Acocella et al. (2003) The 2001 and 2002-2003 eruptions of Mount Etna (Italy)

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Valerio Acocella, Boris Behncke, Salvatore D'Amico, Vincenza Maiolino, Marco Neri, Andrea Ursino and Rosanna Velardita (2003)
The 2001 and 2002-2003 eruptions of Mount Etna (Italy):
Evidence for different triggering mechanisms
Abstract presented at the Annual Workshop 2003, Pantelleria, Sicily (23-28 September 2003)
on: Seismic Phenomena Associated With Volcanic Activity


Mount Etna (Italy) produced two important flank eruptions in 2001 and 2002-2003, which were particular for their high degrees of explosivity and for the simultaneous emission of two compositionally distinct magmas. From a strictly volcanological point of view, the 2001 and 2002-2003 eruptions showed many similarities. Both affected two sides of the volcano (the southern and northeastern flanks), and both were actually "two-eruptions-in-one", with a part of the activity being fed by the lateral draining of the central conduit system (central-lateral activity), while much of the activity was fed from a source independent of the central conduit system (eccentric activity).
However, when placed in a wider geodynamic context, the two eruptions are fundamentally different. While the 2001 eruption was heralded by an intense seismic swarm and vigorous ground deformation, very few such premonitory signs preceded the 2002-2003 eruption, which, however, was accompanied by a major slip of Etna's unstable eastern to southeastern flank, and by widespread seismicity and ground rupturing in the moving sector. This suggests that the dynamics of magma ascent and eruption were anything but identical in the two eruptions.
The deformation of the volcanic edifice during the 2001 eruption clearly indicates forceful dike intrusion, probably under N-S regional compression (tectonic triggering). During the first stage of this eruption, earthquakes began to cluster along the active faults traversing and delimiting the unstable sector on the eastern flank, marking the onset of accelerated spreading of that flank. For much of 2002 (prior to the 2002-2003 eruption), nearly all of the seismicity was concentrated along these faults, mostly on the eastern and southeastern flanks, but in September more vigorous flank slip began along the Pernicana Fault System on the northeastern flank of the volcano. Magma migration into the Northeast Rift began as a response to this event, and a second, much more significant slip event five weeks later permitted the uprise of magma not only on the Northeast Rift, but also on the southern flank. The seismic and deformation data preclude any forceful intrusion of magma in the case of the 2002-2003 eruption, which was mainly triggered by the large-scale slip of the unstable eastern flank of the volcano (slip triggering).

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