Underground storage caverns are cavities in sufficiently thick salt formations (salt layers or salt domes). They are created by drilling a hole, sometimes to a depth of up to 2,000 m, and subsequent solution mining: Water introduced through pipes dissolves the salt, gradually creating a cavity – the cavern. The cavern can reach a height of 300 to 500 m and 50 to 100 m in diameter; volumes range from 500,000 to 800,000 m³.
The specific properties of salt make caverns very tight and stable. Therefore they are ideal for storing gaseous and liquid substances: Carbon compounds such as natural gas, crude oil and its products (fuels, liquefied petroleum gas), as well as
hydrogen or compressed air.