São Miguel

São Miguel Island named for Saint Michael is also referred to locally as “The Green Island”.  It is the largest and most populous island in the Portuguese archipelago of the Azores. The island covers 760 km2 (290 sq mi) and has around 140,000 inhabitants, with 45,000 of these people resident in the largest city in the archipelago: Ponta Delgada.

In the early 15th century, Infante D. Henrique first authorized the settlement of the Azores, and many settlers from the historical provinces of Estremadura, Alto Alentejo, Algarve and Madeira travelled to São Miguel, under the Carta Régia (a decree of the regency). The fertile soils and temperate climate attracted settlers from other countries, notably French people and cultural minorities such as Jews and some Moors.

Its geographic position and fertile soils permitted rapid economic development. The establishment of a military garrison made the island an obligatory port-of-call in the African and Asian commercial trade, while the export of sugar, and later orchil (a dye exported to Flanders for the making of cloth) stabilized the island’s export trade.s such as tea, pineapple, and tobacco. The development of the fishing industry, cultivation of food staples and expansion of the dairy industry permitted the growth of many of the population centres on the island.

The Sete Cidades Massif  an area that occupies the extreme western part of the island, and corresponds to a central volcanic crater and lake-filled caldera, with various cones, deposits of pumice, lava domes and maars. In the northeastern flank of this volcano the Mosteiros Graben, a tectonic structure created from the collapse of lands and located along a northwest to southeast orientation. Along other regional fractures and radial faults there are ancient spatter cones and lava domes;

The Picos Region– is situated along a northwest-southeast alignment, and defines a range of spatter cones and relatively level ground between the Sete Cidades and the Água de Pau Massifs;

The Água de Pau Massif – this central feature corresponds to the central volcano on the island, and includes the Lagoa do Fogo (Lake of Fire), many lava domes and pumice cones. On the northeastern flank of the Massif the Ribeira Grande Graben is visible, representing a tectonic depression oriented northwest to southeast;

The Achada das Furnas Plateau – a region with a central plain marked by cones and maars, with deposits along a west-northwest to east-southeast and northwest to southeast;

Furnas Volcano – located in the eastern part of the island, along the southern coast, and comprising two ancient calderas, occupied by a lake (Lagoa das Furnas). Within the system one can find many pumice cones, maars and lava domes;

Povoação Volcano – comprising a central caldera, generally well-eroded and whose southern rim has disappeared to the southern coast. Within its interior, marked by several river-valleys and cliffs, are several spatter cones;

The Tronqueira Region – it occupies the extreme easterly portion of the island and corresponds to a mountainous region, divided by many river-valleys that are usually delineated by tectonic fractures;

The Northern Coastal Platform – located along the northeastern portion of the island, and marks a zone of relatively moderate topography, limited by the coast to the north and the northern crater rims of Furnas and Povoação volcanoes to the south.

São Miguel comprises six volcanic zones, all are Quaternary in age except the last, which is partly Pliocene. From west to east these zones are: the trachyte stratovolcano of the Sete Cidades Massif; a field of alkali-basalt cinder cones and lava flows with minor trachyte; the trachyte stratovolcano of the Água de Pau Massif; a field of alkali-basalt cinder cones and lava flows with minor trachyte and tristanite; the trachyte stratovolcano of Furnas; and the Nordeste shield, which includes the Povoação caldera and consists of alkali basalt, tristanite and trachyte.  Dormancy ages for these regions include: 400 year for Sete Cidades, 145 for zone 2, 1150 for Água de Pau, and 370 for Furnas, while eruptions in the Nordeste have not occurred in the past 3000 years.

These geomorphological structures have resulted from millions of years of compound growth that began in the eastern portion of the island; around 4 million years ago the Nordeste Volcano burst from the ocean floor in effusive and fissural eruptions. These eruptions were composed of basaltic lava flows and spatter cones whose products reached a height of 1,100 metres (3,600 ft) forming the mountainous region of Tronqueiro, Planalto dos Graminhais, Espigão dos Bois and Pico Verde (finding its maximum extent in Pico da Vara). But, about 950,000 years ago a secondary volcano system (Volcanic Complex of Povoação) supplanted the eruptions of the Nordeste Volcano, responsible for new basaltic lavas and pyroclastic deposits. With an age of 200,000 years the third volcano on São Miguel, the Água de Pau Volcano started erupting on the western flank of Povoação volcano in two phases. The first phase, composed of the older materials, erupted from lava flows and Trachyte pyroclasts, the secondary phase corresponded to volcanic products that began erupting 400,000 years ago. These latter deposits included pyroclastic, trachyte flows (lava and surges), mud flows and a mixture of basalts. In what would become the western portion of the island a fourth volcano formed: the Sete Cidades Volcano erupted 200,000 years ago and continued to erupt until about 36,000 years ago. Between 100,000 and 3,800? years ago fissural eruptions of integrated lava and basaltic pyroclastic deposits occurred in the center of the island between Água de Pau and Povoação, forming the Fissural Volcanic System of Congro. These eruptions were explosive and fed by activities in the neighboring volcanic systems. At about 100,000 years a secondary system developed along the frontier of the Povoação volcano, the “Furnas Volcano” complex (the youngest volcanic system) in three phases mixing pyroclastic surges, trachytes, and lava flows, as well as explosive materials. Finally, two layers of deposits formed the Fissural Volcanic System of Picos between the volcanic Água de Pau and Sete Cidades from 31,000 years ago unifying the island. This formation integrated lavas, basaltic pyroclasts, tuff cones and trachyte domes into two layers (referred to as the Ponta Delgada and Penhal da Paz sub-depoists) and compiled to about 5,000 years ago.

The ancient laurisilva forest has mostly been replaced by cultivated fields and imported trees and plants, such as the ubiquitous cryptomeria trees. There are some hot springs (caldeiras), generally located in the center of the island, in the area stretching from Povoação to Nordeste.

The peak area between Sete Cidades and Fogo is a monogenetic volcanic field composed of 270 volcanoes. They are primarily made up of basaltic cones which were formed during Strombolian and Hawaiian-style eruptions. This is the part of the island with most recent volcanic activity. The youngest volcanoes are relatively well dated. It is estimated by some, that 19 eruptions have occurred during the last 3,000 years. Several eruptions have been witnessed and recorded by people. The last one took place in the 17th century. The most famous eruption is known as Fogo 2, occurring in 1652.

The highest elevation on São Miguel is the Pico da Vara at 1,103 metres (3,619 ft). Lying at the eastern end of the island, it is the focus of a Special Protection Area containing the largest remnant of laurisilva forest on the island, which is home to the endemic and critically endangered bird, the Azores Bullfinch.

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