HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Les Volcans Actifs de Turquie: Guide géologique et itinéraires d'excursions. Réédition océrisée 2026 du Mémoire N° 2 de LAVE de 1994
No full textRéédition 2026 du Mémoire de 1994International audienceLAVE (L'Association Volcanologique Européenne) is a non-profit scientific french association ruled under the 1901-law. It is based near Paris. In 1994, it counted around 700 members, either professional geologists or amateur volcano-lovers, most of them french, and many followers abroad. Very kindly, it accepted a manuscript of my own to be published as its Memoir No. 2, edited unter the title « Les volcans actifs de Turquie ; guide géologique et itinéraires d'excursions ». At that time, these volcanoes (still presently dormant) had already been studied by pioneer geologists of the Turkish universities and by the national Geological Survey of Turkey, the Maden Tetkik ve Arama Enstitüsü (M.T.A.). My Memoir of LAVE thus benefited from those various publications, supplemented by my experience of BRGM exploration geologist on the field. An updating of that Memoir is currently under progress. It will be printed by LAVE as its Memoir N° 15 by the end of 2026 (with a completely new text). Why an updating, 32 years later ?First of all, because as soon as 1992, the scientific knowledge on the active volcanoes of Turkey litteraly exploded. This huge progress resulted in particular from an intense cooperation between the Geological Department of Hacettepe University in Ankara and the french laboratory of Volcanology of the Clermont-Ferrand University. Moreover, other researchers carried out intensive field and laboratory work as well.The Geopark label was given by UNESCO to a first volcanic district, the KULA-SALIHLI area north of Izmir. A second district, the NEMRUT and SÜPHAN Daği area north of Lake Van, is in good way to get this famous international reward as well.Last but not least, every volcano lover will be asthonished and deeply disappointed to learn that the reknown british archaeologist James Mellaart, who had discovered the famous neolithic city of Çatal Höyük near Cappadocia and its extraordinary 7000 BCE fresco of a local volcanic eruption, revealed to be (at the end of his life) a fake maker and a forger. A geological statement is thus needed, in the hope to distinguish the truth.</p
Vocabulaires & Principes FAIR – Cycle de vie vocabulaires - Vocabulaires et cycle de vie des données
No full textMasterPrésentation des vocabulaires, utilité et leur cycle de vie, principes FAIR adaptés aux vocabulaires, et importance des vocabulaires et de leur rôle dans le cycle de vie des données effectuée dans le cadre du MasterGeoData de l'université d'Orléan
Geology and geochronology of the Ubendian belt in Malawi; whither the Nyika Terrane?
No full textInternational audienceThe Palaeoproterozoic Ubendian Domain in Malawi comprises the SE segments of three distinct crustal blocks, namely (from north to south) the Mbozi, Ufipa and Nyika subdomains, apparently confirming the historic crustal subdivisions. Together, they represent about 30 % of the surface area of the entire Ubendian belt, most of which lies in Tanzania. We describe their geology and present 14 new U-Pb zircon dates of representative samples. The Mbozi Subdomain (SD) is predominantly comprised of mafic gneisses (Mbozi Group) with no Palaeoproterozoic granitoid intrusions. The Ufipa SD comprises several units of high grade supracrustal gneisses (Ufipa Group), with a maximum depositional age of ∼1990 Ma, deposited upon an interfoliated “cryptic” tonalite-granodiorite orthogneiss basement dated at ∼2150 Ma and occurring as scattered remnants within the paragneisses. Minor post-Ufipa Group granitoids were emplaced at 1990 Ma. The Nyika SD contains sequences of supracrustal gneiss (Nyika Group) deposited between ∼2100 and 1990 Ma, probably during at least two phases of sedimentation. There are numerous granitoids of varying compositions with an overlapping continuum of emplacement ages from ∼2045 to 1946 Ma, some of which are coeval with Nyika Group deposition. The youngest (post-tectonic) granites intrude the Nyika Group, but the status of the older foliated granitoids is less clear due to poor exposure. In all subdomains high grade regional metamorphism, migmatisation and ductile deformation took place soon after deposition of the supracrustal groups and during granitoid magmatism at c. 1980 Ma. It is argued that the Nyika SD continues westwards into the coeval “Bangweulu Block” of Zambia without break and the existence of a larger contiguous Palaeoproterozoic Bangweulu-Nyika (BaNy) cratonic block is proposed. BaNy is a metacratonic crustal entity which evolved separately from the Congo (west) and Tanzania (east) cratons in Neoarchaen to early Palaeoproterozoic times. The Ubendian belt formed in response to Palaeoproterozoic subduction and an active margin SW of the Archaean Tanzania Craton and eventual collision and amalgamation with the BaNy Block. The U-Pb data show weak evidence of ∼1.1 Ga (Irumide) reworking in the western Nyika SD but extensive and major effects of ∼550 Ma (Pan-African) intense transcurrent deformation and medium-to low-grade metamorphism. The current geometry of this part of the Ubendian Domain is largely controlled by Pan-African structures, dominated by the NNW-striking low-grade Mugesse Shear Zone and in the south by the conjugate WSW-striking Mwembeshi Shear Zone. These shear zone systems form the inter-subdomain contacts and are largely responsible for the observed regional structural grains
Balancing drinking water security and conservation: A spatial multi-objective optimization framework for regional groundwater management under global change
No full textInternational audienceEnsuring long-term drinking water security is a critical challenge for water managers worldwide, fueled by multiple pressures including increasing water demand, deteriorating water quality, and reduced resource availability with climate change. This study addresses the need for integrated and spatially-explicit modeling tools for drinking water management at regional scale. It develops a methodological framework to support management strategies that balance drinking water security and environmental objectives, by combining drinking water supply hydro-economic modeling with high-resolution hydrogeological modeling and multiobjective optimization techniques. The coupling makes it possible to account for the spatial impacts of abstractions on groundwater levels, river-groundwater interaction, risks of salinization and satisfaction of drinking water demand, while optimizing their distribution and allocation. The framework is applied to the plain of Roussillon case study (Mediterranean France), providing insights for water management and demonstrating the scalability of the approach to a large-scale problem (167 decision variables). Results indicate optimal abstractions should be redistributed from the Pliocene toward the Quaternary aquifer (and toward upstream areas) to satisfy drinking water demands while avoiding seawater intrusion. However, results show that it will not be possible to fully satisfy future demand under drier climate without violating seawater intrusion constraints. Implementing demand-side management measures is a win-win-win strategy that reduces water shortages and environmental impacts to aquifers and rivers. Results also suggest that current regulatory abstraction caps are too generous to prevent future decline in piezometric levels under drier climate. The developed methodological framework can generalize to other basins and support analyses of adaptation strategies
Efeitos do suavizamento do lençol freático controlado pela resolução da grade topográfica no fluxo regional simulado de água subterrânea
No full textInternational audienceThe assessment and management of groundwater often depend on large regional numerical models that predict hydrological stresses, such as those caused by climate change and resource exploitation. While regional and continental-scale models have been developed to evaluate these impacts, they typically use coarse grid cells that smooth land surface topography. This study investigates the impact of topography-controlled water table smoothing on simulated groundwater discharge to streams (baseflow) and associated groundwater age. A simplified 2D cross-sectional model of a topographically driven regional aquifer system was developed, under the assumption that the water table is a replica of the land surface topography. Scenarios with varying topography, derived from resampling digital elevation model (DEM) resolutions ranging from 30 to 10,000 m, were analyzed using a consistent, high-resolution numerical hydrogeological model mesh. Results show that baseflow rates decrease significantly as resolution declines, primarily due to reduced hydraulic gradients, with a flux dif- ference of an order of magnitude simulated between resolutions of 30 and 1000 m. Although shallow groundwater flows in more permeable aquifer layers are significantly affected, deeper regional flow remains stable across all scenarios. Regional groundwater flow paths and associated residence times are less sensitive to changes in resolution, particularly at depths greater than 50 m in the model used. The study thus demonstrates that low-resolution models need to overestimate hydraulic conductivity during calibration to accurately match fluxes to streams. This study highlights the critical importance of care- fully considering topographic resolution in regional models to ensure representative predictions of streamflow driven by subsurface–surface interactions
Salinity-driven convection mechanisms in stratified brines
No full textInternational audienceUnderstanding transport and mixing in stratified saline systems is critical for predicting the behavior of brines in natural aquifers, industrial reservoirs, and engineered disposal sites. These multi-ion solutions often exhibit complex instabilities driven by differential diffusion and compositional gradients. The onset and morphology of such convective mixing remain poorly predicted. We investigated double-diffusive (DD) and diffusion-layer convection (DLC) in superimposed aqueous solutions of the salts typical of saline aquifers, sodium chloride (NaCl) and sodium sulphate (Na2SO4). The study combines thermodynamic modeling, optical interferometry experiments, and nonlinear numerical simulations to explore convective instabilities in a ternary system. Our findings reveal a rich variety of convective scenarios depending on salt configuration and concentration ratios. When the faster-diffusing NaCl was placed above Na2SO4, diffusion-layer convection occurred with a delayed and asymmetric onset of instability, an experimentally demonstrated feature not reported previously. In contrast, when the positions were reversed, the system developed double-diffusive fingers that grew slowly due to the small density ratio. These fingers exhibited an unusual morphology, consisting of extremely fine, vertically textured structures that gradually merged away from the interface. This formed a large area of diffuse mixing and suppression of coherent convective structures. In all cases, classical stability criteria failed to fully predict the onset and nature of convection. Instead, we identified the initial position of the system on the stability map, as determined by the full diffusion matrix, as a critical facto
Subsurface variability of sandy coastal geosystems revealed by integrated georadar and cone penetrating testing approach: Insights from the Pays-de-Monts coast (Atlantic France)
No full textInternational audienceBeneath dune fields, the subsurface geology of sandy coastal systems can provide valuable insights for understanding coastal environment. While sandy coasts are often described and monitored through surface geomorphology, their internal structure and geotechnical properties remain poorly documented. To address this limitation, a combined ground-penetrating radar (GPR) and cone penetration testing (CPT) approach was applied along the Pays-de-Monts coast (Atlantic France). This multidisciplinary methodology yields complementary information on the internal architecture, stratigraphic variability, and soil behavior of coastal deposits.Two sectors were investigated, both characterized by dune fields underlain by fractured limestone and bordered inland by low-lying marshes. Despite their apparent similarities, the sites reveal distinct features. Results provide new insights into (i) the sedimentary units anchoring the sandy coastline, (ii) the connection with adjacent marshes and low-lying environments, (iii) the relationships between dune systems and underlying deposits, and (iv) soil behavior properties linked to depositional environment or dune types themself.From these findings, two conceptual models are proposed: (1) a prograding sandy coastline with an inland marshward transition overlain by dune field (La Parée Grollier, northern sector), and (2) a channel-fill and spit development sequence overlain by dunes (La Pège-Les 60 Bornes, southern sector). These results demonstrate the value of integrating geophysical and geotechnical methods to improve understanding of coastal geosystems and enabling the identification of site-specific characteristics. More broadly, this study demonstrates and discusses the benefits of integrating GPR-CPT approach for advancing coastal geology and highlights the relevance of local geological models for management and adaptation strategies under climate change
L’âge de l’eau
No full textInternational audienceL’eau est présente sur Terre depuis au moins quatre milliards d’années. Mais l’âge qui nous intéresse ici est le temps que l’eau passe sous terre. L’eau tombe en pluie ou en neige, s’infiltre dans le sol, alimente les nappes phréatiques, reste donc un certain temps dans les formations géologiques aquifères. Les grands bassins sédimentaires en comportent toute une succession, séparées par des couches peu perméables. Près de la surface l’eau est jeune et vulnérable à la pollution, son âge se comptant en années ou décennies. En profondeur, on entre étage après étage dans le domaine des eaux « fossiles », tombées en pluie lors des temps historiques ou protohistoriques, qui constituent de précieuses archives paléoclimatiques. Nous estimons cet « âge de l’eau » grâce à des horloges géochimiques constituées de radioéléments naturels à décroissance plus ou moins lente. Le krypton-81 ou encore le chlore-36 nous indiquent que des eaux de plus d’un million d’années stagneraient sous nos pieds
How to integrate biology, physics and chemistry for a better description of soil water dynamics?
No full textInternational audienceNumerous and diverse edaphic organisms have the capacity to modify several physical and chemical soil characteristics that influence water transfers. Considering these modifications in modeling approaches would make for more accurate descriptions and modeling of water fluxes in soils. Some impacts of biological activity on soil physical aspects (e.g. modification of the pore space) have been described for 5-10 years now, and are being increasingly accounted for in water transfer models.However, the situation is not the same for biologically-driven chemical modifications linked to the secretion of organic molecules by soil organisms: modeling their consequences on pore space chemical properties and water transfers has just started. We here shortly survey prominent effects of biological activity on water-transfer related soil properties, and describe their coupling with existing water transfer models. We then propose possible ways for a better integration of biological soil modifications into such models. Among these, we point out that an energy-based theoretical framework would not only be consistent with the basic principles of thermodynamics, but would also foster synergies between ecologists, physicists and chemists, to better describe and predict water dynamics in soils and interactions with the soil biota. This would pave the way to model the evolution, on the scale of a few decades, of the water flow regulation services provided by soils</p
Impact of Strain on Carbonaceous Matter Crystallinity: Insights from Raman Spectroscopy and microstructural analysis of strain gradients from exhumed accretionary complexes
No full textInternational audienceHighlights (to remove in a single file after correction)• RSCM parameter R1 reflects CM maturity evolution • CM maturity is increased in ductile and brittle high-strain zones• In shear zones, strain is the main cause of increased CM maturity• In breccia zone frictional heating cannot be ruled out.• RSCM signal stems from ~50-100nm particles distributed throughout the rock 0.</div