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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

PIMENTEL, A., PORRECA, M., PACHECO, J.M., SELF, S. (2011) – The 1000 year BP ignimbrite-forming eruption of Caldeira volcano (Faial, Azores): Event-stratigraphy and paleomagnetic estimation of emplacement temperatures (Poster). IUGG XXV General Assembly 2011, Melbourne, Austrália, 28 Junho – 7 Julho (Poster).


The 1000 year-old eruption of the Caldeira volcano (Faial Island, Azores) generated extensive pyroclastic density currents (PDCs) and was responsible for the subsidence of the 2-km-wide summit caldera. The stratigraphic sequence of this eruption has been studied in detail and emplacement temperatures of PDCs have been estimated by paleomagnetic analyses.
The eruptive succession of this event consists of phreatomagmatic ash, pumice fall, massive to stratified non-welded ignimbrite and lithic breccias. Juvenile clasts from fall and ignimbrite deposits are trachytic in composition and frequently show banded texture.
Three main eruptive phases are present in the stratigraphic record: (1) an initial phase of alternating magmatic/phreatomagmatic short-lived columns that dispersed thin fall deposits over the W flank; (2) a second phase produced a short magmatic column depositing pumice fall onto the N and NW flanks; (3) the final phase, corresponding to the caldera collapse, produced PDCs that spread to the N and to the E into Pedro Miguel graben. PDCs were strongly controlled by topography through valleys and fault scarps spreading from the summit to the sea.
Thermal remanent magnetization analyses carried out on lithic clasts collected from the ignimbrite were used to estimate emplacement temperatures. The temperatures of PDCs emplaced on the N flank were above the Curie temperature of magnetic minerals (more than 520-560ºC), while PDCs channelled along the graben were emplaced at lower temperatures of about 480-520ºC. Field and laboratory data permit reconstruction of the eruptive history and emplacement processes of pyroclastic deposits.