The total area of the island is , while the Autonomous Region of Sicily (which includes smaller surrounding islands) has an area of . The terrain of inland Sicily is mostly hilly and is intensively cultivated wherever possible. Along the northern coast, the mountain ranges of Madonie, , Nebrodi, , and Peloritani, , are an extension of the mainland Apennines. The cone of Mount Etna dominates the eastern coast. In the southeast lie the lower Hyblaean Mountains, . The mines of the Enna and Caltanissetta districts were part of a leading sulphur-producing area throughout the 19th century, but have declined since the 1950s. Sicily and its surrounding small islands have some highly active volcanoes. This is due to the fact Sicily is geographically on the northern edge of the African continental plate. Mount Etna is the largest active volcano in Europe and casts black ash over the island with its recurrent eruptions. It currently stands high, though this varies with summit eruptions; the mountain is lower now than it was in 1981. It is the highest mountain in Italy south of the Alps. Etna covers an area of with a basal circumference of . This makes it by far the largest of the three active volcanoes in Italy, being about two and a half times the height of the next largest, Mount Vesuvius. In Greek mythology, the deadly monster Typhon was trapped under the mountain by Zeus, the god of the sky. Mount Etna is widely regarded as a cultural symbol and icon of Sicily. The Aeolian Islands in the Tyrrhenian Sea, to the northeast of mainland Sicily form a volcanic complex. The three volcanoes of Vulcano, Stromboli and Lipari are also currently active, although the latter is usually dormant. Off the southern coast of Sicily, the underwater volcano of Ferdinandea, which is part of the larger Empedocles volcano, last erupted in 1831. It is located between the coast of Agrigento and the island of Pantelleria (which itself is a dormant volcano). From a geographical perspective, also forming a part of Sicily is the Maltese Archipelago, the islands home to the republic of Malta. The autonomous region also includes several neighbouring islands: the Aegadian Islands, the Aeolian Islands, Pantelleria and Lampedusa. Rivers Several rivers drain the island, most of which flow through the central area and enter the sea at the south of the island. The Salso flows through parts