Gravitational and magma forced spreading of Mount Etna volcano revealed by InSAR data

Mount Etna volcano underwent a cycle of activity over the past ten years from a large flank eruption ending in March 1993, to quiescence, followed by resumed summit activity in August 1995 and recent large flank eruptions in 2001 and 2002-2003. Observations from differential interferometric synthetic aperture radar reveal patterns of surface deformation that result from the changing magma and structural dynamics of the volcano. Here we compute a time series of ground deformation from more than 100 radar interferograms to reveal Mount Etna's time varying surface deformation from 1992 to 2001. We find that during this time interval it experienced magmatic inflation and radial spreading to the West, South, and East. Steady motion between the West-South flanks and between the East-North flanks during this time interval suggests they are related to gravitational spreading of the volcanic edifice. In particular, we find spreading across conjugate, arcuate crossing faults that fit laboratory models of volcano spreading. In contrast, time series analysis shows that southeastern basal anticline growth is not constant, but initiated with the end of magma recharge in 1995, thus showing a direct link between deep-seated magma intrusions and edifice spreading. We will present both results of the time series analysis as well as examples from numerous interferograms. Together these observations support a more complex mode of radial gravitational collapse underlain by deeper magma driven basal spreading.