experiments on conduit flow and eruption behavior of basaltic volcanic eruptions multiphase flow in basaltic volcanic conduits is investigated using analog experiments and theoretical approaches depending on gas supply large gas bubbles gas slugs may rise through basaltic magma in regimes of distinct fluid dynamical behavior ascent of single slugs supplied slugs fed from the gas source during ascent and periodic slug flow an annular flow regime commences at the highest gas supply rates a first set of experiments demonstrates that the growth of gas slugs due to hydrostatic decompression does not affect their ascent velocity and that excess pressure in the slugs remain negligible the applicability of theoretical formulae describing slug ascent velocity as a function of liquid and conduit properties is evaluated in a second set of experiments a third set of experiments with continuous gas supply into a cylindrical conduit are scaled to basaltic conditions over morton eotvos reynolds and froude numbers gas flow rate and liquid viscosity are varied over the whole range of flow regimes to observe flow dynamics and to measure gas and liquid eruption rates foam generation by slug bursting at the surface and partial slug disruption by wake turbulence can modify the bubble content and size distribution of the magma at the transition from slug to annular flow when the liquid bridges between the gas slugs disappear pressure at the conduit entrance drops by 60 from the hydrostatic value to the dynamic flow resistance of the annular flow which may trigger further degassing in a stored magma to maintain the annular flow regime until the gas supply is exhausted and the eruption ends abruptly magma discharge may also terminate when magma ascent is hindered by wall friction in long volcanic conduits and the annular gas flow erodes all magma from the conduit supplied slugs are found to reach much higher rise velocities than unsupplied slugs and to collapse to turbulent annular flow upon bursting at the surface a fourth set of experiments uses a conduit partially blocked by built in obstacles providing traps for gas pockets once gas pockets are filled rising gas slugs deform but remain intact as they move around obstacles without coalescence or significant velocity changes bursting of bubbles coalescing with trapped gas pockets causes pressure signals at least 3 orders of magnitude more powerful than gas pocket oscillation induced by passing liquid our experiments suggest a refined classification of strombolian and hawaiian eruptions according to time dependant behavior into sporadically pulsating lava fountains driven by stochastic rise of single slugs periodically pulsating lava fountains resulting from slug flow and quasi steady lava fountains oscillating at the frequency of annular flow turbulence

coupled textural and compositional characterization of basaltic scoria insights into the transition from strombolian to fire fountain activity at mount etna italy strombolian and fire fountain activities represent a common expression of explosive basaltic eruptions however the transition between these two eruptive styles and their source mechanisms are still debated we use textural and compositional studies to characterize pyroclastic material from both the strombolian and hawaiian style fire fountain phases of the january june 2000 etna activity we find that basaltic scoria presents distinctive textural and compositional features that reflect different modes of magma vesiculation and crystallization in the two eruptive regimes overall magma that forms strombolian scoria is far more crystallized less vesicular and more evolved indicating strong volatile depletion and longer residence time before being erupted fire fountain scoria indicates a fast rising magma with evidence of moderate syneruptive volatile exsolution the new textural and compositional data set is integrated with previous volcanological and geophysical investigations to provide further insights into the dynamics of fire fountains and to frame the transition from strombolian explosions to fire fountain activity into a model that may apply to future eruptions at mount etna as well as other active basaltic volcanoes

seismic insight into explosive paroxysms at stromboli volcano italy abstract at stromboli volcano italy continuous seismic monitoring and periodic visual observations of volcanic activity for surveillance purposes began in the mid 1980s since 1985 two eruptions have occurred one lasting from december 1985 until april 1986 and one in may 1993 there have also been two small overflows in 1990 and 1994 since these episodes of lava effusion the persistent strombolian activity of the volcano has had several fluctuations during the past 15 years some episodes climaxed in powerful explosions according to seismic records these paroxysms consisted of a variable number of explosion quakes in rapid succession i e from tens of seconds to a few minutes associated with a notable increment in the amplitude of volcanic tremor throughout these episodes which are called explosive sequences lapilli fragments of old rock and bombs of varying dimensions were ejected affecting an area greater than the crater terrace where the active craters are located in this article we describe the explosive sequences recorded at stromboli between 1985 and 1999 we provide a characterization in terms of reduced displacement and duration for nine episodes occurring in 1998 and 1999 their reduced displacements range from 15 to 124 cm 2 their durations are between 6 and 18 min we find no change in the frequency content of the seismic signal several minutes before and during the sequences considering medium to long term behavior the spectral amplitude of the seismic signal decreases or has low values over several months preceding the occurrence of the paroxysms this feature is common to 20 of the 22 explosive sequences and is indicative of internal conditions that periodically characterize the feeder we surmise that the paroxysms are the result of the partial obstruction of the volcanic conduit when the magma column is low or dropping the onset of the explosive sequence causing the sudden removal of the material which forms the obstruction would trigger a sudden depressurization of the conduit and the rapid rise of magma from depth

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

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

spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas the eruption of mount etna in 2000 was notable for an exceptional series of 64 periodic lava fountains propelling lava fragments to heights of up to 900 metres it has been difficult to determine which of two suggested sources of power gas release from the magma itself during its rapid ascent or a build up of pressure from gas accumulated at depth is the driving force for these dramatic jets but one of the etna fountains provided volcanologists with the opportunity to use remote sensing not that remote see picture on the following page to determine the infrared spectra of the gas phase this revealed the chemical composition of the gas that powered this fountain as consistent with an origin in an accumulated gas layer lava fountains are spectacular continuous gas jets propelling lava fragments to heights of several hundred metres which occasionally occur during eruptions of low viscosity magmas1 2 3 4 5 whether they are generated by the effervescent disruption of fast rising bubbly melt2 3 4 5 or by the separate ascent of a bubble foam layer accumulated at depth6 7 still remains a matter of debate8 no field measurement has yet allowed firm discrimination between these two models a key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase this composition should differ markedly depending on whether the magma degassing occurs before or during eruption9 10 here we report the analysis of magmatic gas during a powerful 250 600 m high lava fountain measured with fourier transform infrared spectroscopy11 12 13 14 on mount etna sicily the abundances of volcanic gas species determined from absorption spectra of lava radiation reveal a fountain gas having higher co2 s and s cl ratios than other etnean emissions14 15 16 17 18 and which cannot derive from syn eruptive bulk degassing of etna basalt19 20 instead its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1 5 km depth below the erupting crater

experimental study of bubble growth in stromboli basalt melts at 1 atm abstract volcanic eruptions are characterized by intense degassing thus it is imperative to have high quality laboratory data to constrain degassing mechanisms in order to investigate bubble formation and growth at 1 atm degassing experiments using a stromboli basalt were performed on the gsecars x ray beamline at the advanced photon source volatile bearing glasses were synthesized at 1250 c and 1000 mpa in a piston cylinder with h 2 o or mixtures of h 2 o co 2 they were then heated in situ on the x ray beamline at 1 atm bubble growth was observed in situ using x ray radiography the 3d bubble size distributions in the quenched samples and a natural stromboli pumice were studied by synchrotron x ray microtomography the results show that bubble nucleation and growth in basaltic melts are volatile concentration dependent bubbles can easily form in melts initially containing high volatile concentrations the effect of co 2 on bubble nucleation and growth becomes significant at large co 2 concentrations of 880 to 1480 ppm but is not important at lower concentrations multiple nucleation events occur in most of these degassing experiments and they are more pronounced in more supersaturated melts bubble growth is controlled by viscosity near glass transition temperatures and by diffusion at higher temperatures bubbles begin to pop 10 to 20 s after a foam is developed at vesicularities of 65 to 83 bubble size distributions follow power law relations at vesicularities of 1 to 65 and bubble size distributions evolve from power law relations to exponential relations at vesicularities of 65 to 83 this evolution is associated with the change from far from equilibrium degassing to near equilibrium degassing during far from equilibrium degassing multiple nucleation events are pronounced and possibly account for the generation of power law relations when the system reaches near equilibrium degassing coalescence is dominant and leads to the formation of bubbles of similar size therefore bubble size distributions are described by exponential relations

vesiculation in magmas from stromboli and implications for normal strombolian activity and paroxysmal explosions in basaltic systems 1 we performed a series of x ray tomographic experiments and lattice boltzmann permeability simulations on pyroclastic products from explosive activity at stromboli between december 2004 and may 2006 we reconstructed the 3 d textures of vesicles to investigate the relationship between the nature of vesiculation in the erupted products and the dynamics of gas transport in the shallow conduit in order to derive implications for the eruptive behavior of basaltic volcanoes scoriae from normal strombolian explosions display remarkably consistent vesicle volume distributions fit by power laws with an exponent of 1 0 2 we ascribe the origin of such distributions to the combined effect of coalescence and continuous nucleation events in the steady state shallow magma system that supplies normal strombolian activity volume distributions and textures of vesicles in pumice clasts from the 5 april 2003 and 15 march 2007 paroxysmal activity are markedly different from those in the scoriae besides a power law function with a higher exponent portions of these distributions can be also fit by an exponential function suggesting the attempt of the system to reach near equilibrium conditions the investigated pumice clasts also lack the large connecting vesicles responsible for the development of degassing pathways in the stromboli magma that erupts the scoriae this testifies to a decreased degassing efficiency of the magma associated with paroxysmal explosions and potential overpressure buildup at depth by comparison with degassing experiments on basaltic melts we derive a time constraint on the order of minutes to hours for the incubation of paroxysms at stromboli

anomalous magmatic degassing prior to the 5th april 2003 paroxysm on stromboli 1 a major explosion occurred at stromboli on april 5 2003 being the most powerful event over a period of exceptional eruptive activity lasting from december to july here we describe results from a network of diffusive tubes set up on the stromboli s summit area aimed at a characterisation of plume composition so2 hcl hf prior to and after april 5 data analysis revealed anomalous sulphur degassing 2 3 days before the event when so2 hcl ratios 9 significantly higher than those typical of quiescent degassing 1 were recorded we interpret this exceptional plume signature as an evidence of s rich magmas ascending in the shallow plumbing system and propose high so2 hcl as a potential precursor of major explosions on the volcano the post april 5 phase was characterised by time decreasing so2 hcl and so2 hf plume ratios ascribed to declining magma feeding as a prelude to restoration of normal strombolian activity

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

insights into the dynamic processes of the 2007 stromboli eruption and possible meteorological influences on the magmatic system 1 the unrest of stromboli volcano leading to the february 27 april 2 2007 eruptive period and to the march 15 paroxysm is constrained by combining broad band seismic data and 1 hz gps high rate gps hereinafter hrgps measurements during the pre eruptive stage the simultaneous examination of seismic and hrgps data together with weather parameters suggests the possible influence of external perturbations on the magmatic system which evolved toward a critical state after january 2007 some days after the onset of the eruption a sudden change of the seismic and eruptive behaviour was recognized while ground deformation began to show a deflation the march 15 paroxysm was preceded about two days before by a peak of the hrgps spectral power densities a small inflation and by the occurrence of a few vt earthquakes located at depths down to 3 5 km b s l these findings constrain for the first time at stromboli volcano the deep origin of a fast rising magma batch rich in gas that led to a strong explosive event

long term observation of volcanic tremor on stromboli volcano italy a synopsis the features of seismic activity on stromboli are discussed and compared in terms of their relationship with the main changes of volcanic activity from 1990 to 1993

explosive volcanic eruptions ix the transition between hawaiian style lava fountaining and strombolian explosive activity the commonest eruption styles of basaltic volcanoes involve hawaiian lava fountaining or intermittent strombolian explosions we investigate the ways in which magma rise speed at depth magma volatile content and magma viscosity control which of these eruption styles takes place we develop a model of the degree of coalescence between gas bubbles in the magma which allows us to simulate the transition between the two extreme styles of activity we find that magma rise speed is the most important factor causing the transition with gas content and viscosity also influencing the rise speed at which the transition occurs counter to intuitive expectations a decrease in gas content does not cause a transition from hawaiian to strombolian activity but instead causes a transition to passive effusion of vesicular lava rather a change from hawaiian to strombolian style requires a significant reduction in magma rise speed

onset of the persistent activity at stromboli volcano italy stromboli known worldwide as the lighthouse of the mediterranean is commonly believed to have been in a state of persistent activity for the past 2000 2500 years however historical sources older than 1000 a d are not accurate enough to assess if the activity of the volcano was exactly the same as we see at present in order to attempt to identify the onset of the present eruptive regime and assess if it has been maintained with the same characteristics through time stratigraphic and radiometric studies of the recent tephra deposits were undertaken up to 4 m deep stratigraphic trenches dug at a height of approximately 500 m on the ne flank of the volcano exposed a conformable tephra pile containing charcoal fragments one of the most interesting finds was the discovery of a 7 cm thick weathered bed rich in organic matter thin palaeosol approximately 3 m below the surface the sequence underneath the palaeosol consists of decimetre thick lapilli fallout beds alternating with ash deposits bearing small charcoals with calibrated ages of between the fourth century b c and the first century a d the sequence above the palaeosol is charcoal free and consists of coarse ash deposits with discrete centimetre thick lapilli fallout beds composed of crystal poor golden pumice and subordinate crystal rich black scoriae similar to scoria pumice pairs emitted during the more energetic explosions of the present day activity the data collected indicate that between the third and seventh centuries a d after a period of quiescence the activity resumed with an eruptive style identical to the present one we conclude that the lighthouse of the mediterranean actually began its activity in a period much later than previously thought

so2 flux from stromboli during the 2007 eruption results from the flame network and traverse measurements abstract so 2 fluxes emitted by stromboli during the 27th february 2nd april 2007 effusive eruption were regularly measured both by an automatic network of scanning ultraviolet spectrometers and by traverse measurements conducted by boat and helicopter the results from both methodologies agree reasonably well providing a validation for the automatic flux calculations produced by the network approximately 22 000 t of so 2 were degassed during the course of the 35 day eruption at an average rate of 620 t per day such a degassing rate is much higher than that normally observed 150 200 t d because the cross sectional area occupied by ascending degassed magma is much greater than normal during the effusion as descending degassed magma that would normally occupy a large volume of the conduit is absent we propose that the hydrostatically controlled magma level within stromboli s conduit is the main control on eruptive activity and that a high effusion rate led to the depressurisation of an intermediate magma reservoir creating a decrease in the magma level until it dropped beneath the eruptive fissure causing the rapid end of the eruption a significant decrease in so 2 flux was observed prior to a paroxysm on 15th march 2007 suggesting that choking of the gas flowing in the conduit may have induced a coalescence event and consequent rapid ascent of gas and magma that produced the explosion

dynamics of magma mixing and degassing recorded in plagioclase at stromboli aeolian archipelago italy crystal rich materials scoriae and lava flows emitted during the 1985 2000 activity of stromboli were taken into consideration for systematic study of bulk rock matrix glass chemistry and in particular for the study of chemical and textural zoning of plagioclase the most abundant mineral phase over the considered time period bulk rock composition remained fairly constant in both major sio2 49 2 50 9 wt and k2o 1 96 2 18 wt and trace elements the quite constant chemistry of matrix glasses also indicates that the degree of crystallization of magma was maintained at around 50 vol plagioclase ranges in composition between an62 and an88 and is characterized by alternating 10 100 m thick bytownitic and labradoritic concentric layers although the dominant and representative plagioclase of scoriae is an68 the labradoritic layers an62 70 show small scale 1 5 m oscillatory zoning are free of inclusions and appear to record episodes of slow crystal growth in equilibrium with a degassed liquid having the composition of the matrix glass in contrast the bytownitic layers an70 an88 are patchy zoned show sieve structure with abundant micrometric glass inclusions and voids and are attributed to rapid crystal growth

dynamics of the 5 april 2003 explosive paroxysm observed at stromboli by a near vent thermal seismic and infrasonic array 1 on 5 april 2003 an array of thermal infrasonic and seismic sensors tracked the dynamics of a major explosive paroxysmal event at stromboli the thermal signal recorded a decline 1 hour before the paroxysm which itself lasted 6 5 minutes and opened with a 14 s low thermal amplitude phase this was followed by three main explosive phases with gas and ejecta velocities of 324 and 185 m s being calculated for the first phase the delay time between thermal and infrasonic signals indicates a very shallow 150 m source for fragmentation a strong tilt component in the seismic signals shows that the conduit began to expand at least 90 s before the explosion large seismic amplitudes were recorded during the emission onset the seismic signal can thus be related to stress build up followed by release during the ejection of the gas particles mixture we calculate that the cloud of hot gas and ash emitted during the explosion had an overpressure of 3 8 mpa and involved 5 7 105 m3 2 9 106 kg of gas

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

dauphine twinning as evidence for an impact origin of preferred orientation in quartzite an example from vredefort south africa large meteorite impacts cause great changes to geologic features on earth ranging from cratering and ejecta blankets to phase transformations in minerals in this report we describe the effect of a shock wave on the crystallographic orientation of quartz crystals in quartzite from the vredefort impact site in south africa preferred orientation of bulk quartzite samples was measured by time of flight neutron diffraction with a random distribution of c axes a weak but distinct difference between the orientation distribution of positive and negative rhombs was observed as illustrated with pole figures and inverse pole figures results for the natural vredefort sample are compared with deformation

stromboli 2007 eruption deflation modeling to infer shallow intermediate plumbing system 1 during the effusive phase of the stromboli 2007 eruption the gps and tilt stations recorded small but significant changes which for the first time at this volcano clearly indicated a deflation we modeled the deflation inferring a depressurizing vertically elongated source with centre under the volcano edifice about 2 8 km below sea level the model whose position is above the magma source region inferred by petrological studies and the associated rapid deflation suggest a near free pathway for magma ascent from this source to the upper shallow 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

h2s fluxes from mt etna stromboli and vulcano italy and implications for the sulfur budget at volcanoes abstract we present here new measurements of sulfur dioxide and hydrogen sulfide emissions from vulcano etna and stromboli italy made by direct sampling at vents and by filter pack and ultraviolet spectroscopy in downwind plumes measurements at the f0 and fa fumaroles on vulcano yielded so 2 h 2 s molar ratios of 0 38 and 1 4 respectively from which we estimate an h 2 s flux of 6 to 9 t d 1 for the summit crater for mt etna and stromboli we found so 2 h 2 s molar ratios of 20 and 15 respectively which combined with so 2 flux measurements suggest h 2 s emission rates of 50 to 113 t d 1 and 4 to 8 t d 1 respectively we observe that source and plume so 2 h 2 s ratios at vulcano are similar suggesting that hydrogen sulfide is essentially inert on timescales of seconds to minutes this finding has important implications for estimates of volcanic total sulfur budget at volcanoes since most existing measurements do not account for h 2 s emission

persistent polybaric rests of calc alkaline magmas at stromboli volcano italy pressure data from fluid inclusions in restitic quartzite nodules a fluid inclusion study has been performed on quartzite nodules of stromboli volcano hosted by calc alkaline lavas of both the strombolicchio 200 ka and paleostromboli ii 60 ka periods the nodules are mainly composed of quartz crystals with subordinate plagioclase and k feldspar small interstitial minerals such as plagioclase k feldspar clinopyroxene biotite and quartz are also found together with glass muscovite epidote and zircon occur as accessory minerals different quartzite nodules occur 1 equigranular polygonal granoblastic quartzite nodules forming a polygonal texture with clear triple points 2 inequigranular polygonal granoblastic quartzite nodules and 3 break up nodules with strongly resorbed quartz these quartzites are restites from partial melting involving felsic crustal rocks at the magma wall rock contact restitic quartz re crystallises at variable and generally high temperatures leading to the formation of quartzites with different textures quartz grains contain five types of fluid inclusions distinguished on the basis of both fluid type and textural phase relationships at room temperature type i are two phase liquid vapour co2 rich fluid inclusions they are primary and subordinately pseudosecondary in origin and have undergone re equilibration processes type ii mono phase two phase vapour liquid vapour co2 rich fluid inclusions are the most common and based on their spatial distribution and shape they can be divided into two subclasses type iia and type iib type ii inclusions are secondary or pseudosecondary and they are assumed to have formed after decrepitation of type i inclusions and cracking of the host quartz type iii inclusions are mono phase vapour they possibly contain co2 at very low density and surround the inner rims of quartz grains type iv two phase silicate melt inclusions contain glass co2 rich fluid some of them are cogenetic with type ii inclusions finally type v two phase liquid vapour aqueous inclusions are both vapour rich and liquid rich aqueous inclusions microthermometric experiments were performed on both type i and ii inclusions type i inclusions homogenise to liquid between 20 and 30 5 c type iia inclusions homogenise to vapour in the 24 to 30 c range with a maximum peak of frequency at 29 c type iib inclusions also homogenise to vapour between 14 and 25 c there appears to be no difference in homogenisation temperature distribution between the strombolicchio and paleostromboli ii samples the trapping pressures of the fluid inclusions have been obtained by combining the microthermometric data of the strombolicchio and paleostromboli ii samples with the pressure temperature volume i e density characteristics for a pure co2 system the data on the early inclusions type i suggest an important magma rest at a pressure of about 290 mpa i e about 11 km depth type iia co2 inclusions suggest that a second magma rest occurred at a pressure of about 100 mpa i e about 3 5 km depth whereas type iib inclusions were trapped later at a shallower depth during the final magma upwelling no pressure depth differences seem to occur between the strombolicchio and paleostromboli ii periods indicating the same polybaric rests for the calc alkaline magmas of stromboli despite their significantly different ages this persistence in magma stagnation conditions from 200 to 60 ka suggests a similar plumbing system for the present day strombolian activity

characterizing high energy explosive eruptions at stromboli volcano using multidisciplinary data an example from the 9 january 2005 explosion abstract stromboli is well known for its persistent normal explosive activity consisting of intermittent mild to moderate strombolian explosions that typically occur every 10 20 min all tephras erupted during this activity usually fall back into the crater terrace and consist of volatile poor scoriae fed by highly porphyritic hp magma more occasionally large explosions or paroxysms eject a greater quantity of tephra mainly consisting of hp scoriae and pumice clasts of low porphyritic lp magma but also including large lithic blocks in addition to this activity between 2004 and 2006 high energy explosions displaying an intermediate eruptive style between that of normal and paroxysmal explosions in terms of column height duration and tephra dispersal were observed to occur at a frequency of one to eight events per year while many volcanological geochemical and geophysical studies have focused in the last few years on the two end members of activity i e normal or paroxysmal a detailed investigation on these intermediate types of events has not been carried out yet here we report of a study on the 9 january 2005 explosion one of the high energy explosions during which the main fountaining phase lasted nearly a minute causing ejection of coarse bombs up to a height of 120 m and of ash and lapilli to 200 m an accompanying ash plume rose up to 500 m at the end of the explosion we present a multidisciplinary approach that integrates the results from analysis of live camera images with compositional and textural characterization of the erupted products major element composition of glassy groundmass and 3d views of textures in the erupted scoriae support the hypothesis based on volcanological observations that this explosion falls between normal and paroxysmal activity for which we use the term intermediate by comparing the video camera images of the 9 january 2005 explosion with volcanological features of other high energy explosions that occurred at stromboli between june 2004 and october 2006 we find that three additional events can be considered intermediate explosions suggesting that this type of activity may be fairly common on this volcano the results of this study although preliminary given our limited dataset clearly indicate that the methodology used here can be successfully applied to better define the range of eruptive styles typifying the normal explosive activity potentially improving our capability of eruption forecasting and assessing volcanic hazard at stromboli

geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings the tyrrhenian sea and surroundings abstract information on the physical and chemical properties of the lithosphere asthenosphere system las can be obtained by geophysical investigation and by studies of petrology geochemistry of magmatic rocks and entrained xenoliths integration of petrological and geophysical studies is particularly useful in geodynamically complex areas characterised by abundant and compositionally variable young magmatism such as in the tyrrhenian sea and surroundings a thin crust less than 10 km overlying a soft mantle where partial melting can reach about 10 is observed for magnaghi vavilov and marsili which belong to the central tyrrhenian sea backarc volcanism where subalkaline rocks dominate similar characteristics are seen for the uppermost crust of ischia a crust about 20 km thick is observed for the majority of the continental volcanoes including amiata vulsini roccamonfina phlegraean fields vesuvius vulture stromboli vulcano lipari etna and ustica a thicker crust is present at albani about 25 km and at cimino vico sabatini about 30 km the structure of the upper mantle in contrast shows striking differences among various volcanic provinces volcanoes of the roman region vulsini sabatini alban hills sit over an upper mantle characterised by vs mostly ranging from about 4 2 to 4 4 km s at the alban hills however slightly lower vs values of about 4 1 km s are detected between 60 and 120 km of depth this parallels the similar and rather homogeneous compositional features of the roman volcanoes whereas the lower vs values detected at the alban hills may reflect the occurrence of small amounts of melts within the mantle in agreement with the younger age of this volcano the axial zone of the apennines where ultrapotassic kamafugitic volcanoes are present has a mantle structure with high velocity lid vs 4 5 km s occurring at the base of a 40 km thick crust beneath the campanian volcanoes of vesuvius and phlegraean fields the mantle structure shows a rigid body dipping westward a feature that continues southward up to the eastern aeolian arc in contrast at ischia the upper mantle contains a shallow low velocity layer vs 3 5 4 0 km s just beneath a thin but complex crust the western aeolian arc and ustica sit over an upper mantle with vs 4 2 4 4 km s although a rigid layer vs 4 55 km s from about 80 to 150 km occurs beneath the western aeolian arc in sardinia no significant differences in the las structure are detected from north to south the petrological geochemical signatures of italian volcanoes show strong variations that allow us to distinguish several magmatic provinces these often coincide with mantle sectors identified by vs tomography for instance the roman volcanoes show remarkable similar petrological and geochemical characteristics mirroring similar structure of the las the structure and geochemical isotopic composition of the upper mantle change significantly when we move to the stromboli campanian volcanoes the geochemical signatures of ischia and procida volcanoes are similar to other campanian centres but sr pb isotopic ratios are lower marking a transition to the backarc mantle of the central tyrrhenian sea the structural variations from stromboli to the central vulcano and lipari and western aeolian arc are accompanied by strong variations of geochemical signatures such as a decrease of sr isotope ratios and an increase of nd pb isotope and lile hfse ratios the dominance of mafic subalkaline magmatism in the tyrrhenian sea basin denotes large degrees of partial melting well in agreement with the soft characteristics of the uppermost mantle in this area in contrast striking isotopic differences of plio quaternary volcanic rocks from southern to northern sardinia does not find a match in the las geophysical characteristics the combination of petrological and geophysical constraints allows us to propose a 3d schematic geodynamic model of the tyrrhenian basin and bordering volcanic areas including the subduction of the ionian adria lithosphere in the southern tyrrhenian sea and to place constraints on the geodynamic evolution of the whole region

effusive to explosive transition during the 2003 eruption of stromboli volcano the persistent explosive activity of stromboli volcano italy ceased in december 2002 and correlated with the onset of a seven month long effusive eruption on the volcano flank from new vents that opened just below the summit craters we intensively monitored this effusive event collecting and interpreting in real time an extensive multiparametric geophysical data set the resulting data synergy allowed detailed insights into the conduit dynamics that drove the eruption and the transition back to the typical strombolian activity we present a direct link between gas flux magma volume flux and seismicity supporting a gas driven model whereby the balance between gas flux and gas overpressure determines whether the system will support effusive or explosive activity this insight enabled us to monitor the migration of the magma column up the conduit and to explain the onset of explosive activity

stratigraphy and sedimentary petrology of an archean volcanic sedimentary succession at mt goldsworthy in the pilbara block western australia implications of evaporite nahcolite and barite deposition abstract a approximately 3 3 ga sedimentary succession at mt goldsworthy in the northeastern pilbara block australia contains beds composed of silicified pseudomorphs of nahcolite nahco3 or barite baso4 this sedimentary succession correlates with the corboy formation and consists of lower middle and upper sedimentary units which conformably overlie mafic to ultramafic volcanic and volcaniclastic rocks the lower and middle units are predominantly siliciclastic whereas the upper unit is characterized by ferruginous cherts and banded iron formations with minor proportions of intercalated mature sandstone the succession defines an overall upward fining and deepening trend the detrital materials were derived from older greenstone successions volcaniclastics and reworked precipitative beds silicified pseudomorphs of nahcolite crystals up to 40 cm in length occur in a 20 m thick bed in the upper portion of the lower unit the formation of this unit was initiated by deposition of immature terrigenous clastic sediments and followed by the precipitation of nahcolite from na hco3 brines in a closed or semi closed evaporitic basin bladed barite deposits occur mainly in the middle unit which was deposited in a sub aerial to shallow marine environment barite may have precipitated as a result of mixing of so42 rich seawater and ba2 rich hydrothermal fluids the mt goldsworthy sedimentary succession records an archean shallow to sub aerial sedimentary environment that probably developed in a continental margin setting

sulphur dioxide fluxes from mount etna vulcano and stromboli measured with an automated scanning ultraviolet spectrometer gruppo nazionale per vulcanolgia gnv the ec 5th framework project multimo and nerc grant gr9 04655

the 2007 eruption of stromboli volcano insights from real time measurement of the volcanic gas plume co2 so2 ratio abstract the recent eruption of stromboli in february april 2007 offered a unique chance to test our current understanding of processes driving the transition from ordinary persistent strombolian to effusive activity and the ability of instrumental geophysical and geochemical networks to interpret and predict these events here we report on the results of two years of in situ sensing of the co 2 so 2 ratio in stromboli s volcanic gas plume in the attempt to put constraints on the trigger mechanisms and dynamics of the eruption we show that large variations of the plume co 2 so 2 ratio range 0 9 26 preceded the onset of the eruption since december 2007 interrupting a period of relatively steady and low ratios time averaged ratio 4 3 lasting from at least may to november 2006 by contrasting our observations with numerical simulations of volcanic degassing at stromboli derived by use of an equilibrium saturation model we suggest that the pre eruptive increase of the ratio reflected an enhanced supply of deeply derived co 2 rich gas bubbles to the shallow plumbing system this larger than normal ascent of gas bubbles was likely sourced by a 1 3 km deep gas melt separation region probably a magma storage zone and caused faster convective overturning of magmas in the shallow conduit an increase in the explosive rate and in seismic tremor and finally the collapse of the la sciara del fuoco sector triggering the effusive phase the high co 2 so 2 ratios up to 21 observed during the effusive phase and particularly in the days and hours before a paroxysmal explosion on march 15 2007 indicate the persistence of the same gas source and suggest that de pressurization of the same 1 3 km deep magma storage zone could have been the trigger mechanism for the paroxysm itself

the 5 april 2003 vulcanian paroxysmal explosion at stromboli volcano italy from field observations and thermal data abstract the 5 april 2003 paroxysmal explosion at stromboli volcano was one of the strongest explosive events of the last century it occurred while the effusive eruption begun on 28 december 2002 and finished on 22 july 2003 was still on going and the summit craters of the volcano were obstructed in this paper we present a reconstruction of the sequence of events based on thermal and visual images collected from helicopter before during and immediately after the paroxysm one month before the blast ash emission and temperature increase at the bottom of the summit craters were observed an increasing amount of juvenile components in the emitted ash during march suggested that the magma level within the crater was rising accordingly hot degassing vents at the bottom of the summit craters were not persistent and the craters remained almost entirely obstructed by talus accumulation until the paroxysm occurred three minutes before the explosion we recorded a significant increase in temperature inside crater 1 accompanied by a thicker gas plume thirty two seconds before the blast reddish ash was emitted from crater 1 the paroxysm produced a vulcanian explosion that opened the feeder conduit obstructed for over three months the blast was accompanied by a shock wave recorded by the ingv seismic network at 07 13 37 gmt explosions with hot material started from crater 1 and after 15 s propagated to crater 3 about 100 m away the velocity of ejecta was 80 m s 1 and increased when the eruptive plumes from both craters merged together during the vulcanian phase an eruptive column rose 1 km above the top of the volcano and explosions continued mainly at crater 3 the paroxysm lasted about 9 min with bombs up to 4 m wide falling on the village of ginostra on the west flank of the island and destroying two houses this event signalled the start of the declining phase of the effusive eruption suggesting that the feeder conduit was returning to its former steady conditions with open vents and continuous mild strombolian activity

acid gas and metal emission rates during long lived basalt degassing at stromboli volcano the discharge of acid gases and metals from stromboli is determined from airborne and ground based filter sampling of particulate matter in the volcanic plume combined with cospec measurements of so2 fluxes smaller particle sizes and high enrichment factors distinguish the most volatile elements by order s se br cl cd bi in as sb sn f au pb cr cu from those strictly fe mn ree sc sr th ti v or mainly al ba ca co k na u derived from volcanic ash time averaged volatile fluxes show that stromboli is a representative arc emittor producing 1 2 of the global volcanic budget of sulfur halogens and several trace metals while 15 25 of volcanic emissions of bi cd cs pb and sn in southern italy subaerial degassing of its s cl rich shoshonitic magma over the last 2 ky of similar activity may have released as much copper and gold as is encountered in magma derived high sulfidation ore deposits

geochemical precursors of the activity of an open conduit volcano the stromboli 2002 2003 eruptive events 1 marked increases of co2 h2 and he dissolved in thermal waters and changes in the dissolved carbon isotopic composition were observed at stromboli before the 28 december 2002 eruption and before a violent explosive paroxysm occurred on 5 april 2003 high anomalous co2 flux values were recorded at the crater rim since a week before the eruption onset the first anomalies in the thermal waters dissolved co2 amount appeared some months before the eruption when magma column rose at a very high level in the conduit high peaks of dissolved h2 and he were recorded a few days before the paroxysm carbon isotopic composition indicates a magmatic origin of the dissolved co2 whose increase together with those of h2 and he is attributed to an increasing output of deep gases likely produced by depressurization of a rising batch of a deep gas rich magma whose fragments have been emitted during the explosion

the contribution of fluid geochemistry to the volcano monitoring of stromboli abstract the persistent open vent mild explosive activity of stromboli volcano is episodically interrupted by more violent and dangerous explosive events major explosions and paroxysms according to the nature of erupted products paroxysms can be related either to the explosion of overpressured gas pockets located in the proximity of the magma column or to the sudden uprise of hot gas rich magma from a deep part of the plumbing system in both cases these more energetic explosive events should be preceded by an escape or a preferential uprise of the highly mobile volatiles which in turn should produce gas leakage anomalies at the surface in sites of high vertical permeability such as deep reaching faults in order to identify such gas leaking sites a systematic co2 soil flux survey has been carried out on the island using an accumulation chamber four hundred sixty one points have been measured with a high density in the summit crater area where high flux values have been found 10 3 10 2 cm s anomalous points are concentrated along the main ne sw axial feeding system of the volcano co2 soil flux decreases from the crater zone to the base of the volcanic cone where however an interesting gas leakage anomaly occurs pizzillo mofette in the pizzillo area thermal water wells also occur whose chemistry indicates an origin by sea water heated by hot gas soil gases have been sampled in the sites with the highest co2 flux in the crater area and at the base of the cone chemical and isotopic analyses indicate the presence of a deep gas component especially in the crater zone samples high co2 appreciable contents of he and h2 3he 4he values up to 3 55 13c of co2 2 the sc5 low flux fumarole on the crater rim has shown during six years a remarkable persistence of temperature 93 95 c with only minor fluctuations of chemistry appearance of anomalous peaks of h2 in correspondence with strombolian explosions was observed during a 2 h 30 min experiment of continuous recording of hydrogen content of the fumarole together with previous data on h2o co2 and he this experiment confirms that strombolian blasts produce rapid fluctuations in the fumarolic gas composition in the light of this study sc5 fumarole and pizzillo mofette look promising sites for the testing of a continuous geochemical monitoring system of stromboli volcano

three dimensional investigation of volcanic textures by x ray microtomography and implications for conduit processes 1 synchrotron x ray computed microtomography ct was applied for the first time to clasts of pumice and scoria generated by active explosive volcanoes characterized by a range of eruptive styles mild strombolian to plinian and magmatic composition basaltic to trachytic the obtained two dimensional 2d tomographic images corresponding to sample views at different rotation angles were processed to reconstruct three dimensional 3d volumes and then used to make 3d measurements of vesicularity vesicle number density volume and connectivity for quantitative characterization of the investigated tephras the results indicate a positive correlation between vesicle number density and eruption intensity that is used to investigate modes of magma degassing in explosive eruptions in addition the vesicle geometry affecting the connected gas flow pathways in pyroclasts from strombolian eruptions is determined and related to the known permeabilities implications on the dynamics of explosive eruptions is discussed and ultimately used to quantitatively discriminate between different eruptive styles

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

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

triggering basaltic volcanic eruptions by bubble melt separation understanding the processes by which volcanic eruptions are triggered is crucial for volcanic hazard prediction and assessment in intermediate and silicic magmas where water is the dominant volatile phase1 2 second boiling provides an effective eruption trigger1 as the magma cools and crystallizes volatiles are increasingly concentrated in the residual melt where they eventually become saturated and are exsolved thereby raising the magma pressure to the point of eruption1 2 in contrast in basaltic magma chambers in which carbon dioxide is the dominant volatile phase the effect of second boiling is to decrease the chamber pressure but basaltic magmas are also relatively inviscid so volatile bubbles can separate from the turbulently convecting melt to produce a foam layer at the chamber roof3 4 decompression of the rising bubbles can increase the chamber pressure and so trigger an eruption5 6 here we model the complex competition between the processes of magma cooling and bubble ascent we find that in basalt of very low viscosity 1 10pas bubble separation dominates and can increase the reservoir pressure by as much as 10 mpa sufficient to trigger an eruption7 on timescales of 1 10 years comparable to the duration of eruptive episodes at kilauea volcano hawaii4 8

gas bubble dynamics model for shallow volcanic tremor at stromboli volcanic tremor at stromboli aeolian islands italy is correlated to small infrasonic transients ripepe et al 1996 which repeat almost rhythmically in time in a range between 0 8 and 1 2 s we demonstrate that infrasonic transients are associated to small gas bubble 0 5 m burstings which produces no transients in the seismic signal tremor ground displacement attenuates with the inverse of the distance from the craters indicating that the source is shallow short term energy release shows that infrasonic and seismic signals are linked to the same dynamical process while at the long term scale it is evident that the two signals are controlled by two distinctive mechanisms we suggest that the possible physical model acts in two steps first gas coalescence and then gas bursting in our model the seismic signal is related to the coalescence of a gas bubble from a layer of small bubbles while the infrasonic signal is linked to the bursting of the bubble when it reaches the magma surface gas bubbles could form by free coalescence in magma or could be forced to coalesce by a structural barrier we calculate that forced coalescence induces in magma a pressure change 104 pa 2 orders of magnitude higher than free coalescence and it explains best the tremor ground displacement 10 5 m recorded at stromboli moreover forced coalescence evidences the role of a structural barrier such as a dike in volcanic tremor source dynamics in this gas dynamic process the delay time of 1 2 s between infrasonic pulses could reflect the gas nucleation interval of basaltic magma thomas et al 1993 manga 1996 we propose that the source function for the shallow volcanic tremor at stromboli could be the viscoelastic reaction of the magma to the pressure decrease induced by gas bubble growth rate under constant depressurization the spectrum of our source function is controlled by the time duration of the pressure pulse which represents the viscoelastic relaxation time of the magma and gas bubble growth rate the predicted asymptotic decay of the frequency contents fits the spectral behavior of the volcanic tremor ground displacement recorded at stromboli we show that the same spectral behavior can be found in ground displacement spectra of volcanic tremor recorded on different volcanoes

triggering mechanism at the origin of paroxysms at stromboli aeolian archipelago italy the 5 april 2003 eruption 1 the 5 april 2003 paroxysm of stromboli occurred during an ongoing effusive episode that initiated on 28 december 2002 it mainly consisted in two a few seconds apart cannon like explosions followed by a vertical gas pyroclast jet the hk basaltic pumices that were generated mainly contain crystals that were drained back from the shallow parts of the plumbing system few euhedral to anhedral olivines and their melt inclusions testify to crystal fractionation and possible mixing between hk basaltic magmas variable in their volatile content extent of evolution and volume the most primitive volatile rich hk basalt term is sizable at micrometer scale only we propose that the triggering mechanism of the paroxysm was initiated at moderate pressures 240 mpa and was related to bubble driven ascent of magma blobs the latter rose through and interacted with overlying slightly more evolved melts and finally mingled with the shallow crystal rich magma just before the eruption

a note on gas segregation in dykes and sills at high volumetric gas fractions abstract the model of gas segregation in volcanic systems developed by menand and phillips menand t phillips j c 2007 gas segregation in dykes and sills j volcanol geotherm res 159 393 408 show that non vertical elements of the plumbing systems such as dykes and sills act as strong gas segregators and can explain the persistent degassing displayed by many basaltic volcanoes as well as their associated eruptive characteristics however this model is based on laboratory experiments carried out at low volumetric gas fractions