The Dallol Geothermal Area, Northern Afar (Ethiopia)—An Exceptional Planetary Field Analog on Earth

The Dallol volcano and its associated hydrothermal field are located in a remote area of the northern Danakil Depression in Ethiopia. A region only recently appraised after decades of inaccessibility due to severe political instability and the absence of infrastructure. The region is notable for hosting environments at the very edge of natural physical-chemical extremities. It is surrounded by a wide, hyperarid salt plain, and is one of the hottest (ATT: 36-38°C) and most acidic places (< pH 1.0) on Earth. Spectacular geomorphologies and mineral deposits produced by supersaturated hydrothermal waters and brines are the result of complex interactions between active and inactive hydrothermal alteration of the bedrock, sulphuric hot springs and pools, fumaroles and geysers, and recrystallization processes driven by hydrothermal waters, degassing, and rapid evaporation. The study of planetary field analogue environments plays a crucial role for charactering the physical and chemical boundaries in which life can exist on Earth. It is key to the assessment and criteria definition of the conditions of habitability on other planets, including the possibility for biosignature preservation and in situ testing of technologies for life-detection. The Dallol volcano in Ethiopia represents an excellent Mars analogue environment since the active volcanic environment, the associated diffuse hydrothermalism and hydrothermal alterations, the vast acidic-sulphate deposits are reminiscent of past hydrothermal activity on Mars. The work presented in this paper is an overview of the Dallol volcanic area and its hydrothermal field integrating previous literature with observations and results obtained from field surveys and monitoring of the area coupled with sample characterization. In so doing, we highlight its incredible potential as a planetary field analogue environment and as a site for future NASA and ESA astrobiological exploration programs.