High-temperature Volcanic Gases Research Articles

Extremely deuterium depleted methane revealed in high-temperature volcanic gases

Active volcanoes often discharge hot (T ≫ 100 °C) magmatic gases whose original composition has been modified through partial interaction with an externally fed hydrothermal system. The study of methane (CH4) in these volcanic discharges may provide useful information on the interplay between deep magmatic gases and shallow circulation of hydrothermal fluids. However, the origin of CH4 in high-temperature volcanic gases and the factors exerting control on its abundance and stable isotope composition are still largely unknown. Here, we present the abundances and stable isotopic composition of CH4 in hot (99–387 °C) volcanic gases from the La Fossa volcanic crater of Vulcano Island (Southern Italy).Our investigation revealed low (<1.5 μmol/mol) CH4 concentrations and an extraordinarily large variability in CH4 stable isotopic composition, with δ13C and δ2H values being positively correlated and varying from −35 to −9.2 ‰ and −670 to −102 ‰, respectively. Notably, CH4 isotopes measured at Vulcano almost encompasses the global-scale variability observed in natural fluids, with δ2H values ≤ −500 ‰ being the first ever reported in nature. Gases showing extremely negative δ13C-CH4 and δ2H-CH4 values systematically display higher CH4 abundances.We propose two possible scenarios in order to explain the observed huge variation in δ13C and δ2H: (1) mixing of 13C- and 2H-depleted CH4 with 13C- and 2H-enriched CH4 of thermogenic origin formed under hydrothermal conditions; (2) post-genetic removal and isotopic alteration of 13C- and 2H-depleted CH4 occurring during the ascent of volcanic gases. Comparing our dataset with available isotopic data from naturally occurring and artificially produced CH4, a thermogenic origin for the isotopically light CH4 seems unlikely. We postulate that the 13C- and 2H-depleted CH4 may have formed via kinetically-controlled abiotic synthesis through CO (or CO2) hydrogenation reactions in the hot ascending gas phase, possibly at temperatures intermediate between those typical of magmatic and hydrothermal conditions. Further investigations of methane in high-temperature volcanic gases are necessary to test this hypothesis.

Constraints on the sulfur subduction cycle in Central America from sulfur isotope compositions of volcanic gases

The sulfur cycle at convergent margins remains poorly constrained yet is fundamentally important for understanding the redox state of Earth's reservoirs and the formation of ore deposits. In this study we investigate the sulfur isotope composition of high temperature volcanic gases emitted from the Nicaraguan (average of +4.8 ± 1.3‰) and Costa Rican (average of +2.3 ± 1.3‰) arc segments contributing to emissions from the Southern Central American Volcanic Arc (SCAVA; average of +3.8 ± 1.7‰). Along-arc variations in geochemical tracers at SCAVA are widely accepted to reflect variations in subduction parameters and deep fluid sources and correlations between these parameters and gas S isotope compositions are observed. These correlations suggest that gas emissions are sourced from a mixture of mantle S with δ34S ~ 0‰ and isotopically heavy slab-derived sulfur with δ34S ≥ ~ +8‰. We employ Monte Carlo mass balance modeling to constrain S inputs to the subduction zone and relative contributions from mantle and slab to arc sulfur emissions. The models indicate that bulk subduction input in Nicaragua has a S isotope composition of +1.4 ± 0.5‰ compared to −0.2 ± 0.4‰ in Costa Rica, requiring preferential release of isotopically heavy oxidized S from the slab to explain the relatively high δ34S observed in arc outputs. We show that the flux of S from the slab is sufficient to oxidize the entire mantle wedge within the lifetime of the arc, indicating that S is a primary oxidizing agent in subduction zones. Furthermore, the preferential removal of heavy S from the slab requires retention of isotopically light S in the residual slab. Subduction-scale fractionation of S isotopes is fundamentally important in explaining why Earth's bulk surface reservoirs are isotopically positive.

Sulfur sequestration and redox equilibria in volcanic gases

Although It has long been recognized that sub-volcanic gas-solid reactions involving iron play a major role in determining the redox state (RH=logfH2fH2O) of discharging gases, the crucial role played by calcium has only recently been recognized through high temperature gas-solid experimental studies.These show that SO2, which dominates H2S in high temperature (> ~600°C) volcanic gas mixtures, rapidly and efficiently reacts with abundant plagioclase and other calcic rock-forming minerals to simultaneously deposit anhydrite and release reduced sulfur. Coupled with sulfide deposition, these reactions control the total sulfur content of the gas phase through the very low solubilities of sulfides and anhydrite and, via coupled multicomponent reactions, determine the redox state and the H2S/SO2 ratio of the volcanic gas mixtures.Multi-component thermochemical modelling of gas-solid equilibria and titration-precipitation reactions along adiabatic expansion pathways from magma to surface confirm that for fumarole gas mixtures with outlet temperature > 400 °C, RH is primarily controlled by anorthite - pyroxene - anhydrite - sulfide reactions, irrespective of their tectonic location, state of volcanic activity, gas discharge temperature and the composition of the gas mixtures released from the magma.Anhydrite and sulfide deposition through gas-solid reactions result in extensive sulfur sequestration as gas mixtures expand from the magma to the surface as is observed in the many large scale ‘porphyry’ Cu-Mo-Au deposits exposed in ancient, now dissected, volcanoes in magmatic arcs. These volcano-scale alteration processes also imply that high temperature (> 600 °C) volcanic gases have C/S ratios that may have been increased by this process relative to their original magmatic values. The corollary is that current estimates of the total sulfur released annually from the mantle may be significantly underestimated.

Estimation of CO2 Content in the Gas Phase of Melt Inclusions Using Raman Spectroscopy: Case Study of Inclusions in Olivine from the Karymsky Volcano (Kamchatka)

Abstract —Carbon dioxide (CO2) is one of the main volatile components of natural magmas, but estimation of its initial contents remains a challenge. Study of melt inclusions in minerals permits a direct estimation of the content of CO2 in the melts. For the precise determination of its content in melt inclusions, it is necessary to analyze the contents of CO2 both in glass and in the fluid daughter phase of the inclusions. In this work, we constructed a calibration dependence of the density of CO2 in the range 0.01–0.22 g/cm3 on the distance between its characteristic peaks in Raman spectra (Fermi diads). The accuracy of density determination is ±0.03 g/cm3. The calibration plot was used to estimate the density of CO2 in the gas phase of melt inclusions in magnesian olivine (Fo84.8-88.5) from basalts of the Karymskii Volcano, eastern Kamchatka. The estimated density was 0.03–0.21 g/cm3. Using these values, we have first evaluated the minimum initial content of CO2 in the parental magmas of the Karymskii Volcano, 0.45 wt.%. These data, along with the known initial content of water (~4.5 wt.%), indicate that the parental magmas began to crystallize at a pressure of at least 7 kbar (depth of &amp;gt;25 km). To increase the reliability of the above method of estimation of the CO2 content in the gas phase of olivine-hosted melt inclusions, we propose to carry out preliminary experimental reheating of inclusions for the complete homogenization of the fluid phase and determination of the 3D size of melt inclusions. The performed study provides a reliable evaluation of the content of CO2 in parental magmas, the depth of crystallization, and the degree of magma degassing and permits a comparison of the compositions of magmatic fluids and high-temperature volcanic gases.

A novel apparatus for the simulation of eruptive gas-rock interactions

The chemical interactions between hot volcanic gases and co-erupted magmatic and lithic particles within eruption plumes and pyroclastic flows are increasingly investigated for their relevance to the impacts of ash emission on natural and human environments. Laboratory experiments are critical to our understanding of high-temperature gas-ash interactions, but previous studies are yet to replicate the chemical composition of the high-temperature volcanic gases involved. Here, we present a unique apparatus, the Advanced Gas-Ash Reactor, capable of generating an atmosphere of H2O, CO2, SO2 and HCl at temperatures ranging from 200 to 900 °C, under variable heating and cooling rates. Experiments utilising the reactor can inform investigations of a range of topics, from subsurface gas-rock interaction and in-plume gas adsorption processes, to the effect of ash surface chemistry on marine nutrient loadings and atmospheric chemistry. Our results demonstrate the differences in high-temperature gas uptake by volcanic glass powders under both hydrous and anhydrous atmospheres and, accordingly, demonstrate the utility of the new reactor.

Sulphur geodynamic cycle.

Evaluation of volcanic and hydrothermal fluxes to the surface environments is important to elucidate the geochemical cycle of sulphur and the evolution of ocean chemistry. This paper presents S/3He ratios of vesicles in mid-ocean ridge (MOR) basalt glass together with the ratios of high-temperature hydrothermal fluids to calculate the sulphur flux of 100 Gmol/y at MOR. The S/3He ratios of high-temperature volcanic gases show sulphur flux of 720 Gmol/y at arc volcanoes (ARC) with a contribution from the mantle of 2.9%, which is calculated as 21 Gmol/y. The C/S flux ratio of 12 from the mantle at MOR and ARC is comparable to the C/S ratio in the surface inventory, which suggests that these elements in the surface environments originated from the upper mantle.

Imaging the hydrothermal system beneath the Jigokudani valley, Tateyama volcano, Japan: implications for structures controlling repeated phreatic eruptions from an audio-frequency magnetotelluric survey

This study focuses on the results of an audio-frequency magnetotelluric (AMT) survey across the Jigokudani valley, Tateyama volcano, Japan, to investigate the spatial relationship between the distribution of electrical resistivity and geothermal activity and to elucidate the geologic controls on both its phreatic eruption history and recent increase in phreatic activity. The AMT data were collected at eight locations across the Jigokudani valley in September 2013, with high quality data obtained from most sites, enabling the identification of an underground 2D resistivity structure from the transverse magnetic (TM) mode data. The data obtained during this study provided evidence of a large conductive region beneath the surface of the Jigokudani valley that is underlain by a resistive layer at depths below 500 m. The resistive layer is cut by a relatively conductive region that extends subvertically toward the shallow conductor. The shallow conductive region is divided into an uppermost slightly conductive section that is thought to be a lacustrine sediment layer of an extinct crater lake containing hydrothermal fluids and a lower section containing a mix of volcanic gases and hydrothermal fluids. The low permeability of the clay zone means that the uppermost clayey sediments allow the accumulation of gases in the lower section of the conductive region, suggesting the existence of a cap structure. The deep resistive layer likely consists of units similar to the granitic rocks that are widely exposed throughout the Jigokudani valley. We suggest that the relatively conductive zone that separates these granitic rocks represents a high-temperature volcanic gas conduit, given that the most active fumarole in the Jigokudani valley lies directly along the trajectory of this path.

High-temperature volcanic gas flow from the summit lava dome of Tarumai Volcano, Hokkaido, Japan

High-temperature volcanic gas flow from the summit lava dome of Tarumai Volcano, Hokkaido, Japan

A heating process of Kuchi-erabu-jima volcano, Japan, as inferred from geomagnetic field variations and electrical structure

Since August 2000, we have recorded the total intensity of the geomagnetic field at the summit area of Kuchi-erabu-jima volcano, where phreatic eruptions have repeatedly occurred. A time series analysis has shown that the variations in the geomagnetic field since 2001 have a strong relationship to an increase in volcanic activity. These variations indicate thermal demagnetization of the subsurface around the presently active crater. The demagnetization source for the early variations, until summer 2002, was estimated at about 200 m below sea level. For the variations since 2003, the source was modeled on the basis of the expansion of a uniformly magnetized ellipsoid. The modeling result showed that the source is located at 300 m above sea level beneath the crater. We carried out an audio-frequency magnetotelluric survey with the aim of obtaining a relation between the demagnetization source and the shallow structure of the volcano. A two-dimensional inversion applied to the data detected two good conductors, a shallow thin one which is restricted to a region around the summit area, while the other extends over the edifice at depths between 200 and 800 m. These conductors are regarded as clay-rich layers with low permeability, which were assumed to be generated through hydrothermal alteration. The demagnetization source for the early variations was possibly located at the lower part of the deep conductor and the source after 2003 lies between the two conductors, where groundwater is considered to be abundant. Based on these results, as well as on seismological, geodetic, and geochemical information, we propose a heating process of the Kuchi-erabu-jima volcano. In the initial stage, high-temperature volcanic gases supplied from the deep-seated magma remained temporarily at the level around the lower part of the less permeable deep conductor since the ascent path had not yet been established. Then, when the pathway developed as a result of repeated earthquakes, it became possible for a massive flux of volcanic gases to ascend through the conductor. The high temperature gases reached the aquifer located above the conductor and the heat was efficiently transported to the surrounding rocks through the groundwater. As a consequence, an abrupt increase of the gas flux and diffusion of the heat through the aquifer occurred and the high-temperature zone expanded. Since the high-temperature zone is located beneath another conductor, which acts as caprock, we assume that the energy of the phreatic explosion is accumulated there.

Magma degassing process during the eruption of Mt. Unzen, Japan in 1991 to 1995: Modeling with the chemical composition of volcanic gas

During the dome-forming eruption in 1991 to 1995 at Mt. Unzen, Japan high temperature volcanic gases were sampled from fumaroles located at the western basement of the dacitic lava dome. Comparing the composition of volcanic gas, the volatile in the pre-eruptive melt of magma and the groundmass of lava, we propose that the volatile in magma was liberated through three different gas separation steps. The first gas separation happened at depth deeper than 3.9 km. The liberated gas traveled along the conduit then discharged as the observed fumarolic gas. The second gas separation took place beneath the lava dome. The liberated gas was discharged on the top of lava dome. The third gas separation occurred near surface in a so called “open system degassing” process. The large variation in the CO 2/H 2O ratio of fumarolic gas could be explained by the variation of the bubble fraction in the pre-eruptive melt of magma chamber before the gas separations. The estimated bubble fraction in the melt was less than 1.7 vol.%. Such a low fraction of bubbles in the magma chamber of Mt. Unzen would be one of the reasons why the eruption was non-explosive. The fumarolic gas in the later stage of eruption was enriched in HCl and HF due to the effect of open system degassing of magma, although the gas contained CO 2 and H 2S with high concentrations. The CO 2 and H 2S would be derived from a vapor phase of hydrothermal system developed around the conduit.

A preparation zone for volcanic explosions beneath Naka-dake crater, Aso volcano, as inferred from magnetotelluric surveys

The 1st crater of Naka-dake, Aso volcano, is one of the most active craters in Japan, and known to have a characteristic cycle of activity that consists of the formation of a crater lake, drying-up of the lake water, and finally a Strombolian-type eruption. Recent observations indicate an increase in eruptive activity including a decrease in the level of the lake water, mud eruptions, and red hot glows on the crater wall. Temporal variations in the geomagnetic field observed around the craters of Naka-dake also indicate that thermal demagnetization of the subsurface rocks has been occurring in shallow subsurface areas around the 1st crater. Volcanic explosions act to release the energy transferred from magma or volcanic fluids. Measurement of the subsurface electrical resistivity is a promising method in investigating the shallow structure of the volcanic edifices, where energy from various sources accumulates, and in investigating the behaviors of magma and volcanic fluids. We carried out audio-frequency magnetotelluric surveys around the craters of Naka-dake in 2004 and 2005 to determine the detailed electrical structure down to a depth of around 1 km. The main objective of this study is to identify the specific subsurface structure that acts to store energy as a preparation zone for volcanic eruption. Two-dimensional inversions were applied to four profiles across the craters, revealing a strongly conductive zone at several hundred meters depth beneath the 1st crater and surrounding area. In contrast, we found no such remarkable conductor at shallow depths beneath the 4th crater, which has been inactive for 70 years, finding instead a relatively resistive body. The distribution of the rotational invariant of the magnetotelluric impedance tensor is consistent with the inversion results. This unusual shallow structure probably reflects the existence of a supply path of high-temperature volcanic gases to the crater bottom. We propose that the upper part of the conductor identified beneath the 1st crater is mainly composed of hydrothermally altered zone that acts both as a cap to upwelling fluids supplied from deep-level magma and as a floor to infiltrating fluid from the crater lake. The relatively resistive body found beneath the 4th crater represents consolidated magma. These results suggest that the shallow conductor beneath the active crater is closely related to a component of the mechanism that controls volcanic activity within Naka-dake.

Self-potential anomaly of Satsuma-Iwojima volcano

We conducted self-potential (SP) surveys twice at Satsuma-Iwojima volcano where an intense fumarolic activity continued for more than 1000 years from a summit crater of Iwodake, a lava dome of rhyolite. A positive anomaly of 200 ∼ 250 mV was detected on the Iwodake edifice, although the survey area was limited because of the steep topography and existence of high temperature fumaroles. The anomaly seems to be centered at the summit crater of Iwodake and can roughly be explained by a pair of conduction current source and sink located around the sea level beneath the summit crater. Depth of the current source might indicate the upper end of a liquid-phase water upflow zone, where the liquid-phase water vaporizes due to heat and depressurization. The above model does not explain the additional positive SP anomaly around the summit crater and on the western flank. The anomaly around the su mmit might be caused by suppression of meteoric water downflow by high temperature volcanic gases. The positive anomaly on the western flank might be caused by local fluid upflows associated with fumaroles on the flank.

D/H and 18O/16O ratios of water in the crater lake at Kusatsu-Shirane volcano, Japan

The D/H and 18O/16O ratios of water in the active crater lake situated on the Kusatsu-Shirane volcano, Japan are about 20 and 6‰, respectively, higher than local meteoric water. The ratios show seasonal variations superimposed on a gradual change over nine years. The isotopic ratios started to increase in early 1990 and decrease in the spring of 1995. The seasonal variation which is high in winter and low in summer correlates with the temperature difference between lake water and ambient air. The large temperature difference in winter enhances the evaporation of lake water and produces the enriched isotopic ratios relative to the ratios in summer. The accumulation of snow and the decrease in the flux of meteoric water into the lake strengthens the winter-time isotopic enrichment. The enriched isotopic ratios of the lake water over a long time result from the addition of an end member with heavy isotopic ratios contained in a thermal fluid supplied to the lake. Considering the water balance in the lake, the isotopic ratios of the thermal fluid were found to be close to the lake water itself, suggesting the circulation of the lake water seeping through lake floor. Based on the correlation between Cl−concentration and the isotopic ratios, the contribution by the heavy end member was estimated to be 25–36% relative to the enrichment by evaporation. The heavy end member could be a liquid phase evolved from a parental fluid, which is a mixture of local meteoric water and a magmatic fluid as found in high-temperature volcanic gases.

The stable isotope geochemistry of volcanic lakes, with examples from Indonesia

Stable isotope compositions (δD, δ18O and δ34S) of volcanic lake waters, gas condensates and spring waters from Indonesia, Italy, Japan, and Russia were measured. The spring fluids and gas samples plot in a broad array between meteoric waters and local high-temperature volcanic gas compositions. The δD and δ18O data from volcanic lakes in East Indonesia plot in a concave band ranging from local meteoric waters to evaporated fluids to waters heavier than local high-temperature volcanic gases. We investigated isotopic fractionation processes in volcanic lakes at elevated temperatures with simultaneous mixing of meteoric waters and volcanic gases. An elevated lake water temperature gives enhanced kinetic isotope fractionation and changes in equilibrium fractionation factors, providing relatively flat isotope evolution curves in δ18O–δD diagrams. A numerical simulation model is used to derive the timescales of isotopic evolution of crater lakes as a function of atmospheric parameters, lake water temperature and fluxes of meteoric water, volcanic gas input, evaporation, and seepage losses. The same model is used to derive the flux magnitude of the Keli Mutu lakes in Indonesia. The calculated volcanic gas fluxes are of the same order as those derived from energy budget models or direct gas flux measurements in open craters (several 100m3 volcanic water/day) and indicate a water residence time of 1–2decades. The δ34S data from the Keli Mutu lakes show a much wider range than those from gases and springs, which is probably related to the precipitation of sulfur in these acid brine lakes. The isotopic mass balance and S/Cl values suggest that about half of the sulfur input in the hottest Keli Mutu lake is converted into native sulfur.

Volcanic lake systematics II. Chemical constraints

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.

Native gold in mineral precipitates from high-temperature volcanic gases of Colima volcano, Mexico

Trigonal and pentagonal shaped plates and prism, and octahedra of Au crystals 3–40 μm in dimension were found on the inner wall of a silica tube inserted into a 800°C fumarolic vent of Colima volcano, Mexico. Gold precipitates from the high-temperature and highly oxidized volcanic vapor (a mixture of magmatic gas with more than 90% of air) cover a narrow temperature range of 550–600°C, and occur in association with V-rich Na–K-sulfates. The Au concentration in the volcanic gas condensate is between 0.1 and 0.5 μg/kg. Using thermodynamic data for Au(c), Au(g), AuH(g) and AuS(g), open- and closed-system cooling of a simplified volcanic gas has been modeled with the following characteristics of volcanic gas+air mixture: P=1 bar, f SO 2 =0.01 bar; f SO 2 fixed by Fe 2O 3–Fe 3O 4 or Cu 2O–CuO pairs for open-system cooling, and f SO 2 =0.1 bar for closed-system cooling. Volcanic vapor released from the shallow magma body transports Au as AuH(g) and AuS(g). According to calculations, after mixing with air, AuS(g) and AuH(g) oxidize to Au(g), and the temperature of the Au deposition depends only on the initial total concentration of Au species in the vapor. The temperature range of 550–600°C for Au precipitation at a high f SO 2 corresponds to a very low initial Au concentration, about 1 ng/kg in the volcanic gas condensate. This is at least two orders of magnitude lower than the observed Au content in the Colima gas, indicating the presence of other volatile gold species, e.g. AuCl x , Au(OH) x etc., or Au precipitation under non-equilibrium conditions from a volcanic gas+air mixture with coexisting free H 2 and O 2.

Water contents and hydrogen isotopic ratios of rocks and minerals from the 1991 eruption of Unzen volcano, Japan

Water contents and hydrogen isotopic ratios were determined for blocks from pyroclastic flow deposits, and bread-crust bombs and blocks from the 1991 Vulcanian eruptions of Unzen volcano, Japan. Groundmass water contents and δD values of samples were calculated by subtracting the contribution of major hydrous minerals (hornblende and biotite) from the bulk rock analyses, and range from 0.1 to 0.5 wt.% and −83 to −49‰, respectively. The samples do not show a systematic H 2O– δD relationship, although the block samples tend to have lower δD values than the bomb samples. The non-systematic H 2O– δD relationship is likely a result of near surface, kinetically-controlled gas loss. High viscosity of this magma would hinder attainment of hydrogen isotopic equilibrium between exsolved vapor and melt in the final degassing stage. The near surface degassing, however, was accompanied by kinetic fractionation resulting in enrichment of deuterium in the final products as exemplified by bread-crust bombs with high H 2O–low δD margins and low H 2O–high δD cores. Relatively high δD values of the blocks and bombs as well as high temperature volcanic gas (−30 to −35‰) suggest a closed system degassing of an initial water-rich magma (H 2O=6 wt.%) until its water content was reduced to 0.5 wt.%. The pre-eruptive δD value (−46‰) was estimated from the volcanic gas data and D/H analysis of hornblende phenocrysts coupled with assumed isotopic equilibration in the initial hydrous magma.

Changes in Geochemical Characteristics of Thermal water observed at Sumikawa and Akagawa Spas, after the 1997. 5. 11 Sumikawa Landslide, Akita Prefecture

In May 8-11, 1997, a landslide occurred at the Sumikawa Spa, the northern flank and about 4 km northeast from the summit crater of Akita-Yakeyama Volcano, northeastern part of Akita Prefecture. The scale of the landslide was 400 m wide and 800 m long, the volume 2, 500, 000 m3, and the height of the mainscarp was 60 m. In May 11, when the main landslide mass movement occurred, the toe (front unit) of the landslide mass was transformed into the debris avalanche, 500, 000 m3 in volume. The debris avalanche rushed over the River Sumikawa, and to the Akagawa Spa, 1100 m northward and 190 m low of the Sumikawa Spa. The debris avalanche was finally transformed into the debris flow, that flowed about 800 m northward to the confluence with the River Kumazawa, one of the upper reaches of the River Yoneshiro. At the same time, when the main landslide and the debris avalanche occurred, the intermittent phreatic eruptions (hydrothermal explosions) broke out at the Sumikawa and Akagawa Spas. The smoke (fume) of these eruptions rose up to a height of>100 m at the Sumikawa Spa and up to a height of several decades of meter at the Akagawa Spa.Three times of observations of water temperatures and chemical concentrations were carried out for thermal waters and interstitial waters centrifuged from altered clay and ash samples obtained from at and around the Sumikawa and Akagawa Spas, to know the possibility of contribution of high temperature volcanic gas and deepseated hydrothermal water to the occurrence of the 1997 Sumikawa Landslide with phreatic eruptions (hydrothermal explosions).The results lead us to conclude the followings.1) The increase of ground water temperature and chemical concentrations, and the decrease of pH observed at the Sumikawa Spa were caused by the decrease of the rate of the intrusion of subsurface, meteoric and/or river water to the Sumikawa hot spring layer.2) The increase of chloride ion concentrations compared with other reference values observed at the Akagawa Spa were caused by the increase of the rate of the intrusion of interstitial water to the Akagawa hot spring layer, because of the movement of spring head, usually observed in hot spring area.These results obviously denied the possibility of contribution of high temperature volcanic gas and deepseated hydrothermal water to the occurrence of the 1997 Sumikawa Landslide with phreatic eruptions (hydrothermal explosions).

Chemical equilibrium in high temperature volcanic gas

Chemical equilibrium in high temperature volcanic gas

Formula omitted] fractionation in the system methane-hydrogen-water

We report measurements of the equilibrium D H fractionation factor (a) between methane and hydrogen in the temperature range 200–500°C. Isotopic equilibrium was achieved by recycling the gases over a Ni-Thoria catalyst, using an in-line sampling volume for sequestering aliquots of the gas mixture without contributions from adsorbed gases on the catalyst. Equilibrium values of a were approached from both sides by use of (1) enriched CH 3D in the initial mixture and (2) pre-equilibration of the gases at temperatures below that of the final equilibrium mixture. The measured values of a are linear vs. 1 T 2 and fit the equation a = 0.8994 + 183,540/T2, with a standard deviation σ = ±2.5‰. The D H fractionation factors for water vapor-hydrogen exchange measured by Suess (1949) and by Cerrai et al. (1954) are also linear in α vs. 1 T 2 over the temperature range of the data: comparison with published D H ratios in high-temperature (1127°C) volcanic gases at Surtsey volcano shows that the Suess (1949) data are much closer to the observed ratios in H2 and H2O. The Suess (1949) measurements (80– 200°C) are also much closer to the theoretical values calculated by Bardo and Wolfsberg (1976), which fit the observed Surtsey fractionations slightly better than the extrapolated Suess (1949) results. We conclude that (1) the Suess (1949) measurements are the better set of experimental data, (2) the Surtsey gases are close to isotopic equilibrium at the vent temperatures, and (3) the Bardo and Wolfsberg (1976) theoretical equation gives the best representation of the H 2OH 2 fractionation factors. This equation is combined with the Horita and Wesolowski (1994) equation for H 2O liquid-vapor fractionation factors and can be used with the CH 4HZ a values to determine whether concordant temperatures are observed in the system CH 4H 2H 20. Application to the D H ratios in the East Pacific Rise hydrothermal vents measured by Welhan and Craig (1979) shows that concordant temperatures are obtained for both CH 4H 2 and H 2OH 2 data, and are close to the approximate vent temperatures (∼350°C). We note that fractionation equations in which a, rather than In a, is fit to powers of T are much more useful for geochemical studies because the precision estimate is uniform over the entire temperature range of the data.