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

application of video image processing to detect volcanic pressure waves a case study on archived images of aso volcano japan 1 application of video image processing to a volcanic eruption was attempted using video image archives of aso volcano as a result continual flashings in the pale gray plume that appeared to be continual 5 6 times per second and long lived nature more than 20 30 sec were found the speed of their propagation was very high 200 300 m sec they are thought to be due to a phase change of h2o in the plume caused by volcanic pressure waves but they cannot be recognized directly on normal images the video image processing reported here will become increasingly more useful in the field of volcanology as the imaging technology is developed

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

strombolian explosions 1 a large bubble breaking at the surface of a lava column as a source of sound strombolian activity consists of a series of explosions caused by the breaking of large overpressurized bubbles at the surface of the magma column acoustic pressure has been measured for 36 explosions at stromboli we propose that sound is generated by the vibration of the bubble before it bursts oscillations are driven by an initial overpressure inside the bubble assumed to be initially at rest just below the magma air interface inertia effects cause the bubble to overshoot its equilibrium radius then the bubble becomes underpressurized and contracts because of gas compressibility these oscillations are only slightly damped by viscous effects in the magma layer above the bubble the bubble cannot complete more than one cycle of vibration because of instabilities developing on the magma layer that lead to its breaking near the minimum radius assuming a simple geometry we model this vibration and constrain the radius and length of the bubble and the initial overpressure by fitting a synthetic waveform to the measured acoustic pressure the fit between synthetic and observed waveforms is very good both for frequency 60 rad s 1 and amplitude the initial bubble radius is 1 m and the length varies between several and a few tens of meters from the initial overpressure approximately 105 pa we calculate the maximum radial velocity of ejecta 30 m s 1 the generally good agreement between data and predictions of our model leads us to suggest that acoustic measurements are a powerful tool for the understanding of eruption dynamics

dynamics of mild strombolian activity on mt etna abstract here we report the first measurements of gas masses released during a rare period of strombolian activity at the bocca nuova crater mt etna sicily uv camera data acquired for 195 events over an 27 minute period 27th july 2012 indicate erupted so2 masses ranging from 0 1 to 14 kg per event with corresponding total gas masses of 0 1 to 74 kg thus the activity was characterised by more frequent and smaller events than typically associated with strombolian activity on volcanoes such as stromboli events releasing larger measured gas masses were followed by relatively long repose periods before the following burst a feature not previously reported on from gas measurement data if we assume that gas transport within the magma can be represented by a train of rising gas pockets or slugs then the high frequency of events indicates that these slugs must have been in close proximity in this case the longer repose durations associated with the larger slugs would be consistent with interactions between adjacent slugs leading to coalescence a process expedited close to the surface by rapid slug expansion we apply basic modelling considerations to the measured gas masses in order to investigate potential slug characteristics governing the observed activity we also cross correlated the acquired gas fluxes with contemporaneously obtained seismic data but found no relationship between the series in line with the mild form of manifest explosivity

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

a co2 rich gas trigger of explosive paroxysms at stromboli basaltic volcano italy in addition to rhythmic slug driven strombolian activity stromboli volcano occasionally produces discrete explosive paroxysms 2 per year on average for the most frequent ones that constitute a major hazard and whose origin remains poorly elucidated partial extrusion of the volatile rich feeding basalt as aphyric pumice during these events has led to consider their triggering by the fast ascent of primitive magma blobs from possibly great depth here i examine and discuss the alternative hypothesis that most of the paroxysms could be triggered and driven by the fast upraise of co2 rich gas pockets generated by bubble foam growth and collapse in the sub volcano plumbing system data for the so2 and co2 crater plume emissions are used to show that stromboli s feeding magma may originally contain as much as 2 wt of carbon dioxide and early coexists with an abundant co2 rich gas phase with high co2 so2 molar ratio 60 at 10 km depth below the vents compared to 7 in time averaged crater emissions pressure related modelling indicates that the time averaged crater gas composition and output are well accounted for by closed system decompression of the basalt gas mixture until the volcano crust interface 3 km depth followed by open degassing and crystallization in the volcano conduits however both the low viscosity and high vesicularity of the basaltic magma permit bubble segregation and bubble foam growth at deep sill like feeder discontinuities and at shallower physical boundaries such as the volcano crust interface where the gas rich aphyric basalt interacts with the unerupted crystal rich and viscous magma drained back from the volcano conduits gas pressure build up and bubble foam collapse at these boundaries will intermittently trigger the sudden upraise of co2 rich gas blobs that constitute the main driving force of the paroxysms deeper sourced gas blobs driving the most powerful explosions will be the richest in co2 and have highest co2 so2 ratios this mechanism is shown to account well for the dynamic seismic and petrologic features of stromboli s paroxysms and hence to provide a potential alternative interpretation for their genesis and their forecasting enhanced bubble foam leakage prior to a paroxysm or foam emptying in several steps should lead indeed to precursory upstream of co2 rich gas and increasing co2 so2 ratio in crater plume emissions the recent detection of such signals prior to two explosions in december 2006 and march 2007 strongly supports this expectation and the model proposed in this study

single bubble air gun array for deep exploration large tuned air gun arrays operated in off shore petroleum exploration are also used for deep penetration marine seismic reflection surveys conducted to define structures in the earth s crust because of the attenuation of higher frequencies the useful upper frequency limit of these records is usually about 50 60 hz the aim of this paper is to report on a method of seismic pulse generation that preferentially concentrates the air gun s energy in the low range of the seismic frequency band by centering the output on the first bubble pulse instead of the initial primary pulse experimental results show that due to the increased low frequency energy content of this single bubble pulse air gun arrays considerably reduced both in size and volume can generate the necessary acoustic energy for deep seismic exploration

source location of the 19 february 2008 oregon bolide using seismic networks and infrasound arrays 1 on 19 february 2008 a bolide traveled across the sky along a southern trajectory ending in a terminal burst above oregon the event was well recorded by the usarray other seismic networks four infrasound arrays and several video cameras we compare the results of locating the burst using these different sensor networks specifically we reverse time migrate acoustic to seismic coupled signals recorded by the usarray out to 800 km range to image the source in 2 d space and time we also apply a grid search over source altitude and time minimizing the misfit between observed and predicted arrival times using 3 d ray tracing with a high resolution atmospheric velocity model our seismic and video results suggest a point source rather than a line source associated with a hypersonic trajectory we compare the seismic source locations to those obtained by using different combinations of observed infrasound array signal back azimuths and arrival times we find that all locations are consistent however the seismic location is more accurate than the infrasound locations due to the larger number of seismic sensors a more favorable seismic source receiver geometry and shorter ranges to the seismometers for the infrasound array locations correcting for the wind improved the accuracy but implementing arrival times while increasing the precision reduced the accuracy presumably due to limitations of the source location method and or atmospheric velocity model we show that despite known complexities associated with acoustic to seismic coupling aboveground infrasound sources can be located with dense seismic networks with remarkably high accuracy and precision

basaltic thermals and subplinian plumes constraints from acoustic measurements at shishaldin volcano alaska the 1999 basaltic eruption of shishaldin vol cano alaska usa included both strombolian and sub plinian activity as well as a pre subplinian phase inter preted as the local coalescence within a long foam in the conduit although few visual observations were made of the eruption a great deal of information regarding gas ve locity gas flux at the vent and plume height may be inferred by using acoustic recordings of the eruption by relating acoustic power to gas velocity a time series of gas velocity is calculated for the subplinian and pre subplinian phases these time series show trends in gas velocity that are inter preted as plumes or for those signals lasting only a short time thermals the subplinian phase is shown to be com posed of a thermal followed by five plumes with a total expelled gas volume of 1 5 10 7 m 3 the initiation of the subplinian activity is probably related to the arrival of a large overpressurised bubble close to the top of the magma column a gradual increase in low frequency 0 01 0 5 hz signal prior to this trigger bubble may be due to the rise of the bubble in the conduit this delay corresponds to a reservoir located at 3 9 km below the surface in good agreement with studies on other volcanoes the presence of two thermal phases is also identified in the middle of the pre subplinian phase with a total gas release of 4 3 10 6 m 3 and 3 6 10 6 m 3 gas veloc ity at the vent is found to be 82 m s 1 and 90 m s 1 for the subplinian plumes and the pre subplinian thermals respectively the agreement is very good between estimates of the gas flux from modelling the plume height and those obtained from acoustic measurements leading to a new method by which eruption physical parameters may be quantified fur thermore direct measurements of gas velocity can be used for better estimates of the so2 flux released during the eruption

direct video and hydrophone observations of submarine explosive eruptions at nw rota 1 volcano mariana arc 1 extraordinary video and hydrophone observations of a submarine explosive eruption were made with a remotely operated vehicle in april 2006 at a depth of 550 560 m on nw rota 1 volcano in the mariana arc the observed eruption evolved from effusive to explosive while the eruption rate increased from near zero to 10 100 m3 h during the peak in activity cyclic explosive bursts 2 6 min long were separated by shorter non eruptive pauses lasting 10 100 s the size of the ejecta increased with the vigor of the explosions a portable hydrophone deployed near the vent recorded sounds correlated with the explosive bursts the highest amplitudes were 50 db higher than ambient noise at frequencies between 10 and 50 hz the acoustic data allow us to quantify the durations amplitudes and evolution of the eruptive events over time the low eruption rate high gas lava ratio and rhythmic eruptive behavior at nw rota 1 are most consistent with a strombolian eruptive style we interpret that the eruption was primarily driven by the venting of magmatic gases which was also the primary source of the sound recorded during the explosive bursts the rhythmic nature of the bursts can be explained by partial gas segregation in the conduit and upward migration in a transitional regime between bubbly flow and fully developed slug flow the strongest explosive bursts were accompanied by flashes of red glow and oscillating eruption plumes in the vent apparently caused by magma seawater interaction and rapid steam formation and condensation this is the first time submarine explosive eruptions have been witnessed with simultaneous near field acoustic recordings

on the spectral peaks of volcanic tremor at stromboli abstract seismic activity at stromboli volcano is characterized by a variety of signals emanating from three vents for a long time the northwest vent has been in constant activity periodically large explosions occur and material is ejected beyond the crater walls these large explosions are accompanied by sonic and infrasonic pressure waves in the atmosphere and explosion quakes apart from large explosions there is constant activity in the form of continuous gas bursts which are related to low infrasonic pulses in the atmosphere and volcanic tremor we assume that volcanic tremor and low pressure infrasonics are generated by gas bubbles inside the volcanic conduit and accordingly we compute synthetic tremor by modeling the source function as a pressure variation in a spherical cavity that propagates through a finely layered medium by means of haskell s formalism to simulate a tremor we superpose in time domain a large number of such pulses of varying amplitudes and time delays according to the observed infrasonic series in addition to the spectral similarity the observed and synthetic tremor display the same autocorrelation and hurst exponents implying similar long term correlation we present strong evidence in favour of an interpretation of the spectral peaks of the volcanic tremor at stromboli in terms of resonances of the layered structure hence as a path effect rather than a source effect

the gas content and buoyancy of strombolian ash plumes plinian plumes erupt with a bulk density greater than that of air and depend upon air entrainment during their gas thrust phase to become buoyant if entrainment is insufficient the column collapses into a potentially deadly pyroclastic flow this study shows that strombolian ash plumes can be erupted in an initially buoyant state due to their extremely high initial gas content and in such cases are thus impervious to column collapse the high gas content is a consequence of decoupled gas rise in the conduit in which particles are ultimately incidental the relations between conduit gas flow eruption style and plume density are explored here for strombolian scenarios and contrasted with conventional wisdom derived from plinian eruptions considering the inherent relation between gas content and initial plume density together with detailed measurements of plume velocities can help unravel ambiguities surrounding conduit processes eruption styles and hazards at poorly understood volcanoes analysis of plume dynamics at santiaguito volcano guatemala adds further support for a model involving decoupled gas rise in the conduit

canonical model of volcano acoustics a full wave theoretical model is developed for the acoustic field generated by an explosive point source embedded in a magma column that is open to the atmosphere the green s functions for the field in the magma and the atmosphere are derived on the basis of several simplifying assumptions concerning the geometry of the conduit the boundary conditions and the geoacoustic properties of the magma a kinematic model for the acoustic signature of the explosive source is proposed which when combined with the green s functions provides full analytical expressions for the acoustic field in the magma and in the atmosphere as complex functions of frequency by fourier inversion the airborne pressure spectrum is transformed into a pressure time series the predicted sound pulse in the atmosphere and its energy spectrum are highly dispersive showing complicated structure that arises from the coherent addition of many normal modes of oscillation i e depth and radial resonances in the magma column at high frequencies for which the aperture of the vent is many wavelengths across each mode is launched into the atmosphere as a parallel sided beam of sound with a characteristic angle of elevation which through snell s law is determined by the speed of sound in the magma relative to that in air at somewhat lower frequencies the modal beams of sound undergo angular spreading due to diffraction at the edge of the vent in the lowest frequency regime where the wavelength is comparable with the aperture the airborne field shows little angular structure a comparison between airborne acoustic data that we recorded in july 1994 at the western vent of stromboli volcano and the predictions of the theory using parameters that are characteristic of stromboli show compelling agreement the theoretical and observed power spectra both display the following features 1 a concentration of energy below 20 hz associated with the first four longitudinal resonances 2 radial resonances between 35 and 65 hz and 3 a broad minimum around 30 hz arising because the source lies near nulls in longitudinal modes that would otherwise be excited the conclusion is that the airborne sound signature from an explosive volcanic event may be inverted to provide estimates of the depth and radius of the magma conduit the depth spectral shape and peak shock wave pressure of the source and the viscosity of the magma

modeling the failure of magmatic foams with application to stromboli volcano italy abstract the failure of magmatic foams has been implicated as a fundamental process in eruptions occurring at open conduit basaltic volcanoes in order to investigate the failure of magmatic foams we applied the fiber bundle model using global load sharing the strengths of the fibers for the model were taken from bubble wall widths measured in four computer simulated foams of low porosity and from one very low porosity and two high porosity foams produced in the laboratory by heating hydrated basaltic glasses to 1200 c the relative strength of an individual fiber in the model was calculated from the square of a bubble wall s average width and absolute strengths of the foams were calculated based upon the correlation of the strength of one modeled foam with experimental data the fiber bundle model is shown to successfully reproduce measured tensile strengths of porous volcanic rocks studied by other researchers and confirms previous findings of the primary importance of foam porosity as well as the secondary importance of structural details that affect the number and size of bubble walls and permeability because of the success of the fiber bundle model in reproducing experimental foam failure its results are compared to infrasonic measurements associated with bubbles at stromboli italy and demonstrate that within uncertainty the power law exponents of the infrasonic energies and of the fiber bundle model energies are in agreement both show a crossover from an exponent of 5 2 associated with the bursting of small bubbles in the infrasonic measurements to an exponent of 3 2 for normal strombolian eruptions associated with infrasonic signals from meter scale bubbles the infrasonic signals for major explosions and a paroxysmal eruption at stromboli fall near the extrapolation of the power law defined by the low amplitude bubble bursting events and are interpreted to reflect the bursting of multitudes of small bubbles rather than a few large bubbles the measurement of small amplitude infrasonic events at stromboli appears useful in predicting the recurrence interval of paroxysmal eruptions at this volcano and may also provide a tool that uses common small amplitude infrasonic events to constrain the frequency of larger eruptions at other volcanoes

rise dynamics of unsteady laboratory jets with implications for volcanic plumes a b s t r a c t geophysical observations of discrete volcanic eruptions suggest their eruption rates vary rapidly in time to learn how such variations may impact the initial stages of plume rise we conducted a laboratory study of neutrally buoyant jets generated by unsteady source conditions analogous to the volcanic case turbulent jets were generated by quickly injecting a finite volume of water into a large volume of still water the mass injection rates evolved over time with a gaussian like history producing jets with peak reynolds numbers ranging from 10 4 to 10 5 consistent with values estimated for small discrete eruptions except during very early and late times jet heights show a logarithmic dependence on time this trend contrasts with the power law dependence for jets produced by steady state or instantaneous discharge conditions we show that this logarithmic dependence is the similarity form appropriate for impulsive releases from a time varying source and found characteristic length and time scales that consolidate the non dimensional jet heights as functions of non dimensional times from a range of experimental conditions onto a single trend the rise of unsteady volcanic plume fronts from short duration eruptions mori and burton 2009 patrick 2007 s how the same trend as that observed in the laboratory variations in mass eruption rate strongly influence the initial phases of plume rise and may impact related processes such as mixing entrainment and eruption column collapse consequently source unsteadiness must be accounted for in physical plume models before they will reliably estimate trajectory dilution and stability for volcanic plumes from discrete eruptions 2014 elsevier b v all rights reserved

comparing near regional and local measurements of infrasound from mount erebus antarctica implications for monitoring abstract local 100 s of metres from vent monitoring of volcanic infrasound is a common tool at volcanoes characterized by frequent low magnitude eruptions but it is generally not safe or practical to have sensors so close to the vent during more intense eruptions to investigate the potential and limitations of monitoring at near regional ranges 10 s of km we studied infrasound detection and propagation at mount erebus antarctica this site has both a good local monitoring network and an additional international monitoring system infrasound array is55 located 25 km away we compared data recorded at is55 with a set of 117 known strombolian events that were recorded with the local network in january 2006 75 of these events were identified at is55 by an analyst looking for a pressure transient coincident with an f statistic detection which identifies coherent infrasound signals with the data from january 2006 we developed and calibrated an automated signal detection algorithm based on threshold values of both the f statistic and the correlation coefficient application of the algorithm across is55 data for all of 2006 identified infrasonic signals expected to be strombolian explosions and proved reliable for indicating trends in eruption frequency however detectability at is55 of known strombolian events depended strongly on the local signal amplitude 90 of events with local amplitudes 25 pa were identified at is55 compared to only 26 of events with local amplitudes

infrasonic tremor wavefield of the pu u ō ō crater complex and lava tube system hawaii in april 2007 1 long lived effusive volcanism at the pu u crater complex kilauea volcano hawaii produces persistent infrasonic tremor that has been recorded almost continuously for months to years previous studies showed that this infrasonic tremor wavefield can be recorded at a range of 10 km however the low signal power of this tremor relative to ambient noise levels results in significant propagation effects on signal detectability at this range in april 2007 we supplemented a broadband infrasound array at 12 5 km from pu u mene with a similar array at 2 4 km from the source kipu the additional closer range data enable further evaluation of tropospheric propagation effects and provide higher signal to noise ratios for studying volcanic source processes the infrasonic tremor source appears to consist of at least two separate physical processes we suggest that bubble cloud oscillation in a roiling magma conduit beneath the crater complex may produce a broadband component of the tremor low frequency sound sourced in a shallow magma conduit may radiate infrasound efficiently into the atmosphere due to the anomalous transparency of the magma air interface we further propose that more sharply peaked tones with complex temporal evolution may result from oscillatory interactions of a low velocity gas jet with solid vent boundaries in a process analogous to the hole tone or whistler nozzle the infrasonic tremor arrives with a median azimuth of 67 at kipu additional infrasonic signals and audible sounds originating from the extended lava tube system to the south of the crater complex median azimuth 77 coincided with turbulent degassing activity at a new lava tube skylight our observations indicate that acoustic studies may aid in understanding persistent continuous degassing and unsteady flow dynamics at kilauea volcano

dynamics of degassing at kilauea volcano hawaii at kilauea volcano hawaii the recent long lived eruptions of mauna ulu and pu u o o have occurred in two major stages defining a characteristic eruptive pattern the first stage consists of cyclic changes of activity between episodes of fire fountaining and periods of quiescence or effusion of vesicular lava the second stage consists only of continuous effusion of lava we suggest that these features reflect the dynamics of magma degassing in a chamber which empties into a narrow conduit in the volcano chamber gas bubbles rise through magma and accumulate at the roof in a foam layer the foam flows toward the conduit and its shape is determined by a dynamic balance between the input of bubbles from below and the output into the conduit the foam thickness is proportional to lq e2 l g 1 4 where l and l are the viscosity and density of magma e is the gas volume fraction in the foam g is the acceleration of gravity and q is the gas flux the bubbles in the foam deform under the action of buoyancy and the maximum permissible foam thickness is hc 2 e lgr where is the coefficient of surface tension and r is the original bubble radius if this critical thickness is reached the foam collapses into a large gas pocket which erupts into the conduit foam accumulation then resumes and a new cycle begins the attainment of the foam collapse threshold requires a gas flux in excess of a critical value which depends on viscosity surface tension and bubble size hence two different eruption regimes are predicted 1 alternating regimes of foam buildup and collapse leading to the periodic eruption of large gas volumes and 2 steady foam flow at the roof leading to continuous bubbly flow in the conduit the essential result is that the continuous process of degassing can lead to discontinuous eruptive behavior data on eruption rates and repose times between fountaining phases from the 1969 mauna uiu and the 1983 1986 pu u o o eruptions yield constraints on three key variables the area of the chamber roof must be a few tens of square kilometers with a minimum value of about 8 km2 magma reservoirs of similar dimensions are imaged by seismic attenuation tomography below the east rift zone close to the roof the gas volume fraction is a few percent and the gas bubbles have diameters lying between 0 1 and 0 6 mm these estimates are close to the predictions of models for bubble nucleation and growth in basaltic melts as well as to the observations on deep submarine basalts the transition between cyclic and continuous activity occurs when the mass flux of gas becomes lower than a critical value of the order of 103 kg s in this model changes of eruptive regime reflect changes in the amount and size of bubbles which reach the chamber roof

the cerro chopo basaltic cone costa rica an unusual completely reversed graded pyroclastic cone with abundant low vesiculated cannonball juvenile fragments cerro chopo is a partially dissected asymmetric isolated pleistocene pyroclastic cone located in front of the cordillera de guanacaste in northern costa rica the cone consists of similar to 0 09 km 3 of basaltic tephra as well as similar to 0 14 km 3 of lateral lava flows tephras are tholeiitic high alumina olivine basalts and represent minor degrees 5 of crystal fractionation major and trace element compositions are consistent with minor fractionation from a mixture of e morb and oib magmas the cone walls consist of alternating coarser and finer grained well sorted beds containing continuous spectra from breadcrust to smooth surface cannonball bombs but also less frequent cylindric fragments and broken clasts cerro chopo is unique compared to other typical scoria cones because it contains ubiquitous reversely graded layers scarcity of scorias and instead a wide range of dense 1 54 2 49 g cm 3 poorly vesicular 5 40 vol juvenile clast morphologies including abundant cannonball juvenile bombs and lapilli these are bombs with concentric layers surrounding vesiculated dense and lapillistone cores and are interpreted to have repeatedly recycled through the vent the cannonball bombs and lapilli have been described in a few scoria cones but are much less abundant than in chopo the reverse graded sequences are interpreted to have resulted from decreasing explosivity at the vent in addition to local failure of tephra on slopes as the consequence of grain flows elsewhere on the earth most of the poorly vesiculated spherical bombs particularly cannonball accretionary composite and core bombs and its equivalent lapilli size pelletal spinning droplets and ellipsoidal lapilli are all related to mafic to ultramafic low viscosity magmas c 2010 elsevier b v all rights reserved

the role of large bubbles detected from acoustic measurements on the dynamics of erta ale lava lake ethiopia the activity at the surface of the lava lake on erta ale volcano ethiopia shows that large bubbles are regularly breaking at a fixed position on the lava lake this is also where the small lava fountains are sometimes produced since this location is likely to be directly above the volcanic conduit feeding the lava lake we have done continuous measurements between march 22 and 26 2003 to understand the degassing of a volcano in permanent activity the bubble size has been first estimated from videos which once combined with the acoustic pressure can constrain the source of the sound the gas volume and overpressure stayed roughly constant between 36 700 m3 and 4 103 1 8 104 pa respectively simultaneous thermal measurements showed regular peaks which occurred when the crust was broken by a large bubble hence gave a direct indication on the typical return time between the bubbles 1 h these spherical cap bubbles had a high reynolds number 4600 20000 therefore a wake periodically unstable formed and detached from the bubble bottom the bubbly wake if the detachment occurs close to the surface can explain the duration of lava fountains measured on the videos the periodic arrival of bubbly wakes which mostly detach from the driving spherical cap within the lava lake could explain the absence of cooling at erta ale erebus antartica villarica chile and nyiragongo democratic republic of congo without invoking a convective downflow of magma in the conduit as previously done

origin of the sound generated by strombolian explosions during strombolian eruptions large bubbles break at the surface of the lava column and produce sound acoustic pressure recorded during several explosions on the eastern vent of stromboli volcano shows a pattern consistent between explosions the well marked oscillation contains only very low frequencies around 7 hz and is followed by a signal containing now both higher frequencies and lower frequency less than 4 hz the generation of sound is explained by the vibration 7 hz and bursting higher frequencies of large bubbles followed by the drainage of magma down in the conduit less than 4 hz the interpretation suggests that 1 the bubble vibrates before bursting and 2 the vibration prior to bursting yields more energy than the bursting itself the radius of bubbles responsible for explosions is determined to be close to 1 meter in agreement with observations of a few conduit sizes

interaction of seismic and air waves recorded at stromboli volcano explosion quake seismograms recorded at stromboli show that seismic phases with a high amplitude and high frequency content propagate with a velocity of approximately 330 m s the sound speed the analysis of seismograms recorded at a distance of 500 m from one of the three active vents shows for the first onset a low frequency and particle motion characteristic of a p wave which loses its longitudinal polarization with the onset of the air wave recording the explosion quakes simultaneously with a microphone we could ascertain that the high frequency onset coincided with the air wave s in order to better understand the seismic wavefield generated by the atmospheric pressure we performed a controlled source experiment at stromboli using a seismic gun seismograms with the same two phases and particle motions comparable with the volcano seismic data were obtained a second experiment demonstrated that the air wave propagates at least in the uppermost 1 m of the ground we suggest that the seismic source of the corresponding seismograms is an explosion at the top of the magma column and conclude that the p and air waves are both generated in the same point and at the same time

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

flux measurements of explosive degassing using a yearlong hydroacoustic record at an erupting submarine volcano at nw rota 1 are primarily h2o so2 and co2 instantaneous fluxes varied by a factor of 100 over the deployment using melt inclusion information to estimate the concentration of co2 in the explosive gases as 6 9 0 7 wt we calculate an annual co2 eruption flux of 0 4 0 1 tg a 1 this result is within the range of measured co2 fluxes at continuously erupting subaerial volcanoes and represents 0 2 0 6 of the annual estimated output of co2 from all subaerial arc volcanoes and 0 4 0 6 of the mid ocean ridge flux the multiyear eruptive history of nw rota 1 demonstrates that submarine volcanoes can be significant and sustained sources of co2 to the shallow ocean

mineralogy and mineral chemistry of the metamorphosed and precious metal bearing ming deposit canada abstract the ming deposit in the northwestern canadian appalachians is a metamorphosed bimodal mafic precious metal au ag bearing and cu rich volcanogenic massive sulfide vms deposit consisting of several spatially proximal lenses in a sericite to chlorite altered rhyodacitic footwall the various lenses 1807 zone 1806 zone ming south up plunge ming south down plunge and the lower footwall zone have variations in cu au ag and zn grades that reflect varying physico chemical conditions of ore formation this study describes the complex ore mineralogy of the orebodies and constrains the genesis of the deposit using field methods mineralogy whole rock sulfide geochemistry and micro analytical methods the orebodies are predominantly pyrite chalcopyrite with lesser sphalerite pyrrhotite and trace galena and arsenopyrite with the exception of the lower footwall zone which consists of a high temperature 320 c chalcopyrite pyrrhotite pyrite cubanite assemblage the other orebodies 1806 1807 ming south up plunge and down plunge contain trace amounts of tellurides hessite altaite tsumoite unnamed bismuthtelluride sulfosalts ag poor and ag rich tennantite tetrahedrite meneghinite agsb phases stannite and precious metal phases electrum aghg au alloys the 1807 zone is enriched in te bi and se whereas the 1806 zone is telluride free and contains as sb hg au and ag mineral chemistry of sphalerite shows strong variations in fe content 1 12 11 04 wt intermediate fe 4 33 6 33 wt fe and fe rich 7 327 11 04 wt fe sphalerite are common in all orebodies whereas fe poor sphalerite 1 12 3 57 wt fe occurs exclusively in the 1807 and 1806 zones tennantite tetrahedrite is typically ag poor 0 25 2 19 wt in the 1807 zone but is significantly enriched in ag up to 29 3 wt in the 1806 zone galena in the 1807 zone and ming south orebodies is commonly myrmekitically intergrown with tellurides and has high concentrations of te bi se and ag in contrast galena in the 1806 zone is less enriched in te bi and se but high in ag variations in mineralogy epithermal elements as bi hg sb se sn te and precious metal ag au content and mineral chemistry between the different orebodies indicate that they were formed from predominantly reduced acidic hydrothermal fluids with varying te2 s2 se2 s2 and mbi msb ratios as temperatures steadily decreased from 300 c to

infrasound generated by the 2016 2017 shallow submarine eruption of bogoslof volcano alaska the 2016 2017 shallow submarine eruption of bogoslof volcano produced numerous infrasound signals over 9 months that were recorded on six alaska volcano observatory avo arrays at ranges of 59 to over 800 km from the volcano the lack of geophysical monitoring near bogoslof and the repeated production of volcanic clouds to flight levels made monitoring by remote infrasound critical during the eruption for the first time avo relied extensively on automated infrasound detections from regional arrays to dispatch timely notifications of the ongoing activity most of the 70 eruptive events were detected on at least one array but no array detected all of the events mainly because atmospheric conditions were highly variable during the eruption acoustic propagation modeling helps explain some of the variation in array detections but also highlights limitations in regional propagation models to our knowledge this is the first example of well recorded infrasound from an explosive eruption occurring in shallow seawater providing extensive insights into eruption dynamics in this unique environment the dominance of low frequency infrasound 0 1 1 hz is attributed to eruptions occurring beneath tens of meters of seawater higher frequency infrasound signals were mostly limited to eruptions where the vent was isolated from major interaction with seawater or in several cases where a lava dome grew above sea level

volcanological and magmatological evolution of stromboli volcano aeolian islands the roles of fractional crystallization magma mixing crustal contamination and source heterogeneity the present paper reports the results of a detailed stratigraphical petrological and geochemical investigation on the island of stromboli aeolian arc southern tyrrhenian sea major and trace element data determined on a large quantity of samples from well established stratigraphic positions indicate that the magmatological evolution of the island through time was more complex than previously known the activity of the exposed part of stromboli which occurred over a time span of about 100 000 years started with the emission of high k calc alkaline hkca volcanics which were covered by calc alkaline ca shoshonitic sho high k calc alkaline hkca and potassic ks products the most recent activity consists of hkca lavas and the present day sho basaltic volcanics emitted by mildly explosive strombolian activity most of the products are lavas with minor amounts of pyroclastic rocks emplaced mainly during the early stages of activity the transition from the sho to the ks cycle was associated with the collapse of the upper part of the volcanic apparatus the transition from ks to the present day sho activity has been found to have occurred at the time of the sliding of the western portion of the volcano that generated the sciara del fuoco depression the rock series cropping out at stromboli show variable enrichment in potassium incompatible trace elements and radiogenic sr which increase from ca through hkca and sho up to ks rocks major trace element and sr isotopic data agree in indicating that the hkca and sho series evolved by crystal liquid fractionation starting from different parental liquids whereas crustal assimilation appears to have been the leading process during the evolution of ks volcanics mixing processes also played a role although they can be well documented only when they occurred between magmas with different isotopic and geochemical characteristics geochemical modelling based on trace element and isotopic data indicates that the mafic magmas of the different volcanic series may be generated by melting of an upper mantle heterogeneously enriched in incompatible elements and radiogenic sr by addition via subduction of different amounts of crustal material geochemical data however are also in agreement with the alternative hypothesis that the most mafic magmas of the different series have been generated by combined processes of fractional crystallization assimilation and mixing of a ca magma in a deep sited magma chamber the mafic magmas formed by these complex processes were successively emplaced in a shallow reservoir where they evolved by simple fractional crystallization hkca and sho series and by assimilation of crustal material ks the occurrence of changes in the geochemical signatures of the magmas at the time of the structural modification of the volcano is believed to favour the hypothesis that the variable composition observed in the volcanic rocks of stromboli is the result of processes occurring within the volcanic system

life and demise of intrathermocline mesoscale vortices abstractthis study is focused on finescale dissipation mechanisms of intra thermocline mesoscale vortices exemplified by meddies large anticyclonic salt lenses of mediterranean origin commonly observed in the lower north atlantic thermocline high resolution numerical experiments are diagnosed to quantify the rates of temperature t and salinity s dispersion in salt lenses and to determine the relative contribution of various mixing processes in the decay of their thermohaline signatures we find in agreement with observations that meddies dissipate on the characteristic timescale of several years and that their ultimate disintegration can be attributed to thermohaline interleaving driven by double diffusive mixing mechanically generated turbulence on the other hand tends to suppress the interleaving and therefore has an adverse net effect on eddy dispersion it is found that the dispersion properties of static lenses characterized by density compensated t s patterns and their rapidly rotating

strombolian explosions 2 eruption dynamics determined from acoustic measurements strombolian activity consists of a series of explosions due to the breaking of a large overpressurized bubble at the surface of the magma column acoustic pressure due to sound waves has been measured and analyzed at stromboli for more than 50 explosions three parts can be distinguished in the acoustic pressure waveform which are related to the behavior of the bubble before during and after its bursting before the sharp rise in acoustic pressure the signal is dominated by waves with a frequency of 2 hz which develop on the nose of the bubble they produce sound in air by imposing a rapid motion to the interface and one could detect a bubble travelling in the uppermost 30 m of the magma column when the bubble reaches the air magma interface its strong vibration driven by a large overpressure inside the gas generates the main event with a frequency around 9 hz after the bubble has burst kinematic waves of frequency around 4 5 hz are the main source of sound they develop at the surface of the magma left on the conduit side the three types of motion although determined independently give consistent results furthermore combining the results obtained for the two types of kinematic waves the magma viscosity is estimated to be of 300 65 pa s which is in good agreement with petrological constraints and corroborates the validity of our analysis this suggests that acoustic measurements constitute a powerful tool in the understanding of eruption dynamics

predicting eruptions from precursory activity using remote sensing data hybridization abstract many volcanoes produce some level of precursory activity prior to an eruption this activity may or may not be detected depending on the available monitoring technology in certain cases precursors such as thermal output can be interpreted to make forecasts about the time and magnitude of the impending eruption kamchatka russia provides an ideal natural laboratory to study a wide variety of eruption styles and precursory activity prior to an eruption at bezymianny volcano for example a clear increase in thermal activity commonly occurs before an eruption which has allowed predictions to be made months ahead of time conversely the eruption of tolbachik volcano in 2012 produced no discernable thermal precursors before the large scale effusive eruption however most volcanoes fall between the extremes of consistently behaved and completely undetectable which is the case with neighboring kliuchevskoi volcano this study tests the effectiveness of using thermal infrared tir remote sensing to track volcanic thermal precursors using data from both the advanced spaceborne thermal emission and reflection radiometer aster and advanced very high resolution radiometer avhrr sensors it focuses on three large eruptions that produced different levels and durations of effusive and explosive behavior at kliuchevskoi before each of these eruptions tir spaceborne sensors detected thermal anomalies i e pixels with brightness temperatures 2 c above the background temperature high temporal low spatial resolution i e hours and 1 km avhrr data are ideal for detecting large thermal events occurring over shorter time scales such as the hot material ejected following strombolian eruptions in contrast high spatial low temporal resolution i e days to weeks and 90 m aster data enables the detection of much lower thermal activity however activity with a shorter duration will commonly be missed aster and avhrr data are combined to track low level anomalies months prior to an eruption and higher energy events prior to large eruptions to develop a monitoring approach for this eruption style results show that strombolian eruptions produce enough energy in the pre eruptive phase to trigger an avhrr detection paired with aster data the results can be extended back in time to develop a precursory timeline which captures subtle changes in volcanic activity that would commonly go unnoticed in a single data set although these precursors may be volcano and eruption specific the now sixteen year old database from aster allows this methodology to be repeatable at other volcanoes to establish a quantitative precursory baseline which would be an improvement over current eruption classifications

acoustic sounder measurements of the vertical velocity of volcanic jets at stromboli volcano we have used a sodar acoustic doppler sounder to characterize the behavior of volcanoes and in particular to measure the vertical velocities of volcanic jets we have analyzed more than 100 explosions on stromboli volcano eolian islands first results show vertical speeds close to the vent ranging from 20 m s to 80 m s the uncertainty in the measurements is close to 10 due mainly to the inaccurate knowledge of the sound speed in volcanic jets this is small compared to other volcanological methods this method is well suited for monitoring temporal variations during an eruption and should be particularly interesting for the study of the eruptive dynamics of lava fountains the doppler spectrum in explosions appears to be related to different types of echoes and contains information on particle sizes in the jet

influence of near source volcano topography on the acoustic wavefield and implication for source modeling in near source conditions 5 km the atmosphere is often assumed to be fully transparent to acoustic waves and to have a small effect on the acoustic wavefield as a consequence the propagation of the acoustic waves in the atmosphere near the source is often neglected and waveform is compensated only in amplitude by the inverse of the distance from the source however the amplitude distribution at five infrasonic stations deployed around the active craters of the stromboli volcano reveals anomalous decay up to 11 db larger than expected which cannot be explained in terms of energy loss for geometrical spreading the distribution of amplitude decay changes for different source positions suggesting a strong relationship with the source to receiver path geometry by using 2d fdtd modeling we show that the anomalous amplitude distribution of the acoustic waves at stromboli is not necessarily due to the source radiation pattern but it is strongly influenced by the topography of the ground atmosphere interface diffraction and reflection of topography contaminate the acoustic wavefield and have a strong effect in reducing the amplitude and altering the waveform our work demonstrates that line of sight conditions are quite difficult to be achieved in acoustic experiments and that a detailed knowledge of the topography along the crater receiver path is necessary whenever infrasound waveforms are used to invert for the source process

it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity this is the second paper in a two part series examining numerical simula tions of buoyancy driven ow in the presence of large viscosity contrasts in the rst pa per we demonstrated that a combination of three numerical tools an extended ghost uid type method the level set approach and the extension velocity technique accurately simulate complex interface dynamics in the presence of large viscosity contrasts in this paper we use this three fold numerical method to investigate bubble dynamics in the conduits of basaltic volcanos with a focus on normal strombolian eruptions strombolian type activity named after the famously episodic eruptions at stromboli volcano is char acterized by temporally discrete fountains of incandescent clasts the mildly explosive nature of normal strombolian activity as compared to more eusive variants of basaltic volcanism is related to the presence of dissolved gas in the magma yielding a complex two phase ow problem we present a detailed scaling analysis allowing identication of the pertinent regime for a given ow problem the dynamic interactions between gas and magma can be clas sied into three non dimensional regimes based on bubble sizes and magma viscosity re solving the uid dynamics at the scale of individual bubbles is not equally important in all three regimes as long as bubbles remain small enough to be spherical their dy namic interactions are limited compared to the rich spectrum of coalescence and breakup processes observed for deformable bubbles in particular once inertia ceases to be neg ligible one key nding in our simulations is that both large gas bubbles and large conduit lling gas pockets slugs are prone to dynamic instabilities that lead to their rapid breakup during buoyancy driven ascent we provide upper bound estimates for the maximum sta ble bubble size in a given magmatic system and discuss the ramications of our results for two commonly used models of normal strombolian type activity the rise speed dependent rsd model and the collapsing foam cf model

array tracking of infrasonic sources at stromboli volcano 1 infrasonic arrays are a powerful tool for volcanic monitoring and hazard assessment explosions were recorded at stromboli using a small aperture array of 4 infrasonic stations allowing precise vent location the acoustic signals were delayed and summed revealing the existence of two main groups of infrasonic waves the ne crater produces short 3 s high amplitude 20 80 pa pressure waves while the sw crater produces small acoustic pressure 10 30 pa with long 5 15 s coda the two groups reflect different in explosive styles and similar spectral content centered on 5 6 hz when stacked together acoustic waveforms for each crater reveal the same pressure pulse which indicates a common source process we infer that the acoustic onset at both craters is generated by the burst of a large gas bubble while the acoustic coda is controlled by a sustained pressure release

high speed imaging of strombolian explosions the ejection velocity of pyroclasts explosive volcanic eruptions are defined as the violent ejection of gas and hot fragments from a vent in the earth s crust knowledge of ejection velocity is crucial for understanding and modeling relevant physical processes of an eruption and yet direct measurements are still a difficult task with largely variable results here we apply pioneering high speed imaging to measure the ejection velocity of pyroclasts from strombolian explosive eruptions with an unparalleled temporal resolution measured supersonic velocities up to 405 m s are twice higher than previously reported for such eruptions individual strombolian explosions include multiple sub second lasting ejection pulses characterized by an exponential decay of velocity when fitted with an empirical model from shock tube experiments literature this decay allows constraining the length of the pressurized gas pockets responsible for the ejection pulses these results directly impact eruption modeling and related hazard assessment as well as the interpretation of geophysical signals from monitoring networks

airwaves generated by an underwater explosion implications for volcanic infrasound 1 a shallow explosion in a fluid is one of the fundamental processes of airwave generation in volcanic eruptions to better understand the mechanism of the airwave generation underwater explosion experiments were conducted although the underwater explosions have been intensely studied over the last century airwaves have received little attention in this study pressure waves were measured in air and under water and the corresponding motion of the water surface was captured by a high speed video camera airwaves and associated styles of the surface motion show similarities determined by the scaled depth defined as the depth divided by the cubic root of the explosion energy the air waveforms are quite different from the pressure waves measured in the water and cannot be completely explained by linear transmission of pressure waves from water to air the mechanism of airwave generation is a combination of wave transmission and dynamics of the interface boundary the first mechanism directly reflects the explosion source and the same source is also observed as the underwater pressure waves on the other hand the second is not necessarily visible in the underwater pressure waves but will provide information on the mechanical properties and behavior of the material above the explosion source each mechanism is analyzed in the experiments

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

on the volcanic waveguide an analytical solution for the sound field in a resonant magma conduit with depth dependent magma properties provides a versatile interpretative tool for the analysis of seismoacoustic signals generated by fluid processes in active volcanoes expressions are given for the acoustic field in the atmosphere and the seismic field in the ground radiated through the magma conduit vent and walls respectively a new source model allows the resonance in the conduit to be excited by the vertical fluid velocity at the bottom of the conduit this source model represents acoustic excitation induced by low frequency fluid oscillations or large volume fluctuations originating at depth the magma conduit is modeled as a three section duct with each section having a different density sound speed viscosity and dimension the modal structure of the coupled resonant system is retained as the sound field in the conduit propagates into the surrounding bedrock and the overlying atmosphere the source time function permits estimates of the total mass injected or removed from the magmatic system and the source spectrum acts as a band pass filter on the resonant modes of the conduit theoretical or empirical source functions can be used to drive the seismoacoustic wave field and the amplitude of the source velocity may be constrained by the ballistics of pyroclasts and the height of ash plumes the acoustic properties of the melt may be predicted from the temperature composition and flow conditions of the magma as a function of depth comparisons of synthetic waveforms and spectra with those of seismic and acoustic signals recorded on active volcanoes permit estimates of the conduit geometry density sound speed and attenuation properties of the melt and characterize the temporal and spectral features of the source function the ability to extract this information accurately and efficiently from seismic and acoustic data streams may permit near real time modeling of fluid driven processes in active volcanoes

anatomy of a strombolian eruption inferences from particle data recorded with thermal video over the past decade a proliferation of new technologies has pushed forward our ability to measure the dynamics of volcanic emissions as they exit and ascend above the vent measuring parameters of all particles as they exit the vent during an explosive eruption is the best way to gather parameters such as size shape velocity and mass for the solid particulate fraction of the plume in our case this being the lapilli and bomb component we compute particle velocities and size distributions using high spatial resolution centimeter sized pixel thermal infrared imagery collected at 200 hz for small explosive eruptions at stromboli italy our study covers 13 eruptions from stromboli s southwest crater that occured in october 2012 plus 13 eruptions from the southwest crater and 5 eruptions from the northeast crater in may 2014 we obtain a statistically robust database for size mass and velocity of 83 000 particles most particles have sizes of 5 to 15 cm so that the majority of individual particle masses are below 0 4 kg however 4950 6 of the particles are heavier than 5 kg and represent 59 of the total mass erupted we also show that the smallest particles detected have the highest velocities with the maximum recorded vent leaving velocity being 240 m s while the thermal data provide insights into particle emission and launch dynamics correlation with seismic data sheds light on the source mechanism our results lead us to suggest that pyroclast dominated explosions are a consequence of the presence of a viscous degassed cap at the head of the magma column whereas gas dominated events are a consequence of slug bursting in a cleaner conduit the cap having been lost by convective overturn

gas slug ascent in a stratified magma implications of flow organisation and instability for strombolian eruption dynamics the canonical strombolian paradigm of a gas slug ascending and bursting in a homogeneous low viscosity magma cannot explain the complex details in eruptive dynamics recently revealed by field measurements and textural and geochemical analyses evidence points to the existence of high viscosity magma at the top of the conduit of strombolian type volcanoes acting as a plug here new experiments detail the range of flow configurations that develop during the ascent and burst of a slug through rheologically stratified magma within a conduit end member scenarios of a tube fully filled with either high or low viscosity liquid bracket three main flow configurations 1 a plug sufficiently large to fully accommodate an ascending gas slug 2 a plug that can accommodate the intrusion of low viscosity liquid driven by the gas expansion but not all the slug volume so the slug bursts with the nose in the plug whilst the base is still in the low viscosity liquid 3 gas expansion is sufficient to drive the intrusion of low viscosity liquid through the plug with the slug bursting in the low viscosity layer emplaced dynamically above the plug we show that the same flow configurations are viable at volcanic scale through a new experimentally validated 1d model and 3d computational fluid dynamic simulations applied to stromboli our results demonstrate that the key parameters controlling the transition between each configuration are gas volume plug thickness and plug viscosity the flow processes identified include effective dynamic narrowing and widening of the conduit instabilities within the falling magma film transient partial and complete blockage of the conduit and slug disruption these complexities influence eruption dynamics and vigour promoting magma mingling and resulting in pulsatory release of gas

inverting the source mechanism of strombolian explosions at mt yasur vanuatu using a multi parameter dataset abstract the source mechanism of strombolian explosions at mt yasur vanuatu is analyzed using a unique data set which enables us to combine different methodologies the novelty of the approach presented here lies in the combination of seismic acoustic and doppler radar data thus using infrasound and doppler radar observations we are able to provide independent estimates of the volume of the eruptive source in the following we show that a correlation exists between source volume and the maximum particle velocity of the expelled volcanic products in order to determine the source location and the associated mechanism and to compare those two methods we use time reversal imaging and moment tensor inversion while the first method also applies to extended sources the latter might be biased by its intrinsic point source approximation we show that time reversal imaging can deliver an estimate of the source depth without any a priori assumptions even in an unfavorable scenario in terms of topography and receiver setup the inverted source mechanism retrieved from moment tensor inversion is found to be largely isotropic with minor deviatoric components the inverted source location points towards an area to the north west of the active craters indicative of a common feeder system of the activity at mt yasur however it is also evident that to fully locate the source of strombolian activity at yasur location precision must be enhanced

types and mechanisms of strombolian explosions characterization of a gas dominated explosion at stromboli textural and chemical analyses of bombs quenched directly from a normal explosion at stromboli volcano italy were integrated with coincident seismic acoustic and thermal data the data set defines a new gas dominated type of strombolian eruption named type 0 these events are characterized by high velocity emission 150 250 m s 1 of a few relatively small juvenile particles with entrained non juvenile clasts that previously fell back into the vent to be re erupted for the studied event the explosion depth was more than 250 m deep and the particles showed little residence time in the shallow system slug ascent velocities over the final 20 35 m of magma filled conduit and the low viscosity of the resident magma are all consistent with simple bubble burst in a clean conduit this conduit type and eruption style likely fit popular slug ascent and burst models used to explain strombolian eruptions in contrast the ballistic dominated type of explosions type 1 are associated with larger proportions of stagnant material in the shallow system magma mix we argue that the additional volume of this stagnant material pushes the free surface upward because of the larger volume of material available for entrainment into a type 1 slug burst which has to fragment through a thick cap of degassed material type 1 events tend to be rich in particles in contrast the less spectacular gas rich type 0 events have little material to entrain thus being poor in lapilli and bombs

review of ten years of volcano deformations recorded by the ground based insar monitoring system at stromboli volcano a tool to mitigate volcano flank dynamics and intense volcanic activity abstract stromboli volcano southern italy is one of the most monitored volcano in the world with a surveillance network that includes a permanently sited ground based sar interferometer gbinsar this work is the review of the gbinsar data gained from the last decade of monitoring activity the analysis of the entire dataset of gbinsar measurements allowed the assessment of the deformation field of the northern part of the summit crater area and the sciara del fuoco depression in detail the main displacements recognized can be related to different factors 1 the inflation deflation respectively immediately before and after each new effusive event 2 the bulging of localized sectors of the volcano involved in the vent opening 3 the gravitational sliding of the sciara del fuoco infill 4 the movement of lava flows accelerations in this sector are related to sheet intrusions while the possibility of vent opening associated with small sliding or catastrophic flank failure are related to highly overpressurized sheets able to produce high displacement rate in the sciara del fuoco in the summit crater area the increases in the displacement rate are related to the pressurization of the shallow conduit system as the consequence of the variation in the magma level magmastatic pressure or to the lateral magma migration lateral conduit expansion or dike intrusion in response to the increase of the overpressure component fluctuations in the displacement rate in the summit crater area can be related to the magma overturning within the conduit with the increases in displacement rate during the upwelling of less dense magma while displacement rate decreases as the degassed magma column is pushed out from the conduit lava flows or overflows instead the decrease in the displacement rate without coeval lava outpouring could be related to the sink of the degassed magma due to density contrast between the gas poor and the gas charged magmas using the displacement rate in the summit crater area as a proxy for the variation in the pressure condition in conduit both magmastatic and overpressure components thresholds for the crises characterized by the occurrence of overflows eventually associated with major explosions and flank effusions eventually associated with paroxysmal explosions are identified small conduit overpressure will produce overflows sometimes associated with crater rim collapses while large magma overpressure will laterally expand the conduit forming ne sw striking sheets feeding eruptive vents at the base of the summit crater area and within the sciara del fuoco generating conditions of instability that can evolve into catastrophic collapse of the instable flank

the implications of gas slug ascent in a stratified magma for acoustic and ground deformation source mechanisms in strombolian eruptions the interpretation of geophysical measurements at active volcanoes is vital for hazard assessment and for understanding fundamental processes such as magma degassing for strombolian activity interpretations are currently underpinned by first order fluid dynamic models which give relatively straightforward relationships between geophysical signals and gas and magma flow however recent petrological and high speed video evidence has indicated the importance of rheological stratification within the conduit and here we show that under these conditions the straightforward relationships break down using laboratory analogue experiments to represent a rheologically stratified conduit we characterise the distinct variations in the shear stress exerted on the upper sections of the flow tube and in the gas pressures measured above the liquid surface during different degassing flow configurations these signals generated by varying styles of gas ascent expansion and burst can reflect field infrasonic measurements and ground motion proximal to a vent the shear stress signals exhibit timescales and trends in qualitative agreement with the near vent inflation deflation cycles identified at stromboli therefore shear stress along the uppermost conduit may represent a plausible source of near vent tilt and conduit shear contributions should be considered in the interpretation of ground deformation which is usually attributed to pressure sources only the same range of flow processes can produce different experimental infrasonic waveforms even for similar masses of gas escape the experimental data resembled infrasonic waveforms acquired from different vents at stromboli associated with different eruptive styles accurate interpretation of near vent ground deformation infrasonic signal and eruptive style therefore requires detailed understanding of a spatiotemporal magma rheology in the shallow conduit and b shallow conduit geometry as well as bubble overpressure and volume

pressure changes associated with the ascent and bursting of gas slugs in liquid filled vertical and inclined conduits at basaltic volcanoes the sources of long period and very long period seismicity and acoustic signals are frequently described in terms of fluid dynamic processes in particular the formation and ascent of gas slugs within the magma column and their bursting at the surface to investigate pressure changes associated with these processes two phase flow experiments have been carried out in vertical and inclined pipes with both single gas slugs and a continuously supplied gas phase the ascent of individual gas slugs is accompanied by strong dynamic pressure variations resulting from the flow of liquid around the slug these dynamic transients generate sub static pressures below the ascending slug in viscosity controlled systems and produce super static pressures when the slug reaches the surface and motion ceases in inertia dominated systems conduit inclination promotes a change of regime from bubbly to slug flow and favours an increase in size and velocity of the slugs at the expense of their frequency of occurrence during continuously supplied two phase flow the experimental pressure data support previous theoretical analyses of oscillatory sources in ascending slugs as the slugs approach the surface and burst pressure oscillations are also observed during the release of gas slugs and in their wake region

volumetric observations during paroxysmal eruptions at mount etna pressurized drainage of a shallow chamber or pulsed supply abstract the october 17 to november 5 1999 eruption of mount etna s bocca nuova crater emplaced a 15 10 6 m 3 flow field the eruption was characterized by 11 paroxysmal events during which intense strombolian and lava fountain activity fed vigorous channelized a a flows at eruption rates of up to 120 m 3 s 1 each paroxysm lasted between 75 and 450 min and was separated by periods of less intense strombolian activity and less vigorous 3 s 1 effusion ground based satellite and model derived volumetric data show that the eruption was characterized by two periods during which eruption rates and cumulative volume showed exponential decay this is consistent with a scenario whereby the system was depressurized during the first eruptive period october 17 23 repressurized during an october 24 pause and then depressurized again during the second period october 25 28 the imbalance between the erupted and supplied volumes mean that the two periods involved the collection of 1 5 5 7 10 6 m 3 and 1 2 3 6 10 6 m 3 respectively or an increase in the time averaged supply to 11 6 13 6 m 3 s 1 and 12 5 14 9 m 3 s 1 two models are consistent with the observed episodic fountaining derived volumetric trends and calculated volume imbalance a magma collection model and a pulsed supply model in the former case depressurization of a shallow reservoir cause the observed volumetric trends and foam collapse at the reservoir roof powers fountaining in the pulsing case variations in magma flux account for pressurization depressurization and supply the excess volume increases in rise rate and volatile flux coupled with rapid exsolution during ascent trigger fountaining limiting equations that define critical foam layer volumes and magma rise rates necessary for hawaiian style fountaining favor the latter model

interpretation of data from the monitoring thermal camera of stromboli volcano aeolian islands italy twenty eruptive events from the northeast crater of stromboli volcano recorded by a thermal monitoring camera in early 2004 were analysed in order to understand the eruptive dynamics selected events were chosen to be typical of explosions that characterize the steady activity of stromboli in terms of jet height and duration most of the explosions consisted of clast rich single bursts originating from the same vent inside the northeast crater conspicuous ash emission was scarce eruptions were preceded by the flashing of a perturbation wave characterized by low temperatures and an average propagation velocity of about 35 100 m s 1 this perturbation was thought to be caused by the bursting of the gas slug at the bottom of the crater and is interpreted as an air wave this was immediately followed by the expansion of a jet of hot gas and particles at a velocity of 35 75 m s 1 ejecta coarser than 138 cm appeared 1 6 2 s after the onset of the explosion moving at a variable velocity 30 60 m s 1 eruptive events were either vertical or inclined 7 13 towards the nnw this inclination is thought to be a consequence either of the morphology of the conduit following modest rock falls that partially obstructed the uppermost part of the crater or of the displacement of the internal conduit due to the explosive activity of the volcano the instability of the summit area is a further possible cause of the deformation of the conduit

image processing of explosive activity at stromboli abstract a new way to study the dynamics of explosive behaviour at different vents of stromboli volcano is proposed the method is based on computer processing of images taken by an infrared film camera at a rate of 4 pictures per second each picture has been digitized by use of an image scanner with a 75 d p i dots per inch resolution and 256 levels of gray then processed and the total mass of the ejected material has been calculated for each photograph with this procedure the flux of ejected matter throughout every single explosive event has been reconstructed the analysis of trajectories made on adequate samples of ejecta has allowed us to evaluate the ejection velocity the mode of the mass flux distribution and the mean value of the velocities calculated for individual particles quantify the kinetic energy of an explosion vents nos 1 and 3 which remained active after the last effusive eruption of 1985 1986 show several explosive patterns the energy of which is measured the observed flux distributions have been checked both numerically and experimentally by modelling impulsive events the computer simulations of the mass distributions have allowed us to speculate on the possible explosive dynamisms two different models have been used a single impulse model confirms the behaviour actually shown by one of the two vents while the behaviour of the other is better depicted by a cumulative trend of successive impulses in rhythmic sequence moreover through the experimental approach we have had the opportunity to test the overall resolution of the method the observed matter flux distribution has then been associated to the seismic signals in order to correlate the dynamics involved in the explosions with the seismic source mechanisms