laboratory experiments simulating the geomorphic response to tectonic uplift 1 we present the results of an experimental study of topography dynamics under conditions of constant precipitation and uplift rate the experiment is designed to develop a complete drainage network by the growth and propagation of erosion instabilities in response to tectonic perturbations the quantitative analysis of topographic evolution is made possible by using telemetric lasers that perform elevation measurements at an excellent level of precision we focus our study on the effect of initial surface organization and of uplift rate on both the transient dynamics and the steady state forms of topography we show that the transient phase is strongly dependent on the initial internally drained area which is found to decrease exponentially with time the topography always reaches a steady state whose mean elevation depends linearly on uplift rate with a strictly positive value when uplift is zero steady state surfaces are characterized by a well defined slope area power law with a constant exponent of 0 12 and an amplitude that depends linearly on uplift rate with a strictly positive value when uplift is zero these results are consistent with a stream power law erosion model that includes a nonnegligible threshold for particle detachment uncertainty regarding the sediment transport length is resolved by calibrating the transient dynamics with a surface process model reappraising published results on the linear dependency between mean elevation or relief and denudation rate we suggest that an erosion threshold is worth considering for large scale systems

keeping the edge a numerical method that avoids knickpoint smearing when solving the stream power law the stream power equation is commonly used to model river incision into bedrock although specific conditions allow an analytical approach finite difference methods fdms are most frequently used to solve this equation fdms inevitably suffer from numerical smearing which may affect their suitability for transient river incision modeling we propose the use of a finite volume method fvm which is total variation diminishing tvd to simulate river incision in a more accurate way the tvd fvm is designed to simulate sharp discontinuities making it very suitable to simulate river incision pulses we show that the tvd fvm is much better capable of preserving propagating knickpoints than fdms using niagara falls as an example comparison of numerical results obtained using the tvd fvm with analytical solutions shows a very good agreement furthermore the uncertainty associated with parameter calibration is dramatically reduced when the tvd fvm is applied the high accuracy of the tvd fdm allows correct simulation of transient incision waves as a consequence of older uplift pulses this implies that the tvd fvm is much more suitable than fdms to reconstruct regional uplift histories from current river profile morphology and to simulate river incision processes in general

late quaternary mass wasting records in the actively uplifting pa chang catchment southwestern taiwan abstract although dominated by erosion over long term the tectonically active mountains of taiwan commonly contain thick landslide and debris flow gravels capping hillslopes or forming alluvial terraces these deposits and their associated landforms serve to study ancient mass wasting histories and their controls on fluvial processes this study focuses on the pa chang river draining the 50 mm yr 1 are detected further downstream after the recent gravel mining the fact that the obtained bedrock incision rates and patterns are decoupled with the tectonic uplift advises caution in using short term erosion data to interpret the tectonics of the taiwan s mountains

landsliding and the evolution of normal fault bounded mountains much of the tectonic and climatic history in high relief regions such as the mountains of the western u s basin and range province is contained in the morphology of hillslopes drainage networks and other landforms that range in scale from 10 1 to 101km to understand how these landforms evolve we have developed a numerical landscape evolution model that combines a detailed tectonic displacement field with a set of physically based geomorphic rules bedrock landsliding long recognized as a significant geomorphic process in mountainous topography is for the first time explicitly included in the rule set in a series of numerical experiments we generate synthetic landscapes that closely resemble mountainous topography observed in the basin and range the production of realistic landscapes depends critically on the presence of bedrock landslides and landsliding yields rates of long term erosion that are comparable in magnitude to those of fluvial erosion the erosive efficiency of bedrock landsliding implies that hillslopes may respond very quickly to changes in local base level and that fluvial erosion is the rate limiting process in steady state experimental landscapes our experiments generate power law distributions of landslide sizes somewhat similar to both field and laboratory observations thus even a simple model of bedrock landsliding is capable of quantitatively reproducing mountainous topography and landslide distributions and represents a significant step forward in our understanding of the evolution of normal fault bounded ranges

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

supply and removal of sediment in a landslide dominated mountain belt central range taiwan abstract a strong coupling between hillslope and valley systems is often inferred for mountain landscapes dominated by bedrock landsliding we reveal the nature of this link using data sets on landsliding and sediment transport from two montane catchments draining the eastern central range of taiwan here the magnitude frequency distribution of landslides can be modeled by a robust power law but this scale invariance is not mirrored in the sediment discharge at the mountain front instead downstream sediment loads reflect a complex response to both sediment supply and ambient hydraulic conditions the rivers do not transport significant amounts of sediment unless it is provided by hillslope mass wasting in the catchment removal of landslide debris is a function of the transport capacity of the stream at the site of entry thus there is a dual supply and transport control on sediment loads in bedrock floored streams over a monitoring period of 25 yr the bulk of the sediment leaving the mountain bel

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

holocene history of deep seated landsliding in the north fork stillaguamish river valley from surface roughness analysis radiocarbon dating and numerical landscape evolution modeling documenting spatial and temporal patterns of past landsliding is a challenging step in quantifying the effect of landslides on landscape evolution while landslide inventories can map spatial distributions lack of dateable material landslide reactivations or time access and cost constraints generally limit dating large numbers of landslides to analyze temporal patterns here we quantify the record of the holocene history of deep seated landsliding along a 25 km stretch of the north fork stillaguamish river valley washington state usa including the 2014 oso landslide which killed 43 people we estimate the ages of more than 200 deep seated landslides in glacial sediment by defining an empirical relationship between landslide deposit age from radiocarbon dating and landslide deposit surface roughness we show that roughness systematically decreases with age as a function of topographic wavelength consistent with models of disturbance driven soil transport the age roughness model predicts a peak in landslide frequency 1 000 ybp with very few landslide deposits older than 7 000 ybp or younger than 100 ybp likely reflecting a combination of preservation bias and a complex history of changing climate base level and seismic shaking in the study area most recent landslides have occurred where channels actively interact with the toes of hillslopes composed of glacial sediments suggesting that lateral channel migration is a primary control on the location of large deep seated landslides in the valley

cosmogenic nuclide burial ages and provenance of the xigeda paleo lake implications for evolution of the middle yangtze river abstract hundred meter thick lacustrine sediments are widespread along the middle yangtze river the distribution of these sediments suggests that an event blocked the river forming a lake stretching 160 km from east to west and 110 km north to south with a depth of 500 m using the cosmogenic nuclides 10 be and 26 al we have dated the time of burial of the lacustrine sediments and fluvial gravels beneath the sediments our results indicate a deposition age for these sediments between 1 34 and 1 58 ma studies of zircon u pb age distributions within lacustrine sediments and fluvial sands related to the paleo lake formation show diverse provenances from the upper yangtze river and yalong river a major tributary of the yangtze river these deposits contain geologic fingerprints that allow identification of the source region of the lacustrine deposits and fluvial sands our results support the reversal of the middle yangtze river before the paleo lake formation we hypothesize that the geologic event that dammed the originally southward flow was the lateral movement of chenghai fault in the dali fault system initiated in early quaternary water eventually cut through the spillway and flowed to the east

assessment of sediment delivery from successive erosion on stream coupled hillslopes via a time series of topographic surveys in the central high mountain range of taiwan abstract landslides play an important role in the evolution of mountain topography and are a major source of sediment in tectonically active mountain belts for the active orogeny of taiwan erosion rates have been assessed by various methods the discrepancies observed between erosion rates integrated over modern and quaternary time scales may result from various effects related to surface processes more process oriented research on the spatio temporal distribution of hillslope processes and coupling relationships with the fluvial system is needed to reconcile the temporally heterogeneous data in the future this paper assesses and describes the processes of subsequent erosion on hillslopes via a time series of topographic surveys of hillslopes after the initial failure in order to better understand the temporal and spatial variability of landslide erosion sediment fluxes and storage of landslide sediment within channels the results demonstrate that hillslope channel coupling is controlled by the relative frequency of erosive flooding events and the magnitude of rainfall driven hillslope processes the latter is assumed to be disproportionately high on larger failures in periods with less rainfall mass wasting may only affect part of the total failure s area volumes of eroded sediment from gullies on the landslide scar may be as high as the volume estimated for the initial failure the geometry of the sliding masses eroded after the initial failure appears to be uniform and their depths average 6 1 2 2 m

the formation and failure of natural dams of the numerous kinds of dams that form by natural processes dams formed from landslides glacial ice and late neoglacial moraines present the greatest threat to people and property landslide dams form in a wide range of physiographic settings the most common types of mass movements that form landslide dams are rock and debris avalanches rock and soil slumps and slides and mud debris and earth flows the most common initiation mechanisms for dam forming landslides are excessive rainfall and snowmelt and earthquakes landslide dams can be classified into six categories based on their relation with the valley floor type i dams 11 of 184 landslide dams from around the world that we were able to classify do not reach from one valley side to the other type ii dams 44 span the entire valley floor in some cases depositing material high on opposite valley sides type iii dams 41 move considerable distances both upstream and downstream from the landslide failure type iv dams 1 are rare and involve the contemporaneous failure of material from both sides of a valley type v dams 1 also are rare and are created when a single landslide sends multiple tongues of debris into a valley and forms two or more landslide dams in the same reach of river type vi dams 3 involve one or more failure surfaces that extend under the stream or valley and emerge on the opposite valley side many landslide dams fail shortly after formation in our sample of 73 documented landslide dam failures 27 of the landslide dams failed less than 1 day after formation and about 50 failed within 10 days over topping is by far the most common cause of failure the timing of failure and the magnitude of the resulting floods are controlled by dam size and geometry material characteristics of the blockage rate of inflow to the impoundment size and depth of the impoundment bedrock control of flow and engineering controls such as artificial spill ways diversions tunnels and planned breaching by blasting or conventional excavation glacial ice dams can produce at least nine kinds of ice dammed lakes the most dangerous are lakes formed in main valleys dammed by tributary glaciers failure can occur by erosion of a drainage tunnel under or through the ice dam or by a channel over the ice dam cold polar ice dams generally drain supraglacially or marginally by downmelting of an outlet channel warmer temperate ice dams tend to fail by sudden englacial or subglacial breaching and drainage late neoglacial moraine dammed lakes are located in steep mountain areas affected by the advances and retreats of valley glaciers in the last several centuries these late neoglacial dams pose hazards because 1 they are sufficiently young that vegetation has not stabilized their slopes 2 many dam faces are steeper than the angle of repose 3 these dams and lakes are immediately downslope from steep crevassed glaciers and near vertical rock slopes and 4 downstream from these dams are steep canyons with easily erodible materials that can be incorporated in the flow and increase flood peaks the most common reported failure mechanism is overtopping and breaching by a wave or series of waves in the lake generated by icefalls rockfalls or snow or rock avalanches melting of ice cores or frozen ground and piping and seepage are other possible failure mechanisms natural dams may cause upstream flooding as the lake rises and downstream flooding as a result of failure of the dam although data are few for the same potential energy at the dam site ownstream flood peaks from the failure of glacier ice dams are smaller than those from landslide moraine and structed earth fill and rock fill dam failures moraine dam failures appear to produce some of the largest downstream flood peaks for potential energy at the dam site greater than 1011 1012 joules differences in flood peaks natural dam failures appear to be controlled by dam characteristics and failure mechanisms

erosion of a tectonically uplifting coastal landscape ne sicily italy abstract we investigate the relative importance of tectonic uplift climate and bedrock resistance as controls upon channel morphology in the active orogen of ne sicily the study area displays spatial variations in uplift rate precipitation and bedrock resistance the significance of each of these gradients was tested using established morphometric relationships twenty catchments were investigated using the 28 m aster digital elevation model dem for longitudinal profile analysis google earth tm to determine channel widths and schmidt hammer readings to quantify bedrock strength based on channel morphologies and hillslope gradients the basins exhibit three distinct reaches upper middle and lower the upper reaches of the bedrock channels display concave longitudinal profiles positive correlation between uplift rate and steepness and exponents in the width area relationship of 0 4 0 5 indicating that uplift is the major control on the morphology of this reach the middle reaches however display sublinear longitudinal profiles weak correlation between uplift rate and channel steepness and no systematic width area relationship we interpret this to be caused by the presence of a shear zone which through fracturing has tectonically increased the bedrock erodibility irrespective of its lithology in the lower reaches the channels are alluvial neither channel concavity nor steepness seems to be affected by the spatial variation in precipitation in any of the reaches indicating that climate does not noticeably affect channel morphology these observations suggest a strong tectonic influence on channel evolution in this active mountainous region our study illustrates how reach scale morphometric analysis can aid understanding of how fluvial systems vary with potential controlling parameters

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

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

geomorphic imprint of landslides on alpine river systems southwest new zealand an inventory of 846 mass movements mainly landslides in two alpine regions of southwest new zealand was created to explore the geomorphic impacts of slope failure processes on river channels and valley floors in total 213 i e 27 per cent of the slope failures descended to valley floors affecting the geomorphology of trunk channels catchment area ac 10 km2 and valley floors in recurring patterns a nominal classification system is introduced for characterizing a the physical contact nature between landslides and river channels and b the resulting geomorphic consequences for drainage although landslide area a is useful for estimating the length of channel directly impacted by debris it does not necessarily predict the direction of fluvial response or type of impact dominant persistent geomorphic imprints of bedrock landslides include channel occlusions and landslide dams in south westland and fiordland respectively differences in size distribution and geomorphic effects on river systems between the two study regions are attributed to bedrock geology tectonics and sediment flux although south westland rivers are more frequently affected by landslides disrupting long term effects such as blockage are more persistent in fiordland copyright 2005 john wiley sons ltd

storage and weathering of landslide debris in the eastern san gabriel mountains california usa implications for mountain solute flux the weathering of silicate minerals in mountain landscapes provides a critical source of chemical solutes in the global biogeochemical cycles that sustain life on earth observations from across earth s surface indicate that the greatest flux of chemical solute is derived from rapidly eroding landscapes where landsliding often limits the development of a continuous soil cover in this study we evaluate how weathering of landslide debris deposits may supplement the chemical solute flux from rapidly eroding bedrock dominated landscapes we present new measurements of depositional surface and soil morphology soil geochemistry and luminescence based depositional ages from debris stored in cow canyon a tributary to the east fork of the san gabriel river in the eastern san gabriel mountains of california cow canyon deposits include locally derived debris emplaced by dry colluvial and debris flow processes deposits have planar low angle sloping surfaces with soils exhibiting a greater degree of weathering than nearby soils formed on bedrock a 30 40 ka depositional age of cow canyon deposits exceeds the estimated recurrence time for the largest landslides in the san gabriel mountains suggesting the stored landslide debris may be a persistent source of chemical solute in this landscape to quantitatively explore the significance of landslide debris on the landscape solute flux we predict the flux of chemical solute from bedrock and debris soils using a generic time dependent model of soil mineral weathering our modeling illustrates that debris soils may be a primary source of chemical solute for a narrow range of conditions delimited by the initial landslide debris porosity and the comparative soil age broadly we conclude that while landslide debris may be an important local reservoir of chemical solute it is unlikely to dominate the long term solute flux from rapidly eroding bedrock dominated landscapes

mesozoic cenozoic evolution of the danba dome songpan garze east tibet as inferred from la icpms u pb and fission track data abstract the eastern margin of the tibetan plateau is a key region to understand the formation and tectonic evolution of the plateau most studies concentrated on the longmen shan range that corresponds to the tectonically very active boundary between the tibetan plateau and the sichuan basin this work addresses the deformation and exhumation pattern in the poorly understood metamorphic danba dome situated at the conjunction between the southern longmen shan range and the major strike slip xian shui he fault the early mesozoic and cenozoic evolution of the dome are then compared to the regional evolution of eastern tibet the about 830 ma zircon u pb ages obtained on the gezong and gongcai gneiss as well as u pb ages on inherited zircons in the early mesozoic granites confirm the occurrence of neo proterozoic magmatic episodes in the danba basement at 800 900 ma and 650 750 ma following the closure of the palaeotethys ocean granitoids were emplaced in the danba metamorphic basement and triassic cover from about 230 ma to about 170 ma the western part of the lian he kau granitic massif emplaced between 210 and 200 ma within the triassic cover sequence of the dome was only slightly affected by the early mesozoic deformation however in the eastern deeper level compartment of the massif ductile deformation occurred between 200 and 190 ma contemporaneous with the onset of the barrovian type metamorphism dated at 200 180 ma that deformation is compatible with the early mesozoic deformation observed in the longmen shan range and with the development of the large scale decollement level in the songpan garze area apatite fission track data then indicate that following the oligocene middle eocene onset of eastward motion of the songpan garze terrane the danba dome developed as a crustal scale antiform during the late miocene early pliocene 10 4 ma the exhumation was controlled by the lian he kau fault a major transpressive structure parallel to the xian shui he fault and the associated manai thrust faults regionally while the oligocene middle miocene exhumation phase seems to have been of regional extent the late miocene to present day phase is localised along the longmen shan range thrusts as well as along the back thrusts formed by the lian he kau manai and associated faults

reduction of long term bedrock incision efficiency by short term alluvial cover intermittency fluctuations of the sediment volume stored in mountain channels are driven by stochastic variations of discharge and sediment supply and can inhibit bedrock incision if sediment thickness is too large here i study how this short term stochasticity propagates into the long term reduction of bedrock incision efficiency the cover effect at geological time scales i introduce a new numerical model that resolves sediment transport and bedrock incision at daily time scales and is run for thousands of years it incorporates 1 a transport threshold and daily stochastic variations in water discharge and sediment supply 2 a freely evolving channel width and slope and 3 an explicit treatment of alluvial thickness variations and corresponding bed incision reduction for typical mountain river conditions the model predicts that alluvial cover oscillates between complete and negligible incision reduction in this intermittent regime the long term cover effect is mainly set by the fraction of time spent in full cover and the present day extent of alluvial cover is not representative of long term dynamics the long term integrated cover effect law differs strongly from proposed theoretical and experimental models and it is controlled by sediment supply stochasticity rather than the details of cover development at the hydraulic time scale model results also suggest that steady state channel configuration always depends on sediment supply rate while being never limited by transport capacity or strictly detachment limited these results point out that discharge and sediment supply stochasticity should not be considered less important than the intricate details of incision laws to model long term bedrock channel dynamics

late quaternary deposition and incision sequences of the golmud river and their environmental implications abstract golmud river is a large river that originates from the kunlun mountains and drains into the qaidam basin on northern tibetan plateau well developed fluvial terraces in the river valley record complex history of tectonic movements and climate changes in this area the current study investigated fluvial terraces in three cross sections along the river xiaogangou nachitai and sanchahe the ages of the terraces were constrained using optically stimulated luminescence osl and radiocarbon dating methods the results characterize two stages of fluvial landform evolution since the late quaternary the sanchahe deposition stage 82 16 ka and the golmud incision stage 16 ka until now during the deposition stage tectonic movements were relatively stable which drove the deposition meanwhile the enhanced glaciations and precipitation during the last glacial promoted the aggradations in the river valley as well during the incision stage four substages at 16 13 ka 13 11 ka 11 5 ka and 5 ka till now are identified these substages correspond to the incision of the four terraces the incision was mainly driven by the tectonic uplift after the last glacial maximum

tectonic uplift and landslides triggered by the wenchuan earthquake and constraints on orogenic growth a case study from hongchun gully longmen mountains sichuan china abstract many uncertainties need to be taken into account to estimate the relationship between tectonic uplift the landslide volume triggered by the wenchuan earthquake and constraints on the orogenic growth of the longmen shan mountain in this research coseismic tectonic uplift landslides and postseismic debris flows in hongchun gully located at the earthquake epicenter have been studied field data aerial photographs and digital elevation data were used to estimate the quantitative relationship between the tectonic uplift and landslides debris flows and their constraints on the orogenic growth of the longmen mountains the coseismic tectonic uplift volume 667 104 m3 was more than the coseismic landslide volume 380 01 104 m3 only 57 of the volume of the tectonic uplift has been converted to the volume of landslides in hongchun gully indicating new uplift and orogenic growth of the longmen shan the volume of postseismic debris flows was 70 5 104 m3 indicating that 20 of the volume of coseismic landslides was converted into postseismic debris flows by heavy rainfall the volume of materials discharged by minjiang river the main river is 48 5 104 m3 indicating that only 13 of coseismic landslide sediments has been removed from the range by fluvial processes and at least 86 of landslide sediments still remain in the hongchun gully coseismic tectonic uplift volume exceeds coseismic landslides volume and the wenchuan earthquake caused new uplift and geomorphic growth of the longmen mountains this is not consistent with a previous conclusion that mass wasting triggered by the 2008 wenchuan earthquake exceeds orogenic growth and led to a net material deficit in the longmen shan region

the importance of earthquake induced landslides to long term slope erosion and slope failure hazards in seismically active regions abstract this paper describes a general method for determining the amount of earthquake induced landsliding that occurs in a seismically active region over time this determination can be used as a quantitative measure of the long term hazard from seismically triggered landslides as well as a measure of the importance of this process to regional slope erosion rates and landscape evolution the method uses data from historical earthquakes to relate total volume of landslide material dislodged by an earthquake to the magnitude m and seismic moment m0 of the earthquake from worldwide data a linear regression relation between landslide volume v and m0 is determined as v m0 1018 9 0 13 where v is measured in m3 and m0 is in dyn cm to determine the amount of earthquake generated landsliding over time this relation is combined with data on seismic moment release for a particular region which may be derived from either earthquake history or fault slip data the form of the m0 v relation allows the rate of production of earthquake induced landslides over time to be determined from total rate of seismic moment release without regard to the distribution of individual events thus simplifying and generalizing the determination application of the method to twelve seismically active regions with areas ranging from 13 275 to 2 308 000 km2 shows that erosion rates from earthquake induced landslides vary significantly from region to region of the regions studied the highest rates were determined for the island of hawaii new zealand western new guinea and the san francisco bay region of california significantly lower rates were determined for iran tibet the sierra nevada great basin region of california and central japan for the time period from 715 ad to the present intermediate rates were determined for peru southern california onshore california turkey and central japan for the time period from 1586 ad to the present to determine the relative long term importance of seismically triggered landslides these erosion rates are compared to erosion rates calculated for other slope processes and to rates calculated from fluvial sediment discharge comparisons with other slope processes indicate that earthquake induced landslides are the predominant agents of slope erosion on the island of hawaii in the san francisco bay region and in western new guinea for hawaii the san francisco bay region and sierra nevada great basin region of california the erosion rates calculated for earthquake induced landslides also exceed the regional erosion rates calculated from fluvial sediment discharge

surface deformation related to the 2008 wenchuan earthquake and mountain building of the longmen shan eastern tibetan plateau abstract the 12 may 2008 ms 8 0 wenchuan earthquake china was one of largest continental thrusting events worldwide based on interpretations of post earthquake high resolution remote sensing images and field surveys we investigated the geometry geomorphology and kinematics of co seismic surface ruptures as well as seismic and geologic hazards along the longmen shan fold and thrust belt our results indicate that the wenchuan earthquake occurred along the ne sw trending yingxiu beichuan and guanxian anxian faults in the longmen shan fold and thrust belt the main surface rupture zones along the yingxiu beichuan and guanxian anxian fault zones are approximately 235 and 72 km in length respectively these sub parallel ruptures may merge at depth the yingxiu donghekou surface rupture zone can be divided into four segments separated by discontinuities that appear as step overs or bends in map view surface deformation is characterized by oblique reverse faulting with a maximum vertical displacement of approximately 10 m in areas around beichuan county earthquake related disasters e g landslides are linearly distributed along the surface rupture zones and associated river valleys the wenchuan earthquake provides new insights into the nature of mountain building within the longmen shan eastern tibetan plateau the total crustal shortening accommodated by this great earthquake was as much as 8 5 m with a maximum vertical uplift of approximately 10 m the present results suggest that ongoing mountain building of the longmen shan is driven mainly by crustal shortening and uplift related to repeated large seismic events such as the 2008 wenchuan earthquake furthermore rapid erosion within the longmen shan fold and thrust belt occurs along deep valleys and rupture zones following the occurrence of large scale landslides triggered by earthquakes consequently we suggest that crustal shortening related to repeated great seismic events together with isostatic rebound induced by rapid erosion related unloading is a key component of the geodynamics that drive ongoing mountain building on the eastern tibetan plateau

reworking of basin fill deposits along a tributary of the upper yellow river implications for changes to landscape connectivity recent emphasis on sediment connectivity in the literature highlights the need for quantitative baseline studies on the patterns and distribution of sediment stores to facilitate understanding of how sediment moves through the landscape at various temporal and spatial scales this study evaluates the distribution and make up of sediment stores within the dramatically incised landscapes of the upper yellow river where basin fill deposits up to 1200 m in depth have been extensively reworked following incision by the yellow river field and gis analyses highlight the discontinuous distribution of sediment stores in garang catchment a 236 km2 tributary of the upper yellow river volumetric estimates of sediment storage were obtained through a combination of field mapping gpr transects and gis analyses sediment stores cover 20 of the garang catchment with an estimated volume of 474 0 x 106 m3 and inferred residence times from osl and 14c dating of 103 104 years fans and terraces reworked from basin fill deposits and associated cut and fill terrace features are the dominant forms of sediment storage 90 of total a space for time argument is used to assess stages of basin infilling and subsequent landscape responses to incision outlining a dramatic example of changes to sediment dynamics and connectivity relationships within the upper yellow river sediments within the upper catchment lie above the regional basin fill level offering a glimpse of pre incisional conditions this contrasts markedly with the enduring influence of basin incisional history seen within the middle catchment and the contemporary landscapes of the lower catchment where nearly all available sediment has been excavated from the basin and the landscape effectively operates under post incisional conditions the need to contextualize catchment scale studies in terms of landscape history is emphasized

early holocene catastrophic mass wasting event and fan delta development on the hua tung coast eastern taiwan abstract landslides and debris flows rarely occurred during historical times in the tectonically active coastal range of eastern taiwan this topographic stability however contrasts greatly with the widespread existence of terraced alluvial fans and fan deltas on the hua tung coast which fringes the range this study focuses on the two largest fan terrace systems on the hua tung coast both of which consist of alluvial fans plane view areas up to 8 km 2 larger than their contributing catchments stratigraphic data show that both systems were in sandy wave dominated settings during de glacial times the systems were then disturbed by a catastrophic landslide debris flow event or events which brought enormous amounts of gravel facies gm into the systems deforming previously deposited marine sands facies sm and shallowing the seafloor the combined gm sm complex yields multiple radiocarbon dates ranging from 11 3 to 8 3 ka cal bp with a cluster around 8 6 ka cal bp this mass wasting event has been unique since the emergence of its contributing catchment 0 2 0 3 ma ago the low frequency of such an event could reflect the great resistance of rock mass in the source areas to weathering and erosion the common blockage of valley floors by giant boulder piles which limits channel incision and sediment transport could also increase the apparent stability of the mountain the trigger of landslides in the coastal range has been linked to large earthquakes additionally we propose that the great magnitude and duration of the observed early holocene event were caused by the contemporaneous prolonged rainfall and or high frequency of typhoons associated with the east asian summer monsoon maximum

sedimentary provenance constraints on drainage evolution models for se tibet evidence from detrital k feldspar the unusual drainage pattern of the jinsha river upper yangtze is closely linked to the uplift of the tibetan plateau but when this pattern became established is controversial in this study we compare the pb isotopic composition of detrital k feldspars from the modern jinsha river with those from the plio pleistocene xigeda formation a sequence of fluvial and lacustrine deposits widely distributed along the major rivers draining the tibetan plateau to investigate their relationship and to constrain the drainage evolution of the region our results demonstrate that the jinsha river had achieved its current sediment transport pattern by the late pliocene indicating a drainage character similar to that operating at present our findings not only suggest an upper age limit for formation of the jinsha river but also shed new light on the evolution of the whole yangtze system k feldspar grains from the jinsha river have less radiogenic pb than those in the red mekong and salween rivers providing a key test as to whether the jinsha river was previously connected to the paleo red river comparison with published pb isotopic data shows that these characteristically unradiogenic feldspars are absent in the onshore cenozoic archive from the hanoi basin suggesting that there has been no connection between the lower jinsha river and the red river since the eocene

mode of seismic moment release at transform faults abstract seismic moments of oceanic transform fault tf events being the largest ones at various tfs and covering a wide range of spreading rates are obtained by the moment tensor and the scalar moment inversion methods for the p wave first motion amplitudes on wwssn long period records the seismic moment of the largest event at each tf shows a negative correlation with the spreading rate and a positive correlation with the elapse time during which the ocean floor newly created at the ridge passes over ridge offset the seismic moment has a poor correlation with geometrical parameters such as tf length and cumulative moment expected along the tfs in the next step cumulative seismic moments are deduced for three tfs using rayleigh wave excitations relative to those of the largest events to infer seismic moments of small tf events ratios between the cumulative moments and the moments expected by simple plate kinematics amount to about 5 6 at the eltanin fracture zone spreading rate is 9 cm yr 29 at the tasman fracture zone 7 cm yr and 35 at the george v fracture zone 7 cm yr it is clear that the faster the spreading rate is the larger is the amount of tf movement released aseismically this leads to the conclusion that hot mantle materials are supplied by fast moving convection currents and that the mode of the seismic moment release at tfs is principally governed by the thermal state in the uppermost mantle beneath the spreading center

gigantic rockslides induced by fluvial incision in the diexi area along the eastern margin of the tibetan plateau abstract a number of large landslides which have strongly affected fluvial processes in the upstream catchment of the minjiang river along the eastern margin of the tibetan plateau sichuan were investigated with regard to both geological structure and topographic development topographic analysis suggested that there is a major knickpoint that formed not as a result of landslides but via tectonic activity and that the knickpoint propagated upstream forming an inner gorge and undercutting and destabilizing nearby slopes the effects of the knickpoint propagation and inner gorge formation on slope stability are dependent on the geometrical relationships between the river and geological structures when the geological trend is normal or highly oblique to the river axis landslides generally do not occur but gigantic rockslides have occurred on one side of the minjiang valley which can be attributed to a wedge structure consisting of bedding planes and joints with intersections dipping valleyward and tight folds with hinges plunging valleyward when the beds are planar moderately dipping and strike nearly parallel to the river buckling deformation commonly occurs on cataclinal slopes often transforming into catastrophic failure landslide dams form another type of knickpoint on the river channel that gradually disappear from the downstream to upstream as a result of river erosion our findings strongly suggest that the study of slope development by river incision must consider geological structures and that an understanding of geological structures and river incision history can provide a conceptual model for the prediction and mitigation of geohazards in tectonically active drainage basins

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

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

the 1786 earthquake triggered landslide dam and subsequent dam break flood on the dadu river southwestern china abstract chinese historic documents recorded that on june 1 1786 a strong m 7 75 earthquake occurred in the kangding luding area sichuan southwestern china resulting in a large landslide that fell into the dadu river as a result a landslide dam blocked the river ten days later the sudden breaching of the dam resulted in catastrophic downstream flooding historic records document over 100 000 deaths by the flood this may be the most disastrous event ever caused by landslide dam failures in the world although a lot of work has been carried out to determine the location magnitude and intensity of the 1786 earthquake relatively little is known about the occurrence and nature of the landslide dam in this paper the dam was reconstructed using historic documents and geomorphic evidence it was found that the landslide dam was about 70 m high and it created a lake with a water volume of about 50 106 m3 and an area of about 1 7 km2 the landslide dam breached suddenly due to a major aftershock on june 10 1786 the peak discharge at the dam breach was estimated using regression equations and a physically based predictive equation the possibility of a future failure of the landslide seems high particularly due to inherent seismic risk and detailed geotechnical investigations are strongly recommended for evaluating the current stability of the landslide

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

geomorphic evidence of unrecognized balapur fault segment in the southwest kashmir basin of northwest himalayas abstract the balapur fault bf is a high angle thrust fault reverse dipping 60 ne with an established length of 40 km striking nw se of the kashmir basin however geomorphic traces suggest that the strike of the bf propagates beyond what has been documented previously the present investigation aims to identify the unrecognized segment of the bf in the sw of the kashmir basin using hypsometric variability in longitudinal profiles knickpoints zones followed by validation through stream gradient index sl calculations of the rivers draining the area the longitudinal profiles of all the streams indicate prominent and consistent anomalies in the upper and mid reaches even on the coarse resolution data survey of india topographic maps 1 50 000 40 m dem srtm 90 m the profile anomalies in the upper reaches hard rock zone of the streams may be attributed to lithological contacts i e panjal trap agglomeratic slate shale limestone however the river profile convex segments and course deflection specifically in the mid reaches soft rock zone are most likely associated with recent tectonic activity geomorphic signatures suggest that these anomalies coincide with the strike of the recognized segment of the bf moreover the sl values of each stream express a clear agreement with the anomalies shown by the long profiles of the rivers hence we infer that the strike of the bf extends for a significant distance 95 km over the northeastern flank of the pir panjal range in the nw se direction

plugs or flood makers the unstable landslide dams of eastern oregon abstract landslides into valley bottoms can affect longitudinal profiles of rivers thereby influencing landscape evolution through base level changes large landslides can hinder river incision by temporarily damming rivers but catastrophic failure of landslide dams may generate large floods that could promote incision dam stability therefore strongly modulates the effects of landslide dams and might be expected to vary among geologic settings here we investigate the morphometry stability and effects on adjacent channel profiles of 17 former and current landslide dams in eastern oregon data on landslide dam dimensions former impoundment size and longitudinal profile form were obtained from digital elevation data constrained by field observations and aerial imagery while evidence for catastrophic dam breaching was assessed in the field the dry primarily extensional terrain of low gradient volcanic tablelands and basins contrasts with the tectonically active mountainous landscapes more commonly associated with large landslides all but one of the eastern oregon landslide dams are ancient likely of order 10 3 to 10 4 years old and all but one has been breached the portions of the oregon landslide dams blocking channels are small relative to the area of their source landslide complexes 0 4 33 6 km 2 the multipronged landslides in eastern oregon produce marginally smaller volume dams but affect much larger channels and impound more water than do landslide dams in mountainous settings as a result at least 14 of the 17 82 large landslide dams in our study area appear to have failed cataclysmically producing large downstream floods now marked by boulder outwash compared to a 40 70 failure rate for landslide dams in steep mountain environments morphometric indices of landslide dam stability calibrated in other environments were applied to the oregon dams threshold values of the blockage and dimensionless blockage indices calibrated to worldwide data sets successfully separate dam sites in eastern oregon that failed catastrophically from those that did not accumulated sediments upstream of about 50 of the dam sites indicate at least short term persistence of landslide dams prior to eventual failure nevertheless only three landslide dam remnants and one extant dam significantly elevate the modern river profile we conclude that eastern oregon s landslide dams are indeed floodmakers but we lack clear evidence that they form lasting plugs

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

late paleozoic to cenozoic history of the offshore sydney basin atlantic canada the sydney basin covers a large offshore area south of newfoundland with a well exposed outcrop belt on cape breton island the geological history of the poorly known offshore area is interpreted using an industry seismic grid and lithoprobe line 86 5 tied to outcrops and two wells the mid devonian to upper carboniferous permian basin fill is 6 7 km thick and represents three extensional phases with intervening and succeeding compressive phases the mid devonian mcadams lake formation was deposited in a local half graben during early post acadian extension following deformation a suite of early carboniferous extensional basins filled mainly with horton group conglomerates developed on northeast trending and southeast dipping master faults some faults developed along acadian terrane boundaries the windsor group extends over the master faults to onlap basement as a result of thermal sag and visean eustatic rise mid carboniferous deformation linked to the alleghanian orogeny reactivated faults an

controls on valley width in mountainous landscapes the role of landsliding and implications for salmonid habitat a fundamental yet unresolved question in fluvial geomorphology is what controls the width of valleys in mountainous terrain establishing a predictive relation for valley floor width is critical for realizing links between aquatic ecology and geomorphology because the most productive riverine habitats often occur in low gradient streams with broad floodplains working in the oregon coast range western united states we used airborne lidar to explore controls on valley width and couple these findings with models of salmon habitat potential we defined how valley floor width varies with drainage area in a catchment that exhibits relatively uniform ridge and valley topography sculpted by shallow landslides and debris flows in drainage areas 0 1 km 2 valley width increases as a power law function of drainage area with an exponent of 0 6 consequently valley width increases more rapidly downstream than channel width exponent of 0 4 as derived by local hydraulic geometry we used this baseline valley width drainage area function to determine how ancient deep seated landslides in a nearby catchment influence valley width anomalously wide valleys tend to occur upstream of and adjacent to large landslides while downstream valley segments are narrower than predicted from our baseline relation according to coho salmon habitat potential models broad valley segments associated with deep seated landsliding resulted in a greater proportion of the channel network hosting productive habitat because large landslides in this area are structurally controlled our findings indicate a strong link between geologic properties and aquatic habitat

stability of landslide dams and development of knickpoints the wenchuan earthquake triggered many landslides and numerous avalanches and created 100 odd quake lakes the quake lakes may be removed or preserved the removal strategy was applied to several large landslide dams which were dangerous because massive amounts of water pooled up in the quake lakes the dams could eventually fail under the action of dam outburst flooding potentially endangering the lives of people in the downstream reaches this paper studied the stability of landslide dams and the development of knickpoints by field investigations and experiments and analyzing satellite images the study concluded that if landslide dams were preserved they would develop into knickpoints and act as a primary control of riverbed incision and thus reduce the potential of new landslide the stability of landslide dams depends mainly on the development of the step pool system and stream power of the flood flow if a landslide dam consists of many boulders a step pool system may develop on the spillway channel of the dam which would maximize the resistance consume most of the flow energy and consequently protect the dam from incision the development degree of the step pool system is represented by a parameter s p which was measured with a specially designed instrument a preservation ratio of landslide dams is defined as the ratio of preserved height after flood scouring to the original height of the dam for streams with peak flood discharge lower than 30 m3 s the preservation ratio is linearly proportional to s p for rivers with a peak flood discharge higher than 30 m3 s 30 30 000 m3 s the minimum s p value for stable channel increases with log p in which p is the unit stream power for a landslide dam with a poorly developed step pool system s p is smaller than the minimum value and the outburst flood incises the spillway channel and causes failure of the dam for preserved landslide dams sediment deposits in the quake lakes a landslide dam may develop into a knickpoint if it is stabilized by long term action of the flow large knickpoints can totally change the fluvial processes and river morphology uplift of the qinghai tibetan plateau has caused extensive channel bed incision along almost all rivers for many rivers the incision has been partly controlled by knickpoints upstream reaches of a knickpoint have a new and unchanging base level this brings about a transition from degradation to aggradation and from vertical bed evolution to horizontal fluvial process multiple and unstable channels are prominent in the reaches upstream of the knickpoints if hundreds of landslide dams occurred simultaneously on a reach of a mountain river the potential energy of bank failure and the slope erosion would be greatly reduced and sediment yield from the watershed may be reduced to nearly zero the quake lakes may be preserved long term and become beautiful landscapes streams with long term unfilled quake lakes have good aquatic ecology

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

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

controls on strath terrace formation and evolution the lower guadiana river pulo do lobo portugal abstract the lower guadiana river carves a wide canyon in the variscan metamorphic rocks of the sw iberian peninsula and presents an exceptionally homogeneous and well preserved case of a strath terrace st some 40 km long and 400 m wide the rocky surface or strath shows different characteristics and development stages upstream the lateral erosion level forms a flooded riverbed or submerged strath that gradually rises above the thalweg and develops into an active floodplain downstream below the 15 m high pulo do lobo waterfall the strath is incised by an inner canyon that forms a terrace on both sides the inner channel increasingly widens and the st loses its longitudinal continuity yet remains prone to flooding during extraordinary magnitude floods to assess the factors controlling the formation of this st we examined the roles of key drivers of st formation lithological hardness tectonic structures and climate change using cosmogenic data to create a chronologic context the st developed favoured by a monotonous succession of phyllites as shown by schmidt hammer resistance data and interbedded more resistant quartz veins do not significantly alter its flat configuration variscan structures and measured joints determine the main orientation of the river and control the drainage network pattern the intersection of the n s and ne sw fractures promotes a wavy surface due to three dimensional minor fold trains that act as discontinuities and play an important role in st erosion through quarrying and plucking however we detected no evidence of st deformation attributable to recent or late cenozoic tectonic activity the upstream active riverbed progressively changes downstream into an st this implies that be radiometric ages obtained at pulo do lobo may not represent the st s genetic age but rather the time of dismantling of its alluvial or sedimentary cover this means the strath surface formed prior to its cosmogenic age and was therefore controlled by a higher base level indicating a higher sea level than the current one given the downstream area studied the quaternary sea level fluctuations show records of only a few meters above the current level instead the sea level low stand maintains an average depth of 60 m reaching 140 m during the last glacial period this low base level context could justify the strong incision of the inner channel within the st but not the age of strath surface genesis and expansion and thus this surface should have evolved previously the highest possible sea level stand corresponds to the pliocene transgression which reached an elevation of 120 m in the region covering miocene paleorelief the mouth of the guadiana river at that time resembled a fluvio deltaic embayment between the algarve domain and the guadalquivir depression which was infilled with fluvial deposits at the end of the transgression collectively these data suggest that cosmogenic dating would define the time of exhumation of this pliocene sedimentary cover despite great variation of the st ages estimated incision rates at the knickpoint area are consistent with the total entrenchment of the pulo do lobo fall especially if we consider that data correspond to an active erosion site highest erosion rates were found for the pothole area compared to those obtained for the higher st surface radiometric ages correspond to the period of lowest quaternary sea level and during which headward erosion would have been very active in the inner channel the waterfall area shows more resistant lithology in its concentrated quartz veins but this effect is inconspicuous at the st surface the regular gradient of 0 02 m m and vast extension of this perched strath linked upstream to the guadiana riverbed indicates a relic exhumed surface beneath its sedimentary cover notwithstanding the subsiding activity of the gulf of cadiz the continental margin behaves as a tectonically stable block which allows for the persistence of former morphologies in these ancient landscapes reshaped by bedrock river dissection

the formation and impact of landslide dams state of the art abstract the blocking of river courses by mass movements is very common in mountainous areas with deep and narrow valleys landslide dams may pose serious threats to people and their livelihoods downstream in the case of abrupt dam failure since the publication of benchmark reviews of costa and schuster 1988 and korup 2002 there is a growing number of studies focusing on the formation stability and short term impacts of landslide dams this review combines the insights of all these studies builds on current concepts of landslide dams and suggests ways to unify terminologies and classifications we furthermore present a new worldwide database compiled from literature data it contains 410 landslide dams 1 million m3 in volume that were formed since 1900 since these have the most complete data entries these data show that dam longevity is among other factors correlated with the type of landslide forming the dam those formed by rock debris avalanches and rockslides have longest lifespans however the influence of landslide type or material on dam longevity decreases with time after dam formation to ensure consistency in the next database generation we suggest guidelines for data collection to provide a solid basis for evaluating dam stability and governing factors a preliminary classification matrix for landslide dam stability that combines topographic setting and the internal structure of the dam body is another outcome of our review furthermore an evaluation of the various geomorphic stability indices proposed in the literature regarding their suitability and limitations in assessing dam formation and stability shows that they predict the probability of dam formation reasonably well but that their application to longevity estimates requires further assessment the geomorphic impacts of landslide dams in the short medium and long term are summarized and illustrated with key examples finally for a better understanding of the factors controlling dam stability we recommend to 1 include dam composition and sedimentary structures in future case studies 2 maintain and update the worldwide database for sound statistical analyses 3 refine landslide dam stability indices and test them for different landslide types and 4 study hazard cascades related to multiple dams in one watershed for long term landscape evolution studies we suggest to 5 quantify terrestrial sediment flux related to landslide dams 6 detect ancient landslide dams in river profiles and 7 further exploit the sediment archives in former impoundment areas

glacier and landslide feedbacks to topographic relief in the himalayan syntaxes despite longstanding research on the age and formation of the tibetan plateau the controls on the erosional decay of its margins remain controversial pronounced aridity and highly localized rock uplift have traditionally been viewed as limits to the dissection of the plateau by bedrock rivers recently however glacier dynamics and landsliding have been argued to retard headward fluvial erosion into the plateau interior by forming dams and protective alluvial fill here we report a conspicuous clustering of hundreds of natural dams along the indus and the tsangpo rivers where these cross the himalayan syntaxes the indus is riddled by hundreds of dams composed of debris from catastrophic rock avalanches forming the largest concentration of giant landslide dams known worldwide whereas the tsangpo seems devoid of comparable landslide dams in contrast glacial dams such as river blocking moraines in the headwaters of both rivers are limited to where isolated mountain ranges intersect the regional snowline we find that to first order high local topographic relief along both rivers corresponds to conspicuously different knickzones and differences in the type and potential longevity of these dams in both syntaxes glacier and landslide dams act as a negative feedback in response to fluvial dissection of the plateau margins natural damming protects bedrock from river incision and delays headward knickpoint migration thereby helping stabilize the southwestern and southeastern margins of the tibetan plateau in concert with the effects of upstream aridity and localized rock uplift

rock slope failure and the river long profile this study examines the geomorphic effects of large 10 6 m 3 rock slope failures on long profiles of rivers in the swiss alps and the new zealand southern alps regression of channel slope versus drainage basin area objectively highlights knickpoints separating incised from aggraded reaches that often correspond to locations of large rock slope failures for a fixed concavity index the highest values of the steepness index and erosion index along a given profile spatially coincide with breach channels cut into formerly river damming rockslide debris as old as 10 k y assuming that the knickpoints do not predate slope failure data show that high profile steepness and inferred specific stream power are not always the cause but often a result of large river blocking rock slope failure in mountain basins omission of rockslide data from slope area plots lowers the steepness index and increases the concavity index on average yet only in few cases more than one standard deviation

spatial distribution of denudation in eastern tibet and regressive erosion of plateau margins article i nfo the longmen shan range is one of the major topographic and structural features of the eastern margin of the tibetan plateau with an impressive topographic gradient and low convergence rates across the range this region has raised important questions concerning the dynamics of plateau margin settings such as the long term mechanisms of topographic evolution the investigation of the distribution in space and time of denudation can provide critical insight into such dynamics and shed light on still unresolved controversies for that purpose we present a new dataset that documents the intensity and distribution of denudation processes across this plateau margin through field survey of fluvial incision markers quantitative geomorphology and cosmogenic nuclide derived basin wide erosion rates erosion is b0 5 mm year in the frontal region of the longmen shan and between 0 5 and 1 mm year further west with a gradual decrease when reaching the northern headwaters of the min jiang watershed adjacent to the beginning of the tibetan plateau the spatial distribution of denudation inferred from the various methods we use suggests that most of the differential uplift in the central longmen shan is accommodated by the beichuan fault and frontal structures located in the foothills the denudation pattern seems also to reflect the large scale propagation of erosion from the sichuan basin toward the plateau this suggests that the longmen shan range is submitted to the combined influences of slow thrusting activity on the frontal structures and progressive westward regressive erosion as a probable response to a pulse of uplift of the tibetan plateau eastern margin that

landslides threshold slopes and the survival of relict terrain in the wake of the mendocino triple junction establishing landscape response to uplift is critical for interpreting sediment fluxes hazard potential and topographic evolution we assess how landslides shape terrain in response to a wave of uplift traversing the northern california coast ranges united states in the wake of the mendocino triple junction we extracted knickpoints landslide erosion rates and topographic metrics across the region modified by mendocino triple junction migration landslide erosion rates mapped from aerial imagery are consistent with modeled uplift and exhumation while hillslope gradient is invariant across the region suggesting that landslides accommodate uplift as predicted by the threshold slope model landslides are concentrated along steepened channel reaches downstream of knickpoints generated by base level fall at channel outlets and limit slope angles and relief we find evidence that landslide derived coarse sediment delivery may suppress catchment wide channel incision and landscape denudation over the time required for the uplift wave to traverse the region we conclude that a landslide cover effect may provide a mechanism for the survival of relict terrain and orogenic relief in the northern californian coast ranges and elsewhere over millennial time scales

the role of waterfalls and knickzones in controlling the style and pace of landscape adjustment in the western san gabriel mountains california bedrock rivers set the pace of landscape adjustment to tectonic and climatic forcing by transmitting signals of base level change upstream through the channel network and ultimately to hillslopes river incision is typically modeled as a monotonic function of bed shear stress or stream power modulated by sediment tools and cover effects but these models do not apply in channels with steep or vertical bedrock reaches due to changes in flow dynamics hydraulic geometry and bed cover here we investigate how such knickzones oversteepened channel reaches often containing waterfalls influence the propagation of slope break knickpoints that separate relict from adjusting topography and thus the response times of landscapes to external forcing we use a conceptual long profile model to explore the consequences of waterfalls and knickzones on channel response and compare predictions to light detection and ranging lidar topography field observations and cosmogenic radionuclide data from big tujunga creek a 300 km2 watershed in the san gabriel mountains california three prominent knickzones along big tujunga creek characterized by numerous waterfalls show contrasting behavior for the upper knickzone waterfalls align with bands of harder rock exposed on adjacent hillslopes and between waterfalls the channel is mantled by large 2 m boulders indicating knickzone retreat is slow compared to predictions of slope break knickpoint retreat from stream power models enhancing the preservation of an upstream relict landscape the middle knickzone shows evidence for both fast and slow knickzone retreat as well as significant deviations from predictions of uniform tributary knickpoint elevations derived from stream power models the lower knickzone is characterized by a waterfall and knickzone within an incised inner gorge that provide evidence of rapid retreat relative to background channel incision overall we find a pattern of decreasing knickzone and waterfall retreat rate with distance upstream of the range front beyond decreases predicted by simple area dependent celerity models our results highlight that waterfalls and knickzones can both enhance and inhibit landscape adjustment leading to divergent controls on the pace of landscape evolution

landscape analysis of the huang he headwaters ne tibetan plateau patterns of glacial and fluvial erosion the large scale geomorphology of the huang he yellow river headwaters centered around the bayan har shan 5267 m asl in the northeastern part of the tibetan plateau is dominated by an uplifted

multiple landslide clusters record quaternary climate changes in the northwestern argentine andes the chronology of multiple landslide deposits and related lake sediments in the semi arid eastern argentine cordillera suggests that major mass movements cluster in two time periods during the quaternary i e between 40 and 25 and after 5 14 c kyr bp these clusters may correspond to the minchin maximum at around 28 27 14 c kyr bp and titicaca wet periods after 3 9 14 c kyr bp the more humid conditions apparently caused enhanced landsliding in this environment in contrast no landslide related damming and associated lake sediments occurred during the coipasa 11 5 10 14 c yr bp and tauca wet periods 14 5 11 14 c yr bp the two clusters at 40 25 and after 5 14 c kyr bp may correspond to periods where the el nin o southern oscillation enso and tropical atlantic sea surface temperature variability tav were active this however was not the case during the coipasa and tauca wet periods lake balance modelling of a landslide dammed lake suggests a 10 15 increase in precipitation and a 3 4 c decrease in temperature at v30 14 c kyr bp as compared to the present in addition time series analysis reveals a strong enso and tav during that time the landslide clusters in northwestern argentina are therefore best explained by periods of more humid and more variable climates 2003 elsevier science b v all rights reserved

experimental study on the triggering mechanisms and kinematic properties of large debris flows in wenjia gully debris flows are typically caused by natural terrain landslides triggered by intense rainfalls if an incoming mountain torrent flows along sloping channels at high velocity huge amounts of sediment from landslide dams and eroded channel beds will be entrained into the flows to form debris flows it is likely that large debris flows are due to the failure of many landslide dams of different scales due to bank slides or collapses bed erosion and solid transport the catastrophic debris flows that occurred in wenjia gully wenchuan earthquake area china on august 13 2010 two years after the mega earthquake were caused by intense rainfall and the serious erosion of sloping channels in the wake of the incident experimental tests were conducted to better understand the process of sediment erosion and entrainment on the channel bed and the formation of debris flows the results show that the bed erosion bank collapses and channel widening caused by erosion accounted for the triggering and scale amplification of downstream debris flows in the wenjia gully event this study illustrates how the hazardous process of natural debris flows can begin several kilometers upstream and how such a complex cascade of geomorphic events failure of landslide dams and erosion of the sloping bed can lead to catastrophic discharges neglecting recognition of these hazardous geomorphic and hydrodynamic processes may result in high cost c 2014 elsevier b v all rights reserved

lifespan of mountain ranges scaled by feedbacks between landsliding and erosion by rivers an important challenge in geomorphology is the reconciliation of the high fluvial incision rates observed in tectonically active mountain ranges with the long term preservation of significant mountain range relief in ancient tectonically inactive orogenic belts river bedrock erosion and sediment transport are widely recognized to be the principal controls on the lifespan of mountain ranges but the factors controlling the rate of erosion and the reasons why they seem to vary significantly as a function of tectonic activity remain controversial here we use computational simulations to show that the key to understanding variations in the rate of erosion between tectonically active and inactive mountain ranges may relate to a bidirectional coupling between bedrock river incision and landslides whereas fluvial incision steepens surrounding hillslopes and increases landslide frequency landsliding affects fluvial erosion rates in two fundamentally distinct ways on the one hand large landslides overwhelm the river transport capacity and cause upstream build up of sediment that protects the river bed from further erosion on the other hand in delivering abrasive agents to the streams landslides help accelerate fluvial erosion our models illustrate how this coupling has fundamentally different implications for rates of fluvial incision in active and inactive mountain ranges the coupling therefore provides a plausible physical explanation for the preservation of significant mountain range relief in old orogenic belts up to several hundred million years after tectonic activity has effectively ceased

landslides earthquakes and erosion this paper relates landslide inventories to erosion rates and provides quantitative estimates of the landslide hazard associated with earthquakes we do this by utilizing a three parameter inverse gamma distribution which fits the frequency area statistics of three substantially dcompletet landslide event inventories a consequence of this general distribution is that a landslide event magnitude ml lognlt can be introduced where nlt is the total number of landslides associated with the landslide event using this general distribution landslide event magnitudes ml can be obtained from incomplete landslide inventories and the total area and volume of associated landslides as well as the area and volume of the maximum landslides can be directly related to the landslide event magnitude using estimated recurrence intervals for three landslide events and the time span for two historical inventories we estimate regional erosion rates associated with landslides as typically 0 1 2 5 mm year 1 we next give an empirical correlation between the earthquake magnitude associated landslideevent magnitude and the total volume of associated landslides using these correlations we estimate that the minimum earthquake magnitudes that will generate landslides is m 4 3f0 4 finally using gutenberg richter frequency magnitude statistics for regional seismicity we relate the intensity of seismicity in an area and the magnitude of the largest regional earthquakes to erosion rates we find that typical seismically induced erosion rates in active subduction zones are 0 2 7 mm year 1 and adjacent to plate boundary strike slip fault zones are 0 01 0 7 mm year 1

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

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

a signature of transience in bedrock river incision rates over timescales of 10 4 10 7 years measured rates of river incision into bedrock are commonly interpreted as proxies for rates of rock uplift see refs 1 and 2 for example and indices of the strength of climatic forcing of erosion over time see refs 3 and 4 for example this approach implicitly assumes that river incision rates are in equilibrium with external forcings over a wide range of timescales here we directly test this assumption by examining the temporal scaling of bedrock river incision from 155 independent measurements of river incision compiled from 14 sites of these sites 11 exhibit a negative power law dependence of bedrock river incision rate on measurement interval a relationship that is apparent over timescales of 10 4 10 7 years and is independent of tectonic and geomorphic setting thus like rates of sediment accumulation rates of river incision into bedrock exhibit non steady state behaviour even over very long measurement intervals non steady state behaviour can be explained by episodic hiatuses in river incision triggered by alluvial deposition if such hiatuses have a heavy tailed length distribution regardless of its cause the dependence of incision rate on measurement interval complicates efforts to infer tectonic or climatic forcing from changes in rates of river incision over time or from comparison of rates computed over different timescales

effects of tectonic deformation and landslides in the erosion of a mountain plateau in the transitional zone between the central and patagonian andes

alluvial fan aggradation incision history of the eastern tibetan plateau margin and implications for debris flow debris charged flood hazard abstract this paper reconstructs the quaternary aggradation and incision history of a debris flow debris charged flood affected valley in order to detect the impact of climate on alluvial fan dynamics we used optically stimulated luminescence osl dating of quartz to determine the ages of alluvial fan terraces comparison between the aggradation and incision history and regional climatic records suggests that aggradation occurred in cold and or dry climates whereas incision is a feature of warm and wet climates cold climates lead to enhanced frost shattering and dry climates cause deteriorated vegetation both effects caused surplus sediment which was transported by infrequent flood discharges to form alluvial fan terrace deposits incision during wet and warm climates is due to increased vegetation cover and an increase in the frequency of flood discharges this relationship between climate and valley evolution is applied to assess future changes in the present active channel by considering recent climatic records the results show that the valley channel is expected to experience net incision if the average temperature continues increasing while precipitation maintains at a constant level

fluvial response to large rock slope failures examples from the himalayas the tien shan and the southern alps in new zealand we describe remnants of large 10 7 10 10 m 3 late pleistocene to holocene rockslides and rock avalanches that block ed rivers and are preserved in the himalayas the tien shan and the new zealand southern alps despite rates of uplift and erosion of up to 10 mm year 1 these natural dams control fluvial response on 10 1 10 4 year timescales by a storing and releasing sediment during forced alluviation and fluvial re incision b relocating river channels through diversion or seepage c inhibiting river erosion into bedrock d formingpersistentlong profileknickpointsandknickslopesassociatedwithsteephigh energy n10 3 wm 2 breachand epigenetic bypass gorges and fluvial hanging valleys and e shaping valley floor morphology sediments indicate that rockslidedammed lakes may persist up to 10 4 years before being drained or infilled several short lived 10 0 10 2 year historical rockslide dams in the indian and nepal himalayas and the southern alps have had marked volumetric impacts on catchment sediment budgets shortly following failure therefore we caution against the linear extrapolation of sediment delivery from prehistoric rockslide dams through time as a response variable we find reach scale changes to channel gradient to be prominent and persistent indicators of fluvial response to large rock slope failures 2006 elsevier b v all rights reserved

inner gorge slot canyon system produced by repeated stream incision eastern alps significance for development of bedrock canyons abstract many inner bedrock gorges of the alps show abrupt downstream changes in gorge width as well as channel type and gradient as a result of epigenetic incision of slot canyons many slot canyons also are associated with older gorge reaches filled with quaternary deposits the age of slot canyons and inner bedrock gorges however commonly is difficult to constrain for the inner bedrock gorge system of the steinberger ache catchment eastern alps active slot canyons as well as older abandoned gorge reaches filled with upper wurmian proglacial deposits record three phases of gorge development and slot canyon incision a 234u 230th age of cement of 29 7 1 8 ka in fluvial conglomerates onlapping the flank of an inner gorge fits with late wurmian valley bottom aggradation shortly before pleniglacial conditions in addition the age indicates that at least the corresponding canyon reach must be older during advance of ice streams in the buildup of the last glacial maximum lgm the catchment was blocked and a proglacial lake formed bedrock gorges submerged in that lake were filled with fluviolacustrine deposits during the lgm the entire catchment was overridden by ice during post glacial reincision streams largely found again their preexisting inner bedrock canyons in some areas however the former stream course was missed and a slot canyon formed the distribution of pleistocene deposits the patterns of canyon incision and the mentioned u th cementation age however together record a further discrete phase of base level rise and stream incision well before the lgm the present course of steinberger ache and its tributaries is a patchwork of 1 slot canyons incised during post glacial incision 2 vestiges of slot canyons cut upon an earlier middle to late wurmian cycle of base level rise and fall 3 reactivated reaches up to 200 m in width of inner bedrock gorge that are watershed at present and more than at least 30 ka in age and 4 abandoned sediment filled reaches of bedrock canyons that also must be older than 30 ka and that are exposed alongside the active streams multi cyclic bedrock canyon systems composed of reaches of markedly different ages may be common in mountain ranges subject to glaciations and or mass wasting

the establishment and influence of baimakou paleo dam in an upstream reach of the yangtze river southeastern margin of the tibetan plateau abstract landslide damming is an important disturbance factor in the river evolution of mountain belts and may control river morphology at variable timescales this temporal aspect is mostly discussed in terms of the spatial relationships between the dams and river longitudinal profiles within any given region largely lacking are detailed studies of the geomorphic response for individual dams here we present field evidence and 24 optically stimulated luminescence osl ages that show the history of a landslide dam in an upstream reach of yangtze river at the southeastern margin of the tibetan plateau and its influence on river evolution the distribution of lacustrine ages suggests that there was only one long term damming event induced by landslide blocking the river the dammed lake formed at 12 1 ka and disappeared at 7 5 ka the estimated dam height was 120 m lake area was 96 km2 and lake volume was 7 5 km3 in addition the grain size and distribution of lacustrine deposits indicate the dam failed cataclysmically when the lake finally drained today the river long profile upstream of the dam site remains lower and the channel is wider in contrast to the downstream reach consequently the former dam still influences channel morphology our study shows that the interaction of landslide dams with the rivers in the southeastern tibetan plateau may impeded valley incision and headward erosion in those cases where damming continued over periods of several thousand years

evidence of episodically accelerated denudation on the tibetan namche barwa massif by megafloods abstract megafloods cause widespread mobilization of sediments that have strong potential to control the geodynamic evolution of the namche barwa nb massif by changing the landscape morphology within a short time however the impact of catastrophic events on the denudation of the massif over the longer time scale has not been explored in detail this contribution assesses the impact of catastrophic floods on the denudation style of the namche barwa nb massif over millennial time scales towards this 21 optical ages and 1700 detrital thermochronometric ages of zircon and apatite minerals extracted from paleoflood sediments downstream of the massif were integrated with decadal sediment load and aggradation data to estimate the minimum denudation rate during paleoflood events the results indicate that the 7 ka flood eroded 71 m of material from the nb massif this denudation is equivalent to the material that would be produced over 8000 years of erosion at a rate of 9 mm a the 3 5 ka flood eroded 24 m of material equaling 2500 years worth of erosion at a rate of 9 mm a such relatively instantaneous denudations are three orders of magnitude higher than averaged denudation rates over million year time scale this study therefore provides the first evidence of the strong interplay of catastrophic flood events and tectonics for the rapid exhumation of the namche barwa massif megafloods from the failure of dammed lakes provide valuable information to understand the flood surge risk for human settlements in the siang and the assam valleys

field study of a highly active fault zone the xianshuihe fault of southwestern china the xianshuihe fault of western sichuan province china is one of the world s most active faults having produced 4 earthquakes during this century of magnitude 7 along a 350 km length of the fault at least 8 such events have occurred since 1725 in the more limited 150 km long segment including luhuo and daofu major earthquakes in 1904 1923 1973 and 1981 m 7 7 7 6 6 9 were associated with overlapping surficial fault ruptures and with individual left lateral displacements as large as 3 6 m field studies indicate that this high degree of activity is typical of the fault s longer term history the holocene left lateral slip rate on the north western segment of the fault has been 15 5 mm yr decreasing to about 5 mm yr on its southeastern segment based on radiometrically dated offset stream channel and terrace deposits and on offset glacial moraines physiographic features of active faulting are fully as diagrammatic as those of california s san andreas fault mainly because of high altitude preservation and the absence of cultural modification on this eastern margin of the tibetan plateau detailed en echelon tensional and pushup features resulting from surface ruptures in 1973 1955 1923 and 1893 can still be recognized today and new data have been collected bearing on the offsets and fault rupture lengths during these and other events the locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the xianshuihe fault obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events whereas segmentation control for others remains obscure based on the historic record repeat times estimated from slip rates and current seismic gaps two segments are particularly likely sites for m 7 earthquakes in the near future the 65 km long segment between daofu and qianning and the 135 km long segment bracketing kangding continuing creep has been documented along some segments of the fault and this together with the high degree of activity and other unique attributes makes the xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard evaluation studies

the influence of large landslides on river incision in a transient landscape eastern margin of the tibetan plateau sichuan china deep landscape dissection by the dadu and yalong rivers on the eastern margin of the tibetan plateau has produced high relief narrow river gorges and threshold hillslopes that frequently experience large landslides large landslides inundate river valleys and overwhelm channels with large volumes 10 5 m 3 of coarse material commonly forming stable landslide dams that trigger extensive and prolonged aggradation upstream these observations suggest that strong feedbacks among hillslope processes channel morphology and incision rate are prevalent throughout this landscape and are likely characteristic of transient landscapes experiencing large increases in local relief in general landslide effects are a by product of rapid incision initiated by regional uplift however over timescales relevant to landscape evolution 10 4 yr large landslides can also act as a primary control on channel morphology and longitudinal river profiles inhibiting incision and further preventing the complete adjustment of rivers to regional tectonic climatic and lithologic forcing we explore a probabilistic numerical model to provide a quantitative framework for evaluating how landslides influence bedrock river incision and landscape evolution the time average number of landslide dams along a river course and thus the magnitude of the landslide influence is set by two fundamental timescales the time it takes to erode landslide deposits and erase individual dams and the recurrence interval of large landslides that lead to stable dams stable gradually eroding landslide dams create mixed bedrock alluvial channels with spatial and temporal variations in incision ultimately slowing long term rates of river incision thereby reducing the total amount of incision occurring over a given length of river a stronger landslide effect implies that a higher percentage of channel length is buried by landslide related sediment leading to reduced river incision efficiency the longer it takes a river channel to incise into a landslide dam and remove all landslide related sediment the more control these events have on the evolution of the river profile and landscape evolution this can be the result of slow erosion of stable dams or a higher frequency of large events

impulsive alluviation during early holocene strengthened monsoons central nepal himalaya the steep walled bedrock gorges of the greater himalayan rivers currently lack significant stored sediment suggesting that fluvial erosion and transport capacity outpace the supply of sediment from adjacent hillsides despite this appearance of sustained downcutting such rivers can become choked with sediments and aggrade during intervals of higher precipitation cosmogenic dating 10 be and 26 al of fluvially carved bedrock surfaces indicates that sediment at least 80 m thick filled the marsyandi river valley in central nepal during a time of strengthened early holocene monsoons despite threefold differences in height 43 124 m above the modern river these fluvial surfaces display strikingly similar cosmogenic exposure ages clustering around 7 6 1 ka we speculate that enhanced monsoonal precipitation increased pore pressure and the frequency of landsliding thereby generating a pulse of hillslope derived sediment that temporarily overwhelmed this alpine fluvial system s transport capacity after the easily liberated material was exhausted ca 7 ka the hillslope flux dropped and the river incised through the aggraded alluvium it concurrently eroded adjacent rock walls thereby removing previously accumulated 10 be and 26 al and resetting the cosmogenic clock in the bedrock unlike previous studies these exposure ages cannot be used to derive river incision rates instead they record a coupled fluvial hillslope response to climate change

scale amplification of natural debris flows caused by cascading landslide dam failures debris flows are typically caused by natural terrain landslides triggered by intense rainfalls if an incoming mountain torrent collapses a series of landslide dams large debris flows can form in a very short period moreover the torrent can amplify the scale of the debris flow in the flow direction the catastrophic debris flows that occurred in zhouqu china on 8 august 2010 were caused by intense rainfall and the upstream cascading failure of landslide dams along the gullies in the wake of the incident a field study was conducted to better understand the process of cascading landslide dam failures and the formation of debris flows this paper looks at the geomorphic properties of the debris flow gullies estimates the peak flow discharges at different locations using three different methods and analyzes the key modes i e different landslide dam types and their combinations of cascading landslide dam failures and their effect on the scale amplification of debris flows the results show that five key modes in luojiayu gully and two modes in sanyanyu gully accounted for the scale amplification of downstream debris flows in the zhouqu event this study illustrates how the hazardous process of natural debris flows can begin several kilometers upstream as a complex cascade of geomorphic events failure of landslide dams and erosion of the sloping bed can scale to become catastrophic discharges neglecting recognition of these hazardous geomorphic and hydrodynamic processes may result in a high cost

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

catastrophic landslides and their effects on the upper indus streams karakoram himalaya northern pakistan abstract the paper examines the nature and geomorphic influences of deposits from rock avalanches that obstruct rivers most of the 115 rockslide rock avalanche events identified in the karakoram himalaya straddled one or more stream valleys at least 73 of these landslides formerly dammed the indus or its tributaries upstream of the barriers remnants exist of once very extensive lacustrine deposits the stability and long term survival of dams from large rock avalanches is addressed and the reasons for the gradual or phased rather than catastrophic and sudden breaching case histories emphasise the erosional and depositional forms associated with the barriers they are reconstructed in terms of the emplacement and properties of the deposits from rock avalanches and the response of the river to interruption by them these barriers have exerted a substantial control over stream response and development for most of the holocene at least today they are associated with distinctive features of channel form and thalweg river terrace systems intermontane sediment sinks and sources and local erosional forms in bedrock more broadly the landslide barriers have created a naturally fragmented river system deposition and erosion in the lower few tens or hundreds of meters of the upper indus stream valleys have been dominated by epicycles of aggradation trenching and downcutting that mainly reflect the scale timing and history of each barrier the landforms involved are only indirectly related to the late glacial and paraglacial conditions that have hitherto been regarded as the main explanation

tibetan plateau river incision inhibited by glacial stabilization of the tsangpo gorge much attention has focused on how and when the tibetan plateau formed but far less research has been done on the controls on river incision into the plateau itself oliver korup and david montgomery address this issue which also relates to the question of why the tibetan plateau is still there at all despite hosting one of the deepest gorges on earth the plateau edge is extremely well defined and according to widely accepted stream power theory should be heavily dissected by one of asia s most powerful rivers the yarlung tsangp or yarlung zangbo korup and montgomery propose that the southeastern edge of the plateau was preserved in part by the presence of glaciers that were large enough during the holocene to stall aggressive river downcutting along the plateau margin a considerable amount of research has focused on how and when the tibetan plateau formed in the wake of tectonic convergence between india and asia1 although far less enquiry has addressed the controls on river incision into the plateau itself2 widely accepted theory3 predicts that steep fluvial knick points river reaches with very steep gradients in the eastern himalayan syntaxis at the southeastern plateau margin should erode rapidly4 driving a wave of incision back into the plateau preservation of the plateau edge thus presents something of a conundrum that may be resolved by invoking either differential rock uplift matching erosional decay5 6 7 or other mechanisms for retarding bedrock river incision8 9 in this region where high stream power excludes the potential for aridity as a simple limit to dissection of the plateau10 here we report morphologic evidence showing that quaternary depression of the regional equilibrium line altitude where long term glacier mass gain equals mass loss was sufficient to repeatedly form moraine dams on major rivers such damming substantially impeded river incision into the southeastern edge of the tibetan plateau through the coupled effects of upstream impoundment and interglacial aggradation such glacial stabilization of the resulting highly focused river incision centred on the tsangpo gorge could further contribute to initiating and accentuating a locus of rapid exhumation known as tectonic anaeurysm6

timing of granite emplacement and cooling in the songpan garze fold belt eastern tibetan plateau with tectonic implications abstract new u pb and rb sr geochronology on syn and post orogenic granites provide constraints on the timing of major tectonic events in the songpan garze fold belt west sichuan china the ma nai granite was probably syn kinematic with the main deformation and yields an age of 197 6 ma that is interpreted as an upper age limit of the indosinian event zircons and apatites from the post kinematic rilonguan granite also yield jurassic ages 195 6 and 181 4 ma the post orogenic markam massif gives two ages of 188 1 and 153 3 ma both granites are undeformed and cut structures in the triassic sedimentary rocks these results demonstrate that the major deformation and decollement tectonics in the songpan garze fold belt occurred prior to the early jurassic the wide range of ages obtained for post kinematic granites from early jurassic to late jurassic suggests that locally magmatic activity persisted for a long time at least 50 ma after the indosinian compressional tectonism no tertiary ages have been obtained suggesting that these granites were not affected strongly by the india asia collision

late quaternary intensified monsoon phases control landscape evolution in the northwest himalaya the intensity of the asian summer monsoon circulation varies over decadal to millennial time scales and is reflected in changes in surface processes terrestrial environments and marine sedi ment records however the mechanisms of long lived 2 5 k y intensified monsoon phases the related changes in precipitation distribution and their effect on landscape evolution and sedimen tation rates are not yet well understood the arid high elevation sectors of the orogen correspond to a climatically sensitive zone that currently receives rain only during abnormal i e strength ened monsoon seasons analogous to present day rainfall anom alies enhanced precipitation during an intensified monsoon phase is expected to have penetrated far into these geomorphic threshold regions where hillslopes are close to the angle of failure we as sociate landslide triggering during intensified monsoon phases with enhanced precipitation discharge and sediment flux leading to an increase in pore water pressure lateral scouring of rivers and ov ersteepening of hillslopes eventually resulting in failure of slopes and exceptionally large mass movements here we use lacustrine deposits related to spatially and temporally clustered large land slides 0 5 km 3 in the sutlej valley region of the northwest him alaya to calculate sedimentation rates and to infer rainfall patterns during late pleistocene 29 24 ka and holocene 10 4 ka inten sified monsoon phases compared to present day sediment flux measurements a fivefold increase in sediment transport rates re corded by sediments in landslide dammed lakes characterized these episodes of high climatic variability these changes thus em phasize the pronounced imprint of millennial scale climate change on surface processes and landscape evolution

the impact of river capture on the landscape development of the dadu river drainage basin eastern tibetan plateau abstract continental collision between india and eurasia plates and associated compression result in the formation of the tibetan plateau with a mean elevation of 5000 m however how the plateau was formed is still under debate in this study by analyzing multiple topographic metrics in the dadu river drainage basin eastern tibetan plateau together with previous studies we attempt to unravel the landscape development there our results reveal significant differences in the obtained topographic metrics within the dadu river drainage basin higher values of hypsometric integral hi normalized stream length gradient slk topographic relief slope and channel steepness in the middle section of the drainage basin between 29 2 n and 31 n and lower values in the upper north of 31 n and lower sections south of 29 2 n meanwhile these topographic metrics show a good match with the millennial scale erosion rates but the long term exhumation rates contrast between the upper dadu and the lower dadu despite similar topographic metric values we infer that the topographic patterns in the dadu river drainage basin are related to river capture between the dadu and anning rivers which resulted in the adjustment of the landscape in the middle section of the dadu river drainage basin with additional incision occurred but not enough to be recorded by low temperature thermochronometric ages

optical dating of landslide dammed lake deposits in the upper yellow river qinghai tibetan plateau china abstract two large landslides dehenglong and suozi blocked the upper yellow river from longyang gorge to liujia gorge on the qinghai tibetan plateau this research is significant because no relevant chronologies for this landslide dammed lake had been reported twelve osl samples were collected from the lacustrine sediments of the landslide dammed lake deposited on both banks of the upper yellow river samples yielded similar ages of ca 80 ka the dehenglong landslide and suozi landslide are thus inferred to be triggered by ca 80 ka tectonic movements

use of a regional relict landscape to measure vertical deformation of the eastern tibetan plateau 1 field work and topography analysis show that remnant local areas of a low relief landscape or erosion surfaces are geographically continuous across the southeastern tibetan plateau margin we correlate these remnant surfaces as a paleolandscape that formed at low elevation remnants of this paleolandscape are preserved because incision of the fluvial system has been largely limited to major rivers and principal tributaries and has not yet progressed throughout the entire fluvial network the incomplete adjustment of the fluvial system signals initiation of rapid bedrock incision into a developing plateau margin and erosional denudation is concentrated in the major river channels this interpretation contradicts earlier notions that low gradient regional topography is the product of regional elevation reduction by intense landscape dissection due to the presence of several large southeast flowing rivers the modern altitude of the reconstructed paleolandscape or relict landscape constrains the vertical displacement of the plateau surface in response to crustal thickening and subsequent erosion during the lateral growth of the tibetan plateau regional preservation of the relict landscape is consistent with minor surface disruption by late cenozoic thrust faults and folds and supports a model of distributed lower crustal thickening because significant erosion is limited to narrow river gorges an increase in the plateau elevation due to isostatic rebound is minor therefore we propose that the modern elevation of the relict landscape reflects isostatically compensated thickening of the lower crust

colorado river long profile metrics knickzones and their meaning abstract the numerical analysis of river long profiles has a rich history and is experiencing a rejuvenation with the advent of improved terrain models and computational tools the highly variable profile and the unusual hydrology of the green colorado river system crossing the colorado plateau provide an example that is germane to debates about transient versus equilibrium knickzone features about the controls of baselevel change due to drainage integration or differential uplift and the role of adjustments to climate hydrology and changing bedrock in order to explore these controls in more detail we define objective geologic study reaches along the green colorado river calculate unit stream power and develop a discharge adjusted steepness index kqsn that avoids the scaling assumptions in substituting contributing area for discharge which are erroneous in this dryland setting determining the nature of knickzones is key and the colorado plateau is a prime setting for study because of the legacy of previous work and a burst of new research and debate the four canyon knickzones along the green colorado are characterized by energy expenditure an order of magnitude greater than in intervening reaches and our kqsn proxy tracks stream power well the strong coincidence of the grand canyon cataract canyon and eastern uinta knickzones with stronger bedrock and mass movement inputs suggests they are pinned equilibrium adjustments to greater bed resistance with the possible exception of desolation canyon as a transient feature marked by anomalous profile convexity along the trunk drainage the knickzone anomalies become greater downstream this and patterns of kqsn in headwater tributaries correspond to some proposed sources of broad mantle driven uplift but they do not match other proposed uplift patterns thus a poorly understood decoupling of topography and proposed uplift exists in some regions