ETNA 2021 13th December eruption: does SEVIRI data contribute to the early detection of lateral event?

Infrared remotely sensed data can be used to evaluate the surface thermal state of active volcanoes. Because the spectral radiance emitted by hot spots reaches its maximum in the region of Mid Infra-Red (MIR), the early detection of an impending eruption has been highlighted by exploiting the SEVIRI 3.9 mm channel. Despite its spatial resolution (3x3 sqkm at nadir), the presence of a high temperature source, even affecting only a small portion of one large pixel, causes a dramatic increase of the emitted MIR radiance easily detectable also at 4x5 sqKm (mid latitude).

The procedure named MS2RWS (MeteoSat to Rapid Response Web Service) allowed us to identify the Mt Etna summit area eruption since February 2010, when it was developed to detects the beginning and to estimates the duration of an eruption [1,2]. The procedure starts from the assumption that in a remote sensing image a pixel may assume a limited number of radiance values ranging from 0 up to the saturation. The radiance of a given pixel, in clear sky condition and no eruption ongoing, follows a characteristic Gaussian trend related to the Sun elevation and this trend varies during an eruption affecting, in particular, the pixel centred over the summit Mt. Etna craters [3].

On 13^th December 2021 an eruptive vent opened in the eastern flank of Mt. Etna volcano, at an elevation of 2100 m a.s.l., about 3.5 km far from the summit craters. This eruption lasted only one day and produced a small lava flows (less than 1 km length). Thus it might be considered as a “punctual event” in the eruptive history of the volcano and ideal for validating the capability of the MS2RWS procedure in detecting flank eruptions since their beginning. This experiment succeed, demonstrating that the MS2RWS procedure has the capability to detect also lateral eruption, as this was, giving a further contribute on the monitoring of volcanic activity by space.