Dome permeability and fluid circulation at La Soufrière de Guadeloupe implied from soil CO2 degassing, thermal flux and self-potential

Abstract

Abstract Quantifying subsurface fluid flows and related heat and gas fluxes can provide essential clues for interpreting the evolution of volcanic unrest in volcanoes with active hydrothermal systems. To better constrain the distribution of current hydrothermal activity, we mapped diffuse soil CO \(_2\) degassing, ground temperature and self-potential covering the summit of La Soufrière de Guadeloupe during 2022-23. From these mappings, we identify areas of fluid recharge and the zones and extent of major ascending hydrothermal flows. We provide a first estimate for ground CO$_2$ flux of \SI{3.76+-0.52}{\tonne\per\day} (\SI{0.044+-0.006}{\kg\per\s}), representing about half the CO$_2$ emissions from the summit fumaroles. We find an extensive area of ground heating of at least \SI{15175+-4200}{\m\squared} in area and a total ground heat flux of \SI{2.29+-0.88}{\MW} to \SI{2.79+-0.98}{\MW}, dominated by a convective flux of \SI{2.00+-0.86}{\MW}. These observations indicate that conduction is not always the primary mode of heat transport in hydrothermal volcanoes, especially in highly-altered settings. The prominent summit fractures exert significant control over hydrothermal fluid circulation and delimit a main active zone in the NE sector. The observed shift in subsurface fluid circulation towards this sector may be attributed to a changing ground permeability and may also be related to observed fault widening and the gravitational sliding of the dome's SW flank. Our results indicate that the state of sealing of the dome may be inferred from the mapping of hydrothermal fluid fluxes and that such mappings may help evaluate potential hazards associated with fluid pressurisation.