The volcanic episode of Piton de la Fournaise that is of interest for the present study lasted from the 27 th of April 2018 to the 1 st of June 2018, and GEM depletion was observed on the 29 th of April. The main active vent of the eruption was at coordinates of 21.254°S and 55.700°E, at an elevation of 2229 masl (see red cross in Figure ).