Volcanoes produce infrasound –acoustic waves below 20 Hz– during explosive eruptions. Often, these eruptions inject large amounts of ash into the atmosphere, reaching altitudes of commercial flights (~8-12 km), thus posing a direct threat to civil aviation worldwide. Infrasound can travel up to thousands of kilometers through the atmosphere and is therefore a promising tool to remotely (>250 km) detect volcanic eruptions and alert experts and authorities of the danger by an ash cloud. Long-range infrasound records have been investigated for many explosive eruptions, but its efficiency as a monitoring system has not been addressed in details yet. The Volcanic Information System (VIS) was created within the Atmospheric dynamics Research InfraStructure in Europe (ARISE) projects under the European Commission’s programs FP7 and H2020), and originally in collaboration with the Toulouse Volcanic Ash Advisory Centre (VAAC), as a prototype monitoring system that uses long-range (>250 km) infrasound to remotely detect and notify of explosive eruptions. The integration of the VIS into the EPOS Thematic Core Service Volcano Observation (TCS-VO) or HOTVOLC web-GIS interface (OPGC, CNRS-INSU) is currently being discussed within the European Geo-INQUIRE project (HORIZON-INFRA-2021-SERV-01). The VIS is designed to use global observations from the International Monitoring System (IMS) infrasound network (currently comprising 54 of 60 planned stations), and it can also incorporate non-IMS infrasound array data. To remotely detect an eruption, the VIS relies on the Infrasound Parameter (IP), which is a data-derived measure accounting for propagation effects, detection persistency, and amplitude at each detecting station. The efficiency of this methodology has been investigated extensively considering 10 years of global explosive activity. Recently, we have expanded the VIS capabilities to use open-access streamlined and standardized IMS-derived infrasound array signal processing data products, and to allow the incorporation of pre-calculated propagation effects in the form of back-azimuth deviation interpolations for each source-station pair.In the current study, we focus on two similar energetic explosive eruptions (June 2011 at Cordón Caulle and April 2015 at Calbuco, Chile) to assess the reliability of the VIS to detect, locate and raise automatic notifications for the VAACs. We base this on open-access data from 2011 to 2015 of IMS stations up to ~4800 km away from both volcanoes. With operability in mind, we show how this methodology could be implemented in different scenarios, e.g. for monitoring Mount Etna, Italy.

Understanding the internal structure of volcanoes is essential for improving predictions of eruptions and for assessing hazards. However, creating high-resolution models of their interiors remains a significant challenge. At Piton de la Fournaise, we conducted an innovative 3D electrical resistivity tomography to produce a new high-resolution image of the subsurface beneath the Terminal Cone, extending down to 1 km below the summit. Our model not only images a large hydrothermal zone beneath the layered lava flows, but also reveals conductive offshoots extending toward the surface beneath the Bory crater and along faults linked to the Dolomieu crater. These findings suggest that hydrothermal activity is strongly influenced by volcano-tectonic features at the summit. This study provides valuable insights into fluid circulation, magma transfer, and instability, offering a new framework for understanding the present structure of Piton de la Fournaise and proposes a novel approach for studying the spatio-temporal evolution of volcanoes worldwide.

Our understanding of dynamic volcanic processes (fluid transfers at depth and eruptions, collapses and sliding, etc.) relies directly on our knowledge of the geometries of magmatic and hydrothermal systems, mechanical heterogeneities and how these structures evolve in time. Imaging the internal structure and temporal dynamics of volcanoes still represents a real challenge to univocally identify the processes that govern their evolution, including eruptive precursors, instabilities phenomena, surface manifestations and their repercussions. It is therefore necessary to more rigorously constrain the geometry and the spatio-temporal dynamics of these structures, and their activation at different depths. The behaviour of these structural volcanic features strongly depends on physical parameters such as temperature and fluid composition that can be assessed using a range of complementary ground and remote observations. Among these, geophysical methods provide images of the internal structure, which can subsequently be translated in terms of geological structure and evolution. Such constraints are also necessary to provide more realistic numerical models. Recent improvements to the available suite of the instrumentation for volcanological studies, including field geophysics (ground and airborne-Unmanned Aerial Vehicles, UAVs), remote sensing methods and numerical capabilities, allows us to build even more comprehensive analyses of such terrestrial phenomena. In addition, combining several spatial (local and more regional) and temporal scales (one-off studies, time lapse through reiterations, time series) help to better follow the dynamics of the edifices, anticipate eruptive crises and associated hazards. Here we focus on the highly active and well monitored Piton de la Fournaise laboratory volcano, which is an excellent case study to develop and apply new methodologies in order to address both scientific and societal issues. Amongst the most significant parameters, recent studies have evidenced the potential of magnetic field measurements in imaging thermal anomalies (strong influence of temperature on magnetic measurements) and mechanical heterogeneities (fracturing-alteration at depth). Electrical resistivity is also a powerful tool in volcanic contexts, being very sensitive to fluid contents and particularly well suited to image the shallow structure of a volcanic edifice through, for example, innovative 3D surveys, or more in-depth using magnetotellurics measurements. Based on the analysis of combined recent reiterations of ground magnetic measurements, UAV magnetic and thermal infrared acquisitions, as well as high resolution electrical resistivity measurements, we focus on the 3D structure and recent evolution of the summit activity at Piton de la Fournaise, using additional constraints such as seismicity and deformation (InSAR inverse modelling). This study confirms that detecting resistivity and magnetization anomalies, and quantifying their spatiotemporal evolution, can provide powerful tools for imaging volcanic systems at various scales and for providing warning of associated hazards. It also highlights the necessity for 4D monitoring of volcanic edifices using this method to provide greater precision, an important issue that is now made possible using UAV and near real time analyses. These observational datasets aim to be integrated in open databases distributed through French and European research structures and infrastructures, namely the National Volcanology Observation Service (CNRS-INSU), Epos-France and Data Terra Research Infrastructures, as well as the EPOS VOLC-TCS.

Mount Hasan (Türkiye), an active stratovolcano, has had two eruptions during the Holocene and currently exhibits fumarole activities at its summit. Despite its potential hazards, it is not under any monitoring. In a first-of-its-kind study in Türkiye, we utilized VolcFlow and TephraProb (Tephra2) codes to conduct a scenario-based probabilistic hazard assessment and forecast the explosive behavior of Mt Hasan during a volcanic eruption. In our scenario-based hazard assessment study, tephra fall deposits primarily accumulate from plumes dispersing in the NE, E, and SE directions, with occasional accumulation in the SW direction. Eruption source parameters, such as eruption duration, discharged mass, and plume heights, naturally affect the impact rate. The plume heights selected for modeling are (min–max) 5–10 km, 10–15 km, 15–20 km, 20–25 km, and 25–30 km to illustrate related tephra dispersal. All probability and probabilistic isomass maps have been drawn. Volcanic flows were modeled considering the topographic effects using the digital elevation model of the volcano. As a result, an approach was made especially to probable depositional areas and thicknesses. In conclusion, this study identified the areas most likely to be impacted by tephra deposits (fall, flow) given the scenarios applied and developed a comprehensive impact maps. Our findings underscore the urgent need for close monitoring of Mt Hasan.

Volcanic explosive eruptions produce large amounts of low-frequency (250 km) with sustained ash-columns and provide early warnings to mitigate the risk that eruptions pose to civil aviation. Additionally, it can reconstruct the chronology of eruptions, and provide volcanic source constraints (acoustic intensity, gas flow, etc.). The system is designed to integrate the IMS and national infrasound stations to gather all available infrasound detections in the area of interest. The detections rely on the Progressive Multi-Channel Correlation (PMCC) method, which separates coherent infrasound waves (detections) from noise. The VIS is based on the Infrasound Parameter (IP) criterion to establish when an eruption is in course, accounting for atmospheric propagation effects, detection persistency, and amplitude. An operational VIS demonstrator will be deployed on servers of the Observatoire de Physique du Globe de Clermont-Ferrand (OPGC, CNRS-INSU and University Clermont Auvergne) to monitor Mt. Etna and Stromboli in real-time using data from the Amiata infrasound array (AMT) operated by the University of Florence. The data products of the VIS demonstrator will be available through an application programming interface (API) hosted at OPGC, where also an archived catalogue of European volcano eruptions and the real-time data products for AMT will be hosted.As part of the European Geo-INQUIRE project (HORIZON-INFRA-2021-SERV-01), the VIS will be integrated into the Thematic Core Service Volcano Observation (TCS-VO) of the European Plate Observing System (EPOS). Future developments will include integration into web services such as the HOTVOLC web-GIS interface (OPGC, CNRS-INSU) or the EPOS Data Portal.

Energetic volcanic eruptions can inject large amounts of ash into the atmosphere, posing a direct threat to commercial flights and potentially overwhelming populations down the ash plume path. These eruptions also produce infrasound –acoustic waves below 20 Hz– which can propagate over hundreds to thousands of kilometers in the atmosphere due to favorable ducting conditions and its intrinsic low attenuation.Within the Atmospheric dynamics Research InfraStructure in Europe (ARISE) project (FP7, H2020), in collaboration with the Toulouse Volcanic Ash Advisory Centre (VAAC), the Volcanic Information System (VIS) was created as a prototype monitoring system that uses long-range (>250 km) infrasound recordings to remotely detect and notify of explosive eruptions.The VIS was designed to primarily use data recorded by the global International Monitoring System (IMS) infrasound network (53 stations of 60 planned stations), but it can also include non-IMS arrays (e.g., AMT, Florence, Italy) to increase the coverage. At its core, the VIS relies on a data processing output denoted the Infrasound Parameter (IP) to establish when an eruption occurs. The IP value accounts for propagation effects, detection persistency, and infrasound signal amplitude.Currently, we are thoroughly testing the capabilities of the VIS, and considering the future developments that can be implemented to improve its reliability, before it is made publicly available.Our recent efforts have expanded the VIS capabilities to use open-access (OA) streamlined and standardized IMS-derived infrasound array signal processing data products. We found that the eruption notification results using OA data were comparable to the notifications calculated with regular IMS data (i.e., PMCC detections).In this work, we look in detail into the eruptive periods of April 2010 Eyjafjallajökull (Iceland), May 2016 Etna (Italy), and April 2021 La Soufrière (Saint Vincent island, Saint Vincent and the Grenadines), and test how year-long back-azimuth deviation predictions (i.e., pre-calculated back-azimuth bias values) for the nearest IMS stations (

During years 2021–2022, an unusual seismic swarm was recorded at crustal level beneath the Monts Dore volcanic province (France). Complementary field and remote measurements were performed. Together with the time series recorded on the seismological and GNSS national networks, these measurements were fundamental for monitoring the evolution of the seismic swarm and deciphering its origin. Although a potential vertical migration of the seismic events is suggested, the complementary measurements presumably discard the hypothesis of magma intrusion at shallow crustal level. The ascent of a CO2-rich fluid originating from the mantle might instead have reacted with the hydrothermal system beneath the Monts-Dore since at least the summer 2021 leading to the reactivation of pre-existing tectonic structures with known associated seismicity. Feedback on the management of the 2021–2022 seismic swarm prompts for several recommendations that should be considered in future to better face and address at the national level the issues raised at long-dormant volcanic provinces in mainland France.

Long-dormant volcanic provinces remain excellent proxies in studying active edifices. The Monts Dore volcanic province (French Massif Central) has been recently the site of a unique seismic episode. Geophysical surveys were conducted at different horizontal and vertical spatial scales. Magnetic anomalies highlight mechanical heterogeneities consistent with the regional tectonic context. Low-conductive structures imaged suggest the presence of fluid rising along main paths at various depths. Although we cannot strictly exclude a purely tectonic explanation, our data seem to support the origin of seismicity as being linked to the injection of fluids at depth controlled by internal structural constraints.

Volcanic activity disturbs the existing magnetic field, and analysis of the resulting magnetic anomalies provides information about the internal structure and evolution of active systems within edifices. This study focuses on the South-East Rift Zone (SERZ) of Piton de la Fournaise, specifically the eruptive site of September 2022, which offers a unique opportunity to characterise the thermal state, the subsurface structures, and to obtain information about the global fluid dynamics of this highly active area. For this purpose, we performed high-resolution aeromagnetic surveys using an Unmanned Aerial Vehicle (UAV) in November 2022 and May 2024 to investigate the evolution of the eruptive site. At a regional scale, first order 3D modelling of the magnetic anomalies primarily reveals a negative magnetic axis with a N120° orientation. Comparative analysis with 3D Interferometric Synthetic Aperture Radar data modelling shows a significant correlation between this demagnetised axis, the depth, and the volume of magmatic intrusions along the rift-zone. This result suggests the presence of a N120°-trending mechanical weakness intersecting the SERZ that has some control over the internal dynamics of the magmatic and hydrothermal fluids in the area. In addition, we quantify the temporal evolution of the magnetic signals associated with the September 2022 lava flow by means of repeated UAV measurements from May 2024 and estimate a global increase of several hundreds of nanoteslas (between 150 and 900 nT) linked to the magnetisation caused by the lava cooling during this time. We then successfully explore on a more local scale the ability of UAV magnetic prospecting to detect lava tubes using semi-quantitative 2D models. These results demonstrate the potential of UAV magnetic surveys to characterise the spatio-temporal evolution of magnetic signals from Piton de la Fournaise. Such multi-scale analysis of magnetic structures within the edifice indicates the potential of 4D monitoring for obtaining a better understanding of the volcano’s evolution.

Atmospheric composition varies both spatially and temporally, notably in terms of relative humidity and greenhouse gases. Current methods rely on massive and expensive sensors deployed sparsely. Here, we are interested in developing a multi-gas sensor that targets very small atmospheric composition variations. In addition, it intends to be gas specific, lightweight, autonomous and compact. Targeted gases are either greenhouse gases such as CO2, CH4 , and N2O, or toxic gases such as CO and SO2. For this purpose, we have developed a Photoacoustic Spectroscopy sensor, using Mid Infrared QCL laser sources, which achieve a very narrow spectral linewidth and have a good potential for miniaturization. We developed a dedicated electronic device to perform data acquisition. Our prototype is beginning its calibration phase in a lab environment, prior further integration for real time measurement.

For environmental purposes, it is important to measure the temporal and spatial variations of a number of gases. Human-related activities' gases emissions need monitoring relatively to climate change, landfill survey or air pollution. A current limitation is the deficiency of compact and lightweight manufactured sensors capable of selectively quantifying air pollutants, such as CO 2 , CH 4 , CO or N 2 O. Currently used multi-gas sensors are expensive, large and need calibration frequently for each gas to be detected. Photoacoustic Spectroscopy has demonstrated to be a promising technology for addressing downsizing and integration of multi-gas detection. This shows the potential for miniaturization of mid-IR sensors [1], [2].

Current issues on air pollution monitoring or greenhouse gases emissions rely on the sparse use of expensive gas sensors. We target to develop a portable miniaturized sensor with the capacity of being gas-specific, lightweight and autonomous. We present here results obtained with our newly packaged Photoacoustique Module. We also present the development of its dedicated electronic companion system.

The Volcano Observations Thematic Core Service (VOLC-TCS) is one of ten core services forming the European Research Infrastructure Consortium for the European Plate Observing System (EPOS ERIC). The main objective of the VOLC-TCS is the implementation of a technical, financial, and legal framework compliant with EPOS ERIC to (i) strengthen the European volcanology community represented by Volcano Observatories (VOs) and Volcanological Research Institutions (VRIs), and (ii) provide virtual access to the community’s data, data products software and services (DDSSs) from volcanoes in Europe and European overseas territories. The efforts of the VOLC-TCS community began prior to the appointment of EPOS as an ERIC and have followed a long-term work plan that started in 2002. One of the main challenges for the management of volcanological data has consisted in their great heterogeneity regarding technical characteristics and also legal aspects (e.g. different data policies among the data providers, different purposes for the use of data, ranging from science to monitoring, early-warning and crisis response, and communication and outreach). Another challenge has derived from the consistency of the VOLC-TCS’ products with the overall service provision of EPOS, which merges services from different Earth Science communities (seismology, GNSS, geomagnetic, geochemistry, geology, etc.). Some of the services used in volcanology are in common with the other communities, thus the implementation work was also devoted to harmonising the data and products with standards defined by other TCSs. Yet another important task has been the implementation of the community Gateway to expose and enable access to services not fully compliant with EPOS, or to services implemented by institutions outside the EPOS perimeter, as well as to create a platform that can act as an interface between the VOLC-TCS and data infrastructures operating at a global level (e.g. WOVOdat). Based on the experience gained and the results achieved, we report here on the state of the art of the VOLC-TCS implementation since 2018 and propose future actions to address some of the main technical challenges and measures to ensure mid-to-long term sustainability of the services.

The present Self-Potential (SP) dataset acquired in the Chaîne des Puys is the result of four decades of measurements carried out by master's students, PhD students, researchers, and engineering offices under the auspices of the Laboratoire Magmas et Volcans (LMV) and the Observatoire de Physique du Globe de Clermont-Ferrand (OPGC). Acquired in the 1980s by Maurice Aubert and his collaborators (e.g. [1], [2], [3]), this Self-Potential dataset was completed as part of the CAPRICE project focused on the hydrosystem of the Chaîne des Puys. The methodology and equipment used for data acquisition has remained unchanged since the first measurement in 1987. As a result, this dataset compiles more than 20,000 SP measurements and covers an area of almost 200 km². The SP data are intended to serve as the basis for geological models, coupled with geological and other geophysical data, according to the method described in Aubert and Atangana, 1996. After interpolation, SP data can be used to identify preferential groundwater flow paths and to delineate the surface of hydrogeological watersheds. As indicated in the literature, they also be used to identify possible recharge zones or areas of permeability contrast.

Near-real time analysis of magnetization can provide important information for the imaging of volcano systems and their spatiotemporal evolution. This study focuses on the contribution of volcano-magnetic signals from reiterations of ground magnetic measurements to investigate the evolution of active structures at the Piton de la Fournaise volcano from 2017 to 2020. Changes are demonstrated by magnetic anomalies along a reference profile by means of the reiteration periods. These variations are first modeled qualitatively in 2D using electrical resistivity constraints in order to investigate the evolution of magnetization at depth through time, and the model is subsequently compared with the 3D intrusive activity from depth up to the surface from Interferometric Synthetic Aperture Radar (InSAR) inverse modeling. The shallow areas of demagnetization modeled from one reiteration to another are consistent with the geometry and location of the underlying intrusions revealed by the 3D InSAR models, suggesting strong thermal, stress, and electrokinetic effects due to magmatic activity not only at the surface but also at depth, along the main magmatic paths. It also raises a question as to the extent of the associated thermal diffusion processes at the scale of individual magma injections. This study confirms that detecting resistivity and magnetization anomalies, and quantifying their spatiotemporal evolution, can provide powerful tools for imaging volcanic systems at various scales and for providing warning of associated hazards. It also highlights the necessity for 4D monitoring of volcanic edifices using this method to provide greater precision, an important issue that is now made possible by the use of Unmanned Aerial Vehicle measurements.