Geothermal Exploration by Tem-Soundings in the Central Asal Rift in Djibouti, East Africa

Abstract

In 1988 the National Energy Authority of Iceland (NEA) made a resistivity survey in the Asal Rift in Djibouti, East Africa. The survey was a part of a geothermal exploration of the Central Asal Rift. Because of the arid conditions a central loop transient electromagnetic method was applied. The survey revealed a rather complex but clear resistivity structure, which correlates with the geological structure of the area. The level of the highly saline groundwater was mapped with great accuracy. A hydrological barrier that was observed in the active rift zone is most naturally explained by effective self sealing due to mineral deposition at the margins of the geothermal system. The water table, under Lava Lake, is found to be locally above sea level, probably reflecting an upwards convecting plume of geothermal fluids. The resistive basement found in the survey area is locally absent under Lava Lake, most likely due to higher porosity in the geothermal upflow zone.