Cross section of a typical salt dome in Lower Saxony (after Bentz: "Erdöl und Tektonik in Nordwestdeutschland 1949). 

The thickness of a salt dome is up to 3000 m. As can be seen from the figure, the salt dome was formed by the uplift of a previously horizontal salt deposit. With the salt, the other sedimentary deposits above were also dragged up. Large caverns can be leached in the rock salt layers in these salt domes.