Coupled magma chamber inflation and sector collapse slip observed with synthetic aperture radar interferometry on Mt. Etna volcano

Volcanoes deform dynamically due to changes in both their magmatic system and instability of their edifice. Mt. Etna features vigorous and almost continuous eruptive activity from its summit craters and periodic flank eruptions. Even though its shape is that of a large stratovolcano, its structure features two rift systems and a flank collapse structure similar to Hawaiian shield volcanoes. We analyze European remote sensing (ERS) satellite differential interferometric synthetic aperture radar (InSAR) data (1993-1996) for Mt. Etna spanning its quiescence from 1993 through the initiation of renewed eruptive activity in late 1995. We use synthetic aperture radar (SAR) data from both ascending and descending ERS satellite tracks. Comparison of independent interferograms covering the first 2 years of the inflationary period shows a pattern consistent with inflation of the volcano. Calculation of the tropospheric path delay based on meteorological data does not change this interpretation. Interferograms from late summer 1995-1996 show no significant deformation. Joint inversion of interferograms from ascending and descending satellite tracks require both inflation from a spheroidal magmatic source located beneath the summit at 5 km below sea level, and displacement of the east flank of Etna along a basal decollement. Both sources of deformation were contemporaneous within the resolution of our data and suggest that inflation of the central magma chamber acted to trigger slip of Etna's eastern flank. These results demonstrate that flank instability and recharge of a volcano's magma system must both be considered toward understanding how volcanoes work and in their hazard evaluation.