HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Multiple comparisons of point clouds acquired by a permanent LiDAR (PLS) to improve the reliability of a rockfall event catalogue
No full textInternational audienceThe ANR C2R-IA project (www.anrc2ria.fr) aims to develop reliable decision-support tools for the dynamic management of rockfall hazard. Its goal is to understand how meteorological forcing influences rockfall occurrence and to anticipate temporary increases in hazard in order to implement risk reduction measures. To this end, a predictive model of rockfall occurrence as a function of meteorological conditions is being developed using artificial intelligence tools (neural network training), which requires a comprehensive and well-labelled dataset. Several monitoring instruments have been deployed at the Saint-Eynard site (Grenoble, France). Among them, a permanent LiDAR scanner (PLS) acquires point clouds continuously, with one acquisition per hour, providing high temporal resolution representative of what could be used for operational monitoring or crisis management. An automated data-processing workflow has been developed in Python. It is based on a pairwise comparison of the clouds (Manceau et al., 2025) and includes the alignment of successive point clouds, filtering of points outside the cliff area, change detection using M3C2 distances computation, clustering with DBSCAN, and volume quantification of rockfalls using alphashapes. This well-structured processing has significantly reduced the detection threshold, identifying relief change of only 10 cm deep (compared to 40 cm previously; Le Roy et al, 2020) and 10 liters in volume, while the scanner is located approximately 1 km from the cliff. Depending on acquisition quality, the effective temporal resolution of detected rockfall events may range from one hour to several days. Combining relief-change detections with simultaneously deployed seismic monitoring should further refine event timing. The completeness of the event catalogue has therefore improved, increasing from fewer than 10 detected rockfalls per month to around 30. However, some false positives remain, mainly related to recurring artifacts despite preprocessing. To mitigate these errors, the previous pairwise comparison of the clouds has been refined to a multiple point-cloud comparison strategy, enabling the tracking of the temporal persistence of changes. This allows distinguishing changes corresponding to real rockfalls, which persist over time, from transient artifacts. This improvement leads to a more reliable and complete rockfall event database. It includes block shape ratios, identified failure mechanisms, and free-fall heights under overhanging sections, providing a suitable basis for future fusion with seismic data.Manceau, L., Chanut, M.-A., Levy, C., Dewez, T., and Amitrano, D.: Enhancing Rockfall Detection Using Permanent LiDAR Scanner (PLS) Data and Automated Workflows at St. Eynard Cliff (Grenoble, France), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6312, https://doi.org/10.5194/egusphere-egu25-6312 Le Roy, G., Helmstetter, A., Amitrano, D., Guyoton, F., & Le Roux-Mallouf, R. (2019). Seismic analysis of the detachment and impact phases of a rockfall and application for estimating rockfall volume and free-fall height. Journal of Geophysical Research: Earth Surface, 124, 2602-2622. https://doi.org/10.1029/2019JF00499
Coupler les données satellitaires aux données de terrain pour comprendre les dynamiques des socio-hydrosystèmes à différents niveaux d'organisation
No full textNote scientifique du PEPR OneWate
Middle Eocene hyperthermal seasonality from Paris Basin marine mollusks
No full textInternational audienceThe Earth has experienced hyperthermal events in the past, characterized by maximum durations of hundreds thousand years, significant magnitude, global extent, and drivers associated with increases in greenhouse gas concentrations, therefore making them potential analogues for current climate change. The Middle Eocene Climatic Optimum (MECO) that occurred 40 Ma ago, is marked by a CO2-driven global warming of +4 to +6° C, affecting global temperatures. Here, we present a detailed reconstruction of seasonal fluctuations in seawater temperatures during this warming event in littoral environment, based on geochemical analyses (δ18O and Δ47) of shallow-marine mollusks from the Paris Basin. Our data show a stability in mean winter temperatures compared to pre-MECO conditions, but a marked warming of +10°C in maximum estuarine water temperatures, with a seasonal temperature range increasing from 12°C before the MECO to 22°C at the climax of the event. We demonstrate that at mid-latitudes, annual maximum shallow-water temperatures increased from 30 ± 2°C before the event to a maximum of 41 ± 4°C at the warming peak. This pattern is associated with a seasonal regime characterized by dry summers and wet winters, implying that the Paris Basin experienced a super-hot summer Mediterranean climate during the MECO
Long-term bioelectricity generation in microbial fuel cell exposed to perfluorooctanoic acid
No full textInternational audienceThe long-term performance of microbial fuel cells (MFCs) depends on microbial communities whose composition strongly influences electron transfer and substrate utilization. The presence of environmental pollutants can cause changes in microbial abundance and biodiversity and have an effect on the MFC efficacy; however, their long-term operational stability under environmental stress remains insufficiently explored. This study assessed the long-term performance of MFCs using river sediment organic matter as the energy, electron, and carbon source during exposure to perfluorooctanoic acid (PFOA). The MFC-PFOA (MFC with PFOA) system operated effectively for 10 months, achieving a maximum voltage of 461.9 mV and a peak current density of 14.5 mA/m2, significantly outperforming the control cell. Liquid chromatography–tandem mass spectrometry (LC-MS/MS) analysis confirmed a 94.9 % reduction in PFOA concentration and detected perfluoroheptanoic acid (PFHpA) and perfluorohexanoic acid (PFHxA), indicating possible partial transformation and/or redistribution processes within the bioelectrochemical system. Additionally, bacterial community analysis revealed a shift in microbial composition, with Firmicutes and Desulfobacterota becoming dominant, suggesting their roles in current generation and biotransformation of PFOA. Overall, this work demonstrates long-term bioelectricity generation in the presence of per- and polyfluoroalkyl substances (PFAS) pollutants, while indicating partial attenuation and compositional changes of PFOA under bioelectrochemical conditions, thus providing valuable insights into the robustness of bioelectrochemical systems for energy recovery in contaminated environments
The Bondi universe: How negative mass drives the cosmological expansion
No full textWe identify a new cosmological coincidence that parallels the well-known matter/dark-energy coincidence: the present-epoch transition of the universe from a weakly coupled (collisionless) to a strongly coupled (collisional) gravitational regime. Within a cosmological model containing equal amounts of positive and negative Bondi masses -consistent with the weak equivalence principle and momentum conservation -we show that this coupling transition naturally coincides with the shift from a coasting to an accelerating expansion. A linear response analysis of the corresponding Vlasov-Poisson system reveals that mixed positive-negative mass configurations are always unstable, with growth rates that increase at shorter wavelengths, thereby driving the system toward strong coupling. Using long-time, exact one-dimensional N-body simulations, we demonstrate that the universe undergoes three successive expansion phases: an initial ballistic regime, an intermediate random-walk acceleration driven by sporadic Bondi encounters, and finally a uniformly accelerating phase triggered by the formation of stable positive/negative mass pairs. The onset of this last phase occurs precisely when the coupling parameter crosses unity, linking the two cosmological coincidences through a single dynamical mechanism. These results suggest that cosmic acceleration may arise from the nonlinear dynamics of a gravitationally neutral mixed-mass universe, without invoking dark energy or a cosmological constant.</div
Experimental and numerical study of microwave heating in sand columns: Water saturation effects on temperature profiles and heat transfer mechanisms
No full textInternational audienceSubsurface heating finds applications in soil remediation and enhanced resource recovery, with microwave heating offering advantages over conventional methods (conductive heating, hot vapor injection). However, the transition from laboratory-scale studies conducted in microwave ovens to in situ applications using embedded antennas in relevant environments remains poorly studied. This study investigates microwave heating mechanisms of a 2.45 GHz coaxial antenna in sand across varying water saturation levels.Results reveal that the reported advantages of microwave heating-rapid and homogeneous temperature rise-require a critical water content. For near-dry sand (<5% water saturation), temperature increased but exhibited steep, non-constant radial gradients. Conversely, at higher saturation levels (14% and 22%), temperature profiles rapidly developed near-constant, reduced gradients. Despite these differences, modeling indicates that thermal conduction, rather than direct absorption, remains the dominant heat transfer mechanism across all tests. Furthermore, the study identifies a significant discrepancy between nominal power and actual absorbed power, highlighting a low conversion efficiency. These results suggest that while microwave heating is effective for moderately saturated soils, further optimization of power and heat delivery is essential to promote its applicability to thermal desorption of polluted soil
A conceptual architecture for AI-assisted Digital Twins in natural resource management
No full textInternational audienceThe management of natural resources is increasingly critical and challenging due to complex interactions among environmental, industrial, and societal processes. Traditional approaches often fail to integrate heterogeneous data, limiting predictive and decision-support capabilities. This study presents a conceptual architecture for an Artificial Intelligence (AI)-assisted Digital Twin (DT) of the Centre-Val de Loire region, designed to unify time-dependent multi-source data. Based on the ENVRI Reference Model, it covers Science, Information, Computational, Engineering, and Technology layers, defining standardized data exchange, communication protocols, and prototype functionalities. A proof of concept FIWARE implementation supports ingestion, monitoring and analytical services for piezometric and meteorological data, exemplified through groundwater dynamics in the Beauce aquifer. It integrates daily observations from 53 piezometric stations over more than five years, managing approximately 2.8 million records in a containerized environment.Results show that the proposed DT architecture can enhance sustainability-oriented decision making, integrating heterogeneous data and predictive analyses while enabling collaboration across scientific and technical domains. Its modular design offers a replicable template for future AI-assisted environmental DTs, scalable to larger regions. Hence, this work illustrates how DTs can improve environmental monitoring and understanding, providing a pathway toward resilient, data-driven management of natural resources.</p
Exploring the relationships between Electron Spin Resonance (ESR)/Luminescence (OSL/TL) properties and trace element composition from quartz in various bedrocks (Strengbach catchment, Vosges)
No full textInternational audienceQuartz Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) offer valuable quantitative tools both for understanding sediment provenance and surface processes. However, the variability of quartz sensitivity remains an issue, attributed either to the intrinsic properties of source bedrock, to processes during sediment transport and deposition, or to both. This study addresses these questions by investigating quartz from magmatic, metamorphic, and sedimentary formations in the Strengbach catchment (Vosges Massif, France). Using a combination of ESR, TL, OSL, and LA-ICPMS (Laser-Ablation Inductively Coupled Plasma Mass Spectrometry) trace element analyses, our study reveals significant relationships between quartz TL-OSL/ESR sensitivities and source bedrock characteristics, such as lithology, crystallization conditions, and deformation histories. ESR Ti-centre and TL-OSL signals are notably influenced by trace elements like Al, Li, and Ti. Quartz that underwent high pressure during metamorphism along with those located in the tectonic shear zone show both lowest TL-OSL and ESR intensities, while higher sensitivities are observed in quartz from plutonic rocks and sandstones. This suggests that (i) pressure can be one of the prevailing factors driving changes in quartz TL-OSL/ESR sensitivities (ii) enhanced quartz TL-OSL sensitivity in mature and recycled sediments (sandstones) highlight the importance of sedimentary transport and reworking on TL-OSL and ESR signals.Our results highlight the need for careful interpretation of ESR and TL-OSL signals, both for dating or sourcing, particularly in sediments derived from metamorphic terrains.</p
Hydrolytic weakening controls Jurassic to early Cretaceous mylonitisation in the basement of the Pyrenees
No full textInternational audienceThe age of the mylonite belts in the basement rocks of the Pyrenees is a subject of debate in the structural geology and petrology communities because of its potential implication on the regional tectono-thermal history and on the tectonic evolution of SW Europe. Here we address when and how mylonitisation took place in two key areas of the Eastern Pyrenees, where shear zones are associated with Giant Quartz Veins (GQVs). We conducted zircon U-Pb and muscovite 40 Ar/ 39 Ar dating coupled with structural, textural, and crystallographic preferred orientation (CPO) analyses of mylonites from the Cap de Creus and Canigó Massifs. U-Pb zircon dating of a dacite porphyry dyke crosscut by GQVs and mylonitic bands yields a maximum shear zone and GQV formation age of ca. 292 ± 3 Ma. 40 Ar/ 39 Ar analyses of muscovite within mylonitised GQVs yield initial crystallisation ages between ca. 164 and 188 Ma, as well as younger recrystallisation ages of ca. 110-118 Ma. A qualitative assessment of the GQV history is inferred from stepheating spectra of muscovite and quartz CPOs. The results indicate that GQV formation and mylonitisation were coupled, coeval, and long-lasting processes that took place from early Jurassic to early Cretaceous times. A comparative evaluation of quartz CPOs reveals inconsistencies regarding the strain distribution, quartz slip systems activity, and deformation temperatures depending on the deformed rock type. Quartz mylonites have stronger CPOs dominated by basal <a>, prism <a> or prism <c> slip systems, whilst phyllonites and granite mylonites show weaker fabrics mostly dominated by mixed <a> slip. This apparently suggests higher deformation temperatures in quartz mylonites than those inferred from more reliable proxies, such as mineral assemblages, brittle behaviour of K-feldspar, and fluid inclusion data. We suggest that the water-weakening effect caused by coeval formation and deformation of GQVs enabled easier dislocation glide and creep, allowing strain localisation and transitions between slip systems at lower temperatures than commonly inferred due to enhanced ductility. U-Pb zircon dating further suggests the existence of an early Carboniferous (ca. 332 ± 4 Ma; Visean) magmatic episode in the Pyrenees, in agreement with a cyclic, rather than a progressive, geodynamic history of the region during Variscan times.The present work challenges classical interpretations stating that Pyrenean mylonite belts developed during the retrograde stages of the Variscan Orogeny, highlighting that the structural evolution of this region during Mesozoic times deserves further investigation. Results have implications for interpreting deformation localisation mechanisms and conditions in crustal rocks, for the formation mechanisms of GQVs in worldwide orogenic belts, and for the tectono-thermal history of the Pyrenees since late-Variscan times.</div
Etude du transfert potentiel de chlordécone de parcelles à parcelles par ruissellement et érosion
No full textInternational audienceMessages-clés :Déploiement de mesures de terrain multi-échelles, de la placette (~ 10 m 2 ) au bassin versant (~ 100 km 2 ), de l'événement de pluie à l'archive sédimentaire (~ 50 ans), pour analyser le transfert potentiel de chlordécone de parcelles à parcelles par ruissellement et érosion.Persistance de la chlordécone sur le profil des 21 carottes de sol avec présence systématique en surface jusqu'à 40 cm, indiquant que le ruissellement et l'érosion superficielle et en ravine peuvent disperser la chlordécone.Quantification sur le long terme (~ 50 ans) de taux d'érosion significatifs à l'échelle du bassin versant, associé à des teneurs en chlordécone non-nulles, soulignant l'existence du transfert particulaire.Modélisation distribuée du ruissellement et de l'érosion préliminaire déployée à l'échelle de la Martinique et de la Guadeloupe.La modélisation montre la probabilité de transfert potentiel de chlordécone de parcelles à parcelles par ruissellement et érosion, bien qu'une quantification relative de la dispersion par ces processus, relativement à d'autres bien documentés dans la littérature (ex. percolation profonde) n'aient pas été menée.</div