large scale dam removal on the elwha river washington usa river channel and floodplain geomorphic change abstract a substantial increase in fluvial sediment supply relative to transport capacity causes complex large magnitude changes in river and floodplain morphology downstream although sedimentary and geomorphic responses to sediment pulses are a fundamental part of landscape evolution few opportunities exist to quantify those processes over field scales we investigated the downstream effects of sediment released during the largest dam removal in history on the elwha river washington usa by measuring changes in riverbed elevation and topography bed sediment grain size and channel planform as two dams were removed in stages over two years as 10 5 million t 7 1 million m3 of sediment was released from two former reservoirs downstream dispersion of a sediment wave caused widespread bed aggradation of 1 m greater where pools filled changed the river from pool riffle to braided morphology and decreased the slope of the lowermost river the newly deposited sediment which was finer than most of the pre dam removal bed formed new bars largely pebble granule and sand material prompting aggradational channel avulsion that increased the channel braiding index by almost 50 as a result of mainstem bed aggradation floodplain channels received flow and accumulated new sediment even during low to moderate flow conditions the river system showed a two to tenfold greater geomorphic response to dam removal in terms of bed elevation change magnitude than it had to a 40 year flood event four years before dam removal two years after dam removal began as the river had started to incise through deposits of the initial sediment wave 1 2 million t of new sediment 10 of the amount released from the two reservoirs was stored along 18 river km of the mainstem channel and 25 km of floodplain channels the elwha river thus was able to transport most of the released sediment to the river mouth the geomorphic alterations and changing bed sediment grain size along the elwha river have important ecological implications affecting aquatic habitat structure benthic fauna salmonid fish spawning and rearing potential and riparian vegetation the response of the river to dam removal represents a unique opportunity to observe and quantify fundamental geomorphic processes associated with a massive sediment influx and also provides important lessons for future river restoration endeavors

fractional crystallization of mantle derived melts as a mechanism for some i type granite petrogenesis an example from lachlan fold belt australia the mt buller igneous suite in the southeastern lachlan fold belt encompasses a large variety of rock types from gabbros through diorites to granites mafic rocks and enclaves have primitive mantle like initial 87 sr 86 sr values 0 7037 0 7045 and nd values 5 6 to 4 1 the granites do not show distinctively more radiogenic initial 87 sr 86 sr values suggesting they are derived from the same parent as the gabbros most of the mt buller rocks do not show a positive correlation between silica and initial 87 sr 86 sr or between silica and 143 nd 144 nd values indicating that neither crustal contamination nor mixing between mantle and crustal derived melts has been important and that these rock types are likely to have formed by fractional crystallization from a common mantle derived parent some scatter in compatible trace elements particularly in granites and diorites may be explained by mixing geochemical modelling confirms a comagmatic origin of the suite magma generation probably took place in the subduction modified upper mantle this mechanism may play an important role in i type granite petrogenesis in particular tectonic settings such as during an efficient slab roll back or sinking of oceanic crust in divergent subduction conditions

mantle heterogeneity beneath oceanic islands some inferences from isotopes radiogenic isotopes in oceanic basalts are extremely useful as tracers of long lived heterogeneities in the earth9s mantle helium isotopes provide unique information in that high 3 he 4 he ratios are indicative of relatively undegassed mantle reservoirs i e mantle with high time integrated 3 he th u ratios an alternative hypothesis is that high 3 he 4 he ratios may have been produced by ancient melting events if the solid melt partition coefficient k d for he is greater than that for th and u i e yielding relatively high he th u in the residue of melting however the distribution of helium within basaltic phenocrysts and olivine glass helium partitioning within mid ocean ridge basalts suggest that helium behaves as an incompatible element during melting k d olivine glass 3 he 4 he ratios are derived from undegassed mantle reservoirs isotopic measurements of he sr and pb in hawaiian volcanoes lavas demonstrate that the mantle sources have changed on extremely short timescales between 100 and 10 000 years before present the preferred explanation for these variations is that they represent heterogeneities within the hawaiian mantle plume combined with late stage melting in the lithosphere for post shield alkali basalts helium isotopic data from kilauea hualalai and mauna loa suggest that the plume is presently located beneath kilauea and loihi seamount and constrain the melting zone of the hawaiian plume to be less than 40 km in radius

the rates of plate creation and consumption summary an alternative vector derivation of the expression for the rates of plate creation and consumption is given from which it can be seen that the rates are proportional to the scalar product of the edges of the geohedron and plate polyhedron corresponding to the same boundary the plate polyhedron is defined by the set of triple junction vectors this is used together with a recent determination of the angular velocity vectors and a number of auxiliary plate boundary vectors to revise the rates of plate creation and consumption along sections of plate boundaries all plates which have a substantial proportion of their boundary connected to a downgoing slab are found to be decreasing in area the total rate of plate generation is used in estimates of the area of the ocean floor and the total heat loss from the oceans the rate of consumption within a relatively small area around new guinea implies a large mass flux away from this region knowledge of the rates of plate creation and consumption is used in a number of different areas calculating the contribution of plate creation to the total heat loss of the earth calculating geochemical fluxes out of the mantle such as for the rare gases and other volatiles and return fluxes back into the mantle resulting from reactions between sea water and the ocean crust during hydrothermal circulation calculating the area of the ocean floor as a function of age mass fluxes related to the distribution of the rates of creation and destruction along the plate boundaries are important boundary conditions on the flow pattern in the mantle previous estimates of these rates deffeyes 1970 chase 1972 garfunkel 1975 have applied a simple expression derived for spreading ridges deffeyes 1970 using angular distances from the poles of rotation measured graphically on a globe an alternative derivation of the expression for rates of plate creation and consumption which is independent of assumptions about the nature of the boundary is given below in terms of the framework used to describe plate motions by mckenzie parker 1967 1974 this derivation emphasizes that the rates depend on two sets of vectors one the instantaneous rotation vectors defining the relative plate motions the other a set of triple junction and auxiliary vectors defining the plate boundaries

isotopic evolution of mauna loa volcano abstract in an effort to understand the temporal helium isotopic variations in mauna loa volcano we have measured helium strontium and lead isotopes in a suite of mauna loa lavas that span most of the subaerial eruptive history of the volcano the lavas range in age from historical flows to ninole basalt which are thought to be several hundred thousand years old most of the samples younger than 30 ka in age kau basalt are radiocarbon dated flows while the samples older than 30 ka are stratigraphically controlled kahuku and ninole basalt the data reveal a striking change in the geochemistry of the lavas approximately 10 ka before present the lavas older than 10 ka are characterized by high 3 he 4 he 16 20 times atmospheric higher 206 pb 204 pb 18 2 and lower 87 sr 86 sr 0 70365 ratios than the younger kau samples having he pb and sr ratios of approximately 8 5 atmospheric 18 1 and 0 70390 respectively the historical lavas are distinct in having intermediate sr and pb isotopic compositions with 3 he 4 he ratios similar to the other young kau basalt 8 5 atmospheric the isotopic variations are on a shorter time scale 100 to 10 000 years than has previously been observed for hawaiian volcanoes and demonstrate the importance of geochronology and stratigraphy to geochemical studies the data show consistency between all three isotope systems which suggests that the variations are not related to magma chamber degassing processes and that helium is not decoupled from the other isotopes however the complex temporal evolution suggests that three distinct mantle sources are required to explain the isotopic data most of the mauna loa isotopic variations could be explained by mixing between a plume type source similar to loihi and an asthenospheric source with helium isotopic composition close to morb and elevated sr isotopic values an asthenospheric source or variation within the plume source is considered more likely than lithospheric sources due to the elevated 87 sr 86 sr ratios in the recent kau basalts however the distinct isotopic characteristics of the historical lavas are inferred to be related to lithospheric involvement in the latest stages of shield building volcanism

sediment pulses in mountain rivers 2 comparison between experiments and numerical predictions 1 mountain rivers in particular are prone to sediment input in the form of pulses rather than a more continuous supply these pulses often enter in the form of landslides from adjacent hillslopes or debris flows from steeper tributaries the activities of humans such as timber harvesting road building and urban development can increase the frequency of sediment pulses the question as to how mountain rivers accommodate pulses of sediment thus becomes of practical as well as academic significance in part 1 cui et al 2003 the results of three laboratory experiments on sediment pulses are reported it was found there that the pulses were eliminated from the flume predominantly by dispersion of the topographic high significant translation was observed only when the pulse material was substantially finer than the ambient load in the river here the laboratory data are used to test a numerical model originally devised for predicting the evolution of sediment pulses in field scale gravel bed streams the model successfully reproduces the predominantly dispersive deformation of the experimental pulses rates of dispersion are generally underestimated largely because bed load transport rates are underestimated by the transport equation used in the model the model reproduces the experimental data best when the pulse is significantly coarser than the ambient sediment in this case the model successfully predicts the formation and downstream progradation of a delta that formed in the backwater zone of the pulse in run 3 the performance of the model is less successful when the pulse is composed primarily of sand this is likely because the bed load equation used in the study is specifically designed for gravel when the model is adapted to conditions characteristic of large sand bed rivers with low froude numbers it predicts substantial translation of pulses as well as dispersion

influence of bed patchiness slope grain hiding and form drag on gravel mobilization in very steep streams steep streams are a major portion of channel networks and provide a link to transport sediment from hillslopes to lower gradient rivers despite their importance key unknowns remain perhaps foremost of which is evaluating in steep streams empirical laws for fluvial sediment transport developed for low gradient rivers to address this knowledge gap we painted sediment in situ over 3 years to monitor incipient sediment motion and sediment patch development in five small drainage areas of 0 04 2 km 2 and steep slopes of 5 37 tributaries of elder creek california united states we found that channel beds organized into size sorted sediment patches which displayed active fluvial transport of gravel annually consistent year to year patch median grain sizes partial transport of bed material and significantly higher values of critical shields stress for incipient sediment motion compared to that observed for lower gradient rivers the high critical shields stresses up to 0 5 for the median grain size agree within a factor of 3 to theoretical predictions which account for slope dependent hydraulics grain hiding and sediment patches for grains of approximately the same size as the roughness length scale slope dependent hydraulics and bed patchiness are the dominant controls on critical shields stress values while grain hiding is important for grains larger or smaller than the roughness length scale form drag exists in our monitored tributaries but has a smaller influence than the above effects our field observations show fluvial processes contribute to sediment mobilization in steep channels which are often considered to be dominated by debris flows

one dimensional bed wave movement in lowland rivers we show that recent measurements in the east fork river wyoming of annual gravel wave translation annual bedload transport and annual variations in riverbed cross sectional area can be described to within a factor of 2 by using the gradowczyk characteristic velocity for bed waves to describe gravel wave translation the engelund hansen formula for bedload transport and a duboys like formula for changes in cross sectional area no free parameters are needed

numerical simulation of downstream fining by selective transport in gravel bed rivers model development and illustration a numerical model has been developed for the routing of gravel sized sediment along a river channel which is free to adjust both its long profile and surface texture hydraulic calculations use a step backwater approach and sediment transport is predicted with the method of parker 1990a which uses a low degree of size selectivity exchange of sediment between the surface and subsurface is described using the modified exner equation of parker and sutherland 1990 the model is applied to an idealized channel based on the highly concave allt dubhaig scotland in which fining by particle wear is minor the rapid downstream fining observed in this river is closely matched by model predictions after a time equivalent to 102 years under the present flow regime of the river the evolution of the fining pattern during the model run and associated changes in sediment transport and bed aggradation are described it is concluded that strong profile concavity can force rapid downstream fining even though bed load transport is only slightly size selective this run of the model serves as a basis for testing of the sensitivity of downstream fining to alternative choices of parameter values and boundary conditions which are summarized here and will be described in a subsequent paper

sr and nd isotope composition of the metamorphic sedimentary and ultramafic xenoliths of lanzarote canary islands implications for magma sources abstract the lavas produced by the timanfaya eruption of 1730 1736 lanzarote canary islands contain a great many sedimentary and metamorphic metasedimentary and mafic and ultramafic plutonic xenoliths among the metamorphosed carbonate rocks calc silicate rocks csrs are monomineral rocks with forsterite or wollastonite as well as rocks containing olivine orthopyroxene clinopyroxene plagioclase their mineralogical compositions are identical to those of the mafic gabbros and ultramafic dunite wherlite and lherzolite xenoliths the 87sr 86sr around 0 703 and 143nd 144nd around 0 512 isotope ratios of the ultramafic and metasedimentary xenoliths are similar while the 147sm 144nd ratios show crustal values 0 13 0 16 in the ultramafic xenoliths and mantle values 0 18 0 25 in some csrs the apparent isotopic anomaly of the metamorphic xenoliths can be explained in terms of the heat source basaltic intrusion inducing strong isotopic exchange 87sr 86sr and 143nd 144nd between metasedimentary and basaltic rocks petrofabric analysis also showed a possible relationship between the ultramafic and metamorphic xenoliths

sm nd studies of archaean metasediments and metavolcanics from west greenland and their implications for the earth s early history metasedimentary and metavolcanic rocks from the archaean of west greenland have been examined for evidence of crustal components greater than 3 8 ga in age and for their compatibility with the presently adopted bulk earth sm nd parameters sm nd isotopic data have been obtained for the garbenschiefer metagabbro unit metasediments from the isua supracrustal belt gneisses interior to the isua belt and metasediments from the malene supracrustal belt using estimates of emplacement age t of between 3 77 and 3 67 ga for the parental volcanics to the garbenschiefer unit initial143nd 144nd ratios yield positiveendt values between 1 0 and 3 1 relative to the chur parameters for seven out of eight samples model sm nd ages for the isua gneisses and metasediments are only compatible with their estimated stratigraphic ages if their sources were ca 2end relative to chur at those times similarly model sm nd ages for the malene samples are only compatible with stratigraphic age constraints when based on a source evolution with positiveendt implications of these results for the early development of the earth s mantle are discussed

effect of shallow level contamination on the helium isotope systematics of ocean island lavas the bimodal distribution of helium isotope ratios in ocean island lavas has provided powerful constraints on the composition and evolution of the earth s mantle1 3 high 3he hotspot ratios 3he 4he greater than in mid ocean ridge basalt morb found on hawaii4 and iceland5 are thought to trace pristine plumes from the deep er mantle whereas low 3he hotspot values 3he 3he morb value at tristan da cunha6 and st helena7 are considered to characterize plumes composed in part of recycled oceanic or continental crust here we report the observation of both high 3he and 6low 3he characteristics8 in lavas from a single ocean island heard island in the indian ocean whereas the high 3he lavas provide unambiguous evidence for the involvement of a deep seated plume in their genesis we argue that the low 3he 4he ratios in other lavas result from shallow level contamination by radiogenic helium before eruption these observations call into question the presumed association between low 3he ratios at heard island and elsewhere and ancient crustal material recycled back into the mantle

modeling of riverbed evolution for bedload sediment mixtures a new computational methodology for fully coupled simulation of unsteady water and sediment movement in mobile bed alluvial rivers has been developed and tested the one dimensional approach treats bedload transport of nonuniform sediment mixtures with sorting and armoring effects considered spatial lag effects in nonequilibrium bedload transport are taken into account through innovative use of the recently developed notion of a loading law the new system of equations for water and sediment movement is solved in a fully coupled implicit manner using the preissmann finite difference scheme implemented to allow for either upstream or downstream induced mobile bed perturbations formal analysis of the coupled system sheds new light on boundary condition requirements for the multiple size class problem the fully coupled implicit solution has proven to be robust and stable and it respects the underlying volumetric conservation laws remarkably well as demonstrated in continuity analyses of computed bed e

nd and sr systematics in an eclogite xenolith from tanzania evidence for frozen mineral equilibria in the continental lithosphere combined isotopic nd sr and petrographic analyses are reported for an eclogitic xenolith from the vissury mine tanzania an exceedingly large difference in measured nd values in garnet and clinopyroxene 200 units suggest a major mineral equilibration at 1 75 0 014 ga nd isotopic heterogeneities are demonstrated in different generations of garnet and zonation in sr and nd isotope compositions is present within the clinopyroxene the variation in measured nd isotope compositions in different generations of garnet corresponds to 16 units exsolution of garnet from clinopyroxene occurred in an essentially closed system with respect to sr and nd petrographically different generations of garnet are present one garnet with rutile inclusions as well as the rims of clinopyroxene are clearly off the isochron features like this can originate either if a system is not closed e g affected by a migrating fluid or if a remanent isotopic heterogeneity survived the homogenisation at 1 75 ga the subsolidus partitioning of sm and nd between garnet and clinopyroxene results in higher fractionation of the smnd ratio in garnet than in the liquid crystal partitioning since the closure temperature for the sm nd exchange between garnet and clinopyroxene may be around 850 c in a dry system many of the lithospheric ultramafic rocks may exhibit frozen mineral equilibria the isotopic data suggest that this eclogite was emplaced at 1 75 ga into the lithosphere mantle at temperatures of about 1040 c and then cooled as a closed system at a rate of 6 50 c my down to 840 c where all the exchange reactions were efficiently frozen in at 1 75 ga ago the coincidence of the emplacement of granites 1 7 1 8 ga into the central part of the tanzanian craton with the age of the eclogite suggests that lower crustal melting was triggered by a thermal event in the upper lithosphere

the relationship between gravity and bathymetry in the pacific ocean surface ship and satellite derived data have been compiled in new free air gravity anomaly bathymetry and geoid anomaly maps of the pacific ocean basin and its margin the maps are based on smoothed values of the gravity anomaly bathymetry and geoid interpolated on to a 90 x 90km grid the smoothed values of bathymetry and geoid anomaly have been corrected for age the resulting maps show the pacific ocean basin is associated with a number of ene wsw trending geoid anomaly highs with amplitudes of approx or 5m and wavelengths of approx 3000km the most prominent of these highs correlate with the magellan seamounts marshall gilbert islands magellan rise and the hess rise hawaiian ridge regions the correlation between geoid anomaly and bathymetry cannot be explained by models of static compensation but is consistent with a model in which the geoid anomaly and bathymetry are supported by some form of dynamic compensation suggests that the dynamic compensation which characterizes ocean lithosphere older than 80ma is the result of mantle convection on scales that are smaller than the lithospheric plates themselves from authors

helium neon and argon systematics of the european subcontinental mantle implications for its geochemical evolution in this study we present a comprehensive noble gas study of mantle xenoliths from various european cenozoic volcanic provinces the main body of samples is from the massif central france and the eifel germany smaller subsets of samples are from spitsbergen and the graz basin austria in all the helium neon and argon isotopic abundances of a total of forty five mantle xenoliths phenocrysts and xenocrysts were determined the 3he 4he ratios within each volcanic province are very uniform irrespective of the diverse lithologies and p t conditions which are represented by our sample suite mean 3he 4he ratios of the massif central eifel spitsbergen and kapfenstein are 6 53 25 6 03 14 6 65 25 and 6 1 7 1 times the atmospheric ratio ra respectively the strontium and neodymium isotopic composition of some of the cpx separates are highly variable and therefore in contrast to the uniform he signature we thus conclude that he and probably also the other noble gases in the xenoliths are effectively decoupled from the non volatile elements therefore the he signature that is preserved in the xenoliths is actually that of their host magmas published strontium neodymium and lead isotope data of the unevolved host magmas of the xenoliths correlate well with our xenolith he data the position of the fields of the investigated volcanic provinces in hesr hend and hepb variation diagrams depict ternary mixtures between dmm em himu endmembers as the source the host magmas and their volatiles the neon isotopic composition of the gases released from the xenoliths is in most cases atmospheric and probably reflects atmospheric contamination only a few samples reveal indications for morb type ne or evidence of mass fractionation the 40ar 36ar ratios of the xenoliths are mostly radiogenic with the highest ratio being 17 000 however all samples have suffered a certain degree of atmospheric contamination we calculate that the uncontaminated 40ar 36ar ratio of the european subcontinental mantle is 30 000 the4he 40ar ratios have been fractionated since with values around 0 25 they are below both the current production ratio and the morb ratio they cannot be explained by atmospheric contamination as the samples with high 40ar 36ar ratios also have low 4he 40ar ratios helium and ar were probably fractionated during initial closed system degassing of the host magma we calculate the original unfractionated 4he 40ar ratios of the massif central and eifel magma source which are 2 56 18 and 2 71 17 respectively the noble gas systematics are compatible with the notion that addition of crustal material has modified a former morb source signature we use our mean 3he 4 he ratios and reconstructed 4he 40ar ratios to model the time and degree of contamination of a morb like source with crustal material combining our model with evidence from published oxygen strontium neodymium and lead isotope data we judge that the source of the massif central and eifel magmas became enriched in k u and th shortly prior or during the variscan orogeny pre collisional collisional in this case the enrichment in these elements is therefore most probably related to subduction of crustal material in a destructive continental margin setting

more on the evolution of bed material waves in alluvial rivers sediment waves or pulses can form in rivers following variations in input from landslides debris ows and other sources the question as to how rivers cope with such sediment inputs is of considerable practical interest experimental numerical and eld evidence assembled by the authors suggests that in mountain gravel bed streams such pulses show relatively little translation instead mostly dispersing in place this research has recently been the subject of discussion in particular it has been suggested that a the equations of ow and sediment mass balance used in the analyses and in most other morphodynamic analyses require correction b the dominance of dispersion appears only because the hyperbolic nature of the governing equations has not been adequately considered and c the sediment transport equation used in the analyses does not lead to generalizable results here we suggest that a the relations for mass balance do not require the indicated correction b the hyperbolic nature of the governing equations does not preclude the result of dispersion dominating translation in mountain streams and c the general behaviour of an appropriate hyperbolic model of sediment waves pulses includes the relative roles of dispersion and translation and is not affected by the precise choice of a sediment transport relation as long as the choice is reasonable for the case in question copyright 2005 john wiley sons ltd

controls of strength and rate of downstream fining above a river base level we report sensitivity tests on a numerical model of the development of downstream fining by size selective transport and deposition above a base level in a gravelbed river with no lateral inputs of water or sediment strong fining requires deposition mainly to the surface otherwise its amount and streamwise distribution are not highly sensitive to any single factor but vary somewhat with hiding factor excess shear stress and bed sorting low initial concavity inhibits fining but different higher concavities generate fairly similar fining profiles lower sediment supply leads to a coarser bed with less fining but there is no simple relationship between fining and aggradation rate the rate of development of fining is sensitive to all these factors but is always rapid initially followed by a far slower approach towards final equilibrium surface grain size adjustment is potentially an important degree of freedom in river response to any environmental change or human impact which causes overloading

the dominance of dispersion in the evolution of bed material waves in gravel bed rivers bed material waves are temporary zones of sediment accumulation created by large sediment inputs recent theoretical experimental and field studies examine factors influencing dispersion and translation of bed material waves in quasi uniform gravel bed channels exchanges of sediment between a channel and its floodplain are neglected within these constraints two factors influence relative rates of dispersion and translation 1 interactions between wave topography flow and bed load transport and 2 particle size differences between wave material and original bed material our results indicate that dispersion dominates the evolution of bed material waves in gravel bed channels significant translation requires a low froude number which is uncharacteristic of gravel bed channels and low wave amplitude which for a large wave can be achieved only after substantial dispersion wave material of small particle size can promote translation but it primarily increases bed load transport rate and thereby accelerates wave evolution copyright 2001 john wiley sons ltd

the early cretaceous san juan plutonic suite ecuador a magma chamber in an oceanic plateau sections through an oceanic plateau are preserved in tectonic slices in the western cordillera of ecuador south america the san juan section is a sequence of mafic ultramafic cumulates to establish that these plutonic rocks formed in an oceanic plateau setting we have developed criteria that discriminate intrusions of oceanic plateaus from those of other tectonic settings the mineralogy and crystallization sequence of the cumulates are similar to those of intra plate magmas clinopyroxene predominates throughout and orthopyroxene is only a minor component rocks of intermediate composition are absent and hornblende is restricted to the uppermost massive gabbros within the sequence the ultramafic cumulates are very depleted in light rare earth elements lree whereas the gabbros have flat or slightly enriched lree patterns the composition of the basaltic liquid in equilibrium with the peridotite calculated using olivine compositions and ree contents of clinopyroxene contains between 16 and 8

melt depletion and subsequent metasomatism in the shallow mantle beneath koolau volcano oahu hawaii xenoliths from pali oahu hawaii include samples of the mantle lithosphere underlying koolau shield volcano most such xenoliths are spinel peridotites the remainder being plagioclase spinel peridotites and garnet free pyroxenites clinopyroxene separates from pali peridotite xenoliths have relatively depleted 87sr 86sr 0 70309 0 70346 and 143nd 144nd 0 512967 0 513206 the mantle lithosphere beneath the koolau volcano has a range of present day epsilonnd 6 9 11 on a 143nd 144nd versus 147sm 144nd diagram they define a 61 20 ma errorchron within error of the estimated age of 80 85 ma of the pacific lithosphere at oahu and an intercept of epsilonnd 6 8 we interpret the pali spinel peridotites as samples of the pacific lithosphere residual to melt extraction of the pacific crust these rocks were not metasomatized by melts having isotopic composition similar to the shield building koolau volcano but they could have been metasomatized by melts related to the honolulu volcanic series plagioclase mineral separates from two peridotites are in 87sr 86sr isotopic disequilibrium with coexisting clinopyroxenes the plagioclases are light rare earth element depleted and have enriched 87sr 86sr ratios 0 70436 and 0 70443 the delta18o of olivine 5 09 5 12 and clinopyroxene 5 32 5 33 from spinel peridotites are typical for oceanic upper mantle rocks in contrast delta18o of olivine pyroxene and plagioclase in plagioclase bearing peridotites are enriched by 0 5 relative to the spinel peridotites e g delta18o ratios of olivines from plagioclase peridotites are 5 4 5 5 it is here interpreted that the plagioclases represent phases that formed by reaction with or precipitation from a melt that intruded the pacific lithospheric mantle the pacific lithospheric isotopic composition is reflected in the clinopyroxene separates the high delta18o and 87sr 86sr of the plagioclase resemble koolau lavas and suggest that the melt passing through the lithosphere was plume related the elevated delta18o of the plagioclase indicates that the melt from which it fractionated had a component of recycled crustal material not acquired from local crustal contamination it is also estimated here that the duration of the porous melt flow of the koolau like melt though the mantle lithosphere was short lived 10 2 10 4 years

evidence for subduction related components in the subcontinental mantle from low 3he 4he and 40ar 36ar ratio in mantle xenoliths from far eastern russia abstract by applying both vacuum crushing and stepwise heating methods for the extraction of the noble gases we have discovered 3he 4he ratios much lower than the atmospheric ratio 0 3 ra ra is the atmospheric 3he 4he ratio of 1 4 10 6 and relatively low 40ar 36ar ratios spectroscopic and petrographic observations confirm that there are at least two compositionally distinct fluids in these xenoliths liquid co2 inclusions and melt inclusions with shrinkage bubbles based on the crushing experiments it is inferred that the inclusions of liquid co2 have a 3he 4he ratio similar to that of morb and the component with the low 3he 4he ratio is derived from the shrinkage bubbles in the melt inclusions for the present samples the 40ar 36ar ratios obtained by crushing were less than 1000 suggesting incorporation of atmospheric components in the source materials since low 40ar 36ar ratios were observed irrespective of the occurrence of the liquid co2 inclusions the atmospheric component exists in the melt inclusions ne and xe isotopes are also consistent with incorporation of atmospheric components since the far eastern russia area was located at a subduction zone in the jurassic early cretaceous period it is most likely that the melt inclusions displaying atmospheric noble gas characteristics together with low 3he 4he ratios have been derived from the jurassic cretaceous subducted slab although we cannot exclude the possibility that low 3he 4he ratios are due to the existence of minor u bearing minerals in the lithospheric continental mantle caused by metasomatism we have no petrographical evidence for such minerals in this area on the other hand 3he 4he ratios observed in the liquid co2 inclusions which are similar to the morb like value might reflect the general character of the upper mantle the far eastern russian mantle may therefore be a morb like source that has been partly infiltrated by subduction related fluids

evolution of a sediment wave in an experimental channel the routing of bed material through channels is poorly understood we approach the problem by observing and modeling the fate of a low amplitude sediment wave of poorly sorted sand that we introduced into an experimental channel transporting sediment identical to that of the introduced wave the wave essentially dispersed upstream and downstream without translation although there was inconclusive evidence of translation late in the experiment when the wave was only 10 20 grain diameters high alternate bars migrated through zones of differing bed load transport rate without varying systematically in volume celerity or transport rate sediment that overpassed migrating bars was apparently responsible for dispersion of the wave the evolution of the wave was well predicted by a one dimensional model that contains no adjusted empirical constants numerical experiments demonstrate however that the theory does not predict sediment waves that migrate long distances downstream such waves can only be explained by the following processes not represented by the theory selective bed load transport spatial variations in bar and other form roughness the mechanics of mobile armor and perhaps other mechanisms

numerical model of sediment pulses and sediment supply disturbances in mountain rivers sediment pulses in rivers can result from many mechanisms including landslides entering from side slopes and debris flows entering from tributaries artificial sediment pulses can be caused by the removal of a dam this paper presents a numerical model for the simulation of gravel bedload transport and sediment pulse evolution in mountain rivers a combination of the backwater and quasi normal flow formulations is used to calculate flow parameters gravel bedload transport is calculated with the surface based bedload equation of parker in 1990 the exner equation of sediment continuity is used to express the mass balance at different grain size groups and lithologies as well as the abrasion of gravel the river is assumed to have no geological controls such as bedrock outcrops and immobile boulder pavements the results of nine numerical experiments designed to study various key parameters relevant to the evolution of sediment pulses are reported here results of the numerical runs indicate that the evol

a noble gas profile across a hawaiian mantle xenolith coexisting accidental and cognate noble gases derived from the lithospheric and asthenospheric mantle beneath oahu a noble gas profile across a garnet pyroxenite xenolith from salt lake crater oahu hawaii provides information about the scale and origin of noble gas heterogeneities within such rocks variations in both absolute and relative noble gas concentrations are large and comparable to those observed between individual salt lake crater pyroxenite xenoliths 3he 4he varies from 7 7 to 9 4 times the atmospheric value ra and correlates inversely with 40ar 36ar which ranges between 4100 and 9700 neon krypton and xenon isotopes are uniform and indistinguishable from air with the exception of excess 129xe overall the observed noble gas compositions reflect a derivation from depleted morb type mantle sources the spatial distribution of noble gas signatures within the xenolith and the observed correlation between helium and argon isotopes suggest the presence of two different noble gas components which are trapped in different phases and are unevenly distributed within the xenolith 40ar 36ar and 1 36ar correlate inversely indicating that atmospheric contamination is insignificant hence the observed isotopic variations reflect mixing of two mantle derived noble gas components correlations between hear isotopes and co2 h2o in different pyroxenites from salt lake crater including our sample reveal that the first component is characterized by highly radiogenic helium and argon isotopes and related to abundant secondary co2 rich fluid inclusions given the high diffusivity of he at mantle temperatures hart 1984 the observed helium isotope heterogeneities on a sub mm scale require that the fluids were introduced concurrently with eruption this interpretation is supported by the low entrapment depths of fluid inclusions in salt lake crater pyroxenites 30 km murck et al 1978 this implies that the fluids are genetically related to the host magma itself and reflect its composition the second noble gas component is interpreted as being magmatic i e cognate to the basaltic magma from which the pyroxenite precipitated within the mantle it is proposed that this component resides inside the mineral lattices and was trapped during magmatic crystallization our results indicate that the depleted lithospheric mantle source of the post erosional host magma honolulu volcanic series is characterized by 40ar 36ar 10000 r ra 7 5 and excesses in129xe noble gas signatures of the asthenospheric mantle source parental to the pyroxenite producing magma are less radiogenic with respect to these isotopes combining noble gas and strontium neodymium and lead isotope evidence we propose that the asthenosphere beneath oahu was originally similar to depleted morb type mantle but became slightly modified by noble gases and other incompatible trace elements derived from the hawaiian mantle plume prior to partial melting this study provides evidence that noble gas isotopes and solid radiogenic isotopes are coupled in the mantle sources of basalts e g allegre et al 1983 but decoupled in xenoliths e g vance et al 1989

he sr and nd isotopes in xenoliths from hawaii and other oceanic islands abstract isotopic analyses on he whole rock and sr nd separated clinopyroxenes are reported for ultramafic and gabbroic xenoliths from the hawaiian islands canary islands kerguelen gough and madeira the he isotopic compositions in samples of varied petrologic type from hawaii show a remarkably narrow range r ra 8 2 9 5 are within the previously reported range for hawaiian xenoliths and are indistinguishable from the range of 3he 4he ratios seen in morb in contrast sr and nd isotopic compositions show a significant range samples from the canary islands kerguelen gough and madeira considered as a group show a similar trend with a restricted range in 3he 4he 5 2 7 ra contrasted by sr and nd isotopic compositions extending over almost the entire range of oceanic basalts the relationship between he and sr nd isotopes of ocean island xenoliths are strikingly similar to that observed for continental ultramafic xenoliths by porcelli et al 1986 1 these systematics suggest metasomatic introduction of lithophile sr and nd and volatile he elements into the lithosphere beneath ocean islands overprinting depleted mantle isotopic characteristics the addition of volatiles must be accomplished by a different process to that of lithophiles probably due to selective transport most likely migration of a lithophile poor co2 h2o fluid consideration of he sr data for oceanic basalts suggests that similar fluid related processes may operate prior to or during mantle melting if so the interpretation of he sr relationships of oceanic basalts in terms of simple mixing between isotopically well defined sources is likely to be invalid

open system behavior of helium in case of the himu source area lower he 4he than that of mid ocean ridge basalts morbs observed in himu ocean island basalts oibs has been considered to be the evidence that the himu source is related to recycled materials however typical he 4he value of polynesian himu oibs 6 8 ra is too high to be explained by addition of in situ radiogenic 4he in the recycled oceanic crust mixing of the upper mantle material with the recycled oceanic crust cannot explain he 4he of himu oibs as revealed from mixing calculation in the he pb isotope system as another possibility if we assume that large mobility of helium affects he 4he of recycled materials the model calculation indicates that the balance between radiogenic 4he production in the recycled oceanic crust and diffusive loss of 4he to the surrounding mantle accounts for he 4he of himu the model suggests the thickness of himu source body to be in the order of 1 km

incision and morphologic evolution of an alluvial channel recovering from hydraulic mining sediment hydraulic gold mining in the sierra nevada california produced such a large volume of sediment from 1853 to 1884 that channels could not carry a substantial proportion of the delivered sediment the lower bear river aggraded as much as 5 m and underwent a major avulsion during the 1870s channel morphology continues to respond to these changes more than 100 years after the cessation of most hydraulic mining textures of mine tailings and older alluvium are contrasted and channel incision and channel shape changes from 1930 to 1985 are documented unlike the yuba and sacramento rivers the lower bear river had not returned to pre mining base levels by 1950 as sediment loads decreased nor were incision rates or morphological change governed by reduced sediment loads below dams built in 1928 and in the mid 1960s channel stability was due to resistance of a cohesive stratum on the channel bed an episode of channel down cutting was instigated by a moderately large flood in december 1955 that pierced the cohesive layer and was sustained through the 1970s by moderate magnitude floods the 1955 flood did not directly erode large volumes of sediment but it destabilized the channel allowing smaller floods to erode the channel at an accelerated rate episodic channel bed incision is contrasted to progressive morphologic changes cross section shape narrowed and deepened steadily from 1930 through the mid 1970s as the channel was superimposed onto cohesive older alluvium progressive deepening set up a positive feedback that ensured the ultimate penetration of the paved bed channel morphologic readjustment from the avulsion thus was both progressive and episodic

river adjustment to changes in sediment load the effects of tin mining on the ringarooma river tasmania 1875 1984 the mining of alluvial tin in the ringarooma basin began in 1875 reached a peak in 1900 20 and had virtually ceased by 1982 during that time 40 million m3 of mining waste were supplied to the main river quickly replacing the natural bed material and requiring major adjustments to the channel based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load the river s transport history is reconstructed using a mass conservation model because of the lengthy time period 110 years and river distance 75 km involved the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream peak storage is predicted in that part of the river where braiding and anastomosis are best developed aggradation was most rapid in the upper reaches close to major supply points becoming slower and later with distance downstream channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common bridges had frequently to be replaced while bed levels were still rising in lower reaches degradation began in upper ones notably after 1950 and by 1984 had progressed downriver over 30 km rates of incision reached 0 5 m yr 1 especially in the early 1970s when record high flows occurred as a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions also a narrower unbraided channel has developed the river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris

he solubility in silicate melts a tentative model of calculation abstract published data of he solubility in silicate melts of simple composition enable the calculation of he solubility of any melt of natural composition with a fair accuracy the model proposed relates henry s law solubility constant k to the mole fraction of oxide component in the melt according to ln k i x i k i where k i is a constant to be determined and x i the oxide mole fraction of component i k i values are obtained for sio 2 al 2 o 3 k 2 o cao na 2 o li 2 o and mgo and increase in that order these k i values and reasonable assumptions concerning tio 2 feo and fe 2 o 3 make it possible to calculate a model he solubility for a tholeiitic basalt melt which compares fairly well with the previously published result

selective sorting and abrasion of river gravel i theory most gravel rivers show a tendency for characteristic grain size to decrease in the downstream direction over scales of tens or hundreds of kilometers it has been surmised that this downstream fining is due to some combination of selective sorting by which finer grains are preferentially transported downstream and abrasion by which individual particles are reduced in size here a framework for the simultaneous treatment of both phenomena is developed the analysis is restricted to bed load transport of gravel only abrasion due to binary collisions between moving bed load and stationary bed particles is considered the formulation includes the possibility of differential basin uplift and subsidence due to tectonism and mixtures of rock types with differing coefficients of abrasion the formulation of selective sorting is based on the concept of hiding as applied to a surface based bed load transport relation abrasion is first treated in terms of a lagrangian formulation for individual grains and t

ore genesis and fluid evolution of the kaladawan south zn pb cu ore field eastern altyn mountains nw china evidence from fluid inclusions h o isotopes and geochronology abstract the newly discovered kaladawan south zn pb cu orefield in eastern altyn mountains is composed of five zn pb cu deposits with the largest one containing 414 4 thousand tonnes kt zn 265 2 kt pb and 149 2 kt cu stratiform lenticular orebodies are hosted by the ordovician volcanic sedimentary sequences subjected to greenschist facies metamorphism two major ore forming stages with significant cross cutting relationship are identified at kaladawan south stage i of the earlier massive banded disseminated barite rich sulfide ores and stage ii of the later polymetallic sulfide quartz veins with economically less importance fluid inclusions fis locked in quartz of stage i massive sulfide ores are homogenized completely at 226 354 c with calculated seawater like salinities of 2 7 4 2 wt nacl equiv these characteristics of ore forming fluids coupled with ore textures of typical vms deposits are interpreted to be originated from the modified seawater by sea floor volcanic hydrothermal activities in compared the stage ii fis yielded lower homogenization temperatures ranging 251 c 357 c with higher salinities of 0 8 14 4 wt nacl equiv laser raman analyses identified large amounts of co 2 ch 4 n 2 in the hydrothermal fluids of stage ii the 18 o h2o values 0 5 5 7 and d h2o values of 68 1 to 32 3 of stage ii quartz are plotted in the range of metamorphic fluids in the d o isotopic diagram which indicating that the co 2 rich and mesothermal fluids are metamorphic derived the phlogopite paragenetic in the stage ii polymetallic vein yielded a 40 ar 39 ar plateau age of 435 4 3 9 ma similar to the age of the metamorphic muscovite 451 0 4 1 ma from the ore hosting schist based on the ore deposit geology mineral assemblages and fluid geochemistry the kaladawan south zn pb cu mineralization is attributed to be an ordovician vms type deposit overprinted by the silurian metamorphic fluids

chemical and isotopic variations along the superfast spreading east pacific rise from 6 to 30 s chemical data of 39 fresh basaltic glasses from the east pacific rise epr between 6 and 30 s and pb sr and nd isotopic compositions of 12 basalt glasses are presented major and trace element data indicate a wide compositional range including primitive basalts mg 0 67 and highly evolved feti basalts mg 0 34 molmg mg fe2 the compositional range can be attributed to low pressure fractional crystallization fractionation corrected major element concentrations provide evidence for varying mantle melting conditions calculations of the melting conditions suggest melt generation in a rising upper mantle column between 20 and 10 kbar at temperatures between 1430 and 1280 c and total degrees of partial melting between 17 and 20 by weight leached and hand picked basalt glasses display large variations in 87sr 86sr 0 70235 0 70270 143nd 144nd 0 51312 0 51323 and 206pb 204pb 18 064 18 665 but are similar to other n type morb from the epr the isotopic ratios of basalts from 13 to 23 s show strong correlations and delineate two systematic trends from 23 to 17 s 87sr 86sr and pb isotope ratios increase and 143nd 144nd decrease in agreement with previous results mahoney et al 1989 a reverse trend is indicated by basalts from 17 to 13 s however k ti and la sm n continuously increase from 23 to 13 s this opposite behavior indicates a recent decoupling of isotopic and minor element ratios in the mantle between 13 and 17 s north of 13 5 s garrett fracture zone isotopic data show no systematic variation with ridge location and display an overall weaker covariation the results suggest that the isotopic variations and ridge segmentation appear to be unrelated and that major ridge offsets apparently coincide with changes in mantle melting conditions p t f f degrees of melting there is no evidence for a systematic relationship between calculated melting conditions and second order ridge segmentation our isotopic data provide further evidence for regionally confined chemical variations in the mantle at 5 to 30 s we interpret the isotopic trends as reflecting melting of distinct smallvolume and old enriched mantle components in contrast variations in trace elements are attributed to young mantle differentiation processes

partition of noble gases between olivine and basalt melt abstract the distribution coefficients ki of noble gases were determined for synthesized olivine basalt melt pairs seven samples bh series were synthesized at 1370 1300 c under a one atmospheric pressure 105 pa noble gas mixture and four samples hpp and hpg series at 1360 1050 c at high pressures 0 2 1 5 gpa the two different experiments gave consistent results with each other some bh series olivine samples were apparently contaminated with gas rich inclusions or the glass phase and the effects of such interferences on the calculated distribution coefficients were evaluated the possible ranges of the distribution coefficients of noble gases thus obtained are khe 0 07 kne 0 006 0 08 kar 0 05 0 15 kkr 0 15 and kxe 0 3 these show remarkable features compared to solid element distribution coefficients the distribution coefficients of noble gases are rather insensitive to or even positively correlated with the atomic size of noble gases the striking contrast between the partition of noble gases and that of solid elements may be attributed to the electrical neutrality of noble gases and the increasing electronic polarizability from he to xe

trace of the kerguelen mantle plume evidence from seamounts between the kerguelen archipelago and heard island indian ocean 1 the gravity and bathymetric highs on the kerguelen plateau in the southern indian ocean between the kerguelen archipelago and heard island are seamounts formed of miocene alkalic basalts similar to those found on the islands dredging during the kerimis survey cruise recovered 1 ton of mostly basaltic rocks one of the dredges d6 yielded a large volume of in situ alkalic picritic pillow basalts the first picritic lavas recovered that are related to the kerguelen plume k ar and 40ar 39ar ages are between 18 and 21 ma for all but one sample and these ages are only slightly younger than the main phase of volcanism on the archipelago the dredged lavas form three distinct groups based on chemical and isotopic compositions incompatible element abundance ratios overlap with compositional groups defined by lavas from both the kerguelen archipelago and heard island indicating that alkalic volcanism in this region of the kerguelen plateau has been spatially diverse olivine and picritic basalts have sr and nd isotopic characteristics similar to most of the lavas exposed on the archipelago and those proposed for the kerguelen plume however compared to kerguelen archipelago lavas the picritic basalts have relatively low 206pb 204pb which is a characteristic of cretaceous basalt forming some parts of the kerguelen plateau we propose that the apparent age trend of the lavas from 34 ma in the northern kerguelen plateau odp leg 183 site 1140 to 24 30 ma on the kerguelen archipelago to 18 21 ma on the dredged submarine volcanoes and even possibly to recent volcanism on heard and mcdonald islands may correspond to the tertiary hot spot track of the kerguelen plume

evolution of a landslide induced sediment wave in the navarro river california a streamside landslide delivered 60 000 m3 of mixed size sediment to the navarro river a sinuous gravel bed channel drainage area 535 km2 at the end of the annual high runoff period in spring 1995 the deposit formed a 9 m high dam that partially breached within several hours but recessional flows entrained little material until the following high runoff season the landslide afforded the opportunity to measure the evolution of a sediment wave from its inception to near obliteration and particularly to test relative tendencies for translation and dispersion of a sediment wave in a natural gravel bed channel this study represents a simple case the wave originated from a single input the preexisting channel was relatively uniform and resistant banks prevented adjustments in width we surveyed channel topography over a 1 5 4 5 km reach centered on the landslide dam each year from 1995 to 1999 and we sampled bed material downstream of the dam in 1995 and 1997 landslide material was coarser than ambient bed material but all sizes were mobilized by subsequent peak flows abrasion of weathered and fractured graywacke sandstone landslide material was roughly an order of magnitude greater than the ambient river gravel the sediment wave dispersed and mostly disappeared within a few years with no measurable translation sediment filled the reservoir created by the eroding landslide dam until throughput of bed load was restored in 1998 the stationary wave crest eroded until in 1999 it was 1 m higher e mail dsutherl fs fed us than the preslide elevation as the wave profile flattened its detectable leading edge extended downstream from 620 m in 1995 to 1600 m in 1997 downstream advance of the wave was associated with coarsening of bed material the sediment wave created a longitudinal disturbance in sediment transport by using the dam as a reference datum of zero bed load transport we computed longitudinal variations in annual bed load and suspended sediment transport rates in 100 m increments downstream of the dam these longitudinal variations were controlled by scour and fill of the bed and by abrasion of bed load particles bed load transport rates in the first and second years after the landslide increased in the landslide vicinity and then decreased downstream as sediment deposited behind the advancing leading edge of the wave the location of peak bed load transport rate advanced from the first year 400 m to the second 800 m we used a physically based one dimensional model cui et al 2002b to hindcast annual changes in transversely averaged bed elevation over the study reach agreement between measured and predicted bed elevations was very good this result supports our conclusion that once emplaced sediment waves in gravel bed rivers tend to disperse with little or no translation

the isotope systematics of a juvenile intraplate volcano pb nd and sr isotope ratios of basalts from loihi seamount hawaii abstract sr nd and pb isotope ratios for a representative suite of 15 basanites alkali basalts transitional basalts and tholeiites from loihi seamount hawaii display unusually large variations for a single volcano but lie within known ranges for hawaiian basalts nd isotope ratios in alkali basalts show the largest relative variation 0 51291 0 51305 and include the nearly constant tholeiite value 0 51297 pb isotope ratios show similarly large ranges for tholeiites and alkali basalts and continue tatsumoto s 31 loa trend towards higher 206pb 204pb ratios resulting in a substantial overlap with the kea trend 206pb 204pb ratios for loihi and other volcanoes along the loa and kea trends 31 are observed to correlate with the age of the underlying lithosphere suggesting lithosphere involvement in the formation of hawaiian tholeiites loihi lavas display no correlation of nd sr or pb isotope ratios with major element compositions or eruptive age in contrast with observations of some other hawaiian volcanoes 38 isotope data for loihi as well as average values for hawaiian volcanoes are not adequately explained by previously proposed two end member models new models for the origin and the development of hawaiian volcanoes must include mixing of at least three geochemically distinct source regions and allow for the involvement of heterogeneous oceanic lithosphere

238u 230th radioactive disequilibria in historic lavas from the canary islands and genetic implications abstract lava samples from 10 historic or recent eruptions on la palma tenerife and lanzarote canary islands have been analyzed for u and th contents and th sr and o isotopes the sample suite ranges from mantle derived tholeiites and basanites to evolved phonolites a phonolite from la palma has identical th isotope ratio as basanite from the same 1949 eruption and was most probably formed by crystal fractionation of a basanitic magma in contrast the th isotope ratios in the teide phonolites tenerife slightly decrease with differentiation these latter were produced either by crystal fractionation in magma pockets isolated for about 35 000 y or by an assimilation fractional crystallization afc process involving old syenites as contaminants the sr and o isotope ratios show very small variations from 0 7030 to 0 7032 and 5 2 to 5 9 respectively in the analyzed samples except in the most evolved phonolite from tenerife but th isotope ratios are significantly different between the three islands the 230 th 232 th ratios vary from 1 1 in la palma to 0 94 1 01 in lanzarote and to 0 9 or lower in tenerife a possible interpretation of this variation is mixing of melts derived from an undepleted mantle source similar in composition to the tristan da cunha mantle plume with melts of the suboceanic lithosphere the proportion of the plume derived magmas would be higher below the center of the archipelago a variably metasomatized mantle source beneath each island is an alternative explanation the few available 3 he 4 he ratios are correlated with 230 th 232 th ratios and are compatible with both these models they indicate the existence of a mantle source or a metasomatic component with a high th u and th u he ratios below the canary islands

modelling sediment transport as a moving wave the transfer and deposition of mining waste abstract the movement of slugs of bedload from a discrete input point down a river has proved difficult to model using conventional finite difference formulations of equations of motion a model is proposed which makes explicit allowance for the mean sediment velocity and through a dispersion coefficient the distribution of sediment velocity about the mean a second comparative model uses the normal mass conservation or sediment transport continuity approach the models have been tested over a 43 month period using data from seven monitored cross sections of the kawerong river on bougainville island papua new guinea a system which receives waste from a large copper mine the dispersion model performs considerably better than the mass conservation model

he sr and nd isotopes of mantle derived xenoliths in volcanic rocks of ne china abstract abundances and isotopic ratios of he and isotopic ratios of sr and nd have been measured for 18 mantle derived xenoliths from three cenozoic volcanic provinces in ne china the xenoliths are characterized by low he concentrations 2 3 10 9 2 5 10 7 cm3 stp g 1 and large variations of 3he 4he ratios 1 6 10 7 15 8 10 6 or r ra 0 1 11 3he 4he 87sr 86sr and 143nd 144nd ratios in xenoliths from kuandian holocene volcanic provinces are consistent with those observed in mid oceanic ridge basalt morb indicating that the source of he sr nd in the lithospheric mantle is chemically and isotopically identical to that of morb reservoir however xenoliths in huinan pleisteocene holocene volcanic province are characterized by slightly low 3he 4he ratios r ra 4 3 6 5 and more radiogenic sr and nd the age corrected 3he 4he ratios suggest that their time integrated ratio of u th 3he is slightly elevated compared to the depleted upper mantle the hannuoba xenoliths in the miocene volcanic province show much lower and wider variable 3he 4he ratios which is most likely caused by in situ radiogenic 4he accumulation since it erupted on to the surface the he sr nd results suggest chemical and isotopical heterogeneity in the subcontinental mantle beneath ne china

stochastic forcing of sediment routing and storage in channel networks the stochastic field of sediment supply to the channel network of a drainage basin depends on the large scale interactions among climatically driven processes such as forest fire and rainstorms topography channel network topology and basin scale during infrequent periods of intense erosion large volumes of colluvium are concentrated in parts of a channel network particularly near tributary junctions the rivers carry bed material and wash load downstream from these storage sites at different rates the bed material travels slowly creating transient patterns of sediment transport sediment storage and channel morphology along the channel network as the concentrations of bed material migrate along the network their waveforms can undergo changes by diffusion interference at tributary junctions and loss of mass through temporary sediment storage in fans and terraces and through particle abrasion which converts bed material to wash load we investigated how these processes might influence the sediment mass balance in channels of third and higher order in a 215 km 2 drainage basin within the oregon coast range over a simulated 3000 year period with a climate typical of the late holocene we used field measurements and a simulation model to illustrate interactions between the major controls on large scale processes functioning over long periods of time in complex drainage basins

selective sorting and abrasion of river gravel ii applications most gravel rivers show a tendency for characteristic grain size to decrease in the downstream direction over scales of tens or hundreds of kilometers it has been surmised that this downstream fin