The geology of São Miguel is dominated by three volcanic centers, which correspond to the major active trachytic central volcanoes of Fogo, Sete Cidades and Furnas, linked by rift zones. Nevertheless, several volcanic complexes at São Miguel are well defined, and from the older to the younger the following units can be considered: Nordeste Volcanic Complex, Povoação Volcanic Complex, Furnas Volcanic Complex, Sete Cidades Volcanic Complex, Fogo Volcanic Complex and Picos Volcanic Complex.