Halogens are the elements in the seventh main group of the periodic table. The term comes from the Greek and means salt former. Chlorine in particular occurs frequently in nature and forms the important common salt (NaCl). However, other salts are also frequently found, such as potash salts. Salts are found in the sea and are deposited as evaporites (through dehydration and precipitation) under special conditions. Salts also occur as sedimentary rocks. However, salt karst and salt caves are extremely rare. They are formed by the dissolution of salt by rainwater.
The common salts are directly soluble in water in large quantities. From this it is easy to deduce why salt karst is so rare: if salt reaches the area of meteoric water through geological processes, it is very quickly completely dissolved and transported away. Geological movements are usually very slow, whereas salt solution is very fast. This is why salt usually does not reach the earth's surface. In humid (moist) climate zones it is dissolved by the groundwater. It then reaches the earth's surface in brine springs. These have been used by humans for thousands of years to extract salt.
Salt on the earth's surface is therefore only possible in arid (desert) climate zones. Here it can happen that salt layers reach the earth's surface. In some areas, such as the Dead Sea, the formation of huge salt sediments can even occur. But even in these dry climates, precipitation is very rare. During these exceptional events, torrential rivers and mudflows form, which flow down the wadis at high speed. This precipitation causes the salt to dissolve and the formation of karst and karst caves.
Despite the rare rainfall, the life of the salt caves is extremely limited. Apart from the extremely high solubility, this is also due to the lower stability of the salt against sedimentary rocks and the plasticity of the salt. Under high pressure salt can flow very slowly. At the earth's surface, air humidity is sufficient to allow salt to be rearranged, which causes the caves to grow very quickly leaves.
There are two fairly well known salt karst areas on earth. The first is in Sedom in Israel, south of the Dead Sea. Sedom is often thought to be the site of Sodom from the Bible, but there is no archaeological evidence of this. The second salt karst is located in eastern Spain. It is very small in area and is strongly influenced by human mining activity.