par Mazot, Agnès ;Bernard, Alain
Référence Volcanic Lakes, Springer Berlin Heidelberg, page (341-354)
Publication Publié, 2015-01
Partie d'ouvrage collectif
Résumé : Measurements of CO2 flux emitted at the surface of volcanic lakes have been performed using the so-called floating accumulation chamber method. Two statistical methods are used to process data: the graphical statistical and stochastic simulation methods. The results of graphical statistical approach allow the quantification of two degassing processes acting at the lake surface: one corresponding to CO2 fluxes resulting from rising bubbles and the second corresponding to equilibrium diffusion of dissolved CO2 at the water-air surface. The sequential Gaussian simulation method has been used for mapping the CO2 flux and estimating the total CO2 emission rate at the surface of volcanic lakes. The study of two volcanic lakes is presented in this chapter: Kelud, Indonesia and El Chichón, Mexico. Before a lava dome appeared in the middle of Kelud Lake on the 4th November 2007, the lake contained near neutral waters with a pH of 6. The total CO2 emission rate estimated by stochastic simulation ranged from 105 t day−1 for 2001 to 35 t day−1 for 2006. In early July 2007, the total flux for the lake area was estimated at 307 t day−1, showing that CO2 flux monitoring at the surface of volcanic lakes is a powerful tool in the improvement of early warning systems of volcanic eruptions. A significant change in CO2 flux was not detected for El Chichón lake during the period of survey (2007-2008) but the mapping of the CO2 flux on the lake area highlighted lineaments reflecting structures controlled by the main local and regional tectonic patterns.