Mendukilo Caves

GEOLOGY

How have they been formed?
What evidence is there of their creation?

The Mendukilo caves were formed due to the erosion of the limestone rock by which they are formed by CO2, which was dissolved in the ocean water that covered the area 140 million years ago. This happened due to the fact that 140 million years ago in the town of Astitz there was a tropical ocean of which remains are still found, such as certain coral reefs located inside the cave as well as some remains of mollusks and marine animals. that previously inhabited this ocean that was in Navarre.

A karst is produced by the indirect dissolution of calcium carbonate from limestone rocks due to the action of slightly acidic waters. Water becomes acidic when it becomes enriched in carbon dioxide, for example when it passes through soil, and reacts with carbonate, forming bicarbonate, which is soluble. The surface and underground waters dissolve the rock and create galleries and caves that, due to partial subsidence, form sinkholes and, due to total subsidence, form canyons. Many other karst forms, depending on whether they occur on the surface or are geomorphological that appear in underground cavities. (Karst is a slow dissolution process that takes millions of years to develop, every hundred years the advance in the rock is approximately 5 mm, abundant especially in limestone rocks but also in others such as evaporites, such as gypsum and salt or quartzites and dolomites.
This process goes through three main stages. The first is known as juvenile where the dissolution of the limestone massif occurs creating calcium bicarbonate, then surface and underground waters penetrate into the cracks of the rocks, and finally they dissolve little by little until creating caves or other characteristic forms of this relief.)

What endokarst forms are there?

In the Mendukilo cave there are different and very varied endokarstic forms, such as:

Chasms: Deep wells formed from a fissure or crevice in the ground, generally caused by a karst erosive process or collapse of the roof of a cave or lower gallery, through which the water seeps and generates the well.

Sump: it is a type of circular sinkhole that acts as a natural drain for rainwater or for rivers or streams.

Siphons: Place where a gallery descends below the water table (Water level in an aquifer).

Galleries: Duct connecting two or more adjoining rooms, generally narrower than one room and longer.

Rooms: Cavity inside a cave formed by the widening of the horizontal ducts of the cave.

Stalagmites: Endokarstic form formed by the decantation of solutions and the accumulation of calcium carbonate in the soil of a limestone cave.

Stalactites: Endokarstic form that hangs from the roof of a limestone rock cave and is formed by the accumulation of calcium carbonate forming a kind of fang.

Geodes: Rocky cavity, normally closed, covered with crystals and other mineral materials. It is not really a mineral but a composition of magmatic, crystalline and sedimentary formations

Calcite geode: Rocky cavity almost always closed, in which the minerals are crystallized

Columns: Union between a stalactite and a stalagmite that forms a structure that connects the roof to the cave floor, formed by solid sedimented materials.

Macaroni: Straight tubes that have an inner tube. They can reach meters in length and their growth can lead to a stalactite.

Pineapples: Bulbous stalactites that form when a stalactite grows partially submerged in water, creating a thickening by acquiring matter at the tip.

Anemolytes: Endokarstic forms similar to stalactites deformed by air currents that cause the stalactite not to grow straight but with a certain curvature.

Turnips/Udders/Beets: Endokarst form generated by the union of a shield with a stalactite.

Shields: Endokarstic forms formed from the ground by water flowing from a crack in calcite, adding fine layers of this material.

What other geological formations are there?

In the area where the Mendukilo Caves are located, there are also other important geological formations, which we will mention below.

Nacedero de Urederra:

The source of Urederra is a natural area of high environmental quality and with great accessibility that also has beech forests and blue waterfalls. From the source of Urederra the River Ega is born, which later descends down the mountain.

Sierra de Urbasa:

The Urbasa mountain range is a mountainous plateau located in the northwest of Navarra that presents an average altitude of about 1000 m above sea level. It is a great elevated plane in the mountain range of the Basque mountains.

What rocks are on the ground? How important?

The Mendukilo Caves are made up of a soil made of various materials that have allowed the cave to have been formed as it is today and to have acquired those characteristic endokarst forms. Among all these materials are the reef limestone rocks, accumulated in the Cretaceous (between 114 and 96 million years old), although the erosion of the first limestones began 140 million years ago.

In addition, the cave also has clay fillings between the limestone rocks, which allow the flow of water and the formation with the passage of time of different and highly varied endokarst forms.

Apart of these last two essential materials you can also find plaster inside the cave.

Ecosystems

Main biotic and abiotic factors of the ecosystem:

In the ecosystem of the Mendukilo caves we can find various biotic factors that modify the ecosystem in one way or another, such as all its flora and all its fauna. The modification produced by the flora in the cave can be a small accumulation of water, since the plants retain water, or simply a small change in the terrain due to the introduction of its roots and rhizomes into the limestone of its walls.

The fauna of the caves modifies the terrain through, for example, the feces of bats, its most well-known inhabitants, and through the deposition of corpses that are then used as nutrients by plants or simply by the ingestion of vegetables found inside Cave. All these factors modify the ecosystem and are carried out by living beings, so they are biotic factors of the ecosystem.

On the other hand, there are also a series of abiotic factors, as in any other ecosystem, such as the temperature at which the cave is located, which conditions the survival of certain species of animals and plants in its interior and that is 8ºC on average. In addition, it should be noted that the full predominance of darkness in this geographical feature prevents the abundance of plants, by preventing their basic survival function, photosynthesis. On the other hand, the earthly composition is the culprit for the endokarstic forms present in the cave, being predominantly limestone accompanied by clays and mostly gypsum. Fourth, the function of water in the cave is essential, since it is in charge of transporting the nutritive substances to the living beings inside the cave, the latter depending on their flow through the galleries. Here also other factors such as the climate (Humidity) and the acidity of the land among many others would be added.

What flora are there?

In the Mendukilo Cave there are various living beings inhabiting its interior, since like any other ecosystem it also has its living part, and in this section we are going to talk about its flora.

The Mendukilo Cave has various bacteria responsible for the decomposition of other living beings to feed themselves and that also serve as food for other living beings that inhabit the cave. On the other hand, it also highlights the presence of fungi, capable of surviving in very bad conditions, which help bacteria in their decomposition processes to feed themselves. Apart from this flora, which is the most abundant inside the cave due to the impossibility of survival of other species due to the inability to carry out photosynthesis in spaces without light, we can also see different mosses, algae, lichens and ferns in the outermost parts of the cave, where light is capable of reaching and where water is capable of transporting more nutrients.

What fauna are there?

The fauna that we can find in the Mendukilo Cave is quite varied, dividing the animals that we can find into trogloxenos, troglophiles and troglobes.

Trogloxenos: They inhabit caves occasionally.
Troglophiles: They live inside caves but can also live outside them.
Troglobes: They spend their entire lives inside the cave. They could not live outside due to the morphological adaptations of their bodies.

In the group of trogloxen we can distinguish different animals such as dormouse, foxes or some wild boar that can enter the cave at a given moment to take refuge.

In the group of troglophiles we find the “chiropterans”, commonly known as bats, which feed on different insects inside the cave and are capable of moving thanks to waves emitted by themselves that allow them to identify the entire geology inside the cave and somehow orient yourself. On the other hand, certain insects can also live in the cave that normally inhabit the outermost part of the cave, where there is still some light and they can orient themselves, or that enter in times of scarcity of food outside or for some reason. another external cause.

Third and last, in the section on troglobes we can find a large number of tiny bugs and insects, invertebrates, that live in the absolute darkness of the caves. They are blind, they are oriented with long antennae that capture chemical stimuli and have a transparent appearance, since they do not need pigments to give them color because they do not receive any solar radiation. Its menu is made up of organic substances carried by water and bat guano (feces). There are species of troglobes that are endemic, that is, they do not exist anywhere else in the world other than in the Mendukilo Cave, and they are also cave-dwelling species. One of these endemic species is the “Trichoniscoides govillari”, a type of troglobium discovered by one of the guides on the visit to the Mendukilo Cave.