| Abstract |
The Afar triangle has been shown to be the surface expression of the Afro-Arabian plate boundary, having the surface expression of most of the characteristics of a mid-oceanic rift system (Barberi & Varet, 1977). Most of the heat is dissipated at the surface along these major geodynamic features and Afar, like Iceland, therefore represents an exceptional geothermal energy potential. Afar was therefore described as “the future Gulf region for geothermal energy” (Varet, 2006). Many sites have been shown to be of potential geothermal interest on the basis of geological criteria: the presence of a volcanic “axial range” (oceanic-type rift segment) combined with transverse fractures (the surface expression of transform faults) provides both a heat source and a fractured reservoir. In addition, central stratovolcanoes on the Afar Margins also develop favorable conditions similar to those prevailing in the rift valley. Compared to Iceland, Afar suffers from a major handicap: the composition of the geothermal fluids in geothermal reservoir fed by meteoric water. Since there is much less rainfall in Afar (annual rainfall there being one of the world's lowest), and as a former branch of the Red Sea evaporated in Northern Afar in the Pleistocene, brines predominate over fresh meteoritic water both at and below the surface (Kebede et al. 2008), notably in northern and eastern Afar (where open faults allow the sea to penetrate the depression). The noticeable exception in the Awash valley fed by the river itself and its many tributaries descending from the Ethiopian plateau should be underlined. A new approach is proposed that takes into consideration the hydrological basins feeding the potential geothermal sites, as well as new hydrogeological considerations. This enables us to take a new look at potentially favorable geothermal sites. The Dallol, Boina, Manda-Hararo and Asal-Ghoubet geothermal sites are particularly discussed. The technical-economic challenge posed by how geothermal energy might satisfy local needs and aid in the development of this sparsely populated, essentially pastoral region is also addressed. |