sedimentary rhythm of mn carbonate laminae induced by east asian summer monsoon variability and human activity in lake ohnuma southwest hokkaido northern japan abstract past and ongoing precipitations of mn carbonate rhodochrosite have occurred in the freshwater lake ohnuma which is situated about 8 km south of the hokkaido komagatake volcano southwest hokkaido northern japan lake sediments from a surface and a longer 4 m core contain the sedimentary rhythms of rhodochrosite laminae and volcanic deposits which were identified by nondestructive micro xrf fluorescence analyses the three tephra ash layers from the hokkaido komagatake volcano characterized by peaks of al si k ca and ti correspond to regionally recognized tephras 1640 1929 and 1996 ce based on ashfall isopachs and 137cs 210pb and 14c ages determined from the two cores the sedimentation rate showed a drastic change around 1929 ce 0 3 cm yr for 1640 1929 ce and 2 7 cm yr for 1929 2012 ce the mn content record of lake ohnuma sediments composed of rhodochrosite laminae showed a periodic variation with a decadal centennial scale over the interval 1640 2012 ce sediment petrography and hydrochemical measurements suggest that the metastable phase of rhodochrosite was deposited during summer after being precipitated followed by the crystal growth of rhodochrosite within the anoxic sediments on the basis of these results high mn content is interpreted as an indicator of strengthened summer stratification associated with reduced rainfall runoff the ti si ratios are representative of the relative abundance of detrital inputs from the watershed the combined signals of elevated mn content and ti si ratio for 1935 2012 ce indicate eutrophication and hypoxia in the lake and enhanced land erosion in the watershed associated with the post 1970s intensive land use such as livestock farming for 1640 1935 ce the lake ohnuma record shows an antiphase relationship between the mn content and ti si ratio which implies that the detrital inputs reflected the strength of the east asian summer monsoon easm and the reduced rainfall runoff resulted in weaker mixing followed by depleted o2 in the water column the antiphase variation in mn content and ti si ratio suggest weak easm during the little ice age 1850 ce followed by strong easm between 1860 and 1929 ce

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

magmatic evolution of a volcano studied by 230th 238u disequilibrium and trace elements systematics the etna case age determinations of several lava flows from etna through 230th 238u disequilibrium internal isochrons yield a precise chronology of the volcano s history for the last 200 000 years and emphasize the main episodes in the formation of this huge complex strato volcano study of 230th232th 0 initial ratios of lavas together with their trace element compositions yields a consistent model of magmatic evolution implying the existence for 200 000 years of a deep reservoir of alkalic magma periodically mixed with magmas of tholeiitic affinity these short periods of mixing appear to be related to the formation of the large calderas of etna in addition to these processes affecting the deep reservoir fractional crystallization also occurred in more superficial levels of the volcanic edifice thereby yielding several series of differentiation of relatively short duration as for its geochemistry etna s volcanism is of oceanic type but with its own characteristics and in a peculiar geodynamic context at the edge of the african plate

multiple levels of magma storage during the 1980 summer eruptions of mount st helens wa transitions in eruptive style explosive to effusive sustained to pulsatory are a common aspect of volcanic activity and present a major challenge to volcano monitoring efforts a classic example of such transitions is provided by the activity of mount st helens wa during 1980 where a climactic plinian event on may 18 was followed by subplinian and vulcanian eruptions that became increasing pulsatory with time throughout the summer finally progressing to episodic growth of a lava dome here we use variations in the textures glass compositions and volatile contents of melt inclusions preserved in pyroclasts produced by the summer 1980 eruptions to determine conditions of magma ascent and storage that may have led to observed changes in eruptive activity five different pyroclast types identified in pyroclastic flow and fall deposits produced by eruptions in june 12 july 22 and august 7 1980 provide evidence for multiple levels of magma storage prior to each event highly vesicular clasts have h2o rich 4 5 5 5 wt melt inclusions and lack groundmass microlites or hornblende reaction rims characteristics that require magma storage at p 160 mpa until shortly prior to eruption all other clast types have groundmass microlites ph20 estimated from both h2o bearing melt inclusions and textural constraints provided by decompression experiments suggest pre eruptive storage pressures of 75 40 and 10 mpa the distribution of pyroclast types within and between eruptive deposits can be used to place important constraints on eruption mechanisms fall and flow deposits from june 12 1980 lack highly vesicular microlite free pyroclasts this eruption was also preceded by a shallow intrusion on june 3 as evidenced by a seismic crisis and enhanced so2 emissions our constraints suggest that magma intruded to a depth of 4 km beneath the crater floor fed the june eruption in contrast eruptions of july and august although shorter in duration and smaller in volume erupted deep volatile rich magma if modeled as a simple cylinder these data require a step wise decrease in effective conduit diameter from 40 50 m in may and june to 8 12 m in july and august the abundance of vesicular intermediate to deep clast types in july and august further suggests that this change was effected by narrowing the shallower part of the conduit perhaps in response to solidification of intruded magma remaining in the shallow system after the june eruption eruptions from july to october were distinctly pulsatory transitioning between subplinian and vulcanian in character as originally suggested by scandone and malone 1985 a growing mismatch between the rate of magma ascent and magma disruption explains the increasingly pulsatory nature of the eruptions through time recent fragmentation experiments spieler et al 2004 suggest this mismatch may have been aided by the multiple levels at which magma was stored and degassed prior to these events

degassing processes at stromboli volcano inferred from short lived disequilibria 210 pb 210 bi 210 po in volcanic gases abstract volcanic aerosols and gases released by three active craters at stromboli volcano have been regularly collected since 1985 in this paper we present new evidence of the high volatility of some nuclides among radon daughters 210pb 210bi and 210po which are strongly fractionated leading to significant radioactive disequilibria in volcanic exhalations the very low volcanic activity in october 1996 allowed a separate sampling of each crater plume for the first time remote sampling of the bulk plume were also performed these data show that the chemical composition of volcanic aerosols remains constant within the first few hundred meters from their source vents ensuring the validity of remote sampling when the activity does not allow one to approach the active craters moreover it appears that there is no differentiation of gases from one crater to another suggesting that the geometry of the upper plumbing system of the volcano is rather simple gases being directly emitted from a shallow magma chamber without significant cooling inside the edifice on the basis of the assumption of a continuously replenished shallow magma reservoir in steady state we propose a dynamic model of degassing accounting for the variations of radionuclide contents and ratios observed in the gas phase since 1985 this model allows us to relate these variations to changes in the magma chamber dynamics namely the magma residence time inside the chamber and the escape time of gases from it both parameters being closely linked to the volcanic activity while gases are always emitted within a few hours after bubble nucleation suggesting that the chamber is no deeper than a few hundred meters magma residence time varies from less than 20 days during eruptive periods highly explosive or effusive periods to more than 200 days before the 1985 eruption the latter figure is explained by the storage at shallow depth of a poorly renewed magma batch that fed the eruption the variations of the residence time observed over the studied period suggest that the steady state dynamics of the stromboli magma chamber is sustained for rather short periods of a few months at most on basis of the knowledge of the deep undegassed magma supply and the magma residence time we estimate the volume of the shallow magma chamber at about 7 2 10 5 m 3 the good agreement of our results with previous estimates based on both geochemical and geophysical studies suggests that the measurement of radioactive disequilibria in the gas phase provides a robust tool for a deeper understanding of the volcanic activity and the magma dynamics beneath active volcanoes

evidence for decreasing south asian summer monsoon in the past 160 years from varved sediment in lake xinluhai tibetan plateau 1 we report glacial varves in the sediment of lake xinluhai tibetan plateau independent data of 137cs and 210pb indicate that these are annually deposited varves varves appear as rhythmic units of light colored silt layer capped by a dark clay layer under microscope varve thickness in lake xinluhai is sensitive to precipitation because sediment accumulation is strongly affected by monsoon rainfall in the area a general decreasing trend can be observed in the varve thickness over the past 160 years spectral analyses of the varve record are dominated by cycles which are similar to enso periodicities it implies that the decreasing trend of the south asia monsoon may be linking with enso spatially the decreasing trend can be observed across different proxy records in the south of the tibetan plateau although arguments still remain for the dynamic mechanisms and spatial rainfall difference the south asian summer monsoon could be weakened due to rising temperatures

estimates of stress directions by inversion of earthquake fault plane solutions in sicily summary the tectonic stress orientation is estimated in the lithosphere of northern sicily the southern tyrrhenian sea and southern calabria and in the wadati benioff zone below the tyrrhenian by inversion of fault plane solutions of earthquakes covering a magnitude range from 2 5 to 7 1 focal mechanisms of 97 earthquakes are taken from the literature after a critical evaluation of their data quality an average misfit of f 13 indicates that the set of all shallow 50 km earthquakes is generated by a heterogeneous stress field for three subsets based on regional and magnitude separation f was small enough 2 8 lfs5 9 to support the assumption of a homogeneous stress direction for an additional subset with f 7 4 such a condition is close to being fulfilled even though some heterogeneity appears to be present the number of earthquakes in these subsets ranged from nine to 22 and the uncertainties of the principal stress directions were generally of the order of 20 at the 90 per cent confidence level the earthquakes with a425 define a regional stress field with the greatest principal stress ul dipping at a shallow angle to the south in north eastern sicily and south western calabria the stress field estimated by earthquakes is extensional with o3 in a direction of wnw and a near vertical ol in agreement with the graben tectonics mapped geologically in this area in western sicily the c1 direction is oriented wnw but this result is judged less reliable than the others based on the broader confidence limits of the solution and the average misfit of 7 4 the earthquakes in the wadati benioff zone define ol dipping at about 70 to the nw subparallel to the zone with o2 horizontal and striking parallel to the zone

reactivation of stromboli s summit craters at the end of the 2007 effusive eruption detected by thermal surveys and seismicity this paper was partially supported by a grant to s c project ingv dpc paroxysm v2 03 2008 2010 funded by the istituto nazionale di geofisica e vulcanologia and by the italian civil protection

zircon fission track ages from the gasherbrum diorite karakoram range northern pakistan the gasherbrum peaks in the himalaya of pakistan reach elevations of 8000 m the relief between the peaks and the adjacent valley baltoro glacier is in excess of 3000 m eight samples of the early cretaceous gasherbrum diorite at elevations between 4880 and 7165 m on gasherbrum iv were collected for fission track dating zircon fission track ages from the gasherbrum diorite vary from early cretaceous to middle tertiary in age there is no consistent pattern between age and elevation the cretaceous ages indicate that these rocks were never deeply buried i e heated to temperatures in excess of 175 c to reset the zircons during cenozoic time these results also indicate that the uplift of this part of the himalaya has been either very rapid and recent or very slow since early cretaceous time this latter possibility is not consistent with the high relief at gasherbrum and what is known about regional tectonics gasherbrum iv zircons currently at approximately 4880 m have never been at depths greater than 6 km and less than 3 km of material has been removed from the top of the range by erosion since the early cretaceous rapid uplift has occurred very recently and erosion rates have notmore been able to keep pace with this uplift less

volcanic plume and bomb field masses from thermal infrared camera imagery masses erupted during normal explosions at stromboli volcano italy are notoriously difficult to measure we present a method that uses thermal infrared video for cooling bomb fields to obtain the total power emitted by all hot particles emitted during an explosion a given mass of magma m will emit a finite amount of thermal power defined by m cp te t0 cp and te being magma specific heat capacity and temperature and t0 being ambient temperature we use this relation to convert the total power emitted by the bomb field to the mass required to generate that power to do this we extract power flux curves for the field and integrate this through time to obtain total power e this is used to estimate mass q in q e cp te t0 when applied to individual bombs we obtain masses of between 1 and 9 kg per bomb or a volume of 970 and 6500 cm3 these volumes equate to spheres with diameters 12 and 27 cm for the entire bomb field we obtain volumes of 7 28 m3 we calculate masses for 32 eruptions and obtain typical bomb masses of between 103 and 104 kg per eruption in addition we estimate that between 102 and 103 kg of gas and ash are emitted as part of a mixed plume of bombs gas and ash we identify two types of eruption on the basis of the erupted bomb masses and the ratio of the plume s gas and ash component to the bomb component the first type is bomb dominated is characterized by bomb masses of 104 kg and has ash gas bomb ratios of 0 02 the second type is ash and gas dominated is characterized by erupted bomb masses of 103 kg and has ash gas bomb ratios of around one and as high as two there is no correlation between the quantity of bombs and quantity of gas ash erupted in addition while source pressure for each explosion correlates with the quantity of gas and ash erupted the mass of bombs emitted varies independently of pressure

flow to fracture transition in a volcanic mush plug may govern normal eruptions at stromboli stromboli is a model volcano for studying eruptions driven by degassing the current paradigm posits that strombolian eruptions represent the bursting of gas slugs ascending through melt filled conduits but petrological observations show that magma at shallow depth is crystalline enough to form a three phase plug consisting of crystals bubbles and melt we combine a 1d model of gas flushing a crystalline mush with a 3d stress model our results suggest that localized gas segregation establishes hot conduits of mobile magma within a stagnant plug the plug is prone to tensile failure controlled by gas over pressure and tectonic stress with failure most likely beneath the observed vent locations we hence argue that strombolian eruptions are related to plug failure rather than flow our proposed three phase model of the shallow plumbing system may provide a promising framework for integrating geophysical petrological and morphological observations at stromboli and in open system volcanism more generally

a 2000 year record of solar forcing on varved lake sediment in eastern finland abstract a high resolution study was performed on varved sediments from lake lehmilampi in eastern finland varve data was collected by digital image analysis using standard 1 8 mm thick samples impregnated in epoxy and x rayed climatic variability is imprinted on varve properties varve thickness and accumulation of mineral and organic matter during the last 2000 years the cumulative counting error of the varve record is estimated as 2 3 qualitative comparison of varve parameters and residual 14c constructed from tree rings revealed close correspondence between the two records suggesting solar forcing on lake sedimentation classical climatic periods of the last millennia medieval climate anomaly 1060 1280 in the varve record and little ice age cooler phases culminating in 1340 1465 1545 1680 1850 and also in 1930 in the varve record are clearly evident in the varve record at present the physical link between solar activity levels and lake sedimentation has not been established

relationships among crustal structure volcanism and strike slip tectonics in the lipari vulcano volcanic complex aeolian islands southern tyrrhenian sea italy abstract the lipari vulcano volcanic complex lvvc aeolian arc southern tyrrhenian sea italy develops along a strike slip fault system that bisects the aeolian arc the lvvc crustal structure is investigated by applying seismic methods to two data sets p wavefronts generated by local and distant events constrain the shallow velocity structure dss data provide shape and depth of the main crustal discontinuities the obtained velocity model shows that the lvvc shallow structure is characterized by the presence of two sharp lateral discontinuities the northern discontinuity bounds a low velocity basin like structure including the la fossa caldera and mt guardia caldera depressions the southern discontinuity coincides with the southern boundary of a high velocity diffractor located beneath the la fossa cone direct modeling of dss data define three crustal discontinuities showing a complex geometry the intra crustal interfaces and the moho discontinuity show an upheaval beneath the lvvc central sector the estimated crustal velocities are lower than those generally reported for the continental crust this feature is due to the high heat flux and fluid circulation affecting the lvvc area the ratio between the thickness of the upper and lower crust and the presence of the moho upheaval are consistent with that reported for continental areas affected by extensional strain the collected geophysical data combined with volcanological and structural information indicate that a the mt guardia and la fossa caldera depressions represent the surface expression of a single structure whose formation is mainly due to tectonic processes b the lvvc crustal structure and the evolution of the volcanism are consistent with those recognized in zones of transition from arc related to rift volcanism in addition results of a preliminary mechanical analysis based on the available structural data indicate low values of the ratio between magmatic overpressure and tectonic stress this suggests a passive mechanism of mantle upwelling the mantle upwelling is due the post collisional normal strike slip tectonics affecting the aeolian arc

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

the lithosphere asthenosphere system in the calabrian arc and surrounding seas southern italy a fairly detailed structural model of the lithosphere asthenosphere system thickness s and p wave velocities of the crust and of the uppermost mantle layers has been defined in the calabrian arc region southern tyrrhenian sea calabria and the northwestern part of the ionian sea in southern italy using seismic data from literature as a priori constraints of the nonlinear inversion of surface wave data

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

a possible middle pleistocene seasonal deposit in taipei basin taiwan inferred from pollen study abstract laminated sediments in the taipei basin which are tentatively assigned to the antepenultimate glacial period were studied to discern the paleoclimatic significance analyses of multi proxies including pollen mineralogy grain size and loss on ignition loi were carried out on three 50 cm thick intervals of a 23 7 m thick laminated section of the hsinchuan core western taipei the couplets are commonly composed of 2 7 mm light grey layers and 2 3 mm dark grey layers major components in the light grey layer are quartz 70 associated with clay minerals illite clay minerals increase in the dark grey layer and can dominate a pollen study indicates that the light grey layers are characterized by more abundant warm elements such as cyclobalanopsis and castanopsis while the dark grey layers have more abundant cool elements including pinaceae pinus picea tsuga alnus and significant amounts of poaceae study of the present pollen calendar of the taipei basin indicates that pinus appears during winter spring and cyclobalanopsis and castanopsis appear during early summer the studied couplets are thus very possibly seasonal deposits of the ancient lake spectrum analysis for the thickness variation of the light grey laminae believed to represent most of the annual precipitation changes in summer autumn shows prominent el nino southern oscillation enso peaks of 3 4 and 6 7 year periods this may indicate that enso events occurred during the middle pleistocene glaciation

methods of determining the rheological properties of magmas at sub liquidus temperatures non vesicular basaltic melts behave as newtonian fluids at temperatures above their liquidus and their viscosities can be calculated using a method developed by shaw 1972 and bottinga and weill 1972 because many igneous processes involve the flow of silicates at sub liquidus temperatures numerous attempts have been made to calculate the interactive effects of the crystal phase however current methods are appropriate only for relatively low crystal concentrations and they assume newtonian behaviour we argue that this assumption is invalid when bubble or crystal concentrations exceed 30 at higher concentrations factors other than concentration become increasingly important these include particle shape and size distribution a method which takes these factors into account is tested on a range of suspensions including magmas at sub liquidus temperatures and rheological properties calculated using this method agree closely with the measured values we also demonstrate that an equation which was introduced to explain large differences in measured apparent viscosities during the cooling and crystallisation of mount st helens dacite murase et al 1985 and which is currently used to calculate the rheological properties of crystallising lavas generates viscosities which may be in error by several orders of magnitude this difference is argued to be caused by a combination of factors including the ten orders of magnitude range in the strain rates utilised during the mount st helens measurements causing orders of magnitude difference in the resulting apparent viscosities rheological data on crystallising silicic melts are reinterpreted taking into account the non newtonian rheology of the magmas and changes in activation energy of flow during crystallisation

neutral buoyancy and the structure of mid ocean ridge magma reservoirs the mechanical structure of the regions for shallow storage and lateral intrusion of mid ocean ridge basalt morb is explored in part by examining the density range appropriate for picritic to tholeiitic liquids and liquid crystal mixtures and its relationship to the nonlinear density depth structure of the ridge magma density spans the range 2 6 to at least 2 82 mg m 3 and incorporates the effects of fractional crystallization on the density evolution the incorporation of olivine phenocrysts and the contributions of water in melt phase density reductions the melt and melt crystal density band crosses the in situ rock density curve over the 1 to 3 km depth interval beneath the volcanic surface within that averaged interval picritic to tholeiitic melt and melt crystal mixtures are in approximate mechanical equilibrium with their surroundings and the interval is referred to as the morb horizon of neutral buoyancy hnb the detailed locations of the transition regions between the negative and neutral buoyancy and between the neutral and positive buoyancy regimes are dependent on melt phase composition as well as the presence of suspended mineral phases and their identity in the east pacific rise the hnb has a 1 1 correspondence with the inferred location of the sheeted dike complex and the seismically detected minimum compressional wave velocity region in ophiolite complexes the region corresponds to the sheeted dike complex and the uppermost isotropic gabbros above the hnb is the region of negative buoyancy seafloor to an averaged 1 km depth within which negative buoyancy forces may induce the descent of nonvesiculated melt this region corresponds to the pillow basalt sediment sequence the region of positive buoyancy extends from 3 km to the depth of melt generation and picritic melt ascends in dikes and veins of finite height 500 m to 11 km and relatively narrow width 20 mm to 100 cm the finite strengths of high temperature fluid weakened rocks mandate finite height melt parcels along the ascent pathway the magmatic source region is therefore never hydraulically connected with the surface nor with the near surface reservoir thus relatively locally integrated buoyancy has a natural role in the ascent of melt from the source region to the region of neutral buoyancy during the final stages of magma ascent hydrothermal fluid circulation enshrouds the hnb in a three dimensional envelope as suggested by the depth extent of alteration mineralogy in ophiolite complexes while hydrothermal cooling may play an important role in arresting the ascent of magma in very low spreading rate environments gravitational equilibrium represents the effectively dominant theme in intermediate and high spreading rate regions such as the east pacific rise elastic crack penetration of rheological transition zones near the hnb identify modes of crack tip morphologic changes as a function of young s modulus ratios e2 e1 above and beneath the transition and affect the style of intrusion while melt buoyancy determines the ultimate equilibrium resting place elastic crack stability considerations relate the vertical magma pressure gradients for tholeiitic pt and picritic pp magmas to the vertically varying gradient in the horizontal stress component h and suggest further subdivision into two horizons of neutral buoyancy one for tholeiitic magma hnbt and one for the picritic liquid olivine mixtures hnbp these intervals are very approximate but are estimated as 600 m to 1400 m and 1400 to 3000 m depth respectively beneath the east pacific rise axis as oceanic lithosphere is created at the rise axis and spreads laterally the horizons of negative buoyancy and neutral buoyancy ride with it and may continue to modulate the subsurface magma dynamics that influence off axis volcanism

deformation at stromboli volcano italy revealed by rock mechanics and structural geology abstract we approach the reconstruction of the recent structural evolution of stromboli volcano italy and the analysis of the interplay between tectonics gravity and volcanic deformation by tying together structural lithostratigraphic and rock mechanics data we establish that since 100 ka bp the edifice has faulted and jointed mainly along ne striking planes faults mostly dip to the nw with normal displacement taking also into account the presence of a nw trending regional least principal stress and of tectonic earthquake hypocenters inside the cone we suggest that this fracturing can be related to the transmission of tectonic forces from the basement to the cone dyking concentrated along a main ne trending weakness zone nez across the volcano summit resembling a volcanic rift whose geometry is governed by the tectonic field in the past 13 ka stromboli experienced a reorganisation of the strain field which was linked with the development of four sector collapses affecting the nw flank alternating with growth phases the tectonic strain field interplayed with dyking and fracturing related to unbuttressing along the collapse shoulders we propose that tectonics control the geometry of dykes inside the cone and that these in turn contribute to destabilise the cone flanks

dynamics of the december 2002 flank failure and tsunami at stromboli volcano inferred by volcanological and geophysical observations 1 the 2002 effusive flank eruption at stromboli volcano started on december 28 after several months of strong explosive activity at the summit craters on december 30 the seismic network recorded two large flank failures and associated tsunami waves this is the first time that a flank collapse and tsunami and their associated phenomena have been recorded by a multi disciplinary monitoring system volcanological and geophysical monitoring as well as thermal surveys performed immediately before and after the failure allowed us to define and interpret the sequence of events the still on going eruption has provided for the first time the opportunity to look into the dynamics of stromboli s effusive eruptions flank failure and landslide formation and their potential hazard

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

when magmas do not interact paired roman age activity revealed by tephra studies at stromboli volcano detailed stratigraphic and geochemical studies were carried out on remnants of the partially collapsed pizzo o sopra la fossa pizzo scoria cone which represents the best viewpoint for observing the present day activity on top of the stromboli volcano italy the main outcrop is above the active craters and is strongly altered by acid fumarolic gases for this reason the pizzo activity has previously been poorly studied for age and composition we focus mainly on the well preserved le croci fallout succession we show that the pizzo activity occurred in the roman age 2 4 1 8 ka and was fed by two compositionally and genetically distinct magma groups each occupying a separate reservoir shoshonitic basalts pizzo sho were stored at lower depths than high k basalts to high k basaltic andesites pizzo hkca although pizzo sho and pizzo hkca magmas were affected by multiple mafic magma inputs with different dynamics as reflected in variable mineral zoning they did not interact with each other they were however erupted simultaneously suggesting they were emitted by two unconnected conduits and vents located in the summit area stromboli historic activity was thus quite different from present day activity in the roman age the volcano was characterised by paired activity taking place on the summit with similar explosive characteristics from two coeval vents each fed by different and non parental magmas while the pizzo sho magmas still persist in the present day shallow reservoir the pizzo hkca magmas could be quiescent and re activated in the future possibly from an eccentric vent fissure

magma budgets and steady state activity of vulcano and stromboli we present three models for magma budget during steady state volcanic activity by which non erupted magma is emplaced as dykes or cumulates or crystallises in place using gas and thermal data we apply our models at vulcano to calculate degassing cooling and crystallisation of magma at a rate of 40 375 kg s 1 within a magma body with an upper surface at a 2 km depth at stromboli we calculate a steady magma supply of 300 1300 kg s 1 to shallow 1 km depths

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

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

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

dike propagation driven by volcano collapse a general model tested at stromboli italy 1 analogue experiments investigate how flank collapse affects dike propagation within volcanoes water magma analogue is injected within a gelatin cone volcano analogue with a lateral collapse the injections form dikes that away from the collapse become radial the dikes propagating nearby the collapse focus towards the collapse sides becoming subparallel to them because of the stress reorientation due to the unbuttressing only dikes formed along the collapse axis passing through the mean points of the collapse map view propagate radially within the collapse this general model is applied at stromboli the stromboli dikes cluster along and parallel to the collapse sides similar to the experiments nevertheless the current location of the conduit along the collapse axis leads to dike propagation within the collapse infill rather than at its sides this may have occurred during the 2002 03 eruption when diking in the collapse triggered a landslide and tsunami within the collapse

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

recent eruptive history of stromboli aeolian islands italy determined from high accuracy archeomagnetic dating 1 the large sample method of archeomagnetic dating was applied to stromboli 127 samples 10 sites yielded paleofield directions with 95 confidence intervals less than 2 coupled with a reference curve for secular variation in western europe these allow accurate dating of volcanic events a lava flow underlying san bartolo village gave a minimum age of ad 100 100 a lava overflow predating the last sector collapse was dated from 1350 60 suggesting the recent occurrence of highly hazardous events lava spatters and a hot avalanche high on the northern flank were emplaced during the xxth century lava spatters on the lower flanks could date the onset of the still ongoing phase from ad 550 50 these results are different from those obtained in a recent study probably because traditional paleomagnetic sampling cannot yield sufficient precision considering the characteristics of the archeomagnetic secular variation curve

volcanological and magmatological evolution of stromboli volcano aeolian islands the roles of fractional crystallization magma mixing crustal contamination and source heterogeneity the present paper reports the results of a detailed stratigraphical petrological and geochemical investigation on the island of stromboli aeolian arc southern tyrrhenian sea major and trace element data determined on a large quantity of samples from well established stratigraphic positions indicate that the magmatological evolution of the island through time was more complex than previously known the activity of the exposed part of stromboli which occurred over a time span of about 100 000 years started with the emission of high k calc alkaline hkca volcanics which were covered by calc alkaline ca shoshonitic sho high k calc alkaline hkca and potassic ks products the most recent activity consists of hkca lavas and the present day sho basaltic volcanics emitted by mildly explosive strombolian activity most of the products are lavas with minor amounts of pyroclastic rocks emplaced mainly during the early stages of activity the transition from the sho to the ks cycle was associated with the collapse of the upper part of the volcanic apparatus the transition from ks to the present day sho activity has been found to have occurred at the time of the sliding of the western portion of the volcano that generated the sciara del fuoco depression the rock series cropping out at stromboli show variable enrichment in potassium incompatible trace elements and radiogenic sr which increase from ca through hkca and sho up to ks rocks major trace element and sr isotopic data agree in indicating that the hkca and sho series evolved by crystal liquid fractionation starting from different parental liquids whereas crustal assimilation appears to have been the leading process during the evolution of ks volcanics mixing processes also played a role although they can be well documented only when they occurred between magmas with different isotopic and geochemical characteristics geochemical modelling based on trace element and isotopic data indicates that the mafic magmas of the different volcanic series may be generated by melting of an upper mantle heterogeneously enriched in incompatible elements and radiogenic sr by addition via subduction of different amounts of crustal material geochemical data however are also in agreement with the alternative hypothesis that the most mafic magmas of the different series have been generated by combined processes of fractional crystallization assimilation and mixing of a ca magma in a deep sited magma chamber the mafic magmas formed by these complex processes were successively emplaced in a shallow reservoir where they evolved by simple fractional crystallization hkca and sho series and by assimilation of crustal material ks the occurrence of changes in the geochemical signatures of the magmas at the time of the structural modification of the volcano is believed to favour the hypothesis that the variable composition observed in the volcanic rocks of stromboli is the result of processes occurring within the volcanic system

persistent polybaric rests of calc alkaline magmas at stromboli volcano italy pressure data from fluid inclusions in restitic quartzite nodules a fluid inclusion study has been performed on quartzite nodules of stromboli volcano hosted by calc alkaline lavas of both the strombolicchio 200 ka and paleostromboli ii 60 ka periods the nodules are mainly composed of quartz crystals with subordinate plagioclase and k feldspar small interstitial minerals such as plagioclase k feldspar clinopyroxene biotite and quartz are also found together with glass muscovite epidote and zircon occur as accessory minerals different quartzite nodules occur 1 equigranular polygonal granoblastic quartzite nodules forming a polygonal texture with clear triple points 2 inequigranular polygonal granoblastic quartzite nodules and 3 break up nodules with strongly resorbed quartz these quartzites are restites from partial melting involving felsic crustal rocks at the magma wall rock contact restitic quartz re crystallises at variable and generally high temperatures leading to the formation of quartzites with different textures quartz grains contain five types of fluid inclusions distinguished on the basis of both fluid type and textural phase relationships at room temperature type i are two phase liquid vapour co2 rich fluid inclusions they are primary and subordinately pseudosecondary in origin and have undergone re equilibration processes type ii mono phase two phase vapour liquid vapour co2 rich fluid inclusions are the most common and based on their spatial distribution and shape they can be divided into two subclasses type iia and type iib type ii inclusions are secondary or pseudosecondary and they are assumed to have formed after decrepitation of type i inclusions and cracking of the host quartz type iii inclusions are mono phase vapour they possibly contain co2 at very low density and surround the inner rims of quartz grains type iv two phase silicate melt inclusions contain glass co2 rich fluid some of them are cogenetic with type ii inclusions finally type v two phase liquid vapour aqueous inclusions are both vapour rich and liquid rich aqueous inclusions microthermometric experiments were performed on both type i and ii inclusions type i inclusions homogenise to liquid between 20 and 30 5 c type iia inclusions homogenise to vapour in the 24 to 30 c range with a maximum peak of frequency at 29 c type iib inclusions also homogenise to vapour between 14 and 25 c there appears to be no difference in homogenisation temperature distribution between the strombolicchio and paleostromboli ii samples the trapping pressures of the fluid inclusions have been obtained by combining the microthermometric data of the strombolicchio and paleostromboli ii samples with the pressure temperature volume i e density characteristics for a pure co2 system the data on the early inclusions type i suggest an important magma rest at a pressure of about 290 mpa i e about 11 km depth type iia co2 inclusions suggest that a second magma rest occurred at a pressure of about 100 mpa i e about 3 5 km depth whereas type iib inclusions were trapped later at a shallower depth during the final magma upwelling no pressure depth differences seem to occur between the strombolicchio and paleostromboli ii periods indicating the same polybaric rests for the calc alkaline magmas of stromboli despite their significantly different ages this persistence in magma stagnation conditions from 200 to 60 ka suggests a similar plumbing system for the present day strombolian activity

varved lacustrine sediments and diatom assemblages of lake fukami central japan abstract a sediment core taken from lake fukami in southern nagano prefecture in the summer of 1999 contained alternating light and dark colored laminae diatom microstratigraphy was determined for the succession between 60 and 68 cm core depth the frequency of synedra spp varied from more than 40 in the light colored laminae to less than 10 in the dark laminae aulacoseira spp or cyclotella spp were dominant in the dark laminae in which the proportion of synedra spp was relatively low the correlation of these diatom assemblages with alternating lamina color indicates a seasonal succession within the diatom biota each couplet of light and dark colored laminae in the sediment is therefore considered to be an annual sedimentation increment

characteristics of sedimentary varve chronologies a review abstract we constructed a varve data base vdb to study the worldwide distribution of varved sediment records and the fidelity of their varve chronologies clusters of lakes with varved sediments exist in central north america in the canadian arctic and in northern and central europe among the 108 sites included in the vdb varved records are typically 200 500 cm long and cover a period of 1000 2000 years their varve chronologies are often based on counting of annual layers from fresh sediment surfaces and photographs or from epoxy embedded sediment blocks and thin sections the vdb indicates that chronological errors associated with counting sedimentary varves fall generally between 1 and 3 but only 57 of published records are providing quantitative error estimations for their chronologies with a careful documentation of varves and by applying radiometric dating methods to surface sediments as well as using historical events as time markers there is the potential of having centennial long varved records with a very precise age depth control however it is unrealistic to expect errors significantly below 1 from several millennia long sections we found no indication that varve chronologies would have been substantially more accurate and precise in some parts of the world than in others or statistically dependent on varve thickness or temporal extension of a varved sequence according to the vdb close to 90 of the published varve chronologies have been cross checked with some independent dating methods

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

h2o in rhyolitic glasses and melts measurement speciation solubility and diffusion dissolved h2o in silicate melts and glasses plays a crucial role in volcanic eruptions on terrestrial planets and affects glass properties and magma evolution in this paper major progress on several aspects of the h2o melt or glass system is reviewed consistency among a variety of data is investigated discrepancies are evaluated and confusion is clarified on the infrared measurement of total h2o and species concentrations calibration for a variety of glasses has been carried out at room temperature the measurements for h2o in rhyolitic glasses have undergone the most scrutiny resulting in the realization that absorptivities for the near infrared bands depend on total h2o content although the variation of the absorptivities does not seem to significantly affect the determination of total h2o it does affect the determination of molecular h2o and oh species concentrations calibration of the infrared technique for h2o in rhyolitic glasses still needs much improvement especially at high total h2o furthermore it is now almost certain that the molar absorptivities also depend on the measurement temperature in in situ studies hence it will be necessary to carry out calibrations in situ at high temperatures on h2o speciation results from two experimental approaches the quench technique and the in situ technique are very different leading to controversy in our understanding of true speciation a solution is presented to reconcile this controversy it is almost certain that the quench technique does not suffer from a quench problem but interpretation of in situ results suffered from ignoring the dependence of the molar absorptivities on measurement temperature accurate calibration at high temperatures is necessary for the quantitative application of the in situ technique to h2o speciation in silicate melts and glasses on h2o solubility in silicate melts recent experimental work has significantly expanded the t p range of solubility measurements and recent solubility models fill a gap for predicting solubility for a wide range of melt compositions i present a solubility model for rhyolitic and quasi rhyolitic melts over a wide range of t and p 500 1350 c 0 8 kbar by incorporating the role of speciation the solubility model is able to recover the experimental solubility data and has extrapolative value although the partial molar volume of h2o derived from the solubility model differs from that derived from density measurements on h2o diffusion recent studies on h2o diffusion in a quasi rhyolitic melt at 800 1200 c 0 5 5 kbar and up to 7 total h2o not only provide important new diffusion data but are also challenging earlier understanding of h2o diffusion based on data in rhyolitic glasses at 400 550 c 1 bar and 0 2 1 8 total h2o a comparison between the earlier model and recent data is made the recent high temperature diffusivities at total h2o 2 can be predicted by the earlier model however at higher total h2o the earlier model fails new work is under way to understand the diffusion mechanisms at high h2o contents

radiative heat power at stromboli volcano during 2000 2011 twelve years of modis observations abstract twelve years of night time modis moderate resolution imaging spectroradiometer observations has been analysed to detect and quantify the radiative heat power emitted by stromboli volcano from march 2000 to september 2011 using an accurate background subtraction of the modis signal at 4 m we were able to discriminate two main regimes of thermal radiation related to different levels of volcanic activity effusive eruptions occurred on december 28 2002 and february 27 2007 radiated at an average of 186 mw with a frequency of alert detection of 50 95 conversely during the typical strombolian activity an average of 9 mw is radiated with a frequency of alert detection of 0 45 although during the effusive eruptions the radiative power is basically controlled by the lava discharge rate our results suggest that during non effusive periods strombolian regime both the intensity and the frequency of modis alerts are controlled by the height of the magmatic column feeding the activity at the surface in particular we found that a radiative power of 50 mw corresponds to a high magma column which is exposed in the vent area at the same rate in which the deeper gas rich magma is typically supplied within the feeding system of stromboli 0 3 m3 s 1 in this condition the magmatic system approaches steady state regimes above this threshold a transition from strombolian to effusive regimes may occur as shown by the detection of 50 mw 8 10 days before the onset of both the last two major flank eruptions these values were reached after 1 2 months of gradual increase of the radiative power which was likely associated the rising of the magma column within the shallowest portion of the conduit in addition our data suggest that over the years 2000 2011 several cycles of rise and fall of the magma column have occurred which however did not culminate into an effusive eruption but only into recurrent episodes of sustained spattering or fountaining and summit overflows these fluctuations has substantially increased in frequency and intensity after the 2007 eruption thus suggesting that this event has perturbed in some way the shallow plumbing system of stromboli we stress that the detection of a radiative power higher than 50 mw is a clear evidence of a very high magma column which may prelude the onset of an effusive eruption and or periods of sustained vent activity in conclusion we suggest that systematic analysis of modis data can be used to detect variations in the intensity of strombolian activity and may considerably improve volcano surveillance at stromboli as well as at other open system volcanoes

residual topography lithospheric structure and sunken slabs in the central mediterranean abstract the central mediterranean comprises subduction collision and backarc extension all in a relatively small area in this paper we analyze the topography of this region examining the influence of subducting slabs on overriding plates we take the observed surface elevation remove the contribution of the crust to it and use the residual topography to identify regions that are unusually low unusually high or normal then we calculate lithospheric thickness where local isostasy applies the results provide information about the structure of the lithosphere in this complex region and about the vertical tectonics in particular we found a difference between the south tyrrhenian subduction zone and the apennines consistent with the processes of slab rollback and slab break off respectively in the south tyrrhenian the edge of the oceanic plate is strongly pulled down whereas the edge of the overriding plate the calabrian peninsula is uplifted this opposite trend indicates weak plate coupling that is the subducting slab which is rapidly rolling back hangs almost entirely on the oceanic plate and the overriding plate is free in contrast in the apennines high residual topography and uplifting are detected on both sides of the mountain belt consistent with complete break off of the subducted lithosphere

viscosity measurements of subliquidus magmas alkali olivine basalt from the higashi matsuura district southwest japan abstract we carried out viscosity measurements and sampling of a crystal suspension derived from alkali olivine basalt from the matsuura district sw japan at subliquidus temperatures from 1230 c to 1140 c under 1 atm with nno oxygen buffered conditions viscosity increased from 31 to 1235 pa s with a decrease in temperature from 1230 to 1140 c on cooling olivine first appeared at 1210 c followed by plagioclase at 1170 c the crystal content of the sample attained 31 vol at 1140 c plagioclase 22 olivine 9 non newtonian behaviors including thixotropy and shear thinning were pronounced in the presence of tabular plagioclase crystals the cause of such behavior is discussed in relation to shear induced changes in melt crystal textures relative viscosities r s m where s and m are the viscosities of the suspension and the melt respectively were obtained by calculating melt viscosities from the melt composition and temperature at 1 atm using the equation proposed by giordano and dingwell giordano d dingwell d b 2003 non arrhenian multicomponent melt viscosity a model earth and planetary science letters 208 337 349 the obtained relative viscosities are generally consistent with the einstein roscoe relation which represents r for suspensions that contain equant and equigranular crystals even though the crystal suspension analyzed in the present experiments contained tabular plagioclase and granular olivine of various grain sizes this consistency is attributed to the fact that the effect of crystal shape was counterbalanced by the effect of the dispersion of crystal size the applicability of the einstein roscoe equation with respect to crystal shape is discussed on the basis of the present experimental results our experiments and those of sato sato h 2005 viscosity measurement of subliquidus magmas 1707 basalt of fuji volcano journal of mineralogical and petrological sciences 100 133 142 show that the relationship between relative viscosity and crystal fraction is consistent with the einstein roscoe relationship for axial ratios that are smaller than the critical value of 4 6 5 but discrepancies occur for higher ratios

effusive to explosive transition during the 2003 eruption of stromboli volcano the persistent explosive activity of stromboli volcano italy ceased in december 2002 and correlated with the onset of a seven month long effusive eruption on the volcano flank from new vents that opened just below the summit craters we intensively monitored this effusive event collecting and interpreting in real time an extensive multiparametric geophysical data set the resulting data synergy allowed detailed insights into the conduit dynamics that drove the eruption and the transition back to the typical strombolian activity we present a direct link between gas flux magma volume flux and seismicity supporting a gas driven model whereby the balance between gas flux and gas overpressure determines whether the system will support effusive or explosive activity this insight enabled us to monitor the migration of the magma column up the conduit and to explain the onset of explosive activity

varved lacustrine sediments of lake tougou ike western japan with reference to holocene sea level changes in japan abstract eighteen metres of laminated sediments were recovered in a holocene sediment core taken from lake tougou ike in 1992 the lamination evident from the alternation of light and dark coloured laminae records cyclic deposition of biochemical sediments annual environmental changes in and around the lake caused seasonal variations in sediment flux to the lake floor explaining these cyclic variations in sedimentary facies ams 14 c dating of organic remains from 40 horizons in the succession supports the interpretation of each light to dark couplet as an annual increment each laminated couplet is identified as a non glacial varve formed mainly by seasonal changes in diatom productivity varve counting and 14 c dating provide a detailed holocene chronological framework with time resolution on the order of individual years within which to reconstruct paleoenvironmental changes recorded in the sediment core holocene relative sea level changes at lake tougou ike were estimated with 10 yr precision using the variable authigenic iron mineral content of the sediment as a proxy the results demonstrate that the relative sea level at lake tougou ike rose abruptly at about 8900 7700 5600 4000 3600 and 2700 cal yr bp and decreased gradually in the intervening intervals these relative rises in sea level are demonstrated to be coeval with ice sheet discharge events recorded in sediment cores from the north atlantic ocean abrupt coastal environmental changes caused by sea level changes likely took place throughout the japanese islands and will probably be identified in both the holocene and the last glacial interval the latter being a time when dansgaard oeschger cycles were clearly active in the north atlantic region

textural effects of steady state behaviour of the stromboli feeding system abstract the exceptionally persistent activity of stromboli volcano has lasted for at least 1400 years the normal strombolian activity is periodically interrupted by more energetic explosions 1 2 per year and by sporadic effusive episodes every 10 20 years normal activity and effusive episodes are characterized by crystal rich high k to shoshonitic basalts issuing from a volatile poor shallow system crystal poor pumice are emitted only during more violent explosions and are thought to derive from deep pulses of volatile rich magma shallow level degassing induces massive crystallization of deep pulses of feeding magma that continuously mixing with the resident one produces the crystal rich shoshonite of the persistent activity we examined the crystallization history of the crystal rich shallow reservoir using plagioclase crystal size distribution csd analysis of scoriae and lavas emitted in the past twenty years csds show a linear dependence from crystal size in the size interval 0 06 1 2 mm number density of larger crystals is biased by right hand truncation effects csds slopes and intercepts are quite constant during the whole considered time span revealing a system that is close to the equilibrium also from a kinetic point of view the linear crystal size distribution are reached by the system through episodes of growth and resorption respectively occurring in the degassed and undegassed magma during the continuous mixing in the feeding system plagioclase net growth rate 2 10 11 cm s results from a balance of growth 10 10 cm s and resorption episodes which induce spectacular zoning and resorption textures in crystals larger than 200 m csds of mafic phases cannot be accurately acquired on each single sample due to poor counting statistics the evaluation of pyroxene and olivine csd on the whole data set however confirms the conclusions acquired from plagioclase csds

elliptical calderas in active tectonic settings an experimental approach abstract caldera volcanoes form due to collapse of a magma chamber roof into the underlying magma chamber many field theoretical and experimental studies have postulated that calderas are delimited by reverse ring faults and are surrounded by peripheral concentric normal faults in the simplest theoretical scenario circular magma chambers produce circular calderas many calderas however are elliptical in shape particularly those in extensional and compressive tectonic settings several factors may explain elliptical calderas the first is the presence of an elliptical magma chamber established by for instance preferential intrusion along pre existing basement structures or differential spalling of the magma chamber walls the second is the overlap nesting of several discrete calderas to form a single larger elliptical structure the third is asymmetric subsidence the fourth is variable pre collapse topography a fifth possible factor is distortion of the caldera faults by the regional stress field during caldera formation a sixth factor is the post collapse distortion of the caldera structure due to continued regional deformation to better understand relationships between caldera surface expression reservoir geometry and regional tectonic stresses we conducted scaled analogue experiments these experiments examined the impact of regional stress and associated structures on calderas formed during evacuation of reservoirs circular rubber balloons of known dimensions and depths the results show that in principle calderas produced in compression extension experiments are elongated parallel to the direction of minimum horizontal compressive stress despite the chamber beneath being circular in plan view as a consequence model ring fault orientation varied from steeply dipping where striking perpendicular to the minimum horizontal regional compressive stress to shallower dips where striking parallel to the minimum horizontal regional compressive stress this leads us to suggest that the influence of a regional stress field on caldera fault orientation during and or after caldera formation may be significant in the development of elliptical calderas in addition such variation of caldera ring fault dip from steep to relatively shallow could influence location and behaviour of ring fissure eruptions

textural studies of vesicles in volcanic rocks an integrated methodology abstract vesicles in volcanic rocks are frozen records of degassing processes in magmas for this reason their sizes spatial arrangements numbers and shapes can be linked to physical processes that drive magma ascent and eruption although numerous techniques have been derived to describe vesicle textures there is no standard approach for collecting analyzing and interpreting vesicular samples here we describe a methodology for techniques that encompass the entire data acquisition process from sample collection to quantitative analysis of vesicle size and number carefully chosen samples from the lower mean and higher density vesicularity endmembers are characterized using image nesting strategies we show that the texture of even microvesicular samples can be fully described using less than 20 images acquired at several magnifications to cover efficiently the range of existing vesicle sizes a new program foams was designed to perform the quantification stage from vesicle measurement to distribution plots altogether this approach allows substantial reduction of image acquisition and processing time while preserving enough user control to ensure the validity of obtained results we present three cameo investigations on basaltic lava flows scoria deposits and pumice layers to show that this methodology can be used to quantify a wide range of vesicle textures which preserve information on a wide range of eruptive conditions

subduction zone paleoseismology along the pacific coast of northeast japan progress and remaining problems abstract this paper reviews recent progress in tsunami geology and the history of coastal uplift subsidence along the pacific coasts of hokkaido and tohoku facing the kuril and japan trenches respectively in the last 20 years research by tsunami geologists in northeast japan has focused on extending the record of tsunamis beyond the range of historical documents in the region which span too little time to reveal much of the earthquake history over the last millennia along the coast of hokkaido recurrent sandy deposits are evidence of historical and prehistoric large tsunamis at kiritappu marsh for example at least 15 identified tsunami deposits occurred between 200 and 6 000 years ago the spatial distribution of the most recent prehistoric tsunami deposit that of the so called 17th century earthquake and tsunami exceeds historical and recent tsunami inundations in eastern hokkaido numerical simulations of this event require a multi segment fault model with variable slip mw 8 8 encompassing both the tokachi oki and nemuro oki regions to reproduce the observed deposit distribution in eastern hokkaido the recurrence interval of such multi segment earthquakes along the southern kuril trench is estimated to be 100 800 years based on tephrochronological and radiocarbon evidence tsunami deposits are also associated with historical earthquakes in 1843 and 1894 in eastern hokkaido and with the 1640 komagatake eruption in western hokkaido the 17th century earthquake probably triggered postseismic coastal deformation diatom based transfer functions suggest rapid subsidence before the event and gradual uplift afterward and historical volcanic ash layers indicate that gradual postseismic uplift occurred over decades a simple dislocation model can explain such gradual uplift as an aseismic fault extension after the 17th century event in the tohoku region a tsunami deposit associated with the 869 jogan earthquake has been identified and the inundation area of this event has been constrained based on the lateral extent of the tsunami deposit and its stratigraphic position beneath the historical to a tephra 915 ce land level changes at odaka fukushima prefecture associated with the jogan event have been estimated based on changes of fossil diatom assemblages below and above the tsunami deposit numerical simulations based on geological evidence and observations of the 2011 tohoku tsunami deposit suggest that the jogan event was a plate boundary rupture at least 200 km long along the japan trench mw 8 3 8 6 the 1454 kyotoku tsunami is also considered to have been generated by a rupture area including the miyagi oki region part of the jogan rupture it remains unclear whether the 869 1454 and 2011 tsunamis were similar in size and source if they were the recurrence intervals of such events near sendai are less than 600 years and more regular than those for multi segment earthquakes along the kuril trench

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

types and mechanisms of strombolian explosions characterization of a gas dominated explosion at stromboli textural and chemical analyses of bombs quenched directly from a normal explosion at stromboli volcano italy were integrated with coincident seismic acoustic and thermal data the data set defines a new gas dominated type of strombolian eruption named type 0 these events are characterized by high velocity emission 150 250 m s 1 of a few relatively small juvenile particles with entrained non juvenile clasts that previously fell back into the vent to be re erupted for the studied event the explosion depth was more than 250 m deep and the particles showed little residence time in the shallow system slug ascent velocities over the final 20 35 m of magma filled conduit and the low viscosity of the resident magma are all consistent with simple bubble burst in a clean conduit this conduit type and eruption style likely fit popular slug ascent and burst models used to explain strombolian eruptions in contrast the ballistic dominated type of explosions type 1 are associated with larger proportions of stagnant material in the shallow system magma mix we argue that the additional volume of this stagnant material pushes the free surface upward because of the larger volume of material available for entrainment into a type 1 slug burst which has to fragment through a thick cap of degassed material type 1 events tend to be rich in particles in contrast the less spectacular gas rich type 0 events have little material to entrain thus being poor in lapilli and bombs

chronology and sedimentation process of varved lacustrine sediment in lake fukami central japan abstract continuous varve sequences were taken from lake fukami a monomictic lake southern part of nagano prefecture central japan in 2000 total 196 varve units were recognized in the upper 2 m horizon of the sediment core sedimentation rates in the core have some high peaks indicating increments of clastic particles supplied to the lake owing to natural disasters including floods and earthquakes and the artificial construction around lake fukami the results of the correlation between the meteorological records in iida meteorological station and the total carbon flux change based on the varve chronology indicates that the total carbon flux shows an inverse relationship to february mean temperature and precipitation february mean temperature controlled the vertical mixing of lake water column that affects the productivity of phytoplankton in the epilimnion or decomposition of organic matter in the hypolimnion february precipitation probably has affected the activity of denitrifying bacteria in the stagnation period pyrite and siderite minerals are recognized in the core by observation of thin sections and x ray powder diffraction analysis the pyrite was deposited in summer and the siderite was deposited in summer and winter these iron minerals indicate the decomposition processes of organic matters in the water column in each season

tracking precursors and degassing by radon monitoring during major eruptions at stromboli volcano aeolian islands italy 1 we monitored radon anomalies before during and after the recent paroxysmal eruptions of stromboli major eruptive events are preceded by relative minima in radon emissions at stations located at the base of the cone whereas three of the summit stations reached peak values 20 000 bq m3 or higher 12 to 14 days before major eruptions and are nearly coeval with earth tides radon emissions at or above such high threshold values are proposed to result from the dynamic response of the fracture network due to degassing processes associated with magma ascent relative minima recorded at the base of the cone are related to fractures self sealing within the hydrothermal system eventually coupled with the atmospheric stack effect the coexistence of the above anomalies is interpreted as the first precursory signals to major eruptive events

the effects of environmental parameters on diffuse degassing at stromboli volcano insights from joint monitoring of soil co2 flux and radon activity abstract soil co 2 flux and 222 rn activity measurements may positively contribute to the geochemical monitoring of active volcanoes the influence of several environmental parameters on the gas signals has been substantially demonstrated therefore the implementation of tools capable of removing or minimising the contribution of the atmospheric effects from the acquired time series is a challenge in volcano surveillance here we present 4 years long continuous monitoring from april 2007 to september 2011 of radon activity and soil co 2 flux collected on the ne flank of stromboli volcano both gases record higher emissions during fall winter up to 2700 bq m 3 for radon and 750 g m 2 day 1 for co 2 than during spring summer seasons short time variations on 222 rn activity are modulated by changes in soil humidity rainfall and changes in soil co 2 flux that may be ascribed to variations in wind speed and direction the spectral analyses reveal diurnal and semi diurnal cycles on both gases outlining that atmospheric variations are capable to modify the gas release rate from the soil the long term soil co 2 flux shows a slow decreasing trend not visible in 222 rn activity suggesting a possible difference in the source depth of the of the gases co 2 being deeper and likely related to degassing at depth of the magma batch involved in the february april 2007 effusive eruption to minimise the effect of the environmental parameters on the 222 rn concentrations and soil co 2 fluxes two different statistical treatments were applied the multiple linear regression mlr and the principal component regression pcr these approaches allow to quantify the weight of each environmental factor on the two gas species and show a strong influence of some parameters on the gas transfer processes through soils the residual values of radon and co 2 flux i e the values obtained after correction for the environmental influence were then compared with the eruptive episodes that occurred at stromboli during the analysed time span 2007 2011 but no clear correlations emerge between soil gas release and volcanic activity this is probably due to i the distal location of the monitoring stations with respect to the active craters and to ii the fact that during the investigated period no major eruptive phenomena paroxysmal explosion flank eruption occurred comparison of mlr and pcr methods in time series analysis indicates that mlr can be more easily applied to real time data processing in monitoring of open conduit active volcanoes like stromboli where the transition to an eruptive phase may occur in relatively short times

petrological insights into shifts in eruptive styles at volcan llaima chile tephra and lava pairs from two summit eruptions ad 2008 and 1957 and a flank fissure eruption ad 1850 are compared in terms of textures phenocryst contents and mineral zoning patterns to shed light on processes responsible for the shifts in eruption style during typical eruptive episodes at volcan llaima andean southernvolcanic zone chile the mineralogy and whole rock com positions of tephra and lavas are similar within eruptive episodes suggesting a common magma reservoir for strombolian paroxysms and lava effusion the zoning profiles and textures of plagioclase record successive and discrete intrusions of volatile rich mafic magma accompanied by mixing of these recharge magmas with the resident basaltic andesitic crystal mushes that are commonly present at shallow levels in the llaima system each recharge event destabil izes the plagioclase in equilibrium with the resident crystal mush melt and stabilizes relatively an rich plagioclase as is recorded by the numerous resorption zones lavas typically have 15 20 vol more phenocrysts than the tephra differences in plagioclase and olivine textures and zoning combined with different phenocryst contents indicate that a greater volume fraction of recharge magma is present in the explosively erupted magma than in subsequent effu sively erupted magma we propose that strombolian paroxysms at volcan llaima are triggered by interactions with large volume frac tions of recharge magma which decrease the bulk viscosity and in crease the volatile contents of the erupted magmas leading to the conditions required for the fragmentation of basaltic andesite lava effusion ensues from reduced interactions with the recharge magma after it has partially degassed and crystallized thereby impeding rapid ascent this process could be operating at other steady state basaltic volcanoes wherein shallow reservoirs are periodically re filled by fresh volatile rich magmas

viscosity of high k basalt from the 5th april 2003 stromboli paroxysmal explosion abstract the 5th april 2003 paroxysmal event was the strongest explosion that has occurred at stromboli in the last 50 years this event lasted only few minutes and was characterised by two violent explosions followed by gas and pyroclast emission in order to constrain models of the dynamics of the paroxystic event the viscosity of anhydrous and hydrous stromboli high potassium hk basaltic melts have been measured viscosity has been investigated in the low viscosity range with the falling sphere method at superliquidus temperatures 1423 to 1673 k and 0 5 gpa and in the high viscosity range with micropenetration near the glass transition temperature 723 to 1035 k at atmospheric pressure falling sphere experiments were performed in a piston cylinder apparatus with melts whose water content varies from nominally anhydrous 0 02 wt h 2 o to 4 16 wt h 2 o the combination of high and low viscosity data permits a general description of the viscosity as a function of temperature and water contentusing a modified tamman vogel fulcher equation using these new viscosity data an estimation of the flow regime and magma velocity is performed our data suggest that the ascent of magma from the 7 8 km deep reservoir to a shallower reservoir located at about 3 km of depth may occur within minutes moreover we infer a turbulent flow regime finally our estimates of the ascent velocity agree qualitatively with results from petrological studies e g bertagnini a metrich n landi p rosi m 2003 stromboli volcano aeolian archipelago italy an open window on the deep feeding system of a steady state basaltic volcano journal of geophysical research 108 2336 2350 which indicate a turbulent flow regime and rapid ascent velocities such to inhibit volatile loss induced crystallization we conclude that hazard evaluation at stromboli island should incorporate the likelihood of very rapid ascent of less evolved melts from depth

crystal size distribution analysis of plagioclase in experimentally decompressed hydrous rhyodacite magma article i nfo this study presents crystal size distributions csd of plagioclase forming during decompression experiments of hydrous rhyodacite magma samples were annealed at 130 mpa subjected to continuous decompression at either 2 mpa h 1 or 0 5 mpa h 1 and then quenched along their respective decompression paths at 20 mpa intervals samples display concave up curved csd plots which result from a combination of two crystal populations those which formed during the anneal period and those which formed during decompression the csds also display a decrease in crystal number density at 3 7 m a size range that is easily resolvable with the imaging strategy employed the downturn at small sizes is presumably due to insufficient compensation for the intersection probability effect in converting 2d measurements to 3d size distributions crystal nucleation and growth rates derived from csds using standard assumptions are compared with values obtained using 2d measurements of bulk crystal populations batch methods csd calculated nucleation rates are substantially low relative to the batch values in fact csd derived volumetric nucleation rates may underestimate actual nucleation rates by up to two orders of magnitude in contrast growth rates from csds are consistently higher than batch rates although plagioclase growth rates are relatively constant during decompression at a given rate the average growth rate in the rapidly decompressed series is approximately five times faster than the crystal growth rate in the slowly decompressed series because crystal growth rate depends on decompression rate csds are incapable of revealing decompression timescales or magma ascent rates without independent knowledge of crystal growth rate published by elsevier b v

gas bubble dynamics model for shallow volcanic tremor at stromboli volcanic tremor at stromboli aeolian islands italy is correlated to small infrasonic transients ripepe et al 1996 which repeat almost rhythmically in time in a range between 0 8 and 1 2 s we demonstrate that infrasonic transients are associated to small gas bubble 0 5 m burstings which produces no transients in the seismic signal tremor ground displacement attenuates with the inverse of the distance from the craters indicating that the source is shallow short term energy release shows that infrasonic and seismic signals are linked to the same dynamical process while at the long term scale it is evident that the two signals are controlled by two distinctive mechanisms we suggest that the possible physical model acts in two steps first gas coalescence and then gas bursting in our model the seismic signal is related to the coalescence of a gas bubble from a layer of small bubbles while the infrasonic signal is linked to the bursting of the bubble when it reaches the magma surface gas bubbles could form by free coalescence in magma or could be forced to coalesce by a structural barrier we calculate that forced coalescence induces in magma a pressure change 104 pa 2 orders of magnitude higher than free coalescence and it explains best the tremor ground displacement 10 5 m recorded at stromboli moreover forced coalescence evidences the role of a structural barrier such as a dike in volcanic tremor source dynamics in this gas dynamic process the delay time of 1 2 s between infrasonic pulses could reflect the gas nucleation interval of basaltic magma thomas et al 1993 manga 1996 we propose that the source function for the shallow volcanic tremor at stromboli could be the viscoelastic reaction of the magma to the pressure decrease induced by gas bubble growth rate under constant depressurization the spectrum of our source function is controlled by the time duration of the pressure pulse which represents the viscoelastic relaxation time of the magma and gas bubble growth rate the predicted asymptotic decay of the frequency contents fits the spectral behavior of the volcanic tremor ground displacement recorded at stromboli we show that the same spectral behavior can be found in ground displacement spectra of volcanic tremor recorded on different volcanoes

triggering mechanism at the origin of paroxysms at stromboli aeolian archipelago italy the 5 april 2003 eruption 1 the 5 april 2003 paroxysm of stromboli occurred during an ongoing effusive episode that initiated on 28 december 2002 it mainly consisted in two a few seconds apart cannon like explosions followed by a vertical gas pyroclast jet the hk basaltic pumices that were generated mainly contain crystals that were drained back from the shallow parts of the plumbing system few euhedral to anhedral olivines and their melt inclusions testify to crystal fractionation and possible mixing between hk basaltic magmas variable in their volatile content extent of evolution and volume the most primitive volatile rich hk basalt term is sizable at micrometer scale only we propose that the triggering mechanism of the paroxysm was initiated at moderate pressures 240 mpa and was related to bubble driven ascent of magma blobs the latter rose through and interacted with overlying slightly more evolved melts and finally mingled with the shallow crystal rich magma just before the eruption

understanding shallow magma emplacement at volcanoes orthogonal feeder dikes during the 2002 2003 stromboli italy eruption 1 understanding how shallow magma is emplaced within volcanoes is crucial for hazard assessment the 2002 2003 stromboli eruption provides the opportunity to investigate shallow magma emplacement resulting from orthogonal feeder dikes and its possible effects stromboli erupted in 2002 2003 when effusive activity replaced strombolian activity on december 28 a ne sw fissure propagated from the lava filled northernmost summit crater on december 29 a nw se fissure propagated north of the craters feeding nw se aligned vents on december 30 this area collapsed reaching the sea and generating a tsunami in mid february 2003 the nw se fissure became inactive while the ne sw effusive fissure continued until july a model for shallow magma emplacement is proposed the lateral propagation of a ne sw dike from the northernmost crater was triggered below a nw se dike propagating from the magma filled ne tip of the ne sw elongated conduit fed the nw se aligned vents in february the conduit periphery became solidified freezing the nw se dike and the transport of magma was limited to the central part focusing its rise below the craters this fed the ne sw fissure until the supply decreased further july returning to the ordinary level sustaining strombolian activity orthogonal dike emplacement followed the trajectories of the maximum gravitational stress 1 partly controlled by the irregular topography of the uppermost edifice the emplacement of orthogonal dikes in a limited area is feasible at non perfectly conical active volcanoes where the maximum gravitational stress may show variations from a purely radial path

rheological control on the radiant density of active lava flows and domes abstract during an effusive extrusive eruption the capability of an active lava body flow or dome to radiate thermal energy depends on how the lava discharge rate is accommodated by the expansion of the magma body and by the cooling of its surface this feature can be described by a single empirical parameter defined radiant density c rad in j m 3 that for a given discharge rate expresses the efficiency of the lava body to change its area and or to insulate its inner core thus modulating the heat radiated from the active surface by comparing the volcanic radiative energy vre in j detected by modis during 28 eruptions at 18 active volcanoes with their erupted lava volumes vol in m 3 we show that the radiant density c rad vre vol is inversely proportional to the silica content of the erupted lava basic lavas 45 52 wt sio 2 have the highest observed radiant density 1 to 4 10 8 j m 3 while intermediate 52 63 wt sio 2 and acidic 63 wt sio 2 lavas show a gradually lower radiant densities 1 5 to 9 10 7 j m 3 and 0 2 to 1 10 7 j m 3 for intermediate and acidic composition respectively we regard this correlation as the result of the control that the rheology of lavas exerts on cooling and spreading processes of related bodies in particular we found that for any given compositional group the radiant density is essentially related to a characteristic thickness of active lavas at the time of a satellite acquisition we suggest that the radiant density of effusive extrusive lava bodies can be predicted 50 by means of an empirical relationship based on the sio 2 content of the erupted lava this makes this parameter very useful in observing volcanic activity especially in remote regions where access may not be possible by measuring the energy radiated during an eruption and by assuming a lava composition based on the tectonic setting or magmatic province we suggest that the radiant density can be used to estimate lava discharge rates and erupted volumes for volcanoes characterised by effusive or extrusive activity