Mount Etna, Italy--a new model for why it exists where it does

Mount Etna, Italy  (photo from NASA)

Mount Etna, the largest volcano in Europe, has been active for the last half-million years.  It is located near, but not above, the Ionian subducted slab.  A number of theories have been proposed to explain its location and existence: magma migrates up through complex fault systems, aesthenopheric melting from Africa, a deep mantle plume. In a recent paper, Schellart proposes that upper mantle material is flowing around the southern Ionian slab edge and upward (W.P. Schellart, Geology, 38, 691-694, October 19, 2010).  This model incorporates some elements of the older subduction models, and presents a new fluid dynamic model based on experimental results.  In the la experiments, two viscous layers are contained in a rectangular tank.  A high-viscosity upper layer rests on top of a lower layer made of low viscosity glucose syrup.  A subducting slab is placed on the upper layer. At the start of the experiment, subduction was initiated by bending the model slab downward, and the slab is moved to simulate the history of the Ionian slab.  Fluid motions in the surrounding material were documented by the use of sheet lighting.  Schellart observed upwelling at the (scaled) distance of Mount Etna (a few hundred kilometers), and proposes that the melt originates at about a few hundred kilometers depth. The most rapid upwelling is in the middle to upper mantle, but slow upwelling is observed all the way to 660 km depth.