changes in coral reef structure through the miocene in the mediterranean province adaptive versus environmental influence well documented mediterranean examples of miocene carbonate platforms with complete exposures from shallow water to basinal facies provide evidence for temporal changes in reef building capacity of zooxanthellate corals in pre late tortonian platforms small coralgal patches and mounds occur from platform top to the toe of slope but they did not build to sea level in contrast barrier reefs with unequivocal reef crest structures that reached sea level are documented in late tortonian early messinian platforms we suggest that a change in both calcification rates and bathymetric zonation was the result of coevolution of corals and symbiodinium zooxanthellae coeval to global cooling and at least at a regional scale a geochemical change that supported widespread aragonite precipitation through the late miocene

temporal buffering of climate driven sediment flux cycles by transient catchment response abstract the marine sedimentary record can exhibit a systematic cyclicity that is consistent with climate variability driven by milankovitch scale forcing milankovitch band cyclicity is widely interpreted in the hemipelagic and pelagic sediments of the marine realm and in terrestrial paleoenvironments has been observed in lacustrine sediments soils and river floodplain successions it remains unclear however if and how mountain catchments as a primary sediment source respond to these high frequency 6 yr climatic cycles and whether particulate sediment flux signals can be expected to be recorded in the clastic sedimentary record of adjacent basin fills recent field and theoretical studies suggest that mountain catchments respond transiently to high frequency forcing and so sediment discharge from the catchment is a non linear function of forcing variables using a catchment basin model we demonstrate that climate driven cyclicity in particulate sediment discharge is strongly damped when the period of climate variability is shorter than the response timescale of the eroding landscape given that the response timescale of landscapes is of the order of 10 6 yr and that milankovitch driven climate cyclicity is of the order of 10 4 10 5 yr it is likely that climate driven perturbation of upland catchments at these periods will be strongly damped by transient landscape behaviour our results therefore suggest that stratigraphy built by particulate fluxes from upland catchments and long term trends in the sediment delivery to the ocean may be relatively insensitive to short term climate variability

weathering and morphogenesis in a mediterranean climate calabria italy abstract deeply weathered plutonic rocks occur widely in the sila massif calabria southern italy three representative weathering profiles developed on the hilltops indicate that sand represents more than 50 by weight throughout most of the weathering profile and silt and clay size fractions are also well represented filling the interstices among corestones both sand and finer fractions of grus and soil horizons are thought to be derived from a combination of granular disintegration and chemical decomposition developed on relatively flat terrains of the sila massif these slopes are now experiencing transport limited morphodynamics under a montane modified mediterranean climate the depth of the weathered layers that have suffered little erosional truncation typically exceed 15 m and may reach 50 60 m or more major isolated or grouped exfoliation boulders are the most common minor landform feature developed on the sila massif granite boulders have developed as a result of spheroidal weathering and by removal of the sandy textured granite the schmidt hammer sh test on boulders and corestones suggests three distinctive degree of weathering from moderately to completely weathered rock and that biotite content is the major controlling factor of the granite mechanical behaviour understanding of the dynamics of this weathering system is crucial to the interpretation of the complex suite of variables that control landscape evolution of granitoid terrains

shredding of environmental signals by sediment transport 1 landscapes respond to climate tectonic motions and sea level but this response is mediated by sediment transport understanding transmission of environmental signals is crucial for predicting landscape response to climate change and interpreting paleo climate and tectonics from stratigraphy here we propose that sediment transport can act as a nonlinear filter that completely destroys shreds environmental signals this results from ubiquitous thresholds in sediment transport systems e g landsliding bed load transport and river avulsion this morphodynamic turbulence is analogous to turbulence in fluid flows where energy injected at one frequency is smeared across a range of scales we show with a numerical model that external signals are shredded when their time and amplitude scales fall within the ranges of morphodynamic turbulence as signal frequency increases signal preservation becomes the exception rather than the rule suggesting a critical re examination of purported sedimentary signals of external forcing citation jerolmack d j and c paola 2010 shredding of environmental signals by sediment transport geophys res lett 37 l19401 doi 10 1029 2010gl044638

uplift history of the central and northern andes a review the elevation of the andean cordillera is a crucial boundary condition for both climatic and tectonic studies the andes affect climate because they form the only barrier to atmospheric circulation in the southern hemisphere and they intrigue geologists because they have the highest plateau on earth formed at a noncollisional plate margin the altiplano puna yet until recently few quantitative studies of their uplift history existed this study presents both 1 a review of the quantitative paleoelevation estimates that have been made for the central and colombian andes and 2 an examination of the source and magnitude of error for each estimate in the central andes paleobotanical evidence suggests that the altiplano puna had attained no more than a third of its modern elevation of 3700 m by 20 ma and no more than half its modern elevation by 10 7 ma these data imply surface uplift on the order of 2300 3400 m since the late miocene at uplift rates of 0 2 0 3 mm yr paleobotanical and geomorphological data suggest a similar uplift history for the eastern cordillera namely no more than half the modern elevation present by 10 ma no evidence exists for an exponential increase in uplift rate as has been interpreted from fissiontrack data these uplift rates mostly reflect mean surface uplift rather than rock uplift that is uplift of material points because little dissection of the western eastern cordillera has occurred south of lat 19 s and of the altiplano puna thus the central andean plateau appears to be young in the colombian andes paleobotanical data imply rapid uplift of the eastern cordillera between 2 and 5 ma at rates on the order of 0 6 3 mm yr however some of this uplift is likely rock uplift due to erosion driven isostatic rebound rather than mean surface uplift

transient landscapes at fault tips 1 fault growth produces patterns of displacement and slip rate that are highly variable in both space and time this transience is most pronounced near fault tips where along strike displacement gradients vary in time as the fault array lengthens we use a set of statistical and field observations to quantify the response of catchments and their associated fans in three large normal fault arrays to transient patterns of displacement and slip rate catchments near the fault tips show distinct scaling of channel slope with drainage area compared with catchments near the strike center this scaling becomes uniform beyond about 10 km from the fault tips and is therefore like footwall relief largely decoupled from the fault displacement profile the estimated catchment response times to a change in slip rate also vary between fault tips and strike center the response times for tip catchments are much longer than the inferred time since fault activity began indicating that they are unlikely to be in equilibrium with the current fault displacement field this disequilibrium combined with the decoupling of slope area scaling from displacement indicates that landscapes are most sensitive to fault activity near fault tips active faults characterized by along strike variation in slip rate thus provide excellent opportunities to explore the transient response of landscapes to tectonic forcing

river drainage patterns in the new zealand alps primarily controlled by plate tectonic strain the persistence of dendritic drainage patterns implies that rivers reorganize after a tectonic perturbation preserving no long term record of that tectonic event numerical simulations of the evolution of drainage patterns in the southern alps new zealand however reveal rivers that resist reorganization and thus preserve a record of plate tectonic strain over 10 million years

calibrating fluvial erosion laws and quantifying river response to faulting in sardinia italy abstract it is now widely accepted that rivers modify their erosion rates in response to variable rock uplift rates resulting in changes in channel slope that propagate upstream through time therefore present day river morphology may contain a record of tectonic history the simple stream power incision model can in principle be used to quantify past uplift rates over a variety of spatial and temporal scales nonetheless the erosional model s exponents of area and slope m and n respectively and bedrock erodibility k remain poorly constrained in this paper we will use a geologically and geomorphically well constrained plio pleistocene volcanic landscape in central sardinia italy to calibrate the stream power erosion equation and to investigate the slip rate of faults that have been seismically quiescent in the historic past by analysing digital elevation models geological maps and landsat imagery we have identified the geomorphic expression of several volcanic features eruption centres and basaltic lava flows and three normal faults with 6 to 8 km fault traces within the outcrop downstream river longitudinal profiles show a similar transient response to relative base level fall probably as a result of relief inversion at the edge of the volcanic outcrop from measurements of incision local slope and upstream catchment area across eight different rivers we calculate n 1 m 0 50 0 02 and using a landscape age from literature of 2 7 ma bedrock erodibility k 0 10 0 04 m 1 2m myr 1 there are also knickpoints on rivers upstream of two normal faults and we used numerical inverse modelling of the longitudinal profiles to predict the slip rate of these faults since 2 7 ma the results from the inverse model show that the erosional parameter values derived in this study can produce theoretical longitudinal profiles that closely resemble observed river profiles upstream of the faults the lowest misfit theoretical longitudinal profiles were generated by a model of temporally discontinuous footwall uplift with consistently low throw rates

measuring alluvial fan sensitivity to past climate changes using a self similarity approach to grain size fining death valley california the effects of climate change on eroding landscapes and the terrestrial sedimentary record are poorly understood using mountain catchment alluvial fan systems as simple analogues for larger landscapes a wide range of theoretical studies numerical models and physical experiments have hypothesised that a change in precipitation rate could leave a characteristic signal in alluvial fan sediment flux grain size and down system fining rate however this hypothesis remains largely untested in real landscapes this study measures grain size fining rates from apex to toe on two alluvial fan systems in northern death valley california usa which each have well exposed modern and ca 70 ka surfaces and where the long term tectonic boundary conditions can be constrained between them these surfaces capture a well constrained temporal gradient in climate a grain size fining model is adapted based on self similarity and selective deposition for application to these alluvial fans this model is then integrated with cosmogenic nuclide constraints on catchment erosion rates and observed grain size fining data from two catchment fan systems to estimate the change in sediment flux from canyon to alluvial fan that occurred between mid glacial and modern interglacial conditions in a fan system with negligible sediment recycling an approximately 30 decrease in precipitation rate led to a 20 decrease in sediment flux and a clear increase in the down fan rate of fining supporting existing landscape evolution models consequently this study shows that small mountain catchments and their alluvial fan stratigraphy can be highly sensitive to orbital climate changes over 105 year timescales however in the second fan system it is observed that this sensitivity is completely lost when sediment is remobilised and recycled over a time period longer than the duration of the climatic perturbation these analyses offer a new approach to quantitatively reconstructing the effects of past climate changes on sedimentation using simple grain size data measured in the field this article is protected by copyright all rights reserved

drainage basin sensitivity to tectonic and climatic forcing implications of a stochastic model for the role of entrainment and erosion thresholds long term average rates of channel erosion and sediment transport depend on the frequency magnitude characteristics of ood ows that exceed an erosion threshold using a poisson model for rainfall and runoff analytical solutions are developed for average rates of stream incision and sediment transport in the presence of such a threshold solutions are derived and numerically tested for three erosion transport formulas the howard kerby shear stress incision model the bridge dominic sediment transport model and a generic shear stress sediment transport model results imply that non linearity resulting from threshold effects can have a rst order impact on topography and patterns of dynamic response to tectonic and climate forcing this non linearity becomes signi cant when fewer than about half of ood events are capable of detaching rock or sediment predicted morphology and uplift gradient scaling is more closely consistent with observations and laboratory experiments than conventional slope linear or shear linear erosion laws these results imply that particle detachment thresholds are not details that can be conveniently ignored in long term landscape evolution models copyright 2004 john wiley sons ltd

transient fluvial incision as an indicator of active faulting and plio quaternary uplift of the moroccan high atlas one of the challenges facing earth scientists is to determine the extent to which geomorphic features can be used to extract tectonic signals from landscapes here we quantitatively analyse the long profiles of rivers that drain southwards across the south atlas fault saf a thrust fault that forms the southern margin of the high atlas mountains in morocco to derive new data on the late cenozoic activity of this fault system river long profiles were extracted for 32 major rivers flowing southwards into the ouarzazate basin of these eleven exhibit concave up river profiles with a mean concavity of 0 64 and normalized steepness indices in the range 47 5 219 0 m 0 9 by contrast 21 rivers exhibit at least one knickpoint upstream of the thrust front knickpoint height varies from 100 1300 m with calculated incision at the range bounding fault ranging from 80 900 m despite the drainage areas upstream of the knickpoint ranging over several orders of magnitude in map view knickpoint locations generally plot along sub parallel lines and there are no obvious relationships with lithological units for knickpoints exhibiting slope break morphology channel reaches below slope break knickpoints have higher mean concavities 0 76 than above the knickpoint indicative this observation combined with a lithological or river capture origin for the knickpoints having been ruled out suggests that an increase in uplift rate along a planar fault zone during the plio quaternary caused the initiation of the transient response i e knickpoint formation to a change in base level observed in the river profiles this uplift event can be correlated to the convective removal of the lithospheric root to the atlas mountains resulting in the anomalously high topography at the present day

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

beyond threshold hillslopes channel adjustment to base level fall in tectonically active mountain ranges numerous empirical and model based studies argue that in general hillslopes and river channels increase their gradients to accommodate high rates of base level fall to date however few data sets show the dynamic range of both these relationships needed to test theoretical models of hillslope evolution and river incision here we utilize concentrations of 10 be in quartz extracted from river sand on the eastern margin of the tibetan plateau to explore relationships among short term 10 2 10 5 a erosion rate hillslope gradient and channel steepness our data illustrate nonlinear behavior and a threshold in the relationship between erosion rate and mean hillslope gradient confi rming the generalization that hillslopes around the world are limited by slope stability and cease to provide a metric for erosion at high rates 0 2 mm a the relationship between channel steepness index and erosion rate is also nonlinear but channels continue to steepen beyond the point where threshold hillslopes emerge up to at least 0 6 mm a demonstrating that channel steepness is a more reliable topographic metric than mean hillslope gradient for erosion rate and that channels ultimately drive landscape adjustment to increasing rates of base level fall in tectonically active settings

landscape form and millennial erosion rates in the san gabriel mountains ca abstract it has been long hypothesized that topography as well as climate and rock strength exert first order controls on erosion rates here we use detrital cosmogenic 10 be from 50 basins ranging in size from 1 to 150 km 2 to measure millennial erosion rates across the san gabriel mountains in southern california where a strong e w gradient in relief compared to weak variation in precipitation and lithology allow us to isolate the relationship between topographic form and erosion rate our erosion rates range from 35 to 1100 m ma and generally agree with both decadal sediment fluxes and long term exhumation rates inferred from low temperature thermochronometry catchment mean hillslope angle increases with erosion rate until 300 m ma at which point slopes become invariant with erosion rate although this sort of relation has been offered as support for non linear models of soil transport we use 1 d analytical hillslope profiles derived from existing soil transport laws to show that a model with soil flux linear in slope but including a slope stability threshold is indistinguishable from a non linear law within the scatter of our data catchment mean normalized channel steepness index increases monotonically though non linearly with erosion rate throughout the san gabriel mountains even where catchment mean hillslope angles have reached a threshold this non linearity can be mostly accounted for by a stochastic threshold incision model though additional factors likely contribute to the observed relationship between channel steepness and erosion rate these findings substantiate the claim that the normalized channel steepness index is an important topographic metric in active ranges

high latitude forcing of the south american summer monsoon during the last glacial the climate of the last glacial period 10 000 to 110 000 years ago was characterized by rapid millennial scale climate fluctuations termed dansgaard oeschger d o and heinrich events we present results from a speleothem derived proxy of the south american summer monsoon sasm from 16 000 to 50 000 years ago that demonstrate the occurrence of d o cycles and heinrich events this tropical southern hemisphere monsoon reconstruction illustrates an antiphase relationship to northern hemisphere monsoon intensity at the millennial scale our results also show an influence of antarctic millennial scale climate fluctuations on the sasm this high resolution precisely dated tropical precipitation record can be used to establish the timing of climate events in the high latitudes of the northern and southern hemispheres

transient fluvial incision in the headwaters of the yellow river northeastern tibet china 1 we utilize topographic analysis of channel profiles combined with field measurements of erosion rates to explore the distribution of channel incision in the anyemaqen shan a broad mountainous region in the northeastern tibetan plateau tributary channels to the yellow river display systematic downstream increases in channel gradient associated with convex upward longitudinal profiles steep lower reaches of channels are associated with rapid 1 m ka incision rates along the yellow river while upstream reaches are associated with relatively slow 0 05 0 1 m ka erosion of soil mantled uplands covariance between erosion rates and channel steepness indices suggest that channels are adjusted to match long wavelength differential rock uplift across the range geologic constraints indicate that rapid incision downstream of the range is associated with excavation of basin fill driven by changes in relative base level farther downstream the upstream limit of this wave of transient incision is marked by a series of knickpoints that are found at nearly the same elevation throughout the watershed consistent with knickpoint migration as a kinematic rather than diffusional wave tributary channel gradients downstream of knickpoints however display a progressive adjustment to increased incision rates that may reflect the influence of increased sediment flux comparison of observed channel profiles to a stream power model of fluvial behavior reveals that the rate of knickpoint propagation can only be explained if the erosional efficiency coefficient k increases during incision our results thus highlight the utility of channel profile analysis to reconstruct the fluvial response to both active tectonism and external changes in base level

quantifying the slip rates spatial distribution and evolution of active normal faults from geomorphic analysis field examples from an oblique extensional graben southern turkey abstract quantifying the extent to which geomorphic features can be used to extract tectonic signals is a key challenge in the earth sciences here we analyse the drainage patterns geomorphic impact and long profiles of bedrock rivers that drain across and around normal faults in a regionally significant oblique extensional graben hatay graben in southern turkey that has been mapped geologically but for which there are poor constraints on the activity slip rates and plio pleistocene evolution of basin bounding faults we show that drainage in the hatay graben is strongly asymmetric and by mapping the distribution of wind gaps we are able to evaluate how the drainage network has evolved through time by comparing the presence size and distribution of long profile convexities we demonstrate that the northern margin of the graben is tectonically quiescent whereas the southern margin is bounded by active faults our analysis suggests that rivers crossing these latter faults are undergoing a transient response to ongoing tectonic uplift and this interpretation is supported by classic signals of transience such as gorge formation and hill slope rejuvenation within the convex reach additionally we show that the height of long profile convexities varies systematically along the strike of the southern margin faults and we argue that this effect is best explained if fault linkage has led to an increase in slip rate on the faults through time from 0 1 to 0 45 mm yr by measuring the average length of the original fault segments we estimate the slip rate enhancement along the faults and thus calculate the range of times for which fault acceleration could have occurred given geological estimates of fault throw these values are compared with the times and slip rates required to grow the documented long profile convexities enabling us to quantify both the present day slip rate on the fault 0 45 0 05 mm yr and the timing of fault acceleration 1 4 0 2 ma our results have substantial implications for predicting earthquake hazard in this densely populated area calculated potential mw 6 0 6 6 enable us to constrain the tectonic evolution of the graben through time and more widely demonstrate that geomorphic analysis can be used as an effective tool for estimating fault slip rates over time periods 106 years even in the absence of direct geodetic constraints

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

using hilltop curvature to derive the spatial distribution of erosion rates 1 erosion rates dictate the morphology of landscapes and therefore quantifying them is a critical part of many geomorphic studies methods to directly measure erosion rates are expensive and time consuming whereas topographic analysis facilitates prediction of erosion rates rapidly and over large spatial extents if hillslope sediment flux is nonlinearly dependent on slope then the curvature of hilltops will be linearly proportional to erosion rates in this contribution we develop new techniques to extract hilltop networks and sample their adjacent hillslopes in order to test the utility of hilltop curvature for estimating erosion rates using high resolution 1 m digital elevation data published and new cosmogenic radionuclide analyses in the feather river basin california suggest that erosion rates vary by over an order of magnitude 10 to 250 mm kyr 1 hilltop curvature increases with erosion rates allowing calibration of the hillslope sediment transport coefficient which controls the relationship between gradient and sediment flux having constraints on sediment transport efficiency allows estimation of erosion rates throughout the landscape by mapping the spatial distribution of hilltop curvature additionally we show that hilltop curvature continues to increase with rising erosion rates after gradient limited hillslopes have emerged hence hilltop curvature can potentially reflect higher erosion rates than can be predicted by hillslope gradient providing soil production on hilltops can keep pace with erosion finally hilltop curvature can be used to estimate erosion rates in landscapes undergoing a transient adjustment to changing boundary conditions if the response timescale of hillslopes is short relative to channels

spatial patterns of late quaternary river incision along the northern tian shan foreland abstract river incision rate is widely used to track changes in tectonics or climate over time and space however the feasibility of utilizing the spatial variations of river incision to reconstruct past tectonic and climatic processes remains unclear here we focus on the spatial patterns of river incision along the northern chinese tian shan foreland three alluvial fans fp feh and flh are determined as the alluvial fan context of river incision and terrace classification providing the geomorphological framework across the foreland region four rivers i e the kuitun jingou manas and urumqi rivers from the western central and eastern part of the foreland are used to reconstruct the paleogeomorphology from the reference which is the best preserved terrace of each river system with ages clustering in different parts of the latest pleistocene early holocene the depth of incision constrained by the reference terrace of each river is obtained by comparing the present day topography and the reconstructed one the resulting profile of channel incision depth and rate of each analyzed river displays an overall decreasing downstream trend from the maximum where the river exits from the mountain range to zero such a trend has been attributed to the progressive lowering of the river gradient that was caused by the adjusted ratio of sediment input versus water discharge induced by climate change superimposing on the decreasing downstream trend an obvious step can also easily be observed onto the profile of channel incision of each river downstream of which channel incision is significantly less the step occurs near the thrust fault controlling growth of the outermost anticline through which each river cuts thereby implying the key role of local rock uplift in forming the river incision step the former observation implies that at the same timescale more river incision at the exit from the mountain range does not necessarily mean stronger climatic forcing of incision there we thus propose that in a foreland setting it should be the temporal pattern of river incision rather than its spatial variation that is helpful for unraveling the change in the forcing factor of downcutting

geomorphic constraints on landscape sensitivity to climate in tectonically active areas abstract the geomorphology of fluvial landscapes is known to record information about uplift rate spatial patterns of faulting and tectonic history data is far less available when addressing the sensitivity of common geomorphological metrics such as channel steepness to climatic boundary conditions we test the relationship between channel steepness and precipitation rate by measuring a large number of channels in different mountainous areas these regions exhibit a tenfold variation in precipitation rate between them 100 1000 mm y 1 but have similar uplift rates allowing the tectonic variable to be controlled by accounting for the orographic coupling of rainfall with uplifted topography we find that channel steepness is significantly suppressed by higher precipitation rates in a measurable way that conforms to simple stream power erosion laws and empirical constraints on their parameters we demonstrate this using modern and estimated glacial precipitation rates and climate emerges as an important quantifiable control on channel geometry these findings help to explain why highly variable measurements of channel steepness are reported from different locations and provide important empirical constraints on how climate shapes tectonically active landscapes

tectonics climate and mountain topography 1 by regressing simple independent variables that describe climate and tectonic processes against measures of topography and relief of 69 mountain ranges worldwide we quantify the relative importance of these processes in shaping observed landscapes climate variables include latitude as a surrogate for mean annual temperature and insolation but most importantly for the likelihood of glaciation and mean annual precipitation to quantify tectonics we use shortening rates across each range as a measure of topography we use mean and maximum elevations and relief calculated over different length scales we show that the combination of climate negative correlation and tectonics positive correlation explain substantial fractions 25 but 50 of mean and maximum elevations of mountain ranges but that shortening rates account for smaller portions 25 of the variance in most measures of topography and relief i e with low correlations and large scatter relief is insensitive to mean annual precipitation but does depend on latitude especially for relief calculated over small 1 km length scales which we infer to reflect the importance of glacial erosion larger scale averaged over length scales of 10 km relief however correlates positively with tectonic shortening rate moreover the ratio between small scale and large scale relief as well as the relative relief the relief normalized by the mean elevation of the region varies most strongly with latitude strong positive correlation therefore the location of a mountain range on earth with its corresponding climatic conditions not just tectonic forcing appears to be a key factor in determining its shape and size in any case the combination of tectonics and climate as quantified here can account for approximately half of the variance in these measures of topography the failure of present day shortening rates to account for more than 25 of most measures of relief raises the question is active tectonics overrated in attempts to account for present day relief and exhumation rates of high terrain

seasonal precipitation gradients and their impact on fluvial sediment flux in the northwest himalaya abstract precipitation in the form of rain and snowfall throughout the himalaya controls river discharge and erosional processes and thus has a first order control on the fluvial sediment flux here we analyze daily precipitation data 1998 2007 of 80 weather stations from the northwestern himalaya in order to decipher temporal and spatial moisture gradients in addition suspended sediment data allow assessment of the impact of precipitation on the fluvial sediment flux for a 103 km2 catchment baspa we find that weather stations located at the mountain front receive 80 of annual precipitation during summer may oct whereas stations in the orogenic interior i e leeward of the orographic barrier receive 60 of annual precipitation during winter nov apr in both regions 4 6 rainstorm days account for 40 of the summer budgets while rainstorm magnitude frequency relations derived from 40 year precipitation time series indicate a higher storm variability in the interior than in the frontal region this high variability in maximum annual rainstorm days in the orogenic interior is reflected by a high variability in extreme suspended sediment events in the baspa valley which strongly affect annual erosion yields the two most prominent 5 day long erosional events account for 50 of the total 5 year suspended sediment flux and coincide with synoptic scale monsoonal rainstorms this emphasizes the erosional impact of the indian summer monsoon as the main driving force for erosion processes in the orogenic interior despite more precipitation falling during the winter season

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

small valley glaciers and the effectiveness of the glacial buzzsaw in the northern basin and range usa the glacial buzzsaw hypothesis suggests that efficient erosion limits topographic elevations in extensively glaciated orogens studies to date have largely focussed on regions where large glaciers tens of kilometres long have been active in light of recent studies emphasising the importance of lateral glacial erosion in lowering peaks and ridgelines we examine the effectiveness of small glaciers in limiting topography under both relatively slow and rapid rock uplift conditions four ranges in the northern basin and range idaho montana and wyoming usa were chosen for this analysis estimates of maximum pleistocene slip rates along normal faults bounding the beaverhead bitterroot mountains similar to 0 14 mm y 1 lemhi range similar to 0 3 mm y 1 and lost river range similar to 0 3 mm y 1 are an order of magnitude lower than those on the teton fault similar to 2 mm y 1 we compare the distribution of glacial erosion estimated from cirque floor elevations and last glacial maximum lgm equilibrium line altitude ela reconstructions and fault slip rate with three metrics of topography in each range the along strike maximum elevation swath profile hypsometry and slope elevation profiles in the slowly uplifting beaverhead bitterroot mountains and lemhi and lost river ranges trends in maximum elevation parallel elas independent of variations in fault slip rate maximum elevations are offset similar to 500 m from lgm elas in the lost river range lemhi range and northern beaverhead bitterroot mountains and by similar to 350 m in the southern beaverhead bitterroot mountains where glacial extents were less the offset between maximum topography and mean quaternary elas inferred from cirque floor elevations is similar to 350 m in the lost river and lemhi ranges and 200 250 m in the beaverhead bitterroot mountains additionally slope elevation profiles are flattened and hypsometry profiles show a peak in surface areas close to the ela in the lemhi range and beaverhead bitterroot mountains suggesting that small glaciers efficiently limit topography the situation in the lost river range is less clear as a glacial signature is not apparent in either slope elevation profiles or the hypsometry in the rapidly uplifting teton range the distribution of elas appears superficially to correspond to maximum topography hypsometry and slope elevations profiles with regression lines on maximum elevations offset by similar to 700 and similar to 350 m from the lgm and mean quaternary ela respectively however grand teton and mt moran represent high elevation teflon peaks that appear impervious to glacial erosion formed in the hard crystalline bedrock at the core of the range glacier size and drainage density rock uplift rate and bedrock lithology are all important considerations when assessing the ability of glaciers to limit mountain range topography in the northern basin and range it is only under exceptional circumstances in the teton range that small glaciers appear to be incapable of imposing a fully efficient glacial buzzsaw emphasising that high peaks represent an important caveat to the glacial buzzsaw hypothesis c 2008 elsevier b v all rights reserved

controls on the channel width of rivers implications for modeling fluvial incision of bedrock on the basis of the manning equation and basic mass conser vation principles we derive an expression for scaling the steady state width w of river channels as a function of discharge q channel slope s roughness n and width to depth ratio a w 5 a a1 2 2 3 3 8 q 3 8 s 23 16 n 3 8 we propose that channel width to depth ratio in addition to roughness is a function of the material in which the channel is developed and that where a river is con fined to a given material width to depth ratio and roughness can be assumed constant given these simplifications the expression emulates traditional width discharge relationships for rivers incis ing bedrock with uniformly concave fluvial long profiles more sig nificantly this relationship describes river width trends in terrain with spatially nonuniform rock uplift rates where conventional discharge based width scaling laws are inadequate we suggest that much of observed channel width variability in river channels confined by bedrock is a simple consequence of the tendency for water to flow faster in steeper reaches and therefore occupy smaller channel cross sections we demonstrate that using conventional scaling relationships for channel width can result in underestima tion of stream power variability in channels incising bedrock and that our model improves estimates of spatial patterns of bedrock incision rates

continental erosion and large scale relief a worldwide investigation of continental erosion is carried out by the study of large drainage basins on the basis of hydrological data environmental factors and basin relief distribution inside each basin mean geochemical and mechanical denudation rates are defined a multicorrelation analysis shows that the mechanical denudation rates ds are uncorrelated with environmental factors and correlated with mean basin elevation h while chemical denudation rates dd are insensitive to relief but correlated with mean annual precipitation furthermore two linear relationships between h and ds are detected 1 ds m 10 yr 419 10 6 h m 0 245 with v explained variance 95 1 this law concerns basins related to orogenies younger than 250 ma the negative intercept is interpreted as a continental sedimentation rate of 245 m m y an alternative model in which one invokes a critical elevation separating erosion from sedimentation is equally successful and leads to lower sedimentation rates 60 110 m m y for both models one derives from the slope of the adjustments erosion time constants on the order of 2 5 m y 2 ds m 10 yr 61 10 6 h m with v 86 5 this law concerns basins related to older orogenies the null intercept suggests the lack of continental storage because of the more important dispersion of the data the erosion time constant is calculated separately for each basin it ranges from 15 to 360 m y the tectonic implications of these results are discussed in particular the short time constant 2 5 m y agrees with orogenic uplift rates on the order of 1 mm yr observed in active mountain chains

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

bedrock channel adjustment to tectonic forcing implications for predicting river incision rates we present detailed data of channel morphology for a river undergoing a transient response to active normal faulting where excellent constraints exist on spatial and temporal variations in fault slip rates we show that traditional hydraulic scaling laws break down in this situation and that channel widths become decoupled from drainage area upstream of the fault unit stream powers are 4 times higher than those predicted by current scaling paradigms and imply that incision rates for rivers responding to active tectonics may be significantly higher than those heretofore modeled the loss of hydraulic scaling cannot be explained by increasing channel roughness and is an intrinsic response to tectonic forcing we show that channel aspect ratio is a strongly nonlinear function of local slope and demonstrate that fault induced adjustment of channel geometries has reset hillslope gradients the results give new insight into how rivers maintain their course in the face of tectonic uplift and illustrate the first order control the fluvial system exerts on the locus and magnitude of sediment supply to basins

the effect of topography latitude and lithology on rock glacier distribution in the lemhi range central idaho usa abstract statistical analysis of rock glaciers in the lemhi range demonstrates that their development and preservation is controlled primarily by annual insolation and lithology we inspected 171 alpine valleys in the lemhi range using optical remote sensing techniques digital topographic analysis and field examination in those valleys we identified 48 rock glaciers and examined them for lichen cover evidence of ice presence specific evidence of movement and distinctive morphological features in addition to recording the presence or absence of a rock glacier in each alpine valley existing rock glaciers were classified according to their morphology factors such as topographic shading lithology relief aspect and elevation determine the development and preservation of rock glaciers analysis of these factors in the lemhi range shows that elevation 2600 m a north facing aspect 300 60 and multivariate statistical analysis of controlling parameters demonstrates that annual insolation and latitude influence rock glacier occurrence most strongly whereas duration of insolation is a logical controlling factor latitude is more enigmatic additional statistical analysis indicates that the latitude factor is likely a reflection of lithologic changes with latitude along the range lithology may affect rock glacier distribution through its effects on hydrology or air ventilation moreover statistical analysis shows that rock glacier occurrence correlates with protalus lobe occurrence suggesting that protalus lobes play a role in the genesis of rock glaciers in the lemhi range separate analysis of the classification systems shows that each morphologic class inferred to correlate with rock glacier activity is statistically significant and distinguishable from other classes in addition to the effect of insolation statistical analysis of the classification system also shows that latitude influences distribution of existing rock glacier classes independent of lithology

geomorphic constraints on uplift history in the aspromonte massif southern italy abstract the landscape morphology of the aspromonte massif southern italy shows hanging low relief surfaces that correlate with uplifted landsurfaces which are preserved all around the massif the drainage network has deeply incised the high standing low relief landscapes seen here as being the remnants of phases of relief smoothing prior to strong uplift that has affected the area since the middle pleistocene gis aided estimation of the rock volumes eroded since the late early pleistocene indicate high variability in denudation rates between the gently rolling landscapes and the river valleys in this framework longitudinal river profiles are examined for 42 river channels to constrain multiple non equilibrium conditions and to reconstruct the long term uplift history of the massif most profiles consist of three four segments separated by knickpoints and suggest a complex incision pattern longitudinal profiles reveal two upper low gradient channel segments a zone of steep channels further down the low relief landsurface margin and a very steep lower channel segment particularly in the western quadrant upper channel segments correspond to the relict landscape rlandscape a high standing landsurface on top of the massif and the hanging landscape hlandscape a landsurface surrounding the rlandscape respectively steeper middle and lower segments are the result of two phase river incision that is linked to changes in regional uplift rates and subordinately to rock strength properties indeed analysis of river longitudinal profiles could indicate initially relatively slow aspromonte uplift during the early pleistocene and then pulses of rapid uplift during the middle late pleistocene multi segment river longitudinal profiles are therefore evidence of the transient landscapes of aspromonte in response to pulsed massif uplift

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

quaternary alluvial fan development climate and morphologic dating of fault scarps in laguna salada baja california mexico article i nfo late quaternary slip across the canada david detachment has produced an extensive array of quaternary scarps cutting alluvial fans along nearly the entire length 60 km of the range bounding detachment eight regional alluvial fan surfaces q1 youngest to q8 oldest are defined and mapped along the entire sierra el mayor range front terrestrial cosmogenic nuclide 10 be concentrations from individual boulders on alluvial fan surfaces q4 and q7 yield surface exposure ages of 15 5 2 2 ka and 204 11 ka respectively formation of the fans is probably tectonic but their evolution is strongly moderated by climate with surfaces developing as the hydrological conditions have changed in response to climate change on milankovitch timescales systematic mapping reveals that the fault scarp array along active range bounding faults in sierras cucapa and el mayor can be divided into individual rupture zones based on cross cutting relationships with alluvial fans quantitative morphological ages of the laguna salada fault scarps derived from linear diffusive degradation modeling are consistent with the age of the scarps based on cross cutting relationships the weighted means of the maximum mass diffusivity constant for all scarps with offsets b 4 m is 0 051 and 0 066 m 2 ka for the infinite and finite slope solutions of the diffusion equation respectively this estimate is approximately an order of magnitude smaller than the lowest diffusivity constants documented in other regions and it probably reflects the extreme aridity and other microclimatic conditions that characterize the eastern margin of laguna salada

glacial interglacial climate changes recorded by debris flow fan deposits owens valley california abstract it is hotly debated whether and how climate changes are recorded by terrestrial stratigraphy basin sediments produced by catchment alluvial fan systems may record past climate over a variety of timescales and could offer unique information about how climate controls sedimentation unfortunately there are fundamental uncertainties about how climatic variables such as rainfall and temperature translate into sedimentological signals here we examine 35 debris flow fan surfaces in owens valley california that record deposition throughout the past 125 000 years during which climate has varied significantly we show that the last full glacial interglacial cycle is recorded with high fidelity by the grain size distributions of the debris flow deposits these flows transported finer sediment during the cooler glacial climate and became systematically coarser grained as the climate warmed and dried we explore the physical mechanisms that might explain this signal and rule out changes in sediment supply through time instead we propose that grain size records past changes in storm intensity which is responsible for debris flow initiation in this area and is decoupled from average rainfall rates this is supported by an exponential clausius clapeyron style scaling between grain size and temperature and also reconciles with climate dynamics and the initiation of debris flows the fact that these alluvial fans exhibit a strong sustained sensitivity to orbital climate changes sheds new light on how eroding landscapes and their sedimentary products respond to climatic forcing finally our findings highlight the importance of threshold controlled events such as storms and debris flows in driving erosion and sedimentation at the earth s surface in response to climate change

structural and geomorphological constraints on active normal faulting and landscape evolution in calabria italy calabria is one of the fastest uplifting and most seismically active regions in the mediterranean yet the time averaged c 10 6 years rates of normal faulting remain poorly constrained here we use digital elevation model analysis geological cross sections and a compilation of published data to quantify systematically along strike the fault throws and time averaged throw rates of the serre cittanova armo east crati and west crati faults we show that regional uplift has uplifted both their hanging wall and footwall blocks by c 200 400 m and the aspromonte massif by up to c 1150 1300 m we find that these faults have throws between c 640 and 1430 m and throw rates between c 0 6 and 1 4 mm a 1 their footwall ranges have variable proportions of inherited relief up to c 300 800 m the channels draining these ranges reflect the active normal faulting and relief in their steepness indices becoming c 5 8 m 0 9 steeper for each 0 1 mm a 1 throw rate increment and each 100 m relief increase finally the presence of knickpoints suggests that these channels are transiently responding to changes in relative base level which could be due to fault linkage or regional strain rate increases for the southern calabrian faults and to regional uplift acceleration in the case of the crati faults supplementary material topographic profiles of the marine terraces and long profiles of rivers are available at https doi org 10 6084 m9 figshare c 3689464

vegetation modulated landscape evolution effects of vegetation on landscape processes drainage density and topography 1 topography acts as a template for numerous landscape processes that include hydrologic ecologic and biologic phenomena these processes not only interact with each other but also contribute to shaping the landscape as they influence geomorphic processes we have investigated the effects of vegetation on thresholds for channel initiation and landform evolution using both analytical and numerical approaches vegetation is assumed to form a uniform ground cover runoff erosion is modeled based on a power function of excess shear stress in which shear stress efficiency is inversely proportional to vegetation cover this approach is validated using data plant effect on slope stability is represented by additional cohesion provided by plant roots vegetation cover is assumed to reduce sediment transport rates due to physical creep processes rainsplash dry ravel and expansion and contraction of sediments according to a negative exponential relationship vegetation grows as a function of both available cover and unoccupied space by plants and is killed by geomorphic disturbances runoff erosion and landsliding and wildfires analytical results suggest that in an equilibrium basin with a fixed vegetation cover plants may cause a transition in the dominant erosion process at the channel head a runoff erosion dominated landscape under none or poor vegetation cover may become landslide dominated under a denser vegetation cover the sign of the predicted relationship between drainage density and vegetation cover depends on the relative influence of vegetation on different erosion phenomena with model parameter values representative of the oregon coast range ocr numerical experiments conducted using the channel hillslope integrated landscape development child model confirm the findings based on the analytical theory a highly dissected fluvial landscape emerges when surface is assumed bare when vegetation cover is modeled landscape relief increases resulting in hollow erosion dominated by landsliding interestingly our simulations underscore the importance of vegetation disturbances by geomorphic events and wildfires on the landscape structure simulated landscapes resemble real world catchments in the ocr when such disturbances are considered

morphologic evolution of the central andes of peru in this paper we analyze the morphology of the andes of peru and its evolution based on the geometry of river channels their bedrock profiles stream gradient indices and the relation between thrust faults and morphology the rivers of the pacific basin incised mesozoic sediments of the maranon thrust belt cenozoic volcanics and the granitic rocks of the coastal batholith they are mainly bedrock channels with convex upward shapes and show signs of active ongoing incision the changes in lithology do not correlate with breaks in slope of the channels or knick points such that the high gradient indices k with values between 2 000 3 000 and higher than 3 000 suggest that incision is controlled by tectonic activity our analysis reveals that many of the ranges of the western cordillera were uplifted to the actual elevations where peaks reach to 6 000 m above sea level by thrusting along steeply dipping faults we correlate this uplift with the quechua phase of neogene age documented for the subandean thrust belt the rivers of the amazonas basin have steep slopes and high gradient indices of 2 000 3 000 and locally more than 3 000 in those segments where the rivers flow over the crystalline basement of the eastern cordillera affected by vertical faulting gradient indices decrease to 1 000 2 000 within the east vergent thrust belt of the subandean zone here a correlation between breaks in river channel slopes and location of thrust faults can be established suggesting that the young quechua phase thrust faults of the subandean thrust belt which involve neogene sediments influenced the channel geometry in the eastern lowlands these rivers become meandering and flow parallel to anticlines that formed in the hanging wall of quechua phase thrust faults suggesting that the river courses were actively displaced outward into the foreland

modeling topographic and climatic control of east west asymmetry in sierra nevada glacier length during the last glacial maximum 1 glaciers draining westward from the sierra nevada divide california during the last glacial maximum lgm were 7 times longer than east draining glaciers we address the degree to which this difference may be attributed to the topographic asymmetry of the west tilted sierran block and the climate asymmetry resulting from orographic modification of pacific ocean storms we simulate kilometer scale glaciers within the 50 50 km kings canyon region of the southern sierra by employing a two dimensional numerical model that is driven by simple spatially variable climates and treats ice transport by deformation sliding and avalanching in numerical experiments we match simulated termini to lgm moraine positions to constrain the parameters of different climate scenarios the 38 km long lgm glacier in kings canyon was reproduced by a climate specified by an equilibrium line altitude ela of 3170 m a mass balance gradient of 0 01 m yr m and a maximum positive balance of 2 m yr this climate generates much shorter average 6 km long east draining glaciers that however overshoot the lgm moraines by 1 km roughly 97 of the e w difference in glacier lengths can therefore be attributed to topographic asymmetry alone a second experiment suggesting a 120 m higher ela of 3290 m east of the divide can explain the shorter east draining glaciers an experiment in which orographic precipitation is explicitly simulated and melt is prescribed using a positive degree day algorithm matches both kings canyon and the average east draining glacier length with an lgm climate that was 5 6 c cooler and 2 times wetter than the modern sierra nevada

constraints on the long term colluvial erosion law by analyzing slope area relationships at various tectonic uplift rates in the siwaliks hills nepal 1 the large database of topographic form and uplift rates that exists for the siwaliks hills central nepal makes possible a thorough analysis of the long term erosion model the study especially focuses on drainage areas larger than 5 10 3 km2 fixed by the database resolution and smaller than 1 km2 above which a fluvial signature is recorded this area range corresponds to colluvial valleys in which the dominant erosion process is likely debris flow we evaluate a phenomenological model wherein erosion is considered to depend on drainage area and slope we test this model by assuming that the uplift rate is in approximate equilibrium with erosion the stream power law model formulated by analogy to river incision and transport problems is found to be consistent with data since an inverse power law relationship between slope and drainage area is systematically observed between 7 10 3 and 1 km2 with little variability on the exponent 0 24 thanks to the range of uplift rates we obtain constraints on the slope dependency of erosion law which appears linear and which predicts a significant erosion threshold the linear dependence on slope in the debris flow zone is consistent with findings by kirby and whipple 2001 in the fluvial downstream zone and with the linear relationship between local relief and uplift rate documented by hurtrez et al 1999 the transition between this colluvial channel regime and the fluvial regime appears quite sharp in contrast with recent studies but the latter regime is not sufficiently documented to derive definite conclusions

the qs problem sediment volumetric balance of proximal foreland basin systems although the stratigraphy of sedimentary basins depends on the balance between the magnitude and grain size characteristics of the sediment supply qs and the spatial distribution of tectonic subsidence generating accommodation x qs is problematical to measure in present day sediment routing systems and formidably difficult to predict in their ancient counterparts this challenge was tackled by treating the sediment discharge from the outlet of mountain catchments as the result of incision by a drainage network with a bulk diffusivity based on the length over which the mean annual rainfall is concentrated the size relief and slope of palaeo catchments acting as feeders for sediment routing systems are used to run simulations of sediment discharge and bulk diffusivity for a range of annual precipitation values a wide range of observable geological phenomena can be used to converge on the most likely solutions for qs including depositional volumes in the basin and bedrock thermochronology and detrital cosmogenic nuclide dating to constrain catchment erosion rates modelled sediment discharges can be checked with estimates derived from global regressions the sediment efflux of mountain catchments serves as a boundary condition for down system sediment transport and deposition variations in the volumetric ratio of sediment supply to available accommodation qs x determines patterns of transverse versus longitudinal axial sediment dispersal the volumetric ratio may change as a result of variations in climatic parameters tectonic uplift rate and catchment expansion an abrupt climate change to higher precipitation values promotes higher qs x but transient landscape response causes a return to values close to the baseline generating a distinctive down system extension of a gravel spike catchment expansion has a similar but more prolonged effect on gravel progradation in contrast a change in tectonic forcing such as an increase in slip rate on a border fault causes little change in qs x because increased subsidence compensates for the increased sediment supply studies of mid eocene oligocene sediment routing systems in the south central pyrenees allow the discrimination of different types of proximal wedge top sedimentary systems on the basis of the volumetric ratio of qs to accommodation x i small steep local fan systems in tectonically ponded underfilled basins supplied by low sediment discharges ii tectonically guided long range axial systems fed by large sediment discharges from widely spaced palaeovalleys and iii large shallow sloping transverse megafans burying underlying defunct or active tectonic structures supplied by high to very high sediment discharges understanding the role of variations in qs helps to explain the syntectonic evolution of proximal foreland basin systems the oligocene miocene north alpine foreland basin switzerland is qualitatively identified as a high qs example the miocene recent northern apennines of italy as a low qs example and the eocene oligocene southern pyrenees of spain as intermediate in character

variability in erosion rates related to the state of landscape transience in the semi arid chilean andes we quantify erosion rates in the higher sectors of the huasco valley in the main cordillera of the semi arid andes of chile using elevation differences between three successive geomorphic markers pediments and paleo valleys and the present day valley available ar ar ages of neogene pediments are used to estimate mean erosion rates for the three periods 16 to 13 my 13 to 8 my and following 8 my the landscape of the huasco valley is in a transient state as indicated by well preserved pediment surfaces in interfluves valleys deeply incised by fluvial and glacial erosion and scarped head valleys that represent the current knickzones higher erosion rates 45 75 m my are calculated for the more recent period 8 my during which deep incision developed compared to previous periods 6 31 m my quantitative data indicate that glaciers had a much higher erosional capability than fluvial activity in the higher sectors of the main cordillera comparison with erosion rates calculated in other drainage basins of the chilean andes suggests that the variability of erosion rates depends on the landscape s transient erosive state the landscape s geomorphologic response to the uplift of the main cordillera results in the retreat of a knickzone for which retreat velocity depends on precipitation rate pattern and glacial erosion intensity copyright 2011 john wiley sons ltd

andean coastal uplift and active tectonics in southern peru 10be surface exposure dating of differentially uplifted marine terrace sequences san juan de marcona 15 4 s article i nfo along the san juan de marcona bay of southern peru two spectacular sequences of preserved marine terraces record net quaternary uplift previous geomorphic analysis of these paleo shorelines has revealed evidence of upper plate deformation and regional uplift however in the absence of a robust absolute dating method these studies contain substantial uncertainties concerning the numerical dating of these marine markers and thus the corresponding calculated surface uplift rates however field mapping surveying the neotectonic features and 10 be dating of abraded surfaces contained within two sequences of marine terraces along this margin should allow for the robust calculation of pleistocene uplift rates the san juan de marcona bay lies on the southern flank of the subducting and south migrating aseismic nazca ridge where the maximum rates of coastal uplift are expected in this locality we measure high uplift rates ranging from 0 4 m ka to 0 9 m ka during the pleistocene margin parallel normal faults displace several marine terraces and influence the development of bays thereby contributing to the configuration of paleo and present day coastlines the faults have relatively low slip rates b0 1 m ka over 400 ka and have been inactive for the last 80 ka the presence and activity of these normal faults can be directly linked to subduction zone processes with the release and accommodation of short term coseismic compression during megathrust subduction zone events in contrast the regional permanent uplift is probably controlled by post seismic and or interseismic strain accumulation over longer time scales due to inelastic behavior of the upper plate since at least the latest pliocene the san juan de marcona area has experienced long term regional tectonic uplift that has increased since about 800 ka due to the southward migration of the subducting nazca ridge based on migration velocity and geometry of the ridge the influence of the nazca ridge on the uplift of the forearc should account for 0 4 m ka within 145 km south of the ridge axis hence most of the post 400 ka mean uplift rate of the san juan de marcona area could be explained by the nazca ridge subduction

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

natural experiments in landscape evolution a natural experiment in landscape evolution is a case study of landform development in which only one element varies significantly and for which the driving forces initial conditions and or boundary conditions are well constrained natural experiments provide a means of testing landscape evolution theory on the large space and time scales to which that theory applies natural experiments can involve either steady or transient conditions cases with steady conditions allow one to test predictions about the relationships among topography erosion rates and various attributes related to climate and material properties transient cases are valuable for distinguishing between models whose predictions might be similar and therefore indistinguishable under steady conditions essential ingredients of a natural experiment include minimal variation in all but one factor good constraints on timing and or rates well characterized processes and high quality topographic data other useful ingredients include information about intermediate topographic states such as a former valley profile revealed by strath terraces and knowledge of the time history of erosion rates in order to deepen our understanding of the physics and chemistry of long term landscape evolution there is a pressing need to identify natural experiments and develop the necessary databases to take advantage of them copyright 2009 john wiley sons ltd

climatic modulation of timing of systems tract development with respect to sea level changes middle pleistocene of crotone calabria southern italy abstract climate change has traditionally played a secondary role in the literature behind eustasy and tectonics with eustasy regarded as the main controlling factor in development of sedimentary sequences here we emphasize the role of the interaction of climate modulated sediment supply and sea level change particularly its potential impact on sequence development we discuss a case history from the lower middle pleistocene of the highly subsiding valle di manche shelf area crotone basin calabria southern italy where a stack of cyclothems spanning from late marine isotope stage mis 22 to full mis 18 preserves a full record of eustatic cycles glacials included tectonics certainly played a critical role in the creation of local accommodation ultimately controlling the preservation of an almost complete sedimentary record however its role as a factor controlling the sediment flux on milankovian scale can be ruled out direct comparisons between data concerning 18o pollen and physical stratigraphy demonstrate that climate induced changes in sediment load caused significant deviations from the predicted timing and magnitude of the responses to sea level changes in the traditional sequence model a phase lag occurred in the timing of systems tracts leading to a significant delay of one quarter of a sea level cycle specifically climate driven sediment discharge during sea level rise triggered progradation of shelf margin wedges which should thus be considered lowstand in their architecture and transgressive in their timing this was generated by a shift toward drier conditions leading to extensive deforestation and consequent lowering of the threshold for slope erosion and mass wasting processes in the source area due to the reduced extent of the transfer zone sedimentary signals were conveyed rapidly from source to sink with little apparent attenuation suggesting that the milankovitch scale climate changes can lead to rapid source to sink responses on tectonically active margins fed by high gradient short headed streams the studied case history demonstrates that the impact of milankovitch scale climatic forcing on sediment supply in an icehouse world can be more supluential than sediment redistribution due to corresponding sea level fluctuations these findings emphasize that a reconstruction of the timing of systems tract development with respect to sea level changes based on a sequence stratigraphic approach may be misleading whenever independent chronological and climatic constraints are not available

special climatological conditions in the deserts of sinai and the negev during the latest pleistocene abstract results of hydrological and geological investigations carried out during the last ten years in the deserts of the sinai and the negev indicate that unique climatological and hydrological conditions prevailed between ca 100 000 and ca 10 000 yr b p the uniqueness was expressed by the following characteristics 1 1 higher precipitation and recharge rates caused the nubian sandstone aquifers to be filled up through the outcrops in central sinai and to overflow through big springs emerging along the faults of the syrian african rift system this water is of special isotopic composition namely depleted in 18o and deuterium and with a lower excess of the latter 2 2 dust laden rainstorms prevailed probably mainly during the autumn season causing the deposition of thick layers of loess the quantity of rain during the humid periods was double that of the present 3 3 the drainage system of many western and northern wadis of sinai as well as the negev could not drain out all the silt loaded water during the rainy season and shallow lakes and marshes extended in many wadis during this season 4 4 the floods and the springs flowing into the dead sea rift valley contributed to the lisan lake which was 200 m above the level of the contemporary dead sea

influence of precipitation phase on the form of mountain ranges observations of precipitation fall speeds and precipitation patterns suggest that precipitation phase rain versus snow is a significant control on the relationship between precipitation patterns and topography due to the potential for increased downwind advection of snow relative to rain a coupled model of orographic precipitation and surface erosion shows that for a range of climate variables steady state precipitation patterns vary from nearly uniform and maximizing over the highest topography to highly spatially variable closely coupled to topography and reaching a maximum on low slopes precipitation patterns are a first order control on modeled range scale and ridge valley scale relief channel concavity and the position of the drainage divide an association between cool climates spatially uniform precipitation and efficient erosion of high topography is indicated the importance of precipitation phase to the evolution of precipitation patterns and topography further demonstrates the fundamental importance of the coupled climate erosion and tectonic system in the evolution of mountain topography

transformation of tectonic and climatic signals from source to sedimentary archive sedimentary rocks reflect past tectonic and climatic events numerical simulations suggest that changes in precipitation and in the rate of tectonic uplift affect the grain size and the distribution of sediments deposited downstream

early holocene juniper woodland and chaparral taxa in the central baja california peninsula mexico abstract a packrat midden located in the sierra san francisco baja california sur mexico dating to ca 10 200 14c yr b p contains remains of california juniper juniperus californica and other taxa now associated with southern california chaparral california juniper does not occur in the sierra san francisco today although relict populations of a few chaparral taxa still occur at higher elevations this midden record documents the early holocene occurrence of baja california coniferous woodland and chaparral vegetation far south of its present distribution or its previously known extent from other fossil records based on modern climatic tolerances of california juniper and other taxa central baja california experienced a mild mediterranean type climate at least 5 6 c cooler than the climate of today with at least twice the winter precipitation the region now receives

on the importance of higher order ice dynamics for glacial landscape evolution abstract alpine glacial landforms such as u shaped troughs hanging valleys and cirques have been linked to the meltwater modulated sliding motion of glaciers several of these alpine landforms are associated with characteristic length scales for width and spacing indicating that the viscosity of ice exerts a first order control on the processes responsible for their formation here we present the results of three dimensional computational experiments focusing on the influence of higher order ice dynamical effects such as horizontal stress gradients on long term glacial landscape evolution some of the experiments presented have highly simplified bed conditions other experiments use topography from an existing mountain range as basis for simulating glacial erosion the experiments demonstrate how gradients in horizontal stress play a primary role in scaling the bed shear stress of glaciers we also demonstrate how higher order ice dynamics may influence the feedback between glacial sliding and erosion hereby providing important stabilization mechanisms that prevent runaway effects associated with the steepening of longitudinal profiles and the formation of overdeepenings

erosion rates and mechanisms of knickzone retreat inferred from 10be measured across strong climate gradients on the northern and central andes western escarpment escarpment edge deep gorges and distinct knickzones in river profiles characterize the landscape on the western escarpment of the andes between 5 s and 18 s northern peru to northern chile th

expression of active tectonics in erosional landscapes understanding the manner and degree to which topography in active mountain ranges reflects deformation of the earth s surface remains a first order goal of tectonic geomorphology a substantial body of research in the past decade demonstrates that incising channel systems play a central role in setting relationships among topographic relief differential rock uplift rate and climatically modulated erosional efficiency this review provides an introduction to the analysis and interpretation of channel profiles in erosional mountain ranges we show that existing data support theoretical expectations of positive monotonic relationships between channel steepness index a measure of channel gradient normalized for downstream increases in drainage area and erosion rate at equilibrium and that the transient response to perturbations away from equilibrium engenders specific spatial patterns in channel profiles that can be used to infer aspects of the forcing these aspects of channel behavior lay the foundation for a series of case studies that we use to illustrate how focused quantitative analysis of channel morphology can provide insight into the spatial and temporal dynamics of active deformation although the complexities of river response to climate lithology and uplift patterns mean that multiple interpretations of topographic data alone will always possible we show that application of stream profile analysis can be a powerful reconnaissance tool with which to interrogate the rates and patterns of deformation in active mountain belts

new constraints on sediment flux dependent river incision implications for extracting tectonic signals from river profiles we present new field data from rivers draining across active normal faults that incise across the same lithology at the fault have been subjected to similar climatic regimes and tectonic settings and were perturbed by a well documented increase in fault slip rate ca 1 ma in spite of these similarities the rivers exhibit markedly different long profiles and patterns of catchment incision we use channel slope and hydraulic geometry data for each river to calculate bed shear stresses b and show that there is no simple relationship between peak b and the relative uplift rates across the faults u which differ by a factor of four the long term average sediment supply to each channel q s estimated from time averaged catchment erosion rates can explain the b versus u data if bedload modulates bedrock incision rate e in a strongly nonlinear way together these field data allow us for the first time to evaluate theoretical predictions of the role of sediment on river profile evolution and to quantify the magnitude of the effect in natural systems

modeling fluvial incision and transient landscape evolution influence of dynamic channel adjustment 1 channel geometry exerts a fundamental control on fluvial processes recent work has shown that bedrock channel width depends on a number of parameters including channel slope and is not solely a function of drainage area as is commonly assumed the present work represents the first attempt to investigate the consequences of dynamic gradient sensitive channel adjustment for drainage basin evolution we use the channel hillslope integrated landscape development child model to analyze the response of a catchment to a given tectonic perturbation using as a template the topography of a well documented catchment in the footwall of an active normal fault in the apennines italy that is known to be undergoing a transient response to tectonic forcing we show that the observed transient response can be reproduced to first order with a simple detachment limited fluvial incision law transient landscape is characterized by gentler gradients and a shorter response time when dynamic channel adjustment is allowed the differences in predicted channel geometry between the static case width dependent solely on upstream area and dynamic case width dependent on both drainage area and channel slope lead to contrasting landscape morphologies when integrated at the scale of a whole catchment particularly in presence of strong tilting and or pronounced slip rate acceleration our results emphasize the importance of channel width in controlling fluvial processes and landscape evolution they stress the need for using a dynamic hydraulic scaling law when modeling landscape evolution particularly when the relative uplift field is nonuniform

quantitative relationships between uplift and relief parameters for the southern alps new zealand as determined by fission track analysis the southern alps mountain chain new zealand has formed as a consequence of late cenozoic collision of the continental parts of the pacific and australia plates fission track analysis has yielded estimates of the amount age of initiation and rate of late cenozoic rock uplift for 82 surface samples taken from transects across the southern alps the mean surface summit and valley elevations in the vicinity of each of the rock sample sites have also been measured regression of the geomorphic variables on the uplift variables has been used to establish quantitative relationships between uplift and geomorphology there are strong and consistent linear associations between uplift and the elevations of the mean surface summits and valleys the preferred regression models have uniform slope but varying elevation response between transects substitution of space for time has allowed the evolution of landforms to be studied to the east of the main divide elevation and relief are proportional to and closely related to the age of initiation of rock uplift uplift age and the amount of rock uplift r2 0 8 mean surface uplift was delayed for 2 ma after the start of rock uplift a result of the stripping of a soft cover rock succession that prior to rock uplift overlaid the harder greywacke basement inter transect variations in regression response and x intercept are inferred therefore to reflect the variable preuplift thickness of cover rocks however the regular regression slope for the transects reflects the consistent nature of the interaction between uplift and the erodibility of greywacke basement uplift of the mean surface proceeded at 0 4 km km and 0 4 km ma of rock uplift while the rock uplift rate was 0 8 km ma summit elevations have increased at a rate of 0 6 km ma and valley elevations have increased at 0 2 km ma regression lines relating mean surface summit and valley elevations to rock uplift and uplift age diverge from common intercepts it is concluded therefore that the mountains east of the main divide have continued to increase in elevation and relief and change in form over time since the start of mean surface uplift mountain elevation has little relationship with late cenozoic mean rock uplift rates of 0 8 1 0 km ma or inferred contemporary rock uplift rates r2 0 3 in contrast to the west of the main divide elevation is shown to be closely related to rock uplift rate r2 0 3 in contrast to the west of the main divide elevation is shown to be closely related to rock uplift rate r2 0 8 transects with higher rock uplift rates support higher topography landforms are therefore in a stable equilibrium with rock uplift rate and the landscape contains no residual evidence of the total amount of rock uplift or the age of uplift lithological variation appears to have no relationship with elevation

spatiotemporal trends in erosion rates across a pronounced rainfall gradient examples from the southern central andes abstract the tectonic and climatic boundary conditions of the broken foreland and the orogen interior of the southern central andes of northwestern argentina cause strong contrasts in elevation rainfall and surface process regimes the climatic gradient in this region ranges from the wet windward eastern flanks 2 m yr rainfall to progressively drier western basins and ranges 0 1 m yr bordering the arid altiplano puna plateau in this study we analyze the impact of spatiotemporal climatic gradients on surface erosion first we present 41 new catchment mean erosion rates derived from cosmogenic nuclide inventories to document spatial erosion patterns second we re evaluate paleoclimatic records from the calchaquies basin 66 w 26 s a large intermontane basin bordered by high 4 5 km mountain ranges to demonstrate temporal variations in erosion rates associated with changing climatic boundary conditions during the late pleistocene and holocene three key observations in this region emphasize the importance of climatic parameters on the efficiency of surface processes in space and time 1 first order spatial patterns of erosion rates can be explained by a simple specific stream power ssp approach we explicitly account for discharge by routing high resolution satellite derived rainfall this is important as the steep climatic gradient results in a highly nonlinear relation between drainage area and discharge this relation indicates that erosion rates er scale with er ssp1 4 on cosmogenic nuclide time scales 2 we identify an intrinsic channel slope behavior in different climatic compartments channel slopes in dry areas 0 75 m yr with equal drainage areas thus compensating lower amounts of discharge with steeper slopes 3 erosion rates can vary by an order of magnitude between presently dry 0 05 mm yr and well defined late pleistocene humid 0 5 mm yr conditions within an intermontane basin overall we document a strong climatic impact on erosion rates and channel slopes we suggest that rainfall reaching areas with steeper channel slopes in the orogen interior during wetter climate periods results in intensified sediment mass transport which is primarily responsible for maintaining the balance between surface uplift erosion sediment routing and transient storage in the orogen

lake levels and climate for the last 30 000 years in the fucino area abruzzo central italy a review abstract lake fucino was in a closed basin that was drained in 1875 a review of published data as well as new geological and geomorphological studies are used to define changes in lake level over the last 30 000 years the changes are summarized as follows 1 a general rise of level between 33 000 and 18 000 20 000 yr b p 2 a general lowering between 18 000 20 000 and 7500 6500 yr b p 3 a rise between 6000 5000 yr b p 4 a lowering between 5000 2800 yr b p 5 a rise between 2800 2300 yr b p 6 lower between 2300 1800 yr b p 7 very low levels in the 16th century and 8 a rise during the 1750 1861 period of the so called little ice age lake level fluctuations are attributed to climatic variations in particular there is a clear link between fluctuations and changes in seasonal insolation produced by the orbital parameters of the earth precession of the equinoxes and obliquity of the ecliptic and average annual rainfall the fluctuations of lake levels do not seem to have been influenced significantly by tectonic movements affecting the fucino plain or by karst drainage pits present along the periphery

vegetation history along the eastern desert escarpment of the sierra san pedro martir baja california mexico abstract plant macrofossils from 38 packrat middens spanning the last 33 000 cal yr bp record vegetation between 650 and 900 m elevation along the eastern escarpment of the sierra san pedro martir northern baja california the middens span most of the holocene with a gap between 4600 and 1800 cal yr bp but coverage in the pleistocene is uneven with a larger hiatus between 23 100 and 14 400 cal yr bp the midden flora is relatively stable from the pleistocene to holocene exceptions include pinus californiarum juniperus californica and other chaparral elements that were most abundant 23 100 cal yr bp and declined after 14 400 cal yr bp despite being near the chaparral woodland desertscrub ecotone during glacial times the midden assemblages reflect none of the climatic reversals evident in the glacial or marine record and this is corroborated by a nearby semi continuous pollen stratigraphy from lake sediments regular appearance of c4 grasses and summer flowering annuals since 13 600 cal yr bp indicates occurrence of summer rainfall equivalent to modern jas average of 80 90 mm this casts doubt on the claim based on temperature proxies from marine sediments in the guaymas basin that monsoonal development in the northern gulf and arizona was delayed until after 6200 cal yr bp

seismic cycle and rheological effects on estimation of present day slip rates for the agua blanca and san miguel vallecitos faults northern baja california mexico 1 geodesy can be used to infer long term fault slip rates assuming a model for crust and upper mantle rheology we examine the sensitivity of fault slip rate estimates to assumed rheology for the agua blanca and san miguel vallecitos faults in northern baja california mexico part of the pacific north america plate boundary zone the agua blanca fault is seismically quiet but offset alluvial fans indicate young activity current seismicity is confined to the nearby san miguel vallecitos fault a small offset fault better aligned with plate motion gps measurements between 1993 and 1998 suggest that both faults are active with a combined slip rate of 4 8 mm yr 1 regardless of rheological model however slip rate estimates for the individual faults are sensitive to assumed rheology elastic half space models yield 2 3 mm yr 1 for the agua blanca fault and somewhat faster rates for the san miguel vallecitos fault 2 4 mm yr 1 with uncertainties of about 1 mm yr 1 models incorporating viscoelastic rheology and seismic cycle effects suggest a faster slip rate for the agua blanca fault 6 1 mm yr 1 and a slower rate for the san miguel vallecitos fault 1 1 mm yr 1 in better agreement with geological data but these rates are sensitive to assumed rheology numerical simulations with a finite element model suggest that for similar rheological and friction conditions slip on the san miguel vallecitos fault should be favored due to better alignment with plate motion long term faulting processes in the larger offset agua blanca fault may have lowered slip resistance allowing accommodation of motion despite misalignment with plate motion index terms 1206 geodesy and gravity crustal movements interplate 8155 1236 geodesy and gravity rheology of the lithosphere and mantle 8160 8107 tectonophysics continental neotectonics keywords fault slip rates and the seismic cycle northern baja california

uplift of the sierra san pedro martir baja california mexico the sierra san pedro martir of baja california is the highest of the peninsular ranges and has undergone rapid cenozoic uplift recent uplift can be explained as a result of flexural isostasy driven by a previously suppressed crustal root two dimensional modeling of topography and bouguer gravity data for present and preuplift conditions indicates that a flexural isostatic mechanism for uplift is consistent with the available topographic geologic and geophysical data the crustal root underlying the batholithic rocks of the sierra san pedro martir was probably emplaced during cretaceous magmatic arc activity however existence of a vast low relief and low elevation erosion surface mantled with deposits of fluvial systems originating far to the east suggests that by the early tertiary the plutons were unroofed and there was only subtle topographic expression of this crustal thickening we model the remnant crustal root as regionally compensated suppressed beneath a strengthened and continuous elastic plate and topographically expressed as a broad dome the regional distribution of tertiary sediments and preserved drainage patterns are geologic evidence of such doming since the late miocene there has been rapid uplift and apparent drainage reversal near the dome apex the present topography approximates the predicted isostatic response of a doubly broken elastic plate to the previously suppressed root several lines of evidence indicate that a major component of uplift of the sierra san pedro martir has occurred during the pliocene quaternary and that the crustal scale faulting that has allowed the range to rise rapidly toward local isostasy is related to full development of the san andreas gulf of california transform system

middle miocene extension in the gulf extensional province baja california evidence from the southern sierra juarez new geologic mapping structural studies and geochronology of miocene volcanic and sedimentary rocks in the southern sierra juarez baja california shed light on the extensional history of the gulf extensional province prior to sea floor spreading in the gulf of california the southern sierra juarez is underlain by lower middle miocene rocks including fluvial strata intermediate composition volcanic deposits basalt lava flows and cinder cones and dacite pyroclastic deposits and lavas that nonconformably overlie the cretaceous peninsular ranges batholith the 40 ar 39 ar geochronology indicates that basaltic rocks are 16 90 0 05 ma and dacite pyroclastic deposits are between 16 69 0 11 ma and 15 98 0 13 ma these strata were subsequently cut by two generations of faults first generation faults comprise a dominant set of north south striking west dipping normal faults a secondary set of north south striking east dipping normal faults and a lesser set of variably oriented strike slip faults all three fault sets are temporally and spatially related and were produced by east west extension the dominant west dipping faults which are antithetic to and oblique to the east dipping main gulf escarpment may have been a precursor or an early phase accommodation zone along the escarpment west dipping normal faults are cut by a 10 96 0 05 ma dacite hypabyssal intrusion thus bracketing the age of east west extension between 15 98 0 13 ma and 10 96 0 05 ma hence this faulting event clearly indicates a period of extension that predates the onset of oceanic rifting and even predates other dated miocene extension within baja california second generation faults which are comprised of east west striking strike slip faults that cut first generation faults and associated northwest striking northeast dipping normal faults may be related to early development of the transpeninsular strike slip province global plate reconstructions suggest that transtensional motion between the north american and pacific plates along the western margin of baja california began during middle miocene time coeval with east west extension in the southern sierra juarez this observation supports a hypothesis that middle miocene transtensional plate motion was partitioned into two components a strike slip component parallel to active faults along the western offshore margin of baja california and an extensional component normal to the margin but located in what is now the gulf extensional province hence the onset of extension within the circum gulf region was in response to plate boundary processes

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

uplift history of the sila massif southern italy deciphered from cosmogenic 10be erosion rates and river longitudinal profile analysis 1 the sila massif in the calabrian arc southern italy is a key site to study the response of a landscape to rock uplift here an uplift rate of 1 mm yr has imparted a deep imprint on the sila landscape recorded by a high standing low relief surface on top of the massif deeply incised fluvial valleys along its flanks and flights of marine terraces in the coastal belt in this framework we combined river longitudinal profile analysis with hillslope erosion rates calculated by 10be content in modern fluvial sediments to reconstruct the long term uplift history of the massif cosmogenic data show a large variation in erosion rates marking two main domains the samples collected in the high standing low relief surface atop sila provide low erosion rates from 0 09 0 01 to 0 13 0 01 mm yr conversely high values of erosion rate up to 0 92 0 08 mm yr characterize the incised fluvial valleys on the massif flanks the analyzed river profiles exhibit a wide range of shapes diverging from the commonly accepted equilibrium concave up form generally the studied river profiles show two or more frequently three concave up segments bounded by knickpoints and characterized by different values of concavity and steepness indices the wide variation in cosmogenic erosion rates and the non equilibrated river profiles indicate that the sila landscape is in a transient state of disequilibrium in response to a strong and unsteady uplift not yet counterbalanced by erosion

decoding temporal and spatial patterns of fault uplift using transient river long profiles we present detailed observations of rivers crossing active normal faults in the central apennines italy where excellent constraints exist on the temporal and spatial history of fault movement we demonstrate that rivers with drainage areas 10 km2 and crossing faults that have undergone an increase in throw rate within the last 1 my have significant long profile convexities in contrast channels that cross faults that have had a constant slip rate for 3 my have concave up profiles and have similar concavities and steepness indices to rivers that do not cross any active fault structures this trend is consistent across the central apennines and cannot be explained by appeal to lithology or regional base level change the data challenge the belief that active faulting must always be reflected in river profiles instead the long profile convexities are best explained as a transient response of the river system to a change in tectonic uplift rate moreover for these rivers we demonstrate that the height of the profile convexity as measured from the fault scales with the magnitude of the uplift rate increase on the fault and we establish that this relationship holds for throw rate variation along strike for the same fault segment as well as between faults these findings are shown to be consistent with predictions of channel response to changing uplift rate rates using a detachment limited fluvial erosion model and they illustrate that analysis of the magnitude of profile convexities has considerable predictive potential for extracting tectonic information we also demonstrate that the migration rate of the profile convexities varies from 1 5 10 mm y and is a function of the slip rate increase as well as the drainage area this is consistent with n 1 for the slope exponent in a classical detachment limited stream power erosion law but could potentially be explained by incorporating an erosion threshold or an explicit role for sediment in enhancing erosion rates finally we show that for rivers in extensional settings where the response times to tectonic perturbation are long in this case 1 my attempts to extract tectonic uplift rates from normalised steepness indices are likely to be flawed because topographic steady state has not yet been achieved

does climate change create distinctive patterns of landscape incision 1 incised fluvial systems are typically interpreted as recording geologically recent changes in either climate or tectonics however few diagnostic tools exist to evaluate whether particular incised landscapes primarily reflect climatic or tectonic perturbation here we summarize the results of a simple fluvial sediment transport model that allows us to contrast patterns of fluvial incision driven by changes in hydrology and sediment flux climate with those driven by changes in rock uplift patterns relative to sea level tectonics our modeling suggests that there may be diagnostic differences between the spatial and temporal patterns of incision caused by these different processes in particular incision driven by climate change is most commonly accompanied by downstream migrating waves of incision and decreases in channel gradient while under most circumstances incision driven by tectonics will be accompanied by upstream migrating incision and increases in channel gradient we apply our modeling to a case study of the north american high plains where regionally elevated surfaces east of the rockies have been incised up to 500 m by the fluvial systems draining the core of the range although this incision has been interpreted as reflecting a tectonic rejuvenation of the high plains our analysis suggests that climate change is at least as plausible an explanation to explain the incision of this landscape diagnostic differences between the climate and tectonic end member scenarios might be obtained via detailed study of the spatial and temporal patterns of terrace abandonment providing a potentially fruitful target for field investigation

quaternary coastal uplift along the talara arc ecuador northern peru from new marine terrace data marine terrace sequences have been investigated along the talara arc a 1000 km long stretch of the coast of ecuador and northern peru characterized by subduction with a concave plan view seven areas were investigated evidencing flights of up to seven marine terraces with elevations reaching up to 360 in above mean sea level amsl dating of the terraces was made using the infra red stimulated luminescence irsl technique on sands as old as mis 9 similar to 330 ka c 14 and u series dates were obtained from fossil shells for geochronological cross control mean uplift rates along the talara arc range from about 0 10 up to 0 50 mm yr the strongest uplift is observed in the manta peninsula of ecuador in front of the subduction of the carnegie ridge the uplift rate tends to slow down towards the northern and southern ends of the talara arc and then the transition toward the stable or subsiding coasts of central peru and northern ecuador and colombia is sharp the uplift appears to be homogeneous and related to 1 the map view curvature of the are 2 the concave subduction pattern and 3 the carnegie ridge subduction c 2006 elsevier b v all rights reserved

late cenozoic history and slip rates of the fish lake valley emigrant peak and deep springs fault zones nevada and california several well dated stratigraphic markers permit detailed assessment of the temporal and spatial variation in slip rates along the interconnected faults of the fish lake valley emigrant peak and deep springs fault zones in west central nevada and east central california right lateral motion on the fish lake valley fault zone apparently began ca 10 ma 11 9 8 2 ma associated extensional faulting probably began ca 5 ma 6 9 4 ma and resulted in the opening of fish lake valley and deep springs valley the long term lateral slip rate for the fish lake valley fault zone since about 10 ma is 5 mm yr 3 12 mm yr our preferred lateral slip rate for the central most active part of the fish lake valley fault zone decreased from about 6 to 3 mm yr from the late miocene to the early pleistocene increased to about 11 mm yr during the middle pleistocene and decreased to about 4 mm yr during the late pleistocene extension may account for some of the change in lateral slip rate during the pliocene the large increase in lateral slip rate during the middle pleistocene is circumstantially linked to an increase in vertical slip rates on the fish lake valley and deep springs fault zones at about the time of the eruption of the bishop ash 0 76 ma vertical slip rates along the three fault zones are also related to fault strike vertical rates are highest on north striking faults and approach zero on northwest striking faults the long lived slip history of the fish lake valley fault zone fits a tectonic model in which the death valley furnace creek fish lake valley fault system is integrated with right lateral shear on faults of the central walker lane and the eastern california shear zone to accommodate part of the pacific north american relative plate motion our research demonstrates that the fish lake valley fault zone accounts for about half the rate of 10 12 mm yr of pacific north american plate boundary shear accommodated within the basin and range province between about lat 37 and 38 n

a 24 700 yr paleolimnological history from the peruvian andes abstract a new paleolimnological dataset from lake pacucha 13 s 3095 m elevation in the peruvian andes provides evidence of changes in lake level over the past 24 700 yr a late glacial highstand in lake level gave way to an early holocene lowstand this transition appears to have paralleled precessional changes that would have reduced insolation during the wet season the occurrence of benthic salt tolerant diatoms and caco3 deposition suggest that the lake had lost much of its volume by c 10 000 cal yr bp pronounced holocene oscillations in lake level included a second phase of low lake level and heightened volatility lasting from c 8300 to 5000 cal yr bp while a polymictic lake formed at c 5000 cal yr bp these relatively wet conditions were interrupted by a series of drier events the most pronounced of which occurred at c 750 cal yr bp paleolimnological changes in the holocene were more rapid than those of either the last glacial maximum or the deglacial period

hillslope response to tectonic forcing in threshold landscapes hillslopes are thought to poorly record tectonic signals in threshold landscapes numerous previous studies of steep landscapes suggest that large changes in long term erosion rate lead to little change in mean hillslope angle measured at coarse resolution new lidar derived topography data enables a finer examination of threshold hillslopes here we quantify hillslope response to tectonic forcing in a threshold landscape to do so we use an extensive cosmogenic beryllium 10 10 be based dataset of catchment averaged erosion rates combined with a 500 km 2 lidar derived 1 m digital elevation model to exploit a gradient of tectonic forcing and topographic relief in the san gabriel mountains california we also calibrate a new method of quantifying rock exposure from lidar derived slope measurements using high resolution panoramic photographs two distinct trends in hillslope behavior emerge below catchment mean slopes of 30 modal slopes increase with mean slopes slope distribution skewness decreases with increasing mean slope and bedrock exposure is limited above mean slopes of 30 our rock exposure index increases strongly with mean slope and the prevalence of angle of repose debris wedges keeps modal slopes near 37 resulting in a positive relationship between slope distribution skewness and mean slope we find that both mean slopes and rock exposure increase with erosion rate up to 1 mm a in contrast to previous work based on coarser topographic data we also find that as erosion rates increase the extent of the fluvial network decreases while colluvial channels extend downstream keeping the total drainage density similar across the range our results reveal important textural details lost in 10 or 30 m resolution digital elevation models of steep landscapes and highlight the need for process based studies of threshold hillslopes and colluvial channels

modulation of the erosion rate of an uplifting landscape by long term climate change an experimental investigation abstract whether or not climatic variations play a major role in setting the erosion rate of continental landscapes is a key factor in demonstrating the influence of climate on the tectonic evolution of mountain belts and understanding how clastic deposits preserved in sedimentary basins may record climatic variations here we investigate how a change in precipitation influences the erosional dynamics of laboratory scale landscapes that evolved under a combination of uplift and rainfall forcings we consider here the impact of a decrease in the precipitation rate of finite duration on the erosive response of a landscape forced by a constant uplift and initially at a steady state ss1 we performed several experiments with the same amplitude but different durations of precipitation decrease tp we observe that the decrease in precipitation induces a phase of surface uplift of landscapes to a new steady state condition ss2 however the details of the uplift histories timing rate differ between the experiments according to tp we also observe a decrease in the erosion rate induced by the precipitation change however the timing and amplitude of this decrease vary according to tp defining a delayed and damped erosion signal our data show that the landscape response to precipitation change is dictated by a critical water to rock ratio ratio of precipitation over uplift that likely corresponds to a geomorphic threshold our study suggests that variations in precipitation that occur at a geological time scale 106 years may have a weak impact on the erosion of landscapes and on the delivery of siliciclastic material to large rivers and sedimentary basins

climatic control of bedrock river incision bedrock river incision drives the development of much of earth s surface topography and thereby shapes the structure of mountain belts and modulates earth s habitability through its effects on soil erosion nutrient fluxes and global climate although it has long been expected that river incision rates should depend strongly on precipitation rates quantifying the effects of precipitation rates on bedrock river incision rates has proved difficult partly because river incision rates are difficult to measure and partly because non climatic factors can obscure climatic effects at sites where river incision rates have been measured here we present measurements of river incision rates across one of earth s steepest rainfall gradients which show that precipitation rates do indeed influence long term bedrock river incision rates we apply a widely used empirical law for bedrock river incision to a series of rivers on the hawaiian island of kaua i where mean annual precipitation ranges from 0 5 metres to 9 5 metres ref 12 over 70 per cent of the global range and river incision rates averaged over millions of years can be inferred from the depth of river canyons and the age of the volcanic bedrock both a time averaged analysis and numerical modelling of transient river incision reveal that the long term efficiency of bedrock river incision across kaua i is positively correlated with upstream averaged mean annual precipitation rates we provide theoretical context for this result by demonstrating that our measurements are consistent with a linear dependence of river incision rates on stream power the rate of energy expenditure by the flow on the riverbed these observations provide rare empirical evidence for the long proposed coupling between climate and river incision suggesting that previously proposed feedbacks among topography climate and tectonics may occur