Dasht-e Kavir, also known the Great Salt Desert, is a large desert lying in the middle of the Iranian plateau, about 300 kilometers east-southeast of Tehran. The desert is about 800 kilometers long and 320 kilometers wide, and composed of mud and salt marshes (kavirs). Tens of millions of years ago, this region was occupied by a salt-rich ocean that surround a small piece of continent in what is now central Iran. As the ocean dried up, it left behind a layer of salt as much as 6 to 7 kilometers thick.

Over time, the layer of salt was buried under a thick layer of mud. But salt has a fairly low density — lower than the layer of mud and rocks underneath which the salt layer lay. So it started pushing up through the overlying sediment and eventually, over millions of years, the salt broke through and formed domes. The salt domes of Dasht-e Kavir are probably some of the best examples of this geological phenomenon.

Photo credit: George Steinmetz