Continental margin large-scale instability controlling the flank sliding of Etna volcano

Etna volcano is affected by a downward sliding of its eastern flank, as rapid as a few cm/year, whose nature is highly debated. Recently collected marine geological and geophysical data allows a detailed image of the morphostructural setting of the continental margin facing the volcano. Here, a large bulge offsets the margin that is deeply affected by widespread semicircular steps, interpreted as evidence of large-scale gravitational instability. Such features permeate the whole margin and extend inshore to the volcano sector where the larger ground deformations are measured. Both submarine instability and subaerial flank sliding are bounded by two regional tectonic lineaments interpreted as weakness lines. These cross the coastline to accommodate the basinward movement of this large sector of the continental margin topped by the Etna volcanic pile. The new data allows re-interpreting the tectonic setting of the coastal belt and proposing a novel structural model, highlighting the active role of the continental margin instability to drive the seaward sliding of the volcano's eastern flank. This model may suggest why a very active basaltic volcano has so unusually developed in front of an active thrust belt.

Research highlights
► Etna affected by eastern flank sliding has a bulge offsetting its continental margin.
► Submarine and costal slopes are dissected by a wide semicircular faults system.
► Volcano plumbing system inflation caused the continental margin bulge.
► Bulge collapsed creating a gravitational disequilibrium propagates to the volcano.
► Volcano decompression favors the ascent of basic magma without lengthy storage.