REMARKABLE OSCILLATIONS OF TEMPERATURE, H UMIDITY AND ELECTRIC-POTENTIAL OBSERVED IN AN UNDERGROUND QUARRY

Intriguing quasi-sinusoidal variations of electric potential have been measured at the surface and inside the pillars of a limestone undergr ound quarry, the period of which is of the order of a minute, and the amplitude a few millivolts. Similar variations of the temperature of t he air in the gallery-with an amplitude of a few hundredths of a degre e-and of its humidity are also observed. All these signals present tra ins of oscillations over which the period and amplitude are often rema rkably constant; the period changes rather suddently from one train to another. We interpret these signals as due to the reaction of the sys tem gallery-embedding rock (this embedding is made of highly porous an d saturated rock) so thermal perturbations through a flux of water suc cessively outwards and inwards and evaporation and condensation at the surface of the wall. in conclusion we emphasize the extent to which e lectric measurements are suitable for detecting and studying fluid flo ws in natural porous media.