Fogo, also known as Água de Pau, is the largest of the three active central volcanoes of S. Miguel Island and dominates its central part. It is located at the intersection of NW-SE, NE-SW and E-W fault systems and shows a complex morphology with a summit caldera formed as result of numerous collapse and explosive events. The Fogo edifice has been extensively dissected by erosion, presenting deep valleys some of which show a clear tectonic control.

The products of Fogo belong to a potassic alkaline suite ranging from alkali basalt through to trachyte, reflecting withdrawal of melt from a compositionally zoned magma reservoir, where fractionated crystallisation was the dominant process. The oldest subaerial products of Fogo volcano date from about 280 ka BP and were collected from a borehole in its lower northern flank. Older products are poorly exposed, making stratigraphic correlations difficult, particularly in the north flank where considerable subsidence within the NW-SE Ribeira Grande graben has taken place. A more complete stratigraphy for the last 40 ka was established, mainly based on the deposits of the southern flank. During this period some large trachytic plinian eruptions, including those of the Ribeira Chã and Fogo A, were responsible for episodes of caldera collapse. The last major intracaldera eruption, of sub-plinian style, occurred in 1563 AD and this led to accumulation of a considerable thickness of tephra on the eastern part of the island. Four days after this event an effusive basaltic eruption occurred on the north-western lower flank, with pahoehoe lava flows that reached the sea in few days.