Intrusion of eccentric dikes: The case of the 2001 eruption and its role in the dynamics of Mt. Etna volcano

Abstract The 2001 eruption represents one of the most studied events both from volcanological and geophysical point of view on Mt. Etna. This eruption was a crucial event in the recent dynamics of the volcano, marking the passage from a period (March 1993–June 2001) of moderate stability with slow, continuous flank sliding and contemporaneous summit eruptions, to a period (July 2001 to present) of dramatically increased flank deformations and flank eruptions. We show new GPS data and high precision relocation of seismicity in order to demonstrate the role of the 2001 intrusive phase in this change of the dynamic regime of the volcano. GPS data consist of two kinematic surveys carried out on 12 July, a few hours before the beginning of the seismic swarm, and on 17 July, just after the onset of eruptive activity. A picture of the spatial distribution of the sin-eruptive seismicity has been obtained using the HypoDD relocation algorithm based on the double-difference (DD) technique. Modeling of GPS measurements reveals a southward motion of the upper southern part of the volcano, driven by a NNW–SSE structure showing mainly left-lateral kinematics. Precise hypocenter location evidences an aseismic zone at about sea level, where the magma upraise was characterized by a much higher velocity and an abrupt westward shift, revealing the existence of a weakened or ductile zone. These results reveal how an intrusion of a dike can severely modify the shallow stress field, triggering significant flank failure. In 2001, the intrusion was driven by a weakened surface, which might correspond to a decollement plane of the portion of the volcano affected by flank instability, inducing an additional stress testified by GPS measurements and seismic data, which led to an acceleration of the sliding flanks.

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

[2]  M. Favalli,et al.  Impact of the Minoan tsunami of Santorini: Simulated scenarios in the eastern Mediterranean , 2006 .

[3]  Mimmo Palano,et al.  A syn-eruptive ground deformation episode measured by GPS, during the 2001 eruption on the upper southern flank of Mt Etna , 2004 .

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

[5]  G. Puglisi,et al.  Ground deformation patterns on Mount Etna, 1992 to 1994, inferred from GPS data , 2001 .

[6]  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 .

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

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

[9]  S. Gambino.  Continuous dynamic response along a pre-existing structural discontinuity induced by the 2001 eruption at Mt. Etna , 2004 .

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

[11]  Mimmo Palano,et al.  Intrusive mechanism of the 2002 NE-rift eruption at Mt Etna (Italy) modelled using GPS and gravity data , 2007 .

[12]  A. Ferretti,et al.  Dynamics of Mount Etna before, during, and after the July-August 2001 eruption inferred from GPS and differential synthetic aperture radar interferometry data , 2008 .

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

[14]  M. Favalli,et al.  Large submarine landslides offshore Mt. Etna , 2006 .

[15]  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.

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

[17]  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 .

[18]  Mike Burton,et al.  Continuous soil radon monitoring during the July 2006 Etna eruption , 2006 .

[19]  B. Behncke,et al.  Pyroclastic density currents resulting from the interaction of basaltic magma with hydrothermally altered rock: an example from the 2006 summit eruptions of Mount Etna, Italy , 2008 .

[20]  Giuseppe Puglisi,et al.  Dynamics of the eastern flank of Mt. Etna volcano (Italy) investigated by a dense GPS network , 2006 .

[21]  Salvatore Gambino,et al.  Mount Etna 1993–2005: Anatomy of an evolving eruptive cycle , 2006 .

[22]  Giuseppe Puglisi,et al.  Dynamics of Mount Etna Volcano inferred from static and kinematic GPS measurements , 2004 .

[23]  A. Harris,et al.  Volumetric observations during paroxysmal eruptions at Mount Etna: pressurized drainage of a shallow chamber or pulsed supply? , 2002 .

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

[25]  Claudio Chiarabba,et al.  Magma Ascent and the Pressurization of Mount Etna's Volcanic System , 2003, Science.

[26]  F. Waldhauser,et al.  A Double-Difference Earthquake Location Algorithm: Method and Application to the Northern Hayward Fault, California , 2000 .

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

[28]  Mimmo Palano,et al.  Composite ground deformation pattern forerunning the 2004–2005 Mount Etna eruption , 2006 .

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

[30]  Michel Condomines,et al.  Magma changes at Mount Etna: the 2001 and 2002–2003 eruptions , 2004 .

[31]  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 .

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

[33]  D. Patanè,et al.  High‐precision locations of the microseismicity preceding the 2002–2003 Mt. Etna eruption , 2004 .

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

[35]  A. Bonaccorso,et al.  Dike emplacement forerunning the Etna July 2001 eruption modeled through continuous tilt and GPS data , 2002 .

[36]  L. Chiaraluce,et al.  Seismological constraints for the dyke emplacement of the July-August 2001 lateral eruption at Mt. Etna volcano, Italy , 2003 .

[37]  Geometric and kinematic variations along the active Pernicana fault: Implication for the dynamics of Mount Etna NE flank (Italy) , 2007 .

[38]  S. D’Amico,et al.  Intrusive Mechanisms at Mt. Etna Forerunning the July-August 2001 Eruption from Seismic and Ground Deformation Data , 2004 .

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

[40]  Giuseppe Puglisi,et al.  Magma uprising and flank dynamics on Mount Etna volcano, studied using GPS data (1994–1995) , 2003 .

[41]  H. M. Iyer,et al.  Seismic tomography : theory and practice , 1993 .

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

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

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

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

[46]  Valerio Acocella,et al.  The 2004-2005 Etna eruption: Implications for flank deformation and structural behaviour of the volcano , 2006 .

[47]  L. Tanner,et al.  Debris-avalanche deposits of the Milo Lahar sequence and the opening of the Valle del bove on Etna volcano (Italy) , 1998 .

[48]  E. Privitera,et al.  Stress tensor computations in the mount Etna area (Southern Italy) and tectonic implications , 1997 .

[49]  Eugenio Sansosti,et al.  Gravity and magma induced spreading of Mount Etna volcano revealed by satellite radar interferometry , 2004 .

[50]  F. Guglielmino,et al.  Ground deformation modeling of flank dynamics prior to the 2002 eruption of Mt. Etna , 2007 .

[51]  Mimmo Palano,et al.  Feeding system and magma storage beneath Mt. Etna as revealed by recent inflation/deflation cycles , 2008 .

[52]  Boris Behncke,et al.  The exceptional activity and growth of the Southeast Crater, Mount Etna (Italy), between 1996 and 2001 , 2006 .

[53]  Y. Okada.  Surface deformation due to shear and tensile faults in a half-space , 1985 .

[54]  N. Houlié,et al.  Large scale ground deformation of Etna observed by GPS between 1994 and 2001 , 2003 .

[55]  Francesco Guglielmino,et al.  Flank instability on Mount Etna: Radon, radar interferometry, and geodetic data from the southwestern boundary of the unstable sector , 2007 .

[56]  L. Keszthelyi,et al.  A gravitational spreading origin for the Socompa debris avalanche , 2001 .