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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Painéis ► em encontros internacionais


Referência Bibliográfica

PIMENTEL, A., ESPOSTI ONGARO, T., NERI, A., PACHECO J.M. (2008) - Numerical simulation of explosive activity at Sete Cidades Volcano (S. Miguel, Azores). IAVCEI 2008 General Assembly, Reykjavik, Islândia, 17 - 22 de Agosto (Poster).


The dynamics of explosive volcanic activity at Sete Cidades Volcano (S. Miguel, Azores) were analyzed by using multiphase flow simulations. Sete Cidades, located on the western end of S. Miguel Island, is an active central volcano truncated by an approximately circular caldera of about 5 km in diameter, with steep walls ranging up to 500 m high. In the last 16,000 years, since the last caldera forming event, the eruptive history of Sete Cidades has been marked by explosive activity, particularly in the last 5,000 years. The eruptive scenarios investigated in the numerical simulations were constrained by the Sub-Plinian scale events occurred in the recent (< 5,000 years) eruptive history of Sete Cidades, where a VEI 4 event (similar to P11 eruption) may be considered as the maximum expected scenario for an intracaldera eruption. 2D axisymmetric simulations of collapsing columns and propagation of pyroclastic density currents (PDCs) were preformed for different source eruptive conditions and over several topographic profiles of Sete Cidades caldera. The simulations were carried out by running the code PDAC (Pyroclastic Dispersal Analysis Code) on parallel supercomputers available at the CINECA High Performance Computing facilities (Italy). Simulation results showed a marked unsteady behaviour of the eruptive columns. The instabilities generated in the fountains led to oscillations of the collapse height thus producing PDCs that are intermittently fed by batches of collapsed material. As the PDCs propagate along the topography, phoenix clouds rise up due to the deceleration of the flow and the presence of topographic obstacles. Phoenix clouds tend to be conveyed towards the main eruptive column and merge into large buoyant plumes. Highly energetic suspended backflows are generated when the pulsing PDC front reaches the caldera wall producing a complex flow pattern. Simulation results also revealed that, for the eruptive scenarios and vent conditions adopted, the PDCs were not capable of overcoming the obstacles encountered showing a strong control of caldera topography on their propagation.