mudflows and layered basalt rock, from phases associated with Plinian and sub-Plinian eruptions in the interior of the caldera. This group is divided into five formations: Roída da Praia (between 34,000 and 8,000 years ago), Ribeira Chã (created from abrupt eruption 8–12000 years ago), Fogo A (also from an abrupt eruption some 5000 years ago), Lombadas (a complex eruption of Fogo B, C and D sites) and geological eruptions occurring in the last 3000 years. Among the various deposits Fogo A, which dates to roughly 5000 years, corresponds a clear stratigraphy of the island of São Miguel. The flanks of the massif are heavily eroded, with drainage confined to many valleys and gullies. See also List of volcanoes in Azores References Notes Sources Stratovolcanoes of Portugal Calderas of Portugal Volcanic crater lakes São Miguel Island Geology of the Azores Pleistocene stratovolcanoes Pleistocene calderas Holocene stratovolcanoes