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Volcanic sulfur dioxide (SO2) is a gaseous precursor that is transformed into secondary sulfate aerosols (SO42-) by several intricate chemical and physical atmospheric processes. It is currently unclear how quickly sulfate aerosols are produced in volcanic plumes, particularly in tropospheric plumes. We jointly analyze Aura/OMI SO2 observations to constrain the sulfur-rich emissions and identify the volcanic plume dispersion pattern as well as multi-angle, multi-wavelength, and polarizing PARASOL/POLDER-3 observations that are particularly sensitive to fine mode particles to gain a better understanding of the lifecycle of volcanic sulfate aerosols. The GRASP/Component[1] (Generalized retrieval of Aerosol and Surface Properties) algorithm gives us details about the soluble and insoluble aerosol components in both fine and coarse modes based on their complex refractive indices in addition to standard optical characteristics. In order to provide insight into SO2 to particle conversion rate, we analyze the degassing of the Kilauea volcano (Hawaii, USA) between 2006 to 2012, which includes periods of passive and eruptive degassing.We demonstrate that Kilauea SO2-rich pixels from OMI measurements are broadly collocated with poorly-absorbing fine aerosol-rich pixels from POLDER measurements (fine AOD (440nm) ranging from 0.1 to 0.4, SSA (440nm) ranging from 0.95 to 1.0). We show that these volcanic particles also differ from long-distance transported man-made and natural fine-absorbing particles seen across the Kilauea domain from the Asian region in terms of their absorption characteristics. We, therefore attribute these fine mode particles to sulfate aerosols that result from the conversion of Kilauea SO2 emissions.In comparison to SO2-rich plumes, Kilauea aerosol-rich plumes have a significantly wider spread and are characterized by an excess anomaly in fine AOD and high SSA values. Irrespective of the degassing strength, a pattern consistent with the oxidation of SO2 to secondary sulfate aerosols is observed where the SO2 concentration gradually drops with plume dispersion while the fine AOD gradually increases, peaking at a distance of around 800–3000 km from the Kilauea source. Depending on the intensity of volcanic activity, the season, and enduring local meteorological conditions, different time scales for oxidation of SO2 and geographical dispersion of the Kilauea aerosol plumes are observed. We conducted additional analysis on the coarse AOD and coarse components to look for ash signals inside the plume. Furthermore, the complex refractive index of Kilauea particles, retrieved by the GRASP/Component algorithm, indicates an imaginary part (0.003-0.005) that is slightly higher than that of volcanic basaltic ash, as determined by laboratory experiments, while the real part (1.49-1.52) lies well in between pure sulfate (1.40-1.46) and basaltic ash (1.56-1.63). These refractive index values imply that Kilauea particles are not pure sulfate aerosols but instead contain some spectrally absorbing elements that may point to the existence of fine ash or sulfate-coated ash particles within the plume.[1] Li, L., Dubovik, O., Derimian, Y., Schuster, G. L., Lapyonok, T., Litvinov, P., Ducos, F., Fuertes, D., Chen, C., Li, Z., Lopatin, A., Torres, B., and Che, H.: Retrieval of aerosol components directly from satellite and ground-based measurements, Atmos. Chem. Phys., 19, 13409–13443, https://doi.org/10.5194/acp-19- 13409-2019, 2019.

This document describes the landscaping exercise proposed for deliverable 4.2 (D4.2) within Work Package (WP) 4 of the FAIR Earth Sciences & Environment services project (FAIR-EASE, FE). The goal of this exercise is to analyse different special use case (UC) datasets per pilot and the requirements they must meet to be included in the data lake infrastructure proposed in D4.1 (landscaping exercise: the (meta)data, software, and cloud needs for the data lake). The pilots per UC are: UC1 - Earth and Environmental Dynamics: Coastal waters dynamics (Pilot 5.1.1), Earth Critical zones observatory (Pilot 5.1.2), and Volcano Space Observatory (Pilot 5.1.3), UC2 - Environmental Bio-geochemical Assets: Ocean Bio-Geo-Chemical Observatory (Pilot 5.2.1) and, UC3 - Biodiversity Observation: Marine Omics Observatory (Pilot 5.3.1). Datasets from each pilot were selected from Table 1 in Annex A of D5.1 (report on key requirements from Use Cases and Pilots, [1]) and with a prior selection from a representative from each pilot. These datasets were selected to cover as much diversity as possible and to reflect the multidisciplinary nature of each UC. The deliverable aims to analyse and highlight the criticalities of the selected datasets considering their current limitations and needs and how they could fit into the “data provider” view proposed for the “data lakes” architecture in D4.1. Bear in mind that the datasets described should not be taken as the only source for the data lake ingestion. As stated, before a few special UCs datasets were selected using the minimum selection and maximum diversity criteria, to analyse the requirements for them to be ingested in the data lakes proposed.

This presentation is from the FAIR-EASE webinar heldon 6 April 2023, 13:00-14:00 CET.FAIR-EASEpresented the distributed and integrated services for observation and modelling of the Earth system, environment and biodiversity being developed in close cooperation with user-communities, the European Open Science Cloud (EOSC) and research infrastructures in their design and sustainable availability. The meetingspurpose was to involve external communities, share the FAIR-EASEvision and objectives, and receive feedback.

Stratospheric sulfate aerosols play a key role on atmospheric chemistry and Earth’s radiation budget, but their size distribution, a critical parameter in climate models, is generally poorly-known. We address such gap for the 2022 Hunga Tonga-Hunga Ha apai (HT-HH) volcanic eruption by exhaustively analyzing photometric observations from the worldwide open-access AERONET network. We document a rapid growth of HT-HH sulfate aerosols in the days following eruption, faster than observed for other stratospheric eruptions, likely due to the exceptional hydration of the stratosphere by this phreatomagmatic eruption. An unusual aerosol fine mode (peak radius in 0.3-0.5 µm) is identified at >20 stations of the southern hemisphere until December 2022 (time of writing). Nevertheless, one year after eruption, HT-HH sulfate aerosols remain smaller than 1991 Pinatubo particles. Smaller aerosols backscatter more efficiently visible light and sediment more slowly than larger particles, implying stronger and longer-lasting negative radiative forcing.

The overall objective of the EOSC Horizon Europe FAIR-EASE project is to develop and operate distributed and integrated services for observation and modelling of the earth system, environment and biodiversity implemented in close cooperation with user-communities and research infrastructures in their very design and sustainable availability and evolution. The FAIR-EASE WP5 (Work Package) is in charge of coordinating the activities tackling three different use cases (UCs): 1) the Earth and Environment dynamics; 2) The Environmental Biogeochemical Asset; 3) The Biodiversity Observations. As documented in the FAIR-EASE work plan, all the use cases represent “Real Life-Science” challenges. During the progress of the project, specific Pilots will be considered per UC, each of them addressing specific objectives. This deliverable reports on the assessment of the key requirements and the mapping of main resources to be considered in the project to fulfill the aims and scope of the Pilots included in each use case.

L'éruption explosive du volcan Hunga Tonga - Hunga Ha’apai (HTHH), le 15 janvier 2022, a produit la plus puissante explosion enregistrée depuis les explosions du Krakatau et du Tambora dans les années 1800, libérant une énergie équivalente à 110 mégatonnes de TNT. Les ondes générées se sont propagées dans le sol, et dans l’atmosphère jusqu’à l’ionosphère. L'onde atmosphérique la plus énergétique observée sur les baromètres correspond au mode de Lamb. De période supérieure à 2000 s, son amplitude est comparable à celle observée lors de l’éruption du Krakatau en 1883. L’empreinte des perturbations atmosphériques a été caractérisée à l’échelle planétaire par des réseaux de mesures au sol, à bord de satellites ou de plateformes aéroportées. L’analyse combinée de ces observations a permis d’évaluer les conséquences à court terme de l'éruption du HTHH. Les méthodes d'investigation géophysiques présentées dans cette note montrent l’apport d’analyses interdisciplinaires pour caractériser la réponse impulsionnelle des enveloppes fluides planétaires (atmosphère, océans et mers) à une éruption d’une intensité exceptionnelle.

Volcanic sulphur dioxide (SO2), a precursor of sulphate aerosols, can have a deleterious impact on the atmosphere, ecosystems, and air quality at multiple scales. Knowledge of highly variable volcanic SO2 emissions, i.e., mass flux rates and injection heights, would not only aid comprehension of such atmospheric implications but would also provide information on subterranean volcanological processes of magma transport. Furthermore, volcanic SO2, which frequently co-exists in volcanic plumes with ash and sulphate aerosols, can pose a threat to aviation as ash and acidic aerosols are alarming to aircraft. Therefore, comprehensive knowledge of volcanic SO2 emissions is essential for a thorough evaluation of near-source volcanic hazards and large-scale atmospheric impacts.Hyper-spectral nadir-viewing UV and infrared satellite instruments record global SO2 mass-loadings on a daily or bi-daily basis. Geostationary sensors, on the other hand, deliver high temporal information on SO2 emissions but with much lower sensitivity. Consequently, there are still gaps in our knowledge of volcanic SO2 emissions and SO2 to sulphate oxidation rates, notably inside tropospheric plumes, and hence volcanic sulphur-rich compound feedback on the atmosphere.TROPOMI, a hyperspectral UV sensor with increased spatial and spectral resolution than that of the pre-existing UV (OMPS) sensor in the same orbit, was launched in 2017. We discuss how an inverse modelling approach that assimilates TROPOMI SO2 column amounts (CA) improves the retrieval of hourly SO2 emissions when compared to the assimilation of OMPS data acquired at approximately the same time and the new SO2 products (both SO2 CA and layer heights) from IASI. The purpose of using IASI data is to assess the impact of assimilating SO2 data available bi-daily into inverse modelling with additional information on SO2 layer height. The inverse modelling is performed utilizing a time series of daily or bi-daily SO2 CA snapshots from the TROPOMI, OMPS, and IASI satellite instruments, respectively. Contrary to OMPS, which has 50x50 km2 of spatial resolution, and IASI, which has a 12 km circular footprint, TROPOMI has an extraordinary spatial resolution of 5.5x3.5 km2 (7x3.5 km2 before August 2019). We find that because of their sensitivity to low-level SO2 fluxes and thin SO2 plumes, and the numerous SO2-rich pixels defining dense parcels, TROPOMI observations enable better evaluation of SO2 degassing during paroxysmal eruption phases, offering better-resolved SO2 emissions by inverse modelling. However, if meteorological clouds hide the volcanic SO2 plumes, the results can be inconsistent, especially if the clouds are near the source. So the additional data, the SO2 height product from IASI observations, is used to reconcile and offer more robust SO2 emissions. As a second step, we perform inverse modelling using both the SO2 CA and layer heights from IASI. This research investigates the Mount Etna eruption in February 2021, the SO2 plume reaching France, and the 2018 Ambrym eruption, which was the top world-ranking SO2 emitter. In the context of Etna eruption, we use ground-based OHP LIDAR aerosol height measurements to explore the presence of sulphate aerosols and their height in the SO2 plume.

The underwater Hunga Tonga-Hunga Ha-apai (HT) volcano violently erupted on January 15th, 2022, injecting volcanic gases and aerosols at over 50 km altitude. Here we show the stratospheric aerosol and water vapour perturbations due to the HT eruption, the plume evolution during the first month dispersion and we estimate its short-term radiative impact. The HT eruption produced the largest perturbation of stratospheric aerosols and water vapour since the eruption of Pinatubo volcano in 1991. During the first three weeks following the eruption, water vapour radiative cooling dominates the plume’s heating/cooling rates, reaching values as large as -10 K/d and produces a fast plume descent of several km. At the top-of-the-atmosphere (TOA) and surface, volcanic aerosol cooling dominates the radiative forcing (RF) for the fresh plume. After two weeks, due to dispersion/dilution, water vapour heating starts to dominate the TOA RF, leading to a net warming of the climate system, which was never reported before for a volcanic plume. The surface RF, on the contrary, is dominated by the aerosol effect and reaches values of near -2 Wm-2, exceeding the hemispheric-averaged surface impact of stratospheric events of the last 30 years.

International audience

International audience; Surface deformation accompanying dike intrusions is dominated by uplift and horizontal motion directly related to the intrusions. In some cases, it includes subsidence due to associated magma reservoir deflation. When reservoir deflation is large enough, it can form, or reactivate pre-existing, caldera ring-faults. Ring-fault reactivation, however, is rarely observed during moderate-sized eruptions. On February 21st, 2015 at Ambrym volcano in Vanuatu, a basaltic dike intrusion produced more than 1 meter of co-eruptive uplift, as measured by InSAR, SAR correlation, and Multiple Aperture Interferometry (MAI). Here we show that an average of ∼40 cm of slip occurred on a normal caldera ring-fault during this moderate-sized (VEI < 3) event, which intruded a volume of ∼24 million cubic meters and erupted ∼9.3 million cubic meters of lava (DRE). Using the 3D Mixed Boundary Element Method, we explore the stress change imposed by the opening dike and the depressurizing reservoir on a passive, frictionless fault. Normal fault slip is promoted when stress is transferred from a depressurizing reservoir beneath one of Ambrym’s main craters. After estimating magma compressibility, we provide an upper-bound on the critical fraction (f = 7%) of magma extracted from the reservoir to trigger fault slip. We infer that broad basaltic calderas may form in part by hundreds of subsidence episodes no greater than a few meters, as a result of magma extraction from the reservoir during moderate- sized dike intrusions.

International audience; In December 2018, an unusually large intra- and extra-caldera eruption took place at Ambrym volcano (Vanuatu). The eruption drained the volcano’s five active lava lakes and terminated, at least momentarily, the surface activity that had been ongoing for decades to hundreds of years, sustaining the largest recorded persistent degassing on the planet. Here, we investigate the mechanisms and dynamics of this major eruption. We use major elements and volatiles in olivine and clinopyroxene-hosted melt inclusions, embayments, crystals and matrix glasses together with clinopyroxene geobarometry as well as olivine and clinopyroxene geothermometry and diffusion modelling in crystals and embayments to reconstruct the chronology and timing of the subsurface processes that accompanied the eruption. We find that the eruption began with the meeting, mingling and limited chemical mixing of mostly two magma bodies occupying similar vertical but different horizontal locations in the crust, one corresponding to the main plumbing system at Ambrym that fed the lava lakes and the other corresponding to an older, previously cutoff and more chemically evolved branch of the plumbing system. Within the primitive magma, two texturally distinct components—one microlite rich and one microlite poor—can further be identified. The 2018 eruption hence provides a detailed image of Ambrym’s complex plumbing system. Our diffusion timescales and geobarometric estimates coincide closely with geophysical observations. They point to a reconnection of the evolved magmatic branch with the main system occurring less than 10 h prior to the intra-caldera eruption and a period of 2 days for the subsequent > 30-km lateral magma transport along a deeper dike prior to submarine eruption just off the SE coast of the island with the more primitive magma reaching first followed by mingled magma containing both compositions. Magma ascent rates are estimated at 95 ± 24 m/s in the last ~ 2.5 km of ascent during the intra-caldera eruption and at 80 ± 6 m/s in the last ~ 4 km of ascent during the submarine eruption. Comparison with other lava lake draining eruptions reveals striking similarities both in terms of precursory activity, with lake level rising prior to the eruption in all cases, and in terms of plumbing system organization with the presence of peripheral magma pockets, isolated from the main magmatic system but that can be mobilized and erupted when met by dikes propagating laterally from the main system.

Satellite-based UV spectrometers can constrain sulphur dioxide (SO2) fluxes at passively degassing volcanoes over decadal time scales. From 2005 to 2015, more than 15 volcanoes had mean passive SO2 fluxes greater than 1 kiloton per day. Although the processes responsible for such high emission rates are not clearly established, this study aims to investigate the impact of strong degassing on the pressurization state of volcanic systems and the resulting ground deformation. One possible result of high degassing rates is the depressurization of the region where the melt releasing gas is stored, which may result in subsidence at the Earth’s surface. Passive degassing may depressurize pathways between deep and shallow magma storage regions, resulting in magma ascent and possibly eruption.A lumped-parameter model developed by Girona et al., 2014 couples the mass loss by passive degassing with reservoir depressurization in an open volcanic system. However, this model has yet to be tested using real measurements of gas emissions and ground deformation. In our study, we focus on Ambrym volcano, the past decade’s top passive emitter of volcanic SO2, which exhibits intriguing long-term subsidence patterns and no obvious pressurization preceding eruptive periods. We compare subsidence rates measured by InSAR to the system’s average daily SO2 flux, focusing on a subsidence episode spanning 2015 to 2017 that is not clearly linked to magma removal from the system. Using realistic input parameters for Ambrym’s system constrained by petrology and gas geochemistry, a range of reservoir volumes and conduit radii are explored. Large reservoir volumes (greater than 30 km3) and large conduit radii (greater than 300 m) are consistent with depressurization rates obtained from geodetic modelling of InSAR measurements using the Boundary Element method. By comparing these values of reservoir volume and conduit radius with those estimated from geodesy, gas geochemistry, and seismology, we test the applicability and discuss uncertainties of the aforementioned lumped-parameter physical model to interpret the long-term subsidence at Ambrym volcano as a result of sustained passive degassing.

Volcanic eruptions are a natural disaster with significant impact on human activities. The unprecedented European Volcanic Ash Crisis in 2010 demonstrated the vulnerability of the infrastructure and the need for new approaches to enable stakeholders in the aviation sector to obtain fast and accurate information. Currently, there are many data sources available and cutting-edge technology to provide the means to detect and monitor high impact eruptions. However, the information from multiple data sources is not yet efficiently integrated and aviation-specific products incorporating multi-platform datasets is not in place. To this end, the integration of tailored ground-based, satellite, and model data as well as information from volcanic observatories in Europe is essential. The Pilot EO4D_ash – Earth observation data for detection, discrimination & distribution (4D) of volcanic ash – of the e-shape project aims to strengthen the Earth Observation and in-situ data exploitation and multi-source (satellite, remotely sensed, and ground-based network) data integration to derive innovation for ash discrimination and monitoring; to enhance the capability of 4D forecasting volcanic ash dispersal and to foster innovation in the decision making processes and mitigate ash related impact and hazard resilience. The overall pilot structure, tailored products, aerosol lidar profile assimilation and study cases will be presented at the conference.Acknowledgements: This work has been conducted within the framework of the H2020 e-shape (Grant Agreement n. 820852) project.

The adverse impact of volcanic gas and aerosol emission on global climate, air quality and ecosystem is well recognized. A better-refined knowledge of volcanic degassing mechanism and its interaction with the atmospheric environment can lead further to fill the persisting gaps in understanding well the impact of volcanic activities. The key is to monitor continuously the volcanoes at a global scale bearing also in mind the limitations of ground-based instruments during the ash-rich phase of emission. Thus, the space-borne sensors with a high spatial and temporal as well as spectral resolution are emerged but with complications in detecting low-altitude emissions, which are also limited to 12 h to 24 h of data acquisition frequency. Nonetheless, recently launched TROPOMI spectrometer onboard Sentinel 5P is shown to be a game-changer due to its high spatial and spectral resolution albeit the data acquisition frequency of only 24 h. To make further progress in retrieving high temporal SO2 emission, the contemporary inverse modelling method has already been shown to be promising. The obtained modelled parameters, viz., SO2 flux and altitude of injection, are reasonably compatible with the ground-based and space-borne observations [1] showing its importance in volcano monitoring [2] and towards forecasting large-scale plume dispersal [3]. The current work incorporates this advancing method and investigates a recent special volcanic event that occurred at Ambrym, Vanuatu during December 2018. The uniqueness of this eruption is the rapid shut down of decade long SO2 degassing and lava lake just after the eruption with the emplacement of a major dike [4]. Here, the hourly retrieved SO2 flux and altitude of injection are aimed to put to the fore the striking features of this unmonitored volcanic activity by assimilating the observations from several space-borne sensors.To do so, the CHIMERE Eulerian chemistry-transport model (CTM) is used to simulate the Ambrym eruption at a large-scale during 13-19 December 2018. Weather Research and Forecast (WRF) model is used to force the meteorological fields in the CTM simulation, while ERA5 reanalysis data are used to force the initial and boundary conditions of the WRF simulation. The modelled SO2 column amount is then co-located with the TROPOMI, OMPS and GOME2 SO2 column amounts, respectively, to perform the inversion to estimate the modelled flux rates and altitude of injection. The high spatial and spectral resolution SO2 data from TROPOMI is shown to reshape significantly the results obtained from the inverse method in comparison to OMPS and GOME2 SO2 data. Furthermore, a proxy to the SO2 flux is then developed from the geostationary HIMAWARI data to validate the inversion results as the time resolution of HIMAWARI data acquisition is every 20 min. This work is further intended to explore more on the fate of sulphate aerosols formed during this eruption at a large-scale. References:1. Boichu et al., Atmospheric Chemistry and Physics, 15(14):8381–8400, July 2015.2. Boichu et al., Atmospheric Chemistry and Physics, 13(17):8569–8584, September 2013.3. Boichu et al., Geophysical Research Letters, 41(7):2637–2643, 2014.4. Shreve et al., Scientific reports, 9(1):1–13, 2019.

Emission of volcanic gas is thought to be the dominant process by which volatiles transit from the deep earth to the atmosphere. Volcanic gas emissions, remain poorly constrained, and volcanoes of Peru are entirely absent from the current global dataset. In Peru, Sabancaya and Ubinas volcanoes are by far the largest sources of volcanic gas. Here, we report the first measurements of the compositions and fluxes of volcanic gases emitted from these volcanoes. The measurements were acquired in November 2015. We determined an average SO 2 flux of 15.3 ± 2.3 kg s − 1 (1325-ton day − 1 ) at Sabancaya and of 11.4 ± 3.9 kg s − 1 (988-ton day − 1 ) at Ubinas using scanning ultraviolet spectroscopy and dual UV camera systems. In-situ Multi-GAS analyses yield molar proportions of H 2 O, CO 2 , SO 2 , H 2 S and H 2 gases of 73, 15, 10 1.15 and 0.15 mol% at Sabancaya and of 96, 2.2, 1.2 and 0.05 mol% for H 2 O, CO 2 , SO 2 and H 2 S at Ubinas. Together, these data imply cumulative fluxes for both volcanoes of 282, 30, 27, 1.2 and 0.01 kg s − 1 of H 2 O, CO 2 , SO 2 , H 2 S and H 2 respectively. Sabancaya and Ubinas volcanoes together contribute about 60% of the total CO 2 emissions from the Central Volcanic zone, and dominate by far the total revised volatile budget of the entire Central Volcanic Zone of the Andes.

Volcanic sulfate aerosols play a key role in air quality and climate. However, the rate of oxidation of sulfur dioxide (SO2) precursor gas to sulfate aerosols (SO42-) in volcanic plumes is poorly known, especially in the troposphere. Here we determine the chemical speciation as well as the intensity and temporal persistence of the impact on air quality of sulfate aerosols from the 2014–2015 Holuhraun flood lava eruption of Icelandic volcano Bárðarbunga. To do so, we jointly analyse a set of SO2 observations from satellite (OMPS and IASI) and ground-level measurements from air quality monitoring stations together with high temporal resolution mass spectrometry measurements of an Aerosol Chemical Speciation Monitor (ACSM) performed far from the volcanic source. We explore month/year long ACSM data in France from stations in contrasting environments, close and far from industrial sulfur-rich activities. We demonstrate that volcanic sulfate aerosols exhibit a distinct chemical signature in urban/rural conditions, with NO3:SO4 mass concentration ratios lower than for non-volcanic background aerosols. These results are supported by thermodynamic simulations of aerosol composition, using the ISORROPIA II model, which show that ammonium sulfate aerosols are preferentially formed at a high concentration of sulfate, leading to a decrease in the production of particulate ammonium nitrate. Such a chemical signature is however more difficult to identify at heavily polluted industrial sites due to a high level of background noise in sulfur. Nevertheless, aged volcanic sulfates can be distinguished from freshly emitted industrial sulfates according to their contrasting degree of anion neutralization. Combining AERONET (AErosol RObotic NETwork) sunphotometric data with ACSM observations, we also show a long persistence over weeks of pollution in volcanic sulfate aerosols, while SO2 pollution disappears in a few days at most. Finally, gathering 6-month long datasets from 27 sulfur monitoring stations of the EMEP (European Monitoring and Evaluation Programme) network allows us to demonstrate a much broader large-scale European pollution, in both SO2 and SO4, associated with the Holuhraun eruption, from Scandinavia to France. While widespread SO2 anomalies, with ground-level mass concentrations far exceeding background values, almost entirely result from the volcanic source, the origin of sulfate aerosols is more complex. Using a multi-site concentration-weighted trajectory analysis, emissions from the Holuhraun eruption are shown to be one of the main sources of SO4 at all EMEP sites across Europe and can be distinguished from anthropogenic emissions from eastern Europe but also from Great Britain. A wide variability in SO2:SO4 mass concentration ratios, ranging from 0.8 to 8.0, is shown at several stations geographically dispersed at thousands of kilometres from the eruption site. Despite this apparent spatial complexity, we demonstrate that these mass oxidation ratios can be explained by a simple linear dependency on the age of the plume, with a SO2-to-SO4 oxidation rate of 0.23 h−1. Most current studies generally focus on SO2, an unambiguous and more readily measured marker of the volcanic plume. However, the long persistence of the chemical fingerprint of volcanic sulfate aerosols at continental scale, as shown for the Holuhraun eruption here, casts light on the impact of tropospheric eruptions and passive degassing activities on air quality, health, atmospheric chemistry and climate., info:eu-repo/semantics/published

Eruptive activity shapes volcanic edifices. The formation of broad caldera depressions is often associated with major collapse events, emplacing conspicuous pyroclastic deposits. However, caldera subsidence may also proceed silently by magma withdrawal at depth, more difficult to detect. Ambrym, a basaltic volcanic island, hosts a 12-km wide caldera and several intensely-degassing lava lakes confined to intra-caldera cones. Using satellite remote sensing of deformation, gas emissions and thermal anomalies, combined with seismicity and ground observations, we show that in December 2018 an intra-caldera eruption at Ambrym preceded normal faulting with >2 m of associated uplift along the eastern rift zone and 2.5 m of caldera-wide subsidence. Deformation was caused by lateral migration of >0.4 cubic kilometers of magma into the rift zone, extinguishing the lava lakes, and feeding a submarine eruption in the rift edge. Recurring rifting episodes, favored by stress induced by the D’Entrecasteaux Ridge collision against the New Hebrides arc, lead to progressive subsidence of Ambrym’s caldera and concurrent draining of the lava lakes. Although counterintuitive, convergent margin systems can induce rift zone volcanism and subsequent caldera subsidence.

Forecasting the dispersal of volcanic clouds during an eruption is of primary importance, especially for ensuring aviation safety. As volcanic emissions are characterized by rapid variations of emission rate and height, the (generally) high level of uncertainty in the emission parameters represents a critical issue that limits the robustness of volcanic cloud dispersal forecasts. An inverse modeling scheme, combining satellite observations of the volcanic cloud with a regional chemistry-transport model, allows reconstructing this source term at high temporal resolution. We demonstrate here how a progressive assimilation of freshly acquired satellite observations, via such an inverse modeling procedure, allows for delivering robust sulfur dioxide (SO2) cloud dispersal forecasts during the eruption. This approach provides a computationally cheap estimate of the expected location and mass loading of volcanic clouds, including the identification of SO2-rich parts.

Depending on the magnitude of their eruptions, volcanoes impact the atmosphere at various temporal and spatial scales. The volcanic source remains a major unknown to rigorously assess these impacts. At the scale of an eruption, the limited knowledge of source parameters, including time variations of erupted mass flux and emission profile, currently represents the greatest issue that limits the reliability of volcanic cloud forecasts. Today, a growing number of satellite and remote sensing observations of distant plumes are becoming available, bringing indirect information on these source terms. Here, we develop an inverse modelling approach combining satellite observations of the volcanic plume with an Eulerian regional chemistry-transport model (CHIMERE) to characterise the volcanic SO2 emissions during an eruptive crisis. The May 2010 eruption of Eyjafjallajökull is a perfect case study to apply this method as the volcano emitted substantial amounts of SO2 during more than a month. We take advantage of the SO2 column amounts provided by a vast set of IASI (Infrared Atmospheric Sounding Interferometer) satellite images to reconstruct retrospectively the time series of the mid-tropospheric SO2 flux emitted by the volcano with a temporal resolution of ~2 h, spanning the period from 1 to 12 May 2010. We show that no a priori knowledge on the SO2 flux is required for this reconstruction. The initialisation of chemistry-transport modelling with this reconstructed source allows for reliable simulation of the evolution of the long-lived tropospheric SO2 cloud over thousands of kilometres. Heterogeneities within the plume, which mainly result from the temporal variability of the emissions, are correctly tracked over a timescale of a week. The robustness of our approach is also demonstrated by the broad similarities between the SO2 flux history determined by this study and the ash discharge behaviour estimated by other means during the phases of high explosive activity at Eyjafjallajökull in May 2010. Finally, we show how a sequential IASI data assimilation allows for a substantial improvement in the forecasts of the location and concentration of the plume compared to an approach assuming constant flux at the source. As the SO2 flux is an important indicator of the volcanic activity, this approach is also of interest to monitor poorly instrumented volcanoes from space.

The 2014–15 Holuhraun lava-flood eruption of Bárdarbunga volcano (Iceland) has emitted prodigious amounts of sulfur dioxide into the atmosphere. This eruption caused a large-scale episode of air pollution throughout Western Europe in September 2014, the first event of this magnitude recorded in the modern era. We gathered a wealth of complementary observations from satellite sensors (OMI, IASI), ground-based remote sensing (lidar, sunphotometry, differential optical absorption spectroscopy) and ground-level air quality monitoring networks to characterize both the spatial-temporal distributions of volcanic SO2 and sulfate aerosols as well as the dynamics of the planetary boundary layer. Time variations of dynamical and microphysical properties of sulfate aerosols in the aged low-tropospheric volcanic cloud, including loading, vertical distribution, size distribution and single scattering albedo, are provided. Retrospective chemistry-transport simulations capture the correct temporal dynamics of this far-range air pollution event but fail to reproduce the magnitude of SO2 concentration at ground-level. Improving forecasts of large-scale volcanogenic air pollution will require refined emission parameters and adapted model grid resolution to accurately describe both long-range transport and local boundary layer dynamics.

In the 15 years following the last crisis of phreatic type in 1975–77, the hydrothermal and seismic activity of La Soufriere de Guadeloupe has displayed an episodic behavior superimposed on a long-term decay, as inferred from seismicity and degassing, monitored through fumarolic emissions and Cl content in thermal springs. In particular, the evolution of the Cl content can be explained by a succession of magmatic gas injections into the hydrothermal system. This episodic supply of gas may be associated to the thermodynamic evolution of a batch of magma intruded at shallow depth around 1976. Progressive magma cooling, crystallization, gas exsolution and pressure buildup lead to cyclic failure of host rock around the intrusion, and episodic release of gas, with a decreasing frequency as cooling proceeds. This physical model allows to reproduce the pattern of degassing activity of La Soufriere, including the decreasing frequency of Cl pulses with time. Our preferred forward model of Cl pulses involves a magma intrusion volume in the range 0.01– 0.52 km 3 and a tensile strength of the surrounding rock in the range 0.1–0.6 MPa. These results reinforce the hypothesis of a shallow magma intrusion triggering the 1975–77 crisis and provide an explanation for the degassing and seismic activities observed until 1992.

International audience; The measurement of SO2 flux from volcanoes is of major importance for monitoring and hazard assessment purposes, and for evaluation of the environmental impact of volcanic emissions. We propose here a novel technique for accurate and high time resolution estimations of the gas flux. We use two wide field of view UV spectrometers capable of collecting, instantaneously, light from thin parallel cross sections of the whole gas plume, obviating the need for either traversing, scanning or imaging. It enables tracking of inho-mogeneities in the gas cloud from which accurate evaluation of the plume velocity can be made by correlation analysis. The method has been successfully applied on Mt. Erebus volcano (Antarctica). It yields estimations of the plume velocity and gas flux at unprecedented time resolution (1 Hz) and high accuracy (uncertainty of 33%). During a ∼2 h experiment on 26 December 2006, SO2 flux varied between 0.17 and 0.89 ± 0.2 kg s −1 with a vertical plume velocity varying between 1 and 2.5 ± 0.1 m s −1. These measurements provide insight into the short-term variations of the passive degassing of this volcano renowned for its active lava lake. A cyclicity in flux, ranging from about 11-24 min, is evident. We propose two physical mechanisms to explain this degassing pattern, associated to periodic supply of either gas-rich magma or gas alone into the lake. The dual-wide field of view DOAS technique promises better integration of geochemical and geophysical observations and new insights into gas and magma dynamics, as well as processes of magma storage and gas segregation at active volcanoes.

A few lava lakes, like that at Erebus volcano, Antarctica, have been continuously active for decades, reaching a steady-state. We report spectroscopic and thermal observations from Erebus that reveal remarkable, phase-locked cycles of lava lake convection and gas plume composition. We argue that the observed fluctuations in gas ratios, including the SO2/CO2 content in the plume, identify two end-member contributions to the Erebus emission: a sustained source of CO2-rich gas percolating through permeable conduit magma, and a shallower source of H2O-rich gas exsolved from magma pulses that periodically enter the lava lake. The unstable magma flow may reflect the viscosity stratification between rising and descending magma in the conduit, and the resulting oscillatory behaviour of the phonolite lake exemplifies the relative roles of closed- and open-system degassing in persistently active volcanoes.

In this paper we combine SO2 and ash plume dispersion modelling with satellite and surface remote sensing observations to study the regional influence of a relatively weak volcanic eruption from Mount Etna on the optical and micro-physical properties of Mediterranean aerosols. We analyse the Mount Etna eruption episode of 25–27 October 2013. The evolution of the plume along the trajectory is investigated by means of the FLEXible PARTicle Lagrangian dispersion (FLEXPART) model. The satellite data set includes true colour images, retrieved values of volcanic SO2 and ash, estimates of SO2 and ash emission rates derived from MODIS (MODerate resolution Imaging Spectroradiometer) observations and estimates of cloud top pressure from SEVIRI (Spinning Enhanced Visible and InfraRed Imager). Surface remote sensing measurements of aerosol and SO2 made at the ENEA Station for Climate Observations (35.52° N, 12.63° E; 50 m a.s.l.) on the island of Lampedusa are used in the analysis. The combination of these different data sets suggests that SO2 and ash, despite the initial injection at about 7.0 km altitude, reached altitudes around 10–12 km and influenced the column average aerosol particle size distribution at a distance of more than 350 km downwind. This study indicates that even a relatively weak volcanic eruption may produce an observable effect on the aerosol properties at the regional scale. The impact of secondary sulfate particles on the aerosol size distribution at Lampedusa is discussed and estimates of the clear-sky direct aerosol radiative forcing are derived. Daily shortwave radiative forcing efficiencies, i.e. radiative forcing per unit AOD (aerosol optical depth), are calculated with the LibRadtran model. They are estimated between −39 and −48 W m−2 AOD−1 at the top of the atmosphere and between −66 and −49 W m−2 AOD−1 at the surface, with the variability in the estimates mainly depending on the aerosol single scattering albedo. These results suggest that sulfate particles played a large role in the transported plume composition and radiative forcing, while the contribution by ash particles was small in the volcanic plume arriving at Lampedusa during this event.

The 2014-2015 Holuhraun lava-flood eruption of Bároarbunga volcano (Iceland) emitted prodigious amounts of sulfur dioxide into the atmosphere. This eruption caused a large-scale episode of air pollution throughout Western Europe in September 2014, the first event of this magnitude recorded in the modern era. We gathered chemistry-transport simulations and a wealth of complementary observations from satellite sensors (OMI, IASI), ground-based remote sensing (lidar, sunphotometry, differential optical absorption spectroscopy) and ground-level air quality monitoring networks to characterize both the spatial-temporal distributions of volcanic SO2 and sulfate aerosols as well as the dynamics of the planetary boundary layer. Time variations of dynamical and microphysical properties of sulfate aerosols in the aged low-tropospheric volcanic cloud, including loading, vertical distribution, size distribution and single scattering albedo, are provided. Retrospective chemistry-transport simulations at low horizontal resolution (25 km × 25 km) capture the correct temporal dynamics of this far-range air pollution event but fail to reproduce the correct magnitude of SO2 concentration at ground-level. Simulations at higher spatial resolution, relying on two nested domains with finest resolution of 7.3 km × 7.3 km, improve substantially the far-range vertical distribution of the volcanic cloud and subsequently the description of ground-level SO2 concentrations. However, remaining discrepancies between model and observations are shown to result from an inaccurate representation of the planetary boundary layer (PBL) dynamics. Comparison with lidar observations points out a systematic under-estimation of the PBL height by the model, whichever the PBL parameterization scheme. Such a shortcoming impedes the capture of the overlying Bároarbunga cloud into the PBL at the right time and in sufficient quantities. This study therefore demonstrates the key role played by the PBL dynamics in accurately modelling large-scale volcanogenic air pollution., SCOPUS: ar.j, info:eu-repo/semantics/published

In this paper we combine SO2/ash plume dispersion modelling, satellite and surface remote sensing observations to study the regional influence of a relatively weak volcanic eruption from Mount Etna on the optical and micro-physical properties of Mediterranean aerosols. We analyse the Mount Etna eruption episode of 25–27 October 2013. The evolution of the plume along the trajectory is investigated by means of the FLEXPART (FLEXible PARTicle dispersion model) Lagrangian dispersion model. The satellite dataset includes true colour images, retrieved values of volcanic SO2 and ash, and estimates of SO2 and ash emission rates derived from MODIS (MODerate resolution Imaging Spectroradiometer) observations, and estimates of cloud top pressure from SEVIRI (Spinning Enhanced Visible and InfraRed Imager). Surface remote sensing measurements of aerosol and SO2 made at the ENEA Station for Climate Observations (35.52° N, 12.63° E, 50 m a.s.l.) on the island of Lampedusa are used in the analysis. The combination of these different datasets suggests that SO2 and ash, despite the initial injection occurred at about 7.0 km altitude, reached altitudes around 10–12 km and influenced the aerosol size distribution at a distance more than 350 km downwind. This study indicates that even a relatively weak volcanic eruption may produce an observable effect on the aerosol properties at the regional scale. The impact of secondary sulphate particles on the aerosol size distribution at Lampedusa is discussed, and estimates of the clear sky direct aerosol radiative forcing are derived. Daily shortwave radiative forcing efficiencies are calculated with the LibRadtran model. They are estimated between −39 and −48 W m−2 AOD−1 at the top of the atmosphere, and between −66 and −49 W m−2 AOD−1, at the surface, with the variability in the estimates mainly depending on the aerosol single scattering albedo. These results suggest that sulphate particles played a large role, while the contribution by ash particles was small in the volcanic plume arriving at Lampedusa during this event.

National audience

International audience; The 1999 basaltic eruption of Shishaldin volcano (Alaska, USA) displayed both classical Strombolian activity and an explosive Subplinian plume. Strombolian activity at Shishaldin occurred in two major phases following the Subplinian activity. In this paper, we use acoustic measurements to interpret the Strombolian activity. Acoustic measurements of the two Strombolian phases show a series of explosions that are modeled by the vibration of a large overpressurised cylindrical bubble at the top of the magma column. Results show that the bubble does not burst at its maximum radius, as expected if the liquid film is stretched beyond its elasticity. But bursting occurs after one cycle of vibration, as a consequence of an instability of the air-magma interface close to the bubble minimum radius. During each Strombolian period, estimates of bubble length and overpressure are calculated. Using an alternate method based on acoustic power, we estimate gas velocity to be 30-60 m/s, in very good agreement with synthetic waveforms. Although there is some variation within these parameters, bubble length and overpressure for the first Strombolian phase are found to be c 82 F 11 m and 0.083 MPa. For the second Strombolian phase, bubble length and overpressure are estimated at 24 F 12 m and 0.15 MPa for the first 17 h after which bubble overpressure shows a constant increase, reaching a peak of 1.4 MPa, just prior to the end of the second Strombolian phase. This peak suggests that, at the time, the magma in the conduit may contain a relatively large concentration of small bubbles. Maximum total gas volume and gas fluxes at the surface are estimated to be 3.3 Â 10 7 and 2.9 Â 10 3 m 3 /s for the first phase and 1.0 Â 10 8 and 2.2 Â 10 3 m 3 /s for the second phase. This gives a mass flux of 1.2 Â 10 3 and 8.7 Â 10 2 kg/s, respectively, for the first and the second Strombolian phases.

International audience The link between seismicity and degassing is investigated during the VEI 4 eruptions of Merapi volcano (Indonesia) in October and in early November 2010. Seismicity comprised a large number and variety of earthquakes including Volcano-Tectonic events, a sustained period of Long Period Seismicity (LPS), i.e., Long-Period events (LP), Very Long Period events (VLP) and tremor. LPS seismicity is ascribed to the excitation of fluid-filled cavity resonance and inertial displacement of fluids and magma. We investigate here LPS that occurred between 17 October and 4 November 2010 to obtain insights into the volcano eruption processes which preceded the paroxysmal phase of the eruption on 4-5 November. We proceed to the moment tensor inversion of a well-recorded large VLP event during the intrusion phase on 17 October 2010, i.e., before the first explosion on 26 October. By using two simplified models (crack and pipe), we find a shallow source for this VLP event at about 1 km to the south of the summit and less than 1 km below the surface. We analyze more than 90 LP events that occurred during the multi-phase eruption (29 October-4 November). We show that most of them have a dominant frequency in the range 0.2-4 Hz. We could locate 48 of those LP events; at least 3 clusters of LP events occurred successively. We interpret these observations as generated by different fluid-filled containers in the summit area that were excited while magma rose. We also observe significant variations of the complex frequency during the course of the eruption. We discuss these changes in terms of a variable ratio of fluid to solid densities and/or by possible conduit geometry change and/or permeability of the conduit or the edifice and/or by resonance of different fluid-containers during the release of more than 0.4 Tg of SO2 and large but unknown masses of other volcanic gases. Finally, we also discuss how the major explosions of the eruption were possibly triggered by passing waves resulting from regional tectonic earthquakes on 3 and 4 November.

International audience; Merapi volcano (Indonesia) is one of the most active and hazardous volcanoes in the world. It is known for frequent small to moderate eruptions, pyroclastic flows produced by lava dome collapse, and the large population settled on and around the flanks of the volcano that is at risk. Its usual behaviour for the last decades abruptly changed in late October and early November 2010, when the volcano produced its largest and most explosive eruptions in more than a century, displacing a third of a million people, and claiming nearly 400 lives. Despite the challenges involved in forecasting this 'hundred year eruption', we show that the magnitude of precursory signals (seismicity, ground deformation, gas emissions) were proportional to the large size and intensity of the eruption. In addition and for the first time, near-real-time satellite radar imagery played an equal role with seismic, geodetic, and gas observations in monitoring eruptive activity during a major volcanic crisis. The Indonesian Center of Volcanology and Geological Hazard Mitigation (CVGHM) issued timely forecasts of the magnitude of the eruption phases, saving 10,000-20,000 lives. In addition to reporting on aspects of the crisis management, we report the first synthesis of scientific observations of the eruption. Our monitoring and petrologic data show that the 2010 eruption was fed by rapid ascent of magma from depths ranging from 5 to 30 km. Magma reached the surface with variable gas content resulting in alternating explosive and rapid effusive eruptions, and released a total of ~ 0.44 Tg of SO2. The eruptive behaviour seems also related to the seismicity along a tectonic fault more than 40 km from the volcano, highlighting both the complex stress pattern of the Merapi region of Java and the role of magmatic pressurization in activating regional faults. We suggest a dynamic triggering of the main explosions on 3 and 4 November by the passing seismic waves generated by regional earthquakes on these days.

International audience; [1] Episodic magmatic degassing has been observed at numerous volcanoes, especially those of intermediate composition. It can span timescales from years to decades. Here we propose a physical model for the degassing of a shallow magma intrusion to explain this phenomenon. The magma cools by convection, which leads to melt crystallization, volatile exsolution, and magma overpressure. When the pressure reaches a critical value, wall rocks fracture and the exsolved gas escapes. The intrusion then returns to the initial lithostatic pressure and a new cooling-crystallization-degassing cycle occurs. A series of such cycles leads to episodic degassing. The trend and timescale of the degassing process are mainly governed by magma cooling. Two degassing regimes are exhibited: an early phase with a high frequency of gas pulses and a later phase with a lower gas pulse frequency. The transition between these two regimes is caused by the viscosity increase when the magma crystallinity exceeds the crystal percolation threshold. We find that the time to this transition is dependent on magma volume, to a first approximation. Where observations are available from sustained geochemical surveillance, the model provides constraints on key aspects of the subsurface magmatic system, with estimation of the volume of an intrusion and tensile strength of the surrounding rocks. It therefore represents a relevant tool for volcanic surveillance and hazard assessment.

Volcanic sulfate aerosols play a key role on air quality and climate. However, the oxidation of sulfur dioxide (SO2) precursor gas to sulfate aerosols (SO42−) in volcanic clouds is poorly known, especially in the troposphere. Here we determine the chemical speciation, lifetime and impact on air quality of sulfate aerosols from the 2014–15 Holuhraun flood lava eruption of Bárðarbunga icelandic volcano. To do so, we jointly analyze a set of SO2 observations from satellite (OMPS and IASI) and ground-level measurements from air quality monitoring stations together with, for the first time, high temporal resolution mass spectrometry measurements of Aerosol Chemical Speciation Monitor (ACSM) performed far from the source. We explore month/year-long ACSM data in France from stations in contrasted environments, close and far from industrial sulfur-rich activities. We demonstrate that aged volcanic sulfate aerosols exhibit a distinct chemical fingerprint, with NO3 : SO4 and Organic : SO4 concentration ratios higher than freshly-emitted industrial sulfate but lower than background aerosols in urban/rural conditions. Combining AERONET (AErosol RObotic NETwork) sunphotometric data with ACSM observations, we also show a long persistence over weeks of volcanic sulfate aerosols while SO2 disappears in a few days at most. Finally, gathering 6 month-long datasets from 19 sulfur monitoring stations of the EMEP (European Monitoring and Evaluation Programme) network allows us to demonstrate a much broader large-scale European particulate pollution in SO4 associated to the Holuhraun eruption, from Scandinavia to France. Exploiting these in-situ data, we also show the various rates of SO2 oxidation observed in the volcanic cloud, with SO2 : SO4 concentration ratios ranging in 0.6–7, distinct from background conditions of about 50. Most current studies generally focus on SO2, an unambiguous and more readily measured marker of the volcanic cloud. However, our results here on sulfate aerosols raise fundamental questions about the cumulative impact of tropospheric eruptions on air quality, health, atmospheric composition and climate, which may be significantly underestimated.