The Contribution of Multi-Sensor Infrared Satellite Observations to Monitor Mt. Etna (Italy) Activity during May to August 2016

In May 2016, three powerful paroxysmal events, mild Strombolian activity, and lava
emissions took place at the summit crater area of Mt. Etna (Sicily, Italy). During, and immediately after
the eruption, part of the North-East crater (NEC) collapsed, while extensive subsidence affected the
Voragine crater (VOR). Since the end of the May eruptions, a diffuse fumarolic activity occurred from
a fracture system that cuts the entire summit area. Starting from 7 August, a small vent (of ~20–30min
diameter) opened up within the VOR crater, emitting high-temperature gases and producing volcanic
glow which was visible at night. We investigated those volcanic phenomena from space, exploiting
the information provided by the satellite-based system developed at the Institute of Methodologies for
Environmental Analysis (IMAA), which monitors Italian volcanoes in near-real time by means of the
RSTVOLC (Robust Satellite Techniques–volcanoes) algorithm. Results, achieved integrating Advanced
Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer
(MODIS) observations, showed that, despite some issues (e.g., in some cases, clouds masking the
underlying hot surfaces), RSTVOLC provided additional information regarding Mt. Etna activity.
In particular, results indicated that the Strombolian eruption of 21 May lasted longer than reported
by field observations or that a short-lived event occurred in the late afternoon of the same day.
Moreover, the outcomes of this study showed that the intensity of fumarolic emissions changed
before 7 August, as a possible preparatory phase of the hot degassing activity occurring at VOR.
In particular, the radiant flux retrieved from MODIS data decreased from 30 MW on 4 July to an
average value of about 7.5 MW in the following weeks, increasing up to 18 MW a few days before
the opening of a new degassing vent. These outcomes, in accordance with information provided
by Sentinel-2 MSI (Multispectral Instrument) and Landsat 8-OLI (Operational Land Imager) data,
confirm that satellite observations may also contribute greatly to the monitoring of active volcanoes
in areas where efficient traditional surveillance systems exist.

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