Two diffuse soil CO2 flux surveys from the southern Lakki plain show that CO2 is mainly released from the hydrothermal explosion craters. The correspondence between high CO2 fluxes and elevated soil temperatures suggests that a flux of hot hydrothermal fluids ascends towards the surface. Steam mostly condenses near the surface and the heat given off is conductively transferred to the atmosphere through the soil, accompanied by a large CO2 flux. It was calculated, that 68 t d-1 of hydrothermal CO2 are released through the total surveyed area of -1.3 km2. Admitting that a steam flux of 2200 t d-1 accompanies this CO2 flux, the thermal energy released through steam condensation amounts to 58 MW. ¿ 2001 American Geophysical Union