COMPILED BY HAFTU GEBREZGABIHER
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 and most acidic natural systems 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, sulfuric hot springs and pools, fumaroles and geysers, and recrystallization processes driven by hydrothermal waters, degassing, and rapid evaporation.
The Danakil Depression is located in the northern Afar Region of Ethiopia near the borders of Eritrea and Djibouti. The famous British explorer Wilfred Thesiger described the place as “a land of death”, which is a perfectly apt description for any outsider entering the region.
This description not only applies to humans settled in the locality due to the high average temperatures but also to the very harsh conditions faced by the microbial life inhabiting the ecosystems of the area.
The very extreme physicochemical parameters make this site a polyextremophilic environment with the potential to harbor, among others, acidophilic, thermophilic, and/or halophilic microorganisms and metabolic networks.
The physical and compositional features of the Dallol deposits, their mineralogies, sedimentary and alteration features, and their location in a region of basaltic volcanism of planetary-scale importance, are testament to the novelty of this extreme environment and its ability to host life-forms and to preserve biosignatures.
It is therefore also a reliable analog to ancient martian environments and habitats. Deep investigation of the characteristics of this unique geological site will improve our understanding of the limits of life on Earth and inform the search for life on the Red Planet.
Extensive spring deposits associated with salt precipitation have also been noted in the martian terrane of Arabia Terra, where their morphological expression comprises spring deposits and salt flats in craters and on plateau similar to those found in the Dallol area.
The geological similarities between the Dallol area and various potential hydrothermal systems on Mars indicate that this unique region presents an excellent planetary field analog for astrobiology.
The study of planetary field analog environments plays a crucial role in characterizing the physical and chemical boundaries within which life can exist on Earth and other planets. It is essential for the definition and assessment 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 area represents an excellent Mars analog environment given that the active volcanic environment, the associated diffuse hydrothermalism and hydrothermal alteration, and the vast acidic sulfate 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 that integrates previous literature with observations and results obtained from field surveys and monitoring coupled with sample characterization.
In so doing, we highlight its exceptional potential as a planetary field analog as well as a site for future astrobiological and exploration programs.
Dallol geothermal area is part of the Danakil Depression, which straddles the Ethiopia–Eritrea border, between the Ethiopian Plateau and the Danakil microplate (also called Danakil Alps or Mountains) in the northern part of the Afar Depression.
The Afar Depression is an incipient seafloor-spreading center located at the triple junction between the Nubian, Somali, and Arabian plates, atop the developing Danakil microplate that is generating the continental breakup of Africa. Here, the E-W ocean ridge spreading of the Gulf of Aden through Djibouti meets the axes of the Ethiopian Rift and the Red Sea.
Danakil Depression in the northern tectono-magmatic domains of the Afar Depression is a well-defined tectonic feature bordered both to the west and to the east by major faults and dissected escarpments.The attenuated continental crust has a thickness of <15 km with shallow (3–5 km deep) magma chambers beneath its axial.
The main volcano-tectonic features of these magmatic segments are intermittent NNW-SSE axial volcanic edifices and fissure basalts, open extensional fractures and vertical step faulting. The volcanic activity in this region has been intense since the Pliocene but is today mostly restricted to the axial zone with the spectacular shield and stratovolcanoes of the Erta’Ale Range (in the Afar language, ’Ale means mount), which include Ale Bagu, Erta’Ale, Borale’Ale, Dalafilla Alu, and other small volcanic and fumarolic centers. Of the volcanic edifices that constitute the Erta’Ale Range, the Gada’Ale shield volcano and its surrounding fissural eruptions are part of the Dallol area.
To the western border of the Danakil Depression is bounded by the Ethiopian Escarpment or Highland (the highest peaks standing well above 3,500 m above sea level which includes prominent marginal grabens, such as the Maglala-Renda and Dergaha-Sheket grabens, the fill deposits of which accommodate a drop in elevation of up to 3000 m to the ridgeline of the escarpment and less than 1000 m to the marginal areas up to 100–150 m b.s.l. at the floor of the Danakil Depression. The western border has a more distinct rift architecture and morphology than the eastern border, which comprises the Danakil Alps.
To the north, the low volcano-tectonic barriers (including the Jalua and Alid stratovolcanoes, 713 and 904 m a.s.l., respectively) south of the Gulf of Zula and the city of Mersa Fatma protect the Danakil and Afar Depression from marine flooding; and to the south, the Danakil Depression hosts about 100 km long, axial volcanic Erta’Ale Range where the Ale Bagu stratovolcano rises up to 1031 m a.s.l. and Erta’Ale (“smoking mountain” in the Afar language) features a spectacular permanent lava lake.
The age of the Dallol dome is postdated by the age of the thick evaporite deposit of the Assale salt plain, whereas the hydrothermalism of the area (Dallol Hot Springs, Black Pool and Gaet’ale Lake) was possibly generated by a phreatic explosion in 1926. Since then, explosive volcanic episodes, perpetual and ephemeral hydrothermal venting, small geysers and pools, and several seismic events have been reported in the area.
The ellipsoidal Dallol dome features an approximately 1 km main crater atop a wide dome of approximately 5 km E-W diameter, located ca. 80 km NNW from the axially aligned active volcanoes of the Erta’Ale Range. It consists of bedded anhydrite and halite with an elevation of about 45–50 m above the Assale salt plain.
Hydrothermal activity is fueled by water heated and enriched in gases by a shallow magma reservoir that lies primarily beneath the volcano. Field observations permit the recognition of at least three main sites within the Dallol hydrothermal system, each with distinct vent characteristics: the Dallol Hot Springs, the Gaet’ale Lake, and the Black Pool.
Sources: Astrobiology, 2019
The Ethiopian Herald February 26/2021
