experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

are granitic intrusions scale invariant published length l and thickness t data on 135 laccolith and 21 granite intrusions define power law relationships of the form l kt a typical of systems exhibiting scale invariant fractal behaviour both data sets are characterised by an exponent a 1 0 88 0 1 for laccoliths and 0 80 0 20 for plutons that reflects an inherent preference for scale invariant tabular sheet geometries these power law size relationships can be explained in mechanical terms by the need for an incoming magma sheet to travel laterally some distance before vertical thickening can occur sheet thickness is a function of available magma pressure which for an intrusion fed by a feeder dyke is proportional to the vertical magma transport distance

morphology and dynamics of explosive vents through cohesive rock formations shallow explosive volcanic processes such as kimberlite volcanism and phreatomagmatic and phreatic activity produce volcanic vents exhibiting a wide variety of morphologies including vertical pipes and v shaped vents in this study we report on experimental and numerical models designed to capture a range of vent morphologies in an eruptive system using dimensional analysis we identified key governing dimensionless parameters in particular the gravitational stress to fluid pressure ratio 2 p gh and the fluid pressure to host rock strength ratio 3 p c we used combined experimental and numerical models to test the effects of these parameters the experiments were used to test the effect of 2 on vent morphology and dynamics a phase diagram demonstrates a separation between two distinct morphologies with vertical structures occurring at high values of 2 and diagonal ones at low values of 2 the numerical simulations were used to test the effect of 3 on vent morphology and dynamics in the numerical models we see three distinct morphologies vertical pipes are produced at high values of 3 diagonal pipes at low values of 3 and horizontal sills at intermediate values of 3 our results show that vertical pipes form by plasticity dominated yielding in high energy systems high 2 and 3 whereas diagonal and horizontal vents dominantly form by fracturing in lower energy systems low 2 and 3 although our models are two dimensional they suggest that circular pipes result from plastic yielding of the host rock in a high energy regime whereas v shaped volcanic vents result from fracturing of the host rock in lower energy systems

experimental modelling of ground deformation associated with shallow magma intrusions abstract active volcanoes experience ground deformation as a response to the dynamics of underground magmatic systems the analysis of ground deformation patterns may provide important constraints on the dynamics and shape of the underlying volcanic plumbing systems nevertheless these analyses usually take into account simplistic shapes sphere dykes sills and the results cannot be verified as the modelled systems are buried in this paper i present new results from experimental models of magma intrusion in which both the evolution of ground deformation during intrusion and the shape of the underlying intrusion are monitored the models consisted of a molten vegetable oil simulating low viscosity magma injected into cohesive fine grained silica flour simulating the brittle upper crust oil injection resulted is sheet intrusions dykes sills and cone sheets the initial topography in the models was flat while the oil was intruding the surface of the models slightly lifted up to form a smooth relief which was mapped through time after an initial symmetrical development the uplifted area developed asymmetrically at the end of the experiments the oil always erupted at the steepest edge of the uplifted area after the experiment the oil solidified the intrusion was excavated and the shape of its top surface mapped the comparison between the uplifted zone and the underlying intrusions showed that 1 the complex shapes of the uplifted areas reflected the complex shapes of the underlying intrusions 2 the time evolution of the uplifted zone was correlated with the evolution of the underlying intrusion and 3 the early asymmetrical evolution of the uplifted areas can be used to predict the location of the eruption of the oil the experimental results also suggest that complex intrusion shapes inclined sheet cone sheet complex sill may have to be considered more systematically in the analyses of ground deformation patterns on volcanoes

mechanisms and timescales of felsic magma segregation ascent and emplacement in the himalaya we combine field petrological geochemical and experimental observations to evaluate the time scales of compaction driven and shear assisted melt extraction and ascent in the himalayas the results show that melt migration via compaction and channelling is inescapable and operates on timescales less than 1 m y and possibly as short as 0 1 m y field and petrological data show that such a fast and efficient melt transfer result from a combination of favourable factors including 1 low but constant melt viscosity 104 5 pa s during extraction and ascent 2 grain size coarsening of the source rocks in response to prolonged heating prior to melting and 3 high source fertility and thus high melt fraction owing to elevated modal amounts of muscovite of leucogranite sources all three factors dramatically increase source permeability calculations show that shear assisted melt extraction had a time interval recurrence in the 10 100 kyr range leading to sill thicknesses of 1 30 m yet melts falling at the low end of the viscosity range when coupled to high shear velocities may lead to veins several hundred meters thick the deepest structural levels eg central zanskar range show that in situ melts formed where pure shear compaction was greatest and where simple shear was also operative magma extracted from migmatite leucosomes was injected along planes of weakness parallel to the ductile shear fabric probably by some sort of hydraulic fracturing crack propagation mechanism large hhl eg c 5 km thick sills at manaslu makalu and northern bhutan may thus represent inflated laccoliths assembled via dykes that tapped a 100 300 m melt layer produced by compaction of ghs thermal simulations show that such melt layers may have incubation times of several m y although transport time for magmas associated with the hhl is short the time for assembly may take several m y for the largest hhl as geochronological data indicate up to 5 m y for manaslu shisha pangma transport of leucogranite melt from mid crust levels towards the surface was concomitant with active low angle normal faulting along the south tibetan detachment normal fault a structure that effectively formed the lid to the extrusion of a partially molten layer of mid crustal rocks channel flow rapid cooling of the granites emplaced on top of ghs implies rapid extrusion and lateral flow of greater himalayan sequence rocks beneath the std during the period 20 17 ma weakening of the crust by partial melting is thus likely to be pulsatory in time and future thermomechanical models should incorporate such aspects to model tectonic evolution of hot orogens

petrologic and experimental evidence for the movement and heating of the pre eruptive minoan rhyodacite santorini greece hydrothermal experiments combined with petrologic observations form the basis for a new two stage model for the evolution of the pre eruption minoan magma chamber at santorini greece ninety nine percent of the erupted volume is two pyroxene rhyodacitic magma that had been stored at a temperature of 885 c based on magnetite ilmenite and quilf geothermometry the rest of the volume is basaltic to andesitic magma which occurs as 200 mpa in addition the composition of the plagioclase hosts an56 6 of the inclusions require temperatures of 825 25 c at pressures 200 mpa this demonstrates that the minoan rhyodacitic magma underwent a two stage evolution first crystallizing at 825 c and 200 mpa and then rinsing to a shallow 50 mpa storage region with a concomitant rise in temperature to 885 c we suggest that the episodic intrusion of mafic magmas provided the necessary heat and perhaps contributed to the ascent of the magma to shallow crustal depths where it reequilibrated before the cataclysmic eruption phase equilibria suggest that much of the heating of the rhyodacite occurred in the shallow storage region thermal budget calculations suggest that the rhyodacite magma could have been heated by intrusions of basalt rising at reasonable upwelling rates and injected into the storage zone over several hundred years preservation of amphibole in the mafic scoria indicate that injection of mafic magma continued up until days before the cataclysmic eruption perhaps triggering the event

fragmentation efficiency of explosive volcanic eruptions a study of experimentally generated pyroclasts abstract products of magma fragmentation can pose a severe threat to health infrastructure environment and aviation systematic evaluation of the mechanisms and the consequences of volcanic fragmentation is very difficult as the adjacent processes cannot be observed directly and their deposits undergo transport related sorting however enhanced knowledge is required for hazard assessment and risk mitigation laboratory experiments on natural samples allow the precise characterization of the generated pyroclasts and open the possibility for substantial advances in the quantification of fragmentation processes they hold the promise of precise characterization and quantification of fragmentation efficiency and its dependence on changing material properties and the physical conditions at fragmentation we performed a series of rapid decompression experiments on three sets of natural samples from unzen volcano japan the analysis comprised grain size analysis and surface area measurements the grain size analysis is performed by dry sieving for particles larger than 250 m and wet laser refraction for smaller particles for all three sets of samples the grain size of the most abundant fraction decreases and the weight fraction of newly generated ash particles up to 40 wt increases with experimental pressure potential energy for fragmentation this energy can be estimated from the volume of the gas fraction and the applied pressure the surface area was determined through argon adsorption the fragmentation efficiency is described by the degree of fine particle generation results show that the fragmentation efficiency and the generated surface correlate positively with the applied energy

new insights into the initiation and venting of the bronze age eruption of santorini greece from component analysis the late seventeenth century bc minoan eruption of santorini discharged 30 60 km3 of magma and caldera collapse deepened and widened the existing 22 ka caldera a study of juvenile cognate and accidental components in the eruption products provides new constraints on vent development during the five eruptive phases and on the processes that initiated the eruption the eruption began with subplinian phase 0 and plinian phase 1 phases from a vent on a ne sw fault line that bisects the volcanic field during phase 1 the magma fragmentation level dropped from the surface to the level of subvolcanic basement and magmatic intrusions the fragmentation level shallowed again and the vent migrated northwards during phase 2 into the flooded 22 ka caldera the eruption then became strongly phreatomagmatic and discharged low temperature ignimbrite containing abundant fragments of post 22 ka pre minoan intracaldera lavas phase 3 phase 4 discharged hot fluidized pyroclastic flows from subaerial vents and constructed three main ignimbrite fans northwestern eastern and southern around the volcano the first phase 4 flows were discharged from a vent or vents in the northern half of the volcanic field and laid down lithic block rich ignimbrite and lag breccias across much of the nw fan about a tenth of the lithic debris in these flows was subvolcanic basement new subaerial vents then opened up probably across much of the volcanic field and finer grained ignimbrite was discharged to form the e and s fans if major caldera collapse took place during the eruption it probably occurred during phase 4 three juvenile components were discharged during the eruption a volumetrically dominant rhyodacitic pumice and two andesitic components microphenocryst rich andesitic pumices and quenched andesitic enclaves the microphenocryst rich pumices form a textural mineralogical chemical and thermal continuum with co erupted hornblende diorite nodules and together they are interpreted as the contents of a small variably crystallized intrusion that was fragmented and discharged during the eruption mostly during phases 0 and 1 the microphenocryst rich pumices hornblende diorite andesitic enclaves and fragments of pre minoan intracaldera andesitic lava together form a chemically distinct suite of ba rich zr poor andesites that is unique in the products of santorini since 530 ka once the minoan magma reservoir was primed for eruption by recharge generated pressurization the rhyodacite moved upwards by exploiting the plane of weakness offered by the pre existing andesite diorite intrusion dragging some of the crystal rich contents of the intrusion with it

structure and evolution of hydrothermal vent complexes in the karoo basin south africa the karoo large igneous province formed at c 183 ma is characterized by the presence of voluminous basaltic intrusive complexes within the karoo basin extrusive lava sequences and hydrothermal vent complexes these last are pipe like structures up to several hundred metres in diameter piercing the horizontally stratified sediments of the basin detailed mapping of two sediment dominated hydrothermal vent complexes shows that they are composed of sediment breccias and sandstone the breccias cut and intrude tilted host rocks and are composed of mudstone and sandstone fragments with rare dolerite boulders sandstone clasts in the breccias are locally cemented by zeolite which represents the only hydrothermal mineral in the vent complexes our data document that the hydrothermal vent complexes were formed by one or a few phreatic events leading to the collapse of the surrounding sedimentary strata we propose a model in which hydrothermal vent complexes originate in contact metamorphic aureoles around sill intrusions heating and expansion of host rock pore fluids resulted in rapid pore pressure build up and phreatic eruptions the hydrothermal vent complexes represent conduits for gases and fluids produced in contact metamorphic aureoles slightly predating the onset of the main phase of flood volcanism

exsolution of magmatic volatile phases from cl enriched mineralizing granitic magmas and implications for ore metal transport abstract to understand cl dissolution in aluminosilicate liquids and the exsolution of cl rich magmatic volatile phases experiments were conducted to determine the solubility of nacl kcl and h2o in felsic liquids at 0 5 and 2 kbar the cl content of h2o poor nacl saturated and kcl saturated silicate liquids is low i e 1 3 wt to very low i e 0 2 wt and varies with changes in pressure and composition the cl concentration increases with the f concentration and the molar al na ca mg si ratio of the liquid and decreases with increasing activity of h2o in the system exsolution of a volatile phase depends on the partial pressures of all dissolved volatiles and low cl solubilities in nacl saturated and kcl saturated silicate liquids imply that exsolution of a cl bearing volatile phase will occur early in cl bearing granitic magmas i e prior to extensive melt crystallization and or at comparatively low water fugacities the solubility behavior of h2o and cl is very similar to that of co2 and h2o in felsic liquids small quantities of co2 are known to facilitate volatile phase exsolution holloway 1976 and in a similar manner volatile phases may exsolve early in cl enriched granite magmas whereas 5 to 6 wt dissolved h2o is necessary for volatile phase exsolution from a co2 free and cl free haplogranite liquid at 2 kbar and 800 c a cl rich brine will exsolve if the liquid contains only 1 wt h2o and 0 26 wt cl at the same conditions these new solubility data are interpreted in light of h2o f and cl concentrations in felsic liquids determined from silicate melt inclusions to constrain the exsolution of cl bearing magmatic volatile phases from mineralizing granitic magmas felsic magmas genetically associated with cu porphyry and mo porphyry mineralization contain sufficient h2o and cl to become saturated with respect to a hypersaline brine without strong pressure reduction boiling of the volatile phase i e exsolution of immiscible vapor and brine or strong volatile enrichment resulting from extensive crystal fractionation experiments were also conducted to investigate the solubility of mo in highly saline volatile phases coexisting with granitic liquids at 2 and 0 5 kbar the apparent partition coefficient for mo in the volatile phase s relative to silicate liquid d mo is defined as the computed concentration of mo in a volatile phase or phases the measured concentration of mo in granite glass d mo ranges from 8 to 80 as the nacl and kcl content of the volatile phase s increases from 15 to 90 wt because mo does not complex with cl in aqueous fluids it appears that mo solubility may be a strong function of the activity of na and k in alkali chloride rich volatile phases

storage and interaction of compositionally heterogeneous magmas from the 1986 eruption of augustine volcano alaska compositional heterogeneity 56 64 wt sio2 whole rock in samples of tephra and lava from the 1986 eruption of augustine volcano alaska raises questions about the physical nature of magma storage and interaction beneath this young and frequently active volcano to determine conditions of magma storage and evolutionary histories of compositionally distinct magmas we investigate physical and chemical characteristics of andesitic and dacitic magmas feeding the 1986 eruption we calculate equilibrium temperatures and oxygen fugacities from fe ti oxide compositions and find a continuous range in temperature from 877 to 947 c and high oxygen fugacities nno 1 2 for all magmas melt inclusions in pyroxene phenocrysts analyzed by fourier transform infrared spectroscopy and electron probe microanalysis are dacitic to rhyolitic and have water contents ranging from 1 to 7 wt matrix glass compositions are rhyolitic and remarkably similar 75 9 76 6 wt sio2 in all samples all samples have 25 phenocrysts but lower silica samples have much higher microlite contents than higher silica samples continuous ranges in temperature and whole rock composition as well as linear trends in harker diagrams and disequilibrium mineral textures indicate that the 1986 magmas are the product of mixing between dacitic magma and a hotter more mafic magma the dacitic endmember is probably residual magma from the previous 1976 eruption of augustine and we interpret the mafic endmember to have been intruded from depth mixing appears to have continued as magmas ascended towards the vent we suggest that the physical structure of the magma storage system beneath augustine contributed to the sustained compositional heterogeneity of this eruption which is best explained by magma storage and interaction in a vertically extensive system of interconnected dikes rather than a single coherent magma chamber and or conduit the typically short repose period 10 years between augustine s recent eruptive pulses may also inhibit homogenization as short repose periods and chemically heterogeneous magmas are observed at several volcanoes in the cook inlet region of alaska

quantitative experiments on phreatomagmatic explosions abstract an experimental set up for controlled generation of thermal explosions fuel coolant interactions has been built by an interdisciplinary research group of volcanologists physicists and engineering scientists the tee haus thermal explosion experiment during the last 3 years more than 500 experimental runs were performed aim of the project was not to build a mini volcano but to produce igniteable mixtures of water and hot melt on a small scale in order to investigate basic physical aspects such small scale mixtures however most probably also occur during phreatomagmatic events in nature mixtures of water and magma on a large scale may be modelled by combination of small elements earlier experimental studies of thermal explosions were carried out with the use of metal melts nearly exclusively therefore a carbonate melt approx 0 3 kg of 1 1 mass ratio na2co3 k2co3 was used for initial experimental series because of easy handling and more magma similarity by injection of water into this melt explosive mixtures were produced and ignited self triggering explosive interactions occurred in a wide melt temperature range 720 to 1040 c at melt temperatures exceeding 1000 c co2 increasingly degassed presence of non condensible gas bubbles in the melt strongly reduced the explosivity the intensity of explosions only slightly increased with higher melt temperatures but strongly increased with higher water injection velocities because of more intensive mixing a minimum injection velocity was found to be approx 0 7 m s 1 experiments with silicate melts derived from diverse remelted volcanic rocks were carried out with a slightly modified set up explosions were ignited by an additional trigger a shock wave of approx 8 j in volcanic systems shock waves of this magnitude are abundant volcanic tremor etc strong explosions with silicate melts were produced at melt temperatures between 1350 and 1750 c the produced explosions exerted repulsion forces of up to 24 000 n with a typical pulse duration of 1 ms carbonate melt resp 1 5 ms silicate melts the ejection velocity was found to be in a range between 200 and 400 m s 1 explosion energy values up to 500 j were calculated the maximum explosion pressure was calculated to be in the range between 10 and 100 mpa only part of the melt so called interactive melt reacts explosively with injected water most of the melt is passively ejected by and after the thermal explosion different fragmentation processes result in specific grain size and grain shape populations that can be distinguished from each other particles resulting from the fine fragmentation process that precedes and causes the thermal explosion are characterized by angular to subrounded shapes and grain sizes ranging from 20 m to 180 m the amount of interactive melt is proportional to the intensity of the explosion the maximum amount of water vapourized at the explosive interaction so called interactive water was estimated thus the water melt mass ratio for explosive interactions could be calculated the values range between 1 25 and 1 35 carbonate melt resp between 1 6 and 1 25 silicate melts

influence of decompression rate on fragmentation processes an experimental study a key for an effective early warning or even a forecasting system for volcanic eruptions lies in the understanding of volcanic processes and the correct interpretation of monitoring data here we investigate the processes occurring in the upper conduit at the phase transition between melt and the surrounding rock characterizing the fragmentation threshold and speed fragmentation experiments using a shock tube were performed to address the following questions 1 how does sample conduit size affect fragmentation processes 2 what is the impact of different decompression rates and differing stress distributions in the sample on fragmentation threshold and speed the observed fragmentation behaviour is analyzed in terms of energy density and compared with recent related studies a 2d fragmentation mechanism is presented based on the arrangement of cracks in fragmented samples a numerical model for the estimation of the first principle stress distribution before the magma failure is provided

generation of volcanic ash by basaltic volcanism 1 the recent eruptions of eyjafjallajokull and grimsvotn volcanoes in iceland demonstrate the importance of a better understanding of processes leading to the formation of volcanic ash specifically of fine volcanic ash that poses a threat to air traffic continuous deformation and brittle type experiments were carried out to better constrain these processes the studies on short time continuous deformation behavior of basaltic melt showed viscoelastic properties deviating from hydrodynamic newtonian models by more than 5 orders of magnitude high temperature deformation experiments on basaltic rock samples revealed an increase of elastic strengths as approaching the melting regime also pointing to a very complex behavior at the solid ductile boundary understanding magma fragmentation from the liquid side is a challenge but meanwhile we propose a pragmatic solution a thermodynamic model based on fracture mechanics this model is in agreement with experiments and observations that show that fine volcanic ash is produced by brittle type fragmentation of magma a critical material property was defined characterizing the conditions for brittle fragmentation the fracture surface energy density which represents the critical fragmentation energy short term fracture experiments using silicate glass have been performed to investigate the formation of ash sized particles by brittle failure and to extract this critical physical property which was found to range between 40 and 130 j m2 this value is in good agreement to fragmentation energies determined from experiments using remelted volcanic rocks now there is a tool to define critical conditions for the production of volcanic ash of a specific magma type

explosive fragmentation criteria and velocities for vesicular magma abstract we present a new criterion for primary fragmentation of natural rock samples in shock tube experiments and new formulae for the effective strength of natural rock samples for the size of primary fragments and for fragmentation velocities these formulae and the fragmentation criterion are given in terms of the physical properties of the rock and in terms of experimental parameters the formulae and criterion are derived from numerical solutions and asymptotic analytic solutions to a novel recently published mathematical model for the explosive fragmentation of vesicular magma in shock tube experiments this model is singularly successful in accounting for the length scales observed in these experiments the criterion and formulae provide good matches to data from shock tube experiments on natural samples

p and s velocity structures of the santorini coloumbo volcanic system aegean sea greece obtained by non linear inversion of travel times and its tectonic implications abstract one of the most prominent tectonic features of the eastern mediterranean region is the hellenic volcanic arc in the southern aegean sea with the santorini island being one of the most active volcanic centers recent seismic studies show that the main seismic activity of the santorini volcanic center is strongly associated with the volcanic processes as well as with the seismo tectonic regime of the broader southern aegean sea area the main cluster of local seismicity is located near the northeastern edge of the santorini island beneath the coloumbo reef which is a submarine volcanic seamount of the santorini island volcanic system the p and s wave velocity structures of the santorini coloumbo volcanic system is studied by inverting travel times of local earthquakes recorded by two independent dense seismic arrays installed in the broader area of santorini islands during the period of september 2002 september 2005 in particular 137 local earthquakes with 1600 p phases and 1521 s phases recorded by 25 seismological stations have been selected for the inversion the inversion technique applied is non linear since three dimensional ray tracing is incorporated the reliability of the final tomographic results is demonstrated through resolutions tests using synthetic seismic data the obtained results confirm the strong variations of the p and s wave velocity structures in the area of santorini coloumbo volcanic system as well as the connection between the tectonic setting of the study area with the magmatic processes taking place beneath the two volcanoes the tomographic models show that a low velocity zone extends along the northeastern edge of the santorini island parallel to the kameni coloumbo fracture zone ne sw direction which corresponds to the western termination of the major ene wsw santorini amorgos fault zone evidence is presented that this structural lineament corresponds to a tecto volcanic fracture zone which probably links the volcanic center of santorini with the submarine volcano at coloumbo reef furthermore the tomographic results show indications that the magmatic chamber beneath the coloumbo volcanic seamount is located at a depth of 6 7 km in good agreement with recent independent studies in the area though this feature is not within the resolving power of the employed data set

evolution of santorini volcano dominated by episodic and rapid fluxes of melt from depth santorini volcano in greece was thought to be continually charged by small injections of magma measurements of surface deformation show that magma equivalent to 10 50 of that emitted in previous small eruptions has been injected beneath santorini since january 2011 implying that the volcano is instead charged by rapid episodic fluxes of melt

marine tephra from the cape riva eruption 22 ka of santorini in the sea of marmara abstract a discrete tephra layer has been discovered in three marine sediment cores from the sea of marmara eastern mediterranean the rhyodacitic glass chemistry and the stratigraphical position suggest a santorini provenance and in particular a correlation with the marine y 2 tephra that is known from the southern aegean sea and eastern levantine basin this tephra represents the distal facies of the cape riva eruption of santorini which has been dated by 14c on land at 21 950 cal yr bp hitherto the y 2 tephra has been detected only in marine sediment cores recovered south to southeast of its volcanic source the new occurrence in the sea of marmara approximately 530 km nne of the santorini eruptive centre suggests a more north easterly dispersal of fallout products of the cape riva eruption than previously supposed

petrological and experimental constraints on the pre eruption conditions of holocene dacite from volcan san pedro 36 s chilean andes and the importance of sulphur in silicic subduction related magmas we present an experimental and petrological study aimed at estimating the pre eruptive conditions of a holocene dacitic lava from volcan san pedro 36 s chilean andes phase equilibrium experiments were performed at temperatures t from 800 to 950 c and mainly at 200 mpa but also at 55 150 and 406 mpa oxygen fugacity fo2 ranged from the ni nio buffer nno to 3 5 log units above nno 3 5 and water contents from 3 to 6 wt we also report several experiments where we added sulphur 0 1 1 wt s to the dacite the main mineral assemblage of the dacite hornblende orthopyroxene plagioclase is stable at 200 50 mpa 850 10 c with 4 5 5 5 wt h2o in the melt and at fo2 of nno 1 2 0 2 in accord with the crystallinity mineral proportions and t fo2 determination from fe ti oxides of the lava however biotite which is also present in the dacite is stable at these same t fo2 conditions only in experiments with 0 1 wt s added this result is in accord with the occurrence of pyrrhotite in the lava and with the presence of s in glass inclusions and biotite 300 ppm and up 170 ppm respectively moreover the zoning patterns and compositions of plagioclase phenocrysts together with the presence of high temperature minerals e g clinopyroxene in the lava suggest that the petrological history of the dacite is more complex than a single near equilibrium crystallization stage and could be explained by short lived 100 years temperature fluctuations 50 c in the magma reservoir

a study of clast size distribution ash deposition and fragmentation in a hawaiian style volcanic eruption ash deposits from hawaiian style eruptions are generally of small volume but are important in understanding the mechanisms of these eruptions an analysis of the ash deposit from the 1959 kilauea iki eruption of kilauea volcano is presented and the whole deposit grain size distribution for the eruption is calculated the grain size distribution is found to be heavily skewed towards the coarsest clast sizes and to differ considerably from size distributions for plinian deposits

influence of the fragmentation process on the dynamics of vulcanian eruptions an experimental approach abstract the dynamics of magma fragmentation is a controlling factor in the behavior of explosive volcanic eruptions if porous magma is sufficiently decompressed a fragmentation front develops and travels through the magma at a certain speed fragmentation speed while the resulting particles are being ejected to investigate the influence of the fragmentation process on eruption dynamics we have performed fragmentation experiments in a shock tube apparatus using natural volcanic samples with diverse porosities and different applied pressures 4 20 mpa for each experiment we simultaneously measured the fragmentation speed and ejection velocities the results are consistent with a theoretical model based on a 1 d shock tube theory considering the conservation laws across the fragmentation front our results show that a certain pressure threshold has to be exceeded for fragmentation and ejection of the particles to take place and that the fragmentation speed determines the initial conditions of the expansion of the gas particle mixture the fragmentation process has a controlling influence on the velocity density and mass discharge rate per unit area of the gas particle mixture all factors which can affect eruption dynamics significantly the model presented herein may help describe the dynamics of vulcanian eruptions and improve hazard assessment

experimental investigations on the explosivity of steam driven eruptions a case study of solfatara volcano campi flegrei steam driven eruptions both phreatic and hydrothermal expel exclusively fragments of non juvenile rocks disintegrated by the expansion of water as liquid or gas phase as their violence is related to the magnitude of the decompression work that can be performed by fluid expansion these eruptions may occur with variable degrees of explosivity in this study we investigate the influence of liquid fraction and rock petrophysical properties on the steam driven explosive energy a series of fine grained heterogeneous tuffs from the campi flegrei caldera were investigated for their petrophysical properties the rapid depressurization of various amounts of liquid water within the rock pore space can yield highly variable fragmentation and ejection behaviors for the investigated tuffs our results suggest that the pore liquid fraction controls the stored explosive energy with an increasing liquid fraction within the pore space increasing the explosive energy overall the energy released by steam flashing can be estimated to be 1 order of magnitude higher than for simple argon gas expansion and may produce a higher amount of fine material even under partially saturated conditions the energy surplus in the presence of steam flashing leads to a faster fragmentation with respect to gas expansion and to higher ejection velocities imparted to the fragmented particles moreover weak and low permeability rocks yield a maximum fine fraction using experiments to unravel the energetics of steam driven eruptions has yielded estimates for several parameters controlling their explosivity these findings should be considered for both modeling and evaluation of the hazards associated with steam driven eruptions

a fragmentation criterion for highly viscous bubbly magmas estimated from shock tube experiments abstract when a highly viscous bubbly magma is sufficiently decompressed layer by layer fracturing propagates through the magma at a certain speed fragmentation speed on the basis of a recent shock tube theory by koyaguchi and mitani koyaguchi t mitani n k 2005 a theoretical model for fragmentation of viscous bubbly magmas in shock tubes journal of geophysical research 110 b10 b10202 doi 10 1029 2004jb003513 gas overpressures at the fragmentation surface are estimated from experimental data on fragmentation speed in shock tube experiments for natural volcanic rocks with various porosities the results show that gas overpressure at the fragmentation surface increases as initial sample pressure increases and sample porosity decreases we propose a new fragmentation criterion to explain the relationship between the gas overpressure at the fragmentation surface the initial pressure and the porosity our criterion is based on the idea that total fragmentation of highly viscous bubbly magmas occurs when the tensile stress at the midpoint between bubbles exceeds a critical value we obtain satisfactory agreement between our simulation and experiment when we assume that the critical value is inversely proportional to the square root of bubble wall thickness this fragmentation criterion suggests that long micro cracks or equivalent flaws e g irregular shaped bubbles that reach the midpoints between bubbles are a dominant factor to determine the bulk strength of the bubbly magma

experimental estimates of the energy budget of hydrothermal eruptions application to 2012 upper te maari eruption new zealand sudden hydrothermal eruptions occur in many volcanic settings and may include high energy explosive phases ballistics launched by such events together with ash plumes and pyroclastic density currents generate deadly proximal hazards the violence of hydrothermal eruptions or explosive power depends on the energy available within the driving fluids gas or liquid which also influences the explosive mechanisms volumes durations and products of these eruptions experimental studies in addition to analytical modeling were used here to elucidate the fragmentation mechanism and aspects of energy balance within hydrothermal eruptions we present results from a detailed study of recent event that occurred on the 6th of august 2012 at upper te maari within the tongariro volcanic complex new zealand the eruption was triggered by a landslide from this area which set off a rapid stepwise decompression of the hydrothermal system explosive blasts were directed both westward and eastward of the collapsed area with a vertical ash plume sourced from an adjacent existing crater all explosions ejected blocks on ballistic trajectories hundreds of which impacted new zealand s most popular hiking trail and a mountain lodge 1 4 km from the explosion locus we have employed rocks representative of the eruption source area to perform rapid decompression experiments under controlled laboratory conditions that mimic hydrothermal explosions under controlled laboratory conditions an experimental apparatus for 34 by 70 mm cylindrical samples was built to reduce the influence of large lithic enclaves up to 30 mm in diameter within the rock the experiments were conducted in a temperature range of 250 degrees c 300 degrees c and applied pressure between 4 mpa and 6 5 mpa which span the range of expected conditions below the te maari crater within this range we tested rapid decompression of pre saturated samples from both liquid dominated conditions and the vapor dominated field further we tested dry samples at the same pressure and temperature conditions results showed that host rock lithology and state of the interstitial fluid was a major influence on the fragmentation and ejection processes as well as the energy partitioning clasts were ejected with velocities of up to 160 m s as recorded by high speed camera in addition to rare large clasts analogous to ballistics a large amount of fine and very fine 63 mu m ash was produced in all experiments the efficiency of transformation of the total explosive energy into fragmentation energy was estimated between 10 to 15 depending on the host rock lithology while less than 0 1 of this was converted into kinetic energy our results suggest that liquid to vapor flashing expansion provides an order of magnitude higher energy release than steam expansion which best explains the dynamics of the westward and most energetic directed blast at te maari considering the steam flashing as the primary energy source the experiments suggested that a minimum explosive energy of 7 x 10 10 to 2 x 10 12 j was involved in the te maari blast experimental studies under controlled conditions compared closely to a field example are thus highly useful in providing new insights into the energy release and hazards associated with eruptions in hydrothermal areas c 2016 the author s published by elsevier b v

phase equilibria of the lyngdal granodiorite norway implications for the origin of metaluminous ferroan granitoids the proterozoic 950 ma lyngdal granodiorite of southern norway belongs to a series of hornblende biotite metaluminous ferroan granitoids hbg suite coeval with the post collisional rogaland anorthosite mangerite charnockite amc suite this granitoid massif shares many geochemical characteristics with rapakivi granitoids yet granodiorites dominate over granites to constrain both crystallization p t fo2 h 2o in melt and magma generation conditions we performed crystallization experiments on two samples of the lyngdal granodiorite with 60 and 65 wt sio2 at 4 2 kbar mainly at fo2 of nno nickel nickel oxide to nno 1 and under fluid saturated conditions with various h2o co2 ratios for each temperature comparison between experimental phase equilibria and the mineral assemblage in the lyngdal granodiorite indicates that it crystallized between 4 and 2 kbar from a magma with 5 6 wt h2 oa t an fo2 of nno to nno 1 these oxidized and wet conditions sharply contrast with the dry and reduced conditions inferred for the petrogenesis of the amc suite and many other rapakivi granites worldwide the high liquidus temperature and h2o content of the lyngdal granodiorite imply that it is not a primary magma produced by the partial melting of the crust but is derived by the fractionation of a mafic magma lyngdal type magmas appear to have volcanic equivalents in the geological record in particular our results show that oxidized high silica rhyolites such as the bishop tuff could be derived via fractionation of oxidized intermediate magmas and do not necessarily represent primary crustal melts this study underlines the great variability of crystallization conditions from anhydrous to hydrous and reduced to oxidized and petrogenetic processes among the metaluminous ferroan magmas of intermediate compositions granodiorites quartz mangerites quartz latites suggesting that there is not a single model to explain these rocks

fragmentation of magma during plinian volcanic eruptions the ratio of the volume of vesicles gas to that of glass liquid in pumice clasts v g v l reflects the degassing and dynamic history experienced by a magma during an explosive eruption v g v l in pumices from a large number of plinian eruption deposits is shown here to vary by two orders of magnitude even between pumices at a given level in a deposit these variations in v g v l do not correlate with crystallinity or initial water content of the magmas or their eruptive intensities despite large ranges in these variables gas volume ratios of pumices do however vary systematically with magma viscosity estimated at the point of fragmentation and we infer that pumices do not quench at the level of fragmentation but undergo some post fragmentary evolution on the timescale of plinian eruptions pumices with viscosities 109 pa s can expand after fragmentation as long as their bubbles retain gas at a rate inversely proportional to their viscosity once the bubbles connect to form a permeable network and lose their gas expansion halts and pumices with viscosities 105 pa s can collapse under the action of surface tension textural evidence from bubble sizes and shapes in pumices indicates that both expansion and collapse have taken place the magnitudes of expansion and collapse therefore depend critically on the timing of bubble connectivity relative to the final moment of quenching we propose that bubbles in different pumices become connected at different times throughout the time span between fragmentation and quenching after accounting for these effects we derive new information on the fragmentation process from two characteristics of pumices the most important is a relatively constant minimum value of v g v l of 1 78 64 vol vesicularity in all samples with viscosities 105 pa s this value is independent of magma composition and thus reflects a property of the eruptive mechanism the other characteristic is that highly expanded pumices 85 vol vesicularities are common which argues against overpressure in bubbles as a mechanism for fragmenting magma we suggest that magma fragments when it reaches a vesicularity of 64 vol but only if sheared sufficiently strongly the intensity of shear varies as a function of velocity in the conduit which is related to overpressure in the chamber so that changes in overpressure with time are important in controlling the common progression from explosive to effusive activity at volcanoes

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

experimental modelling of fragmentation applied to volcanic explosions abstract explosions during volcanic eruptions cause fragmentation of magma and host rock resulting in fragments with sizes ranging from boulders to fine ash the products can be described by fragment size distributions fsd which commonly follow power laws with exponent d the processes that lead to power law distributions and the physical parameters that control d remain unknown we developed a quantitative experimental procedure to study the physics of the fragmentation process through time the apparatus consists of a hele shaw cell containing a layer of cohesive silica flour that is fragmented by a rapid injection of pressurized air the evolving fragmentation of the flour is monitored with a high speed camera and the images are analysed to obtain the evolution of the number of fragments n their average size a and the fsd using the results from our image analysis procedure we find transient empirical laws for n a and the exponent d of the power law fsd as functions of the initial air pressure we show that our experimental procedure is a promising tool for unravelling the complex physics of fragmentation during phreatomagmatic and phreatic eruptions

textural analysis of magmatic enclaves from the kameni islands santorini greece abstract the kameni islands have been the focus of historic volcanic activity on santorini greece the islands comprise a series of dacite lavas the erupted compositions of which have remained approximately constant for the last 2200 years the dacite lava flows of nea kameni contain a variety of mafic enclaves distinguished by differences in texture composition and mechanical behaviour the mafic enclaves represent chilled fragments of mafic magma that crystallised rapidly on contact with the cooler more silicic host magma the absence of chilled margins on the enclaves suggests that the replenishing magma initially formed a dense layer at the base of the chamber groundmass textures are interpreted as an indication of the degree of undercooling between the enclaves and the host groundmass textural information obtained from the enclaves has been used to determine the relative volumes of replenishing magmas injected into the host magma before eruption which indicates that the volume of erupted magma is directly proportional to the volume of replenishing magma emplaced in the chamber prior to eruption which thus may act as a potential eruption trigger the variety of replenishing magmas implies the existence of a complex conduit and chamber system beneath santorini volcano andesitic enclaves with linear crystal size distributions are thought to have originated as an aphyric andesitic melt expelled from a crystal mush by filter pressing disequilibrium phenocryst assemblages in the lavas and phenocryst bearing enclaves provide evidence for the entrainment and recycling of older phenocryst populations

premixing of magma and water in mfci experiments experimental studies have been performed to evaluate pre explosive water melt mixes with respect to explosive volcanic molten fuel coolant interaction mfci i e phreatomagmatic explosion remolten ultrabasic volcanic rock was used as a magma simulant measurement of the explosion intensity was used to determine optimal premixing conditions a well defined optimal range was found for the hydrodynamic mixing energy differential flow speed of 4 2 m s as well as for the water melt mass ratio 0 03 to 0 04 under experimental conditions the mass flux of water had a minor influence on the explosion intensity additionally transparent mixing experiments with silicon oil and inked water were carried out they indicate a direct dependence of the pre explosive water melt interface area on the explosion intensity the experimental results show that the contact conditions of water and melt required for explosive mfci may easily be established in natural volcanic systems thus explosive mfci is a probable mechanism of explosive volcanism

using the sr isotope compositions of feldspars and glass to distinguish magma system components and dynamics the individual components of magmatic rocks are being increasingly targeted to gain insight into volcanic systems here we demonstrate the use of sr isotope microsampling to distinguish distinct populations of glass and plagioclase that represent the sources of components liquids and crystals within each erupted magma batch we analyzed glasses and plagioclase feldspar crystal cores to characterize crystal cargoes and host liquids from pumice fall units from the minoan cycle santorini greece using this approach we identify the magmatic components that interacted prior to eruption and formation of pumice clasts allowing us to interpret the magma dynamics associated with each eruption varying degrees of complexity can be identified from relatively simple cases where the crystals are in isotopic equilibrium with the glass to more complex such as the large caldera forming minoan eruption which is characterized by at least two liquid components and three different crystal provenances

the contribution of experimental volcanology to the study of the physics of eruptive processes and related scaling issues a review abstract the experimental approach has become a major tool increasingly used by volcanologists in recent decades to investigate the physics of eruptive processes in complement to field and theoretical works researchers have developed various methodologies to study volcanic phenomena at reduced length scale the works involve natural or analogue materials and their types range from first order tests to identify fundamental processes and make qualitative comparison with field observations to more sophisticated experiments in which precise data obtained in a controlled environment can be used to validate outputs of theoretical models scaling is a central issue to ensure dynamic similarity between the small scale experiments and the large scale volcanic phenomena when natural conditions cannot be simulated due to inherent length scale difference and or technical limitations in this respect dimensionless numbers are used to map physical regimes and to define scaling laws which allow experimental results to be extrapolated to natural scale this review presents the variety of experimental studies conducted to investigate subterraneous and aerial volcanic phenomena involving in particular fluid particle mixtures we focus on the major scaling issues and the physical regimes investigated and we also highlight in a historical perspective some of the major advances achieved through experimental studies finally we conclude on some perspectives for future works

recent volatile evolution in the magmatic system of hekla volcano iceland estimates of the volatile budgets for volcanic eruptions are often based on volatile concentrations measured in melt inclusions mis versus groundmass glass here we present new measurements and estimates of pre eruptive volatile concentrations in magma from the hekla volcano in iceland based on mis in recent basalts and basaltic icelandites from the 2000 eruption the last eruption at hekla occurred from 26 february to 8 march 2000 it began with a short sub plinian phase followed by lava effusion that produced 0 17 km 3 of basaltic icelandite volatile s cl f and h2o and major element concentrations were measured in mis trapped in olivine and plagioclase phenocrysts contained in the basaltic icelandite from the 2000 eruption and in basalt erupted in 1913 from a fissure adjacent to the hekla volcano same elements were measured in the groundmass glass from the 2000 tephra the observed compositional range of mis from the basalt mgo 7 73 to the basaltic icelandite mgo 2 51 is readily explained by fractional crystallisation allowing the prediction of the evolution of dissolved volatile concentrations within the magma plumbing system beneath hekla the incompatible behaviour of the volatile elements controls their concentrations in mis during the crystal fractionation and consequently the highest concentrations are found in the most evolved basaltic icelandite mis with the notable exception of sulphur volatile concentrations in the basaltic mis exhibit strong linear correlations with k2o and this relationship can be used to estimate the theoretical expected volatile contents in the basaltic icelandite melt just prior to eruption such an approach avoids underestimation of the pre eruptive volatile contents measured in mis and improves constraints on the volatile mass release into the atmosphere the difference of volatile contents between expected concentrations and those present in the groundmass scaled to the mass of erupted magma yields maximum atmospheric mass loading of 0 10 mt hcl 0 17 mt hf and 3 77 mt so2 during the 2000 hekla eruption whereas calculations using the measured values in the inclusions give a significant lower mass yields of 0 05 mt hcl 0 17 mt hf and 0 6 mt so2 these results are discussed and compared to the data derived from remote sensing and snow proxy of the gas phase measurements 2007 elsevier b v all rights reserved

experimental and analytic modeling of piercement structures 1 piercement structures such as mud volcanoes hydrothermal vent complexes pockmarks and kimberlite pipes form during the release of pressurized fluids the goal of this work is to predict under which conditions piercement structures form from the insights gained by sand box experiments injecting compressed air through an inlet of width w at the base of a bed of glass beads of height h at an imposed critical velocity vf a fluidized zone consisting of a diverging cone like structure formed with morphological similarities to those observed in nature dimensional analysis showed that vf is correlated to the ratio of h over w in addition we derived an analytical model for vf which is compared to the experimental data the model consists of a force balance between the weight and the seepage forces imparted to the bed by the flowing gas the analytic model reproduces the observed correlation between vf and h w although a slight underestimate was obtained the results suggest that the gas particle seepage force is the main triggering factor for fluidization and that the commonly used proxy which the fluid pressure must equal or exceed the lithostatic weight needs to be reconsidered by combining the experiments and the model we derived critical pressure estimates which were employed to a variety of geological environments comparing the estimated and measured pressures prior to the lusi mud volcano shows that the presented model overestimates the critical pressures the model paves the way for further investigations of the critical conditions for fluidization in earth systems

explosive energy during volcanic eruptions from fractal analysis of pyroclasts abstract despite recent advances by means of experiments and high resolution surveys and the growing understanding of the physical processes before and during volcanic eruptions duration and type of eruptive activity still remain highly unpredictable this uncertainty hinders appropriate hazard and associated risk assessment tremendously in an effort to counter this problem experimentally generated pyroclasts have been studied by fractal statistics with the aim of evaluating possible relationships between eruption energy and fragmentation efficiency rapid decompression experiments have been performed on three differently porous sample sets of the 1990 1995 eruption of unzen volcano japan at 850 c and at initial pressure values above the respective fragmentation threshold u kueppers b scheu o spieler d b dingwell fragmentation efficiency of explosive volcanic eruptions a study of experimentally generated pyroclasts j volcanol geotherm res 153 2006 125 135 o spieler b kennedy u kueppers d b dingwell b scheu j taddeucci the fragmentation threshold of pyroclastic rocks epsl 226 2004 139 148 the size distribution of generated pyroclasts has been studied by fractal fragmentation theory and the fractal dimension of fragmentation df a value quantifying the intensity of fragmentation has been measured for each sample results show that size distribution of pyroclastic fragments follows a fractal law i e power law in the investigated range of fragment sizes indicating that fragmentation of experimental samples reflects a scale invariant mechanism in addition df is correlated positively with the potential energy for fragmentation pef while showing a strong influence of the open porosity of the samples results obtained in this work indicate that fractal fragmentation theory may allow for quantifying fragmentation processes during explosive volcanic eruptions by calculating the fractal dimension of the size distribution of pyroclasts it emerges from this study that fractal dimension may be utilised as a proxy for estimating the explosivity of volcanic eruptions by analysing their natural pyroclastic deposits

granite intrusion in a metamorphic core complex the example of the mykonos laccolith cyclades greece abstract the aegean domain is a well suited place to study the formation of metamorphic core complex mcc and to investigate the role of syn tectonic granites on their development in the northern cyclades the mykonos delos rhenia mcc is characterized by the intrusion of a kilometer scale late miocene pluton of i type granitoids within a migmatitic gneiss dome new combined ams anisotropy of magnetic susceptibility and microstructural studies on the mykonos granitoids together with recently published thermochronological data allow us to use the granitoids as strain markers the mykonos granitoids form a laccolith like intrusion with a n70 e long axis the laccolith is strongly asymmetric with an outlying root zone to the sw and a major body mainly developed to the ne the laccolith construction is due to successive pulses of more or less differentiated magma that intruded the cycladic blueschist unit the attitude of stretching markers suggests an important about 60 vertical axis local rotation phenomenon in the cycladic upper crust during the exhumation of the mykonos mcc structural data suggest a four stage evolution of the mykonos mcc i a first stage characterized by flat shearing toward the n ne and by the formation of a domal structure in migmatitic paragneisses with multi scale generation of folds with axes either perpendicular or parallel to the regional stretching as a result of the interplay between regional n20 e directed extension and ew shortening ii a second stage marked by the emplacement of the mykonos laccolith at 13 5 0 3 ma at the top of the migmatitic paragneisses iii the third stage corresponding to the development of protomylonitic foliations and lineations in the whole laccolith in high to medium temperature conditions and iv the late stage marked by an acceleration of the exhumation of the mykonos mcc this exhumation was accommodated by important rotations of upper crustal blocks during the end of the exhumation processes around 10 ma deformation localized at the top of the laccolith in semi ductile conditions and then in brittle conditions in the major detachment plane our study shows that the cycladic plutonism event had no role on the initiation of the mcc however the geometry of the mykonos intrusion supports that the magmas are sucked into the direction of regional extension and that the intrusion of magmas has caused an acceleration of the last stages of the mcc development this acceleration was marked by a very fast exhumation of the laccolith after its emplacement

water solubility and chlorine partitioning in cl rich granitic systems effects of melt composition at 2 kbar and 800 c abstract experiments have been conducted in the system na2o k2o al2o3 sio2 h2o cl2o 1 at 2 kbar and 800 c to determine the effects of melt composition on the solubility of water in haplogranite melt and on the distribution of cl between aqueous fluid and haplogranite melt the melts studied include peraluminous subaluminous and peralkaline haplogranites and quartz albite and quartz orthoclase compositions the solubility of water at 2 kbar and 800 c in water saturated haplogranite melts varies strongly as a function of melt composition water solubility in melt decreases in the order strongly peralkaline haplogranite quartz albite composition moderately peralkaline haplogranite peraluminous haplogranite subaluminous haplogranite quartz orthoclase composition d cl wt cl in fluid wt cl in melt is a strong function of system composition d cl increases as the concentration of cl in the system increases a comparison of the distribution of cl between haplogranite melts of subaluminous peraluminous and peralkaline compositions and aqueous fluids shows that with similar concentrations of cl in the system d cl is largest for subaluminous melts a nk 1 having relatively high k2o concentrations as the a nk of melt increases or decreases from 1 or as the n nk of the melt increases both d cl and the concentration of cl in the fluid decrease the experimental data imply that complexes involving cl and na in hydrous subaluminous granite melts are dominant furthermore the data imply that in hydrous peraluminous granite melts cl complexes with network modifying a13 and in hydrous peralkaline granite melts cl complexes with network modifying na k on a molar basis cl apparently complexes with network modifying a13 in peraluminous melts as strongly as it does with na and k in peralkaline melts experimental studies of cl partitioning in granitic systems suggest that the strongest enrichment of magmatic hydrothermal fluids in cl and ore metals complexed with cl will most likely occur in fluids exsolved from subaluminous granite magmas that are relatively enriched in k2o sio2 and cl and relatively depleted in f co2 and na2o

saturated and olefinic terrigenous triterpenoid hydrocarbons in a biodegraded tertiary oil of northeast alaska abstract dinorlupanes norlupanes olean 12 ene 18 olean 12 ene and urs 12 ene occur in a heavily biodegraded tertiary oil tested from the ocs y 0849 1 well drilled on the hammerhead prospect in the beaufort sea offshore northeast alaska these indicators and other source related characteristics of the hammerhead oil ring a degraded oleanoids ursanoids and lupanoids v and ni less than 2 0 ppm v v ni less than 0 5 indicate a land plant angiospermous character in the source facies the olefins in the hammerhead and canadian oils are considered to be contributed directly from the source rather than extracted from adjacent immature non source sediments during migration as indicated by a the accompanying presence in the oil of saturated angiosperm markers and b the absence of measurable amounts of other olefins characteristic of immature organic matter e g diasterenes and hopenes

caldera formation on santorini and the physiography of the islands in the late bronze age the caldera of santorini is a composite structure with a subsidence history extending over 100 ka or more geomorphological mapping shows that the present day caldera wall is a complex assemblage of cliff surfaces of different ages and that collapse at santorini has repeatedly exhumed earlier caldera cliffs and unconformities cliffs bounding the southern southeastern and northwestern rims of the caldera are morphologically fresh and probably formed during or soon after the minoan eruption in the late bronze age the well scalloped shape of these cliffs is attributed to large scale rotational landslip around the margins of the minoan caldera the deposit from one landslip is preserved subaerially minoan landslips in southeast santorini detached along the basement unconformity exposing a cliff of the prevolcanic island the caldera wall in the north northeast and east preserves evidence for three generations of cliff those of minoan age and two earlier generations of caldera wall the two early calderas can be dated relative to a well established statigraphy of lavas and tuffs the presence of in situ minoan tephra plastered onto the present day caldera wall provides evidence that these ancient caldera cliffs had already been exhumed prior to the minoan eruption field relationships permit reconstruction of the physiography of bronze age santorini immediately before the minoan eruption the reconstruction differs from some previously published versions and is believed to be the most accurate to date bronze age sa ntorini had a large flooded caldera formed 21 ka ago this caldera must have acted as an excellent harbour for the bronze age inhabitants of the island the 3 6 ka minoan eruption deepened and widened the extant caldera the volume of minoan collapse 25 km3 is in good agreement with published estimates for the volume of discharged magma if between 5 and 8 km3 of minoan ignimbrite ponded as intracaldera tuff

geochemistry and evolution of the calc alkaline volcanic complex of santorini aegean sea greece abstract volcanic activity on santorini started in upper pliocene times and is still in progress the last eruption occurred in 1950 at least seven eruptive centers were active at various times and some centers were active contemporaneously the overall chemical variations displayed by lavas and pyroclastics from the volcanic complex are largely explicable in terms of fractional crystallization involving removal of the observed phenocryst phases together with variable amounts of magma mixing and assimilation comparison of the chemistry of volcanic products from different eruption centers indicates long term variations in magma chemistry progressive depletion in lil elements and enrichment in compatible elements with time that cannot be explained in terms of fractionation mixing and assimilation such variations are attributed to processes occurring within the upper mantle trace element data require that the primitive lavas erupted on santorini were derived from an upper mantle source which was relatively depleted in lil elements compared with other calc alkaline volcanics and it is proposed that the source region contained a dominant refractory component which had experienced earlier events and a component derived from the subducted slab as magmatism progressed the contribution to the source region from the slab decreased due to either 1 cessation of subduction and hence a decrease in the proportion of slab derived material in the source region 2 a rise in geothermal gradient during melting so that the earliest melts contained a higher proportion of low melting slab derived material or 3 a combination of these processes we conclude that it is possible to see through intracrustal processes and to evaluate the processes which occur in the upper mantle beneath island arcs and we also conclude that the time integrated history of the mantle wedge above the subducted slab beneath island arcs must be taken into account when constructing viable models for are magmatism

the solubility of sulphur in hydrous rhyolitic melts experiments performed at 2 kbar in the temperature range 800 1000 c with fo2 between nno 2 3 and nno 2 9 where nno is the nickel nickel oxide buffer and varying amounts of sulphur added to hydrous metaluminous rhyolite bulk compositions were used to constrain the solubility of sulphur in rhyolite melts the results show that fs2 exerts a dominant control on the sulphur solubility in hydrous silicate melts and that depending on fo2 a rhyolitic melt can reach sulphur contents close to 1000 ppm at high fs2 at fo2 below nno 1 the addition of iron to a sulphur bearing rhyolite magma produces massive crystallization of pyrrhotite and does not enhance the sulphur solubility of the melt for a given fo2 the melt sulphur content increases with fs2 for fixed fo2 and fs2 temperature exerts a positive control on sulphur solubilities at least for fo2 below nno 1 the mole fraction of dissolved sulphur exhibits essentially linear dependence on fh2s at low fo2 and although the experimental evidence is less clear on fso2 at high fo2 the minimum in sulphur solubility corresponds to the redox range where both fh2s and fso2 are approximately equal a thermodynamic model of sulphur solubility in hydrous rhyolite melts is derived assuming that total dissolved sulphur results from the additive effects of h2s and so2 dissolution reactions the model reproduces well the minimum of sulphur solubility at around nno 1 in addition to the variation of the sulphide to sulphate ratio with fo2 a simple empirical model of sulphur solubility in rhyolitic melts is derived and shows good correspondence between model and observations for high silica rhyolites

experimental constraints on parameters controlling the difference in the eruptive dynamics of phonolitic magmas the case of tenerife canary islands we have performed phase equilibrium experiments to determine the pre eruptive conditions of the explosive eruption of montana blanca 2020 bp that occurred from a satellite vent located in the east flank of teide volcano tenerife island crystallization experiments were performed using a phonolitic obsidian from the fall out deposit that contains 5 wt anorthoclase diopside and magnetite with minor amounts of biotite and ilmenite set in a glassy matrix that contains microlites of ca rich alkali feldspars temperature was varied between 850oc and 800oc and pressure between 200mpa to 50 mpa the oxygen fugacity fo2 was varied between nno 0 2 0 2 log units above to the ni nio solid buffer to nno 2 whilst dissolved water contents varied from 7 to 1 5 wt comparison between natural and experimental phase proportions and compositions indicates that the main body of phonolite magma was stored at 850 15oc 50 20mpa 2 5 0 5wt h2o at an fo2 around nno 0 5 prior to eruption equivalent to depths between 1 to 2 km below the surface some clinopyroxene hosting h2o rich melt inclusions possibly originates from intermittent supply of phonolitic magma stored at somewhat deeper levels 100 mpa the ca and fe rich composition of alkali feldspar phenocrysts rims and microlites attests to the intrusion of a mafic magma in the reservoir just prior to eruption as borne out by banded pumices appearing in the later products of the eruptive sequence the comparison with other phonolitic magmas from tenerife and elsewhere e g vesuvius laacher see shows that differences in the eruptive dynamic of phonolitic magmas can be correlated to differences in storage depths along with variation in pre eruptive volatile contents

shear test results for cohesion and friction coefficients for different granular materials scaling implications for their usage in analogue modelling abstract laboratory tests have been carried out on dry granular materials such as quartz sand glass microspheres and sugar with different grain size rounding and sphericity the measurements have been made with a simple shear test machine for different values of normal stress 50 900 pa shear stress has been plotted against normal stress in order to determine the cohesion and coefficient of internal friction for the investigated materials resulting values of cohesion and coefficient of internal friction are mainly dependent on rounding and sphericity while grain size has a less significant influence further the behaviour of the materials for very small normal stresses 0 400 pa is more complex than previously assumed the fracture envelopes for all materials investigated are convex outward for this small range and converge towards a straight failure envelope with increasing normal stress finally in extensional faulting experiments there is no significant change in fault dip with increasing depth therefore the non linear behaviour for small normal stresses is best described as a dependence of the cohesion on the normal stress and not as a dependence of the coefficient of internal friction on the normal stress values for cohesion increase from 0 pa 15 pa at zero normal stress to 137 247 pa 15 pa for normal stresses greater than 250 400 pa the results show that well rounded spherical material is better suited to model brittle behaviour of rocks in crustal and lithospheric scale analogue models than less well rounded material since it has a smaller cohesion and a coefficient of internal friction which is closer to values of natural rocks

total grain size distribution and volume of tephra fall deposits on 17 june 1996 ruapehu volcano new zealand produced a sustained andesitic sub plinian eruption which generated a narrow tephra fall deposit extending more than 200 km from the volcano the extremely detailed data set from this eruption allowed methods for the determination of total grain size distribution and volume of tephra fall deposits to be critically investigated calculated total grain size distributions of tephra fall deposits depend strongly on the method used and on the availability of data across the entire dispersal area the voronoi tessellation method was tested for the ruapehu deposit and gave the best results when applied to a data set extending out to isomass values of 1 g m 2 the total grain size distribution of a deposit is also strongly influenced by the very proximal samples and this can be shown by artificially constructing subsets from the ruapehu database unless the available data set is large all existing techniques for calculations of total grain size distribution give only apparent distributions the tephra fall deposit from ruapehu does not show a simple exponential thinning but can be approximated well by at least three straight line segments or by a power law fit on semi log plots of thickness vs area 1 2 integrations of both fits give similar volumes of about 4 106 m3 integration of at least three exponential segments and of a power law fit with at least ten isopach contours available can be considered as a good estimate of the actual volume of tephra fall integrations of smaller data sets are more problematic

modification of the regional stress field by magma intrusion and formation of tabular granitic plutons granitic intrusions typically have large aspect ratios with an horizontal major axis about 4 8 times the vertical one combined structural and geophysical gravity data allows distinction between two main types of plutons flat floored plutons the most represented are rather thin 3 4 km and extend in every horizontal direction with a gently dipping floor toward several root zones these contrast with the thick 10 km wedge shaped plutons more elongated in one direction with a few root zones we interpret the shape of flat floored plutons as the result of a switch in the stress pattern caused by the emplacement of magma magma is preferentially emplaced into the plane 1 2 perpendicular to the least principal stress component 3 this plane is initially vertical except for compressional conditions this dilation causes a local re organization of the stress field by increasing the minor and intermediate principal stress components when they overcome the lithostatic load a drastic change in the orientation of the opening plane results switching from vertical to horizontal this constitutes a change from vertically oriented dike shaped intrusions to sub horizontal laccoliths crustal anisotropies vertical faults or horizontal zones of different rheology also contribute to modify the shape of the intrusions the continual exchange of the intermediate stress components also explains the rounded shape of intrusions in strongly extended regions our analysis suggests that the concept of magmas rising to a level of neutral buoyancy is not applicable to many settings rather we suggest that the feedback between displacements resulting from magma intrusion and the local stress pattern controls the geometry of magma emplacement

hydrothermal breccias in vein type ore deposits a review of mechanisms morphology and size distribution abstract breccias are among the most widely distributed rock textures found in hydrothermal vein type deposits previous studies have mainly been interested in developing qualitative descriptive approaches leading to a confusing profusion of terms brecciation originates in numerous ways resulting in highly complex classification systems and frequent misinterpretations of facies field observations are difficult to reconcile with physical theories of fragmentation partly due to the fact that few satisfactory quantitative tools have been developed a review of the main brecciation processes occurring in hydrothermal vein type deposits allows for the discrimination between chemical and physical mechanisms including tectonic comminution wear abrasion two types of fluid assisted brecciation hydraulic and critical volume expansion or reduction impact and collapse each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry including fragment morphology size distribution of the fragments fabric and dilation ratio the first two parameters are especially important because 1 the morphology of the fragments allows chemical and physical mechanical breccias to be distinguished and 2 the particle size distribution psd is a function of the energy input during breccia formation the slope of the cumulative psd fractal dimension ranges from high values for high energy brecciation processes to low values for low energy processes indicated by an isometric distribution the evolution of a vein system can be divided into three stages propagation wear and dilation these stages are separated by one threshold of mechanical discontinuity and one of hydraulic continuity these two thresholds also mark the transition between different types of brecciation mineralization occurs during all three stages and may display different textures due to pressure variations the use of quantitative parameters in fault related hydrothermal breccias allows a better understanding of the physical parameters related to a vein environment including structural setting and crustal level as well as fluid rock interactions recognition of the different breccia types could also be important during the early stages of mineral exploration

experimental study of chlorine behavior in hydrous silicic melts chlorine solubility in silicate melts has been investigated at 830 850 plus minus 5c and at pressures ranging from 50 to 200 mpa using both natural pantellerite rhyolite phonolite and synthetic sio sub 2 al sub 2 o sub 3 k sub 2 o na sub 2 o compositions and a stated h sub 2 o nacl kcl fluid phase near 4 molal at 100 mpa cl contents in pantelleritic melts reach a solubility plateau at initial aqueous phase molality near 2 this plateau coincides with a large immiscibility gap between aqueous and chloride rich fluids with the coexisting cl saturated aqueous phase cl ranges from 2 720 plus minus 120 ppm in rhyolite to 8 960 plus minus 85 ppm in pantellerite and reaches 6 270 plus minus 170 ppm in phonolite at 100 mpa between 50 and 200 mpa the cl content in pantelleritic melt decreases from 9 640 plus minus 200 ppm to 5 040 plus minus 150 ppm although cl solubility increases with increasing feo sup in high sio sub 2 melts it is mainly controlled by the al si and na k al molar ratios of the melt with a minimum at na k al 1 in a series of synthetic rhyolitic to pantelleritic melts the experimental results suggest that chlorine occurs as alkali chloride complexes in high sio sub 2 more melts they also indicate that cl is concentrated in the aqueous fluids in equilibrium with sio sub 2 rich melts the exact value of d depending on melt composition and melt chlorine concentration volcanic degassing will create chlorine rich hydrothermal fluids and decrease chlorine melt content less

s velocity structure and radial anisotropy in the aegean region from surface wave dispersion summary the lithospheric structure of the aegean region is investigated by analysis of rayleigh wave fundamental mode dispersion measurements isotropic 1 d models for almost 100 two station ray paths across the region display distinct variations in the moho depth and crustal s wave velocities the descending slab of the subducting african plate can be resolved down to 120 km depth beneath the volcanic arc three different regions are distinguished in terms of moho depth 1 the forearc with large crustal thicknesses between 38 and 48 km and an average of 43 km 2 the northern aegean with an average moho depth of 28 km and 3 the southern aegean central volcanic arc i e cyclades and sea of crete with an even thinner crust of around 25 km lateral variations in structure between 25 and 55 km depth indicate a marked difference between the western and eastern forearc collocated with pronounced changes in trench and slab geometry as well as published deformation rates s velocities between 25 and 55 km depth are low everywhere beneath the forearc but increase from the peleponnesus to crete an abrupt change occurs between western and central crete in terms of the visibility of the aegean moho and the seismic structure of the lithospheric mantle wedge an aegean mantle wedge with s velocities above 4 4 km s 1 is only observed to the east of central crete whereas to the west velocities of less than 4 0 km s 1 occur down to the plate contact these low velocities above the slab may indicate the presence of a melange of metamorphic rocks at the depths a low velocity asthenospheric layer is observed beneath the sea of crete and the cyclades below 40 km depth between the thinned lithosphere above and the slab below the observed radial anisotropy in the northern part of the aegean is likely to be due to preferred orientation of anisotropic minerals within the lower crust possibly caused by lateral ductile flow associated with recent lithospheric extension

recent geodetic unrest at santorini caldera greece 1 after approximately 60 years of seismic quiescence within santorini caldera in january 2011 the volcano reawakened with a significant seismic swarm and rapidly expanding radial deformation the deformation is imaged by a dense network of 19 survey and 5 continuous gps stations showing that as of 21 january 2012 the volcano has extended laterally from a point inside the northern segment of the caldera by about 140 mm and is expanding at 180 mm yr a series of spherical source models show the source is not migrating significantly but remains about 4 km depth and has expanded by 14 million m3since inflation began a distributed sill model is also tested which shows a possible n s elongation of the volumetric source while observations of the current deformation sequence are unprecedented at santorini it is not certain that an eruption is imminent as other similar calderas have experienced comparable activity without eruption

magma storage conditions of large plinian eruptions of santorini volcano greece the intensive variables of dacitic rhyodacitic magmas prior to four large plinian eruptions of santorini volcano over the last 200 kyr minoan cape riva lower pumice 2 and lower pumice 1 were determined by combining crystallization experiments with study of the natural products including the volatile contents of melt inclusions trapped in phenocrysts phase equilibria of the silicic magmas were determined at pressures of 1 2 and 4 kbar temperatures of 850 900 c fluid h2o co2 saturation xh2o molar h2o h2o co2 between 0 6 and 1 melt h2o contents of 2 10 wt and redox conditions of fmq fayalite magnetite quartz buffer or nno 1 where nno is ni nio buffer experiments were generally successful in reproducing the phenocryst assemblage of the natural products the phase relationships vary significantly among the investigated compositions revealing a sensitivity to small variations in whole rock compositions our results show that the pre eruptive storage conditions of the four silicic magmas were all very similar the magmas were stored at t 850 900 c and p 2 kbar under moderately reduced conditions nno 0 9 to 0 1 and were poor in fluorine 500 800 ppm and sulphur 100 ppm but rich in water and chlorine 5 6 wt and 2500 3500 ppm respectively in all cases the melts were slightly undersaturated with respect to h2o but most probably saturated with respect to h2o cl co2 and a brine the santorini magma plumbing system appears to be dominated by a large long lived 200 kyr predominantly silicic magma storage region situated at 8 km depth from which crystal poor melt batches were extracted during the largest caldera forming eruptions of the volcanic system

fractionation of metaluminous a type granites an experimental study of the wangrah suite lachlan fold belt australia abstract crystallisation experiments were performed on two metaluminous a type granite compositions ab412 and ab422 from the wangrah suite a representative a type granite suite from the lachlan fold belt south eastern australia ab412 is more mafic than ab422 and zircon saturation temperatures are 897 and 843 c respectively experiments were performed at 200 mpa f o 2 between nno and nno 1 05 in a temperature range between 700 and 900 c for various melt h 2 o contents experimental results were compared to the natural phase compositions to constrain the water content of the melt and the phases involved in fractionation processes in the wangrah suite with decreasing temperature fe ti oxide orthopyroxene and plagioclase are the first phases to crystallise followed by biotite the orthopyroxene stability is mainly restricted to temperatures above 750 c hornblende is only stable in the less evolved composition if the water content of the melt is at least 4 5 wt h 2 o the initial water content in the more mafic melt ab412 was between 2 and 3 wt h 2 o although orthopyroxene is not observed in the natural assemblages of the wangrah suite it has influenced the early fractionation of the wangrah suite granites mass balance calculations show that composition ab422 can be obtained after the crystallisation of 4 7 wt iron rich orthopyroxene plus 8 5 wt plagioclase from ab412

simulations of the explosive eruption of superheated fluids through deformable media the sudden release of superheated fluids at depth can cause surface disturbances in the form of vents mud volcanoes or seafloor pockmarks i have performed calculations with the sage hydrocode from los alamos and science applications international of superheated venting in an idealised geometry varying the pressure and velocity of hot fluid injected at depth the simulations show several different patterns of propagation and fracturing in the deformable overburden the simulations performed so far show for different conditions upward propagating cylindrical pipes with hardened walls narrowly diverging conical pipes cone sheets downward propagating cracks and funnel shaped craters

mfci experiments on the influence of nacl saturated water on phreatomagmatic explosions abstract molten fuel coolant interaction mfci experiments were performed using remelted foiditic rock samples from the west eifel volcanic field germany two experimental series were carried out with one magmatic melt and two water compositions bi distilled water was used in the first series dw 1 to dw 5 in the second series sw 1 to sw 5 the bi distilled water was saturated 350 g l 1 with sodium chloride nacl for both experimental series the fragmentation history and the energy release were recorded and compared the smallest particles 125 m were studied using scanning electron microscopy sem most mfci experiments with bi distilled water reached higher explosion intensities than the experiments with the saline water this was accompanied by higher particle ejection velocities as well as the formation of more fine grained and more interactive particles of angular shape additionally the smallest artificial pyroclasts were examined by evolved gas analyses ega the particles from the mfci experiments with salt solutions are found to contain more sodium hydroxide naoh these observations can be explained by thermodynamic arguments in contrast to the mfci experiments with pure water an additional reaction occurs with saline water that results in evolution of hydrogen chloride hcl gas and leaves a residue of sodium hydroxide the mfci process with saline water consumes more enthalpy and gibbs free energy so that less energy is available for the explosion with other sodium halides dissolved in the water naf nabr or nai the additional reaction can be predicted to have greater or lesser effects on phreatomagmatic explosions

comparative analyses of glass fragments from brittle fracture experiments and volcanic ash particles explosive volcanic eruptions are characterized by the rapid fragmentation of a magmatic melt into ash particles in order to describe the energy dissipation during fragmentation it is important to understand the mechanism of material failure a quantitative description of fragmentation is only possible under controlled laboratory conditions industrial silicate glasses have a high structural affinity with magmatic melts and have the advantage of being transparent which allows the study of the evolution of fractures by optical methods on a time scale relevant for explosive volcanism with this aim a series of low speed edge on hammer impact experiments on silicate glass targets has been conducted leading to the generation of fragments in the grain size spectra of volcanic ash in order to verify the general transferability of the experimentally generated fragmentation dynamics to volcanic processes the resulting products were compared by means of statistical particle shape analyses to particles produced by standardized magma fragmentation experiments and to natural ash particles coming from deposits of basaltic and rhyolitic compositions from the 2004 grimsvotn and the quaternary tepexitl tuff ring eruptions respectively natural ash particles from both grimsvotn and tepexitl show significant similarities with experimental fragments of thermally pre stressed float glasses indicating a dominant influence of preexisting stresses on particle shape and suggesting analogous fragmentation processes within the studied materials

intrusion triggering of the 2010 eyjafjallajokull explosive eruption the ash cloud that brought chaos to european air traffic in april this year was the result of emissions from an icelandic volcano that had been intermittently active for about 18 years a combination of detailed space based geodetic measurements and seismic monitoring of the eyjafjallajkull volcano in the run up to the ash producing explosive summit eruption reveals an unusual deformation pattern that may be attributed to its off rift setting with relatively cool subsurface structure and limited magma at shallow depth as to the predictability of such a dramatic reawakening the immediate precursors to the initial eruption of the volcano in 2010 were subtle and difficult to detect but the clear signs of volcanic unrest during the weeks months and years preceding it may provide better clues to the catastrophic explosion

the size distribution of pyroclasts and the fragmentation sequence in explosive volcanic eruptions in an explosive eruption the atmospheric column dynamics depend strongly on the mass fraction of gas in the erupting mixture which is fixed by fragmentation in the volcanic conduit at fragmentation gas present in vesicular magmatic liquid gets partitioned between a continuous phase separating magma clasts and a dispersed phase in individual bubbles within the clasts as regards flow behavior it is the former continuous gas phase which matters and we show that its amount is determined by the fragment size analysis of 25 fall deposits and 37 flow deposits demonstrates that ash and pumice populations follow a power law size distribution such that n the number of fragments with radii larger than r is given by n r d d values range from 2 9 to 3 9 and are always larger than 3 0 in fall deposits d values for pyroclastic flow deposits are systematically smaller than those of fall deposits we show that at fragmentation the amount of continuous gas phase is an increasing function of the d value large d values cannot be attributed to a single fragmentation event and are due to secondary fragmentation processes laboratory experiments on bubbly magma and on solid pumice samples demonstrate that primary breakup leads to d values of 2 5 0 1 and that repeated fragment collisions act to increase the d value a model for size dependent refragmentation accounts for the observations we propose that in a volcanic conduit fragmentation proceeds as a sequence of events primary breakup releases a small amount of gas and is followed by fragment collisions due to refragmentation and decompression both the mass and volume fractions of continuous gas increase the final d value and hence the mass fraction of continuous gas at the vent depends on the time spent between primary fragmentation and eruption out of the vent

partitioning behavior of chlorine and fluorine in the system apatite silicate melt fluid the partitioning behavior of cl among apatite mafic silicate melt and aqueous fluid and of f between apatite and melt have been determined in experiments conducted at 1066 to 1150 c and 199 205 mpa the value of dclapatite melt wt fraction of cl in apatite cl in melt 0 8 for silicate melt containing less than 3 8 wt cl at higher melt cl contents small increases in melt cl concentration are accompanied by large increases in apatite cl concentration forcing dclapatite melt to increase as well melt containing less than 3 8 cl coexists with water rich vapor that containing more cl coexists with saline fluid the salinity of which increases rapidly with small increases in melt cl content analogous to the dependency of apatite composition on melt cl content this behavior is due to the fact that the solubility of cl in silicate melt depends strongly on the composition of the melt particularly its mg ca fe and si contents once the melt becomes saturated in cl additional cl must be accommodated by coexisting fluid apatite or other phases rather than the melt itself because cl solubility depends on composition the cl concentration at which dclapatite melt and dclfluid melt begin to increase also depends on composition the experiments reveal that dfapatite melt 3 4 in contrast to cl the concentration of f in silicate melt is only weakly dependent on composition mainly on melt ca contents so dfapatite melt is constant for a wide range of composition the experimental data demonstrate that the fluids present in the waning stages of the solidification of the stillwater and bushveld complexes were highly saline the cl rich apatite in these bodies crystallized from interstitial melt with high cl f oh ratio the latter was generated by the combined processes of fractional crystallization and dehydration by its reaction with the relatively large mass of initially anhydrous pyroxene through which it percolated

breaking news on the formation of volcanic ash fracture dynamics in silicate glass abstract in explosive volcanic eruptions magmatic melts behave like brittle solids under rapid loading volcanic ash particles predominantly are generated by brittle fragmentation induced within pre stressed magma in volcanic conduits here we present straightforward measurements of fracture area velocity i e surface generation rates in analog materials under volcanic time and deformation rates using a high resolution high speed camera at up to 2 5 million frames per second surface generation rates are directly linked to energy dissipation and can be related to pyroclast formation during explosive volcanism according to our findings pre existing stress fields play a crucial role for the evolution of cracks control the dynamics of fracture area growths during fragmentation and thus strongly modify the production of volcanic ash

experimental modelling of shallow magma emplacement application to saucer shaped intrusions abstract saucer shaped dolerite and sandstone intrusions are common in sedimentary basins world wide we have conducted a series of scaled experiments simulating the process of magma emplacement in sedimentary basins with particular attention on the formation of saucer shaped sills the model materials were 1 cohesive fine grained silica flour representing brittle crust and 2 molten low viscosity oil representing magma the experiments were performed in both homogeneous and layered models in all the experiments oil injection resulted in doming of the surface in the homogeneous models the injected oil formed cone sheets and sub vertical dykes cone sheets formed for shallow injection 1 3 cm and vertical dykes formed for deeper injection 4 5 cm in layered models the injected oil always formed saucer shaped intrusions our experimental results show that 1 sill intrusion results in the formation of a dome with melt erupting at the rim 2 layering controls the formation of sills and saucer shaped sills 3 saucer shaped sills are fed from the bottom and the fluid flows upward and outward and 4 the diameter of saucer shaped sills increase with increasing emplacement depth the systematic relation between domes and sills and the depth dependence of sill diameters show that saucer shaped intrusions result from the interaction between a growing flat lying shallow sill and doming of the free surface we conclude that saucer shaped intrusions represent fundamental geometries formed by shallow magma intrusion in stratified basins

the fragmentation threshold of pyroclastic rocks in response to rapid decompression porous magma may fragment explosively this occurs when the melt can no longer withstand forces exerted upon it due to the overpressure in included bubbles this occurs at a critical pressure difference between the bubbles and the surrounding magma in this study we have investigated this pressure threshold necessary for the fragmentation of magma here we present the first comprehensive high temperature experimental quantification of the fragmentation threshold of volcanic rocks varying widely in porosity permeability crystallinity and chemical composition we exposed samples to increasing pressure differentials in a high temperature shock tube apparatus until fragmentation was initiated experimentally we define the fragmentation threshold as the minimum pressure differential that leads to complete fragmentation of the pressurized porous rock sample our results show that the fragmentation threshold is strongly dependent on porosity high porosity samples fragment at lower pressure differentials than low porosity samples the fragmentation threshold is inversely proportional to the porosity of the other factors permeability likely affects the fragmentation threshold at high porosity values whereas chemical composition crystallinity and bubble size distribution appear to have minor effects the relationship for fragmentation threshold presented here can be used to predict the minimum pressure differential necessary for the initiation or cessation of the explosive fragmentation of porous magma

the effect of total grain size distribution on the dynamics of turbulent volcanic plumes abstract the impact of explosive volcanic plumes on climate and on air traffic strongly depends on the concentration and grain size distribution gsd of pyroclastic fragments injected into the atmosphere accurate and robust modelling of the evolution of gsd during pyroclast transport from the vent to the ash cloud is therefore crucial for the assessment of major volcanic hazards analysis of field deposits from various recent plinian eruptions shows that their total gsd is well described by a power law as expected from the physics of magma fragmentation with an exponent d ranging from 3 0 to 3 9 by incorporating these measured gsd into the initial conditions of a steady state 1d model of explosive eruption columns we show that they have a first order impact on the dynamical behaviour of explosive eruption columns starting from an initial value of d the model tracks the evolution of gsd in the column and calculates the dynamical consequences of particle sedimentation the maximum height reached by the column one of the first order results relevant to aircraft safety changes by 30 for mass fluxes of 10 7 kg s 1 or larger and by 45 85 for mass fluxes between 105 and 10 7 kg s 1 depending on exponent d we compare our predictions to a specially assembled set of geologic field data and remote sensing observations from 10 plinian eruptions for which maximum column height and mass flux are known independently the incorporation of realistic power law gsd in the model greatly improves the predictions which opens new perspectives for estimation of ash load and gsd in volcanic clouds from near real time measurements available from satellite payloads our results also contribute to the improvement of volcanic source term characterization that is required input for meteorological dispersion models

conditions for the growth of a long lived shallow crustal magma chamber below mount pelee volcano martinique lesser antilles arc 1 the compositional homogeneity of silicic andesites emitted during the 13 500 year long last eruptive cycle of mount pelee suggests that the physical state of the magma chamber was largely unmodified during this period experimental phase equilibria on mount pelee recent products indicate that pre eruptive magma temperatures and pressures were in the range of 875 900 c and 2 0 5 kbar respectively the estimated average eruption rate was 7 5 10 4 km3 a with an average volume of about 0 3 km3 per eruption an analytical model for a spherical magma chamber indicates that a magma flux of 4 5 10 4 km3 a can maintain a magma chamber of 0 3 km3 above 875 c below mount pelee however observations of plutons suggest that magma chambers may grow by addition of sheet like intrusions with numerical simulation we show that a minimum sheet accretion rate of a few centimeters per year is required to grow a persistently active magma chamber independently of the intruded volumetric flux this minimum injection rate is higher if the heat transfer is enhanced by convection processes the limited ability of an arc crust to extend and accommodate dikes suggests that magma injections are sills or if they are dikes that most of the volume injected in the magma chamber is eventually erupted in a conductively cooling igneous body formed by sills injected at a rate of a few centimeters per year most of the injected magma completely solidifies and only a small part of the body about 10 20 is above 875 c and able to feed eruptions

implications of incremental emplacement of magma bodies for magma differentiation thermal aureole dimensions and plutonism volcanism relationships abstract field observations and geophysical data indicate that many igneous bodies grow by amalgamation of successive magma pulses that commonly take the shape of horizontal sheets sills emplacement styles and emplacement rates of magma bodies have fundamental implications on magma differentiation country rock metamorphism and assimilation and for the formation of large magma chambers in the upper crust when a magma body begins to grow by slow accretion of sills each successive intrusion solidifies before the injection of the next one when the system is thermally mature sill temperatures equilibrate above the solidus melts accumulate and older sills can re melt the time needed for each magma injection to cool down and equilibrate with its surrounding is short relatively to the total emplacement time of the body the transition from a mafic crystal poor magma to a partially molten rock that retains a highly differentiated melt is fast whereas the resulting evolved residual melt can reside in the crust for protracted periods as long as temperatures in the system are relatively low highly differentiated melts are generated which may explain the bi modal character and the absence of intermediate compositions in some magmatic provinces the level of emplacement of successive magma pulses controls the shape of the thermal anomaly associated with the magma body growth metamorphism partial melting and assimilation of the country rock are favoured if successive magma sheets are emplaced at or close to the country rock magma body boundary if the magma emplacement rate is low the size of the thermal aureole is controlled by the size of one pulse and not by the size of the entire igneous body understanding emplacement of magma bodies is fundamental for our understanding of the plutonism volcanism relationship magma emplacement rates of several centimetres per year are needed for a magma body to evolve into a large magma chamber able to feed large silicic explosive eruptions the time averaged emplacement rates of plutons are lower than this critical emplacement rate eruptions of 100s to 1000s cubic kilometres of silicic products show that such high volumes of magmas can accumulate in the upper crust this suggests that the emplacement of magma bodies is a multi timescale process with the development of large magma chambers corresponding to the highest magma fluxes because they control magmatic processes and the impact of magma intrusion on the country rock future studies should focus on magma emplacement rates and on magma emplacement geometries these studies should integrate field observation on plutons and geophysical data on active magmatic systems coupled with laboratory experiments and numerical simulations

use of vegetable oil and silica powder for scale modelling of magmatic intrusion in a deforming brittle crust in the upper crust intrusive bodies adopt different configurations depending on the tectonic setting this paper describes a new technique for analogue modelling of such intrusions specifically of low viscosity magma into a deforming brittle crust proper dynamic scaling is an important consideration if the crust has a coulomb failure envelope the model material should have a cohesion c of 40 pa to 7500 pa if the intruding magma is highly mobile the model fluid should have a viscosity of 4 10 9 pa s to 75 pa s for the model crust we have used crystalline silica powder si crystal siliceous microspheres si sphere of grain size 30 m and a mixture si mix of both materials the mechanical properties of these powders have been obtained by shear and tension shear tests si crystal powder is cohesive c 300 pa angle of internal friction 45 and represents competent rock si sphere powder is much less cohesive c 10 pa 25 and represents incompetent rock si mix has intermediate properties the model magma is a vegetable oil which solidifies at room temperature its viscosity when molten is 2 10 2 pa s at 50 c using these materials we have done some preliminary experiments to investigate the intrusion of low viscosity magma into sedimentary basins in non deformed settings intrusions were saucer shaped cone sheets in horizontal extension they were steep dykes finally in horizontal shortening intrusions were basal sills that branched into thrust faults

decadal to monthly timescales of magma transfer and reservoir growth at a caldera volcano caldera forming volcanic eruptions are low frequency highimpact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days with devastating effects on local and global scales1 because no such eruption has been monitored during its long build up phase the precursor phenomena are not well understood geophysical signals obtained during recent episodes of unrest at calderas such as yellowstone usa and campi flegrei italy are difficult to interpret and the conditions necessary for large eruptions are poorly constrained2 3 here we present a study of pre eruptive magmatic processes and their timescales using chemically zoned crystals from the minoan caldera formingeruption of santorini volcano greece4 which occurred in the late 1600s bc the results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption5 6 despite the large volume of erupted magma4 40 60 cubic kilometres and the 18 000 year gestation period between the minoan eruption and the previous major eruption most crystals in the minoan magma record processes that occurred less than about 100 years before the eruption recharge of the magma reservoir by large volumes of silicic magma and some mafic magma occurred during the century before eruption and mixing between different silicicmagmabatches was still taking place during the final months final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period with major growth phases immediately before eruption these observations have implications for the monitoring of long dormant but potentially active caldera systems

grain size characteristics of experimental pyroclasts of 1980 mount st helens cryptodome dacite effects of pressure drop and temperature using the fragmentation bomb we analysed the effects of temperature and pressure drop on the grain size characteristics of experimentally produced pyroclasts experiments performed on vesicular samples of grey dacite of the 1980 mount st helens cryptodome at t 20 900 c and initial pressure differential up to 18 5 mpa provide clear evidence of the influence of these physical conditions upon fragment size and character cylindrical dacite samples diameter 17 mm length 50 mm are placed in the high pressure temperature section of the apparatus heated and saturated by argon gas the disruption of a diaphragm located between the high and low pressure sections of the apparatus initiates the rapid depressurisation of the sample the main results may be summarised as follows 1 increasing tempera ture from 20 to 900 c results in a decrease in the fragmentation threshold value from 9 to 3 mpa and an increase in the median diameter of the experimental pyroclasts these observations imply a decrease in the dynamic tensile strength of dacite at higher temperatures which in turn influences the characteristic size of fragments 2 increasing initial pressure differential yields a decrease of the median diameter thus a higher initial elastic potential energy in the magma generates a higher degree of fragmentation 3 fragments of angular shape are observed from experiments at all investigated temperatures 20 900 c including thereby temperatures significantly higher than the classical dilatometrically or calorimetrically determined glass transition temperature determined for this dacite of 810 c thus brittle response of the dacite is observed under rapid decom pression 4 fragment size distributions do not corre spond to log normal distributions and are more closely described by rosin rammler distributions with a de crease of temperature and increase of the initial pressure differential fragment size distributions approach a rosin rammler distribution dependence 5 microscopic and grain size comparison of particle characteristics of ex perimental and natural fragments of the 1980 mount st helens cryptodome dacite demonstrate similar median diameters and shapes

two models for the formation of magma reservoirs by small increments abstract it is now clear that magma reservoirs develop over long time intervals out of a large number of individual intrusions evidence from some large volcanic deposits including those of the bishop tuff california and fish canyon tuff colorado indicates that such reservoirs may experience pervasive and rapid heating before catastrophic eruptions injection of hot primitive melt in the reservoir is often invoked to explain these observations but this requires the rapid emplacement of a large magma volume at least 25 km 3 in less than 100 years for the bishop tuff and efficient heat transfer through a thick cumulate pile within a magma body that grows incrementally temperatures rise progressively and may eventually lead to a permanent volume of melt temperature and crystallization follow two completely different paths depending on the thickness of individual intrusive sheets in one limit corresponding to thick sheets crystallization proceeds at equilibrium initial magma batches crystallize completely and a permanent body of melt develops progressively once ambient temperatures in the complex rise above the solidus in the other limit corresponding to thin sheets crystallization is kinetically controlled such that initial intrusions do not crystallize completely and preserve a glassy residue once temperatures within the growing magma pile reach a certain threshold value nucleation and growth of crystals get reactivated in the residual glass crystallization then proceeds catastrophically in a positive feedback loop involving latent heat release and temperature rise thus an initial phase with no evolved melt present ends with the sudden formation of a large volume of evolved melt in a crystal mush after this initial phase new intrusions get emplaced in heated surroundings and follow a thermal path similar to that of the equilibrium case with melts that become increasingly more primitive with time evidence for kinetic controls on crystallization in the natural environment is provided by the significant amounts of glass up to 40 that are found in thin isolated basaltic sills and dykes owing to sluggish crystallization kinetics more glass should be generated in andesitic and dacitic magmas emplaced in similar conditions devitrification of such quantities of glass accounts for the rapid heating of a thick sill complex the two models of magma reservoir formation involve different requirements the intrusion thickness must be smaller than a critical value in the kinetic model and the average magma input rate must exceed a threshold value in the equilibrium model for a given injection rate a permanent magma reservoir forms in a shorter time interval and over a smaller cumulative magma thickness in the kinetic model than in the equilibrium one the kinetic model is such that the amount of evolved melt generated increases with decreasing injection rate in contrast to the equilibrium model for which the opposite relationship holds