Volcanic processes detected by tiltmeters: A review of experience on Sicilian volcanoes

A review of the experience gained in the use of tiltmeters on Mt. Etna, Stromboli and Vulcano during the last 30 years is reported here. Tilt data represent a fundamental contribution towards understanding volcanic processes such as dike intrusions, fracture propagation, lava fountains and volume changes in magmatic or hydrothermal systems causing a deflation/ inflation of the edifice. Intrusive processes preceding lateral eruptions show large variations (up to over 100 microradians), while minor variations (not exceeding 2.5 microradians) are linked to lava fountains that form ash plumes and lead to fallout deposits that cause severe hazards to aviation. High precision tilt also allows detecting the slight ground deformation linked to strombolian activity (0.01–0.2 microradians) as well as co-seismic variations (0.1–1.5 microradians) and tidal effects (0.1–0.2 microradians) that may have a role in the evolution of a volcanic system. Time–amplitude tilt ranges linked to each process are generally different allowing to discriminate, in real time, between a signal associated to one process and another one. This fact is important in terms of early warning particularly during the first phases of dikes propagation that precede a lateral eruption by hours–days