A unique geological heritage
In the world of evaporitic rocks, halite, also known as rock salt, is a rock in which karst phenomena develop with a speed several orders of magnitude greater than what we are used to.
However, its extreme solubility, which reaches approximately 360 grams per liter of water, makes these phenomena practically confined to arid climates.
Furthermore, halite banks, although present in large quantities in the earth’s crust, in most cases do not emerge, but are found buried even kilometers deep.
This makes salt caves a rather rare and uncommon phenomenon.
Fortunately, salt has a tendency to rise to the surface, mostly in the form of extrusions, which are large salt domes or columns, known as salt diapirs.
Around the world, it is possible to find a fair amount of these diapirs, like islands of salt of varying sizes.
Some of them are still affected by a push capable of generating real “fountains” and salt glaciers that flow slowly, such as the Namakier in Iran, while others are now immobile.
In Italy, in the context of the Messinian salinity crisis, in addition to the sequence of chalk banks, powerful halite banks were also generated.
Unfortunately, the latter lie buried deep and have only been reached by mining activity.
However, there is a fortunate exception in Calabria, in the Crotone basin, where within the well-known evaporitic series, there are several small salt diapirs that emerge on the surface, mainly in the territory of the municipality of Casabona.
The presence of these diapirs has been known in the bibliography since at least the 1960s and has been cited in several works on karst formation in chalks.
Recently, some research has addressed the characterization of the different facies present and the study of fluid inclusions in the crystals to reconstruct their original paleoclimatic conditions.
In the context of the national geological heritage, this is a practically unique case, and in fact the area has achieved a certain visibility in recent years as a geosite and geological tourism destination.
From a speleological point of view, however, the existence of caves in these formations is not documented in the bibliography.
Recently, a group of researchers made up of Andrea Benassi, Roberto Pettirossi and Mauro Masci went to the site to evaluate the potential of the area.
Their brief research focused on the four main points where the salt matrix emerges, partly protected by a thin breccia caprock and partly overlain by clays.
Here, they documented the existence of at least six caves including wells, resurgences and sinkholes that develop in the halite, for a total of approximately 200 meters in extension.
In the current state of knowledge, this is certainly the most important phenomenon present.
Locally known as the Caves of Mandria Vecchia, it was known by the inhabitants of Zinga from one entrance to the other for at least 60-70 years and was visited occasionally at least until 15-20 years ago, when some landslides made it difficult to access.
The solubility of salt makes halite speleothems something very ephemeral and changeable, but also fascinating in their shapes and types.
Alongside stalactites, crusts, rims, rafts and many other microcrystalline forms, several macrocrystalline speleothems based on cubic halite crystals are also on display in the explored caves, including a whole series of stalactites composed of a sequence of skeletal and euhedral crystals.
Given the extension of the diapirs, from an exploratory point of view it is difficult to imagine the presence of large underground systems.
At the same time, the documentation of these caves, even if of limited extension, undoubtedly adds value to the context and its uniqueness on the national territory.
We can also imagine interesting research and monitoring on the evolution of these phenomena over time, both with regards to the speleothem cycle and the morphological evolution of these small systems, which lend themselves well to becoming models to study.
Researchers will certainly return to Zinga’s diapirs, perhaps even in the company of those interested in documenting a different type of speleology than usual.
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