggest that sinuosity and the rate at which it increases depends upon the location of maximum uplift the geometry of the preescarpment drainage system and margin age all data suggest that the location of passive margin escarpments does not change significantly over time

the humped soil production function eroding arnhem land australia we report erosion rates and processes determined from in situ produced beryllium 10 10be and aluminum 26 26al across a soil mantled landscape of arnhem land northern australia soil production rates peak under a soil thickness of about 35 cm and we observe no soil thicknesses between exposed bedrock and this thickness these results thus quantify a well defined humped soil production function in contrast to functions reported for other landscapes we compare this function to a previously reported exponential decline of soil production rates with increasing soil thickness across the passive margin exposed in the bega valley south eastern australia and found remarkable similarities in rates the critical difference in this work was that the arnhem land landscapes were either bedrock or mantled with soils greater than about 35 cm deep with peak soil production rates of about 20 m ma under 35 40 cm of soil thus supporting previous theory and modeling results for a humped soil production function we also show how coupling point specific with catchment averaged erosion rate measurements lead to a better understanding of landscape denudation specifically we report a nested sampling scheme where we quantify average erosion rates from the first order upland catchments to the main sixth order channel of tin camp creek the low 5 m ma rates from the main channel sediments reflect contributions from the slowly eroding stony highlands while the channels draining our study area reflect local soil production rates 10 m ma off the rocky ridge 20 m ma from the soil mantled regions quantifying such rates and processes help determine spatial variations of soil thickness as well as helping to predict the sustainability of the earth s soil resource under different erosional regimes copyright 2009 john wiley sons ltd

a review of numerical modeling studies of passive margin escarpments leading to a new analytical expression for the rate of escarpment migration velocity abstract passive margins are geomorphological features that have historically attracted much attention from the modeling community in particular many numerical modeling studies have attempted to explain the longevity of steep escarpments that formed along continental edges at the transition between low elevation coastal plains and high elevation continental interiors such as along the coasts of africa and south america on both sides of the south atlantic ocean in this paper i review the wide and diverse body of observational constraints gathered to constrain the formation and evolution of passive margins escarpments as well as the various mechanisms that have been proposed to explain their anomalously high topography i then compile and summarize the findings of numerous numerical modeling studies that have been performed in the past twenty years to explain their formation and evolution i show that many of these studies converged to agree that the longevity of passive margin escarpments depends on how rapidly they become and remain regional drainage divides and that this is primarily controlled by the flexural isostatic rebound associated with the erosion of the high elevation continental interior to better quantify these findings i derive and present a new analytical expression for the migration velocity of an escarpment once it has become a drainage divide this expression is validated by a series of numerical experiments using 1d and 2d high resolution landscape evolution models interestingly these models also predict that the rate of erosion at or near escarpments can be several orders of magnitude smaller than the rate of escarpment retreat this may explain the apparent discrepancy between the low estimates of present day erosion rates obtained mostly from cosmogenic nuclide studies 10m myr and the long term rates of escarpment retreat 1km myr

a 1 d mechanistic model for the evolution of earthflow prone hillslopes 1 in mountainous terrain deep seated landslides transport large volumes of material on hillslopes exerting a dominant control on erosion rates and landscape form here we develop a mathematical landscape evolution model to explore interactions between deep seated earthflows soil creep and gully processes at the drainage basin scale over geomorphically relevant 10 3 year timescales in the model sediment flux or incision laws for these three geomorphic processes combine to determine the morphology of actively uplifting and eroding steady state topographic profiles we apply the model to three sites one in the gabilan mesa california with no earthflow activity and two along the eel river california with different lithologies and varying levels of historic earthflow activity representative topographic profiles from these sites are consistent with model predictions in which the magnitude of a dimensionless earthflow number based on a non newtonian flow rheology reflects the magnitude of recent earthflow activity on the different hillslopes the model accurately predicts the behavior of earthflow collection and transport zones observed in the field and estimates long term average sediment fluxes that are due to earthflows in agreement with historical rates at our field sites finally our model predicts that steady state hillslope relief in earthflow prone terrain increases nonlinearly with the tectonic uplift rate suggesting that the mean hillslope angle may record uplift rate in earthflow prone landscapes even at high uplift rates where threshold slope processes normally limit further topographic development

controls on post mid cretaceous landscape evolution in the southeastern highlands of australia insights from numerical surface process models the tectonic and geomorphic evolution of the southeastern australian highlands has been a subject of controversy among geophysicists geologists and geomorphologists for several decades we employ a numerical surface process model that includes long range fluvial transport hillslope diffusion and landsliding in order to quantitatively assess the tectonic lithological and structural controls on the landscape evolution and denudation history of se australia we constrain fluvial erosion parameters for our model by fitting river profiles rockfall and landsliding are the most important processes controlling the concentration of erosion in river valleys we therefore model hillslope evolution using a very low diffusion coefficient and a threshold slope for landsliding the initial prebreakup topography of the highlands provides a fundamental control on their subsequent evolution together with the style and rate of fluvial incision secondary controls are exerted by lateral variations in lithology and local tectonic uplift along faults our modeling results indicate that 1 the observed highlands morphology requires that the drainage divide was established at its present location prior to opening of the tasman sea whether the divide is inherited from paleozoic orogeny or resulted from mesozoic syn rift uplift cannot be established however 2 in contrast to traditional interpretations escarpment retreat does not appear to be the fundamental process eroding the highlands and 3 the observed barbed river drainage may be imprinted as a result of lithological variation it does not necessarily evolve through capture the driving mechanism that is most consistent with the inferred uplift pattern of the southeastern highlands appears to be magmatic underplating

post gondwana geomorphic evolution of southwestern africa implications for the controls on landscape development from observations and numerical experiments the relationship between morphology and surficial geology is used to quantify the denudation that has occurred across southwestern africa since the fragmentation of gondwana during the early mesozoic two main points emerge significant denudation of the order of kilometers is widespread except in the kalahari region of the continental interior the denudation is systematically distributed so that the continental exterior catchment draining directly to the cape basin is denuded to a greater depth than the interior catchment inland of the great escarpment the analysis also implies that the majority of the denudation occurred before the beginning of the cenozoic for both the exterior and interior catchments existing models of landscape development are reviewed and implications of the denudation chronology are incorporated into a revised conceptual model this revision implies that the primary effect of rifting on the subsequent landscape evolution is that it generates two distinct drainage regimes a marginal upwarp or rift flank uplift separates rejuvenated rivers that drain into the subsiding rift from rivers in the continental interior that are deflected but not rejuvenated the two catchments evolve independently unless they are integrated by breaching of the marginal upwarp if this occurs the exterior baselevel is communicated to the interior catchment that is denuded accordingly denudation rates generally decrease as the margin evolves and this decrease is reinforced by the exposure of substrate that is resistant to denudation and or a change to a more arid climate the observations do not reveal a particular style of smaller scale landscape evolution such as escarpment retreat that is responsible for the differential denudation across the region it is proposed that numerical model experiments which reflect the observational insights at the large scale may identify the smaller scale controls on escarpment development if the model and natural systems are analogous four numerical experiments are presented in which the roles of antecedent topography resistant substrate climate change and lowering the baselevel of the interior catchment are investigated for an initially high elevation margin bordered by an escarpment the model results suggest several styles of landscape evolution that are compatible with the observations escarpments may retreat in a regular manner but they also degrade and are destroyed only to reform at the drainage divide between exterior and interior catchments

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

present day trends of vertical ground motion along the coast lines vertical ground motion vgm rates stand as crucial information either for predicting the impact of the actual sea level rise along low lying coasts or refining geodynamic problems because present day vgm rates have a magnitude smaller than 10 mm yr they remain challenging to quantify and often elusive we focus on the quantification of global scale vgm rates in order to identify global or regional trends we computed vgm rates by combining tide gauges records and local satellite altimetry which yield a new dataset of 634 vgm rates we further compare this database to previous studies that use geodetic techniques and tide gauges records in order to evaluate the consistency of both our results and previous ones the magnitudes differ by less than 5 mm yr and similar subsidence and uplift general tendencies appear even if the asset of our database stands in the greater number of sites the combination of all studies each with different pros and cons yields a hybrid dataset that makes our attempt to extract vgm trends more robust than any other independent study fennoscandia the west coast of north america and the eastern coast of australia are uplifting while the eastern coast of north america the british isles and western europe the eastern mediterranean sea japan and the western coast of australia are subsiding glacial isostatic adjustment gia is expected to provide a major contribution to the present day signal aside from fennoscandia observed vgm often depart from the gia model predictions of peltier 2004 this either results from an underestimate of the model predictions or from the influence of other processes indeed the influence of the geodynamic setting appears in particular along the coasts of western north america or japan where the alternation of transform faults and subduction zones makes it possible to assign contrasted behaviours to the local geodynamic context local mechanisms like anthropogenic processes or sediment compaction also contribute to vgm this remains true for the critical cases of venice the gulf of mexico the ganges delta and the maldives which are particularly exposed to the current sea level rise

cenozoic landscape development in the blue mountains se australia lithological and tectonic controls on rifted margin morphology abstract cenozoic landscape development on the southeastern australian rifted margin as recorded by mid tertiary basalt flows that preserve ancient landforms is generally considered to be very slow eocene miocene basalts of the southeastern australian highlands flowed down paleovalleys indicating that landscape dissection was already well under way at the time of their eruption within the deeply incised blue mountains however miocene basalts cap relatively flat hilltops suggesting that most incision postdates their emplacement we have studied the controls on these apparent lateral variations in cenozoic landscape development using both field observations and numerical models we have mapped the blue mountains basalts in detail to reconstruct the miocene landscape and to quantify both the amount of subbasalt relief and postbasalt incision rates new geochemical and k ar geochronological data indicate that most of the blue mountains basalts were derived from a common magma source and were erupted i

multiple postorogenic denudation events an example from the eastern lachlan fold belt australia fission track results from 40 surface samples from the eastern part of the lachlan fold belt australia suggest that two distinct episodes of rapid kilometre scale denudation have occurred since the middle carboniferous when deformation within the fold belt is believed to have ceased the first episode during the early triassic was possibly in response to the hunter bowen orogeny which affected the new england fold belt and the sydney bowen basin but the effects of which have previously not been recognized within the lachlan fold belt the second episode occurred during the middle cretaceous possibly in response to the onset of continental extension in the tasman sea ca 96 ma uplift at this time resulted in kilometre scale denudation over much of the southeastern highlands of australia and may have been caused by underplating inward of the rift these results indicate that the lachlan fold belt has remained tectonically active long after the last recognized deformational event in the region and highlight the importance of fission track data in elucidating the posttectonic histories of orogens previously undetected due to a lack of stratigraphic and structural crosscutting relationships

soil production on a retreating escarpment in southeastern australia the functional dependence of bedrock conversion to soil on the overlying soil depth the soil production function has been widely recognized as essential to understanding landscape evolution but was quantified only recently here we report soil production rates for the first time at the base of a retreating escarpment on the soil mantled hilly slopes in the upper bega valley southeastern australia concentrations of 10 be and 26 al in bedrock from the base of the soil column show that soil production rates decline exponentially with increasing soil depth these data define a soil production function with a maximum soil production rate of 53 m m y under no soil mantle and a minimum of 7 m m y under 100 cm of soil thus constraining landscape evolution rates subsequent to escarpment retreat the form of this function is supported by an inverse linear relationship between topographic curvature and soil depth that also suggests that simple creep does not adequately characterize the hillslope processes spatial variation of soil production shows a landscape out of dynamic equilibrium possibly in response to the propagation of the escarpment through the field area within the past few million years in addition we present a method that tests the assumption of locally constant soil depth and lowering rates using concentrations of 10 be and 26 al on the surfaces of emergent tors

episodic post rift deformation in the south eastern australian passive margin evidence from the lapstone structural complex identifying the influence of neotectonics on the morphology of elevated passive margins is complicated in that major morpho structural patterns might plausibly be explained by processes related to late mesozoic to early cenozoic rifting and or differential erosion induced by cenozoic epeirogenic uplift the proportional contribution of each process can vary from continent to continent and potentially even within the same passive margin in the passive margin setting of the southeast australian highlands the documented occurrence of neotectonic deformation is rare and accordingly its role in landscape evolution is difficult to establish the results of investigations within the lapstone structural complex which forms the eastern range front of the blue mountains plateau provide evidence for two periods of cenozoic neotectonic uplift in this part of the highlands the first demonstrated by seismic and structural evidence is suggested to have occurred in the paleogene and is thus unrelated to cretaceous rifting the second period demonstrated by evidence from the kurrajong fault presented herein suggests that uplift occurred in both the mio pliocene and the middle pleistocene the cumulative neogene and younger uplift of 15 m determined for the kurrajong fault is less than 10 of the 130 m of total measured throw across the fault the apparently minor contribution of neotectonism to the current elevation of the blue mountains plateau supports a predominantly erosional exhumation origin for the topographic relief at the plateau s eastern edge this finding contrasts with evidence from fault complexes associated with similar topographic relief elsewhere in the south eastern highlands indicating that present day topography cannot be directly related to relief generated by neogene and younger uplift even from relatively closely spaced 150 km structures within the same passive margin these findings have implications for understanding the spatio temporal variability of post rift faulting in continental passive margin settings and the evolution of landscapes therein commonwealth of australia earth surface processes and landforms 2014 john wiley sons ltd

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

topographic signatures and a general transport law for deep seated landslides in a landscape evolution model a fundamental goal of studying earth surface processes is to disentangle the complex web of interactions among baselevel tectonics climate and rock properties that generate characteristic landforms mechanistic geomorphic transport laws can quantitatively address this goal but no widely accepted law for landslides exists here we propose a transport law for deep seated landslides in weathered bedrock and demonstrate its utility using a two dimensional numerical landscape evolution model informed by study areas in the waipaoa catchment new zealand and the eel river catchment california we define a non dimensional landslide number which is the ratio of the horizontal landslide flux to the vertical tectonic flux that characterizes three distinct landscape types one is dominated by stochastic landsliding whereby discrete landslide events episodically erode material at rates exceeding the long term uplift rate another is characterized by steady landsliding in which the landslide flux at any location remains constant through time and is greatest at the steepest locations in the catchment the third is not significantly affected by landsliding in both the stochastic landsliding and steady landsliding regimes increases in the non dimensional landslide number systematically reduce catchment relief and widen valley spacing producing long low angle hillslopes despite high uplift rates the stochastic landsliding regime captures the frequent observation that deep seated landslides produce large sediment fluxes from small areal extents while being active only a fraction of the time we suggest that this model is adaptable to a wide range of geologic settings and is useful for interpreting climate driven changes in landslide behavior

apatite u th he age constraints on the development of the great escarpment on the southeastern australian passive margin the southeast australian margin like other high elevation passive margins is characterised by a steep escarpment that separates a dissected coastal plain from a low relief inland plateau quantitative constraints on the generation of escarpments can be provided by apatite u th he ages here we use a coast perpendicular traverse across the coastal lowlands escarpment and plateau to test the three prevailing models of se australian escarpment formation namely retreat into a downwarped rift shoulder escarpment retreat and down wearing on high elevation rift shoulder with flexural rebound apatites from the coastal plain have he ages of between 87 and 112 ma suggesting that the coastal lowlands developed very rapidly after rifting and continental break up at 85 100 ma the he age data are inconsistent with the erosion of a downwarped rift margin and cannot be explained by a constant post break up rate of lateral escarpment retreat across the coastal plain or by constant down wearing the data require either rapid escarpment retreat or rapid in place excavation of the escarpment soon after break up in response to rifting and the lowering of base levels on the margin of the new continent at break up followed by a period of landscape stability and low erosion combined with the existing apatite fission track record the he data are consistent with erosion of 3 4 km within a maximum of 28 myr of break up at a minimum vertical erosion rate of 130 m myr 1 along the coast the rapid denudation period across the coastal plain in this region took less than 48 myr from the coast to the escarpment base which corresponds to an average vertical erosion rate of 45 m myr 1 this is equivalent to a mean escarpment retreat rate of 5 10 km myr 1 apatite he ages from the plateau 183 247 ma indicate that the highlands remained stable throughout continental break up experiencing average erosion rates of less than 10 m myr 1 since the late palaeozoic early mesozoic

morphotectonic evolution of rifted continental margins inferences from a coupled tectonic surface processes model and fission track thermochronology we use a numerical model to study the topographic evolution and erosional history of rifted continental margins the model combines a kinematic description of lithospheric extension tectonic model with a surface processes model that includes short range hillslope and long range fluvial transport the tectonic model predicts the evolution of the lithospheric temperature and strength elastic thickness distribution as well as the tectonic uplift through time this is input into the surface processes model which calculates the degradation of topography and associated isostatic rebound modeled denudation histories across the margin are used to predict apatite fission track age and length patterns modeling results indicate that depending on the adopted parameters an uplifted rift flank should degrade by erosion within 50 100 m y without significant retreat of the topographic elevation maximum the development of an escarpment system at rifted continental margins is in itself not an indication of tectonic rift flank uplift but results from the existence of a high elevation interior plateau erosional base level lowering as a consequence of rifting and regional isostatic response to erosion of the margin however apatite fission track thermochronology reveals that the areas seaward of the escarpment at a number of rifted margins have been exhumed from several kilometers depth such amounts of denudation cannot be accommodated with isostatic rebound alone and require additional tectonic uplift of the rift flanks modeling of apatite fission track patterns suggests that fission track thermochronology dates the onset of rapid erosion which coincides with the initiation of strong relief i e initiation of rifting fission track ages which are younger than the age of rifting thus cannot be unambiguously interpreted as excluding prerift uplift the timing of margin uplift can be established only by careful track length analysis and integration with regional stratigraphic data the model is applied to the saudi arabian red sea margin and the southeastern australian highlands where it is constrained by present day topography and apatite fission track data as well as seismic and gravity data for the saudi arabian red sea margin synrift regional plateau uplift with a magnitude of approximately 1 km is inferred possibly as a result of asthenospheric upwelling flexurally induced tectonic uplift of the rift flank with a magnitude of 2 km is superimposed on this regional uplift the relatively high elevation of the southeastern australian highlands their steep front and the relatively high amounts of erosion suggest that apart from mesozoic synrift flexural uplift tertiary rejuvenation of topography has occurred possibly as a result of renewed lithospheric thinning and underplating the low elevation of the australian interior would inhibit the evolution of a major escarpment in the absence of such renewed uplift

extensional neotectonics around the bend of the western central alps an overview the western alps active tectonics is characterized by ongoing widespread extension in the highest parts of the belt and transpressive compressive tectonics along its borders we examine these contrasting tectonic regimes using a multidisciplinary approach including seismotectonics numerical modeling gps morphotectonics fieldwork and brittle deformation analysis extension appears to be the dominant process in the present day tectonic activity in the western alps affecting its internal areas all along the arc shortening in contrast is limited to small areas located along at the outer borders of the chain strike slip is observed throughout the alpine realm and in the foreland the stress orientation pattern is radial for 3 in the inner extensional zones and for 1 in the outer transcurrent tranpressional ones extensional areas can be correlated with the parts of the belt with the thickest crust quantification of seismic strain in tectonically homogeneous areas shows that only 10 20 of the geodesy documented deformation can be explained by the alpine seismicity we propose that alpine active tectonics are ruled by isostasy buoyancy forces rather than the ongoing shortening along the alpine europe adria collision zone this interpretation is corroborated by numerical modeling the neogene extensional structures in the alps formed under increasingly brittle conditions a synthesis of paleostress tensors for the internal parts of the west alpine arc documents major orogen parallel extension with a continuous change in 3 directions from ene wsw in the simplon area to n s in the vanoise area and to nnw sse in the briancon area minor orogen perpendicular extension increases from n to s this second signal correlates with the present day geodynamics as revealed by focal plane mechanisms analysis the orogen parallel extension could be related to the opening of the ligurian sea during the early middle miocene and to compression rotation of the adriatic indenter inducing lateral extrusion

post rift influence of small scale convection on the landscape evolution at divergent continental margins abstract after decades of geological and geophysical data acquisition along with quantitative modeling of the long term evolution of the landscape at divergent continental margins the search for an explanation for the formation and evolution of steep escarpments bordering the coast is still a challenging task one difficult aspect to explain about the evolution of these escarpments is the expressive variability of denudation rate through the post rift phase observed in many margins here i propose that the interaction of small scale convection in the asthenosphere with the base of the continental lithosphere can create intermittent vertical displacements of the surface with magnitude of a few hundreds of meters at the continental margin these topographic perturbations are sufficient to produce an expressive variability in the rate of erosion of the landscape through the post rift phase similar to the exhumation history observed along old divergent margins i show that the vertical motion of the surface is amplified when a mobile belt is present at the continental margin with lithospheric mantle less viscous than the cratonic lithosphere and consequently more prone to be partially eroded by the convective asthenosphere i conclude that the influence of small scale convection is not the primary explanation for the formation of high topographic features at divergent continental margins but can be an important component contributing to sustain a preexistent escarpment the present results are based on numerical simulations that combine thermochemical convection in the mantle flexure of the lithosphere and surface processes of erosion and sedimentation

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

evolution of the santa cruz mountains california through tectonic growth and geomorphic decay i describe a strategy for modeling a specific large scale topographic feature that recognizes the discrepancy between tectonic and geomorphic scales and allows for important feedbacks between these processes in the geomorphic model the largest channel in each 4 4 km cell is explicitly treated the channel incision being driven by a stream power rule hillslopes internal to each cell respond rapidly to incision of the local channel prompting their treatment in the model as steady state forms i present analytic expressions for the local relief which is controlled by the local channel incision rate and rate constants associated with the dominant hillslope process either diffusive or landsliding initial conditions include any preexisting topography and a lightly etched a channel network the model is illustrated using the santa cruz mountains california i show that an earlier hypothesis that the santa cruz mountains are due to advection of topography past an uplift source related to a restraining bend in the san andreas fault remains viable when more specific geomorphic processes are considered the local tectonics are represented by crustal thickening necessitated by conservation of mass in the bend right lateral translation of crust with respect to the bend and flexural response to the distributed load the model produces reasonable geographic and statistical distributions of topography using rates of tectonic and geomorphic processes that are within the range of those measured locally this argues that this restraining bend is a long lived feature of the san andreas fault the slightly higher crest and shorter length of the southern santa cruz mountains may potentially be explained by slightly faster slip of the crust west of the fault with respect to the bend than of that to the east deflection is minimal beneath these relatively small mountains disallowing the interesting feedback of erosionally driven uplift the predicted pattern of exhumation could be used to guide the search for fission track sites that could aid in the testing of the model

normal fault control on bedrock channel incision and sediment supply insights from numerical modeling 1 the evolution of footwall drainage basins sediment supply and hanging wall stratigraphy in rift basins is investigated using a coupled numerical model of detachment limited stream network evolution and coarse grained fan delta deposition the response of bedrock channel networks to repeated footwall uplift events leads to increasing sediment supply over tens of thousands of years as the networks initiate and then expand followed by relatively constant sediment supply as the stream networks reach their maximum spatial extent the distinct time lag between the onset of tectonic activity and attainment of maximum sediment supply leads to stratigraphies that are initially aggradational and then progradational much of the variation in sediment supply is the product of the complex response and reorganization of the stream networks to faulting related perturbations and is not directly related to specific faulting events increasing fault displacement drives the system toward a new steady state with a higher sediment supply but is initially expressed as a retrogradation as sediment supply lags behind increased displacement the converse is true for a decrease in fault displacement which is initially expressed as progradation continual stochastic variation in recurrence interval leads to a system that does not achieve a steady state and as a result exhibits continual variation in sediment supply the model results emphasize the local tectonic controls on stratigraphic architectures developed within extensional basins and the complex manner in which stream network growth and response to tectonic activity can be expressed in the stratigraphic record

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

long term drainage evolution in the shoalhaven catchment southeast highlands australia the long term evolution of streams in the shoalhaven catchment of southeast new south wales has been a contentious issue for decades several authors have suggested that the shoalhaven river was captured at the sharp eastward bend near tallong this has been used as evidence for the westward migration of the east australian divide in this area other workers however have argued that capture did not occur and that the location of the divide has been stable throughout the tertiary a vast sheet of sediments which spread across and infill a palaeovalley network cut into a broad undulating plain in the middle shoalhaven catchment provides a record of stream behaviour since at least the start of the tertiary this record shows that the shoalhaven river and many of its tributaries have maintained almost the same courses since at least the very early tertiary this provides strong evidence against the capture hypothesis the record further suggests that during the paleogene these streams were graded to a level within the southeast australian highlands their depths of incision thus cannot be used as evidence for the extent of uplift of the southeast australian highlands during this time

sediment flux from a mountain belt derived by landslide mapping in humid uplands landsliding is the dominant mass wasting process in the western southern alps of new zealand landslides are scale invariant and have a power law magnitude frequency distribution independent studies from other regions suggest that this is a general property of landsliding this observation is of critical importance to the evaluation of the impact of events of different length scales over different time intervals on landscape evolution it is particularly useful when estimating regional geomorphic rates because it constrains the frequency and overall significance of extreme events which cannot otherwise be evaluated by integrating the complete response of the system we estimate the regional denudation rate due to landsliding to be 9 4 mm yr 1 sediment discharge from the western southern alps is dominated by landslide derived material

upper mantle shear velocity beneath eastern australia from inversion of waveforms from skippy portable arrays in 1993 the research school of earth sciences of the australian national university commenced a nationwide seismometry project skippy for a comprehensive study of the upper mantle beneath the australian continent we applied a waveform inversion technique to broad band data recorded while the skippy portable arrays were positioned in eastern australia in order to construct a 3 d model of shear velocity in the upper mantle and transition zone beneath eastern australia and the adjacent oceanic regions the skippy data were augmented by data from the permanent seismological observatories in the region the first step of the waveform inversion used involved the matching of the waveforms of fundamental and higher mode rayleigh waves with waveforms synthesized from radially stratified models in the second stage the linear constraints on radial variations in shear velocity were combined in a tomographic inversion for aspherical variations in shear velocity the preferred model reduces the data variance by 90 per cent owing to the dense data coverage structural features with dimensions larger than 250 km laterally and 50 km vertically are resolved the major structural features inferred from the tomographic images are 1 a substantial increase in the thickness of the high velocity lid from the oceanic region to the phanerozoic continental and proterozoic continental regions 2 a pronounced low velocity zone centred at 140 km depth beneath the part of eastern australia often referred to as the tasman fold belt which confirms previous inferences from rayleigh wave dispersion curves 3 a prominent zone of low wave speeds beneath the eastern margin of the continent that coincides with locations of cenozoic volcanism and regions of enhanced heat flow 4 deep low wave speed anomalies beneath both the coral and tasman seas and 5 localized high wave speed perturbations in the mantle transition zone 410 660 km depth beneath eastern australia in particular beneath the new england fold belt and the mount isa block from the images we infer that the eastern boundary of the precambrian shields does not coincide with a sharp seismic contrast unless this boundary is located further to the east than is commonly assumed the structure of the upper mantle and transition zone beneath eastern australia as inferred from the images is more complex than that beneath the precambrian cratons of central and western australia which could be due to subduction beneath the eastern continental margin prior to opening of the tasman sea if correct this interpretation would imply that part of the upper mantle has moved along laterally with the lithosphere during the relatively fast northward motion of the plane

effect of shaking strength on the seismic response of liquefiable level ground abstract shaking strength is one of the most important parameters that characterize earthquake events in the past it was common to apply shaking of different strengths consecutively on a soil model to investigate the effect of shaking level on seismic ground response without considering the effect of loading history in this study a series of dynamic centrifuge tests under different shaking levels was performed on fresh saturated sand models with the same initial conditions to investigate the effect of shaking strength on the seismic response of liquefiable level ground the experimental observations indicate the following effects 1 shaking strength has pronounced effect on the excess pore pressure buildup in the saturated sand deposit the maximum excess pore pressure at the deep part of the deposit increased by 184 and 109 as the peak input acceleration along the x direction increased from approximately 0 064 g to 0 098 g and from 0 098 g to 0 189 g respectively 2 shaking strength has significant effect on the development of shear strain in soil however the permanent settlement is sensitive to the shaking strength at low shaking level but the increment rate tends to slow down as the shaking strength becomes stronger 3 the peak acceleration along the x direction at the ground surface was 0 126 0 079 and 0 087 g at peak input accelerations of 0 064 0 098 and 0 189 g respectively the peak acceleration at the ground surface under slight shaking was greater than that under strong shaking 4 the amplification pattern of acceleration varied continuously during shaking the amplification factor decreased quickly as the excess pore pressure accumulated under strong shaking but continued to increase at an early stage under low strength earthquake the natural frequency of the soil column also evolved with the development of the shaking induced excess pore pressure which had adversely affected the wave propagation and ground response the data presented in this paper enrich the ground response database and can be used to validate the current site response analysis methods

rapid incision of the mekong river in the middle miocene linked to monsoonal precipitation the uplift of orogenic plateaus has been assumed to be coincident with the fluvial incision of the gorges that commonly cut plateau margins the mekong river which drains the eastern qiangtang terrane and southeastern tibetan plateau is one of the ten largest rivers in the world by water and sediment discharge when the mekong river was established remains highly debated with estimates that range from more than 55 to less than 5 million years ago despite being a key constraint on the elevation history of the tibetan plateau here we report low temperature thermochronology data from river bedrock samples that reveal a phase of rapid downward incision 700 m of the mekong river during the middle miocene about 17 million years ago long after the uplift of the central and southeastern tibetan plateau however this coincides with a period of enhanced east asian summer monsoon precipitation over the region compared with the early miocene using stream profile modelling we demonstrate that such an increase in precipitation could have produced the observed incision in the mekong river in the absence of an obvious tectonic contribution we suggest that the rapid incision of the tibetan plateau and the establishment of the mekong river in the middle miocene may be attributed to increased erosion during a period of high monsoon precipitation incision of the mekong river that occurred after the uplift of the tibetan plateau may have been driven by a period of high monsoon precipitation as suggested by age data from river bedrock samples and stream profile modelling

thermal evolution of rifted continental margins new evidence from fission tracks in basement apatites from southeastern australia the palaeozoic granitic basement of southeastern australia shows a regular pattern of apatite fission track ages which is dominated by a rapid decrease in apparent age towards the rifted continental margin apparent ages away from the margin vary between about 230 and 360 myr but drop sharply to minimum values of around 80 myr near the coast just south of the sydney basin and 150 175 myr elsewhere along the coast fission track length information allows the age pattern to be interpreted as the result of partial to complete resetting of the older ages by a widespread thermal event at about 80 100 myr this event accompanied the rift phase of passive margin development and peaked just before the onset of sea floor spreading in the adjacent tasman sea the zone of reduced apatite ages is deeply embayed around the gippsland basin supporting the suggestion that it originated as a cretaceous failed arm of the tasman rift system the thermal event has affected apatites up to about 130 km from the margin and has produced a characteristic set of bimodal track length distributions in apatites with partially reset ages the bimodality gradually disappears towards the oldest apatite ages which have negatively skewed unimodal distributions the youngest apatites also tend towards unimodal length distributions indicating that thermal annealing of pre existing tracks in these samples went almost to completion maximum temperatures reached in samples presently exposed in the coastal area were thus probably about 110 120 c thermal activity was accompanied by considerable uplift across the region followed by gradual erosion to expose the present land surface post breakup erosion was generally greater towards the new coastline with near coastal samples being previously buried a probable 1 5 2 5 km

rock uplift and erosion rate history of the bergell intrusion from the inversion of low temperature thermochronometric data the bergell intrusion european alps was one of the first locations where thermochronometry was used to resolve changes in erosion rate yet relating these changes to variations in climate or in local tectonics remains challenging one approach that enables changes in erosion rate to be related to changes in climate or rock uplift rate is to utilize landscape evolution models as topographic response to these forcing parameters is unique furthermore low temperature thermochronometric systems have the potential to resolve topography through time and thus topographic response we present new u th he data for samples collected across 2 km of relief from the bergell the ages range from 2 to 16 ma and define an age elevation with an apparent exhumation rate of 0 1 km myr in order to infer erosion rates we use a thermokinematic model to solve the heat equation in the crust track material points through time and predict thermochronometric data paleo topography and erosion rate are parameterized using the stream power model we find that rock uplift rates were 0 4 km myr from 25 to 20 ma and subsequently decreased to 0 05 km myr this results in a gradual decrease in erosion rate from rates of 0 4 to 0 1 km myr a recent increase in rock uplift rate at 4 ma to 0 6 km myr is required to explain the youngest ages and high topographic relief

cenozoic river profile development in the upper lachlan catchment se australia as a test of quantitative fluvial incision models 1 we have used early miocene valley filling basalts to reconstruct fluvial long profiles in the upper lachlan catchment se australia in order to use these as well constrained initial conditions in a forward model of fluvial incision many different fluvial incision algorithms have been proposed and it is not clear at present which one of these best captures the behavior of bedrock rivers we test five different formulations the ability of these models to reproduce the observed present day stream profiles and amounts of incision is assessed using a weighted mean misfit criterion as well as the structure of the misfit function the results show that for all models parameter combinations can be found that reproduce the amounts of incision reasonably well however for some models these best fit parameter combinations do not seem to have a physical significance whereas for some others best fit parameter combinations are such that the models tend to mimic the behavior of other models overall best fit model predictions are obtained for a detachment limited stream power model or an undercapacity model that includes a river width term that varies as a function of drainage area the uncertainty in initial conditions does not have a strong impact on model outcomes the model results suggest however that lithological variation may be responsible for variations in parameter values of a factor of 3 5

modeling postbreakup landscape development and denudational history across the southeast african drakensberg escarpment margin 1 we employ a numerical surface processes model to study the controls on postbreakup landscape development and denudational history of the southeast african margin apatite fission track data presented in the companion paper suggest that the drakensberg escarpment formed by rapid postbreakup river incision seaward of a preexisting drainage divide located close to its present position and subsequently retreated at rates of only 100 m m y 1 numerical modeling results support such a scenario and show that the prebreakup topography of the margin has exerted a fundamental control on subsequent margin evolution the rheology of the lithosphere lithological variations in the eroding upper crust and inland base level falls provided secondary controls a relatively low flexural rigidity of the lithosphere te 10 km is required to explain the observed pattern of denudation as well as the observed geological structure of the southeast african margin lithological variations have contributed to the formation of flat topped ridges buttressing the main escarpment as well as major fluvial knickpoints both these features have previously been interpreted as supporting significant cenozoic uplift of the margin an inland base level fall possibly related to back cutting of the orange river drainage system and occurring 40 50 m y after breakup explains the observed denudation inland of the escarpment as well as the development of inland drainage parallel to the escarpment our model results suggest that in contrast to widely accepted inferences from classical geomorphic studies the southeast african margin has remained tectonically stable since breakup and escarpment retreat has been minimal 25 km

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

denudation along the atlantic passive margin new insights from apatite fission track analysis on the western coast of south africa apatite fission track aft data from two traverses across the great escarpment of the western coast of south africa are used to reconstruct the tectonic evolution and denudation history of this sector of the atlantic passive margin fission track ages range between 180 and 86 ma modelling of this data identifies two distinct cooling events the first event between 160 and 138 ma is recorded only by the rocks above the escarpment in the karoo area and is tentatively linked to post karoo magmatism 180 ma thermal relaxation the second between 115 and 90 ma results instead from a tectonically induced denudation episode responsible for the removal of up to 2 5 km of crust across the coastal zone in front of the escarpment and less than 1 km on the elevated interior plateau based on these results it is suggested that the cretaceous is the time when most of the elevated topography of southern africa was generated with only a minor cenozoic contribution

wearing down wearing back and gorge extension in the long term denudation of a highland mass quantitative evidence from the shoalhaven catchment southeast australia the long standing issue of the dominance of scarp retreat versus summit lowering in the denudation of a highland mass is investigated with supporting evidence provided by tertiary basalts throughout the shoalhaven catchment in southeast australia both of these forms of denudation are found to be insignificant compared to the role of fluvial gorge extension over the last 30 m y headward advancement of the shoalhaven gorge has been occurring at approximately 15 times the rate of major escarpment retreat 250 times the average rate of summit lowering and over 500 times the rate of interfluve consumption these estimates show that the headward erosion of gorges is the most important process denuding the highlands in the shoalhaven region and possibly elsewhere in the highlands of eastern australia over the long term the highlands in this region will become considerably more dissected well before they decrease substantially in height or are narrowed this conclusion has important implications for models p

influence of rock strength properties on escarpment retreat across passive continental margins we examine the influence of bedrock strength properties imparted by jointing and fracturing on the retreat of erosional escarpments across passive continental margins two types of escarpment are identified and focus is placed on the gorge head knickpoint form of escarpment where upland streams drain across the escarpment along the macleay river system of eastern australia major knickpoints associated with escarpment retreat are currently located about 200 km upstream from the river mouth despite differences in bedrock lithology and order of magnitude differences in drainage areas upstream of the gorge heads implying an average escarpment retreat rate of 2 km m y since the margin formed 85 m y ago field observations from apsley river gorge a macleay river tributary indicate that bedrock jointing profoundly affects the evolution of the gorge headwall and sidewalls where dominant jointing dips into hillslopes failure occurs by block and column toppling conversely where jointing dips out of hillslopes mass wasting occurs by joint parallel rock sliding allowing slopes to remain steep as material is shed from the gorge sidewalls the toppling slopes develop lower overall gradients the gorge becomes asymmetric in cross section and the channel remains nearer to the steeper sidewall affected by joint parallel sliding coupling between fluvial and hillslope processes is essential to maintain headward propagation of the knickpoint gorge head and to facilitate mass wasting from the gorge sidewalls peak stream discharge across the gorge head must exceed a threshold sufficient to transport debris away from the gorge head to keep the knickpoint rock face free of talus to incise the stream channel and to erode the toes of the sidewalls if these conditions on fluvial processes are met then hillslope processes including rockslope failure mechanisms are the rate controlling processes for knickpoint propagation and therefore determine the rate of escarpment retreat across the passive margin

soil production in heath and forest blue mountains australia influence of lithology and palaeoclimate an erratum has been published for this article in earth surfaces processes and landforms 25 13 2005 1683 1686 recent determinations of soil production from in situ cosmogenic nuclides indicate that production decreases exponentially with soil depth this contrasts with a long held assumption that maximum soil production occurs under a soil cover of finite depth sites in the blue mountains australia show a sharp decrease of soil depth where vegetation changes from forested plateau surfaces to heath covered spurs and bands of bare rock in the heath suggest that soil production depends on presence of a finite depth of soil the substrate varies from hard ferruginized sandstone to soft saprolite in situ 10be determinations indicate that apparent rates of erosion and soil production are greater under the relatively thin heath soil than under the thicker forest soil but in contrast to other studies these sites do not show significant depth dependence of apparent soil production the pattern reflects both hardness variation in the rock substrate and the effect of late quaternary climatic change optically stimulated luminescence osl dating indicates that soil 30 cm depth is of holocene age whereas the deeper soil is substantially older the age break coincides with a stone line interpreted as a former surface lag deposit assuming that pre holocene soil depths were 30 cm less than today recalculated soil production tends to decrease with increasing depth soil production at this site requires soil cover but bare rock patches and vegetation comprise a shifting mosaic in the long term average rates of erosion and soil production decrease with increasing soil depth copyright 2005 john wiley sons ltd

the role of climate during high plateau formation insights from numerical experiments abstract high plateaus are elevated areas of low relief mostly associated with compressional tectonics and characterized by dry climatic conditions results from a novel computer modeling technique integrating surface and tectonic processes suggest that a pre existing dry climate through its effects on surface transport and orogenic evolution can significantly contribute to the formation of high plateaus according to these results dry climatic conditions promote sediment trapping within the orogen transferring the accommodation of tectonic shortening towards the external parts of the orogen and leading to the formation of a high plateau this feedback operates in the following steps 1 dry climatic conditions at the early stages of orogenesis favor the tectonic defeat of rivers draining the orogen promoting internal drainage endorheism 2 endorheism extends the life of intramountain basins maximizing the mass trapped within the orogen and expelling deformation further into the foreland and 3 this propagation of deformation further isolates the central parts of the orogen from incoming precipitation reinforcing sediment trapping and topographic leveling of the intramountain region this phenomenon allows reproduction of basic topographic drainage and tectonic differences between orogens lacking a high plateau such as the alps and orogens with a well developed high plateau like the andes without invoking inherited heterogeneities in the crust or other tectonic processes it also suggests that internal drainage and high plateaus might be a natural stage of orogenesis undergoing dry climatic conditions in the light of recent data reporting dry climate prior to the formation of the andean high plateau aridity can be seen as one of the causes for the formation of the altiplano rather than just as a consequence of topographic growth

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

interplay between tectonics climate and fluvial transport during the cenozoic evolution of the ebro basin ne iberia 1 three dimensional modeling that integrates fluvial sediment transport crustal scale tectonic deformation and lithospheric flexural subsidence is carried out to simulate the landscape and drainage evolution of the ebro sedimentary basin ne iberia the ebro basin underwent a long period of closed intramountain drainage as a result of tectonic topography generation at the pyrenees the iberian range and the catalan coastal range in the late oligocene the catalan coastal range underwent extension leading to the formation of the valencia trough nw mediterranean but the ebro basin remained closed for nearly 15 myr more before the ebro river cut through the remnants of the topographic barrier this drainage opening caused widespread basin incision that shaped spectacular outcrops of the syntectonic and posttectonic infill here we investigate the processes controlling these major drainage changes the modeling results constrained by a large data set on the tectonic and transport evolution of the area predict a closed phase characterized by a large lake in the central eastern ebro basin dry climatic conditions probably lowered the lake level and contributed together with rift flank uplift to prolong this endorheic basin stage the age and amount of reworked sediment after the opening are consistent with an onset of basin incision between 13 and 8 5 ma as a result of lake capture by escarpment erosion and lake level rise associated with sediment accumulation and wetter climatic conditions sea level changes in the mediterranean had no major impact in the large scale drainage evolution of the ebro basin index terms 1625 global change geomorphology and weathering 1824 1886 1815 hydrology erosion and sedimentation 3210 mathematical geophysics modeling 3344 meteorology and atmospheric dynamics paleoclimatology 8102 tectonophysics continental contractional orogenic belts keywords pyrenees drainage evolution lake sediment budget erosion flexure

the influence of rifting on escarpment migration on high elevation passive continental margins 1 using numerical models that couple surface processes flexural isostasy faulting and the thermal effects of rifting we show that fault bounded escarpments created at rift flanks by mechanical unloading and flexural rebound have little potential to survive as retreating escarpments if the lower crust under the rift flank is substantially stretched in this configuration a drainage divide that persists through time appears landward of the initial escarpment in a position close to a secondary bulge that is created during the rifting event at a distance that depends on the flexural rigidity of the upper crust moreover the migration of the escarpment to the secondary bulge occurs when the pre rift topography dips landward otherwise the evolution of the escarpment is guided by the pre existing inland drainage divide to illustrate this new mechanism for the evolution of passive margins we study the examples of southeastern australia and southeastern brazil we propose that a pre existing inland drainage divide with rift related flank uplift can produce the double drainage divide observed in southeastern australia on the other hand we conclude that it is possible that the serra do mar escarpments on the southeastern brazilian margin originated as a secondary flexural bulge during rifting that persisted through time in both cases the retreating escarpment scenario is unlikely and the present day margin morphology can be explained as resulting from rift related vertical motions alone without requiring significant post rift rejuvenation

andean growth and monsoon winds drive landscape evolution at sw margin of south america abstract in the atacama desert the driest place on earth located at the subduction margin of the andes the landscape evolves very slowly and changes in tectonic or erosion processes remain for a long time in the memory of topography at latitude 19 30 s a threshold between exoreic and endoreic drainage regimes is clearly associated with the latitudinal gradient imposed by the modern monsoon carrying humidity from the atlantic and disposed obliquely over catchments draining the andes to the pacific we summarize the geomorphic geological and climatic data in the threshold area we then use these data to constrain numerical experiments of drainage evolution data and experimental results are consistent with the development of a flat low energy morphology close to sea level interrupted at 10 ma by tectonic uplift prevailing to the present suggesting trench ward relief growth by incorporation of the coastal atacama region to the andes mountain belt

unraveling rift margin evolution and escarpment development ages along the dead sea fault using cosmogenic burial ages abstract the dead sea fault dsf is one of the most active plate boundaries in the world understanding the quaternary history and sediments of the dsf requires investigation into the neogene development of this plate boundary dsf lateral motion preceded significant extension and rift morphology by 10 ma sediments of the sedom formation dated here between 5 0 0 5 ma and 6 2 2 1 inf ma yielded extremely low 10be concentrations and 26al is absent these reflect the antiquity of the sediments deposited in the sedom lagoon which evolved in a subdued landscape and was connected to the mediterranean sea the base of the overlying amora formation deposited in the terminal amora lake which developed under increasing relief that promoted escarpment incision was dated at 3 3 0 8 0 9 ma burial ages of fluvial sediments within caves 3 4 0 2 ma and 3 6 0 4 ma represent the timing of initial incision initial dsf topography coincides with the earliest red sea morb s and the east anatolian fault initiation these suggest a change in the relative arabian african plate motion this change introduced the rifting component to the dsf followed by a significant subsidence margin uplift and a reorganization of relief and drainage pattern in the region resulting in the topographic framework observed today