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

characteristics of two phreatoplinian ashes and their water flushed origin abstract the whole deposit grain size populations have been determined for two phreatoplinian ashes of the rhyolitic taupo volcano new zealand one is much finer than plinian pumice deposits studied from the same volcano and the other differs in having a lower content of coarse pumice the poor sorting of the two ashes is attributed mainly to water scavenging of the ash cloud the very limited fractionation with distance from source combined with the very regular exponential thickness decrease indicates that the scavenging water was an integral part of the ash cloud and was derived from lake taupo at times when the proportion of erupted water to magma became particularly high erosion of the underlying deposits took place and to this is attributed the striking gullying of the surface which separates the two ashes

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

large explosive basaltic eruptions at katla volcano iceland fragmentation grain size and eruption dynamics abstract katla volcano in iceland produces hazardous large explosive basaltic eruptions on a regular basis but very little quantitative data for future hazard assessments exist here details on fragmentation mechanism and eruption dynamics are derived from a study of deposit stratigraphy with detailed granulometry and grain morphology analysis granulometric modeling componentry and the new quantitative regularity index model of fragmentation mechanism we show that magma water interaction is important in the ash generation process but to a variable extent by investigating the large explosive basaltic eruptions from 1755 and 1625 we document that eruptions of similar size and magma geochemistry can have very different fragmentation dynamics our models show that fragmentation in the 1755 eruption was a combination of magmatic degassing and magma water interaction with the most magma water interaction at the beginning of the eruption the fragmentation of the 1625 eruption was initially also a combination of both magmatic and phreatomagmatic processes but magma water interaction diminished progressively during the later stages of the eruption however intense magma water interaction was reintroduced during the final stages of the eruption dominating the fine fragmentation at the end this detailed study of fragmentation changes documents that subglacial eruptions have highly variable interaction with the melt water showing that the amount and access to melt water changes significantly during eruptions while it is often difficult to reconstruct the progression of eruptions that have no quantitative observational record this study shows that integrating field observations and granulometry with the new regularity index can form a coherent model of eruption evolution

explosive felsic volcanism on el hierro canary islands the canary islands consist of seven basaltic shield volcanoes whose submerged portion is much more voluminous than the subaerial part of each island like so many other volcanic oceanic islands the indicative deposits of explosive felsic volcanism are not a common feature on the canary archipelago hitherto they have only been documented from the central islands of gran canaria and tenerife which are the largest volcanic complexes of the islands on the other canary islands the presence of felsic rocks is mostly restricted to intrusions and a few lava flows generally within the succession in the oldest parts of individual islands in this paper we present a detailed stratigraphic lithological and sedimentological study of a significant felsic pumice deposit on the island of el hierro referred here as the malpaso member which represents the only explosive episode of felsic volcanism found on the canary islands outside of gran canaria and tenerife the products of the eruption indicate a single eruptive event and cover an area of about 15 km2 this work provides a detailed stratigraphic and chronological framework for el hierro and four subunits are identified within the member on the basis of lithological and granulometric characteristics the results of this study demonstrate the importance of an explosive eruption in a setting where the activity is typified by effusive basaltic events given the style and the spatial distribution of the malpaso eruption and its products a future event with similar characteristics could have a serious impact on the population infrastructure and economy of the island of el hierro

the baia fondi di baia eruption at campi flegrei stratigraphy and dynamics of a multi stage caldera reactivation event the baia fondi di baia eruption is one of the sporadic events that have occurred in the western sector of the campi flegrei caldera it dates back to 9525 9696 bp and opened epoch 2 of the caldera activity after a 1000 year long period of quiescence although relatively small in terms of erupted volume with respect to most of the events of the past 15 ka the baia fondi di baia eruption was characterized by a complex series of events which have led to different interpretations in the literature we present a detailed stratigraphic study of 40 outcrops in a sector of about 90 km2 coupled with sedimentological grain size componentry physical density vesicularity textural and compositional analyses of the erupted deposits based on these data we interpret the stratigraphic succession as being related to two distinct eruptive episodes baia and fondi di baia these were separated by a short time interval and each was characterized by different eruptive phases the baia eruptive episode started in a shallow water environment with an explosive vent opening phase that formed a breccia deposit unit i rapidly followed by alternating fallout activity and dense pyroclastic density current deposits generation unit ii sedimentological features and pumice textural analyses suggest that deposition of unit ii coincided with the intensity peak of the eruption with the fallout deposit being characterized by a volume of 0 06 0 008 km3 corresponding to a total erupted mass of 4 06 0 5 1010 kg a column height of 17 km and a corresponding mass flow rate of 1 8 107 kg s 1 the associated tephra also shows the highest vesicularity up to 81 vol the highest vesicle number density 1 01 108 cm 3 and decompression rate 0 69 mpa s 1 this peak phase waned to turbulent surge like activity possibly associated with vulcanian explosions and characterized by progressively lower intensity as shown by density vesicularity and textural properties of the erupted juvenile material unit iii this first eruptive episode was followed by a short quiescence interrupted by the onset of a second eruptive episode fondi di baia whose vent opening deposited a breccia bed unit iv which at some key outcrops directly overlies the fallout deposit of unit ii the final phase of the fondi di baia episode strongly resembles unit ii although sedimentological presence of obsidian clasts which are absent in the baia deposits and textural lower vesicularity vesicle number density and decompression rate values features together with a more limited dispersal suggest that this phase of the eruption had a lower intensity the large range of groundmass glass compositions associated with variable proportions of highly phonolitic trachytic and mildly tephriphonolitic latitic evolved end members in the erupted products also suggests that these eruptive episodes were fed by at least two different magma batches that interacted during the different phases with an increase of tephriphonolitic latitic magma occurring during the fondi di baia stage

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

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

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

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

architectural analysis of a volcaniclastic jokulhlaup deposit southern iceland sedimentary evidence for supercritical flow the 1918 eruption of the glacially capped katla volcano southern iceland generated a violent jokulhlaup or glacial outburst flood inundating a large area of m rdalssandur the proglacial outwash plain where it deposited ca 1 km3 of volcaniclastic sediment the character of the 1918 jokulhlaup is contentious having been variously categorized as a turbulent water flow a hyperconcentrated flow or as a debris flow based on localized outcrop analysis in this study outcrop based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi stationary antidunes and down current migrating antidunes and from regular based bedsets associated with transient chute and pool bedforms all of which are associated with turbulent transcritical to supercritical water flow conditions antidune wavelengths range from 24 to 96 m corresponding to flow velocities of 6 to 12 m sec 1 and average flow depths of 5 to 19 m this range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts architectural analysis of the 1918 jokulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 jokulhlaup that could not have been achieved through localized outcrop analysis the observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions the physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations regarding modes of deposition and formative flow hydraulics are to be made

silicic phreatomagmatism in the snake river plain the deadeye member non welded rhyolitic pyroclastic units in the central snake river plain are interbedded with the much better exposed large volume snake river type rheomorphic welded rhyolitic ignimbrites and rhyolite lavas we document one such unit to investigate why it is so different from the interbedded welded ignimbrites the newly recognised deadeye member of southern idaho is a soil bounded eruption unit that comprises ashfall layers and a 4 m thick ignimbrite that extends for 35 km the ignimbrite is non welded lithic clast poor and varies from massive to diffuse low angle cross bedded it contains abundant angular clasts of non vesicular black glass and upper parts contain accretionary lapilli the ashfall layers above it contain coated ash pellets and ash clumps which record moist aggregation of fine ash the magmas of the deadeye eruption were closely similar in composition and temperature to those that generated the intensely welded rheomorphic ignimbrites of the central snake river plain we infer that the marked contrast in physical appearance of the deadeye ignimbrite compared to the other more typical snake river type welded ignimbrites was the result of emplacement at relatively low temperatures during an eruption in a lacustrine environment magmatic volatile driven fragmentation of the rhyolitic magma was influenced by interaction with lake water that also led to cooling the deadeye member is the first recorded example of explosive silicic phreatomagmatism in the central snake river plain

large scale phreatomagmatic silicic volcanism a case study from new zealand abstract pyroclastic deposits of the 20 000 year old wairakei formation occur in the region surrounding lake taupo in the central north island of new zealand recent advances in the correlation of both proximal and distal equivalents of the wairakei deposits show that they were the result of one large eruption the ash layers once covered most of new zealand they are also present in deep sea cores from the sw pacific and on the chatham islands the dispersal and grain size parameters of the ash fall members indicate that their vent area was within the taupo volcano tectonic depression which for a long period has contained a large lake the wairakei eruption is interpreted to have been phreatomagmatic throughout each phase of the eruption sequence generated its own characteristic deposits the sequence of events can be summarized as follows 1 eruption and deposition of a white fine grained bedded fall deposit 2 eruption and deposition of a medium grained pumice fall deposit 3 generation of ultra fine wet ash clouds with a fall deposit accumulating largely as aggregates and accretionary lapilli accompanied by base surges 4 formation of water cooled pyroclastic flows and deposition of an extensive ignimbrite 5 return to a dominantly vertical eruption column and deposition of a medium grained bedded ash fall immediately followed by another wet ultra fine fall deposit charged with accretionary lapilli finally 6 an ignimbrite less widespread than that of phase 4 was produced co ignimbrite fall deposits of fine vitric dust and medium grained pumice were laid down over a huge area there may have been a short hiatus in activity between phases 4 and 5

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

the influence of water on the strength of neapolitan yellow tuff the most widely used building stone in naples italy neapolitan yellow tuff nyt has been used in construction in naples italy since the greeks founded the city then called neapolis in the sixth century bce we investigate here whether this popular building stone is weaker when saturated with water an issue important for assessments of weathering damage and monument preservation to this end we performed 28 uniaxial compressive strength measurements on dry and water saturated samples cored from a block of the lithified upper member of the nyt our experiments show that the strength of the zeolite rich nyt is systematically reduced when saturated with water the ratio of wet to dry strength is 0 63 complementary experiments show that two other common neapolitan building stones piperno tuff and the grey campanian ignimbrite both facies of the campanian ignimbrite deposit devoid of zeolites do not weaken when wet from these data and previously published data for tuffs around the globe we conclude that the water weakening in nyt is a consequence of the presence of abundant zeolites the block tested herein contains 46 wt of zeolites these data may help explain weathering damage in nyt building stones due to rainfall rising damp and proximity to the sea or water table and the observed link between rainfall and landslides rock falls and sinkhole formation in naples and the weathering of other buildings built from zeolite rich tuffs worldwide

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

structure of volcanic glasses from the nmr epr perspective a preliminary application to the neapolitan yellow tuff glass samples from alkali trachytic pumice of the lower member lm level lm1 and upper member um of the neapolitan yellow tuff at campi flegrei caldera were studied by nuclear magnetic resonance nmr and electron paramagnetic resonance epr spectroscopy the epr data show that the relative occupancy of the different iron sites varies in samples from the lower member lm1 and upper member of the eruptive sequence the lm1 glasses are characterized by a more homogeneous distribution of the cationic site population of iron compared with um and by a different fe3 al3 substitution in the c2v symmetrical sites of the silicate framework 29si mas nmr spectra on glasses indicate that lm1 glasses are more depolymerized than um glasses indicating the existence of structurally distinct magma batches 27al mas nmr spectra indicate the occurrence in um glasses of aluminum in both tetrahedral and octahedral coordination the observed alvi is believed to be a primary feature of the glass since 27al cp mas nmr experiments do not reveal detectable esa hydrated al the al in sixfold coordination could be ascribed either to the more abundant alkali oh terminations in um in which alkalies would be extracted from their charge balance role for al thus altering its fourfold structural position or to permanent compaction during fast cooling and decompression of high pressure melts 23na cp mas nmr experiments indicate the existence of na oh groups in both lm1 and um glasses relatively more abundant in the latter although preliminary the results indicate the possible application of atomic scale studies to variables that determine the regimes of explosive volcanism

statistical analysis of textural data from complex pyroclastic sequences implications for fragmentation processes of the agnano monte spina tephra 4 1 ka phlegraean fields southern italy the agnano monte spina eruption 4 1 ka generated pyroclastic deposits with complex internal stratigraphy that reflects variations in eruptive style to obtain constraints on the fragmentation processes we analysed grain size and scanning electron microscopy sem data by means of multivariate statistical techniques of the cluster and factor analysis types the results allow the identification of end member deposits related to either pure magmatic activity or pure phreatomagmatic activity in addition some deposits show evidence of the contemporaneous operation of both end member fragmentation modes the presence of the two contrasting fragmentation processes during the various phases of explosive activity is tentatively interpreted to be a function in inhomogeneities in gas exsolution processes within the magma column that feeds the eruption

depositional mechanisms and alteration processes in different types of pyroclastic deposits from campi flegrei volcanic field southern italy the campi flegrei volcanic field southern italy is composed of a large variety of pyroclastic deposits related to both magmatic and hydromagmatic activity in spite of similarities of composition grain size age and pre eruptive environment the various deposits exhibit great differences in terms of degree and type of alteration of the juvenile components in particular detailed analyses of pyroclasts collected in the numerous monogenetic volcanic cones show the broad range of alteration from fresh glass to complete replacement of the glass by the zeolites the comparative analysis of 17 different deposits has allowed us to conclude that the eruptive and emplacement conditions were the major controls on the zeolitization processes the relationships between volcanological features of deposits and secondary mineralization are consistent with the glass fluid phase reaction in a near closed post depositional system eruptions characterised by separation of water vapour from the pyroclastic particles produce unaltered or poorly altered deposits in contrast eruptions characterised by mechanisms that permit the capture and retention of pore water and water vapour produce zeolitized deposits according to these lines of evidence the zeolitization of pyroclastic products of campi flegrei took place immediately after emplacement during the cooling of wet deposits

viscosity of partial melts in the upper mantle the viscosity and density of melts of composition close to primary olivine tholeiite and alkali olivine basalt have been measured at pressures between 0 7 and 1 5 gpa and at temperatures between 1300 and 1475 c using the falling floating sphere method the viscosity of the olivine tholeiite melts decreases only slightly from 1 atm to 1 0 gpa whereas that of the alkali olivine basalt melts decreases by a factor of about 2 in the same pressure range and they become very close to one another about 2 0 pa s at 1 0 1 25 gpa at 1400 c the activation energy for viscous flow of the olivine tholeiite melt is about 250 kj mol at 1 0 gpa the viscosity of partial melts melts formed by partial melting in the upper mantle can be estimated based on the viscosities of the melts and the activation energy for viscous flow obtained by the present experiments the viscosity of the partial melts along the anhydrous solidus of peridotite decreases from about 2 5 pa s at 0 8 gpa 1220 c to only about 0 2 pa s at 3 5 gpa 1580 c thus the partial melts must be extremely fluid at depths greater than 100 km even under anhydrous conditions such partial melts might not ascend because of their high density and play an important role in the movement of the lithosphere the viscosities of the partial melts in the upper mantle may decrease with increasing depth until completion of the transformation of si to six fold coordination the viscosities of magmas and the diffusivity of oxygen in them have an inverse relation which is approximated by the eyring s equation the diffusivity of oxygen in the partial melts estimated from this relation and the viscosity increases from 10 7 cm2 s at 0 8 gpa to 10 5 cm2 s at 3 5 gpa along the anhydrous solidus of peridotite homogenization of partial melts or magmas would be greatly enhanced with increasing depth down to the viscosity minimum

sequential fragmentation transport theory pyroclast size density relationships and the emplacement dynamics of pyroclastic density currents a case study on the mt st helens usa 1980 eruption abstract pyroclastic density currents pdcs are the most dangerous hazard associated with explosive volcanic eruptions despite recent advancements in the general understanding of pdc dynamics limited direct observation and or outcrop scarcity often hinder the interpretation of specific transport and depositional processes at many volcanoes this study explores the potential of sequential fragmentation transport theory sft cf wohletz et al 1989 a modeling method capable of predicting particle mass distributions based on the physical principles of fragmentation and transport to retrieve the transport and depositional dynamics of well characterized pdcs from the size and density distributions of individual components within the deposits the extensive vertical and lateral exposures through the may 18th 1980 pdc deposits at mt st helens msh provide constraints on pdc regimes and flow boundary conditions at specific locations across the depositional area application to msh deposits suggests that sft parameter distributions can be effectively used to characterize flow boundary conditions and emplacement processes for a variety of pdc lithofacies and deposit locations results demonstrate that 1 the sft approach reflects particle fragmentation and transport mechanisms regardless of variations in initial component distributions consistent with results from previous studies 2 sft analysis reveals changes in particle characteristics that are not directly observable in grain size and fabric data and 3 sft parameters are more sensitive to regional transport conditions than local outcrop scale depositional processes the particle processing trends produced using sft analysis are consistent with the degree of particle processing inferred from lithofacies architectures for all lithofacies examined in this study suspension sedimentation products exhibit much better processing than concentrated current deposits integrated field observations and sft results provide evidence for increasing density segregation within the depositional region of the currents away from source as well as for comparable density segregation processes acting on lithic concentrations and pumice lenses within the current these findings further define and reinforce the capability of sft analysis to complement more conventional pdc study methods significantly expanding the information gained regarding flow dynamics finally this case study demonstrates that the sft methodology has the potential to constrain regional flow conditions at volcanoes where outcrop exposures are limited

source processes of the thermal waters from the phlegraean fields naples italy by means of the study of selected minor and trace elements distribution abstract the geochemical characteristics of hydrothermal waters from the phlegraean fields p f naples italy were analysed for minor and trace elements selectively mobilised in hydrothermal systems such as b f hg as pb and tl the water samples collected from a shallow aquifer likely to be fed by deeper fluids showed various geochemical features resulting from the mixing of three components 1 surface waters of meteoric origin 2 hot deep waters deriving from water rock interaction and including deep waters of marine origin 3 magmatic fluids rising from the local magma chamber lying a few kilometres below the town of pozzuoli this setting although very complex provides a reliable means of studying the distribution of the investigated trace elements in particular within the phlegraean area high contents of b 0 1 48 mg l f 0 5 8 mg l as 16 6050 g l and hg 0 7 232 g l were observed the levels of thallium in the springs close to solfatara about 7 g l were in line with those normally recorded in hydrothermal areas whereas high levels of this element up to 23 3 g l were identified in other wells of the study area lead 1 3 to 29 1 g l appears to be anomalous with respect to its normal content in groundwater about 1 g l owing to the presence of high density brines at depth which enhance the solubility of pb in volcanic rocks under hydrothermal conditions the distribution of the investigated trace elements in the phlegraean fields thermal area is probably related to the different ascent pathways of the fluids clearly apart from the influence exerted by anomalous thermal conditions each element shows a different behaviour depending on its geochemical affinity with mineral phases and as a consequence of the different enthalpy values which determine ion partitioning in gaseous phases based on geochemical evidences and on the distribution of minor and trace elements the source processes of the investigated hydrothermal waters were defined five main groups were identified 1 acid sulphate waters resulting from mixing of meteoric water with magmatic gases mainly h 2 s 2 high sulphate chloride waters from a deep reservoir located in the major upflow zone 3 waters associated with significant degassing of magmatic co 2 4 waters from a deep geothermal neutral chloride reservoir resulting from heating of marine water modified by water rock interaction processes 5 cold waters from the inner area influenced by low temperature water rock interaction processes

a facies interpretation of the eruption and emplacement mechanisms of the upper part of the neapolitan yellow tuff campi flegrei southern italy this study focuses on the upper part member b of the neapolitan yellow tuff nyt detailed measurements of stratigraphic sections within the unlithified pozzolana facies show that member b is composed of at least six distinct depositional units which each record a complex fluctuation between different styles of deposition from pyroclastic density flows six lithofacies have been identified 1 massive valleyponded facies the product of non turbulent flows 2 inverse graded facies formed by flows that were turbulent for the majority of transport but were deposited through a non tubulent basal regime 3 regressive sand wave facies the product of high concentration turbulent flows 4 stratified facies the product of deposition from turbulent low particle concentration flows 5 particle aggregate and 6 vesicular ash lithofacies both of which are considered to have formed by deposition from turbulent low concentration flows although the whole eruption may have been phreatomagmatic facies 1 4 are interpreted to be the product of dry eruptive activity whereas facies 5 and 6 are considered to be of wet phreatomagmatic eruptive phases small scale horizontal variations between facies include inverse graded lithofacies that pass laterally into regressive sand wave structures and stratified deposits this indicates rapid transition from non turbulent to turbulent deposition within the same flow thin vesicular ash and particle aggregate layers pass laterally into massive valley ponded vesicular lithofacies suggesting contemporaneous wet pyroclastic surges and cohesive mud flows three common vertical facies relations were recognised 1 massive valley ponded and inverse graded facies are overlain by stratified facies suggesting decreasing particle concentration with time during passage of a flow 2 repeated vertical gradation from massive up into stratified facies and back into massive beds is indicative of flow fluctuating between non turbulent and turbulent depositional conditions 3 vertical alternation between particle aggregates and vesicular facies is interpreted as the product of many flow pulses each of which involved deposition of a single particle aggregate and vesicular ash layer it is possible that the different facies record stages in a continuum of flow processes the deposits formed are dependent on the presence thickness and behaviour of a high concentration non turbulent boundary layer at the base of the flow the end members of this process are a flows that transported and deposited material from a non turbulent flow regime and b flows that transported and deposited material from a turbulent flow regime

linkages between holocene paleoclimate and paleohydrogeology preserved in a yucatan underwater cave abstract three sediment cores spanning the last 4200 years from aktun ha cave on the yucatan peninsula mexico demonstrate that underwater caves can document changes to regional hydrogeology and climate benthic microfossils testate amoebae foraminifera organic matter geochemistry 13 c 15 n c n and particle size distributions were analyzed however microfossil paleoecology proved the most useful for indicating three salinity phases in the aktun ha sediment cores phase 1 4300 yr bp contains predominantly foraminifera physalidia simplex 78 that indicate the meteoric lens flooding the cave was initially brackish salinity 3 5 g l 1 phase 2 2800 4300 cal yr bp has both freshwater testate amoebae centropyxis spp 40 and p simplex 42 which indicates a slight freshening of the meteoric lens to 1 5 2 g l 1 phase 3 lagenodifflugia vas and difflugia oblonga with a reduction in p simplex 10 this last faunal shift represents the initiation of modern freshwater conditions in the cave 1 5 g l 1 this final freshening is synchronous with a significant reduction in the c n ratio e g core 2 27 to 19 which suggests an expansion of primary productivity in the adjacent cenote the 15 n values ranged from 1 5 to 3 5 with observed cycles likely from intervals of increased terrestrial om input into the cave during high rainfall events e g hurricanes the observed paleoenvironmental shifts in the cave correlate well with regional precipitation patterns aquifer recharge and storm activity caused by southward migration of the intertropical convergence zone therefore regional climate change impacted eastern yucatan groundwater during the mid to late holocene however decelerating holocene sea level rise and aquifer occlusion are likely contributing factors these results demonstrate that underwater cave sediments and microfossils can be useful proxies for aquifer evolution and climate change

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

the 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

particle size density relationships in pyroclastic deposits inferences for emplacement processes in moving pyroclastic systems particles are sorted as a function of their sizes densities and shapes the analysis of the distribution of these characteristics in particle populations of pyroclastic deposits is a major tool in evaluating properties and regimes of parent transport systems this paper reports a study of size density relationships of component subpopulations from selected quaternary pyroclastic deposits of the latera volcanic complex vulsini italy by means of integrated field and laboratory investigations including grain size and component analyses density measurements and sem crystal morphoscopy three kinds of particle size density relationships characterize the studied deposits as follows 1 a significant correlation of decreasing sizes with increasing component densities exists for direct suspension sedimentation products including plinian fall and pyroclastic surge deposits 2 a wide data dispersion with poor correlation normally occurs for the main zones of deposits from high concentration pyroclastic flows and 3 component subpopulations occur in a narrow size range irrespective of density in granular systems dominated by grain collisions such as traction zones beneath low concentration pyroclastic surges and sheared basal layers of pyroclastic flows the regression coefficients of size density relationships appear as a comparative measure of particle concentration in the parent systems consistent with that inferred from the degree of sorting and abrasion of crystal subpopulations from sequential fragmentation transport analysis of grain size data and quantitative morphoscopy the crystal component becomes less sorted and more abraded as the fit to the size density relationship decreases from plinian fall to pyroclastic surge to pyroclastic flow consistent with increasing particle concentration in the transporting current

turbulent boundary layer shear flows as an approximation of base surges at campi flegrei southern italy abstract small volume base surge deposits of astroni and agnano monte spina eruptions at campi flegrei consist of sets of beds formed by the passage of multiple pyroclastic density currents each set is made by a fining upward sequence consisting from base to top of 1 an inversely graded layer made of bombs and lapilli 2 a finely laminated layer with wavy bedforms made of coarse ash and fine lapilli 3 a structureless fine ash bed lack of discontinuities at layer contacts allows us to hypothesize that each set of beds represents the passage of one pyroclastic density current the sequence formed as a function of the decreasing particle transportation capability of the base surge during the waxing sustained waning phases of flowage we make the simplifying assumptions that the flow on passing from the deposition of the inversely graded layer to the deposition of the finely laminated layer had low particle concentration was quasi steady and incompressible by such assumptions some of the equations that regulate sediment mechanics are applicable to the base surges of campi flegrei to reconstruct flow density and shear velocity in between the deposition of the two layers structural and textural features of deposits stress the importance of shear and turbulence during transportation and suggest that the turbulent boundary layer shear flow is a good approximation to such pyroclastic density currents we used the coles formula to reconstruct velocity as a function of flow height during the formation of the finely laminated layer of astroni and agnano monte spina base surges the methodology we used allows the reconstruction of flow parameters just at a particular point in time and space of base surge evolution and does not provide the complete picture of the flow history of pyroclastic density currents nevertheless flow velocity and density data as obtained with the proposed approach point to dynamic pressure values that are compatible with those reported for similar currents on other volcanoes we conclude therefore that the results obtained give approximate but helpful information on the nature of such hazardous events at campi flegrei

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

vent area and depositional mechanisms of the upper member of the neapolitan yellow tuff campi flegrei italy new insights from directional fabric through image analysis in order to provide new information about the source area and depositional mechanisms of the upper member of the neapolitan yellow tuff nyt a prominent pyroclastic deposit of the campi flegrei volcanic district southern italy statistics on directional fabric by means of computer assisted image analysis on 32 rock samples were compiled seventeen samples were collected along vertical direction on two selected exposures and fifteen were taken from outcrops widely distributed all around the campi flegrei volcanic district fabric measurements within the investigated successions reveal a vertically homogeneous direction of the mean particle iso orientation with considerable variability in the strength of particle iso orientation even at cm scale the existence of particle iso orientation can be related to continuous sedimentation from a concentrated bedload region beneath suspension currents producing massive or inversely graded beds by traction carpet sedimentation the considerable vertical variability in the strength of iso orientation is the result of very unstable flow regimes up to the extreme condition of discrete depositional events with a variable combination of traction carpet and or direct suspension sedimentation the vertical homogeneity in the mean orientation values found in the investigated sections may derive from the sequential deposition of laminae to thin beds whose relatively flat upper surfaces were unable to significantly deflect the depositional system of the following currents according to the observed homogeneous mean particle orientation values along the investigated vertical profiles samples collected through areal distribution are considered representative of the local paleo flow directions of the whole deposit the mean directions of the samples collected areally show two different coherent patterns which point to the existence of two different source areas the first which includes all samples from the northern outcrops appears to converge in a narrow area about 2 km ne of the town of pozzuoli largely in coincidence with the inferred area on the basis of the pumice fall distribution the second which includes samples from capo miseno and posillipo areas points to the central part of the pozzuoli bay about 4 km offshore the town of pozzuoli

hazard of pyroclastic density currents at the campi flegrei caldera southern italy as deduced from the combined use of facies architecture physical modeling and statistics of the impact parameters abstract pyroclastic density currents of the recent eruptions at campi flegrei caldera cfc southern italy have been studied with the aim of assessing the potential impact of similar events in the future eruptions of different scales have been investigated by means of the combined use of facies architecture laboratory analysis and physical modeling both in the small averno 2 and intermediate astroni scales facies analysis indicates that deposits result from the emplacement of pyroclastic density currents like base surge formed by multiple closely timed impulses of phreatomagmatic origin in the large scale event agnano monte spina the facies architecture suggests that the currents started as concentrated flows near the vent as originating from the collapse of a dense eruptive column and evolved laterally into expanded flows by the propagation of the basal shear current laboratory analyses on samples from the main layers of deposits allowed obtaining the input data for the pyflow code which was used for reconstructing the flow dynamic characteristics of the currents the expected damage is discussed in terms of the probability density function of dynamic pressure and particle volumetric concentration in this way the range of potential impact that similar pyroclastic density currents could cause to buildings infrastructures and population is defined in the large scale event the dynamic pressure ranges from 9 38 to 1 00 kpa integrating the basal 10 m of the current at distances of 1 5 and 4 0 km from the vent respectively the values are highly influenced by the local topography in the intermediate scale event the dynamic pressure ranges from 2 43 to 0 26 kpa at distances of 1 1 and 1 4 km from the vent respectively in the small scale event the dynamic pressure ranges from 1 49 to 0 39 kpa at distances of 0 5 and 1 1 km from the vent respectively the particle volumetric concentration at a height of 2 m within the current is always lower than 0 01 but typically it is higher than 0 001 inside the caldera and could have severe effects on the unsheltered population also at locations topographic highs where velocity and dynamic pressures are low in distal reaches outside the caldera the widespread fine ash originated by buoyancy from the currents which was transported by lower atmosphere winds is to be considered as a fallout load slowly accumulating on the ground surface and building roofs during the waning stage of the current

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

stable isotope relations in an open magma system laacher see eifel frg 18o 16o and d h ratios have been measured for matrix glasses and phenocrysts from the zoned phonolitic laacher see tephra sequence 11000 y b p east eifel volcanic field frg to study open system behaviour of the associated magma system mineral and glass 18o values appear to be largely undisturbed by low temperature secondary alteration record isotopic equilibrium and confirm previous conclusions based on radiogenic isotope evidence of early small scale crustal assimilation during differentiation of parental magmas in a crustal magma chamber one sanidine glass pair possibly documents the late stage influx of meteoric fluids into the topmost magma layer prior to eruption a sealing carapace of chilled magma which itself was strongly contaminated prevented large scale fluid exchange up to the point prior to eruption when this carapace was fractured and meteoric water gained access to parts of the magma system d h measurements of various glass types glass inclusions dense and pumiceous glass and amphiboles gave conflicting results suggesting a combination of degassing volatile exchange with country rocks and hydration stable isotope ratios for primitive parental magmas 18o 5 5 to 7 0 and mantle megacrysts 18o 5 5 to 6 0 d 21 to 38 for amphiboles and phlogopite resp suggest a rather variable fluid composition for the sub eifel mantle

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

ianthasaurus hardestii n sp a primitive edaphosaur reptilia pelycosauria from the upper pennsylvanian rock lake shale near garnett kansas a new small pelycosaur ianthasaurus hardestii has been discovered in the well known richly fossiliferous locality in the upper pennsylvanian missourian stanton formation near garnett kansas it is represented by a partial semi articulated skeleton and scattered elements of at least three other individuals the small insectivorous ianthasaurus possesses a number of primitive pelycosaurian features but also shares several derived characters with the large early permian herbivore edaphosaurus justifying its inclusion in the family edaphosauridae and its recognition as the oldest and most primitive member of that group