Abstract
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 ~20–30 m in 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.
Highlights
Advanced Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS), where hot magmatic surfaces reach the peak of thermal emissions [39,40]
MODIS data uncorrected for atmospheric effects.(e.g., In more detail, in Figure 4b, we running the algorithm) under different observational conditions show eruption chronology and overcast periods, for better assessing the impact of clouds on the
We estimated the radiant flux from infrared AVHRR data by outputs of a dual bandachieved three components method [44]; the mean value calculated from two end-members was
Summary
22 of of 14 observation, in remote areas where ground-based surveillance systems are often lacking observation,. In remote areas where ground-based surveillance systems are often lacking (e.g., [1,2,3,4,5]). Sensors such as TM (Thematic Mapper) and ASTER (Advanced Spaceborne Thermal Emission suchRadiometer), as TM Reflection that Mapper) have a repeat cycle(Advanced of 16 daysSpaceborne and offer Thermal channelsEmission in the SWIR Reflection. Radiometer), thatTIR have a repeatinfrared) cycle of 16 dayswith and offer channels in the SWIR (shortwave (shortwave infrared) and (thermal bands a spatial resolution of 30–90 m, were infrared) and TIR (thermal infrared) withanomalies a spatial resolution. (e.g., [1,2,3,4,5]). in remote areas where ground-based surveillance systems are often lacking (e.g., [1,2,3,4,5]).
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