Syn- and Post-eruptive movement at a major Mt Etna flank eruption

Abstract

The aims of this project were to investigate the long-term ground deformation of Mt Etna. More specifically, loan 898 was to measure the ground deformation in the wake of the 2008-9 eruption to see if gravitational spreading had resumed, and also to extend back the record of Etna’s ground deformation to include pre-GPS trilateration data by making GPS and geodetic measurements at the same points. The latter aim was carried out by a different method from that planned for 16 stations across the volcano. The location of the field area is shown in Fig. 1. Mt Etna, Sicily, had completed its longest flank eruption in 17 years (13th May 2008 – 6th July 2009) two months before the trip started. Like the eruptions of 2004 and 2006 October, the main eruptive vents were associated with the Southeast Crater, and were situated in the upper reaches of the Valle del Leone in its southern part. The lavas from these three eruptions have covered much of the lower part of the Valle del Leone, and the central Valle del Bove. All three ground deformation networks: levelling, dry tilt and GPS, were measured. The movements recorded in 2008 after the start of the eruption had showed large horizontal movements of 50 cm or more. The disposition of these vectors indicated the presence of a dyke injected NW-SE between the summit and the eruption site. However, an unusual feature of this eruption was the fact that the lower flank stations showed no evidence of gravitational spreading, suggesting that this event might have been driven by magma pressure rather than depressurisation caused by spreading, so the 2009 results were awaited with particular interest to see if spreading was still arrested. The movement vectors conclusively show that spreading had resumed at about an average annual rate of non-eruptive periods of 2-4 cm.