The 2004-2005 Etna eruption: Implications for flank deformation and structural behaviour of the volcano

The development of the 2004–2005 eruption at Etna (Italy) is investigated by means of field surveys to define the current structural state of the volcano. In 2004–2005, a fracture swarm, associated with three effusive vents, propagated downslope from the SE summit crater towards the SE. Such a scenario is commonly observed at Etna, as a pressure increase within the central conduits induces the lateral propagation of most of the dikes downslope. Nevertheless, some unusual features of this eruption (slower propagation of fractures, lack of explosive activity and seismicity, oblique shear along the fractures) suggest a more complex triggering mechanism. A detailed review of the recent activity at Etna enables us to better define this possible mechanism. In fact, the NW–SE-trending fractures formed in 2004–2005 constitute the southeastern continuation of a N–S-trending fracture system which started to develop in early 1998 to the east of the summit craters. The overall 1998–2005 deformation pattern therefore forms an arcuate feature, whose geometry and kinematics are consistent with the head of a shallow flank deformation on the E summit of Etna. Similar deformation patterns have also been observed in analogue models of deforming volcanic cones. In this framework, the 2004–2005 eruption was possibly induced by a dike resulting from the intersection of this incipient fracture system with the SE Crater. A significant acceleration of this flank deformation may be induced by any magmatic involvement. The central conduit of the volcano is presently open, constantly buffering any increase in magmatic pressure and any hazardous consequence can be expected to be limited. A more hazardous scenario may be considered with a partial or total closing of the central conduit. In this case, magmatic overpressure within the central conduit may enhance the collapse of the upper eastern flank, triggering an explosive eruption associated with a landslide reaching the eastern lower slope of the volcano.

[1]  B. Behncke,et al.  An exceptional case of endogenous lava dome growth spawning pyroclastic avalanches: the 1999 Bocca Nuova eruption of Mt. Etna (Italy) , 2003 .

[2]  M. Burton,et al.  Etna 2004–2005: An archetype for geodynamically‐controlled effusive eruptions , 2005 .

[3]  A. Rittmann.  Vulkanismus und Tektonik des Ätna , 1964 .

[4]  Daniele Andronico,et al.  A multi-disciplinary study of the 2002–03 Etna eruption: insights into a complex plumbing system , 2005 .

[5]  J. Bousquet,et al.  Nouvelle interpretation des fractures des eruptions laterales de l'Etna; consequences pour son cadre tectonique , 2001 .

[6]  S. Martel.  Mechanics of landslide initiation as a shear fracture phenomenon , 2004 .

[7]  Agust Gudmundsson,et al.  Formation and geometry of fractures, and related volcanism, of the Krafla fissure swarm, northeast Iceland , 1989 .

[8]  Pierre Briole,et al.  Active spreading and regional extension at Mount Etna imaged by SAR interferometry , 2001 .

[9]  E. L. Giudice,et al.  Very shallow earthquakes and brittle deformation in active volcanic areas: The Eatnean region as an example , 1992 .

[10]  M. Neri,et al.  Effusion rate estimations during the 1999 summit eruption on Mount Etna, and growth of two distinct lava flow fields , 2003 .

[11]  D. Pollard,et al.  Surface deformation in volcanic rift zones , 1983 .

[12]  David D. Pollard,et al.  Field relations between dikes and joints: Emplacement processes and paleostress analysis , 1986 .

[13]  M. Neri,et al.  Structural features of an active strike-slip fault on the sliding flank of Mt. Etna (Italy) , 2005 .

[14]  M. Neri,et al.  What makes flank eruptions? The 2001 Etna eruption and its possible triggering mechanisms , 2003 .

[15]  V. Acocella.  Modes of sector collapse of volcanic cones: Insights from analogue experiments , 2005 .

[16]  B. Behncke,et al.  Nested zones of instability in the Mount Etna volcanic edifice, Italy , 2005 .

[17]  G. Giordano,et al.  Structural features of the July–August 2001 Mount Etna eruption: evidence for a complex magma supply system , 2003, Journal of the Geological Society.

[18]  Mike Burton,et al.  2001 flank eruption of the alkali- and volatile-rich primitive basalt responsible for Mount Etna's evolution in the last three decades , 2004 .

[19]  S. Saunders,et al.  Recent dyke-induced large-scale block movement at Mount Etna and potential slope failure , 1990, Nature.

[20]  Boris Behncke,et al.  The July–August 2001 eruption of Mt. Etna (Sicily) , 2003 .

[21]  Giancarlo Neri,et al.  Satellite analysis and PUFF simulation of the eruptive cloud generated by the Mount Etna paroxysm of 22 July 1998 , 2002 .

[22]  B. Behncke,et al.  Lava flow hazard at Mount Etna (Italy): New data from a GIS-based study , 2005 .

[23]  R. A. Corsaro,et al.  Dynamics of 2004–2005 Mt. Etna effusive eruption as inferred from petrologic monitoring , 2005 .

[24]  M. Neri,et al.  The boundaries of large-scale collapse on the flanks of Mount Etna, Sicily , 1996, Geological Society, London, Special Publications.

[25]  Stephen J. Martel,et al.  Numerical Models of Translational Landslide Rupture Surface Growth , 2000 .

[26]  Boris Behncke,et al.  Contrasting triggering mechanisms of the 2001 and 2002-2003 eruptions of Mount Etna (Italy) , 2005 .

[27]  Donald A. Swanson,et al.  Thrust faults and related structures in the crater floor of Mount St. Helens volcano, Washington , 1989 .

[28]  A. Borgia,et al.  Importance of gravitational spreading in the tectonic and volcanic evolution of Mount Etna , 1992, Nature.

[29]  B. Voight,et al.  Discussion: Nature and mechanics of the Mount St Helens rockslide-avalanche of 18 May 1980 , 1985 .

[30]  Harry Pinkerton,et al.  Instabilities in the summit region of Mount Etna during the 1999 eruption , 2002 .

[31]  Boris Behncke,et al.  The role of the Pernicana Fault System in the spreading of Mt. Etna (Italy) during the 2002–2003 eruption , 2004 .

[32]  Michael Manga,et al.  Kinematics and dynamics of lava flows , 2005 .

[33]  Ciro Del Negro,et al.  Volcanomagnetic changes accompanying the onset of the 2002–2003 eruption of Mt. Etna (Italy) , 2004 .

[34]  A. Tibaldi,et al.  Volcano-tectonic activity along structures of the unstable NE flank of Mt. Etna (Italy) and their possible origin , 2002 .

[35]  M. Tesauro,et al.  Actively growing anticlines beneath catania from the distal motion of Mount Etna's Decollement measured by SAR interferometry and GPS , 2000 .

[36]  M. Burton,et al.  High spatial resolution radon measurements reveal hidden active faults on Mt. Etna , 2004 .

[37]  B. Voight,et al.  Slope movement crisis on the east flank of Mt. Etna volcano: Models for eruption triggering and forecasting , 1994 .

[38]  Salvatore D'Amico,et al.  Link between major flank slip and 2002–2003 eruption at Mt. Etna (Italy) , 2003 .

[39]  Thomas R. Walter,et al.  Feedback processes between magmatic events and flank movement at Mount Etna (Italy) during the 2002-2003 eruption , 2005 .

[40]  G. Giordano,et al.  Mechanisms for ground-surface fracturing and incipient slope failure associated with the 2001 eruption of Mt. Etna, Italy: analysis of ephemeral field data , 2003 .

[41]  Boris Behncke,et al.  Cycles and trends in the recent eruptive behaviour of Mount Etna (Italy) , 2003 .

[42]  A. Rittmann,et al.  Structure and Evolution of Mount Etna [and Discussion] , 1973 .