a new approach to the relief of great britain ii a classification of rocks based on relative resistance to denudation abstract we have assembled a digital database for great britain containing square by square data for the 1 km squares of the national grid on altitude and geology age and lithology as well as other variables it is used here to classify the 71 most common rocks of great britain i e all outcrops over 500 km2 in terms of the degree to which they form high ground the empirical classification utilised a large number of measures eventually 19 to allow for the varying location and spatial pattern coastal vs inland large continuous outcrops vs scattered patches of these outcrops and several different combinations of variables produced very similar sequences when the rocks were arranged in rank order a six fold classification provides a basis for further work which will seek to remove the influence of varying resistance to denudation from the pattern of relief for rocks of similar age rank order is determined by lithology but for all rocks age is a stronger influence than lithology it is shown that variations in the resistance of rocks to erosion account for a large part of the local relative relief of britain the pattern of mean altitude predicted from river distance values using regressions for each rock resistance class simulates remarkably closely the overall pattern of british relief

the history of the major rivers of southern britain during the tertiary the evolution of the drainage system of lowland britain is discussed on the basis of available geological evidence including that from terrestrial sites and that which has more recently become available from offshore exploration of the north sea the english and bristol channels and the irish sea tertiary stratigraphy throws considerable light on landform and river development paleocene destruction of a chalk cover which seems to have been incomplete in western britain was accompanied by basin sedimentation under a tropical climate the major elements the thames solent hampshire proto avon river irish sea river and possibly an early trent river existed almost throughout the cenozoic the influence of atlantic rifting and thermal doming in nw britain appears to have been stronger and more temporally focused than the persistent flexuring that determined and maintained tertiary drainage lines in the se here also the folded mesozoic terrains on the surface contrast with the more dominant block faulted relief of the palaeozoic oldlands the rivers of the se can be shown to have extended or reduced their lengths in response to relative sea level change and gentle warping drainage antecedence the destruction of the solent system and the breaching of the english channel are also evident by contrast the major river systems of the west are now entirely submerged long term stability of the drainage pattern reflects a persistent tectonic regime in the south with a subdued low relief landscape having a weathered regolith and dense vegetation cover meandering river channels and alluvial styles predominated although channel forms varied according to sediment load slope and discharge variability coarse gravel dominated accumulations are rare and localized chemically stable lithologies dominate the clastic component throughout it is apparent that the deeply incised river valleys seen today are related to high predominantly coarse sediment yields encouraged by substantial rapid climate changes in the pleistocene this emphasizes the significance of mechanical compared with chemical weathering for the rate and nature of landscape dissection and the modifications that have arisen as a result of glaciation frost climate weathering rapidly changing climates and sea levels the stratigraphical evidence here reviewed is at variance with older largely geomorphologically based landform evolution models denudational chronology but gives considerable support to the recent proposals emphasizing the significance of paleocene erosion and enduring low relief landscapes and drainage systems evolving alongside fold development during the paleogene given the depobasin evidence now available postulated fluvially active episodes can and must be linked to contemporaneous deposition some at least of the many controversies involving the identity of erosion surfaces the dating of them using only residual deposits and weathering mantles and the selection of particular tertiary episodes as ones of landscape development can now be resolved

climate tectonics and the morphology of the andes large scale topographic analyses show that hemisphere scale climate variations are a first order control on the morphology of the andes zonal atmospheric circulation in the southern hemisphere creates strong latitudinal precipitation gradients that when incorporated in a generalized index of erosion intensity predict strong gradients in erosion rates both along and across the andes cross range asymmetry width hypsometry and maximum elevation reflect gradients in both the erosion index and the relative dominance of fluvial glacial and tectonic processes and show that major morphologic features correlate with climatic regimes latitudinal gradients in inferred crustal thickening and structural shortening correspond to variations in predicted erosion potential indicating that like tectonics nonuniform erosion due to large scale climate patterns is a first order control on the topographic evolution of the andes

systematic variation of bedrock channel gradients in the central oregon coast range implications for rock uplift and shallow landsliding abstract in tectonically active regions bedrock channels play a critical role in dictating the pace of landscape evolution models of fluvial incision into bedrock provide a means of investigating relationships between gradients of bedrock channels and patterns of active deformation variations in lithology orographic precipitation sediment supply and erosional processes serve to complicate tectonic inferences derived from morphologic data yet most tectonically active landscapes are characterized by these complexities in contrast the central oregon coast range ocr which is situated above the cascadia subduction zone has experienced rock uplift for several million years did not experience pleistocene glaciation boasts a relatively uniform lithology and exhibits minor variations in precipitation although numerous process based geomorphic studies suggest that rates of erosion across the ocr are relatively constant it has not been demonstrated that bedrock channel gradients in the region exhibit spatially consistent values analysis of broadly distributed small drainage basins 5 20 km in the central ocr enables us to explore regional variability in bedrock channel gradients resulting from differential rock uplift or other sources consistent with previous studies that have documented local structural control of deformed fluvial terraces in the western portion of our study area our data reveal a roughly 20 km wide band of systematically elevated channel slopes roughly twice the background value roughly coincident with the strike of n s trending mapped folds although many factors could feasibly generate this pattern including variable rock strength precipitation gradients or temporal or spatial variations in forearc deformation the elevated bedrock channel slopes likely reflect differential rock uplift related to activity of local structures importantly our analysis suggests that rock uplift and erosion rates may vary systematically across the ocr although our calculations were focused on the fluvial dominated portion of study basins our results have implications for upstream areas including unchanneled valleys that often serve as source areas for long runout debris flows zero order basins or topographic hollows within the n s trending band of elevated channel slopes tend to be steeper than adjacent areas and may experience more frequent evacuation by shallow landsliding thus this region of the ocr may be highly sensitive to land use practices and high intensity rainstorms

quantifying differential rock uplift rates via stream profile analysis despite intensive research into the coupling between tectonics and surface processes our ability to obtain quantitative information on the rates of tectonic processes from topography remains limited due primarily to a dearth of data with which to test and calibrate process rate laws here we develop a simple theory for the impact of spatially variable rock uplift rate on the concavity of bedrock river profiles application of the analysis to the siwalik hills of central nepal demonstrates that systematic differences in the concavity of channels in this region match the predictions of a stream power incision model and depend on the position and direction of the channel relative to gradients in the vertical component of deformation rate across an active fault bend fold furthermore calibration of model parameters from channel profiles argued to be in steady state with the current climatic and tectonic regime indicates that 1 the ratio of exponents on channel drainage area and slope m n is 0 46 consistent with theoretical predictions 2 the slope exponent is consistent with incision either linearly proportional to shear stress or unit stream power n 0 66 or n 1 respectively and 3 the coefficient of erosion is within the range of previously published estimates mean k 4 3 10 4 m 0 2 yr application of these model parameters to other channels in the siwalik hills yields estimates of spatially variable erosion rates that mimic expected variations in rock uplift rate across a fault bend fold thus the sensitivity of channel gradient to rock uplift rate in this landscape allows us to derive quantitative estimates of spatial variations in erosion rate directly from topographic data

sediment loads and sources in heavily modified irish catchments a move towards informed management strategies abstract implementation of the eu water framework directive 2000 60 ec has forced regulatory authorities to take an integrated view of the link between water quality and catchment management in northern ireland concern over progressive habitat degradation of one of the province s prime salmon rivers the river bush provided the stimulus for a sediment monitoring programme the aims of this study were to quantify instream sediment loads and to identify sources of fine sediment feeding into the river channel this information would then be used to justify changes in the way the catchment s resources were managed sediment loads were assessed at four sampling stations on the river bush system over a one year period between 18 07 02 and 24 07 03 using sediment collection tubes and pit type traps these ranged between 0 196 and 4 98 t yr 1 for bed load and 1 70 and 102 t yr 1 for suspended load a combination of desktop studies erosion potential mapping monitoring visual observations bank erosion magnitude and yield and analytical work sediment fingerprinting was then applied in order to elucidate links between catchment sediment erosion and downstream sediment delivery bank erosion was highest in regions of the catchment with the least cohesive bank materials during high flow conditions livestock poaching and peak flows caused damage to banks at a localised scale and led to selective patches of bare land being susceptible to further erosion augmenting the sediment load approximately 2 of the annual suspended sediment and 60 of the annual bed load drainage maintenance work 60 and 30 forest clearfell 1 and 2 and ploughed land 37 and 8 also contributed to the annual suspended sediment and bed load respectively nine key actions were suggested in order to improve habitat quality in relation to sediment supply in the river bush these included wetland restoration prohibiting drainage maintenance work strategies to control conifer plantation felling reducing bare ground livestock access restrictions construction site management macrophyte clearance employment of a river warden and systematic dissemination of project recommendations to the general public to generate community involvement it was essential that these actions were both cost effective and practical in order to maximise catchment stakeholder uptake

tectonic and lithologic controls on bedrock channel profiles and processes in coastal california 1 recent theoretical models suggest that topographic characteristics of bedrock channels are products of interactions among tectonics substrate resistance and the climatically modulated erosive ability of the river the degree to which these factors influence the form of channel profiles is poorly quantified at present here we investigate bedrock channels developed across the southern flank of the santa ynez mountains california uniform climate and systematic variations in lithology and rock uplift rate along the range allow comparison of channel morphology between 1 channels eroding rocks of uniform and nonuniform strength and 2 channels experiencing differences in tectonic forcing we combine field observations surveys and analysis of digital data to determine topographic and hydraulic characteristics of bedrock channels at a constant rock uplift rate streams flowing from resistant to less resistant bedrock exhibit highly concave profiles and increased gradients along lower reaches relative to channels developed in uniform bedrock these effects are interpreted as responses to 1 an increase in substrate resistance to channel incision in the upper reaches and 2 transport limited gradients along lower reaches comparisons of channels developed across uniform lithology but experiencing an approximately sevenfold difference in rock uplift rate reveal an approximately twofold increase in gradient and an approximately threefold decrease in width in this landscape the combined channel adjustments of gradient and width are consistent with a fluvial incision model in which channel incision rate is linearly proportional to mean bed shear stress

effects of riparian vegetation on stream bank subaerial processes in southwestern virginia usa riparian vegetation is frequently used for stream bank stabilization but the effects of vegetation on subaerial processes have not been quantified subaerial processes such as soil desiccation and freeze thaw cycling are climate related phenomena that deliver soil directly to the stream and make the banks more vulnerable to fluvial erosion by reducing soil strength this study compares the impact of woody and herbaceous vegetation on subaerial processes by examining soil temperature and moisture regimes in vegetated stream banks soil temperature and water tension were measured at six paired field sites in southwestern virginia usa for one year results showed that stream banks with herbaceous vegetation had higher soil temperatures and a greater diurnal temperature range during the summer compared to forested stream banks daily average summer soil water tension was 13 to 57 per cent higher under herbaceous vegetation than under woody vegetation probably due to evapotranspiration from the shallow herbaceous root system on the bank in contrast to summer conditions the deciduous forest buffers provided little protection for stream banks during the winter the forested stream banks experienced diurnal temperature ranges two to three times greater than stream banks under dense herbaceous cover and underwent as many as eight times the number of freeze thaw cycles during the winter the stream banks under the deciduous forests were exposed to solar heating and night time cooling which increased the diurnal soil temperature range and the occurrence of freeze thaw cycling study results also indicated that freeze thaw cycling and soil desiccation were greater on the upper stream bank due to thermal and moisture regulation of the lower bank by the stream therefore subaerial erosion and soil weakening may be greater on the upper stream banks additional research is needed on the influence of subaerial processes on both subaerial and fluvial erosion copyright 2006 john wiley sons ltd

aspects of basin inversion in southern britain the wessex basin of southern england a permian to cretaceous extensional basin can be structurally divided into a set of constituent asymmetrical graben bounded by major e w trending zones of en echelon syn depositional normal faults the graben were inverted in late cretaceous and tertiary times by compressive stresses oriented roughly north south inversion structures fall into two related categories regional upwarps overlie earlier graben depocentres and were formed by bulk shortening of the graben fill superimposed upon and geographically delimiting the regional upwarps are roughly east west trending linear zones of en echelon inversion structures these coincide with the earlier graben bounding faults and typically have the form of monoclinal or periclinal flexures each underlain by a partially reversed normal fault the linear reverse fault monocline inversion structures were a relatively inefficient method of basin shortening because upper crustal faults in the region steepen upward markedly reversal of these faults under compression resulted in a shortening discrepancy at shallow depths locally particularly in south dorset this was overcome by bucklefolding and low angle reverse faulting which increased the amount of shortening attainable across the linear inversion structures elsewhere however the shortening discrepancy was accommodated by bulk shortening and regional upwarp of the graben sedimentary fill this occurred preferentially in those graben containing young poorly lithified and therefore weak sediments thus the early cretaceous depocentres of the weald and channel basins were strongly upwarped with axial uplifts of over 1000 m conversely graben having older more lithified sequences suffered little regional upwarp shortening primarily by fault reversal along the linear inversion structures the amount of crustal shortening which accompanied inversion was considerably less than the earlier crustal extension

stability of streambanks formed in partially saturated soils and effects of negative pore water pressures the sieve river italy abstract streambanks of alluvial channels are usually composed of loose materials which are unsaturated in ambient conditions unsaturated soils are subject to negative pore water pressures which cause an apparent cohesion the latter is the main factor in allowing the stability of near vertical banks even during moderate in bank flow events the apparent cohesion can be strongly reduced as the material approaches full saturation therefore during the drawdown phase as the confining pressure of the water in the channel disappears a bank failure is likely to occur channel bed level lowering along the sieve river central italy has caused widespread bank instability a geomorphological reconnaissance of forms and processes was followed by in situ tests to determine the shear strength of the banks interpretation of the tests and a streambank stability analysis were based on concepts of soil mechanics for unsaturated soils in order to obtain relations between bank angle and height in limit equilibrium conditions a stability chart was obtained with curves for different apparent cohesion values and a stability analysis was performed taking into account the effects of flow events in order to investigate the pore pressure effects a series of piezo tensiometers were installed in a streambank of the sieve river data from a 1 year monitoring period show variations in pore water pressure and matric suction as a consequence of rainfall evapotranspiration and water stage variations a planar failure with a tension crack occurred in the upper cohesive part of the bank during december 1996 the safety factor has been expressed as a function of the geometry of the bank and of the shear strength of the material safety factor variations through time are therefore shown as a function of seasonal variations in matric suction

effects of orographic precipitation variations on the concavity of steady state river profiles the concavity or curvature of river profiles has long been taken to be a fundamental indicator of the underlying processes governing fluvial erosion and thereby of landscape evolution however erosion laws have generally been derived without accounting for the strong orographically driven gradients in precipitation typically found in mountainous regions in addition field measurements have found discrepancies between the form of measured stream profiles and theoretically derived values introducing a simple physically based feedback we find that orographically induced variations in precipitation strongly affect the curvature of steady state river profiles this feedback complicates efforts to infer the form of erosion laws from observed profile concavities but could help explain discrepancies between observations and theory our results demonstrate a strong feedback through which climate influences the form of river profiles and show how such climatic effects act to limit the relief of unglaciated mountain ranges

linking paleogene denudation and magmatic underplating beneath the british isles a simple flexural model is used to explore the relationship between magmatic underplating and denudation first we show how denudation can be calculated as a function of underplating the distribution and density of underplate are obviously important parameters in determining the wavelength and amplitude of denudation however the denudational pattern can be considerably modulated by the flexural rigidity of the lithosphere several other parameters also play a significant role for example we show how variations in pre existing bathymetry and in present day topography affect denudational calculations we have applied our simple algorithm to the problem of paleogene underplating beneath the british isles forward and inverse modelling of travel time data from a wide angle seismic experiment which traversed the british isles suggests that a large pod of high velocity material occurs at moho depths beneath the irish sea the shape and inferred density of this pod are used to calculate the amplitude and wavelength of denudation for different flexural rigidities we compare our predictions with the observed pattern of paleogene denudation and conclude that the bulk of the observed denudation can be accounted for by magmatic underplating associated in a general way with the iceland plume notwithstanding this agreement there is compelling evidence for additional mild uplift events especially during the neogene these mild events may reflect fluctuating dynamic topography associated with the iceland plume

sedimentary basin inversion caused by igneous underplating northwest european continental shelf a considerable body of evidence indicates that many of the extensional sedimentary basins in the vicinity of the british isles underwent permanent exhumation during the tertiary the most dramatic indicator of this process is the present day absence of as much as 4 km of anticipated postrift thermal subsidence in basins just north and west of scotland any explanation of this observation must take into account the fact that the entire region has very small long wavelength free air gravity anomalies this important constraint implies either that the crust has been thickened or that low density material has been added to or formed from the lithosphere and rules out models that invoke flexural effects arising from the opening of the north atlantic tertiary epeirogeny is often attributed to compression that is assumed to be related in a general sense to alpine mountain building however to remove 3 km of sedi mentary rock from a basin 100 km wide requires 15 km of shortening minor tertiary compression is observed all over the continental shelf but nowhere is it sufficient to account for the required amount of uplift and erosion in addition exhumation dramatically increases from south to north whereas the observed compression decreases markedly in the same direction at the beginning of the tertiary rifting associated with the initiation of the iceland plume generated substantial volumes of melt inversion of rare earth element concentrations of mgorich igneous rocks suggests that a minimum of 5 km of melt was produced beneath at least part of the continental shelf we infer that much of this melt remains trapped within the lithosphere presumably close to the moho which acted as a density filter such underplating will generate rapid uplift

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

accelerated uplift resulting from anglian glacioisostatic rebound in the middle thames valley uk evidence from the river terrace record abstract a relatively simple analysis of the terraces of the middle thames valley reveals a complex sequence of responses to late anglian late middle pleistocene drainage disruption a decrease in the amounts of vertical incision separating the later post anglian terraces strongly suggests a major change in the rate of incision in the middle thames area in the post anglian a late anglian and early post anglian incision rate of 1 45 m ka 1 was quickly replaced by incision at a rate of 0 089 m ka 1 in the later post anglian period the lower incision rate of the later post anglian compares favourably with previous estimates of regional uplift two plausible explanations for the enhanced incision in the late anglian and early post anglian are recognized one related to ponding of the river by anglian ice and the other to glacio isostatic rebound in the latter case the mismatch between expected and actual heights of late anglian deposits would suggest glacio isostatic uplift of the order of 22 25 m

a latest cretaceous hotspot and the southeasterly tilt of britain the southeasterly regional dip of england and wales is usually ascribed to miocene movements loss of up to 2 km of cover from northern england shown by apatite fission track analysis has been related to uplift and erosion induced by a mantle hotspot but its effects were far more widespread than considered hitherto outcrop patterns throughout much of england wales and eastern ireland can be related to a hotspot beneath the irish sea uplift occurred within the late maastrichtian and erosion continued into the late palaeogene after post oligocene down faulting of the irish sea the modern drainage was initiated on the eroded surface unconformities provide the best means of dating orogenic movements in some localities the time interval between the youngest rocks preserved beneath the unconformity and the oldest preserved above may be small enough to enable the dating of fold movements to be determined with some precision thus in southeastern britain the major e w structures of the hampshire basin the weald and the london basin can be dated as miocene as rocks of oligocene age are involved in the folding in the hampshire basin and pliocene sands rest in erosional pockets of the chalk of se england because fold movements tend to affect large areas of the crust at discrete intervals of time the southeasterly tilt of britain evident from the fact that a nw se transect from anglesey to london crosses outcrops of rocks getting progressively younger from the precambrian of anglesey to the tertiary of the london basin has

thames river sediments of the british early and middle pleistocene abstract the thames drainage system contains the most complete record of fluvial sediments in the british quaternary the kesgrave sands and gravels form the main body of this sediment having been deposited over an interval that spans the later part of the early pleistocene and most of the middle pleistocene conventional stages pre pastonian a through to early anglian ca 1 2 ma this deposit provides a stratigraphic context for related bio morpho and pedostratigraphic evidence and for the recognition of pre anglian pre oi stage 12 upland glaciation in the welsh mountains and intense periglaciation in lowland england it also facilitates correlation with the stratigraphy of northern europe and the global pattern of orbitally forced climatic change this paper describes the first catchment wide correlation of thames river sediments and proposes a formal redefinition of the lithostratigraphic units concerned the scheme outlined here is based on two lithologically distinctive formations defined at type areas reflecting significant changes in catchment dimensions the earlier sudbury formation was formed when the thames catchment extended into wales and drained northwards across east anglia the later colchester formation was formed after the upper catchment had been reduced in extent to that of the present river but continued to flow across east anglia the whole sediment body is now named the kesgrave group

extraction of a lithospheric cooling signal from oceanwide geoid data abstract the geoid an equipotential surface of earth s gravity field reflects the distribution of mass within the planet and hence a variety of geodynamic processes because these data are dominated by sublithospheric processes notably mantle convection they have not played a major role in the ongoing debate concerning models of the thermal evolution of oceanic lithosphere application of spatial filtering to the age derivative of the geoid however extracts an age dependent signal which reflects lithospheric thermal evolution the data are much better fit by a thin about 100 km thick thermal plate than by a cooling halfspace and so provide a valuable constraint complementary to and consistent with the variations in oceanic depth and heat flow with age

quaternary river terraces in england forms sediments and processes abstract flights of quaternary river terraces in south and east england have common characteristics involving low gradient planed or irregular bedrock surfaces and single or multi storey gravel deposits rather than depending on warm cold or cold warm transitions it is suggested that bedrock planation working depths of gravel and later stage relatively shallow aggradations are all dominantly of cold climate origin basal sediments show active incorporation of plucked and periglacially shattered materials whilst super incumbent units incorporating up catchment and slope derived materials demonstrate later cold stage sediment influx and consequent cessation of active bedrock erosion channel activity effecting both planation and deposition are reviewed together with the detailed sedimentology of gravelly sediments which show evidence of both autogenic processes bar migration channel switching and infilling and truncation of upper sedimentation units cold climate indicators turbation ice wedge casts and frozen block transport and specifically for the last glacial interglacial cycle varying sediment flux as climates changed both interglacial and transitional activities are believed to be of lesser morphological significance whilst prior uplift is taken as enabling rather than being a generator of terrace within the timescale of a glacial interglacial cycle variations within cold stage climates varying sediment influx and channel belt bedrock erosion are stressed as dominating mid catchment and mid latitude quaternary terracing at the glacial interglacial scale

on the recovery of effective elastic thickness using spectral methods examples from synthetic data and from the fennoscandian shield there is considerable controversy regarding the long term strength of continents te while some authors obtain both low and high te estimates from the bouguer coherence and suggest that both crust and mantle contribute to lithospheric strength others obtain estimates of only 25 km using the free air admittance and suggest that the mantle is weak at the root of this controversy is how accurately te can be recovered from coherence and admittance we investigate this question by using synthetic topography and gravity anomaly data for which te is known we show that the discrepancies stem from comparison of theoretical curves to multitaper power spectral estimates of free air admittance we reformulate the admittance method and show that it can recover synthetic te estimates similar to those recovered using coherence in light of these results we estimate te in fennoscandia and obtain similar results using both techniques te is 20 40 km in the caledonides 40 60 km in the swedish svecofennides 40 60 km in the kola peninsula and 70 100 km in southern karelia and svecofennian central finland independent rheological modeling using a xenolith controlled geotherm predicts similar high te in central finland because te exceeds crustal thickness in this area the mantle must contribute significantly to the total strength te in fennoscandia increases with tectonic age seismic lithosphere thickness and decreasing heat flow and low te correlates with frequent seismicity however in proterozoic and archean lithosphere the relationship of te to age is ambiguous suggesting that compositional variations may influence the strength of continents copyright 2004 by the american geophysical union

the cenozoic uplift and earthquake belt of mainland britain as a response to an underlying hot low density upper mantle a belt of hot low density uppermost mantle underlying mainland britain down to at least 200 km depth revealed by seismic tomography may be the prime cause of the cenozoic uplift and exhumation we use finite element modelling to demonstrate how isostatic uplift can occur in response to such a low density hotspot beneath continental crust to explain the narrow width of the uplift of northern britain the lower crust must be ductile power law rheology assumed and the asymmetrical uplift may be bounded at least on the west side by a pre existing fault or faults of appropriate polarity faulting has probably been reverse under nw se regional compression since the onset of the cenozoic with the assistance of continuing denudation inferred gross cenozoic exhumation of up to 3000 m can be explained british earthquakes concentrate along a similar north south belt with the strongest events in the west we suggest that the earthquakes result from the continuing tectonics associated with the hot upper mantle the uplift it causes and the weakened crust the underlying low density region gives rise to tensional loading stress in all directions and bending stresses are associated with the upper crustal flexuring accompanying uplift these large stresses supplement nw se regional compression available earthquake mechanisms are approximately consistent with this stress environment

recognition of tectonic events in undeformed regions contrasting results from the midland platform and east midlands shelf central england apatite fission track and vitrinite reflectance data from central england demonstrate how these techniques can reveal otherwise unrecognized tectonic and or palaeothermal episodes in apparently tectonically stable areas the results document the transition from an inverted basinal region in the north east midlands shelf to a tectonically stable platform in the south midland platform afta data from the region reveal two discrete cooling episodes in the early and late tertiary maximum palaeotemperatures from afta and vr data in outcrop samples define a consistent increase from 50 c in lower cretaceous and upper jurassic units in the se to around 80 90 c in triassic and older units in the nw these early tertiary palaeotemperatures reflect a combination of deeper burial and elevated basal heat flow results from the rufford 1 well define an early tertiary palaeogeothermal gradient of 40 5 c km 1 32 50 c km 1 at 95 confidence limits corresponding to deeper burial by 1450 m of additional section 1 1 2 2 km at 95 confidence limits subsequently removed by tertiary erosion in contrast geological considerations suggest a maximum overburden of 800 900 m above the base of the lower jurassic in the vicinity of rugby where palaeotemperatures at outcrop are similar to those near the rufford 1 location the discrepancy between stratigraphic and palaeo thermal reconstruction of former burial depths often noted in earlier studies remains unresolved the late tertiary episode is much less well constrained but results from rufford 1 may require between 910 and 1650 m of eroded section thus much of the total amount of removed overburden may have been removed during the late tertiary results from the apley barn borehole oxfordshire reveal a late tertiary palaeothermal episode characterized by a highly non linear palaeotemperature profile which probably reflects local heating due to passage of hot fluids despite stratigraphic evidence for some early tertiary erosion results from this borehole show no evidence of early tertiary effects major early and late tertiary exhumation was limited to regions underlain by older palaeozoic basins while regions overlying palaeozoic basement were more stable experiencing significantly less exhumation we suggest this reflects the preferential reactivation of the weaker basinal regions as a result of compressional events at plate margins our results emphasize the importance of incorporating results from both inverted and non inverted areas in understanding the causal mechanisms of uplift and inversion and highlight the importance of testing apparent stability using palaeo thermal methods

measuring streambank erosion due to ground water seepage correlation to bank pore water pressure precipitation and stream stage limited information exists on one of the mechanisms governing sediment input to streams streambank erosion by ground water seepage the objective of this research was to demonstrate the importance of streambank composition and stratigraphy in controlling seepage flow and to quantify correlation of seepage flow erosion with precipitation stream stage and soil pore water pressure the streambank site was located in northern mississippi in the goodwin creek watershed soil samples from layers on the streambank face suggested less than an order of magnitude difference in vertical hydraulic conductivity ks with depth but differences between lateral ks of a concretion layer and the vertical ks of the underlying layers contributed to the propensity for lateral flow goodwin creek seeps were not similar to other seeps reported in the literature in that eroded sediment originated from layers underneath the primary seepage layer subsurface flow and sediment load quantified using 50 cm wide collection pans were dependent on the type of seep intermittent low flow lf seeps flow rates typically less than 0 05 l min 1 persistent high flow hf seeps average flow rate of 0 39 l min 1 and buried seeps which eroded unconsolidated bank material from previous bank failures the timing of lf seeps correlated to river stage and precipitation the hf seeps at goodwin creek began after rainfall events resulted in the adjacent streambank reaching near saturation i e soil pore water pressures greater than 5 kpa seep discharge from hf seeps reached a maximum of 1 0 l min 1 and sediment concentrations commonly approached 100 g l 1 buried seeps were intermittent but exhibited the most significant erosion rates 738 g min 1 and sediment concentrations 989 g l 1 in cases where perched water table conditions exist and persistent hf seeps occur seepage erosion and bank collapse of streambank sediment may be significant copyright 2007 john wiley sons ltd

crustal trace of a hot convective sheet the iceland plume has played an influential role in the evolution of the north atlantic ocean and margins over the past 60 m y it is believed that this plume formed at the conjunction of a tetrad of hot subvertical convective sheets the impingement of these hot sheets at the base of the lithospheric lid caused decompressional melting generating substantial quantities of high temperature magma that were injected into the cold overlying lid over the next 10 m y these sheets partly coalesced to form a crudely axisymmetric plume head here we analyze the lithospheric fingerprint of one of these hot convective sheets by forward and inverse modeling of densely sampled wide angle seismic data in conjunction with gravity observations we determined the three dimensional shape of magmatic underplating trapped within the lithosphere the injection of this melt into the lithosphere generated substantial permanent and minor transient uplift of earth s surface predicted and measured amounts of consequent denudation and sedimentation agree within error temporal variations in the patterns of deposition and oceanic circulation adjacent to the convective sheet show its evolution through time and space our results suggest that this linear sheet has probably been directly and indirectly responsible for cyclical events over 60 m y these events have 0 5 1 and 4 6 m y periodicities the existence of which may help to elucidate the dynamic behavior of convective sheets during and after impingement thus in particular circumstances surficial geological processes yield an indirect record of mantle convection and melt generation processes

geoarchaeology the four dimensional 4d fluvial matrix and climatic causality abstract geoarchaeology is the application of geological and geomorphological techniques to archaeology and the study of the interactions of hominins with the natural environment at a variety of temporal and spatial scales geoarchaeology in the uk over the last twenty years has flourished largely because it has gone beyond technological and scientific applications over the same period our ability to reconstruct the 3 dimensional stratigraphy of fluvial deposits and the matrix of fluvial sites has increased dramatically because of a number of technological advances these have included the use of lidar laser imaging and radar to produce high resolution digital surface models the use of geophysics particularly ground penetrating radar and electrical resistivity to produce sediment depth models and the use of gis and data visualisation techniques to manipulate and display the data these techniques along with more systematic and detailed sedimentological recording of exposed sections have allowed the construction of more precise 3 dimensional volumetric models of the matrix of artefacts within fluvial deposits additionally a revolution in dating techniques particularly direct sediment dating by luminescence methods has enabled the creation of 4 dimensional models of the creation and preservation of these sites these 4 dimensional models have the ability to provide far more information about the processes of site creation preservation and even destruction and also allow the integration of these processes with independent data sources concerning cultural evolution and climatic change all improvements in the precision of dating fluvial deposits have archaeological importance in our need to translate events from a sequential or geological timeframe to human timescales this allows geoarchaeology to make a more direct contribution to cultural history through the recognition of agency at the individual or group level this data can then form a component of biocomplexity or agent based modelling which is becoming increasingly used in the natural sciences particularly ecology and geomorphology and which can be used to test scenarios including the impact on and response of hominins to abrupt or catastrophic environmental change whilst catastrophic events clearly represent the atypical they can be illuminating in revealing cognitive processes resulting in abandonment coping mitigation and innovation these points are exemplified using two in depth case studies one from the holocene geoarchaeological record of the river trent in central england and the other from the palaeolithic record from rivers in south west britain in the former the interaction between climate change and human activity is illustrated at the year to century timescale whilst in the other the timescale is millennial these case studies have deliberately been chosen to be as different as possible in temporal and spatial scale with the aim of examining the applicability of methodological and theoretical aspects of geoarchaeology lastly the paper considers the problem of scale in geoarchaeology and concludes it is process dependency which ultimately affects the questions we can ask and that questions of human response to climate change are fundamentally a product of materiality and cognitive processes this demands an in depth contextual approach to such questions rather than database driven assertions of causality

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

variations of elastic plate thickness at continental thrust belts after examining 15 reliable estimates of the elastic thickness of the lithosphere where it underthrusts mountain belts in europe asia and the americas we conclude that the strength of continental lithosphere as a function of depth must be very different from that of oceanic lithosphere depending on the state of stress continental lithosphere may be either very much stronger or very much weaker than would be predicted for oceanic lithosphere of the same thermal age we explain this observation as the result of two competing effects a thicker thermal plate beneath the continents which allows a deeper elastic ductile transition for plates more than 100 million years old and a low activation energy for ductile creep in the continental crust which leads to massive failure of the upper elastic lithosphere at high bending stresses the 100 km values for elastic plate thickness of billion year old lithosphere require a thermal plate thickness of at least 250 km the magnitude of apparent thinning of the elastic plate at high stress is consistent with that calculated from a simple yield envelope which includes a ductile zone in the lower crust the low yield strength of continental materials leads to correlations between effective elastic plate thickness and all of the following dip of the underthrust plate radius of curvature of the thrust front in map view and total length of the mountain belt using insight derived from laboratory experiments on the buckling of spherical shells and drawing analogies with the geophysical characteristics of oceanic subduction zones we arrive at the following sequence of causes and effects the primary variable is the dip of the downgoing plate presumably prescribed by its own excess mass and pressure exerted by dynamic flow in the mantle where this dip is steep the rigidity of the plate is weakened due to inelastic yielding the weakened plate can then buckle at small wavelengths into short arcuate mountain belts thus we believe that the mantle ultimately controls the pattern of surface tectonics but that the nonelastic rheology of the lithosphere is the mechanism by which that control is imposed

an analysis of cotswold topography insights into the landscape response to denudational isostasy we have used the nextmap britain digital terrain model dtm to determine the lithospheric response to erosional unloading and the contribution of tectonics in the form of elastic plate flexure to the cotswold scarp and vale landscape the calculations take into account lithology variations and along strike changes in escarpment retreat we show that flexural rock uplift as a result of erosional unloading varies spatially and may contribute up to 50 of the relief in the cotswold region this is supported by morphometric analysis of concavity and steepness for 66 longitudinal river profiles that drain the scarp and dip slope of the escarpment viscoelastic plate models suggest that the uplift is initially rapid up to 8 m ka 1 and essentially complete within 50 ka these initial rates are compatible with an early post anglian incision rate inferred from the thames terraces the staircase terrace pattern suggests however that there have been a number of denudational isostatic events each associated with a climate cycle finally the analysis reveals an inherited proto landscape that has a subdued relief when compared with the modern dtm such a relief is consistent with an early extension of the river thames through the vale of moreton to the north of the present day cotswold hills

influence of seepage undercutting on the stability of root reinforced streambanks several mechanisms contribute to streambank failure including fluvial toe undercutting reduced soil shear strength by increased soil pore water pressure and seepage erosion recent research has suggested that seepage erosion of noncohesive soil layers undercutting the banks may play an equivalent role in streambank failure to increased soil pore water pressure however this past research has primarily been limited to laboratory studies of non vegetated banks the objective of this research was to utilize the bank stability and toe erosion model bstem in order to determine the importance of seepage undercutting relative to bank shear strength bank angle soil pore water pressure and root reinforcement the bstem simulated two streambanks little topashaw creek and goodwin creek in northern mississippi simulations included three bank angles 70 to 90 four pore water pressure distributions unsaturated two partially saturated cases and fully saturated six distances of undercutting 0 to 40 cm and 13 different vegetation conditions root cohesions from 0 0 to 15 0 kpa a relative sensitivity analysis suggested that bstem was approximately three to four times more sensitive to water table position than root cohesion or depth of seepage undercutting seepage undercutting becomes a prominent bank failure mechanism on unsaturated to partially saturated streambanks with root reinforcement even with undercutting distances as small as 20 cm consideration of seepage undercutting is less important under conditions of partially to fully saturated soil pore water conditions the distance at which instability by undercutting became equivalent to instability by increased soil pore water pressure decreased as root reinforcement increased with values typically ranging between 20 and 40 cm at little topashaw creek and between 20 and 55 cm at goodwin creek this research depicts the baseline conditions at which seepage undercutting of vegetated streambanks needs to be considered for bank stability analyses copyright 2008 john wiley sons ltd

testing 3d landform quantification methods with synthetic drumlins in a real digital elevation model metrics such as height and volume quantifying the 3d morphology of landforms are important observations that reflect and constrain earth surface processes errors in such measurements are however poorly understood a novel approach using statistically valid synthetic landscapes to quantify the errors is presented the utility of the approach is illustrated using a case study of 184 drumlins observed in scotland as quantified from a digital elevation model dem by the cookie cutter extraction method to create the synthetic dems observed drumlins were removed from the measured dem and replaced by elongate 3d gaussian ones of equivalent dimensions positioned randomly with respect to the noise e g trees and regional trends e g hills that cause the errors then errors in the cookie cutter extraction method were investigated by using it to quantify these synthetic drumlins whose location and size is known thus the approach determines which key metrics are recovered accurately for example mean height of 6 8 m is recovered poorly at 12 5 0 6 2 m but mean volume is recovered correctly additionally quantification methods can be compared a variant on the cookie cutter using an un tensioned spline induced about twice 1 79 as much error finally a previously reportedly statistically significant p 0 007 difference in mean volume between sub populations of different ages which may reflect formational processes is demonstrated to be only 30 50 likely to exist in reality critically the synthetic dems are demonstrated to realistically model parameter recovery primarily because they are still almost entirely the original landscape results are insensitive to the exact method used to create the synthetic dems and the approach could be readily adapted to assess a variety of landforms e g craters dunes and volcanoes

lithospheric flexure uplift and landscape evolution in south central england the high level river gravels in oxfordshire the northern drift group which range in age from early pleistocene to around 450 ka contain pebbles that were derived from a source area to the north near birmingham the pebbles could not have been transported across the upper triassic and lower jurassic clay outcrops of the midlands unless the region was at or close to sea level the present day cotswold escarpment ranges from 70 to 215 m this uplift must therefore have occurred after deposition of the northern drift group when the drainage of the midlands appears to have shifted from towards the thames basin to the bristol channel area it is concluded that lithospheric flexure due to the removal of 500 km 3 of soft late triassic and early jurassic clays and marls from large areas of the midlands and their re deposition in the celtic deep might account for this late pleistocene uplift uplift in the midlands is the likely explanation for both the tilted approximately 0 3 plateau surface in north oxfordshire and the change in strike of the jurassic beds sw of northamptonshire although some uplift occurred in se england during the early cenozoic and miocene we demonstrate here that there has been significant uplift of the region in the late pleistocene the tilted plateau surface in north oxfordshire may therefore be a relatively young i e post 450 ka feature related to tectonic uplift in the midlands

a structural transect between the central north sea dome and the south swedish dome middle jurassic quaternary uplift subsidence reversal and exhumation across the eastern north sea basin

late devensian and holocene records of relative sea level changes in northwest scotland and their implications for glacio hydro isostatic modelling raised tidal marshes and isolation basins lakes that were once connected to the sea in northwest scotland record changes in relative sea level following deglaciation during the late devensian to the present the kentra to arisaig area which was covered by relatively thick ice c 900 m at the last glacial maximum lgm shows a regression from a marine limit between 36 5 m od and 40 m od at c 15 9 kyr cal bp range 15 6 16 3 kyr cal bp through to an early holocene minimum a range of sites in the same area record a mid holocene maximum indicative of mean sea level c 6 5 m above present the maximum is not a well developed and short duration highstand as predicted by a number of models but is an extended period 8 0 5 0 kyr cal bp with sea level within c 1 m of the maximum sites to the north in kintail show no late devensian record because much of the area lies within the younger dryas ice limit the altitude of the mid holocene maximum in kintail is not well constrained but occurred 7 9 8 1 kyr cal bp further north sites on the applecross peninsula record a late devensian fall in sea level and a holocene maximum for mean sea level no higher than c 3 0 m above present in coigach the furthest north of the new sites and well outside the younger dryas ice limit there is no evidence recorded of late devensian sea levels above present the holocene maximum here was around c 2 5 m above present these observations of sea level change all standardised to change in mean sea level relative to present constrain the glacio hydroisostatic rebound model parameters earth models comprising three mantle layers with lateral viscosity and elastic parameters give a satisfactory description of rebound the parameters h lithosphere thickness 65 km g 6 upper mantle viscosity 4 1020 pa 14c seconds and g lower mantle viscosity 1022 pa 14c seconds give the best overall agreement but discrepancies between observations and predictions remain an increase of 10 in ice thickness north of the great glen compared to the previous optimum ice model provides good agreement for many sites but important discrepancies remain for the northern sites and indicate inadequacies in the model of the british ice sheet several alternative ice models are examined but the various combinations of earth and ice model illustrate the non uniqueness of the solution a combination of more extensive ice limits especially onto the hebridean shelf and west shetland shelf and some changes to ice thicknesses over the mainland should produce a better agreement but the spatial coverage of observations remains a limitation to producing a unique solution the characteristics of the holocene highstand age duration and amplitude at the di erent sites refutes the assumption that globally deglaciation ceased abruptly 7000 yr ago the observations are consistent with an ice model that includes c 3 m of melting over the last 7000 yr 2000 elsevier science ltd all rights reserved

climatic influences on profile concavity and river incision 1 longitudinal profiles of alluvial and bedrock rivers are typically concave up and the precise shape of their concavity is known to integrate tectonic climatic and channel grain size distribution factors we isolate climatic hydrologic effects on profile concavity through a spatial analysis of large watersheds with mixed bedrock alluvial trunk channels spanning a steep climatic hydrologic gradient in a tectonically stable landscape forty watersheds on the eastern american high plains were selected to minimize variability in base level relief vegetation rock type and drainage area we calculate stream concavity by two complementary methods an area normalized stream concavity index sci and the slope of a line regressed through log log plot of channel slope and basin area the sci and covary more importantly a positive correlation exists between profile concavity and climatic hydrologic factors such as precipitation intensity and peak annual discharge however modeled profile steepness has no correlation to climate or watershed hydrology we conclude that in tectonically stable settings higher intensity rainfall and greater mean annual precipitation lead to more concave profiles we do not have data to know if the concavity changes reflect primarily bedrock or alluvial grain size processes but generally a doubling of rainfall intensity on the high plains leads to a tripling in concavity manifest as tens of meters of incision such climatically influenced profile concavity could explain some of the often cited late cenozoic incision and increase in local relief for the high plains and rocky mountains traditionally ascribed to tectonics

major river systems of central and southern britain during the early and middle pleistocene central and southern britain was drained by two main river systems during the larger part of the early and middle pleistocene the thames and bytham rivers evidence for these rivers and their quaternary history is represented by their sediments the kesgrave and bytham sands and gravels respectively the geomorphological position of the sediments biostratigraphy and amino acid geochronology evidence from the earlier parts of the early pleistocene tiglian c4b and earlier indicates low energy river systems and marine conditions over much of east anglia for most of the early pleistocene tiglian c4c to the cromerian complex the ancestral thames was the main river with at its maximal extent a catchment that extended into wales and across east anglia and what is now the north sea to join the ancestral rhine during this period glaciers in the uplands of wales and periglacial mass movement elsewhere supplied material to the catchment and it was at this time that the bulk of the sorted quaternary ssediments of lowland britain were deposited the bytham river system has no successor because the landscape now in existence has been fundamentally altered by glacial erosion this catchment drained most of midland england and joined the thames in central east anglia initially the bytham river was a tributary of the thames but over time it extended its catchment and at the beginning of the cromerian complex it became the main river of southern britain with the anglian glaciation 01 stage 121 the bytham river was destroyed and the thames was diverted to its present route through london

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

flow in the lower continental crust as a mechanism for the quaternary uplift of south east england constraints from the thames terrace record abstract the sequence of terraces of the river thames in south east england has been shown to date from the early pleistocene onwards and to provide an indication of the quaternary uplift history of the region using this evidence supplemented by altitudes of pliocene and early pleistocene marine sediments we have determined the pliocene and quaternary uplift histories of five representative localities clacton colchester and dartford for the lower thames and cookham and reading for the middle thames these uplift histories have been modelled using a physics based technique which calculates the isostatic response involving flow in the lower continental crust induced by cyclic loading at the earth s surface our results suggest that the late pliocene and early pleistocene part of the uplift history of our study region was initiated following the deterioration in climate starting at 3 1 ma which marked the start of upland glaciation elsewhere in europe the later increase in uplift rates in the middle pleistocene followed the start of intensified cyclic loading by very large continental ice sheets during and after oxygen isotope stage ois 22 at 0 87 ma dartford cookham and reading in the interior of south east england are all shown to have begun to uplift quite rapidly at rates of up to 0 1 mm a 1 following the start of forcing at 3 1 ma they have since uplifted by distances which increase gradually westward from 200 to 250 m of which a uniform 70 m has occurred since ois 22 at 0 87 ma in contrast clacton and colchester near the present north sea coastline experienced slow subsidence until the late early pleistocene but have nonetheless uplifted since ois 22 by similar distances to the other sites

a numerical modelling technique that can account for alternations of uplift and subsidence revealed by late cenozoic fluvial sequences abstract alternations between fluvial incision and aggradation in response to switches between uplift and subsidence and occurring over timescales of many hundreds of thousands of years have been documented in many regions worldwide contrasting markedly with the monotonic histories of uplift or subsidence evident elsewhere it has been noted that this pattern of reversals in vertical crustal motion is only observed in regions where the mobile lower crustal layer is thin 6 km thick suggesting a cause and effect connection with the physical properties of the underlying continental lithosphere it is proposed that these reversals result from the interplay between the isostatic responses to erosional unloading by lower crustal flow and by mantle lithosphere relaxation estimates of the characteristic timescale for relaxation of the continental mantle lithosphere range from several hundred thousand years in regions of cold crust with a thin mobile lower crustal layer to a few tens of thousands of years in regions of hot crust where the mobile lower crustal layer is thicker in regions of hot crust relaxation of the mantle lithosphere requires a shorter characteristic timescale than flow within the lower crust the complex interaction between these processes means that isostatic compensation of crustal thickening in regions of hot crust will typically involve surface uplift the development of a lower crustal root and thinning of the mantle lithosphere the observation of alternations between uplift and subsidence in long timescale fluvial sequences and the proposed physical interpretation demonstrate the importance of fluvial records for providing unique high resolution control on deformation of the continental lithosphere and for constraining its layered rheology

localized quaternary uplift of south central england the early quaternary of south central england is characterized by uplift as is indicated by the river gravels that extend intermittently from oxfordshire through northamptonshire to lincolnshire the earliest of these gravels contain abundant quartz and quartzite clasts derived from lower triassic conglomerates in the west midlands but later deposits contain progressively larger amounts of locally derived jurassic sediments this compositional change is associated with the incision of the rivers that flowed eastwards from the west midlands subsequently the headwaters of some of these rivers were diverted towards the bristol channel and their suspended material was deposited on the outer parts of the uk continental shelf and slope the area of incised drainage gloucestershire to lincolnshire did not extend to east anglia in the east or to somerset in the west both these coastal regions contain several marine horizons showing that the area of uplift did not include the whole of southern england the uplift cannot therefore be attributed to eustatic changes in sea level the area of uplift is centred on the broad topographic depression of the english midlands and corresponds approximately to the outcrop of thick c 1 km upper triassic and lower jurassic mudrocks we have used an ordnance survey 50 m 50 m topographic grid to estimate the amount of mudrocks that has been removed from the depression and 2d flexural unloading models to calculate the tectonic uplift that resulted for various assumptions of the effective elastic thickness which is determined by the flexural rigidity of the lithosphere the amount of material removed is in accord with what is known of the volume of quaternary deposits offshore and the uplift accounts for the incised plateau surfaces of the flanking cotswold hills and the high ground of northamptonshire to the east and the forest of dean and the hills of herefordshire to the west

assessment of river bank erosion in southern minnesota rivers post european settlement article i nfo river bank erosion is one of the major sources of sediment for many rivers around the world with the cur rent emphasis on developing total maximum daily loads tmdls for impaired waters in the united states there is heightened interest in quantifying background sediment levels in rivers in this study we assessed variations in river bank erosion over time using a combination of 1855 public land survey system plats aerial photographs from 1938 to 2009 and light detection and ranging lidar data from 2005 to 2009 for sediment impaired rivers in southern minnesota results showed that bank erosion was episodic making comparisons of erosion rates from dissimilar time intervals unreliable for comparable time intervals average river bank retreat rates 0 51 m yr 1 from 1855 to 1938 vs 0 37 m yr 1 from 1938 to 2009 were statistically similar t 2 13 p 0 14 suggesting that bank erosion rates have remained stable since european settlement comparisons over shorter time intervals of 1938 1971 and 1971 2009 also showed similar statistical trends t 0 76 p 0 45 with average river bank retreat rates of 0 57 and 0 50 m yr 1 respectively however additional 145 observations of bank retreat were found in the period 1971 2009 relative to 1938 1971 in dicating that the number of actively eroding river banks may have increased over time contrary to assump tions made in the literature bank erosion measurements using lidar data showed a poor relationship r 2

seepage induced mass wasting in coarse soil slopes an expression is derived for the critical shear stress of surface flow on a noncohesive soil slope subjected to seepage induced mass wasting i e erosion caused by a successive mobilization of flake aggregates of surficial grains the expression is supported with data from experiments with stone fill subjected to throughflow in current theories for hill slope erosion of riprap protection on slopes buoyancy is assumed to be a constant vector directed vertically or the seepage force is omitted as a variable however the present analysis shows that for many conditions buoyancy should be described in accordance with the dynamic pressure distribution and the seepage force should be included as a variable in the theory furthermore a parameter denoted minimum stable volume per unit width of stone fill is introduced as a measure of global stability of the stone fill along with seepage height on the downstream face and grain size experimental results indicate that the minimum stable volume decreases with increase in grain size and for the materials investigated is about 20 lower for crushed rock than for gravel

discussion on an analysis of cotswold topography insights into the landscape response to denudational isostasy journal vol 165 85 103 lane et al 2008 interestingly interpret the evolution of the cotswold scarp and vale landscape in terms of lithospheric response to erosional unloading denudational isostasy and elastic plate flexure tectonics they attribute up to 50 of the relief in the cotswolds to erosional unloading and discuss viscoelastic plate models which predict initial uplift rates as high as 8 m ka 1 they note that late anglian and early post anglian incision rates inferred from the thames terrace sequence by maddy bridgland 2000 are consistent with this high rate against a longer term last 2 ma

late devensian and holocene shorelines of the british isles and north sea from models of glacio hydro isostatic rebound sea level change around the british isles since the time of the last glacial maximum is largely due to of the crustal rebound from the glacial unloading of northern britain and the concomitant melt water loading of the adjacent seas and atlantic ocean minor but not insignificant contributions also result from the rebound caused by the unloading of the distant ice sheets including fennoscandia and north america observations of sea level change for this period constrain the glacio hydro isostatic rebound model parameters describing the effective lithospheric thickness or rigidity and the effective mantle viscosity as well as certain ice sheet characteristics such as the ice thickness at the time of the last glacial maximum the models permit palaeobathymetry and palaeoshorelines to be predicted for the british isles region including the north sea the resulting evolution of the coastlines exhibits a complex behaviour through time one that is quite different from the usual models in which sea level change is assumed to be a function of time only in part this is because of the delayed response of the mantle to the spatially variable and time dependent ice and water loads and in part because the unloading history of the british ice sheet is different from those of the major global ice sheets thus maximum emergence of the north sea occurred after deglaciation had started and lasted for an extended period from about 15 000 to 12 000 radiocarbon years bp during this relative sea level still stand shoreline features could have formed for example along the western edge of the norwegian trough when access to the firths of eastern scotland would have been via a long and shallow marine inlet shoreline retreat across the north sea became relatively rapid after about 10000 years the model predictions for the irish and celtic seas also suggest a complex behaviour with the formation of a wide land bridge between about 20000 and 13 000 years ago the model also suggests that as long as the scottish ice extended across the northern irish sea until about 14 000 years ago there would have been a large freshwater periglacial lake located further south both the predicted sea level height age relations and the shoreline positions are consistent with a large body of observational evidence but some discrepancies occur particularly in northern scotland and ireland where the ice heights may have been somewhat greater than assumed in the model

a synthetic stratigraphic model of foreland basin development the processes of erosion and deposition must be included in foreland basin models to predict correctly basin geometry and stratigraphy we present a synthetic stratigraphic model of the development of nonmarine foreland basins that predicts progressive geometry topography and facies patterns in the model steady crustal shortening occurs according to a wedgethickening model erosion and deposition follow a diffusive process and the lithosphere is compensated elastically erosion and deposition are controlled by the transport coefficients r of the diffusion equation for a range of thrust velocities and lithospheric rigidities transport coefficients are of order 102 103 m yr in the mountain belt these values are much higher than those derived from the study of scarp degradation in the sedimentary basin transport coefficients of order 104 m2 yr are appropriate and are compatible with previous studies of fluvial and deltaic deposition rapid thrusting results in a narrow underfilled basin while slow thrusting results in a wide overfilled basin in addition by varying the erosional and depositional transport coefficients while holding other parameters constant we generate both overfilled and underfilled basins these results suggest that changes in the rate of thrust loading the climate or the source rock lithology can create stratigraphic signatures that have been interpreted to record viscoelastic relaxation of the lithosphere clearly to understand either the long term behavior of the lithosphere or to interpret orogenic history from preserved foreland strata the manner in which a basin was filled must be considered we apply the model to the evolution of the modern sub andean foreland and find that an erosional transport coefficient of 3000 m2 yr and a depositional transport coefficient of 20 000 m2 yr successfully predict the observed basin geometry

the elastic thickness of the british isles free air gravity and topography data from the british isles have been analysed in the frequency domain to determine the mechanisms of topographic support first we calculate how the admittance between measured free air gravity and topography varies as a function of wavelength a simple model which consists of a crust with two layers of different densities overlying a higher density mantle was then used to calculate admittance functions the misfit between observed and calculated admittance was minimized by varying elastic thickness and the proportion of the total load due to internal loading at short wavelengths c 0 2 the general behaviour of the observed admittance suggests that topography is primarily supported by elastic stresses in the crust a small departure between observed and calculated admittance at the longest wavelengths 400

observations of flexure and the rheology of oceanic lithosphere the principal evidence for the long term i e 1 myr mechanical behaviour of the oceanic lithosphere has come from studies of how it deforms in response to large loads such as volcanoes and sediments a model widely used to explain the deformation is an elastic plate in which flexural rigidity depends on the thermal age of the lithosphere at the time of loading an elastic model however is time invariant and does not take into account temporal changes that may occur in the flexural rigidity as a consequence of loading there is evidence for example that the flexural rigidity of the oceanic lithosphere also depends on load age being large at short times and small at long times thus competing effects may exist between thermal cooling which strengthens the lithosphere and some form of load induced stress relaxation which weakens it in order to investigate the relative roles of these processes we have developed a multilayered viscoelastic model which is based on the results of experimental rock mechanics that creep in the lithosphere is a thermally activated process and on a thermal structure that is given by the plate cooling model by comparing the predictions of the model with a new compilation of flexural rigidity estimates we have found that if the upper mantle viscosity is 1020 pa s the activation energy that best describes the long term mechanical behaviour of the oceanic lithosphere is 120 kj mol 1 this parameter pair explains the dependence of flexural rigidity on both plate and load age it also helps account for the subsidence and uplift history of oceanic islands and the stratigraphic patterns that develop in the flexural moats that flank them at atolls a multilayered viscoelastic model explains the rapid subsidence that follows shield building and does not require that the age of the lithosphere that supports a volcano is thermally re set to a younger value our studies suggest that while the oceanic lithosphere has viscoelastic properties the viscosity of its upper layers is so much higher than that of its lower layers that in effect it behaves as a thin elastic plate on long timescales there will therefore be a certain permanence to the observations of oceanic flexure such that they may be used with some confidence to evaluate the tectonic setting of individual features of the seafloor and in some cases their age

isostatic response and anisotropy of the eastern himalayan tibetan plateau a reappraisal using multitaper spectral analysis 1 we estimate the variation in strength of the eastern himalayan tibetan lithosphere from 2d gravity and topography coherence functions calculated with the thomson slepian multitaper technique the coherence shows evidence of structural weakness of the plate in the n s direction aligned with the direction of maximum compression the tibetan plateau is characterized by an effective elastic thickness te that is much lower than would be expected from its large crustal thickness and the additional strength contributed by a coherently folded mantle inferred from shear wave splitting the seismogenic thickness indicates that only the upper crust is contributing to the elastic strength and not the mantle the predominant weakness of the lithosphere in the n s direction revealed from the anisotropy in the coherence function suggests that the mantle may not be directly coupled to crustal deformation beneath the tibetan plateau

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

channel response to tectonic forcing field analysis of stream morphology and hydrology in the mendocino triple junction region northern california abstract an empirical calibration of the shear stress model for bedrock incision is presented using field and hydrologic data from a series of small coastal drainage basins near the mendocino triple junction in northern california previous work comparing basins from the high uplift zone huz uplift rates around 4 mm year to ones in the low uplift zone luz 0 5 mm year indicates that the huz channels are about twice as steep for a given drainage area this observation suggests that incision processes are more effective in the huz it motivates a detailed field study of channel morphology in the differing tectonic settings to test whether various factors that are hypothesized to influence incision rates discharge channel width lithology sediment load change in response to uplift or otherwise differ between the huz and luz analysis of regional stream gaging data for mean annual discharge and individual floods yields a linear relationship between discharge and drainage area increased orographic precipitation in the huz accounts for about a twofold increase in discharge in this area corresponding to an assumed increase in the erosional efficiency of the streams field measurements of channel width indicate a power law relationship between width and drainage area with an exponent of 0 4 and no significant change in width between the uplift rate zones although interpretation is hampered by a difference in land use between the zones the huz channel width dataset reveals a scaling break interpreted to be the transition between colluvial and fluvial dominated incision processes assessments of lithologic resistance using a schmidt hammer and joint surveys show that the rocks of the study area should be fairly similar in their susceptibility to erosion the huz channels generally have more exposed bedrock than those in the luz which is consistent with protection by sediment cover inhibiting incision in the luz however this difference is likely the result of a recent pulse of sediment due to land use in the luz therefore the role of sediment flux in setting incision rates cannot be constrained with any certainty to summarize of the four response mechanisms analyzed the only factor that demonstrably varies between uplift rate zones is discharge although this change is likely insufficient to explain the relationship between channel slope and uplift rate the calibrated model allows us to make a prediction of channel concavity that is consistent with a previous estimate from slope drainage area data we show that the inclusion of nonzero values of critical shear stress in the model has important implications for the theoretical relationship between steady state slope and uplift rate and might provide an explanation for the observations this analysis underscores the importance of further work to constrain quantitatively threshold shear stress for bedrock incision

testing the tectonic significance of some parameters of longitudinal river profiles the case of the ardenne belgium nw europe the longitudinal profiles of 24 rivers of 3rd to 5th order have been analyzed in order to recognize the regional tectonic differentiation pattern of the ardenne a paleozoic massif of nw europe data collected exclusively from 1 25 000 topographic maps were used to define a set of parameters related to the geometry of the profile and proxies for river bedload and drainage area validation of the proxy defined for the bedload discharge ratio demonstrates its potential use for inter river comparison based on its value at the river mouth it is however inadequate to estimate the ratio changes along a given stream course this proxy has been computed to estimate the portion accounted for by hydrodynamic factors in the river bed profiling thus outliers to the correlation function linking it to the river bed gradient have been considered as undergoing other influences principally of lithologic or tectonic origin most indicative of the computed profile parameters are those related to the concavity of the profile four more or less regional longitudinal profile types are recognized which are partly determined by differential tectonic movement the combined analysis of all the parameters confirms the current uplift of the ne ardenne and points to a subsidence of the namur area with respect to its sw and se surroundings whether periglacial or tectonic in origin the upper pleistocene lowering of a local base level has also been identified in the famenne another conclusion of this study is that in order to evidence tectonic influences and to avoid any misinterpretation in a region of complex geologic and geomorphic history and moderate tectonic activity it is essential to consider a number of parameters and to consider their significance within the framework of detailed geologic setting and morphogenetic history

coupled simulations of fluvial erosion and mass wasting for cohesive river banks the erosion of sediment from riverbanks affects a range of physical and ecological issues bank retreat often involves combinations of fluvial erosion and mass wasting and in recent years bank retreat models have been developed that combine hydraulic erosion and limit equilibrium stability models in related work finite element seepage analyses have also been used to account for the influence of pore water pressure in controlling the onset of masswasting this paper builds on these previous studies by developing a simulation modeling approach in which the hydraulic erosion finite element seepage and limit equilibrium stability models are for the first time fully coupled application of the model is demonstrated by undertaking simulations of a single flow event at a single study site for scenarios where i there is no fluvial erosion and the bank geometry profile remains constant throughout ii there is no fluvial erosion but the bank profile is deformed by simulated mass wasting and iii the bank profile is allowed to freely deform in response to both simulated fluvial erosion and mass wasting the results are limited in scope to the specific conditions encountered at the study site but they nevertheless demonstrate the significant role that fluvial erosion plays in steepening the bank profile or creating overhangs thereby triggering mass wasting however feedbacks between the various processes also lead to unexpected outcomes specifically fluvial erosion also affects bank stability indirectly as deformation of the bank profile alters the hydraulic gradients driving infiltration into the bank thereby modulating the evolution of the pore water pressure field consequently the frequency magnitude and mode of bank erosion events in the fully coupled scenario differ from the two scenarios in which not all the relevant bank process interactions are included

on the postglacial isostatic adjustment of the british isles and the shallow viscoelastic structure of the earth summary observations of postglacial relative sea level rsl history at sites beyond the margins of the main accumulations of wu rm wisconsin devensian ice may be invoked to test the accuracy of global models of the glacial isostatic adjustment process the existing database of rsl time series for the british isles forms a continuous network of sites that sample the coasts of scotland england and wales fairly uniformly and which may be especially important in this regard not only are these 14c data for the holocene epoch of very high quality in terms of our knowledge of the coastal environment and relationship to palaeo sea level of each age measurement but they are especially numerous and relate to an island that was itself partly glaciated in the north essentially ice free in the south and located well outboard of the massive ice sheet that covered fennoscandia at the last glacial maximum lgm taken together the time series from 55 distinct locations allow us to perform a fairly stringent test of the recently formulated ice 4g vm2 global model of the isostatic adjustment process even without modification this model has been shown to fit most of the time series in the uk data set rather well in order to satisfy very recently published a priori constraints on the maximum thickness of the scottish ice sheet however we find that the lithospheric thickness the feature of the radial viscoelastic structure to which the rebound data from scotland are most sensitive must be somewhat reduced whereas the assumed thickness of the lithosphere in ice 4g vm2 was near to 120 km best fits to the scottish data require a lithospheric thickness near to 90 km this reduced value for lithospheric thickness agrees exceedingly well with the latest estimates of this earth property based on the inversion of oceanic geoid and topography data as the asymptotic thickness characteristic of the oldest ocean floor this would appear to be the best possible a priori estimate for the thickness of the cratonic lithospheres upon which the largest ice sheets of the late pleistocene are known to have rested we also demonstrate explicitly that inferences of the shallow viscoelastic structure beneath the british isles are strongly influenced by the details of the history of deglaciation at remote locations at antarctica in particular

a new approach to the relief of great britain iii derivation of the contribution of neotectonic movements and exceptional regional denudation to the present relief abstract this paper builds on the contribution of relative rock resistance to contrasts in the relief of britain to establish the contribution of other factors these include the slope of the major rivers towards the sea itself in part a function of the size of material eroded from the headwater uplands and thus of their lithology and the steepness of their valleyside slopes the pattern of denudational unloading and thus of isostatic uplift is mapped and compared with actual mean altitude it is shown that the sum of predicted isostatic uplift and local base level is closely related to the current mean altitude of our uplands the predicted mean height based on the six equations for each rock resistance class relating mean altitude to river distance can also be compared with actual mean elevation this shows positive departures which are most readily explained by neotectonic uplift notable in the scottish highlands the alston block of the northern pennines and fforest fawr in south wales negative departures may be due to relative neotectonic subsidence as in buchan where there is coincidence with positive gravity anomalies however most negative departures can be linked with severe glacial erosion especially in such areas as westernmost scotland the lake district the vale of belvoir and the wash fens basin where evidence for deep glacial erosion is already strong regional height differences related to the major structural regions of britain are calculated they make a smaller contribution to differences in average elevation and thus to the overall relief of britain

uplift driven valley incision and river terrace formation in southern england outside the limits of middle pleistocene glaciation the river basins of southern england contain long cenozoic terrestrial sedimentary records of greatest importance are the river terrace sequences which contain biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary however trends in valley development cannot easily be accommodated within the framework of quaternary climatic change it is argued in this paper that episodic incision and terrace development result from uplift a consequence of the interplay between continuing alpine orogenic movements and erosion driven isostasy using a simple linear model height age an uplift rate of ca 7 cm ka 1 is estimated for the terrace sequence in the upper thames valley this preliminary model is evaluated using the records of adjacent basins 1997 john wiley sons ltd

bank and near bank processes in an incised channel abstract gravitational forces acting on in situ bank material act in concert with hydraulic forces at the bank toe to determine rates of bank erosion the interaction of these forces control streambank mechanics hydraulic forces exerted by flowing water on in situ bank toe material and failed cohesive material at the bank toe are often sufficient to entrain materials at relatively frequent flows and to maintain steep lower bank profiles seepage forces exerted on in situ bank material by groundwater downward infiltration of rainwater and lateral seepage of streamflow into and out of the bank are critical in determining bank strength data from a study site on goodwin creek ms usa clearly show the temporal variability of seepage forces and the lag time inherent in reductions in shear strength due to losses of matric suction and generation of positive pore water pressures negative pore water pressures matric suction have also been shown to increase the resistance of failed cohesive blocks to entrainment by fluid shear a stable bank can be transformed into an unstable bank during periods of prolonged rainfall through 1 increase in soil bulk unit specific weight 2 decrease or complete loss of matric suction and therefore apparent cohesion 3 generation of positive pore water pressures and therefore reduction or loss of frictional strength 4 entrainment of in situ and failed material at the bank toe and 5 loss of confining pressure during recession of stormflow hydrographs relatively small frequent flows during the winter have the ability to erode failed bank materials maintain oversteepened unstable bank surfaces and promote prolonged periods of bank retreat channel migration and high yields of fine grained sediment confining pressures provided by stormflow are not as significant in maintaining bank stability as the counteracting force of fluid shear on the bank toe which steepens the bank for example more than 2 m of bank retreat occurred during the study period at the research site on goodwin creek northern mississippi the loss of matric suction negative pore pressures due to infiltrating precipitation has been found to be as significant as the development of excess pore pressures in contributing to mass bank instability apparent cohesion friction angle soil bulk unit weight and moisture content were measured in situ matric suction was measured continuously in situ with a series of five pressure transducer tensiometers a bank failure algorithm which combines the mohr coulomb approach for saturated conditions and the fredlund modification for unsaturated conditions was developed for layered cohesive streambanks the resulting equation has been used successfully to investigate the role of matric suction positive pore water pressures and confining pressure for layered streambanks composed of cohesive materials

soil properties controlling seepage erosion contributions to streambank failure the majority of sediment leaving catchments may be from streambank failure seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams that leads to streambank failure by undercutting banks the objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern mississippi using field observations as a guide the soil profile conditions of a shallow 45 cm streambank consisting of 30 cm of topsoil a 10 cm conductive layer and a 5 cm restrictive layer were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head the time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer seepage erosion began within minutes of flow initiation and resulted in substantial 3 to 34 cm undercutting of the bank sediment concentrations of seeps were as high as 660 g l 1in situ and 4500 g l 1 in the lysimeters sediment concentrations were related to the layer slope thereby indicating the importance of detailed site characterization the usda ars streambank stability model demonstrated the increase in instability of banks due to undercutting by seepage erosion but failed to account for the sediment loss due to sapping for stable banks and overestimated the sediment loads for failed banks published in 2006 by john wiley sons ltd

geometric optical bidirectional reflectance modeling of a conifer forest canopy a geometric optical forest canopy model that treats conifers as cones casting shadows on a contrasting background explains the major anisotropies in bidirectional reflectance measurements of a conifer forest canopy taken from the literature the model uses parallelray geometry to describe the illumination and viewing of conifers as three dimensional cones cones are randomly placed and overlap freely cone size height is distributed lognormally and cone form described by the apex angle of the cone is a negative exponential function of height the cones are first presumed to be solid dark gray lambertian objects located on a lighter gray lambertian background to add realism translucence is added and light is allowed to pass through cones with negative exponential attenuation both computer simulation and analytical closed form expressions are implemented the results show a good qualitative agreement with the directional reflectance measurements of the conifer stand indicating that the three dimensional nature of the canopy is a key factor in determining its directional reflectance

geologic constraints on bedrock river incision using the stream power law denudation rate in unextended terranes is limited by the rate of bedrock channel incision often modeled as work rate on the channel bed by water and sediment or stream power the latter can be generalized as ka m s n where k represents the channel bed s resistance to lowenng whose variation with lithology is unknown a is drainage area a surrogate for discharge s is local slope and m and n are exponents whose values are debated we address these uncertainties by simulating the lowering of ancient river profiles using the finite difference method we vary m n and k to match the evolved profile as closely as possible to the corresponding modern river profile over a time period constrained by the age of the mapped paleoprofiles we find at least two end member incision laws ka 0 3 0 5 s for australian rivers with stable base levels and k f a 0 1 0 2 s n for rivers in kauai subject to abrupt base level change the long term lowering rate on the latter expression is a function of the frequency and magnitude of knickpoint erosion characterized by k f incision patterns from japan and california could follow either expression if they follow the first expression with m 0 4 k varies from 10 7 10 6 m 0 2 yr for granite and metamorphic rocks to 10 5 10 4 m 0 2 yr for volcaniclastic rocks and 10 4 10 2 m 0 2 yr for mudstones this potentially large variation in k with lithology could drive strong variability in the rate of long term landscape change including denudation rate and sediment yield

sediment and rock strength controls on river incision into bedrock recent theoretical investigations suggest that the rate of river incision into bedrock depends nonlinearly on sediment supply challenging the common assumption that incision rate is simply proportional to stream power our measurements from laboratory abrasion mills support the hypothesis that sediment promotes erosion at low supply rates by providing tools for abrasion but inhibits erosion at high supply rates by burying underlying bedrock beneath transient deposits maximum erosion rates occur at a critical level of coarse grained sediment supply where the bedrock is only partially exposed fine grained sediments provide poor abrasive tools for lowering bedrock river beds because they tend to travel in suspension experiments also reveal that rock resistance to fluvial erosion scales with the square of rock tensile strength our results suggest that spatial and temporal variations in the extent of bedrock exposure provide incising rivers with a previously unrecognized degree of freedom in adjusting to changes in rock uplift rate and climate furthermore we conclude that the grain size distribution of sediment supplied by hillslopes to the channel network is a fundamental control on bedrock channel gradients and topographic relief

numerical simulation of widening and bed deformation of straight sand bed rivers ii model evaluation in this paper the numerical model presented in the companion paper is tested and applied assessment of model accuracy was based on two approaches first predictions of evolution of a 13 5 km reach of the south fork of the forked deer river in west tennessee were compared to observations over a 24 yr period results suggest that although the model was able to qualitatively predict trends of widening and deepening quantitative predictions were not reliable simulated widths and depths were within 15 of the corresponding observed values but observed change in these parameters at the study sites were also close to these values simulated rates of depth adjustment were within 15 of observed rates but observed rates of channel widening at the study sites were approximately three times those simulated by the model in the second approach the model was used to generate relationships between stable channel width and bank full discharge the model was able to successfully replicate the form of empirically

the long term strength of europe and its implications for plate forming processes field based geological studies show that continental deformation preferentially occurs in young tectonic provinces rather than in old cratons this partitioning of deformation suggests that the cratons are stronger than surrounding younger phanerozoic provinces however although archaean and phanerozoic lithosphere differ in their thickness and composition their relative strength is a matter of much debate one proxy of strength is the effective elastic thickness of the lithosphere te unfortunately spatial variations in te are not well understood as different methods yield different results the differences are most apparent in cratons where the bouguer coherence method yields large te values 60 km whereas the free air admittance method yields low values or 1 5 gyr old is much larger mean te 60 km than that of younger lithosphere mean te 30 km we propose that this strength difference reflects changes in lithospheric plate structure thickness geothermal gradient and composition that result from mantle temperature and volatile content decrease through earth s history

speleothem u series constraints on scarp retreat rates and landscape evolution an example from the severn valley and cotswold hills gull caves uk modelling landscape evolution requires quantitative estimates of erosional processes dating erosional landscape features such as escarpments is usually difficult because of the lack of datable deposits some escarpments and valley margins are associated with the formation of mass movement caves sometimes known as gull or crevice caves which are typically restricted to within 0 5 km of the valley margin or scarp edge as in other caves these mass movement cavities may host speleothems as gull caves develop only after valley incision uranium series dating of speleothems within them can provide a minimum age for the timing of valley excavation and scarp formation here we present data from several gull caves in the cotswold hills which form the eastern flank of the severn valley in southern england u series ages from these gull caves yield estimates for both the minimum age of the cotswold escarpment and the maximum scarp retreat rate this is combined with data from geological modelling to propose a model for the evolution of the severn valley and the cotswold hills the data suggest that the location of the escarpment and regional topography is determined not by valley widening and scarp retreat but by the in situ generation of relief by differential erosion

piping sapping erosion ii identification diagnosis although erosion of streambanks and other shorelines by emergent seepage is widespread this erosion mechanism termed piping or sapping has not been recognized as important to the overall erosion process the mechanism is complex and interactions with other bank and shore processes tend to mask the effects of piping sapping direct evidence water emerging from a soil face and carrying away soil particles is rarely encountered several types of indirect evidence are presented and illustrated in this paper including cavities formed by piping deposits of dislocated particles below piping zones blind gullies staining produced by persistent seepage outflow and particular types of localized failures slab toppling block shearing and tensile falls caused by undercutting due to piping sapping the interactions of this erosion mechanism with other erosion deposition processes are described the purpose of this paper is to facilitate identification and evaluation of piping sapping erosion particularly

uplift driven valley incision and climate controlled river terrace development in the thames valley uk abstract the sequence of terraces of the river thames in southeast england has previously been shown to span the period from the earliest pleistocene to the present this terrace sequence contains biostratigraphical and sedimentary evidence that testifies to the high amplitude climatic changes of the quaternary large scale fluvial incision resulting in basin wide terrace formation appears to have been concentrated at the warming limbs of the major climatic glacial interglacial cycles when sediment supply was greatly reduced this incision and subsequent valley floor widening created the accommodation space for the later aggradation of the terrace sediments during the following warm cold transitions and during the cold stages when high sediment supply conditions prevailed although the timing of terrace aggradation may be controlled by climate change the progressive valley incision recorded by terrace staircases cannot easily be explained in terms of quaternary climatic change alone and recently developed models suggest that long term incision by the thames has been driven by uplift this paper presents an overview of the available terrace data and tabulates incision amounts and rates between key stratigraphic horizons superimposed upon these broad changes revealed by the complex internal sedimentary architecture of many terrace sediments are the geomorphological system responses to both higher frequency climate driven changes and more localized intrinsic fluvial system adjustments

intraplate deformation and 3d rheological structure of the rhine rift system and adjacent areas of the northern alpine foreland the lithosphere of the northern alpine foreland has undergone a polyphase evolution during which interacting stress induced intraplate deformation and upper mantle thermal perturbations controlled folding of the thermally weakened lithosphere in this paper we address relationships among deeper lithospheric processes neotectonics and surface processes in the northern alpine foreland with special emphasis on tectonically induced topography we focus on lithosphere memory and neotectonics paying special attention to the thermo mechanical structure of the rhine graben system and adjacent areas of the northern alpine foreland lithosphere we discuss implications for mechanisms of large scale intraplate deformation and links with surface processes and topography evolution

holocene land and sea level changes in great britain analysis of more than 1200 radiocarbon dated samples that constrain relative sea levels in great britain over the past 16 000 yr provides estimates of current land level changes negative of relative sea level change maximum relative land uplift occurs in central and western scotland ca 1 6 mm yr 1 and maximum subsidence is in southwest england ca 1 2 mm yr 1 sediment consolidation arising from autocompaction as the sediment accumulates and from land drainage increases the subsidence in areas with thick sequences of holocene sediments with an average effect equivalent to at least an extra ca 0 2 mm yr 1 land subsidence but more in parts of southeast england 0 5 1 1 mm yr 1 modelled changes in tidal range during the mid to late holocene in eastern england suggest that the calculated rate of land subsidence is overestimated unless such changes are quantified the effect is most significant for large coastal lowlands the fenland and humber ca 0 5 and 0 6 mm yr 1 that were tidal embayments during the mid to late holocene

distribution of active rock uplift along the eastern margin of the tibetan plateau inferences from bedrock channel longitudinal profiles 1 current models of long term river incision into bedrock suggest that the local rate of differential rock uplift should exert a primary control on the gradient of channel longitudinal profiles however discrimination of this effect from the influence of variations in substrate erodibility sediment flux precipitation and transient changes in profile shape has proved difficult in practice here we investigate the controls on the spatial distribution of bedrock channel gradients adjacent to the sichuan basin in an effort to assess the degree and nature of active deformation along this margin of the tibetan plateau analysis of river longitudinal profiles utilizing a channel steepness index a measure of profile gradient normalized for drainage area reveals a zone of anomalously steep channels adjacent to the topographic front of the plateau margin channel profiles are systematically less steep in their headwater reaches on the plateau and in their lower reaches east of the plateau margin comparison of steepness indices to mapped lithologic variations reveals that lithology has only a limited influence on channel gradient in this field area we observe no systematic relationship between steepness indices and upstream drainage area channels of all size are steeper near the plateau margin we argue that these systematic changes are not readily explained as a consequence of increased sediment flux or of orographic precipitation we are led to conclude that steep channel profiles along the topographic front of the plateau reflect active differential rock uplift between this region and the foreland

landscape response to climate change insights from experimental modeling and implications for tectonic versus climatic uplift of topography we present the results of an experimental investigation of the concurrent action of tectonic uplift and climate variation on relief evolution we designed an experimental apparatus that allows the study of erosion of laboratory scale topographies that evolve under given uplift and rainfall rates for constant uplift and rainfall rates the experimental topography evolves toward a statistical steady state defined by a mean elevation constant with time starting from such a steady state and keeping the input uplift rate constant a subsequent change in the rainfall rate yields a change in the mean elevation of the landscape to a new equilibrium elevation an increase in precipitation yields a lower mean steady state elevation whereas for a decrease in precipitation the surface is uplifted we define this phenomenon as a climatically induced surface uplift as opposed to a tectonically induced surface uplift the climatically and tectonically induced surface uplifts correspond to different dynamics of denudation so that it is theoretically possible to differentiate between the climatic or tectonic causes of surface uplift from records of output sediment fluxes

reply to discussion on an analysis of cotswold topography insights into the landscape response to denudational isostasy journal vol 165 85 103 we thank scourse and preece for their interest in our paper we agree that we should have included a reference to gale et al 1999 who used stratigraphic data to quantify the uplift history of the northern limb of the sandown pericline isle of wight we did however include a reference to green et al 2001 who used an apatite fission track analysis of outcrops of palaeozoic basement rocks to determine the uplift history of the english midlands together these studies suggest a mean long term uplift rate of c 0 10 m ka 1 for the