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

the effect of inertial accelerations on the higher frequency components of the signal from spring gravimeters summary experimental and theoretical studies have shown that due to the magma gas dynamics in the upper part of a volcano s plumbing system gravity changes can develop over periods between a few tens of seconds and several hours the mass transport implied by certain fast evolving volcanic processes also constitute the source mechanism of seismic waves with frequencies over the lower limit of the seismic band these seismic waves could affect the measuring system of spring gravimeters that are increasingly used as continuously running devices to monitor and study active volcanoes as a consequence under some circumstances the signal from a continuously running spring gravimeter will be the combination of the gravity field component and the inertial acceleration component the latter due to the ground motion in such cases the inertial acceleration must be separated from the gravity signal to assess the amount of mass redistributed during the studied process to achieve this separation the frequency response curve of the spring gravimeter to inertial accelerations must be calculated since it is not supplied by manufacturers in this paper we present a method to retrieve the above curve using simultaneous recordings during the transit of teleseismic waves of a lacoste romberg d gravimeter and a nanometrics trillium 40 broad band seismometer whose frequency response curve to ground acceleration is known ap riori the use of teleseismic waves is particularly useful for our purpose since teleseisms are not associated with a local mass redistribution the gravimeter will thus be affected only by the ground motion making the above calculation possible our results show that because of the instrumental damping the effect of the inertial acceleration is reduced in the output signal from the gravimeter to 0 5 and 0 1 of its original value at frequencies between 0 02 and 0 07 hz respectively the robustness of the calculated frequency response curve is proven using independent simultaneous signals from gravimeter and broad band seismometer

very long period oscillations of mount erebus volcano as the signal decays vlp scalar moments up to 5 10 11 n m exceed sp moments by an order of magnitude or more suggesting distinct though genetically related sp and vlp source mechanisms we conclude that vlp signals arise from excitation of a quasi linear resonator that is intimately associated with the conduit system and is excited by gravity and inertial forces associated with gas slug ascent eruption and magma recharge vlp signal stability across hundreds of eruptions spanning 5 years the persistence of the lava lake and the rapid posteruptive lava lake recovery indicate a stable near summit magma reservoir and vlp source process index terms 4544 oceanography physical internal and inertial waves 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms 8419 volcanology eruption monitoring 7280 keywords strombolian very long period volcano seismology

willemite zn2sio4 as a possible rb sr geochronometer for dating nonsulfide zn pb mineralization examples from the otavi mountainland namibia abstract the zinc silicate willemite zn 2 sio 4 is the main carrier of zinc in a number of high grade carbonate hosted nonsulfide deposits located in the southern hemisphere that have been recently reinterpreted to be of hypogene hydrothermal origin the timing of willemite mineralization in these deposits is only poorly constrained in this pilot study willemite has been evaluated as a potential rb sr geochronometer that can be used to directly date nonsulfide ore deposits we have analyzed samples of economic stage willemite from the berg aukas and abenab west deposits otavi mountainland namibia which are hosted by neoproterozoic dolomitized and tectonized carbonate rocks rb sr elemental concentration levels and ranges of 87 rb 86 sr and 87 sr 86 sr ratios in these willemite samples are comparable to those observed for the zn sulfide sphalerite which has been already successfully used for direct rb sr dating of carbonate hosted mvt deposits this reflects similar rb sr partitioning mechanisms into zn ore minerals that precipitate either as sulfides from reduced or as silicates from oxidized hydrothermal fluids respectively the rb sr results on willemite presented here reflect mostly low but variable 87 rb 86 sr ratios sufficient to generate radiogenic 87 sr over time this clearly shows that willemite is suitable as an rb sr geochronometer and should be further evaluated for direct rb sr dating of nonsulfide zn deposits isochron regressions combining samples from berg aukas and abenab west willemites yield rb sr ages in the range of ca 500 to 560 ma these values are geochronologically doubtful at first sight due to high excess data scatter mswd 2000 to 3000 massive fine grained willemite samples from abenab west alone n 3 give a still statistically unacceptable mswd 60 isochron regression corresponding to an rb sr age of 574 84 ma more reliable ages are obtained from two statistically adequate small scale rb sr isochron regressions for samples of coarse grained well crystallized berg aukas willemite which yield 499 63 ma mswd 2 6 and 493 2 ma mswd 1 2 respectively regardless of the quality of isochron regressions in terms of mswd the rb sr ages obtained in this study are fully compatible with other available geochronological data that reflect distinct tectonothermal events in the study area therefore on a regional scale they appear to be at least geologically reasonable which has yet to be verified by further studies comparable mineralization ages in the range of ca 490 to 550 ma are also reflected by the few other known economic hypogene willemite deposits in the southern hemisphere for which direct geochronological information is mostly lacking this may point to a global period of hydrothermal activity in the cambrian to lower ordovician under conditions that favored the formation of hypogene nonsulfide zn mineralization

quantitative geomorphic modeling of martian bedrock shorelines 1 multiple researchers have identified shoreline features such as scarps on mars these features occur in both paleocrater lake basins and the northern hemispheric basin here we use a simple numerical model to investigate the viability of forming martian bedrock scarps via wind wave action we use the pierson moskowitz equation modified for martian gravity to generate wave fields under a variety of wind speeds and use those wave fields to drive a terrestrial bedrock shore erosion model modified for martian conditions our results indicate that even with conservative assumptions for the key parameters of wind speed slope and substrate it is difficult to form shoreline features of sufficient magnitude to be captured by spacecraft imaging under many combinations of reasonable initial conditions no shoreline features are formed in cases where shoreline features do develop the largest equilibrium scarp height is 5 m and the shorelines require nearly 2000 model years to form in light of these results and the difficulty of maintaining warm wet climates on mars it seems unlikely that the putative shoreline features identified in images are a result of water wave erosion and alternative hypotheses such as ice cover should be entertained

viscosity of hydrous etna basalt implications for plinian style basaltic eruptions water dissolved in a silicate melt can strongly influence its physical properties and thus magma behavior during crystallization degassing foaming and fragmentation etna is a basaltic volcano whose activity is dominated by effusive eruptions which have long represented a threat to the densely populated surrounding area recently recognition of the products of a plinian eruption 122 b c has raised further issues for hazard assessment at etna and other basaltic volcanoes constraining the behavior of etna magma under conditions relevant to both effusive and explosive hazards requires viscosity data under conditions near the glass transition here we have investigated the viscosity of hydrous etna lava in order to better understand eruptive processes which characterize this volcano the experimental methods which have been used include piston cylinder synthesis of the hydrated melts micropenetration viscometry for low temperature viscosity measurements and near infrared spectroscopy for the evaluation of sample homogeneity and measurements of water content additionally scanning calorimetric determinations were performed to check whether incipient crystallization had occurred sample compositions were determined using electron microprobe analysis and 57fe mossbauer spectroscopy results from this study are compared with previous reports of trachytic phonolitic and model calc alkaline rhyolite hpg8 compositions the viscosity of the basaltic melt dry and wet has been parameterized in terms of temperature and water content via the non arrhenian equation log10 4 643 5 812 44 427 04 h2o t k 499 31 28 74 ln h2o where is the viscosity in pa s h2o is the water content in wt and t is the temperature in kelvin we observe that the viscosity of alkali basalt at more than 0 5 wt h2o is similar to that of an alkaline trachyte agnano monte spina eruption phlegrean fields and much higher than that of a peralkaline phonolite teide tenerife at similar silica contents and nbo t for water contents above 1 5 wt the viscosity of the basalt is similar to that of rhyolitic melts with similar water contents at temperatures ranging from 1 050 to 1 150 c and with water contents between 0 5 and 2 3 wt eruptive conditions the viscosities calculated using the equation defined in this study are 1 in reasonable agreement with those calculated using shaw s model and 2 much lower than those experimentally determined in a previous study however outside these temperature and water content ranges the agreement with shaw s model 1972 breaks down

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

geophysical indications of magma uprising at mt etna during the december 2005 to january 2006 non eruptive period 1 during the december 2005 january 2006 non eruptive period the tremor amplitude at etna markedly increased and negatively correlated with the gravity signal from one of the two summit station over 2 3 hour periods no correlation was found with the signal from the other gravity station we locate the tremor source by inverting the spatial distribution of seismic amplitudes relying on the relative position of the two stations we define a volume within which the gravity source must lie during the period of marked anti correlation the tremor sources intersect this volume in a region located 1 km s se of the summit craters and about 2 km beneath the surface this finding suggests that the anti correlation marks the activation of a joint source process possibly related to the arrival of fresh magma and the consequent gas separation our study has implications for the early recognition of gas segregation processes at active volcanoes

decrypting geophysical signals at stromboli volcano italy integration of seismic and ground based insar displacement data we present the integration of seismic and ground based interferometric synthetic aperture radar system gbinsar displacement data at stromboli volcano ground deformation in the area of summit vents is positively correlated with both seismic tremor amplitude and cumulative amplitudes of very long period vlp signals associated with strombolian explosions changes in vlp amplitudes precede by a few days the variations in ground deformation and seismic tremor we propose a model where the arrival of fresh gas rich magma from depth enhances gas slug formation promoting convection and gas transfer throughout the conduit system at the shallowest portion of the conduit an increase in volatile content causes a density decrease expansion of the magmatic column and augmented degassing activity which respectively induce inflation of the conduit and increased tremor amplitudes the temporal delay between increase of vlp and tremor amplitudes conduit inflation can be interpreted in terms of the different timescales characterizing bulk gas transfer versus slug formation and ascent

magma dynamics crystallization and chemical differentiation of the 1959 kilauea iki lava lake hawaii revisited abstract using constraints from an extensive database of geological and geochemical observations along with results from fluid mechanical studies of convection in magma chambers we identify the main physical processes at work during the solidification of the 1959 kilauea iki lava lakes in turn we investigate their quantitative influence on the crystallization and chemical differentiation of the magma and on the development of the internal structure of the lava lake in contrast to previous studies vigorous stirring in the magma driven predominately by the descent of dense crystal laden thermal plumes from the roof solidification front and the ascent of buoyant compositional plumes due to the in situ growth of olivine crystals at the floor is predicted to have been an inevitable consequence of very strong cooling at the roof and floor the flow is expected to have caused extensive but imperfect mixing over most of the cooling history of the magma producing minor compositional stratification at the roof and thermal stratification at the floor the efficient stirring of the large roof cooling is expected to have resulted in significant internal nucleation of olivine crystals which ultimately settled to the floor additional forcing due to either crystal sedimentation or the ascent of gas bubbles is not expected to have increased significantly the amount of mixing in addition to convection in the magma circulation driven by the convection of buoyant interstitial melt in highly permeable crystal melt mushes forming the roof and the floor of the lava lake is envisaged to have produced a net upward flow of evolved magma from the floor during solidification in the floor zone mush convection may have caused the formation of axisymmetric chimneys through which evolved magma drained from deep within the floor into the overlying magma and potentially the roof we hypothesize that the highly evolved pipe like vertical olivine rich bodies vorbs bull volcanol 43 1980 675 observed in the floor zone of the lake are fossil chimneys in the roof zone buoyant residual liquid both produced at the roof solidification front and gained from the floor as a result of incomplete convective mixing is envisaged to have percolated or leaked into the overlying highly permeable cumulate displacing less buoyant interstitial melt downward the results from rayleigh fractionation type models formulated using boundary conditions based on a quantitative understanding of the convection in the magma indicate that most of the incompatible element variation over the height of the lake can be explained as a consequence of a combination of crystal settling and the extensive but imperfect convective mixing of buoyant residual liquid released from the floor solidification front the remaining chemical variation is understood in terms of the additional influences of mush convection in the roof and floor on the vertical distribution of incompatible elements although cooling was concentrated at the roof of the lake the floor zone is found to be thicker than the roof zone implying that it grew more quickly the large growth rate of the floor is explained as a consequence of a combination of the substantial sedimentation of olivine crystals and more rapid in situ crystallization due to both a higher liquidus temperature and enhanced cooling resulting from imperfect thermal and chemical mixing

a case history of paroxysmal explosion at stromboli timing and dynamics of the april 5 2003 event abstract on april 5 2003 stromboli volcano italy produced the most violent explosion of the past 50 years the event was exceptionally well documented thanks to the presence on the island of several scientists and a large number of instruments deployed over the preceding months to monitor the effusive eruption that began in december 2002 integration of visual documentation deposit features and geophysical data allowed an accurate reconstruction of the explosive event and its dynamics the eruption consisted of a 8 min long explosive event which evolved through four phases whose timing was precisely recorded by an infrared thermometer located about 450 m from the summit crater phases 2 and 3 lasted 39 and 42 s respectively both had an impulsive character were responsible for ejecting almost the entire mass of the pyroclastic products phases 1 and 4 represented respectively a short lived precursory event and a waning tale during phase 2 meter sized ballistic blocks were launched with velocities of 170 m s to altitudes of up to 1400 m above the craters these fell on the volcano flanks and on the village of ginostra about 2 km distant from the vent a vertical jet rose above the craters which developed to feed a convective plume that reached a height of up to 4 km the calculated mass of the phase 2 fallout deposit and mass discharge rate were 1 1 1 4 108 kg and 2 8 3 6 106 kg s respectively during phase 3 a scoria flow deposit with an estimated volume of 0 9 1 1 104 m3 was erupted from the same vent that fed the ongoing sustained lava flow the average mass discharge rate for this phase was 2 5 3 1 105 kg s products emitted during phases 2 and 3 consisted of lithic and fresh magmatic material in similar proportions the juvenile fraction consisted of a deep originated almost aphyric highly vesicular pumice mingled with a shallow derived crystal rich moderately vesicular scoria similarities with the eruption dynamics of other historical paroxysms at stromboli makes the april 5 2003 explosion representative of these highly energetic events that constitute the most hazardous volcanic phenomena at stromboli volcano

experimental constraints on the deep magma feeding system at stromboli volcano italy new experiments have been performed on a high k basalt pst 9 from stromboli volcano italy to constrain the physical conditions of golden pumice magmas at their storage level and discuss their petrogenesis fluid present h2o and co2 bearing near liquidus experiments were performed at 11508c between 100 and 400mpa and under oxidizing conditions glasses were analyzed by fourier transform ir spectroscopy and their h2o and co2 concentrations compared with those in glass inclusions most glass inclusions cluster near the 200mpa isobar suggesting entrapment at a depth of 8 km golden pumice magmas have viscosities of 7 9 pa s and densities of 2 48 2 57 g cm3 compositions of experimental fluids coexisting with melts along the liquidus have been estimated by mass balance they range from co2 rich xh2o 0 2 at 400mpa to h2o rich xh2o 0 8 at 100mpa the free fluid phase present at the reservoir level has an xh2o of 0 6 consistent with equilibration with a near liquidus golden pumice magma below 300mpa clinopyroxene is the liquidus phase in all highpressure experiments either fluid absent h2o or fluid present h2o co2 in contrast at 0 1mpa cpx and ol appear together on the liquidus and olivines are more fo rich up to 89 1 than those crystallizing at high pressures up to 87 3 the composition of cotectic liquids multiply saturated in cpx and ol has been experimentally determined most pumices and a majority of melt inclusions have compositions of cotectic melts in contrast pst 9 plots in the cpx field and is representative of less evolved ankaramitic magmas parental to golden pumices melt inclusions trapped in fo 487 olivines form a group of ultra calcic compositions plotting in the cpx field interpreted as boundary layer melts locally generated by cpx dissolution in the deep reservoir ankaramitic melts in the stromboli feeding system are proposed to derive from primitive mantle melts by combined crystallization mixing wall rock interaction and assimilation

a peritidal evaporite environment in the neoproterozoic of south gabon schisto calcaire subgroup nyanga basin the neoproterozoic 630 ma nsc3 or sciii formation schisto calcaire subgroup of the nyanga basin is a muddy peritidal carbonate dolomite shelf succession that is exposed in the old mouila quarry keri quarry south gabon its 20 m thick lower member is dominated by microbially laminated dolomites and domal stromatolites representing shallow subtidal to supratidal environments abundant pseudomorphs after gypsum and anhydrite relicts indicate carbonate precipitation in sulphate rich hypersaline environments dolomitization of the muddy microbial sediments probably occurred by the evaporite reflux of groundwaters silica precipitates constitute the ultimate diagenetic phase dolomites of the nsc3 formation retain a pattern of oxygenic isotopic variation that reflects the depositional environment shallow subtidal microbialites and stromatolites record the lightest values 18o 5 1 consistent with the isotopic values of neoproterozoic marine waters whereas strongly dolomitized facies display heavier oxygen isotope values 18o 1 3 with the heaviest values in subaerially exposed caps enrichment of 3 8 fungal hyphae and spores have been discovered in these upper parts the 18o pattern through the plurimetric recognized sequences thicknesses from 2 to 6 m suggests a constant exposure in a sabkha like environment although the timing of the series is poorly constrained the c isotopic values of the nsc3 carbonates with values of 2 and 3 approximate depositional conditions minor variations in c isotopes have been observed the evolution of the succession from the stromatolitic lower member to the oolitic upper member of the nsc3 formation could record the progradation of a low energy evaporitic tidal flat that migrated seaward from oolitic shoal crests

identification of variable convective regimes at erta ale lava lake abstract during february 17 19 2002 we collected a combined thermal and seismic data set for persistent lava lake activity at erta ale volcano ethiopia these data indicate that the lake cycled between periods characterized by low 0 01 0 08 m s 1 and high 0 1 0 4 m s 1 surface velocities typically lasting tens to hundreds of minutes these periods of high and low velocity motion define periods of vigorous and sluggish convection respectively spectral analysis revealed that vigorous convection periods were characterized by high frequencies and energies in the thermal data and an increased presence of high frequency energy in the seismic data the data show that vigorous periods were characterized by formation of hot short lived plastic crusts and sluggish periods by cooler longer lived brittle crusts here the higher transit velocity across the lake surface from upwelling zones of crust formation to downwelling zones of crust destruction during the vigorous periods decreases the crust lifetime this in turn decreases the total cooling and thickening experienced by a plate of crust moving across the lake surface two scenarios can be envisaged to explain such convection cycles the first relates variable convection rates to changes in the volume flux and rheology of magma entering the lake in the second cyclic convection is set up by the generation of convective instabilities within the lake in this case cooling of a surface layer generates a slow moving viscous increasingly dense convection layer at the lake surface which is consumed and replaced during overturn

source mechanism of long period events at kusatsu shirane volcano japan inferred from waveform inversion of the effective excitation functions abstract we investigate the source mechanism of long period lp events observed at kusatsu shirane volcano japan based on waveform inversions of their effective excitation functions the effective excitation function which represents the apparent excitation observed at individual receivers is estimated by applying an autoregressive filter to the lp waveform assuming a point source we apply this method to seven lp events the waveforms of which are characterized by simple decaying and nearly monochromatic oscillations with frequency in the range 1 3 hz the results of the waveform inversions show dominant volumetric change components accompanied by single force components common to all the events analyzed and suggesting a repeated activation of a sub horizontal crack located 300 m beneath the summit crater lakes based on these results we propose a model of the source process of lp seismicity in which a gradual buildup of steam pressure in a hydrothermal crack in response to magmatic heat causes repeated discharges of steam from the crack the rapid discharge of fluid causes the collapse of the fluid filled crack and excites acoustic oscillations of the crack which produce the characteristic waveforms observed in the lp events the presence of a single force synchronous with the collapse of the crack is interpreted as the release of gravitational energy that occurs as the slug of steam ejected from the crack ascends toward the surface and is replaced by cooler water flowing downward in a fluid filled conduit linking the crack and the base of the crater lake

magmatic differentiation examined with a numerical model considering multicomponent thermodynamics and momentum energy and species transport abstract magmatic differentiation processes in a cooling magma body were examined using a numerical model considering multicomponent thermodynamics and momentum energy and species transport the model accounts for melt transport induced by its density variation resulting primarily from solid liquid phase change the equilibrium mineral assemblages their mass fractions and their chemical compositions are determined by multicomponent thermodynamic models and these parameters are linked with the calculations of velocity pressure temperature and species fields at each iteration and time step for simplicity solid phases are assumed to be stationary and only olivine and plagioclase that are the earliest crystallization phases in common basaltic magmas are considered as fractionating phases application of the model to natural magmatic system shows that crystallization occurs selectively along the chilled boundaries soon after the cooling and the magma body is separated into high crystallinity mush zones and mostly crystal free main magma because of the melt exchange between the mush zones and the main magma by compositional convection the main magma evolves progressively in composition and the spatial chemical heterogeneity is grown with time the melt segregated from the sidewall mush zone is accumulated below the roof mush zone forming compositional stratification in the upper part of the main magma on the other hand the fractionated melt from the floor mush zone principally mixes with the overlying ambient magma in the middle and lower parts of the main magma body this study shows that the direct treatment of nonlinear coupling among momentum energy and species transport provides useful information of the thermal and chemical evolution of magma chambers as a function of time and space

a numerical model for temporal variations during explosive central vent eruptions an axisymmetrical numerical model has been developed in order to find the temporal evolution of pressure the position of the exsolution level the velocity field the eruption rate and the amount of erupted material of a shallow volatile rich felsic magma chamber during a plinian central vent eruption the overpressure necessary to trigger the eruption is assumed to result from crystallization driven volatile oversaturation we solve the resulting set of equations using a finite element method the results obtained show that the pressure at the conduit entrance decreases exponentially as the eruption proceeds this produces a shifting of the exsolution level so that deeper parts of the chamber become progressively volatile oversaturated during the eruption we assess the influence of chamber geometry and the physical properties of the magma on the computed parameters using several numerical examples the results are also compared with those predicted by previous models from the literature and are found to be in good agreement with documented eruptions the model constitutes a first attempt to numerically model the dynamics and the temporal evolution of the most relevant physical parameters during withdrawal from a closed magma chamber

an expanded non arrhenian model for silicate melt viscosity a treatment for metaluminous peraluminous and peralkaline liquids we present new viscosity measurements for melts spanning a wide range of anhydrous compositions including rhyolite trachyte moldavite andesite latite pantellerite basalt and basanite micropenetration and concentric cylinder viscometry measurements cover a viscosity range of 10 1 to 10 12 pas and a temperature range from 700 to 1650 c these new measurements combined with other published data provide a high quality database comprising 800 experimental data on 44 well characterized melt compositions this database is used to recalibrate the model proposed by giordano and dingwell giordano d dingwell d b 2003a non arrhenian multicomponent melt viscosity a model earth planet sci lett 208 337 349 for predicting the viscosity of natural silicate melts the present contribution clearly shows that 1 the viscosity temperature relationship of natural silicate liquids is very well represented by the vft equation log a b t c over the full range of viscosity considered here 2 the use of a constant high t limiting value of melt viscosity e g a is fully consistent with the experimental data 3 there are 3 different compositional suites peralkaline metaluminous and peraluminous that exhibit different patterns in viscosity 4 the viscosity of metaluminous liquids is well described by a simple mathematical expression involving the compositional parameter sm but the compositional dependence of viscosity for peralkaline and peraluminous melts is not fully controlled by sm for these extreme compositions we refitted the model using a temperature dependent parameter based on the excess of alkalies relative to alumina e g ae sm the recalibrated model reproduces the entire database to within 5 relative

geology mineralogy and geochemistry of the vazante northern extension zinc silicate deposit minas gerais brazil thesis master geological sciences geological engineering queen s university 2012 02 29 16 45 36 41

numerical simulation of convection and mixing in magma chambers replenished with co2 rich magma 1 magma convection and mixing and periodic refilling commonly occur in magma chambers we show here that the presence of co2 in the refilling magma is a very efficient mean of inducing buoyant driven plume rise and large scale convection numerical simulations performed with an appositely developed code for the transient 2d dynamics of multicomponent compressible to incompressible fluids reveal several features of the processes of plume rise convection and mixing in magma chambers associated with chamber refilling a parametric study on co2 abundance in the refilling magma shows that progressively larger amounts of this volatile produce a shift from simple plume rise and spreading near the chamber top to complex patterns of flow circulation and large scale vorticity and mixing lower chamber depth and lower magma viscosity largely enhance the efficiency of mixing and convection favoring the formation of multiple vortexes migrating with time

modelling the time dependent frequency content of low frequency volcanic earthquakes abstract low frequency volcanic earthquakes and tremor have been observed on seismic networks at a number of volcanoes including soufriere hills volcano on montserrat single events have well known characteristics including a long duration several seconds and harmonic spectral peaks 0 2 5 hz they are commonly observed in swarms and can be highly repetitive both in waveforms and amplitude spectra as the time delay between them decreases they merge into tremor often preceding critical volcanic events like dome collapses or explosions observed amplitude spectrograms of long period volcanic earthquake swarms may display gliding lines which reflect a time dependence in the frequency content using a magma filled dyke embedded in a solid homogeneous half space as a simplified volcanic structure we employ a 2d finite difference method to compute the propagation of seismic waves in the conduit and its vicinity we successfully replicate the seismic wave field of a single low frequency event as well as the occurrence of events in swarms their highly repetitive characteristics and the time dependence of their spectral content we use our model to demonstrate that there are two modes of conduit resonance leading to two types of interface waves which are recorded at the free surface as surface waves we also demonstrate that reflections from the top and the bottom of a conduit act as secondary sources that are recorded at the surface as repetitive low frequency events with similar waveforms we further expand our modelling to account for gradients in physical properties across the magma solid interface we also expand it to account for time dependence of magma properties which we implement by changing physical properties within the conduit during numerical computation of wave propagation we use our expanded model to investigate the amplitude and time scales required for modelling gliding lines and show that changes in magma properties particularly changes in the bubble nucleation level provide a plausible mechanism for the frequency variation in amplitude spectrograms

modelling low frequency volcanic earthquakes in a viscoelastic medium with topography summary magma properties are fundamental to explain the volcanic eruption style as well as the generation and propagation of seismic waves this study focusses on magma properties and rheology and their impact on low frequency volcanic earthquakes we investigate the effects of anelasticity and topography on the amplitudes and spectra of synthetic low frequency earthquakes using a 2 d finite difference scheme we model the propagation of seismic energy initiated in a fluid filled conduit embedded in a homogeneous viscoelastic medium with topography we model intrinsic attenuation by linear viscoelastic theory and we show that volcanic media can be approximated by a standard linear solid sls for seismic frequencies above 2 hz results demonstrate that attenuation modifies both amplitudes and dispersive characteristics of low frequency earthquakes low frequency volcanic earthquakes are dispersive by nature however if attenuation is introduced their dispersion characteristics will be altered the topography modifies the amplitudes depending on the position of the seismographs at the surface this study shows that we need to take into account attenuation and topography to interpret correctly observed low frequency volcanic earthquakes it also suggests that the rheological properties of magmas may be constrained by the analysis of low frequency seismograms

seismological insight into the kinematics of the 5 april 2003 vulcanian explosion at stromboli volcano southern italy 1 on 5 april 2003 at 07 13 gmt 09 13 local time a violent vulcanian explosion occurred at stromboli volcano at the time of the event an eruptive crisis was ongoing at the volcano with a lava flow outpouring along the sciara del fuoco flank the seismic signals related to the event were recorded by 8 permanent broadband stations and gives information about the eruption kinematics an ultra long period signal period 20 s that we interpret as the effect of the ground tilt on the broadband sensors starts about 4 min before and terminates about 1 min after the explosion on the basis of the radial pattern of tilt directions we conclude that this signal is the effect of the deformation of the volcanic edifice due to the rapid rising of a batch of magma its ejection and the magma column readjustment about 1 min before the explosion we observe an high frequency signal period 0 1 s that we believe to be related to the vesiculation of the rising batch of gas rich magma at 07 13 35 gmt a powerful very long period signal period 2 20 s marking the onset of the explosive fragmentation is recorded this is confirmed by a blast wave following few seconds later the remaining seismic signal more than 3 min shows an higher frequency content being related only to the fall of ballistic ejecta and to landslides along sciara del fuoco we propose the implementation of an early warning system for the short term forecast of such explosions based on the real time automatic detection of the tilt signals preceding such events

on the dynamics of magma mixing by reintrusion implications for pluton assembly processes many plutons have formed by repeated intrusion with complex internal contacts characterized by sharp and diause kinematic and compositional domains we performed numerical experiments of mixing following magma chamber recharge that explicitly considers the fluid dynamics of multiphase mixtures in the limit of zero diausivity of intensive scalar quantities and low stokes number mingling by fluid instability is equivalent to deformation and persistent fluid structures are kinematic attractors three distinct regimes are exemplified and can be described by their multiphase reynolds or grashof number for a reynolds number greater than about 100 an internal intrusive contact will collapse by internal wave breaking and chaotic magma mingling and mixing yield a nearly chamber wide stratification this flow may scour mushy regions at the walls and widely distribute previously crystallized material for reynolds numbers from 10 to 100 the internal wave does not break and the stratification occupies less of the chamber leaving islands of unmixed material for reynolds numbers around 1 internal slumping and folding can occur and is the most likely to be preserved by a mineral fabric internal sub vertical contacts require a high absolute viscosity in the resident magma representing a time break between episodes of reintrusion the shape of perched mafic domains captures the progress of sinking from higher levels into regions of increasing strength and crystallinity 7 2000 elsevier science ltd all rights reserved