rabaul caldera papua new guinea volcanic hazards surveillance and eruption contingency planning abstract planning for volcanic contingencies at the rabaul caldera complex is a difficult task requiring urgent attention in view of the results of volcano surveillance and historical eruption frequency historical eruption periodicities have ranged from about 2 to 59 years the most recent eruptions were in 1937 1943 and caused more than 500 fatalities in may 1937 surveillance since 1971 has revealed uplift of part of the caldera floor and increasing seismicity in a ring structure believed to define the caldera bounding fault or faults these phenomena are interpreted as the prelude to a possible eruption potential eruption sites are all close to rabaul town and outlying residential areas and include the volcanoes of sulphur creek last active about 1850 vulcan and tavurvur 1937 1943 and rabalanakaia but new sites should also be considered in relation to the results of volcano surveillance a wide range of volcanic hazards accompanying different scales of eruption must be considered for the rabaul area the most likely types of eruption may be similar to the relatively small events that have been witnessed over the last century whose hazards included air fall tephra pumice rafts pyroclastic flows and surges volcanic earthquakes volcanic gas discharges tsunamis lightning strikes and the fall of mud rain torrential run off and mudflows as a result of accompanying rain storms other potential eruption types of much larger scale could involve cauldron subsidence which could cause destructive tsunamis and could be accompanied by explosive activity of major proportions air fall tephra is considered to be one of the main hazards from a future eruption and its effects in and around rabaul are primary influences in the choice of evacuation routes and points of refuge hence theoretical tephra dispersal patterns have been considered in some detail air fall tephra deposition from rabaul eruption clouds at heights of less than about 4 km is determined by a biannual change in wind direction from southeast in may to october november trade winds to northwest during the monsoon from december to march april in contrast clouds that rise higher than about 4 km are blown by east winds all year round another principal hazard is pyroclastic flows and surges which took place during the 1937 vulcan eruption but have until recently been overlooked although flows or surges or both are clearly distinguishable on eruption photographs the lack of suitable evacuation routes and problems in choosing safe and reasonably accessible refuge points compound the difficulties in preparing a practicable contingency plan however in small moderate eruptions the safest areas around rabaul are considered to be at the duke york islands about 30 km to the east and at cape gazelle about 25 km to the southeast seaborne evacuation to main ports in central new britain or on the neighbouring islands of new ireland and bougainville or overland evacuation using a southwards expanded road system would be necessary in the event of forewarning of a major eruption

first 13c 12c isotopic characterisation of volcanic plume co2 we describe analytical details and uncertainty evaluation of a simple technique for the measurement of the carbon isotopic composition of co2 in volcanic plumes data collected at solfatara and vulcano where plumes are fed by fumaroles which are accessible for direct sampling were first used to validate the technique for both volcanoes the plume derived carbon isotopic compositions are in good agreement with the fumarolic compositions thus providing confidence on the method and allowing its application at volcanoes where the volcanic component is inaccessible to direct sampling as a notable example we applied the same method to mount etna where we derived a 13c of volcanic co2 between 0 9 0 27 and 1 41 0 27 bocca nuova and voragine craters the comparison of our measurements to data reported in previous work highlights a temporal trend of systematic increase of 13c values of etna co2 from 4 in the 1970 s and the 1980 s to 1 at the present time 2009 this shift toward more positive 13c values matches a concurrent change in magma composition and an increase in the eruption frequency and energy we discuss such variations in terms of two possible processes magma carbonate assimilation and carbon isotopic fractionation due to magma degassing along the etna plumbing system finally our results highlight potential of systematic measurements of the carbon isotopic composition of the co2 emitted by volcanic plumes for a better understanding of volcanic processes and for improved surveillance of volcanic activity

fumarolic and diffuse soil degassing west of mount epomeo ischia italy abstract fumarolic fluid compositions and diffuse soil emissions of hydrothermal fluids of the donna rachele area 0 86 km 2 western flank of mt epomeo ischia island have been studied in order to develop a conceptual geochemical model of the hydrothermal system the degassing area was mapped and the total release of hydrothermal gas and heat associated with the diffuse emission of hydrothermal fluids was estimated a mesostructural study was carried out in order to investigate the relations between the brittle structures and the main pathways of the uprising vapor the fumarolic compositions are typical of hydrothermal fluids and water 99 represents the major component all gas species in the h 2 o h 2 co ch 4 co 2 h 2 s system are close to equilibrium concentrations at temperatures of 300 c and at redox conditions slightly more oxidizing than expected the compositions of the donna rachele fumarolic gas approach the pure liquid equilibrium composition this indicates a high fraction of separated vapor and suggests the presence of a highly energetic hydrothermal system at depth the pure liquid equilibrium compositions of the donna rachele fumaroles along with the historical records of shallow seismicity the explosion of a well in 1995 the occurrence of intense acoustic phenomena and of shallow wells discharging vapor indicate that the internal pressure of the hydrothermal system is occasionally larger than the hydrostatic pressure to quantify the energy dissipated in the donna rachele area by the emission of fumarolic fluids the hydrothermal diffuse degassing was studied by means of 336 soil co 2 flux measurements the highest co 2 fluxes were measured in hydrothermally altered areas along the faults that border mt epomeo structural data indicate that the vapor rises up along nw se striking normal faults related to gravity induced stresses and affecting highly fractured lavas the older faults which are related to the mt epomeo resurgence act as a permeability barrier and bound the donna rachele diffuse degassing structure the total hydrothermal co 2 output was estimated to be 9 t d 1 assuming that the h 2 o co 2 ratio of the fluids that feed the diffuse degassing is the same as that of fumarolic effluents the calculated heat flux is 40 mw this value which represents an important energy release is only a part of the total thermal energy release of ischia where other fumarolic areas occur the results obtained at ischia indicate the importance of thermal energy released by diffuse degassing structures in the energy balance of quiescent volcanoes values of the thermal energy release from the ischia hydrothermal system are comparable with those estimated on other quiescent volcanoes

three dimensional seismic tomography from p wave and s wave microearthquake travel times and rock physics characterization of the campi flegrei caldera 1 the campi flegrei cf caldera experiences dramatic ground deformations unsurpassed anywhere in the world the source responsible for this phenomenon is still debated with the aim of exploring the structure of the caldera as well as the role of hydrothermal fluids on velocity changes a multidisciplinary approach dealing with three dimensional delay time tomography and rock physics characterization has been followed selected seismic data were modeled by using a tomographic method based on an accurate finite difference travel time computation which simultaneously inverts p wave and s wave first arrival times for both velocity model parameters and hypocenter locations the retrieved p wave and s wave velocity images as well as the deduced v p v s images were interpreted by using experimental measurements of rock physical properties on cf samples to take into account steam water phase transition mechanisms affecting p wave and s wave velocities also modeling of petrophysical properties for site relevant rocks constrains the role of overpressured fluids on velocity a flat and low v p v s anomaly lies at 4 km depth under the city of pozzuoli earthquakes are located at the top of this anomaly this anomaly implies the presence of fractured overpressured gas bearing formations and excludes the presence of melted rocks at shallow depth a high v p v s anomaly located at 1 km suggests the presence of rocks containing fluids in the liquid phase finally maps of the v p v s product show a high v p v s horseshoe shaped anomaly located at 2 km depth it is consistent with gravity data and well data and might constitute the on land remainder of the caldera rim detected below sea level by tomography using active source seismic data

observations and analysis of b type earthquakes explosions and volcanic tremor at pavlof volcano alaska an eight station network of short period seismometers has been operated near pavlof volcano 55 25 n 161 54 w alaska peninsula since 1976 high quality analog to digital and direct digital data were recorded during eruptions in 1980 through 1983 data are analyzed from explosions with distinct air phases b type volcanic earthquakes shallow low frequency events lacking clear s phases and volcanic tremor to determine source and propagation effects between zero and several hundred b type events and explosions per day are recorded with higher numbers during eruptions magnitudes range between 0 5 and 1 3 and b values range between 1 9 0 1 and 2 6 0 1 with no systematic relation to eruptive activity six results are most important 1 data from a recently installed three component station reveal that the highest amplitude waves of the b type events show retrograde elliptical particle motion and normal dispersion and are hence probably rayleigh waves 2 stacking of the events enhances the p wave which has a velocity of 3 1 0 1 km sec 1 3 the explosions and b type events have similar hypocenters as evidenced by signal characteristics and wave arrival times 4 the b type events contain virtually no high frequency energy even when allowing for attenuation effects in particular we estimate the anelastic attenuation coefficient q to have a value of 45 20 for rayleigh waves in the shallow part of the volcano 5 volcanic tremor spectra exhibit evenly spaced narrow peaks which we model as eigenvalues of organ pipe resonance in the magma conduit we estimate the length of the conduit to be a maximum of 1 6 km 6 the volcano shows evidence of extreme lateral variation of velocity and attenuation in its shallow structure

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

source mechanism of volcanic tremor low frequency 10 hz volcanic earthquakes originate at a wide range of depths and occur before during and after magmatic eruptions the characteristics of these earthquakes suggest that they are not typical tectonic events physically analogous processes occur in hydraulic fracturing of rock formations low frequency icequakes in temperate glaciers and autoresonance in hydroelectric power stations we propose that unsteady fluid flow in volcanic conduits is the common source mechanism of low frequency volcanic earthquakes tremor the fluid dynamic source mechanism explains low frequency earthquakes of arbitrary duration magnitude and depth of origin as unsteady flow is independent of physical properties of the fluid and conduit fluid transients occur in both low viscosity gases and high viscosity liquids a fluid transient analysis can be formulated as generally as is warranted by knowledge of the composition and physical properties of the fluid material properties geometry and roughness of the conduit and boundary conditions to demonstrate the analytical potential of the fluid dynamic theory we consider a single phase fluid a melt of mount hood andesite at 1250 c in which significant pressure and velocity variations occur only in the longitudinal direction further simplification of the conservation of mass and momentum equations presents an eigenvalue problem that is solved to determine the natural frequencies and associated damping of flow and pressure oscillations for a simple constant pressure reservoir conduit orifice fluid system a change in orifice size can cause the source signal duration due to a single disturbance to change from several seconds to in excess of an hour fluid kinematic viscosity 0 412 m2 s is both included and neglected in the analysis to illustrate its effect upon system damping tremor magnitude is related to the magnitude of the conduit wall motion occurring in response to oscillating fluid pressures the entire volcanic fluid system does not generally experience a transient flow condition at a given time closed end and constant pressure fluid system boundaries reflect pressure waves and isolate components of the fluid system total fluid movement may not be accurately monitored by tremor data alone since steady state and slowly changing flows are aseismic

texture and composition of pumices and scoriae from the campi flegrei caldera italy implications on the dynamics of explosive eruptions 1 the campi flegrei cf caldera is one of the most dangerous quiescent volcanic systems in the world its activity mostly resulted in low magnitude explosive eruptions such as that of the monte nuovo tuff cone that represents the last eruptive event within the caldera a d 1538 however there have been more energetic plinian events e g the agnano monte spina eruption 4 1 ka and very highly explosive caldera forming eruptions e g the campanian ignimbrite eruption 39 ka here we integrate new and literature data on the groundmass texture and composition of pyroclastic products from the three above eruptions with the aim of unraveling how volatiles content degassing mechanisms and crystallization processes influence magma explosivity and eruption dynamics at cf previous studies indicate that the investigated rocks share similar major element bulk and phenocryst chemistry also similar is the water content of their trapped melt inclusions these observations suggest that the magmas feeding these eruptions had comparable physicochemical properties during storage in the shallow crust however our investigations indicate that the studied rocks differ in texture and composition of the groundmass and viscosity of the related magmas we ascribe such differences to the variable style of volatile exsolution and outgassing from the melt primarily in response to changes of the rate of magma ascent to the surface we conclude that the magma ascent rate was the key parameter in driving explosive eruptions at cf and we suggest that this parameter may be influenced by magma water interaction and or magma chamber geometry and replenishment

earthquake activity related to the 1991 eruption of the hekla volcano iceland the 1991 eruption of the hekla volcano started unexpectedly on 17 january no long term precursory seismicity was observed the first related activity was a swarm of small earthquakes that began approximately half an hour before the eruption intensive seismicity both earthquakes and volcanic tremor accompanied the violent onset of the eruption almost 400 events up to ml magnitude 2 5 were recorded during the first few hours during the later phases of the eruption the earthquake activity was modest and the main volcano related seismic signal was the persistent volcanic tremor the tremor died away together with the eruption on 11 march and hekla was seismically quiet until the beginning of june 1991 when a sudden swarm of numerous small shallow earthquakes occurred this activity is atypical for hekla and is interpreted to be a failed attempt to resume the eruption

origin of the fumarolic fluids of vulcano island italy and implications for volcanic surveillance variations in d and 18o values with h2o contents and outlet temperatures indicate that the fumaroles of la fossa crater have discharged mixtures of magmatic water and marine hydrothermal water since 1979 the contribution of meteoric water was low in the period 1979 1982 and very low afterwards the 18o values of the marine hydrothermal component of 5 to 7 2 are due to isotopic exchange with the 18o rich silicates of the rocks under high temperature and low permeability conditions the 18o value of the magmatic end member is generally 3 5 to 4 3 although values as high as 5 5 to 6 5 were reached in the summer of 1988 when magma degassing appears to have extended into the core of the magma body the d values of the end member were close to 20 typical of andesitic waters both the isotopic values and chemical data strongly support a dry model consisting of a central magmatic gas column and a surrounding hydrothermal envelope in which marine hydrothermal brines move along limited fracture zones to undergo total evaporation on approaching the conduits of magmatic fluids the vents at the eastern and western boundaries of the fumarolic field are fed by fluids whose pressure is governed by the coexistence of vapor liquid and halite giving rise to a high risk of phreato magmatic explosions should magma penetrate into these wet environments most la fossa eruptions were triggered by an initial hydrothermal blast and continued with a series of phreatomagmatic explosions the fluids discharged by the forgia vecchia fumaroles are mixed with meteoric water which is largely evaporated although subordinate loss of condensed steam may be responsible for scrubbing most of the acidic gas species the temperatures and pressures and the risk of a sudden pressure increase are low a boiling hydrothermal aquifer at 230 c is present underneath the baia di levante beach this area has a minor risk of hydrothermal explosions

evolution of santorini volcano dominated by episodic and rapid fluxes of melt from depth santorini volcano in greece was thought to be continually charged by small injections of magma measurements of surface deformation show that magma equivalent to 10 50 of that emitted in previous small eruptions has been injected beneath santorini since january 2011 implying that the volcano is instead charged by rapid episodic fluxes of melt

hydrogen in the gas plume of an open vent volcano mount etna italy 1 we report here on the first hydrogen determinations in the volcanic gas plume of mount etna in italy which we obtained during periodic field surveys on the volcano s summit area with an upgraded multigas using a specific ezt3hyt electrochemical sensor we resolved h2 concentrations in the plume of 1 3 ppm above ambient background atmosphere and derived h2 so2 and h2 h2o plume molar ratios of 0 002 0 044 mean 0 013 and 0 0001 0 0042 mean 0 0018 respectively taking the above h2 so2 ratios in combination with a time averaged so2 flux of 1600 gg yr 1 we evaluate that etna contributes a time averaged h2 flux of 0 65 gg yr 1 suggesting that the volcanogenic contribution to the global atmospheric h2 budget 70 000 100 000 gg yr 1 is marginal we also use our observed h2 h2o ratios to propose that etna s passive plume composition is at least partially representative of a quenched temperatures between 750 c and 950 c equilibrium in the gas magma system at redox conditions close to the nickel nickel oxide nno mineral buffer the positive dependence between h2 so2 h2 h2o and co2 so2 ratios suggests that h2 is likely supplied at least in part by deeply rising co2 rich gas bubbles fluxing through a co2 depleted shallow conduit magma

an approach to problems on energy sources at mount etna based on seismological and volcanological data based on seismograms from the most continuously operating station of the seismic network at mt etna monte vetore 1665 m a s l the energy release patterns through time have been obtained for volcanic tremors and earthquakes which occurred between 1978 1982 both energies range between 1011 1013 j a but their release patterns are not strictly correlated to each other considering only the eruptions which occurred during the same time span the amount of thermal energy released and the associated potential energy needed to raise the magma to the surface from a 2 km deep hydrostatic equilibrium level were estimated to be about 1017 and 1015 j a respectively the computed energies for earthquakes and tremors are at least one order of magnitude less than what is needed to match a model of magma transport based solely on the jerky propagation of melt filled cracks the energy needed to raise the magma to the surface could be supplied by expanding gases in the upper levels of the magma column and or by tectonic stresses acting on shallow batches of magma

carbon dioxide earth degassing and seismogenesis in central and southern italy 1 we present the first regional map of co2 earth degassing from a large area most of central and south italy derived from the carbon of deep provenance dissolved in the main springs of the region the investigation shows that a globally significant amount of deeply derived co2 10 of the estimated global co2 emitted from subaerial volcanoes is released by two large areas located in western italy the anomalous flux of co2 suddenly disappears in the apennine in correspondence to a narrow band where most of seismicity concentrates here at depth the gas accumulates in crustal traps generating co2 overpressurized reservoirs which induce seismicity

weather radar observations of the hekla 2000 eruption cloud iceland the hekla eruption cloud on 26 27 february 2000 was the first volcanic cloud to be continuously and completely monitored advecting above iceland using the c band weather radar near the keflavik international airport real time radar observations of the onset advection and waning of the eruption cloud were studied using time series of ppi plan position indicator radar images including vmi normal echotop and cappi level 2 displays the reflectivity of the entire volcanic cloud ranges from 0 to 60 dbz the eruption column above the vent is essentially characterised by vmi normal and cappi level 2 values 30 dbz due to the dominant influence of lapilli and ash tephra on the overall reflected signal the cloud generated by the column was advected downwind to the north northeast it is characterised by values between 0 and 30 dbz and the persistence of these reflections likely result from continuing water condensation and freezing on ash particles echotop radar images of the eruption onset document a rapid ascent of the plume head with a mean velocity of 30 to 50 m s 1 before it reached an altitude of 11 12 km the evolution of the reflected cloud was studied from the area change in pixels of its highly reflected portions 30 dbz and tied to recorded volcanic tremor amplitudes the synchronous initial variation of both radar and seismic signals documents the abrupt increase in tephra emission and magma discharge rate from 18 20 to 19 00 utc on 26 february from 19 00 the 45 dbz and 30 45 dbz portions of the reflected cloud decrease and disappear at about 7 and 10 5 h respectively after the eruption began indicating the end of the decaying explosive phase the advection and extent of the reflected eruption cloud were compared with eyewitness accounts of tephra fall onset and the measured mass of tephra deposited on the ground during the first 12 h differences in the deposit map and volcanic cloud radar map are due to the fact that the greater part of the deposit originates by fallout off the column margins and from the base of the cloud followed by advection of falling particle in lower level winds

first observations of the fumarolic gas output from a restless caldera implications for the current period of unrest 2005 2013 at campi flegrei 1 the fumarolic gas output has not been quantified for any of the currently deforming calderas worldwide due to the lack of suitable gas flux sensing techniques in view of resumption of ground uplift since 2005 and the associated variations in gas chemistry campi flegrei in southern italy is one of the restless calderas where gas flux observations are especially necessary here we report the first ever obtained estimate of the campi flegrei fumarolic gas output based on a set of multigas surveys performed in 2012 and 2013 with an ad hoc designed measurement setup we estimate that the current campi flegrei fumarolic sulphur s flux is low on the order of 1 5 2 2 tons day suggesting substantial scrubbing of magmatic s by the hydrothermal system however the fumarolic carbon dioxide co2 output is 460 160 tons day mean sd which is surprisingly high for a dormant volcano in the hydrothermal stage of activity and results in a combined fumaroles soil co2 output of 1560 tons day assuming magma to be the predominant source we propose that the current co2 output can be supplied by either i a large 0 6 4 6 km3 deeply stored 7 km magmatic source with low co2 contents 0 05 0 1 wt or ii by a small to medium sized 0 01 0 1 km3 but co2 rich 2 wt magma possibly stored at pressures of 100 to 120 mpa independent geophysical evidence e g inferred from geodetic and gravity data is needed to distinguish between these two possibilities

temporal and spatial characteristics of volcanic tremor wave fields abstract detailed volcanic tremor studies were carried out with portable seismic stations installed both in the near and distant zones at klyuchevskoy volcano in 1984 1986 and 1987 it has been determined that the coherence of wave field decreases with distance to 0 5 km and does not change at greater distances based on coherence and phase spectra the frequency dependence of the phase velocities has been determined the dispersion of phase velocity points to the surface character of the wave field the behaviour of volcanic tremor characteristics through time is stationary which implies stability of the parameters of the volcanic tremor source a detailed spectral study has demonstrated that when the intensity of volcanic tremor varies by a few orders of magnitude parts of the low frequency and high frequency spectra change which is likely due to the variations in source dimensions the detailed spectral characteristics of tremor may be used for both determining the source parameters and studying the structure of the medium

isotopic study of the origin of sulfur and carbon in solfatara fumaroles campi flegrei caldera abstract isotopic study of the origin of sulfur and carbon in the hottest solfatara fumaroles of campi flegrei caldera southern italy was carried out on gas samples collected between 1983 and 1988 i e during and after the 1982 1984 seismo volcanic crisis the results for sulfur h2s the first ever reported on these gases indicate a mean 34 s of 0 3 0 3 range 0 7 to 0 1 versus canyon diablo troilite standard consistent with an igneous derivation of this element from either active magma degassing or and leaching of reduced sulfur bearing minerals in the volcanic layers the lack of peculiar 34s variation during and after the crisis suggests that the chemical variation of h2s and s c ratio in the fumaroles increase and then decrease by a factor 3 were not due to a changing origin of sulfur the mean 13c of carbon co2 over the period of survey 1 6 0 2 range 1 9 to 1 3 versus pdb standard is similar to the values obtained before the crisis since 1970 such an isotopic constancy requires a large and stable source of carbon feeding the fumaroles the measured 13c values are much higher than those typical of primary mantle magmatic carbon 6 2 and plot within the 13c range for marine carbonates 0 2 such high values may reflect either a 13c fractionation during degassing of co2 from the underlying 5 km depth magma chamber or b the contribution of heavy co2 of sedimentary origin derived from either thermometamorphism of mesozoic limestone series embedding the magma chamber or possibly past contamination of the local mantle by subducted sediments various arguments among which volcanological evidence of an isolated and cooling magma reservoir which would have been extensively degassed and so depleted in 13c along with time the low 3he 4he ratios and the broad 13c enrichment of volcanic fluids in the region and geochemical evidence of crust magma fluid interactions suggest that a considerable fraction 60 of co2 in solfatara fumaroles derives from carbonate sediments in the basement the contribution of magma derived co2 may be higher within the central part of the caldera including solfatara crater than toward its western margin where fumarolic and geothermal well gases exhibit lower 3he 4he ratios and still higher 13c values such a geochemical pattern is consistent with the central distribution of ground deformation and seismicity during the 1982 1984 crisis and with the idea of a residual magma body confined beneath the central part of the structure alternatively higher 13c and lower 3he 4he ratios toward the western margin may result from dilution of solfatara type gas during progressively deeper water boiling finally accepting that solfatara co2 derives from simple crustal mixing between magmatic and sedimentary carbon its constant isotopic composition together with the constant he isotope ratio would restrict the possibility of magma intrusion and or higher magmatic gas input as mechanisms responsible for the 1982 1984 events however this conclusion would no more hold true if the magma itself or even its mantle source were previously contaminated by crustal carbon

excitation mechanism of large amplitude volcanic tremor associated with the 1989 ito oki submarine eruption central japan abstract unusually large amplitude volcanic tremor was observed in association with the 1989 ito oki submarine eruption off the east coast of izu peninsula central japan the largest amplitude tremor occurred on july 13 1989 and was studied by using digital seismic data national research institute for earth science and disaster prevention in the distance range of 6 250 km spectral analysis shows that the seismograms have two kinds of predominant spectral peaks low frequency peaks around 1 hz and middle frequency peaks between 2 and 7 hz the relative amplitude ratios of these peaks show distinctive spatial variation depending primarily on the distances from the crater low frequency waves are predominant at close stations distances less than 50 km from the crater similar to typical low frequency volcanic tremor while at more distant stations the middle frequency waves are more prominent than low frequency waves propagation velocity analysis for narrow frequency bands on the basis of correlation of envelopes of seismograms reveals that the middlefrequency waves are compressional body waves and the excitation of shear wave was ineffective suggesting an explosive or implosive source as the simplest source model in contrast to the middle frequency waves our analysis showed no evidence for the low frequency waves to have propagated with any body wave velocity consideration of the spatial pattern of both waves suggests that surface waves were trapped in sedimentary layers from the shallow source and that no lowfrequency oscillations dominated at the source

volcanic tremor related to the 1991 eruption of the hekla volcano iceland volcanic tremor at the hekla volcano is directly related to eruptive activity it starts simultaneously with the eruptions and dies down at the end of them no tremor at hekla has been observed during non eruptive times the 1991 hekla eruption began on 17 january after a short warning time local seismograph stations recorded small premonitory earthquakes from 16 30 gmt on at 17 02 gmt low frequency volcanic tremor became visible on the seismograph records marking the onset of the eruption the initial plinian phase of the eruption was short lived during the first day several fissures were active but by the second day the activity was already limited to a segment of one principal fissure the eruption lasted almost 53 days at the end of it during the early hours of 11 march volcanic tremor disappeared under the detection threshold and was followed by a swarm of small earthquakes at the start of the eruption the tremor amplitude rose rapidly and reached a maximum in only 10 min the tremor was most vigorous during the first hour and started to decline sharply during the next hour and later on more gently during the eruption as a whole the tremor had a continuous declining trend with occasional increases lasting up to about 2 days spectral analysis of the tremor during the first 7 h of the eruption shows that it settled quickly within a couple of minutes to its characteristic frequency band 0 5 1 5 hz the spectrum had typically one dominant peak at 0 7 0 9 hz and a few subdominant peaks hekla tremor likely has a shallow source particle motion plots suggest that it contains a significant component of surface waves the tremor started first when the connection of the magma conduit with the atmosphere was reached suggesting that degassing may contribute to its generation

the deep magmatic system of the campi flegrei caldera italy 1 melt inclusions in phenocrysts of the minopoli2 shoshonite and fondo riccio latite eruptive products campi flegrei caldera 10 2 to 9 5 ka bp constrain the nature of deep phlegraean magmatic fluids their role in volcanism and give new insights into the magmatic plumbing system the analyzed melt inclusions show that co2 is an abundant gaseous species confirming the results of geochemical studies on the magmatic gas fraction involved in present day fumarolic emissions volatile concentrations within the melt inclusions require gas melt equilibria between 8 and 9 km depth and closed system degassing in presence of ascending co2 rich fluids of deep provenance magmas later re equilibrate at depths up to 3 2 km i e above the top of the carbonate basement these observations correlate well with independent geophysical and geochemical evidence and are useful constraints for volcanic hazards assessment at campi flegrei

echo resonance and hydraulic perturbations in magma cavities application to the volcanic tremor of etna italy in relation to its eruptive activity a study is presented of spectral features of volcanic tremor recorded at mount etna sicily italy following the methods of analysis suggested by the resonant scattering formalism of gaunaurd and uberall 1978 1979a 1979b and the model for hydraulic origin of seidl et al 1981 the periods investigated include summit and flank eruptions that occurred between 1984 and 1993 recordings from a permanent station located near the top of the volcano were used and the temporal patterns associated with a the average spacing bar delta between consecutive spectral peaks in the frequency range 1 6 hz b the spectral shape and c the overall spectral amplitude were analyzed bar delta values are thought to depend on the physical properties of magma such as its density which in turn is controlled by the degree of gas exsolution variations in the spectral shape are tentatively attributed to changes in the geometrical scattering from the boundary of resonant conduits and magma batches finally the overall amplitude at the station should essentially reflect the state of turbulence of magma within the superficial ascending path a limit in the application of the resonant scattering formalism to the study of volcanic tremor is given by the fact that the fundamental modes and integer harmonics are difficult to identify in the frequency spectra as tremor sources are likely within cavities of very complex geometry rather than in spherical or cylindrical chambers as expected by theory this study gives evidence of some correlations between the analyzed temporal patterns and the major events in the volcanic activity related to both lava flow and explosions at the summit vents in particular relatively high values of bar delta have been attained during the se crater eruption of 1984 the complex eruptive phases of september october 1989 and the 1991 1993 flank eruption suggesting the presence of a relatively dense magma for all of these events conversely very low values have been recorded in coincidence with the december 1985 activity and the paroxysmal explosions at the summit craters of early 1990 which are interpreted here as fed by fluid vesiculated magma appreciable modifications in the spectral shape have been observed in relation to changes of the volcanic activity that probably preceded the opening and disactivation of shallow dykes or magma batches finally the overall amplitude seems to be a sensitive indicator of the state of gas turbulence within the shallow conduits as is suggested by the high values attained during phases of intense volcanic activity

seismic activity related to the 2000 eruption of the hekla volcano iceland the 2000 hekla eruption took place from february 26 to march 8 its seismic expressions were a swarm of numerous small earthquakes related to its onset and low frequency volcanic tremor that continued throughout the eruption a swarm of small earthquakes was observed some 80 min before the onset of the eruption and the size of the events increased with time low frequency volcanic tremor with a characteristic frequency band of 0 5 1 5 hz and dominant spectral peak s at 0 7 0 9 hz became visible at 18 19 gmt on february 26 marking the onset of the eruption the tremor amplitude rose quickly and was very high in the beginning of the eruption however it soon began to decrease after about an hour in general the seismic activity related to the 2000 hekla eruption was very similar to what was observed in the previous eruption in 1991 based on knowledge gained from seismicity and strain observations from 1991 this was the first time that a hekla eruption was predicted

history of earthquakes and vertical ground movement in campi flegrei caldera southern italy comparison of precursory events to the a d 1538 eruption of monte nuovo and of activity since 1968 abstract the record of felt earthquakes around naples bay in southern italy is probably complete since the mid 15th century according to this record intense earthquake swarms originating beneath campi flegrei an explosive caldera located along the north coast of naples bay have occurred only twice 1 before the only historical eruption in campi flegrei in 1538 and 2 from mid 1983 to december 1984 earthquake activity during the earlier period which began at least a few years and possibly as many as 30 years before the 1538 eruption damaged many buildings in the city of pozzuoli located near the center of campi flegrei minor seismic activity which consisted of only a few felt earthquakes occurred from 1970 to 1971 the second period of intense earthquake swarms lasted from mid 1983 to 1984 again damaging many buildings in pozzuoli two periods of uplift along the shoreline within campi flegrei have also been noted since the mid 15th century 1 during the few decades before the 1538 eruption and 2 as two distinct episodes since 1968 uplift of a few meters probably occurred a few decades before the 1538 eruption uplift of as much as 3 0 m has occurred in pozzuoli since 1968 these similarities strongly suggest that for the first time in 440 years the same process that caused intense local earthquake swarms and uplift in the early 1500 s and led to an eruption in 1538 has again occurred beneath campi flegrei though no major seismicity or uplift has occurred since december 1984 because of the large amount of extensional strain accumulated during the past two decades if a third episode of seismicity and rapid uplift occurs it may lead to an eruption within several months after the resumption of activity

the hekla eruption 1980 1981 the sixteenth eruption of hekla since 1104 began on august 17th 1980 after the shortest repose period on record only ten years the eruption started with a plinian phase and simultaneously lava issued at high rate from a fissure that runs along the hekla volcanic ridge the production rate declined rapidly after the first day and the eruption stopped on august 20th a total of 120 million m3 of lava and about 60 million m3 of airborne tephra were produced during this phase of the activity in the following seven months steam emissions were observed on the volcano activity was renewed on april 9th 1981 and during the following week additional 30 million m3 of lava flowed from a summit crater and crater rows on the north slope

geoconservation and geotourism in arxan chaihe volcano area inner mongolia china abstract in east inner mongolia the arxan chaihe volcano area acva constitutes an important component part of the cenozoic volcanic eruption area in northeast china with great scientific and aesthetic value the area has received much attention since the 1980s the arxan national geopark was established in 2004 and the zalantun autonomous geopark in 2010 and volcanic geoconservation and geotourism developed to a certain degree along with some common problems in geopark development this paper analyzes the characteristics geoconservation and geotourism of volcanic geoheritage in the area the main problems identified are the inefficient conservation management uncoordinated development and the limited interpretation system we provide some suggestions on the problems in order to promote the local development such as strengthening legislation training tour guides as volcanologists with a background in geology who can interpret volcano geoheritage correctly building a web site and combining the two geoparks to apply for designation as a global geopark

quantitative model for magma degassing and ground deformation bradyseism at campi flegrei italy implications for future eruptions campi flegrei phlegrean fields is an active volcanic center near naples italy numerous eruptions have occurred here during the quaternary and repeated episodes of slow vertical ground movement bradyseism have been documented since roman times here we present a quantitative model that relates deformation episodes to magma degassing and fracturing at the brittle ductile transition in a magmatic hydrothermal environment the model is consistent with fi eld and laboratory observations and predicts that uplift between 1982 and 1984 was associated with crystallization of 0 83 km 3 of h 2 o saturated magma at 6 km depth during crystallization 6 2 10 10 kg of h 2 o and 7 5 10 8 kg of co 2 exsolved from the magma and generated 7 10 15 j of mechanical p v energy to drive the observed uplift for comparison 10 17 j of thermal energy was released during the 18 may 1980 lateral blast at mount st helens

mechanisms of activity and unrest at large calderas large caldera collapses represent catastrophic natural events second only to large meteoritic impacts in addition some calderas are densely populated making the risk extreme even for moderate eruptions understanding caldera mechanisms unrest and the danger of eruption is therefore a crucial challenge for earth sciences several key features of caldera behaviour have yet to be fully understood through a combination of case studies and theoretical modelling the following topics are addressed in this volume the conditions required to produce and to release large volumes of magma erupted during caldera formation how magmatic feeding systems evolve before and after a caldera has formed the processes that limit the behaviour of precursors to eruptions how pre emptive precursors can be distinguished from those that drive unrest without an eruption and given that post collapse eruptions may occur across a wide area the optimum procedures for designing hazard maps and mitigation strategies

unusually large magmatic co2 gas emissions prior to a basaltic paroxysm 1 the low intensity activity of basaltic volcanoes is occasionally interrupted by short lived but energetic explosions which whilst frequently observed are amongst the most enigmatic volcanic events in nature the combination of poorly understood and deep challenging to measure source processes make such events currently impossible to forecast here we report increases in quiescent degassing co2 emissions 10 000 t day prior to a powerful explosive event on stromboli volcano on 15 march 2007 we interpret such large co2 flux as being sourced by passive gas leakage from a deeply 4 km stored magma whose depressurization possibly caused by the onset of an effusive eruption on 28 february 2007 was the explosion trigger our observations suggest that continuous co2 flux monitoring may allow anomalously large explosions to be accurately forecast at basaltic volcanoes

monitoring and modelling hydrothermal fluid emission at la solfatara phlegrean fields italy an interdisciplinary approach to the study of diffuse degassing discharge of hydrothermal fluids at la solfatara is one of the many pieces of evidence testifying to the level of activity and the potential danger characterizing the volcanic complex of the phlegrean fields recent measurements of diffuse degassing shed light on the unexpected magnitude of this process and prompted further research to improve our understanding of the hydrothermal system feeding the surface phenomenon at la solfatara in this work we first present new data on co2 diffuse degassing that were collected during a campaign in july 2000 and confirm previous measurements of the degassing rate these data together with other information on subsurface structures and conditions provided the necessary constraints to perform physical modelling of the hydrothermal fluid circulation at la solfatara numerical simulations describe the ascent and evolution of a hot multi phase and multi component fluid composed of water and carbon dioxide through a homogeneous porous medium when certain system properties and conditions are used this model reproduces some of the main features which characterize the natural system including the energy budget associated with the ascent and condensation of hot fluids and the development of a single phase gas region whose existence was inferred from independent chemical data further simulations investigated the effects associated with changes in rock properties and fluid injection rates results showed that an increase in the permeability at shallow depth may have an important influence on the system conditions and fluid discharge they imply that surface phenomena accompanied by very high temperatures at shallow depths may survive long after deep feeding has ceased

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

monitoring super volcanoes geophysical and geochemical signals at yellowstone and other large caldera systems earth s largest calderas form as the ground collapses during immense volcanic eruptions when hundreds to thousands of cubic kilometres of magma are explosively withdrawn from the earth s crust over a period of days to weeks continuing long after such great eruptions the resulting calderas often exhibit pronounced unrest with frequent earthquakes alternating uplift and subsidence of the ground and considerable heat and mass flux because many active and extinct calderas show evidence for repetition of large eruptions such systems demand detailed scientific study and monitoring two calderas in north america yellowstone wyoming and long valley california are in areas of youthful tectonic complexity scientists strive to understand the signals generated when tectonic volcanic and hydrothermal hot ground water processes intersect one obstacle to accurate forecasting of large volcanic events is humanity s lack of familiarity with the signals leading up to the largest class of volcanic eruptions accordingly it may be difficult to recognize the difference between smaller and larger eruptions to prepare ourselves and society scientists must scrutinize a spectrum of volcanic signals and assess the many factors contributing to unrest and toward diverse modes of eruption

climate and biogeochemical response to a rapid melting of the west antarctic ice sheet during interglacials and implications for future climate interglacials onto the global climate carbon cycle system using the earth system model of intermediate complexity loveclim prescribing a meltwater pulse in the southern ocean that mimics a rapid disintegration of the wais a substantial cooling of the southern ocean is simulated that is accompanied by an equatorward expansion of the sea ice margin and an intensification of the southern hemispheric westerlies the strong halocline around antarctica leads to suppression of antarctic bottom water aabw formation and to subsurface warming in areas where under present day conditions aabw is formed this subsurface warming at depths between 500 and 1500 m leads to a thermal weathering of the wais grounding line and provides a positive feedback that accelerates the meltdown of the wais our model results further demonstrate that in response to the massive expansion of sea ice marine productivity in the southern ocean reduces significantly a retreat of the wais however does not lead to any significant changes in atmospheric co2 the climate signature of a wais collapse is structurally consistent with available paleoproxy signals of the last interglacial mis5e citation menviel l a timmermann o e timm and a mouchet 2010 climate and biogeochemical response to a rapid melting of the west antarctic ice sheet during interglacials and implications for future climate paleoceanography 25 pa4231 doi 10 1029 2009pa001892

seismic attenuation imaging of campi flegrei evidence of gas reservoirs hydrothermal basins and feeding systems 1 passive high resolution attenuation tomography is used here to image the geological structure in the first upper 4 km of the shallow crust beneath the campi flegrei caldera southern italy the inverse q was estimated for each source receiver path using the coda normalization method s waves and the slope decay method p waves and s waves inversion was performed using a multi resolution method which ensures a minimum cell size resolution of 500 m the study of the resolution matrix as well as the synthetic tests guarantee an optimal reproduction of the input anomalies in the center of the caldera between 0 and 3 5 km in depth high attenuation vertical structures are connected at the surface with the main volcanological features e g the solfatara and mofete fumarole fields and depict vertical q contrast imaging important geological structures such as the la starza fault these high attenuation volumes extend between the surface and a depth of about 3 km where a hard rock layer is imaged by the sharp contrast of the quality factors the retrieved image of the campi flegrei has been jointly interpreted taking into account evidence from seismological geological volcanological and geochemical investigations this analysis has allowed an unprecedented view of the feeding systems in this area and in particular it recognizes the vertically extending high attenuation structures that correspond to gas or fluid reservoirs beneath pozzuoli solfatara solfatara mofete mt nuovo and agnano this high attenuation system is possibly connected with the magma sill revealed at about 7 km in depth by passive travel time tomography

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

the 1991 eruption of hekla iceland the eruption that started in the hekla volcano in south iceland on 17 january 1991 and came to an end on 11 march produced mainly andesitic lava this lava covers 23 km2 and has an estimated volume of 0 15 km3 this is the third eruption in only 20 years whereas the average repose period since 1104 is 55 years earthquakes as well as a strain pulse recorded by borehole strainmeters occurred less than half an hour before the start of the eruption the initial plinian phase was very short lived producing a total of only 0 02 km3 of tephra the eruption cloud attained 11 5 km in height in only 10 min but it became detached from the volcano a few hours later several fissures were active during the first day of the eruption including a part of the summit fissure by the second day however the activity was already essentially limited to that segment of the principal fissure where the main crater subsequently formed the average effusion rate during the first two days of the eruption was about 800 m3 s 1 after this peak the effusion rate declined rapidly to 10 20 m3 s 1 then more slowly to 1 m3 s 1 and remained at 1 12 m3 s 1 until the end of the eruption site observations near the main crater suggest that the intensity of the volcanic tremor varied directly with the force of the eruption a notable rise in the fluorine concentration of riverwater in the vicinity of the eruptive fissures occurred on the 5th day of the eruption but it levelled off on the 6th day and then remained essentially constant the volume and initial silica content of the lava and tephra the explosivity and effusion rate during the earliest stage of the eruption as well as the magnitude attained by the associated earthquakes support earlier suggestions that these parameters are positively related to the length of the preceeding repose period the chemical difference between the eruptive material of hekla itself and the lavas erupted in its vicinity can be explained in terms of a density stratified magma reservoir located at the bottom of the crust we propose that the shape of this reservoir its location at the west margin of a propagating rift and its association with a crustal weakness all contribute to the high eruption frequency of hekla

magma ascent and eruptive processes from textural and compositional features of monte nuovo pyroclastic products campi flegrei italy geochemical and textural studies were carried out on alkaline products of the ad 1538 monte nuovo eruption due to the integration of the volcanological study with eyewitness reports the dynamics and timing of each phase of the eruption and the volume of emitted magmas are known in detail on this basis unique in campi flegrei the relations between magma chamber mechanisms eruptive styles magma ascent dynamics and volatile exsolution processes have been explored glass and phenocryst compositions indicate that the erupted magma has a homogeneous phono trachytic composition textures and compositions of phenocrysts indicate that they crystallised at equilibrium with the melt in the magma chamber likely as a mushy boundary layer along the chamber wall where the temperature was below the liquidus temperature of the crystal free chamber core the estimated crystallisation temperature is 850 40 c the magma phase relations in petrogeny s residua system suggest that phenocryst crystallisation occurred at text p text h 2 text o between 100 and 200 mpa corresponding to depths ranging from 3 to 8 km the microlite composition and their close genetic relations with vesicles indicate that groundmass crystallisation occurred during the eruption as a consequence of magma degassing and vesiculation induced by decompression during its ascent toward the surface crystal size distributions reveal that microlites grew in two stages of undercooling that we define as 1 magma migration onset upward from the chamber and 2 magma rising through the conduit to the surface possibly lasting tens of days and few days respectively these results provide information on the physical conditions that characterise pre and syn eruptive processes which may be useful in order to define eruptive scenarios and to evaluate short term precursors furthermore the collected data provide for the first time information on degassing induced crystallisation during the eruption of a highly evolved alkaline magma

the phlegraean fields structural evolution volcanic history and eruptive mechanisms abstract the main event within the volcanic history of the phlegraean fields was the eruption about 35 000 years ago of a huge alkali trachytic ignimbrite 80 km 3 dre followed by caldera collapse the pre caldera activity evidence from geothermal wells and surface outcrops changed from submarine to subaerial shortly before the ignimbrite eruption the caldera was subsequently invaded by the sea and became progressively filled with tuffites and subordinate submarine flows in its northern half the last submarine explosive activity dates back to 12000 10500 yr with the eruption of mostly hydroplinian yellow tuffs recent mostly subaerial activity consists of a series of explosive eruptions whose volume decreases with time until the last eruption of mt nuovo in 1538 a d two peaks in recent activity occur at 10000 8000 and 4700 3000 years ago during post caldera activity eruptive vents migrated from the caldera rim toward the center where there are two distinct zones of recent vents minor collapses occurred within the caldera after the main eruptions often they are eccentric to the vent and displaced toward the caldera center phlegraean explosive activity is characterized by water magma interaction eruptive events without a hydromagmatic component are extremely rare in most cases the evolved trachytic magmas interacted with surface water either the sea or intracaldera lakes however there is evidence of interaction of magma with deep seated aquifers for some plinian events explosivity i e the efficiency of the transformation of thermal into kinetic energy during magma water interaction is largely controlled by the primary fragmentation of the magmatic melt

the origin of the fumaroles of la solfatara campi flegrei south italy abstract the analysis of gaseous compositions from solfatara campi flegrei south italy fumaroles since the early 1980s clearly reveals a double thermobarometric signature a first signature at temperatures of about 360 c was inferred by methane based chemical isotopic geoindicators and by the h2 ar geothermometer these high temperatures close to the critical point of water are representative of a deep zone where magmatic gases flash the hydrothermal liquid forming a gas plume a second signature was found to be at around 200 240 c at these temperatures the kinetically fast reactive species h2 and co re equilibrate in a pure vapor phase during the rise of the plume a combination of these observations with an original interpretation of the oxygen isotopic composition of the two dominant species i e h2o and co2 shed light on the origin of fumarolic fluids by showing that effluents are mixture between fluids degassed from a magma body and the vapor generated at about 360 c by the vaporization of hydrothermal liquids a typical andesitic water type d 20 18o 10 and a co2 rich composition x co 2 0 4 has been inferred for the magmatic fluids while for the hydrothermal component a meteoric origin and a co2 fugacity fixed by fluid rock reaction at high temperatures have been estimated in the time the fraction of magmatic fluids in the fumaroles increased up to 0 5 at each seismic and ground uplift crisis bradyseism which occurred at campi flegrei suggesting that bradyseismic crises are triggered by periodic injections of co2 rich magmatic fluids at the bottom of the hydrothermal system

unrest at campi flegrei a contribution to the magmatic versus hydrothermal debate from inverse and finite element modeling 1 we present results from the modeling of ground deformation and microgravimetric data recorded at campi flegrei in order to assess the causative phenomena of caldera unrest between 1981 and 2001 we find that residual gravity changes during ground uplift 1982 1984 are indicative of mass changes in a hybrid of magmatic and hydrothermal sources during deflation between 1985 and 2001 the inversion of gravity residuals for a single source does not provide convincing results we then performed the joint inversion of gravity and deformation data for multiple spherical sources and refined source parameters by finite element modeling in order to mitigate against limitations of the analytical solutions the data recorded during inflation and rapid deflation may be best explained by mass and pressure changes in a deep magmatic source at about 5 km depth and a shallow 2 km deep hydrothermal source both sources contribute equally to the gravity changes observed between 1982 and 1984 the contemporary uplift appears to be mainly caused by the shallow source the subsequent deflation is dominated by a pressure decrease in the hydrothermal source the magmatic source contributes chiefly to the observed gravity changes pressure and density variations within multiple shallow seated hydrothermal sources provide acceptable fits to the deflation and accompanying gravity changes recorded since 1988 these shallow level dynamics also appear to trigger spatially and temporarily random short term reversals of the overall mode of ground subsidence since 1985 our analysis does not support the idea of magmatic contributions to these short lived periods of inflation

helium strontium isotope constraints on mantle evolution beneath the roman comagmatic province italy european social fund scottish universities carnegie trust for the universities of scotland

lithology of the basement underlying the campi flegrei caldera volcanological and petrological constraints abstract a geologically reasonable working hypothesis is proposed for the lithology of the basement underlying the campi flegrei caldera in the ca 4 8 km depth range in most current geophysical modeling this portion of crust is interpreted as composed of meso cenozoic carbonate rocks underlain by a ca 1 km thick sill of partially molten rock thought to be a main magma reservoir shallower magma reservoirs likely occur in the 3 4 km depth range however the lack of carbonate lithics in any campi flegrei caldera volcanic rocks does not support the hypothesis of a limestone basement considering the major caldera forming eruptions which generated widespread and voluminous ignimbrites during late quaternary times including the campanian ignimbrite and neapolitan yellow tuff eruptions the total volume of trachytic to phonolitic ejected magma is conservatively estimated at not less than 350 km 3 results of least squared mass balance calculations suggest that this evolved magma formed through fractional crystallization from at least 2500 km 3 of parent shoshonitic magma in turn derived from even more voluminous more mafic k basaltic magma calculations suggest that shoshonitic magma likely emplaced at ca 8 km depth must have crystallized about 2100 km 3 of solid material dominated by alkali feldspar and plagioclase with a slightly lower amount of mafic minerals during its route toward shallower magma reservoirs before feeding the campi flegrei large volume eruptions the calculated volume of cumulate material likely syenitic in composition at least in its upper portions is more than enough to completely fill the basement volume in the 4 8 km depth range beneath the campi flegrei caldera estimated at ca 1250 km 3 thus it is proposed that the basement underlying the campi flegrei caldera below 4 km is composed mostly of crystalline igneous rocks as for many large calderas worldwide syenite sensu lato would meet physical properties requirements for geophysical data interpretations explain some geochemical and isotopic features of the past 15 ka volcanics and justify the carbon isotopic composition of fumaroles at the campi flegrei caldera this implies that meso cenozoic limestones if still present today beneath the campi flegrei caldera no longer constitute significant portions of its basement

volcanic tremor wave field during quiescent and eruptive activity at mt etna sicily abstract this paper reports the results of an analysis of volcanic tremor at etna in the years 1987 to 1992 the data utilized were obtained from the osservatorio vesuviano s serra la nave permanent station and several seismic surveys carried out by means of portable digital seismic stations equipped with three component geophones the spatial temporal patterns of main parameters such as intensity spectral content polarization and wave composition of volcanic tremor in different phases of etna s activity were studied eruptive activity appears to be significantly correlated with volcanic tremor in particular it is worth pointing out that the magma upwelling in the terminal part of the conduit is characterized by a marked increase in low frequency components 3 4 hz of the spectrum of volcanic tremor hence volcanic tremor at etna can be considered as a short period precursor of eruptions an analysis of polarization and propagation velocity of volcanic tremor shows the presence of love waves overlapping other seismic phases

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

modelling of volcanic tremor wave fields abstract the comparison of the temporal variations of the volcanic tremor for various eruptions shows stable connection between tremor intensity and volcanic activity we have determined the wave pattern of seismic signals produced by individual explosions in the crater during eruption of the tolbachik volcano kamchatka considering an explosion in the crater as the source for formation of the seismic wave field we determined the relation between the spectrum of the source and volcanic tremor spectra theoretical seismograms for the unit source of explosion type in various medium models correlate well with the real volcanic tremor seismograms and explain the formation of the volcanic tremor wave fields in real conditions volcanic tremor frequency range of 0 6 5 hz forms as a result of disturbances near the surface in the active crater explosions pressure variations at sustained flow etc and consist mostly of surface waves a comparative estimation of transfer functions for the system explosion in the crater volcanic tremor and for theoretical models with the isolated source of explosion type has been done

volcanic tremors at etna a model for hydraulic origin spectral analysis of volcanic tremors at etna reveals 2 characteristic features 1 the escaping vapor and gas streams drive the magma in random turbulent motion generating a seismic wave emission according toa f n exp m f k wherea amplitude f frequency n m k parameters 2 sudden transients in the boundary conditions of the piping system generate hydraulic pressure pulses which in the seismogram appear as wave packages their monochromatic frequency content suggests that their origin is associated with strong resonance phenomena it is conclusive that volcanic eruptions may be distinguished and classified according to different eigenfrequencies of the fissure and pipe network involved in the volcanic activity furthermore positions of active dykes may be traced following the amplitude distributions associated with pronounced spectral lines in the tremor spectra

spectral analysis of harmonic tremor signals at mt semeru volcano indonesia a detailed spectral analysis of tremor signals recorded at mt semeru volcano indonesia in october 1992 by the german indonesian volcano expedition give 92 reveals clearly harmonic spectra containing up to 11 integer harmonics the spectral features can be explained by any rhythmically pulsating source producing a temporarily stable source signal as one realisation of this concept we model the source as a resonating gas volume generating seismic signals similar to the sound generated in a recorder

the opening subplinian phase of the hekla 1991 eruption properties of the tephra fall deposit the 1991 hekla eruption started on 17th of january with an intense 50 min long explosive phase that transitioned into fire fountain activity lasting for 2 days the eruptive plume rose to maximum height in about 10 min and the total mass of tephra deposited from the opening phase was 8 6 109 kg vei 3 event the principal axis of tephra fall is to the nne of hekla and grain size analysis reveals a systematic decrease in grain size away from source majority of sample sites show typically unimodal grain size distributions although a few have bimodal distributions where the secondary mode is a subtle finer peak the calculated total grain size distribution tgsd is bimodal with a coarse primary peak 3 5 to 2 5 and a subordinate fine peak 2 5 to 3 5 the coarse peak is lapilli dominated and was deposited within the first 25 km of transport whereas the fine peak is coarse ash dominated and fits well with the modal grain size of samples deposited 65 km from hekla ascent rate of the magma and conditions for vesiculation in the shallow conduit became increasingly uniform with time through the 1991 opening phase

genesis and evolution of unrest episodes at campi flegrei caldera the role of thermal fluid dynamical processes in the geothermal system we develop a model for describing water flow in a porous medium under the effect of thermal and pressure gradients the model simulates geothermal systems in calderas given the boundary conditions and the fluid dynamical properties of the medium the model allows computation in fluid dynamical stationary states of parameters characterizing the flow such as flow velocity and temperature and pressure distributions at depth the model is applied to investigate the effects of the local geothermal system on the unrest episodes at campi flegrei caldera using experimentally determined fluid dynamical parameters for the caldera rocks we show that changes of water flow in shallow aquifers under the effect of pressure and or temperature variations within the geothermal system can be very important in the genesis and evolution of unrest crises in particular they can strongly amplify the effect of pressure increase in the magma chamber on ground uplift they can also explain the timescales of evolution of ground movements in terms of transit times of the water front and of the connected temperature fronts due to advective transport on such grounds an integrated mechanic thermal fluid dynamical model was built allowing us to give a semiquantitative global explanation to the genesis and evolution of unrest phenomena results obtained here can be generalized to other similar calderas

ground motion in the near field of a fluid driven crack and its interpretation in the study of shallow volcanic tremor we present a study of the motion of the ground in the near field of a fluid driven tensile crack embedded in a layered half space the source that we consider is the jerky opening of a channel connecting two fluid filled cracks and the cause of this opening is the excess pressure of fluid in one of the cracks we make a complete representation of the three components of ground motion in the space time and frequency domains and analyze the effects of fluid compressibility source depth and medium structure on the ground response the calculations show the presence of a dominant frequency of motion which depends not only on the source geometry and bulk modulus of the fluid but also on medium characteristics receiver position and the component of motion being considered using this source model we view an episode of volcanic tremor as a continuous sequence produced by numerous jerky openings of channels occurring randomly in time along a chain of cracks our results are applied to the october 5 6 1963 east rift eruption of kilauea volcano hawaii and found to be compatible with available seismic data suggesting that magma is transported through an ensemble of cracks with the area of 1 1 km each pair of cracks constituting an individual dike segment which opens in discrete increments at a rate of 1 s we obtain the following parameters for each dike segment opening increase in cavity volume 40 m3 stress drop 0 004 bar seismic moment 1019 dyn cm and force applied by the fluid to open the dike 1014 dyn the total moment integrated over the entire duration of tremor for the eruption is 0 5 1024 dyn cm roughly equivalent to a single magnitude m 5 earthquake the seismic source parameters and other field observations offer constraints on the process of mass transport and are compatible with the excess pressure and viscosity of magma of about 40 bars and 102 p respectively

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

geochemical modeling of mixing between magmatic and hydrothermal gases the case of vulcano island italy abstract in this study we present a geochemical approach to model the mixing of magmatic and hydrothermal gases our model is based on a rigorous formulation of a perfectly dimensioned system of mass and energy balance equations inputs of the equation set are the h2o and co2 content and gas emission temperature at the surface together with some constraints gained from the chemical physical features of the hydrothermal system the output data give the composition of magmatic gas mixing fractions and temperatures of gas mixtures in the mixing zone the comparison of the emission temperature of fumarolic gases with their calculated mixing temperatures provides valuable indications on the expansion process that gases undergo during their ascent towards the surface our mixing model is exemplified by the fumarolic system of vulcano island italy we calculate the thermodynamic parameters of the hydrothermal system by means of an h2o co2 nacl equation of state while the thermo baric conditions of the magma have been assessed by previous geophysical and petrologic investigations the obtained results show that during volcanic crises at vulcano island and in agreement with magma degassing processes both the co2 and the he contents of magmatic gas display peaks with a progressively declining amplitude suggesting a progressive magmatic impoverishment of volatiles strongly partitioned in the gas phase mixing fractions of various fumaroles are normally variable while they display almost homogeneous values during periods of increased volcanic activity on the basis of results gained some implications regarding the hazard of phreato magmatic explosions are also discussed the high temperature reached by fumarolic gases strongly constrains their probable expansion process during the ascent towards the surface a comparison between the temperature of the fumarolic gas and the calculated mixing temperature at depth indicates that the expansion process can be reasonably described as almost iso enthalpic although field evidences suggest that the fumarolic emission temperature could be affected by the sharp permeability changes in the last few hundred meters therefore our results and field evidences clearly indicate that variations in gas emission temperature cannot be considered a good indicator of volcanic activity as it is strongly dependent on expansion process and ultimately on rock permeability changes the model greatly improves the knowledge of the volcanic system of vulcano island and provides an important tool for the interpretation and evaluation of volcanic activity moreover a similar approach can be considered for other volcanic systems having analogous characteristics