The Realmonte Salt Mine in Sicily

In the southern cost of Sicily, the largest island in the Mediterranean Sea, lies the town of Realmonte where there is a huge underground salt mine with tunnels that goes on for 25 km some 100 meters below the ground. The walls of the salt mine are naturally adorned with alternating bands of dark and light colored rocks arranged in concentric circles and stripes. These colored bands were formed approximately 5 million years ago by deposition of salt when seawater evaporated away leaving large quantities of dissolved salt as precipitate. During this period the Mediterranean Sea was undergoing a cycle of partly or nearly complete desiccation, which geologists call the Messinian Salinity Crisis. The precursor of the Strait of Gibraltar had closed tight and the Mediterranean Sea was blocked off from the Atlantic, resulting in the increase in salinity of the water. Because of the generally dry climate conditions, within a millennium the Mediterranean basin nearly completely dried out, forming a deep dry basin that reached 3 to 5 km below the world ocean level. Photo credit: Giuseppe Fallica/500px “The temperature at which a solution is evaporating can affect the type of salt which precipitates, meaning that a different type of salt is formed during the winter than during the summer,” explains The Earth Story . “Thus, the light and dark salts seen in the walls of the mine actually represent summer vs. winter deposits respectively. These seasonal cycles are known as varves in the geological world, and create fascinating patterns in many outcrops worldwide. Here, subsequent deformation of these varve deposits has resulted in the extraordinary outcrop seen in the photo above” In addition to its natural wonder, the Realmonte Salt Mine also contains a church embedded deep in the salt mine complete with altar, steps, frescos and crucifix all painstakingly carved out of the salt face by the mine workers.