Abstract
After a month-long increase in activity at the summit craters, on 24 December 2018, the Etna volcano experienced a short-lived lateral effusive event followed by a rapid resumption of low-level explosive and degassing activity at the summit vents. By combining space (Moderate Resolution Imaging Spectroradiometer; MODIS and SENTINEL-2 images) and ground-based geophysical data, we track, in near real-time, the thermal, seismic and infrasonic changes associated with Etna’s activity during the September–December 2018 period. Satellite thermal data reveal that the fissural eruption was preceded by a persistent increase of summit activity, as reflected by overflow episodes in New SouthEast Crater (NSE) sector. This behavior is supported by infrasonic data, which recorded a constant increase both in the occurrence and in the energy of the strombolian activity at the same crater sectors mapped by satellite. The explosive activity trend is poorly constrained by the seismic tremor, which shows instead a sudden increase only since the 08:24 GMT on the 24 December 2018, almost concurrently with the end of the infrasonic detections occurred at 06:00 GMT. The arrays detected the resumption of infrasonic activity at 11:13 GMT of 24 December, when tremors almost reached the maximum amplitude. Infrasound indicates that the explosive activity was shifting from the summit crater along the flank of the Etna volcano, reflecting, with the seismic tremor, the intrusion of a gas-rich magma batch along a ~2.0 km long dyke, which reached the surface generating an intense explosive phase. The dyke propagation lasted for almost 3 h, during which magma migrated from the central conduit system to the lateral vent, at a mean speed of 0.15–0.20 m s−1. Based on MODIS and SENTINEL 2 images, we estimated that the summit outflows erupted a volume of lava of 1.4 Mm3 (±0.5 Mm3), and that the lateral effusive episode erupted a minimum volume of 0.85 Mm3 (±0.3 Mm3). The results presented here outline the support of satellite data on tracking the evolution of volcanic activity and the importance to integrate satellite with ground-based geophysical data in improving assessments of volcanic hazard during eruptive crises.
Highlights
Multidecadal satellite data from different platforms have provided great support for volcano monitoring, and are enlarging our knowledge on the processes that drive the eruptions (e.g., [1,2,3,4,5])
SENTINEL-2 images show that the MODIS-detected thermal alerts were sourced by two distinct vents hosted within BN crater and from New SouthEast Crater (NSE) sector with a sustained degassing from NE and Central Craters (Figure 3a–c)
Our measurements showed that this short-lived activity has been heralded by monthly-long thermal precursor, tracked by MODIS and SENTINEL-2 satellite data, which clearly detect the overflow episodes at NSE crater sector
Summary
Multidecadal satellite data from different platforms have provided great support for volcano monitoring, and are enlarging our knowledge on the processes that drive the eruptions (e.g., [1,2,3,4,5]). Etna is an open-vent basaltic volcano, characterized by a persistent degassing and frequent explosive activity, ranging from low strombolian explosions to lava fountaining and sub-plinian ash-rich paroxysms [27,28,29] This activity occurs at several active vents located at three main sectors of the summit area, named: Bocca Nuova–Voragine (BN/VOR, cited as Central Craters—CC; [29]), NorthEast Crater (NEC) and Southeast Crater–New Southeast Crater (SEC/NSEC) ([30,31]; see Figure 1). The eccentric flank eruptions may be promoted by magma reaching the surface via new, secondary conduits and/or dike intrusions, successively being erupted from propagating lateral fissures with multiple aligned vents [29,36] In this view, a main hazard source at the Etna volcano is related to the opening of distal eruptive fissures with lava flows that potentially threatened nearby villages, infrastructures and tourist facilities [37]
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