Hydrothermal fluid circulation at La Soufrire de Guadeloupe inferred from soil CO2 degassing, thermal flux, and self-potential

Quantifying subsurface fluid circulation and the associated heat and gas fluxes provides crucial clues for interpreting the evolution of volcanic unrest in volcanoes with active hydrothermal systems. To better constrain the distribution of current hydrothermal activity on La Soufrire de Guadeloupe, we conducted repeated mapping of diffuse ground CO2 degassing, ground temperature, and self-potential on the dome summit in 2022-2023. We produced maps by interpolating these data, which allowed us to identify areas of fluid recharge into the hydrothermal system and the areas of ascending hydrothermal flows. We were also able to quantify the convective and conductive ground heat fluxes and the area affected by ground heating. Our measurements allowed us, for the first time, to quantify the ground CO2 flux of the dome, estimate the condensation depth of ascending fluids, and relate it to soil permeability. We found diffuse ground CO2 degassing corresponds to about half of the CO2 emissions from the summit fumaroles. Further, we performed continuous self-potential measurements at the summit to analyse the temporal variability of underground fluid fluxes. The combination of these measurements and comparison with high-resolution thermal images taken in recent years allows us to track the spatial and temporal evolution of the shallow hydrothermal fluid circulation. Moreover, we were able to constrain the controlling factors of the observed changes in the surface manifestations in the NE sector of the summit, where a fumarole field has been developing since 2012. Our results imply that monitoring soil degassing and ground temperature gradients can enhance understanding of the sealing state of the dome, which is crucial for assessing potential hazards linked to fluid pressurisation.