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Etna discrete geodetic networks

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Etna discrete geodetic networks (reference: Alessandro Bonforte)

On Mount Etna, the first trilateration networks, dedicated to monitoring ground deformations by using Electronic Distance Meters (EDM) and theodolites, were installed during the seventies. These early network provided data relevant to eruptions taking place near the summit of the volcano, especially around the North East Crater between 1974 and 1978. Due to their limited extent, these geodetic networks were not able to properly sample any medium-scale deformation induced by changes in the deep internal plumbing system, preventing any clear understanding of the medium-term evolution of the volcanic activity. Moreover, the survey and the maintenance of these networks were difficult, due to the lack of facilities such as good roads or observatories, to the prohibitive environmental conditions in winter time, to the benchmarks being frequently destroyed by volcanic activity and to difficulties in connecting those networks to stable areas. Following this pioneering epoch, and in order to overcome some of the above limitations, three EDM (networks were installed on the intermediate flanks of the volcano, on the northeastern (in 1978), southwestern (in 1980) and southern (in 1983) sides. Those networks aimed to monitor ground deformation patterns related to deformation sources located at medium depth inside the volcano. They were surveyed at least yearly, and more frequently during eruptive periods (e.g. 1978 - 1979). The combination of those efforts ensured that, at the beginning of the 1980’s, Etna was densely covered by geodetic networks. Data from these networks were used to study and interpret the volcanic deformation for more than a decade, in particular during the eruptions of 1981. 1989, and 1991-93. Leveling data collected on recent lava flows in the summit area showed the existence of still ongoing subsidence of these flows, several years after their emplacement. After the 1983 and 1985 eruptions, large horizontal displacements were observed in the upper southeastern part of the volcano, stimulating a debate on the possible risk of slope failure in the eastern part of the volcano.