Geology of the National Park
The Plitvice lakes National Park belongs to Dinaric karst area and due to its specific geology, geomorphology and hydrology it truly is one of the most impressive karst entities in the world. Apart from dolomitic rock, mesosoic limestones with dolomite inserts prevail. The ratio between less porous or water-retaining dolomites and porous Jurassic limestone sediments in the karst has influenced the landscape of the overall area today. Specific hydrology properties of rock have enabled water retention on Triassic dolomite rocks, as well as canyon formation by water cutting through Cretaceous limestone deposits. Tufa barriers are a phenomenon enabling water to remain inside the lakes.
Plitvice lake waters are supersaturated with dissolved calcium carbonate, in the form of calcium bicarbonate. As water is dispersed at a large scale at tufa barriers, it mineralises and calcium carbonate (calcite) is emitted in the form of tiny agglomerating crystals. The basic chemical formula for tufa sedimentation is the following:
Ca (HCO3)2+water dispersion → CO2+H2O+CaCO3↓ (tufa)
The invisible and at the same time essential element of this specific and complex tufa creation process are the so-called ‘blue-green algae’ (Cyanobacteria), eukaryotic algae (Diatomeae), various bacteria, Protozoa (single-cell organisms) and multi-cell microscopic organisms. These organisms represent a life community developing on rocks, plants (mosses) and submerged debris. Calcite micro-crystals are glued on mucopolysacharide mucus excreted by algae and bacteria. Crystals glued in such a way are crystal-forming agglomerate, around which calcium carbonate from water settles, helping the precipitation of well-known tufa barriers. The most prevalent moss, covering steep and vertical tufa barriers is Cratoneuron comutatum. This moss lithifies fast, and its contours remain well preserved in the tufa. At quieter places, a ‘Bryum pseudotriquetrum’ moss forms a Bryum-type tufa. The process of tufa formation dates far back into geologic history, to the conditions of warm and humid climate, similar to today. The age of active tufa barriers precipitation is estimated at 6.000 - 7.000 years, which corresponds to their formation after the latest ice age. Growth and development of tufa barriers is threatened if there are disturbances in physical, chemical and biological balance, important to the precipitation process.