crystallization and welding variations in a widespread ignimbrite sheet the rattlesnake tuff eastern oregon usa the 7 05 ma rattlesnake tuff covers ca 9000 km2 but the reconstructed original coverage was between 30000 and 40000 km2 thicknesses are remarkably uniform ranging between 15 and 30 m for the most complete sections only 13 of the area is covered with tuff thicker than 30 m to a maximum of 70 m the present day estimated tuff volume is 130 km3 and the reconstructed magma volume of the outflow is 280 km3 dre dense rock equivalent the source area of the tuff is inferred to be in the western harney basin near the center of the tuff distribution based mainly on a radial exponential decrease in average pumice size and is consistent with a general radial decrease in welding and degree of post emplacement crystallization rheomorphic tuff is found to a radius of 40 60 km from the inferred source four facies of welding and four of post emplacement crystallization are distinguishable they are non welded incipiently welded partially welded and densely welded zones and vapor phase pervasively devitrified spherulite and lithophysae zones the vapor phase pervasively devitrified and lithophysae zones are divided into macroscopically distinguishable subzones at constant thickness 20 3 m and over a distance of 1 3 km nonrheomorphic sections can cary between two extremes a entirely vitric sections grading from nonwelded to incipiently welded and b highly zoned sections highly zoned sections have a basal non to densely welded vitric tuff overlain by a spherulite zone that grades upward through a lithophysae dominated zone to a zone of pervasive devitrification which in turn is overlain by a zone of vapor phase crystallization and is capped by partially welded vitric tuff a three dimensional welding and crystallization model has been developed based on integrating local and regional variations of 85 measured sections strong local variations are interpreted to be the result of threshold governed welding and crystallization controlled by residence time above a critical temperature which is achieved through differences in thickness and accumulation rate

infrasonic tremor in the diffraction zone 1 volcanic tremor signals recorded by an infrasound array 12 5 km from the active vent of k lauea volcano show clear diurnal amplitude variations and originate from a well defined direction pointing to the active pu u crater complex spectral amplitudes between 0 02 0 3 hz a proxy for wind speed increase when the wind speeds increase during the daytime spectral amplitudes between 0 5 3 hz where infrasonic tremor is concentrated increase when the wind speeds decrease at night power spectrum analysis shows that when ambient noise levels drop infrasonic tremor amplitudes rise array processing confirms this relationship and reveals tremor detections and amplitudes decrease during the day these changes in infrasonic tremor spectral amplitude and coherence are most likely due to diurnal variations in atmospheric boundary layers affecting infrasonic propagation within the diffraction zone recognition of these regional atmospheric patterns is necessary to permit robust infrasonic remote sensing of volcanic processes

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

acoustic source inversion to estimate volume flux from volcanic explosions we present an acoustic waveform inversion technique for infrasound data to estimate volume fluxes from volcanic eruptions previous inversion techniques have been limited by the use of a 1 d green s function in a free space or half space which depends only on the source receiver distance and neglects volcanic topography our method exploits full 3 d green s functions computed by a numerical method that takes into account realistic topographic scattering we apply this method to vulcanian eruptions at sakurajima volcano japan our inversion results produce excellent waveform fits to field observations and demonstrate that full 3 d green s functions are necessary for accurate volume flux inversion conventional inversions without consideration of topographic propagation effects may lead to large errors in the source parameter estimate the presented inversion technique will substantially improve the accuracy of eruption source parameter estimation cf mass eruption rate during volcanic eruptions and provide critical constraints for volcanic eruption dynamics and ash dispersal forecasting for aviation safety application of this approach to chemical and nuclear explosions will also provide valuable source information e g the amount of energy released previously unavailable

structure and emplacement of a rhyolitic obsidian flow little glass mountain medicine lake highland northern california many rhyolitic obsidian flows show consistent stratigraphic relations among textural units exposed in the flow fronts of undissected flows and in cross sections of older flows the stratigraphy of the holocene little glass mountain rhyolitic obsidian flow consists of from bottom to top air fall tephra deposits basal breccia coarsely vesicular pumice obsidian finely vesicular pumice and surface breccia slightly crystalline rhyolite occurs near the vent areas a model of obsidian flow emplacement based on these textural relations is presented this stratigraphy may reflect the distribution of volatiles within the magma source region with the interlayered contact between coarsely vesicular pumice and overlying obsidian indicating stratification of volatiles in the magma body the distribution of pumiceous and glassy zones along with the orientations of flow banding can be used to map the surface structure of rhyolitic obsidian flows this complex structure as mapped on the little glass mountain flow reflects both the initial flow stratigraphy and subsequent deformational processes during emplacement of the lava three processes disrupt the initial flow configuration the rise of coarse pumice diapirs from the base of the flow the inward propagation of fractures in areas of extension and surface folding in sites of flow parallel compression subvertical flow banding in vent areas indicates that fracturing accompanies the emergence of lava most of the observed upper surface of a dome originates as a fracture plane the structure of domes that form over vent areas may reflect the orientation of dike like conduits as well as the local state of stress during extrusion

rheomorphic ignimbrites of the rogerson formation central snake river plain usa record of mid miocene rhyolitic explosive eruptions and associated crustal subsidence along the yellowstone hotspot track rogerson graben usa is critically placed at the intersection between the yellowstone hotspot track and the southern projection of the west snake river rift eleven rhyolitic members of the re defined 420 m thick rogerson formation record voluminous high temperature explosive eruptions emplacing extensive ashfall and rheomorphic ignimbrite sheets yet each member has subtly distinct field chemical and palaeomagnetic characteristics new regional correlations reveal that the brown s view ignimbrite covers 3300 km2 and the wooden shoe ignimbrite covers 4400 km2 and extends into nevada between 11 9 and 8 ma the average frequency of large explosive eruptions in this region was 1 per 354 ky about twice that at yellowstone the chemistry and mineralogy of the early rhyolites show increasing maturity with time possibly by progressive fractional crystallisation this was followed by a trend towards less evolved rhyolites that may record melting and hybridisation of a mid crustal source region contemporaneous magmatism induced crustal subsidence of the central snake river basin is recorded by successive ignimbrites offlapping and thinning up the n facing limb of a regional basin margin monocline which developed between 10 59 and 8 ma the syn volcanic basin topography contrasted significantly with the present day elevated yellowstone hotspot plateau concurrent basin and range extension produced the n trending rogerson graben early uplift of the shoshone hills 10 34 ma was followed by initiation of the shoshone fault and an e sloping half graben 10 3 10 1 ma the graben asymmetry then reversed with initiation of the brown s bench fault 8 ma which remained intermittently active until the pliocene

emplacement of the rocche rosse rhyolite lava flow lipari aeolian islands the rocche rosse lava flow marks the most recent rhyolitic extrusion on lipari island italy and preserves evidence for a multi stage emplacement history due to the viscous nature of the advancing lava 108 to 1010 pa s indicators of complex emplacement processes are preserved in the final flow this study focuses on structural mapping of the flow to highlight the interplay of cooling crust formation and underlying slope in the development of rhyolitic lavas the flow is made up of two prominent lobes small 0 2 m scale folding and a channelled geometry foliations dip at 2 4 over the flatter topography close to the vent and up to 30 50 over steeper mid flow topography brittle faults tension gashes and conjugate fractures are also evident across flow heterogeneous deformation is evident through increasing fold asymmetry from the vent due to downflow cooling and stagnation a steeper underlying topography mid flow led to development of a channelled morphology and compression at topographic breaks resulted in fold superimposition in the channel we propose an emplacement history that involved the evolution through five stages each associated with the following flow regimes 1 initial extrusion crustal development and small scale folding 2 extensional strain stretching lineations and channel development over steeper topography 3 compression at topographic break autobrecciation lobe development and medium scale folding 4 progressive deformation with stagnation large scale folding and re folding and 5 brittle deformation following flow termination the complex array of structural elements observed within the rocche rosse lava flow facilitates comparisons to be made with actively deforming rhyolitic lava flows at the chilean volcanoes of chaiten and cordon caulle offering a fluid dynamic and structural framework within which to evaluate our data

growth of megaspherulites in a rhyolitic vitrophyre megaspherulites occur in a rhyolitic vitrophyre near the base of a thick rhyolitic vitrophyre that occupies a late eocene to early oligocene volcanic tectonic basin near silver cliff colorado diameters of the megaspherulites range from 0 3 to over 3 66 m including an alteration layer the megaspherulites are compound spherulites they are holocrystalline very fine to fine grained composed of sanidine and quartz and surrounded by a thin sanidine quartz rind and an alteration layer containing mordenite and 15 a montmorillonite megaspherulite crystallization began soon after the vitrophyre was emplaced as the result of sparse heterogeneous nucleation under highly nonequilibrium conditions spherulite growth proceeded in a diffusion controlled manner under lowered viscosity as a result of a high water content 5 to 7 wt which also contributed to sparse nucleation when nucleation did occur it was at a large t 245 350 c on near critical sized nuclei once the spherulites began to grow continued nucleation was on existing growth cones and new independent spherulites did not form sanidine crystals grew with a fibrous habit which is favored by a large t restricting fibril lengths and diameters between 10 30 and 3 7 m respectively during crystallization these growth cones impinged upon each other resulting in fibril cone free areas these cone free interconal areas consist of coarser fine grained phases dominated by quartz which crystallized from the melt as it accumulated between the crystallizing sanidine fibrils of the cones the anhydrous nature of the sanidine and quartz suggests that their crystallization concentrated a water rich residual fluid enriched in ca mg and fe and depleted in si k and na at the megaspherulite vitrophyre interface this fluid phase enclosed the megaspherulites resulting in the hydrothermal alteration of the vitrophyre forming a hydrothermal alteration layer as indicated by the presence of the minerals mordenite and montmorillonite

compressive strength and failure modes of lithophysae rich topopah spring tuff specimens and analog models containing cavities the presence of lithophysae in some units of topopah spring tuff at yucca mountain nevada the u s high level nuclear waste repository have a detrimental effect on the engineering properties of the rock mass and its performance the lithophysae were formed by pockets of gas trapped within the falling volcanic ash that formed the tuff units the porosity associated with the lithophysae is termed macroporosity because of the large pore size as compared with traditional rock pores in this paper lithophysae rich tuff and analog models both cylindrical and cubic made of plaster of paris containing artificially created cavities were tested to assess the effect of macroporosity on both the uniaxial compressive strength and failure modes of the specimens as expected compressive strength decreases with increasing porosity due to lithophysae in tuff and cavities in plaster analog specimens failure modes of cylindrical specimens were also investigated the failure modes observed were grouped into four distinct categories spalling axial splitting shear failure and web failure the failure modes transition from spalling through web failure as the percentage of macroporosity within the specimen increased

diffusion controlled spherulite growth in obsidian inferred from h2o concentration profiles spherulites are spherical clusters of radiating crystals that occur naturally in rhyolitic obsidian the growth of spherulites requires diffusion and uptake of crystal forming components from the host rhyolite melt or glass and rejection of non crystal forming components from the crystallizing region water concentration profiles measured by synchrotron source fourier transform spectroscopy reveal that water is expelled into the surrounding matrix during spherulite growth and that it diffuses outward ahead of the advancing crystalline front we compare these profiles to models of water diffusion in rhyolite to estimate timescales for spherulite growth using a diffusion controlled growth law we find that spherulites can grow on the order of days to months at temperatures above the glass transition the diffusion controlled growth law also accounts for spherulite size distribution spherulite growth below the glass transition and why spherulitic glasses are not completely devitrified

thermal interaction between lava lobes pahoehoe lava may be emplaced as lobes which flow on top of each other a cross section was investigated through two lava lobes from the active pu u o o vent kilauea hawaii consisting of a 6 6 cm thick top lobe and the upper part of a 3 2 cm thick underlying bottom lobe the top lobe cooled at the contact with air and has a quenched glassy margin which is almost 1 cm thick the underlying lobe although originally also in contact with air is entirely crystalline suggesting that the bottom lobe experienced crystallization during reheating by the top lobe based on published data experimental results on reheating show that crystallization of basalt glass requires temperatures above 920 c and knowing that the pu u o o melt is initially at about 1 160 c the minimum temperature of the bottom lobe should have been 700 c prior to emplacement of the top lobe crystal size distribution csd theory demonstrates an oscillation of grain size which is superposed on an overall increase in size with depth cooling rates estimated from simple modeling and growth rates derived from csd suggest a thermal interaction of the bottom lobe on the top lobe to about 2 cm from the contact

infrasonic harmonic tremor and degassing bursts from halema uma u crater kilauea volcano hawaii 1 the formation evolution collapse and subsequent resurrection of a vent within halema uma u crater kilauea volcano produced energetic and varied degassing signals recorded by a nearby infrasound array between 2008 and early 2009 after 25 years of quiescence a vent clearing explosive burst on 19 march 2008 produced a clear complex acoustic signal near continuous harmonic infrasonic tremor followed this burst until 4 december 2008 when a period of decreased degassing occurred the tremor spectra suggest volume oscillation and reverberation of a shallow gas filled cavity beneath the vent the dominant tremor peak can be sustained through helmholtz oscillations of the cavity while the secondary tremor peak and overtones are interpreted assuming acoustic resonance the dominant tremor frequency matches the oscillation frequency of the gas emanating from the vent observed by video tremor spectra and power are also correlated with cavity geometry and dynamics with the cavity depth estimated at 219 m and volume 3 106 m3 in november 2008 over 21 varied degassing bursts were observed with extended burst durations and frequency content consistent with a transient release of gas exciting the cavity into resonance correlation of infrasound with seismicity suggests an open system connecting the atmosphere to the seismic excitation process at depth numerous degassing bursts produced very long period 0 03 0 1 hz infrasound the first recorded at kilauea indicative of long duration atmospheric accelerations kilauea infrasound appears controlled by the exsolution of gas from the magma and the interaction of this gas with the conduits and cavities confining it

spherulites and thundereggs from pitchstones of the deccan traps geology petrochemistry and emplacement environments spherulites and thundereggs are rounded typically spherical polycrystalline objects found in glassy silicic rocks spherulites are dominantly made up of radiating microscopic fibers of alkali feldspar and a silica mineral commonly quartz they form due to heterogeneous nucleation in highly supercooled rhyolitic melts or by devitrification of glass associated features are lithophysae stone bubbles which have an exterior sometimes concentric shells of fine quartz and feldspar and internal cavities left by escaping gas when filled by secondary silica these are termed thundereggs here we describe four distinct occurrences of spherulites and thundereggs in pitchstones mostly rhyolitic some trachytic of the deccan traps india the thundereggs at one locality were previously misidentified as rhyolitic lava bombs and products of pyroclastic extrusive activity we have character ized the thundereggs petrographically and geochemically and have determined low contents of magmatic water 0 21 0 38 wt in them using fourier transform infrared spectros copy we consider that the spherulite bearing outcrops at one of the localities are of lava flows but the other three represent subvolcanic intrusions based on the structural disposition of the deccan sheet intrusions studied here and considerations of regional geology we suggest that they are cone sheets emplaced from a plutonic center now submerged beneath the

the continuing story of etna s new southeast crater 2012 2014 evolution and volume calculations based on field surveys and aerophotogrammetry abstract during the years 2013 2014 the new southeast crater nsec at the summit of mount etna produced frequent episodes of lava fountaining paroxysms and its cone continued to grow at unprecedented rates many of the episodes were of rather brief duration and violently explosive producing mostly pyroclastic material and minor volumes of lava other episodes especially those since mid december 2013 were characterized by violent strombolian activity without producing sustained lava fountains and significant amounts of tephra but emitting more voluminous lava flows one episode of intense strombolian and effusive activity that was possibly fed from the nsec conduit occurred from vents located approximately 1 km north of the crater on the east flank of the northeast crater in july august 2014 the evolution of the nsec cone between 2012 and 2014 was documented by repeated gps surveys carried out both from a distance and on the cone itself by the acquisition of comparison photographs and by two aerophotogrammetric surveys from these surveys the highest point of the nsec results to have grown from 190 m may 2012 to 215 m october 2014 above the pre cone surface reaching an elevation of 3290 m and its volume more than doubled to 50 0 6 5 10 6 m 3 representing the 40 of the total bulk volume of the volcanic products including pyroclastic fallout erupted in 2011 2014 which is 147 2 10 6 m 3 101 3 10 6 m 3 dense rock equivalent the whole of the 2011 2014 nsec activity marks an unusually high frequency of rather explosive tephra rich eruptive episodes compared to etna s activity in past decades and centuries although the average magma production rate in this interval is close to the supposed long term output rate of the volcano the latest eruptive episodes show a tendency of the nsec coalescing with the old southeast crater cone which therefore represents a miniature example of a growing compound volcano at the summit of etna

infrasound reveals transition to oscillatory discharge regime during lava fountaining implication for early warning 1 we present the analysis of 4 million infrasonic signals which include 39 episodes of lava fountains recorded at 5 5 km from the active vents we show that each eruptive episode is characterized by a distinctive trend in the amplitude waveform and frequency content of the acoustic signals reflecting different explosive levels lava fountain starts with an 93 min long violent phase of acoustic transients at 1 25 hz repeating every 2 5 s infrasound suddenly evolves into a persistent low frequency quasi monochromatic pressure oscillation at 0 4 hz we interpret this shift as induced by the transition from the slug discrete strombolian to churn flow sustained lava fountain regime that is reflecting an increase in the gas discharge rate we calculate that infrasonic transition can occur at a gas superficial velocity of 76 m s and it can be used to define infrasonic based thresholds for an efficient early warning system

infrasonic evidences for branched conduit dynamics at mt etna volcano italy an edited version of this paper was published by agu copyright 2009 american geophysical union

flow banding in basaltic pillow lavas from the early archean hooggenoeg formation barberton greenstone belt south africa well preserved pillow lavas in the uppermost part of the early archean volcanic sequence of the hooggenoeg formation in the barberton greenstone belt exhibit pronounced flow banding the banding is defined by mm to several cm thick alternations of pale green and a dark green conspicuously variolitic variety of aphyric metabasalt concentrations of relatively immobile tio2 al2o3 and cr in both varieties of lava are basaltic compositional differences between bands and variations in the lavas in general have been modified by alteration but indicate mingling of two different basalts one richer in tio2 al2o3 mgo feot and probably ni and cr than the other as the cause of the banding the occurrence in certain pillows of blebs of dark metabasalt enclosed in pale green metabasalt as well as cores of faintly banded or massive dark metabasalt suggest that breakup into drops and slugs in the feeder channel to the lava flow initiated mingling the inhomogeneous mixture was subsequently stretched and folded together during laminar shear flow through tubular pillows while diffusion between bands led to partial homogenisation the most common internal pattern defined by the flow banding in pillows is concentric in some pillows the banding defines curious mushroom like structures commonly cored by dark variolitic metabasalt which we interpret as the result of secondary lateral flow due to counter rotating transverse dean vortices induced by the axial flow of lava towards the flow front through bends generally downward in the tubular pillows other pillows exhibit weakly banded or massive dark variolitic cores that are continuous with wedge shaped apophyses and veins that intrude the flow banded carapace these cores represent the flow of hotter and less viscous slugs of the dark lava type into cooled and stiffened pillows

varying seismic acoustic properties of the fluctuating lava lake at villarrica volcano chile villarrica volcano outgasses through an open lava lake with bubbles ranging in size from submillimeter to several meters the largest of which produce strombolian bursting events that are visible from the crater rim thousands of shallow strombolian events identified through seismic waveform cross correlation were found to produce discrete and repetitive long period seismic and infrasonic signals we identified variations of up to 0 7 s in seismic acoustic arrival delay times between april and july 2010 at a station 750 m from the vent which we interpret as due to fluctuations in the level of lava lake during time periods interpreted as having high lava lake levels based on reduced time delays interevent times were also reduced and average seismic amplitude measurements seismic and acoustic event energies and volcano acoustic seismic ratios were all high as compared to times when the lava lake was lower the crater is also a source of nearly continuous monotonic infrasonic tremor we found that the peak frequency of this infrasonic tremor typically around 0 5 1 0 hz was inversely correlated with seismic acoustic delay times and therefore an indicator of lava lake level we use this correlation to propose a new model for infrasonic tremor generation namely using crater geometry to approximate a bessel horn we interpret the two clearest cycles of elevated seismicity and lava lake level as due to an increase in exsolved gas resulting from an injection of volatile rich magma or an overturn in a deeper magma reservoir

textural characterization major and volatile element quantification and ar ar systematics of spherulites in the rocche rosse obsidian flow lipari aeolian islands a temperature continuum growth model spherulitic textures in the rocche rosse obsidian flow lipari aeolian islands italy have been characterized through petrographic crystal size distribution csd and in situ major and volatile elemental analyses to assess the mode temperature and timescales of spherulite formation bulk glass chemistry and spherulite chemistry analyzed along transects across the spherulite growth front glass boundary reveal major oxide and volatile h2o co2 f cl and s chemical variations and heterogeneities at a 5 m scale numerous bulk volatile data in non vesicular glass spatially removed from spherulitic textures reveal homogenous distributions of volatile concentrations h2o 0 089 0 012 wt f 950 40 ppm and cl 4 100 330 ppm with co2 and s consistently below detection limits suggesting either complete degassing of these volatiles or an originally volatile poor melt volatile concentrations across the spherulite boundary and within the spherulitic textures are highly variable these observations are consistent with diffusive expulsion of volatiles into melt leaving a volatile poor rim advancing ahead of anhydrous crystallite growth which is envisaged to have had a pronounced effect on spherulite crystallization dynamics argon concentrations dissolved in the glass and spherulites differ by a factor of 20 with ar sequestered preferentially in the glass phase petrographic observation csd analysis volatile and ar data as well as diffusion modeling support continuous spherulite nucleation and growth starting at magmatic emplacement temperatures of 790 825 c and progressing through the glass transition temperature range tg 750 620 c being further modified in the solid state we propose that nucleation and growth rate are isothermally constant but vary between differing stages of spherulite growth with continued cooling from magmatic temperatures such that there is an evolution from a high to a low rate of crystallization and low to high crystal nucleation based on the diffusion of h2o across these temperature ranges 800 300 c timescales of spherulite crystallization occur on a timescale of 4 days with further modification up to 400 years growth is prohibitively slow 400 c and would become diffusion reliant selective deformation of spherulites supports a down temperature continuum of spherulite formation in the rocche rosse obsidian indeed petrographic evidence suggests that high strain zones may have catalyzed progressive nucleation and growth of further generations of spherulites during syn and post emplacement cooling

new perspectives on graptolite distributions and their use as indicators of platform margin dynamics graptolite distributions in ordovician shelf slope and basinal facies in the great basin indicate that graptolites were scarce in open oceanic waters oceanward of the cordilleran shelf margin and that they thrived in waters above the margin this pattern is consistent with that of most zooplankton in modern oceans it follows from these observations that the depositional setting of typical graptolitic shale was the area of the sea floor under continental margin upwelling zones where graptolites flourished and within the oxygen minimum zone where their rhabdosomes were preserved with changes over time in relative sea level deep oceanic circulation and wind driven surface circulation the upwelling and oxygen minimum zones may have thickened or thinned migrated landward or oceanward and expanded laterally contracted or even disappeared the observed graptolite occurrences suggest that the primary graptolite biotope that is the habitat of diverse and abundant faunas was a relatively narrow belt of upwelling waters along and extending somewhat open oceanward from the continental margin provinces were maintained only to the extent that species could disperse along continental margins distribution of typical graptolitic strata may be used to interpret development of continental margins because such distribution incorporates a signal of sea level rise or fall oceanographic changes especially upwelling and tectonic events that led to creation and deterioration of upwelling conditions in which graptolites flourished

infrasound observations of the 2008 explosive eruptions of okmok and kasatochi volcanoes alaska 1 the recent explosive eruptions of okmok and kasatochi volcanoes provide an opportunity to use seismic local infrasound distant infrasound array and remote sensing data in concert to better monitor volcanoes in the aleutian arc and to better understand the source processes the eruption of okmok volcano began on 12 july 2008 and included a seismically active phase that lasted continuously for about 10 h in contrast the eruption of kasatochi which began on 7 august 2008 consisted of five explosive events that lasted from 26 to 68 min each and had a cumulative duration of 3 4 h given the event times by local seismic stations the corresponding infrasound signals were found in the data recorded by local infrasound sensors and by distant infrasound arrays signals from the okmok eruption were detected by three international monitoring system ims arrays as far away as 4400 km signals from the kasatochi eruption were detected at greater distances up to 5200 km away by seven infrasound arrays including the ones that detected the event at okmok volcano back azimuth propagation and a simple acoustic wave propagation model in unison with known event times were used to confirm that the planar acoustic signals recorded at the arrays had originated from the eruptions the infrasound array data reflected the differences in eruption styles between okmok and kasatochi as the signals from kasatochi were of shorter duration of greater amplitude and detected over greater distances the infrasound array data were also able to distinguish between two types of tremor episodes that occurred at kasatochi volcano based on atmospheric disturbance

eruption mass estimation using infrasound waveform inversion and ash and gas measurements evaluation at sakurajima volcano japan abstract eruption mass and mass flow rate are critical parameters for determining the aerial extent and hazard of volcanic emissions infrasound waveform inversion is a promising technique to quantify volcanic emissions although topography may substantially alter the infrasound waveform as it propagates advances in wave propagation modeling and station coverage permit robust inversion of infrasound data from volcanic explosions the inversion can estimate eruption mass flow rate and total eruption mass if the flow density is known however infrasound based eruption flow rates and mass estimates have yet to be validated against independent measurements and numerical modeling has only recently been applied to the inversion technique here we present a robust full waveform acoustic inversion method and use it to calculate eruption flow rates and masses from 49 explosions from sakurajima volcano japan six infrasound stations deployed from 12 20 february 2015 recorded the explosions we compute numerical green s functions using 3 d finite difference time domain modeling and a high resolution digital elevation model the inversion assuming a simple acoustic monopole source provides realistic eruption masses and excellent fit to the data for the majority of the explosions the inversion results are compared to independent eruption masses derived from ground based ash collection and volcanic gas measurements assuming realistic flow densities our infrasound derived eruption masses for ash rich eruptions compare favorably to the ground based estimates with agreement ranging from within a factor of two to one order of magnitude uncertainties in the time dependent flow density and acoustic propagation likely contribute to the mismatch between the methods our results suggest that realistic and accurate infrasound based eruption mass and mass flow rate estimates can be computed using the method employed here if accurate volcanic flow parameters are known application of this technique could be broadly applied to enable near real time calculation of eruption mass flow rates and total masses these critical input parameters for volcanic eruption modeling and monitoring are not currently available

volcanic glass in cretaceous dacites and rhyolites of the parana magmatic province southern brazil characterization and quantification by xrd rietveld abstract acidic rocks are a significant component of the cretaceous parana magmatic province occurring in different stratigraphic positions and often forming deposits of complex and as yet poorly defined architecture vitrophyric varieties are surprisingly abundant for a volcanic sequence of this age and are composed of predominant glass plus plagioclase labradorite andesine pyroxenes augite pigeonite and orthopyroxene ti rich magnetite and traces of apatite hypocrystalline rocks largely derived from devitrification additionally contain sanidine cristobalite and quartz the negative correlation between the abundance of these minerals and the amount of glass suggests that these latter phases formed by devitrification modal analysis using a combined xrd rietveld rir method detected glass contents between 0 and 85 wt in a set of representative samples of palmas type acidic rocks from southern brazil with dacite to rhyolite composition modal compositions determined by xrd and by scanning electron microscope are in good agreement with each other and were checked against whole rock xrf chemical data water contents up to 4 wt show a positive linear correlation with the amount of glass and are inferred to be mostly secondary as original pre eruptive h2o dissolved in melts is inferred to have been

the effects of heterogeneity in magma water concentration on the development of flow banding and spherulites in rhyolitic lava abstract this study focuses on the origin of flow banded rhyolites that consist of compositionally similar darker and lighter flow bands of contrasting texture and color infrared radiation was used to obtain fourier transform infrared ftir spectra from which water concentrations were calculated and to map variations in water concentrations across zones of spherulites and glass from the 23 million year old sycamore canyon lava flow of southern arizona lighter colored thicker flow bands consist of gray glass fine grained quartz and large 1 0 to 1 5 mm spherulites darker colored thinner flow bands consist of orange glass and smaller 0 1 to 0 2 mm spherulites the centers of both large and small spherulites are occupied by either 1 a quartz or sanidine crystal 2 a granophyric intergrowth or 3 a vesicle mapping of water concentration dominantly oh in glass and oh and h2o in sanidine crystals illustrates fluctuating water availability during quenching of the host melt textures of large spherulites in the lighter gray bands in some cases indicate complex quenching histories that suggest that local water concentration controlled the generation of glass versus crystals small spherulites in darker orange bands have only one generation of radiating crystal growth both the glass surrounding spherulites and the crystals in the spherulites contain more water in the gray flow bands than in the orange flow bands flow banding in the sycamore canyon lava flow may have originated by the stretching of a magma that contained pre existing zones vesicles or proto vesicles of contrasting water concentration as the magma flowed in the conduit and on the surface variation in the original water concentration in the alternating layers is interpreted to have resulted in differences in undercooling textures in spherulites in the lighter compared to the darker flow bands

an overview of volcano infrasound from hawaiian to plinian local to global abstract volcano infrasound is an increasingly useful technique for detecting locating characterizing and quantifying eruptive activity and can be used to constrain eruption source parameters in recent years studies of infrasound data from active volcanoes have shown clear progress towards mitigating volcanic hazards and understanding volcanic source processes volcano acoustic sources are shallow or aerial thus volcano infrasound data provide valuable information on eruption dynamics and are readily combined with direct and remote observations of gas ash and other eruptive phenomena the infrasound signals produced by volcanoes are indicative of the eruption style and dynamics here we review the diversity of infrasound signals generated by a wide variety of volcanic eruptions from hawaiian to plinian and the physical processes inferred to produce them we place particular emphasis on regional 15 250 km distance and global 250 km distance volcano infrasound studies as recent work in this area has made significant advances in monitoring and characterizing remote and difficult to monitor eruptions long range infrasonic detection of explosive volcanic eruptions is possible due to the energetic source mechanisms involved minor atmospheric attenuation at low frequencies and the existence of waveguides in the atmosphere however accurate characterization of the atmosphere and its spatiotemporal variability is required for reliable long range sound propagation modeling and correct interpretation of global infrasound recordings conversely because volcanic explosions are energetic and sometimes repetitive infrasound sources they can be used to validate atmospheric and acoustic propagation models

simulation and inversion of harmonic infrasound from open vent volcanoes using an efficient quasi 1d crater model abstract volcanic activity excites low frequency acoustic waves termed infrasound in the atmosphere infrasound observations can be used to provide constraints on eruption properties such as crater geometry and volume flux at open vent volcanoes such as erebus antarctica and villarrica chile the infrasound signal is modulated by the crater properties eruptive activity at the bottom of the crater such as unsteady degassing or explosions can excite the air mass within the crater into resonance leading to infrasound generation with signals possessing clear spectral peaks termed harmonics therefore the effect of the crater on the infrasound signal or crater acoustic response must be accounted for when inverting harmonic infrasound observations for eruption properties at open vent volcanoes here we develop a linearized model of quasi one dimensional 1d wave propagation inside volcanic crater coupled with 3d axisymmetric radiation into the atmosphere from the crater with waves generated by a volumetric flow rate source at the bottom of the crater we perform simulations for a range of volcanic crater geometries temperature profiles gas compositions and source descriptions to explore the influence of these properties on the infrasound signal the observed infrasound signal depends on the flow rate source time function but interference of up and down going waves within the crater selectively amplifies the signal at the resonant frequencies of the crater the crater resonance model presented here is verified by comparison with an established three dimensional 3d infrasound code and is shown to be appropriate for realistic crater geometries when the crater radius is less than approximately one quarter of the acoustic wavelength the model presented here is more computationally efficient and can be used to invert infrasound observations for a range of properties such as crater geometry or volumetric flow rate associated with eruptions we demonstrate the utility of our efficient modeling framework by inverting harmonic infrasound observations for the crater geometry and position of the lava lake at villarrica volcano this technique may be used at other open vent volcanoes to constrain dynamic crater geometry and provide insights about lava lake motions and infrasound producing eruption sources

telkibanya lava domes lithofacies architecture of a miocene rhyolite field tokaj mountains carpathian pannonian region hungary abstract this work focuses on the miocene telkibanya lava dome field tokaj mountains hungary proposed as an example of poorly investigated lithofacies architecture of old silicic lava dome fields a detailed fieldwork combined with petrographic and radiometric k ar dating analyses allows us the redefinition of the volcano stratigraphy of a 25 km2 area and the recognition of two temporary different generation of domes that grew in a subaerial environment 12 cohesive and autoclastic lithofacies are identified and grouped together to document the internal variability of the domes as well as the erosional phases that affected the lithofacies architecture furthermore stratigraphy lithofacies association and morphology allow recognizing the areal distribution of 5 lithosomes lava flows coulees or domes all these findings represent a major breakthrough in the identification and interpretation of the volcanic processes that control the growth of silicic lava domes and their products in late miocene environment of carpathian pannonian region

spherulites and lithophysae 200 years of investigation on high temperature crystallization domains in silica rich volcanic rocks high temperature crystallization domains htcds including spherulites and lithophysae form during cooling of silica rich lava and welded ignimbrites spherulites grow in silicate melts or hot glass and they display a radiating or microcrystalline texture typically consisting of cristobalite tridymite and sanidine lithophysae are htcds comprising one or more cavities this contribution reviews the research and discussions on htcds carried out over the last 200 years the emphasis here is on lithophysae and summarizes current knowledge of their formation a number of parameters influence the initiation and growth of lithophysae as well as their shapes and internal textures the most likely cause of cavity formation is transient tensional stress that produces a mechanical opening and widening at the interface between the crystallization front and the host melt e g where t tg cavity growth and expansion forced by rising vapor pressure is considered less important in some cases further growth of htcd cavities results from vapor phase corrosion and brecciation

origin and geochemistry of agates in permian volcanic rocks of the sub erzgebirge basin saxony germany abstract mineralogical and geochemical investigations of agates from permian volcanic rocks of the sub erzgebirge basin saxony germany were made to constrain the genesis and characteristics of these spectacular forms of silica in acidic volcanic host rocks samples from the main agate occurrences of chemnitz hohenstein ernstthal st egidien and zwickau were selected for detailed analyses the results of the study show that agate formation can be related to volcanic activity rochlitz ignimbrite and the subsequent alteration of the volcanic rocks most agates originate from the infill of silica into cavities of lithophysae high temperature crystallization domains which formed during cooling of welded ignimbrite agate formation temperatures of probably 150 c were calculated from fluid inclusion and oxygen isotope studies which indicate that the mobilization and accumulation of silica started already during a late phase of or soon after the volcanic activity the trace element composition of chalcedony and macrocrystalline quartz in agates is different from that of quartz from magmatic or metamorphic rocks and pegmatites elements of the volcanic rock matrix al ca fe na k were released during the alteration processes and accumulated in the sio 2 matrix of the agates extraordinary high contents of ge 90 ppm b 46 ppm and u 18 ppm were also detected which can exceed the clark concentration and sometimes the element concentration in the surrounding host rocks in addition chondrite normalized ree distribution patterns of the agates show strong negative eu anomalies enriched hree as well as tetrad effects these patterns are different from the ree patterns of the volcanic host rocks and point to fractionation processes during agate formation the specific geochemical features indicate interactions of the host rocks with magmatic volatile fluids and heated meteoric water and transport of sio 2 and other elements both in aqueous solution and via stable fluorine and chlorine compounds such as sif 4 bf 3 gef 4 and uo 2 f 2 the results of cathodoluminescence cl microscopy and spectroscopy revealed a microstructure of the agates that is similar for all occurrences characteristic features are irregular internal textures and sector zoning in quartz as well as luminescence colours and spectra respectively which are caused by a typical high defect density oxygen vacancies silanol groups according to these results the formation of agates can be explained by crystallization via an amorphous silica precursor under non equilibrium conditions

hydrogen isotope analysis of rehydrated silicic lavas implications for eruption mechanisms abstract bulk and step heating hydrogen isotope measurements of glassy and vesicular samples from three young rhyolite lavas demonstrate for the first time that magmatic h 2 o can be distinguished from meteoric h 2 o added during rehydration step heat extractions of gases obtained at five temperatures show that most meteoric h 2 o is released at around 400 c while magmatic h 2 o comes off during the fusion step at 1100 1200 c magmatic h 2 o contents from vertically arrayed lava samples show a downward increase consistent with the equilibrium pressure dependence of h 2 o solubility these gradients imply that volatile concentrations high enough to generate pyroclastic flows during front collapse may be found in the upper portions of silicic domes produced by relatively high eruption rates

using unsupervised machine learning to identify changes in eruptive behavior at mount etna italy abstract volcanoes frequently generate infrasound signals that need to be processed before they can be used to monitor and track changes in eruptive activity unsupervised machine learning is complementary to existing processing methods and can be used for data exploration to identify features of interest in the data here i examine three days of infrasound data from mount etna italy that encompasses the 24 december 2018 fissure eruption the continuous infrasound data is divided into overlapping windows and for each window i extract seven features in the time and frequency domains that characterize the signal i apply the k means clustering algorithm to group the data into seven clusters and generate a discrete time series of cluster labels the cluster labels clearly identify a change in eruptive activity from strombolian explosions at the summit to lava fountaining at the fissure feature distributions and representative waveforms for each cluster are analyzed and source mechanisms are hypothesized this work illustrates how advances in unsupervised machine learning can be leveraged to explore volcano infrasound data sets and demonstrates the potential of these techniques for monitoring eruptive activity

textures formed during emplacement and cooling of a palaeoproterozoic small volume rhyolitic sill the 52 m thick rhyolitic sill at onedin in northwestern australia intruded wet unconsolidated sediment of the koongie park formation during the palaeoproterozoic the sill is composed of five main zones a thin 1 2 m thick basal peperitic contact zone with sparse large 61 cm amygdales and abundant spherulites grades up over 1 m into the lower zone the lower zone is 10m thick and made up of radiating feldspar laths surrounded by granophyric quartz and feldspar and has less than 5 amygdales in the overlying middle zone 20m thick amygdales increase in abundance from 5 near the base to 20 near the top this zone is dominated by spherulitic rhyolite the 18 m thick upper zone is complex with alternating 10 cm thick layers containing abundant spherulites lithophysae amygdales and perlite amygdales make up to 40 of the rock a pumiceous 2 3 cm thick layer occurs at the upper contact fluidal and blocky peperite marks the 1 2 m thick upper contact zone the five zones formed in response to different cooling rates within the sill the lower zone experienced the slowest cooling rate whereas the upper and basal contact zones with abundant glass cooled rapidly there is an overall upward increase in the amygdale abundance in many cases early formed bubbles became nucleation sites for lithophysae spherical bubbles formed in melt above the glass transition temperature as crystallisation proceeded irregularly shaped bubbles formed relatively late in crystalline zones textural zones in the rhyolitic sill at onedin are most similar to those in large volume rhyolitic lavas even though it is a small volume intrusion this similarity may be related to efficient heat retention beneath covering sediments for the sill or beneath a thick crust for large volume lavas the presence of the crystalline lower zone immediately above the base and a high proportion of crystalline rhyolite and the lack of autobreccia and sub vertical flow banding near the top distinguish this rhyolite as a sill rather than a lava

cooling and crystallization of lava in open channels and the transition of pāhoehoe lava to a ā samples collected from a lava channel active at kilauea volcano during may 1997 are used to con strain rates of lava cooling and crystallization during early stages of flow lava erupted at near liquidus tem peratures f1150 7c cooled and crystallized rapidly in upper parts of the channel glass geothermometry indi cates cooling by 12 14 7c over the first 2 km of trans port at flow velocities of 1 2 m s this translates to cooling rates of 22 50 7c h cooling rates this high can be explained by radiative cooling of a well stirred flow consistent with observations of non steady flow in proximal regions of the channel crystallization of plag ioclase and pyroxene microlites occurred in response to cooling with crystallization rates of 20 50 per hour crystallization proceeded primarily by nucleation of new crystals and nucleation rates of f10 4 cm 3 s are similar to those measured in the 1984 open channel flow from mauna loa volcano there is no evidence for the large nucleation delays commonly assumed for plagioclase crystallization in basaltic melts possibly a reflection of enhanced nucleation due to stirring of the flow the transition of the flow surface morphology from pahoehoe to a aoccurred at a distance of 1 9 km from the vent at this point the flow was thermally stratified with an interior temperature of f1137 7c and crystallinity of f15 and a flow surface tempera ture of f1100 7c and crystallinity of f45 a afor mation initiated along channel margins where crust was continuously disrupted and involved tearing and clotting of the flow surface both observations suggest that the transition involved crossing of a rheological threshold we suggest this threshold to be the develop ment of a lava yield strength sufficient to prevent vis cous flow of lava at the channel margin we use this concept to propose that a aformation in open chan nels requires both sufficiently high strain rates for con tinued disruption of surface crusts and sufficient groundmass crystallinity to generate a yield strength equivalent to the imposed stress in hawai i where lava is typically microlite poor on eruption these combined requirements help to explain two common observations on a aformation a a aflow fields are generated when effusion rates are high thus promoting crustal disruption and b under most eruption conditions lava issues from the vent as pahoehoe and changes to a aonly after flowing some distance thus permitting sufficient crystallization

fayalite oxidation processes in obsidian cliffs rhyolite flow oregon this study investigates the oxidation of fayalite fe22 sio4 that is present in lithophysae from a rhyolite flow obsidian cliffs oregon textural chemical and structural analyses of the successive oxidation zones are used to constrain 1 the oxidation processes of olivine and 2 the role of temperature chemical diffusion and meteoric infiltration petrologic analyses and thermodynamic modeling show that the rhyolite flow emplaced at 800 950 c fayalite bearing lithophysae formed only in the core of the lava flow variations in the gas composition inside the lithophysae induced the oxidation of fayalite to a laihunite 1 m zone fe12 fe23 1 sio4 2 this zone is made of nano lamellae of amorphous silica sio2 and laihunite 3 m fe2 1 6fe3 1 6 0 8 sio4 2 hematite fe2o3 it probably formed by a nucleation and growth process in the fayalite fractures and defects and at fayalite crystal edges the laihunite 1 m zone then oxidized into an oxyfayalite zone with the composition fe2 0 52fe3 2 32 1 16 sio4 2 this second oxidation zone is made of lamellae of amorphous silica sio2 and hematite fe2o3 with a possible small amount of ferrosilite fe2 sio3 a third and outer zone composed exclusively of hematite is also present the successive oxidation zones suggest that there may be a mineral in the olivine group with higher fe3 content than laihunite 1 m the transformation of laihunite 1 m to this oxyfayalite phase could occur by a reaction such as formula 1 this would imply that fe3 can also be incorporated in the m1 site of olivine 1 embed mml math 1 gif

distribution and significance of crystalline perlitic and vesicular textures in the ordovician garth tuff wales diverse spherulitic and granular crystalline fabrics perlitic textures and fabrics related to the growth and migration of vesicles occur in the garth tuff a largely welded ordovician ignimbrite defining the distribution of such textures helps to constrain the ignimbrite s cooling and degassing history suites of spherulitic and perlitic textures closely reflect variation in cooling rates seven facies are defined based on the style and intensity of crystallisation 1 a medium to coarsely crystalline equigranular facies 2 an intensely spherulitic facies 3 a sparsely spherulitic facies 4 a pectinate facies 5 a microcrystalline to cryptocrystalline equigranular facies 6 a lithophysal facies and 7 a transitional perlite pectinate facies textural changes from facies 1 to 5 reflect progressively higher cooling rates facies 1 occurs in proximal settings in the ignimbrite s core facies 2 to 5 successively envelop facies 1 with facies 2 becoming the dominant fabric in the ignimbrite s core in medial settings facies 5 is typically developed in the originally glassy perlitic zones at the ignimbrite s welded margins crystallisation under hydrous conditions is reflected by second boiling textures in the sporadically developed lithophysal facies the seventh facies reflects a subtle interplay between cooling hydration and crystallisation which locally prevented perlitic fracturing the distribution of amygdales reflects patterns of volatile migration and entrapment in the lower levels of the ignimbrite amygdales occur in irregular concentrations or rare subvertical pipe like structures pipe like structures attest to fumarolic activity while the ignimbrite was in a rheomorphic state amygdales are widespread and evenly distributed in the upper levels of the ignimbrite however the top of the welding profile is characterised by a thin poorly vesiculated originally vitrophyric horizon that abruptly caps an intense concentration of amygdales ductile and brittle fabrics developed during the upward migration of gas microscopic drag folds occur around some amygdales jigsaw fit to clast rotated breccias originated through both late stage pneumatic fracturing and autobrecciation vaporisation of water at the flow base provided a significant source of volatiles in addition to gas released during cooling and crystallisation secondary alteration has enhanced or modified some fabrics perlitic zones were susceptible to patchy chlorite sericite carbonate diagenetic alteration diagenesis and metamorphism have contributed to the infilling of vesicles

monitoring seismo volcanic and infrasonic signals at volcanoes mt etna case study volcanoes generate a broad range of seismo volcanic and infrasonic signals whose features and variations are often closely related to volcanic activity the study of these signals is hence very useful in the monitoring and investigation of volcano dynamics the analysis of seismo volcanic and infrasonic signals requires specifically developed techniques due to their unique characteristics which are generally quite distinct compared with tectonic and volcano tectonic earthquakes in this work we describe analysis methods used to detect and locate seismo volcanic and infrasonic signals at mt etna volcanic tremor sources are located using a method based on spatial seismic amplitude distribution assuming propagation in a homogeneous medium the tremor source is found by calculating the goodness of the linear regression fit r 2 of the log linearized equation of the seismic amplitude decay with distance the location method for long period events is based on the joint computation of semblance and r 2 values and the location method of very long period events is based on the application of radial semblance infrasonic events and tremor are located by semblance brightness and semblance based methods respectively the techniques described here can also be applied to other volcanoes and do not require particular network geometries such as arrays but rather simple sparse networks using the source locations of all the considered signals we were able to reconstruct the shallow plumbing system above sea level during 2011

insights into explosive activity at closely spaced eruptive vents using infrasound signals example of mt etna 2008 eruption abstract on 13 may 2008 an eruptive fissure opened on mount etna s eastern flank feeding both explosive activity and lava effusion from multiple vents for about 14 months during the investigated may september 2008 eruptive period infrasound recordings from a 4 station sparse network allowed tracking of the explosive activity in terms of location and dynamics in order to focus on activity from the eruptive fissure the infrasonic events generated by the summit craters were selected by using both spectral features and time delays between pairs of stations and excluded from our analysis then to accurately locate events from the fissure we used a composite method based on the semblance and brightness functions this enabled the study of the co existence of more than one infrasound source and or its migration along the eruptive fissure hence results permitted us to discriminate the number of active vents and their location along the fissure even when due to poor weather conditions it was not possible to access the vents or carry out direct observations the eruptive activity was characterised by variations in the number of active vents according to the overall intensity of the eruptive event variability of the infrasound waveforms highlighted either that distinct vents produced signals with different waveforms or that single vents generated different events during distinct periods of time or finally both the previous phenomena we applied the strombolian bubble vibration model to model waveform differences and attributed the signal variations to bubble radius changes

infrasonic precursors to a vulcanian eruption at sakurajima volcano japan the may 1998 eruption sequence of sakurajima volcano was monitored by ten infrasonic stations ten seismometers and a video camera during this seismo acoustic experiment we recorded hundreds of infrasonic tremor and long period events associated with seismic signals and observed a progression from relative quiescence to a vulcanian eruption the number of infrasonic events increased with escalating volcanic activity and the dominant character of the infrasonic signals changed from impulsive to emergent at 22 17 of may 19 sakurajima released ash and gases to a height of 2 km above the vent an event that was recorded continuously by one infrasonic and two seismic stations we present the experimental setup as well as a procedure through which infrasonic signals may be incorporated into future eruption monitoring and forecasting algorithms for open vent volcanic systems in addition our recordings suggest that infrasonic signals are more representative of processes occurring within the volcanic interior than are seismic signals which are strongly altered by diffraction and scattering in the volcanic edifice

tracking eruptive phenomena by infrasound may 13 2008 eruption at mt etna 1 active volcanoes produce inaudible infrasound due to the coupling between surface magmatic processes and the atmosphere monitoring techniques based on infrasound measurements have been proved capable of producing information during volcanic crises we report observations collected from an infrasound network on mt etna which enabled us to detect and locate a new summit eruption on may 13 2008 when poor weather inhibited direct observations three families of signals were identified that allowed the evolution of the eruption to be accurately tracked in real time each family is representative of a different active vent producing different waveforms due to their varying geometry several competitive models have been developed to explain the source mechanisms of the infrasonic events but according to our studies we demonstrate that two source models coexist at mt etna during the investigated period such a monitoring system represents a breakthrough in the ability to monitor and understand volcanic phenomena

geochemistry of agates a trace element and stable isotope study abstract agate samples of acidic intermediate and basic volcanics from 18 localities around the world and of different age precambrian to tertiary were studied by trace element and stable isotope analysis to provide information about the process of agate formation and the origin of mineral forming fluids trace element data are similar for agates from acidic and basic volcanics the general chondrite normalized ree distribution pattern is characterized by a slope from la to lu with enriched lree and a positive eu anomaly in some samples the similarity in the shape of the ree patterns between agates and the parent volcanic rocks suggests that the elements are mobilized by circulating fluids during syn and postvolcanic alteration of the volcanic wall rocks observed positive eu anomalies in agates probably originate from feldspar alteration deuterium and oxygen isotope analyses of agates and associated quartz incrustations d 44 to 130 18o 16 4 to 33 4 reveal variations in isotopic composition between samples of different localities but also within single agate samples up to 10 for 18o in general oxygen isotope compositions become heavier as volcanic host rocks grow more acidic furthermore agates have higher 18o values than associated quartz incrustations variations within single agate samples can be explained either by kinetic effects during isotope fractionation e g the formation of agate from a noncrystalline precursor or by mixing processes of meteoric and magmatic fluids remarkably high 18o values of the parent volcanic rocks up to 19 5 suggest that the circulation of 18o enriched hydrothermal fluids originated from heated meteoric water and or residual magmatic fluids this conclusion is supported by 13c and 18o data of paragenetic calcite the temperature of agate formation was calculated for different fluid compositions and they indicate a temperature range of ca 50 c to 250 c

internal textures of rhyolite flows as revealed by research drilling recent drilling of 550 and 140 000 yr old rhyolite lava flows in the inyo dome chain california and valles caldera new mexico and field inspection of 8 ma flows in western arizona reveal a more detailed vertical zonation of lava textures in glassy rhyolite flows than has previously been recognized the upper vitrophyre of a flow can usually be subdivided into a surficial finely vesicular pumice underlain by obsidian coarsely vesicular pumice and a second obsidian layer beneath these layers is the crystalline center of the flow which in turn is underlain by a basal obsidian layer lower vitrophyre differences in lava vesicularity and crystallinity between zones in a flow result from primary effervescence devitrification lava rheology and migration of water vapor

seismic and infrasound signals at mt etna modeling the north east crater conduit and its relation with the 2008 2009 eruption feeding system abstract on 13 may 2008 an eruption began at mt etna from an eruptive fissure that opened on the upper eastern flank of the volcano during 12 13 may 157 infrasonic events together with the related seismic transients were collected we carried out several analyses to obtain dominant frequencies pseudospectrograms peak to peak amplitudes source locations and time lags between infrasonic and seismic events spectra of the infrasonic events show two main spectral peaks in the frequency bands 0 4 0 7 hz and 1 5 2 0 hz respectively both infrasonic and seismic events were separately located below the north east crater where no eruptive activity was observed moreover significant changes in infrasound spectral content as well as in the infrasonic seismic lags were found a few hours before the beginning of the eruption on the basis of the collected information the infrasound source mechanism was modeled as a superposition of pipe and helmholtz resonance also leading to outline the geometry of the shallower portion of the north east crater plumbing system the occurrence of these seismo infrasonic events together with other geological and geophysical evidences led us to inferring a direct link between north east crater activity and the eruptive fissure further based on variations over time of both spectral features and seismic infrasonic time lag shallowing phenomena of the free magma column inside north east crater conduit were hypothesized such an uprise of magma was likely caused by a pressure increase inside the plumbing system occurring before the beginning of the 2008 2009 eruption

crystallization kinetics of rhyolitic melts using oxygen isotope ratios crystals provide themeans to understand igneous systems but natural constraints on crystallization kinetics are rare because thermal conditions and crystallization timescales are typically unknown oxygen isotope ratios in quartz and alkali feldspar crystals in spherulites provide a natural record of the temperature interval of crystallization and crystal growth rates in rhyolitic melts oxygen isotope compositions in both phases change progressively with position from the spherulite core to rim quartz o increases from 5 0 0 3 in the core to 5 6 0 3 at the rims whereas alkali feldspar decreases from 3 7 0 4 in the core to 2 7 0 9 at the rims fractionation therefore increases from 1 3 0 7 in the cores to 2 9 1 1 at the rims oxygen isotope thermometry tracks crystallization temperature with position spherulites nucleate at 578 160 c and continue to grow until 301 88 c the in situ analyses demonstrate that spherulites self contain a record of their thermal history and that of the host lava

estimates of eruption velocity and plume height from infrasonic recordings of the 2006 eruption of augustine volcano alaska abstract the 2006 eruption of augustine volcano alaska began with an explosive phase comprising 13 discrete vulcanian blasts these events generated ash plumes reaching heights of 3 14 km the eruption was recorded by a dense geophysical network including a pressure sensor located 3 2 km from the vent infrasonic signals recorded in association with the eruptions have maximum pressures ranging from 13 111 pa eruption durations are estimated to range from 55 350 s neither of these parameters however correlates with eruption plume height the pressure record however can be used to estimate the velocity and flux of material erupting from the vent assuming that the sound is generated as a dipole source eruptive flux in turn is used to estimate plume height assuming that the plume rises as a buoyant thermal plume heights estimated in this way correlate well with observations events that exhibit strongly impulsive waveforms are underestimated by the model suggesting that flow may have been supersonic

infrasound from tungurahua volcano 2006 2008 strombolian to plinian eruptive activity abstract strombolian to plinian activity from tungurahua volcano ecuador has been recorded by the autonomous infrasound arrays of the acoustic surveillance for hazardous eruptions ashe project since early 2006 our studies suggest that acoustic energy release during large eruptions does appear to broadly scale with eruption intensity this manuscript provides a detailed chronology and characterization of tungurahua s eruptive activity between 2006 and 2008 and demonstrates the ability to constrain source parameters of significant eruptions such as onset duration and escalation at regional distances by combining infrasound and remote sensing techniques the ashe system in ecuador automatically detected over 20 000 volcanic explosions at an array 37 km from tungurahua and was successful at notifying the onset escalation and cessation of a hazardous february 2008 eruption with a latency of 5 min elevated infrasonic energy from sustained and intense tungurahua eruptions correlates well with ash column heights and their lateral extent during the study period the spectra of these sustained explosive eruptions appear to be recurrent readily recognizable and indicative of volcanic jetting and significant atmospheric ash injection the paroxysmal plinian phase of the august 2006 eruption produced an ash cloud that extended well into the stratosphere 24 km coinciding with a shift of the dominant jetting frequency from 0 25 hz to below 0 1 hz and radiation of over 5 107 w of acoustic power transient explosions were often marked by minor or no ash release and are presumed to be more gas rich a change in the acoustic spectrum of volcanic jetting was also detected in the transition from a sustained to collapsed eruption column at the end of the july 14 2006 eruption the jetting spectrum at tungurahua during a period of sustained pyroclastic density current production changes from a typical double peaked to a single peaked spectrum suggesting remote acoustic monitoring can help ascertain the stability and dynamics of an eruptive column

fabrics facies and flow through a large volume ignimbrite pampa de oxaya chile the miocene oxaya formation exposed along the western andean slope in northern chile represents one of the largest ignimbrite provinces on earth in this study magnetic fabric data were acquired from a 1 km long core drilled vertically through a single cooling unit of the oxaya formation the ca 22 ma cardones ignimbrite samples for magnetic analysis were obtained every 20 m from the fine grained matrix of the core detailed measurements of the variation in bulk magnetic properties including natural remanent magnetization nrm susceptibility and anisotropy of magnetic susceptibility ams were used to monitor changes in magnetic mineralogy as well as changes in the strength and orientation of the magnetic fabric throughout the flow ams ellipsoid orientation and shape reflect rapid deposition from a concentrated granular fluidized flow and constrain both the location of the source caldera for this catastrophic eruption and processes of transport and deposition in this large volume ignimbrite after utilizing the magnetic remanence to correct for rotation about the core axis well grouped and imbricated petrofabric orientations reveal a well defined sw 247 transport direction down a proto western andean slope indicating syn or post welding flow and confirming the deformed lauca caldera as the likely source of the eruption systematic variations in fabric shape t and intensity p with depth reveal a predominately oblate fabric toward the top and base of the flow and predominately prolate fabrics in the center these vertical changes in fabric reveal that this massive apparently homogeneous deposit has a systematic layering this layering reflects depth dependent temperature variations temporal changes in the flow boundary zone during deposition and post depositional processes

silicic volcanism on mars evidenced by tridymite in high sio2 sedimentary rock at gale crater tridymite a low pressure high temperature 870 c sio2 polymorph was detected in a drill sample of laminated mudstone buckskin at marias pass in gale crater mars by the chemistry and mineralogy x ray diffraction instrument onboard the mars science laboratory rover curiosity the tridymitic mudstone has 40 wt crystalline and 60 wt x ray amorphous material and a bulk composition with 74 wt sio2 alpha particle x ray spectrometer analysis plagioclase 17 wt of bulk sample tridymite 14 wt sanidine 3 wt cation deficient magnetite 3 wt cristobalite 2 wt and anhydrite 1 wt are the mudstone crystalline minerals amorphous material is silica rich 39 wt opal a and or high sio2 glass and opal ct volatile bearing 16 wt mixed cation sulfates phosphates and chlorides perchlorates chlorates and has minor tio2 and fe2o3t oxides 5 wt rietveld refinement yielded a monoclinic structural model for a well crystalline tridymite consistent with high formation temperatures terrestrial tridymite is commonly associated with silicic volcanism and detritus from such volcanism in a lake gale catchment environment can account for buckskin s tridymite cristobalite feldspar and any residual high sio2 glass these cogenetic detrital phases are possibly sourced from the gale crater wall rim central peak opaline silica could form during diagenesis from high sio2 glass as amorphous precipitated silica or as a residue of acidic leaching in the sediment source region or at marias pass the amorphous mixed cation salts and oxides and possibly the crystalline magnetite otherwise detrital are primary precipitates and or their diagenesis products derived from multiple infiltrations of aqueous solutions having variable compositions temperatures and acidities anhydrite is post lithification fracture vein fill

dense welding caused by volatile resorption welding of pyroclastic rocks is generally thought to occur by mechanical expulsion of interstitial gas from a deposit as it compacts under its own weight we propose here that volatile resorption and compression can also be important factors in welding we describe densely welded rocks which cannot be explained by loading and re evaluate the welding process taking into account the effects of volatile resorption into the glassy fragments intra caldera oligocene ignimbrites from the rhodope mountains bulgaria and intrusive tuffs of the loch ba ring dyke mull in scotland are intensely welded but some samples lack foliation eutaxitic texture fiamme and glass shards show no preferred orientation in thin section or on outcrop scale fiamme are sometimes complexy deformed into u or s shapes we propose that these textures are the consequence of volatile dissolution in the glass and gas compression scaling analysis indicates that there are two regimes for gas behaviour following emplacement of hot pyroclastic deposits which depend on the relative characteristic time scales of compaction gas escape and gas resorption a gas escape regime and a gas retention regime during explosive eruption glassy pyroclasts are decompressed to less than one atmosphere pressure and are outgassed during deposition and subsequent burial in a thick hot deposit volatiles will be retained and soluble gases h 2 o can be resorbed back into the glass defining the gas retention regime poorly soluble gases air are compressed to small fractions of their original volume resulting in destruction of pore spaces and vesicles in pumice in some circumstances such as volcanic vents the volume changes involve isotropic strain and implosion of the tuff resorption of water greatly speeds up welding during compactional loading by reducing the viscosity of the glass welding is inhibited not only by lower temperatures but also by entrainment of insoluble atmospheric gases the two regimes also can explain the common presence of post emplacement gas escape pipes in non welded ignimbrites and their rarity in densely welded ignimbrite factors that are likely to promote the gas retention regime include fine grain size low collapsing columns a large thickness of tuff and incorporation of external water

timescales of spherulite crystallization in obsidian inferred from water concentration profiles we determined the kinetics of spherulite growth in obsidians from krafla volcano iceland we measured water concentration profiles around spherulites in obsidian by synchrotron fourier transform infrared spectroscopy the distribution of oh groups surrounding spherulites decreases exponentially away from the spherulite glass border reflecting expulsion of water during crystallization of an anhydrous paragenesis plagioclase sio2 clinopyroxene magnetite this pattern is controlled by a balance between the growth rate of the spherulites and the diffusivity of hydrous solute in the rhyolitic melt we modeled advective and diffusive transport of the water away from the growing spherulites by numerically solving the diffusion equation with a moving boundary numerical models fit the natural data best when a small amount of post growth diffusion is incorporated in the model comparisons between models and data constrain the average spherulite growth rates for different temperatures and highlight size dependent growth among a small population of spherulites

crystallization history of obsidian dome inyo domes california samples obtained by u s department of energy research drilling at the 600 year old obsidian dome volcano provide the rare opportunity to examine the transition from volcanic dome to plutonic intrusion textures in a silicic magma system textures in the lavas from obsidian dome record multiple periods of crystallization initiated in response to changes in undercooling t related to variable degassing in the mag ma phenocr ysts formed first at low t a drastic increase in t related to loss of a vapor phase during initial stages of eruption caused nucleation of microlites all of the lavas thus contain phenocrysts and microlites extrusion and subsequent devitrification of the dry 0 1 wt h2o magma crystallized spherulites and fine grained rhyolite at high t a granophyric texture representing crystallization at a moderate t formed in the intrusions beneath obsidian dome textures in the intrusion apparently represent crystallization of hydrous 1 2 wt h2o rhyolitic magma at shallow depths

insights into mt etna s shallow plumbing system from the analysis of infrasound signals august 2007 december 2009 previous studies performed on mt etna on short and discontinuous time intervals indicate the north east crater nec as the most active source of infrasound the source mechanism of nec infrasound events was modeled as a double resonance this lead to infer the connection between the nec and both the southeast crater sec and the eruptive fissure ef that opened at the beginning of the 2008 2009 eruption nevertheless there are still several open questions that need to be addressed for instance the steadiness of nec event features should be studied as well as the orderliness of spectral changes of nec events time related to eruptive activity of other vents the investigation of such topics is strongly enhanced by the possibility of analysing infrasound signals during year long time periods with this aim about 40 000 infrasound events recorded at mt etna from august 2007 to december 2009 were analysed by using spectral and location techniques it was noted in particular that the nec events featured periods with very steady waveforms and spectral characteristics lasting from days to months with slow or sudden variations the most important eruptive episodes occurring at the sec or the ef were accompanied by significant spectral changes in nec events in light of such systematic behaviour the connection between the nec and the sec ef plumbing systems was not considered temporary but rather stable even during a relatively long time interval 2006 2009 moreover study of nec event spectral features and their changes over multiple years supports the double resonance source model such a model together with the inferred connections between nec and sec ef feeding systems implies that level fluctuations of a magma column inside the nec conduit correspond to magmastatic pressure decrease increase inside the main plumbing system these findings open up new and interesting possibilities for monitoring magma pressure changes inside the mt etna plumbing system