eduction extension and exhumation of ultrahigh pressure rocks in metamorphic core complexes due to subduction initiation the controversy over the exhumation of ultrahigh pressure uhp rocks centers on whether it involves rising of pieces of crust detached from subducted continental lithosphere or an entire subducted plate that undergoes eduction i e reverse subduction we present a new thermomechanical model of continental subduction showing that these apparently contrasting mechanisms can occur together crust subducted deep enough is heated and weakened causing limited diapiric rise while crust subducted to shallower depths retains strength and is exhumed only by eduction the model also shows for the first time how eduction followed by seafloor spreading can occur in a zone of regional convergence this occurs spontaneously when subduction of buoyant crust causes a subduction zone to lock up in one place causing a new subduction zone to form in another the model is consistent with many features of the youngest region of uhp rock exhumation on earth the d entrecasteaux islands uhp exhumation and the amount of regional extension as well as the seismic structure around the islands can be explained by eduction ductile flow fabrics seen on the islands would result from exhumation of the most deeply subducted crust heated enough to undergo partial melting reversal of motion on the north dipping continental subduction zone required by this model was likely triggered by initiation of the new britain trench as suggested previously our model implies that the crust of goodenough basin south of the islands was exhumed by eduction in the last 5 ma and this hypothesis can be tested by drilling

a multidisciplinary effort to assign realistic source parameters to models of volcanic ash cloud transport and dispersion during eruptions during volcanic eruptions volcanic ash transport and dispersion models vatds are used to forecast the location and movement of ash clouds over hours to days in order to define hazards to aircraft and to communities downwind those models use input parameters called eruption source parameters such as plume height h mass eruption rate duration d and the mass fraction m63 of erupted debris finer than about 4 or 63 m which can remain in the cloud for many hours or days observational constraints on the value of such parameters are frequently unavailable in the first minutes or hours after an eruption is detected moreover observed plume height may change during an eruption requiring rapid assignment of new parameters this paper reports on a group effort to improve the accuracy of source parameters used by vatds in the early hours of an eruption we do so by first compiling a list of eruptions for which these parameters are well constrained and then using these data to review and update previously studied parameter relationships we find that the existing scatter in plots of h versus yields an uncertainty within the 50 confidence interval of plus or minus a factor of four in eruption rate for a given plume height this scatter is not clearly attributable to biases in measurement techniques or to well recognized processes such as elutriation from pyroclastic flows sparse data on total grain size distribution suggest that the mass fraction of fine debris m63 could vary by nearly two orders of magnitude between small basaltic eruptions 0 01 and large silicic ones 0 5 we classify eleven eruption types four types each for different sizes of silicic and mafic eruptions submarine eruptions brief or vulcanian eruptions and eruptions that generate co ignimbrite or co pyroclastic flow plumes for each eruption type we assign source parameters we then assign a characteristic eruption type to each of the world s 1500 holocene volcanoes these eruption types and associated parameters can be used for ash cloud modeling in the event of an eruption when no observational constraints on these parameters are available

using simple plume models to refine the source mass flux of volcanic eruptions according to atmospheric conditions abstract a simple three dimensional volcanic plume model that incorporates the effects of moisture and ambient wind is presented and used iteratively to refine the source mass flux obtained from an empirical relationship between the plume rise height and source mass flux according to the prevailing atmospheric conditions it is applied to the eruption of eyjafjallajokull in may 2010 using realistic atmospheric profiles appropriate to the time of the eruption it is shown that the ambient wind has the largest effect on the refined source mass flux with moisture playing a secondary though still important role it is also shown that significant differences in the values of the revised source mass fluxes can arise when the realistic atmospheric profiles are approximated by idealised profiles the revised source mass flux is used to initialise a long range dispersion model of ash in the atmosphere

uncertainty analysis of a model of wind blown volcanic plumes mathematical models of natural processes can be used as inversion tools to predict unobserved properties from measured quantities uncertainty in observations and model formulation impact on the efficacy of inverse modelling we present a general methodology history matching that can be used to investigate the effect of observational and model uncertainty on inverse modelling studies we demonstrate history matching on an integral model of volcanic plumes that is used to estimate source conditions from observations of the rise height of plumes during the eruptions of eyjafjallajokull iceland in 2010 and grimsvotn iceland in 2011 sources of uncertainty are identified and quantified and propagated through the integral plume model a preliminary sensitivity analysis is performed to identify the uncertain model parameters that strongly influence model predictions model predictions are assessed against observations through an implausibility measure that rules out model inputs that are considered implausible given the quantified uncertainty we demonstrate that the source mass flux at the volcano can be estimated from plume height observations but the magmatic temperature exit velocity and exsolved gas mass fraction cannot be accurately determined uncertainty in plume height observations and entrainment coefficients results in a large range of plausible values of the source mass flux our analysis shows that better constraints on entrainment coefficients for volcanic plumes and more precise observations of plume height are required to obtain tightly constrained estimates of the source mass flux

uncertainty quantification and sensitivity analysis of volcanic columns models results from the integral model plume mom the behavior of plumes associated with explosive volcanic eruptions is complex and dependent on eruptive source parameters e g exit velocity gas fraction temperature and grain size distribution it is also well known that the atmospheric environment interacts with volcanic plumes produced by explosive eruptions in a number of ways the wind field can bend the plume but also affect atmospheric air entrainment into the column enhancing its buoyancy and in some cases preventing column collapse in recent years several numerical simulation tools and observational systems have investigated the action of eruption parameters and wind field on volcanic column height and column trajectory revealing an important influence of these variables on plume behavior in this study we assess these dependencies using the integral model plume mom whereby the continuous polydispersity of pyroclastic particles is described using a quadrature based moment method an innovative approach in volcanology well suited for the description of the multiphase nature of magmatic mixtures application of formalized uncertainty quantification and sensitivity analysis techniques enables statistical exploration of the model providing information on the extent to which uncertainty in the input or model parameters propagates to model output uncertainty in particular in the framework of the iavcei commission on tephra hazard modeling inter comparison study plume mom is used to investigate the parameters exerting a major control on plume height applying it to a weak plume scenario based on 26 january 2011 shinmoe dake eruptive conditions and a strong plume scenario based on the climatic phase of the 15 june 1991 pinatubo eruption

deep subduction and rapid exhumation role of crustal strength and strain weakening in continental subduction and ultrahigh pressure rock exhumation 1 the exhumation of crustal ultra high pressure uhp material depends on temporal and spatial variations in its detachment within the subduction channel this dependence is investigated using numerical models with variable initial crustal strengths representing a range of initial crustal compositions and parameterized strain weakening representing a range of processes that reduce effective crustal viscosity during deformation competition between down channel shear traction favoring subduction and up channel buoyancy favoring exhumation is expressed as the exhumation number e which can vary with time and position along the channel exhumed lower strength crust which resists subduction owing to weak down channel traction records peak conditions 38 kbar given sufficient strain weakening exhumation proceeds at 60 km ma 1 indicating that buoyancy e 1 drives exhumation in these models in all models exhuming uhp material forms a deforming ductile plume with a range of possible structural relationships predicted between exhumed uhp and hp materials

the terminal velocity of volcanic particles with shape obtained from 3d x ray microtomography new experiments of falling volcanic particles were performed in order to define terminal velocity models applicable in a wide range of reynolds number re experiments were carried out with fluids of various viscosities and with particles that cover a wide range of size density and shape particle shape which strongly influences fluid drag was measured in 3d by high resolution x ray microtomography by which sphericity 3d and fractal dimension d3d were obtained they are easier to measure and less operator dependent than the 2d shape parameters used in previous papers drag laws that make use of the new 3d parameters were obtained by fitting particle data to the experiments and single equation terminal velocity models were derived they work well both at high and low re 3 10 2 re 104 while earlier formulations made use of different equations at different ranges of re the new drag laws are well suited for the modelling of particle transportation both in the eruptive column where coarse and fine particles are present and also in the distal part of the umbrella region where fine ash is involved in the large scale domains of atmospheric circulation a table of the typical values of 3d and d3d of particles from known plinian subplinian and ash plume eruptions is presented graphs of terminal velocity as a function of grain size are finally proposed as tools to help volcanologists and atmosphere scientists to model particle transportation of explosive eruptions

operational prediction of ash concentrations in the distal volcanic cloud from the 2010 eyjafjallajokull eruption 1 during the 2010 eruption of eyjafjallajokull improvements were made to the modeling procedure at the met office uk enabling peak ash concentrations within the volcanic cloud to be estimated in this paper we describe the ash concentration forecasting method its rationale and how it evolved over time in response to new information and user requirements the change from solely forecasting regions of ash to also estimating peak ash concentrations required consideration of volcanic ash emission rates the fraction of ash surviving near source fall out and the relationship between predicted mean and local peak ash concentrations unresolved by the model to validate the modeling procedure predicted peak ash concentrations are compared against observations obtained by ground based and research aircraft instrumentation this comparison between modeled and observed peak concentrations highlights the many sources of error and the uncertainties involved despite the challenges of predicting ash concentrations the ash forecasting method employed here is found to give useful guidance on likely ash concentrations predicted peak ash concentrations lie within about one and a half orders of magnitude of the observed peak concentrations a significant improvement in the agreement between modeled and observed values is seen if a buffer zone accounting for positional errors in the predicted ash cloud is used sensitivity of the predicted ash concentrations to the source properties e g the plume height and the vertical distribution of ash at the source is assessed and in some cases seemingly minor uncertainties in the source specification have a large effect on predicted ash concentrations

the fate of subducted sediments a case for backarc intrusion and underplating subduction of oceanic and continental sediments into the mantle is fundamental to the geochemical evolution of earth using thermal mechanical models we examine the dynam ics of sediments that are subducted below continental lithosphere owing to their low density relative to the mantle model sediments detach from the subducting plate at 100 km depth with ongoing subduction a subhorizontal sediment plume develops and intrudes the conti nental lithosphere this occurs for a wide range of sediment densities and rheologies suggest ing that sediment detachment may be important for regions where the subducted sediment thickness is larger than 350 m in these areas a reservoir of sediments may be found in the shallow backarc mantle in contrast to models of sediment transport to the deep mantle the detachment model predicts chemical and mechanical interactions between the sediments and backarc mantle lithosphere and a shallow sediment source for arc and backarc magmas

metasomatism and the crystallization of zircon megacrysts in archaean peridotites from the lewisian complex nw scotland zircon megacrysts are locally abundant in 1 40 cm thick orthopyroxenite veins within peridotite host rocks in the archaean lewisian gneiss complex from nw scotland the veins formed by metasomatic interaction between the ultramafic host and si rich melts are derived from partial melting of the adjacent granulite facies orthogneisses the interaction produced abundant orthopyroxene and within the thicker veins phlogopite pargasite and feldspathic bearing assemblages two generations of zircon are present with up to 1 cm megacrystic zircon and a later smaller equant population located around the megacryst margins patterns of zoning rare earth element abundance and oxygen isotopic compositions indicate that the megacrysts crystallized from crustal melts whereas the equant zircon represents new neocryst growth and partial replacement of the megacryst zircon within the ultramafic host both zircon types have u pb ages of ca 2464 ma broadly contemporaneous with granulite facies events in the adjacent gneisses zircon megacrysts locally form 10 of the assemblage and may be associated to zones of localized nucleation or physically concentrated during movement of the siliceous melts their unusual size is linked to the suppression of zircon nucleation and increased zr solubility in the si undersaturated melts the metasomatism between crustal melts and peridotite may represent an analog for processes in the mantle wedge above subducting slabs as such the crystallization of abundant zircon in ultramafic host rocks has implications for geochemistry of melts generated in the mantle and the widely reported depletion of high field strength elements in arc magmas

interaction between volcanic plumes and wind during the 2010 eyjafjallajokull eruption iceland 1 estimates of volcanic source mass flux currently deduced from observations of plume height are crucial for ash dispersion models for aviation and population hazard this study addresses the role of the atmospheric wind in determining the height at which volcanic plumes spread in the atmosphere and the relationship between source mass flux and plume height in a wind field we present a predictive model of volcanic plumes that describes the bending over of the plume trajectory in a crosswind and show that model predictions are in accord with a dataset of historic eruptions if the profile of atmospheric wind shear is described the wind restricts the rise height of volcanic plumes such that obtaining equivalent rise heights for a plume in a windy environment would require an order of magnitude increase in the source mass flux over a plume in a quiescent environment our model calculations are used to calibrate a semi empirical relationship between the plume height and the source mass flux that explicitly includes the atmospheric wind speed we demonstrate that the model can account for the variations in plume height observed during the first explosive phase of the 2010 eyjafjallajokull eruption using independently measured wind speeds and show that changes in the observed plume height are better explained by changing meteorology than abrupt changes in the source mass flux this study shows that unless the wind is properly accounted for estimates of the source mass flux during an explosive eruption are likely to be very significant underpredictions of the volcanic source conditions

continental subduction and exhumation of high pressure rocks insights from thermo mechanical laboratory modelling abstract thermo mechanical physical modelling of continental subduction is performed to investigate the exhumation of deeply subducted continental crust the model consists of two lithospheric plates made of new temperature sensitive analogue materials the lithosphere is underlain by liquid asthenosphere the continental lithosphere contains three layers the weak sedimentary layer the crust made of a stronger material and of a still stronger lithospheric mantle the whole model is subjected to a constant vertical thermal gradient causing the strength reduction with depth in each lithospheric layer subduction is driven by both push force and pull force during subduction the subducting lithosphere is heating and the strength of its layers reduces the weakening continental crust reaches maximal depth of about 120 km and cannot subduct deeper because its frontal part starts to flow up the subducted crust undergoes complex deformation including indicated upward ductile flow of the most deeply subducted portions and localised failure of the subducted upper crust at about 50 km depth this failure results in the formation of the first crustal slice which rises up between the plates under the buoyancy force this process is accompanied by the delamination of the crustal and mantle layers of the subducting lithosphere the delamination front propagates upwards into the interplate zone resulting in the formation of two other crustal slices that also rise up between the plates average equivalent exhumation rate of the crustal material during delamination is about 1 cm year the crust asthenosphere boundary near the interplate zone is uplifted the subducted mantle layer then breaks off removing the pull force and thereby stopping the delamination and increasing horizontal compression of the lithosphere the latter produces shortening of the formed orogen and the growth of relief the modelling reveals an interesting burial exhumation evolution of the sedimentary cover during initial stages of continental subduction the sediments of the continental margin are dragged to the overriding plate base and are partially accreted at the deep part of the interplate zone at 60 70 km depth these sediments remain there until the beginning of delamination during which the pressure between the subducted crust and the overriding plate increases this results in squeezing the underplated sediments out part of them is extruded upwards along the interplate zone to about 30 km depth at an equivalent rate of 5 10 cm year

effect of wind on the rise height of volcanic plumes a theoretical model of a volcanic plume based on applying the equations of motion in a plume centered coordinate system suggests that the interaction between a volcanic plume and wind causes enhanced entrainment of air and horizontal momentum plume bending and a decrease in plume rise height at constant eruption rate because of rapid dilution in the high windspeeds of the polar jet plumes that vary over more than one order of magnitude in mass eruption rate 106 to 107 108 kg s if injected into the polar jet may all attain rise heights only slightly different from that of the core of the jet 10 km as opposed to 17 33 km in a still atmosphere

the flow structure of jets from transient sources and implications for modeling short duration explosive volcanic eruptions we used laboratory experiments to examine the rise process in neutrally buoyant jets that resulted from an unsteady supply of momentum a condition that defines plumes from discrete vulcanian and strombolian style eruptions we simultaneously measured the analog jet discharge rate the supply rate of momentum and the analog jet internal velocity distribution a consequence of momentum transport and dilution then we examined the changes in the analog jet velocity distribution over time to assess the impact of the supply rate variations on the momentum driven rise dynamics we found that the analog jet velocity distribution changes significantly and quickly as the supply rate varied such that the whole field distribution at any instant differed considerably from the time average we also found that entrainment varied in space and over time with instantaneous entrainment coefficient values ranging from 0 to 0 93 in an individual unsteady jet consequently we conclude that supply rate variations exert first order control over jet dynamics and therefore cannot be neglected in models without compromising their capability to predict large scale eruption behavior these findings emphasize the fundamental differences between unsteady and steady jet dynamics and show clearly that i variations in source momentum flux directly control the dynamics of the resulting flow ii impulsive flows driven by sources of varying flux cannot reasonably be approximated by quasi steady flow models new modeling approaches capable of describing the time dependent properties of transient volcanic eruption plumes are needed before their trajectory dilution and stability can be reliably computed for hazards management

paradigms new and old for ultrahigh pressure tectonism regional ultrahigh pressure uhp metamorphic terranes exhibit a spectrum of lithological structural and petrological characteristics that result from the geodynamic processes that formed and exhumed them at least six geodynamic processes can be envisioned to have carried continental rocks to mantle depths i continental margin subduction ii microcontinent subduction iii sediment subduction iv intracontinental subduction v subduction erosion and vi foundering of a crustal root most of these processes have been investigated through numerical or analog models and most have been invoked for one or more specific occurrences of uhp rocks at least six geodynamic processes can be envisioned to have exhumed uhp continental rocks i eduction ii microplate rotation iii crustal stacking iv slab rollback v channel flow and vi trans mantle diapirs most of these processes have also been investigated through numerical or analog models and all have been invoked to explain the exhumation of at least one uhp terrane more detailed and systematic field investigations are warranted to assess the predictions of numerical models and more sophisticated and realistic numerical models are required to replicate and explain the petrological structural and chronological data obtained from uhp terranes

estimating the total mass emitted by the eruption of eyjafjallajokull in 2010 using plume rise models abstract the volcanic plume rise model of devenish 2013 is applied to the duration of the 39 day eruption of eyjafjallajokull in 2010 to produce a time series of the estimated source mass flux this in turn is integrated to give the total emitted mass which is found to lie within the error bounds of an observational estimate made by gudmundsson et al 2012 the calculation uses realistic profiles of key atmospheric variables such as wind speed temperature and humidity taken from a numerical weather prediction model and appropriate to the time of the eruption the sensitivity of the model results to changes in the values of the entrainment coefficients is discussed it is shown that including the radius of the plume when it is strongly affected by the wind in the comparison of the modelled and observed rise heights not only improves the accuracy of the estimated total emitted mass compared with neglecting the radius but also reduces the sensitivity of this estimate to the value of the entrainment coefficient associated with velocity differences normal to the plume axis

the grain size dependency of vesicular particle shapes strongly affects the drag of particles first results from microtomography investigations of campi flegrei fallout deposits abstract acknowledging the grain size dependency of shape is important in volcanology in particular when dealing with tephra produced and emplaced during and after explosive volcanic eruptions a systematic measurement of the tridimensional shape of vesicular pyroclasts of campi flegrei fallout deposits agnano monte spina astroni 6 and averno 2 eruptions varying in size from 8 00 to 0 016 mm has been carried out by means of x ray microtomography data show that particle shape changes with size especially for juvenile vesicular clasts since it is dependent on the distribution and size of vesicles that contour the external clast outline two drag laws that include sphericity in the formula were used for estimating the dependency of settling velocity on shape results demonstrate that it is not appropriate to assume a size independent shape for vesicular particles in contrast with the approach commonly employed when simulating the ash dispersion in the atmosphere

relationship between volcanic ash fallouts and seismic tremor quantitative assessment of the 2015 eruptive period at cotopaxi volcano ecuador understanding the relationships between geophysical signals and volcanic products is critical to improving real time volcanic hazard assessment thanks to high frequency sampling campaigns of ash fallouts 15 campaigns 461 samples the 2015 cotopaxi eruption is an outstanding candidate for quantitatively comparing the amplitude of seismic tremor with the amount of ash emitted this eruption emitted a total of 1 2e 9 kg of ash 8 6e 5 m3 during four distinct phases with masses ranging from 3 5e 7 to 7 7e 8 kg of ash we compare the ash fallout mass and the corresponding cumulative quadratic median amplitude of the seismic tremor and find excellent correlations when the dataset is divided by eruptive phase we use scaling factors based on the individual correlations to reconstruct the eruptive process and to extract synthetic eruption source parameters daily mass of ash mass eruption rate and column height from the seismic records we hypothesize that the change in scaling factor through time associated with a decrease in seismic amplitudes compared to ash emissions is the result of a more efficient fragmentation and transport process these results open the possibility of feeding numerical models with continuous geophysical data after adequate calibration in order to better characterize volcanic hazards during explosive eruptions

taiwan mountain building insights from 2 d thermomechanical modelling of a rheologically stratified lithosphere summary the taiwan orogen has long been regarded as a case example for studying mountain building in association with subduction processes in this paper we present a fully coupled thermomechanical modelling of the taiwan collision based on a realistic viscous elastic plastic rheology it satisfactorily reproduces available thermochronometric data long short term deformation patterns heat flux and erosion sedimentation distribution across the taiwan orogeny we found that a deep seated flux of asian crustal material into the orogenic wedge should be invoked to counter balance observed exhumation and erosion in the central range however in contrast with recent thermokinematic models of exhumation and deformation suggesting that underplating plays a significant role we show that most constraints on exhumation and deformation can be more straightforwardly interpreted by the frontal accretion of the rheologically layered asian crust we finally infer that such a model is in better agreement with the basic expectation that the hot young and buoyant chinese continental margin should hardly be subducted beneath the cold old and dense oceanic plate of the philippines sea

sensitivity analysis of dispersion modeling of volcanic ash from eyjafjallajokull in may 2010 1 we analyze the sensitivity of a mathematical model of volcanic ash dispersion in the atmosphere to the representation of key physical processes these include the parameterization of subgrid scale atmospheric processes and source parameters such as the height of the eruption column the mass emission rate the size of the particulates and the amount of ash that falls out close to the source by comparing the results of the mathematical model with satellite and airborne observations of the ash cloud that erupted from eyjafjallajokull volcano in may 2010 we are able to gain some insight into the processes and parameters that govern the long range dispersion of ash in the atmosphere the structure of the ash cloud particularly its width and depth appears to be sensitive to the source profile i e whether ash is released over a deep vertical column or not and to the level of subgrid diffusion of central importance to the quantitative estimates of ash concentration in the distal ash cloud is the fallout of ash close to the source by comparing the mass of the ash and the column loadings in the modeled and observed distal ash cloud we estimate the fraction of fine ash that survives into the distal ash cloud albeit with considerable uncertainty the processes that contribute to this uncertainty are discussed

refir a multi parameter system for near real time estimates of plume height and mass eruption rate during explosive eruptions abstract meaningful forecasting of the atmospheric concentration and ground accumulation of volcanic ash during explosive eruptions requires detailed knowledge of the eruption source parameters however due to the large uncertainties in observations and limitations of current models used to make inferences from these monitoring an ongoing eruption and quantifying the mass eruption rate in real time is a considerable challenge within the eu supersite project futurevolc an integrated approach has been applied to develop a quasi autonomous multi parameter system denoted refir for monitoring volcanic eruptions in iceland and assessing the eruption mass flow rate by inverting the plume height information and taking account of these uncertainties refir has the capability to ingest and process streaming plume height data provided by a multitude of ground based sensors including c and x band radars and web cam based plume height tracking systems these observational data are used with a suite of plume models that also consider the current wind and other atmospheric conditions providing statistically assessed best estimates of plume height and mass eruption rate provided instrumental data is available near real time estimates are obtained the delay corresponding to the scan rate of data providing instruments presently of the order of minutes using the hekla 2000 and eyjafjallajokull 2010 eruptions in iceland the potential of refir is demonstrated and discussed through application to three scenarios the system has been developed to provide maximum flexibility a setup script assists the user in adapting to local conditions allowing implementation of refir for any volcanic eruption site worldwide refir is designed to be easily upgradable allowing future extension of monitoring networks learning from new events and incorporation of new technologies and model improvements this article gives an overview of the basic structure models implemented functionalities and the computational techniques of refir

evidence for two upper mantle sources driving volcanism in central kamchatka article i nfo article history volcanoes of the central kamchatka depression ckd form the most active arc volcano system in the world volcanoes of the ckd are positioned 170 km above the subducting pacific plate in excess of the typical glob al value of 100 km for arc volcanism we present results of a combined geophysical and petrological study of the main volcanic center in the ckd and argue for the presence of a second contributing melt source within the mantle wedge this region of melt generation is separate from the fluid fluxed region above the subduct ing pacific plate it may explain the presence of the active ckd arc in its current location results of receiver function imaging of the upper mantle beneath ckd reveal a distinct area of low velocities at approximately 110 km depth that is clearly distinct from the crust of the subducting pacific plate results of petrological modeling suggest presence of pyroxenite source melt contribution to ckd lavas alongside pre viously described peridotite source melts we contend that our results advance the notion that melting at two separate sources rather than the simple flux induced melting within the mantle wedge drives volca noes of the ckd

uncertainties in volcanic plume modeling a parametric study using fplume we carry out a parametric study in order to identify and quantify the effects of uncertainties on pivotal parameters controlling the dynamics of volcanic plumes the study builds upon numerical simulations using fplume an integral steady state model based on the buoyant plume theory generalized in order to account for volcanic processes particle fallout and re entrainment water phase changes effects of wind etc as reference cases for strong and weak plumes we consider the cases defined during the iavcei commission on tephra hazard modeling inter comparison study costa et al 2016 the parametric study quantifies the effect of typical uncertainties on total mass eruption rate column height mixture exit velocity temperature and water content and particle size moreover a sensitivity study investigates the role of wind entrainment and intensity atmospheric humidity water phase changes and particle fallout and re entrainment results show that the leading order parameters that control plume height are the mass eruption rate and the air entrainment coefficient especially for weak plumes

dynamics of wind affected volcanic plumes the example of the 2011 cordon caulle eruption chile the 2011 cordon caulle eruption represents an ideal case study for the characterization of long lasting plumes that are strongly affected by wind the climactic phase lasted for about 1 day and was classified as subplinian with plumes between 9 and 12 km above the vent and mass flow rate mfr on the order of 107 kg s 1 eruption intensity fluctuated during the first 11 days with mfr values between 106 and 107 kg s 1 this activity was followed by several months of low intensity plumes with mfr 106 kg s 1 plume dynamics and rise were strongly affected by wind during the whole eruption with negligible upwind spreading and sedimentation the plumes that developed on 4 6 and 20 22 june can be described as transitional i e plumes showing transitional behavior between strong and weak dynamics while the wind clearly dominated the rise height on all the other days resulting in the formation of weak plumes individual phases of the eruption range between volcanic explosivity indices veis 3 and 4 while the cumulative deposit related to 4 7 june 2011 is associated with veis 4 and 5 crosswind cloud and deposit dispersal of the first few days are best described by a linear combination of gravitational spreading and turbulent diffusion with velocities between 1 and 10 m s 1 downwind cloud velocity for the same days is best described by a linear combination of gravitational spreading and wind advection with velocities between 17 and 45 m s 1 results show how gravitational spreading can be significant even for subplinian and small moderate eruptions strongly advected by wind and with low richardson number and low mfr

anomalous seismic structure beneath the klyuchevskoy group kamchatka 1 the klyuchevskoy group is among the most active volcanic features on earth yet its position within the kamchatka subduction zone is hard to explain with a simple tectonic mechanism the geochemistry of klyuchevskoy group lavas is typical for volcanic products resulting from flux melting in the mantle wedge yet the depth to the subducting pacific plate beneath it is much larger than the average depth of volatile release in subduction zones we present new seismological constraints on the upper mantle structure beneath the klyuchevskoy group and identify a planar dipping seismic feature in the mantle wedge which is 100 km deep and appears to be sharply bounded we hypothesize that this upper mantle structure may be the true source of melts erupting at the klyuchevskoy group and that the presence of this feature may explain both the extraordinary productivity of the klyuchevskoy group and its unusual location

a user friendly one dimensional model for wet volcanic plumes 1 this paper presents a user friendly graphically based numerical model of one dimensional steady state homogeneous volcanic plumes that calculates and plots profiles of upward velocity plume density radius temperature and other parameters as a function of height the model considers effects of water condensation and ice formation on plume dynamics as well as the effect of water added to the plume at the vent atmospheric conditions may be specified through input parameters of constant lapse rates and relative humidity or by loading profiles of actual atmospheric soundings to illustrate the utility of the model we compare calculations with field based estimates of plume height 9 km and eruption rate 4 105 kg s during a brief tephra eruption at mount st helens on 8 march 2005 results show that the atmospheric conditions on that day boosted plume height by 1 3 km over that in a standard dry atmosphere although the eruption temperature was unknown model calculations most closely match the observations for a temperature that is below magmatic but above 100 c

u th and ra disequilibria sr nd and pb isotope and trace element variations in sunda arc lavas predominance of a subducted sediment component the time scales of magma formation transfer and storage beneath island arc volcanoes are important because of the insights they provide into the physical processes of magma formation and evolution with possible links to the prediction of eruptive hazards here we present new mass spectrometric u th and ra and sr nd and pb isotope data along with major and trace element data from 19 lavas along the sunda arc indonesia the lavas range in sio2 from 49 to 75 and the combination of high sio2 and low 143nd 144nd indicates an important role for shallow level contamination by ancient crustal materials in sumatra diagrams of 143nd 144nd versus th ce and u th versus 87sr 86sr reveal negative trends which allow contributions from both subducted sediments and fluids to be identified the fluid component as expressed in elevated u th 238u 230th and 226ra 230th o ratios is ubiquitous in all of the lavas including near primary lavas from galunggung sr isotope data indicate that the fluids had variable composition and derived from altered oceanic crust and the u th and ra isotope data suggest that some fluid components must have been added less than 8 000 years ago tholeiitic lavas from flores have the lowest th contents in the arc and accordingly the highest 226ra 230th o and 238u 230th for these there is evidence that both u and ra addition probably occurred less than a few thousand years ago this suggests that the onset of melting was linked to fluid fluxing and cannot have been due to decompression alone in contrast the sediment component may have been added as a partial melt and sediment addition can account for the observed along arc variations in sr nd pb and th isotopes there is no requirement in our data for an oib component in the mantle wedge increases in sio2 in the galunggung lavas are accompanied by decreases in both 238u 230th and 226ra 230th o which are inferred to reflect mixing with melts of pre existing mafic lavas mixing and differentiation must have occurred faster than could be recorded by either the 238u 230th or 226ra 230th systems there is little evidence in our data for any effect of the australia indonesia collision on the composition of the lavas across arc trends in lava composition indicate an increasing relative contribution from subducted sediment a correspondingly weaker fluid signal and probable decreases in the degree of partial melting residual aluminous clinopyroxene or garnet may become important in controlling ree and u th fractionation in the far back arc

moist convection and the injection of volcanic ash into the atmosphere if unsaturated water vapor is carried upward by a volcanic eruption column it may eventually become saturated owing to the decrease in temperature of the column as it expands through decompression and transfers heat to entrained air heat released as a result of the subsequent condensation of water vapor causes the air within the column to expand we show that this increases the buoyancy and therefore the total height of rise of the column the increase in height is significant in relatively small sub plinian and strombolian eruptions in which mass eruption rates lie in the range 103 to 106 kg s in such eruptions the latent heat released as the entrained water vapor condenses may provide the main source of heat which drives the ash and clasts upward the height of rise then becomes relatively insensitive to the mass flux erupted at the vent and depends primarily upon the vapor loading of the atmosphere in a moist atmosphere ash may rise several kilomtres higher than in an eruption of comparable strength in a dry environment moist convection leads to much wider ash dispersal particularly from very small eruptions subsequently rain flushing of ash from umbrella clouds may result from the water which forms through the condensation of entrained vapor the ash provides natural condensation nuclei for some of this entrained vapor whose mass may be much greater than that of the ash in small columns 107 kg s the latent heat released by condensation of vapor is relatively small in comparison with the thermal energy provided by the hot clasts and therefore moisture has no significant effect upon the eruption column dynamics furthermore the mass of water vapor originating from the erupted volatiles is usually comparable to or greater than that entrained from the ambient air our model also shows that if the erupting mixture becomes buoyant then the eruption columns associated with phreatomagmatic eruptions ascend nearly as high as plinian columns with the same mass eruption rate this is because the water which is vaporized by the hot ash at the source condenses higher in the column and thereby restores its latent heat to the ascending ash

testing the accuracy of a 1 d volcanic plume model in estimating mass eruption rate during volcanic eruptions empirical relationships are used to estimate mass eruption rate from plume height although simple such relationships can be inaccurate and can underestimate rates in windy conditions one dimensional plume models can incorporate atmospheric conditions and give potentially more accurate estimates here i present a 1 d model for plumes in crosswind and simulate 25 historical eruptions where plume height hobs was well observed and mass eruption rate mobs could be calculated from mapped deposit mass and observed duration the simulations considered wind temperature and phase changes of water atmospheric conditions were obtained from the national center for atmospheric research reanalysis 2 5 model simulations calculate the minimum maximum and average values mmin mmax and mavg that fit the plume height eruption rates were also estimated from the empirical formula mempir 140hobs4 14 mempir is in kilogram per second hobs is in kilometer for these eruptions the standard error of the residual in log space is about 0 53 for mavg and 0 50 for mempir thus for this data set the model is slightly less accurate at predicting mobs than the empirical curve the inability of this model to improve eruption rate estimates may lie in the limited accuracy of even well observed plume heights inaccurate model formulation or the fact that most eruptions examined were not highly influenced by wind for the low wind blown plume of 14 18 april 2010 at eyjafjallajokull where an accurate plume height time series is available modeled rates do agree better with mobs than mempir

polyphase formation and exhumation of high to ultrahigh pressure rocks in continental subduction zone numerical modeling and application to the sulu ultrahigh pressure terrane in eastern china 1 high to ultrahigh pressure hp uhp metamorphic rocks commonly form and exhume during the early continental collision and many questions related to their origin still remain unresolved we focus our study on explaining the poly metamorphic origins of many hp uhp terranes composed of tectonic units having strongly variable ages peak metamorphic conditions and p t paths these features are especially well characterized for the sulu uhp terrane in eastern china which we have chosen therefore as the reference case we conducted 2 d thermomechanical numerical modeling of continental subduction associated with formation and exhumation of hp uhp rocks our experiments suggest existence of several consequent episodes of u hp rocks exhumation related to the inherently cyclic origin of continental crust subduction detachment exhumation processes three major phases of these processes are identified in our reference model for the sulu uhp terrane 1 first and 2 second exhumation episodes of hp rocks originated in the subduction channel at lithospheric depths and 3 exhumation of uhp rocks originated at asthenospheric depths numerical models also suggest that subducted uhp rocks which are positively buoyant compared to the mantle may detach from the slab forming a flattened plume underplating the overriding lithosphere this sublithospheric plume may exist for several million years being heated to 800 900 c by the surrounding hot mantle at the later stage upward extrusion of hot partially molten rocks from the plume may exhume high temperature ht uhp complexes toward the surface

cross arc geochemical variations in the kurile arc as a function of slab depth lavas from transects across the kurile islands arc showed geochemical variations related to changes in the compositions of fluids derived from the subducting slab enrichment factors for boron cesium arsenic and antimony all elements with strong affinities for water decreased across the arc this decrease is presumably related to losses of water rich fluids during the dehydration of the subducting plate enrichments of potassium barium beryllium 10 and the light rare earth elements remained constant these species may move in silica rich fluids liberated from the slab at greater depths

impact of wind on the condition for column collapse of volcanic plumes the collapse of volcanic plumes has significant implications for eruption dynamics and associated hazards we show how eruptive columns can collapse and generate pyroclastic density currents as a result of not only the source conditions but also of the atmospheric environment the ratio of the potential energy and the kinetic energy at the source quantified by the richardson number and the entrainment efficiency quantified by the radial entrainment coefficient have already been identified as key parameters in controlling the transition between a buoyant and collapsing plume here we quantify how this transition is affected by wind using scaling arguments in combination with a one dimensional plume model air entrainment due to wind causes a volcanic plume to lower its density at a faster rate and therefore to favor buoyancy we identify the conditions when wind entrainment becomes dominant over radial entrainment and quantify the effect of wind on column collapse these findings are framed into a generalized regime diagram that also describes previous regime diagrams for the specific case of choked flows many observations confirm how bent over plumes typically do not generate significant collapses a quantitative comparison with the 1996 ruapehu and the 2010 eyjafjallajokull eruptions shows that the likelihood of collapse is reduced even at moderate wind speeds relative to the exit velocity at the vent

linking the alps and apennines subduction systems new constraints revealed by high resolution teleseismic tomography abstract we report a new model of the upper mantle structure beneath italy obtained by means of p wave teleseismic tomography besides the recent and remarkable development of the italian seismic network a high model resolution has been achieved improving the inversion method upon the ach method used in previous investigations and picking high quality arrival times with the multi channel cross correlation technique the finer details of our vp model yield new insights into the heterogeneous structure of the adria continental lithosphere involved in the collision between the africa and europe plates a wide low vp anomaly located in the northern adria mantle facing the alpine high vp slab supports the idea that the adria lithosphere has been hydrated and thinned during the alpine subduction we argue that this mantle softening may have played a key role in favoring the subsequent delamination of the adria lithosphere in the northern apennines we hypothesize that delamination of continental lithosphere previously thinned in a back arc setting may be considered a key process to favor subduction polarity reversal and recycling of continental material into the mantle circulation conversely in the central southern apennines the velocity structure is consistent with the existence of a deeper oceanic slab that flattens at the base of the upper mantle in agreement with the widely accepted geodynamic evolution of the central mediterranean by slab retreat and back arc spreading the oceanic slab is discontinuously detached from the surface plate suggesting a different structure of the adria lithosphere which resists subduction instead of favoring delamination

charge structure in volcanic plumes a comparison of plume properties predicted by an integral plume model to observations of volcanic lightning during the 2010 eruption of eyjafjallajokull iceland observations of volcanic lightning made using a lightning mapping array during the 2010 eruption of eyjafjallajokull allow the trajectory and growth of the volcanic plume to be determined the lightning observations are compared with predictions of an integral model of volcanic plumes that includes descriptions of the interaction with wind and the effects of moisture we show that the trajectory predicted by the integral model closely matches the observational data and the model well describes the growth of the plume downwind of the vent analysis of the lightning signals reveals information on the dominant charge structure within the volcanic plume during the eyjafjallajokull eruption both monopole and dipole charge structures were observed in the plume by using the integral plume model we propose the varying charge structure is connected to the availability of condensed water and low temperatures at high altitudes in the plume suggesting ice formation may have contributed to the generation of a dipole charge structure via thunderstorm style ice based charging mechanisms though overall this charging mechanism is believed to have had only a weak influence on the production of lightning

petrogenesis of the postcollisional middle devonian monzonitic to granitic magmatism of the sierra de san luis argentina abstract middle devonian granitoids intruded the eastern sierras pampeanas basement ca 600 km east of the inferred proto pacific margin of gondwana along which a ca 390 ma collisional event developed in the sierra de san luis voluminous middle devonian 393 382 ma batholiths are composed of i to a type hybrid monzonite and granite suites shoshonite and subordinated high k series stocks synplutonic dikes and enclaves make up the monzonite suite rocks are metaluminous alkali calcic magnesian porphyritic or equigranular monzonite quartz monzonite monzodiorite and scarce monzogabbro high k and subordinated shoshonite series metaluminous to mildly peraluminous magnesian alkali calcic to calc alkalic porphyritic or equigranular quartz monzonite granodiorite monzogranite and equigranular leucomonzogranites make up the granite suite plutons and batholiths only a small group of highly evolved granites are ferroan sio 2 46 62 cr ni v sc lile lree th zr and variable sr y la yb n and tb yb n smooth eu eu moderate na 2 o ca 3 5 and troughs at nb and ta for monzonite suite rocks suggest an subduction related enriched lithospheric mantle source sm nd data t dm 0 98 1 08 ga end 380 ma 0 66 1 47 and 87 sr 86 sr i 0 703520 0 704203 are compatible with an enriched mantle source the metaluminous porphyritic quartz monzonite monzogranite and the mildly peraluminous equigranular biotite monzogranites of the granite suite are characterized by relatively moderate al 2 o 3 cao and 87 sr 86 sr i high lile cr variable sr y la yb n and eu eu and low rb sr dm 1 20 1 28 ga end 380ma 3 02 to 3 3 87 sr 86 sr i 0 706578 0 707027 and the biotite monzogranites t dm 1 31 ga end 380ma 3 3 87 sr 86 sr i 0 707782 would share a common source the equigranular alkali calcic leucomonzogranites are characterized by rb sr 1 5 asi 1 05 1 18 and ga al 2 6 3 9 end 380 ma 3 74 to 3 95 and 87 sr 86 sr i 0 710743 0 712955 which would point to metasedimentary or felsic igneous crustal sources nevertheless their t dm 1 36 1 38 ga is considerably younger than the mean 1 8 1 6 ga eastern sierras pampeanas crustal residence age and less radiogenic middle devonian magmatism would record an episode of crustal growth by enriched mantle derived magma input and variable degrees of partial melting of a lower crustal source at the waning stages of the achalian orogeny

grain size distribution in the mantle wedge of subduction zones 1 mineral grain size plays an important role in controlling many processes in the mantle wedge of subduction zones including mantle flow and fluid migration to investigate the grain size distribution in the mantle wedge we coupled a two dimensional 2 d steady state finite element thermal and mantle flow model with a laboratory derived grain size evolution model in our coupled model the mantle wedge has a composite olivine rheology that incorporates grain size dependent diffusion creep and grain size independent dislocation creep our results show that all subduction settings lead to a characteristic grain size distribution in which grain size increases from 10 to 100 m at the most trenchward part of the creeping region to a few centimeters in the subarc mantle despite the large variation in grain size its effect on the mantle rheology and flow is very small as 90 of the deformation in the flowing part of the creeping region is accommodated by grain size independent dislocation creep the predicted grain size distribution leads to a downdip increase in permeability by 5 orders of magnitude this increase is likely to promote greater upward migration of aqueous fluids and melts where the slab reaches 100 km depth compared with shallower depths potentially providing an explanation for the relatively uniform subarc slab depth seismic attenuation derived from the predicted grain size distribution and thermal field is consistent with the observed seismic structure in the mantle wedge at many subduction zones without requiring a significant contribution by the presence of melt

subduction zone recycling processes and the rock record of crustal suture zonesthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent offshore observations at modern ocean margin subduction zones omszs reveal that bodies of accreted material are commonly volumetrically small or missing that crustal thinning and subsidence 3 5 km has occurred and that most trench axes lie close 5 30 km to the seaward tapering edge of coastal basement rock onshore mapping commonly documents missing or only narrow terranes of former forearc rock and the inboard migration of the arc magmatic front these observations are evidence that subduction is accompanied by the removal of sediment and crustal material from the submerged forearc by the kindred tectonic processes respectively of sediment subduction and subduction erosion subduction erosion truncates the margin migrates the trench inboard at 2 5 km ma onshore observations at ancient crust suturing subduction zones csszs imply that collisional suturing is accompanied by sediment subduction and truncation of both upper and lower plates during a protracted period of suturing 20 50 millio

transport of atmospheric water vapor by volcanic eruption columns contrary to assumptions often made in the literature explosive volcanic eruptions are capable of transporting significant amounts of water into the stratosphere in addition to the magmatic water component atmospheric water vapor is entrained by the column at lower levels a theoretical model for the conservation of mass momentum and thermal energy of four separate components dry air water vapor liquid condensates and solid particles is used to determine the extent of atmospheric water redistribution we examine the effects of water vapor condensation on dynamical characteristics and ambient water vapor transport a simple technique is presented for deriving canonical forms for the complex system of ordinary differential equations governing the column components solutions of this model are presented that show the influence of different volcanic boundary conditions and a range of ambient water vapor distributions on transport of the buoyant column we show that the water component vapor liquid of small eruption columns rising through a wet atmosphere is dominated by entrained water whereas larger columns are dominated by the magmatic water this is due in part to the proportionately smaller entrainment surface area in relation to the control volume for the larger columns we also show that a maintained column with an initial mass flux of 2 7 108 kg s 1 erupted into a wet atmosphere would inject 96 mt of water vapor into the stratosphere over 24 hours comparable to the annual input from methane oxidation or 100 midlatitude thunderstorms this increase may accelerate the conversion of simultaneously erupted volcanic so2 into sulfuric acid

results of the eruptive column model inter comparison study this study compares and evaluates one dimensional 1d and three dimensional 3d numerical models of volcanic eruption columns in a set of different inter comparison exercises the exercises were designed as a blind test in which a set of common input parameters was given for two reference eruptions representing a strong and a weak eruption column under different meteorological conditions comparing the results of the different models allows us to evaluate their capabilities and target areas for future improvement despite their different formulations the 1d and 3d models provide reasonably consistent predictions of some of the key global descriptors of the volcanic plumes variability in plume height estimated from the standard deviation of model predictions is within 20 for the weak plume and 10 for the strong plume predictions of neutral buoyancy level are also in reasonably good agreement among the different models with a standard deviation ranging from 9 to 19 the latter for the weak plume in a windy atmosphere overall these discrepancies are in the range of observational uncertainty of column height however there are important differences amongst models in terms of local properties along the plume axis particularly for the strong plume our analysis suggests that the simplified treatment of entrainment in 1d models is adequate to resolve the general behaviour of the weak plume however it is inadequate to capture complex features of the strong plume such as large vortices partial column collapse or gravitational fountaining that strongly enhance entrainment in the lower atmosphere we conclude that there is a need to more accurately quantify entrainment rates improve the representation of plume radius and incorporate the effects of column instability in future versions of 1d volcanic plume models