theory of acoustic propagation in a multi phase stratified liquid flowing within an elastic walled conduit of varying cross sectional area abstract a theoretical solution is derived for the sound field in an arbitrarily layered viscous fluid moving with the non negligible mach number within a duct with elastic walls and varying cross sectional area the solution is applied to the interpretation of infrasonic and seismic signals preceding and accompanying volcanic eruptions and can be used to study the acoustic response of various types of volcanic fluids including magma gas mixtures ash gas mixtures and bubble rich liquids the acoustic field in a magma conduit can be propagated into the atmosphere through an open vent and coupled into the ground through the displacement of the magma conduit walls the theoretical solutions predict that fluids moving with the non negligible mach number will exhibit significant attenuation in the upstream direction thereby reducing the quality factor of the conduit resonance thus acoustic energy generated during an eruption may be preferentially radiated downstream exacerbating the acoustic decoupling between the upper and lower parts of a stratified magma column a source model for a repeated cavitation process is introduced as a possible excitation mechanism for tremor signals

applications of autoregressive models and time frequency analysis to the study of volcanic tremor and long period events volcanic tremor and long period lp events are characterized by sharp spectral peaks that generally result from resonance effects at the source and which concentrate most of the radiated energy the understanding of these seismovolcanic phenomena requires good descriptions of the distribution in time and frequency of the different spectral components included in the signals as well as a separation of the resonance effects from less energetic effects such as excitation and propagation we address the issue of extracting from individual records information as detailed as possible on the physical processes involved at the source we introduce and compare several time frequency analysis methods and we describe the application of autoregressive modeling and deconvolution methods to the characterization and separation of the main spectral components we propose a signal analysis approach based on the joint use of a set of complementary methods and we present applications to several examples of volcanic tremor and lp events the time frequency analysis of some of the lp events taken as examples reveals short duration components at the seismogram onsets with energy concentrated at frequencies either higher or lower than the main resonance frequencies these seismic phases are probably related to the excitation processes of the volcanic resonators in several cases the arrival of the main spectral peak has a delay of a few tenths of a second with respect to the first arrival the residual signals obtained by deconvolving and eliminating the main spectral components contain information about the excitation such as duration delay or frequency band the residual signals are short for lp events and continuous for volcanic tremor the autoregressive modeling of the sample records gives precise estimations of the frequency and quality factor of the main spectral peaks the measured parameters cover a wide range of values which is consistent with the great variety of fluids filling resonating cavities in volcanoes

temporal and spectral characteristics of seismicity observed at popocatepetl volcano central mexico abstract popocatepetl volcano entered an eruptive phase from december 21 1994 to march 30 1995 which was characterized by ash and fumarolic emissions during this eruptive episode the observed seismicity consisted of volcano tectonic vt events long period lp events and sustained tremor before the initial eruption on december 21 vt seismicity exhibited no increase in number until a swarm of vt earthquakes was observed at 01 31 hours local time visual observations of the eruption occurred at dawn the next morning lp activity increased from an average of 7 events a day in october 1994 to 22 events per day in december 1994 at the onset of the eruption lp activity peaked at 49 events per day lp activity declined until mid january 1995 when no events were observed tremor was first observed about one day after the initial eruption and averaged 10 h per episode by late february 1995 tremor episodes became more intermittent lasting less than 5 min and the number of lp events returned to pre eruption levels 7 events per day using a spectral ratio technique low frequency oceanic microseismic noise with a predominant peak around 7 s was removed from the broadband seismic signal of tremor and lp events stacks of corrected tremor episodes and lp events show that both tremor and lp events contain similar frequency features with major peaks around 1 4 hz frequency analyses of lp events and tremor suggest a shallow extended source with similar radiation pattern characteristics the distribution of vt events between 2 5 and 10 km also points to a shallow source of the tremor and lp events located in the first 2500 m beneath the crater under the assumption that the frequency characteristics of the signals are representative of an oscillator we used a fluid filled crack model to infer the length of the resonator

infrasonic waves and volcanic tremor at stromboli the origin of the volcanic tremor is still under debate many theories have been proposed in the last years but none has yet been completely accepted in 1993 highly sensitive pressure sensors 2 175 pa volt used to monitor the explosive activity at stromboli have revealed unexpected correlation between small spike shaped pressure signals 1 2 pa and volcanic tremor these pressure pulses repeat regularly in time with a recurrent period of ca 1 s video camera images allowed us to correlate the pressure pulses with small gas bursts occurring at one of the active vents the striking correlation 0 971 between infrasonic and seismic energy fluctuations is particularly meaningful in the frequency domain infrasonic and seismic signal share the same spectral content 3 hz for every station within a range of 700 m around the craters correlations in time and frequency domain remained unaltered during the 1994 field experiments moreover during 1994 the increased degassing activity has been followed by an increase in pressure release 7 8 pa and by a shift towards higher frequencies 8 hz both in the infrasonic and seismic records infrasonic waves and volcanic tremor show similar energy fluctuations and frequency contents appearing therefore to be produced by the same dynamical process on this basis we claim that volcanic tremor at stromboli originates by continuous outbursting of small gas bubbles in the upper part of the magmatic column

theory of the airborne sound field generated in a resonant magma conduit abstract explosive sources triggered inside a magma conduit may excite the conduit into acoustic resonance the acoustic field in the conduit can propagate into the atmosphere through an open vent and ensonify the overlying atmosphere the character of the airborne sound field is determined by a combination of propagation and source effects the resonance of the magmatic conduit and the diffraction of the sound field at the volcanic vent are acoustic propagation effects whereas the explosion pressure signature and the firing rate of the explosions define the source characteristics for wavelengths larger than the conduit radius only the longitudinal resonances of the magmatic conduit are relevant and the open vent radiates like a piston surrounded by an infinite baffle in this case the fluid particle velocities are directed along the axis of the conduit and the sound field may propagate into the surrounding bedrock through the conduit wall displacement induced by the fluid overpressure this coupling may produce seismic signals with banded spectra such as volcanic tremor and long period events the airborne pressure field retains the modal structure of the sound field in the magmatic conduit which contains information on the conduit geometry and geo acoustic properties of the magma the seismic wavefield is driven by the acoustic field in the magma and also contains this information although it may be filtered by propagation effects in the bedrock the theoretical sound field in the magma conduit is used to interpret seismic tremor signals recorded at mt spurr volcano alaska rapid variations in the acoustic impedance of the magma conduit terminations can create systematic changes in the tremor spectra which can be used to monitor changes in the magmatic system the results of the modelling illustrate the difference between source effects and conduit resonance as well as the value of seismoacoustic measurements in volcanic environments

on the relation between infrasound seismicity and small pyroclastic explosions at karymsky volcano 1 ground and atmospheric propagating elastic waves are integrated with digitized video to reconstruct important parameters during the onset of eruptions at karymsky volcano in 1999 muzzle velocities which range from 10 to 55 m s for 34 analyzed explosive events are found to be very well correlated with eruption velocities synthesized from infrasonic trace data acoustic modeling proposed here invokes a linear acoustic source consistent with a 3 m piston that accelerates upwards timing of acoustic arrivals relative to video records of material emission is used to constrain fragmentation sources depths which are assumed to be coincident with infrasound generation these sources are generally shallow with an observed vertical range of about 15 m systematic changes in source depth are observed during two nights of data collection and are attributed to variations in the depth of the magma free surface relative timing of acoustic and seismic arrivals is used to identify the presence of seismicity prior to fragmentation this seismicity is emergent and low intensity but significant because it precedes the presumed fragmentation events by variable amounts up to 4 s the primary short period seismic phases appear coincident with the initiation of fragmentation and infrasound generation because of the complexity of the seismic green s function it is not possible to correlate amplitude from a specific seismic pulse with observed eruption intensity

multiple ruptures for long valley microearthquakes a link to volcanic tremor despite several episodes of ground deformation and intense seismic activity starting in 1978 the long valley california volcanic area has not produced clearly recognized volcanic tremor instead a variety of atypical microearthquakes have been recorded during these episodes including events dominated by low frequency long period or mixed high and low frequency hybrid signals during a 1997 episode a number of unusual microearthquakes occurred within a temporary 40 station seismic network surrounding the casa diablo area allowing the events to be precisely located and analyzed as a function of azimuth offset and source characteristics eight prime examples lie within two 7 km deep clusters of seismicity separated by about 1 km with four events in each cluster empirical green s function deconvolution shows that these events are composed of two to three sub events the sub events consisting of ordinary single rupture double couple microearthquakes the delay times between the sub events are constant within each cluster equaling 0 092 s in one and 0 06 s in the other events from other clusters show similar delays the signal interference produced by the closely spaced sub events gives rise to modulated delay dependent source spectra the regularity of the delays suggests that the sub events are being triggered by a fixed length and or time scale process an example being the length inflation rate of a magmatic or hydrothermal flow structure with continued action of the triggering process the sub events could proliferate and evolve into observable volcanic tremors at mammoth

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

observations of volcanic tremor during the january february 2005 eruption of mt veniaminof alaska mt veniaminof alaska peninsula is a stratovolcano with a summit ice filled caldera containing a small intracaldera cone and active vent from january 2 to february 21 2005 mt veniaminof erupted the eruption was characterized by numerous small ash emissions vei 0 to 1 and accompanied by low frequency earthquake activity and volcanic tremor we have performed spectral analyses of the seismic signals in order to characterize them and to constrain their source continuous tremor has durations of minutes to hours with dominant energy in the band 0 5 4 0 hz and spectra characterized by narrow peaks either irregularly non harmonic tremor or regularly spaced harmonic tremor the spectra of non harmonic tremor resemble those of low frequency events recorded simultaneously with surface ash explosions suggesting that the source mechanisms might be similar or related we propose that non harmonic tremor at mt veniaminof results from the coalescence of gas bubbles while low frequency events are related to the disruption of large gas pockets within the conduit harmonic tremor characterized by regular and quasi sinusoidal waveforms has duration of hours spectra containing up to five harmonics suggest the presence of a resonating source volume that vibrates in a longitudinal acoustic mode an interesting feature of harmonic tremor is that frequency is observed to change over time spectral lines move towards higher or lower values while the harmonic nature of the spectra is maintained factors controlling the variable characteristics of harmonic tremor include changes in acoustic velocity at the source and variations of the effective size of the resonator

low attenuation resonance of a spherical magma chamber source mechanism of monotonic volcanic tremor at asama volcano japan some volcanic tremor has the extreme persistence of oscillation that may be attributed to resonance our theoretical analysis suggests that a spherical resonator consisting of volcanic fluid has a low attenuation mode lam at some of the lowest frequencies which can be as low as 0 01 times the attenuation factors of higher modes in some cases the monotonic waveforms of volcanic tremor lp events at asama volcano japan can be explained by the lam excitation in the spherical resonator model which well fits both characteristic frequencies and attenuation factors the resonator size velocity and the density contrasts between the fluid inside and the elastic medium outside are estimated

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

propagation of acoustic waves in a visco elastic two phase system influences of the liquid viscosity and the internal diffusion abstract the main purpose of the present paper is to present the mathematical expression for the frequency dependent effective acoustic properties of a liquid bubble mixture effects of the bubble resonance the heat and mass transfer between the liquid and bubbles and the viscoelasticity of the liquid are included in the expression several characteristic frequencies associated with these internal processes are represented by simple functions of the material and condition parameters using these expressions the acoustic properties of bubbly magmas are calculated and analyzed it is shown that the dispersion and attenuation of the pressure wave are particularly considerable in the frequency range lower than the characteristic frequency of the mass transfer and in the range near the characteristic frequency of the viscous response of the bubble radius in the frequency range bounded by these two frequencies the bubbly magma can be regarded as an elastic medium with the slow sound speed the significance of such acoustic properties on resonance of a body of bubbly magma is demonstrated in a simple one dimensional system

relationship between the flank sliding of the south east crater mt etna italy and the paroxysmal event of november 16 2006 over the last 2 years the south east crater sec at mt etna italy has been characterised by the intermittent emission of lava flows often accompanied by paroxysmal episodes with violent strombolian activity and or lava fountains one of the most intense and intriguing episodes occurred on november 16 2006 during strombolian and effusive activity from the very top of the sec at the eastern base of the crater a violent and short lasting outburst generated a 300 m high eruptive curtain of finely fragmented magma and steam which collapsed in a few seconds giving rise to a small but significant pyroclastic flow the paroxysm was preceded by progressive sliding of the eastern flank of the sec edifice which led to the formation of a large niche previously published models explain the outburst as due to rapid vaporisation of water contained in sediments on contact with hot lava flowing along the flank of the sec or alternatively to gravitational collapse of a destabilised portion of the eastern flank of the crater however several lines of evidence suggest that these models do not adequately explain the paroxysm which we propose was associated with the explosive emission of magma during the rapid opening of an ese wnw oriented fracture at the eastern base of the sec moreover geochemical data of the products associated with this episode show that they are the most primitive and gas rich among those erupted during the entire 2006 period we suggest that the paroxysm of november 16 2006 which occurred at base of the sec was a magma outburst due to rapid ground fracturing related to a drop in confining pressure upon the underlying dyke consequent to the sliding of the eastern flank of the sec cone specifically the unloaded shallow portion of the feeding dyke did not restrain the arrival of a new batch of gas rich magma which worked its way out by fracturing the base of the niche at its weakest point this paroxysm appears significant because it reveals the potential development of syn eruptive dynamics acting directly on the uppermost portion of the plumbing system which is able to generate pyroclastic flows even on basaltic volcanoes such as mount etna

degassing explosions at karymsky volcano kamchatka during the summer of 1997 karymsky vol cano produced summit explosions about six times each hour typical explosive episodes lasted between 30 seconds and three minutes produced gas and ash columns several hun dred meters high and ejected some incandescent material to better understand the physical source mechanisms re sponsible we recorded hundreds of explosions with a three component broad band seismometer and microphone lo cated 1650 meters from the active vent nearly every explo sion is recorded as an emergent yet identical seismic wavelet which is followed 4 15 s later by an impulsive acoustic ar rival we interpret the signals as a near surface gas volume burst which fractures the vent plug lowers the lithostatic pressure within the magma column and often induces fur ther degassing when degassing continues it is generally manifested as either a series of regular one second chug ging 1 explosions steady higher frequency jetting or a hy brid combination we believe that the seismic signature for chugs short duration harmonic tremor with integer over tones is the result of repeated gas volume bursts at the vent in contrast seismograms for jetting are non harmonic and contain higher frequencies we believe that the competing degassing behaviors are influenced by the gas flux as well as the plug conduit characteristics we propose that a plug exists due to a viscosity gradient caused by volatile depletion in the upper conduit

acoustic multipole source model for volcanic explosions and inversion for source parameters summary volcanic explosions are accompanied by strong acoustic pressure disturbances in the atmosphere with a proper source model these acoustic signals provide invaluable information about volcanic explosion dynamics far field solutions to volcanic infrasound radiation have been derived above a rigid half space boundary and a simple inversion method was developed based on the half space model acoustic monopole and dipole sources were estimated simultaneously from infrasound waveforms stability of the inversion procedure was assessed in terms of variances of source parameters and the procedure was reliable with at least three stations around the infrasound source application of this method to infrasound observations recorded at tungurahua volcano in ecuador successfully produced a reasonable range of source parameters with acceptable variances observed strong directivity of infrasound radiation from explosions at tungurahua are successfully explained by the directivity of a dipole source model the resultant dipole axis in turn shows good agreement with the opening direction of the vent at tungurahua which is considered to be the origin of the dipole source the method is general and can be utilized to study any monopole dipole or combined sources generated by explosions

dynamic behaviour of the east antarctic ice sheet during pliocene warmth warm intervals within the pliocene epoch 5 33 2 58 million years ago were characterized by global temperatures comparable to those predicted for the end of this century1 and atmospheric co2 concentrations similar to today2 3 4 estimates for global sea level highstands during these times5 imply possible retreat of the east antarctic ice sheet but ice proximal evidence from the antarctic margin is scarce here we present new data from pliocene marine sediments recovered offshore of adelie land east antarctica that reveal dynamic behaviour of the east antarctic ice sheet in the vicinity of the low lying wilkes subglacial basin during times of past climatic warmth sedimentary sequences deposited between 5 3 and 3 3 million years ago indicate increases in southern ocean surface water productivity associated with elevated circum antarctic temperatures the geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the wilkes subglacial basin an area today buried beneath the east antarctic ice sheet we interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the east antarctic ice sheet was sensitive to climatic warmth during the pliocene

vent discrimination at stromboli volcano italy eruptive activity at stromboli volcano was significantly elevated over background levels in may 2001 during 63 h of observation eight vents produced on average 17 explosions h with an average repose interval of 3 min during this period the stromboli vents exhibited consistent seismic and acoustic signatures based on cross correlation cluster analysis dendrogram clustering based on waveform cross correlation was used to illustrate the complexity of the near surface plumbing system of stromboli s multi vent edifice cross correlations of displacement seismograms produced by explosions at specific craters such as the northeast crater nec form dense waveform clusters with correlation coefficients between 0 96 and 0 99 while displacement waveforms from other craters such as the southwest crater swc exhibit loose clusters with correlations between 0 88 and 0 96 the inconsistency of swc events as compared to the nec suggests that the vent system there is more heterogeneous cluster linkage distance between the nec cluster and the central crater cc cluster is shorter than the linkage distance between the nec and swc clusters indicating that nec and cc are more closely related infrasonic observations were used to locate vent explosions confirming that the clusters of events are associated with specific vents or craters qualitative analyses of acoustic waveforms from approximately 500 explosions reveal that impulsive acoustic signals were associated with short mechanically simple ground displacement responses these events may correspond to the bursting of an individual gas slug similar degassing mechanisms from vents in the nec and the cc show common characteristics in their displacement waveforms

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

modeling of volcanic tremor as explosive point sources in a single layered elastic half space i investigate path effects on the waveform of a volcanic tremor using a model that consist of an impulsive dilatational point source embedded in a single layered elastic half space such a source may arise during a variety of volcanic conditions such as a sequence of rapid explosions at a volcanic vent as well as gas piston activity observed in basaltic lava lakes using acoustic signals recorded during the 1975 tolbachik eruption the 1983 klyuchevskoy eruption and the 1989 tokachi dake eruption i propose a general impulsive time function for the tremor source consisting either of a single impulse or a sequence of identical impulses computed seismograms illustrate the influence of a low velocity surface layer on the shape and spectra of the waveforms for the same layered model a single impulse produces a dispersive wave while a sequence of identical impulses produces a wave of multiple harmonics for a single impulse the peak in the seismograms shifts to higher frequencies when the surface layer is very thin for multiple impulses spectral peaks shift to higher frequencies as the time between successive impulses increases indicating an increasing importance of higher order harmonics

the first second of volcanic eruptions from the erebus volcano lava lake antarctica energies pressures seismology and infrasound 1 we describe a multiparameter experiment at erebus volcano antarctica employing doppler radar video acoustic and seismic observations to estimate the detailed energy budget of large up to 40 m diameter bubble bursts from a persistent phonolite lava lake these explosions are readily studied from the crater rim at ranges of less than 500 m and present an ideal opportunity to constrain the dynamics and mechanism of magmatic bubble bursts that can drive strombolian and hawaiian eruptions we estimate the energy budget of the first second of a typical erebus explosion as a function of time and energy type we constrain gas pressures and forces using an analytic model for the expansion of a gas bubble above a conduit that incorporates conduit geometry and magma and gas parameters the model consistent with video and radar observations invokes a spherical bulging surface with a base diameter equal to that of the lava lake the model has no ad hoc free parameters and geometrical calculations predict zenith height velocity and acceleration during shell expansion during explosions the energy contained in hot overpressured gas bubbles is freed and partitioned into other energy types where by far the greatest nonthermal energy component is the kinetic and gravitational potential energy of the accelerated magma shell 10 9 j seismic source energy created by explosions is estimated from radar measurements and is consistent with source energy determined from seismic observations for the generation of the infrasonic signal a dual mechanism incorporating a terminally disrupted slug is proposed which clarifies previous models and provides good fits to observed infrasonic pressures a new and straightforward method is presented for determining gas volumes from slug explosions at volcanoes from remote infrasound recordings

source location variability and volcanic vent mapping with a small aperture infrasound array at stromboli volcano italy stromboli volcano in italy is a persistently active complex volcanic system in may 2002 activity was confined to 3 major summit craters within which several active vents hosted multiple explosions each hour during a 5 day field campaign an array of 3 low frequency microphones was installed to investigate the coherent infrasound produced by degassing from these vents consistent phase lags across the 3 stations indicate distinct sources that are subsequently investigated to determine the associated vent location apparent depth and origin time the cross correlation routine allows for variations in comparison window length waveform filtering bandwidth and correlation and consistency thresholds allowing for improved detection of certain types of degassing sources identification of activity at the various vents could be subsequently corroborated with 3 channels of synchronously acquired thermal data and video during the may 2002 experiment persistent energetic infrasound was observed from a passive degassing source within the central crater cc and transient infrasound produced by discrete strombolian explosions was identified at 4 additional vents the continuous infrasound produced by the cc exhibits variable frequency dependent correlation lag times that are interpreted as a diffraction effect due to the acoustic radiator s recessed location within a steep walled crater such dispersion has important implications for accurate eruption source modeling because it indicates that infrasonic waveforms may be significantly filtered during propagation transient explosion signals from the northeast crater nec and southwest crater swc vents also exhibit dynamic correlation lag times but this scatter may be more reasonably attributed to variable epicentral locations explosions from the nec west vent for instance appear to emanate from a diffuse zone with a lateral extent in excess of 10 m

infrasound connecting the solid earth oceans and atmosphere the recently reinvigorated field of infrasonics is poised to provide insight into atmospheric structure and the physics of large atmospheric phenomena just as seismology has shed considerable light on the workings and structure of earth s solid interior although a natural tool to monitor the atmosphere and shallow earth for nuclear explosions it is becoming increasingly apparent that infrasound also provides another means to monitor a suite of natural hazards the frequent observation of geophysical sources such as the unsteady sea surface volcanoes and earthquakes that radiate energy both up into the atmosphere and down into the liquid or solid earth and transmission of energy across earth s boundaries reminds us that earth is an interconnected system this review details the rich history of the unheard sound in the atmosphere and the role that infrasonics plays in helping us understand the earth system

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

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

volcano infrasound a review abstract exploding volcanoes which produce intense infrasound are reminiscent of the veritable explosion of volcano infrasound papers published during the last decade volcano infrasound is effective for tracking and quantifying eruptive phenomena because it corresponds to activity occurring near and around the volcanic vent as opposed to seismic signals which are generated by both surface and internal volcanic processes as with seismology infrasound can be recorded remotely during inclement weather or in the dark to provide a continuous record of a volcano s unrest moreover it can also be exploited at regional or global distances where seismic monitoring has limited efficacy this paper provides a literature overview of the current state of the field and summarizes applications of infrasound as a tool for better understanding volcanic activity many infrasound studies have focused on integration with other geophysical data including seismic thermal electromagnetic radiation and gas spectroscopy and they have generally improved our understanding of eruption dynamics other work has incorporated infrasound into volcano surveillance to enhance capabilities for monitoring hazardous volcanoes and reducing risk this paper aims to provide an overview of volcano airwave studies from analog microbarometer to modern pressure transducer and summarizes how infrasound is currently used to infer eruption dynamics it also outlines the relative merits of local and regional infrasound surveillance highlights differences between array and network sensor topologies and concludes with mention of sensor technologies appropriate for volcano infrasound study

interpretation and utility of infrasonic records from erupting volcanoes abstract in the most basic seismo acoustic studies at volcanoes infrasound monitoring enables differentiation between sub surface seismicity and the seismicity associated with gas release under optimal conditions complicated degassing signals can be understood relative explosion size can be assessed and variable seismo acoustic energy partitioning can be interpreted the extent to which these points may be investigated depends upon the quality of the infrasonic records a function of background wind noise microphone sensitivity and microphone array geometry and the type of activity generated by the volcano frequency of explosions bandwidth of the signals and coupling efficiency of the explosion to elastic energy to illustrate the features benefits and limitations of infrasonic recordings at volcanoes we showcase acoustic and seismic records from five volcanoes characterized by explosive degassing these five volcanoes erebus in antarctica karymsky in russia and sangay tungurahua and pichincha in ecuador were the focus of seismo acoustic experiments between 1997 and 2000 each case study provides background information about the volcanic activity an overview of visual observations during the period of monitoring and examples of seismo acoustic data we discuss the benefits and utility of the infrasound study at each respective volcano finally we compare the infrasound records and eruptive activity from these volcanoes with other volcanoes that have been the focus of previous seismo acoustic experiments

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

precursory swarms of long period events at redoubt volcano 1989 1990 alaska their origin and use as a forecasting tool abstract during the eruption of redoubt volcano from december 1989 through april 1990 the alaska volcano observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long period lp seismic events dominant period of about 0 5 s the initial eruption on december 14 occurred after 23 years of quiescence and was heralded by a 23 hour swarm of lp events that ended abruptly with the eruption after a series of vent clearing explosions over the next few days dome growth began on december 21 another swarm with lp events similar to those of the first began on the 26th and ended in a major tephra eruption on january 2 eruptions continued over the next two weeks and then ceased until february 15 when a large eruption initiated a long phase of repetitive dome building and dome destroying episodes that continued into april warnings were issued before the major events on december 14 and january 2 but as the eruptive sequence continued after january 2 the energy of the swarms decreased and forecasting became more difficult a significant but less intense swarm preceded the february 15 eruption which was not forecast this eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until march 4 when the first of three new stations was installed within 3 km of the active vent from march 4 to the end of the sequence on april 21 there were eight eruptions six of which were preceded by detectable swarms of lp events although weak these swarms provided the basis for warnings issued before the eruptions on march 23 and april 6 the initial swarm on december 13 had the following features 1 short duration 23 hours 2 a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm followed by a decline of activity during the 5 hours preceding the eruption 3 a magnitude range from 0 4 to 1 6 4 nearly identical lp signatures with a dominant period near 0 5 s 5 dilatational first motions everywhere and 6 a stationary source location at a depth of 1 4 km beneath the crater this occurrence of long period events suggests a model involving the interaction of magma with groundwater in which magmatic gases steam and water drive a fixed conduit at a stationary point throughout the swarm the initiation of that sequence of events is analogous to the failure of a pressure relief valve connecting a lower supercharged magma dominated reservoir to a shallow hydrothermal system a three dimensional model of a vibrating fluid filled crack recently developed by chouet is found to be compatible with the seismic data and yields the following parameters for the lp source crack length 280 380 m crack width 140 190 m crack thickness 0 05 0 20 m crack stiffness 100 200 sound speed of fluid 0 8 1 3 km s compressional wave speed of rock 5 1 km s density ratio of fluid to rock 0 4 and ratio of bulk modulus of fluid to rigidity of rock 0 03 0 07 the fluid filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0 4 to 40 bar such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack

seismoacoustic investigations of paroxysmal activity at mt etna volcano new insights into the 16 november 2006 eruption 1 on 16 november 2006 a 1 day long paroxysmal eruption occurred at the summit craters of mt etna volcano a multiparametric approach consisting of analyzing infrasonic seismic and video camera recordings was carried out to follow its evolution volcanological and geophysical observations identified three eruptive phases in the first phase infrasonic and seismic characteristics reflected the highly explosive nature of the activity waveform characterization of infrasound events confirmed the activity of the several explosive vents at the summit of southeast crater sec during the second phase results highlighted the decoupling between seismic and infrasonic sources which was due to the decrease in explosive activity and the reactivation of effusive vents located south of bocca nuova and on the saddle between bocca nuova and sec the third phase was the most intense and was characterized by various volcanic phenomena pyroclastic flows jets of dark ash and white steam the very high radiated infrasonic energy together with infrasound event features led us to infer a gas enrichment of the shallow magma column preceding by a few minutes and likely related to the pyroclastic flows in the sec area after the eruption at sec variations in infrasound events related to the activity of northeast crater nec were found the observed spectral changes and the source mechanism modeling of the nec infrasound events suggest the existence of a link in the plumbing system feeding the two craters

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

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

excitation of a buried magmatic pipe a seismic source model for volcanic tremor recent observations of seismic events at various volcanoes suggest that harmonic tremor results from the sustained occurrence of so called long period or low frequency events accordingly we can view the long period volcanic event as the elementary process of tremor and interpret it as the impulse response of the tremor generating system we present a seismic model in which the source of tremor is the acoustic resonance of a fluid filled volcanic pipe triggered by excess gas pressure the model consists of three elements namely a triggering mechanism a resonator and a radiator for simplicity we assume a hemispherical trigger cylindrial resonator and circular radiator set in a vertical configuration with the trigger capping the top of the pipe and the disk shaped radiator shutting off its bottom considering the simple case of a source buried in a homogeneous half space we then apply the discrete wave number method to obtain a complete representation of the ground motion response at near and intermediate distances the results demonstrate that the displacement attributed to the pipe dominates the near field motion while that due to the disk is representative of the intermediate and far fields the trigger itself has a smaller contribution mainly limited to the field in the proximity of the source the characteristics displayed by the free surface response evolve from a strong impulsive signature in the immediate vicinity of the epicenter to a well developed harmonic wave train dominated by rayleigh waves at larger distances no clear shear arrival can be detected in the synthetic seismograms the displacement spectrum reflects the organ pipe modes of the conduit and the bandwidth associated with the dominant spectral peak of motion is controlled by the combined losses due to viscous attenuation in the fluid and elastic radiation into the solid in the case of the cylindrical magma column considered the radiation loss is proportional to the square of the pipe radius while the loss related to viscous damping is inversely proportional to the same factor indicating that the relative importance of the two loss mechanisms is critically dependent on the geometry of the magma reservoir the relative importance of the pipe and disk elements likewise is a function of the conduit cross section this suggests the possibility of determining the geometry of the source as well as the radiation loss and in situ magma viscosity from a comparison of near and far field observations

finite difference time domain modeling of transient infrasonic wavefields excited by volcanic explosions 1 numerical modeling of waveform diffractions along the rim of a volcano vent shows high correlation to observed explosion signals at karymsky volcano kamchatka russia the finite difference modeling assumed a gaussian source time function and an axisymmetric geometry a clear demonstration of the significant distortion of infrasonic wavefronts was caused by diffraction at the vent rim edge data collected at karymsky in 1997 and 1998 were compared to synthetic waveforms and variations of vent geometry were determined via grid search karymsky exhibited a wide range of variation in infrasonic waveforms well explained by the diffraction and modeled as changing vent geometry rim diffraction of volcanic infrasound is shown to be significant and must be accounted for when interpreting source physics from acoustic observations

detecting geyser activity with infrasound abstract we monitored geyser activity in the lower geyser basin lgb of yellowstone national park with dual four element microphone arrays separated by 600 m the arrays were independently used to identify incident coherent plane wave energy then conjoint cross beam back azimuths from the two arrays were used to precisely locate signal sources during a week in august 2011 we located repeating infrasound events peaked in energy between 1 and 10 hz originating from at least five independent geothermal features including the episodically erupting great fountain fountain and kaleidoscope geysers as well as periodic infrasound from nearby botryoidal and persistent sound from firehole spring although activity from nearby cone type geysers was not detected in the infrasound band up through 50 hz the major fountain type geysers i e with columns greater than 10 m could be detected at several kilometers and two minor geysers i e a few meters in eruption height could be tracked at distances up to a few hundred meters detection of geyser activity was especially comprehensive at night when ambient noise was low we conclude that infrasound monitoring of fountain type geysers permits convenient tracking of geyser activity episodicity signal duration energy content and spectral content these parameters enable objective statistical quantification of geyser behavior and changes over time that may be due to external forcing infrasonic study of geyser activity in an individual basin has great monitoring utility and can be reasonably accomplished with two or more distributed sensor arrays

acoustic measurements of the 1999 basaltic eruption of shishaldin volcano alaska 1 origin of strombolian activity the 1999 basaltic eruption of shishaldin volcano alaska usa displayed both classical strombolian activity and an explosive subplinian plume strombolian activity at shishaldin occurred in two major phases following the subplinian activity in this paper we use acoustic measurements to interpret the strombolian activity acoustic measurements of the two strombolian phases show a series of explosions that are modeled by the vibration of a large overpressurised cylindrical bubble at the top of the magma column results show that the bubble does not burst at its maximum radius as expected if the liquid film is stretched beyond its elasticity but bursting occurs after one cycle of vibration as a consequence of an instability of the air magma interface close to the bubble minimum radius during each strombolian period estimates of bubble length and overpressure are calculated using an alternate method based on acoustic power we estimate gas velocity to be 30 60 m s in very good agreement with synthetic waveforms although there is some variation within these parameters bubble length and overpressure for the first strombolian phase are found to be c82f11 m and 0 083 mpa for the second strombolian phase bubble length and overpressure are estimated at 24f12 m and 0 15 mpa for the first 17 h after which bubble overpressure shows a constant increase reaching a peak of 1 4 mpa just prior to the end of the second strombolian phase this peak suggests that at the time the magma in the conduit may contain a relatively large concentration of small bubbles maximum total gas volume and gas fluxes at the surface are estimated to be 3 3 10 7 and 2 9 10 3 m 3 s for the first phase and 1 0 10 8 and 2 2 10 3 m 3 s for the second phase this gives a mass flux of 1 2 10 3 and 8 7 10 2 kg s respectively for the first and the second strombolian phases

geoarchaeology in action a sedimentological analysis of anthropogenic shell mounds from the cape york region of australia abstract large mounded deposits of shell are prominent archaeological features across much of the north australian tropical coast many of the shell mounds are composed almost entirely of the bivalve anadara granosa linnaeus 1758 a food source for aboriginal people in the past a relatively long history of inquiry into the nature and significance of the shell mounds has focussed primarily on analysing the shell component as clues to australian aboriginal coastal economies in the past this paper presents results of new analyses on the non shell sediments examining the physical and chemical signatures of depositional and post depositional processes within shell mounds near weipa in far north queensland australia with a view to obtaining insights into how they formed and for what purposes and how their morphology structure and content may have changed since they ceased accumulating we also consider how such changes might relate to past and present environmental conditions physical and chemical analyses indicate that the primary purpose of mound building was most likely to discard the large volumes of shell resulting from a granosa harvesting and consumption post depositional diagenetic alteration has strongly influenced the present day composition and form of the shell mounds in particular the accession of carbon and silica to the mounds by environmental burning aided by strong leaching under the seasonal high rainfall conditions as such the mound chemistry is more likely to reflect modern environmental conditions rather than provide an archive of or an opening to the past

explosions and periodic tremor at karymsky volcano kamchatka russia summary the explosions of karymsky volcano often produce signals containing a sequence of repeating pulses recorded on acoustic and seismic sensors known as chugging the amplitudes of these pulses correlate with the time interval between pulses for a given measured acoustic pressure seismic amplitudes take on arbitrary values up to a specific empirically determined threshold conversely events with a small seismic amplitude yielded acoustic waves with large variations and large amplitude seismic events corresponded to large acoustic waves these observations are not consistent with a source modelled by a resonating conduit rather a model consisting of a sequence of discrete pulses explains the data and provides a framework for understanding the dynamics of degassing at the vent the physical model for chugging involves a time varying narrowing vent where gasses are released in a series of oscillations which appear to be harmonic but instead are modelled as short term transients or discrete pulses suggestive of choked flow

waveform analysis of seismoacoustic signals radiated during the fall 1996 eruption of pavlof volcano alaska theoretical modeling of acoustic and seismic signals associated with the 1996 strombolian eruption of pavlof volcano suggests that volcanic tremor at pavlof originates in the deeper part of the magma conduit and is generated by random fluid oscillations in the magma flow explosions are believed to occur in the shallower part of the magma conduit and to be caused by the rapid and violent expansion of metastable magma gas mixtures the effect of increasing the exsolved quantities of h2o and co2 gas with reduced pressure in the melt is to decrease the sound speed and density of the magma gas mixture this causes an acoustic decoupling of the upper and lower parts of the magma conduit the reduced sound speed and density of the melt at shallow depths present a sharp impedance contrast which strongly reflects acoustic energy originating at depth and traps it in the lower part of the magma conduit alternatively acoustic energy originating from the upper part of the conduit remains trapped in the low velocity region formed by the exsolved gas in the melt and hence shallow explosions may preferentially couple into the atmosphere explosion signals may be triggered by an increased flow of melt at depth and may be preceded and accompanied by vigorous mass flux transients

volcanic eruptions observed with infrasound 1 infrasonic airwaves produced by active volcanoes provide valuable insight into the eruption dynamics because the infrasonic pressure field may be directly associated with the flux rate of gas released at a volcanic vent infrasound also enhances the efficacy of volcanic hazard monitoring and continuous studies of conduit processes here we present new results from erebus fuego and villarrica volcanoes highlighting uses of infrasound for constraining quantitative eruption parameters such as eruption duration source mechanism and explosive gas flux

long period seismicity and very long period infrasound driven by shallow magmatic degassing at mount pagan mariana islands long period lp seismicity and very long period infrasound ivlp were recorded during continuous degassing from mount pagan mariana islands in july 2013 to january 2014 the frequency content of the lp and ivlp events and delay times between the two arrivals were remarkably stable and indicate nearly co located sources using phase weighted stacking over similar events to dampen noise we find that the lp source centroid is located 60 m below and 180 m west of the summit vent the moment tensor reveals a volumetric source modeled as resonance of a subhorizontal sill intersecting a dike we model the seismoacoustic wavefields with a coupled earth air 3 d finite difference code the ratios of pressure to velocity measured at the infrasound arrays are an order of magnitude larger than the synthetic ratios so the ivlp is not the result of lp energy transmitting into the atmosphere at its epicenter based on crater shape and dimensions determined by structure from motion we model the ivlp as acoustic resonance of an exponential horn the source of the continuous plume from gas analysis is shallow magmatic degassing which repeatedly pressurized the dike sill portion of the conduit over the 7 months of observation periodic gas release caused the geologically controlled sill to partially collapse and resonate while venting of gas at the surface triggered resonance in the crater lp degassing only accounts for 12 of total degassing indicating that most degassing is relatively aseismic and that multiple active pathways exist beneath the vent

towards an automatic monitoring system of infrasonic events at mt etna strategies for source location and modeling active volcanoes characterized by open conduit conditions generate sonic and infrasonic signals whose investigation provides useful information for both monitoring purposes and studying the dynamics of explosive processes in this work we discuss the automatic procedures implemented for a real time application to the data acquired by a permanent network of five infrasound stations running at mt etna volcano the infrasound signals at mt etna consist in amplitude transients called infrasound events the adopted procedure uses a multi algorithm approach for event detection counting characterization and location it is designed for an efficient and accurate processing of infrasound records provided by single site and array stations moreover the source mechanism of these events can be investigated off line or in near real time by using three different models 1 strombolian bubble 2 resonating conduit and 3 helmholtz resonator the infrasound waveforms allow us to choose the most suitable model to get quantitative information about the source and to follow the time evolution of the source parameters

sound channel observations of ice generated tremor in the indian ocean 1 mid to low southern latitude hydrophone stations within the indian ocean have recorded two distinct types of low frequency 100 hz tremor that can be correlated with drifting icebergs and glacial features along the wilkes land coast of eastern antarctica the most common of these signals is a variable harmonic tremor vht with spectral peaks that exhibit frequency fluctuations through time these signals typically display a 4 to 10 hz fundamental frequency and may have as many as ten harmonic bands individual vht signal packets have durations of up to 30 min and occur throughout the year in clusters that continue for hours to days a second less commonly observed signal is characterized by shorter duration 25 to 90 s pulses with a convex upward spectrogram appearance these cusped pulse tremors cpt often exhibit a near uniform pulse spacing with episodes continuing for minutes to hours tremor received levels at hydrophones near 32 s 114 e and 7 s 72 e reach as high as 142 and 133 db re 1 pa peak to peak respectively propagation likely occurs as a sea surface reflected phase at high latitudes and a sound channel phase north of the convergence zone with low frequency transmission loss estimates suggesting maximum acoustic source levels of 245 db re 1 pa at 1 m source locations for a subset of the loudest vht signals correlate with the satellite derived locations of a large iceberg b 15d that migrated westward along the wilkes land shelf region during 2002 and early 2003 most vht sources however cannot be correlated with known iceberg locations suggesting that these signals also may be sourced from smaller unnamed icebergs and or associated with outlet glaciers distributed along the wilkes land coast cpt signals have a more limited spatial distribution originating from five specific regions where ice streams are observed the harmonic nature of both signal types is consistent with the resonance of an ice layer or fluid filled cavity within an ice mass

acoustic measurements of the 1999 basaltic eruption of shishaldin volcano alaska 2 precursor to the subplinian phase the 1999 eruption of shishaldin volcano alaska usa displayed both strombolian and subplinian basaltic activity the subplinian phase was preceded by a signal of low amplitude and constant frequency c2 hz lasting 13 h this bhumming signalq is interpreted as the coalescence of the very shallow part of a foam building up in the conduit which produces large gas bubbles before bursting the acoustic waveform of the hum event is modelled by a helmholtz resonator gas is trapped into a rigid cavity and can only escape through a tiny upper hole producing sound waves at shishaldin the radius of the hole c 5m is close to that of the conduit c6 m the cavity has a length of c60 m and gas presents only a small overpressure between c1 2 10 3 and 4 5 10 3 mpa such an overpressure is obtained by the partial coalescence of a foam formed by bubbles with a diameter from c2 3 mm at the beginning of the episode towards c0 64 mm very close to the end of the phase the intermittency between hum events is explained by the ripening of the foam induced by the h2o diffusion through the liquid films the two extreme values from 600 to 10 s correspond to a bubble diameter from 2 2 to 0 3 mm at the beginning and end of the pre subplinian phase respectively the extremely good agreement between two independent estimates of bubble diameters in the shallow foam reinforces the validity of such an interpretation the total gas volume lost at the surface during the humming events is at most 5 9 10 6 m 3 at the very end of the presubplinian phase there is a single large bubble with an overpressure of c0 42 mpa the large overpressure suggests that it comes from significant depth unlike other bubbles in the pre subplinian phase this deep bubble may be responsible for the entire foam collapse resulting in the subplinian phase d 2004 elsevier b v all rights reserved

acoustic source characterization of impulsive strombolian eruptions from the mount erebus lava lake abstract we invert for acoustic source volume outflux and momentum imparted to the atmosphere using an infrasonic network distributed about the erupting lava lake at mount erebus ross island antarctica by modeling these relatively simple eruptions as monopole point sources we estimate explosively ejected gas volumes that range from 1 000 m 3 to 24 000 m 3 for 312 lava lake eruptions recorded between january 6 and april 13 2006 though these volumes are compatible with bubble volumes at rupture as estimated from explosion video records departures from isotropic radiation are evident in the recorded acoustic wavefield for many eruptions a point source acoustic dipole component with arbitrary axis orientation and strength provides precise fit to the recorded infrasound this dipole source axis corresponding to the axis of inferred short duration material jetting varies significantly between events physical interpretation of dipole orientation as being indicative of eruptive directivity is corroborated by directional emissions of ejecta observed in erebus eruption video footage although three azimuthally distributed stations are insufficient to fully characterize the eruptive acoustic source we speculate that a monopole with a minor amount of oriented dipole radiation may reasonably model the primary features of the recorded infrasound for these eruptions

array measurements and modeling of sources of shallow volcanic tremor at kilauea volcano hawaii we show that resonances in near surface layers path effects or a combination of near surface resonances and source resonances source effects could be responsible for the sharp spectral peaks found in the records of gas piston activity and volcanic tremor recorded near puu oo crater on kilauea volcano hawaii two types of sources are found to be compatible with observations and can not be distinguished using our data in one model impulsive explosion point sources are embedded in the puu oo structure in the other model impulsive point sources of pressure excite the resonances of a fluid filled crack embedded in that structure both models require shallow sources z 100 m and display a strong dependence of the radiated spectrum on source depth over a depth range comparable to the overall thickness of the surficial layers based on these results it may be possible to track changes in source depth through temporal changes in observed spectra a potentially useful tool for monitoring volcanic activity at this site we estimate the depth and spatial extent of volcanic tremor and gas piston activity using two dense arrays with respective apertures of 800 and 120 m located near puu oo measurements of slowness ray parameter and azimuth as a function of time clearly indicate that the sources of volcanic tremor and gas piston activity are located beneath or in close proximity to the puu oo crater at depths shallower than approximately 1 km based on slowness and particle motion analyses we find that the records of volcanic tremor and gas piston events at puu oo consist of a complex combination of body and surface waves

generation and propagation of infrasonic airwaves from volcanic explosions abstract analysis of infrasonic pressure waves generated by active volcanoes is essential to the understanding of volcanic explosion dynamics unlike seismic waves propagating in the earth infrasonic airwaves offer a relatively unfiltered representation of source motions at the vent during an eruption time varying acoustic propagation filters caused by changeable atmospheric conditions are minimal for microphones deployed at intermediate distances johnson et al j volcanol geotherm res in press