Chemical characteristics of the crater lakes of Popocatetetl, El Chichon, and Nevado de Toluca volcanoes, Mexico

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 Chichón at a post-eruptive stage, and Popocatépetl 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 (<3.0) were measured in the water from the active volcanoes, while a pH of 5.6 was measured at the Nevado de Toluca Sun lake. Changes with time were observed at Popocatépetl and El Chichón. Concentrations of volcanic-gas derived species like Cl⁻, SO₄²⁻ and F⁻ decreased irregularly at El Chichón from 1983 until 1997. Major cations concentrations also diminished at El Chichón. A 100% increase in the SO₄²⁻ content was measured at Popocatépetl 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 Popocatépetl, 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.     

A reassessment of current volcanic emissions from the Central American arc with specific examples from Nicaragua

The Central American volcanic arc supplies a significant proportion of the persistent annual global sulphur dioxide emissions from volcanoes. In November/December 2003, we completed a survey of the arc section from Mombacho to San Cristóbal in Nicaragua recording individual mean fluxes of 800, 530 and 220 Mg day^− 1 in the plumes from San Cristóbal, Telica and Masaya, respectively. An assessment of fluxes published since 1997 along the entire Central America arc yields a mean total arc flux of SO₂ of 4360 Mg day^− 1 or 8–16% of the annual estimated global volcanic SO₂ flux to the troposphere. New field data shows that Masaya volcano continues to show stable HCl/SO₂ and HF/SO₂ ratios, suggesting a sustained flux of these components of ∼ 220 and 30 Mg day^− 1, respectively (1997 to 2004). Masaya's plume composition also appears to have been stable, between 2001 and 2003, with respect to all the particulate species measured, with significant fluxes of SO₄²⁻ (4 Mg day^− 1), Na⁺ (0.9–1.3 Mg day^− 1) and K⁺ (0.7 Mg day^− 1). Extrapolating the Masaya plume species ratios to the entire Central American arc gives mean HCl and HF fluxes of 1300 and 170 Mg day^− 1 and a particulate sulphate flux of 40 Mg day^− 1 for 1997 to 2004, although without further understanding of the degassing processes and sources at depth of these different volatiles, these arc-scale estimates should be treated with caution. Combining our arc scale mean SO₂ flux with published measurements of volcanic gas compositions with respect to CO₂ and H₂O allows us to estimate mean CO₂ fluxes of 4400–9600 Mg day^− 1 and H₂O fluxes of 70,000–78,000 Mg day^− 1 for the arc. Preliminary comparisons of these estimates of outgassing rates with published volatile input fluxes into the Central American subduction zone, suggest that Cl is more efficiently recycled through the subduction zone than CO₂. The results for H₂O are inconclusive.     

Using Crater Lake chemistry to predict volcanic activity at Poás Volcano,Costa Rica

Monitoring of crater lake chemistry during the recent decline and disappearance of the crater lake of Poás 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 (H₂S_xO₆, 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.     

Forecast of volcanic eruptions by chemical methods

From the magmatic emanations differentiation point of view it is possible to calculate some ratios such as F/CO₂, Cl/CO₂, SO₂/CO₂, SO₂/H₂S, H₂S/CO₂ and CO₂/N₂ in the tumarolic gases for the forecasting of volcanic activity. In order to predict the cruptions of a volcano it is needed to select several fumaroles or hot springs having different regimes of variation of the above ratios. The study of some fumaroles composition at the Asama. Mihara, Kirishima and other volcanoes in Japan showed a close connection between volcanic gas compositions and state of the volcanoes.     

Downstream composition changes of acidic volcanic waters discharged into the Banyupahit stream, Ijen caldera, Indonesia

The crater lake of Kawah Ijen volcano contains extremely low pH (<0.4) waters with high SO₄ (70000 mg/kg), Cl (21000 mg/kg), F (1500 mg/kg), Al (5000 mg/kg), Fe (2000 mg/kg) and trace metal (Cu 0.5, Zn 4, Pb 3 mg/kg) contents. These brines seep outward through the western crater rim and reappear on the other side as streamlets, which form the headwaters of the Banyupahit stream. The Banyupahit first mixes with fresh rivers and thermal springs in the Ijen caldera and then irrigates a coastal agricultural plain which is 30 km from the summit crater.We discuss the downstream composition changes affecting the Banyupahit waters by using stable isotope, chemical and mineralogical data collected from sites along the stream length. The saturation of the stream waters with respect to minerals was evaluated with SOLVEQ and WATEQ4F and compared with the geochemical observations. An aluminous mineralogy (alunogen, pickeringite, tamarugite and kalinite) develops in the upper part of the Banyupahit due to concentration of the headwaters by evaporation. Downstream attenuation of dissolved element concentrations results principally from dilution and from mineral precipitation. The stream pH changes from 0 at the source to >4 close to the mouth. The δD and δ¹⁸O values and the relative SO₄–Cl–F contents of the Banyupahit waters indicate that the tributaries are mostly meteoric. Dissolved SO₄ in the acidic stream come only from the crater lake seepages and are not involved later in microbially mediated reactions, as shown by their δ³⁴S and δ¹⁸O values. Re-equilibration of the stream SO₄ oxygen-isotope composition with H₂O from tributaries does not occur.Calcium, SiO₂, Al, Fe, K and SO₄ behave non-conservatively in the stream waters. Gypsum, silica (amorphous or poorly ordered), a basic aluminum hydroxysulfate (basaluminite?), K-jarosite and amorphous ferric hydroxide may exert a solubility control on these elements along the entire stream length, or in certain stream sections, consistent with the thermochemical model results. Downstream concentration trends and mineral saturation levels suggest that precipitation of Sr-, Pb-rich barite and celestite consume Ba, Sr and Pb, whereas dissolved Cu, Pb and Zn may adsorb onto solid particles, especially after the junctions of the acidic stream with non-acidic rivers. We calculated that significant fluxes of SO₄, F, Cl, Al, SiO₂, Ti, Mn and Cu may reach the irrigation system, possibly causing serious environmental impacts such as soil acidification and induration.     

New clues on the contribution of Earth’s volcanism to the global mercury cycle

Active volcanoes are thought to be important contributors to the atmospheric mercury (Hg) budget, and this chemical element is one of the most harmful atmospheric pollutants, owing to its high toxicity and long residence time in ecosystems. There is, however, considerable uncertainty over the magnitude of the global volcanic Hg flux, since the existing data on volcanogenic Hg emissions are sparse and often ambiguous. In an attempt to extend the currently limited dataset on volcanogenic Hg emissions, we summarize the results of Hg flux measurements at seven active open-conduit volcanoes; Stromboli, Asama, Miyakejima, Montserrat, Ambrym, Yasur, and Nyiragongo.. Data from the dome-building Soufriere Hills volcano are also reported. Using our determined mercury to SO₂ mass ratios in tandem with the simultaneously-determined SO₂ emission rates, we estimate that the 7 volcanoes have Hg emission rates ranging from 0.2 to 18 t yr^-1 (corresponding to a total Hg flux of ~41 t·yr^-1). Based on our dataset and previous work, we propose that a Hg/SO₂ plume ratio ~10^-5 is best-representative of gas emissions from quiescent degassing volcanoes. Using this ratio, we infer a global volcanic Hg flux from persistent degassing of ~95 t·yr^-1 .     

The mass estimation of volatile emission during 1199–1200 AD eruption of Baitoushan volcano and its significance

On the basis of the study of volcanic products during 1199–1200AD eruption of Baitou Mountain (Baitoushan), the released volatile content was estimated by comparing Cl, F, S, H₂O concentrations of undegassed glass inclusions with those of degassed matrix glasses. The calculations show that volatile yields, released from the melt, are 109.88 × 10⁶ ton of HCl, 196.80 × 10⁶ ton of HF, 1477.84 × 10⁶ ton of H₂O, 23.14 × 10⁶ ton of SO₂, which could have formed 35.43 x10⁶ ton of H²SO₄ aerosol in the atmosphere. They could have substantial effect on paleoclimate and paleo-environment.     

Leaching characteristics of ash from the May 18, 1980, eruption of Mount St. Helens volcano,Washington

Leaching of freshly erupted air-fall ash, unaffected by rain, from the May 18, 1980, eruption of Mount St. Helens volcano, Washington, shows that Ca²⁺, Na⁺, Mg²⁺, SO ₄ ^2? , and Cl^? are the predominant chemical species released on first exposure of the ash to water. Extremely high correlation of Ca with SO₄ and Na with Cl in water leachates suggests the presence of CaSO₄ and NaCl salts on the ash. The amount of water soluble material on ash increases with distance from source and with the weight fraction of small (less than 63 micrometers) ash particles of high-surface area. This suggests that surface reactions such as adsorption are responsible for concentrating the soluble material. CaSO₄, NaCl, and other salts are probably formed as microscopic crystals in the high-temperature core of the eruption column and are then adsorbed by silicate ash particles. The environmentally important elements Zn, Cu, Cd, F. Pb, and Ba are released by a water leach in concentrations which could pose short-term hazards to some forms of aquatic life. However, calculated concentrations are based on a water-to-ash ratio of 4:1 or less, which is probably an underestimation of the regionally operative ratio. A subsequent leach of ash by warm alkaline solution shows dramatic increases, in the amount of dissolved SiO₂, U, and V, which are probably caused by increased dissolution of the glassy component of ash. Glass dissolution by alkaline ground water is a mechanism for providing these three elements to sedimentary traps where they may coaccumulate as uraniferous silica or U-V minerals. Leaching characteristics of ash from Mount St. Helens are comparable to characteristics of ash of similar composition from volcanoes in Guatemala. Ashes from each locality show similar ions predominating for a given leachate and similar fractions of a particular element in the ash removed on contact with the leach solution.     

SO2 emission of the 1974 eruption of Volcán Fuego,Guatemala

Volcán Fuego in the Central American Republic of Guatemala erupted violently in October, 1974. A remote sensing correlation spectrometer. COSPEC IV, which utilizes the characteristic molecular absorption of SO₂ in the ultraviolet was used to monitor the SO₂ content of the volcanic plume. Over a 60-day period measurements were made on 37 days between and following major eruptive phases. SO₂ emission rates corrected for atmospheric scattering of the spectral signal average 423 metric tons/day with a standard deviation of 252 metric tons/days. Late stage peaks in SO₂ emission at Fuego are consistent with the presence of anomalously high contents of soluble materials on the stratigraphically highest ashes from other Central American eruptions. Indications are that the SO₂ concentration within the volcanic plume increased as activity waned. These features imply that remote spectroscopic sensing of SO₂ and perhaps other gases in a volcanic plume may provide a relatively easy and inexpensive means of determining the cessation of violent eruptive activity.     

Evaluation of gases,condensates, and SO2 emissions from Augustine volcano,Alaska: the degassing of a Cl-rich volcanic system

After the March–April 1986 explosive eruption a comprehensive gas study at Augustine was undertaken in the summers of 1986 and 1987. Airborne COSPEC measurements indicate that passive SO₂ emission rates declined exponentially during this period from 380±45 metric tons/day (T/D) on 7/24/86 to 27±6 T/D on 8/24/87. These data are consistent with the hypothesis that the Augustine magma reservoir has become more degassed as volcanic activity decreased after the spring 1986 eruption. Gas samples collected in 1987 from an 870°C fumarole on the andesitic lava dome show various degrees of disequilibrium due to oxidation of reduced gas species and condensation (and loss) of H₂O in the intake tube of the sampling apparatus. Thermochemical restoration of the data permits removal of these effects to infer an equilibrium composition of the gases. Although not conclusive, this restoration is consistent with the idea that the gases were in equilibrium at 870°C with an oxygen fugacity near the Ni–NiO buffer. These restored gas compositions show that, relative to other convergent plate volcanoes, the Augustine gases are very HCl rich (5.3–6.0 mol% HCl), S rich (7.1 mol% total S), and H₂O poor (83.9–84.8 mol% H₂O). Values of D and ¹⁸O suggest that the H₂O in the dome gases is a mixture of primary magmatic water (PMW) and local seawater. Part of the Cl in the Augustine volcanic gases probably comes from this shallow seawater source. Additional Cl may come from subducted oceanic crust because data by Johnston (1978) show that Cl-rich glass inclusions in olivine crystals contain hornblende, which is evidence for a deep source (>25km) for part of the Cl. Gas samples collected in 1986 from 390°–642°C fumaroles on a ramp surrounding the inner summit crater have been oxidized so severely that restoration to an equilibrium composition is not possible. H and O isotope data suggest that these gases are variable mixtures of seawater, FMW, and meteoric steam. These samples are much more H₂O-rich (92%–97% H₂O) than the dome gases, possibly due to a larger meteoric steam component. The 1986 samples also have higher Cl/S, S/C, and F/Cl ratios, which imply that the magmatic component in these gases is from the more degassed 1976 magma. Thus, the 1987 samples from the lava dome are better indicators than the 1986 samples of degassing within the Augustine magma reservoir, even though they were collected a year later and contain a significant seawater component. Future gas studies at Augustine should emphasize fumaroles on active lava domes. Condensates collected from the same lava-dome fumarole have enrichments ot 10⁷–10² in Cl, Br, F, B, Cd, As, S, Bi, Pb, Sb, Mo, Zn, Cu, K, Li, Na, Si, and Ni. Lower-temperature (200°–650°C) fumaroles around the volcano are generally less enriched in highly volatile elements. However, these lower-termperature fumaroles have higher concentration of rock-forming elements, probably derived from the wall rock.     

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 SO₄–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 ¹⁸O 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 ¹⁸O content. The large Δ_SO4–S⁰ (23.8–26.4‰) measured in the lake suggest that dissolved SO₄ forms during disproportionation of magmatic SO₂ in the hydrothermal conduit at temperatures of 250280°C. The lake δ¹⁸O_SO4 and δ¹⁸O_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 SO₂-rich gas input to the lake system.Thermal springs at Kawah Ijen consist of acidic SO₄–Cl waters on the lakeshore and neutral pH HCO₃–SO₄–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 SO₄/Cl ratios and water and sulfur isotopic compositions support the idea that these springs are mixtures of summit acidic SO₄–Cl water and ground water.The lakeshore fumarole discharges (T=170245°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, SO₂-dominated magmatic vapor and of the reduced, H₂S-dominated hydrothermal vapor in the fumaroles varied between 1979 and 1996. This may be the result of interaction of SO₂-bearing magmatic vapors with the summit acidic hydrothermal reservoir. This idea is supported by the lower H₂S/SO₂ ratio deduced for the gas producing the SO₄–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 H₂S 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 H₂S- 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 δ³⁴S 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.     

Effects of ultrafiltration on salt migration and isotopic composition of pore water in groundwater depression area in Hengshui,NCP

Clay aquitards are semipermeable membranes that allow groundwater flow while retarding solute migration has been researched extensively but also subjected to much debate. At present, there is no evidence of whether the physical and chemical properties of clay soil and the isotopic composition of pore water affect the semipermeable membrane effect. In this study, we collected clay samples from drilling cores (30–90 m) in the Hengshui area located in the North China Plain (NCP), then extracted pore water using a high-pressure squeezing device. Vertical hydrochemical and isotopic profile variation trends for the pore water were revealed using hydrochemical (Cl⁻, Na⁺, Ca²⁺, K⁺, Mg²⁺, and SO₄²⁻) and stable isotopic measurements of H, O and Cl. The results showed that the hydrochemical clay interlayer pore water of the saline aquifer is Cl/SO₄-Na/Mg type and the average total dissolved solids (TDS) are 10.17 g/L. However, the hydrochemical clay aquitard pore water is of the Cl/SO₄-Na/Ca type with an average TDS of 1.90 g/L. The hydrochemical clay interlayer pore water of aquifer II is of Cl-Na/Ca type with an average TDS of 1.10 g/L. Our results showed that the water quality of the aquifer II is not affected by the upper part of the saline aquifer, thus the clay aquitard acts as a significant barrier to salt movement. A polarization layer concentrated in ions was formed between the upper part of the saline aquifer and the clay aquitard. The concentration polarization layer increases the salt-inhibition effect. H, O and Cl isotopic composition results showed significant fractionation. The pore water of aquifer II lacked heavy isotopes (²H, ¹⁸O, ³⁷Cl), but had significant heavy isotope enrichment in the concentrated polarized layer (the δ²H value was −76‰, the δ¹⁸O value was −8.4‰, and the δ³⁷Cl value was 1.59‰). Hyperfiltration thus played a significant role in isotope fractionation.     

Ground-Water Chemistry of Dibdiba Formation, North Kuwait

Chemical studies have been carried out on a number of water wells from the Dibdiba Formation northeast of Kuwait. Water salinity of this formation ranges between 3,300 mg/l to 7,000 mg/l, increasing with depth. The water entrapped in Dibdiba Formation is mainly sodium chloride type which can be differentiated into three different groups according to the ranges of concentration of the main cations and anions. These groups are: (3331113) sodium chloride water type in which Cl > Na, group (3333113) sodium chloride water type in which Na > Cl. In both groups the sequence of dominant cations is Na > Ca > Mg. Group (3333111) sodium chloride water type has Na > Cl and the sequence of dominant cations is Na > Mg > Ca. Chemical ratios of Ca/Mg, Na/Cl, and C1/HCO₃ were worked out for Dibdiba ground water. The ratio of Ca/Mg Dibdiba Formation ranges from 0.4 to 8.58, the ratio of Na/Cl ranges between 0.98 to 1.33, and the ratio of C1/HCO₃ is 232. A plot of chemical analysis on a trilinear diagram shows that Dibdiba Formation ground-water chemical properties are dominated by alkalies (Na > Ca) and strong acid (Cl > SO₄). Water chemistry may reflect the history of the flow path, indicating regional flow as shown by increasing Na⁺, Cl^-, SO^–₄ and where Ca⁺, Mg⁺ achieve equilibrium.     

Anomalous Emissions of SO2 During the Recent Eruption of Santa Ana Volcano, El Salvador, Central America

Santa Ana volcano in western El Salvador, Central America, had a phreatic eruption at 8:05 am (local time) on October 1, 2005, 101 years after its last eruption. However, during the last one hundred years this volcano has presented periods of quiet degassing with fumarolic activity and an acidic lake within its crater. This paper presents results of frequent measurements of SO₂ degassing using the MiniDOAS (Differential Optical Absorption Spectroscopy) system and a comparison with the volcanic seismicity prior to the eruption, during, and after the eruption. Vehicle measurements of SO₂ flux were taken every hour during the first nine days of the eruption and daily after that. The period of time reported here is from August to December, 2005. Three periods of degassing are distinguished: pre-eruptive, eruptive, and post-eruptive periods. The intense activity at Santa Ana volcano started in July 2005. During the pre-eruptive period up to 4306 and 5154 ton/day of SO₂ flux were recorded on October 24 and September 9, 2005, respectively. These values were of the same order of magnitude as the recorded values just after the October 1^st eruption (2925 ton/day at 10:01 am). Hourly measurements of SO₂ flux taken during the first nine days after the main eruptive event indicate that explosions are preceded by an increase in SO₂ flux and that this parameter reaches a peak after the explosion took place. This behavior suggests that increasing accumulation of exsolved magmatic gases occurs within the magmatic chamber before the explosions, increasing the pressure until the point of explosion. A correlation between SO₂ fluxes and RSAM (Real Time Seismic Amplitude Measurements) is observed during the complete sampling period. Periodic fluctuations in the SO₂ and RSAM values during the entire study period are observed. One possible mechanism explaining these fluctuations it that convective circulation within the magmatic chamber can bring fresh magma periodically to shallow levels, allowing increasing degasification and then decreasing degasification as the batch of magma lowers its gas content, becomes denser, and sinks to give space to a new magma pulse. These results illustrate that the measurements of SO₂ flux can provide important warning signals for incoming explosive activity in active volcanoes.     

A summary of sulfur dioxide emission rate measuremnts from Guatemalan volcanoes

Measurements of the sulfur dioxide (SO₂) emission rate from three Guatemalan volcanoes provide data which are consistent with theoretical and laboratory studies of eruptive and shallow magma chamber processes. In particular, unerupted magma makes a major contribution to the measured SO₂ emission rates at Santiaguito, a continuously erupting dacitic volcanic dome. Varying shallow magma convection rates can explain the variations in SO₂ emission rates at Santiaguito. At Fuego, a basaltic volcano currently in repose, SO₂ emission rate measurements are consistent with a high level magma body that is crystallizing and releasing volatiles. At Pacaya, a continuously erupting basaltic volcano, recent SO₂ emission rate measurements support laboratory simulation studies of strombolian eruptions; these studies indicate that the majority of gas escapes during eruptions and little gas escapes between eruptions.Average SO₂ emission rates over the last 20 years for Santiaguito, Fuego and Pacaya are 80, 160 and 260 Mg/d, respectively. On a global scale, these three volcanoes account for 1% of the annual global volcanic output of SO₂. Santiaguito and Pacaya, together, emit 6% of the total annual SO₂ emitted by continuously erupting volcanoes.Even though SO₂ measurements at these volcanoes have been made infrequently and by different investigators, the collective data help to establish a useful baseline by which to judge future changes. A more complete record of SO₂ emission rates from these volcanoes could lead to a better understanding of their eruption mechanisms and reduce the impact of their future eruptions on Guatemalan society.     

Origin and chemical and isotopic evolution of dissolved inorganic carbon (DIC) in groundwater of the Okavango Delta,Botswana

The origin and the chemical and isotopic evolution of dissolved inorganic carbon (DIC) in groundwater of the Okavango Delta in semi-arid Botswana were investigated using DIC and major ion concentrations and stable oxygen, hydrogen and carbon isotopes (δD, δ¹⁸O and δ¹³C_DIC). The δD and δ¹⁸O indicated that groundwater was recharged by evaporated river water and unevaporated rain. The river water and shallow (<10 m) groundwater are Ca–Na–HCO₃ type and the deep (≥10 m) groundwater is Na–K–HCO₃ to HCO₃–Cl–SO₄ to Cl–SO₄–HCO₃. Compared to river water, the mean DIC concentrations were 2 times higher in shallow groundwater, 7 times higher in deep groundwater and 24 times higher in island groundwater. The δ¹³C_DIC indicate that DIC production in groundwater is from organic matter oxidation and in island groundwater from organic matter oxidation and dissolution of sodium carbonate salts. The ionic and isotopic evolution of the groundwater relative to evaporated river water indicates two independent pools of DIC.     

Petrology and sulfur and chlorine emissions of the 1963 eruption of Gunung Agung,Bali, Indonesia

 The 1963 eruption of Gunung Agung produced 0.95 km³ dense rock equivalent (DRE) of olivine±hornblende-bearing, weakly phyric, basaltic andesite tephra and lava. Evidence for magma mixing in the eruptive products includes whole-rock compatible and incompatible trace element trends, reverse and complex compositional zoning of mineral phases, disequilibrium mineral assemblages, sieve-textured plagioclase phenocrysts, and augite rims on reversely zoned orthopyroxene. Basalt magma mixed with pre-existing andesite magma shortly before eruption to yield basaltic andesite with a temperature of 1040–1100  °C at an assumed pressure of 2 kb, f O₂>NNO, and an average melt volatile content (H₂O±CO₂) of 4.3 wt.%. Magma-mixing end members may have provided some of the S and Cl emitted in the eruption. Glass inclusions in phenocrysts contain an average of 650 ppm S and 3130 ppm Cl as compared with 70 ppm and 2220 ppm, respectively, in the matrix glass. Maximum S and Cl contents of glass inclusions approach 1800 and 5000 ppm, respectively. Application of the petrologic method to products of the 1963 eruption for estimating volatile release yields of 2.5×10¹²g (Mt) of SO₂ and 3.4 Mt of Cl released from the 0.65 km³ of juvenile tephra which contributed to stratospheric injection of H₂SO₄ aerosols on 17 March and 16 May, when eruption column heights exceeded 20 km above sea level. An independent estimate of SO₂ release from atmospheric aerosol loading (11–12 Mt) suggests that approximately 7 Mt of SO₂ was injected into the stratosphere. The difference between the two estimates can be most readily accounted for by the partitioning of S, as well as some Cl, from the magma into a water-rich vapor phase which was released upon eruption. For other recent high-S-release eruptions of more evolved and oxidized magmas (El Chichón, Pinatubo), the petrologic method gives values two orders of magnitude less than independent estimates of SO₂ emissions. Results from this study of the Agung 1963 magma and its volatile emissions, and from related studies on eruptions of more mafic magmas, suggest that SO₂ emissions from eruptions of higher-S-solubility magma may be more reliably estimated by the petrologic method than may those from more-evolved magma eruptions. Received: 29 June 1994 / Accepted: 25 April 1996     

Major-ion bulk deposition around an active volcano (Mt. Etna, Italy)

Bulk atmospheric deposition of major cations (Na, K, Ca, Mg) and anions (Cl, F, SO₄) were measured at 15 sites around an active volcano, Mount Etna, from 2001 to 2003. Their composition indicates several natural sources, among which deposition of plume-derived volcanogenic gas compounds is prevalent for F, Cl and S. Plume-derived acidic compounds are also responsible for the prevailing acidic composition of the samples collected on the summit of the volcano (pH in the 2.45–5.57 range). Cation species have complex origin, including deposition of plume volcanogenic ash and aerosols and soil-dust wind re-suspension of either volcanic or carbonate sedimentary rocks. Variation of the deposition rates during the March 2001–March 2003 period, coupled with previous measurements from 1997 to 2000 (Appl Geochem 16:985–1000, 2001), were compared with the variation of SO₂ flux, volcanic activity and rainfall. The deposition rate was mainly controlled by rainfall. Commonly, about 0.1–0.9% of HF, HCl and SO₂ emitted by the summit crater's plume were deposited around the volcano. We estimate that ∼2 Gg of volcanogenic sulphur were deposited over the Etnean area during the 2002–2003 flank eruption, at an average rate of ∼24 Mg day⁻¹ which is two orders of magnitude higher than that typical of quiescent degassing phases.     

Behavioral patterns of Fuego volcano, Guatemala

The times of activity at Fuego (one of the most active volcanoes in the world) since 1800 correlate with the activity of other Central American volcanoes. Approximately 0.7 km³ of olivine-bearing, high-Al₂O₃ basalt has been erupted since 1932, and about 1.7 km³ has been produced during 450 years of historic records. A minimum of 13,000 years and a maximum of 100,000 years were required to build Fuego's cone of 50 km³. Within the recent cluster of activity since 1932, rates of magma production have increased to 0.5 m³/s and the trend has been toward more eruptions (shorter reposes) of progressively more mafic basalt. 47% of the eruptions occurred within 2 days of the fortnightly tidal maximum and 56% occurred within 2 hours of the semi-diurnal minimum of the vertical tidal gravity acceleration. Thus the maximum compressional component of the tidal cycles can trigger an eruption at Fuego. Eruptions with higher effusion rates produce larger volumes of materials, although they only last a few hours. The 20–70 year clusters of activity beginning at 80–170-year intervals are interpreted as reflecting the ascent of primary batches of magma. A deeper (8–16 km), larger (> 1 km³) primary chamber and a shallower (2–5 km), smaller (0.1 km³), dike-like secondary chamber best explain Fuego's behavioral pattern.