the role of bore collapse and local shear stresses on the spatial distribution of sediment load in the uprush of an intermediate state beach abstract spatial variations in sediment load in the swash uprush and textural properties of sediment in transport were evaluated to investigate the mechanisms responsible for sediment transport during wave uprush four streamer traps were deployed at 2 0 m intervals across the swash zone of a sheltered microtidal sandy beach at port beach western australia over a 4 day period during these trapping experiments offshore significant wave heights were 0 3 0 5 m and wave periods were about 10 s the average width of the uprush zone was 6 9 m and the average uprush duration was 5 9 s cross shore distributions of sediment load for 70 uprush events reveal a maximum in sediment load landward of the base of the swash at about 20 of swash width during single events and a maximum closer to mid swash at about 40 of swash width during multiple events characterized by swash interactions settling velocity distributions of trap samples during individual uprush events are similar to distributions found on the beach surface with the lowest settling velocities finest sediments near the base of the swash zone and maximum settling velocities coarsest sediments around the mid swash position it was found that sediment transport during wave uprush occurs through two distinct mechanisms 1 sediment entrainment during bore collapse seaward of the base of the swash zone and subsequent advection of this bore entrained sediment up the beach by wave uprush and 2 in situ sediment entrainment and transport induced by local shear stresses during wave uprush both mechanisms are considered important but the first mechanism is considered most significant during the early stages of wave uprush when sediment is transported mainly in suspension while the second mechanism is likely to dominate the mid to later stages of wave uprush when sediment is transported mainly by sheet flow the relative importance of the two mechanisms will vary between different beaches with the morphodynamic state of the beach reflective versus dissipative expected to play a major role

net sediment transport and morphological change in the swash zone of a high energy sandy beach from swash event to tidal cycle time scales abstract a field experiment was conducted on a high energy sandy beach truc vert france to examine swash zone processes and shoreline erosion accretion in response to changing wave and tide conditions beachface morphological changes were measured at the swash by swash timescale using an array of ultrasonic bed level sensors and at the tidal timescale through total station surveys hydrodynamic and sediment dynamic data were collected using arrays of pressure transducers electromagnetic current meters optical backscatter sensors and total load sediment traps data were collected for 16 consecutive days 33 tides over a spring neap spring tidal cycle with offshore significant wave heights of 1 4 m and periods of 5 12 s the swash motion was predominantly at infragravity wave frequencies over the measurement period the upper beach experienced phases of accretion erosion and stability trapped sediment loads for the uprush and backwash were predicted reasonably well by cross shore velocity skewness but the prediction of net transport over individual swash events by velocity based models was more problematic particularly lower in the swash zone where swash interactions were more prevalent net sediment fluxes over individual swash events often exceeded 100 kg per unit meter beach width and such rates were only one order of magnitude less than the net transport typically experienced across the high tide swash zone over complete tidal cycles upper beach erosion accretion at the tidal timescale was reasonably well predicted by the dean criterion based on offshore wave steepness and dimensionless fall velocity but the beach gradient also played a significant role in controlling the occurrence of erosion and accretion

advances in swash zone research small scale hydrodynamic and sediment transport processes abstract extensive research efforts in the last decade have improved knowledge of swash zone processes this paper reviews and synthesizes from 2004 onward the research advances of small scale hydrodynamics and sediment transport processes considering field laboratory and numerical modeling efforts swash zone hydrodynamics are examined by means of shoreline motions fluid velocities pressure gradients flow structure bed shear stress friction coefficients and turbulence subsequently advances related to sediment transport mechanisms and morphological changes are described detailed descriptions of measuring techniques novel findings and the strengths and weaknesses of the different approaches are discussed the review also acknowledges the major advances in the development of instrumentation to collect highly resolved flow and sediment concentration measurements in direct proximity of the bed and the experimental framework for analyzing local dynamics on a wave by wave time scale e g dam break

sand transport processes and bed level changes induced by two alternating laboratory swash events abstract sand transport processes and net transport rates are studied in a large scale laboratory swash zone bichromatic waves with a phase modulation were generated producing two continuously alternating swash events that have similar offshore wave statistics but which differ in terms of wave swash interactions measured sand suspension and sheet flow dynamics show strong temporal and spatial variability related to variations in flow velocity and locations of wave capture and wave backwash interactions suspended and sheet flow layer transport rates in the lower swash zone are generally of same magnitude but sheet flow exceeds the suspended load transport by up to a factor four during the early uprush the bed level near the inner surf zone is relatively steady during a swash cycle but changes of o cm s are measured near the mid swash zone where wave swash interactions lead to strongly non uniform flows the two alternating swash events produce a dynamic equilibrium with bed level changes up to a few mm induced by single swash events but with net morphodynamic change over multiple events that is two orders of magnitude lower most of the intra swash and the single event averaged bed level changes in the swash zone are caused by a redistribution of sediment within the swash the transport of sediment across the surf swash boundary is minor at intra swash time scale but becomes increasingly significant at swash averaged time scales or longer i e averaged over multiple swash events

a semianalytical model for sheet flow layer thickness with application to the swash zone a new semianalytical model for the time dependent thickness of the sheet flow layer that includes the effects of pressure gradients bed slope boundary layer growth and bore turbulence is presented the shear stress and boundary layer growth are computed using the boundary layer integral method the model is expressed as two coupled ordinary differential equations that are solved numerically given a prescribed time series of free stream velocity horizontal pressure gradient and bore turbulence which together represent the hydrodynamic forcing the model was validated against two data sets of sheet flow layer thickness collected in oscillatory flow tunnels and one data set collected in the swash zone of a prototype scale laboratory experiment in the oscillatory flow tunnel data sets sheet flow is mostly generated by shear stress with pressure gradients providing an important secondary forcing around flow reversal in the swash zone pressure gradients and shear stresses alone are not sufficient to generate the large sheet flow layer thickness observed at the initial stages of uprush bore turbulence is most likely the dominant generation mechanism for this intense sheet flow

the influence of wave groups and wave swash interactions on sediment transport and bed evolution in the swash zone abstract large scale laboratory measurements of sediment dynamics in the swash zone are presented two bichromatic wave group conditions were generated having the same energy content but different wave group period t g 15 0 s and 27 7 s for the shortest wave group due to bore focusing the shoreline fluctuates predominantly at the t g time scale showing a large runup and the presence of wave swash interactions with strong momentum exchange in contrast for the longer wave groups the swash excursion is dominated by the individual waves the uprush generally promotes onshore sediment advection with consequent erosion at the rundown location but accretion close to the runup on the contrary the backwash promotes seaward sediment advection and accretion at the rundown location the presence of repeated wave swash interactions modifies these patterns slightly a wave overrunning a previous uprush promotes a reduction in onshore sediment advection while weak wave backwash interactions reduce seaward advection consequently the measured sediment dynamics shows stronger intra swash cross shore sediment advection for the swash events produced by the short wave groups measurements of the sheet flow layer near the shoreline show that for the shortest wave groups the vertical structure of the concentration is influenced by horizontal advection leading to large sheet flow layer thickness however for the longer wave groups the local vertical exchange of sediment in the sheet flow layer is dominant with the presence of a pick up and mirroring upper layer similar to oscillatory sheet flow measurements these results reaffirm the important effects of the wave group structure and the wave swash interactions on the swash zone sediment dynamics and beach face evolution

a fiber optic sensor for monitoring suspended sediment a new instrument that can be used to continuously monitor concentration of suspended particulates in close proximity to the sea bed z 3 5 cm is described the instrument is composed of a narrow band source light a photodiode detector and glass fibers that transmit and receive light individual sensors can be sampled rapidly 8 hz and respond linearly to increasing concentrations of sediment over the range 0 100 gl 1 an array of sensors can be deployed from z 0 5 to 3 5 cm above the seabed providing simultaneous time series of suspended sediment concentration at five discrete elevations results of a field deployment in the swash zone of a dissipative beach indicate that the performance of the instrument is comparable to that of the standard optical backscatter sensor obs the data show that se the standard optical backscatter sensor obs the data show that sediment resuspension in the swash zone is strongly correlated with low frequency cross shore flows with peak concentrations exceeding 200 gl 1

swash zone sediment fluxes field observations abstract this paper describes newly obtained high frequency observations of beach face morphological change over numerous tidal cycles on a macrotidal sandy beach made using a large array of ultrasonic altimeters these measurements enable the net cross shore sediment fluxes associated with many thousands of individual swash events to be quantified it is revealed that regardless of the direction of net morphological change on a tidal time scale measured net fluxes per event are essentially normally distributed with nearly equal numbers of onshore and offshore directed events the majority of swash events cause net cross shore sediment fluxes smaller than 50 kg m 1 and the mean sediment flux per swash event is only o 1 kg m 1 leading to limited overall morphological change however much larger events which deposit or remove hundreds of kilograms of sand per meter width of beach occur at irregular intervals throughout the course of a tide it was found that swash swash interactions tend to increase the transport potential of a swash event and the majority of the swash events that cause these larger values of sediment flux include one or more interactions the majority of the larger sediment fluxes were therefore measured in the lower swash zone close to the surf swash boundary where swash swash interactions are most common despite the existence of individual swash events that can cause fluxes of sediment that are comparable to those observed on a tidal time scale frequent reversals in transport direction act to limit net transport such that the beach face volume remains in a state of dynamic equilibrium and does not rapidly erode or accrete

measurement of wave by wave bed levels in the swash zone abstract a technique is described to observe and quantify wave by wave bed level changes in the swash zone the ultrasonic instrument system is non contact with the beach face surface being measured and the sensors remain outside of the fluid flows causing sediment movement sensor resolution combined with the electronic noise inherent within a digital network data logging system results in a conservative measurement accuracy of 1 mm equating to a couple of sand grain diameters in height illustrative field results demonstrate the practical use of the instrumentation and a simple data pre processing method to separate swashes and intervening bed level events is discussed these example data reveal rather complex fluctuations of the bed observed over time periods of minutes to hours rather strikingly gross bed level changes per wave are revealed to be up to many orders of magnitude larger than the observed net rate of beach face evolution it is outlined how observations of successive bed level changes at multiple locations within a dense grid combined with a consideration of sediment continuity will now enable the total net sediment transported per uprush backwash to be quantified

subaqueous deposition of accretionary lapilli significance for palaeoenvironmental interpretations in archaean greenstone belts abstract accretionary lapilli from phreatomagmatic eruptions are abundant in the late archaean fortescue group of the pilbara region western australia where the sequence is uncleaved and gently folded well preserved depositional structures include densely packed accretionary lapilli in trough cross beds and sparse accretionary lapilli in trough and wedge to tabular cross beds accretionary lapilli also occur in conglomerate layers and localised pebbly channel fills associated with granite and pegmatite clasts up to 10 cm in diameter these lapilli are clearly robust being capable of withstanding fairly energetic aqueous transport in contrast to the opinion of many authors who consider that all accretionary lapilli would disintegrate if settled through extensive water columns or incorporated in turbidite deposits accretionary lapilli indicate subaerial or very shallow water eruption but their presence cannot be used alone to support very shallow water or subaerial deposition accretionary lapilli are found throughout many volcanic piles and are probably widespread in archaean greenstone successions but their environmental significance has to be assessed carefully using a variety of associated features

large scale experimental observations of sheet flow on a sandbar under skewed asymmetric waves a novel large wave flume experiment was conducted on a fixed barred beach with a sediment pit on the sandbar allowing for the isolation of small scale bed response to large scale forcing concurrent measurements of instantaneous sheet layer sediment concentration profiles and near bed velocity profiles were obtained on a sandbar for the first time two sediment distributions were used with median grain diameters d50 of 0 17 mm and 0 27 mm sheet flow occurred primarily under wave crests where sheet thickness increased with increasing wave height a proportionality constant was used to relate maximum shields parameter to maximum sheet thickness normalized by d50 with bed shear stress computed using the quadratic drag law an enhanced sheet layer thickness was apparent for the smaller sediment experiments 18 7 when directly compared to closed conduit oscillatory flow tunnel data 10 6 however varied significantly 5 31 depending on the procedure used to estimate grain roughness ds and wave friction factor fw three models for ks were compared keeping the model for fw fixed constant ks 2 5d50 and two expressions dependent on flow intensity derived from steady and oscillatory sheet flow experiments values of ks d50 varied by two orders of magnitude and exhibited an inverse relationship with where 30 for ks d50 of o 1 while 5 for ks d50 of o 100 two expressions for fw were also tested with the steady flow based model for ks yielding a difference of 69 13 versus 22

swash overtopping and sediment overwash on a truncated beach new experimental laboratory data are presented on swash overtopping and sediment overwash on a truncated beach approximating the conditions at the crest of a beach berm or inter tidal ridge runnel the experiments provide a measure of the uprush sediment transport rate in the swash zone that is unaffected by the difficulties inherent in deploying instrumentation or sediment trapping techniques at laboratory scale overtopping flow volumes are compared with an analytical solution for swash flows as well as a simple numerical model both of which are restricted to individual swash events the analytical solution underestimates the overtopping volume by an order of magnitude while the model provides good overall agreement with the data and the reason for this difference is discussed modelled flow velocities are input to simple sediment transport formulae appropriate to the swash zone in order to predict the overwash sediment transport rates calculations performed with traditional expressions for the wave friction factor tend to underestimate the measured transport additional sediment transport calculations using standard total load equations are used to derive an optimum constant wave friction factor of f w 0 024 this is in good agreement with a broad range of published field and laboratory data however the influence of long waves and irregular wave run up on the overtopping and overwash remains to be assessed the good agreement between modelled and measured sediment transport rates suggests that the model provides accurate predictions of the uprush sediment transport rates in the swash zone which has application in predicting the growth and height of beach berms c 2005 elsevier b v all rights reserved

an unusual occurrence of mafic accretionary lapilli in deep marine volcaniclastics on eua tonga palaeoenvironment and process reports of occurrences of accretionary lapilli on earth whether in historic time or in the geological record are restricted to subaerial environments or to shallow marine environments when faunal evidence exists to determine palaeodepths the proximity of the deep ocean to subduction zones island arcs where moist explosive volcanism conducive to ash aggregate formation is common makes this surprising in this paper accretionary lapilli are reported within middle miocene mafic glass rich volcaniclastics on eua the island closest to the tonga trench a persistent high in the frontal arc basin the glass in the accretionary lapilli has been subjected to advanced palagonitisation but concentric layers marked by micro aggregates containing shard shaped particles survive to determine one group of occurrences as layered accretionary lapilli the palaeoenvironment as established by pelagic microfauna is clearly deep marine not less than 1600 m the host rocks typically gravel sand in grain size contain sedimentary structures normal grading to inverse and normal to inverse grading lack of grading large scale cross bedding slump bedding and sedimentary dykes suggesting that the full spectrum of sediment gravity flow types including less ordered debris flows has been active in an island arc environment a range of sediment gravity flow types can be initiated some by pyroclastic flows entering the sea however the thin beds of accretionary lapilli do not exhibit features of sediment gravity flow deposits or those of submarine pyroclastic flows possible transport processes must account for the matrix between the ash aggregates which is either coarse grained or absent modelling of particle descent times to 1600 m through a sea water column provides one explanation for the features displayed

bedload and suspended load contributions to breaker bar morphodynamics abstract this study presents measurements of sheet flow processes grain sorting and bedload plus suspended load transport rates around a medium sand breaker bar in a large scale wave flume the results offer insights in effects of wave breaking on bedload and grain sorting processes and in the quantitative contributions by bedload and suspended transport to breaker bar morphodynamics sheet flow layer dynamics are highly similar to observations under non breaking waves revealing clear effects by velocity asymmetry but no evident effects by breaking generated turbulence bed slope or the cross shore non uniform flow the sheet flow layer thickness can be predicted using existing empirical formulations based on local hydrodynamic forcing at locations covering the shoaling region up to the bar crest the cross shore variation in bedload transport rates is explained by variations in wave shape i e velocity skewness and asymmetry at locations between bar crest and bar trough bedload transport rate magnitudes correlate positively with bed slope and turbulent kinetic energy bedload and suspended load transport rates are of similar magnitude but of opposite sign bedload transport is onshore directed and dominates in the shoaling zone but after wave breaking the offshore directed suspended sediment transport increases in magnitude and exceeds bedload transport rates in the breaking and inner surf zones bedload and suspended load transport contribute notably differently to bed profile evolution bedload transfers sand grains from the offshore slope to the bar crest and additionally leads to erosion of the shoreward bar slope and deposition at the bar trough while suspended load transport induces an opposite pattern of erosion at the bar trough and accretion at the bar crest grain size analysis of suspended sediment samples reveals size selective entrainment and vertical size segregation in the inner surf zone but suggest size indifferent entrainment and vertical mixing by energetic vortices in the breaking region size selective transport by bedload and suspended load leads to a cross shore coarsening of the bed from shoaling to inner surf zone with local additional sorting mechanisms around the breaker bar due to bed slope effects

bed level motions and sheet flow processes in the swash zone observations with a new conductivity based concentration measuring technique ccm detailed measurements of bed level motions and sheet flow processes in the lower swash are presented the measurements are obtained during a large scale wave flume experiment focusing on swash zone sediment transport induced by bichromatic waves a new instrument ccm provides detailed phase averaged measurements of sheet flow concentrations particle velocities and bed level evolution during a complete swash cycle the bed at the lower swash location shows a clear pattern of rapid erosion during the early uprush and progressive accretion during the middle backwash phase sheet flow occurs during the early uprush and mid and late backwash phases sheet flow sediment fluxes during these instances are highest in the pick up layer sediment entrainment from the pick up layer occurs not only during instances of high horizontal shear velocities but also in occurrence of wave backwash interactions as opposed to oscillatory sheet flow the pivot point elevation of the sheet flow layer is time varying during a swash event moreover the upper sheet flow layer concentrations do not mirror the concentrations in the pick up layer both differences suggest that in the lower swash zone the dynamics of the upper sheet flow layer are not only controlled by vertical sediment exchange such as in oscillatory sheet flows but are strongly affected by horizontal advection processes induced by the non uniformity of the flow

ascent dynamics of large phreatomagmatic eruption clouds the role of microphysics 1 we examine the impact of abundant surface water interaction on the development of volcanic clouds from large scale 108 kg s 1 magma phreatomagmatic eruptions presenting the first 2 d large eddy simulations of wet volcanic plumes that incorporate the effects of microphysics the active tracer high resolution atmospheric model was forced with field derived inputs from an exceptionally large phreatomagmatic eruption the 27 ka oruanui supereruption taupo volcano new zealand surface water contents were varied from 0 to 40 wt for eruptions with equivalent magma eruption rates of 1 3 108 and 1 1 109 kg s 1 our findings confirm that increased surface water has a pronounced impact on column stability leading to transitional column behavior and hybrid clouds resulting from simultaneous ascent of material from stable columns and pyroclastic density currents pdcs contrary to the suggestion of previous workers however abundant surface water does not systematically lower the spreading level or maximum height of volcanic clouds owing to vigorous microphysics assisted lofting of pdcs the simulated behavior and ash cloud dimensions provide a close match to field evidence from the oruanui case study cloud heights from the collapsing eruption columns also show a notable sensitivity to changes in the altitude of the tropopause while ambient humidity primarily impacts the abundance of airborne hydrometeors particularly ice associated with the volcanic clouds general relationships between eruption style meteorological conditions and the resulting vertical profiles of volcanic emissions outlined here could also be adapted for use in operational volcanic ash forecasting and deposit reconstruction techniques already in existence

concentrations in oscillatory sheet flow for well sorted and graded sands in wave generated sheet flow conditions oscillatory near bed flow is large ripples are washed out and sand is mainly transported in a thin layer a few centimetres thick close to and below the no flow bed level new experiments in the aberdeen oscillatory flow tunnel have produced a comprehensive dataset of transport processes for well sorted and graded sands in large scale sinusoidal and asymmetric oscillatory sheet flow conditions in this paper detailed time and height varying concentration measurements are analysed the range and level of detail in the measurements make it possible to quantitatively analyse concentration behaviour more rigorously than before a new empirical equation is presented which characterises the time dependent concentration profile in the sheet flow layer the equation involves two time dependent parameters erosion depth and reference concentration the dependence of both parameters on flow and bed conditions is analysed new results are presented which make it possible to estimate time dependent erosion depth reference concentration and therefore concentration profile the effects of grading on sheet flow concentrations are analysed by comparing results from the large range of sand beds tested

the morphodynamics of a swash event on an erodible beach a high accuracy numerical solution coupling one dimensional shallow water and bed evolution equations with for the first time a suspended sediment advection equation thereby including bed and or suspended load is used to examine two swash events on an initially plane erodible beach the event of peregrine williams j fluid mech vol 440 2001 pp 391 399 and that of a solitary wave approaching the beach equations are solved by the method of characteristics and the numerical model is verified full coupling of suspended load to beach change for peregrine williams j fluid mech vol 440 2001 pp 391 399 yields only slightly altered swash flows depending on beach mobility and sediment response time a series of similar final beach change patterns results for different beach mobilities suspended and bed load transport have distinct morphodynamical signatures for the solitary wave a backwash bore is created hibberd peregrine j fluid mech vol 95 1979 pp 323 345 this morphodynamical bore propagates offshore initially and leads to the creation of a beach bed step larson sunamura j sedimentary petrology vol 63 1993 pp 495 500 primarily due to bed load transport its height is directly related to bed load mobility and also depends strongly on the bed friction coefficient the shock dynamics of this bed step is explained and illustrated bed and suspended load mobilities are quantified using field data and an attempt is made to relate predictions to measurements of single swash events on a natural beach average predicted bed change magnitudes across the swash are of the order of 2 mm with maximum bed changes of up to approximately 10 cm at the bed step

measurements of sheet flow transport in acceleration skewed oscillatory flow and comparison with practical formulations near bed oscillatory flows with acceleration skewness are characteristic of steep and breaking waves in shallow water in order to isolate the effects of acceleration skewness on sheet flow sand transport new experiments are carried out in the aberdeen oscillatory flow tunnel the experiments have produced a dataset of net transport rates for full scale oscillatory flows with varying degrees of acceleration skewness and three sand sizes the new data confirm previous research that net transport in acceleration skewed flow is non zero is always in the direction of the largest acceleration and increases with increasing acceleration skewness large transport rates for the fine sand conditions suggest that phase lag effects play an important role in augmenting positive net transport a comparison of the new experimental data with a number of practical sand transport formulations that incorporate acceleration skewness shows that none of the formulations performs well in predicting the measured net transport rates for both the fine and the coarser sands the new experimental data can be used to further develop practical sand transport formulations to better account for acceleration skewness

bed level fluctuations in the inner surf and swash zone of a dissipative beach abstract a field study was conducted on a dissipative beach to quantify inner surf and swash zone bed level change during periods of inundation and throughout a tidal cycle elevation changes were acquired at millimeter resolution with a new conductivity concentration profiler that allowed quantification of the bed level throughout the duration of the wave swash cycle and also during periods of bed exposure bed level change spectra showed the highest energy at low frequencies even though event scale net bed level changes were observed to exceed the tidal scale net bed level change net bed level change for individual events was nearly normally distributed with most individual events displaying little or no net bed level change large erosion and accretion events with bed level elevation magnitudes that exceeded net tidal elevation change occurred with similar frequency the similarity between the frequency of large erosion and large accretion events suggests that a few events may be ultimately responsible for the observed net elevation change over the tidal cycle the large events displayed different hydrodynamic characteristics erosion events had longer duration onshore directed flow and higher maximum onshore directed velocity magnitude than offshore directed velocity magnitude the opposite was found for accretion events that had longer duration offshore directed flow and a higher maximum offshore directed velocity magnitude than onshore directed velocity magnitude

inversion of an oligocene volcano tectonic basin and uplifting of its superimposed miocene magmatic arc in the chilean central andes first seismic and gravity evidences abstract a new structural model is presented for the cenozoic part of the main range east of santiago a chain made up of thick miocene ignimbrites and andesitic lavas overlying primitive oligocene volcanoclastics deposited on a thin continental crust because the latter coya machali formation locally show tight folding close to the margins of the miocene volcanics they had previously been described as deformed prior to construction of the arc our field observations analysed along two profiles at 33 and 34 15 s however support the conclusion hinted at by ongoing geochronological and geochemical studies deformation of both formations is synchronous and related to late miocene inversion of the coya machali intra arc basin uplift of the rigid arc rocks and part of its volcanoclastic basement took place mainly along two northward shallowing boundary structures that seem to share a lower decollement the eastern fierro out of sequence thrust and a series of western back thrusts that resemble triangle zones seismic data obtained from el teniente porphyry copper mine 34 s rockbursts and two gravimetric profiles at the western end of the southern profile are compatible with a decollement located at that locality 2 3 km under the surface

a precambrian proximal ejecta blanket from scotland ejecta blankets around impact craters are rarely preserved on earth although impact craters are ubiquitous on solid bodies throughout the solar system on earth they are rapidly effaced and few records exist of the processes that occur during emplacement of ejecta the stac fada member of the precambrian stoer group in scotland has previously been described as volcanic in origin however shocked quartz and biotite provide evidence for high pressure shock metamorphism while chromium isotope values and elevated abundances of platinum group metals and siderophile elements indicate addition of meteoritic material thus the unit is reinterpreted here as having an impact origin the ejecta blanket reaches 20 m in thickness and contains abundant dark green vesicular devitrified glass fragments field observations suggest that the deposit was emplaced as a single fluidized flow that formed as a result of an impact into water saturated sedimentary strata the continental geological setting and presence of groundwater make this deposit an analogue for martian fluidized ejecta blankets

sediment flux based model of instantaneous sediment transport due to pure velocity skewed oscillatory sheet flow with boundary layer stream abstract velocity skewed oscillatory sheet flow transport is studied by an approximate model for instantaneous sediment transport resulting from exponential profiles of sediment concentration and velocity over a mobile bed the phase lag effect and asymmetry in wave friction factor oscillatory flow orbital amplitude roughness height bed shear stress and wave boundary layer thickness are modelled so that the net boundary layer stream of pure velocity skewed oscillatory flow can be obtained the proposed model is found consistent with the previous classical formulas and qualitatively refines a series of exponents of velocity power function for the approximation of instantaneous sediment transport rate under different flow conditions the sediment fluxes can be well predicted with accuracy as that of a two phase numerical model the net boundary layer stream and sediment transport rates are also well predicted especially the negative net stream and rates with large phase residual the phase residual is shown a useful but insufficient factor in the net sediment transport in pure velocity skewed flows in addition the net boundary layer stream resulting from velocity skewed wave boundary layer development difference between onshore and offshore flow durations is an essential factor as well

on the transport of suspended sediment by a swash event on a plane beach we develop solutions for the transport of suspended sediment by a single swash event following the collapse of a bore on a plane beach and we investigate the morphodynamical role that such transport may play although the intrinsic asymmetry between uprush and backwash velocities tends to encourage the export of sediment we find that swash events may be effective in distributing across the swash zone much or all of the sediment mobilised by bore collapse additionally settling lag effects may promote a weak onshore movement of sediment we quantify both effects in terms of the properties of the sediment and of the swash event and comment on the relationship between our findings and recent field studies of swash zone sediment transport

swash zone sediment suspension and transport and the importance of bore generated turbulence a study of swash zone sediment transport was conducted at gleneden beach oregon during february 25 28 1994 the data collected included suspended sediment concentration ssc sea surface elevation and velocity initially 4 and 8 cm above the bed at three cross shore locations within the swash zone spanning high tides ensemble averages of 6 9 and 12 s duration swash events showed that the uprush suspension was high concentrated in the leading edge and nearly vertically uniform above the lower 1 2 cm of the water column shortly after the sensors were inundated by run up the sediment rapidly settled out of the water during flow reversal the ssc was small but increased again in the backwash backwash vertical profiles were markedly different from uprush profiles with much of the suspension being confined to very near the bed where strong vertical gradients in ssc existed these marked differences show that the backwash is not simply the reverse of the uprush implying significant differences in the underlying fluid dynamics and sediment transport mechanisms backwash sediment suspension increased with flow duration however ensemble averaged ssc profiles of varying duration showed that the backwash concentrations were not consistent at the same temporal phases which suggests that water depth in addition to flow duration may be a controlling factor strong cross shore gradients in ssc suggest that bore derived turbulence may affect local sediment transport specifically our data show this bore generated turbulence turbulent kinetic energy directly influences local sediment suspension hence standard bed shear bagnold type sediment transport models may no longer be valid in the vicinity of the bore in the vicinity of the bore a higher correlation between bore generated turbulence and suspended sediment transport was found than between a bagnold type formulation and suspended sediment transport

an experimental study on sediment transport and bed evolution under different swash zone morphological conditions in this study new large scale experimental data are presented showing evidences of a link between the swash zone dynamics and the surf zone morphodynamics two sets of large scale experiments are presented the first set of experiments investigates the swash and surf dynamics under the same hydrodynamic forcing but with two different swash zone morphological conditions one of which was created by manual reshaping of the sub aerial beach face it is shown that more dissipative swash zone conditions a more mildly sloping beach face significantly reduce the rate of seaward sandbar migration such that it almost ceases during the performed experimentation time this behavior is compared to a second set of experiments which shows the natural sand bar offshore migration under almost identical hydrodynamic forcing the changes in the sandbar migration are investigated in terms of the differences in the swash zone dynamics the more reflective swash zone is characterized by more intense backwashes that in turn promote significant quantities of sediment suspension during the interaction of the backwash with the subsequent bore the dissipative swash zone leads to a larger number of wave swash interactions reducing the backwash magnitudes and the magnitude of suspended sediment concentration events in the swash zone with a corresponding reduction in the offshore suspended sediment transport the total offshore sediment transport rates are also shown to reduce leading to the observed modification of the sandbar migration

sand transport beneath waves the role of progressive wave streaming and other free surface effects recent large scale wave flume experiments on sheet flow sediment transport beneath stokes waves show more onshore directed sediment transport than earlier sheet flow experiments in oscillating flow tunnels for fine sand this extends to a reversal from offshore tunnels to onshore flumes directed transport a remarkable hydrodynamic mechanism present in flumes with free water surface but not in tunnels rigid lid is the generation of progressive wave streaming an onshore wave boundary layer current this article investigates whether this streaming is the full explanation of the observed differences in transport in this article we present a numerical model of wave induced sand transport that includes the effects of the free surface on the bottom boundary layer with these effects and turbulence damping by sediment included our model yields good reproductions of the vertical profile of the horizontal mean velocities as well as transport rates of both fine and medium sized sediment similar to the measurements the model reveals the reversal of transport direction by free surface effects for fine sand a numerical investigation of the relative importance of the various free surface effects shows that progressive wave streaming indeed contributes substantially to increased onshore transport rates however especially for fine sands horizontal gradients in sediment advection in the horizontally nonuniform flow field also are found to contribute significantly we therefore conclude that not only streaming but also inhomogeneous sediment advection should be considered in formulas of wave induced sediment transport applied in morphodynamic modeling we propose a variable time scale parameter to account for these effects

large scale experiments on beach profile evolution and surf and swash zone sediment transport induced by long waves wave groups and random waves new large scale laboratory data are presented on the influence of long waves bichromatic wave groups and random waves on sediment transport in the surf and swash zones physical model testing was performed in the large scale ciem wave flume at upc barcelona as part of the susco swash zone response under grouping storm conditions experiment in the hydralab iii program vicinanza et al 2010 fourteen different wave conditions were used encompassing monochromatic waves bichromatic wave groups and random waves the experiments were designed specifically to compare variations in beach profile evolution between monochromatic waves and unsteady waves with the same mean energy flux each test commenced with approximately the same initial profile the monochromatic conditions were perturbed with free long waves and then subsequently substituted with bichromatic wave groups with different bandwidth and with random waves with varying groupiness beach profile measurements were made at half hourly and hourly intervals from which net cross shore transport rates were calculated for the different wave conditions pairs of experiments with slightly different bandwidth or wave grouping show very similar net cross shore sediment transport patterns giving high confidence to the data set consistent with recent small scale experiments the data clearly show that in comparison to monochromatic conditions the bichromatic wave groups reduce onshore transport during accretive conditions and increase offshore transport during erosive conditions the random waves have a similar influence to the bichromatic wave groups promoting offshore transport in comparison to the monochromatic conditions the data also indicate that the free long waves promote onshore transport but the conclusions are more tentative as a result of a few errors in the test schedule and modifications to the setup which reduced testing time the experiments suggest that the inclusion of long wave and wave group sediment transport is important for improved near shore morphological modeling of cross shore beach profile evolution and they provide a very comprehensive and controlled series of tests for evaluating numerical models it is suggested that the large change in the beach response between monochromatic conditions and wave group conditions is a result of the increased significant and maximum wave heights in the wave groups as much as the presence of the forced and free long waves induced by the groupiness the equilibrium state model concept can provide a heuristic explanation of the influence of the wave groups on the bulk beach profile response if their effective relative fall velocity is larger than that of monochromatic waves with the same incident energy flux

geology and tectonostratigraphy of the onverwacht suite barberton greenstone belt south africa abstract a synthesis of new and existing data reveals that at least seven major shear zones and an unconformity separate the rocks of the southern barberton greenstone belt into seven units with different geological histories current views that these units constitute a continuous stratigraphic sequence and their subdivision into successive formations cannot be maintained we argue here that the status of the traditional formations of the onverwacht group of the barberton greenstone belt be changed to complexes and collectively these complexes be referred to as the onverwacht suite the total age range and tectonostratigraphic thickness of the suite is about 120 million years and 15 km respectively the precise age range of the rocks present in each complex is largely unknown the original spatial relationships between the complexes can in most cases only be inferred all of the complexes include significant volumes of intrusions that were emplaced into the volcanic and volcaniclastic host rocks the ages of the intrusions in the different complexes vary in some complexes the intrusions and volcanic rocks have similar geochemistry and are probably co magmatic others provide stitching ages between complexes four of the complexes display internal relationships that resemble ophiolites basaltic pillowed and massive lavas are the most common rock types sheeted dykes are generally absent whilst multiple mafic sills are common and dominate one of the complexes the volcanology and geochemistry of the complexes suggest that they formed predominantly in oceanic spreading and intra oceanic arc environments at water depths of 1 7 4 km the complexes were tectonically stacked during the final stages of their development and during two subsequent orogenic events one complex the hooggenoeg complex was uplifted and deeply eroded between about 3460 and 3470 ma with a minimum uplift rate ca 0 5 mm yr similar to that during emplacement of phanerozoic ophiolites unconformably overlying sub aerial coarse clastic sedimentary rocks part of the newly distinguished noisy complex overlap in age with felsic intermediate igneous activity dated between 3445 and 3460 ma that in turn is genetically related to tonalite trondjemite plutons exposed farther to the south the emergence of the deep water hooggenoeg complex above sea level the start of its erosion and fluvial sedimentation on top of it at ca 3458 ma represents the onset of its obduction onto older complexes some of which are now preserved as enclaves in the granitoid terrains to the south other oceanic slabs the kromberg and the mendon complexes were subsequently emplaced onto the noisy complex during latitudinal displacements ca 12 cm yr that were not notably faster than today exhumation with up to 18 km of unroofing along the southern margin of the greenstone belt took place during a second orogenic episode of subduction and accretion between 3140 and 3230 ma this episode was associated with folding thrusting and molasse type sedimentation within the greenstone belt coupled to extension and ductile faulting at a lower crustal level during this period younger complexes were assembled and the older complexes re cycled and eroded at rates and with geotherms comparable to those in modern orogenic belts in the barberton region between 3 2 and 3 5 ga tectonic processes appear to have operated at rates similar to those within modern evolving plate boundaries

measurements and modelling of the advection of suspended sediment in the swash zone by solitary waves novel laboratory experiments and numerical modelling have been performed to study the advection scales of suspended sediment in the swash zone an experiment was designed specifically to measure only the sediment picked up seaward of the swash zone and during bore collapse the advection scales and settling of this sediment were measured during the uprush along a rigid sediment free beach face by a sediment trap located at varying cross shore positions measurements were made using a number of repeated solitary broken waves or bores approximately 25 of the pre suspended sediment picked up by the bores reaches the mid swash zone 50 of the horizontal run up distance indicating the importance of the sediment advection in the lower swash zone the pre suspended sediment is sourced from a region seaward of the shoreline still water line which has a width of about 20 of the run up distance an eulerian lagrangian numerical model is used to model the advection scales of the suspended sediment the model resolves the hydrodynamics by solving the non linear shallow water equations in an eulerian framework and then solves the advection diffusion equation for turbulence and suspended sediment in a lagrangian framework the model provides good estimates of the measured mass and distribution of sediment advected up the beach face the results suggest that the correct modelling of turbulence generation prior to and during bore collapse and the advection of the turbulent kinetic energy into the lower swash is important in resolving the contribution of pre suspended sediment to the net sediment transport in the swash zone c 2009 elsevier b v all rights reserved

sediment suspension and turbulence in the swash zone of dissipative beaches abstract this paper investigates mechanisms for stirring and transport of suspended sediment by infragravity scale swash using high frequency field measurements of horizontal and vertical flow velocities water depths and sediment concentration profiles the field data suggest that vertical velocity fluctuations generated by coherent eddies can be important to the process of sediment suspension and can contribute to asymmetrically distributed sediment transport rates between the uprush and backwash phases of the swash cycle this result indicates that the traditional and often used proxy for bed shear stress based solely on measurements of the horizontal component of flow u i e b fu 2 where is the water density and f is a friction factor may be inadequate when used in energetics type sediment transport models applied to the swash which is indeed the case we demonstrate that a bed shear stress formulation which is more consistent with the physics leads to improved predictive capability for energetics type transport models this formulation is based on the correlation between the horizontal and turbulent vertical components of the flow i e b uw despite the improvement it is evident that considerable amounts of calibration data are still required before each application of this model type moreover our data shows that the issue of calibration coefficients is more problematic than generally appreciated the calibration coefficients for energetics type models on a given beach not only differ between uprush and backwash but also vary with position within the swash zone particularly on the uprush phase

intra swash hydrodynamics and sediment flux for dambreak swash on coarse grained beaches the paper reports on dambreak type swash experiments in which intra swash hydrodynamics and sediment flux are measured for swash on a coarse sand beach and a gravel beach flow velocity and depth are measured using piv and lif respectively the intra swash sediment flux is measured using sediment traps comparison of measured hydrodynamics with the immobile permeable bed experiments of kikkert et al 2013 indicates that bed mobility impacts on the swash hydrodynamics reducing the maximum run up by approximately 8 for both beaches compared to the maximum run up on the corresponding immobile beach the measured intra swash sediment flux at a given location is characterised by high flux at the moment of bore arrival followed by rapid decay during uprush becoming zero at some time before flow reversal for the gravel beach the backwash sediment flux is negligibly small while for the sand beach the backwash flux increases slowly as the flow accelerates down the beach and peaks at about the time of maximum backwash velocity intra swash sediment flux calculated using the meyer peter and muller bed load transport formula with measured hydrodynamics as input and bed shear stress estimated using both the swart and colebrook formulae is within a factor 2 of the measured intra swash flux the agreement between the calculated and measured flux is better for the sand beach than for the gravel beach and better for uprush than for backwash for the sand beach there is good agreement between calculated and measured total uprush and total backwash sediment volumes the agreement is less good for the gravel beach for which calculated and measured uprush volumes show a similar trend but the calculated backwash volumes over estimate the negligible volumes observed in the experiments

laboratory investigation of coastal beach erosion processes under storm waves of slowly varying height abstact storm induced large coastal waves are a predominant driver for coastal erosion problems but the physical processes of storm erosion have not been fully understood due to some technical difficulty in simulating storm waves with timely varying heights in the laboratory and collecting storm beach profiles in the field in this study novel series of experiments are proposed to study sandy beach processes under coastal storm conditions in a laboratory wave flume of 60 m long 3 m wide and 1 5 m high two water depths of h 0 5 m and h 0 7 m were used to investigate beach response under low and high tidal levels two initially uniform plane beach slopes of tan 1 15 for dissipation beach and tan 1 5 for reflection beach were used to study beach profile changes additionally intermediate beach tan 1 10 was also experimentally investigated under regular waves in another wave flume of 30 m long 0 6 m wide and 1 m high non intrusive instrumentation of high resolution cameras was used to record time series photo images on beach profile evolution in spatial resolution of 0 2 cm and a temporal resolution of 0 1 s image analyzing techniques were also developed to transform the recorded photo images to digital data on both beach and water surface profiles in analyzing the collected data it is found that the variation of storm wave height results in changes of wave breaking point and also sediment transport direction before and after the wave breaking point sediment transport direction was found to move onshore initially under small storm waves and then a sand bar was generated and a certain portion of sediment also moved offshore under large waves but such monotonic relationship between sediment transport and wave forcing could transform as morphology feedback and phase lags between wave orbital fluid velocity and sediment concentration the wave energy flux at the breaking point is shown to be suitable parameter in predicting beach mass change or storm erosion rate while the dimensionless sediment settling velocity parameter may not be a suitable criterion for predicting beach erosion or accretion under storm waves