on the nonuniqueness of sediment yield at the catchment scale the effects of soil antecedent conditions and surface shield the understanding of reasons leading to nonuniqueness of soil erosion susceptibility is still inadequate yet indispensable for establishing general relations between runoff volume and sediment yield to obtain relevant insights we performed a series of numerical simulations with a detailed hydrodynamic model using synthetic storms of varying intensity duration and lag time between events as representations of different hydrologic response conditions in a zero order catchment the design targeted to generate surface flow and perturb soil substrate by a first rainfall event creating a set of initial conditions in terms of flow and deposited sediment prior to the onset of a subsequent rainfall event due to the differential effect of re detachment and re entrainment processes on soil particles of varying sizes the deposited sediment mass formed shielding layer one of the essential results is that unless the initial condition of flow and sediment is identical the same volume of runoff can generate different total sediment yields and their variation can reach up to 200 the effect is attributed to two major conflicting effects exerted by the deposited initialization soil antecedent condition sediment mass erosion enhancement because of supply of highly erodible sediment and erosion impediment because of constrain on the availability of lighter particles by heavier sediment consistently with this inference long term simulations with continuous rainfall show that a peculiar feature of sediment yield series is the existence of maximum before the steady state is reached the two characteristic time scales the time to peak and the time to steady state separate three characteristic periods that correspond to flow limited source limited and steady state regimes these time scales are log linearly and negatively related to the spatially averaged shields parameter the smaller the rainfall input and the heavier a given particle is the larger the two scales are the results provide insights on how the existence of shield operates on erosion processes possibly implying that accurate short term predictions of geomorphic events from headwater areas may never become a tractable problem the latter would require a detailed spatial characterization of particle size distribution prior to precipitation events

spatial and temporal patterns of debris flow deposition in the oregon coast range usa patterns of debris flow occurrence were investigated in 125 headwater basins in the oregon coast range time since the previous debris flows was established using dendrochronology and recurrence interval estimates ranged from 98 to 357 years tributary basins with larger drainage areas had a greater abundance of potential landslide source areas and a greater frequency of scouring events compared to smaller basins the flux rate of material delivered to the confluence with a larger river influenced the development of small scale debris flow fans fans at the mouths of tributary basins with smaller drainage areas had a higher likelihood of being eroded by the mainstem river in the interval between debris flows compared to bigger basins that had larger more persistent fans valley floor width of the receiving channel also influenced fan development because it limited the space available to accommodate fan formation of 63 recent debris flows 52 delivered sediment and wood directly to the mainstem river 30 were deposited on an existing fan before reaching the mainstem and 18 were deposited within the confines of the tributary valley before reaching the confluence spatial variation in the location of past and present depositional surfaces indicated that sequential debris flow deposits did not consistently form in the same place instead of being spatially deterministic results of this study suggest that temporally variable and stochastic factors may be important for predicting the runout length of debris flows

the control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment the study of a sample of river sediment enables the determination of spatially averaged denudation rates that provide an exceptional perspective on erosion and weathering processes that have taken place within a landscape these measurements are done with in situ produced cosmogenic nuclides e g 10be 26al mostly in quartz from alluvial sediment cosmogenic nuclides are produced when secondary cosmic rays interact with the very uppermost layer of the earth s surface they are produced within a characteristic depth scale of about 1 m which means that the measured concentrations record an integrated denudation history while material passed through this depth interval depending on the denudation rate the resulting integration time scales are 103 to 105 years and one obtains a robust long term estimate of natural denudation that is relatively insensitive to short term changes the last 10 years have seen significant research activity using these methods and an array of fascinating tectono geomorphologic and geochemical insights are emerging amongst these is the ability to identify the physical and chemical processes with which a landscape responds to tectonic activity or climate change a compilation of world wide denudation rates in non glaciated areas that however does not yet include some of the world s most active mountain belts has resulted in the following findings some of which have been unexpected 1 no obvious relationship between precipitation or mean annual temperature and total denudation is apparent 2 topographic relief alone does not result in high rates of denudation 3 denudation rates are high in areas of landscape rejuvenation that is triggered and controlled by tectonic activity faulting escarpment formation and retreat rifting surface uplift 4 rates of weathering using a combination of cosmogenic nuclides and zirconium normalised cation loss balances co vary primarily with physical erosion rates and much less with temperature or precipitation 5 in some areas of high land use short term rates from river load gauging exceed those from cosmogenic nuclides by several orders of magnitude which serves to highlight the severity of geomorphic change caused by human action in the future the control mechanisms over denudation will be determined on all spatial scales ranging from the single soil section to entire river basins the same analysis can be done back through time on well dated terraces lake records and marine sediment cores which is possible with 10be for the past 1 2 my the rates obtained will be used to develop a quantitative understanding of tectonic geomorphologic and geochemical landscape processes which in turn is a prerequisite to design and calibrate models of the response of landscapes to tectonic climate and anthropogenic forcing

geological relationships and u pb zircon and 40 ar 39ar tourmaline geochronology of gneisses and tourmalinites from the nevado filabride complex western sierra nevada spain tectonic implications abstract the nevado filabride complex the lowest complex in the betic hinterland forms a stack of alpine nappes the tectonic units consist of metasedimentary sequences whose ages are not well constrained gneiss bodies included in the sequences have been one of the few sources of geochronological data in this metamorphic complex new radiometric data from u pb zircon dating on gneisses from the western sierra nevada confirm the presence of late carboniferous intrusive rocks in the betic hinterland these results combined with available data from the literature and a detailed structural analysis suggest that the gneisses represent a single late variscan magmatic event evidence for a close genetic relation between gneisses and tourmalinites is provided by field and petrographic observations in conjunction with geochemical data u pb zircon 314 7 304 23 ma and 40 ar 39 ar tourmaline 319 85 5 81 317 85 3 67 ma geochronology a pre late carboniferous age for the basal formation of the nevado filabride sequence can be inferred the gneiss protolith and the graphite schist are considered to be the boron source and the precursor of the tourmalinites respectively superposed tectonic units rather than a continuous palaeozoic sequence is supported by the occurrence of palaeozoic rocks at the top of the nevado filabride complex the nappe tectonics as evidenced from the contractional character of the unit boundaries and the superposition of higher grade on lower grade metamorphic rocks is additionally supported by the superposition of older on younger rocks as revealed from radiometric data

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

contemporary versus long term denudation along a passive plate margin the role of extreme events short term contemporary and long term denudation rates were determined for the blue mountains plateau in the western sydney basin australia to explore the role of extreme events wildfires and catastrophic floods in landscape denudation along a passive plate margin contemporary denudation rates were reconstructed using 40 years of river sediment load data from the nattai catchment in the south west of the basin combined with an analysis of hillslope erosion following recent wildfires long term denudation rates 10 kyr 10 myr were determined from terrestrial cosmogenic nuclides apatite fission track thermochronology and post basalt flow valley incision contemporary denudation rates average several times lower than the long term average 5 5 4 mm kyr 1 versus 21 5 7 mm kyr 1 erosion of sediment following wildfires accounts for only a small proportion 5 of the contemporary rate most post fire sediment is stored on the lower slopes and valley floor with the amount transported to the river network dependent on rainfall run off conditions within the first few years following the fire historical catastrophic floods account for a much larger proportion 35 of the contemporary erosion rate and highlight the importance of these events in reworking stored material evidence for palaeofloods much larger than those experienced over the past 200 years suggests even greater sediment export potential mass movement on hillslopes along valleys incised into softer lithology appears to be a dominant erosion process that supplies substantial volumes of material to the valley floor it is possible that a combination of infrequent mass movement events and high fluvial discharge could account for a significant proportion of the discrepancy between the contemporary and long term denudation rates copyright 2006 john wiley sons ltd

thresholds for bed load transport and channel initiation in a chert area in ashio mountains japan an empirical approach from hydrogeomorphic observations 1 we examined the effect of bed load transport on channel head locations where shallow landsliding is infrequent area slope thresholds for bed load transport estimated from hydrogeomorphic observations were compared with certain area slope relations at 24 channel heads in a chert area the ashio mountains japan the hydrogeomorphic observations include 1 spring discharge at 12 sites 2 rainfall intensity and 3 peak discharge and bed load transport immediately below two channel heads of differing gradient we confirmed an increase of spring discharge in proportion to drainage area during a stormflow we performed regression analyses involving the peak 4 hour rainfall and the peak discharge per unit area to give the optimal rainfall runoff equation the bed load yield increases abruptly when the peak discharge exceeds a critical discharge we calculated area slope thresholds for bed load transport for 1 year and 100 year rainfalls combining the rainfall runoff equation with the critical discharge more than half of all channel heads are located where peak discharge produced by frequent rainstorms return intervals of less than 100 years is sufficient to transport bed load in mountains where shallow landsliding is infrequent bed load transport has a strong influence on channel head location

denudation rates on cratonic landscapes comparison between suspended and dissolved fluxes and 10be analysis in the nyong and sanaga river basins south cameroon south cameroon is located in a tropical and tectonically quiescent region with landscapes characterized by thick highly weathered regolith indicative of the long term predominance of chemical weathering over erosion currently this region undergoes huge changes due to accelerated mutations related to a growing population and economical developments with associated needs and increasing pressures on land and natural resources we analysed two of the main south cameroon rivers the nyong river and sanaga river the sanaga catchment undergoes a contrasted tropical climate from sub humid mountainous and humid climate and is impacted by deforestation agriculture damming mining and urbanization especially in the mbam sub basin draining the highly populated volcanic highlands by contrast the nyong catchment only under humid tropical climate is preserved from anthropogenic disturbance with low population except in the region of yaounde mefou sub basin moreover the nyong basin is dam free and less impacted by agriculture and logging we explore both denudation temporal variability and the ratio between chemical and physical denudation through two catchment averaged erosion and denudation datasets the first one consists of an 11 year long gauging dataset while the second one comes from cosmogenic radionuclides crns here beryllium 10 be 10 from sand sampled in the river mainstreams timescale of tens to hundreds of thousands of years modern fluxes estimated from gauging data range from 5 to 100m ma 10 to 200t km 2 yr our calculations indicate that the usual relative contribution of chemical versus physical denudation is 60 and 40 respectively of the total denudation beryllium 10 denudation rates and sediment fluxes range from 4 8 to 40 3m ma or 13 to 109t km 2 yr respectively after correction for quartz enrichment these fluxes are slightly less than the modern fluxes observed in cameroon and other stable tropical areas the highest be 10 derived fluxes and the highest physical versus chemical denudation ratios are attributed to anthropogenic impact copyright c 2016 john wiley sons ltd

role of debris flows in long term landscape denudation in the central appalachians of virginia four major storms that triggered debris flows in the virginia west virginia appalachians provide new insights into the role of high magnitude low frequency floods in longterm denudation and landscape evolution in mountainous terrain storm denudation in the blue ridge mountain drainage basins is approximately an order of magnitude greater compared to basins located in the mountains of the valley and ridge province this difference is probably the result of higher storm rainfall from the blue ridge storms radiocarbon dating of debris flow deposits in the blue ridge indicates a debris flow return interval of not more than 2 4 k y in mountainous river basins this finding combined with measurements of basin denudation suggests that approximately half of the long term denudation from mechanical load occurs episodically by debris flow processes although floods of moderate magnitude are largely responsible for mobilizing sediment in lowgradient streams our data suggest that high magnitude low frequency events are the most significant component in delivering coarse grained regolith from mountainous hollows and channels to the lowland floodplains

initiation conditions for debris flows generated by runoff at chalk cliffs central colorado abstract we have monitored initiation conditions for six debris flows between may 2004 and july 2006 in a 0 3 km 2 drainage basin at chalk cliffs a band of hydrothermally altered quartz monzonite in central colorado debris flows were initiated by water runoff from colluvium and bedrock that entrained sediment from rills and channels with slopes ranging from about 14 to 45 the availability of channel material is essentially unlimited because of thick channel fill and refilling following debris flows by rock fall and dry ravel processes rainfall exceeding i 6 61 d 0 77 where i is rainfall intensity mm h and d is duration h was required for the initiation of debris flows in the drainage basin the approximate minimum runoff discharge from the surface of bedrock required to initiate debris flows in the channels was 0 15 m 3 s colluvium in the basin was unsaturated immediately prior to antecedent and during debris flows antecedent volumetric moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 4 9 and 4 7 respectively during debris flows peak moisture levels in colluvium at depths of 1 cm and 29 cm ranged from 10 20 and 4 12 respectively channel sediment at a depth of 45 cm was unsaturated before and during debris flows antecedent moisture ranged from 20 22 and peak moisture ranged from 24 38 although we have no measurements from shallow rill or channel sediment we infer that it was unsaturated before debris flows and saturated by surface water runoff during debris flows our results allow us to make the following general statements with regard to debris flows generated by runoff in semi arid to arid mountainous regions 1 high antecedent moisture levels in hillslope and channel sediment are not required for the initiation of debris flows by runoff 2 locations of entrainment of sediment by successive runoff events can vary within a basin as a function of variations in the thickness of existing channel fill and the rate of replenishment of channel fill by rock fall and dry ravel processes following debris flows and 3 rainfall and simulated surface water discharge thresholds can be useful in understanding and predicting debris flows generated by runoff and sediment entrainment

lithological effects in soil formation and soil slips on weathering limited slopes underlain by granitic bedrocks in japan abstract soil slips occur every few years due to heavy rains on biotite granite gb and hornblende biotite granite ghb slopes in the taga mountains ibaraki prefecture japan the occurrence density of soil slips per unit area is 2 7 times greater in the gb slopes than that in ghb slopes we examined the chemical mineral physical and mechanical properties of two soil profiles on soil slip scars in these slopes to study the effect of bedrock mineral composition on the density of soil slips for a given size of mineral grain the amount of biotite which is susceptible to chemical weathering in granitic bedrocks strongly influenced the density of soil slips in the gb slope the soil layer becomes thinner because of the smaller proportion of biotite in the bedrock this restricts the downward movement of soil water into the material below the slip plane during heavy rainfall the water surface then rises toward the slope surface above the slip plane this promotes soil slips increasing the density of soil slip scars in contrast in the ghb slope with more biotite in the bedrock the soil layer becomes thicker so that soil water moves easily into the material beneath the slip plane this limits the rise of water surface toward the slope surface above the slip plane even during heavy rainfalls there are consequently fewer soil slips and density of soil slip scars

increase of human over natural erosion rates in tropical highlands constrained by cosmogenic nuclides we quantify the difference between the human caused sediment yield and the natural rates of soil production and bedrock erosion in a now largely deforested tropical highland the present day rate of soil loss in the upper mahaweli catchment sri lanka is calculated by using suspended river load fluxes these data provide spatially averaged sediment yields of 130 2100 t km 2 yr 1 local rates of soil loss from agricultural plots on hillslopes are as high as 7000 t km 2 yr 1 by comparison natural rates of sediment generation as determined by measuring cosmogenic 1 0 be in quartz from sediments and soils are only 13 30 t km 2 yr 1 the natural rates presented here provide a benchmark against which recent erosion rates determined by various sediment gauging techniques can be referenced in the sri lankan highlands these results suggest that soil is now being lost 10 100 times faster from agriculturally utilized areas than it is being produced

influence of rock fragment coverage on soil erosion and hydrological response laboratory flume experiments and modeling two laboratory flume experiments on the effect of surface rock fragments on precipitation driven soil erosion yields were carried out the total sediment concentration the concentration of seven individual size classes and the flow discharge were measured digital terrain models dtms were generated before and after one of the experiments the results revealed that the rock fragments protected the soils from raindrop detachment and retarded the overland flow therefore decreasing its sediment transport capacity rock fragments were found to affect selectively the different size classes in a manner that changed according to the time scale for short times the rock fragment coverage reduced erosion of the finer particles 100 m was unaffected at long times the rock fragment cover decreased the concentration of the individual size classes in proportion to effective rainfall intensity and the area exposed to raindrops an area based modification of the hairsine and rose h r soil erosion model was employed to analyze the experimental data the h r model predictions agreed well with the measured sediment concentrations when high rainfall intensity and low rock fragment cover were used predictions were instead less accurate with low rainfall intensity and high rock fragment cover the dtm results showed that the presence of rock fragments on the soil surface led to increased soil compaction perhaps due to higher soil moisture content from greater infiltration within the rock fragment covered flumes

debris flows from small catchments of the ma ha tuak range metropolitan phoenix arizona abstract debris flows debauch from tiny but steep mountain catchments throughout metropolitan phoenix arizona usa urban growth in the past half decade has led to home construction directly underneath hundreds of debris flow channels but debris flows are not recognized as a potential hazard at present one of the first steps in a hazard assessment is to determine occurrence rates the north flank of the ma ha tuak range just 10 km from downtown phoenix was selected to determine the feasibility of using the varnish microlaminations vml method to date every debris flow levee from 127 catchment areas only 152 of the 780 debris flow levees yielded vml ages in a first round of sampling this high failure rate is due to erosion of vml by microcolonial fungi the temporal pattern of preserved debris flow levees indicates anomalously high production of debris flows at about 8 1 ka and about 2 8 ka corresponding to northern hemisphere climatic anomalies because many prior debris flows are obliterated by newer events the minimum overall occurrence rates of 1 3 debris flows per century for the last 60 ka 2 2 flows century for the latest pleistocene and 5 flows century for the last 8 1 ka has little meaning in assessment of a contemporary hazard this is because newer debris flows have obliterated an unknown number of past deposits more meaningful to a hazards analysis is the estimate that 56 flows have occurred in the last 100 years on the north side of the range an estimate that is consistent with direct observations of three small debris flows resulting events from a january 18 22 2010 storm producing 70 mm of precipitation in the ma ha tuak range and a 500 m long debris flow in a northern metropolitan phoenix location that received over 150 mm of precipitation in this same storm these findings support the need for a more extensive hazard assessment of debris flows in metropolitan phoenix

mountain erosion over 10 yr 10 k y and 10 m y time scales we used cosmogenic 10 be to measure erosion rates over 10 k y time scales at 32 idaho mountain catchments ranging from small experimental watersheds 0 2 km 2 t o large river basins 35 000 km 2 these long term sediment yields are on average 17 times higher than stream sediment fluxes measured over 10 84 yr but are consistent with 10 m y erosion rates measured by apatite fission tracks our results imply that conventional sediment yield measurements even those made over decades can greatly underestimate long term average rates of sediment delivery and thus overestimate the life spans of engineered reservoirs our observations also suggest that sediment delivery from mountainous terrain is extremely episodic sporadically subjecting mountain stream ecosystems to extensive disturbance

rainfall thresholds for shallow landsliding derived from pressure head monitoring cases with permeable and impermeable bedrocks in boso peninsula japan rainfall thresholds for shallow landslide initiation were determined for hillslopes with two types of bedrock permeable sandstone and impermeable mudstone in the boso peninsula japan the pressure head response to rainfall was monitored above a slip scarp due to earlier landslides multiple regression analysis estimated the rainfall thresholds for landsliding from the relation between the magnitude of the rainfall event and slope instability caused by the increased pressure heads the thresholds were expressed as critical combinations of rainfall intensity and duration incorporating the geotechnical properties of the hillslope materials and also the slope hydrological processes the permeable sandstone hillslope has a greater critical rainfall and hence a longer recurrence interval than the impermeable mudstone hillslope this implies a lower potential for landsliding in sandstone hillslopes corresponding to lower landslide activity copyright 2007 john wiley sons ltd

spatially averaged long term erosion rates measured from in situ produced cosmogenic nuclides in alluvial sediment spatially averaged erosion rates of small catchments can be accurately inferred from the concentrations of cosmogenic nuclides in stream sediment here we test this technique at two catchments by comparing erosion rates inferred from cosmogenic nuclides with rates of alluvial fan deposition over the past 16 000 years these two independent estimates agree within one standard error demonstrating that cosmogenic nuclide signatures of stream sediment can be used to measure spatially averaged long term erosion rates using this technique we show that long term erosion rates are an exponential function of average hillslope gradient at these sites

in situ produced 10be measurements at great depths implications for production rates by fast muons in situ cosmogenic 10be values have been used to investigate a brazilian quartz vein from the surface to a depth of 15 m at depths greater than 1000 g cm2 deep enough for neutron induced reactions to be insignificant there is only a slight decrease in 10be concentration with increasing depth our results are consistent with deep production of 10be by a mechanism presumably induced by fast muons with an attenuation length of 5300 950 g cm2 and a contribution of 0 65 0 25 to the total surface production results are compared with values from the literature and implications of this re evaluation are discussed

hydrological responses on saline sodic soil slopes in a coastal reclamation area of china abstract evaluation of the effects of slope gradient and rainfall intensity on the hydrological responses on slopes can provide important information for soil and water conservation we conducted simulated rainfall experiments to study the hydrological response of a saline sodic soil on slopes with different gradients 6 11 22 and 35 and rainfall intensities 85 95 110 and 125 mm h 1 higher effective rainfall intensities significantly reduced the times to ponding and runoff while the infiltration coefficient did not always increase with increasing slope gradient it consistently increased with increasing rainfall intensity on slopes of 6 11 or 22 the mean flow velocities and stream power values tended to increase with increasing slope gradient but did not change consistently with changes in rainfall intensity hydraulic shear stress and its logarithm could predict sediment losses that were 1 h 1 however stream power and its logarithm were better predictors of a wider range of sediment losses from slopes with saline sodic soil these results suggest that existing hydrological and erosion models should be adjusted to take into account the effects of salinity and sodicity

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