flux and fate of small mountainous rivers derived sediments into the taiwan strait article i nfo high resolution chirp sonar profiles across the taiwan strait reveal a large silt sand dominated deltaic clinoform up to 50 m thick overlying the postglacial transgressive sea floor across the southeastern central and northern strait delta like configuration and internal depositional sequences indicate a northwestward progradation from western taiwan primarily from the choshui zhuoshui river grain size and mineral data confirm the sediment s taiwanese derivation the chirp profiles together with existing radiocarbon and geomagnetic dates suggest that the clinoform has formed over the past 10 kyr the estimated volume of 375 km 3 of sediment mainly sand and silt suggests a mean annual accumulation of 60 10 6 t yr presumably much of fine mud delivered by taiwanese rivers has been washed away by the local currents and escaped either northeastward into the southern okinawa trough or southward into the south china sea numerous shallow borings onshore over the central western taiwan coastal plain reveal an additional 350 km 3

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

distal tephra record for the last ca 105 000 years from core prad 1 2 in the central adriatic sea implications for marine tephrostratigraphy abstract core prad 1 2 located on the western flank of the mid adriatic deep contains a continuous sediment record extending back to upper mis 11 the upper part of the record which spans the mid holocene to mis 5 4 the last ca 105 000 years has been investigated for tephra content a total of 25 discrete tephra layers were discovered only one of which was visible in the core sequence the other 24 are not visible to the naked eye nor were the majority detected by routine down core scanning methods a total of 625 geochemical measurements obtained from individual glass shards using wds epma enabled 21 of the 25 tephras to be assigned to known volcanic events emanating from the campanian province campi flegrei somma vesuvius and ischia island the results provide an independent basis for establishing an age depth profile for the upper part of the prad 1 2 record this study demonstrates that the number of non visible tephra layers can significantly exceed the number of visible layers in some deep marine sequences routine testing for the presence of non visible tephra layers can therefore prove rewarding leading to the detection of additional isochrons for dating and correlating marine sequences and for their synchronisation with terrestrial records

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

segmentation pattern and structural complexities in seismogenic extensional settings the north matese fault system central italy abstract we investigated the northern slope of the matese mts molise central italy with the aim of characterizing the n to ne dipping active normal fault system in the bojano basin a sector of primary importance from a seismic hazard perspective we collected field data to define the geometry and segmentation pattern of two sub systems patalecchia colle di mezzo and bojano campochiaro new evidence of late quaternary faulting was obtained by exploiting well log interpretations kinematic analysis revealed the interaction of pre quaternary inherited mainly e w striking and newly formed nw se striking normal faults slip accommodation through linkage was clearly noted in the case of the patalecchia colle di mezzo sub system detailed topographic profiles across the active fault segments provided post lgm 15 3 kyr slip rates up to 2 mm yr which agree with the high deformation rates based on different approaches in the literature finally the instrumental seismicity analysis constrained the bottom of the seismogenic layer to depths of 13 14 km and the gathered information allowed us to reconstruct the north matese seismogenic source its 3d geometry and dimensions agree with both the dimension magnitude relationships and macroseismic information available for the 1805 earthquake mw 6 6 the main historical earthquake to have struck the bojano basin

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

hydrovolcanic explosions the systematics of water pyroclast equilibration the initial contact of external water with erupting magma and the mass ratio of water to magma govern the development of hydrovolcanic phenomena the phase relations of water within the runout system and the separation of vapor or liquid from the pyroclasts explain gradational transitions between some pyroclastic flows base surges mud hurricanes mudflows and sheetfloods

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

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

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

the ilopango tierra blanca joven tbj eruption el salvador volcano stratigraphy and physical characterization of the major holocene event of central america abstract the ilopango caldera is the source of the large tierra blanca joven tbj eruption that occurred about 1 5 ka years ago between ca ad270 and ad535 the eruption dispersed volcanic ash over much of the present territory of el salvador and pyroclastic density currents pdcs extended 40 km from the volcano in this study we document the physical characteristics of the deposits from all over el salvador to further constrain the eruption processes and the intensity and magnitude of the different phases of the eruption the succession of deposits generated by the tbj eruption is made of 8 units the eruption started with pdcs of hydromagmatic origin unit a0 followed by fallout deposits units a and b that are

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 active portion of the campi flegrei caldera structure imaged by 3 d inversion of gravity data 1 we present an improved density model and a new structural map of the neapolitan yellow tuff caldera the active portion of the nested campi flegrei caldera the model was built using a new 3 d inversion of the available high precision gravity data and a new digital terrain and marine model the inversion procedure based on a variable depth lumped assembling of the subsurface gravity distribution via cell aggregation gives better defined insights into the internal caldera architecture that well agree with the available geological geophysical and geochemical data the adopted 3 d gravity method is highly efficient for characterizing the shallow caldera structure down to 3 km depth and defining features related to regional or volcano tectonic lineaments and dynamics in particular the resulting density distribution highlights a pronounced density low in correspondence of the central portion of the caldera with a detail not available till now the joint interpretation of the available data suggests a subsurface structural setting that supports a piecemeal collapse of the caldera and allows the identification of its headwall positive gravity anomalies localize dense intrusions presently covered by late volcanic deposits along the caldera marginal faults and the main structural lineaments both bordering the resurgent block and cutting the caldera floor these results allow us to both refine the current geological structural framework and propose a new structural map that highlights the caldera boundary and its internal setting this map is useful to interpret the phenomena occurring during unrest and to improve both short term and long term volcanic hazards assessment

calderas and caldera structures a review abstract calderas are important features in all volcanic environments and are commonly the sites of geothermal activity and mineralisation yet it is only in the last 25 years that a thorough three dimensional study of calderas has been carried out utilising studies of eroded calderas geophysical analysis of their structures and analogue modelling of caldera formation as more data has become available on calderas their individuality has become apparent a distinction between caldera caldera complex cauldron and ring structure is necessary and new definitions are given in this paper descriptions of calderas based on dominant composition of eruptives basaltic peralkaline andesitic dacitic rhyolitic can be used and characteristics of each broad group are given styles of eruption may be effusive or explosive with the former dominant in basaltic calderas and the latter dominant in andesitic dacitic rhyolitic and peralkaline calderas four end member collapse styles occur plate or piston piecemeal trapdoor and downsag but many calderas have multiple styles features of so called funnel and chaotic calderas proposed in the literature can be explained by other collapse styles and the terms are considered unnecessary ground deformation comprises subsidence or collapse essential characteristics of a caldera and uplifting doming and fracturing due to tumescence and or resurgence frequent but not essential collapse may occur on pre existing structures such as regional faults or on faults created during the caldera formation and the shape of the collapse area will be influenced by depth size and shape of the magma chamber the final morphology of a caldera will depend on how the caldera floor breaks up whether collapse takes place in one event or multiple events whether vertical movement is spasmodic or continuous throughout the eruptive sequence and whether blocks subside uniformly or chaotically at one or more collapse centres a meaningful description of any caldera should therefore include number of collapse events presence or absence of resurgence caldera floor coherency caldera floor collapse geometry and dominant composition of eruptives

controls on terrigenous sediment supply to the arabian sea during the late quaternary the makran continental slope the input of terrigenous sediment along the tectonically active makran continental margin off south western pakistan gulf of oman northern arabian sea is studied on the basis of sediment cores distributed along a transect from the upper slope to the abyssal plain spatial and temporal variations in sediment composition sedimentation rate and turbidite frequency in late pleistocene holocene time last 20 14c ka will be discussed and related to changes in sea level and climate and tectonic activity end member modelling of the grain size distributions of the hemipelagic and turbiditic sediments indicate that the sediments are adequately described as mixtures of three end members which represent turbidite sand turbidite silt or eolian dust and fluvial mud the geochemical and mineralogical compositions of the hemipelagic sediments indicate that the eolian dust was dominantly supplied from the northern arabian peninsula and the persian gulf region and that the fluvial input is from the makran margin the ratio of contributions of eolian and fluvial sediment in the hemipelagic intervals is used as an indicator of continental aridity i e summer monsoon intensity highest holocene turbidite frequencies and sedimentation rates are recorded at the deepest coring sites they are related to the proximity of the deformation front of the accretionary prism turbidite sedimentation on the upper continental slope was most frequent during the last glacial period of sea level lowstand and continued during the entire deglaciation and sea level rise infrequent turbidite sedimentation occurred during the holocene highstand of sea level turbidite sedimentation during the period of late sea level rise and the holocene sea level highstand is inferred to be due to the strong impact of episodic events i e flash floods and earthquakes and because of the narrow shelf of the active makran continental margin

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

soil formation in kettle holes from high altitudes in central apennines italy abstract kettle holes are relatively common features of glaciated landscapes and have been widely reported in the literature the work reported here documents the presence of kettle holes at high altitude and low latitude in the central apennines italy and describes the geomorphic and pedogenic processes that originated the soils infilling these depressions the areas selected for this study were located on three of the main massifs of the central apennines italy gran sasso majella and sibillini the kettle holes on these massifs formed at the end of the wurm glaciation appear smaller and shallower than those reported from elsewhere in the northern hemisphere are roughly circular in form and do not contain bogs or lakes in each area the dimensions of 40 kettle holes were measured and three kettle holes were excavated to examine the soils developed inside them the size of the kettle holes was highest in the sibillini massif where the glaciers reached altitudes as low as 1700 m in the very narrow low lying valleys it is hypothesised that at lower elevations the glacier receded more rapidly generating larger blocks of ice and consequently larger kettle holes once formed the kettle hole depressions were very effective as sediment traps and acted as sink for materials washed in from the surrounding slopes or from more distant wind blown sources in the kettle holes from gran sasso and majella massifs small fragments of woody charcoal were found the material filling the kettle holes accumulated inside them in the form of layers soils formed inside the kettle holes showed horizons whose thickness and properties appeared mostly inherited from the amassed layers the only pedogenic process common to the kettle holes of the three massifs was the incorporation of organic matter that as expected from the rather cold climatic conditions was subjected to slow dynamics in the kettle holes of the majella massif the horizons developed from layers rich of materials of volcanic origin and the formation of short range order minerals occurred we conclude that the soils inside the kettle holes are a repository of geomorphic pedogenic and in reference to the source of the charcoal paleo environmental information

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

a new lateglacial chronostratigraphic tephra marker for the south eastern alps the neapolitan yellow tuff nyt in langsee austria in the context of a regional biostratigraphy and palaeoclimate langsee is a small meromictic lake in carinthia se alps with partially varved lateglacial sediments the langsee tephra correlates to the neapolitan yellow tuff nyt an eruption from the campanian volcanic province italy this tephra provides a lateglacial chronostratigraphic time marker from central italy across the adriatic sea to the southeastern alps the langsee tephra is discussed in the context of pollen geochemical and microstratigraphical data from a profundal sediment core from langsee the age of 14 120 cal yr bp for the nyt has been accepted from the monticchio chronology the timescale for the lateglacial in the langsee record is based on laminae counts and has been linked to calendar year ages using the nyt tephrachronological marker consequently the mass expansion of betula has been dated at 14 270 cal yr bp the expansion of p sylvestris started concurrent with the nyt and about 180 yr later at 13 940 cal yr bp p sylvestris forests were established the younger dryas biozone at langsee is characterized only by a slight increase in non arboreal pollen and dominated by pine with visible variations only in pine pollen types differentiation of pine pollen types allowed the recognition of three minor fluctuations during the lateglacial interstadial two of these oscillations tentatively have been correlated with the aegelsee and gerzensee oscillations in switzerland as well as with vegetation changes in nw germany

quaternary silicic pyroclastic deposits of atitlan caldera guatemala abstract atitlan caldera has been the site of several silicic eruptions within the last 150 000 years following a period of basalt andesite volcanism the silicic volcanism began with 5 10 km3 of rhyodacites erupted as plinian fall and pyroclastic flows about 126 000 yr b p at 85 000 yr b p 270 280 km3 of compositionally distinct rhyolite was erupted in the los chocoyos event which produced widely dispersed plinian fall deposits and widespread mobile pyroclastic flows in the latter parts of this eruption rhyodacite and minor dacite were erupted which compositionally resembled the earliest silicic magmas of the atitlan center as a result of this major eruption the modern atitlan iii caldera formed following this event rhyodacites were again erupted in smaller 5 13 km3 volumes partly through the lake and mafic volcanism resumed forming three composite volcanoes within the caldera the bimodal mafic silicic atitlan volcanism is similar to that which has occurred elsewhere in the guatemalan highlands but is significantly more voluminous mafic lavas are thought to originate in the mantle but rise intrude and underplate the lower crust and partly escape to the surface eventually silicic melts form in the crust possibly partly derived from underplated basaltic material rise crystallize and erupt the renewed mafic volcanism could reflect either regional magmato tectonic adjustment after the large silicic eruption or the onset of a new cycle

hydrothermal fluid venting in the offshore sector of campi flegrei caldera a geochemical geophysical and volcanological study the ongoing unrest at the campi flegrei caldera cfc in southern italy is prompting exploration of its poorly studied offshore sector we report on a multidisciplinary investigation of the secca delle fumose sdf a submarine relief known since antiquity as the largest degassing structure of the offshore sector of cfc we combined high resolution morpho bathymetric and seismo stratigraphic data with onshore geological information to propose that the present day sdf morphology and structure developed during the initial stages of the last cfc eruption at monte nuovo in ad 1538 we suggest that the sdf relief stands on the eastern uplifted border of a n s trending graben like structure formed during the shallow emplacement of the monte nuovo feeding dike we also infer that the high angle bordering faults that generated the sdf relief now preferentially allow the ascent of hot brines with an equilibrium temperature of 179 c thereby sustaining hydrothermal degassing on the seafloor systematic vertical seawater profiling shows that hydrothermal seafloor venting generates a sizeable co2 ph and temperature anomaly in the overlying seawater column data for the seawater vertical profile can be used to estimate the co2 and energy heat outputs from the sdf area at 50 tons day 0 53 kg s and 80mw respectively in view of the cause effect relationship with the monte nuovo eruption and the substantial gas and energy outputs we consider that the sdf hydrothermal system needs to be included in monitoring programs of the ongoing cfc unrest this article is protected by copyright all rights reserved

late quaternary tephra derived paleosols in central italy s carbonate apennine range stratigraphical and paleoclimatological implications abstract detailed stratigraphical pedological and geochronological 14c dating research was carried out on numerous sections located in the carbonate apennine range of central italy two paleosols late pleistocene pedomarker a and holocene pedomarker b in age were recognized as having developed from air fall pyroclastic material given their special properties and widespread distribution both soils represent valuable markers in the late quaternary stratigraphy of central italy information about the climatic conditions that have influenced their pedogenesis through time has been obtained pedomarker a formed under temperate wet conditions related to the last interstadial fluctuations of the pleniglacial its development ceased after ca 30 ka because of the onset of last glacial maximum dry cold conditions pedomarker b formed at the beginning of the holocene under udic and perudic soil moisture regimes its development ceased in some localities because of a change towards a drier climate after ca 4 5 ka petrographic and geochemical characteristics of the parent materials are discussed and correlations with the campanian ignimbrite pedomarker a and neapolitan yellow tuff pedomarker b both related to activity in the phlegrean fields are proposed

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

geochemical characterization of quaternary tephras from the campanian province italy the campanian province has a rich history of human interaction with volcanic eruptions in a region currently inhabited by 3 million people it is crucial to have precise and accurate geochemical characterization of volcanic units within the region so as to identify the spatial distribution of past events furthermore tephrochronology is becoming an important tool in the region for correlating past environmental records unfortunately many of the key units have been geochemically analysed using relatively imprecise methods making correlation problematic although robust correlations have been established in the campanian province using a range of methods including stratigraphy and geochronology more distal correlation requires precise geochemical characterisation of individual glass shards here we report major oxide data geochemically characterising 17 key tephra units within the campanian province using wavelength dispersive spectrometry wds the new data confirm the trachytic nature of most of the eruptions to effect more precise correlations between units especially in distal locations proximal units must be individually analysed for major oxides using wds on the vitreous phase and statistically analysed for robust correlations in cases where similar geochemistry exists analysis of trace and rare earth elements may be necessary

linking the north atlantic to central europe a high resolution holocene tephrochronological record from northern germany a high resolution holocene tephrochronology for northern germany has been established based on systematic tephrostratigraphical analysis of three peat bogs microscopic volcanic ash layers have been traced and characterised petrographically and by the chemical composition of the glass shards at least 37 ash horizons representing 16 different explosive volcanic eruptions have been identified and many can be correlated between the three sites up to 100 km apart the tephra layers can be related to icelandic volcanic sources and some correlated to the eruptions of askja 1875 hekla 3 hekla selsund hekla 4 and hekla 5 as well as to unspecified eruptions of icelandic volcanic systems e g torfajokull the source volcanoes for some tephra layers remain unidentified some tephra layers were known previously from the north atlantic region e g sluggan glen garry others have not been recorded previously in the literature e g microlite tephra this study provides the first comprehensive holocene tephrostratigraphical record for northern germany complementing the north atlantic tephrostratigraphical dating framework effectively extending it into central europe the study shows that icelandic ash layers are even more widespread than hitherto thought copyright 2002 john wiley sons ltd

interpretation of gravity and magnetic data in the phlegraean fields geothermal area naples italy abstract available gravity and magnetic data of the phlegraean fields geothermal area naples italy have been interpreted and the obtained structural models discussed in the light of the other available geological volcanological and geophysical data on the basis of the results of a previous seismic reflection survey in the gulf of naples and in the pozzuoli bay which delineated a basement characterized by a seismic velocity of 4 6 km s it has been possible to evaluate the gravity anomaly connected with the morphology of this horizon 2 7 g cm3 the residual anomaly map obtained after subtraction of the regional long wavelength components relative to mantle and deep crustal structures and the computed components relative to the above mentioned seismic basement shows up as a circular low with an amplitude of 10 mgal centred in the pozzuoli bay this gravity low has been interpreted as due to the occurrence in the centre of pozzuoli bay of light 0 2 g cm3 material with a maximum thickness of about 2 km however a contribution to the anomaly due to a narrow magmatic body intruded in the basement as suggested by volcanological and ground deformation data cannot be excluded the aeromagnetic map of the phlegraean fields is characterized by three main anomalies which have been fitted by superficial tridimensional parallelepipedic bodies schematically representing lava flows and domes their anomalies have been subsequently subtracted from the observed field obtaining as a residual a large anomaly centred in the southwestern area of the pozzuoli bay it has been interpreted as being due to a lowmagnetized body which taking into account the thermal state of the area should represent that part of the pyroclastic sequence which has lost part of its magnetization by thermo chemical alteration

the jiulong river plume as cross strait exporter and along strait barrier for suspended sediment evidence from the endmember analysis of in situ particle size abstract the influences of the jiulong river on taiwan strait sediment resuspension and transport systems was conducted to reveal the extent to which longshore gradients in fine sediments could be related to the existence of a fresh water plume from the jiulong river an endmember model was used in the analysis of in situ suspended particle size data obtained by a lisst particle analyzer device in order to understand the effect of jiulong river plume on taiwan strait waters during the summer period of 2010 three in situ suspended particle endmembers associated with particular sediment dynamic processes are identified endmember 1 associated with estuarine waters endmember 2 associated with a fine sediment zone over longshore clinothem and endmember 3 associated with a coarse sediment zone over outer shelf and main channel of the strait the spatial distribution of the endmember 1 shows the adjustment of estuarine related suspended particles from the upper water layer to the halocline layer when they were transported along the plume the spatial distribution of endmember 1 can also indicate how the jiulong river estuarine related suspended particles transport across the taiwan strait although such a relatively small amount of river derived suspended particle transport provides limited fine sediment source to the inner shelf of the west taiwan strait the distribution of the reworking fine sediment dominating endmember 2 illustrates that the jiulong river plume acts as a barrier to alter the along strait transport of fine particles and the strengthened cross strait transport traps them into the distal depocenter in west part of taiwan strait

tephrostratigraphy study for the last 18 000 14 c years in a deep sea sediment sequence for the south adriatic abstract a detailed tephrostratigraphy supported by accelerator mass spectrometry ams 14c dating and isotopic and geochemical analyses has been carried out for a deep sea core collected from the southern adriatic sea which spans the last 18 14c kyr fourteen ash layers have been recognized in the marine core and the origin was determined by comparing their age and geochemistry with tephra detected in terrestrial deposits the geochemical signatures of marine ash layers indicate a prevailing campanian and subordinate etnean and eolian provenances collectively they are attributed to sources in the phlegraean fields lam lagno amendolare ln1 ln2 gm1 c 2 nyt neapolitan yellow tuff c 1 agnano pomici principali ams pf agnano monte spina ast astroni somma vesuvius l9 pomici di base l8 greenish mount etna et1 y1 biancavilla ignimbrite lipari e 1 gabellotto fiumebianco and palinuro seamount pal 1 some of these eruptions have been detected for the first time in marine cores astroni lam l9 l8 and three were detected and dated by marine tephra ln1 ln2 and pal 1 providing new more precise stratigraphic markers for the last 18 kyr in the south adriatic marine record

primary and redeposited facies from a large magnitude rhyolitic phreatomagmatic eruption cana creek tuff late carboniferous australia the cana creek tuff is one of four rhyolitic ignimbrite members of the late carboniferous currabubula formation a volcanogenic conglomeratic braidplain sequence exposed along the western margin of the new england orogen in northeastern new south wales the source is not exposed but was probably located tens of kilometres to the west of existing outcrops the medial to distal parts of the tuff average about 70 m in thickness are widespread minimum present area 1400 km2 and comprise a primary pyroclastic facies ignimbrite ash fall tuff and a redeposited volcaniclastic facies sandstone conglomerate both facies are composed of differing proportions of crystal fragments quartz plagioclase k feldspar pumiceous clasts pumice shards fine ash and accidental lithics the eruption responsible for this unit was explosive and of large magnitude dense rock equivalent volume about 100 km3 that it was also phreatomagmatic in character is proposed on the basis of the intimate association of primary and redeposited facies the presence of accretionary lapilli both in ignimbrite and in ash fall tuff the fine grain size of juvenile pyroclasts the low grade of the ignimbrite and the close similarity in facies composition and magnitude to the deposits from the 20 000y b p phreatomagmatic eruption at taupo new zealand the wairakei and parts of the hinuera formations the eruption began and ended from a vent with excess water available possibly submersed in a caldera lake and generated volcaniclastic sheet floods and debris flows the emplacement of the primary pyroclastic facies is correlated with an intervening stage when the water magma mass ratio was lower the deposits from a large magnitude phreatomagmatic eruption are predicted to show systematic lateral variations in facies primary pyroclastic facies predominate near the source although the preserved stratigraphy is an incomplete record because of widespread contemporaneous erosion volcaniclastic facies redeposited from proximal sites by floods dominate at medial and distal locations in areas hundreds of kilometres from the source the eruption is registered by thin layers of fine grained airfall ash

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

sediment resuspension flocculation and settling in a macrotidal estuary national natural science foundation of china 40876043 papd fund china scholarship council 2010832427 mel young scientist visiting fellowship melrs0938

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

a unique yellow river derived distal subaqueous delta in the yellow sea abstract newly acquired high resolution chirp sonar profiles reveal a unique yellow river derived alongshore distributed bidirectional landward and seaward across shelf transported omega shaped distal subaqueous deltaic lobe deposited around the eastern tip of the shandong peninsula in the yellow sea this clinoform deposit directly overlies the postglacial transgressive surface featured by convex up seafloor morphology up to 40 m thick locally radiocarbon 14 dates from the underlain pre holocene and transgressive sediments indicate this distal lobe has formed since the middle holocene highstand under a relatively stable sea level this along shelf distributed distal clinoform has been deposited mainly by the resuspended yellow river sediments carried down by the coastal current interacting with the local waves tides and upwelling collectively over the past 7000 years nearly 30 of the yellow river derived sediment has been re suspended and transported out of the bohai sea into the yellow sea overall the yellow river derived sediment could reach the 80 m water depth in the central south yellow sea about 700 km from the river mouth in contrast a very small fraction of the modern riverine sediment could escape the outer shelf or reach the okinawa trough

towards a european tephrochronological framework for termination 1 and the early holocene the record of deposition of tephras in europe and the north atlantic during the period 18 5 8 0 14 c ka bp the last termination and early holocene is reviewed altogether 34 tephras originating from four main volcanic provinces iceland the eifel district the massif central and italy have been identi ed so far in geological sequences spanning this time interval most of the records have been based until very recently on observations of visible layers of tephras here we report on the potential for extending the areas over which some of the tephras can be traced by the search for layers of micro tephra which are not visible to the naked eye and on the use of geochemical methods to correlate them with known tephra horizons this approach has greatly extended the area in northern europe over which the vedde ash can be traced the same potential exists in southern europe which is demonstrated for the rst time by the discovery of a distinct layer of micro tephra of the neapolitan yellow tu in a site in the northern apennines in italy far to the north of the occurrences of visible records of this tephra the paper closes by considering the potential for developing a robust european tephrostratigraphy to underpin the chronology of records of the last termination and early holocene thereby promoting a better understanding of the nature timing and environmental e ects of the abrupt climatic changes that characterized this period

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

syn and posteruptive hazards of maar diatreme volcanoes abstract maar diatreme volcanoes represent the second most common volcano type on continents and islands this study presents a first review of syn and posteruptive volcanic and related hazards and intends to stimulate future research in this field maar diatreme volcanoes are phreatomagmatic monogenetic volcanoes they may erupt explosively for days to 15 years above the preeruptive surface a relatively flat tephra ring forms below the preeruptive surface the maar crater is incised because of formation and downward penetration of a cone shaped diatreme and its root zone during activity both the maar crater and the diatreme grow in depth and diameter inside the diatreme which may penetrate downwards for up to 2 5 km fragmented country rocks and juvenile pyroclasts accumulate in primary pyroclastic deposits but to a large extent also as reworked deposits ejection of large volumes of country rocks results in a mass deficiency in the root zone of the diatreme and causes the diatreme fill to subside thus the diatreme represents a kind of growing sinkhole due to the subsidence of the diatreme underneath the maar crater is a subsidence crater and also grows in depth and diameter with ongoing activity as long as phreatomagmatic eruptions continue the tephra ring grows in thickness and outer slope angle syneruptive hazards of maar diatreme volcanoes are earthquakes eruption clouds tephra fall base surges ballistic blocks and bombs lahars volcanic gases cutting of the growing maar crater into the preeruptive ground formation of a tephra ring fragmentation of country rocks thus destruction of area and ground changes in groundwater table and potential renewal of eruptions the main hazards mostly affect an area 3 to possibly 5 km in radius distal effects are comparable to those of small eruption clouds from polygenetic volcanoes syneruptive effects on infrastructure people animals vegetation agricultural land and drainage are pointed out posteruptive hazards concern erosion and formation of lahars inside the crater a lake usually forms and diverse types of sediments accumulate in the crater volcanic gases may be released in the crater compaction and other diagenetic processes within the diatreme fill result in its subsidence this posteruptive subsidence of the diatreme fill and thus crater floor is relatively large initially but will decrease with time it may last millions of years various studies and monitoring are suggested for syn and posteruptive activities of maar diatreme volcanoes erupting in the future the recently formed maar diatreme volcanoes should be investigated repeatedly to understand more about their syneruptive behaviour and hazards and also their posteruptive topographic limnic and biologic evolution and potential posteruptive hazards for future maar diatreme eruptions a hazard map with four principal hazard zones is suggested with the two innermost ones having a joint radius of up to 5 km areas that are potentially endangered by maar diatreme eruptions in the future are pointed out

mechanisms for the generation of compositional heterogeneities in magma chambers although there is general agreement that systematic variations of composition temperature and crystallinity in pyroclastic deposits provide strong evidence for chemical heterogeneities inside of magma chambers no hypothesis for the origin of these heterogeneities is widely accepted the chemical boundary layer flow hypothesis receives the most attention in the literature but other potentially valuable hypotheses are ignored in this paper we review the representative hypotheses and attempt to quantitatively evaluate their potential for producing compositional heterogeneities our conclusions can be summarized as follows based on volcanological data for compositionally zoned eruptions evolved magma is generated at a rate between 10 2 and 10 4 km3 a with a typical value of 10 3 km3 a melting of silicic country rock by intrusion of basaltic magma is a viable hypothesis because evolved melt is produced at a rate consistent with the volcanological observations some systems however do not show the extensive isotopic contamination predicted by this model mechanisms which involve porous media flow separation of partial melts from the source region and boundary layers in a magma chamber s marginal liquid crystal mush are unlikely due to low permeability of the porous media diffusion limited chemical boundary layers are capable of transporting significant quantities of h2o rich melt to the roof of a magma chamber components which diffuse more slowly for example sio2 are transported in sufficient quantities only if diffusively coupled to more mobile species in the melt cross coupling effects will be important if the off diagonal diffusion coefficients are 10 of the on diagonal coefficients or larger

compression along the northern apennines evidence from the mw 5 3 monghidoro earthquake in this paper we present the seismological data recorded during the deployment of a dense three component seismic network installed a few hours after the 2003 mw 5 3 monghidoro earthquake in northern apennines the main shock focal solutions derived from polarities distribution and body wave modelling of regional broadband data show a ne sw striking reverse mechanism accurate relative locations of aftershocks and the inversion of focal mechanisms show that earthquakes occurred on a nw dipping backthrust within the adria lithosphere under a nw trending horizontal compression the observed compression is a secondary process possibly explained by differential motion within the adriatic lithosphere fault geometry and kinematics is controlled by pre existing structures

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

the hazards of eruptions through lakes and seawater abstract eruptions through crater lakes or shallow seawater referred to here as subaqueous eruptions present hazards from hydromagmatic explosions such as base surges lahars and tsunamis which may not exist at volcanoes on dry land we have systematically compiled information from eruptions through surface water in order to understand the circumstances under which these hazards occur and what disastrous effects they have caused in the past subaqueous eruptions represent only 8 of all recorded eruptions but have produced about 20 of all fatalities associated with volcanic activity in historical time excluding eruptions that have resulted in about a hundred deaths or less lahars have killed people in the largest number of historical subaqueous eruptions 8 followed by pyroclastic flows excluding base surges 5 tsunamis 4 and base surges 2 subaqueous eruptions have produced lahars primarily on high 1000 m steep sided volcanoes containing small

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

the taupo eruption new zealand i general aspects the ca a d 186 taupo eruption was the latest eruption at the taupo volcanic centre occurring from a vent at horomatangi reefs now submerged beneath lake taupo in the central north island of new zealand minor initial phreatomagmatic activity was followed by the dry vent 6 km 3 hatepe plinian outburst large amounts of water then entered the vent during the 2 5 km 3 hatepe phreatoplinian ash phase eventually stopping the eruption though large amounts of water continued to be ejected from the vent area causing gullying of the ash deposits after a break of several hours to weeks phreatoplinian activity resumed generating the 1 3 km 3 rotongaio ash notable for its fine grainsize and for containing significant quantities of non or poorly vesicular juvenile material the vent area then became dry again and eruption rates and power markedly increased into the 23 km 3 taupo ultraplinian phase which is the most powerful plinian outburst yet documented synchronous with this ultraplinian activity lesser volumes of non to partially welded ignimbrite were generated by diversion of ejecta from or partial collapse of the eruption column the rapid rate of magma withdraw al during this phase removed support from the vent area to trigger local vent collapse and initiate the catastrophic eruption of the ca 30 km 3 taupo ignimbrite finally after some years lava was extruded on to the floor of the reformed lake taupo and floating fragments derived from the lava carapace were driven ashore the known eruption volume is more than 65 km 3 while additional volumes are represented by primary material now beneath lake taupo and layer 3 to the ignim brite phases a total volume of more than 105 km 3 is likely equivalent to more than 35 km 3 of magma plus more than 3 km 3 of lithic debris airfall deposits more than 10 cm thick blanketed 30000 km 2 of land east of the vent while ignimbrite covers a near circular area of 20000 km 2 widespread and locally severe ground shaking occurred during but mostly after the eruption associated with subsidence in the lake taupo basin secondary deposits are abundant above and extending beyond the taupo ignimbrite consisting of the products of surface water interacting with the still hot ignimbrite and subsequent water reworking of the light pumiceous materials the complexity and size of this eruption preclude accurate forecasting of the size nature and return period of the inevitable next eruption from the taupo volcanic centre