Zumaia » Location » Natural surroundings » Cliffs and Coastal Erosion at Algorri



Cliffs from Algorri

The coastal strip of cliffs described begins in the western section of the town limits of Deba, and extends to the beach of Itzurun and Mariantón point, in Zumaia, at its eastern end. The rocky slopes are almost vertical in some sections and reach heights of up to 150 metres.

Geology



Debris from the cliffs

The materials found in this coastal section were formed between the Cretaceous period (around 100 million years ago) and the Tertiary Era (50 million years ago). At that time, the Guipuzcoan territory was submerged and subjected to marine sedimentation processes. The pressure and the temperature of the bottom of the sea shaped the rocks which, after being warped and lifted up, remained above sea level, exposed to the wind and waves which have formed the landscape since then, known as flysch.

The materials of the Lower Cretaceous, that appear between Deba and Aitzuri, are made up of sandstone, shale, limestone and marly limestone. From Aitzuri to Algorri the materials are of the Upper Cretaceous, marl and marlaceous lime. The last section, up to Mariantón point, is made up of marly limestone, limestones, marl, sandstone and shale from the Tertiary period. The fossils of ammonites and bivalves, among others, and the traces and prints of digging or perforation, are testament to there being living creatures, now trapped by time and rock. Each sediment layer, now vertical, is a page of an immense book that tells part of the fascinating history of life on Earth. Geologists and students from all over the world visit here to find out its secrets and try to understand mysteries such as the disappearance of numerous species that populated the planet some 65 million years ago.



Reddish sedimentation

Marine erosion in this area has been intense; during the seasons, above all in winter, the lower parts of the cliff are subjected to continuous and powerful onslaughts from the waves and wind, so little by little it is wearing away with the upper layers losing their support and collapsing towards the sea. The harder lithological layers are more resistant and form points or ends, and the most feeble ones are literally eaten by the sea, giving rise to large coves. This has allowed the sea to gain territory from the land throughout thousands of years, leaving evidence of the old mountain in the base, the so-called erosion platform or tidal erosion.

Small valleys lined by short streams, that long ago would have arrived gently to the sea, hanging there at more than 10 metres up, forming waterfalls or cascading down the cliff walls.

Flora and Fauna



Erosion platform

When describing the flora and the fauna of the area of Algorri, it is necessary to distinguish between two very different habitats: on the one hand, the walls of the cliff and on the other, the platform, subjected every day to the action of the tides.

In general, the rocky scree, with its steep slopes and crumbling material, does not allow the formation of soil. The force of the waves drags it in and frequently destroys the plants. Only in small cracks and shelves can a few plants adapt and settle down.

In the higher, less steep areas not so influenced by the tide, where the land allows a greater accumulation of soil, small areas of grass grow, sprinkled with plants typical of these coastal environments.



Spanish broom

In the upper part of cliffs, where the sea's influence is reduced and the soil more developed, scrubs of broom and heather (Erica vagans) settle, accompanied by holm oaks and small strawberry trees stunted by the pressure of the strong, salty winds arriving from the sea.

With regard to the flora of the erosion platform, seaweed is the most notable, followed by some tide-resistant lichen. Depending on the level of resistance of the seaweed on remaining exposed to the open air, they can form extensive belts at the different levels of the tide marks, or take refuge in pools.

The coastal flysch constitutes a quite inhospitable place for terrestrial birds. The steep slopes of the layers and their instability mean that birds are rarely seen on the cliffs. Also, few terrestrial birds venture into the erosion platform and, if they do, it is to feed in the multitude of pools that form in it.

However, for marine birds and some waders, the erosion platform has considerable value, offering them the sustenance that is difficult to obtain on the beaches. Here oystercatchers, turnstones, common sandpipers or phalaropes, take advantage of the resources offered by the breaking waves and pools.



Gull

The marine birds most inclined to approach this coastal zone are the divers, the cormorants, razorbills or guillemots, that during the winter pass over the coastal waters of the Cantabrian coast.

The fauna in the coastal erosion area is characterised by its diversity (more than 200 species of animals) and by the high population density of certain species, as well as for the presence of representatives of the majority of groups of marine invertebrates.



Sea fennel Rock samphire

Some filter feeding polychaetes form coral structures and, in the voids that are formed, a rich and varied fauna is found. The populations of molluscs, limpets, periwinkles and octopuses are numerous. In addition, due to its wide range of colours and beauty, one must draw attention to the nudibranches.

Crustaceans also constitute a good part of the inhabitants of the eroded zones at the foot of the cliff; shrimps are frequent, the porcelain crab, the velvet crabs, the aggressive "cangrejo moruno" (eriphia verrucosa), or the squat lobster. Several species of starfish and especially the common sea urchins are abundant in the tidal area and the pools. In some of these, up to 600 sea urchins per square metre can be counted.

Communities of tidal fish display a certain originality in relation to other zones of the Cantabrian coast. "Chafarrocas" (Cyclopterus lepadogaster), the small red scorpion fish, gobies and blennies are frequent inhabitants of the pools beneath the cliffs.