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How it all began: travertine

After the karst, limestone rock rose up out of the ancient sea, flattening the surrounding lands and cutting a deep canyon, the Krka River waterfalls were formed,

thus creating the present day appearance of the river bed, and the characteristics of the living world. The waterfalls are the youngest formations in the canyon.

The travertine building process began in the Pleistocene, and has continued to the present day, with some interruptions. At the end of the last glacial age called Würm, the climate became warmer, water flow slowed and the conditions were created for the colonisation of algae, mosses and other organisms that take part in the travertine building process. In the Krka River Valley and its tributaries, the Pleistocene travertine is found up to 20 metres higher than today's riverbed, which tells us of the level at which the water flowed during that time. This travertine is called fossil travertine.

The majority of the travertine at the waterfalls is less than 10,000 years old. With the creation of travertine deposits in the post-Würm period, Skradinski buk, Roški slap and the other waterfalls began to rise up above the water level, creating Visovac Lake and other accumulations in the canyon sections of the present-day Krka River.

The travertine forms differ in their age. The youngest travertine formations are the thresholds that form under the water surface. There are also barriers, travertine curtains, cones and many other forms. In terms of the structure and size of travertine barriers, we know that the most travertine is deposited near the end of the river course, where the water flow rate was slower. Skradinski buk waterfall is the longest travertine barrier on the Krka River and in Europe.

Travertine is also called tufa. This is the name for calcium carbonate (limestone) that settles out of running waters onto various types of substrates. Travertine will settle only in waters that have sufficient quantities of dissolved calcium bicarbonate. The waters in karst are rich in this mineral, as karst landscapes are made up of limestone and associate rock, which together are called carbonate rocks. They are easily dissolved and create very strange forms, both on the surface and underground. In order for these chemical processes to unfold unhindered, temperature, water flow rate, pH value of the water, dissolved oxygen concentrations and the organic matter content in the water are also important variables.

The travertine building process requires travertine building organisms, which are aquatic algae and mosses upon which these minerals settle. Without them, the calcium carbonate would not be retained, as it would be washed downstream, especially in places where the water flows quickly, mostly at sites with an uneven river bottom. The slope and structure of the riverbed are not uniform at any of the waterfalls, meaning that today we can enjoy the uniqueness of each.

The travertine growth conditions are most favourable in the present day, and this process can be seen along the entire course of the river, with new travertine deposits being continually formed on the Krka River, which make new waterfalls. However, it should be stressed that travertine is highly sensitive to water pollution and increase concentrations of organic matter in the water. Therefore, our primary function is to preserve the travertine barriers as vulnerable parts of the natural system, and to ensure the water and surroundings areas are clean.