gas emission strength and evolution of the molar ratio of bro so2 in the plume of nyiragongo in comparison to etna airborne and ground based differential optical absorption spectroscopy observations have been carried out at the volcano nyiragongo democratic republic of congo to measure so2 and bromine monoxide bro in the plume in march 2004 and june 2007 respectively additionally filter pack and multicomponent gas analyzer system multi gas measurements were carried out in june 2007 our measurements provide valuable information on the chemical composition of the volcanic plume emitted from the lava lake of nyiragongo the main interest of this study has been to investigate for the first time the bromine emission flux of nyiragongo a rift volcano and the bro formation in its volcanic plume measurement data and results from a numerical model of the evolution of bro in nyiragongo volcanic plume are compared with earlier studies of the volcanic plume of etna italy even though the bromine flux from nyiragongo 2 6t d is slightly greater than that from etna 1 9t d the bro so2 ratio maximum 7x10 5 is smaller than in the plume of etna maximum 2 1x10 4 a one dimensional photochemical model to investigate halogen chemistry in the volcanic plumes of etna and nyiragongo was initialized using data from multi gas and filter pack measurements model runs showed that the differences in the composition of volcanic volatiles led to a smaller fraction of total bromine being present as bro in the nyiragongo plume and to a smaller bro so2 ratio

volcanic lightning as a source of reactive radical species in eruption plumes volcanic lightning has accompanied most recent major explosive eruptions and provides a source of intense thermal energy to drive the formation of reactive radical species these radicals may have an impact upon the chemical evolution of the eruption plume and its interaction with the atmosphere equilibrium modeling shows that within each lightning channel 1 of total n o and f and 100 of h cl br and i may remain as radicals after quenching the production of radicals generally increases with the quenching temperature of the gas mixture and the dilution of the eruption plume and decreases with increasing atmospheric pressure despite the small volume fraction of the plume directly exposed to volcanic lightning i e 10 4 the production of o h f and no is predicted to be quantitatively significant over the entire plume furthermore these radicals may indirectly lead to the production of br cl ho2 and o3 through reactions occurring at low temperature we suggest that volcanic lightning may promote the oxidation of magmatic gases e g hbr and so2 and result in a wide range of atmospheric impacts including tropospheric ozone depletion the production of fixed nitrogen species and the formation of cloud condensation nuclei

atmospheric chemistry of a 33 34 hour old volcanic cloud from hekla volcano iceland insights from direct sampling and the application of chemical box modeling 1 on 28 february 2000 a volcanic cloud from hekla volcano iceland was serendipitously sampled by a dc 8 research aircraft during the sage iii ozone loss and validation experiment solve i it was encountered at night at 10 4 km above sea level in the lower stratosphere and 33 34 hours after emission the cloud is readily identified by abundant so2 1 ppmv hcl 70 ppbv hf 60 ppbv and particles which may have included fine silicate ash we compare observed and modeled cloud compositions to understand its chemical evolution abundances of sulfur and halogen species indicate some oxidation of sulfur gases but limited scavenging and removal of halides chemical modeling suggests that cloud concentrations of water vapor and nitric acid promoted polar stratospheric cloud psc formation at 201 203 k yielding ice nitric acid trihydrate nat sulfuric acid tetrahydrate sat and liquid ternary solution h2so4 h2o hno3 sts particles we show that these volcanically induced pscs especially the ice and nat particles activated volcanogenic halogens in the cloud producing 2 ppbv clox this would have destroyed ozone during an earlier period of daylight consistent with the very low levels of ozone observed this combination of volcanogenic pscs and chlorine destroyed ozone at much faster rates than other pscs that arctic winter elevated levels of hno3 and noy in the cloud can be explained by atmospheric nitrogen fixation in the eruption column due to high temperatures and or volcanic lightning however observed elevated levels of hox remain unexplained given that the cloud was sampled at night

emission of bromine and iodine from mount etna volcano 1 constraining fluxes of volcanic bromine and iodine to the atmosphere is important given the significant role these species play in ozone depletion however very few such measurements have been made hitherto such that global volcanic fluxes are poorly constrained here we extend the data set of volcanic br and i degassing by reporting the first measurements of bromine and iodine emissions from mount etna these data were obtained using filter packs and contemporaneous ultraviolet spectroscopic so2 flux measurements resulting in time averaged emission rates of 0 7 kt yr 1 and 0 01 kt yr 1 for br and i respectively from april to october 2004 from which we estimate global br and i fluxes of order 13 range 3 40 and 0 11 range 0 04 6 6 kt yr 1 observed changes in plume composition highlight the coherent geochemical behavior of hcl hf hbr and hi during magmatic degassing and strong fractionation of these species with respect to so2

atmospheric chemistry of an antarctic volcanic plume 1 we report measurements of the atmospheric plume emitted by erebus volcano antarctica renowned for its persistent lava lake the observations were made in december 2005 both at source with an infrared spectrometer sited on the crater rim and up to 56 km downwind using a twin otter aircraft with the two different measurement platforms plume ages were sampled ranging from 1 min to as long as 9 h three species co carbonyl sulfide ocs and so2 were measured from both air and ground while co and ocs were conserved in the plume consistent with their long atmospheric lifetimes the downwind measurements indicate a so2 co ratio about 20 of that observed at the crater rim suggesting rapid chemical conversion of so2 the aircraft measurements also identify volcanogenic h2so4 hno3 and recognized for the first time in a volcanic plume ho2no2 we did not find nox in the downwind plume despite previous detection of no2 above the crater this suggests that near source nox was quickly oxidized to hno3 and ho2no2 and probably no3 aq possibly in tandem with the conversion of so2 to sulfate these fast processes may have been facilitated by cloud processing in the dense plume immediately downwind from the crater a further striking observation was o3 depletion of up to 35 in parts of the downwind plume this is likely to be due to the presence of reactive halogens bro and clo formedthrough heterogeneous processes in the young plume our analysis adds to the growing evidence for the tropospheric reactivity of volcanic plumes and shows that erebus volcano has a significant impact on antarctic atmospheric chemistry at least locally in the southern ross sea area

evidence for a new shallow magma intrusion at la soufriere of guadeloupe lesser antilles insights from long term geochemical monitoring of halogen rich hydrothermal fluids more than three decades of geochemical monitoring of hot springs and fumaroles of la soufriere of guadeloupe allows the construction of a working model of the shallow hydrothermal system this system is delimited by the nested caldera structures inherited from the repeated flank collapse events and the present dome built during the last magmatic eruption 1530 ad and which has been highly fractured by the subsequent phreatic or phreatomagmatic eruptions because it is confined into the low volume highly compartmented and partially sealed upper edifice structure the hydrothermal system is highly reactive to perturbations in the volcanic activity input of deep magmatic fluids the edifice structure sealing and fracturing and meteorology wet tropical regime the current unrest which began with a mild reactivation of fumarolic activity in 1990 increased markedly in 1992 with seismic swarms and an increase of degassing from the summit of the dome in 1997 seismic activity increased further and was accompanied by a sudden high flux hcl rich gas from summit fumaroles we focus on the interpretation of the time series of the chemistry and temperature of fumarolic gases and hot springs as well as the relative behaviours of halogens f cl br and i this extensive geochemical time series shows that the deep magmatic fluids have undergone large changes in composition due to condensation and chemical interaction with shallow groundwater scrubbing it is possible to trace back these processes and the potential contribution of a deep magmatic source using a limited set of geochemical time series t co2 and total s content in fumaroles t and cl in hot springs and the relative fractionations between f cl br and i in both fluids coupling 35 years of geochemical data with meteorological rainfall data and models of ion transport in the hydrothermal aquifers has allowed us to identify a series of magmatic gas pulses into the hydrothermal system since the 1976 1977 crisis the contrasting behaviours of s and cl bearing species in fumarolic gas and in thermal springs suggests that the current activity is the result of a new magma intrusion which was progressively emplaced at shallow depth since 1992 although it might still be evolving the characteristics of this new intrusion indicate that it hasalready reached a magnitude similar to the intrusion that was emplaced during the 1976 1977 eruptive crisis the assessment of potential hazards associated with evolution of the current unrest must consider the implications of recurrent intrusion and further pressurization of the hydrothermal system on the likelihood of renewed phreatic explosive activity moreover the role of hydrothermal pressurization on the basal friction along low strength layers within the upper part of the edifice must be evaluated with regards to partial flank collapse at this stage enhanced monitoring research and data analysis is required to quantify the uncertainties related to future scenarios of renewed eruptive activity and magmatic evolution

characterization and interpretation of volcanic activity at karymsky volcano kamchatka russia using observations of infrasound volcanic emissions and thermal imagery 2 a multiparameter data set including measurements of infrasound volcanic emissions and thermal imagery is used to characterize and interpret diverse volcanic activity observed during field campaigns in august 2011 and july 2012 at karymsky volcano kamchatka russia four activity types are visually identified and characterized according to so2 emission rate ash mass event duration peak temperature thermal radiation energy infrasound onset and frequency reduced infrasonic pressure and acoustic energy these activity types include 1 ash explosions 2 pulsatory degassing 3 gas jetting and 4 explosive eruption unique infrasound signals are associated with all four activity types suggesting that infrasound can be used to help remotely and continuously detect and characterize volcanic activity at karymsky and other similar volcanoes our observations suggest that so2 is emitted continuously though in varying abundance while ash is emitted discontinuously and is only associated with certain types of activity our data set supports previous models that attribute variations in surface activity to changes in conduit permeability at karymsky volcano evidence for a decrease in conduit permeability as a trigger for ash explosions and explosive eruption activity types is supported by weakened but still detectable so2 emission rates prior to eruption along with the highly impulsive infrasonic onset and large reduced infrasound pressure indicating high pressure at the vent we speculate that changes in conduit permeability at karymsky volcano result from changes in magma supply from the shallow crustal storage region though additional measurements are required to validate this hypothesis

so2 bro ratios studied in five volcanic plumes abstract the distribution of bromine monoxide bro and sulphur dioxide so2 was measured by ground based max doas scattered light multi axis differential optical absorption spectroscopy in the plume of five volcanoes soufriere hills volcano on montserrat in may 2002 masaya volcano in nicaragua in march 2003 etna volcano on sicily in september october 2003 and august october 2004 stromboli volcano in italy in september 2003 and villarica in chile in november 2004 maximum slant column densities scds of several 1014 molecules cm2 of bro were observed bromine monoxide sulphur dioxide ratios of 10 0 10 4 0 8 10 4 4 8 10 4 2 1 10 4 2 1 10 4 and 1 3 10 4 were found in the plumes of soufriere hills masaya etna 2003 etna 2004 stromboli and villarica respectively causes for the differences in the bro so2 ratios for the various volcanic sites are discussed

andesitic magma degassing investigated through h2o vapour melt partitioning of halogens at soufriere hills volcano montserrat lesser antilles magma degassing at soufriere hills volcano shv is characterised by an almost permanent so2 flux and a hcl production rate which mainly depends on dome growth rate degassing processes have been studied through textural h2o and halogen analyses of clasts collected between 1995 and 2006 on the dome and in pyroclastic flows and vulcanian eruption deposits cl br and i are strongly depleted in melts during h2o degassing with no significant cl br i fractionation whereas f is almost unaffected all magmas erupted at shv have followed a multi step degassing path from the magma chamber up to a shallow depth 1 km p 20 mpa from that depth however effusive and explosive paths are distinct vulcanian eruptions are the result of closed system degassing csd while effusive dome growth is the result of csd up to a very shallow depth 200 m p 5 2 mpa followed by open system degassing osd csd is modelled using the h2o solubility law the perfect gas law and partition coefficients of halogens between a rhyolitic melt and h2o vapour dv li gas loss characteristic of osd is modelled using a rayleigh law degassing induced crystallisation is introduced through the ratio of crystallisation and degassing rates which ranges from 150 500 dv lcl for osd ranges between 50 300 increasing with melt cl content for csd the lower effective dv lcl 20 is attributed to kinetic effects dome forming activity has a greater impact on atmospheric chemistry than vulcanian eruptions because osd is much more efficient at extracting halogens the model shows that hcl flux is a good proxy for the dome forming eruption rate comparison between model and measured gas compositions suggests a high hbr bro conversion rate bro total br 1 3 in the shv gas plume the degassing behaviour of cl br and i implies similar cl br 160 and br i 90 in initial melts volcanic clasts and high temperature gases the low cl br at shv compared to other island arcs 250 300 is attributed to a shallow pre eruptive br enrichment the almost permanent dome extrusion at shv since 1995 has likely had a significant regional atmospheric impact because of the very efficient effusive degassing and the high conversion rate of halogens into reactive species within the gas plume

pre and syn eruptive geochemistry of volcanic gases from soufriere hills of montserrat west indies soufriere hills fumaroles contained magma derived volatiles before and during the eruption initiated in 1995 but also preserved a typical and quite steady hydrothermal composition chemical changes due to increased boiling and a greater input of oxidizing magmatic gas occurred only at galway s soufriere the most active fumarolic field hydrothermal buffering of the fumaroles has been favoured by their remote location 1 2 km from the eruptive vents and by a preferential degassing of the uprising magma through intrusive conduits under the crater high temperature 720 c gas collected from the extruding lava dome in feb 1996 was chemically and isotopically representative of the magmatic gas stream its composition allows assessment of average eruptive fluxes of h2o co2 and hcl which require the degassing of only 2 5 3 times more magma than erupted

volcanic degassing of bromine and iodine experimental fluid melt partitioning data and applications to stratospheric chemistry abstract in order to understand the degassing behavior of heavy halogens in volcanic processes we experimentally studied the distribution of cl br and i between albite melt and hydrous fluids containing 0 01 2 wt of nacl nabr or nai respectively all experiments were carried out at 2 kbar and 900 c in rapid quench cold seal autoclaves with a run duration of 7 days the major element compositions and cl contents of the glassy run products were measured by electron microprobe bromine and iodine were measured by proton induced x ray emission fluid compositions were obtained by mass balance all halogens investigated were found to partition strongly into the fluid phase over the range of concentrations studied the halogen contents in the melt are proportional to the concentrations in the fluid the fluid melt partition coefficients df m are 8 1 0 2 for cl 17 5 0 6 for br and 104 7 for i the logarithm of df m is linearly correlated with the ionic radius of the halogenide ion on the basis of our experimental data we estimate the amount of bromine injected into the stratosphere by major volcanic explosions for the 1991 mount pinatubo eruption we obtain br yields of 11 25 kt as minimum estimates these numbers are comparable to the total annual influx of bromine into the stratosphere from all other natural and anthropogenic sources about 100 kt year since bromine is much more efficient in destroying stratospheric ozone than chlorine it could at least be partially responsible for the massive ozone depletion observed after the 1991 mount pinatubo eruption

modelling reactive halogen formation and ozone depletion in volcanic plumes in this paper we present a purpose built model plumechem to simulate the reactive halogen chemistry in plumes from persistently degassing volcanoes the model includes photolytic gas phase and aqueous phase chemical reactions and dispersion of the plume into the background atmosphere we investigate how high temperature chemistry close to the vent believed to enhance plume nox hox brox and clox affects bro formation in the downwind plume plumechem simulations initialised using output from thermodynamic calculations at 1000 c with atmospheric magmatic gas ratio 0 1 above the compositional discontinuity are in good quantitative agreement with observations of bro so2 and also provide a mechanism whereby clo and oclo may be formed in the plume the model reproduces the observed magnitudes and rates of increase of bro so2 at several volcanoes the hbr content of the initial plume is shown to be an important control in determining the bro so2 ratio and ozone depletion in the downwind plume the model simulates conversion of nox to hno3 and destruction of ozone in the plume providing an explanation for observed elevated hno3 in volcanic plumes and in agreement with an in plume observation of depleted ozone the predicted ozone depletion was locally and regionally significant for three different volcanic plume compositions therefore we present a new model of volcanic plume chemistry supported by observations of volcanic bro and hno3 which identifies hbr emission as a key determinant in ozone depletion by volcanoes

reactive halogens bro and oclo detected in the plume of soufriere hills volcano during an eruption hiatus volcanic plumes are sites of dynamic chemistry involving halogen gases here we present new data on the relative abundances of so2 bro and oclo gases emitted from soufriere hills volcano shv they were collected during an eruptive hiatus but during sustained degassing at this halogen rich volcano by comparison with data from a previous study during an eruptive phase and application of the data and modeling of villemant et al 2008 we suggest that after consideration of errors either the rate of hbr conversion to bro is variable ranging from 30 to 15 and or the relative partitioning of cl and br into the gas phase from the melt changes according to eruptive activity we examine the potential implications of this for fluid melt partitioning and compare our results with data from the experimental literature our work contributes toward understanding the controls on the bro so2 ratio for volcano monitoring purposes the changes in plume chemistry with regard to bromine at the onset of lava extrusion may be large and rapid oclo was detected in the plume at shv for the first time this species has only previously been detected in emissions from mount etna using ground based methods and from puyehue cordon caulle using satellite based methods no hcho or noy species were detected in the spectra

chlorine isotope and cl br fractionation in fluids of poas volcano costa rica insight into an active volcanic hydrothermal system abstract halogen rich volcanic fluids issued at the surface carry information on properties and processes operating in shallow hydrothermal systems this paper reports a long term record of cl br concentrations and 37cl signatures of lake water and fumaroles from the active crater of poas volcano costa rica where surface expressions of magmatic hydrothermal activity have shown substantial periodic changes over the last decades both the hyperacid water of its crater lake laguna caliente and subaerial fumaroles show significant temporal variability in cl br concentrations br cl ratios and 37cl reflecting variations in the mode and magnitude of volatile transfer the 37cl signatures of the lake covering the period 1985 2012 show fluctuations between 0 02 0 06 and 1 15 0 09 condensate samples from adjacent fumaroles on the southern shore collected during the interval 2010 2012 with strong changes in gas temperature 107 763 c display a much larger range from 0 43 0 09 to 14 09 0 08 most of the variations in cl isotope br cl and concentration signals can be attributed to interaction between magma derived gas and liquid water in the volcanic hydrothermal system below the crater the 37cl were lowest and closest to magmatic values in 1 fumarolic gas that experienced little or no interaction with subsurface water and followed a relatively dry pathway and 2 water that captured the bulk of magmatic halogen output so that no phase separation could induce fractionation in contrast elevated 37cl can be explained by partial scavenging and fractionation during subsurface gas liquid interaction hence strong cl isotope fractionation leading to very high 37cl in poas fumaroles indicates that they followed a wet pathway highest 37cl values in the lake water were found mostly in periods when it received a significant input from subaqueous fumaroles or when high temperatures and low ph caused hcl evaporation it is concluded that combined monitoring of 37cl and br cl in laguna caliente and adjacent fumaroles provides valuable information on activity in the subsurface hydrothermal system with significant relevance for volcanic surveillance of poas

volatilization transport and sublimation of metallic and non metallic elements in high temperature gases at merapi volcano indonesia abstract condensates silica tube sublimates and incrustations were sampled from 500 800 c fumaroles and lava samples were collected at merapi volcano indonesia in jan feb 1984 with respect to the magma merapi gases are enriched by factors greater than 105 in se re bi and cd 104 105 in au br in pb and w 103 104 in mo cl cs s sn and ag 102 103 in as zn f and rb and 1 102 in cu k na sb ni ga v fe mn and li the fumaroles are transporting more than 106 grams day g d of s cl and f 104 106 g d of al br zn fe k and mg 103 104 g d of pb as mo mn v w and sr and less than 103 g d of ni cu cr ga sb bi cd li co and u with decreasing temperature 800 500 c there were five sublimate zones found in silica tubes 1 cristobalite and magnetite first deposition of si fe and al 2 k ca sulfate acmite halite sylvite and pyrite maximum deposition of cl na k si s fe mo br al rb cs mn w p ca re ag au and co 3 aphthitalite k na sulfate sphalerite galena and cs k sulfate maximum deposition of zn bi cd se and in higher deposition of pb and sn 4 pb k chloride and na k fe sulfate maximum deposition of pb sn and cu and 5 zn cu and k pb sulfates maximum deposition of pb sn ti as and sb the incrustations surrounding the fumaroles are also chemically zoned bi cd pb w mo zn cu k na v fe and mn are concentrated most in or very close to the vent as expected with cooling atmospheric contamination and dispersion the highly volatile elements br cl as and sb are transported primarily away from high temperature vents ba si p al ca and cr are derived from wall rock reactions incomplete degassing of shallow magma at 915 c is the origin of most of the elements in the merapi volcanic gas although it is partly contaminated by particles or wall rock reactions the metals are transported predominantly as chloride species as the gas cools in the fumarolic environment it becomes saturated with sublimate phases that fractionate from the gas in the order of their equilibrium saturation temperatures devolatilization of a cooling batholith could transport enough acids and metals to a hydrothermal system to play a significant role in forming an ore deposit however sublimation from a high temperature high velocity carrier gas is not efficient enough to form a large ore deposit re se cd and bi could be used as supporting evidence for magmatic fluid transport in an ore deposit

in situ measurements of tropospheric volcanic plumes in ecuador and colombia during tc4 a nasa dc 8 research aircraft penetrated tropospheric gas and aerosol plumes sourced from active volcanoes in ecuador and colombia during the tropical composition cloud and climate coupling tc 4 mission in july august 2007 the likely source volcanoes were tungurahua ecuador and nevado del huila colombia the tc 4 data provide rare insight into the chemistry of volcanic plumes in the tropical troposphere and permit a comparison of so 2 column amounts measured by the ozone monitoring instrument omi on the aura satellite with in situ so 2 measurements elevated concentrations of so 2 sulfate aerosol and particles were measured by dc 8 instrumentation in volcanic outflow at altitudes of 3 6 km estimated plume ages range from 2 h at huila to 22 48 h downwind of ecuador the plumes contained sulfate rich accumulation mode particles that were variably neutralized and often highly acidic a significant fraction of supermicron volcanic ash was evident in one plume in plume o 3 concentrations were 70 80 of ambient levels downwind of ecuador but data are insufficient to ascribe this to o 3 depletion via reactive halogen chemistry the tc 4 data record rapid cloud processing of the huila volcanic plume involving aqueous phase oxidation of so 2 by h 2o 2 but overall the data suggest average in plume so 2 to sulfate conversion rates of 1 2 h 1 so 2 column amounts measured in the tungurahua plume 0 1 0 2 dobson units are commensurate with average so 2 columns retrieved from omi measurements in the volcanic outflow region in july 2007 the tc 4 data set provides further evidence of the impact of volcanic emissions on tropospheric acidity and oxidizing capacity

gas and particle emissions from soufriere hills volcano montserrat west indies characterization and health hazard assessment the soufriere hills volcano montserrat erupting since 18 july 1995 intensified its degassing in early 1996 with the continuing growth of the lava dome inside the summit crater during this period of increased activity between 11 and 18 march 1996 we measured gases and particles within the visible plume to determine whether at that time it posed a health risk to the population of plymouth the capital town which is 5 km southwest downwind and was then still occupied gravimetric measurements were made of total suspended particles tsp and particles having an aerodynamic diameter of less than 10 m pm10 measurements were made of sulphur dioxide so2 hydrochloric acid hcl hydrofluoric acid hf nitric acid hno3 acetic acid ch3cooh formic acid hcooh and particulate sulphate so4 2 chloride cl nitrate no3 fluoride f methanesulphonate ch3so3 acetate ch3coo formate hcoo ammonium nh4 sodium na and acidity h trace metals having human health implications chromium cr nickel ni cobalt co copper cu zinc zn arsenic as selenium se cadmium cd tin sn mercury hg and lead pb were also determined mean concentrations of hcl so2 and hf obtained in the town of plymouth were 14 0 5 9 and 0 8 ppbv respectively corresponding concentrations in the mixed plume on the crater edge were 533 168 and 22 ppbv there were no direct emissions of hno3 although nitrate was detected in coarse particles at the source higher concentrations of ch3cooh and hcooh were measured close to the crater mean tsp and pm10 were 64 and 15 g m 3 in plymouth and 455 and 47 g m 3 on the upper volcano slope aerosols were highly acidic at the source but rapidly neutralised during transport trace metals were enriched in the aerosol relative to crater surface material the concentrations of the acid gases sulphur dioxide in particular and particles were found to be too small to pose a health hazard at the time of these measurements when relatively modest volcanic activity was occurring

india asia convergence insights from burial and exhumation of the xigaze fore arc basin south tibet the composite fore arc syncollisional xigaze basin in south tibet preserves a key record of india asia collision new apatite fission track and zircon u th he data from an n s transect across the preserved fore arc basin sequence near xigaze show a consistent northward late cretaceous to middle miocene younging trend while coexisting apatite u th sm he ages are all miocene corresponding detrital zircon u pb data are also reported for constraining the cretaceous depositional ages of the xigaze basin sequence in the region thermal history modeling indicates that the basin experienced northward propagating episodic exhumation along with a northward migration of the depocenter and a pre existing cenozoic syncollisional basin sequence which had been removed in the southern part fore arc exhumation commenced in the late cretaceous 89 2 ma following transition to a syncollisional basin in the paleocene sedimentation in the central and northern xigaze basin continued until the latest eocene 34 4 ma ongoing folding and thrusting e g great counter thrusts caused by progressive plate convergence during late oligocene early miocene time resulted in regional uplift and considerable basin denudation which fed two fluvial basins along its northern and southern flanks and exposed the basement ophiolite subsequent incision of the yarlung river resulted in miocene cooling in the region different episodes in the exhumation history of the xigaze basin caused by thrusting of an accretionary wedge and ophiolitic basement can be linked to changes in india asia convergence rates and the changing subduction pattern of the indian and neo tethyan slabs

aerosol formation in basaltic lava fountaining eyjafjallajokull volcano iceland 1 a short lived episode of basaltic lava fountaining at eyjafjallajokull volcano march april 2010 produced a low altitude ash poor plume we measured the composition of aerosol particles sampled using a cascade impactor and filter packs gases sampled using filter packs and volatile species scavenged by scoria and external water in order to investigate the formation and speciation of near source aerosol 0 4 m and its composition was dominated by chloride rather than sulfate we used two thermodynamic equilibrium models e aim and hsc chemistry v5 1 to show that the formation of particulate cl by condensation of hcl gas is more responsive to changes in ambient temperature than the oxidation of so2 to so42 so that a low so42 cl ratio in aerosol particles is characteristic of volcanic emissions in cold climates field measurements suggested that the efficiency of so2 to so42 conversion inside the vent increased with lower explosivity volatiles adsorbed on the surface of scoria had significantly higher so42 halogen molar ratios than the aerosol samples several potential explanations for these differences are discussed

reconciling discrepancies between uk37 and mg ca reconstructions of holocene marine temperature variability significant discrepancies exist between the detrended variability of late holocene marine temperatures inferred from mg ca and uk37 proxies with the former showing substantially more centennial scale variation than the latter discrepancies exceed that attributable to differences in location and persist across various calibrations indicating that they are intrinsic to the proxy measurement we demonstrate that these discrepancies can be reconciled using a statistical model that accounts for the effects of bioturbation sampling and measurement noise and aliasing of seasonal variability the smaller number of individual samples incorporated into mg ca measurements relative to uk37 measurements leads to greater aliasing and generally accounts for the differences in the magnitude and distribution of variability an inverse application of the statistical model is also developed and applied in order to estimate the spectrum of marine temperature variability after correcting for proxy distortions the correction method is tested on surrogate data and shown to reliably estimate the spectrum of temperature variance when using high resolution records applying this inverse method to the actual mg ca and uk37 data results in estimates of the spectrum of temperature variance that are consistent this approach provides a basis by which to accurately estimate the distribution of intrinsic marine temperature variability from marine proxy records

oxygen buffering of kilauea volcanic gases and the oxygen fugacity of kilauea basalt volcanic gases collected during episode 1 of the puu oo eruption along the east rift zone of kilauea volcano hawaii have uniform c o h s cl f compositions that are sharply depleted in co2 the co2 poor gases are typical of type ii volcanic gases gerlach and graeber 1985 and were emitted from evolved magma stored for a prolonged period of time in the east rift zone after releasing co2 rich gases during an earlier period of temporary residence in the summit magma chamber the samples are remarkably free of contamination by atmospheric gases and meteoric water thermodynamic evaluation of the analytical data shows that the episode 1 gases have equilibrium compositions appropriate for temperatures between 935 and 1032 c open and closed system equilibrium models of species distributions for the episode 1 gases show unequivocally that coexisting lavas buffered the gas oxygen fugacities during cooling these models indicate that the fo2 buffering process occurs by transfer of oxygen from the major species in the gas phase h2o co2 so2 to the lava during cooling and that the transfer of oxygen also controls the fugacities of several minor and trace species h2 co h2s s2 cl2 f2 in addition to o2 during cooling gas lava exchanges of other components are apparently insignificant and exert little influence compared to oxygen exchange during cooling oxygen transfer during cooling is variable presumably reflecting short term fluctuations in gas flow rates higher flow rates restrict the time available for gas lava oxygen transfer and result in gases with higher equilibrium temperatures lower flow rates favor fo2 constrained equilibration by oxygen transfer down to lower temperatures thus the chemical equilibrium preserved in these gases is a heterogeneous equilibrium constrained by oxygen fugacity and the equilibrium temperatures implied by the compositions of the gases reflect the temperatures at which gas lava oxygen exchange ceased this conclusion challenges the common assumption that volcanic gases are released from lava in a state of chemical equilibrium and then continue equilibrating homogeneously with falling temperature until reaction rates are unable to keep pace with cooling no evidence is found moreover that certain gas species are kinetically more responsive and able to equilibrate down to lower temperatures than those of the last gas lava oxygen exchange homogeneous reaction rates in the gas phase are apparently slow compared to the time it took for the gases to move from the last site of gas lava equilibration to the site of collection an earlier set of data for higher temperature co2 rich type i volcanic gases which come from sustained summit lava lake eruptions supplied by magma that experienced substantially shorter periods of crustal storage shows fo2 buffering by oxygen transfer up to 1185 c oxygen fugacity measurements in drill holes into ponded lava flows suggest that buffering by oxygen transfer may control the fo2 of residual gases down to several hundred degrees below the solidus in the early stages of cooling although the details of the fo2 buffering mechanisms for oxygen transfer are unknown the fact that fo2 buffering is effective from molten to subsolidus conditions suggests that the reaction mechanisms must change with cooling as the reactants change from predominantly melt to melt plus crystals to glass plus crystals mass balance calculations suggest that redox reactions between the gas and ferrous ferric iron in the lava are plausible mechanisms for the oxygen transfer and that the fo2 of the gases is buffered by sliding ferrous ferric equilibria in the erupting lavas contrary to expectations based on models predicting the oxidation of basalt by h2 and co escape during crustal storage co2 rich type i gases and co2 poor type ii gases have identical oxygen fugacities despite greatly different crustal storage and degassing histories volcanic gas data give a tightly constrained log fo2 of nno 0 5 0 05 for subaerially erupted kilauea basalt from liquidus to solidus temperatures consistent with recent fo2 determinations for the mantle source regions of ocean island basalts because the oxygen fugacities of volcanic gases emitted by subaerial lavas imply that the fo2 of kilauea basalt is unchanged during crustal storage kilauea basalt either arrives in the crust with an oxygen fugacity between nno and fmq or it develops an oxygen fugacity in this range immediately upon arrival in the summit chamber

rapid chemical evolution of tropospheric volcanic emissions from redoubt volcano alaska based on observations of ozone and halogen containing gases abstract we report results from an observational and modeling study of reactive chemistry in the tropospheric plume emitted by redoubt volcano alaska our measurements include the first observations of br and i degassing from an alaskan volcano the first study of o 3 evolution in a volcanic plume as well as the first detection of bro in the plume of a passively degassing alaskan volcano this study also represents the first detailed spatially resolved comparison of measured and modeled o 3 depletion in a volcanic plume the composition of the plume was measured on june 20 2010 using base treated filter packs for f cl br i and s at the crater rim and by an instrumented fixed wing aircraft on june 21 and august 19 2010 the aircraft was used to track the chemical evolution of the plume up to 30 km downwind 2 h plume travel time from the volcano and was equipped to make in situ observations of o 3 water vapor co 2 so 2 and h 2 s during both flights plus remote spectroscopic observations of so 2 and bro on the august 19th flight the airborne data from june 21 reveal rapid chemical o 3 destruction in the plume as well as the strong influence chemical heterogeneity in background air had on plume composition spectroscopic retrievals from airborne traverses made under the plume on august 19 show that bro was present 6 km downwind 20 min plume travel time and in situ measurements revealed several ppbv of o 3 loss near the center of the plume at a similar location downwind simulations with the plumechem model reproduce the timing and magnitude of the observed o 3 deficits and suggest that autocatalytic release of reactive bromine and in plume formation of bro were primarily responsible for the observed o 3 destruction in the plume the measurements are therefore in general agreement with recent model studies of reactive halogen formation in volcanic plumes but also show that field studies must pay close attention to variations in the composition of ambient air entrained into volcanic plumes in order to unambiguously attribute observed o 3 anomalies to specific chemical or dynamic processes our results suggest that volcanic eruptions in alaska are sources of reactive halogen species to the subarctic troposphere

halogen diffusion in magmatic systems our current state of knowledge diffusion of halogens has the potential to influence petrogenetic processes in magma chambers and conduit degassing processes this contribution reviews our current state of knowledge concerning halogen diffusion and the influence of halogens on the diffusion of major elements in silicate melts the addition of halogens to silicate melts at common natural concentration levels will have little effect on the diffusion of major elements however the differences between the diffusivity of water the diffusivities of halogens and the diffusivity of sulfur are significant enough that during melt inclusion entrapment or during rapid bubble or crystal growth diffusive fractionation between water and the halogens and between halogens and sulfur are expected to occur and can influence the compositions of melt inclusions crystals and volcanic gases

rapid oxidation of mercury hg at volcanic vents insights from high temperature thermodynamic models of mt etna s emissions a major uncertainty regarding the environmental impacts of volcanic hg is the extent to which hg is deposited locally or transported globally an important control on dispersion and deposition is the oxidation state of hg compounds hg 0 is an inert insoluble gas while hg ii occurs as reactive gases or in particles which deposit rapidly and proximally near the volcanic vent using a new high temperature thermodynamic model we show that although hg in etna s magmatic gases is almost entirely hg 0 i e gaseous elemental mercury significant quantities of hg ii are likely formed at etna s vents as gaseous hgcl2 when magmatic gases are cooled and oxidised by atmospheric gases these results contrast with an earlier model study and allow us to explain recent measurements of hg speciation at the crater rim of etna without invoking rapid 1 min low temperature oxidation processes we further model hg speciation for a series of additional magmatic gas compositions compared to etna hg ii production i e hg ii hgtot is enhanced in more hcl rich magmatic gases but is independent of the hg hbr and hi content of the magmatic gases hg ii production is not strongly influenced by the initial oxidation state of magmatic gases above nno although production is hindered in more reduced magmatic gases the model and results are widely applicable to other open vent volcanoes and may be used to improve the accuracy of chemical kinetic models for low temperature hg speciation in volcanic plumes

petrologic evidence for pre eruptive pressure temperature conditions and recent reheating of andesitic magma erupting at the soufriere hills volcano montserrat w i the recent eruption of the soufriere hills volcano in montserrat july 1995 to present september 1997 has produced an andesitic dome sio 2 59 61 wt the eruption has been caused by invasion of mafic magma into a preexisting andesitic magma storage region p 130 mpa 5 km depth the composition of the andesite has remained essentially constant throughout the eruption but heating by the mafic magma increased the andesite temperature from 830 c to 880 c prior to being heated the stable mineral assemblage in the andesite was plagioclase amphibole orthopyroxene titanomagnetite ilmenite quartz the rise in temperature from 830 c to 880 c fo 2 1 log unit above nno has caused quartz to become unstable and has also caused changes in silicate and fe ti oxide mineral compositions the andesitic magma is likely saturated with an h 2 o rich vapor phase in the upper part of the magma storage region melt h 2 o content is 4 7 wt

degassing processes during lava dome growth insights from santiaguito lava dome guatemala abstract eruptions of intermediate magma may be explosive or effusive the development of open system degassing has been proposed as a pre requisite for effusion of intermediate magma however processes leading to open system degassing are poorly understood to better understand degassing processes during lava dome extrusion we report high temporal resolution so2 emission rate measurements collected with an ultra violet imaging camera at santiaguito guatemala santiaguito is an ideal case study as the dome lava is compositionally very similar to products of the 1902 plinian eruption of the parental santa maria volcano we find that degassing is weak 0 4 1 kg s 1 but continuous and explosions are associated with small increases in emission rates up to 2 3 kg s 1 continuous repose degassing occurs through a shallow cap rock which likely represents a proto crust on the block lava flow which is extruded from the same vent the continual permeability of the upper conduit argues against a mechanism of explosion triggering in which gas pressure builds beneath a viscous cap rock or plug rather we consider degassing data better consistent with a model of shear fracturing at the conduit margins using field constraints we model the viscosity of santiaguito magma as a function of depth and show that conditions for shear fracturing are met from 150 600 m to the surface this is in line with independent estimates of explosion initiation depth we show that repose timescales are orders of magnitude longer than the timescale for shear fracture and suggest that explosions are triggered when a continuous network of smaller scale fractures develops at which point decompression occurs and an explosion is triggered fracture healing occurs by viscous relaxation however near to the surface where viscosity is highest an unconsolidated gouge layer may develop our model implies that the observed explosions are a by product of extrusion shear fracturing can drive open system degassing of crystal rich intermediate magma at shallow levels in the conduit as high magma viscosity is able to overcome the low strain rates associated with slow ascent of magma

halogen oxide measurements at masaya volcano nicaragua using active long path differential optical absorption spectroscopy active long path differential optical absorption spectroscopy lp doas measurements of halogen oxides were conducted at masaya volcano in nicaragua from april 14 to 26 2007 the active lp doas system allowed night time halogen measurements and reduced the clo detection limit by an order of magnitude when compared to previous passive doas measurements as wavelengths below 300 nm could be used for the doas retrievals bro was detected with an average bro so2 molecular ratio of approximately 3 10 5 during the day however bro values were below the detection limit of the instrument for all night time measurements a strong indication that bro is not directly emitted but rather the result of photochemical formation in the plume itself according to the autocatalytic bromine explosion mechanism despite the increased sensitivity both clo and oclo could not be detected the achieved upper limits for the x so2 ratios were 5 10 3 and 7 10 6 respectively a rough calculation suggests that clo and oclo should be present at similar abundances in volcanic plumes since the doas technique is orders of magnitude more sensitive for oclo than for clo this indicates that oclo should always be detectable in plumes in which clo is found however further lp doas studies are needed to conclusively clarify the role of chlorine oxides in volcanic plumes

high temperature mixtures of magmatic and atmospheric gases recent measurements of bro nox and near source sulfate in volcanic plumes suggest that volcanic vents might not simply act as point sources of emissions into the troposphere but may also act as high temperature reaction sites where mixtures of magmatic and ambient atmospheric gases may combine giving new and previously unexpected reaction products the detection of such species demands that a more complex model be developed for the interaction of volcanoes and atmospheres we show that general thermodynamic models can be applied successfully to volcanic gas equilibria by comparing the results from hsc chemistry with those from two volcanic gas equilibrium models solvgas and gasmix using a thermodynamic model optimized for volcanic gas chemistry c o s h f cl br i n ar speciation we show that the volume ratio of atmospheric gas to magmatic gas in a high temperature mixture is an important parameter of the volcanic plume chemistry and our results suggest that even small amounts of air a few for an h2o rich magmatic gas in the high temperature mixture are sufficient to yield elevated levels of reactive nitrogen halogen cl br and i and sulfur species within the volcanic plume further modifications of the plume chemistry may also occur due to low temperature reactions and chemical schemes for the modification of halogen cl br i nitrogen and sulfur chemistry are suggested within the constraints imposed by recent measurements

hcl emissions at soufriere hills volcano montserrat west indies during a second phase of dome building november 1999 to october 2000 hcl so2 mass ratios measured by open path fourier transform spectroscopy op ftir in the volcanic plume at soufriere hills volcano montserrat are presented for the second phase of dome building between november 1999 and november 2000 hcl so2 mass ratios of greater than 1 and hcl emission rates of greater than 400 t day 1 characterise periods of dome building for this volcano the data suggest that chlorine partitions into a fluid phase as the magma decompresses and exsolves water during ascent this is substantiated by a correlation between chlorine and water content in the melt derived from the geochemical analysis of plagioclase melt inclusion and matrix glasses from phase i and ii of dome growth the matrix glass from the november 1999 and march 2000 domes indicate an open system degassing regime with a fluid melt partition coefficient for chlorine of the order of 250 300 september 1997 glasses have higher chlorine contents and may indicate a switch to closed system degassing prior to explosive activity in september and october 1997 the op ftir hcl time series suggests that hcl emission rate is strongly related to changes in eruption rate and we infer an emission rate of over 13 5 kt day 1 hcl during a period of high extrusion rate in september 2000 a calculation of the hcl emission rate expected for varying extrusion rates from the open system degassing model suggests a hcl emission rate of the order of 1 4 kt day 1 is indicative of an extrusion rate of between 2 and 8 m3 s 1 monitoring of hcl at soufriere hills volcano provide a proxy for extrusion rate with changes in ratio between hcl and so2 occurring rapidly in the plume order of magnitude changes occur in hcl emission rates over the time scale of hours to days making these changes easy to detect during the day to day monitoring of the volcano mean water emission rates are calculated to range from 9 24 kt day 1 during dome building activity calculated from the predicted mass ratio of h2o hcl in the fluid at the surface and ftir derived hcl emission rates

so2 photoexcitation mechanism links mass independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism natural climate variation such as that caused by volcanoes is the basis for identifying anthropogenic climate change however knowledge of the history of volcanic activity is inadequate particularly concerning the explosivity of specific events some material is deposited in ice cores but the concentration of glacial sulfate does not distinguish between tropospheric and stratospheric eruptions stable sulfur isotope abundances contain additional information and recent studies show a correlation between volcanic plumes that reach the stratosphere and mass independent anomalies in sulfur isotopes in glacial sulfate we describe a mechanism photoexcitation of so2 that links the two yielding a useful metric of the explosivity of historic volcanic events a plume model of s iv to s vi conversion was constructed including photochemistry entrainment of background air and sulfate deposition isotopologue specific photoexcitation rates were calculated based on the uv absorption cross sections of 32so2 33so2 34so2 and 36so2 from 250 to 320 nm the model shows that uv photoexcitation is enhanced with altitude whereas mass dependent oxidation such as so2 oh is suppressed by in situ plume chemistry allowing the production and preservation of a mass independent sulfur isotope anomaly in the sulfate product the model accounts for the amplitude phases and time development of 33s 34s and 36s 33s found in glacial samples we are able to identify the process controlling mass independent sulfur isotope anomalies in the modern atmosphere this mechanism is the basis of identifying the magnitude of historic volcanic events

geochemistry of metallic trace elements in fumarolic condensates from nicaraguan and costa rican volcanoes metallic trace element composition of volcanic gas from cerro negro momotombo san cristobal telica and masaya volcanoes in nicaragua and poas volcano in costa rica is indicated by analyses of fumarolic condensates for alkalis alkaline earths transition elements precious metals halogens and sulphate the temperatures of the fumaroles varied from 85 to 852 c element concentrations range from 104 to 10 3 ppm statistical tests indicate that the trace element constituents of the condensates are log normally distributed although there are variations in element concentrations in individual condensates the general order of decreasing elemental abundances in nicaraguan and costa rican fumarolic gas is cl so4 certain igneous rock forming elements si al fe ti f and alkalis li na k alkaline earths mg ca ba br and transition elements cr mn co ni cu zn other ore forming elements mo cd sn pb semi metals as sb sc hg and precious metals au ag li mn cr and pb were found to be near or below detection limits in many of the condensates analyzed so4 ti al k na zn sn cr and br all tend to decrease in abundance as mean fumarolic temperature between volcanoes decreases the remaining elements remain constant in abundance or behave erratically the metallic trace element composition of the nicaraguan and costa rican fumarolic condensates is very similar to condensates from subduction zone volcanoes around the pacific margin and the mediterranean metals in volcanic gas are postulated to have been transported as halogen sulphate and oxide compounds chloride and fluoride compounds are considered to be the primary transporters of metals in volcanic gas correlations between metal and halogen content vary considerably between volcanoes statistically significant correlations between metal content and both chlorine and bromine are found in the cerro negro and between metal content and bromine and fluorine in the momotombo condensates metal bearing compounds in volcanic gas are postulated from correlation matrices bromine though seldom reported in condensates is a minor but important constituent of volcanic gas with concentrations similar to those of fluorine metal bromide compounds have higher volatilities than fluoride compounds and volatilities similar to chloride compounds significant correlations between bromine content and metal concentration suggests that bromide compounds play a role in the transportation of metals in volcanic gas

volcanic sources of tropospheric ozone depleting trace gases 1 recent investigations report mixing ratios of bro gas reaching 1 ppb in plume 4 7 km downwind of the summit of soufriere hills volcano montserrat the detection of bro in volcanic plumes is potentially important evidence of halogen catalyzed tropospheric ozone destruction and suggests that volcanoes either directly emit bro or emit bromine species that are rapidly converted to reactive bromine in volcanic plumes species distribution models constrained by volcanic gas and condensate analytical data for arc rift and hot spot volcanoes demonstrate that shallow magma degassing generates volcanic gases with ppb to ppm levels of reactive radicals br cl h and ho but no significant bro or clo the conversion of volcanic br and cl by reaction with ozone in gas phase catalytic reaction cycles during plume transport can lead to secondary bro and clo at mixing ratios of a ppt and higher possibly approaching a ppb for especially halogen rich volcanic gases several kilometers downwind of degassing sources in general however ppb bro and clo levels in volcanic plumes several kilometers downwind probably require near vent high temperature reaction of magmatic gases with air and or in plume heterogeneous chemical processes involving aerosols during plume transport these processes oxidize bromine and chlorine in hbr and hcl giving rise to increased levels of reactive br cl and ho in addition to nox they can also produce significant amounts of the photochemically active precursors br2 brcl and cl2 which are photolyzable to reactive br and cl the precursors may build up in nighttime volcanic plumes and accelerate ozone destruction and bro and clo production after sunrise downwind conversion of reactive br cl h and ho from volcanic gas sources by catalytic reaction chains to hobr and hocl may trigger heterogeneous chemical processes which are probably essential for sustaining ozone destruction in volcanic plumes gas phase reactions of hbr and hcl with ho in volcanic plumes might also boost bro and clo downwind thus in plume processes that generate reactive halogens may contribute significantly to ozone destruction in volcanic plumes enhanced levels of hox and nox in volcanic emissions may trigger nonhalogen catalytic cycles depleting ozone in tropospheric volcanic plumes

a total volatile inventory for masaya volcano nicaragua nerc project magma dynamics at persistently degassing basaltic volcanoes a novel approach to linking volcanic gases and magmatic volatiles within a physical model ne f004222 1 and ne f005342 1

emissions of trace elements during the 2012 2013 effusive eruption of tolbachik volcano kamchatka enrichment factors partition coefficients and aerosol contribution abstract gases and aerosols from the 2012 13 effusive eruption of tolbachik basaltic volcano kamchatka were sampled in february and may 2013 from a lava tube window located 300 m from the eruptive crater temperature at the sampling point was 1060 1070 c the chemical and isotopic compositions of the sampled gases 92 4 h 2 o 3 5 co 2 2 3 so 2 on average d from 25 0 to 38 6 correspond to a typical volcanic arc gas without dilution by meteoric or hydrothermal water halogen contents in the gases 1 37 hcl 0 5 hf were higher than average arc values the total amount of analyzed metallic and metalloid trace elements in the gas exceeded 665 ppm six most abundant trace elements k 250 ppm na 220 ppm si 74 ppm br 48 ppm cu 21 ppm and fe 12 ppm accounted for 95 of the total content of trace elements in the gas the gases contained 24 ppb re 12 ppb ag 4 9 ppb au and 0 45 ppb pt refractory rock forming elements mg al ca and some other elements such as ba and th were transported mainly in the form of silicate microspheres and altered rock particles the concentrations of metals in the eruptive tolbachik gases are higher than the corresponding concentrations in high temperature fumaroles worldwide although the mutual ratios of the elements are approximately the same the gas magma partition coefficients of eleven elements exceed unity including the non metals f s cl br as se and te and the rare metals cd re tl and bi despite the relatively low concentrations of trace elements in the volcanic gases at the highest temperatures superficial magma degassing provides information on the sources and sinks of metals

evaluation of gases condensates and so2 emissions from augustine volcano alaska the degassing of a cl rich volcanic system after the march april 1986 explosive eruption a comprehensive gas study at augustine was undertaken in the summers of 1986 and 1987 airborne cospec measurements indicate that passive so2 emission rates declined exponentially during this period from 380 45 metric tons day t d on 7 24 86 to 27 6 t d on 8 24 87 these data are consistent with the hypothesis that the augustine magma reservoir has become more degassed as volcanic activity decreased after the spring 1986 eruption gas samples collected in 1987 from an 870 c fumarole on the andesitic lava dome show various degrees of disequilibrium due to oxidation of reduced gas species and condensation and loss of h2o in the intake tube of the sampling apparatus thermochemical restoration of the data permits removal of these effects to infer an equilibrium composition of the gases although not conclusive this restoration is consistent with the idea that the gases were in equilibrium at 870 c with an oxygen fugacity near the ni nio buffer these restored gas compositions show that relative to other convergent plate volcanoes the augustine gases are very hcl rich 5 3 6 0 mol hcl s rich 7 1 mol total s and h2o poor 83 9 84 8 mol h2o values of d and 18o suggest that the h2o in the dome gases is a mixture of primary magmatic water pmw and local seawater part of the cl in the augustine volcanic gases probably comes from this shallow seawater source additional cl may come from subducted oceanic crust because data by johnston 1978 show that cl rich glass inclusions in olivine crystals contain hornblende which is evidence for a deep source 25km for part of the cl gas samples collected in 1986 from 390 642 c fumaroles on a ramp surrounding the inner summit crater have been oxidized so severely that restoration to an equilibrium composition is not possible h and o isotope data suggest that these gases are variable mixtures of seawater fmw and meteoric steam these samples are much more h2o rich 92 97 h2o than the dome gases possibly due to a larger meteoric steam component the 1986 samples also have higher cl s s c and f cl ratios which imply that the magmatic component in these gases is from the more degassed 1976 magma thus the 1987 samples from the lava dome are better indicators than the 1986 samples of degassing within the augustine magma reservoir even though they were collected a year later and contain a significant seawater component future gas studies at augustine should emphasize fumaroles on active lava domes condensates collected from the same lava dome fumarole have enrichments ot 107 102 in cl br f b cd as s bi pb sb mo zn cu k li na si and ni lower temperature 200 650 c fumaroles around the volcano are generally less enriched in highly volatile elements however these lower termperature fumaroles have higher concentration of rock forming elements probably derived from the wall rock

fumarolic emissions from mount st augustine alaska 1979 1984 degassing trends volatile sources and their possible role in eruptive style gas samples were collected from high temperature rooted summit vents at mount st augustine in 1979 1982 and 1984 all of the gas samples exhibit various degrees of disequilibrium thermodynamic restoration of the analyzed gases permits partial or complete removal of these disequilibrium effects and allows inference of equilibrium gas compositions long term 1979 1984 degassing trends within resampled or adjacent vents are characterized by increases from 97 4 to 99 8 mole in the h2o fraction and major decreases in the residual gases over this same period total gas hcl contents decreased by a factor of 3 to 10 while dry gas h2o free recalculated hcl contents increased by a factor of 1 6 to 3 dry gas mole proportions at these sites changed from being co2 dominated 46 co2 24 h2 in 1979 to h2 dominated 49 h2 22 co2 in 1984 the overall trends in gas chemistry and the stable isotope patterns in gases and condensates from the summit fumaroles can be explained by progressive magmatic outgassing coupled with increasing proportions of seawater in the fumarole emissions