Geological wealth

Beyond Ortegal

The Cape Ortegal Geological Complex belongs to the geological area of Galicia Tras-Os-Montes, one of the geological sectors into which the Iberian Mazizo is divided. It comprises the north-southwest axis from Os Aguillóns point to San Sadurniño and the west-east axis from Pantín beach to Espasante.  The scientific relevance of this area has been known for almost fifty years, due to the presence of rocks that millions of years ago were in the upper mantle of the Earth, more than 70 kilometers deep.

The geopark project extends the enhancement of geological resources to other places of interest located outside the scientific delimitation of the complex. This is the case, for example, of the arsenic mineralizations of Meirás, the faults of Valdoviño and As Pontes-Pedroso, the granitic block of O Forgoselo -lower limit of the project-, or even the volcanism of the coast of Loiba.

Depending on their scientific interest, these sites may qualify as Sites of Geological Interest or, if they are very exclusive, as Global Geosites. Having one of these geosites is enough to obtain the geopark declaration. In our area we already have 6 and we may soon reach a total of 9.

To learn more

But… what are the conditions of the Cape Ortegal Geopark Project area, why is it so special, what do our rocks have to make it worth dedicating so much effort to promote a geopark?.

Let’s go by parts. Let’s imagine that the Earth is like a boiled egg where the shell would be the Earth’s crust or lithosphere -up to about 70 km deep on the continents and about 7 km deep on the ocean floor-, the shell would be the crust of the Earth. at the ocean floor-, the clear would be the mantle -from 70 to 2,890 kilometers deep- and the yolk would be the core, the center with liquid and solid part of the planet, about 3,481 kilometers in radius and extremely high temperatures.

Our planet is not a rigid ball, but each of its layers has different behaviors caused by pressure and materials in contact. Moreover, that shell is fragmented into plates that move driven by the immense energy generated by the molten magma inside the planet. They collide, rub against each other, some get under others… and the Earth, although we do not notice it -except for earthquakes and volcanoes-, is a place that is constantly changing due to the so-called “plate tectonics” that has been changing the appearance of the planet for millions of years.

The current lands of Ortegal were close to the Equator 340 million years ago (Source: Ancient Earth - http://www.ianww.com)

The geological uniqueness of the Cape Ortegal Geopark Project comes precisely from that transforming, slow and unstoppable movement of the Earth. A movement that left us on the surface rocks that are usually more than 70 kilometers deep. A gift for researchers, who in few places in the world can see with the naked eye what happened and still happens inside the globe.

This is due to the formation of the largest mountain range that has existed in the history of our planet, approximately 350 million years ago. A set of mountains higher even than the present Himalayas produced by the collision between two continents, Laurussia and Gondwana, which were initially separated by the Rheic Ocean and which would end up united in the supercontinent Pangea. This collision and its result are known in the world of geological science as the “Variscan Orogeny” which, among other things, resulted in the elevation in this area of materials from the upper mantle.

From the ocean in the middle of Laurussia and Gondwana -or from its depths- emerged most of the rocks that today make up the Cape Ortegal Geopark Project: peridotites, serpentinites -the “toelo”-, metavulcanites and metasediments. The geology of the area has been extensively studied in different investigations since the mid-twentieth century and all agree in assuring its exceptional scientific value.

A journey into the interior of the Earth

Here there are also amphibolites, granulites and gneisses, along with the largest and best outcrops of eclogites in the world, which are just that, rocks produced for a long time by high pressures -more than 10,000 atmospheres- and temperatures above 800 ºC. There are also beaches with black sands of non-volcanic origin -the one of Teixidelo, unique in the world- and others of reddish color due to their richness in garnet particles. 

We also have “speleothems“, which is the technical word to define accumulations of certain minerals inside caves or, as in the case of Cerdido and Moeche, the blue and green stalactites and stalagmites found inside the old copper mines.

Herbeira Massif, formed by rock types usually found in the Earth's mantle. In the image, the highest cliffs of continental Europe (615 m.).
Ortegal is rich in eclogites and one of the few places where they can be seen on the surface (Photo: eclogite outcrop crossed by a white feldspar vein).

In our area we also have faults that were very active until 20 million years ago, a relatively close time in the geological scale, and in short, in just over 600 km² of territory we witness one of the most exciting chapters in the history of the planet. 

To tell that story, or rather, those chapters of the Earth’s history, is what the UNESCO Geoparks aim to do, and for that very reason they must be different from each other in terms of the knowledge they make available to the public. In the case of the Cape Ortegal Geopark Project, the differentiation lies precisely in the appearance of mantle rocks on the surface, hence the motto “A journey into the interior of the Earth” has been chosen as the main theme of the project.

LIG and Geosites

The geology of the Cape Ortegal Geopark project is a real journey into the interior of our planet, with which you can discover and learn about the rocks that are in the innermost parts of the Earth, something exceptional that can be seen in very few places.
In the 80’s the Geological and Mining Institute of Spain (IGME) made an inventory of places of geological interest (LIG) with the idea of knowing and making known those areas with an outstanding geological heritage. At that time, two sites were catalogued, which were later expanded into three more within an international project to define Geosites, that is, enclaves of geological interest worldwide that the IGME chose as illustrative of the Iberian Variscan Orogeny, one of the 21 geological contexts of the State with international relevance. 
Recently the IGME was asked to include four other sites in the Global Geosites project, of which one has been accepted, so that the Cape Ortegal Geopark Project has 6 internationally outstanding geological sites, something extraordinary in such a small geographic space (remember that to qualify as a geopark it would be enough to have only one Geosite) and there is a possibility of reaching 9 in the near future.
On the occasion of the preparation of the Cape Ortegal Geopark Project, several inventories of outstanding points were made. The most recent one shows the presence of up to 108 Places of Geological Interest distributed throughout the territory. Their interest can be scientific, didactic or touristic, according to a series of valuation parameters.

Geological curiosities of Cape Ortegal Project

The geological richness of the project is concentrated in the coastal area, as this is where the results of the Variscan Orogeny and the rocks that emerged from the depths of the Earth almost 400 million years ago can be appreciated in greater detail. But scientific research has left us with a wealth of data that allows us to understand what we have under our feet in the area of the seven municipalities. And they are not exactly few things: 

  • Most of the Sierra de A Capelada was an ancientvolcanic island, similar to the current archipelago of Japan.
  • The Sierra de O Forgoselo was a large magma bubble that cooled 290 million years ago at a depth of over 15 kilometers.
  • The river valleys, the creeks and the dune systems are, chronologically, the most recent landscape elements that can be seen in this territory.
  • The rocks of the environment of the Cedeira estuary, part of Moeche, south of Ortigueira and the coastline between Ladrido and Espasante, formed part of the seabed more than 400 million years ago. In the latter locality, submarine volcanic lavas are preserved.
  • The copper that was exploited in the different mines of Cerdido and Moeche originated as a result of intense thermal activity on the seabed, where there were volcanic chimneys -called fumaroles- through which gases and minerals were released at high temperature and cooled on contact with water.
  • On the coastline of Valdoviño we find two outstanding scars in the terrain: theAs Pontes-Pedroso and Valdoviño faults, the latter more than 150 kilometers long and cutting Galicia in two.
  • Between Cerdido and Cariño there is an alignment of mountain ridges that reaches Os Aguillóns. This is due to the presence of the extremely hard and unique eclogites, which constitute here the largest outcrop known on Earth.
  • At the meeting of the Sierra de A Capelada with the Atlantic Ocean we find the third highest cliffs in Europe and the first in continental Europe, which began to form at the same time as the Alps and the Himalayas.
  • The Moeche Stone or “toelo” is a rare rock on the earth’s surface, since it is normally found at a depth of more than 70 kilometers. It enjoys great fame in the regions of Ferrolterra and Ortegal as constructive and ornamental material.
  • In the coastal Loiba there was an important volcanic activity of explosive and violent character. But there was also the trace of icebergs in the form of small boulders embedded in the rocks.

All this shows that this territory has a remarkable geology both at the level of the Iberian Peninsula and internationally, as well as a great potential in the field of geological tourism.

Teixidelo beach, the only one in the world with black sand of non-volcanic origin
Cape Ortegal and Os Aguillóns, a point that marks the geographical division between the Atlantic and the Cantabrian Sea.

A journey into the interior of the Earth

© Mancomunidade de Concellos da Comarca de Ferrol

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