impact of particle shape on saltating mode of bedload transport sheared by turbulent flow abstractthe saltating mode of sediment transport is the dominant mechanism of bedload transport in a fluvial stream especially in mountainous rivers in most simulation studies the actual shapes

experiments on saltation of sand in water a high speed video system was used to study saltation of sand in an open channel flow high rates of image acquisition provided the information needed to resolve details of the lagrangian properties of particle motion saltation of sand is described in terms of statistical properties of particle trajectories such as mean values and standard deviations of saltation length height and streamwise particle velocity results are compared with available empirical data saltation height seems to be independent of particle size when made dimensionless with the particle diameter however the dimensionless saltation length appears to increase as the particle size decreases particle collision with the bed is also analyzed observations of this process indicate that most of the interactions between saltating particles and the bed are of the collision rebound type which contradicts previous discussions on the subject the estimated value of the dynamic friction coefficient is about half that proposed by bagnold i

lobal interactions rheologic superposition and implications for a pleistocene ice stream on the continental shelf of british columbia abstract data on structures stone striae clast pavements fabrics morphology provenance and matrix grain size of four pre late wisconsinan diamictons are presented from the lower accessible part of an 855 m long sea cliff at cape ball east coast of graham island queen charlotte archipelago british columbia the data indicate that an ice stream crossed the continental shelf from the british columbian mainland to the queen charlotte islands local queen charlotte piedmont ice coalesced with the western edge of the cordilleran ice sheet resulting in northward flow deflection along the east coast of graham island generally consistent structural and stone data indicate that diamictons were deposited as primary subglacial tills and that subglacial dynamics and rheologic conditions were complex two of the tills can be traced continuously over the cape ball section which provides a north south transect oblique to ice flow each of the two tills reveals five major changes in rheology and genesis ranging from a strong lodgement component to dominantly deformation mainly by subglacial squeeze flow true end member tills are rare and in almost all places the tills are hybrids that formed within a continuum of till forming processes commonly involving stone rotation and superposition of structures and rheologic states this could have occurred mainly in response to fluctuating till pore water content along the transect two dimensional stretches of contrasting till types probably represent a three dimensional patchwork of contrasting till rheologies and pore waters if patches of ductily deforming till were common and or widespread they could have accounted for much of the movement of cordilleran ice over glaciomarine mud on the continental shelf when sea level was much lower than present deforming probably saturated muddy till reconstituted glaciomarine would have possessed negligible shear strength resulting in a thin rapidly moving glacier most likely an ice stream that reached cape ball but failed to remove the record of previous glacial events the ice stream probably issued out of the mainland s skeena valley which is aligned with cape ball and is approximately the size of valleys in antarctica that today conduct small outlet glaciers and ice streams evidence for this and other ice streams on the northwestern continental shelf of north america imply that destabilization and rapid decay of the western edge of the cordilleran ice sheet may have been accomplished by a combination of ice streams sea level rise and extensive calving

do critical stresses for incipient motion and erosion really exist the concept of critical stress for the initial motion of noncohesive sediment beds under turbulent flow conditions is reviewed observational definitions of incipient motion are many and not entirely compatible some laboratory flume observations of sediment movement suggest that no true threshold exists current understanding of turbulent fluid motion at a sediment bed suggests that some particle movement must occur at all nonzero time mean velocities a combined model for flume flow and sediment transport having no threshold is seen to explain features of data that have been previously used to support the threshold concept

investigations of continuous bed load saltating process particle saltating motions during bed load transport are dominated by the forces acting upon particles and the random process of the particles impacting on and rebounding from the channel bed a real time flow visualization technique is developed in this study to measure particle saltating trajectories corresponding velocities and impacting and rebounding angles based on the experimental data regression equations for the dimensionless saltating length height and velocity were obtained a numerical model that is able to simulate the continuous saltating process of a single particle was developed the model was calibrated and verified with the experimental data and the results were satisfactory the model was also used to generate a series of synthetic data based on these data and the flume data collected by previous investigators a bed load equation was derived

ocean drilling program leg 169s surficial geology stratigraphy and geomorphology of the saanich inlet area southeastern vancouver island british columbia abstract this paper provides i a descriptive overview of the late pleistocene and holocene geology and geomorphology of the region surrounding saanich inlet and ii the palaeogeographic setting for discussion of the oceanographic record at odp leg 169s sites 1033 and 1034 the dominant deposits and landforms in the saanich inlet area are similar to those of late pleistocene marine influenced glacial environments and modern fjord inlets dominated by retreating tide water glaciers patterns of ice retreat meltwater drainage and sea level change are reconstructed for the interval 4000 15 000 calendar years before present yrbp the flux of meltwater and sediment into saanich inlet was greatest between ca 12 000 and 15 000 yrbp at that time sea level was up to 90 m higher relative to land than today during deglaciation tidewater glaciers occupying chemainus cowichan and koksilah valleys entered a marine embayment that formed in the vicinity of cowichan bay satellite channel saanich inlet and saanich peninsula in the early holocene relative sea level fell to a low stand perhaps tens of metres below the present datum and the surface area of saanich inlet and satellite channel was much reduced by the middle holocene sea level had risen to near its present position and modern drainage patterns and oceanographic conditions were established

bed load grain velocities and sediment transport rates theoretical consideration of the dynamics of bed load sediment transport leads to expressions for bed grain velocity and sediment transport rate as respectively ub a u u c and ib a tan u u c 0 c agreeing in form with many previous analyses the grain velocity equation agrees well with all experimentally determined velocities of single grains moving over fixed rough beds if a is allowed to vary with bed roughness and saltation height values of u c for such overriding grains are substantially less than normally accepted values the sediment transport rate equation predicts plane bed experimental data well over five orders of magnitude of ib values of a tan increase significantly from lower to upper stage plane beds due to an increase in a with suspended sediment concentration but also due to a decrease in tan with increasing transport stage and grain size as predicted by bagnold

saltation in water dynamics an evaluation of the fluid forces exerted on a bed load particle is presented the study used strobe photography to measure the kinematics of a sphere moving via saltation along the bed of an open channel flow the experiment showed that the forces of bouyancy added mass and drag could predict the particle motion the added mass force included an unusual component due to the mean shear of the open channel flow

role of near bed turbulence structure in bed load transport and bed form mechanics the interactions between turbulence events and sediment motions during bed load transport were studied by means of laser doppler velocimetry and high speed cinematography sweeps u 0 w 0 w 0 which contribute negatively to the bed shear stress and are relatively rare individually move as much sediment as sweeps of comparable magnitude and duration however and much more than bursts u 0 and inward interactions u 0 w 0 when the magnitude of the outward interactions increases relative to the other events therefore the sediment flux increases even though the bed shear stress decreases thus although bed shear stress can be used to estimate bed load transport by flows with well developed boundary layers in which the flow is steady and uniform and the turbulence statistics all scale with the shear velocity it is not accurate for flows with developing boundary layers such as those over sufficiently nonuniform topography or roughness in which significant spatial variations in the magnitudes and durations of the sweeps bursts outward interactions and inward interactions occur these variations produce significant peaks in bed load transport downstream of separation points thus supporting the hypothesis that flow separation plays a significant role in the development of bed forms

mineralogical analyses and in vitro screening tests for the rapid evaluation of the health hazard of volcanic ash at rabaul volcano papua new guinea the continuous ash and gas emissions from the tavurvur cone in rabaul caldera papua new guinea during 2007 08 raised concerns regarding how exposure would affect the respiratory health of nearby populations and impact on the environment as part of a formal evaluation of the effects of volcanic emissions on public health we investigated the potential health hazard of the ash using a suite of selected mineralogical analyses and in vitro toxicity screening tests the trachy andesitic ash comprised 2 1 6 7 vol respirable sub 4 m diameter particles the crystalline silica content was 1 9 5 0 wt cristobalite in the bulk sample with trace amounts of quartz and or tridymite scanning electron microscopy showed that the ash particles were angular with sparse fibre like particles 3 60 m max diameter observed in some samples which we confirmed to be caso4 gypsum at 6 wt in the bulk samples and not asbestiform fibres the ash specific surface area was low 0 1 2 7 m2 g 1 the leached solution from one of the ash samples was slightly acidic ph 5 6 but did not contain high levels of toxic metals such as f cu zn mn as ni and cd when compared to previously tested volcanic ash leachates ash samples generated potentially harmful hydroxyl radicals through an iron mediated catalytic reaction in the range of 0 15 2 47 mol m 2 after 30 min of reaction however measurement of particle oxidative capacity potential oxidative stress reaction using ascorbic acid and silica like injury to red blood cells erythrolysis assay i e measurement of cell death nevertheless revealed low biological reactivity the findings suggest that acute exposure to the ash would have a limited potential to exacerbate pre existing conditions such as asthma or chronic bronchitis and the potential for chronic exposure leading to silicosis was low

sediment transport and shear stress partitioning in a vegetated flow vegetation is a common feature in natural coastal and riverine water ways interacting with both the water flow and sediment transport however the physical processes governing these interactions are still poorly understood which makes it difficult to predict sediment transport and morphodynamics in a vegetated environment we performed a simple experiment to study how sediment transport responds to the presence of flexible single blade vegetation and how this response is influenced by the vegetation density we found that the skin friction and sediment transport are reduced in a plant patch and that this effect is larger for denser vegetation we then evaluated several methods to calculate the skin friction in a vegetated flow which is the key to sediment transport prediction among these the inversion of bed load transport formulas and the einstein and banks 1950 methods appeared to produce the most reasonable values of the skin friction finally we suggest using the parameter which is the ratio of the skin friction computed by these methods to the total bed shear stress to make more realistic sediment transport predictions in morphodynamic models

using lagrangian particle saltation observations for bedload sediment transport modelling a lagrangian model for the saltation of sand in water is proposed simulated saltation trajectories neglecting particle rotation and turbulence effects compare fairly well with experimental observations the model for particle motion is coupled with a stochastic model for particle collision with the bed such that a number of realizations of the saltation process can be simulated numerically model predictions of mean values and standard deviations of saltation height length and streamwise particle velocity agree fairly well with experimental observations model predictions of the dynamic friction coefficient are also in good agreement with experimental observations but they underestimate the value of 0 63 proposed by bagnold for this coefficient the saltation model is applied to the estimation of bedload transport rates of sand using a bagnoldean formulation modelled values of the bedload transport rates overestimate those predicted by commonly used bedload formulae which appears to be a consequence of problems in the definition of the dynamic friction coefficient these results seem to indicate a few problems with the bagnoldean formulation particularly regarding the continuum assumption for the bedload layer which would be valid only for very high particle concentrations and small particle diameters and also regarding the evaluation of the shear stress exerted on the bed by the saltating particles 1998 john wiley sons ltd

large eddy simulation of sediment transport currents over ripples a large eddy simulation has been performed to study the detailed sediment dynamics that occur in channel flow over ripples the code solves the navier stokes equations and an advection diffusion equation for the sediment and has been verified to produce quantitatively accurate hydrodynamic results for the flow domains used in this study the main features of interest in this flow are seen because of the high resolution of the grid especially near the ripple boundary this yields a detailed bottom shear stress distribution properly identified coherent structures and resolved sharp gradients in the sediment concentration globally the sediment is carried up into the flow from locations where the shear stress is high on the upslopes of ripple crests and is advected downstream by the current and upward by the vertical velocity component regions of positive vertical velocity are associated with gortler vortices which represent a significant sediment transport mechanism in this flow

discrete particle model for sheet flow sediment transport in the nearshore fully three dimensional discrete particle computer simulations of high concentration sheet flow transport in oscillatory flows quantify the effect of fluid acceleration on bed load transport in highly unsteady flows typical of nearshore marine environments a simple impulse momentum approach explains simulation results and forms the basis for adding an acceleration related term to widely used energetics sediment transport formulae transport predicted by the acceleration term becomes increasingly significant as wave shape approaches the sawtooth profile characteristic of surf zone bores simulations integrate f ma and a corresponding set of equations for the torques for each sphere normal and tangential forces between contacting particles are linear functions of the distance between sphere centers and the relative tangential displacement at the contact point respectively particle interactions are both inelastic and frictional pressure gradient forces generated by the passage of surface gravity waves drive fluid and particle motion in a stack of thin horizontal fluid layers that exchange momentum and exert fluid drag added mass and buoyancy forces on particles transport properties of the simulated granular fluid assemblage are robust to large variations in material properties of the particles simulated transport rates agree with available experimental data for unsteady transport of coarse sands the mode of bed load motion dispersion of bed load particles and particle segregation by size and density are qualitatively consistent with available particle scale observations of bed load transport of natural particles

the dwyka group in the northern part of kwazulu natal south africa sedimentation during late palaeozoic deglaciation abstract multiple sedimentary sequences up to and over 300 m thick and comprising the late palaeozoic dwyka group in the southeastern part of the african subcontinent were deposited during deglaciation of the gondwana ice sheet attention is focused on the northern part of kwazulu natal in south africa where the dwyka group represented by glaciogenic deposits rests on an uneven surface of archaean basement rocks these deposits occur on the northwestern flank of an elongate pre dwyka crustal downwarp which had a significant influence on the mode of sedimentation as it progressively subsided stratigraphic sections from selected localities in northern kwazulu natal display the thickness variations and marked vertical and lateral lithofacies changes that characterise the dwyka group of this region diamictite consistently occurs at the base of the dwyka sequences but is also interstratified with mainly arenaceous and conglomeratic lithotypes which predominate in the upper 60 160 m these heterolithic sequences reflect sedimentation from a retreating marine ice sheet during a rise in relative sea level which commenced towards the close of the carboniferous period in southwestern gondwana as the margin of the ice sheet receded towards an archaean upland region in the northwest this ice mass was locally grounded and stabilised on bathymetric highs of the irregular basement topography release of glacial debris produced diachronous sedimentary sequences as the ice sheet was temporarily pinned on successive basement highs during its episodic retreat matrix and clast supported conglomerates and associated sandstones testify to a plexus of sediment gravity flow and subaqueous outwash processes that occurred near the grounding line thick homogeneous blanket like diamictite facies in the southeastern and southern part of the region suggest an unimpeded retreat of the sediment laden marine sheet in the deeper parts of the basin rapid dissipation of the ice in the closing stages of deglaciation was followed by accumulation of postglacial muds which mantled the glaciogenic sediments in the northernmost part of the study area proximal products of deglaciation represented by conglomeratic deposits and associated sandstones are preserved in deep partly exhumed glaciated valleys and depressions along the southern periphery of the archaean upland the distinctive character of the dwyka group in northern kwazulu natal is partly attributable to the complex tectonic setting in which it occurs and reflects an interplay of various factors that controlled the styles of sedimentation during deglaciation

the nature and formation of cristobalite at the soufriere hills volcano montserrat implications for the petrology and stability of silicic lava domes cristobalite is commonly found in the dome lava of silicic volcanoes but is not a primary magmatic phase its presence indicates that the composition and micro structure of dome lavas evolve during and after emplacement nine temporally and mineralogically diverse dome samples from the soufriere hills volcano shv montserrat are analysed to provide the first detailed assessment of the nature and mode of cristobalite formation in a volcanic dome the dome rocks contain up to 11 wt cristobalite as defined by x ray dif fraction prismatic and platy forms of cristobalite identified by scanning electron microscopy sem are commonly found in pores and fractures suggesting that they have precipitated from a vapour phase feathery crystallites and micro crystals of cristobalite and quartz associated with vol canic glass identified using sem raman are interpreted to have formed by varying amounts of devitrification we dis cussmechanismsof silicatransport and cristobaliteformation and their implications for petrological interpretations and domestability we conclude 1 that silica maybetransported in the vapour phase locally or from one part of the magmatic system to another 2 that the potential for transport of silica into the dome should not be neglected in petrological and geochemical studies because the addition of non magmatic phases may affect whole rock composition and 3 that the extent of cristobalite mineralisation in the dome at shv is sufficient to reduce porosity hence permeability and may impact on the mechanical strength of the dome rock thereby potentially affecting dome stability

numerical simulation of turbulence and sediment transport of medium sand a model of sand transport in water is produced by combining a turbulence resolving large eddy simulation les with a discrete element model dem prescribing the motion of individual grains of medium sand the momentum effect of each particle on the fluid is calculated at the les cell containing the particle and the fluid velocity and pressure interpolated to each particle center is used to derive fluid force on each particle in the dem eleven numerical experiments are conducted of an initially flat bed of particles the experiments span a range of motion from essentially no motion to vigorous suspension hydraulic roughness is found to increase abruptly at the transition from bed load to suspended load transport suspended sediment extracts momentum from the flow and decreases the rate of shear whereas slightly higher in the flow vertical drag by suspended grains damps turbulence and increases the rate of shear vertical sediment diffusivity and effective particle settling velocity are much smaller than is commonly assumed in suspended sediment models the bed load experiments suggest that saltation by itself is a poor model of bed load sand transport in contrast to expectations from saltation models the peak bed load flux occurs at essentially the same level as the bed and grains move slowly in frequent contact with other grains higher and faster moving bed load grains that can be considered to be in saltation represent a smaller portion of the total flux entrainment of bed load grains occurs in response to fluid penetration of the bed by high vorticity turbulence structures embedded within broader high speed fluid regions referred to as a sweeps or high speed wedges

late wisconsinan glaciomarine deposition and isostatic rebound northern puget lowland washington the distribution and age of glaciomarine and marine sediment in the northern puget lowland washington demonstrate that rapidretreatofcontinentalice theeverson marineincursion andhighratesofisostatic reboundoccurredbetweenabout13 600and 11 300 14 c yr b p 11 3 ka glaciomarine and marine deposits are thickest in zones where retreating ice lobes grounded in the northeast puget lowland and near large drainages glaciomarine sediment was depositedmainlyfrom 1 submarineoutwash in ice proximal zones 2 turbid underflows dispersed melt water icebergs and resedimentation in transitional zones and 3 dispersedmeltwaterandcurrentsinicedistal zones marine estuarine and emergence intertidalandbeach faciesaccumulated in areas more than 10 km from ice margins particularly near major rivers molluscan and foraminiferal assemblages intheglaciomarineandmarinedepositsindicate that turbid cool brackish water covered much of the puget lowland during the everson interval water was generally shallower 30 m in the southern part of the area and deeper 15 60 m to the north mineralogy and geochemical properties such as boron or sodium content of the gravel free fraction do not clearly distinguish glaciomarine and marine deposits from terrestrial deposits isostatic rebound rapidly lifted the glaciomarine and marine deposits through sea level between about 13 5 and 11 3 ka the presentaltitudesofradiocarbon datedshell and the marine limit show that initial rates of isostatic rebound exceeded 10 cm yr 21 in thenorthernpugetlowland butdroppedto 2cmyr 21 before 11 ka the uplift gradient is about 0 6 m km 21 to the north and steepens locally to at least 1 3 m km 21 the pattern of emergence in the northern puget lowland is anomalous locally perhaps as a result of complex isostatic effects near the glacier margin rapid rise of sea level or tectonic deformation

the respiratory health hazards of volcanic ash a review for volcanic risk mitigation studies of the respiratory health effects of different types of volcanic ash have been undertaken only in the last 40 years and mostly since the eruption of mt st helens in 1980 this review of all published clinical epidemiological and toxicological studies and other work known to the authors up to and including 2005 highlights the sparseness of studies on acute health effects after eruptions and the complexity of evaluating the long term health risk silicosis non specific pneumoconiosis and chronic obstructive pulmonary disease in populations from prolonged exposure to ash due to persistent eruptive activity the acute and chronic health effects of volcanic ash depend upon particle size particularly the proportion of respirable sized material mineralogical composition including the crystalline silica content and the physico chemical properties of the surfaces of the ash particles all of which vary between volcanoes and even eruptions of the same volcano but adequate information on these key characteristics is not reported for most eruptions the incidence of acute respiratory symptoms e g asthma bronchitis varies greatly after ashfalls from very few if any reported cases to population outbreaks of asthma the studies are inadequate for excluding increases in acute respiratory mortality after eruptions individuals with pre existing lung disease including asthma can be at increased risk of their symptoms being exacerbated after falls of fine ash a comprehensive risk assessment including toxicological studies to determine the long term risk of silicosis from chronic exposure to volcanic ash has been undertaken only in the eruptions of mt st helens 1980 usa and soufriere hills montserrat 1995 onwards in the soufriere hills eruption a long term silicosis hazard has been identified and sufficient exposure and toxicological information obtained to make a probabilistic risk assessment for the development of silicosis in outdoor workers and the general population a more systematic approach to multi disciplinary studies in future eruptions is recommended including establishing an archive of ash samples and a website containing health advice for the public together with scientific and medical study guidelines for volcanologists and health care workers

identification of varying time scales in sediment transport using the hilbert huang transform method sediment transport processes vary at a variety of time scales from seconds hours days to months and years multiple time scales exist in the system of flow sediment transport and bed elevation change processes as such identification and selection of appropriate time scales for flow and sediment processes can assist in formulating a system of flow and sediment governing equations representative of the dynamic interaction of flow and particles at the desired details recognizing the importance of different varying time scales in the fluvial processes of sediment transport we introduce the hilbert huang transform method hht to the field of sediment transport for the time scale analysis the hht uses the empirical mode decomposition emd method to decompose a time series into a collection of the intrinsic mode functions imfs and uses the hilbert spectral analysis hsa to obtain instantaneous frequency data the emd extracts the variability of data with different time scales and improves the analysis of data series the hsa can display the succession of time varying time scales which cannot be captured by the often used fast fourier transform fft method this study is one of the earlier attempts to introduce the state of the art technique for the multiple time sales analysis of sediment transport processes three practical applications of the hht method for data analysis of both suspended sediment and bedload transport time series are presented the analysis results show the strong impact of flood waves on the variations of flow and sediment time scales at a large sampling time scale as well as the impact of flow turbulence on those time scales at a smaller sampling time scale our analysis reveals that the existence of multiple time scales in sediment transport processes may be attributed to the fractal nature in sediment transport it can be demonstrated by the hht analysis that the bedload motion time scale is better represented by the ratio of the water depth to the settling velocity h w in the final part hht results are compared with an available time scale formula in literature

microstructures within a modern debris flow deposit derived from quaternary glacial diamicton a comparative micromorphological study abstract examination of a modern debris flow in comparison with a quaternary diamicton from which it has been derived reveals significant differentiating sedimentological characteristics the two sediments were examined using micromorphological analyses thin sections of the debris flow show distinct primary microstructure sets that appear indicative of debris flow processes of turbate micro deformation during flow and subsequent flow deceleration comparison of the micromorphological character of both sediments reveal many similarities but the differences seem indicative of flow processes within the active debris flow large turbate structures are common within the debris flow sediment and although many more turbate structures occur within the in situ diamicton they are smaller in size possibly indicative that those structures within the debris flow sediment are not inherited but are neo formed perhaps the most distinctive and individual characteristic separating the debris flow sediment from the older diamicton is the presence of tiled structures these structures result from downslope flow deceleration and dewatering resulting in transverse bands of clays developing in rhythmic like patterns likewise the debris flow sediment exhibits a marbled appearance presumably indicative of intense deformation a characteristic not found in the in situ quaternary diamicton

characterization of ultrafine aerosol particles in mt etna emissions particulate emissions from mt etna in the fine size range below 100 nm were studied in june and september 1989 the aerosol particles were characterized by size concentration and photoelectric activity these quantities are sensitive to the physical and chemical properties of the magma concentrations varied from 104 to 107 cm 3 the size distributions peak below 20 nm radius and are very narrow the particles are generated mainly by nucleation and condensation of magmatic volatiles in a strong temperature gradient the photoelectric activity of these particles can indicate high magma levels and increased exsolution of volatiles it is therefore related to the observed activity of the respective crater and may be helpful as a prediction tool when used in conjunction with other volcano monitoring techniques

a past millennium maximum in postglacial activity from volcan chaiten southern chile volcan chaiten southern chile 43 s initiated an historically unprecedented eruption in a d 2008 surprising the local inhabitants chilean and argentine authorities and the geologic community available data at the time indicated an absence of explosive eruptions from this rhyolitic volcano since a large magnitude eruptive event dated at ca 10 500 yr b p we present lake sediment data from lago teo a small closed basin lake located in the immediate vicinity of both chaiten township and the volcano that spans the past 10 000 yr and contains 26 pyroclastic fallout deposits glass shard electron microprobe analyses revealed ten rhyolitic tephras indistinguishable in composition from the 2008 volcan chaiten eruption and ten others potentially derived from the michinmahuida volcanic complex among the rhyolites we detected three closely spaced tephras deposited between ca 9460 and 9680 yr b p followed by two thick tephras dated at ca 7700 and ca 5080 yr b p three other closely spaced tephras occur between ca 600 and 850 yr b p the most recent prehistoric event at ca 420 yr b p and a 3 cm thick tephra deposited during the 2008 event we calculate a median recurrence of 310 yr between eruptive events from all sources over the past 10 000 yr and 200 yr between volcan chaiten events over the past millennium our results not only challenge the notion of an 10 500 yr long quiescence for volcan chaiten activity but also suggest that the 2008 eruption was an overdue phenomenon in the context of its postglacial eruptive history illustrating the advantage and absolute necessity of utilizing lake sediment archives for developing continuous well dated time series inventories of explosive volcanic events

a systematic classification of glacial and periglacial environments facies and deposits abstract several aspects of the deposits formed in the glacial and periglacial environments are presented in order to establish a framework that can be used in various disciplines dealing with sedimentation under glacial and periglacial conditions the almost unlimited number of different deposits are grouped into 37 types that are all described briefly most of them are also illustrated by field examples mainly from poland these 37 types are grouped within 23 facies belonging to 3 continental glacial 3 continental periglacial and 3 marine periglacial subenvironments all environments subenvironments facies and deposits are defined and presented with a hierarchic code that enables unambiguous definition attention is paid to both the general characteristics of the various deposits as they have been described by previous investigators and to specific deposits that have been studied by the present authors the factors influencing peri glacial sedimentation are discussed briefly

revisiting slope influence in turbulent bedload transport consequences for vertical flow structure and transport rate scaling gravity driven turbulent bedload transport has been extensively studied over the past century in regard to its importance for earth surface processes such as natural riverbed morphological evolution in the present contribution the influence of the longitudinal channel inclination angle on gravity driven turbulent bedload transport is studied in an idealised framework considering steady and uniform flow conditions from an analytical analysis based on the two phase continuous equations it is shown that i the classical slope correction of the critical shields number is based on an erroneous formulation of the buoyancy force ii the influence of the slope is not restricted to the critical shields number but affects the whole transport formula and iii pressure driven and gravity driven turbulent bedload transport are not equivalent from the slope influence standpoint analysing further the granular flow driving mechanisms the longitudinal slope is shown to not only influence the fluid bed shear stress and the resistance of the granular bed but also to affect the fluid flow inside the granular bed responsible for the transition from bedload transport to debris flow the relative influence of these coupled mechanisms allows us to understand the evolution of the vertical structure of the granular flow and to predict the transport rate scaling law as a function of a rescaled shields number the theoretical analysis is validated with coupled fluid discrete element simulations of idealised gravity driven turbulent bedload transport performed over a wide range of shields number values density ratios and channel inclination angles in particular all the data are shown to collapse onto a master curve when considering the sediment transport rate as a function of the proposed rescaled shields number

sedimentation in a subglacial lake enniskerry eastern ireland abstract field relationships between a subglacial lake fill from the enniskerry basin eastern ireland provide evidence for dynamic links between the sedimentary fill regional subglacial meltwater flow and regional ice dynamics the basin fill 6 7 km2 forms an integral part of an extensive 30 km subglacial meltwater system which developed parallel to north south ice flow along the western marginal sector of the late pleistocene irish sea glacier high magnitude sediment fluxes were directed into the subglacial lake southwards across the northern basin rim from two nye type channels and westwards by a rothlisberger type channel the resulting subaqueous fans typically consist of cones of coarse boulder gravels deposited by jet effluxes overlain by cross bedded sands and foreset gravels in places these are eroded and overlain by multistorey dish shaped channels cut and filled by subglacial meltwaters driven by a high hydrostatic head a variety of gravelly and sandy bedforms indicate that sediment migrated over efflux cores towards deeper parts of the basin facies variability within the ice proximal fans and spreads record deposition from a wide range of high and low density turbulent flows traction currents density underflows suspension and sediment gravity flows a surficial drape of winnowed diamict is related to areal resedimentation as jet effluxes closed down at one site the gravelly sequence shows a largely conformable transition upwards into glaciotectonised gravel and basal till in the lee of the basin rim elsewhere the upper part of the sediment pile is occasionally deformed by the drag of the ice roof a series of sequential events is postulated for the evolution of the subglacial drainage system and subglacial lake development initially a rock ridge transverse to ice flow resulted in the development of a relatively low pressure lee zone along the northern margin of the basin ice sheet decoupling within the basin was enhanced by water migration into this low pressure lee zone which also melted an ice roof cavity closure and maintenance of the ice roof was prevented by a fast ice flux generated by intense marine downdraw in the main ice lobe centred in the irish sea basin regional ice directed meltwater pressure gradients and erosion enhanced subglacial lake development in the lowest topographic point of the system major inlet and outlet nye type channels incised transverse to the rims of the basin testify to the intensity of ice directed drainage along the marginal sector of the irish sea glacier in a wider context the concepts of high magnitude subglacial meltwater flow coupled with high rates of debris flux invoked for the subglacial basin fill are also necessary to explain the thick tidewater sequences present in adjacent sectors of the irish sea basin

grain scale nonequilibrium sediment transport model for unsteady flow abstracta one dimensional 1d finite volume model is developed for simulating nonequilibrium sediment transport in unsteady flow the governing equations are the 1d mass and momentum conservation equations for sediment laden flow and the sediment continuity equation for both bed load and suspended load transport the rouse profile is modified to consider the nonequilibrium transport of suspended sediment the spatial lag between the instantaneous flow properties e g velocity bed shear stress and the rate of bed load transport in unsteady flow is quantified by using an adaptation length which is derived theoretically by applying the momentum principle in the bed load layer this new method for calculating the adaptation length is verified using data from several experiments and yields better results than other empirical formulas for a wide range of shear stress the nonequilibrium model is applied to simulate a series of laboratory dam break flows over erodible beds and the simulated results agree

emission of elemental gold particles from mount erebus ross island antarctica volcanoes are an important source of gases and aerosols in the atmosphere significant quantities of trace elements are emitted as vapor species nriagu 1989 symonds et al 1987 and are strongly enriched in the gas relative to the magma tazieff and sabroux 1983 crowe et al 1987 after eruption the trace elements condense on ash and other particles or they form sublimates and agglomerates here we report on the emission of gold au from mount erebus antarctica although the flux of emitted au is low compared to other volcanoes crystalline particulate au has been found in the plume near the crater in ambient air up to 1000 km from the volcano and in near surface samples vapor phase transport of au may occur as a chloride species and could be an important transport mechanism in crystallizing magmatic intrusions

resistance in flat bed sediment laden flows the effect on flow resistance in uniform flat bed open channel flows due to suspended sediment is investigated flows with and without an equilibrium sand bed are studied in a laboratory channel three well sorted natural sands are used point velocity measurements as well as estimates of local wall shear are obtained with a laser doppler anemomentry system and are used to evaluate friction factors the results indicate that contrary to recent models the presence of suspended sediment does not necessarily lead to a reduction in flow resistance but will generally result in an increase the relation between changes in the velocity profile and changes in friction factors is discussed

nanogeoscience in ore systems research principles methods and applications introduction and preface to the special issue martin reich robert m hough artur deditius satoshi utsunomiya cristiana l ciobanu and nigel j cook

occurrence of silica polymorphs nanocrystals in tuffaceous rocks province of the mesa central mexico and their formation from subcritical si rich fluids cristobalite tridymite blade nanocrystals cemented by sio2 glass and tridymite nanocrystals fill separately sio2 glass spherules released by explosive volcanism in rhyolitic tuffs from the province of the mesa central mexico this paper presents the mineralogy of silica polymorphs occurrence and process of formation in the province of the mesa central the understanding of the origin of these pure sio2 polymorphs their association with high temperature minerals fractionation of magmas and role of volatiles contribute to our knowledge on silica minerals their technological implications and damaging health effects results indicate that a precursor magma from which kyanite crystallized partitioned into an immiscible fe rich magmatic liquid that crystallized fe cordierite fe amphiboles and fayalite and into a siliceous melt that led to low temperature glasses of 78 22 80 01 wt sio2 and si al ratio 4 07 5 65 presence of amphiboles sulfur in cristobalite tridymite crystals and alunite suggest association of volatiles the crystallization of silica polymorphs is associated with the dissolution of water vapor and volatiles in the precursor magma establishing a silicate melt water system of two critical points one of them at pressure and temperature near the critical point of water and another close to the critical point of sio2 and defining a critical curve between them and supercriticality at pressures and temperatures lower than the critical point of sio2 decreasing the ambient conditions from supercritical to subcritical would have allowed the separation of liquid and gases and the crystallization of cristobalite tridymite and tridymite nanocrystals from the vapor phase cristobalite single crystals were not formed and transformation of cristobalite and trydimite to quartz did not occur we conclude that glasses did not crystallize cristobalite or tridymite components in excess of the pure phases precipitated as nanoparticles of siliceous glass forming agglomerates some containing iron hydroxides and alunogen

multiple flow and support mechanisms and the development of inverse grading in a subaquatic glacigenic debris flow subaquatic glacigenic debris flows of late wisconsinan age occur as lobes within an ice marginal glaciomarine lithofacies at victoria british columbia flow was initiated by release of supraglacial debris during an interval of glacial ablation prior to advance and deposition of lodgement till many of the lobes developed a common morphology during deposition consisting of an outer layer surrounding an inner core of rafted material in the largest lobe reworking of the sediment during flow produced improved sorting a coarsening of mean grain size and a shift in skewness toward the negative this occurred simultaneously within the core and outer layer as a result of different transformations in mechanisms of flow and support normal grading produced in the outer layer was conveyed around the nose and buried in an inverse position along the base of the flow these data enable us to present a model that may be applicable to similar flows elsewhere the flow studied demonstrates that transformations between flow types and sediment support mechanisms can occur simultaneously and serially in subaquatic debris flows

sediment suspension with rippled bed experiments on the suspension of sediment were performed in flume with and without sediment layer on the bottom for movable bed runs three dimensional sand ripples were found to affect seriously the features of suspended sediment the horseshoe vortices and the resulting bursts in the lee of the ripples entrain intermittently a large amount of sediment into the outer layer of flow details of the suspension process were studied using a sand ripple model made of plaster the result revealed that the vertical component of turbulent eddies is responsible for the suspension of sediment and the statistical distribution of the component was found to be the gaussian law the statistical distribution of the concentration fluctuation was observed to be highly skewed and the reason was determined to be the fact that the concentration increases with the power of eight against the vertical fluid velocity the period of the intermittent ejection of sediment agreed reasonably with those reported for natural geophysical flows thus the suspension of sediment in flows with rippled beds was proved to be significantly correlated with bursting phenomenon behind sand ripples

physically realistic roughness closure scheme to simulate turbulent channel flow over rough beds within the framework of les a physically realistic roughness closure method for the simulation of turbulent open channel flow over natural beds within the framework of large eddy simulation les is proposed the description of bed roughness in les is accomplished through a roughness geometry function together with forcing terms in the momentum equations the major benefit of this method is that the roughness is generated from one physically measurable parameter i e the mean grain diameter of the bed material a series of flows over rough beds for which mean flow and turbulence statistics are available from experiments is simulated measured and computed values are compared to validate the proposed roughness closure approach it is found that predicted streamwise velocity profiles turbulence intensities and turbulent shear stress profiles match the measured values fairly well furthermore the effect of roughness on the overall flow resistance is predicted in reasonable agreement with experimental values

inception of bed load motion beneath a bore abstract a tidal bore is a series of waves propagating upstream in the river mouth as the tidal flow turns to rising in macro tidal conditions some related geophysical processes include the tsunami induced bores and uprushing bores on beaches in the present study the inception of sediment motion beneath tidal bores was investigated physically no sediment motion was observed in the initially steady flow and beneath undular bores a transient sheet flow motion was observed beneath breaking bores and the onset of sediment motion was closely linked with the passage of the roller toe the forces acting on the movable gravel bed particles were estimated from the physical measurements the results showed that the longitudinal pressure gradient force was the dominant contribution de stabilising the particles and inducing the onset of sediment motion the drag force added a sizeable contribution to maintain the upstream particle motion although the entire sheet flow motion was brief

late quaternary stratigraphy and seafloor geology of eastern juan de fuca strait british columbia and washington abstract a combination of shallow sediment cores and high resolution seismic reflection data were used to identify and map four main surficial geologic units in eastern juan de fuca strait these units comprise bedrock unit 1 till diamict unit 2 glacial marine unit 3 and post glacial sediments unit 4 bedrock crops out only in nearshore environments off vancouver island diamicton forms the numerous morainal and drumlin like banks in the region a series of banks including middle and hein banks and the offshore extension of dungeness spit divide the strait into two major areas based on the dominant surficial sedimentary units post glacial sediments are most common to the east and glacial marine sediments to the west glacial marine sediments are represented by several seismo lithologic subunits that suggest progression from ice proximal to ice distal depositional environments radiocarbon dates indicate these sediments are a product of the last phase of glacier retreat there is relatively little modern sediment input to eastern juan de fuca strait so most post glacial sediments are thought to consist of material reworked from glacial outwash or eroded from shallow bank deposits this conclusion is supported by radiocarbon ages from the post glacial sediments most of which are early holocene or younger also there are sandwave fields sediment drifts and barrier spits that appear to be actively maintained the source of sediment to these features is probably the pre existing deposits that occur in banks and extensive coastal exposures

sediment characteristics and sea level history of royal roads anchorage victoria british columbia high resolution and airgun seismic reflection mapping of the approaches to esquimalt harbour juan de fuca strait reveal that offshore sea floor sediments consist of a widespread glaciomarine unit recognizable to the entrance of the strait the upper part of the unit has been dated at approximately 10 000 radiocarbon years bp an early postglacial sea level low of at least 50 m appears to have formed a widespread unconformity nearshore sediments above the unconformity consist of sands muddy fine sands and minor gravel that were deposited in a prograding marine environment sediments have been accumulating off esquimalt harbour at a rate of approximately 1 9 cm per 100 years

punctuated sand transport in the lowermost mississippi river 1 measurements of sand flux and water flow in the mississippi river are presented for a portion of the system 35 50 km upstream from the head of its subaerial delta these data are used to provide insight into how nonuniform flow conditions present in the lower reaches of large alluvial rivers affect the timing and magnitude of sand transport near the river outlet field surveys during both low and high water discharge include 1 sequential digital bathymetric maps defining mobile river bottom topography which were used to estimate bed material flux 2 multiple water velocity profiles and 3 multiple suspended sediment profiles collected using a point integrated sampler these data show that total sand transport increases by two orders of magnitude over the measured range in water discharge 11 300 to 38 400 m3 s 1 during low water discharge no sand is measured in suspension and sand discharge via bed form migration is minimal during high water discharge 54 of the sand discharge is measured in suspension while 46 of the sand discharge is part of bed form migration the component of boundary shear stress associated with moving this sediment is estimated using a set of established sediment transport algorithms and values for the total boundary shear stress are predicted by fitting logarithmic velocity functions to the measured profiles the estimates of boundary shear stress using measurements of suspended sand transport bed form transport and downstream oriented velocity profiles are internally consistent moreover the analyses show that boundary shear stress increases by nearly 10 fold over the measured water discharge range we show how this increase in shear stress is consistent with backwater flow arising where the river approaches its outlet the hydrodynamic properties of backwater flow affect the timing and magnitude of sand flux and produce punctuated sand transport through the lowermost mississippi river our field data are used to evaluate the influence of this sand transport style on development of the mixed bedrock alluvial channel for the lowermost mississippi river

gravel saltation 2 modeling a lagrangian model for the motion of a sediment particle in a water flow is proposed the particle motion equation is averaged over flow turbulence specialized to the case of coarse sediment particles saltating in water and coupled with a stochastic model for particle collision with the bed model predictions of statistics of gravel saltation generally agree well with experimental observations as an application of the saltation model bed load transport rates are estimated from modeled mean saltation streamwise velocity and a dynamic friction coefficient the results obtained compare favorably with typical bed load equations but they overestimate experimental measurements of gravel transport which would suggest that a bagnoldean formulation for bed load transport of coarse material by saltating particles may not be valid

sand transportation and reverse patterns over leeward face of sand dune abstract sand saltation has complex interactions with turbulent flow and dune form most models of wind blown sand consider ideal circumstances such as steady wind velocity and a flat surface and the bulk of data on wind flow and sand transport over an individual dune has focused mostly on the influence of dune shape or inter dune space on the wind flow neglecting the effect of morphology on sand saltation particularly airflow and sand transportation over the leeward slope wind flow structures over the leeward slope of sand dunes have a fundamental influence on the organization of sand dunes in order to understand sand dune dynamics lee face airflow and sediment transportation should be paid more attention previous field observations could not measure turbulent flow structure well because of the limited observation points and the influence of experiment structure on wind field in addition the reverse sand particles over leeward face could not be collected by sand trap in field numerous field observations could not measure turbulent flow structure because of the limited observation points and the influence of experimental structures on the wind field in addition the reverse transport of sand particles over leeward face could not be collected by sand traps in field therefore this paper aims to investigate the turbulent flow structure and sand transport pattern over the leeward slope a numerical model of sand saltation over slope terrain is constructed which also considers the coupling effects between air flow and sand particles the large eddy simulation method is used to model turbulent flow sand transport is simulated by tracking the trajectory of each sand particle the results show that terrain significantly alters the turbulent air flow structure and wind blown sand movement especially over the leeward slope here mass flux increases initially and then decreases with height in the reversed flow region in the direction of wind flow and the mass flux decreases with height in the reversed direction the height of 0 5 h is the height of vortex core in the reversed flow region the vortex core is a critical point in the flow region where few particles are transited in the reversed region the reversed mass flux of sand particles is 25 of the mass flux in the flow direction this research may contribute to scientific understanding of the mechanisms of sand motion and wind flow over leeward of dune and it is likely to be significant in desertification control

the respiratory health hazard of tephra from the 2010 centennial eruption of merapi with implications for occupational mining of deposits ashfall into heavily populated areas during the october november 2010 eruption of merapi volcano indonesia created anxiety regarding the growing impacts to health as the eruption escalated and the hazard zone widened we made a preliminary assessment of the respiratory hazards to human health of the tephra deposits ashfall lahar and pdc surge from the eruption using a laboratory protocol specifically developed to study the toxic potential of volcanic ash particles twenty samples collected from a range of locations were analysed for health pertinent mineralogical parameters grain size crystalline silica content morphology surface area bulk chemistry and leachable elements and bio reactivity hydroxyl radical generation haemolytic potential oxidative capacity pro inflammatory response the grain size pertinent to respiratory health was variable ranging from 1 4 15 6 vol sub 4 m and 3 0 28 9 vol sub 10 m diameter material no fibre like particles were observed cristobalite was present in all samples ranging from 1 9 9 5 wt but surface reactivity and in vitro toxicity assays showed low reactivity for all samples tested the risk of direct exposure to ash from fallout was in any case low due to seasonal rains limiting its re suspension and the immediate and effective clean up of communities by local people who supplied the ash to the indonesian construction industry for use as aggregate however mining of the lahar and thick pdc deposits in the valleys draining the volcano is performed on a vast industrial scale which could result in high occupational exposure to thousands of sand miners at merapi during the dry seasons further study of the health hazard of the mined merapi deposits is warranted

nature and classification of waterlain glaciogenic sediments exemplified by pleistocene late paleozoic and late precambrian deposits this study of waterlain glaciogenic sediments is designed to present both a review and new information on glaciogenic subaquatic deposits of differing age in a number of localities in north and south america and south africa the late paleozoic glaciogenic deposits of the parana basin in brazil and the karoo basin of south africa are singled out for special attention as they show a reasonably complete lateral sequence of terrestrial to off shore glaciogenic sedimentation although the environment of subaquatic glaciogenic sedimentation varies from one area to the next certain common elements are found which can be used to develop a generalized model for both glaciomarine and glaciolacustrine sedimentation for descriptive purposes the model is divided into two broad categories a shelf facies and a basinal facies the shelf facies is marked by massive diamicton ite which may be 200 m or more in thickness and which is frequently overlain by a complex of clastic sediments consisting primarily of gravity and fluid flows the basinal facies is marked by products of subaquatic slumps and more distal turbidites and glaciomarine sediments new terminology is introduced the massive diamicton ite which is diagnostic of the shelf facies probably represents deposition from the base of active ice in a subaquatic environment and is termed undermelt diamicton ite the gravity and fluid flows which are usually found overlying undermelt diamicton ite and in the basinal facies are subdivided into six categories glaciogenic subaquatic outwash glaciogenic suspension flow glaciogenic chaotic debris flow glaciogenic subaquatic debris flow glaciogenic slurry flow and glaciogenic turbidity flow the relative abundance of undermelt diamicton ite and the various types of gravity and fluid flows can be used to define inner shelf outer shelf inner basin and outer basin facies of glaciomarine sedimentation

submarine flow tills at victoria british columbia sea cliffs at victoria expose submarine flow tills within an ice contact complex of flow till outwash proglacial cones interbedded with dinoflagellate bearing glaciomarine fine sediments glacial debris flow lobes mainly flow tills were formed by supraglacially englacially and basally transported sediment slumping off an ice margin grounded in the strait of juan de fuca the structures and textures reveal that lobes formed by a conveyor mechanism in some lobes a double sorting phenomenon apparently developed involving an outer winnowed layer of pseudo plastic flow around an inner core of till that was sorted by dewatering and expulsion of fines outward from the centre during flow structures and fabric data indicate lobe travel was gravitationally controlled down cone flanks and independent of ice movement a depositional model for the complex proposes the ice margin produced a proglacial apron of interdigitating cones which accumulated on the sea floor sediment facies variations were probably c

late pleistocene glaciolacustrine sedimentation and paleogeography of southeastern michigan usa abstract the geomorphic stratigraphic and sedimentological characteristics of glaciolacustrine sediments in the metropolitan detroit michigan area were studied to determine environments of deposition and make paleogeographic reconstructions nine lithofacies were identified and paleoenvironments interpreted based on their morphostratigraphic relationships with relict landforms the sediments studied are found southeast of the defiance and birmingham moraines lying beneath a lowland characterized by a low morainal swell detroit moraine and a series of lacustrine terraces that descend progressively in elevation southeastward the glaciolacustrine sediments were deposited approximately 14 3 12 4 ka bp during the port bruce and port huron glacial phases of late wisconsinan time and are related to proglacial paleolakes maumee arkona whittlesey warren wayne grassmere lundy and rouge the glaciolacustrine section is typically 2 4 m thick and consists of a basal unit of wavy bedded clayey diamicton overlain by a surficial deposit of stratified and cross stratified sand and gravel the basal unit is comprised of subaqueous debris flow deposits that accumulated as subaqueous moraine in paleolake maumee along the retreating front of the huron lobe the surficial deposits of sand and gravel were formed by traction resulting from lacustrine wave activity and fluvial processes in lakebed plain beach ridge and deltaic depositional settings much of the lake margin sand and gravel was derived from clayey diamicton by lacustrine wave action and winnowing and that associated with paleolakes of the port huron phase is largely reworked port bruce sediment paleogeographic reconstructions show that the defiance birmingham and detroit moraines defiance and rochester channels and the rochester delta were deposited penecontemporaneously as paleolake maumee expanded northward across the map area a unique type of wavy bedform is characteristic of clayey diamicton deposited by subaqueous mass flow in the study area that is useful for differentiating sediment 1 deposited by mass flow in subaqueous vs subaerial settings and 2 deposited by subaqueous mass flow vs basal till these bedforms are a useful tool for identifying subglacial meltwater deposits and facilitate the mapping and correlation of glacial sediments based on till sheets the map area provides a continental record of ice sheet dynamics along the southern margin of the laurentide ice sheet during heinrich event h 1 the record reveals rapid glacial retreat 0 8 km yr contemporaneous with the discharge of a large volume of meltwater evidence in the study area for subglacial meltwater is problematic but indications that periglacial conditions persisted in the map area until 12 7 ka bp and extended for 200 km or more south of the ice front suggest that a frozen substrate may have contributed to instability of the lis

terrestrial or waterlain glacial diamictites three case studies from the late precambrian and late ordovician glacial drifts in west africa abstract three examples of extensive diamictites within glacial sequences well exposed in the sedimentary cover of the west african cratonic platform are described they belong to the late precambrian and upper ordovician glacial periods and the paleogeography is summarized the late precambrian diamictites of the jbeliat group in adrar of mauritania displays characteristics of tillite deposited as lodgement or melt out till detail studies on structure clast shape nature and fabric texture in thin section clay mineralogy and carbonate content are given and discussed in order to delimitate useful criteria for tillite identification compared to this first example the two other diamictites from the late precambrian bakoye group in western mali and from the upper ordovician tichit group in southeastern mauritania have obviously been deposited in an aquatic environment waterlain glacial diamictites by the action of ice rafting bottom current and flow processes these examples show that for such ancient deposits sedimentological interpretations are partly solved by broad scale stratigraphical relationships however detailed sedimentological analyses remain essential for precise facies identification especially structural and petrographic studies must be encouraged in the lights of modern glaciodynamic processes

glacimarine processes and inductive lithofacies modelling of ice shelf and tidewater glacier sediments based on quaternary examples abstract three variables control the type of glacial debris source and where and when debris is introduced to an ocean 1 type of glacial ice source ice sheet or valley glacier 2 condition of a grounded glacier melting freezing or frozen base and cold or warm internal ice and 3 type of glacier front ice shelf or tidewater using these variables in different combinations eight glacimarine regimes are postulated to exist by integrating information from holocene sediment and pleistocene glacimarine sequences with the eight inductive regimes lithofacies relationships are predicted and modelled the models show a complexity of glacimarine lithofacies the importance of recognizing this complexity lies in realistic interpretations of ancient sequences ice shelf sediment may be limited in the geologic record because of tectonic and climatic constraints required for ice shelf formation alternatively in some tidewater glacier regimes larger volumes of glacimarine sediment are produced than in ice shelf regimes ice proximal sediment is distinctive especially near subglacial meltwater stream effluxes ice shelves and tidewater glaciers may produce similar ice proximal lithofacies e g morainal bank associations and laminites in certain regimes however details of lithofacies may aid in distinguishing ice shelf from tidewater regimes ice shelf and tidewater iceberg zone sediment can be distinguished from each other if basal and high level englacial debris can be distinguished ice shelf zone sediment out from the grounding line has a basal debris source high level englacial debris is deposited in more distal ice shelf zones resulting in sediment by pass in corresponding positions of a tidewater glacier regime iceberg rafted debris comprises mixed basal and high level englacial debris deeper water zones receive large volumes of sediment when a melting freezing base grounding line is at the edge of a continental shelf when the grounding line retreats sediment supply may be drastically reduced because of a back sloping continental shelf and trapping by morainal banks cool water bioclastic carbonates may accumulate once a grounding line has retreated although ice shelf iceberg zones are more extensive than those in tidewater regimes ice shelf icebergs have low debris content and resulting ice rafted debris may be scarce the smallest volume of sediment is produced by a frozen base ice sheet ending as a tidewater front and the largest volume by a melting freezing base valley tidewater glacier glacimarine sediment has a relatively high preservation potential near continental interiors or margins however at continental margins mass flow olistostrome and tectonic melange deposits may be preserved with glacimarine diamictites these deposits may be difficult to distinguish from each other especially if metamorphosed such as at a convergent margin the models presented do not fully represent the glacimarine environment because many other variables are omitted however the principal concepts of generating glacimarine lithofacies associations are considered continued research will verify if each regime exists and will provide data on those regimes that exist today to compare and modify these models

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

entrainment and motion of coarse particles in a shallow water stream down a steep slope we investigate the entrainment deposition and motion of coarse spherical particles within a turbulent shallow water stream down a steep slope this is an idealization of bed load transport in mountain streams earlier investigations have described this kind of sediment transport using empirical correlations or concepts borrowed from continuum mechanics the intermittent character of particle transport at low water discharges led us to consider it as a random process sediment transport in this regime results from the imbalance between entrainment and deposition of particles rather than from momentum balance between water and particles we develop a birth death immigration emigration markov process to describe the particle exchanges between the bed and the water stream a key feature of the model is its long autocorrelation times and wide frequent fluctuations in the solid discharge a phenomenon never previously explained despite its ubiquity in both nature and laboratory experiments we present experimental data obtained using a nearly two dimensional channel and glass beads as a substitute for sediment entrainment trajectories and deposition were monitored using a high speed digital camera the empirical probability distributions of the solid discharge and deposition frequency were properly described by the theoretical model experiments confirmed the existence of wide and frequent fluctuations of the solid discharge and revealed the existence of long autocorrelation time but theory overestimates the autocorrelation times by a factor of around three particle velocity was weakly dependent on the fluid velocity contrary to the predictions of the theoretical model which performs well when a single particle is moving for our experiments the dependence of the solid discharge on the fluid velocity is entirely controlled by the number of moving particles rather than by their velocity we also noted significant changes in the behaviour of particle transport when the bed slope or the water discharge was increased the more vigorous the stream was the more continuous the solid discharge became moreover although 90 of the energy supplied by gravity to the stream is dissipated by turbulence for slopes lower than 10 particles dissipate more and more energy when the bed slope is increased but surprisingly the dissipation rate is nearly independent of fluid velocity a movie is available with the online version of the paper

coeval brittle and ductile deformation beneath the late wisconsinan puget lobe washington state usa late wisconsinan glacial sediments exposed on whidbey island and camano island puget sound washington state usa were deposited in a proglacial shallow marine outwash environment during northward retreat of the puget lobe of the cordilleran ice sheet sediments mainly comprise massive and cross bedded sand and gravels and rhythmically bedded clay and silt fine sand couplets interbedded with diamictons that were deposited by a range of mass flows of different viscosities although sediment stratigraphy and ice advance retreat patterns are well established for the puget lobe brittle and ductile deformation structures within and separating these sediment units are less well understood these structures record the nature of ice bed interactions taking place in subglacial and proglacial environments this study examines evidence for these processes and environments key deformation structures identified include open to overturned folds normal and reverse faults clastic dikes and hydrofractures and passive loading structures evidence for coeval development of ductile and brittle deformation structures shows the close relationship between porewater changes sediment rheology and sediment system responses to changes in strain caused by ice bed interactions

the fluid dynamics of river dunes a review and some future research directions 1 dunes are present in nearly all fluvial channels and are vital in predicting flow resistance sediment transport and deposition within many rivers progress in understanding the fluid dynamics associated with alluvial dunes has been significant in the last 15 years and has witnessed huge advances in field laboratory and numerical investigations progress has been made in detailing the principal features of mean and turbulent flow over asymmetric dunes that possess flow separation in their leesides and how these forms affect both downstream boundary layer structure and stress partitioning over the dune additionally the links between sediment transport over dunes and instantaneous coherent flow structures are being increasingly understood with the feedback of dune three dimensionality upon flow and sediment dynamics over these bed forms beginning to be recognized as vital such research now provides an outstanding background for beginning to address areas of greater complexity that will enable a fuller understanding of these important natural features this review paper summarizes the principal features of mean and turbulent flow over alluvial sand dunes five areas are then highlighted and discussed as a possible focus for future research 1 the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field 2 the influence of three dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress 3 flow field modification resulting from bed form superimposition and amalgamation 4 the scale and topology of dune related turbulence and its interactions with sediment transport and the flow surface and 5 the influence of suspended sediment on the dune flow field and dune morphology

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

grain size variations in north atlantic non carbonate sediments and sources of terrigenous components abstract fine silt to medium sand grain size spectra of the carbonate free fractions of 115 sea bed samples from the northern north atlantic the labrador sea and baffin bay can be explained as mixtures of five distinct end members the five end members resemble combinations of grain size modes which are characteristic of till matrix dreimanis and vagners 1972 therefore the ultimate source of most of the terrigenous deep sea sediments in the study area is probably the veneer of glacial comminution products on the surrounding continents three sand rich end members exhibit patterns of distribution that are largely compatible with the modern transport of ice rafted debris as inferred from iceberg drift observations the best sorted of those sandy end members however also appears to be concentrated in regions characterized by high energy turbidity and contour currents and so may also represent hydraulically winnowed sediment the distribution of two lutite end members appears in general to reflect the transport of fines by moderate to low energy thermohaline currents although in baffin bay and the northeastern north atlantic the lutite could have accumulated primarily in turbidites ice rafting by icebergs calved from greenland glaciers the reworking of glacigenic sediments on the iceland faeroes ridge and injection of turbid glacial meltwater into deep baffin bay from west greenland fiords are suggested as the principal means of introduction of clastic particles into the sediment distribution redistribution budget of the deep north atlantic

cristobalite in a rhyolitic lava dome evolution of ash hazard prolonged and heavy exposure to particles of respirable crystalline silica rich volcanic ash could potentially cause chronic fibrotic disease such as silicosis in individuals living in areas of frequent ash fall here we show that the rhyolitic ash erupted from chaiten volcano chile in its dome forming phase contains increased levels of the silica polymorph cristobalite compared to its initial plinian eruption ash erupted during the initial explosive phase 2 5 may 2008 contained approximately 2 wt cristobalite whereas ash generated after dome growth began from 21 may 2008 contains 13 19 wt the work suggests that active obsidian domes crystallise substantial quantities of cristobalite on time scales of days to months probably through vapour phase crystallisation on the walls of degassing pathways rather than through spherulitic growth in glassy obsidian the ash is fine grained 9 7 17 7 vol 4 m in diameter the respirable range and the particles are mostly angular sparse fibre like particles were confirmed to be feldspar or glass

submarine flow tills at victoria british columbia reply during winter to maintain the same average position over a year perhaps these cones originated by slumps on the foreslope of subaquatic outwash fans similar to those postulated by aario 1972 and rust and romanelli 1975 for a glacimarine setting the small proportion of traction current deposits may be due to subglacial streams not having a sufficiently high sediment concentration to maintain an underflow away from the efflux occasionally the streams were sufficiently dense to deposit outwash sand and gravel in the foreslope area the gravity flows may have incorporated the stream gravel sand and mud as well as melt out debris from englacial and basal debris layers mixing of these sources during liquefaction perhaps induced by iceberg calving powell 1980 p 70 may produce poorly sorted sediment flows thick accumulation by supraglacial melt out from debris layers in a tidewater glacier may best occur where the glacier has almost retreated from the sea and ablation occurs primarily by surface melting rather than iceberg calving the situation in facies association 111 of powell 1981 a similar situation of ice in shallow water under mid latitude temperature conditions was envisaged by evenson et al 1977 to explain stratified quaternary tills although their interpretation has been questioned gibbard 1980 here the glacial regime and processes are similar to those of the terrestrial environment mudflows and debris flows may occur from the ice surface and retain their integrity whilst flowing down a shallower though still relatively steep slope into shallow water if such deposits are not modified by wave action and remain preserved then they may indicate proximity to sea level in a similar way to deltaic plains

cristobalite in volcanic ash of the soufriere hills volcano montserrat british west indies crystalline silica mostly cristobalite was produced by vapor phase crystallization and devitrification in the andesite lava dome of the soufriere hills volcano montserrat the sub 10 micrometer fraction of ash generated by pyroclastic flows formed by lava dome collapse contains 10 to 24 weight percent crystalline silica an enrichment of 2 to 5 relative to the magma caused by selective crushing of the groundmass the sub 10 micrometer fraction of ash generated by explosive eruptions has much lower contents 3 to 6 percent of crystalline silica high levels of cristobalite in respirable ash raise concerns about adverse health effects of long term human exposure to ash from lava dome eruptions

ice marginal sedimentation and processes of diamicton deposition in large proglacial lakes lake erie ontario canada detailed studies of coastal cliff exposures through two end moraines form the basis for a model of ice marginal sedimentation in large ice contact glacier fed lakes the input to the ice marginal environment directly from the glacier included subglacial till and subaquatic flow tills the subaquatic flow till thinly bedded diamicton was deposited in an apron up to 1 km wide along the ice margin an upward gradient of pore water pressure immediately beyond the ice margin causing heaving and dilation of the sediments initiated debris flows of glacially derived debris subaquatic flow tills most of the stratified sediments in the ice marginal zone entered the lake by way of a large proglacial stream sedimentation was dominated by quasi or near continuous density underflows that resulted in the deposition of a sequence of thick rhythmites the glacier in the lake erie basin most likely behaved like an ice stream with its movement controlled predominantly by a deforming bed of glacial debris separa

glacial and postglacial stratigraphy of dinosaur provincial park and surrounding plains southern alberta canada abstract thirty one stratigraphic logs from the dinosaur provincial park area reveal seven major lithofacies associations lfa s lfa 1 is a preglacial fluvial deposit recording deposition on a sandy braided floodplain this lfa fines upwards to lfa 2 a glacilacustrine deposit which records the first advance of laurentide glacier ice into the region erosional contacts between lfa s 1 and 2 and bedrock suggest that large expanses of badlands may have existed prior to glaciation lfa 3 is a grey till which together with glacitectonized bedrock records ice movement from the northeast lfa 4 represents supraglacially derived diamictons and outwash its oxidized colour indicates either a considerable period of subaerial weathering or groundwater activity and the deposit is tentatively assigned an interstadial or interglacial age a second glaciation is recorded by lfa 5 heterogeneous diamicton and lfa 6 homogeneous diamicton lfa 5 records a period of subglacial molding and then cavity filling by fluvial and debris flow deposits lfa 6 records lodgement and melt out of the same glacier ice after it had glacitectonically thrust large rafts of older lfa s the sequence of molding cavity fill tectonism melt out represents large scale decoupling of the glacier from its bed and later surges creating extensive deformation of the substrate melt out was interrupted in some places by remobilization caused by surges which continued throughout ice retreat lfa s 7a 7e record deposition in glacilacustrine fluvial pond and aeolian environments after deglaciation some previously reported and new radiocarbon dates on regional and local surface drainage are discussed with reference to fluvial incision and holocene climate all lfa s are tentatively correlated with stratigraphic sequences reported from adjacent areas of southern alberta and former regional glaciodynamics are assessed

influence of turbulence on bed load sediment transport this paper summarizes the results of an experimental study on the influence of an external turbulence field on the bed load sediment transport in an open channel the external turbulence was generated by 1 a horizontal pipe placed halfway through the depth ih 2 a series of grids with a clearance of about one third of the depth from the bed and extending over a finite length of the flume and 3 a series of grids with a clearance in the range 0 1 1 0 ih from the bed but extending over the entire length of the flume two kinds of experiments were conducted plane bed experiments and ripple covered bed experiments in the former case the flow in the presence of the turbulence generator was adjusted so that the mean bed shear stress was the same as in the case without the turbulence generator in order to single out the effect of the external turbulence on the sediment transport in the ripple covered bed case the mean and turbulence quantities of the streamwise component of the velocity were measured and the shields parameter due to skin friction was determined the shields parameter together with the rms value of the streamwise velocity fluctuations was correlated with the sediment transport rate the sediment transport increases markedly with increasing turbulence level

characterization of respirable volcanic ash from the soufriere hills volcano montserrat with implications for human health hazards volcanic ash generated in the long lived eruption of the soufriere hills volcano montserrat is shown to contain respirable sub 4 m particles and cristobalite a crystalline silica polymorph respirable particles of cristobalite can cause silicosis raising the possibility that volcanic ash is a respiratory health hazard this study considers some of the main factors which affect human exposure to respirable volcanic ash namely the composition and proportions of respirable ash and the composition and concentrations of airborne suspended particulates the composition size distribution and proportion by weight of respirable particles in representative samples of the soufriere hills tephra dome collapse ash fall deposits dome collapse pyroclastic flow matrix vulcanian explosion ash and mixed ash have been characterized dome collapse ash fall deposits are significantly richer in respirable particles 12 wt than the other tephra samples in particular the matrices of dome collapse pyroclastic flow deposits 3 wt within the respirable fraction dome collapse ash contains the highest proportion of crystalline silica particles 20 27 number of which 97 wt is cristobalite compared with other primary tephra types 0 4 5 6 number this enrichment of crystalline silica in the dome collapse ash is most pronounced in the very fine particle fraction sub 2 m the results are explained as being due to significant size fractionation during fragmentation of pyroclastic flows resulting in a fines depleted dome collapse matrix and a fines rich dome collapse ash deposit for all sample types the sub 4 m fraction comprises 45 55 wt of the sub 10 m fraction aeolian deposit lahar deposit and airborne samples of suspended ash collected on filters were characterized these samples show enrichment of crystalline silica in the respirable fraction 10 18 number the results are consistent with ash in the environment having a mixed origin but originating predominantly from dome collapse eruptions the reworked ash however contains low proportions of respirable ash 3 wt compared to primary ash samples the concentration of ash particles re suspended by road vehicles on montserrat is found to decrease exponentially with height above the ground indicating higher exposure for children compared with adults pm4 concentration at 0 9 m height of two year old child is 3 times that at 1 8 m adult height the composition of the re suspended road particles is similar to that re suspended by the wind

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

formation of cristobalite nanofibers during explosive volcanic eruptions high resolution transmission electron microscopy hrtem observations of unaltered volcanic air fall deposits from the ongoing lava dome explosive eruption at chaiten volcano chilean patagonia revealed the presence of highly crystalline silica nanofibers in the respirable fraction of the volcanic ash 240 c beta form of cristobalite with average lengths of hundreds of nanometers and widths on the order of tens of nanometers we propose that the beta cristobalite nanofibers are formed during explosive eruptions by the reduction of amorphous silica by carbon monoxide to its reactive suboxide sio which is later oxidized to form one dimensional crystalline silica nanostructures nucleation and growth of the nanofibers are enhanced by the high surface area of the micrometer to nanometer sized fragments of silica glass in the volcanic column the formation of nanocrystalline cristobalite fibers during explosive lava dome eruptions poses new challenges for the assessment of the short and long term health hazards associated with the respirable nanofibrous components of volcanic ash

submarine debris flow deposits from the upper carboniferous dwyka tillite formation in the kalahari basin south africa four types of sediment gravity flow deposits occur interbedded with rhythmite shale siltsone mudstone and minor diamictite in a 230 m thick carboniferous glacial sequence shear and plug zones are present in the cohesive debris flow deposits which have a diamictic texture the high density turbidity flow deposits which consist of coarse to medium grained clastics are characterized by both normal and reverse grading the medium to fine grained low density turbidity flow deposits show normal grading and consist of bouma units a b d and e deposition occurred by gravity flow suspension settling and minor basal melt out during ice retreat along the southern margin of the kalahari basin immediately basinwards of the ice grounding line a proximal diamictite facies consisting predominantly of cohesive and high density turbidity flow deposits and minor melt out tills formed a distal sedimentary facies of graded sandstone and siltstone units deposited by low density turbidity flows and suspension settling of muds with ice rafted debris is located basinwards

cristobalite in the 2011 2012 cordon caulle eruption chile cristobalite is a low pressure high temperature polymorph of sio2 found in many volcanic rocks its volcanogenic formation has received attention because 1 pure particulate cristobalite can be toxic when inhaled and its dispersal in volcanic ash is therefore a potential hazard and 2 its nominal stability field is at temperatures higher than those of magmatic systems making it an interesting example of metastable crystallization we present analyses by xrd sem epma laser raman and synchrotron ct of representative rhyolitic pyroclasts and of samples from different facies of the compound lava flow from the 2011 2012 eruption of cordon caulle chile cristobalite was not detected in pyroclasts negating any concern for respiratory hazards but it makes up 0 23 wt of lava samples occurring as prismatic vapour deposited crystals in vesicles and or as a groundmass phase in microcrystalline samples textures of lava collected near the vent which best represent those generated in the conduit indicate that pore isolation promotes vapour deposition of cristobalite mass balance shows that the sio2 deposited in isolated pore space can have originated from corrosion of the adjacent groundmass textures of lava collected down flow were modified during transport in the insulated interior of the flow where protracted cooling additional vesiculation events and shearing overprint original textures in the most slowly cooled and intensely sheared samples from the core of the flow nearly all original pore space is lost and vapour deposited cristobalite crystals are crushed and incorporated into the groundmass as the vesicles in which they formed collapse by strain and compaction of the surrounding matrix holocrystalline lava from the core of the flow achieves high mass concentrations of cristobalite as slow cooling allows extensive microlite crystallization and devitrification to form groundmass cristobalite vapour deposition and devitrification act concurrently but semi independently both are promoted by slow cooling and it is ultimately devitrification that most strongly contributes to total cristobalite content in a given flow facies our findings provide a new field context in which to address questions that have arisen from the study of cristobalite in dome eruptions with insight afforded by the fundamentally different emplacement geometries of flows and domes

particles in the great pinatubo volcanic cloud of june 1991 the role of ice 1 pinatubo s 15 june 1991 eruption was earth s largest of the last 25 years and it formed a substantial volcanic cloud we present results of analysis of satellite based infrared remote sensing using advanced very high resolution radiometer avhrr and tiros operational vertical sounder high resolution infrared radiation sounder 2 tovs hirs 2 sensors during the first few days of atmospheric residence of the pinatubo volcanic cloud as it drifted from the philippines toward africa an so2 rich upper 25 km portion drifted westward slightly faster than an ash rich lower 22 km part though uncertainty exists due to difficulty in precisely locating the ash cloud the pinatubo clouds contained particles of ice ash and sulfate which could be sensed with infrared satellite data multispectral ir data from hirs 2 were most useful for sensing the pinatubo clouds because substantial amounts of both ice and ash were present ice and ash particles had peak masses of about 80 and 50 mt respectively within the first day of atmospheric residence and declined very rapidly to values that were 10 mt within 3 days ice and ash declined at a similar rate and it seems likely that ice and ash formed mixed aggregates which enhanced fallout sulfate particles were detected in the volcanic cloud by ir satellites very soon after eruption and their masses increased systematically at a rate consistent with their formation from so2 which was slowly decreasing in mass during the same period the initially detected sulfate mass was 4 mt equivalent to 3 mt so2 and after 5 days was 12 16 mt equivalent to 9 12 mt so2

bed load at low shields stress on arbitrarily sloping beds failure of the bagnold hypothesis 1 the bagnold hypothesis has been a major tool in the development of mechanistic models of bed load transport according to the hypothesis a necessary constraint for the maintenance of equilibrium bed load transport is that the fluid shear stress at the bed must be reduced to the critical or threshold value associated with incipient motion of grains the constraint determines a functional form for the areal concentration of bed load grains as a function of flow parameters it is shown here however that the bagnold hypothesis breaks down when applied to equilibrium bed load transport on beds with transverse slopes above a relatively modest value that is well below the angle of repose in particular under such conditions it is shown that no areal concentration no matter how large is sufficient to reduce the fluid shear stress at the bed to the critical value this failure motivates the abandonment of the bagnold constraint even for nearly horizontal beds the framework presented here however provides a natural basis for an entrainment based model of sediment transport that neither satisfies nor suffers from the drawbacks of the bagnold constraint

quantification of the bed load effects on turbulent open channel flows with a computational model combining large eddy simulation and a discrete element model detailed quantification of the bed load effects on turbulent open channel flows is presented the objective is the revelation of bed load particle impact on the mean flow properties and coherent structures two comparative numerical experiments with mobile and immobile beds are conducted mean properties e g velocity and reynolds stress profiles show good agreement with experimental data comparing the mobile and immobile cases the effective bed position is nearly the same whereas the equivalent sand roughness is changed the flow experiences higher bottom shear stress over immobile bed to quantify impact on turbulent structures a revised quadrant analysis is performed to calculate four key parameters of ejection and sweep events duration maximum shear stress transported momentum and period results show that the ejection and sweep events have comparable importance in the outer region however sweep becomes dominant in the near wall region the motion of particles enhances the sweep dominance by breaking up the ejection structures and decreasing their occurrence ratio the results also suggest that the ejection events are easier to be influenced by the particle motions because they originate from the near wall region the duration maximum shear stress and transported momentum decrease close to the bed the period remains relatively constant in the outer region but decreases near the bed visualization of the coherent structure reveals that the instantaneous particle motion has strong correlation with the bursting cycle events

facies architecture in depositional systems resulting from the interaction of acidic springs alkaline springs and acidic lakes case study of lake roto a tamaheke rotorua new zealand the facies architecture in hot spring systems tends to become more varied and complicated as the degrees of freedom in the system increase discharge aprons fed by waters from a single vent will for example be characterized by predictable downslope facies changes that reflect downslope changes in water chemistry and temperature the facies architecture however becomes exponentially more intricate when more factors start to impact the system this phenomenon is readily apparent in the geothermal area around lake roto a tamaheke located in the whakarewarewa thermal village rotorua new zealand where the facies architecture developed in response to the interactions between acid lake acid hot spring and alkaline hot spring depositional regimes with additional extraneous sediment being brought into the area by volcanic ash clouds wind blown pollen and surface run off from the surrounding drainage basin much of the complexity in the facies architecture of this system stems from the temporal varianc

sakurajima volcano a physico chemical study of the health consequences of long term exposure to volcanic ash regular eruptions from sakurajima volcano japan repeatedly cover local urban areas with volcanic ash the frequency of exposure of local populations to the ash led to substantial concerns about possible respiratory health hazards resulting in many epidemiological and toxicological studies being carried out in the 1980s however very few mineralogical data were available for determination of whether the ash was sufficiently fine to present a respiratory hazard in this study we review the existing studies and carry out mineralogical geochemical and toxicological analyses to address whether the ash from sakurajima has the potential to cause respiratory health problems the results show that the amount of respirable 4 m material produced by the volcano is highly variable in different eruptions 1 1 18 8 vol the finest samples derive from historical plinian eruptions but considerable amounts of respirable material were also produced from the most recent vulcanian eruptive phase since 1955 the amount of cristobalite a crystalline silica polymorph which has the potential to cause chronic respiratory diseases is 3 5 wt in the bulk ash scanning electron microscope and transmission electron microscope imaging showed no fibrous particles similar to asbestos particles surface reactivity tests showed that the ash did not produce significant amounts of highly reactive hydroxyl radicals 0 09 1 35 mol m 2 at 30 min in comparison to other volcanic ash types a basic toxicology assay to assess the ability of ash to rupture the membrane of red blood cells showed low propensity for haemolysis the findings suggest that the potential health hazard of the ash is low but exposure and respiratory conditions should still be monitored given the high frequency and durations of exposure