melting relationships in the fe fe3s system up to the outer core conditions abstract in situ x ray diffraction experiments in the fe fe 3 s system were performed up to 175 gpa and 3500 k using a laser heated diamond anvil cell to investigate melting relationships in the system partial melting in the fe fe 3 s system was observed based on the disappearance of x ray diffraction peaks of solid fe 3 s and texture observation of the recovered samples the melting relationship of the fe fe 3 s system as a function of pressure is evaluated based on kraut kennedy law our results of melting relationships suggest that the temperature at the inner core boundary is between 4700 160 and 4930 330 k if sulfur is the only light element in the earth s core assuming the adiabatic temperature gradient in the outer core the temperature at the core mantle boundary is estimated to be in the range of 3600 3770 k the present temperature profile of the core is consistent with the core mantle boundary temperature that can explain the core heat flux to maintain the core dynamo and the seismic structure at the base of the lower mantle

rapid releases of metal salts and nutrients following the deposition of volcanic ash into aqueous environments deposition of volcanic ash into aqueous environments leads to dissolution of adsorbed metal salts and aerosols increasing the bioavailability of key nutrients volcanogenic fertilization events could increase marine primary productivity leading to a drawdown of atmospheric co2 here we conduct flow through experiments on unhydrated volcanic ash samples from a variety of locations and sources measuring the concentrations and fluxes of elements into de ionized water and two contrasting ocean surface waters comparisons of element fluxes show that dissolution of adsorbed surface salts and aerosols dominates over glass dissolution even in sustained low ph conditions these surface ash leachates appear unstable decaying in situ even if kept unhydrated volcanic ash from recent eruptions is shown to have a large fertilization potential in both fresh and saline water fluorine concentrations are integral to bulk dissolution rates and samples with high f concentrations display elevated fluxes of some nutrients particularly fe si and p bio limiting micronutrients are released in large quantities suggesting that subsequent biological growth will be limited by macronutrient availability importantly acidification of surface waters and high fluxes of toxic elements highlights the potential of volcanic ash leachates to poison aqueous environments in particular large ph changes can cause undersaturation of caco3 polymorphs damaging populations of calcifying organisms deposition of volcanic ash can both fertilize and or poison aqueous environments causing significant changes to surface water chemistry and biogeochemical cycles

agronomic impact of tephra fallout from the 1995 and 1996 ruapehu volcano eruptions new zealand eruptions from ruapehu volcano on 11 and 14 october 1995 and 17 june 1996 distributed at least 36 106 m3 of sulphur s rich tephra over the central and eastern north island of new zealand the tephras added between 30 1500 kg ha 1 s to at least 25 000 km2 of land in primary production smaller but beneficial amounts of selenium se and in some areas potassium and magnesium were also supplied addition of s to the soils in the form of sulphate and elemental s resulted in a drop in soil ph and an increase in pasture s contents within seven weeks of the eruptions the soils affected by the tephra are naturally low in s and se but following the eruptions s was not required in fertilizer applications in many areas the strongest and longest lasting effects of s and se deposition were in high anion retention soils particularly hapludands moist moderately weathered soils derived from volcanic ash soluble fluorine concentrations within the tephras were low compared to historic icelandic and chilean examples however pastoral livestock deaths were apparently caused by fluorosis in addition to starvation when tephra covered feed the ruapehu tephra contained very low concentrations of other soluble toxic elements

phase relationships of the fe fes system in conditions up to the earth s outer core abstract in situ x ray diffraction experiments in the fe fes system were performed up to 220 gpa and 3300 k using a laser heated diamond anvil cell fe 3 s and e fe coexisted stably up to 220 gpa and 3300 k and thus fe 3 s is likely to be the stable s bearing iron alloy under the earth s core conditions the solid iron e fe also contained 7 6 0 8 at of sulfur at 86 gpa and 2200 k the amount of sulfur in the solid iron increased with increasing pressure at the eutectic temperatures if the sulfur content obtained in this study is extrapolated to the conditions at the inner core all the sulfur in the solid inner core can be stored in e fe the eutectic composition becomes nonsensitive to pressure and seems to be constant around 20 at of sulfur at pressures above 40 gpa the pressure gradient of the melting curve of the fe fes system is 13 4 0 7 k gpa based on our results of melting relationship the temperature at the core mantle boundary should be greater than 2850 100 k assuming that sulfur is the only light element in the earth s liquid outer core

temporal magnetotellurics reveals mechanics of the 2012 mount tongariro nz eruption monitoring dynamics of volcanic eruptions with geophysics is challenging in august and november 2012 two small eruptions from mount tongariro provided a unique opportunity to image subsurface changes caused by the eruptions a detailed magnetotelluric survey of the tongariro volcanic complex completed prior to the eruption 2008 2010 provides the pre eruption structure of the magmatic system a subset of the initial measurement locations was reoccupied in june 2013 significant changes were observed in phase tensor data at sites close to the eruptive centre although subsurface electrical resistivity changed geometry of the pre eruptive reservoir did not these subsurface resistivity variations are interpreted as being predominantly caused by interaction of partial melt and the overlying brine layer causing volume reduction of the brine layer through phreatic eruption the ability to detect significant changes associated with the magma reservoir suggests that magnetotellurics can be a valuable volcano monitoring tool

posteruptive impacts of pyroclastic deposits from basaltic andesite stratovolcanoes on surface water composition volcanic ash deposition following explosive eruptions can pose significant hazards for water quality human health agriculture and infrastructure functionality many studies have examined how fresh ash deposition may lower the ph of and introduce a range of potentially toxic elements into exposed surface waters however no study has yet determined the effects on water composition as a result of mechanical pyroclast disaggregation and production of new fresh particle surfaces and increasingly fine grained particles such disaggregation could result from natural posteruptive processes such as debris avalanches lahars or fluvial aeolian transport and human activities such as cleanup efforts or mining of pyroclastic deposits the posteruption time scales of pyroclast disaggregation may vary from months in moist tropical or temperate environments to years or decades in arid settings here we show for the first time in experimental studies that mechanical milling of pyroclasts will introduce a range of elements into exposed waters including al which can be toxic at elevated levels and na which increases the electrical conductivity of solutions the ph of leaching solutions also increases by several log units such dramatic changes on the experimental scale may have implications for surface water composition in posteruptive settings necessitating longer term risk assessments for ecosystem health and consideration of the role of pyroclastic deposits in element cycling in volcanically active regions

precursory characteristics of the seismicity before the 6 august 2012 eruption of tongariro volcano north island new zealand abstract the 6 august 2012 eruption from the upper te maari crater of tongariro volcano followed approximately three weeks of precursory seismic activity earthquake relocations including data from extra temporary stations indicated that nearly all events were in a small area very close to upper te maari most of these relocated events were very shallow with nearly all events being between 1000 and 1500 m below the ground surface the pre eruption seismicity occurred in three main swarms during the first swarm on 12 13 july 2012 all the earthquakes had consistent inter event times of 71 8 min while in the later swarms 17 20 and 29 30 july many events had a similar pattern of consistent inter event times the stationary quasi periodic clockwork earthquake process suggests that a single fracture point was excited by a nearly constant rate flux process the dominant type of earthquake observed in these swarms had a sharp onset and a broad spectrum with strong energy from 2 to 10 hz most events seen had a local magnitude of 1 5 to 2 5 with virtually no smaller events most of these earthquakes appeared to belong to a main earthquake family whose characteristics included a strong spectral component at about 2 hz and three bursts of energy spaced at intervals of about 1 5 s of the 116 located earthquakes 75 had a correlation coefficient greater than 0 70 with a master event the spectra of these events did not change with size with matching frequency peaks for all the events with a high correlation the last event of this type was the day before the 6 august 2012 eruption none have been seen since and there has been very little seismicity under tongariro this seismicity alerted gns science and other organisations to the unrest of tongariro and the volcanic alert level and aviation colour code were raised to publicise this gns science also increased its monitoring of tongariro and discovered that the magmatic gas concentrations had increased compared to previous measurements in may 2012 however the seismicity did not show any accelerating trend that suggested an immediate eruption threat indicating the difficulty of predicting small eruptions in tongariro and similar volcanoes

eutectic melting in the system fe s to 44 gpa abstract melting relations in the fe s system were measured in the laser heated diamond cell by analyzing recovered samples using scanning electron microscopy the eutectic melting temperatures are lower than in previous diamond cell studies using in situ melt detection and are in good agreement with recent multi anvil measurements at lower pressures the new measurements ranging from 22 to 44 gpa show that the eutectic composition becomes increasingly iron rich with increasing pressure thus if sulfur is the main light component in the earth s core the sulfur content would have to be below 10 wt because the density contrast between the inner and outer cores implies that the core composition is on the iron rich side of the eutectic at 44 gpa we find eutectic melting temperatures that are about 1000 k below that of pure iron those eutectic temperatures suggest even lower temperatures in the earth s core than previous measurements on pure iron and for mars they imply a liquid core

dual polarisation c band weather radar imagery of the 6 august 2012 te maari eruption mount tongariro new zealand abstract the 6 august 2012 eruption of mt tongariro from upper te maari crater in the central north island of new zealand was the first volcanic eruption observed by an operational weather radar in new zealand and is believed to be one of only a small number of eruptions observed by a dual polarisation radar worldwide the eruption was also observed by a geonet webcam and detailed ash deposit studies have permitted analysis of the plume characteristics a combination of radar and webcam imagery show 5 pulses within the first 13 min of the eruption and also the subsequent ash transport downwind comparison with ash samples show the radar was likely detecting ash particles down to about 0 5 mm diameter the maximum plume height estimated by the radar is 7 8 1 0 km above mean sea level amsl although it is possible this may be a slight under estimation if very small ash particles not detected by the radar rose higher and comprised the very top of the plume the correlation coefficient and differential reflectivity fields that are additionally measured by the dual polarisation radar provide extra information about the structure and composition of the eruption column and ash cloud the correlation coefficient easily discriminates between the eruption column and the ash plume and provides some information about the diversity of ash particle size within both the ash plume and the subsequent detached ash cloud drifting downwind the differential reflectivity shows that the larger ash particles are falling with a horizontal orientation and indicates that ice nucleation and aggregation of fine ash particles was probably occurring at high altitudes within 20 25 min of the eruption

gas aerosol ash interaction in volcanic plumes new insights from surface analyses of fine ash particles the reactions occurring between gases aerosols and silicate ash particles in volcanic eruption plumes remain poorly understood despite the fact that they are at the origin of a range of volcanic environmental atmospheric and health effects in this study we apply x ray photoelectron spectroscopy xps a surface sensitive technique to determine the chemical composition of the nearsurface region 2 10 nm of nine ash samples collected from eight volcanoes in addition atomic force microscopy afm is used to image the nanometer scale surface structure of individual ash particles isolated from three samples we demonstrate that rapid acid dissolution of ash occurs within eruption plumes this process is favoured by the presence of fluoride and is believed to supply the cations involved in the deposition of sulphate and halide salts onto ash afm imaging also has permitted the detection of extremely thin 10 nm coatings on the surface of ash this material is probably composed of soluble sulphate and halide salts mixed with sparingly soluble fluoride compounds the surface approach developed here offers promising aspects for better appraising the role of gas aerosol ash interaction in dictating the ability of ash to act as sinks for various volcanic and atmospheric chemical species as well as sources for others c 2007 elsevier b v all rights reserved

geochemistry of fluids associated with the 1995 1996 eruption of mt ruapehu new zealand signatures and processes in the magmatic hydrothermal system abstract the 1995 1996 eruption of mt ruapehu has provided a number of insights into the geochemical processes operating within the magmatic hydrothermal system of this volcano both pre eruption degassing of the rising magma and its eventual intrusion into the convective zone of the hydrothermal system beneath the lake were clearly reflected in lake water compositions the eruptions of september october 1995 expelled the lake and provided the first ever opportunity to characterise gas discharges from this volcano the fumarolic discharges revealed compositions typical of andesite volcanoes and strong interaction with the enclosing meteoric and hydrothermal system fluids some 1 1 mt of so 2 gas was released from the volcano between september 1995 and december 1996 whereas ca twice this amount 2 2 mt equivalent so 2 was erupted as soluble i e leachable oxyanions of sulphur significantly more sulphur was released from the volcano over this period than can be accounted for from the magma volume actually erupted the evidence suggests that a sizable component of the evolved sulphur was remobilised from the long lived hydrothermal system within the volcano during the 1995 1996 activity

the effect of volcanic eruptions on the chemistry of surface waters the 1991 and 2000 eruptions of mt hekla iceland abstract the mt hekla eruptions in 1991 and 2000 have provided a unique opportunity to study the local environmental effects of high latitude volcanic eruptions in the middle of winter both eruptions started around sunset at sub zero temperatures in order to define better these effects we studied the chemistry of surface waters in the vicinity of the volcano additionally we describe and predict the environmental consequences of these volcanic eruptions on the chemistry of surface waters on land and in the ocean several dissolved elements in the polluted snow melt from the 2000 eruption cl f al fe mn as cd pb zn and u exceeded the limits for water intended for human consumption the volcanic ash the primary minerals and secondary mineral phases that commonly form in the weathering environment of iceland were undersaturated in the polluted snow melts with the exception of fluorite barite goethite and amorphous feooh these minerals can constrain the maximum initial concentration of the respective dissolved constituents in the meltwaters it took few days after the first rainfall on the volcanic ash to flush out the readily soluble constituents in the vicinity of the headwaters of the ytri ranga river the polluted river waters were oversaturated with respect to several secondary minerals resulting in precipitation of amorphous al hydroxide and feooh and further scavenging of some trace elements on the al and fe surfaces dissolved al and f were the main contaminants in the ytri ranga river water previous studies have shown that combined al f toxicity is directly related to the predominance of specific al f species in solution model calculations for mixing of a hekla type volcanic cloud with 4 surface water end members shows al f species to be most important in rain and dilute river waters this makes al and f phyto available but diminishes the concentration of the al 3 species the most toxic al species mixing with high alkalinity river waters or seawater results in the domination of non toxic al oh 4 species at dilutions greater than 800 thus hindering al toxicity and bioavailability this study indicates that h 2 so 4 contamination from volcanic eruptions is time and place dependent volcanic eruptions that take place during winter at high latitudes result in relatively high global sulfur contamination and relatively low local sulfur contamination due to the low oxidation rate of so 2 into h 2 so 4 because of the low solar radiation

water storage and early hydrous melting of the martian mantle abstract we report an experimental investigation of the near solidus phase equilibria of a water saturated analog of the martian mantle experiments were performed at low temperatures 700 920 c and high pressure 4 7 gpa using multi anvil apparatus and piston cylinder device 4 gpa the results of this study are used to explore the role of water during early melting and chemical differentiation of mars and to further our understanding of the near solidus behavior in planetary mantle compositions at high pressure water has a significant effect on the temperature of melting and therefore on accretion and subsequent differentiation processes experiments locate the wet solidus at 800 c and is isothermal between 4 gpa and 7 gpa the martian primitive mantle can store significant amounts of water in hydrous minerals stable near the solidus humite group minerals and phase e represent the most abundant hydrous minerals stable in the 4 7 gpa pressure range the amount of water that can be stored in the mantle and mobilized during melting ranges from 1 to up to 4 wt near the wet solidus we discuss thermal models of mars accretion where the planet formed very rapidly and early on in solar system history we incorporate the time constraint of dauphas and pourmand 2011 that mars had accreted to 50 of its present mass in 1 8 myr and include the effects of 26al radioactive decay and heat supplied by rapid accretion when accretion has reached 30 of mars current mass 70 of its present size melting starts and extends from 100 to 720 km depth below this melt layer water can still be bound in crystalline solids the critical stage is at 50 accretion 80 of its size where mars is above the wet and dry solidi with most of its interior melted this is earlier in the accretion process than what would be predicted from dry melting we suggest that water may have promoted early core formation on mars and rapidly extended melting over a large portion of mars interior

using the spatial distribution and lithology of ballistic blocks to interpret eruption sequence and dynamics august 6 2012 upper te maari eruption new zealand the ballistic ejection of blocks during explosive eruptions constitutes a major hazard near active volcanoes fields of ballistic clasts can provide important clues towards quantifying the energy dynamics and directionality of explosive events but detailed datasets are rare during the 6 august 2012 hydrothermal eruption of upper te maari tongariro new zealand three explosions occurred in rapid succession within less than 20 s the first two produced laterally directed pyroclastic density currents pdc and the final vertical explosion generated an ash plume each of these explosions was associated with the ejection of ballistic blocks we present detailed maps of the resulting 5 1 km2 block impact field and the distribution of the 2200 impact craters with diameters 2 5 m there are two distinct regions of high crater concentration where crater densities reach more than six times the average background density these occur at distances of 500 700 m east and 1000 1350 west of a 430 m long fissure that was created during the eruption the high density fields are characterized by a narrow radial spread of 45 and are located along the proximal transport direction of the pyroclastic density currents a provenance analysis of ballistic blocks allowed us to reconstruct two different eruptive vents for the explosions the first two laterally directed explosions were sourced from the fissure while the third explosion occurred through the pre existing upper te maari crater generating a roughly axisymmetric shower of ballistics stratigraphic relationships between impact craters pdc and fall deposits suggest that the ballistic blocks were initially coupled with the rapidly expanding gas particle mixtures that produced the pdcs ballistic trajectory modeling reproducing the lateral extent and main impact density pattern of the western impact field allows estimation of the vertical expansion angle of the second and largest explosion the calculations show that the largest proportion of the explosion energy was strongly focused as a narrow and extremely shallow from 3 to 15 from the horizontal laterally expanding hydrothermal blast the results presented here constitute an important data set for ballistic hazard assessment at tongariro volcano and they can provide further clues towards better understanding highly energetic laterally directed volcanic explosions at similar hydrothermal fields

thermal state and solidification regime of the martian core insights from the melting behavior of feni s at 20 gpa abstract a series of multi anvil experiments have been conducted to define the iron rich liquidus of the iron nickel sulfur feni s system at 20 gpa the estimated pressure of the martian core mantle boundary cmb the liquidus curve of feni s containing about 9 wt ni has a concave up shape and is as much as 400 k lower than the liquidi previously applied to the martian core with sparse experimental constraints unlike existing liquidi of fe s and feni s at 23 gpa which predict a fully molten core for a narrow range of sulfur content between 14 and 15 wt s our results are consistent with a molten state for all proposed core compositions and establishes a new minimum cmb temperature of 1500 k for 10 wt s and 1250 k for 16 wt s extrapolating our feni s liquidus to high pressures and comparing it to calculated areotherms we find that three core crystallization regimes are possible for a martian core with moderate sulfur content 10 to 13 wt or lower crystallization takes the form of iron snow near the cmb while for cores with higher sulfur content 15 16 wt solidification occurs near the center of the planet in the form of solid fe3s at an intermediate sulfur content of 14 wt fe3s would precipitate over a broad depth range and may appear fully molten to surface observations

integrating multidisciplinary science modelling and impact data into evolving syn event volcanic hazard mapping and communication a case study from the 2012 tongariro eruption crisis new zealand abstract new zealand s tongariro national park volcanoes produce hazardous eruptions every few years to decades on 6 august 2012 the te maari vent of tongariro volcano erupted producing a series of explosions and a fine ash of minor volume which was dispersed rapidly to the east this manuscript presents a summary of the eruption impacts and the way these supported science communication during the crisis particularly in terms of hazard map development the most significant proximal impact was damage from pyroclastic surges and ballistics to the popular and economically important tongariro alpine crossing track the only hazard to affect the medial impact zone was a few mms of ashfall with minor impacts field testing indicated that the te maari ash had extremely low resistivity when wetted implying a very high potential to cause disruption to nationally important power transmission networks via the mechanism of insulator flashover this was not observed presumably due to insufficient ash accumulation on insulators virtually no impacts from distal ashfall were reported post event analysis of pm10 data demonstrates the additional value of regional air quality monitoring networks in quantifying population exposure to airborne respirable ash while the eruption was minor it generated a high level of public interest and a demand for information on volcanic hazards and impacts from emergency managers the public critical infrastructure managers health officials and the agriculture sector meeting this demand fully taxed available resources we present here aspects of the new zealand experience which may have wider applicability in moving towards improved integration of hazard impact information mapping and communication these include wide use of a wiki technical clearinghouse and email listservs a focus on multi agency consistent messages and a recently developed environment of collaboration and alignment of both research funding and technical science advice hazard maps were integral to science communication during the crisis but there is limited international best practice information available on hazard maps as communication devices as most volcanic hazard mapping literature is concerned with defining hazard zones we propose that hazard maps are only as good as the communications framework and inter agency relationships in which they are embedded and we document in detail the crisis hazard map development process we distinguish crisis hazard maps from background hazard maps and ashfall prediction maps illustrating the complementary nature of these three distinct communication mechanisms we highlight issues that arose and implications for the development of future maps

the 1975 1977 crisis of la soufriere de guadeloupe f w i a still born magmatic eruption on july 8 1976 eruptive activity broke out at la soufriere de guadeloupe f w i after about one year of increasing seismic activity seismic activity continued to increase until august 1976 reaching more than 1500 events a 200 fold increase over the preceding quiet period of a few years and an energy output of about 1017 ergs in a day a total of 26 major phreatic eruptions similar to the july 8 outburst took place during an eight months period the steam blasts that characterized the eruptions gave rise to particle and sometimes block charged plumes that deposited an estimated 106 m3 of solids the h2o rich gases emitted during the blasts presumably contained other gases h2s so2 co2 that were partly adsorbed on solid particles all material was erupted at temperatures of the order of 100 to 200 c the observation of vertical migration of earthquake foci in less than a few hours and over about 6 km depth and of abnormal variations of the geomagnetic field indicate a deep energy source for the phreatic eruptions a small proportion of the gases adsorbed on solid particles had a magmatic origin however most of the steam and the tephra seemed to originate from superficial levels of a hydrothermal system similar phreatic eruptions have occurred several times in recorded history in the case of la soufriere the origin of the phreatic eruptions is best described by an abnormal energy input versus steady state from a crustal magma chamber the occurrence of truly magmatic eruptions is presumably inhibited by an extensive hydrothermal system the abrupt release of more power from the magma chamber could have resulted in an explosive pyroclastic eruption substantial improvement of the guadeloupe volcano observatory has followed the 1975 1977 crisis permanent telemetered geophysical networks and regular geochemical observations have provided a five year data base of the volcano behavior in its noneruptive state which can be compared to crisis situations

deformation in the diffuse india capricorn somalia triple junction from a multibeam and magnetic survey of the northern central indian ridge 3 s 10 s 1 we use new multibeam and magnetic observations from 3 s 10 s along the central indian ridge to describe morphotectonic features and spreading fabrics within the study area and quantify deformation across the diffuse india capricorn somalia triple junction a megamullion adjacent to the vityaz transform fault is the first reported for the northern central indian ridge the principal transform displacement zone ptdz of the vema transform fault consists of several closely spaced faults that can be traced for more than 150 km serpentinite or volcanic intrusions that are offset by the vema pdtz have inferred ages of 30 000 45 000 years testifying to the youth of active features on the valley floor abyssal hill orientations throughout the study area have remained constant since at least 4 ma implying little or no change in the opening direction during this period abyssal hills from opposite sides of the ridge have the same orientations within our 1 3 errors implying that slip along reactivated fracture zones in the diffuse triple junction neither significantly rotates nor shears the intervening seafloor transform fault azimuths in the survey area agree with the nuvel 1 africa australia slip direction but are 5 9 clockwise from the africa india direction in contrast seafloor spreading rates in the study area agree better with the nuvel 1 africa india predictions these seemingly conflicting observations are reconciled by a model in which seafloor within the diffuse triple junction rotates about the india capricorn pole at angular rotation rates that increase monotonically from zero to the full rotation rate across the deforming zone

debris flow evolution and the activation of an explosive hydrothermal system te maari tongariro new zealand abstract analysis of the pre and post eruption topography together with observations of the avalanche deposition sequence yields a triggering mechanism for the 6 august 2012 eruption of upper te maari the avalanche was composed of a wedge of c 683 000 774 000 m 3 of coarse breccia spatter and clay rich tuffs and diamictons which slid from the western flanks of the upper te maari crater the failure plane is considered to be a hydrothermally altered clay layer this landslide led to a pressure drop of up to 0 5 mpa enough to generate an explosive eruption from the hydrothermal system below which had been activated over the months earlier by additional heat and gas from a shallow intrusion the landslide transformed after c 700 m into a clay rich cohesive debris flow eroding soils from steep narrow stretches of channel before depositing on intermediate broad flatter reaches after each erosive reach the debris flow contained greater clay and mud contents and became more mobile at c 2 km flow distance however the unsaturated flow stopped due to a lack of excess pore pressure this volume controlled flow deposited thick steep sided lobes behind an outer levee accreting inward and upward to form a series of curved surface ridges

liquidus and solidus temperatures of a fe o s alloy up to the pressures of the outer core implication for the thermal structure of the earth s core abstract the solidus and liquidus temperatures of the fe75o5s20 alloy are determined up to 157 gpa using a laser heated diamond anvil cell combined with in situ x ray diffraction technique fe fcc hcp fe3s2 fe3s and feo b1 b8 rhombohedral phases are stable under subsolidus conditions first fe3s2 or fe3s phase melts at a temperature close to the eutectic point of the fe fe3s system suggesting that the alloying effect of 5 at oxygen on the eutectic temperature in the fe fe3s system is minor then feo melts at several hundreds of degrees kelvin higher than the solidus and fe is a liquidus phase in this system the liquidus temperature is 260 670 k lower than the melting temperature of pure fe because of the alloying effect of s and o on the melting temperature of fe based on our results the temperatures at the core mantle boundary tcmb and at the boundary of the inner outer core ticb are estimated to be 3600 200

dynamics of surges generated by hydrothermal blasts during the 6 august 2012 te maari eruption mt tongariro new zealand abstract the 6 august 2012 te maari eruption produced violent and widespread cold pyroclastic density currents pdcs following unroofing of the pressurized hydrothermal system despite an erupted volume of only 5 10 5 m 3 and lacking any juvenile component the 340 000 m 3 of pdcs spread over an area of 6 1 km 2 and had mobilities that were on the order of volcanic blasts or blast like pdcs this great mobility was due to strong lateral focussing of explosion energy producing jets with initial velocities 100 m s we present a type stratigraphy for these hydrothermal derived low temperature pdcs that show a tripartite deposit sequence each of the deposit units dominates respectively three outward gradational sedimentary facies reflecting transitions in the propagating pdc transport and depositional mechanisms the largest pdcs directed west and east of the upper te maari area were generated from outer cone breccias and tuffs that were mostly highly hydrothermally altered landsliding and the geometry of the hydrothermal area led to the directed jetting initial particle laden jets laid sheets grading into lobes of proximal massive sand to gravel rich facies dominated by unit a and extending up to 1 km from the vents as the jets were collapsing a vertically and longitudinally stratified pdc developed within the first few hundred metres from source exponential thinning and coarse tail grading dominated fining with radial distance of massive unit a resulted from fast deposition and progressive depletion of the most concentrated flow region behind the pdc head markedly slower tractional sedimentation from the passing pdc body and tail deposited the highly stratified and ripple bedded fine coarse ash of unit b this formed distinctive dune fields of the medial dune bedded ash rich facies upwards in depositional sequences the waning of the current can be seen by replacement of higher energy bedforms to progressively lower ones downstream progressive waning and further depletion are characterised by the development of the distal wavy to planar bedded ash rich facies this is increasingly dominated by the uppermost deposition unit c of laminated fine med ash deposited by gently turbulent dilute phoenix clouds these high energy pdcs sourced from flank hydrothermal systems should be regarded as a serious threat in any multihazard assessment of a stratovolcano even though they may not be one of the major magmatic vent sites in addition further detailed studies of these hydrothermal jetting events and their deposits should be pursued in order to better understand large volume volcanic blasts which appear to be a larger scale sibling phenomenon

solution to the volume problem in serpentinization kernel pattern consists of a rim of completely serpentinized peridotite surrounding a core of partly serpentinized or unserpentinized peridotite it is found adjacent to shear zones in some serpentinites kernels are commonly rectangular with length width ratios of 1 to 3 the boundary between the completely serpentinized rim and the unserpentinized core is commonly cut at a high angle by cross fractures the cross fractures which contain either picrolite or chrysotile asbestos taper out in the core and widen in the rim they are almost always perpendicular to the core rim boundary and point into the core of the kernel in this sense they are radially distributed in the rim the kernel pattern can be observed in thin section in outcrop and on the megascopic scale of tens of metres cross fractures represent expansion fractures in serpentinite in the rim of the kernel caused by an increase in volume acompanying serpentinization of the peridotite in the core of the kernel as the serpentinization front penetrates into the kernel the serpentinized peridotite expands however the serpentinite in the rim cannot expand and must fracture to accommodate the increase in volume as serpentinization proceeds more expansion occurs extending the fractures farther into the core and requiring the fractures in the existing serpentinite to widen these fractures are subsequently filled by serpentine minerals the resulting pattern consists of a rim of serpentinite cut by serpentine veins that surrounds a core of peridotite measured densities of cross fractures in the rims of kernels are consistent with those expected from the magnitude of the volume change accompanying serpentinization of peridotite

30 000 years of hydrothermal activity at the lost city vent field strontium carbon and oxygen isotope data and radiocarbon ages document at least 30 000 years of hydrothermal activity driven by serpentinization reactions at lost city serpentinization beneath this off axis field is estimated to occur at a minimum rate of 1 2 10 4 cubic kilometers per year the access of seawater to relatively cool fresh peridotite coupled with faulting volumetric expansion and mass wasting processes are crucial to sustain such systems the amount of heat produced by serpentinization of peridotite massifs typical of slow and ultraslow spreading environments has the potential to drive lost city type systems for hundreds of thousands possibly millions of years

the effects of serpentinization on density and magnetic susceptibility a petrophysical model abstract new measurements are presented of initial magnetic susceptibility and density for serpentinized harzburgites from the josephine peridotite oregon an inverse correlation between density and susceptibility which is typical of these rocks and similar rocks from other localities is not explained by simple serpentinization reactions calculations of density and susceptibility as a function of reaction progress for reactions that produce magnetite show susceptibilities that are larger than those observed at low degrees of serpentinization susceptibilities of fe bearing serpentine and brucite are calculated from a molecular field model initially developed for the olivine and orthopyroxene solid solutions at high degrees of serpentinization susceptibilities that are lower than those observed are predicted by reactions where iron is sequestered by serpentine and brucite observed density susceptibility trends of serpentinized harzburgites fall between the values predicted by these limiting reactions the observed properties may be modelled by multiple reactions involved in multi stage serpentinization processes such that the production of magnetite increases with the degree of serpentinization the empirical and calculated properties provide a complementary characterization of density and susceptibility values of serpentinites

environmental hazards of fluoride in volcanic ash a case study from ruapehu volcano new zealand abstract the vent hosted hydrothermal system of ruapehu volcano is normally covered by a c 10 million m3 acidic crater lake where volcanic gases accumulate through analysis of eruption observations granulometry mineralogy and chemistry of volcanic ash from the 1995 1996 ruapehu eruptions we report on the varying influences on environmental hazards associated with the deposits all measured parameters are more dependent on the eruptive style than on distance from the vent early phreatic and phreatomagmatic eruption phases from crater lakes similar to that on ruapehu are likely to contain the greatest concentrations of environmentally significant elements especially sulphur and fluoride these elements are contained within altered xenolithic material extracted from the hydrothermal system by steam explosions as well as in residue hydrothermal fluids adsorbed on to particle surfaces in particular total f in the ash may be enriched by a factor of 6 relative to original magmatic contents although immediately soluble f does not show such dramatic increases highly soluble naf and casif6 phases demonstrated to be the carriers of available f in purely magmatic eruptive systems are probably not dominant in the products of phreatomagmatic eruptions through hydrothermal systems instead slowly soluble compounds such as caf2 alf3 and ca5 po4 3f dominate fluoride in these phases is released over longer periods where only one third is leached in a single 24 h water extraction this implies that estimation of soluble f in such ashes based on a single leach leads to underestimation of the f impact especially of a potential longer term environmental hazard in addition a large proportion of the total f in the ash is apparently soluble in the digestive system of grazing animals in the ruapehu case this led to several thousand sheep deaths from fluorosis

gas and ash emissions associated with the 2010 present activity of sinabung volcano indonesia abstract sinabung volcano sumatra indonesia awoke from over 1200 years of dormancy with multiple phreatic explosions in 2010 after a period of quiescence sinabung activity resumed in 2013 producing frequent explosions lava dome extrusion and pyroclastic flows from dome and lava flow collapses becoming one of the world s most active volcanoes and displacing over 20 000 citizens this study presents a compilation of the geochemical datasets collected by the indonesian center for volcanology and geological hazard mitigation cvghm from 2010 current 2016 which provides insights into the evolution of the eruption based on observations of so2 emissions ash componentry ash leachate chemistry and bulk ash geochemistry the eruption can be split into six distinct geochemical phases the initial stage of phreatic summit explosions phase a occurred from august september 2010 during which background so2 emissions averaged 550 180 t d 1 s d an eruptive pause phase b starting in october 2010 abruptly ended in september 2013 with a resumption of conduit clearing eruptions phase c this third phase had a relatively modest background so2 emission rate avg 430 310 t d and produced ash consisting of accidental ejecta with high s cl leachate molar ratios 12 0 8 2 max 34 suggestive of deep sourced magma and or the incorporation of hydrothermal sulfur bearing phases lava extrusion at the summit phase d began in mid december 2013 and was accompanied by relatively low so2 emission rates 360 200 t d and lower but variable s cl leachate ratios 6 3 8 5 the most intense phase of the eruption phase e occurred from mid january to late february 2014 following a major lava dome collapse this period included increased lava extrusion rates dozens of large eruptions per day high so2 emission rates average 1680 1070 t d peak 3800 t d and a dramatic drop in s cl ash leachates to ratios average 1 4 0 5 consistent with increased degassing from shallow magma and the clearing out of sulfurous phases from the old hydrothermal system from march 2014 through the time of writing september 2016 sinabung settled into a relatively steady state of lower activity phase f ash emissions now consist of dominantly juvenile andesitic dacitic material with low s cl leachate ratios average 1 1 0 6 in august 2016 so2 emissions started being measured in a continuous manner using a network of permanent scanning doas instruments background so2 emission rates average 450 290 t d for the entirety of phase f but have been progressively decreasing to an average of 250 300 t d since june 2016 this long term gradual decline in so2 emission rates at sinabung since early 2014 is consistent with an apparent decrease in magma supply and lava effusion rates our conceptual degassing model suggests that large explosions and pyroclastic flows could continue in the near term owing to conduit plugging and dome collapses remaining a major threat until the magma supply rate decreases further and the eruption ends

assessment of leachable elements in volcanic ashfall a review and evaluation of a standardized protocol for ash hazard characterization abstract volcanic ash presents a widespread and common hazard during and after eruptions complex interactions between solid ash surfaces and volcanic gases lead to the formation of soluble salts that may be mobilized in aqueous environments a variety of stakeholders may be concerned about the effects of ash on human and animal health drinking water supplies crops soils and surface runoff as part of the immediate emergency response rapid dissemination of information regarding potentially hazardous concentrations of soluble species is critical however substantial variability in the methods used to characterize leachable elements makes it challenging to compare datasets and eruption impacts to address these challenges the international volcanic health hazard network www ivhhn org organized a two day workshop to define appropriate methods for hazard assessment the outcome of this workshop was a consensus protocol for analysis of volcanic ash samples for rapid assessment of hazards from leachable elements which was subsequently ratified by leading volcanological organizations the purpose of this protocol is to recommend clear standard and reliable methods applicable to a range of purposes during eruption response such as assessing impacts on drinking water supplies and ingestion hazards to livestock and also applicable to research purposes where possible it is intended that the methods make use of commonly available equipment and require little training to evaluate method transferability an interlaboratory comparison exercise was organized among six laboratories worldwide each laboratory received a split of pristine ash and independently analyzed it according to the protocol for a wide range of elements collated results indicate good repeatability and reproducibility for most elements thus indicating that the development of this protocol is a useful step towards providing standardized and reliable methods for ash hazard characterization in this article we review recent ash leachate studies report the outcomes of the comparison exercise and present a revised and updated protocol based on the experiences and recommendations of the exercise participants the adoption of standardized methods will improve and facilitate the comparability of results among studies and enable the ongoing development of a global database of leachate information relevant for informing volcanic health hazards assessment

fesi melting curve up to 70 gpa abstract the melting curve of iron monosilicide fesi has been determined in a laser heated diamond anvil cell from 6 up to 70 gpa by direct visual observation of the continuous laser speckle motion in the liquid state at 12 gpa and 1700 k a discontinuous change in the slope of the melting curve indicates the first order phase transition between the fesi b20 and the cscl type fesi structures b2 during the phase transition the coordination number of both fe and si atoms increases from 7 to 8 above this pressure the melting curve rises steeply but shows significant flattening at higher pressures a comparison with the melting curve of fe shows that both curves cross at 32 3 gpa fesi having higher melting temperatures about 100 k at high pressures

serpentinization of cumulate ultramafic rocks from the north arm mountain massif of the bay of islands ophiolite abstract partially serpentinized dunites and wehrlites comprise the bulk of the cumulate ultramafic unit at the north arm mountain massif of the bay of islands ophiolite complex newfoundland in a suite of 59 dunites and werhlites from the base of the unit the serpentinized portions consist of lizardite chrysotile brucite accessory magnetite the ratio of lizardite chrysotile to brucite 8 2 weight percent petrographic observations show that most serpentinization occurred at the expense of olivine only limited amounts of clinopyroxene were serpentized an estimated volume increase of 32 accompanied serpentinization of the peridotites reconstructions of the primary modal proportions of wehrlites made taking this volume increase into account contain an average of 6 more clinopyroxene and 6 less olivine than do modal reconstructions that ignore the volume increase mass balance calculations provide no clear evidence for appreciable metasomatism of al2o3 cao feo mgo or sio2 during serpentinization the presence of brucite the evidence that most serpentinization occurred at the expense of olivine and the lack of appreciable metasomatism suggest that the primary reaction that controlled serpentinization of the peridotites is 2mg 2 sio 2 3h 2 o mg 3 si 2 o 5 oh 4 mg oh 2 olivine added serpentine brucite

time dependent convection models of mantle thermal structure constrained by seismic tomography and geodynamics implications for mantle plume dynamics and cmb heat flux summary one of the outstanding problems in modern geodynamics is the development of thermal convection models that are consistent with the present day flow dynamics in the earth s mantle in accord with seismic tomographic images of 3 d earth structure and that are also capable of providing a time dependent evolution of the mantle thermal structure that is as realistic earth like as possible a successful realization of this objective would provide a realistic model of 3 d mantle convection that has optimal consistency with a wide suite of seismic geodynamic and mineral physical constraints on mantle structure and thermodynamic properties to address this challenge we have constructed a time dependent compressible convection model in 3 d spherical geometry that is consistent with tomography based instantaneous flow dynamics using an updated and revised pseudo spectral numerical method the novel feature of our numerical solutions is that the equations of conservation of mass and momentum are solved only once in terms of spectral green s functions we initially focus on the theory and numerical methods employed to solve the equation of thermal energy conservation using the green s function solutions for the equation of motion with special attention placed on the numerical accuracy and stability of the convection solutions a particular concern is the verification of the global energy balance in the dissipative compressible mantle formulation we adopt such validation is essential because we then present geodynamically constrained convection solutions over billion year timescales starting from present day seismically constrained thermal images of the mantle the use of geodynamically constrained spectral green s functions facilitates the modelling of the dynamic impact on the mantle evolution of 1 depth dependent thermal conductivity profiles 2 extreme variations of viscosity over depth and 3 different surface boundary conditions in this case mobile surface plates and a rigid surface the thermal interpretation of seismic tomography models does not provide a radial profile of the horizontally averaged temperature i e the geotherm in the mantle one important goal of this study is to obtain a steady state geotherm with boundary layers which satisfies energy balance of the system and provides the starting point for more realistic numerical simulations of the earth s evolution we obtain surface heat flux in the range of earth like values 37 tw for a rigid surface and 44 tw for a surface with tectonic plates coupled to the mantle flow also our convection simulations deliver cmb heat flux that is on the high end of previously estimated values namely 13 tw and 20 tw for rigid and plate like surface boundary conditions respectively we finally employ these two end member surface boundary conditions to explore the very long time scale evolution of convection over billion year time windows these billion year scale simulations will allow us to determine the extent to which a memory of the starting tomography based thermal structure is preserved and hence to explore the longevity of the structures in the present day mantle the two surface boundary conditions along with the geodynamically inferred radial viscosity profiles yield steady state convective flows that are dominated by long wavelengths throughout the lower mantle the rigid surface condition yields a spectrum of mantle heterogeneity dominated by spherical harmonic degree 3 and 4 and the plate like surface condition yields a pattern dominated by degree 1 our exploration of the time dependence of the spatial heterogeneity shows that for both types of surface boundary condition deep mantle hot upwellings resolved in the present day tomography model are durable and stable features these deeply rooted mantle plumes show remarkable longevity over very long geological time spans mainly owing to the geodynamically inferred high viscosity in the lower mantle

contamination of water supplies by volcanic ashfall a literature review and simple impact modelling abstract volcanic ash is the most widely distributed product of explosive volcanic eruptions and can disrupt vital infrastructure on a large scale previous studies of effects of ashfall on natural waters and water supplies have focused mainly on the consequences of increased levels of turbidity ash suspended in water acidity and fluoride with very little attention paid to other contaminants associated with volcanic ash the aims of this paper are twofold firstly to review previous studies of the effects of volcanic ashfall on water supplies and identify information gaps and secondly to propose a simple model for predicting effects of ashfall on water supplies using available information on ash composition we reviewed reported impacts of historic eruptions on water supplies drawing on case studies from new zealand vanuatu argentina the usa costa rica montserrat iceland and guadeloupe elevated concentrations of fluoride iron sulphate and chloride as well as turbidity and acidity have been reported in water supplies from a public health perspective the two main issues appear to be 1 outbreaks of infectious disease caused by the inhibition of disinfection by high levels of suspended ash and 2 elevated fluoride concentrations we devised a simple model using volcanic ash leachate composition data to predict effects on receiving waters applying this model to the effects of ruapehu ash from the 1995 1996 eruptions suggests that the primary effects of concern are likely to be an increase in acidity decrease in ph and increases in concentrations of the metals aluminium iron and manganese these metals are not normally considered to pose health risks and are regulated only by secondary non enforceable guidelines however exceedences of guideline values for al mn fe and ph will cause water to become undrinkable due to a bitter metallic taste and dark colour and may also cause corrosion staining and scale deposition problems in water tanks and pipes therefore the main issues following volcanic ashfall of similar composition to ruapehu ash are likely to be shortages of potable water and damage to distribution systems rather than risks to public health

aspects of historical eruptive activity and volcanic unrest at mt tongariro new zealand 1846 2013 abstract the 6 august and 21 november 2012 eruptions from upper te maari crater have heightened interest in past activity at mt tongariro new zealand risks caused by volcanic hazards are increasingly being quantified by using probability estimates through expert elicitation partly based on the frequency of past eruptions to maximise the accuracy of these risk values at mt tongariro a historical eruption catalogue is required this paper presents the findings of a detailed historical chronology of unrest and eruptions at mt tongariro between 1846 ad and 2013 ad it builds on the findings of previous researchers highlighting that volcanic eruptions and unrest have occurred frequently from this volcano eruptions are now thought to have occurred at mt tongariro in 1869 1892 1896 97 1899 1926 1927 1934 and 2012 eruptions also potentially occurred in 1846 1855 1886 and 1928 in addition to frequent eruptions from neighbouring mt ngauruhoe the number of recognised eruptions during the 1896 97 episode has increased to 18 and the red crater area has been found to be more active than previously appreciated multiple episodes of unrest not resulting in eruptions have also been identified new eruption recurrence rates are derived from this catalogue with the baseline probability of the onset of an eruption episode calculated to be 0 07 per year if 1896 97 and 2012 are considered as one episode each and all others separately and the maximum eruption rate within an eruption episode is 18 per year these new data contribute towards risk assessments for future eruptions at mt tongariro

compositional controls on hydrogen generation during serpentinization of ultramafic rocks abstract where ultramafic rocks are exposed to water at temperatures 2 formation are not well established we used thermodynamic computations to examine the equilibrium mineral assemblages mineral compositions and the chemistry of fluids during serpentinization of 21 different ultramafic rock compositions and 10 distinct compositions of olivine between 25 c and 400 c at 50 mpa our models predict some systematic differences between serpentinization of olivine dominated lithologies i e peridotite and of orthopyroxene dominated lithologies i e pyroxenite most notably it is predicted that serpentinization of peridotite causes the formation of serpentine having elevated fe 3 fe 3 fe 2 values fe bearing brucite at temperatures ca 320 c and magnetite at temperatures ca 200 c while serpentinization of pyroxenite does not produce magnetite but instead forms fe rich serpentine with relative low fe 3 fe 3 fe 2 values and fe poor talc the predicted activities of dissolved hydrogen a h 2 aq dissolved silica a sio 2 aq as well as the ph vary accordingly at temperatures ca 350 c fluids interacting with peridotite are more reducing have lower a sio 2 aq and higher ph than fluids interacting with pyroxenite a direct correlation between the iron content of olivine its stability relative to water temperature and a h 2 aq is apparent from our calculations in contrast to forsterite rich olivine fayalite rich olivine can be stable to temperatures as low as 180 c in the presence of water as a consequence the predicted ah 2 aq for serpentinization of fayalite is maximal at temperatures 180 c

reaction induced fracturing during replacement processes replacement processes are common transformation mechanisms in minerals and rocks at a variety of conditions and scales the underlying mechanisms are in general poorly understood but both mechanical and chemical processes are thought to be important replacement of leucite kalsi2o6 by analcime naalsi2o6 h2o is common in silica poor igneous rocks a 10 increase in volume is associated with the replacement process and this generates stresses that eventually cause fracturing of the reacting leucite experimentally reacted leucite samples display characteristic fracturing patterns that include both spalling of concentric onion skin like layers near the reacting interface and the formation of cross cutting often hierarchically arranged sets of fractures that divide the remaining leucite into progressively smaller domains these structures may explain the patchy alteration patterns observed in natural leucite samples and similar so called mesh textures associated with the serpentinization of olivine grains during hydration of mafic or ultramafic rocks they are also strikingly similar to larger scale patterns formed during spheroidal weathering processes a simple discrete element model illustrates the mechanics that control the formation of such systems and shows how these replacement processes may be accelerated due to the generation of new reactive surface area by hierarchical fracturing processes

volcanic ash leachate compositions and assessment of health and agricultural hazards from 2012 hydrothermal eruptions tongariro new zealand abstract after almost 80 years of quiescence the upper te maari vent on mt tongariro erupted suddenly at 2352 h nz time on 6 august 2012 the short lived hydrothermal eruption distributed a fine ash of minor volume 5 10 5 m 3 over 200 km from source the threat of further eruptions prompted an investigation of the possible health and agricultural impacts of any future eruptions from this volcano particularly since the most recent large scale ash falls in new zealand in 1995 1996 had generated significant agricultural problems including livestock deaths deposited ash was sampled between 5 and 200 km from the volcano as soon as possible after the eruption two sub lobes of ash were identified from different vent areas and displayed subtly different leaching properties the first was an initial small lobe directed nne likely formed from drifting low level clouds associated with the initial lateral explosive blast and surges the main fall lobe directed eastward was sourced from a short lived vertical plume that rose up to c 8 km ash from the initial fall lobe had higher concentrations of f and al in single step leaches as well as in the totals of three sequential extractions further the initial lobe showed a higher proportion of soluble f and al extracted in the first leach compared to totals a linear relationship between concentrations of al and f in single leaches from the 6 august eruption was highly significant pearson correlation coefficient r 0 987 for 1 20 leaching ratios and r 0 971 for 1 100 suggesting the presence of soluble alumino fluoride complexes alf x 3 x an even more significant 1 1 ratio is displayed for the largest concentration leached ions of ca and so 4 which correspond to the presence of crystalline gypsum throughout the newly excavated hydrothermal system although no fresh magma was erupted in this event a shallow intrusion prior to the hydrothermal explosion apparently provided significant contents of volcanic gas that was dissolved within the hydrothermal fluids and adhering to ejected particles this and the ubiquitous presence of gypsum dominated the soluble components of these ash deposits leading to a complex leaching profile the leaching study carried out here showed that agricultural and human health hazard assessment particularly of f and s is not straightforward particularly because f solubility may be complex and not well characterised by simple leaching studies in the case of s which is agriculturally important saturation effects are apparent using normal leaching protocols and also imply a need for modification of standard methods

evolution of a vent hosted hydrothermal system beneath ruapehu crater lake new zealand a two year chemical monitoring program of ruapehu crater lake shows that it has evolved considerably since the volcano s more active eruptive periods in the early 1970s the present ph 20 c of 0 6 is about one half unit more acid than the baseline values in the 1970s whereas s cl ratios have increased markedly owing in part to declining hcl inputs into the lake but also to absolute increases in so4 levels which now stand at the highest values ever recorded increases in k mg and na mg ratios over the 20 year period are attributed to hydrothermal reaction processes in the vent which are presently causing dissolution of previously formed alteration phases such as natroalunite these observations combined with results of a recent heat budget analysis of the lake have led to the development of hydrothermal convection model for the upper portion of the vent possible vent lake chemical reaction processes between end member reactants have been modelled with the computer code chiller the results are consistent with the view that variations in lake chemistry which are initiated by the introduction of fresh magmatic material into the vent reflect the extent of dissolution reaction progress on the magmatic material and or its alteration products the results also provide insights into the role of such vent processes in the formation of high sulfidation type ore deposits

potential impacts of tephra fallout from a large scale explosive eruption at sakurajima volcano japan we present an exposure analysis of infrastructure and lifeline to tephra fallout for a future large scale explosive eruption of sakurajima volcano an eruption scenario is identified based on the field characterization of the last subplinian eruption at sakurajima and a review of reports of the eruptions that occurred in the past six centuries a scenario based probabilistic hazard assessment is performed using the tephra2 model considering various eruption durations to reflect complex eruptive sequences of all considered reference eruptions a quantitative exposure analysis of infrastructures and lifelines is presented primarily using open access data the post event impact assessment of magill et al earth planets space 65 677 698 2013 after the 2011 vei 2 eruption of shinmoedake is used to discuss the vulnerability and the resilience of infrastructures during a future large eruption of sakurajima results indicate a main eastward dispersal with longer eruption durations increasing the probability of tephra accumulation in proximal areas and reducing it in distal areas the exposure analysis reveals that 2300 km of road network 18 km2 of urban area and 306 km2 of agricultural land have a 50 probability of being affected by an accumulation of tephra of 1 kg m2 a simple qualitative exposure analysis suggests that the municipalities of kagoshima kanoya and tarumizu are the most likely to suffer impacts finally the 2011 vei 2 eruption of shinmoedake demonstrated that the already implemented mitigation strategies have increased resilience and improved recovery of affected infrastructures nevertheless the extent to which these mitigation actions will perform during the vei 4 eruption presented here is unclear and our hazard assessment points to possible damages on the sakurajima peninsula and the neighboring municipality of tarumizu

variations in grain size and viscosity based on vacancy diffusion in minerals seismic tomography and geodynamically inferred mantle rheology the effect of grain size on mantle viscosity is comparable to that of temperature and pressure the current 3 d distribution of grain size in the mantle is however unknown to explore the possible variability of grain size we use the following geodynamic inferences of effective viscosity vacancy diffusion rates in upper mantle minerals and perovskite in the lower mantle lateral variations in temperature derived from seismic images and different geotherms an important outcome of this modeling is a new mapping of lateral viscosity variations throughout the mantle the corresponding 3 d variations in grain size are characterized by 2 orders of magnitude changes we find a correlation between grain size variability in the mantle and absolute viscosity changes with depth our findings suggest that the traditional assumption of arrhenius temperature dependence for vacancy diffusion in the lower mantle is not sufficient to constrain the deformation mechanisms that determine its effective bulk viscosity

chemistry of ash leachates to monitor volcanic activity an application to popocatepetl volcano central mexico abstract monitoring volcanic activity and assessing volcanic risk in an on going eruption is a problem that requires the maximum possible independent data to reduce uncertainty a quick relatively simple and inexpensive method to follow the development of an eruption and to complement other monitoring parameters is the chemical analysis of ash leachates particularly in the case of eruptions related to dome emplacement here the systematic analysis of so 4 2 cl and f concentrations in ash leachates is proposed as a valuable tool for volcanic activity monitoring however some results must be carefully assessed as is the case for s cl ratios since eruption of hydrothermally altered material may be confused with degassing of incoming magma sulfur isotopes help to identify so4 produced by hydrothermal processes from magmatic so2 lower s isotopic values correlated with higher f percentages represent a better indicator of fresh magmatic influence that may lead to stronger eruptions and emplacement of new lava domes additionally multivariate statistical analysis helps to identify different eruption characteristics provided that the analyses are made over a long enough time to sample different stages of an eruption

melting temperature of the earth s mantle and core earth s thermal structure abstract although the temperature at the top of the lower mantle is well constrained by phase equilibrium data for the transformation of transition zone minerals to the denser perovskite polymorphs the temperature distribution in the lower mantle is poorly known models depend strongly on the assumptions of the amount of internal heating and the viscosity profile new melting data on iron to pressures of the outer core 2 mbar and the observed strong decrease of eutectic melting depression in the fe feo fes system with increasing pressure however tightly constrain the temperature at the inner core boundary to slightly less than 5000 k this estimate can be reconciled with all recent static melting measurements on iron and lays within the uncertainty of shock temperature measurements the resulting temperature at the core mantle boundary of about 4000 k then requires a large temperature gradient at the bottom of the lower mantle of about 1500 k recent findings of the very high melting temperatures o

the immediate environmental effects of tephra emission the earth s history is punctuated by large explosive eruptions that eject large quantities of magma and silicate rock fragments into the atmosphere these tephra particles can sometimes be dispersed across millions of square kilometres or even entire continents the interaction of tephra with or in receiving environments may induce an array of physical chemical and biological effects the consequences for affected systems and any dependent communities may be chronic and localised in the event of frequent small eruptions while larger and rarer events may have acute regional scale impacts it is therefore necessary to document the range of possible impacts that tephra may induce in receiving environments and any resulting effects in interconnected systems we collate results from many studies to offer a detailed multidisciplinary and interdisciplinary review of the immediate post eruptive effects of tephra emission into the atmosphere onto vegetation soil or ice snow surfaces and in aquatic systems we further consider the repercussions that may be induced in the weeks to years afterwards in the atmosphere tephra can influence cloud properties and air chemistry by acting as ice nuclei in or by offering sites for heterogeneous reactions respectively tephra on vegetation causes physical damage and sustained coverage may elicit longer term physiological responses tephra deposits on soils may alter their capacity to exchange gas water and heat with the atmosphere or may have a specific chemical effect such as nutrient input or acidification on sensitive soils tephra deposition onto snow or ice may affect ablation rates rivers and lakes may experience turbidity increases and changes in their morphology as a result of fallout and prolonged months or years erosion from the tephra covered catchment in the first weeks after deposition tephra leaching may affect river chemistry the abundance and speciation of phytoplankton populations in lakes may be altered by tephra induced changes in water chemistry or sediment water nutrient cycling in the oceans tephra deposition may fertilise fe limited waters with potential impacts on the global carbon cycle embracing the full complexity of environmental effects caused by tephra fall demands a renewed investigative effort drawing on interdisciplinary field and laboratory studies combined with consideration of the interconnectivity of induced impacts within and between different receiving environments

perils in distinguishing phreatic from phreatomagmatic ash insights into the eruption mechanisms of the 6 august 2012 mt tongariro eruption new zealand abstract the weak geophysical precursors of the 6 august 2012 te maari eruption of mt tongariro and a lack of obvious juvenile components in its proximal ballistic deposits imply that the eruption was caused by the sudden decompression of a sealed hot hydrothermal system strong magmatic signals in pre and post eruption gas emissions indicate that fresh magma had intruded to shallow levels shortly before this eruption here we examine the volcanic ash produced during the august eruption with the aim of determining whether juvenile magma was erupted or not the widely applied criteria for identifying fresh juvenile pyroclasts provided inconclusive results the te maari ash sorting and trend towards a unimodal grain size distribution increase with distance along the dispersal axis proximal to intermediate sites showing polymodal grain size distributions can be related to the re fragmentation of different pre existing lithologies overlapped erupted pulses and transport mechanisms and to particle aggregation between 69 and 100 vol of particles coarser than 3 and 45 75 vol of grains finer than 3 were sourced from the pre existing commonly hydrothermally altered vent area lavas and pyroclasts free crystals pyroxene plagioclase magnetite pyrite make up 0 23 vol of particles coarser than 3 and 22 41 vol of grains finer than 3 brown to black fragments of fresh glass are a small 1 15 vol but notable component under sem these blocky glassy particles are poorly vesicular and irregularly shaped some with fluidal or bubble wall surfaces and others with fragmented stepped surfaces and fine adhering ash in thin section they contain variable amounts of microlites within an isotropic groundmass the range in silica content of the microprobe analysed glass is very wide 56 77 wt and cannot be correlated to any specific particle textural type these chemically and texturally diverse glassy fragments are identical to mechanically broken pieces of country rock lavas and pyroclasts both their diversity and their match with vent country rocks argue strongly against a juvenile origin for the glassy fragments we conclude that rising magma provided only heat and gas into the overlying sealed vapour dominated hydrothermal system a landslide from this area led to a rapid decompression and ash was produced by top down hydrothermal explosions careful attention must be paid to the combination of compositions and textures of fine ash particles in such situations as well as to the context of their source vent in order to be confident that new magma has reached the surface

volcanic ash leachates a review and recommendations for sampling methods tephra in plumes can scavenge and thereby rapidly deposit volatiles including sulphur halogen and metal species these may then be leached e g by rainfall potentially releasing heavy loadings to soils and water bodies several eruptions have resulted in contamination of pasture sometimes with serious impacts on livestock water quality has also been an issue in some areas affected by tephra fall this work synthesises the literature on volcanic ash leachates and considers the controls on volatile adsorption general trends emerge for basaltic intermediate and silicic tephra as well as for variable particle size and transport distance the applications of ash leachate data to plume gas geochemistry calculation of volatile budgets and environmental impact assessment are evaluated comparisons for different eruptions are hampered by disparities in leachate analysis techniques a standardised methodology is therefore proposed to facilitate future health impact assessment and volcanological interpretation of results from different sites

dynamic control on serpentine crystallization in veins constraints on hydration processes in oceanic peridotites deformation and hydration processes are intimately linked in the oceanic lithosphere but the feedbacks between them are still poorly understood especially in ultramafic rocks where serpentinization results in a decrease of rock density that implies a volume increase and or mass transfer serpentinization is accompanied by abundant veining marked by different generations of vein filling serpentines with a high variety of morphologies and textures that correspond to different mechanisms and conditions of formation we use these veins to constrain the role of deformation and mass transfer processes during hydration of oceanic peridotites at slow spreading ridges we have selected a representative set of veins from ocean floor serpentinites of the mid atlantic ridge near kane transform fault 23 n and characterized these in detail for their microstructures and chemistry by coupling optical and electron microscopy sem tem with electron microprobe analyses four main veining episodes v1 to v4 accompany the serpentinization the first episode identified as vein generation v1 is interpreted as the tectonically controlled penetration of early seawater dominated fluid within peridotites enhancing thermal cracking and mesh texture initiation at 3 4 km up to 8 km depth and at t 300 350 c the two following vein stages v2 and v3 formed in a closed diffusive system and accommodate volume expansion required to reach almost 50 serpentinization of the protolith the cracks exploited by these veins were caused by the progressive unroofing at depths of 4 to 2 km along a detachment fault degree and rate of serpentinization seem to be controlled by the capacity of the system to create space and to drive the mass transfer needed for ongoing serpentinization and this capacity is in turn linked to the exhumation rate and local tectonics during this period water consumed by hydration may prevent the establishment of convective hydrothermal cells the onset of an open hydrothermal system in the shallow lithosphere 2 km where brittle fracturing and advective transfer dominate and enable the completion of serpentinization is marked by the last vein generation v4 these results show a complete history of alteration with the crystallization of different types of serpentine recording different tectonic events chemical conditions and modes of hydrothermal alteration of the lithosphere

melting of the fefeo and the fefes systems at high pressure constraints on core temperatures melting temperatures of feo fes and fes2 have been accurately determined in a hydrostatic inert pressure environment up to about 0 5 mbar using a new yttrium lithium fluoride ylf heating laser the melting curve for feo is in perfect agreement with data obtained from multi anvil experiments at 160 kbar 1 but is in stark disagreement with previous laser heating experiments 2 preliminary measurements show strong melting depression on mixtures of fe and fes whereas mixtures of fe and feo were observed to melt close to the melting curve of iron the kraut kennedy melting relationship 3 in which the melting temperature is a linear function of volume is successfully tested in this study for li na k fe fes fes2 and feo to compressions up to 30 at 1 36 mbar core mantle boundary cmb feo fe and fes are estimated to melt at 3670 3260 and 3060 100 k respectively assuming outer core compositions with about 60 fe and about 40 feo or fes and a solid solution system the melting temperature at the cmb on the core side would be 3300 k 200 k compared to a temperature at the bottom of the mantle of 2650 100 k if these systems exhibit eutectic behaviour the melting gradient through the outer core would have to be substantially higher than the adiabatic gradient in order to maintain a thermal boundary at the cmb the present melting data and experimental constraints on the adiabatic gradient in the outer core suggest a temperature at the inner core outer core boundary of nearly 4200 k

unraveling the sequence of serpentinization reactions petrography mineral chemistry and petrophysics of serpentinites from mar 15 n odp leg 209 site 1274 1 the results of detailed textural mineral chemical and petrophysical studies shed new light on the poorly constrained fluid rock reaction pathways during retrograde serpentinization at mid ocean ridges uniformly depleted harzburgites and dunites from the mid atlantic ridge at 15 n show variable extents of static serpentinization they reveal a simple sequence of reactions serpentinization of olivine and development of a typical mesh texture with serpentine brucite mesh rims followed by replacement of olivine mesh centers by serpentine and brucite the serpentine mesh rims on relic olivine are devoid of magnetite conversely domains in the rock that are completely serpentinized show abundant magnetite we propose that low fluid flux serpentinization of olivine to serpentine and ferroan brucite is followed by later stages of serpentinization under more open system conditions and formation of magnetite by the breakdown of ferroan brucite modeling of this sequence of reactions can account for covariations in magnetic susceptibility and grain density of the rocks citation bach w h paulick c j garrido b ildefonse w p meurer and s e humphris 2006 unraveling the sequence of serpentinization reactions petrography mineral chemistry and petrophysics of serpentinites from mar 15 n odp leg 209 site 1274 geophys res lett 33 l13306

hydrothermal eruptions at el humazo domuyo geothermal field argentina insights into the eruptive dynamics and controls abstract hydrothermal eruptions are explosive events driven by the sudden and violent vaporization of the water present in many hot water geothermal fields worldwide over recent years thermodynamical conditions of fluids and petrophisical geomechanical features of host rocks were mentioned as responsible of the wide range of eruptive styles and deposits of hydrothermal eruptions nevertheless geological and historical records show that pdc and fallout processes are underestimated as common processes linked to hydrothermal eruptions this paper analyzes from a multi disciplinary approach virtual outcrops modeling sedimentology petrographic and xdr studies facies modeling eye witness source analysis and stratigraphy the pristine holocene historic hydrothermal eruptive record of el humazo manifestation domuyo geothermal field patagonia argentina different eruptive scenarios are characterized by ballistic ejection pdc and or fallout mechanisms with discernible tefra composition and granulometry associated with both excavational and or aggradational landforms we show how diverse eruptive dynamics are controlled by pre eruptive internal and external factors such as reservoir energy depth of the explosion fragmentation levels physical properties and structural anisotropy of the host rocks and eruptive center migrations we consider that this case study may be useful not only for the application in the assessment of the volcanic hazard associated with the domuyo geothermal field but also contributes to the knowledge of the eruptive dynamics in other geothermal systems with similar characteristics

in situ determination of fe fe3s phase diagram and liquid structural properties up to 65 gpa abstract lighter elements than iron such as sulphur are required in the earth s core to account of the core density deficit accurate determination of the evolution of the fe fes phase diagram at high pressure is essential to determine sulphur amount in the earth s core ab initio calculations predict extensive solubility of s in solid fe at core pressures of 330 gpa whereas multi anvil quench analysis exhibits deep eutectic system at moderate pressure of 21 gpa in this study we investigated the fe rich part of fe fes phase diagram up to 65 gpa and 2200 k using in situ angle dispersive x ray diffraction we report a uniform increase with pressure of the eutectic temperatures t eut of about 15 k gpa above 50 gpa we evidence a decrease of s content in eutectic liquid with increasing pressure extrapolating this trend to inner core boundary pressures suggests that s cannot account for the 10 wt outer core density deficit and that other light elements such as si and o are needed diffraction pattern recorded at 42 gpa and 2150 k was selected for structural investigations of the fe s liquid by applying liquid structure simulation based on gaussian distribution of atoms around crystalline positions a good agreement has been found with hcp fe model structure rather than with fe 3 s structure it suggests that s acts as an interstitial impurity in the liquid state therefore s could have a relatively minor effect on sound velocities in liquid outer core

vegetation dieback as a proxy for temperature within a wet pyroclastic density current a novel experiment and observations from the 6th of august 2012 tongariro eruption abstract the 6th of august 2012 eruption of te maari mt tongariro new zealand generated wet pyroclastic density currents pdcs which caused widespread dieback of vegetation singed brown foliage in their path an absence of significant charcoal formation suggests that pdc temperatures were mostly below 250 c textural evidence for liquid water being present in the matrices during emplacement vesicles suggests that temperatures were

hydrovolcanic ash emission between august 14 and 24 2015 at cotopaxi volcano ecuador characterization and eruption mechanisms abstract cotopaxi is an active hazardous and ice covered stratovolcano 60 km southeast of quito ecuador whose last major eruption occurred in 1877 during 2001 2002 volcanic unrest characterized by volcanic seismicity and deformation ended without eruptive activity on april 2015 a new increase of seismicity so2 emissions thermal anomalies and edifice deformation evolved into the onset of a new eruptive cycle beginning august 14 we sampled and measured the ash fall deposits to the west of cotopaxi between august 14 and 24 2015 the ash collected was analyzed using grain size x ray fluorescence x ray diffraction and scanning electron microscope sem eds revealing the eruptive products to be compound of dense fragments mostly lithics diverse types of scoria pumice free fractured crystals glassy particles and aggregates most of hydrothermal alteration is observed during the initial stage of the eruption 14 15 august including cu oxides and fe minerals in the lithics the glassy particles were blocky morphology and textural changes were recognized over 10 days of eruption varying from null or low vesicularity to low to moderate vesicularity occasionally exhibiting molten or subrounded textures the bulk ash has a basaltic andesitic composition 55 67 wt of sio2 while clusters of selected particles likely juvenile analyzed through sem eds reveal dacitic composition 65 67 and 65 8 wt sio2 plagioclase clinopyroxene and orthopyroxene are the main minerals present with accessory anhydrite melanterite and pyrite these typically observed during the initial stage of eruption these variations in addition to the geophysical background led us to interpret this eruption as the result of the volcano s hydrothermal system disruption due to a shallow low volume magma input which initially evolved into phreatic activity at surface level further activity up to 24 august was triggered by the indirect interaction between magma and the depleted hydrothermal system generating a magmatic hydrothermal eruption the issue is important for evaluating unrest periods at active stratovolcanoes and the impact of their initial low volume ash falls in neighboring communities

fate and agricultural consequences of leachable elements added to the environment from the 2011 cordon caulle tephra fall abstract the june 2011 eruption of cordon caulle volcano chile dispersed tephra over 350 000 km 2 including productive agricultural land this resulted in the death of nearly one million livestock two distinct environments were affected a proximal temperate andean setting and the semi arid argentine steppe farther from the volcano the purpose of this study was to better understand the fate and agricultural consequences of leachable elements added to the environment by this large silicic tephra fall tephra soil and surface water samples across the depositional area were collected both immediately after the eruption tephra and water and nine months afterwards tephra soil and water tephra samples were analysed following a new hazard assessment protocol developed by the international volcanic health hazard network ivhhn water extractable element concentrations in freshly collected tephra were very low to low compared to other eruptions and showed no trends with distance from the volcano surface water analyses suggested short term changes to water composition due to the release of elements from tephra no effect on the fertility of soils underlying tephra was apparent after nine months water extractable fluorine f in freshly collected tephra ranged from 12 to 167 mg kg with a median value of 67 mg kg based on parallels with the 11 12 october 1995 eruption of ruapehu volcano new zealand we conclude that f toxicity was a possible contributing factor to the large scale livestock deaths as well as to chronic fluorosis widely reported in wild deer populations across the cordon caulle tephra depositional area finally we recommend that effective response to widespread tephra fall over agricultural areas should include 1 rapid statistically representative field sampling of tephra soils surface water supplies and forage crops 2 analysis using appropriate and reliable laboratory methods 3 modelling both short and long term impacts on the ecosystem especially for elements that may generate chronic hazard 4 timely dissemination of results to agricultural agencies 5 longitudinal sampling and monitoring to adapt impact models and 6 developing reliable animal fatality diagnoses through autopsies and chemical analysis

effects of volcanic eruptions on the co2 content of the atmosphere and the oceans the 1996 eruption and flood within the vatnajokull glacier iceland abstract the october 1996 eruption within the vatnajokull glacier iceland provides a unique opportunity to study the net effect of volcanic eruptions on atmospheric and oceanic co2 volatile elements dissolved in the meltwater that enclosed the eruption site were eventually discharged into the ocean in a dramatic flood 35 days after the beginning of the eruption enabling measurement of 50 dissolved element fluxes the minimum concentration of exsolved co2 in the 1 1012 kg of erupted magma was 516 mg kg s was 98 mg kg cl was 14 mg kg and f was 2 mg kg the ph of the meltwater at the eruption site ranged from about 3 to 8 volatile and dissolved element release to the meltwater in less than 35 days amounted to more than one million tonnes equal to 0 1 of the mass of erupted magma the total dissolved solid concentration in the floodwater was close to 500 mg kg ph ranged from 6 88 to 7 95 and suspended solid concentration ranged from 1 to 10 according to h o c and s isotopes most of the water was meteoric whereas the c and s were of magmatic origin both c and s went through isotopic fractionation due to precipitation at the eruption site creating short cuts in their global cycles the dissolved fluxes of c ca na si s and mg were greatest ranging from 1 4 1010 to 1 4 109 mol the dissolved c flux equaled 0 6 million tonnes of co2 the heavy metals ni mn cu pb and zn were relatively mobile during condensation and water rock interactions at the eruption site about half of the measured total carbon flood flux from the 1996 vatnajokull eruption will be added to the long term co2 budget of the oceans and the atmosphere the other half will eventually precipitate with the ca and mg released thus for eruptions on the ocean floor one can expect a net long term c release to the ocean of less than half that of the exsolved gas this is a considerably higher net c release than suggested for the oceanic crust by staudigel et al geochim cosmochim acta 53 1989 3091 in fact they suggested a net loss of c therefore magma degassed at the ocean floor contributes more c to the oceans and the atmosphere than magma degassed deep in the oceanic crust the results of this study show that subglacial eruptions affecting the surface layer of the ocean where either mn fe si or cu are rate determining for the growth of oceanic biomass have a potential for a transient net co2 removal from the ocean and the atmosphere for eruptions at high latitudes timing is crucial for the effect of oceanic biota eruptions occurring in the wintertime when light is rate determining for the growth of biota have much less potential for bringing about a transient net negative co2 flux from the ocean atmosphere reservoir

serpentinization of olivine gabbro in central indian ridge insights into h2 production during alteration in lower oceanic crust and sustenance of life at slow spreading ridges abstract we investigated the textural compositional characteristics across olivine interfaces in variably serpentinized olivine gabbro samples dredged from the vityaz megamullion in the northern central indian ridge cir the results are used to understand the role temperature and different chemical properties in infiltrating fluid e g seawater hydrothermal solution on the pattern of compositional evolution during progressive alteration in olivine gabbro the development of two distinct types of replacement rims i e type 1 and type 2 are conspicuous in our samples type 1 pseudomorphic mesh rim that formed within individual olivine grains occurs in two different textural modes a as successive layers of fe rich xmg 0 89 0 02 lizardite magnetite clay and calcite towards the olivine interface and b as homogeneous rim of comparatively fe poor lizardite xmg 0 93 0 01 magnetite replacement of olivine by talc and chlorite is evident towards the clinopyroxene and plagioclase grain boundaries respectively local precipitation of clay minerals is also observed at the inner interface of talc layer and within intra olivine fractures type 2 rim is characterized by the development of inter olivine mg rich lizardite xmg 0 97 0 01 magnetite layer cross cutting type 1 veins thus post dates type 1 replacement the process of cir olivine gabbro alteration records at least two stages of serpentinization any presence of brucite has not been observed suggesting relatively higher silica activity at reacting interfaces during olivine gabbro alteration than that of peridotite serpentinization at temperature log a sio 2 aq log a h 2 o log a al 3 a h 3 and log a ca 2 a h 2 and or temperature during progressive alteration of olivine type 2 replacement attests greater extent of magnetite precipitation as compared to type 1 serpentinization which may indicate increasing fluid rock ratio in the system and or decreasing magnitude of fe intake into serpentine structure with ongoing alteration importantly it implies release of h2 aq during olivine gabbro serpentinization which is consistent with that observed during peridotite serpentinization this corroborates that alteration in the deepest part of the oceanic crust may play an important role on the sustenance of biosphere in slow spreading ridges

experimental constraints on fluid rock reactions during incipient serpentinization of harzburgite the exposure of mantle peridotite to water at crustal levels leads to a cascade of interconnected dissolution precipitation and reduction oxidation reactions a process referred to as serpentinization these reactions have major implications for microbial life through the provision of hydrogen h 2 to simulate incipient serpentinization under well constrained conditions we reacted centimeter sized pieces of uncrushed harzburgite with chemically modified seawater at 300 oc and 35 mpa for ca 1 5 yr 13 441 h monitored changes in fluid chemistry over time and examined the secondary mineralogy at the termination of the experiment approximately 4 mol of the protolith underwent alteration forming serpentine accessory magnetite chlorite and traces of calcite and heazlewoodite alteration textures bear remarkable similarities to those found in partially serpentinized abyssal peridotites neither brucite nor talc precipitated during the experiment given that the starting material contained 4 times more olivine than orthopyroxene on a molar basis mass balance requires that dissolution of orthopyroxene was significantly faster than dissolution of olivine coupled mass transfer of dissolved si mg and h between olivine and orthopyroxene reaction fronts was driven by steep activity gradients and facilitated the precipitation of serpentine hydrogen was released in significant amounts throughout the entire experiment however the h 2 release rate decreased with time serpentinization consumed water but did not release significant amounts of dissolved species other than h 2 suggesting that incipient hydration reactions involved a volume increase of 40 the reduced access of water to fresh olivine surfaces due to filling of fractures and coating of primary minerals with alteration products led to decreased rates of serpentinization and h 2 release while this concept might seem at odds with completely serpentinized seafloor peridotites reaction driven fracturing offers an intriguing solution to the seemingly self limiting nature of serpentinization indeed the reacted sample revealed several textural features diagnostic of incipient reaction driven fracturing we conclude that fracturing must have far reaching impacts on the rates of serpentinization and h 2 release in peridotite hosted hydrothermal systems

fluid mixing and the deep biosphere of a fossil lost city type hydrothermal system at the iberia margin subseafloor mixing of reduced hydrothermal fluids with seawater is believed to provide the energy and substrates needed to support deep chemolithoautotrophic life in the hydrated oceanic mantle i e serpentinite however geosphere biosphere interactions in serpentinite hosted subseafloor mixing zones remain poorly constrained here we examine fossil microbial communities and fluid mixing processes in the subseafloor of a cretaceous lost city type hydrothermal system at the magma poor passive iberia margin ocean drilling program leg 149 hole 897d brucite calcite mineral assemblages precipitated from mixed fluids ca 65 m below the cretaceous paleo seafloor at temperatures of 31 7 4 3 c within steep chemical gradients between weathered carbonate rich serpentinite breccia and serpentinite mixing of oxidized seawater and strongly reducing hydrothermal fluid at moderate temperatures created conditions capable of supporting microbial activity dense microbial colonies are fossilized in brucite calcite veins that are strongly enriched in organic carbon up to 0 5 wt of the total carbon but depleted in 13c 13ctoc 19 4 we detected a combination of bacterial diether lipid biomarkers archaeol and archaeal tetraethers analogous to those found in carbonate chimneys at the active lost city hydrothermal field the exposure of mantle rocks to seawater during the breakup of pangaea fueled chemolithoautotrophic microbial communities at the iberia margin possibly before the onset of seafloor spreading lost city type serpentinization systems have been discovered at midocean ridges in forearc settings of subduction zones and at continental margins it appears that wherever they occur they can support microbial life even in deep subseafloor environments

stacked gabbro units and intervening mantle a detailed look at a section of iodp leg 305 hole u1309d hole u1309d integrated ocean drilling program iodp legs 304 305 penetrated 1415 m into the seafloor of the atlantis massif an oceanic core complex at 30 n mid atlantic ridge more than 96 of all recovered rocks are gabbroic on the basis of a mineral chemical overview we suggest that between 800 and 1100 m below sea floor mbsf a magmatic unit occurs ranging from olivine gabbro and troctolite in the lower part to gabbronorite and oxide gabbro in the upper part below 1235 mbsf massive gabbronorites oxide gabbros were drilled and they may represent the roof of an underlying magmatic unit the focus here is on the zone where both units interact and screens totaling 50 m of a microstructurally distinct olivine rich troctolite occur we argue that the olivine rich troctolite is a former mantle rock which was converted to a crust mantle transition zone dunite at the base of the upper magmatic unit later as melts derived from the lower magmatic unit percolated through it it was equilibrated to a more evolved chemistry and transformed to a fine grained olivine rich troctolite our main arguments against a possible cumulate nature of the olivine rich troctolite are the lack of a systematic downhole trend in compatible elements within the olivine rich troctolite its distinctly fine grained microstructure the high cr content of cpx and its ni rich olivine composition the high nio for a given mg mg fe in the olivine rich troctolite can be modeled by simple equilibration of relict mantle olivine with a mildly evolved melt evidence for the percolation of evolved melts through the olivine rich troctolites are ti rich interstitial pyroxenes and as inclusions in cr spinel highly evolved amphiboles and orthopyroxenes plus the occurrence of millimeter scale noritic veins the percolation by evolved melts would also be the major difference to otherwise conceptually similar rocks from the ophiolitic crust mantle transition zone

extending the upper temperature limit for life the upper temperature limit for life is a key parameter for delimiting when and where life might have evolved on a hot early earth the depth to which life exists in the earth s subsurface and the potential for life in hot extraterrestrial environments a combination of geological and

clay mineral organic matter relationships in the early solar system as the solar system formed it inherited and perpetuated a rich organic chemistry the molecular products of which are preserved in ancient extraterrestrial objects such as carbonaceous chondrites these organic rich meteorites provide a valuable and tangible record of the chemical steps taken towards the origin of life in the early solar system chondritic organic matter is present in the inorganic meteorite matrix which in the cm and ci chondrites contains evidence of alteration by liquid water on the parent asteroid an unanswered and fundamental question is to what extent did the organic matter and inorganic products of aqueous alteration interact or display interdependence we have used an organic labelling technique to reveal that the meteoritic organic matter is strongly associated with clay minerals this association suggests that clay minerals may have had an important trapping and possibly catalytic role in chemical evolution in the early solar system prior to the origin of life on the early earth