<p>By 2021, Vulcano, Aeolian Islands (Italy), experienced a dramatic increase in different monitoring parameters, including microseismicity, ground deformation, fumarole temperatures, and volatile emissions of steam, carbon, and sulfur dioxide. The volcanic unrest was noticeable in September 2021, causing the Civil Protection to raise the alert level from green to yellow on October 1st. Here we present a number of ground- and satellite-based thermal methodologies used to detect and characterize the change of state of the La Fossa hydrothermal system between January 2021 and January 2022. We analyzed: (i) the temperature and (ii) CO2 flux data acquired at 15 cm&#8208;depth on a N-S profile N-S and grid in the geothermally heated area during three field surveys in June, September 2021 and January 2022; (iii) a time series acquired with a radiometer including temperatures and number of vents inside the fumarole field from 1994 to 2022; (v) thermal images acquired by a hand-held thermal camera during four field surveys in March, June and September 2021, plus January 2022; (v) nighttime multi-spectral satellite images acquired by ASTER, ECOSTRESS and VIIRS sensors from January 2021 to January 2022. Satellite images show a clear increase in the radiant heat flux/land surface temperature as well as in the number of thermally anomalous pixels, this thermal anomaly has been observed from mid-September. However, by combining ground and satellite techniques the starting point of this change can be tracked thermally from at least June 2021. Our experience suggests that the methods, essentially based on the thermal monitoring,&#160;<span>could be used to herald upcoming crises. This method </span><span>has been applied on a close conduit volcano and highlighted changes of trend in the solfataric release. Further tests, aiming to reduce (filter or define) the external effects on the land surface temperature, and to define the correlations with the long term monitoring data (either ground-based or by remote sensing) in this area, would assess a standardized methodology to monitoring the subtle, but diffuse fluid release. The assessed methodology could then be applied to other active hydrothermal systems, to herald thermal changes on the surface, related to the increasing energy released from a deep source.</span></p>
The development of a resilient society is a major challenge for growing human population faced with abundant natural hazards. During and after the May 22, 2021 eruption of Nyiragongo, the local population was surprised and scared by the subsequent seismicity and associated surface fracturing, coupled with the alert of a possible new eruptive vent opening in Goma (Democratic Republic of Congo) and/or Gisenyi (Rwanda). The creation of a toll-free phone number enabled the population to record fractures and gas/thermal anomalies affecting the area. Such work was fundamental in enabling scientists and authorities to assess the associated risks. Crucially, gas data showed that the degassing through fractures did not represent direct transfer of magmatic volatiles but was more likely of superficial origin. Surprisingly, this participatory work revealed that the first fractures appeared several weeks before the eruption and their opening was not detected by the monitoring system. This firmly underlines the need for scientists to anchor citizen science in monitoring strategies.
Hydrothermal systems can generate phreatic and/or phreatomagmatic explosions with little warning. Understanding the temporal and spatial evolution of geophysical and geochemical signals at hydrothermal systems is crucial for detecting precursors to unrest and to inform on hazard. Thermal signatures of such systems are poorly defined because data records are often too short or punctual compared to activity timescales, which can be decadal. La Fossa system of Vulcano has been monitored since the 1980s and entered a period of unrest in 2021. We assessed the thermal signature using ground- and satellite-based data with temporal and spatial scales ranging from minutes to days. While continuously-recording stations provided continuous but point-based measurements, fumarole field vent surveys and ASTER and VIIRS images allowed lower temporal resolution but synoptic records to be built. By integrating this multi-resolution data set, precursory signals to the unrest could retrospectively be placed ranging from February to June 2021. Intensity of unrest increased during summer 2021, with an onset over a few days in September 2021. By September, seismic, CO2, SO2 and geochemical metrics also indicated unrest, leading Civil Protection to raise the alert level to yellow on October 1. Heat flux, having been 4 MW in May 2019, peaked at 90 MW in September, and increased to 120 MW by March 2022. This ranked Vulcano as one of the highest intensity hydrothermal systems like Reykjanes, well ahead of Yellowstone and Nysiros We thus convolved our thermal data sets with all other monitoring data to validate a Vulcano Unrest Index (VUI) that can be potentially applied to any hydrothermal system. The VUI highlighted four stages of unrest, none of which were clear in any single data set: baseline, precursory, onset and unrest. Onset was characterized by sudden release of fluids, likely caused by failure of sealed zones that had become pressurized during the precursory phase that began possibly as early as February 2021. Unrest has been ongoing for more than 18 months, and may continue for several more years. Our understanding of this system behavior has been due to hindsight, but demonstrates how multiparametric surveys can track and forecast unrest.
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