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Authors: Neri, M.* 
Acocella, V.* 
Behncke, B.* 
Maiolino, V.* 
Ursino, A.* 
Velardita, R.* 
Title: Contrasting triggering mechanisms of the 2001 and 2002–2003 eruptions of Mount Etna (Italy)
Journal: Journal of Volcanology and Geothermal Research 
Series/Report no.: 1-4/144(2005)
Publisher: Elsevier
Issue Date: 15-Jun-2005
DOI: 10.1016/j.jvolgeores.2004.11.025
Keywords: eruption triggering
central–lateral vs. eccentric eruptions
flank instability and slip
Mt. Etna
instrumental monitoring
Subject Classification04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics 
04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring 
05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions 
04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk 
Abstract: Mount Etna produced two significant eruptions in 2001 and 2002–2003, which we have analysed using geological, seismic and deformation data. These eruptions showed some similarities, such as the activating of two magmatic plumbing systems (central–lateral and eccentric), but they differed in their triggering mechanisms. While the 2001 eruption was largely the result of the emplacement of a N–S eccentric dike (independent from the central conduits) consistent with E–W regional extension, the 2002–2003 eruption occurred in response to a major flank slip on the eastern and southeastern sides of the volcano. This is demonstrated by the spatial and temporal distribution of seismicity and deformation preceding and accompanying the two eruptions. During the months prior to the 2001 eruption, most epicenters were concentrated on the southern flank, at depths of 5–15 km below sea level. During the 4 days before the eruption, earthquake hypocenters migrated to shallower levels (from 5 km bsl. upward) indicating the emplacement of the eccentric dike. This is confirmed by the patterns of ground fracturing observed in the field and deformation documented by electronic distance measurements (EDM). In contrast, the months before the 2002–2003 eruption were characterised by shallower seismicity, mainly concentrated along the active faults bordering the slipping flank sector. Flank slip accelerated in September 2002 and a second, more vigorous acceleration of flank slip occurred on 26–27 October 2002, accompanying the opening of eruptive vents. The very short (2 h) seismic crisis preceding the onset of eruptive activity stands in neat contrast with the 4 days of intense seismicity before the 2001 eruption. Subsequently, flank slip-deformation extended all over the eastern and southeastern flanks of the volcano, causing serious damage in this sector. The events of 2001–2003 can be seen as a continuous chain of intimately interacting processes including regional tectonics, magma accumulation and eruption, and flank instability. In this scenario the 2001 eruption led to increased flank instability that subsequently accelerated and culminated with the massive flank slip, which in turn facilitated the 2002–2003 eruption. This sequence of events points to a long-term feedback mechanism between magmatism and flank instability at Etna.
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