São Miguel Island

Lagoa do Fogo (English: Lake of Fire), as seen from Miradouro da Serra da Barrosa, along the Água de Pau Massif

Lagoa das Furnas

Pasturelands in the Picos region: the debris field that joined the Sete Cidades Massif and Água de Pau Massif that united the island of São Miguel.

Detailed map of São Miguel Island

São Miguel is bisected by many faults from the northwest to southeast in the direction of the Terceira Rift, a triple junction of the African, Eurasian, and North American tectonic plates. This system is best expressed in the western part of the island with extensive geological formations, such as the Mosteiros Graben (along the western flank of the Sete Cidades Massif), the Ribeira Grande Graben (along the northern flank of the Água de Pau Massif), and the many cones and fissural structures along the interior of the island. In the ancient crater of Furnas the faults are aligned west-northwest to east-southeast. Zbysewsky (1959), among others (note references) identifies eight geomorphological structures on São Miguel that correspond to the formative features that built the island, including:

• 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 Volcanic System or 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.[2] 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.[2]

Ginetes, situated in the westernmost part of the island, near the coast

A species of common dolphins seen during one of whale watching tours

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-deposits) and compiled to about 5,000 years ago.

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 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, which occurred in 1652.

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. There is also an ocean hot spring called Ponta da Ferraria.[3][4]

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.

Whale watching tours, starting from Ponta Delgada and Vila Franca do Campo are available. One may see sea turtles, dolphins and humpback whales.

São Miguel has a mild maritime climate, which is drier in the summer and wetter in the winter, though according to the Köppen climate classification, four different climatic classifications can be found throughout the island. At lower elevations, the hot-summer Mediterranean climate (Csa) dominates over the Humid subtropical climate (Cfa) typical of the more westerly islands and truly only found around Capelas. Above 100 m (330 ft) altitude, the Mediterranean climate transitions into its warm-summer variant (Csb), and past 200 m (660 ft) the climate is strictly oceanic (Cfb).[5]

The western half of the island is generally drier, due to the lower topography. Precipitation varies from less than 800 mm (31 in) in the Northwest coastline between Mosteiros and Ajuda da Bretanha, to over 3,200 mm (130 in) around Pico da Vara in the east.[6]

Similar to other islands in the archipelago, São Miguel is influenced by ocean currents and winds, and, in particular, the cyclonic Gulf Stream. This stream functions as a moderating force in the islands, keeping temperatures hovering between 14 °C (57 °F) and 23 °C (73 °F) throughout the year. The island's location also makes it susceptible to some Atlantic storms, and precipitation tends to be elevated during the winter periods. Winters are very mild by European standards and summers are warm (sometimes very warm due to the high humidity) and relatively dry. Temperatures above 30 °C (86 °F) or below 5 °C (41 °F) have never been recorded at the coast.

The Fonte de Buraco Belvedere overlooking the village of Maia, in the northern municipality of Ribeira Grande

Owing to the predominance of volcanic cones and craters in the interior, human settlement has developed primarily along coastal and interior plains. In addition, there are several communities that have developed within ancient craters (such as Sete Cidades, Furnas or Povoação), river-valleys (such as Ribeira Chã, Pilar da Bretanha) or coastal deltas (Mosteiros). Regardless, these settlements were largely agrarian and concentrated around the parish churches and the many fertile parcels of land. The communities were largely isolated throughout the year, owing to the great distances and rough landscape of the island, and only became integrated with the development of the many road networks that circle and bisect the island. Two cities have developed, largely because the island was divided by mountainous volcanic cones in the interior: Ponta Delgada and Ribeira Grande. Administratively, the island is governed by five municipalities, with Ponta Delgada and Ribeira Grande having more administrative functions associated with their larger populations:

The center of Ponta Delgada, as seen from the marina complex, Portas do Mar

Lagoa, the youngest of the municipalities of São Miguel, has a populationp of about 14,126 inhabitants (2008 census), incorporating the south-central parishes east of Ponta Delgada; Nordeste, literally the north-eastern municipality, well known for an abundance of natural vegetation and the highest point on the island, Pico da Vara; Ponta Delgada, includes not only the industrial/commercial city of Ponta Delgada, but also many rural parishes, as well as the large crater of Sete Cidades; Povoação, home to the first colony on the island, Povoação is located in the south-east corner of the island, and includes active and dormant volcanic features, including Furnas and the crater of Povoação; Ribeira Grande, the second largest municipality, with approximately 30,852 inhabitants, received its charter in 1981, and incorporates an extensive area of the northern coast (including the parish of Rabo de Peixe, the largest parish by population); and Vila Franca do Campo, once the seat of the historical capital of São Miguel (until it was almost destroyed by earthquake and landslides in 1522), it is located along the southern coast between Lagoa and Povoação.

Chá Gorreana's main plant

The cult of the Lord Holy Christ of the Miracles is the most popular devotion in São Miguel island.

Government is administered at the local level by the civil parish (Portuguese: freguesias), which are responsible for the provision of services and implementation of municipal initiatives. Based on the historical ecclesiastical limits established after settlement, the civil parishes are run by a president, treasurer and secretary (at the head of a parish council). These presidents have municipal council standing and represent their constituencies in the assemblies of the Câmara Municipal. On the island of São Miguel there are 64 local area authorities, that include: