Water and fire coexist under volcanoes to generate "hydrothermal" systems: complex "steam engines" producing white smoke called "fumaroles" that is sometimes observed at the surface. Scientists have just demonstrated why these reservoirs are not always found under the volcanic peaks. For certain structures such as the Ticsani and Ubinas in Peru, where the volcanologists conducted their study, resurgences occur more than 10 km from the top of the dome. Their numerical model shows that the position of the hydrothermal systems depends on regional topography, which may significantly deviate subsurface flows....