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> Etna, the good giant Issue: 2006-3 Section: Science



All started about 130 million years ago.

It was the Mesozoic Era (in particular the Cretaceous Period) and, from a geologic point of view, the earth surface was subdivided into two big plates that started to split into several slabs similar to the present continents: Laurasia in the North and Gondwana in the South. They derived from the division of the super continent Pangaea and they were separated by Tetide’s waters (the Mediterranean Sea is today what remains of the Tetide Ocean).

Owing to the continental drift, 80 million years ago the African plate began to move in the direction of the North-East towards the Eurasian plate that pushed to the South: all this determined the partial disappearance of the Tetide Ocean and the compression of the two plates of a series of cays; which in the future would be part of the Italian peninsula.

In general, convergence or divergence phenomena can change physical parameters (pressure, temperature, etc.) and they can result in the emerging of magma from the depths of the Earth.

In the light of these considerations, in the Mediterranean area a particular phenomenon took place: the magma erupted in the divergence zones have a basaltic composition like the one of the Sicilian eruptions magma (both in the eruptions dating back to about 10 million years ago and Etna eruptions), but Sicily was in a compression area. A possible explanation that justifies this anomalous phenomenon is the probable and contemporaneous making, through fracture, of microplates in several points of the principal plate. These split up and created depression zones perpendicular to the general compression event. So, in one of these areas the removal of the microplates allowed the magma to surface and to originate Etna.

Between 700.000 and 500.000 years ago, Etna volcanic activity started and developed in three stages:

  • the pre-Etna activity (from 700.000 to 200.000 years ago) during which there wasn’t a real volcanic body; and when the earliest submarine eruptions took place inside a gulf, called pre-etnean gulf, which extended from Peloritani Mountains to Iblei Mountains. Besides, the oriental area of Sicily began to rise (because of the pillow lava hoard on the sea floor) till when the volcanic manifestations took place over the sea level with the appearance of the earliest cones;

  • Primordial or old Etna: dating back to 150.000 - 80.000 years ago, it is little known because the lava flows and the several explosive products of the eruptions (that formed Etna’s primordial structure) were covered with materials of following activities. Studies about primordial Etna volcanic compounds state that early eruptions were effusive while the following eruptions were explosive. This first volcanic body was the result of two overlapping apparatuses: one broad, with little steep sides and constituted of lava flows; the other cone-shaped, with steep and fragile sides. The irregular outline of the Catanesi’s Mountains is due to the landslide, towards the sea, of old Etna east side; the explosive eruptions started from all this;

  • Old and intermediate centres and Mongibello: at this stage several eruptive centres formed and covered the one over the others, they heightened and widened the shape of the volcano. The reading of the origin of these centres has been possible thanks to the Valle del Bove, a natural section of one of the volcano sides. Calanna, Trifoglietto I and Trifoglietto II were part of the old centres (what remains is today in the lower part of the Valle del Bove) while Trifoglietto, Valaci and Cuvigghiuni’s products constitute the intermediate centres. After a long activity, 65.000 years ago Trifoglietto II’s volcanic cones collapsed giving rise to a huge caldera (the present Valle del Bove), and the volcanic activity moved more inland, thus Mongibello , the most recent eruptive centre, was created This big cone covers the central zone of the volcano and its activity has formed the present volcanic building throughout the centuries. The North-East crater is the highest of the volcano and it was formed in 1911 at 3100 metres of height. Today this crater is about 3350 metres high and it makes Etna the highest European active volcano.


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