Raphaël Grandin

The Kerguelen Islands (49°S, 69°E), a volcanic archipelago in the southern Indian Ocean, have experienced substantial environmental change over recent decades, including significant retreat of the Cook ice cap. The rapid ice loss is expected to induce measurable crustal deformation.In this study, we use the complete archive of Sentinel-1 SAR imagery acquired since 2015 to examine the present-day deformation field of the Kerguelen Islands. Our small-baseline InSAR time-series analysis reveals a broad ~ 100 km-wide pattern of crustal uplift centered on the Cook ice cap, reaching up to ~ 6 mm/yr. To investigate the physical processes driving this uplift, we combine observed change in ice elevation inferred from multiple Digital Elevation Model over the 2015-2025 period with local estimates of shallow elastic properties derived from seismic experiments. Using a layered Cartesian elastic Earth model, we predict the surface deformation resulting from present-day unloading of the Cook ice cap, and compare model predictions to the InSAR-derived deformation field.We then explore time-dependent deformation scenarios by considering viscoelastic deformation of the solid Earth induced by a range of plausible ice-loss histories over recent decades, and show that recent ice melting in the Kerguelen island can be used to place constraints on the rheology of the Earth’s upper mantle at decadal timescales. Finally, given the volcanic setting of the Kerguelen Islands, we also investigate whether magmatic sources could contribute to the observed long-wavelength uplift pattern.Overall, this work highlights the potential of InSAR observations in remote subpolar environments to quantify ice-driven deformation and to infer solid Earth rheological properties on decadal timescales.

Spectacular natural hazards such as large earthquakes or volcanic eruptions are accompanied by smaller-amplitude processes that produce millimeter-scale ground deformation. Although subtle, these signals provide critical insight into the physical state of the system and their associated hazards. Interferometric Synthetic Aperture Radar (InSAR) offers the spatial resolution required to observe such deformation, but its exploitation over long time spans remains challenging due to centimeter-scale noise and systematic biases. Here, we demonstrate how state-of-the-art interferometric processing combined with a Kalman Filter–based Time Series analysis (KFTS) enables the extraction of millimeter-scale deformation from 10 years of Sentinel-1A/B data. We present two case studies: the Chaman fault system (Pakistan–Afghanistan) and the Natron rift (northern Tanzania) in the East African Rift. Careful step-by-step corrections of the interferograms include tropospheric and ionospheric corrections, azimuth shift compensation, and rigorous assessment of closure phase biases. Measurement uncertainties derived from coherence are propagated within the KFTS time-series inversion, allowing iterative estimation of phase evolution with associated uncertainties.In the Chaman fault zone, we detect aseismic deformation characterized by fault creep rates of about 5 mm/yr, as well as a slow-slip event with ~1 cm of cumulative displacement resolved using combined ascending and descending geometries. In northern Tanzania, we resolve long-term rift opening of only a few millimeters per year between 2015 and 2025, consistent with GNSS campaign measurements. We further assess the potential of Independent Component Analysis (ICA) for InSAR signal separation and discuss current limitations imposed by residual noise and vegetation-related biases.

Globally, over 800 million people live within 100 km of a volcano. The contrast between geological and human timescales makes it notoriously difficult to predict when and where the next eruption will occur. However, the timescales of magma ascent mean that monitoring systems can detect changes, allowing scientists to judge changing likelihoods of hazardous events, to raise (and lower) volcanic alert levels if they are in place, and advise authorities, who may in turn decide to call evacuations. Thus volcano monitoring and advice saves lives and supports economic development. Despite this, many volcanoes near large population centres have little or no ground-based monitoring meaning most alerts do not accurate reflect hazard levels. Recent developments in satellite technology and machine learning are transforming the way we study our planet, changing our perception of volcanic activity and revolutionising the ways in which volcanoes are monitored. Here, we focus on the East African Rift system, where exposure is high and ground-based monitoring is scarce.First, we showcase how satellite data has enabled the systematic identification and characterisation of deformation at 16 otherwise unmonitored volcanoes, demonstrating a previously unrecognised, but extensive hazard. Then we discuss the scientific response to the 2024-2025 seismic crisis in the Fentale-Dofen Region, Ethiopia, which was caused by a sequence of magmatic intrusions over 6 months. UNOCHA report that 75,000 people were evacuated. The largest intrusion was ~ 50 km in length causing ~ 3 m of surface displacement and extensive surface fracturing. Satellite data and analysis provided by international organisations including the UK Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET), the ERC Grant MAST (PI Biggs) and the GVEWERS programme of the CEOS Working Group on Disasters played a critical role in informing and supporting crisis response efforts. Real-time analysis was discussed with partners at Addis Ababa University and used by the Ethiopian Scientific Advisory Committee comprising scientists from Addis Ababa University, the Geological Institute of Ethiopia and other relevant institutions to monitor the events and keep the Ethiopian Disaster Risk Management Commission (EDRMC) and the public continuously informed. The advisory committee provided a highly simplified zoned map summarising the most likely scenarios and zones of hazard. Alongside this, a series of open-access Event Response Reports was published on the COMET website to support situational awareness and decision making by international stakeholders. For example, these reports supported the British Geological Survey (BGS) International Natural Hazards Forward Look (INHFL) reports and volcano advisory assessments for the UK’s Foreign, Commonwealth and Development Office (FCDO).This event highlights two pathways for scientists to address societal challenges, by engaging and supporting the process of decision-making. Firstly, that there is an urgent need for enhanced scientific monitoring, scientific expertise and preparedness in the East African Rift, particularly the infrastructural, and institutional capacities to support these efforts. Secondly satellite technology now provides monitoring data at sufficient spatial and temporal resolution to be used during crises, and if properly supported, could provide the foundation for global volcano monitoring systems.

Magmatic intrusions into sedimentary rocks can mobilise carbon-based greenhouse gases, through the interaction between magma and organic-rich sediments. These processes have been linked to rapid climate changes in the past. However, we lack appropriate modern analogues for these systems, as most volcanic systems emit very little methane. In this study, we present the first confirmed satellite detection of methane emissions associated with a volcanic system, resulting from interactions between magma and sedimentary rocks. In early 2025, Fentale Volcano, Ethiopia, released >38.2 ± 3.9 kilo tonnes of methane, with 90% emitted within one month. Peak methane emission rates reached 157 ± 41 tonnes per hour, comparable to major industrial blowouts and orders of magnitude higher than typical volcanic systems emission rates, making this, to date, the largest observed natural point-source methane emission. The emissions followed the intrusion of ~1 km3 of magma into a 50 km long dyke that did not erupt. The release of methane and carbon dioxide coincided with localised ground subsidence, thermal anomalies and a persistent low-lying plume within Fentale’s caldera. We infer that the intrusion disrupted an impermeable cap, allowing for the sudden mobilisation of previously trapped gases. This single outburst, while small relative to annual emissions from natural and anthropogenic sources, demonstrates that some volcanoes can release methane episodically. These observations highlight the importance of satellite monitoring for detecting transient volcanic degassing and provide new insights into the mechanisms by which magmatic intrusions release carbon-based greenhouse gases.

The faulting caused by dyke intrusions provide a novel opportunity to study the way natural fault systems respond to time-varying changes to the stress field. The recent 2024-2025 Fentale-Dofen dyking episode in the northern Main Ethiopian Rift (NMER) offers a rare opportunity to investigate these processes, as the surface deformation was captured in unusually high spatial and temporal resolution by satellite radar. In our study, we combine Interferometric Synthetic Aperture Radar (InSAR) data from the COSMO-SkyMed satellite, high resolution Digital Elevation Model (DEM), with a catalogue of >150 relocated moderated-sized earthquakes (M4.5-6) to study the spatio-temporal evolution of seismic and aseismic fault slip linked to dyking in the NMER. We focus on an area ~15 km north of the tip of the dyke, where we find fault patches showing both repeated seismic and aseismic slip occurring in close proximity, associated with surface deformation of

The 2019 Raikoke eruption injected material directly into the stratosphere and had major impact on climate. The particle composition of the volcanic aerosols still remains debated today. The eruption generated usual hemispherically-dispersed plumes, but also a long-lived, compact and vorticized volcanic plume (VVP). While this type of plume is usually observed for biomass burning aerosol smoke plumes, it is identified for the first time after a volcanic eruption. A synergistic analysis of S5P/TROPOMI, MetOp/IASI, CALIPSO/CALIOP and AERONET data is conducted to retrieve particle size in the VVP and in the dispersed plumes. In the VVP, fine particle peak radii increased to a record size within three months after the eruption. It is three times greater than the particle radius retrieved in the dispersed plumes, and even greater than the one reached by the strongest eruption of the last decades, i.e., the 1993 Mt Pinatubo eruption. The growth coincides with the decrease in SO2 concentration, suggesting the growth of sulfate aerosols. However, dynamical, optical and radiative signatures point to a more complex composition, where submicronic ash become coated by sulfates. This phenomenon is enhanced in the VVP where SO2 concentration is initially one order of magnitude higher than in the dispersed plumes, because of its vorticized nature. It means that the local SO2 concentration is the critical factor limiting sulfate aerosols growth, and not the total eruption SO2 emission budget. Finally, this unprecedented particle size observed in the VVP with persisting submicronic ash calls for a re-evaluation of the current approach for modeling impacts of stratospheric eruptions on climate.

Recent advances in satellite remote sensing, particularly high-resolution and high-temporal-frequency SAR systems, provide new opportunities for capturing rapidly evolving deformation. X-band InSAR (Interferometric Synthetic Aperture Radar) data from the COSMO-SkyMed (CSK) and COSMO-SkyMed Second Generation (CSG) constellations offer dense temporal sampling and high spatial resolution, making them particularly valuable for monitoring complex, rapidly evolving deformation signals. However, the short wavelength of X-band data can make phase unwrapping – the step required to convert wrapped interferometric phase into continuous surface displacement – challenging when the signal has a large footprint, large deformation gradients and surface discontinuities.Here we present an enhanced X-band InSAR monitoring framework applied to the 2024-2025 Fentale-Dofen dyke intrusion in Ethiopia. The dyke measured ~50 km in length and produced complex surface deformation spanning ~10,500 km², with InSAR line-of-sight displacements up to ~3 m over ~60 days. Monitoring dyke intrusion-related deformation is important for understanding magma movement, assessing volcanic hazards, and supporting rapid response during period of unrest. We address limitations of conventional phase unwrapping in areas of complex deformation, including dense fringes caused by dyke-opening and discontinuous deformation within the graben. By integrating pixel-offset tracking with interferometric phase, we develop a reliable offset-supported unwrapping strategy that allows robust recovery of surface displacement associated with both dyke opening and graben subsidence, with consistency evaluated by loop-closure tests. The resulting deformation products provide a consistent basis for InSAR time-series analysis using dense CSK observations, allowing the temporal evolution of intrusion-related deformation to be resolved at high spatial and temporal resolution. Ongoing work extends this framework toward integrated deformation modeling, combining geodetic observations with physics-based representations of dyke-driven magma transport to better constrain subsurface processes.This study demonstrates how advanced InSAR processing strategies and multi-technique data integration can unlock the full potential of high-resolution X-band SAR data for environmental hazard monitoring. The proposed framework contributes to the development of robust remote sensing tools for deformation analysis, supporting both near-real-time monitoring and post-event assessment of volcanic and other hazards.

The Committee on Earth Observation Satellites (CEOS) Working Group on Disasters (WGD) has coordinated multiple initiatives to enhance volcano disaster risk management through improved access to satellite data. Historically, access to high-resolution synthetic aperture radar (SAR) and optical imagery—critical for monitoring volcanic activity—has been restricted by costs or limited research-focused allocations. To overcome these limitations, CEOS-WGD launched the Volcano Pilot Project (2014–2017), which demonstrated the feasibility of systematic, integrated volcano monitoring in Central and South America using space-based observations. Through coordinated contributions from multiple space agencies, regional observatories gained unprecedented access to SAR and high-resolution optical datasets, enabling more effective monitoring of active volcanoes.Building on this success, the Volcano Demonstrator Project (2019–2023) expanded coverage to Southeast Asia and Africa, further confirming the benefits of collaborative satellite data sharing for volcano monitoring. In 2023, CEOS approved the Global Volcano Early Warning and Eruption Response from Space (GVEWERS) initiative—a permanent, sustainable framework uniting international space agencies, academic institutions, and volcano observatories. GVEWERS aims to ensure timely, free, and low-latency access to critical satellite datasets for forecasting, detecting, and tracking volcanic activity worldwide. This capability is essential for mitigating hazards and providing early warnings of potential eruption impacts, as illustrated by the role of satellite data in monitoring unrest at Fentale, Ethiopia (2024–2025), and in tracking volcanic products emplacement and redeposition at Fuego Volcano, Guatemala, since 2024.The success of GVEWERS depends on strong engagement from the global volcanology community. We invite international participation to advance this collaborative effort, which represents a transformative step toward reducing volcanic risk through space-based Earth Observation and fulfilling the vision of the United Nations’ Early Warning 4 All program.

Magmatic intrusions into sedimentary rocks can release carbon-based greenhouse gases, dominantly methane, and have been linked to rapid changes in past climate. However, we lack appropriate modern analogues, as most volcanic systems emit very little methane. Here, we report the first confirmed satellite detection of methane emissions from a volcanic system, likely resulting from interactions between magma and sedimentary rocks. In early 2025, Fentale Volcano (Ethiopia) released >38.2 ± 3.9 kilo tonnes of methane, of which 90% was emitted within 31 days. The peak emission rate of 157 ± 41 tonnes per hour is comparable to major industrial blowouts and ~4 orders of magnitude higher than the methane emission rates of other volcanic systems. The emissions followed the intrusion of ~1 km ³ of magma into a dyke which did not erupt. Subsequent emissions of methane and carbon dioxide coincided with localised ground subsidence and thermal anomalies within Fentale’s caldera. We infer that the intrusion disrupted an impermeable cap beneath which methane, derived from hydrocarbon-rich sediments, was trapped. This single outburst is small compared to annual emissions from natural and anthropogenic sources, but demonstrates that some volcanoes can release methane episodically, providing insight into the mechanism of greenhouse gas release in magmatic-sedimentary systems