tour guide
Ángel P Olivares Espinosa
16th April 2020

The UNESCO Basque Coast Geopark is a territory in the shires of Deba Barrena and Urola Kosta, which is very important in Europe and is due to many reasons. One of them is that this Geopark; which is conformed by the municipalities of Mutriku, Deba and Zumaia, it has a rock formation called Flysch.
These rocks contain millions of years of the Earth’s history, such as important information about unique past events that changed the course of the world’s biodiversity and climate forever.

Flysch at Itzurun beach

What is the importance of the flysch rock formations?

In addition to the beautiful scenery created by these rock formations, the cliffs are a scientifically important place. That is why a world institution like the UNESCO has named this territory as world heritage under the figure of a Geopark. This means, developing the territory in a sustainable way around the geological heritage.

The secret of this designation and the importance of the site lies within the rocks, but it is also the fact that they are very accessible and orderly.

There are many places in the world where you can find Flysch type rock formations and even other places where the rock layers are much older. The earth itself is circa 4.6 billion years old and here, in the Geopark, you can find rocks that are up to 300 million years old. Impressive, but comparatively, very young rocks.

However, like nowhere else in the world, here is a very accessible open book on earth’s history, which includes full chapters of this history.

Thus, on the coast you can find entire sections of about 14 kilometers wide that have 60 million years of history of the earth; almost page by page, year after year … That is something unique.

In Zumaia, for example and next to Itzurun beach, you can easily walk 16 million years of history and the most interesting thing is that within those rocks you can find important and unique information about past events that were recorded in these layers and that today they are used for defining the chapters of the history of our planet. For example, the extinction of dinosaurs!

Many geologists have scoured these cliffs to study and propose what the earth was like in the past, finding fossils, chemical molecules, and isotopes that would hint at past climates, but also mass extinctions.

That is why the Basque Coast Geopark and the Flysch rock formations that you can find here are so interesting and unique.

Flysch at Algorri rocky cove

What is a Flysch rock formation?

The Flysch rock formation is found in many parts of the world and in fact practically the entire Basque Coast. In general and also here in the Geopark, the Flysch is an intercalation of sedimentary rocks, and in this case: limestones, marls and sandstones mainly

Sedimentary rocks are one of three types of rocks you can find anywhere, and as the name implies, they are rocks made of sediment.

The interesting thing here is that you can find different sedimentary rocks interspersed and not a single rock and that’s it. This is because the variations in the climates and the environment were causing different sediments that accumulated one after another, during millions of years.

Limestone was originally and mainly many small shells and also some clay, the marls were basically the same, but with a higher proportion of clay rather than small shells and sandstones, as the name suggests, it was originally sand. What happened to them to move from sediment to rocks? well … time and pressure.

These sedimentary rocks alternate between softer layers of rock and harder layers of rock, creating an intercalation of beautiful colours and textures. That is the Flysch.

Flysch at Sakoneta

Why can we find these rocks here and now?

Now you know that these rocks were once sediments, but why do we see them here and now? The answer is incredibly interesting, especially if you consider that sand, clay, and small shells are closely related to the ocean.

Believe it or not, all of these cliffs that we can find in Mutriku, Deba and Zumaia were once the bottom of a shallow sea that accumulated tons of sediment and was then pushed upwards by the forces of the earth.

To understand this process, we must first review some concepts from the school.

Lithosphere and tectonic plates. You may remember that the earth is divided into three main layers, such as an orange, an apple, or whatever fruit your school teacher mentioned trying to explain these concepts. The earth has a core in the middle, a mantle that covers the core, and a crust that covers the mantle and the planet’s surface, the latter can also be called the lithosphere. A sphere of rock. The latter is like a multi-piece puzzle called continents or plates and they are floating on the mantle, crushing each other and constantly moving creating earthquakes and shaping the landscape.

So why can we find these rocks here and now?

More than a hundred million years ago (not that much), due to the movement of the continents and the tectonic plates, the Iberian Peninsula separated from Europe and where we now find the entire Basque Country and mountain ranges such as the Pyrenees there was a shallow ocean. For the bulk of millions of years after that happened, the accumulated sediment layers, as it happens today, rivers transport sediment to the ocean and also everything that lives there at some point dies and moves slowly towards the bottom of the ocean. But then things moved again, colliding the Iberian Peninsula with Europe, creating great pressure and lifting these rocks and creating the Pyrenees, which by the way are ancient coral reefs!

Time passed and these exposed rocks have been eroded by natural forces such as the ocean, wind and ice, but also carved and shaped by humans.

Would you like to know more and see these rocks up close?

Book an excursion with Basque Nomads!

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