a new estimate for present day cocos caribbean plate motion implications for slip along the central american volcanic arc velocities from 153 continuously operatinggps sites on the caribbean north american and pacic plates arecombinedwith61newlyestimatedpacic cocosseafloor spreading rates and additional marine geophysical data to deriveanewestimate of present daycocos caribbean plate motion acomparisonofthepredictedcocos caribbean di rectiontoslipdirectionsofnumerousshallow thrustsubduc tion earthquakes from the middle america trench between costa rica and guatemala shows the slip directions to be deflected 10 clockwise from the plate convergence direc tion supporting thehypothesisthatfrequentdextralstrike slip earthquakes along the central american volcanic arc result from partitioning of oblique cocos caribbean plate convergence linear velocity analysis for forearc locations in nicaragua and guatemala predicts 14 2m m yr 1 of northwestward trench parallel slip of the forearc relative to thecaribbean plate possibly decreasing inmagnitude inel salvador and guatemala where extension east of the vol canic arc complicates the tectonic setting

wave attenuation over coastal salt marshes under storm surge conditions salt marshes protect coastlines against waves wave flume experiments show that marsh vegetation causes substantial wave dissipation and prevents erosion of the underlying surface even during extreme storm surge conditions

debris flows and debris torrents in the southern canadian cordillera in canada debris torrents also referred to as channelized debris flows occur in parts of british columbia alberta and the yukon at least 17 deaths and an estimated 100 million of damage to bridges and property can be attributed to this natural hazard the debris mainly comprises large boulders rock fragments gravel to clay sized material tree and wood mulch materials that accumulate in the mountain creeks to be susceptible to a debris torrent a creek must have a drainage area within a critical range a profile that is sufficiently steep an accumulation of debris and some form of triggering mechanism the most common triggering mechanism is an extreme water discharge which may result from a very intense rainfall or a temporary damming of the creek in western canada the resulting torrents involve masses of debris typically less than 50 000 m3 that travel down creeks at speeds between 3 and 12 m s several passive and active forms of mitigation can be used to reduce the impact of debris to

geochemistry of silicic magmas in the macolod corridor sw luzon philippines evidence of distinct mantle derived crustal sources for silicic magmas silicic volcanic deposits 65 wt sio2 which occur as domes lavas and pyroclastic deposits are relatively abundant in the macolod corridor sw luzon philippines at makiling stratovolcano silicic domes occur along the margins of the volcano and are chemically similar to the silicic lavas that comprise part of the volcano pyroclastic flows are associated with the laguna de bay caldera and these are chemically distinct from the domes and lavas at makiling stratovolcano as a whole samples from the laguna de bay caldera contain lower concentrations of mgo and higher concentrations of fe2o3 t than the samples from domes and lavas the laguna de bay samples are more enriched in incompatible trace elements the silicic rocks from the domes makiling volcano and laguna de bay caldera all contain high alkalis and high k2o na2o ratios melting experiments of primitive basalts and andesites demonstrate that it is difficult to produce high k2o na2o silicic magmas by fractional crystallization or partial melting of a low k2o na2o source however recent melting experiments sisson et al contrib mineral petrol 148 635 661 2005 demonstrate that extreme fractional crystallization or partial melting of k rich basalts can produce these silicic magmas our model for the generation of the silicic magmas in the macolod corridor requires partial melting of mantle derived evolved moderate to k rich crystallized calc alkaline magmas that ponded and crystallized in the mid crust major and trace element variations along with oxygen isotopes and ages of the deposits are consistent with this model

flow adjustment and interior flow associated with a rectangular porous obstruction the flow at the leading edge and in the interior of a rectangular porous obstruction is described through experiments and scaling the porous obstruction consists of an emergent rectangular array of cylinders in shallow flow a configuration that mimics aquatic vegetation the main features of the flow depend upon the non dimensional canopy flow blockage which is a function of the obstruction width and porosity for the ranges of canopy flow blockage tested in this paper the fluid decelerates upstream of the obstruction over a length scale proportional to the array width for high flow blockage the interior adjustment length within the porous obstruction is set by the array width for low flow blockage the array s frontal area per unit volume sets the interior adjustment length downstream of the adjustment regions the interior velocity is governed by a balance between the lateral divergence of the turbulent stress and canopy drag or by a balance between the pressure gradient and canopy drag depending on the lateral penetration into the array of kelvin helmholtz kh vortices which is set by the non dimensional canopy flow blockage for a porous obstruction with two stream parallel edges the kh vortex streets along the two edges are in communication across the width of the array a phenomenon that results in cross array vortex organization which significantly enhances the vortex strength and creates significant lateral transport within the porous obstruction

holocene vegetation climate and lake level changes in the interior douglas fir biogeoclimatic zone british columbia chilhil phair fishblue and horseshoe lakes in the southern interior of british columbia were cored and analyzed for pollen phair lake was also examined for plant macrofossils and aquatic molluscs two dated volcanic tephras mazama and bridge river are present in three of the four lakes and together with radiocarbon dates provide an absolute chronology for pollen influx calculations and stratigraphic correlation abrupt changes in sediment type at phair lake about 5650 and 2000 years ago correlate with neoglacial advances near the coast interior transition pollen changes suggestive of moister conditions and the presence of an aquatic mollusc valvata sincera helicoidea at phair and chilhil lakes are consistent with the neoglacial evidence of cooler and wetter conditions after about 2400 years ago the driest part of the holocene was the early pre mazama ca 6600 6800 years ago interval when the vegetation was more open and herb rich and the lake levels were lower than at present wetter clima

depth averaged drag coefficient for modeling flow through suspended canopies aquatic suspended canopies are porous obstacles that extend down from the free surface but have a gap between the canopy and bed examples of suspended canopies include those formed by aquaculture structures or floating vegetation the major difference between suspended canopies and the more common submerged canopies which are located on the bottom boundary is the influence of the bottom boundary layer beneath the suspended canopy data from laboratory experiments are presented which explore aspects of the flow through and beneath suspended canopies constructed from rigid cylinders the experiments using both acoustic doppler and two dimensional 2d particle tracking velocimetry give details of the flow structure that may be divided vertically into a bottom boundary layer a canopy shear layer and an internal canopy layer the experimental data show that the penetration of the shear layer into the canopy is limited by the distance between the canopy and bottom boundary layer peaks in velocity spectra indicate an interaction between the bottom boundary and canopy shear layer an analytical model is also developed that can be used to calculate a drag coefficient that includes the effect of both canopy drag and bed friction this drag coefficient is suitable for use in 2d depth averaged hydrodynamic modeling the model also allows the average velocity within and beneath the canopy to be calculated and is used to investigate the effect of canopy density and thickness on both total drag and bottom friction

applying the mixing layer analogy for flow resistance evaluation in gravel bed streams abstract previous studies show that the flow velocity profile is s shaped for low submergence flows in gravel bed streams as a consequence the power or logarithmic flow resistance equations cannot be theoretically deduced for a low submergence flow in this study the mixing layer analogy in an accurate and innovative way is applied to express the flow resistance in gravel bed streams laboratory experiments over 12 uniform gravel bed runs the relative submerged height ranging from 2 6 to 4 6 are used to determine the physical rationality and accuracy of the analogy that statistical flow turbulent properties are closer to typical values in the mixing layer than in the surface layer the key parameters of shear strength ls applied by an incomplete self similarity analysis for the dimensionless groups and difference coefficient cu defined as the ratio of velocity at the reference level to shear velocity deduced by the simplified darcy forchheimer brinkman equation are expressed and tested using experimental data the new approach is further underpinned by using 104 field measured reaches located in 40 different natural streams which adds to the more widely ranged field data with the relative submerged height ranging from 0 9 to 20 the analysis shows that the flow layer subdivisions theoretical approach based on the multivariable mixing layer analogy and optimized katul law characterized by the lowest root mean square error relative error and closest 1 nash sutcliffe index has potential in future research

the source of central american lavas inferences from geochemical inverse modeling the rate earth element chemistry of a large suite of samples from the central american volcanic front has been determined to understand their petrogenesis different segments of the volcanic front are compared on the basis of their calculated source rare earth patterns as deduced from inverse modeling the results yield a range in the extent of light rare earth enrichment of the source as well as in source mineralogy moderateto strong lree enrichment and high modal garnet contents are observed for the sources of both guatemala and central costa rica whereas slight lree depletion and little or no garnet occurs in the nicaraguan source region although distinct source regions beneath each central american segment are permitted by the modeling it is more likely that the mantle wedge is broadly homogeneous but locally heterogeneous small volume relatively enriched garnet bearing veins surrounded by a matrix of isotopically depleted mantle periodotite could exist throughout the mantle wedge apparently distinct sources occur due to the variation in partial melting beneath the different segments controlled by the amount of subduction generated flux per unit wedge volume which in turn is a function of the dip of the subducted lithosphere

estimating ages of late quaternary stream terraces from analysis of weathering rinds and soils rates of growth of rock weathering rinds and rates of changes of soil morphologic and chemical properties that are calibrated at sites of known ages produce powerful tools for estimating ages of geomorphic surfaces particularly when materials datable by conventional methods are not widespread sequences of latest quaternary stream terraces from the south island of new zealand are ideally suited for application of these calibrated age techniques because climate and source materials for terrace deposits are internally consistent within two regions west land and marlborough modal and mean thicknesses of weathering rinds formed in surface cobbles of torlesse graywacke provide age estimates for latest pleistocene and holocene stream terraces in marlborough with uncertainties estimated at 5 to 40 modal rind thickness of subsurface cobbles provides age estimates for latest quaternary westland sites with uncertainties of 10 to more than 50 few dated soils are available to constrain rates of soil development in westland and marlborough furthermore soils were sampled from only one pedon on each surface morphologic data however provide least squares age estimates for westland sites with uncertainties typically greater than 100 and the calibration data can further bracket likely soil ages to less than 50 uncertainty the regression data from marlborough are less reliable but profile index ratios help bracket ages to at least 50 distributions of oxalate extractable fe and ai and total major element concentrations allow age estimates for westland and marlborough soils with uncertainties estimated at 15 to 50 despite these uncertainties the three techniques combine to provide age estimates with the high resolution needed to examine details of fault slip rates or stream downcutting the calibration data and weathering rates used herein are applicable only to the new zealand region studied although similar calibrated age techniques should provide high resolution dating in many other regions such techniques are particularly useful when multiple approaches are available to provide independent cross checks

improved parameterization of seagrass blade dynamics and wave attenuation based on numerical and laboratory experiments seagrass blade dynamics were explored through numerical and laboratory experiments in order to improve parameterization of wave attenuation by submerged aquatic vegetation in the presence of a background current in the numerical model a single blade was modeled as a series of rigid plates attached by torsion springs for the laboratory model strips of low density polyethylene were placed in a recirculating wave flume a new form of the keulegan carpenter number based on the horizontal excursion of the blade tip was found to be an excellent predictor of drag coefficient an algebraic model for predicting wave attenuation was developed based on the following observations during the portion of the wave period when the fluid velocities are highest the blade motion is almost completely arrested and the vast majority of the turbulence production occurs during this time turbulence production when the blade is pronated is accurately predicted by the maximum fluid velocity over the wave period the relative contribution to the total turbulence production over the wave period is determined by the relative strength of the waves and the current therefore using a simple algebraic fit the total depth integrated time averaged turbulence production can be accurately predicted by two flow parameters the maximum fluid velocity over the wave period and a non dimensional number that compares the wave and current velocities by fitting the algebraic model to data from a particular site it can be used to efficiently estimate wave attenuation and drag coefficient in seagrass exposed to waves with a background current

extension and rotation of crustal blocks in northern central america and effect on the volcanic arc sinistral displacements across the north american caribbean plate boundary in northern central america are distributed among major arcuate faults that have been active in neogene time south of the jocotan and motagua faults in guatemala extensional tectonics has accompanied rotation of the trailing edge of the caribbean plate around these faults segmentation of the volcanic arc in northern central america hitherto attributed to transverse breaks in the subducting cocos plate may instead be a result of this block rotation accompanying changes along the arc are observed in seismicity gravity anomaly patterns volume and composition of volcanic products and topography therefore the complex volcano tectonic geology south of the main boundary faults may be explained by interaction and rotation of crustal blocks in the overriding caribbean plate above the magma production zone along the downgoing cocos slab

experimental study on vegetation flexibility as control parameter for wave damping and velocity structure abstract vegetation can contribute to coastal defence by damping incoming waves however prior studies have shown that attenuation varies greatly among plant species plant flexibility is a mechanical property that is commonly omitted but varies considerably between shrubs and grasses on salt marshes therefore we present an experimental study in a laboratory wave flume with artificial vegetation that differs in flexibility only we measured wave attenuation and water particle velocities around rigid and flexible salt marsh vegetation waves were measured using a series of gauges and particle image velocimetry piv was used to measure spatio temporal variations of water particle velocities in the x z plane around the vegetation our results show that flexible vegetation attenuates waves up to 70 less than rigid vegetation due to swaying of flexible plants furthermore we find that rigid vegetation modifies the velocity structure whereas flexible vegetation does not specifically a mean current in the direction of wave propagation develops around the canopy and the horizontal particle velocities are amplified directly above the canopy these results indicate that plant flexibility is a key parameter in the wave vegetation interaction that controls wave damping and velocity structure

geometrical and mechanical properties of four species of northern european brown macroalgae abstract aquatic vegetation interacts with the flow by posing an obstruction and in return experiences drag and is reconfigured by acting forces it is suggested that plant buoyancy and stiffness affect these bio physical interactions and hence should be considered when including vegetation in physical and numerical hydrodynamic models however data on these parameters is either lacking for many species or existing information is insufficient to model flexible aquatic vegetation correctly previous studies have focused on plant stems but did not take plant foliage into account the present study extends the existing knowledge base by providing data for four northern european brown macroalgae and also provides a comparison between the mechanical properties of stem and blade tissue for these species specimens of alaria esculenta laminaria digitata fucus serratus and fucus vesiculosus were collected from a small tidal inlet in norway other than f serratus the macroalgae were positively buoyant and all stems showed bending moduli in agreement with previous studies with respect to their order of magnitude only l digitata exhibited a significant difference between bending moduli for stems and blades and also between the tip and the base of the blades however there were differences in flexural rigidities product of bending modulus and second moment of cross sectional area of both stems and blades and the tip and the base of blades of all but f serratus this highlights the important influence of cross sectional area and cross sectional shape on stiffness

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

holocene migration of lodgepole pine pinus contorta var latifolia in southern yukon canada a palynological reconstruction n 25 profiles suggests that the northern extent of lodgepole pine pinus contorta var latifolia engelmann ex s watson occurred between 59 and 60 n latitude in

upper plate stress controls the distribution of mariana arc volcanoes we present a spatial analysis of volcano distribution and morphology in the young intraoceanic mariana arc both the quality of fit to idealised models and the divergence from those ideals indicate that mariana arc volcanoes are arranged into five great circle segments rather than a single small circle or multiple small circles the alignment of magmatic centres suggests that magma transport is controlled by the stress regime in the deep crust and or lithospheric mantle of the philippine sea plate into which the arc is emplaced and that arc normal tension is the dominant process operating in the deep lithosphere along the whole arc volcano morphologies indicate that the stress regime in the shallow crust varies between arc normal tension and compression which also implies that the stress field can vary with depth in the arc lithosphere we show that this horizontal and vertical stress partitioning can be related to the changing dip of the subducting plate and the breadth of the zone where it is coupled with the overriding plate the variation in stress regime is consistent with both the distribution of seismicity in the philippine sea plate and with the structural fabrics of the non volcanic part of the plate margin to the south our analysis suggests that the upper plate exerts the principal control on the distribution of volcanoes in the mariana arc where tension in the deeper parts of arc lithosphere is sufficiently concentrated then a distinct volcanic front is produced

numerical study of turbulence and wave damping induced by vegetation canopies article i nfo vegetation canopies control mean and turbulent flow structure as well as surface wave processes in coastal regions a non hydrostatic rans model based on nhwave ma et al 2012 is developed to study turbulent mixing surface wave attenuation and nearshore circulation induced by vegetation a nonlinear k e model accounting for vegetation induced turbulence production is implemented to study turbulent flow within the vegetation field the model is calibrated and validated using experimental data from vegetated open channel flow as well as nonbreaking and breaking random wave propagation in vegetation fields it is found that the drag related coefficients in the k e model cfk and cf can greatly affect turbulent flow structure but seldom change the wave attenuation rate the bulk drag coefficient cd is the major parameter controlling surface wave damping by vegetation canopies using the empirical formula of mendez and losada 2004 the present model provides accurate predictions of vegetation induced wave energy dissipation wave propagation through a finite patch of vegetation in the surf zone is investigated as well it isfound that the presenceof a finite patch of vegetation may generate strong pressure driven nearshore currents with an onshore mean flow in the unvegetated zone and an offshore return flow in the vegetated zone published by elsevier b v

large scale 3 d experiments of wave and current interaction with real vegetation part 2 experimental analysis abstract this paper assesses the influence of different flow and vegetation parameters on the wave attenuation provided by two contrasting salt marsh species puccinellia maritima and spartina anglica different water depths and wave parameters height and period are considered for both regular and irregular waves with and without an underlying uniform current coming from different directions the study of the submergence ratio h h v influence shows that wave damping coefficient rapidly decreases as the plant submergence ratio increases the high nonlinearities found in the wave current interaction lead to different wave damping patterns in comparison to wave only conditions a smaller wave damping is found for waves and current acting in the same direction and an increase in the wave damping rate is obtained for waves and current flowing in the opposite direction these wave and current tests allow for the studying of the energy dissipation produced by the vegetation increasing our knowledge about flow and plant interaction in estuarine conditions the biomechanical properties of the two real salt marshes used in the experiments are also evaluated and related to wave damping revealing a higher attenuation for stiffer vegetation both the vegetation density and the biomass strongly influence wave damping higher density and biomass values lead to higher attenuation rates for both species

the importance of accurately representing submerged vegetation morphology in the numerical prediction of complex river flow this paper reports a novel method for the incorporation of complex plant morphologies into a computational fluid dynamics cfd model allowing the numerical prediction of flows around individual plants the morphological complexity which comprises the vertical and lateral distribution of individual branches and leaves is captured through terrestrial laser scanning tls and is maintained in the numerical prediction of flow fields this is achieved where the post processed voxelised plant representation is incorporated into a cfd scheme through a mass flux scaling algorithm mfsa flow around prunus laurocerasus has been modelled under foliated and defoliated states following the removal of leaves the complex plant morphologies are shown to produce spatially heterogeneous downstream velocity fields with velocity profiles that deviate significantly from the idealised inflected shape rapid transition between the high velocity free stream zone and the zone of reduced velocity in the plant wake indicate shearing of flow with the point of reattachment extending up to seven plant lengths downstream the presence of leaves significantly modifies the flow field response with development of a second more pronounced wake structure around the dense foliage this approach provides a full flow numerical description of the pressure field enabling the vegetative drag force to be quantified for the example given here drag force is an order of magnitude greater for the foliated state the methodology outlined here demonstrates the importance of accurately representing complex plant morphology in hydraulic models and allows drag forces and coefficients to be calculated for specific plant species this article is protected by copyright all rights reserved

linear volcanic segments in the central sunda arc indonesia identified using hough transform analysis implications for arc lithosphere control upon volcano distribution abstract hough transform analysis is used as an objective means to constrain volcano distribution in the central sunda arc indonesia most volcanoes in the arc define four en echelon linear segments each of 500 700 km length javan volcanoes that do not lie on these segments either i formed at an early stage in the history of the arc and erupted products that are petrologically and geochemically distinct from typical arc magma or ii lie along other mapped structures the en echelon distribution of volcanoes in the central sunda arc is best explained as originating from two possible sources first interaction with the subducting indo australian plate may induce stress in the arc lithosphere generating pathways for magma to exploit second downward flexure of the arc lithosphere as a result of mantle flow or loading by the arc would also establish arc normal tension towards the base of the lithosphere where magma is supplied to volcanic systems to the west and east of the central sunda arc deviations from the distribution of long en echelon linear segments can be understood as responses to specific stress fields in the arc lithosphere of sumatra and eastern nusa tenggara respectively control of volcano distribution by arc lithosphere explains why there are large variations in the depth from volcanoes to the zone of slab seismicity in the central sunda arc where there is little variation in slab geometry or the rate of plate convergence

flow resistance in natural turbulent channel flows the need for a fluvial fluid mechanics in fluvial environments feedbacks among flow bed forms sediment and macrophytes result in a complex fluid dynamics the assumptions underpinning standard tools in hydraulics are commonly violated and alternative approaches must be formulated i argue that we should question the assumption that classical notions in fluid mechanics provide the foundations for the techniques of the future recent work on turbulent dissipation interscale modulation of the dynamics intermittency and the role of complex forcings is discussed an agenda for future work is proposed that involves improving our characterization of complex forcings and developing better understanding of the behavior of the velocity gradient tensor in complex fluvial environments this leads to the formulation of modeling tools relevant to fluvial fluid mechanics rather than a reliance on methods developed elsewhere one avenue by which such methods might be developed is suggested based on the stretched spiral vortex as a baseline topology this would result in a nonequilibrium model for turbulence that has greater potential to capture the dynamics in which we are interested although these ideas are raised in the context of a future fluvial fluid mechanics they are applicable to any situation where turbulent flows are forced in complicated ways

the limited growth of vegetated shear layers 1 in contrast to free shear layers which grow continuously downstream shear layers generated by submerged vegetation grow only to a finite thickness because these shear layers are characterized by coherent vortex structures and rapid vertical mixing their thickness controls exchange between the vegetation and the overlying water experiments conducted in a laboratory flume show that the growth of these obstructed shear layers is arrested once the production of shear layer scale turbulent kinetic energy ske is balanced by dissipation of ske within the canopy this equilibrium condition along with a mixing length closure scheme was used in a one dimensional numerical model to predict the mean velocity profiles of the experimental shear layers the agreement between model and experiment is very good but field application of the model is limited by a lack of description of the drag coefficient in a submerged canopy

waving plants and turbulent eddies new large eddy simulations of flow over a flexible plant canopy by dupont et al j fluid mech 2010 this issue vol 652 pp 5 44 have produced apparently paradoxical results work over the last three decades had suggested that turbulent eddies could lock onto to the waving frequency of uniform cereal canopies their new simulations contradict this view although a resolution may lie in the essentially three dimensional nature of the instability process that generates the dominant eddies above plant canopies

hydrodynamics of flow through double layer rigid vegetation vegetation in riparian environment varies in size from grass to shrubs to trees a double layer approach with an array of short and tall acrylic dowels is employed here to simulate such an environment the focus of the present work is to study the response of the flow as it travels through a double layer arrangement for a variety of conditions for this purpose instantaneous measurements of velocity were collected using a one dimensional laser doppler velocimeter at multiple locations to create velocity and turbulence intensity profiles the results indicate that velocity is nearly constant within the short and tall dowel array and increases significantly at the top of the arrays the velocity profile behind a dowel is characterized by multiple inflection points and velocity spikes near the bed especially for locations directly behind a tall dowel where a bulge in the velocity at the top of the short dowel array is present followed by a significant drop in velocity the region immediately behind a tall dowel where the highest turbulence intensities are found is very unstable especially at the dowel boundaries where significant mass and momentum exchange occurs the better known case of submerged single layer flow is included for comparison

epeirogenic uplift above a detached slab in northern central america p wave tomographic images reveal that the northern central america highlands east of the modern volcanic arc overlie a detached slab hypsometric analysis of the highlands in honduras demonstrates that the region is a dissected plateau that is disrupted by normal faults near the north american caribbean plate margin the dissected central american plateau contains a network of superimposed rivers with meanders cut into bedrock such a geomorphic character indicates that the regional uplift occurred in the absence of tilting we propose that the epeirogenic uplift of northern central america is the buoyant upper plate response to the influx of mantle asthenosphere following the break off and sinking of the slab

flow structure in canopy models dominated by progressive waves summary laboratory experiments were carried out to study the flow structure both inside and above different canopy models which were dominated by progressive waves a set of experimental conditions were considered in a laboratory flume three vegetation models submerged rigid submerged flexible and emergent rigid three plant densities 128 640 and 1280 stems m 2 and three wave frequencies f 0 8 1 and 1 4 hz the progressive waves followed the second order stokes theory in the intermediate depth range the observations revealed that submerged and emergent rigid vegetation models modified the wave induced velocities i e both mean current and wave velocity the submerged rigid vegetation model for plant densities higher than 640 plants m 2 and wave frequency higher than 1 hz acted akin to a false floor confining the mean current to above the plant bed a penetration depth around 2 cm below the top of submerged rigid vegetation was found for the other runs the vertical profile of mean current did not present changes with respect to runs without plants the emergent rigid vegetation model reversed the direction of the induced mean current with the highest velocity corresponding to the highest plant density in contrast the submerged flexible vegetation model had a weak effect on the mean current with the vertical velocity profile similar to that found in experiments without vegetation the wave velocities inside the vegetation for the densest submerged rigid vegetation were found to be reduced by 20 when compared to the wave velocities without vegetation while in emergent rigid vegetation this reduction was of 45

correlating geochemistry tectonics and volcanic volume along the central american volcanic front the central american volcanic front consists of several distinct volcanic lineaments or segments separated by right steps and or changes in strike each volcanic line is rotated slightly counterclockwise from the strike of the inclined seismic zone right stepping volcanic lines oblique to the strike of the slab create a sawtooth pattern in the depth to the slab zr nb is the first geochemical signature with consistent large offsets at the right steps in the volcanic front moreover zr nb mirrors the sawtooth variation in depth to the slab within a segment it increases from se to nw and at the right steps separating segments it abruptly decreases unfortunately there is no simple negative correlation between zr nb and depth to the slab because zr nb also has a regional variation similar to previously documented regional variations in slab tracers in central america e g ba la u th and 87sr 86sr within a segment zr nb decreases with increasing depth to slab this can be explained in two ways a nb retaining mineral e g amphibole in the subducting slab is breaking down gradually with increasing depth causing more nb to be released and consequently a smaller nb depletion in deeper melts alternatively all melts have the same initial nb depletion which is then diluted by acquiring nb from the surrounding mantle wedge as melts rise and react deeper melts have longer paths and therefore more reaction with the mantle wedge diluting the initial nb depletion within each volcanic segment there is variation in eruptive volume the largest volcanoes generally occur in the middle of the segments and the smaller volcanoes tend to be located at the ends connecting the largest volcanoes in each segment suggests an axis of maximum productivity this is likely the surface projection of the center of the melt aggregation zone the largest volcanoes tap the entire melt zone those with shallow depths to the slab tap just the front part of the melt zone and have very large nb depletions those at greater depths tap the back part of the melt zone and have much smaller nb depletions

modeling the effect of wave vegetation interaction on wave setup aquatic vegetation in the coastal zone attenuates wave energy and reduces the risk of coastal hazards e g flooding besides the attenuation of sea swell waves vegetation may also affect infragravity band ig waves and wave setup to date knowledge on the effect of vegetation on ig waves and wave setup is lacking while they are potentially important parameters for coastal risk assessment in this study the storm impact model xbeach is extended with formulations for attenuation of sea swell and ig waves and wave setup effects in two modes the sea swell wave phase resolving nonhydrostatic and the phase averaged surfbeat mode in surfbeat mode a wave shape model is implemented to capture the effect of nonlinear wave vegetation interaction processes on wave setup both modeling modes are verified using data from two flume experiments with mimic vegetation and show good skill in computing the sea swell and ig wave transformation and wave setup in surfbeat mode the wave setup prediction greatly improves when using the wave shape model while in nonhydrostatic mode nonlinear intrawave effects are directly accounted for subsequently the model is used for a range of coastal geomorphological configurations by varying bed slope and vegetation extent the results indicate that the effect of wave vegetation interaction on wave setup may be relevant for a range of typical coastal geomorphological configurations e g relatively steep to gentle slope coasts fronted by vegetation

the managua graben and las sierras masaya volcanic complex nicaragua pull apart localization by an intrusive complex results from analogue modeling abstract there is a well documented association between pull apart basins in strike slip zones and large volcanic caldera complexes las sierras masaya volcanic complex nicaragua is a large basaltic lava and ignimbrite shield with nested calderas the widest caldera is partly underlain by a large and dense intrusive complex evidenced by a positive gravity anomaly the las sierras caldera relating to this cumulate complex is less than 30 000 years old and is probably still hot and ductile the inner masaya caldera hosts an active magmatic system the volcanic complex is in a dextral transtensional tectonic context of the nicaraguan depression the highly active managua graben is on the northern part of the volcano we speculate that the graben and volcano are linked tectonically with the graben initiating in response of a regional stress field modified around the dense ductile intrusive complex previous field work and reappraisal of structures with digital elevation model morphological analysis show that the volcano is surrounded by a rhombic fault pattern that may form a nascent pull apart basin we have done scaled analogue models to test the effect of intrusion density and rheology anomalies on strike slip fault geometries the models show that intrusion density variations alone do not significantly change fault patterns in contrast ductile rocks silicone in the models as analogue for hot mafic intrusive rocks markedly alter strike slip fault patterns in transtension the presence of a ductile intrusion causes the formation of a pull apart while in pure strike slip or transpression uplift and thrusting is generated pull apart and uplift structures are rhomb shaped even when the ductile inclusion is circular we conclude that a pull apart is developing at las sierras masaya volcanic complex in response to the transtensive regional deformation regime and the dense ductile intrusive complex we suggest that the volcano and graben are one dynamic system and should be monitored as one entity

plant patch hydrodynamics in streams mean flow turbulence and drag forces 1 this paper investigates the effects of a finite size vegetation patch on flow turbulence variations in drag forces experienced by individual plants within the patch and flow drag interrelations the experiments were conducted in a 32 m long laboratory flume with a 2 8 m long artificial patch the plants were arranged to form a staggered pattern and three flow scenarios were tested velocities were recorded with an acoustic doppler velocimeter whereas specifically designed devices were used to simultaneously measure the drag forces acting on nine plants within the patch for all studied cases the results show zones of increased turbulent energy close to the leading edge and along the patch canopy top where turbulence shear production is enhanced zones of negative reynolds stresses u w are found inside the patch and they reflect the influence of plant morphology which affects the shape of the longitudinal velocity profile and associated turbulent fluxes modifications to the power spectral densities of velocity by the plants indicate the emergence of two plant induced mechanisms of energy production which are most likely related to the wake turbulence and shear layer turbulence drag fluctuations appear to be correlated with the velocity field with this correlation being especially profound at the highest studied flow rate the data suggest that the highlighted correlation stems from flow plant interactions at the top of the vegetation canopy likely due to the presence of large three dimensional coherent structures

trace element incorporation in titanite constraints from experimentally determined solid liquid partition coefficients titanite liquid partition coefficients for most of the trace elements relevant in petrogenetic studies are provided for titanite saturated liquids equilibrated at 1 5 gpa and 850 c starting from lamproitic compositions the high compatibility observed for ree hfse sr v and sc and the strong incompatibility observed for actinides large ion lithophile and light elements are discussed in terms of available crystal chemical mechanisms for incorporation and crystal structure control the exchange vectors na1ca 1 and al1ti 1 allow local charge balance to be achieved after incorporation of ree3 and r5 at the ca and ti site respectively the significant amounts of h measured are also relevant in this regard the exchange mechanism being oh 1o 1 at the o1 site the incorporation of u4 and th4 at the ca site is scarce and is likely balanced by that of mg2 at the ti site both these substitutions are responsible for strong structural strain titanite can thus be considered an important repository for ree and hfse in metamorphic and igneous rocks and its role must be accounted for when modelling trace element residence during metamorphic reactions and late magmatic crystallisation history due to the measured differences in compatibility titanite crystallisation increases the values of nb ta and lree hree ratios in residual liquids the similar compatibility of u and pb makes titanite suitable for u pb geochronology of igneous rocks only after common pb correction finally this study confirms that the titanite end member is not suitable for radioactive waste disposal due to the discussed crystal chemical constraints and that titanite based waste forms should contain high amounts of na and mg2

analytical solutions of velocity profile in flow through submerged vegetation with variable frontal width abstract flow within vegetation is one of the main driving forces for material exchange and energy transfer in wetland systems impacted by vegetation the flow velocity profile illustrates distortions to the classic logarithmic velocity profile and has attracted much attention among researchers different from analytical models of velocity distribution in literature which is mainly suitable for vegetation with uniform frontal width this paper establishes new analytical solutions of the velocity profile for vegetation such as shrub and sedge that have a variable frontal width in the vertical direction a new shape function is proposed under these conditions in which the frontal width exhibits a gradual increase in the vertical direction from bottom up in the vegetation along with different closure models for eddy viscosity in the vegetation layer and surface layer analytical solutions of the velocity profile are derived from the momentum equations good agreement between calculated and measured data shows our analytical model is effective in predicting velocity profiles

modeling flow in coral communities with and without waves a synthesis of porous media and canopy flow approaches both canopy flow and porous media theories have been developed independent of one another to predict flow through submerged porous structures these approaches are very similar albeit with some key differences in how canopy resistance forces are parameterized canopy models provide a means of parameterizing the shear stresses that occur at the top of the canopy whereas porous media models can often provide a simpler and more tractable way of parameterizing turbulent form drag based on simple morphological metrics and empirical relationships already in the hydrology literature we developed a set of equations combining aspects of both models and applied this hybridized model to predict the flow structure within an experimental canopy formed by the branching coral porites compressa using model parameter values obtained from the literature results from the model predictions agreed well with direct measurements of flow speed and flow forces derived from particle image velocimetry under conditions of both unidirectional and wave driven oscillatory flow

late quaternary sequence stratigraphy of the mackenzie delta the late wisconsinan and holocene sequence stratigraphy of the mackenzie delta provides insights into the glacial history of the region the base of the described succession is a hummocky regional reflector interpreted to be a flooding surface formed immediately after retreat of glacial ice from the mackenzie trough above this flooding surface two progradational parasequences are present the first assigned to the transgressive systems tract is correlated with the tutsieta lake readvance of the ice sheet at approximately 13 000 bp a flooding surface forming the upper boundary of this parasequence extends inland to at least inuvik developing as a response to glacial retreat and early holocene relative sea level rise the second parasequence of holocene deltaic deposits is assigned to the highstand systems tract and is characterized by progressive progradation of the delta into the mackenzie trough to a position seaward of the present delta coastline a distinct reduction in gradient of the most recen

single parameter model of vegetated aquatic flows coupled flows through and over permeable layers occur in a variety of natural phenomena including turbulent flows over submerged vegetation in this work we employ a two domain approach to model flow through and over submerged canopies the model amenable of a closed form solution couples the log law and the darcy brinkman equation and is characterized by a novel representation of the drag force which does not rely on a parametrization through an unknown drag coefficient this approach limits to one i e the obstruction permeability the number of free parameters analytical expressions for the average velocity profile through and above the canopies volumetric flow rate penetration length and canopy shear layer parameter are obtained in terms of the canopy layer effective permeability the model suggests that appropriately rescaled velocities in the canopy and surface layers follow two different scaling laws the analytical predictions match with the experimental data collected by ghisalberti and nepf 2004 and nepf et al 2007

laboratory measurements of flow and turbulence in discontinuous distributions of ligulate seagrass turbulent flow characteristics were investigated in laboratory flume studies of a ligulate plant canopy interrupted by a gap representing discontinuities observed in seagrass prairies the reliability of velocity measurements obtained using an acoustic doppler velocimeter within the canopy was shown using specifically designed experiments in relatively fast flow mean velocity 5 5 cm s 1 the mean flow profile was logarithmic above the canopy had an inflection point near its top and uniformly low values within it within the gap a recirculation cell formed reynolds stress maxima were approximately coincident with the mean flow inflection point quadrant analysis revealed an ejection dominated upper layer a sweep dominated region around the top of the canopy and within the gap and no dominant quadrant within the canopy in slower flow mean velocity 1 7 cm s 1 the plants were quasiemergent and the flow fields more uniform sweeps similarly dominated the region near the top of the canopy and within the gap in both flows autocorrelation of longitudinal velocity fluctuations showed a lagrangian time scale maximum at the downstream end of the gap

submarine fernandina magmatism at the leading edge of the galapagos hot spot new multibeam and side scan sonar surveys of fernandina volcano and the geochemistry of lavas provide clues to the structural and magmatic development of galapagos volcanoes submarine fernandina has three well developed rift zones whereas the subaerial edifice has circumferential fissures associated with a large summit caldera and diffuse radial fissures on the lower slopes rift zone development is controlled by changes in deviatoric stresses with increasing distance from the caldera large lava flows are present on the gently sloping and deep seafloor west of fernandina fernandina s submarine lavas are petrographically more diverse than the subaerial suite and include picrites most submarine glasses are similar in composition to aphyric subaerially erupted lavas however these rocks are termed the normal series and are believed to result from cooling and crystallization in the subcaldera magma system which buffers the magmas both thermally and chemically these normal series magmas are extruded laterally through the flanks of the volcano where they scavenge and disaggregate olivine gabbro mush to produce picritic lavas a suite of lavas recovered from the terminus of the sw submarine rift and terraces to the south comprises evolved basalts and icelandites with mgo 3 1 to 5 0 wt this evolved series is believed to form by fractional crystallization at 3 to 5 kb involving extensive crystallization of clinopyroxene and titanomagnetite in addition to plagioclase high k lavas were recovered from the southwest rift and are attributed to hybridization between normal series basalt and evolved series magma the geochemical and structural findings are used to develop an evolutionary model for the construction of the galapagos platform and better understand the petrogenesis of the erupted lavas the earliest stage is represented by the deep water lava flows which over time construct a broad submarine platform the deep water lavas originate from the subcaldera plumbing system of the adjacent volcano after construction of the platform eruptions focus to a point source building an island with rift zones extending away from the adjacent buttressing volcanoes most rift zone magmas intrude laterally from the subcaldera magma chamber although a few evolve by crystallization in the upper mantle and deep crust

a vortex based model of velocity and shear stress in a partially vegetated shallow channel 1 this paper presents a method for predicting the distributions of velocity and shear stress in shallow channels with a boundary of emergent vegetation experiments in a laboratory channel with model vegetation show that the velocity profile exhibits a distinct two layer structure consisting of a rapidly varying shear layer across the vegetation interface and a more gradual boundary layer in the main channel in addition coherent vortices are observed which span both layers and are the dominant contributors to lateral momentum fluxes from these observations we propose a model for the vortex induced exchange and find expressions for the width of momentum penetration into the vegetation the velocity and shear stress at the vegetation edge and the width of the boundary layer in the main channel these variables along with a momentum balance in the main channel comprise a modeling framework which accurately reproduces the observed velocity and shear stress distributions the predictions for the velocity and shear stress can provide a basis for modeling flood conveyance overbank sediment transport and scalar residence time in the vegetated layer

bromine and chlorine emissions from plinian eruptions along the central american volcanic arc from source to atmosphere highlights data set of br and cl emissions from 29 large cava eruptions vei 5 melt inclusions are strongly enriched in chlorine and bromine compared to their respective matrix glasses fluid partitioning is 4 to 68 times more efficient for br than for cl subducted calcareous sediments are the major control on the arc magmatic bromine contents average cava eruption would add 368 eesc of recent annual loading to stratosphere abstract large explosive volcanic eruptions inject gases aerosols and fine ashes into the stratosphere potentially influencing climate and atmosphere composition on a global scale although the potential climate effect of chlorine cl and bromine br injections into the stratosphere is known the global mass fluxes are poorly constrained in this study we focus on the magmatic degassing systematics and budgets of br and cl and on constraining the major sources of br in a subduction setting we therefore present a regional time series of br and cl emissions from 29 highly explosive eruptions throughout the central american volcanic arc cava covering the last 200 ka and a range of magmatic compositions and eruption magnitudes we have measured br and cl in matrix glasses and melt inclusions using synchrotron radiation micro x ray fluorescence spectrometry sr micro xrf and electron microprobe respectively melt inclusions of the cava tephras generally have higher br 0 9 to 17 9 ppm and cl 770 to 3800 ppm contents than the matrix glasses 0 39 to 1 5 ppm br 600 to 2800 ppm cl moreover the difference between maximum and minimum concentrations observed in melt inclusions of a given sample ranges between 9 and 90 of the maximum observed concentration for br and between 2 and 40 for cl such intra sample variations arise from variable pre eruptive degassing of these halogens into a magmatic fluid phase the relative loss of br from the melt is 4 to 68 times higher than that of cl the masses of br 2 1100 kt and cl 0 1 to 800 mt emitted by the eruptions generate instantaneous additions to the stratosphere potentially amounting to 6 5600 of the present day stratospheric annual global loading of equivalent effective stratospheric chlorine as the size of the stratospheric impact is primarily a function of eruption magnitude we use magnitude frequency relationships to estimate that eruptions adding 10 to resident eesc loading would occur every 40 years while every 200 years an eruption would double the eesc loading comparing the variations in br and cl concentrations and particularly minimum cl br ratios in melt inclusions with geochemical trace element proxies e g u la ba th and lead isotope compositions which change along the arc in response to changing subduction conditions we suggest that subducted calcareous sediment is a major source of magmatic br but also infer an important role of fluids expelled from serpentinized subducted mantle extrapolation of cava volcanic br emissions to the global subduction system thus needs to consider variations in the nature of subducted lithologies

the impact of air mass circulation dynamics on late holocene paleoclimate in northwestern north america paleoclimate records from northern british columbia southwestern yukon and adjacent alaska suggest that late holocene climate may have been influenced by specific air mass circulation dynamics the aleutian lowpressure index alpi is a measure of sea level pressure fluctuations in the pacific northwest associated with the aleutian low al pressure system in this study we show that the al has a strong influence on historical climate change in the study area and explore the relationships between alpi polarity and changes in late holocene paleoclimate records analyses of weather station data in the study area indicate positive correlations r 0 63 between mean wintertime december march temperature and alpi values total wintertime snowfall accumulation and total precipitation show moderate and weak negative correlations respectively a late holocene increase in exotic western hemlock tsuga heterophylla pollen has been observed in regional paleoclimate studies a sustained positive alpi phase during the late holocene is considered as a causative mechanism under such conditions warm maritime air masses would more frequently penetrate inland potentially resulting in eastward pollen transfer enhanced growing conditions at coastal sites and an increase eastwards in the range limit of these species this study indicates that apparent conflicts in the timing and magnitude of late holocene climate change may be the result of a strong regional climate forcing mechanism that exhibits both temporal and geographical variation r 2002 elsevier science ltd and inqua all rights reserved

highest natural bed forms 1 fluid flow interacts with sedimentary beds forming waves of different kinds which are of considerable practical importance since they influence significantly the near bed flow both over and below the bed sediment transport and wave height attenuation we focus here on steep bed forms capable of producing flow separation in this case the large scale vorticity generated in the phenomenon of separation rules the process of friction which appears to be practically unaffected by sediment motion under the crests of the bed forms the mean shear force due to friction is balanced by the force that bed forms exert on the flow via pressure which can be calculated from the work of gimenez curto and corniero 2002 bed forms grow until they have a height such that friction at their troughs is negligible thus ceasing the motion of fluid and sediment this condition leads to a very simple expression for the limiting steepness which compares favorably with existing observations on bed form geometry under steady open channel flow as well as under oscillatory flow

vegetated mixing layer around a finite size patch of submerged plants 1 theory and field experiments 1 dynamics of a vegetated mixing layer around a patch of submerged plants was examined theoretically and experimentally in a lowland river theoretical analysis explored analogy with hydrodynamic mixing layers and introduced equations that describe expansion of the layers and alterations in mean flow field experiments provided empirical data for validation of the theory and examination of the effects of population density on the mixing layer dynamics detailed measurements assessed the structure of turbulent flow plant morphology biomechanical properties bending and streamlining due to interaction with the flow the theory was compared with the field experiments and an agreement was concluded it was found that near the upstream edge of the patch the vegetated mixing layer expands similar to the canonical mixing layers although its statistics scale on the velocity differential characteristic for the stabilized part downstream mean momentum flux reduces in magnitude and reverses in direction while turbulence became dominant this was observed to stabilize the velocity differential and increase the mean velocity of the layer that result in its limited growth described by a logarithmic function the population density of vegetation was found to control the flow in dense vegetation the analogy with mixing layers resembled best while in sparse vegetation the flow behaved similar to the boundary layers this theory can be used for quantitative assessment of seasonal effects in natural vegetated rivers because the population density of vegetation varies during the vegetation season the companion paper focuses on the structural properties of turbulence in the vegetated shear layers

evolution of geochemical variations along the central american volcanic front 1 new geochemical analyses of volcanic rocks in el salvador add to existing data from nicaragua and costa rica to create a comprehensive set of geochemical data for central american volcanics these data coupled with previously published 40ar 39ar ages covering the past 30 ma show that costa rica and nicaragua had similar u th and ba la values until 10 ma when the region developed the distinctive along arc variations that made this margin famous u th values increased in nicaragua since the miocene while remaining unchanged along the rest of the volcanic front this coincides temporally with the carbonate crash which caused a transition in cocos plate sediments from low u carbonates to high u organic rich hemipelagic muds increases in uranium are not observed in costa rica because its lower slab dip produces a more diffuse zone of partial melting and because of the contribution from galapagos derived tracks dilutes this signal ba la has been used as a geochemical proxy for contributions from the subducting slab however our analyses indicate that the ba concentrations do not vary significantly along strike either in the subducting sediment or the volcanic front along arc variation is controlled by changes in la an indicator of the degree of partial melting or source enrichment trace element models of five segments of the volcanic front suggest that a subducting sediment component is more important to magmas produced in el salvador and nicaragua than in costa rica where the geochemistry is controlled by recent 10 ma recycling of galapagos tracks

seismic cycle and plate margin deformation in costa rica gps observations from 1994 to 1997 global positioning system gps observations in costa rica from 1994 to 1997 reveal a complex pattern of motion consistent with the superposition of seismic cycle and secular plate margin deformation in the south velocity vectors are consistent with motion of the panama block plus postseismic deformation following the 1991 limon earthquake and interseismic strain due to partial locking of the middle america trench mat thrust in the northwest sites west of the volcanic arc are moving to the nw as a forearc sliver superimposed on this sliver motion are vertical and horizontal interseismic deformations from the adjacent nicoya segment of the mat we apply two different inverse methods to understand the source of the seismic strain in nw costa rica we compare fault locking models derived using a singular value decomposition inversion with that of a simulated annealing global optimization approach both methods yield similar models for partial locking of the thrust interface beneath the nicoya peninsula our results define an area of nearly fully locked fault beneath the outer coast of the southern portion of the peninsula with somewhat lower coupling beneath the northern half and with low coupling elsewhere these initial results show the promise for detailed imaging of the locked portion of a thrust interface responsible for future large subduction zone earthquakes

influence of permeable beds on hydraulically macro rough flow in this study macro rough flows over beds with different permeability values are simulated using the large eddy simulation and the results are analysed by applying the double averaging da methodology spheres of different sizes and arrangements were used to form the beds which are deemed to be permeable granular beds the influence of bed permeability on the turbulence dynamics and structure is investigated it was observed that the scales of the spanwise vortical structures over more permeable beds are larger than those over less permeable beds this is attributed to large scale spanwise alternate strips of varying reynolds shear stress rss emerging from the surface of macro rough elements for the permeable beds the da stress balance suggests that the time averaged spanwise vortical structure leads to a damping in da rss and an unusual peak of the form induced stress in the main flow in the streamwise direction both large turbulent structures that originate from the kelvin helmholtz type instability and small turbulent structures that are associated with the turbulent transport across the gaps of the roughness elements are more prevalent over highly permeable beds near the bed the relative magnitude of turbulent events shows a transition from a ejections dominating to sweeps dominating zone with vertical distance further several hydrodynamic characteristics normalized by inner scales kinematic viscosity to shear velocity ratio show a greater dependency on permeability reynolds number than those normalized by sediment size the study provides an insight into the mechanism of mass transfer near the fluid particle interface which is vital to benthic and aquatic ecology

the wet nicaraguan slab 1 nicaraguan volcanoes show globally high concentrations of geochemical tracers from dehydration of subducting crust which may reflect a slab with unusually high amounts of h2o to test this possibility we measure seismic velocities at the top of the subducted plate and compare them with predictions for hydrated mafic rocks regional seismic p waves for intraslab events at 100 150 km depth show a high frequency late arrival apparently trapped in a low velocity waveguide 2 5 6 km thick at the top of the downgoing plate 14 5 2 2 slower than surrounding mantle the velocities can be explained by 5 wt h2o in the subducted crust 2 3 times the hydration inferred for other slabs by similar methods this interpretation implies extensive hydration of the cocos plate off nicaragua perhaps enhanced by up dip fluid flow within the slab at 100 km depth

late cenozoic tephrostratigraphy offshore the southern central american volcanic arc 1 tephra ages and provenance we studied the tephra inventory of 18 deep sea drill sites from six dsdp odp legs legs 84 138 170 202 205 206 and two iodp legs legs 334 and 344 offshore the southern central american volcanic arc cava eight drill sites are located on the incoming cocos plate and ten drill sites on the continental slope of the caribbean plate in total we examined 840 ash bearing horizons and identified 650 of these as primary ash beds of which 430 originated from the cava correlations of ash beds were established between marine cores and with terrestrial tephra deposits using major and trace element glass compositions with respect to relative stratigraphic order as a prerequisite for marine terrestrial correlations we present a new geochemical data set for significant neogene and quaternary costa rican tephras moreover new ar ar ages for marine tephras have been determined and marine ash beds are also dated using the pelagic sedimentation rates the resulting correlations and provenance analyses build a tephrochronostratigraphic framework for costa rica and nicaragua that covers the last 8 myr we define 39 correlations of marine ash beds to specific tephra formations in costa rica and nicaragua from the 4 15 ma lower sandillal ignimbrite to the 3 5 ka rincon de la vieja tephra from costa rica as well as another 32 widely distributed tephra layers for which their specific region of origin along costa rica and nicaragua can be constrained this article is protected by copyright all rights reserved

wave attenuation by flexible idealized salt marsh vegetation abstract wave attenuation by vegetation is a highly dynamic process and its quantification is important for understanding shore protection potential and modeling coastal hydrodynamics data documenting the interactions of spartina alterniflora represented by polyolefin tubing and single and double peaked irregular waves were collected in a large scale laboratory flume the laboratory provided a controlled environment to evaluate wave attenuation including the parameters of stem density submergence wave height and peak period wave attenuation appeared to be most dependent on stem density and the ratio of stem length to water depth wave attention increased slightly with wave height while no clear trend with respect to wave period was seen treating double peaked spectra as superimposed wave systems revealed a preferential dissipation of the higher frequency wave system relative to the lower frequency wave system under emergent conditions wave energy loss occurred at all frequencies of both spectral types with dissipation increasing with frequency above the spectral peak parameterizing the spectral equilibrium range as a function of frequency showed a steepening of the spectral tail compared to the 4 power law under emergent conditions an empirical relationship defining the bulk drag coefficient for s alterniflora as a function of the stem reynolds number is found to serve as a first estimate for engineering applications

turbulence structure in open channel flow with partially covered artificial emergent vegetation abstract an innovative approach was recently proposed to increase water depth and improve navigation in rivers by increasing overall roughness through an adaptive placement of artificial vegetation in this approach a section of the river width is covered with artificial vegetation constructed from an array of dampers that can be added or removed while maintaining sufficient width for navigational purposes the goal of the work here is to explore the mean flow and turbulent momentum transport properties of such flow in a controlled flume setting where the flow rate is steady the vegetation placement is uniform and the froude number is maintained at sub critical conditions the focus is on vegetation induced roughness alterations to the bulk flow statistics as well as the structure of turbulence impacted by the presence of such artificially engineered vegetation the canopy flow experimentally explored here differs from the well studied planar uniform emergent canopy flow because the interface between the vegetation and non vegetation areas occurs along a lateral direction instead of the vertical direction the flume experiments were conducted by partially covering the channel width with emergent artificial vegetation that is flexible and can interact with the flow the quantities studied are the equilibration distance of the flow statistics from the leading vegetation edge as such distance is essential to any engineering design moreover the mean flow and turbulence regimes at several longitudinal sections were analyzed using spectral analysis and conditional sampling to identify the main vortical structures and their contribution to momentum transport spectral analysis demonstrated that the sizes of the dominant vortices can be classified into stem scale small scale and shear scale larger scale vortices as conventional in canonical canopy flows the shear layer formed in the planar direction and its associated coherent vortices are spawned near the edge of the vegetated area in a manner analogous to a plane mixing layer quadrant analysis showed two contributions to the overall shear stress and lateral momentum exchange between the vegetated and non vegetated zone namely ejections and sweeps the measured ejection sweep contributions are short lived but significant to the overall turbulent momentum transport consistent with other canopy flow studies approximately 80 of the turbulent stress contributions at the interface occur within 30 of the time because the flume experiments were conducted at sufficiently high reynolds number and sufficiently low froude number the scalability of the experimental findings here to much larger settings encountered in engineering practice are briefly discussed

observations of amplified roughness from crystal accretion in the sub ice ocean boundary layer ice crystal accretion on the underside of sea ice and ice shelves a signature of pressure induced supercooling has the potential to alter the energy balance in the ocean boundary layer through enhanced hydrodynamic roughness here we present estimates of crystal driven ocean boundary layer roughness in supercooled water beneath sea ice adjacent to the mcmurdo ross ice shelf data were collected from four sites in mcmurdo sound antarctica between 2007 and 2015 and represent a range of ice shelf affected conditions the results show that drag of the rough ice underside in the presence of platelets is 6 30 times larger than typical levels homogeneously applied in ice ocean interaction models the crystal enhanced drag promotes increased entrainment into the boundary layer from the upper ocean which has the potential to affect ice shelf evolution and sea ice growth through enhanced turbulent exchange of heat and momentum

crustal and mantle shear velocity structure of costa rica and nicaragua from ambient noise and teleseismic rayleigh wave tomography the costa rica nicaragua subduction zone shows systematic along strike variation in arc chemistry geology tectonics and seismic velocity and attenuation presenting global extremes within a few hundred kilometres in this study we use teleseismic and ambient noise derived surface wave tomography to produce a 3 d shear velocity model of the region we use the 48 stations of the tucan array and up to 94 events for the teleseismic rayleigh wave inversion and 18 months of continuous data for cross correlation to estimate green s functions from ambient noise in the shallow crust 0 15 km we observe low shear velocities directly beneath the arc volcanoes 40 km thick crust beneath the costa rican arc and the nicaraguan highlands thinned crust 20 km beneath the nicaraguan depression and increasing crustal thickness in the backarc region consistent with receiver function studies the region of thinned seismically slow and likely weakened crust beneath the arc in nicaragua is not localizing deformation associated with oblique subduction at mantle depths 55 120 km depth we observe lower shear velocities up to 3 per cent beneath the nicaraguan arc and backarc than beneath costa rica our low shear velocity anomaly beneath nicaragua is in the same location as a low shear velocity anomaly and displaced towards the backarc from the high vp vs anomaly observed in body wave tomography the lower shear velocity beneath nicaragua may indicate higher melt content in the mantle perhaps due to higher volatile flux from the slab or higher temperature finally we observe a linear high velocity region at depths 120 km parallel to the trench which is consistent with the subducting slab

paraglacial and postglacial debris flows on a little ice age terminal moraine jamapa glacier pico de orizaba mexico the study area is located on the northern face of pico de orizaba mexico 5700 m asl on the terminal moraine of jamapa glacier which dates from the little ice age large debris flows are recurrent on the proglacial ramp the comparison of lichen colonies growing on the deposits of the flows reveals that two generations of flows are present an old one and a very recent one that occurred between 1994 and 1995 studies were made of the sedimentologic characteristics of the flows and ground temperatures were recorded to a depth of 70 cm on the floor of the channels comparison of the lichen growth on the exposed surfaces of the deposits led to the relative dating of the older debris flow which is associated with the beginning of the retreat of the glacier and the saturation of the terminal moraine deposits by meltwater the more recent flow has less transport capacity and is identified with the formation of an impermeable layer of permafrost that covers the bottom of the channel of the old debris flow the permafrost layer formed when snow accumulations on the bottom of the channel were covered by ash that fell from the slopes

an eruptive history of maderas volcano using new 40ar 39ar ages and geochemical analyses maderas volcano is a small andesitic stratovolcano located on the island of ometepe in lake nicaragua nicaragua with no record of historic activity twenty one samples were collected in 2010 from lava flows of maderas the selected samples were analyzed for whole rock geochemistry using icp aes and or were dated using the 40ar 39ar method the results of these analyses were combined with previously collected data from maderas as well as field observations to determine the eruptive history of the volcano and create a geologic map the results of the geochemical analyses indicate that maderas has higher concentrations of alkalies than most nicaraguan and costa rican volcanoes including its nearest neighbor concepcion volcano it is also different from concepcion in that it displays higher incompatible elements determined age dates range from 179 2 16 4 ka to 70 5 6 1 ka based on these ages and the geomorphology of the volcano which is characterized by a bisecting graben it is proposed that maderas experienced two generations of development initial build up of the older cone including pre graben lava flows followed by post graben lava flows the ages also indicate that maderas is markedly older than concepcion which is historically active volcanic hazards were also assessed the 40ar 39ar ages indicate that maderas has likely been inactive for tens of thousands of years and future volcanic eruptions are not considered an immediate hazard however earthquake and lahar hazards exist for the communities around the volcano the steep slopes of the eroded older cone are the most likely sources of lahar hazards

hydrodynamics of model posidonia oceanica patches in shallow water the hydrodynamics of simulated patches of the mediterranean seagrass posidonia oceanica were studied in laboratory flume experiments in which the height of the pronated canopy was always greater than half the total water depth the effects of variations in speed from 0 08 m s 21 to 0 24 m s 21 and patch configuration on the hydrodynamics were investigated significant speeds penetrated the patches to approximately half their height reducing speed did not change the flow patterns observed except to weaken and blur them flow encountering a single patch formed a turbulent wake at the height of the top of the canopy within this wake the vertical shear stress decreased monotonically downstream but the reynolds stress increased initially and then decayed when a second patch was positioned within the region where reynolds stress increased referred to as the 06 patch the wake center penetrated it causing average turbulent velocities with horizontal components 3 3 times higher and vertical components 4 2 times higher than in the upstream patch when this patch was positioned where the reynolds stress decayed referred to as the 14 patch the wake center rose above it nevertheless the turbulence in the 14 patch had horizontal components 12 higher and vertical components 22 higher on average than in the 06 patch because its upstream end was closer to the reynolds stress maximum thus the ratio of the patch separation to the length of wake in which the reynolds stress increased was identified as central to quantifying the turbulence within the downstream patch the increased turbulence is likely to be important in determining sedimentary and ecological patch characteristics by increasing retention of particulates in suspension and thus reducing depositional rates of for example larvae nutrients and dead organic matter

the lillooet terraces of fraser river a palaeoenvironmental enquiry the history of holocene fluvial terraces was investigated by stratigraphic morphological and palaeohydrologic methods the terraces were formed in glaciofluvial and glaciolacustrine sediments by the fraser river degradation alternated with episodes of stability and aggradation the uppermost terraces four nonpaired surfaces were occupied by a braided river vertical stability was controlled either by the water and sediment discharge of the river or by backwater effects from downstream landslides the lower terraces two paired surfaces and associated fluvial sediments provide evidence for at least two cycles of aggradation and downcutting these can be attributed to the effects of landslides that occurred a short distance downstream climatic variations may also have influenced terrace formation but direct evidence is lacking palaeohydraulic investigations based on gravel texture terrace gradients and geometry of palaeochannels provide results that although approximate conform with conclusions

the influence of macrophyte growth typical of eutrophic conditions on river flow velocities and turbulence production the influence of emergent and submerged macrophytes on flow velocity and turbulence production is demonstrated in a 140 m reach of the river blackwater in farnborough hampshire uk macrophyte growth occurs in patches and is dominated by sparganium erectum and sparganium emersum in may 2001 patches of s erectum were already established and occupied 18 of the channel area the flow adjusted to these predominantly lateral patches by being channelled through a narrower cross section the measured velocity profiles showed a logarithmic form with deviations attributable to topographic control the channel bed was the main source of turbulence in september 2001 in stream macrophytes occupied 27 of the channel and overhanging bank vegetation affected 32 of the area overall flow resistance described by manning s n showed a threefold increase that could be attributed to the growth of s emersum in the middle of the channel velocity profiles showed different characteristic forms depending on their position relative to plant stems and leaves the overall velocity field had a three dimensional structure turbulence intensities were generally higher and turbulence profiles tended to mirror the velocity profiles evidence for the generation of coherent eddies was provided by ratios of the root mean square velocities spectral analysis identified deviations from the kolmogorov 5 3 power law and provided statistical evidence for a spectral short cut indicative of additional turbulence production this was most marked for the submerged vegetation and in some instances the overhanging bank vegetation the long strap like leaves of s emersum being aligned approximately parallel to the flow and the highly variable velocity field created by the patch arrangement of macrophytes suggest that the dominant mechanism for turbulence production is vortex shedding along shear zones wake production around individual stems of s emersum close to the bed may also be important locally

sedimentary processes of the kusawa lake torrent system yukon canada as revealed by the september 16 1982 flood event abstract the kusawa lake torrent system is located in the northern canadian cordillera of southwestern yukon it is holocene in age and consists of a catchment area gorge and alluvial fan complex the north compartment of the catchment is a third order basin covering an area of 13 2 km 2 it is characterized by active slumping of quaternary glacial deposits that supply sediment for the torrent system the gorge is approximately 800 m long and distinguished by 10 m high vertical walls cut into granitic bedrock the fan complex is semiconical in shape and covers an area of 1 52 km 2 the active part of the fan is plano convex in longitudinal profile covers an area of 0 75 km 2 and is subdivided into an upper middle and lower fan based on the occurrence of seven sedimentary facies that were deposited by a catastrophic flood in 1982 the upper fan is characterized by boulder gravel levees and boulder gravel lobes that were deposited by debris flows it is also characterized by sandy boulder gravel that may represent a transition from debris flow to dominantly hyperconcentrated flow processes the middle fan is distinguished by sandy cobble gravel and sandy pebble gravel that is interbedded with horizontally laminated sand these sediments were deposited by hyperconcentrated flows the lower fan is characterized by horizontally bedded and laminated sand that may represent a transition from hyperconcentrated flow to sheetflood dominant processes and by sand channels that represent rechannelized waning flood discharge the fan displays downfan trends in grain size boulders to sand slope style plano concave and slope value 4 1 typical of sheetflood dominated fans the initiation of sedimentation in the kusawa lake torrent system was due to a combination of rainfall flooding and flooding related to catastrophic slope failure in the catchment area slope failure leads to the formation of a landslide dam and lake and when the dam fails the draining lake results in a flood many times larger than a rainfall flood the frequency of these catastrophic flood events may be once every 200 years although the kusawa lake torrent system is now dormant the potential for further landslide dams and subsequent catastrophic floods is high and could result in further damage to a campground and private property in the area

flow and deposition in and around a finite patch of vegetation this laboratory study describes the flow and deposition observed in and around a finite patch of vegetation located at the wall of a channel two patch densities are considered with 2 and 10 solid volume fraction the velocity field measured in and around the patch by acoustic doppler velocimetry revealed three distinct zones first there is a diverging flow region at the leading edge of the patch where the flow in line with the patch decelerates and the bulk of the flow is diverted toward the open channel second there is a fully developed region within the vegetation where the velocity is uniform across the patch width and along the length of the patch third a shear layer forms at the interface between the patch and adjacent open channel the pattern of deposition in and around the vegetation was characterized by releasing 12 micron spherical glass particles and recording net deposition on a set of glass slides in the diverging region net deposition increases in the stream wise direction as the local velocity decreases in the fully developed region of the patch deposition decreases with longitudinal position as the concentration in the water column is depleted the deposition pattern is nearly uniform across the patch width consistent with the velocity field and suggesting that turbulent diffusive flux across the lateral edge of the patch is not a significant source of particles to the patch under the conditions studied here

hydrodynamics induced by wind waves in a vegetation field the wave induced kinematics and dynamics of a submerged or emerged vegetation field is analyzed using potential flow and an eigenfunction expansion the problem is solved considering regular as well as irregular incident waves the model takes into account the vegetation motion and solves for the complete wave system on the vegetation field and in its vicinity the model is validated against experimental laboratory data obtained by other authors showing a much better agreement than previous theoretical models in this paper the model is used to evaluate wave height evolution damping vegetation and fluid motion and forces and moments on the vegetation furthermore the inclusion of irregular waves provides force and moment distributions on the vegetation field depending on the wave climate statistics

shear induced instabilities of flows through submerged vegetation we consider the instabilities of flows through a submerged canopy and show how the full governing equations of the fluid structure interactions can be reduced to a compact framework that captures many key features of vegetative flow first by modelling the canopy as a collection of homogeneous elastic beams we predict the steady configuration of the plants in response to a unidirectional flow this treatment couples the beam equations in the canopy to the fluid momentum equations subsequently a linear stability analysis suggests new insights into the development of instabilities at the surface of the vegetative region in particular we show that shear at the top of the canopy is a dominant factor in determining the onset of instabilities known as monami based on numerical and asymptotic analysis of the quadratic eigenvalue problem the system is shown to be stable if the canopy is sufficiently sparse

the role of hydrodynamic forcing sediment transport processes and bottom substratum in the shoreward development of posidonia oceanica meadow abstract this paper investigates the combined role of hydrodynamic forcing sediment transport processes and sea bottom features in determining the location of the meadow upper limit of the endemic mediterranean seagrass posidonia oceanica for this purpose an approach including extreme wave analysis and numerical modelling is applied to two sandy beach systems located in southern sardinia italy information about bathymetry p oceanica meadow extension and bottom features has been made available by previous published studies based on the 30 year long noaa hindcast dataset a wave climate analysis is carried out to identify the incoming storm wave conditions 1 year return period to be simulated with the delft3d model package the simulation results extend the current knowledge highlighting the importance of wave induced hydrodynamic parameters as limiting factors for the survival of p oceanica meadows in particular the results suggest that on sandy substrata the meadow upper limit lies well offshore of the surf zone in areas with little morphological activity where the wave orbital velocities associated to storms are on the order of 0 8 m s and the mean current magnitude does not exceed 0 5 m s on rocky bottoms the p oceanica meadow can extend up to the outer surf zone of storms and is thus able to colonize shallow areas subject to stronger hydrodynamic forcings than those observed on sand this difference in the plant tolerance to wave forcing depending on the substratum type shows how both hydrodynamic and geological factors play a key role in defining the environmental conditions for the development of seagrass meadows

mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition 1 the transport of fine sediment and organic matter plays an important role in the nutrient dynamics of shallow aquatic systems and the fate of these particles is closely linked to vegetation we describe the mean and turbulent flow near circular patches of synthetic vegetation and examine how the spatial distribution of flow is connected to the spatial distribution of suspended sediment deposition patches of rigid emergent and flexible submerged vegetation were considered with two different stem densities for the rigid emergent vegetation flow adjustment was primarily two dimensional with flow deflected in the horizontal plane horizontal shear layers produced a von karman vortex street flow through the patch shifted the vortex street downstream resulting in a region directly downstream of the patch in which both the mean and turbulent velocities were diminished net deposition was enhanced within this region in contrast for the flexible submerged vegetation flow adjustment was three dimensional with shear layers formed in the vertical and horizontal planes because of strong vertical circulation turbulent kinetic energy was elevated directly downstream of the patch consistent with this deposition was not enhanced at any point in the wake this comparison suggests that morphological feedbacks differ between submerged and emergent vegetation further enhanced deposition occurred only in regions where both turbulent and mean velocities were reduced relative to the open channel reduced deposition indicating enhanced resuspension occurred in regions of high turbulence kinetic energy regardless of local mean velocity these observations highlight the importance of turbulence in controlling deposition

holocene debris flows and environmental history hazelton area british columbia debris flow deposits of chicago creek and the sediment pollen and macrofossil records of seeley lake were studied to elucidate the holocene history of the northwest flank of the rocher dcboulc range near hazelton british columbia the chicago creek drainage has experienced numerous rockfalls debris slides and debris flows a large debris flow covering approximately 300 ha occurred about 3580 2 150 bp this flow was two to three orders of magnitude larger than historic debris flows in this drainage it traveled about 3 km down chicago creek and dammed the outlet stream of seeley lake a debris deposit along lower chicago creek is interpreted as the product of debris torrents that formed during or soon after the damming of seeley lake its surface exhibits soil development rubification and profile development comparable to that on the large debris flow suggesting equivalent age pollen and plant macrofossils are described from a core taken in seeley lake this core spans the period from ca 9200 bp to the present a disturbance event in 3380 2 110 bp correlative with the large chicago creek debris flow is recorded by a clastic sediment layer and changes in the microfossil and rnacrofossil assemblages the chicago creek debris flow and debris torrent ca 3500 bp may be the catastrophic event recorded in the story of the medeek an oral history or ada ok of the gitksan people of hazelton

mixing layers and coherent structures in vegetated aquatic flows 1 to date flow through submerged aquatic vegetation has largely been viewed as perturbed boundary layer flow with vegetative drag treated as an extension of bed drag however recent studies of terrestrial canopies demonstrate that the flow structure within and just above an unconfined canopy more strongly resembles a mixing layer than a boundary layer this paper presents laboratory measurements obtained from a scaled seagrass model that demonstrate the applicability of the mixing layer analogy to aquatic systems specifically all vertical profiles of mean velocity contained an inflection point which makes the flow susceptible to kelvin helmholtz instability this instability leads to the generation of large coherent vortices within the mixing layer observed in the model at frequencies between 0 01 and 0 11 hz which dominate the vertical transport of momentum through the layer the downstream advection of these vortices is shown to cause the progressive coherent waving of aquatic vegetation known as the monami when the monami is present the turbulent vertical transport of momentum is enhanced with turbulent stresses penetrating an additional 30 of the plant height into the canopy

preservation of contrasting geothermal gradients across the caribbean north america plate boundary motagua fault guatemala 1 strike slip plate boundaries juxtapose crustal blocks that may have different geodynamic origins and therefore different thermal structures thermo kinematic modeling of this type of strike slip plate boundary predicts an asymmetric signature in the low temperature thermochronologic record across the fault age elevation profiles of zircon u th he ages across the motagua fault a 500 km long segment of the transform boundary between the north american and caribbean plates document a sharp cooling age discontinuity across the fault this discontinuity could be interpreted as a difference in denudation history on each side of the fault however a low relief miocene erosional surface extends across the fault this surface has been uplifted and incised and provides a geomorphic argument against differential denudation across the fault by integrating magmatic volcanic and heat flow data age elevation profiles and thermo kinematic modeling we propose that large horizontal displacement along the motagua fault has offset a persistent geothermal asymmetry across the fault and explains both the age discontinuities and the age elevation patterns this study illustrates how thermochronology can be used to detect large strike slip displacements and more generally opens new perspectives in understanding the impact of nonuniform thermal structures on thermochronologic results

an experimental study of flow through rigid vegetation 1 better understanding of the role of vegetation in the transport of fluid and pollutants requires improved knowledge of the detailed flow structure within the vegetation instead of spatial averaging this study uses discrete measurements at multiple locations within the canopy to develop velocity and turbulence intensity profiles and observe the changes in the flow characteristics as water travels through a vegetation array simulated by rigid dowels velocity data was collected with a one dimensional laser doppler velocimeter under emergent and submerged flow conditions the effects of dowel arrangement density and roughness were also examined the results show that the velocity within the vegetation array is constant with depth and the velocity profile is logarithmic above it however the boundaries are marked by inflection points the strongest vortices and turbulence intensities can be found there especially in the region immediately downstream of a dowel these results support the idea that the flow in the region near the bed and at the top of the dowel array is very unstable leading to the formation of coherent structures and are areas of significant mass and momentum exchange

persistent growth of a young andesite lava cone bagana volcano papua new guinea abstract bagana an andesite lava cone on bougainville island papua new guinea is thought to be a very young central volcano we have tested this idea by estimating the volumes of lava extruded over different time intervals 1 2 3 9 15 70 years using digital elevation models dems mainly created from satellite data our results show that the long term extrusion rate at bagana measured over years to decades has remained at about 1 0 m3 s 1 we present models of the total edifice volume and show that if our measured extrusion rates are representative the volcano could have been built in only 300 years it could also possibly have been built at a slower rate during a longer earlier period of growth six kilometres nnw of bagana an andesite dacite volcano billy mitchell had a large caldera forming plinian eruption 437 years ago we consider the possibility that as a result of this eruption the magma supply was diverted from billy mitchell to bagana it seems that bagana is a rare example of a very youthful polygenetic andesite volcano the characteristics of such a volcano based on the example of bagana are a preponderance of lava products over pyroclastic products a high rate of lava extrusion maintained for decades a very high rate of so2 emission evidence of magma batch fractionation and location in a trans tensional setting at the end of an arc segment above a very steeply dipping and rapidly converging subduction zone

lead isotope composition of central american volcanoes influence of the galapagos plume 1 lead isotopic analyses of lavas from central america both along and behind the volcanic arc help to clarify source components in the mantle wedge analysis of previous pb isotopic data had implied that little or no marine sediment lead was added to the central american source region as all samples fell within the morb field in contrast to other information e g ba la 10be 87sr 86sr that indicated a high subduction component the data presented here include several analyses of local marine sediment showing it to be exceptionally unradiogenic in pb and thus permitting high sediment contributions to the mantle source region without significant changes in pb isotopes combined pb nd and pb sr isotopic diagrams clearly illustrate the influence of crustal contamination for samples from guatemala and honduras and of subducted sediment for all lavas of the volcanic front samples collected behind the volcanic front are derived from mixing between enriched and depleted mantle sources and in central costa rica extending to the back arc overlap pb sr and nd isotope values for both cocos island and some components of the galapagos hot spot the restricted geographical occurrence of the enriched mantle signature in central america coupled with the persistence of the signal well into the back arc region imply that these lavas are sampling galapagos plume influenced mantle the presence of this plume component beneath southern central america and extending to the northeast beneath the caribbean confirms a galapagos hot spot origin for this part of caribbean plate

velocity profiles in vegetated open channel flows combined effects of multiple mechanisms abstractvertical profile of longitudinal velocity in vegetated channels reflects complex mechanics of flow vegetation interactions and determines the bulk flow velocity and flow rate most available models of velocity profiles in vegetated channels are based on a single physical concept that underpins theoretical considerations and data interpretation however measured velocity profiles suggest that the use of a single concept is not sufficient to cover all possible scenarios of flow vegetation interactions as a result a number of models in which different concepts are applied to different flow regions have been recently developed within this framework the overall velocity profile is represented with a set of linked segments although such segment based models have improved velocity profile description there is a need for more robust approaches and better analytical formulations this paper proposes a new approach where a vertical velocity profile in vegetated channels is modelled as a linear superp

petrogenesis of a voluminous quaternary adakitic volcano the case of baru volcano the origin of adakite magmas remains controversial because initially the term adakite had petrogenetic significance implying an origin by direct melting of the eclogitized subducting oceanic crust many models have been produced for their origin and until now there has not been a straightforward method to discriminate between these models in a given adakite suite here we use detailed chronological and geochemical studies of selected adakitic edifices that allows for the determination of the magmatic output rate parameter qe which has been correlated with the rates of magma generation deep within subduction zones by providing temporal and eruption rate estimates we provide constraints on the possible petrogenetic processes involved in the generation of adakite like signatures adakite magmas derived from the melting of the subducting slab should be volumetrically insignificant when compared to the adakite like magmas produced by typical arc magma generation processes in this study we use this observation and the extraordinary stratigraphic exposure from miocene to present in an adakitic volcano in panama and to study the temporal and chemical variation in erupted magmas to estimate rates of magma generation detailed chemical and geochronological analyses of baru volcano indicate that the volcanic edifice was constructed in its entirety during the quaternary and magmas display adakite like features such as steep rare earth elements patterns pronounced depletions in the heavy rare earth elements low y high sr and high sr y the magmatic output rates qe that we have calculated show that compared to other typical adakitic volcanoes most of the volcanic edifice of baru volcano was constructed extremely rapidly 213 k a and in time frames that are similar to typical arc volcanoes the observed chemical and mineralogical variation coupled with the high magma production rates indicate that baru volcano is more representative of a typical arc volcano than a small volume melt of the subducting oceanic crust the technique we outline may have broader application in determining the petrogenetic conditions of other adakite suites

wind flow and sedimentation in artificial vegetation field and wind tunnel experiments abstract the flow dynamics within and immediately above an artificial plastic vegetation canopy are measured in the field and wind tunnel artificial plants created from wooden dowels and cable zip ties were arranged in a variety of arrays on pegboards where plant cover or lateral cover could be accurately controlled plant covers examined ranged from 12 to 60 wind velocity profiles and the bedforms incipient dunes that developed within and beyond the vegetation in a few hours were measured the results indicate that flow deceleration and drag increases within the canopy as plant density increases in general there is a marked reduction and inflection in velocity at the canopy top and a second major inflection in the velocity profiles occurs immediately below the base of the four arrays equal or 23 density tall vegetation allows flow to sweep under the canopy and local high speed maxima flows may develop leading to minimal sedimentation in those canopies but deposition downwind beyond the canopies short vegetation where the leaves fill the canopy close to the ground display significantly greater drag and rapid rates of sand deposition flow velocities above the canopy increase as plant cover or density increases due to flow compression and acceleration bedform development is strongly correlated with plant cover density or lateral cover and short plants such that shorter length higher bedforms develop in higher density and or shorter plants the relationship between plant cover density or lateral cover and within canopy velocity is non linear and a new tentative flow regime is proposed canopy flow which may occur between wake interference flow and skimming flow this study further confirms that plant density plays a defining role in determining bedform and dune morphology the results also apply to flow in semi arid grasslands

holocene climate and seasonality of shell collection at the dundas islands group northern british columbia canada a bivalve sclerochronological approach article i nfo to analyze environmental changes and the seasonality of shell collection in british columbia during the ho locene oxygen isotopes were measured from modern and archeological 1337 7438 cal yr bp shells of the butter clam saxidomus gigantea 1697 discrete isotope samples were taken from two modern and 27 arche ological shells with a high temporal resolution sub seasonal up to daily archeological shells were collected from five shell midden sites on the dundas islands group northern british columbia canada the oxygen iso tope data reveal clear annual cycles with the most positive 18 oshell values occurring during the cold season slower growth annual growth line formation and the most negative 18 oshell values during the warm sea son period of faster growth whereas the most positive 18 oshell values remained relatively constant throughout the holocene the warm season 18 oshell values reflected considerable variability summer values observed in the early and late holocene became approximately 1 more negative around 2500 3000 and 5500 6000 bp implying lower salinity during the mid holocene variations in the oxygen isotopic composi tion of marine shells reflect changes in temperature and salinity such large changes in 18 oshell are unlikely being caused by temperature changes alone furthermore the large annual 18