Hydrothermal activity of the Lake Abhe geothermal field (Djibouti): Structural controls and implications for geothermal exploration

This study investigates the structurally-controlled fluid flow of the Lake Abhe Geothermal Field (LAGF), using multiscale structural lineament distribution mapping and field observations. The LAGF lies within the Gob Aad graben in the Afar depression, at the junction of three rifts, along the Djibouti-Ethiopia border. Numerous hydrothermal surface manifestations on the lake’s eastern shore, including steam vents, hot springs and carbonate chimney structures, reflect the geothermal activity of this area. Structural features of the LAGF area are dominated by ESE-extensional faults that form a series of narrow elongated horst, graben and half-graben structures. Fault interaction and accommodation zones, such as fault intersections and relay ramps, as well as possible breaching faults are also identified in the area. The control of the main ESE-structural direction over the distribution of hydrothermal chimneys and hot springs indicates these faults to be the primary permeability fluid pathways of the LAGF. Signs of enhanced hydrothermal activity at fault intersections further suggest that structural intersections locally increase fracture-related permeability. Field observations combined with satellite image analysis also reveal a lateral migration of the hydrothermal outflows over a short period of time (during the past several thousands to tens of thousands of years) from the SE to the NW. Finally, this study discusses the potential role of N-striking faults, which may either act as vertical drains channeling fluids from south to north or as barriers preventing eastward fluid migration. Overall, this study provides new insights into the tectonically driven fluid flow dynamics of the LAGF, which may support further exploration of this remarkable site and promote its geothermal development.