Drilling into the Danakil Depression to witness the birth of a future ocean

Deep beneath the salt pans of Ethiopia’s Danakil Depression, one of the most hostile landscapes on Earth, an international team of scientists is preparing to drill more than two kilometres into the crust of a continent that is actively tearing itself apart. The Afar Dallol Drilling project, known as ADD-ON, took a decisive step forward in August 2023 when sixty-four researchers from ten countries gathered in Addis Ababa for a workshop sponsored by the International Continental Scientific Drilling Program. Their goal is nothing less than to recover the first complete sedimentary archive from the heart of an active rift basin, a place where the final stages of continental breakup can be observed on land and where a future ocean may one day flood the desert floor.

The Afar Triangle occupies a singular position in the Earth sciences. Sitting at the junction of the Nubian, Arabian, and Somalian plates, it forms the meeting point of the Red Sea Rift, the Gulf of Aden Rift, and the Main Ethiopian Rift. Since the era of continental drift theory, the region has served as the archetypal natural laboratory where the transition from continental rifting to seafloor spreading can be studied subaerially. The Danakil Depression, the northern portion of the Afar Depression, is bounded by the western Ethiopian Plateau and the Danakil Horst, a block of continental crust rotating away from the rift axis. Rifting began in the Oligocene, and extension has localized in the depression since Middle to Late Miocene times as the Danakil Block, also described as the Arrata Microplate, rotated eastward.

Kinematic modelling supported by geological and geophysical observations suggests that the Danakil Depression has formed in faulted, stretched, and thinned continental crust that has been heavily modified by intrusions of mafic magma and the flow of volatiles. Combined with thick, young syn-rift evaporites and basaltic lava flows in a near-sea-level basin, this makes the region one of the few modern analogues for the development of a classic magma-rich rifted margin, the kind of structure that flanks much of the world’s oceans. Accelerated subsidence along the central axis of the depression over at least the past 120,000 years has preserved an exceptional stratigraphic record. Repeated cycles of marine flooding, during which the Red Sea transgressed into the basin, deposited kilometre-thick successions of halite interlayered with gypsum, anhydrite, and economically significant potash-bearing minerals, making the Danakil Depression one of the youngest salt giants on the planet.

At the centre of the depression lies the Dallol volcano, born from the direct interaction between magmatism and sedimentary processes. Its hydrothermal brine pools, sulfuric acidic springs, and fumaroles create a geochemical environment of extraordinary intensity, where temperatures, acidity, and salinity combine to push life to its apparent limits. Previous studies have revealed hyperdiverse communities of archaea thriving near the boundaries of habitability, and the site has become a leading terrestrial analogue for the search for extraterrestrial life. Yet despite decades of research focused on tectonics, volcanology, and geophysics, the deep subsurface of the basin remains essentially unexplored by science. Industrial potash exploration in the 1960s produced early structural and stratigraphic maps, and recent industry seismic and borehole data have refined the picture, but no sedimentary core has ever been recovered from the central basin, which is filled with more than 2.2 kilometres of sediments recording the basin’s evolution.

The workshop in Addis Ababa was the culmination of a process that began with an online ICDP meeting in June 2021, attended by seventy participants, and continued with a European Geosciences Union splinter meeting in 2022. The in-person gathering, held from 28 to 31 August 2023 at Addis Ababa University, brought together sedimentologists, stratigraphers, structural geologists, volcanologists, geochemists, geophysicists, hydrologists, palaeo-climate scientists, biologists, biogeochemists, and engineers. More than half of the participants were Ethiopian, representing Addis Ababa University, Addis Ababa Science and Technology University, Mekelle University, and Semera University, alongside delegates from the potash, geothermal, and petroleum industries, national and regional government, and non-governmental organizations. Around twenty postgraduate students were invited to participate, reflecting a deliberate emphasis on diversity, inclusion, and early-career involvement.

Over three days of presentations, lightning talks, poster sessions, and break-out discussions, the participants refined the science plan and settled on a single drilling site, designated Dallol-01A, located in the central depression between the Dallol volcano and the Erta Ale volcanic range. The choice was strategic: the site avoids major faults and fault zones as well as gas pockets, and available industrial seismic profiles reveal four distinct seismo-stratigraphic units spanning roughly the past 500,000 years. The target depth of 2.2 kilometres is designed to intercept the full syn-rift sedimentary sequence through continuous coring down to the rift basement. The upper part of the sequence consists of alternating halite and clay-silt layers, underlain by a thick upper halite unit, a potash-bearing formation, a lower halite unit, and basal sandstones locally enriched with anhydrite, which can be correlated with Middle to Late Pleistocene carbonate outcrops at the basin margins.

The scientific payoff of such a core is expected to be profound across at least five thematic fronts. First, the record will unravel rapid palaeo-environmental change in a rift basin near breakup, quantifying non-linear sedimentation rates and clarifying how cycles of marine flooding and desiccation are expressed in the basin centre. It may also illuminate how the Danakil evaporites formed, offering a modern analogue for understanding other great salt giants such as the Messinian deposits of the Mediterranean. Second, a well-dated core will constrain subsidence rates and fault slip histories, challenging traditional models that assume extension by magma intrusion increases steadily during breakup; recent work in the Danakil Basin instead points to significant subsidence driven by plate thinning and faulting. Third, the core will test the origin and limits of life in the deep biosphere, revealing whether halophilic microbes inhabit anoxic brines at depth and how their metabolism shapes biogeochemical cycles under poly-extreme conditions.

Fourth, the drilling will characterize one of the most vigorous hydrothermal systems on the planet. The region possesses all the key ingredients for high-enthalpy geothermal fields: shallow magmatic heat sources, fault and fracture permeability, and potential aquifers fed by meteoric water infiltrating from the Ethiopian Plateau. Subsurface petrophysical data on rock properties, microfractures, fluids, and heat flow are currently lacking, and the core will provide the inputs needed for realistic three-dimensional models of fluid and heat flow. Hydrothermal circulation through the evaporites also raises the possibility of commercially viable concentrations of lithium and other metals required for the global transition to renewable energy. Fifth, after drilling is complete, the borehole is intended to become a permanent downhole Earth observatory, equipped with a broadband borehole seismometer and a surface GPS station feeding real-time data to the Addis Ababa Geophysical Observatory, improving Ethiopia’s capacity to monitor earthquakes, ground deformation, and gas and fluid flux in a seismically and volcanically active region.

The workshop also placed strong emphasis on societal relevance and community engagement. Discussions involved the Energy Office of the Afar National Regional Government, the Afar Geothermal Alternative Power company, potash and geothermal sector representatives, and the universities of Addis Ababa, Mekelle, and Semera. Participants explored links with community-based schemes promoting geothermal energy development compatible with Afar pastoralist lifestyles and culture, the so-called green geothermal village concept, as well as geo-tourism and educational materials for local schools. The universities expressed a strong desire to use the project to strengthen student training in subsurface characterization, to archive core samples and downhole data locally, and to establish a field camp at the drill site. Recognizing the Danakil as a national heritage site was also discussed. Beyond science, the project promises direct economic benefits: identifying deep potash deposits, quantifying potential water aquifers, and informing the commercial development of geothermal energy in one of the most energy-rich but underexplored regions of Africa.

As the ADD-ON team moves toward compiling a full drilling proposal, the Danakil Depression stands poised to yield answers to some of the most fundamental questions in Earth science: how continents rupture and new oceans are born, how climate and tectonics interact to shape sedimentary basins, and how far the boundaries of life can stretch. The sediments beneath the salt pans hold a half-million-year ledger of flooding, desiccation, volcanism, and faulting, written in halite and clay. Reading that ledger, scientists hope, will not only reconstruct the birth of a future ocean but also inform hazard monitoring, energy development, and water resource management for the people who live at the edge of the rift today.

Subject of Research: Scientific drilling of the Danakil Depression in the Afar rift, Ethiopia, to study continental breakup, sedimentary basin evolution, the deep biosphere, and geohazards

Article Title: Workshop report: Afar Dallol Drilling – ONset of sedimentary processes in an active rift basin (ADD-ON)

Article References: Workshop report: Afar Dallol Drilling – ONset of sedimentary processes in an active rift basin (ADD-ON). (n.d.). https://doi.org/10.5194/sd-33-207-2024

Image Credits: AI Generated

DOI: 10.5194/sd-33-207-2024

Keywords: Afar, Danakil Depression, scientific drilling, ICDP, continental rifting, salt giants, Dallol, deep biosphere, geothermal energy, evaporites, seafloor spreading, geohazards