Geology of Madeira

 

Basaltic Dikes of Madeira Island Mountains
© B&C

Discover Madeira's origins and the Archipelago vulcanic heritage treasures


Geology Tour

Archipelago of Madeira belonging to Portugal, is compound by Madeira, Desertas, Porto Santo, and Selvagens Islands. Biogeographical this archipelago together with Azores, Canary and Cape Verde form the region of Macaronesia in the North Atlantic.

quoting  Madeira is an archipelago of volcanic islands, which never had contact with the mainland.

The island of Madeira, a volcanic edifice with about 6 km high, that rising from the Madeira Abyssal in the intra-plate region of the African Tectonic Plate, is located in 500km south of Azores – Gibraltar Fracture and about 1600 km from Middle Atlantic Ridge.

The only exposed part of the Madeira Volcanic Mountain Chain, aligned by NE-SW direction, is compound by Madeira with Desertas and Porto Santo Islands. These islands and isolated submerse mountains, shall correspond to hotspot track and the movement of African plate toward NE. The beginning of the chain is dated with about 72 Ma and is located in Portugal mainland. The origin of Selvagens Island is related with the geologic formation of archipelago of Canaries.

quoting  The stratigraphy of Madeira is compound by three main stages dating from Miocene to the Quaternary: Lower Volcanic Complex (< 5,7 Ma), Intermediate Volcanic Complex (5,57 Ma-1,8 Ma) and Higher Volcanic Complex (1,8-0,007 Ma)  
Submarine Explosive Eruption - Porto Moniz, madeira island
Submarine Explosive Eruption, Porto Moniz
© B&C 

The lavas that forming this island, with more than 6Ma, are alkaline predominantly basalts and basanites, but also rare outcrops of intermediate rocks such as trachytes and mugearites. These rocks are very hard, heavy, compact, with very small grain size and rarely vascular structures, developed by cooling off slowly. The basalt are the main rock of this group compound by ferromagnesian minerals, such us olivine (green crystals), pyroxenes and amphiboles (black crystals), giving the dark colour usual of these rocks. Could be found also small crystals of plagioclases, giving a more or less grey colour to the rock, like trachytes.

quoting  Another common rock in Madeira is pyroclasts obtained from explosive eruptions.

Pyroclasts are softer rocks with lots of cavities, usually loose, and sometimes with a spongy structure. In Madeira, according the size and composition can be found tuff and breccias of bombs, block, lapilli and ashes, scoria and pumice, these last ones very vesiculated.

Geomorphology

Madeira Island Volcanic Rock Mountains Peaks
© B&C

Find unique biodiversity in Madeira Island highest mountains and peaks


Mountains and Peaks Tour

Volcanicity together with periods of tectonic uplift, tilting, erosion and sedimentation, origin the present island of Madeira. This edifice is a shield volcano with about 4000 meters submerse and 1862 meters in surface (highest peak of the island - Pico Ruivo) corresponding to 4,2 % of the volume of edifice.

Madeira it’s the biggest island of the archipelago with about 736 Km2, has an elongated form with 57 km direction E-W and about 23 Km by N-S.

quoting  Madeira is a fascinating mountainous island, dissected by steep and deep ravines and narrow valleys.

The inner of the island is compound by two Massive Volcanic Complexes, the Oriental one with the highest peaks of the island, as Pico Ruivo (1862 m), Pico das Torres (1851 m) and Pico do Arieiro (1818 m).

These mountains are the result of erosion of the rocks, mainly the softer pyroclastic rocks that surround vents and the intrusive basalt dykes. The swarm of dykes weather more slowly than pyroclastic rocks, forming a dense and spectacular network structure.

The Occidental one is compound by the biggest plateau of the island – Paul da Serra, with about 22 km2 on 1400m of the altitude, where the youngest eruptions of Madeira taken place. About the middle of these formations, Encumeada pass cuts giving origin to the valley of Ribeira Brava to south and the valley of São Vicente to north side of the island.

quoting  Morphologically the coastline of Madeira island, with exception of São Lourenço Peninsula, is in general steep, formed by tall sea cliffs specially in the western and northern coasts.
Onion Skin Weathering, São Lourenço peninsula Madeira Island
Onion Skin, São Lourenço © B&C
quoting  One of the highest sea cliff of the Europe is Cabo Girão with 633 m, located in southern of Madeira.

The northern coast is more rugged, because of the action of the trade winds that causes rapid retreat of the cliffs, induce to dismantling, sliding and accumulation of debris on the bottom of the cliff – fajã.

 

 

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