Anatomy of an unstable volcano from InSAR: Multiple processes affecting flank instability at Mt. Etna, 1994–2008

Abstract

Volcano deformation may occur under different conditions. To understand how a volcano deforms, as well as relations with magmatic activity, we studied Mt. Etna in detail using interferometric synthetic aperture radar (InSAR) data from 1994 to 2008. From 1994 to 2000, the volcano inflated with a linear behavior. The inflation was accompanied by eastward and westward slip on the eastern and western flanks, respectively. The portions proximal to the summit showed higher inflation rates, whereas the distal portions showed several sectors bounded by faults, in some cases behaving as rigid blocks. From 2000 to 2003, the deformation became nonlinear, especially on the proximal eastern and western flanks, showing marked eastward and westward displacements, respectively. This behavior resulted from the deformation induced by the emplacement of feeder dikes during the 2001 and 2002–2003 eruptions. From 2003 to 2008, the deformation approached linearity again, even though the overall pattern continued to be influenced by the emplacement of the dikes from 2001 to 2002. The eastward velocity on the eastern flank showed a marked asymmetry between the faster sectors to the north and those (largely inactive) to the south. In addition, from 1994 to 2008 part of the volcano base (south, west, and north lower slopes) experienced a consistent trend of uplift on the order of ∼0.5 cm/yr. This study reveals that the flanks of Etna have undergone a complex instability resulting from three main processes. In the long term (103–104 years), the load of the volcano is responsible for the development of a peripheral bulge. In the intermediate term (≤101 years, observed from 1994 to 2000), inflation due to the accumulation of magma induces a moderate and linear uplift and outward slip of the flanks. In the short term (≤1 year, observed from 2001 to 2002), the emplacement of feeder dikes along the NE and south rifts results in a nonlinear, focused, and asymmetric deformation on the eastern and western flanks. Deformation due to flank instability is widespread at Mt. Etna, regardless of volcanic activity, and remains by far the predominant type of deformation on the volcano.

Long-period seismicity in the shallow volcanic edifice formed from slow-rupture earthquakes

“…On Mt Etna, flank instability in the form of East-West spreading is by far the predominant type of deformation 21,22 …”

Evaluation of the SBAS InSAR Service of the European Space Agency’s Geohazard Exploitation Platform (GEP)

“…DInSAR was originally applied to analyze the deformation related to earthquakes [3]. In the last decades it has proved to be a powerful tool to detect and monitor active processes such as rock dissolution-and human-induced subsidence [4][5][6][7][8], slow-moving slope instabilities [9,10], or volcano inflation and/or destabilization [11], among others. These slow movements not only can generate damages on buildings or infrastructures [6,12], but also may be precursors of volcanic eruptions [13] or other hazardous fast-moving phenomena such as ground sudden collapses [14,15] or landslides [16,17].…”

A method for multi-hazard mapping in poorly known volcanic areas: an example from Kanlaon (Philippines)

“…On Mount Cameroon, landslides that are not related to contemporary volcanic activity are a major concern (Ayonghe et al, 2004). On Etna and Stromboli, several zones are affected by landslides at various scales, triggered by vol- canic activities and/or by seismicity (Acocella et al, 2006b;Solaro et al, 2010;Barreca et al, 2013). In a multi-hazard assessment procedure, it is thus necessary to equally consider the adverse events that may occur during both the rest and unrest periods.…”