review of holocene glacial chronologies based on radiocarbon dating in tibet and its surrounding mountains a compilation of 53 14c ages on moraines constrains the holocene glacial history of tibet and the surrounding mountains several holocene glacial stages are identified the little ice age had three substages at 1 0 0 13 cal ka bp however the glacial advances may have occurred 200 600 a earlier in southern and eastern bordering mountains than in the northern bordering mountains the earlier glacial advance might have been driven by humid conditions in bordering areas of tibet most glacial advances in the neoglaciation occurred at 3 5 1 4 cal ka bp they can be identified in almost every mountain range an early holocene glacial advance occurred 9 4 8 8 cal ka bp in both central tibet and bordering mountains the timings of holocene glacial advances are synchronous with the cooling periods in the 18o record from ice cores and with the results of optically stimulated luminescence dating and cosmogenic exposure dating in tibet copyright 2008 john wiley sons ltd

late stage groundmass differentiation as a record of magma stagnation fragmentation and rewelding in the 2011 eruption of shinmoedake of the kirishima volcano group sub plinian eruptions were followed by lava extrusion with intermittent vulcanian explosions the interstices of microlites and relatively large nanolites 0 4 nm width in the groundmass of pyroclasts groundmass interstices were studied to reveal shallow magmatic processes that lead to different eruption styles the pumice of the sub plinian eruption has the least differentiated groundmass interstices composition the groundmass interstices of the dense juvenile fragments of the vulcanian explosions are divided into two groups the first group is the most differentiated as expected from their lava like texture whereas the second group is less differentiated and covers the range of sub plinian pumice the vulcanian pumice overlaps the dense juvenile fragments despite their high vesicularity this seemingly contradictory relationship of composition in the interstitial groundmass indicates the clastogenic lava origin of the less differentiated group of dense juvenile fragments in contrast magmas stagnated in the shallow conduit maintained elevated temperature and water content allowing groundmass interstices to differentiate by microlite growth these magmas then erupted as pumice in the vulcanian explosions and were effused as lava that was fragmented by subsequent explosions to be later sampled as a dense juvenile fragment the groundmass crystallinity increased by 9 1 vol in 5 45 days between the sub plinian and vulcanian eruptions increasing initial melt and magma viscosity from 106 1 7 4 and 107 0 8 3 pa s to 106 9 8 4 and 108 2 9 7 pa s respectively this viscosity increase by nanolite crystallization could have facilitated the stress fragmentation of conduit magma leading to vulcanian explosions post fragmentation expansion of the sub plinian pumice could have been suppressed by this viscosity increase resulting in their low vesicularity late stage groundmass differentiation can thus control shallow magmatic processes

oceanic forcing of the marine isotope stage 11 interglacial the interglacial known as marine isotope stage 11 has been proposed to be analogous to the holocene owing to similarities in the amplitudes of orbital forcing it has been difficult to compare the periods however because of the long duration of stage 11 and a lack of detailed knowledge of any extreme climate events that may have occurred here we use the distinctive phasing between seasurface temperatures and the oxygen isotope records of benthic foraminifera in the southeast atlantic ocean to stratigraphically align the holocene interglacial with the first half of the marine isotope stage 11 interglacial optimum this alignment suggests that the second half of marine isotope stage 11 should not be used as a reference for pre anthropogenic greenhouse gas emissions by compiling benthic carbon isotope records from sites in the atlantic ocean on a single timescale we also find that meridional overturning circulation strengthened about 415 000 years ago at a time of high orbital obliquity we propose that this mechanism transported heat to the high northern latitudes inhibiting significant ice sheet build up and prolonging interglacial conditions we suggest that this mechanism may have also prolonged other interglacial periods throughout the past 800 000 years

field based density measurements as tool to identify preeruption dome structure set up and first results from unzen volcano japan for an improvement in the quality of conduit flow and dome related explosive eruption models knowledge of the preeruption or precollapse density of the rocks involved is necessary as close investigation is impossible during eruption the best substitute comes from quantitative investigation of the eruption deposits the porosity of volcanic rocks is of primary importance for the eruptive behaviour and accordingly a key parameter for realistic models of dome stability and conduit flow fortunately this physical property may be accurately determined via density measurements we developed a robust battery powered device for rapid and reliable density measurements of dry rock samples in the field the density of the samples sealed in plastic bags at 250 mbar is determined using the archimedean principle we have tested the device on the deposits of the 1990 1995 eruption of unzen volcano japan short setup and operation times allow up to 60 measurements per day under fieldwork conditions the rapid accumulation of correspondingly large data sets has allowed us to acquire the first statistically significant data set of clast density distribution in block and ash flow deposits more than 1100 samples with a total weight of 2 2 tons were measured the data set demonstrates that the deposits of the last eruptive episode at unzen display a bimodal density distribution with peaks at 2 0 0 1 and 2 3 0 1 g cm3 corresponding to open porosity values of 20 and 8 vol respectively we use this data set to link the results of laboratory based fragmentation experiments to field studies at recently active lava domes

transitions between explosive and effusive eruptions of silicic magmas water rich silicic magmas may erupt explosively giving rise to massive columns of fragmented ash1 5 or effusively as viscous bubbly lavas to form lava domes6 8 complex cycles of explosive and effusive eruptions are often observed8 12 although these two eruption mechanisms have been modelled independently1 8 the conditions under which a volcano exhibits a particular style of eruption are not known and the transitions between eruption styles are poorly understood by modelling the ascent of magma along a permeable conduit we show here that for small magma chamber overpressures the style of eruption explosive or effusive is dependent on the magma flow rate we also identify a critical overpressure above which only explosive eruptions occur complex eruption sequences follow naturally for example if a shallow magmatic system is supplied with magma at an intermediate flow rate the eruption will be slow and effusive until the chamber over pressure becomes too large an explosive eruption then relieves the overpressure and an effusive eruption style resumes we suggest that monitoring of temporal variations in chamber overpressure for example by measuring ground deformation can be used to assess whether a passively effusing volcano has the potential to erupt explosively

the effects of topography on magma chamber deformation models application to mt etna and radar interferometry we have used a three dimensional elastic finite element model to examine the effects of topography on the surface deformation predicted by models of magma chamber deflation we used the topography of mt etna to control the geometry of our model and compared the finite element results to those predicted by an analytical solution for a pressurized sphere in an elastic half space topography has a significant effect on the predicted surface deformation for both displacement profiles and synthetic interferograms not only are the predicted displacement magnitudes significantly different but also the map view patterns of displacement it is possible to match the predicted displacement magnitudes fairly well by adjusting the elevation of a reference surface however the horizontal pattern of deformation is still significantly different thus inversions based on constant elevation reference surfaces may not properly estimate the horizontal position of a magma chamber we have investigated an approach where the elevation of the reference surface varies for each computation point corresponding to topography for vertical displacements and tilts this method provides a good fit to the finite element results and thus may form the basis for an inversion scheme for radial displacements a constant reference elevation provides a better fit to the numerical results

growth process of the lava dome flow complex at sinabung volcano during 2013 2016 abstract mount sinabung north sumatra indonesia erupted for the first time in 2010 and reactivated again in 2013 the eruption started with a phreatic phase changed to phreatomagmatic and then andesite lava appeared at the summit crater in late december 2013 lava effusion continued and has been associated with partial to complete collapses of the lava complex which successively generated pyroclastic density currents pdcs the lava complex grew first as a lava dome and then developed into a lava flow lava extension stage it extended up to about 3 km in horizontal runout distance by late 2014 when the front of the lava complex moved onto the middle and lower slope of the volcano pdc events were initially replaced by simple rock falls inflation of the upper part of the lava complex began in mid 2014 when the movement of the lava flow front stagnated the inflation was associated with hybrid seismic events and frequent partial collapses of the upper part of the lava complex generating pdc events with long travel distances from mid september 2014 new lobes repeatedly appeared near the summit and collapsed cyclic vulcanian events began in august 2015 when hybrid events peaked and continued 1 5 years vulcanian stage these events sometimes triggered pdcs whose deposits contained vesiculated lava fragments the distribution of pdc deposits which extended over time mostly overlapped in areal extent with that of the 9th 10th century eruption eruption volumes were estimated based on measurements with a laser distance meter during 6 periods digital surface model dsm analysis of satellite images during one period and the cumulative number of seismically detected pdc events assuming a constant volume of each pdc event the total volume of eruption products reached about 0 16 km 3 dre as of the end of 2015 the lava discharge rate was largest during the initial stage 7 m 3 s and decreased exponentially over time the discharge rate during the vulcanian stage was 1 m 3 s the trend of decreasing discharge rate is in harmony with that of ground deflation recorded by a gps measurement the chemical composition of lava slightly evolved with time cyclic vulcanian events may have been triggered by limited degassing conditions in the upper conduit and by unloading of the conduit by lava dome collapses

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

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

magma discharge variations during the 2011 eruptions of shinmoe dake volcano japan revealed by geodetic and satellite observations we present precise geodetic and satellite observation based estimations of the erupted volume and discharge rate of magma during the 2011 eruptions of kirishima shinmoe dake volcano japan during these events the type and intensity of eruption drastically changed within a week with three major sub plinian eruptions on january 26 and 27 and a continuous lava extrusion from january 29 to 31 in response to each eruptive event borehole type tiltmeters detected deflation of a magma chamber caused by migration of magma to the surface these measurements enabled us to estimate the geodetic volume change in the magma chamber caused by each eruptive event erupted volumes and discharge rates were constrained during lava extrusion using synthetic aperture radar satellite imaging of lava accumulation inside the summit crater combining the geodetic volume change and the volume of lava extrusion enabled the determination of the erupted volume and discharge rate during each sub plinian event these precise estimates provide important information about magma storage conditions in magma chambers and eruption column dynamics and indicate that the shinmoe dake eruptions occurred in a critical state between explosive and effusive eruption

the mechanism of volcanic eruptions a steady state approach a theory of a volcanic eruption as a steady magma flow from a magma chamber to the surface is described magma is considered as a two component two phase medium and magma flow is steady one dimensional and isothermal mass and momentum exchange between condensed and gaseous phases is assumed to be in equilibrium with nucleation of bubbles as a fast process at small oversaturations three basic flow structures in a conduit are recognized and three resulting types of eruption are described 1 in the discrete gas separation dgs flow melt with discrete gas bubbles erupts this type includes lava eruptions and strombolian activity 2 in the dispersion regime there is continuous eruption of a gas pyroclastic suspension catastrophic explosive eruptions are included in this type 3 here a partly destroyed foam is erupted with permeable structure that allows gas escape near the surface this structure evolves with an increase in permeability and a decrease in the total porosity this type corresponds to lava dome extrusions a criterion dividing dgs flow from the other two regimes is obtained di u n1 3a c0 where u is the magma ascent velocity is magma viscosity n is number of bubble nuclei in a unit mass of magma a is the solubility coefficient for volatiles in magma and c0 is the volatile content the boundary between the dispersion regime and the partly destroyed foam regime depends on u c0 and particle size dp for the dispersion regime the basic governing parameters are magma chamber depth h conduit conductivity b2 b is the characteristic cross dimension of the conduit and excess pressure in the magma chamber instability of the dispersion regime is investigated numerically the dependence of magma discharge rate on the governing parameters is described as a combination of equilibrium surfaces with cusp catastrophes magma chamber depth is a splitting parameter in most cusps and controls the existence of unstable magma flow with sharp regime changes catastrophic rise of eruption intensity is possible if h hcr the critical chamber depth hcr depends approximately linearly on c0 and is about 15 km at c0 0 05 some scenarios of eruption evolution are described in a steady state approximation and the mechanism of catastrophic explosive eruptions is proposed the theory is applied to well documented eruptions tolbachik 1975 1976 and mount st helens 1980 the theory can also describe changes in a volcanic system such as destruction of the conduit or chamber walls destruction of the edifice changes in magma composition and caldera subsidence due to magma evacuation

recent progress of geophysical and geological studies of mt fuji volcano japan abstract mt fuji located in central japan near the triple junction of the philippine sea eurasia or amurian and north american or okhotsk plates is one of the arc volcanoes associated with the subduction of the pacific plate mt fuji has unique features including an average eruption rate in the last 100 000 years of 4 6 km3 ka which is much higher than that of other volcanoes along the same arc 0 01 and 0 1 km3 ka basaltic rocks dominate in mt fuji while other arc volcanoes are dominated by intermediate and felsic compositions and mt fuji has erupted both explosively and effusively with the two largest eruptions in the last 2000 years having different styles the 864 866 ce jogan eruption was effusive while the 1707 hoei eruption the most recent eruption was explosive mt fuji is not only interesting from a scientific point of view but also important from a societal point of view because it is only 100 km from the tokyo metropolitan region one of the biggest cities in the world hosting more than 30 million people the hoei eruption resulted in more than a few tens of millimeters of ashfall in tokyo by more than 150 mm with this background mt fuji has been studied intensively using geological and geophysical methods to understand the evolution magma plumbing system and current activity of the volcano this article synthesizes the current knowledge about mt fuji in particular we provide background information required to understand the jogan and hoei eruptions and discuss how to assess the size timing and style of the next eruption statistical insights suggest that the next eruption of mt fuji is more likely to be voluminous with a long precursor given a repose time of more than 300 years

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

short time scales of magma mixing processes prior to the 2011 eruption of shinmoedake volcano kirishima volcanic group japan we estimated time scales of magma mixing processes just prior to the 2011 sub plinian eruptions of shinmoedake volcano to investigate the mechanisms of the triggering processes of these eruptions the sequence of these eruptions serves as an ideal example to investigate eruption mechanisms because the available geophysical and petrological observations can be combined for interpretation of magmatic processes the eruptive products were mainly phenocryst rich 28 vol andesitic pumice sio2 57 wt with a small amount of more silicic pumice sio2 62 63 wt and banded pumice these pumices were formed by mixing of low temperature mushy silicic magma dacite and high temperature mafic magma basalt or basaltic andesite we calculated the time scales on the basis of zoning analysis of magnetite phenocrysts and diffusion calculations and we compared the derived time scales with those of volcanic inflation deflation observations the magnetite data revealed that a significant mixing process mixing i occurred 0 4 to 3 days before the eruptions pre eruptive mixing and likely triggered the eruptions this mixing process was not accompanied by significant crustal deformation indicating that the process was not accompanied by a significant change in volume of the magma chamber we propose magmatic overturn or melt accumulation within the magma chamber as a possible process a subordinate mixing process mixing ii also occurred only several hours before the eruptions likely during magma ascent syn eruptive mixing however we interpret mafic injection to have begun more than several tens of days prior to mixing i likely occurring with the beginning of the inflation december 2009 the injection did not instantaneously cause an eruption but could have resulted in stable stratified magma layers to form a hybrid andesitic magma mobile layer this hybrid andesite then formed the main eruptive component of the 2011 eruptions of shinmoedake

implications of magma transfer between multiple reservoirs on eruption cycling volcanic eruptions are episodic despite being supplied by melt at a nearly constant rate we used histories of magma efflux and surface deformation to geodetically image magma transfer within the deep crustal plumbing of the soufriere hills volcano on montserrat west indies for three cycles of effusion followed by discrete pauses supply of the system from the deep crust and mantle was continuous during periods of reinitiated high surface efflux magma rose quickly and synchronously from a deflating mid crustal reservoir at about 12 kilometers augmented from depth during repose the lower reservoir refilled from the deep supply with only minor discharge transiting the upper chamber to surface these observations are consistent with a model involving the continuous supply of magma from the deep crust and mantle into a voluminous and compliant mid crustal reservoir episodically valved below a shallow reservoir at about 6 kilometers

non equilibrium processes in ash laden volcanic plumes new insights from 3d multiphase flow simulations abstract in the framework of the iavcei international association of volcanology and chemistry of the earth interior initiative on volcanic plume models intercomparison we discuss three dimensional numerical simulations performed with the multiphase flow model pdac pyroclastic dispersal analysis code the model describes the dynamics of volcanic and atmospheric gases in absence of wind and two pyroclastic phases by adopting a non equilibrium eulerian eulerian formulation accordingly gas and particulate phases are treated as interpenetrating fluids interacting with each other through momentum drag and heat exchange numerical results describe the time wise and spatial evolution of weak mass eruption rate 1 5 106 kg s and strong mass eruption rate 1 5 109 kg s plumes the two tested cases display a remarkably different phenomenology associated with the different roles of atmospheric stratification compressibility and mechanism of buoyancy reversal reflecting in a different structure of the plume of the turbulent eddies and of the atmospheric circulation this also brings about different rates of turbulent mixing and atmospheric air entrainment the adopted multiphase flow model allows to quantify temperature and velocity differences between the gas and particles including settling preferential concentration by turbulence and thermal non equilibrium as a function of their stokes number i e the ratio between their kinetic equilibrium time and the characteristic large eddy turnover time of the turbulent plume as a result the spatial and temporal distribution of coarse ash in the atmosphere significantly differs from that of the fine ash leading to a modification of the plume shape finally three dimensional numerical results have been averaged in time and across horizontal slices in order to obtain a one dimensional picture of the plume in a stationary regime for the weak plume the results are consistent with one dimensional models at least in the buoyant plume region and allow to reckon a variable effective entrainment coefficient with a mean value around 0 1 consistently with laboratory experiments for the strong plume analysis of the results reveals that the two most critical assumptions of one dimensional integral models are the self similarity and the pressure equilibrium in such a case the plume appears to be controlled by the dynamics in the jet stage below the buoyancy reversal and by mesoscale vorticity associated with the development of the umbrella

time lapse monitoring of seismic velocity associated with 2011 shinmoe dake eruption using seismic interferometry an extended kalman filter approach seismic interferometry is a powerful tool to monitor the seismic velocity change associated with volcanic eruptions for the monitoring changes in seismic velocity with environmental origins such

effects of wind on entrainment efficiency in volcanic plumes the entrainment of air by turbulent mixing plays a central role in the dynamics of volcanic eruption clouds as the amount of entrained air controls the height of the plume in one dimensional models of volcanic plumes the efficiency of entrainment under a wind field is parameterized using two empirical constants the first is the coefficient associated with the entrainment caused by the shear between the volcanic plume and the ambient air i e the radial entrainment coefficient and the other is associated with the entrainment caused by wind i e the wind entrainment coefficient in this study we used three dimensional numerical simulations of volcanic plumes to determine the effective values of these empirical constants from the relationship between eruption conditions and plume heights these simulations suggest that the value of the radial entrainment coefficient is 0 05 0 06 which is slightly smaller than that of pure jets or plumes seen in laboratory experiments 0 07 0 15 the value of the wind entrainment coefficient was estimated to be 0 1 0 3 which is significantly smaller than those estimated from laboratory experiments 0 3 1 0 the entrainment coefficients derived from these simulations successfully explain the observations made during the 2011 shinmoe dake eruptions in which the volcanic plumes were significantly distorted by the wind

explosive activity associated with the growth of volcanic domes abstract domes offer unique opportunities to measure or infer the characteristics of magmas that at domes and elsewhere control explosive activity a review of explosive activity associated with historical dome growth shows that 1 1 explosive activity has occurred in close association with nearly all historical dome growth 2 2 whole rock sio 2 content a crude but widely reported indicator of magma viscosity shows no systematic relationship to the timing and character of explosions 3 3 the average rate of dome growth a crude indicator of the rate of supply of magma and volatiles to the near surface enviornment shows no systematic relationship to the timing or character of explosions and 4 4 new studies at arenal and mount st helens suggest that water content is the dominant control on explosions from water rich magmas whereas the crystal content and composition of the interstitial melt and hence magma viscosity are equally or more important controls on explosions from water poor magmas new efforts should be made to improve current rather limited techniques for monitoring pre eruption volatile content and magma viscosity and thus the explosive potential of magmas

conduit processes during the climactic phase of the shinmoe dake 2011 eruption japan insights into intermittent explosive activity and transition in eruption style of andesitic magma abstract the climactic phase of the shinmoe dake 2011 eruption was characterized by sub plinian events january 26 p m 27 a m and 27 p m and lava accumulation in the crater late on january 27 to january 29 all of which were accompanied by vulcanian events the magma discharge rate for lava accumulation was close to that of the sub plinian events we discuss evolution of syneruptive magma ascent through the climactic phase on the basis of decompression induced crystallization of groundmass microlites in order to reveal how the final eruption style was determined at the explosive effusive transition we examined pumice and lava like pyroclasts from three sub plinian events the january 28 vulcanian event and a lava block ballistically ejected during the february 1 vulcanian event the samples exhibit variable groundmass textures due to variable syneruptive ascent conditions not due to pre eruptive inhomogeneity of the andesitic magma and different degrees of syneruptive volatile exsolution preceding quenching eruptive units were first characterized according to bulk density assuming that slower ascent resulted in higher density a decrease in the magma ascent rate led to a gradual shift to an effusive eruption style there was little variation in ascent rate among magmas erupted simultaneously during the first and second sub plinian events bulk density 0 8 2 1 g cm3 but differences increased in the third sub plinian and january 28 vulcanian eruptions with minor appearance of slow magma 0 9 2 8 g cm3 only slow magma occupied the shallow conduit at the completion of lava accumulation february 1 lava 2 1 g cm3 among the first and second sub plinian units the early stage of the second sub plinian event had the greatest variation in ascent rate with extension to a slightly higher bulk density 1 0 2 1 g cm3 than the other events 0 8 1 7 g cm3 ascent rate variations in the early stage of the second sub plinian event the third sub plinian event and the january 28 vulcanian event are all due to the preceding calm phase in the intermittent explosive activity the moving magma column which showed a vertical zonation in the degree of degassing formed in the shallow conduit during the calm phase due to a decrease in the discharge rate and this resulted in the co ejection of magmas with variable degassing upon the start of explosive events the crystal size distribution csd of plagioclase microlites constrains the syneruptive branching i e a point of divergence in ascent rate and eruption style which occurred after the start of microlite crystallization the csds of the different samples show differences only in small crystal sizes slope at these size fractions is smallest for low density 2 0 g cm3 of the january 28 and february 1 events and greatest for high density pyroclasts 2 0 g cm3 of the third sub plinian event we propose based on the similarity in csd that the shallow magma feeding system was common for the two craters active during the january 28 explosive effusive hybrid activity where the vulcanian event and emplacement of lava of the later february 1 event occurred in different parts of the original crater the samples have variable plagioclase microlite number densities 1 4 105 3 5 106 mm 3 based on variations in small crystal sizes among different csds this variability resulted not only from the usual increasing trend in number density with increasing degree of undercooling but also the decreasing trend associated with the strong undercooling during explosive eruptions

evidence of a shallow persistent magmatic reservoir from joint inversion of gravity and ground deformation data the 25 26 october 2013 etna lava fountaining event

three dimensional resistivity structure and magma plumbing system of the kirishima volcanoes as inferred from broadband magnetotelluric data broadband magnetotelluric mt measurements were conducted in 2010 and 2011 in the vicinity of shinmoe dake volcano in the kirishima volcano group japan where sub plinian eruptions took place 3 times during 26 27 january 2011 by combining the new observations with previous mt data it is found that an anomalous phase in excess of 90 is commonly observed in the northern sector of the kirishima volcano group because the anomalous phase is not explained by 1 d or 2 d structure with isotropic resistivity media 3 d inversions were performed by applying small errors to the anomalous phase we successfully estimated a 3 d resistivity structure that explains not only the normal data but also the anomalous phase data the final model shows a vertical conductor that is located between a deep seated conductive body at a depth greater than 10 km and a shallow conductive layer by applying the findings of geophysical and petrological studies of the 2011 sub plinian eruptions we infer that the subvertical conductor represents a zone of hydrothermal aqueous fluids at temperatures over 400 c in which a magma pathway interconnected melt is partially and occasionally formed before magmatic eruptions to the north of the deep conductor earthquake swarms occurred from 1968 to 1969 suggesting that these earthquakes were caused by volcanic fluids

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

viscoelastic crustal response to magma supply and discharge in the upper crust implications for the uplift of the aira caldera before and after the 1914 eruption of the sakurajima volcano abstract crustal viscoelasticity is expected to influence volcano deformation as the crustal viscosity at volcanoes is lowered from regional values by higher crustal temperatures and the eventual presence of magma in this study we examine viscoelastic crustal response to continuous magma supply into and sudden discharge from a sill emplaced in the upper crust using a three dimensional 3 d finite element model composed of an elastic layer underlain by a linear maxwell viscoelastic layer with spatially uniform viscosity we find that viscoelastic response to sill deflation due to magma discharge is an important driving force for post eruption surface displacement influenced both by how much viscoelastic relaxation occurs in response to sill inflation due to magma supply in the pre eruption period and by the amount of co eruptive sill deflation following an eruption the surface elevation is always recovered later than the sill volume because the viscoelastic response to the sill inflation detracts from the uplift we apply this viscoelastic model to geodetic observations in the aira caldera southern kyushu japan over a time span of more than 100 yr it is found that a sill emplacement with constant inflation rate can well explain the observed first order exponential like surface recovery after the 1914 eruption until 1975 if the effective crustal viscosity is 5 10 18 pa s the sill emplacement with an equatorial radius of 2 km occurs at a depth of 11 km and the sill is deflated by 0 4 km3 during the 1914 eruption 4 times less than the eruptive volume the sill emplacement is also required to have begun 50 yr before the 1914 eruption with a constant inflation rate of 0 009 km3 yr in the post eruption period the accumulation of magma in the sill during the first 50 yr is lower than that estimated by an elastic model but larger thereafter it is necessary to introduce temporal variation of the inflation rate for higher order improved fitting to the geodetic data after 1975 our results suggest that geodetic signals observed before and after magma discharge due to an eruption need to be revisited considering the effects of crustal viscoelasticity

effects of gas escape and crystallization on the complexity of conduit flow dynamics during lava dome eruptions 1 we investigated the coupled effects of gas escape and crystallization on the dynamics of lava dome eruptions using a one dimensional conduit flow model the relationship between chamber pressure pch and mass flow rate q for steady conduit flow commonly has a regime of negative differential resistance i e dpch dq 0 5 feedback 1 is the main mechanism that forms negative differential resistance in this case the transition from lava dome to explosive eruption occurs when the magma supply rate exceeds a fixed critical value for low phenocryst content magma volume fraction 0 5 feedback 2 plays a key role so that the transition is controlled by the permeability of the surrounding rocks the critical magma supply rate remarkably decreases with decreasing permeability transition due to feedback 2 is associated with a change in the chemical composition of volcanic gas a drastic increase in magma porosity from nearly 0 to greater than 0 8 and overpressure at a shallower level which can be detected from geochemical and geophysical field observations

inter comparison of three dimensional models of volcanic plumes abstract we performed an inter comparison study of three dimensional models of volcanic plumes a set of common volcanological input parameters and meteorological conditions were provided for two kinds of eruptions representing a weak and a strong eruption column from the different models we compared the maximum plume height neutral buoyancy level where plume density equals that of the atmosphere and level of maximum radial spreading of the umbrella cloud we also compared the vertical profiles of eruption column properties integrated across cross sections of the plume integral variables although the models use different numerical procedures and treatments of subgrid turbulence and particle dynamics the inter comparison shows qualitatively consistent results in the weak plume case mass eruption rate 1 5 106 kg s 1 the vertical profiles of plume properties e g vertical velocity temperature are similar among models especially in the buoyant plume region variability among the simulated maximum heights is 20 whereas neutral buoyancy level and level of maximum radial spreading vary by 10 time averaging of the three dimensional 3d flow fields indicates an effective entrainment coefficient around 0 1 in the buoyant plume region with much lower values in the jet region which is consistent with findings of small scale laboratory experiments on the other hand the strong plume case mass eruption rate 1 5 109 kg s 1 shows greater variability in the vertical plume profiles predicted by the different models our analysis suggests that the unstable flow dynamics in the strong plume enhances differences in the formulation and numerical solution of the models this is especially evident in the overshooting top of the plume which extends a significant portion 1 8 of the maximum plume height nonetheless overall variability in the spreading level and neutral buoyancy level is 20 whereas that of maximum height is 10 this inter comparison study has highlighted the different capabilities of 3d volcanic plume models and identified key features of weak and strong plumes including the roles of jet stability entrainment efficiency and particle non equilibrium which deserve future investigation in field laboratory and numerical studies

vesicle connectivity in pyroclasts and implications for the fluidisation of fountain collapse pyroclastic flows montserrat west indies abstract pyroclastic flows are noted for their highly mobile behaviour being able to flow on slopes as low as a few degrees and this has been attributed to fluidisation or partial fluidisation by escaping gases the three types of pyroclastic flows generated during the eruption of soufriere hills volcano on montserrat dome collapse fountain collapse and surge derived differ in their apparent mobility suggesting different degrees of fluidisation and friction reduction in the flowing granular materials several possible sources of fluidising gas operate in pyroclastic flows the purpose of this paper is to assess the feasibility of one mechanism the release during flow of pressurised gases trapped in the vesicles of juvenile clasts measurements with a helium pycnometer show that all vesicles in dense lava blocks from dome collapse pyroclastic flows are connected so that the mechanism is probably not viable for such flows on the other hand pumices from fountain collapse pyroclastic flows from soufriere hills and other volcanoes contain up to 10 vol of isolated vesicles this is confirmed by sem imagery which shows that soufriere hills pumices contain two vesicle populations with a bimodal size distribution the large vesicles are mostly interconnected whereas about two thirds of the smaller population

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

numerical determination of the efficiency of entrainment in volcanic eruption columns 1 entrainment of air by turbulent mixing plays a central role in the dynamics of eruption clouds the amount of entrained air controls eruption styles and heights of eruption columns the efficiency of entrainment is quantified by the entrainment coefficient the ratio between mean inward radial velocity at the edge and the mean vertical velocity we directly determined the entrainment coefficient of eruption columns as a function of height on the basis of three dimensional numerical simulations the value of entrainment coefficient is similar to that for pure jets 0 07 just above the vent and approaches that for pure plumes 0 10 0 15 far from the vent between these two regions we identify a new transitional zone with a significantly small entrainment coefficient 0 05 this spatial variation in the entrainment coefficient is correlated with the change in vortical structure accompanying the addition of off source buoyancy in the transitional zone

constraining tephra dispersion and deposition from three subplinian explosions in 2011 at shinmoedake volcano kyushu japan constraining physical parameters of tephra dispersion and deposition from explosive volcanic eruptions is a significant challenge because of both the complexity of the relationship between tephra distribution and distance from the vent and the difficulties associated with direct and comprehensive real time observations three andesitic subplinian explosions in january 2011 at shinmoedake volcano japan are used as a case study to validate selected empirical and theoretical models using observations and field data tephra volumes are estimated using relationships between dispersal area and tephra thickness or mass area a new cubic b spline interpolation method is also examined magma discharge rate is estimated using theoretical plume models incorporating the effect of wind results are consistent with observed plume heights 6 4 7 3 km above the vent and eruption durations estimated tephra volumes were 15 34 106 m3 for explosions on the afternoon of 26 january and morning of 27 january and 5 0 7 6 106 m3 for the afternoon of 27 january magma discharge rates were in the range 1 2 106 kg s for all three explosions clast dispersal models estimated plume height at 7 1 1 km above the vent for each explosion the three subplinian explosions occurred with approximately 12 h reposes and had similar mass discharge rates and plume heights but decreasing erupted magma volumes and durations

a retrospective analysis of the shinmoedake japan eruption of 26 27 january 2011 by means of japanese geostationary satellite data abstract during the sub plinian eruptions of mt shinmoedake japan on 26 27 january 2011 a significant amount of ash was emitted into the atmosphere destroying thousands of hectares of farm land causing air traffic disruption and forcing the closure of four railroad lines located around the volcano in this work a retrospective analysis of these eruptive events is presented exploiting the high temporal resolution of the japanese multi functional transport satellites mtsat data to study thermal volcanic activity to identify and track volcanic ash and to determine the cloud top height inferring information about eruption features and space time evolution we show that a strong and sudden increase in the thermal signal occurred at mt shinmoedake as a consequence of above mentioned eruptive events generating hot spots timely detected by the rst volc algorithm for the first time implemented here on data provided by geostationary satellites this study also shows that the emitted ash plume identified by means of the rst ash algorithm strongly fluctuated in altitude reaching a maximum height around 7 4 km above sea level in agreement with information provided by the tokyo vaac the plume heights derived in this work by implementing the widely accepted cloud top temperature method appear also compatible with the values provided by independent weather radar measurements with the main differences characterizing the third sub plinian event that occurred in the afternoon of 27 january the estimates of discharge rate the temporal trend of ash affected areas and the results of thermal monitoring reported in this work seem to indicate that the third sub plinian event was the least intense in spite of some limitations this study confirms the potential of japanese geostationary satellites in effectively monitoring volcanoes located in the west pacific region providing continuous information also about such critical parameters of ash clouds as the plume height such information is useful not only for driving numerical models forecasting ash dispersion into the atmosphere but also for characterizing eruption features and dynamics

seismic and infrasonic eruption tremors and their relation to magma discharge rate a case study for sub plinian events in the 2011 eruption of shinmoe dake japan

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