Driving around the island visitors can see the different aspects of the rocks that arise from a number of various geological events that, during the millenniums, have defined the original profiles of the coast. Therefore, fans of geology will appreciate the features of the rocks and the history of the origin of the island of through this detailed technical report.

The island of San Pietro was formed between 18 and 13 million years ago by intense volcanic activity, both effusive and explosive, whose products can currently be seen on the entire island. Until today many rock types have been recognized as both lavic and pyroclastic, whose variety and unique composition make the island an extremely attractive destination for a geological excursion.

The San Pietro Island rocks are formed primarily of ignimbrites streams (composition that varies from dacite to rhyolite to comenditic) from domes and lava flows of comenditic composition which are a rarity in this type of volcanic activity.

The official scientific name for Comendite originates from a region called Comende island, where they were discovered for the first time in 1895.

The island of San Pietro can be divided into four sectors based on geological and morphological characteristics:

• Center-Western Sector

Featuring more marked high grounds, formed by succession of domes and of lavic and comenditic flows

that can be observed in the areas of Borrona, Nasca and of Tortoriso which underlie the various layers of younger riolitic and of dacite ignimbrites (erroneously called by some trachytes). This type of geological structure forms in the north and in the South of the island. Often have a columnar fracturing and are well sealed, so as to resemble the lava.

• Northwestern Sector

Characterized by hills formed by small plateau of younger ignimbrite, near tall cliffs along the coastline where ash, pumice and tuffs deposits are located (the Bianche Tacche site).  At the summit, accessible from the ground, one can observe the ignimbrites rocks with large cavities, due to the presence of gas bubbles and magma that originated them.

• Center-Western Sector

 In this area you can find the most ancient volcanites of the island, whose flows are clearly visible in the Becco bay. To the north can be found ignimbrites rocks of a younger age, very fractured (the area of Capo Sandalo).  Walking down the path that leads to the sea in Capo Sandalo it's possible to reach a little plaza where you can observe both comenditic ignimbrite and younger lavic ignimbrite.

• South-Eastern Sector

The oldest volcanic succession of the island, emerges on the south coast only in Punta Nera area. The sector is mainly dominated by layers of younger ignimbrites rocks, and of a low pressure area covered by recent sedimentary deposits. This old volcanic succession is visible along the south coast, in Punta Nera.  Near a couple of beaches (like Girin beach ) it's possible to see the few island outcrops of sedimentary rocks formed during the lowering of the sea level .

Retrieved from: Unica.it
To know more about the terminology: Gruppo Nazionale di Vulcanologia


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