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Cerknisko jezero is an intermittent lake and covers 26 km2 , when is full - even up to 38 km2! It is 10 km long and 5 km wide. That makes it the largest lake in Slovenia. It lies in the heart of Notranjska region in a karst field near Cerknica.
Cerknica Lake is situated on the borderline between Dinaric and Alpine world. Basin Cerknica field is formed in carbonate rocks, that is Triassic and Jurassic dolomites and the Jurassic and Cretaceous limestones. Water that flow in this area caused a chemical weathering (dissolution of limestone), a process where water is bind CO2 and generate carbonic acid which then dissolves the limestone. Results are holes through which water drains now. When inflow is greater than outflow, than we have the lake.
Cerknisko jezero is an intermittent lake, filled mainly by autumn rains and the early spring thaw, which stops in May or June, sometimes even in mid-winter. The water comes from karst springs bubbling up at the lake’s edge and flows out underground, through sinkholes. Its surface level varies by over 7 meters (it lies between 546 and 553 meters above sea level). When the water is low, it spans over 20 square kilometers, but when high waters set in, it is over 10 kilometers in length, almost 5 kilometers wide, and its surface area exceeds 30 square kilometers.
The most interesting phase in the lake's annual cycle is when it fills up. Water starts bursting from vent holes and the streams rise immediately, flooding the field at the bottom of the valley. When it starts receding, the water disappears into picturesque sinkholes and into swallow-holes, entrances to the hollow karst underground which is embellished with stalagmites and stalactites.
On Losko polje (field) water disappears underground as stream Obrh and comes of the earth as river Strzen. Water from one of the most marvellous caves in Slovene karst – Krizna jama and water from Javornik mountains also flow in the lake.
All that water disappears in swallow holes on Cerknica field in a diferent directions: one section fills (stream Rak) the valley and nature reserve Rakov Skocjan and continues below ground level to the Planina cave where it connects with the river Pivka from Postojna Cave and becomes river Unica. The other part disappears opposite Planina field; the longest path of water comes of the earth in the springs in the Bistra near Borovnica. Some of the outflow water resurfaces at Mocilnik, the source of the Ljubljanica river.
Cerknica Lake is an important fish habitat and as a nesting ground for many species of birds. It is increasingly popular as a recreational area, ideal for fishing, hiking, nature excursions (speleology), wind-surfing, swimming, and ice-skating – depending on the season and the water level. The constantly changing landscape makes it worth a visit in any season.
Stories about the miraculous lake have inspired artists for centuries, in whose imagination it acquired a sense of the divine and unfathomable; Dante Alighieri saw it in this way in his Divine Comedy. The lake became known globally, when the intermittence mechanism was first described over 300 years ago by the Slovene polymath, historian, topographer, ethnographer and sketcher, baron Janez Vajkard Valvasor (1641-1693), which earned him membership in the Royal Society. He also published a lengthy summary of his description in his most comprehensive work, The Glory of the Duchy of Carniola.
Lake is wonderful in all year seasons: In winter you can see nice ice ruptures, spring storms show you high waves on water, in summer, when water disappears, the bottom of the lake looks like Moon area. After autumn rains all nature around lake puts on wonderful colours and many birds stop here on their way to the south.
Above the lake you can see the hill, name XXXXXXXX, the witch nest (1114 m a.s.l.). To log the cache, mail me the name and in the log upload the picture of you with the lake panorama.The log without mail will be delete.
At the beginning of mail please write your geocache nick name and the name of this GC20PFY earth cache.
(No hints available.)