normal and anomalous diffusion of gravel tracer particles in rivers received 12 december 2008 revised 16 november 2009 accepted 10 december 2009 published 4 may 2010 1 one way to study the mechanism of gravel bed load transport is to seed the bed with marked gravel tracer particles within a chosen patch and to follow the pattern of migration and dispersal of particles from this patch in this study we invoke the probabilistic exner equation for sediment conservation of bed gravel formulated in terms of the difference between the rate of entrainment of gravel into motion and the rate of deposition from motion assuming an active layer formulation stochasticity in particle motion is introduced by considering the step length distance traveled by a particle once entrained until it is deposited as a random variable for step lengths with a relatively thin e g exponential tail the above formulation leads to the standard advection diffusion equation for tracer dispersal however the complexity of rivers characterized by a broad distribution of particle sizes and extreme flood events can give rise to a heavy tailed distribution of step lengths this consideration leads to an anomalous advection diffusion equation involving fractional derivatives by identifying the probabilistic exner equation as a forward kolmogorov equation for the location of a randomly selected tracer particle a stochastic model describing the temporal evolution of the relative concentrations is developed the normal and anomalous advection diffusion equations are revealed as its long time asymptotic solution sample numerical results illustrate the large differences that can arise in predicted tracer concentrations under the normal and anomalous diffusion models they highlight the need for intensive data collection efforts to aid the selection of the appropriate model in real rivers

celldym a room temperature operating cryogenic cell for the dynamic monitoring of snow metamorphism by time lapse x ray microtomography monitoring the time evolution of snow microstructure in 3 d is crucial for a better understanding of snow metamorphism we therefore designed a cryogenic cell that precisely controls the experimental conditions of a sample while it is scanned by x ray tomography based on a thermoelectrical regulation and a vacuum insulation the cell operates at room temperature it is thus adaptable to diverse scanners offering advantages in terms of imaging techniques resolution and speed three dimensional time lapse series were obtained under equitemperature and temperature gradient conditions at a 7 8 m precision the typical features of each metamorphism and the anisotropic faceting behavior between the basal and prismatic planes known to occur close to 2 c were observed in less than 30 h these results are consistent with the temperature fields expected from heat conduction simulations through the cell they confirm the cell s accuracy and the interest of relatively short periods to study snow metamorphism

silk producing stream insects and gravel erosion significant biological effects on critical shear stress there is growing evidence for impacts of small stream organisms on the transport of fine sediments however such impacts on the transport of coarser sediments remained unconsidered therefore we studied whether a silk producing stream insect hydropsyche siltalai consolidated gravel through silk fixed among gravel pieces we exposed gravel for 2 months in a stream along a gradient of hydropsyche abundance and measured the critical shear stress for this gravel in a laboratory flume the critical gravel shear stress was very significantly p 7 7 10 11 related to a variable overall biomass describing gravel consolidation by hydropsyche silk we showed that hydropsyche in a range of abundance typical of many streams increases critical shear stress for gravel by as much as a factor of 2 surface gravel arrangement i e the spatial distribution and orientation of different gravel sizes and forms had a less significant impact on critical shear stress while other sediment variables so far considered in erosion had no significant impact future studies on the transport of solids and on habitat conditions should consider the high potential of stream invertebrates to consolidate gravel

soil moisture wind speed and depth hoar formation in the arctic snowpack basal depth hoar that forms in arctic snowpacks often has a low thermal conductivity strongly contributing to the snowpack thermal insulance and impacting the permafrost thermal regime at ward hunt island canadian high arctic 83 05 n 74 07 w almost no depth hoar was observed in spring 2016 despite favorable thermal conditions we hypothesize that depth hoar formation was impeded by the combination of two factors 1 strong winds in fall that formed hard dense wind slabs where water vapor transport was slow and 2 low soil moisture that led to rapid ground cooling with no zero curtain period which reduced soil temperature and the temperature gradient in the snowpack comparisons with detailed data from the subsequent winter at ward hunt and from bylot island 73 09 n 80 00 w and with data from barrow and alert indicate that both high wind speeds after snow onset and low soil moisture are necessary to prevent arctic depth hoar formation the role of con vection to form depth hoar is discussed a simple preliminary strategy to parameterize depth hoar thermal conductivity in snow schemes is proposed based on wind speed and soil moisture finally warming induced vegetation growth and soil moisture increase should reduce depth hoar thermal conductivity potentially affecting permafrost temperature

particle clusters in gravel bed rivers an experimental morphological approach to bed material transport and stability concepts structured gravel river beds clearly exert a major influence on bed stability indexing structural stability by field measurements of bed strength neglects the processes operating to entrain and transport bed material in different parts of each structure this study takes a morphological approach to interpreting the critical processes using particle tracing to determine the movement of individual cluster particles over a range of flood event magnitudes and durations the experiment was carried out on the river south tyne uk it uses flow hydrographs measured nearby and also benefits from previous studies of historical development channel morphology and sediment transport at the same site more than 30 clusters were monitored over a seven month period during which clusters occupied 7 16 per cent of the bed threshold flows delimiting three apparently contrasting bed sediment process regimes for cluster particles are tentatively set at 100 m3 s 1 and 183 m3 s 1 durations of flow at these levels are critical for cluster development rather than flow peak values wake particles are transported most easily flow straightening in the wandering channel planform reduces the stability of clusters since mechanical strength is markedly reduced by this change of direction the overall area covered by clusters between significant transport events varies little implying a dynamic equilibrium condition copyright 2005 john wiley sons ltd

grain size and topographical differences between static and mobile armour layers a series of laboratory flume experiments under conditions of sediment starvation zero sediment feeding and recirculation were conducted in order to identify the temporal evolution and surface properties of static and mobile armour layers the experiments were carried out in an 8 m long flume using a bimodal grain size mixture d50 6 2 mm and a range of shear stresses ranging from 4 0 to 8 6 n m 2 the results confirm that a static armour layer is coarser than a mobile one and that the grain size of a mobile armour layer is rather insensitive to changes in the imposed flow strength an analysis of laser scan bed surveys revealed the highly structured and imbricated nature of the static armour layer under these conditions the vertical roughness length scale of the bed diminished and it became topographically less complex at higher forming discharges the topography of mobile armour layers created by rising discharges differed they exhibited a greater roughness length scale and were less organized despite the fact that the grain size of the surface material maintained an approximately constant value during recirculation also the mobile armour tended to create larger cluster structures than static armour layers when formed by higher discharges these differences were mainly due to the transport of the coarser fraction of bed sediments which diminished to zero over the static armour because of being hidden within the bed whereas in the mobile armour the coarser particles protruded into the flow and were actively transported increasing the vertical roughness length scale overall the results show that an examination of the grain size characteristics of armour layers cannot be used to infer sediment mobility and bed roughness detailed elevation models of exposed surfaces of gravel bed rivers are required to provide critical insight on the sediment availability and sedimentation processes copyright 2011 john wiley sons ltd

a nonlocal theory of sediment buffering and bedrock channel evolution 1 bedrock erosion in mountain river channels ultimately sets the erosion rate of the surrounding hillslopes and the rate of sediment supply to the channels the supply of coarse bed sediment acts as a dampening effect on further erosion by depositing an alluvial cover that temporarily obscures the bedrock for landscapes where the residence time of the alluvial bed cover is comparable to the timescale of bedrock incision coarse sediment supply and transport generate a strong negative feedback on fluvial downcutting and the coupled process of hillslope channel erosion is inherently self buffering here we study a simple model of self buffered bedrock channel erosion that incorporates the spreading of bed sediment cover downstream in a way that allows for a broad tailed power law probability distribution of transport velocities of bed sediment over the long term this leads us to consider a nonlocal transport law fractional advection parameterized by a scaling exponent 0 1 which collapses to local advection for 1 for strong sediment buffering we find that nonlocality 1 has a direct control on the power law scaling of channel slope s with upstream area a giving s a 1 2 at steady state empirical observations of slope area scaling are consistent with 1 and nonlocal transport in general the model predicts linear logarithmic or power law stream profiles depending on the extent of buffering the degree of nonlocality and the scaling of the bedrock erosion law it also predicts somewhat counterintuitively that bed cover should thicken with distance x downstream slower than linearly as x i e the more nonlocal the bed sediment spreading process 0 the slower the bed cover increases downstream we deduce that long range heterogeneous transport of coarse sediment in mixed bedrock alluvial rivers may be a key element of landscape scaling and an important factor in landscape dynamics

tomography based characterization of ice air interface dynamics of temperature gradient snow metamorphism under advective conditions snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow which alters its microstructure and physical properties a functional understanding of this process is essential for many disciplines from modeling the effects of snow on regional and global climate to assessing avalanche formation time lapse x ray microtomography was applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions experiments specifically analyzed sublimation and deposition of water vapor on the ice structure in addition an analysis of the ice air interface dynamics was carried out using a macroscopic equivalent model of heat and water vapor transport through a snow layer the results indicate that sublimation of the ice matrix dominated for flow rates 10 6 m3 s 1 while during increased mass flow rates the water vapor deposition supplied by the advective flow counteracted sublimation a flow rate dependence of water vapor deposition at the ice interface was observed asymptotically approaching an average estimated maximum deposition rate on the whole sample of 1 05 10 4 kg m 3 s 1 the growth of microsized whisker like crystals on larger ice crystals was detected on microscope photographs leading to an increase of the specific surface area and thus suggest a change of the physical and optical properties of the snow the estimated values of the curvature effect of the ice crystals and the interface kinetic coefficient are in good agreement with previously published values

modeling sediment entrainment and transport processes limited by bed armoring abstract a sediment transport model including a bed armoring algorithm is used to ascertain the potential importance of bed armoring processes the parameters that control the bed armoring effects on the suspension of granular sediments in the marine environment are examined using the numerical model and data from the eel shelf results for the shelf indicate that bed armoring controls the total suspended sediment load and affects the across shelf gradients of suspended material the armoring effects are too significant to be neglected in most analyses of shelf and nearshore sediment transport and this is especially relevant for models that are developed to represent large scale and long term sedimentary regimes a principal controlling parameter is the thickness of the active layer and the dynamics of this layer are not well known

stabilizing self organized structures in gravel bed stream channels field and experimental observations stable reticulate structures which we call stone cells have been observed in cobble gravel channel beds with low bed material transport rates experiments show that such structures develop simultaneously with the armor layer during an extended period when flows do not exceed the shields threshold by more than 2 times so that bed material transport is low they are constructed by particles moving from less stable positions into more stable configurations against each other intermediate developments include clusters and stone lines they reduce sediment transport by orders of magnitude and are evidently a major stability promoting mechanism in gravel channels the timescale for their development suggests that the boundaries of many gravel bed channels are not in equilibrium with recent competent flows but reflect the history of recent dominant flows

chemical characteristics of the crater lakes of popocatetetl el chichon and nevado de toluca volcanoes mexico abstract three crater lakes from mexican volcanoes were sampled and analyzed at various dates to determine their chemical characteristics strong differences were observed in the chemistry among the three lakes nevado de toluca considered as dormant el chichon at a post eruptive stage and popocatepetl at a pre eruptive stage not surprisingly no influence of volcanic activity was found at the nevado de toluca volcano while the other volcanoes showed a correlation between the changing level of activity and the evolution of chemical trends low phs so 4 2 and f decreased irregularly at el chichon from 1983 until 1997 major cations concentrations also diminished at el chichon a 100 increase in the so 4 2 content was measured at popocatepetl between 1985 and 1994 an increase in the mg cl ratio between 1992 mg cl 0 085 and 1994 mg cl 0 177 was observed at popocatepetl before the disappearance of the crater lake in 1994 it is concluded that chemical analysis of crater lakes may provide a useful additional tool for active volcano monitoring

field evidence for rapid downstream fining of river gravels through selective transport doubts have been expressed about the ability of either abrasion or sorting to explain strong downstream fining of river gravels we describe pronounced fining over a short distance in a scottish river that has no human disturbance or lateral input of water and sediment measured abrasion rates are far too small to explain observed downstream fining but bed load trap measurements and the dispersion of magnetic tracer pebbles in six subreaches both show sorting during transport the observed downstream fining is also simulated well by a numerical sediment routing model using hydraulic and transport laws consistent with our field measurements the geomorphological cause of the strong fining is slope reduction above a local base level control in this common situation the development of downstream fining is part of the river9s tendency to minimize downstream variation in bed load transport rates and can proceed far more rapidly than the major aggradation otherwise required for equilibration

temperature measurements and heat transfer in near surface snow at the south pole to study near surface heat flow on the antarctic ice sheet snow temperatures were measured at south pole station to a depth of 3 m at 15 min intervals during most of 1992 solar heating and water vapor transport were negligible during the 6 month winter as was inter grain net thermal radiation leaving conduction as the dominant heat transport mechanism the rate of temperature change at depth over 15 min intervals was smaller than that at the surface by one order of magnitude at 20 cm depth and two orders of magnitude at 1 m depth a finite difference model with conduction as the only heat transfer mechanism and measured temperatures as the upper and lower boundary conditions was applied to foursets of three thermistors each the thermal conductivity was estimated as that which minimized the difference between modeled and measured 15 min changes in temperatures at the center thermistor the thermal conductivity obtained at shallow depths above 40 cm was lower than that given by existing parameterizations based on density probably because the snow grains were freshly deposited cold and poorly bonded a model using only vertical conduction explains on average 87 ofthe observed 15 min temperature changes at less than 60 cm depth and 92 below 60 cm the difference between modeled andmeasured temperature changes decreased with depth the discrepancies between model and observation correlated more strongly with the air snow temperature difference than with the product of that difference with the square of the wind speed suggesting that the residual errors are due more to non vertical conduction and to sub grid scale variabilis of the conductivity than to windpumping the residual heating rate not explained by the model of vertical conduction exceeds 0 2 w m 3 only in the top 60 cm of the near surface snow

a tempered multiscaling stable model to simulate transport in regional scale fractured media 1 accurate and efficient simulation of contaminant transport in fractured rock is practically important yet current approaches suffer from numerical constraints that limit the full inclusion of fracture network properties at the regional scale we propose a multidimensional transport model nonlocal in space and time which describes complex transport behavior in fractured media at regional scales without introducing the computational burden of explicitly incorporating individual rock fractures the model utilizes a direction dependent tempered stable process to describe the transition of multiscaling anomalous diffusion to asymptotic diffusion limits applications show that the model can capture efficiently the transient superdiffusion found in two dimensional synthetic fracture networks and suggest that the truncation of leading plume edges is related to fracture network properties

early formation of preferential flow in a homogeneous snowpack observed by micro ct we performed x ray microtomographic observations of wet snow metamorphism during controlled continuous melting and melt freeze events in the laboratory three blocks of snow were sieved into boxes and subjected to cyclic superficial heating or heating cooling to reproduce vertical water infiltration patterns in snow similarly to natural conditions periodically samples were taken at different heights and scanned results suggest that wet snow metamorphism dynamics are highly heterogeneous even in an initially homogeneous snowpack consistent with previous work we observed an increase with time in the thickness of the ice structure which is a measure of grain size however this was coupled with large temporal scatter between consecutive measurements of the specific surface area and of the statistical moments of grain thickness distributions because of marked differences in the right tail grain thickness distributions did not show shape invariance with time contrary to previous analyses in our experiments wet snow metamorphism showed two strikingly different patterns homogeneous coarsening superimposed by faster heterogeneous coarsening in areas that were affected by preferential percolation of water liquid water movement in snow and fast structural evolution may be thus intrinsically coupled by early formation of preferential flow at local scale these observations suggest that further experiments are highly needed to fully understand wet snow metamorphism and infiltration patterns in a natural snowpack

snow metamorphism under alternating temperature gradients morphology and recrystallization in surface snow 1 the composition of the lower atmospheric boundary layer can be strongly influenced by snow photochemistry surface snow where air snow interactions take place is viewed as slowly changing quasi isothermal snow implied by the observation of mainly rounded snow crystals the role of snow for photochemistry is therefore expected to be purely geometric however large temperature gradients are often observed in these layers which would imply high recrystallization and faceting in controlled laboratory experiments we showed that temperature gradients on the order of 100 k m 1 do not lead necessarily to faceting if their sign changes with a daily cycle the shape of snow crystals does not reflect necessarily the metamorphic process with time lapse x ray tomography recrystallization rates as high as 60 of the total ice mass were observed during 12 hours the high recrystallization rates in apparently isothermal snow not only contradict the current understanding of snow metamorphism they also might influence chemical air snow interactions

bedload entrainment travel lengths step lengths rest periods studied with passive iron magnetic and active radio tracer techniques this paper reports results from bedload transport investigations with active radio and passive iron magnetic tracers in the lainbach a step pool mountain river in bavaria southern germany the spatial distributions of the iron tracers after flood events can be best described by exponential or gamma distributions there is some indication of a tendency of size selective transport of the iron tracers but there is also a considerable amount of scatter in the correlations between weight size and travel length owing to the masking influence of other variables such as the shape of the particles and different positions in the river bed the experiments with artificial magnetic tracers showed that elongated pebbles rods had the longest mean transport distance platy ones discs remained relatively close to the starting points the particles from the pool showed the greatest transport lengths and a 100 per cent chance of being eroded the pebble transmitter system petsy consists of transmitters implanted into individual pebbles a computerized receiver a stationary antenna system with an antenna switchboard and a data logging system the particles do not move continuously but in a series of transport steps and non movement intervals a single value for a given size class is not adequate to describe the critical conditions of entrainment under natural circumstances a probability approach is much more suitable the critical unit discharges total discharge divided by active channel width along the measuring reach are dependent on river bed morphology in the steps bedload needs higher unit discharges to be entrained once entrained the transport of bedload is stochastic in nature and the single particle transport is controlled by the step lengths and the duration of rest periods the distributions of both parameters can be approximated by exponential functions applying the stochastic concept proposed by einstein the mean values of the random variables step length and duration of rest period measured with the petsy technique were used for the simulation of spatial distributions of bedload particles from point sources more field and laboratory data are needed to include varying flow and roughness conditions with tracers representing different particle characteristics

a general power equation for predicting bed load transport rates in gravel bed rivers 1 a variety of formulae has been developed to predict bed load transport in gravel bed rivers ranging from simple regressions to complex multiparameter formulations the ability to test these formulae across numerous field sites has until recently been hampered by a paucity of bed load transport data for gravel bed rivers we use 2104 bed load transport observations in 24 gravel bed rivers in idaho to assess the performance of eight different formulations of four bed load transport equations results show substantial differences in performance but no consistent relationship between formula performance and degree of calibration or complexity however formulae containing a transport threshold typically exhibit poor performance furthermore we find that the transport data are best described by a simple power function of discharge from this we propose a new bed load transport equation and identify channel and watershed characteristics that control the exponent and coefficient of the proposed power function we find that the exponent is principally a factor of supply related channel armoring transport capacity in excess of sediment supply whereas the coefficient is related to drainage area a surrogate for absolute sediment supply we evaluate the accuracy of the proposed power function at 17 independent test sites

first study of the heat and gas budget for sirung volcano indonesia with at least four eruptions over the last 20 years sirung is currently one of the more active volcanoes in indonesia however due to its remoteness very little is known about the volcano and its hyperacid crater lake we report here on the first measurements of gas and heat emissions from the volcano notable is the substantial heat loss from the crater lake surface amounting to 220 mw in addition 17 gg of so2 representing 0 8 of indonesian volcanic so2 contribution into the atmosphere 11 gg of h2s 17 gg of co2 and 550 gg of h2o are discharged into the atmosphere from the volcano annually the volatiles degassed from sirung magmas are subjected to hydrothermal fluid rock interactions and sulfide depositions initiated by the disproportionation of so2 these processes lead to distinct gas compositions and changing lake water chemistry in the sub craters and the main crater lake however the occurrence of so2 rich fluids and strong gas flux appear to highlight a rapid fluid transfer to surface avoiding re equilibration with lower temperature rocks fluids in the conduits

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

fractional dispersion equation for sediment suspension this study proposes a stochastic approach to simulate sediment vertical dispersion in turbulent solid liquid flows by developing a fractional advection diffusion equation fade to characterize the dynamics of sediment suspension the fade is a generalization of the traditional advection diffusion equation ade where the first order spatial derivative is replaced with a fractional derivative of order alpha 0 alpha 1 many previous investigations of sediment suspension in steady sediment laden flows apply the classic or improved rouse equation which was derived from the traditional ade by assuming fick s first law for the sediment dispersive flux recent observations in field and laboratory studies however have indicated that large errors may arise from the traditional ade when applied to flows with coarse sediments instead the vertical dispersion of suspended sediment is most likely a space nonlocal transport process in flows with turbulent bursting because particle vertical jumps with ejection events are no longer constrained to a small distance defined by the representative elementary volume in other words the vertical random displacements of suspended particles follow levy motion instead of brownian motion after validating against field measurements in the las vegas wash as well as a set of published experimental data we find that the proposed fractional model can describe the real world vertical distribution of suspended sediment concentration in steady turbulent flows c 2013 elsevier b v all rights reserved

the temperature gradient metamorphism of snow vapour diffusion model and application to tomographic images a simple physical model describing the temperature gradient metamorphism of snow is presented this model based on kelvin s equation and fick s law takes into account the local variation of the saturating vapour pressure with temperature it can determine locally whether the ice is condensing or subliming depending on both the pressure and temperature fields in the snow structure this model can also explain the formation of facets that occurs during the metamorphism using x ray microtomo graphic images of snow samples obtained under low to moderate temperature gradient conditions this model has been tested and compared to the reaction limited model proposed in a previous work

an assessment of sediment transport processes in the lower mekong river based on deposit grain sizes the cm technique and flow energy data abstract the lower mekong river has been an important research topic for at least 15 years notably in the fields of hydrology fluvial geomorphology and the impact of dams recent papers refer mostly to the impact of the lancang chain of hydroelectric dams constructed on the chinese section of the river among the pending scientific questions are 1 the upstream downstream variations in the concentration and yield of suspended sediment and 2 the relative importance of sand in the total yield the general consensus among the scientific community is that the relative importance of sand in suspended load is not the main scientific concern despite its extensive presence in the mekong river channel as noted by geomorphologists and despite its extreme importance for the stability of the delta shoreline in viet nam this paper contradicts the general consensus its objective is to present new information on the processes of sand transport in the lower mekong channel imagery field observations sampling on the river banks and grain size analysis of sand deposits have been carried out between chiang sean downstream of the chinese border and the delta the c m image technique served to discriminate between the various transport processes bedload and different types of suspension this technique helps in understanding the changing processes responsible for downstream sediment transfer in river channels the results of this study are the following 1 discrepancies in the values of annual suspended sediment load detected by different gauging stations have not yet been satisfactorily explained the cm image technique indicates that grain size and the quantity of sand transiting in suspension vs bedload vary from upstream to downstream 2 these upstream downstream differences may be related to the energy of floods energy helps to explain longitudinal variations in the relative importance of the different modes of transport and serves to distinguish between bedload graded and uniform suspension and wash load 3 the mekong is seen as a river carrying mostly silt and clay however the results suggest that sand plays a major role in downstream sediment transfer during floods this result is in line with the large amounts of sand present in the channel its relative importance in the total yield must be reassessed as suggested by walling 2005 2008 as may be expected the role of sand in the stability of the delta shoreline is of prime importance

radio tracking gravel particles in a large braided river in new zealand a field test of the stochastic theory of bed load transport proposed by einstein hans a einstein initiated a probabilistic approach to modelling sediment transport in rivers his formulae were based on theory and were stimulated by laboratory investigations the theory assumes that bed load movement occurs in individual steps of rolling sliding or saltation and rest periods so far very few attempts have been made to measure stochastic elements in nature for the first time this paper presents results of radio tracing the travel path of individual particles in a large braided gravel bed river the waimakariri river of new zealand as proposed by einstein it was found that rest periods can be modelled by an exponential distribution but particle step lengths are better represented by a gamma distribution einstein assumed an average travel distance of 100 grain diameters for any bed load particle between consecutive points of deposition but larger values of 6 7 m or 150 grain diameters and 6 1 m or 120 grain diameters were measured for two test particle sizes together with other available large scale field data a dependence of the mean step length on particle diameter relative to the d50 of the bed surface was found during small floods the time used for movement represents only 2 7 of the total time from erosion to deposition the increase in percentage of time being used for transport means that it then has to be regarded in stochastic transport models tracing the flow path of bed load particles between erosion and deposition sites is a step towards explaining the interactions between sediment transport and river morphology copyright 2001 john wiley sons ltd

volcano hydrothermal system and activity of sirung volcano pantar island indonesia abstract sirung is a frequently active volcano located in the remote parts of western timor indonesia sirung has a crater with several hydrothermal features including a crater lake we present a timeseries of satellite images of the lake and chemical and isotope data from the hyperacid hydrothermal system the fluids sampled in the crater present the typical features of hyperacidic systems with high tds low ph and 34s h s o 4 34s s 0 among the highest for such lakes the cations concentrations are predominantly controlled by the precipitation of alunite jarosite silica phases native sulfur and pyrite which dominate the shallow portions of the hydrothermal system these minerals may control shallow sealing processes thought to trigger phreatic eruptions elsewhere sparse mg cl and so4 cl ratios and lake parameters derived from satellite images suggest gradual increase in heat and gas flux most likely so2 rich prior to the 2012 phreatic eruption an acidic river was sampled 8 km far from the crater and is genetically linked with the fluids rising toward the active crater this river would therefore be a relevant target for future remote monitoring purposes finally several wells and springs largely exceeded the world health organization toxicity limits in total arsenic and fluoride

evolution of the specific surface area of snow during high temperature gradient metamorphism the structural evolution of low density snow under a high temperature gradient over a short period usually takes place in the surface layers on clear cold nights in this paper x ray computed microtomography microct was combined with numerical simulations to investigate the temperature gradient metamorphism tgm on different types of snow precipitation particles pp small rounded particles rgsr and large rounded particles rglr were each observed in high temperature gradients 100 500 k m 1 at a mean temperature of 4 c the specific surface area ssa was used to characterize the tgm which were influenced by both the magnitude of the temperature gradient and the initial snow structures pp samples experienced a logarithmic decrease of ssa with time and the depth hoar structures created under high tgm 500 k m 1 have higher ssa compared to those under lower tgm unlike previous observations for initial rounded and connected structures like rglr samples the ssa increased during tgm simulated normal vapor flux distributions for different snow types were used to help understand the structural evolution under tgm understanding the ssa increase is important in order to predict the enhanced uptake of chemical species by snow or increase in snow albedo

sediment transport storage relations for degrading gravel bed channels 1 in a drainage network sediment is transferred through a series of channel valley segments natural sediment storage reservoirs that are distinguished from their neighbors by their particular capacity to store and transport sediment we propose that the sediment transport capacity of each reservoir is a unique positive function of storage volume which influences sediment mobility and availability through variations in bed surface texture channel gradient and availability of valley floor sediments for erosion examinations of the form of transport storage relations of degrading alluvial reservoirs using published field studies flume experiments and simulations support a conceptual model that includes two phases in phase i filled channels respond to variations in supply primarily by changes in stored sediment volume with little change in transport rate in phase ii channel mobility is responsive to supply through armoring and form roughness although these phases could represent idealized transport limited phase 1 or supply limited phase ii states we propose that every alluvial reservoir responds to changes in sediment inputs by changing both storage and transport rate the propensity for either depending on reservoir characteristics and the sediment exchange processes in the channel transport storage relations for phase ii are approximately linear but examination of numerical simulations and flume experiments indicates that armoring imparts positive curvature simulations of degradation of an alluvial reservoir with channel and valley floor surfaces indicate that interactions between channel lowering and lateral erosion are critical in the manifestation of a transport storage relation better knowledge of transport storage relations could lead to improved sediment routing models for drainage basins wherein component sediment reservoirs dynamically adjust to varying sediment loads

size selective entrainment of bed load in gravel bed streams entrainment of mixed size gravel bed material was studied in nine reaches of three high power streams in scotland and norway paired measurements of at a point shear stress estimated from velocity profiles and bed load transport by hand held sampler were made they extended to very high values 400 n m 2 3 5 kg m x s x analyses of maximum bed load diameter mean bed load diameter transport rates of individual size fractions and tracer pebble movements all show some dependence of threshold shear stress for entrainment on absolute particle size despite strong relative size effects precise equal mobility of all sizes was approached in the data set with the highest shear stresses and transport rates size selective transport in the streams studied is also indicated by clear downstream and downbar reductions in surface sediment size over distances too short for abrasion to be significant

sediment feed and recirculating flumes fundamental difference two standard modes of laboratory sediment transport flume operation are sediment feed and recirculating in the case of uniform sediment the final equilibriums achieved in the two modes are equivalent and independent of initial conditions even though the specified flow and sediment constraints differ when the sediment consists of a mixture of sizes however this symmetry breaks down in a sediment feed flume both the feed rate and size distribution are specified by the user and must be identical to those of the bed load at final equilibrium the final state thus becomes independent of initial conditions in a recirculating flume however the equilibrium size distribution of neither the bed load nor the bed surface material can be specified in advance as a result the final state depends on the initial conditions and can include the possibility of partial transport the equilibriums themselves are equivalent in that they obey the same laws of flow and sediment transport their ia priori n predictability however differs due to the difference in governing constraints when fractional transport is scaled by the bulk size distribution the two flume modes may produce very different transport relations even for the same sediment a consistent approach requires that the transport be scaled by the size distribution of the bed surface

chemical and isotopic compositions of volcanic gases from the east sunda and banda arcs indonesia the easternmost sunda arc and the banda arc represent a continent arc collision zone where magma genesis is influenced by subducted continent derived material chemical and isotopic studies of volcanic gas samples from this environment provide information on the sources of volatiles in arc magmas these volcanic gases some of which last equilibrated at magmatic temperatures are characterized by anomalous low sup 3 he sup 4 he values but by common arc values of c s approx 2 4 delta sup 13 c approx minus 3 per thousand and delta sup 34 s sub tot approx 5 per thousand abundant helium and high he ar ratios are consistent with the subduction of terrigenous components in local sediments or slivers of continental crust although individual concentration and isotope ratios of volatile components may be explicable by complex fractionation in the recycling process the combined data are in agreement with an important role of subducted sedimentary source components comparison of the authors results with volcanic gas data from other arcs indicates that the carbon and sulfur signals in arc gases are relatively insensitive to the amount and nature of sediment on the subsiding plate hence a contribution to arc volcanic gases from subducted altered oceanic crust cannot be excluded

surveillance of ruapehu crater lake new zealand by aqueous polythionates abstract aqueous sulfur speciation of samples of crater lake water from crater lake collected at mt ruapehu new zealand since 1968 has been determined using high performance liquid chromatography polythionates s x o 6 2 are produced in the lake through reactions between sulfur dioxide and hydrogen sulfide gases from the subaqueous fumaroles their concentrations vary from 0 to a few hundred mg l corresponding to the activity of the volcano the concentration of the total polythionates s x o 6 2 s 4 o 6 2 s 5 o 6 2 s 6 o 6 2 is found to be a good indicator of changes in the subaqueous fumarolic activity at crater lake the molar s x o 6 2 cl ratios of the lake water can be used to divide the volcanic activity of crater lake into four stages 1 stage i period of weak volcanic activity with no hydrothermal explosions this stage is characterized by low total s x o 6 2 with a distribution order of s 5 o 6 2 s 4 o 6 2 s 6 o 6 2 h 2 s is predominant among dissolved gases in the lake water 2 stage iia quiescent period with minor hydrothermal explosions the lake water contains high s x o 6 2 with a distribution order of s 5 o 6 2 s 4 o 6 2 s 6 o 6 2 dissolved h 2 s and so 2 gases are very low 3 stage iib increased fumarolic activity with frequent hydrothermal explosions low s x o 6 2 with a distribution order of s 4 o 6 2 s 5 o 6 2 s 6 o 6 2 sulfur dioxide but no h 2 s is detected in the water 4 stage iii period of phreatomagmatic eruptions with lahars and intensive seismic activity no s x o 6 2 exists but dissolved so 2 is high in the lake water the moderate sized explosion of december 8 1988 which was not preceded by any changes in lake water polythionate chemistry or seismic activity is hypothesized to be a vent cleaning eruption caused by blockage of ascending magmatic gases that was caused by solidification of a molten sulfur pool at the bottom of crater lake

condensation of volatile elements in high temperature gases of mount st helens abstract the cooling of high temperature 675 650 c volcanic gases in silica tubes produces successive condensation of volatile elements as solids on the inner walls of the tubes the chemistry of the solid phases obtained by these reactions varies along the temperature gradient 675 400 c fe3o4 and sio2 occur above 570 c mos2 and fewo4 are mainly enriched between 570 and 480 c nacl and kcl occur in the range 550 450 c and cds occurs at 520 450 c pb and bi sulfides are typical of the low temperature zone 480 400 c thermodynamic calculations performed to define the nature of the stable solid phases in equilibrium with the oxygen sulfur and chlorine fugacities of the gas phase show that the observed solid phases reflect a formation in a low o2 fugacity environment the chemistry of fumarolic incrustations collected around high temperature vents 300 c 5 15 cm below the surface reveals that condensation processes similar to those observed in the tubes occur naturally in the ground these incrustations show marked differences with those generally collected at the outlet of fumarolic vents where reactions with atmospheric gases and wall rocks are the major processes leading to the formation of these incrustations

channel stability in bed load dominated streams with nonerodible banks inferences from experiments in a sinuous flume 1 experimental and computational evidence shows that bed state adjustments can accommodate a twofold to fourfold change in sediment supply without otherwise affecting the morphology of a sinuous gravel bed stream channel with nonerodible banks in contrast previously published experiments of the same kind but with erodible channel banks suggest that changes in sediment supply are taken up almost exclusively by changes in channel sinuosity and hence the reach average water surface gradient it appears that stream channel response to changes in sediment supply is strongly conditioned by the nature of the stream boundary and that determines which of several potential adjustments are possible

effect of kcl on melting in the mg2sio4 mgsio3 h2o system at 5 gpa to examine the effect of kcl bearing fluids on the melting behavior of the earth s mantle we conducted experiments in the mg2sio4 mgsio3 h2o and mg2sio4 mgsio3 kcl h2o systems at 5 gpa in the mg2sio4 mgsio3 h2o system the temperature of the fluid saturated solidus is bracketed between 1 200 1 250 c and both forsterite and enstatite coexist with the liquid under supersolidus conditions in the mg2sio4 mgsio3 kcl h2o systems with molar cl cl h2o ratios of 0 2 0 4 and 0 6 the temperatures of the fluid saturated solidus are bracketed between 1 400 1 450 c 1 550 1 600 c and 1 600 1 650 c respectively and only forsterite coexists with liquid under supersolidus conditions this increase in the temperature of the solidus demonstrates the significant effect of kcl on reducing the activity of h2o in the fluid in the mg2sio4 mgsio3 h2o system the change in the melting residues indicates that the incongruent melting of enstatite enstatite forsterite silica rich melt could extend to pressures above 5 gpa in kcl bearing systems in contrast to the behavior in the kcl free system

recent 1999 2003 canadian research on contemporary processes of river erosion and sedimentation and river mechanics contributions by canadian fluvial geomorphologists between 1999 and 2003 are discussed under four major themes sediment yield and sediment dynamics of large rivers cohesive sediment transport turbulent flow structure and sediment transport and bed material transport and channel morphology the paper concludes with a section on recent technical advances during the review period substantial progress has been made in investigating the details of fluvial processes at relatively small scales examples of this emphasis are the studies of flow structure turbulence characteristics and bedload transport which continue to form central themes in fluvial research in canada translating the knowledge of small scale process related research to an understanding of the behaviour of large scale fluvial systems however continues to be a formidable challenge models play a prominent role in elucidating the link between small scale processes and large scale fluvial geomorphology and as a result a number of papers describing models and modelling results have been published during the review period in addition a number of investigators are now approaching the problem by directly investigating changes in the system of interest at larger scales e g a channel reach over tens of years and attempting to infer what processes may have led to the result it is to be expected that these complementary approaches will contribute to an increased understanding of fluvial systems at a variety of spatial and temporal scales

geochemistry of the acid kawah putih lake patuha volcano west java indonesia abstract kawah putih is a summit crater of patuha volcano west java indonesia which contains a shallow 300 m wide lake with strongly mineralized acid sulfate chloride water the lake water has a temperature of 26 34 c ph s tot 2500 4600 ppm and cl 5300 12 600 ppm and floating sulfur globules with sulfide inclusions are common sulfur oxyanion concentrations are unusually high with s 4 o 6 2 s 5 o 6 2 s 6 o 6 2 2400 4200 ppm subaerial fumaroles thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases barite pyrite and various pb sb cu as bi bearing sulfides when sulfur saturation is assumed precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur rich bottom sediments and their identified mineral phases much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases as indicated by a comparison of the fluids volcanic rocks and lake bed sediment flank springs on the mountain at different elevations vary in composition and are consistent with local rock dissolution as a dominant factor and ph dependent element mobility discharges of warm sulfate and chloride rich water at the highest elevation and a near neutral spring at lower level may contain a small contribution of crater lake water the acid fluid induced processes at patuha have led to the accumulation of elements that are commonly associated with volcano hosted epithermal ore deposits the dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern

the sirung volcanic boiling spring an extreme chloride rich acid brine on pantar lesser sunda islands indonesia abstract the sirung volcano with a history of phreatomagmatic outbreaks has its present active center within a 1000 m wide subsidence crater the sirung crater lake scl has 15 g l 1 cl and 19 g l 1 so4 ph 0 75 temperature 40 c a highly saline brine sirung boiling spring sbs boils to the surface beside the lake it contains 116 g l 1 cl ph 1 4 chemical geothermometers indicate a reservoir temperature of 240 c the maximum depth of this reservoir is estimated to be 400 m the stable isotope composition is d 12 and 18o 5 0 to 6 0 tritium in the sbs is 0 0 tu in the scl 4 6 tu evidence against invading seawater as a source is the negative d value in addition to the six times higher cl concentration of the sbs evaporites are rejected as a source of the cl because of the geologic setting the average cl h 2 o ratio in sirung volcanic glasses as estimated by microprobe is very close to the cl h 2 o ratio of 0 047 for the sbs the zero tritium level in the sbs its high cl concentration and the acid character are other evidences for magmatic water as source for the sbs the acid sbs is poor in sulphur which may have been precipitated at depth as sulphides theories on porphyry cu formation in volcanic arc environments invoke highly saline brines as the transporting agent the acid saline brines from the sirung and white island new zealand craters and cl rich crater lakes associated with andesitic volcanism in subduction zones indicate that such fluids occur more frequently at the surface than has been possibly realized hitherto

effect of bed sand content on the turbulent flows associated with clusters on an armored gravel bed surface abstractas a gravel bed river armors a bed surface often develops clusters as part of its structure the influence of sand on armoring and the impact of clusters on the surrounding flow processes were investigated through flume experiments armored beds were created from four different sediments which progressively increased from 1 38 sand in the bed sediment extending from gravel framework to sand matrix beds turbulent kinetic energy tke and xz direction reynolds stress calculated from velocity profiles showed the clusters increased turbulence and induced formation of recirculation cells similar recirculation cells formed downstream of every cluster but the strength and orientation of these cells varied with bed condition the increase in sediment sand content and change in bed condition from gravel framework to sand matrix correlated to an increase in the energy and momentum in the recirculation cell but a reduction in cluster influence across the flow profile results show that the sand conten

crater lake and post eruption hydrothermal activity el chichon volcano mexico abstract explosive eruptions of volcan el chichon in chiapas mexico on march 28 and april 3 4 1982 removed 0 2 km3 of rock to form a 1 km wide 300 m deep summit crater by late april 1982 a lake had begun to form on the crater floor and by november 1982 it attained a maximum surface area of 1 4 105 m2 and a volume of 5 106 m3 accumulation of 4 5 m of rainfall between july and october 1982 largely formed the lake in january 1983 temperatures of fumaroles on the crater floor and lower crater walls ranged from 98 to 115 c by october 1983 the maximum temperature of fumarole emissions was 99 c in january 1983 fumarole gas emissions were greater than 99 vol h2o with traces of co2 so2 and h2s the water of the lake was a hot t 52 58 c acidic ph 0 5 dilute solution 34 046 mg l 1 dissolved solids cl s 20 5 sediment from the lake contains the same silicate minerals as the rocks of the 1982 pyroclastic deposits together with less than 1 of elemental sulfur the composition and temperature of the lake water is attributed to 1 solution of fumarole emissions 2 reaction of lake water with hot rocks beneath the lake level 3 sediments washed into the lake from the crater walls 4 hydrothermal fluids leaching sediments and formational waters in sedimentary rocks of the basement 5 evaporation and 6 precipitation

theory of metamorphism of dry snow the growth of ice particles in dry seasonal snow is caused by vapor diffusion among particles due to temperature gradients imposed on the snow cover the diffusion is calculated by using the potential field solutions for electrostatically charged particles the stereography of snow is represented by using a log normal distribution function for a geometrical enhancement factor defined here reasonable crystal growth rates and supersaturations are found the transition between the growth of highly faceted crystals and the growth of highly rounded crystals is determined by the critical supersaturation for the onset of dislocation aided growth thermal convection and the continuous movement of vapor around the particles due to the imposed temperature gradient are accommodated in the theory although both have little effect relative to the interparticle diffusion the growth of a layer of faceted crystals just below semi permeable crusts is explained by showing that crusts can cause the local supersaturation to exceed the critical value faceted crystals are shown to grow most rapidly in the lower warmer portions of the snow cover because of temperature effects on growth rate

volcanic lake systematics ii chemical constraints abstract a database of 373 lake water analyses from the published literature was compiled and used to explore the geochemical systematics of volcanic lakes binary correlations and principal component analysis indicate strong internal coherence among most chemical parameters compositional variations are influenced by the flux of magmatic volatiles and or deep hydrothermal fluids the chemistry of the fluid entering a lake may be dominated by a high temperature volcanic gas component or by a lower temperature fluid that has interacted extensively with volcanic rocks precipitation of minerals like gypsum and silica can strongly affect the concentrations of ca and si in some lakes a much less concentrated geothermal input fluid provides the mineralized components of some more dilute lakes temporal variations in dilution and evaporation rates ultimately control absolute concentrations of dissolved constituents but not conservative element ratios most volcanic lake waters and presumably their deep hydrothermal fluid inputs classify as immature acid fluids that have not equilibrated with common secondary silicates such as clays or zeolites many such fluids may have equilibrated with secondary minerals earlier in their history but were re acidified by mixing with fresh volcanic fluids we use the concept of degree of neutralization as a new parameter to characterize these acid fluids this leads to a classification of gas dominated versus rock dominated lake waters a further classification is based on a cluster analysis and a hydrothermal speedometer concept which uses the degree of silica equilibration of a fluid during cooling and dilution to evaluate the rate of fluid equilibration in volcano hydrothermal systems

comparison of turbulent flows over clusters of varying density abstractgravel bed rivers commonly form an armored surface layer within which cluster bedforms develop clusters can form in isolation or develop cluster groups of increasing density flume experiments are presented in which a clustered armored surface was formed on a gravel bed flows were measured over an area without a cluster and areas with an isolated cluster a coupling of two clusters and a group of three clusters turbulent flow parameters reynolds stresses and turbulent kinetic energy were calculated from acoustic doppler velocimeter measured flows and visualizations of the flow patterns around clusters flow separated over the cluster crest creating an increase in the turbulent flow properties and a high turbulence intensity region when flow reattached downstream turbulent kinetic energy increased around the coupled clusters but around the grouped clusters the flow field was distinguished by a high degree of uniformity the net effect of increasing density of cluster grouping was an incr

a numerical model to simulate snow cover stratigraphy for operational avalanche forecasting laws of snow metamorphism have been introduced in a numerical model which simulates the evolution of temperature density and liquid water profiles of snow cover as a function of weather conditions to establish these laws the authors have summarized previous studies on temperature gradient and on wet snow metamorphism and they have also conducted metamorphism experiments on dry or wet fresh snow samples an original formalism was developed to allow a description of snow with parameters evolving continuously throughout time the introduction of laws of metamorphism has improved significantly the derivation of the settlement of internal layers and of snow covered albedo which depend on the simulated stratigraphy i e the type and size of snow grains of different layers of the snow cover the model was tested during a whole winter season without any re initialization comparison between the simulated characteristics of the snow cover and the observations made in the field are described in detail the model proved itself to be very efficient in simulating accurately the evolution of the snow cover stratigraphy throughout the whole winter season

thermal effects due to air flow and vapor transport in dry snow the thermal effects of air flow forced through a snow sample are investigated numerically a new method for calculating vapor transport in snow is presented which allows for the determination of the effects of sublimation in this method the snow is not assumed to be saturated with water vapor results of the model show very good agreement with analytical and experimental results

the stable isotope geochemistry of volcanic lakes with examples from indonesia abstract stable isotope compositions d 18o and 34s of volcanic lake waters gas condensates and spring waters from indonesia italy japan and russia were measured the spring fluids and gas samples plot in a broad array between meteoric waters and local high temperature volcanic gas compositions the d and 18o data from volcanic lakes in east indonesia plot in a concave band ranging from local meteoric waters to evaporated fluids to waters heavier than local high temperature volcanic gases we investigated isotopic fractionation processes in volcanic lakes at elevated temperatures with simultaneous mixing of meteoric waters and volcanic gases an elevated lake water temperature gives enhanced kinetic isotope fractionation and changes in equilibrium fractionation factors providing relatively flat isotope evolution curves in 18o d diagrams a numerical simulation model is used to derive the timescales of isotopic evolution of crater lakes as a function of atmospheric parameters lake water temperature and fluxes of meteoric water volcanic gas input evaporation and seepage losses the same model is used to derive the flux magnitude of the keli mutu lakes in indonesia the calculated volcanic gas fluxes are of the same order as those derived from energy budget models or direct gas flux measurements in open craters several 100 m3 volcanic water day and indicate a water residence time of 1 2 decades the 34s data from the keli mutu lakes show a much wider range than those from gases and springs which is probably related to the precipitation of sulfur in these acid brine lakes the isotopic mass balance and s cl values suggest that about half of the sulfur input in the hottest keli mutu lake is converted into native sulfur

the thermal conductivity of seasonal snow twenty seven studies on the thermal conductivity of snow k eff have been published since 1886 combined they comprise 354 values of k eff and have been used to derive over 13 regression equation and predicting k eff vs density due to large and largely undocumented differences in measurement methods and accuracy sample temperature and snow type it is not possible to know what part of the variability in this data set is the result of snow microstructure we present a new data set containing 488 measurements for which the temperature type and measurement accuracy are known a quadratic equation where is in g cm 3 and k eff is in w m 1 k 1 can be fit to the new data r 2 0 79 a logarithmic expression can also be used the first regression is better when estimating values beyond the limits of the data the second when estimating values for low density snow within the data set snow types resulting from kinetic growth show density independent behavior rounded grain and wind blown snow show strong density dependence the new data set has a higher mean value of density but a lower mean value of thermal conductivity than the old set this shift is attributed to differences in snow types and sample temperatures in the sets using both data sets we show that there are well defined limits to the geometric configurations that natural seasonal snow can take

experiments on surface structure and partial sediment transport on a gravel bed eight flume experiments were conducted to study the development of bed surface texture and structure in the presence of partial bed material transport the experiments have two phases a no feed degradational phase followed by a feeding phase a surface structure of irregular reticulate stone nets and clusters was developed before sediment feeding commenced bed load transport equaled or slightly exceeded the fed supply except at the highest feed rate the bed structure was maintained but bed surface texture fined with increasing sediment load the two phenomena may coexist because the largest grains on the bed moved only very sporadically the actual sediment transport rates were much less than the expected rate calculated from the ratio of bed surface grain size to transported grain size the difference reflects the increase in bed stability introduced by the bed structure between 17 and 47 of the bed shear stress is estimated to be carried by the structure 4 being absorbed by the load while the bed grains carried the balance of the stress bed material transport is exceedingly sensitive to bed surface structure and grain size which raises concerns about the realizable precision of grain size measurements and characterization of the structure

extreme snow metamorphism in the allan hills antarctica as an analogue for glacial conditions with implications for stable isotope composition understanding physical processes in near zero accumulation areas can help us to better understand polar ice core records particularly during periods when accumulation rates were lower than today we report measurements from a 5 m firn core from the allan hills antarctica which include physical properties using computer tomography stable isotope ratios d and 18 o and 210 pb activity the core shows a highly metamorphosed firn with homogeneous and stable structure but with discrete layers near the surface the observed firn structure is caused by a combination of unique depositional and post depositional processes the irregular d and 18 o signal does not follow the stratigraphic sequence and implies post depositional modification caused by microscopic pressure gradients in the firn that can result from either forced ventilation over rough surfaces in the presence of wind or alternating temperature gradients between the firn and the atmosphere our results also indicate impact snow deposition under high winds and with a high initial density and air exchange between the atmosphere and the snowpack 210 pb activity below 0 3 m falls below the detection limit implying that most of the core is more than 100 years old we conclude that the allan hills record provides a unique opportunity to investigate important processes that would have affected ice core records from glacial periods

acid sulfate chloride volcanic waters formation and potential for monitoring of volcanic activity abstract this paper deals mainly with acidic sulphate chloride asc waters that are discharged at volcanic edifices generally not associated with crater lakes geographically the largest number of such manifestations were found on japanese and kuril islands these waters are formed by 1 condensation of magmatic vapor under shallow conditions and or 2 dissolution of magmatic gases in underground waters 3 near surface mixing of steam heated sulphate waters with sodium chloride waters of deeper formation 4 interaction of sodium chloride waters with the rocks undergone by argillic and advanced argillic alteration including hydrolysis of elemental sulfur 5 a combination of several of the listed processes criteria to assess the nature of such waters using their chemical and isotopic composition are based on the relative abundances of major species and trends in isotopic compositions generally controlling by mixing of magmatic host rock meteoric endmembers an overview of available data on temporal chemical variations of such waters shows that usually volcanic activity is marked by an increase in the so4 cl ratio during or after the eruptive event the response on the volcanic activity depends on hydrogeological conditions that control the appearance of the asc springs

carbon sources in arc volcanism with implications for the carbon cycle new co2 3 he data from the east sunda arc indonesia confirm earlier observations that arc volcanic gases have higher co2 3 he ratios than mor environments on average 80 of arc volcanic co2 is recycled exogene carbon addition of a few percent of carbonate bearing sediments to the mantle wedge explains much of the carbon abundance andcarbon isotopic data of arc gases but can not explain the he isotope observations the co2 3he in arc volcanoes is not strongly dependent on the composition of modem trough sediments e g deep sea clays vs carbonate rich sequences and calcite veins in the hydrothermally altered subducted slab may provide a contribution to the recycled carbon flux of arcs the sum of globally deep subducted sediment and slab carbon exceeds the estimated arc co2 flux and approximately 3 5 teramole of carbon may return annually to the mantle in convergent zones the modem combined processes of mor volcanism slab alteration and subduction volcanism do not produce a substantial carbon flux into the exosphere and rate changes in ocean floor spreading are unlikely to cause major changes in atmospheric co2 as a result of changes in the volcanic co2 fluxes intense pulses of flood basalt volcanism however may alter the co2 contents of the atmosphere over the course of a millenium or so and influence global climate

bed clusters in humid perennial and mediterranean ephemeral gravel bed streams the effect of clast size and bed material sorting summary a short review of the literature on particle clusters on gravel river beds reveals investigations of both process and form dominated by the intensive study approach using a restricted geographical sample or evidence from flumes an alternative presented here is extensive sampling from three climatic zones several channels in each and at multiple transects at each site it uses insights provided by a more intensively studied base station wittenberg l newson m d 2005 particle clusters in gravel bed rivers an experimental morphological approach to bed material transport and stability concepts earth surface processes and landforms 30 11 1351 1368 transect surveys were completed in each selected reach to establish flow depth bed material size and bed structure a total of more than 5000 sample points reveals the vital presence of bed material of 100 mm d50 for all sub types of clusters to occur thereafter cluster frequency relates directly to the d90 with an improving correlation at d90 256 mm a better integration of data from the diverse hydrological hydraulic regimes can be achieved by correlating cluster frequency with a sorting index for bed material further analysis of hydrological and hydraulic data for all sites is required to develop a dynamic explanation

particle geochemistry of volcanic plumes of etna and mount st helens particles in volcanic plumes include vapor condensates and reaction products of ash with vapors or condensed liquids in addition to abundant silicate particles in the 1980 mount st helens plume we detected abundant na k cl crystals as well as ca sulfates the latter commonly as overgrowths on ash or anthropogenic particles many of the chloride particles contained zinc and cadmium high temperature fumarolic incrustations showed strong enrichments of arsenic zinc alkalis and iron at etna we did not detect chloride crystals but found abundant al fe and ca sulfates sulfuric acid droplets were ubiquitous in both plumes bulk analyses of fumarole incrustations at etna showed an enrichment in the rare earth elements ree the chemical and textural data of the plume particles indicate that chloride particles form relatively early and react later with sulfuric acid droplets to form sulfates at etna aluminum as well as some ree are probably transported as volatile fluorine compounds the differences in plume chemistry between etna and mount st helens are most likely related to differences in f cl ratios of the vapors based on the abundance of particulate chlorine in plumes we suggest that only a small fraction of the total chlorine released during an eruption might reach the stratosphere in the vapor phase

fluid immiscibility in volcanic environments volatile components enter the atmosphere oceans and other surface waters through pre syn and post eruptive volcanic processes that involve a variety of fluids aluminosilicate poor fluids include aqueous or carbonic to sulfide sulfate chloride fluoride carbonate and phosphate rich compositions in volcanic environments but other more complex combinations of these constituents may be involved giggenbach 1977 roedder 1984 1992 lowenstern 1995 other rare gases and dissolved constituents e g h2 n2 he ar h3bo3 hg ch4 and other hydrocarbon compounds metals and metalloids are also present but in general they are not sufficiently concentrated to form their own phases or control bulk fluid composition and volcanic processes as a result of their diverse compositions volcanic fluids ranging from vapor to liquid exhibit widely different densities and show strong distinctions in heat capacity dielectric behavior viscosity and other chemical and physical characteristics geiger et al 2006a the density of a saline liquid in the system nacl h2o at 50 mpa and 800 c for example is more than 7 times that of the coexisting aqueous vapor e g 0 2 gm cm3 henley and mcnabb 1978 multiple fluids move mix and or unmix in magma chambers and volcanic conduits in the root zone of fumaroles and in the convective hydrothermal systems that are ubiquitous to volcanic environments hydrothermal systems are typically centered on magmatic intrusions and may include crater lakes at the top of eruptive conduits hydrothermal processes involving two or more fluid phases operate through a variety of geologically relevant shallow crustal pressure temperature composition conditions volcanic fluids occur at supersolidus to subsolidus conditions meaning that the dense aluminosilicate melt that is common to volcanism may or may not be present this chapter addresses the evidence for and occurrence of two or more low density aluminosilicate poor fluids

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

linking fluvial bed sediment transport across scales 1 we present a new random walk model for bed load sediment transport that explains the scale dependency generally observed in transport rates and captures the transient anomalous dispersion often seen in rivers particles alternate between mobile and resting phases with a tempered stable probability distribution for both particle step length and resting time tempered fractional mobile immobile differential equations model the ensemble average of particle dynamics the model is tested against data from three sediment dispersion experiments using tempering in both space and time the new model is able to capture the full range of observed ensemble particle dynamics the random walk model illuminates the physical meaning of all transport parameters in the mobile immobile equations and explains transitions between observed super diffusive sub diffusive and regular diffusive ensemble particle dynamics by explicitly predicting the effects of spatial and temporal averaging on particle dynamics this method can be used to link observations of fluvial sediment dynamics across scales this approach is also generally applicable to a wide variety of geophysical and ecological dynamics such as ecological dispersal pathogen transmission in rivers nutrient export from watersheds and large scale geomorphodynamics associated with infrequent phenomena such as avalanches and turbidity currents