magma chamber of the campi flegrei supervolcano at the time of eruption of the campanian ignimbrite a supereruption that occurred in the campi flegrei area italy ca 39 ka had regional and global scale environmental impacts and deposited the campanian ignimbrite ci we attempt to shed light on critical aspects of the eruption depth of magma chamber intensive pre eruptive magma conditions and the large volume magma plumbing system on the basis of information derived from analyzing melt inclusion mi data to achieve these aims we provide new measurements of homogenization temperatures and values of dissolved h2o within phenocryst hosted mis from pumices erupted during different phases of the ci eruption the mi data indicate that a relatively homogeneous overheated trachytic magma resided within a relatively deep magma chamber dissolved water contents in mis indicate that prior to the eruption the magma chamber underwent radical changes related to differential upward movement of magma decompression of the rising trachytic magma caused a decrease in water solubility and crystallization and trachytic bodies were emplaced at very shallow depths the proposed eruptive model links portions of the main magma chamber and apophyses with specific eruptive units

structural setting of the bay of naples italy seismic reflection data implications for campanian volcanism abstract this paper focuses on the recent tectonic evolution of the bay of naples with the aim of exploring the connection between local tectonics and volcanism we reprocessed the seismic reflection dataset acquired in the area in the late 1973 the new processing was highly successful in obtaining a decisive strong reduction of random noise removal of coherent noise and reduction of spatial aliasing classical interpretative schemes and complex attributes of seismic traces were used to reconstruct fault kinematics and reflector patterns the results show that the faults affecting the bay of naples exhibit prevailing ne structural strikes with the exception of the pozzuoli caldera where nw patterns are also common many faults are subvertical and show seismic evidence of volcanic activity along them a main alignment of conjugate ne sw faults named here as magnaghi sebeto line intersects several submarine volcanic banks and separates the bay into two sectors characterized by important geological geophysical and petrochemical differences the structural configuration of the bay may reflect the occurrence of either oblique extension or a transfer zone of the nw se fault system along which in the campanian lucanian apennine chain great vertical displacements occur

statistical analysis and clustering features of the phlegraean fields earthquake sequence may 1983 may 1984 abstract the seismic activity at the phlegraean fields volcanic area southern italy during the period may 1983 may 1984 5 301 selected events has been analyzed from a statistical point of view the analysis of the time series associated to the microearthquakes shows a high degree of interdependence among the events the main feature being the occurrence of dense swarms the generalized poisson process provides a good fit for the sequence the clustering of the events has not substantially changed during the analyzed period while the mean rate of occurrence of the swarms has generally increased the distribution of the magnitudes within the swarms shows pronounced maxima of energy around the center of the subsequences in agreement with theoretical models of fractures in highly heterogeneous media

new gas geothermometers for geothermal exploration calibration and application calibration of five gas geothermometers is presented three of which used co2 h2s and h2 concentrations in fumarole steam respectively the remaining two use co2h2 and h2sh2 ratios the calibration is based on the relation between gas content of drillhole discharges and measured aquifer temperatures after establishing the gas content in the aquifer gas concentrations were calculated in steam formed by adiabatic boiling of this water to atmospheric pressure to obtain the gas geothermometry functions it is shown that the concentrations of co2 h2s and h2 in geothermal reservoir waters are fixed through equilibria with mineral buffers at temperatures above 230 c epidote prehnite calcite quartz are considered to buffer co2 two buffers are involved for h2s and h2 and two functions are therefore presented for the geothermometers involving these gases for waters containing less than about 500 ppm chloride and in the range 230 300 c pyrite pyrrholite epidote prehnite seem to be involved but pyrite epidote prehnite magnetite or chlorite for waters above 300 c and waters in the range 230 300 c if containing over about 500 ppm the gas geothermometers are useful for predicting subsurface temperatures in high temperature geothermal systems they are applicable to systems in basaltic to acidic rocks and in sediments with similar composition but should be used with reservation for systems located in rocks which differ much in composition from the basaltic to acidic ones the geothermometry results may be used to obtain information on steam condensation in upflow zones or phase separation at elevated pressures measured aquifer temperatures in drillholes and gas geothermometry temperatures based on data from nearby fumaroles compare well in the five fields in iceland considered specifically for the present study as well as in several fields in other countries for which data were inspected the results of the gas geothermometers also compare well with the results of solute geothermometers and mixing models in three undrilled icelandic fields

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

magma chamber evolution prior to the campanian ignimbrite and neapolitan yellow tuff eruptions campi flegrei italy the campi flegrei campanian region italy experienced two cataclysmic caldera forming eruptions which produced the campanian ignimbrite 39 ka ci and the neapolitan yellow tuff 15 ka nyt we studied the minor eruptions before both these large events to understand magma chamber evolution leading towards such catastrophic eruptions major trace element and sr and nd isotope compositions of pre campanian ignimbrite and pre neapolitan yellow tuff products define distinct geochemical groups which are here interpreted as distinct magma batches these batches do not show any transitional trend towards the ci and nyt eruptions the ci and nyt systems are decoupled geochemically and isotopically at least one of the pre ci and one of the pre nyt erupted magma batches qualifies as mixing endmembers for the large ci and nyt eruptions and thus must have been stored in reservoirs for some time to remain available for the ci and nyt eruptions the least evolved isotopically distinct magma compositions that are typical of the last phases of the nyt and ci eruptions did not occur before caldera forming events based on the new data we propose the following scenario multiple magma chambers with distinct compositions existed below the campi flegrei before the ci and nyt eruptions and remained generally separated for some time unless new magma was recharged in each case one of the residing magma reservoirs was recharged by a new large volume magma input of intermediate composition from a deeper differentiating magma reservoir this may have triggered the coalescence of the previously separated reservoirs into one large chamber which fed the cataclysmic caldera forming eruption large magma chambers in the campi flegrei may therefore be ephemeral features interrupted by periods of evolution in individual separated magma reservoirs

a geochemical and geophysical reappraisal to the significance of the recent unrest at campi flegrei caldera southern italy volcanic unrest at calderas involve complex interaction between magma hydrothermal fluids and crustal stress and strain campi flegrei caldera cfc located in the naples italy area and characterised by the highest volcanic risk on earth for the extreme urbanisation undergoes unrest phenomena involving several meters of uplift and intense shallow micro seismicity since several decades despite unrest episodes display in the last decade only moderate ground deformation and seismicity current interpretations of geochemical data point to a highly pressurized hydrothermal system we show that at cfc the usual assumption of vapour liquid coexistence in the fumarole plumes leads to largely overestimated hydrothermal pressures and accordingly interpretations of elevated unrest by relaxing unconstrained geochemical assumptions we infer an alternative model yielding better agreement between geophysical and geochemical observations the model reconciles discrepancies between what observed 1 for two decades since the 1982 84 large unrest when shallow magma was supplying heat and fluids to the hydrothermal system and 2 in the last decade compared to the 1980 s unrest the post 2005 phenomena are characterized by much lower aquifers overpressure and magmatic involvement as indicated by geophysical data and despite large changes in geochemical indicators our interpretation points out a model in which shallow sills intruded during 1969 1984 have completely cooled so that fumarole emissions are affected now by deeper co2 richer magmatic gases producing the modest heating and overpressure of the hydrothermal system our results have important implications on the short term eruption hazard assessment and on the best strategies for monitoring and interpreting geochemical data this article is protected by copyright all rights reserved

the volcanic and geothermally active campi flegrei caldera an integrated multidisciplinary image of its buried structure the campi flegrei caldera in southern italy is one of the greatest geohazard areas on earth evidence of an active magmatic and geothermal system is provided by ongoing ground uplift with volcano tectonic and long period lp seismicity the persistent degassing of 1500 tonnes of co2 per day the presence of hot fumaroles at temperatures of 90 150 c brine rich aquifers with total dissolved solids up to 33 g l 1 and high thermal gradients in the crust with temperatures reaching 420 c at 3 050 m b s l since the 1940s more than 100 exploratory boreholes have been drilled in the area to depths of 80 3 100 m by the azienda geologica italiana petroli agip and the societa anonima forze endogene napoletane safen to date however no systematic reanalysis of the drilling data has been carried out and the buried volcanic structure has not been updated using the most recent scientific results and previous findings by integrating unpublished data from the agip and safen reports with published information from geological volcanological petrological petrophysical and geophysical studies this paper presents an improved picture of the campi flegrei caldera that will be useful for volcanic hazard assessment and mitigation in the naples area and for future research planning the results suggest that intra caldera activity has been influenced by how the magmatic system at depths greater than about 4 km has determined the transfer of magma volatiles and heat to the overlying geothermal system and ultimately to the surface in particular intriguing is that the most volcanically active central eastern sector of the caldera which is subject to intense bradyseismic ground movement and gas emission coincides with a structurally delimited subsurface rock volume characterized by an uprising of the 100 c isotherm a deep water supply to the shallower aquifer the early disappearance of secondary calcite lp seismicity and high seismic s wave attenuation in this area we also document evidence of repeated injection at depths of c 1 5 3 0 km of isolated and small volume batches of magma where occurred their crystallization and degassing shallow intrusions and degassing of magma are thus identified as two of the key processes that drive unrest in campi flegrei

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

accurate fault mechanism determinations for a 1984 earthquake swarm at campi flegrei caldera italy during an unrest episode implications for volcanological research we have analyzed 42 microearthquakes 1 ml 3 that occurred at campi flegrei volcanic area during an intense swarm like activity more than 500 events in half a day in the last period of strong ground uplift 1982 1984 focal mechanisms of these earthquakes have been computed by a probability method which uses p wave polarity and s wave polarization data composite focal mechanisms for different groups of earthquakes have also been computed by the same technique results show a well defined fault plane in agreement with the elongation of the epicentral pattern the orientation and dip of this fault plane together with other observations about hypocenter locations and focal mechanisms of the whole seismicity accompanying the ground uplift episode suggest the presence of an elliptical fracture system at the caldera center this fracture system dipping toward the center of the caldera should represent the limit of the most recent caldera collapse which is also indicated by a negative bouguer gravity anomaly moreover an important differential feature among various groups of earthquakes has been shown namely a rotation up to about 30 of the strike of the compressive stress axis between the easternmost and the westernmost events the resulting pattern indicates that the axis is always oriented towards the town of pozzuoli which roughly represents the very center of the caldera and also the center of symmetry of the ground deformation these observations strongly suggest that earthquakes are generated by the variation of the stress field associated with the deformation along prefractured zones because of their greater weakeness this study provides then the first direct evidence that both seismicity and ground deformations have a common origin

the lithosphere asthenosphere system in the calabrian arc and surrounding seas southern italy a fairly detailed structural model of the lithosphere asthenosphere system thickness s and p wave velocities of the crust and of the uppermost mantle layers has been defined in the calabrian arc region southern tyrrhenian sea calabria and the northwestern part of the ionian sea in southern italy using seismic data from literature as a priori constraints of the nonlinear inversion of surface wave data

the age of the neapolitan yellow tuff caldera forming eruption campi flegrei caldera italy assessed by 40ar 39ar dating method abstract the neapolitan yellow tuff nyt is the product of the largest known trachytic phreatoplinian eruption it covered an area larger than 1000 km2 with an estimated volume of about 40 km3 of erupted magma during the course of the eruption a caldera collapsed within the previously formed campanian ignimbrite caldera the resulting nested structure strongly influenced the following volcanic activity in the campi flegrei caldera as previous dating of the nyt does not converge toward a unique result a new set of 40ar 39ar age determinations has been carried out to better constrain the age of the eruption two variants of the 40ar 39ar dating method were applied to determine the age of the nyt eruption 1 single crystal total fusion sctf on an individual phenocryst of feldspar and 2 laser incremental heating lih on bulk aliquots of feldspar phenocrysts the results of the sctf analyses show that the overall sample weighted mean age derived from the conventional age calculation is 15 6 0 8 ka a weighted mean of the isochron age is 15 3 1 2 ka 2 and has been assumed as the best indicator of age to be derived from the sctf analyses the lih analyses results show that plateau ages vary from 15 4 0 5 to 14 5 0 5 ka the overall weighted mean age of the isochron results is 14 9 0 4 ka 2 this result has been assumed as the reference age for the nyt eruption and agrees with the sctf age the new age obtained for the nyt deposits is of great relevance for the understanding of the evolution and the present state of the campi flegrei caldera and collocates the nyt in a crucial stratigraphical position to date the climatic oscillations that occurred between the late glacial and the holocene

geochemical and b sr nd isotopic evidence for mingling and mixing processes in the magmatic system that fed the astroni volcano 4 1 3 8 ka within the campi flegrei caldera southern italy abstract the astroni volcano was built through seven eruptions that generated pyroclastic deposits and lava domes within the campi flegrei caldera southern italy 4 1 3 8 ka bp whole rock geochemical and b sr nd isotopic investigations were carried out on representative samples of all seven eruptions the products vary from tephriphonolites to phonolites and from latites to trachytes they show textural mineralogical and isotopic evidence of disequilibrium including distinct clinopyroxene populations rounded and or resorbed plagioclase and alkali feldspar and reverse zoned phenocrysts of all these mineral phases the sr nd and b isotopic composition of whole rocks is variable and correlated with the degree of chemical evolution suggesting open system processes in addition to fractional crystallisation moreover significant sr isotopic disequilibrium between the phenocrysts and glass has been documented for one sample the chemostratigraphy of the products indicates that astroni eruptions 1 through 5 were fed by magmas of trachytic to phonolitic composition that were less enriched in radiogenic sr and 11b up section this variability has been interpreted as the result of mingling between at least two distinct magmatic end members one more evolved and the other less evolved another heterogeneous batch of magma resulting from almost complete mixing between the same two end members was drained during eruptions 6 and 7 the more evolved end member characterised by 87sr 86sr 0 7075 143nd 144nd 0 51247 and 11b 8 was very similar to the magma that fed the final phases of the agnano monte spina eruption which occurred a few centuries earlier in the astroni vent area the less evolved end member had 87sr 86sr 0 70726 143nd 144nd 0 51251 and 11b 10 and was likely derived by fractional crystallisation of a mantle derived magma an abrupt decrease in both the sr isotope ratio and the th content detected at the transition between unit 4 and 5 suggests that another magma with a 87sr 86sr ratio intermediate between those of the two identified end members may have been involved in astroni activity the more evolved end member is interpreted as a residue of the agnano monte spina eruption that was invaded by either the intermediate or the less evolved magmatic end member promoting mingling and triggering astroni activity this study of astroni provides insights for both short and long term volcanic hazard assessment as the astroni volcano is the best example of a very close sequence of eruptions from the same vent area in the campi flegrei caldera

intrusion and deformation at campi flegrei southern italy sills dikes and regional extension 1 the campi flegrei volcanic district in southern italy has been uplifted since 1968 by a net maximum of 3 m during the intervals 1968 1972 and 1982 1984 the uplift represents a permanent deformation against a background rate of subsidence of about 17 mm a 1 previous models have reproduced the observed vertical deformation but not the full pattern of horizontal movements the 1982 1983 deformation is here reanalyzed in terms of a penny shaped sill on its own with a tabular surface protrusion or in an extensional stress field it can be explained best by the intrusion of a sill of 0 03 0 04 km3 at a depth of 2 75 km in a crust that is being stretched ese wnw at a strain rate of about 5 6 10 5 a 1 the sill s volume is similar to the common volumes of campi flegrei s eruptions since the neapolitan yellow tuff nyt caldera was formed 15 6 ka ago this similarity and the permanent nature of the uplift favor magmatic intrusion as the primary source of unrest sill formation may thus reflect the spreading of magma at a level of neutral buoyancy or along lateral discontinuities in the crust the southern part of the caldera has been shielded from post nyt eruptions despite some 33 m of permanent uplift since roman times precursors to eruptions may thus be related not to caldera wide uplift but to the preceding conditions that determine whether magma ascends beneath the southern part of the caldera favoring sill intrusion or elsewhere favoring an eruption

the role of transfer structures on volcanic activity at campi flegrei southern italy abstract the tyrrhenian margin of central italy underwent extension during pliocene and quaternary extension occurred mainly through nw se normal faults bordering a sequence of plio quaternary basins these basins are offset by coeval ne sw faults which show strike slip and normal motions and have been interpreted as transfer faults plio quaternary volcanic activity along the margin occurred along a nw se belt systematically in correspondence with ne sw transverse systems the campi flegrei volcanic district cfvd on the southern tyrrhenian margin consists of an active ne sw volcanic ridge developed along ne sw fractures we performed a structural field analysis with analogue and mechanical models to investigate the role of transverse structures upon volcanism at campi flegrei field analysis at campi flegrei recognized ne sw and to a lesser extent coeval nw se active fractures analogue experiments have simulated the development of transfer fault systems in brittle extensional domains the experiments show that subvertical transfer faults connect offset adjacent normal faults dipping 60 the mechanical model is based on the stress equations in uniaxial lithostatic conditions and absence of regional stresses it shows how pre existing subvertical fractures require the smallest magmatic pressures to be penetrated for a given magmatic pressure subvertical fractures might be penetrated more deeply tapping more easily primitive magmas these results suggest that the cfvd is located along a ne sw transfer zone connecting nw se regional normal faults volcanic activity along such ne sw trend would be induced by the subvertical dip of the transfer faults the subvertical dip of transfer faults also suggests an explanation for the emission of the more primitive products along ne sw systems at campi flegrei these considerations find a wider application on the remaining volcanic districts of the margin located in the same overall structural setting

deformation regime and long term precursors to eruption at large calderas rabaul papua new guinea eruptions at large calderas are normally preceded by variable rates of unrest that continue for decades or more a classic example is the 1994 eruption of rabaul caldera in papua new guinea which began after 23 years of surface uplift and volcano tectonic vt seismicity at rates that changed unevenly with time by an order of magnitude although the vt event rate and uplift rate peaked in 1983 1985 eruptions only began a decade later and followed just 27 hours of anomalous changes in precursory signal here we argue that the entire 23 years of unrest belongs to a single sequence of damage accumulation in the crust and that in 1991 1992 the crust s response to applied stress changed from quasi elastic elastic deformation with minor fault movement to inelastic deformation predominantly by fault movement alone the change in behaviour yields limiting trends in the variation of vt event rate with deformation and can be quantified with a mean field model for an elastic crust that contains a dispersed population of small faults the results show that identifying the deformation regime for elastic brittle crust provides new criteria for using precursory time series to evaluate the potential for eruption they suggest that in the quasi elastic regime short term increases in rates of deformation and vt events are unreliable indicators of an imminent eruption but that in the inelastic regime the precursory rates may follow hyperbolic increases with time and offer the promise of developing forecasts of eruption as much as months beforehand

the campi flegrei deep drilling project cfddp new insight on caldera structure evolution and hazard implications for the naples area southern italy the 501 m deep hole of the campi flegrei deep drilling project located west of the naples metropolitan area and inside the campi flegrei caldera gives new insight to reconstruct the volcano tectonic evolution of this highly populated volcano it is one of the highest risk volcanic areas in the world but its tectonic structure eruptive history and size of the largest eruptions are intensely debated in the literature new stratigraphic and 40ar 39ar geochronological dating allow us to determine for the first time the age of intracaldera deposits belonging to the two highest magnitude caldera forming eruptions i e campanian ignimbrite ci 39 ka and neapolitan yellow tuff nyt 14 9 ka and to estimate the amount of collapse tuffs from 439 m of depth yield the first 40ar 39ar age of ca 39 ka within the caldera consistent with the ci volcanic rocks from the nyt were moreover detected between 250 and 160 m our findings highlight i a reduction of the area affected by caldera collapse which appears to not include the city of naples ii a small volume of the infilling caldera deposits particularly for the ci and iii the need for reassessment of the collapse amounts and mechanisms related to larger eruptions our results also imply a revaluation of volcanic risk for the eastern caldera area including the city of naples the results of this study point out that large calderas are characterized by complex collapse mechanisms and dynamics whose understanding needs more robust constraints which can be obtained from scientific drilling

chemical and isotopic compositions of minerals and waters from the campi flegrei volcanic system naples italy abstract based on their 34 s signature sulfate minerals and native sulfur around fumaroles and hot water pools from the campi flegrei volcanic area derive from supergenic oxidation of volcanic h 2 s their mean 34 s value 0 2 1 7 matches with that of fumarolic h 2 s at solfatara 0 3 0 3 as well as with the 34 s of 1 4 obtained for total sulfur in fresh trachyte from the area all 34 s values indicate a mostly deep seated origin for sulfur thermal waters were analysed for major and minor chemistry and for oxygen hydrogen and sulfur isotope compositions pools at pisciarelli are filled with evaporated meteoric water heated by rising magmatic gases the water 18 o 3 8 1 3 and 2 h 6 5 2 2 values in these steam heated waters are controlled by mixing and evaporation effects and the 34 s value of dissolved sulfate 1 3 0 3 basically agrees with supergenic oxidation of deep seated h 2 s as the major source of sulfur instead water from thermal springs and wells elsewhere in the campi flegrei appears to be a mixture between dilute meteoric and saline marine components the latter may be local seawater from the bay of pozzuoli the 18 o and 2 h values of waters sampled during 1993 1994 range from 5 6 to 0 3 and from 33 to 3 4 respectively the 34 s values of dissolved sulfate range between 0 1 and 19 5 in general sulfate is probably derived essentially from two sources both within the volcanic cover i e oxidation dissolution of pyrite and anhydrite and marine water an occasional source of water and sulfate is represented by magmatic gases which directly interact with shallow meteoric water as in the case of the hotel tennis well yielding steam heated water with 18 o 1 5 0 2 2 h 17 1 and 34 s 0 1

understanding the seismic velocity structure of campi flegrei caldera italy from the laboratory to the field scale we report laboratory measurements of p and s wave velocities on samples of tuff from campi flegrei italy and a new tomographic velocity map of the campi flegrei caldera laboratory measurements were made in a hydrostatic pressure vessel during both increasing and decreasing effective pressure cycles selected samples were also thermally stressed at temperatures up to 600 c to induce thermal crack damage acoustic emission output was recorded throughout each thermal stressing experiment and velocities were measured after thermal stressing laboratory p and s wave velocities are initially low for the tuff which has an initial porosity of 45 but both increase by between 25 and 50 over the effective pressure range of 5 to 80 mpa corresponding to a decrease of porosity of 70 marked velocity hysteresis due to inelastic damage processes is also observed in samples subjected to a pressurization depressurization cycle tomographic seismic velocity distributions obtained from field recordings are in general agreement with the laboratory measurements integration of the laboratory ultrasonic and seismic tomography data indicates that the tuffs of the campi flegrei caldera can be water or gas saturated and shows that inelastic pore collapse and cracking produced by mechanical and thermal stress can significantly change the velocity properties of campi flegrei tuffs at depth these changes need to be taken into account in accurately interpreting the crustal structure from tomographic data

merging active and passive data sets in traveltime tomography the case study of campi flegrei caldera southern italy we propose a strategy for merging both active and passive data sets in linearized tomographic inversion we illustrate this in the reconstruction of 3d images of a complex volcanic structure the campi flegrei caldera located in the vicinity of the city of naples southern italy the caldera is occasionally the site of significant unrests characterized by large ground uplifts and seismicity the p and s velocity models of the caldera structure are obtained by a tomographic inversion based on travel times recorded during two distinct experiments the first data set is composed of 606 earthquakes recorded in 1984 and the second set is composed of recordings for 1528 shots produced during the serapis experiment in 2001 the tomographic inversion is performed using an improved method based on an accurate finite difference traveltime computation and a simultaneous inversion of both velocity models and earthquake locations in order to determine the adequate inversion parameters and relative data weighting factors we perform massive synthetic simulations allowing one to merge the two types of data optimally the proper merging provides high resolution velocity models which allow one to reliably retrieve velocity anomalies over a large part of the tomography area the obtained images confirm the presence of a high p velocity ring in the southern part of the bay of pozzuoli and extends its trace inland as compared to previous results this annular anomaly represents the buried trace of the rim of the campi flegrei caldera its shape at 1 5 km depth is in good agreement with the location of hydrothermalized lava inferred by gravimetric data modelling the vp vs model confirms the presence of two characteristic features at about 1 km depth a very high vp vs anomaly is observed below the town of pozzuoli and is interpreted as due to the presence of rocks that contain fluids in the liquid phase a low vp vs body extending at about 3 4 km depth below a large part of the caldera is interpreted as the top of formations that are enriched in gas under supercritical conditions

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

geochemical monitoring of the thermal waters of the phlegraean fields abstract thermal waters from the phlegraean fields pf caldera area have been periodically sampled and analysed during the period 1990 1999 for major chemical constituents and chemico physical parameters to define the most useful variables for geochemical surveillance the variations observed in waters from different locations were compared with ground movements and microseismic events recorded at the time of observation the discontinuous monitoring of the hydrothermal system of the pf has given indications about the geochemical variations brought about by changes in the chemical and physical characteristics of the deep aquifers because of the complexity of the pf geothermal system in each sampling location different variations have been observed and then evaluated on the basis of the different kinds and degrees of deep fluid supply characterising waters sampled in the different zones in some cases a good correspondence between vertical soil movements and chemical changes in the waters has been observed in particular in pools and wells located around the solfatara crater interesting variations in some chemical parameters ph ammonia and or so 4 2 cl ratios have been recorded variations can be observed in all of the sampling locations but pools and wells located near the solfatara crater are the best sites for detecting changes occurring in the deep hydrothermal system and possibly in the activity of the underlying magma chamber

the averno 2 fissure eruption a recent small size explosive event at the campi flegrei caldera italy the averno 2 eruption 3 700 50 a b p was an explosive low magnitude event characterized by magmatic and phreatomagmatic explosions generating mainly fall and surge beds respectively it occurred in the western sector of the campi flegrei caldera campanian region south italy at the intersection of two active fault systems oriented ne and nw the morphologically complex crater area largely filled by the averno lake resulted from vent activation and migration along the ne trending fault system the eruption generated a complex sequence of pyroclastic deposits including pumice fall deposits in the lower portion and prevailing surge beds in the intermediate upper portion the pyroclastic sequence has been studied through stratigraphical morphostructural and petrological investigations and subdivided into three members named a through c member a was emplaced during the first phase of the eruption mainly by magmatic explosions which generated columns reaching a maximum height of 10 km during this phase the eruption reached its climax with a mass discharge rate of 3 2 106 kg s intense fracturing and fault activation favored entry of a significant amount of water into the system which produced explosions driven by variably efficient water magma interaction these explosions generated wet to dry surge deposits that emplaced member b and c respectively isopachs and isopleths maps as well as areal distribution of ballistic fragments and facies variation of surge deposits allow definition of four vents that opened along a ne oriented 2 km long fissure the total volume of magma extruded during the eruption has been estimated at about 0 07 km3 dre the erupted products range in composition from initial weakly peralkaline alkali trachyte to last emplaced alkali trachyte isotopic data and modeling suggest that mixing occurred during the averno 2 eruption between a more evolved less radiogenic stored magma and a less evolved more radiogenic magma that entered the shallow reservoir to trigger the eruption the early phases of the eruption during which the vent migrated from sw to the center of the present lake were fed by the more evolved uppermost magma while the following phases extruded the less evolved lowermost magma integration of the geological and petrological results suggests that the averno 2 complex eruption was fed from a dyke shaped shallow reservoir intruded into the ne sw fault system bordering to the west the la starza resurgent block within the caldera floor

a proposal for the kinematic modelling of w dipping subductions possible applications to the tyrrhenian apennines system in w dipping subduction zones there is a general eastward progression of the back arc basin accretionary wedge foredeep complex with the forward progression early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle a major shear zone should form at the new moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle the mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt the retreating of the subduction hinge is interpreted as due to the push generated by the eastward mantle flow detected in the hot spot reference frame the foredeep depth is mainly a function of the radius of curvature of the subduction hinge the frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension in order to preserve volume balance the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates laterally stretched subducted lithosphere is predicted at depth w dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere the thin back arc which are a key factor in controlling and generating new subductions both e and w dipping this model is applied to the apennines tyrrhenian sea system

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

seismicity associated with the 2004 2006 renewed ground uplift at campi flegrei caldera italy abstract following the significant ground uplift 1 8 m of the 1982 1984 bradyseismic crisis the recent history of campi flegrei volcanic complex italy has been dominated by a subsidence phase recent geodetic data demonstrate that the subsidence has terminated and that positive ground deformation renewed in november 2004 at a low but accelerating rate leading to about 4 cm of uplift by the end of october 2006 as in previous episodes ground uplift has been accompanied by swarms of micro earthquakes m 1 4 in three distinct episodes october 2005 october 2006 and december 2006 hypocenters of these earthquakes are mainly located beneath the solfatara volcano at depths ranging between 0 5 and 4 km inversion of s wave spectra indicates source radius and stress drop on the order of 30 60 m and 104 9 105 pa respectively fault plane solutions indicate predominantly normal mechanisms accompanying the october 2006 swarm we detected intense long period lp activity for about 1 week these signals consist of weak monochromatic oscillations whose spectra exhibit a main peak at frequency 0 8 hz this peak is common to all the stations of the network and not present in the noise spectra suggesting that it is a source effect about 75 of the detected lps cluster into three groups of mutually similar events adjustment of waveforms using cross correlation allows for precise alignment and stacking which enhances signal onsets and permits accurate absolute arrival picks and thus better absolute as well as relative locations locations associated with the three different clusters are very similar and appear to delineate the se rim of the solfatara volcano at a depth of about 500 m the most likely source process for the lp events involves the resonance of a fluid filled buried cavity quality factors of the resonator cluster in a narrow interval around 4 which is consistent with the vibration of a buried cavity filled with a water vapour mixture at poor gas volume fractions we propose a conceptual model to interpret the temporal and spatial patterns of the observed seismicity

three dimensional seismic image of a geothermal reservoir the geysers california three dimensional seismic travel time tomography of the geysers geothermal area in the coast ranges of northern california shows a strong 9 anomaly in vp vs the ratio of the compressional and shear wave speeds that is not evident in vp alone and corresponds closely to the most intensively exploited part of the geothermal reservoir this anomaly probably indicates low pore pressure and relatively dry conditions caused partly by boiling of pore water as steam is extracted steam pressure decreases over the last decade have probably caused seismologically measurable changes in wave speeds tomographic measurement of vp vs is a promising technique both for identifying geothermal resources and for monitoring them during exploitation

three dimensional kernel based coda attenuation imaging of caldera structures controlling the 1982 84 campi flegrei unrest abstract coda wave attenuation imaging has risen as a state of the art technique to depict volcanic structures using their dispersion effects the 1982 84 seismic and deformation unrest at campi flegrei caldera italy is a unique example of non eruptive volcanic activity in a structured caldera here we propose the first application of 3d coda attenuation kernels to image caldera structures at multiple frequencies during unrest using sensitivity kernels is necessary to assess the effective resolution of coda imaging in highly heterogeneous volcanoes the technique relies on the solution of paasschens equations in the framework of radiative transfer theory the results map coda attenuation in the 3d space without need of pre existent velocity models the resolution and stability of the inversion solutions were examined by changing the damping parameters and outputting the corresponding images inverting for different node spacings and performing checkerboard tests these tests show that the resolution of the multiple scattering model is much lower than that provided by a standard isotropic scattering and or single scattering technique the best resolution in our model is obtained between depths of 1 km and 3 km in the centre of the model between pozzuoli town and solfatara crater the results are discussed at a frequency of 3 hz due to both longer coda durations and broader kernel illumination in this frequency range coda based 3d imaging had so far failed to provide stable results the interpretation is performed based on the extensive geological and geophysical knowledge of the caldera high attenuation anomalies below solfatara and monte nuovo mark areas either saturated with water or enriched in molten rocks feeding the respective fumarole fields the flattening and horizontal elongation of these anomalies below 2 km depth is a manifestation of the blocking and spreading around of the rising hot magmatic fluids below a previously inferred high velocity low attenuation and highly deforming caprock this caprock is not uniform likely due to the remnants of erupted structure a sw to ne trending low attenuation and high velocity anomaly deeps down to 3 km under pozzuoli we infer that the high seismicity in the region is a consequence of the stress sustained by the caprock from a 4 km deep deformation source in 1983 84 on top of this source high coda attenuation corresponds to high vp vs ratios and high direct wave attenuation the region s characteristics are likely due to the accumulation of magmatic fluids above a magmatic sill

seismic images and rock properties of the very shallow structure of campi flegrei caldera southern italy in september 2001 an extensive active seismic investigation serapis experiment was carried out in the gulfs of naples and pozzuoli with the aim of investigating and reconstructing the shallow crustal structure of the campi flegrei caldera and possibly identifying its feeding system at depth the present study provides a joint analysis of the very shallow seismic reflection data and tomographic images based on the serapis dataset this is achieved by reflection seismic sections obtained by the 3d data gathering and through refined p velocity images of the shallowest layer of pozzuoli gulf z 3 500 m s correlates with units made up of agglomerate tuffs and interbedded lava which form the southern edge of the caldera which was probably formed following the two large ignimbritic eruptions that marked the evolutionary history of the area under study the upper part of the anomaly that tends to split into two parallel arcs is correlated with dikes volcanic mounds and hydrothermal alteration zones noted in previous shallow reflection seismic analyses the depth of the transition between the upper and lower parts of the anomaly is characterized by an abrupt vp increase on the one dimensional 1d profiles extracted from the 3d tomographic model and by the presence of a strong reflector located at about 0 6 0 7 s two way time twt on common mid point gathers the move out velocity analysis and stack of the p p and p s reflections at the layer bottom allowed to estimate relatively high vp vs values 3 7 0 9 this hypothesis has been tested by a theoretical rock physical modeling of the vp vs ratio as a function of porosity suggesting that the shallow layer is likely formed by incoherent water saturated volcanic and marine sediments that filled pozzuoli bay during the post caldera activity

calc silicate mineralization in active geothermal systems detailed study of the calc silicate mineralogy in the cerro prieto geothermal system was used to demonstrate examples for thermodynamic evaluation of phase relations among minerals of variable composition and to calculate the chemical characteristics of hydrothermal solutions compatible with the observed calc silicate assemblages in general there is a close correlation between calculated and observed fluid compositions calculated fugacities of o 2 at about 320 degrees c in the cerro prieto geothermal system are about five orders of magnitude less than those at the nearby salton sea geothermal system this observation is consistent with the occurrence of fe super 3 rich epidotes and andradite garnets in the latter system and the presence of prehnite at cerro prieto modified journal abstract

significance of the 1982 2014 campi flegrei seismicity preexisting structures hydrothermal processes and hazard assessment we find that the double difference relocated seismicity which occurred over the last 30 years at campi flegrei was triggered by the uprising of fluids preferentially concentrated along onshore and offshore nw striking preexisting caldera faults focal volumes of the 2005 2014 seismicity do not overlap that of the 1982 1984 period when a major uplift of 1 8 m occurred in the central sector of the caldera this indicates a transition from an elastic to a plastic behavior due to fluid saturation and heating of the rocks in the hydrothermal reservoir the 2012 2014 deeper earthquakes are located in a low vp vs zone at the western boundary of the hydrothermal reservoir where a volume increase from a magmatic body at 3 5 km depth has been recognized the progressive rheological change from elastic to plastic in the upper 4 km of the crust implies that a slow upward migration of magma may not necessarily be preceded by earthquakes or swarms

chemical and isotopic signatures of the basement rocks from the campi flegrei geothermal field naples southern italy inferences about the origin and evolution of its hydrothermal fluids abstract the campi flegrei naples campanian plain southern italy geothermal system is hosted by quaternary volcanic rocks erupted before during and after the formation of the caldera that represents one of the major structural features in the neapolitan area the volcanic products rest on a mesozoic carbonate basement cropping out north east and south of the area chemical major minor and trace elements and stable isotope c h o analyses were conducted on drill core samples recovered from geothermal wells mf 1 mf 5 sv 1 and sv 3 at depths of 1100 to 2900 m the study was complemented by petrographic and sem examination of thin sections the water which feeds the system is both marine and meteoric in origin mineral zonation typical of a high temperature geothermal system exists in all the geothermal wells measured temperatures in wells are as high as 400 c the chemical composition of the waters suggests the existence of two reservoirs a shallow reservoir depth 2000 m of hypersaline water the drill cores are mainly hydrothermally altered volcanics of trachy latitic affinity but some altered pelites and limestones are also present published na mg and k concentrations of selected geothermal waters indicate that the hydrothermal fluids are in equilibrium with their host rocks with respect to k feldspar albite sericite and chlorite the measured 18 o smow values of rocks range from 4 3 to 16 5 the measured d smow values range from 79 to 46 the calculated isotopic composition of the fluids at equilibrium with the samples vary from 1 to 8 3 18 o and from 52 to 1 d the estimated isotopic composition of the waters at equilibrium with the studied samples confirmed the existence of two distinct fluid types circulating in the geothermal system the shallower has a marine water signature while the deeper water has a signature consistent both with magmatic and meteoric origins in the latter case the recharge of this aquifer likely occurs at the outcrop of the mesozoic limestones surrounding the campanian plain after infiltration the water percolates through evaporitic layers becoming hypersaline and d depleted

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 bay of naples southern italy constraints on the volcanic structures inferred from a dense seismic survey 1 the bays of naples and pozzuoli host volcanic areas that have been active within recent history in addition the vicinities areas around the vesuvius volcano and the campi flegrei caldera are extremely densely inhabited over the past decade this situation has prompted several active seismic experiments focused on the vesuvius volcano more recently the serapis active seismic survey covered the entire bay of naples with particular attention to pozzuoli bay the processed serapis p wave travel time collection extended with a previously acquired data set has allowed the computation of the most comprehensive three dimensional p wave velocity distribution for the bay of naples which includes a small scale high resolution model of the campi flegrei caldera the joint interpretation of the velocity distribution together with both the available gravity measurements and models and the geothermal drilling information has allowed us to locate and map lithological units at depths we propose a model of the campi flegrei caldera in relation to the underlying mesozoic limestone unit in this model no magma chamber exists in the upper 6 km beneath the bay of naples the feeding system of the campi flegrei caldera is directly controlled by the tectonic structures affecting the limestone unit beneath the bay of naples two ne sw normal faults run beneath the vesuvius volcano and campi flegrei which are related to the pre pleistocene apenninic tectonics

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

structure and evolution of the bay of pozzuoli italy using marine seismic reflection data implications for collapse of the campi flegrei caldera digital marine seismic reflection data acquired in 1973 in the bay of pozzuoli and recently reprocessed were used to study the volcanological evolution of the marine sector of campi flegrei caldera during the last 37 ka in order to gain more information interpretation also involved estimation of the pseudo velocity and the pseudo density from the resistivity logs of two onshore deep exploration wells the main results are 1 discovery of ancient pre 18 ka and post 37 ka submarine and mainly effusive volcanic activity along coeval emission centers located at the edges of campi flegrei caldera 2 confirmation that the caldera collapse in the marine sector of campi flegrei seems strongly controlled by regional ne sw and nw se structural discontinuities 3 the finding of at least two episodes of collapse in the bay and 4 identification of a post 18 ka volcanic deflation phase that has caused about 150 200 m of subsidence in the central sector of the bay of pozzuoli in the last 18 ka

active deformation and volcanism offshore campi flegrei italy new data from high resolution seismic reflection profiles abstract the interpretation of high resolution seismic reflection profiles permitted the identification of many geologic features in the inner shelf of pozzuoli bay this area corresponds to the offshore of campi flegrei a classically active volcanic area that experienced earthquakes and meter scale vertical ground uplift before the 1538 monte nuovo eruption and in the period from 1970 to 1985 the detected undersea features include two small debris flows that are located in a submarine valley in the western part of pozzuoli bay they may be the result of a pyroclastic flow and a pyroclastic surge that entered the sea the younger debris flow in the uppermost marine deposits of pozzuoli bay formed during the 1538 monte nuovo eruption and the older debris flow during the 3 8 ka old averno eruption other features detected by our survey are an undersea 8 m high and 1 km wide cryptodome corresponding to a near surface intrusion located off pozzuoli that warped post 4 ka marine deposits the interpretation of the cryptodome is based on seismic facies analysis deformation geometry and correspondence to a magnetic high it is suggested that this undersea dome formed during the uplift phases associated with the 1538 monte nuovo eruption and the two more recent bradyseismic crises of 1970 1972 and 1982 1984 surface breaking faults with maximum vertical offset of 1 m were recognized in very shallow waters near the coast of pozzuoli it is suggested that some of these faults were active during the 1982 1984 bradyseismic earthquake sequence

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

the sieving of heavy mineral sands abstract an investigation has been undertaken of the sieving of natural heavy mineral sands from a beach placer to determine the effects of the differing shapes of the several mineral types the measurements agree with an equation derived by sahu 1965 based on the passage of ellipsoidal grains through a square sieve opening demonstrating that the ratio of the grain s smallest axial diameter dc to its intermediate diameter db controls grain passage through the sieves empirical relationships are established between the average db values of the grains and the sieve size on which they are captured during sieving these relationships are sufficiently close to that for quartz grains to conclude that there would be little separation of the several minerals by s ape during the sieving process the results further permit evaluations of the db distributions of the heavy mineral sands rather than the standard practice of reporting distributions in terms of sieve sizes

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

source parameters and three dimensional attenuation structure from the inversion of microearthquake pulse width data qp imaging and inferences on the thermal state of the campi flegrei caldera southern italy the three dimensional p wave attenuation structure of the campi flegrei caldera and the estimate of source parameters for 87 local microearthquakes is obtained by the nonlinear inversion of pulse width and rise time measurements by using the method described by zollo and de lorenzo this issue source radii represent the better resolved parameters with values ranging from 70 m to 230 m the dip and strike angles defining fault orientations are usually affected by larger uncertainties and are well constrained only for 11 events the dip fault is usually confined in the range 30 60 with an average uncertainty of 12 the fault strikes mainly range between 60 and 60 and seem to define preferential directions oriented radially from the symmetry axis of the ground deformation stress drop estimates indicate rather low values 0 01 1 mpa which suggest low strength properties of the incoherent and brittle materials filling the caldera primarily yellow tuffs the three dimensional qp images obtained from the inversion of p pulse durations show two significant low qp anomalies between 0 and 1 km of depth in the north eastern sector and at 2 3 km of depth in the central eastern sector of the caldera the high degree of spatial correlation of the low qp zone and low vs as inferred by aster and meyer 1988 at 0 1 km in depth and other geophysical and geochemical observations suggest that this anomaly can be related to the presence of densely fractured porous and fluid filled rocks in the ne sector of the caldera the deeper low qp anomaly is interpreted as being related to a dominant thermal effect we used the surface and deep borehole temperature measurements available in the area to obtain a local calibration curve to convert qp in temperature at campi flegrei the retrieved t qp map shows a high thermal deep disturbance 450 500 c at depths between 2 and 3 km in the eastern sector of the caldera where the most recent eruptive activity is concentrated the present day temperature field retrieved by qp images has been interpreted by using a three dimensional thermal conduction model assuming an extended heat source initial temperature of 800 c located underneath the attenuation anomalous region the results indicate that the qp inferred temperature field can be related to the heat conduction effect of one or more molten bodies whose top should be at about 4 km depth consistent with recent seismic estimates of the magma chamber top at campi flegrei ferrucci et al 1992 this study suggests that the present thermal state and rock rheology of the inner caldera could be controlled by the cooling of molten bodies that originally intruded at depths of 1 4 1 6 km during one or more recent time of 10 kyr eruptive events

upper mantle properties of the tuscan tyrrhenian area a framework for its recent tectonic evolution abstract within the alpine mediterranean deformational system several interesting features in the physical properties of the upper mantle have been recognized through the regional analysis of surface wave dispersion a large upper mantle anomaly uma here called the tuscan uma has been identified in the area northeast of corsica which includes part of the northern tyrrhenian sea and part of the north central apennines this anomalous upper mantle area together with the upper mantle characteristics of the tyrrhenian sea located further to the south provides a natural framework for comprehensive interpretation of the large data set of geological and geophysical observations such as land and marine geology volcanism gravity magnetic data seismic data and seismology deep temperatures and surface heat flow

a geochemical and sedimentological perspective of the life cycle of neapolis harbor naples southern italy since the discovery of the ancient harbor of naples in 2004 during construction work on an underground railway geoarchaeological studies undertaken on the archaeological excavation have revealed the main stratigraphic and paleo environmental levels of the harbor site near the piazza municipio however knowledge of the dynamics and paleoenvironmental changes in the water column of the harbor as well as the processes of transport and deposition of sediments that led to siltation and infilling of the harbor basin has been lacking due to the absence of high resolution data to fill these gaps we have undertaken a threedimensional study longitudinal transverse and vertical of the harbor deposits by carrying out geochemical and sedimentological analyses of four stratigraphic sections of the archaeological excavation the results show that after a phase of relative calm during the first half of the 1st c ad siltation of the harbor progressed exponentially up to the 5th c ad when dredging operations were carried out to obtain a water level sufficient for the development of maritime and harbor activities we attribute this acceleration of siltation to a combination of climatic anthropic and volcanic factors volcanic activity was responsible for a high energy tsunami type event during the eruption of vesuvius in 79 ad from the 5th c ad onwards the harbor basin of neapolis does not appear to have been functional as evidenced by its transformation into a lagoon following coastal progradation the last stage of infilling was the development of a flood dominated fan delta under the combined influences of climatic cooling in the early medieval cool period and agro pastoral activities in the catchment area of the harbor several generations of paleo channels containing flash flood deposits as well as sheet wash from sheet floods are indicative of high environmental instability in this period

ground deformation at campi flegrei italy implications for hazard assessment campi flegrei caldera west of naples in southern italy has an exceptional documented record of ground deformation from roman times onwards systematic recording began in the nineteenth century for earlier dates information has been obtained from archaeological studies and from contemporary descriptions of the locations of buildings usually roman with respect to sea level especially important have been accounts related to the serapis a roman market place built in the second century bc and now incorporated within the modern town of pozzuoli the long term patterns of ground deformation have conventionally been investigated on the premise that campi flegrei naturally tends to a state of static equilibrium this study argues that instead the area naturally tends to a steady rate of subsidence at about 17 mm a 1 after this background rate has been removed the data indicate that a permanent uplift of some 33 m has occurred from roman times up until the present day 2005 at the time of writing attributable to the intrusion of 1 85 km3 of magma of which only 1 has been erupted uplift has occurred in three episodes the third of which is still in progress the behaviour can be interpreted in terms of the intermittent ascent of magma between a reservoir of c 102 103 km3 at depths of 8 15 km or greater to a much smaller shallower system at depths of about 3 4 km should the current pattern of deformation follow previous trends uplift is expected to continue for another 80 90 years during whieh time campi flegrei will be characterized by an elevated possibility of eruption the geological society of london

laboratory measurements of ultrasonic wave velocities in rocks from the campi flegrei volcanic system and their relation to other field data the campi flegrei caldera located near the city of naples italy has shown signs of unrest characterized by large ground deformation seismic activity and changes in the hydrothermal system since 1970 any attempt to model the processes giving rise to these phenomena requires some knowledge of the subsurface structure and of the physical properties of the rocks at depth in this study we report the results of laboratory measurements of ultrasonic compressional and shear wave velocities in rock samples cored in 4 different geothermal wells reaching a maximun depth of 3 km the wells are located in the san vito sv and mofete mf areas at about 3 km north and 4 km west respectively from the center of the caldera we selected 10 core samples 7 from the sv wells and 3 from the mf wells the attention being focused on the most important rock formations underneath campi flegrei and on the lower sections of the wells where data had been lacking the measurements involved the transmission of ultrasonic waves along three orthogonal directions through dry and water saturated rocks at room conditions the samples are only moderately anisotropic 13 for one sv sample and 8 for all the other samples wave velocities generally increase with the depth of the sample the range of velocities is 3 5 4 km s 1 for p waves and 1 5 2 9 km s 1 for s waves for the sv samples water saturation generally implies slightly larger 10 vp values and smaller 20 vs values as compared with dry velocities for the mf samples water saturation implies both higher vp and vs velocities up to 35 and 18 respectively these results may be explained by the different type of porosity of the sv samples vesicular and the mf samples fissurai the ultrasonic measurements on water saturated samples are slightly higher than the available in situ vp sonic measurements 25 for one sv sample and 15 for all the other samples these differences can be explained by velocity dispersion between ultrasonic and sonic frequencies and by the different pressure temperature conditions existing at depth

3d scattering image of the campi flegrei caldera southern italy new hints on the position of the old caldera rim abstract a scattering image of the campi flegrei caldera has been obtained using coda wave envelopes from local microearthquake data recorded at a portable 12 station digital network this was operated during the paroxysmic phase of the ground uplift bradyseism that occurred in the years 1983 1984 the nishigami technique has been used to obtain the 3d distribution of the strong scatterers in an earth volume with a horizontal extension of 20 km 20 km and a vertical thickness of 6 km this earth volume was segmented in blocks of 2 km 2 km 2 km for the outer section and in blocks of 1 km 1 km 1 km for the inner section the inversion was performed using a hybrid jackknife svd method that has allowed qualitative control of the stability and robustness of the solution the results show that the scatterers revealed by the coda envelopes which were band pass filtered at a center frequency of 18 hz match the inner border of the caldera rim which is well outlined on land by geological observations the scatterer position also delineates this border well beneath sea level these results are in close agreement with recently obtained seismic velocity tomography the scatterers imaged at the 6 and 12 hz band pass frequencies are located around the zone of maximum uplift beneath solfatara crater where most of the present residual volcanic activity is concentrated

the influence of paleogeographic setting and crustal subsidence on the architecture of ignimbrites in the bay of naples italy abstract the margin of campania including campania plain and the bay of naples featured recurrent large scale ignimbrite eruptions between 270 and 15 ka these ignimbrite deposits are exposed in the valleys of the apennines and in limited areas along the margin of campania whereas are covered by younger deposits in the campania plain and the bay of naples of all these eruptions the campania ignimbrite 39 ka and the neapolitan yellow tuff 15 ka are the best studied and are considered to be the most important numerous papers suggest that these two eruptions originated from one or two nested calderas located in campi flegrei and the bay of pozzuoli in the northern part of the bay of naples the recognition of the way the site and the timing of a volcano tectonic collapse is of paramount importance to establish which of the structures were active during the eruption our study demonstrates that the recognition of the areas involved in volcano tectonic collapses is possible by means of a three dimensional basin analysis in the bay of naples the sequence stratigraphy interpretation of more than 4000 km of single channel and multi channel seismic reflection profiles made it possible to reconstruct the three dimensional architecture of the ignimbrite units basin analysis reveals that before ignimbrite eruptions the physiography of the bay of naples was characterised by a lateral variation in depositional environment ranging from shelf to deep marine our structural and stratigraphic analysis documents volcano tectonic deformations that occurred during the eruptions of the pre campania ignimbrite tuffs and of the campania ignimbrite these deformations were controlled by normal faults with planar geometry the overall features of the campania ignimbrites and the quantitative evaluation of crustal subsidence support a model of fissural emission associated to an asymmetrical crustal subsidence of the campania margin

monitoring changes in velocity and q using non physical arrivals in seismic interferometry application of seismic interferometry to records from receivers at the earth s surface from sources in wells retrieves the reflection response measured at the receivers as if from virtual sources located also at the surface when the wavefields experience intrinsic losses during propagation non physical arrivals ghosts would appear in the retrieved result these ghosts appear due to waves that reflect inside a subsurface layer thus a ghost contains information about the seismic properties of the specific layer we show how such ghosts can be used to monitor layer specific changes in the velocity and intrinsic losses in the subsurface we show how to identify the ghosts using numerical modelling results from a vertical well and how to estimate the layer specific velocity and quality factor changes using numerical modelling results from a horizontal well as well as ultrasonic s wave laboratory data

the present state of the magmatic system of the campi flegrei caldera based on a reconstruction of its behavior in the past 12 ka abstract new geochemical and sr isotope data have been acquired on samples representative of volcanic units erupted inside the resurgent campi flegrei caldera cfc over the past 12 ka these data integrated with previous published petrological and with newly acquired geochronological volcanological and geothermal data shed light on the nature and timing of the processes that controlled the evolution of the phlegraean magmatic system in the past 12 ka three isotopically and geochemically distinct magmatic components were erupted at the cfc as either homogeneous or mixed magma batches one component campanian ignimbrite component cic 87 sr 86 sr 0 70735 0 70740 is similar to the trachytic magma extruded during the first phase of the campanian ignimbrite ci eruption 37 ka a second component neapolitan yellow tuff component nytc 87 sr 86 sr 0 70750 0 70757 is similar to the latitic alkali trachytic magma batches extruded during the course of the neapolitan yellow tuff nyt eruption 12 ka a third component minopoli component mic 87 sr 86 sr 0 7086 is similar to the trachybasaltic magma of the minopoli 2 mi eruption 9 7 ka these components were erupted as either single batches of magma or mixed ci nyt or mi nyt batches of magma through vents located either along the structural boundary of the nyt caldera or inside the nyt caldera mainly on portions of the resurgent block under extensional stress the ci and nyt components represent residual portions of older large volume magma reservoirs which have fed eruptions since about 60 and 15 ka respectively the least evolved mi component was erupted only during the 12 9 5 ka and 8 6 8 2 ka epochs of activity through vents located on a ne sw regional fault system this component could represent a deeper reservoir tapped by the ne sw regional fault system reactivated after the nyt caldera collapse deeper mi and shallower ci and nyt magmatic systems interacted by mixing among batches of magma during their rise to surface overall the data suggest that the cfc magmatic system today is characterized by the presence of two larger independent reservoirs filled by residual portions of the ci and nyt magmas these generated many smaller shallower pockets of evolved magma that fed most of the eruptions that occurred in the cfc over the past 12 ka moreover a deeper reservoir mi tapped by the ne sw regional fault system provided batches of less evolved magma that mixed with magma present in the shallower pockets

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

mineral control of arsenic content in thermal waters from volcano hosted hydrothermal systems insights from island of ischia and phlegrean fields campanian volcanic province italy this paper documents arsenic concentrations in 157 groundwater samples from the island of ischia and the phlegrean fields two of the most active volcano hosted hydrothermal systems from the campanian volcanic province southern italy in an attempt to identify the environmental conditions and mineral solution reactions governing arsenic aqueous cycling on ischia and in the phlegrean fields groundwaters range in composition from nacl brines which we interpret as the surface discharge of deep reservoir fluids to shallow depth circulating fluids the latter ranging from acid sulphate steam heated to hypothermal cold bicarbonate groundwaters arsenic concentrations range from 1 6 to 6900 g l 1 and from 2 6 to 3800 g l 1 in the phlegrean fields and on ischia respectively they increase with increasing water temperature and chlorine contents and in the sequence bicarbonate groundwatersbsteam heated groundwatersbnacl brines according to thermochemical modeling we propose that high as concentrations in nacl brines form after prolonged water rock interactions at reservoir t fo2 and fh2s conditions and under the buffering action of an arsenopyrite pyrite pyrrhotite rock assemblage on their ascent toward the surface nacl brines become diluted by as depleted meteoric derived bicarbonate groundwaters giving rise to hybrid water types with intermediate to low as contents steam heated groundwaters give their intermediate to high as concentrations to extensive rock leaching promoted by interaction with as bearing hydrothermal steam 2005 elsevier b v all rights reserved

ultrasonic velocity measurements in volcanic rocks correlation with microtexture summary this paper summarizes results of a study of porosity permeability microstructure and acoustic properties of volcanic and pyroclastic rocks from campi flegrei cf and mt etna et italy we have measured the hydraulic transport and acoustics properties of 28 room dry samples at ambient conditions 25 room dry samples under confining pressure up to 60 mpa and 5 brine saturated samples under pressure up to 45 mpa effective pressure we established the following range of porosity permeability and vp and vs variations as functions of mineralogy and differential pressure in cf and et lithologies 1 porosity cf pyroclastic rocks 30 60 per cent cf and et lava rocks 2 20 per cent 2 permeability cf pyroclastic rocks 10 1000 md cf and et lava rocks 0 01 100 md 3 velocity and quality factor cf pyroclastic rocks vp 2 3 km s x1 vs 1 2 km s x1 qp 5 80 cf and et lava rocks vp 3 5 5 5 km s x1 vs 2 3 km s x1 qp 10 115 mineralogy and microstructure govern the acoustic and petrophysical properties of these rocks under pressure in pyroclastic rocks changes in acoustic response are directly related to presence of zeolites and pumice and their reactions with the pore fluid in dry conditions collapse of the internal texture of pumice leads to decreasing velocity with pressure in saturated conditions the water zeolite interactions compete with effects due to collapsing internal textures and so velocity change with pressure is not as pronounced the microstructural changes were confirmed by analyses of optical hydraulic and transport properties after pressure ct scans show a macroscopically more compact structure under optical microscopy pumice and zeolitized pumice appear shredded a significant reduction in porosity and permeability is measured after pressurization in lava rock samples acoustic velocities increase in function of pressure and the velocity pressure relationships are characteristic of samples with rounded pores our results emphasize the importance of conducting velocity measurements at simulated in situ conditions by constraining the computations using site and depth specific rock physics properties differences between ground deformation models in volcanic areas can be assessed and predicted more reliably thus reducing volcanic hazard

tectonic stress and renewed uplift at campi flegrei caldera southern italy new insights from caldera drilling deep drilling is a key tool for the investigation of active volcanoes in the modern earth sciences as this provides the only means to obtain direct information on processes that occur at depth data acquired from drilling projects are fundamental to our understanding of volcano dynamics and for mitigation of the hazards they pose for millions of people who live close to active volcanoes we present here the first borehole measurement of the stress field in the crust of campi flegrei southern italy a large active caldera and one of the highest risk volcanoes worldwide measurements were performed to depths of 500 m during a pilot study for the campi flegrei deep drilling project these data indicate an extensional stress field with a minimum horizontal stress of ca 75 to 80 of the maximum horizontal stress which is approximately equal to the vertical stress the deviation from lithostatic conditions is consistent with a progressive increase in applied horizontal stress during episodes of unrest since at least 1969 as the stress field is evolving with time the outcome of renewed unrest cannot be assessed by analogy with previous episodes interpretations of future unrest must therefore accommodate the possibility that campi flegrei is approaching conditions that are more favourable to a volcanic eruption than has previously been the case such long term accumulation of stress is not expected to be unique to campi flegrei and so might provide a basis for improved forecasts of eruptions at large calderas elsewhere