Salt Caves


Salt caves are karst caves which are formed by the dissolution of salt by rain water. In other words, salt caves form inside salt deposits.


Salt in the chemical sense is an ionic compound of metals with non-metals. Another definition is an ionic compound that can be formed by the neutralization reaction of an acid and a base. The chemical group of salts is quite big and includes limestone and gypsum. But on this page we are talking about the salt in salt water, those ionic compounds which are easily dissolved by water and which you can get by evaporating seawater in a bowl. During Earth's history, many times geographic conditions existed which created huge depressions with sporadic inflow of seawater. The results are massive deposits of salt. The main mineral of the so-called "salt rocks" is the well known table salt which is used in the kitchen. The chemical name is sodium chloride (NaCl), as a mineral it is called halite. But the rock also contains various other salt varieties with similar chemical characteristics. Some are used as mineral fertilizer, others are unhealthy in higher doses.

As rainwater dissolves salt so easily, there should actually be millions of huge salt caves all over the world. But the reality is quite the opposite, there are only a few salt caves on earth in a few specific locations. The reason is the same: salt is dissolved so easily, any occurrence of salt gets washed away very fast. Much faster than the movements of the crust exposing the salt. Salt normally does not even reach the surface in areas with humid climates (high precipitation). The salt is dissolved by the groundwater which causes salt water springs. Man used such springs for thousands of years to produce salt.

The main prerequisite for the formation of salt caves is salt outcrops at the surface, which actually restricts them to arid (desert) climates. Even in arid climates with their low precipitation, there are some rare events with rain. At these events, the rain water forms huge and wild rivers running down the wadis, the desert valleys. This water forms solution caves in salt deposits. This process is so fast, salt caves change considerably with each rainfall. And despite the rareness of rainfalls, the life of salt caves is very short. The life of a salt cave may take several thousand years or only some years.

Salt caves - in contrary to gypsum caves - have speleothems. There are no dripstones as in limestone caves, but salt crystals formed by the evaporating of salt rich water at the end of the rain fall. Remaining puddles of water evaporate, the solution becomes supersaturated, and halites grow in multiple forms, but mostlly in cubic form.

There are three famous salt karst areas on the world, in Israel, Spain, and Iran:

  1. At the southern end of the Dead Sea in Israel, a place called Mt Sedom after the biblical town Sedom, is actually a mass of salt. It contains Malham Cave which was the longest salt cave of the world until 2006, and after further explorations it is again since 2019.
  2. The island Queshm in Hormus which belongs to Iran has a huge diapir with the Tri Nahacu Cave or 3n Cave. It was surveyed in 2006 and was the longest salt cave until 2019.
  3. Spain has many salt karst areas, some have caves, others just salt springs and sinkholes. A karstified salt outcrop in Cardona, the Cardona diapir, hosts salt caves whose genesis is related to flooding of mine galleries. The Cova dels Meandres de Sales is 4,300 m long and is the third-longest salt cave, other long caves are Sorbas Caves and Estremera Maze Cave. The deepest salt cave in Spain is El Sumidor Cave, VR=210 m.
  4. And finally there is a salt karst in Romania, which is artificial, as it developed in the salt bearing slag heaps of a salt mine. It hosts the Pestera 6S de la Mânzálesti, 3,100 m long and the fourth-longest salt cave. As it developed in the spoil heaps, it is extremely young, only a few decades. And in a humid climate, the cave development and the solution of the salt are extremely fast. So this cave might be gone in a few decades!


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