electrical conductivity of orthopyroxene and its high pressure phases electrical conductivity of orthopyroxene clinopyroxene and ilmenite garnet with the same starting material san carlos orthopyroxene mg 0 92 fe 0 08 sio 3 containing 2 89 al 2 o 3 by weight were measured within their respective stability fields in a multi anvil press in the formula for conductivity 0 exp h kt pre exponential factors 0 of orthopyroxene clinopyroxene and ilmenite garnet are 5248 1778 2239 s m respectively and the activation enthalpies are 1 80 1 87 and 1 66 ev respectively these results are required for defining a laboratory based conductivity depth profile of the upper mantle

magmatic precursors to the 18 may 1980 eruption of mount st helens usa perhaps the most difficult task facing volcanologists today is that of distinguishing between low level volcanic restlessness and activity that presages a full scale eruption we illustrate these difficulties by reexamining the sequence of events that led to the 18 may 1980 eruption of mount st helens activity that is often presented as a classic example of early phreatic explosions leading to a magmatic eruption this interpretation is problematic however given the known ascent of juvenile magma to within 250 m of the surface prior to the climactic event reexamination of ash samples from several precursory events shows that small amounts of juvenile material were erupted as early as 28 march 1980 just two weeks after the first seismic signals of reawakening and that the juvenile content of the ash had probably increased by early may the magmatic component of these eruptions was not recognized at the time because of the high crystallinity of the juvenile material a signature of extensive degassing induced crystallization during magma ascent identification of juvenile material in the precursory ash from mount st helens has important implications for initiation of eruptive activity

effect of iron content on electrical conductivity of ringwoodite with implications for electrical structure in the transition zone abstract electrical conductivity of ringwoodite with various iron contents fe fe mg 0 09 0 2 and 0 3 was measured at pressure 20 gpa and temperature up to 1900 k conditions of the lower part of the mantle transition zone in a kawai type multi anvil apparatus the conductivity increased with increasing total iron content all electrical conductivity data were fitted to the formula of electrical conductivity 0 xfe exp h kt where 0 is the pre exponential term xfe is the mole fraction of iron content in the mg site h is the activation enthalpy k is the boltzmann constant and t is absolute temperature the activation enthalpy becomes higher at a certain temperature at high temperatures the activation enthalpy decreased from 1 44 to 0 92 ev with increasing total fe content at low temperatures less than 1000 k the activation enthalpy also decreases from 1 15 to 0 74 ev with total fe content dependence of the activation enthalpy on fe content suggests that the dominant mechanism of charge transport is fe2 fe3 hopping small polaron recent electrical conductivity depth profiles of the transition zone beneath the pacific ocean obtained from the electromagnetic induction study shows that the conductivity values between 520 and 660 km depths may be explained by ringwoodite with fe fe mg 0 10 on the other hand assuming a normal geotherm conductivity values beneath the continent or stable craton are considerably lower than those of ringwoodite with fe fe mg 0 10 taking into consideration results from the global seismic tomographic studies relatively low conductivity in these regions can be explained by the existence of a cooler region compared with the surrounding mantle rather than the presence of iron poor ringwoodite or a combination of both

mud plumbing system of an isolated phreatic eruption at akita yakeyama volcano northern honshu japan abstract a small phreatic eruption occurred on 16 august 1997 at the flank of a dacite lava dome of akita yakeyama northern honshu japan air falls and viscous mudflows were discharged from two craters mudflow effusion preceded discrete explosions followed by a fine ash discharge the air fall deposit consists of an upper fine ash deposit and a lower ballistic dominated poorly sorted tephra in which ranges in grain size from fine ash to blocks of ca 50 cm both air fall and mudflow deposits were composed of fine mud and coarse lithic fragments which contained abundant liquid water lithic fragments comprise fresh dacite of the host lava dome and hydrothermally altered stratocone andesite intensely altered andesite fragments contain quartz cristobalite andalusite pyrophyllite 7 a kaolin and anhydrite some mineral assemblages indicate hydrothermal temperatures greater than 300 c rare sandstone fragments are likely to be lacustrine from ca 1000 m depth the surface morphology of the mudflow deposits indicates that the mud contained ca 30 vol water the cube root similarity rules on crater size and the cloud shape of buried explosions provided energy of 3 5 10 9 j at depths of 6 10 m based on the observed crater size 20 m and fountain like cloud shape the depth estimate is consistent with the abundance of coarse dacite fragments derived from shallow lava in the explosion deposit thermodynamic energy release of ca 1 10 11 j was calculated based on the following estimated parameters product volume of 1 10 3 m 3 hydrothermal temperatures of 300 350 c and pressures of 11 24 mpa corresponding to the estimated source depth the thermodynamic estimation represents the total energy released during the eruption whereas the similarity rule yields an energy value as created by discrete explosions mud ascended from a hot aquifer at 1000 m depth first effused as a mudflow and was then expelled explosively from another crater explosivity depends on the shallow geologic structures reduction of pressure within the shallow permeable breccia resulted in effusive mudflow whereas overpressure confined by rigid dacite lava yielded explosive eruptions the mud plumbing system which includes deep aquifer mud and shallow explosions seems to be typical of phreatic eruptions

emplacement of pyroclastic density currents pdcs in a deep sea environment the val d aveto formation case northern apennines italy abstract the occurrence of pdc deposits in a foredeep basin sequence named val d aveto formation 32 29 ma northern apennines italy provides new information on the behavior of pyroclastic density currents entering the water in this work stratigraphic petrographic and mineralogical features that characterize three pyroclastic deposits have been described and analyzed in the field facies and lithological analysis on the blocky size fraction and in the laboratory image analyses on the blocky size detritus optical analyses of the microtextures mineralogical analyses through x ray powder diffraction xrpd and scanning electron microscope with energy dispersive x ray spectometry sem eds the deposits are lapilli to blocky size with a blocky size fraction constituted of accidental detritus in thin sections their groundmass texture varies from porphyritic to eutaxitic where coarser particles become close each others growth rims have been also detected around plagioclase crystals pyrite habits and oxidation and plagioclase albitization are consistent with hydrothermal temperature conditions of 200 c all these results have been compared with the information provided by modern examples of pdc deposits and laboratory experiments on the behavior of water hot particles mixing grain to grain collision has been considered as the main flow mechanism that sustained and avoided the disaggregation of the pdcs entering the water

a review on phreatic eruptions and their precursors abstract an analysis of the reported information on 132 historical phreatic events indicates that most of these 115 were not followed by a magmatic or phreatomagmatic eruption only in 18 cases precursory phenomena are reportedly lacking whereas they are recognized for the majority 72 of the considered cases these precursors have been analyzed as a function of the kind of phreatic event and of its possible triggering mechanism unfortunately the quality of the available information is poor however data suggest that anomalous seismicity ground deformation changes in the output chemistry and temperature of fumaroles and thermal springs are potential mid term precursors whereas seismic tremor is a common short term precursor

investigation of the failure mechanism and stabilization of a landslide in weathered tuffite giresun northeastern turkey this study investigates the causes and failure mechanism of the aksu landslide that occurred during the construction of the giresun espiye road between km 1 030 1 170 in northern turkey and recommends proper stabilization techniques for the purpose of investigating the causes and mechanism of this slope failure engineering geological mapping geotechnical investigation and rock mass characterization were performed from top to bottom weathered tuffite tuffite flysch and dacitic tuffite were the major units in the study area the disturbance of the slope by the excavations performed at the toe of the slope i e due to the foundation excavation for the tunel restaurant building and for the road cut led to a translational slide the translational slide occurred in completely weathered tuffite due to the disturbance of the stability of the slope by the excavations performed at the toe of the slope particularly for the foundation excavation of the tunel restaurant building and for the road cut along the giresun espiye road the rise in the groundwater level was also another important factor that has contributed to the occurrence of the landslide after establishing the geometry of the landslide in detail the shear strength parameters of the failure surface were determined by the back analysis method sensitivity analyses were performed and landslide failure mechanisms were modeled to quantify the contributing factors that have caused the formation of the aksu landslide the influence of an earthquake was investigated through pseudostatic slope stability analysis toe buttressing ground water drainage and surface water drainage alternatives were considered for stabilizing the slope

on the heterogeneous electrical conductivity structure of the earth s mantle with implications for transition zone water content 1 we have investigated the lateral variations in mantle electrical conductivity structure using electromagnetic sounding data for this purpose we used very long time series up to 51 years of geomagnetic observatory data at six locations encompassing different geological settings to compute response functions that cover the broadest possible frequency range 3 9 to 95 2 days furstenfeldbruck fur europe hermanus her south africa langzhou lzh china alice springs asp australia tucson tuc united states north america and honolulu hon united states north pacific we inverted the response functions beneath each observatory for a local radial conductivity profile using a stochastic sampling algorithm specifically we found significant lateral variations in conductivity throughout the mantle with resolution limited to the depth range 500 1200 km at 600 km depth conductivity varies between 0 1 and 0 4 s m and increases to 1 3 2 0 s m at 800 km depth beneath all stations except her 0 5 s m at 900 km depth conductivity increases further to 1 4 2 4 s m with her hon and asp being most conductive this trend persists to a depth of 1200 km comparison with conductivity profiles constructed from laboratory measurements of mantle mineral conductivities and models of earth s mantle composition and thermal state reveal that significant thermochemical variations are at the origin of the observed heterogeneities in mantle conductivity found here because of the somewhat large error bounds on sampled conductivity profiles and the reduced sensitivity of the electromagnetic sounding data above 500 km depth constraints on transition zone water content are less conclusive although h2o contents 0 5 wt in the midtransition zone appear less likely

electrical conductivity of pyrope rich garnet at high temperature and high pressure garnet is one of the important constituent minerals in the upper mantle and the transition zone of the earth s mantle however there were very few previous works on its electrical conductivity we have measured the electrical conductivity of single crystal of pyrope rich garnet py73 alm14 grs13 under the conditions of 4 16 gpa 873 1473 k and frequency range from 10 2 to 106 hz with a range of water content from less than 10 to 7000 h 10

the eclogite garnetite transformation at high pressure and some geophysical implications mineral assemblages displayed by morb and alkali poor olivine tholeiites have been investigated over the pressure interval 4 6 18 gpa at 1200 c both compositions crystallize to form normal eclogites between 4 6 and 10 gpa and there is little change in the relative proportions of garnet and pyroxene over this range however the proportion of garnet increases rapidly above 10 gpa as pyroxene dissolves in the garnet structure and pyroxene free garnetites stishovite are produced by 14 15 gpa dependent upon composition the garnetite facies for both compositions possess zero pressure densities of 3 75 g cm3 implying that subducted oceanic crust remains appreciably denser than surrounding mantle to depths exceeding 600 km it is demonstrated that the seismic velocity distributions in the mantle between 400 and 650 km are inconsistent with anderson s hypothesis that this region is of eclogitic composition

3 d modelling and analysis of dst c responses in the north pacific ocean region revisited summary during the last decade a number of one dimensional 1 d conductivity profiles have been constructed for the upper and mid mantle of the north pacific ocean region these profiles differ significantly and from our point of view it is still unclear which profile is the best candidate for the upper and mid mantle conductivity reference model for this region keeping the differences in mind and inspired by recent findings that the ocean effect is a major contributor to the anomalous behaviour of c responses up to the period of 20 days especially at coastal observatories the goal of this paper has been three fold 1 to understand on the basis of systematic model studies using 3 d ocean models which of the published 1 d upper and mid mantle profiles is in best agreement with the available observations 2 to try to reduce the misfit between the observed and modelled responses by using dense grids in modelling by considering 3 d models which include not only an inhomogeneous surface layer but also inhomogeneous deeper structures 3 to derive an alternative 1 d upper and mid mantle section for the north pacific ocean by carefully selecting the data for interpretation and by using 3 d models that are as realistic and detailed as possible in order to perform the simulations using realistic 3 d models on a routine basis a novel 3 d spherical forward solution has been elaborated in this paper the solution combines the modified iterative dissipative method with a conjugate gradient iteration and allows one to compute efficiently the electromagnetic fields in full 3 d spherical models with very high lateral contrasts of conductivity and for very dense grids during the 3 d simulations a systematic shift of observed c responses at honolulu compared with those at other observatories was detected the reason for this shift is still unclear even if a very detailed grid of 0 3 0 3 is used the 3 d simulations using a model of the inhomogeneous surface has no notable ocean effect to c responses at this site an attempt has been made to reduce the misfit between observed and modelled c responses by incorporating a 3 d model with inhomogeneous lithosphere and upper mantle however this has resulted only in a slight change in responses the main conclusion drawn from our 3 d model studies is that there exists a significant disagreement between observed and 3 d modelled c responses if the published 1 d sections with conducting uppermost 400 km are considered as the upper and mid mantle sections our 3 d simulations and reinterpretation of the data also confirm the recent finding that the upper and mid mantle beneath north pacific ocean in the depth range down to 400 km is much more resistive than hitherto assumed

water solubility in majoritic garnet in subducting oceanic crust 1 water in majoritic garnet synthesized in the mid oceanic ridge basalt morb h2o composition at 20 gpa and 1400 1500 c was measured by secondary ion mass spectrometry sims and infrared spectroscopy we found that the majorite contains 1130 to 1250 ppm oh by weight the infrared absorption band showed that incorporation of the hydroxyl in majorite is most likely due to the hydrogarnet substitution our results indicate that water can be transported into the mantle transition zone by nominally anhydrous minerals such as omphacite and majorite in the subducting basaltic crust such water may have great influences on the physical properties of slab in the transition zone

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

volcanic hazards from bezymianny and bandai type eruptions major slope failures are a significant degradational process at volcanoes slope failures and associated explosive eruptions have resulted in more than 20 000 fatalities in the past 400 years the historic record provides evidence for at least six of these events in the past century several historic debris avalanches exceed 1 km3 in volume holocene avalanches an order of magnitude larger have traveled 50 100 km from the source volcano and affected areas of 500 1500 km2 historic eruptions associated with major slope failures include those with a magmatic component bezymianny type and those solely phreatic bandai type the associated gravitational failures remove major segments of the volcanoes creating massive horseshoe shaped depressions commonly of caldera size the paroxysmal phase of a bezymianny type eruption may include powerful lateral explosions and pumiceous pyroclastic flows it is often followed by construction of lava dome or pyroclastic cone in the new crater bandai type eruptions begin and end with the paroxysmal phase during which slope failure removes a portion of the edifice massive volcanic landslides can also occur without related explosive eruptions as at the unzen volcano in 1792 the main potential hazards from these events derive from lateral blasts the debris avalanche itself and avalanche induced tsunamis lateral blasts produced by sudden decompression of hydrothermal and or magmatic systems can devastate areas in excess of 500km2 at velocities exceeding 100 m s 1 the ratio of area covered to distance traveled for the mount st helens and bezymianny lateral blasts exceeds that of many pyroclastic flows or surges of comparable volume the potential for large scale lateral blasts is likely related to the location of magma at the time of slope failure and appears highest when magma has intruded into the upper edifice as at mount st helens and bezymianny debris avalanches can move faster than 100 ms 1 and travel tens of kilometers when not confined by valley walls avalanches can affect wide areas beyond the volcano s flanks tsunamis from debris avalanches at coastal volcanoes have caused more fatalities than have the landslides themselves or associated eruptions the probable travel distance l of avalanches can be estimated by considering the potential vertical drop h data from a catalog of around 200 debris avalanches indicates that the h l rations for avalanches with volumes of 0 1 1 km3 average 0 13 and range 0 09 0 18 for avalanches exceeding 1 km3 h l ratios average 0 09 and range 0 5 0 13 large scale deformation of the volcanic edefice and intense local seismicity precede many slope failures and can indicate the likely failure direction and orientation of potential lateral blasts the nature and duration of precursory activity vary widely and the timing of slope faliure greatly affects the type of associated eruption bandai type eruptions are particularly difficult to anticipate because they typically climax suddenly without precursory eruptions and may be preceded by only short periods of seismicity

grain growth kinetics of majorite and stishovite in morb abstract grain growth rates of majorite and stishovite in their aggregates with morb composition were studied at 18 gpa and temperatures ranging from 1873 to 2223 k the rates of grain growth were expressed by g n g 0 n k 0 t exp h r t where g is the grain size at time t s and g 0 is the initial grain size we determined the grain growth kinetic parameters for majorite where n 9 1 1 3 h 950 249 kj mol and log k 0 32 5 2 3 m 9 1 s for the graphite capsule and log k 0 31 3 3 9 m 9 1 s for the re capsule kinetic parameters for stishovite were determined to be n 6 6 0 9 h 599 226 kj mol and log k 0 30 6 0 9 m 6 6 s for the graphite capsule and log k 0 29 0 1 1 m 6 6 s for the re capsule

connectivity of molten fe alloy in peridotite based on in situ electrical conductivity measurements implications for core formation in terrestrial planets abstract the connectivity of molten fe s in peridotite has been experimentally investigated by means of in situ electrical conductivity measurements at high temperatures and 1 gpa starting materials were powdered mixtures of peridotite klb 1 with various amounts 0 3 6 13 19 24 vol of the 1 gpa eutectic composition in the fe fes binary system at temperatures above the eutectic point in the fe fes system 980 c and below the solidus of klb1 1200 c molten fe s in a solid silicate matrix interconnects when the volume fraction is over 5 conductivity temperature paths indicate that in the presence of partial silicate melting the connectivity of molten fe s in a peridotite matrix is inhibited based on observations of retrieved samples the percolation threshold of fe s melts in the presence of low to moderate degrees of silicate melt is estimated at 13 2 vol these results indicate that if the volume fraction of fe alloy in a planetesimal was initially greater than 5 and if early heating by decay of radionuclides raised the temperature of the interior above the fe alloy melting point initial metal segregation was controlled by permeable flow of molten iron alloy in a solid silicate matrix these conditions were likely met by many terrestrial objects in the early solar nebula efficient removal of residual fe alloy 5 vol from silicate requires high degree melting of silicate so that metal can segregate as droplets giant impacts during the final stage of accretion of large planetary objects could supply the energy required for high degrees of melting alternatively if initial metal segregation were delayed until a planetary object grew to large size 1000 km in diameter release of gravitational potential energy due to metal segregation could contribute enough heat to form a magma ocean

first gas and thermal measurements at the frequently erupting gamalama volcano indonesia reveal a hydrothermally dominated magmatic system abstract the first gas and thermal measurements at the summit of the gamalama volcano indicate that the system is dominated by hydrothermal processes this is highlighted by the prevalence of h2s over so2 h2s so2 2 8 a high co2 so2 ratio 76 201 and a low heat transfer 3 0 mw to the surface a relative variation in gas composition is observed along the degassing fracture zone possibly due to partial s scrubbing despite this surface hydrothermal signature the system exhibits high gas equilibrium temperatures 425 480 c indicating that fluids are not exclusively derived from a boiling hydrothermal aquifer but also sourced by cooling and crystallizing basaltic magma at deep that continues to inject magmatic fluids into the system this hydrothermally dominated activity on gamalama possibly persisted over the last two decades during which a high number of eruptive events were witnessed the period coincides with the opening of large fractures at the summit that subsequently shifted the volcanic activity from the crater center to the peripheral fractures zones these fractures that possibly developed in response to the regional geodynamics have weakened the hydrothermal seal allowing the pressure developed by the hydrothermal magmatic system and promoted by the high annual rainfall to rapidly exceeds the tensile strength of the seal leading to the numerous phreatic eruptions

continuous mixing of crystal mush and replenished magma in the ongoing unzen eruption zoning profiles of magnetite phenocrysts in the successively effused dacite of the ongoing unzen eruption from 1991 wereanalyzed to estimate the time scale of magma mixing the dacite was formed by mixing of relatively high and low temperature t end member magmas the magnetite phenocrysts derived from the low t magma are reversely zoned by the mixing with high t magma a diffusion calculation for reequilibration of the reverse zonings gives the time interval from magma mixing to quenching for the mixed dacite erupted from may 1991 to may 1993 the typical diffusion time was estimated to be a few months regardless of the effused sequence for 2 yr this indicates that the mixing was continuous during the effusion the invariability of the other mixing signatures such as the thickness of reaction rims around biotite phenocrysts also supports the continuous mixing model low t end member magma is estimated by mass balance calculation to be a crystal rich mush of dacitic composition these observations lead to a model wherein the highly crystallized remnant magma of the preceding activity has been mixed with the newly injected hot magma of similar bulk composition just prior to the effusion the proposed mechanism implies that this type of magma mixing is an inevitable process in periodically erupting polygenetic volcanoes

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

design of anchorage and assessment of the stability of openings in silty sandy limestone a case study in turkey abstract this study presents a procedure for the design of anchorage and for the assessment of the stability of openings in silty sandy limestone through investigating the geotechnical problems of the hasankeyf historical settlement area in southeastern turkey of which a good portion will stay below the reservoir of the proposed ilisu dam rock mass characterization was performed the rmr and gsi methods were utilized for rock mass classification the roclab software was used to determine the shear strength parameters and the geomechanical properties of the rock mass according to the gsi method the cohesion and angle of internal friction of the rock mass was determined as 257 kpa and 52 respectively a back analysis was applied to a structurally controlled planar failure block supporting one of the prominent historical structures in the area to determine the shear strength parameter pairs that satisfy limit equilibrium along the sliding surface of the planar block a sensitivity analysis of the most likely shear strength pairs satisfying limit equilibrium was performed as a function of reservoir water condition i e rapid drawdown dry and wet reservoir condition and the expected earthquake generated peak horizontal ground acceleration coefficient the results of the back analysis led to a cohesion of 161 kpa and an angle of internal friction of 40 along the failure surface of the planar block a limit equilibrium sensitivity analysis of the unstable rock block was performed as a function of the water condition of the reservoir expected earthquake generated peak horizontal ground acceleration coefficient and rock anchor inclination angle the minimum anchor force required for the stabilization of the planar block was calculated for a rapid drawdown condition as 4000 kn m a total of fifty six 56 rock anchors each with a service load capacity of 1000 kn and spaced at 1 m are recommended for stability finite element analysis was utilized to analyze the collapse of some of the roofs of the adjacent man made cave dwellings carved in rock due to insufficient pillar thicknesses and to determine the minimum pillar thickness required between adjacent caves in the region for stability nine different pillar thicknesses ranging from 0 1 to 0 93 m were analyzed the stages included in the finite element analysis of the caves were a gravity loading due to the thickness of the overburden followed by applying the far field horizontal stresses and inserting the planar block fracture b excavating the caves in stressed rock assuming full face excavation and c applying a uniform traction load the results of the finite element analysis led to a recommendation to apply a steel arch support to one of the adjacent caves located at hasankeyf in case the wall thickness was less than or equal to 0 5 m

mantle transition zone beneath a normal seafloor in the northwestern pacific electrical conductivity seismic thickness and water content abstract we conducted a joint electromagnetic em and seismic experiment to reveal the mantle structure beneath a normal seafloor at 130 145 ma in the northwestern pacific where the seafloor is relatively flat and the underlying mantle is expected to be normal free from tectonic perturbations in the experiment we deployed state of the art instruments in two arrays from 2010 2015 here we report the result of analyses of the em and seismic data for investigating the mantle transition zone mtz structure the em data analysis revealed that an electrical conductivity structure below both arrays was approximated by an average 1 d model of the north pacific and showed a possible downward increase in conductivity at the top of the mtz from the p wave receiver function analysis perturbations in the mtz thickness from a global average were estimated to be 20 km and 2 km below the northern and southern arrays respectively from which temperature profiles in the mtz below these two arrays were then estimated we jointly interpreted the profiles of electrical conductivity and thus estimated temperature with reference to the experimental values of the effects of water on the electrical conductivities of mtz minerals wadsleyite and ringwoodite from mineral physics the upper bound of the water content below the northern array was determined to be 0 4 wt or 0 04 wt depending on different results of mineral physics and that below the southern array was determined to be slightly smaller the lower bound of the water content was not constrained by our data our results indicate that the mtz beneath the normal seafloor in the northwestern pacific is drier than subduction zones and may be a water poor region in a plum pudding mantle model

phase transformations in subducted oceanic crust and buoyancy relationships at depths of 600 800 km in the mantle abstract phase transformations in a representative oceanic crust composition morb have been studied at pressures up to 28 gpa at 1200 c and 1500 c using a multi anvil apparatus the assemblage of majorite casio 3 rich perovskite stishovite which is displayed by the morb composition at pressures above 20 gpa was found to transform further into an assemblage containing a new aluminous phase at pressures above 25 gpa this al phase has a complex composition and is also relatively sodium rich its x ray diffraction pattern is similar to that observed for mgal 2 o 4 calcium ferrite type and is tentatively indexed on the basis of an orthorhombic cell yielding a zero pressure density of 3 87 2 g cm 3 majorite garnet was found to remain as the most abundant phase at the highest pressure studied 28 gpa and does not appear likely to transform to perovskite until pressures exceed 29 30 gpa these results imply that the basaltic crust component of subducted oceanic lithosphere would be 0 1 0 2 g cm 3 less dense than surrounding mantle pyrolite between the depths of 660 800 km thereby confirming an earlier hypothesis of anderson moreover the underlying layer of harzburgite would be 0 05 g cm 3 less dense than pyrolite throughout most of this depth interval these buoyancy relationships contribute to a barrier which impedes and may sometimes prevent the entry of slabs into the lower mantle

experimental constraints on phreatic eruption processes at whakaari white island volcano vigorous hydrothermal activity interspersed by sequences of phreatic and phreatomagmatic eruptions occur at whakaari white island volcano new zealand here we investigate the influence of sample type hydrothermally altered cemented ash tuffs and unconsolidated ash lapilli and fragmentation mechanism steam flashing versus gas expansion on fragmentation and ejection velocities as well as on particle size and shape our rapid decompression experiments show that fragmentation and ejection speeds of two ash tuffs cemented by alunite and amorphous opal increase with increasing porosity and that both are significantly enhanced in the presence of steam flashing ejection speeds of unconsolidated samples are higher than ejection speeds of cemented tuffs as less energy is consumed by fragmentation fragmentation dominated by steam flashing results in increased fragmentation energy and a higher proportion of fine particles particle shape analyses before and after fragmentation reveal that both steam flashing and pure gas expansion produce platy or bladed particles from fracturing parallel to the decompression front neither fragmentation mechanisms nor sample type show a significant influence on the shape our results emphasize that under identical pressure and temperature conditions eruptions accompanied by the process of liquid water flashing to steam are significantly more violent than those driven simply by gas expansion therefore phase changes during decompression and cementation are both important considerations for hazard assessment and modeling of eruptions in hydrothermally active environments

electrical conductivity anisotropy of deformed talc rocks and serpentinites at 3 gpa abstract the electrical conductivity anisotropy of deformed natural talc rocks and serpentinites was investigated using a kawai type multi anvil press in the temperature range of 500 1000 k at 3 gpa the electrical conductivities of the samples were measured by an impedance analyzer with a frequency range of 10 3 10 6 hz along three sample directions the direction parallel to the lineation of oriented minerals x direction the direction perpendicular to the lineation on the foliation plane y direction and the direction perpendicular to the foliation z direction for both rock types electrical conductivities parallel to the x and the z directions were the highest and the lowest respectively electrical conductivities of talc rocks and serpentinites were at least two orders of magnitude lower than previous reports electrical conductivities of the serpentinites were higher than those of the talc rocks electrical conductivity anisotropy for the talc rocks was stronger than that for the serpentinites at the same oxygen buffer condition electrical conductivity and its anisotropy of the serpentinites become higher with higher oxygen fugacity the activation enthalpy of talc rocks was the lowest 0 59 ev in the x direction and highest 0 68 ev in the z direction the activation enthalpies of the serpentinites in different directions show similar values about 0 74 ev and 0 68 ev for the experiments using mo and ni electrodes respectively impedance spectra for both rock types show the presence of two conduction paths grain interior and grain boundary conductions the total electrical conductivities were reduced by grain boundary conduction electrical conductivities of hydrous minerals show strong dependence on hydrogen concentration and hydrogen mobility the conduction mechanism probably was proton migration through extrinsic vacancies derived from a presence of ferric iron perpendicular to the c axis of the crystals and through interstitial mechanisms parallel to the c axis in both warm and cold subduction zones high electrical conductors 10 1 5 s m cannot be explained by the presence of talc or serpentinites the electrical conductivity anisotropy in a subduction zone would be inconspicuously small within one order unless we consider other well aligned high conductive phases

source mechanism of a very long period event at mt ontake central japan response of a hydrothermal system to magma intrusion beneath the summit abstract a very long period vlp volcanic event which occurred on 25 january 2007 beneath mt ontake central japan was recorded by nearby broadband seismometers as well as the japanese nationwide hi net and f net seismic networks the vlp waveforms show a pulse like shape with a duration of approximately 1 min the vlp event was accompanied by a burst sequence of long period lp events we carried out waveform inversion to determine the source mechanism and location of the vlp event our analysis indicates volumetric changes in an inclined crack seismic moment of 10 14 nm at the vlp source which is located at 0 6 km above sea level beneath the summit of mt ontake and above dikes determined from gps data the source time functions of the vlp event showed a pulse like triangular shape indicating inflation followed by deflation of the crack at the source we interpreted the result of the waveform inversion as follows gases released from the intruded magma heated an aquifer system beneath the summit of mt ontake a break of unstable superheated water in a hydrothermal crack in the system caused vaporization of water and associated crack inflation which was followed by discharge of steam from the crack resulting in its collapse these processes caused the vlp event which may have been a precursor of a small phreatic eruption that occurred in late march 2007

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

hydrothermal alteration of surficial rocks at solfatara campi flegrei petrophysical properties and implications for phreatic eruption processes abstract solfatara crater is located within the campi flegrei caldera to the west of naples italy it is one of the largest fumarolic manifestations known and the rocks hosting the hydrothermal system are affected by intense hydrothermal alteration alteration can result in changes of degassing behavior and in the formation of a cap rock thereby increasing the probability of phreatic eruptions here we investigate the effects of alunitic solfataric alteration on the mineralogy the physical properties porosity density permeability and the mechanical properties strength of the rocks involved as well as its influence on fragmentation and ejection behavior our results show that the pristine mineralogy of deposits from the vicinity of the solfatara cryptodome and from pisciarelli is almost completely replaced by amorphous silica and alunite the differences in the degree of alteration among the samples series are reflected in the investigated properties and behavior as well as in the analysis of the experimentally generated particles alunitic alteration increases porosity and permeability whereas it reduces density elastic wave velocity and strength leading to higher fragmentation and ejection speeds for the sample series examined in this study our results also show that alteration results in the generation of a high fraction of fines particle sizes

variations in the electrical conductivity of the upper mantle beneath north america and the pacific ocean variations in the electrical conductivity of the mantle beneath carty lake in the canadian shield tucson in the southwest united states and honolulu and midway in the north central pacific were determined through the inversion of long period magnetotelluric and geomagnetic depth sounding data inversion of computed response functions is carried out using a minimum structure regularized approach the upper mantle beneath carty lake is approximately an order of magnitude more resistive than the upper mantle beneath tucson and nearly 1 5 orders of magnitude more resistive than honolulu and midway island inversions were also carried out where the minimum structure constraint was removed at known upper mantle discontinuities these models show a jump in conductivity of 1 5 orders of magnitude across the 660 km discontinuity a result that is consistent with laboratory experiments on realistic mantle assemblages mantle conductivity profiles at carty lake are significantly more resistive than those at tucson honolulu and midway to depths of 300 400 km these observations likely reflect differing thermal states the presence or absence of partial melt and volatiles and may also be related to chemical differences between depleted and undepleted upper mantle the observed conductivity variations may be interpreted as lateral variations in temperature partial melt and or dissolved hydrogen in olivine

the 1989 submarine eruption off eastern izu peninsula japan ejecta and eruption mechanisms the submarine eruption of a new small knoll which was named teishi knoll off eastern izu peninsula behind the izu mariana arc occurred in the evening of 13 july 1989 this is the first historic eruption of the higashi izu monogenetic volcano group the eruption of 13 july followed an earthquake swarm near ito city starting on 30 june there were subsequent volcanic tremors on 11 and 12 july and the formation of the teishi knoll on the 100 m deep insular shelf 4 km northeast of ito city there were five submarine explosions which were characterized by intermittent domelike bulges of water and black tephra jets which occurred within 10 min on 13 july ejecta of the eruption was small in volume and composed of highly crystalline basalt scoria highly vesiculated pumice and lithic material petrographical features suggest that the pumice was produced by vesiculation of reheated wet felsic tuff of an older formation the teishi knoll before the eruption was a circular dome 450 m across and 25 m high with steep sides and a flat summit considerations of submarine topographic change indicate the knoll was raised by sill like intrusion of 106 m3 of magma beneath a 30 m thick sediment blanket this shallow intrusion is assumed to have started on 11 july when volcanic tremors were observed for the first time but there was no indications of violent interaction between wet host sediments and intruding magma the submarine eruption of 13 july appears to have been friggered by a major lowering of the magma column the basalt scoria having crystal contents of more than 60 is assumed to be derived from the cooled plastic margin of the shallow intrusive body however glassy scoria which would indicate the interaction between hot fluidal magma and external water was not observed a scenario for the 1989 submarine eruption is as follows when rapid subsidence of the hot interior of the intrusive magma occurred reduced pressure caused the implosion of cooled plastic magma adjacent pressurized hot host material and wet sediment the mixing of these materials triggered the vigorous vapor explosions

water in the mantle results from electrical conductivity beneath the french alps 1 a deep magnetotelluric sounding in the french alps provided a vertical electrical conductivity profile between 200 1000 km two prominent features are observed first the conductivity in the depth range 400 800 km is smaller than the conductivity of a pyrolite mantle obtained from laboratory results for a normal geotherm second the data do not require the conductivity to change throughout the transition zone 410 660 km in this part of the mantle a temperature of 350 450 c less than normal explains the magnetotelluric conductivity profile at 200 400 km our model favors a cold mantle with 1000 1500 ppm of water dissolved in olivine if correct this model suggests that the subducted slab is dehydrated before reaching the transition zone

electrical conductivity of stishovite as a function of water content abstract the electrical conductivity of stishovite with various al2o3 and h2o contents was measured at 12 gpa of pressure p and temperatures t up to 1900 k in a kawai type multi anvil apparatus starting materials were pre synthesized at 12 gpa and 1673 k from various mixtures of sio2 al2o3 and al oh 3 the synthesized stishovite aggregates contained various h2o concentrations up to 0 25 wt the conductivity of relatively dry stishovite was almost constant independently of al content whereas the conductivity significantly increased with increasing h2o content in stishovite all electrical conductivity data fit the formula for electrical conductivity 0 c w exp h 0 c w 1 3 kt where 0 is the pre exponential term cw is the h2o concentration h0 is the activation enthalpy at very low h2o concentration and k is the boltzmann constant the activation enthalpy decreased from 1 22 to 0 90 ev with increasing h2o content from 0 01 to 0 22 wt a nearly linear correlation of the conductivity values on the h2o content suggests that the dominant mechanism of charge transport in stishovite is proton conduction although electrical conductivity of hydrous stishovite is higher than that of garnet in the subducted oceanic crust small amount of hydrous stishovite is insufficient to raise conductivity on the other hand hydrous stishovite can contribute to the high conductivity occasionally observed at the mantle transition zone if the subducted archean continental crusts with tonalite trondhjemite granodiorite ttg composition were accumulated above the 660 km seismic discontinuity

a geophysical perspective on mantle water content and melting inverting electromagnetic sounding data using laboratory based electrical conductivity profiles abstract this paper applies electromagnetic sounding methods for earth s mantle to constrain its thermal state chemical composition and water content we consider long period inductive response functions in the form of c responses from four stations distributed across the earth europe north america asia and australia covering a period range from 3 9 to 95 2 days and sensitivity to 1200 km depth we invert c responses directly for thermo chemical state using a self consistent thermodynamic method that computes phase equilibria as functions of pressure temperature and composition in the na 2 o cao feo mgo al 2 o 3 sio 2 model system computed mineral modes are combined with recent laboratory based electrical conductivity models from independent experimental research groups yoshino 2010 and karato 2011 to compute bulk conductivity structure beneath each of the four stations from which c responses are estimated to reliably allocate water between the various mineral phases we include laboratory measured water partition coefficients for major upper mantle and transition zone minerals this scheme is interfaced with a sampling based algorithm to solve the resulting non linear inverse problem this approach has two advantages 1 it anchors temperatures composition electrical conductivities and discontinuities that are in laboratory based forward models and 2 at the same time it permits the use of geophysical inverse methods to optimize conductivity profiles to match geophysical data the results show lateral variations in upper mantle temperatures beneath the four stations that appear to persist throughout the upper mantle and parts of the transition zone calculated mantle temperatures at 410 and 660 km depth lie in the range 1250 1650 c and 1500 1750 c respectively and generally agree with the experimentally determined temperatures at which the measured phase reactions olivine spinel and spinel ferropericlase perovskite occur the retrieved conductivity structures beneath the various stations tend to follow trends observed for temperature with the strongest lateral variations in the uppermost mantle for depths 300 km conductivities appear to depend less on the particular conductivity database conductivities at 410 km and at 660 km depth are found to agree overall with purely geophysically derived global and semi global one dimensional conductivity models both electrical conductivity databases point to 2 o in the upper mantle for transition zone minerals results from the laboratory database of yoshino 2010 suggest that a much higher water content up to 2 wt h 2 o is required than in the other database karato 2011 which favors a relatively dry transition zone 2 o incorporating laboratory measurements of hydrous silicate melting relations and available conductivity data allows us to consider the possibility of hydration melting and a high conductivity melt layer above the 410 km discontinuity the latter appears to be 1 regionally localized and 2 principally a feature from the yoshino 2010 database further there is evidence of lateral heterogeneity the mantle beneath southwestern north america and central china appears wetter than that beneath central europe or australia

phreatomagmatism and its relevance abstract phreatomagmatic explosive volcanism results from the interaction of magma with external water groundwater or surface water close to or at the earth s surface magma of any composition acid to ultrabasic may be involved in this type of explosive activity at present the relevance of phreatomagmatism is realized increasingly because it takes place in many diverse environments and affects not only small monogenetic volcanoes but also large volcanoes at some volcanoes as for example at lake taupo new zealand a volume of several tens of km 3 of magma may have been mixed with several km 3 of external water phreatomagmatism has thus become an important aspect in volcanic hazard assessments other fields involving the interaction of water with a melt are the study of nuclear and other industrial safety hazards of magma mixing of diamond carrying volcanism and of hydrothermal ore deposits as well as geothermal and groundwater reservoirs experiments on the dynamics of magma water interactions provide increasing insight into the principles and hazards of phreatomagmatic explosions this type of research will become a new field in experimental petrology

a semi global reference model for electrical conductivity in the mid mantle beneath the north pacific region 1 one dimensional electrical conductivity structure in the mid mantle of the one fourth of the earth beneath the north pacific ocean was obtained by a semi global electromagnetic induction study electromagnetic response functions estimated from electric field variations measured by submarine cables and geomagnetic field variations obtained by magnetic observatories and long term observations sites were inverted into radially symmetric conductivity distribution by taking the distribution of land and ocean at the surface into account as a most preferred model a smooth conductivity depth profile was obtained with two abrupt increases that possibly correspond to the seismic discontinuities at 410 and 660 km

casio3 perovskite may cause electrical conductivity jump in the topmost lower mantle the electrical conductivity of casio3 perovskite was measured in situ between 17 24 gpa and 1300 2000 k using a multi anvil apparatus and solartron 1260 impedance gain phase analyzer in the frequency range of 107 1 hz the activation energies are 95 100 and 100 120 kj mol and the activation volumes are 0 06 0 08 and 0 46 0 03 cm3 mol at 1300 1800 and 1800 2000 k respectively conduction under lower mantle conditions may be dominated by the ionic diffusion of oxygen the electrical conductivity of casio3 perovskite is higher than that of bridgmanite majoritic garnet and ferropericlase the main constituents of the topmost lower mantle therefore casio3 perovsktie may significantly contribute to the electrical structure of the topmost lower mantle in spite of its relatively small volume proportion

heat source of the 2014 phreatic eruption of mount ontake japan we present petrological evidence of the shallow magmatic processes that may have supplied heat and gas to the eruption of mount ontake japan on 27 september 2014 which resulted in 63 fatalities ash from the eruption comprises primarily hydrothermally altered white toned rock fragments however the ash contains trace amounts 0 7 wt of vitreous less altered particles laps which are only altered on their surfaces suggesting rapid ascent through the hydrothermal system the laps are classified into two categories glassy and crystalline glassy laps comprise high silica rhyolitic glass 74 83 wt sio2 with rounded quartz chalcedony free vesicles and reversely zoned plagioclase cores 47 mol an rims 70 mol an indicating magma re heating crystalline laps have a groundmass like texture that suggests eutectic crystallization at shallow depths thermodynamic calculations indicate that the pre eruptive temperatures of the glassy and crystalline laps were 700 1300 c and 700 c respectively and that the storage depth was 4 km pressure 100 mpa the observed petrological features suggest that the laps were sourced from a magma recently intruded at shallow depths although crustal deformation i e the volume change associated with magmatic intrusion was insignificant prior to the 2014 eruption a clear signature of crustal deformation was observed in 2007 the source of which was located 3 km below the summit we suggest that the magma that was intruded 3 km below the summit in 2007 supplied the heat and gas for the 2014 phreatic eruption

hydrothermal eruptions of nisyros dodecanese greece past events and present hazard abstract the detailed analysis of the craters of hydrothermal eruptions and related products present on nisyros island demonstrates the ephemerality of these morphological forms in other words the mere recognizable existence of the craters and associated deposits implies recency of hydrothermal activity the minimum temperature required to cause the explosive phenomenon and possibly the depth of the reservoir which can be evaluated on the basis of the correlation between the diameter of the crater and the depth of explosion as proposed by fytikas and marinelli 1976 are therefore closely representative of the current hydrothermal circulation both field evidence and historical records indicate that all the deposits of hydrothermal eruption recognized on nisyros island were emplaced as debris flows almost all the ballistic ejecta were entrained in these debris flows and either redeposited far from their landing sites or involved in later crater collapse and erosion this emplacing mechanism implies that the original products were characterized by a water content higher than about 5 by weight steam driven hydrothermal eruptions one of which took place in 1871 originated deposits of limited dispersion as no sign of these erodible products can be found in the field today surface geology and fluid geochemistry together with subsurface information e g primary and hydrothermal lithologies distribution of temperature with depth physical chemical characteristics of deep water bearing zones indicate that two distinct hydrothermal aquifers are present underneath the southeastern part of the caldera floor both aquifers were probably involved in the most important historically documented hydrothermal eruptions which occurred in 1873 at that time violent earthquakes fractured the brittle aquiclude separating the two aquifers and caused a sudden transfer of fluids from the deep to the shallow aquifer thus triggering the hydrothermal eruptions hydrothermal eruptions will probably occur in future and this hazard must be taken into serious consideration the southern half of lakki plain where all past eruptions took place and active fumaroles are concentrated is the zone at highest risk at present gas geochemistry represents an effective tool to detect changes in the p t conditions of the shallow aquifer and particularly the phenomena of pressure build up that may lead to a hydrothermal eruption

magnetotelluric evidence of the tectonic boundary between the rio de la plata craton and the pampean terrane chaco pampean plain argentina the extension of the transbrasiliano lineament abstract the transbrasiliano lineament represents a continental shear belt that transversely intersects the south american platform from nne to ssw much evidence of this lineament exists to the north but it remains uncharacterized in the distal andean foreland to the south where it is associated with the tectonic boundary between the rio de la plata craton and the pampean terrane this tectonic boundary is mostly unexposed in the chaco pampean plain argentina debate continues about the existence of an east or west dipping subduction zone and a later collisional event between the terranes here we report the results of a magnetotelluric survey along a w e profile at 27 s between 63 45 and 60 30 w to characterize the geoelectric structure the magnetotelluric data were processed the dimensionality and distortion of the geoelectrical medium were analyzed and a 2 d inversion model was developed the distribution of the resistivities at the lithospheric scale indicates a highly resistive crust 20 000 m on the east side of the profile that is correlated with the rio de la plata craton on the west side of the profile a less resistive but still highly resistive crust 12 000 m is correlated with the pampean terrane the highly resistive blocks are separated by an east dipping conductive anomaly 150 250 m that is correlated with the transbrasiliano lineament this conductive feature is consistent with the east dipping subduction model and can be explained by the presence of graphite in paleosutures in long stable geological terranes oblique convergence between the terranes may have developed the transpressional shear belt the results provide new geophysical evidence of the tectonic boundary between the rio de la plata craton and the pampean terrane beneath the chaco pampean plain that extends southward into the transbrasiliano lineament the study also improves the knowledge of the amalgamation of western gondwana

the electrical conductivity of the mantle beneath europe derived from c responses from 3 to 720 hr summary the c response which connects the magnetic vertical component and the horizontal gradient of the horizontal components of electromagnetic fluctuations forms the basis for estimating the conductivity depth profile of the earth this paper describes new estimates of the c response obtained from observatory hourly mean values the z y method is applied which means that the vertical component is used locally whereas the horizontal components are used globally by expansion into terms of spherical harmonics a special evort is made to obtain unbiased estimates of c when applied to 90 months of hourly mean values from about 90 observatories the method yields consistent results for european observatories in the entire period range from 3 to 720 hr and for two diverent source mechanisms s and d st a good description of the source structure for individual time segments is essential this was achieved by a separate spherical harmonic analysis of the data for each month for d st or each day for s and by estimating a large number 120 of expansion coeycients the results are interpreted by means of 1 d conductivity models which show that the upper mantle has remarkably little structure with a monotonic decrease of resistivity from 100 v m near z 200 km to 0 7 v m below z 1000 km

are the ashes from the latest eruptions 2010 2016 at turrialba volcano costa rica related to phreatic or phreatomagmatic events abstract the initial eruptive episodes of explosive eruptions are classified as phreatic if the amount of juvenile material scoria glass pumice is null and the amount of fresh accidental lithics and hydrothermally altered lithics is substantial phreatic eruptions have been in some cases recognized as precursory events preceding phreatomagmatic and magmatic eruptive phases usually the lithological features of tephra deposits are investigated and sampled in the field investigation of ash samples under binocular microscope or by back scattered electron bse microscope images of polished sections is usually considered sufficient to typify the fragmentation mechanism of the eruption the opening eruptive phases at turrialba volcano together with the formation of new intracraters i e 2010 2012 2014 and the enlargement of the western crater 29 october 2014 to present were classified in previous papers and internal reports as phreatic we studied a series of ash samples erupted from 2010 to 2016 with the aim of understanding the fragmentation processes characterizing the vent opening phases we used sem eds analyses in addition to field and microscopic investigation results showed a composition of accidental lithics of fresh to hydrothermally altered clasts and secondary minerals 82 98 besides juvenile andesite fragments 2 18 which leads us to revisit the classification of the initial eruptive phases of turrialba as phreatomagmatic our method allowed the detection of a juvenile component directly involved in an effective magma water interaction which was possible only by a scrutinous examination of the glass surface textures by sem in the range size between 3 and 3 5 phi we recommend such a type of investigation when the identification of fresh magma in a new eruption is crucial for the preparedness and hazard evaluation at active volcanoes

a preliminary stable isotope study of volcanic ashes discharged by the 1979 eruption of ontake volcano nagano japan sulphur isotopic compositions of pyrite anhydrite and native sulphur in volcanic ashes discharged by the 1979 eruption of ontake volcano nagano japan were determined the isotopic data indicate that sulphate in anhydrite and a part of native sulphur were produced by the disproportionation reaction of sulphite formed by dissolution of so2 in volcanic gases into water which filled a mud reservoir probably located just below the crater zone some part of h2s in volcanic gases was fixed as pyrite and some was oxidised to form native sulphur hydrothermal alteration of country rocks to form pyrite anhydrite and clay minerals had proceeded in the mud reservoir before eruption at temperatures ranging from 110 to 185 c which were estimated by oxygen isotopic fractionation between anhydrite and water

the geochemical and petrological characteristics of prenatal caldera volcano a case of the newly formed small dacitic caldera hijiori northeast japan evaluating the magma depth and its physical properties is critical to conduct a better geophysical assessment of magma chambers of caldera volcanoes that may potentially cause future volcanic hazards to understand pre eruptive conditions of a magma chamber before its first appearance at the surface this paper describes the case of hijiori caldera volcano in northeastern japan which emerged approximately 12 000 years ago at a place where no volcano ever existed we estimated the depth density bulk modulus vesicularity crystal content and bulk h 2 o content of the magma chamber using petrographic interpretations bulk and microchemical compositions and thermodynamic calculations the chemical mass balance calculations and thermodynamic modeling of the erupted magmas indicate that the upper portion of the hijiori magmatic plumbing system was located at depths between 2 and 4 km and had the following characteristics 1 pre eruptive temperature about 780 circ c 2 bulk magma composition 66 1 5 wt sio 2 3 bulk magmatic h 2 o approximately 2 5 wt and variable characteristics that depend on depth 4 crystal content le 57 vol 5 bulk modulus of magma 0 1 0 8 gpa 6 magma density 1 8 2 3 g cm3 and 7 amount of excess magmatic h 2 o 11 32 vol or 48 81 mol the range of melt water contents found in quartz hosted melt inclusions 2 9 wt suggests the range of depth phenocrysts growth to be wide 2 sim 13 km our data suggest the presence of a vertically elongated magma chamber whose top is nearly solidified but highly vesiculated this chamber has probably grown and re mobilized by repeated injections of a small amount of hot dacitic magma originated from the depth

electrical conductivity of wadsleyite at high temperatures and high pressures abstract the electrical conductivity of wadsleyite aggregates has been determined under the broad range of thermodynamic conditions using the impedance spectroscopy for a frequency range of 10 2 to 10 6 hz two branches are observed in the complex impedance one at high frequency range showing a half circle originated at z real part of impedance z imaginary part of impedance 0 in the z z plot and another branch in the low frequency range the results from high frequency semi circles correspond to the electric properties of a sample whereas the results from a low frequency branch correspond to the electrode effects from the analysis of the results from the semi circles we have identified two distinct mechanisms of electrical conduction having different activation enthalpies and different sensitivity to oxygen fugacity and water content one mechanism dominating at water poor condition has a high activation enthalpy 147 kj mol and the conductivity increases with oxygen fugacity we suggest that electrical conduction in this regime is due to charge transfer involving ferric iron polaron conduction under water rich conditions electrical conductivity increases with water content but decreases with oxygen fugacity and the activation enthalpy is smaller 88 kj mol we infer that electrical conduction in this regime is due to protons the activation enthalpy in this regime is insensitive to water content and the conductivity is proportional to water content c w as c w r with r 0 72 the value of r is smaller than one suggests that minority defects such as h m or h are responsible for electrical conduction our results show that a completely dry transition zone is incompatible with most of the geophysical observations on the mantle transition zone and some water 0 1 0 3 wt in the pacific is required to explain the observed electrical conductivity

a temperature profile of the mantle transition zone the temperature distribution across the transition zone has been determined on the high pressure phase equilibria in the system mg2sio4 fe2sio4 recently determined by katsura and ito 1988 and ito and takahashi 1988 the temperature at the base of the transition zone 655 km depth is estimated to be about 1600 c assuming that the spinel dissociation is responsible for the sharp seismic discontinuity implied by study of reflected waves this estimation would be little modified for the chemically stratified mantle models since the lower mantle is characterized by the stability of perovskite the temperatures in the region from 350 km to 655 km depth are calculated for a peridotitic mantle model assuming an adiabatic temperature gradient the and transformations in mg fe 2sio4 make the temperature profile steep in the depth regions of 390 415 km and 500 530 km respectively the temperature would increase from about 1400 c to 1600 c over the depths interval 350 between 655 km

spatial and temporal variations of gas geochemistry at mt ontake japan abstract this report describes spatial and temporal variations of helium carbon and nitrogen isotopes measured in co2 rich bubbling gases from natural springs associated with mt ontake central honshu japan from november 1981 through september 2015 during the entire period the 3he 4he ratio decreased concomitantly with increasing distance of the sampling site from the central cone in contrast the co2 3he ratios and the 13c values of co2 increased with distance these spatial trends became more pronounced after the september 27 2014 ontake eruption suggesting reactivation of the volcano plumbing system with enhanced emission of magmatic volatiles although the spatial trend of nitrogen isotopes disappeared the 3he 4he ratios of the most proximal site to the central cone remained constant until 2000 apparently increasing from june 2003 through october 2014 they became constant soon after the eruption until september 2015 the ten year 3he enhancement might have been a precursor of the 2014 ontake eruption in contrast 13c values of co2 at the same site remained constant through this period the lack of 13c anomaly might be attributable to 1 negligibly small amounts of magmatic co2 introduced into the source of hot springs compared to ambient co2 in the air saturated aquifer or 2 close resemblance of the carbon signature of magmatic co2 to that of ambient co2 therefore its addition cannot change the overall 13c value of the sampled hot springs at distal sampling sites no measurable change of helium carbon or nitrogen isotopes was observed in relation to the 2014 ontake eruption suggesting that the effect of this eruption on the ontake hydrothermal system was geographically localized

short period volcanic gas precursors to phreatic eruptions insights from poas volcano costa rica abstract volcanic eruptions involving interaction with water are amongst the most violent and unpredictable geologic phenomena on earth phreatic eruptions are exceptionally difficult to forecast by traditional geophysical techniques here we report on short term precursory variations in gas emissions related to phreatic blasts at poas volcano costa rica as measured with an in situ multiple gas analyzer that was deployed at the edge of the erupting lake gas emitted from this hyper acid crater lake approaches magmatic values of so2 co2 1 6 days prior to eruption the so2 flux derived from magmatic degassing through the lake is measureable by differential optical absorption spectrometry sporadic campaign measurements which allows us to constrain lake gas output and input for the major gas species during eruptive and non eruptive periods we can further calculate power supply to the hydrothermal system using volatile mass balance and thermodynamics which indicates that the magmatic heat flux into the shallow hydrothermal system increases from 27 mw during quiescence to 59 mw during periods of phreatic events these transient pulses of gas and heat from the deeper magmatic system generate both phreatic eruptions and the observed short term changes in gas composition because at high gas flux scrubbing of sulfur by the hydrothermal system is both kinetically and thermodynamically inhibited whereas co2 gas is always essentially inert in hyperacid conditions thus the so2 co2 of lake emissions approaches magmatic values as gas and power supply to the sub limnic hydrothermal system increase vaporizing fluids and priming the hydrothermal system for eruption our results suggest that high frequency real time gas monitoring could provide useful short term eruptive precursors at volcanoes prone to phreatic explosions

electrical conductivity of a natural mg fe sio3 majorite garnet the electrical conductivity of meteoritic majorite measured at 10 hz under a nitrogen atmosphere at ambient pressure is 3 8 1 8 10 7 s m at room temperature and displays an arrhenius behavior with an activation energy of 0 55 0 1 ev over the temperature range 290 370 k extrapolating these values to conditions of the earth s mantle suggests that majorite and spinel can account for the increase in electrical conductivity observed from the upper mantle to the transition zone where these phases are stable

re evaluation of electrical conductivity of anhydrous and hydrous wadsleyite abstract recent laboratory electrical conductivity measurements of the main mantle constituent minerals have represented considerable efforts to determine the effects of water content on electrical conductivity however there are large discrepancies between the results of yoshino et al 2008a and those of dai and karato 2009a on hopping conduction and the effects of water on the electrical conductivity of wadsleyite to investigate the cause of these discrepancies the electrical conductivity of anhydrous and hydrous wadsleyite were newly measured under low and high temperature conditions by impedance spectroscopy the conductivity values of dry wadsleyite aggregates with less than 2 ppm h2o by weight were similar to those for hopping conduction reported by yoshino et al 2008a and distinctly higher than those of dai and karato 2009a for hydrous wadsleyite at temperatures below 1000 k the electrical conductivity in an arrhenius plot was repeatable along the heating cooling paths and was similar to the results of yoshino et al 2008a the impedance spectrum in the complex impedance plane of hydrous wadsleyite showed a semicircular shape and the infrared spectrum did not show any shape change after the conductivity measurements in contrast when the temperature exceeds 1000 k the electrical conductivity in an arrhenius plot showed higher activation enthalpy the impedance spectra were greatly distorted and the impedance arc contained at least two relaxation processes this shape is similar to those reported by dai and karato 2009a who measured the conductivity above 1000 k the infrared spectra showed a large contribution from molecular water after conductivity measurements suggesting significant dehydration during the conductivity measurements in summary the results obtained from conductivity measurements at higher temperatures 1000 k do not represent the proton conduction in the grain interior

petrology of philippine geothermal systems and the application of alteration mineralogy to their assessment abstract philippine geothermal systems occur in the vicinity of large holocene calc alkaline volcanic complexes wells drilled in these areas encountered multiple intrusions the latest dikes are the subsurface manifestations of the youngest heat source commonly at least two hydrothermal regimes are juxtaposed in a single area with the latest being in equilibrium with the present temperature and chemical regime alteration by neutral ph water is pervasive and abundant a contact metamorphic aureole also occurs near intrusives alteration due to acid sulfate fluids is generally confined to permeable structures neutral ph alteration is divided into four zones on the basis of key clay minerals and two subzones are defined by calc silicates these are the smectite ambient to 180 c transition 180 230 c illite 230 320 c and biotite 270 340 c zones subzones are defined by epidote 250 340 c and amphibole 280 340 c the four main zones of acid alteration are kaolinite ambient to 120 c dickite kaolinite 120 200 c dickite pyrophyllite 200 250 c and pyrophyllite illite 230 320 c where relict high temperature alteration reaches the surface the area being drilled is usually the outflow zone of the present system these hydrothermal mineral assemblages are used 1 as geothermometers 2 to assist in determining the depth at which the production casing will be set during drilling 3 to estimate fluid ph and other chemical parameters 4 to predict possible corrosion and scaling tendencies of the fluids 5 as a measure of permeability and possible cold water influx into wells 6 as a guide to field hydrology and 7 to estimate roughly the thickness of the eroded overburden

petrology and fe ti oxide reequilibration of the 1991 mount unzen mixed magma a dacitic magma 64 5 wt sio2 a mixture of phenocryst rich rhyodacite and an aphyric mafic magma was erupted during the recent 1991 1995 mount unzen eruptive cycle the experimental and analytical results of this study reveal additional details about conditions in the premixing and postmixing magmas and the nature of the mixing process the preeruption rhyodacitic magma was at a temperature of 790 20 c according to fe ti oxide phenocryst cores and at a depth of 6 to 7 km 160 mpa according to al in hornblende geobarometry the mafic magma that mixed with the rhyodacite is found as andesitic 54 to 62 wt sio2 enclaves in the erupted magma and was essentially aphyric when intruded phase equilibria indicate that an aphyric andesite at 160 mpa is 1030 c h2o saturated and possibly as high as 1130 c 2 wt h2o the composition of the rhyodacite which was mixed with the andesite is estimated to lie between 67 and 69 wt sio2 using these compositions and temperatures the temperature of the unzen magma after mixing is estimated to be at least 850 to 870 c the groundmass fe ti oxide microphenocrysts and those in pargasite bearing reaction zones around biotite phenocrysts both give 890 20 c temperatures the oxide oxide contacts give temperatures of 910 20 c the 900 30 c postmixing temperatures are consistent with phase equilibria experiments which show that the magma was not above 930 c at 160 mpa our fe ti oxide reequilibration experiments suggest that the mixing of the two magmas began within a few weeks of the eruption which is a shorter time than is calculated using available diffusion data there is also evidence that some mixing took place much closer to the time of extrusion based on the presence of unrimmed biotite phenocrysts in the magma

high hydrogen solubility in al rich stishovite and water transport in the lower mantle abstract stishovite is an important phase in subducting oceanic crust the post garnet assemblage from a precursor eclogite lithology contains up to 25 stishovite at pressures above 25 gpa this stishovite may contain up to 5 wt al 2 o 3 we measured the hydrogen contents of stishovite samples synthesized at 20 25 gpa and 1200 1800 c from several starting materials containing up to 10 wt al 2 o 3 ftir spectra of stishovite show major bands at 3111 3134 cm 1 with the frequencies increasing as h 2 o and al 2 o 3 contents increase and several minor bands at 2659 2667 3240 3261 3312 3334 and 3351 cm 1 the h 2 o content of al free stishovite is in the range of 16 30 wt ppm the maximum h 2 o content of al bearing stishovite 4 4 wt al 2 o 3 synthesized at 20 gpa and 1400 c is 3010 300 wt ppm most hydrogen in stishovite is associated with al 3 substitutional defects on the octahedral si 4 site the hydrogen can occupy 40 of vacancies created by incorporation of al 3 at 20 gpa this observation along with some anomalies in the ftir spectra may indicate an alternative mechanism of al 3 incorporation into stishovite via the formation of oxygen vacancies or interstitial al i defects we report the highest h 2 o concentrations in al stishovite to date and argue that it is the most important carrier of water into the lower mantle post garnet eclogitic assemblages

effect of water on the electrical conductivity of lower crustal clinopyroxene 1 the electrical conductivity of lower crustal clinopyroxene was measured at 6 12 kbar 250 1000 c and ni nio buffer conditions the dependence of electrical conductivity on water content was studied using both natural and preannealed samples separated from a fresh xenolith granulite with water contents from 0 to 375 ppm an end loaded piston cylinder apparatus and a solarton 1260 impedance gain phase analyzer were used in the study over a frequency range of 0 01 106 hz to obtain the complex impedance spectra the results show that the influence of pressure is very weak relative to temperature and water content and that two distinct mechanisms with different activation enthalpies dominate electrical conduction under dry and wet conditions for the dry sample the activation enthalpy is 102 kj mol and the main charge carriers are small polarons i e hopping of electron holes between ferrous and ferric irons for wet samples the electrical conductivity is significantly enhanced with an activation enthalpy of 70 kj mol and the charge carriers are likely to be protons under hydrous conditions the activation enthalpies are nearly independent of water content and the conductivity is a function of water content with an exponent of 1 as a major constituent of granulites with 60 modal volume in some regions clinopyroxene containing minor amounts of water may contribute significantly to the high electrical conductivity in the lower crust especially under stable continental regions

transport of water into the lower mantle role of stishovite when subjected to lower mantle pressures and temperatures natural anhydrous basalt containing 0 2 wt h sub 2 o forms a phase assemblage in which sio sub 2 stishovite is a significant carrier of hydrogen up to 500 ppm h sub 2 o by weight as hydroxide whereas the coexisting mg fe al ca sio sub 3 perovskite appears to be not upper bound of 50 ppm wt h sub 2 o contrary to the devolatilization characteristically observed at lower pressures we find that the abundance of h sub 2 o in residual stishovite increases from approx 100 to approx 400 ppm by weight upon partially melting the high pressure mineral assemblage at 28 60 gpa we infer that the trace concentration of al within residual stishovite increases upon partial melting thereby increasing the coupled abundance of h in this crystalline phase the anhydrous component of subducted oceanic crust can thus recycle a significant amount of water into the lower mantle over the age of the earth with subducted stishovite potentially returning approx 10 sup 2 times the amount of water present in today s atmosphere

upper mantle conductivity structure of the back arc region beneath northeastern china the upper mantle electrical conductivity structure of the pacific back arc beneath northeastern china was investigated through long period magnetotelluric mt and geomagnetic depth sounding gds experiments mt and gds responses were obtained up to periods of 105 106 seconds and were inverted to one dimensional 1 d models with minimum and smooth structure constraints respectively the resulting conductivity model was compared with past models and the mantle transition zone beneath northeastern china is more conductive than those of other tectonic settings by almost one order of magnitude in the depth range of 400 600 km this feature may correspond to the presence of a stagnant slab beneath this region in the mantle at a depth of less than 400 km the conductivity profile has a similar feature to that in the thermal and extensional tectonic region in the southwestern united states

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

juvenile magma recognition and eruptive dynamics inferred from the analysis of ash time series the 2015 reawakening of cotopaxi volcano forecasting future activity and performing hazard assessments during the reactivation of volcanoes remain great challenges for the volcanological community on august 14 2015 cotopaxi volcano erupted for the first time in 73 years after approximately four months of precursory activity which included an increase in seismicity gas emissions and minor ground deformation here we discuss the use of near real time petrological monitoring of ash samples as a complementary aid to geophysical monitoring in order to infer eruption dynamics and evaluate possible future eruptive activity at cotopaxi twenty ash samples were collected between august 14 and november 23 2015 from a monitoring site on the west flank of the volcano these samples contain a range of grain types that we classified as hydrothermal altered lithic juvenile and free crystals the relative proportions of theses grains evolved as the eruption progressed with increasing amounts of juvenile material and a decrease in hydrothermally altered material in samples from the initial explosion juvenile grains are glassy microlite poor and contain hydrothermal minerals opal and alunite the rising magma came in contact with the hydro thermal system under confinement causing hydro magmatic explosions that cleared the upper part of the plumbing system subsequently the magmatic column produced a thermal aureole in the conduit and dried out the hydrothermal system allowing for dry eruptions magma ascent rates were low enough to allow for efficient outgassing and microlite growth constant supply of magma from below caused quasi continuous disruption of the uppermost magma volume through a combination of shear deformation and gas expansion the combination of increasing crystallinity of juvenile grains and high measured so2 flux indicate decreasing integrated magma ascent rates and clearing of the hydrothermal system along transport pathways in a system open to gas loss the near real time monitoring of ash samples combined with traditional geophysical monitoring techniques during the reawakening of cotopaxi allowed us to gain a much clearer understanding of events than when using traditional geophysical monitoring alone c 2016 elsevier b v all rights reserved

kar age determination of late quaternary volcanic rocks using the mass fractionation correction procedure application to the younger ontake volcano central japan abstract we propose an age derivation procedure for the k ar dating method to be applied to late quaternary volcanic rocks of low to medium k 2 o content whose k ar ages calculated by the conventional derivation procedure provide insufficient age information in this procedure which we call the mass fractionation correction procedure mfcp the initial 40 ar 36 ar ratios of the samples are estimated from the stable 38 ar 36 ar ratios determined by the unspiked technique assuming that the initial argon isotope ratios of all the samples should lie on a theoretical mass fractionation line of argon in the atmosphere to examine the usefulness of the mfcp systematic k ar age determinations using this procedure were made on volcanic rocks from the stratigraphically well known younger ontake volcano in central japan which has erupted repeatedly over the past 100 ka the k ar ages determined for these volcanics by this procedure generally have analytical uncertainties within 25 1 level and are consistent with the volcanostratigraphy exceptions were the large phenocrysts in pumice fall deposits these may contain significant amounts of excess 40 ar and we considered them to be unsuitable for accurate k ar age determinations of young volcanic rocks in the cases of lava flows which underlie a widespread fallout tephra the k ar ages determined by the mfcp were consistent with the 14 c age of the tephra 21 22 ka

electrical conductivity of majorite garnet and its implications for electrical structure in the mantle transition zone abstract electrical conductivities of majorite garnet with compositions of pyrolite minus olivine pyrolite majorite and mid ocean ridge basalt morb majorite were measured under physical conditions of the mantle transition zone 18 and 23 gpa and temperatures up to 2000 k in a kawai type multi anvil apparatus the samples with morb composition are mainly composed of majorite which has higher fe and al contents and contain a small amount of stishovite the conductivity of the morb majorite is more than twice higher than those of the pyrolite majorite at the same temperature the activation energies of these majorites are both 1 4 ev at temperature of 1000 1600 k suggesting that the dominant mechanism of charge transportation is fe 2 fe 3 hopping small polaron conduction at higher temperatures 1600 k corresponding to temperature conditions of the transition zone conduction mechanism of the pyrolite majorite would change from small polaron to ionic conduction the pyrolite majorite has only slightly higher and lower conductivity than dry wadsleyite and ringwoodite respectively and will not largely change the conductivity depth profile predicted for the dry mantle transition zone the laboratory based conductivity profile of the mantle transition zone with pyrolitic composition can explain well the current semi global conductivity depth profile obtained from electromagnetic study beneath pacific on the other hand the garnetite originating from the oceanic crust has remarkably higher conductivity than the surrounding mantle because the conductivity of morb majorite is significantly higher than those of wadsleyite and ringwoodite conductivity values of morb majorite agree with those of the stagnant slab beneath the northeastern china

water partitioning between nominally anhydrous minerals in the mgo sio2 h2o system up to 24 gpa implications for the distribution of water in the earth s mantle multi anvil experiments have been conducted in the mgo sio2 h2o system at pressures of 15 24 gpa and temperatures of 1200 1600 c to investigate the partitioning of water between mantle phases the water contents were obtained from fourier transform infrared spectroscopy on doubly polished and clear crystals most of the mineral phases coexisted with a hydrous melt the results show that among all magnesium silicate phases 1 mgsio3 perovskite is the only phase which does not dissolve a detectable amount of water and 2 the high pressure polymorphs of mg2sio4 wadsleyite and ringwoodite dissolve about one order of magnitude more water than the polymorphs of mgsio3 clinoenstatite majorite and akimotoite the following partition coefficients of water were measured dwadsleyite clinoenstatite 3 8 at 15 gpa and 1300 c dringwoodite akimotoite 21 at 19 gpa and 1300 c dakimotoite perovskite 1 at 24 gpa and 1600 c and dpericlase perovskite 1 at 24 gpa and 1500 c these results suggest that most of the water in the earth s mantle is partitioned in the transition zone

electrical conductivity model of al bearing bridgmanite with implications for the electrical structure of the earth s lower mantle electrical conductivity measurements of bridgmanite with various al contents and a constant mg of 90 were performed at temperatures ranging from room temperature up to 2000 k at pressures of 26 28 gpa in a kawai type multianvil apparatus by impedance spectroscopy analysis the incorporation of al into bridgmanite raises its electrical conductivity significantly but it is a small conductivity variation with respect to the quantity of al synchrotron mossbauer spectroscopy of recovered samples showed significant amounts of ferric iron in aluminous bridgmanite the mobility of the charge carriers in bridgmanite was calculated based on the conductivity and the fe3 fe ratio the relationship between the logarithm of the electrical conductivity and the reciprocal temperature is consistent with fe2 fe3 electron hopping small polarons as the dominant conduction mechanism at low temperatures 1600 k by taking various conduction mechanisms into account we develop an electrical conductivity model for aluminous bridgmanite as a function of the al and fe contents the small polaron conduction model indicates that the electrical conductivity of aluminous bridgmanite has a maximum at around 0 06 al atoms per formula unit and any further increase in the al content in bridgmanite reduces the conductivity in contrast the ionic conduction model indicates that the electrical conductivity simply increases with increasing al content the resulting conductivity of al bearing bridgmanite first increases up to 0 06 al atoms per formula unit and then remains constant or increases with increasing al content at higher temperatures the increase in conductivity observed in the uppermost part of the lower mantle by electromagnetic studies can be explained by the gradual decomposition of majorite garnet the deeper lower mantle conductivity would be controlled by small polaron conduction because of the large positive activation volume required for ionic conduction

helium and carbon isotope systematics at ontake volcano japan we have measured chemical compositions he ne ratios and he and c isotopic compositions of 47 gas samples collected from crater fumaroles and hot springs associated with ontake volcano japan geographical and temporal variations of chemical compositions 3he 4he ratios and 13c values of co2 are reported here between 1981 and 1993 3he 4he ratios decreased with increasing distance from the central cone of the volcano while 13c values increased with the distance magmatic he and co2 are probably carried by a fluid flowing through the volcanic edifice and are diluted by crustal he and co2 a negative correlation of 3he 4he ratios and 13c values suggests two component mixing between magmatic and crustal end members at the sampling sites close to the fault formed by a m6 8 earthquake that occurred in september 1984 3he 4he ratios have increased significantly with time from 1984 to 1993 while except for three sites close to the fault no systematic change of 13c values is found on the other hand he and c isotopes have been constant at the sites distant from the fault the temporal variations of 3he 4he ratios may be related to the recent reactivation of ontake volcano

effects of pore fluid pressure and tectonic stress on diverse seismic activities around the mt ontake volcano central japan abstract to understand the effects of pore fluid pressure and tectonic stress in generating diverse seismicity we deployed 11 temporary seismic stations around an active volcano mt ontake in central japan during the summers of 2009 2011 we obtained well constrained focal mechanism solutions from the seismic data recorded at the temporary stations and permanent stations located within 50 km around mt ontake we estimated the 3 d pore fluid pressure field taking into consideration spatial changes in the tectonic stress pattern by applying the method of focal mechanism tomography to the dataset we found overpressurized fluid reservoirs with a peak of 100 150 mpa at depths between 5 and 12 km in the southeast and east flanks of mt ontake this region has experienced earthquake swarm activity since 1976 many seismic events concentrated at the edge of the overpressurized fluid reservoirs where pore fluid pressure gradients are steep this indicates that a large amount of fluid flow would trigger seismic events by decreasing fault strength caused by an increase in pore fluid pressures many small events m

geology geochemistry and origin of high sulfidation cu au mineralization in the nansatsu district japan the nansatsu district of southern kyushu has been the site of calc alkaline volcanism for the last 10 m y shifting eastward with time associated hydrothermal activity followed deposition of the volcanic host rocks by about 0 5 m y and was characterized by interaction of magmatic fluids with meteoric water under epithermal conditions resulting in the formation of high sulfidation cu au deposits at kasuga iwato and akeshi the orebodies consist of 95 wt percent sio 2 and result from leaching of the original andesite lava and pyroclastic flows by acid chloride sulfate waters these are inferred to have formed when magmatic vapors containing hcl and so 2 condensed into meteoric water the residual silica now quartz orebodies are best developed where the host was initially permeable the margins of the quartz bodies are abrupt with narrow 1 2 m halos representing the reaction front of acid waters isochemically dissolving the host rock the halo comprises alunite strongly zoned in na and k with p rich cores dickite and or kaolinite or pyrophyllite grading out into illite and interlayered illite smectite clays and finally propylitic alteration this pattern is characteristic of deposits of this type throughout the world for example at summitville colorado and lepanto philippines mineralization occurred after initial leaching by the vapor condensates with metals transported by a dense magmatic fluid mixing with meteoric water and the subsequent temperature decrease caused the general decrease in grade toward the margin of the quartz bodies ore grades are restricted to the quartz bodies gold is most closely associated with enargite and pyrite later minerals include covellite and then sulfur the last stage of activity was steam heated with descending waters oxidizing sulfides to goethite and locally remobilizing au into fractures this varies in degree between deposits erosion exposed the orebodies to supergene weathering continuing the sulfide oxidation and au remobilization stable isotope results indicate that hypogene alunite formed from a mixture of magmatic fluid delta 18 o 7 or 2 per thousand delta d 25 or 5 per thousand similar to nearby active volcanic discharges with local meteoric water in contrast the clays in the marginal halo have isotopic compositions indicating a delta 18 o shift of 6 to 8 per mil from local meteoric water values probably due to water rock interaction and the delta 18 o values of residual silica quartz may also be due to meteoric water domination fluid inclusion study of postmineralization quartz crystals indicates that the fluids had a salinity of about 1 wt percent nacl equiv during late quartz growth though there is evidence in one sample for higher salinity fluid having been present up to 30 wt percent nacl equiv some inclusions contain daughter minerals of halite and sulfur the t h values of over 1 000 measurements on late quartz from the ore zones indicate that the mean temperature during that stage ranged from 200 degrees c at akeshi to about 200 degrees c at iwato and 230 degrees c at kasuga the presence of vapor rich inclusions some with t hv similar to t hl indicate the presence at times of a two phase fluid in the center of the ore zones with depths of about 150 to 300 m below the paleowater table the mineralizing fluid was relatively oxidized sulfide sulfate ratio about 3 1 close to pyrite alunite coexistence under these redox conditions a ph of 3 and over a temperature range of 200 degrees to 300 degrees c aucl 2 super complexing may dominate over hau sh 2 at salinities above about 2 wt percent nacl several conditions are conducive for high sulfidation mineralization to occur 1 a crystallizing magma exsolves a fluid with lower pressure conditions favoring metal fractionation from melt to fluid 2 the exsolved fluid separates into vapor and saline liquid phases due to immiscibility with the latter being metal rich 3 the gas rich hcl and so 2 h 2 s vapor ascends to the surface with at least a portion condensed into meteoric water forming an acid fluid which leaches the host rock to create permeable zones for later mixing and 4 the dense metal bearing fluid also ascends into this leached zoned and precipitates cu sulfosalts sulfides and au upon mixing with meteoric water if the saline liquid is not released from its source adjacent to the magma due to lack of fracturing or if there is a strong hydraulic gradient caused by high relief only the vapor related stage may occur this will leave leached barren rock which is characteristic of many eroded volcanic terranes

electrical conductivity of dense hydrous magnesium silicates with implication for conductivity in the stagnant slab abstract electrical conductivities of dense hydrous magnesium silicates dhms phase a super hydrous phase b sub and phase d were measured by means of impedance spectroscopy in the frequency range of 10 1 106 hz at temperatures up to 775 700 and 700 k and pressures of 10 18 and 22 gpa respectively for all phases the increase in electrical conductivity with temperature follows the arrhenian formula 0 exp h k t the pre exponential factors 0 and activation enthalpies h of phase a sub and phase d yield values of 7 28 0 82 s m and 0 77 0 01 ev 292 48 s m and 0 83 0 01 ev and 1342 154 and 0 75 0 01 ev respectively higher pressure dhms phases show higher conductivity values the electrical conductivities of phase d and super hydrous phase b are about two and one orders of magnitude higher than that of phase a in the same temperature range respectively although the proton conduction is considered to be a dominant mechanism there is no clear relationship between water content and conductivity rather the conductivity of dhms phase is closely related to the o o distance the conductivity depth profiles for a cold subduction zone were constructed based on the phase proportion predicted in the descending slab the results show distinctly lower conductivity values than those geophysically observed beneath the northeastern china and the philippine sea where the cold slab stagnates in the mantle transition zone consequently the dhms phases themselves cannot be a main contributor to enhance the conductivity in the stagnant slab dehydration of the stagnant slab would strongly enhance the conductivities in the transition zone beneath northeastern china and philippine sea

electrical conductivity measurement of granulite under mid to lower crustal pressure temperature conditions summary we have developed a technique to measure electrical conductivity of crustal rocks with relatively low conductivity and complicated mineral components in order to compare with results given by magneto telluric mt measurements a granulite from hidaka metamorphic belt hmb in hokkaido japan at high temperature and pressure conditions was obtained the granulite sample was ground and sintered under the conditions similar to those of mid to lower crust we have observed smooth and reversible change of conductivity with temperature up to about 900 k at 1 gpa the results were consistent with the electrical conductivity structures suggested by the mt data analysis considering pore fluid conduction mechanism or the role of accessory minerals in the rock the mechanisms of electrical conductivity paths in dry or basic rocks should be reconsidered

thermodynamics of gas and steam blast eruptions eruptions of gas or steam and non juvenile debris are common in volcanic and hydrothermal areas from reports of non juvenile eruptions or eruptive sequences world wide at least three types or end members can be identified 1 those involving rock and liquid water initially at boiling point temperatures boiling point eruptions 2 those powered by gas primarily water vapor at initial temperatures approaching magmatic gas eruptions and 3 those caused by rapid mixing of hot rock and ground or surface water mixing eruptions for these eruption types the mechanical energy released final temperatures liquid water contents and maximum theoretical velocities are compared by assuming that the erupting mixtures of rock and fluid thermally equilibrate then decompress isentropically from initial near surface pressure 10 mpa to atmospheric pressure maximum mechanical energy release is by far greatest for gas eruptions 1 3 mj kg of fluid rock mixture about one half that of an equivalent mass of gunpowder and one fourth that of tnt it is somewhat less for mixing eruptions 0 4 mj kg and least for boiling point eruptions 0 25 mj kg the final water contents of crupted boiling point mixtures are usually high producing wet sloppy deposits final erupted mixtures from gas eruptions are nearly always dry whereas those from mixing eruptions vary from wet to dry if all the enthalpy released in the eruptions were converted to kinetic energy the final velocity v max of these mixtures could range up to 670 m s for boiling point eruptions and 1820 m s for gas eruptions highest for high initial pressure and mass fractions of rock m r near zero for mixing eruptions v max ranges up to 1150 m s all observed eruption velocities are less than 400 m s largely because 1 most solid material is expelled when m r is high hence v max is low 2 observations are made of large blocks the velocities of which may be less than the average for the mixture 3 heat from solid particles is not efficiently transferred to the fluid during the eruptions and 4 maximum velocities are reduced by choked flow or friction in the conduit