Vuataz, François

2003, Wilhelm, Jules, Bianchetti, Gabriele, Vuataz, François

1993, Bianchetti, Gabriele, Zuber, Frédéric, Vuataz, François, Rouiller, Jean-Daniel

1997, Bianchetti, Gabriele, Vuataz, François

1993, Vuataz, François, Rouiller, Jean-Daniel, Dubois, Jean-Daniel, Bianchetti, Gabriele, Besson, Olivier

1993, Pahud, Daniel, Vuataz, François, Bianchetti, Gabriele

1992, Bianchetti, Gabriele, Roth, Philippe, Vuataz, François, Vergain, Jean

The recent occurence (end of 1953) of the thermal springs of Val d'Illiez, Wallis, is linked to exceptional events. During this year indeed, numerous seismic events were felt by the local population. These springs, located on the left bank of the Vieze River, outflow from Tertiary flysch of the Helvetic domain. Since 1988, all thermal and subthermal waters of the study area were measured, sampled and analyzed systematically. Their temperatures reach a maximum of 30-degrees-C and the total discharge of the various exsurgences amounts to 1200 l/mn. The water chemistry of Ca-SO4 type with total dissolved solids of 1850 mg/l is characterized by a low content of alkalis and chlorides. The thermal springs temperature and discharge are varying with time and the warm fluids are mixed during their ascent by a cold and dilute groundwater, problably originating from a karstic aquifer in the Malm. The calcium and sulphate come from the dissolution of gypsum and anhydrite present in the Triassic cellular dolomite of the autochthonous cover of the Aiguilles Rouges Massif. The authors present an hypothesis based on the interpretation of hydrogeological, geological, seismic and isotopic data, which suggests a link between these thermal springs and major water losses (> 1 m3/s) at the artificial lake of Salanfe, located 9 km south-east of the spring discharge zone. This hypothesis is supported by several observations: 1) The water losses of the lake of Salanfe do not converge to existing cold springs of the region, as shown by tracer tests carried out during the mid 1950's. This tends to reinforce the hypothesis that the water losses percolate to a deep confined aquifer; 2) The presence in the Salanfe cirque of autochthonous Triassic outcrops from the Helvetic domain, dipping towards the Val d'Illiez area: these layers are responsible for the major water losses of the lake and it is thought that the water flows in the same direction; 3) The abnormally high seismicity recorded in the Val d'Illiez in 1953 at the end of the complete initial filling of the reservoir and the occurence of the thermal springs seem to be contemporaneous; 4) The elevation of the lake catchment basin corresponds to the elevation of the thermal water catchment area, based on stable isotope data; Chemical geothermometers calculations applied to the thermal springs analyses do not indicate a temperature at depth over 35-degrees-C. Nevertheless, due to their yield (1200 l/min) and emergence temperature (30-degrees-C), the geothermal potential of the springs readily available for an integrated exploitation of water and heat of at least 1.7 MW, and should not be neglected.