Chapter 8 Eruptive history of Fogo Volcano, São Miguel, Azores

Abstract Fogo is the largest of the three active central volcanoes on Sao Miguel and dominates the centre of the island. It is located at the intersection of NW–SE, NE–SW and east–west-trending fault systems, showing a complex morphology with a Summit Caldera formed as a result of explosive and collapse events. The edifice of Fogo has been extensively dissected by erosion, with deep valleys that show clear tectonic control. The products of Fogo range from basalt to trachyte and belong to a potassic alkaline suite. The oldest subaerial products of Fogo are >200 ka. Older products are poorly exposed, making stratigraphic correlation difficult, particularly on the north flank where considerable subsidence within the NW–SE Ribeira Grande graben has occurred. A more complete stratigraphy for the last 40 ka was established on the southern flank of the volcano. During this period there were large trachytic Plinian eruptions, including those of the Ribeira Cha (8–12 ka BP) and Fogo A (4.6 ka BP). The last intracaldera eruption was historic and occurred in 1563, and 4 days afterwards there was an effusive basaltic eruption on the northwestern lower flank of the volcano.