Geothermal energy, the cheapest amorlY ttl~ differeDt soutced of power, is thought to provide a solution for the rising demand of electricity in Ethiopia, because the Ethiopian Rift Valley and Afar area have been identified to have one of the greatest geothermal potential in the world. The Nvl Lake Abaya geothermal province, situated in the southern part of the Ethiopian Rift Valley near to its western man'in, is one of the target areas singlE'd out for detailed exploration purposes. The area:i.s characterized by high heat flo", indicated by the presence of a number of hot-"l'rings. fumaroles and a geysE'r. '-.- The volcano-tectonic evolution \·'hich started in early 1110cene, has been in progress throughout Plio-Pleistocene and Quaternary activity has been evidenced 'in the most active part of the Rift. 1'he volcanic products, represented by basal ts and rhyolitic products, vary from alkaline to mildly alkaline and the recent fissural b'lsaltic volcanism sho\'ls a transitional nature. The final silicic products', are represented by peralkaline rhyolites, probably commendites. The hydrogeological evidence suggests that quite abundant amount of \~ater is recharged from the surrounding highland areas in the north and N\'I into the reservoir system and that the hot springs are all of meteoric origin. Important circulation of \~ater at depth is evidenced from isotopic data. The chemical characteristics of the the,rmal manifestations suggest the presence of two groups of thermal waters \'lith different geochemical histories. A high temperature reservoir is represented by the first group while different degrees of mixing and dilution of the original