gas evolution in eruptive conduits combining insights from high temperature and pressure decompression experiments with steady state flow modeling abstract in this paper we examine the consequences of bubble nucleation mechanism on eruptive degassing of rhyolite magma we use the results of published high temperature and pressure decompression experiments as input to a modified version of conflow the numerical model of mastin and ghiorso 2000 u s g s open file rep 00 209 53 pp and mastin 2002 geochem geophys geosyst 3 10 1029 2001gc000192 for steady two phase flow in vertical conduits synthesis of the available experimental data shows that heterogeneous nucleation is triggered at p 120 150 mpa and leads to disequilibrium degassing at extreme h2o supersaturation in this latter case nucleation is an ongoing process controlled by changing supersaturation conditions exponential bubble size distributions are often produced with number densities of 106 109 bubbles cm3 our numerical analysis adopts an end member approach that specifically compares equilibrium degassing with delayed disequilibrium degassing characteristic of homogeneously nucleating systems the disequilibrium simulations show that delaying nucleation until p 150 mpa restricts degassing to within 1500 m of the surface fragmentation occurs at similar porosity in both the disequilibrium and equilibrium modes 80 vol but at the distinct depths of 500 m and 2300 m respectively the vesiculation delay leads to higher pressures at equivalent depths in the conduit and the mass flux and exit pressure are each higher by a factor of 2 0 residual water contents in the melt reaching the vent are between 0 5 and 1 0 wt roughly twice that of the equilibrium model

rapid circulation of warm subtropical waters in a major glacial fjord in east greenland the recent rapid increase in mass loss from the greenland ice sheet is primarily attributed to an acceleration of outlet glaciers oceanographic data obtained in summer 2008 show that subtropical waters that reside year round in the shelf ocean off greenland continuously enter a large glacial fjord in east greenland and contribute to melting at the glacier terminus the recent rapid increase in mass loss from the greenland ice sheet1 2 is primarily attributed to an acceleration of outlet glaciers3 4 5 one possible cause of this acceleration is increased melting at the ice ocean interface6 7 driven by the synchronous warming8 9 10 of subtropical waters offshore of greenland however because of the lack of observations from greenland s glacial fjords and our limited understanding of their dynamics this hypothesis is largely untested here we present oceanographic data collected in sermilik fjord east greenland by ship in summer 2008 and from moorings our data reveal the presence of subtropical waters throughout the fjord these waters are continuously replenished through a wind driven exchange with the shelf where they are present all year the temperature and renewal of these waters indicate that they currently cause enhanced submarine melting at the glacier terminus key controls on the melting rate are the volume and properties of the subtropical waters on the shelf and the patterns of along shore winds suggesting that the glaciers acceleration has been triggered by a combination of atmospheric and oceanic changes our measurements provide evidence for a rapid advective pathway for the transmission of oceanic variability to the ice sheet margins

conduit enlargement during the precursory plinian eruption of aira caldera japan increase in magma flux as the result of conduit enlargement is one of the key processes that triggered caldera collapse and eruption of the ito ignimbrite from aira caldera at 29 ka we examine the total volume of the pumice fall deposit vertical variations in grain size of pumice and the lithic content in the osumi pumice deposit to investigate the trigger for caldera collapse wider distribution of the later stage unit and the upward coarsening of grain size throughout the osumi pumice fall deposit indicate an increase in magma discharge toward the onset of collapse the total volume of lithic fragments in the osumi pumice fall deposit is estimated as 1 6 km3 based on the lithic content in several representative outcrops and the total volume of the osumi pumice fall deposit the lithic fragments in the osumi pumice fall deposit indicate intense mechanical erosion of the conduit during the plinian eruption prior to caldera collapse caldera collapse requires decompression of the magma chamber by withdrawal of magma effective enlargement of the conduit diameter during precursory eruptive phases is one of the important processes that subsequently allow the rapid discharge of a large volume of magma which in turn facilitates decompression of the reservoir and induces caldera collapse

volcanic conduit controls on effusive explosive transitions and the 2010 eruption of merapi volcano indonesia abstract individual volcanoes can produce both effusive and explosive eruptions a transition between these two eruption styles dramatically changes the hazards and can occur either between distinct eruption events or within one eruption episode the causes of these transitions are difficult to determine due to the number of system parameters that can influence whether or not magma fragments in a runaway process we apply a numerical model of magma ascent in a volcanic conduit to isolate and test the effects of key parameters related to magma rheology and system geometry we find that for a given volcanic system parameters that control magma viscosity such as initial water mass fraction initial crystal volume fraction and temperature have the greatest influence on whether or not magma fragments during ascent and erupts explosively we also define a critical condition for the full set of initial parameters under which a transition in eruption style from effusive to explosive or the reverse is more likely to occur under these conditions small heterogeneities in the water or crystal content of the magma or small perturbations to the conduit pressure gradient due to magma chamber overpressure or dome growth or collapse can disrupt the magmatic conditions and cause a transition in eruption style the 2010 vei 4 eruption of merapi volcano included both effusive and explosive phases and was larger by an order of magnitude than its eruptions during the previous century we constrain our model for the merapi system using published literature values and show that between the previous eruption in 2006 and the 2010 eruption the shallow magmatic system at merapi reached critical conditions due to the ascent from depth of a large hotter more volatile rich magma under these critical conditions and according to our model results small changes in the volatile content of the magma small dome collapses subtle changes in degassing rate or the addition of co2 to the magma through decarbonation of the bedrock are all feasible mechanisms for triggering rapid transitions between effusive and explosive activity during the 2010 eruption period

dynamics of magma flow in volcanic conduits with variable fragmentation efficiency and nonequilibrium pumice degassing numerical models of volcanic conduit dynamics assume that the foamy structure of magma is totally destroyed at fragmentation neglecting the presence of vesicular fragments in the above gas particle flow region the abundance of pumice among the volcanic pyroclasts is however the outstanding evidence that such a complete atomization assumption is an oversimplification the present one dimensional multiphase nonequilibrium magma ascent modeling rejects such an assumption taking into account the presence of pumice ash and loose crystals in the turbulent flow region above fragmentation a parametric study is conducted on the role of pumice abundance related to a fragmentation efficiency parameter in affecting the magma ascent dynamics additionally different hypotheses on pumice degassing behavior are evaluated the numerical results show that the presence of even relatively small amounts of pumice translates into a large decrease of continuous gas volume fraction while other flow quantities are mainly affected by the efficiency of pumice degassing a decreased degassing efficiency translates into significant velocity and pressure decrease mixture density increase and further gas volume fraction decrease that overall result in a decrease of the mechanical energy content of the erupted magma by an amount comparable to that due to water content decrease by several weight percent postprocessing of numerical results based on the dynamics of porous flow of gas in pumice allows one to relate the efficiency of pumice degassing to a measurable pumice texture parameter namely the degree of gas bubble coalescence which is therefore identified as a major factor affecting the ascent dynamics of silicic magma

non newtonian rheology of igneous melts at high stresses and strain rates experimental results for rhyolite andesite basalt and nephelinite the stress strain rate relationships of four silicate melt compositions high silica rhyolite andesite tholeiitic basalt and nephelinite have been studied using the fiber elongation method measurements were conducted in a stress range of 10 400 mpa and a strain rate range of 10 6 to 10 3 s 1 the stress strain rate relationships for all the melts exhibit newtonian behavior at low strain rates but non newtonian nonlinear stress strain rate behavior at higher strain rates with strain rate increasing faster than the applied stress the decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt the decrease in viscosity observed at the high strain rates of the present study ranges from 0 25 to 2 54 log10 pa s the shear relaxation times of these melts have been estimated from the low strain rate newtonian shear viscosity using the maxwell relationship s g non newtonian shear viscosity is observed at strain rates time 1 equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time brittle failure of the fibers occurs 2 log10 units of time above the relaxation time this study illustrates that the occurrence of non newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate high silica rhyolite melts involved in ash flow eruptions are expected to undergo a non newtonian phase of deformation immediately prior to brittle failure

forensic recovery of transient eruption parameters for the 2360 bp fall deposit mount meager british columbia abstract the 2360 bp eruption of mount meager canada featured an explosive subplinian onset resulting in dacitic fallout tephra and associated pumiceous pyroclastic flow deposits followed by the effusion of dacite lava and the deposition of a thick sequence of block and ash flow deposits fall deposits are distributed to the ne of the vent onto a rugged deeply incised landscape the central axis of deposition is 063 az the lateral margins of the fall deposit are massive to unbedded whereas deposits underlying the plume axis feature complex bedding relationships we present componentry and granulometry data for eight outcroppings of the fall deposit four on plume axis and four off plume axis vertical cross sections based on surface outcrops and drill core logs from local commercial drilling programs are used to relate the accessory lithics to their source depth in the underlying subvolcanic basement these combined datasets inform on the dynamics of this explosive phase of the eruption including variations in column height eruption intensity atmospheric conditions and depth to fragmentation front the lateral variations within the fall strata reflect the effects of the prevailing atmospheric conditions on the form and dispersal pattern of the subplinian plume vertical variations in granulometry and componentry of the fall deposits are used to track temporal changes in eruption intensity and column height and the transient influence of the jetstream on the dispersal pattern of the plume lastly vertical variations in lithic componentry combined with our knowledge of the subsurface geology are used to quantitatively track the deepening of the fragmentation front our computed results show that the fragmentation front migrated from 640 m to 1160 m below the vent over the course of the 2360 bp mount meager eruption

rheology of bubble bearing magmas the rheology of bubble bearing suspensions is investigated through a series of three dimensional boundary integral calculations in which the effects of bubble deformation volume fraction and shear rate are considered the behaviour of bubbles in viscous flows is characterized by the capillary number ca the ratio of viscous shear stresses that promote deformation to surface tension stresses that resist bubble deformation estimates of ca in natural lava flows are highly variable reflecting variations in shear rate and melt viscosity in the low capillary number limit e g in carbonatite flows bubbles remain spherical and may contribute greater shear stress to the suspension than in high capillary number flows in which bubble deformation is significant at higher ca deformed bubbles become aligned in the direction of flow and as a result contribute less shear stress to the suspension calculations indicate that the effective shear viscosity of bubbly suspensions at least for ca 0 5 is a weakly increasing function of volume fraction and that suspensions of bubbles are shear thinning field observations and qualitative arguments however suggest that for sufficiently large ca ca greater than about 1 the effective shear viscosity may be less than that of the suspending liquid bubbles reach their quasi steady deformed shapes after strains of order one for shorter times the continuous deformation of the bubbles results in continual changes of rheological properties in particular for small strains the effective shear viscosity of the suspension may be less than that of the liquid phase even for small ca results of this study may help explain previous experimental theoretical and field based observations regarding the effects of bubbles on flow rheology

sub sample time shift and horizontal displacement measurements using phase correlation method in time lapse seismic hydrocarbon production and fluid injection affect the level of subsurface stress and physical properties of the subsurface and can cause reservoir related issues such as compaction and subsidence monitoring of oil and gas reservoirs is therefore crucial time lapse seismic is used to monitor reservoirs and provide evidence of saturation and pressure changes within the reservoir however relative to background velocities and reflector depths the time lapse changes in velocity and geomechanical properties are typically small between consecutive surveys these changes can be measured by using apparent displacement between migrated images obtained from recorded data of multiple time lapse surveys apparent displacement measurements by using the classical cross correlation method are poorly resolved here we propose the use of a phase correlation method which has been developed in satellite imaging for sub pixel registration of the images to overcome the limitations of cross correlation phase correlation provides both vertical and horizontal displacements with a much better resolution after testing the method on synthetic data we apply it to a real dataset from the norne oil field and show that the phase correlation method can indeed provide better resolution

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

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

relating vesicle shapes in pyroclasts to eruption styles vesicles in pyroclasts provide a direct record of conduit conditions during explosive volcanic eruptions although their numbers and sizes are used routinely to infer aspects of eruption dynamics vesicle shape remains an underutilized parameter we have quantified vesicle shapes in pyroclasts from fall deposits of seven explosive eruptions of different styles using the dimensionless shape factor omega a measure of the degree of complexity of the bounding surface of an object for each of the seven eruptions we have also estimated the capillary number ca from the magma expansion velocity through coupled diffusive bubble growth and conduit flow modeling we find that omega is smaller for eruptions with rm ca ll 1 than for eruptions with ca gg 1 consistent with previous studies we interpret these results as an expression of the relative importance of structural changes during magma decompression and bubble growth such as coalescence and shape relaxation of bubbles by capillary stresses among the samples analyzed strombolian and hawaiian fire fountain eruptions have rm ca ll 1 in contrast to vulcanian plinian and ultraplinian eruptions interestingly the basaltic plinian eruptions of tarawera volcano new zealand in 1886 and mt etna italy in 122 bc for which the cause of intense explosive activity has been controversial are also characterized by rm ca gg 1 and larger values of omega than strombolian and hawaiian style fire fountain eruptions we interpret this to be the consequence of syn eruptive magma crystallization resulting in high magma viscosity and reduced rates of bubble growth our model results indicate that during these basaltic plinian eruptions buildup of bubble overpressure resulted in brittle magma fragmentation

bubble deformation in magma under transient flow conditions abstract we investigate the transient behavior of bubble deformation in magma previous studies have used the relationships between capillary number and equilibrium shape for a single bubble under either steady simple shear or steady pure shear to estimate strain rates in pyroclasts and to calculate bubble shapes in a conduit flow we developed a deformation model for a bubble by adjusting the empirical functions used in an existing model for a droplet to fit experimental data for bubble deformation the modified model was used to calculate transient large deformations of a single bubble in arbitrary shear flows in this paper we demonstrate the significance of the modified model through two different applications firstly using this model we are able to simulate the entire history of the evolution of bubble shapes in a time dependent flow using the computational code conflow in this simulation we further include the effect of gas expansion on the bubble shape from this simulation we show that bubble deformation in conduit flow is controlled by the history of both capillary number and strain secondly by using this model to analyze bubble shapes observed in natural magma samples we are able to better estimate the strain rates and deformation durations we apply this model to certain transient features in the relationship between bubble shape and radius in the published data of obsidian clasts from newberry volcano and estimate a deformation duration of 2 7 4 0 min

extraction of crystal poor rhyolite from a hornblende bearing intermediate mush a case study of the caldera forming matahina eruption okataina volcanic complex the matahina ignimbrite 160 km3 rhyolite magma 330 ka was deposited during a caldera forming eruption from the okataina volcanic centre taupo volcanic zone tvz new zealand juvenile clasts are divided into three groups group 1 the dominant crystal poor rhyolite type group 2 a minor coarse grained mingled mixed intermediate type and group 3 a rare fine grained basalt the ignimbrite consists of the group 1 type and is divided into three members a lower and middle member which is high silica crystal poor 10 vol rhyolite and the upper member which is low silica and slightly more crystal rich up to 21 vol cognate crystal rich up to 50 vol basalt to intermediate pumice occurs on top of lag breccias and within lithic rich pyroclastic density current deposits along the caldera margin groups 2 and 3 several lines of evidence indicate that the intermediate clasts represent the cumulate complement to the melt rich rhyolite 1 continuity in the compositions of plagioclase orthopyroxene hornblende and oxides and normal zoning of individual phenocrysts 2 the silicic glass from the intermediate magma interstitial melt overlaps compositionally with the bulk rock rhyolite and glass 3 high zr and a slight positive eu anomaly in the intermediate magma relative to quenched enclaves from other intermediate tvz eruptions indicates zircon and plagioclase accumulation respectively 4 an increase in the cl contents in glass from the least evolved to most evolved is consistent with the concentration of volatiles during magma evolution most of the compositional variations in the low to high silica rhyolites can be accounted for by continued rayleigh fractionation up to 15 following melt extraction from the underlying mush under varying fo2 fh2o conditions to form a slightly compositionally zoned rhyolitic cap this link to the varying fo2 fh2o conditions is evidenced by the strong correlation between key geochemical parameters e g dy y that qualitatively reflect fh2o conditions presence or absence of hornblende biotite and fo2 estimated from fe ti oxide equilibrium magma mingling mixing between the basalt andesite and the main slightly compositionally zoned rhyolitic magma occurred during caldera collapse modifying the least evolved rhyolite at the lower portion of the reservoir and effectively destroying any pre eruptive gradients

experimental study of analogue vent erosion towards nozzle shapes abstract volcanic vent shapes evolve over the course of an explosive eruption as the high pressure ejecta erode the solid conduit walls the changing shape affects the fluid behavior of the expelled gases potentially the plume rise column collapse and the type and amount of accidental debris ejected field observations of evolving vent shape are difficult or impossible while the mechanics of this process have been studied numerically almost no laboratory studies have examined these behaviors thus a series of test samples was manufactured using 3d printing techniques which were eroded using high pressure compressed air four material combinations were considered using stainless steel and alumina powders consolidated with binder concentrations of 16 and 38 material properties were evaluated using compression testing while the erosion behavior was studied through high speed visualization and pressure measurements with identical samples at constant inflow conditions in all cases the erosion showed an initial rapid erosion of the vent exit followed by quasi steady state conditions all samples produced converging diverging nozzle shapes with exit areas increasing by 1 5 to 6 times depending on the sample properties behavior correlated strongly with binder concentration as low binder materials had significant increases in nozzle area when using high density particles these weaker samples disintegrated due to particle abrasion from higher kinetic energy impacts the nozzle shapes produced supersonic exit conditions with mach numbers from 1 48 to 2 51 for the various samples however exit pressures were not balanced suggesting that the optimum is not the isentropic pressure balanced shape previously postulated

groundmass crystallization of mount st helens dacite 1980 1986 a tool for interpreting shallow magmatic processes the 1980 1986 eruption of mount st helens volcano provides an unprecedented opportunity to observe the evolution of a silicic magma system over a short time scale groundmass plagioclase size measurements are coupled with measured changes in matrix glass plagioclase and fe ti oxide chemistry to document increasing groundmass crystallinity and thus to better constrain proposed physical models of the post may 18 1980 magmatic reservoir measurements of plagioclase microlite and microphenocryst sizes demonstrate that relatively rapid growth approximately 10 9 cm s of groundmass plagioclase occurred immediately subsequent to may 18 relatively rapid plagioclase growth continued through the end of 1980 at an average rate of 3x10 11 cm s plagioclase growth rates then decreased to 1x10 11 cm s through 1986 changes in groundmass crystallinity are reflected in changes in both matrix glass and plagioclase microphenocryst rim chemistry although the matrix glass composition appears to have remained approximately constant from 1981 1986 after a rapid compositional change from may 18 until the end of 1980 plagioclase microphenocrysts show increasingly more complex zoning patterns with time microphenocryst core compositions are commonly positively correlated with crystal size both of these observations indicate continuous groundmass plagioclase growth through 1986 magmatic temperatures estimated from fe ti oxide pairs are approximately constant through 1981 at eruption temperatures of 930 c and at log fo2 of 10 8 by 1985 1986 oxide temperatures decreased to 870 c chemical and textural changes can be explained by 1 rapid degassing and crystallization in response to the intrusion of magma into a shallow 4 5 km reservoir toward the end of the may 18 1980 eruption 2 continued crystallization at a much reduced rate through 1986 due to slow cooling of the shallow magma reservoir growth rates and consequent chemical changes appear to decrease at the end of 1980 this is coincident with the change in eruption style from explosive eruptions sometimes followed by dome growth to solely extrusive dome building events and can be explained by the expected viscosity increase of both degassing and increasing crystallinity the model of twostage crystallization of magma in a shallow reservoir is consistent with conclusions from gas studies casadevall et al 1983 gerlach and casadevall 1986 a b patterns of crater deformation chadwkck et al 1988 and post 1980 seismicity endo et al 1990 although it does not explain the experimental data of hill and rutherford 1989 on the growth rate of amphibole reaction rims textural measurements on mount st helens dacite can also be used to evaluate crystallization kinetics in silicic magmas systems for which experimental data is almost non existent plagioclase growth rates are 5 10 times slower than estimated plagioclase growth rates in basaltic systems a result consistent with the higher viscosity of a more silicic melt furthermore patterns of textural change both average crystal size and number density are similar to those observed during the 1984 mauna loa eruption by lipman and banks 1987 suggesting that the only modification to the crystallization behavior of plagioclase required in extrapolation from basaltic systems is a moderate decrease in rates such that the rate of crystallization scales with the melt viscosity

three fragmentation mechanisms for highly viscous magma under rapid decompression abstract analysis of the behavior of viscous magma under short term tensile stresses demonstrates that the strain rates anticipated in the eruptive stages of collapse related events may be high enough under certain circumstances to provide fragmentation of the melt by brittle failure mechanisms of fragmentation of a highly viscous vesicular magma by the propagation of an unloading wave by layer by layer vesicle bursting fragmentation wave propagation and by rapid filtration gas flow are outlined fragmentation scenarios involving possible combinations of the three fragmentation mechanisms are evaluated for two models of magma with isolated and with connected pores experimental results for magma fragmentation under high decompression rates appear to support such mechanisms these mechanisms of highly viscous magma fragmentation by rapid decompression probably have their greatest application in cases of explosive disintegration of lava domes and cryptodomes caused by collapse events

linking reservoir geomechanics and time lapse seismics predicting anisotropic velocity changes and seismic attributes seismic technology has been used successfully to detect geomechanically induced signals in repeated seismic experiments from more than a dozen fields to explain geomechanically induced time lapse 4d seismic signals we use results from coupled reservoir and geomechanical modeling the coupled simulation yields the 3d distribution over time of subsurface deformation and triaxial stress state in the reservoir and the surrounding rock predicted changes in triaxial stress state are then used to compute changes in anisotropic p and s wave velocities employing a stress sensitive rock physics transform we predict increasing vertical p wave velocities inside the reservoir accompanied by a negative change in p wave anisotropy e 0 a stress sensitive rock physics transform that predicts a

what makes hydromagmatic eruptions violent some insights from the keanakāko i ash kilauea volcano hawai i abstract volcanic eruptions at the summit of kilauea volcano hawai i are of two dramatically contrasting types 1 benign lava flows and lava fountains and 2 violent mostly prehistoric eruptions that dispersed tephra over hundreds of square kilometers the violence of the latter eruptions has been attributed to mixing of water and magma within a wet summit caldera however magma injection into water at other volcanoes does not consistently produce widespread tephras to identify other factors that may have contributed to the violence of these eruptions we sampled tephra from the keanak ko i ash the most recent large hydromagmatic deposit and measured vesicularity bubble number density and dissolved volatile content of juvenile matrix glass to constrain magma ascent rate and degree of degassing at the time of quenching bubble number densities 9 10 4 1 10 7 cm 3 of tephra fragments exceed those of most historically erupted kilauean tephras 3 10 3 1 8 10 5 cm 3 and suggest exceptionally high magma effusion rates dissolved sulfur average 330 ppm and water 0 15 0 45 wt concentrations exceed equilibrium saturation values at 1 atm pressure 100 150 ppm and 0 09 respectively suggesting that clasts quenched before equilibrating to atmospheric pressure we interpret these results to suggest rapid magma injection into a wet crater perhaps similar to continuous uprush jets at surtsey estimates of reynolds number suggest that the erupting magma was turbulent and would have mixed with surrounding water in vortices ranging downward in size to centimeters such fine scale mixing would have ensured rapid heat exchange and extensive magma fragmentation maximizing the violence of these eruptions

a model for calculating the viscosity of natural iron bearing silicate melts over a wide range of temperatures pressures oxygen fugacites and compositions a new general model that takes into account the pressure and redox state effect is presented to calculate melt viscosities of natural fe bearing melts this new model is applicable to melts that span a wide range of temperatures from 733 to 1873 k pressures 0 001 15 kbar h2o content from 0 to 12 3 wt and compositions from ultramafic mafic to silicic melts the accuracy of the model is calculated to be 0 23 log units of viscosity which is within or close to experimental uncertainty the transport properties including glass transition temperature and melt fragility can also be calculated from this model a spreadsheet to calculate the viscosity is provided in an electronic supplement

observing silicic magma transport in dykes at depths of 8 19 km evidences from crustal xenoliths and numerical modelling abstract within the context of magma transport processes in a dyke this paper integrates petrography and thermodynamic modelling together with fluid dynamics to model the melting of the wall rock in three magma dykes at crustal depths from 8 to 19 km using this combination we explore the interaction between thermal and mechanical processes during silicic magma ascent and the implications for the relative abundance of different crustal xenoliths erupted at the surface we utilize a two dimensional thermal model of dacitic magma injection and flow in dykes of different thickness lengths and depths and associated partial melting of the wall rock and compare the results with field examples from the neogene volcanic province se spain the modelling results open the possibility to relate the range of observed xenoliths information microstructures size distribution at the surface p t evolution to their position in a transient thermal regime in the wall rock of a magma conduit and to the time spent immersed in magma in addition the effects of the modelled stress in the wall rock during magma ascent by the presence or absence of planar features in the xenoliths reveal that the stress patterns are independent of the dyke length and thickness

thermal and dynamical regimes of single and two phase magmatic flow in dikes finite element calculations of magma flow in dikelike channels with length to width ratios of 1000 1 or more have been used to investigate the coupling between thermal and dynamical regimes due to temperature dependent viscosity and dissipation steady state solutions with realistic thermal and dynamical parameter values have been obtained the models show that the onset of solidification on the boundaries of a basaltic or andesitic dike as predicted by idealized laminar flow models can be prevented or significantly delayed by a small amount of transverse flow induced by rising bubbles boundary roughness or turbulence this effect will reduce the critical initial widths of dikes estimated by bruce and huppert 1989 in the absence of transverse flow the bulk temperature of the magma may actually increase slightly with distance along the dike as a result of viscous dissipation even while solidification is occurring on the walls of the dike with converging or necking dike walls it is found that boundary temperatures fall to a minimum and then increase with distance along a dike even if viscous heating is neglected for viscous heating to offset significant rates of heat loss 2 kw m2 in a plane parallel 1 m wide basaltic dike an average flow velocity of 2 7 m s driven by a pressure gradient of 1 7 mpa km is required a 7 void fraction caused by exsolution of volatiles or chamber gas in the magma will produce this pressure gradient the ease of producing such a gradient by reducing the density of the magmatic column with addition of a gas phase makes it likely that flows of basaltic magma could be maintained in dikes tens of kilometers long furthermore a gas phase may be important for the propagation of the fracture prior to the initial injection of magma during dike emplacement rapid transport of more silicic magmas through dikes is inhibited by the requirement of large driving pressure gradients exceeding several hundred megapascals per kilometer however the pressure gradient can be substantially reduced if the magma is a heterogenous mixture of a predominantly silicic component with a more mafic component pipe flow experiments involving molten polymers that exhibit dynamical similarity to magmas strongly suggest that unmixing occurs when a two component magma mixture in which the components have different viscosities rises within a dike within a few dike widths of the inlet the less viscous mafic component encapsulates the more viscous silicic part effectively lubricating the passage of the more viscous component compositional variations in the obsidian dome volcano support the occurrence of this pressure reduction or self lubrication mechanism such a self lubrication process often may be necessary to permit very viscous magmas to reach earth s surface if so chemical and lithologic zoning would be anticipated as a common feature of near surface intrusions or lava flows that are characterized by a high silica and or high crystal content such as at deadman dome in long valley california

dynamics and energetics of bubble growth in magmas analytical formulation and numerical modeling we have developed a model of diffusive and decompressive growth of a bubble in a finite region of melt which accounts for the energetics of volatile degassing and melt deformation as well as the interactions between magmatic system parameters such as viscosity volatile concentration and diffusivity on the basis of our formulation we constructed a numerical model of bubble growth in volcanic systems we conducted a parametric study in which a saturated magma is instantaneously decompressed to one bar and the sensitivity of the system to variations in various parameters is examined variations of each of seven parameters over practical ranges of magmatic conditions can change bubble growth rates by 2 4 orders of magnitude our numerical formulation allows determination of the relative importance of each parameter controlling bubble growth for a given or evolving set of magmatic conditions an analysis of the modeling results reveals that the commonly invoked parabolic law for bubble growth dynamics r t1 2 is not applicable to magma degassing at low pressures or high water oversaturation but that a logarithmic relationship r log t is more appropriate during active bubble growth under certain conditions a second aspect of our study involved a constant decompression bubble growth model in which an initially saturated magma was subjected to a constant rate of decompression model results for degassing of initially water saturated rhyolitic magma with a constant decompression rate show that oversaturation at the vent depends on the initial depth of magma ascent on the basis of decompression history explosive eruptions of silicic magmas are expected for magmas rising from chambers deeper than 2 km for ascent rates 1 5 m s 1

the influence of geometry on the ascent of magma in open fissures during steady eruption the flow conditions emitted mass flux exit velocity and exit pressure depend on the geometry of the conduit in which the eruption occurs this dependence is examined for the onedimensional isothermal ascent of a homogeneous basaltic magma with an aqueous volatile phase and newtonian rheology by fixing the geometry of the feeding fissure the mass flux flowing in steady conditions can be determined at any depth as well the magma pressure and vertical velocity flow behaviour is analysed for three fissure shapes constant width slowly upward narrowing and lenticular in all the cases examined the magma arrives at the earth s surface with a pressure greater than atmospheric the results are compared with those obtained when a lithostatic pressure gradient is assumed for the magma column some speculations are made moreover about the change in eruption style if conduit geometry varies during a non steady phase

magma fragmentation by rapid decompression the processes leading to magma fragmentation and the generation of pyroclastic debris during explosive volcanic eruptions are of fundamental importance in volcanology observations of explosive eruptions1 3 as well as theoretical analyses of the underlying processes4 have raised the question of whether the rapid decompression of highly viscous vesicular magma that results from the collapse of a lava dome or volcanic edifice can in itself produce explosive magma fragmentation and pyroclast formation here we report the results of a laboratory investigation of pyroclast formation following rapid decompression samples of magma from the 1980 eruption of mount st helens when rapidly depressurized from initial pressures of up to 12 mpa and at temperatures in the range 750 825 c fragmented to form pyroclastic products that are in many respects similar to those formed in real eruptions moreover we observe explosive fragmentation at temperatures well below those normally associated with magmatic processes suggesting that even relatively cool magma bodies can be very hazardous when subjected to rapid unloading events

analysis of time lapse travel time and amplitude changes to assess reservoir compartmentalization fluid depletion within a compacting reservoir can lead to significant stress and strain changes and potentially severe geomechanical issues both inside and outside the reservoir we extend previous research of time lapse seismic interpretation by incorporating synthetic near offset and full offset common midpoint reflection data using anisotropic ray tracing to investigate uncertainties in time lapse seismic observations the time lapse seismic simulations use dynamic elasticity models built from hydro geomechanical simulation output and a stress dependent rock physics model the reservoir model is a conceptual two fault graben reservoir where we allow the fault fluid flow transmissibility to vary from high to low to simulate non compartmentalized and compartmentalized reservoirs respectively the results indicate time lapse seismic amplitude changes and travel time shifts can be used to qualitatively identify reservoir compartmentalization due to the high repeatability and good quality of the time lapse synthetic dataset the estimated travel time shifts and amplitude changes for near offset data match the true model subsurface changes with minimal errors a 1d velocity strain relation was used to estimate the vertical velocity change for the reservoir bottom interface by applying zero offset time shifts from both the near offset and full offset measurements for near offset data the estimated p wave velocity changes were within 10 of the true value however for full offset data time lapse attributes are quantitatively reliable using standard time lapse seismic methods when an updated velocity model is used rather than the baseline model

the controlling effect of viscous dissipation on magma flow in silicic conduits nearly all volcanic conduit models assume that flow is newtonian and isothermal such models predict that during high flux silicic eruptions gradients in pressure with depth increase upward as magma accelerates and becomes more viscous leading to extremely low pressure and fragmentation at a depth of kilometers below the surface in this paper i show that shear heating also known as viscous dissipation dramatically reduces the pressure gradient required for flow and concentrates shear in narrow zones along the conduit margin the reduction in friction may eliminate the zone of low pressure predicted by isothermal models and move the fragmentation level up to the surface

recent large increases in freshwater fluxes from greenland into the north atlantic 1 freshwater fw fluxes from river runoff and precipitation minus evaporation for the pan arctic seas are relatively well documented and prescribed in ocean gcms fluxes from greenland on the other hand are generally ignored altogether despite their potential impacts on ocean circulation and marine biology here we present a reconstruction of the spatially distributed fw flux from greenland for 1958 2010 we find a modest increase into the arctic ocean during this period fluxes into the irminger basin however have increased by fifty percent 6 3 0 5 km3 yr 2 in less than twenty years this greatly exceeds previous estimates for the ice sheet as a whole the rate of increase since 1992 is 16 9 1 8 km3 yr 2 the cumulative fw anomaly since 1995 is 3200 358 km3 which is about a third of the magnitude of the great salinity anomaly gsa of the 1970s if this trend continues into the future the anomaly will exceed that of the gsa by about 2025

solidification and turbulence non laminar during magma ascent insights from 2d and 3d analyses of bubbles and minerals in an etnean dyke

volcanic tremor and plume height hysteresis from pavlof volcano alaska the march 2016 eruption of pavlof volcano alaska produced an ash plume that caused the cancellation of more than 100 flights in north america the eruption generated strong tremor that was recorded by seismic and remote low frequency acoustic infrasound stations including the earthscope transportable array the relationship between the tremor amplitudes and plume height changes considerably between the waxing and waning portions of the eruption similar hysteresis has been observed between seismic river noise and discharge during storms suggesting that flow and erosional processes in both rivers and volcanoes can produce irreversible structural changes that are detectable in geophysical data we propose that the time varying relationship at pavlof arose from changes in the tremor source related to volcanic vent erosion this relationship may improve estimates of volcanic emissions and characterization of eruption size and intensity

evidence for the development of permeability anisotropy in lava domes and volcanic conduits the ease at which exsolving volatiles can migrate though magma and outgas influences the explosivity of a volcanic eruption volcanic rocks often contain discrete discontinuities providing snapshots of strain localisation processes that occur during magma ascent and extrusion whether these features comprise pathways for or barriers to fluid flow is thus of relevance for volcanic eruption and gas emission modelling we report here on nine discontinuity bearing andesite blocks collected from volcan de colima mexico we present a systematic porosity and permeability study of fifty cores obtained from the blocks collected and interpret the genetic processes of the discontinuities through detailed microstructural examination bands in pumiceous blocks were inferred to be relicts of inhomogeneous bubble expansion which despite significantly increasing porosity do not markedly affect permeability other discontinuities in our blocks are interpreted to be shear strain induced flow banding cavitation porosity and or variably healed fractures in each of these cases an increase in permeability up to around three orders of magnitude was measured relative to the host material a final sample contained a band of lower porosity than the host rock characterised by variably infilled pores in this case the band was an order of magnitude less permeable than the host rock highlighting the complex interplay between dilatant and densifying processes in magma we therefore present evidence for significant permeability anisotropy within the conduit and or dome of a volcanic system we suggest that the abundance and distribution of strain localisation features will influence the escape or entrapment of volatiles and therefore the evolution of pore pressure within active volcanic systems using a simple upscaling model we illustrate the relative importance of permeable structures over different lengthscales strain localisation processes resulting in permeability anisotropy are likely to play an important role in the style magnitude and recurrence interval of volcanic eruptions

confort 15 model of conduit dynamics applications to pantelleria green tuff and etna 122 bc eruptions numerical simulations are useful tools to illustrate how flow parameters and physical processes may affect eruption dynamics of volcanoes in this paper we present an updated version of the conflow model an open source numerical model for flow in eruptive conduits during steady state pyroclastic eruptions mastin and ghiorso in a numerical program for steady state flow of magma gas mixtures through vertical eruptive conduits u s geological survey open file report 00 209 2000 in the modified version called confort 15 the rheological constraints are improved incorporating the most recent constitutive equations of both the liquid viscosity and crystal bearing rheology this allows all natural magma compositions including the peralkaline melts excluded in the original version to be investigated the crystal bearing rheology is improved by computing the effect of strain rate and crystal shape on the rheology of natural magmatic suspensions and expanding the crystal content range in which rheology can be modeled compared to the original version conflow is applicable to magmatic mixtures with up to 30 vol crystal content moreover volcanological studies of the juvenile products crystal and vesicle size distribution of the investigated eruption are directly incorporated into the modeling procedure vesicle number densities derived from textural analyses are used to calculate through toramaru equations maximum decompression rates experienced during ascent finally both degassing under equilibrium and disequilibrium conditions are considered this allows considerations on the effect of different fragmentation criteria on the conduit flow analyses the maximum volume fraction criterion porosity criterion the brittle fragmentation criterion and the overpressure fragmentation criterion simulations of the pantelleritic and trachytic phases of the green tuff pantelleria and of the plinian etna 122 bc eruptions are performed to test the upgrades in the confort 15 modeling conflow and confort 15 numerical results are compared analyzing the effect of viscosity decompression rate temperature fragmentation criteria critical strain rate porosity and overpressure criteria and equilibrium versus disequilibrium degassing in the magma flow along volcanic conduits the equilibrium simulation results indicate that an increase in viscosity a faster decompression rate a decrease in temperature or the application of the porosity criterion in place of the strain rate one produces a deepening in fragmentation depth initial velocity and mass flux of the mixture are directly correlated with each other inversely proportional to an increase in viscosity except for the case in which a faster decompression rate is assumed taking into account up to date viscosity parameterization or input faster decompression rate a much larger decrease in the average pressure along the conduit compared to previous studies is recorded enhancing water exsolution and degassing disequilibrium degassing initiates only at very shallow conditions near the surface brittle fragmentation i e depending on the strain rate criterion in the pantelleritic green tuff eruption simulations is mainly a function of the initial temperature in the case of the etna 122 bc plinian eruption the viscosity strongly affects the magma ascent dynamics along the conduit using confort 15 and therefore incorporating the most recent constitutive rheological parameterizations we could calculate the mixture viscosity increase due to the presence of microlites results show that these seemingly low viscosity magmas can explosively fragment in a brittle manner mass fluxes resulting from simulations which better represent the natural case i e microlite bearing are consistent with values found in the literature for plinian eruptions 106 kg s the disequilibrium simulations both for green tuff and etna 122 bc eruptions indicate that overpressure sufficient for fragmentation if present occurs only at very shallow conditions near the surface

the architecture of intrusions in magmatic mush abstract magmatic reservoirs located in the upper crust have been shown to result from the repeated intrusions of new magmas and spend much of the time as a crystal rich mush the geometry of the intrusion of new magmas may greatly affect the thermal and compositional evolution of the reservoir despite advances in our understanding of the physical processes that may occur in a magmatic reservoir the resulting architecture of the composite system remains poorly constrained here we performed numerical simulations coupling a computational fluid dynamics and a discrete element method in order to illuminate the geometry and emplacement dynamics of a new intrusion into mush and the relevant physical parameters controlling it our results show that the geometry of the intrusion is to first order controlled by the density contrast that exists between the melt phases of the intrusion and resident mush rather than the bulk density contrast as is usually assumed when the intruded melt is denser than the host melt the intrusion pounds at the base of the mush and emplaced as a horizontal layer the occurrence of rayleigh taylor instability leading to the rapid ascent of the intruded material through the mush was observed when the intruded melt was lighter than the host one and was also unrelated to the bulk density contrast in the absence of density contrasts between the two melt phases the intrusion may fluidize the host crystal network and slowly ascend through the mush the effect of the viscosity contrast between the intruded and host materials was found to have a lesser importance on the architecture of intrusions in a mush analyzing the eruptive sequence of well documented eruptions involving an intrusion as the trigger shows a good agreement with our modeling results highlighting the importance of specifically considering granular dynamics when evaluating magmas and mush physical processes

the structure of basaltic scoria and reticulite and inferences for vesiculation foam formation and fragmentation in lava fountains in this investigation pyroclast structures are used to constrain degassing in basaltic lava fountains vesicle size shape number density interconnectedness and packing character are quantified and related to 1 the kinetics of bubble nucleation and growth 2 the structural evolution of magmatic foams and 3 the influence of vesiculation rate on magma fragmentation measurements made on a diverse suite of pyroclasts from kilauea volcano indicate that basaltic foams evolve through an initially disordered closed celled spherical state to a well ordered open celled polyhedral state as the vesicularity rises from 75 to 98 the structural changes occur rapidly 10 s in the conduit and fountain in response to an intense vesiculation burst vesicle size distribution systematics indicate bubble nucleation rates 2 104 events cm 3s 1 that are approximately three orders of magnitude greater than those found for effusive eruptive activity bubble growth rates 9 10 4 cm s exceed effusive estimates by a factor of 3 the observed runaway rate of bubble production indicates strong supersaturations at the onset of nucleation we speculate that the rise speed of the magma as it reaches the level where significant volatile exsolution begins determines the intensity of the vesiculation burst and hence the vigor of the eruption rapid expansion and acceleration of the magma under these conditions may provide the impetus for fragmentation

magma degassing during the plinian eruption of novarupta alaska 1912 1 we have modeled the nucleation and isothermal growth of bubbles in dacite from the 1912 plinian eruption of novarupta alaska bubble growth calculations account for the exsolution of h2o and co2 beginning with bubble nucleation and ending when bubble sizes reproduced the observed size distribution of vesicles in novarupta pumice clasts assuming classical nucleation theory bubbles nucleated with a diameter of the order of 10 8 m and grew to sizes ranging from 10 6 m to greater than 10 3 m the typical range of vesicle sizes found in novarupta pumice the smallest vesicles in novarupta pumices are also the most abundant and bubbles with radii of 10 6 m to 10 5 m comprise almost 90 of the entire bubble population we find that these bubbles must have nucleated and grown to their final size within a few 100 milliseconds despite these extremely fast growth rates the pressures of exsolved volatiles contained within the bubbles remained high up to about 107pa in excess of ambient pressure assuming a closed system the potential energy of these compressed volatiles was sufficient to cause magma fragmentation even though only a fraction of the pre eruptive volatiles had exsolved unless the matrix glasses of novarupta pyroclasts retains a large fraction of pre eruptive volatiles the majority of magmatic volatiles 80 90 was likely lost by open system degassing between magma fragmentation and quenching

non newtonian flow of bubbly magma in volcanic conduits the dynamics of magma ascent along volcanic conduits toward the earth s surface affects eruptive styles and contributes to volcanic hazard the rheology of ascending magmatic mixtures is known to play a major role on mass flow rate as well as on pressure and exit velocity at the vent even determining effusive versus explosive eruptive behavior in this work we explore the effects of bubble induced non newtonian rheology on the dynamics of magma flow in volcanic conduits we develop a quasi 2 d model of magma ascent that incorporates a rheological constitutive equation describing the strain dependent effect of gas bubbles on the viscosity of the multiphase magma non newtonian magma flow is investigated through a parametric study where the viscosity of the melt and the water content are varied over natural ranges our results show that non newtonian rheology leads to greater exit velocity mass flow and density the pressure distribution along the conduit remains very similar to the newtonian case deviating only at the conduit exit plug like velocity profiles develop approaching the conduit exit when mixture velocity is high and are favored by smaller liquid viscosity since the mass flow rate the density and the velocity of the mixture exiting from the conduit are fundamental for quantifying and assessing the transport and emplacement dynamics neglecting that the non newtonian effect of bubble bearing magmas may result in misinterpretation of the deposit and consequently eruptive behavior

local diurnal wind driven variability and upwelling in a small coastal embayment the oceanic response to high frequency local diurnal wind forcing is examined in a small coastal embayment located along an understudied stretch of the central california coast we show that local diurnal wind forcing is the dominant control on nearshore temperature variability and circulation patterns a complex empirical orthogonal function ceof analysis of velocities in san luis obispo bay reveals that the first mode ceof amplitude time series which accounts for 47 9 of the variance is significantly coherent with the local wind signal at the diurnal frequency and aligns with periods of weak and strong wind forcing the diurnal evolution of the hydrographic structure and circulation in the bay is examined using both individual events and composite day averages during the late afternoon the local wind strengthens and results in a sheared flow with near surface warm waters directed out of the bay and a compensating flow of colder waters into the bay over the bottom portion of the water column this cold water intrusion into the bay causes isotherms to shoal toward the surface and delivers subthermocline waters to shallow reaches of the bay representing a mechanism for small scale upwelling when the local winds relax the warm water mass advects back into the bay in the form of a buoyant plume front local diurnal winds are expected to play an important role in nearshore dynamics and local upwelling in other small coastal embayments with important implications for various biological and ecological processes

fault textures in volcanic conduits evidence for seismic trigger mechanisms during silicic eruptions it is proposed that fault textures in two dissected rhyolitic conduits in iceland preserve evidence for shallow seismogenic faulting within rising magma during the emplacement of highly viscous lava flows detailed field and petrographic analysis of such textures may shed light on the origin of long period and hybrid volcanic earthquakes at active volcanoes there is evidence at each conduit investigated for multiple seismogenic cycles each of which involved four distinct evolutionary phases in phase 1 shear fracture of unrelaxed magma was triggered by shear stress accumulation during viscous flow forming the angular fracture networks that initiated faulting cycles transient pressure gradients were generated as the fractures opened which led to fluidisation and clastic deposition of fine grained particles that were derived from the fracture walls by abrasion fracture networks then progressively coalesced and rotated during subsequent slip phase 2 developing into cataclasite zones with evidence for multiple localised slip events fluidisation and grain size reduction phase 2 textures closely resemble those formed on seismogenic tectonic faults characterised by friction controlled stick slip behaviour increasing cohesion of cataclasites then led to aseismic distributed ductile deformation phase 3 and generated deformed cataclasite zones which are enriched in metallic oxide microlites and resemble glassy pseudotachylite continued annealing and deformation eventually erased all structures in the cataclasite and formed microlite rich flow bands in obsidian phase 4 overall the mixed brittle ductile textures formed in the magma appear similar to those formed in lower crustal rocks close to the brittle ductile transition with the rheological response mediated by strain rate variations and frictional heating fault processes in highly viscous magma are compared with those elsewhere in the crust and this comparison is used to appraise existing models of volcano seismic activity based on the textures observed it is suggested that patterns of long period and hybrid earthquakes at silicic lava domes reflect friction controlled stick slip movement and eventual healing of fault zones in magma which are an accelerated and smaller scale analogue of tectonic faults

the effect of nonlinear decompression history on h2o co2 vesiculation in rhyolitic magmas magma ascent rate is one of the key parameters that controls volcanic eruption style tephra dispersion and volcanic atmospheric impact many methods have been employed to investigate the magma ascent rate in volcanic eruptions and most rely on equilibrium thermodynamics combining the mixed h2o co2 solubility model liu et al 2005 with the diffusivities of both h2o and co2 for normal rhyolitic melt zhang et al 2007 behrens and zhang 2009 we model the kinetics of h2o and co2 in rhyolitic eruptions that involve non linear decompression rates our study focuses on the effects of the total magma ascent time the non linearity of decompression paths and the influence of different initial co2 h2o content on the post eruptive h2o and co2 concentration profiles around bubbles within the melt our results show that under most circumstances volatile diffusion profiles do not constrain a unique solution for the decompression rate of magmas during an eruption but instead provide a family of decompression paths with a well defined trade off between ascent time and non linearity an important consequence of our analysis is that the common assumption of a constant decompression rate averaged value tends to overestimate the actual magma ascent time

influence of magma composition on the eruptive activity of mount st helens washington the relation of eruptive intensity with magma composition and viscosity has been investigated for mount st helens washington where eruptive activity has ranged from basaltic lava flows to dacitic plinian eruptions the plinian eruptions have varied in eruptive intensity from 10 6 to 10 8 kg s yet all erupted dacitic magma these dacites however differ greatly in temperature water content and crystallinity and thus magma viscosity varies by two orders of magnitude the variation in viscosity is correlated inversely with intensity demonstrating the control of composition on intensity in addition more mafic magmas erupted at lower intensities showing that the wide range in eruptive behavior is linked to magma composition changes in composition result mainly from mixing of basaltic and dacitic magmas and occur in cycles the rate of change during a cycle depends upon the length of the preceding repose period and the flux of basalt to the reservoir because the supply of dacite has been relatively constant when the flux of basalt is low cycles progress from dacite to andesite over extended periods whereas a higher flux leads to more rapid changes because composition controls eruptive intensity the eruptive behavior of the volcano also varies through a cycle

effects of caldera collapse on magma decompression rate an example from the 1800 14c yr bp eruption of ksudach volcano kamchatka russia abstract caldera collapse changes volcanic eruption behavior and mass flux many models of caldera formation predict that those changes in eruption dynamics result from changes in conduit and vent structure during and after collapse unfortunately no previous studies have quantified or described how conduits change in response to caldera collapse changes in pumice texture coincident with caldera formation during the 1800 14c yr bp ks1 eruption of ksudach volcano kamchatka provide an opportunity to constrain magma decompression rates before and after collapse and thus estimate changes in conduit geometry prior to caldera collapse only white rhyodacite pumice with few microlites and elongate vesicles were erupted following collapse only gray rhyodacite pumice containing abundant microlites and round vesicles were erupted bulk compositions phase assemblages phenocryst compositions and geothermometry of the two pumice types are indistinguishable thus the two pumice types originated from the same magma geothermobarometry and phase equilibria experiments indicate that magma was stored at 100 125 mpa and 895 5 c prior to eruption decompression experiments suggest microlite textures observed in the white pumice require decompression rates of 0 01 mpa s 1 whereas the textures of gray pumice require decompression at 0 0025 mpa s 1 balancing those decompression rates with eruptive mass fluxes requires conduit size to have increased by a factor of 4 during caldera collapse slower ascent through a broader conduit following collapse is also consistent with the change from highly stretched vesicles present in white pumice and to round vesicles in gray pumice numerical modeling suggests that the mass flux and low decompression rates during the gray phase can be accommodated by the post collapse conduit developing a very broad base and narrow upper region

magma decompression rates during explosive eruptions of kīlauea volcano hawaii recorded by melt embayments the decompression rate of magma as it ascends during volcanic eruptions is an important but poorly constrained parameter that controls many of the processes that influence eruptive behavior in this study we quantify decompression rates for basaltic magmas using volatile diffusion in olivine hosted melt tubes embayments for three contrasting eruptions of k lauea volcano hawaii incomplete exsolution of h2o co2 and s from the embayment melts during eruptive ascent creates diffusion profiles that can be measured using microanalytical techniques and then modeled to infer the average decompression rate we obtain average rates of 0 05 0 45 mpa s 1 for eruptions ranging from hawaiian style fountains to basaltic subplinian with the more intense eruptions having higher rates the ascent timescales for these magmas vary from around 5 to 36 min from depths of 2 to 4 km respectively decompression exsolution models based on the embayment data also allow for an estimate of the mass fraction of pre existing exsolved volatiles within the magma body in the eruptions studied this varies from 0 1 to 3 2 wt but does not appear to be the key control on eruptive intensity our results do not support a direct link between the concentration of pre eruptive volatiles and eruptive intensity rather they suggest that for these eruptions decompression rates are proportional to independent estimates of mass discharge rate although the intensity of eruptions is defined by the discharge rate based on the currently available dataset of embayment analyses it does not appear to scale linearly with average decompression rate this study demonstrates the utility of the embayment method for providing quantitative constraints on magma ascent during explosive basaltic eruptions

pre eruptive reheating during magma mixing at quizapu volcano and the implications for the explosiveness of silicic arc volcanoes effusive explosive transitions are observed in volcanoes erupting water rich magmas that lack mineralogical evidence of degassing suggesting that gas loss occurred rapidly and ascent was fast despite the high viscosity of rhyodacitic to rhyolitic melts here we show that pre eruptive heating of water rich silicic magma by mixing with hot recharge in subvolcanic chambers controls the effusive explosive transition volcan quizapu chile emitted a 5 km3 mingled dacite andesite lava flow in a d 1846 1847 that was 130 c hotter than the 5 km3 of the same dacite that lead to a plinian eruption in a d 1932 we explain the suppression of explosive fragmentation in the 1846 1847 lavas by enhanced syneruptive magma degassing as a consequence of late reheating following mixing with andesite recharge higher magma temperatures led to the transitioning into effusive eruptive behavior by significantly accelerating volatile diffusion and lowering melt viscosity which facilitated bubble nucleation growth and coalescence while also inhibiting brittle fragmentation thus recharge by mafic magmas in subvolcanic magma chambers may reduce the risk of explosive eruptions in cases where heat can be efficiently transferred to cold volatile rich silicic magmas

earthquake induced variations in extrusion rate a numerical modeling approach to the 2006 eruption of merapi volcano indonesia abstract extrusion rates during lava dome building eruptions are variable and eruption sequences at these volcanoes generally have multiple phases merapi volcano java indonesia exemplifies this common style of activity merapi is one of indonesia s most active volcanoes and during the 20th and early 21st centuries effusive activity has been characterized by long periods of very slow

explosive volcanic eruptions viii the role of magma recycling in controlling the behaviour of hawaiian style lava fountains explosive eruptions of mafic magmas produce lava fountains whose heights are a function of the exsolved volatile content of the magma its erupted mass flux and the geometry of the vent which may be an elongate fissure or a localized near circular conduit the geometry of the initial vent and the eruptive behaviour can be distinctly modified by lava drainback and accumulating ejecta hot pyroclasts landing near the vent may coalesce to form rootless flows some of which may drain back into the vent to be recycled into the eruption products rootless flows may be at least partially confined by pre existing topographic features or by spatter or cinder ramparts being built up by the eruption itself so that they accumulate into a lava pond over and around the vent the erupting jet of magmatic gas and pyroclasts must force its way through such a pond and will entrain some of the pond lava as it does so the energy expended in entraining and accelerating previously erupted materials will reduce the eruption velocity and the lava fountain height by an amount which can be calculated as a function of the eruption conditions and the lava pond depth or lava drainback rate the results of such calculations are presented and are used to assess the influence of this process on attempts to infer magma volatile contents from field observations of lava fountain heights

spatial variability of diapycnal mixing and turbulent dissipation rates in a stagnant fjord basin two microstructure profilers two ships and four moorings with acoustic doppler current profilers and conductivity temperature loggers were used in an intensive effort to map the spatial and temporal variations of vertical mixing in the stagnant deep basin of gullmar fjord sweden during three days in the beginning of august 2001 a continuous time series of turbulent kinetic energy dissipation profiles was obtained with one microstructure profiler at a fixed position near the deepest part of the fjord during the same period the other microstructure profiler was used to obtain six sections of dissipation through the length of the basin two moorings were deployed in the fjord basin for one month from the end of july to the end of august the mapping of dissipation rates reveals that the dissipation in the deep basin is confined to areas just inside the sill more than 77 of the dissipation in the fjord basin happens above the sloping bottoms closest to the sill

viscous heating in rhyolite an in situ experimental determination viscous heating during magmatic flow may play a major role in eruption dynamics in order to document viscous heating during deformation of magma we have conducted a series of rheological experiments where viscous heating is directly monitored via thermocouples in high viscosity magmas we observe experimentally the strain rate dependence of viscous heating viscous heating becomes rheologically significant in the highly viscous lavas investigated at strain rates above ca 10 3 s 1 a simple analysis shows that the temperature increase generated through viscous heating during deformation of melts with viscosities ranging from 108 to 1012 pa s can account for their apparent non newtonian rheology in these experiments this thermal correction transforms apparent non newtonian strain rate dependent rheology of magma to a newtonian behavior over the range of conditions accessed in this work in this manner this study provides an experimental basis for separating the relative roles of structural relaxation and viscous heating in the generation of apparent non newtonian rheology at high strain rates here viscous heating dominates and the observation of the structural onset of non newtonian behavior is precluded by a viscous heating induced lowering of the newtonian viscosity the interplay of viscous heating and structural relaxation in melts in nature is discussed briefly

fragmentation of a porous viscoelastic material implications to magma fragmentation fragmentation of vesicular magma by rapid decompression is one of the most likely triggers for explosive eruptions in this phenomenon the decompression rate and the viscoelastic nature of magma are considered to be key factors in order to obtain a clear idea on the effects of these two factors controlled fragmentation experiments have been conducted these experiments have three advantages first the specimen is made of a viscoelastic material with controlled porosity and geometry second the fragmentation process is directly monitored finally both the magnitude and rate of decompression are controlled brittle fragmentation and ductile expansion were both observed in the same porous material at different timescales the various mechanical responses of the specimen elastic flow and fragmentation were correlated with the pressure profile measured at the base of the specimen fragmentation was noted to occur when the decompression exceeded a critical value within a critical time two relevant timescales are discussed in terms of physical mechanisms of relaxation the first is the measured glass transition time the second is the estimated timescale for the onset of viscous bubble expansion the observed phenomena bear several similarities with natural magma fragmentation it is thus considered that the present results are a useful step toward constructing a model for magma fragmentation

pre explosive conduit conditions of the 1997 vulcanian explosions at soufriere hills volcano montserrat i pressure and vesicularity distributions an authoritative case of vulcanian eruptive dynamics is the series of 88 explosions that occurred between august and october 1997 at soufriere hills volcano on montserrat island the state of the magmatic column just before a vulcanian explosion is still poorly understood but conditions the eruptive style this study establishes such a pre explosive stratigraphy by 1 documenting the textures covering the range of the 1997 products 2 quantitative analysis of h2o content in interstitial glass measured by karl fischer titration and 3 combining these data with a simple model linking pre and post explosive vesicularities the model shows that syn explosive degassing affects greatly the way porosity evolves by decompression during an explosion the stratigraphy reconstruction shows a three part vertical layering of the conduit prior to explosion with overall denser values than those previously suggested a dense and strongly degassed plug caps the column it is underlain by a shallow transition zone featuring complex mingling between vesicular and dense magma up to 10 mpa at higher pressure up to 80 mpa lies a more homogeneous zone of relatively dense 10 20 vol magma which was emplaced under partly open system degassing this conduit stratigraphy gives the vision of a strongly heterogeneous magma column immediately prior to its disruption our analysis suggests that fragmenting such a composite magma cannot happen in a single coherent pulse but rather as stages the transition zone contains heterogeneous amounts of exsolved gas that could explain the pulsatory nature of the vulcanian jets at the beginning of the explosions this contrasts with the nearly constant vesicularities of the deeper part of the pre explosive magma column which are propitious to a general short lived disruption

high frequency internal waves in large stratified lakes observations are presented from lake biwa and lake kinneret showing the ubiquitous and often periodic nature of high frequency internal waves in large stratified lakes in both lakes high frequency wave events were observed within two distinct categories 1 vertical mode 1 solitary waves near a steepened kelvin wave front and vertical mode 2 solitary waves at the head of an intrusive thermocline jet were found to have wavelengths 64 670 m and 13 65 m respectively and were observed to excite a spectral energy peak near 10 23 hz 2 sinusoidal vertical mode 1 waves on the crests of kelvin waves vertically coherent in both phase and frequency and bordering the thermocline jets in the high shear region trailing the vertical mode 2 solitary waves vertically incoherent in both phase and frequency were found to have wavelengths between 28 37 and 9 35 m respectively and excited a spectral energy peak just below the local maximum buoyancy frequency near 10 22 hz the waves in wave event categories 1 and 2 were reasonably described by nonlinear wave and linear stability models respectively analysis of the energetics of these waves suggests that the waves associated with shear instability will dissipate their energy rapidly within the lake interior and are thus responsible for patchy turbulent events that have been observed within the metalimnion conversely the finite amplitude solitary waves which each contain as much as 1 of the basinscale kelvin wave energy will propagate to the lake perimeter where they can shoal thus contributing to the maintenance of the benthic boundary layer

investigating lava flow rheology using video analysis and numerical flow models abstract lava rheology is a major control on lava flow behavior and a critical parameter in flow simulations but is very difficult to measure at field conditions or correctly extrapolate from the lab scale we present a new methodology for investigating lava rheology through a combination of controlled experiments image analysis and numerical forward modeling our experimental setup part of the syracuse university lava project http lavaproject syr edu includes a large furnace capable of melting up to 450 kg of basalt at temperatures well above the basalt liquidus the lava is poured onto either a tilted bed of sand or a steel channel to produce meter long flows this experimental setup is probably the only facility that allows such large scale controlled lava flows made of natural basaltic material we document the motion of the lava using a high resolution video camera placed directly above the flows and the temperature using infrared probes and cameras after collecting the footage we analyze the images for lava deformation and compare with numerical forward models to constrain the rheological parameters and laws which best describe the flowing lava for the video analysis we employ the technique of differential optical flow which uses the time variations of the spatial gradients of the image intensity to estimate velocity between consecutive frames an important benefit for using optical flow compared with other velocimetry methods is that it outputs a spatially coherent flow field rather than point measurements we demonstrate that the optical flow results agree with other measures of the flow velocity and estimate the error due to noise and time variability to be under 30 of the measured velocity our forward models are calculated by solving the stokes flow equations on an unstructured finite element mesh defined using the geometry of the observed flow itself we explore a range of rheological parameters including the lava s apparent viscosity the power law exponent m and the thermal activation energy our measurements of apparent viscosity agree well with predictions of the composition based shaw 1972 and grd model giordano russell and dingwell 2008 we find that for the high temperature portion of the flow a weakly shear thinning or newtonian rheology m 0 7 with an effective activation energy of b 5500 j gives the best fit to the data our methodology is the first time that high resolution optical flow analysis of flowing lava is combined with numerical flow models to constrain rheology the methodology we present here can be used in field conditions to obtain in situ information on lava rheology without physical interaction with the flow and without being limited to point wise low strain rate local measurements currently available through the use of rotational viscometers in the field

time lapse tomographic inversion using a gaussian parameterization of the velocity changes most seismic studies of changes in traveltimes are of a qualitative nature and a major challenge in four dimensions is to use the information contained in time shifts to quantify the nature of velocity changes in the subsurface layers we propose a 4d tomographic inversion method that uses time shifts from prestack seismic data to estimate parameters describing the 2d velocity field after changes have occurred prestack data allow for the usage of many offsets thus increasing the information input for the inversion the velocity changes are parameterized by a chosen number of gaussian functions in two dimensions and weighted least squares inversion is used to estimate the parameters describing these functions we have found that the parameters describing the position and shape of the gaussian velocity anomalies can be estimated with this method for simple synthetic cases for more complex cases with overlapping gaussian functions resolution of the parameters can be difficult and in these cases our recom

the effect of magma flow on nucleation of gas bubbles in a volcanic conduit abstract we solve the dynamics of magma ascent and the kinetics of bubble nucleation and growth simultaneously which allow us to predict bubble sizes and number densities under ascent conditions as magma rises toward the surface the pressure decreases and eventually becomes less than the solubility pressure when the degree of supersaturation becomes great enough bubbles nucleate nucleation will stop as the concentration of volatiles in the melt decreases due to growth of existing bubbles and hence the degree of supersaturation decreases we show that a second nucleation event may occur just below the fragmentation level near that level the degree of supersaturation continuously increases as the magma is rapidly decompressed as a result nucleation will not stop until fragmentation occurs this second nucleation event should be taken into account when interpreting bubble size distribution measurements made on natural pumices the bubbles of the second nucleation event have high internal gas pressures up to 2 mpa greater than the liquid pressure suggesting that the second nucleation event may enhance fragmentation of magma we apply the model to the calculation protocol defined at the volcanic eruption mechanism modeling workshop durham 2002 we found that as a result of disequilibrium degassing fragmentation occurs higher in the conduit than under equilibrium degassing

a multimethod global sensitivity analysis to aid the calibration of geomechanical models via time lapse seismic data time lapse seismic attributes are used extensively in the history matching of production simulator models however although proven to contain information regarding production induced stress change it is typically only loosely i e qualitatively used to calibrate geomechanical models in this study we conduct a multimethod global sensitivity analysis gsa to assess the feasibility and aid the quantitative calibration of geomechanical models via near offset time lapse seismic data specifically the calibration of mechanical properties of the overburden via the gsa we analyse the near offset overburden seismic traveltimes from over 4000 perturbations of a finite element fe geomechanical model of a typical high pressure high temperature hpht reservoir in the north sea we find that out of an initially large set of material properties the near offset overburden traveltimes are primarily affected by young s modulus and the effective stress i e biot coefficient the unexpected significance of the biot coefficient highlights the importance of modelling fluid flow and pore pressure outside of the reservoir the fe model is complex and highly nonlinear multiple combinations of model parameters can yield equally possible model realizations consequently numerical calibration via a large number of random model perturbations is unfeasible however the significant differences in traveltime results suggest that more sophisticated calibration methods could potentially be feasible for finding numerous suitable solutions the results of the time varying gsa demonstrate how acquiring multiple vintages of time lapse seismic data can be advantageous however they also suggest that significant overburden near offset seismic time shifts useful for model calibration may take up to 3 yrs after the start of production to manifest due to the nonlinearity of the model behaviour similar uncertainty in the reservoir mechanical properties appears to influence overburden traveltime to a much greater extent therefore reservoir properties must be known to a suitable degree of accuracy before the calibration of the overburden can be considered

relating 4d seismics to reservoir geomechanical changes using a discrete element approach a modified discrete element method is briefly introduced and used for modelling reservoir geomechanical response during fluid injection and depletion the modified approach works as a continuum method until some local failure is initiated after which it behaves like a discrete element method on a polygonal lattice the method is advantageous for modelling fracture developments in rocks it is applied here to synthetic models of two reservoirs taken from the north sea gullfaks and elginfranklin for gullfaks two cases of water injection were modelled one with low horizontal effective stress and the other with low vertical effective stress vertical fractures are developed in the first case whereas horizontal fractures are developed in the second case this would not have been seen using traditional methods based on 4d seismics data for the gullfaks field one may envision that horizontal fractures could have been formed the elgin franklin synthetic model is used to study various scenarios of changing stress field around the depleting reservoir based on 4d seismics data from this field one may see changes that could be interpreted in terms of possible fault reactivation

dynamics of deep submarine silicic explosive eruptions in the kermadec arc as reflected in pumice vesicularity textures abstract despite increasing recognition of silicic pumice bearing deposits in the deep marine environment the processes involved in explosive silicic submarine eruptions remain in question here we present data on bubble sizes and number densities number of bubbles per unit of melt matrix for deep submarine erupted pumices from three volcanoes healy raoul sw and havre along the kermadec arc sw pacific to investigate the effects of a significant 1 km overlying water column and the associated increased hydrostatic pressure on magma vesiculation and fragmentation we compare these textural data with those from chemically similar subaerially erupted pyroclasts from nearby raoul volcano as well as submarine erupted tangaroan fragments derived by non explosive buoyant detachment of foaming magma from macauley volcano also along the kermadec arc deep submarine erupted pumices are macroscopically similar colour density texture to subaerial or shallow submarine erupted pumices but show contrasting microscopic bubble textures deep submarine erupted pyroclasts have fewer small

excitation and resonance of acoustic gravity waves in a column of stratified bubbly magma oscillations of magma in volcanic conduits are thought to be the source of certain seismic and infrasonic signals observed near active volcanoes however the multiphase and stratified nature of magma within the conduit complicates the calculation of resonant modes that is required to interpret observations here we present a linearized mathematical framework to describe small amplitude oscillations and waves in a stably stratified column of two phase magma liquid melt and gas bubbles with a traction free upper surface a lava lake we explore the role of time dependent mass exchange between the phases depth varying fluid properties and gravity on the modes of oscillation of inviscid magma within an axisymmetric vertical conduit non equilibrium phase exchange which we refer to as bubble growth and resorption bgr is parameterized by introduction of a kinetic time scale quantifying mass exchange between the liquid and gas phases that evolves the mixture towards a state of thermodynamic equilibrium using a provably stable finite difference method we solve the eigenvalue problem for the resonance frequencies decay rates and spatial structure of the conduit eigenmodes the numerical method is then extended to time domain simulations of waves excited by internal volumetric sources in the conduit or forces applied to the surface of the lava lake we connect time dependent wave propagation simulations to the modal analysis by identifying the primary modes that are excited by representative excitation processes waves propagating through bubbly magma are dispersive and their behaviour is determined by three dimensionless parameters one quantifies the importance of buoyancy and gravitational restoring forces relative to compressibility the second quantifies differences between fluid properties e g mixture compressibility under equilibrium and non equilibrium conditions and the third compares the wave period to the bgr time scale pronounced depth variations in background fluid properties such as the transition from liquid melt with dissolved volatiles at the high pressures at depth to bubbly magma above the gas exsolution depth segment the conduit into distinct regions the longest period modes which are expressed with the largest amplitudes for typical excitation processes are most sensitive to the length of the bubbly region and properties of the bubbly magma within it while the boundary condition at the bottom of the conduit determines whether the fundamental mode is affected by the total conduit length modes localized above the exsolution depth are remarkably insensitive to the overall conduit length our analysis suggests that parameters affecting eruption style such as total volatile content and kinetic time scales of bgr along with excitation source characteristics are imprinted on long period seismic and infrasonic signals at active volcanoes

the effect of particle shape on suspension viscosity and implications for magmatic flows 1 the rheology of crystal bearing magma and lava depends on both the shape and volume fraction of the suspended crystals we present the results of analogue rheometric experiments on monodisperse suspensions of solid particles in a newtonian liquid in which particle volume fraction and aspect ratio rp are varied systematically we find that the effect of on viscosity is well captured by the maron pierce model and that this model is valid across the range of particle aspect ratios investigated 0 04 rp 22 i e strongly oblate to strongly prolate when the maximum packing fraction m is treated as a fitting parameter the value of m derived from fitting to our experimental data depends strongly and systematically on particle aspect ratio hence m represents an effective proxy for the influence of particle shape on suspension rheology we present a simple relationship for m rp which allows the viscosity of a suspension to be calculated as a function of and rp only we investigate the impact of accounting for crystal shape when modelling volcanic flows by simulating the eruption of magma carrying crystals of different aspect ratio and conclude that the effect of crystal shape should not be neglected

review paper a semi empirical model of strain sensitivity for 4d seismic interpretation we reformulate the original model of hatchell and bourne and roste stovas and landro that couples fractional velocity change to subsurface strain via a fundamental constant r the new model combines elastic compressibility of a dual porosity system for a sand shale mixture with horizontal planes of inter granular weakness the majority of observed r factor magnitudes from post stack 4d seismic data in both the reservoir and overburden can thus be explained r is predicted to depend strongly on lithology and also initial strain state the model is also extended to predict the observed angle dependence of time lapse time shifts from pre stack data an expression for the gradient of time shift with incidence angle is obtained in terms of the background vp vs and also the ratio of tangential to normal compliances bt bn representing loss or creation of inter granular coupling if accurately estimated from data this compliance ratio can be used as an additional parameter to assess the post production state of the overburden it is concluded that whilst r remains the over arching parameter controlling the magnitude of time shifts measured from 4d seismic data bt bn is a subtler parameter that may also prove of future value

a mathematical model of vulcanian eruptions summary the problem of an expansion wave propagating into a saturated magma is solved and used as a model of a vulcanian eruption in our model for an explosive eruption we assume that a drop in pressure leads to the exsolution of magmatic volatiles initially the exsolved vapours create bubbles in the magma we model the subsequent part of the exsolution process in which a foam is created this is believed to be an essential feature of explosive volcanic eruptions the foam also has the advantage that it can be modelled as a mixture or pseudo gas without slippage between the phases eventually the foam breaks up and becomes volcanic ash assuming that the exsolution of vapour is given by henry s law that the temperature is constant that the magma and vapour have equal velocities and neglecting wall friction and gravitational effects an analytic solution for pressure velocity and vapour fraction is obtained for the expanding mixture in a constant area duct the exit velocity u for the mixture is u o0rt0 1 2in p0 p where o0 is the original mass fraction of dissolved vapour r is the gas constant for the vapour t0 the constant temperature and p0 p the pressure ratio across the expansion with o0 1 per cent t0 1000 k and p0 p 100 we find u0 300ms 1 consistent with observations for vulcanian eruptions

ascent and decompression of viscous vesicular magma in a volcanic conduit during eruption lava domes and flows may become unstable and generate dangerous explosions fossil lava filled eruption conduits and ancient lava flows are often characterized by complex internal variations of gas content these observations indicate a need for accurate predictions of the distribution of gas content and bubble pressure in an eruption conduit bubbly magma behaves as a compressible viscous liquid involving three different pressures those of the gas and magma phases and that of the exterior to solve for these three different pressures one must account for expansion in all directions and hence for both horizontal and vertical velocity components we present a new two dimensional finite element numerical code to solve for the flow of bubbly magma even with small dissolved water concentrations gas overpressures may reach values larger than 1 mpa at a volcanic vent for constant viscosity the magnitude of gas overpressure does not depend on magma viscosity and increases with the conduit radius and magma chamber pressure in the conduit and at the vent there are large horizontal variations of gas pressure and hence of exsolved water content such variations depend on decompression rate and are sensitive to the exit boundary conditions for the flow for zero horizontal shear stress at the vent relevant to lava flows spreading horizontally at the surface the largest gas overpressures and hence the smallest exsolved gas contents are achieved at the conduit walls for zero horizontal velocity at the vent corresponding to a plug like eruption through a preexisting lava dome or to spine growth gas overpressures are largest at the center of the vent the magnitude of gas overpressure is sensitive to changes of magma viscosity induced by degassing and to shallow expansion conditions in conduits with depth dependent radii

insights into volcanic conduit flow from an open source numerical model 1 numerical models that calculate the fluid dynamics of explosive volcanic eruptions have been used with increasing frequency to understand volcanic processes and evaluate volcanic hazards yet those who develop such models rarely make them publicly available so that they can be verified used and possibly improved by other scientists in this paper i present a visual interactive open source numerical model that calculates steady state flow of magma and gas in vertical eruptive conduits and contains user friendly utilities for quickly determining physical thermodynamic and transport properties of silicate melts h2o gases and melt gas crystal mixtures the model represents an advance over previously published conduit models by incorporating a non arrhenian viscosity relation for hydrous silicate melts a relation between viscosity and volume fraction of gas that depends on capillary number and adiabatic temperature changes in the mixture using established thermodynamic relations for melts and h2o gas respectively volcanologists who have not had access to conduit models have frequently approximated conduit flow using an analytical equation for incompressible laminar newtonian pipe flow which predicts that the mass flux is proportional to the fourth power of conduit radius and inversely proportional to mixture viscosity the model presented here which is not much more difficult to use than a back of the envelope calculation shows that the pipe flow approximation significantly overestimates the sensitivity of mass flux to both conduit radius and mixture viscosity results from the model also show that viscous heating in the lower conduit which is not considered in most other models may increase the mass flux of large silicic eruptions by several percent and decrease the viscosity of the mixture at the fragmentation depth by a few tens of percent

effects of wall rock elasticity on magma flow in dykes during explosive eruptions abstract magma flow during explosive volcanic eruptions has been described assuming rigid conduits with simple cylindrical or planar geometries here we study the dynamics of explosive volcanic flows to take account of the role of elastic deformation of the conduit influenced by local magmatic pressure three cases are investigated a dyke with elliptical cross section a cylindrical conduit and a deep dyke connected to a shallow cylinder the model cpiuc macedonio et al 2005 was used for simulations and generalized to account for elastic deformations of the conduit cross section area due to magmatic overpressure fragmentation level is typically deeper in a dyke than in a cylinder for flows in wide dykes pressure at the fragmentation depth can be lower than the surrounding lithostatic pressure by several tens of mpa indicating that the wall rocks of the dyke will be unstable constraining the dyke width and eventually blocking the eruption on the other hand when the fragmentation level is shallow the corresponding lithostatic pressure is not large enough to close the dyke and eruptions from wide dykes are possible the behaviour changes drastically when we assume the conduit is a dyke at depth that evolves to a cylinder near the surface in this case even very wide dykes can be stable because the fragmentation level moves into the cylindrical region where deformation is negligible

subglacial intermediate volcanism at kerlingarfjoll iceland magma water interactions beneath thick ice the products of andesite and dacite glaciovolcanism at kerlingarfjoll are unlike others previously described in the literature three sequences of lithofacies are described and interpreted here the andesitic deposits at campsite gully are divided into massive vitriclastic lapilli tuff with intrusions fluidal clast bearing vitriclastic lapilli tuff and stratified pumice rich vitriclastic lapilli tuff at tindur andesitic eruptions produced contorted pillow fragment breccia and the clast supported lithic breccia finally pillow lava with intrusions and crudely bedded vitriclastic lapilli tuff of dacitic composition are described at haraldur abundant vitriclasts the presence of pillow lavas hackly fracturing of lava bodies and lack of oxidation of clasts demonstrate that each of these lithofacies formed in the presence of abundant water this contrasts with all other descriptions of subglacially erupted intermediate magmas which are characterised by jointed and glassy lava flows and domes with a marked scarcity of fragmental material the kerlingarfjoll sequences therefore demonstrate that it is possible for intermediate magmas to generate and interact with significant volumes of water at the base of a glacier preliminary estimates of volatile contents in glassy clasts correspond to quenching pressures equivalent to 500 m water or 550 m ice this is consistent with eruption beneath an ice sheet that was thick enough to overwhelm the underlying topography and where meltwater drainage was controlled by the morphology of the glacier surface it is argued that the drainage of water due to steep topography and or thin and fractured ice as opposed to thermodynamic considerations is the most likely explanation for the absence of evidence for significant magma water interaction in previously described instances of intermediate glaciovolcanism the apparent low viscosity of the kerlingarfjoll magmas may relate to relatively high eruption temperatures and or the inhibition of degassing of the magma due to high ambient pressures and the consequent limitation of groundmass crystallisation

externally forced fluctuations in ocean temperature at greenland glaciers in non summer months the factors that control the submarine melt rate at greenland s glaciers are uncertain and largely inferred from brief summer surveys in the fjords where glaciers terminate continuous records of water properties and velocity for the months september to may from two large greenland fjords reveal strong variability on 3 to 10 day timescales as a result of pulses of water that are propagated from the shelf ocean

petrological insights into shifts in eruptive styles at volcan llaima chile tephra and lava pairs from two summit eruptions ad 2008 and 1957 and a flank fissure eruption ad 1850 are compared in terms of textures phenocryst contents and mineral zoning patterns to shed light on processes responsible for the shifts in eruption style during typical eruptive episodes at volcan llaima andean southernvolcanic zone chile the mineralogy and whole rock com positions of tephra and lavas are similar within eruptive episodes suggesting a common magma reservoir for strombolian paroxysms and lava effusion the zoning profiles and textures of plagioclase record successive and discrete intrusions of volatile rich mafic magma accompanied by mixing of these recharge magmas with the resident basaltic andesitic crystal mushes that are commonly present at shallow levels in the llaima system each recharge event destabil izes the plagioclase in equilibrium with the resident crystal mush melt and stabilizes relatively an rich plagioclase as is recorded by the numerous resorption zones lavas typically have 15 20 vol more phenocrysts than the tephra differences in plagioclase and olivine textures and zoning combined with different phenocryst contents indicate that a greater volume fraction of recharge magma is present in the explosively erupted magma than in subsequent effu sively erupted magma we propose that strombolian paroxysms at volcan llaima are triggered by interactions with large volume frac tions of recharge magma which decrease the bulk viscosity and in crease the volatile contents of the erupted magmas leading to the conditions required for the fragmentation of basaltic andesite lava effusion ensues from reduced interactions with the recharge magma after it has partially degassed and crystallized thereby impeding rapid ascent this process could be operating at other steady state basaltic volcanoes wherein shallow reservoirs are periodically re filled by fresh volatile rich magmas

shallow plumbing systems for small volume basaltic volcanoes eruptive dynamics in basaltic volcanoes are controlled in part by the conduit geometry however uncertainties in conduit shape and dike to conduit transition geometry have limited our predictive capability for hazards assessments we characterize the subvolcanic geometry of small volume basaltic volcanoes magmatic volatile driven eruptions 0 1 to 0 5 km3 based on a synthesis of field studies of five basaltic volcanoes exposed to varying degrees by erosion and exhibiting feeder dikes conduits and vent areas 250 m depth study areas include east grants ridge new mexico usa basalt ridge east basalt ridge paiute ridge and southeast crater flat nevada usa basaltic feeder dikes 250 to 100 m deep have typical widths of 4 12 m with smooth host rock contacts rhyolite tuff at depths less than 100 m heterogeneities in the host rock form preferential pathways for small dike splays and sills resulting in a 30 m effective width at 50 m depth the development of a complex conduit at depths less than 70 m is reflected in bifurcating dikes and brecciation and incorporation of the country rock the overall zone of effect at depths less than 50 m is 110 m wide 220 m elongated along the feeder dike based on comparisons with theoretical conduit flow models the width of the feeder dike at depths from 250 to 500 m is expected to range from 1 to 10 m and is expected to decrease to about 1 2 m at depths greater than 500 m the flaring shape of the observed feeder systems is similar to results of theoretical modeling using lithostatic pressure balanced flow conditions sizes of observed conduits differ from modeled dimensions by up to a factor of 10 in the shallow subsurface 50 m depth but at depths greater than 100 m the difference is a factor of 2 to 4 this difference is primarily due to the fact that observed eroded conduits record the superimposed effects of multiple eruptive events while theoretical model results define dimensions necessary for a single steady eruption phase the complex details of magma host rock interactions observed at the study areas contact welding brecciation bifurcating dikes and sills and stoping represent the mechanisms by which the lithostatic pressure balanced geometry is attained the similarity in the normalized shapes of theoretical and observed conduits demonstrates the appropriateness of the pressure balanced modeling approach consistent with the conclusions of wilson and head j geophys res 86 2971 3001 1981 for this type of volcano

circulation of prince william sound alaska the circulation of prince william sound alaska is described using hydrographic 1974 1989 current meter 1977 1979 and acoustic doppler current profiler 1986 1990 observations from both the sound and the adjacent gulf of alaska ancillary data include data for winds freshwater runoff and satellite tracked drifters prince william sound is a small inland sea in that it is wide enough to have appreciable horizontal cyclonic circulation it is also a fjord in that it has basin depths to 700 m but is stilled at 180 m to the open ocean the general circulation pattern is defined by a portion of the westward flowing alaska coastal current on the gulf of alaska shelf that enters prince william sound through hinchinbrook entrance and transits the sound from east to west before exiting through montague strait and rejoining the coastal current however there is much variability in this circulation especially in the transport through hinchinbrook entrance in addition some of the water entering the sound becomes involved in the cyclonic circulation in the northern sound and so has a longer residence time the circulation is strongly mediated by seasonal and interannual variations in winds and freshwater runoff as well as by local topography both inside and outside the sound in winter the strong cyclonic winds over the gulf of alaska cause coastal downwelling and strong flow in the upper layers into prince william sound through hinchinbrook entrance and out through montague strait in summer the downwelling ceases allowing subsurface denser water to rise above the sill and flow into the sound through the bottom layers of hinchinbrook entrance we conclude that the best transport data came from montague strait from which we estimate that 40 of the volume of prince william sound is flushed in summer may september this estimated volume rises to about 200 in winter october april

magmatic storage conditions decompression rate and incipient caldera collapse of the 1902 eruption of santa maria volcano guatemala abstract phase equilibria experiments and analysis of natural pumice and phenocryst compositions indicate the 1902 santa maria dacite was stored at 140 170 mpa and 840 850 c prior to eruption h2o saturated cold seal experiments conducted in vessels with an intrinsic log fo2 of nno 1 0 5 show that the natural phase assemblage melt plagioclase amphibole orthopyroxene fe ti oxides apatite is stable from approximately 115 140 mpa at temperatures below 825 c to 840 860 c at 150 mpa to 850 and 50 mpa and 50 c greater than experimental run conditions precise estimates of magmatic conditions based solely upon amphibole composition are likely inaccurate the experimental results and analysis of natural crystals suggest that although the natural amphiboles likely record a broad range of magmatic conditions only the lower bounds of that range reflect pre eruptive storage conditions comparison of santa maria microlite abundances with decompression experiments examining other silicic systems from the literature suggests that the 1902 dacite decompressed at the rate of 0 005 to 0 01 mpa s during the eruption applying the decompression rate with the previously described eruption rate of approximately 2 3 108 kg s williams and self 1983 carey and sparks 1986 to the conduit model conflow reveals that the eruption conduit was dike like with an along strike length 1 km despite depositing 20 km3 of dacite tephra equivalent to 8 5 km3 magma the 1902 eruption did not form an obvious caldera this work suggests that collapse of the dike like conduit terminated the eruption preventing full caldera collapse

production induced stresses from time lapse time shifts a geomechanics case study from franklin and elgin fields franklin and elgin fields were discovered in 1986 and 1991 respectively within the u k north sea central graben blocks 22 30 and 29 5 the producing reservoirs are contained in the jurassic fulmar shallow marine and pentland fluvial formations at depths of 5100 5600 m subsea the fields presented significant development challenges both in terms of seismic imaging complexity and being in a state of exceptionally high pressure high temperature hpht addressing these challenges meant that production could not commence until 2001

kinetics of cooling and decompression induced crystallization in hydrous mafic intermediate magmas article i nfo the crystallization of a hydrous basaltic andesite magma was investigated using cooling and decompression experiments these experiments were designed so that the driving force for crystallization of feldspar the undercooling is equal whether in the direction of cooling or decompression after initial equilibration steps at conditions t 1 025 c and ph2o 150 mpa charges were either cooled or decompressed near instantaneously to final conditions corresponding to undercoolings t 5 2 154 c with dwell times of 12 24 and 48 h at the final p t t his single step experimental strategy ssd for decompression experiments ssc for cooling allowed derivation of kinetic parameters such as nucleation and growth rates as a function of undercooling even though our setup was primarily designed to investigate feldspar crystallization we report kinetic and geochemical data for all phases present glass feldspar clinopyroxene olivine and amphibole at low to intermediate undercoolings the solidification behavior of mafic intermediate magmas is very similar texturally and compositionally whether the crystallization mechanism is cooling or decom pression at high degrees of undercooling feldspar and clinopyroxene nucleation rates are nevertheless higher in ssd compared to ssc runs perhaps due to slower diffusivities or larger nucleation barriers in the cooling runs minerals transition from interface limited growth to diffusion limited growth with increasing undercooling while nucleation regimes shift from homogeneous to heterogeneous crystal morphologies are highly variable but can be used qualitatively to assess the extent of undercooling relative to more silicic melts with similar crystal contents feldspar formed in andesitic melts nucleate at a lower rate but grow to larger sizes published by elsevier b v

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