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

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

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

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

uniqueness of modeling results from teleseismic p wave tomography in project tor within project tor which is about teleseismic tomography across the tomquist zone in germany denmark sweden we have confirmed very significant deep lithosphere differences and modeling is substantiated via completely independent methods in 1996 1997 our 130 seismographs constituted the largest seismic antenna ever in europe the tor area was chosen along a well studied crustal profile of an earlier project and the modeling efforts were concentrated on the deep lithosphere and asthenosphere differences to depths around 300 km the tor data have been subjected to p wave travel time tomography surface wave and receiver function analysis as well as anisotropy and scattering measurements an important goal of the project was to make several independent inversions of the tomography data and compare the results in an attempt to evaluate uniqueness resolution and accuracy of these inversions the comparisons of this paper involve more diversity in methods than any previous comparison the geological outcome is a substantiation of earlier statements that the transition is interpreted to be sharp and steep in two places it goes all through the lithosphere at the northern rim of the tornquist zone near the border between sweden and denmark and here the lithosphere difference is large to depths more than 200 km the other lithosphere difference of smaller scale is found near the southern edge of the ringkobing fyn high near the border between denmark and germany also this transition is sharp and steep and goes all through the lithosphere to depths around 120 km these two sharp transitions divide the tor region into 3 different lithosphere structures distinguishable in p wave travel time tomography surface wave dispersion p and s wave anisotropy and partly in p wave scattering the mentioned broad scale features are judged to be unambiguously determined with well described resolution and accuracy unfortunately a detail like the slope of the subcrustal lithosphere transition right under the tronquist zone cannot be constrained even if this is where the resolution is best and the curiosity largest c 2009 elsevier b v all rights reserved

exploding lakes and maleficent water in grassfields legends and myth abstract in august 1984 lake manoun exploded killing 37 people in august 1986 lake nyos exploded killing more than 1700 people both explosions occurred in the rainy season two years and six days apart have there been similar explosions in the cameroon grassfields in the past this paper argues that such explosions have occurred and have been recorded in area folklore in the form of migration stories that point unmistakably to the maleficent activities of lakes and other bodies of water two migration stories are considered and compared an ephemeral exploding lake that destroys the bamessi people in the kom story and a crater lake in the oku story in which the lake is said to have left its bed to destroy the people of kijem in examining the category of maleficent water several types of potentially maleficent water are considered including indigenous classifications of lakes as good or bad and stories about devils or witches associated with water all suggest that the folklore motif of dangerous destructive water may have its basis in observed fact while this evidence is not conclusive it is highly suggestive and in combination with evidence that the area around nyos is very recently settled it lends credence to the supposition that the crater lakes of the area may have a life cycle that involves changes of sometimes stupendous often dangerous proportions

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

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

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

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

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

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

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

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

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

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