Evolution of gas content with time for the fumaroles of Site 4 within the Asal–Ghoubbet rift. Orange points 21/11/2019; blue points 12/08/2020; gray points 13/08/2020. (a) H₂ (ppm) in situ as a function of time. (b) CO₂ (%) in situ as a function of time. (c) Balance/O2 as a function of time for air variation in the analysis. (d) Diurnal variation in H₂, after correction. (e) Diurnal variation in CO₂, after correction. (f) Corrected H₂ as a function of corrected CO₂ (Pasquet et al., 2021).