All of the volcanicity in Italy is the result of the subduction of the African crustal plate beneath southern Italy. Italy itself appears to be rotating in an anticlockwise direction. Twisting and stretching the continental crust to breaking point about 7 to 8 million years ago. Huge volumes of basalt escaped from the mantle to coat the thinning and sinking crust and to provide the nucleus of the present Tyrrhenian Basin. The reduced crustal thickness allowed the underlying mantle to rise to shallower depths, and the combination of general mantle uplift and eastward crustal motion produced a crude three-way zone of preferred crustal failure (approximately to the north, east and southwest) centred about 100km west of the modern day Campanian coast.
Across southern Italy and Sicily, rotation has been distorted by a strong south-eastward stretching which has fragmented the original southwest fracture zone and favoured the migration towards Sicily.
The south-eastward stretching has forced the subduction of the African plate beneath Calabria, inducing crustal melting and the formation of the Aeolian island arc. 50km south, local tension along the edge of the southeast unit has allowed magma to escape beneath Mt Etna. Rotation of the northern unit has triggered major block faulting and continued activity from the Neapolitan volcanoes, Somma-Vesuvius, and the Campi Flegrei.
(Ref. “Italian Volcanoes”. Chris Kilburn & Bill McGuire)
By Gordon Hensman
Dudley, West Midlands