modelling shoreface profile evolution current knowledge of hydro sediment and morpho dynamics in the shoreface environment is insufficient to undertake shoreface profile evolution modelling on the basis of first physical principles we propose a simple panel type model to map observed behaviour the internal dynamics are determined by slope dependent wave induced cross shoreface transports while the external driving factors are lateral sediment supply and sea level rise this model concept is tested with reasonable success against the observed behaviour of the central holland coast considering two hindcast periods one covering the evolution over the last century the other the subboreal subatlantic evolution a limitation of this model is that the cross shoreface dynamics are solely steered by the variations of shoaling short waves since a variety of other wave and current dynamics may be expected to be present in the coastal boundary layer it may well be that the effects of the mechanisms and conditions which are not represented are hidden in the coefficients of the sediment transport formula this limits the accuracy of the coefficients as used and our findings should be considered as an order of magnitude estimate only indeed behaviour oriented modelling implies that generalization of results to arbitrary situations and conditions is not straightforward yet we expect that some of the conclusions are more generally applicable this concerns the substantiation of the assumption that the upper shoreface responds on a much smaller time scale than the lower shoreface and the idea that the shoreface profile is not always and everywhere in equilibrium with its forcing a worthwhile observation from the holland coast application is that the bottom slope effect on the transport is only important at geological time scales the profile evolution at the engineering time scales say 10 to 100 years is effectively quasi static in that there is no feedback between the long term averaged transport and the state of the profile this implies that at these smaller scales the profile changes can be predicted on the basis of a static sediment balance this does not mean that the gravitational downslope transport is unimportant as a physical phenomenon in coastal profile evolution it is only unimportant if a highly aggregated model like this is applied at relatively short time scales

storm influences on a tidal sandbank s surface middelkerke bank southern north sea the results are presented of two types of pre storm and post storm surveys carried out on the middelkerke bank southern north sea the first type of survey was planned to detect detailed morphological changes in two selected areas of the bank totalling 3 km2 for the survey in these shallow waters to be completed in a fast and accurate way use was made of a special hovercraft based hydrographic system the other type of survey concerned grab samplings covering the sandbank in order to study spatial variations in surficial grain size the pre storm and post storm morphological surveys showed that small and medium dunes disappear under stormy conditions a 5 m westerly displacement of most of the large and very large dunes has been interpreted as the result of bedform migration under normal fair weather locally dominant ebb flow the lowering of the large dunes crests by up to 1 2 m is considered an effect of the storms the accretion of the lower part of the northwestern flank is attributed to the deposition of sand derived from shallow parts of the sandbank during storms the grain size surveys showed that especially the central and northern parts of the sandbank were affected by grain size changes the northwestern flank showing a clear coarsening and the landward southeastern flank a fining with respect to the fair weather situation it is put forward that the waves approaching from the north cause an extra winnowing on the exposed flank of the bank on the southeastern flank of the bank which is better protected against the wave action fine particles are then deposited

sediment transport predictions for the english channel using numerical models output from an hydrodynanmic numerical model salomon breton 1991 a b has been combined with various empirical formulae to derive sediment transport rates and directions the predictions are compared with radioactive sand tracer experiments demonstrating the applicability of gadd et al s 1978 expression the derived bedload transport pattern for the area is consistent with sedimentological and geomorphological evidence but provides improved resolution a bedload parting zone is identified for the central english channel this is well defined for sand movement but seabed material present over this area gravel is not predicted to move significantly the area is non erosive over which fine grained sediments are being transported a bedload convergence is located to the southwest of the dover strait not in the strait itself as proposed previously a transport pathway bypassing the convergence along the french coastline which is supported by radioactive tracer experiments could be responsible for sand transfer from the english channel to the southern north sea

sequential evolution of sn zn in mineralization at the skarn hosted hammerlein deposit erzgebirge germany from fluid inclusions in ore and gangue minerals skarn hosted deposits can be important high grade resources for a variety of metals but sn skarns are still of subordinate importance for global mining because of their complex mineralogy and evolution as part of recent exploration efforts the economic potential of the sn zn in mineralization at the hammerlein skarn hosted deposit is currently being re evaluated the temporal and spatial evolution of the ore forming hydrothermal system is still debated we analyzed fluid inclusion assemblages fia in ore and gangue minerals using conventional and infrared microthermometry and laser ablation inductively coupled plasma mass spectrometry la icp ms we further estimated alteration temperatures with chlorite thermometry and compared the fluid inclusion fi record at hammerlein with a mineralized greisen sample of the nearby eibenstock granite cassiterite in skarn forms the major mineralization at hammerlein during stage i and hosts fis showing homogenization temperatures of up to 500 c and salinities between 30 and 47 wt nacl eq cassiterite from schists and the additional greisen sample from the eibenstock granite of the later stage ii show lower homogenization temperatures 350 400 c and considerably lower salinities varying from 1 9 to 6 wt nacl eq despite the different homogenization temperatures and salinities the chemical compositions of fis hosted in both generations of cassiterite show that both cassiterite in skarn and in schist and greisen are similar which points to a common source the gangue minerals mainly contain low temperature fia max 330 c and 2 9 wt nacl eq and are interpreted to form during further cooling of the system in stage iii intergrown chlorite has compositions indicating similar temperatures of around 260 c and is thus also related to stage iii fia in sphalerite homogenize around 200 c with salinities between 2 and 6 7 wt nacl eq and show decreasing trace element contents despite having the same salinity range as the gangue minerals indicating dilution of the ore fluid during stage iv as a possible precipitation mechanism stage i inclusions are solely hosted in cassiterite from skarn which shows the importance of fluid inclusion analyses in ore minerals and record remarkable high mineralization temperatures exceeding the typically temperature range reported in other studies by at least 100 c our results suggest that this main ore stage is related to the early expulsion of a high salinity brine phase from an underlying magmatic intrusion at depths greater than 3 km which likely is a relatively short lived event within the evolution of the hydrothermal system

response of the seabed to storm generated combined flows on a sandy arctic shoreface canadian beaufort sea abstract wave and current measurements in 3 4 and 5 0 m water depths on a sandy shoreface of the canadian beaufort sea showed that a down welling circulation accompanied by strong offshore flowing near bottom currents develops during storm surges induced by northwesterly winds because fine to medium sand prevails on the shoreface a significant sediment load is probably moved down the shoreface by such currents during major storms a sidescan sonar profile recorded in 4 4 m water depth the day after a storm with seaward directed currents with mean velocity up to 0 49 ms 1 revealed the presence of narrow bands of large ripples 0 7 0 8 m wavelength with crests almost parallel to shore on the basis of theoretical calculations relating the wavelength of wave formed ripples to w ve orbital diameter the observed ripples were probably formed or reactivated during a storm in response to bed orbital motion of surface gravity waves on the sonograph the ripple bands were separated by less reflective areas interpreted as current parallel sand patches formed by seaward flowing bottom currents cores taken on the shoreface at the end of the wave and current measurement period showed the presence of thick graded sand beds which are thought to be the products of rapid deposition of sand from suspension during the waning phase of a recent storm such beds may he the modern analogues of graded sand beds in ancient wave dominated sequences and could indicate waning storm sedimentation in shallow fetch limited environments

hydrothermal mineral replacement reactions for an apatite monazite assemblage in alkali rich fluids at 300 600 c and 100 mpa mineral replacement reactions are common in the various environments where rocks have undergone re equilibration with geologic fluids replacement reactions commonly take the form of fluid aided coupled dissolution precipitation and often result in pseudomorph formation one class of environment that frequently shows significant examples of mineral replacements is hydrothermal ore deposit systems the goal of this study was to test the simultaneous reactivity of fluorapatite and monazite in na and si rich hydrothermal fluids which partially mimic the mineralogy and fluid chemistry of the llallagua tin deposit in bolivia a series of experiments were performed at 300 to 600 c and 100 mpa utilizing various combinations of monazite fluorapatite and h 2 o na 2 si 2 o 5 reaction products were evaluated using scanning electron microscopy electron microprobe analysis and single crystal x ray diffraction the results of this experimental study show that fluorapatite and monazite are differentially reactive under the conditions studied the reaction products pathways and kinetics have a large temperature dependence the 300 and 400 c experiments show variable amounts of monazite replacement and only minor if any dissolution or reactivity of fluorapatite the high temperature 500 and 600 c experiments are characterized by massive replacement of monazite by vitusite and britholite exclusively at 600 c monazite alteration takes the form of symplectite development at the reaction front as vermicular intergrowths of vitusite and britholite the higher temperature experiments also show substantially more reactivity by fluorapatite which is partially pseudomorphically altered into britholite this is an example of regenerative mineral replacement where both fluorapatite and britholite share the same atomic structure and are crystallographically coherent after the partial replacement the britholite replacement is characterized by the presence of oriented nanochannels which facilitate fluid based mass transfer between the bulk solution and the reaction front the fluorapatite replacement is enhanced by monazite alteration through a self perpetuating positive feedback mechanism between these two reactions which enhance the ree mobility in alkali bearing fluids and further drives bulk re equilibration these results have potential geochronologic implications and may be significant in the evaluation of monazite and fluorapatite as potential solid nuclear waste forms they also give us deeper insights into the mechanism of mineral replacement reactions and porosity development

hydrodynamics and sediment dynamics of north sea sand waves and sand banks and discussion seabed drag coefficients have been measured at a site within the norfolk banks and at a site within the sand wave field in the southern north sea using pressure sensors and moored current meters at the sand banks site a seabed tripod measuring turbulent flows within 1 m of the bed was also used the results are generally in agreement with values used in numerical models at the sand banks site the drag coefficient increases with wind conditions but at the sand waves site there is a reduction during the highest wave conditions attributed to the drag reduction caused by sand resuspension from the bed this result suggests that sediment effects must be considered if wave current interaction is included in numerical models of the region the drag coefficient for reversing tidal flows over the asymmetric sand waves is found to be larger for flow towards the steeper face suggesting a small form drag component studies of sand movement used bedform mapping fluorescent sand tracing and photography of migrating ripples there is evidence for the early stages of formation of a new bank between broken bank and well bank at the sand waves site ripple migration is found to be a useful estimator of bedload transport under conditions of negligible suspension over the sand banks a definite correlation of surface water properties notably the turbidity with the topography of the banks was observed the mechanism for this surface effect is not known but it is consistent with the observation of features seen in satellite visible light images which outline the shapes of the banks

depth of emplacement fluid provenance and metallogeny in granitic terranes a comparison of western thailand with other tin belts the most important tin mineralization in thailand is associated with the late cretaceous to middle tertiary western thai granite belt a variety of deposit types are present in particular pegmatite vein and greisen styles of mineralization a feature common to most of the deposits is that they are associated with granites that were emplaced into the khang krachan group which consists of poorly sorted carbonaceous pelitic metasediments most of the deposits contain low to moderately saline aqueous fluid inclusions and aqueous carbonic inclusions with variable ch4 co2 ratios low salinity aqueous inclusions represent trapped magmatic fluid in at least one case the nong sua pegmatite based on their occurrence as primary inclusions in magmatic garnet aqueous carbonic inclusions are commonly secondary and neither the co2 nor nacl contents of these inclusions decrease in progressively younger inclusions implying that they are not magmatic in origin reduced carbon is depleted in the metasediments adjacent to granites and the d values greisen muscovites are variable but are as low as 134 per mil indicative of fluid interaction with organic graphitic material this suggests that the aqueous carbonic fluid inclusions represent fluids that were produced at least in part during contact metamorphism metasomatism by comparing the western thai belt with other sn w provinces it is evident that there is a strong correlation between fluid composition and pressure in general low to moderately saline aqueous inclusions and aqueous carbonic inclusions are characteristic of mineralization associated with relatively deep plutonic belts mineralized pegmatites are also typically of deeper plutonic belts and pegmatite hosted deposits may contain cassiterite that is magmatic crystallized from granitic melt or is orthomagmatic hydrothermal crystallized from aqueous or aqueous carbonic fluids in origin the magmatic aqueous fluids those that were exsolved from granitic melts are interpreted to have had low salinities as a consequence of the low salinities tin is partitioned in favour of the melt on vapour saturation thus with a high enough degree of fractionation the crystallization of a magmatic cassiterite or different sn phase such as wodginite is inevitable because tin is not partitioned in favour of the vapour phase upon water saturation of the granitic melts it is proposed that relatively deep vein and greisen systems tend to form by remobilization processes in addition many deeper greisen systems are hosted in part by carbonaceous pelitic metasediments and the reduced nature of the metasediments may play a key role in remobilizing tin sub volcanic systems by contrast are characterized by high temperature high salinity fluids owing to the high chlorinity tin is strongly partitioned in favour of the vapour and cassiterite mineralization can form by of orthomagmatic hydrothermal processes similar relationships between the depth of emplacement and fluid composition also appear to apply to other types of granite hosted deposits such as different types of molybdenum deposits

a suspended sediment stratification correction for combined wave and current flows a simple model for the near bottom combined wave and current flow over a moveable sediment bed is presented the model is an extension of the grant and madsen 1979 combined wave and current model with moveable bed effects on the physical bottom roughness included as by grant and madsen 1982 the unsteady conservation of fluid momentum and sediment mass equations which are coupled through an eddy diffusivity closure scheme are solved for the wave and current velocity profiles along with the suspended sediment concentration and transport profiles sample runs are presented to illustrate the effect of varying wave conditions on the current the mean sediment concentration and the mean sediment transport results show that for fine to medium sands self stratification of the flow can be important during storms owing to the large amount of sediment suspended by the waves and the enhanced turbulent mixing associated with the wave current interaction the theory easily can be generalized for inclusion in a full ekman layer model

tidal influence on the intertidal bar morphology of two contrasting macrotidal beaches abstract analyses of morphological and hydrodynamic data from two macrotidal beaches mean spring ranges respectively 5 6 and 6 4 m with intertidal bars and troughs were carried out in order to detect and explain the relationship between tides and bar morphological attributes bar crest height and location and morphological change the following four aspects are treated in the paper 1 tidal levels vertical tidal translation rates and bar morphology 2 tidal range and morphological relaxation 3 the neap spring tidal variation and 4 tide generated longshore currents bar distribution and bar heights across the profile are not related in a straightforward manner to tidal levels and expected vertical tidal translation rates at these levels because the wave process domains involved in bar formation and bar morphological change are strongly modulated by wave energy by tide modulated water levels which vary with the neap spring cycle and by the beach morphology the variability of these conditions may explain the large variability of bar trough beach morphology the relatively large tidal ranges and rapidly shifting wave domains across the profile imply long periods of non exposure of the bars to wave processes during each semi diurnal tidal cycle and this tide generated effect reduces the scope for prolonged wave reworking while contributing to enhancing the long relaxation times and morphological feedback which minimise change on these beaches the effects of the neap spring tidal range variation on wave activity on these beaches are subordinate to those due to the random wave energy regime but this neap spring variation appears to influence the morphologically important intertidal drainage channels associated with bar trough topography although longshore tidal currents are relatively strong on these beaches digital elevation models show no significant longshore bar and tidal channel migration over time due to the absence of sustained strong wind conditions which considerably reinforce such longshore tidal currents and which therefore are the dominant control on longshore processes on these beaches it is also tentatively suggested that there is no established relationship between tidal range and the number of intertidal bars on these beaches

fe solubilities in very saline hydrothermal fluids their relation to zoning in some ore deposits the fe concentrations in fluids present in very saline fluid inclusions from the king island w skarn hole 16 f sn w deposit and the mary kathleen u rare earth element skarn have been determined using the phase deposit volume method fe bearing daughter minerals include magnetite pyrite amarantite fe super 3 so 4 oh 3h 2 o and hydrated ferrous chloride the fluid inclusion liquid compositions are inferred from a combined analysis of first melting temperatures eutectic temperatures of the salt system daughter crystal identification by scanning electron microscopy in conjunction with an energy dispersive x ray analyzer and relevant published experimental salt solubilities maximum fe solubilities show an exponential increase to 9 wt percent fe with increasing total anion content of the fluid especially in the 20 to 30 wt percent interval fe solubility is mainly dependent on total chloride contents with fluoride contributing very little to increasing the fe solubility temperature f sub o 2 and f sub s 2 appear to have a minor influence on the total fe solubilities some of the samples contain solid fe bearing crystals which coexisted with the fluid inclusions and probably buffered fe at the appropriate a fe values during genesis but the fe contents of most fluids were probably undersaturated with respect to fe bearing minerals over the range for which the total anion content of the fluid is 25 to 35 wt percent the apparent maximum fe content of fluids tends to decrease in the following order when the fe bearing daughter crystals are present magnetite pyrite hydrated ferrous chloride raquo amarantite although anomalies to this trend occur the fe solubility data are used to explain some fe mineral overprints stages ii and iii of skarns the magnetite fe chlorite cassiterite veins in tin granites and the zonal pattern present in porphyry copper systems the fe data suggest that the highly saline fe bearing solutions present in the cores of porphyry systems and other near contact deposits are not a result of increased salinity of hydrothermal fluids due to boiling of meteoric solutions but are inherent from an orthomagmatic source

rip current type spacing and persistence narrabeen beach australia abstract long term daily rip observations on narrabeen beach australia were made together with daily measurements of wave height period direction surf zone width and beach state a total of 3513 rips were observed on 270 days over a 19 month period results show that rips accompany moderate to high waves and are associated with intermediate beach types rip spacing follows wave conditions increasing in spacing size and intensity as waves rise and conversely as they fall rips are a function of both the prevailing and antecedent wave conditions and the rate and direction of change in wave conditions rips are classified into three types erosion mega and accretion erosion rips are initiated by rising seas in the transverse bar and rip and higher beach states they accompany general beach erosion they are widely spaced narrabeen ys 300 500 m 100 200 m increasing in size and intensity with the waves until the fully dissipative ripless state is reached they are both temporally and spatially highly variable persisting in one location for only hours to a day or so except where topographically controlled they are a major mechanism for the seaward transport of sediment and under extreme conditions may extend over a kilometer seaward of the breaker zone mega rips are large scale 1 km topographically controlled erosion rips that persist when nearshore and or embayment topography prevents the development of the fully dissipative state by inducing wave refraction and persist longshore gradients in surf zone dynamics that in turn drive the rip circulation accretion rips prevail during stable or falling wave conditions usually following erosion rip formation they are associated with general beach accretion are more closely spaced narrabeen ys 170 250 m 100 m less intense and become increasingly topographically arrested by crescentic bars and rhythmic bar beach morphology of the longshore bar trough rhythmic bar and beach and transverse bar and rip beach states they are relatively stable both spatially and temporally and may persist in one location for days to weeks if wave conditions remain favorable they are fair weather rips which may disappear by infilling in the low tide terrace beach state or be destroyed by rising seas rips generally are absent from the reflective low tide terrace and fully dissipative beach states

medium term frequency distributions of cross shore suspended sediment transport rates in water depths of 3 to 9 m abstract a data set of several thousands of hours of near bed flow obtained at three cross shore positions in 3 to 9 m water depth in the multiple bar system of terschelling netherlands was used to estimate the medium term years frequency distribution of the cross shore suspended sediment transport rates induced by short waves infragravity waves and cross shore mean flows predictions of an energetics based transport model were categorised into groups of the local height over depth ratio with a width of 0 02 and were subsequently coupled to the discrete medium scale probability distribution of this ratio at all depths the estimated medium scale sediment transport rate by the short waves q ms h and mean flows q ms mf were of approximately equal magnitude and were about three times as large as that of the infragravity waves in general the medium term sediment transport rates were dominated neither by the most extreme conditions nor by day to day situations this was related to the infrequent recurrence of the most energetic events and by the predicted negligible transport rates under daily conditions in 9 m depth breaking conditions contributed to about 90 of both q ms h and q ms mf in shallower water 3 5 m non breaking conditions became increasingly important for q ms h whereas q ms mf remained fully dominated by surf zone conditions this observation as well as literature findings for water depths less than about 3 m suggest that the range of small scale conditions that contribute most to q ms h and q ms mf changes in the onshore direction from mainly breaking conditions at depths in excess of 5 7 m towards prolonged non breaking periods for q ms h and short breaking events for q ms mf on the beach

modes of cross shore sediment transport on the shoreface of the middle atlantic bight the mechanisms responsible for onshore and offshore sediment fluxes across the shoreface zone seaward of the surf zone were examined in a 3 year field study the study was conducted in the southern part of the middle atlantic bight in the depth region 7 17 m using instrumented tripods supporting electromagnetic current meters pressure sensors suspended sediment concentration sensors and sonar altimeters the observations embraced fairweather moderate energy swell dominated and storm conditions cross shore mean flows ranged from near zero during fairweather to 20 cm s 1 during the storm oscillatory flows were on the order of 10 cm s 1 during fairweather and 100 cm s 1 during the storm suspended sediment concentrations at about 10 cm above the bed were 5 kg m 3 during the storm three methods were applied to evaluate the relative importance of incident waves long period oscillations mean flows and gravity in effecting shoreward or seaward sediment flux 1 an energetics transport model was applied to instantaneous near bottom velocity data 2 higher moments of near bottom flows were estimated and compared and 3 suspended sediment fluxes were estimated directly from the instantaneous products of cross shore velocity and suspended sediment concentration the results show that measurable contributions were made by all four of the processes most significantly mean flows were seen to dominate and cause offshore fluxes during the storm and to contribute significantly to onshore and offshore flux during fairweather and moderate energy incident waves were in all cases the major source of bed shear stress but also caused shoreward as well as seaward net sediment advection low frequency effects involving wave groups and long period waves made secondary contributions to cross shore sediment flux contrary to expectations low frequency fluxes were just as often shoreward as seaward whereas cross correlations between suspended sediment concentration and the instantaneous near bottom current speed were high and in phase under storm conditions they were weak and out of phase during fairweather conditions this suggests that simple energetics models are probably inadequate for predicting fairweather transport of suspended sediment

dynamics of large and small scale bedforms on a macrotidal shoreface under shoaling and breaking waves abstract bedform dimensions bed position changes near bed velocities and suspended sand concentrations are analyzed from measurements at a single location on a macro tidal beach in the south west of england the study was conducted in 0 5 2 25 m water depth under both swell and wind generated storm waves with both weak and strong currents present bed positions and suspended sand concentrations were measured using the 3 transducers of a multi frequency acoustic backscatter sensor with 5 mm vertical resolution two distinct bed types based on wavelength were observed each with two or more subtypes possible i small scale bedforms 20 cm which include two dimensional 5 forms and three dimensional vortex 6 forms small scale forms were dominant under non breaking conditions while the large scale forms occurred under both non breaking and breaking waves the large scale forms dominate under breaking conditions both types but particularly low steepness forms were highly mobile with maximum horizontal migration rates of 5 cm min 1 large upto 15 cm and rapid upto 3 0 cm min 1 changes in vertical bed elevation were also observed in association with the development and migration of large scale forms large scale bedforms were also highly variable spatially often being interspersed with smaller scale forms under decaying flow regimes and with areas of flat bed under increasing regimes observations suggest these forms are present even under high energy surf zone conditions wave shields 1 models for predicting ripple dimensions did not perform well in this environment this lack of agreement reflects the complex hydrodynamic regimes associated with random grouped shoaling and breaking waves together with the presence of currents often at large angles to the waves as well as the rapid rates of change in the wave forcing associated with tidal cycle oscillations in this macrotidal environment suspended sediment concentrations and transport rates are particularly sensitive to the bedforms present and also to bed position changes associated with ripple migration estimates of transport rates are subject to potentially large errors upto 30 without compensation for bed elevation changes relative to sensor position

frequency dependent cross shore suspended sediment transport 1 a non barred shoreface abstract the local time varying and time averaged suspended sediment transports across a marine non barred shoreface were obtained from field measurements of the near bed velocity and sediment concentration vectors using electromagnetic current meters and optical backscatterance suspended solids sensors co spectral analyses of velocity and sediment concentration revealed the contributions of waves of different frequencies to the total transport the transport attributable to quasi steady currents was determined from the product of the time averaged cross shore velocity and sediment concentration estimates of the local time integrated sediment volume flux total and net and the associated erosion or accretion were determined using depth of activity rods suspended sediment transport was associated with 1 local wind forced waves 2 swell 3 low frequency waves group bound long waves and 4 offshore directed mean currents undertow these transport components varied spatially and temporally in response to changes in the wave height to water depth ratio the local net oscillatory transport rate at wind wave and swell wave frequencies was directed onshore predominantly and increased as water depth decreased in association with wave shoaling the local mean sediment transport rate was predominantly offshore and dominated the net transport rate wherever wave induced components were weak relative to the mean currents under breaking waves the suspended sediment transport contribution associated with wind waves and swell waves was reduced as a result of dissipation the net suspended sediment transport rate exhibited a distinct vertical structure reflecting the balance at each elevation between the opposing mean and oscillatory components of transport the local time averaged total and net sediment volume flux and resulting erosion and accretion patterns support the hypothesis of a near balance in sediment flux for the complete storm event

shoreface morphodynamics on wave dominated coasts abstract an open ocean shoreface typical of long wave dominated sandy coasts has been examined through a combination of extensive field measurements of wave and current patterns with computations of marine bedload transport and sedimentation sand transport on the upper shoreface is dominantly controlled by waves with only secondary transport by currents sand on the middle and lower shoreface as well as the inner continental shelf is entrained by storm waves and transported by a complex pattern of bottom boundary layer currents storm events have been studied and modeled for the shoreface off tiana beach long island the dominant effect of coastal frontal storms is to cause significant shore parallel bedload transport with important shore normal secondary components these storms tend to result in net offshore transport of sand removed from the beach and surf zone systems the bedload transport during a storm is convergent on the shoreface leading to accretion most accretion occurs on the upper shoreface with lesser deposits covering the middle and lower shoreface as well as the inner continental shelf longer term equilibrium can be maintained by slow return of sand up the shoreface during non storm conditions annual and geologic time scale budgets of shoreface sand transport and sedimentation yield equilibrium net accretion or net deposition the annual balance results from an integration of the event scale bedload transport patterns and morphologic responses these processes and responses have feedback mechanisms which stabilize the system over longer but not geologic time scales geologic time scale balances are controlled by relative sea level changes and relative availability of sediment supply with the event scale shoreface and transporting processes providing the mechanism to produce the changes in long term morphology and sedimentation patterns in the area of study the long term pattern is one of net shoreface erosion and the permanent loss of sand to the shelf floor

maintenance of the shoreface by wave orbital currents and mean flow observations from the long island coast waves and currents were observed for a total of 36 days in august 1976 and 1977 calculations of wave transport of sediment using a bagnold equation for transport and second order stokes theory show that wave orbital current asymmetry results in landward sediment transport in 10 m or less water depth but does not significantly effect transport at greater depths calculations of sand transport using the madsen grant formulation show that during a 36 day observation period sediment in less than 10 m of water generally moved landward into the breaker and then along coast with the wave driven littoral flow the calculations show that below 10 m the generally upwelling coast parallel mean flow did not move sediment however during two days of a mild summer northeaster storm a downwelling coastal jet developed with 60 cm sec sup 1 maximum current the calculations show that if this flow had been combined with the intense wave regime of the succeeding several days sediment would have been entrained across the lower as well as the upper shoreface movement would have been offshore and alongshore such storm transport is believed to be typical of the more intense winter storms and to be responsible for the erosionalmore shoreface retreat that has caused up to a kilometer of shoreline retreat on the long island coast in the last century less

storm generated morphological change and longshore sand transport in the intertidal zone of a multi barred macrotidal beach abstract the morphology hydrodynamics and sediment transport processes of a multi barred macrotidal beach were surveyed over 21 semi diurnal tides the first eight of which were dominated by storm conditions with offshore wave heights ranging from 1 2 to nearly 3 5 m the hydrodynamic conditions prevailing over the intertidal beach showed a rapid response to these storm conditions notably through strong longshore currents that attained peak velocities of 1 6 m s 1 i e over three times the peak spring tide velocities of tide generated longshore currents during calm conditions the bars showed no cross shore migration during the storm events morphological mapping of the beach tracer dispersal patterns and calculations of potential sand transport rates using the energetics based model of bailard bailard j a 1981 an energetics total load sediment transport model for a plane sloping beach j geophys res 86 10938 10954 showed significant longshore sand transport as well as longshore migration of an intertidal drainage channel these longshore movements were bi directional responded to changes in incident wind and wave directions and involved wave stirring coupled with longshore advection of sand along the bar crests in particular strong trough and cross shore channel flows also led to the longshore migration of crescentic dunes the longshore sediment movements were embedded in a cross shore gradient associated with increasing overall profile mobility from the lower to the upper beach in response to wave shoaling and post breaking processes assessed through examination of the relative wave height hs h 1 based on the relationship between significant wave height hs and water depth h longshore sediment transport is a characteristic feature of the long term evolution of wissant bay which is dominated by a net northeastward residual sand transport within a bay sediment cell characterised by significant updrift erosion and downdrift accumulation longshore transport should be considered as an essential element of the morphodynamics of bar trough beaches subject to large tidal ranges and significant wind stress but there is a need for a better understanding of the role of wind stress on longshore currents in the shallow intertidal zone of these beaches

the systematic contribution of transporting mechanisms to the cross shore sediment transport in water depths of 3 to 9 m the systematic contributions of short waves infragravity waves and mean flows to the cross shore sediment transport were studied with direct measurements of instantaneous near bed sediment concentrations and velocities as well as with an energetics based sediment transport model using measured time series of near bed cross shore flow as input the study was conducted at four cross shore positions in the multiple bar system of terschelling netherlands during three field campaigns each with a five week duration the data were collected in 3 to 9 m water depth during a wide range of conditions from low energy non breaking conditions to almost fully saturated breakers the height over depth ratio hs h was applied at all four measuring stations as a local conditional parameter all model predictions were grouped into hs h classes with a width of 0 02 to highlight the generality of the data the energetics approach predicted that the suspended load dominated over the bedload at all four stations both the sediment flux measurements as well as the model predictions showed that the largest contributors to the gross suspended sediment transport were made by the short waves and the undertow inducing an onshore and offshore transport respectively their contributions to the gross suspended transport were about 40 to 50 under surf zone conditions bound infragravity waves were observed and predicted to result in an offshore directed transport that was of subordinate magnitude compared to the observed and estimated magnitudes by the short waves and the undertow however as these transports almost cancelled out because of their about equal magnitude but opposite sign the suspended transport by bound infragravity waves may not be ignored and may rather paradoxically have a relatively large influence on the net suspended sediment transport hydrodynamical processes that do not seem to be of importance to the onshore and offshore sediment transport in 3 to 9 m water depth in the long run are mean flows under non breaking conditions and free infragravity motions a direct comparison between measured sediment fluxes and the model predictions suggests that simple energetics models are suitable for predicting cross shore sediment transport in 3 to 9 m water depth

sediment supply from shoreface to dunes linking sediment transport measurements and long term morphological evolution a significant problem in current coastal research is the understanding of linkages between morphological phenomena occurring on different temporal and spatial scales morphodynamic processes in the nearshore typically exhibit nonlinear behaviour and consequently phenomena which occur on short temporal event scales as e g observed during field experiments have generally been difficult to upscale to provide an understanding of the long term behaviour of the coast on the time scale of seasons or decades this paper documents a persistent onshore migration of nearshore bar features over a period of 3 decades using a set of cross shore profile surveys from a barrier on the danish north sea coast the observed behaviour is consistent with experimental data obtained during weeklong field campaigns when sediment transport and bar migration were found to be landward directed during high energy dissipative conditions hydrodynamic and sediment transport processes leading to onshore bar migration and eventually welding of the bars are documented to provide an explanation for the observed long term evolutionary trends in addition bar welding and the resulting intertidal bar formation represent an onshore sediment storage which is subsequently available for aeolian transport observations on aeolian sediment transport indicate that transport rates and sediment supply to the foredunes critically depend on the presence of dry sand sources as represented by well drained intertidal bars measurements of long term accretion rates in foredunes indicate that volumes deposited on the crest and lee slope of the dunes are in reasonable correspondence with volumes supplied to the subaerial beach through the process of bar welding hence the data suggest that a persistent onshore directed sediment supply occurs from the shoreface across the surf and intertidal zones and into the dunes of the investigated barrier

short term beach dune sand budgets on the north sea coast of france sand supply from shoreface to dunes and the role of wind and fetch abstract three experimental plots covering the transition from the upper beach to the dune on the north sea coast of france were monitored at various intervals over a period of 18 24 months via high resolution terrain surveys in order to determine inter site sand budget variability as well as patterns and processes involved in sand exchanges between the upper beach and dune the wind regime consists of a fairly balanced mix of moderate 80 of winds are below 8 m s onshore offshore and shore parallel winds sustained dune accretion over several years depends on the periodic local onshore welding of shoreface tidal banks that have developed in the storm and tide dominated setting of the southern north sea the only site where this has occurred in the recent past is calais where bank welding has created a wide accreting upper beach sand flat at this site significant sand supply from the subtidal sand bank reservoir to the upper beach flat occurred only once over the 18 month survey following a major storm the bulk of the sand deposited over this large flat is not directly integrated into the adjacent embryo dunes by onshore winds but is progressively reworked in situ into developing dunes or transported alongshore by the balanced wind regime thus resulting in alongshore stretching of the embryo dune system the leffrinckoucke site near belgium shows moderate beach dune mobility and accretion while the wissant site exhibits significant upper beach bedform mobility controlled by strong longshore currents that result in large beach budget fluctuations with little net budget change to the detriment of the adjacent dunes accretion at these two sites which are representative of the rest of the north sea coast of france is presently constrained by the absence of a shore attached sand bank supply reservoir while upper beach dune sand exchanges are further limited by the narrow wave affected upper beach the intertidal morphology of bars and troughs which segments the aeolian fetch and the moderate wind energy conditions the balanced wind regime limits net sand mobilisation in favour of either the beach or the dune and may explain the relatively narrow longshore morphology of the dune ridges bounding this coast

cross shore distribution of longshore sediment transport comparison between predictive formulas and field measurements abstract the skill of six well known formulas developed for calculating the longshore sediment transport rate was evaluated in the present study formulas proposed by bijker bijker e w 1967 some considerations about scales for coastal models with movable bed delft hydraulics laboratory publication 50 delft the netherlands journal of the waterways harbors and coastal engineering division 97 4 1971 687 engelund hansen engelund f hansen e 1967 a monograph on sediment transport in alluvial streams teknisk forlag copenhagen denmark ackers white journal of hydraulics division 99 1 1973 2041 bailard inman journal of geophysical research 86 c3 1981 2035 van rijn journal of hydraulic division 110 10 1984 1431 110 11 1984 1613 110 12 1984 1733 and watanabe watanabe a 1992 total rate and distribution of longshore sand transport proceedings of the 23rd coastal engineering conference asce 2528 2541 were investigated because they are commonly employed in engineering studies to calculate the time averaged net sediment transport rate in the surf zone the predictive capability of these six formulas was examined by comparison to detailed high quality data on hydrodynamics and sediment transport from duck nc collected during the duck85 superduck and sandyduck field data collection projects measured hydrodynamics were employed as much as possible to reduce uncertainties in the calculations and all formulas were applied with standard coefficient values without calibration to the data sets overall the van rijn formula was found to yield the most reliable predictions over the range of swell and storm conditions covered by the field data set the engelund hansen formula worked reasonably well although with large scatter for the storm cases whereas the bailard inman formula systematically overestimated the swell cases and underestimated the storm cases the formulas by watanabe and ackers white produced satisfactory results for most cases although the former overestimated the transport rates for swell cases and the latter yielded considerable scatter for storm cases finally the bijker formula systematically overestimated the transport rates for all cases it should be pointed out that the coefficient values in most of the employed formulas were based primarily on data from the laboratory or from the river environment thus re calibration of the coefficient values by reference to field data from the surf zone is expected to improve their predictive capability although the limited amount of high quality field data available at present makes it difficult to obtain values that would be applicable to a wide range of wave and beach conditions

sediment transport under wave and current combined flows on a tide dominated shoreface northern coast of france abstract hydrodynamic circulation and sediment transport patterns were investigated on a macrotidal shoreface off the southern north sea coast of france from in situ directional wave and current measurements and through numerical modeling of sediment flux current meters equipped with wave gauges were deployed at two sites on the mid upper shoreface in approximately 5 6 m water depth during 6 and 15 days sediment flux was estimated using the sedtrans96 numerical model li m z amos c l 2001 sedtrans96 the upgraded and better calibrated sediment transport model for continental shelves comp geosc 27 619 645 based on grant and madsen s grant w d madsen o s 1986 the continental shelf bottom boundary layer ann rev fluid mech 18 265 305 combined flow boundary layer theory the hydrodynamic measurements and modeling results show that sediment on the shoreface is essentially transported alongshore in response to shore parallel tidal currents the direction of the net sediment transport is largely determined by the asymmetry of the tidal flows which can be flood or ebb dominated but during important wind speed events winds blowing in the same direction as tidal flow can significantly reinforce tidal currents or conversely can limit tidal current speeds when acting in the opposite direction although sediment transport on this macrotidal shoreface is strongly controlled by tidal processes waves can significantly enhance bed shear stresses resulting in increased sediment remobilization and hence higher sediment flux wave induced onshore sediment transport may occasionally occur but is several orders of magnitude lower than longshore transport this macrotidal shoreface is thus characterized by a hydraulic regime strongly dominated by shore parallel tidal flows that favour longshore sediment dispersal rather than shore normal transport our results imply that the water depths from which sediment may be transported shoreward to beaches is certainly much more restricted on a macrotidal shoreface such as the one bordering the northern coast of france than on micro and mesotidal shoreface environments where weaker tidal currents do not significantly limit cross shore sediment movements

barrier formation on an actively prograding delta system the red river delta vietnam abstract an extensive barrier spit system 20 to 30 km long developed on the delta front platform of the ba lat delta within a relatively short period 10 20 years however it was not evident whether the formation was related to river floods typhoons or calm weather conditions or to cross shore or alongshore sediment transport mechanisms therefore a process based numerical model that simulates sediment transport and morphologic changes by waves tides wind and river flow is used to analyze the processes that govern this barrier formation the mechanism that initiates the barrier formation is concluded to be onshore transport by wave asymmetry of sediment previously transported seaward in the buoyant river plume the main mechanism that counteracts the barrier formation is probably destruction of the barrier by river flow during the subsequent transformation from a subaqueous barrier into a sub aerial barrier spit system overwashes and alongshore sediment transport become increasingly important this spit system therefore appears to be dominated by alongshore processes even though its initial formation is more strongly regulated by cross shore processes the importance of cross shore processes results in a minor contribution of typhoons to the initial formation of these barriers typhoons are not very important to destruction of barriers as well because wave energy is gradually dissipated over the gentle offshore profile which in turn results from river plume sedimentation

duration of magmatic hydrothermal and supergene activity at cerro rico de potosi bolivia new high precision 40ar 39ar dating of sanidine and biotite from two rhyolitic domes and an ignimbrite combined with existing fission track data and a hydrothermal sericite age suggests that the world class ag deposit at cerro rico was emplaced during a protracted period of magma related hydrothermal activity beginning at 13 77 0 03 ma and continuing for at least 0 2 m y this may have been sustained by a large single injection or repeated injections of fractionated ag enriched magma into a high level magma chamber k ar dating of alunite indicates that supergene oxidation had begun by about 13 5 ma soon after dome emplacement and progressed semicontinuously for at least 7 5 m y this oxidation while not leading to significant enrichment has significantly enhanced the economic viability of the disseminated part of the orebody

environmental setting morphology and volumetric evolution of the middelkerke bank southern north sea abstract the middelkerke bank a tidal sandbank located in the southern north sea on the belgian continental platform has been the object of a multidisciplinary and international research project the morphological and hydrodynamical setting of the study area is presented a complete side scan sonar coverage of the bank allowed a detailed analysis of the morphology of the bank and of its superimposed bedforms large dunes cover the flanks and summit of the middelkerke bank they have a constant orientation a height ranging from 0 5 to 5 m a wavelength from 75 to 150 m and in most cases an asymmetrical profile the slopes of both lee and stoss flanks are very low small and medium dune fields occur on the entire bank and in the adjacent swales they are 2 d and present a wavelength ranging from 1 to 15 m flood and ebb oriented small dunes cover respectively the western and eastern flank of the bank bathymetric surveying of the middelkerke bank was carried out to assess the importance of volumetric variations of the bank mass caused by seasonal factors results show that changes in the bank volume can be quite important the bank s volume decreases in periods of heavy weather after which the process of sand uppiling acting during long periods of fair weather conditions causes the bank to restore itself volumetric variations of the total bank volume in a winter summer period can range along certain sections of the bank from 21 to 26 despite these large seasonal volumetric variations the bank shows a long term dynamic equilibrium as proven by the obtained evolution trend

fluid inclusion studies of the polymetallic hydrothermal ore deposits in bolivia homogenization temperature and salinity were determined for fluid inclusions in mostly quartz and partly sphalerite cassiterite and barite from the 28 tin polymetallic ore deposits in bolivia generally the homogenization temperatures and salinities of these fluid inclusions are comparatively high for ore deposits formed by cassiterite mineralization such as morococala and avicaya in the oruro district frequently indicating a temperature higher than 300 c and salinity higher than 20 equiv wt nacl particularly it is quite possible that tin deposits associated with the w bi and tourmaline mineralizations such as viloco and caracoles have been produced by such high temperature hypersaline fluid ranging up to 500 c and 56 equiv wt nacl similar to the porphyry copper type this feature reveals that the hydrothermal fluid related to the sn w bi mineralization may be of magmatic origin homogenization temperatures for the pb zn deposits with no tin minerals are low mostly ranging 170 300 c at the avicaya bolivar mining area in the oruro district as well as at the tasna and chocaya animas mining areas in the quechisla district temperature gradients consistent with the zonal distributions of ore minerals were confirmed

formation of epithermal sn ag zn vein type mineralization at the pirquitas deposit nw argentina fluid inclusion and noble gas isotopic constraints abstract the pirquitas sn ag zn deposit in northwestern argentina is thought to be an analogue to the miocene polymetallic epithermal sn ag deposits of the southern bolivian tin belt but little is known in detail about the origin and evolution of ore forming fluids at pirquitas this paper reports on a microthermometric study of fluid inclusions in quartz sphalerite ag sn sulfides and ag rich sulfosalts using transmitted near infrared and visible light combined with noble gas isotope analyses of fluids released from mineral separates the study focused on the vein hosted mineralization which formed during two major mineralization events whereby the first event i comprises two stages i 1 and i 2 all studied minerals exclusively contain aqueous two phase inclusions indicating that the ore forming fluids did not undergo two phase phase separation boiling salinity of fluid inclusions in i 1 quartz that precipitated along with pyrite and pyrrhotite ranges between 0 and 7 5 wt nacl equiv and homogenization temperatures th are between 233 and 370 c stage i 2 is characterized by abundant sn ag pb zn sulfides and a variety of ag rich sulfosalts fluid inclusions in stage i 2 ag sn sulfides have salinities up to 10 6 wt nacl equiv and th between 213 and 274 c the deposition of stage i 2 ore is likely related to a new pulse of saline magmatic fluids to the hydrothermal system the mineralization event ii deposited the richest ag ores at pirquitas colloform sphalerite and pyrargyrite deposited during event ii contain two phase aqueous fluid inclusions with homogenization temperatures between 190 and 252 c and salinities between 0 9 and 4 3 wt nacl equiv noble gas concentrations and isotopic compositions of ore hosted fluid inclusions were determined from crushing hand picked ore minerals from both mineralization events with one exception all samples yielded 3he 4he ratios between 1 9 and 4 1 ra which is within the range of published data from the volcanic arc and somewhat higher than typical values of meteoric water derived hot springs in the region this demonstrates a significant contribution of magmatic fluids to the pirquitas mineralization although no intrusive rocks are exposed in the mine region taking the noble gas evidence for a magmatic fluid source we interpret the trends of decreasing th and salinity values in fluid inclusions from events i and ii to represent waning of the magmatic hydrothermal system and or increased admixing of meteoric water to the magmatic fluids

trace elements of indium bearing sphalerite from tin polymetallic deposits in bolivia china and japan a femto second la icpms study abstract indium bearing tin polymetallic base metal deposits in japan toyoha ashio and akenobe china dulong and dachang and bolivia potosi huari huari bolivar and porco were studied using femto second laser ablation icpms fsla icpms and epma analyses for major and minor elements in sphalerite paying special attention to in concentrations sphalerite is a principal mineral in these tin polymetallic deposits and a broad range of in concentration is measured in the ores there are distinct differences in mode of occurrence of the sphalerite and the distribution of in the highest in concentration up to 18 wt occur as a zn in mineral within black sphalerite zones in an oscillatory zoned sphalerite from the huari huari deposits additionally jamesonite from the huari huari deposit also contains anomalous in values ranging from several hundreds to thousands g g sphalerite from the toyoha and the other bolivian deposits are characterized by oscillatory and chemical zoning whereas those from akenobe and the chinese deposits are represented by homogeneous distribution of in the 1000in zn values of sphalerite are in good agreement with those of the ore grade for each of the selected tin polymetallic deposits indicating that sphalerite is the principal host of in the in bearing sphalerite principally involves the combined coupled substitutions 2zn2 cu in3 3zn2 cu ag sn4 and 3zn2 2cu sn4 the first of these is apparent in sphalerite from huari huari and bolivar whereas the second is prominent in sphalerite from toyoha ashio potosi porco and dachang akenobe and dulong sphalerite features the dominant coupled substitution of 2zn2 cu or ag in3 owing to their poor sn content occasionally sub micron inclusions of minerals such as stannite and pb sb bearing sulfides can occur in sphalerite contributing to high cu sn and high ag contents respectively the observed correlations of each element in the in cu ag sn bearing sphalerite can be proposed as a fundamental reason for the indium enrichment related to sulfur rich oxidized magmatism in addition the ag content in sphalerite is considered a possible indicator of formation depth which ranges from plutonic to subvolcanic environments

barrier island evolution middle atlantic shelf u s a part i shoreface dynamics abstract in part i of this paper near bottom fluid velocity and sediment concentration measurements from the shoreface of a middle atlantic barrier long island coast are analyzed to provide insight into the dynamics of erosional shoreface retreat in part ii these data are combined with observations of coastal stratigraphy in order to construct a model for the evolution and behavior of middle atlantic barriers wave motions on the long island shoreface tend to drive sediment onshore calculations of the onshore sediment flux driven by asymmetrical shoaling waves show that for the wave states commonly encountered on the middle atlantic shelf values become strongly positive landward of approximately 10 m water depth upper shoreface but drop to very low values shortly seaward of that isobath on the lower shoreface and inner shelf floor fair weather wave current interaction tends to cause a landward creep of sediment even though the wave orbital component of the near bottom velocity field is nearly symmetrical this movement occurs because the wave approach direction generally lies within 90 of the direction up coast or down coast of the alongshore wind driven current therefore fluid shear stress acting on the sediments tends to be reinforced during the shoreward stroke of the wave orbital motion and partially cancelled during the seaward stroke during major storms the rate of sediment transport increases by at least an order of magnitude and the role of wind driven currents becomes important much more sediment is resuspended by the wave orbital current component because storm waves are more powerful than fair weather swells but the wind driven flow component is also much stronger and is now available for transporting the resuspended sediment storm flows over the shoreface occur in distinct dynamic zones surf zone friction dominated zone transition zone geostrophic zone the zones are defined by dynamical considerations and expand or contract with the intensity of the causative wind stress during peak flow events the characteristic length scales of the friction dominated and geostrophic zones tend to correspond with the morphologic zones of the shoreface and inner shelf the storm intensified wind driven alongshore flows of the lower shoreface are frequently jet like in nature and may be upwelling or downwelling wind driven coastal flows with a strong downwelling component occur during most storms on the long island coast and are particularly important to the coastal sand budget during these events sand is entrained by the storm intensified upper shoreface circulation system of wave driven alongshore currents and rip currents and is fed into the main wind driven coastal current because of the offshore component of bottom flow sand is swept down the lower shoreface and onto the adjacent inner shelf fair weather processes may be unable to return storm deposited sand to the beach from such an offshore position the shoreface transport regime of the long island barrier coast thus consists of long periods of time months during which sand moves slowly toward the beach punctuated by short intense periods hours or days during which sand is transferred from the shoreface to the adjacent inner shelf the long term sense of movement of the shoreface whether retreating the long island case or prograding must depend on the loss or gain of sand by shoreface with respect to the inner shelf the data shows that the coastal sand budget is controlled not only by the upper shoreface cycle withdrawl of sand from the beach prism storage in the breakpoint bar and its subsequent return to the beach but by a cycle of larger spatial and temporal scale in which sand is exchanged between the shoreface as a whole and the adjacent inner shelf

boundary layer dynamics and sediment transport under storm and non storm conditions on the scotian shelf abstract near bed measurements of waves currents seabed responses and ripple migration rates were obtained using an instrumented tripod at a water depth of 39 m on the scotian shelf during the winter of 1992 93 these data and the grant and madsen s 1986 grant w d madsen o s 1986 the continental shelf bottom boundary layer annu rev fluid mech 18 265 305 combined flow boundary layer model are used to examine wave current interaction various sediment dynamic thresholds and sediment transport on an exposed high energy continental shelf the seabed was found to be rippled for most time of the deployment and thus the ripple enhanced combined skin friction shear velocity had to be used to determine the initiation of bedload transport under combined flows this indirectly indicates adequate predictions of the skin friction shear velocities inside the wave boundary layer by the grant and madsen model at high transport stages bedload roughness must be added to the grain size roughness to obtain a transportrelated combined shear velocity in order to predict correctly the onsets of saltation suspension and sheet flow transports otherwise the initiation of suspended load transport and the total sediment transport rates will be severely under estimated the comparison between the prediction by the grant and madsen 1986 model and the calculation of a quadratic stress law suggests that the total current shear velocity was enhanced by a factor of 2 3 due to the wave current interaction during storms while the apparent bottom roughness was increased by more than an order of magnitude the non linear coupling between waves and currents also causes a 20 increase of the combined skinfriction shear velocity inside the wave boundary layer this non linear coupling is most important when waves and currents are roughly equal in magnitude and the angles between them are less than 30 four sediment transport formulae were tested while the engelund hansen total load and yalin bedload methods did not perform well the einstein brown and bagnold formulae were found to respectively give reasonable predictions of the bedload and total load sediment transport rates under the observed combined flow conditions the predicted sediment transport direction is also in good agreement with the observed ripple migration direction the gsc sediment transport model sedtrans92 predicts that the net daily transport rates during the storms reached 822 kg m 1 day 1 and were 2 3 orders of magnitude higher than the non storm transport suggesting the dominance of storm processes in sediment transport on the scotian shelf these values are in good agreement with the results from sand tracer experiments conducted in this region we thus conclude that sedtrans92 can properly simulate boundary layer dynamics and sediment transport on continental shelves

suspended sediment reference concentration under waves field observations and critical analysis of two predictive models two commonly adopted but fundamentally different approaches for predicting time averaged suspended sediment reference concentration cref under waves are tested against field measurements and compared with each other the first model relates cref to the cube of the non dimensional skin friction whereas the second model adopts a more complex function of excess skin friction incorporating the empirical constant 0 the dataset is from the zone of wave shoaling seaward of an open coast surfzone and includes measurements of waves currents suspended sediment and bedforms estimates of cref are derived from acoustic backscatter data and the seabed and suspension process are described from video footage when waves were energetic the bed was deformed into large hummocks during less energetic conditions the bed was rippled the time averaged concentration profiles over the ripples were consistent with settling flux balanced by pure gradient diffusion and a sediment diffusivity that is constant with elevation above the bed cref in that case is shown to apply at z 0 where z is the elevation above the bed over the hummocks there was a sheet flow at the base of the suspension and cref is shown to apply at z 1 cm the concentration profiles over the hummocks implied sediment diffusivity that varied linearly with elevation within 10 cm of the bed and constant sediment diffusivity above that level for both rippled and hummocky beds 0 derived from the field data was found to be sensitive to the value assumed for critical stress for initiation of sediment motion which could explain the range of values reported in the literature for 0 0 was also found to vary in a complex way with skin friction which suggests that the reference concentration model based on excess skin friction is not correctly formulated nevertheless two functions for 0 one applying to rippled beds and the other to hummocky beds were contrived to make the model fit the data the model based on non dimensional skin friction was found to be a good predictor of cref when a correction was made for flow contraction over ripples the correction was not required for the hummocky bed where sediment was being entrained in a thin sheet flow layer the model based on non dimensional skin friction correctly portrayed the relationship between flow and sediment response without contrivance and therefore should be the favoured approach in predicting reference concentration

the grain size characterisation of coastal sand from the somme estuary to belgium sediment sorting processes and mixing in a tide and storm dominated setting abstract sand rich holocene to modern clastic deposits in the eastern english channel and the southern north sea coasts of france and belgium occur extensively as nearshore sand bank estuarine tidal flat aeolian dune and beach sub environments sand samples n 665 collected from these deposits suggest the presence of three different populations a largely dominant 83 medium to fine quartz sand population b and finer 14 and coarser grained 4 populations respectively c and a the distribution of these populations among the four sub environments reflects tide and storm dominated sorting and transport processes and a variable degree of mixing these populations are derived from a mixture of very fine to very coarse grained fluvial outwash and paraglacial sediments deposited on the beds of the eastern english channel and southern north sea during the late pleistocene lowstand the nearshore sand bank environment which also corresponds to the main offshore source area of the coastal deposits exhibits population heterogeneity reflecting the variability of hydrodynamic conditions and sediment sorting in this zone the nearshore topography of tidal ridges banks and troughs in these tidal seas leads to variable bed and tide and storm induced shear stress conditions these conditions only allow for the mobilisation and onshore transport of some of the finer fractions populations b and c leaving an offshore mixture of these finer populations with coarser less mobilisable sediments population a once in the coastal zone these two finer populations undergo further hydrodynamic sorting and segregation variably sorted very fine sands to silts population c are trapped in the low energy estuarine tidal flat sub environment while the highly homogeneous population b is further sorted in aeolian dune and beach sub environments this sorting occurs via a coastal sand transport pathway linking the somme estuary mouth to the southern north sea bight where tidal range and wave energy decrease relative to the english channel since this sand transport pathway enables longshore transport of hydrodynamically sorted medium to fine sand derived directly from the immediate nearshore zone it has further contributed to a net flux of this sand population from the eastern english channel sea bed to the southern north sea

acoustic measurements of suspended sand on the shoreface and the control of concentration by bed roughness acoustic backscatter measurements of the concentrations of sand in suspension on the shoreface seawards of the breaking zone during a mild storm event show that sand concentrations increase initially but then rapidly decrease as the wave energy increases it is suggested that the bed roughness is a major control on suspended sand concentration and that the decrease in concentration is due to decreasing ripple steepness after the break off bed shear stress is exceeded no direct measurements of bedforms were available and the combined wave current interaction model of grant and madsen j geophys res vols 84 1979 and 87 1982 with extensions to movable bed roughness ripple dimensions from carstens et al s 1969 laboratory data u s army corps eng cerc tech mem 28 and to sediment induced self stratification glenn and grant j geophys res vol 92 1983 was used to predict the current and suspended sand concentration profile matching the measured and modeled concentrations at 2 cm above the bed the values of the resuspension coefficient 0 were found to decrease as excess skin friction increased in a manner similar to that suggested by drake and cacchione cont shelf res vol 9 1989 but were an order of magnitude larger using the much smaller ripple dimensions of nielsen j geophys res vol 86 1981 changed the model results very little significant differences were found between the time averaged suspended sand profiles and those predicted by the model sand transport fluxes have also been computed using the instantaneous products of measured suspended concentrations and currents the current being the sum of steady and wave induced components the wave induced fluxes show considerable variability from run to run but the general pattern is of a transport profile having a shoreward maximum at 5 10 cm above the bed and offshore transport in the few centimetres closest to the bed little net transport occurred above 15 cm these fluxes show a weak dependence on the wave energy becoming more shoreware and the height of the maximum shoreward transport decreasing as the wave energy increased again consistent with the influence of the ripple steepness

the age and thermal history of cerro rico de potosi bolivia cerro rico de potosi bolivia is the world s largest silver deposit and has been mined since the sixteenth century for silver and for tin and zinc during the twentieth century together with by product copper and lead the deposit consists primarily of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and explosion breccia the deposit is compositionally and thermally zoned having a core of cassiterite wolframite bismuthinite and arsenopyrite surrounded by a peripheral lower temperature mineral assemblage consisting principally of sphalerite galena lead sulfosalt and silver minerals the low temperature assemblage also was superimposed on the high temperature assemblage in response to cooling of the main hydrothermal system both the dacite dome and the ore fluids were derived from a larger magmatic hydrothermal source at depth the dome was repeatedly fractured by recurrent movement on the fault system that guided its initial emplacement the dome was extruded at 13 8 0 2 ma 2 based on u th pb dating of zircon mineralization and alteration occurred within about 0 3 my of dome emplacement as indicated by a 40ar 39ar date of 13 76 0 10ma 1 for sericite from the pervasive quartz sericite pyrite alteration associated with the main stage high temperature mineralization the last thermal event able to reset zircon fission tracks occurred no later than 12 5 1 1 ma 1 as indicated by fission tract dating minor sericite and magmatic steam alunite veins were episodically formed around 11 ma and between 8 3 and 5 7 ma the younger episodes occurring at the time of extensional fracturing at cerro rico and wide spread volcanism in the adjacent los frailes volcanic field none of these younger events appear to be significant thermal mineralizing events the exceptionally flat thermal release pattern of 39ar from sericite and the results of the fission tract dating of zircon show that none of the younger events was hot enough and lasted long enough to cause significant loss of ar or annealing of zircon fission tracks u th pb dating of zircon cores indicates a precambrian progenitor for some zircons and ree analyses of dated samples of hydrothermally altered dacite show the presence of a prominent positive eu anomaly which constrains interpretations of the origin and evolution of the magmatic hydrothermal system

predicting ripple roughness and sand resuspension under combined flows in a shoreface environment ripple measurements and flow and sediment dynamical data obtained from the shoreface of the middle atlantic bight using instrumented tripods were analyzed to evaluate various predictors of ripple geometry and roughness ripple roughness controls on sand resuspension and suspended sediment concentration profiles under combined waves and currents were also evaluated the limited observation of sand ripples in the field indicates that the grant and madsen 1982 method overestimates ripple roughness while the nielsen 1981 method tends to under predict ripple roughness a modified ripple predictor is thus proposed based on the grant and madsen method and it is shown to give reasonable predictions under the present experiment conditions this modified ripple prediction along with wave current and suspended sediment concentration data recorded by the tripods were then brought into the combined flow bottom boundary layer model of grant and madsen 1986 and the modified rouse equation of glenn and grant 1987 to calculate sand resuspension coefficient 0 and to predict suspended sediment concentration profiles it was found that under low energy fair weather conditions sand ripples are in the equilibrium range and ripple roughness increases with the bed shear stress this causes strong vortex activity close to seabed and thus higher resuspension coefficient reference concentrations are moderate due to this high resuspension coefficient even though bed shear stresses are low under moderate storm conditions ripple break off occurs and ripple roughness will decrease with bed shear stress this reduces the vortex activity and hence sand resuspension coefficient 0 the combination of this moderately high bed shear stress and reduced but still moderate ripple roughness favours sand suspension and produces the highest reference concentration for the encountered experimental conditions as bed shear stress is further increased ripples are nearly washed out and sand resuspension coefficient is further decreased approaching the previously suggested constant value of 1 3 10 4 this corresponds with the lowest reference concentration despite the high bed shear stress suspended sediment concentrations predicted by the modified rouse equation using this time variable resuspension coefficient and properly calculated bottom boundary layer parameters are reasonable compared to the field measured concentration profiles

wave formed sand ripples at duck north carolina a recently developed acoustic multiple transducer array was utilized to measure small scale bed forms in the nearshore and inner shelf regions at duck north carolina two populations of wave formed ripples were observed short wave ripples swr with heights ranging from 3 mm to 2 cm and lengths ranging from 4 to 25 cm and long wave ripples lwr with heights ranging from 3 mm to 6 cm and lengths ranging from 35 to 200 cm the swr were only present sometimes and their presence or absence was determined by a critical value of the near bed mobility number the swr were highly dynamic sometimes flattening during wave groups and reforming over several incident wave periods the lwr in contrast were almost always present they were longer and lower relief than predicted by models or generally observed previously both swr and lwr were often observed to migrate shoreward but were rarely observed to migrate seaward the dimensions of the swr when they were present were predictable by the nielsen 1981 model or the wiberg and harris 1994 model to within approximately a factor of 2

sand suspension and transport on the middelkerke bank southern north sea by storms and tidal currents abstract estimates have been made of the suspended sand transport at two sites on the middelkerke bank in the southern north sea from suspended sand profiles and current meter measurements over a period of approximately 40 days sand resuspension was mainly due to waves while transport was dominated by a few hours when large waves coincided with peak flood currents soulsby s relationships for the stress under combined currents and waves were found to be poor predictors for the observed near bed concentrations the mean stress m predicting 45 of the variance while the maximum stress max predicted just 15 and overestimate the effects of the waves when the influence of the stress due to the waves is reduced the variance explained increases to 67 the sand transport rate on the steep slope of the bank was 10 times that of the southern end and was up slope at 25 to the bank axis in the direction of the major axis of the tidal ellipse the transport on the steep slope was mainly in the size range 100 140 m which did not occur in any significant proportion in samples of the sea bed at that site but was advected from deeper water to the southeast excluding this finer component the transport rates of coarser sand 200 m at the two sites were similar over the 40 day period the up slope transport during storms suggests that waves play an important part in the bank maintenance and are not simply the mechanism which prevents the continual growth of the sand bank due to asymmetrical transport by the tidal currents alone the transport rates are consistent with a time scale of 10 2 10 3 years for the formation of the middelkerke bank

regime and trace element evolution of open magma chambers o hara and co workers1 2 have recently summarized some of the evidence accumulated for open system cyclic magmatic systems and provided useful geochemical equations for the replenishment eruption cycles of an ideal magma reservoir i show here that o hara s theory fits the situation where the volcanic eruption taps the more differentiated magma before the mixing stage an alternative ideal model is discussed which is applicable to the more common process of hybrid magma eruption in mid ocean ridge basalts this new model may explain why large variations in incompatible elements coexist with moderate depletion of compatible elements