evaluation of the applicability of acid leaching for the 238u 230th internal isochron method abstract the 238 u 230 th internal isochron method has great potential for determining eruption ages of young volcanic materials if the separated groundmass phases have a sufficiently wide range of u th ratios we examined the fractionation behavior of u and th in aged i e 0 5 ma basaltic samples by 6 m hydrochloric acid leaching to evaluate the applicability of acid leaching treatment for the 238 u 230 th internal isochron method acid leaching of aged basaltic rocks in 238 u 234 u 230 th secular equilibrium at the bulk rock scale results in 230 th 238 u and 234 u 238 u radioactive disequilibria for both leachates and residues these radioactive disequilibria can be explained by redistribution of 234 th parent of 234 u and 230 th between acid soluble and acid resistant phases due to recoil the number of 230 th atoms redistributed by recoil can be calculated by using a mass conservation equation for 234 u atoms and by the relative amount of recoiled 230 th and 234 th the latter proportional to the kinetic energy of the recoiled nuclide when the fraction of daughter nuclide 234 u remaining in either the residue or leachate after recoil redistribution of 238 u is large enough 95 the corrected 230 th 238 u values of leachate and residue show radioactive equilibria this result demonstrates that preferential fractionation between u and th does not occur during acid leaching for basaltic samples if there is no selective etching of the recoil track this study implies that acid leaching can be used in conjunction with the 238 u 230 th internal isochron method for dating young volcanic rocks by evaluating the degree of the recoil redistribution of 234 u

the 1891 submarine eruption offshore pantelleria island sicily channel italy identification of the vent and characterization of products and eruptive style high resolution bathymetry and seafloor sampling have been used to characterize the 1891 submarine eruption of the pantelleria volcanic complex this submarine eruption has been documented mainly by historical reports describing basaltic scoria bombs floating on the sea surface i e lava balloons in this study the 1891 eruptive vent has been identified as a small cone volume of 700 000 m3 rising 90 m from 350 m w d and located within a newly discovered submarine volcanic field covering a wide area offshore from the nw coast of pantelleria recently kelly et al 2012 confirmed this location by a multibeam and rov survey pyroclasts from the 1891 eruption crop out directly on the seafloor and are fresh scoria clasts i e small bombs bomb fragments and lapilli and glass ash sized grains both have been characterized in their morphology textures and geochemistry the distinctive vesicularity and crystallization characteristics displayed by the scoriaceous pyroclasts reflect modes of degassing in both syn and posteruptive regimes these characteristics along with the distribution of deposits suggest for the strongest eruptive phase of the 1891 eruption a style analogous to hawaiian fountaining glass grains from a buoyant plume were dispersed northward from the vent up to distances of 1 5 km redirected by the levantine intermediate water the identification of the 1891 submarine eruptive vent offshore pantelleria as well as the features of erupted pyroclasts improve our knowledge of submarine explosive eruptions that occur at shallow intermediate depths and among these of the rare eruptions producing lava balloons

quantitative hazard assessment of phreatomagmatic eruptions at vulcano aeolian islands southern italy as obtained by combining stratigraphy event statistics and physical modelling abstract the detailed analysis of stratigraphy allowed the reconstruction of the complex volcanic history of la fossa di vulcano an eruptive activity mainly driven by superficial phreatomagmatic explosions emerged a statistical analysis of the pyroclastic successions led to the identification of dilute pyroclastic density currents base surges as the most recurrent events followed by fallout of dense ballistic blocks the scale of events is related to the amount of magma involved in each explosion events involving about 1 million cm 3 of magma occurred during recent eruptions they led to the formation of hundreds of meters thick dilute pyroclastic density currents moving down the volcano slope at velocities exceeding 50 m s the dispersion of density currents affected the whole vulcano porto area the vulcanello area they also overrode the fossa caldera s rim spreading over the piano area for the aim of hazard assessment deposits from la fossa cone and la fossa caldera were studied in detail to depict the eruptive scenarios at short term and at long term by means of physical models that make use of deposit particle features the impact parameters have been calculated they are dynamic pressure and particle volumetric concentration of density currents and impact energy of ballistic blocks a quantitative hazard map based on these impact parameters is presented it could be useful for territory planning and for the calculation of the expected damage

late pleistocene paleoclimates and sea level change in the mediterranean as inferred from stable isotope and u series studies of overgrowths on speleothems mallorca spain abstract phreatic overgrowths on speleothems form at the surface of brackish pools which are present in many coastal caves of mallorca spain unlike common vadose speleothems formed in subaerial environments their occurrence directly identifies the height of the sea level at the time of the carbonate deposition because such pools are physically connected with the sea these deposits from the late pleistocene have recorded the same global variations in oxygen isotopes as planktonic and benthonic foraminifera corals and cave deposits a number of phreatic overgrowths on speleothems have been dated using the th u method in order to determine the position of the sea level during late quaternary the same samples as well as some subaerial speleothems have been analysed for 18 o 16 o and 13 c 12 c ratios the former samples allow the analysis of variations in sea water component in the brackish pools associated with glacio eustatic mediterranean fluctuations and the latter permit inferences concerning past continental climate changes some high sea stands have been recognized in correspondence with oxygen isotope stages ois 9 or older 7 5e 5c and 5a phreatic overgrowths on speleothems have also been formed during a colder phase ois 4 demonstrating that also in that period there were environmental conditions favourable for this kind of carbonate precipitation vadose crystallizations have recorded a cold period at 36 ka corresponding with the end of ois 3

coupling of millennial scale changes in sea surface temperature and precipitation off northeastern brazil with high latitude climate shifts during the last glacial period 1 high resolution records of alkenone derived sea surface temperatures and elemental ti ca ratios from a sediment core retrieved off northeastern brazil 4 s reveal short term climate variability throughout the past 63 000 a large pulses of terrigenous sediment discharge caused by increased precipitation in the brazilian hinterland coincide with heinrich events and the younger dryas period terrigenous input maxima related to heinrich events h6 h2 are characterized by rapid cooling of surface water ranging between 0 5 and 2 c this signature is consistent with a climate model experiment where a reduction of the atlantic meridional overturning circulation amoc and related north atlantic cooling causes intensification of ne trade winds and a southward movement of the intertropical convergence zone resulting in enhanced precipitation off northeastern brazil during deglaciation the surface temperature evolution at the core site predominantly followed the antarctic warming trend including a cooling prior to the younger dryas period an abrupt temperature rise preceding the onset of the bolling allerod transition agrees with model experiments suggesting a southern hemisphere origin for the abrupt resumption of the amoc during deglaciation caused by southern ocean warming and associated with northward flow anomalies of the south atlantic western boundary current

preferential leaching and the age of radiation damage from alpha decay in minerals preferential release into solution of radionuclides that result from alpha decay is a contributor to natural isotopic disequilibrium such release is critical to geochemical understanding of alpha decay products and would be an undesirable characteristic of solidified nuclear waste in deep geological formations spontaneous annealing of the radiation damage that is responsible for the preferential release is shown to diminish the effect in thorianite and uraninite which we have found to be 550 to 1000 m y old respectively leaching experiments and measurements of the thorium and uranium isotopes show that there is strongly enhanced release of short lived 228th relative to 232th but only slight enhancement of long lived 234u and 230th relative to 238u and 232th these results are interpreted in terms of natural annealing of damage occurring on a time scale between the 10 and 105 years of the alpha decay products with a simple assumption actual times for the survival of the enhanced leaching in these minerals are 15 000 years

the late holocene tephra record of the central mediterranean sea mapping occurrences and new potential isochrons for the 4 4 2 0 ka time interval five cores from the southern tyrrhenian and ionian seas were studied for their tephra and cryptotephra content in the 4 4 2 0 ka time interval the chronological framework for each core was obtained by accelerator mass spectrometry 14c dating the occurrence of distinct marker tephra and stratigraphic correlation with adjacent records tephrochronology allowed us to correlate the analyzed deposits with tephra markers associated with somma vesuvius 79 ad ischia island cretaio mt etna fg fl and fs and campi flegrei astroni agnano monte spina events for the first time in the marine setting a large single glass data set is provided for the late holocene etnean marker beds including the fs tephra ca 4 3 ka moreover unknown deposits from lipari ca 2 2 2 0 ka and vulcano 3 6 3 3 ka are also recognized at more distal sites than previously reported these results contribute to improve the high resolution tephrostratigraphic framework of the central mediterranean sea they also provide new insights into the chemical composition and dispersal pattern of tephras that can be used as inter archive tools for regional and local stratigraphic correlations and for addressing paleoclimate research

volcanic hazards at fossa of vulcano data from the last 6 000 years stratigraphic reconstruction of the complete sequence of deposits that formed the fossa cone of vulcano has distinguished four principal eruptive cycles punte nere palizzi commenda and pietre cotte at least three additional eruptive cycles one of which ends with the campo sportivo lava occur between deposits of the punte nere and palizzi cycles however exposure is inadequate for their characterization the assignment of the modern deposits that follow the pietre cotte lava is uncertain

u series isochron dating a generalized method employing total sample dissolution the age of a sedimentary deposit can be determined by measuring 238u 234u 232th and 230th in two or more samples of the deposit with the requirement that these samples have different u th ratios but an identical 230th232th ratio when deposited this paper presents the theoretical and experimental aspects of the dating method the latter involves techniques for securing samples of varied u th ratios from the same deposit plotting isochrons of the radiochemical data obtained on totally dissolved samples for age analysis and estimating the errors involved although applications to impure carbonates and lacustrine evaporite sediments are given as examples in this paper the method potentially can be generalized for dating a variety of authigenic deposits such as rock varnish peat opal sulfate minerals and marine phosphorites

volcaniclastic debris flows at la fossa volcano vulcano island southern italy insights for erosion behaviour of loose pyroclastic material on steep slopes abstract this paper describes a qualitative model of erosion of loose volcaniclastic material on steep slopes of la fossa cone vulcano island italy that generates small volume debris flows the loose volcaniclastic cover rests on an almost impermeable substratum which comprises a fine grained hydromagmatic tuff morphologically three sectors were distinguished 1 a water supply zone slope 32 where rain water is enriched in mud and concentrated in the initiation zone 2 an initiation zone or source area sensu stricto slope with 30 where debris flows form and 3 a transport and deposition zone where debris flows deposited levees and terminal lobes slope 30 main episodes of erosion of loose volcaniclastic cover and debris flow generation occur in response to thunderstorms the erosion of tuff from superficial water added a significant amount of fines mud fraction to the initiating flows debris flow stoppage on steep slopes was interpreted as the result of a loss of mass estimated between 35 and 53 of total mass to form levees from field and laboratory data the density of debris flows was estimated at about 1950 kg m3 morphological data matrix texture mass number nm and clay content of debris flow deposits suggest that they were deposited by saturated granular slurries

glass geochemistry of pyroclastic deposits from the aeolian islands in the last 50 ka a proximal database for tephrochronology abstract volcanic ash 1000 analyses provides a basis for proximal distal and distal distal tephra correlations tephra deposits from the different aeolian islands are geochemically diverse with some individual eruptions showing diagnostic geochemical heterogeneity recognised both stratigraphically and or spatially major element glass analyses reveal that vulcano 0 21 ka and stromboli 4 13 ka have erupted potassic shoshonitic and k series tephra with broadly overlapping compositions but data presented here demonstrates that their eruptive products can be distinguished using either tio2 contents or their hfse th ratios whilst individual volcanic sources often produce successive tephra deposits with near identical major and minor element compositions through time i e lipari vulcano trace element glass data can help to decipher successive eruptions changes in lree and th concentrations of volcanic glasses erupted spanning approximately the last 50 ka greatly enhance the potential to discriminate successive eruptive units on lipari the new proximal glass database has been used to verify new ionian sea core m25 4 12 and existing distal occurrences of aeolian island derived tephra enabling the reassessments of past ash dispersals finally proximal and distal data have been used to establish an integrated proximal distal eruptive event stratigraphy for the aeolian islands

middle late holocene caribbean aridity inferred from foraminifera and elemental data in sediment cores from two cuban lagoons abstract coastal lagoons are rarely used as paleoclimate archives because of their complex geomorphic histories which can be affected by both climate and sea level change combined foraminiferal and xrf element analysis of sediment cores from punta de cartas and playa bailen cuba isolated the effects of climate change wet vs dry on the lagoon environments foraminiferal assemblages from both punta de cartas and playa bailen show increasing diversity over the past 4000 yr bp with a prominent increase at 1400 1100 yr bp assemblages were initially dominated by ammonia spp e g ammonia tepida and elphidium spp e g elphidium excavatum indicating brackish conditions but increased miliolid species e g triloculina spp quinqueloculina spp indicate a shift to more marine conditions up core correspondingly terrigenous input to the lagoon fe ti ti ca and k declined over the past 4000 yr bp with a flexion at 1200 1100 yr bp that is likely a consequence of decreasing precipitation fe ti and k have been used as proxies for detrital erosion and transport rates in tropical and sub tropical basins with greater input during wet periods but have rarely been applied to shallow lagoon systems coincident changes in the xrf and foraminiferal data indicate decreased freshwater input to the lagoon and support an inference for the onset of drier climate conditions similar temporal patterns in the foraminifera and xrf records from the two lagoons which are 10 km apart suggest a regional climate influence with increasingly arid conditions developing since the middle holocene 4 kyr bp a pronounced drying over the last 1200 years agrees with other climate records from the caribbean

adiabatic temperature profile in the mantle abstract the temperature at the 410 km discontinuity is re evaluated by comparing the depth of the discontinuity with the olivine wadsleyite transition pressure obtained using in situ x ray diffraction experiments by katsura et al 2004a and equation of state eos of mgo by tange et al 2009 tange scale and matsui et al 2000 the newly estimated temperature is 1830 48 k 70 k higher than that by our previous estimation the eoses of the major mantle minerals olivine wadsleyite ringwoodite and perovskite are also recalculated using the tange scale the adiabatic temperature gradient is calculated using the thermal expansion coefficient obtained from these eoses the adiabatic temperature gradient gradually decreases with increasing depth without a phase transition and abruptly increases in association with phase transitions the adiabatic temperature gradients are found to be 04 0 5 and 0 3 k km in the upper and lower parts of the mantle respectively the temperatures at a depth of 200 km the bottom of the mantle transition zone the top of the lower mantle and a depth of 2700 km are found to be 1720 40 2010 40 1980 40 and 2730 50 k the mantle potential temperature is found to be 1610 35 k

marine continental tephra correlations volcanic glass geochemistry from the marsili basin and the aeolian islands southern tyrrhenian sea italy abstract major minor and trace element analysis of volcanic glass in proximal and distal it is evident that correlation of proximal continental and distal marine tephras at a high level of confidence requires a full complement of major minor and trace element data in conjunction with considerations of the mineralogy and morphology of juvenile deposits these data help define petrological lineages such that precise provenance can be established whilst a precise proximal distal match must be based on identical major minor and trace element concentrations it is clear that resurgent activity from a single volcano can produce magmas with identical compositions in such cases stratigraphic relationships must complement any geochemical study occasionally proximal stratigraphies may be unrepresentative of the complete eruptive history because of a lack of exposure due to burial by more recent effusive and explosive activity or sector collapse which can remove vital stratigraphy particularly on volcanic islands

leaching procedure used in dating young potassic volcanic rocks by the 226ra 230th method a method for determining the ages of shoshonitic volcanics erupted within the last 5000 years is presented and assessed this method is based on 226ra 230th radioactive disequilibrium and on a leaching procedure and counting of volcanics containing th enriched rainitial depleted mineral phases detected by microprobe analyses k is used as a ra stable chemical analogue the data are plotted on 226ra 228ra k 228ra osmond type diagrams in order to evaluate the 226raradiogenic230th activity ratio of the th enriched rainitial depleted phases four samples of volcanics from vulcano island southern italy gave ages consistent with historical reports andk ar chronology

mineralogical and geochemical study of granular xenoliths from the alban hills volcano central italy bearing on evolutionary processes in potassic magma chambers granular xenoliths ejecta from pyroclastic deposits emplaced during the latest stages of activity of the alban hills volcano range from ultramafic to salic ultramafic types consist of various proportions of olivine spinel clinopyroxene and phlogopite they show low sio2 alkalies and incompatible element abundances and very high mgo however cr co and sc are anomalously low at a few ppm level olivine is highly magnesian up to fo 96 and has rather high cao 1 ca and very low ni around a few tens ppm contents these characteristics indicate a genesis of ultramafic ejecta by thermal metamorphism of a siliceous dolomitic limestone probably with input of chemical components from potassic magma the other xenoliths have textures and compositional characteristics which indicate that they represent either intrusive equivalents of lavas or cumulates crystallized from variably evolved ultrapotassic magmas one sample of the former group has major element composition resembling ultrapotassic rocks with kamafugitic affinity some cumulitic rocks have exceedingly high abundances of th 81 84 ppm and light rare earth elements lree la ce 421 498 ppm and extreme ree fractionation la yb 288 1393 not justified by their modal mineralogy which is dominated by sanidine leucite and nepheline finegrained phases are dispersed through the fractures and within the interstices of the main minerals semiquantitative eds analyses show that th and lree occur at concentration levels of several tens of percent in these phases indicating that their presence is responsible for the high concentration of incompatible trace elements in the whole rocks the interstitial position of these phases and their association with fluorite support a secondary origin by deposition from fluorine rich fluids separated from a highly evolved potassic liquid the nd isotopic ratios of the cjecta range from 0 51182 to 0 51217 87sr 86sr ratios range from 0 70900 to 0 71036 with the exception of one sample these values are lower than those of the outcropping lavas which cluster around 0 7105 3 this indicates either the occurrence of several isotopically distinct potassic magmas or a variable interaction between magmas and wall rocks however this latter hypothesis requires selective assimilation of host rocks in order to explain isotopic and geochemical characteristics of lavas and xenoliths the new data indicate that the evolutionary processes in the potassic magmas of the alban hills were much more complex than envisaged by previous studies interaction of magmas with wall rocks may be an important process during magmatic evolution element migration by gaseous transfer often invoked but rarely constrained by sound data is shown to have occurred during the latest stages of magmatic evolution such a process was able to produce selective enrichment of th u lree and to a minor degree ta and hf in the wall rocks of potassic magma chamber finally the occurrence of xenoliths with kamafugitic composition points to the existence of this type of ultrapotassic magma at the alban hills

multiple hazards and paths to eruptions a review of the volcanic system of vulcano aeolian islands italy abstract vulcano is one of the 7 volcanic islands and 6 seamounts forming the aeolian volcanic district italy vulcano has a long eruptive record and its last eruption 1888 90 originated the definition of the vulcanian eruptive style like most volcanic islands vulcano generates many potentially interconnected hazards determining a potentially high risk here we review the state of knowledge on its geology eruptive activity historical accounts structural setting geophysical and geochemical surveillance and available hazard quantifications in order to have an updated picture of the state knowledge on volcanic hazard we follow a prototypal reviewing scheme based on three standardized steps i review of the volcanic system ii review of available eruptive and non eruptive hazard quantifications iii development of a conceptual interpretative model we find that while a rather vast literature is dedicated to the volcanic system of vulcano and the reconstruction of past events few quantitative hazard assessments exist in addition the range of natural variability considered for each hazard is potentially underestimated e g limited range of considered eruption magnitude and style and of vent position as it is the potential effect of multi hazard impact the developed conceptual model for the feeding system provides a synthetic picture of the present knowledge about the system as emerged from the review in addition it allows for the identification of potential paths to eruption and provides a first order link among the main hazards this review provides an up to date snapshot of existing knowledge on volcanic hazard at vulcano on which to build future hazard quantifications as well as to support present and future decision making

stratigraphy and significance of brown tuffs on the aeolian islands southern italy abstract brown tuffs bt are volcaniclastic ash deposits prominently represented in the stratigraphic profiles of all the aeolian islands and capo milazzo on the northern coast of sicily detailed stratigraphy and tephrochronology together with available radiometric ages suggest that they were emplaced over a long time interval spanning from the end of the last interglacial period ca 80 ka bp up to 4 5 ka bp age of the overlying punte nere pyroclastic products on vulcano the most complete bt succession is documented on lipari where 14 distinct and successive units are subdivided by the interbedding of widespread tephra layers local volcanic products paleosols and epiclastic deposits and the occurrence of local erosive surfaces inter island occurrence of ischia tephra a widely known tephra layer in the aeolian archipelago dated at 56 ka bp and monte guardia pyroclastics from lipari dated at 22 20 ka bp subdivides the bt succession in upper ubt intermediate ibt and lower bt units lbt which can be correlated at regional level the lbt was emplaced between 80 and 56 ka bp the ibt between 56 and 22 ka bp and the ubt between 20 and 4 5 ka bp on the basis of stratigraphy similarity in lithology and textural features morphology of glass fragments composition and consistency of thickness and grain size variations ubt units correlate with piano grotte dei rossi tuffs on vulcano island they were generated by pulsating hydromagmatic explosive activity giving rise to pyroclastic density currents spreading laterally from a source located inside the la fossa caldera on vulcano island composition is in agreement with this hypothesis since ubt compositional features match those of vulcano magmas erupted in that period the effect of co ignimbrite ash clouds or associated fallout processes from sustained eruptive columns is seen to explain the presence of ubt in areas further away from the suggested source e g salina and lipari islands and capo milazzo the origin of ubt exposed on panarea island is still a matter of debate due to contrasting compositional data due to large uniformity of lithological textural and componentry characters with respect to the ubt the lower portions of the bt succession lbt ibt are considered to be the result of recurrent large scale hydromagmatic eruptions of similar type moreover for the ibt units the correlation with monte molineddo 3 pyroclastics of vulcano island on the basis of lithological compositional and stratigraphic matching again suggests source s related to the vulcano plumbing system and located within the la fossa caldera

u series disequilibrium radionuclides in sulphur incrustations from the fumarolic field of vulcano island abstract u series disequilibrium radionuclides 238 u 234 u 210 pb 210 po in sulphur incrustations deposited at la fossa cone vulcano island italy were measured over the period 1990 1995 to collect information about changes in the feeding system of the fumarolic field the 210 po 210 pb and 210 pb pb ratios of the sulphur incrustations allowed the identification of a fumarolic vent which is free from magmatic contribution and remobilized sublimate contamination in spite of the low temperature of the selected fumarole 280 350 c kinetic data show that 210 po is almost fully volatilized due to the relatively high velocity of the gas as a result the 210 po 222 rn activity ratio of the gas can be used to estimate fluid rising times about 100 days 234 u 238 u activity ratios of sulphur incrustations deposited in 1991 1993 showed a shift toward high values typical of nonmagmatic fluids both short lived and long lived u series disequilibrium radionuclides contribute to volcanic forecasting and give information on fluid sources and rising times as well as the residence times of the aquifers involved in the degassing process of the fumarolic field

genesis evolution and tectonic significance of k rich volcanics from the alban hills roman comagmatic region as inferred from trace element geochemistry trace element data are reported in 21 lava samples from the alban hills one of the most important volcanic complexes of the roman comagmatic region the samples consist mostly of tephritic leucitites with minor phonolitic tephrites and tephritic phonolites emplaced during two distinct phases of activity separated by a caldera collapse