The Aeolian Islands or Lipari Islands (Isole Eolie) are a volcanic archipelago in the Tyrrhenian Sea north of Sicily, named after the demigod of the winds Aeolus. The locals residing on the islands are known as Eolians (Italian: Eoliani). The Aeolian Islands are a popular tourist destination in the summer, and attract up to 200,000 visitors annually. The largest island is Lipari. The other islands include Vulcano, Salina, Stromboli, Filicudi, Alicudi, Panarea and Basiluzzo. The present shape of the Aeolian Islands is the result of volcanic activity over a period of 260,000 years. There are two active volcanoes - Stromboli and Vulcano. The volcanic activity of steaming fumaroles and thermal waters are on most of the islands. Only the one on Stromboli, the northernmost island, is still active. Scientifically the archipelago is defined as a "volcanic arc". Geology explains the origin of the Aeolian Islands is due to movement of the Earth's crust as a result of plate tectonics. The African continental shelf is in constant movement towards Europe. The resulting collision has created a volcanic area with ruptures in the Earth's crust with consequent eruptions of magma. The "Eolian Arc" extends for more than 140 kilometres, but the area of geological instability caused by the collision of Africa and Europe is very much larger. It includes Sicily, Calabria, Campania together with Greece and the Aegean islands. The complex of the eight Aeolian Islands, covering an area of 1,600 square kilometres, originated from a great plain at the bottom of the Tyrrhenian sea. Emissions of lava from depths of up to 3,600 metres resulted in the formation of the Eolian Islands, together with Ustica and a series of submarine volcanoes named Magnani, Vavilov, Marsili and Palinuro, as well as two that are unnamed. The Aeolian Islands are listed by UNESCO as World Heritage Sites. However, inaccuracy, the missing closure of a pumice quarry, and the oncoming building of some four harbours by the shore of the sole town of Lipari pose a threat to the islands' place on the list, according to the Italian UNESCO Commission