volcano monitoring by microgravity and energy budget analysis microgravity monitoring of active volcanoes can provide evidence of sub surface mass and or density changes that precede eruptions if in addition precursory increases in thermal emissions are observed an integrated mechanistic model for volcanic activity may be developed with the potential for forecasting eruptions crater lake volcanoes provide an interesting target for such studies since thermal output can be monitored simply through lake water calotimetry here we summarize 10 years of gravity and thermal data from poas volcano costa rica mass energy balance calculations demonstrate that in the steady state the large thermal inertia of the crater lake acts as a buffer to short term changes in the energy input from the cooling magma feeder pipe since february 1986 it is postulated that there has been gradual emplacement of a shallow magma intrusion associated with vesiculation and gas loss to the surface this follows from unambiguous gravity increases constrained by elevation control that are coincident in time with a period of long term increased energy input to the crater lake progressive reduction of the lake volume by evaporation seepage culminated in an april 1989 ash eruption providing a good documented record of combined gravity and thermodynamic precursors to volcanic activity

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

hydrogeochemical surveillance at el chichon volcano crater lake chiapas mexico abstract el chichon volcano has an eruptive record of at least 12 major eruptions in the holocene the latest one in march april 1982 causing the worst volcanic disaster in the history of mexico after about 6 centuries of quiescence this eruption destroyed a large dome and opened a 1 km wide crater a lake formed within the crater shortly after the eruption has been an important source of information about the evolution of the post eruptive processes the fluctuations of the crater lake water physicochemical parameters observed since 1983 have allowed in identifying hydrothermal waters and h 2 s rich gases influenced by tectonic and meteorological effects as the main contributors to its composition here we propose some methods to help in assessing the state of the volcano derived from the relative contribution of these factors as an easy to implement volcanic surveillance method in potentially active volcanoes with crater lakes or other volcano influenced water sources

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

late quaternary paleohydrology in the north american great plains inferred from the geochemistry of endogenic carbonate and fossil ostracodes from devils lake north dakota usa abstract devils lake north dakota is a closed basin lake in which water chemistry is responsive to hydrological changes making it a valuable resource for documenting paleoclimate conditions ostracode trace element and bulk carbonate geochemistry in a core are used to generate a 12 000 year record of salinity fluctuations the relative amounts of sr ca and ba in the bulk carbonate fraction can be linked mechanistically to changes in sediment mineralogy calcite aragonite and or solute chemistry whereas the elemental geochemistry of ostracode valves reflect solute chemistry associated minima in sr ca and maxima in mg ca in ostracode valves from the devils lake core may be due to aragonite mediation of sr chemistry during the precipitation of multiple mineral phases during more saline intervals the devils lake record can be divided into four hydrological periods on the basis of the geochemical proxies a 12 5 9 k y low salinity b 9 5 4 5 k y fluctuating saline conditions with a maximum at about 8 k y c 4 5 3 5 k y low salinity phase but probably not as fresh as at 12 5 9 k y d 3 5 k y present saline phase although generally less so than 9 5 4 5 k y however a large degree of variability characterizes the entire record suggesting the absence of long term climatic stability in this region

leakage of active crater lake brine through the north flank at rincon de la vieja volcano northwest costa rica and implications for crater collapse abstract the active crater at rincon de la vieja volcano costa rica reaches an elevation of 1750 m and contains a warm hyper acidic crater lake that probably formed soon after the eruption of the rio blanco tephra deposit approximately 3500 years before present the active crater is buttressed by volcanic ridges and older craters on all sides except the north which dips steeply toward the caribbean coastal plains acidic above ambient temperature streams are found along the active crater s north flank at elevations between 800 and 1000 m a geochemical survey of thermal and non thermal waters at rincon de la vieja was done in 1989 to determine whether hyper acidic fluids are leaking from the active crater through the north flank affecting the composition of north flank streams results of the water chemistry survey reveal that three distinct thermal waters are found on the flanks of rincon de la vieja volcano acid chloride sulfate acs acid sulfate as and neutral chloride nc waters the most extreme acs water was collected from the crater lake that fills the active crater chemical analyses of the lake water reveal a hyper acidic ph 0 chloride sulfate brine with elevated concentrations of calcium magnesium aluminum iron manganese copper zinc fluorine and boron the composition of the brine reflects the combined effects of magmatic degassing from a shallow magma body beneath the active crater dissolution of andesitic volcanic rock and evaporative concentration of dissolved constituents at above ambient temperatures similar cation and anion enrichments are found in the above ambient temperature streams draining the north flank of the active crater the ph of north flank thermal waters range from 3 6 to 4 1 and chloride sulfate ratios 1 2 1 4 that are a factor of two greater than that of the lake brine 0 60 the waters have an acs composition that is quite different from the as and nc thermal waters that occur along the southern flank of rincon de la vieja the distribution of thermal water types at rincon de la vieja strongly indicates that formation of the north flank acs waters is not due to mixing of shallow steam heated as water with deep seated nc water more likely hyper acidic brines formed in the active crater area are migrating through permeable zones in the volcanic strata that make up the active crater s north flank dissolution and shallow subsurface alteration of north flank volcanoclastic material by interaction with acidic lake brine particularly in the more permeable tephra units could weaken the already oversteepened north flank of the active crater sector collapse of the active crater with or without a volcanic eruption represents a potential threat to human lives property and ecosystems at rincon de la vieja volcano

water chemistry of lake quilotoa ecuador and assessment of natural hazards a geochemical survey carried out in november 1993 revealed that lake quilotoa was composed by a thin 14 m oxic epilimnion overlying a 200 m thick anoxic hypolimnion dissolved co2 concentrations reached 1000 mg kg in the lower stratum loss of co2 from epilimnetic waters followed by calcite precipitation and a consequent lowering in density was the apparent cause of the stratification the cl so4 and hco3 contents of lake quilotoa are intermediate between those of acid so4 cl crater lakes and those of neutral hco3 crater lakes indicating that lake quilotoa has a memory of the inflow and absorption of hc1 and s bearing volcanic magmatic gases the mg ca ratios of the lake waters are governed by dissolution of local volcanic rocks or magmas but k na ratios were likely modified by precipitation of alunite a typical mineral in acid so 4 cl crater lakes the constant concentrations of several conservative chemical species from lake surface to lake bottom suggest that physical chemical and biological processes did not have enough time after the last overturn to cause significant changes in the contents of these chemical species this lapse of time might be relatively large but it cannot be established on the basis of available data besides the lake may not be close to steady state mixing of lake quilotoa waters could presently be triggered by either cooling epilimnetic waters by 48c or providing heat to hypolimnetic waters or by seismic activity although quilotoa lake contains a huge amount of dissolved co2o 3 10 11 gu at present the risk of a dangerous limnic eruption seems to be nil even though some gas exsolution might occur if deep lake waters were brought to the surface carbon dioxide could build up to higher levels in deep waters than at present without any volcanic re awakening due to either a large inflow of relatively cool co 2 rich gases or possibly a long interval between overturns periodical geochemical surveys of lake quilotoa are therefore recommended q 2000 elsevier science b v all rights reserved

geochemistry of ostracode calcite part 2 the effects of water chemistry and seasonal temperature variation on candona rawsoni abstract reconstruction of lake paleochemistry from the isotope and trace element composition of fossil ostracodes requires an understanding of geochemical variations induced by the seasonality of shell formation monthly field collections of live candona rawsoni from two hyposaline lakes in the eastern dakotas reveal large variations in 18 o values 2 5 o and mg ca and sr ca ratios up to 35 among individual adults within the same assemblage because the measured variations in water chemistry were small the amplitude of ostracode 18 o and mg ca variations must result from seasonal temperature variation ostracode sr ca ratios which should be temperature independent shows strong positive covariance with shell mg ca these results imply that sr uptake in ostracode calcite increases with the mg content of the shell the partitioning coefficient for mg on the other hand appears to decreases at high values of mg ca in the host water the geochemical variability in the field collections indicates that c rawsoni populations are composed of multiple overlapping generations that attain maturity at different times many juveniles apparently undergo several molts in mid summer and persist as penultimate instars a 1 into the following spring geochemical analysis of late instar juvenile c rawsoni from lacustrine sedimentary records is likely to provide information on mid summer conditions large numbers of fossil ostracodes should be analyzed from each stratigraphic interval to eliminate seasonal noise from the paleochemistry records of temperate region lakes

origin of native sulfur ball from the kueishantao hydrothermal field offshore northeast taiwan evidence from trace and rare earth element composition we first report the trace and rare earth element compositions of native sulfur ball with sulfur contents varying from 97 08 wt to 99 85 wt from the kueishantao hydrothermal field off ne taiwan we then discuss the sources of trace and rare earth elements incorporated into the native sulfur ball during formation comparison of our results with native sulfur from crater lakes and other volcanic areas shows the sulfur content of native sulfur ball from the kueishantao hydrothermal field is very high and that the rare earth element ree and trace element constituents of the native sulfur balls are very low sigma ree 35 ppb in the native sulfur ball v cr co ni nb rb cs ba pb th u al ti and ree are mostly derived from andesite mg k and mn are mostly derived from seawater and fe cu zn and ni are partly derived from magma based on the sulfur contents trace and rare earth element compositions and local environment we suggest that the growth of the native sulfur ball is significantly slower than that of native sulfur chimneys which results in the relatively higher contents of trace and rare earth element contents in the native sulfur ball than in the native sulfur chimneys from the kueishantao hydrothermal field finally we suggest a glue pudding growth model for understanding the origin of the native sulfur ball in the kueishantao hydrothermal field whereby the native sulfur ball forms from a mixture of oxygenated seawater and acidic low temperature hydrothermal fluid with h 2 s and so 2 gases and is subsequently shaped by tidal and or bottom currents c 2010 elsevier ltd all rights reserved

poas volcano crater lake acts as a condenser for acid metal rich brine models of formation of volcanic hosted metal deposits hypothesize that subsurface brines transport metals to sites of deposition laguna caliente in the active crater of poas volcano central costa rica consists of acid sulphate chloride brine with extreme ph 0 0 lake water sampled between 9 and 12 january 1987 at eight sites within the 40 m deep 210 m wide lake revealed temperatures between 58 and 64 c and densities measured in the laboratory at 60 c of 1 0575 0 0015g cm 3 the water s extreme acidity reflects the dominating input of acid fumaroles the presence of precipitated silica gypsum and sulphur as sediments reflects lake water equilibrium with those phases mass balance considerations require that dense brines percolate downwards from the lake into the volcano these may act as a source of metal rich brine feeding an underground ore forming hydrothermal system

chemical characteristics of the crater lakes of popocatetetl el chichon and nevado de toluca volcanoes mexico abstract three crater lakes from mexican volcanoes were sampled and analyzed at various dates to determine their chemical characteristics strong differences were observed in the chemistry among the three lakes nevado de toluca considered as dormant el chichon at a post eruptive stage and popocatepetl at a pre eruptive stage not surprisingly no influence of volcanic activity was found at the nevado de toluca volcano while the other volcanoes showed a correlation between the changing level of activity and the evolution of chemical trends low phs so 4 2 and f decreased irregularly at el chichon from 1983 until 1997 major cations concentrations also diminished at el chichon a 100 increase in the so 4 2 content was measured at popocatepetl between 1985 and 1994 an increase in the mg cl ratio between 1992 mg cl 0 085 and 1994 mg cl 0 177 was observed at popocatepetl before the disappearance of the crater lake in 1994 it is concluded that chemical analysis of crater lakes may provide a useful additional tool for active volcano monitoring

sulphur eruptions at volcan poas costa rica since the recent desiccation of the crater lake at volcan poas costa rica vigorous fumarolic activity on the exposed lake bed has been associated with the manifestation of miniature sulphur volcanoes sulphur flows and sulphur pools in this paper observations of 2 3 m high active sulphur volcanoes are reported and mechanisms for their formation proposed and discussed their ejecta composed of milled particles crystals and accretionary lapilli of sulphur are unlike previously described pyroclastic sulphur deposits and probably form from a spray of crystallised sulphur forced to the surface by fumarolic gases passing upwards through shallow bodies of liquid sulphur while much of the erupted material is recycled the reservoir of molten sulphur can also be replenished by influxing magmatic hydrothermal fluids 34s isotope ratios of several samples of native sulphur collected at poas range between 9 4 and 12 3 cdt these are among the isotopically lightest volcanic deposits of elemental sulphur reported although this pronounced depletion is readily explained by the likely formation of the sulphur under the acidic conditions of the aqueous lake and hydrothermal system the total amount of native sulphur deposits contained within lake sediments at poas and perhaps at other active volcanoes with crater lakes is potentially substantial a large explosive eruption could by volatilisation and oxidation of this sulphur inject large volumes of sulphur dioxide into the atmosphere the greenish colouration of the sulphur reminiscent of other documented terrestrial sulphur eruptions is probably due to impurities this emphasises the point that interpretation of spectral reflectances of the jovian moon io regarding the possible contribution of sulphur cannot rely on extrapolation of laboratory data for pure materials

characteristics and petroleum origin of the carboniferous volcanic rock reservoirs in the shixi bulge of junggar basin western china abstract shixi bulge of the central junggar basin in western china is a unique region that provides insight into the geological and geochemical characteristics of large scale petroleum reservoirs in volcanic rocks of the western central asian orogenic belt carboniferous volcanic rocks in the shixi bulge mainly consist of striped lava and agglomerate as well as breccia lava and tight tuff volcanic rocks differ in porosity and permeability striped lava exhibits the highest porosity average 14 2 but the lowest permeability average 0 67 10 15 m among the rock types primary gas pores are widely developed and mostly filled secondary dissolution pores and fractures are two major reservoir storage spaces capillary pressure curves suggest the existence of four pore structure types of reservoir rocks several factors namely lithology pore structure and various diagenesis govern the physical properties of volcanic rocks the oil is characterized by a high concentration of tricyclic terpane a terpane distribution of c 23 21 c 20 and sterane distributions of c 27 28 29 and c 27 c 28 29 oil and gas geochemistry revealed that the oil is a mixture derived primarily from p 2 w source rock and secondarily from p 1 j source rock in the sag west of pen 1 well the gases are likely gas mixtures of humic and sapropelic organic origins with the sapropelic gas type dominant in the mixture the gas mixture is most likely cracked from kerogen rather than oils the carboniferous volcanic reservoirs in shixi bulge share some unique characteristics that may provide useful insights into the various roles of different volcanic reservoir types in old volcanic provinces the presence of these reservoirs will undoubtedly encourage future petroleum exploration in volcanic rocks up to the deep parts of sedimentary basins

eruption of the nevado del ruiz volcano colombia on 13 november 1985 gas flux and fluid geochemistry the 13 november 1985 eruption of nevado del ruiz volcano in colombia released a small volume of pyroclastic material and a disproportionately large volume of volcanic gas before the eruption summit fumarole gases became less water rich and the sulfur chlorine ratio increased remote measurements of sulfur dioxide flux after the eruption indicated active degassing at levels associated with eruptive or inter eruptive stages of other volcanoes thermal water analyses revealed increases in magnesium calcium and potassium and an increase in the magnesium chlorine ratio suggesting that these elements may have been leached from new magma ash leachate data showed sulfate and chloride concentrations and ratios that would be expected for the late stages ofa major plinian eruption water from the lahar contained high concentrations of sulfate and had a sulfur chlorine ratio of 4 67 suggesting that water ejected from the crater lake and turbulent mixing of pyroclasts and glacial ice triggered the lahar microprobe analyses of pumice from this eruption and the most recent previous event showed similar mixed andesites the uniform composition of the pumices and the unusually high ratio of gas to magma suggest that although a new batch of magma triggered this eruption the pumice that erupted may actually be old large volumes of new magma and glacial ice make the volcano dangerous and should stimulate development of an integrated long term monitoring program to include tolima volcano 25 kilometers to the south

first study of the heat and gas budget for sirung volcano indonesia with at least four eruptions over the last 20 years sirung is currently one of the more active volcanoes in indonesia however due to its remoteness very little is known about the volcano and its hyperacid crater lake we report here on the first measurements of gas and heat emissions from the volcano notable is the substantial heat loss from the crater lake surface amounting to 220 mw in addition 17 gg of so2 representing 0 8 of indonesian volcanic so2 contribution into the atmosphere 11 gg of h2s 17 gg of co2 and 550 gg of h2o are discharged into the atmosphere from the volcano annually the volatiles degassed from sirung magmas are subjected to hydrothermal fluid rock interactions and sulfide depositions initiated by the disproportionation of so2 these processes lead to distinct gas compositions and changing lake water chemistry in the sub craters and the main crater lake however the occurrence of so2 rich fluids and strong gas flux appear to highlight a rapid fluid transfer to surface avoiding re equilibration with lower temperature rocks fluids in the conduits

gravity changes as a precursor to volcanic eruption at poas volcano costa rica monitoring of gravity changes at active volcanoes has considerable potential for understanding magma chamber dynamics and for detecting eruptive precursors the technique essentially aims to identify changes in sub surface mass or density corresponding to departures from the free air gradient fag or bouguer corrected terrain corrected fag bcfag respectively1 2 such gravity changes of the order of 10 100 gal have been reported previously through eruptive periods3 6 here we present a ten year data set measured at poas volcano costa rica in which gravity increases in 1987 1989 relative to both the fag and the bcfag preceded the ash cloud eruptions of april may 1989 these results constitute the first unambiguous detection of gravity changes as a precursor to eruption and we interpret them in terms of the intrusion of an ascending relatively dense magma body

climate and vegetation in northeastern alaska 18 000 yr b p present changing abundances of taxa in the pollen record of northeastern alaska contain a climate signal and may be compared with gcm simulations of paleoclimates cold dry conditions indicated by full glacial pollen spectra are in broad agreement with model simulations successive expansion of betula and salix and later populus during the deglacial period 14 000 11 000 yr b p are likely correlated with the crossing of temperature thresholds determined largely by the size and position of the laurentide ice a degree of asynchroneity between sites probably reflects differential site responses to regional effects plus inaccuracies of radiocarbon dating the early holocene was probably the warmest period of the present interglacial as summer climate was influenced by a strong positive insolation anomaly picea glauca expanded in majorr river valleys ca 9000 yr ago and slightly later at upland sites in the brooks and alaska ranges at some sites a juniperus subzone which suggests particularly warm and dry conditions occurs between ca 10 000 and 8000 yr b p early mid holocene expansions of alnus 8500 7000 yr b p and picea mariana 7500 5000 yr b p suggest the subsequent development of moister conditions which have continued to the present temporal patterns in picea treeline position during the holocene are different in northern alaska northwestern canada and central canada in alaska the treeline is currently at its furthest holocene extent in northwestern canada the treeline has retreated since the mid holocene and in central canada a mid holocene advance and retreat occurred such differences between regions suggest a complex response of this taxon to climatic controls and underscore the need to interpret vegetation changes in relation to regional scale climate phenomena if the pollen chronology is calibrated with reference to u th dates the relationship of vegetational events to the insolation maximum at ca 10 000 yr b p is significantly altered the changed chronology also affects the interpretation of pollen records in relation to gcm simulations which are partly keyed to calendar years

superficial alteration mineralogy in active volcanic systems an example of poas volcano costa rica abstract the alteration mineralogy in the crater area of poas volcano costa rica has been studied to constrain acid fluid rock interaction processes and conditions relevant for the formation of sulphate bearing mineral assemblages found on the surface of mars individual sub environments which include the hyperacid lake laguna caliente ephemeral hot springs fumarole vents and areas affected by acid rain and or spray from the lake are marked by distinct secondary mineral associations with sulphates commonly as prevailing component the sulphates occur in a wide mineralogical diversity comprising gypsum anhydrite various polyhydrated al sulphates alunite jarosite group minerals halotrichite voltaite and copiapite group minerals epsomite and romerite depending on the sub environment they are variably associated with clay minerals kaolinite group and smectite group zeolites sio 2 polymorphs fe hydro oxides ti oxides native sulphur sulphides chlorides fluorides phosphates and carbonates geochemical modelling was performed to identify mechanisms responsible for the formation of the secondary minerals found in the field and to predict their possible stability under conditions not seen at the surface the results indicate that the appearance of amorphous silica hematite anhydrite gypsum pyrite anatase and kaolinite is relatively insensitive to the degree of acidity of the local aqueous system on the other hand alunite jarosite group minerals elemental sulphur and al oh so 4 only form under acidic conditions ph 2 sulphates is restricted to olivine bearing rocks exposed to acid rain or brine spray modelling suggests that their formation required a repetitive sequence of olivine dissolution and evaporation in an open system involving limited amounts of fluid the mineral variety in the crater of poas is remarkably similar to sulphate bearing assemblages considered to be the product of acid sulphate alteration on mars the analogy suggests that comparable fluid rock interaction controls operated in martian volcanic environments

thermal evolution of the crater lake of copahue volcano with aster during the last quiescence period between 2000 and 2012 eruptions abstract active crater lakes are the surface expression of volcanic activity at the top of complex magmatic hydrothermal systems the volcanic and hydrothermal system copahue is one of the most important active systems in argentina it lies at the border of argentina and chile and is very important since the copahue and caviahue towns are very close and constitute important touristic resources including a ski center the aim of this work is to improve the temperature register of the volcano and contribute towards a better understanding of the thermal behavior of the system during the quiescence period between the 2000 and 2012 eruptions the surface temperature of the crater lake was estimated by using the normalized emissivity method nem on 70 images acquired by the advanced spaceborne thermal emission and reflection radiometer aster and we combined them with field measurements in order to capture the fundamental variations of the system the analysis allowed the identification of two different thermal periods i january 2001 august 2003 and ii december 2004 november 2011 characterized by temperature ranges of 43 50 c and 30 45 c respectively beyond these ranges temperature anomalies or moments of high temperature variability occurred which corresponded to surface expressions of volcanic activity in august 2004 the lake froze almost completely whereas in march 2012 peak temperatures were recorded however a significant drop in temperature prior to the eruption of december 22 2012 was observed which might constitute a characteristic feature of the system furthermore the crater lake of copahue volcano is classified as a lake of high activity the observations and interpretations presented constitute a useful baseline and a significant contribution towards a better understanding of the functioning of the volcano the mitigation of volcanic hazards and the identification of volcanic unrest

strontium content of ostracods indicates lacustrine palaeosalinity individual non marine ostracod valves contain sr in proportion to the sr content of their host lake water two commonly coexisting large planktonic species mytilocypris praenuncia and australocypris robusta have a sr distribution coefficient kd sr ca of 0 082 which is independent of temperature in the range 10 18 c if the relationship between salinity and the sr content of a hydrologically simple lake is known palaeosalinities can be calculated from fossil ostracods we present here palaeosalinities for the past 10 000 yr for lake keilambete victoria calculated from ostracod sr ca of fossil material which are in striking agreement with independent interpretations of palaeosalinity the range of salinity spans 14 95 we also show that a reliable quantitative continuous indicator of lacustrine palaeosalinity is important for the elucidation of continental palaeoenvironments for palaeoclimatology and archaeology and ocean continent climatic correlations and interactions

magnesium content of non marine ostracod shells a new palaeosalinometer and palaeothermometer abstract ostracods are microcrustaceans with calcitic carapaces each consisting of two valves or shells that grow by moulting and regeneration of sequentially larger valves up to nine times before reaching maturity the mg content of these valves is species dependent and is a function of their growth stage and the temperature salinity mg content and mg ca ratio of their host water newly formed partly calcified valves of the non marine nektic ostracod mytilocypris henricae have high mg contents 100 000 ppm mg in caco3 at individual shell weights of 2 g this relative mg content decreases as calcification proceeds until shell weights exceed 120 g whereupon the mg content is constant and useful as an indicator of the ostracod s environment mg ca ratios in individual ostracod valves from several species of the genera mytilocypris and australocypris from culture experiments and a series of australian lakes indicate that the valve s mg content increases as a function of increasing temperature and salinity within the range 11 25 c and for waters containing 24 2325 ppm mg the molar mg ca ratio in these ostracods fully calcified valves increases by 0 0015 or 370 ppm mg in caco3 per 1 c and per change of 125 ppm mg in solution for most mainland australian lakes a change in water composition of 125 ppm mg corresponds to a change of 3 5 in salinity for a given mg content of a lake the mg ca ratio of the water may vary within the range of common lacustrine values without significantly affecting mg uptake in the ostracod valves these relationships can provide palaeosalinities and or palaeotemperatures for ostracods recovered from continental sediments for mg partitioning an increase in temperature and salinity produce increased mg content in ostracods whereas for 18o fractionation in biogenic calcite an increase in temperature produces a decrease in 18o of the ostracod and an increase in salinity leads to an increase in 18o of the ostracod thus a combination of 18o and mg measurements on non marine ostracods should enable unique resolution of palaeotemperature and palaeosalinity variations

the volcanic acidification of glacial lake caviahue province of neuquen argentina abstract lake caviahue northern patagonia argentina is a large glacial lake acidified by volcanic fluids from copahue volcano the lake and the feeding rivers were sampled annually from 1997 till early 2006 including the eruptive period of 2000 lake caviahue waters evolved over time with the most concentrated waters in 2000 during the eruptive period followed by gradual dilution that was interrupted by renewed acidification in 2003 2004 inversion of the lake water data and application of a dynamic non steady state model for the lake provides our best quantitative estimates for the variation in element fluxes over the 9 year period the model flux results agree well with most of the measured fluxes the copahue hydrothermal system had gently declining element fluxes between 1997 and mid 1999 although the lake was still becoming more concentrated about 2 3 months before the 2000 eruption element fluxes increased strongly but the hydrothermal fluxes almost shutoff directly after the main eruptive events the fluxes of several elements recovered post 2001 with an increase in element fluxes in 2003 2004 the lake became more dilute between 2004 and 2006 the intrusion of new magma into the hydrothermal system just prior to the 2000 eruption led to enhanced water rock interaction with higher concentrations of the rock forming elements in the fluids and the hot spring flow rate increased as a result of the higher pressure in the reservoir the fluids became saturated in alunite and jarosite and they were already saturated with anhydrite precipitation of these minerals possibly led to a decreased permeability of the hydrothermal reservoir leading to the strongly reduced element fluxes just after the eruption in addition k al and s were retained in the newly precipitated minerals as well further diminishing their export the acidification in 2003 2004 may have resulted from a new small intrusion of magma or resulted from seismic activity that created new permeability and fresh rock surfaces for water rock interaction the volcano is a significant source of toxic trace elements such as f as b and li as well as a nutrient p for the local watershed monitoring of the hydrothermal fluids in the river that drains copahue especially the s cl mg cl and mg k values as well as the magnitude of the element fluxes would provide the best information for eruption forecasting for this volcano

crater lake temperature changes of the 2005 eruption of santa ana volcano el salvador central america a sudden eruption at santa ana occurred on 1 october 2005 producing an ash and gas plume to a height in excess of 10 km above the volcano several days before thermal infrared images of the crater provided precursory signals of the eruption a significant increase in the extent and intensity of the fumarolic field inside the crater rim and of the surface temperature of the crater s lake was observed changes in energy input was also estimated to explain the increase in lake temperature based on energy mass balance calculations

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

sulfur geochemistry of hydrothermal waters in yellowstone national park wyoming usa ii formation and decomposition of thiosulfate and polythionate in cinder pool abstract cinder pool is an acid sulfate chloride boiling spring in norris geyser basin yellowstone national park the pool is unique in that its surface is partially covered with mm size black hollow sulfur spherules while a layer of molten sulfur resides at the bottom of the pool 18 m depth the sulfur speciation in the pool was determined on four different days over a period of two years samples were taken to evaluate changes with depth and to evaluate the importance of the sulfur spherules on sulfur redox chemistry all analyses were conducted on site using a combination of ion chromatography and colorimetric techniques dissolved sulfide h 2 s thiosulfate s 2 o 3 2 polythionates s x o 6 2 and sulfate were detected the polythionate concentration was highly variable in time and space the highest concentrations were found in surficial samples taken from among the sulfur spherules with depth the polythionate concentrations dropped off the maximum observed polythionate concentration was 8 m thiosulfate was rather uniformly distributed throughout the pool and concentrations ranged from 35 to 45 m total dissolved sulfide concentrations varied with time concentrations ranged from 16 to 48 m sulfate was relatively constant with concentrations ranging from 1150 to 1300 m the sulfur speciation of cinder pool is unique in that the thiosulfate and polythionate concentrations are significantly higher than for any other acid sulfate spring yet sampled in yellowstone national park complementary laboratory experiments show that thiosulfate is the intermediate sulfoxyanion formed from sulfur hydrolysis under conditions similar to those found in cinder pool and that polythionates are formed via the oxidation of thiosulfate by dissolved oxygen this last reaction is catalyzed by pyrite that occurs as a minor constituent in the sulfur spherules floating on the pool s surface polythionate decomposition proceeds via two pathways 1 a reaction with h 2 s yielding thiosulfate and elemental sulfur and 2 by disproportionation to sulfate and thiosulfate this study demonstrates that the presence of a subaqueous molten sulfur pool and sulfur spherules in cinder pool is of importance in controlling the pathways of aqueous sulfur redox reactions some of the insights gained at cinder pool may be relevant to acid crater lakes where sulfur spherules are observed and variations in polythionate concentrations are used to monitor and predict volcanic activity

diffuse emission of hydrogen from poas volcano costa rica america central we report the results of four soil h2 surveys carried out in 2000 2003 at poas volcano costa rica to investigate the soil h2 distribution and evaluate the diffuse h2 emission as a potential surveillance tool for poas volcano soil gas h2 contents showed a wide range of concentration from 0 2 to 7 059 ppmv during the four surveys maps of soil gas h2 based on sequential gaussian simulation showed low h2 concentration values in the soil atmosphere 0 7 ppmv for most of the study area whereas high soil gas h2 values were observed inside the active crater of poas a significant increase in soil gas h2 concentration was observed inside the active crater during 2001 and 2002 with respect to year 2000 followed by a decrease in 2003 the observed spatial and temporal variations of soil h2 concentration have been well correlated with seismicity microgravimetry and fumarolic chemistry changes which occurred during this study these observations evidence changes in the shallow magmatic hydrothermal system of poas and it might be related to a potential magmatic intrusion during the period 1998 2004 therefore monitoring diffuse h2 emission of poas has become an important geochemical tool for the monitoring of its volcanic activity

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

geochemistry of the magmatic hydrothermal system of kawah ijen volcano east java indonesia samples from kawah ijen crater lake spring and fumarole discharges were collected between 1990 and 1996 for chemical and isotopic analysis an extremely low ph 0 3 lake contains so 4 cl waters produced during absorption of magmatic volatiles into shallow ground water the acidic waters dissolve the rock isochemically to produce immature solutions the strong d and 18 o enrichment of the lake is mainly due to enhanced evaporation at elevated temperature but involvement of a magmatic component with heavy isotopic ratios also modifies the lake d and 18 o content the large so4 s d 23 8 26 4 measured in the lake suggest that dissolved so 4 forms during disproportionation of magmatic so 2 in the hydrothermal conduit at temperatures of 250 280 c the lake 18 o so4 and 18 o h2o values may reflect equilibration during subsurface circulation of the water at temperatures near 150 c significant variations in the lake s bulk composition from 1990 to 1996 were not detected however we interpret a change in the distribution and concentration of polythionate species in 1996 as a result of increased so 2 rich gas input to the lake system thermal springs at kawah ijen consist of acidic so 4 cl waters on the lakeshore and neutral ph hco 3 so 4 cl na waters in blawan village 17 km from the crater the cation contents of these discharges are diluted compared to the crater lake but still do not represent equilibrium with the rock the so 4 cl ratios and water and sulfur isotopic compositions support the idea that these springs are mixtures of summit acidic so 4 cl water and ground water the lakeshore fumarole discharges t 170 245 c have both a magmatic and a hydrothermal component and are supersaturated with respect to elemental sulfur the apparent equilibrium temperature of the gas is 260 c the proportions of the oxidized so 2 dominated magmatic vapor anti of the reduced h 2 s dominated hydrothermal vapor in the fumaroles varied between 1979 and 1996 this may be the result of interaction of so 2 bearing magmatic vapors with the summit acidic hydrothermal reservoir this idea is supported by the lower h 2 s so 2 ratio deduced for the gas producing the so 4 cl reservoir feeding the lake compared with that observed in the subaerial gas discharges the condensing gas may have equilibrated in a liquid vapor zone at about 350 c elemental sulfur occurs in the crater lake environment as banded sediments exposed on the lakeshore and as a subaqueous molten body on the crater floor the sediments were precipitated in the past during inorganic oxidation of h 2 s in the lake water this process was not continuous but was interrupted by periods of massive silica poorly crystallized precipitation similar to the present day lake conditions we suggest that the factor controlling the type of deposition is related to whether h 2 s or silica rich volcanic discharges enter the lake this could depend on the efficiency with which the lake water circulates in the hydrothermal cell beneath the crater quenched liquid sulfur products show 34 s values similar to those found in the banded deposits suggesting that the subaqueous molten body simply consists of melted sediments previously accumulated at the lake bottom

subaqueous geothermal activity revealed by lacustrine sediments of the acidic nakadake crater lake aso volcano japan abstract lacustrine sediments were sampled from the inaccessible acidic ph 0 43 nakadake crater lake of aso volcano japan by a simple method the sediments contain an extremely high content 74 wt of sulfur which exits as elemental sulfur gypsum and anhydrite the abundant elemental sulfur is likely formed by the reaction of so 2 and h 2 s gases and by the so 2 disproportionation reaction in magmatic hydrothermal system below the crater lake based on the sulfur content of sediments and measurements of elevation change of the crater bottom the sulfur accumulation rate at the nakadake crater lake was calculated as 250 tonne day which is comparable with the so 2 emission rate 200 600 tonne day from the nakadake crater the sediments include a small amount 9 of clear glass shards that are apparently not altered in spite of the high reactivity of hyperacid lake water this finding suggests that the clear glass shards are fragments of recently emitted magmas from fumaroles on the bottom of the crater lake and the magma emissions continuously occur even in quiescent periods

surveillance of ruapehu crater lake new zealand by aqueous polythionates abstract aqueous sulfur speciation of samples of crater lake water from crater lake collected at mt ruapehu new zealand since 1968 has been determined using high performance liquid chromatography polythionates s x o 6 2 are produced in the lake through reactions between sulfur dioxide and hydrogen sulfide gases from the subaqueous fumaroles their concentrations vary from 0 to a few hundred mg l corresponding to the activity of the volcano the concentration of the total polythionates s x o 6 2 s 4 o 6 2 s 5 o 6 2 s 6 o 6 2 is found to be a good indicator of changes in the subaqueous fumarolic activity at crater lake the molar s x o 6 2 cl ratios of the lake water can be used to divide the volcanic activity of crater lake into four stages 1 stage i period of weak volcanic activity with no hydrothermal explosions this stage is characterized by low total s x o 6 2 with a distribution order of s 5 o 6 2 s 4 o 6 2 s 6 o 6 2 h 2 s is predominant among dissolved gases in the lake water 2 stage iia quiescent period with minor hydrothermal explosions the lake water contains high s x o 6 2 with a distribution order of s 5 o 6 2 s 4 o 6 2 s 6 o 6 2 dissolved h 2 s and so 2 gases are very low 3 stage iib increased fumarolic activity with frequent hydrothermal explosions low s x o 6 2 with a distribution order of s 4 o 6 2 s 5 o 6 2 s 6 o 6 2 sulfur dioxide but no h 2 s is detected in the water 4 stage iii period of phreatomagmatic eruptions with lahars and intensive seismic activity no s x o 6 2 exists but dissolved so 2 is high in the lake water the moderate sized explosion of december 8 1988 which was not preceded by any changes in lake water polythionate chemistry or seismic activity is hypothesized to be a vent cleaning eruption caused by blockage of ascending magmatic gases that was caused by solidification of a molten sulfur pool at the bottom of crater lake

volcanic lakes of the azores archipelago portugal geological setting and geochemical characterization abstract a representative set of 30 lakes from the azores archipelago portugal has been studied to obtain data on their volcanic setting and water geochemistry the majority of the studied lakes are located inside volcanic craters and subsidence calderas while the remaining lakes are located in topographic depressions not associated with volcanic centres in depressions of tectonic origin and inside lava caves in general the azorean volcanic lakes are small with surface areas between 8 94 10 4 km 2 and 4 35 km 2 and volumes between 2 4 10 3 and 4 78 10 7 m 3 median 3 99 10 4 m 3 presenting maximum depths between 0 8 and 33 m mostly of the na cl to na hco 3 type the lake waters are generally low temperature 11 9 24 6 c very dilute tds range between 11 0 and 356 2 mg l median 36 8 mg l and a clear exception is furna do enxofre lake graciosa island that shows a mg trend two types of lake waters can be recognized 1 one is characterized by na cl ratio close to the seawater value and have evolved and evolve by marine contribution and 2 na hco 3 type waters that in addition to sea salt input have been influenced by other processes e g water rock interaction hydrothermal seepage into the lake bottom evident from higher total co 2 content 365 1 mg l and sio 2 content 74 9 mg l as well demonstrated by in the furna do enxofre lake nevertheless volcanic contribution cannot be excluded for some lakes as furna do enxofre vertical profiles made at the deepest lakes of sao miguel reveal that major ion content varies little with depth largely independent of the occurrence of thermally driven density stratification in summer for some lakes however dissolved co 2 increases with depth and is kept in the hypolimnion in summer whereas the hco 3 content is stable suggesting that co 2 release exceeds acidity neutralization by water rock interaction during winter without stratification the dissolved co 2 increase is less sharp for the majority of the lakes with the exception of furnas and furna do enxofre lakes the co 2 enrichment observed for certain lakes e g furna do enxofre and furnas implies a volcanic input moreover as these lakes themselves are located near hydrothermal surface manifestations they therefore offer good targets of volcano monitoring in the azores

hematite breccia hosted iron oxide copper gold deposits require magmatic fluid components exposed to atmospheric oxidation evidence from prominent hill gawler craton south australia

relationship of pyroclastic volcanism and lake water acidification to jehol biota mass mortality events early cretaceous northeastern china abstract geochemical analysis of the 14 4 m thick lacustrine succession of the lower cretaceous yixian formation jehol group has yielded new insights concerning vertebrate mass mortality events in the lake sihetun volcanic caldera in western liaoning province northeastern china that produced the jehol biota fossil lagerstatten the long term evolution of the caldera system resulted in a shift from felsic to mafic magma chemistry accompanied by a reduced frequency of pyroclastic eruptions declining hydrothermal activity and lower lacustrine productivity the basal tetrapod beds exhibit strong hydrothermal influence as indicated by enrichments of boron b certain alkalis rb cs rare earth elements rees yttrium y and many metals e g co cr cu ge mo ni sb u v and w and by strongly negative molybdenum isotope compositions 98mo to 2 50 that may record large fractionations between molybdate and thiomolybdate species in the sihetun caldera hydrothermal system in contrast the overlying fish beds and non fossiliferous beds have an elemental and mo isotopic composition similar to calc alkaline basalts 98mo 0 29 0 04 in the surrounding watershed suggesting weathering of yixian formation volcanic rocks as the major source of sediment during its

investigating crater lake warming using aster thermal imagery case studies at ruapehu poas kawah ijen and copahue volcanoes abstract a two channel or split window algorithm designed to correct for atmospheric conditions was applied to thermal images taken by the advanced spaceborne thermal emission and reflection radiometer aster of lake yugama on kusatsu shirane volcano in japan in order to measure the temperature of its crater lake these temperature calculations were validated using lake water temperatures that were collected on the ground overall the agreement between the temperatures calculated using the split window method and ground truth is quite good typically 1 5 c for cloud free images data from fieldwork undertaken in the summer of 2004 at kusatsu shirane allow a comparison of ground truth data with the radiant temperatures measured using aster imagery further images were analyzed of ruapehu poas kawah ijen and copahue volcanoes to acquire time series of lake temperatures a total of 64 images of these 4 volcanoes covering a wide range of geographical locations and climates were analyzed results of the split window algorithm applied to aster images are reliable for monitoring thermal changes in active volcanic lakes these temperature data when considered in conjunction with traditional volcano monitoring techniques lead to a better understanding of whether and how thermal changes in crater lakes aid in eruption forecasting

ostracode geochemical record of holocene climatic change and implications for vegetational response in the northwestern alaska range abstract trace element analysis of the calcareous shells of ostracodes in a sediment core from farewell lake provides the first limno geochemical record for climatic reconstructions in alaska when compared with pollen data from the same site this record offers new insights into climatic controls over vegetation dynamics during the holocene the low mg ca ratios and high sr ca ratios suggest that a relatively cold dry climate prevailed in this region between 11 000 and 9000 yr b p uncalibrated14c ages are used throughout the paper this result contrasts with previous interpretations of a thermal maximum at this time corresponding to the widespread establishment ofpopuluswoodland forest the trace element record suggests instead that the warmest period of the early holocene at farewell lake was between 8500 and 8000 yr b p during the decline ofpopulus marked decreases in sr ca and mg ca suggest a major increase in effective moisture around 6500 yr b p which coincided with the establishment ofpiceaboreal forests in the farewell lake region this climatic change was probably widespread throughout much of alaska and adjacent canada and might have induced the rapid spread ofalnusand the shift frompicea glaucatop marianadominance across that region our geochemical record also suggests that the late holocene climate history was more complex than previously thought on the basis of palynological studies according to this record growing season temperatures increased 6000 4500 yr b p decreased 4500 1500 yr b p and increased with fluctuations afterward after 6000 yr b p stratigraphic changes in pollen percentages ofpiceaappear to be positively related with those of mg ca this relationship implies that once the threshold of effective moisture was crossed for the establishment ofpiceaforests temperature was the primary control ofpiceapopulation density

bathymetric and geochemical investigation of kawah ijen crater lake east java indonesia abstract a bathymetric survey of kawah ijen crater lake was conducted by acoustic sounding in 1996 to compare the lake morphology with those measured in 1922 1925 and 1938 and to calculate the present lake volume even though the lake experienced several hydrothermal eruptions the maximum depth became shallower 182 m than before 200 m resulting in a reduced lake volume 3 0 10 7 m 3 fifty two major and minor constituents including rare earth elements and polythionates pt of the lake waters at various depths were determined by icp aes icp ms and hplc respectively these ions except for several volatile elements are taken up by lake fringe through congruent dissolution of pyroclastics of kawah ijen volcano most ions are homogeneously distributed throughout the lake although pt showed a considerable vertical variation rare earth elements ree in the kawah ijen water as well as those from other hyper acidic crater lakes show distribution patterns likely due to the three rock dissolution preferential congruent and residual types and their logarithmic concentrations linearly depend upon the ph values of the lake waters using the pt degradation kinetics data production rates of pt injection rates of so 2 and h 2 s into the lake were estimated to be 114 86 and 30 tons day respectively also travel time of the spring water at the banyupahit riverhead from kawah ijen was estimated to be 600 1000 days through the consideration of decreasing rates of pt molten sulfur stocks containing sn cu bi sulfides and pb barite exposed on the inner crater slope were presumed to be extinct molten sulfur pools at the former lake bottom this was strongly supported by the barite precipitation temperature estimated through the consideration of the temperature dependence of pb chlorocomplex formation

monitoring of volcanic eruptions at yugama crater lake by aqueous sulfur oxyanions abstract variations of polythionates sulfane disulfonates and sulfate in the yugama crater lake japan have been monitored for more than 25 years just before the 1982 eruption at the crater lake polythionate ions decreased to zero from the normal level of about 2000 ppm and sulfate ions increased from 2500 to 5000 ppm during the 1982 eruption polythionate and sulfate ions varied inversely in concentration and the variations exactly coincided with the frequency of volcanic earthquakes and subsequent explosions these observations are interpreted in terms of aqueous reactions of fumarolic so2 h2s gases resulting in precipitation of alunite the behavior of polythionate and sulfate ions strongly suggests that they are useful indicator for prediction of impending volcanic hazards from active crater lakes

volatiles of mount st helens and their origins abstract analyses have been made of gases in clouds apparently emanating from mount st helens despite appearances most of the water in these clouds does not issue from the volcano even directly above a large fumarole d and 18o data indicate that only half the water can come from the volcano isotopic and chemical evidence also shows the steam in the volcano 33 0 per mol d from which a condensate of 0 2 n hci was obtained is not a major cause of the explosions the steam in the volcano is derived from a metamorphic brine in the underlying tertiary meta andesite the gas that caused the explosive eruptions is carbon dioxide

water and dissolved gas geochemistry at coatepeque ilopango and chanmico volcanic lakes el salvador central america abstract coatepeque on the e slope of santa ana volcano ilopango inside ilopango caldera and chanmico associated with san salvador volcano are volcanic lakes in el salvador showing a thermocline at a relatively shallow depth from 30 to 40 m from 20 to 40 m and from 5 to 15 m depth respectively and anoxic conditions below 33 24 and 4 m depth respectively the na cl composition of the coatepeque and ilopango lakes displaying tds values up to 1226 and 1216 mg l respectively is likely due to hydrothermal fluids that feed these two lakes as also confirmed by cl br molar ratios 650 high as b li and si contents and cl so42 ratio 1 the mg2 hco3 water composition of lake chanmico whose tds values were between 566 and 856 mg l suggests water rock interaction processes with mafic ultramafic rocks variably affected by serpentinization processes which produced high mg2 si and b concentrations waters at depth were characterized by the presence of co2 from an extra lacustrine source as suggested by 13c co2 values significantly less negative than those typically related to biogenic processes albeit this gas was found in smaller quantities when compared to those recorded in other meromictic lakes hosted in quiescent volcanic systems e g lake kivu in drc monticchio albano and averno lakes in italy hule and rio cuarto lakes in costa rica lake pavin in france the occurrence of ch4 whose concentrations in lake chanmico were up to two orders of magnitude higher than those recorded in coatepeque and ilopango lakes suggests bacterial methanogenesis

geochemistry of the acid kawah putih lake patuha volcano west java indonesia abstract kawah putih is a summit crater of patuha volcano west java indonesia which contains a shallow 300 m wide lake with strongly mineralized acid sulfate chloride water the lake water has a temperature of 26 34 c ph s tot 2500 4600 ppm and cl 5300 12 600 ppm and floating sulfur globules with sulfide inclusions are common sulfur oxyanion concentrations are unusually high with s 4 o 6 2 s 5 o 6 2 s 6 o 6 2 2400 4200 ppm subaerial fumaroles thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases barite pyrite and various pb sb cu as bi bearing sulfides when sulfur saturation is assumed precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur rich bottom sediments and their identified mineral phases much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases as indicated by a comparison of the fluids volcanic rocks and lake bed sediment flank springs on the mountain at different elevations vary in composition and are consistent with local rock dissolution as a dominant factor and ph dependent element mobility discharges of warm sulfate and chloride rich water at the highest elevation and a near neutral spring at lower level may contain a small contribution of crater lake water the acid fluid induced processes at patuha have led to the accumulation of elements that are commonly associated with volcano hosted epithermal ore deposits the dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern

a model for episodic degassing of an andesitic magma intrusion 1 episodic magmatic degassing has been observed at numerous volcanoes especially those of intermediate composition it can span timescales from years to decades here we propose a physical model for the degassing of a shallow magma intrusion to explain this phenomenon the magma cools by convection which leads to melt crystallization volatile exsolution and magma overpressure when the pressure reaches a critical value wall rocks fracture and the exsolved gas escapes the intrusion then returns to the initial lithostatic pressure and a new cooling crystallization degassing cycle occurs a series of such cycles leads to episodic degassing the trend and timescale of the degassing process are mainly governed by magma cooling two degassing regimes are exhibited an early phase with a high frequency of gas pulses and a later phase with a lower gas pulse frequency the transition between these two regimes is caused by the viscosity increase when the magma crystallinity exceeds the crystal percolation threshold we find that the time to this transition is dependent on magma volume to a first approximation where observations are available from sustained geochemical surveillance the model provides constraints on key aspects of the subsurface magmatic system with estimation of the volume of an intrusion and tensile strength of the surrounding rocks it therefore represents a relevant tool for volcanic surveillance and hazard assessment

geological constraints on the 2003 2005 ash emissions from the nakadake crater lake aso volcano japan abstract the active crater of nakadake at aso volcano southwestern japan has been occupied by a lake during its dormant periods multiple ash emissions were observed from the crater lake between july 2003 and august 2005 the largest events occurred on 10 july 2003 and 14 january 2004 on 10 july 2003 ash 41 tons was dispersed throughout an area extending 14 km east northeast of the vent and on 14 january 2004 ash 32 tons extended 8 km to the east southeast thereafter small ash emissions were frequent at the crater lake in which the water level fell considerably from april to august 2005 during this period major ash emitting events producing mostly white aggregated ash occurred on june 10 12 june 21 4 2 tons and july 25 1 2 tons ash emissions at the nakadake crater in 2003 2005 were classified into three types gentle release of white aggregated ash from fumaroles inside the crater lake e g daytime of 14 april 10 12 june and 25 july 2005 emission of black ash from an almost dried up vent 21 june 2005 and short time ca 20 s small explosion triggered gas and ash emission through the crater lake 10 july 2003 14 january 2004 and 14 april 20h41m 2005 all products from these ash emissions consisted of fine grained

degassing at la soufriere de guadeloupe volcano lesser antilles since the last eruptive crisis in 1975 77 result of a shallow magma intrusion in the 15 years following the last crisis of phreatic type in 1975 77 the hydrothermal and seismic activity of la soufriere de guadeloupe has displayed an episodic behavior superimposed on a long term decay as inferred from seismicity and degassing monitored through fumarolic emissions and cl content in thermal springs in particular the evolution of the cl content can be explained by a succession of magmatic gas injections into the hydrothermal system this episodic supply of gas may be associated to the thermodynamic evolution of a batch of magma intruded at shallow depth around 1976 progressive magma cooling crystallization gas exsolution and pressure buildup lead to cyclic failure of host rock around the intrusion and episodic release of gas with a decreasing frequency as cooling proceeds this physical model allows to reproduce the pattern of degassing activity of la soufriere including the decreasing frequency of cl pulses with time our preferred forward model of cl pulses involves a magma intrusion volume in the range 0 01 0 52 km 3 and a tensile strength of the surrounding rock in the range 0 1 0 6 mpa these results reinforce the hypothesis of a shallow magma intrusion triggering the 1975 77 crisis and provide an explanation for the degassing and seismic activities observed until 1992

crater lake and post eruption hydrothermal activity el chichon volcano mexico abstract explosive eruptions of volcan el chichon in chiapas mexico on march 28 and april 3 4 1982 removed 0 2 km3 of rock to form a 1 km wide 300 m deep summit crater by late april 1982 a lake had begun to form on the crater floor and by november 1982 it attained a maximum surface area of 1 4 105 m2 and a volume of 5 106 m3 accumulation of 4 5 m of rainfall between july and october 1982 largely formed the lake in january 1983 temperatures of fumaroles on the crater floor and lower crater walls ranged from 98 to 115 c by october 1983 the maximum temperature of fumarole emissions was 99 c in january 1983 fumarole gas emissions were greater than 99 vol h2o with traces of co2 so2 and h2s the water of the lake was a hot t 52 58 c acidic ph 0 5 dilute solution 34 046 mg l 1 dissolved solids cl s 20 5 sediment from the lake contains the same silicate minerals as the rocks of the 1982 pyroclastic deposits together with less than 1 of elemental sulfur the composition and temperature of the lake water is attributed to 1 solution of fumarole emissions 2 reaction of lake water with hot rocks beneath the lake level 3 sediments washed into the lake from the crater walls 4 hydrothermal fluids leaching sediments and formational waters in sedimentary rocks of the basement 5 evaporation and 6 precipitation

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

volcanic 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

iron and aluminum hydroxysulfates from acid sulfate waters acid sulfate waters are produced mostly by the oxidation of common sulfide minerals such as pyrite chalcopyrite pyrrhotite and marcasite in rocks soils sediments and industrial wastes this spontaneous process of mineral weathering plays a fundamental role in the supergene alteration of ore deposits the formation of acid sulfate soils and the mobilization and release of acidity and metals to surface and ground waters the purely natural process of acid rock drainage is often intensified by human activities related to mining mineral processing construction soil drainage and dredging geochemical reaction rates are accelerated because physical disturbance gives greater exposure of mineral surfaces to air and water and to microbes that catalyze the reaction process large quantities of reactive sulfides are also concentrated and exposed to air as a result of mining and mineral processing acid sulfate waters produce a number of fairly insoluble hydroxysulfate and oxyhydroxide minerals that precipitate during oxidation hydrolysis and neutralization the objective of this chapter is to describe the formation properties fate and environmental implications of the nano to microphase hydroxy sulfates of fe and al that are precipitated from acid sulfate waters these minerals are commonly of poor crystallinity and difficult to characterize much remains to be learned about their occurrence formation and properties mine drainage the best known examples of acid sulfate waters are those released from mines where coal and metallic sulfide ores have been exploited ash et al 1951 barton 1978 nordstrom 1982a rose and cravotta 1998 nordstrom and alpers 1999 there may be as many as 500 000 inactive or abandoned mine sites in the united states alone lyon et al 1993 although most of these pose no immediate water quality problem kleinmann 1989 estimated that about 19 300 km of streams and more than 72 000 ha of lakes and reservoirs have been

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

co2 emissions from fogo intracaldera volcanic lakes sao miguel island acores a tool for volcanic monitoring abstract a geochemical study was carried out at fogo lake during june 2016 in one of the deepest lakes on sao miguel island as well as on small associated pond in order to identify possible anomalous degassing areas fogo lake is located inside the summit caldera of fogo volcano one of the three active central volcanoes that dominate sao miguel geology the hydrogeochemical profile carried out along the water column of the fogo lake suggests that the lake was thermally stratified corresponding to poorly mineralized and cold na cl type waters the same composition is found in the small pond but with a slight ca enrichment to measure the co2 flux at the lake surface the modified accumulation chamber method was used and a total of 1696 measurements were accomplished covering an area of approximately 1 56 km2 measured co2 flux values are relatively low ranging from 0 to 28 4 g m 2 d 1 mean 2 6 g m 2 d 1 and from 2 1 to 15 0 g m 2 d 1 mean 6 3 g m 2 d 1 respectively at fogo lake and at the small pond the very low values measured in the central area of fogo lake are associated with the monomictic character of the lake as the co2 is not able to ascend into the surface when the water column is stratified during the warmer period statistical analyses suggest that the co2 emission is associated with a single source of co2 probably biogenic a similar signature is pointed by the water 13c isotopic content the estimated total co2 emissions from the fogo lake was approximately 4 04 t d 1 much higher than the value observed at the small pond 0 19 t d 1

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

chemical evolution and volcanic activity of the active crater lake of poas volcano costa rica 1993 1997 abstract concentrations of chloride and sulfate and ph in the hot crater lake laguna caliente at poas volcano and in acid rain varied over the period 1993 1997 these parameters are related to changes in lake volume and temperature and changes in summit seismicity and fumarole activity beneath the active crater during this period lake level increased from near zero to its highest level since 1953 lake temperature declined from a maximum value of 70 c to a minimum value of 25 c and ph of the lake water increased from near zero to 1 8 in may 1993 when the lake was nearly dry chloride and sulfate concentrations in the lake water reached 85 400 and 91 000 mg l 1 respectively minimum concentrations of chloride and sulfate after the lake refilled to its maximum volume were 2630 and 4060 mg l 1 respectively between january 1993 and may 1995 most fumarolic activity was focused through the bottom of the lake after may 1995 fumarolic discharge through the bottom of the lake declined and reappeared outside the lake within the main crater area the appearance of new fumaroles on the composite pyroclastic cone coincided with a dramatic decrease in type b seismicity after january 1996 between may 1995 and december 1997 enhanced periods of type a seismicity and episodes of harmonic tremor were associated with an increase in the number of fumaroles and the intensity of degassing on the composite pyroclastic cone adjacent to the crater lake increases in summit seismic activity type a b and harmonic tremor and in the height of eruption plumes through the lake bottom are associated with a period of enhanced volcanic activity during april september 1994 at this time visual observations and remote fumarole temperature measurements suggest an increase in the flux of heat and gases discharged through the bottom of the crater lake possibly related to renewed magma ascent beneath the active crater a similar period of enhanced seismic activity that occurred between august 1995 and january 1996 apparently caused fracturing of sealed fumarole conduits beneath the composite pyroclastic cone allowing the focus of fumarolic degassing to migrate from beneath the lake back to the 1953 1955 cone changes in the chemistry of summit acid rain are correlated changes in volcanic activity regardless of whether fumaroles are discharging into the lake or are discharging directly into the atmosphere

temporal changes in the chemistry of lake water within yugama crater kusatsu shirane volcano japan implications for the evolution of the magmatic hydrothermal system abstract the chemical composition and temperature of lake water within yugama crater kusatsu shirane volcano japan have fluctuated markedly over the period 1966 to 2005 from 1966 to 1981 water temperature was relatively low and cl and so 4 2 concentrations gradually decreased these trends are explained by the growth of a sealing zone that formed between the region of hot rock surrounding the degassing magma and cool crust saturated with groundwater the sealing zone acted to restrict the emission of magmatic volatiles in 1982 and 1983 several steam driven explosive eruptions occurred within yugama crater following the eruptions lake temperature increased and so 4 2 and cation concentrations increased markedly although no increase in cl was recorded these changes are attributed to a breach of the sealing zone the increased interaction of groundwater with the hot rock region surrounding the magma chamber including the sealing zone produced a cation and sulfate rich fluid that was transported to yugama lake a large number of earthquakes occurred in the region of the volcano in 1990 at this time cl concentrations in lake water increased rapidly while water ph dropped these changes are explained by the invasion of groundwater through the breached sealing zone the invading water interacted with the inner region of hot rock close to the molten magma and cl stored in the hot rock was leached to the water as hcl the hcl enriched water was then transported to yugama lake resulting in the observed increase in cl concentration and decrease in ph the sequence of hot rock water interaction followed by the extraction of hcl from hot rock recurred in 1996 to 2005 although the degree of the interaction was much smaller than the former sequence in 1982 to 1995 resulting in no occurrence of significant eruptions

aqueous sulfur speciation possibly linked to sublimnic volcanic gas water interaction during a quiescent period at yugama crater lake kusatsu shirane volcano central japan after the phreatic eruption in 1982 83 volcanic activities at kusatsu shirane volcano had been decreasing and reached a minimum in 1990 had turned to a temporal rise in activity up to 1994 and then decreased again at least up to 1997 during this low activity period we observed a relatively short 1 y cyclic variation in polythionates ft in the yugama lake water spectral power density analysis of the ft time series by an autoregressive maximum entropy spectral estimation mese method indicates that the major frequency in the ft variations is 1 0 y 1 and the minor is 2 3 y 1 1 0 and 0 3 0 5 y in periodicity respectively annual variations in the lake temperature are ruled out for explaining these periodicities we attribute these cyclic variations to a cyclic magnification reduction in meteoric water injection into a hydrothermal regime where volcanic gases from cooling magma bodies at depth and cooler oxidized groundwater come into contact with each other this interaction may result in a periodical change in the composition and flux of so 2 and h 2 s gases being discharged into the lake and forming ft from a phase deviation 2 3 months in the cycles between the annual precipitation including snowmelt and the ft time series we estimated the maximal depth of a hydrothermal reservoir beneath the lake assuming a vertical hydraulic conductivity 5 10 3 cm s of the volcanic detritus around the summit hydrothermal system chloride in the lake water reached a maximum 1 5 years faster than ft this is most likely due to a gradual elevation of the potentiometric front of a concentrated sublimnic solution in the hydrothermal reservoir variations of dissolved so 2 and h 2 s in the lake water were not consistent with those of the fumarolic gases on the north flank of the volcano this fact together with additional observations strongly suggests that these fumaroles may have the same origin but are chemically modified by a subsurface aquifer the ft monitoring at active crater lakes during a quiescent period can provide insight into the annual expansions and reductions of a volcano hosted hydrothermal reservoir a simple analytical method in the field for the semi quantitative determination of dissolved so 2 and h 2 s in crater lake waters is given in appendix 2

fluid volcano interaction in an active stratovolcano the crater lake system of poas volcano costa rica rowe g l jr brantley s l fernandez m fernandez j f borgia a and barquero j 1992 fluid volcano interaction in an active stratovolcano the crater lake system of po is volcano costa rica j volcanol geotherm res 49 2351 seismic and geochemical data collected at po is volcano costa rica since 1978 suggest that temperature and chemical variations recorded in subaerial fumaroles and the crater lake are related to episodic release of heat and volatiles associated with hydrofracturing of the upper margin of the shallow magma body power outputs associated with these events approach 600 mw and are superimposed on a baseline energy flux of approximately 200 mw the baseline heat flux suggests a magma solidification rate of 0 012 km3 yr and background volatile release rates of 1000 t d h20 66 t d s 13 t d ci and 0 5 t d f these fluxes are comparable to fluxes of f c1 and s exiting the magmatic hydrothermal system through acidic flank springs and are about a factor of five less than estimated volatile fluxes through summit fumaroles during the high temperature event of 1981 1983 mass balance considerations suggest that heat released at the lake surface is primarily supplied by the ascent of heated brines supplemented by condensation of fumarolic steam calculated average seepage rates out of the lake 450 kg s indicate rapid convection of acidic lake brine through underlying lake sediments and pyroclastic deposits circulation of the extremely corrosive lake brine through the volcanoclastic material beneath the lake may enhance subsurface permeabilities fluxes of rock forming elements observed in the rio agrio basin on the northwest flank of po is suggest that dissolution and removal of volcano elastic material occurs at a rate of approximately 1650 m3 yr however estimated sulfur fluxes from the cooling magma body suggest that porosity created by this dissolution could quickly be filled by the deposition of native sulfur finally analysis of heat and water budgets for the crater lake over the period 1978 1989 indicates that the recent decline and disappearance of the lake was caused by variations in summit rainfall combined with an increase in subsurface heat flow to the lake in 1987 1988 the increase in heat flow is related to continued degassing of high temperature volatiles following a hydrofracturing magma ascent episode that occurred in 1986

ree fractionation during the gypsum crystallization in hyperacid sulphate rich brine the poas volcano crater lake costa rica exploited as laboratory abstract the critical role of rare earth elements lanthanides plus yttrium hereafter ree in high tech technologies and consequently their increasing demand from the industry in addition to the capability of ree to trace water rock interaction processes boosted the study of ree in unconventional extreme environments this study is focused on the geochemical behaviour of ree in the hyperacid sulphate rich brine of the crater lake of poas volcano costa rica where the precipitation of gypsum occurs this system can hence be considered as a natural laboratory to evaluate the fractionation of ree between the lake water mother brine and the precipitating gypsum mineral total ree concentrations dissolved in waters range from 1 14 to 2 18 mg kg 1 calculated distribution coefficients kd for ree between the gypsum and the mother brine indicate a preferential removal of the light ree lree with respect to the heavy ree hree with kd values mainly decreasing from la to lu during the observation period 2007 2009 the distributions of ree concentrations dissolved in lake water normalized to the average local volcanic rock show two different trends i lree depleted patterns and ii flat patterns the identification of the lree depleted pattern is justified by the kd calculated in this study we demonstrate that the precipitation of gypsum is able to strongly fractionate the ree in hyperacid sulphate rich brine inducing changes in ree concentrations and distributions over time x ray computed tomography imaging was performed on gypsum crystal precipitated from the lake waters to gain insights on crystal scale processes possibly controlling the ree geochemistry i e surface processes vs structural substitution accordingly the heavy metals and possibly the ree seem to be mainly located on the crystal surface rather than inside the crystal suggesting that a surface process could be the major process controlling ree removal from the water to the crystal

color and temperature of the crater lakes at kelimutu volcano through time we investigated the color and temperature of three volcanic crater lakes that co exist at kelimutu volcano indonesia using 30 years of landsat data these satellite data were obtained through google earth engine time series of surface reflectance visible wavelengths and brightness temperature above background thermal infrared wavelengths were calculated color was defined in the rgb red green blue and hsv hue saturation value color spaces and we introduce a visualization concept called hue stretch to consistently represent hue through time these parameters display long term trends seasonal cycles and short duration bursts of activity at the lakes we demonstrate that the color of the lakes are related over a period of months to years and discovered a previously unreported but significant episode around 1997 which included large agglomerations of floating elemental sulfur globally speaking these techniques could reveal trends at any of the 100 crater lakes on active volcanoes furthermore they could apply to any target whose color changes through time e g forests crops and non volcanic water bodies we have open sourced the code necessary to perform these analyses

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

late quaternary pollen records from the kobuk and noatak river drainages northwestern alaska abstract pollen diagrams from joe and niliq lakes date to ca 28 000 and 14 000 yr b p respectively mesic shurb tundra grew near joe lake ca 28 000 to 26 000 yr b p with local populus populations prior to ca 27 000 yr b p shrub communities decreased as climate changed with the onset of itkillik ii glaciation 25 000 to 11 500 yr b p and graminoid dominated tundra characterized vegetation ca 18 500 to 13 500 yr b p herb tundra was replaced by shrub betula tundra near both sites ca 13 500 yr b p with local expansion of populus ca 11 000 to 10 000 yr b p and alnus ca 9000 yr b p mixed picea glauca p mariana woodland was established near joe lake ca 6000 yr b p these pollen records when combined with others from northern alaska and northwestern canada indicate 1 mesic tundra was more common in northwestern alaska than in northeastern alaska or northwestern canada during the duvanny yar glacial interval 25 000 to 14 000 yr b p 2 with deglaciation shrub betula expanded rapidly in northwestern alaska but slowly in areas farther east 3 an early postglacial thermal maximum occurred in northwestern alaska but had only limited effect on vegetation and 4 pollen patterns in northern alaska and northwestern canada suggest regional differences in late quaternary climates

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

geophysical studies of the recent 15 year eruptive cycle at poas volcano costa rica abstract the recent eruptive cycle at poas volcano was notable for the dramatic disappearance and subsequent reappearance of the summit crater lake this cycle consisted of discrete phases of activity associated with a range of geophysical and geochemical signatures that illustrate the relative value of the various techniques for identifying precursory phenomena intrusive episodes in 1980 and 1986 1989 at poas were preceded by a type seismicity magma rose close to the surface on both occasions but the focus shifted from the dome 1980 when the lake remained stable to the crater lake 1986 1989 the 1986 1989 event which culminated in the complete loss of the crater lake and explosive eruptions was characterised by concurrent increases in micro gravity on the southern crater floor b type seismicity and lake temperature and by changes in lake geochemistry the calculated mass of magma intruded in this period is far too small to account for the observed increase in surface heat flux and subsequent loss of the lake we suggest that a series of magma filled dendritic conduits intruded beneath the lake facilitated enhanced heat and gas flux from a deeper magma feeder body a model is envisaged where brittle fracture of the magma carapace at about 500 m depth allows magma to rise up through the conduit system beneath the crater and to fall again or solidify in situ when pressure drops whilst active this process transfers heat and gas upwards driven by the convection of buoyant volatile rich magma displacing colder relatively volatile poor magma as magma pressure from below decreases the link between the deeper magma feeder and the upper conduit system is broken and the hydrothermal system resumes its role of cooling the magma feeder the role of the lake as a physical and chemical buffer to the volcanic system was clearly demonstrated when its disappearance in 1989 was accompanied by enhanced eruptive activity and gas emissions with considerable local environmental impact the lake therefore acts as both a moderator and index of volcanic processes at poas

naturally acid waters from copahue volcano argentina volcanic acid sulfate chloride brines form through absorption of volcanic vapors in shallow reservoirs of meteoric water reaction with surrounding volcanic rocks leads to partial neutralization of the fluids and precipitation of secondary minerals chemical data of such acid waters from copahue volcano argentina covering 8 years of observations show evidence for changes in composition related to water rock interaction at depth prior to emergence of the fluids at the surface the chemical composition changed dramatically during the 2000 eruption of copahue with enhanced concentrations and fluxes of mg na fe and al followed in 2001 by rapidly declining concentrations and element fluxes the subsequent 5 years saw more variable element ratios and strong depletions in k and al most incompatible elements are released from the rock matrix stochiometrically whereas some elements are enriched through vapor input from the magma as pb zn most fluids have lree enrichments relative to the rock matrix but during periods of new magma intrusion the lree enrichment decreases as does the magnitude of the negative eu anomaly in the fluids these observations are interpreted assuming early dissolution of plagioclase olivine and volcanic glass that occurs during intrusion of new magma into the hydrothermal system the high field strength elements are virtually immobile even in these hot acid fluids with nb and ta more so than hf and zr the mobility of u and th in these fluids is comparable at variance with th behavior in neutral fluids the local rivers and lakes of copahue are fertilized by volcanic dissolved p and most surface waters with ph 3 have high levels of as the acid fluids from copahue may be surficial analogs for deep subduction fluids that evolve below zones of arc magma generation as well as for early mars environments that are thought to have had large acid lakes