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

Sabkhas form under arid to hyper-arid climates where evaporation persistently exceeds rainfall and groundwater lies close enough to the surface for capillary rise to deliver moisture into the evaporation zone. The review distinguishes two dominant types in the UAE. Coastal sabkhas, exemplified by the Abu Dhabi shoreline, sit within supratidal to marginal intertidal zones and are sustained by episodic marine flooding, tidal pumping, lagoonal exchange and saline groundwater circulation. Inland sabkhas, such as the vast Sabkha Matti that extends roughly 150 kilometres from western Abu Dhabi into Saudi Arabia, occupy continental depressions and interdune corridors where groundwater discharge and intense evaporation dominate, with little direct marine input. Both settings share the same fundamental process chain: capillary ascent, evaporative concentration, evaporite crystallization and early cementation, yet their differing hydrologic connectivity produces distinct brine chemistries and mineral assemblages.

The geological setting of the UAE gives these systems unusual scientific richness. The Abu Dhabi coastal plain is an exceptionally low-gradient carbonate ramp where offshore shoals, barrier islands and restricted lagoons dampen wave energy and allow broad tidal flats to prograde seaward. Facies belts trace an orderly progression from subtidal carbonate shoals through lagoons and tidal channels into a shoreline-parallel belt of polygonal microbial mats and finally onto supratidal sabkha plains. Because these belts are preserved as vertically stacked Holocene packages, geologists can walk laterally across modern environments and read the same succession downward in cores. This direct process-to-product linkage is why the Abu Dhabi sabkhas became the type analogue for ancient carbonate–evaporite reservoir–seal systems across the Arabian Plate, including the Upper Jurassic Arab Formation.

The Mussafah Channel, a man-made canal cut through the coastal plain, has proven especially instructive. Its walls expose a well-constrained Holocene succession in which Pleistocene aeolian deposits are overlain by lagoonal and tidal-channel carbonates, microbial mat facies and supratidal sediments overprinted by evaporite mineralization. The stacking records a post-glacial marine transgression followed by regression and progressive sabkha development, providing a high-resolution template for reconstructing facies architecture and early diagenesis in subsurface reservoirs. Quantitative comparisons between modern surfaces and shallow subsurface successions have shown that many environmentally diagnostic structures, from microbial polygons to halite crust morphologies, retain recognizable signatures during early burial, strengthening confidence in facies-based analog applications.

One of the most celebrated contributions of the UAE sabkhas lies in addressing the long-standing Dolomite Problem: the puzzle of how abundant dolomite forms at low temperatures when laboratory experiments struggle to precipitate it. Cryo-scanning electron microscopy has revealed authigenic dolomite crystals nucleating within the extracellular polymeric substances of Abu Dhabi microbial mats, and laboratory studies with sulfate-reducing bacteria isolated from the sabkha have reproduced poorly ordered Ca-dolomite and very high-Mg calcite under simulated pore-water conditions. These findings establish microbial mats as geochemical micro-reactors that locally modify pH, alkalinity and magnesium-to-calcium ratios, demonstrating that low-temperature dolomitization in evaporitic settings is fundamentally microbially mediated rather than a simple consequence of evaporation.

The hydrogeochemistry of the coastal sabkha is equally counterintuitive. Water-budget and mass-balance analyses show that most water entering the shallow sabkha aquifer is meteoric, derived from infrequent but efficiently infiltrating rainfall, whereas more than 95 percent of the dissolved solutes ascend from continental brines in underlying Tertiary formations. This decoupling between water sources and solute sources explains why marine-like evaporite assemblages develop even where modern marine flooding is sporadic. The characteristic mineral sequence of carbonate, gypsum and anhydrite, then halite, reflects recurrent concentration–reset cycles driven by evaporation, flooding and brine–sediment interaction rather than a single linear evaporation path. Density contrasts between concentrated near-surface brines and dilute underlying groundwater even drive free convection, first documented at field scale in the Abu Dhabi aquifer, redistributing solutes and shaping cementation patterns.

The review also brings radiogeochemistry into the framework. Natural radioelement distributions prove strongly facies-dependent: potassium-40 and thorium-232 track detrital inputs of K-bearing silicates, clays and heavy minerals inherited from desert dunes and the ophiolite-dominated Hajar Mountains, while uranium behaves far more dynamically, migrating as uranyl–carbonate complexes in oxidizing alkaline brines and immobilizing in reducing microbial mat microenvironments. Radium, by contrast, can be trapped through substitution into the abundant gypsum and anhydrite that pervade sabkha soils, making sulfate horizons potential radiogeochemical sinks. The authors argue that robust environmental baselines therefore require sampling stratified by facies and depth rather than treating sabkhas as uniform salt flats.

On the question of critical elements, particularly lithium, the synthesis is deliberately cautious. Lithium remains in solution through early evaporation and concentrates mainly in late-stage, bittern-like residual brines enriched in magnesium, potassium, bromine and boron. Whether UAE sabkhas reach that stage depends on hydrologic restriction, residence time and flushing frequency, and the reviewers note that facies-resolved lithium datasets for UAE sabkhas are effectively absent from the open literature. Regional benchmarks, including lithium concentrations of roughly 0.2 to 0.3 milligrams per litre measured in Arabian Gulf desalination brines, and the persistent technical obstacle posed by high magnesium-to-lithium ratios in direct extraction technologies, all counsel against assuming inherent high-grade enrichment. The authors instead propose a staged screening strategy: vertical porewater profiling across representative facies, quantification of lithium alongside its chemical companions, seasonal repetition to capture evaporation and flooding cycles, and integration with techno-economic and environmental assessments before any resource claims are made.

Finally, the review elevates the sabkhas to geoheritage priorities. Abu Dhabi Sabkha is listed on UNESCO’s World Heritage Tentative List, recognized for the completeness of its roughly 7,000-year-old system, where subtidal lagoon muds, intertidal microbial mats and supratidal gypsum and anhydrite nodules co-occur within a single locality. Yet the scientific archive is disappearing fast: studies estimate that of about 150 kilometres of coastal sabkha present in the 1960s, only around 36 percent remained by the early 2010s, lost to industrial and urban encroachment. The reviewers call for protected reference zones, controlled access and integration of research with public interpretation, framing the sabkhas not as wasteland but as irreplaceable outdoor laboratories. From reservoir calibration and lithium screening to radon baselines and geotechnical risk in sulfate-cemented soils, they conclude, the fate of these reactive evaporitic systems now matters far beyond the shorelines of the southern Gulf.

Subject of Research: Integrated sedimentology, hydrogeochemistry, geomicrobiology and resource potential of UAE sabkha carbonate–evaporite systems

Article Title: Sabkha systems of the United Arab Emirates as integrated carbonate–evaporite laboratories: facies architecture, brine evolution, critical-element potential, and geoheritage significance

Article References: Abukhadra, M. R., Al-zharani, M., Allam, A. A., Hamdan, M. A., Szűcs, P., & Eid, M. H. (2026). Sabkha systems of the United Arab Emirates as integrated carbonate–evaporite laboratories: facies architecture, brine evolution, critical-element potential, and geoheritage significance. Environmental Earth Sciences, 85(16), Article 411. https://doi.org/10.1007/s12665-026-13146-2

Image Credits: AI Generated

DOI: 10.1007/s12665-026-13146-2

Keywords: sabkha, United Arab Emirates, evaporites, carbonate sedimentology, brine geochemistry, dolomite, microbial mats, lithium, radioactivity, Abu Dhabi, geoheritage, reservoir analogue