sub volcanic crystallization at stromboli aeolian islands southern italy preceding the sciara del fuoco sector collapse evidence from monzonite lithic suite we describe texture mineralogy and whole rock composition of cognate monzonite sub volcanic clasts within debris flow deposits related to the 5000 years catastrophic phreatomagmatic eruption probably linked to the sciara del fuoco sector collapse the debris flows are at the top of accretionary lapilli rich ash deposits overlying potassic ks shoshonites lavas of the neostromboli period the monzonites are inferred to be crystallized in situ at low p at the side walls and or roof margins of a shallow magma chamber and to be cogenetic with the ks neostromboli extrusives they can be considered ideal orthocumulates since they approximately retain a bulk liquid composition and possibly represent slowly cooled equivalents of their ks shoshonite host rock the closure temperature of final solidification of the monzonite lithic suite was estimated through ternary feldspar geothermobarometry plagioclase k feldspar and k feldspar biotite equilibria and is in the range of 750 790 c with a maximum logfo2 around 15 1 15 3 the estimated pressure of crystallization is 0 5 kbar potassic lavas and dikes previously emplaced during the neostromboli period also resemble the monzonites in both major trace elements and mineral chemistry the cogenetic relationship between ks neostromboli extrusives and the monzonite host rock magma from which the sub volcanic clasts were derived is clear evidence that a shallow magma chamber existed between the caldera collapse of the vancori period and the sciara del fuoco sector collapse i e between 13 000 and 5000 years the monzonite clasts were derived from crystallization at very shallow depth ca 1 km and strongly support the hypothesis of violent decompression of the shallow magmatic plumbing system during the sciara del fuoco sector collapse climax of the regressive landslide event with maximum disruption of the chamber walls took place during emplacement of the debris flows i e during the late stage of the neostromboli phreatomagmatic eruption

the december 2002 july 2003 effusive event at stromboli volcano italy insights into the shallow plumbing system by petrochemical studies abstract on 28 december 2002 the persistent strombolian activity at stromboli was interrupted by the sudden onset of lava emission onto the sciara del fuoco slope a horseshoe shaped depression on the nw flank of the volcano the effusive episode went on until 22 july 2003 and produced a cumulative volume of lavas of 11 106 m3 ranking the event as the largest occurred in the past 30 years the eruptive vents were mainly located in the ne sector of the sciara del fuoco depression at an elevation of 550 600 m a s l on 30 december the eastern portion of the sciara del fuoco collapsed producing a tsunamigenic landslide on 5 april 2003 a paroxysmal eruption occurred at the summit craters during which crystal poor pumiceous products were emitted the paroxysm did not interrupt the lava emission the strombolian activity at the summit craters gradually resumed starting from march 2003 and fully recovered by the end of july periodic sampling of the lava at the active vents was carried out during the entire effusive event all the analysed samples are shoshonitic basalts sio2 48 5 50 4 wt k2o 2 1 2 4 wt in the range of composition observed in the products erupted during the past 20 years they bear about 50 vol zoned crystals of plagioclase an90 60 diopside augite and olivine fo70 73 in a compositionally homogeneous shoshonitic groundmass bulk rock major and trace element contents measured with different methodologies at different laboratories show only minor variations sr and nd isotope ratios are close to those of the crystal rich scoriae erupted in the previous years despite of small compositional variations related to the emptying of the zoned topmost portion of the conduit the data show that the switch from strombolian explosive to effusive activity is not associated with changes of the textures and composition of the erupted products slight but somehow systematic variation of trace elements and isotope ratios between products erupted before and after the 5 april eruption are likely accounted by limited mixing between the fresh volatile rich crystal poor magma erupted as pumice during the paroxysm and the volatile poor crystal rich magma feeding the lava flow the uniform composition of the erupted lava indicates the presence of a large volume of well mixed crystal rich homogeneous magma residing in the shallow plumbing system of the volcano two possible trigger mechanism of the effusive event are here proposed i a discrete input of fresh magma into the lower part of the shallow magmatic system occurred some months before the eruption and was followed by crystallisation degassing and mixing with the crystal rich shallow magma which re homogenised the system these processes eventually led to the rise of the magma at a higher level and failure of the conduit walls ii the onset of the effusion may represent the consequence of a gradual rise of the magma level in the conduits occurred in the past two decades the process of progressive refilling initiated after the 1985 effusive eruption ultimately culminated on 28 december 2002 with the failure of the conduit wall and the opening of vents 100 150 m below the summit craters

sulfur diffusion in basaltic melts abstract we measured the diffusion coefficients of sulfur in two different basaltic melts at reduced conditions i e in the sulfide stability field temperatures from 1225 c to 1450 c pressures of 0 5 and 1 gpa and water concentrations of 0 and 3 5 wt although each melt is characterized by slightly different sulfur diffusion coefficients the results can be combined to create a general equation for sulfur diffusion in anhydrous basalts d 2 19 10 4 exp 226 3 58 3 r t where d is the diffusion coefficient in m2s 1 the activation energy is in kj mol 1 r is the gas constant and t is the temperature in k sulfur diffusion in basalts with 3 5 wt water is a factor of three to seven higher than in anhydrous melts and can be described by d 5 91 10 7 exp 130 8 82 6 r t at the conditions of this study the pressure does not measurably affect sulfur diffusion sulfur diffusion in dry basaltic melts is one order of magnitude higher than sulfur diffusion in dry andesitic and dacitic melts whereas sulfur diffusion in hydrous basaltic and andesitic melts is within the same order of magnitude when compared to the diffusivity of other volatile species in nominally dry basaltic melts sulfur diffusion appears to be two times lower than co2 diffusion and two orders of magnitude lower than h2o diffusion

pyrometamorphic processes at the magma hydrothermal system interface of active volcanoes evidence from buchite ejecta of stromboli aeolian islands italy pyrometamorphic ejecta erupted during recent paroxysmal explosions and hydrothermally altered volcanic and subvolcanic rocks from stromboli volcano aeolian islands italy were studied by combined polarizing microscopy electron microprobe scanning electron microscope x ray diffraction transmission electron microscope and whole rock inductively coupled plasma optical emission spectrometry mass spectrometry analysis the pyrometamorphic ejecta are compositionally heterogeneous at the macroand micro scale and are classified as buchites that is glass coupled with a high temperature low pressure modal mineralogy three distinct facies i e cordierite plagioclase mullite plagioclase palisade and tridymite clinopyroxene are recognized among the buchites whose bulk rock chemistry is compatible with aluminousto silica rich protoliths abundant mineral growth e g plagioclase palisades and clinopyroxene coronae occurs at the contact between the ejecta and the crystal rich host shoshonitic basalt which typically coats the pyrometamorphic blocks mineral constraints pseudoporphyritic microstructures plagioclase relict phenocrysts and major and trace element compositions strongly support the origin of the buchite ejecta as hydrothermally altered rocks from thevancori edifice a period of activity spanning 410 kyr which underwent high temperature low pressure contact metamorphism in the uppermost magmatic system of an active island arc volcano such as stromboli volcanic and subvolcanic rocks usually undergo alteration processes induced by acid sulphate hydrothermal systems the circulation of acidic fluids results in leaching of the stromboli rocks in the upper part of the volcano edifice and depending on the ph temperature and exposure time to the hydrothermal fluids production of different alteration facies the hydrothermally altered stromboli rocks show facies consistent with argillic to silicic alteration containing abundant hydrous sulphate and hydroxy sulphate minerals such as the alunite group minerals hexahydrite millosevichite pickeringite and kieserite the hydrothermally altered wall rocks heated by contact with the basaltic magma of the feeder dyke system of stromboli can easily undergo pyrometamorphic processes inducing partial melting and subsolidus crystallization of the volcanic protoliths this results in the development of buchite rocks at the magma hydrothermal system interface

ash erupted during normal activity at stromboli aeolian islands italy raises questions on how the feeding system works ash fallout collected during 4 days of sampling at stromboli confirms that a crystal rich hp degassed magma erupts during the strombolian explosions that are characteristic of the normal activity of this volcano we identified 3 different types of juvenile ash fragments fluidal spongy and dense which formed through different mechanisms of fragmentation of the low viscosity physically heterogeneous in terms of the size and spatial distribution of bubbles shoshonitic magma a small amount less than 3 vol of volatile rich magma with low porphyricity lp erupted as highly vesicular ash fragments has been collected together with the hp magma during normal strombolian explosions laboratory experiments and the morphological textural and compositional investigations of ash fragments reveal that the lp ash is fresh and not recycled from the last paroxysm 15 march 2007 we suggest that small droplets of lp magma are dragged to the surface by the time variable but persistent supply of deep derived co2 rich gas bubbles this coupled ascent of bubbles and lp melts is transient and does not perturb the dynamics of the hp magma within the shallow reservoir this finding provides a new perspective on how the stromboli volcano works and has important implications for monitoring strategies

what controls sheet intrusion in volcanoes structure and petrology of the stromboli sheet complex italy abstract a multidisciplinary study has been conducted on 109 intrusive sheets of stromboli the relation between sheet injection conditions with the magmatic and structural variations of the volcano and the parameters governing the preferential intrusion geometry inside the volcano in a time perspective have been determined during its subaerial activity the last 100 ka stromboli experienced periods of extrusive growth and sheet intrusions alternated to caldera and lateral collapses of the nw sciara del fuoco flank the sheet intrusions similar to the extrusive rocks span a large compositional range from calc alkaline to potassic through high k calc alkaline and shoshonitic series the most evolved compositions of the effusive rocks however have not been found as intrusions whereas some mafic and basic magmas of sheets were never erupted the repeated time change of location of the intrusions from strombolicchio to the ne sw trend passing trough the inferred paleostromboli summit cone and the southern flank could represent the expression of the shift of the magma chamber towards the southeast and the subsequent onset of a clear ne sw elongated magma chamber located along the main stromboli weakness zone the stromboli evolution in the last 100 ka has been characterized by the persistent n 10 55 e intrusion direction which reflects the influence of the edifice s state of stress on the magma feeding paths after 13 ka ago sheets mainly intruded along to the sector collapse scarps in a circum amphitheatre geometry which has been demonstrated to be influenced by the new cone morphostructure and not by different magma rheological characters

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

unusual lapilli tuff ejecta erupted at stromboli during the 15 march 2007 explosion shed light on the nature and thermal state of rocks forming the crater system of the volcano abstract textural and mineralogical study of high temperature angular blocks erupted during the stromboli explosion of 15 march 2007 was used to make inferences on the nature and thermal state of rocks forming the subsurface of the volcano summit crater terrace the studied ejecta consist of lapilli tuff that formed as a result of the transformation and high temperature induration sintering of the basaltic scoriae lapilli and ash originally accumulated as loose tephra during the current activity of the volcano the main processes leading to the tephra transformation were investigated through microstructural observations mineral and glass analyses sem eds and emp analyses investigations revealed that subsolidus reactions and partial melting of the tephra occurred at temperatures higher than 600 c and under variable fo 2 conditions from qfm to hm buffering curves in some blocks evidence of high t reheating and partial melting at the expense of secondary hydrothermal minerals was also observed in order to track the subsolidus reheating history of the basaltic pyroclasts a detailed study of the pseudomorphic phases and reactions after olivine driven by iron oxidation under high t conditions was performed the observed mineralogical transformation suggests that the lapilli tuff material originating from the burial of tephra routinely accumulated by persistent strombolian explosions within the crater terrace were in some cases altered by the circulation of acidic fluids and were in any case reheated due to isotherm rise forced by high heat flux and gas streaming delivered by the underlying magma system it is worth noting that the ejection of these unusual volcanic lithotypes was possible because a few days before the 15 march 2007 event the craters were clogged with lapilli tuff material that slid into the crater bottom between 7 and 9 march findings of this study suggest that the scattered permanently active vents and shallow conduits of stromboli are surrounded sideways and underneath the crater terrace by a fairly large volume of high temperature rocks with variable degree of compaction sintering up to partially melted such a spectrum of rock types is in good agreement with the conceptual model of prominent thermal zoning all around sideway and upwards the active magmatic system we speculate that continuous migration upwards of isotherms led to transformation and partial melting of the normal strombolian tephra

the onset of the 2007 stromboli effusive eruption recorded by an integrated geophysical network abstract the stromboli volcano erupted on february 27 2007 after an intense strombolian activity lasted about 2 months the eruption was characterized by a series of rapidly evolving phenomena like the propagation of an effusive fracture along the crater rim the opening of lateral effusive vents an unusually large effusive flux 10 m 3 s the collapse of the crater system and a major strombolian explosion this eruption was monitored by an integrated network of multiparameter instruments broad band seismometers infrasonic array thermal cameras and bore hole tiltmeters all the information collected and processed in real time allowed to draw a clear picture of the eruption dynamics thermal imagery documented in real time how the effusive fracture propagated at 12 24 gmt of february 27 along the northern rim of the ne crater towards the ne direction the infrasonic array showed that explosive and degassing activity ceased at 10 32 gmt a couple of hours before the opening of the effusive fractures the end of the explosive activity coincided with an intense phase of high frequency 4 22 hz tremor which showed two episodes of harmonic spectrum gliding from 4 7 hz to 22 hz the end of this phase was characterized at 18 26 gmt by a strong infrasonic signal located by the array in the sciara del fuoco and associated with the landslide induced by the opening of a lateral effusive vent at 400 m of elevation this eruption provided a clear example on how the strategy of integrating in near real time geophysical information can pinpoint the transition from explosive to effusive activity of the shallow volcanic system at stromboli

magma dynamics during the 2007 stromboli eruption aeolian islands italy mineralogical geochemical and isotopic data abstract after the 6 month long effusive event of 2002 2003 a new lava effusion occurred at stromboli between 27 february and 2 april 2007 despite the different durations approximately the same volume of magma was emitted in both eruptions in the order of 107 m3 a paroxysmal eruption occurred at the summit craters in both the 2002 2003 and 2007 episodes during which a significant amount of low porphyritic lp volatile rich magma was erupted in both cases the paroxysm did not interrupt the lava emission here we present compositional data including texture mineralogy chemistry and sr and nd isotope ratios of bulk rock groundmass and separated minerals of lavas erupted in 2007 together with chemistry and sr and nd isotope composition of the pumices emitted during the 15 march paroxysm as a whole the lavas have the same texture and chemistry that characterize the highly porphyritic hp products usually erupted at stromboli during normal strombolian activity and effusive events compared to the previous hp products the 2007 lavas show minor but systematic mineralogical and isotopic variations which are consistent with a modest increase of the magma supply rate of the volcano compositional variations during the entire duration of the event are very modest glass chemistry changes in lavas erupted in the second half of march can be explained by the minor mixing between the volatile rich lp magma rising through the shallow magmatic system during the 15 march paroxysm and the degassed residing hp magma a first conclusion of this study is that there is no compositional evidence supporting major changes in the magma dynamics of the volcano accompanying the effusive activity as also suggested for the 2002 2003 event the activity of stromboli is controlled by a steady state feeding system in which refilling mixing degassing and crystallization at shallow level continuously operate with modest oscillations in the magma supply rate switching between normal strombolian and effusive activity is related to periods of relatively more vigorous refilling of the shallow system leading to progressive pressure increase in the upper conduits associated with only minor compositional variations in the erupted products

origin of high silica liquids at stromboli volcano aeolian islands italy inferred from crustal xenoliths high silica igneous xenoliths granophyre and obsidian fragments with sio2 ca 75 wt and high silica glass sio2 between ca 64 and 75 wt within glass bearing tonalitic and dioritic xenoliths have been discovered at stromboli they are well beyond the silica range of the volcanic rocks erupted during the subaerial activity of the volcano the granophyre and the obsidian fragments occur within the petrazza pyroclastics high k andesite pumiceous scoriae of the paleostromboli i period 61 ka whereas the glass bearing tonalites and diorites are hosted in the omo basaltic andesite lava flows of the paleostromboli ii period 64 55 ka the obsidian represents an extremely evolved liquid derived from low pressure fractional crystallization of high k calc alkaline magmas of stromboli coupled with minor assimilation of upper crust or terrigenous sediments the other studied high silica products have an anatectic origin the granophyre composition is compatible with a genesis by low degree melting of leucotonalites similar to some calabrian arc lithotypes partial melting of crustal rocks from the stromboli basement is also demonstrated by interstitial glass in the tonalite and diorite xenoliths textural evidence and the presence of variable glass compositions suggest that in these plutonic xenoliths the melt chemistry was controlled by dehydration melting of biotite and non modal melting of local mineralogy high degree undercooling of granophyre melt and of the partially melted xenoliths is consistent with rapid rise of the host magmas leading to eruption whether partial melting was initiated during stoping and transport of xenoliths within the rising magma or in situ during magma storage within the crust has not been unequivocally established

thermal interaction between lava lobes pahoehoe lava may be emplaced as lobes which flow on top of each other a cross section was investigated through two lava lobes from the active pu u o o vent kilauea hawaii consisting of a 6 6 cm thick top lobe and the upper part of a 3 2 cm thick underlying bottom lobe the top lobe cooled at the contact with air and has a quenched glassy margin which is almost 1 cm thick the underlying lobe although originally also in contact with air is entirely crystalline suggesting that the bottom lobe experienced crystallization during reheating by the top lobe based on published data experimental results on reheating show that crystallization of basalt glass requires temperatures above 920 c and knowing that the pu u o o melt is initially at about 1 160 c the minimum temperature of the bottom lobe should have been 700 c prior to emplacement of the top lobe crystal size distribution csd theory demonstrates an oscillation of grain size which is superposed on an overall increase in size with depth cooling rates estimated from simple modeling and growth rates derived from csd suggest a thermal interaction of the bottom lobe on the top lobe to about 2 cm from the contact

the restricted stability of osumilite under hydrous conditions in the system k 2 o mgo al 2 o 3 sio 2 h 2 o osumilitess was synthesized as a single phase product in the model system k2o mgo al2o3 sio2 at 800 c 0 5 kbar water pressure and at 800 to 840 c 1 0 kbar total pressure with x text co text 2 0 3 in the gas phase the experimentally determined solid solubility range of synthetic osumilites can be expressed by the formula kmg2 al3 xmgx al2 xsi10 x o30 with 0 x 0 4 a survey of sixteen chemical analyses of natural osumilites from eleven occurrences shows a solid solubility characterized by 0 x 0 6 reversed stability experiments for the synthetic osumilite kmg2 al2 75mg0 25 al1 75si10 25 o30 determined at water pressure equal to total pressure demonstrate its restriction to water pressures below 0 8 kbar at 0 5 kbar the stability range is between 765 and 800 c at the lower thermal stability limit osumilite h2o vapor break down to cordierite k feldspar phlogopitess quartz at the higher one to cordierite k feldspar phlogopite liquid reduction of water fugacity will expand the stability field largely by shifting the lower and higher thermal stability limits to lower and higher temperatures respectively the dependence of osumilite stability on water fugacity makes osumilite a sensitive indicator mineral for dry conditions in rocks formed at total pressures higher than about 0 8 kbar

the summit hydrothermal system of stromboli new insights from self potential temperature co2 and fumarolic fluid measurements with structural and monitoring implications accurate and precisely located self potential sp temperature t and co2 measurements were carried out in the summit area of stromboli along 72 straight profiles sp data were acquired every metre and t data every 2 5 m co2 concentrations were acquired with the same density as t but only along seven profiles the high density of data and the diversity of the measured parameters allows us to study structures and phenomena at a scale rarely investigated the shallow summit hydrothermal activity pizzo fossa area is indicated by large positive sp t and co2 anomalies these anomalies are focused on crater faults suggesting that the fracture zones are more permeable than surrounding rocks at stromboli the analysis of the distribution of these linear anomalies coupled with the examination of the geologic photographic and topographic data has led us to propose a new structural interpretation of the summit of stromboli this newly defined structural framework comprises 1 a large pizzo circular crater about 350 m in diameter 2 a complex of two concealed craters nested within the pizzo crater the large and the small fossa craters thought to have formed during the eruption of the pizzo pyroclastites unit the small fossa crater is filled with highly impermeable material that totally impedes the upward flow of hydrothermal fluids and 3 the present complex of active craters on the floor of the fossa short wavelength sp lows are organized in drainage like networks diverging from the main thermal anomalies and converging toward the topographic low in the fossa area inside the small fossa crater they are interpreted as the subsurface downhill flow of water condensed above the thermal anomalies we suspect that water accumulates below the small fossa crater as a perched water body representing a high threat of strong phreatic and phreatomagmatic paroxysms t and co2 anomalies are highly correlated the two types of anomalies have very similar shapes but the sensitivity of co2 measurements seems higher for lowest hydrothermal flux above t anomalies a pronounced high frequency sp signal is observed isotopic analyses of the fluids show similar compositions between the gases rising through the faults of the pizzo and large fossa craters this suggests a common origin for gases emerging along different structural paths within the summit of stromboli a site was found along the large fossa crater fault where high gas flux and low air contamination made gas monitoring possible near the active vents using the alkaline bottle sampling technique

deformation of stromboli volcano italy during the 2007 eruption revealed by radar interferometry numerical modelling and structural geological field data abstract the activity of stromboli volcano is characterized by very low energy explosions occurring every 10 15 min throwing out lava above the crater rim during 2007 the volcano showed an anomalous activity in which new effusive vents developed 27 february and 9 march and a major explosion took place on 15 march this paper presents an integrated study based on a structural geological field survey interferometric radar monitoring and numerical modelling on the deformations of the upper nw flank of the volcano sciara del fuoco sdf the field survey carried out during the 2007 events shows the development of mainly ne striking fissures and fractures on the northern part of the upper sdf in january 2007 the ground based synthetic aperture radar gb insar installed on the flank of the sdf showed a progressive acceleration of movement on the ne crater preceding the eruption of 27 february 2007 by the first half of february the acceleration also involved the upper portion of the sdf and on 27 february the eruption started with the opening of new vents and deformation rates higher than the measurement capability of the radar device on 8 9 march 2007 the gb insar highlighted the formation of a bulge on the nw sector of the sdf preceding the opening of an additional vent to understand the deformation pattern recorded during the eruption a numerical simulation was carried out by using the flac 3d code based on the integration of all the data the deformations observed in the pre effusive phase before 27 february seem to be related to the intrusion of a sw ne striking dyke the bulging recorded before the 9 march vent opening is instead to be associated with the intrusion of a sub horizontal sill

fluid circulation at stromboli volcano aeolian islands italy from self potential and co2 surveys this work addresses the study of fluid circulation of the stromboli island using a dense coverage of self potential sp and soil co2 data a marked difference exists between the northern flank and the other flanks of the island the northern flank exhibits 1 a typical negative sp altitude gradient not observed on the other flanks and 2 higher levels of co2 the general sp pattern suggests that the northern flank is composed of porous layers through which vadose water flows down to a basal water table in contrast to the other flanks where impermeable layers impede the vertical flow of vadose water in the sciara del fuoco and rina grande le schicciole landslide complexes breccias of shallow gliding planes may constitute such impermeable layers whereas elsewhere poorly permeable fine grained pyroclastites or altered lava flows may be present this general model of the flanks also explains the main co2 patterns concentration of co2 at the surface is high on the porous north flank and lower on the other flanks where impermeable layers can block the upward co2 flux the active upper part of the island is underlain by a well defined hydrothermal system bounded by short wavelength negative sp anomalies and high peaks of co2 these boundaries coincide with faults limiting ancient collapses of calderas craters and flank landslides the hydrothermal system is not homogeneous but composed of three main subsystems and of a fourth minor one and is not centered on the active craters the latter are located near its border this divergence between the location of the active craters and the extent of the hydrothermal system suggests that the internal heat sources may not be limited to sources below the active craters if the heat source strictly corresponds to intrusions at depth around the active conduits the geometry of the hydrothermal subsystems must be strongly controlled by heterogeneities within the edifice such as craters caldera walls or gliding planes of flank collapse as suggested by the correspondence between sp co2 anomalies and structural limits the inner zone of the hydrothermal subsystems is characterized by positive sp anomalies indicating upward movements of fluids and by very low values of co2 emanation this pattern suggests that the hydrothermal zone becomes self sealed at depth thus creating a barrier to the co2 flux in this hypothesis the observed hydrothermal system is a shallow one and it involves mostly convection of infiltrated meteoric water above the sealed zone finally on the base of co2 degassing measurements we present evidence for the presence of two regional faults oriented n41 and n64 and decoupled from the volcanic structures

crystal recycling in the steady state system of the active stromboli volcano a 2 5 ka story inferred from in situ sr isotope and trace element data in situ sr isotope data by microdrilling coupled with major and trace element analyses have been performed on plagioclase and clinopyroxene from seven samples collected during the 2002 2003 eruptive crisis at stromboli volcano aeolian islands italy on 28 december 2002 the persistent moderate explosive activity was broken by an effusive event lasting about 7 months a more violent explosion paroxysm occurred on 5 april 2003 two magma types were erupted namely a volatile poor and highly porphyritic magma hp magma poured out as scoria or lava and a volatile rich phenocryst poor magma lp magma found as pumice lp magma differs from the hp magma also for its slightly less evolved chemistry the groundmass composition and the lower sr isotope ratios micro sr isotope data show the presence of zoned minerals in strong isotope disequilibrium as previously found in products erupted in 1984 1985 and 1996 ad with 87sr 86sr values generally decreasing from cores to rims of minerals only some outer rims testify for equilibrium with the host groundmass the internal mineral zones with high sr isotope ratios 0 70665 0 70618 are interpreted as antecrysts crystallised during the previous activity and recycled in the present day system since the opening shoshonitic activity of the recent period which occurred at about 2 5 ka ago this result has implications for the dynamics of the present day plumbing system of stromboli at intermediate pressure about 2 3 km depth and allows us to propose a model whereby an hp magma reservoir is directly interconnected at the bottom with a cumulate crystal much reservoir efficient mixing between residing hp and input lp magmas can occur in this reservoir due to more similar rheological characteristics of the two magmas than in the conduit where crystallisation is enhanced by degassing antecrysts and possibly melts re enter in the hp magma reservoir both from the bottom recycled by ascending lp magmas crossing the crystal mush and from the top recycled by descending degassed and dense hp magma residual of the periodic strombolian explosions at the surface the isotope variation measured in the groundmasses allows calculating the proportion of the lp magma entering the shallow hp magma reservoir at 20 from this proportion we estimate that the total volume of lp magma input during 2002 2003 closely matches the magma volume erupted in the effusive event suggesting a steady state system at broadly constant volume the comparison with estimates of the lp magma volume ejected by the paroxysm indicates that the lp magma amount directly reaching the surface during the 5 april paroxysm is minimal with respect to that entering the system

growth after collapse the volcanic and magmatic history of the neostromboli lava cone island of stromboli italy this study focuses on the holocene neostromboli lava cone which is part of the stromboli volcano aeolian islands italy it represents an important example of the structure and behaviour of lava cone re growth shortly after a large scale volcano sector collapse neostromboli s eruptive style is dominated by extrusion of sheet like a a lava flows and associated autoclastic breccias the lava cone developed during five phases of activity phases a to e representing discrete episodes of lava effusion characterised by rapid changes in magma composition spatial development of the feeder system and physical properties of erupted lavas through time although they all belong to the potassic series ks with sio2 49 55 wt and mgo 2 50 6 25 wt the neostromboli lavas have distinct petrogenetic characteristics ranging from leucite free and low sr shoshonitic basalts phases a and b to leucite bearing shoshonitic basalts with high phase c and intermediate phase d sr contents and to leucite free biotite bearing shoshonites phase e three different batches of mantle derived relatively primitive basic magmas fed the activity of phases a c and d the evolution phases a to b is inferred to have occurred in a continuously replenished tapped and crystallizing rtf magma chamber whereas phase e products were dominantly generated by fractional crystallization from phase d magmas the neostromboli cone shows summit flank and satellite vents and sheet intrusions with different geometry and location through time reflecting the interplay of regional tectonics precursory instability processes and volcano load

the 2007 stromboli eruption event chronology and effusion rates using thermal infrared data accepted for publication in journal of geophysical research copyright 2009 american geophysical union further reproduction or electronic distribution is not permitted

influence of fo2 and cooling rate on the kinetics and energetics of fe rich basalt crystallization cooling rate and fo2 are each varied over several orders of magnitude in a matrix of 1 atm constant rate cooling experiments using synthetic basalt the modes and compositions of olivine pyroxene and titanomagnetite are sensitive to oxygen fugacity ranging from qfm 4 to qfm 5 log units whereas their textures respond to the degree of undercooling as modulated by cooling rate ranging from 2 8 to 231 c h 1 key results pertain to the trends in mineral composition melt differentiation and

glass bearing crustal xenoliths buchites erupted during the recent activity of stromboli aeolian islands abstract three xenoliths erupted as ejecta during recent violent explosion of stromboli volcano aeolian islands were investigated in this paper they consist of high temperature mineral association cordierite hercynite spinels sillimanite plagioclase mullite corundum and abundant glass 10 70 vol and may be classified as buchites the peraluminous composition of the xenoliths their trace element distribution and ree patterns support their origin from granulite and amphibolite facies metapelites of the calabrian continental crust which is considered the crystalline basement beneath stromboli buchites have an isotopic composition comparable to that of stromboli extrusives and significantly different from that of the calabrian basement the glass is generally colourless and has a si al alkali rich composition except for one sample where a fe mg ca rich reddish brown glass also occurs these two kinds of glass show complicated textures where patches of reddish brown glass are often surrounded by plagioclase and or cordierite or forms streaks and swirls with the colourless glass cordierite plagioclase and oxides have different compositions according to their position in the xenoliths ca rich plagioclase an72 95 mg poor cordierite mg values 47 66 and al rich spinels are in the inner portions of the xenoliths and associated with colourless glass on the contrary close to the contact with the host lava or associated with coloured glass cordierite shows higher mg values ti fe bearing oxides occur and plagioclase is chemically similar to the basalt phenocrysts an66 71 the abundant and fresh glass and the idiomorphic shape of the high temperature minerals suggest that the xenoliths were hold in the basaltic magma before its extrusion for a significant time to allow their partial or nearly complete melting and subsequent nucleation and growth of new phases during this stage the interaction between the anatectic liquid and the basaltic magma affected the original isotopic composition of the xenoliths and in some cases produced glass and mineral phases cordierite plagioclase and oxides with different composition

onset of the persistent activity at stromboli volcano italy stromboli known worldwide as the lighthouse of the mediterranean is commonly believed to have been in a state of persistent activity for the past 2000 2500 years however historical sources older than 1000 a d are not accurate enough to assess if the activity of the volcano was exactly the same as we see at present in order to attempt to identify the onset of the present eruptive regime and assess if it has been maintained with the same characteristics through time stratigraphic and radiometric studies of the recent tephra deposits were undertaken up to 4 m deep stratigraphic trenches dug at a height of approximately 500 m on the ne flank of the volcano exposed a conformable tephra pile containing charcoal fragments one of the most interesting finds was the discovery of a 7 cm thick weathered bed rich in organic matter thin palaeosol approximately 3 m below the surface the sequence underneath the palaeosol consists of decimetre thick lapilli fallout beds alternating with ash deposits bearing small charcoals with calibrated ages of between the fourth century b c and the first century a d the sequence above the palaeosol is charcoal free and consists of coarse ash deposits with discrete centimetre thick lapilli fallout beds composed of crystal poor golden pumice and subordinate crystal rich black scoriae similar to scoria pumice pairs emitted during the more energetic explosions of the present day activity the data collected indicate that between the third and seventh centuries a d after a period of quiescence the activity resumed with an eruptive style identical to the present one we conclude that the lighthouse of the mediterranean actually began its activity in a period much later than previously thought

dynamics of magma mixing and degassing recorded in plagioclase at stromboli aeolian archipelago italy crystal rich materials scoriae and lava flows emitted during the 1985 2000 activity of stromboli were taken into consideration for systematic study of bulk rock matrix glass chemistry and in particular for the study of chemical and textural zoning of plagioclase the most abundant mineral phase over the considered time period bulk rock composition remained fairly constant in both major sio2 49 2 50 9 wt and k2o 1 96 2 18 wt and trace elements the quite constant chemistry of matrix glasses also indicates that the degree of crystallization of magma was maintained at around 50 vol plagioclase ranges in composition between an62 and an88 and is characterized by alternating 10 100 m thick bytownitic and labradoritic concentric layers although the dominant and representative plagioclase of scoriae is an68 the labradoritic layers an62 70 show small scale 1 5 m oscillatory zoning are free of inclusions and appear to record episodes of slow crystal growth in equilibrium with a degassed liquid having the composition of the matrix glass in contrast the bytownitic layers an70 an88 are patchy zoned show sieve structure with abundant micrometric glass inclusions and voids and are attributed to rapid crystal growth

transient processes in stromboli s shallow basaltic system inferred from dolerite and magmatic breccia blocks erupted during the 5 april 2003 paroxysm we describe the mineralogy geochemistry and mesomicrostructure of fresh subvolcanic blocks erupted during the 5 april 2003 paroxysm of stromboli aeolian islands italy these blocks represent 50 vol of the total erupted ejecta and consist of fine to medium grained basaltic lithotypes ranging from relatively homogeneous dolerites to strongly or poorly welded magmatic breccias the breccia components are represented by angular fragments of dolerites entrapped in a matrix of vesiculated lava like to scoriae crystal rich cr basalt all of the studied blocks are cognates with the cr basalt of the normal strombolian activity or lavas and they are often coated by a few centimeter thick layer of crystal poor cp basaltic pumice erupted during the paroxysm we suggest that they result from the rapid increase of pressure and related subvolcanic rock failure that occurred shortly before the 5 april 2003 explosion when the uppermost portion of the edifice inflated and suffered brecciation as the result of the sudden rise of the gas rich cp basalt that triggered the eruption dolerites and magmatic matrix of the breccias show major and trace element compositions that match those of the cr basalts erupted during normal strombolian activity and effusive events at stromboli volcano dolerites consist of a phenocrysts normally found in the cr basalts and b late stage magmatic minerals such as sanidine an60 28 plagioclase fe mn rich olivines fo68 48 phlogopite apatite and opaque mineral pairs magnetite and ilmenite most of which are never found both in lava flows and scoriae erupted during the persistent explosive activity that characterizes typical strombolian behavior subvolcanic crystallization of the stromboli cr magma leading to slowly cooled equivalents of basalts could result from transient drainage of the magma from the summit craters to lower levels fingering and engulfing of the material that collapsed from the summit crater floor into the shallow basaltic system during the late evening of 28 december 2002 coupled with the short break in the summit persistent explosions between december 2002 and march 2003 permitted the cr magma pockets to solidify as dolerites which were confined to the uppermost portion of the system and thus not involved in the ongoing flank effusive activity crystal size distribution of the basaltic blocks and crystallization of the finer grained 0 1 mm mafic minerals of the dolerites over a time interval of 100 days closely agrees with the above interpretation vesicle filling miarolitic cavities locally found in some dolerites with minerals deposited as vapor phase crystallization is a result of continuous gas percolation through the rocks of the uppermost portion of the volcanic system poorly welded magmatic breccias formed during syn eruptive processes of 5 april 2003 when the paroxysm strongly shattered the shallow subvolcanic system and many dolerite fragments were entrapped in the cr magma in contrast the high degree of welding between the dolerite clasts and the cr basaltic matrix in the strongly welded magmatic breccias provides a snapshot of subvolcanic intrusions of the cr basalt into the dolerite when after a 2 month break in activity cr magmas started to rise again to the summit craters blocks similar to these subvolcanic ejecta of 5 april 2003 were also erupted during previous paroxysms e g 1930 suggesting that changes in the usual strombolian activity e g short breaks in the persistent mild explosions and or flank effusive activity lead to transient crystallization of dolerites in the shallow plumbing system

the 15 march 2007 explosive crisis at stromboli volcano italy assessing physical parameters through a multidisciplinary approach basaltic volcanoes are dominated by lava emission and mild explosive activity nevertheless many basaltic systems exhibit from time to time poorly documented and little understood violent explosions a short lived multiblast explosive crisis paroxysmal explosion occurred on 15 march 2007 during an effusive eruptive crisis at stromboli italy the explosive crisis which started at 20 38 14 ut had a total duration of 5 min the combined use of multiparametric data collected by the permanent instrumental networks seismic acoustic and thermal records and a field survey carried out immediately after the event enabled us to constrain the eruptive dynamics and quantify physical parameters the eruption consisted of three major pulses in the first lithic blocks and ash were ejected at speeds of 100 155 m s and 130 210 m s respectively the high solid load of the eruptive jet resulted in the partial collapse of the column with the formation of a small volume pyroclastic density current the second 12 s long pulse emitted 2 2 2 7 107 kg of tephra mass discharge rate 1 9 2 3 106 kg s forming a 3 km high convective plume dispersing tephra up to the west coast and a dilute density current with limited dispersal downslope of the craters a final 30 s long phase formed a scoria flow with a volume of 1 5 1 7 104 m3 mass discharge rate 5 9 6 7 105 kg s a total runout of 200 m and a velocity of 45 m s the total gas volume involved in the explosion was 1 3 1 9 104 m3 with an initial overpressure of 7 9 0 4 mpa we compared the 15 march 2007 event with historical paroxysms in particular with that of 5 april 2003 which was remarkably similar

conditions of magma storage degassing and ascent at stromboli new insights into the volcano plumbing system with inferences on the eruptive dynamics stromboli is known for its persistent degassing and rhythmic strombolian activity occasionally punctuated by paroxysmal eruptions the basaltic pumice and scoria emitted during paroxysms and strombolian activity respectively differ in their textures crystal contents and glass matrix compositions which testify to distinct conditions of crystallization degassing and magma ascent we present here an extensive dataset on major elements and volatiles co2 h2o s and cl in olivine hosted melt inclusions and embayments from pyroclasts emplaced during explosive eruptions of variable magnitude magma saturation pressures were assessed from the dissolved amounts of h2 oa nd co2 taking into account the melt composition evolution both pressures and melt inclusion compositions indicate that 1 ca basaltic melts entrapped in high mg olivines fo89 90 generate stromboli basalts through crystal fractionation and 2 the stromboli plumbing system can be imaged as a succession of magma ponding zones connected by dikes the 7 10 km interval where magmas are stored and differentiate is periodically recharged by new magma batches possibly ranging from ca basalts to basalts with a co2 rich gas phase these deep recharges promote the formation of bubbly basalt blobs which are able to intrude the shallow plumbing system 2 4 km where co2 gas fluxing enhances h2o loss crystallization and generation of crystal rich dense degassed magma chlorine partitioning into the h2o co2 bearing gas phase accounts for its efficient degassing 69 under the open system conditions of strombolian activity paroxysms however are generated through predominantly closed system ascent of basaltic magma batches from the deep storage zone in this situation crystallization is negligible and sulfur exsolution starts at 170 mpa chlorine remains dissolved in the melt until lower pressures only 16 being lost upon eruption finally we propose a continuum in explosive eruption energy from strombolian activity to large paroxysmal events ultimately controlled by variable pressurization of the deep feeding system associated with magma and gas recharges

chronology of the 2007 eruption of stromboli and the activity of the scientific synthesis group abstract on 27 february 2007 at 12 49 gmt a new eruption of stromboli took place with the effusion of a lava flow from a fracture cutting the flank of the ne cone which rapidly reached the sea the eruption had been heralded by an increase in the amplitude of tremor and flank movement since at least the 14th of february short term precursors were an increase in the rate of occurrence of small landslides within the sciara del fuoco scar on the north western flank of the volcano a new effusive vent opened at 18 30 gmt on the sciara del fuoco at an height of 400 m asl the new lava emission caused the sudden termination of the summit flow and initiated a period of non stationary lava outpouring which ended on 2 april 2007 the eruption has been characterized by a rapid decrease in the eruption rate after the first days and subsequently by episodic pulse increases on the 15th of march the increase in lava outpouring monitored by a thermal camera heralded by 9 min the occurrence of a violent paroxysmal explosion with the formation of an impulsive eruption column and the emission of small pumices mingled with black scoriae the pumice had a bulk composition similar to that of the lava and of the black scoriae but with a distinct lower content of phenocrysts a similar feature has been repeatedly observed during the major explosive paroxysms of stromboli short term precursors of the paroxysm were recorded by strainmeter and tiltmeter stations the volcano monitoring activity has been made by a joint team of researchers from the ingv sections of catania napoli palermo and rome along with researchers from the universities of florence pisa roma tre and palermo the scientific activity was coordinated by a synthesis group made up by scientists responsible for the different monitoring techniques of ingv and universities and by the volcanic experts of commissione nazionale grandi rischi of the prime minister office civil protection department the group made a daily evaluation of the state of the volcano and transmitted its recommendations to the civil protection department dpc several prevention measures were adopted by dpc the main of which were the evacuation of the coast zone when strong acceleration of the sciara del fuoco slope motion occurred twice could led to a dangerous tsunami by flank collapse as last occurred on 30 december 2002 and four days before the 15 march paroxysm when access was prohibited to the part of the volcano above 290 m asl

a case history of paroxysmal explosion at stromboli timing and dynamics of the april 5 2003 event abstract on april 5 2003 stromboli volcano italy produced the most violent explosion of the past 50 years the event was exceptionally well documented thanks to the presence on the island of several scientists and a large number of instruments deployed over the preceding months to monitor the effusive eruption that began in december 2002 integration of visual documentation deposit features and geophysical data allowed an accurate reconstruction of the explosive event and its dynamics the eruption consisted of a 8 min long explosive event which evolved through four phases whose timing was precisely recorded by an infrared thermometer located about 450 m from the summit crater phases 2 and 3 lasted 39 and 42 s respectively both had an impulsive character were responsible for ejecting almost the entire mass of the pyroclastic products phases 1 and 4 represented respectively a short lived precursory event and a waning tale during phase 2 meter sized ballistic blocks were launched with velocities of 170 m s to altitudes of up to 1400 m above the craters these fell on the volcano flanks and on the village of ginostra about 2 km distant from the vent a vertical jet rose above the craters which developed to feed a convective plume that reached a height of up to 4 km the calculated mass of the phase 2 fallout deposit and mass discharge rate were 1 1 1 4 108 kg and 2 8 3 6 106 kg s respectively during phase 3 a scoria flow deposit with an estimated volume of 0 9 1 1 104 m3 was erupted from the same vent that fed the ongoing sustained lava flow the average mass discharge rate for this phase was 2 5 3 1 105 kg s products emitted during phases 2 and 3 consisted of lithic and fresh magmatic material in similar proportions the juvenile fraction consisted of a deep originated almost aphyric highly vesicular pumice mingled with a shallow derived crystal rich moderately vesicular scoria similarities with the eruption dynamics of other historical paroxysms at stromboli makes the april 5 2003 explosion representative of these highly energetic events that constitute the most hazardous volcanic phenomena at stromboli volcano

transmission electron microscopy of subsolidus oxidation and weathering of olivine olivine crystals in basaltic andesites which crop out in the abert rim south central oregon have been studied by high resolution and analytical transmission electron microscopy the observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of olivine oxidation the olivine crystals contain rare dense arrays of coherently intergrown ti free magnetite and inclusions of a phase inferred to be amorphous silica we interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava the second olivine alteration assemblage contains complex ordered intergrowths on 001 of forsterite rich olivine and laihunite distorted olivine structure with fe3 charge balanced by vacancies based on experimental results for laihunite synthesis kondoh et al 1985 these intergrowths probably formed by olivine oxidation between 400 and 800 c the third episode of alteration involves the destruction of olivine by low temperature hydrothermal alteration and weathering elongate etch pits and channels in the margins of fresh olivine crystals contain semi oriented bands of smectite olivine weathers to smectite and hematite and subsequently to arrays of oriented hematite crystals the textures resemble those reported by eggleton 1984 and smith et al 1987 we find no evidence for a metastable phase intermediate between olivine and smectite m eggleton 1984 the presence of laihunite exerts a strong control on the geometry of olivine weathering single laihunite layers and laihunite forsteritic olivine intergrowths increase the resistance of crystals to weathering preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine rather than where coherency strain is associated with laihunite olivine interfaces

multiple sector collapses at stromboli volcano italy how they work this paper demonstrates that four large sector collapses have affected the nw flank of the stromboli volcano in the past 13 ka alternating with growth phases in order to contribute to the evaluation of the critical conditions which trigger lateral collapses a reconstruction of the geometry of each collapse of the volcano edifice in the four stages that preceded the relative collapse events is also presented and a computation of the landslide volume this reconstruction is based on new field data plotted in three dimensions prior to the initial 13 ka collapse the volcano was 1125 100 m high above sea level the collapse had a volume of 2 23 0 87 km3 whereas the pre collapse volcano volume was 218 8 7 7 km3 the next edifice that failed was 900 70 m high a s l the collapse volume was 1 0 54 km3 with a precollapse volcano volume of 201 4 5 4 km3 the edifice then grew to 1000 60 m a s l the third collapse had a volume of 1 08 0 39 km3 and occurred within a volcano with a volume of 209 1 4 6 km3 this was followed by a new growth phase followed by the last collapse with a volume of 0 73 0 22 km3 the volcano volume was about the same as the present one the present active crater zone is at 780 m a s l in the first three collapses sliding surfaces cut the main magma conduit in the last collapse the upper scarp coincided with the conduit location dyking along a main ne trending weakness zone across the volcano summit exerted a lateral force for collapse inception the decrease of the landslide volumes with the age and the concentric scarps of the four collapses suggest that the younger sliding planes tended to become more superficial and to decrease the areal extent this is interpreted as due to a successively weaker eruptive products from dominantly lavas to dominantly pyroclastics and b the feedback effects between collapses and dykes that injected along the lateral segments of the first collapse slide plane

effects of the ground surface on polarimetric features of broadband radar scattering from subsurface metallic objects throughout the world the problem of buried unexploded ordnance uxo poses an enormous persistent and expensive problem while uxo generally consists of sizable bodies of ferrous metal and can therefore be detected with current technology it is extremely difficult to distinguish them reliably from typically widespread pieces of clutter thus the problem is one of subsurface discrimination the authors previous modeling work on scattering of ground penetrating radar gpr from metallic objects surrounded by an infinite soil like medium has suggested the utility of a number of key discriminants in broadband fully polarimetric sensing in particular resonance structure induced field rotation and ellipticity and bistatic observation of scattered signals were shown to offer key information about target shape and size the authors investigate the effects on signature features of the proximity of a ground surface to the target for the common case of shallow burial 1 m overall their analyses suggest that the key discriminants seen in scattering in an infinite medium survive the complex interactions with the ground surface in some instances these revealing signatures appear to be strengthened by the presence of a nearby surface multiposition backscatter also allows fundamental inferences about target elongation and symmetry when those cannot be obtained from single position viewing

experimental constraints on the deep magma feeding system at stromboli volcano italy new experiments have been performed on a high k basalt pst 9 from stromboli volcano italy to constrain the physical conditions of golden pumice magmas at their storage level and discuss their petrogenesis fluid present h2o and co2 bearing near liquidus experiments were performed at 11508c between 100 and 400mpa and under oxidizing conditions glasses were analyzed by fourier transform ir spectroscopy and their h2o and co2 concentrations compared with those in glass inclusions most glass inclusions cluster near the 200mpa isobar suggesting entrapment at a depth of 8 km golden pumice magmas have viscosities of 7 9 pa s and densities of 2 48 2 57 g cm3 compositions of experimental fluids coexisting with melts along the liquidus have been estimated by mass balance they range from co2 rich xh2o 0 2 at 400mpa to h2o rich xh2o 0 8 at 100mpa the free fluid phase present at the reservoir level has an xh2o of 0 6 consistent with equilibration with a near liquidus golden pumice magma below 300mpa clinopyroxene is the liquidus phase in all highpressure experiments either fluid absent h2o or fluid present h2o co2 in contrast at 0 1mpa cpx and ol appear together on the liquidus and olivines are more fo rich up to 89 1 than those crystallizing at high pressures up to 87 3 the composition of cotectic liquids multiply saturated in cpx and ol has been experimentally determined most pumices and a majority of melt inclusions have compositions of cotectic melts in contrast pst 9 plots in the cpx field and is representative of less evolved ankaramitic magmas parental to golden pumices melt inclusions trapped in fo 487 olivines form a group of ultra calcic compositions plotting in the cpx field interpreted as boundary layer melts locally generated by cpx dissolution in the deep reservoir ankaramitic melts in the stromboli feeding system are proposed to derive from primitive mantle melts by combined crystallization mixing wall rock interaction and assimilation

mineralogy at the magma hydrothermal system interface in andesite volcanoes new zealand ejecta from phreatomagmatic eruptions of ruapehu and white island andesite volcanoes in new zealand provide insight into the mineralogical reactions that occur when magma invades a vent hosted hydrothermal system at the surface and in ejected blocks from shallow depths hydrothermal alteration mineralogies are dominated by silica polymorphs anhydrite natroalunite and pyrite blocks from greater depths are composed mainly of cristobalite anhydrite halite and magnetite where altered material was heated to magmatic temperatures thermal decomposition reactions produced mullite wollastonite and indialite some ejected breccias contain osumilite cordierite sanidine and hypersthene indicative of reactions occurring near the osumilite cordierite phase boundary at 800 c and water pressure 0 2 kbar hedenbergite wollastonite andradite and magnetite are found in rare skarn fragments possibly formed by metasomatism of silica poor sulfate rich hydrothermal deposits high temperature parageneses of these types have not been reported before in shallow acidic volcano hydrothermal systems however they may be typical of the magma hydrothermal contact zone at many andesite volcanoes

adventive hydrothermal circulation on stromboli volcano aeolian islands italy revealed by geophysical and geochemical approaches implications for general fluid flow models on volcanoes on march 15th 2007 a paroxysmal explosion occurred at the stromboli volcano this event generated a large amount of products mostly lithic blocks some of which impacted the ground as far as down to 200 m a s l about 1 5 km far away from the active vents two days after the explosion a new vapour emission was discovered on the north eastern flank of the volcanic edifice at 560 m a s l just above the area called nel cannestra this new vapour emission was due to a block impact in order to investigate the block impact area to understand the appearance of the vapour emission we conducted on may 2008 a multidisciplinary study involving electrical resistivity tomography ert ground penetrating radar gpr self potential sp co2 soil diffuse degassing and soil temperature surveys this complementary data set revealed the presence of an anomalous conductive body probably related to a shallow hydrothermal level at about 10 15 m depth more or less parallel to the topography it is the first time that such a hydrothermal fluid flow with a temperature close to the water boiling point 76 c has been evidenced at stromboli at this low elevation on the flank of the edifice the ert results suggest a possible link between 1 the main central hydrothermal system of stromboli located just above the plumbing system feeding the active vents with a maximum of subsurface soil temperature close to 90 c and limited by the neostromboli summit crater boundary and 2 the investigated area of nel cannestra at 500 m a s l a buried eruptive fissure active 9 ka ago in parallel sp and co2 soil diffuse degassing measurements suggest in this sector at slightly lower elevation from the block impact crater a magmatic and hydrothermal fluid rising system along the n41 regional fault a complementary ert profile on may 2009 carried out from the neostromboli crater boundary down to the block impact crater displayed a flank fluid flow apparently connected to a deeper system the concept of shallow hydrothermal level have been compared to similar ert results recently obtained on mount etna and la fossa cone of vulcano this information needs to be taken into account in general fluid flow models on volcanoes in particular peripheral thermal waters as those bordering the north eastern coast of stromboli could be contaminated by hydrothermal and magmatic fluids coming from regional faults but also from the summit

a reply to the comment on assessing discrepancies between previous plate kinematic models of mesozoic iberia and their constraints by barnett moore et al we welcome the comments of van hinsbergen et al 2017 on the recent efforts of barnett moore et al 2016 specifically van hinsbergen et al 2017 raise concerns about two of the major conclusions made by barnett moore et al 2016 firstly barnett moore et al 2016 choose to negate the cretaceous iberian paleomagnetic database as a viable plate kinematic constraint on the plate motions of mesozoic iberia this conclusion criticized by van hinsbergen et al 2017 was based on citing the previous efforts of neres et al 2012 2013 which exposed several shortcomings elaborated on below within this dataset secondly van hinsbergen et al 2017 criticize barnett moore et al 2016 for dismissing mantle tomographic interpretations in support of a preserved cretaceous pyrenean subducted slab beneath northern africa below we have addressed each of these major criticisms from van hinsbergen et al 2017 in a two section layout similar to their comment above

kinetics of crystallization example of micro crystallization in basalt lava the kinetics of crystallization of basalt glass from kilauea hawaii was investigated to derive time and temperature dependence of growth rates and to relate these results to crystallization characteristics that develop during in place cooling of lava and isothermal re heating in the lab the choice of temperatures of re heating was based on observations that pyroxene and fe ti oxide production starts at about 850 c and plagioclase above 920 c crystallization parameters were determined by the crystal size distribution method csd which allows one to derive growth g and nucleation j rates if the residence time within the temperature interval of crystallization is known for the in place cooled lava the residence time was determined from cooling rates that could be derived from literature data of temperature measurements in the upper 2 cm of lava lobes re heating of basalt glass as a function of time shows a linear relationship between log g and log time log g a log t k 1 this observation was possible because the time scale of crystallization was similar to the observational time scale a condition usually not given for cooling processes the time dependence of g is shown to correspond to a decrease in g and j from the original surface air interface to the interior of the lava a change that occurs concomitant with an increase in crystal size and number density hence it is the time dependence of g that explains the hitherto well observed relationship with cooling rate along a temperature gradient in magmatic bodies moreover the log linear relationship between time and growth rate is suggested to describe heterogeneous nucleation and growth which is independent of the process i e cooling or metamorphism isothermal re heating extinguishes the high growth rate signatures of cooling temperature dependence of growth rates carried out at 24 h shows minimum temperatures of 900 950 c which because of the time dependence of growth refers to the nucleation and crystallization maximum and is in agreement with results from differential scanning calorimetry

generation of forsteritic olivine fo99 8 by subsolidus oxidation in basaltic flows we identify olivine grains with compositions up to fo99 8 which are found in multiple primitive basaltic lava flows from a monogenetic volcano in the big pine volcanic field california usa in this study we show that the forsterite in these basalts formed by subsolidus recrystallization in a high fo2 environment olivine compositions are bimodal with flows having either all normal compositions fo74 9 94 4 or highly forsteritic fo97 2 99 8 compositions in many grains the subhedral forsteritic olivine has a hematite and clinopyroxene rim and internal parallel oriented planes of hematite clinopyroxene and orthopyroxene results of isotopic chemical crystallographic petrographic and mineralogical analyses show that the forsterite formed through subsolidus oxidation of olivine phenocrysts the forsteritic olivines generally occur in the thinner flows we infer that a rapidly emplaced sequence of thin vesicular spatter fed flows allowed the original olivine phenocrysts to become repeatedly reheated while exposed to air our study required sampling each flow so it was difficult to avoid the altered portions of the thinner flows other studies would tend to avoid such flows which may account for why such forsteritic olivines have not been more widely recognized

buchitic metagreywacke xenoliths from mount ngauruhoe taupo volcanic zone new zealand abstract buchitic sedimentary xenoliths a few centimetres to several decimetres diameter occur in recent andesite from mount ngauruhoe tongariro volcanic center taupo volcanic zone new zealand bulk chemistry and sr isotope compositions of the xenoliths indicate that they are greywacke and argillite derived from mesozoic torlesse terrane basement that partly underlies the taupo volcanic zone the xenoliths contain up to 80 glass with quartz apatite and zircon remaining as unmelted phases glasses within the xenoliths are peraluminous a cnk 1 0 1 4 have high normative corundum 2 7 appreciable feo 2 4 wt mgo 0 2 1 5 wt tio 2 0 17 0 84 wt relatively high normative an 1 0 5 3 and do not represent s type granitic melts in the argillite the glass has higher amounts of ai 2 o 3 feo mgo cao and k 2 o and has less sio 2 and na 2 o than glass in the greywacke silica rich glass up to 80 wt sio 2 surrounds partially melted quartz variable glass chemistry reflects the heterogeneous layered nature of the xenoliths cordierite mg mg fe mn 0 78 0 58 orthopyroxene en 43 56 mg rich ilmenite rutile pleonaste v cr ti spinel and pyrrhotite occur in the glass of the xenoliths the dominant cordierite orthopyroxene spinel assemblage can be accounted for by disequilibrium breakdown reactions under low oxidation conditions

cooling kinetics experiments on different stromboli lavas effects on crystal morphologies and phases composition abstract controlled cooling experiments at atmospheric pressure and fo2 of the nno buffer were performed on three stromboli lavas of calcalkaline ca high k calcalkaline hkca and shoshonitic sho affinities the experiments were conducted at cooling rates of 900 c h fast cooling rate fcr and 1 c h slow cooling rate scr respectively to investigate the kinetic factors governing textural and compositional features such as phase growth morphology phase relations and phase compositions the experiments produced different types of textures as both the cooling rate and the quenching temperatures were varied in general fcr experiments show a decrease of crystal size as well as a change in crystal shape from euhedral to granular to skeletal up to dendritic morphology with decreasing temperatures scr experiments produce less variable crystal size and crystal morphology measurements of plagioclases indicate that the crystal size and calculated crystal growth are functions of cooling rate crystal growth rates are about two orders of magnitude higher in fcr experiments than scr ones such textural responses are in agreement with the empirical calibration based on the plagioclase size dependence on cooling rate developed by cashman 1993 experimental phase relations display three main features of the crystallization process 1 the delay in the crystallization of the liquidus phase in the fcr experiments with respect to the scr ones 2 crystallization controlled by the multiphase cotectic relations plagioclase pyroxenes olivine is more enhanced for fcr experiments compared to that of scr ones at the lowest experimental temperature 1100 c 3 crystallization of augite and pigeonite is sensitive to cooling rate and system compositions pigeonite not found in the natural rocks crystallizes in the ca sample across scr and fcr runs and in the hkca sample just in the scr experiments fcr and scr experiments produce similar liquid lines of descent for both ca and hkca starting materials suggesting that the processes of nucleation and growth play reciprocal roles through mass balance as cooling rate varies this is not true for the sho composition where the trends of melt composition appear to be especially influenced by the different amounts of olivine crystallization at the different cooling rates data on mineral compositions show that plagioclase and clinopyroxene are the phases more strongly affected by the cooling gradients crystals from scr experiments and to a lesser extent from fcr experiments show zoning patterns mainly at the lowest experimental temperature

structural features of the 2007 stromboli eruption abstract on 27 february 2007 two ne sw and nnw sse dike fed effusive vents opened to the north at 650 and 400 m above sea level asl of the summit craters at stromboli forming a fissure parallel to the inner walls of the sciara del fuoco sdf sector collapse depression the formation of these vents was soon followed by rapid subsidence of the summit crater area this partly obstructed the central conduit temporarily choking the fissure and increasing the deformation of the upper part of sdf the reactivation of the nnw sse vent and the opening of a new vent located at 500 m asl fed by a second dike released the internal pressure and surface deformation ceased the eruption then continued again from the 400 m vent after a summit explosion on 15 march until ending in early april after a progressive decrease of magma output repeated ne sw dike intrusions have occurred in recent years close to the upper se limit of the sdf in that zone named bastimento the eruptive fractures traced the discontinuities that borders the sdf increasing the risk of triggering new sector collapse whereas the ne sw trending structures lie along the regional volcano structural trend of the aeolian arc through stromboli the nnw sse vents are oblique to this trend and may be controlled by the anomalous stress field within the unstable flank of the sdf another fundamental aspect of the 2007 eruption is the collapse of the central conduit due to the rapid and deep magma drainage linked to the opening of the 400 m vent the intrusion of dikes and development of flank vents during the 2007 eruption could possibly have triggered catastrophic landslides and related tsunami or eruptive paroxysms but the opening of new effusive vents released the internal pressures diminishing the hazard

the contribution of fluid geochemistry to the volcano monitoring of stromboli abstract the persistent open vent mild explosive activity of stromboli volcano is episodically interrupted by more violent and dangerous explosive events major explosions and paroxysms according to the nature of erupted products paroxysms can be related either to the explosion of overpressured gas pockets located in the proximity of the magma column or to the sudden uprise of hot gas rich magma from a deep part of the plumbing system in both cases these more energetic explosive events should be preceded by an escape or a preferential uprise of the highly mobile volatiles which in turn should produce gas leakage anomalies at the surface in sites of high vertical permeability such as deep reaching faults in order to identify such gas leaking sites a systematic co2 soil flux survey has been carried out on the island using an accumulation chamber four hundred sixty one points have been measured with a high density in the summit crater area where high flux values have been found 10 3 10 2 cm s anomalous points are concentrated along the main ne sw axial feeding system of the volcano co2 soil flux decreases from the crater zone to the base of the volcanic cone where however an interesting gas leakage anomaly occurs pizzillo mofette in the pizzillo area thermal water wells also occur whose chemistry indicates an origin by sea water heated by hot gas soil gases have been sampled in the sites with the highest co2 flux in the crater area and at the base of the cone chemical and isotopic analyses indicate the presence of a deep gas component especially in the crater zone samples high co2 appreciable contents of he and h2 3he 4he values up to 3 55 13c of co2 2 the sc5 low flux fumarole on the crater rim has shown during six years a remarkable persistence of temperature 93 95 c with only minor fluctuations of chemistry appearance of anomalous peaks of h2 in correspondence with strombolian explosions was observed during a 2 h 30 min experiment of continuous recording of hydrogen content of the fumarole together with previous data on h2o co2 and he this experiment confirms that strombolian blasts produce rapid fluctuations in the fumarolic gas composition in the light of this study sc5 fumarole and pizzillo mofette look promising sites for the testing of a continuous geochemical monitoring system of stromboli volcano

review of ten years of volcano deformations recorded by the ground based insar monitoring system at stromboli volcano a tool to mitigate volcano flank dynamics and intense volcanic activity abstract stromboli volcano southern italy is one of the most monitored volcano in the world with a surveillance network that includes a permanently sited ground based sar interferometer gbinsar this work is the review of the gbinsar data gained from the last decade of monitoring activity the analysis of the entire dataset of gbinsar measurements allowed the assessment of the deformation field of the northern part of the summit crater area and the sciara del fuoco depression in detail the main displacements recognized can be related to different factors 1 the inflation deflation respectively immediately before and after each new effusive event 2 the bulging of localized sectors of the volcano involved in the vent opening 3 the gravitational sliding of the sciara del fuoco infill 4 the movement of lava flows accelerations in this sector are related to sheet intrusions while the possibility of vent opening associated with small sliding or catastrophic flank failure are related to highly overpressurized sheets able to produce high displacement rate in the sciara del fuoco in the summit crater area the increases in the displacement rate are related to the pressurization of the shallow conduit system as the consequence of the variation in the magma level magmastatic pressure or to the lateral magma migration lateral conduit expansion or dike intrusion in response to the increase of the overpressure component fluctuations in the displacement rate in the summit crater area can be related to the magma overturning within the conduit with the increases in displacement rate during the upwelling of less dense magma while displacement rate decreases as the degassed magma column is pushed out from the conduit lava flows or overflows instead the decrease in the displacement rate without coeval lava outpouring could be related to the sink of the degassed magma due to density contrast between the gas poor and the gas charged magmas using the displacement rate in the summit crater area as a proxy for the variation in the pressure condition in conduit both magmastatic and overpressure components thresholds for the crises characterized by the occurrence of overflows eventually associated with major explosions and flank effusions eventually associated with paroxysmal explosions are identified small conduit overpressure will produce overflows sometimes associated with crater rim collapses while large magma overpressure will laterally expand the conduit forming ne sw striking sheets feeding eruptive vents at the base of the summit crater area and within the sciara del fuoco generating conditions of instability that can evolve into catastrophic collapse of the instable flank

monitoring of the volcanic rock compositions during the 2012 2013 fissure eruption at tolbachik volcano kamchatka abstract here we present the results from monitoring of the composition of rocks produced during the 2012 2013 fissure eruption at tolbachik volcano fte major and trace element concentrations in 75 samples are reported products of this eruption are represented by high alumina basaltic trachyandesites with higher alkalis and titanium contents than in all previously studied rocks of the tolbachik monogenetic volcanic field rocks erupted during the first three days 27 30 november from the northern also called menyailov group of vents are the most silica and alkali rich sio2 concentrations up to 55 35 wt and k2o up to 2 67 wt from december onwards when the eruptive activity switched from the menyailov vents to the southern naboko group of vents silica content dropped by 2 wt concentrations of mgo feo tio2 and mg increased and k2o and na2o concentrations and k2o mgo ratio decreased for the rest of the eruption the compositions of rocks remained constant and homogeneous no systematic compositional differences between lava bombs and scoria samples are evident trace element distributions in the rocks of the menyailov and naboko vent lavas are relatively uniform menyailov lavas have slightly higher th nb hf y and hree concentrations than the naboko vent lavas at more or less constant element ratios we explain the initial change in geochemistry by tapping of a slightly cooler and fractionated 3 mt and 8 cpx upper part of the magma storage zone before the main storage area began to feed the eruption thermodynamic constraints show that apparent liquidus temperatures varied from 1142 c to 1151 c and thermodynamic modeling shows that variations in compositions are consistent with a high degree of low pressure 100 300 mpa nominally anhydrous fractionation of a parent melt compositionally similar to the 1975 northern breakthrough high mg basalt geochemistry petrological observations and modeling are in agreement with the newly erupted material being derived from remnant high al magma from the 1975 76 southern breakthrough eruption with only slight amounts of cooling less than 1 c per year during the intervening 36 years

integrated petrochemical and geophysical data reveals thermal distribution of the feeding conduits at stromboli volcano italy 1 samples of scoriae erupted at stromboli volcano during its persistent strombolian activity were collected between 2005 and 2008 chemical and mineralogical compositions were obtained on products erupted from the three main crater sectors sw central and ne small chemical variations indicate a different degree of evolution coupled with small difference of magma temperature 10 c analysis of the acoustic data for the same time period as the scoria sampling indicates that puffing a persistent overpressurized bubble degassing was on average mainly observed at the central craters and at times moved to the ne sector the cross check of the two independent data sets allowed us to assess correlation between composition of products and puffing activity at vents the hotter products are always erupted from the vents where puffing occurs indicating that slightly higher temperature can be the expression of an enhanced two phase bubble flow dynamics