Jarkko KARI


Jonathan MILLS

James M. NYCE


Gabriela QUEIROZ


Philip WELCH

The Geology of the Island

Abstract. The Azores archipelago comprises nine islands of volcanic origin, located in the North Atlantic Ocean, in the area where the Eurasian, African and American tectonic plates meet. Due to this complex geodynamic setting, volcanic eruptions and earthquakes marked the History of the Azores. Since the beginning of the settlement, in the XV century, more than 30 eruptions and about 22 strong earthquakes were recorded. São Miguel is the main island of the archipelago with an area of 745 km2 and approximately 132000 inhabitants. Regarding its morphology distinct regions can be defined. In the easternmost part of the island, Nordeste and Povoação regions are volcanically inactive and exhibit the oldest terrains. The former is distinguished by a strongly eroded landscape and the latter corresponds to a large caldera partially filled with younger volcanic deposits from neighbour volcanoes. To the west, three active central volcanoes have developed – Furnas, Fogo, and Sete Cidades, all with impressive summit calderas partially occupied by lakes. Between those volcanoes, fissure eruptions developed in the Achada das Furnas and Picos regions, originating a distinct landscape marked by the formation of several scoria cones, often aligned according to regional tectonic trends. In historical times 5 volcanic eruptions took place in S. Miguel Island. Present day volcanic activity is marked by hydrothermal manifestations like fumaroles, thermal springs and extensive soil degassing, particularly in Fogo and Furnas regions.