Modification of fumarolic gases by the ice-covered edifice of Erebus volcano, Antarctica

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.

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Geochemical evidence of volcanic plumbing system processes from fumarolic gases and diffuse CO2 degassing of Taal volcano, Philippines, prior to the January 2020 eruption

10.5194/egusphere-egu21-15073 ◽

2021 ◽

Author(s):

Pedro A. Hernández ◽

Gladys Melian ◽

María Asensio-Ramos ◽

Eleazar Padron ◽

Hirochicka Sumino ◽

...

Keyword(s):

Hydrothermal System ◽

Temporal Variations ◽

Average Value ◽

Taal Volcano ◽

Magmatic Intrusion ◽

Volcanic Plumbing System ◽

Wide Range ◽

Fumarolic Gases ◽

Co2 Degassing ◽

Increasing Trends

Significant temporal variations in the chemical and isotopic composition of Taal fumarolic gas as well as in diffuse CO2 emission from Taal Main Crater Lake (TMLC) have been observed across the ~12 years of geochemical monitoring (Arpa et al., 2013; Hern&#225;ndez et a., 2017), with significant high CO2 degassing rates, typical of plume degassing volcanoes, measured in 2011 and 2017. In addition to these CO2 surveys at the TCML, soil CO2 efflux continuous monitoring was implemented at Taal volcano since 2016 and a clear increasing trend of the soil CO2 efflux in 2017 was also observed. Increasing trends on the fumarolic CO2/St, He/CO2, CO/CO2 and CO2/CH4 ratios were recorded during the period 2010-2011 whereas increasing SO2/H2S, H2/CO2 ratios were recorded during the period 2017-2018. A decreasing on the CO2/CH4 and CO2/St ratios was observed for 2017-2018. These changes are attributed to an increased contribution of magmatic fluids to the hydrothermal system in both periods. Observed changes in H2 and CO contents suggest increases in temperature and pressure in the upper parts of the hydrothermal system of Taal volcano. The 3He/4He ratios corrected (Rc/Ra), and &#948;13C of fumarolic gases also increased during the periods 2010-2011 and 2017-2018 before the eruption onset. During this study, diffuse CO2 emission values measured at TMCL showed a wide range of values from >0.5&#8201;g&#8201;m&#8722;2 d&#8722;1 up to 84,902 g&#8201;m&#8722;2 d&#8722;1. The observed relatively high and anomalous diffuse CO2 emission rate across the ~12 years reached values of 4,670 &#177; 159 t d-1 on March 24, 2011, and 3,858 &#177; 584 t d-1 on November 11, 2017. The average value of the soil CO2 efflux data measured by the geochemical station showed oscillations around background values until 14 March, 2017. Since then at 22:00 hours, a sharp increase of soil CO2 efflux from ~0.1 up to 1.1 kg m-2 d-1 was measured in 9 hours and continued to show a sustained increase in time up to 2.9 kg m-2 d-1 in 2 November, that represents the main long-term variation of the soil CO2 emission time series. All the above variations might be produced by two episodes of magmatic intrusion which favored degassing of a gas-rich magma at depth. During the 2010-2011 the magmatic intrusion of volatile-rich magma might have occurred from the mid-crustal storage region at shallower depths producing important changes in pressure and temperature conditions, whereas a new injection of more degassed magma into the deepest zone of the hydrothermal system occurring in 2017-2018 might have favored the accumulation of gases in the subsurface, promoting conditions leading to a phreatic eruption. These geochemical observations are most simply explained by magma recharge to the system, and represent the earliest warning precursor signals to the January 2020 eruptive activity.Arpa, M.C., et al., 2013. Bull. Volcanol. 75, 747. https://doi.org/10.1007/s00445-013-0747-9.Hern&#225;ndez, P.A., et al.,&#160; 2017. Geol. Soc. Lond. Spec. Publ. 437:131&#8211;152. https://doi.org/10.1144/SP437.17.

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