Flysch Rock Formation in Zumaia: Longest Continuous Rock Strata in the World

According to some geologists, the flysch formation in Zumaia can be dated back to around 100 million years.

The Earth's surface across the world holds intact several awe-inspiring and incredible natural features. Some like the rivers, gorges, mountain tops, waterfalls, or beaches, are more known than other landforms, which are actually equally magnificent. One such 'rarely-heard about' feature on the Earth's surface is the flysch rock formation. Have a look at what this 'flysch' formation is all about.

Flysch is basically a sedimentary rock deposition. Shale and sandstone conglomerate is interbedded, due to which the rock strata appears dark, with thin and thick layers of fine-grained clay material.

Flysch formations appear like parallel and slanted draped rock curtains. There are unevenly pointed cliffs, vertical walls of rock with alternate strata of sedimentary rocks forming a long landform on Zumaia's coasts.

These formations alongside the waters resemble long tracts of plowed farm land. It looks like nature has carved out narrow aisles on the beach surface leading to the waters. Just like its beauty of form, the geology of flysch deposits is worth a glance too.

Flysch rocks are believed to have existed since the mid-cretaceous period of geological history (somewhere between 145 to 66 million years ago).

The Swiss geologist Bernhard Studer introduced the term 'flysch' in 1827. It was named from the word 'fliessen' in German, meaning 'to flow', as he thought it was deposited by rivers. That flysch are a type of marine sedimentation, was known much later.

Flysch rocks are a marine facies (a specific rock type that has distinct characteristics, and has formed due to sedimentation). The flysch is usually a rock structure that is deposited in the foreland basin during the process of mountain formation.

A foreland basin refers to the basin that is created adjacent and parallel to a mountain belt. This foreland basin becomes shallower as orogenesis (mountain building) progresses.

The flysch deposits, also called molasse, consisting of shale, sandstone, and conglomerates (coarser fragments of broken rocks), are deposited in the initial phase of orogenesis itself. In Zumaia, geologists gave found fossils of ammonites (marine invertebrate animals) at the Itzurun beach.

Flysch rocks are known to be formed at the convergent plate boundaries. The Zumaia flysch formation has the convergent Iberian and Eurasian plates underneath it.

During tectonic movements, the crust gets forced and squeezed, leading to a landslide-like scenario. Huge amounts of deposits get arranged and sorted naturally, leaving the coarser rock at the bottom, and finer materials rising to surface.

Why these flysch depositions are tilted or angular is also answered by plate tectonics. During convergence, the plate movement causes immense destruction, resulting in thrusts, faults, folds, and tilting of the surface, so also of depositions.

This deformation has led to the tilting of some rock beds to almost slanting parallels. The characteristic long, narrow, and somewhat hollow or grove-like structure of the flysch is because of the different resistance put up by the interbedded rocks to sea waves, wind, and heat. The softer, fragile, and brittle of them weathered away easily.

Two beaches along the Basque coast, named Itzurun and Santiago, are the most visited locations in Zumaia. Interestingly, these beaches are a part of the longest set of continuous rock strata in this world. The flysch formations at the Itzurun beach extends to a length of around 8 km. This long stretch lies between the towns of Deba and Getaria, linking Zumaia in the center.

Another way to entertain yourself when in Zumaia is through activities like surfing, kayaking, and underwater fishing. A walk along these intricate looking rock cliffs is part of the famous 'Way of St. James' pilgrimage, or what is also called 'Camino de Santiago'.

Besides flysch rocks, the town has another significant geographical attribute. Urola and Narrondo are two rivers that come together in Zumaia. Also, the San Telmo Chapel is a very popular destination for tourists, as it offers a picturesque view of the flysch rocks from the top.