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With more than 30 million people living within 10 km of active or dormant volcanoes, eruptions are a natural socio-economic hazard that can have devastating consequences for society. Hence, the timely forecasting of volcanic unrest has real-world, and potentially, life and death implications. A major challenge is the identification and monitoring of precursors to forthcoming volcanic eruptions. The observation and measurement of thermal anomalies is one of the answer to this challenge, with some volcanoes exhibiting signs of thermal unrest over extensive areas of their edifice for several years prior to an eruptive event. Glaciers that sits on volcanoes are likely to respond to the increased heat and could therefore be used as complementary volcano thermometers but a large scale study is missing. Our study, which covers 600 Andean glaciers and 37 ice-clad volcanoes, demonstrate glacier mass balance sensitivity to volcanic heat. We distinguish between ‘volcanic-glaciers’ (located ≤1 km from volcanic centres), and ‘proximal glaciers’ (1-15 km) and calculate their equilibrium line altitude (ELA). In most instances, proximal glacier ELAs are lower than those of nearby volcanic-glaciers. In some cases, the ELA decrease proportionally with increasing glacier distance from the volcanic edifice, and a quantitative relationship between ΔELAmean (i.e., the difference in mean ELA between the proximal and volcanic-glaciers) and ASTER-based measurements of volcanic thermal anomalies could be established. These results highlight the impact of volcanic heat on glacier mass balance; emphasise the need to exclude volcanic-glaciers from glacier-climate investigations; and demonstrate the first-order potential of glaciers as ‘volcanic thermometers’, with the ΔELAmean representing a proxy for volcanic heat.

Long-lasting, hybrid eruptions can be of complex description and classification, especially when associated with multiple eruptive styles and multiple products. The 2021 Tajogaite eruption of La Palma, Canary Islands, was associated with a magma-gas decoupled system that resulted in the simultaneous emission of lava flows and tephra plumes from various vents. Even though the tephra blanket (∼2 × 107 m3) represents only 7%–16% of the total erupted volume, it provides fundamental insights into the overall eruptive dynamics. Tephra was mostly dispersed NE-SW due to a complex regional and local wind patterns and was subdivided into 3 units and 11 layers that well correlate at different distances from the vent and with both tremor data and lava emission rate. While plume height varied at the temporal scale of a few hours, the average mass eruption rate associated with the tephra blanket of the different units remained relatively constant (∼3–4 × 103 kg s−1). In contrast, the emission rate of lava largely increased after the first week and remained higher than the overall emission of tephra throughout the whole eruption (average value of ∼6 × 104 kg s−1). Based on a detailed characterization of the tephra blanket in combination with atmospheric wind, tremor, and lava emission trend, we demonstrate the need of (a) multidisciplinary strategies for the description of hybrid eruptions that account for both the duration of individual phases and the quantification of the mass of multiple products, and of (b) dedicated ash dispersal forecasting strategies that account for the frequent variations of eruptive and atmospheric conditions., Research activities were supported by Swiss National Science Foundation (Grant 200020_188757) and by the projects (a) VOLRISKMAC (MAC/3.5b/124) and (b) VOLRISKMAC II (MAC2/3.5b/328), financed by the Program INTERREG VA Spain-Portugal MAC 2014–2020 of the European Commission; (c) Cumbre Vieja Emergencia, financed by the Science and Innovation Ministry, Spanish Government; and (d) Tfassistance, financed by the Cabildo Insular de Tenerife. JER fieldwork was partially financed through NSFGEONERC-DisEqm (NERC Reference: NE/N018575/1) and V-PLUS projects (Prof. Mike Burton).

The 1982 and 2015 eruptions are the first at Wolf volcano, Galápagos Archipelago, with eyewitness accounts and satellite imagery. Both eruptions are characterized by a rapid, intense initial phase and multiple eruptive vents leading to the formation of large ‘a‘ā lava fields with scarce pāhoehoe deposits, mostly associated with the waning phases. The 1982 eruption started on 28 August from an intra-caldera vent that produced high lava fountaining, but also occurred from a radial fissure on the SE flank. This eruption lasted for at least 9 days and generated approximately 70E+6 m3 of lava. The 2015 eruption started on 25 May from a circumferential fissure that also produced high lava fountaining and deposited reticulite scoria on the flanks of the volcano. For the first time since monitoring Galápagos eruptions, we observed cryptotephra from the 2015 eruption reaching and depositing in mainland Ecuador, 1400 km away from the source. Lava from the 2015 circumferential vents covered large areas on the SE and E flanks. On 13 June 2015 the eruption switched to an intra-caldera vent that was active until 30 June, which produced lava flows that covered most of the caldera floor. This eruption lasted 36 days and produced ~116E+6 m3 of lava, making it one of the largest eruptions in the Galápagos since the eruption of Sierra Negra in 1979. The combination of ground-based geophysical surveillance, remote sensing, eyewitness accounts, and detailed field work allows us, for the first time, to constrain the eruptive dynamics of this remote volcano with a day-by-day time resolution. In particular, our approach allows quantification of eruption rates, which represents critical information for understanding volcanic systems and for hazard assessment. First order rheological calculations further enable us to constrain the eruption dynamics and emplacement of the lava fields.

Volcanoes switching from quiescence to eruption shortly after catastrophic earthquakes have raised interest for volcanic triggering and the influence of earthquakes on volcanic activity. Its influence on already active systems and especially at open-vent volcanoes is more difficult to apprehend. A number of recent observations suggest an influence of tectonic earthquakes on Popocatépetl’s activity, the importance of which remains unknown. To further investigate this, we introduce an index, based on the near-field concept, identifying the earthquakes with the highest potential to promote volcanic activity (hereafter termed “significant earthquakes”). The time series of significant earthquakes is compared with the intensity of the volcanic activity, as characterized by the number and energy of volcano-tectonic earthquakes, the number of dome extrusions, the intensity of thermal and degassing fluxes, and ash production. Three main periods with contrasting activity stand out showing that Popocatépetl presents intense activity when significant tectonic earthquakes are frequent. Enhanced extrusion apparently follows significant earthquakes quickly with pulses of dome extrusion that peak after 1.3 ± 0.3 years. Conversely, extrusive activity vanishes when significant seismicity disappears, as during the period 2003–2011, which coincides with a 12-year-long significant seismicity gap. Hence, we propose that the 1994–2022 open-vent activity at Popocatépetl is in part modulated by the repetitive occurrence of significant earthquakes that periodically promote volcanic activity., We thank three anonymous reviewers for their remarks and the editorial handling by N. Metrich and A. Harris that significantly improved the original manuscript. This manuscript also benefitted from constructive discussions with P.J. González. The earthquakes catalogue of the Servicio Sismológico Nacional (Mexico) is possible thanks to its personnel and product of the calculations made by its Analysis and Interpretation of Seismic Data Department. We thank all the personnel of the CENAPRED for realizing the reports. MIROVA is a collaborative project between the Universities of Turin and Florence (Italy). We acknowledge the LANCE-MODIS data system for providing MODIS Near Real-Time products. The manuscript was edited by G. Jones, currently funded by the Cabildo de Tenerife under the TFinnova Programme supported by MEDI and FDCAN funds. TB gratefully acknowledges the invitation of J. Solé at the Noble Gases Geochronology Laboratory of the LANGEM and their fruitful discussions there. TB and NT acknowledge the hospitality and assistance of Rancho del Castillo and D. Belmont during fieldwork campaigns. DL is funded by the PAPIIT project number # IN106019 and SV by the PAPIIT project number #IA102221 and RC by the CONACYT-SEP project number A1-S-30127.

International audience; Sangay is one of the most active volcanoes in Ecuador, as it has been almost continuously erupting at least since the seventeenth century. However, because of its remote location and low associated risk to human population, little is known about its eruptions. Here we summarize Sangay's volcanic activity from January 2001 to May 2020, based on ground-based data, satellite-derived observations and chemical analysis of its erupted products. During the analyzed period, Sangay's activity changed from continuous to episodic, as revealed by seismic, thermal and ash emission data. We identified three main eruptive periods: the first, from 2001 to 2013, extruded a cumulative volume of 100 ± 50 million m3 of lava through long-lived activity; the second emitted 54 ± 27 million m3 in four short-lived episodes, which occurred once every year from 2015 to 2018; and finally, a third period since 2019, which has continuous but fluctuating intensity, and shows a significant increase in the extruded lava volume (172 ± 86 million m3 until May 31, 2020). Our results show a marked change in the eruption frequency and a significant increase in average discharge rate over time, although surface activity remained similar, with lava flows, small explosions and ash venting. We propose that three magmatic processes acted to explain the observed changes: between 2001 and 2013 the long-living low-intensity eruptions were promoted by buoyancy, while since 2019 similar but more intense activity was triggered by mass injections. In contrast, the episodic activity in between probably resulted from volatile exsolution due to crystallization (second boiling). Transitions between these three regimes are presumably the result of varying mass inflow rates. Our results provide insights into eruptive style transitions commonly observed at volcanoes of intermediate composition, such as Sangay, over a timescale of several years.

The atmospheric injection of gas and material produced by an explosive volcanic eruption determines a rapid compression of the atmosphere, which subsequently propagates as longitudinal elastic waves (sound). The size of the source, generally greater than tens of meters, and its duration, longer than few seconds, result into an emitted signal that is particularly rich in low frequency (f < 20 Hz), thus determining an efficient infrasound radiation. Thanks to the low spectral content and the reduced attenuation in the atmosphere, infrasound is capable of propagating for very large distances.In this study we show how the infrasonic monitoring of volcanoes at regional distances (> 100 km) is efficient in recording and characterizing volcanic events. For the purpose of our study, detections from the Yasur volcano (Tanna Island, Vanuatu) registered at a source-to-receiver distance of 400 km by the IS22 infrasound array, located in New Caledonia and part of the Comprehensive nuclear Test Ban Treaty (CTBT) International Monitoring System (IMS), were studied for a period of eleven years (2008-2018). The predominantly explosive Strombolian activity of this volcano makes it a perfect subject to be studied by infrasound technology.Detections of infrasound signals from Yasur volcano, that are modulated according to the seasonal variation of stratospheric winds, are corrected for attenuation accounting for real atmospheric specification between the source and the receiver to retrieve the pressure at the source: next, they are used to evaluate long term (yearly) and short term (hourly) variations of activity over the period of analysis. Results are eventually compared with thermal anomalies recorded by the MODIS (MODerate resolution Imaging Spectroradiometer) installed on NASA's Terra and Aqua satellites and computed by the MIROVA hotspot detection system.We show that even at regional (400 km) distances it is possible to follow the fluctuations of ordinary explosive activity during periods of optimal propagation of infrasonic waves in the atmosphere, In addition, we show that, when the signal is recorded, the time resolution retrieved from the analysis allows following variations of activity at hourly time scale, thus representing a valuable source of information, in particular in areas where local geophysical observation is missing.

Recently, numerous agencies and administrations in their latest reports show how it’s impossible to overlook the negative impact of atmospheric air pollution on human health. In this regard, it’s essential to be able to understand the spatial and temporal distribution of the concentration of main pollutants, and its ways to change. Among the numerous strategies proposed to tackle this problem, from the ’70s the study of satellite data assumed a key role, extending the analyzes carried out only with ground tools.In this work we analyzed the data acquired by TROPOMI (TROPOspheric Monitoring Instrument), a multispectral imaging spectrometer mounted onboard the ESA Copernicus Sentinel-5P satellite (orbiting since October 2017) and specifically focused on mapping atmospheric composition. In particular, we processed the TROPOMI NO2 products acquired over Piedmont Region (Italy) between 2018 and 2021. We obtain preliminary results by comparing the satellite-derived tropospheric NO2 columns data with ground-based NO2 concentration acquired by the ARPA-Piemonte network in different urban and geomorphological contexts. In particular, we compared the TROPOMI-derived time series with the acquisitions of ground stations located in urban and suburban areas (e.g. in the city of Turin), identified as “traffic stations”, and in rural areas (low population density and countryside areas) identified as “background stations”. The results allow us to investigate the correlation and coherence between the two datasets and discuss the added values and limits of satellite data in different environmental contexts, with the prospective of providing NO2 concentration maps of the Piedmont Region.

Open-vent volcanic activity is typically sustained by ascent and degassing of shallow magma, in which the rate of magma supply to the upper feeding system largely exceeds the rate of magma eruption. Such unbalance between supplied (input) and erupted (output) magma rates is thought to result from steady, degassing-driven, convective magma overturning in a shallow conduit/feeding dyke. Here, we characterize shallow magma circulation at Stromboli volcano by combining independent observations of heat (Volcanic Radiative Power; via satellite images) and gas (SO2, via UV camera) output in a temporal interval (from August 1, 2018 to April 30, 2020) encompassing the summer 2019 effusive eruption and two paroxysmal explosions (on July 3 and August 28, 2019). We show that, during the phase of ordinary strombolian explosive activity that preceded the 2019 effusive eruption, the average magma input rate (0.1-0.2 m3/s) exceeds the magma eruption rate (0.001-0.01 m3/s) by ∼2 orders of magnitude. Conversely, magma input and output rates converge to an average of ∼0.4 m3/s during the summer 2019 summit effusion, implying an overall suppression of magma recycling back into the feeding system, and hence of excess degassing. We find that, during the effusive eruption, the peak in SO2 emissions lags behind the thermal emission peak by ∼27 days, suggesting that magma output, feeding the lava flow field, initially dominates over magma input in the conduit. We propose that this conduit mass unloading, produced by this initial phase of the effusive eruption, leads to an overall decompression (of up to 30 Pa/s) of the shallow plumbing system, ultimately causing ascent of less-dense, volatile-rich magma batch(es) from depth, enhanced explosive activity, and elevated SO2 fluxes culminating into a paroxysmal explosion on August 28. Our results demonstrate that combined analysis of thermal and SO2 flux time-series paves the way to improved understanding of shallow magmatic system dynamics at open-vent volcanoes, and of the transition from explosive to effusive activity regimes.

Thermal spaceborne remote sensing has been used to study, monitor, and forecast volcanic activity for decades. But these data have not been used systematically at high spatial resolution to study changes in volcano temperatures across an entire region spanning multiple decades to understand background thermal activity and its relation to unrest and eruption. We have developed a first-of-a-kind database that uses manual analysis to identify and collect data for volcanic thermal output with 90 m/pixel spatial resolution for 330 potentially active volcanoes found in Latin America between the years 2000–2017. This database is reliant on the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor due to its high spatial resolution data, capability of detecting low-level thermal features, its accessibility and reliability compared to similar data types, and the long time series available at multiple volcanoes. A total of 88 Latin American volcanoes were found to have some type of volcanic thermal feature detected by ASTER, and here we document thermal features at 16 of these volcanoes detected from space for the first time. We have recorded these thermal features, including the temperature above background, area above background, and the timing and location of detection in the ASTER Volcanic Thermal Output Database (AVTOD). By comprehensively analyzing such a large dataset, we are able to quantitatively analyze some of the issues with these data, including 24% of all volcanoes in this study failing to meet the acquisition rates proposed by the current acquisition plan and 44.5% of all acquisitions being unusable due to interference from clouds. We provide recommendations of how to update future acquisition plans that would focus on night-time and cloud-free acquisitions. In order to confirm the validity of AVTOD it was tested against the existing Moderate Resolution Imaging Spectroradiometer (MODIS)-based MIROVA database. In some cases, we found a high degree of correlation between the two datasets (r2 = 0.87). In other cases, however, correlation was limited due to the difference in spatial resolution of these two data types. By examining the maximum temperature detected by every volcano in the database we found 46 that never reach a temperature high enough to be detected by MODIS-class thermal sensors. The information in this database provides new insights about volcanic activity both on its own, and in combination with other data types, as well as a data-driven approach to improve key features in future sensors.

Ambrym is an active volcanic island, located in the Vanuatu archipelago, consisting of a 12 km-wide summit caldera. This open vent volcano is characterized by an almost persistent degassing activity which occurs in the Benbow and Marum craters, which were also the site of recent lava lakes. On 15 December 2018, about three years after an intense lava effusion, the first recorded since 1989, a small-scale intra-caldera fissure eruption occurred. On 16 December, the eruption stopped, and the lava lakes at the Benbow and Marum craters were drained. In this work, we investigated the thermal activity of the Ambrym volcano, before, during, and after the 15 December 2018 eruption, using daytime Sentinel-2 (S2) Multispectral Instruments (MSI) and Landsat-8 (L8) Operational Land Imager (OLI) data, at a mid-high spatial resolution. The results were integrated with Moderate Resolution Imaging Spectroradiometer (MODIS) observations. Outputs of the Normalized Hotspot Indices (NHI) tool, retrieved from S2-MSI and L8-OLI data, show that the thermal activity at the Ambrym craters increased about three weeks before the 15 December 2018 lava effusion. This information is consistent with the estimates of volcanic radiative power (VRP), which were performed by the Middle Infrared Observation of Volcanic Activity (MIROVA) system, by analyzing the nighttime MODIS data. The latter revealed a significant increase of VRP, with values above 700 MW at the end of the October–November 2018 period. Moreover, the drastic reduction of thermal emissions at the craters, marked by the NHI tool since the day of the fissure eruption, is consistent with the drop in the lava lake level that was independently suggested in a previous study. These results demonstrate that the S2-MSI and L8-OLI time series, combined with infrared MODIS observations, may contribute to detecting increasing trends in lava lake activity, which may precede effusive eruptions at the open vent volcanoes. This study addresses some challenging scenarios regarding the definition of possible threshold levels (e.g., in terms of VRP and total Short Wave Infrared radiance) from the NHI and MIROVA datasets, which could require special attention from local authorities in terms of the occurrence of possible future eruptions.

At open-vent basaltic volcanoes, resolving the activity escalation that heralds larger, potentially harmful eruptions is challenged by the persistent mild ordinary activity, which often masks the precursory unrest signals related to heightened magma transport from depth. Gas (SO2 and CO2) fluxes at surface are controlled by rate of magma transport and degassing within the magma plumbing system, and thus constitute key parameters to infer deep magma budget and dynamics. Here, we use several year-long (2014-present) gas observations at Etna and Stromboli volcanoes, in Sicily, to provide new evidence for the utility of long-term instrumental gas monitoring in real-time detecting the early phase of unrest prior eruption, and for characterizing syn-eruptive dynamics. To this aim, we use information from a gas monitoring network of permanent ultraviolet (UV) cameras and automatic Multi-Gas instruments that, combined with geophysical observations, allow characterizing changes in degassing and eruptive dynamics at high temporal/spatial resolution. Our results show that the paroxysmal (lava fountaining) explosions that periodically interrupted persistent open-vent activity on Etna (during 2014-2020) were accompanied by systematic, repetitive SO2 emission patterns prior, during, and after eruptions. These allow us identifying the characteristic pre- syn- and post- eruptive degassing regimes, and to establish thresholds in the SO2 flux record that mark phases of unrest. On Stromboli, the much improved temporal/spatial resolution of UV cameras allows resolving the escalation of regular strombolian activity, and its concentration toward its North-east crater, that heralds onset of effusive eruptions. During effusive eruption, although magma level drops in the conduit and explosive summit activity ceases, UV camera observations can still detect explosive gas bursts deep in the conduit while no infrasonic activity is detected. Combining the UV camera-derived SO2 fluxes with CO2/SO2 ratio records measured by the Multi-Gas, the CO2 flux can be inferred. We find that such CO2 flux time-series can allow tracking degassing of deeply stored mafic magma months before Stromboli’s eruptions. We finally show that remotely sensed gas emission and thermal activity can be combined together to characterize the dynamics of shallow magmatic system prior to and during unrest, ultimately helping to define timing of magma re-charging events driving the eruptions.

During the last two decades, Sangay has been one of the most active Ecuadorian volcanoes. However, because of its remote location and logistically difficult access, monitoring Sangay is a challenging task. The IG-EPN tackled this problem by expanding its terrestrial monitoring network and complementing it with the available satellite data. On 7th May 2019, the most recent and ongoing eruptive episode commenced. Compared to the previously monitored and observed eruptive activity at Sangay since the 2000’s, this episode is by far the most intense and the first to affect populated areas due to ash fallouts and numerous lahars. Surface activity is generally characterized by frequent low-to-moderate magnitude ash emissions and a semi-continuous viscous lava flow extrusion. This activity is punctuated by occasional lava flow collapse events, probably associated with pulses of high lava extrusion and that produced long-runout pyroclastic density currents towards the southeastern flank.Here, we present the most complete data set of long-term instrumental observations performed at Sangay. SO2 degassing, seismic activity, ground deformation, ash emissions and thermal anomalies are depicted as a multiparametric sequence to better understand the link between these parameters and the dynamism and eruptive style of this isolated volcano. Correlations between the depicted parameters are not straight-forward, making it hard to identify patterns that might lead to enhanced eruptive activity. High values of SO2 recorded by the DOAS instruments as well as the TROPOMI satellite sensor seem to coincide with periods of increased eruption rate. Nevertheless, increases in SO2 flux do not occur systematically before or after these episodes. Seismic activity, characterized by daily counts of individual seismic events, does not demonstrated a clear precursory pattern either. These results indicate that none of the available monitoring parameters currently allow for a timely forecast of the largest and potentially most dangerous eruptions. However, looking at the entire time series we are able to distinguish a slightly but progressive change in the ground deformation displacement associated with a higher number of earthquakes per day prior to the 20 September 2020 paroxysmic event. This eruption produced regional ash fallout which affected significant swaths of farming lands and livestock. Since then, a different ground deformation pattern has taken hold, and coincides with a step decrease in the number of daily earthquakes and a significant increase in the SO2 mass measured by TROPOMI.This behavior matches an open-vent system, where punctual increases in eruptive activity show few precursory signals. The observed increase in all the parameters compared to previous eruptions before 2019 allows us to propose that this eruptive phase is fed by batches of deep and volatile-rich magma which rise to the surface at high ascent rates. The interpretations presented here are an important step towards a better understanding of the dynamism and eruptive style of this very active and isolated volcano. Moreover, the various monitoring parameters from terrestrial to satellite provide a better picture of the behavior of Sangay that could be applied to other remote and open-system volcanoes.

Piton de la Fournaise (La Réunion, France) is one of the most active volcanoes in the world, producing frequent effusive basaltic eruptions of varying duration. These eruptions are accompanied by strong thermal infrared (TIR) signals and significant sulfur dioxide (SO2) emissions detected by satellite instruments. The high frequency of eruptions provides an extensive dataset, which allows us to explore the relationships between eruptive heat, mass and gas fluxes. Five eruptions with different temporal trends of erupted mass flux have been selected for this study: April 2007, May 2015, August-October 2015, February 2019 and April 2020. For each of them, we estimated SO2 emission from three ultraviolet satellite instruments (the Ozone Monitoring Instrument OMI, the Ozone Mapping and Profiler Suite OMPS and the Tropospheric Monitoring Instrument TROPOMI). The total SO2 emission for each eruption has been estimated for an extensive range of sulfur (S) content within melt inclusions and the matrix using a petrological approach and the erupted magma masses obtained from MODIS TIR satellite data. Preliminary results show that, assuming the estimated SO2 emission falls within the 30% error of the SO2 mass detected by each satellite instrument, the implied magmatic sulfur contents are in good agreement with expected values for basaltic eruptions. Given pre-eruptive S contents between 200 and 750 ppm, estimated SO2 emissions for the May 2015 eruption are consistent with an eruption largely fed by degassed magma. However, for the February 2019 eruption, there is a discrepancy between the three satellite sensors. Whereas the TROPOMI and the OMI instruments provide almost the same range of magmatic sulfur content (300-1100 ppm), the OMPS gives a higher range (700 to 1900 ppm) suggesting that fresh, undegassed magma was also involved in this eruption. Petrologic analysis of the pre-eruptive sulfur content will allow us to validate the satellite data and, in turn, to validate the ground-based SO2 data from the NOVAC network operated by the Observatoire Volcanologique du Piton de la Fournaise (OVPF). Our approach yields insights into the characteristics of the magma reservoir supplying effusive events (e.g., eruptive degassing processes and the ratio of intrusive to extrusive magma) from space-based sensors.

co-auteur étranger; International audience; The rise and fall of magma columns is a process commonly observed in volcanoes hosting lava lakes and serves as proxy of magmatic reservoir pressure and warning for potential eruptions. This dynamic process typically involves the filling and emptying of a “pit crater” -a cylindrical depression usually formed by one or more collapses of a structure lying above an emptied surficial reservoir. Between 2016 and 2020, the 300 m deep pit crater located within Nyamulagira volcano (Democratic Republic of Congo) underwent an unusual filling dynamic. In May 2019 while filled to about 90% the crater floor collapsed by 90 m within two months, followed by the rapid emergence of a sub-circular solidified block overlooking the crater rim in less than 6 months. Using numerical simulations of models based on thermal energy and constrained by multiparametric data, we account for the incremental filling of the crater by successive intra-crateric lava flows and the subsequent collapse of the crater floor. We further characterize this unconventional filling mode based on thermal budget considerations.

Description, Escalating CO2 emissions precede basaltic explosive eruptions on time scales of weeks to months., The ordinarily benign activity of basaltic volcanoes is periodically interrupted by violent paroxysmal explosions ranging in size from Hawaiian to Plinian in the most extreme examples. These paroxysms often occur suddenly and with limited or no precursors, leaving their causal mechanisms still incompletely understood. Two such events took place in summer 2019 at Stromboli, a volcano otherwise known for its persistent mild open-vent activity, resulting in one fatality and damage to infrastructure. Here, we use a post hoc analysis and reinterpretation of volcanic gas compositions and fluxes acquired at Stromboli to show that the two paroxysms were preceded by detectable escalations in volcanic plume CO2 degassing weeks to months beforehand. Our results demonstrate that volcanic gas CO2 is a key driver of explosions and that the preparatory periods ahead of explosions in basaltic systems can be captured by precursory CO2 leakage from deeply stored mafic magma.

The Virunga Volcanoes is the first Supersite established on the African continent in a highly populated Multi-hazards region. This permanent Supersite was established in a critical context as little was known about the Virunga hazards sources and their dynamics, and little done as measures to evaluate, mitigate and reduce their impacts. Similarly, the active volcanoes are poorly studied and monitored, because of the lack of both qualified human resources and appropriate infrastructures. Therefore, the establishment of the “Virunga Volcanoes Supersite” aimed mostly at helping put together local and international scientists and agencies; support them to access to Earth Observatory (EO) data and potentially to equipment for ground-based data collection, as well as the building of a pool of collaboration. The expectation was that the above-mentioned collaborations and supports would improve the early warning capacity of the local scientists and agencies involved in Natural Hazards Assessment and volcano monitoring, risk reduction and management. After two years of existence, the Virunga Volcanoes Supersite has allowed the building of institutional collaboration between the Goma Volcano Observatory and some of the world leading institutes specialized in the study and monitoring of active volcanoes, and the assessment of related hazards (e.g. Italian INGV, United Stated USGS-VDAP, discussions are ongoing for others). The supersite has also allowed the access-free of charge- to a variety of EO data, e.g. COSMO-SkyMed SAR data from the Agenzia Spaziale Italiana, Pleiades from the Centre National d’Etudes Spaciales. More importantly, the Virunga Volcanoes Supersite has brought a large number of local and international scientists and agencies work together to and study Nyiragongo and Nyamulagira active volcanoes in order to better understand their eruptive mechanism, and hence better assess the related hazards and manage risks. Through this pool of collaboration, numerus activities have been successfully conducted, going from field works to assistance ordering and processing EO data, which yielded the production of useful hazards maps. Thus, the Virunga has requested and successfully obtained the activation of the Copernicus EMS services for the Virunga volcanoes for risk analyses with a focus on volcanic hazard. The later has yielded the production of hazards maps for future eruptions management, the collection of ground-based data used to produce Risk and Recovery mapping of Virunga volcanoes, as well as the production of thorough natural hazards assessment in the Virunga region and Lake Kivu. However, similar works have to be conducted in other parts of the Area of Interest of the Virunga Volcanoes Supersite, and hence the future works that use EO data (InSAR and Pleiades, principally) will aim at (1) continuing the ongoing study and monitoring of ground deformation of Nyiragongo and Nyamulagira volcanoes; (2) mapping and monitoring earthquakes and earthquake-triggered landslides in Lake Kivu Basin; (3) mapping of normal and non-normal faults in the Lake Kivu Basin, (4) along with geohazards assessment and forecast in Virunga and Lake Kivu Basin regions Most of these results were obtained while the Virunga Volcanoes Supersite has any budget, as they were conducted through voluntary international partnership, as are all the GEO Geohazard Supersites and Natural Laboratory initiative (GSNL). On the other hand, this prevented the Virunga Supersite from realizing some key activities such as long-term trainings abroad or acquiring infrastructures and equipment useful for ground-based data collection, and data processing in general. However, some of the activities that required funding have benefited from the support from INGV, the USGS-VDAP, the Volcano Active foundation, the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) which for instance supported short trainings, the donation of some equipment for some ground-based data collection, the processing of EO data and the attendance to meetings and workshops. Therefore, the Virunga Volcanoes Supersite is lacking of funds to support its mid to long-term objectives which are to permit local scientists access the strong trainings, skills and experience for both ground based and EO data continuous acquisition and analysis for volcano monitoring, to continuously assess natural hazards, vulnerability and risks in the region and regularly produce the related updated maps.&nbsp

The Dutch islands of Saba and St. Eustatius are located in the far north of the Lesser Antilles arc, a subduction zone hosting seventeen active volcanoes. The volcanoes of Saba and St. Eustatius: Mount Scenery and The Quill, are currently monitored using a ground based network, operated by KNMI, comprising broadband seismometers, continuous GNNS stations and a temperature sensor in the hotspring on Saba. Satellite observations are complementary to these ground based measurements and are especially useful for these volcanoes as they are located in a remote area.InSAR observations can be used to monitor surface deformation of volcanoes. Because considerable areas are observed with each satellite passing, subtle signals, which may be missed by continuously recording ground based GNSS stations, may be picked up. However, research using TerraSAR X-band and Sentinel-1 C-band data in the Caribbean region has shown that monitoring with InSAR is hampered due to the loss of radar coherence caused by tropical rain forest covering the Caribbean islands. Moreover many of the islands have steep slopes resulting in layover and shadowing effects. We generate interferograms and time series of ALOS-2 L-band data and Sentinel C-band data to identify which mission is more suitable for long term monitoring of the volcanoes on Saba and St. Eustatius.The Terra satellite carries five instruments that take coincident measurements of the Earth system, among those is MODIS: a Moderate Resolution Imaging Spectroradiometer. MODIS data are used by MIROVA (Middle Infrared Observation of Volcanic Activity): an automatic volcano hot spot detection system, able to detect, locate and quantify thermal anomalies in near real-time, by providing, infrared images and thermal flux time-series on over 200 volcanoes worldwide (www.mirovaweb.it). A volcano in a non-eruptive state such as Mount Scenery on Saba would typically be checked on a monthly basis. As Saba is a very small island (12 km2) automatic triggering is challenging and therefore observations are still in a test phase.Satellite observations can be a useful addition to the ground based monitoring of small island volcanoes although small adaptions to currently used techniques may be needed. As such they may be crucial for timely warning of local authorities in case of unrest at a remote volcano.

In the satellite thermal remote sensing, the new generation of sensors with high-spatial resolution SWIR data open the door to an improved constraining of thermal phenomena related to volcanic processes, with strong implications for monitoring applications. In this paper, we describe a new hot-spot detection algorithm developed for SENTINEL-2/MSI data that combines spectral indices on the SWIR bands 8a-11-12 (with a 20-meter resolution) with a spatial and statistical analysis on clusters of alerted pixels. The algorithm is able to detect hot-spot-contaminated pixels (S2Pix) in a wide range of environments and for several types of volcanic activities, showing high accuracy performances of about 1% and 94% in averaged omission and commission rates, respectively, underlining a strong reliability on a global scale. The S2-derived thermal trends, retrieved at eight key-case volcanoes, are then compared with the Volcanic Radiative Power (VRP) derived from MODIS (Moderate Resolution Imaging Spectroradiometer) and processed by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system during an almost four-year-long period, January 2016 to October 2019. The presented data indicate an overall excellent correlation between the two thermal signals, enhancing the higher sensitivity of SENTINEL-2 to detect subtle, low-temperature thermal signals. Moreover, for each case we explore the specific relationship between S2Pix and VRP showing how different volcanic processes (i.e., lava flows, domes, lakes and open-vent activity) produce a distinct pattern in terms of size and intensity of the thermal anomaly. These promising results indicate how the algorithm here presented could be applicable for volcanic monitoring purposes and integrated into operational systems. Moreover, the combination of high-resolution (S2/MSI) and moderate-resolution (MODIS) thermal timeseries constitutes a breakthrough for future multi-sensor hot-spot detection systems, with increased monitoring capabilities that are useful for communities which interact with active volcanoes.

Deciphering eruptive dynamics in near-real time is essential when dealing with hazard assessment and population evacuation. Recognition of specific patterns in time-series measured during volcanic activity may help decipher distinctive behavior at active volcanoes, providing insights into the underlying driving mechanisms. Multi-parameter data sets usually agree on the overall trend characterizing the temporal evolution of an eruption providing insights into the first-order eruptive dynamics. However, second-order variations detected in different data sets remain often poorly understood. The 2014-2015 Holuhraun eruption (Iceland) offers an excellent opportunity to investigate the dynamics of a long-lasting effusive eruption. We analyze the seismic tremor and the volcanic radiated power emitted by the lava field during the 6 months of the eruption using Singular Spectrum Analysis (SSA). In both geophysical time-series, we identify periods from ∼5 to ∼32 days coinciding with periods of Earth tides. Here we show that ∼50% of both signals are composed of tidal periods suggesting that magma movements follow frequencies imposed by lunisolar forces within the crust and at Earth's surface.

The Miravalles-Guayabo caldera is located in the Guanacaste Cordillera and its genesis and evolution is related with the geodynamic setting of northwestern Costa Rica. The development of a N-S graben, and related NE-trending fracture zones, was essentially coeval with caldera forming eruptions and the multiple collapses which dismembered earlier volcanoes. The lavas of the Miravalles-Guayabo Complex (MGC) are two-pyroxene calc-alkaline andesites and basaltic andesites with subordinate high alumina basalts and rare dacites. Interstitial matrix glasses span from andesite (in basalts) to dacite (in andesite s.l.) and rhyolite (in dacite) that overlap the bulk chemical compositions of the lavas. REE patterns and spider diagrams show typical features of a subduction-related volcanism at convergent plate boundaries with spiked incompatible-element patterns, negative anomalies for Nb and Ti in spider diagrams, enrichment in LILE (with the exclusion of Sr) and LREE, and relative depletion in HFSE. The geochemical signatures of the MGC volcanic rocks are essentially consistent with recent petrogenetic models. Thermobarometric estimates suggest that basaltic and magmas equilibrated with their phenocrystic phases at 1080–1120 °C, and pressures ranges of 380–430 MPa, whereas andesitic melts are confined at 200–230 MPa and temperatures of 1050–1070 °C. In turn, amphibole-biotite dacites equilibrated at 240–290 MPa and temperatures of 920–950 °C approaching water saturated conditions (with H2O contents up to 5.7–7.2 wt%). Thermobarometry indicate that contiguous andesitic-dacitic magma lenses are stored within the subvolcanic region at depths below 10 km, whereas basaltic magmas are stored and degas at slightly higher depths (up to ~15 km). Single eruptions associated with the emplacement of lava flows seem to be related to the tapping of portions of single magma lenses during minor unrest episodes. Conversely, caldera forming eruptions involved the ejection of differentiated rhyolitic pumices (of La Ese member) and likely occurred during recharge and pressurization of this heterogeneous reservoir under critical stress conditions.

During emplacement, lavas modify the pre-existing topography and release a large amount of heat. In spite of the relevance of both heat and mass release, combined morphological and thermal analyses have been seldom carried out at a flow-field scale. Here, we consider a channelised lava flow unit formed at Mt Etna during the 2001 flank eruption, and we show that, by combining a morphological analysis of the pre- and post-emplacement topography with the analysis of the syn-eruptive thermal signature, critical insights about the processes driving mass and heat dissipation can be derived. Our results suggest that, in the considered lava flow, the pre-emplacement slope controls heat dissipation and can influence the thickness of the final lava deposit, with possible implications for hazard assessment. The width of the lava channel, instead, appears less sensitive to the pre-emplacement slope, and tends to regularly increase with increasing distance from the vent.

A vigorously degassing lava lake appeared inside the Santiago pit crater of Masaya volcano (Nicaragua) in December 2015, after years of degassing with no (or minor) incandescence. Here we present an unprecedented-long (3 years) and continuous volcanic gas record that instrumentally characterizes the (re)activation of the lava lake. Our results show that, before appearance of the lake, the volcanic gas plume composition became unusually CO 2 rich, as testified by high CO 2 /SO 2 ratios (mean: 12.2 ± 6.3) and low H 2 O/CO 2 ratios (mean: 2.3 ± 1.3). The volcanic CO 2 flux also peaked in November 2015 (mean: 81.3 ± 40.6 kg/s; maximum: 247 kg/s). Using results of magma degassing models and budgets, we interpret this elevated CO 2 degassing as sourced by degassing of a volatile-rich fast-overturning (3.6–5.2 m 3 s −1 ) magma, supplying CO 2 -rich gas bubbles from minimum equivalent depths of 0.36–1.4 km. We propose this elevated gas bubble supply destabilized the shallow (

International audience; On October 1st, 2005, Santa Ana volcano (El Salvador) underwent a VEI 3 phreatomagmatic eruption after approximately one century of rest. Casualties and damages to some of the local infrastructures and surrounding plantations were followed by the evacuation of the nearby communities. The analysis of MODIS (Moderate Resolution Imaging Spectroradiometer) infrared data reveals that the main explosion was preceded by a one-year-long thermal unrest, associated to the development of a fumaroles field, located at the western rim of the summit crater lake. By combining space-based thermal flux and ground-based measurements (seismicity, sulfur emissions and lake temperatures), we suggest that the activity observed at Santa Ana between 2004 and 2005 was driven by the gradual intrusion of an undegassed magma body at a very shallow depth. Magma injection induced thermal anomalies associated with sustained degassing from the fumaroles field and promoted the interaction between the magmatic-hydrothermal system and the overlying water table. This process culminated into the VEI 3 phreatomagmatic eruption of October 2005 that strongly modified the shallow structure of the crater area. The subsequent three-years-long activity resulted from self-sealing of the fracture system and by the opening of a new fracture network directly connecting the deeper hydrothermal system with the crater lake. Our results show that satellite-based thermal data allow us to detect the expansion of the high-temperature fumarolic field. This may precede an explosive eruption and/or a lava dome extrusion. In particular, we show that thermal records can be analyzed with other geochemical (i.e. SO2 emissions) and geophysical (seismicity) data to track a shallow magmatic intrusion interacting with the surrounding hydrothermal system. This provides a remarkable support for volcano monitoring and eruption forecasting, particularly in remote areas where permanent ground data acquisition is hazardous, expensive and difficult.