Geology of the Island ofVolcanoes andLakes


The fascinating world of geology in São Miguel, Azores - the island that was once two

São Miguel Island is the largest island in the Azores archipelago and also the largest among the islands that belong to Portugal. The island has an area of 746.82 km² and, from a geometric perspective, roughly resembles a rectangular shape, with a maximum length of 62 km and a maximum width of 16 km. It is located at coordinates 37º 43' - 37º 55' North latitude and 25º 8' - 25º 52' West longitude from Greenwich, 57 miles north of the island of Santa Maria, with which it forms the Eastern Group of Islands.

Fondly nicknamed the "green island" due to the predominant color of its vegetation and extensive pasture areas, São Miguel is a testament to the power of nature in creating impressive and diverse environments.

The birth of Sao Miguel Island

Approximately 8 to 10 million years ago, volcanic activity began to occur in the Atlantic Ocean, leading to the eruption of a series of underwater volcanoes. Over time, these volcanoes grew and emerged above the surface, forming the islands of the Azores archipelago, including São Miguel Island.

Location of the main volcanic complexes in São Miguel Island

São Miguel Island was born and formed from east to west. The oldest part of the island is the area currently known as the northeast, which originated from the volcanoes of the Nordeste volcanic complex that emerged 4.1 million years ago, forming a small island in that location. Approximately 1.1 million years later, the Povoação volcanic complex added more land to the small primordial island.

It is approximately at the boundaries of the meeting of these two large volcanic complexes that the Serra da Tronqueira is located, where the Pico da Vara rises to a height of 1,105 meters, the highest point of the island. Both volcanic complexes are extinct, but their dimensions and existence have left impressive geological features and landscape marks.

The terrains in these areas include deep ravines, plateaus, high mountains, flowing streams, hills, and cliffs in a charming succession of landscapes. These are the areas of the island where vegetation is denser and better preserved.

Arnel Lighthouse - Northeastern Tip - São Miguel Island
Arnel Lighthouse - Northeastern Tip - São Miguel Island

 As the chain of major volcanic events that contributed to the formation of São Miguel Island continued, the emergence of the Furnas Volcano occurred approximately 800,000 years ago, followed by the Sete Cidades volcanic complex that emerged about 500,000 years ago, located in the extreme southwest of the island's current configuration.

Volcanic activity in Furnas - Thermal fields and fumaroles
Volcanic activity in Furnas - Thermal fields and fumaroles

 In terms of landscape and tourism, Furnas Volcano is known for its visible volcanic activity, including the lake that covers the crater depression where the famous "Cozidos das Furnas" (Furnas Stew) is cooked, as well as geysers, hot springs, and fumaroles along the lake's margin and within the village of Furnas, located in the heart of the valley with the same name, the volcano's caldera. The mineral and thermal waters, vegetation, and gardens in this area are also highly appreciated and characteristic of the region.

Suggestions for exploring the geology of São Miguel.

The Sete Cidades volcano, which also boasts lush vegetation, is an active volcano, although its volcanic activity is not as noticeable. The impressive size of the crater, filled with water and forming the famous Blue Lagoon and Green Lagoon, is the most prominent feature of the landscape and geology.

The scenic beauty of this area is so striking that it has become one of the most well-known tourist icons of the Azores. Contributing to this are, on one hand, the majestic lake, approximately 5 km in diameter, surrounded by picturesque settlements and encompassed by verdant hills called Cumeeiras. On the other hand, within the area of the ancient crater, there are two more lakes - Santiago Lake and Rasa Lake - adding to the stunning beauty of this region. The unique and idyllic landscape makes this area considered one of the most beautiful landscapes in the world.

Sete Cidades Volcanic Complex
Sete Cidades Volcanic Complex

The attentive reader who is familiar with the current geological characteristics of São Miguel island or has examined the above map may have noticed the absence of mention of a large volcano. In fact, the Água de Pau volcanic complex, located approximately in the center of the island, where the famous Lagoa do Fogo (Fire Lake) is located, is more recent than the other described volcanoes, having emerged about 250,000 years ago, and still exhibits evident volcanic activity.

Thermal waterfall of Caldeira Velha - Lagoa do Fogo
Thermal waterfall of Caldeira Velha - Lagoa do Fogo

This volcanic activity allows for tourist recreational activities, such as exploring the landscapes and hot springs, as well as the production of approximately 70% of the electricity consumed on the island.

The hot water waterfalls of Caldeira Velha, the thermal baths of Ribeira Grande, and Lagoa do Fogo, located at an altitude of 575m, are the most well-known tourist spots of this volcano. The Lagoa do Fogo is fed by 18 watercourses, surrounded by dense endemic vegetation, and is considered one of the must-visit tourist attractions on the island. Classified as a Natural Reserve in 1974, it is part of the Regional Network of Protected Areas and is also classified as a Site of Community Importance within the Natura 2000 network, as well as a Ramsar site.

Lagoa do Fogo
Lagoa do Fogo

It is interesting to note that for approximately half a million years, the current island was not a single island, but two separate land masses.

Between the southeastern edge of the caldera of the Sete Cidades Volcano and the western slope of the Água de Pau Volcano, there extends a 23 km wide strip of land that took shape due to the fissural volcanic system of the Picos, forming the Ponta Delgada Plateau.

This is the most recent geological area of the island and is responsible for closing the channel that previously existed between the volcanic complexes of Sete Cidades and Água de Pau. This occurred approximately 50,000 years ago.

Suggestions for exploring the geology of São Miguel.
Sistema fissural dos Picos
The fissure system of Picos

 The geological processes that have shaped the island over millennia, including volcanic eruptions, tectonic movements, and erosion of natural elements, have been responsible for creating the current configuration of São Miguel Island, which boasts around 500 volcanoes, five of which are still active. 

This treasure reveals the fascinating history of its formation over millions of years. Its breathtaking landscapes, rich biodiversity, and unique culture make it an unforgettable tourist destination.

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