GEOPHYSICAL, GEOLOGICAL AND HYDROGEOLOGICAL INVESTIGATIONS OF BOKU THERMAL FIELD, NAZARETH, ETHIOPIA

Abstract

This paper presents the results of a multidisciplinary research program involving geological, hydrogeological and geophysical surveys carried out over the Boku fumaroles, Nazareth (Rift floor of the Main Ethiopian Rift).
The results show that the Boku thermal field is a vapor-dominated, dry type geothermal system tapping the deep-seated heat reservoirs of the shallow acidic volcanic center of Quaternary volcanics of the Rift floor.
The cap rock is formed by the self-sealing process through hydrothermal alterations of the major rock units in the area as witnessed by the surface manifestations of calcite, silica and extensive kaolinization that are suggestive of such an environment.
The aquifer system consists of the Quaternary fractured Rift floor ignimbrites. The necessary supply for the replenishment of the reservoirs is derived from the closed basin system of the Nazareth watershed and/or from the large open irrigated grounds of the Wonji state farm. The investigations have clearly mapped the Quaternary Fault Systems that are the major tectonic structures for the propagation of the deep-seated superheated vapor to the surface, and the recharging of the geothermal reservoir.