Characterization and modeling of the complete volcanic gas phase.

Abstract

During the survey on the eruption of the volcano "La Soufriere de la Guadeloupe" (French West Indies), the behaviour of sulfur in volcanic gases was examined. Matsuo (1962) studied chemical equilibrium in volcanic gases which led us to develop the "in situ" gas analysis. A field gas chromatograph allowed direct injection of hot gases, before water and sulfur condensation occurred. A silica tube equipped with thermocouples was used for sublimates sampling and for measuring the con densation temperature. Conventional condensors and caustic soda bottles were used for sampling and later complementary analyses in the laboratory. A free energy minimisation computational method modelled the physical and chemical changes that occurred during cooling of volcanic gases. The high temperature composition of the .gas mixture was recalculated from the concentrations of the gaseous and solid components obtained during sampling. The equilibrium composition was first calculated at the collection temperature for 22 elements. The model then calculated the equilibrium compositions at 50°C intervals using the residual gas composition after condensation at the previous temperature. The depositional sequence observed in the silica tube depend on the temperature and the concentration of elements in the initial mixture. The computational method was applied to gases sampled from Mt. St Helens. The calculated results agree with observed sublimates. A new method for volcano monitoring is proposed which allow to determine the magmatic origin of volcanic gases and their emission tempera ture from remote plume analysis. The model is also applicable to estimate the temperature and the com position of the gases entering hydrothermal systems or participating in ore deposits in the basement of the volcano. The model predicts the behaviour of the main and minor species emitted in the volcanic gases. This approach is not only restricted to the volcanic gas studies but can be applied to studies of high temperature reactive gas reactor to simulate cooling reactions.

Uptake of gaseous thallium, tellurium, vanadium and molybdenum into anhydrous alum, Lascar volcano fumaroles, Chile

“…Several studies have collected gas sublimates and condensates at the mouth of fumaroles to document the condensation sequence of elements (e.g., Bernard and Le Guern, 1986;Symonds et al, 1987;Taran et al, 2001). In agreement with thermochemical data, they showed that semi-volatile elements (Cd, Pb, Bi, Cu, Zn) condense over a wide temperature range, from 800 to less than 400°C, depending on gas composition and oxidation state (e.g., Symonds et al, 1987;Le Guern et al, 1993;Churakov et al, 2000). Fewer studies noted that fumarolic incrustations are also enriched in some volatile metals (e.g.…”

“…The other fraction is trapped within the volcanic edifices, due to the dissolution of magmatic gases into groundwater (Doukas and Gerlach, 1995) and/or hydrothermal system (Symonds et al, 1992), formation of secondary sulphate minerals during gas-rock reactions (Zimbelman et al, 2005), condensation of sulpho-salt melts during gas expansion in fractures (Henley and Berger, 2013) and precipitation of gas sublimates at fumaroles vents as gas cools and mixes with air (Bunsen 1851;Stoiber and Rose, 1974). The extent of element uptake in the ground has implications for volcano monitoring (Symonds et al, 2001;Le Guern et al, 1993), and also controls the global versus local environmental impact of magmatic gases, especially regarding toxic heavy metals.…”

Noble gas isotopes in hydrothermal volcanic fluids of La Soufrière volcano, Guadeloupe, Lesser Antilles arc

“…A condenser was connected to the tube to remove water. Before introducing the gas we flushed the system several times (LeGuern et al, 1993). In April 2007 gas was collected using a glass-bottle; analyses were conducted two weeks after the sampling to avoid helium diffusion.…”