The island of Pantelleria is situated 70 km from the African coast and 85 km from Sicily. Its area is circa 83 sq. Km, the height at the highest point is 836 m, the peak of the Montagna Grande (Great Mountain), which constitutes the emerged part of a volcanic formation elevating at 2000 m over an oceanic crust of about 20 kms in thickness. The shape of the island, elongated towards NW on one side and SE on the other, follows the general direction of the tectonic rift of the Sicilian Channel.  The island is exclusively made up of two kinds of volcanic rocks. One can infact distinguish acid vulcanites (rich in silica) and basic vulcanites (poor in silica). Acid vulcanites, such as trachite and riolite, rich in alkalines (sodium and potassiun), constitute 98% of emerged rocks. Because of the peculiarity, riolite is also known as pantellerite. These rocks are formed by high viscosity lavae with a high percentage of glass, or by pyroplastic materials (ignimbrites) deriving from explosive activities. Basic vulcanites constitute 2% of emerged rocks, and are represented by olivinic basalt and hawaite, which are very fluid and dark lavae.
Thirty to forty eruptive spots have been detected: cones and domes are
characteristic of acid lavae, while parallel cones are of basic lavae.

Pantelleria’s geological history can thus be synthesized:
 
  about 220,000 years ago, extrusion of a trachitic disc;
  220,000 to 50,000 years ago, eruptions rich in silica, which is found especially in the area covered by Kuddia Attalora, on the southern part of the island;
  120,000 years ago, birth of a caldera in the zone of the main volcanic area; minor basaltic events particularly at Cala dell’Alca;
  50,000 years ago, emission of so-called green ignimbrite, which covers an area of 48 sq. Km, with a maximum thickness of 20 m; following this, collapse of the main volcanic area, creating a caldera;
  35,000 years ago, inside the caldera, ascent of the trachitic dome of the Montagna Grande, causing a collapse of the top part and birth of secondary craters such as Monte Gibele and Kuddia di Mida (made of pumice);
  about 30,000 years ago, basaltic eruptions NW of the caldera;
  22,000 years ago, a spill out of the endogenous dome of Monte Gelkhammar, which cleaving apart, causes a spill out of riolitic lavae which reach the sea (punta Fram);
  16,000 years ago, explosive activities at Kuddia di Mida;
  9,000 years ago, emissions of basaltic lavae at Kuddie Rosse creating formations of waste cones.

 

The general morphology of the island, from the above information, is the consequence of four main factors:
- The presence in the central part of the island of two calderas of different ages;
- The lift of the Montagna Grande
- The presence of faults which make the high coasts on the southern and eastern parts of the island;
- The basaltic lavaflow on the northwestern part of the island.

 

 

 Capt. Dr. Marco Belogi, geologist, Military Geographical Institute of Florence