Long-term investigation of Mt Etna`s eruptive mechanism

Abstract

A 94-station dual-frequency GPS network on Mt Etna was occupied between 8th September and 14th October 2008, to measure deformation in association with the current series of eruptions, using 7 Leica system 530 sets. The 181-station precise levelling network was also occupied, using a Leica NA2000 digital level and invar staff, and we measured the 27 Dry Tilt stations on the flanks of the volcano using the same level and staff. The measurements were made at a critical time, beginning 4 months after the start of the longest Etna eruption since 1991-3. The results showed an interesting new type of deformation not seen since the whole-volcano network of GPS stations was set up in 1995. The summit movements were similar to previous eruptions in that there were horizontal movements of >1 metre at locations close to the emplaced subsurface dyke, with vectors normal to the dyke indicating fracture opening of more than 2 metres. But instead of the spreading of the flanks that has been the general rule accompanying such activity, this time the stations below 2000 metres altitude generally showed random small horizontal movements of less than 2cm since October 2007, i.e. there was no evidence of gravitational spreading. The implication is that contrary to previous recent eruptions, this event was not driven by flank spreading opening fissures to passive lava escape, but by magmatic pressure alone.