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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

QUEIROZ, G., GASPAR, J.L., GUEST, J.E. (2004) - The last 5,000 years of intracaldera volcanic activity at Sete Cidades Volcano (S. Miguel Island, Azores): implications for hazard assessment. IAVCEI General Assembly, Pucon, México, Novembro (Comunicação Oral).


Sete Cidades Volcano is located in the westernmost part of S. Miguel Island, Azores. Its subaerial eruptive history has more than 200,000 years old and comprised the built up of a basaltic shield volcano that evolved to a trachytic central volcano with caldera. At least three major caldera-forming events occurred in the last 36,000 years, producing pyroclastic flows, surges and pumice fall deposits.
5,000 years ago the intracaldera volcanic activity changed from a magmatic to a hidromagmatic dominant character, enhancing the role of the hydrologic system characterized by the existence of aquifers and crater lakes. For that period a detailed field survey allowed to recognize the deposits of at least 17 intracaldera eruptions identified as P1 to P17. Such deposits are mainly composed by alternated ash and lapilli pumice fall layers sometimes accompanied by small surge beds. Pyroclastic flow units were identified within three of them.
The recent eruptive history of Sete Cidades makes it the most active central volcano known in the region. The style of the eruptions, its frequency and magnitude were analyzed for hazard assessment. A future intracaldera event will probably have an hydromagmatic character producing pyroclastic fall deposits and minor surges and/or pyroclastic flows.