4. Where do volcanic eruptions occur?

There are three main types of locations for volcanoes :

  • At the boundaries of plates
    • divergent plates: the progressive separation of the plates opens fractures in the crust through which magma rises out. In these zones magmas are in general basaltic (e.g. Mid-Atlantic ridge);
    • convergent plate: the colliding and overriding plates produce very high pressure and temperatures that melt the rocks and form the most dangerous volcanoes in the world. In these zones, in general, magmas are rhyolitic and rich in gases (e.g. the North Pacific area, Vesuvius in Italy);
  • Far from the boundaries of plates: Hot spots, rare volcanoes, with very deep magma reservoirs, giving less explosive basaltic volcanoes (e.g. the Hawaii islands).
Different types of Plate Boundaries - This image is in the public domain because it contains materials that originally came from the United States Geological Survey, an agency of the United States Department of Interior. For more information, see the official USGS copyright policy. Source: Wikipedia
Different types of Convergent Boundaries - Source: Wikipedia
Distribution of volcanoes and earthquakes in the world. Source: United States Geological Survey

The largest volcanic risks in the world are concentrated in densely populated areas located on the hills or near active volcanoes.

The most impressive example on Earth is the “Ring of Fire”, a 40,000 km long zone of frequent earthquakes and volcanic eruptions that encircles the basin of the Pacific Ocean, also called the circum-Pacific belt or the circum-Pacific seismic belt.

The Ring of Fire involves the western coast of North America continent and the Pacific Ocean islands: Kuril, Japan, Philippines. It accounts for 90% of the world’s earthquakes and 81% of the world’s largest earthquakes.

The next most seismic region (5-6% of earthquakes and 17% of the world’s largest earthquakes) is the Alpide belt which extends from Indonesian islands of Java and Sumatra through the Himalayas, the Mediterranean and out into the Atlantic.

The Mid-Atlantic Ridge is the third most prominent earthquake belt.

In Europe, volcanic risk is concentrated in:

  • the Mediterranean region: Southern Italy (Vesuvius near Naples, Stromboli and Vulcano in the Aeolian Islands, Etna in Sicily, etc.), Greece (Methana on the Peloponnese peninsula, Milos and Santorini in the Cyclades, Nisyros in the Dodecanese) and Turkey (Mt Ararat, Nemrut Dagi and Tendurek Dagi in Eastern Anatolia);
  • the Northern Atlantic Ocean region: Canary Islands (Teide, Teneguía, Tanganasoga), Açores Islands (Capelinhos, Mount Pico) and Iceland (with 130 volcanic mountains: Hekla, Eyjafjallajökull, Surtsey, etc.).

France has some active volcanoes but only in its overseas departments: the “Mount Pelée” in the Martinique and “La Grande Soufrière” in Guadeloupe (Carribean Sea), the “Piton de la Fournaise” in the Réunion island (Indian Ocean) and both submarine and emerged volcanoes in the French Polynesia (Pacific Ocean). The United Kingdom also has some in its overseas territories: for exemple, the very dangerous Soufriere Hills volcano is located on the island of Montserrat (Carribean Sea).