Volcanic Geology of São Miguel Island (Azores Archipelago)

The Azores archipelago in the Atlantic Ocean is composed of nine volcanic islands and São Miguel is the largest and most volcanically active. During the past 5000 years several eruptions have taken place on the three active central volcanoes – Sete Cidades, Fogo and Furnas – and in the basaltic fissure systems of Picos and Congro. There is evidence that Furnas was in eruption when the first settlers arrived some time between 1439 and 1443. In the sixteenth and seventeenth centuries there were two explosive sub-Plinian eruptions, Fogo in 1563 and Furnas in 1630. The last eruption on land occurred in the Picos Fissural Volcanic System in 1652, involving the extrusion of lava domes. In 22 chapters, this volume considers the volcanic geology of the island under the headings of geological setting, volcanic history, geological hazards and risk assessment, volcano monitoring and natural resources.
The structure of the Azores Triple Junction: implications for São Miguel Island Available to Purchase
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Published:January 01, 2015
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CiteCitation
J. M. Miranda, J. F. Luis, N. Lourenço, R. M. S. Fernandes, 2015. "The structure of the Azores Triple Junction: implications for São Miguel Island", Volcanic Geology of São Miguel Island (Azores Archipelago), J. L. Gaspar, J. E. Guest, A. M. Duncan, F. J. A. S. Barriga, D. K. Chester
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Abstract
To date, a lack of reliable morphological and geophysical data has been a major limitation to understanding the tectonic and magmatic processes that shape the Azores Triple Junction and the Terceira Rift. This situation has changed recently: for the first time both areas are covered by high-quality swath bathymetry surveys and marine magnetic data with GPS quality positioning. This provides a good description of the surface morphology, and also of magnetic chrons that give fundamental information for the timing of spreading processes in a geological time frame. There is also a large amount of data from GPS stations that provide accurate estimations of present-day velocities for most of the islands. It is shown that only two main rift systems can be found on the plateau, the older one matching the Princess Alice Basin, and the newer one matching Terceira Rift; the shift between the two probably occurs close to c. 3 Ma. It is shown that extension is currently concentrated on the Terceira Rift, progressively attaching Graciosa and Terceira islands to Eurasia, while São Miguel is being strained by rifting. It is also shown that no right lateral strike-slip fault connects the Terceira Rift to the Mid-Atlantic Ridge.