Francesco Massimetti

Lascar volcano, located in the Central Andes Volcanic Zone, is one of the most active volcanoes in Northern Chile, characterized by recurrent minor explosive events. We have analyzed the volcanic degassing process at Lascar between August 2017 and August 2021 using a multiparametric approach that integrates seismicity, visual observations, satellite thermal data, and ground-based SO2 flux measurements, which were deseasonalized to remove meteorological artifacts.This correction revealed intrinsic volcanic variations that allowed us to identify three distinct patterns: i) Pattern I - Overpressure and System Sealing (August 2017-January 2018), characterized by low deseasonalized SO2, emission rates despite frequent valid measurements, minimal thermal activity, and increasing long-period seismicity, indicating progressive sealing of the shallow system and internal pressurization, ii) Pattern II - Pressurization, Fracturing, and Partial Unsealing (February 2018-November 2018), involves pressurization and mechanical failure of the conduit, marked by the appearance of tornillo and volcano-tectonic seismicity, followed by partial unsealing and increased gas release, iii) Pattern III - Explosion, Decompression, and Cycle Reset (November 2018-February 2020), correspond to explosive decompression, starting in the November 22nd, 2018 with ash emission event, followed by peak SO2 fluxes and transient thermal anomalies.Post-eruptive observations show that this event did not establish a stable equilibrium but reset the volcanic cycle, with the repetition of sealing and pressurization phases between 2020 and 2021. These results indicate that conduit sealing and rupture are recurrent processes that control Lascar's recent activity and highlight the importance of integrated gas, seismic, and thermal monitoring for identifying pressurization phases preceding minor explosive events.

Ordinary, moderately explosive activity at Stromboli is sporadically interrupted by larger effusive and explosive events that can trigger hazardous phenomena such as sector collapses, tsunamis, and ballistic fallout. We analyze 25 years of satellite infrared data to characterize the thermal pattern associated with these larger events, including: (1) effusive eruptions, (2) lava overflows, (3) major explosions, and (4) paroxysms. Increased heat flux precedes effusive eruptions and overflow sequences, and is interpreted to reflect the progressive rise of the magma column in the conduit accompanying the transition between Strombolian and effusive regimes. Conversely, major explosions are not preceded by any detectable thermal increase, although they statistically occur during periods of frequent overflows in which the Volcanic Radiative Power (VRP) is punctuated by higher values. Paroxysms (which occurred at the beginning, during and at the end of the effusive eruptions) do not show systematic thermal patterns in the preceding days, but in most cases are followed by a VRP increase. Major explosions and paroxysmal events contribute minimally to the long-term energy released by the volcano. Instead, the energy output is primarily governed by the recurrent transitions between Strombolian- and effusive-dominated regimes, sustaining a long-term, steady-state VRP of approximately 14.5 MW. Overall, only ~ 25% of the thermal energy is radiated during Strombolian activity, whereas overflows and effusions account for ~ 15% and ~ 60%, respectively. Results highlight that satellite thermal analysis is a useful tool for tracking changes of surface activity at open-vent basaltic volcanoes with frequent switching from ordinary low-energy activity to more energetic explosive or effusive eruptions.

On 3 March 2024, a new effusive eruption began from a sub-circular fissure on the southeast upper flank of the Fernandina volcano (Galápagos archipelago, Ecuador). Although the eruption posed no threat to people, as the island is uninhabited, it provided an opportunity to test a rapid response system for effusive eruptions, based on satellite infrared (IR) data. In this work, we illustrate how the analysis of data from multiple IR sensors allowed us to monitor the eruption in near real-time (NRT), providing recurrent updates on key parameters, such as (i) lava discharge rate and trend, (ii) erupted lava volume, (iii) lava field area, (iv) active flow front position (v) flow velocity, (vi) location of active vents and breakouts, and (vii) emplacement style. Overall, the eruption lasted 68 days, during which 58.5 ± 29.2 Mm³ of lava was erupted and an area of 14.9 ± 0.5 km² was invaded. The eruption was characterized by a peak effusion rate of 206 ± 103 m³/s, an initial velocity of ~2.3 km/h, and by an almost exponential decline in the effusion rate, accompanied by a transition from channel- to tube-fed emplacement style. The advance of the lava flow was characterized by three lengthening phases that allowed the front to reach the coast (~12.5 km from the vent) after 36 days (at an average velocity of ~0.015 km/h). The results demonstrate the efficiency of satellite thermal data in responding to effusive eruptions and maintaining situational awareness at remote volcanoes where ground-based data are limited or completely unavailable. The requirements, limitations, and future perspectives for applying this rapid response protocol on a global scale are finally discussed.

Open‐vent volcanoes continuously emit magmatic products and frequently feature multiple adjacent craters. Temporal shifts of thermal emissions between craters are especially detectable by InfraRed satellites. Here, SENTINEL‐2 and LANDSAT‐8/9 Short Wave InfraRed (SWIR) high‐spatial resolution satellite data, are combined to investigate 10 years (2013–2023) of thermal activity at Stromboli volcano (Italy). The correlation between Volcanic Radiative Power (VRP, in Watts) and Volcanic Radiative Energy (VRE, in Joules), retrieved by moderate MODIS and VIIRS Middle InfraRed (MIR) data, with the Thermal Index SWIR (TI_SWIR) data, allows us to quantify long‐term series of heat fluxes (VRP_SWIR) and energy (VRE_SWIR). Combining moderate and higher spatial resolution data and fitting cumulative trends of TI_SWIR with VRE_MIR allows to measure thermal activity sourced by single craters during Strombolian activity. Long‐term results highlight that thermal emissions are clustered in the northern and southern parts of the crater terrace, with total energy emitted (∼12 × 10¹⁴ J) equally distributed. The thermal increase since April 2017 marked a reactivation of shallow magma transportation and an intensification of the activity after the 2014 eruption. Distinct thermal behaviors are shown by the NE, C, and SW craters, related to mechanisms of explosions. We found that short‐term thermal variations match well those resolved by ground‐based signals, and the NE crater as the most sensitive to the transition to higher‐intensity activity. Our multispatial/multisensory investigation allows, for the first time, the long‐term quantification of heat flux from Stromboli's craters, with an improved understanding of open‐vent dynamics and a new approach to monitor multiple active craters.

Taking prompt and effective actions to mitigate risks associated with an effusive eruption greatly depends on the monitoring of lava flow emplacement. Here we report on the monitoring of the lava flow emplaced during the 19 September to 05 October 2022 eruption at Piton de la Fournaise (La Réunion) that involves an unprecedentedly large data set acquired using multiple techniques and sensors. These include aerial photogrammetry to construct digital surface models and define lava flow geometry during and after emplacement. Complementary use of multiple satellite sensors (visible, infrared, and radar) allowed lava flow field contour definition and an estimation of time-averaged discharge rate with daily frequency. Evolution of the eruptive cone morphology was also monitored through aerial photogrammetry and radar multi-viewing angle imagery. This combination of data obtained from several institutes and using various techniques—from ground, air and space—allowed detailed tracking of lava flow advance and serves as an example for future eruptions at Piton de La Fournaise and at other active volcanic sites.

Satellite data provide crucial information to better understand volcanic processes and mitigate associated risks. In recent years, exploiting the growing number of spaceborne polar platforms, several automated volcanic monitoring systems have been developed. These, however, rely on good geometrical and meteorological conditions, as well as on the occurrence of thermally detectable activity at the time of acquisition. A multiplatform approach can thus increase the number of volcanological-suitable scenes, minimise the temporal gap between acquisitions, and provide crucial information on the onset, evolution, and conclusion of both transient and long-lasting volcanic episodes. In this work, we assessed the capabilities of the MEdium Resolution Spectral Imager-II (MERSI-II) sensor aboard the Fengyun-3D (FY-3D) platform to detect and quantify heat flux sourced from volcanic activity. Using the Middle Infrared Observation of Volcanic Activity (MIROVA) algorithm, we processed 3117 MERSI-II scenes of Mount Etna acquired between January 2020 and February 2023. We then compared the Volcanic Radiative Power (VRP, in Watt) timeseries against those obtained by MODIS and VIIRS sensors. The remarkable agreement between the timeseries, both in trends and magnitudes, was corroborated by correlation coefficients (ρ) between 0.93 and 0.95 and coefficients of determination (R²) ranging from 0.79 to 0.84. Integrating the datasets of the three sensors, we examined the effusive eruption of Mount Etna started on 27 November 2022, and estimated a total volume of erupted lava of 8.15 ± 2.44 × 10⁶ m³ with a Mean Output Rate (MOR) of 1.35 ± 0.40 m³ s⁻¹. The reduced temporal gaps between acquisitions revealed that rapid variations in cloud coverage as well as geometrically unfavourable conditions play a major role in thermal volcano monitoring. Evaluating the capabilities of MERSI-II, we also highlight how a multiplatform approach is essential to enhance the efficiency of satellite-based systems for volcanic surveillance.

The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of the most-used sensors for monitoring volcanoes and has been providing time series of Volcanic Radiative Power (VRP) on a global scale for two decades now. In this work, we analyzed the data provided by the Visible Infrared Imaging Radiometer Suite (VIIRS) by using the Middle Infrared Observation of Volcanic Activity (MIROVA) algorithm, originally developed to analyze MODIS data. The resulting VRP is compared with both the MIROVA_MODIS data as well as with the Fire Radiative Power (FRP), distributed by the Fire Information for Resource Management System (FIRMS). The analysis on 9 active volcanoes reveals that VIIRS data analyzed with the MIROVA algorithm allows detecting ~60% more alerts than MODIS, due to a greater number of overpasses (+30%) and improved quality of VIIRS radiance data. Furthermore, the comparison with the nighttime FIRMS database indicates greater effectiveness of the MIROVA algorithm in detecting low-intensity (<10 MW) thermal anomalies (up to 90% more alerts than FIRMS). These results confirm the great potential of VIIRS to complement, replace and improve MODIS capabilities for global volcano thermal monitoring, because of the future end of Terra and Aqua Earth-observing satellite mission of National Aeronautics and Space Administration’s (NASA).