Localized crater deformation can shed insight into shallow magma processes and eruption hazards. To study localized crater deformation at Nyiragongo volcano (Democratic Republic of the Congo), we processed Interferometric Synthetic Aperture Radar (InSAR) time series using RADARSAT-2 Ultra-Fine satellite data spanning 2012–2016. This observation was possible thanks to a period between mid-2012 and early 2016 during which the lava lake did not overflow the bottom of the crater. We observed persistent crater floor subsidence and inverted the InSAR displacements during August 2013–December 2015 to model candidate deformation sources with analytic solutions in a homogeneous elastic half-space. We identified a deflating source modeled as a sill at 90 m depth beneath the crater surface. The sill solution is an oversimplified but useful model of the observed deformation rather than a physically realistic intrusion. Thus, we instead interpret the model to represent a composite signal of cooling lava lake overflows accumulated in the crater. Our study demonstrates the capabilities of imaging localized deformation patterns using high spatial resolution SAR data.

The high susceptibility to geo-hydrological hazards in tropical Africa and their impacts remain poorly documented in existing disaster databases. Only impactful events with high attention are manually reported, creating systematic biases. Natural Language Processing has the potential to automate the documentation of geo-hydrological disasters. This research focuses on developing a semi-automated tool to extract information from online press and social media posts. Fine-tuned Large Language Models perform a series of tasks, such as question-answering, zero-shot classification, and near-entity recognition, to extract information from these online sources. A three-step approach is proposed for the detection of events: (1) filtering posts or articles on their relevancy, (2) extracting information on the location, timing, and impact and (3) merging and sorting information to document identified events into a structured disaster database. Shortcomings compared to a manual approach remain. These mainly relate to the complexity of the text or toponymic ambiguity when geocoding events. The tool is therefore complementary to other information-gathering approaches. These new sources of information will improve our understanding of the distribution of disasters related to geo-hydrological hazards, especially in data scarce context. Future work will combine this semi-automated tool with remote sensing and citizen science data, to further reduce systematic biases in disaster datasets.

Satellite-based thermal remote sensing is a useful tool for monitoring volcanoes. It involves detecting thermal anomalies, called 'hotspots,' and calculating the radiative energy emitted by volcanic activity. Various volcanic hot spot detection algorithms already exist in the literature. However, every algorithm has its advantages and disadvantages, as they are limited depending on the tradeoffs made during algorithm development, the sensor used for aquisition, and the geometry of acquisition. Depending on the algorithm used, different results are obtained from the same data and, hence, different interpretations can be made in terms of, e.g., energy emitted, effusion rates, and eruption duration. In the present work, we aim at creating a new hotspot detection algorithm using MODIS and VIIRS imagery, which allows us to efficiently look at the dynamics of thermal emissions coming from persistent lava lakes, i.e., bassins of lava maintained molten through thermal convection and outgassing. We investigate the applicability of sensor fusion ideas, using multiple bands, and incorporating cloud cover information. We expect that by combining all available data the robustness of the detection process will increase.

The acquisition of aerial photographs for cartographic applications started in the 1930s, and more intensively after World War II. Such old, often panchromatic, imagery offers metre to sub-metre scale spatial resolution over landscapes that have significantly evolved over the decades. Before the appearance of the first digital aerial camera systems at the end of the 20th Century, surveys were performed with analogue metric cameras, with images acquired on films or glass plates and, next, developed on photo papers. In Europe and North America, several institutions hold unique collections of historical aerial photographs having local, national and, in some cases, colonial coverages. They represent invaluable opportunities for environmental studies, allowing the comparison with today’s land use land cover, and the analysis of long-term surface displacements. Initially, the photogrammetric processing of analogue aerial photographs would require expensive equipment, specialised operators, and significant processing time. Thanks to the digital revolution of the past two decades and the development of modern digital photogrammetric approaches, the processing of this type of image datasets has become less cumbersome, time consuming and expensive, at least in theory. In practice, this is more complex, with digitising and processing issues related to the ageing and quality of conservation of the aerial photographs, the potential distortions created during the digitising process, and the lack of ancillary data, such as, flight plans, and camera calibration reports. The limited overlap between photographs, typically 60 % and 10-20 %, along-track and across-track, respectively, make their processing with Structure-from-Motion Multi-View Stereo (SfM-MVS) photogrammetry poorly reliable to accurately reconstruct the topography and orthorectify the images. Given the fact that some collections reach up to millions of historical aerial photographs, the digitising, pre-processing, and photogrammetric processing of these images remain a challenge that must be properly tackle if we would like to ensure their preservation and large-scale valorisation. In the present work, we describe the mass-digitising, digital image pre-processing and photogrammetric processing approaches implemented at the Royal Museum for Central Africa (RMCA, Belgium) to preserve and valorise the collection of >320,000 historical aerial photographs conserved in this federal institution. This imagery was acquired between the 1940’s and the 1980’s, over Central Africa, and mostly D.R. Congo, Rwanda and Burundi. For the digitising, a system of parallelized flatbed scanners controlled by a Linux computer and a self-developed software allows speeding-up the scanning of the entire collection in only few years. A series of Python scripts were developed and combined to allow a swift pre-processing that prepare and optimise the digitised images for photogrammetric processing. Finally, a SfM-MVS photogrammetric approach adapted to historical aerial photos is used. Examples of application for geo-hydrological hazards studies in the western branch of the East African Rift are shown.

Slow-moving landslides (SML; mm year−1 to 100 m year−1) can be a ubiquitous geomorphic process in tropical mountain landscapes. Yet, answer to crucial questions such as what landscape characteristics exert the most important control on their spatial distribution (e.g., slope, connection to rivers, climate, lithology, tectonic setting, recent deforestation, degree of anthropogenic activity, etc.), or how does their dynamic behaviour responds to landscape changes (urbanisation, deforestation, etc.), remains elusive – and is typically relying on information collected on single or a few landslide(s). Intrinsically complex, obtaining large-scale datasets with dense surface displacement measurements is even more so in the tropics, where field access is typically difficult, and rapid vegetation changes and persistent cloud cover hamper the use of satellite remote sensing. In this work, we attempt to overcome these limitations by exploiting synergies between spaceborne sensors (i.e., radar and optical) and deformation measurement techniques (i.e., interferometry and sub-pixel image correlation), to obtain multi-year datasets of the activity of SML in the western branch of the East African Rift (wEAR). Characterised by a large natural landscape and climatic diversity, the wEAR is exemplative of many tropical mountain regions, i.e., i) affected by large-scale land use changes and ii) disproportionately high landslide impacts and iii) largely overlooked in landslide research. We collected a spatio-temporal inventory containing characterised by varying level of activity and behaviours, and located in contrasting environments. This regional-scale dataset will form the foundation for untangling the intricate influences of climate, lithology, tectonics and man-made environmental changes on the occurrence and activity of SML. By investigating their interaction with river system, we also aim at estimating how they contribute to controls on river sediment budgets, regional erosion rates, channel network evolution and flooding patterns – key for our understanding of landscape evolution, sediment budgets and geo-hydrological hazards. Overall, this work aims at moving forward our understanding of a key geomorphic process in severely under-researched types of environments subject to rapid changes. This is not only essential for a better hazard assessment, but also for comprehending how (human-induced and/or natural) environmental changes affect these landscapes and the sediment dynamics.

Nyamulagira volcano (eastern Democratic Republic of the Congo) is one of Africa's most active volcanoes and poses a significant threat to the nearby rapidly expanding population centers. Situated in the Virunga Volcanic Province in the western branch of the East African Rift System, Nyamulagira's frequent eruptions offer a valuable opportunity to study effusive rift volcanism. However, understanding its subsurface processes remains challenging, impeding monitoring efforts. Here, we report a comprehensive mineralogical, petrological, and geochemical study of rocks from historical eruptions at Nyamulagira. Mineral textures and compositions show strong spatial and temporal variations. We identify multiple active magma reservoirs in which magma compositions and textures evolve via crystal accumulation, fractional crystallization, magma recharge, mixing, and convection. We distinguish three distinct reservoirs: a deep reservoir at similar to 22-30 km depth, the main storage region at similar to 13-18 km depth, and a shallow reservoir at similar to 2-9 km depth. We propose that differentiation at Nyamulagira integrates olivine and clinopyroxene crystallization and accumulation in the deep reservoir, and fractional crystallization and magma mixing/homogenization in the interconnected intermediate and shallow reservoirs. Primitive magmas from the deep reservoir are predominantly emitted via distal eruptions, whereas more evolved magmas from the shallower reservoirs have been erupted on the flanks or at the summit caldera in recent decades.

Many regions of Africa are exposed to a large variety of geo-hydrological hazards such as earthquakes, volcanic eruptions, landslides, floods, karst collapses and large urban gullies. Despite the soaring impacts on population, infrastructure and the environment associated with the occurrence of these hazard risks, most regions are under-studied. In addition to this lack of information, stakeholders, policy makers and the public at large remain relatively poorly aware of the hazard and risk problems, whether it is about their causes, their impact, and/or their mitigation. This overall lack of knowledge and awareness is associated with an aggravation of the impacts as the growing and vulnerable population of these regions, in search for new settlements and opportunities, is often moving towards areas that are more prone to natural hazards. This is in this context that UNESCO supports the preparation and dissemination of a guide booklet on geo-hydrological hazards for stakeholders, policy makers and the general public. The booklet targets ten African countries (Angola, Burundi, Cameroon, Central African Republic, Chad, Democratic Republic of the Congo, Equatorial Guinea, Gabon, Republic of the Congo, São Tomé and Príncipe) that are covered by the UNESCO regional office of Yaoundé. The aim of this work is to raise collective awareness of the need to prevent natural hazard risks at local, regional and national levels in order to ensure the protection of populations and promote the sustainable development of territories. In this way, UNESCO aims to guide and advise the ten African countries by providing them with useful and practical information.

Assessing volcanic hazards in locations exposed to multiple central volcanoes requires to consider multiple potential eruption sources and their respective characteristics. While this is common practice in ashfall hazard assessment, this is generally not considered for topography-controlled volcanic flow processes. Yet, in volcanic areas with closely spaced volcanic systems, eruptions fed from several contrasted volcanic systems might threaten one given area. Considering the case of the Nyiragongo and Nyamulagira volcanoes in the Virunga Volcanic Province (D.R.Congo), we present a method to produce a combined lava flow inundation susceptibility map that integrates both volcanoes. The spatial distribution of the probability of vent opening for the next eruption is separately constrained for both volcanoes based on the mapping of historical and pre-historical eruptive vents and fissures. The Q-LavHa lava flow probability model is then calibrated separately for each volcano, considering several historical lava flows of Nyamulagira (2004, 2006, 2010) and Nyiragongo (2002). The maps for the two volcanoes are thereafter integrated based on a weighted sum of both individual lava flow inundation probability maps, assuming historically-based relative eruption frequency of the two volcanoes. The accuracy of this probabilistic susceptibility map for the most active volcanic region in Africa was unfortunately validated by the May 2021 lava flow produced by Nyiragongo. This map was discussed and validated in 2019 with local scientists, as well as representatives of disaster management and urban planning institutions, but was not included in the regional contingency plan ahead of the 2021 eruption crisis. Updating the volcanic crisis and evacuation management plans with this lava flow probability map could contribute to reinforce risk awareness among the population and inform the future development of the city of Goma.

Landslides are hillslope processes controlled by natural changing topographic conditions. Landslides are also influenced by human activities. Yet, understanding the space-time occurrence of landslides and their interactions with these typically long-term natural and short-term human-induced controls remains a key challenge in many regions, especially in tropical environments where data scarcity is commonplace. Here we decipher these dynamic processes in the Ruzizi Gorge located in the Kivu Rift (Central Africa), that is an exceptional geomorphological landmark whose origin is associated with the rerouting of >7000 km(2) of drainage area from Lake Kivu during the Holocene. This bedrock river has also seen its landscape disturbed over the past decades by the development of the city of Bukavu (DR Congo). In this study, we combine detailed field observations, historical aerial photographs, archive analysis and satellite imagery to compile a multi-temporal inventory of 385 landslides and constrain their dynamics. We show that extremely high incision rates during the early stage of the formation of the gorge explain the space-time clustering of thousand-year-old large (up to similar to 2 km(2)) landslides, independently from the lithological context. These landslides are currently non-active and poorly eroded. Their deposit areas partly cover the riverbed with boulders, armouring the channel and inhibiting further incision. The landslides that occurred over the last 60 years are shallower slope failures of smaller size and higher mobility. They tend to disappear rather quickly from the landscape, sometimes within a few years. Their distribution is primarily controlled by threshold slopes, lithology, and the past large landslides, the influence of the land use being less pronounced. Overall, the sediment mobilization rates associated with these high frequency landslides significantly outpace the extreme landslide erosion pulse associated with the gorge formation. Our results provide insight on interactions between channel-hillslope coupling and feedbacks among landslide processes and river gorge formation in a unique environment.

The Nyiragongo volcano is one of the most alkali-rich volcanic centres on the planet (Na2O + K2O generally >10 wt.%, agpaitic index up to 1.34), characterized by a semi-permanently active lava lake which hosts silica-undersaturated (SiO2 <40 wt.%), low viscosity lavas. To improve our understanding of this unique magmatic system, we present a set of 291 samples, acquired during new field excursions between 2017 and 2021. The major and trace element composition of all samples was measured, revealing a lithological range extending from primitive picrites (Mg# 82) erupted from parasitic cones to a variety of highly evolved nephelinites, leucitites, and melilitites erupted from the main edifice as recently as 2002, 2016, and 2021. We measured major and trace element compositions from the full spectrum of minerals present in all sampled lithologies. From these we calculated that the main magma reservoirs feeding Nyiragongo are at approximately 9 – 15 and 21 – 33 km depth, in agreement with recent seismic observations. Fractional crystallization modelling using observed mineral compositions and proportions was performed to quantitatively link the lithologies to specific residual liquid fractions assuming evolution from an olivine-melilite parental melt. Our modelling indicates that fractionation cumulate formation in deep chambers reduces the melt fraction remaining to ~60%, after which melts are injected into upper, liquid dominated magma chambers where fractionation and accumulation of clinopyroxene, melilite, and feldspathoids dominate. Characterisation of mineral textures and geochemistry reveals high crystal mobility in a repeatedly recharging plumbing system split between liquid-dominated, evolved magma chambers and more solid-dominated, primitive mushes, decreasing in liquid fraction with depth.

The impact of humans on Earth surface processes strongly increased since the offset of the 20th century, often surpassing the importance of natural drivers. In most mountainous regions, landslide mobilization rates may have increased due to human disturbances of the landscape such as deforestation, mining, and road construction. However, assessing the impact of these human disturbances is not straightforward, especially in the Global South where data-scarcity is commonplace. In this study, we use historical aerial imagery to assess the mobilization rates of rapidly-formed landslides and their sensitivity to human impacts over six decades and 21,000 km(2) in the North Tanganyika-Kivu Rift region (NTK Rift) in Africa. This tropical region is characterized by rapid societal changes which have drastically altered the natural environment. By estimating the volume of thousands of rapidly-formed landslides, we find that the average mobilization rate in the landscapes rejuvenated by the retreat of rifting-related knickpoints is three times higher as compared to the relict landscapes (ca. 31 [29.2-34.2] m(3) km(2) year(-1) vs 13 [11.9-13.7] m(3) km(2) year(-1)). These mobilization rates are dominated by deep-seated landslides. Our mobilization rates are relatively low as compared to observations in other mountainous regions. Yet, the tropical NTK rift also has a more moderate topography and degree of tectonic activity. In addition, our research covers an unprecedented large area and a long period, as such being not biased by local extreme events. In rejuvenated landscapes, roughly 5 % of the sediment mobilization by rapidly-formed landslides is linked to human activity, while in relict landscapes this figure rises to 18 %, notably due to mining and road construction. The role of human activity is limited as compared to the recent occurrence of some large landslides, which seem linked to natural causes and dominate the overall mobilization rates. Moreover, the limited role of human activity must be balanced with the fact that the NTK Rift, although highly populated, remains relatively untouched by major road infrastructure constructions. While previous studies have found that deforestation has a large impact on the landslide risk in the region, its impact on the mobilization rates is much less important. Overall, our results significantly contribute to a better understanding of landslide mobilization and its controlling factors in the context of human-induced environmental change, especially by providing much-needed long-term observations for a currently under-researched type of environment.

Active volcanic craters are highly dynamic geological features that undergo morphological changes on a broad range of spatial and temporal scales. Such changes have implications for the stability of the edifice, the eruptive style and the associated hazards. However, monitoring the morphological evolution of active craters at high spatial resolution and over long periods of time can be challenging, especially at remote volcanoes. In this study, we demonstrate the potential of Structure-from-Motion Multi-View Stereo photogrammetry technique based on crowd-sourced data, applied to the case study of Oldoinyo Lengai (OL) volcano in northern Tanzania. Following the 2007-08 paroxysm, OL volcano resumed its characteristic effusive activity and started to fill in with lava the newly-formed 300 m wide and 130 m deep pit crater. Monitoring capability is limited at OL due to its location in a remote non-urbanized area, therefore, the eruptive and morphological evolution is poorly constrained (e.g., lava emission rates, number of vents, location of unstable areas), with hazard implications for tourists visiting the summit area. Here we use crowd-sourced images, including Unoccupied Aircraft System (UAS) images, ground-based videos and pictures collected between October 2014 and June 2022, to reconstruct high-resolution topographic time-series of OL's summit crater. With these data, we have generated 7 Digital Elevation Models (DEMs) of OL's pit crater spanning the past 8 years, and estimated the emitted volume of lava and the corresponding time averaged discharge rates (TADR). From this we characterize the geomorphological evolution of OL pit crater since the 2007-08 paroxysm and perform a preliminary hazard assessment of the crater area. InSAR COSMO-SkyMed and Sentinel-1 data covering the periods 2013-2014 and 2018-2019 were also used in this study to complement our observations. Our results indicate that the main location of lava emission within the crater floor has repeatedly shifted over the years and that the 2008 cone has experienced a subsidence over time. OL's TADR has increased over the years, reaching values one order of magnitude higher in the period 2021-2022 compared to 2014-2018. Assuming similar TADR in the coming years, the crater could be filled in by lava within the next decade, leading to new lava overflows on the flanks of the volcano.

Abstract During eruptions, volcanoes produce air‐pressure waves inaudible for the human ear called infrasound, which are very helpful for detecting early signs of magma at the surface. Compared to violent ash‐rich explosions, recording more discrete atmospheric disturbances from effusive eruptions remains a practical challenge depending on the distance to the source. At Nyiragongo volcano (D.R. Congo), towering above a 1‐million urban area, we analyzed local infrasonic records between January 2018 and April 2022. An acoustic signature from this open‐vent volcano is detected up to the volcano observatory facilities in Goma city center about 17 km from its crater. We compared infrasound signals with space‐based observations of the intra‐crater activity (SO2 emissions, thermal anomalies, crater depth/radius). We thus obtain a comprehensive picture of Nyiragongo's eruptive activity during this period, encompassing the drainage of its lava lake during its third known flank eruption on 22 May 2021.

Human activities transform Earth's ecosystems and landscapes at unprecedented rates and scales. Land use changes are particularly drastic in economically developing countries of the tropics, where major demographic and economic shifts are driving unparalleled rates of agricultural expansion, deforestation and urbanisation. These changes to the environment are increasing the incidence of geo-hydrological hazards such as landslides. Dramatic increase in the occurrence of shallow, high-velocity landslides has been comprehensively demonstrated on recently deforested and/or urbanised steep slopes. Yet, our understanding of how such constraints – typical for the tropics – interact and affect larger (often > 0.2 km²), slow-moving (mm year−1 to 100 m year−1), deep-seated (> 5 m) landslides (SML) remains very limited. Often manifesting as long-term, persistent slope failures, these SML can nevertheless permanently affect the livelihood of local communities in mountain regions. Their connectivity to river networks also places them as a dominant geomorphic process in mountain landscapes: they shape the morphology of hillslopes and can exert very strong controls on river sediment budgets, regional erosion rates, channel network evolution and flooding patterns. Nevertheless, estimations of landslide mobilisation rates over sufficient spatiotemporal scales are very scarce, especially in tropical environments. As a result, the potential interactions between rivers and landslide dynamics remain poorly constrained while being key for our understanding of landscape evolution, sediment budgets and geo-hydrological hazards.Untangling the intricate influences of climate, lithology, tectonics and man-made environmental changes on the activity of SML will require a large and robust dataset across diverse landscape conditions. Here, we aim to present and discuss our strategy is to quantify SML spatio-temporal patterns over the western branch of the East African Rift System (wEARS), a > 1000 km north-south region exemplary of many tropical mountain areas, i.e., affected by large-scale land use changes and disproportionately high landslide impacts – as well as largely overlooked in landslide research. Synergies between different space-borne remote sensing tools (combined use of optical and radar imagery, historical aerial photographs, etc.), which proved effective in our recent work in the region, will be exploited to gather a large dataset on the activity of SML across diverse time scales, landscapes and climatic conditions in the wEARS. Overall, this work aims at moving forward our understanding of a key geomorphic process in severely under-researched types of environments subject to rapid changes. This is not only essential for a better hazard assessment, but also for comprehending how (human-induced and/or natural) environmental changes affect these landscapes and the sediment dynamics.

Karthala shield volcano (Grande Comore) is the most frequently active volcano of the Comoros Archipelago. On a centennial scale, Karthala alternates phases of dominantly eccentric activity, when eruptive fissures open along the rift zones cutting the northern and southern volcano flanks, with phases of dominantly summit activity. As a whole, the volcano alternates periods of intense activity (4 eruptions in the 2005-2007 period) with decade-long periods of total rest. Since 1926, the activity of the volcano has occurred inside or close to the summit caldera, with the notable exception of the 1977 eruption located at a low altitude on the SW flank, close to the village of Tsingani. The last eruption occurred in 2007 in the northern part of the summit caldera.The Centre National de Documentation et de Recherche Scientifique (CNDRS) of Comoros is in charge of volcanic and seismic monitoring for the three islands of Grande Comore, Anjouan and Moheli. The headquarters of the Karthala Volcano Observatory (OVK) are located on Grande Comore. Geophysical and geochemical volcano monitoring and educational programs are performed in collaboration with international partners, while communication during seismo-volcanic events is performed in collaboration with the Civil Defence and a panel of stakeholders.Since November 2021, the OVK seismic network has detected the beginning of a new phase of unrest, after 14 years of quiescence. Swarms of deep eccentric seismicity below the western flank and minor shallow seismicity below the summit during June-October 2022 have been associated with significant movement of the western flank of the volcano towards the satellite as detected by satellite radar interferometry. A continuous trend of subsidence is measured inside the summit crater, possibly related to cooling of the 2007 lava lake. Geochemical monitoring has confirmed the absence of major changes in composition or temperature of the summit intra-caldera fumaroles and the occurrence of CO2 soil emissions mostly focused on the volcano flanks.On one side, the early detection of a possible dyke injection below the edifice, the progressive awakening of the volcano and the existence of major international cooperation programs (Interreg “Hatari”) have facilitated the rapid consolidation of the scientific and operational framework and have permitted to inform the national authorities and the population regularly. Conversely, the long duration of the alert represents a major challenge in maintaining a permanent and efficient scientific-operational interface able to face the several possible scenarios associated with the reawakening of Karthala volcano.

The Nyiragongo volcano is one of the most alkali-rich magmatic systems on the planet, currently characterized by the presence of a persistent lava lake in the summit crater which hosts silica-undersaturated (SiO 2 < 40 wt.%), low viscosity lavas with a significantly elevated alkali content (Na 2 O + K 2 O > 10 wt.%). In order to better understand this exotic magmatic system, we present a set of 244 samples of the Nyiragongo volcano, acquired during a field expedition performed in 2017. Lithologies range from primitive picrites (Mg# 82) erupted by parasitic cones to a variety of highly evolved nephelinites, leucitites, and melilitites erupted from the main edifice as recently as 2016. Extensive mineralogical characterisation in terms of major and trace element geochemistry is presented for the full lithological diversity of Nyiragongo, revealing a compositional range in olivine from forsteritic (Fo = 91) to Ca-rich (Fo = 2, 31 wt.% CaO). Similarly, clinopyroxene crystals cover a compositional range of Mg# = 89 to Mg# = 2. Melilite is dominantly alumo-åkermanitic, with only minor compositional variation driven by Ca-Na substitution, and additionally acts as a carrier of Sr and Ba. Trace element patterns indicate significant enrichment (up to 100*E-MORB concentrations) of LREE and LILE increasing with fractionation, coinciding with comparative depletions

&lt;p&gt;Sensitive and accurate detection of SO&lt;sub&gt;2&lt;/sub&gt; from remote sensing is essential to monitor volcanic degassing. The main objective of this study is to understand the dynamics of SO&lt;sub&gt;2&lt;/sub&gt; gas emissions at open-vent volcanoes between major eruptive events, using Sentinel-5P TROPOMI-based SO&lt;sub&gt;2&lt;/sub&gt; measurements.&lt;/p&gt; &lt;p&gt;Time-series of SO&lt;sub&gt;2&lt;/sub&gt; mass are analysed at 10 open-vent volcanoes (Ambrym, Erebus, Erta Ale, Kilauea, Masaya, Nyamuragira, Nyiragongo, Stromboli, Villarica, Yasur) using a newly developed TROPOMI SO&lt;sub&gt;2&lt;/sub&gt; product generated by the Covariance Based Retrieval Algorithm (COBRA; Theys et al., 2021). Compared to the current operational SO&lt;sub&gt;2&lt;/sub&gt; TROPOMI product (which uses the Differential Optical Absorption Spectroscopy technique), the COBRA dataset has improved performances and reduce both the noise and bias on the data, allowing a more refined study of degassing from open-vent volcanoes.&lt;/p&gt; &lt;p&gt;Time-series have been obtained for SO&lt;sub&gt;2 &lt;/sub&gt;emissions over a period from 2018 to early 2023. For the 10 selected persistently active volcanoes, the SO&lt;sub&gt;2 &lt;/sub&gt;behaviours are analysed and compared, showing cyclic and sporadic variations, as well as peaks of emission when a flank or major eruption occur. Patterns in SO&lt;sub&gt;2&lt;/sub&gt; time-series during and between major eruptive events are discussed to assess the potential use (and limitations) of these measurements as a tool for early warning and volcanic crisis management.&lt;/p&gt; &lt;p&gt;Reference:&lt;/p&gt; &lt;p&gt;Theys, N., Fioletov, V., Li, C., De Smedt, I., Lerot, C., McLinden, C., Krotkov, N., Griffin, D., Clarisse, L., Hedelt, P., Loyola, D., Wagner, T., Kumar, V., Innes, A., Ribas, R., Hendrick, F., Vlietinck, J., Brenot, H., Van Roozendael, M. (2021). A sulfur dioxide Covariance-Based Retrieval Algorithm (COBRA): application to TROPOMI reveals new emission sources. &lt;em&gt;Atmospheric Chemistry and Physics&lt;/em&gt;, &lt;em&gt;21&lt;/em&gt;(22), 16727-16744.&lt;/p&gt;

Volcano monitoring requires simple techniques to rapidly identify the cause of volcanic unrest. The so-called RSAM (real-time seismic amplitude measurements) technique, used in many observatories, is a good example of extracting information from seismograms with minimal processing. Built on a similar principle, the more recent seismic amplitude ratio analysis (SARA) technique allows locating migrating seismicity at high frequency (> 2 Hz, e.g., due to dike intrusions) under certain assumptions. However, such analysis generally requires a dense distribution of stations close to the seismic sources (depending on the magnitude) and/or station sites undisturbed by human activity. In a more straightforward and qualitative approach, computing amplitude ratios between station pairs can also allow for the detection of temporal and (2D) spatial changes of volcanic activity. In this work, we adopt such a simplified approach of SARA in order to characterize seismic tremors originating from two open-vent neighboring volcanoes, Nyiragongo and Nyamulagira, in the Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo (DRC). In contrast with previous studies, we focus here on the low-frequency band (0.3–1 Hz), free from anthropogenic noise and sensitive to shallow volcanic tremors linked to intermittent or permanent intra-crater eruptive activity recorded through the large-aperture local network. We apply for the first time the SARA methodology for volcanic sources predominantly generating surface waves and propagating over long distances. The analysis is performed on more than two years of continuous seismic data. Seismic amplitude analysis in this frequency band is strongly influenced by the short-period microseisms originating from nearby Lake Kivu. Despite this diurnal to seasonal amplitude variability, SARA successfully detects continuous volcanic tremor activity and its arrest at both volcanoes. In light of these findings, we discuss the applicability of the method to the continuous, real-time detection, and characterization of long-period shallow volcanic tremor sources in this region.

Between 2015 and 2021, Nyiragongo's lava lake level experienced a linear increase punctuated by fast intermittent drops. These drops occurred synchronously to seismic swarm at approximately 15 km below the surface and extending laterally NE from the volcano. To interpret these lava lake level patterns in terms of reservoirs pressure evolution within Nyiragongo, we consider the following simplified plumbing system: a central reservoir is fed by a constant flux of magma, distributing the fluid up into the lava lake and laterally into a distal storage zone. Magma transport is driven by a pressure gradient between the magma storage bodies, accommodating influx and outflow of magma elastically, and the lava lake. Lateral transport at depth occurs through a hydraulic connection for which the flow resistance is coupled to the magma flux. When the right conditions are met, lateral magma transport occurs intermittently and triggers intermittent lava lake level drops matching the observations.

Alkaline magmatism is an important chemical end-member of magmatic activity that typically occurs in response to small volume melting of asthenospheric-and/or lithospheric mantle material in intra-continental settings. Understanding trace element partitioning and phase equilibria during alkaline mag-matism can therefore provide constraints on intra-continental geodynamic settings. However, the parti-tioning of trace elements between alkaline melts and their dominant equilibrium mineral phases remains poorly constrained. Feldspathoids in particular have received limited attention with regards to their trace element contents, hampering our ability to interpret geochemical trends in alkaline magmatic systems. In this study, we performed a series of 1 atmosphere experiments in a gas-mixing furnace using a variety of highly alkaline (Na2O + K2O = 4.15-14.97 wt%) and silica-undersaturated (SiO2 = 36.73-45.96 wt%) lava compositions from Nyiragongo, Democratic Republic of Congo, in order to investigate the partitioning behaviour of trace elements in minerals from alkaline magmas. Experimental runs were performed with oxygen fugacity buffered at both QFM (quartz-fayalite-magnetite equilibrium) and QFM + 1 and cover a range of geologically-relevant temperatures (1025-1200 degrees C). The quenched products of these experi-ments contained leucite, nepheline, melilite, clinopyroxene, olivine, and rhonite crystals, of which glass-crystal pairs were analysed for rare earth elements, large-ion lithophile elements, and high-field -strength elements. Leucite and nepheline host considerable quantities of large-ion lithophile elements but take up negligible amounts of more highly charged cations. Akermanitic melilite readily incorporates mono-to trivalent cations with a preference for light over heavy rare earth elements, but incorporates only select divalent cations. Rhonite and clinopyroxene have analogous partitioning behaviours, with a strong preference for heavy over light rare earth elements. Fractionation modelling using the reported partitioning behaviours reproduces the 2021 eruption products of Nyiragongo, with 48% fractionation from an olivine-melilitic parental melt composition. Crystallization of trace-element poor feldspathoid amplifies pre-existing high LREE/MREE ratios of the parental magma and progressively increase trace ele-ment abundances for all but monovalent cations.@ 2023 Elsevier Ltd. All rights reserved.