Monthly Geological Pics

FEBRUARY 17  - 
AJUY NATURAL MONUMENT - 
(FUERTEVENTURA, CANARY ISLANDS)

Although we have grown accustomed to the fact that the Canary Islands have always been there, 
only an hour later than the Iberian peninsula, the fact is that, 
in geological terms, its origin goes back only about 20 million years ago ... quite little, as a matter of fact. 

Aunque desde niños, nos hemos acostumbrado a que las Canarias siempre han estado ahí, solamente una hora más tarde que en la Península, lo cierto es que, en términos geológicos, su origen se remonta solamente a unos 20 millones de años… poca cosa, para entendernos.

The volcanism of the Canaries, as a propagation of a "hot spot" under the oceanic crust, has its origin in the most eastern islands, which share platform: Lanzarote and Fuerteventura, whose volcanism below sea level occurred during 50 million years, until 17 million years ago, the submarine volcanic building surfaced and there appeared what would be the islands themselves.

There have been several theories about the formation of the Canary Islands. The most recent Unifying Model (Anguita and Hernán, 2000) considers that the magma, originated in a hot spot of residual character, reaches the outside as a consequence of tectonic origin compression and distension movements. During the distension the crust is fractured and compression rises the blocks.

On the oldest "Basal Complex" of Fuerteventura (Left) , formed from the bottom of the ocean, three large stratovolcanoes grew: first the Central Building, then the Jandía Building in the south, and finally the North Building. These volcanoes would be very high, but due to problems of instability or great earthquakes, disappeared by sliding, their material accumulating in the bottom of the sea.

Natural monument of Puerto de La Peña (Ajuy - Fuerteventura)
Due to this cataclysm, the rocks of the Basal Complex were exposed, being possible its study and visit in the zone of Betancuria and Ajuy. The following geological units can be seen here.

Monumento natural de Puerto de La Peña (Ajuy – Fuerteventura)  - Debido a este cataclismo, las rocas del Complejo Basal quedaron al descubierto, siendo posible su estudio y visita en la zona de Betancuria y Ajuy.

1.- The Basal complex is formed by oceanic sediments, volcanic deposits and lava, traversed by intrusive dikes and plutonic rocks. The oldest rocks date from the Jurassic-Cretaceous period. They are the oldest rocks in the Canary islands.

2.- An old beach raised more than 14 meters above the present sea level. Its sediments contain fossils of 5 million years of age. (Left down)

3.- Pliocene basaltic pillow lavas are visible, which origin is a flow from Morro Valdés volcano in Betancuria. (Left up)

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4.- Recent alluvium consist of water transported rock fragments, from inland to the sea side. (Right)

5.- Pliocene dunes consist of calcarenites, formed by the fossil remains of shells and seaweed, indicators of the existence of a warmer climate.