Active volcanoes emit high temperature gases that modify the chemical composition of the Earth’s atmosphere. It is crucial to be able to quantify the contribution of volcanogenic gases to the atmosphere so that the global atmospheric effects of a major eruption can be predicted and so that volcanogenic effects can be discriminated from anthropogenic emissions. At the scale of one volcano, monitoring of gas plumes is a major tool in volcanic risk management. Volcanologists have long measured gas composition and fluxes between and during eruptions and often noted a decoupling between degassing flux and magmatic flux. In parallel, experimental petrologists are now able to calculate the gas composition that is in equilibrium with the magma at depth. However, when the calculated gas composition is compared to that measured at the surface, a general disagreement arises. As a result, it is currently impossible to determine whether a plume is generated in response to passive degassing or to magma ascent. This is a serious drawback as these processes have opposite implications for volcanic activity. Such difficulties are mainly due to the fact that the interplay between degassing mechanisms and gas chemistry has not been addressed. To improve the application of volcanic gas analyses to understanding global geochemical budgets and for the mitigation of volcanic risk, we propose to link deep magmatic processes and surface emissions. Our objective is to model the quantity and composition of volcanic gases as a function of the petrology of the magma at depth and the eruptive regime, and compare those calculations with new measures of plumes at active volcanoes. We will achieve this by modeling the chemical kinetics of degassing in volcanic conduits by using a combination of experimental, field, and numerical approaches. We anticipate building a tool linking flux and composition of gases to eruptive regime, thus opening the door to inverse modeling of volcanic gas observations.
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