The lakes of Plitvice are a result of century-old processes and the
sedimentation of
chalk, which is abundantly available in the waters of this karst area. These sedimentations are called
tufa or
travertine (both are called
sedra or
tuf in
Croatian, apart from many other names like
bigar or
vapneni mačak).
Alteration processes In geological terms, the actual phenomena molding the Plitvice Lakes are quite young. The complex processes of dissolution and sedimentation of limestone require specific climatic preconditions. These have only existed since the end of the ice age about 12,000 to 15,000 years ago, according to tufa
radiocarbon datings. The quantity of calcium hydrogencarbonate (calcium bicarbonate) dissolved in water depends on the quantity of dissolved carbon dioxide in the water. Generally, the following could be said: The colder the water, the higher the quantity of dissolved calcium hydrogencarbonate. Depending on the conditions for the alteration processes, scientists identified limestone dissolution rates of 0.01 to 4 millimeters a year (it is possible that by the effect of rainwater about 1 m3 of limestone is dissolved in about 10,000 years).
Preconditions for sedimentation river at the Lower Lakes Measurements of carbon dioxide quantities in the water show that they correspond with continuous sedimentation processes in the Plitvice Lakes area. Carbon dioxide quantities at the springs are about twenty times higher than in the atmosphere. The quantity of carbon dioxide decreases along the water route. The Plitvica river, for example, loses even up to 97% of its original quantity of carbon dioxide along its route. The area of a river, in which the formation of tufa occurs, is called precipitation area. Along the Korana river, for example, measured from its origins, tufa is being formed only along the first 10 to , even if according to pH measurements the conditions would be favorable further down the river. At the ground of Lake Kozjak a constant yearly sedimentation of 0,8 millimeters during the past 3,000 years has been ascertained. Yearly, the barriers are growing up to 13 millimeters in height. Tufa formation processes thus surpass erosion activities, which would destroy the sensitive barriers of the lakes. It is estimated that the tufa sedimentations at the ground of the lakes date back 6,000 or even 7,000 years. The precipitation of calcium carbonate, however, does not occur right at the springs of the rivers that flow into the Plitvice Lakes. For the precipitation of carbonate chalk (calcium carbonate) the water needs to reach a certain mineral saturation level. At the springs this saturation level is about 1. For the precipitation, the water saturation level needs to be higher than 3. At the same time, the pH value of the water needs to be above 8,0 (slightly alkaline).
Influence of vegetation Mosses, algae and water plants play a major role in forming the unique landscape of the Plitvice Lakes and its
tufa barriers. Up until the 21st century, it was supposed by scientists, including the botanist who initially argued for conservation efforts at Plitvice in 1926, that plants extract carbon dioxide from the water for photosynthesis purposes and that in return oxygen is released, thus resulting in the sedimentation of hydrogen carbonate
phytogenesis. Recent scientific evidence indicates that vegetation is not primarily responsible for the extraction of carbonate from the flowing water. However, plants indirectly contribute to
tufa formation. For sedimentation to occur it is essential that the water be decelerated, aerated and sprayed. The mosses of the Plitvice Lakes waterfalls provide a
substrate for sedimentation, generating travertine (
tufa). Depending on the species found locally, various biological types of
travertine can be differentiated.
Types of rock == Biodiversity ==