A number of electric and magnetic signals have been observed on La Fournaise volcano, which are attributed to electrokinetic effects induced by the heavy rains which fall in this area. A general modeling of the flow in the unsaturated and saturated zones is proposed for an arbitrary topography, arbitrary spatial distributions of physical properties, and arbitrary rains. This flow generates an electrical field and an associated current which itself induces a variable magnetic field. Variations of water masses inside the volcano are also determined to predict gravity variations. Saturation, electric, magnetic, and gravity fields are given and discussed for various rain distributions including real ones.