hydrothermal element fluxes from copahue argentina a beehive volcano in turmoil copahue volcano erupted altered rock debris siliceous dust pyroclastic sulfur and rare juvenile fragments between 1992 and 1995 and magmatic eruptions occurred in july october 2000 prior to 2000 the copahue crater lake acid hot springs and rivers carried acid brines with compositions that reflected close to congruent rock dissolution the ratio between rock forming elements and chloride in the central zone of the volcano hydrothermal system has diminished over the past few years reflecting increased water rock ratios as a result of progressive rock dissolution magmatic activity in 2000 provided fresh rocks for the acid fluids resulting in higher ratios between rock forming elements and chloride in the fluids and enhanced mg fluxes the higher mg fluxes started several weeks prior to the eruption model data on the crater lake and river element flux determinations indicate that copahue volcano was hollowed out at a rate of about 20 000 25 000 m 3 yr but that void space was filled with about equal amounts of silica and liquid elemental sulfur the extensive rock dissolution has weakened the internal volcanic structure making flank collapse a volcanic hazard at copahue

volatile transport of metals and the cu budget of the active white island magmatic hydrothermal system new zealand abstract evidence of metal transport by volcanic gases is found amongst others in volcanic plumes and sublimates growing around fumaroles the transport mechanisms i e volatile metal compounds are however not well constrained here we present results on the volatile transport of metals at the scale of a magmatic hydrothermal system white island volcano we studied metal emissions from the main vent through the crater lake covering the conduit volcanic gases injected in the lake are responsible for the waters and sediments enrichment in various metals while elemental sulfur forming at the bottom appears as the main sink for chalcophile metals metal chloride complexes are the dominant species in the hot and acidic crater lake waters nearby low temperature fumarolic gases are lower in metals than higher temperature gases reported in the 1970s emphasizing precipitation at depth and sequestration by condensing elemental sulfur efficient gaseous transport of metals by hcl and hbr is revealed by thermodynamic modeling whereas the role of sulfur is restrained to controlling redox conditions a copper budget for white island magmatic hydrothermal system is assessed taking into consideration all the potentials sinks about 3900 tons of copper are estimated to be retained in the subsurface environment every year over the 10 000 years lifetime of the magmatic hydrothermal system this adds up to 40 megatons depicting white island as a potential cu porphyry forming deposit

the bimodal ph distribution of volcanic lake waters abstract volcanic lake waters have a bimodal ph distribution with an acidic mode at ph 0 5 1 5 and a near neutral mode at ph 6 6 5 with relatively few samples having ph 3 5 5 to investigate the reasons for this distribution the irreversible water rock mass exchanges during the neutralization of acid so4 cl waters with andesite under both low and high temperature conditions were simulated by means of the eq3 6 software package version 7 2 reaction path modeling under low temperature and atmospheric pco2 and fo2 suggests that several homogeneous and or heterogeneous ph buffers exist both in the acidic and neutral regions but no buffer is active in the intermediate central ph region again the same titration under high temperature hydrothermal magmatic conditions is expected to produce comparatively infrequent aqueous solutions with ph values in the 3 5 5 range upon their cooling below 100 c substantially different ph values are obtained depending on the cooling paths either through boiling or conductive heat losses these distinct ph values are governed by either hso4 and hcl aq in poorly neutralized aqueous solutions or the co2 aq hco3 couple and the pco2 value as well in neutralized aqueous solutions finally mixing of the acid lake water with the aqueous solutions produced through high temperature titration and cooled below 100 c is unlikely to generate mixtures with ph values higher than 3 unless the fraction of the acidic water originally present in the lake becomes very small which means its virtually complete substitution summing up the evidence gathered through reaction path modeling of the neutralization of acid lake waters with andesite both at low and high temperatures explains the scarcity of volcanic lake waters with measured ph values of 3 5 5

geochemical and isotopic evidences of magmatic inputs in the hydrothermal reservoir feeding the fumarolic discharges of tacora volcano northern chile abstract tacora volcano is a nearly unknown and understudied 5980 m high volcano located on the northernmost border between chile and peru tacora is characterized by intense fumarolic activity with extensive white colored hydrothermal areas along the nw and w flanks of the volcanic structure the chemical and isotopic features of gas emissions indicate that the hydrothermal reservoir is significantly affected by contributions from magmatic degassing despite relatively low outlet temperatures 82 93 c water and gas isotopic signatures stem from degassing of andesitic magmas produced from the sediment poor subducting slab isotopic data suggests ch 4 co 2 isotopic equilibration occurs at 400 c likely in the deepest portion of the hydrothermal magmatic fluid reservoir the h 2 h 2 o co co 2 h 2 ar ch 4 co 2 and c 2 c 3 alkenes alkanes pairs tend to approach a chemical equilibrium at temperatures between 200 and 320 c when redox conditions are more oxidizing than those determined by the typical feo feo 1 5 rock buffer system boiling occurs at shallow depth at 85 c within a discontinuous thin aquifer enough as thermal buffer but not able to scrub the uprising magmatic related acidic gases

evolution of fluid geochemistry at the turrialba volcano costa rica from 1998 to 2008 turrialba 10 02 n 83 45 w is a 3 349 m high stratovolcano belonging to the holocene cordillera central volcanic belt of costa rica the summit consists of three ew oriented craters east central and west since its last eruptive phase 1864 1866 the central and west craters have displayed modest fumarolic activity with outlet temperatures clustering around 90 c in 2001 seismic swarms ground deformation and increasing fumarolic activity occurred from 2005 to 2008 new fumarolic vents opened between and within the central and west craters and along the western and southwestern outer flanks of the volcanic edifice these physical changes were accompanied by a drastic modification in the gas chemistry that can be divided in three stages 1 hydrothermal from 1998 to autumn 2001 characterized by the presence of h2o co2 h2s and to a very minor extent hcl and hf 2 hydrothermal magmatic autumn 2001 2007 with the appearance of so2 and a significant increase of hcl and hf and 3 magmatic dominated 2007 2008 characterized by increased so2 content so2 h2s 100 and temperatures up to 282 c accordingly gas equilibrium in the co2 ch4 h2 system suggests a progressive evolution of the deep fluid reservoir toward higher temperatures and more oxidizing conditions the chemical physical modifications of turrialba in the last decade can be interpreted as part of a cyclic mechanism controlling the balance between the hydrothermal and the magmatic systems nevertheless the risk of rejuvenation of the volcanic activity cannot be excluded and an appropriate seismic ground deformation and geochemical monitoring program is highly recommended turrialba lies at a distance of 35 and 15 km from san jose and cartago respectively the two largest cities in costa rica

role of the tectonic facies concept in orogenic analysis and its application to tethys in the eastern mediterranean region abstract the purpose of this paper is to advocate the use of a tectonic facies concept which aids systematic and objective analysis of orogenic belts the tectonic facies concept as discussed here focuses on the recognition of discrete tectonic settings mainly those exposed at high crustal levels in orogenic belts application of the tectonic facies concept can help field geologists to relate plate scale processes to outcrop geology tectonic facies are recognised based on knowledge of the modern oceans and margins and well constrained land settings tectonic facies analogous to sedimentary facies can be identified from integrated sets of field data and related laboratory studies a number of tectonic facies models can be recognised in this way their identification aids interpretation and comparisons of orogenic belts palinspastic reconstructions require additional information particularly age kinematic and palaeomagnetic data in this paper the tectonic facies concept is tested by application to a well documented mainly high level orogenic segment tethys in the eastern mediterranean area and is found to be an effective way both of the describing and interpreting this region other methods of tectonic analysis e g recognition of tectono stratigraphic terranes may also be found useful in certain settings and can be used in conjunction with the tectonic facies concept

precise 40ar 39ar ages from the metamorphic sole of the mersin ophiolite southern turkey abstract the mersin ophiolite is located on the southern flank of the e w trending central tauride belt in turkey it is one of the late cretaceous neotethyan oceanic lithospheric remnants the mersin ophiolite formed in a suprasubduction zone tectonic setting in southern turkey at the beginning of the late cretaceous the mersin ophiolite is one of the best examples in turkey in order to study reconstruction of ophiolite emplacement along the alpine himalayan orogenic belt 40ar 39ar incremental heating measurements were performed on seven obduction related subophiolitic metamorphic rocks hornblende separates yielded isochron ages ranging from 96 0 0 7 ma to 91 6 0 3 ma all errors 1 five of the seven hornblende age determinations are indistinguishable at the 95 confidence level and have a weighted mean age of 92 6 0 2 2 ma we interpret these ages as the date of cooling below 500 c intraoceanic thrusting occurred 4 ma soon after formation of oceanic crust the sole was crosscut by microgabbro diabase dikes less than 3 m y later the final obduction onto the tauride platform occurred during the late cretaceous early paleocene our new high precision ages constrain intraoceanic thrusting for a single ophiolite mersin in the tauride belt

turmoil at turrialba volcano costa rica degassing and eruptive processes inferred from high frequency gas monitoring eruptive activity at turrialba volcano costa rica has escalated significantly since 2014 causing airport and school closures in the capital city of san jose whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material here we use high frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions pulses of deeply derived co2 rich gas co2 s total 4 5 precede explosive activity providing a clear precursor to eruptive periods that occurs up to 2weeks before eruptions which are accompanied by shallowly derived sulfur rich magmatic gas emissions degassing modeling suggests that the deep magmatic reservoir is similar to 8 10km deep whereas the shallow magmatic gas source is at similar to 3 5km two cycles of degassing and eruption are observed each attributed to pulses of magma ascending through the deep reservoir to shallow crustal levels the magmatic degassing signals were overprinted by a fluid contribution from the shallow hydrothermal system modifying the gas compositions contributing volatiles to the emissions and reflecting complex processes of scrubbing displacement and volatilization h2s so2 varies over 2 orders of magnitude through the monitoring period and demonstrates that the first eruptive episode involved hydrothermal gases whereas the second did not massive degassing 3000t d so2 and h2s so2 1 followed suggesting boiling off of the hydrothermal system the gas emissions show a remarkable shift to purely magmatic composition h2s so2 0 05 during the second eruptive period reflecting the depletion of the hydrothermal system or the establishment of high temperature conduits bypassing remnant hydrothermal reservoirs and the transition from phreatic to phreatomagmatic eruptive activity

metal transport in volcanic plumes a case study at white island and yasur volcanoes abstract we report new data on trace metal emissions at white island volcano 2015 2016 the first estimates from yasur volcano 2016 and a brief review of global volcanic metal fluxes bi cd tl se sb te and au are the most enriched metals and metalloids in the particulate phase of volcanic plumes observations of the particulate phase from the volcanic plumes of white island yasur and etna reveal abundant silicates and sulfates sulfuric acid and more interestingly zn oxide containing variable amounts of cu thermodynamic speciation calculations show chloride species to be very important in terms of gaseous metal transport complexation with sulfur in contrast appears significant only in s rich and cl poor gases at high 700 c temperature bromine despite being a minor component of volcanic gases is very efficient at complexing with metals and especially with cu pb bi zn and cr metal emission rates in the study period at white island are one to two orders of magnitude lower than reported previously with 6 10 kg d of cu as se and zn and

counterclockwise p t t trajectory from the metamorphic sole of a neo tethyan ophiolite turkey abstract the kiziltepe ophiolitic thrust sheet in the bolkar mountains of turkey occurs between two subparallel ophiolite belts bounding the tauride carbonate platform and represents a remnant of the cretaceous neo tethyan oceanic lithosphere it is underlain by foliated amphibolite that represents a metamorphic sole developed at the inception of an intra oceanic subduction zone in the neo tethys 92 90 ma blueschist facies overprinting of the amphibolite indicates that the metamorphic sole was dragged deeper into the subduction zone where it experienced increasing p t with cooling regional tectonic constraints suggest a maastrichtian age for the timing of this blueschist facies metamorphism sodic amphibole rich veins and crossite mg riebeckite rims on hornblende suggest that growth of blueschist facies minerals was facilitated by infiltration of fluid along fractures and grain boundaries we infer a counterclockwise p t t trajectory during which metamorphism was accompanied succeeded by rapid uplift along the northern edge of the tauride belt in late cretaceous early tertiary time

the ophiolite related mersin melange southern turkey its role in the tectonic sedimentary setting of tethys in the eastern mediterranean region the mersin melange underlies the intact mersin ophiolite and its metamorphic sole to the south of the mesozoic tauride carbonate platform in southern turkey the melange varies from chaotic melange to broken formation in which some stratigraphic continuity can be recognized based on study of the broken formation four lithological associations are recognized 1 shallow water platform association dominated by upper palaeozoic lower cretaceous neritic carbonates 2 rift related volcanogenic terrigenous pelagic association mainly upper triassic andesitic acidic volcanogenic rocks siliciclastic gravity flows basinal carbonates and radiolarites 3 within plate type basalt radiolarite pelagic limestone association interpreted as upper jurassic lower cretaceous seamounts with associated radiolarian sediments and upper cretaceous pelagic carbonates 4 ophiolite derived association including fragments of the upper cretaceous mersin ophiolite and its metamorphic sole locally the ophiolitic melange includes granite that yielded a k ar radiometric age of 375 7 10 5 ma late devonian this granite appears to be subduction influenced based on immobile element composition the mersin melange documents the following history 1 triassic rifting of the tauride continent 2 jurassic cretaceous passive margin subsidence 3 oceanic seamount genesis 4 cretaceous supra subduction zone ophiolite genesis 5 late cretaceous intra oceanic convergence metamorphic sole formation and 6 latest cretaceous emplacement onto the tauride microcontinent and related backthrusting regional comparisons show that the restored mersin melange is similar to the beysehir hoyran nappes further northwest and a northerly origin best fits the regional geological picture these remnants of a north neotethys inner tauride ocean were formed and emplaced to the north of the tauride carbonate platform they are dissimilar to melanges and related units in northern syria western cyprus and southwestern turkey which are interpreted as remnants of a south neotethys early high temperature ductile transport lineations within amphibolites of the metamorphic sole of the mersin ophiolite are generally orientated e w possibly resulting from vertical axis rotation of the ophiolite while still in an oceanic setting by contrast the commonly northward facing later stage brittle structures are explained by backthrusting of the ophiolite and melange related to exhumation of the partially subducted northern leading edge of the tauride continent

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

chemical and isotopic composition of fumarolic gases and the so2 flux from volcan de colima mexico between the 1994 and 1998 eruptions volcan de colima is the most active volcano in mexico including a significant effusive eruption in 1991 and a weak explosive event in 1994 geochemical monitoring of the volcano started in january 1996 with collection of fumarolic gases approximately every 3 months from two sites in the summit crater z3 800 c and z2 400 c chemical compositions of volcanic gases from the z2 fumarole showed a peak in s cl in the middle of 1997 14 15 months before the start of the 1998 lava eruption high temperature volcanic vapors from z3 changed progressively in water isotopic composition and showed a weak trend of increasing hcl hf and a peak in s cl at the same time starting from the summer of 1997 the volcanic water became gradually enriched in deuterium which probably indicated an increasing contribution from deep less degassed magma a negative correlation between d and cl content for the z3 fumarolic gases is explained by shallow degassing of the colima hot lava plug this hypothesis is consistent with published data on cl contents and solubilities in magmas and supported by the observed positive trends of s cl and hcl hf with d for the z3 fumarole until september 1998 the so2 flux from the volcano was at a low level 100 tons day and often below the detection limit of the instrument 30 tons day a sharp increase in the so2 flux was recorded 1 month before the eruption started it jumped from 400 50 tons day to 1600 tons day 2 days before new lava emerged on 20 november 1998 the so2 flux correlated well with seismicity

dynamic fluid recycling at laguna caliente poas costa rica before and during the 2006 ongoing phreatic eruption cycle 2005 10

stratification at the earth s largest hyperacidic lake and its consequences volcanic lakes provide windows into the interior of volcanoes as they integrate the heat flux discharged by a magma body and condense volcanic gases volcanic lake temperatures and geochemical compositions therefore typically serve as warnings for resumed unrest or prior to eruptions if acidic and hot these lakes are usually considered to be too convective to allow any stratification within their waters kawah ijen volcano featuring the largest hyperacidic lake on earth volume of 27 million m3 is less homogeneous than previously thought hourly temperature measurements reveal the development of a stagnant layer of cold waters 30 c overlying warmer and denser water generally above 30 c and density 1 083 kg m3 examination of 20 yrs of historical records and temporary measurements show a systematic thermal stratification during rainy seasons the yearly rupture of stratification at the end of the rainy season causes a sudden release of dissolved gases below the cold water layer which appears to generate a lake overturn i e limnic eruption and a resonance of the lake i e a seiche highlighting a new hazard for these extreme reservoirs a minor non volcanic event such as a heavy rainfall or an earthquake may act as a trigger the density driven overturn requires specific salinity temperature conditions for the colder and less saline top water layer to sink into the hot saline water spectacular degassing occurs when the dissolved gases progressively stored during the rainy season due to a weakened diffusion of carbon dioxide in the top layer are suddenly released these findings challenge the homogenization assumption at acidic lakes and stress the need to develop appropriate monitoring setups

the role of manganese in the paragenesis of magmatic garnet an example from the old woman piute range california a reply strongly peraluminous plutons of the old woman piute range southeastern california display the differentiation sequence muscovite biotite granite rightarrow muscovite garnet biotite granite rightarrow garnet muscovite granite rightarrow garnet muscovite aplite and pegmatite the garnets show no evidence of reaction but biotites in garnet bearing rocks are rimmed by muscovite metamorphic assemblages in the country rocks suggest pressures of emplacement less than 4 5 kb the plutons become relatively enriched in manganese with differentiation whole rock ratios of molar mn fe mg increase from 0 01 in least felsic garnet free rocks to 0 3 in most felsic garnet rich rocks mno concentrations show a corresponding rise in biotites 0 4 to 1 8 wt and less clearly in garnets 9 to 25 the differentiation sequence textural relations and mineral and whole rock compositions suggest that garnet paragenesis was controlled by the reaction biotite mn rich liquid rightarrow garnet

volcanic lake systematics ii chemical constraints abstract a database of 373 lake water analyses from the published literature was compiled and used to explore the geochemical systematics of volcanic lakes binary correlations and principal component analysis indicate strong internal coherence among most chemical parameters compositional variations are influenced by the flux of magmatic volatiles and or deep hydrothermal fluids the chemistry of the fluid entering a lake may be dominated by a high temperature volcanic gas component or by a lower temperature fluid that has interacted extensively with volcanic rocks precipitation of minerals like gypsum and silica can strongly affect the concentrations of ca and si in some lakes a much less concentrated geothermal input fluid provides the mineralized components of some more dilute lakes temporal variations in dilution and evaporation rates ultimately control absolute concentrations of dissolved constituents but not conservative element ratios most volcanic lake waters and presumably their deep hydrothermal fluid inputs classify as immature acid fluids that have not equilibrated with common secondary silicates such as clays or zeolites many such fluids may have equilibrated with secondary minerals earlier in their history but were re acidified by mixing with fresh volcanic fluids we use the concept of degree of neutralization as a new parameter to characterize these acid fluids this leads to a classification of gas dominated versus rock dominated lake waters a further classification is based on a cluster analysis and a hydrothermal speedometer concept which uses the degree of silica equilibration of a fluid during cooling and dilution to evaluate the rate of fluid equilibration in volcano hydrothermal systems

lycian melange southwestern turkey an emplaced late cretaceous accretionary complex the lycian thrust belt is an important part of the tethyan orogenic belt in the eastern mediterranean region it includes a unit of internally disrupted thin skinned thrust sheets layered tectonic melange and a melange rich in ophiolitic material ophiolitic melange the layered tectonic melange is dominated by mesozoic distal deep water sedimentary rocks and the ophiolitic melange includes disrupted thrust sheets of early mesozoic shallow water limestone and blocks of basalt of both mid ocean ridge and within plate geochemical affinities a complete record of closure of a tethyan oceanic basin began with late cretaceous intraoceanic subduction followed by latest cretaceous trench continental collision and ended with mid tertiary continental collision and orogenic collapse

the crater lake of ilamatepec santa ana volcano el salvador insights into lake gas composition and implications for monitoring we here present the first chemical characterization of the volcanic gas plume issuing from the santa ana crater lake a hyper acidic crater lake ph of 0 2 to 2 5 in north western el salvador our results obtained during regular surveys in 2017 and 2018 using a multi gas instrument demonstrate a hydrous gas composition h2o so2 ratios from 32 to 205 and so2 as the main sulfur species h2s so2 0 03 0 1 we also find that gas composition evolved during our investigated period with the co2 so2 ratio decreasing by one order of magnitude from march 2017 37 2 9 7 to november 2018 3 this compositional evolution toward more magmatic so2 rich compositions is interpreted in the context of the long term evolution of the volcano following its 2005 and 2007 eruptions we find that in spite of reduced background level seismicity the magmatic gas supply into the lake was one order of magnitude higher in march 2017 total volatile flux 20 200 30 200 t day than in the following periods total volatile flux 900 10 167 t day we propose that the elevated magmatic hydrothermal transport in march 2017 combined with a 15 reduction in precipitation caused the volume of the lake to decrease ultimately reducing its sulfur absorbing and scrubbing capacity and hence causing the gas plume co2 so2 ratio to decrease the recently observed increases in temperature acidity and salinity of the lake are consistent with this hypothesis we conclude that the installation of a continuous fully automated multi gas is highly desirable to monitor any future change in lake plume chemistry and hence the level of degassing activity

intense magmatic degassing through the lake of copahue volcano 2013 2014 here we report on the first assessment of volatile fluxes from the hyperacid crater lake hosted within the summit crater of copahue a very active volcano on the argentina chile border our observations were performed using a variety of in situ and remote sensing techniques during field campaigns in march 2013 when the crater hosted an active fumarole field and in march 2014 when an acidic volcanic lake covered the fumarole field in the latter campaign we found that 566 to 1373 t d 1 of so2 were being emitted from the lake in a plume that appeared largely invisible this combined with our derived bulk plume composition was converted into flux of other volcanic species h2o 10989 t d 1 co2 638 t d 1 hcl 66 t d 1 h2 3 3 t d 1 and hbr 0 05 t d 1 these levels of degassing comparable to those seen at many open vent degassing arc volcanoes were surprisingly high for a volcano hosting a crater lake copahue s unusual degassing regime was also confirmed by the chemical composition of the plume that although issuing from a hot 65 c lake preserves a close to magmatic signature eq3 6 models of gas water rock interaction in the lake were able to match observed compositions and demonstrated that magmatic gases emitted to the atmosphere were virtually unaffected by scrubbing of soluble s and cl species finally the derived large h2o flux 10 988 t d 1 suggested a mechanism in which magmatic gas stripping drove enhanced lake water evaporation a process likely common to many degassing volcanic lakes worldwide

magma hydrothermal system interaction inferred from volcanic gas measurements obtained during 2003 2008 at meakandake volcano hokkaido japan phreatic eruptions occurred at the meakandake volcano in 1988 1996 1998 2006 and 2008 we conducted geochemical surveillance that included measurements of temperature so2 emission rates and volcanic gas composition from 2003 to 2008 at the nakamachineshiri nm northwest nw and akanuma ak fumarolic areas and the 96 1 vent where historical eruptions had occurred the elemental compositions of the gases discharged from the different areas are similar compared with the large variations observed in volcanic gases discharged from subduction zones all the gases showed high apparent equilibrium temperatures suggesting that all these gases originated from a common magmatic gas the gases discharged from each area also exhibited different characteristics which are probably the results of differences in the conditions of meteoric water mixing quenching of chemical reactions and vapor liquid separation the highest apparent equilibrium temperatures about 500 c were observed in the case of nw fumarolic gases despite the low outlet temperature of about 100 c at these fumaroles since the nw fumaroles were formed as a result of the 2006 phreatic eruption the high temperature gas supply to the nw fumarole suggests that the phreatic eruption was caused by the ascent of high temperature magmatic gases the temperatures compositions and emission rates of the nm and 96 1 gases did not show any appreciable change after the 2006 eruption indicating that each fumarolic system had a separate magmatic hydrothermal system the temperatures compositions and emission rates of the nm fumarolic gases were apparently constant and these fumaroles are inferred to be formed by the evaporation of a hydrothermal system with a constant temperature of about 300 c the 96 1 gas compositions showed large changes during continuous temperature decrease from 390 to 190 c occurred from 2003 to 2008 but the sulfur gas emission rates were almost constant at about four tons day at the 96 1 vent the so2 h2s ratio decreased while the h2 h2o ratio remained almost constant this was probably caused by the rock buffer controlled chemical reaction during the temperature decrease

geochemistry mineralogy and chemical modeling of the acid crater lake of kawah ijen volcano indonesia the kawah ijen volcano with a record of phreatic eruptions has its 1000 m wide crater filled with a lake that has existed for at least one century at present the lake waters are hot t 37 c strongly mineralized tds 105 g l and extremely acidic ph 0 4 by its volume the javanese lake is probably the largest accumulation in the world of such acidic waters mineralogy of the suspended solids within the lake waters suggests that concentrations of si ca ti and ba are controlled by precipitation of silica gypsum anatase and barite lake sediment is composed of chemical precipitates with composition similar to the suspended solids thermodynamic calculations predict that the lake waters have reached equilibrium with respect to cristobalite barite gypsum anglesite celestite and amorphous silica in agreement with the analytical observations significant concentrations of ferric iron suggest that the current lake waters are fairly oxidized sulfides are absent in the water column but are always present in the native s spherules that form porous aggregates which float on the lake the presence of native s provides direct evidence of more reduced conditions at the lake floor where h 2 s is probably being injected into the lake with progressive addition of h 2 s to the acid waters native s pyrite and enargite are theoretically predicted to be saturated reactions between upward streaming h 2 s bearing gases discharged by subaqueous fumaroles and metals dissolved in the acidic waters could initiate precipitation of these sulfides a model of direct absorption of hot magmatic gases into cool water accounts for the extreme acidity of the crater lake results show that strongly acidic sulfate rich solutions are formed under oxidizing conditions at high gas water ratios reactions between the acidic fluids and the ijen andesite were modeled to account for elevated cation concentrations in lake water current concentrations of conservative rockforming elements are produced by dissolution of approximately 60 g of andesite per kg of acid solution complete neutralization of the acid lake waters by reaction with the wallrock produces a theoretical alteration assemblage equivalent to that observed in volcano hosted acid sulfate epithermal ore deposits

using crater lake chemistry to predict volcanic activity at poas volcano costa rica monitoring of crater lake chemistry during the recent decline and disappearance of the crater lake of poas volcano revealed that large variations in so4 cl f cl and mg cl ratios were caused by the enhanced release of hcl vapor from the lake surface due to increasing lake temperature and solution acidity variation in the concentration of polythionic acids h2sxo6 x 4 6 was the most reliable predictor of renewed phreatic eruptive activity at the volcano exhibiting sharp decreases three months prior to the initiation of phreatic eruptions in june 1987 polythionic acids may offer a direct indicator of changing subsurface magmatic activity whereas chloride based element ratios may be influenced by surface volatilization of hcl and subsequent recycling of acidic fluids in crater lake volcanoes

hydrological evolution and chemical structure of a hyper acidic spring lake system on whakaari white island nz abstract white island has a long and varied history of acid spring discharge and shallow ephemeral lake formation on its main crater floor in the 12 months prior to the onset of the 1976 2000 eruptive episode mass discharge from the spring system increased ca 10 fold pointing to a strong coupling of the hydrothermal environment to the evolving magmatic system between 1976 and 1978 the formation of numerous eruption vents to 200 m depth in the western sub crater abruptly changed the hydraulic gradients in the volcano resulting in the reversal of groundwater flow in the massif towards the newly formed crater s this affected not only the style of volcanic activity leading to phreatic phreatomagmatic magmatic eruption cycles but also led to the demise of the spring system with discharge from the main crater declining by a factor 100 by 1979 eruptive activity ended shortly after a moderate strombolian eruption in mid 2000 after which ephemeral lakes started to form in the eruption crater complex between 2003 and 2015 there were three complete lake filling and evaporative cycles reflecting varying heat flow through the conduit system beneath the lake over these cycles lake water concentrations of cl and so 4 varied between ca 35 150 and 5 45 g l respectively with ph values temporally ranging from 1 5 to 1 springs appeared on the main crater floor in 2004 and their discharges varied with lake level pointing to the lake level being a primary control over the piezometric surface in the crater area springs closest to the crater complex show direct evidence of crater lake water infiltration into the crater floor aquifer whereas distal spring discharges show compositional variations reflecting vertical displacement of the interface between shallow dilute condensate and underlying acidic brine fluids source components for the spring fluids include magmatic vapour dissolved andesitic host rocks seawater and meteoric water lake waters on the other hand consist predominantly of magmatic vapour meteoric water and solutes derived from host andesites and their altered derivatives 2 h and 18 o signatures of the enclosing acid brine fluids indicate they are predominantly seawater which have been affected by both vapour loss but also mixing with arc type vapour an interesting finding of this study is that crater floor deformation correlates directly to both lake level and volatile emissions in an apparent poroelastic response to the establishment of a hydrostatic water column in the eruption crater complex and a net decrease in permeability owing to hydrothermal mineralization in the conduit predominantly elemental sulfur and sulfate minerals the hydrostatic pressurization of the vent environment also leads to increased gas pressures and flows through fumarolic channels and consequent expansion of fumarolic areas on the main crater floor a period of unrest which commenced in august 2012 and lasted until october 2013 included the extrusion of a small dome into the eruption crater complex this activity and related high heat flow led once again to evaporation of the lake and ongoing phreatic eruption activity which has provided interesting insights into the role which elemental sulfur associated hydrothermal alteration minerals and of course water play in regulating pressures in the magmatic hydrothermal environment

the 2012 2016 eruptive cycle at copahue volcano argentina versus the peripheral gas manifestations hints from the chemical and isotopic features of fumarolic fluids this study presents the chemical and isotopic compositions of hydrothermal gases from fumaroles discharging around copahue volcano argentina gas samples including those from two fumaroles at the active summit crater were collected during 13 surveys carried out by different research teams from 1976 to february 2016 the time series of h2 co and light hydrocarbons showed episodic increases related to the main events of the last eruptive cycle that started on 19 july 2012 concentration peaks were likely caused by enhanced input of hot magmatic fluids affecting the hydrothermal reservoir these data contrast with the temporal variations shown by rc ra and 13c co2 values in 2012 2014 which indicated an increasing input from a crustal fluid source in 2015 2016 however these isotopic parameters showed opposite trends their composition became closer to that of the two summit fumaroles which possibly corresponds to that of the deep magmatic related end member the delayed and reduced compositional changes in the peripheral hydrothermal fluid discharge in response to the 2012 2016 eruptive events suggest that geochemical surveys of these emissions are unlikely to provide premonitory signals of volcanic unrest if the volcanic activity remains centered in the main crater instead an instrument which is able to provide measurements of volcanic gases in the air e g multigas may be used to detect changes at the summit crater otherwise monitoring of seismic activity and ground deformation as well as the periodic measurement of the chemistry of the water in the rio agrio which is fed by thermal discharge from the summit crater seem to represent the most reliable means of monitoring at copahue however the relative compositional stability of the hydrothermal reservoir is a great advantage in terms of geothermal resource exploitation and could encourage new investments in the copahue geothermal project which was abandoned in the 1990s