decoding downstream trends in stratigraphic grain size as a function of tectonic subsidence and sediment supply downstream grain size fining in stratigraphy is driven primarily by selective deposition of sediment and the long term efficiency of this process is determined by 1 the magnitude and characteristics of the input sediment supply 2 the spatial distribution of subsidence rate which creates accommodation for sediment preservation and 3 the dynamics of sediment transport and deposition a key challenge is to determine how these first two factors control the caliber and spatial distribution of deposits over time scales of 10 4 10 6 yr without incorporating sediment transport details that are largely unknowable for time averaged stratigraphy in the geological past we address this using grain size data collected from fluvial conglomerates in the eocene pobla basin spanish pyrenees a synorogenic basin where the timing of sediment deposition is well constrained the sediment budget is closed and good exposure enables time lines within stratigraphy to be picked out unambiguously for successive stratigraphic horizons downstream trends in grain size and composition are derived for basin filling sediment routing systems with length scales of 6 and 40 km respectively our data show that the rate of grain size fining varies over time and with system length and can be linked to changes in source area these results are contrasted with grain size data from the antist group a 60 km long oligocene system that mantles the southern pyrenees where very slow rates of grain size fining on the wedge top of this fold and thrust belt are observed we apply a self similarity based selective deposition model to quantify the competing controls of tectonic subsidence and sediment supply on derived grain size trends and model results are compared with independent constraints on the eocene oligocene evolution of the pyrenees our results suggest that it is now possible to invert time averaged grain size trends in stratigraphy to gain quantitative information on the geological boundary conditions governing the evolution of sedimentary basins

the downstream gradation of particle sizes in the squamish river british columbia the exponential downstream decline in particle size predicted by sternberg 1875 is examined within a highly active alpine fluvial environment the gravel bed squamish river in southwestern british columbia transect survey procedures for sampling within the coarse alluvial gravels are described in detail downstream trends for various particle size statistics plotted with distance from a major sediment source are considered according to two scenarios evaluation of overall trends indicates that the downstream expression derived by sternberg 1875 is not the most appropriate rather curves are better described by power functions this reflects a very rapid decline in particle size immediately downstream of the major sediment source secondly evaluation of downstream trends in relation to channel planform determines that exponential functions with different coefficients describe adequately relations within individual planform reaches there is insufficient evidence to suggest which of these two scenarios may be appropriate several lines of evidence suggest that the trends found are more the result of selective sediment transport phenomena than of abrasion a condition attributed to channel competence within a system dominated by sediment supply conditions

long term bedload mobility in gravel bed rivers using iron slag as a tracer abstract bedload dispersion is evaluated in gravel bed rivers using slag elements from ironworks established along rivers in the ardenne region between the fourteenth and the nineteenth centuries large quantities of slag were dumped close to these rivers or even directly into the channels for centuries slag elements were dispersed in the bedload and transported by floods of varying importance consequently slag may be considered as a reliable tracer to analyze bedload dispersion over several centuries the size of slag elements was studied along 16 ardenne rivers the longitudinal size trend of the largest slag particles allows the effective competence of these rivers to be determined between 19 and 129 mm for rivers where specific stream power for the bankfull discharge ranges between 20 and 134 w m a direct relationship doesn t exist between these two parameters as the size of slag elements must be considered with regard to the d 50 of the bed selective transport was analyzed directly downstream of the input sites the sorting distance varies from river to river and depends on the velocity of the coarse elements introduced into the river since the inception of the iron industry downstream of two metallurgic sites the slag propagation fronts were located as the periods of activity at these sites are known from historical studies the virtual velocity of bedload movement in these rivers was estimated to be 2 4 km century

successful predictions of river characteristics across england and wales based on ordination predictions of river channel form under current conditions or in response to environmental or management changes and the rapid comparison of different channel reaches are important tasks in river management river classification is a common and valuable framework to address these aims but may suffer from the necessity to force a continuum of channel morphology into discrete groups more generally the scope to test the ability of predictive tools has been limited because of a shortage of field data in this study we used principal component analysis pca to identify the main sources of variation among river reaches in england and wales based on a set of 20 variables expected to correlate with channel morphology the pca scores were then used to predict the distributions of a wide range of hydromorphic features based on 4000 reaches surveyed in the river habitat survey baseline for comparison the predictive ability of three pairs of variables channel slope discharge slope catchment area and specific power catchment area was also tested the pca identified specific stream power channel size and groundwater input as the main sources of variation among reaches regression models using pca scores or paired variables were effective predictors of a range of channel characteristics including predominant substrate flow biotopes and channel vegetation channel cross sections and anthropogenic modifications were less predictable all of the approaches permitted simple plots of river reaches and quantitative comparisons of the dis similarity among individual reaches whilst the paired variables also minimised the data requirements our work reiterates the value of simple paired variables as a basis for rapidly comparing river reaches and for the first time quantifies the predictive ability of these approaches across a wide range of channel characteristics at a national scale principal component analysis provides a valuable exploratory tool for identifying the main sources of variation in complex multivariate data from which a simplified version e g specific power and area could be adopted

bed material texture in low order streams on the queen charlotte islands british columbia low order channels comprise a large proportion of the links of every drainage basin and are often at the centre of land management concerns they exhibit hydrological and geomorphological characteristics atypical of higher order links this paper examines the nature and causes of variations in the bed material texture of two streams on the queen charlotte islands british columbia the extant functional exponential model is found to be inadequate for explaining observed changes in grain size parameters with distance downstream recurrent disruption of sediment transport by large organic debris jams and the sporadic contamination of the fluvial sediment population by colluvial inputs preclude the development of longitudinal structure rather grain size varies erratically over short distances a stochastic model best describes the observed variations and should be adopted as an alternative to the exponential model in low order links characteristic variances are controlled by the degree of hillslope channel coupling and the extent and characteristics of non alluvial storage mechanisms

evaluation of the physical and chemical properties of eyjafjallajokull volcanic plume using a cloud resolving model the eyjafjallajokull volcanic eruption which occurred on april 14 2010 caused many environmental air traffic and health problems an attempt has been made to demonstrate for the first time that certain improvements could be made in the quantitative prediction of the volcanic ash parameters and in the accounting of the processes in the immediate vicinity of the volcano using a cloud resolving model this type of explicit modeling by treatment of volcanic ash and sulfate chemistry parameterization with input of a number parameters describing the volcanic source is the way forward for understanding the complex processes in plumes and in the future plume dispersion modeling results imply that the most significant microphysical processes are those related to accretion of cloud water cloud ice and rainwater by snow and accretion of rain and snow by hail the dominant chemical conversion rates that give a great contribution to the sulfate budget are nucleation and dynamic scavenging and oxidation processes a three dimensional numerical experiment has shown a very realistic simulation of volcanic ash and other chemical compounds evolution with a sloping structure strongly influenced by the meteorological conditions in cloud oxidation by h2o2 is the dominant pathway for so2 oxidation and allows sulfate to be produced within the so2 source region the averaged cloud water ph of about 5 8 and rainwater ph of 4 5 over simulation time show quantitatively how the oxidation may strongly influence the sulfate budget and acidity of volcanic cloud compared to observations model results are close in many aspects information on the near field volcanic plume behavior is essential for early preparedness and evacuation this approach demonstrates a potential improvement in quantitative predictions regarding the volcanic plume distribution at different altitudes it could be a useful tool for modeling volcanic plumes for better emergency measures planning

ice formation in ash influenced clouds after the eruption of the eyjafjallajokull volcano in april 2010 1 the influence of volcanic ash on heterogeneous ice nucleation in tropospheric clouds is investigated on the basis of 90 observed cloud cases the clouds were observed with polarization lidars at the two central european earlinet stations leipzig 51 3 n 12 4 e and maisach 48 2 n 11 3 e 25 km northwest of munich germany in volcanic aerosol layers which originated from the strong eruptions of the icelandic eyjafjallajokull volcano in april 2010 case studies of evolving boundary layer cumuli and long lasting free tropospheric cloud events with unusual behavior mixed phase cloud complex cirrus deck are discussed a clear impact of ash is observed the ice nuclei concentration derived from the lidar observations has been estimated to range from 2 20 per liter in the boundary layer and from 100 300 per liter at cirrus level the statistical analysis based on the 90 evaluated cloud cases revealed that all observed cloud layers with cloud top temperatures of below 15 c contained ice typically under non volcanic aerosol conditions such a high fraction of ice containing clouds is not reached before temperatures decrease below 25 c over central europe

an experimental study of wind abrasion rocks were abraded by a sand laden air jet in the laboratory to examine the quantitative relationships between wind abrasion and wind velocity quantity and grain size of windblown sand particles and physical properties of the target rocks the results of 101 runs are expressed by an experimental equation with dimensionless constant which indicates that the rate of abrasion is directly related to the kinetic energy of the sand projectiles and inversely proportional to the compressive strength of the target rocks a tentative extension of the experimental equation to field condition leads to an equation for the wind abrasion in fields an application of the latter equation to the natural settings is preliminarily examined by comparing it with sharp s 1964 field experiments and a plausible result is obtained

sex that moves mountains the influence of spawning fish on river profiles over geologic timescales abstract a key component of resilience is to understand feedbacks among components of biophysical systems such as physical drivers ecological responses and the subsequent feedbacks onto physical process while physically based explanations of biological speciation are common e g mountains separating a species can lead to speciation less common is the inverse process examined can a speciation event have significant influence on physical processes and patterns in a landscape when such processes are considered such as with ecosystem engineers many studies have focused on the short term physical and biological effects rather than the long term impacts here we formalized the physical influence of salmon spawning on stream beds into a model of channel profile evolution by altering the critical shear stress required to move stream bed particles we then asked if spawning and an adaptive radiation event similar to the one that occurred in pacific salmon species could have an effect on channel erosion processes and stream profiles over geological timescales we found that spawning can profoundly influence the longitudinal profiles of stream beds and thereby the evolution of entire watersheds the radiation of five pacific salmon from a common ancestor additionally could also cause significant geomorphic change by altering a wider section of the profile for a given distribution of grain sizes this modeling study suggests that biological evolution can impact landscape evolution by increasing the sediment transport and erosion efficiency of mountain streams moreover the physical effects of a species on its environment might be a complementary explanation for rapid radiation events in species through the creation of new habitat types this example provides an illustrative case for thinking about the long and short term coupling of biotic and abiotic systems

downstream changes in the channel geometry of a large gravel bed river 1 field data obtained on a nearly contiguous segment of the colorado river in western colorado and eastern utah are used to examine the mechanisms driving downstream changes in channel geometry measurements characterizing the bank full hydraulic geometry bed material grain size and average channel gradient were made at closely spaced intervals in 10 alluvial and quasi alluvial reaches covering 260 km of the river these data indicate that changes in surface and subsurface grain sizes are small in relation to the change in channel slope over the full length of the study area the median grain size of the surface sediment decreases by a factor of a little more than 2 whereas the average channel slope decreases by a factor of about 5 the decreases in slope and median grain size are offset by a large increase in bank full depth relative to width such that the bank full shields stress b is constant downstream for the reach as a whole b averages 0 049 which is roughly 50 higher than the threshold for bed load transport

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

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

trends of grain sizes on gravel bars in the rio chagres panama abstract we examined the trends of grain sizes along the upper 414 km 2 of the mountainous rio chagres drainage basin in panama gravel bars were sampled along 40 km of the rio chagres and five major tributary streams using a transect pebble count of median diameter lithology and clast rounding although previous investigators have found that downstream fining can be obscured by inputs of colluvial sediment and other local controls in mountain drainages we decided to examine the trends of grain sizes along a tropical mountain river where rapid weathering and high capability of transport might be capable of overriding the input effects of colluvium specifically we tested the hypotheses that downstream fining would be present as a result of selective sorting and that weak felsic particles would decrease in size preferentially to strong mafic particles because of abrasion statistical analyses reveal a weak downstream decrease of sediment size on gravel bars along the study reach of the rio chagres with a sternberg diminution coefficient for felsic and mafic grains of 0 013 and 0 017 respectively felsic clasts have thicker weathering rinds and become rounded downstream faster than mafic particles but tumbling mill tests of abrasion show no significant differences in rate of mass loss in relation to lithology and downstream decreases in grain size are similar between lithologies dividing the study reach into six sub reaches bounded by major tributary junctions we further tested the hypothesis that downstream trends in fining might be obscured at the basin scale by sediment input from tributaries but that trends in grain sizes might be more visible at the reach scale between tributaries we did not find any consistent trends in grain size between tributaries stream width appears to assert a local control on grain size coarse particles are associated with narrow channel reaches whereas smaller particles are associated with wide channel reaches

the morphology of graded gravel rivers a network perspective analytical hydraulic geometry equations are combined with a watershed model to quantify downstrem trends in equilibrium fluvial morphology in gravel streams the hydraulic geometry equations relaet fluvial morphology to discharge bedload transport rate and grain size these independent variables are in turn determined by routing gravel supplied at zero order basins through a channel network as gravel is routed downstream it decreases in size according to an empirical power law the resulting model specifies the discharge bedload transport rate grain size width depth slope and river bed elevation at every point in the drainage basin when the downstream fining law is calibrated using data from central pennsylvania dowstream hydraulic geometry exponents for the width and depth are accurately reproduced longitudinal profiles calculated from the model fit observed profiles in largerwatersheds but are inaccurate in smaller watersheds the model also reproduces hack s 1957 empirical result relating slope to the 0 6 power of a ds where a is the drainage basin area and ds is the mean grain size unfortunately the model requires an equilibrium time scale which is unreasonably long suggesting that the channels of the study area are best described as systems with multiple time scales and multiple rates of response the model probably is successful because the width and depth have relatively short relaxation times and also because downstream trends in discharge and sediment transport rate are controlled by network topology thus downstream hydraulic geometry equations do not necessarily provide strong evidence for the equilibrium of fluvial landscapes rather they reflect the constancy of network topology and the rapid response times of width and depth

a case study of observations of volcanic ash from the eyjafjallajokull eruption 2 airborne and satellite radiative measurements 1 an extensive set of airborne and satellite observations of volcanic ash from the eyjafjallajokull icelandic eruption are analyzed for a case study on 17 may 2010 data collected from particle scattering probes and backscatter lidar on the facility for airborne atmospheric measurements faam bae 146 aircraft allow estimates of ash concentration to be derived using radiative transfer simulations we show that airborne and satellite infrared radiances can be accurately modeled based on the in situ measured size distribution and a mineral dust refractive index furthermore airborne irradiance measurements in the 0 3 1 7 m range are well modeled with these properties retrievals of ash mass column loading using infrared atmospheric sounding interferometer iasi observations are shown to be in accord with lidar derived mass estimates giving for the first time an independent verification of a hyperspectral ash variational retrieval method the agreement of the observed and modeled solar and terrestrial irradiances suggests a reasonable degree of radiative closure implying that the physical and optical properties of volcanic ash can be relatively well constrained using data from state of the science airborne platforms such as the faam bae 146 aircraft comparisons with iasi measurements during recent grimsvotn and puyehue volcanic eruptions demonstrate the importance of accurately specifying the refractive index when modeling the observed spectra

weathering controlled abrasion in a coarse grained meandering reach of the rio grande implications for the rock record abrasion mill analysis of fluvial clast 4 0 mm abrasion in a meandering reach of the rio grande south central colorado indicates that 1 abrasion rates of natural clasts from various locations in the channel and flood plain differ very little 2 abrasion rates in the first few hours are high then drop to much lower levels for these natural clasts and 3 a previously experimentally abraded clast sample otherwise identical to natural samples had a much lower initial abrasion rate than any natural samples the initial high abrasion rate of all natural clasts can be attributed to the presence of an easily abraded weathered layer we interpret the relatively abrupt drop in abrasion rate after a few hours of abrasion to the complete removal of the weathered layer and the exposure of more resistant rock the low initial abrasion rate of the previously experimentally abraded sample supports this interpretation and also indicates that none of the clasts in the river have been abraded as extensively as the experimentally abraded samples from this we infer that clasts have not traveled very far in the channel these results have led to the development of a weathering controlled abrasion model to explain the effect of abrasion on downstream fining size reduction over distance downstream weathering controlled abrasion is essentially a step function in time composed of the alternation of long periods of weathering with no abrasion flood plain storage with very brief but intense periods of mechanical abrasion channel transport this alternation of weathering and abrasion can produce a net abrasion rate sufficient to generate the amount of downstream fining present along the rio grande and also can explain why many abrasion mill experiments which simulate abrasion but not weathering fail to reproduce natural abrasion rates changes in the amount of fluvial downstream fining in an aggrading basin margin and thus in the rock record can result from variation in selective deposition temporary or permanent flood plain storage or from changes in the abrasion rate experiments demonstrate however that the complex interaction between these two processes may in some cases obscure the tectonic signal that is commonly interpreted from basin margin depositional geometries

from grain size to tectonics 1 regional grain size trends in fluvial successions can reveal important information regarding the dynamics of sediment routing systems self similar solutions for down system grain size fining have recently been proposed to explore how key variables such as the spatial distribution of deposition sediment discharge and sediment supply characteristics control spatial distribution of grain size in fluvial successions over time scales of 104 106 years we explore the sensitivity of these solutions to changes in key variables and assess their applicability to ancient fluvial successions several sensitivity analyses are presented to investigate the relative control of the key model variables on the spatial pattern of down system grain size fining in fluvial successions sensitivity analyses demonstrate that 1 an increase in the initial value of sediment discharge to a basin causes a decrease in the rate of grain size fining in fluvial successions an effect that becomes nonlinear for large values of initial sediment discharge 2 a short wavelength high amplitude subsidence regime generates a greater rate of down system grain size fining and a long wavelength lower amplitude subsidence regime generates a lesser rate of down system grain size fining in fluvial successions and 3 an increase in the spread of grain sizes in the sediment supply generates a greater rate of down system grain size fining we apply this modeling technique to grain size data sets collected from two time surfaces within conglomerates of the upper eocene montsor fan succession of the pobla basin spanish pyrenees these data sets exhibit approximately self similar grain size distributions further the observed increase in down system grain size fining associated with smaller depositional system lengths provides support for the application of self similar solutions to fluvial successions by applying these solutions to carefully collected grain size data from fluvial successions we are able to relate explicitly the initial grain size supplied to the system the spatial distribution of subsidence and the sediment discharge into the basin to the rate of grain size fining in fluvial successions this method thus offers a powerful means of elucidating sediment routing system dynamics over time

flow and sediment dynamics in channel confluences confluences with relatively low discharge and momentum flux ratios where a small steep tributary with a high supply of poorly sorted sediment joins a large low gradient main channel commonly occur in nature but they have not yet been investigated measurements of the three dimensional velocity field turbulence sediment transport bed material grain size and morphology are reported in a laboratory setting that is representative of confluences on the upper rhone river switzerland the difference between the low flow depth in the steep tributary and the higher flow depth in the main channel creates a marked bed discordance in the tributary zone due to this bed discordance the tributary flow penetrates into the main channel mainly in the upper part of the water column whereas the main channel flow is hardly hindered by the tributary in the lower part of the water column giving rise to a two layer flow structure in the confluence zone in confluences with high supply of coarse sediment from the tributary the development of a deposition bar downstream from the confluence reduces the flow area and causes flow acceleration that contributes to an increase in sediment transport capacity the sediment supplied by the tributary is mainly sorted and transported on the face of the bar by the near bed flow originating from the main channel the sediment transport capacity is further increased by the three dimensionality of the flow which is characterized by maximum velocities occurring near the bed and by a considerable increase in turbulent kinetic energy generated in the shear layer at the interface of the flows originating from the main channel and the tributary a conceptual model is proposed for the hydro morpho sedimentary processes and compared to existing conceptual models for confluences with different characteristics

high levels of particulate matter in iceland due to direct ash emissions by the eyjafjallajokull eruption and resuspension of deposited ash 1 the dangers to people living near a volcano due to lava and pyroclastic flows and on glacier or snow covered volcanoes jokulhlaups are well known the level of risk to human health due to high concentrations of ash from direct emission and resuspension from the ground is however not as well known the eruption at eyjafjallajokull 14 april to 20 may 2010 produced abundant particulate matter due to its explosive eruption style even after the volcanic activity ceased high particulate matter pm concentrations were still measured on several occasions due to resuspended ash the 24 hour mean concentration of pm10 in the small town of vik 38 km se of the volcano reached 1230 g m 3 which is about 25 times the health limit on 7 may 2010 with 10 min average values over 13 000 g m 3 even after the eruption ceased values as high as 8000 g m 3 10 min and 900 g m 3 24 h were measured because of resuspension of freshly deposited fine ash in reykjavik 125 km wnw of the volcano the pm10 concentration reached over 2000 g m 3 10 min during an ash storm on 4 june 2010 which should have warranted airport closure summarizing our study reveals the importance of ash resuspension compared to direct volcanic ash emissions this likely has implications for air quality but could also have detrimental effects on the quality of ash dispersion model predictions which so far generally do not include this secondary source of volcanic ash

downstream patterns of bed material grain size in a large lowland alluvial river subject to low sediment supply 1 a new data set of bimodal subaqueous channel bed sediments was analyzed for longitudinal patterns in grain size it yielded two interesting observations 1 separate fining trends in d50 exist for gravel and fines that overlap for 175 river kilometers and 2 this overlap in fining trends results in a protracted nonabrupt gravel to sand transition these suggest bed patchiness that is interpreted in the context of inherent grain size bimodality localized hydraulic sorting due to spatially heterogeneous and low sediment supply and local deviations in channel gradient the data also show that tributaries have a minor impact on main stem downstream fining due to basin shape and tectonic history in addition subaqueous channel sediments were observed to be finer than nearby sediments collected from exposed bars which may indicate a narrow active zone of transport where bars are disconnected from sediment movement this research has implications for bed material collection and theories of downstream fining

quantitative shape measurements of distal volcanic ash 1 large scale volcanic eruptions produce fine ash 200 m which has a long atmospheric residence time 1 hour or more and can be transported great distances from the volcanic source thus becoming a hazard to aircraft and public health ash particles have irregular shapes so data on particle shape size and terminal velocities are needed to understand how the irregular shaped particles affect transport processes and radiative transfer measurements in this study a methodology was developed to characterize particle shapes sizes and terminal velocities for three ash samples of different compositions the shape and size of 2500 particles from 1 distal fallout 100 km of the 14 october 1974 fuego eruption basaltic 2 the secondary maxima 250 km of the 18 august 1992 spurr eruption andesitic and 3 the miocene ash hollow member nebraska rhyolitic were measured using image analysis techniques samples were sorted into 10 to 19 terminal velocity groups 0 6 59 0 cm s using an air elutriation device grain size distributions for the samples were measured using laser diffraction aspect ratio feret diameter and perimeter measurements were found to be the most useful descriptors of how particle shape affects terminal velocity these measurement values show particle shape differs greatly from a sphere commonly used in models and algorithms the diameters of ash particles were 10 120 larger than ideal spheres at the same terminal velocity indicating that irregular particle shape greatly increases drag gas adsorption derived surface areas are 1 to 2 orders of magnitude higher than calculated surface areas based on measured dimensions and simple geometry indicating that particle shapes are highly irregular correction factors for surface area were derived from the ash sample measurements so that surface areas calculated by assuming spherical particle shapes can be corrected to reflect more realistic values

a case study of observations of volcanic ash from the eyjafjallajokull eruption 1 in situ airborne observations on 17 may 2010 the faam bae 146 aircraft made remote and in situ measurements of the volcanic ash cloud from eyjafjallaja kull over the southern north sea the falcon 20e aircraft operated by deutsches zentrum fa r luft und raumfahrt dlr also sampled the ash cloud on the same day while no a wingtip to wingtipa co ordination was performed the proximity of the two aircraft allows worthwhile comparisons despite the high degree of inhomogeneity e g column ash loadings varied by a factor of three over 100 km the range of ash mass concentrations and the ratios between volcanic ash mass and concentrations of so2 o3 and co were consistent between the two aircraft and within expected instrumental uncertainties the data show strong correlations between ash mass so2 concentration and aerosol scattering with the faam bae 146 data providing a specific extinction coefficient of 0 6a 0 8 m2 g 1 there were significant differences in the observed ash size distribution with faam bae 146 data showing a peak in the mass at 3 5 mm volume equivalent diameter and dlr data peaking at 10 mm differences could not be accounted for by refractive index and shape assumptions alone the aircraft in situ and lidar data suggest peak ash concentrations of 500a 800 mg m 3 with a factor of two uncertainty comparing the location of ash observations with the ash dispersion model output highlights differences that demonstrate the difficulties in forecasting such events and the essential nature of validating models using high quality observational data from platforms such as the faam bae 146 and the dlr falcon

impact of coarse sediment supply from hillslopes to the channel in runoff dominated dryland fluvial systems sediment supply from hillslopes to channels is an important control on basin functioning and evolution however current theoretical frameworks do not adequately consider processes of runoff driven hillslope sediment supply which affect river channels spatially and temporally mountainous dryland basins exhibit an important manifestation of these processes because their debris mantled hillslopes produce coarse sediment and because rainfall is delivered as infrequent high intensity short duration rainstorms this paper combines field measurements and modeling to explore runoff driven coarse sediment supply from hillslopes to the channel and assesses a range of plausible storms on the longitudinal patterns of sediment load and its caliber over a dryland basin reach our results show that modeled sediment load and its grain size distribution are determined by the nonlinear interaction between rainfall characteristics and hillslope attributes resulting in longitudinal fluctuations in sediment supply the relative magnitude and location of which varies between storms results suggest that long hillslopes are most sensitive to rainfall and they exhibit large variations in supplied sediment load and grain size for different runoff characteristics short and steep hillslopes are less sensitive to rainfall variations as gradient effects dominate over the role of length in modulating runoff accumulation furthermore the signal of the median fraction d50 of modeled sediment supplied by the hillslope is preserved in the coarse fraction of the measured in channel grain sizes d90 finally we propose a simple index which provides new insights into the effectiveness of different rainstorms in terms of the impact of hillslope sediment supply on the channel

subsidence control on river morphology and grain size in the ganga plain the ganga plain represents a large proportion of the current foreland basin to the himalaya the himalayan sourced waters irrigate the plain via major river networks that support approximately 10 percent of the global population however some of these rivers are also the source of devastating floods the tendency for some of these rivers to flood is directly linked to their large scale morphology in general the rivers that drain the east ganga plain have channels that are perched at a higher elevation relative to their floodplain leading to more frequent channel avulsion and flooding in contrast those further west have channels that are incised into the floodplain and are historically less prone to flooding understanding the controls on these contrasting river forms is fundamental to determining the sensitivity of these systems to projected climate change and the growing water resource demands across the plain here we present a new basin scale approach to quantifying floodplain and channel topography that identifies areas where channels are super elevated or entrenched relative to their adjacent floodplain we explore the probable controls on these observations through an analysis of basin subsidence rates sediment grain size data and sediment supply from the main river systems that traverse the plain yamuna ganga karnali gandak and kosi rivers subsidence rates are approximated by combining basement profiles derived from seismic data with known convergence velocities results suggest a more slowly subsiding basin in the west than the east grain size fining rates are also used as a proxy for relative subsidence rates along the strike of the basin the results also indicate higher fining rates and hence subsidence rates for given sediment supply in the east by integrating these observations we propose that higher subsidence rates are responsible for a deeper basin in the east with perched low gradient river systems that are relatively insensitive to climatically driven changes in base level in contrast the lower subsidence rates in the west are associated with a higher elevation basin topography and entrenched river systems recording climatically induced lowering of river base levels during the holocene

longitudinal profiles in simple alluvial systems theoretical considerations suggest that exponential or quadratic functions are apt for describing the longitudinal profiles of aggrading alluvial systems that are unaffected by significant lateral inputs of water or sediment a new set of field data confirms this for individual sedimentary links along a wandering gravel bed river in british columbia canada each link is viewed as a simple alluvial system without major water or sediment inputs within which grain size typically fines downstream in a relatively systematic manner such homogeneous reaches are suitable for the investigation of simple profile form it is found that quadratic approximations are the most flexible descriptor for link longitudinal profiles overall the river forms an irregularly cuspate long profile structured by these fundamental length scale units both link gradients and link fining rate reflect size selective aggradation associated with the bounding lateral inputs

grain size along two gravel bed rivers statistical variation spatial pattern and sedimentary links a new set of field data facilitates a detailed analysis of variations in bed material grain size within two confluent gravel bed rivers in northeastern british columbia canada a preliminary assessment of grain size variability establishes a basis for examination of the spatial pattern of grain size change standard anova techniques are inappropriate because individual samples have unequal variances and are not normally distributed alternative tests for homoscedasticity and comparison of means are therefore utilized within site between sample variability is not significant the grain size distributions that were obtained at individual sites are therefore representative of the depositional environments that were sampled in both rivers mean grain size does vary significantly between sites and there is therefore a basis for examining the data for spatial patterns such as downstream fining textural variations along the two rivers studied here are complex and show negligible overall fining in over 100 km this is the consequence of a large number of tributary inputs and non alluvial sediment sources which are the legacy of late pleistocene glaciation the identification of lateral sources like these is fundamental for understanding textural changes within rivers the sedimentary link a channel reach between significant lateral sediment inputs provides a means of isolating fluvial maturation processes abrasion and sorting from contingent lateral inputs strong fining trends are apparent in most links and classification of grain size measurements according to their location within particular links greatly improves the statistical explanation of textural variation identification of sedimentary links provides a means of applying models of fluvial fining processes so isolation of link networks will aid the development of basin scale models of textural variation 1998 john wiley sons ltd

a model for wet aggregation of ash particles in volcanic plumes and clouds 2 model application 1 the occurrence of particle aggregation has a dramatic effect on the transport and sedimentation of volcanic ash the aggregation process is complex and can occur under different conditions and in multiple regions of the plume and in the ash cloud in the companion paper costa et al develop an aggregation model based on a fractal relationship to describe the rate particles are incorporated into ash aggregates the model includes the effects of both magmatic and atmospheric water present in the volcanic cloud and demonstrates that the rate of aggregation depends on the characteristics of the initial particle size distribution the aggregation model includes two parameters the fractal exponent df which describes the efficiency of the aggregation process and the aggregate settling velocity correction factor e which influences the distance at which distal mass deposition maxima form both parameters are adjusted using features of the observed deposits here this aggregation model is implemented in the fall3d volcanic ash transport model and applied to the 18 may 1980 mount st helens and the 17 18 september 1992 crater peak eruptions for both eruptions the optimized values for df 2 96 3 00 and e 0 27 0 33 indicate that the ash aggregates had a bulk density of 700 800 kg m 3 the model provides a higher degree of agreement than previous fully empirical aggregation models and successfully reproduces the depositional characteristics of the deposits investigated over a large range of scales including the position and thickness of the secondary maxima

an approach for measuring confinement and assessing the influence of valley setting on river forms and processes valley setting and confinement or lack thereof are primary controls on river character and behaviour although there are various proxies for valley confinement direct measures that quantify the nature and extent of confinement are generally lacking and or inconsistently described as such they do not lend themselves to consistent analysis over large spatial scales here we clearly define forms of confinement to aid in quantification of degrees of confinement types of margin that can induce confinement are differentiated as a valley margin valley bottom margin and or anthropogenic margin such margins sometimes overlap and share the same location and in other situations are separated giving immediate clues as to the valley setting we apply this framework to examples from australia united states and new zealand showing how this framework can be applied across the spectrum of river diversity this method can help to inform interpretations of reach scale river behaviour highlighting the role of antecedent controls on contemporary forms and processes clear definitions of confinement are shown to support catchment scale analysis of river patterns along longitudinal profiles and appraisals of the geomorphic effectiveness of floods and sediment flux in catchments e g process zone distribution lateral sediment inputs and dis connectivity copyright 2015 john wiley sons ltd

evaluating the structure and magnitude of the ash plume during the initial phase of the 2010 eyjafjallajokull eruption using lidar observations and name simulations 1 the eyjafjallajokull volcano in iceland erupted explosively on 14 april 2010 emitting a plume of ash into the atmosphere the ash was transported from iceland toward europe where mostly cloud free skies allowed ground based lidars at chilbolton in england and leipzig in germany to estimate the mass concentration in the ash cloud as it passed overhead the uk met office s numerical atmospheric dispersion modeling environment name has been used to simulate the evolution of the ash cloud from the eyjafjallajokull volcano during the initial phase of the ash emissions 14 16 april 2010 name captures the timing and sloped structure of the ash layer observed over leipzig close to the central axis of the ash cloud relatively small errors in the ash cloud position probably caused by the cumulative effect of errors in the driving meteorology en route result in a timing error at distances far from the central axis of the ash cloud taking the timing error into account name is able to capture the sloped ash layer over the uk comparison of the lidar observations and name simulations has allowed an estimation of the plume height time series to be made it is necessary to include in the model input the large variations in plume height in order to accurately predict the ash cloud structure at long range quantitative comparison with the mass concentrations at leipzig and chilbolton suggest that around 3 of the total emitted mass is transported as far as these sites by small 100 m diameter ash particles

rock type controls on downstream changes in clast parameters in sandur systems in southeast iceland abstract the role of rock type in controlling downstream variation in clast parameters in non jokulhlaup affected oraefi sandar in iceland was evaluated clast changes in the svinafellsa are simple but the effects of tributary sources complicate the clast parameter distance relationships in the morsardalur kjos system the behavior of individual rock types must be studied to understand the changes both selective sorting and abrasion are taking place and the relative importance of these processes is evaluated the volcanic rocks are rounding relatively rapidly with variation among individual rock types but there are no significant changes in sphericity and clast form with distance the compressive strength of the volcanic suite is variable and significant weathering changes must be takin place during transport from rock face to distal sandur the influence of such weathering changes on changes in clast parameters needs further research

the impact of the atmosphere on the eyjafjallajokull 2010 eruption plume 1 the eruption of eyjafjallajokull volcano in 2010 lasted 39 days 14 april 23 may the eruption had two explosive phases separated by a phase with lava formation and reduced explosive activity during the explosive phases there were episodes of strong winds that advected ash to the south and southeast leading to widespread disruptions in air traffic the height of the eruption plume was monitored with a weather radar and with web cameras mounted with a view of the volcano three different types of the impact of the ambient atmosphere on the eruption plume are described first the weather situation throughout the eruption has been analyzed the frequency of northerly wind component is found to be unusually high or 71 in comparison to 49 on average in spring secondly during the effusive phase of the eruption diurnal variation was observed in the plume altitude and there is evidence that suggest that nocturnal inversions may have played a role limiting the rise of the weak plume thirdly images from a web camera were analyzed and the rise of individual cloud heads associated with explosions at the volcano vent mapped the velocity profiles obtained largely agree with conceptual models of volcanic plumes

simultaneous retrieval of volcanic ash and so2 using msg seviri measurements 1 volcanic ash and sulphur dioxide masses from the november 2005 eruption of karthala volcano comoros islands are simultaneously retrieved using rapid scan multispectral infrared measurements from the spin enhanced visible and infrared imager on board the meteosat second generation geosynchronous satellite retrievals are made every 15 min which show that the ash and so2 separate in the vertically sheared atmosphere producing a fast moving upper level 12 km so2 cloud a slower moving middle level 8 km ash cloud and a boundary layer 3 km so2 plume the total mass of fine ash is 0 1 0 05 tg sio2 the upper level so2 mass is 0 19 0 01 tg s while the boundary layer so2 mass is 0 009 0 01 tg s these are the first simultaneous satellite measurements of ash and so2 from an erupting volcano and confirm previous ideas about vertical separation we suggest care must be exercised when using so2 as a tracer for volcanic ash in aviation hazard warning systems

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

within catchment variability in landscape connectivity measures in the garang catchment upper yellow river abstract the degree of landscape connection has wide ranging implications for sediment availability frequency of transport and the nature of sediment storage within a basin two methodological approaches for assessing landscape connectivity are applied within the garang subcatchment of the upper yellow river a gis based geomorphometric index was calculated for the catchment and compared to a methodology linking interpretation of satellite imagery and field mapping of sediment storage to slope threshold analysis landscapes of the garang catchment are highly contrasting and can be separated into three zones i a highly disconnected upper catchment of low relief with large inactive sediment stores ii a transitional zone where present landscape dynamics are controlled in large part by past incisional processes in the form of large alluvial fan terrace deposits and iii a highly connected and highly dissected landscape within the lower catchment that has little accommodation space for sediment storage the geomorphometric index shows general agreement with the patterns in landscape connectivity observed through imagery and field investigations however it estimates similar levels of connectivity in landscapes with observed dis connectivity reflecting limitations of the calculation while rapidly calculated geomorphometric indices of landscape connectivity provide useful appraisals of relative within catchment variability in systems such as the garang catchment caution is urged in conducting broader scale analyses using the same tools findings from this study highlight the importance of field informed appraisals of landscape dynamics site specific characteristics and the imprint of historical evolutionary context in making such comparative assessments

stream geomorphology in a mountain lake district hydraulic geometry sediment sources and sinks and downstream lake effects lakes are common in glaciated mountain regions and geomorphic principles suggest that lake modifications to water and sediment fluxes should affect downstream channels lakes in the sawtooth mountains idaho usa were created during glaciation and we sought to understand how and to what extent glacial morphology and lake disruption of fluxes control stream physical form and functions first we described downstream patterns in channel form including analyses of sediment entrainment and hydraulic geometry in one catchment with a lake to expand on these observations and understand the role of glacial legacy we collected data from 33 stream reaches throughout the region to compare channel form and functions among catchments with lakes meadows filled lakes and no past or present lakes downstream hydraulic geometry relationships were weak for both the single catchment and regionally our data show that downstream patterns in sediment size channel shape sediment entrainment and channel hydraulic adjustment are explained by locations of sediment sources hillslopes and tributaries and sediment sinks lakes stream reaches throughout the region are best differentiated by landscape position relative to lakes and meadows according to channel shape and sediment size where outlets are wide and shallow with coarse sediment and inlets are narrow and deep with finer sediment meadow outlets and lake outlets show similarities in the coarse sediment fraction and channel capacity but meadow outlets have a smaller fine sediment fraction and nearly mobile sediment estimates of downstream recovery from lake effects on streams suggest 50 per cent recovery within 2 4 km downstream but full recovery may not be reached within 20 km downstream these results suggest that sediment sinks such as lakes in addition to sources such as tributaries are important local controls on mountain drainage networks copyright 2006 john wiley sons ltd

change in the mathematical function type describing the longitudinal profile of a river through an evolutionary process japanese rivers where a large amount of sediment accumulates along the middle reaches are today not at grade nevertheless most of their longitudinal profiles can be described by one of the mathematical functions proposed for graded rivers for these rivers the mathematical function should show an aspect of fluvial processes different from the explanations of grade theories the geomorphological significance of differences in the mathematical functions describing the longitudinal profiles of rivers is discussed here a dynamic change in the shape of longitudinal profile of a river accompanying the change in mathematical function type is proposed in relation to changes in fluvial processes and stage of evolution of a river most japanese rivers can be described by either exponential or power functions the fluvial processes of the rivers described by exponential functions are in the depositional state the front of depositional area of gravels increases in altitude and migrates downstream the rivers exp

the nature and controls on downstream fining within sedimentary links abstract at scales of 100 to 102 km grain size change in gravelly alluvial systems is characterized by punctuated downstream fining significant lateral sediment inputs define a sequence of sedimentary links within which fluvial processes produce fining trends using a new set of surface grain size data eighteen such links along two canadian gravel bed rivers are examined negative exponential functions are found to be most appropriate for describing within link grain size changes development of a pragmatic means of predicting grain size is then pursued by searching for a means to relate model diminution coefficients to link attributes consideration of lithologically differentiated fining trends indicates that lithology plays an insignificant role in controlling fining rate examination of within link longitudinal profiles indicates a reasonable relation between fining rate and the rate of change of channel slope the predictive value of this relation is limited by the regional nature of the data upon which it is based and the relative difficulty of obtaining accurate gradient information however as previously noted for alluvial fans although for different reasons channel gradient is correlated with link length and a reasonable predictive tool is apparent in a relation between link length and diminution rate the validity of the derived relation cannot be tested for want of a suitable data set several lines of evidence indicate that abrasion is unimportant as a fining mechanism on these rivers and it is argued that this may be typical of sedimentary links fining rate must then be a function of the efficiency with which sorting processes operate and it is suggested that this efficiency is dependent on aggradation rates associated with the lateral sediment influxes at the head and terminus of individual links

meso scale catchment sediment budgets combining field surveys and modeling in the dragonja catchment southwest slovenia in this paper we present a methodology to construct a sediment budget for meso scale catchments we combine extensive field surveys and expert knowledge of the catchment with a sediment delivery model the meso scale mediterranean drainage basin of the dragonja 91 km2 southwest slovenia was chosen as case study area during the field surveys sheet wash was observed on sloping agricultural fields during numerous rainfall events which was found to be the main source of sediment with the sediment yield model watem sedem the estimated net erosion on the hillslopes 4 1 t ha 1 y 1 91 of inputs the second source bank erosion 4 2 0 25 t ha 1 y 1 was monitored during several years with erosion pins and photogrammetric techniques the last source channel incision was derived from geomorphological mapping and lichenomery and provided 3 8 0 17 t ha 1 y 1 of the sediment input the river transports its suspended sediment mainly during high flow events sampled with automated water samplers about 27 1 2 t ha 1 y 1 of the sediment delivered to the channel is deposited on floodplains and low terraces downstream estimated with geomorphological mapping coring and cesium 137 measurements the sediment transported as bedload disintegrates during transport to the outlet due to the softness of the bedrock material as a result the river carries no bedload when it reaches the sea the results imply a build up of sediment in the valleys catchment however extreme flood events may flush large amounts of sediment stored in the lower parts of the system geomorphological evidence exists in the catchment that such high magnitude low frequency events have happened in the past

atmospheric distribution and removal of volcanic ash after the eruption of kasatochi volcano a regional model study 1 in august 2008 kasatochi volcano on the aleutian islands erupted without much advance warning volcanic ash released during this eruption quickly settled out of the atmosphere mainly into the ne pacific ocean the amount of volcanic ash as well as the ash fall area and volume into the ne pacific ocean remains speculative as only a limited number of measurements is available we used a three dimensional atmosphere chemistry aerosol model to determine the atmospheric distribution of so2 and volcanic ash and its fallout after the eruption of kasatochi volcano in a first step modeled atmospheric so2 distributions are compared with satellite data thereby evaluating the model capabilities to reasonably reproduce atmospheric transport patterns for modeled volcanic ash mass a considerable reduction of the atmospheric content already occurred by 10 august the second day after the eruption in accordance with satellite observations gravitational settling is the most efficient removal process for volcanic ash mass exceeding dry and wet deposition by far assuming an ash volume of 0 3 km3 released during the eruption of kasatochi volcano and a median ash particle diameter of 4 m the mass of volcanic ash removed at ground within the 0 1 mm isopach covers an area of 7 6 105 km2 over the ne pacific ocean and makes up 49 of the removed material out of the atmosphere the amount of ash and that of iron attached to it is sufficient to explain measured seawater co2 decrease at the ocean station papa in august 2008 induced by iron fertilization and subsequent phytoplankton production

re evaluation of so2 release of the 15 june 1991 pinatubo eruption using ultraviolet and infrared satellite sensors 1 in this study ultraviolet toms total ozone mapping spectrometer satellite data for so2 are re evaluated for the first 15 days following the 15 june 1991 pinatubo eruption to reflect new data retrieval and reduction methods infrared satellite so2 data from the tovs hirs 2 tiros television infrared observation satellite optical vertical sounder high resolution infrared radiation sounder 2 sensor whose data sets have a higher temporal resolution are also analyzed for the first time for pinatubo extrapolation of so2 masses calculated from toms and tovs satellite measurements 19 118 hours after the eruption suggest initial so2 releases of 15 3 mt for toms and 19 4 mt for tovs including so2 sequestered by ice in the early pinatubo cloud tovs estimates are higher in part because of the effects of early formed sulfate the toms so2 method is not sensitive to sulfate but can be corrected for the existence of this additional emitted sulfur the mass of early formed sulfate in the pinatubo cloud can be estimated with infrared remote sensing at about 4 mt equivalent to 3 mt so2 thus the total s release by pinatubo calculated as so2 is 18 4 mt based on toms and 19 4 mt based on tovs the so2 removal from the volcanic cloud during 19 374 hours of atmospheric residence describes overall e folding times of 25 5 days for toms and 23 5 days for tovs these removal rates are faster in the first 118 hours after eruption when ice and ash catalyze the reaction and then slow after heavy ash and ice fallout so2 mass increases in the volcanic cloud are observed by both toms and tovs during the first 70 hours after eruption most probably caused by the gas phase so2 release from sublimating stratospheric ice ash gas mixtures this result suggests that ice sequestered so2 exists in all tropical volcanic clouds and at least partially explains so2 mass increases observed in other volcanic clouds in the first day or two after eruption

lateral sediment sources and knickzones as controls on spatio temporal variations of sediment transport in an alpine river modern mixed alluvial bedrock channels in mountainous areas provide natural laboratories for understanding the time scales at which coarse grained material has been entrained and transported from their sources to the adjacent sedimentary sink where these deposits are preserved as conglomerates this article assesses the shear stress conditions needed for the entrainment of the coarse bed particles in the glogn river that drains the 400 km2 val lumnezia basin eastern swiss alps in addition quantitative data are presented on sediment transport patterns in this stream the longitudinal stream profile of this river is characterized by three ca 500 m long knickzones where channel gradients range from 0 02 to 0 2 m m 1 and where the valley bottom confined into a 10 m wide gorge downstream of these knickzones the stream is flat with gradients 0 01 m m 1 and widths 30 m measurements of the grain size distribution along the trunk stream yield a mean d84 value of ca 270 mm whereas the mean d50 is ca 100 mm the consequences of the channel morphology and the grain size distribution for the time scales of sediment transport were explored by using a one dimensional step backwater hydraulic model hydrologic engineering centre river analysis system the results reveal that along the entire trunk stream a two to 10 year return period flood event is capable of mobilizing both the d50 and d84 fractions where the shields stress exceeds the critical shields stress for the initiation of particle motion these return periods however varied substantially depending on the channel geometry and the pebble boulder size distribution of the supplied material accordingly the stream exhibits a highly dynamic boulder cover behaviour it is likely that these time scales might also have been at work when coarse grained conglomerates were constructed in the geological past