page_title: Plitvice Lakes National Park
section_title: Thresholds become barriers
hierarchical_section_title: Plitvice Lakes National Park / The dissolution and creation of rock / Sedimentation processes / Thresholds become barriers
caption_attribution_description: Hrvatski: Nacionalni park Plitvička jezera, Hrvatska. English: Plitvice Lakes National Park, Croatia Deutsch: Nationalpark Plitvicer Seen, Kroatien
context_page_description: Plitvice Lakes National Park is one of the oldest and largest national parks in Croatia. In 1979, Plitvice Lakes National Park was added to the UNESCO World Heritage register.
  The national park was founded in 1949 and is in the mountainous karst area of central Croatia, at the border to Bosnia and Herzegovina. The important north–south road that passes through the national park area connects the Croatian inland with the Adriatic coastal region.
  The protected area extends over 296.85 square kilometres. About 90% of this area is part of Lika-Senj County, while the remaining 10% is part of Karlovac County.
  Each year, more than 1 million visitors are recorded. Entrance is subject to variable charges, up to 250 kuna or around €34 per adult per day in summer 2018.
context_section_description: Tufa barriers are the result of continuous sedimentation processes along natural thresholds. As the water flows in thin layers over thresholds, it is splashed up. This disturbs the chemical balance and causes precipitation of the carbonates, which then creates sedimentary deposits. Since the water forms larger surfaces at these places, increased quantities of carbon dioxide (CO₂) are released. Calcium carbonate is secreted in the form of microcrystals that are deposited, eventually creating tufa sediments (CaCO₃). This phenomenon particularly occurs on abundantly available mosses, enabling better adherence of the crystals.
  In the course of time, older barriers can be flooded by rising water levels since other barriers have outgrown the older ones. 400 years ago, there were two lakes in the place of today's Kozjak lake. In the lowest third of the lake, at the level of Matijaševića draga, a crown of an underwater barrier that is 40 m high, is stretching 4 m below the water surface. This barrier certainly formed a magnificent waterfall in the past. The travertine barrier at the Kozjak bridges (at the current end of the Kozjak lake), however, grew faster. Thus, 400 years ago two lakes merged in one. That is why the greatest depths of Kozjak lake are in its lower basin (north from the little island).
caption: The cascades of Milka Trnina
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