Sicilia (Sicily) is the largest island in the Mediterranean Sea and one of the 20 regions of Italy. It is separated from the Italian Peninsula by the narrow Strait of Messina, about 3 km wide in the north, and about 16 km wide in the south. Its most prominent landmark is Mount Etna (3,329 m asl), one of the tallest active volcanoes in Europe. It is also the most active volcano in the world and produces lots of lava tubes, several may be visited.
Sicily is located at the collision of the Eurasian and the African plates during westward-dipping subduction of the African slab since late Oligocene. It has four major tectonic units, the Hyblean foreland, the Gela foredeep, the Apenninic-Maghrebian orogen, and the Calabrian Arc. The Hyblean foreland is the southeastern part of the island is a northward-dipping monocline with a rather high dip of 16–18°. It consists of limestones and other carbonatic rocks, ike turbidites, chalk, and calcarenite. The younger limestones are interbedded with basalt. The Gela foredeep is a series of Late Miocene-Pleistocene sediments, including marly limestones, Messinian evaporites and sandy clays. It is located along the southern coast of Sicily. The Apenninic-Maghrebian orogen is the central and western part of Sicily. It is the fold and thrust belt of the subduction system between African and European plate. The rocks consist of a stack of detached nappes composed mostly of Mesozoic carbonates. All three units are karstified.
The fourth unit is completely different. The Calabrian crystalline basement in the northeastern part of Sicily is a part of the Calabrian Arc. Paleozoic igneous and metamorphic basement rocks with the active stratovolcano Mount Etna. There is no karstification but numerous rather young lava tubes.