a method for the calculation of the impact parameters of dilute pyroclastic density currents based on deposit particle characteristics 1 a new method for the reconstruction of the physical characteristics of dilute pyroclastic density currents is introduced the velocity density and particle volumetric concentration profiles of the stratified current are calculated together with the profile of dynamic pressure which is a useful parameter for checking resistance of buildings the model links turbulent boundary layer shear flow theory with particle coupling to gas turbulence the working procedure starts with the recognition in the field of the fining upward sequence of layers formed during the time integrated depositional history of an individual current distinct processes of particle transportation and deposition are associated with the different particle modes composing the bedset the system of equations for the solution of the fluid dynamic parameters is implemented in two alternative ways the first one uses data of particles coming from both the basal coarse layer and the overlying laminated layer of the bedset the second uses features of two distinct components of the laminated layer a statistical test is performed for checking model results against experimental data of actual particles model calculations give the average solution as well as solutions corresponding to a range of 68 of probability around the average value the maximum solution can be considered as a safety value for impact parameters the methodology is applied to deposits of recent eruptions of vesuvius and campi flegrei in italy and results are discussed in terms of hazard and expected damage

geochemical properties and environmental impacts of seven campanian tephra layers deposited between 40 and 38 ka bp in the varved lake sediments of lago grande di monticchio southern italy abstract we present the results of new tephrostratigraphical and environmental impact studies of the 40 38 ka varved sediment section of lago grande di monticchio southern italy the sediments in this time zone are correlated with the heinrich h4 stadial that occurred between greenland interstadials gi 9 and gi 8 and include the widespread campanian ignimbrite ci 39 3 ka as a thick tephra layer in the middle of the h4 stadial the ci in the monticchio record is overlain by the schiava tephra from vesuvius c 1240 varve years younger than the ci and preceded by four tephras from small scale eruptions of the phlegrean fields and by an ischia derived tephra the four phlegrean field derived tephras were deposited 600 varve years or fewer prior to the deposition of the ci and show very similar major minor and trace element glass compositions to those of the ci this close similarity in composition and age could compromise the accurate linking and synchronisation of palaeoenvironmental records in the central mediterranean area microfacies analyses and xrf core scanning were used to characterise primary and secondary depositional features of all seven tephra layers and to evaluate environmental and ecological responses after tephra deposition higher concentrations of tephra derived material mainly glass shards and pumices in primary and reworked layers were detected by elevated k counts in xrf elemental core scans reworked tephra derives mainly from in washing from the littoral zone and the catchment and occurs within five to 30 years and up to 1240 varve years after the deposition of thinner 1 5 mm and thicker 5 230 mm tephra fallout deposits respectively an obvious response of diatom population growth directly after the primary tephra deposition was observed for the thicker tephra layers 1 mm during the first 1 8 years after deposition of the primary deposit indicating that the additional input of potential nutrients glass shards temporarily affected the ecological lake system

water solubility and speciation in shoshonitic and latitic melt composition from campi flegrei caldera italy abstract we report new data on water solubility in two melt compositions representative of volcanic units of the campi flegrei caldera italy the first composition is a primitive shoshonite and the second one is a more evolved latitic composition that have been chosen because of their less evolved nature compared to the other erupted products of campi flegrei water solubility was investigated at pressures from 25 to 200 mpa and 1200 c following synthesis in an internal heated pressure vessel ihpv the glasses obtained from water saturated experiments were analysed using both fourier transform infra red spectroscopy ftir and karl fischer titration kft kft was used as an independent method to obtain water concentration for the calibration of molar absorptivities of infrared bands at 3550 cm 1 total water 4500 cm 1 hydroxyl groups and 5200 cm 1 molecular water water solubility in the shoshonitic melts is similar to that of a basalt while a slightly higher water solubility is observed for the latitic composition as regards the speciation we have investigated the water speciation for the shoshonitic composition only and we have made a comparison between the data resulting using different molar absorptivities obtained for basaltic compositions similar to our shoshonite

lava stones from neapolitan volcanic districts in the architecture of campania region italy results of a research carried out on the lavas from campi flegrei and somma vesuvius volcanic districts are reported here the lavas have been widely employed since roman age in several important monumental buildings of the campania region mainly in the town of naples and in its province they are classified as trachytes campi flegrei products tephri phonolites and phono tephrites somma vesuvius complex from a petrographical point of view sampling was carried out from well known exploitation districts a substantial chemical difference between the products of the two sectors was confirmed while petrophysical characterization evidenced similarity among the two different materials although some differences were recorded even in samples coming from the same exploitation site

step filling and development of a three layer magma chamber the neapolitan yellow tuff case history abstract the neapolitan yellow tuff the product of the largest known trachytic phreatoplinian eruption gives a good opportunity to investigate the filling mechanisms and internal dynamics of a trachytic magma chamber a detailed study of the geochemical mineralogical and isotopical features of the deposit was carried out to investigate the behaviour of the magma chamber before the eruption the collected data show three distinct compositional groups separated by gaps single depositional units contain glass shards formed contemporaneously although each of these shards is homogeneous they display the same compositional variations and gaps detected in pumice clasts this feature is taken as an evidence for interpreting the detected compositional gaps as real gaps in the chamber therefore the chamber was filled by three distinct magma bodies separated by compositional gaps the uppermost magma was alkali trachyte and highly homogeneous likely a consequence of vigorous convection the intermediate magma was trachyte with a slight and continuous compositional variation likely resulting from less intense convection the lowermost magma was compositionally zoned from alkali trachyte to latite downward this compositional zonation was most likely acquired during uprise from a deeper reservoir the three magmas entered the chamber sequentially from the uppermost to the lowermost the latter entered the chamber short before the beginning of the eruption its input was interpreted as a possible triggering factor for the eruption the results of this study strongly support a step filling mechanism for the neapolitan yellow tuff magma chamber and allow definition of the temporal succession of input of magma batches furthermore they also suggest that the magma bodies did not mix although at least the uppermost two coexisted inside the chamber for a time long enough to allow internal homogeneization by convection

time scales of recent phlegrean fields eruptions inferred from the application of a diffusive fractionation model of trace elements the variation of chemical element compositions in two pyroclastic sequences astroni 6 and averno 2 phlegrean fields italy is studied both sequences are compositionally zoned indicating a variability of melt compositions in the magma chamber prior to eruption a clear dichotomy between the behaviour of major vs trace elements is also observed in both sequences with major elements displaying nearly linear inter elemental trends and trace elements showing a variable scattered behaviour together with previous petrological investigations these observations are consistent with the hypothesis that magma mixing processes played a key role in the evolution of these two magmatic systems recently it has been suggested that mixing processes in igneous systems may strongly influence the mobility of trace elements inducing a diffusive fractionation phenomenon whose extent depends on the mixing time scale here we merge information from 1 numerical simulations of magma mixing and 2 magma mixing experiments using as end members natural compositions from phlegrean fields to derive a relationship relating the degree of diffusive fractionation to the mixing time scales application of the diffusive fractionation model to the two studied pyroclastic sequences allowed us to apply the relationship derived by numerical simulations and experiments to estimate the mixing time scales for these two magmatic systems results indicate that mixing processes in astroni 6 and averno 2 systems lasted for approximately 2 and 9 days respectively prior to eruption

simple shearing block resurgence in caldera depressions a model from pantelleria and ischia abstract similar resurgent blocks occur in caldera depressions at the islands of pantelleria and ischia the two blocks which are tilted show similar deformation patterns and similar distributions of volcanic vents related to resurgence the remaining parts of the floors of the two calderas are not deformed similarities between the two features are so striking that the resurgence mechanism must have been alike a dynamic model for resurgence is presented and called simple shearing block resurgence the triggering mechanism is an increase of the magmatic pressure in the upper part of a shallow magma chamber which results in a vertical direction of the maximum stress applied on the roof rocks the block is first defined by high angle inland dipping marginal detachments and then deformed through a simple shearing mechanism reverse faults on its mostly uplifted side determine an horizontal shortening of the block which is balanced on the opposite side by normal faults oblique movements take place along the other two sides due to this distribution of the stress around the block magmas can reach the surface only through the extensional faults on the less uplifted side

the thermal regime of the campi flegrei magmatic system reconstructed through 3d numerical simulations abstract we illustrate a quantitative conductive convective thermal model incorporating a wide range of geophysical petrological geological geochemical and isotopical observations that constrain the thermal evolution and present state of the campi flegrei caldera cfc magmatic system the proposed model has been computed on the basis of the current knowledge of 1 the volcanic and magmatic history of the volcano over the last 44 ka 2 its underlying crustal structure and 3 the physical properties of the erupted magmas 3d numerical simulations of heat conduction and convection within heterogeneous rock magma materials with evolving heat sources and boundary conditions that simulate magma rise from a deep 8 km depth to shallow 2 6 km reservoirs magma chamber formation magma extrusion caldera collapse and intra caldera hydrothermal convection have been carried out the evolution of the cfc magmatic system through time has been simulated through different steps related to its changes in terms of depth location and size of magma reservoirs and their replenishment the thermal modeling results show that both heat conduction and convection have played an important role in the cfc thermal evolution although with different timing the simulated present heat distribution is in agreement with the measured geothermal profiles agip 1987 reproduces the thermal gradient peaks at the cfc margins in correspondence to the anomalies in surface gradients corrado et al 1998 and suggests temperatures of 700 c at depth of 4 km in the central portion of the caldera in agreement with the estimated temperature for the brittle ductile transition hill 1992

eruptive mechanisms of the neapolitan yellow tuff interpreted from stratigraphie chemical and granulometric data abstract the neapolitan yellow tuff 12 ka is the second largest pyroclastic deposit of the campanian volcanic area covering at least 1000 km 2 with conservative estimates of volume placed at 40 km 3 previous studies showed that this mainly trachytic deposit composed of two members was erupted by 1 a central vent mostly phreatoplinian phase lower member that generated pyroclastic surges and fallout reaching 34 km from the vent followed by 2 a multiple vent phreatomagmatic and magmatic phase upper member associated with onset of caldera collapse that produced surges extending 14 km from the vent the lower member is well bedded and comprises 13 subunits that alternate between phreatoplinian surges flows and plinian pumice and ash fallout the upper member is relatively lithic rich and more massive in character for both members magma compositions vary from alkali trachyte through trachyte to latite which does not fit a simple inversion of magma chamber gradients calculations based on magma chemistry show an increase in magma density a decrease followed by an increase in viscosity and a general decrease of gas fraction during the course of both eruptive phases after migrating to a depth of about 400 m calculated fragmentation depths gradually rise during each phase application of sequential fragmentation transport analysis to granulometric data shows for the lower member an average ratio of phreatomagmatic to magmatic components of 70 30 while the upper member shows an average ratio of 80 20 however considering the tephra volume represented by samples computed water magma interaction ratios r are shown to fluctuate but generally decrease from about 0 65 to 0 05 during eruption of the lower member while the upper member shows r fairly constant at about 0 1 furthermore surge flow runout distances and estimates of eruptive velocities from r values show that column collapse heights were extremely high 6 to 7 km during the first phase and were substantially lower during the second phase 2 to 3 km vent radii required for calculated eruption velocities of 180 to 370 m s are between 70 and 300 m suggesting a cumulative eruption duration of over 10 hours perhaps spanning of one to several days

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

hydrogeochemistry of the campania region in southern italy abstract a geochemical study of thermal springs cold springs stream waters and natural gas emissions has been carried out in the campania region of southern italy this region hosts four quaternary volcanic areas and thermal springs and gas emissions occur in three of them most thermal springs discharge na cl composition waters of connate origin derived from post orogenic volcanic and sedimentary formations although high enthalpy systems are present in two of the four volcanic areas there appear to be no magmatic contributions to the thermal springs solute geothermometers are unreliable as spring waters are strongly affected by mixing with shallow brines before discharging thermal springs and gas emissions also occur in non volcanic areas where an extensive carbonate unit acts as a regional aquifer for cold low salinity bicarbonate waters thermal features in these areas occur in fractured zones associated with active faults their compositions are determined only by the type of rock encountered by solutions before surface discharge as in other areas of north central italy the widespread occurrence of hot and cold co2 rich springs and gas emissions in both volcanic and non volcanic zones suggests a deep origin for the co2

first integrated tephrochronological record for the last 190 kyr from the fucino quaternary lacustrine succession central italy we present the first integrated tephrochronological study major and trace elemental glass composition sr and nd isotope analyses and 40ar 39ar dating for the last one tenth 82 m of the 900 m thick quaternary lacustrine succession of the fucino basin the largest and probably only central apennine intermountain tectonic depression that hosts a continuous lacustrine succession documenting the plio quaternary sedimentary history up to historical times major element glass compositions determined using a wavelength dispersive electron microprobe wds empa yielded the geochemical fingerprinting needed for a reliable identification of most of the 23 stratigraphically ordered tephra layers under investigation these include tephra from italian volcanoes such as campi flegrei etna colli albani ischia vico sabatini and undefined volcanic sources in the neapolitan area and latium region the recognition of key mediterranean marker tephra layers e g x 5 and x 6 is supported by trace element data acquired by laser ablation inductively couple plasma mass spectrometry la icp ms the sr and nd isotope compositions of selected layers where also determined for circumscribing the volcanic source of distal tephra and for supporting correlations with individual eruptive units we also propose a new more expeditious covariation diagram cao feotot vs cl for identifying the volcanic source of trachytic to phonolitic and tephrytic to phonolitic tephra that are the most common compositions of pyroclastic rocks from volcanoes of campania and latium regions finally we present five new 40ar 39ar age determinations including a new analytically well supported and more precise 40ar 39ar age for the widespread y 7 tephra and the first 40ar 39ar age determinations for one tephra from the sabatini volcanic district 126 ka and one tephra from neapolitan volcanic area campi flegrei 159 ka these newly dated tephra are widely dispersed e g monticchio southern italy adriatic sea and lake ohrid macedonia abania and have thus the potential to become important mediterranean mis 5 and mis 6 tephrochronological markers altogether the new geochemical data and 40ar 39ar ages precisely constrain the chronology of the investigated fucino succession spanning the last 190 ka in light of these results and by considering that this sedimentary succession possibly extends back to 2 ma fucino is likely to provide a very long continuous tephrostratigraphic record for the mediterranean area and become a key node in the dense network of tephra correlations of this region

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

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

magnetic modeling of the phlegraean volcanic district with extension to the ponza archipelago italy abstract a 3d modeling of the residual aeromagnetic anomalies of the area including the phlegraean volcanic district pvd campi flegrei caldera cfc and ischia and procida vivara islands and two volcanic islands of the ponza archipelago ventotene and s stefano has been carried out the observed residual anomalies have been reproduced with several large magnetized bodies located at 2 10 km depth in the crust a volcanological interpretation has been made possible only for those bodies that have been constrained by geological geothermal and other geophysical data the magnetized structures associated with cfc and ischia procida vivara ventotene and santo stefano islands have been interpreted as igneous bodies that may be solidified intrusions or magma reservoirs on the basis of magnetic data volcanological and magmatological history and geothermal heat flux distribution the existence of a partially solidified magma chamber is suggested at ischia a speculation shows that the magnetization intensity assumed for the magnetic bodies located at procida and south west of ventotene matches quite well with the calculated composition of a cooled residual magma resulting from crystallization processes within a chamber

uplift shortening and steady state topography in active mountain belts we present a tectonic surface process model used to investigate the role of horizontal shortening in convergent orogens and the effects on steady state topography the tectonic model consists of a specified velocity field for the earth9s surface and includes a constant uplift rate and a constant horizontal strain rate which varies to reflect the relative importance of frontal accretion and underplating in an orogenic wedge the surface process model includes incision of a network of rivers formed by collection of applied precipitation and diffusive hillslope mass transfer three non dimensional parameters describe this model a ratio of the maximum horizontal velocity to the vertical velocity a peclet number expressing the efficiency of the hillslope diffusion relative to the uplift rate and a fluvial erosion number reflecting the fluvial incision efficiency relative to the uplift rate a series of models are presented demonstrating the resultant steady state landforms parameterized by these three numbers a finite velocity ratio results in an asymmetric form to the model mountain range although the magnitude of the asymmetry also depends on the peclet number topographic steady state is achieved faster for models with no horizontal component to the velocity field with finite horizontal velocity topographic steady state is achieved only at the scale of the entire mountain range even the first order drainage basins are unstable with time in the presence of horizontal shortening we compare our model results to topographic profiles from active mountain ranges in taiwan new zealand and the olympic mountains of washington state all these examples exhibit asymmetric topographic form with the asymmetry consistent with the polarity of subduction suggesting that horizontal tectonic motion is affecting the macro geomorphic form of these ranges

geochemical evidences of magma dynamics at campi flegrei italy abstract campi flegrei caldera within the neapolitan area of italy is potentially one of the most dangerous volcanoes in the world and during the last decade it has shown clear signs of reactivation marked by the onset of uplift and changes in the geochemistry of gas emissions we describe a 30 year long data set of the co2 he ar n2 compositions of fumarolic emissions from la solfatara crater which is located in the center of the caldera the data display continuous decreases in both the n2 he and n2 co2 ratios since 1985 paralleled by an increase in he co2 these variations cannot be explained by either processes of boiling condensation in the local hydrothermal system or with changes in the mixing proportions between a magmatic vapor and hydrothermal fluids we applied the magma degassing model of nuccio and paonita 2001 earth planet sci lett 193 467 481 using the most recent inert gas solubilities in order to interpret these peculiar features in accordance with petrologic constraints derived from the ranges of the melt compositions and reservoir pressures at campi flegrei the model simulations for mafic melts trachybasalt and shoshonite show a remarkably good agreement with the measured data both decompressive degassing of an ascending magma and mixing between magmatic fluids exsolved at various levels along the ascent path can explain the long term geochemical changes recalling that i a sill like reservoir of gases at a depth of 3 4 km seems to be the main source of ground inflation and ii there is petrologic and geophysical evidence for a reservoir of magma at about 8 km below campi flegrei we suggest that the most intense episodes of inflation occur when the gas supply to the sill like reservoir comes from the 8 km deep magma although fluids exsolved by magma bodies at shallower depths also contribute to the gas budget our work highlights that in caldera systems where the presence of hydrothermal aquifers commonly masks the magmatic signature of reactive volatiles inert gases are the preferred species to use when seeking information on the melt composition dynamics and structure of the plumbing systems

mobility of a large volume pyroclastic flow emplacement of the campanian ignimbrite italy abstract the trachytic campanian ignimbrite originally exposed over a 30 000 km 2 area around naples italy is the product of a highly energetic gas rich eruption the deposit lies in valleys and isolated watersheds and in its medial and distal extent to the south north and east of naples the campanian pyroclastic current encountered mountains exceeding 1000 meters anisotropy of magnetic susceptibility ams measurements indicate that the campanian pyroclastic current the transport system traveled radially outward from the phlegrean fields area but the ignimbrite forming flow the deposition system that developed from the base of the transport system moved downslope from mountainsides to valleys including slopes facing the eruption source and flowed down drainage systems from intermontane basins the campanian pyroclastic current flowed 35 km over the water of the bay of naples to deposit 43 m of ignimbrite on the south shore and also overtopped a 685 1000 m high ridge of the sorrento peninsula to deposit more on the other side the distribution of the ignimbrite and the measured flow directions suggest that the campanian pyroclastic current moved across the landscape as an expanded and therefore turbulent decompressing flow rather than as a high density nonturbulent sheet like current moving over mountains by momentum acquired by eruption column collapse strong expansion is corroborated by shard morphology that indicates derivation from highly inflated pumice and suggests vesicles must have been at least 80 by volume of the original magma

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

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

isotopic evidence for open system processes within the campanian ignimbrite campi flegrei italy magma chamber new sr and nd isotope data for whole rocks glasses and minerals are combined to reconstruct the nature and origin of mixing end members of the 200 km3 trachytic to phonolitic campanian ignimbrite campi flegrei italy magmatic system the least evolved magmatic end member shows equilibrium between host glass and the majority of the phenocrysts and is less radiogenic in sr and nd than the most evolved magma on the contrary only the fe rich pyroxene from the most evolved erupted magma is in equilibrium with the matrix glass while all other minerals are in isotopic disequilibrium these magmas mixed prior to and during the campanian ignimbrite eruption and minerals were freely exchanged between the magma batches combining the results of the geochemical investigations on magma end members with geophysical and geological data we develop the following scenario in stage 1 a parental less differentiated magma rose into the middle crust and evolved through combined crustal assimilation and crystal fractionation in stage 2 the differentiated magma rose to shallower depth fed the pre campanian ignimbrite activity and evolved by further open system processes into the most evolved and most radiogenic campanian ignimbrite end member magma in stage 3 new trachytic magma isotopically distinct from the pre campanian ignimbrite magmas rose from ca 6 km to shallower depth recharged the most evolved pre campanian ignimbrite magma chamber and formed the large and stratified campanian ignimbrite magmatic system during the course of the campanian ignimbrite eruption the two layers were tapped separately and or simultaneously and gave rise to the range of chemical and isotopic values displayed by the campanian ignimbrite pumices glasses and minerals

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

reply to comment by a rapolla on the bay of naples southern italy constraints on the volcanic structures inferred from a dense seismic survey 1 judenherc and zollo 2004 hereinafter referred to as jz2004 describe the analysis and three dimensional 3 d tomographic inversion of first p arrival times from data sets obtained during the controlled source seismic experiments carried out in 1997 mareves and 2001 serapis in the neapolitan volcanic bay area 2 thirty years after the 2 d near vertical seismic reflection survey of the neapolitan bay area made by osservatorio geofisico sperimentale di trieste ogs and whose results are described in the pioneering work of finetti and morelli 1974 the serapis exploration project provides an unique 3 d global offset simultaneous near vertical and wide angle data acquisition data set allowing the investigation of crustal structure in the area with a detail not achievable using previous available data 3 as detailed in jz2004 the dense spatial coverage provided by more then 6000 air gun sources and 150 threecomponent seismic stations deployed both on land and at the sea bottom allowed reconstruction of the highresolution three dimensional image of the shallow crustal structure beneath campi flegrei caldera and bay of naples down to 6 7 km depth 4 the comment by rapolla 2005 hereinafter referred to as rap2005 does not bring the results of jz2004 into question but mainly focuses on the claim that some of the 3 d seismic tomography results could be already known from the existent literature and not referred in jz2004 5 in particular rap2005 debates two major points 6 1 jz2004 shows the existence of the pozzuoli banco di fuori fault pbf fault a 30 km long se nw normal fault cutting the limestone top at 4 5 km depth which rap2005 associates with a ne sw trending shallow fault fracture system previously reported by bruno et al 2003 and bruno 2004 called the magnaghi sebeto ms line 7 2 jz2004 does not give proper credit to a number of papers cited in rap2004 dealing with the geochemical geological geophysical investigation of the campi flegrei caldera

p sv conversions at a shallow boundary beneath campi flegrei caldera italy evidence for the magma chamber seismograms from an active seismic experiment carried out at campi flegrei caldera near naples italy show a large amplitude 5v polarized shear wave following by less than 1 5 s p waves reflected at wide angle from a deep crustal interface early arriving sv polarized waves with the same delay to direct p waves are also observed in seismograms from a regional 280 km deep magnitude 5 1 earthquake such short delays of s to p waves are consistent with a p sv conversion on transmission occurring at a shallow boundary beneath the receivers the large amplitude of the converted sv phase along with that the p waves are near vertical requires a boundary separating a very low rigidity layer from the upper caldera fill the converted phases are interpreted as a seismic marker of a magma chamber the top of this magma chamber is located slightly deeper than the deepest earthquakes observed during the 1982 1984 unrest of campi flegrei

evidence of crystallization in residual cl f rich agpaitic trachyphonolitic magmas and primitive mg rich basalt trachyphonolite interaction in the lava domes of the phlegrean fields italy the lava domes in the northwestern cuma northern punta marmolite and central accademia parts of the phlegrean fields are the subject of this study the cuma and punta marmolite trachyphonolitic lava domes are among the oldest phlegrean products cropping out the cuma rocks have an agpaitic groundmass with early alkali feldspar fe rich clinopyroxene fe edenite and sodalite and late rosenbuschite fluorite baddeleyite pyrochlore britholite monazite aegirine often zr rich and exceptionally fe mn rich olivine the bulk rock compositions at cuma have some of the highest concentrations of zn mn zr nb th u and lanthanides among the phlegrean fields rocks and some of the lowest mgo p 2 o 5 sr eu and ba the punta marmolite dome is chemically less evolved and lacks characteristic agpaitic minerals but features alkali feldspar sodalite nepheline and relatively na poor fe rich hedenbergite with rare ca rich plagioclase xenocryst cores the accademia dome belonging to the recent activity is latitic to trachytic in composition has highly forsteritic olivine with chromiferous spinel inclusions calcic plagioclase and mg rich diopside phlogopite xenocrysts in an evolved host rock with phenocrysts and microlites of alkali feldspar fe rich clinopyroxene fe rich amphibole magnetite fe rich olivine and accessory baddeleyite zirconolite and fluorite there is clear evidence of open system magma crystallization in the form of interaction between a crystallizing primitive shoshonitic basalt in a reservoir already filled by rather evolved trachytic magma the magmatic evolution towards the evolved compositions is dominated by crystallization of more and more na rich alkali feldspar in a cl f rich and relatively h 2 o poor environment input of mafic magma is evident in many trachytic eruptions of the phlegrean fields and even in the products of the campanian ignimbrite but eruptions having mineral assemblages rich in xenocryst phases as well as eruptions virtually free of mafic magma input are also frequently observed throughout the history this suggests a variable pattern of open and closed system crystallization which may or may not be linked to explosive activity and that can be caused by intermittent supply of basaltic magma from depth

the neapolitan yellow tuff a large magnitude trachytic phreatoplinian eruption eruptive dynamics magma withdrawal and caldera collapse the results of a detailed stratigraphical and volcanological study has allowed the definition of the neapolitan yellow tuff nyt as the largest known trachytic phreatoplinian eruption with an estimated volume of not less than 30 km3 dre the nyt sequence can be subdivided in a lower and an upper member sedimentological and textural variations in time and space indicate that different eruptive and depositional mechanisms operated during the eruption the lower member eruptive phase was characterized by alternating phreatoplinian and magmatic explosions while the upper member eruptive phase was characterized by a random sequence of phreatomagmatic and magmatic explosions particles produced by the same explosion were deposited contemporaneously by fallout and surge mechanisms either at different or at the same distance from the vent compositional variations show that the nyt sequence cannot be modeled as an inverted compositionally zoned magma body with magma becoming more basic in the course of the eruption the chamber composed of three geochemically distinct magma layers was tapped at different depths according to the eruption dynamics each phreatoplinian explosion tapped concurrently all the magma layers while magmatic explosions tapped only one of them the onset of the nyt caldera collapse is well constrained between lower and upper member eruptive phases the collapse which is only gravimetrically detectable occurred inside the larger phlegrean fields caldera which therefore can be defined as a nested caldera

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

a general viscosity model of campi flegrei italy melts abstract viscosities of shoshonitic and latitic melts relevant to the campi flegrei caldera magmas have been experimentally determined at atmospheric pressure and 0 5 gpa temperatures between 840 k and 1870 k and h2o contents from 0 02 to 3 30 wt the concentric cylinder technique was employed at atmospheric pressure to determine viscosity of nominally anhydrous melts in the viscosity range of 101 5 103 pa s the micropenetration technique was used to determine the viscosity of hydrous and anhydrous melts at atmospheric pressure in the high viscosity range 1010 pa s falling sphere experiments were performed at 0 5 gpa in the low viscosity range from 100 35 to 102 79 pa s in order to obtain viscosity data of anhydrous and hydrous melts the combination of data obtained from the three different techniques adopted permits a general description of viscosity as a function of temperature and water content using the following modified vft equation l o g a b t c d t e e x p g w t where is the viscosity in pa s t the temperature in k w the h2o content in wt and a b c d e and g are the vft parameters this model reproduces the experimental data 95 measurements with a 1 standard deviation of 0 19 and 0 22 log units for shoshonite and latite respectively the proposed model has been applied also to a more evolved composition trachyte from the same area in order to create a general model applicable to the whole compositional range of campi flegrei products moreover speed data have been used to constrain the ascent velocity of latitic shoshonitic and trachytic melts within dikes using petrological data and volcanological information geometrical parameters of the eruptive fissure and depth of magma storage we estimate a time scale for the ascent of melt from 9 km to 4 km depth where deep and shallow reservoirs respectively are located in the order of few minutes such a rapid ascent should be taken into account for the hazard assessment in the campi flegrei area

three dimensional electrical resistivity tomography of the solfatara crater italy implication for the multiphase flow structure of the shallow hydrothermal system the solfatara volcano is the main degassing area of the campi flegrei caldera characterized by 60 years of unrest assessing such renewal activity is a challenging task because hydrothermal interactions with magmatic gases remain poorly understood in this study we decipher the complex structure of the shallow solfatara hydrothermal system by performing the first 3 d high resolution electrical resistivity tomography ert of the volcano the 3 d resistivity model was obtained from the inversion of 43 432 resistance measurements performed on an area of 0 68 km2 the proposed interpretation of the multiphase hydrothermal structures is based on the resistivity model a high resolution infrared surface temperature image and 1 136 soil co2 flux measurements in addition we realized 27 soil cation exchange capacity cec and ph measurements demonstrating a negligible contribution of surface conductivity to the shallow bulk electrical conductivity hence we show that the resistivity changes are mainly controlled by fluid content and temperature the high resolution tomograms identify for the first time the structure of the gas dominated reservoir at 50 m depth that feeds the bocca grande fumarole through a 10 m thick channel in addition the resistivity model reveals a channel like conductive structure where the liquid produced by steam condensation around the main fumaroles flows down to the fangaia area within a buried fault the model delineates the emplacement of the main geological structures mt olibano solfatara crypto dome and tephra deposits it also reveals the anatomy of the hydrothermal system especially two liquid dominated plumes the fangaia mud pool and the pisciarelli fumarole respectively

comment on the bay of naples southern italy constraints on the volcanic structures inferred from a dense seismic survey by s judenherc and a zollo