Behavior of magmatic components in fumarolic gases related to the 2018 phreatic eruption at Ebinokogen Ioyama volcano, Kirishima Volcanic Group, Kyushu, Japan

Direct sampling and analysis of fumarolic gas was conducted at Ebinokogen Ioyama volcano, Japan, between December 2015 and July 2020. Notable changes in the chemical composition of gases related to volcanic activity included a sharp increase in SO2 and H2 concentrations in May 2017 and March 2018. The analyses in March 2018 immediately preceded the April 2018 eruption at Ioyama volcano. The isotopic ratios of H2O in fumarolic gas revealed the process of formation. Up to 49% high-enthalpy magmatic vapor mixed with 51% of cold local meteoric water to generate coexisting vapor and liquid phases at 100–160 °C. Portions of the vapor and liquid phases were discharged as fumarolic gases and hot spring water, respectively. The CO2/SO2 ratio of the fumarolic gas was higher than that estimated for magmatic vapor due to SO2 hydrolysis during the formation of the vapor phase. When the flux of the magmatic vapor was high, effects of hydrolysis were small resulting in low CO2/SO2 ratios in fumarolic gases. The high apparent equilibrium temperature defined for reactions involving SO2, H2S, H2 and H2O, together with low CO2/SO2 and H2S /SO2 ratios were regarded to be precursor signals to the phreatic eruption at Ioyama volcano. The apparent equilibrium temperature increased rapidly in May 2017 and March 2018 suggesting an increased flux of magmatic vapor. Between September 2017 and January 2018, the apparent equilibrium temperature was low suggesting the suppression of magmatic vapor flux. During this period, magmatic eruptions took place at Shinmoedake volcano 5 km away from Ioyama volcano. We conclude that magma sealing and transport to Shinmoedake volcano occurred simultaneously in the magma chamber beneath Ioyama volcano.

Gas monitoring of a hydrothermal-magmatic volcano in a tropical environment: the example of La Soufriere de Guadeloupe (FWI)

<p>Fumarolic gas survey of dormant volcanoes is fundamental because the compositional and flux changes in gas emissions are recognised signals of unrest and may even be precursors of eruptions on several dormant volcanoes in hydrothermal unrest [1-5].</p><p>Here we report on the chemical compositions (CO<sub>2</sub>, H<sub>2</sub>S, SO<sub>2</sub>, H<sub>2</sub>) and mass fluxes of fumarolic gas emissions from the low-temperature (from 97° to 104°C) volcanic-hydrothermal system of La Soufrière de Guadeloupe (Lesser Antilles). This present study covers the period 2016 to present, encompassing the peak activity of April 2018. Long-term trends are acquired from both portable MultiGAS measurements (performed monthly) and two permanent MultiGAS stations (4 automated 20’ measurements per day). These MultiGAS data are discussed along with other geochemical and geophysical parameters monitored at OVSG, such as complete fumarole chemistry via Giggenbach bottles, fumarole temperatures, volcanic seismicity and deformation in order to track the deep-sourced magmatic signal contribution compared to the one of the hydrothermal system and detect potential signs of unrest [6].</p><p>Dealing with MultiGAS data from a low-T fumarolic system in a tropical environment is not straightforward due to external forcing effect of meteoric water on gas composition. Hence, interpretation of the observed chemical changes must consider (i) the role of water-gas-rock interactions and gas scrubbing processes by the hydrothermal system and the perched volcanic pond [7], which particularly affect sulphur precipitation and remobilization and (ii) how these processes vary with rainfall and groundwater circulation (i.e. rainy vs non-rainy seasons, extreme events).</p><p>[1] Giggenbach and Sheppard, 1989; [2] Symonds et al., 1994; [3] Hammouya et al., 1998; [4] De Moor et al., 2016; [5] Allard et al., 2014; [6] Moretti et al., submitted; [7] Symonds et al., 2001</p>

Dioskouriite, CaCu4Cl6(OH)4∙4H2O: A New Mineral Description, Crystal Chemistry and Polytypism

A new mineral, dioskouriite, CaCu4Cl6(OH)4∙4H2O, represented by two polytypes, monoclinic (2M) and orthorhombic (2O), which occur together, was found in moderately hot zones of two active fumaroles, Glavnaya Tenoritovaya and Arsenatnaya, at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. Dioskouriite seems to be a product of the interactions involving high-temperature sublimate minerals, fumarolic gas and atmospheric water vapor at temperatures not higher than 150 °C. It is associated with avdoninite, belloite, chlorothionite, eriochalcite, sylvite, halite, carnallite, mitscherlichite, chrysothallite, sanguite, romanorlovite, feodosiyite, mellizinkalite, flinteite, kainite, gypsum, sellaite and earlier hematite, tenorite and chalcocyanite in Glavnaya Tenoritovaya and with avdoninite and earlier hematite, tenorite, fluorophlogopite, diopside, clinoenstatite, sanidine, halite, aphthitalite-group sulfates, anhydrite, pseudobrookite, powellite and baryte in Arsenatnaya. Dioskouriite forms tabular, lamellar or flattened prismatic, typically sword-like crystals up to 0.01 mm × 0.04 mm × 0.1 mm combined in groups or crusts up to 1 × 2 mm2 in area. The mineral is transparent, bright green with vitreous luster. It is brittle; cleavage is distinct. The Mohs hardness is ca. 3. Dmeas is 2.75(1) and Dcalc is 2.765 for dioskouriite-2O and 2.820 g cm−3 for dioskouriite-2M. Dioskouriite-2O is optically biaxial (+), α = 1.695(4), β = 1.715(8), γ = 1.750(6) and 2Vmeas. = 70(10)°. The Raman spectrum is reported. The chemical composition (wt%, electron microprobe data, H2O calculated by total difference; dioskouriite-2O/dioskouriite-2M) is: K2O 0.03/0.21; MgO 0.08/0.47; CaO 8.99/8.60; CuO 49.24/49.06; Cl 32.53/32.66; H2O(calc.) 16.48/16.38; -O=Cl −7.35/−7.38; total 100/100. The empirical formulae based on 14 O + Cl apfu are: dioskouriite-2O: Ca1.04(Cu4.02Mg0.01)Σ4.03[Cl5.96(OH)3.90O0.14]Σ10∙4H2O; dioskouriite-2M: (Ca1.00K0.03)Σ4.03(Cu4.01Mg0.08)Σ4.09[Cl5.99(OH)3.83O0.18]Σ10∙4H2O. Dioskouriite-2M has the space group P21/c, a = 7.2792(8), b = 10.3000(7), c = 20.758(2) Å, β = 100.238(11)°, V = 1531.6(2) Å3 and Z = 4; dioskouriite-2O: P212121, a = 7.3193(7), b = 10.3710(10), c = 20.560(3) Å, V = 1560.6(3) Å3 and Z = 4. The crystal structure (solved from single-crystal XRD data, R = 0.104 and 0.081 for dioskouriite-2M and -2O, respectively) is unique. The structures of both polytypes are based upon identical BAB layers parallel to (001) and composed from Cu2+-centered polyhedra. The core of each layer is formed by a sheet A of edge-sharing mixed-ligand octahedra centered by Cu(1), Cu(2), Cu(3), Cu(5) and Cu(6) atoms, whereas distorted Cu(4)(OH)2Cl3 tetragonal pyramids are attached to the A sheet on both sides, along with the Ca(OH)2(H2O)4Cl2 eight-cornered polyhedra, which provide the linkage of the two adjacent layers via long Ca−Cl bonds. The Cu(4) and Ca polyhedra form the B sheet. The difference between the 2M and 2O polytypes arises as a result of different stacking of layers along the c axis. The cation array of the layer corresponds to the capped kagomé lattice that is also observed in several other natural Cu hydroxychlorides: atacamite, clinoatacamite, bobkingite and avdoninite. The mineral is named after Dioskouri, the famous inseparable twin brothers of ancient Greek mythology, Castor and Polydeuces, the same in face but different in exercises and achievements; the name is given in allusion to the existence of two polytypes that are indistinguishable in appearance but different in symmetry, unit cell configuration and XRD pattern.

Elevated CO2 Emissions during Magmatic-Hydrothermal Degassing at Awu Volcano, Sangihe Arc, Indonesia

Awu is a remote and little known active volcano of Indonesia located in the northern part of Molucca Sea. It is the northernmost active volcano of the Sangihe arc with 18 eruptions in less than 4 centuries, causing a cumulative death toll of 11,048. Two of these eruptions were classified with a Volcanic Explosivity Index (VEI) of 4. Since 2004, a lava dome has occupied the centre of Awu crater, channelling the fumarolic gas output along the crater wall. A combined Differential Optical Absorption Spectroscopy (DOAS) and Multi-component Gas Analyzer System (Multi-GAS) study highlight a relatively small SO2 flux (13 t/d) sustained by mixed magmatic–hydrothermal emissions made-up of 82 mol.% H2O, 15 mol.% CO2, 2.55 mol.% total S (ST) and 0.02 mol.% H2. The CO2 emission budget, as observed during a short observation period in 2015, corresponds to a daily contribution to the atmosphere of 2600 t/d, representing 1% of the global CO2 emission budget from volcanoes. The gas CO2/ST ratio of 3.7 to 7.9 is at the upper limit of the Indonesian gas range, which is ascribed to (i) some extent of S loss during hydrothermal processing, and perhaps (ii) a C-rich signature of the feeding magmatic gas phase. The source of this high CO2 signature and flux is yet to be fully understood; however, given the peculiar geodynamic context of the region, dominated by the arc-to-arc collision, this may result from either the prolonged heating of the slab and consequent production of carbon-rich fluids, or the recycling of crustal carbon.

Time Variation in the Chemical and Isotopic Composition of Volcanic Gas at Mt. Mihara of Izu-Oshima Island, Japan

Volcanic gas was sampled at three fumaroles and one borehole on Mt. Mihara, Izu-Oshima volcano. The fumarolic gas and the borehole steam possessed an excess enthalpy relative to the air saturated with water vapor. The fumarolic gas located west of the pit crater on Mt. Mihara showed a time variation in chemical and isotopic composition. The cause of the variation seems to be an enhancement of water vapor condensation. No similar variation was observed in the fumarolic gas located east of the pit crater, suggesting the above variation is a phenomena localized around the western fumarole. Hydrogen gas was detected in the sampled gases with low concentration. The change in the H2 concentration synchronized among the three fumaroles, suggesting the H2 gas originated in the hydrothermal system developed beneath Mt. Mihara.

Trace Elements and Minerals in Fumarolic Sulfur: The Case of Ebeko Volcano, Kuriles

Native sulfur deposits on fumarolic fields at Ebeko volcano (Northern Kuriles, Russia) are enriched in chalcophile elements (As-Sb-Se-Te-Hg-Cu) and contain rare heavy metal sulfides (Ag2S, HgS, and CuS), native metal alloys (Au2Pd), and some other low-solubility minerals (CaWO4, BaSO4). Sulfur incrustations are impregnated with numerous particles of fresh and altered andesite groundmass and phenocrysts (pyroxene, magnetite) as well as secondary minerals, such as opal, alunite, and abundant octahedral pyrite crystals. The comparison of elemental abundances in sulfur and unaltered rocks (andesite) demonstrated that rock-forming elements (Ca, K, Fe, Mn, and Ti) and other lithophile and chalcophile elements are mainly transported by fumarolic gas as aerosol particles, whereas semimetals (As, Sb, Se, and Te), halogens (Br and I), and Hg are likely transported as volatile species, even at temperatures slightly above 100°C. The presence of rare sulfides (Ag2S, CuS, and HgS) together with abundant FeS2 in low-temperature fumarolic environments can be explained by the hydrochloric leaching of rock particles followed by the precipitation of low-solubility sulfides induced by the reaction of acid solutions with H2S at ambient temperatures. The elemental composition of native sulfur can be used to qualitatively estimate elemental abundances in low-temperature fumarolic gases.