A unique nature of wonder looking like snow white cotton balls. Travertine terraces on the slope of the ancient city of Hierapolis were formed by thermal spring waters coming up onto surface. Forming only under the right set of conditions coming together Pamukkale Terraces date back to the quaternary period that is, several million years ago. Back then, a west-east fault line cut across the Cokelez Mountain a mountain of limestone. Today, at the point where waters emerge from the fault line, there is the Pool of Cleopatra. Tourists from all over the world look for treatment in its mineral-rich water.
The water flows through the skirt of the mountain, forming travertine terraces. 1 liter of the water at a temperature of 35°C (95 F) contains 2.2 grams of calcareous. 0.84 grams of it become travertine after precipitation. This means that for a flow rate of 40 m3 of water per minute, a total of 20 m3 travertine is deposited every day. But, for the formation of travertine, first of all, groundwater on its way to surface should absorb dissolved calcite (CaCO3) while flowing through lime stone and marble.
But, how? Let’s take a closer look. Surface water soaks into soil and reacts with carbon dioxide, creating carbonic acid which is geologically a significant corrosive. High pressure deep underground helps carbon dioxide maintain its dissolved form just like soda and its high-pressure can. Flowing through rocks, the groundwater with carbonic acid melts lime stone, producing calcium bicarbonate.
Again, just like the gas in soda can escapes when the can is opened, carbon dioxide in water escapes when the groundwater containing carbon bicarbonate reaches surface and pressure falls. After carbon dioxide escapes, calcium bicarbonate precipitates once again. The groundwater that creates dense and broad travertine is generally hot since the hotter the karstic water, the more the precipitation.
The color of travertine often depends on the chemical composition or pureness of the rocks the ground water flows through. There are a few regions where limestone or marbles are pure enough to produce snow white travertine just like in Pamukkale. There are some external factors, too, that affect the formation of travertine. The speed of precipitation is directly proportionate to the decrease in pressure, evaporation and the speed of carbon dioxide’s escape into air.
And since these are peculiar to warmer regions, travertine in such regions is formed near its source and on a large scale. The shape and physical characteristics of travertine are related to the speed of precipitation. When it’s faster, travertine becomes spongy and perishable. When it’s slower, travertine becomes dense. Structural properties of the ground where precipitation occurs also play an important role in formation of travertine. If spring waters flow on a flat surface and form a thin layer, pressure decrease, cooling, evaporation, and escape of Co2 will be faster. So is the precipitation. If the ground slopes down, the water’s flow will be rapid and mass.
In that case, precipitation will occur slowly and far from the source. Various speeds of precipitation have a direct effect on physical characteristics of travertine. When waters flow down a waterfall, the precipitation will be more and terraces will get broader in time. The depositions that are formed this way are called stalactites. Pamukkale displays perfect samples of travertine terraces and stalactites. As a result of this, Pamukkale Travertine Terraces are one of the unique wonders of nature.
Please note that Hierapolis is an ancient city called “Pamukkale” in Turkey and located on hot springs in classical Phrygia in southwestern Anatolia.