Geothermal energy, the cheapest amorlY ttl~ differeDt soutcedrnof power, is thought to provide a solution for the rising demandrnof electricity in Ethiopia, because the Ethiopian Rift Valley andrnAfar area have been identified to have one of the greatest geothermalrnpotential in the world. The Nvl Lake Abaya geothermalrnprovince, situated in the southern part of the Ethiopian Rift Valleyrnnear to its western man'in, is one of the target areas singlE'd outrnfor detailed exploration purposes. The area:i.s characterized byrnhigh heat flo", indicated by the presence of a number of hot-"l'rings.rnfumaroles and a geysE'r.rn'-.-rnThe volcano-tectonic evolution Â·'hich started in early 1110cene,rnhas been in progress throughout Plio-Pleistocene and Quaternaryrnactivity has been evidenced 'in the most active part of the Rift.rn1'he volcanic products, represented by basal ts and rhyolitic products,rnvary from alkaline to mildly alkaline and the recent fissural b'lsalticrnvolcanism sho'ls a transitional nature. The final silicic products', arernrepresented by peralkaline rhyolites, probably commendites.rnThe hydrogeological evidence suggests that quite abundant amountrnof ~ater is recharged from the surrounding highland areas in the northrnand N'I into the reservoir system and that the hot springs are all ofrnmeteoric origin. Important circulation of ~ater at depth is evidencedrnfrom isotopic data.rnThe chemical characteristics of the the,rmal manifestations suggestrnthe presence of two groups of thermal waters 'lith different geochemicalrnhistories. A high temperature reservoir is represented by the firstrngroup while different degrees of mixing and dilution of the original