The Eruptions of Mount ETNA

Bearing in mind that every eruption has its own characteristics that distinguish it from any others, the Etna eruptions can be divided, on the basis of their site and eruptive mechanism, into terminal, sub terminal, lateral and eccentric.

The terminal eruptions, connected to the summit craters, are characterized by violent and often brief explosive activity (lava fountains, throw of bombs and incandescent scoriae), at times accompanied by generally not very consistent overflow of lava. Apart from the above-mentioned paroxysmal phenomena at the two chasms of the central crater (the Voragine Est or the Voragine and the Voragine Ovest or Bocca Nuova) and on the North-east and South-east craters, there is a continuous and more or less intense emission of vapour and gas, at times accompained by more or less violent and impressive emissions of ash and lapillus. This latter phenomenon is due to an almost continuous explosive activity at the bottom of the same chasms (at depths varying from 100 to 400 m), or to collapses of the steep internal walls.

Sub terminal eruptions are those in which the explosive activity occurs mostly on the summit craters, or on an explosive crater formed during the same eruption, while the effusive lavas are emitted quietly for a certain distance (sometimes for several kilometres).

Lateral or flank eruptions are those in which, along an eruptive fissure, opened on the flanks of the volcano, a single eruptive cone or a series of spatter and cinder cones (the so called “bottoniera”) are formed, owing to an intense explosive activity, at the base of which an effusion of lava takes place and it causes numerous lava flows that, generally, reach long distances (several kilometres) and cover vast land areas.

Finally, Eccentric eruptions are those where the rising magma conduit is completely independent of the central crater feeder system, and the very infrequent eruptions take place at low altitudes at a certain distance from the summit area. Generally, some isolated cones form and, from their base, more or less consistent lava streams are emitted.

Studies of past and recent eruptions, carried out on all the reconstructible historic eruptions, have also shown that, on Mount Etna, two distinct types of eruption may generally occur:

paroxysmal eruptions of short duration (days or weeks), characterized by abundant initial emission and by the fluidity of the lavas which give rise to long (7-15 km) and not very thick (less than 10 m) lava flows;

quiet or slow eruptions characterized by constant, but not very abundant emissions of lava, which last for long periods of time (months or years) and which cause lava flows extended in breadth (some km), rather than in length (up to 7 km), and generally very thick (more than 15 m).