response of roll wave to suspended load and hydraulics of overland flow on steep slope abstract a roll wave is frequently observed in overland flow and it can accelerate the soil erosion on slopes however the feedback effect of eroded sediment on roll wave has not been studied the aim of this study was to investigate the response of roll wave to sediment concentration and overland flow hydraulics on steep slope the experiment was carried out in a hydraulic flume the unit flow rate varied from 1 0 to 3 0 10 3 m 3 s 1 and sediment concentration from 0 to 400 kg m 3 the sediment transport was dominated by suspension slope gradient was 9 as the sediment concentration increased the critical slope length for roll wave formation increased implying that the suspended sediment in flow could inhibit the formation of a roll wave the roll wave in overland flow is a short water long wave the roll wave length increased with the increasing sediment concentration while the wave frequency and velocity decreased the decreased wave velocity meant a decrease in flow erosion potential caused by a roll wave roll wave frequency and velocity significantly increased with reynolds number froude number and mean flow velocity and decreased with the hydraulic resistance while there were no notable relationships between roll wave length and overland flow hydraulics both roll wave frequency and velocity had the strongest dependency on froude number and could be estimated by the linear equations between them when the sediment concentration was larger than 300 kg m 3 all the roll waves in overland flow disappeared due to the high sediment supply the results indicated that the suspended sediment can ease the acceleration influence of a roll wave on soil erosion and should be considered in the soil erosion models

sea level change and storm surge deposition in a late holocene florida salt marsh abstract a 300 km length of west florida s coastline is dominated by an open marine coastal marsh system located along the central part of this sediment poor region waccasassa bay is presently a broad shallow embayment rimmed by an expansive juncus roemerianus salt marsh in this system sediments were first deposited in a forested swamp from 4400 to 1800 cal yr bp contemporaneously large oyster reefs grew in the embayment near a paleo river mouth these deposits indicate a period of slow sea level rise during the late holocene that correlates with the establishment or regression of other west florida coastal systems circa 1800 cal yr bp a rapid transgression of 2 4 km led to salt marsh growth over the former swamp and a brackish marsh developed over a previously unflooded upland surface calculated rates of shoreline retreat are 10 to 20 m yr at this time and compare to 3 0 m yr during most of the late holocene timing of the event in waccasassa bay corresponds with transgressive sequences in other atlantic and gulf coast systems and supports a relative sea level fluctuation ca 1800 cal yr bp following this event sediments overstepped during the transgression were reworked onto the low lying tidal marsh rapid accretion along the shore edge outpaced sea level rise and led to the local development of high intertidal and supratidal levees evidence indicates that storm driven surge was the principal mechanism of sediment transport for these deposits in waccasassa bay storm surge deposition has played a significant role in marsh surface accretion distinguishing the system from more typically tide dominated wetlands within the past 150 years most of the supratidal environment became tidally inundated and there was a widespread transition into the modern salt marsh this change and evidence from adjacent portions of the florida coast implicate a rise in sea level within the past several hundred years

constraining sediment transport to deep marine basins through submarine channels the levant margin in the late cenozoic abstract the recent world class gas discoveries in early miocene sand units offshore israel raises the question of their origin apparently the simplest explanation is to relate them to a fluvial system that arrived from arabia at that time this system predated the modern pliocene nile river supply and existed until captured by the dead sea valley interestingly however very little sedimentation occurred along the levant continental margin before the pliocene in spite of its stepped structure that provided much space for accommodation the only way that sediments could have bypassed the continental margin and arrive at the deep basin without being trapped in the middle is through submarine channels that crossed the continental margin here we explore this possibility using 3 d stratigraphic modeling techniques that quantify the sediment load and the water discharge required to fill the basin by pushing enough sediment through submarine channels we show that such a scenario requires a fluvial system in the order of the largest rivers that exist today on earth in terms of drainage area and water discharge alternatively it requires extreme hydraulic conditions in terms of diffusion coefficients and an elevated drainage basin that could not have existed in the study area we therefore challenge the traditional view of arabia as the main source for oligo miocene deposits in the levant basin and suggest that the basin was mainly fed by a proto nile system that transported clastic material to the north african margin and then farther east by ocean currents in a wider view we demonstrate how numerical modeling can constrain sediment transport through submarine channels as a function of basin geometry and hydraulic conditions and how paleogeographic knowledge can be combined with current data on world rivers to evaluate if modeling results are plausible

depositional facies and stratal geometry of an upper carboniferous prograding and aggrading high relief carbonate platform cantabrian mountains n spain seismic scale continuous exposures of an upper carboniferous bashkirian moscovian carbonate platform n spain provide detailed information about the lithofacies and stratal geometries quantified with differential global positioning system measurements of microbial boundstone dominated steep prograding and aggrading platform margins progradational and aggradational platform to slope transects are characterized by distinct lithological features and stratal patterns that can be applied to the understanding of geometrically comparable high relief depositional systems the bashkirian is characterized by rapid progradation at rates of 415 970 m my 1 characteristic outerplatform facies are high energy grainstones with coated intraclasts ooids and pisoids moderate energy algal skeletal grainstones to packstones and lower energy algal packstone and boundstone units the moscovian aggradational phase is characterized by aggradation rates of 108 m my 1 coated grain shoals are less common whereas crinoidal bars nucleated in well circulated settings below wave base boundstones form a belt 30 300 m wide at the platform break and interfinger inwards with massive algal skeletal wackestones mud rich banks the progradational phase has divergent outer platform strata with basinward dips of 12 to 2 steep clinoforms with dips of 20 28 are 650 750 m in relief and possibly sigmoidal to concave in the lower part the basinward dipping outer platform strata might be depositional for less than 6 consistent with lithofacies deepening seaward the basinward dip is attributed to the downward shift of upperslope boundstone forced by late highstand and relative sea level fall and to compaction induced differential subsidence during progradation the aggradational phase is characterized by horizontally layered platform strata clinoforms steepen to 30 45 reaching heights of 850 m and are planar to concave the evolution from progradation to aggradation at the bashkirian moscovian boundary is attributed to increased foreland basin subsidence and decreased boundstone accumulation rates progradation was primarily controlled by boundstone growth rather than by highstand shedding from the platform top within the major phases aggradational progradational increments are produced by third to fourth order relative sea level

coupling between northward propagating intraseasonal oscillations and sea surface temperature in the indian ocean using a hybrid atmosphere ocean coupled model it is shown that during the boreal summer northwardpropagating intraseasonal oscillations npisos are strongly coupled to the underlying sea surface temperature sst in the indian ocean sector on the one hand the intraseasonal atmospheric convection changes the sst through solar radiation latent heat flux and mixed layer entrainment on the other the induced sst fluctuations feed back to affect the intraseasonal convection the preferential northward rather than southward propagation of boreal summer isos in the indian ocean is partially explained by an interaction among the summer mean climate state the atmospheric disturbances and the ocean surface temperature a solution to an atmosphere only model forced with daily sst produces much stronger npisos than a similar solution forced with monthly mean sst amip type run the atmosphere only model however even when it is forced by daily sst from the coupled model with a small amount of noise in the initial and or boundary conditions is unable to reproduce the npisos in the coupled case in the coupled system intraseasonal sst anomalies are forced by intraseasonal atmospheric convection and hence are in quadrature with the convection in the stand alone atmospheric model however sst acts only as a boundary forcing and the resultant atmospheric convection has almost the same phase with the underlying sst one consequence is that the intensity of the sst forced intraseasonal convection in the stand alone atmospheric model is considerably weaker than in the coupled model finally solutions indicate that the northward movement of the off equatorial convection in the northern indian ocean is more closely related to local intraseasonal sst anomalies than to the equatorial eastward moving madden julian oscillation positive negative sst anomalies in the northern indian ocean lead the active break phases of the intraseasonal convection by about 2 pentads 10 days therefore intraseasonal sst anomalies in the northern indian ocean are potentially a useful index to forecast active break spells of the south asian summer monsoon

comparing the smooth parabolic shapes of interfluves in continental slopes to predictions of diffusion transport models abstract computer models of stratigraphic development at continental margins often include elements in which sediment topography evolves according to a diffusion equation representing effects of down slope sediment transport however there has been little effort to verify the model for example by showing whether deposit geometries are as expected from it or by considering whether transport is consistent with the model s assumptions the issue is important for understanding transport erosion and deposition in continental slopes more generally and the extent to which such processes are recorded in seabed morphology examples of slope topography illustrating diffusive like characteristics are examined here in the uppermost slope of the usa central atlantic margin sandy areas between canyon heads are smoothly convex upwards and almost parabolic a morphology similar to subaerial soil mantled hillslopes known to evolve according to a diffusion equation other data of interfluves in muddy sediment from both atlantic and pacific usa margins also show this smooth convex upwards form in subaerial hill crests the upwards convex parabolic shape arises where steady erosion by streams along channels provide constant flux boundary conditions i e the parabola is the steady state solution to the diffusion equation although submarine processes will likely be different the similar morphology of submarine interfluves prompts the question as to whether erosion along channels and movements of sediment between channels can also sometimes occur to cause a diffusive like evolution of topography the discussion therefore focuses on submarine processes affecting erosion and deposition in particular to address whether the morphology results from true diffusion which requires that sediment moves down slope with a transport flux proportional to local bed gradient or is fortuitous sediment transport is instead unrelated to local bed gradient and the morphology arises from other effects on accumulation rates

a re examination of the mechanism and human impact of catastrophic mass flows originating on nevado huascaran cordillera blanca peru in 1962 and 1970 abstract the 1962 and 1970 huascaran mass movements originated as rock ice falls from the mountain s north peak transformed into higher volume high velocity mud rich debris flows by incorporation of snow from the surface of a glacier below huascaran and the substantial entrainment of morainic and colluvial material from slopes below the glacier terminus water for fluidization of the entrained material originated in the melting of incorporated snow and the liberation of soil moisture contained within the entrained materials eyewitness reports indicate very high mean velocities for the events 17 35 m s 1962 and 50 85 m s 1970 the runout distances and velocity profiles of both events were simulated using dan w both mass movements continued downstream in the rio santa as debris floods aluviones that in 1970 reached the pacific at a distance of 180 km in strong contrast to publications in the geosciences literature 1961 peru census data indicates that the death toll of the 1970 event is ca 6000 and that total life loss in the two events did not exceed 7000 people

two dimensional stratigraphic forward modeling reconstructing high relief clinoforms in the northern taranaki basin clinoforms the basic large scale architectural form within which sediments are stored and eventually fed down depositional dip in clastic wedges exist in many shapes and sizes understanding how they form evolve and degrade is critical to understanding how transport mechanisms affect the shelf margin and sediment partitioning and distribution and their implications on the presence of a working petroleum system the neogene stratigraphic succession of the taranaki basin in new zealand contains clinoform packages that display a variety of architectures well imaged on seismic data quantitative characterization of this interval was performed to unravel the processes by which clinoforms evolve under the influence of tectonic and isostatic driven subsidence sea level change and sediment supply fluctuations nine different clinoform packages were identified on the basis of changes in their seismic stratigraphic characteristics two dimensional stratigraphic forward modeling was used to conduct a sensitivity analysis and determine the relative importance of different geologic controls on their genesis our results show that during the early to late pliocene clinoform architectures were influenced by the opening of a back arc rifting structure in the taranaki basin northern graben which controlled sediment redistribution and partitioning at the same time a drop in global sea level allowed sediment bypass to distal parts of the basin during the late pliocene changes in the australian pacific subduction zone forced rapid uplifting of the southern alps generating a significant increase in sediment supply model simulations suggest that clinoform architectures during the late pliocene were controlled by this increase in sediment supply and associated loading

instability and surge development in debris flows 1 debris flows are often described as a succession of surges which are characterized by enhanced peak depth and velocity and therefore by a tremendous increase of their destructive power for given characteristics of the base flow if the channel is sufficiently long to allow an appreciable wave development the linear stability analysis in shallow streams is shown to provide a reasonable prediction of the critical flow condition and of the instability growth rate the one dimensional 1 d theory however does not allow the determination of the wave period of the fastest growing perturbations debris waves most frequently develop following a mechanism similar to water roll waves instabilities grow up becoming clearly distinguishable waves and then waves overtake one another with increasing wave period and amplitude the typical hydrograph of a multiple peak event is shown to be composed of a first surge which is usually characterized by the highest depth the longest duration the greatest erosive power and the most symmetrical shape and of secondary waves that burst on the flow tail in the recession phase the characteristics of the first surge can be explained by two different mechanisms all waves that rise up near the flood crest run faster than this first surge and coalesce into it causing its high depth and great volume moreover segregation during the flow induces the concentration of boulders at the fronts contributing to its depth enhancement erosive power and symmetrical shape when a debris surge impacts a structure the force pattern can be interpreted as the superposition of the reflection of the bouldery front and the formation of a vertical muddy jet due to the impact of the front wedge wave reflection can be described by a 1 d mass and momentum balance across the front whereas the pressure impulse due to the incompressibility of the interstitial fluid can be analyzed through inviscid formulations validated for the representation of tsunami forces

real time observation of an active debris flow watershed in the wenchuan earthquake area abstract debris flows occur frequently and cause considerable damage in the wenchuan earthquake area however there has been no systematic real time monitoring of such events this study used a monitoring system to consider the spatial variation of meteorological and flow processes in a 39 4 km2 watershed the system comprised three rainfall gauges at different locations and three hydrological monitoring stations located on the mainstream and tributaries with instruments to measure the velocity height and density of debris flows based on the monitoring data the debris flow events were categorized and the general runoff velocity discharge and density were analysed we proposed empirical methods for estimating the velocity and the total volume of debris flows based on other easily obtainable parameters e g maximum flow depth and duration comparison of the results derived using the monitoring data and empirical formulas with those obtained in other small watersheds worldwide revealed the debris flow characteristics in this relatively large watershed rainfall threshold for the debris flows was proposed which is higher than those proposed for the same region for periods shortly after the wenchuan earthquake 2008 2013 and the temporal evolution of the rainfall conditions necessary for debris flows was addressed

hydrologic conditions responsible for triggering the stože landslide slovenia in two events on november 15 and 17 2000 near the mangart mountain 2679 m a s l nw slovenia two translational landslides debris flow slides with a total volume of more than 1 5 million m3 occurred on the sto e slope composed of morainic material filled with silt fraction the first landslide was associated with a dry and the second landslide with a wet debris flow respectively the rain gauging station in the village of log pod mangartom recorded 1638 4 mm of rainfall more than 60 of the average annual precipitation in the 48 days before the events rainfall intensity of 1 42 mm h in 1152 h the recorded rainfall depth has a recurrence interval of more than 100 years other recorded rainfall depths of shorter duration 481 6 mm in 7 days 174 0 mm in 24 h 70 mm in 1 h have recurrence intervals of much less than 100 years a hydrological analysis of the event showed that the increase in runoff coefficients during the wet period in autumn 2000 before the landslide was as high as two to threefold an analysis using natural isotopes of 18o and tritium of water samples from the sto e landslide area has shown permanent but slow exfiltration of underground waters from a reservoir in the slope in the case of low intensity and long duration rainfall in autumn 2000 relatively low permeable 10 7 m s morainic material was nearly saturated but remained stable average porosity 21 water content 20 liquid limit 25 until high artesian pressures up to 100 m developed in the slope by slow exfiltration from the relatively high permeable 10 5 m s massive dolomite the sto e landslide two debris flow slides was triggered by high artesian pressures built in the slope after long duration rainfall the devastating debris flows formed from the landslide masses by infiltration of rainfall and surface runoff into the landslide masses and by their liquefaction

occurrence conditions of roll waves for three grain fluid models and comparison with results from experiments and field observation for the flow and deposition behaviour of debris flows phenomena like particle sorting levee formation and the development of roll waves are expected to be important processes however these processes are not well understood and hardly implemented in modelling approaches in this study we focus on the development of roll waves and derive advanced criteria separating stable and instable flow regimes for three debris flowmodels these criteria are expressed using critical froude numbers each of these simple flow models reflect different sources of flow resistance laminar viscous stress bingham type dispersive stress due to particle collision bagnold type and a model combining turbulent and dispersive stresses subsequently we compare the predictions from these models with results from laboratory experiments with grain fluid mixtures in a straight flume and with observations from a debris flow monitoring site at the lattenbach creek in austria the experimental flows match with a turbulent flow model including particle collisions for the natural flows the connection between models and observations is not clear due to limited field data the results of our study contribute to an improved determination of critical flow conditions and provide data for model testing

carbonate platform flanks slope angle and sediment fabric more than 20 examples of fossil carbonate platform systems were compared for slope angle and sediment fabric plots of slope angle versus sediment fabric show that grainy non cohesive mud free sediments build steeper slopes than muddy cohesive sediments examples near the end members of grainy and muddy carbonate platform flanks are found in the triassic of the dolomites in northern italy and in the bahamas respectively they document the flank geometry and the processes readjusting the slope profile once the limiting slope angle is exceeded the grainy flank sediments in the dolomites modified by shearing and avalanching produce straight slope profiles with declivities up to 35 whereas the muddy bahamian flank sediments modified by large scale creep and rotational to translational sliding and slumping produce a concave upwards slope profile inclined at less than 4 the comparison between slope angle and sediment fabric indicates that the physical behaviour of sediments in the gravity field angle of shearing and mode of readjustment processes is linked to the composition of the slope sediment among the variables such as sea level subsidence climate plate motion and oceanographic setting windward leeward sediment fabric is suggested to be a major if not the major control on slope angle and slope curvature of carbonate platform flanks besides the recently documented tendency of carbonate sediments to build steeper slopes than siliciclastics this proposed relation sheds new light on the analysis and quantification of the variables influencing the geometry and depositional evolution of carbonate systems furthermore it provides an opportunity to deduce sediment composition from seismic lines and predict lithology prior to drilling

depths of modern coastal sand clinoforms abstract clinoforms are classical geological features examples in the rock record or in seismic reflection data that originally formed in shallow water can potentially help to locate paleo sea level but their precise links with sea level need to be established using modern examples before such inferences can be made accurately some near shore areas of high wave energy and steep coasts host sand bodies with upwards convex surfaces these clinoforms have been suggested to have been created from sand exported from the upper shoreface during stormy conditions and deposited at depths where wave action diminishes below the threshold of motion field and roy 1984 hernandez molina et al 2000 we have compiled the shapes of these bodies in a variety of wave environments in order to test this idea the interpreted depths at which the sand surface steepens i e the clinoform rollover vary from 21 m off southern california to deeper than 50 m off se australia to assess the link with wave action rollover depths were compared with adjacent deep water wave properties over the period 1992 2001 in the era 40 reanalysis dataset rollover bed shear stresses were computed from properties representing average wave conditions and from properties associated with upper percentile conditions stresses were found to reach 0 1 0 5 pa during upper 5 percentile wave conditions exceeding the sediment threshold of motion estimated from reported grain size data sediment to below the rollover is therefore mobile during extreme wave conditions

topographic characteristics of the submarine taiwan orogen a complete digital elevation and bathymetry model of taiwan provides the opportunity to characterize the topography of an emerging mountain belt the orogen appears to form a continuous wedge of constant slope extending from the subaerial peaks to the submarine basin we compare submarine channel systems from the east coast of taiwan with their subaerial counterparts and document a number of fundamental similarities between the two environments the submarine channel systems form a dendritic network with distinct hillslopes and channels there is minimal sediment input from the subaerial landscape and sea level changes are insignificant suggesting that the submarine topography is sculpted by offshore processes alone we implement a range of geomorphic criteria widely applied to subaerial digital elevation models and explore the erosional processes responsible for sculpting the submarine and subaerial environments the headwaters of the submarine channels have steep straight slopes and a low slope area scaling exponent reminiscent of subaerial headwaters that are dominated by bedrock landslides the main trunk streams offshore have concave up longitudinal profiles extensive knickpoints and a slope area scaling exponent similar in form to the onshore fluvial domain we compare the driving mechanisms of the likely offshore erosional processes primarily debris flows and turbidity currents with subaerial fluvial incision the results have important implications for reading the geomorphic signals of the submarine and subaerial landscapes for understanding the links between the onshore and offshore environments and more widely for focusing the future research of the submarine slope

stratigraphic modeling of the western taiwan foreland basin sediment flux from a growing mountain range and tectonic implications abstract sediment flux signals from source to sink in foreland basins preserve a record of tectonics sea level and climate through erosion and sedimentation however longitudinal sediment transport often occurs in foreland basins thus removing part of the orogenic material flux from foreland basin records here we use mass balance calculation and stratigraphic simulations of sediment fluxes for the taiwan orogen to provide an order of magnitude estimate of how much orogenic material may bypass a foreland basin our results indicate a significant potentially more than 50 mismatch between sediment volume currently preserved in the basin and the amount of material presumably eroded from the orogen since the onset of collision in taiwan this suggests either a significant overestimation of average erosion rates over the period concerned with orogenic development of taiwan or it supports previous paleogeographic work suggesting that longitudinal sediment transport in the paleo taiwan strait served as a major bypass conduit of importance for the establishment of a steady state orogen we identify candidate submarine topography in the south china sea that may preserve taiwan s missing erosional mass

the effects of topography on sedimentation from particle laden turbulent density currents abstract we present results from a series of laboratory experiments that illustrate the influence of changes in channel topography depth or width on the sedimentation patterns produced by steady particle laden currents on a planar surface in a channel with constant width such currents created deposits that thinned exponentially with distance as long as a current was not blocked to produce a bore topographic features consisting of constrictions ridges and sudden openings caused no significant deviation from exponential deposit thinning or discontinuity in thickness even when there was a transition in flow regime caused by the topographic feature changes in the channel width did affect the distance over which the deposit thinned with the deposits associated with wider parts of the channel thinning more rapidly with distance in contrast if the topographic change was large enough to partially reflect the flow producing an upstream propagating bore then the deposit did not thin exponentially the results are consistent with a model in which the current is assumed to be turbulent and well mixed in this case sedimentation occurs at a rate proportional to the channel width the settling speed of the particles and their concentration within the current and inversely proportional to the current discharge such a model predicts that as a flow passes through a topographic control that does not produce a bore the deposit continues to thin exponentially even if the flow undergoes a transition from the subcritical to the supercritical regime the results suggest that in natural systems changes in current speed and flow regime do not in themselves produce changes in deposit thickness or gradient in thickness unless the flow is partially blocked and a fraction of the flow is reflected upstream

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

submarine slopes with an exponential curvature abstract the curvature of submarine slopes is a little used source of information on transport processes and sediment composition in a survey of modern submarine slopes selected from all over the world about 15 are characterized by very regular profiles with sharp shelfbreaks and concave upward curvature an exponential function describes this morphology very well these exponential profiles are from three very different depositional settings a continental margin close to a young mountain belt with very high rates of sedimentation high latitude continental margins with evidence of ice cover during quaternary glacial intervals and a carbonate platform margin we propose that the curvature is controlled by the exponential decay of transport capacity with increasing distance from the shelf edge while exponential decrease of transport may be a general property of most slopes the development of a regular exponential profile is commonly disturbed by other factors in particular by the interplay with wave dominated transport at the upper boundary during sea level fluctuations and with turbidite dominated sedimentation at the lower boundary the good exponential fit of the profiles described here results from the fact that vertical shifts of the shelfbreak are very small compared to the horizontal progradation the three depositional settings mentioned above prevent the shelf edge from fluctuations in the vertical high rates of sedimentation and therefore rapid progradation result in minimal movements of the shelfbreak ice covered margins are limited by the grounding level of the ice and margins built by reef organisms are stationary because the hard limestone is relatively resistant to erosion during lowstands of sea level the numerical value of the exponent is distinctly different for sandy and muddy slopes indicating the possibility of using the curvature to deduce sediment composition of submarine slopes

the perfect debris flow aggregated results from 28 large scale experiments 1 aggregation of data collected in 28 controlled experiments reveals reproducible debris flow behavior that provides a clear target for model tests in each experiment 10 m3 of unsorted water saturated sediment composed mostly of sand and gravel discharged from behind a gate descended a steep 95 m flume and formed a deposit on a nearly horizontal runout surface experiment subsets were distinguished by differing basal boundary conditions 1 versus 16 mm roughness heights and sediment mud contents 1 versus 7 percent dry weight sensor measurements of evolving flow thicknesses basal normal stresses and basal pore fluid pressures demonstrate that debris flows in all subsets developed dilated coarse grained high friction snouts followed by bodies of nearly liquefied finer grained debris mud enhanced flow mobility by maintaining high pore pressures in flow bodies and bed roughness reduced flow speeds but not distances of flow runout roughness had these effects because it promoted debris agitation and grain size segregation and thereby aided growth of lateral levees that channelized flow grain size segregation also contributed to development of ubiquitous roll waves which had diverse amplitudes exhibiting fractal number size distributions despite the influence of these waves and other sources of dispersion the aggregated data have well defined patterns that help constrain individual terms in a depth averaged debris flow model the patterns imply that local flow resistance evolved together with global flow dynamics contradicting the hypothesis that any consistent rheology applied we infer that new evolution equations not new rheologies are needed to explain how characteristic debris flow behavior emerges from the interactions of debris constituents

clinoform development by advection diffusion of suspended sediment modeling and comparison to natural systems clinoforms are the building blocks of prograding stratigraphic sequences these sig moid shaped surfaces can be found forming today on modem deltas sedimentation rate profiles over the clinoform surface of these deltas show low rates of sediment accumulation on both topset and bottomset regions with a maximum accumulation rate on the upper foreset region we pres ent a model for the formation of clinoforms that relies on the interpretation of modem clinoform sedimentation as a result of the distribution of shear stresses at the mouth of a river model clino form surfaces are generated using an equation for the conservation of suspended sediment concentration together with a conservation of fluid equation for simple time averaged flow velocity fields in the model suspended sediment is advected horizontally into a basin and gravitational settling of sediment particles is counteracted by vertical turbulent diffusion in shallow water shear stresses are too large to allow deposition and sediment bypasses the topset region with increasing water depth near bed shear stresses decrease and sediment is allowed to deposit at the foreset region with gradually decreasing rates toward deeper water this sedimentation pattern leads to progradation of the clinoform surfaces through time the clinoform surfaces produced by the model capture the fundamental morphological characteristics of natural clinoforms these include the gradual slope rollover at the topset and bottomset steeper foreset slopes with increased grain size and an increase in foreset slope through time as clinoforms prograde into deeper water because the parameters controlling the model clinoforms have a direct relation to physical quantities that can be measured in natural systems the model is an important step toward unraveling the physical processes associated with these deposits

modeling the rollovers of sandy clinoforms from the gravity effect on wave agitated sand abstract clinoforms on coasts exposed to ocean waves form from sand exported from the shoreface during extreme wave conditions and deposited where wave action diminishes elsewhere it is shown that during upper 5 percentile wave conditions wave induced shear stresses exceed the sediment threshold of motion to below the clinoform rollovers experiments and theory suggest that where bed sediments are agitated by waves the effect of gravity should move particles down slope with a flux proportional to the slope combined with considerations of continuity this implies a diffusion of the sediment topography a property that would explain the smooth seabed morphology found at sandy rollovers where recorded with multibeam sonar for situations where this gravity effect dominates a simple analytical expression developed here shows how the rollover curvature should relate to wave properties and to the offshore component of sediment flux more sharply curved rollovers are expected where waves have short periods or where the sediment flux is large relative sediment fluxes were calculated using the model from rollover curvature and wave properties for sites from california southeast australia and atlantic and mediterranean iberia the relative magnitudes of the fluxes are roughly as would be expected from local physiography and coastal erosion rates for sandy clinoforms developed under mainly wave influences the model could be useful for exploring variations within clinoform datasets e g how varied convexity in an area of uniform wave properties reflects varied sediment flux and for interpreting how varied curvatures of rollovers within seismic stratigraphy reflect how wave climate and flux have varied in the past

the triggering of debris flow due to channel bed failure in some alpine headwater basins of the dolomites analyses of critical runoff the debris deposits at the bottom of very steep natural channels and streams in high mountain areas can be mobilized by runoff triggering a water sediment mixture flow known as debris flow the routing of debris flow through human settlements can cause damage to civil structures and loss of human lives the prediction of such an event or the runoff discharge that triggers it assumes an interest in risk analyses and the planning of defence measures the object of this study is to find a method to determine the critical runoff value that triggers debris flow as a result of channel bed failure historical and rainfall data on 30 debris flows that occurred in six watersheds of the dolomites north eastern italian alps were collected from different sources field investigations at the six sites together with the hydrologic response to the rainfalls that triggered the events were performed to obtain a realistic scenario of the formation of the debris flow there occurred field observations include a survey along the channel of the triggering reach of debris flow with measurements of the channel slope and cross section and sampling of debris deposits for grain size distribution simulated runoff discharge values based on the rainfall recorded by pluviometers were then compared with values obtained through experimental criteria on the initiation and formation of debris flow by bed failure the results are discussed to provide a plausible physical based method for the prediction of the triggering of debris flow by channel bed failure copyright 2007 john wiley sons ltd

large scale stratigraphic architecture eustatic variation and unsteady tectonism a theoretical evaluation we incorporate a process based depositional model with basin subsidence models to predict stratigraphic records this allows us to investigate the importance of subsidence geometry on coastal stratigraphy and thus to characterize and compare the stratigraphic architecture of two categories of tectonic basins the models demonstrate that the correlation of stratigraphic sequences to eustatic cycles is not the same in passive margin basins as in foreland basins and that in a foreland basin the record of episodic tectonism is distinct from that of eustatic sea level change in the model sediment transport is approximated by slope controlled diffusion nonmarine transport is treated as more efficient diffusion than marine transport three different subsidence and sediment supply models are examined a simple passive margin basin a simple foreland basin and then a foreland basin for which vertical motions are driven by thrust shortening that is compensated flexurally and for which sediment supply is related to relief predicted passive margin stratigraphies for cases of varying eustatic sea level are similar to those of natural basins and include progradational packages and subaerial unconformities which are used to define sequence boundaries that form during sea level fall we explore the timing relationships between stratigraphic features and a sinusoidal sea level history showing that the phase relationship depends on subsidence sediment flux efficiency of sediment transport and period and amplitude of sea level when the basic geometry of the basin is inverted placing the sediment supply on the side with maximum subsidence as is the case in foreland basins the sequence character changes markedly subaerial erosion does not generate unconformities in the models of a dynamic foreland basin sediment supply and subsidence are linked to the structure of the flanking thrust belt and are not necessarily constant for steady thrusting and variable sea level unconformities that define sequence boundaries form only on the distal or forebulge side of the basin and the ages of the sequence boundaries correlate to limes of rising sea level in cases of constant sea level but variable thrusting subaerial unconformities are cut locally on both the proximal margin of the basin and the distal margin of the basin yet the ages of the proximal margin and distal margin unconformities are out of phase in the tectonic cycle erosion is most pronounced during quiescence on the proximal side and during thrusting on the distal side

evolution of a natural debris flow in situ measurements of flow dynamics video imagery and terrestrial laser scanning many theoretical and laboratory studies have been undertaken to understand debris flow processes and their associated hazards however complete and quantitative data sets from natural debris flows needed for confirmation of these results are limited we used a novel combination of in situ measurements of debris flow dynamics video imagery and pre and postflow 2 cm resolution digital terrain models to study a natural debris flow event our field data constrain the initial and final reach morphology and key flow dynamics the observed event consisted of multiple surges each with clear variation of flow properties along the length of the surge steep highly resistant surge fronts of coarse grained material without measurable pore fluid pressure were pushed along by relatively fine grained and water rich tails that had a wide range of pore fluid pressures some two times greater than hydrostatic surges with larger nonequilibrium pore fluid pressures had longer travel distances a wide range of travel distances from different surges of similar size indicates that dynamic flow properties are of equal or greater importance than channel properties in determining where a particular surge will stop progressive vertical accretion of multiple surges generated the total thickness of mapped debris flow deposits nevertheless deposits had massive vertically unstratified sedimentological textures

the role of subsidence in shelf widening around ocean island volcanoes insights from observed morphology and modeling abstract on reefless volcanic islands insular shelves are thought to have formed essentially by the combined effects of wave erosion and glacio eustatic sea level oscillations subsidence however has also been recognized as having an important role in the development of these morphologies yet few studies have quantified the relative contribution of subsidence to shelf generation and development particularly to shelf width a better understanding of this contribution however is key to understand the long term evolution of coasts at volcanic islands particularly given that subsidence may exacerbate the effects of marine erosion in this study we assess quantitatively the role of subsidence in shelf development by comparing real cross shore shelf profiles with modeled profiles using varied rates of subsidence to achieve this we used shelf bathymetric profiles from faial and sao jorge islands in the azores which we compared with predictions of a numerical model of coastal erosion that has been calibrated previously against other field data the first set of model runs was made to calibrate the model by determining the values that produced shelves with break depths widths and profile shapes that were similar to those observed the second set of runs which served to evaluate the contribution of subsidence to shelf widening revealed that subsidence may have been responsible for increasing shelf widths by almost 2 5 times relative to shelves formed only by the combined effects of wave erosion and glacio eustatic oscillations modeling shelf formation on the same islands but with increased subsidence rates up to 2 2 mm yr resulted in shelf profiles up to 19 km wide a value 3 to 6 times greater than observed on these islands our study therefore reinforces the idea that subsidence is a key contributor to the generation of broad insular shelves given its role in enhancing coastal retreat our shelf evolution modeling also suggests that notwithstanding the crucial role subsidence plays in increasing the width of shelves on islands subjected to energetic wave regimes as it happens in the azores and hawaii modification by erosion is important enough to result in shelf morphologies that are not constructional in essence but rather dominantly erosive surfaces this study therefore contributes to a better understanding of how insular shelves and submarine terraces form and develop by proving important new quantitative insights of the role of subsidence on the generation of these morphologies

the kolka karmadon rock ice slide of 20 september 2002 an extraordinary event of historical dimensions in north ossetia russian caucasus on 20 september 2002 an enormous rock ice slide and subsequent mud flow occurred on the northern slope of the kazbek massif northern ossetia russian caucasus it started on the north northeast wall of dzhimarai khokh 4780 ma s l and seriously affected the valley of genaldon karmadon immediate governmental actions available scientific information first reconstructions hazard assessments and monitoring activities as well as initial expert judgments recommendations are documented in order to enable more detailed analyses and modelling of the event by the wider scientific community among the most remarkable aspects related to this event are 1 the relation between the recent event and somewhat smaller but quite similar events that occurred earlier in historical times 1835 1902 2 the interactions between unstable local geological structures and complex geothermal and hydraulic conditions in the starting zone with permafrost cold to polythermal hanging glaciers and volcanic effects hot springs in close contact with each other 3 the erosion and incorporation of a debris covered valley glacier largely enhancing the sliding volume of rocks ice firn snow water and probably air to a total of about 100 106m3 and 4 the astonishingly high flow velocities up to 300 km h 1 and enormous length of travel path 18 km plus 15 km of debris mud flow this extraordinary case illustrates that large catastrophic events in high mountain regions typically involve a multitude of factors and require integrated consideration of complex chains of processes a task which must be undertaken by qualified groups of experts

model for the sigmoidal curvature of submarine slopes sigmoidal slope profiles are common on the margins of continents and intracratonic basins we propose that these profiles consist of two genetically different segments the lower concave part reflects the exponential decrease of the sedimentation rate with increasing distance from the source at the shelf edge the upper convex part represents the gradational boundary between the shelf domain where sediment is moved by waves and wave induced currents and the slope domain where sediment is moved by gravity the boundary is narrow and the shelf edge is sharp if sedimentary base level remains stationary during progradation the boundary becomes gradational and the shelf edge becomes rounded if storms and sea level cycles induce significant fluctuations of base level this model is supported by observations on holocene sedimentary systems as well as numerical simulations with the program strata based on the diffusion equation for sediment dispersal

effects of strong ground motion on the susceptibility of gully type debris flows abstract typhoon herb in 1996 caused widespread debris flows in central taiwan the 7 3 chi chi earthquake on september 21 1999 which also took place in central taiwan induced many landslides in the region these landslides turned into debris flows when typhoon toraji struck taiwan in 2001 this research selects three regions which suffered a ground motion class of 5 6 and 7 on the richter scale during the chi chi earthquake as study areas air photos from 1997 and 2001 of these regions are used to map the gully type debris flows that took place after typhoons herb and toraji respectively the gullies adjacent to the debris flow but without a trace of debris flows are also mapped as the non debris flow data the topography hydrogeology and rainfall factors where debris flow occurred and in which there was no occurrence of debris flows in these gullies were retrieved from dtm geological maps and iso countour maps and of rainfall through gis processing these characteristic are introduced into a probabilistic neural network to build a predicting model for the probability of the occurrence of debris flows three series of cross analyses are conducted to compare the probability of the occurrence of debris flows of the same dataset predicted by different prediction models the results reveal that the susceptibility of debris flows was elevated after the chi chi earthquake struck the upsurge of susceptibility was more obvious for the regions that received a higher class of ground motion

surface slopes velocity profiles and fluid pressure in coarse grained debris flows saturated with water and mud data on the internal velocity distribution of flowing sediment fluid mixtures such as debris flows are rare but necessary for model development and testing a probe to measure the mean particle velocity at different depths and different locations within experimental debris flows in a 4 m diameter rotating drum was developed in addition the flow depth basal normal stress and basal pore fluid pressure were also measured results show that for a given sediment fluid mixture the velocity profiles collapse to distinct non dimensional profiles macroscopic flow behaviour shows great similarity with mean surface slopes weakly dependent on the shear rate for water saturated gravel but strongly shear rate dependent when pores are filled with mud poorly sorted material with a high content of fines produced fluid pressures close to normal stress and sidewall friction had a strong effect on the flow pattern our results reveal variability in profile characteristics for flows displaying similar macro dynamics and provide data for model testing

the record of oligocene middle miocene paleoenvironmental changes in a carbonate platform iodp exp 359 maldives indian ocean abstract the carbonate edifice of the maldives has an exceptional record of the global climate and ocean current reconfigurations during the neogene that set the path for the establishment of the present day global climate system the study of seismic profiles sedimentary facies microfacies and ichnofabrics of the oligocene miocene platform slopes allows reconstructing the different stages of basin evolution the focus is on the characterization of paleoenvironmental conditions along the slope at iodp expedition 359 drill sites as well as subtle changes of the slope depositional regime controlled by variations in the frequency and intensity of the platform shedding and the basin oxygenation natural gamma radiation and ichnofabric logs are used as a proxy for sea floor ventilation in the inner sea area which is today surrounded by atolls from the oligocene 25 5 ma to the end of the middle miocene climate optimum 15 ma the maldives carbonate platform slopes were poorly oxygenated the opening of the eastern passages through the maldives carbonate platform at 17 5 ma led to an improvement of the sea floor oxygenation sea level fluctuations controlled the sediment input from the platform onto the slope that resulted in changes of the fossil and trace fossil assemblages after the evolution from a ramp to a flat topped platform with well defined bank edges the platform developed hanging shoulder and more sigmoidal clinoforms this correlates to the global decline of coral reefs during the middle miocene climate transition 15 ma and a general sea level lowering the associated slope deposits show abundant channels and cyclic steps are rich in reworked bioclasts and have ichnofabrics pointing towards a good oxygenation of the sea floor the example of the maldives carbonate platform therefore shows how integrating seismic geometries and compositional changes i e microfacies and ichnofabrics allow identifying changes in sea level and in the current pattern as the main controlling factors on carbonate platform evolution

grain size segregation and levee formation in geophysical mass flows 1 data from large scale debris flow experiments are combined with modeling of particle size segregation to explain the formation of lateral levees enriched in coarse grains the experimental flows consisted of 10 m3 of water saturated sand and gravel which traveled 80 m down a steeply inclined flume before forming an elongated leveed deposit 10 m long on a nearly horizontal runout surface we measured the surface velocity field and observed the sequence of deposition by seeding tracers onto the flow surface and tracking them in video footage levees formed by progressive downslope accretion approximately 3 5 m behind the flow front which advanced steadily at 2 m s 1 during most of the runout segregation was measured by placing 600 coarse tracer pebbles on the bed which when entrained into the flow segregated upwards at 6 7 5 cm s 1 when excavated from the deposit these were distributed in a horseshoe shaped pattern that became increasingly elevated closer to the deposit termination although there was clear evidence for inverse grading during the flow transect sampling revealed that the resulting leveed deposit was strongly graded laterally with only weak vertical grading we construct an empirical three dimensional velocity field resembling the experimental observations and use this with a particle size segregation model to predict the segregation and transport of material through the flow we infer that coarse material segregates to the flow surface and is transported to the flow front by shear within the flow head coarse material is overridden then recirculates in spiral trajectories due to size segregation before being advected to the flow edges and deposited to form coarse particle enriched levees

analysis of debris wave development with one dimensional shallow water equations the objective of this contribution is to analyze the formation of debris waves in natural channels numerical simulations are carried out with a 1d code based on shallow water equations and on the weighted averaged flux method the numerical code represents the incised channel geometry with a power law relation between local width and flow depth and accounts for all source terms in the momentum equation the debris mixture is treated as a homogeneous fluid over a fixed bottom whose rheological behavior alternatively follows herschel bulkley bingham or generalized viscoplastic models the code is first validated by applying it to dam break tests on mudflows down a laboratory chute and verifying its efficiency in the simulation of rapid transients then following the analytical method developed by trowbridge the stability of a uniform flow for a generalized viscoplastic fluid is examined showing that debris flows become unstable for froude numbers well below 1 applications of the code to real debris

debris flow velocities and superelevation in a curved laboratory channel the vortex equation is often used to estimate the front velocity of debris flows using the lateral slope of the flow surface through a channel bend of a given radius here we report on laboratory e