tour guide
Ángel P Olivares Espinosa
7th November 2019

The UNESCO’s Basque Coast Geopark is an incredible territory in Europe and it is due to many reasons. One of the many reasons is that by the coast and specifically here in Zumaia, you can find the Flysch rock formation that holds millions of years of the earth’s history. But also, inside those rocks, there is important information about unique past events that changed the course of biodiversity and the world’s climate for ever.

What is a Flysch rock formation?

The flysch rock formation here in the Basque Geopark and in Zumaia is an intercalation of sedimentary rocks, in this case: limestones, marls and sandstones.

Sedimentary rocks are one of the three kinds of rock that you could find anywhere and as they name say, these are rocks made out of sediments.

Nonetheless, the interesting thing here is that you can find different sedimentary rocks, because they were originally different sediments accumulating one after another, for millions of years.

Limestone was originally sediments of clay and plenty of little shells, marls were basically the same but with a higher proportion of clay rather than little shells and sandstone as the name says, was originally sand. What happened to them in order to go from sediment to rocks? well… time and pressure.

These sediments, now being rocks, are alternated between softer layers of rocks and harder layers of rocks, creating an intercalation of beautiful colours and textures. That is the Flysch.
Flysch rock formation in Zumaia at the Basque Coast Geopark. this imagen was taken in Itzurun Beach, Zumaia, Gipuzkoa, Basque Country, Spain.Flysch rock formation in Zumaia at the Basque Coast Geopark. this imagen was taken in Itzurun Beach, Zumaia, Gipuzkoa, Basque Country, Spain.
Flysch rock formation in Zumaia at the Basque Coast Geopark

Why can we find these rocks here?

Now you know that once upon a time these rocks were sediment, but, why do we see them here now? The answer is incredibly interesting, specially if you consider that sand, clay and little shells are very related to the ocean…

Believe it or not, all these cliffs that we can find in Zumaia and the Basque Coast Geopark, once upon a time were the bottom of a shallow sea that accumulated tons of sediment and then was pushed up by the forces of the earth.

In order to understand this process we need to first revise a few concepts from school.

Lithosphere and Tectonic plates. Perhaps you remember that the earth is divided in three main layers, like and orange, apple or any fruit that your school teacher came up to that they he/she mentioned these concepts. The earth has a nucleus in the middle, a mantle covering the nucleus and a crust covering the mantle and the surface of the planet, this last one can also be called the lithosphere. An sphere of rock. This last one is like a puzzle of many pieces called continents or plates and are floating and drifting on top of the mantle, crushing between 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, because of the movement of the continents and tectonic plates, the Iberian peninsula was separated from Europe and where now we find the whole of the Basque country and mountain ranges like the Pyrenees there was a shallow ocean. During the coarse of millions of years after that happened, layers of sediment built up, just like nowadays happen, rivers carry sediment to the ocean and also everything that lives there at some point dies and slowly drift to the bottom of the ocean. But then things moved around again, crashing the nowadays Iberian peninsula with Europe, creating a hell lot of pressure and lifting these rocks and creating the Pyrenees, which by the way are ancient coral reefs!

Time went by and these exposed rocks have been eroded by natural forces like the ocean, the wind and the ice, but also, carved and shaped by humans.
Exposed flysch cliffs in Itzurun beach, Zumaia.

Why are the Flysch rock formations in Zumaia so important?

Apart from the beautiful scenery that this rock formations creates, the Flysch rock formations in Zumaia inside the Basque Coast Geopark are an incredibly important geological site. That’s why a worldwide institution like the UNESCO has named this territory as world heritage under the figure of a Geopark.

The secret for this designation and the importance of the site is inside the rocks but it is also the fact that they are all together here.

There are many places in the world where you can find Flysch rock formations and even other places where the layers of rocks are much older, but like no other place in the world, here you have a very accessible open book of the history of the earth, including full chapters of this book.

The earth itself is 4.6 billions years old and here at the Geopark you can find rocks that are up to 300 millions years old. Impressive, but comparably, very young rocks.

Nonetheless, by the coast you can find a whole sections of around 14 kilometres wide that has got 60 million years of the earth’s history; almost page by page, year by year… and that, is something unique.

Here in Zumaia, just by the beach you can easily walk 16 millions years of history and the very interesting thing too is that inside those rocks you can find important and unique information about past events that were recorded in these layers and that nowadays are used to define the chapters of the earth’s history. For example, the extinction of the dinosaurs!

Many geologists have walked these cliffs in order to study and propose what was the earth like in the past, finding fossils, chemical molecules and isotopes that would give clues of past climates, but also mass extinctions.

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

Would you like to know more and see these rocks by yourself?

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