the role of climate in the accumulation of lithium rich brine in the central andes abstract lithium rich brine within the sub surface of the salar del hombre muerto shm salt pan in the andes of northwestern argentina has a chemical and isotopic composition which is consistent with li derived from several sources the modern halite saturated lagoon li rich salts and brines formed recently and dissolution of halite which precipitated from ancient saline lakes shm lies in the closed basin that includes part of the massive cerro galan caldera which is drained by the rio los patos which is responsible for 90 of surface runoff into the salar the low li isotope composition 3 4 of this river is consistent with significant contributions of geothermal spring water as water drains through the volcaniclastic deposits which cover a large proportion of the basin li removal as indicated by decreasing li na occurs but without significant isotope fractionation this indicates a mechanism of surface sorption onto smectite or ferrihydrite rather than li incorporation into octahedral structural sites of clays these observations suggest that conditions in this high altitude desert have limited the dilution of hydrothermal spring water as well as the formation of clay minerals which jointly have allowed the li resource to accumulate rapidly changes in climate on a multi millennial time scale specifically in the hydrologic budget have resulted in solute accumulation rates that have been variable through time and decoupled li and na fluxes inflow to the salar under modern conditions has high li na 7 9 10 3 by wt with 7 li indistinguishable from basement rocks 0 3 to 6 4 while under pluvial climate conditions the li na of the saline lake was 40 times lower than the modern lagoon 0 1 0 3 10 3 compared to 10 6 13 4 10 3 with slightly higher 7 li 6 9 to 12 3 reflecting the uptake of 6 li into secondary minerals which formed under a wetter climate

rapid releases of metal salts and nutrients following the deposition of volcanic ash into aqueous environments deposition of volcanic ash into aqueous environments leads to dissolution of adsorbed metal salts and aerosols increasing the bioavailability of key nutrients volcanogenic fertilization events could increase marine primary productivity leading to a drawdown of atmospheric co2 here we conduct flow through experiments on unhydrated volcanic ash samples from a variety of locations and sources measuring the concentrations and fluxes of elements into de ionized water and two contrasting ocean surface waters comparisons of element fluxes show that dissolution of adsorbed surface salts and aerosols dominates over glass dissolution even in sustained low ph conditions these surface ash leachates appear unstable decaying in situ even if kept unhydrated volcanic ash from recent eruptions is shown to have a large fertilization potential in both fresh and saline water fluorine concentrations are integral to bulk dissolution rates and samples with high f concentrations display elevated fluxes of some nutrients particularly fe si and p bio limiting micronutrients are released in large quantities suggesting that subsequent biological growth will be limited by macronutrient availability importantly acidification of surface waters and high fluxes of toxic elements highlights the potential of volcanic ash leachates to poison aqueous environments in particular large ph changes can cause undersaturation of caco3 polymorphs damaging populations of calcifying organisms deposition of volcanic ash can both fertilize and or poison aqueous environments causing significant changes to surface water chemistry and biogeochemical cycles

surface based transport model for mixed size sediment we present a transport model for mixed sand gravel sediments fractional transport rates are referenced to the size distribution of the bed surface rather than subsurface making the model completely explicit and capable of predicting transient conditions the model is developed using a new data set of 48 coupled observations of flow transport and bed surface grain size using five different sediments the model incorporates a hiding function that resolves discrepancies observed among earlier hiding functions the model uses the full size distribution of the bed surface including sand and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models the model shares some common elements with two previous surface based transport models but differs in using the full surface size distribution and in that it is directly developed from a relatively comprehensive data set with unambiguous measurement of surface grain size over a range of flow transport rate and sediments

an experimental investigation of mechanisms involved in bed load sheet production and migration 1 field measurements indicate that in gravel bed rivers bed load may not be a one to one response to shear stress but may instead fluctuate a great deal over time for a given flow condition both in flume and field experiments these fluctuations were often associated with migration of low relief bed forms called bed load sheets whereas several studies have described bed load sheets as a consequence of grain sorting little is known about the mechanisms responsible for their production and migration these were investigated in flume experiments a set of 20 experiments was conducted under constant feeding rate conditions with mixtures of different uniform sediments and for slopes varying from 0 8 to 9 except for runs performed in high flow conditions we observed periodic bed load sheet production and migration associated with fluctuations of bed slope bed state bed fining and paving and bed load observations allowed us to conclude that bed load sheets resulted from very efficient vertical and longitudinal grain sorting that produced periodic local bed aggradation and erosion clearly observed in the upstream section of the flume fractional transport rates were measured in one run combined with the results of experiments previously conducted by authors with uniform sediments this experiment showed that the highest peak solid discharges were essentially caused by the much greater mobility of the coarser gravels when transported within bed load sheets a scenario is proposed for the mechanisms involved in bed load sheet production and migration

stabilization of a gravel channel by large streamside obstructions and bedrock bends jacoby creek northwestern california jacoby creek bed width 12 m bankfull discharge 32 6 m 3 s contains stationary gravel bars that have forms and positions controlled by numerous large streamside obstructions bedrock outcrops large woody debris and rooted bank projections and bedrock bends bank projection width and bar volume measured in 104 channel segments 1 bed width long are significantly cross correlated at lags of 1 3 and 4 indicating the tendency for large obstructions and bends to form bars 3 to 4 bed widths downstream and 1 bed width upstream all of the 18 bars downstream of large obstructions or bends in the study reach were along the obstruction side of the channel or outside bank of the bend most of the pools 85 were next to large obstructions or in bends conversely 92 of large obstructions or bends had pools comparison of the volume of four bars with volumetric bar changes and volume of bedload transported during four high flow events suggests that rates of sediment transport were sufficient to cause major changes in bars during bankfull events the only important channel changes observed in 4 yr however have been associated with the movement of large woody debris and with changes in the angle at which the flow approaches an obstruction a general model is proposed that large obstructions and nonalluvial bends stabilize the form and location of gravel bars bars are stabilized by two related mechanisms 1 large obstructions and bends cause intense quasi steady secondary circulation in scour holes that terminate upstream bars at fixed locations obstruction width channel deflection scour hole width and bed width were measured at 26 obstructions these data show that obstructions wider than approximately one third of the bed form pools spanning the entire channel and thus terminating bars smaller obstructions form scour holes contained within a single bar 2 bars are deposited upstream of large obstructions and sharp bends because of backwater reductions in stream power bars are deposited downstream because flow energy is expended around obstructions and bends and because the flow expands downstream of constrictions that result from large obstructions the formation of bars and pools inherent in many gravel channels can thus be enhanced and fixed in position by flow structures set up around large obstructions and bends formed of resistant materials

predicting incipient motion including the effect of turbulent pressure fluctuations in the bed 1 incipient motion of particles on a river bed can in principle be understood and predicted from a balance of the forces acting on the particles on a natural river bed the exposure of particles to the flow is variable the effect of exposure on the initiation of motion including the case of deep embedding is studied in this paper so far the turbulence induced lifting force has been derived exclusively from examinations of the surface flow the understanding of destabilization processes of the riverbed is improved when turbulence induced vertical pressure gradients in the upper sediment layer are included this is particularly important for particles that lie in the lee of larger ones an analytical solution for the critical shields parameter of spherical particles is found including the effects of pressure fluctuations in the bed macroscale flow structures average bed slope and shallow flow existing laboratory data designed to test the effect of exposure and roughness conditions are in excellent agreement with the new model

petrology of pumices of april 1993 eruption of lascar atacama chile lascar volcano atacama chile erupted on 18 20 april 1993 several sub plinian explosions occurred and some were mushroom shaped the highest column rose up to 23 km ash clouds crossed south america eastwards dacite pumice falls made of blocks and ashes were deposited on the flanks of the volcano as a result of collapsed columns the pumice contains phenocrysts of plagioclase enstatite augite biotite magnetite and ilmenite and small crystals of apatite the 1992 previous andesite dome inside the crater was destroyed banded blocks resulting from mingling of the dacitic pumice and andesite from the dome are found in the pumice flow both the lava dome and the pumice are representative of the lascar high k magma unit dacitic pumice is a product of crystal fractionation of the andesitic magma

leachate analyses of volcanic ashes from stromboli volcano a proxy for the volcanic gas plume composition 1 many volcanoes show a change in chemical composition of the gas phase prior to periods of eruptive activity fine grained tephra erupted from active vents and transported through volcanic plumes can adsorb and therefore rapidly scavenge volatile elements such as sulfur halogens and metal species in the form of soluble salts adhering to ash surfaces analysis of such water soluble surface materials is a suitable supplement for remote monitoring of volcanic gases at inaccessible volcanoes in this work ash samples of the 2004 to 2009 eruptive activity of stromboli volcano were sampled leached and analyzed for major and trace elements data analysis and interpretation was focused on determining the relationship between chemical composition of water soluble components adhering to volcanic ash and the volcano s activity state first results show significant temporal variations in ash leachate compositions reflecting changes in the eruptive style of the volcano in particular we reveal that ash leachates s f and mg na ratios showed marked increases prior to a large scale explosion on 15 march 2007

the origin of solutes within the groundwaters of a high andean aquifer abstract this paper investigates the origin of solutes within the groundwaters of the monturaqui negrillar tilopozo mnt aquifer system within the high andes of the atacama desert that discharges into the salar de atacama key questions include the relative significance of volcanic hydrothermal processes and evaporitic brine recycling over solute supply as well as the pathways of solute ingress to the mnt aquifer system groundwaters were analysed for elemental major minor and trace and isotopic 18o 2h 13c dic 34s so4 87sr 86sr constituents to which various hydrochemical and multivariate statistical methods have been applied groundwaters are all classified as thermal and show increasing temperatures 27 35 c and concentrations of hco3 4 4 10 4 mmol l 1 dissolved inorganic carbon dic with increasing proximity to volcano socompa resulting from an increasing mass flux of steam and magmatic co2 pco2 0 016 to 0 10 atm 13c co2 9 3 to 3 6 v pdb boiled off a deep hydrothermal reservoir superimposed upon this gradational and relatively smooth spatial increase in heat and mass flow is a sharp structurally controlled increase in tds 826 3632 mg l 1 and a concomitant change in 34s so4 0 79 to 4 9 v cdt and 87sr 86sr values 0 707375 0 706859 associated with the inflow of evaporitic solutes evaporitic inputs are chemically and isotopically distinct from localised secondary hydrothermally derived solutes with major minor and trace element data suggesting an origin within a highly oxidising alkaline evaporitic lake receiving dilute inflows enriched in volcanic fumarolic sulfur mineralisation probably from volcanoes socompa salin or pular that delimit the eastern topographic extent of the aquifer system the conceptual model presented in this paper proposes that basal leakage of evaporitic brines from active salar s within the high altiplano volcanic arc are actively entrained by sub regional groundwater flow and conveyed to the mnt aquifer system where they mix with solutes derived from localised secondary hydrothermal gas water rock interaction this work provides detail on the origin and processes controlling the solute composition of groundwater inflows to the salar de atacama within the volcanically active and hyperarid atacama desert and may be of significance to conceptual models of evaporitic brine evolution recycling of evaporitic brines and hydrothermalism in arid regions

simple method for calculating reach averaged bed load transport abstracta simple and robust method is proposed for calculating reach averaged bed load transport in sand and gravel bed rivers with no calibration the data required are the bed surface d50 and d84 measured with the nontruncated pebble count technique the slope the width and the flow depth or discharge the method is illustrated by comparison with bed load samples measured in 15 river reaches

controls on organic matter accumulation in the triassic chang 7 lacustrine shale of the ordos basin central china abstract the triassic chang 7 formation is a rich lacustrine source rock in the ordos basin central china petrographic and geochemical analyses were performed in order to research the mechanism of organic matter om enrichment in the chang 7 shales bulk geochemical data indicate that the om rich shales were formed in a fresh and brackish water which is not usually the case for high toc total organic carbon content sediments therefore there must be some special conditions favorable for om enrichment in chang 7 shales petrography and element geochemistry show that the chang 7 om rich shales are abundant in om enriched laminae framboidal pyrites collophanes and some elements including iron fe diphosphorus pentoxide p2o5 copper cu vanadium v molybdenum mo and uranium u high bio productivity algae blooming and anoxic depositional environments are critical for om enrichment as the organic carbon contents increase the fe p2o5 cu v mo and u element contents increase as well and the ratios of u th and v v ni are growing many geochemical data demonstrate that the water was oxic while the environment under the sediment water interface was anoxic as a result of a high organic supply that sufficiently consumed oxygen taking into account the geological settings and our previous studies we propose that the frequent volcanic events and hydrothermal activity caused by the collision of the north china landmass with the yangtze landmass and consequential formation of the qingling mountains had a significant role in the om enrichment in the fresh and brackish lacustrine shales deposition of volcanic ash into aqueous environments might lead to the increase of some key nutrients such as fe and p2o5 which might enhance primary bio productivity new evidence for hydrothermal activity the reddingite was demonstrated in this study not only can the hydrothermal activity provide elements necessary for life but is also favorable for formation of anoxic settings the deposition of the chang 7 lacustrine om rich shales can be explained using the high bio productivity driven model which is related to volcanic events and hydrothermal activity as a consequence of regional tectonic movements an anoxic depositional setting is beneficial for om preservation and slow sedimentation rates in the deep lacustrine environments are favorable for om enrichment

a comparison between flume and field bed load transport data and consequences for surface based bed load transport prediction 1 the ability of simple equations to predict bed load transport with limited knowledge of the bed surface material was investigated this was done using a data set consisting of 7 636 bed load transport values from the flume 1 317 data and from 84 river reaches 6 319 field data it was possible to collapse field and flume data by correcting the ratio between the shields number and its critical value with a very simple hiding function proposed as a power law of the d84 d50 ratio in so doing a surface based bed load transport formula was proposed it was successfully tested on an independent data set comprising sand and gravel bed rivers with slope in the range 0 0002 0 08 with 86 of the values predicted within a precision of 1 order of magnitude moreover the formula reproduced the low transport rates well contrary to the usual surface based formulas also tested and is particularly well suited for estimating low transport rates associated with near bankfull flow discharge this new formula is neither time consuming no fractionwise calculation nor data consuming the required parameters are the flow discharge the active width the slope and the surface grain diameters d50 and d84

dynamics of bedload transport in turkey brook a coarse grained alluvial channel automatic and continuously recording samplers are deployed in a hertfordshire gravel bed stream to show that bedload transport is related to stream power the pattern is similar to that already established for north american channels but because the record is so detailed it is possible to identify the cause of the considerable scatter that is normal in such relationships a major factor is the occurrence of rhythmic pulses in bedload discharge that are not matched by similar fluctuations in hydraulic variables it is suggested that these pulses reflect downstream differences in the concentration of mobile particles in a slow moving traction carpet and that they may be likened to kinematic waves the record also reveals that the threshold of sediment transport always presumed hithero to be associated with incipient motion is related to the cessation of bedload transport in a river flood indeed the mean value of stream power at the finish of bedload transport is only 20 percent of that prevailing at the moment of incipient sediment motion because of this there is an inevitably poor correlation between actual bedload transport rates and those predicted by bedload equations which rely upon a single traction threshold these new data show that the general inverse relationship between bedload discharge and water depth grain size ratio proposed by bagnold 1977 1980 is not universal transport efficiency for this gravel bed stream is typically 0 05 per cent of available stream power which compares with 1 6 per cent for a river moving both gravel and sand and 5 per cent for another channel where bedload is composed predominantly of sand sized particles it is argued that coarse and fine grained alluvial channels may need to be considered separately by allowing for differences in traction threshold at the beginning and end of bedload events and by averaging bedload discharge flood by flood in order to smooth out the effect of pulses it is possible to achieve a reasonably good prediction of average bedload transport rate in terms of stream power

river channel slope flow resistance and gravel entrainment thresholds 1 river beds are traditionally assumed to become mobile at a fixed value of nondimensional shear stress but several flume and field studies have found that the critical value is higher in steep shallow flows explanations for this have been proposed in terms of the force balance on individual grains the trend can also be understood in bulk flow terms if total flow resistance has base and additional components the latter due to protruding immobile grains as well as any bedforms and the stress corresponding to additional resistance is not available for grain movement in threshold conditions a quantitative model based on these assumptions predicts that critical shields stress increases with slope critical stream power is near invariant with slope and each has a secondary dependence on bed sorting the proposed slope dependence is similar to what force balance models predict and consistent with flume data and most field data possible explanations are considered for the inability of this and other models to match the very low critical values of width averaged stress and power reported for some low gradient gravel bed rivers

relation between flow surface layer armoring and sediment transport in gravel bed rivers this study investigates trends in bed surface and substrate grain sizes in relation to reach scale hydraulics using data from more than 100 gravel bed stream reaches in colorado and utah collocated measurements of surface and substrate sediment bankfull channel geometry and channel slope are used to examine relations between reach average shear stress and bed sediment grain size slopes at the study sites range from 0 0003 to 0 07 bankfull depths range from 0 2 to 5 m and bankfull widths range from 2 to 200 m the data show that there is much less variation in the median grain size of the substrate d50s than there is in the median grain size of the surface d50 the ratio of d50 to d50s thus decreases from about four in headwater reaches with high shear stress to less than two in downstream reaches with low shear stress similar trends are observed in an independent data set obtained from measurements in gravel bed streams in idaho a conceptual quantitative model is developed on the basis of these observations to track differences in bed load transport through an idealized stream system the results of the transport model suggest that downstream trends in total bed load flux may vary appreciably depending on the assumed relation between surface and substrate grain sizes copyright 2007 john wiley sons ltd

sediment transport along lower fraser river 1 measurements and hydraulic computations a comprehensive program of sediment transport measurements was conducted along lower fraser river british columbia between 1966 and 1986 the data yield a detailed sediment budget annual total suspended loads at three stations are virtually identical averaging 17 106 tonnes year t yr 1 the suspended sand load is about 5 5 106 t yr 1 about one third of the total in the gravel bed reach of the river the sand behaves as wash load significant transport of gravel begins at agassiz at a discharge of about 5000 m3 s 1 the annual gravel transport was estimated to be about 0 23 106 t yr 1 only 1 of the total load all of this material is deposited in the reach upstream of mission at mission sands finer than 0 177 mm make up more than 50 of the suspended sand load but are virtually absent from the sand bed therefore a portion of the sand load at mission is wash load the total bed material load here was estimated to be 3 0 106 t yr 1 about 18 of the total sediment load virtually all of the bed material load was transported in intermittent suspension near the bed less than 5 occurring as bed load in the long term the suspended sand load upstream is approximately equal to the total sand load at mission however within individual years some of the sand is stored within the reach temporarily and then reentrained later

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

sulfate oxygen 17 anomaly in an oligocene ash bed in mid north america was it the dry fogs 1 the oxygen and sulfur isotope compositions of sulfate particularly the oxygen 17 anomaly provide clues to the origin of sulfate we report a variable oxygen 17 anomaly for water and acid leached sulfate from an oligocene volcanic ash bed in the northern high plains u s a we find no sulfate o 17 anomaly however in freshly collected ashes from recent eruptions around the world the oligocene paleoclimatic and sedimentary evidence argues against a hyperarid condition in the high plains thus a long term background atmospheric sulfate accumulation is less likely the origin combining sulfur isotope data we suggest that the anomalous sulfate was associated with volcanic eruptions in the west but was not directly carried by ash falls extreme dry fog sulfate haze events resulting from tropospheric oxidation of volcanic sulfur gases might provide a viable explanation for the sulfates in the ash bed that carry the oxygen 17 anomaly

the magmatic and hydrothermal dominated fumarolic system at the active crater of lascar volcano northern chile low to high temperature fumaroles discharging from the active crater of lascar volcano northern chile have been collected in november 2002 may 2005 and october 2006 for chemical and isotopic analysis to provide the first geochemical survey on the magmatic hydrothermal system of this active volcano chemical and isotopic gas composition shows direct addition of high temperature fluids from magmatic degassing mainly testified by the very high contents of so2 hcl and hf up to 87 800 29 500 and 2 900 mol mol and the high r ra values up to 7 29 contributions from a hydrothermal source mainly in gas discharges of the active crater rim has also been detected significant variations in fluid chemistry mainly consisting of a general decrease of magmatic related compounds i e so2 have affected the fumarolic system during the period of observation indicating an increase of the influence of the hydrothermal system surrounding the ascending deep fluids the chemical composition of active crater fumaroles has been used to build up a geochemical model describing the main processes that regulate the fluid circulation system of lascar volcano to be utilized in volcanic surveillance

oxygen isotope evidence for chemical interaction of kilauea magmas with basement rocks david green has shown us that the geochemistry of basaltic volcanoes is largely governed by mantle processes however kilauea volcano one of the most active volcanoes on earth also records interaction with its crustal rocks kilauea is built on a 6 km thick crustal basement of 100 ma oceanic crust 1 overlain by 8 10 km of young lavas 1 ma from the adjacent growing shield volcano mauna loa the contribution of these basaltic basement rocks on the geochemistry of kilauea magma was thought to be negligible based on major trace element and pb nd and sr isotope analyses of historical lavas from this volcano 2 new oxygen isotope results provide evidence for extensive exchange between kilauea magmas and the volcano s basement this exchange is documented by analyses of basalt matrix material and olivine matrix pairs for historical lavas the matrix oxygen isotope ratios are lower and the disequilibrium between olivine and matrix is greatest following summit explosions and collapses in 1790 and 1924 the source of this contamination is not likely to be shallow because blocks from the 1924 explosions derived from depths 400 m have relatively high o isotope ratios 5 5 per mil in contrast lavas from the volcano s deeper 2 3 km and hotter interior at least 300 c have much lower o isotope ratios 1 7 2 3 per mil these deeper rocks are more appropriate for lowering o matrix ratios following summit collapses via assimilation of hydrothermally altered rock the positive correlation between pb and o isotopes is consistent with mauna loa basement rocks being contaminants for recent kilauea lavas our results show that oxygen isotopes are a sensitive indicator of crustal interaction in basaltic lavas and can help eliminate an exotic mantle source component as the cause for isotopic variations

response and recovery of a subalpine stream following a catastrophic flood the july 15 1982 lawn lake flood in rocky mountain national park colorado was caused by the failure of a 79 yr old earthen dam peak discharges of the flood far exceeded naturally occurring flows and it caused severe channel disturbance along most of roaring river and some parts of fall river this study documents the geomorphic response of a 5 km reach of fall river in the 5 yr following the flood in 1983 the first year after the lawn lake flood snowmelt flows were well above average these high flows together with very high sediment yields from roaring river resulted in significant geomorphic changes on reaches of fall river downstream during the 1983 snowmelt runoff 15 5 x 106 kg of bed load sediment was eroded from the upper part of the study area these loads were at least 1 000 times higher than before the lawn lake flood most of this sediment was then deposited in a highly sinuous reach of fall river in the lower part of the study area this reach had not been much affected by the lawn lake flood but sedimentation during the period of high flow in 1983 completely filled in the channel resulting in the formation of a continuous 2 3 km long depositional zone in 1984 sediment yield from roaring river declined dramatically and this trend continued for the next 3 yr by 1987 the bed load sediment yield in the upper reaches of fall river was only about 0 4 x 106 kg yr the decline in sediment loads resulted in progressive erosion and recovery of the original channel of fall river in the depositional zone reach recovery in the upstream part of the depositional zone was complete by 1985 recovery in the downstream part of the depositional zone took longer because of the continued supply of sediment and because the sediment was mobile less of the time as of 1987 about 80 of the material initially stored in the sedimentation zone had been eroded bed load sediment yields at a sampling site 1 km downstream of the terminus of the depositional zone ranged from 5 x 106 to 11 x 106 kg yr but showed no significant decline over the 5 yr study period the average rate of bed load transport through this reach was at least 100 times greater than before the lawn lake flood but few discernible channel changes resulted from the higher loads

feedback between bed load transport and flow resistance in gravel and cobble bed rivers 1 to calculate bed load engineers often use flow resistance equations that provide estimates of bed shear stress in these equations on the basis of the estimate of the appropriate hydraulic radius associated with the bed only the bed roughness ks is commonly set as a constant whatever the bed load intensity however several studies have confirmed the existence of feedback mechanisms between flow resistance and bed load suggesting that a flow dependent bed roughness should be used therefore using a data set composed of 2282 flume and field experimental values this study investigated the importance of these feedback effects new flow resistance equations were proposed for three flow domains domain 1 corresponds to no bed load and a constant bed roughness ks d where d is a representative grain diameter whereas domain 3 corresponds to a high bed load transport rate over a flat bed with a constant bed roughness ks 2 6d between these two domains a transitional domain 2 was identified for which the bed roughness evolved from d to 2 6d with increasing flow conditions in this domain the darcy weisbach resistance coefficient f can be approximated using a constant for a given slope the results using this new flow resistance equation proved to be more accurate than those using equations obtained from simple fittings of logarithmic laws to mean values the data set indicates that distinguishing domains 2 and 3 is still relevant for bed load in particular the data indicate a slope dependence in domain 2 but not in domain 3 a bed load model based on the tractive force concept is proposed finally flow resistance and bed load equations were used together to calculate both shear stress and bed load from the flow discharge the slope and the grain diameter for each run of the data set efficiency tests indicate that new equations implicitly taking a feedback mechanism into account can reduce the error by a factor of 2 when compared to other equations currently in use showing that feedback between flow resistance and bed load can improve field bed load modeling

influence of coarse lag formation on the mechanics of sediment pulse dispersion in a mountain stream squire creek north cascades washington united states 1 mountain channels closely coupled to landslide prone hillslopes often exhibit bed surface grain sizes coarser than transportable by annual high flows coarse particles within poorly sorted sediment delivered to channels by mass wasting processes may not be readily transported as bed load and can consequently form lag deposits that influence the morphology hydraulic roughness and sediment storage within mountain channel networks a tracer study and comparison of supply and bed grain size distributions from a valley spanning landslide in the north cascades of washington state were used to derive relations between shear stress and the probability of particle entrainment and erosion from the sediment pulse rapid bed surface armoring formed a relatively immobile lag deposit within 2 years covering of 20 of the bed by lag boulders with 5 probability of entrainment was sufficient to retard vertical incision and force considerable channel widening during a flood with an 8 to 152 year recurrence discharge on locally gauged streams our results imply that numerical models of sediment pulse evolution that do not explicitly incorporate the influence of lag formation may substantially overestimate long term dispersion rates the grain size distribution and lithology of a sediment input relative to the flow competence of the receiving channel are important factors influencing the rates and mechanisms of sediment pulse dispersion and the sediment capacitance provided by coarse grained sediment pulses in mountain drainage basins

evaluation of flow resistance in gravel bed rivers through a large field data set 1 a data set of 2890 field measurements was used to test the ability of several conventional flow resistance equations to predict mean flow velocity in gravel bed rivers when used with no calibration the tests were performed using both flow depth and discharge as input since discharge may be a more reliable measure of flow conditions in shallow flows generally better predictions are obtained when using flow discharge as input the results indicate that the manning strickler and the keulegan equations show considerable disagreement with observed flow velocities for flow depths smaller than 10 times the characteristic grain diameter most equations show some systematic deviation for small relative flow depth the use of new definitions for dimensionless variables in terms of nondimensional hydraulic geometry equations allows the development of a new flow resistance equation the best overall performance is obtained by the ferguson approach which combines two power law flow resistance equations that are different for deep and shallow flows to use this approach with flow discharge as input a logarithmic matching equation in terms of the new dimensionless variables is proposed for the domains of intermediate and large scale roughness the field data indicate a considerable increase in flow resistance as compared with the domain of small scale roughness the ferguson approach is used to discuss the importance of flow resistance partitioning for bed load transport calculations at flow conditions with intermediate and large scale roughness in natural gravel cobble and boulder bed streams

quaternary geochemical evolution of the salars of uyuni and coipasa central altiplano bolivia risacher f and fritz b i99 i quaternary geochemical evolution ofthe salars of uyuni and coipasa central altiplano bolivia chem geol 90 21 1 231 the central trough of the bolivian altiplano is occupied by two wide salt crusts the salar of uyuni which is probably the largest salt pan in the world 10 000 km and the salar of coipasa 2 500 km both crusts are essentially made of porous halite filled with an interstitial brine very rich in li k mg b up to 4 7 g l li 4 3 g l b 30 g l k and 75 g l mg lithium reserves are the highest known in the world around 9x io6 tons potassium magnesium and boron reserves in brines are also important around 194x io6 tons k 8x 10 tons b and 21 1 x io6 tons mg the cnists are the remnant of saline lake tauca 13 000 10 000 yr bp its salinity was estimated approximately at 80 g l its paleochemistry was derived in two ways 1 by dissolving the present amounts of all chemical components in the former lake volume and 2 by simulating the evaporation of the major inflows to the basin the resulting chemical compositions are quite different the dissolution derived one is 5 to 50 times less concentrated in li k mg b than the evaporation simulated ones however all compositions present the same na and ci contents this suggests either a removal of bittern salts or an enrichment of the former lake water in na and ci the most probable interpretation is that lake tauca redissolved a salt crust akin to that existing today several older lakes have been detected on the altiplano nevertheless such an explanation only pushes the problem back it is likely that the anomaly was transferred from one lake to an other three hypotheses may be put forward 1 bittern seepage through bottom sediments 2 uptake of the missing components by minerals and 3 leaching of ancient evaporites from the catchment area at the beginning of the lacustrine history of the basin the excess halite could have been recycled from lake to lake this latter process seems to be the most effective to explain the large excess of na and ci over the bittern solutes li k mg and b the occurrence of almost pure na ci saline springs flowing out from a gypsum diapir in the northern altiplano gives substantial support to this hypothesis

occurrence of cluster microforms in mountain rivers the occurrence of cluster microforms in natural rivers is examined using data collected from three mountain streams the study was conducted under the premise that the occurrence of clusters is strongly tied to local reach scale conditions and that prediction of clustered sites therefore can be made through identification of particular reach conditions that are conducive to cluster development for the study reach scale variables were measured at 50 sites and the presence or absence of clusters at each of these sites was recorded a statistical analysis using logistic regression was performed to examine the correlation between the occurrence of clusters and various combinations of reach scale parameters it was found that clustering was best predicted by the bankfull channel width scaled with the d84 of the bed sediment w d84 and the non dimensional parameter wq2 gd it is thought that these variables work best at predicting the presence of clusters because they are descriptive of the reach hydraulic and sedimentary conditions and work well at discriminating between reach morphology types it was found that clustering was most strongly tied to riffle pool type reaches observations from this study suggest that clusters can be described as bed features that form out of the structural organization of grains in cobble size sediment within depositional mountain reaches for which the majority of the sediment can become mobilized by yearly peak flows copyright 2008 john wiley and sons ltd

theoretical development on the effects of changing flow hydraulics on incipient bed load motion 1 several decades of flume and field measurements have indicated that in rough turbulent flows the critical shields stress increases with increasing slope and associated decreasing relative depth this result contradicts the usual consideration of a decreased critical shields value on very steep slopes because of increased gravitational effects however recent studies have demonstrated that these experimental results could be reproduced with a force balance model if the classical logarithmic velocity profile was replaced with a velocity profile that was more compatible with available velocity measurements over gravel beds these measurements indicate the existence of a roughness layer that is a zone of almost constant velocity close to the bed whose properties mean velocity and turbulence depended on the flow s relative depth unfortunately velocity profile measurements for low relative depth associated with steep slopes are scarce and it is still difficult to include such flow properties in a force balance model flow resistance data on the basis of depth average velocity measurements are very common and cover a wide range of slopes and relative depths in this paper these data are used to fit a velocity profile including a roughness layer when used in a force balance model for incipient motion it adequately reproduced a data set composed of 270 critical shields values measured in a flume with near uniform sediments the relevance of this research to field problems is discussed using a data set composed of 92 critical shields stresses obtained from field measurements finally a model is proposed for field applications taking into account the slope effect

geochemistry of bolivian salars lipez southern altiplano origin of solutes and brine evolution abstract the southern bolivian altiplano is a volcanic area which contains numerous undrained basins occupied by playas and saline lakes locally named salars solutes carried by springs and rivers into the salars originate mostly from the alteration of the volcanic rocks and the re solution of ancient buried evaporites both weathering and hydrothermal alteration lead to na hco 3 inflow waters of similar composition high contents of lithium and boron are not specifically related to hydrothermal activity evaporite leaching leads to na cl inflow waters of higher salinity atmospheric precipitation contributes only a small amount of ca and so 4 and very little na or cl the calculated evaporative evolution of the inflow waters shows that about half of them should become highly alkaline brines and the other half should end as near neutral brines however alkaline soda lakes are rare in this region most lake brines are of the na cl and na cl so 4 types to understand this anomaly one characteristic sequence of evaporating waters was studied in detail precipitation of calcite and mg smectites accounts only partially for the reduction of alkalinity a further loss of alkalinity is probably related to the oxidation of wind blown native sulfur in peripheral ponds wind blown sulfur is also deposited around the lakes on the drainage basins in the rainy season ephemeral streams carry along sulfur particles in permanent pools of the preconcentration areas a hydrologic control of brine chemistry is suspected inflow waters that should become alkaline appear to evolve to neutral brines if they remain in contact with atmospheric dust and peripheral colluvium for a long time on the contrary inflow waters to soda lakes are generally close to the shore and have only minimal contact with atmospheric dust and peripheral sediments presently all lakes are at relatively low levels and inflow waters often drain an important area of the drainage basin before reaching the topographic low in the past lakes were at higher levels and less interaction occurred between inflow waters atmospheric dust and peripheral sediments as a result the chemistry of some lakes may have changed during the quaternary

surface height adjustments in pyroclastic flow deposits observed at unzen volcano by jers 1 sar interferometry abstract pyroclastic flows from the 1990 1995 eruption of unzen a dacitic volcano in the southwest of japan descended the mountain along a variety of routes causing widespread damage and loss of life interferograms constructed from jers 1 l band synthetic aperture radar sar images show a number of features related to these pyroclastic flows and their secondary effects the most useful interferogram in this respect is based on images acquired on 22 july 1993 and 1 december 1993 and shows the descent paths for pyroclastic flows occurring in four valley systems within this time window as zones of decorrelation caused by the repeated resurfacing the 22 july 1993 sar image was through considerable good fortune acquired only 2 6 days after a major pyroclastic flow had descended into the mizunashi valley so that in the absence of rainfall the fresh 2 m thick deposits were dry when first imaged the largest differential surface height changes observed in the interferogram represent height decreases in the vertical of 12 cm and significantly lie within a small region of the mizunashi valley which was resurfaced by the pyroclastic flow of 19 july 1993 but not subsequently within this small region radar coherence is higher maximum correlation value of 0 75 in a center valley site where ash but relatively few large boulders are present in a qualitative sense the new ash surfaces exhibit higher levels of radar coherence than the older pre 19 july deposits in other unzen valleys visited by pyroclastic flows smaller differential surface height decreases 4 cm are observed where the surface deposits were emplaced by events taking place between 1 3 months before the acquisition date of the 22 july 1993 image the extra 8 cm of surface height decrease observed in the case of the freshly laid mizunashi deposits must result from a deflationary mechanism or mechanisms operating in a spatially uniform manner in order for radar coherence to be maintained a number of possible causative mechanisms including hydroconsolidation initiated by the seepage of rainwater into a newly deposited ash sheet deflation on gas release basal erosion settlement and substrate relaxation are discussed here given the relatively low emplacement temperatures of the unzen ash 300 500 c it is unlikely that viscous deformation within the body of the fresh ash deposits is responsible for the subsidence comparison of the 22 july 1993 1 december 1993 interferogram with a landsat 4 thematic mapper image of unzen acquired on 10 january 1994 highlights a ribbon like zone of radar decorrelation running along the course of the mizunashi valley which marks the path of debris flows that occurred within the time interval between the two sar images used in the construction of the interferogram overall these results demonstrate the utility of interferometric sar derived surface height and coherence measurements for monitoring the pyroclastic and debris flow regimes of active volcanoes

miocene to recent history of the western altiplano in northern chile revealed by lacustrine sediments of the lauca basin 18 15 18 40 s 69 30 69 05 w the intramontane lauca basin at the western margin of the northern chilean altiplano lies to the west of and is topographically isolated from the well known plio pleistocene lake system of fluvio lacustrine origin that covers the bolivian altiplano from lake titicaca to the north for more than 800 km to the salar de uyuni in the south the lauca basin is filled by a sequence of some 120 m of mainly upper miocene to pliocene elastic and volcaniclastic sediments of lacustrine and alluvial origin volcanic rocks partly pyroelastic provide useful marker horizons in the first period 6 4 ma of its evolution the lago lauca was a shallow ephemeral lake evaporites indicate temporarily closed conditions after 4 ma the lake changed to a perennial water body surrounded by alluvial plains in the late pleistocene and holocene 2 0 ma there was only marginal deposition of alluvial and glacial sediments the basin formed as a half graben or by pull apart between 10 and 15 ma tectonic displacement of the basal ignimbrite sequence during the quechua phase and 6 2 ma maximum k ar ages of biotites of tuff horizons in the deepest part of the basin apart from this early basin formation there has been surprisingly little displacement during the past 6 ma close to the western cordillera of the altiplano also climate indicators pollen evaporites sedimentary facies suggest that an arid climate has existed for the past 6 ma on the altiplano together these pieces of evidence indicate the absence of large scale block faulting tilt and major uplift during the past 5 6 ma in this area

hydrogeochemical fluxes and processes contributing to the formation of lithium enriched brines in a hyper arid continental basin abstract the accumulation of solutes delivered via shallow groundwater and surface water in arid to hyper arid closed basins and the complex hydrogeochemical processes associated with their transport are key to deciphering mechanisms responsible for the formation of brines and salts in these environments a rigorous investigation of the hydrogeochemical fluxes and the formation of the li enriched brine in the hyper arid basin of the salar de atacama chile is presented water fluxes within the salar de atacama basin range from 0 003 m3 s to 1 50 m3 s with a poor correlation between discharge and drainage basin area the inflowing waters have major elemental and li concentrations that are within the same order of magnitude over a period of several decades the element fluxes indicate for example that 58 of the li in the halite nucleus and brines is derived from the south and southeast parts of the basin the average 18ovsmow and dvsmow of inflow waters indicate that there are varied sources of recharge corresponding to the defined sub watershed regions the average water flux weighted 87sr 86sr of inflow waters allows further definition of where in the regional watershed the solutes are derived the predicted water flux weighted 87sr 86sr of the brines 0 70813 compared to the measured average 87sr 86sr 0 70801 indicates that there may be unaccounted sources of water and solutes to the basin brines elemental accumulation time scales for the volume of halite and brine in the nucleus balance on time frames of 0 5 ma mg 1 0 ma ca 1 9 ma li and 2 2 ma k as compared to 47 ma na and 53 ma cl further evidence that na and cl require additional sources not accounted for in the modern inflows to the topographic watershed dissolved noble gas concentrations of marginal and nucleus brines specify that the brines formed in an atmospheric equilibrated state and have since been isolated below the salt crust a process based model is presented to explain the extremely high concentrations of li in brines which incorporates the 7li isotope signatures of waters in the basin to further decipher on a first order the contributions of processes such as low temperature weathering and secondary phase formation

the origin of continental carbonates in andean salars a multi tracer geochemical approach in laguna pastos grandes bolivia abstract in continental volcanic settings abundant carbonate precipitation can occur with atypical facies compared to marine settings the bio chemical processes responsible for their development and early diagenesis are typically complex and not fully understood in the bolivian altiplano laguna pastos grandes hosts a 40 km2 carbonate platform with a great diversity of facies and provides an ideal natural laboratory to understand the processes responsible for the precipitation of carbonates in a continental province dominated by volcanism in order to trace the origin of both water and solutes in the lagoon the major element and stable isotope compositions 2h 18o 37cl 7li 11b and 87sr 86sr of the spring and stream waters were characterized as well as the stable isotope compositions 13c 15n and noble gas isotope ratios of hydrothermal gases associated with spring waters the results show that thermal springs discharging on the carbonate platform are close to saturation with calcite phreeqc modeling together with fluid geochemistry and temperature estimated from a combination of geothermometers indicate that ca in these springs is inherited from the alteration of the volcanic bedrock by aqueous fluids heated at 225 c and enriched in magmatic mantle derived co2 our results clearly show that the main driver for the precipitation of modern carbonates in laguna pastos grandes is the deeply sourced co2 which boosts the alteration of volcanic rocks at depth

degassing at anatahan volcano during the may 2003 eruption implications from petrology ash leachates and so2 emissions abstract on 10 may 2003 anatahan volcano located at 16 21 n 145 40 e on the mariana arc entered its first historical eruptive episode sending ash to 12 km into the atmosphere abundant accretionary lapilli quenched pumice textures and hydrothermal minerals in the earliest eruptive deposits indicate hydromagmatic interaction and active mining of the pre eruptive hydrothermal system whole rock compositions of the products erupted within the first week are chemically homogenous with sio 2 61 mgo 2 1 k 2 o 1 4 na 2 o 4 1 and fe 2 o 3 9 1 the products are classified as medium k andesites with tholeiitic affinity slightly more silicic matrix glass compositions up to 63 sio 2 in microlite rich matrices overlap with whole rock suggesting limited crystal fractionation with microlite crystallization responsible for the more evolved residual melt decreasing corrected loi values 2 3 1 4 wt upsection are consistent with waning hydrothermal mineral contributions as the eruption progressed oxygen fugacity calculations based on the ferric to ferrous iron ratio of bulk samples indicate an oxidized magma with nno 1 two pyroxene equilibrium thermometry suggests magmatic temperatures of 1050 1100 c matrix glass volatile contents show a degassed residual melt with 2 o 1000 2000 ppm cl 480 780 ppm f 50 150 ppm s and 2 a magmatic so 2 flux of 3 4 5 kt day was measured by cospec on 21 may ash leachate data indicate a decreasing s cl ratio 3 3 0 7 in the eruptive plume between 10 and 21 may with a relatively constant cl concentration assuming a constant cl flux an so 2 flux of 14 22 kt day is calculated for 10 may the average s concentration from ash leachates 1230 mg kg suggests that at least 25 of the so 2 60 kt erupted from anatahan between 10 and 21 may was removed from the plume by the precipitation of sulphate salts in the eruption column adsorbtion onto ash particles and subsequent deposition molar ratios in ash leachates elucidate caso 4 and nacl as the most likely soluble salts formed in the plume total element abundances molar s ca 1 and ca mg na and k ratios in the leachates suggest a hydrothermal fluid contribution to elements present as water soluble salts adsorbed onto ash sulfur budget calculations based on estimates of pre eruptive magmatic and residual melt s contents mass of erupted magma and total so 2 output fluxes require an additional source of s other than the erupted magma multiple lines of evidence including high so 2 emissions early in the eruption the presence of accretionary lapilli and hydrothermal minerals in the early eruptive deposits quenched pumice textures and cation and anion ratios and abundances in ash leachates suggest that a s rich free volatile phase exsolved from a large magma body magmatic volatiles were stored as components of the hydrothermal system pressurized gases hydrothermal fluids and or hydrothermal minerals to be remobilized early in the eruption to contribute to the total so 2 output

is the critical shields stress for incipient sediment motion dependent on channel bed slope data from laboratory flumes and natural streams show that the critical shields stress for initial sediment motion increases with channel slope which indicates that particles of the same size are more stable on steeper slopes this observation is contrary to standard models that predict reduced stability with increasing slope due to the added downstream gravitational force processes that might explain this discrepancy are explored using a simple force balance model including increased drag from channel walls and bed morphology variable friction angles grain emergence flow aeration and changes to the local flow velocity and turbulent fluctuations surprisingly increased drag due to changes in bed morphology does not appear to be the cause of the slope dependency because both the magnitude and trend of the critical shields stress are similar for flume experiments and natural streams and significant variations in bed morphology in flumes is unlikely instead grain emergence and changes in local flow velocity and turbulent fluctuations seem to be responsible for the slope dependency due to the coincident increase in the ratio of bed roughness scale to flow depth i e relative roughness a model for the local velocity within the grain roughness layer is proposed based on a 1 d eddy viscosity with wake mixing in addition the magnitude of near bed turbulent fluctuations is shown to depend on the depth averaged flow velocity and the relative roughness extension of the model to mixed grain sizes indicates that the coarser fraction becomes increasingly difficult to transport on steeper slopes

turbulent velocity profiles and boundary shear in gravel bed rivers vertical profiles of turbulent streamwise velocities in several new zealand gravel bed rivers are investigated field measurements made at high and low flows with electronic pitot tubes show logarithmic velocity profiles to extend over much of the flow depth for the gravel bed rivers studied the velocity at 0 6 of the total depth was generally a good indicator of depth averaged flow velocity an unambiguous definition of flow depth is adopted to deal with situations where the bed is uneven or moving when hydraulic roughness z sub 0 is defined as a fitted parameter of a logarithmic velocity profile the river data indicate that the profile origin displacement below the tops of roughness elements scales with z sub 0 no direct relation between z sub 0 and bed material size is evident under mobile bed conditions for these conditions a relation between hydraulic roughness and u squared is identified with u also derived as a log profile parameter a flow resistance equation using this relation is verified by comparison with mobile bed laboratory measurements in which u is not fitted from velocity profiles

persistence of the surface texture of a gravel bed river during a large flood we present herein clear field evidence for the persistence of a coarse surface layer in a gravel bed river during flows capable of transporting all grain sizes present on the channel bed detailed field measurements of channel topography and bed surface grain size were made in a gravel bed reach of the colorado river prior to a flood in 2003 runoff produced during the 2003 snowmelt was far above average resulting in a sustained period of high flow with a peak discharge of 27 m3 s 170 of normal peak flow all available grain sizes within the study reach were mobilized in this period of time during the 2003 peak flow the river avulsed immediately upstream of the study reach thereby abandoning approximately one half kilometer of the former channel the abandonment was rapid probably within a few hours leaving the bed texture essentially frozen in place at the peak of the flood all locations sampled prior to the flood were resampled following the stream abandonment in response to the high flow the surface median grain size d50s coarsened slightly in the outer part of the bend while remaining nearly constant along the inner part of the bend resulting in an overall increase from 18 to 21 mm for the study reach thus the coarse bed surface texture persisted despite shear stresses throughout the bend that were well above the critical entrainment value this may be explained because the response of the bed texture to increases in flow strength depends primarily upon the continued availability of the various grain size percentiles in the supply which in this case was essentially unlimited for all sizes present in the channel copyright 2007 john wiley sons ltd

chemistry of ash leachates to monitor volcanic activity an application to popocatepetl volcano central mexico abstract monitoring volcanic activity and assessing volcanic risk in an on going eruption is a problem that requires the maximum possible independent data to reduce uncertainty a quick relatively simple and inexpensive method to follow the development of an eruption and to complement other monitoring parameters is the chemical analysis of ash leachates particularly in the case of eruptions related to dome emplacement here the systematic analysis of so 4 2 cl and f concentrations in ash leachates is proposed as a valuable tool for volcanic activity monitoring however some results must be carefully assessed as is the case for s cl ratios since eruption of hydrothermally altered material may be confused with degassing of incoming magma sulfur isotopes help to identify so4 produced by hydrothermal processes from magmatic so2 lower s isotopic values correlated with higher f percentages represent a better indicator of fresh magmatic influence that may lead to stronger eruptions and emplacement of new lava domes additionally multivariate statistical analysis helps to identify different eruption characteristics provided that the analyses are made over a long enough time to sample different stages of an eruption

the immediate environmental effects of tephra emission the earth s history is punctuated by large explosive eruptions that eject large quantities of magma and silicate rock fragments into the atmosphere these tephra particles can sometimes be dispersed across millions of square kilometres or even entire continents the interaction of tephra with or in receiving environments may induce an array of physical chemical and biological effects the consequences for affected systems and any dependent communities may be chronic and localised in the event of frequent small eruptions while larger and rarer events may have acute regional scale impacts it is therefore necessary to document the range of possible impacts that tephra may induce in receiving environments and any resulting effects in interconnected systems we collate results from many studies to offer a detailed multidisciplinary and interdisciplinary review of the immediate post eruptive effects of tephra emission into the atmosphere onto vegetation soil or ice snow surfaces and in aquatic systems we further consider the repercussions that may be induced in the weeks to years afterwards in the atmosphere tephra can influence cloud properties and air chemistry by acting as ice nuclei in or by offering sites for heterogeneous reactions respectively tephra on vegetation causes physical damage and sustained coverage may elicit longer term physiological responses tephra deposits on soils may alter their capacity to exchange gas water and heat with the atmosphere or may have a specific chemical effect such as nutrient input or acidification on sensitive soils tephra deposition onto snow or ice may affect ablation rates rivers and lakes may experience turbidity increases and changes in their morphology as a result of fallout and prolonged months or years erosion from the tephra covered catchment in the first weeks after deposition tephra leaching may affect river chemistry the abundance and speciation of phytoplankton populations in lakes may be altered by tephra induced changes in water chemistry or sediment water nutrient cycling in the oceans tephra deposition may fertilise fe limited waters with potential impacts on the global carbon cycle embracing the full complexity of environmental effects caused by tephra fall demands a renewed investigative effort drawing on interdisciplinary field and laboratory studies combined with consideration of the interconnectivity of induced impacts within and between different receiving environments

the origin of brines and salts in chilean salars a hydrochemical review abstract northern chile is characterized by a succession of north south trending ranges and basins occupied by numerous saline lakes and salt crusts collectively called salars fossil salt crusts are found to the west in the extremely arid central valley while active salars receiving permanent inflows fill many intravolcanic basins to the east in the semiarid cordillera sea salts and desert dust are blown eastward over the cordillera where they constitute an appreciable fraction of the solute load of very dilute waters salt content evaporative concentration of inflow waters leads to sulfate rich or calcium rich near neutral brines alkaline brines are almost completely lacking the alkalinity calcium ratio of inflow waters is lowered by the oxidation of native sulfur reducing alkalinity and the deposition of eolian gypsum increasing ca concentration theoretically so4 rich inflow waters and their derived so4 rich brines should be found in the intravolcanic basins of the cordillera because of the ubiquity of native sulfur while ca rich brines should prevail in sedimentary basins where ca rich minerals are abundant this relation is perfectly observed in the salar de atacama the largest in chile however several salars located within the volcanic cordillera belong to the ca rich group inflows and brines may have acquired their ca rich composition in pleistocene time when their drainage basins were mainly sedimentary later on recent lava flows and ignimbrites covered the sedimentary formations underground waters may have kept their early sedimentary signature by continuous recycling however the weathering of volcanic rocks tend to slowly shift the water compositions from the ca rich to the so4 rich type

a critical perspective on 1 d modeling of river processes gravel load and aggradation in lower fraser river 1 we investigate how well a width averaged morphodynamic model can simulate gravel transport and aggradation along a highly irregular 38 km reach of lower fraser river and discuss critical issues in this type of modeling bed load equations with plausible parameter values predict a gravel input consistent with direct measurements and a sediment budget simulations using spatially varying channel width and forced by dominant discharge or a 20 year hydrograph match the observed downstream fining well they reproduce major qualitative features of a 47 year sediment budget and match maximum local rates of aggradation and degradation to well within a factor of 2 locations and rates of aggradation and degradation are influenced by channel constrictions runs for single years of unusually high or low peak discharge suggest that the main transfers of gravel occur in different parts of the reach in different years one dimensional morphodynamic modeling of highly nonuniform rivers has serious conceptual limitations but may be a valuable complement to empirical approaches

the missing dimension effects of lateral variation on 1 d calculations of fluvial bedload transport most calculations of bedload transport in rivers including those in numerical models of aggradation and degradation are 1 d all hydraulic and transport rate calculations are averaged over the channel width because bedload transport laws are nonlinear width averaged calculations will underestimate the true bedload flux if there is any local spatial variation in either the bed or the flow this paper analyses the effects on bedload transport capacity of spatial variation in applied and critical c shear stress separately and in combination a simple but versatile statistical model is used to represent variability in with allowance for differences between sand and gravel bed rivers and for below bankfull flow bedload flux is shown to increase greatly with the variance of especially in gravel bed rivers variability in c through bed patchiness may increase reduce or make little difference to bedload flux depending on the correlation between and c simple width averaging leads to severe underestimation of bedload transport in most conditions some alternatives are considered the findings have implications for sediment routing models srms but further research is needed to explore the issue fully

volcanic ash leachates a review and recommendations for sampling methods tephra in plumes can scavenge and thereby rapidly deposit volatiles including sulphur halogen and metal species these may then be leached e g by rainfall potentially releasing heavy loadings to soils and water bodies several eruptions have resulted in contamination of pasture sometimes with serious impacts on livestock water quality has also been an issue in some areas affected by tephra fall this work synthesises the literature on volcanic ash leachates and considers the controls on volatile adsorption general trends emerge for basaltic intermediate and silicic tephra as well as for variable particle size and transport distance the applications of ash leachate data to plume gas geochemistry calculation of volatile budgets and environmental impact assessment are evaluated comparisons for different eruptions are hampered by disparities in leachate analysis techniques a standardised methodology is therefore proposed to facilitate future health impact assessment and volcanological interpretation of results from different sites

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

bedload sheets in heterogeneous sediment field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin migrating accumulations of sediment and coarse grains cluster at their leading edge these accumulations are one or two coarse grains high and are much longer 0 2 0 6 m long in sand 0 5 2 0 m in fine gravel than their height the authors propose the term bedload sheet for these features and the authors argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment in essence coarse particles in the bedload slow or stop each other trap finer particles in their interstices and thus cause the coarse particles to become mobile again bedload sheets develop on the stoss side of dunes causing the dune to advance incrementally with the arrival of each sheet successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain size sorting that distinguishes cross bedding available flume experiments and field observations indicate that bedload sheets are a common but generally unrecognized feature of heterogeneous sediment transport

magma solidification processes beneath kilauea volcano hawaii a quantitative textural and geochemical study of the 1969 1974 mauna ulu lavas sents a late magma component formed in the summit magma storage region our results are consistent with the hypothesis that the components of the mu magmas followed two different routes the deformed olivine bearing magma moved along the deep basal

sediment supply and the development of the coarse surface layer in gravel bedded rivers the bed surface of most gravel rivers is considerably coarser than the sub surface or the gravel load transported over it a phenomenon affecting river dynamics morphology and ecology the coarse surface layer often called an armour or pavement has been attributed to an inherent tendency for small grains to settle between larger ones during active transport of all sizes1 2 and to selective erosion or trapping of finer particles when the coarse grains are relatively immobile3 4 where bedload supply is cut off below dams selective erosion causes coarsening5 6 using a simple quantitative model we propose that surface coarsening develops in gravel bedded rivers when local bedload supply from upstream is less than the ability of the flow to transport that load we present laboratory results which support this hypothesis and show that supply reduction causes changes in bedforms and progressive confinement of active bedload transport to a narrow band of finer bed surface bordered by a coarse less active bed it may therefore be possible to relate the degree of river bed surface coarsening to sediment supply resulting from land use

geochemistry of ash leachates from the 1993 lascar eruption northern chile implication for recycling of ancient evaporites abstract volcanic formations in the central andes overlie extensive amounts of ancient evaporites of cenozoic age recycling of buried salts in present closed basins through the hydrological cycle is a well known process another salt recycling process through volcanic activity has been detected in a recent eruption of the lascar volcano in northern chile about 10 9 metric tons of air fall tephra was deposited over the surrounding closed basins leaching experiments were carried out on ashes deposited near the summit and in a lower neighbouring valley summit ash leachates are almost pure caso 4 solutions whereas the valley ashes leachates are enriched in minor components leachates of the summit ash are near neutral whereas those of the valley ash have ph as high as 10 5 sulfur isotope composition of the leached sulfate is consistent with the volcanic recycling of tertiary gypsum present in the sedimentary section beneath the volcanic cordillera as a rough estimate about 700 000 tons of easily soluble caso 4 were added in only three days to the surrounding closed basins the high ph of the valley ash leachates is due to the hydration of alkali and alkaline earth metal oxides formed during pyrolysis of vegetation by hot ash efflorescent salts encrusted on plants and dissolution of volcanic glass provided some of the minor components the almost pure caso 4 composition of the leach waters is compositionally distinct from any present inflow waters in the central andes addition of caso 4 may explain some of the differences between the observed brine compositions and those predicted by simulating the evaporation of regular inflows the recycling of sedimentary gypsum is probably not restricted to lascar volcano the recycling of ancient salts and possibly also the pyrolysis of vegetation may have been crucial processes in the salt balance of closed basins during the intense volcanic activity of the tertiary

resistance equation for large scale roughness a theory of flow resistance for large scale roughness is developed the main points of which are supported by a flume study from which the outline of a process based resistance equation is determined rivers with large scale roughness have steep slopes and depths of the same order of magnitude as the bed material size flow resistance depends on the form drag of the roughness elements and their disposition in the channel theoretical considerations show resistance to be a function of reynolds number froude number roughness geometry and channel geometry these processes are examined using the results of flume experiments based on five different roughness beds and a wide range of flows semi empirical analysis supports the theory and allows the development of a theoretical power law resistance equation which accounts for most of the processes a summary of the data is presented for use in other research studies

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

intra and intercrystalline oxygen isotope variations in minerals from basalts and peridotites igneous phenocrysts commonly exhibit zoning in major and trace element composition reflecting and potentially constraining the differentiation and or mixing histories of their parent melts to date little work has been done characterizing zonation of oxygen isotopes in minerals from mafic and ultramafic rocks we present 259 ion probe cameca ims 1280 measurements of 18 o in 34 natural magmatic and mantle olivines and pyroxenes from five hand samples from diverse igneous environments we compare 18 o variations with zonation in other elements especially p analyzed by electron microprobe analysis empa and nano secondary ionization mass spectrometry nanosims there is generally a close average within 0 1 0 2 agreement between average 18 o values of olivines measured by sims standardized against san carlos olivine and independently known values for bulk separates from the same samples measured by laser fluorination these data demonstrate that current ion microprobe techniques are not only precise but also accurate enough for study of sub per mil oxygen isotope variations in silicates within 0 2 provided samples are prepared and analyzed following strict guidelines all but one of the 34 studied grains are homogeneous in 18 o within a small multiple of analytical precision estimated 0 2 1 for most data poorer for a subset of measurements made on small 5 m spots this population of isotopically homogeneous grains includes some with oscillatory micrometer scale p banding the lack of 18 o variations suggests that whatever factors lead to this common mode of trace element zonation have no detectable effect on melt crystal partitioning of oxygen isotopes large 2 oxygen isotope variations are observed in one olivine glomerocryst from mauna kea hawaii this glomerocryst contains p rich domains that are either equant or skeletal or feathery in outline and these p rich domains are systematically low in 18 o compared with adjacent later grown p poor olivine this unusual oxygen isotope zonation pattern might reflect a kinetic fractionation during nucleation and growth of the cores of some olivine phenocrysts we tested this hypothesis through measurements of 18 o distributions in synthetic olivines grown at a range of rates and exhibiting diverse patterns of p zoning these synthetic olivines are homogeneous in 18 o within the limits of our analyses 0 3 0 4 in this case and show no connection between p zonation and oxygen isotope heterogeneity we therefore think it more plausible that unusual o isotope zonation in the mauna kea glomerocryst reflects addition of a low 18 o component to some hawaiian magmas just before nucleation of olivine more generally this study demonstrates the utility of modern sims techniques for in situ study of the subtle 1 range oxygen isotope variations characteristic of common mafic and ultramafic rocks

giant evaporite belts of the neogene central andes large volumes of continental evaporites accumulated within the central andes during neogene uplift of the altiplano puna plateau and development of the andean volcanic arc halite and gypsum are dominant minerals along with local and economically important borates playa conditions have existed since ca 15 ma halite and borate deposition has occurred for the past 7 to 8 m y evaporites formed in salar environments e g playa lakes and are characterized by complex mineral assemblages occurrence zonation and geochemistry evaporite deposition was controlled by volcanism geothermal activity closed drainage and climate these andean deposits and their controls differ from evaporites in other continental and marine environments

sediment transport and resulting deposition in spawning gravels north coastal california incubating salmonid eggs in streambeds are often threatened by deposition of fine sediment within the gravel to relate sedimentation of spawning gravel beds to sediment transport infiltration of fine sediment 2 mm in diameter into clean gravel beds bed material size distributions scour fill depths and sediment transport during 10 storm flow events were measured in three streams of north coastal california although suspended sediment comprised most 75 94 of the clastic load during storm flows bed load material 0 25 2 mm accounted for most 70 78 of the fine sediment accumulated in experimental gravel implanted in the streambeds sand trapped in the interstices of the top several centimeters formed a seal that impeded deeper deposition of very fine sand and finer material the seal was responsible at least in part for a decrease in the rate of fine sediment accumulation with increasing cumulative bed load transport areas of the streambeds commonly scoured or filled 0 1 m or more during storm flows and thus scour and fill commonly created a sandy layer at least as thick as the seal formed by sediment infiltration scour could erode eggs laid in the bed and expose deeper levels of the bed to infiltration by fine sediment but at the same time could allow fine sediment to be winnowed away great temporal and spatial variation in sedimentation in these streams suggests that individual storms of moderate size pose a threat to eggs in many but not all areas selected by fish for spawning

variation in the reference shields stress for bed load transport in gravel bed streams and rivers 1 the present study examines variations in the reference shear stress for bed load transport r using coupled measurements of flow and bed load transport in 45 gravel bed streams and rivers the study streams encompass a wide range in bank full discharge 1 2600 m3 s average channel gradient 0 0003 0 05 and median surface grain size 0 027 0 21 m a bed load transport relation was formed for each site by plotting individual values of the dimensionless transport rate w versus the reach average dimensionless shear stress the reference dimensionless shear stress r was then estimated by selecting the value of corresponding to a reference transport rate of w 0 002 the results indicate that the discharge corresponding to r averages 67 of the bank full discharge with the variation independent of reach scale morphologic and sediment properties however values of r increase systematically with average channel gradient ranging from 0 025 0 035 at sites with slopes of 0 001 0 006 to values greater than 0 10 at sites with slopes greater than 0 02 a corresponding relation for the bank full dimensionless shear stress bf formulated with data from 159 sites in north america and england mirrors the relation between r and channel gradient suggesting that the bank full channel geometry of gravel and cobble bedded streams is adjusted to a relatively constant excess shear stress bf r across a wide range of slopes

the stable isotope composition of halite and sulfate of hyperarid soils and its relation to aqueous transport halite nacl and gypsum or anhydrite caso4 are water soluble minerals found in soils of the driest regions of earth and only modest attention has been given to the hydrological processes that distribute these salts vertically in soil profiles the two most notable chloride and sulfate rich deserts on earth are the dry valleys of antarctica and the atacama desert of chile while each is hyperarid they possess very different hydrological regimes we first show using previously published s and o isotope data for sulfate minerals that downward migration of water and sulfate is the primary mechanism responsible for depth profiles of sulfate concentration and s and o isotopes in both deserts in contrast we found quite different soluble cl concentration and cl isotope profiles between the two deserts for antarctic soils with an ice layer near the soil surface the cl concentrations increase with decreasing soil depth whereas the ratio of 37 cl 35 cl increases based on previous field observations by others we found that thermally driven upward movement of brine during the winter described by an advection diffusion model qualitatively mimics the observed profiles in contrast in the atacama desert where rare but relatively large rains drive cl downward through the profiles cl concentrations and 37 cl 35 cl ratios increased with depth the depth trends in cl isotopes are more closely explained by a rayleigh like model of downward fluid flow the isotope profiles and our modeling reveal the similarities and differences between these two very arid regions on earth and are relevant for constraining models of fluid flow in arid zone soil and vadose zone hydrology 2012 elsevier ltd all rights reserved

leachability of uranium and other elements from freshly erupted volcanic ash abstract a study of leaching of freshly erupted basaltic and dacitic air fall ash and bomb fragment samples unaffected by rain shows that glass dissolution is the dominant process by which uranium is initially mobilized from air fall volcanic ash si li and v are also preferentially mobilized by glass dissolution gaseous transfer followed by fixation of soluble uranium species on volcanic ash particles is not an important process affecting uranium mobility gaseous transfer however may be important in forming water soluble phases adsorbed to ash surfaces enriched in the economically and environmentally important elements zn cu cd pb b f and ba quick removal of these adsorbed elements by the first exposure of freshly erupted ash to rain and surface water may pose short term hazards to certain forms of aquatic and terrestrial life such rapid release of material may also represent the first step in transportation of economically important elements to environments favorable for precipitation into deposits of commercial interest ash samples collected from the active guatemalan volcanoes fuego and pacaya high al basalts and santiaguito hornblende hypersthene dacite bomb fragments from augustine volcano andesite dacite alaska and heimaey basalt vestmann islands iceland and fragments of rhyolitic pumice from various historic eruptions were subjected to three successive leaches with a constant water to ash weight ratio of 4 1 the volcanic material was successively leached by 1 distilled deionized water ph 5 0 5 5 at room temperature for 24 h which removes water soluble gases and salts adsorbed on ash surfaces during eruption 2 dilute hcl solution ph 3 5 4 0 at room temperature for 24 h which continues the attack initiated by the water and also attacks acid soluble sulfides and oxides 3 a solution 0 05 m in both na co and nahco ph 9 9 at 80 c for one week which preferentially dissolves volcanic glass the first two leaches mimic interaction of ash with rain produced in the vicinity of an active eruption the third leach accelerates the effect of prolonged contact of volcanic ash with alkaline ground water present during ash diagenesis

continuous monitoring of bedload flux in a mountain gravel bed river an automatic bedload monitoring station has been established on the perennial tordera river a mediterranean mountain gravel bed stream located in ne spain bedload fluxes were obtained automatically at 1 min intervals using two birkbeck type pit bedload samplers aligned across the width of the channel flow depth and water surface slope were both measured continuously and synchronously with bedload data for five flow events show that bedload flux varies considerably bedload flux is high when it is compared with other perennial streams for a 15 min interval maximum channel average bedload flux was 0 83 kg m 1 s 1 bedload records also show that there is no direct relationship between bedload flux and grain shear stress the low correlation between bedload flux and hydraulics arises due to the different thresholds of initiation of motion for each flow event and the variable character of the bed between events for two individual floods there is a reasonable relationship between bedload flux and grain shear stress in part as a consequence of individual particle entrainment and patch movement over a stable coarse gravel bed during moderately high discharges these results demonstrate that the birkbeck system functions well in a mediterranean mountain gravel bed stream with a longitudinal slope of 2

coarse sediment transport in mountain streams in colorado and wyoming usa since the early 1990s us forest service researchers have made thousands of bedload measurements in steep coarse grained channels in colorado and wyoming usa in this paper we use data from 19 of those sites to characterize patterns and rates of coarse sediment transport for a range of channel types and sizes including step pool plane bed pool riffle and near braided channels this effort builds upon previous work where we applied a piecewise regression model to 1 relate flow to rates of bedload transport and 2 define phases of transport in coarse grained channels earlier the model was tested using bedload data from eight sites on the fraser experimental forest near fraser colorado the analysis showed good application to those data and to data from four supplementary channels to which the procedure was applied the earlier results were however derived from data collected at sites that for the most part have quite similar geology and runoff regimes in this paper we evaluate further the application of piecewise regression to data from channels with a wider range of geomorphic conditions the results corroborate with those from the earlier work in that there is a relatively narrow range of discharges at which a substantial change in the nature of bedload transport occurs the transition from primarily low rates of sand transport phase i to higher rates of sand and coarse gravel transport phase ii occurs on average at about 80 per cent of the bankfull 1 5 year return interval discharge a comparison of grain sizes moved during the two phases showed that coarse gravel is rarely trapped in the samplers during phase i transport moreover the movement and capture of the d16 to d25 grain size of the bed surface seems to correspond with the onset of phase ii transport particularly in systems with largely static channel surfaces however while there were many similarities in observed patterns of bedload transport at the 19 studied sites each had its own bedload signal in that the rate and size of materials transported largely reflected the nature of flow and sediment particular to that system published in 2005 by john wiley sons ltd