rates and processes of bedrock incision by the upper ukak river since the 1912 novarupta ash flow in the valley of ten thousand smokes alaska the rates and patterns of bedrock channel incision significantly influence landscape evolution and long term interactions among climate tectonics and erosion unfortunately only sparse field data are available to quantify the controls on river incision rates we exploit the diversion of the upper ukak river by an ash flow in 1912 to measure rates of incision along a newly formed bedrock channel minimum estimates of the rate of incision into intact rock vary from 0 01 to 0 10 m yr 1 this variation reflects differences in channel slope channel width lithologic facies and intensity of jointing as well as the effects of upstream knickpoint migration a streampower type incision model adequately explains the incision rate data provided 1 variations in channel width are prescribed on the basis of field measurements 2 the slope exponent is significantly less than unity n 0 4 0 2 and 3 observed downstream changes in lithologic facies and the intensity of jointing account for the apparent twofold downstream decrease in the coefficient of erosion despite the very rapid rate of incision calibrated stream power erosion coefficients for the ukak river k 2 4 10 4 m 0 2 yr 1 to 9 0 10 4 m 0 2 yr 1 are within the range of previously published estimates two plausible explanations for the low values of the slope exponent n are that incision rate is limited by either 1 a combination of physical weathering and hydrodynamic joint block extraction or 2 block fracture due to bedload impacts modulated on steeper channel segments by suspension of a significant fraction of the sediment load

flow of abyssal water into wake island passage properties and transports from hydrographic surveys 1 water mass characteristics and volume transports of abyssal water flowing northward into wake island passage in the north pacific ocean were examined by carrying out high quality hydrographic surveys in may 2003 october 2004 and december 2005 along with mooring observations from may 2003 to december 2005 close linear relationships between potential temperature and salinity dissolved oxygen and silicate were seen below 1 1 c 4000 m the relationships above 1 1 c were scattered and were separated into relatively salty oxygen rich silicate poor water to the south and water with the opposite properties to the north the results suggested that there was a boundary between water masses at 1 1 c in the deep passage in addition to the three hydrographic sections two hydrographic sections previously surveyed in the deep passage in 1975 and 1999 were reexamined for transport estimates geostrophic calculations relative to the 1 1 c surface indicated northward transports of the abyssal water from 0 5 to 2 2 sv 1 sv 106 m3 s 1 below this surface when 1 year mean estimated velocities at 1 1 c surface were used for reference mean transport from the five estimates increased from 1 4 to about 4 sv the temperature of abyssal water colder than 1 1 c was found to have increased by an average of 0 012 c between 1975 and 2005 this warming is greater than double the standard deviation from the temporal mean temperature profile obtained from mooring observations

fluvial bedrock incision in the active mountain belt of taiwan from in situ produced cosmogenic nuclides the concentration of cosmogenic nuclides in rocks exposed at the earth s surface is proportional to the total duration of their exposure this is the basis for bedrock surface exposure dating and has been used to constrain valley lowering rates in the taroko gorge eastern central range taiwan taroko gorge contains a uniquely complete geomorphic record of fluvial valley lowering continuous fluvially sculpted surfaces are present in the lower 200 m of this marble gorge assuming no post fluvial erosion of the gorge wall the concentration of in situ produced cosmogenic 36 cl measured in gorge wall marbles reveals exposure ages from 0 2 ka in the active channel to 6 5 ka at 165 m above the present river these ages imply an average fluvial incision rate of 26 3m m a 1 throughout the middle and late holocene taking into account lateral gorge wall retreat after initial thalweg lowering would give rise to calculated older exposure ages without considering gorge wall retreat our estimates therefore represent maximum incision rates estimated maximum holocene incision rates are higher than the long term exhumation rates derived from fission track dating the longterm gorge development governed by tectonic uplift is superimposed by short term variations in incision rates caused by climatic or regional tectonic changes copyright 2005 john wiley sons ltd

late cenozoic relief evolution under evolving climate a review abstract the present review paper is an attempt to summarize quantitative evidence of late cenozoic changes in topographic relief different meanings of the word relief as it is commonly used and detail the metrics used to quantify it we then specify methodological tools used to quantify relief change primarily low temperature thermochronometry and terrestrial cosmogenic nuclides and analyze published evidence for different regions our review first shows that relief changes and rates of changes are more important at mid than high or low latitudes and appear to be insensitive to mean precipitation rates it also show that relief change is positive relief increases in most of the reported cases 80 we subsequently define two functional relationships between relief and erosion depending on the chosen definition of relief and propose a conceptual model of landscape memory we conclude following others that erosion rates depend non linearly on relief evolution itself being a function of the spatial distribution and rates of erosion the relief increases documented in this review may be to erosion rate increases during the same timescales lastly we discuss the importance of glacial and periglacial processes on late cenozoic relief and erosion rate changes and stress the importance of frost shattering and glacial erosion at mid and high latitudes

deepening of inner gorges through subglacial meltwater an example from the unesco entlebuch area switzerland this paper explores the mechanisms by which inner gorges in the alps were formed it focuses on the ca 1 5 km long 80 m deep and a few hundred meter wide lammschlucht located in the northern foothills of the central alps we reconstructed the glacial cover using lateral moraines and hanging talus cones that record the elevation of the ice surface at the deglaciation stage of the lgm last glacial maximum we used the reconstructed ice thickness patterns to calculate the erosional potential of the subglacial meltwater the applied model is based on the principle of energy conservation and yields the pattern of downstream changes of the dynamic pressure which is considered a measure for erosion potential the model results suggest a maximum of the dynamic pressure at the end of the inner gorge we interpret therefore that the subglacial meltwater scoured the reach toward the end of the lammschlucht because of the enhanced dynamic pressure which was ultimately controlled by the ice overburden post glacial fluvial erosion then resulted in a readjustment through a regressive shift of the erosional front along the inner gorge farther upstream the current location of this front lies almost in the middle of the lammschlucht inner gorge where a step pool channel changes into a straight plane bed channel flowing on a deeply scoured bedrock

quantifying sediment supply at the end of the last glaciation dynamic reconstruction of an alpine debris flow fan in this paper we quantify the sediment dynamics in the formerly glaciated zielbach catchment in the italian alps from the end of the last glacial maximum lgm until today as a basis for our quantification we use the stratigraphic record offered by a 3 5 km2 large fan that we explore with a seismic survey stratigraphic analyses of drillhole material and 14c ages measured on organic matter encountered in these drillings in addition we calculate past denudation rate variability in the fan deposits using concentrations of cosmogenic 10be we merge this information into a scenario of how the sediment flux has changed through time and how this variability can be related to climatic variations framed within well known paraglacial models the results document a highly complex natural system from the lgm to the very early holocene ice melted discharge and climate variability promoted a high sediment flux sedimentation rate up to 40 mm yr this flux then dramatically decreased toward interglacial values 0 8 mm yr at 5 4 calibrated kyr b p however in contrast to the trend of classic paraglacial models the flux recorded at zielbach shows secondary peaks at 6 5 ka and 2 5 ka with values of 13 mm yr and 1 5 mm yr respectively paleo denudation rates also decrease from 33 mm yr at the beginning of the holocene to 0 42 mm yr at 5 ka with peaks of 6 mm yr and 1 1 mm yr at 6 5 ka and 2 5 ka high amplitude climate change is the most likely cause of the secondary peaks but anthropogenic activities may have contributed as well the good correlation between paleo sedimentation and paleo denudation rates suggests that the majority of the deglaciated material destocked from the zielbach catchment is stored in the alluvial fan

rate of fluvial incision in the central alps constrained through joint inversion of detrital 10be and thermochronometric data abstract we integrate constraints from published detrital thermochronometry and detrital 10 be concentrations in a single catchment to infer how erosion is shaping alpine topography we apply this analysis to the codera watershed in the bergell intrusion central european alps where rivers have incised into a glacial valley because thermochronometric ages of bedrock samples increase with elevation a distribution of detrital ages in river sediment provides a tracer for the source elevations of sediment within the catchment while detrital 10 be concentrations provide constraints on rates of erosion we find that modern erosion rates within the fluvial portion of the landscape are too low to permit the inferred 500 m of incision during the most recent interglacial based on the spatial pattern of modern erosion rates we predict that if the incised fluvial valley was formed during interglacial periods only it has formed over the last approximately 400 000 years

valley formation by fluvial and glacial erosion cross valley profiles from the west slope of the olympic peninsula washington are used to investigate the relative effects of fluvial and glacial erosion on valley formation unlike most ranges where glaciers and rivers sequentially occupied the same valleys neighboring valleys in the olympic mountains developed in similar lithologies but were subject to different degrees of glaciation allowing comparison of the net effect of glacial and fluvial processes integrated over many glacial cycles upslope drainage area was used to normalize comparisons of valley width ridge crest to valley bottom relief and valley cross sectional area as measures of net differences in the mass of rock excavated from below ridgelines for 131 valley spanning transects valley width relief and cross sectional areas are similar for glaciated partly glaciated and unglaciated fluvial valleys with drainage areas of 10 km 2 but diverge downslope glaciated valleys draining 50 km 2 reach two to four times the cross sectional area and have to 500 m greater relief than comparable fluvial valleys partly glaciated valleys have intermediate dimensions at distances of 5 km from valley heads the cumulative upstream volume of rock removed to form valleys is two to four times greater in glacially incised valleys than in fluvial valleys the finding of strong differences in the net result of valley excavation by fluvial and glacial erosion supports the interpretation that alpine glaciers are more effective erosional agents than are rivers and implies that large alpine valleys deepened and enlarged in response to pleistocene glaciation

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

long term fluvial incision rates and postglacial river relaxation time in the french western alps from 10be dating of alluvial terraces with assessment of inheritance soil development and wind ablation effects studying river long profile development as a response to tectonic and climatic controls requires reliable age dating of paleo profile remnants preserved as river terraces cosmic ray exposure cre dating often represents the only method available to date river terraces but the interpretation of cosmogenic nuclide concentrations is complicated by pre depositional inheritance and post depositional disturbance of the terrace deposits through pedogenesis and surface inflation or deflation here we use cosmogenic 10be measurements to date alluvial terraces in the french western alps in order to estimate river incision rates and to infer river response to climatic fluctuations and tectonic forcing we assess inheritance by constructing 10be concentration vs pebble depth profiles and use a monte carlo technique to estimate terrace ages we find that inheritance is negligible on all terraces enabling us to date terraces as young as 5 ky terraces that predate the last glaciation experienced intense pedogenesis and wind ablation which led to significant scatter in the 10be concentrations of surface samples we assess these effects using a model of 10be ingrowth and show that the oldest cre ages of surface clasts are close to the probable terrace age we study two catchments which have undergone varying degrees of glacial disruption the buech river experienced variations in runoff and sediment flux during the last glaciation as well as occasional ice dammings of its outlet its upper terraces record incision rates averaged over 190 ky of 0 8 mm yr consistent with denudation rates estimated in the surrounding areas and suggesting long term stability of river incision rates climatic forcing is well documented for the drac river which was repeatedly dammed by glaciers during cold periods its postglacial incision history was triggered by an 800 m drop in base level following ice dam disappearance long profile development by knickpoint propagation explains the time lag of 2 5 ky between this base level drop and terrace abandonment upstream as well as subsequent peak incision rates of 6 cm yr followed by a gradual decrease in incision rates the present knickpoint location 55 km upstream from the glacial damming site enables us to calculate a fluvial response time of 15 20 ky controlled by knickpoint propagation rates of several meters per year within the drac river

a quantification of the glacial imprint on relief development in the french western alps abstract the morphology of the western alps has been strongly influenced by quaternary glaciations on the basis of observations of glacial morphology in the belledonne grandes rousses taillefer and pelvoux ecrins massifs south eastern france we reconstitute the glacial trimline and equilibrium line altitude ela during the most extensive glaciation meg our best estimate of the meg ela is 1800 100m using digital elevation models we compare our glacial reconstruction with the relief structure of nine major catchments draining the massifs modal elevations of the largest catchments occur at 2000 2500m and coincide with minima in plots of mean slope angles as a function of elevation modal elevations and slope minima occur between the modern and meg elas confirming a strong glacial imprint on relief in order to quantify glacial valley carving in the massifs we isolated high elevation low relief surfaces that form rock shoulders adjacent to the glacial valleys from a digital elevation model and constructed an interpolated surface passing through these subtracting the present day topography from this surface allows us to quantify the maximum glacial valley depths maximum valley depths determined in this manner are typically 1000m with spatial maxima occurring around the location of the meg ela in most valleys these numbers do not take into account glacial valley widening and local glacial overdeepenings the also neglect however potential pre glacial fluvial valley incision which could account for 20 50 of the measured valley depths in spite of these problems inferred valley depths are reasonably well correlated with the mean reconstructed ice thickness and constitute about half of the sub ridgeline relief of the studied catchments these results lead us to propose a significant quaternary increase in the relief of the french western alps controlled by climate and associated with the initiation of alpine glaciations for reasonable values of the effective elastic thickness of the lithosphere the isostatic response to glacial valley carving reaches values of 300m across the massifs this number is insufficient to substantially offset topographic lowering due to regional denudation and we conclude that the isostatic response to glacial valley carving has not increased peak elevations significantly

deciphering the driving forces of erosion rates on millennial to million year timescales in glacially impacted landscapes an example from the western alps in many regions tectonic uplift is the main driver of erosion over million year myr timescales but climate changes can markedly affect the link between tectonics and erosion causing transient variations in erosion rates here we study the driving forces of millennial to myr scale erosion rates in the french western alps as estimated from in situ produced cosmogenic 10be and a newly developed approach integrating detrital and bedrock apatite fission track thermochronology millennial erosion rates from 10be analyses vary between 0 27 and 1 33 m kyr similar to rates measured in adjacent areas of the alps significant positive correlations of millennial erosion rates with geomorphic measures in particular with the lgm ice thickness reveal a strong transient morphological and erosional perturbation caused by repeated quaternary glaciations the perturbation appears independent of myr scale uplift and erosion gradients with the effect that millennial erosion rates exceed myr scale erosion rates only in the internal alps where the latter are low 0 4 km myr these areas moreover exhibit channels that clearly plot above a general linear positive relation between myr scale erosion rates and normalized steepness index glacial erosion acts irrespective of rock uplift and thus not only leads to an overall increase in erosion rates but also regulates landscape morphology and erosion rates in regions with considerable spatial gradients in myr scale tectonic uplift our study demonstrates that climate change e g through occurrence of major glaciations can markedly perturb landscape morphology and related millennial erosion rate patterns even in regions where myr scale erosion rates are dominantly controlled by tectonics

river incision and migration deduced from 36cl cosmic ray exposure durations the clue de la cerise gorge in southern french alps abstract we estimate recent 20 ka incision and lateral migration rate on a spectacular n s striking gorge cross cutting n dipping limestones in a fold and thrust belt of the external southern french alps upstream of the gorge the river makes a right angle turn and follows the limestone surface parallel to the bedding direction ew eighteen samples were gathered along two vertical river polished profiles and three others on the denuded north dipping surface layer in order to determine river incision and lateral migration timing and rates surface age exposures of polished river cliff and bedding surface have been obtained from 36cl cosmogenic nuclide dating and allow us to constrain the rate of vertical incision and of surface denudation of the jurassic limestone layer fifteen 36cl exposure ages have been obtained and range from 21 ka to 3 ka samples clearly define two age height linear trends which slopes correspond to incision rates of 1 and 0 3 mm yr respectively the transition from low to high incision rate occurs at about 12 ka i e during the younger dryas glacial phase data also indicate that the vertical incision of the n s branch of the gorge is coeval with the lateral northward river migration of its e w branch associated with the denudation of the limestones surface extrapolating incision rates deduced from 36cl exposure ages through time suggests that the incision of the clue and denudation of the jurassic limestones started about 500 600 ka ago

deep water flow in the mariana and caroline basins two major water masses dominate the deep layers in the mariana and caroline basins the lower circumpolar water lcpw arriving from the southern ocean along the slopes north of the marshall islands and the north pacific deep water npdw reaching the region from the northeastern pacific ocean hydrographic and moored observations and multibeam echosounding were performed in the east mariana and the east caroline basins to detail watermass distributions and flow paths in the area the lcpw enters the east mariana basin from the east at about 13 n however in the southern part of the basin a part of this water mass arrives in a southward western boundary flow along the izu ogasawara mariana ridge both hydrographic observations and moored current measurements lead to the conclusion that this water not only continues westward to the west mariana basin as suggested before but also provides bottom water to the east caroline basin the critical throughflow regions were identified by multibeam echosounding at the yap mariana junction between the east and west mariana basins and at the caroline ridge between the east mariana and east caroline basins the throughflow is steady between the east and west mariana basins whereas more variability is found at the caroline ridge at both locations throughflow fluctuations are correlated with watermass property variations suggesting layer thickness changes the total transport to the two neighboring basins is only about 1 sverdrup 1sv 106 m3 s 1 but has considerable impact on the watermass structure in these basins estimates are given for the diapycnal mixing that is required to balance the inflow into the east caroline basin farther above in the water column the high silica tongue of npdw extends from the east to the far southwestern corner of the east mariana basin with transports being mostly southward across the basin

distribution and inferred age of exfoliation joints in the aar granite of the central swiss alps and relationship to quaternary landscape evolution abstract exfoliation joints are well known natural fractures limited to near the ground surface relatively few details however are known about their distribution and age in the swiss alps exfoliation joints follow the landscape surface at the time of their formation the age of the associated landscape feature then provides a maximum age of exfoliation joints while landscape forms can change through time exfoliation joints preserve elements of former landscape morphologies by their undisturbed orientations the grimsel region of the central alps is well suited for analyzing the impact of erosional episodes and accompanying stress changes on exfoliation joint formation in granitic rocks mapping above and below ground revealed that exfoliation joints are widespread and occur between valley bottoms and mountain crests within glacial inner and hanging u shaped trough valleys glacial cirques and steep mountain crests and predominantly fluvial landforms gently inclined linear slopes above the inner trough valleys narrow inner valley gorges and steep v shaped side gullies based primarily on their geometric properties at the ground surface three exfoliation joint types were distinguished in our study area 1 closely spaced

woce section p1w in the sea of okhotsk 1 oceanographic data description we describe the results of a world ocean circulation experiment woce survey line p1w from the open pacific ocean through the bussol strait and across the sea of okhotsk observations are presented of distributions of temperature and salinity dissolved oxygen and nutrients and some derived quantities discussion centers on the distribution of the sea of okhotsk component of the north pacific intermediate water mass and its properties the sea of okhotsk has been suggested as the only location where deep convection may occur within the north pacific or its marginal seas our analysis suggests that the surface 26 85 has recently been ventilated and arguments might be made to suggest that ventilation has occurred to 27 05 this is discussed here but detailed evidence is covered in a companion paper analyzing cfc observations the okhotsk component of the north pacific intermediate water extends to substantially greater depths and densities and so some other process is needed to create the denser water mass

river incision into bedrock mechanics and relative efficacy of plucking abrasion and cavitation improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed we present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion e g plucking abrasion cavitation solution is a strong function of substrate lithology and that joint spacing fractures and bedding planes exert the most direct control the relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks and their spatial distributions we find that plucking dominates wherever rocks are well jointed on a submeter scale hydraulic wedging of small clasts into cracks bashing and abrasion by bedload and chemical and physical weathering all contribute to the loosening and removal of joint blocks in more massive rocks abrasion by suspended sand appears to be rate limiting in the systems studied here concentration of erosion on downstream sides of obstacles and tight coupling between fluid flow patterns and fine scale morphology of erosion forms testify to the importance of abrasion by suspended load rather than bedload particles mechanical analyses indicate that erosion by suspended load abrasion is considerably more nonlinear in shear stress than erosion by plucking in addition a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive unjointed rocks that is otherwise attributed to suspended load abrasion direct field evidence of cavitation erosion is however lacking in terms of the well known shear stress or stream power erosion law erosion by plucking is consistent with a slope exponent n of 2 3 to 1 whereas erosion by suspended load abrasion is more consistent with a slope exponent of 5 3 given that substrate lithology appears to dictate the dominant erosion process this finding has important implications for long term landscape evolution and the models used to study it

present day vertical displacements in the north western alps and southern jura mountains data from leveling comparisons two high precision leveling networks were successively surveyed in france the ngf measured during the 1886 1907 period and the ign69 measured from 1965 to 1979 the accuracy of these levelings standard deviation of 1 8mm km to 3 8mm km allows us to compute the vertical displacements of the benchmarks between two different eras the results indicate the occurrence of discrete zones of uplift and subsidence 1 a regional uplift up to 1 4 mm yr of the subalpine massifs 2 an important uplift of the internal jura up to 2 mm yr 3 a relative subsidence of the southern part of the jura 0 8 mm yr and 4 a relative subsidence of the bresse basin with respect to the external jura comparing the spatial distribution of zones of uplift and their respective vertical displacement rates with a regional structural cross section leads to the conclusion that present day uplift of the belledonne and bornes massifs and of the internal parts of the jura mountains can be explained by crustal shortening along a major basement involving thrust fault this fault ramps up under the bornes massif from a depth of 12 km to 7 km turns into a flat under the molasse basin ramps up to the top of the basement at the north eastern margin of the internal jura mountains and reaches the surface in the external jura the saleve ramp anticline is carried by a bifurcation of this thrust horizontal displacement rates of 6 mm yr at the bornes ramp 2 mm yr at the saleve ramp and 4 mm yr at the internal jura ramp have been determined by inversion of profiles of uplift rates whether this basement involving thrust fault was already active during the miocene main folding phase of the jura mountains or whether it was activated only during pliocene pleistocene times is subject to debate

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

post glacial entrenchment and knickpoint migration of the yarlung tsangpo gorge southeastern tibetan plateau abstract the formation of the yarlung tsangpo river system is commonly thought to be controlled by tectonic processes initiated several million years ago however climate change may also play an important role in guiding drainage evolution here we reconstruct the drainage history of the yarlung tsangpo gorge using field observations age constraints from optically stimulated luminescence and radiocarbon dating paleosalinity reconstruction and grain size analysis of lacustrine deposits and river valley characteristics field observations clay boron derived paleosalinity reconstruction and grain size analysis of lacustrine deposits demonstrate that a closed inland saline lake existed upstream of the yarlung tsangpo gorge implying that cutting of the gorge postdated this paleolake optically stimulated luminescence and radiocarbon dating suggest that the paleolake formed at least 51 ka and terminated after 13 ka with a shift in global climate following the last glacial maximum the paleolake drained by river capture and the gorge entrenchment commenced at the village of jiala northwest of the namche barwa peak approximately 13 10 ka ago the evolution of the yarlung tsangpo occurred on a remarkably short timescale of just tens of thousands of years in response to drainage system reorganization the yarlung tsangpo incised at an average rate of at least 26 mm yr the rapid fluvial incision initiated at jiala 13 ka ago propagated rapidly upstream at 2 12 m yr the yarlung tsangpo knickpoint has not stabilized but will likely continue to migrate upstream

erosion driven uplift of the modern central alps abstract we present a compilation of data of modern tectono geomorphic processes in the central european alps which suggest that observed rock uplift is a response to climate driven denudation this interpretation is predominantly based on the recent quantification of basin averaged late holocene denudation rates that are so similar to the pattern and rates of rock uplift rates as determined by geodetic leveling furthermore a gps data based synthesis of adriatic microplate kinematics suggests that the central alps are currently not in a state of active convergence finally we illustrate that the central alps have acted as a closed system for holocene redistribution of sediment in which the peri alpine lakes have operated as a sink for the erosional products of the inner central alps while various hypotheses have been put forward to explain central alpine rock uplift e g lithospheric forcing by convergence mantle processes or ice melting we show with an elastic model of lithospheric deformation that the correlation between erosion and rock uplift rates reflects a positive feedback between denudation and the associated isostatic response to unloading thus erosion does not passively respond to advection of crustal material as might be the case in actively converging orogens rather we suggest that the geomorphic response of the alpine topography to glacial and fluvial erosion and the resulting disequilibrium for modern channelized and associated hillslope processes explains much of the pattern of modern denudation and hence rock uplift therefore in a non convergent orogen such as the central european alps the observed vertical rock uplift is primarily a consequence of passive unloading due to erosion

cosmetic isotope analyses applied to river longitudinal profile evolution problems and interpretations the use of cosmogenic isotopes to determine surface exposure ages has grown rapidly in recent years the extent to which cosmogenic nuclides can distinguish between mechanistic hypotheses of landscape evolution is an important issue in geomorphology we present a case study to determine whether surface exposure dating techniques can elucidate the role knickpoint propagation plays in longitudinal profile evolution cosmogenically produced 10be 26al 36cl 3he and 21ne were measured in olivines collected from 5 2 ma basalt flows on kauai hawaii several obstacles had to be overcome prior to the measurement of in situ produced radionuclides including removal of meteoric 10be from the olivine grains discrepancies between the radionuclide and noble gas data may suggest limits for exposure dating approximate surface exposure ages calculated from the nuclide concentrations indicate that large boulders may remain in the hawaiian valley below the knickpoint for hundreds of thousands of years the ages of samples collected above the knickpoint are consistent with estimates of erosion based on the preservation of palaeosurfaces although the exposure ages can neither confirm nor reject the nickpoint hypothesis boulder ages downstream of the knickpoint are consistent with a wave of incision passing upvalley the long residence time off the coarse material in the valley bottom further suggests that knickpoint propagation beneath a boulder pile is necessary for incision of the bedrock underlying the boulders to occur 1997 by john wiley sons ltd

fluvial incision into bedrock insights from morphometric analysis and numerical modeling of gorges incising glacial hanging valleys western alps france bedrock gorges incising glacial hanging valleys potentially allow measurements of fluvial bedrock incision in mountainous relief using digital elevation models topographic maps and field reconnaissance we identified and characterized 30 tributary hanging valleys incised by gorges near their confluence with trunk streams in the romanche watershed french western alps longitudinal profiles of these tributaries are all convex and have abrupt knickpoints at the upper limit of oversteepened gorge reaches we reconstructed initial glacial profiles from glacially polished bedrock knobs surrounding the gorges in order to quantify the amount of fluvial incision and knickpoint retreat from morphometric analyses we find that mean channel gradients and widths as well as knickpoint retreat rates display a drainage area dependence modulated by bedrock lithology however there appears to be no relation between horizontal retreat and vertical downwearing of knickpoints assuming a postglacial origin of these gorges our results imply high postglacial fluvial incision 0 5 15 mm yr 1 and knickpoint retreat 1 200 mm yr 1 rates that are however consistent with previous estimates numerical modeling was used to test the capacity of different fluvial incision models to predict the inferred evolution of the gorges results from simple end member models suggest transport limited behavior of the bedrock gorges a more sophisticated model including dynamic width adjustment and sediment dependent incision rates predicts present day channel geometry only if a significant supply of sediment from the gorge sidewalls 10 mm yr 1 is triggered by gorge deepening combined with pronounced inhibition of bedrock incision by sediment transport and deposition

examination of surface exposure ages of antarctic moraines using in situ produced 10be and 26al concentrations of 10be t12 1 5 106 y and 26a1 t12 0 72 106 y have been determined by accelerator mass spectrometry ams in a suite of quartz samples taken from sandstone boulders in several moraines in arena valley a dry valley adjacent to the taylor glacier in the quatermain mountains southern victoria land east antarctica these isotopes are produced in surficial quartz by cosmic ray spallation of o and si the concentrations in these samples ranged from 6 1 105 to 3 0 107 at g 1 for 10be and from 9 4 106 to 1 2 108 at g 1 for 26a1 depending upon the extent of exposure at the surface analyses of 10be in several samples from a single moraine at altitudes ranging from 1300 to 1650 m permitted an estimation of the air attenuation pathlength of cosmic ray neutrons the value of 142 96 41 g cm 2 is consistent with other published values production rates of 17 6 4 at g 1 y 1 for 10be and 113 54 16 at g 1 y 1 for 26a1 at 1300 m and 87 s and a 26al 10be production ratio of 6 5 1 3 1 3 were calculated from the data these values correspond to sea level production rates at high geomagnetic latitude of 6 4 at g 1 y 1 and 41 7 at g 1 y 1 for 10be and 26a1 respectively consistent with determinations based on 11 ky glacially polished surfaces in the sierra nevada in california these production rates imply exposure ages for the various moraines ranging from 50 ky to 2 5 my in accordance with other geological evidence the 10be and 26al ages of these rocks compare favorably with those found using a similar dating method based on in situ production of 3he examination of the 3he concentrations in conjunction with the present data set yields an estimate of 3he production of 230 8540 at g 1 y 1 corresponding to 85 31 15 at g 1 y 1 at sea level this is lower than previously reported values of 240 60 at g 1 y 1 and 190 at g 1 y 1 scaled to sea level and high geomagnetic latitude based respectively on volcanic flows less than 2000 years old at low latitude and samples collected from 14 400 year old volcanic flows this discrepancy is likely due to diffusive losses which may become significant up to 50 for surface exposure ages on the order of 2 0 my nevertheless the general correlations among the three isotopes suggest that 3he does not suffer gross losses through diffusion

interaction between normal fault slip and erosion on relief evolution insights from experimental modelling the growth of relief in active tectonic areas is mainly controlled by the interactions between tectonics and surface processes erosion and sedimentation the study of long lived morphologic markers formed by these interactions can help in quantifying the competing effects of tectonics erosion and sedimentation in regions experiencing active extension river long profiles and faceted spurs triangular facets can help in understanding the development of mountainous topography along normal fault scarps in this study we developed analogue experiments that simulate the morphologic evolution of a mountain range bounded by a normal fault this paper focuses on the effect of the fault slip rate on the morphologic evolution of the footwall by performing three analogue experiments with different fault slip rates under a constant rainfall rate a morphometric analysis of the modelled catchments allows comparing with a natural case tunka half graben siberia after a certain amount of fault slip the modelled footwall topographies of our models reaches a dynamic equilibrium i e erosion balances tectonic uplift relative to the base level close to the fault whereas the topography farther from the fault is still being dissected due to regressive erosion we show that the rates of vertical erosion in the area where dynamic equilibrium is reached and the rate of regressive erosion are linearly correlated with the fault throw rate facet morphology seems to depend on the fault slip rate except for the fastest experiment where faceted spurs are degraded due to mass wasting a stream power law is computed for the area wherein rivers reach a topographic equilibrium we show that the erosional capacity of the system depends on the fault slip rate finally our results demonstrate the possibility of preserving convex river long profiles on the long term under steady external tectonic uplift and rainfall conditions

epigenetic gorges in fluvial landscapes epigenetic gorges form when channels that have been laterally displaced during episodes of river blockage or aggradation incise down into bedrock spurs or side walls of the former valley rather than excavating unconsolidated fills and reinhabiting the buried paleovalley valley filling events that promote epigenetic gorges can be localized such as a landslide dam or an alluvial debris flow fan deposit at a tributary junction or widespread such as fluvial aggradation in response to climate change or fluctuating base level the formation of epigenetic gorges depends upon the competition between the resistance to transport strength and roughness of valley filling sediments and a river s ability to sculpt and incise bedrock the former affects the location and lateral mobility of a channel incising into valley filling deposits the latter determines rates of bedrock incision should the path of the incising channel intersect with bedrock that is not the paleovalley bottom epigenetic gorge incision by definition post dates the incision that originally cut the valley strath terraces and sculpted bedrock walls that form in relation to epigenetic gorges should not be used to directly infer river incision induced by tectonic activity or climate variability rather they are indicative of the variability of short term bedrock river incision and autogenic dynamics of actively incising fluvial landscapes the rate of bedrock incision associated with an epigenetic gorge can be very high 1 cm yr typically orders of magnitude higher than both short and long term landscape denudation rates in the context of bedrock river incision and landscape evolution epigenetic gorges force rivers to incise more bedrock slowing long term incision and delaying the adjustment of rivers to regional tectonic and climatic forcing copyright 2008 john wiley sons ltd

variation and paleoclimatic significance of organic carbon isotopes of ili loess in arid central asia as an indicator for terrestrial paleovegetation the stable isotopic composition of total organic matter delta c 13 org in loess sediments has been widely used for paleoclimatic reconstruction in western europe the great plains of north america and the chinese loess plateau clp however little is known about the variation and paleoclimatic significance of the loess delta c 13 org in arid central asia aca we report delta c 13 org data from an axike axk loess paleosol profile from the eastern ili basin eastern central asia along the profile the delta c 13 org values were more negative in the paleosol layers observed in the field and were confirmed by environmental magnetic proxies and a higher concentration of total organic carbon toc consistent with results for western europe and the northwestern clp our results demonstrate that the loess delta c 13 org in this region documents mainly the response of delta c 13 of locally predominant c 3 plants to paleoclimatic variation especially paleoprecipitation our results also suggest that the loess delta c 13 org values in the area have the potential for quantitative paleoprecipitation reconstruction on the basis of detailed delta c 13 org results from modern plants and surface soils in the future c 2013 elsevier ltd all rights reserved

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

topographic control of oceanic flows in deep passages and straits saddle points between neighboring deep ocean basins are the sites of unidirectional flow from one basin to the next depending on the source of bottom water flow in these sites appears to be topographically controlled so the interface between the bottom water and the water above adjusts itself to permit bottom water flow from the basin that contains a source of bottom water into the next examples in the atlantic include flow in the romanche fracture zone the vema channel the ceara abyssal plain the anegada jungfern passage and the discovery gap but there are many more theoretical predictions of volume flux using a method that requires only conductivity temperature depth data archives and detailed knowledge of bathymetry near the saddle point are compared with volume flux estimates using current meters and or geostrophic estimates for seven cases the ratio of prediction to volume flux estimate ranges from 1 0 to 2 7 some ocean straits that separate adjacent seas are also found to critically control bidirectional flows between basins theory of the influence of rotation on such critical flows is reviewed predictions of volume flux in eight cases are compared with ocean estimates of volume flux from traditional methods

unusual early morning development of the equatorial anomaly in the brazilian sector during the halloween magnetic storm 1 the solar events that occurred at the end of october 2003 gave rise to very strong geomagnetic disturbances that peaked twice with dst values reaching 345 nt around 0000 ut on 30 october and 400 nt around 2300 ut on the same day disturbances in several ionospheric parameters were observed over brazil this work will focus on the ionospheric response to the initial westward prompt penetration electric field and on the strong intensification of the equatorial ionization anomaly that occurred because of the electric field polarity reversal that followed in the early morning hours of 29 october the f layer peak height over the equator first decreased under the strong prompt penetration westward electric field which was followed by significant height increase under eastward electric field we have used sheffield university plasmasphere ionosphere model supim with an intensified westward disturbed electric field in the presunrise hours presumably due to prompt penetration from the magnetosphere in order to study the effect of such a field in the ionosphere the simulation results showed that prompt penetration of magnetospheric electric fields of westward polarity to the nightside equatorial region seems to be the most probable cause of the initial f layer height decreases the intensification of the equatorial ionization anomaly and the unusual enhancement on f layer peak density which was not modeled by the supim are explained as caused by the strong eastward electric field that followed the initial phase in combination with a highly variable disturbed meridional transequatorial wind system as inferred from the f2 layer peak height variations the highly dynamic wind pattern with a short term response 2 4 hours is compatible with the predictions of some previous theoretical model calculations reported in the literature

frost cracking control on catchment denudation rates insights from in situ produced 10be concentrations in stream sediments ecrins pelvoux massif french western alps the potential tectonic and climatic controls on erosion rates in the european alps and other mountain belts remain strongly debated we have quantified denudation rates at catchment scales using in situ produced cosmogenic nuclides 10be in stream sediments sampled at the outlets of twelve variously sized 27 1072 km2 catchments of the ecrins pelvoux massif french western alps with average elevations ranging from 1700 to 2800 m spatially averaged denudation rates corrected for potential shielding by little ice age glaciers vary from 0 27 0 05 to 1 07 0 20 mm yr on millennial timescales our results exhibit a correlation 2 0 56 between denudation rate and mean catchment elevation in the absence of significant correlation with any other morphometric parameters relief slope catchment size hypsometry etc although such variations in erosion rates have been previously linked to variations in tectonic uplift rate the relatively small size and tectonic homogeneity of our study area exclude a strongly variable tectonic control we interpret the increase in erosion rate with elevation as the effect of frost controlled processes which are strongly temperature dependent we use a one dimensional heat flow model driven by high resolution instrumental temperature records from the study area to correlate the variability in denudation rates with the integral of the absolute temperature gradient within the frost cracking window 3 to 8 c a proxy of the frost cracking intensity for each catchment the results imply that the efficiency of frost cracking constitutes a major control on catchment wide denudation rates in the study area explaining more than half the measured variability in these rates our study shows that present day denudation of the ecrins pelvoux massif is controlled by a climatically driven factor and suggests that frost cracking processes impose an important control on the post glacial topographic evolution of mid latitude mountain belts

alluvial cover dynamics in response to floods of various magnitudes the effect of the release of glaciogenic material in a swiss alpine catchment abstract fluvial incision into formerly glaciated landscapes is commonly affected by the release of glaciogenic sediments from the hillslopes via landsliding hillslope failure and debris flow activity these deposits typically comprise abundant block size clasts here we determine the ability of the fluvial processes to evacuate glacially derived sediments in an alpine hanging valley blanketed by 100 m thick glacial till we assess along stream profiles of basal shear stress during annual decadal and centennial floods by means of the hydrological model hec ras we use bed surface grain size data to i evaluate the shields stress profiles for these floods ii determine at which timescale the bed undergoes significant changes and to iii predict transport capacity patterns for each flood in addition we present digital photogrammetry based estimates of bed elevation changes over two selected time intervals that experienced low and high magnitude floods respectively the results indicate that floods with return periods of 10 years are capable of mobilizing the coarse fraction of the bed material thereby substantially altering the channel geometry the predicted near critical shields stress values for these floods in the area where the glacial deposits are thickest suggest a strong hillslope channel coupling which may have resulted in the formation of the knickzone observed in this sector however decadal to centennial floods are required to transport the material over long distances and scour the bed in the upper part of the inner gorge in addition the observed downstream trend from bed scouring to deposition in the inner gorge for these floods and the opposite trend for low magnitude floods suggest that these patterns are not directly controlled by downstream variations of transport capacity we propose that the supply of sediment through hillslope failure and bank collapse significantly contributes to the sediment flux for high magnitude floods we conclude that the morphology and the timescale of sediment transport in this glacially conditioned landscape have been substantially controlled by the hillslope derived supply of coarse grained material

buried preglacial fluvial gorges and valleys preserved through quaternary glaciations beneath the eastern laurentide ice sheet the geomorphology geometry and sedimentary infill of buried gorges and v shaped valleys observed at the base of major river valleys in the formerly glaciated southeastern canadian shield region have been revealed from excavation and drilling data acquired during the construction of hydro electric dams and seismic data collected on lakes and offshore compilation of these previously published and unpublished data provided an exceptional opportunity to examine the morphology and spatial distribution of buried bedrock gorges and the mechanical processes responsible for their erosion in some valleys detailed observations of deep gorges have been allowed by their exhumation over large areas archive photographs show deep and large potholes natural pillars furrows flutes and scallops on the well polished bedrock walls of the gorges they also reveal that gorges and valleys have a sharp ending v shape and very narrow base and are superimposed by a u shaped valley forming a buried valley within valley topography the narrow and deep cross profile of these gorges their well polished slopes and the type of bedforms observed within them are typical features of fluvial bedrock channels drilling operations at many sites have also provided data on bedrock topography of these gorges within valleys and on the nature of their sedimentary infill the different lines of evidence presented in this paper indicate that gorges and v shaped valleys of the region were not eroded by the laurentide ice sheet during quaternary glaciations but are relics of a preserved preglacial fluvial system eroded during a lower base level this paleofluvial system is interpreted to be linked to fluvially cut channels observed on the seafloor of the estuary and gulf of st lawrence

substrate sediment and slope controls on bedrock channel geometry in postglacial streams the geometry of channels controls the erosion rate of rivers and the evolution of topography following environmental change we examine how sediment slope and substrate interact to constrain the development of channels following deglaciation and test whether theoretical relationships derived from streams reacting to tectonic uplift apply in these settings using an extensive data set of channel geometry measurements from postglacial streams in the scottish highlands we find that a power law width drainage area scaling model accounts for 81 of the spatial variation in channel width substrate influences channel form at the reach scale with bedrock channels found to be narrower and deeper than alluvial channels bedrock channel width does not covary with slope which may be due to downstream variations in sediment flux bedrock channel width to depth ratios increase with discharge or area and sediment flux consistent with increasing bed cover promoting lateral widening we find steep wide and shallow bedrock channels immediately below lakes which we interpret as the result of limited erosion due to a lack of sediment tools where sediment supply is sufficient to exceed transport capacity alluvial channels develop wider shallower geometries constrained primarily by flow hydraulics our results indicate that simple scaling models of channel width with drainage area are applicable at regional scale but locally channel width varies with substrate and in the case of bedrock channels with sediment flux

turbulent mixing and hydraulic control of abyssal water in the samoan passage 1 we report the first direct turbulence observations in the samoan passage sp a 40 km wide notch in the south pacific bathymetry through which flows most of the water supplying the north pacific abyssal circulation the observed turbulence is 1000 to 10 000 times typical abyssal levels strong enough to completely mix away the densest water entering the passage confirming inferences from previous coarser temperature and salinity sections accompanying towed measurements of velocity and temperature with horizontal resolution of about 250 m indicate the dominant processes responsible for the turbulence specifically the flow accelerates substantially at the primary sill within the passage reaching speeds as great as 0 55 m s 1 a strong hydraulic response is seen with layers first rising to clear the sill and then plunging hundreds of meters downward turbulence results from high shear at the interface above the densest fluid as it descends and from hydraulic jumps that form downstream of the sill in addition to the primary sill other locations along the multiple interconnected channels through the samoan passage also have an effect on the mixing of the dense water in fact quite different hydraulic responses and turbulence levels are observed at seafloor features separated laterally by a few kilometers suggesting that abyssal mixing depends sensitively on bathymetric details on small scales

northward abyssal transport through the samoan passage and adjacent regions a conductivity temperature depth hydrographic survey in january february 1994 and a 17 month deployment of current meter moorings from september 1992 to march 1994 were carried out to determine the volume transport water mass characteristics and diathermal fluxes of northward flowing abyssal waters in the samoan passage and adjacent regions of the south pacific ocean geostrophic calculations relative to 1 2 c potential temperature indicated northward transport of 7 8 sv in the samoan passage 1 1 sv through a gap in robbie ridge and 2 8 sv along the eastern flank of the manihiki plateau all of the total of 11 7 sv of northward geostrophic transport was in waters colder than 1 1 c the northward transport distribution was bimodal in temperature with a cold mode of 3 6 sv in the range 0 65 0 70 c occurring entirely in the samoan passage and a warm mode of 3 0 sv in the range of 0 80 0 85 c occurring mainly along the manihiki plateau within the samoan passage 7 1 sv of the northward transport was below 4000 m where the geostrophic calculation was confirmed by an equal estimate of transport from current meters during the simultaneous 3 day period the 17 month mean transport from the moored array was 6 0 sv 0 5 by using the observed temporally varying flow within the samoan passage together with the hydrographic snapshot across the region an estimate of the total mean northward transport of 10 6 sv 1 7 was obtained estimates of the flow across near bottom potential temperature surfaces indicate extraordinarily high rates of mixing with heating of the abyssal layer up to 20 w m 2 corresponding to diffusivities up to 10 1 m2 s 1

direct velocity measurements in the samoan passage an array of six current meter moorings was deployed in the samoan passage 10 s 170 w from september 1992 to february 1994 with the goal of determining the northward abyssal transport the 17 month mean transport beneath 4000 m was 6 0 sv 106 m3 s 1 the time series were low passed at a period of 100 hours to remove near inertial and tidal variability and the resulting transport had a standard deviation of 1 5 sv a minimum of 1 1 sv and a maximum of 10 7 sv the dominant low frequency variability in transport and area averaged temperature was at a period of 30 days where the temperature led the transport as would be expected if the heat balance were advective the temporal and spatial variability suggested that the mean transport is known to within a 1 standard deviation error of 0 5 sv the along passage flow was intensified to the west and toward the bottom as might be expected in a rotating geostrophic system three pathways through the sill region were identified on the basis of bathymetry and current direction the flow was strongly controlled by topography as indicated by the flow s orientation and directional steadiness the 30 day variability in transport might be described as a resonance of the northward abyssal flow

scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth on sloped surfaces abstract the decrease in rates of production of cosmogenic nuclides occurs because of shielding of cosmic rays by mountains sloped surfaces and local rock formations that block them when a large part of the sky is blocked this correction is large and requires detailed model calculations this paper considers three geometries a rectangular obstruction a triangular obstruction and a sloped surface other geometries can be considered as a combination of these the results are presented in terms of formulas and graphs so that the reader can easily apply them to common field situations any use of cosmogenic nuclides in the study of geomorphic processes or forms must consider factors that introduce variations in the production of nuclides

relation between rock uplift and denudation from cosmogenic nuclides in river sediment in the central alps of switzerland 1 a north south traverse through the swiss central alps reveals that denudation rates correlate with recent rock uplift rates in both magnitude and spatial distribution this result emerges from a study of in situ produced cosmogenic 10be in riverborne quartz in central alpine catchments as a prerequisite we took care to investigate the potential influence of shielding from cosmic rays due to snow glaciers and topographic obstructions to calculate a possible memory from last glacial maximum lgm glaciation and to identify a watershed size that is appropriate for systematic sampling mean denudation rates are 0 27 0 14 mm a for the alpine foreland and 0 9 0 3 mm a for the crystalline central alps the measured cosmogenic nuclide derived denudation rates are in good agreement with post lgm lake infill rates and are about twice as high as denudation rates from apatite fission track ages that record denudation from 9 to 5 ma in general denudation rates are high in areas of high topography and high crustal thickness the similarity in the spatial distribution and magnitude of denudation rates and those of rock uplift rates can be interpreted in several ways 1 postglacial rebound or climate change has introduced a transient change in which both uplift and denudation follow each other with a short lag time 2 the amplitude of glacial to interglacial changes in both is small and is contained in the scatter of the data 3 both are driven by ongoing convergence where their similarity might hint at some form of long term quasi steady state or 4 enhanced continuous quaternary erosion and isostatic compensation of the mass removed accounts for the distribution of present day rock uplift

pacific abyssal transport and mixing through the samoan passage versus around the manihiki plateau abstractthe main source feeding the abyssal circulation of the north pacific is the deep northward flow of 5 6 sverdrups sv 1 sv 106 m3 s 1 through the samoan passage a recent field campaign

quaternary erosion induced isostatic rebound in the western alps the high elevation and deep incision of the alps have traditionally been used as an argument for recent tectonic activity that has elevated the belt and increased erosion rates normal faulting and horizontal extension however dominate current tectonic activity and isostatic compensation of thinning crust should lead not to increased but to decreased mean elevations here we test the idea that enhanced quaternary erosion of the alps and isostatic compensation of the mass removed can account for the distribution of present day geodetically measured rates of vertical movement in the western alps using geophysical relief and kuhlemann s estimated average erosion rate for the alps we quantify the spatial distribution of erosion and the volume of eroded rock respectively from these we obtain a map of rock eroded within a given time span the calculated isostatic response of the alpine lithosphere to erosional unloading for a variety of values of the flexural rigidity of the alpine lithosphere reaches a maximum of 500 m since 1 ma in the inner swiss alps and vertical movement extends across the entire belt including peri alpine basins assuming a steady erosion rate since 1 ma this rebound accounts for half of the measured vertical motion of 1 1 mm yr in the southern valais thus a significant fraction 50 of the present day vertical movement results from the isostatic response to enhanced erosion during plio quaternary time

the initiation of northern hemisphere glaciation for well over a century scientists have speculated that variations in the atmospheric concentration of radiatively important trace gases such as carbon dioxide could control the earth s climate e g arrhenius 1 896 recent observations of significant glacial interglacial variation in atmo spheric co2 in ice cores put this idea on a firm observational as well as theoretical footing e g barnola et ai1 987 in this century as atmospheric co2 levels creep steadily upwards in response to the burning of fossil fuels and forests the specter of manmade global climate change looms before us ipcc 1990 a possibility that has heightened interest in the natural variability of climate in the past in particular the 3 c warming pre dicted for the next century has stimulated interest in past warm climates such as the middle pliocene around 3 0 million years ma ago an interval that has often been invoked as a greenhouse world budyko et al 1985 in this paper the climate transition from the warm mid pliocene around 3 2 ma to the onset of northern hemisphere ice ages around 2 4 ma is examined evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe while the cause of individual glacial interglacial oscillations is tied to milankovitch variations in the earth s orbit around the sun e g imbrie et ai 1 992 these insolation changes cannot account for the long term cooling trend which culminated in northern hemisphere glaciation in the final section of this paper mechanisms of long term climate change

features of glacial valley profiles simply explained 1 glacial occupation of alpine valleys results in a distinct signature in the long valley profile including steepening of the profile in the headwaters flattening at lower elevations and a step in the profile at the convergence of headwater tributaries we present analytic results for glacial erosion patterns by making the following assumptions 1 the initial profile is linear 2 the width of the valley is uniform 3 the annual mass balance varies linearly with elevation 4 the glacier at any time is quasi steady 5 the erosion rate is proportional to ice discharge per unit valley width and 6 glacial erosion rates far exceed fluvial erosion rates a steady glacier under these conditions would erode a parabolic divot in the longitudinal valley profile with its maximum depth coinciding with the down valley position of the equilibrium line altitude ela the calculated flattening of the valley floor down valley of the ela and the steepening of it up valley captures the essence of the glacial signature when a reasonable probability distribution of elas is allowed the predicted erosion peaks at 30 40 of the down valley distance to the glacial limit and the pattern merges smoothly with the steeper fluvial profile downstream of the glacial limit profiles of mass balance that are capped at a maximum value produce shorter glaciers and a slight asymmetry in the expected erosion pattern only when we mimic the tributaries of glacial headwaters by specifying a valley width distribution do we obtain the upper step observed in many valley profiles

bedrock landsliding river incision and transience of geomorphic hillslope channel coupling evidence from inner gorges in the swiss alps 1 the formation of inner gorges cut into bedrock has been explained as relief rejuvenation by fluvial incision in response to rapid base level drop repeated glaciations frequent pore pressure driven landsliding focused at hillslope toes or catastrophic outburst flows from natural dam failures prominent inner gorges occur in soft mesozoic bundner schist and lower tertiary flysch units of the formerly glaciated alpenrhein catchment eastern swiss alps their channel and hillslope morphologies differ from basins characterized by strong glacial or landslide imprints while formally resembling the theoretically predicted transient response of detachment limited bedrock rivers to rapid base level fall by headward knickpoint migration assuming a postglacial onset of fluvial bedrock incision into a last glacial maximum surface in response to base level drop induced by downwasting of trunk valley glaciers requires downcutting rates e 20 mm yr 1 and requires hillslopes to adjust by frequent landsliding toward development of a threshold state we test this scenario using data on surface uplift geomorphometry geomorphic hillslope coupling and probabilistic slope stability models we find that adjustment of inner gorge walls through landsliding is mainly strength limited and structurally controlled and threshold conditions are restricted to the lower 25 of local hillslope relief mass movement processes on upper hillslopes remain largely decoupled from channel incision despite inferred postglacial specific sediment yields of 104 m3 km 2 yr 1 from the studied basins conversely several constraints imposed by fluvial bedrock detachment postglacial sediment yields and bedrock landsliding argue for a pre holocene origin for at least some of the inner gorges in the area this implies partial protection of fluvial gorge topography by subglacial sediment fill during the last wurm extensive glaciation and implies that glaciers were insufficient to fully eradicate fluvially sculpted bedrock topography this leads us to conclude that lithology and major climate oscillations should be considered as further alternative controls on inner gorge formation

cosmogenic nuclide based investigation of spatial erosion and hillslope channel coupling in the transient foreland of the swiss alps abstract transient landscape disequilibrium is a common response to climatic fluctuations between glacial and interglacial conditions such landscapes are best suited to the investigation of catchment wide response to changes in incision the geomorphology of the trub and grosse fontanne adjacent stream systems in the napf region of the swiss molasse was analyzed using a 2 m lidar dem the two catchments were impacted by the last glacial maximum lgm even though the glaciers never overrode this region they did however cause base levels to drop by as much as 80 m despite their similar tectonic lithologic and climatic settings these two basins show very different responses to the changing boundary conditions stream profiles in the trub tend to be smooth while in the fontanne numerous knickzones are visible similarly cut and fill terraces are abundant in the trub watershed but absent in the fontanne where deep valleys have been incised the trub appears to be a coupled hillslope channel system because the morphometrics throughout the basin are uniform the morphology of hillslopes upstream of the knickzones in the fontanne is identical to that of the trub basin but different downstream of the knickzones suggesting that the lower reaches of the fontanne have been decoupled from the hillslopes however the rapid incision of the fontanne is having little effect on the adjacent upper hillslopes we tested this interpretation using cosmogenic 10 be derived basin averaged denudation rates and terrace dating the coupled nature of the trub basin is supported by the similarity of denudation rates 350 50 mm ky 1 at a variety of spatial scales upstream of the knickzones rates in the fontanne 380 50 mm ky 1 match those of the trub downstream of the knickzones denudation rates increase to 540 100 mm ky 1 the elevated rates in the downstream areas of the fontanne are due to rapid incision causing a decoupling of the hillslope from the channel basin response time and the magnitude of base level drop exert the principal control over the difference in geomorphic response between the two basins the timing of the filling of the trub valley 17 2 ka and the initial incision of the fontanne 16 3 ka were calculated verifying that these are responses to late glacial perturbations unique lithologic controls allow for one of the fastest regolith production rates yet to be reported 380 mm ky 1

glacial conditioning as an erosional driving force in the central alps unparalleled data availability in the european alps has led to an ongoing debate about the driving mechanism behind the concurrent patterns of surface denudation and modern rock uplift analysis of stream channels reveals that oversteepened stream segments are primarily located in landscapes with strong glacial inheritance this leads to a transient signal in the landscape with the result that erosion is spatially focused by a combination of glacial conditioning and lithologic controls we postulate that the effect of glacial forcing is a positive feedback cycle between erosion and rock uplift driving rapid rates of both in the alpine landscape this mechanism may explain the observed increases in sediment flux since the late pliocene

observations of the flow of abyssal water through the samoa passage abstract during the fall of 1994 a conductivity temperature depth hydrographic survey was carried out as part of the world ocean circulation experiment one time survey line p15n the survey included standard water properties required by woce line p15n extended southward from the aleutian islands along 165 w into the vicinity of the samoa passage the line was adjusted to follow the axis of the passage and time was found to complete a cross section survey across the passage this paper will present geostrophic computations of flow velocities through the gap including transport estimates and will present longitudinal plots of properties the longitudinal plots show evidence of hydraulic control at the sill in the samoa passage a best estimate of northward transport of water colder than 1 2 c potential temperature is determined to be 8 4 sv

climate induced rebound and exhumation of the european alps foreland basins record the regional isostatic compensation of mountain belts during periods of crustal thickening they subside and when erosion unloads the mass of the mountains the basins rebound and are eroded in order to evaluate this mechanism for rebound it is critical that the timing and magnitude of erosion are documented we present data estimating the timing and magnitude of late orogenic or postorogenic erosion in the north alpine foreland basin of switzerland mineral cooling ages demonstrate that the basin underwent 1 3 km of erosion soon after 5 ma this erosion coincided with a decline in structural deformation in the swiss alps and a doubling of sediment accu mulation rates in surrounding depocenters we propose that accelerated erosional un roofing of the swiss alps triggered isostatic rebound and erosion of the foreland basin after 5 ma a projection of the isostatic rebound of the basin into the mountains suggests that at least 6 5 km of erosion should have occurred in the high topography of the aar massif accelerated erosion in the swiss alps at that time is explained by an increase in atmospheric moisture driven by an intensification of the atlantic gulf stream at 4 6 ma consequently we propose that the changing erosional capacity of the climate triggered late orogenic to postorogenic mass reduction and isostatic rebound of the swiss alps and their neighboring foreland basin

10be derived assessment of accelerated erosion in a glacially conditioned inner gorge entlebuch central alps of switzerland inner gorges often result from the propagation of erosional waves related to glacial interglacial climate shifts however only few studies have quantified the modern erosional response to this glacial conditioning here we report in situ 10be data from the 64 km2 entlen catchment swiss alps this basin hosts a 7 km long central inner gorge with two tributaries that are 100 m deeply incised into thick glacial till and bedrock the 10be concentrations measured at the downstream end of the gorge yield a catchment wide erosion rate of 0 42 0 04 mm yr 1 while erosion rates are consistently lower upstream of the inner gorge ranging from 0 14 0 01 mm yr 1 to 0 23 0 02 mm yr 1 however 10be based sediment budget calculations yield rates of similar to 1 3 mm yr 1 for the inner gorge of the trunk stream likewise in the two incised tributary reaches erosion rates are similar to 2 0 mm yr 1 and similar to 1 9 mm yr 1 moreover at the erosional front of the gorge we measured bedrock incision rates ranging from similar to 2 5 mm yr 1 to similar to 3 8 mm yr 1 these rates however are too low to infer a post glacial age 1520 ka for the gorge initiation this would require erosion rates that are between 2 and 6 times higher than present day estimates however the downcutting into unconsolidated glacial till favored high erosion rates through knickzone propagation immediately after the retreat of the lgm glaciers and subsequent hillslope relaxation led to a progressive decrease in erosion rates this hypothesis of a two to sixfold decrease in erosion rates does not conflict with the 10be based erosion rate budgets because the modern erosional time scale recorded by 10be cover the past 23 ka only these results point to the acceleration of holocene erosion in response to the glacial overprint of the landscape

geomorphology deceptively old alpine gorges the timing and origins of alpine gorge formation are controversial a high resolution analysis of the inner gorges of the swiss alps suggests that these landforms were carved over successive interglacial periods and survived the intervening glaciations

mid holocene cluster of large scale landslides revealed in the southwestern alps by 36cl dating insight on an alpine scale landslide activity abstract although it is generally assumed that the internal structure of a slope e g lithology and rock mass properties inherited faults and heterogeneities etc is preponderant for the progressive development of large scale landslides the ability to identify triggering factors responsible for final slope failures such as glacial debuttressing seismic activities or climatic changes especially when considering landslide cluster at an orogen scale is still debated highlighting in this study the spatial and temporal concordant clustering of deep seated slope failures in the external southwestern alps we discuss and review the possible causes for such wide spread slope instabilities at both local and larger alpine scale high resolution field mapping coupled with electrical resistivity tomography first allows establishing an inventory of large landslides in the southwestern alps determining their structural model precising their depth limit 100 200 m as well as the involved rock volumes 10 7 m 3 we show that they developed in the same geostructural context of thick mudstone layers overlain by faulted limestone and followed a block spread model of deformation that could evolve in rock collapse events cosmic ray exposure dating cre using both 36 cl and 10 be in coexisting limestone and chert respectively has been carried out from the main scarps of six deep seated landslides dsl and leads to landslide failure cre ages ranging from 3 7 to 4 7 ka they highlighted i mainly single and fast ruptures and ii a possible concomitant initiation with a main peak of activity between 3 3 and 5 1 ka centered at ca 4 2 ka because this region was not affected by historical glaciations events landslide triggering by glacial unloading can be excluded the presented data combined with field observations preferentially suggest that these failures were climatically driven and were most likely controlled by high pressure changes in the karstic medium in effect the chronicle of failure ages is concomitant to a well known climatic pulse the 4 2 ka climate event characterized by intense hydrological perturbations associated to the heaviest rainfall period of the entire holocene despite requiring further investigations and discussions the dating of numerous events across the entire alps during the middle holocene period suggests a potential synchronous triggering of several large scale gravitational failures induced by the mid holocene climatic transition

dating bedrock gorge incision in the french western alps ecrins pelvoux massif using cosmogenic 10be terra nova 22 18 25 2010 abstract we report in situ produced 10be data from the gorge du diable french western alps to date and quantify bedrock gorge incision into a glacial hanging valley we sampled gorge sidewalls and the active channel bed to derive both long term and present day incision rates 10be ages of sidewall profiles reveal rapid incision through the late holocene ca 5 ka at rates ranging from 6 5 to 13 mm yr 1 present day incision rates are significantly lower and vary from 0 5 to 3 mm yr 1 within the gorge our data imply either delayed initiation of gorge incision after final ice retreat from internal alpine valleys at ca 12 ka or post glacial surface reburial of the gorge our results suggest that fluvial incision rates 1 cm yr 1 into crystalline bedrock may be encountered in transient landscape features induced by glacial interglacial transitions

increase in late neogene denudation of the european alps confirmed by analysis of a fission track thermochronology database abstract a sharp increase in deposited sediment volume since pliocene times has been observed worldwide and in particular around the european alps this phenomenon has been linked to a rise in denudation rates controlled by an increase of either climatic or tectonic forcing observation of in situ cooling histories for orogens is critical to assess the reality of the inferred increase in denudation rates and to determine whether this phenomenon is widespread or localized at active tectonic structures we exploit the unique density of fission track ages in the western european alps to reconstruct cooling isoage surfaces and to estimate exhumation rates on the orogen scale between 13 5 and 2 5 ma our novel technique is based on the association of isoage contours with age elevation relationships it uses map view interpolation enabling a spatio temporal analysis of exhumation rates over the entire western alps the resulting exhumation histories reconstructed for eight areas of the western alps display strong similarities in timing and rates with orogen wide average denudation rates inferred from sediment volumes this consistency validates the use of both techniques for the study of an orogen characterized by strong relief and high recent exhumation rates we conclude that exhumation rates in the western alps have increased more than twofold since late miocene times this increase may have been locally modulated by the distinct response of different tectonic units