Jean-Christophe Komorowski

Pedestrian tsunami evacuation depends on wave arrival time, warning dissemination, the spatial configuration of the exposed area and population response. These factors, studied by distinct disciplines, are rarely integrated within a single framework, limiting the use of evacuation models for local planning. We present TsunaWAVE (Web interface for Agent-based modelling and Visualisation of Evacuation), an open web interface that links tsunami hazard scenarios with agent-based evacuation scenarios through a one-way sequential coupling, in which simulated arrival times define the time budget against which precomputed evacuation outputs are read, making both explorable by decision-makers. The agent-based model simulates warning dissemination, pre-evacuation delay and movement towards safe areas, while the published surrogate model (Landslide-Tsurrogate v1.0) provides first-wave arrival times for submarine landslide scenarios. The framework is applied to the Mamoudzou waterfront (Mayotte, France), where lead times are 10 to 16 minutes in two reference scenarios and 759 exposed individuals were counted using drone imagery, video line-crossing and manual counts. Ninety scenarios, each replicated 42 times, rank three operational levers (warning, safe-area accessibility and social contagion). Warning reliability is the first-order control. Under degraded warning without social contagion and a 10 min lead time, fewer than 8% of agents reach safety, whatever the safe-area configuration. Social contagion, implemented as neighbourhood-based imitation, ranks second; it cannot substitute for a reliable warning but partially compensates for a degraded one when time allows, raising the share reaching safety at 16 min from 19.4% to 43.8%. TsunaWAVE makes these findings openly available to local authorities at https://geodata.univ-montp3.fr/web-app/irima-mayotte/.

Monitoring data are critical for understanding volcanic unrest and eruption, but they often lack the ability to constrain the pre‐eruptive magma processes. As such, an increasing number of studies couple monitoring data with petrological tools to obtain insights into the causes and durations of magmatic processes. The 2018–2020 eruption of the submarine Fani Maoré (FM) volcano, Comoros Archipelago, is an excellent location to correlate diffusion chronometry with real‐time monitoring data. Zoned olivine in FM testify that deep basanitic magma interacted with a more evolved reservoir. Diffusion modeling in olivine shows an increase in the magma interaction times (0.5–3 to ∼20 months) as the eruption progresses, implying that basanitic magma stalled near the more evolved reservoir. Additionally, two major intrusive events were identified—in March 2019 and March 2020. The first intrusion occurred as seismic and deformation signals decreased possibly due to enhanced mixing and unlocking of the more evolved mushy reservoir after intrusion. The second intrusion correlates with a change in the locations of seismic events before seismicity and deformation become minor, implying that this intrusion occurred before magma drainage and waning of the eruption. Lastly, by coupling diffusion geochronometry and geophysical monitoring, the magmatic reservoir at FM can be placed at a greater depth (∼30 km) than previously thought, which is consistent with seismic events. Hence, our integrated approach of petrologic tools and real‐time monitoring aids in providing new insights into the magma storage locations and magma‐mush interactions at submarine volcanos.

La Soufrière de Guadeloupe volcano exhibits microseismic activity dominated by volcano‐tectonic repeaters, mainly occurring in swarms clustered in a sub‐vertical conduit beneath the Tarissan acid lake (TAS) at depths less than 800 m. Following the April 2018 earthquake (Mlv 4.1), which likely damaged the dome, swarms intensified and show seasonal modulation with more events in October–November. We analyze 5 years of daily seismicity, GNSS‐derived deformation, and hydrological data to investigate controls on this modulation. We enhance groundwater level resolution by modeling TAS level from daily rainfall. To isolate local seasonal deformation, we compute Global Navigation Satellite Systems (GNSS) baselines and derive regional strain time series. Using Multichannel Singular Spectrum Analysis, we identify annual and sub‐annual oscillations in seismicity, groundwater, and vertical strain, highlighting hydrological forcing. Elastic deformation from surface load cannot explain observed strain or stress at depth. In contrast, a poroelastic model calibrated with GNSS strain and lake‐level variations shows pore pressure fluctuations modulate Coulomb stresses by several kPa at microseismic depths. Stress amplitude and phase match seismicity peaks, supporting pore pressure as the main driver of seasonal modulation. Effective elastic moduli from geodetic data are an order of magnitude lower than laboratory rock values, consistent with a fractured dome. Our multi‐parameter time series analysis separates hydrologically driven background seismicity from residual signals, potentially linked to thermoelastic effects or magmatic fluid migration, offering a framework to detect departures from external forcing and improve monitoring of hydrothermal unrest and phreatic eruption precursors.

Volcano unrest associated to ascent of magmatic fluids at shallow depths in the presence of a very active hydrothermal system can promote or enhance extensive hydrothermal rock alteration and form low-strength layers within the edifice. This process can favour flank instability and culminate in partial flank collapse with emplacement of debris-avalanches and pyroclastic-density-currents from potential laterally-directed explosions, engendering significant risks to the surrounding population. In the MYGALE ANR project, we focus on hydrothermal alteration timescales of andesitic rocks to better assess the hazard of volcano flank instability at La Soufrière de Guadeloupe volcano (Eastern Caribbean, France). We characterised the mineral chemistry and the 3D porosity of a suite of unaltered to highly altered andesite samples from the volcanic dome of La Soufrière. Chemical and textural investigation shows the progressive deterioration of plagioclase into kaolinite and Na-alunite, the dissolution of the volcanic glass, and silica precipitation. By comparing the natural products with geochemical computations, we suggest that hydrothermal alteration prevailing at the base of the dome is primarily dominated by the reactive fluid composition (H2O, HCl, and H2SO4) and to a lesser extent by water/rock (W/R) ratio (from 0.5 to 10), pressure close to 100 bars, and temperature (from 150 to 250 °C). We propose that acidic aqueous solutions containing 0.1 mmol/L HCl and 0.15–0.5 mmol/L H2SO4, corresponding to pH of 3.0–3.5, are mandatory to co-precipitate kaolinite, Na-alunite, and silica. We also investigate the alteration of the volcanic dome of La Soufrière under these acidic hydrothermal conditions, using both batch and reactive percolation experiments, combined with kinetic modelling using PHREEQC. The experimental results highlight a strong reactivity of the rhyolitic residual glass and the plagioclase phenocrysts, leading to the formation of clay minerals such as illite, while the pyroxenes and the Fe-Ti oxides remain largely unaltered. Spatial mineralogical heterogeneities develop along the reacted cores, with intense dissolution and secondary mineral precipitation near the fluid inlet and preservation of primary phases toward the outlet. Kinetic simulations of plagioclase dissolution in either pure water or HCl highlight the influence of temperature, W/R ratio, grain-size, and pH on silicon release. Increased temperature and a lower W/R ratio enhance the dissolution rate, while larger grain-sizes reduce the reactive surface area and slow reaction progress. Anorthite dissolution kinetics and alteration extent are also strongly pH-dependent, remaining negligible at pH ≥ 2, becoming rapidly self-limited at pH~1, and evolving continuously under extremely acidic conditions (pH = 0). The alteration sequence simulated following the conditions of the reactivation of La Soufrière since 2018 (i.e., temperature increase, fluid acidification, and rainfall reduction) predicts the preferential formation of Na-alunite and silica precipitation, which reduces the formation of slippery argillic discontinuities and imparts some internal cohesion on the dome rocks. In contrast, an increase in the W/R ratio, as predicted by global warming, would result in preferential formation of phyllosilicates that would serve to increase dome instability. The combined experimental and modelling approach provides a detailed view of the controls on hydrothermal alteration sequence in volcanic systems.

Dating submarine volcanic rocks is essential for understanding the relationship between tectonics and volcanism, as well as for characterizing the evolution of volcanic systems, for instance. The K-Ar chronometer is generally used but dating young rocks (

Submarine volcanoes make up ~75% of volcanism on Earth, yet they are one of the least explored volcanic features. Our understanding of these eruptions is limited due to challenges in monitoring these often remote volcanos with summits deep underwater. Nonetheless, consequences of their eruption can pose significant risks to the local economy and society (e.g. tsunamis) [1]. The recent (2018-2020), unanticipated submarine eruption of Fani Maoré ~50 km East of Mayotte island (Comoros Archipelago) [2] demonstrates this. Monitoring of the area increased only after its eruption, leading to the discovery of a submarine volcanic chain near the island of Mayotte. After the Fani Maoré eruption ended, seismicity and CO2 fluid emissions still continues below the so-called Horseshoe complex [3,4]. This complex is composed of recent phonolitic pyroclastic cones and lava flows, a number of them are of Holocene age and significant volume. Thus, it poses a critical risk to the >320000 inhabitants of Mayotte, as it is only ~10 km from the island [5]. Scenarios for future increased unrest and eruptive activity need to be considered. To contribute to this, we use diffusion chronometry in olivine to determine the maximum interaction times of Holocene magmas with peridotite and gabbro xenoliths in the Horseshoe phonolites. We find extremely short diffusion times on the order of minutes to hours (

The 1257 CE eruption of Mount Samalas (Indonesia) caused the largest stratospheric sulfur injection of the Common Era, as recorded by Greenland and Antarctic ice cores, and led to strong climate perturbations. About 80% of the eruption’s sulfur output likely came from vapor stored in the magma reservoir. However, the factors that controlled prodigious excess sulfur buildup at Samalas remain enigmatic. To address this problem, we analyzed sulfur and iron speciation, along with sulfur isotopes, in plagioclase-hosted melt inclusions and matrix glasses from 1257 pumice samples, and we modeled magma reservoir processes. Our results indicate that intermediate redox conditions, with sulfur as both sulfate and sulfide, and progressive magma recharge maximized pre-eruptive sulfur accumulation at Samalas. Redox-controlled sulfur speciation in the magma and magma reservoir growth via incremental recharge may thus modulate the sulfur emissions and climate impacts of large explosive volcanic eruptions.

The 2018–2020 lava flow field that built the submarine Fani Maoré volcano (Mayotte, north Mozambique Channel) at a water depth of 3,300 m was extensively sampled. We use the petrological analysis of samples collected at high spatial and temporal resolution to provide information on the textural evolution of the submarine lavas and its impacts on lava rheology, and thus on flow emplacement. Although the crystal content is lower than 10%, we observed two populations of crystals: (a) the micro‐phenocrysts which mostly display skeletal shapes suggesting rapid growth upon magma ascent most likely due to decompression‐driven crystallization, (b) the microlites resulting from post‐emplacement groundmass crystallization. Combining both petrological and geochemical analyses, and applying rheological models, we show that lava viscosity increases from 158 ± 21 to 608 ± 134 Pa·s considering rigid bubbles or from 36 ± 5 to 485 ± 130 Pa·s considering deformable bubbles. Together with the waning ascent velocity and the decreasing effusion rates, this correlates with the evolution of lava flow emplacement dynamics, from long sheet lava flows to shorter flows exhibiting pillow mounts and multiple breakouts.

Volcanic eruptions necessitate precise monitoring of magma pressure and inflation for improved forecasting. Understanding deep magma storage is crucial for hazard assessment, yet imaging these systems is challenging due to complex heterogeneities that disrupt standard seismic migration techniques. Here we map the magmatic and hydrothermal system of the La Soufrière volcano in Guadeloupe by analyzing seismic noise data from a sparse geophone array under a matrix formalism. Seismic noise interferometry provides a reflection matrix containing the signature of echoes from deep heterogeneities. Using wave correlations resistant to disorder, matrix imaging successfully unscrambles wave distortions, revealing La Soufrière's internal structure down to 10 km with 100 m resolution. This method surpasses the diffraction limit imposed by geophone array aperture, providing crucial data for modeling and high-resolution monitoring. We see matrix imaging as a revolutionary tool for understanding volcanic systems and enhancing observatories' abilities to monitor dynamics and forecast eruptions.