Geothermal Systems Along the East-African Rift

Abstract

Crustal deformation of the African Plate and in f d hot spot activity (Upper Mantle) have produced anomalously hot, upper crustal rocks and local intrusions beneath the c. 2000 km rift. Geothermal and volcanic activity is moderately intense; 30 major hydrothermal systems with significant natural heat discharge have been found (5 of these have been explored by drilling), 14 volcanic centres have heen active during the past 2000 yr, and 10 centres are probably volcanic-hydrothermal systems. There are c. 50% more geothermal systems per unit length in the Ethiopian than in the Kenyan Rift. The arid to semi-arid climate of the rift favours the development of two types of hydrothermal systems, namely steaming ground and advective. Steaming ground systems are associated with older volcanic dome complexes where heat transfers at shallow levels dominantly by steam. In advective systems, beat is swept from hot rocks within the rift by deeply penetrating groundwater and the heat transfers to the surface by hot water only. Leaching of saline sediments may lead to the development of thermal brine lakes.