The Caves of Artá are not simply a tourist attraction. This underground landscape is the result of the long and complex geological history that has modelled them over time. The cave is situated in limestone rock (mostly comprising calcium carbonate, CaCO3) which was deposited on the ancient seabed during the Jurassic period 200 - 150 million years ago. The rocks contain the remains of shells and skeletons of the organisms that inhabited these seas.
Over time, around 15 million years ago, these marine sediments rose to the surface where they formed the large mountain ranges of the Alps and the Pyrenees. At that time, as a result of the collision between the African and European continents, these marine rocks were raised, deformed and fractured due to enormous geological forces. Hence, the compacted limestone rock has been compartmentalised by a multitude of fractures and discontinuities which has allowed the penetration of water filtering through.
These rock fractures are visible on the roof of the cave where you can see that the stalactites have grown in a line following the discontinuities of the Jurassic rock material.
This is a natural cave formed by dissolving limestone rock caused by the underground waters. These phenomena are due to the presence of carbon dioxide (CO2) which gives a slightly acidic character to the waters that infiltrate the mountains. The above limestone dissolving processes are what geologists call Karst modelling (or simply karst), a name which derives from the Karst region in Slovenia where, in past centuries, these processes were researched for the first time.
These underground waters flow over impermeable beds and slowly erode away the top clayey layers until they finally collapse, leaving a hollow covered by other limestone layers which remain in place because to their arched shape. The water that flows over the arch is loaded with calcium bicarbonate and it slowly filters through the small cracks to produce the following phenomena:
- As the droplets of water appear on the roof of the cave due to the loosening of the excess carbonic acid, they deposit the dissolved limestone matter around them. This gradually forms the stalactite.
- When the drops fall, the calcium bicarbonate is preserved and, in turn, is deposited on the ground to form the stalagmite.
- With the passage of time, these two actions combine to form a column of luxurious and wonderful shapes.
The dissolving of the rock by underground waters in the presence of carbon dioxide (CO2) is the process that has led to the formation of the cave (Karstic modelling). This same chemical process is responsible for the cave’s exuberant natural decor (stalagmites, stalactites, etc.) due to the fact that this chemical reaction is reversible, meaning it can go in one direction or the other. So, the same calcium carbonate that has been dissolved by the infiltration of water is deposited inside the cave when the chemical reaction is reversed.
This is how spectacular limestone deposits are formed, such as the well-known stalagmites (that grow on the ground), stalactites (that hang from the ceiling), columns (joining of stalactites and stalagmites), flowstones (layers of limestone that have developed on walls and/or floors), and the hangings or flags (that create twisted shapes that hang from the ceiling). All these precipitated limestone rocks are known by geologists as speleothems. All these speleothems, that we could define as classics, grow following vertical paths imposed by the force of gravity, which controls the dripping and flow of the filtering water.
It is also worth noting a speleothem that is quite rare within the Earth's Karst caves. These are called discs or shields (circular sloping surfaces) and they are plentiful in the Caves of Artá, reaching some truly spectacular sizes. Some examples can be seen in the vicinity of the Queen of Columns, as well as in the Theatre and Hall of Flags.
Equally, the bulb-like crystalline overgrowths are of great interest. They can be seen in some of the halls, such as Purgatory, where you can find the formation known as the Baptistery, or the sector comprising the Theatre and the entrance to the Hall of Flags. These speleothems feature horizontal lines corresponding to episodes of phreatic flooding of the cave, which occurred during phases of high sea levels that took place throughout the Upper Miocene and Pliocene periods, between 3 and 6 million years ago.
Visitors often ask about the growth rate for these speleothems. This is an aspect about which it is hard to generalise although, in general, they usually grow at a rate of less than a few millimetres per millennium. However, no significant formations can be seen in the Artá caves which are still in the growth stage. In contrast, the deposits are quite ancient and inactive. They were formed at least in the Lower Pleistocene period or in the Pliocene period, and in some cases in the Upper Miocene period. This is the case for some examples that can be found coated by the above mentioned phreatic precipitated limestone.
In conclusion, there are many physical and chemical factors that influence the formation of speleothems. The most important factors include pluviometry (abundance or lack of rain), temperature, concentration of CO2 in the cave's atmosphere, etc. These factors control both the scale of the ornamentation of the speleothems and the speed at which they form.
Although the age of the rock is between 175-150 million years old, the formation of the cave is a much more recent phenomenon, occurring in the last 15 million years. From that date, when Mallorca’s mountains were already formed, the rain waters started to form a series of underground hollows and conduits due to the dissolution of the limestone rock.
In the lower Pliocene period, 5 million years ago, the cave was already formed and decorated by an abundance of speleothems. Later, in the mid Pliocene period, between 4 and 3 million years ago, the cave was flooded due to successive rising sea levels, which caused the bulbous phreatic speleothems present within the cavity.
During the Pleistocene period, which is the last 2.6 million years, the cave took on its present form with the opening of the spectacular entrance on the cliffs of Cap Vermell.
In September 2019 Cuevas de Artà made headlines for the study published in the prestigious journal Nature, it was carried out by an international team of researchers that includes members of the University of the Balearic Islands (UIB), the University of New Mexico and Columbia University.
Analysis of a series of deposits found inside these spectacular geological formations shows that 3.3 million years ago the sea level was sixteen meters higher than it is now. And the temperature then was only two to three degrees warmer than in the pre-industrial era, when changes in temperature were not yet influenced by human beings.
Knowing the climates of the past provides valuable information to develop prediction models that help to make projections of the future with a lower degree of uncertainty.
See article
"Joan J. Fornós y Joaquín Ginés, de la Universidad de las Islas Baleares y Societat Espeleològica Balear, y al fotógrafo Miquel Àngel Gual, de la Societat Espeleològica Balear y Societat d'Història Natural de les Balears."