Salt Domes are the result of large deposits of salts laid down millions of years ago and subsequently covered by layers of sediment that in time became stratified rock. Over time the deposits push upwards, as they are usually less dense than the overlying rock, creating domes. Erosion of these domes can produce a feature that has the appearance of a series of concentric circles. These domes can be many kilometres in diameter and in Kazakhstan have been numbered at 1,200.
Salt domes have been recently put forward as an explanation for the circular waterways of Atlantis, as described by Plato. Ulf Richter has proposed(a) that if one such dome had originally been overlaid with strata of varying hardness the effects of erosion could have produced a number of concentric depressions that could have been adapted as canals. Richter provides a diagram demonstrating the process and gave the Richat Structure in Mauretania as a good example of the process.
*Richter outlined this in a paper presented to the 2005 Atlantis Conference [629.451].