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    Emission rates of sulfur dioxide and carbon dioxide from Redoubt Volcano, Alaska during the 1989–1990 eruptions
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    Soufriere Hills fumaroles contained magma‐derived volatiles before and during the eruption initiated in 1995 but also preserved a typical and quite steady hydrothermal composition. Chemical changes due to increased boiling and a greater input of oxidizing magmatic gas occurred only at Galway's Soufriere, the most active fumarolic field. Hydrothermal buffering of the fumaroles has been favoured by their remote location (1–2 km) from the eruptive vents and by a preferential degassing of the uprising magma through intrusive conduits under the crater. High temperature (720°C) gas collected from the extruding lava dome in Feb. 1996 was chemically and isotopically representative of the magmatic gas stream. Its composition allows assessment of average eruptive fluxes of H 2 O, CO 2 and HCl which require the degassing of only 2.5–3 times more magma than erupted.
    Fumarole
    Lava dome
    Volcanic Gases
    Phreatic eruption
    Dome (geology)
    Magma chamber
    Citations (70)
    Volcanic plumes, discharging from craters or fumaroles, are usually observed at active volcanoes. These plumes are divided into two categories from their appearance; one is a transparent invisible plume, composed of volcanic gases, and the other is a white, visible plume, containing water droplets in addition to the vapors. The difference in plume visibility is caused by changes in the conditions that control water condensation in the plume. We present a simple model describing the condition for the water condensation in the plume as a function of the exit temperature, volcanic gas composition, atmospheric temperature and humidity, and tested the model with a field observation. The result indicates that we can estimate the exit temperature from the visibility of the plume under known atmospheric conditions.
    Fumarole
    Panache
    Volcanic Gases
    Visibility
    Citations (17)
    The ratio between fumarole gas species of predominant magmatic origin (i.e., CO2, He) and CH4, which is typically produced in the hydrothermal environment, is a powerful indicator of the upflow of magmatic fluids towards the surface. The analysis of time series of fumarolic composition from different dormant volcanoes (e.g., Campi Flegrei, Vesuvius, Vulcano, Panarea, Nisyros, Mammoth Mt) reveals similar anomalous peaks of the CO2/H2O, CO2/CH4, and He/CH4 ratio during unrests, suggesting recurrent events of magma degassing. The sudden upflow of deep magmatic fluids causes pressure buildup and heating of the hydrothermal systems, earthquakes and ground deformations, which precede the fumarole gas compositional anomalies. These anomalies, once normalized to the time and to the amplitude of the curve, show the same shape: a rapid increase in the geochemical indicator followed by an exponential decrease.An intriguing consideration based on these examples (almost all the volcanoes for which a long time series of fumarolic compositions are available) is that episodes of magma degassing probably reflect the normal background activity of volcanoes, making the interpretation of volcanic unrests challenging. Concurrently with magma degassing events, a significant increase in the CO2 degassing process was either measured or qualitatively observed in these systems. A better knowledge of these degassing episodes is needed to improve our understanding of the volcanic behavior and to better constrain the release of CO2 from quiescent volcanoes.  
    Fumarole
    Magma chamber