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    Evaluation of results from Second and Third IAVCEI Field Workshops on Volcanic Gases, Mt Usu, Japan, and White Island, New Zealand
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    We analyzed gas samples collected from fumaroles and bubbling pools at Irruputuncu, Putana, Olca and Alitar volcanoes located in the central Andes volcanic zone (northern Chile). The Irruputuncu and Putana fumarolic discharges showed outlet temperatures ranging from 83 ˚C to 240 ˚C and from 82 ˚C to 88 ˚C, respectively. The chemical and isotopic (3He/4He, d13C-CO2, d18O-H2O and dD-H2O) compositions of these discharges were similar to medium-to-high temperature volcanic gases from other active volcanoes in this sector of the Andean volcanic chain (e.g. Lascar volcano). Inorganic and organic gas geothermometers for the H2O-CO2-CO-H2, CO2-CH4 and C2-C3 alkenes-alkanes systems indicated equilibrium temperatures that exceed 500 ˚C at the gas sources. These relatively high temperatures are in agreement with the presence of relevantly high concentrations of magmatic gas emissions, including SO2. Olca and Alitar volcano fluid chemistries indicated lower amounts of magmatic-derived gas species, while both the helium and the water isotopic compositions suggested significant fractions of shallow, crustal/meteoric-originated fluids. These indicate contributions from a hydrothermal environment with temperatures <400 ˚C. The geochemical and isotopic features derived from the present study show that the Irruputuncu, Putana, Olca and Alitar volcanoes should be considered as active and thus warrant periodic geochemical monitoring to determine the evolution of these systems and their potential hazards.
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    We investigated the gas geochemistry of fumaroles close to the Voragine crater of Mt Etna that have a temperature of 90–95°C, are CO 2 ‐dominated, and have an air content as low as <1%. This is the first report of the monitoring of such air‐free fumaroles at the Etnean crater area—previous studies indicated an air contribution of 70% or more. The helium and carbon isotopes (Rc/Ra = 6.5 ± 0.4, δ 13 C CO2 = −1.7 ± 0.5‰) suggest that the released gas is directly related to the magmatic degassing. The fumaroles were sampled 12 times between June 2007 and June 2008, which revealed an increase in Rc/Ra from 6.1 to 6.9 that can be related to the increasing volcanic activity at the summit area of Mt Etna. These fumaroles offer a new tool for detecting magmatic processes (magma ascent, refilling, degassing, etc.), and will be useful for volcano surveillance.
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    Abstract There have been substantial advances in the ability to monitor the activity of hazardous volcanoes in recent decades. However, obtaining early warning of eruptions remains challenging, because the patterns and consequences of volcanic unrests are both complex and nonlinear. Measuring volcanic gases has long been a key aspect of volcano monitoring since these mobile fluids should reach the surface long before the magma. There has been considerable progress in methods for remote and in-situ gas sensing, but measuring the flux of volcanic CO 2 —the most reliable gas precursor to an eruption—has remained a challenge. Here we report on the first direct quantitative measurements of the volcanic CO 2 flux using a newly designed differential absorption lidar (DIAL), which were performed at the restless Campi Flegrei volcano. We show that DIAL makes it possible to remotely obtain volcanic CO 2 flux time series with a high temporal resolution (tens of minutes) and accuracy (<30%). The ability of this lidar to remotely sense volcanic CO 2 represents a major step forward in volcano monitoring and will contribute improved volcanic CO 2 flux inventories. Our results also demonstrate the unusually strong degassing behavior of Campi Flegrei fumaroles in the current ongoing state of unrest.
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    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.
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