laboratory experiments of forced plumes in a density stratified crossflow and implications for volcanic plumes the mass eruption rate feeding a volcanic plume is commonly estimated from its maximum height winds are known to affect the column dynamics causing bending and hence reducing the maximum plume height for a given mass eruption rate however the quantitative predictions including wind effects on mass eruption rate estimates are not well constrained to fill this gap we present a series of new laboratory experiments on forced plumes rising in a density stratified crossflow we identify three dynamical regimes corresponding to increasing effect of wind on the plume rise the transition from one regime to another is governed by two dimensionless velocity scales defined as a function of source and environmental parameters the results are found consistent with the conditions of historical eruptions and provide new empirical relationships to estimate mass eruption rate from plume height in windy conditions leading to valuable tools for eruption risk assessment

an evaluation of volcanic cloud detection techniques during recent significant eruptions in the western ring of fire we examined recent volcanic cloud events in the western pacific and indonesian area to validate the performance of remote sensing techniques used to support the international airways volcano watch iavw five events were considered during which eruptions from eight volcanoes injected ash into the upper troposphere or lower stratosphere for one of the eruptions at miyakejima japan at least five aircraft encountered volcanic ash clouds and the cost to three operators alone exceeded us 12 000 000 in aircraft repairs diversions and lost operating time we performed reverse absorption and pattern analysis using gms 5 vissr modis and avhrr data and we examined toms so2 and aerosol index data surface based observations pilot reports and dispersion model output our results verify that the introduction of reverse absorption using the geostationary gms 5 platform significantly enhanced our capacity to monitor volcanic ash clouds in the region in one case we tracked an eruption cloud for approximately 80 h the primary impediment to remote monitoring is the presence of overlying cloud or substantial amounts of ice within the volcanic clouds toms data showed success in identifying volcanic clouds during these conditions but was limited by the infrequency of observations more effective future operation of the iavw relies on developing complementary methods of volcanic cloud remote sensing and greatly increasing the amount and quality of available surface and air observations including observations of precursor activity an understanding of the likely future limitations of remote sensing techniques will aid in the refining of iavw procedures

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

tracing marine cryptotephras in the north atlantic during the last glacial period protocols for identification characterisation and evaluating depositional controls abstract tephrochronology is increasingly being utilised as a key tool for improving chronological models and correlating disparate palaeoclimatic sequences for many sedimentary environments however there is an increased recognition that a range of processes may impart a delay in deposition and or rework tephra these processes can affect the integrity of tephra deposits as time synchronous markers therefore it is crucial to assess their isochronous nature especially when cryptotephras are investigated in a dynamic marine environment a methodology for the identification and characterisation of marine cryptotephras alongside a protocol for assessing their integrity is outlined this methodology was applied to a wide network of north atlantic marine sequences covering the last glacial period a diverse range of cryptotephra deposits were identified and based on similarities in physical characteristics e g glass shard concentration profiles and geochemical homogeneity heterogeneity indicative of common modes of tephra delivery and post depositional reworking a deposit type classification scheme was defined the presence and dominance of different deposit types within each core allowed an assessment of spatial and temporal controls on tephra deposition and preservation overall isochronous horizons can be identified across a large portion of the north atlantic due to preferential atmospheric dispersal patterns however the variable influence of ice rafting processes and an interplay between the high eruptive frequency of iceland and relatively lower sedimentation rates can also create complex tephrostratigraphies in this sector sites within a wide sector to the south and east of iceland have the greatest potential to be repositories for isochronous horizons that can facilitate the synchronisation of palaeoclimatic records

a model of the plumes above basaltic fissure eruptions a simple model of the ascent of the volatiles above basaltic fissure eruptions shows that atmospheric moisture may play an important role in injecting volatiles high into the atmosphere as ambient water vapour is entrained and carried upwards by the plume it decompresses and some condensation may occur this causes the release of latent heat which heats up the air and thereby increases the buoyancy of the plume enabling it to ascend several kilometres higher than in a dry atmosphere the height of such plumes also increases with the mass fraction of fine ash in the fountain although very simple the model predictions are in accord with observations of plume heights during historical eruptions including the 1984 eruption of mauna loa

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

a prognostic turbulence scheme for the nonhydrostatic plume model atham the presented turbulence scheme was developed for the active tracer high resolution atmospheric model atham to parameterize the effect of subgrid scale turbulence in contrast to the commonly used assumption of local isotropy in high resolution atmospheric modeling this scheme differentiates between horizontal and vertical turbulent exchange to represent the strong influence of buoyancy forces and vertical transports its computational efficiency is similar to classical turbulent kinetic energy approaches while preserving one of the main feature of higher order schemes the present extensions to include anisotropic effects in a turbulent kinetic energy approach do not need any ad hoc assumptions and are equivalent to the classical formulation in the isotropic limit the presence of high tracer concentrations in a particle laden plume is taken into account as well as supersonic effects at low mach numbers the turbulent exchange coefficients used in the equations of motion are derived from a set of three coupled differential equations for the horizontal and vertical turbulent energy and the turbulent length scale no turbulent equilibrium is assumed all turbulent quantities are treated prognostically numerical simulations of convective plumes of a typical plinian volcanic eruption with the nonhydrostatic plume model atham reveal that a complex treatment of turbulent quantities is necessary in order to capture the bulk characteristics of the plume such as the plume height the horizontal extent and plume development in time anisotropic effects of turbulence have a significant impact on the stability and internal structure of the plume for the first time results from a fully three dimensional simulation of a volcanic plume are presented because of its general formulation the presented turbulence scheme is suitable for a wide range of atmospheric applications

sage ii measurements of early pinatubo aerosols sage ii satellite measurements of the mt pinatubo eruption cloud in the stratosphere during june july and early august 1991 show that aerosols in the tropics reached as high as 29 km altitude with most of the cloud between 20 and 25 km the most optically thick portions of the cloud covered latitudes from 10 s to 30 n during the early part of this period by late july high stratospheric optical depths were observed to at least 70 n with the high values north of about 30 n from layers below 20 km high pressure systems in both hemispheres were observed to be correlated with the movement of volcanic material at 21 km into the westerly jet stream at high southern latitudes and similarly to high northern latitudes at 16 km by august the entire southern hemisphere had experienced a 10 fold increase in optical depth relative to early july due to layers above 20 km initial mass calculations using sage ii data place the aerosol produced from this eruption at 20 to 30 megatonnes well above the 12 megatonnes produced by el chichon

injection of gases into the stratosphere by explosive volcanic eruptions 1 explosive eruptions can inject large amounts of volcanic gases into the stratosphere these gases may be scavenged by hydrometeors within the eruption column and high uncertainties remain regarding the proportion of volcanic gases which eventually reach the stratosphere these are caused by the difficulties of directly sampling explosive volcanic eruption columns and by the lack of laboratory studies in the extreme parameter regime characterizing them using the nonhydrostatic nonsteady state plume model active tracer high resolution atmospheric model atham we simulated an explosive volcanic eruption we examined the scavenging efficiency for the climatically relevant gases within the eruption column the low concentration of water in the plume results in the formation of relatively dry aggregates more than 99 of these are frozen because of their fast ascent to low temperature regions consideration of the salinity effect increases the amount of liquid water by one order of magnitude but the ice phase is still highly dominant consequently the scavenging efficiency for hcl is very low and only 1 is dissolved in liquid water however scavenging by ice particles via direct gas incorporation during diffusional growth is a significant process the salinity effect increases the total scavenging efficiency for hcl from about 50 to about 90 the sulfur containing gases so2 and h2s are only slightly soluble in liquid water however these gases are incorporated into ice particles with an efficiency of 10 to 30 despite scavenging more than 25 of the hcl and 80 of the sulfur gases reach the stratosphere because most of the particles containing these species are lifted there sedimentation of the particles would remove the volcanic gases from the stratosphere hence the final quantity of volcanic gases injected in a particular eruption depends on the fate of the particles containing them which is in turn dependent on the volcanic and environmental conditions

new insights on entrainment and condensation in volcanic plumes constraints from independent observations of explosive eruptions and implications for assessing their impacts abstract the turbulent entrainment of atmosphere and the condensation of water vapor govern the heights of explosive volcanic plumes these processes thus determine the delivery and the lifetime of volcanic ash and aerosols into the atmosphere predictions of plume heights using one dimensional integral models of volcanic plumes however suffer from very large uncertainties related to parameterizations for entrainment and condensation in particular the wind entrainment coefficient which governs the contribution of crosswinds to turbulent entrainment is subject to uncertainties of one order of magnitude leading to relative uncertainties of the order of 50 on plume height in this study we use a database of 94 eruptive phases with independent estimates of mass eruption rate and plume height to constrain and evaluate four popular 1d models we employ re sampling methods to account for observational uncertainties we show that plume height predictions are significantly improved when i the contribution of water vapor condensation to the plume buoyancy flux is excluded and ii the wind entrainment coefficient is held constant between 0 1 and 0 4 we explore implications of these results for predicting the climate impacts of explosive eruptions and the likelihood that eruptions will form stable umbrella clouds or devastating pyroclastic flows last we discuss the sensitivity of our results to the definition of plume height in the model in light of a recent set of laboratory experiments and draw conclusions for improving future databases of eruption parameters

geochemistry u pb geochronology and sr nd isotopes of the neogene igneous rocks at the iju porphyry copper deposit nw shahr e babak iran abstract the iju porphyry copper deposit is located in the kerman copper belt in the northwest of shahr e babak city within the southern extension of the urumieh dokhtar magmatic arc based on a cut off grade of 0 15 the deposit contains 24 million tonnes mt of ore with an average grade of 0 4 wt cu the igneous rocks at the iju deposit are primarily made up of upper miocene sub volcanic and volcanic sequences that intruded eocene volcanic rocks sub volcanic rocks comprise barren quartz monzonite porphyry and syn mineralized granodiorite porphyry along with andesitic volcanic rocks geochemical evidences show that they are co genetic medium to high potassium calc alkaline and likely part of a subduction zone i type granitoid magma these rocks are characterized by enrichment in lrees relative to hrees with negative nb ta anomalies similar to subduction zone magmatism all samples exhibit enriched uniform chondrite normalized ree patterns without noticeable eu anomalies similar to magnetite series granitoids the igneous rocks of the iju deposit exhibit geochemical features similar to adakites the u pb zircon dating shows 9 33 0 19 ma tortonian stage for quartz monzonite oldest unit 9 01 0 20 ma for granodiorite and 8 83 0 19 ma for andesite youngest unit unit the initial 87sr 86sr and 143nd 144nd ratios and end t values for the quartz monzonites are 0 704234 0 512819 and 3 75 respectively similar to the values for the granodiorite which are 0 704278 0 512813 and 3 64 respectively in most discrimination diagrams the iju samples show characteristics of both oceanic slab derived and delaminated collisional thickened lower crust derived adakites the geochronological geochemical and isotopic data for the igneous rocks of the iju deposit indicate that after long term subduction of the neo tethys oceanic crust beneath the central iranian plate continental collision between the arabian and eurasian plates during the miocene pliocene led to crustal thickening breaking off of a subducted slab and development of an asthenospheric window thereby facilitating partial melting of the subduction contaminated sub continental lithospheric mantle and thickened lower crust and generating the cu bearing adakites in the iju region

observational evidence for remote forcing of the west india coastal current 1 circulation in the north indian ocean is influenced by both local and remote wind forcing so far however determining the contribution of these two forcing mechanisms at a location has been possible only in numerical experiments here we separate remote and local forcing in observations using field measurements current sea level and wind for a month during march april 2003 off goa in the near coast regime of the west india coastal current wicc we show that the current was driven by local winds only at periods less than 10 days with remote forcing contributing at longer periods the high passed hp period less than 10 days component of the along shore current was strongly correlated with the hp component of the along shore wind the current lagging the wind by half a day the low passed lp components of the wind and current were not correlated the former was unidirectional but the latter reversed during the period of observation the relationship between the hp wind and current was used to estimate the locally forced lp current permitting an estimate of the remote current the lp residual this separation of locally forced and remotely forced currents showed that remote forcing contributed as much as local forcing to the wicc the local current behaved like a classical eastern boundary current forced by local winds the reversal in the remote current was due to winds 700 km farther south along the coast frictional damping had an impact only at periods less than 10 days there being no remotely forced hp current

cenozoic evolution of neotethys and implications for the causes of plate motions africa north america eurasia plate circuit rotations combined with red sea rotations and new estimates of crustal shortening in iran define the cenozoic history of the neotethyan ocean between arabia and eurasia the new constraints indicate that arabia eurasia convergence has been fairly constant at 2 to 3 cm yr since 56 ma with slowing of africa eurasia motion to 1 cm yr near 25 ma coeval with the opening of the red sea ocean closure occurred no later than 10 ma and could have occurred prior to this time only if a large amount of continental lithosphere was subducted suggesting that slowing of africa significantly predated the arabia eurasia collision these kinematics imply that africa s disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern eurasia slowed its motion the slow steady rate of northward subduction since 56 ma contrasts with strongly variable rates of magma production in the urumieh dokhtar arc implying magma production rate in continental arcs is not linked to subduction rate

particle sedimentation and diffusive convection in volcanic ash clouds 1 understanding the longevity of volcanic ash clouds generated by powerful explosive eruptions is a long standing problem for assessing volcanic hazards and the nature and time scale of volcanic forcings on climate change it is well known that the lateral spreading and longevity of these clouds is influenced by stratospheric winds particle settling and turbulent diffusion observations of the recent 2010 eyjafjallajokull and 2011 grimsvotn umbrella clouds as well as the structure of atmospheric aerosol clouds from the 1991 mt pinatubo event suggest that an additional key process governing the cloud dynamics is the production of internal layering here we use analog experiments on turbulent particle laden umbrella clouds to show that this layering occurs where natural convection driven by particle sedimentation and the differential diffusion of primarily heat and fine particles give rise to a large scale instability where umbrella clouds are particularly enriched in fine ash this particle diffusive convection strongly influences the cloud longevity more generally cloud residence time will depend on fluxes due to both individual settling and diffusive convection we develop a new sedimentation model that includes both sedimentation processes and which is found to capture real time measurements of the rate of change of particle concentration in the 1982 el chichon 1991 mt pinatubo and 1992 mt spurr ash clouds a key result is that these combined sedimentation processes enhance the fallout of fine particles relative to expectations from individual settling suggesting that particle aggregation is not the only mechanism required to explain volcanic umbrella longevity

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

experimental and model constraints on degassing of magma during ascent and eruption surface volcanic gases may reflect volatile budgets of magma and forecast impending eruptions and their release to the atmosphere may affect climate the dynamics of magma degassing is complicated however by differences in the solubility partitioning and diffusion of the various volatiles all of which can vary with pressure temperature and melt composition to constrain possible gas outputs we carried out experiments to determine how cl partitions between water bubbles and silicate melt and decompression experiments to examine how cl behaves during closed and open system degassing we incorporate our findings and those from the literature for co2 and s into a steady isothermal and homogeneous flow model to estimate fluxes of gases at the vent from ascending water rich magma assuming different scenarios for the onset and development of permeability in bubbly magma we find that for given permeability scenarios total gas fluxes vary with magma flux but ratios of gas species do not change the s cl and so2 co2 ratios do change however depending on whether the magma is oxidized or reduced after magma fragments into a plinian eruption column gases continue to escape from cooling pumice in the plume but here the rate of gas release is controlled by diffusion which varies with temperature degassing of pumice and ash was modeled by linking a steady state plume model which gives the vertical variation of mean temperature and velocity of particles inside the plume to a conductive cooling model of pumices which controls diffusion of cl co2 and s in pumice we find that gas loss increases with column height mass flux and initial temperature because in both cases pumices cool over a longer time period allowing more gas to diffuse out of the matrix glass the amount of gas released also depends on the size distribution of particles in the erupting mixture with less being released for a finely skewed distribution

combined use of seviri and modis for detecting measuring and monitoring active lava flows at erupting volcanoes multispectral data acquired by spinning enhanced visible and infrared imager seviri onboard the geostationary platform meteosat second generation msg2 located at 0deg longitude were analyzed to assess the payload suitability for quantitative volcano monitoring in times of good infrared transparency of the troposphere seviri data proved particularly suited to detect the onset of effusive eruptions and to monitor the related lava flows with 15 min refresh rates after development of a code allowing for fast automated processing of the 96 data streams downlinked daily by msg2 thorough monitoring tests were carried out on the 2007 eruptions of stromboli aeolian islands italy and piton de la fournaise reunion island france the results in radiant flux and effusion rate provided by use of thermal mid and short infrared bands of seviri were validated by exploiting simultaneous modis overpasses by terra and aqua up to four times daily

improved space borne detection of volcanic ash for real time monitoring using 3 band method abstract for over 25 years thermal infrared data supplied by satellite based sensors are used to detect and characterize volcanic ash clouds using a commonly accepted method the 2 band reverse absorption technique this method is based on a two channel difference model using the opposite extinction features of water ice and ash particles at 11 and 12 m wavelengths although quite efficient with the supervision of a user this method shows however some limitations for reliable automated detection of volcanic ash in a real time fashion here we explore a method dedicated to the operational monitoring of volcanic ash that combines the 11 12 m brightness temperature difference btd11 12 with a second brightness temperature difference between channels 8 7 m and 11 m btd8 7 11 we first achieve a detailed microphysics analysis of different atmospheric aerosols volcanic ash water ice sulfuric acid mineral dust using optical properties e g extinction efficiency single scattering albedo and asymmetry parameter calculated by mie theory and showing that btd8 7 11 can be particularly efficient to remove most of artifacts then we tested this method for eight different eruptions between 2005 and 2011 from six different volcanoes mount etna piton de la fournaise karthala soufriere hills eyjafjallajokull and grimsvotn using data from the spinning enhanced visible and infrared imager seviri on board meteosat second generation msg geostationary satellite we show that between 95 6 and 99 9 of ash contaminated pixels erroneously identified by the btd11 12 method i e artifacts were detected and removed by the 3 band method for all eruptions the 3 band method shows a high and constant reliability having a false alarm rate in the range 0 002 0 08 hence allowing operational implementation for automated detection in case of a volcanic crisis

estimation of ash injection in the atmosphere by basaltic volcanic plumes the case of the eyjafjallajokull 2010 eruption 1 during explosive eruptions volcanic plumes inject ash into the atmosphere and may severely affect air traffic as illustrated by the 2010 eyjafjallajokull eruption quantitative estimates of ash injection can be deduced from the height reached by the volcanic plume on the basis of scaling laws inferred from models of powerful plinian plumes in less explosive basaltic eruptions there is a partitioning of the magma influx between the atmospheric plume and an effusive lava flow on the ground we link the height reached by the volcanic plume with the rate of ash injection in the atmosphere via a refined plume model that 1 includes a recently developed variable entrainment law and 2 accounts for mass partitioning between ground flow and plume we compute the time evolution of the rate of injection of ash into the atmosphere for the eyjafjallajokull eruption on the basis of satellite thermal images and plume heights and use the dispersion model of the volcanic ash advisory center of toulouse to translate these numbers into hazard maps the classical plinian model would have overestimated ash injection by about 20 relative to the refined estimate which does not jeopardize risk assessment this small error was linked to effective fragmentation by intense interactions of magma with water derived from melting of ice and hence strong mass partitioning into the plume for a less well fragmented basaltic dry eruption the error may reach 1 order of magnitude and hence undermine the prediction of ash dispersion which demonstrates the need to monitor both plume heights and ground flows during an explosive eruption

fine ash content of explosive eruptions abstract in explosive eruptions the mass proportion of ash that is aerodynamically fine enough to cause problems with jet aircraft or human lungs 50

caliop observations of the transport of ash from the eyjafjallajokull volcano in april 2010 1 the cloud aerosol lidar with orthogonal polarization caliop is an elastic backscatter lidar carried on the calipso satellite caliop observations between 15 and 20 april 2010 of volcanic ash plumes following the eruption of the icelandic eyjafjallajokull volcano are reported here while caliop has limited spatial coverage due to nadir only sampling ash plumes were observed by caliop over a wide region from the north atlantic ocean to eastern europe during both day and night due to its nadir only view however caliop did not sample the densest ash plumes which were observed by passive satellite sensors and ground based lidar lidar depolarization and spectral backscatter signatures are used to discriminate ash layers from clouds most ash was observed in thin layers of laminar appearance with thicknesses ranging from 0 4 km to a little more than 1 km and at relatively low altitudes between 1 and 7 km most layers reported here produced strong lidar depolarization indicating a predominance of ash over sulfate aerosol in the plumes estimates of lidar extinction to backscatter ratio allow the retrieval of profiles of ash optical properties layers were observed with mean optical extinction ranging from 0 03 km 1 to nearly 1 km 1 combined with an estimate of mass extinction efficiency mass concentration profiles can also be estimated these observations of the three dimensional dispersion of the plume are complementary to observations from passive satellite instruments and ground based lidars and can be useful for verification of dispersion models such as those used by the volcanic ash advisory centers

the 12 900 years bp laacher see eruption estimation of volatile yields and simulation of their fate in the plume we estimated the volatile emissions of the 12 900 years bp eruption of laacher see volcano germany using a modified petrological method glass inclusions in phenocrysts and matrix glasses sampled over the laacher see tephra profile were analysed by synchrotron x ray fluorescence microprobe and electron microprobe to obtain the emitted masses of halogens sulphur and water these data were used to initialize the numerical plume model atham in order to investigate the fate of volcanic gases in the plume and to estimate volatile masses injected into the stratosphere the scavenging efficiency of each volatile component depends on its interactions with both liquid water and ice we found a scavenging efficiency of c 5 for the sulphur species and of only c 30 for hydrogen halides despite their high water solubility our simulations showed that the greatest fraction of hydrometeors freeze to ice due to the fast plume rise and great height of the eruption column for the dry atmospheric conditions of the laacher see eruption the amount of liquid water was not sufficient to completely scavenge hcl and hbr so that a large proportion could reach the stratosphere

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

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

experimental constraints on the distinct effects of ash lapilli and larger pyroclasts on entrainment and mixing in volcanic plumes the rate at which atmosphere is entrained and mixed into relatively dense explosive volcanic jets of gas and pyroclasts ash lapilli determines whether they rise into the atmosphere as buoyant plumes or collapse to form pyroclastic flows here we use analog experiments on grid stirred turbulence to isolate particle inertial effects related to the motions of ash and lapilli on the quantitative dynamical conditions for the onset of turbulent entrainment and mixing from energetic considerations we estimate the distinct effects of ash and lapilli on the entrainment rate we find that whereas large ash and lapilli sized pyroclasts contribute angular momentum to entraining eddies and may enhance entrainment into volcanic jets by 37 compared to expectations without inertial particles ash is dissipative and may reduce entrainment by 14 we also show that the internal turbulent mixing properties are largely insensitive to particle inertial effects our results predict that highly explosive events involving water or ice should for example feed plumes that rise higher than eruption columns that are enriched in larger pyroclasts although these events are also more likely to produce pyroclastic flows

triassic nb enriched basalts magnesian andesites and adakites of the qiangtang terrane central tibet evidence for metasomatism by slab derived melts in the mantle wedge new chronological geochemical and isotopic data are reported for triassic 219 236 ma adakite magnesian andesite nb enriched basaltic rock associations from the tuotuohe area central qiangtang terrane the adakites and magnesian andesites are characterized by high sr y 25 45 la yb 14 42 and na2o k2o 12 49 ratios high al2o3 15 34 18 28 wt and moderate to high sr concentrations 220 498 ppm and end t 0 86 to 1 21 values low enrichments of th rb relative to nb and subequal normalized nb and la contents and enrichments of light rare earth elements combine to distinguish a group of nb enriched basaltic rocks nebs they have positive end t 2 57 to 5 16 values positive correlations between th la and nb and an absence of negative nb anomalies on mantle normalized plots indicate the nebs are products of a mantle source metasomatized by a slab melt rather than by hydrous fluids a continuous compositional variation between adakites and magnesian andesites confirms slab melt interaction with mantle peridotite the spatial association of the nebs with adakites and magnesian andesites define an adakitic metasomatic volcanic series recognized in many demonstrably subduction related environments e g mindanao arc philippines kamchatka arc russia and southern baja california arc mexico the age of the touhuohe suite and its correlation with triassic neb to the north indicates that volcanism derived from subduction modified mantle was abundant prior to 220 ma in the central qiangtang terrane

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

petrogenesis of adakitic porphyries in an extensional tectonic setting dexing south china implications for the genesis of porphyry copper mineralization the dexing adakitic porphyries quartz diorite granodiorite porphyries associated with giant porphyry cu deposits are located in the interior of a continent south china they exhibit relatively high mgo cr ni and sr contents high la yb and sr y ratios but low yb and y contents similar to adakites produced by slab melting associated with subduction however they are characterized by bulk earth like nd sr isotope compositions end t 1 14 to 1 80 and 87 sr 86 sr i 0 7044 0 7047 and high th 12 6 27 2ppm contents and th ce 0 19 0 94 ratios which are different from those of cenozoic slab derived adakites sensitive high resolution ion microprobe shrimp geochronology studies of zircons reveal that the dexing adakitic porphyries have a crystallization age of 171 3ma this age is contemporaneous with middle jurassic extension within the shi han rift zone and within plate magmatism elsewhere in south china indicating that the dexing adakitic porphyries were probably formed in an extensional tectonic regime in the interior of the continent rather than in an arc setting their high th contents and th ce ratios and middle jurassic age argue against an origin from a neoproterozoic 1000ma stalled slab in the mantle taking into account available data for the regional metamorphic magmatic rocks and the present day crustal thickness 31km in the area we suggest that the dexing adakitic porphyries were most probably generated by partial melting of delaminated lower crust which was possibly triggered by upwelling of the asthenospheric mantle due to the activity of the shi hang rift zone moreover the dexing adakitic magmas must have interacted with the surrounding mantle peridotite during their ascent which elevated not only their mgo cr and ni contents but also the oxygen fugacity fo2 of the mantle the high fo2 could have induced oxidation of metallic sulfides in the mantle and mobilization of chalcophile elements which are required to produce associated cu mineralization therefore the cu metallogenesis associated with the dexing adakitic porphyries is probably related to partial melting of delaminated lower crust similar to the metallogenesis accompanying slab melting

investigation of the complex dynamics and structure of the 2010 eyjafjallajokull volcanic ash cloud using multispectral images and numerical simulations 1 we investigated the structure and evolution of the 2010 eyjafjallajokull volcanic cloud and its dispersal over iceland and europe integrating satellite multispectral images and numerical simulations data acquired by medium resolution imaging spectrometer meris and advanced spaceborne thermal emission and reflection radiometer aster have been analyzed to quantify the cloud extent and composition the vol calpuff dispersal code was applied to reconstruct the transient and 3 d evolution of the cloud source parameters estimated on the base of available a posteriori volcanological data sets have been used quantitative comparisons between satellite retrievals and modeling results were performed for two selected instants of time during the first and third eruptive phases on a regional scale sensitivity of the model to initial volcanological conditions has been analyzed at continental scale several complex non intuitive features of cloud dynamics have been highlighted and strengths and limitations of the adopted methods identified the main findings are the level of quantitative agreement between satellite observations and numerical results depends on ash cloud composition particle sizes and concentration with better agreement for smaller particles and higher concentrations the agreement between observations and modeling outcomes also depends on the temporal stability of volcanological conditions and the complexity of the meteorological wind field the irregular dispersion of ash as reconstructed from satellite data and numerical modeling can be well explained by the different response of particle sizes to strong vertical wind shear and by resuspension processes acting at ground level eruptive source conditions are the main source of uncertainty in modeling especially during an ongoing crisis and at long range scales

on the rise of turbulent plumes quantitative effects of variable entrainment for submarine hydrothermal vents terrestrial and extra terrestrial explosive volcanism 1 the maximum height reached by a turbulent plume rising in a stratified environment is a key tool to estimate the flux released at its source particularly for large scale flows because flux can often be very hard to measure directly this height is known to be mainly controlled by the stratification of the ambient fluid source buoyancy flux and the efficiency of turbulent mixing between the plume and the external fluid the latter effect has been only superficially explored in spite of its fundamental control on the dynamics here we show that commonly used one dimensional models incorporating a constant entrainment coefficient do not provide satisfying predictions we propose a new model allowing for variable entrainment which gives excellent predictions of maximum heights reached by laboratory plumes in stratified environments we then apply our formalism to natural plumes produced by explosive volcanic eruptions under terrestrial paleo martian and venusian conditions and by submarine hydrothermal activity at mid ocean ridges source mass discharge rates deduced from maximum volcanic column heights for terrestrial eruptions are found to be greater than those estimated with the commonly used constant entrainment parameterization by a factor of 2 in the paleo martian atmosphere existing models overestimate plume heights by 14 27 in the current atmosphere of venus the maximum height reached by a volcanic plume is also found to be smaller than previously estimated for large eruption rates the source heat flux released by the tag field atlantic ocean deduced from several submarine hydrothermal plumes is found greater by a factor 3 with our model

discrimination of productive and nonproductive porphyritic intrusions in the chilean andes a geochemical comparison between productive intrusions those associated with mineralization and nonproductive intrusions those unrelated to mineralization has been made on the basis of over 100 fresh granitoid rocks from the chilean porphyry copper belt the study was carried out on the scale of a mining district el salvador potrerillos then on the scale of a single traverse el salvador chilean coast and finally on the scale of the andes itself the productive intrusions are best characterized by large negative anomalies in y mn th and the heavy rare earth elements a discriminant diagram of y against mno is recommended for predicting whether an apparently fresh intrusion has associated peripheral mineralization the low values of y and mn in productive intrusions can be partly explained by the early crystallization of y and mn rich hydrous phases such as hornblende and by the loss of mn rich fluids from the magma the same elements make useful discriminants in other porphyry copper provinces although the exact position of the discriminant boundary varies from island arcs through continental margin to continental settings

volcanic eruption plume top topography and heights as determined from photoclinometric analysis of satellite data photoclinometry a shape from shading technique is applied to satellite data to determine the three dimensional height and morphology of the upper optical surface of a plume from the eruption of redoubt volcano alaska the technique can be applied to visible images of volcanic plumes that have uniform scattering properties and is most effective on images with moderate incident sun angles and plume transport perpendicular to the azimuth of the sun the two most significant sources of error are the finite resolution of the image data and the choice of image data number dn value for a flat plume element provided the plume spans at least 10 image pixels useful results can be obtained for the central portion of the plume the closest approximation to a flat plume element is found to be the visible dn value corresponding to the coldest pixel along a transect errors in the element altitude due to uncertainty in the dn value for a flat pixel amount to 10 20 m per pixel and are cumulative along the plume transect for redoubt this results in an uncertainty of approximately 300 m at the highest points the method indicates that the redoubt plume rose to an altitude of approximately 3 km while traveling a distance of 150 km from the vent and that the surface topography of the plume exhibits influences of the ambient wind through simple wave structures this technique will have a tremendous impact on studies of plume spreading dynamics and the time integrated evolution of plumes

particle recycling in volcanic plumes we have developed a new theoretical model of an eruption column that accounts for the re entrainment of particles as they fall out of the laterally spreading umbrella cloud the model illustrates how the mass flux of particles in the plume may increase with height in the plume by a factor as large as 2 5 because of this recycling three important consequences are that 1 the critical velocity required to generate a buoyant eruption column for a given mass flux increases 2 the total height of rise of the column may decrease and 3 we infer that in relatively wind free environments for eruption columns near the conditions for collapse the recycling of particles may lead to an unsteady oscillating motion of the plume which in time may lead to the formation of interleaved fall and flow deposits

abrupt termination of indian ocean dipole events in response to intraseasonal disturbances 1 we have investigated the role of atmospheric intraseasonal disturbances on termination of the indian ocean dipole iod using multiple datasets we observed significant 30 60 day atmospheric disturbances associated with equatorial westerly zonal winds prior to termination of all iod events except for the 1982 and 1997 events the westerlies excite anomalous downwelling kelvin waves that terminate the basin wide coupled processes by warming the eastern indian ocean the 1982 and 1997 iod events coincide with the strongest el nino events during those years the intraseasonal disturbances are weak

volcanic plume heights on mars limits of validity for convective models 1 previous studies have overestimated volcanic plume heights on mars in this work we demonstrate that volcanic plume rise models as currently formulated have only limited validity in any environment these limits are easily violated in the current mars environment and may also be violated for terrestrial and early mars conditions we indicate some of the shortcomings of the model with emphasis on the limited applicability to current mars conditions specifically basic model assumptions are violated when 1 vertical velocities exceed the speed of sound 2 radial expansion rates exceed the speed of sound 3 radial expansion rates approach or exceed the vertical velocity or 4 plume radius grossly exceeds plume height all of these criteria are violated for the typical mars example given here solutions imply that the convective rise model is only valid to a height of 10 km the reason for the model breakdown is that the current mars atmosphere is not of sufficient density to satisfy the conservation equations it is likely that diffusion and other effects governed by higher order differential equations are important within the first few kilometers of rise when the same criteria are applied to eruptions into a higher density early mars atmosphere we find that eruption rates higher than 1 4 109 kg s also violate model assumptions this implies a maximum extent of 65 km for convective plumes on early mars the estimated plume heights for both current and early mars are significantly lower than those previously predicted in the literature therefore global scale distribution of ash seems implausible

marginal stability of atmospheric eruption columns and pyroclastic flow generation explosive volcanic eruptions frequently generate fall and flow deposits simultaneously which can be attributed to a marginally stable atmospheric column in transitional conditions between the buoyant and collapse regimes this behavior is reproduced by laboratory experiments and numerical simulations ten well documented eruptions are used to test theoretical models of explosive eruptions three types of deposits fall flow and composite deposits made of intercalated flow and fall units are observed in these eruptions estimates of mass discharge rate and initial volatile concentration in the magma are available for each eruptive phase using the simple assumptions that 1 the mass fraction of gas in the mixture is equal to the initial volatile content of magma and 2 jet expansion outside the vent is unconstrained by crater dimensions theoretical predictions are not consistent with the data agreement between data and theory may be achieved by appealing to imperfect degassing of pyroclasts which lowers the gas content of the erupted mixture the effective amount of continuous gas phase carrying pyroclasts in suspension depends on the size distribution of pyroclasts in coarse pyroclast populations a large amount of magmatic gas remains trapped in bubbles within the pyroclasts and is not involved in the bulk volcanic flow a new regime diagram based on estimates of the effective gas content in the erupted mixture allows good agreement with the observations for given mass flux and initial dissolved volatile content changes of the size distribution of pyroclasts may have a strong effect on atmospheric column behavior

explosive volcanic eruptions v observations of plume dynamics during the 1979 soufriere eruption st vincent summary during the 1979 eruption of the soufritre of st vincent west indies a 14min period of explosive activity occurred on april 22 the first three minutes of this activity were filmed five individual explosions formed distinct plumes which fed an eruption column which eventually ascended to a height of over 18 km the ascent velocities of the fronts of these plumes ranged from 8 5 to 61 7m s the half angle of spreading of the plume fronts ranged from 21 5 to 24 one of the plumes was observed to 8 km height and decelerated steadily from 5 1 5 to 23 m s l the main column fed by individual explosions was however observed to accelerate from 8 5 to 58 m s l in the same height interval a theoretical treatment of volcanic plume motion is presented measurements of dimensions velocities and spreading rates from the film are used to estimate plume parameters such as temperature particle content and volume discharge rate of magma from the theoretical relationships these calculations show that the individual plumes became hotter and richer in juvenile ash with time the acceleration of the main eruption column was the result of being fed by increasingly hotter and more ash rich explosions an average volume discharge rate of 12600m3s is estimated from the analysis of the plume motions this value agrees closely with an estimate of discharge rate based on the heat flux required to form an 18 km high column this agreement suggests that theories of convective motions in plumes can be successfully adapted to the volcanic case as long as the effect of hot entrained ash particles is considered

the 1980 eruptions of mount st helens physical and chemical processes in the stratospheric clouds we investigate the physical and chemical properties of the stratospheric clouds produced by the recent eruptions of the mount st helens volcano the large and diverse set of observational data collected in the high altitude plumes of the may 18 may 25 and june 13 1980 eruptions is organized and analyzed for evidence of the processes at work the data are used to guide and constrain detailed model simulations of the volcanic clouds for this purpose a comprehensive one dimensional model of stratospheric sulfate aerosols sulfur precursor gases and volcanic ash and dust is utilized the model accounts for gas phase and condensed phase heterogeneous chemistry in the clouds aerosol nucleation and growth and cloud expansion computational results are given for the time histories of the gaseous species concentrations aerosol size distributions and ash burdens of the eruption clouds the long term buildup of stratospheric aerosols in the northern hemisphere and the persistent effects of injected chlorine and water vapor on stratospheric ozone are also investigated we conclude that so2 water vapor and ash were probably the most important substances injected into the stratosphere by the mount st helens volcano both with respect to their widespread effects on composition and their impact on climate despite the seemingly large magnitude of the mt st helens eruption we also find that the volcano had little influence on the climate 0 05 k surface cooling in the northern hemisphere or on stratospheric ozone 0 2 maximum hemispherical depletion the remaining problems in the field of volcanic cloud physics and chemistry and the requirements for future experimental work are also discussed

reducing discrepancies in ground and satellite observed eruption heights abstract the plume height represents a crucial piece of evidence about an eruption feeding later assessment of its size character and potential impact and feeding real time warnings for aviation and ground based populations there have been many observed discrepancies between different observations of maximum plume height for the same eruption a comparison of maximum daily height estimates of volcanic clouds over indonesia and papua new guinea during 1982 2005 shows marked differences between ground and satellite estimates and a general tendency towards lower height estimates from the ground without improvements in the quality of these estimates reconciled among all available methods warning systems will be less effective than they should be and the world s record of global volcanism will remain hard to quantify examination of particular cases suggests many possible reasons for the discrepancies consideration of the satellite and radar cloud observations for the 1991 pinatubo eruptions shows that marked differences can exist even with apparently good observations the problem can be understood largely as a sampling issue as the most widely reported parameter the maximum cloud height is highly sensitive to the frequency of observation satellite and radar cloud heights also show a pronounced clumping near the height of the tropopause and relative lack of eruptions reaching only the mid troposphere reinforcing the importance of the tropopause in determining the eruption height in convectively unstable environments to reduce the discrepancies between ground and satellite estimates a number of formal collaboration measures between vulcanological meteorological and aviation agencies are suggested

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

influence of particle aggregation on deposition of distal tephra from the may 18 1980 eruption of mount st helens volcano the may 18 1980 eruption of mount st helens msh produced an extensive ashfall deposit in washington idaho and montana with a minumum volume of 0 55 km3 tephra an unusual feature of the deposit is the occurrence of a second thickness maximum 325 km ene of msh near ritzville washington grain size and component abundance analysis of samples along the main dispersal axis indicates that ash in this region is very fine grained mean size 22 m poorly sorted polymodal and rich in glass shards and pumice fragments a computer simulation of ash fallout from an atmospherically dispersed eruption plume was developed to evaluate various hypotheses for the origin of the distal ash characteristics particularly the thickness versus distance relationship the model was constrained by observations of the eruption column height elevation of major ash transport lateral spreading of the eruption plume and atmospheric wind structure in the vicinity of msh results of different simulations indicate that the second thickness maximum cannot be attributed to either decreased wind velocities over central washington or injection of fine ash above the horizontal wind velocity maximum near the tropopause for the model to fit the observed characteristics of the deposit significant particle aggregation of ash finer than 63 m must be invoked the best fit occurs when ash less than 63 m is aggregated into particles several hundred microns in diameter with a settling velocity of 0 35 m s support for this process comes from the observation and collection of fragile ash clusters of similar size which fell at pullman washington during the may 18 eruption sorem 1982 the premature fallout of fine ash as particle aggregates is a fundamental process in the origin of the grain size characteristics variations in component abundances and thickness versus distance relationship of the may 18 msh ash fall deposit

retrieval of tephra size spectra and mass flow rate from c band radar during the 2010 eyjafjallajokull eruption iceland the eruption of the eyjafjallajokull volcano in april may 2010 was continuously monitored by the keflavik c band weather radar the keflavik radar is located at a distance of about 156 km from the volcano vent and it has sensitivity of about 5 dbz at 2 km range resolution over the volcanic area the time series of radar volume data which was available every 5 min is quantitatively analyzed by using the volcanic ash radar retrieval varr technique the latter is a physically based methodology that is applied to estimate ash fall rate and mass concentration within each radar volume the varr methodology is here extended with respect to the previous formulation to provide an approximate estimate of both mean particle diameter and airborne tephra particle size distribution under some assumptions deposited tephra at ground is also extrapolated together with an estimate of the magma mass flow rate mfr at the volcano vent derived from the implementation of the mass continuity equation in the radar reference system the varr based retrievals are compared with those derived from a direct tephra sampling at the ground experimentally carried out in terms of ash grain size and loading during the eyjafjallajokull eruption activity on may 5 7 2010 varr based particle diameter estimates may suggest that a sorting of airborne particles during the downwind transport is taking place without observing aggregation processes during the ash fall varr derived daily ash mass loadings in the period between april 14 and may 10 are also evaluated with respect to integrated ground and model based data in the eyjafjallajokull area varr retrieved mfrs are finally compared with corresponding values obtained from analytical 1 d eruption models using radar estimated plume height and radio sounding wind fields a fairly good agreement is obtained thus opening the exploitation of weather radar retrievals for volcanic eruption quantitative studies and ash dispersion model initialization

an experimental study of the surface thermal signature of hot subaerial isoviscous gravity currents implications for thermal monitoring of lava flows and domes received 22 july 2011 revised 23 november 2011 accepted 23 november 2011 published 7 february 2012 1 management of eruptions requires a knowledge of lava effusion rates for which a safe thermal proxy is often used however this thermal proxy does not take into account the flow dynamics and is basically time independent in order to establish a more robust framework that can link eruption rates and surface thermal signals of lavas measured remotely we investigate the spreading of a hot isoviscous axisymmetric subaerial gravity current injected at constant rate from a point source onto a horizontal substrate we performed laboratory experiments and found that the surface thermal structure became steady after an initial transient we develop a theoretical model for a spreading fluid cooled by radiation and convection at its surface that also predicts a steady thermal regime we show that despite the model s simplicity relative to lava flows it yields the correct order of magnitude for the effusion rate required to produce the radiant flux measured on natural lava flows for typical thermal lava properties and an effusion rate between 0 1 and 10 m 3 s 1 the model predicts a steady radiated heat flux ranging from 10 8 to 10 10 w the assessed effusion rate varies quasi linearly with the steady heat flux with much weaker dependence on the flow viscosity this relationship is valid only after a transient time which scales as the diffusive time ranging from a few days for small basaltic flows to several years for lava domes the thermal proxy appears thus less reliable to follow sharp variations of the effusion rate during an eruption

lava effusion rate definition and measurement a review measurement of effusion rate is a primary objective for studies that model lava flow and magma system dynamics as well as for monitoring efforts during on going eruptions however its exact definition remains a source of confusion and problems occur when comparing volume flux values that are averaged over different time periods or spatial scales or measured using different approaches thus our aims are to 1 define effusion rate terminology and 2 assess the various measurement methods and their results we first distinguish between instantaneous effusion rate and time averaged discharge rate eruption rate is next defined as the total volume of lava emplaced since the beginning of the eruption divided by the time since the eruption began the ultimate extension of this is mean output rate this being the final volume of erupted lava divided by total eruption duration whether these values are total values i e the flux feeding all flow units across the entire flow field or local i e the flux feeding a single active unit within a flow field across which many units are active also needs to be specified no approach is without its problems and all can have large error up to 50 however good agreement between diverse approaches shows that reliable estimates can be made if each approach is applied carefully and takes into account the caveats we detail here there are three important factors to consider and state when measuring giving or using an effusion rate first the time period over which the value was averaged second whether the measurement applies to the entire active flow field or a single lava flow within that field and third the measurement technique and its accompanying assumptions

postsubduction porphyry cu au and epithermal au deposits products of remelting of subduction modified lithosphere porphyry cu mo au and some epithermal au deposits are formed from hydrothermal fluids exsolved from cooling water rich calc alkaline magmas emplaced in volcanoplutonic arcs above subduction zones these magmas originate by partial melting of the metasomatized asthenospheric mantle wedge however there is increasing evidence for the existence of a suite of porphyry cu au and epithermal au deposits related to magmas generated after subduction beneath the arc has ceased associated magmas tend to be mildly alkaline relatively sulfur poor and emplaced as isolated complexes rather than in voluminous volcanoplutonic arcs they are likely formed by remelting of previously subduction modified arc lithosphere triggered by postsubduction lithospheric thickening lithospheric extension or mantle lithosphere delamination metasomatized mantle lithosphere or hydrous lower crustal cumulates residual from first stage arc magmatism contain small amounts of chalcophile and siderophile element rich sulfides and constitute a fertile source for hydrous au rich but relatively sulfur poor magmas during later remelting the recognition that porphyry cu au and related epithermal au systems can also form in postsubduction and collisional tectonic settings expands the range of geological environments and geographical terranes that are prospective for such deposits

experimental constraints on degassing and permeability in volcanic conduit flow this study assesses the effect of decompression rate on two processes that directly influence the behavior of volcanic eruptions degassing and permeability in magmas we studied the degassing of magma with experiments on hydrated natural rhyolitic glass at high pressure and temperature from the data collected we defined and characterized one degassing regime in equilibrium and two regimes in disequilibrium equilibrium bubble growth occurs when the decompression rate is slower than 0 1 mpa s 1 while higher rates cause porosity to deviate rapidly from equilibrium defining the first disequilibrium regime of degassing if the deviation is large enough a critical threshold of super saturation is reached and bubble growth accelerates defining the second disequilibrium regime we studied permeability and bubble coalescence in magma with experiments using the same rhyolitic melt in open degassing conditions under these open conditions we observed that bubbles start to coalesce at 43 vol porosity regardless of decompression rate coalescence profoundly affects bubble texture and size distributions and induces the melt to become permeable we determined coalescence to occur on a time scale 180 s independent of decompression rate we parameterized and incorporated our experimental results into a 1d conduit flow model to explore the implications of our findings on eruptive behavior of rhyolitic melts with low crystal contents stored in the upper crust compared to previous models that assume equilibrium degassing of the melt during ascent the introduction of disequilibrium degassing reduces the deviation from lithostatic pressure by 25 the acceleration at high porosities 50 vol by a factor 5 and the associated decompression rate by an order of magnitude the integration of the time scale of coalescence to the model shows that the transition between explosive and effusive eruptive regimes is sensitive to small variations of the initial magma ascent speed and that flow conditions near fragmentation may significantly be affected by bubble coalescence and gas escape

early cretaceous subduction related adakite like rocks of the gangdese belt southern tibet products of slab melting and subsequent melt peridotite interaction abstract the limited geochronology and geochemistry data available for the early cretaceous igneous rocks of the southern gangdese belt southern tibet has resulted in the proposal of conflicting geodynamic models for the generation of the widespread cretaceous igneous rocks in the middle and northern parts of the belt to explore this issue we present shrimp u pb zircon data and geochemical and sr nd pb hf isotopic data for the mamen andesites from the southern margin of the gangdese belt the mamen andesites emplaced at 136 5 ma are sodic na2o k2o 1 2 2 3 and have geochemical characteristics typical of adakites i e high al2o3 high la yb ratios and sr contents low y and hree contents and positive eu anomalies except for high cr ni and mgo contents the andesites have initial 87sr 86sr t ratios of 0 70413 0 70513 positive end t values of 3 7 5 8 and 206pb 204pb t ratios of 18 37 18 51 207pb 204pb t ratios of 15 59 15 65 and 208pb 204pb t ratios of 38 43 38 72 in situ hf isotopic analyses of zircons that had previously been dated by shrimp yielded positive initial ehf t values ranging from 11 0 to 15 5 a model calculation using trace element and sr nd pb isotopic data indicates that several percent of subducted sediment is required to generate the mamen andesites which were derived via the partial melting of subducted neo tethyan slab morb sediment fluid and subsequently hybridized by peridotite in the mantle wedge our data indicate that the neo tethyan oceanic crust was subducted northward beneath the gangdese belt during the early cretaceous at a high angle our results are inconsistent with a tectonic model that advocates the low angle or flat slab subduction of neo tethyan oceanic crust in generating the widespread cretaceous magmatism recorded in the gangdese belt

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

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

the size distribution of pyroclasts and the fragmentation sequence in explosive volcanic eruptions in an explosive eruption the atmospheric column dynamics depend strongly on the mass fraction of gas in the erupting mixture which is fixed by fragmentation in the volcanic conduit at fragmentation gas present in vesicular magmatic liquid gets partitioned between a continuous phase separating magma clasts and a dispersed phase in individual bubbles within the clasts as regards flow behavior it is the former continuous gas phase which matters and we show that its amount is determined by the fragment size analysis of 25 fall deposits and 37 flow deposits demonstrates that ash and pumice populations follow a power law size distribution such that n the number of fragments with radii larger than r is given by n r d d values range from 2 9 to 3 9 and are always larger than 3 0 in fall deposits d values for pyroclastic flow deposits are systematically smaller than those of fall deposits we show that at fragmentation the amount of continuous gas phase is an increasing function of the d value large d values cannot be attributed to a single fragmentation event and are due to secondary fragmentation processes laboratory experiments on bubbly magma and on solid pumice samples demonstrate that primary breakup leads to d values of 2 5 0 1 and that repeated fragment collisions act to increase the d value a model for size dependent refragmentation accounts for the observations we propose that in a volcanic conduit fragmentation proceeds as a sequence of events primary breakup releases a small amount of gas and is followed by fragment collisions due to refragmentation and decompression both the mass and volume fractions of continuous gas increase the final d value and hence the mass fraction of continuous gas at the vent depends on the time spent between primary fragmentation and eruption out of the vent

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

failures in detecting volcanic ash from a satellite based technique abstract immediate and accurate detection of airborne volcanic ash is an operational imperative of the aviation industry especially jet aircraft ash encounters place passengers aboard these aircraft at severe risk and significantly impact via forced rerouting both the safety and profit margins of freight carriers due to their limited fuel supply moreover the airlines can suffer high economic costs for repair and replacement of equipment operational detection and tracking of volcanic ash by most national weather services has relied heavily on a split window differencing technique of thermal longwave infrared channels on currently operational satellites unfortunately prior work on volcanic ash detection has not emphasized the dynamical interaction between the erupting volcano and the effects of overlying atmospheric water vapor phreatic and phreatomagmatic water sources six volcanic ash eruptions from around the globe were chosen for study because they have wide variation in ambient atmospheric water vapor available ground and surface water and different magma types results show that the present differencing technique is not uniformly effective in properly classifying volcanic ash pixels in the satellite scene and often falsely interprets meteorological clouds as volcanic ash clouds and conversely moreover it is not always a robust early detector an operational aviation requirement seasonal variability in global integrated atmospheric water vapor coupled with the geographical distribution of currently active volcanoes suggests the concerns discussed herein with regard to six specific eruptions have applicability to the global aviation industry operational implications are discussed and a strategic proposal is presented on necessary steps to improve detection

a simple explanation for the space based calculation of lava eruption rates abstract knowing how lava effusion rates vary during basaltic eruptions can be of great significance when trying to provide preliminary forecasts regarding how far lava will flow however problems exist in accurately determining effusion rates using conventional field based techniques to ameliorate this problem harris et al j geophys res 102 1997 7985 8003 bull volcanol 59 1997 49 64 j volcanol geotherm res 102 2000 237 269 developed a method for determining effusion rates using infrared satellite data and showed how the method could be used to provide realistic estimates of effusion rates repeatedly during several eruptions at kilauea hawai i krafla iceland etna and stromboli italy harris et al j geophys res 102 1997 7985 8003 bull volcanol 59 1997 49 64 indicate that their method allows instantaneous lava effusion rates to be determined thermodynamically by equating the amount of heat lost by an active lava flow derived from the satellite data to the amount of heat liberated by the cooling mass of lava the purpose of this paper is to provide a simpler alternative explanation we find that rather than being used to calculate heat loss harris et al j geophys res 102 1997 7985 8003 bull volcanol 59 1997 49 64 j volcanol geotherm res 102 2000 237 269 actually use the satellite data to estimate the area of active lava present within the satellite s field of view at the movement of data acquisition thus changes in the effusion rates they present can only be proportional to changes in this area the active flow areas were then multiplied by a constant the value of which is obtained from a crude approximation of the lava flows heat balance crucially the absolute value of this term falls within the range of an empirically derived parameter that was found by pieri and baloga j volcanol geotherm res 30 1986 29 45 to explain strong linear correlations between eruption rate i e the time averaged effusion rate and lava flow area for 34 historic hawaiian flows as a result we find that the method of harris et al j geophys res 102 1997 7985 8003 does not yield instantaneous effusion rates but instead provides a valid and useful way to estimate average effusion rates i e the eruption rate from measurements of flow area

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

electric potential gradient changes during explosive activity at sakurajima volcano japan we report electric potential gradient measurements carried out at sakurajima volcano in japan during 1 explosions which generated ash plumes 2 steam explosions which produced plumes of condensing gases and 3 periods of ashfall and plume induced acid rainfall sequential positive and negative deviations occurred during explosions which generated ash plumes however no deflections from background were found during steam explosions during periods of ashfall negative electric potential gradients were observed while positive potential gradients occurred during fallout of plume induced acid rain from the same eruption these results suggest that a dipole arrangement of charge develops within plumes such that positive charges dominate in the volcanic gas rich top and negative charges in the following ash rich part of the plume the charge polarity may be reversed for other volcanoes hatakeyama and uchikawa 1952 we suggest that charge is generated by fracto emission donaldson et al 1988 processes probably during magma fragmentation within the vent rather than by frictional effects within the plume

constraints on cooling and degassing of pumice during plinian volcanic eruptions based on model calculations during explosive volcanic eruptions pumice clasts are transported into the atmosphere and their thermal and degassing histories determine how much volatiles are lost syneruptively this process is studied by combining a steady state eruption column model with a model for the cooling and degassing of pumice in the model we investigate the impact of various parameters e g mass eruption rate biot number eruption temperature and geometry on the cooling and degassing of pumice and find that the biot number and the eruption temperature are the most influential during typical risetimes of pumices inside eruption columns 200 300 s those smaller than 0 5 cm in diameter are found to lose little of their volatiles syneruptively and remain in thermal equilibrium with the plume in the case of larger pumices the ratio of the cooling timescale r p 2 where rp is the pumice radius and is the thermal diffusivity to the degassing timescale w 2 d 0 where w is the vesicle wall thickness and d 0 is the species diffusivity controls degassing if this ratio is larger than 50 degassing of the pumice will be nearly complete with a few percent of the original volatiles left in the outer rind of the pumice for a ratio of less than 0 1 no volatiles escape the pumice typical values for thermal and species diffusivity as well as vesicle wall thickness indicate that in the case of degassing cl and h 2 o the transition from 0 1 to 50 will be in the pumice size range of 1 10 cm here volatile concentration is a strong function of position inside the pumice suggesting that values for volatile contents measured on picked matrix glass from crushed samples may not be the best way to estimate the volatile content of matrix glass a number which is frequently used to estimate the total volatile input of volcanic eruptions this effect is even more pronounced when looking at hydrogen isotopic fractionation with larger pumices tending toward d 80

can slab melting be caused by flat subduction slab melting has been suggested as a likely source of adakitic arc magmas i e andesitic and dacitic magmas strongly depleted in y and heavy rare earth elements existing numerical and petrologic models however restrict partial melting to very young 5 ma oceanic crust typically at 60 80 km depth paradoxically most of the known pliocene quaternary adakite occurrences are related to subduction of 10 45 ma lithosphere which should not be able to melt under normal subduction zone thermal gradients we propose an unusual mode of subduction known as flat subduction occurring in 10 of the world s convergent margins that can produce the temperature and pressure conditions necessary for fusion of moderately old oceanic crust of the 10 known flat subduction regions worldwide eight are linked to present or recent 6 ma occurrences of adakitic magmas observations from chile ecuador and costa rica suggest a three stage evolution 1 steep subduction produces a narrow calc alkaline arc typically 300 km from the trench above the asthenospheric wedge 2 once flat subduction begins the lower plate travels several hundred kilometers at nearly the same depth thus remaining in a pressure temperature window allowing slab melting over this broad distance and 3 once flat subduction continues for several million years the asthenospheric wedge disappears and a volcanic gap results as in modern day central chile or peru the proposed hypothesis which reconciles thermal models with geochemical observations has broad implications for the study of arc magmatism and for the thermal evolution of convergent margins

expansion and quenching of vesicular magma fragments in plinian eruptions the conditions of pumice generation in plinian eruptions are studied a physical model describes the behavior of gas bubbles in a magma fragment which is carried upward in a volcanic conduit and an atmospheric eruption column the effects of pressure release and cooling are calculated for a range of eruption conditions the magma fragment expands in the conduit and stops expanding soon after leaving the vent when a thin viscous rind forms against the cold mixture of magmatic gas and air this rind prevents further volume changes pumice vesicularity is a function of the decompression rate in the conduit which depends on ascent velocity and fragmentation depth it is also sensitive to the cooling rate in the atmospheric column which depends on vent radius and mass discharge rate different fragments follow different trajectories in the column and are subjected to different cooling rates this generates a range of vesicularities which reflects the eruptive conditions all else being equal pumice vesicularity increases as magma viscosity decreases these predictions are consistent with observations pumices provide quantitative constraints on conduit flow conditions and mass discharge rate these concepts are applied to two plinian eruptions vesicularity values for the bishop tuff long valley caldera require a mass discharge rate between 108 and 109 kg s 1 vesicularity variations during plinian phase 1 of the minoan eruption santorini are explained by the conduit radius increasing from about 30 m to 120 m both cases require large decompression rates in the eruption conduit suggesting that flow pressures were close to lithostatic values

why were cool sst anomalies absent in the bay of bengal during the 1997 indian ocean dipole event 1 the most important center of atmospheric convection associated with the indian summer monsoon is located in the bay of bengal this tendency was enhanced during the 1997 indian ocean dipole iod event and cool sst anomalies due to upwelling in the east were restricted to the south of about 5 n in the bay however sea surface height anomalies associated with the upwelling propagated all the way to the north bay using xbt data collected in the bay and a high resolution ocean general circulation model simulation we propose that the permanent low salinity highly stratified near surface pool in the bay prevented the iod related upwelling from influencing the sst the strong near surface stratification in the bay cannot be broken down by the observed winds there therefore it ensures that internal ocean dynamics cannot have an impact on sst as a result atmospheric convection over the bay may be decoupled from ocean dynamics

automated monitoring of high temperature volcanic features from high spatial to very high temporal resolution developments in spaceborne earth observation eo sensor technology over the last decade combined with well tested physical models and multispectral data processing techniques developed from the early 1980s have paved the way to the global monitoring of volcanoes by sensors of metric decametric kilometric and multi kilometric spatial resolution such variable geometries provide for revisit intervals ranging from about monthly at high spatial resolution in low earth orbit to less than 5 min at low spatial resolution from geostationary platforms there are currently about 20 spacecrafts available for carrying out 24 7 quantitative observations of volcanic unrest at all resolutions and as close as possible to real time we show some successful examples of synergetic eo on volcanoes on three continents from 10 different payloads automatically processed with three end to end unsupervised procedures on eight major eruptions and a lava lake between 2006 and 2014

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

comments on arc magmatism and subduction history beneath the zagros mountains iran a new report of adakites and geodynamic consequences by j omrani p agard h whitechurch m bennoit g prouteau l jolivet abstract based on the imprecise geochemical data for 62 samples from qom anar and baft regions in central iranian magmatic arc omrani et al omrani j agard p witechurch h benoit m prouteau g jolivet l 2008 arc magmatism and subduction history beneath the zagsros mountains iran a new report of adakites and geodynamic consequences lithos 106 380 398 suggested that all studied magmatic rocks display the geochemical affinity of subduction related calc alkalic rock suites here we demonstrate that the incorrect altered and variable geochemical data e g al 2 o 3 sr y ni cr sio 2 na 2 o la yb and th ce show that most of the samples actually display calc alkaline shoshonitic and calc alkalic adakitic affinities furthermore as a result of alteration rock samples of similar age e g qom indicate both adakitic and non adakitic compositional signatures which is misleading on the basis of more than 400 previously published geochemical analyses we suggest that after eliminating the false geochemical signatures the calc alkaline and adakitic affinities of the central iranian magmatic arc are due to flat subduction and might be related to a second phase of miocene pliocene porphyry copper mineralization which is a considerable exploration target and thus merits further investigation

characterization of aerosols from eruptions of mount st helens measurements of mass concentration and size distribution of aerosols from eruptions of mount st helens as well as morphological and elemental analyses were obtained between 7 april and 7 august 1980 in situ measurements were made in early phreatic and later minor phreatomagmatic eruption clouds near the vent of the volcano and in plumes injected into the stratosphere from the major eruptions of 18 and 25 may the phreatic aerosol was characterized by an essentially monomodal size distribution dominated by silicate particles larger than 10 micrometers in diameter the phreatomagmatic eruption cloud was multimodal the large size mode consisted of silicate particles and the small size modes were made up of mixtures of sulfuric acid and silicate particles the stratospheric aerosol from the main eruption exhibited a characteristic narrow single mode with particles less than 1 micrometer in diameter and nearly all of the mass made up of sulfuric acid droplets

structure and evolution of the passive margin of the eastern tethys abstract an extensive passive margin was formed in the triassic along the periphery of arabia including the tauric carbonate platform this event is related to the opening of the mesozoic tethys when a number of microcontinents split off from gondwana triassic extension and continental rifting resulted in the formation of a structural pattern which is uniform from the dinarides to oman it includes the following elements 1 1 shelf 2 2 continental slope 3 3 deep basin probably with a floor of attenuated sialic crust 4 4 inner carbonate platform in the jurassic cretaceous stable conditions prevailed influenced only by eustatic oscillations of the sea level turbidites accumulated on the continental rise while cherts and radiolarites were deposited in the deep basins hawasina pichakun antalya pindus below the ccd level sedimentation on the shelf was controlled by north northeast transverse tectonic elements which also continued across the passive margin dividing it into a number of segments collision with an island arc led to obduction of the oceanic crust deformation of the passive margin and overthrusting of its sedimentary cover onto the arabian shelf obduction and deformation lasted for about 10 m y and created a new tectonic pattern with concentric structural zones surrounding the arabian promontory these zones include 1 1 the flysch basin a remnant of the closing tethys 2 2 an uplift a site of periodical emergence and erosion corresponding to the frontal part of the ophiolitic nappes 3 3 the border furrow a depocenter of low energy calcareous marls 4 4 the arabian shield constantly emerged during the tertiary tectonic deformation of these zones caused by the collision of arabia with eurasia began prior to the early miocene and it is still going on data on afghanistan demonstrate that its central part the gelmend argandab and kabul blocks belonged during the paleozoic and early mesozoic to the continental shelf of india

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

sensitivity of the dynamics of volcanic eruption columns to their shape this paper presents a one dimensional steady state model to investigate the sensitivity of the dynamics of sustained eruption columns to radius variations with height due to thermal expansion of the entrained air and decreases in atmospheric pressure with height in contrast to a number of previous models using an equation known as the entrainment assumption the new model is based on similarity arguments to derive an equation set equivalent to the model proposed by woods bull volcanol 50 169 193 1988 this approach allows investigation of the effect of gas compressibility on the entrainment rate of ambient air which has been little examined for a system in which a decrease in pressure significantly affects the density stratification of a compressible fluid the new model provides results that include two end members one in which the volume change within the eruption columns affects only the radial expansion without changing the vertical motion and the other is the converse the woods bull volcanol 50 169 193 1988 model can be regarded as being between those two end members the range of uncertainty arises because the extremely high temperature of discharged materials from a volcanic vent and the exceptional terminal height of the eruption columns allow significant expansion of the gas component in the eruption columns making them behave differently from common turbulent plumes this study indicates that the maximum height of the eruption columns is affected considerably by this uncertainty particularly when the eruption columns extend above a height of 10 km at which the pressure is about one fourth the pressure at the ground surface column collapse may also be suppressed in wider parameter ranges than previously estimated however the uncertainty can be reduced by measuring column radii through a vertical profile during actual volcanic eruptions accordingly this paper suggests that appropriate observation of eruption column shapes is essential for improving our understanding of the dynamics of eruption columns

the possible effects of large 19th and 20th century volcanic eruptions on zonal and hemispheric surface temperatures abstract the contribution of volcanic material to the stratosphere from major eruptions within the last two centuries has been estimated using volcanological criteria including eruption type eruption column height volume and duration of eruption and composition and degree of fragmentation of magma the chronology of major explosive volcanic eruptions is compared with a record of mean surface temperature deviation t for the same interval constructed from all available temperature data the temperature records are divided into 6 latitudinal zones allowing analysis for individual zones where temperature changes induced by aerosol perturbation might be intensified we focus on the explosive volcanic events which by our estimates injected the most material into the stratosphere these include tambora 1815 krakatau 1883 santa maria 1902 katmai 1912 and quizapu 1932 such eruptions appear to have produced a consistent but small temperature decrease on the order of 0 2 to 0 5 c on a hemispheric scale for periods ranging from one to five years although these changes are similar to background temperature variations the maximum change in t after some of these explosions appears to lag by up to three years in going from equatorial to polar latitudes somewhat smaller eruptions e g agung 1963 and possibly cosiguina 1835 seem to have produced about the same perturbation in t as the larger eruptions this suggests either a limiting mechanism on loading of the aerosol layer after a volcanic eruption or that the composition of injected material i e the ratio of silicate dust to volatiles and composition of the volatiles may significantly effect stratospheric optical depth perturbation temperatures do not remain depressed for a longer period after a series of closely timed eruptions e g the 1881 1889 or the 1902 1903 sequences than after single events

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