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Case Study 13. The Azores – Volcanic Islands in the Atlantic

ByH. Gaudru

Pico volcano overlies an older linear volcano with a number of flank cones making up most of the 48km long island. The volcano rises 3500m above the surrounding ocean floor and has a subaerial volume of 97km3 as compared with the total subaerial volume of Pico Island of 207km3. The conical Pico volcano is dominantly basaltic and developed above the Montanha volcanic complex on the eastern side of Pico Island with a 500m wide summit crater and a small steep sided cone (Global Volcanism Program, 2009). Historical eruptions have been limited to the sides of Pico volcano as well as to the south-east-trending rift zone, the São Roque Piedade volcanic complex, which is covered with pyroclastic cones. During 1562-64 an eruption from the south -east rift zone formed lava flows that reached the northern coast. An erupting nearby vent produced lava flows that moved into the sea on the south side of

Introduction The nine volcanic islands of the Azores are located in the Atlantic Ocean about two hours flying time and 1500km from Lisbon (Portugal), and about five hours flying time or 3900km from the eastern coast of North America (Azores.com, 2009a). The Azores have a total area of 355km2, sit on top of the Mid-Atlantic Ridge, where mountains sometimes reach above sea level (Encyclopaedia Britannica, 2009), thus forming islands of volcanic origin. The Azores have been created by outpourings of lava from the ocean floor, due to the high level of activity in the area which is a result of three major tectonic plates meeting at this point (Siebert and Simkin, 2002). The North American Plate to the north-west of the Azores is gradually drifting west, the Eurasian Plate to the north-east is drifting east and south and finally the African Plate is drifting east and north. The small Azores Microplate, which is drifting westwards, further complicates the picture. The last volcano to erupt in the archipelago was the Capelinhos volcano (Vulcão dos Capelinhos) in 1957, in the western part of Faial Island, increasing the size of that island by 2.4km.