Monday, November 3, 2014

Madeira Island

Executive summary by darmansjah

The island of Madeira is at the top of a massive shield volcano that rises about 6 km (3.7 mi) from the floor of the Atlantic Ocean, on the Tore underwater mountain range. The volcano formed atop an east-west rift in the oceanic crust along the African Plate, beginning during the Miocene epoch over 5 million years ago, continuing into the Pleistocene until about 700,000 years ago. This was followed by extensive erosion, producing two large amphitheatres open to south in the central part of the island. Volcanic activity later resumed, producing scoria cones and lava flows atop the older eroded shield. The most recent volcanic eruptions were on the west-central part of the island only 6,500 years ago, creating more cinder cones and lava flows.

Madeira Island represents 93% of the archipelago's area, with 90% of the landmass above 500 m. It is the largest island of the group with an area of 741 km2 (286 sq mi), a length of 57 km (35 mi) (from Ponte de São Lourenço to Ponte do Pargo), while approximately 22 km (14 mi) at its widest point (from Ponte da Cruz to Ponte São Jorge), with a coastline of 150 km (93.21 mi). It has a mountain ridge that extends along the centre of the island, reaching 1862 meters (6,107 ft) at its highest point (Pico Ruivo), while much lower (below 200 meters) along its eastern extent. The primitive volcanic foci responsible for the central mountainous area, consisted of the peaks: Ruivo (1862 meter), Torres (1851 meter), Areeiro (1818 meter), Cidrão (1802 meter), Cedro (1759 meter), Casado (1725 meter), Grande (1657 meter), Ferreiro (1582 meter). At the end of this eruptive phase, an island circled by reefs was formed, its marine vestiges are evident in a calcareous layer in the area of Lameiros, in São Vicente (which was later explored for calcium oxide production). Sea cliffs, such as Cabo Girão, valleys and ravines extend from this central spine, making the interior generally inaccessible. Daily life has concentrated in the many villages at the mouths of the ravines, through which the heavy rains of autumn and winter usually travel to the sea. A long, narrow, and comparatively low rocky promontory forms (Paul da Serra) the western extremity of the island, on which lies a tract of calcareous sand known (1300-1500 meter). It is a fossil bed, that contains shells and numerous bodies resembling the roots of trees, probably produced by infiltration.

The island was formed from a base volcanic complex, forming to two massifs:

The Base Volcanic Complex was formed during the Miocene period from submarine and sub-aerial eruptions in the central part of the island, and is associated with some of the deeper valleys (São Vicente, Boaventura, Socorridos). The complex extends to the east into the (Porto da Cruz and Machico) ravines until Ponta de São Lourenço and consists of accumulated block pyroclasts, lapilli and ash, layered with basaltic lava. The volcanic material is essentially effusive, of non-viscous compact basalts; the lava formed flows that were not dense which covered the topography and substrata. These first flows were extensive, occupying a large part of the plateau, filling many of the valleys and ending at the sea. More recent episodes were confined into the valley of the São Vicente, Seixal and Porto Moniz ravines. The basaltic flows correspond to the last period of volcanic activity on Madeira (around 500,000-200,000 of years). The flows were boxed into the valleys, and fossilised, sometimes, such as in the valley of São Vicente, forming morphological terraces. The island is covered in faults, and easily identifiable in the area around Ribeira Brava, near Encumeada. The spatial distribution of these faults is varied and their align is also diverse, although it is common to encounter some faults from west-northwest to east-south-southeast to northwest to southeast (coincident with the direction of some volcanic cones). Between many of pyroclastic cliffs, there exists a great variability in materials, from large blocks to fine ash, and an intermediary layer referred to locally as feijoco, or lapilli, of a consistency that is more porous. The material is normally dark to black rocks, yellow and reddish materials, and is used in some construction for their refractive characteristics (as well as used in the construction of blast ovens).

The Central Massif which occupies the central region of the island, consists of explosive material (large blocks, lapilli and ash) and deposited chaotically around volcanic centres of the eruptions, but today mostly hidden and unrecognisable. This massif is crossed by several dense faults, basaltic and trachyte, oriented in many directions, converging on Pico Ruivo. The peak which includes many dykes, has resisted erosion, in contrast to many of the surrounding deposits; the weak cohesion of pyroclastic materials permitted the easy carving of the terrain in this area, constituting the morphology of many of the ravines: Brava, Socorridos, Machico, São Vicente, Porco (Boaventura) and Faial.

The Paul da Serra Massif corresponds to a similar structural platform of basaltic flows oriented towards the southwest.

Madeira has been classified as a Mediterranean climate (Köppen climate classification: Csa/Csb), but based on differences in sun exposure, humidity, and annual mean temperature there are clear variations between north- and south-facing regions, as well as between some islands. Other microclimates are expected to exist, from the constantly humid wettest points of the mountains, to the desert and arid Selvagens islands. The islands are strongly influenced by the Gulf Stream and Canary Current, giving mild year-round temperatures; according to the Instituto de Meteorologia or IM the average annual temperature at Funchal weather station is 19.6 °C (67.3 °F) for the 1980-2010 period. For the 1960-1990 period, IM published an article, showing that some regions in the South Coastline surpass 20 °C (68 °F) in annual average. Porto Santo has at least one weather station with a semiarid climate.

Drought conditions coupled with hot and windy weather in summer have caused numerous wildfires in recent years. The largest of the fires in August, 2010 burned through 95 percent of the Funchal Ecological Park, a 1,000-hectare preserve set aside to restore native vegetation to the island. In July, 2012 Madeira was suffering from severe drought and wildfires began burning on July 18, in the midst of temperatures up to 40 degrees Celsius (more than 100 degrees Fahrenheit) and high winds. By July 20, fires had spread to the nearby island of Porto Santo, and firefighters were sent from mainland Portugal to contain the multiple blazes.
In August, 2013 a hospital and some homes were evacuated as a wildfire approached Funchal. A number of homes were destroyed when the fire hit Monte, a suburb of Funchal.

The Macaronesia region harbours an important floral diversity. In fact, the archipelago's forest composition and maturity are quite similar to the forests found in the Tertiary period that covered Southern Europe and Northern Africa millions of years ago. The great biodiversity of Madeira is phytogeographically linked to the Mediterranean region, Africa, America and Australia, and interest in this phytogeography has been increasing in recent years due to the discovery of some epiphytic bryophyte species with non-adjacent distribution.

Madeira also has many endemic species of fauna – mostly invertebrates which include the extremely rare Madeiran Large White but also some vertebrates such as the native bat, some lizards species, and some birds as already mentioned. The biggest tarantula of Europe is found on Desertas islands of Madeira and can be as wide as a man's hand. These islands have more than 250 species of land molluscs (snails and slugs), some with very unusual shell shape and colours, most of which are endemic and vulnerable.

Madeira has three endemic bird species: Zino's Petrel, the Trocaz Pigeon and the Madeira Firecrest, while the Madeiran Chaffinch is an endemic subspecies. It is also important for breeding seabirds, including the Madeiran Storm-petrel, North Atlantic Little Shearwater and Cory's Shearwater.

In the south, there is very little left of the indigenous subtropical rainforest which once covered the whole island (the original settlers set fire to the island to clear the land for farming) and gave it the name it now bears (Madeira means "wood" in Portuguese). However, in the north, the valleys contain native trees of fine growth. These "laurisilva" forests, called lauraceas madeirense, notably the forests on the northern slopes of Madeira Island, are designated as a World Heritage Site by UNESCO. The critically endangered vine Jasminum azoricum is one of the plant species that is endemic to Madeira.

No comments:

Post a Comment