geomorphological significance of at many stations hydraulic geometry the critically important at a station hydraulic geometry ahg relationships relate hydraulic variables depth width or velocity to discharge in power law form the recently discovered at many stations hydraulic geometry amhg states that ahg exponents and coefficients are strongly correlated removing one parameter and lending amhgs to remote sensing discharge estimation despite the excitement there is an urgent need to clarify amhg s geomorphological significance for different hydraulic variables using data from 57 rivers in the u s and perturbation experiments we show that the width amhg is weak arising mainly from the mathematical construct involving the exponent in both the regressor and the regressand in contrast the depth amhgs result from geomorphological coevolution the similar time mean condition as argued for in the literature is sufficient but not necessary for rating curve convergence and in turn amhg for depth and velocity the predictive accuracy of amhgs whose coefficient of determination is unit dependent is similar to the flow percentile based downstream hydraulic geometry

verifying the prevalence properties and congruent hydraulics of at many stations hydraulic geometry amhg for rivers in the continental united states abstract hydraulic geometry hg has long enabled daily discharge estimates flood risk monitoring and water resource and habitat assessments among other applications at many stations hg amhg is a newly discovered form of hg with an evolving understanding amhg holds that there are temporally and spatially invariant congruent depth width velocity and discharge values that are shared by all stations of a river furthermore these river wide congruent hydraulics have been shown to link at a station hg ahg in space contrary to previous expectation of ahg as spatially unpredictable to date amhg has only been thoroughly examined on six rivers and its congruent hydraulics are not well understood to address the limited understanding of amhg we calculated amhg for 191 rivers in the united states using usgs field measured data from over 1900 gauging stations these rivers represent nearly all geologic and climatic settings found in the continental u s and allow for a robust assessment of amhg across scales over 60 of rivers were found to have amhg with strong explanatory power to predict ahg across space defined as r 2 0 6 118 191 rivers we also found that derived congruent hydraulics bear little relation to their observed time varying counterparts and the strength of amhg did not correlate with any available observed or congruent hydraulic parameters we also found that amhg is expressed at all fluvial scales in this study some statistically significant spatial clusters of rivers with strong and weak amhg were identified but further research is needed to identify why these clusters exist thus this first widespread empirical investigation of amhg leads us to conclude that amhg is indeed a widely prevalent natural fluvial phenomenon and we have identified linkages between known fluvial parameters and amhg our work should give confidence to future researchers seeking to perform the necessary detailed hydraulic analysis of amhg

the significance of channel recharge rates for estimating debris flow magnitude and frequency the quantification of debris flow hazard requires estimates of debris flow frequency and magnitude several methods have been proposed to determine the probable volume of future debris flows from a given basin but most have neglected to account for debris recharge rates over time which may lead to underestimation of debris flow volumes in basins with rare debris flows this paper deals with the determination of debris recharge rates in debris flow channels based on knowledge of debris storage and the elapsed time since the last debris flow data are obtained from coastal british columbia and a relation is obtained across a sample of basins with similar terrain and climatic conditions for rennell sound on the west coast of the queen charlotte islands the power law relation for area normalized recharge rate rt versus elapsed time te was rt 0 23te 0 58 with an explained variance of 75 per cent a difference in recharge rates may exist between creeks in logged and unlogged forested terrain the power function for undisturbed terrain was rt 0 20te 0 49 while the function for logged areas was rt 0 30te 0 77 this result suggests that for the same elapsed time since the last debris flow clearcut gullies tend to recharge at a slower rate than creeks in old growth forest this finding requires verification particularly for longer elapsed times since debris flow but would have important implications for forest resource management in steep coastal terrain this study demonstrates that commonly used encounter probability equations are inappropriate for recharge limited debris flow channels copyright 2005 john wiley sons ltd

coupling glacial lake impact dam breach and flood processes a modeling perspective glacial lake outburst floods glofs are highly mobile mixtures of water and sediment that occur suddenly and are capable of traveling tens to hundreds of kilometers with peak discharges and volumes several orders of magnitude larger than those of normal floods they travel along existing river channels in some instances into populated downstream regions and thus pose a risk to people and infrastructure many recent events involve process chains such as mass movements impacting glacial lakes and triggering dam breaches with subsequent outburst floods a concern is that effects of climate change and associated increased instability of high mountain slopes may exacerbate such process chains and associated extreme flows modeling tools can be used to assess the hazard of potential future glofs and process modeling can provide insights into complex processes that are difficult to observe in nature a number of numerical models have been developed and applied to simulate different types of extreme flows but such modeling faces challenges stemming from a lack of process understanding and difficulties in measuring extreme flows for calibration purposes here we review the state of knowledge of key aspects of modeling glofs with a focus on process cascades analysis and simulation of the onset propagation and potential impact of glofs are based on illustrative case studies numerical models are presently available for simulating impact waves in lakes dam failures and flow propagation but have been used only to a limited extent for integrated simulations of process cascades we present a spectrum of case studies from patagonia the european alps central asia and the himalayas in which we simulate single processes and process chains of past and potential future events we conclude that process understanding and process chain modeling need to be strengthened and that research efforts should focus on a more integrative treatment of processes in numerical models

mineral chemical and isotopic studies of namaqualand granulites south africa a grenville analogue the northwestern part of south africa and southern south west africa namibia is amongst the most extensive granulite terranes in africa this work reports the results of electron microprobe studies of minerals from two pyroxene cordieriteorthopyroxene gedrite sapphirine and garnet and or cordierite parageneses from namaqualand in the n w cape province of south africa determined pt conditions of prograde metamorphism based on thermodynamic calculations are 800 900 c and ca 6 7 kb and it is argued that rocks of unusual composition notably cordierite orthopyroxene rocks are restites after the extraction of granitic liquid from former argillites this interpretation is consistent with previously published data on similar rocks and with mccarthy s 1976 suggestion of extensive partial melting in the quartzofeldspathic rocks in the area

avulsions and the spatio temporal evolution of debris flow fans debris flows are water laden masses of sediment that move rapidly through channel networks and over alluvial fans where they can devastate people and property episodic shifts in the position of a debris flow channel termed avulsions are critical for debris flow fan evolution and for understanding flow hazards because avulsions distribute debris flow deposits through space and time however both the mechanisms of flow avulsion and their effects on the long term evolution of debris flow fans are poorly understood here we document and analyze the spatial and temporal patterns of debris flow activity obtained by repeat topographic analyses dendrogeomorphic and lichenometric reconstructions and cosmogenic radionuclide dating on 16 fans from japan usa switzerland france and kyrgyzstan where possible we analyze the observed spatio temporal patterns of debris flow activity in conjunction with high resolution topographic data to identify the main controls on avulsion we identify two main processes that control avulsions on debris flow fans operating over distinct time scales first during individual flows or flow surges deposition of sediment plugs locally blocks channels and forces subsequent flows to avulse into alternative flow paths plug deposition is a stochastic process but appears to depend in part on the sequence of flow volumes the geometry of the channel and the composition of the flows second over time scales of tens of events the average locus of debris flow deposition gradually shifts toward the topographically lower parts of a fan highlighting the importance of topographic compensation for fan evolution our documented debris flow avulsions often but not always follow a pattern of channel plugging backstepping of deposition toward the fan apex over one or more flows avulsion and establishment of a new active channel large flows can have contrasting impacts depending on whether or not they follow smaller flows that have deposited channel plugs these results suggest that avulsions and spatio temporal patterns of debris flow fan formation strongly depend on both the magnitude frequency distribution and the sequence of the flows feeding a fan while individual avulsions are generally abrupt and difficult to predict the presence of debris flow plugs and patterns of backstepping may be useful as indicators of impending avulsions over longer time scales the compensational tendency of flows to avulse into topographic depressions on the fan may also be used to identify sectors of the fan that are at risk of future inundation

an empirical statistical model for debris flow travel distance an empirical model is presented for analysis of debris flows based on field observations of landslides from clear cuts in the queen charlotte islands british columbia given an initial failure volume changes in event magnitude arising from entrainment and deposition along the path of movement are used to establish the point at which the cumulative flow volume diminishes to zero and therefore the total travel distance hillslope morphology is used to assign three types of flow behaviour unconfined confined and transition flow flow behaviour and slope angle determine the occurrence of entrainment or deposition in the model for every reach of the event path volume change in a reach is calculated from regression analysis of the queen charlotte islands field observations predictor variables are reach length width of entrainment and or deposition and slope angle together with a bend angle function and the incoming flow volume key words slope stability debris flow travel distance runout ris

fan surface evidence for debris flow avulsion controls and probabilities saline valley california debris flow fans form by shifts of the active channel termed avulsions field and experimental evidence suggest that debris flow avulsions may be induced by depositional lobes that locally plug a channel or super elevation of the channel bed above the surrounding fan surface by analogy to fluvial fans to understand debris flow avulsion processes we differentiate between these controls by quantifying the spatial distribution of debris flow lobe and channel dimensions along with channel bed super elevation on nine debris flow fans in saline valley california usa channel beds are generally super elevated by 2 5 channel depths above the fan surface and locally by more than 7 channel depths thereby substantially exceeding super elevation on fluvial fans depositional lobe thickness and channel depth decrease with distance from the fan apex although both are highly variable across the fans median channel depths roughly correspond to the 50 75th percentiles of lobe thicknesses while minimum channel depths roughly correspond to the 10 25th percentiles in contrast the thicknesses of lobes that have triggered avulsions roughly equal local channel depths and are on average twice as thick as the local median lobe thickness the spatial correspondence between avulsion locations and thick lobe deposits and the lack of correlation with channel bed super elevation leads us to infer that avulsions on these fans are mostly caused by thick lobes forming channel plugs although results may vary with climatic and tectonic setting our findings indicate that avulsion hazard assessment on populated fans should include mapping and monitoring of channel depths relative to typical deposit thicknesses on a given fan

dendrogeomorphic evidence of debris flow frequency and magnitude at mount shasta california debris flow deposits and woody vegetation adjacent to and growing within the channels of whitney bolam mud ash and panthe creeks provide a 300 year record of debris flow frequency at mount shasta dendrochronologic tree ring dating methods for the debris flows proved consistent with available documented records of debris flows nine debris flows not reported in the historic record were documented and dated dendrochronologically the oldest tree ring date for a mudflow was about 1670

surficial patterns of debris flow deposition on alluvial fans in death valley ca using airborne laser swath mapping data debris flows are a common event in mountainous environments they often possess the greatest potential for destruction of property and loss of lives in these regions delimiting the spatial extent of potential damage from debris flows relies on detailed studies of the location of depositional zones current research indicates debris flow fans have two distinct depositional zones however the two zones were derived from studies containing detailed analyses of only a few fans high resolution airborne laser swath mapping alsm data is used to calculate profile curvature and surface gradient on 19 debris flow fans on the eastern side of death valley the relationship between these parameters is assessed to 1 identify if debris flow fans are accurately represented by two depositional zones and 2 to assess how these terrain parameters relate to one another at the individual fan scale the results show at least three zones of deposition exist within the sampled fans these zones do not hold consistent when individual fan morphometry is analyzed in conjunction with localized fan surface gradients fans with consistently shallower gradients exhibit numerous depositional zones with more subtle changes in profile curvature steeper gradient fans exhibit significantly fewer zones with more pronounced local changes in profile curvature the surface complexity of debris flow fans is evident from these analyses and must be accounted for in any type of hazard studies related to these features

the role of debris flow on total denudation in small basins of the ashio mountains japan abstract total and continuing denudation rates were estimated using cosmogenic nuclides and intensive field observations of sediment transport in two small basins c3 and s3 from the ashio mountains japan the c3 basin underlain by triassic bedded chert while the s3 basin has evolved in altered jurassic sandstone shale continuing denudation rates were estimated from the records of coarse sediment transport and stream discharge for 6 years 2004 2009 soil grain size distribution and dissolved load in stream water a debris flow was observed and the volume was measured in c3 chert concentrations of cosmogenic 10be and 26al in fluvial sand were measured to determine spatially averaged total denudation rates for these basins on the basis of steady state assumption continuing denudation rate for c3 chert basin excluding the debris flow mass accounted for 75 of the total denudation rate as measured from the cosmogenic nuclides assuming a difference between the total and continuing denudation rates indicates the impact of repeat debris flows the debris flows with the observed magnitude the mass of 24 t occur with the recurrence intervals of 100 550 years mean 167 years for c3 chert basin for s3 sandstone basin the continuous denudation rates were significantly smaller than the total rates where debris flow had not occurred for at least 17 years the large gap in the denudation rates with different time scales shows contribution of higher magnitude debris flow events with longer recurrence intervals

effects of debris flow magnitude frequency distribution on avulsions and fan development shifts in the active channel on a debris flow fan termed avulsions pose a large threat because new channels can bypass mitigation measures and cause damage to settlements and infrastructure recent but limited field evidence suggests that avulsion processes and tendency may depend on the flow size distribution which is difficult to constrain in the field here we investigate how the flow magnitude frequency distribution and the associated flow magnitude sequences affect avulsion on debris flow fans we created three experimental fans with contrasting flow size distributions 1 a uniform distribution 2 a steep double pareto distribution with many flows around the mean and a limited number of large flows and 3 a shallow double pareto distribution with fewer flows around the mean and more abundant large flows the fan formed by uniform flows developed through regular sequences of stepwise channelization backstepping of deposition toward the fan apex and avulsion over multiple flows in contrast the wide range of sizes in the double pareto distributions led to distinct avulsion mechanisms and fan evolution here large flows could overtop channels creating levee breaches that could initiate avulsion immediately or in subsequent events moreover sequences of small to moderately sized flows could deposit channel plugs triggering avulsion in the next large flow this mechanism was most common on the fan formed by a steep double pareto distribution but was rare on the fan formed by a shallow double pareto distribution where large flows were more frequent we infer that some flow size distributions are more likely to cause avulsions especially those that produce abundant sequences of small flows followed by a large flow critically avulsions in our experiments could occur by either large single events or over multiple flows this observation has important implications for hazard assessment on debris flow fans suggesting that attention should be paid to flowhistory as well as flow size

debris flow recurrence periods and multi temporal observations of colluvial fan evolution in central spitsbergen svalbard abstract fan shaped accumulations of debris flow deposits are common landforms in polar regions such as svalbard although depositional processes in these environments are of high interest to climate as well as mars analog research several parameters e g debris flow recurrence periods remain poorly constrained here we present an investigation based on remote sensing as well as in situ data of a 0 4 km2 large colluvial fan in hanaskogdalen central spitsbergen we analyzed high resolution satellite and aerial images covering five decades from 1961 to 2014 and correlated them with lichenometric dating as well as meteorological data image analyses and lichenometry deliver consistent results and show that the recurrence period of large debris flows 400 m3 is about 5 to 10 years with smaller flows averaging at two per year in the period from 2008 to 2013 while this is up to two orders of magnitude shorter than previous estimates for svalbard 80 to 500 years we found the average volume of 220 m3 per individual flow to be similar to previous estimates for the region image data also reveal that an avulsion took place between 1961 and 1976 when the active part of the fan moved from its eastern to its western portion a case study of the effects of a light rain event 5 mm day in the rainy summer of 2013 which triggered a large debris flow further shows that even light precipitation can trigger major flows this is made possible by multiple light rain events or gradual snow melt pre saturating the permafrost ground and has to be taken into account when predicting the likelihood of potentially hazardous mass wasting in polar regions furthermore our findings imply a current net deposition rate on the colluvial fan of 480 m3 year which is slightly less than the integrated net deposition rate of 576 to 720 m3 year resulting from the current fan volume divided by the 12 500 to 10 000 years since the onset of fan build up after the area s deglaciation however the actual deposition rate which should increase in a warmer climate including more rain cannot be constrained due to effects like ongoing toe cutting of the debris fan and some flows only causing internal redistributions

hydrogeomorphic processes in a steep debris flow initiation zone 1 many debris flows initiate in steep channels 20 degrees yet studies have focused on lower gradient streams where failure is controlled by water height above channel deposits multiple debris flows in a steep channel in ohya landslide central japan were linked to infilling processes i e freeze thaw and dry ravel and partial saturation of accumulated sediment because of very active geomorphic processes in this catchment 39 debris flows were observed in the past 6 yr pre and post event imagery indicates selective transport of finer materials during most debris flows that comprise saturated and unsaturated flows however fluvial sediment processes important in relation to debris flow initiation in gentler channels were minimal critical conditions for the movement of such unsaturated materials are derived by equating shear stress with solid friction of the channel bed

effects of forest harvesting on the occurrence of landslides and debris flows in steep terrain of central japan landslides and debris flows associated with forest harvesting can cause much destruction and the influence of the timing of harvesting on these mass wasting processes therefore needs to be assessed in order to protect aquatic ecosystems and develop improved strategies for disaster prevention we examined the effects of forest harvesting on the frequency of landslides and debris flows in the sanko catchment central japan using nine aerial photo periods covering 1964 to 2003 these photographs showed a mosaic of different forest ages attributable to the rotational management in this area since 1912 geology and slope gradient are rather uniformly distributed in the sanko catchment facilitating assessment of forest harvesting effects on mass wasting without complication of other factors trends of new landslides and debris flows correspond to changes in slope stability explained by root strength decay and recovery the direct impact of clearcutting on landslide occurrence was greatest in forest stands that were clearcut 1 to 10 yr earlier with progressively lesser impacts continuing up to 25 yr after harvesting sediment supply rate from landslides in forests clearcut 1 to 10 yr earlier was about 10 fold higher than in control sites total landslide volume in forest stands clearcut 0 to 25 yr earlier was 5 8 10 3 m 3 km 2 compared with 1 3 10 3 m 3 km 2 in clearcuts 25 yr indicating a fourfold increase compared with control sites during the period when harvesting affected slope stability because landslide scars continue to produce sediment after initial failure sediment supply from landslides continues for 45 yr in the sanko catchment to estimate the effect of forest harvesting and subsequent regeneration on the occurrence of mass wasting in other regions changes in root strength caused by decay and recovery of roots should be investigated for various species and environmental conditions copyright 2007 john wiley sons ltd

parallel retreat of rock slopes underlain by alternation of strata abstract characteristic landscapes e g cuesta cliff and overhang of caprock or stepped terrain formed by differential erosion can be found in areas composed of variable geology exhibiting different resistances to weathering parallel retreat of slopes defined as recession of slopes without changes in their topography is sometimes observed on slopes composed of multiple strata however the conditions needed for such parallel retreat have not yet been sufficiently clarified in this study we elucidated the conditions for parallel retreat of rock slopes composed of alternating layers using a geometric method in addition to evaluate whether various rock slopes fulfilled the conditions for parallel retreat we analyzed topographic data obtained from periodic measurement of rock slopes in the aka kuzure landslide central japan our geometric analysis of the two dimensional slopes indicates that dip angle slope gradient and erosion rate are the factors that determine parallel retreat conditions however dip angle does not significantly affect parallel retreat conditions in the case of steep back slopes slope gradient 40 in contrast dip angle is an important factor when we consider the parallel retreat conditions in dip slopes and gentler back slopes slope gradient

linkage of sediment supply and transport processes in miyagawa dam catchment japan 1 linkages between sediment supply by episodic geomorphic processes obtained from aerial photographs and field surveys and sediment transport estimated from changes in sediment deposition behind a large dam were investigated in the miyagawa dam catchment central japan a total of 6667 landslides were confirmed in the period from 1965 to 2000 on the basis of seven temporal pairs of aerial photographs both the occurrence of landslides and discharge into the dam lake affect sediment yield indicating that fluvial systems in miyagawa dam catchment are supply limited with respect to sediment sediment yields are affected by not only the initial failed volume of landslides but also the mobility of landslides and debris flows in miyagawa dam catchment percentages of landslides reaching channels varied from 56 in 1997 2000 to 75 in 1976 1981 and were correlated with maximum hourly rainfall in addition the mobility of debris flows was higher during periods with high maximum instantaneous discharge compared to lower discharge suggesting that the water content both in initially failed materials and transported sediment controlled their mobility topography also affected the mobility of landslides debris flows for catchments 0 1 km2 the percentage of channel network length impacted by debris flows decreased with increasing catchment area due to reduced channel gradient thus both the magnitude of rainfall runoff events and the catchment topography affect how landslide sediment contributes to sediment yield at the large catchment scale

the influence of debris flow rheology on fan morphology owens valley california we have investigated factors controlling the surface morphology of debris flow fans comprising the bajada along the western slope of owens valley california these fans have average slopes of 4 an extensive network of abandoned boulder lined channels rough undulatory surfaces near the range front and smooth distal surfaces field relationships and mechanical considerations indicate that the channels of the bajada are products of fluvial incision and not debris flow scour this is significant because detailed geomorphic maps indicate that the channels strongly influence the pattern of debris flow deposition the locus of debris flow deposition on a channelized fan surface is set by the interaction of debris flows with the channel system and is controlled by channel size channel gradient flow volume flow hydrograph and flow rheology debris flow behavior is most directly controlled by variations in bulk sediment concentration and its influence on flow rheology whereas low sediment concentration debris flows tend to smooth the surface of the lower fan spreading into thin sheets and filling channels and surface undulations repeated deposition of high sediment concentration debris flows produces the rugged topography of the upper fan the texture of the fan surface rough or smooth is determined by the relative volumetric importance of these two types of debris flow in addition channel avulsions and the associated long term shifting of depositional loci are driven by in channel deposition of debris flows with the highest sediment concentrations these debris flows therefore play a critical role in determining both the structure of the channel network and the long term pattern of deposition on the fan surface as a whole we infer that the frequency distribution of debris flow rheologies set by source terrain geology and hydrology is an important control on fan morphology

combining airborne and terrestrial laser scanning for quantifying erosion and deposition by a debris flow event abstract we quantified the sediment volume transported by a major debris flow event in the halltal austrian alps using a combination of terrestrial tls and airborne laser scanning als which has rarely been carried out before a digital terrain model dtm derived from als data pre event surface was combined with a dtm derived from tls data post event surface both datasets were aligned and compared in a cut and fill analysis estimating differential volumes the main focus lay on the evaluation and accuracy assessment of the applied method tie point based registration of both datasets proved to be insufficient additional alignment by multi station adjustment was necessary to minimise the averaged height error between both datasets amounting for a volumetric error of less than 10 which is comparable to pure als campaigns larger errors were estimated for complex terrain with low scanning resolutions a particular problem in data processing was the low and dense shrub vegetation in the study area which required a specifically adapted filter algorithm an insufficient ground representation was observed for the als data overestimating ground heights for averaged 70 cm despite these limitations the approach proved to be suitable for accurate extreme event quantification the starting zones of the debris flows lie at the bedrock debris interface where runoff is concentrated volumes of 5000 to 12 000 m3 were assessed volume estimation worked better for the erosional than for the depositional features this is because the erosional gullies are relatively deep and the calculation is not affected by pre event vegetation while erosion and sedimentation are balanced for one of the three catchments investigated the deposited volumes are higher than the detected eroded volumes for the other two the reasons are not fully understood the magnitude of the flows was determined by catchment size topographical characteristics and deforestation by a major wildfire in 1946

ten years of debris flow monitoring in the moscardo torrent italian alps abstract field data on debris flows are of utmost importance for improving knowledge of these hazardous phenomena and for the development of attenuation measures in alpine basins debris flows generally occur with a frequency high enough to create serious risk to human settlements and transportation routes but too low to justify monitoring activity capable of providing enough data in a sufficiently short time the moscardo torrent a small stream in the eastern italian alps is an exception to this general situation since it displays a high frequency of debris flows commonly at least one event per year in 1989 this torrent was instrumented and the results of the following 10 years 1989 1998 of debris flow monitoring are presented with an analysis of collected data the equipment installed allowed measurement of rainfall flow stage and ground vibrations caused by debris flows other important debris flow variables that is mean front velocity peak discharge and flowing volume were estimated from instrumental records video pictures have proved to be useful for the visual interpretation of debris flow waves and have made it possible to estimate the surface velocity of debris flows recorded data are compared with other experimental data sets collected and documented worldwide advantages and shortcomings of different types of sensors are discussed with relevance both for research monitoring purposes and for possible use in debris flow warning systems

linking debris flow hazard assessments with geomorphology debris flow hazard assessment schemes are commonly based on empirical physical or numerical methods and techniques inherent in all methods is generally the assumption of unlimited sediment supply this study compares model inputs of sediment requirements for debris flows with estimated sediment reproduction from both solifluction and rockwall retreat the analysis is carried out in bildudalur a community in the westfjords of iceland geomorphic techniques are applied to determine the set of natural processes acting in this landscape to estimate spatial distribution of relevant processes to approximate level of processes activity and to provide information for scenario modeling debris flow volumes are determined by coupling rainfall magnitudes and catchment sizes with average sediment contents rockwall retreat and solifluction rates are based on literature reviews for a rainstorm with a 10 year return period debris flow volumes are calculated for 12 different creeks rates are assumed for solifluction with a velocity of 0 25 m yr at an average depth of 0 5 m and for rockwall retreat with 2 mm yr comparing sediment requirements with estimated sediment reproduction leads to a factor of deficit ranging between 6 2 and 8 5 thus the sediment storage is not refilled as fast as the next potential triggering rainfall occurs consequently if a debris flow has occurred in the past all sediment is removed and the following rainstorm event is djustt causing a flood which is by far less destructive than a debris flow event the challenge of future debris flow hazard assessment schemes is to include geomorphic analysis to be able to obtain more sustainable results d 2004 elsevier b v all rights reserved

theoretical basis for at many stations hydraulic geometry citation gleason c j wang j 2015 theoretical basis for at many stations hydraulic geometry geophysical research letters 42 17 7107 7114 doi 10 1002 2015gl064935

the copper bearing basic rocks of namaqualand south africa copper mineralisation is associated with rocks of basic intermediate composition which occur as a widespread swarm of relatively small irregularly shaped bodies within the gneissic terrain of the okiep district these basic rocks comprise the so called koperberg noritoid suite of namaqualand and constitute one of the three major copper producers in south africa while a metasomatic origin was briefly favoured for the noritoids most researchers have emphasized the cross cutting nature of the noritoids relative to their host rocks and prefer an origin involving magmatic injection high noritoid 87sr 86sr initial ratio values indicated to some workers that mobilisation of suitable crustal materials was more attractive than intrusion of mantle derived melts to account for the origin of the noritoid suite the present study has shown that the structure texture and mineralogy of the noritoids do not lend themselves to interpretation of the noritoids as pristine intrusive rocks and indicate that the noritoids have undergone high grade metamorphism after emplacement the geochemistry of the noritoid suite reveals a pronounced alkaline affinity and mineralogical control of the chemistry characterises the rocks as cumulates the dimensions of the noritoids appear unfavourable for development of cumulate rocks and it is considered possible that the present configuration of the noritoids results from dismemberment of larger intrusive bodies as a result of shear deformation during high grade metamorphism it has not been possible to identify a magma parent to the noritoid suite but we believe the parent to have been an alkaline mantle derived magma which suffered contamination by granitic anatects in the lower crust recognition of the metamorphic history of the namaqualand noritoids renders a comparison between them and the caraiba noritoids of interest

controls on modern alluvial fan processes in the central alps northern italy alluvial fan development in alpine areas is often affected by catastrophic sedimentary processes associated with extreme oods events causing serious risks for people living on the fans hazard assessment in these areas depends on proper identi cation of the dominant sedimentary processes on the fans data from a set of 209 alluvial fans from the central alps of italy are presented in this paper and analysed with the help of various statistical techniques linear regression principal components analysis cluster analysis discriminant analysis and logistic regression first we used modern sedimentary facies and historical records ood events since 15th century to distinguish between the two dominant sedimentary processes on alluvial fans debris ows and stream ows then in order to analyse the main controls on past and present fan processes 36 morphological geological and land use variables were analysed as with observations for arid environment fans catchment morphology is the most in uential factor in the study area whereas geology and land use are minor controls the role of climatic change and landsliding within the catchments also seems to be very important and is discussed statistical techniques also help in differentiating groups of alluvial fans by sets of controlling factors including stage and type of evolution finally by using discriminant analysis and logistic regression we classi ed alluvial fans according to the dominant sedimentary process with a success rate ranging between 75 and 92 per cent copyright 2004 john wiley sons ltd

sediment yield spatial characteristics and the long term evolution of active earthflows determined from airborne lidar and historical aerial photographs eel river california in mountainous landscapes with weak fine grained rocks earthflows can dominate erosion and landscape evolution by supplying sediment to channels and controlling hillslope morphology to estimate the contribution of earthflows to regional sediment budgets and identify patterns of landslide activity earthflow movement needs to be quantified over significant spatial and temporal scales presently there is a paucity of data that can be used to predict earthflow behavior beyond the seasonal scale or over spatially extensive study areas across 226 km 2 of rapidly eroding franciscan complex rocks of the eel river catchment northern california we used a combination of lidar light detection and ranging and orthorectified historical aerial photographs to objectively map earthflow movement between 1944 and 2006 by tracking the displacement of trees growing on earthflow surfaces we find that 7 3 of the study area experienced movement over this 62 yr interval preferentially in sheared argillaceous lithology this movement is distributed across 122 earthflow features that have intricate elongate planform shapes a preferred south southwesterly aspect and a mean longitudinal slope of 31 the distribution of mapped earthflow areas is well approximated by a lognormal distribution with a median size of 36 500 m 2 approximately 6 of the study area is composed of earthflows that connect to major channels these flows generated an average sediment yield of 19 000 t km 2 yr 1 rock erosion rate of 7 6 mm yr over the 62 yr study period equating to a regional yield of 1100 t km 2 yr 1 0 45 mm yr if distributed across the study area as such a small fraction of the landscape can account for half of the regional denudation rate estimated from suspended sediment records 2200 t km 2 yr 1 or 0 9 mm yr we propose a conceptual model for long term earthflow evolution wherein earthflows experience intermittent activity and long periods of dormancy when limited by the availability of readily mobilized sediment on upper slopes ultimately high order river channels and ephemeral gully networks may serve to destabilize hillslopes controlling the evolution of earthflow prone terrain

initiation and runout characteristics of debris flow surges in ohya landslide scar japan abstract the characteristics of debris flows e g velocity discharge kinematic energy are highly dependent on surges incurring abrupt changes to flow height velocity and boulder concentration therefore understanding the initiation and runout characteristics of surges is essential when planning debris flow mitigation monitoring performed using 10 time lapse cameras tlcs in ohya landslide central japan where debris flows occur frequently due to mobilization of storage i e talus cone and channel deposits allowed us to obtain data on a series of surge processes from initiation to termination which occurred during each debris flow event we also analyzed temporal changes in the spatial distribution of storage in the debris flow initiation zone associated with sediment supply from hillslopes and evacuation of sediment by the occurrence of debris flows through periodic measurements of topography using unmanned aerial vehicles uavs debris flow surges were mainly induced by repetitive mass movement of storage through the erosion of channel deposits by overland flow sliding of channel deposits and sediment and water supply from channel banks and tributaries development of a spontaneous wave on the flow surface was not an important formation process of surges in the ohya landslide many debris flow surges initiated at channel sections with deep storage 2 m in depth located

hydraulic characterization of river networks based on flow patterns simulated by 2 d shallow water modeling scaling properties multifractal interpretation and perspectives for channel heads detection

real time measurement and preliminary analysis of debris flow impact force at jiangjia ravine china impact forces associated with major debris flows jiangjia ravine china august 25 2004 were recorded in real time by a system consisting of three strain sensors installed at different flow depths this provides the first real time and long duration record of impact forces associated with debris flows a comprehensive approach including low pass filtering and moving average methods were used to preprocess the recorded signals the upper limit of impact frequency in the debris flows was estimated at 188 66 hz under the assumption that only coarse grains cause effective impact loadings thus a low pass filter with a 200 hz cut off frequency was needed to denoise the original data in order to extract the impact force then the moving average method was applied to separate long term and random components of the filtered data these were interpreted as respectively the fluid pressure and grain impact loading it was found that the peak grain impacts at different depths were non synchronous within the debris flows the impact loadings were far greater than and not proportional to the fluid pressures analysis of the impact force of 38 debris flow surges gives an empirical value for the ratio of the hydrodynamic pressure to the momentum flow density i e the product of debrisflow density and mean velocity square which provides a very valuable basis for understanding debris flow dynamics and designing debris flow management systems copyright c 2011 john wiley sons ltd

direct measurement of channel erosion by debris flows illgraben switzerland 1 the timing and magnitude of channel bed erosion by three debris flows was measured in 2008 at the illgraben catchment switzerland using a scour sensor which consisted of a vertical array of erodible sensor elements during the largest debris flow sediment was entrained progressively and stepwise at the flow head within 20 s after front arrival and onset of erosion started before maximum values for flow height and normal and shear stress measured nearby were reached erosion in one of the two smaller debris flows also occurred at the head of the flow but the magnitude of erosion was at the detection limit for the sensor for the other small debris flow we were not able to determine the timing of erosion due to the presence of a sediment layer covering the sensors measurements of pressure fluctuations along the channel sidewall which are produced by interparticle collisions within the flow indicate that the entrainment of sediment is coincident with the largest mean and fluctuating pressures suggesting that interparticle collisions may drive the erosion process at the front of debris flows after erosion at the head of the debris flows sediment was deposited on top of the erosion sensor columns indicating that the bed was reworked to a larger depth than directly visible at the surface after the event observations from elsewhere along the channel support our measurements of the magnitude of net debris flow erosion and indicate that significant erosion can be expected on debris fans when the flow is confined to a channel debris flow entrainment and subsequent bulking of the flow influence the flow dynamics and therefore should be considered in debris flow models and hazard assessment

colluvial sediment dynamics in mountain drainage basins abstract colluvial sediment dynamics are examined using a 70 year landslide inventory in formerly glaciated mountain drainage basins of coastal british columbia canada landslide sediment transfer is documented by identifying landslide types and by characterizing preferential sites of landslide initiation delivery and storage across spatial scales data analysis reveals that open slope landslides delivering material to seasonal or perennial channels and fluvial terraces are the dominant mechanisms of sediment transfer this finding suggests high instability of the low order channel network and its ongoing re organization degradation after generalized sediment recharge occurred in the last glacial maximum in the study period landslide activity across the landscape has generated net degradation on planar slopes and first order colluvial channels whereas unchannelled valleys higher order colluvial channels and alluvial channels have accumulated material the scaling relation of the landslide sediment yield appears to be controlled by the spatial arrangement of the relict glacial macro forms landslide yield is highest in unchannelled topography decreases at the scale of channel initiation ad 0 002 km2 and remains constant for drainage areas where length scales of cirque valley walls and hanging valley floors overlap 0 002

recognition classification and mechanical description of debris flows abstract various types of flow or mass movement involving water and sediments occur on steep slopes in mountainous areas among them debris flows are peculiar events during which a large volume of a highly concentrated viscous water debris mixture flows through a stream channel throughout the world these phenomena cause considerable damage but remain poorly understood although a basic knowledge is already available concerning their recognition and propagation firstly a synthesis of the useful practical criteria of recognition is proposed debris flows must be seen as intermediate phenomena between hyperconcentrated flows intense bed load transport and landslides separated from them by sharp transitions of some characteristics celerity deposit nature and flow type two parameters solid fraction and material type thought to be appropriate for a sound and practical classification are brought out and the corresponding complete classification of flow and mass movements in mountain areas is presented two extreme debris flow types are thus distinguished muddy debris flows and granular debris flows a critical review of recent advances in debris flow dynamic is then proposed it is pointed out that adequate work must be carried out in the field of non newtonian fluid mechanics in particular one fundamental rheological property of debris flow materials is the yield stress which explains thick deposits on steep slopes and can be inferred from field measurements furthermore it can be used to estimate viscous dissipation within the bulk during flow relevant models predicting muddy debris flow dynamics are already available whereas further progress is needed concerning granular flows

mass movements and tree rings a guide to dendrogeomorphic field sampling and dating abstract trees affected by mass movements record the evidence of geomorphic disturbance in the growth ring series and thereby provide a precise geochronological tool for the reconstruction of past activity of mass movement the identification of past activity of processes was typically based on the presence of growth anomalies in affected trees and focused on the presence of scars tilted or buried trunks as well as on apex decapitation for the analyses and interpretation of disturbances in tree ring records in contrast clear guidelines have not been established with largely differing or no thresholds used to distinguish signal from noise at the same time processes with a large spatial footprint e g snow avalanches landslides or floods will likely leave growth anomalies in a large number of trees whereas a falling rock would only cause scars in one or a few trees along its trajectory based on the above considerations we examine issues relating to the interpretation and dendrogeomorphic dating of mass movements particular attention is drawn to sampling in terms of sample distribution across a study site the actual selection of trees as well as to sample size i e number of trees sampled based on case studies from snow avalanche debris flow and landslide sites we demonstrate that thresholds can indeed improve dating quality and at the same time minimize noise in time series we also conclude that different thresholds need to be used for different processes and different periods of the reconstruction especially for the early stages of the reconstruction when the number of potentially responding trees will be much smaller this paper seeks to set standards for dendrogeomorphic fieldwork analysis and interpretation for different processes of mass movements

debris flow dominance of alluvial fans masked by runoff reworking and weathering arid alluvial fan aggradation is highly episodic and fans often comprise active and inactive sectors hence the morphology and texture of fan surfaces are partly determined by secondary processes of weathering and erosion in addition to primary processes of aggradation this introduces considerable uncertainty in the identification of formative processes of terrestrial and martian fans from aerial and satellite imagery the objectives of this study are i to develop a model to describe the sedimentological and morphological evolution of inactive fan surfaces in arid settings and ii to assess the relative importance of primary processes of aggradation and secondary processes of weathering and reworking for surface morphology and sedimentology and for the stratigraphic record we studied an alluvial fan characterized by a recently active sector and a long abandoned inactive sector along the coast of the hyperarid atacama desert here rates of primary geomorphic activity are exceptionally low because of extreme aridity while weathering rates are relatively high because of the effects of coastal fogs long term processes of fan aggradation and reworking were determined through sedimentological facies analysis of stratigraphic sections ground surveys for textural and morphological patterns at the fan surface were integrated with remote sensing by an unmanned airborne vehicle uav discharges and sediment transport capacities were calculated to estimate the efficiency of secondary runoff in reshaping the inactive fan sector stratigraphic sections reveal that the fan was dominantly aggraded by debris flows whereas surface morphology is dominated by debris flow signatures in the active sector and by weathering and runoff on the inactive sector on the latter rapid particle breakdown prevents the formation of a coarse desert pavement furthermore relatively frequent local runoff events erode proximal debris flow channels on the inactive sector to form local lag deposits and accumulate fine sediment in low gradient distal channels forming a well developed drainage pattern that would suggest a runoff origin from aerial images nevertheless reworking is very superficial and barely preserved in the stratigraphic record this implies that fans on earth and mars that formed dominantly by sporadic mass flows may be masked by a surface morphology related to other processes

exploring debris flow history and process dynamics using an integrative approach on a dolomitic cone in western austria the evolution of a debris flow cone depends on a multitude of factors in the hydrogeomorphic system investigations of debris flow history and cone dynamics in highly active catchments therefore require an integrative approach with a temporal and spatial resolution appropriate for the goals of the study we present the use of an orthophoto time series to augment standard dendrogeomorphic techniques to describe the spatio temporal dynamics of debris flows on a highly active cone in the western austrian alps analysis of seven orthophotos since 1951 revealed a migration of active deposition areas with a resulting severe loss of forest cover 80 and a mean tree loss per year of 10 4 range 1 3 16 6 trees per year analysis of 193 pinus mugo ssp uncinata trees allowed the identification of 161 growth disturbances corresponding to 16 debris flows since 1839 and an average decadal frequency of 0 9 events as a result of the severe loss of forest cover we speculate that 20 of the more recent events were actually captured in the tree ring record giving a decadal return interval of 7 5 events for a period of 60 years based on three annual field observations it is evident that this catchment the barenrufe produces very frequent 1 yr small in the order of a few 10 to 100 m3 debris flows with minor material relocation the specific challenges of tree ring analysis in this tree species and in highly active environments are explicitly addressed in the discussion and underline the necessity of employing complementary methods of analysis in an integrative manner copyright 2012 john wiley sons ltd

the corsica sardinia massif as source area for the early northern apennines foredeep system evidence from debris flows in the macigno costiero late oligocene italy large isolated gravity flows debrites are widely present in the stratigraphic record of the northern apennines foreland basin system these strata may be useful for provenance signals and dispersal pathways during foreland evolution this paper examines a cohesive debris flow bed interbedded with turbidite strata of the macigno formation late oligocene tuscany italy in order to obtain new data on the provenance of the clastic material clasts in the debris flow are predominantly plutonic granodiorite tonalite and s granite and subordinately metamorphic gneiss and schist and sedimentary calcareous clasts the composition of the clasts within the debris flow is similar to the clastic composition of the interbedded turbidite sandstones of the macigno costiero the depositional features of the debris flow suggest that it traveled for a short distance within the basin before it was deposited not far from the slope the absence of a high pressure low temperature hp lt paragenesis in the plutonic and metamorphic clasts of the debris flow indicates a provenance from a crystalline basement not involved in the high pressure phases of the alpine orogenesis previous studies have indicated the central western alps as potential source areas for the macigno formation sediments the lack of hp lt metamorphic signatures in our studied samples excludes the pennidic and austroalpine nappes of the western alps as possible sources for the debris flows of the macigno costiero these new data sedimentological petrographical and microstructural suggest that the corsica sardinia hercynian basement lacking a hp lt paragenesis is the more accredited source area of the debris flow and of the related turbidite sandstones of the macigno costiero succession these foredeep feeding sediments were probably before deposited within an episutural basin developed close to the northern apennines orogenic wedge

interpretation of recent alpine landscape system evolution using geomorphic mapping and l band insar analyses abstract alpine landscapes are typically characterized by inherited features of past glaciations and for the more recent past by the interplay of a multitude of types of geomorphic processes including permafrost creep rockfalls debris flows and landslides these different processes usually exhibit large spatial and temporal variations in activity and velocity the understanding of these processes in a wide alpine area is often hindered by difficulties in their surveying in this study we attempt to disentangle recent changes in an alpine landscape system using geomorphic mapping and l band dinsar analyses alos palsar in the zermatt valley swiss alps geomorphic mapping points to a preferential distribution of rock glaciers on north facing slopes whereas talus slopes are concentrated on south facing slopes field based interpretation of ground deformation in rock glaciers and movements in talus slopes correlates well with the ratio of insar images showing potential ground deformation moraines formed during the little ice age rock glaciers and talus slopes on north facing slopes are more active than landforms on south facing slopes implying that the presence of permafrost facilitates the deformation of these geomorphic units such deformations of geomorphic units prevail also at the elevation of glacier termini for rock cliffs the ratio of images indicating retreat is affected by slope orientation and elevation linkages between sediment supply from rock cliffs and sediment transport in torrents are different among tributaries affected by relative locations between sediment supply areas and the channel network we conclude that the combined use of field surveys and l band dinsar analyses can substantially improve process understanding in steep high mountain terrain

characterizing arid region alluvial fan surface roughness with airborne laser swath mapping digital topographic data 1 range front alluvial fan deposition in arid environments is episodic and results in multiple fan surfaces and ages these distinct landforms are often defined by descriptions of their surface morphology desert varnish accumulation clast rubification desert pavement formation soil development and stratigraphy although quantifying surface roughness differences between alluvial fan units has proven to be difficult in the past high resolution airborne laser swath mapping alsm digital topographic data are now providing researchers with an opportunity to study topography in unprecedented detail here we use alsm data to calculate surface roughness on two alluvial fans in northern death valley california we define surface roughness as the standard deviation of slope in a 5 m by 5 m moving window comparison of surface roughness values between mapped fan surfaces shows that each unit is statistically unique at the 99 confidence level furthermore there is an obvious smoothing trend from the presently active channel to a deposit with cosmogenic 10be and 36cl surface exposure ages of 70 ka beyond 70 ka alluvial landforms become progressively rougher with age these data suggest that alluvial fans in arid regions smooth out with time until a threshold is crossed where roughness increases at greater wavelength with age as a result of surface runoff and headward tributary incision into the oldest surfaces

accuracy assessment of georectified aerial photographs implications for measuring lateral channel movement in a gis aerial photographs are commonly used to measure planform river channel change we investigated the sources and implications of georectification error in the measurement of lateral channel movement by testing how the number 6 30 and type human versus natural landscape features of ground control points gcps and the order of the transformation polynomial first second and third order affected the spatial accuracy of a typical georectified aerial photograph error was assessed using the root mean square error rmse of the gcps as well as error in 31 independent test points the rmse and the mean and median values of test point errors were relatively insensitive to the number of gcps above eight but the upper range of test point errors showed marked improvement i e the number of extreme errors was reduced as more gcps were used for georectification using more gcps thus improved overall georectification accuracy but this improvement was not indicated by the rmse suggesting that independent test points located in key areas of interest should be used in addition to rsme to evaluate georectification error the order of the transformation polynomial also influenced test point accuracy the second order polynomial function yielded the best result for the terrain of the study area gcp type exerted a less consistent influence on test point accuracy suggesting that although hard edged points e g roof corners are favored as gcps some soft edged points e g trees may be used without adding significant error based upon these results we believe that aerial photos of a floodplain landscape similar to that of our study can be consistently georectified to an accuracy of approximately f5 m with 10 chance of greater error the implications of georectification error for measuring lateral channel movement are demonstrated with a multiple buffer analysis which documents the inverse relationship between the size of the buffers applied to two channel centerlines and the magnitude of change detected between them this study demonstrates the importance of using an independent test point analysis in addition to the rsme to evaluate and treat locational error in channel change studies d 2005 published by elsevier b v

reconstructing spatio temporal patterns of debris flow activity using dendrogeomorphological methods debris flows are a major threat in many parts of the alps where they repeatedly cause severe damage to infrastructure and transportation corridors or even loss of life nonetheless the spatial behavior of past debris flow activity and the analysis of areas affected during particular events have been widely neglected in reconstructions so far it was therefore the purpose of this study to reconstruct spatio temporal patterns of past debris flows on a forested cone in the swiss alps bruchji torrent blatten valais the analysis of past events was based on a detailed geomorphic map 1 1000 of all forms related to debris flows as well as on tree ring series from 401 heavily affected trees larix decidua mill and picea abies l karst growing in or next to deposits the samples were analyzed and growth disturbances related to debris flow activity assessed such as tangential rows of traumatic resin ducts the onset of reaction wood or abrupt growth suppression or release in total 960 growth disturbances were identified in the samples belonging to 40 different event years between a d 1867 and 2005 in addition the coupling of tree ring data with the geomorphic map allowed reconstruction of eleven formerly active channels and spatial representation of individual events based on our results we believe that before 1935 debris flows preferentially used those channels located in the western part of the cone whereas the eastern part of the cone remained widely unaffected the spatial representation of the 40 events also allowed identification of five different spatial patterns for debris flows at the study site 2006 elsevier b v all rights reserved

a regional reconstruction of debris flow activity in the northern calcareous alps austria dendrogeomorphic dating of historical debris flow events is a highly valuable tool for improving historical records in the field of natural hazard management previous dendrogeomorphic investigations generally have focused on case studies of single torrents however regional investigations may offer a more accurate reconstruction of regional patterns of activity and therefore may have an advantage over individual cases the aim of the study is to provide a regional reconstruction of debris flow events for a site in the northern calcareous alps of western austria gamperdonatal vorarlberg and to document spatial and temporal morphological changes in individual and neighboring torrents analysis of 442 trees 268 pinus mugo ssp uncinata 164 picea abies and 10 abies alba allowed identification of 579 growth disturbances corresponding to 63 debris flow events since a d 1839 the majority of growth disturbances were in the form of growth suppression or release 76 owing to the nature of both the deposited material and the process characteristics regional patterns of event frequency indicated a paucity of activity in the early to mid twentieth century and increased activity since a d 1948 whereby large events were followed by subsequent years of continued activity of smaller magnitude patterns of frequency could be attributed primarily to spatiotemporal changes in channel morphology but may also be reflective of changes in transport conditions within the valley this study provides the first regional investigation in the austrian alps and contributes to the documentation of tree responses to geomorphic disturbances in calcareous material

landslide inventory in a rugged forested watershed a comparison between air photo and field survey data abstract landslide inventories are routinely compiled by means of aerial photo interpretation api when examining photo pairs the forest canopy notably in old growth forest hides a population of not visible landslides in the present study we attempt to estimate how important is the contribution of landslides not detectable from aerial photographs to the global mass of sediment production from mass failures on forested terrain of the capilano basin coastal british columbia api was coupled with intensive fieldwork for identification and measurement of all landslides a 30 year framework was adopted we show that not visible landslides can represent up to 85 of the total number of failures and account for 30 of the volume of debris mobilised such percentages display high sub basin variability with rates of sediment production varying by one order of magnitude between two sub basins of the study area this is explained qualitatively by gis based analysis of slope frequency distributions drainage density and spatial distribution of surficial materials such observations find further support in the definitions of transport limited and supply limited basins as a practical consideration to land managers we envisage that supplementary fieldwork for landslide identification is mandatory in transport limited systems only fieldwork has demonstrated that gully related failures have a greater importance than one could expect from api

biographical sketch of a giant deciphering recent debris flow dynamics from the ohya landslide body japanese alps abstract debris flow frequency discharge and travel distance are highly catchment dependent and typically controlled by topography hydrological conditions and sediment supply as a consequence detailed and case specific investigations are needed to decipher debris flow histories in order to improve hazard mitigation this study documents past ca 10 years debris flow occurrences originating from the ohya landslide central japan by using a large set of methods including field monitoring repeat airborne lidar orthophoto interpretation and tree ring reconstructions we demonstrate that the different approaches generally agree on the occurrence of debris flows but that mismatches may exist when it comes to the assessment of areas affected by individual events these differences may even exceed the usual errors in precision inherent to each of the methods used in the present case high resolution orthophoto interpretation tends to underestimate areas affected by debris flows especially in the vertical direction in the absence of lateral movement of the channel bed and as a result of shade and areas under trees on the other hand we realize that lidar data cannot necessarily be used to distinguish local changes in topography from noise tree ring analyses can help to improve the temporal resolution of the analysis but may have limitations when it comes to the definition of areas affected by an event because of the point type nature of data we conclude that the best and most complete results are obtained by combining multiple methods to improve the spatial and temporal resolution of past debris flows and to delimit areas affected by individual events

earthquake triggered increase in sediment delivery from an active mountain belt in tectonically active mountain belts earthquake triggered landslides deliver large amounts of sediment to rivers we quantify the geomorphic impact of the 1999 mw 7 6 chi chi earthquake in taiwan which triggered 20 000 landslides coseismic weakening of substrate material caused increased landsliding during subsequent typhoons most coseismic landslides remained confined to hillslopes downslope transport of sediment into the channel network occurred during later storms the sequential processes have led to a factor of four increase in unit sediment concentration in rivers draining the epicentral area and increased the magnitude and frequency of hyperpycnal sediment delivery to the ocean four years after the earthquake rates of hillslope mass wasting remain elevated in the epicentral area

a 38 000 year record of floods and debris flows in the ilo region of southern peru and its relation to el nino events and great earthquakes abstract previous work throughout the ilo region of south coastal peru has documented the existence of flood and debris flow deposits produced by two el nino events evidently much more severe than any in recent history these two events have been dated to ca ad 1300 1400 and ad 1607 08 the late pleistocene to holocene record of older sedimentary deposits in this region is dominated by flood and debris flow deposits of similar scale these older deposits have been described and dated from three coastal alluvial fan sites these deposits which are as old as 38 200 years are dominated by massive debris flow deposits several tens of cm thick typically composed of cobble and boulder sized clasts in a matrix of silty sand with characteristics indicating generation by heavy rainfall in an arid environment twenty two radiocarbon dates and a single infrared stimulated luminescence date show that particularly severe el nino events occurred throughout the late pleistocene and two of three divisions of the holocene with significantly different frequencies the period of greatest activity was during the early holocene when at least six such events took place during a period of ca 3600 years beginning near the end of the younger dryas ca 12 000 years ago one of these events produced a debris flow that may have caused abandonment of the paleo indian site at quebrada tacahuay one of the oldest on the andean coast no severe events took place during the middle holocene between ca 8400 and 5300 years ago when a wide variety of other paleoclimate proxy records indicate that the el nino southern oscillation regime was particularly weak since ca 5300 years ago four of these severe events have taken place the late pleistocene sequence is constrained by only two dates which indicate that at least ten severe events took place between ca 38 200 and 12 900 years ago mechanisms probably responsible for generating these large scale deposits include 1 mega ninos that produced anomalously heavy rainfall along most or all of the central andean coast 2 el ninos that occurred shortly after great earthquakes that produced large amounts of sediment or 3 el ninos that produced anomalously heavy local rainfall the existence of these large scale deposits in the ilo region implies a level of hazard much higher than indicated by the historical record alone

floods in mountain environments a synthesis floods are a crucial agent of geomorphic change in the channels and valley floors of mountains watercourses at the same time they can be highly damaging to property infrastructure and life because of their high energy mountain watercourses are highly vulnerable to environmental changes affecting their catchments and channels many factors have modified and frequently still tend to modify the environmental conditions in mountain areas with impacts on geomorphic processes and the frequency magnitude and timing of floods in mountain watercourses the ongoing climate changes vary between regions but may affect floods in mountain areas in many ways in many mountain regions of europe widespread afforestation took place over the twentieth century considerably increasing the amounts of large wood delivered to the channels and the likelihood of jamming bridges at the same time deforestation continues in other mountain areas accelerating runoff and amplifying the magnitude and frequency of floods in foreland areas in many countries in channel gravel mining has been a common practice during recent decades the resultant deficit of bed material in the affected channels may suddenly manifest during flood events resulting in the failure of scoured bridges or catastrophic channel widening during the past century many rivers in mountain and foreland areas incised deeply the resultant loss of floodplain water storage has decreased attenuation of flood waves hence increasing flood hazard to downstream river reaches on the other hand a large amount of recent river restoration activities worldwide may provide examples of beneficial changes to flood risk attained as a result of increased channel storage or reestablished floodplain water storage relations between geomorphic processes and floods operate in both directions which means that changes in flood probability or the character of floods e g increased wood load may significantly modify the morphology of mountain rivers but morphological changes of rivers can also affect hydrological properties of floods and the associated risk for societies this paper provides a review of research in the field of floods in mountain environments and puts the papers of this special issue dedicated to the same topic into context it also provides insight into innovative studies methods or emerging aspects of the relations between environmental changes geomorphic processes and the occurrence of floods in mountain rivers

behaviour of debris flows located in a mountainous torrent on the ohya landslide japan although information on the behaviour of debris flow in the initiation zone is important for the development of mitigative measures field data regarding this behaviour are scarce this research examines the behaviour of debris flow in the initiation zone based on field observations in the upper ichinosawa catchment of the ohya landslide in ja pan in spring 1998 a monitoring system consisting of video cameras ultrasonic sensors capacitive water depth probes and water pressure sensors wps was installed to assess the behaviour of debris flows in the initiation zone on the basis of video image analysis we found that main flow phases during debris flow events consisted of flow con taining largely muddy water and flow containing largely cobbles and boulders data obtained from ultrasonic sensors and wps show that the former flow type muddy flow has large amounts of interstitial water throughout its mass whereas the latter flow type has an unsaturated layer in the upper portion results indicate that the concentration of solids in debris flows differs from flow to flow debris flows in the upper ichinosawa catchment cause both erosion and deposition and exhibit changes in their concentration of solids

sediment transfer patterns at the illgraben catchment switzerland implications for the time scales of debris flow activities debris flows strongly control sediment transfer patterns in mountainous catchments we quantify sediment transfer at the illgraben switzerland where debris flows are frequent and geomorphic change is rapid four sequential aerial image series from fall 2007 to fall 2009 were used to measure landscape change in relation to debris flows the debris often originating from bedrock landslides was transported in patterns of erosion storage and remobilization the landslides typically stopped on the downslope hillslope or in the channel and they did not transform directly into debris flows the magnitude and nature of sediment transfer patterns show large spatial and temporal variability and the storage time of the deposits was shorter than one year landslide volumes were an order of magnitude smaller than the debris flows at the catchment outlet while the mechanism of debris flow initiation could not be determined unambiguously clearly debris flows must entrain substantial amounts of sediment along the flow path to attain the volumes estimated at the distal end of the fan

bam bayesian amhg manning inference of discharge using remotely sensed stream width slope and height the forthcoming surface water and ocean topography swot nasa satellite mission will measure water surface width height and slope of major rivers worldwide the resulting data could provide an unprecedented account of river discharge at continental scales but reliable methods need to be identified prior to launch here we present a novel algorithm for discharge estimation from only remotely sensed stream width slope and height at multiple locations along a mass conserved river segment the algorithm termed the bayesian amhg manning bam algorithm implements a bayesian formulation of streamflow uncertainty using a combination of manning s equation and at many stations hydraulic geometry amhg bayesian methods provide a statistically defensible approach to generating discharge estimates in a physically underconstrained system but rely on prior distributions that quantify the a priori uncertainty of unknown quantities including discharge and hydraulic equation parameters these were obtained from literature reported values and from a usgs dataset of acoustic doppler current profiler adcp measurements at usgs stream gauges a dataset of simulated widths slopes and heights from 19 rivers was used to evaluate the algorithms using a set of performance metrics results across the 19 rivers indicate an improvement in performance of bam over previously tested methods and highlight a path forward in solving discharge estimation using solely satellite remote sensing

counting scars on tree stems to assess rockfall hazards a low effort approach but how reliable rockfall is a widespread and hazardous process in mountain environments but data on past events are only rarely available growth ring series from trees impacted by rockfall were successfully used in the past to overcome the lack of archival records dendrogeomorphic techniques have been demonstrated to allow very accurate dating and reconstruction of spatial and temporal rockfall activity but the approach has been cited to be labor intensive and time consuming in this study we present a simplified method to quantify rockfall processes on forested slopes requiring less time and efforts the approach is based on a counting of visible scars on the stem surface of common beech fagus sylvatica l data are presented from a site in the inn valley austria where rocks are frequently detached from an 200 m high south facing limestone cliff we compare results obtained from i the classical analysis of growth disturbances in the tree ring series of 33 norway spruces picea abies l karst and ii data obtained with a scar count on the stem surface of 50 f sylvatica trees a total of 277 rockfall events since a d 1819 could be reconstructed from tree ring records of p abies whereas 1140 scars were observed on the stem surface of f sylvatica absolute numbers of rockfalls and hence return intervals vary significantly between the approaches and the mean number of rockfalls observed on the stem surface of f sylvatica exceeds that of p abies by a factor of 2 7 on the other hand both methods yield comparable data on the spatial distribution of relative rockfall activity differences may be explained by a great portion of masked scars in p abies and the conservation of signs of impacts on the stem of f sylvatica besides data indicate that several scars on the bark of f sylvatica may stem from the same impact and thus lead to an overestimation of rockfall activity