prediction of alluvial channel pattern of perennial rivers abstract purely braided meandering and straight channels can be considered as end members of a continuum of alluvial channel patterns several researchers have succeeded in separating channel patterns in fields defined by flow related parameters however the discriminators of the principal channel patterns derived from these diagrams all require some a priori knowledge of the channel geometry in this paper a method is presented which enables prediction of the equilibrium conditions for the occurrence of braided and high sinuosity meandering rivers in unconfined alluvial floodplains the method is based on two almost channel pattern independent boundary conditions median grain size of the river bed material and a potential specific stream power parameter related to bankfull discharge or mean annual flood and valley gradient this can be regarded as a potential maximum of the available flow energy corresponding to the minimum sinuosity condition p 1 based on an analysis of 228 datasets of measurement sites along rivers from many parts of the world an independent discriminating function was found that separates the occurrence of braided rivers and meandering rivers with p 1 5 the function applies to equilibrium conditions of rivers that neither incise nor show rapid aggradation with a bankfull or mean annual flood discharge above 10 m3 s and a median bed material grain size between 0 1 and 100 mm

anisotropy beneath the pyrenees range from teleseismic shear wave splitting results from a test experiment we have investigated the seismic anisotropy from sks and skks wave splitting along a n s profile perpendicular to the pyrenean mountain belt the line crossed the north pyrenean fault npf which probably represents the plate boundary between the european and the iberian plates we observed large delay times t 1 3 to 1 5 s and uniform fast polarization directions n100e at three stations located on the iberian plate on the other hand t are smaller 0 5 1 0 s and the scattered at stations located north of the npf the small scale variability the relation with surface geology and the correlation of the t with lithospheric thickness suggest that the anisotropy could be predominantly of lithospheric origin however an asthenospheric contribution cannot be ruled out in the north pyrenean zone an important thermal event before the pyrenean compression has likely erased the former mantle fabric the observed anisotropy is then likely related to the pyrenean orogeny on the iberian plate our splitting parameters are similar to those obtained at two stations located on hercynian structures in central spain this suggests that two contributions are likely superposed to that of the pyrenean built up one related to the hercynian orogeny and the other one related to the rotation of the iberian plate

microfabric analysis of mn carbonate laminae deposition and mn sulfide formation in the gotland deep baltic sea the manganese carbonate deposits of the anoxic littorina sediments of the gotland deep have been commonly related to the periodic renewal of deep water by inflowing saline water from the north sea the use of scanning electron microscopy based techniques allows identification of small scale sedimentary and geochemical features associated with mn carbonate laminae which has significant implications for models of mn carbonate formation varves occurring in the littorina sequence contain up to four laminae that may be placed in a seasonal cycle and kutnahorite laminae occur within varves only as a winter early spring deposit this kutnahorite laminae seasonality is in agreement with the seasonal distribution of major baltic inflow events recorded in historical records and a direct causal link between inflows and kutnahorite deposition is implied benthic foraminifera tests are found to be heavily encrusted in kutnahorite implying that benthic recolonization during oxidation events occurs concurrently with kutnahorite formation the relatively common occurrence of small 50 to 100 m hexagonal mn sulfide pseudomorphs associated with 13 of kutnahorite laminae studied is reported in gotland deep sediments for the first time although mn sulfide crystals are not usually preserved in the sediment the discovery of mn sulfide pseudomorphs suggests that initial formation of mn sulfide in the gotland deep may occur much more commonly during the process of kutnahorite formation than previous reports of mn sulfide occurrence have implied

the implications of geology soils and vegetation on landscape morphology inferences from semi arid basins with complex vegetation patterns in central new mexico usa abstract this paper examines the relationship between land surface properties e g soil vegetation and lithology and landscape morphology quantified by the catchment descriptors the slope area s a relation curvature area c a relation and the cumulative area distribution cad in two semi arid basins in central new mexico the first site is composed of several basins located in today s desert elevations with mesic north facing and xeric south facing hillslopes underlain by different lithological formations the second site is a mountainous basin exhibiting vegetation gradients from shrublands in the lower elevations to grasslands and forests at higher elevations all three land surface properties were found to have significant influences on the s a and c a relations while the power law exponents of the cads for these properties did not show any significant deviations from the narrow range of universal scaling exponents reported in the literature among the three different surface properties we investigated vegetation had the most profound impact on the catchment descriptors in the s a diagrams of the aspect controlled ecosystems we found steeper slopes in north facing aspects than south facing aspects for a given drainage area in elevation controlled ecosystems forested landscapes exhibited the steepest slopes for the range of drainage areas examined followed by shrublands and grasslands in all soil textures and lithologies in the c a diagrams steeper slopes led to a higher degree of divergence on hillslopes and a higher degree of convergence in the valleys than shallower slopes the influence of functional types of vegetation detected on observed topography provided some initial understanding of the potential impacts of life on the organization of topography this finding also emphasizes the critical role of climate in catchment development we suggest that climatic fluctuations that are capable of replacing vegetation communities could lead to highly amplified hydrological and geomorphic responses

post saalian transformation of dry valleys in eastern europe an example from ne poland the studies were conducted in a dry valley in ne poland they were aimed at determining the origin of this structure and tracing the processes that have shaped the dry valley in a time span of about 130 ka the research included detailed geological mapping including piercing of a number of boreholes and electrical resistivity tomography ert surveys the obtained material was pollen analysed osl dated and the grain size distribution and the morphoscopy of sand quartz grains were investigated additionally the organic matter om content was determined based on the obtained results it was concluded that the structure currently occupied by sediments of the dry valley was formed during the warta stadial of the odranian glaciation saalian mis 6 as a glacial tunnel valley small probably isolated depressions functioned in the dry valley bottom after the ice sheet retreat the sediments record a full succession of climate oscillations from the eemian interglacial mis 5e pollen zones e1 to e7 through the early vistulian mis 5a 5d to mis 4 in the early vistulian the depressions functioned as lakes or got shallower and were replaced by peat bogs depending on the climate conditions during mis 4 the bottom of the dry valley was subjected to erosion as a result of concentrated water flow this caused draining of the existing depressions and their incorporation within the flow probably during mis 3 solifluction was activated on the slopes of the dry valley during lgm permafrost aggradation occurred in the study area recorded by two generations of epigenetic sand wedges and development of aeolian processes in contrast to analogous processes within the european sand belt the latter processes acted for a short time and only locally the final record are holocene soils it seems that the analysed valley is a good example of palaeoenvironmental conditions in eastern europe

interpreting climate modulated processes of terrace development along the colorado front range using a landscape evolution model flights of terraces that flank range fronts throughout the rocky mountains record episodic stream incision over the past 1 5 ma studies dating terraces in the denver basin along the colorado front range suggest that these high surfaces were formed during glacial intervals and were rapidly incised and abandoned during interglacials modulation of sediment supply or transport capacity associated with climate change related to glacial interglacial cycles have been suggested as possible drivers for the repeated aggradation and abandonment of these high surfaces potential mechanisms for increasing sediment supply and transport in rivers include variations over time in sediment flux from intermittently glaciated major valleys the efficiency of hillslope sediment transport and the magnitude and timing of rainfall intensity and stream flow in this study we use a landscape evolution model to determine whether any of these processes in isolation or in combination is sufficient to explain the observed rates and patterns of terrace formation and abandonment along the colorado piedmont cycles of channel aggradation and incision are apparent in the models when either mean rainfall intensity is varied or a glacial source of sediment is added the models suggest that in the absence of a large addition of sediment to the streams changes in stream power are necessary to allow channel aggradation and the planation of bedrock surfaces and increased sediment flux from hillslopes is necessary to match observations of increased denudation rates that coincide with the deposition of terrace capping gravels

terrace styles and timing of terrace formation in the weser and leine valleys northern germany response of a fluvial system to climate change and glaciation abstract in glaciated continental basins accommodation space is not only controlled by tectonics and sea level but also by the position of ice sheets which may act as a regional base level for fluvial systems although the pleistocene terrace record of major river systems in northwestern europe has been investigated by many authors relatively little attention has been paid to base level changes related to glacier advance retreat cycles and how these regional changes in base level interacted with river catchment processes this study provides a synthesis of the stratigraphic architecture of middle pleistocene to holocene fluvial terraces in the upper weser and middle leine valley in northern germany and links it to glaciation climate and base level change the depositional architecture of the fluvial terrace deposits has been reconstructed from outcrops and high resolution shear wave seismic profiles the chronology is based on luminescence ages 230 th u ages 14 c ages and middle palaeolithic archaeological assemblages the drainage system of the study area developed during the early miocene during the pleistocene up to 170 m of fluvial incision took place a major change in terrace style from strath terraces to cut and fill terraces occurred during the early middle pleistocene before marine isotope stage mis 12 which may correlate with climate deterioration and the onset of glaciation in northern central europe during this time a stable buffer zone was established within which channels avulsed and cut and filled freely without leaving these vertical confines climate was the dominant driver for river incision and aggradation whereas the terrace style was controlled by base level changes during ice sheet growth and decay a major effect of glacio isostatic processes was the post elsterian re direction of the river weser and river leine the middle pleistocene fluvial terraces are vertically stacked indicating a high aggradation to degradation ratio corresponding with a regional base level rise during glacier advance at the beginning of the late pleistocene the terrace style changed from a vertical to a lateral stacking pattern which is attributed to a decrease in accommodation space during glacier retreat the formation of laterally attached terraces persisted into the holocene major incision phases took place during mis 5e 5d 5c and probably early mis 4 early mis 3 and mis 2 lateglacial during mis 5e and the lateglacial the braided river systems changed into meandering rivers indicated by preserved organic rich flood plain and point bar deposits the late pleistocene braided river systems mis 5c to mis 3 are characterized by a high sinuosity which may be a direct effect of an increased downstream gradient after deglaciation when the channel lengthened and the river adjusted to the increased gradient by increasing sinuosity these middle pleniglacial fluvial deposits are unconformably overlain by lateglacial to holocene meandering river deposits which form laterally attached terraces recording millennial scale channel shifts the lack of late pleniglacial deposits might be related to late weichselian forebulge formation

debris flows as a factor of hillslope evolution controlled by a continuous or a pulse process flood effectiveness observations imply that two families of processes describe the formation of debris flow volume one is related to the rainfall erosion relationship and can be seen as a gradual process and one is related to additional geological geotechnical events those named hereafter extraordinary events in order to discuss the hypothesis of coexistence of two modes of volume formation some methodologies are applied firstly classical approaches con sisting in relating volume to catchments characteristics are considered these approaches raise questions about the quality of the data rather than providing answers concerning the controlling processes secondly we consider statistical approaches cumulative number of events distribution and cluster analysis and these suggest the possibility of having two distinct families of processes however the quantitative evaluation of the threshold differs from the one that could be obtained from the first approach but they all agree in the sense of the coexistence of two families of events thirdly a conceptual model is built exploring how and why debris flow volume in alpine catch ments changes with time depending on the initial condition sediment production the model shows that large debris flows i e with important volume are observed in the beginning period before a steady state is reached during this second period debris flow volume such as is observed in the beginning period is not observed again integrating the results of the three approaches two case studies are presented showing 1 the possibility to observe in a catchment large volumes that will never happen again due to a drastic decrease in the sediment availability sup porting its difference from gradual erosion processes 2 that following a rejuvenation of the sediment storage by a rock avalanche the magnitude frequency relationship of a torrent can be differentiated into two phases the beginning one with large and frequent debris flow and a later one with debris flow less intense and frequent supporting the results of the conceptual model although the results obtained cannot identify a clear threshold between the two families of processes they show that some debris flows can be seen as pulse of sediment differing from that expected from gradual erosion

the relation between climate and river processes landforms and deposits during the quaternary abstract the extent to which river processes and morphology are dependent on climate is an old question when looking at large time scales climatic cyclicity seems to coincide with alternating events in fluvial development however the shorter the time scales at which fluvial development is considered the more it is difficult to find a close correspondence with climate evolution ultimately it appears that the response time of river processes to climatic change may restrict the sensitivity of the fluvial systems to adapt to short climatic oscillations the impact of climate on fluvial systems is largely transferred to these systems by the climate determined soil cohesion and peak discharges the latter factors are especially related to vegetation cover and permafrost conditions finally a number of basin characteristics are discussed that demonstrate that fluvial systems are not completely controlled by climate

transient landscape and stratigraphic responses to drainage integration in the actively extending central italian apennines abstract drainage networks in continental rifts are generally reported as dynamic features that produce transitions between endorheic and exorheic conditions while this is of major importance for landscape development sediment dispersal and basin stratigraphy the controls of drainage network evolution across an array of normal fault bounded basins are still not well understood in this study we use the central italian apennines an area that has been affected by active normal faulting and regional uplift over the last 3 myrs to determine the controls on drainage network evolution and its impact on transient landscape evolution and basin stratigraphy we compile previously published stratigraphic and fault related data with new geomorphological constraints for the aterno river system 1300 km2 for which a wealth of data has been collected following the destructive l aquila earthquake in 2009 we use this compilation to demonstrate how the different basins along the river system were initially isolated during the early pleistocene but became fluvially integrated with one another and the adriatic coast between ca 1 2 and 0 65 ma we conclude that the spatial and temporal pattern of drainage integration is mostly explained by a long term increase in sediment and water supply relative to basin subsidence due to the early to middle pleistocene climatic transition the progressive increase in fault related topography and the transport of sediment and water down system as drainage integration occurred overall we conclude that rates of sedimentation and basin subsidence in the central apennines are well matched allowing tipping points between over and under filled conditions to be easily reached we also show that consecutive drainage integration events produce discrete waves of river incision and terrace formation and conclude that drainage integration is of major importance at least equivalent to tectonics and climate in controlling transient landscape evolution and rift basin stratigraphy

constraints on the lithospheric structure beneath the north pyrenean fault from teleseismic observations the pyrenean range is bordered to the north by the north pyrenean fault which represents the boundary between the european and the iberian plates reflection profiles have shown that the moho is vertically offset by 15 km at the latitude of the fault in order to determine the structure beneath the crust we have recorded teleseismic events on seismic stations deployed on both sides of the fault large p wave traveltime residual variations are observed over a very short distance the residuals given by the rays coming from the south are close to those predicted from the known moho offset southern stations are 0 5 s later they rule out a stacking of the iberian and european crusts underneath the north pyrenean zone as postulated in some models in contrast rays coming from the north give residual variations opposite to those expected from the known crustal structure southern stations are as much as 0 9 s earlier the simplest model fitting the data introduces an abrupt change in lithospheric thickness about 30 km north of the north pyrenean fault i e the southern lithosphere is about 60 70 km thicker than the northern lithosphere the p wave residual variations as a function of incidence angle suggest the existence of an anisotropy a low velocity vertical axis is in the vicinity of the fault this simple structure can be explained by the collision of a thick iberian plate with a thinned aquitaine plate margin a collision involving the imbrication of the crusts and a small decoupling of the lithosphere at the base of the iberian moho

climate forcing of fluvial system development an evolution of ideas starting from traditional ideas on the climatic steering of fluvial system dynamics it appears that there are different kinds of climatic influences on system dynamics they vary from direct climatic forcing like peak precipitation to indirect like permafrost and partial forcing like vegetation vegetation or its absence and not directly climate is considered as the main cause of fluvial incision or deposition during temperate or cold periods however other external factors than climate and non climatic factors such as local basin characteristics like subsoil lithology and relief express their effects on the fluvial systems by their role in the energy balance of the river catchment finally internal factors in fluvial system evolution like thresholds and response time should not be neglected

quantification of soil production and downslope creep rates from cosmogenic 10be accumulations on a hillslope profile average soil transport rates over a period of 3500 yr on a convex soil mantled hillslope have been quantified using a mass balance model that incorporates the soil concentration of the cosmogenic isotope 10 be the 10 be model results support the assumption used in most geomorphic models that the soil creep rate is proportional to surface gradient the predicted diffusion coefficient is 360 55 cm 3 yr 1 cm 1 contour length and the average rate of soil production is 0 026 0 007 cm yr within the uncertainty of this technique the data do not reject g k gilbert9s hypothesis that some hillslopes may exist in a condition of dynamic equilibrium with a uniform soil production rate however the model does not require an assumption of dynamic equilibrium and may be an approach that uniquely allows the quantification of a local soil production rate law

a new numerical framework for simulating the control of weather and climate on the evolution of soil mantled hillslopes abstract we present a new numerical framework for simulating short to long term hillslope evolution this modeling framework to which we have given the name cliche climate control on hillslope evolution aims to better capture the control of climate on soil dynamics it allows the use of realistic forcing that involves through a specific time discretization scheme the variability of both the temperature and precipitation at time scales ranging from the daily rainfall events to the climatic oscillations of the quaternary also including seasonal variability two simple models of soil temperature and soil water balance permit the link between the climatic inputs and derived quantities that take part in the computation of the soil flux such as the surface water discharge and the depth of the non frozen soil layer using this framework together with a multi process parameterization of soil transport we apply an original method to calculate hillslope effective diffusivity as a function of climate this allows us to demonstrate the ability of the model to simulate observed rates of hillslope erosion under different climates cold and temperate with a single set of parameter values numerical experiments furthermore suggest a potential high peak of sediment transport on hillslopes during the glacial interglacial transitions of the quaternary we finally discuss the need to improve the parameterization of the soil production and transport processes in order to explicitly account for other key controlling factors that are also climate sensitive such as biological activity

modelling the long term fluvial erosion of the river somme during the last million years a process based model that simulates fluvial erosion in the river somme valley over the last million years is presented here the model takes into account lithology and climatic influences and allows the simulating of undercapacity and overcapacity sediment transport behaviour the model has been calibrated to a family of terraces within the river somme valley when matched to this field data simulation trials suggest that bedrock incision occurred principally from 120 to 60 40 kyr during the last climatic cycle and before the last glaciation the impact of a progressive tectonic uplift c 60 m over c 1 million years on the river somme has also been studied here extended over a longer period of time the simulations suggest that 1 million years ago the profile of the river somme had a lower slope gradient than today with little relief throughout the paris basin

the concept of cryo conditioning in landscape evolution recent accounts suggest that periglacial processes are unimportant for large scale landscape evolution and that true large scale periglacial landscapes are rare or non existent the lack of a large scale topographical fingerprint due to periglacial processes may be considered of little relevance as linear process landscape development relationships rarely can be substantiated instead periglacial landscapes may be classified in terms of specific landform associations we propose cryo conditioning defined as the interaction of cryotic surface and subsurface thermal regimes and geomorphic processes as an overarching concept linking landform and landscape evolution in cold regions by focusing on the controls on processes this concept circumvents scaling problems in interpreting long term landscape evolution derived from short term processes it also contributes to an unambiguous conceptualization of periglacial geomorphology we propose that the development of several key elements in the norwegian geomorphic landscape can be explained in terms of cryo conditioning

the role of sediment in controlling steady state bedrock channel slope implications of the saltation abrasion incision model abstract the saltation abrasion model is a mechanistic model for river incision into bedrock by saltating bedload which we have previously derived and used experimental data to constrain all parameter values here we develop a method for applying the saltation abrasion model at a landscape scale and use the model as a reference for evaluating the behavior of a wide range of alternative incision models in order to consider the implications of the saltation abrasion model as well as other models for predicting topographic steady state channel slope to determine the single valued discharge that best represents the effects of the full discharge distribution in transporting sediment and wearing bedrock we assume all runoff can be partitioned between a low flow and a high flow discharge in which all bedload sediment transport occurs during high flow we then use the gauged discharge record and measurements of channel characteristics at a reference field site and find that the optimum discharge has a moderate magnitude and frequency due to the constraints of the threshold of grain motion and bed alluviation by high relative sediment supply incision models can be classified according to which of the effects of sediment on bedrock incision are accounted for using the predictions of the saltation abrasion model as a reference we find that the threshold of motion is the most important effect that should be represented explicitly followed in order of decreasing importance by the cover effect the tools effect and the threshold of suspension effect models that lack the threshold of motion over predict incision rate for low shear stresses and under predict the steady state channel slope for low to moderate rock uplift rates and rock strengths models that lack the cover effect over predict incision rate for high sediment supply rates and fail to represent the degree of freedom in slope adjustment provided by partial bed coverage models that lack the tools effect over predict incision rate for low sediment supply rates and do not allow for the possibility that incision rate can decline for increases in shear stress above a peak value overall the saltation abrasion model predicts that steady state channel slope is most sensitive to changes in grain size such that the effect of variations in rock uplift rate and rock strength may affect slope indirectly through their possible but as yet poorly understood influence on the size distribution of sediments delivered to channel networks by hillslopes

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

lithospheric anisotropy beneath the pyrenees from shear wave splitting we investigate upper mantle anisotropy beneath the pyrenean range along three n s profiles across the mountain belt the results of a first profile that operated in 1993 in the central part of the belt have been presented elsewhere we present the results of two other profiles that ran in 1995 1996 and 1996 1997 in the eastern and western part of the belt respectively and propose an interpretation of the whole results teleseismic shear waves sks skks and pks are used to determine splitting parameters the fast polarization direction and the delay time t teleseismic shear wave splitting in the eastern pyrenees displays homogeneous values trending n100 e and t values in the range 1 1 to 1 5 s a station located in the southern massif central 100 km north of the range is characterized by different splitting parameters n70 e t 0 7 s in the western part of the belt anisotropy parameters are similar across the whole belt n110 e and t 1 3 to 1 5 s most of the measured delay times including those obtained in the central part of the range are above the global average of the sks splitting around 1 s at the belt scale is generally poorly correlated with recent estimations of the absolute plate motion which predicts a fast direction ranging between n50 e and n80 e instead the orientation of n100 e is parallel to the trend of the pyrenean belt but also to hercynian preexisting structures this parallelism supports an anisotropy primarily related to frozen or active lithospheric structures we show that a signature related to the pyrenean orogeny is likely for the stations located in the internal domains of the belt by contrast the anisotropy measured at the stations located on the external parts of the belt could reflect a pre pyrenean hercynian deformation we suggest that a late hercynian strike slip deformation is responsible for this frozen upper mantle anisotropy and that the pyrenean tectonic fabric developped parallel to this preexisting fabric finally no particularly strong splitting is related to the north pyrenean fault commonly believed to represent the plate boundary between iberia and eurasia

hillslope and channel evolution in a marine terraced landscape santa cruz california a flight of marine terraces along the central california coastline provides a unique setting for the study of topographic evolution wavecut platforms mantled by 2 6 m of marine terrace cover deposits are separated by 10 50 m tall decaying sea cliffs paleocliff edges become more rounded with age yet the details of the profiles and frequent bedrock exposure on the upper slopes imply weathering limited transport five bedrock stream channels etched through the marine terrace sequence display one to three distinct convexities in their longitudinal profiles detailed hand level surveys of the hillslopes and of the stream channel longitudinal profiles constrain hillslope evolution and channel incision components of a numerical model of landscape evolution we account for regolith production as a function of regolith depth in accord with the field observation that hillslope processes are presently dominated by the activities of burrowing rodents the transport process is taken to be diffusive stream incision is assumed to be controlled by stream power for which we use the surrogate of local drainage area slope product best fits of the numerical model to field data imply hillslope diffusivity is 10 m2 kyr 1 regolith production rate on bare bedrock is 0 3 m kyr 1 and falls off rapidly with regolith cover and the constant controlling the efficiency of stream incision is 5 to 7 10 7m 1 kyr1

tectonic and climatic controls on knickpoint retreat rates and landscape response times 1 the rate at which transient knickpoints propagate through a landscape fundamentally controls the rate of geomorphic response to tectonic and climatic perturbation here we present knickpoint retreat rates upstream of active faults for 19 bedrock catchments in turkey and 11 bedrock catchments in italy where we have very good constraints on both the magnitude and timing of the tectonic perturbation and where climate histories are well documented we show that the knickpoints have average retreat rates of between 0 2 and 2 mm yr for catchments with drainage areas between 6 and 65 km2 and we test whether differences in rock mass strength and catchment size are sufficient to explain this range in retreat rates our analysis suggests that even accounting for these two variables knickpoint propagation velocities differ markedly and we show that channels crossing faults with higher throw rates have knickpoints that are retreating faster the dependence of knickpoint retreat velocity on throw rate is at least as important as catchment drainage area these results indicate counterintuitively that landscapes forced by large amplitude tectonic perturbations will have shorter response times than those perturbed by smaller amplitude changes the link between the knickpoint propagation velocity and throw rate is largely but not completely explained by channel narrowing in areas of high uplift rate channel steepening upstream of the active faults may explain all of the residual dependency of knickpoint retreat rate on fault throw rate but only if the slope exponent n in the standard stream power model is greater than 1 3 however we cannot rule out a role for sediment supply in driving enhanced knickpoint retreat rate in addition to the well documented channel narrowing effect finally we find that mean knickpoints retreat rates in turkey are only half of those in italy for catchments of equivalent size crossing faults with similar throw rates this difference in fluvial response time is accounted for by long term differences in the ratio of precipitation to infiltration in the two areas over the last 1 my

climatic reconstruction of the weichselian pleniglacial in northwestern and central europe a multiproxy approach is applied to reconstructing accurately the weichselian pleniglacial climate 72 13 ka in northwestern and central europe standardised translations are used to transform proxy data into climate parameter values for six characteristic time windows quantitative reconstructions of the temperature regime are derived from periglacial coleoptera and botanical evidence while aeolian and fluvial evidence provide qualitative information on wind activity and precipitation respectively the early pleniglacial 74 59 ka the cold period between 41 38 ka and the late pleniglacial 27 13 ka are characterised by a strong north to south climatic gradient over northwestern europe during the last glacial maximum discontinuous permafrost was established in northern france whereas the continuous permafrost zone extended from the uk belgium the netherlands germany and poland to the nordic ice sheets prominent wind activity and a relatively low precipitation typify these periods in contrast an indistinct west to east climate gradient was present in the relatively more temperate intervals e g 50 41 ka seasonally frozen ground conditions prevailed in northwestern europe whereas discontinuous permafrost may be suggested for central germany it appears that the climate conditions in northwest and central europe were controlled by three major factors the scandinavian ice sheet the north atlantic surface water circulation and the russian continent 1998 john wiley sons ltd

modelling cockpit karst landforms the purpose of this article is to present a model of the formation processes of cockpit karst landscapes the child software was used to simulate landscape evolution including dissolution processes of carbonate rocks after examining briefly how the child model operates two applications of this model involving dissolution of carbonate rocks are presented the simulated landscapes are compared with real landscapes of the cockpit country jamaica using morphometric criteria the first application is based on the hypothesis that dissolution of carbonate rocks is isotropic over time and space in this case dissolution is constant throughout the whole area studied and for each time step the simulated landscapes based oil this hypothesis have morphometric features which are quite different from those of real landscapes the second application considers that dissolution of carbonate rocks is anisotropic over time and space in this case it is necessary to take into account subsurface and under round processes by coupling surface runoff and water infiltration into the fractured carbonates

extensive amazonian aged fluvial channels on mars evaluating the role of lyot crater in their formation widespread amazonian aged fluvial channels have been mapped proximal to lyot crater a 225 km diameter impact basin in the northern lowlands of mars comparable in area to some noachian hesperian fluvial systems their morphology differs being dominated by broad shallow braided channels using new developments in the study of cratering water inventory and climate history we assess eight different models for their origin dewatering of excavated ice rich lyot ejecta and contact melting from hot lyot ejecta superposed on surface ice deposits are the most plausible channel origins the existence of this extensive amazonian fluvial system is attributed to 1 the large size of lyot and its consequent hot ejecta and 2 the presence of surface ice at the time of impact attributed to obliquity changes redistributing polar ice to the mid latitudes a relatively common occurrence in martian geologic history

geomorphic significance of postglacial bedrock scarps on normal fault footwalls the existence of well preserved holocene bedrock fault scarps along active normal faults in the mediterranean region and elsewhere suggests a dramatic reduction in rates of rock weathering and erosion that correlates with the transition from glacial to interglacial climate we test and quantify this interpretation using a case study in the italian central apennines holocene rates are derived from measurements of weathering pit depth along the magnola scarp where previous cosmogenic cl 36 analyses constrain exposure history to estimate the average hillslope erosion rate over similar to 10 5 years we introduce a simple geometric model of normal fault footwall slope evolution the model predicts that the gradient of a weathering limited footwall hillslope is set by fault dip angle and the ratio of slip rate to erosion rate if either slip or erosion rate is known the other can be derived applying this model to the magnola fault yields an estimated average weathering rate on the order of 0 2 0 4 mm yr more than 10 times higher than either the holocene scarp weathering rate or modern regional limestone weathering rates a numerical model of footwall growth and erosion in which erosion rate tracks the oxygen isotope curve reproduces the main features of hillslope and scarp morphology and suggests that the hillslope erosion rate has varied by about a factor of 30 over the past one to two glacial cycles we conclude that preservation of carbonate fault scarps reflects strong climatic control on rock breakdown by frost cracking

modeling the response of the rhine meuse fluvial system to late pleistocene climate change abstract we use a landscape evolution model to infer the effect of late pleistocene climate change on the incision aggradation behaviour of the rhine meuse fluvial system we model the routing of runoff and sediment in the catchment in order to predict grainsize trends and the incision and aggradation behaviour in the downstream reach where we compare it to the sequence of events and grainsize characteristics inferred from borehole corings this sequence starts with an important incision taking place around the mis 3 to mis 2 climatic transition during the coldest part of mis 2 a coarse grained sedimentary unit is deposited that shows an upward increase in the sand gravel ratio the model experiments do not predict an incision at the mis 3 to mis 2 transition therefore the incision should be attributed to other causes most likely effects of glacio isostatic uplift however a relative upward increase in sand content of the sediments is predicted by the model this increase is the result of the difference in transport rates between sand and gravel starting from a homogeneous pre existing mis 3 deposit the gravel content in the active layer increases because the sand is removed quickly and transported further downstream whereas the gravel travels slowly and piles up with gravel originating from immediately upstream resulting in a net accumulation at a later stage sand originating from much further upstream progrades fan like over the gravelly deposits according to the record during the early late glacial warming part of mis 2 bolling allerod interstadial neither incision nor aggradation has taken place this is in accordance with modelling results which show that despite the reduction of sediment input due to re vegetation of hillslopes sufficient sediment remains available for fluvial transport in the channel network itself it takes several thousands of years before effects of sediment depletion in the catchment are noted downstream that is why we argue that the inferred incision at the late late glacial the start of the younger dryas in our downstream study area might reflect depletion effects related to the preceding early late glacial conditions in general our modelling results show that terraces along one large fluvial system are diachronic features in particular terrace surfaces are older upstream compared to downstream in addition complex responses to climate change are likely to occur in a large fluvial system like the rhine meuse and correlation of morphological features in the fluvial record to specific short term palaeo climatic events for example dansgaard oeschger events could be risky without consideration of catchment size characteristics and associated response times

channel network morphology and sediment dynamics under alternating periglacial and temperate regimes a numerical simulation study the occurrence of permafrost in a highly permeable catchment has a profound effect on runoff generation the presence of permafrost effectively makes the subsoil impermeable therefore overland flow can be the dominant runoff generating process during periglacial conditions the absence of permafrost will promote subsurface drainage and therefore saturation excess overland flow can become the dominant runoff generating process during temperate conditions in this paper we present a numerical modelling study in which the effect of alternating climate related phases of permafrost and nonpermafrost on catchment hydrology and geomorphology is investigated special attention is given to the characteristics of the channel network being formed and the sediment yield from these catchments we find that channel networks expand under permafrost conditions and contract under nonpermafrost conditions a change from permafrost to nonpermafrost conditions is characterised by a decrease in sediment yield while a change towards permafrost conditions is marked by a peak in sediment yield this peak is explained by the build up of a reservoir of erodible sediment during the nonpermafrost phase the driving force behind this reservoir build up may be local base level change due to tectonic uplift or eustacy we present a number of experiments which show the details of this process the results are in line with existing reconstructions of climate and fluvial dynamics during the pleistocene in europe and offer a new explanation to these observations

gravity anomaly map of the pyrenean region and a comparison of the deep geological structure of the western and eastern pyrenees abstract a gravity anomaly map based on over 13 000 observations accurately delineates the major features of the pyrenean region an extensive gravity anomaly low in the south of the region appears to result from crustal thickening associated with the pyrenean mountain building episode several large positive gravity anomalies are apparent in the north pyrenean zone in the centre and west of the mountain chain but are absent in the east the interpretation of a series of gravity anomaly profiles along the pyrenees has been controlled by existing geophysical data the interpretations confirm the cause of the southern gravity anomaly low as thickened iberian crust and demonstrate as shown by previous seismic investigations that the transition to much thinner european crust is quite abrupt the sources of the positive anomalies in the north pyrenean zone are bodies in the upper crust with densities too high to be explained in terms of crustal materials these are interpreted as segments of upper mantle that originated in transtensional n s separation across the north pyrenean fault and were emplaced at shallow levels by thrusting during pyrenean orogenesis this is the first time that evidence has been presented for the presence of such mantle bodies in the pyrenees it is suggested that their absence in the east is caused by less extension between iberia and europe in this region during the transform motion between them prior to orogenesis allowing only limited ascent of deep material the greater extension in the west would have allowed the ascent of upper mantle into the space between iberia and europe which would have been further elevated during the thrusting associated with pyrenean orogenesis

geological controls on the geometry of incised valley fills insights from a global dataset of late quaternary examples incised valleys that develop due to relative sea level change are common features of continental shelves and coastal plains assessment of the factors that control the geometry of incised valley fills has hitherto largely relied on conceptual experimental or numerical models else has been grounded on case studies of individual depositional systems here a database driven statistical analysis of 151 late quaternary incised valley fills has been performed the aim being to investigate the geological controls on their geometry results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised valley fills through their effect on the degree and rate of river incision and on river size and mobility the studied incised valley fills developed along active margins are thicker and wider on average than those along passive margins suggesting that tectonic setting exerts a control on the geometry of incised valley fills likely through effects on relative sea level change and river behaviour and in relation to distinct characteristics of basin physiography water discharge and modes of sediment delivery valley fill geometry is positively correlated with the associated drainage basin size confirming the dominant role of water discharge climate is also inferred to exert a potential control on valley fill dimensions possibly through modulations of temperature peak precipitation vegetation and permafrost which would in turn affect water discharge rates of sediment supply and valley margin stability shelves with slope breaks that are currently deeper than 120 m contain incised valley fills that are thicker and wider on average than those hosted on shelves with breaks shallower than 120 m no correlation exists between valley fill thickness and present day coastal prism convexity which is measured as the difference in gradient between lower coastal plains and inner shelves these findings challenge some concepts embedded in sequence stratigraphic thinking and have significant implications for analysis and improved understanding of source to sink sediment route ways and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs

width of mantle deformation across a continental transform evidence from upper mantle pn seismic anisotropy measurements seismic anisotropy v p of at least 6 5 2 5 in the upper mantle pn phase is reported 200 km east of the alpine fault in south island new zealand when these new data are combined with a previous pn study and published sks splitting results two distinct domains of mantle deformation are inferred within south island in southern south island the deforming zone in the mantle lithosphere is as wide as 335 km whereas in mid south island the deforming zone narrows to 200 km both regions display wider zones of seismic anisotropy than found at other continental transforms of the world the width and orientation of mantle anisotropy in southern south island are consistent with a model of simple shear in a zone that has undergone 800 200 km of right lateral shear displacement a value close to that predicted by geological reconstructions hence displacement can be accommodated by distributed shear without faulting being required in the mantle