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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Artigos em livros de atas ► Internacionais


Referência Bibliográfica

GASPAR, J.L., QUEIROZ, G., FERREIRA, T., COUTINHO, R., PACHECO, J.M., WALLENSTEIN, N., ALMEIDA, M.H. (2001) - The Significance of Basaltic Lava Balloons Produced during Submarine Eruptions: Facts from the 1998-2000 Azores Volcanic event. Journal of Conference Abstracts, (6), 1, EUG XI, 800.​


The Azores islands are located in the middle of the Atlantic Ocean and rise from the so-called Azores Platform, a deeply irregular submarine area delimited by the 2000 meters bathymetric line. The tectonic setting of the region is dominated by the Azores triple junction, a point where the American, Eurasian and African lithospheric plates meet. This complex geodynamic frame together with the presence of a deep mantle plume explains why seismic and volcanic phenomena are frequent in the area. Since the settlement of the islands, early in the XV century, several strong earthquakes and about 30 volcanic eruptions occurred being sometimes responsible for many deaths and severe damages. The most recent volcanic event started on December 1998 on the Serreta Submarine Ridge, about 10 km west of Terceira island, and lasted for more than one year. This submarine fissural eruption was preceded by some days of low magnitude seismic activity and displayed up to 7 active spots, defining NE-SW and NW-SE trends, in an area with estimated depths between 300 and 800 metres. Lava balloons were the most singular features observed during the eruption. They are void volcanic blocks of basaltic composition with spherical to ellipsoidal shapes and sizes up to 3 metres long that were emerging at the sea surface and kept floating for several minutes until they released the hot filling gas. These peculiar structures are interpreted as the result of the formation of lava blisters at vent level due to the degassing of a very fluid gas-rich magma during lava lakes and/or lava fountain episodes. This remarkable phenomenon may not be so uncommon in submarine eruptions and explain a few existent descriptions of historical submarine eruptions not only in the Azores but also in other volcanic regions.