With about 100000-year history, the Furnas volcano is the youngest of the active volcanoes of São Miguel. The rock and mineral deposits are divided into three groups, consisting essentially of trachyte materials, constituted by pyroclastic deposits and flows resulting from explosive eruptions, lava flows and surges. The inferior layer includes most pyroclastic materials and volcanic products in the formation of the Povoação Ignimbrite (some 30000 years ago). The intermediate layer includes material produced between 30,000 years and 5,000 years ago (reaching the Fogo A depoists). Finally, the superior layer includes all activities until 5000 years ago.