The Dallol Geothermal Area Northern Afar, Ethiopia. Surface Geology and Fluid Chemistry

Abstract

This paper deals with surface geological and geochemical exploration of the Dallol geothermal area in the Danakil depression in northern Ethiopia. The 60 m high Dallol Mountain is an updomed salt structure with a subsidence crater on top, the latter formed by the escape of geothermal brine from below. Geothermal manifestations are largely confined to the subsidence crater in the central part of the mountain and around the Black mountain southwest of Dallol. The manifestations consist of pillar formations, ponding of acid geothermal fluids, circular or semi-circular disintegrated areas of steam and gas emissions and gas explosion craters. The aerial extent of the surface manifestations in Dallol is about 1,2 km2. A deeper, more extensive geothermal system is proposed to be around 10 km2. Geochemical and isotopic data of the surface fluids suggest two different water systems; meteoric ultrasaline surface waters and geothermal aquifer fluid at depth, which may have a magmatic component. Gas geothermometers suggest temperature of 280-290°C at depth.