The Azores volcanology. Part 1

The Azores archipelago (Wikimedia Commons)

The Azores Islands

The Azores is an autonomous region of Portugal, situated in the Atlantic Ocean 1500 km west of Lisbon. It’s an archipelago of nine islands, scattered over 600 km.

The Azores settlements began first on two eastern islands, Santa Maria and São Miguel (grupo oriental) in 1439 and then on Terceira in 1450, on Pico and Faial in 1466, on Garciosa and Sao Jorge (grupo central) in 1480, and on Flores and Corvo (grupo ocidental) at the start of the next century. Historical records of eruptions therefore extend back only between 500 and  600 years, but over 30 eruptions have taken place during this period, either on the islands or off shore.

All the islands are active except Santa Maria, which is the farthest from the Ridge. Fumaroles are their only persistent manifestation. They make their best displays in the Caldeira das Furnas in São Miguel. Weak fumes usually issue from the summit of Pico do Pico, and the earthquake in May 1958 briefly revived those in the caldera of Faial.

All except Sao Jorge has been stratovolcanoes and all except one have been decapitated by calderas. Pico do Pico soaring to 2351 m above sea level, is the only stratovolcano which still exists on Azores archipelago.

Mount Pico or Ponta de Pico. Photo by Marco Derksen (CC-NC).

The Azores and their submarine plinth grew up on the Mid-Atlantic Ridge near the triple juction of the north American, Eurasian and African plates. Their activity is probably related to a hotspot “The volcanic activity in the Azores was  most probably also intensified by one large, or several small, hotspot plumes [Feraud et al. 1980]” and perhaps also to a secondary band of seafloor spreading. Whatever the reasons behind the growth of the Azores, all display a common and impressive predominance of stratovolcanoes, rifts, faults, fissures and volcanic alignments, running parallel to the spreading axis, that have been the leitmotifs in the development of their scenery. Magmatic emission in the archipelago are much less frequent; the last formed Capelinhos in Faial in 1957-8, although other eruptions have since occurred below sea level.

The Azores are young. The eastern group contains the oldest rock, which reach about 5 million years old in Santa Maria and 4 million years old in eastern São Miguel. No lavas on any of the remaining islands are apparently more than a millions years old. The oldest rock commonly outcrop in the southeast of each island, and the more recent eruptions have tended to occur in the northwest, nearest the Mid-Atlantic Ridge.

Nevertheless, there was no regular progression of eruptions from island to island towards this ridge. Thus, for instance, Faial, in the west, and São Miguel, in the east, both have some of the oldest and some of the youngest lavas in the archipelago.

The eruptions in the Azores produced a predominance of alkali basalts, hawaiites and mugearites, but some evolution to trachytes and pantellerites was associated with the violent explosions that formed the calderas. The basaltic rocks, commonly erupted from fissures, formed many cinder cones and lava flows, and Surtseyan eruptions took place where these fissures extended into shallow water.

This photo was taken by friends of Renato Rio and sent to Spica by him. This is a German article from Wikipedia explaining the rocks on the photos:
http://de.wikipedia.org/wiki/Ilhéus_dos_Mosteiros

ilel100

Sources:
Volcanoes of Europe. ISBN 1-903544-03-3 (Alwyn Scarth, Jean-Claude Tanguy)
Self 1976
Ridley et al. 1974
Moore 1991
McKenzie 1972
Laughton & Whitmarsh 1974
Weijermars 1987
Krause & Watkins 1970
Searle 1980
Feraud et al. 1980
Abdel-Monem et al.1975
Booth & Croasdale 1978

Riddles

Once again there is 3 volcanoes, one famous volcanologist and a volcanologic term to be found. In the lead it is very tight with Sissel grabbing a 1 point lead before Evan Chugg.

1. Ultimate dragon with the heart of a + image – Katla the Dragon from Astrid Lindgrens book Brothers Lionheart (Dinojura44, 2pt) Sidenot, the Lion on the image has the same hairdo as the author had.
2. From Gubbio to Eyfjallajökull while watching Dante’s Peak – Erik Sturkell, papers on Eyjafjallajökull and Gubbio, favourite movie is Dante’s Peak (Dorkviking, 2pt)
3. In this abode I rest – Magma reservoir (chamber) – (Sissel, 2pt)
4. Symmetrical (Italian) dessert next to infamous apple – Paranicota near Pomerape (Evan Chugg, 1pt)
5. Take your sails down, you are at home – Home Reef in Tonga (Edward, 2pt)

Score board
6 Sissel 5 Evan Chugg 4 Pyter 4 Cryphia	3 Dorkviking 3 Matt 2 Edward 2 Inannamoon	2 Kelda 2 Lughduniense 2 UKViggen 1 KarenZ

Advertisement