The 2021 unrest at Vulcano: insights from ground-based and satellites observations

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‐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, could be used to herald upcoming crises. This method 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.