This study presents a detailed characterization of the temporal evolution of diffuse carbon dioxide (CO2) and hydrogen sulfide (H2S) degassing at the crater lake and peripheral soils of El Chichón volcano (Chiapas, Mx́ico). El Chich’ ́volcano hosts an active hydrothermal system, which is covered by an acidic crater lake. Utilizing the Graphical Statistical Approach (GSA), databases collected between 2013 and 2025 were processed to identify and partition gas flux populations into background groups and anomalies of hydrothermal/magmatic origin. The results reveal a significant shift in the system’s dynamics: while in previous periods (2014-2015) the H2S flux in the high-emission group (Group 2) presented a mean of only 0.226,g m-2 d-1, by January 2025 this value rose drastically to 6.7,g m-2 d-1, now representing 70% of the total data population. In parallel, CO2 exhibited intense degassing pulses with mean values in Group 2 reaching 12,734,g m-2 d-1 in 2021 and stabilizing at 5957,g m-2 d-1 in early 2025. This substantial increase in degassing thresholds and the proportion of anomalous populations suggest enhanced advection of deep fluids or a reduction in the scrubbing capacity of the shallow hydrothermal system. This increase is also reflected in the total degassing fluxes, reaching nearly 900,t d-1of CO2 and approximately 1,t d-1 of H2S, indicating an enhancement in degassing compared to measurements carried out in 2008 and 2013-2021. Additionally, two recent seismic swarms (2021 and since June 2025) coincide with this increase in degassing, pointing to renewed permeability and volatile transfer at the hydrothermal interface. These findings evidence a state of geochemical unrest that underscores the critical need to implement a continuous and automated monitoring system to strengthen volcanic surveillance and risk management in the region.
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