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Rheological and topographic implications of thermal insulation created by supercontinents
No full textInternational audienceThick continental lithosphere represents a thermal insulator, promoting less efficient conductive heat transfer to the surface. As a consequence, the mantle temperature under supercontinents can increase relative to surrounding regions. Conversely, hot asthenospheric mantle can modify the thermal and rheological structure of the base of the lithosphere. The understanding of how the lithosphere and asthenosphere co-evolve considering lateral variable lithospheric thickness depends on the appropriate representation of the mechanical properties of the upper mantle in the geological time scale. Using thermo-mechanical numerical scenarios, we investigate how thick continental lithosphere, here referred to as cratonic keel, can affect heat flow to the surface, the convective pattern inside the asthenospheric mantle and the impacts of thermal evolution of a cratonic keel over time scales of hundreds of millions of years. We considered different lateral positions for the cratonic keel and relative movement between lithosphere and the base of upper mantle to emulate lateral movement over geological time. The numerical results indicate that the thermal insulation promoted by the thick continental lithosphere induces the development of positive thermal anomalies in the asthenosphere, which eventually induce the weakening of the base of the continental lithosphere. The heating of the sublithospheric mantle under cratonic keels is only relevant when the continental lithosphere presents low relative velocity with respect to the base of the upper mantle. Additionally, the presence of a mobile belt with lower effective viscosity than the surrounding cratonic lithosphere contributes to basal erosion due to thermal insulation and upwelling divergent flow in the asthenosphere, inducing the weakening of the continental lithosphere between cratonic blocks. Our results help the understanding of how thermal insulation can affect the evolution of cratonic keels and invite us to revisit natural examples to test the current interpretations of the unconformities present in intracratonic basins that are commonly explained by tectonic and/or dynamic processes
The Ganymede Laser Altimeter (GALA) on the Jupiter Icy moons Explorer (JUICE) Mission
No full textInternational audienceThe Ganymede Laser Altimeter (GALA) on the Jupiter Icy Moons Explorer (JUICE) mission, is in charge of a comprehensive geodetic mapping of Europa, Ganymede, and Callisto on the basis of Laser range measurements. While multiple topographic profiles will be obtained for Europa and Callisto during flybys, GALA will provide a high-resolution global shape model of Ganymede while in orbit around this moon based on at least 600 million range measurements from altitudes of 500 km and 200 km above the surface. By measuring the diurnal tidal deformation of Ganymede, which crucially depends on the decoupling of the outer ice shell from the deeper interior by a liquid water ocean, GALA will obtain evidence for (or against) a subsurface ocean on Ganymede and will provide constraints on the ice shell thickness above the ocean. In combination with other instruments, it will characterize the morphology of surface units on Ganymede, Europa, and Callisto providing not only topography but also measurements of surface roughness on the scale of the laser footprint, i.e. at a scale of about 50 m from 500 km altitude, and albedo values at the laser wavelength of 1064 nm. GALA is a single-beam laser altimeter, operating at a nominal frequency of 30 Hz, with a capability of reaching up to 48 Hz. It uses a Nd:YAG laser to generate pulses with pulse lengths of 5.5 ± 2.5 ns. The return pulse is detected by an Avalanche Photo Diode (APD) with 100 MHz bandwidth and the signal is digitized at a sampling rate of 200 MHz providing range measurements with a sub-sample resolution of 0.1 m. Research institutes and industrial partners from Germany, Japan, Switzerland and Spain collaborated to build the instrument. JUICE, conducted under responsibility of the European Space Agency (ESA), was successfully launched in April 2023 and is scheduled for arrival at the Jupiter system in July 2031. The nominal science mission including multiple close flybys at Europa, Ganymede, and Callisto, as well as the final Ganymede orbit phase will last from 2031 to 2035. In May 2023 GALA has completed its Near-Earth Commissioning, showing full functionality of all units. Here we summarize the scientific objectives, instrument design and implementation, performance, and operational aspects of GALA
Benefits of GNSS Local Observations Compared to Global Weather-Based Models for InSAR Tropospheric Corrections Over Tropical Volcanoes: Case Studies of Piton De La Fournaise and Merapi
No full textInternational audienceFrom repeat-pass interferometry, tropospheric signals often prevent the detection of ground deformation signals. In recent years, tropospheric corrections derived from global weather-based models have been implemented in several InSAR processing chains. In this study, we evaluate the performance of two weather-based models (ERA5 and GACOS) on two tropical volcanoes: Piton de la Fournaise and Merapi. For Piton de la Fournaise, the reduction of the tropospheric noise is efficient for 30% and 60% of the data sets for GACOS and ERA5, respectively. For Merapi, the performance reaches 40% for GACOS and 50% for ERA5. Although GNSS local stations provide real-time information about tropospheric delays, their potential for improving InSAR corrections on active volcanoes is under-exploited. Here, we produce local GNSS-based tropospheric corrections and compare their performance to global weather-based models. For Piton de la Fournaise, the gain of performance with 34 GNSS stations is about 25% compared to ERA5 models. GNSS-based corrections increase the signal-to-noise ratio in InSAR time series allowing the detection of ground displacements between July and December 2021. For Merapi, GNSS-based models with only 5 stations spatially distributed at different elevations are as efficient as ERA5 models. GNSS-based corrections induce a decrease in the noise level from values { >} 1–0.5 cm in a period of quiescence. Here, we show that GNSS-based models are an efficient alternative to global weather-based models for instrumented volcanoes. The proposed approach paves the way toward near real-time InSAR monitoring of volcanic unrest and other processes (landslides, groundwater extraction)
Glacial ring forms on Axel Heiberg Island, Nunavut, Canada
No full textInternational audienceRing forms are a type of landform consisting of a series of ridges and troughs with a circular, sinuous, and anastomosing morphology. This striking landform was initially identified in the Canadian High Arctic on the south coast of Devon Island, Nunavut, Canada. Here, we report on the identification of ring forms near Mokka Fiord on Axel Heiberg Island, Nunavut, Canada. Utilizing field observations, ultra-high-resolution light detection and ranging (lidar), and ground-penetrating radar (GPR), we characterize and compare the morphometry and sedimentology of ring forms at Mokka Fiord with other similar periglacial, paraglacial, and glacial landforms. The Mokka Fiord ring forms range in diameter from 6 to 37 m and reach up to 1.5 m in height and are composed of clast-rich glaciofluvial sediment and till. Based on both regional and local observations, results from nearby field investigations of glacial outwash plains on Axel Heiberg Island, and comparisons to other periglacial and glacial features sharing a similar morphology, we interpret Mokka Fiord ring forms as glacial in origin. Specifically, we propose Mokka Fiord ring forms are ice-marginal glaciofluvial kame terraces formed from the passive ablation of buried glacial ice, leading to the formation of hummocky ring forms. This formation mechanism supports a predominantly polythermal glacial environment with limited water supply throughout much of the Holocene
Induced Polarization of Clay Under Freeze-Thaw Cycling and Desiccation Processes: Effect of Surface Cracking Propagation
No full textInternational audienceFreeze-thaw cycles and desiccation drastically affect soil surface cracking and shrinkage processes, altering soil pore structures and hydraulic properties. However, studies using geophysical methods to assess how soil crack patterns and shrinkage respond to climate change remain scarce. Induced polarization, a non-intrusive geophysical technique, is highly sensitive to the moisture content and pore structure of the porous media. For the first time, we investigate the effect of soil surface crack patterns on complex conductivity under freeze-thaw cycling and desiccation processes using a new experimental set-up. Results show that Y-junction-dominated crack patterns form on the sample surface after freeze-thaw cycling, and surface cracking network extends along existing cracks until desiccation ceases. Our findings from induced polarization experiments reveal that two components of complex conductivity are linearly sensitive to surface crack ratio and gravimetric water content. Additionally, they both exhibit a similar decay behavior with drying time. In summary, these results indicate that induced polarization provides a preliminary approach for monitoring the surface crack patterns of clayey soils
Comprehensive Assessment of the Jebel Zaghouan Karst Aquifer (Northeastern Tunisia): Availability, Quality, and Vulnerability, in the Context of Overexploitation and Global Change
No full textInternational audienceKarst aquifers in the Mediterranean region are crucial for water supply and agriculture but are increasingly threatened by climate change and overexploitation. The Jebel Zaghouan aquifer, historically significant for supplying Carthage and Tunis, serves as the focus of this study, which aims to evaluate its availability, quality, and vulnerability to ensure its long-term sustainability. To achieve this, various methods were employed, including APLIS and COP for recharge assessment and vulnerability mapping, SPEI and SGI drought indices, and stable and radioactive isotope analysis. The findings revealed severe groundwater depletion, primarily caused by overexploitation linked to urban expansion. Minimal recharge was observed, even during wet periods. APLIS analysis indicated moderate infiltration rates, consistent with prior reservoir models and the MEDKAM map. Isotopic analysis highlighted recharge from the Atlantic and mixed rainfall, while Tritium and Carbon-14 dating showed a mix of ancient and recent water, emphasizing the aquifer’s complex hydrodynamics. COP mapping classified 80% of the area as moderately vulnerable. Monitoring of nitrate levels indicated fluctuations, with peaks during wet years at Sidi Medien Spring, necessitating control measures to safeguard water quality amid agricultural activities. This study provides valuable insights into the aquifer’s dynamics, guiding sustainable management and preservation efforts
Multi-technique estimation of ice mass balance in Greenland: impact of the uncertainties on firn densification and GIA models
No full textInternational audienceWe conduct a comprehensive comparison of ice mass balance (IMB) estimates for Greenland derived from satellite observations of ice surface elevation changes (SEC), gravity and global navigation satellite system (GNSS) observations. Our analysis integrates data from the ICESat and CryoSat-2 satellite altimetry missions, augmented by optical stereo-imagery for peripheral glaciers, and GRACE satellite gravimetry mission, spanning the 2003-2008 and 2011-2015 periods. We also consider three firn densification models (FDM) and five glacial isostatic adjustment (GIA) models for correcting the data sets for these effects when necessary. Our results reveal significant differences among FDM corrections applied to SEC observations, with particularly large variations in IMB estimates reaching up to 90 Gt yr-1. To address this, we develop an innovative method for estimating equivalent firn corrections to the ice elevation observations, based on a least-squares fit of filtered ice SEC observations to GRACE mass-change estimates. This approach is both simple and independent from climate models assumptions and shows minimal sensitivity to GIA model differences. Using this method, we estimate IMBs for Greenland at -217.6 15.7 Gt yr-1 for 2003-2008 and -253.2 18.8 Gt yr-1 for 2011-2015. Importantly, these values indicate an acceleration of the thinning rate, not consistently captured by the IMB estimates inferred from the ice SEC observations corrected by FDMs. Finally, we compute elastic ground deformation induced by ice mass change during 2011-2015, using the four proposed mass-variation distributions and compare the predicted vertical velocities with GNSS observations in Greenland, accounting for all GIA models. While all models are consistent with most of the GNSS-derived uplift rates, they cannot fully explain the observed vertical velocities, especially in the South-East Greenland, which confirms the need to refine our understanding of GIA contributions in this region
Melt inclusion bubbles provide new insights into crystallisation depths and CO<sub>2</sub> systematics at Soufrière Hills Volcano, Montserrat
No full textInternational audienceImproved understanding of the magmatic system of Soufrière Hills Volcano, Montserrat (SHV) is needed to inform future hazard management strategy, and remaining uncertainties include the depth of magma storage and the source of ongoing gas emissions. Eruptive activity between 1995 and 2010 has been proposed to be sourced from either a dual chamber or transcrustal mush-based magmatic system, with volatile solubility models using H2O and CO2 from melt inclusion (MI) glass estimating depths of 5–6 km. To date, published SHV MI volatile data have neglected the vapour bubbles now known to sequester the bulk of MI magmatic carbon. Total CO2 concentrations in SHV magma are therefore underestimated, together with volatile-derived entrapment pressures and inferred magma storage depths. Here, we present a new dataset of volatile (H2O and total CO2) and major element concentrations in plagioclase- and orthopyroxene-hosted SHV MI, that span almost all of the eruptive activity (Phases 1, 2, 4, and 5), and include the first measurement of bubble-hosted CO2 for SHV and indeed the Lesser Antilles Arc. Analyses were conducted using Raman spectroscopy, ion microprobe, and electron probe analysis. Dacitic–rhyolitic MI occur within andesitic whole rock compositions. Volatiles in MI glass are similar to published studies (H2O 2.47–7.26 wt%; CO2 13–1243 ppm). However, bubble-hosted CO2 contributes 9–3,145 ppm, to total inclusion CO2 with 5%–99% (median 90%) of CO2 sequestered within bubbles, and total CO2 concentrations (131–3,230 ppm) are significantly higher than previously published values. Inferred entrapment depths from our dataset range from 5.7 to 17 km – far greater than previous estimates – and support a vertically elongated magmatic system where crystallisation spanned both upper- and mid-crustal depths. Our CO2 measurements enable new estimation of CO2 sources and fluxes. As a total of 4.5 Mt of CO2 was held in SHV magma during the aforementioned phases, the maximum amount of CO2 that can be emitted from a batch of SHV magma is ∼1500–1750 tonnes/day. Measured CO2 fluxes are significantly higher, indicating additional input of CO2 into the system from greater depths. Our study shows that including bubble-hosted CO2 redefines understanding of the SHV plumbing system
Current research on aquifer thermal energy storage (ATES) in Germany
No full textInternational audienceZusammenfassung Die vorliegende Arbeit stellt die aktuelle Forschung in Deutschland zu thermischen Aquiferspeichern (ATES, engl.: aquifer thermal energy storage) und thermischen Bergwerksspeichern (MTES, engl.: mine thermal energy storage) vor. Es werden drei Forschungsstandorte zu Niedertemperatur-ATES (NT-ATES), acht zu Hochtemperatur-ATES (HT-ATES) sowie zwei zu MTES beschrieben. Trotz einer breit gefächerten Forschungslandschaft mit unterschiedlichen räumlichen Untersuchungsskalen, Forschungszielen und -methoden zeichnet sich der Großteil der Forschungsvorhaben durch einen niedrigen Technologie-Reifegrad (TRL, engl: technology readiness level) aus. Die große Anzahl an HT-ATES-Forschungsstandorten weist auf ein erhöhtes Forschungsinteresse im Vergleich zu LT-ATES hin. Einen aktuellen Forschungsschwerpunkt stellt insbesondere die ATES-Integration in Wärmenetze dar, wobei jedoch fast keines der Projekte konkret auf eine praktische Umsetzung abzielt. Im Rahmen künftiger Forschungsarbeiten sollten daher prioritär praxisnahe Demonstrationsanlagen errichtet sowie Schlüsselstandorte identifiziert werden. Abschließend wird in dieser Arbeit die Notwendigkeit optimierter regulatorischer Rahmenbedingungen diskutiert, welche Umweltrisiken adressieren sowie eine hohe Anlagenqualität und effiziente Genehmigungsverfahren sicherstellen.Abstract This paper reviews the current research on aquifer thermal energy storage (ATES) and mine thermal energy storage (MTES) in Germany providing descriptions of 3 low-temperature ATES (LT-ATES), 8 high-temperature ATES (HT-ATES), and 2 MTES research sites. While the overview reveals a diverse field of investigations spanning various spatial scales, research objectives, and methodologies, the predominant focus is limited to early-stage research with low technology readiness levels (TRL). The high number of HT-ATES research sites suggests greater research interest compared to LT-ATES. The integration of ATES into district heating (DH) grids in particular is a prominent research focus, yet almost none of the projects are specifically intended for practical implementation. Future research should therefore prioritize real-world demonstration projects and identify key locations, which is crucial for showcasing the benefits of ATES. The need for a streamlined regulatory framework that addresses environmental risks and ensures installation quality and efficient permit procedures is also discussed
Dempster-Shafer theory for object matching under data imperfection constraints: Application to wastewater networks' line matching
No full textInternational audienceThe goal of object matching is to identify objects representing the same real entity across multiple spatial datasets. This involves comparing and linking data from different sources using similarity measures, with the final matching decision made by combining these measures. Object matching is especially valuable for creating accurate and complete spatial datasets for underground networks, where data often come from various sources and may have imperfections like imprecision or incompleteness. The Dempster-Shafer (DS) theory, which uses mass functions to model data imperfections, is considered the best method for combining imperfect data. However, previous DS-based approaches produced highly conflicting results when many potential candidates for an object existed. In this work, we present an improved DS-based line matching approach for wastewater networks. Our key contributions include introducing candidate ranking, bidirectional measure combination, and mixed models to convert similarity measures into masses. We validated our approach through experiments on both synthetic and real-world datasets. The results demonstrate that our contributions significantly reduce conflict and improve the accuracy and correctness of the matching decision