ice nucleation and overseeding of ice in volcanic clouds 1 water is the dominant component of volcanic gas emissions and water phase transformations including the formation of ice can be significant in the dynamics of volcanic clouds the effectiveness of volcanic ash particles as ice forming nuclei in is poorly understood and the sparse data that exist for volcanic ash in have been interpreted in the context of meteorological rather than volcanic clouds in this study single particle freezing experiments were carried out to investigate the effect of ash particle composition and surface area on water drop freezing temperature measured freezing temperatures show only weak correlations with ash in composition and surface area our measurements together with a review of previous volcanic ash in measurements suggest that fine ash particles equivalent diameters between approximately 1 and 1000 m from the majority of volcanoes will exhibit an onset of freezing between 250 260 k in the context of explosive eruptions where super micron particles are plentiful this result implies that volcanic clouds are in rich relative to meteorological clouds which typically are in limited and therefore should exhibit distinct microphysics we can expect that such overseeded volcanic clouds will exhibit enhanced ice crystal concentrations and smaller average ice crystal size relative to dynamically similar meteorological clouds and that glaciation will tend to occur over a relatively narrow altitude range

estimating volcanic plume heights from depositional clast size 1 tephra deposits retain a considerable amount of information about the nature of volcanic eruptions with plume height commonly inferred from maximum clast size measurements however current methods for inferring plume height from maximum clast size lose some of the accuracy in measurements made in the field and have limited application when trying to constrain the uncertainty in these parameters here a predictive numerical model is used to determine plume height from maximum clast size found in a deposit plume height is an essential parameter for inferring eruption magnitude as it is explicitly related to mass eruption rate we investigate the effects of different atmospheric and wind profiles allowing the input conditions to be location specific for each eruption the use of a predictive model reduces the uncertainty in determining plume height as it retains the detail of measurements made in the field and incorporates the uncertainty in these measurements in the results in the form of a probability distribution we have applied this approach to fall deposits from the 1991 eruption of pinatubo one of the few plinian eruptions in which the true height of the plume is well known the predicted plume heights are in good agreement with those found from satellite measurements this new approach provides a method for determining plume height from poorly preserved fall deposits from which a limited amount of data can be sampled leading to large uncertainties in the field measurements

separation of ash and sulfur dioxide during the 2011 grimsvotn eruption modeling the transport of volcanic ash and gases released during volcanic eruptions is crucially dependent on knowledge of the source term of the eruption that is the source strength as a function of altitude and time for the first time an inversion method is used to estimate the source terms of both volcanic sulfur dioxide so2 and ash it was applied to the explosive volcanic eruption of grimsvotn iceland in may 2011 the method uses input from the particle dispersion model flexpart flexible particle dispersion model a priori source estimates and satellite observations of so2 or ash total columns from infrared atmospheric sounding interferometer to separately obtain the source terms for volcanic so2 and fine ash the estimated source terms show that so2 was emitted mostly to high altitudes 5 to 13 km during about 18 h 22 may 00 18 utc while fine ash was emitted mostly to low altitudes below 4 km during roughly 24 h 22 may 06 utc to 23 may 06 utc flexpart simulations using the estimated source terms show a clear separation of so2 transported mostly northwestward and the fine ash transported mostly southeastward this corresponds well with independent satellite observations and measured aerosol mass concentrations and lidar measurements at surface stations in scandinavia aircraft measurements above iceland and germany confirmed that the ash was located in the lower atmosphere this demonstrates that the inversion method in this case is able to distinguish between emission heights of so2 and ash and can capture resulting differences in transport patterns key points ash and so2 source terms estimated using inverse techniques and satellite data the transport and separation of ash and so2 are modeled model simulations correspond well with a range of independent observations 2014 the authors

ash plume dynamics and eruption source parameters by infrasound and thermal imagery the 2010 eyjafjallajokull eruption during operational ash cloud forecasting prediction of ash concentration and total erupted mass directly depends on the determination of mass eruption rate mer which is typically inferred from plume height uncertainties for plume heights are large especially for bent over plumes in which the ascent dynamics are strongly affected by the surrounding wind field here we show how uncertainties can be reduced if mer is derived directly from geophysical observations of source dynamics the combination of infrasound measurements and thermal camera imagery allows for the infrasonic type of source to be constrained a dipole in this case and for the plume exit velocity to be calculated 54 142 m s based on the acoustic signal recorded during the 2010 eyjafjallajokull eruption from 4 to 21 may exit velocities are converted into mer using additional information on vent diameter 50 10 m and mixture density 5 4 1 1 kg m3 resulting in an average 9 105 kg s mer during the considered period of the eruption we validate our acoustic derived mer by using independent measurements of plume heights icelandic meteorological office radar observations acoustically derived mer are converted into plume heights using field based relationships and a 1d radially averaged buoyant plume theory model using a reconstructed total grain size distribution we conclude that the use of infrasonic monitoring may lead to important understanding of the plume dynamics and allows for real time determination of eruption source parameters this could improve substantially the forecasting of volcano related hazards with important implications for civil aviation safety

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

estimation and propagation of volcanic source parameter uncertainty in an ash transport and dispersal model application to the eyjafjallajokull plume of 14 16 april 2010 data on source conditions for the 14 april 2010 paroxysmal phase of the eyjafjallajokull eruption iceland have been used as inputs to a trajectory based eruption column model bent this model has in turn been adapted to generate output suitable as input to the volcanic ash transport and dispersal model puff which was used to propagate the paroxysmal ash cloud toward and over europe over the following days some of the source param eters specifically vent radius vent source velocity mean grain size of ejecta and standard deviation of ejecta grain size have been assigned probability distributions based on our lack of knowledge of exact conditions at the source these probability distributions for the input variables have been sampled in a monte carlo fashion using a technique that yields what we herein call the polynomial chaos quad rature weighted estimate pcqwe of output parameters from the ash transport and dispersal model the advantage of pcqwe over monte carlo is that since it intelligently samples the input parameter space fewer model runs are needed to yield estimates of moments and probabilities for the output variables at each of these sample points for the input variables a model run is performed output moments and probabilities are then computed by properly summing the weighted values of the output parameters of interest use

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

a review of tephra transport and dispersal models evolution current status and future perspectives abstract tephra transport models try to predict atmospheric dispersion and sedimentation of tephra depending on meteorology particle properties and eruption characteristics defined by eruption column height mass eruption rate and vertical distribution of mass models are used for different purposes from operational forecast of volcanic ash clouds to hazard assessment of tephra dispersion and fallout the size of the erupted particles a key parameter controlling the dynamics of particle sedimentation in the atmosphere varies within a wide range largest centimetric to millimetric particles fallout at proximal to medial distances from the volcano and sediment by gravitational settling on the other extreme smallest micrometric to sub micrometric particles can be transported at continental or even at global scales and are affected by other deposition and aggregation mechanisms different scientific communities had traditionally modeled the dispersion of these two end members volcanologists developed families of models suitable for lapilli and coarse ash and aimed at computing fallout deposits and for hazard assessment in contrast meteorologists and atmospheric scientists have traditionally used other atmospheric transport models dealing with finer particles for tracking motion of volcanic ash clouds and eventually for computing airborne ash concentrations during the last decade the increasing demand for model accuracy and forecast reliability has pushed on two fronts first the original gap between these different families of models has been filled with the emergence of multi scale and multi purpose models second new modeling strategies including for example ensemble and probabilistic forecast or model data assimilation are being investigated for future implementation in models and or modeling strategies this paper reviews the evolution of tephra transport and dispersal models during the last two decades presents the status and limitations of the current modeling strategies and discusses some emergent perspectives expected to be implemented at operational level during the next few years improvements in both real time forecasting and long term hazard assessment are necessary to loss prevention programs on a local regional national and international level

using picosatellites for 4 d imaging of volcanic clouds proof of concept using iss photography of the 2009 sarychev peak eruption abstract volcanic ash clouds can present an aviation hazard over distances of thousands of kilometres and to help to mitigate this hazard advanced numerical models are used to forecast ash dispersion in the atmosphere however forecast accuracy is usually limited by uncertainties in initial conditions such as the eruption rate and the vertical distribution of ash injected above the volcano here we demonstrate the potential of the telematics earth observation mission tom picosatellite formation due for launch in 2020 to provide valuable information for constraining ash cloud dispersion models through simultaneous image acquisition from three satellites tom will carry commercial frame cameras using photogrammetric simulations we show that such data should enable ash cloud heights to be determined with a precision 30 140 m depending on configuration comparable to the vertical resolution of lidar observations 30 180 m depending on the cloud height to support these estimates we processed photographs taken from the international space station of the 2009 sarychev peak eruption as a proxy for tom imagery structure from motion photogrammetric software successfully reconstructed the 3 d form of the ascending ash cloud as well as surrounding cloud layers direct estimates of the precision of the ash cloud height measurements as well as comparisons between independently processed image sets indicate that a vertical measurement precision of 200 m was achieved image sets acquired at different times captured the plume dynamics and enabled a mean ascent velocity of 14 m s 1 to be estimated for regions above 7 km in contrast the uppermost regions of the column at a measured cloud top height of 11 km were not ascending significantly enabling us to constrain a 1 d plume ascent model from which estimates for the vent size 50 m and eruption mass flux 2 6 106 kg s 1 could be made thus we demonstrate that nanosatellite imagery has the potential for substantially reducing uncertainties in ash dispersion models by providing valuable information on eruptive conditions

eruptions at lone star geyser yellowstone national park usa 1 energetics and eruption dynamics 1 geysers provide a natural laboratory to study multiphase eruptive processes we present results from a 4 day experiment at lone star geyser in yellowstone national park usa we simultaneously measured water discharge acoustic emissions infrared intensity and visible and infrared video to quantify the energetics and dynamics of eruptions occurring approximately every 3 h we define four phases in the eruption cycle 1 a 28 3 min phase with liquid and steam fountaining with maximum jet velocities of 16 28 m s 1 steam mass fraction of less than 0 01 intermittently choked flow and flow oscillations with periods increasing from 20 to 40 s are coincident with a decrease in jet velocity and an increase of steam fraction 2 a 26 8 min posteruption relaxation phase with no discharge from the vent infrared ir and acoustic power oscillations gliding between 30 and 40 s 3 a 59 13 min recharge period during which the geyser is quiescent and progressively refills and 4 a 69 14 min preplay period characterized by a series of 5 10 min long pulses of steam small volumes of liquid water discharge and 50

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

did ice charging generate volcanic lightning during the 2016 2017 eruption of bogoslof volcano alaska the 2016 2017 shallow submarine eruption of bogoslof volcano in alaska injected plumes of ash and seawater to maximum heights of 12 km more than 4550 volcanic lightning strokes were detected by the world wide lightning location network wwlln and vaisala s global lightning dataset gld360 over 9 months lightning assisted monitoring efforts by confirming ash producing explosions in near real time but only 32 out of the 70 explosive events produced detectable lightning what led to electrical activity within some of the volcanic plumes but not others and why did the lightning intensity wax and wane over the lifetime of individual explosions we address these questions using multiparametric observations from ground based lightning sensors satellite imagery photographs acoustic signals and 1d plume modeling detailed time series of monitoring data show that the plumes did not produce detectable lightning until they rose higher than the atmospheric freezing level approximated by 20 c temperatures for example on 28 may 2017 event 40 the delayed onset of lightning coincides with modeled ice formation in upper levels of the plume model results suggest that microphysical conditions inside the plume rivaled those of severe thunderstorms with liquid water contents 5 g m 3 and vigorous updrafts 40 m s 1 in the mixed phase region where liquid water and ice coexist based on these findings we infer that thunderstorm style collisional ice charging catalyzed the volcanic lightning however charge mechanisms likely operated on a continuum with silicate collisions dominating electrification in the near vent region and ice charging taking over in the upper level plumes a key implication of this study is that lightning during the bogoslof eruption provided a reliable indicator of sustained ash rich plumes and associated hazards above the atmospheric freezing level

unraveling the presence of multiple plagioclase populations and identification of representative two dimensional sections using a statistical and numerical approach many plagioclase phenocrysts from volcanic and plutonic rocks display quite complex chemical and textural zoning patterns understanding the zoning patterns and variety of crystal populations holds clues to the processes and timescales that lead to the formation of the igneous rocks however in addition to a true natural complexity of the crystal population the large variety of plagioclase types can be partly artifacts of the use of two dimensional 2d petrographic thin sections and random cuts of three dimensional 3d plagioclase crystals thus the identification of the true number of plagioclase populations and the decision of which are representative crystal sections to be used for detailed trace element and isotope analysis is not obvious and tends to be subjective here we approach this problem with a series of numerical simulations and statistical analyses of a variety of plagioclase crystals zoned in 3d we analyze the effect of increasing complexity of zoning based on 2d chemical maps e g backscattered electron images bse we first analyze the random sections of single crystals and then study the effect of mixing of different crystal populations in the samples by quantifying the similarity of the compositional histogram of about a hundred 2d plagioclase sections it is possible to identify the so called reference and ideal sections that are representative of the real 3d crystal populations these section types allow filtering out the random cut effects and explain more than 90 of the plagioclase compositional data of a given sample our method allows the identification of the main crystal populations and representative crystals that can then be used for a more robust interpretation of magmatic processes and timescales

on the formation of eruption columns following explosive mixing of magma and surface water when magma vents into the sea or a crater lake the ensuing magma water interaction can affect the style of eruption dramatically if the mass of surface water incorporated into the erupting material is small 108 kg s the height progressively decreases with surface water content this occurs when the magma and surface water begin to constitute a significant fraction of the mass at the top of the column so that an increasing fraction of the initial magmatic thermal energy is converted to the surface water rather than the entrained air the transitions in eruption style which result from changes in the mass of surface water mixing with the magma may account for observations of both buoyant plumes and wet surge during the eruptions of taal in 1965 and miyake jima in 1983 and for the changes in the eruptive activity at surtsey in 1963 1964 as the access of seawater to the vent became more restricted we also present calculations which suggest that the accretionary lapilli which are often found in wet flow deposits may result from condensation of vapor in both the cold wet collapsing fountains and in the flows themselves

the decompression of volcanic jets in a crater during explosive volcanic eruptions during explosive volcanic eruptions fragmented silicic magma and volatiles exit the vent with pressures typically in the range 10 100 atm and at the speed of sound of the mixture we show that for magmatic volatile contents no in the range 0 03 no 0 06 this has the approximate value 0 95 0 05 nort 12 where r is the gas constant and t is the eruption temperature this speed is nearly independent of the vent pressure and vent radius by assuming there is negligible mixing with the air we have modelled the decompression of such jets following eruption from the vent for free decompression into the atmosphere the velocity of the decompressed jet has the approximate value 1 85 0 05 nort 12 this is nearly independent of the eruption rate for decompression into a crater the process is more complex at low eruption rates with low vent pressure the material becomes underpressured as it rises in the crater a shock then forms in the crater this recompresses the magma volatile mixture which then issues from the crater as a relatively slow subsonic jet at atmospheric pressure as the eruption rate increases such shocks move towards the top of the crater and ultimately cannot form in the crater instead the material issues from the crater as a high speed supersonic jet the upward thrust provided by the crater walls on this high pressure jet then increases the upward velocity above that of a freely decompressing jet the presence of a crater may therfore cause collapse in relatively small eruptions whereas it may promote formation of buoyant eruption columns at higher eruption rates if a crater grows through erosion during an eruption column collapse will typically ensue even if the mass flux remains steady

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

volcanic controls on ash iron solubility new insights from high temperature gas ash interaction modeling abstract recent studies strongly suggest that volcanic ash can fertilize the surface ocean by releasing soluble iron however the volcanic and atmospheric processes that solubilize ash iron during its transport from the volcano to the ocean are poorly understood using thermodynamic equilibrium calculations we investigate the influence of gas ash interaction within the hot core t 600 c of the volcanic plume and the consequences of this for ash iron solubility simulations are performed by considering the plume hot core as a box model in which 1000 c magmatic gas ash and 25 c ambient air are mixed together we show that mixing and the resulting cooling of the gas ash air mixture affect the mineralogy and oxidation state of iron in the ash surface rim iron mineralogy in the ash surface layer after high temperature plume processing is primarily governed by the ratio of the h2 and h2s content of the magmatic gas to the amount of entrained o2 into the hot plume xmix the model results indicate that most of the iron in the ash surface layer is oxidized to ferric iron fe iii when log xmix drops below 3 5 in the hot core such conditions may be encountered at convergent plate volcanoes which release h2o rich magmatic gases in contrast high temperature gas ash interaction at divergent plate and hot spot volcanoes which tend to be associated with co2 rich and so2 rich magmatic gases respectively may produce ash surfaces where iron mostly occurs as ferrous fe ii these volcanoes seem to be more favorable for iron fertilization because log xmix does not fall below 3 5 and 80 of the iron in the ash surface remains ferrous fe ii which is more soluble in water than fe iii

volcanic ash concentration during the 12 august 2011 etna eruption mount etna in italy is one of the most active volcanoes in the world and an ideal laboratory to improve volcano ash monitoring and forecasting during the volcanic episode on 12 august 2011 an eruption column rose up to several kilometers above sea level asl and the volcanic plume dispersed to the southeast from the video surveillance system we were able to estimate variations in the column height peak value of 9 5 0 5 km above sea level with time we derived the time varying discharge rate peak value of 60 m3 s 1 and determined the ash concentration using a volcanic ash dispersal model the modeled ash concentration was compared with lidar measurements using different particle effective radius and differences are within the error bars volcanic ash concentrations range from 0 5 to 35 5 10 3 g m 3 the comparison highlights that to improve volcanic ash forecasting during volcanic crises it is necessary to take into account the time varying discharge rate of explosive eruptions

thermodynamics of gas and steam blast eruptions eruptions of gas or steam and non juvenile debris are common in volcanic and hydrothermal areas from reports of non juvenile eruptions or eruptive sequences world wide at least three types or end members can be identified 1 those involving rock and liquid water initially at boiling point temperatures boiling point eruptions 2 those powered by gas primarily water vapor at initial temperatures approaching magmatic gas eruptions and 3 those caused by rapid mixing of hot rock and ground or surface water mixing eruptions for these eruption types the mechanical energy released final temperatures liquid water contents and maximum theoretical velocities are compared by assuming that the erupting mixtures of rock and fluid thermally equilibrate then decompress isentropically from initial near surface pressure 10 mpa to atmospheric pressure maximum mechanical energy release is by far greatest for gas eruptions 1 3 mj kg of fluid rock mixture about one half that of an equivalent mass of gunpowder and one fourth that of tnt it is somewhat less for mixing eruptions 0 4 mj kg and least for boiling point eruptions 0 25 mj kg the final water contents of crupted boiling point mixtures are usually high producing wet sloppy deposits final erupted mixtures from gas eruptions are nearly always dry whereas those from mixing eruptions vary from wet to dry if all the enthalpy released in the eruptions were converted to kinetic energy the final velocity v max of these mixtures could range up to 670 m s for boiling point eruptions and 1820 m s for gas eruptions highest for high initial pressure and mass fractions of rock m r near zero for mixing eruptions v max ranges up to 1150 m s all observed eruption velocities are less than 400 m s largely because 1 most solid material is expelled when m r is high hence v max is low 2 observations are made of large blocks the velocities of which may be less than the average for the mixture 3 heat from solid particles is not efficiently transferred to the fluid during the eruptions and 4 maximum velocities are reduced by choked flow or friction in the conduit

evolution of the calabrian accretionary wedge central mediterranean 1 the neogene tectonics of the central mediterranean are related to the subduction and trench rollback of the ionian basin under eurasia causing the opening of the liguro provencal and tyrrhenian back arc basins and the formation of the calabrian accretionary wedge the calabrian accretionary wedge is a partially submerged accretionary complex located in the ionian offshore and laterally bounded by the apulia and malta escarpments while the history of the back arc extension process is fairly well defined the structure and evolution of the wedge are still poorly known we have analyzed and interpreted the available reflection multichannel and single channel seismic profiles in the ionian offshore and integrated them with other geological and geophysical data acquired in the last 40 years here we present unpublished seismic profiles to provide a new map of the tectonic structure of the ionian offshore and to define the structure of the wedge and its evolution during the last 15 myr our reconstruction points out that the messinian salinity crisis represents an important break in the evolution of the wedge as the basal decollement ramps up onto the messinian salt deposits producing a dramatic and fast forward propagation of the frontal thrust and resulting underplating of the underlying crustal ionian sequence during progressive trench rollback our results provide new insight into the style of accretion in a weakly converging setting which is typical for the mediterranean region

particle fallout thermal disequilibrium and volcanic plumes we develop a model of a volcanic eruption column that includes the effects of fallout of pyroclasts and thermal disequilibrium we show that clast fallout with no thermal disequilibrium has only a small effect upon the column however disequilibrium changes column behaviour significantly and can even induce collapse our results may explain the lower plume heights and less widely dispersed fallout of cone forming eruptions contrasted with sheet forming eruptions the model also predicts that the transition from the gas thrust to the convective region in a column results in an inflection in dispersal curves that some features of the stratigraphy common to many fall deposits may result from column velocity structure and that there may exist a region near the volcanic vent in which maximum pyroclast size does not decrease significantly with distance

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

misr observations of etna volcanic plumes 1 in the last twelve years mt etna located in eastern sicily has produced a great number of explosive eruptions volcanic plumes have risen to several km above sea level and created problems for aviation and the communities living near the volcano a reduction of hazards may be accomplished using remote sensing techniques to evaluate important features of volcanic plumes since 2000 the multiangle imaging spectroradiometer misr on board nasa s terra spacecraft has been extensively used to study aerosol dispersal and to extract the three dimensional structure of plumes coming from anthropogenic or natural sources including volcanoes in the present work misr data from several explosive events occurring at etna are analyzed using a program named minx misr interactive explorer minx uses stereo matching techniques to evaluate the height of the volcanic aerosol with a precision of a few hundred meters and extracts aerosol properties from the misr standard products we analyzed twenty volcanic plumes produced during the 2000 2001 2002 03 2006 and 2008 etna eruptions finding that volcanic aerosol dispersal and column height obtained by this analysis is in good agreement with ground based observations misr aerosol type retrievals 1 clearly distinguish volcanic plumes that are sulphate and or water vapor dominated from ash dominated ones 2 detect even low concentrations of volcanic ash in the atmosphere 3 demonstrate that sulphate and or water vapor dominated plumes consist of smaller sized particles compared to ash plumes this work highlights the potential of misr to detect important volcanic plume characteristics that can be used to constrain the eruption source parameters in volcanic ash dispersion models further the possibility of discriminating sulphate and or water vapor dominated plumes from ash dominated ones is important to better understand the atmospheric impact of these plumes

controls on the surface chemical reactivity of volcanic ash investigated with probe gases increasing recognition that volcanic ash emissions can have significant impacts on the natural and human environment calls for a better understanding of ash chemical reactivity as mediated by its surface characteristics however previous studies of ash surface properties have relied on techniques that lack the sensitivity required to adequately investigate them here we characterise at the molecular monolayer scale the surfaces of ash erupted from eyjafjallajokull tungurahua pinatubo and chaiten volcanoes interrogation of the ash with four probe gases trimethylamine tma n ch3 3 trifluoroacetic acid tfa cf3cooh hydroxylamine ha nh2oh and ozone o3 reveals the abundances of acid base and redox sites on ash surfaces measurements on aluminosilicate glass powders as compositional proxies for the primary constituent of volcanic ash are also conducted we attribute the greater proportion of acidic and oxidised sites on ash relative to glass surfaces evidenced by comparison of tma tfa and ha o3 uptake ratios in part to ash interaction with volcanic gases and condensates e g h2o so2 h2so4 hcl hf during the eruption the strong influence of ash surface processing in the eruption plume and or cloud is further supported by particular abundances of oxidised and reduced sites on the ash samples resulting from specific characteristics of their eruptions of origin intense interaction with water vapour may result in a higher fraction of oxidised sites on ash produced by phreatomagmatic than by magmatic activity this study constitutes the first quantification of ash chemical properties at the molecular monolayer scale and is an important step towards better understanding the factors that govern the role of ash as a chemical agent within atmospheric terrestrial aquatic or biotic systems

improved prediction and tracking of volcanic ash clouds abstract during the past 30 years more than 100 airplanes have inadvertently flown through clouds of volcanic ash from erupting volcanoes such encounters have caused millions of dollars in damage to the aircraft and have endangered the lives of tens of thousands of passengers in a few severe cases total engine failure resulted when ash was ingested into turbines and coating turbine blades these incidents have prompted the establishment of cooperative efforts by the international civil aviation organization and the volcanological community to provide rapid notification of eruptive activity and to monitor and forecast the trajectories of ash clouds so that they can be avoided by air traffic ash cloud properties such as plume height ash concentration and three dimensional ash distribution have been monitored through non conventional remote sensing techniques that are under active development forecasting the trajectories of ash clouds has required the development of volcanic ash transport and dispersion models that can calculate the path of an ash cloud over the scale of a continent or a hemisphere volcanological inputs to these models such as plume height mass eruption rate eruption duration ash distribution with altitude and grain size distribution must be assigned in real time during an event often with limited observations databases and protocols are currently being developed that allow for rapid assignment of such source parameters in this paper we summarize how an interdisciplinary working group on eruption source parameters has been instigating research to improve upon the current understanding of volcanic ash cloud characterization and predictions improved predictions of ash cloud movement and air fall will aid in making better hazard assessments for aviation and for public health and air quality

spatial analysis of mount st helens tephra leachate compositions implications for future sampling strategies tephra particles in physically and chemically evolving volcanic plumes and clouds carry soluble sulphate and halide salts to the earth s surface ultimately depositing volcanogenic compounds into terrestrial or aquatic environments upon leaching of tephra in water these salts dissolve rapidly previous studies have investigated the spatial and temporal variability of tephra leachate compositions during an eruption in order to gain insight into the mechanisms of gas tephra interaction which emplace those salts however the leachate datasets analysed are typically small and may poorly represent the natural variability and complexity of tephra deposits here we have conducted a retrospective analysis of published leachate analyses from the 18 may 1980 eruption of mount st helens washington analysing the spatial structure of the concentrations and relative abundances of soluble ca cl na and s across the deposits we have identified two spatial features 1 concentrated tephra leachate compositions in blast deposits to the north of the volcano and 2 low s cl and na cl ratios around the washington idaho border by reference to the bulk chemistry and granulometry of the deposit and to current knowledge of gas tephra interactions we suggest that the proximal enrichments are the product of pre eruptive gas uptake during cryptodome emplacement we speculate that the low s cl and na cl ratios reflect a combination of compositional dependences on high temperature so2 uptake and preferential hcl uptake by hydrometeor tephra aggregates manifested in terrestrial deposits by tephra sedimentation and fallout patterns however despite our interrogation of the most exhaustive tephra leachate dataset available it has become clear in this effort that more detailed insights into gas tephra interaction mechanisms are prevented by the prevalent poor temporal and spatial representativeness of the collated data and the limited characterisation of the tephra deposits future leachate studies should aim to extensively sample across tephra deposit limits whilst simultaneously characterising deposit stratigraphy and tephra chemistry mineralogy and granulometry taking steps to ensure the quality and comparability of collected leachate datasets

improving on mass flow rate estimates of volcanic eruptions 1 we introduce a novel analytical expression that allows for fast assessment of mass flow rate of both vertically rising and bent over volcanic plumes as a function of their height while first order physical insight is maintained this relationship is compared with a one dimensional plume model to demonstrate its flexibility and then validated with observations of the 1980 mount st helens and of the 2010 eyjafjallajokull eruptions the influence of wind on the dynamics of volcanic plumes is quantified by a new dimensionless parameter and it is shown how even vertically rising plumes such as the one associated with the mount st helens 1980 eruption can be significantly affected by strong wind comparison between a one dimensional model and the analytical equation gives anr2 value of 0 88 while existing expressions give negativer2 values due to their inability to adapt to different source and atmospheric conditions therefore this new expression has important implications both for current strategies of real time forecasting of ash transport in the atmosphere and for the characterization of explosive eruptions based on the study of tephra deposits in addition this work provides a framework for the application of more complete three dimensional numerical models as it greatly reduces the parameter space that needs to be explored

subevents of long period seismicity implications for hydrothermal dynamics during the 2004 2008 eruption of mount st helens 1 one of the most striking aspects of seismicity during the 2004 2008 eruption of mount st helens msh was the precise regularity in occurrence of repetitive long period lp or drumbeat events over sustained time periods however this precise regularity was not always observed and at times the temporal occurrence of lp events became more random in addition accompanying the dominant lp class of events during the 2004 2008 msh eruption there was a near continuous randomly occurring series of smaller seismic events these subevents are not always simply small amplitude versions of the dominant lp class of events but appear instead to result from a separate random process only loosely coupled to the main lp source mechanism we present an analysis of the interevent time and amplitude distributions of the subevents using waveform cross correlation to separate lp events from the subevents we also discuss seismic tremor that accompanied the 8 march 2005 phreatic explosion event at msh this tremor consists of a rapid succession of lps and subevents triggered during the explosion in addition to broadband noise from the sustained degassing immediately afterward seismicity returned to the pre explosion occurrence pattern this triggering in relation to the rapid ejection of steam from the system and subsequent return to pre explosion seismicity suggests that both seismic event types originated in a region of the subsurface hydrothermal system that was 1 in contact with the reservoir feeding the 8 march 2005 phreatic explosion but 2 not destroyed or drained by the explosion event finally we discuss possible thermodynamic conditions in a pressurized hydrothermal crack that could give rise to seismicity pressure drop estimates for typical lp events are not generally large enough to perturb pure water in a shallow hydrothermal crack into an unstable state however dissolved volatiles such as co2 may lead to a more unstable system increasing the seismogenic potential of a hydrothermal crack subject to rapid heat flux the interaction of hydrothermal and magmatic systems beneath msh in 2004 2008 thus appears able to explain a wide range of observed phenomena including subevents lp events larger md 2 events and phreatic explosions

satellite observations of the 2016 2017 eruption of bogoslof volcano aviation and ash fallout hazard implications from a water rich eruption satellite data goes viirs modis avhrr were used in near real time during the 2016 2017 eruption of bogoslof volcano alaska to detect explosive eruptive activity and to characterize the resulting volcanic clouds this study examines satellite data to estimate volcanic cloud heights and mass eruption rates for 47 of the 70 explosive events eighteen of the volcanic clouds reached an altitude in excess of 8 5 km asl where they posed a potential hazard to aviation we estimate eruption rates were in the range of 104 107 kg s eruption durations were available for 28 events and the total mass of these events was 5 7 1010 kg most of the explosions occurred from submarine vents producing volcanic clouds with water rich characteristics in satellite data we infer that these water rich phreatomagmatic events contained ice coated ash particles which changed their visible and multispectral characteristics only two of the explosions produced clouds with satellite characteristics that would be considered ash rich we conclude that these events were relatively dry eruptions with limited access to ocean water although some of the explosive events transitioned from submarine to subaerial vents we observed no change in the character of the volcanic clouds during these transitions we speculate that enhanced removal of fine grained volcanic ash likely occurred due to aggregation with implications for modeling ash transport and fallout we conclude that the majority of bogoslof s water rich volcanic clouds did contain volcanic ash despite the lack of conventional ash signature in satellite data this has implications for satellite monitoring of future water rich shallow submarine eruptions

ascent dynamics of large phreatomagmatic eruption clouds the role of microphysics 1 we examine the impact of abundant surface water interaction on the development of volcanic clouds from large scale 108 kg s 1 magma phreatomagmatic eruptions presenting the first 2 d large eddy simulations of wet volcanic plumes that incorporate the effects of microphysics the active tracer high resolution atmospheric model was forced with field derived inputs from an exceptionally large phreatomagmatic eruption the 27 ka oruanui supereruption taupo volcano new zealand surface water contents were varied from 0 to 40 wt for eruptions with equivalent magma eruption rates of 1 3 108 and 1 1 109 kg s 1 our findings confirm that increased surface water has a pronounced impact on column stability leading to transitional column behavior and hybrid clouds resulting from simultaneous ascent of material from stable columns and pyroclastic density currents pdcs contrary to the suggestion of previous workers however abundant surface water does not systematically lower the spreading level or maximum height of volcanic clouds owing to vigorous microphysics assisted lofting of pdcs the simulated behavior and ash cloud dimensions provide a close match to field evidence from the oruanui case study cloud heights from the collapsing eruption columns also show a notable sensitivity to changes in the altitude of the tropopause while ambient humidity primarily impacts the abundance of airborne hydrometeors particularly ice associated with the volcanic clouds general relationships between eruption style meteorological conditions and the resulting vertical profiles of volcanic emissions outlined here could also be adapted for use in operational volcanic ash forecasting and deposit reconstruction techniques already in existence

volcanic lightning and plume behavior reveal evolving hazards during the april 2015 eruption of calbuco volcano chile soon after the onset of an eruption model forecasts of ash dispersal are used to mitigate the hazards to aircraft infrastructure and communities downwind however it is a significant challenge to constrain the model inputs during an evolving eruption here we demonstrate that volcanic lightning may be used in tandem with satellite detection to recognize and quantify changes in eruption style and intensity using the eruption of calbuco volcano in southern chile on 22 and 23 april 2015 we investigate rates of umbrella cloud expansion from satellite observations occurrence of lightning and mapped characteristics of the fall deposits our remote sensing analysis gives a total erupted volume that is within uncertainty of the mapped volume 0 56 0 28 km3 bulk observations and volcanic plume modeling further suggest that electrical activity was enhanced both by ice formation in the ash clouds 10 km above sea level and development of a low level charge layer from ground hugging currents

injection transport and deposition of tephra during event 5 at redoubt volcano 23 march 2009 abstract among the events of the 2009 eruption at redoubt volcano alaska event 5 was the best documented by radar satellite imagery and deposit mapping we use the new eulerian tephra transport model ash3d to simulate transport and deposition of event 5 tephra at distances up to 350 km the eruption which started at about 1230 utc on 23 march 2009 sent a plume from the vent elevation estimated at 2 3 0 1 km above sea level or a s l to about 16 2 km above sea level in 5 min the plume was a few kilometers higher than would be expected for the estimated average mass eruption rate and atmospheric conditions possibly due to release of most of the eruptive mass in the first half of the 20 minute event the eruption injected tephra into a wind field of high shear with weak easterly winds below 3 km elevation strong southerly winds at 6 10 km and weak westerlies above 16 km model simulations in this wind field predicted development of a northward migrating inverted v shaped cloud with a southwest trending arm at a few kilometers elevation which was not visible in ir satellite images due to cloud cover and a southeast trending arm at 10 km elevation that was clearly visible simulations also predicted a deposit distribution that strongly depended on plume height a plume height below 15 km predicted ash deposits that were located west of those mapped whereas good agreement was reached with a modeled plume height of 15 18 km field sampling of the deposit found it to contain abundant tephra aggregates which accelerated the removal of tephra from the atmosphere we were able to reasonably approximate the effect of aggregation on the deposit mass distribution by two methods 1 adjusting the grain size distribution taking the erupted mass 2 isomass lines that was within a few tens of percent of mapped area however they under predicted deposit mass at very proximal 250 km locations modeled grain size distributions at sample locations are also generally coarser than observed the mismatch may result from a combination of limitations in field sampling approximations inherent in the model errors in the numerical wind field and aggregation of particles larger than 0 063 mm

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

color change processes of a plinian pumice and experimental constraints of color change kinetics in air of an obsidian colors of plinian pumices were measured by spectrocolorimetry and their quantitative color parameters in the l a b color space were determined a series of heating experiments of obsidian was conducted to simulate the color change processes of rhyolitic glasses in these experiments following three stages of color change processes were observed stage i showed a rapid b yellowishness increase associated with fast dehydration controlled by water diffusivity dwater in stage ii a reddishness increase was accompanied by fe2 decrease both a increase and fe2 decrease can be simulated by a diffusion model obtained diffusivity doxidation were about two orders of magnitude smaller than dwater the a value increase after the oxidation in stage iii appeared to be quasi linear with time indicating the zeroth order reaction corresponding to the formation of hematite like structures in rhyolitic glasses the diffusion limited a increase model in stage ii was applied to a natural plinian pumice fall unit to evaluate time periods of color change processes through oxidation by air of fragmented rhyolitic materials

investigating the origin of continual radio frequency impulses during explosive volcanic eruptions volcanic lightning studies have revealed that there is a relatively long lasting source of very high frequency radiation associated with the onset of explosive volcanic eruptions that is distinct from radiation produced by lightning this very high frequency signal is referred to as continual radio frequency crf due to its long lasting nature the discharge mechanism producing this signal was previously hypothesized to be caused by numerous small 10 100m leader forming discharges near the vent of the volcano to test this hypothesis a multiparametric data set of electrical and volcanic activity occurring during explosive eruptions of sakurajima volcano in japan was collected from may to june 2015 our observations show that a single crf impulse has a duration on the order of 160ns giving an upper limit on discharge length of 10m and is distinct from near vent lightning discharges that were on the order of 30m in length crf impulses did not produce discernible electric field changes and occurred in the absence of a net static electric field lightning mapping data and infrared video observations of the eruption column showed that crf impulses originated from the gas thrust region of the column these observations indicate that crf impulses are not produced by small leader forming discharges but rather are more similar to a streamer discharge likely on the order of a few meters in length plain language summary this paper investigates the origin of a radio frequency rf signal previously termed continual rf that has been detected from the ash plumes of explosive volcanic eruptions continual rf had been hypothesized to be caused by many very small lightning like discharges on the order of 100m in length occurring at the vent of the volcano to test this hypothesis we conducted a multiparametric observational experiment at sakurajima volcano in japan we measured continual rf during eruptions of sakurajima in 2015 and found that continual rf is a collection of short duration rf impulses on the order of 160ns in duration these rf impulses are distinct from those typically produced by lightning we also observed small 30 m lightning discharges occurring near the volcanic vent that were distinct from the source of continual rf our observations show that continual rf is caused by an electrical discharge that is more simple than even a very small approximate to 100m lightning discharge we conclude that continual rf is caused by numerous small electrical discharges similar to streamer discharges on the order of a few meters in length

assessing eruption column height in ancient flood basalt eruptions a buoyant plume model is used to explore the ability of flood basalt eruptions to inject climate relevant gases into the stratosphere an example from the 1986 izu oshima basaltic fissure eruption validates the model s ability to reproduce the observed maximum plume heights of 12 16 km above sea level sustained above fire fountains the model predicts maximum plume heights of 13 17 km for source widths of between 4 16 m when 32 by mass of the erupted magma is fragmented and involved in the buoyant plume effective volatile content of 6 wt assuming that the miocene age roza eruption part of the columbia river basalt group sustained fire fountains of similar height to izu oshima 1 6 km above the vent we show that the roza eruption could have sustained buoyant ash and gas plumes that extended into the stratosphere at 45 n assuming 5 km long active fissure segments and 9000 mt of so2 released during explosive phases over a 10 15 year duration the 180km of known roza fissure length could have supported 36 explosive events phases each with a duration of 3 4 days each 5 km fissure segment could have emitted 62 mt of so2 per day into the stratosphere while actively fountaining the equivalent of about three 1991 mount pinatubo eruptions per day each fissure segment could have had one to several vents which subsequently produced lava without significant fountaining for a longer period within the decades long eruption sensitivity of plume rise height to ancient atmospheric conditions is explored although eruptions in the deccan traps 66ma may have generated buoyant plumes that rose to altitudes in excess of 18 km they may not have reached the stratosphere because the tropopause was substantially higher in the late cretaceous our results indicate that some flood basalt eruptions such as roza were capable of repeatedly injecting large masses of so2 into the stratosphere thus sustained flood basalt eruptions could have influenced climate on time scales of decades to centuries but the location i e latitude of the province and relevant paleoclimate is important and must be considered

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

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

infrasonic jet noise from volcanic eruptions 1 the lowermost section of a vulcanian or plinian volcanic eruption column may be thought of as a momentum driven turbulent free shear jet flow we propose that large amplitude and long duration infrasonic 20 hz signals recorded at ranges of tens of kilometers during powerful eruptions at mount st helens usa and tungurahua ecuador represent a low frequency form of jet noise a preliminary test of this hypothesis is made by comparing the observed infrasonic spectra to the empirically derived similarity spectra for pure air jets although the spectral shapes are in approximate agreement the observed volcanic signals have additional complexities not present in the pure air laboratory data these features may result from multiphase flow containing solid particles and liquid droplets very high temperatures and perhaps complex crater morphology however the overall similarity between the volcanic signals and jet noise indicates that broadband infrasound measurements at volcanoes may provide a quantitative link to eruption jet dynamics and would aid substantially in the remote assessment of volcanic hazard

estimation of eruption source parameters from umbrella cloud or downwind plume growth rate abstract we introduce a new method to estimate mass eruption rate mer and mass loading from the growth of a volcanic umbrella cloud or downwind plume using satellite images or photographs where ground based observations are available this new method is compared with pre existing models and documented mass eruption rate given in the research literature we applied the method to five well studied eruptions mount st helens 1980 redoubt 1990 pinatubo 1991 hekla 2000 and eyjafjallajokull 2010 and to five less well documented eruptions kliuchevsko i 1994 okmok 2008 kasatochi 2008 sarychev peak 2009 and bezymianny 2012 the mass eruption rate is obtained by estimation of the radius of the umbrella cloud with time or by estimation of the width of the downwind plume with distance from the volcano the results given by the new method show a more fully characterized mer as a function of time than do the results given by pre existing methods and allow a faster remote assessment of the mass eruption rate even for volcanoes that are difficult to study the method thus may provide an additional important path to the estimation of source parameters and the forecasting of ash cloud propagation in addition in cases where numerous methods are available use of the method yields new independent measures of mass eruption rate hence an ability to estimate uncertainty in mass eruption rate which could be used in probabilistic estimations of ash cloud propagation

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

numerical simulations of volcanic jets importance of vent overpressure journal of geophysical research vol 113 b02204 doi 10 1029 2007jb005133 2008 numerical simulations of volcanic jets importance of vent overpressure darcy e ogden 1 kenneth h wohletz 2 gary a glatzmaier 1 and emily e brodsky 1 received 24 april 2007 revised 5 october 2007 accepted 5 november 2007 published 29 february 2008 1 explosive volcanic eruption columns are generally subdivided into a gas thrust region and a convection dominated plume where vents have greater than atmospheric pressure the gas thrust region is overpressured and develops a jet like structure of standing shock waves using a pseudogas approximation for a mixture of tephra and gas we numerically simulate the effects of shock waves on the gas thrust region these simulations are of free jet decompression of a steady state high pressure vent in the absence of gravity or a crater our results show that the strength and position of standing shock waves are strongly dependent on the vent pressure and vent radius these factors control the gas thrust region s dimensions and the character of vertical heat flux into the convective plume with increased overpressure the gas thrust region becomes wider and develops an outer sheath in which the erupted mixture moves at higher speeds than it does near the column center the radius of this sheath is linearly dependent on the vent radius and the square root of the overpressure the sheath structure results in an annular vertical heat flux profile at the base of the convective plume which is in stark contrast to the generally applied gaussian or top hat profile we show that the magnitude of expansion is larger than that predicted from previous 1d analyses resulting in much slower average vertical velocities after expansion these new relationships between vent pressure and plume expansion may be used with observations of plume diameter to constrain the pressure at the vent citation ogden d e k h wohletz g a glatzmaier and e e brodsky 2008 numerical simulations of volcanic jets importance of vent overpressure j geophys res 113 b02204 doi 10 1029 2007jb005133 1 introduction 2 in large explosive volcanic eruptions the eruptive fluid issues from the vent as a high speed compressible gas with entrained solid particulates it is important to quantify the behavior of this gas thrust region because it provides a connection between the fluid dynamics in the conduit and that of the buoyant column if the eruptive fluid velocity is at or greater than sonic and vent pressure is higher than atmospheric pressure the dynamics will be complicated by the presence of standing shock waves that can drastically alter the distribution of the vertical heat flux necessary for eruption column stability the fluid dynamics and structure of a compressible jet issuing from a sonic nozzle into an ambient atmosphere of lower pressure are well known from experimental analytical and computational studies e g crist et al 1966 young 1975 norman et al 1982 figure 1 although application of compressible jet dynamics to explosive volcanic eruptions was first sug gested over 25 years ago by kieffer 1981 the concept has earth planetary sciences department university of california at santa cruz santa cruz california usa los alamos national laboratory los alamos new mexico usa copyright 2008 by the american geophysical union 0148 0227 08 2007jb005133 09 00 yet to be widely applied in modeling and analysis of explosive eruption columns 3 in this paper we present computational results that quantify the important effects of vent pressure on the fluid dynamics of volcanic jets and show that overpressured jets produce vertical heat flux profiles that are drastically different than those of pressure balanced jets note to avoid confusion here we use the physics convention and consider heat flux the thermal energy transfer per area per unit time j m 2 s 1 and heat flow the thermal energy transfer integrated over an entire area per time j s 1 in volcanology literature the term heat flux is often used to mean either of these things e g woods 1988 mastin 2007 the simulations shown here are time dependent though they assume a steady vent condition through these simulations we quantify the effects of vent pressure and radius on plume radius and heat flux distribution after expansion of the jet this may allow the prediction of major features of the eruptive structure we do not consider the effects of variations in conduit dynamics buoyancy or the presence of a crater in order to focus only on the effects of vent pressure and radius alone this study is not a complete picture of the complicated flow dynamics of a volcanic eruption rather the results presented here could be consid ered the simplest case to which one could compare the dynamics resulting from more complicated simulations and observations of high pressure volcanic jets b02204 1 of 18

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

the effect of total grain size distribution on the dynamics of turbulent volcanic plumes abstract the impact of explosive volcanic plumes on climate and on air traffic strongly depends on the concentration and grain size distribution gsd of pyroclastic fragments injected into the atmosphere accurate and robust modelling of the evolution of gsd during pyroclast transport from the vent to the ash cloud is therefore crucial for the assessment of major volcanic hazards analysis of field deposits from various recent plinian eruptions shows that their total gsd is well described by a power law as expected from the physics of magma fragmentation with an exponent d ranging from 3 0 to 3 9 by incorporating these measured gsd into the initial conditions of a steady state 1d model of explosive eruption columns we show that they have a first order impact on the dynamical behaviour of explosive eruption columns starting from an initial value of d the model tracks the evolution of gsd in the column and calculates the dynamical consequences of particle sedimentation the maximum height reached by the column one of the first order results relevant to aircraft safety changes by 30 for mass fluxes of 10 7 kg s 1 or larger and by 45 85 for mass fluxes between 105 and 10 7 kg s 1 depending on exponent d we compare our predictions to a specially assembled set of geologic field data and remote sensing observations from 10 plinian eruptions for which maximum column height and mass flux are known independently the incorporation of realistic power law gsd in the model greatly improves the predictions which opens new perspectives for estimation of ash load and gsd in volcanic clouds from near real time measurements available from satellite payloads our results also contribute to the improvement of volcanic source term characterization that is required input for meteorological dispersion models

a three dimensional numerical simulation of spreading umbrella clouds 1 during explosive volcanic eruptions an eruption column buoyantly rises as a turbulent plume and an umbrella cloud spreads laterally as a gravity current at the neutral buoyancy level the source conditions of explosive eruptions such as mass discharge rates of magma at vents have been estimated from the field observations e g satellite images on the height of the eruption columns and the spreading rate of umbrella clouds on the basis of the one dimensional 1 d plume model and the gravity current model however these simplified models contain empirical constants entrainment coefficient of turbulent plume k and froude number of gravity current that should be justified we developed a time dependent three dimensional 3 d numerical model of eruption clouds to independently determine the values of these constants the 3 d model is designed to calculate quantitative features of turbulent mixing between an eruption cloud and the ambient air without any a priori empirical constants by applying a sufficiently fine grid size with a third order accuracy scheme it has reproduced the fundamental features of eruption clouds including eruption columns pyroclastic flows coignimbrite ash clouds and umbrella clouds the altitudes of the spreading umbrella clouds in the 3 d simulations are consistent with those of the neutral buoyancy level of eruption columns estimated by the 1 d plume model with the entrainment coefficient k 0 1 the relationship between the volumetric flow rate and the spreading rate of the umbrella cloud in the 3 d simulations is explained by the axisymmetrical gravity current model with 0 2 for eruption clouds in the tropical atmosphere and 0 1 for those in the midlatitude atmosphere on the other hand the total column height in the 3 d simulations strongly oscillates even for a constant mass discharge rate and its time average tends to be substantially greater than the column height estimated by the 1 d plume model with k 0 1 particularly for large scale eruption clouds in the midlatitude atmosphere we recommend a method to estimate the mass discharge rate from the observation of the column height or the spreading rate of umbrella cloud the method and the accuracy of the 3 d simulations are tested on the basis of the field data e g the total height of the eruption column the altitude and the spreading rate of the umbrella cloud and the mass discharge rate of the pinatubo 1991 eruption

volcanic plume height measured by seismic waves based on a mechanical model journal of geophysical research vol 116 b01306 doi 10 1029 2010jb007620 2011 volcanic plume height measured by seismic waves based on a mechanical model stephanie g prejean 1 and emily e brodsky 2 received 4 april 2010 revised 3 november 2010 accepted 23 november 2010 published 26 january 2011 1 in august 2008 an unmonitored largely unstudied aleutian volcano kasatochi erupted catastrophically here we use seismic data to infer the height of large eruptive columns such as those of kasatochi based on a combination of existing fluid and solid mechanical models in so doing we propose a connection between a common observable short period seismic wave amplitude to the physics of an eruptive column to construct a combined model we estimate the mass ejection rate of material from the vent on the basis of the plume height assuming that the height is controlled by thermal buoyancy for a continuous plume using the estimated mass ejection rate we then derive the equivalent vertical force on the earth through a momentum balance finally we calculate the far field surface waves resulting from the vertical force the model performs well for recent eruptions of kasatochi and augustine volcanoes if v the velocity of material exiting the vent is 120 230 m s 1 the consistency between the seismically inferred and measured plume heights indicates that in these cases the far field 1 s seismic energy radiated by fluctuating flow in the volcanic jet during the eruption is a useful indicator of overall mass ejection rates thus use of the model holds promise for characterizing eruptions and evaluating ash hazards to aircraft in real time on the basis of far field short period seismic data this study emphasizes the need for better measurements of eruptive plume heights and a more detailed understanding of the full spectrum of seismic energy radiated coeruptively citation prejean s g and e e brodsky 2011 volcanic plume height measured by seismic waves based on a mechanical model j geophys res 116 b01306 doi 10 1029 2010jb007620 1 introduction and motivation 2 empirical studies have suggested that the amplitude of high frequency or broadband seismic waves radiated during large volcanic eruptions generally scales with the height of an eruption column mcnutt 1994a however a direct calculation of the expected seismic wave amplitude based on physical models has not yet been successful connecting commonly observable data such as seismic wave amplitudes to a model of the flow in the eruptive jet would provide a new tool to test and improve our understanding of eruptive physics for instance small scale turbulence is thought to play a major role in the entrainment of hot particles and gases and hence the buoyancy of eruptive columns yet there are few measurements of the strength or distribution of small scale features in real eruptive columns andrews and gardner 2009 using seismic data to provide observational constraints on eruption column flow processes is particularly attractive as seismic data are often available even in remote u s geological survey alaska volcano observatory anchorage alaska usa department of earth and planetary sciences university of california santa cruz california usa copyright 2011 by the american geophysical union 0148 0227 11 2010jb007620 settings thus use of the seismic database would greatly increase the number and type of eruptions amenable to study 3 pragmatically a physical model connecting plume height and seismic data would allow the use of seismology as a remote sensing technology to infer volcanic plume height it would be a particularly useful tool for exploring eruption dynamics in remote environments where direct observation is not possible such as the volcanoes of the northern pacific ocean although many volcano observa tories worldwide are gradually replacing short period seismometers with broadband seismometers we still largely rely on short period instruments for forecasting monitoring and analyzing eruptions these realities motivate the development of the model described below 4 in this study we build on previous work to develop a physical model for the expected amplitude of seismic waves from an eruption that generates a plume of a given height as a cautionary note we explore the potential errors in this formulation and describe situations where the model is not applicable such as small eruptions or eruptions where most mass ejected is not entrained in the plume after reviewing previous work on coeruptive seismology and the char acteristics of the 2008 kasatochi and 2006 augustine eruptions we use the connection between plume height and b01306 1 of 13

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

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

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

an unusually energetic basaltic phreatomagmatic eruption using deposit characteristics to constrain dilute pyroclastic density current dynamics abstract multiple highly erosive base surges of the table rock complex tuff ring trc2 oregon produced dune bedded deposits with crest to crest bedform wavelengths up to 200 m which are amongst the largest ever recognized in the deposits of pyroclastic density currents here we use bedform wavelength surmounted obstacles and a large chute and pool feature to estimate near source velocities 118 233 m s 1 lower bound velocities at radial distances of 1 6 2 and 4 7 km from source 34 29 and 20 m s 1 respectively and corresponding column collapse heights up to 2 8 km this paper represents one of the few studies that attempt to quantify flow characteristics such as emplacement velocities at different distances from source eruption column collapse height and eruptive energy based on deposit characteristics

sedimentation from strong volcanic plumes 1 we develop descriptions of the key processes influencing tephra dispersal from strong volcanic plumes these are characterized by the development of a subvertical eruption column in the atmosphere that forms a spreading current at a level of neutral buoyancy we describe the propagation of the spreading current due to both gravity and wind advection using scaling arguments and a simplified geometry to model particle sedimentation in a windy as well as a wind free environment new parameterizations are used to describe the wind field below the spreading current particle aggregation and particle density variations we conducted a broad study to investigate the effects of these processes and made comparisons with field observations the greatest variations resulted from wind advection below the spreading current which shifts the plume corner mass accumulation and the position of transitions in fallout regimes downwind particle aggregation strongly depends on the initial grain size distribution and significantly affects deposit thinning depending on the aggregate size and density and on the relative amount of aggregating particles small aggregates can reproduce secondary maxima of mass accumulation when sedimenting in a wind field variation of particle density also affects the resulting thinning trend the model provides acceptable reproduction of observations of the propagation of the spreading current tested with the plinian phase of the 18 may 1980 eruption of mount st helens and of observed thinning of tephra fallout deposits tested with deposits from mount st helens 1980 askja d 1875 quizapu 1932 minoan eruption 3 6 ka b p novarupta a 1912 and hudson 1991

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

a global sensitivity analysis of the plumerise model of volcanic plumes abstract integral models of volcanic plumes allow predictions of plume dynamics to be made and the rapid estimation of volcanic source conditions from observations of the plume height by model inversion here we introduce plumerise an integral model of volcanic plumes that incorporates a description of the state of the atmosphere includes the effects of wind and the phase change of water and has been developed as a freely available web based tool the model can be used to estimate the height of a volcanic plume when the source conditions are specified or to infer the strength of the source from an observed plume height through a model inversion the predictions of the volcanic plume dynamics produced by the model are analysed in four case studies in which the atmospheric conditions and the strength of the source are varied a global sensitivity analysis of the model to a selection of model inputs is performed and the results are analysed using parallel coordinate plots for visualisation and variance based sensitivity indices to quantify the sensitivity of model outputs we find that if the atmospheric conditions do not vary widely then there is a small set of model inputs that strongly influence the model predictions when estimating the height of the plume the source mass flux has a controlling influence on the model prediction while variations in the plume height strongly effect the inferred value of the source mass flux when performing inversion studies the values taken for the entrainment coefficients have a particularly important effect on the quantitative predictions the dependencies of the model outputs to variations in the inputs are discussed and compared to simple algebraic expressions that relate source conditions to the height of the plume