Azores - Geography
The Azores straddle the Mid-Atlantic Ridge. Historic eruptions have occurred on five islands during the past 500 years. Islands east of the Ridge, including Sao Miguel, are near the Azores fracture zone (called the Terceira Rift or Terceira Ridge by some workers), a seismically active spreading center near the triple junction of the African, Eurasian, and North American plates. The zone of plate divergence underlying the Azores archipelago changes to one of convergence· between the Azores and the Iberian Peninsula.
The Azores lie between 36°55' and 39°43 north latitude and 25° and 31°30' West longitude and are the only island chain in the mid-Atlantic. They are located some 2,000 miles east of Massachusetts, 700 miles off the coast of Portugal and 750 miles from Africa. Yhry are located in the North Atlantic Ocean about 2,200 miles east of New York City and approximately 850 miles west of Lisbon, Portugal. The total land area is 922 square miles or roughly equivalent to three-fourths the size of Rhode Island. The islands range in size from 297 square miles--Sao Miguel, to seven square miles--Corvo.
From Flores, the most westerly,island, the archipelago extends along a northwest-southeast line some 375 miles to Santa Maria, the most southeasterly island. Collectively known as the Azores. the chain actually consists of three groups of islands: Santa Maria and Sao Miguel - the most easterly pair; Terceira. Gracioga, Sao Jorge. Pico and Faial - the central group; and Cotvo and Flores - situated on the northwest peciphery of the archipelago.
The only beach is a short, sandy strip bordering Praia Bay about three miles from the field. Except for the towns and hamlets, the land is broken up into small plots of cultivated ground by stone fences and narrow, winding roads which crisscross the island. The hilly terrain is dominated by volcanic ranges which are covered with lush, green vegetation. Innumerable stone walls set off small farm plots throughout the island. The farmers clear their fields of volcanic rock, which is then used for building farm structures. The islands contain spectacular scenes of emerald green "carpets" draped over volcanic mountains, covered by a "net" of rock walls. Flowers are abundant, and the seascape is ever present. It is not uncommon for someone to be heard saying that Terceira bears a distinct resemblance to Ireland.
The Azores are spread out over a distance of 600 km in the middle of the Atlantic Ocean. Their climate is mainly oceanic with mild temperatures all year round and a high average rainfall. Being the wettest of the Macaronesian islands, they have an unusually high number of lakes, pools, temporary ponds and mountain streams. This abundance of water has also allowed for the formation of local mires and wet woods which do not exist on any of the other islands in the region.
The indented coastlines support a range of coastal habitats including rocky shores, saltmarshes, inlets, lagoons and vegetated sea cliffs. This latter is where many endemic species are found, such as the priority Azorina vidalii, a type of bellflower Campanulaceae. Other terrestrial habitats include ericaceous heaths, dry scrub, lava fields, rocky slopes and areas of laurel and juniper forest. Altogether there are 26 habitat types of the Habitats Directive in the Azores. Because of their relatively gentle relief and rich soils, many of the islands have been used extensively for agriculture and are now heavily deforested. As a consequence, only 2% of the original laurel forests remain.
The genesis of the Azores is found upon volcanoes, nine of which are still active. Underground, almost three hundred volcanic cavities, including caves, ravines and cracks, have been surveyed. The landscape is filled with dry calderas, craters lakes, fumaroles and thermal water springs. In the sea, there are submarine geothermal springs. The mountain of Pico, majestic and with an intact cone, appears to be protecting all this geological wealth. The volcanism of the archipelago impresses for its diversity and creates its own magnetism. It is a witness to the power of Nature, and the basis for very special experiences.
Three Quaternary trachytic stratovolcanoes - Sete Cidades, Agua de Pau, and Furnas - are located on the island of Sao Miguel, Azores. Mafic vent deposits and associated lava flows are between the stratovolcanoes and on their flanks. Each volcano consists of interbedded ankaramite, basanitoid, alkali olivine basalt, hawaiite, mugearite, and tristanite cones and flows, as well as trachyte domes, flows, and pyroclastic deposits. Detailed geologic mapping and new radiocarbon and K~Ar ages indicate that Furnas, constructed entirely within the past 100,000 years, is somewhat younger than the other two volcanoes.
All three volcanoes have calderas that formed in the late Pleistocene as a consequence of voluminous eruption of trachytic pyroclastic flows and fall deposits. The outer caldera of Agua de Pau volcano is the oldest (26,500-46,000 years). The progression then is from west to east: the caldera of Sete Cidades is about 22,000 years old, the inner caldera of Agua de Pau is about 15,000 years old, and the caldera of Furnas is about 12,000 years old.
Each volcano has erupted during the past 500 years. Holocene eruptions have been most frequent on Sete Cidades and Furnas. Future eruptions present significant risk because a large population (150,000) now inhabits Sao Miguel. Furnas is particularly dangerous, partly because it has erupted five times during the past 1,100 years, most recently in AD 1630.
Pico is a relatively recent volcano, and the largest in the central Atlantic, and as recently as the 18th century flank eruptions of lava flows were observed. High heat flow from fumaroles at its summit have been routinely observed (i.e., ~ 70 C), and evidence of a summit lava lake and scoria cone that must have formed in the past 1000 years is abundant. . Uncharacteristicly quiet during the past few decades, Pico last erupted in 1963. Pico makes up a significant portion of the island of Pico, and is reminiscent of the stratocones of the Pacific rim. However, Pico rises 7700 feet above sea level, and displays a summit region topographically more akin to an oceanic shield than to a pyroclastic stratocone.
In 1811 a new island was temporarily formed in the Azores group, off St Michael, by the throwing-up of ashes, and the formation of a cone about 300 feet high, with a crater in the centra This island, to which the name Sabrina was given, was soon washed away by the waves. And only a few years since, another submarine eruption in this neighborhood was indicated by earthquakes, jets of steam and columns of smoke, and floating masses of scorise.
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