ERS InSAR Observations of Mt. Etna Volcano: Magma Inflation and Radial Spreading

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We present a synthesis of ERS-1 and ERS-2 differential SAR interferometry (InSAR) observations of Mt. Etna volcano over roughly the past ten years from 1002- 2002. Through this time period Mount Etna underwent a cycle of eruptive activity starting with a large flank eruption that ended in March 1993, followed by two years quiescence, with resumed summit activity starting in the summer of 1995, culminating in the recent large flank eruptions of 2001 and 2002/2003. InSAR observations reveal patterns of surface deformation that result from the changing magma and structural dynamics of the volcano. Individual interferograms spanning each of these major volcanic episodes during the last ten years reveal the essential deformation patterns. Similarities between groups of similar time-span interferograms for both ascending and descending ERS satellite passes show common fringe patterns among each group and distinctive differences between the ascending and descending interferograms are related to true ground deformation and are not dominated by atmospheric effects. In general the deformation patterns are related to a combination of magma chamber inflation/deflation plus nearly radial flank motion to the W, S, and E. To make sense of the large number of interferograms computed and the temporal behavior of Etna s deformation, we compute a time series of ground deformation from 1992-2001. We find that during this time interval Mt. Etna experienced magmatic deflation from thew initiation of measurements in 1992 through the spring of 1993, followed by major inflation from 1993-1995, with smaller deflation and inflation episodes from 1996-2000. During the entire time period Etna experienced varying amounts of radial spreading to the West, South, and East. Steady relative motion between the West and South flanks, and between the East and North flanks, during this time interval, suggests they are related to gravitational spreading of the volcanic edifice. In contrast, time series analysis shows that growth of a southeastern basal anticline began with the end of magma recharge in 1995, thus showing a direct link between deep-seated magma intrusions and edifice spreading. Together these observations support a complex mode of radial gravitational collapse underlain by deeper magma driven basal spreading, although ultimately the two must be related. The distinct ascending and descending interferograms accompanying the 2001 flank eruption support this model and demonstrate the direct connection between the magmatic and structural components of the volcano. Mt. Etna is a large, highly active volcano that is structurally complex (Fig. 1). It features two well-developed rift systems extending to the north and south from the summit craters through a series of fault systems as its eastern and southern flanks move away from the volcano s center [Rust and Neri, 1996; Borgia et al., 1992, 2000; Froger et al., 2001].

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