The sources of thermal water for Pamukkale are about 20 km from Denizli. The ancient city of Hierapolis is also located in the same place. The water comes from underground karstic caverns and creates the cascades through precipitation of CaCO3 (calcium bicarbonate ) as the CO2 (carbon dioxide) evaporates. Thermal spring water is beneficial for myocardium and cardiac complaints. The curative value of this thermal spring was understood in ancient times as well. It has been used for centuries. During the Roman Era religious ceremonies and festivals were held at the thermal pools, and important statesmen and rich people came to Hierapolis to be cured. Religious functionaries and ancient physicians administered healing. The spring waters are rich in calcium, magnesium sulfate, bicarbonate and carbon dioxide. They also have a radioactive content of 1,537 picocuries/liter. The pH is 6.0. more infowww.pamukkale.gov.tr
Travertine is a kind of rock which is formed as calcium bicarbonate precipitates out of hot spring water. It may be formed in many ways under different atmospheric conditions. Geological activity of the past affected a large area in which the Pamukkale thermal springs are found. There are 17 thermal sources in this special area with temperatures ranging between 35-100 BC. The source of Pamukkale is only one unit of that whole area. The thermal water flows to the top of the cascades by a 320-meter-long channel and then flows on the cascades about 240-300 m. CaCO3 begins to precipitate on the cascades as the carbon dioxide evaporates, but in the beginning the precipitate is soft like gel. It needs time to completely dry and harden. In order to protect the cascades from destruction and to preserve their natural beauty, entrance to the travertine area has been prohibited since 15 May 1997.