Sunday, 1 February 2009

Geological Origin and Volcanism

The island’s location is the Atlantic Ocean and its coordinates are 32°44′00″N 16°58′00″W/ 32.733333, -16.966667 and 32°44′00″N 16°58′00″W/32.733333, -16.966667.

Madeira and its sister islands (archipelagos) are actually just the peaks of an impressive mountain range rising thousands of meters from the ocean floor. Madeira Island was formed by a massive shield volcano, rising 6 km from off the Atlantic Ocean. The underwater mountain range is called Tore, which is on the African plate. Its rock age is 5 million years and its last eruption was 6,500 years ago, the volcano formed on top of an east-west rift in the oceanic crust. Construction of the bulk of the volcano began during the Miocene Epoch. This continued into the Pleistocene until 700,000 years ago. A study carried out in 1976 by the scientist Mitchell-Thome shows several distinct stages in the development of the archipelago, dividing its formation into four periods and structures. The fourth and final eruption was decisive in forming the current archipelago and its basalt-rich soil layers and the permanent geographical structure of Madeira was formed. After this there was extensive erosion producing two large amphitheaters open to south in the central part of the island. Later volcanic activity resumed, producing scoria cones and lava flows.


The island's highest peaks are the Pico Ruivo de Santana (1,861 m), Pico das Torres (1,851 m), Pico do Arieiro (1,818 m), Ruivo do Paúl (1,640 m) and the Bica de Cana (1,620 m).Also one third of the island is more than 1,000 metres above sea level and with its 580-metre steep vertical cliff, the Cabo Girão is one of the highest headlands in the world.!

Soil conditions.

On Madeira, volcanic soil is rich in basalt, lava, trachite, tuff, scoria and conglomerate. Over the centuries, these rocks eroded under the weather's influence. This is how clusters of weathering clay gradually emerged. The clay is rich in organic materials such as iron and magnesium, as well as phosphorus, yet poor in potassium. Seeds transported by the wind and birds were responsible for sowing on the island. The island is densely populated with forests. On Madeira, the rivers have a strong sloping gradient: up to 10%. Due to this difference in levels and the composition of the soil, Madeira has deep valleys and large basins eroded by water. The water falls on the island are fantastic. On the northern part of the island they can reach 100 meters deep.

Sao Vincent.

If you are really interested in volcanic activity, you can visit the caves at Sao Vincent on the north side of the island. The caves are not so interesting for sightseers as it is just a tour, and the caves are not very exciting. But in the caves plants grow, the seeds having crept through the volcanic rock. What really was breath taking is a virtual show before the walk through the caves during which you see a fantastically built earth’s crust (all done with mirrors and very convincing) and its volcanic activity. They show you in a lot of detail how the volcano formed the island, period by period. I was flabbergasted by this show and tried to get a film of it. No such luck, they are keeping it to themselves. If you do go to see the caves, and you are short of time, like I was, turning up too late, you should consider missing the caves and just seeing the show.


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